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| abstract
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|---|---|---|---|---|
2023ApJ...954...82G
|
Post-outburst Evolution of Bona Fide FU Ori-type V2493 Cygnus: A Spectro-photometric Monitoring
|
We present here the results of 8 yr of our near-simultaneous optical-near-infrared spectro-photometric monitoring of the bona fide FU Ori (FUor)-type candidate V2493 Cygnus (V2493 Cyg) starting from 2013 September to 2021 June. During our optical monitoring period (between 2015 October 16 and 2019 December 30), the V2493 Cyg is slowly dimming with an average dimming rate of ~26.6 ± 5.6 mmag yr<SUP>-1</SUP> in the V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing toward a gradual expansion of the emitting region post the second outburst. The mid-infrared colors, on the contrary, exhibit a blueing trend, which can be attributed to the brightening of the disk due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the Hα line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca II infrared triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilized compared to the early days of the outburst. The evolution of the O I λ7773 Å line also points toward the stabilization of the circumstellar disk post the second outburst.
|
[
430,
476,
1834
] |
[
"early-type stars",
"eruptive variable stars",
"young stellar objects"
] |
2021AJ....161..204B
|
Astrometric Membership Tests for the Zinn-Newell-Gibson UV-bright Stars in Galactic Globular Clusters
|
In 1972, Zinn, Newell, & Gibson (ZNG) published a list of 156 candidate UV-bright stars they had found in 27 Galactic globular clusters (GCs), based on photographs in the U and V bands. UV-bright stars lie above the horizontal branch (HB) and blueward of the asymptotic giant branch (AGB) and red giant branch in the clusters' color-magnitude diagrams. They are in rapid evolutionary phases—if they are members and not unrelated bright foreground stars. The ZNG list has inspired numerous follow-up studies, aimed at understanding late stages of stellar evolution. However, the ZNG candidates were presented only in finding charts, and celestial coordinates were not given. Using my own collection of CCD frames in u and V, I have identified all of the ZNG objects, and have assembled their coordinates, parallaxes, and proper motions from the recent Gaia Early Data Release 3 (EDR3). Based on the Gaia astrometry, I have determined which objects are probable cluster members (45% of the sample). For the members, using photometry from EDR3, I have assigned the stars to various evolutionary stages, including luminous post-AGB stars, and stars above the HB. I point out several ZNG stars of special interest that have still, to my knowledge, never been studied in detail. This study is an adjunct to a forthcoming survey of the Galactic GCs in the uBVI photometric system, designed for detection of low-gravity stars with large Balmer discontinuities.
|
[
656,
911,
2121,
746,
1541
] |
[
"globular star clusters",
"late stellar evolution",
"post-asymptotic giant branch stars",
"horizontal branch stars",
"space astrometry"
] |
2023ApJ...950..114H
|
The Evolving Effect of Cosmic Web Environment on Galaxy Quenching
|
We investigate how cosmic web structures affect galaxy quenching in the IllustrisTNG (TNG100) cosmological simulations by reconstructing the cosmic web within each snapshot using the DISPERSE framework. We measure the comoving distance from each galaxy with stellar mass $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 8$ to the nearest node (d <SUB>node</SUB>) and the nearest filament spine (d <SUB>fil</SUB>) to study the dependence of both the median specific star formation rate (<sSFR>) and the median gas fraction (<f <SUB>gas</SUB>>) on these distances. We find that the <sSFR> of galaxies is only dependent on the cosmic web environment at z < 2, with the dependence increasing with time. At z ≤ 0.5, $8\leqslant \mathrm{log}({M}_{* }/{M}_{\odot })\lt 9$ galaxies are quenched at d <SUB>node</SUB> ≲ 1 Mpc, and have significantly suppressed star formation at d <SUB>fil</SUB> ≲ 1 Mpc, trends driven mostly by satellite galaxies. At z ≤ 1, in contrast to the monotonic drop in <sSFR> of $\mathrm{log}({M}_{* }/{M}_{\odot })\lt 10$ galaxies with decreasing d <SUB>node</SUB> and d <SUB>fil</SUB>, $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 10$ galaxies-both centrals and satellites-experience an upturn in <sSFR> at d <SUB>node</SUB> ≲ 0.2 Mpc. Much of this cosmic web dependence of star formation activity can be explained by an evolution in <f <SUB>gas</SUB>>. Our results suggest that in the past ~10 Gyr, low-mass satellites are quenched by rapid gas stripping in dense environments near nodes and gradual gas starvation in intermediate-density environments near filaments. At earlier times, cosmic web structures efficiently channeled cold gas into most galaxies. State-of-the-art ongoing spectroscopic surveys such as the Sloan Digital Sky Survey and DESI, as well as those planned with the Subaru Prime Focus Spectrograph, JWST, and Roman, are required to test our predictions against observations.
|
[
594,
2040,
811,
330,
902,
1569,
595,
767,
1966
] |
[
"galaxy evolution",
"galaxy quenching",
"intergalactic filaments",
"cosmic web",
"large-scale structure of the universe",
"star formation",
"galaxy formation",
"hydrodynamical simulations",
"magnetohydrodynamical simulations"
] |
2022ApJ...941..166X
|
Search for Quasiperiodic Oscillations in Precursors of Short and Long Gamma-Ray Bursts
|
The precursors of short and long gamma-ray bursts (SGRBs and LGRBs) can serve as probes of their progenitors, as well as shedding light on the physical processes of mergers or core-collapse supernovae. Some models predict the possible existence of quasiperiodic oscillations (QPOs) in the precursors of SGRBs. Although many previous studies have performed QPO searches in the main emission of SGRBs and LGRBs, so far there were no systematic QPO searches in their precursors. In this work, we perform a detailed QPO search in the precursors of SGRBs and LGRBs detected by Fermi/Gamma-ray Burst Monitor (GBM) from 2008 to 2019 using the power density spectrum (PDS) in the frequency domain and Gaussian processes in the time domain. We do not find any convinced QPO signal with significance above 3σ, possibly due to the low fluxes of precursors. Finally, the PDS continuum properties of both the precursors and main emissions are also studied for the first time, and no significant difference is found in the distributions of the PDS slope for precursors and main emissions in both SGRBs and LGRBs.
|
[
629
] |
[
"gamma-ray bursts"
] |
2023RNAAS...7...46M
|
The Behavior of BpSi Stars in the Far UV-Paper II: HD 9996 (HR 465)
|
The analysis of IUE spectra of the B9 SiCrEu star HD 9996 recorded by the SWP and the LWP camera on board the International Ultraviolet Explorer collected at two phases of its very long rotational period (separated by Δϕ = 0.40), reveals large variations of the far and mid ultraviolet flux. The FUV flux seems to vary in opposition with the optical brightness recorded by the Fine Error Sensor near the V band. At ultraviolet maximum, the lines of Mg II, Cr II and Fe II are definitely stronger than at minimum, which suggests that these elements are distributed in a non uniform manner on the stellar disk with large horizontal gradients. However, the changing aspect of the magnetic field between the two rotational phases observed could also cause part of the ultraviolet variability.
|
[
226,
178
] |
[
"chemically peculiar stars",
"bp stars"
] |
2023ApJ...948...39R
|
HOPS 361-C's Jet Decelerating and Precessing through NGC 2071 IR
|
We present a two-epoch Hubble Space Telescope study of NGC 2071 IR highlighting HOPS 361-C, a protostar producing an arced 0.2 parsec-scale jet. The proper motions for the brightest knots decrease from 350 to 100 km s<SUP>-1</SUP> with increasing distance from the source. The [Fe II] and Paβ emission line intensity ratio gives a velocity jump through each knot of 40-50 km s<SUP>-1</SUP>. A new [O I] 63 μm spectrum, taken with the German REciever for Astronomy at Terahertz frequencies instrument aboard Stratospheric Observatory for Infrared Astronomy, shows a low line-of-sight velocity indicative of high jet inclination. Proper motions and jump velocities then estimate 3D flow speed for knots. Subsequently, we model knot positions and speeds with a precessing jet that decelerates. The measurements are matched with a precession period of 1000-3000 yr and half opening angle of 15°. The [Fe II] 1.26-to-1.64 μm line intensity ratio determines visual extinction to each knot from 5 to 30 mag. Relative to ~14 mag of extinction through the cloud from C<SUP>18</SUP>O emission maps, the jet is embedded at a 1/5-4/5 fractional cloud depth. Our model suggests the jet is dissipated over a 0.2 pc arc. This short distance may result from the jet sweeping through a wide angle, allowing the cloud time to fill cavities opened by the jet. Precessing jets contrast with nearly unidirectional protostellar jets that puncture host clouds and can propagate significantly farther.
|
[
803,
840,
412,
851,
1302,
1095,
1834,
722,
837,
1295,
870
] |
[
"intercloud medium",
"interstellar emissions",
"dust continuum emission",
"interstellar plasma",
"protostars",
"nebulae",
"young stellar objects",
"herbig-haro objects",
"interstellar dust extinction",
"proper motions",
"jets"
] |
2022ApJ...937..120W
|
CN 2-1 and CS 5-4 Observations toward Arp 299 with the SMA
|
Dense gas is the key to understanding star formation in galaxies. We present high-resolution (~3″) observations of CN 2-1 and CS 5-4 as dense gas tracers toward Arp 299, a mid-stage major merger of galaxies, with the Submillimeter Array. The spatial distribution of CN 2-1 and CS 5-4 are generally consistent with each other, as well as HCN 1-0 in the literature. However, different line ratios of CS 5-4 and CN 2-1 are found in the A, B, and C regions, with the highest value in B. Dense gas fraction decreases from IC 694 (A) to NGC 3690 (B) and the starburst in the overlap regions (C and C'), which indicates that circumnuclear upcoming starburst in A and B will be more efficient than that in the overlap region of Arp 299.
|
[
608
] |
[
"galaxy mergers"
] |
2020AJ....160..175S
|
BVR<SUB>C</SUB>I<SUB>C</SUB> Observations and Analysis of the UV LEO-type Binary, the Pre-WUMa, V1023 Persei
|
V1023 Per is a polar spotted, but well-detached dwarf binary, very likely a Pre-WUMa eclipsing binary. It was observed on 11 nights in 2015 October, November, and December at Dark Sky Observatory in North Carolina with the 0.81 m reflector of Appalachian State University. The period behavior is complex and may be increasing with a cubic or quadratic ephemeris. Its odd light curves are of high amplitude but have no totality and reach maximum light just before and following the secondary eclipse, indicating that it has polar spots similar to UV Leo. The 28 yr orbital period study calls the attention of observers to further monitor this binary to understand the complex nature of the period evolution. Its presently fixed polar spot does indicate that it must have a strong magnetic field and that it is synchronously rotating. The BVR<SUB>c</SUB>I<SUB>c</SUB> simultaneous 2016 Wilson-Devinney program (W-D) solution gives fillouts of 68% and 75% for the primary and secondary components, respectively. The polar position of the spot, its radius (24°), and T-fact (0.75) indicate that a strong magnetic field is present. The small ΔT in the components (∼289 K) show that the stars are similar in spectral type despite them being well detached. The inclination is high, ∼85°19 ± 0°04, but there is not a total eclipse due to the high mass ratio (∼0.739 ± 0.001). Due to the low galactic position (longitude = 150°390, latitude = -1°023), its reddening is addressed. The primary components temperature is estimated to be 5250 ± 250 K.
|
[
254,
444,
375,
1783,
1416
] |
[
"close binary stars",
"eclipsing binary stars",
"detached binary stars",
"w ursae majoris variable stars",
"rs canum venaticorum variable stars"
] |
2022AJ....164..161K
|
Tying Spitzer's IRS Calibration to IRAC: Observations of IRS Standard Stars
|
We present 3.6 and 4.5 μm photometry for a set of 61 standard stars observed by Spitzer's Infrared Spectrograph (IRS). The photometry was obtained with the Infrared Array Camera (IRAC) on Spitzer in order to help tie the calibration of IRAC and the IRS, which had been anchored to the calibration of the Multiband Infrared Photometer for Spitzer. The wavelength range of the IRS data only slightly overlaps with the IRAC 4.5 μm band and not at all with the 3.6 μm band. Therefore, we generated synthetic spectra from spectral templates of stars with the same spectral types and luminosity classes as our sample stars, normalized to the IRS data at 6-7 μm, and compared those to the observed photometry. The new IRAC observations of IRS standard stars demonstrate that the two instruments are calibrated to within 1% of each other.
|
[
792,
1232,
544,
1556,
1555
] |
[
"infrared photometry",
"photometric standard stars",
"flux calibration",
"spectrophotometry",
"spectrophotometric standards"
] |
2023ApJS..267...22P
|
The LSST Cadence Impact on Non-time-critical Eclipsing Binary Science
|
The Legacy Survey of Space and Time (LSST) is slated to commence in 2025 at the Vera Rubin Observatory. One of the crucial parts of preparing the survey is the choice of observing cadence in an effort to optimize auxiliary science goals while maintaining the core project requirements. Here we look at the impact of proposed cadences, encoded in different operation simulations (opsims), on non-time-critical eclipsing binary science. This is particularly pertinent because LSST is the first large-scale survey that will provide us with color information in addition to high-precision coverage of faint targets. We study the differences between the baseline opsim v2.1 and the latest opsim v3.0 runs. We find that all runs provide sufficient data coverage to enable in-depth studies in the field of eclipsing binaries, and that there are no adverse impacts from any proposed opsim modification studied here.
|
[
1776,
444,
1170
] |
[
"optical astronomy",
"eclipsing binary stars",
"optical observatories"
] |
2020AJ....160...37M
|
Effective Opacity of the Intergalactic Medium from Galaxy Spectra Analysis
|
We measure the effective opacity ( ${\tau }_{\mathrm{eff}}$ ) of the intergalactic medium from the composite spectra of 281 Lyman-break galaxies in the redshift range 2 ≲ z ≲ 3. Our spectra are taken from the COSMOS Lyα Mapping And Tomographic Observations survey derived from the Low Resolution Imaging Spectrometer on the W.M. Keck I telescope. We generate composite spectra in two redshift intervals and fit them with spectral energy distribution (SED) models composed of simple stellar populations. Extrapolating these SED models into the Lyα forest, we measure the effective Lyα opacity ( ${\tau }_{\mathrm{eff}}$ ) in the 2.02 ≤ z ≤ 2.44 range. At z = 2.22, we estimate ${\tau }_{\mathrm{eff}}\,=0.159\pm 0.001$ from a power-law fit to the data. These measurements are consistent with estimates from quasar analyses at z < 2.5 indicating that the systematic errors associated with normalizing quasar continua are not substantial. We provide a Gaussian processes model of our results and previous ${\tau }_{\mathrm{eff}}$ measurements that describes the steep redshift evolution in ${\tau }_{\mathrm{eff}}$ from z = 1.5-4.
|
[
813,
812,
979
] |
[
"intergalactic medium",
"intergalactic gas",
"lyman-break galaxies"
] |
2023ApJ...957...89O
|
Identification of 1RXS J165424.6-433758 as a Polar Cataclysmic Variable
|
We present the results of our X-ray, ultraviolet, and optical follow-up campaigns of 1RXS J165424.6-433758, an X-ray source detected with the Swift Deep Galactic Plane Survey. The source X-ray spectrum (Swift and NuSTAR) is described by thermal bremsstrahlung radiation with a temperature of kT = 10.1 ± 1.2 keV, yielding an X-ray (0.3-10 keV8) luminosity L <SUB> X </SUB> = (6.5 ± 0.8) × 10<SUP>31</SUP> erg s<SUP>-1</SUP> at a Gaia distance of 460 pc. Spectroscopy with the Southern African Large Telescope revealed a flat continuum dominated by emission features, demonstrating an inverse Balmer decrement, the λ4640 Bowen blend, almost a dozen He I lines, and He II λ4541, λ4686, and λ5411. Our high-speed photometry demonstrates a preponderance of flickering and flaring episodes, and revealed the orbital period of the system, P <SUB>orb</SUB> = 2.87 hr, which fell well within the cataclysmic variable (CV) period gap between 2 and 3 hr. These features classify 1RXS J165424.6-433758 as a nearby polar magnetic CV.
|
[
32,
203,
1810
] |
[
"am herculis stars",
"cataclysmic variable stars",
"x-ray astronomy"
] |
2024ApJ...966....6O
|
Initiation and Eruption of a Two-turn Helical Quiescent Filament on 2013 August 2
|
We investigate a quiescent filament that erupted on 2013 August 2; the eruption was observed in EUV and Hα by the Solar Dynamics Observatory and GONG. After a B9.7 flare in the nearby active region, the dark filament materials near its eastern footpoint start to move in the direction of eruption, and are followed by a counterclockwise rotation identified as the motion of a combination of dark and bright filament materials. Then the entire filament rises up and keeps rotating in a clockwise direction during the eruption. More interestingly, the filament exhibits an unusual two-helix structure near its western footpoint during the eruption, which indicates the existence of a highly twisted flux rope. This hypothesis is confirmed by magnetic field modeling using the flux rope insertion method. In the best-fit unstable model, the lower limits of the estimated maximum and average twist numbers of the erupting flux rope reach 7.5π and 4π, which suggests that kink instability plays an important role in the eruption. During these magnetically coupled sympathetic eruptions, the highly twisted filament under the western lobe of a pseudo-streamer-like structure becomes unstable and erupts due to the removal of confinement by magnetic reconnection at the overlying hyperbolic flux tube, which is initiated by the B9.7 flare in the nearby active region. The initial filament motion occurs at the more unstable eastern footpoint, where the surrounding fields are weaker and decrease with height more rapidly.
|
[
1981,
1475,
1321,
1503
] |
[
"solar filament eruptions",
"solar activity",
"quiescent solar prominence",
"solar magnetic fields"
] |
2021ApJ...914..100D
|
Two Populations of Carbon-enhanced Metal-poor Stars in the Disk System of the Milky Way
|
We present a chemodynamical analysis of low-resolution (R ~ 1300) spectroscopy of ~50,000 stars from the AAOmega Evolution of Galactic Structure survey, focusing on two key populations of (in total) 650 carbon-enhanced metal-poor (CEMP) stars within the disk system of the Milky Way: a mildly prograde population (L<SUB>z</SUB> < 1000 kpc km s<SUP>-1</SUP>) and a strongly prograde population (L<SUB>z</SUB> > 1000 kpc km s<SUP>-1</SUP>). Based on their chemical and kinematic characteristics, and on comparisons with similar populations found in the recent literature, we tentatively associate the former with an ex situ inner-halo population originating from either the Gaia Sausage or Gaia-Enceladus. The latter population is linked to the metal-weak thick disk. We discuss their implications in the context of the formation history of the Milky Way.
|
[
1050,
1052,
1053,
2105,
1608
] |
[
"milky way disk",
"milky way evolution",
"milky way formation",
"cemp stars",
"stellar kinematics"
] |
2020ApJ...896..158T
|
Early Evolution of Disk, Outflow, and Magnetic Field of Young Stellar Objects: Impact of Dust Model
|
The formation and early evolution of low-mass young stellar objects (YSOs) are investigated using three-dimensional non-ideal magnetohydrodynamics simulations. We investigate the evolution of YSOs up to $\sim {10}^{4}\,\mathrm{yr}$ after protostar formation, at which protostellar mass reaches $\sim 0.1{M}_{\odot }$ . We particularly focus on the impact of the dust model on the evolution. We found that a circumstellar disk is formed in all simulations, regardless of the dust model. Disk size is approximately 10 au at the protostar formation epoch, and it increases to several tens of au at $\sim {10}^{4}\,\mathrm{yr}$ after protostar formation. The disk mass is comparable to the central protostellar mass, and gravitational instability develops. In simulations with small dust sizes, the warp of the pseudodisk develops $\sim {10}^{4}\,\mathrm{yr}$ after protostar formation. The warp strengthens magnetic braking in the disk and decreases disk size. Ion-neutral drift can occur in the infalling envelope when the typical dust size is $a\gtrsim 0.2\,\mu {\rm{m}}$ and the protostar (plus disk) mass is $M\gtrsim 0.1{M}_{\odot }$ . The outflow activity is anticorrelated to the dust size, and the strong outflow appears with small dust grains.
|
[
1300,
235,
1966
] |
[
"protoplanetary disks",
"circumstellar disks",
"magnetohydrodynamical simulations"
] |
2020ApJ...900....2K
|
Atmospheric Temperature Inversions and He I 5876 Core Profile Structure in White Dwarfs
|
We report distinctive core profiles in the strongest optical helium line, He I λ5876, from high-resolution high-sensitivity observations of spectral type DB white dwarfs. By analyzing a sample of 40 stars from Keck/HIRES and VLT/UVES, we find the core appearance to be related to the degree of hydrogen and heavy element content in the atmosphere. New Ca K-line measurements or upper limits are reported for about half the sample stars. He I λ5876 emission cores with a self-reversed central component are present for those stars with relatively low hydrogen abundance, as well as relatively low atmospheric heavy element pollution. This self-reversed structure disappears for stars with higher degrees of pollution and/or hydrogen abundance, giving way to a single absorption core. From our model atmospheres, we show that the self-reversed emission cores can be explained by temperature inversions in the upper atmosphere. We propose that the transition to a single absorption core is due to the additional opacity from hydrogen and heavy elements that inhibits the temperature inversions. Our current models do not exactly match the effective temperature range of the phenomenon or the amplitude of the self-reversed structure, which is possibly a result of missing physics such as 3D treatment, convective overshoot, and/or non-LTE effects. The He I λ5876 line structure may prove to be a useful new diagnostic for calibrating temperature profiles in DB atmosphere models.
|
[
1799,
358,
1584,
1585,
1748,
511,
1597,
2096
] |
[
"white dwarf stars",
"db stars",
"stellar atmospheres",
"stellar atmospheric opacity",
"upper atmosphere",
"extrasolar rocky planets",
"stellar effective temperatures",
"high resolution spectroscopy"
] |
2021PSJ.....2..145C
|
In Situ Geochronology for the Next Decade: Mission Designs for the Moon, Mars, and Vesta
|
Geochronology is an indispensable tool for reconstructing the geologic history of planets, essential to understanding the formation and evolution of our solar system. Bombardment chronology bounds models of solar system dynamics, as well as the timing of volatile, organic, and siderophile element delivery. Absolute ages of magmatic products provide constraints on the dynamics of magma oceans and crustal formation, as well as the longevity and evolution of interior heat engines and distinct mantle/crustal source regions. Absolute dating also relates habitability markers to the timescale of evolution of life on Earth. However, the number of terrains important to date on worlds of the inner solar system far exceeds our ability to conduct sample return from all of them. In preparation for the upcoming Decadal Survey, our team formulated a set of medium-class (New Frontiers) mission concepts to three different locations (the Moon, Mars, and Vesta) where sites that record solar system bombardment, magmatism, and habitability are uniquely preserved and accessible. We developed a notional payload to directly date planetary surfaces, consisting of two instruments capable of measuring radiometric ages, an imaging spectrometer, optical cameras to provide site geologic context and sample characterization, a trace-element analyzer to augment sample contextualization, and a sample acquisition and handling system. Landers carrying this payload to the Moon, Mars, and Vesta would likely fit into the New Frontiers cost cap in our study (~$1B). A mission of this type would provide crucial constraints on planetary history while also enabling a broad suite of complementary investigations.
|
[
436,
1441,
1007,
2036,
954,
332
] |
[
"earth-moon system",
"selenology",
"mars",
"main belt asteroids",
"lunar geochronology",
"cosmochronology"
] |
2024ApJ...969..156S
|
Discovery of a 100 kpc Narrow Curved Twin Jet in the S-shaped Giant Radio Galaxy J0644+1043
|
We report the discovery of an S-shaped morphology of the radio galaxy J0644+1043 imaged with a 30 μJy beam<SUP>‑1</SUP> sensitive 525 MHz broadband (bands 3 + 4) uGMRT map. Dedicated spectroscopic observations of the host galaxy carried out with the 2 m Rozhen telescope yielded a redshift of 0.0488, giving a projected linear size of the peculiar radio structure of over 0.7 Mpc. This giant radio galaxy is powered by a black hole of mass M <SUB>⊙</SUB>, from the vicinity of which emanate well-collimated and knotty jets, each ∼100 kpc long. The entire radio structure, presumably due to the effective jet precession, is less than 50 Myr old, has a power of ∼6 × 10<SUP>24</SUP> W Hz<SUP>‑1</SUP> at 1.4 GHz, and has observed morphological characteristics that do not strictly conform to the traditional Fanaroff–Riley (FR) FR I or FR II categories.
|
[
654,
17,
1119
] |
[
"giant radio galaxies",
"active galaxies",
"non-thermal radiation sources"
] |
2020ApJ...897..117M
|
Black Hole Masses of Weak Emission Line Quasars Based on the Continuum Fit Method
|
We studied optical-ultraviolet spectral energy distribution of 10 weak emission-line quasars (WLQs) that lie at redshifts z = 0.19 and 1.43 < z < 3.48. The theoretical models of their accretion disk continua are created based on the Novikov-Thorne equations. It allows us to estimate masses of their supermassive black holes ( ${M}_{\mathrm{BH}}$ ) and accretion rates. We determined the virial factor for WLQs and note its anticorrelation with the FWHM of the Hβ emission line $(f\propto {\mathrm{FWHM}}^{\alpha },\alpha =-1.34\pm 0.37$ ). By comparison with the previously estimated BH masses, the underestimation of ${M}_{\mathrm{BH}}$ is noticed with a mean factor of 4-5, which depends on the measured full width. We proposed a new formula to estimate ${M}_{\mathrm{BH}}$ in WLQs based on their observed $\mathrm{FWHM}$ (Hβ) and luminosities at 5100 Å. In our opinion, WLQs are also normal quasars visible in a reactivation stage.
|
[
1319,
16,
162
] |
[
"quasars",
"active galactic nuclei",
"black holes"
] |
2020ApJ...893...14D
|
Prescriptions for Correcting Ultraviolet-based Redshifts for Luminous Quasars at High Redshift
|
High-redshift quasars typically have their redshift determined from rest-frame ultraviolet (UV) emission lines. However, these lines, and more specifically the prominent C IV λ1549 emission line, are typically blueshifted yielding highly uncertain redshift estimates compared to redshifts determined from rest-frame optical emission lines. We present near-infrared spectroscopy of 18 luminous quasars at 2.15 < z < 3.70 that allows us to obtain reliable systemic redshifts for these sources. Together with near-infrared spectroscopy of an archival sample of 44 quasars with comparable luminosities and redshifts, we provide prescriptions for correcting UV-based redshifts. Our prescriptions reduce velocity offsets with respect to the systemic redshifts by ∼140 km s<SUP>-1</SUP> and reduce the uncertainty on the UV-based redshift by ∼25% with respect to the best method currently used for determining such values. We also find that the redshifts determined from the Sloan Digital Sky Survey Pipeline for our sources suffer from significant uncertainties, which cannot be easily mitigated. We discuss the potential of our prescriptions to improve UV-based redshift corrections given a much larger sample of high-redshift quasars with near-infrared spectra.
|
[
590,
1319,
16
] |
[
"galaxy distances",
"quasars",
"active galactic nuclei"
] |
2021ApJ...917...69S
|
Multiwavelength Evidence for a New Flare-mode Transitional Millisecond Pulsar
|
We report the discovery of a new low-mass X-ray binary near the center of the unassociated Fermi GeV γ-ray source 4FGL J0540.0-7552. The source shows the persistent presence of an optical accretion disk and exhibits extreme X-ray and optical variability. It also has an X-ray spectrum well-fit by a hard power law with Γ = 1.8 and a high ratio of X-ray to γ-ray flux. Together, these properties are consistent with the classification of the binary as a transitional millisecond pulsar (tMSP) in the subluminous disk state. Uniquely among the candidate tMSPs, 4FGL J0540.0-7552 shows consistent optical, X-ray, and γ-ray evidence for having undergone a state change, becoming substantially brighter in the optical and X-rays and fainter in GeV γ-rays sometime in mid-2013. In its current subluminous disk state, and like one other candidate tMSP in the Galactic field, 4FGL J0540.0-7552 appears to always be in an X-ray "flare mode," indicating that this could be common phenomenology for tMSPs.
|
[
1062
] |
[
"millisecond pulsars"
] |
2020ApJ...901..140H
|
Asteroid Thermal Inertia Estimates from Remote Infrared Observations: The Effects of Surface Roughness and Rotation Rate
|
The thermal inertia of an asteroid's surface can provide insight into regolith properties, such as the presence of a layer of fine dust, the density and thermal conductivity of a rocky surface, and, together with other observational data, mineralogy. Knowledge of the surface characteristics of asteroids is important for planetary defense initiatives and the extraction of resources ("asteroid mining"). A simple means of estimating asteroid thermal inertia has been proposed by Harris & Drube, which is suitable for application to large sets of thermal-infrared observational data, such as those obtained by infrared space telescopes. We compare results from the Harris-Drube estimator with recently published values of asteroid thermal inertia from detailed thermophysical modeling, and provide an explanation in terms of reduced surface roughness for some discrepant results. Smooth surfaces covered in fine dust may provide an explanation for the unexpectedly low values of thermal inertia derived from thermophysical modeling for some slowly rotating main-belt asteroids. In the case of near-Earth objects (NEOs) we show that results from the estimator are in good agreement with those from thermophysical modeling, with just a few exceptions. We discuss the special cases of the NEOs (101955) Bennu, (162173) Ryugu, and (29075) 1950 DA in the context of results from our estimator. Given the data requirements and complexity of thermophysical modeling, data-analysis tools based on relatively simple concepts can play an important role in allowing "quick-look" assessment of thermal-infrared data of asteroids, especially NEOs.
|
[
2036,
1092,
786,
1065
] |
[
"main belt asteroids",
"near-earth objects",
"infrared astronomy",
"minor planets"
] |
2023RNAAS...7...93M
|
The Behavior of Bp Si Stars in the Far UV-Paper V: HD 187473
|
The analysis of five spectra of the B9 SiSrEu HD 187473 recorded by the Short Wavelength Prime camera on board the International Ultraviolet Explorer reveals large amplitude variations of the far ultraviolet spectral energy distribution over a time interval of about half the rotation period. In contrast, the level of the mid-UV flux does not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations. The iron-peak elements, chromium, manganese and iron probably also contribute to these variations.
|
[
226,
178
] |
[
"chemically peculiar stars",
"bp stars"
] |
2022RNAAS...6..246O
|
Kepler K2 Observations of the Faint, Understudied Polar SDSS J092122.84+203857.1
|
SDSS J092122.84+203857.1 is a polar-type cataclysmic variable system, consisting of a strongly magnetized white dwarf that accretes from its red dwarf companion. It is also one of just five polars known to have been observed by Kepler during its K2 mission. We analyzed the K2 short-cadence light curve of J0921 and identified a weak, but highly coherent, signal at a frequency of 17.099 cycles day<SUP>-1</SUP>, corresponding with the system's reported orbital period. We see no overall variation in the accretion rate across the K2 observation, and both our measurement of the period and the binned orbital profile are very consistent with previous ground-based data.
|
[
203,
32
] |
[
"cataclysmic variable stars",
"am herculis stars"
] |
2024PASP..136a4502E
|
A Novel Eccentricity Parameterization for Transit-only Models
|
We present a novel eccentricity parameterization for transit-only fits that allows us to efficiently sample the eccentricity and argument of periastron, while being able to generate a self-consistent model of a planet in a Keplerian orbit around its host star. With simulated fits of 330 randomly generated systems, we demonstrate that typical parameterizations often lead to inaccurate and overly precise determinations of the planetary eccentricity. However, our proposed parameterization allows us to accurately—and often precisely—recover the eccentricity for the simulated planetary systems with only transit data available.
|
[
441,
1177,
86,
1709
] |
[
"eccentricity",
"orbital elements",
"astronomical models",
"transit photometry"
] |
2022ApJS..262...21F
|
3D Selection of 167 Substellar Companions to Nearby Stars
|
We analyze 5108 AFGKM stars with at least five high-precision radial velocity points, as well as Gaia and Hipparcos astrometric data, utilizing a novel pipeline developed in previous work. We find 914 radial velocity signals with periods longer than 1000 days. Around these signals, 167 cold giants and 68 other types of companions are identified, through combined analyses of radial velocity, astrometry, and imaging data. Without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit brown dwarfs to be 1.3%, and find a significant brown-dwarf valley around 40 M <SUB>Jup</SUB>. We also find a power-law distribution in the host binary fraction beyond 3 au, similar to that found for single stars, indicating no preference of multiplicity for brown dwarfs. Our work also reveals nine substellar systems (GJ 234 B, GJ 494 B, HD 13724 b, HD 182488 b, HD 39060 b and c, HD 4113 C, HD 42581 d, HD 7449 B, and HD 984 b) that have previously been directly imaged, and many others that are observable at existing facilities. Depending on their ages, we estimate that an additional 10-57 substellar objects within our sample can be detected with current imaging facilities, extending the imaged cold (or old) giants by an order of magnitude.
|
[
2130,
1332,
489,
486,
185,
488
] |
[
"astrometric exoplanet detection",
"radial velocity",
"exoplanet detection methods",
"exoplanet astronomy",
"brown dwarfs",
"exoplanet catalogs"
] |
2022ApJ...941...28S
|
The Double White Dwarf Merger Progenitors of SDSS J2211+1136 and ZTF J1901+1458
|
Double white dwarf (DWD) mergers are possibly the leading formation channel of massive, rapidly rotating, high-field magnetic white dwarfs (HFMWDs). However, a direct link connecting a DWD merger to any observed HFMWD is still missing. We here show that the HFMWDs SDSS J221141.80+113604.4 (hereafter J2211+1136) and ZTF J190132.9+145808.7 (hereafter J1901+1458) might be DWD merger products. J2211+1136 is a 1.27 M <SUB>⊙</SUB> white dwarf (WD) with a rotation period of 70.32 s and a surface magnetic field of 15 MG. J1901+1458 is a 1.327-1.365 M <SUB>⊙</SUB> WD with a rotation period of 416.20 s, and a surface magnetic field in the range 600-900 MG. With the assumption of single-star evolution and the currently measured WD masses and surface temperatures, the cooling ages of J2211+1136 and J1901+1458 are, respectively, 2.61-2.85 Gyr and 10-100 Myr. We hypothesize that these WDs are DWD merger products and compute the evolution of the postmerged configuration formed by a central WD surrounded by a disk. We show that the postmerger system evolves through three phases depending on whether accretion, mass ejection (propeller), or magnetic braking dominates the torque onto the central WD. We calculate the time the WD spends in each of these phases and obtain the accretion rate and disk mass for which the WD rotational age, i.e., the total time elapsed since the merger to the instant where the WD central remnant reaches the current measured rotation period, agrees with the estimated WD cooling age. We infer the mass values of the primary and secondary WD components of the DWD merger that lead to a postmerger evolution consistent with the observations.
|
[
1627,
1799,
2157,
283,
288,
1629
] |
[
"stellar remnants",
"white dwarf stars",
"stellar mergers",
"compact binary stars",
"compact objects",
"stellar rotation"
] |
2020ApJ...889L..20L
|
On the Habitable Lifetime of Terrestrial Worlds with High Radionuclide Abundances
|
The presence of a liquid solvent is widely regarded as an essential prerequisite for habitability. We investigate the conditions under which worlds outside the habitable zones of stars are capable of supporting liquid solvents on their surface over geologically significant timescales via combined radiogenic and primordial heat. Our analysis suggests that super-Earths with radionuclide abundances that are ≳10<SUP>3</SUP> times higher than Earth can host long-lived water oceans. In contrast, the requirements for long-lived ethane oceans, which have been explored in the context of alternative biochemistries, are less restrictive: relative radionuclide abundances of ≳10<SUP>2</SUP> could be sufficient. We find that this class of worlds might be detectable (10σ detection over ∼10 day integration time at 12.8 μm) in principle by the James Webb Space Telescope at distances of ∼10 pc if their ages are ≲1 Gyr.
|
[
74,
491,
2022,
511,
549,
695,
1248,
1258
] |
[
"astrobiology",
"exoplanet evolution",
"exoplanet surface composition",
"extrasolar rocky planets",
"free floating planets",
"habitable planets",
"planetary interior",
"planetary theory"
] |
2021PSJ.....2..212A
|
OSSOS. XXIII. 2013 VZ<SUB>70</SUB> and the Temporary Coorbitals of the Giant Planets
|
We present the discovery of 2013 VZ<SUB>70</SUB>, the first known horseshoe coorbital companion of Saturn. Observed by the Outer Solar System Origins Survey for 4.5 yr, the orbit of 2013 VZ<SUB>70</SUB> is determined to high precision, revealing that it currently is in "horseshoe" libration with the planet. This coorbital motion will last at least thousands of years but ends ~10 kyr from now; 2013 VZ<SUB>70</SUB> is thus another example of the already-known "transient coorbital" populations of the giant planets, with this being the first known prograde example for Saturn (temporary retrograde coorbitals are known for Jupiter and Saturn). We present a theoretical steady-state model of the scattering population of trans-Neptunian origin in the giant planet region (2-34 au), including the temporary coorbital populations of the four giant planets. We expose this model to observational biases using survey simulations in order to compare the model to the real detections made by a set of well-characterized outer solar system surveys. While the observed number of coorbitals relative to the scattering population is higher than predicted, we show that the number of observed transient coorbitals of each giant planet relative to each other is consistent with a trans-Neptunian source.
|
[
893,
1705,
1396,
215,
1469,
1715,
874,
1097,
1430,
1181,
2210,
2173
] |
[
"kuiper belt",
"trans-neptunian objects",
"resonant kuiper belt objects",
"centaur group",
"small solar system bodies",
"trojan asteroids",
"jupiter trojans",
"neptune trojans",
"scattered disk objects",
"orbital resonances",
"asteroid dynamics",
"planetary dynamics"
] |
2024PSJ.....5...62M
|
Dynamic Secondary Illumination in Permanent Shadows within Artemis III Candidate Landing Regions
|
Investigations that can be conducted at the Artemis III candidate landing regions will benefit from the knowledge of the thermal environment within permanently shadowed regions (PSRs). Within PSRs, secondary illumination controls the surface temperature, varying diurnally and seasonally, affecting the stability and concentration of volatiles cold-trapped within the PSRs. In this case study, we characterize the dynamic nature of secondary illumination at four PSRs that overlap five of the Artemis III candidate landing regions. Our analysis is based on secondary illumination model-generated images paired with PSR images acquired by ShadowCam on board the Korean Pathfinder Lunar Orbiter. We find that illumination and thermal conditions can change rapidly within the PSRs, and knowledge of time-variable secondary illumination can be decisive for the efficient design of investigations and sample collection operations at the PSRs.
|
[
972,
952,
974
] |
[
"lunar science",
"lunar evolution",
"lunar surface"
] |
2021ApJ...910..103L
|
On the Observational Difference between the Accretion Disk-Corona Connections among Super- and Sub-Eddington Accreting Active Galactic Nuclei
|
We present a systematic X-ray and multiwavelength study of a sample of 47 active galactic nuclei (AGNs) with reverberation mapping measurements. This sample includes 21 super-Eddington accreting AGNs and 26 sub-Eddington accreting AGNs. Using high-state observations with simultaneous X-ray and UV/optical measurements, we investigate whether super-Eddington accreting AGNs exhibit different accretion disk-corona connections compared to sub-Eddington accreting AGNs. We find tight correlations between the X-ray-to-UV/optical spectral slope parameter (α<SUB>OX</SUB>) and the monochromatic luminosity at 2500 Å (L<SUB>2500Å</SUB>) for both the super- and sub-Eddington subsamples. The best-fit α<SUB>OX</SUB>-L<SUB>2500Å</SUB> relations are consistent overall, indicating that super-Eddington accreting AGNs are not particularly X-ray weak in general compared to sub-Eddington accreting AGNs. We find dependences of α<SUB>OX</SUB> on both the Eddington ratio (L<SUB>Bol</SUB>/L<SUB>Edd</SUB>) and black hole mass (M<SUB>BH</SUB>) parameters for our full sample. A multivariate linear regression analysis yields ${\alpha }_{\mathrm{OX}}=-0.13\mathrm{log}({L}_{\mathrm{Bol}}/{L}_{\mathrm{Edd}})-0.10\mathrm{log}{M}_{\mathrm{BH}}-0.69$ <!-- --> , with a scatter similar to that of the α<SUB>OX</SUB>-L<SUB>2500Å</SUB> relation. The hard (rest-frame >2 keV) X-ray photon index (Γ) is strongly correlated with L<SUB>Bol</SUB>/L<SUB>Edd</SUB> for the full sample and the super-Eddington subsample, but these two parameters are not significantly correlated for the sub-Eddington subsample. A fraction of super-Eddington accreting AGNs show strong X-ray variability, probably due to small-scale gas absorption, and we highlight the importance of employing high-state (intrinsic) X-ray radiation to study the accretion disk-corona connections in AGNs.
|
[
14,
2035,
1354
] |
[
"accretion",
"x-ray active galactic nuclei",
"radio quiet quasars"
] |
2022ApJ...935...65Y
|
Prospect of Detecting TeV Halos with LHAASO: In the Framework of the Anisotropic Diffusion Model
|
The particle diffusion coefficients of TeV pulsar halos observed so far are inferred to be significantly smaller than the typical value of the interstellar medium (ISM). The anisotropic diffusion model ascribes the slow diffusion to the cross-field diffusion, assuming sub-Alfvénic turbulence in the ISM around the pulsar if the viewing angle between the observer's line-of-sight (LOS) to the pulsar and the local mean field direction is small. In general, the TeV halo's morphology under this model highly depends on the viewing angle, and an elongated, asymmetric morphology is predicted if the LOS is not approximately aligned with the local mean field direction. While the specific requirement of a small viewing angle is supposedly established only for a small fraction of TeV halos, TeV halos with apparent asymmetric morphology have not been detected. In this paper, we will study the expectation of TeV halos measured by the TeV-PeV gamma-ray detector LHAASO in the framework of anisotropic diffusion model, with a particular focus on the influence of the viewing angle on the detectability. We show that a TeV halo is more detectable with a smaller viewing angle, and this selection effect may explain why the morphologies of all three detected TeV halos so far are consistent with being spherical. We also demonstrate that LHAASO is capable of detecting asymmetric TeV halos after several years of operation with reasonable source parameters. This can serve as a critical test of the anisotropic diffusion model.
|
[
1306,
633,
328,
504
] |
[
"pulsars",
"gamma-ray sources",
"cosmic ray sources",
"extended radiation sources"
] |
2021RNAAS...5..165W
|
Middle Corona Magnetic Field Strength Determined by Spacecraft Radio Faraday Rotation
|
Faraday rotation (FR) of MESSENGER spacecraft X-band transcoronal radio transmissions were studied to evaluate the mid-coronal magnetic field strength, with the line-of-sight closest solar approach at heliocentric altitudes ranging 1.647-1.817 R<SUB>⊙</SUB>. A Community Coordinated Modeling Center (CCMC) CORHEL-MAS 3D coronal field map revealed this region to contain closed magnetic fields. By FR analysis we found a field strength of 118,000 nT at r = 1.647 R<SUB>⊙</SUB>, with fall-off to 40,000 nT by r = 1.817 R<SUB>⊙</SUB>. These values straddle estimates provided by the CCMC model. The mean value of 79,000 nT at r = 1.732 R<SUB>⊙</SUB> is comparable to the value provided by an established empirical model for average coronal magnetic field strength. FR can be used to evaluate middle coronal magnetic fields, but improved methods to constrain concurrent electron column density will be needed to produce the most accurate results.
|
[
1483,
1503
] |
[
"solar corona",
"solar magnetic fields"
] |
2022ApJ...929....9X
|
Please Repeat: Strong Lensing of Gravitational Waves as a Probe of Compact Binary and Galaxy Populations
|
Strong gravitational lensing of gravitational wave sources offers a novel probe of both the lens galaxy and the binary source population. In particular, the strong lensing event rate and the time-delay distribution of multiply imaged gravitational-wave binary coalescence events can be used to constrain the mass distribution of the lenses as well as the intrinsic properties of the source population. We calculate the strong lensing event rate for a range of second- (2G) and third-generation (3G) detectors, including Advanced LIGO/Virgo, A+, Einstein Telescope (ET), and Cosmic Explorer (CE). For 3G detectors, we find that ~0.1% of observed events are expected to be strongly lensed. We predict detections of ~1 lensing pair per year with A+, and ~50 pairs per year with ET/CE. These rates are highly sensitive to the characteristic galaxy velocity dispersion, σ <SUB>*</SUB>, implying that observations of the rates will be a sensitive probe of lens properties. We explore using the time-delay distribution between multiply imaged gravitational-wave sources to constrain properties of the lenses. We find that 3G detectors would constrain σ <SUB>*</SUB> to ~21% after 5 yr. Finally, we show that the presence or absence of strong lensing within the detected population provides useful insights into the source redshift and mass distribution out to redshifts beyond the peak of the star formation rate, which can be used to constrain formation channels and their relation to the star formation rate and delay-time distributions for these systems.
|
[
675,
670
] |
[
"gravitational wave astronomy",
"gravitational lensing"
] |
2024ApJ...969...88M
|
Exploring Gamma-Ray Burst Diversity: Clustering Analysis of the Emission Characteristics of Fermi- and BATSE-detected Gamma-Ray Bursts
|
Gamma-ray bursts (GRBs), often attributed to massive star collapse or binary compact object mergers, exhibit diverse emission characteristics hinting at multiple GRB classes based on various factors like progenitors, radiation mechanisms, and central engines. This study employs unsupervised clustering using the nested Gaussian mixture model algorithm to analyze data from Fermi and BATSE, identifying four classes (A–D) based on duration, spectral peak, and spectral index of time-integrated spectra of GRBs. Class proportions are approximately 70%, 10%, 3%, and 17%, respectively, with A and B comprising mostly long GRBs, C mainly short GRBs, and D encompassing both types. The classes are further assessed based on spectral index α, indicating distinct radiation mechanisms: α > ‑0.67 for photospheric emission, α ≤ ‑1.5 for fast-cooling synchrotron, and ‑1.5 < α ≤ ‑0.67 for slow-cooling synchrotron. Classes B and C align with photospheric emission, while A and D predominantly exhibit synchrotron radiation. Short GRBs are predominantly photospheric emission, whereas long GRBs tend to favor synchrotron emission. Overall, 63% of the total bursts exhibit α profiles indicative of synchrotron emission, with the remaining 37% associated with photospheric emission. Considering the limited data of kilonova and supernova associated with GRBs, classes are examined for progenitor origins, suggesting a hybrid nature for A and D, and collapsar and merger origins for B and C, respectively. This clustering analysis results in four GRB classes, which, upon investigation, reveal the diverse and complex nature of GRBs in terms of their radiation, duration, and progenitor.
|
[
629,
1913,
205,
1908
] |
[
"gamma-ray bursts",
"multivariate analysis",
"catalogs",
"clustering"
] |
2024RNAAS...8...95X
|
A Spectroscopic Characterization of a Blazar Candidate Excluded by Automated Morphology Classification
|
Blazars are radio-loud Active Galactic Nuclei (AGNs) with their jets pointing at us at a very small angle. J064334.60–331430.29 (hereafter J0643–3314) was selected as a blazar candidate by its colors and compactness in archival radio images. In Xie et al. 2024, we introduce an algorithm to recognize likely blazars using the morphology observed in the 3 GHz Very Large Array Sky Survey. According to our algorithm, J0643–3314 is unlikely a blazar based on the two-sided jet seen in VLASS. To validate the result of our algorithm, we investigate this source further. From the extended two-sided jet lobes, the upturn radio spectrum, and the broad emission lines in the follow-up spectrum, we robustly conclude that J0643–3314 is not a blazar. We spectroscopically confirm it as a radio-loud AGN at z = 0.3, with a projected jet size of 100.4 kpc. We estimate its bolometric luminosity to be ∼6×10<SUP>44</SUP> erg s<SUP>‑1</SUP>, black hole mass of ∼2×10<SUP>8</SUP> M <SUB>⊙</SUB>, and Eddington ratio of ∼0.02 from Hβ and Hα broad emission lines.
|
[
164,
16
] |
[
"blazars",
"active galactic nuclei"
] |
2023ApJ...953..100L
|
The Nature of γ-Ray Emission from HESS J1912+101
|
Since the discovery of HESS J1912+101 at teraelectronvolt energies, its nature has been extensively studied. Due to the absence of X-ray and radio counterparts, whether its γ-ray emission is produced by relativistic electrons or ions is still a matter of debate. We reanalyze its megaelectronvolt to gigaelectronvolt γ-ray emission using 14 yr of Pass 8 data of the Fermi-LAT, and find that the gigaelectronvolt γ-ray emission is more extended than the teraelectronvolt shell detected by H. E. S. S. and flux above 10 GeV from the northern half is much higher than that from the southern half, where there is evident interaction between shocks and molecular clouds. As a consequence, the gigaelectronvolt spectrum of the northern half (with an index of 2.19 ± 0.12) is much harder than that in the south (with an index of 2.72 ± 0.08), and the overall gigaelectronvolt spectrum shows a concave shape, which is distinct from most γ-ray supernova remnants (SNRs). In combination with the teraelectronvolt spectrum, the overall γ-ray spectrum can be fitted with a broken power-law model for trapped ions and a low energy component due to escaping ions. The diffusion coefficient for escaping ions however needs to be proportional to the energy, implying that the low energy component may also be attributed to ions accelerated via recent shock-cloud interactions. A hadronic origin for the γ-ray emission is therefore favored and the overall emission properties are consistent with ion acceleration by SNR shocks. On the other hand, it is still undeniable that stellar cluster or PWN may have some contribution in some parts of this extended source.
|
[
1667,
1072,
739
] |
[
"supernova remnants",
"molecular clouds",
"high energy astrophysics"
] |
2024ApJ...969...52S
|
High-precision Transition Energy Measurements of Neon-like Fe XVII Ions
|
We improve by a factor of 4–20 the energy accuracy of the strongest soft X-ray transitions of Fe XVII ions by resonantly exciting them in an electron beam ion trap with a monochromatic beam at the P04 beamline of the PETRA III synchrotron facility. By simultaneously tracking instantaneous photon-energy fluctuations with a high-resolution photoelectron spectrometer, we minimize systematic uncertainties down to 10–15 meV, or velocity equivalent ±∼5 km s<SUP>‑1</SUP> in their rest energies, substantially improving our knowledge of this key astrophysical ion. Our large-scale configuration-interaction computations include more than 4 million relativistic configurations and agree with the experiment at a level without precedent for a 10-electron system. Thereby, theoretical uncertainties for interelectronic correlations become far smaller than those of quantum electrodynamics (QED) corrections. The present QED benchmark strengthens our trust in future calculations of many other complex atomic ions of interest to astrophysics, plasma physics, and the development of optical clocks with highly charged ions.
|
[
2064,
2004,
2085,
2099,
2371,
2093,
1544
] |
[
"atomic data benchmarking",
"laboratory astrophysics",
"line positions",
"atomic spectroscopy",
"experimental data",
"theoretical techniques",
"space plasmas"
] |
2023PSJ.....4..221S
|
Material around the Centaur (2060) Chiron from the 2018 November 28 UT Stellar Occultation
|
A stellar occultation of Gaia DR3 2646598228351156352 by the Centaur (2060) Chiron was observed from the South African Astronomical Observatory on 2018 November 28 UT. Here we present a positive detection of material surrounding Chiron from the 74-inch telescope for this event. Additionally, a global atmosphere is ruled out at the tens of microbars level for several possible atmospheric compositions. There are multiple 3σ drops in the 74-inch light curve: three during immersion and two during emersion. Occulting material is located between 242 and 270 km from the center of the nucleus in the sky plane. Assuming the ring-plane orientation proposed for Chiron from the 2011 occultation, the flux drops are located at 352, 344, and 316 km (immersion) and 357 and 364 km (emersion) from the center, with normal optical depths of 0.26, 0.36, and 0.22 (immersion) and 0.26 and 0.18 (emersion) and equivalent widths between 0.7 and 1.3 km. This detection is similar to the previously proposed two-ring system and is located within the error bars of that ring-pole plane; however, the normal optical depths are less than half of the previous values, and three features are detected on immersion. These results suggest that the properties of the surrounding material have evolved between the 2011, 2018, and 2022 observations.
|
[
215,
2135,
1254,
1469
] |
[
"centaur group",
"stellar occultation",
"planetary rings",
"small solar system bodies"
] |
2021ApJ...910...34G
|
Convective Overshooting in the Envelopes of A-type Stars Using the k-ω Model
|
Mixing between convective zones is quite uncertain in the envelopes of A-type stars. To study the mixing in A-type envelopes, we use a new convection model, the k-ω model, in the MESA stellar evolution code. Using the k-ω model, we find that the overshooting regions of the He II and H/He I convection zones are integrated with each other. There is material exchange between the He II and H/He I convection zones through overshooting, in agreement with recent numerical simulations.We obtain the overshooting distance of about 3.5H<SUB>p</SUB> below the base of the H/He I convection zone in a 2.3 M<SUB>⊙</SUB> star. There are two overshooting regions beyond the He II convection zone in the same stellar model. We obtain that the overshooting distance of the upper one is about 3.9H<SUB>p</SUB> and about 2.0H<SUB>p</SUB> for the lower one. We find that the turbulent diffusion effect is particularly strong in the convective envelopes of A-type stars. In addition, we find that the typical size of the convective rolling cells is restricted by the actual thickness of the convective zones, because the thickness of the convection zones are usually smaller than or approximately equal to the local pressure scale height. Through comparisons with the results of the k-ω model, we find that a suitable value of f<SUB>ov</SUB> is about 0.45 for the H/He I convective overshooting region. It is about 0.27 for the upper He II convective overshooting region and about 0.25 for the lower one.
|
[
299,
5,
1599
] |
[
"stellar convection envelopes",
"a stars",
"stellar evolution"
] |
2023PSJ.....4..196N
|
Fitting Thermal Evolution Models to the Chronological Record of Erg Chech 002 and Modeling the Ejection Conditions of the Meteorite
|
The history of accretion and differentiation processes in the planetesimals is provided by various groups of meteorites. Sampling different parent body layers, they reveal the circumstances of the metal-silicate segregation and the internal structures of the protoplanets. The ungrouped achondrite Erg Chech 002 (EC 002) added to the suite of samples from primitive igneous crusts. Here we present models that utilize thermochronological data for EC 002 and fit the accretion time and size of its parent body to these data. The U-corrected Pb-Pb pyroxene, Pb-Pb phosphate, and Ar-Ar ages used imply a best-fit planetesimal with a radius of 20-30 km that formed at 0.1 Ma after calcium-aluminum-rich inclusions. Its interior melted early and differentiated by 0.5 Ma, allowing core and mantle formation with a transient lower mantle magma ocean and a melt fraction of <25% at the meteorite layering depth. EC 002 formed from this melt at a depth of 0.8 km in a partially differentiated region covered by an undifferentiated crust. By simulating collisions with impactors of different sizes and velocities, we analyzed the minimum ejection conditions of EC 002 from its original parent body and the surface composition of the impact site. The magma ocean region distinct from the layering depth of EC 002 implies that it was not involved in the EC 002 genesis. Our models estimate closure temperatures for the Al-Mg ages as 1030-1200 K. A fast parent body cooling attributes the late Ar-Ar age to a local reheating by another, late impact.
|
[
1248,
1259,
72,
1038,
15,
332,
14,
779
] |
[
"planetary interior",
"planetesimals",
"asteroids",
"meteorites",
"achondrites",
"cosmochronology",
"accretion",
"impact phenomena"
] |
2020PSJ.....1...63C
|
The Effects of Waves on the Meridional Thermal Structure of Jupiter's Stratosphere
|
A thermal oscillation in Jupiter's equatorial stratosphere, thought to have ∼4 Earth year period, was first discovered in 7.8 μm imaging observations from the 1980s and 1990s. Such imaging observations were sensitive to the 10-20 hPa pressure region in the atmosphere. More recent 7.8 μm long-slit high-spectroscopic observations from 2012 to 2017 taken using the Texas Echelon cross-dispersed Echelle Spectrograph (TEXES), mounted on the NASA Infrared Telescope Facility (IRTF), have vertically resolved this phenomenon's structure, and show that it spans a range of pressure from 2 to 20 hPa. The TEXES instrument was mounted on the Gemini North telescope in March 2017, improving the diffraction-limited spatial resolution by a factor of ∼2.5 compared with that offered by the IRTF. This Gemini spatial scale sensitivity study was performed in support of the longer-termed Jupiter monitoring being performed at the IRTF. We find that the spatial resolution afforded by the smaller 3 m IRTF is sufficient to spatially resolve the 3D structure of Jupiter's equatorial stratospheric oscillation by comparing the thermal retrievals of IRTF and Gemini observations. We then performed numerical simulations in a general circulation model to investigate how the structure of Jupiter's stratosphere responds to changes in the latitudinal extent of wave forcing in the troposphere. We find our simulations produce a lower limit in meridional wave forcing of ±7° (planetocentric coordinates) centered about the equator. This likely remains constant over time to produce off-equatorial thermal oscillations at ±13°, consistent with observations spanning nearly four decades.
|
[
873,
1640,
791
] |
[
"jupiter",
"stratosphere",
"infrared observatories"
] |
2024ApJ...966..226K
|
On Innermost Stable Spherical Orbits near a Rotating Black Hole: A Numerical Study of the Particle Motion near the Plunging Region
|
According to general relativity, astrophysical black holes are described by a small number of parameters. Apart from the mass of the black hole (M), among the most interesting characteristics is the spin (a), which determines the degree of rotation, i.e., the angular momentum of the black hole. The latter is observationally constrained by the spectral and timing properties of the radiation signal emerging from an accretion disk of matter orbiting near the event horizon. In the case of the planar (standard, equatorial) accretion disk, this is the location of the innermost stable circular orbit that determines the observable radiation characteristics and allows us to measure the spin. In this paper, we discuss a more general case of the innermost stable spherical orbits (ISSOs) extending above and below the equatorial plane. To this end, we study the nonequatorial geodesic motion of particles following inclined, spherical, relativistically precessing trajectories with the aim of exploring the boundary between the regions of stable (energetically bound) and escaping (energetically unbound) motion. The concept of the radius of the ISSO should play a role in determining the inner rim of a tilted or geometrically thick accretion flow. We demonstrate that the region of inclined bound orbits has a complicated structure due to enhanced precession near the inner rim. We also explore the fate of particles launched below the radius of the marginally bound spherical orbit: these may either plunge into the event horizon or escape to radial infinity.
|
[
98,
641,
645,
14,
886
] |
[
"astrophysical black holes",
"general relativity",
"geodesics",
"accretion",
"kerr black holes"
] |
2022ApJ...929L..30H
|
Signature of Supersonic Turbulence in Galaxy Clusters Revealed by AGN-driven Hα Filaments
|
The hot intracluster medium (ICM) is thought to be quiescent with low observed velocity dispersions. Surface brightness fluctuations of the ICM also suggest that its turbulence is subsonic with a Kolmogorov scaling relation, indicating that the viscosity is suppressed and the kinetic energy cascades to small scales unscathed. However, recent observations of the cold gas filaments in galaxy clusters find that the scaling relations are steeper than that of the hot plasma, signaling kinetic energy losses and the presence of supersonic flows. In this work we use high-resolution simulations to explore the turbulent velocity structure of the cold filaments at the cores of galaxy clusters. Our results indicate that supersonic turbulent structures can be "frozen" in the cold gas that cools and fragments out of a fast, ~10<SUP>7</SUP> K outflow driven by the central active galactic nucleus (AGN), when the radiative cooling time is shorter than the dynamical sound-crossing time. After the cold gas formation, however, the slope of the velocity structure function (VSF) flattens significantly over short, ~10 Myr timescales. The lack of flattened VSF in observations of Hα filaments indicates that the Hα-emitting phase is short-lived for the cold gas in galaxy clusters. On the other hand, the ubiquity of supersonic turbulence revealed by observed filaments strongly suggests that supersonic outflows are an integral part of AGN-ICM interaction, and that AGN activity plays a crucial role at driving turbulence in galaxy clusters.
|
[
626,
535,
584,
858
] |
[
"galaxy winds",
"filamentary nebulae",
"galaxy clusters",
"intracluster medium"
] |
2020RNAAS...4..164L
|
A Search for the Guest Star Associated with Swift J1818-5937
|
We searched the possible historical records for the young magnetar Swift J1818-5937, and found a guest star in AD 1798 that might be associated with it.
|
[
1868,
1108,
992,
1668
] |
[
"history of astronomy",
"neutron stars",
"magnetars",
"supernovae"
] |
2024ApJ...966...32E
|
Early Planet Formation in Embedded Disks (eDisk). XIII. Aligned Disks with Nonsettled Dust around the Newly Resolved Class 0 Protobinary R CrA IRAS 32
|
Young protostellar binary systems, with expected ages less than ∼10<SUP>5</SUP> yr, are little modified since birth, providing key clues to binary formation and evolution. We present a first look at the young, Class 0 binary protostellar system R CrA IRAS 32 from the Early Planet Formation in Embedded Disks ALMA large program, which observed the system in the 1.3 mm continuum emission, <SUP>12</SUP>CO (2‑1), <SUP>13</SUP>CO (2‑1), C<SUP>18</SUP>O (2‑1), SO (6<SUB>5</SUB>‑5<SUB>4</SUB>), and nine other molecular lines that trace disks, envelopes, shocks, and outflows. With a continuum resolution of ∼0.″03 (∼5 au, at a distance of 150 pc), we characterize the newly discovered binary system with a separation of 207 au, their circumstellar disks, and a circumbinary disklike structure. The circumstellar disk radii are 26.9 ± 0.3 and 22.8 ± 0.3 au for sources A and B, respectively, and their circumstellar disk dust masses are estimated as 22.5 ± 1.1 M <SUB>⊕</SUB> and 12.4 ± 0.6 M <SUB>⊕</SUB>, respectively. The circumstellar disks and the circumbinary structure have well-aligned position angles and inclinations, indicating formation in a smooth, ordered process such as disk fragmentation. In addition, the circumstellar disks have a near/far-side asymmetry in the continuum emission, suggesting that the dust has yet to settle into a thin layer near the midplane. Spectral analysis of CO isotopologues reveals outflows that originate from both of the sources and possibly from the circumbinary disklike structure. Furthermore, we detect Keplerian rotation in the <SUP>13</SUP>CO isotopologues toward both circumstellar disks and likely Keplerian rotation in the circumbinary structure; the latter suggests that it is probably a circumbinary disk.
|
[
1300,
254
] |
[
"protoplanetary disks",
"close binary stars"
] |
2021ApJ...921L..24F
|
Transport of Interstellar Neutral Helium throughout the Heliosphere
|
A number of physical processes accompanying the solar wind interaction with the local interstellar medium (LISM) are governed by charge exchange between ions and neutral atoms of interstellar origin. A new, 3D, MHD-plasma/kinetic-neutral model is developed that self-consistently includes both neutral hydrogen and helium atoms, and their feedback on the plasma, through charge exchange and photoionization. Focusing on the transport of interstellar neutral helium, quantitative estimates are provided for bulk properties, deflection angles, and velocity distribution functions (VDFs) along the upwind direction. It is shown that the average deflection of secondary He atoms born in the outer heliosheath (OHS) from their original direction in the LISM is ~12° in front of the heliopause, and occurs in the directions parallel to the plane formed by the velocity and magnetic field vectors in the unperturbed LISM. While these properties are consistent with Interstellar Boundary Explorer observations of the "warm breeze," we show that charge exchange in the OHS leads to remarkable deviations of their VDF from the Maxwellian distribution. He atom filtration in the OHS results in a significant temperature anisotropy and VDF asymmetries, even for the primary helium atoms that experience no charge exchange at all. This is an entirely kinetic phenomenon that shows that primary He atoms observed at 1 au have distributions substantially different from those in the LISM.
|
[
847,
833,
851,
106,
2056,
707,
711
] |
[
"interstellar medium",
"interstellar atomic gas",
"interstellar plasma",
"astrosphere interstellar medium interactions",
"charge exchange ionization",
"heliopause",
"heliosphere"
] |
2022ApJ...939L..22V
|
The Challenge of Ruling Out Inflation via the Primordial Graviton Background
|
Recent debates around the testability of the inflationary paradigm raise the question of how to model-independently discriminate it from competing scenarios. We argue that a detection of the cosmic graviton background (CGB), the relic radiation from gravitons decoupling around Planck time, would rule out the inflationary paradigm, as realistic inflationary models would dilute the CGB to an unobservable level. The CGB contribution to the effective number of relativistic species, ΔN <SUB>eff,g </SUB> ≈ 0.054, is well within the reach of next-generation cosmological probes. We argue that detecting the high-frequency stochastic gravitational wave background associated to the CGB will be challenging but potentially feasible. We briefly discuss expectations within alternatives to inflation, focusing on bouncing cosmologies and emergent scenarios.
|
[
319,
678,
343,
1146,
29
] |
[
"cosmic inflation",
"gravitational waves",
"cosmology",
"observational cosmology",
"alternatives to cosmic inflation"
] |
2023ApJ...944L..53B
|
A Potential Site for Wide-orbit Giant Planet Formation in the IM Lup Disk
|
The radial transport, or drift, of dust has taken a critical role in giant planet formation theory. However, it has been challenging to identify dust drift pileups in the hard-to-observe inner disk. We find that the IM Lup disk shows evidence that it has been shaped by an episode of dust drift. Using radiative transfer and dust dynamical modeling we study the radial and vertical dust distribution. We find that high dust drift rates exceeding 110 M <SUB>⊕</SUB> Myr<SUP>-1</SUP> are necessary to explain both the dust and CO observations. Furthermore, the bulk of the large dust present in the inner 20 au needs to be vertically extended, implying high turbulence (α <SUB> z </SUB> ≳ 10<SUP>-3</SUP>) and small grains (0.2-1 mm). We suggest that this increased level of particle stirring is consistent with the inner dust-rich disk undergoing turbulence triggered by the vertical shear instability. The conditions in the IM Lup disk imply that giant planet formation through pebble accretion is only effective outside of 20 au. If such an early, high-turbulence inner region is a natural consequence of high dust drift rates, then this has major implications for understanding the formation regions of giant planets including Jupiter and Saturn.
|
[
1300,
492
] |
[
"protoplanetary disks",
"exoplanet formation"
] |
2023ApJ...953....9Z
|
Asteroseismic Investigation on KIC 10526294 to Probe Convective Core Overshoot Mixing
|
In the overshoot mixing model with an exponentially decreasing diffusion coefficient, the initial value of the diffusion coefficient plays a crucial role. According to the turbulent convective mixing model, the characteristic length of convection in the convection zone differs from that in the overshoot region, resulting in a rapid decrease of the diffusion coefficient near the convective boundary. To investigate this quick decrease, we conducted an asteroseismic study on the intermediate-mass slowly pulsating B-type star KIC 10526294. We generated stellar models with varied input parameters, including the overshoot parameters, and compared the resulting stellar oscillation periods with observations. To mitigate the potential issue arising from large steps in the stellar parameters and stellar age, we employed a comprehensive interpolation scheme for the stellar oscillatory frequencies, considering all stellar parameters and stellar age. Our analysis revealed that the quick decreasing of the diffusion coefficient has discernible effects on the stellar oscillations, and a quick decrease with 4 orders of magnitude shows the best oscillatory frequencies compared with the observations. This provides weak evidence in support of the prediction made by the turbulent convective mixing model. Furthermore, we examined the residuals of the oscillation periods and discovered a potential association between abundance anomalies in the buoyancy frequency profile and the oscillation-like patterns observed in the residuals.
|
[
73,
1606,
1605,
301
] |
[
"asteroseismology",
"stellar interiors",
"stellar inner cores",
"stellar convective zones"
] |
2020RNAAS...4..194L
|
Optical Transients Found by MASTER during the Observation of LIGO/VIRGO S200219ac Gravitational-wave Event
|
We present the results of MASTER Global Robotic Net optical observations of the region within the LIGO/Virgo S200219ac error-box, triggered during the O3 run. We observed 1124 square degrees inside the 3σ error box during a half month. We present the identified optical transients found during this study, which are not related to gravitational waves, and briefly discuss the MASTER observation strategy.
|
[
1957,
675,
1464,
920,
122
] |
[
"transient detection",
"gravitational wave astronomy",
"sky surveys",
"ligo",
"automatic patrol telescopes"
] |
2023ApJ...943...45M
|
A Red Giants' Toy Story. II. Understanding the Red-giant Branch Bump
|
The Red-Giant Branch Bump (RGBB) is one of the most noteworthy features in the red-giant luminosity function of stellar clusters. It is caused by the passage of the hydrogen-burning shell through the composition discontinuity left at the point of the deepest penetration by the convective envelope. When crossing the discontinuity the usual trend in increasing luminosity reverses for a short time before it increases again, causing a zig-zag in the evolutionary track. In spite of its apparent simplicity the actual physical reason behind the decrease in luminosity is not well understood and several different explanations have been offered. Here we use a recently proposed simple toy model for the structure of low-mass RGs, together with previous results, to show beyond reasonable doubt that the change in luminosity at the RGBB can be traced to the change in the mean molecular weight of the layers on top of the burning shell. And that these changes happen on a nuclear timescale. The change in the effective mean molecular weight, as the burning shell approaches the discontinuity, causes a drop in the temperature of the burning shell which is attenuated by the consequent feedback contraction of the layers immediately below the burning shell. Our work shows that, when applied correctly, including the feedback on the structure of the core together with the increase in the mass of the core, shell-source homology relations do a great quantitative job in explaining the properties of full evolutionary models at the RGBB.
|
[
1631,
1372,
1606,
1368,
1369
] |
[
"stellar structures",
"red giant stars",
"stellar interiors",
"red giant branch",
"red giant bump"
] |
2023ApJ...951..151C
|
Understanding Sun-as-a-Star Variability of Solar Balmer Lines
|
Precise, high-cadence, long-term records of stellar spectral variability at different temporal scales lead to better understanding of a wide variety of phenomena including stellar atmospheres and dynamos, convective motions, and rotational periods. Here, we investigate the variability of solar Balmer lines (Hα, β, γ, δ) observed by space-borne radiometers (OSIRIS, SCIAMACHY, OMI, and GOME-2), combining these precise, long-term observations with high-resolution data from the ground-based NSO/ISS spectrograph. We relate the detected variability to the appearance of magnetic features on the solar disk. We find that on solar-rotational timescales (about 1 month), the Balmer line activity indices (defined as line-core to line-wing ratios) closely follow variations in the total solar irradiance (which is predominantly photospheric), thus frequently (specifically, during passages of sunspot groups) deviating from behavior of activity indices that track chromospheric activity levels. On longer timescales, the correlation with chromospheric indices increases, with periods of low correlation or even anticorrelation found at intermediate timescales. Comparison of these observations with estimates from semiempirical irradiance reconstructions helps quantify the contributions of different magnetic and quiet features. We conclude that both the lower sensitivity to network and in part the higher sensitivity to filaments and prominences, may result in complex, time-dependent relationships between Balmer and other chromospheric indices observed for the Sun and solar-like stars. The fact that core and wings contribute in a similar manner to the variability, and current knowledge of Balmer-lines formation in stellar atmospheres, supports the notion that Balmer line core-to-wing ratio indices behave more like photospheric rather than chromospheric indices.
|
[
1475,
1487,
1490,
1494,
1495,
1521,
1501,
1650,
1553
] |
[
"solar activity",
"solar cycle",
"solar electromagnetic emission",
"solar faculae",
"solar filaments",
"solar radiation",
"solar spectral irradiance",
"sunspot cycle",
"spectral index"
] |
2023ApJ...958..136T
|
Identifying Physical Structures in Our Galaxy with Gaussian Mixture Models: An Unsupervised Machine Learning Technique
|
We explore the potential of the Gaussian mixture model (GMM), an unsupervised machine-learning method, to identify coherent physical structures in the interstellar medium. The implementation we present can be used on any kind of spatially and spectrally resolved data set. We provide a step-by-step guide to use these models on different sources and data sets. Following the guide, we run the models on NGC 1977, RCW 120, and RCW 49 using the [C II] 158 μm mapping observations from the SOFIA telescope. We find that the models identified six, four, and five velocity coherent physical structures in NGC 1977, RCW 120, and RCW 49, respectively, which are validated by analyzing the observed spectra toward these structures and by comparison to earlier findings. In this work we demonstrate that GMM is a powerful tool that can better automate the process of spatial and spectral analysis to interpret mapping observations.
|
[
1565,
1937
] |
[
"star forming regions",
"gaussian mixture model"
] |
2022ApJ...940...38H
|
Saturation Level of Turbulence in Collapsing Gas Clouds
|
We investigate the physical mechanism that determines the saturation level of the turbulence in collapsing gas clouds. We perform a suite of high-resolution numerical simulations that follow the collapse of turbulent gas clouds, with various effective polytropic exponents γ <SUB>eff</SUB>, initial Mach numbers ${{ \mathcal M }}_{0}$ , and initial turbulent seeds. Equating the energy injection rate from gravitational contraction and the dissipation rate of the turbulence, we obtain an analytic expression for the saturation level of the turbulence, and compare it with the numerical results. Consequently, the numerical results are well described by the analytic model, given that the turbulent driving scale in collapsing gas clouds is one-third the Jeans length of the collapsing core. These results indicate that the strength of the turbulence at first-core formations in the early universe/the present-day star formation process can be estimated solely by γ <SUB>eff</SUB>.
|
[
1285,
1282,
435,
1963,
267,
662
] |
[
"population iii stars",
"population i stars",
"early universe",
"hydrodynamics",
"collapsing clouds",
"gravitational collapse"
] |
2023ApJS..267...35Y
|
Advanced Γ Method for Small-scale Vortex Detection in the Solar Atmosphere
|
Ubiquitous vortical structures are considered to act as a natural source of various solar plasma phenomena, for example, a wide range of magnetohydrodynamic waves and jet excitations. This work aims to develop an advanced vortex detection algorithm based on the Γ method and using a separable convolution kernel technique. This method is applied to detect and analyze the photospheric vortices in 3D realistic magnetoconvection numerical and observational data. We present the advanced Γ method (AGM), and our results indicate that the AGM performs with better accuracy in comparison with the original Γ method. The AGM allows us to identify small- and large-scale vortices with no vortex interposition and without requiring the changing of the threshold. In this way, the nondetection issue is mostly prevented. It was found that the Γ method failed to identify the large and longer-lived vortices, which were detected by the AGM. The size of the detected vortical structures tends to vary over time, with most vortices shrinking toward their end. The vorticity at the center is also not constant, presenting a sharp decay as the vortex ceases to exist. Due to its capability of identifying vortices with minimum nondetection, the vortex properties-such as lifetime, geometry, and dynamics-are better captured by the AGM than by the Γ method. In this era of new high-resolution observation, the AGM can be used as a precise technique for identifying and performing statistical analysis of solar atmospheric vortices.
|
[
1477,
1478
] |
[
"solar atmosphere",
"solar atmospheric motions"
] |
2024ApJS..271...20C
|
A Study of Broad Emission Line and Doppler Factor Estimation for Fermi Blazars
|
In this work, we obtained a sample of 979 Fermi blazars with broad emission lines, including 701 objects collected from published works and 278 objects developed in this work. For the 278 objects, we made a crossmatch from three catalogs, the Fermi Large Area Telescope Fourth Source Catalog (4FGL), the Sloan Digital Sky Survey, and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, and calculated the broad-line region (BLR) luminosity. Then, we estimated the Doppler factor and studied the correlations between the BLR luminosities and the γ-ray luminosities, the synchrotron peak frequency (ν <SUB> p </SUB>), and Doppler factor (δ) for the whole sample. Our analyses and discussions came to the following main conclusions: For the 278 blazars, their BLR luminosity (log L <SUB>BLR</SUB>) ranges from 40.44 to 45.45 erg s<SUP>‑1</SUP>, with a mean value of 43.39 erg s<SUP>‑1</SUP>. The Doppler factor ranges from δ = 0.45 to δ = 88.52, with a mean value of 12.99 for the 979 Fermi blazars, which is consistent with the results in the literature. Both the BLR luminosity and the Doppler factor exhibit positive correlations with the γ-ray luminosity. The BLR luminosity is anticorrelated with synchrotron peak frequency, implying a Compton cooling. A line of $\mathrm{log}{L}_{\mathrm{BLR}}=1.58\mathrm{log}{\nu }_{p}-19.46$ separating BL Lacertae objects and flat-spectrum radio quasars was obtained in the diagram of $\mathrm{log}{\text{}}{L}_{\mathrm{BLR}}$ against $\mathrm{log}{\nu }_{p}$ using a machine-learning method. Based on the analysis of the equivalent width and the Doppler factors, we proposed five changing-look blazar candidates.
|
[
164,
16,
739,
870
] |
[
"blazars",
"active galactic nuclei",
"high energy astrophysics",
"jets"
] |
2020ApJ...899...59H
|
Magnetohydrodynamics with Post-Newtonian Corrections
|
Using the fully nonlinear and exact perturbation formulation with magnetohydrodynamics (MHD) in the Minkowski background, we derive first-order, post-Newtonian (1PN) equations without imposing the slicing (temporal gauge) condition. The 1PN-MHD formulation is complementary to our recently presented fully relativistic MHD combined with 0PN gravity available only in the maximal slicing. We present the 1PN-MHD equations in two gauge conditions previously used in the literature and provide gauge transformation relations between different gauges. We derive the PN effects on MHD waves in a static homogeneous medium.
|
[
1261,
1393,
1964,
101
] |
[
"plasma astrophysics",
"relativity",
"magnetohydrodynamics",
"astrophysical fluid dynamics"
] |
2022ApJ...937..116K
|
Comprehensive Analysis of the Neutrino Process in Core-collapsing Supernovae
|
We investigate the neutrino flavor change effects due to neutrino self-interaction and shock wave propagation, as well as the matter effects on the neutrino process in core-collapsing supernovae (CCSNe). For the hydrodynamics, we use two models: a simple thermal bomb model and a specified hydrodynamics model for SN1987A. For the presupernova model, we take an updated model, adjusted to explain SN1987A, which employs recent developments in the (n, γ) reaction rates for nuclei near the stability line (A ~ 100). As for the neutrino luminosity, we adopt two different models: equivalent neutrino luminosity and nonequivalent luminosity models. The latter is taken from a synthetic analysis of CCSN simulation data, which quantitatively presented the results obtained by various neutrino transport models. Relevant neutrino-induced reaction rates are calculated using a shell model for light nuclei and a quasiparticle random phase approximation model for heavy nuclei. For each model, we present abundances of the light nuclei (<SUP>7</SUP>Li, <SUP>7</SUP>Be, <SUP>11</SUP>B, and <SUP>11</SUP>C) and the heavy nuclei (<SUP>92</SUP>Nb, <SUP>98</SUP>Tc, <SUP>138</SUP>La, and <SUP>180</SUP>Ta) produced by the neutrino process. The light nuclei abundances turn out to be sensitive to the Mikheyev-Smirnov-Wolfenstein (MSW) region around O-Ne-Mg layer while the heavy nuclei are mainly produced prior to the MSW region. Through detailed analyses, we find that neutrino self-interaction becomes a key ingredient, in addition to the MSW effect, for understanding the neutrino process and the relevant nuclear abundances. The normal mass hierarchy is shown to be more compatible with the meteorite data. The main nuclear reactions for each nucleus are also investigated in detail.
|
[
1666,
1104,
503,
1102,
304
] |
[
"supernova neutrinos",
"neutrino oscillations",
"explosive nucleosynthesis",
"neutrino masses",
"core-collapse supernovae"
] |
2020ApJ...893...46V
|
The Fourth Fermi-GBM Gamma-Ray Burst Catalog: A Decade of Data
|
We present the fourth in a series of catalogs of gamma-ray bursts (GRBs) observed with Fermi's Gamma-ray Burst Monitor (Fermi-GBM). It extends the six year catalog by four more years, now covering the 10 year time period from trigger enabling on 2008 July 12 to 2018 July 11. During this time period GBM triggered almost twice a day on transient events, 2356 of which we identified as cosmic GRBs. Additional trigger events were due to solar flare events, magnetar burst activities, and terrestrial gamma-ray flashes. The intention of the GBM GRB catalog series is to provide updated information to the community on the most important observables of the GBM-detected GRBs. For each GRB the location and main characteristics of the prompt emission, the duration, peak flux, and fluence are derived. The latter two quantities are calculated for the 50-300 keV energy band, where the maximum energy release of GRBs in the instrument reference system is observed and also for a broader energy band from 10-1000 keV, exploiting the full energy range of GBM's low-energy detectors. Furthermore, information is given on the settings of the triggering criteria and exceptional operational conditions during years 7 to 10 in the mission. This fourth catalog is an official product of the Fermi-GBM science team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center.
|
[
205,
629
] |
[
"catalogs",
"gamma-ray bursts"
] |
2020ApJ...892...58H
|
M-dwarf Eclipsing Binaries with Flare Activity
|
The physical properties of 12 eclipsing binaries of M-type dwarfs with superflare activity are characterized by combining the ground-based spectroscopic measurements and the photometric light curves obtained by the Kepler Space Telescope. All of these binary systems have Algol-type orbital configurations. The primary components are mostly of the early M-type dwarfs (M0-M3). Even though the occurrence rate of large flares with energy >10<SUP>34</SUP> erg of the EBs is less than the hyperflaring M dwarfs, the corresponding cumulative flare frequency is in general about a factor of 10 higher than the single M dwarfs with flare activity. This might be the consequence of magnetic interaction between the primary and secondary component of individual binaries. The slow rotators are not as active as the fast rotators, some of which display a possible eclipsing effect in their flare activity.
|
[
1603
] |
[
"stellar flares"
] |
2022ApJ...933..232T
|
Radio Emission of Pulsars. II. Coherence Catalyzed by Cerenkov-unstable Shear Alfvén Waves
|
This paper explores small-scale departures from force-free electrodynamics around a rotating neutron star, extending our treatment of resistive instability in a quantizing magnetic field. A secondary, Cerenkov instability is identified: relativistic particles flowing through thin current sheets excite propagating charge perturbations that are localized near the sheets. Growth is rapid at wavenumbers below the inverse ambient skin depth k <SUB> p,ex</SUB>. Small-scale Alfvénic wavepackets are promising sources of coherent curvature radiation. When the group Lorentz factor ${\gamma }_{\mathrm{gr}}\lesssim {({k}_{p,\mathrm{ex}}{R}_{c})}^{1/3}\sim 100$ , where R <SUB> c </SUB> is the magnetic curvature radius, a fraction ~10<SUP>-3</SUP>-10<SUP>-2</SUP> of the particle kinetic energy is radiated into the extraordinary mode at a peak frequency ~10<SUP>-2</SUP> ck <SUB> p,ex</SUB>. Consistency with observations requires a high pair multiplicity (~10<SUP>3-5</SUP>) in the pulsar magnetosphere. Neither the primary, slow resistive instability nor the secondary, Alfvénic instability depend directly on the presence of magnetospheric gaps, and may activate where the mean current is fully supplied by outward drift of the corotation charge. The resistive mode is overstable and grows at a rate comparable to the stellar spin frequency; the model directly accommodates strong pulse-to-pulse radio flux variations and coordinated subpulse drift. Alfvén mode growth can track the local plasma conditions, allowing for lower-frequency emission from the outer magnetosphere. Beamed radio emission from charged packets with γ <SUB>gr</SUB> ~ 50-100 also varies on submillisecond timescales. The modes identified here will be excited inside the magnetosphere of a magnetar, and may mediate Taylor relaxation of the magnetic twist.
|
[
2089,
1353,
992,
994,
289
] |
[
"plasma physics",
"radio pulsars",
"magnetars",
"magnetic fields",
"compact radiation sources"
] |
2022ApJ...929...73L
|
The Regulated NiCu Cycles with the New <SUP>57</SUP>Cu(p,γ)<SUP>58</SUP>Zn Reaction Rate and Its Influence on Type I X-Ray Bursts: the GS 1826-24 Clocked Burster
|
During the X-ray bursts of GS 1826-24, a "clocked burster", the nuclear reaction flow that surges through the rapid-proton capture process path has to pass through the NiCu cycles before reaching the ZnGa cycles that moderate further hydrogen burning in the region above the germanium and selenium isotopes. The <SUP>57</SUP>Cu(p,γ)<SUP>58</SUP>Zn reaction that occurs in the NiCu cycles plays an important role in influencing the burst light curves found by Cyburt et al. We deduce the <SUP>57</SUP>Cu(p,γ)<SUP>58</SUP>Zn reaction rate based on the experimentally determined important nuclear structure information, isobaric-multiplet-mass equation, and large-scale shell-model calculations. Based on the isobaric-multiplet-mass equation, we propose a possible order of ${1}_{1}^{+}$ - and ${2}_{3}^{+}$ -dominant resonance states and constrain the resonance energy of the ${1}_{2}^{+}$ state. The latter reduces the contribution of the ${1}_{2}^{+}$ -dominant resonance state. The new reaction rate is up to a factor of 4 lower than the Forstner et al. rate recommended by JINA REACLIB v2.2 at the temperature regime sensitive to clocked bursts of GS 1826-24. Using the simulation from the one-dimensional implicit hydrodynamic code KEPLER to model the thermonuclear X-ray bursts of the GS 1826-24 clocked burster, we find that the new <SUP>57</SUP>Cu(p,γ)<SUP>58</SUP>Zn reaction rate, coupled with the latest <SUP>56</SUP>Ni(p,γ)<SUP>57</SUP>Cu and <SUP>55</SUP>Ni(p,γ)<SUP>56</SUP>Cu reaction rates, redistributes the reaction flow in the NiCu cycles and strongly influences the burst ash composition, whereas the <SUP>59</SUP>Cu(p,α)<SUP>56</SUP>Ni and <SUP>59</SUP>Cu(p,γ)<SUP>60</SUP>Zn reactions suppress the influence of the <SUP>57</SUP>Cu(p,γ)<SUP>58</SUP>Zn reaction and diminish the impact of nuclear reaction flow that bypasses the important <SUP>56</SUP>Ni waiting point induced by the <SUP>55</SUP>Ni(p,γ)<SUP>56</SUP>Cu reaction on the burst light curve.
|
[
1131,
503,
1129,
1108,
1128,
1814,
1965,
2077
] |
[
"nucleosynthesis",
"explosive nucleosynthesis",
"nuclear astrophysics",
"neutron stars",
"nuclear abundances",
"x-ray bursts",
"computational methods",
"nuclear physics"
] |
2020ApJ...889...79Y
|
On Using Inspiraling Supermassive Binary Black Holes in the PTA Frequency Band as Standard Sirens to Constrain Dark Energy
|
Supermassive binary black holes (SMBBHs) in galactic centers may radiate gravitational waves (GW) in the nano-Hertz frequency band, which are expected to be detected by pulsar timing arrays (PTAs) in the near future. GW signals from individual SMBBHs at cosmic distances, if detected by PTAs, are potentially powerful standard sirens that can be used to independently measure distances and thus put constraints on cosmological parameters. In this paper, we investigate the constraint that may be obtained on the equation of state (w) of dark energy by using those SMBBHs, expected to be detected by the PTAs in the Square Kilometre Array (SKA) era. By considering both the currently available SMBBH candidates and mock SMBBHs in the universe resulting from a simple galaxy major merger model, we find that ∼200-3000 SMBBHs with chirp mass >10<SUP>9</SUP> M<SUB>⊙</SUB> are expected to be detected with a signal-to-noise ratio >10 by SKA-PTA with conservative and optimistic settings and they can be used to put a constraint on w to an uncertainty of Δw ∼ 0.02-0.1. If further information on the mass and mass ratio of those SMBBHs can be provided by electromagnetic observations (e.g., chirp mass uncertainty ≲50%), the constraint may be further improved to a ≲0.01 level, as many more SMBBHs will be detected by SKA-PTA with relatively better distance measurements and can be used as the standard sirens.
|
[
1663,
678,
675,
351,
339,
16,
1922,
159,
1305
] |
[
"supermassive black holes",
"gravitational waves",
"gravitational wave astronomy",
"dark energy",
"cosmological parameters",
"active galactic nuclei",
"fisher's information",
"black hole physics",
"pulsar timing method"
] |
2020ApJ...905..133Z
|
Characterizing the Circumgalactic Medium of the Lowest-mass Galaxies: A Case Study of IC 1613
|
Using 10 sight lines observed with the Hubble Space Telescope/Cosmic Origins Spectrograph, we study the circumgalactic medium (CGM) and outflows of IC 1613, which is a low-mass (M<SUB>*</SUB> ∼ 10<SUP>8</SUP> M<SUB>⊙</SUB>), dwarf irregular galaxy on the outskirts of the Local Group. Among the sight lines, four are pointed toward UV-bright stars in IC 1613, and the other six sight lines are background QSOs at impact parameters from 6 kpc (<0.1R<SUB>200</SUB>) to 61 kpc (0.6R<SUB>200</SUB>). We detect a number of Si II, Si III, Si IV, C II, and C IV absorbers, most of which have velocities less than the escape velocity of IC 1613 and thus are gravitationally bound. The line strengths of these ion absorbers are consistent with the CGM absorbers detected in dwarf galaxies at low redshifts. Assuming that Si II, Si III, and Si IV comprise nearly 100% of the total silicon, we find 3% (∼8 × 10<SUP>3</SUP> M<SUB>⊙</SUB>), 2% (∼7 × 10<SUP>3</SUP> M<SUB>⊙</SUB>), and 32%-42% [∼(1.0-1.3) × 10<SUP>5</SUP> M<SUB>⊙</SUB>] of the silicon mass in the stars, interstellar medium, and within 0.6R<SUB>200</SUB> of the CGM of IC 1613. We also estimate the metal outflow rate to be ${\dot{{\rm{M}}}}_{\mathrm{out},{\rm{Z}}}\geqslant 1.1\times {10}^{-5}\,{{\rm{M}}}_{\odot }\,{\mathrm{yr}}^{-1}$ and the instantaneous metal mass loading factor to be η<SUB>Z</SUB> ≥ 0.004, which are in broad agreement with available observation and simulation values. This work is the first time a dwarf galaxy of such low mass is probed by a number of both QSO and stellar sight lines, and it shows that the CGM of low-mass, gas-rich galaxies can be a large reservoir enriched with metals from past and ongoing outflows.
|
[
1879,
929,
991,
1031,
417
] |
[
"circumgalactic medium",
"local group",
"magellanic stream",
"metallicity",
"dwarf irregular galaxies"
] |
2021ApJ...910..121N
|
On the Color-Metallicity Relation of the Red Clump and the Reddening toward the Magellanic Clouds
|
The zero point of the reddening toward the Large Magellanic Cloud (LMC) has been the subject of some dispute. Its uncertainty propagates as a systematic error for methods that measure the extragalactic distance scale through knowledge of the absolute extinction of LMC stars. In an effort to resolve this issue, we used three different methods to calibrate the most widely used metric to predict LMC extinction, the intrinsic color of the red clump, (V - I)<SUB>RC,0</SUB>, for the inner ∼3° of that galaxy. The first approach was to empirically calibrate the color zero points of the BaSTI isochrones over a wide metallicity range of Δ[Fe/H] ≈ 1.10 using measurements of red clump stars in 47 Tuc, the solar neighborhood, and NGC 6791. From these efforts, we also measure these properties of the solar neighborhood red clump, (V - I, G<SUB>BP</SUB> - K<SUB>s</SUB>, G - K<SUB>s</SUB>, G<SUB>RP</SUB> - K<SUB>s</SUB>, J - K<SUB>s</SUB>, H - K<SUB>s</SUB>, M<SUB>I</SUB>, M<SUB>Ks</SUB>)<SUB>RC,0</SUB> = (1.02, 2.75, 2.18, 1.52, 0.64, 0.15, -0.23, -1.63). The second and third methods were to compare the observed colors of the red clump to those of Cepheids and RR Lyrae in the LMC. With these three methods, we estimated the intrinsic color of the red clump of the LMC to be (V - I)<SUB>RC,0,LMC</SUB> = {≈0.93, 0.91 ± 0.02, 0.89 ± 0.02}, respectively, and similarly, using the first and third methods, we estimated (V - I)<SUB>RC,0,SMC</SUB> = {≈0.85, 0.84 ± 0.02}, respectively, for the Small Magellanic Cloud. We estimate the luminosities to be M<SUB>I,RC,LMC</SUB> = -0.26 and M<SUB>I,RC,SMC</SUB> = -0.37. We show that this has important implications for recent calibrations of the tip of the red giant branch in the Magellanic Clouds used to measure H<SUB>0</SUB>.
|
[
394,
1595,
2048,
903,
1468,
1410,
1413,
218,
2046
] |
[
"distance indicators",
"stellar distance",
"horizontal branch",
"large magellanic cloud",
"small magellanic cloud",
"rr lyrae variable stars",
"rrab variable stars",
"cepheid variable stars",
"stellar evolutionary models"
] |
2023PSJ.....4..246M
|
Deep Dielectric Breakdown of Silicates: Microstructural Damage and Implications for Lunar Space Weathering
|
Solar energetic particle events electrically charge the lunar surface and may produce electric fields sufficient to induce dielectric breakdown in regolith grains. We irradiated series of silicate minerals with electrons to determine their physical and chemical response to deep dielectric charging and subsequent breakdown. Two electrical phenomena, flashovers and subsurface dielectric breakdown, produced damage including erosional and eruptive channels, surface pits, comminuted grains, and melt and vapor deposits. Iron abundances strongly affected the scale of damage and the minimum fluence required to reach dielectric breakdown; higher iron abundances required higher fluences to reach the breakdown threshold and produced more areally dense damage with each event. If dielectric breakdown is a prominent space-weathering process on the Moon, it should contribute to differential weathering signatures across the lunar surface as a function of target composition.
|
[
2315,
1491
] |
[
"lunar regolith",
"solar energetic particles"
] |
2022RNAAS...6..268W
|
A VLA Light Curve Spanning 43.8 yr for the Compact Symmetric Object OQ 208
|
Compact symmetric objects are young, jetted active galactic nuclei defined in part by their slow radio continuum variability. Radio light curves spanning decades can help characterize their evolutionary trends. Here, we present a preliminary VLA light curve at 1.465 GHz for the compact symmetric object OQ 208, a frequently observed calibrator. The light curve spans 43.8 yr, or about 17% of OQ 208's estimated age. The light curve shows two distinct steady levels separated by a decade-long rise at a rate of about 1% yr<SUP>-1</SUP>, corresponding to a cumulative increase of about 12% in flux density.
|
[
16,
53,
1340,
1347,
2109
] |
[
"active galactic nuclei",
"aperture synthesis",
"radio continuum emission",
"radio jets",
"time domain astronomy"
] |
2022ApJ...938...64R
|
Active Learning for Computationally Efficient Distribution of Binary Evolution Simulations
|
Binary stars undergo a variety of interactions and evolutionary phases, critical for predicting and explaining observations. Binary population synthesis with full simulation of stellar structure and evolution is computationally expensive, requiring a large number of mass-transfer sequences. The recently developed binary population synthesis code POSYDON incorporates grids of MESA binary star simulations that are interpolated to model large-scale populations of massive binaries. The traditional method of computing a high-density rectilinear grid of simulations is not scalable for higher-dimension grids, accounting for a range of metallicities, rotation, and eccentricity. We present a new active learning algorithm, psy-cris, which uses machine learning in the data-gathering process to adaptively and iteratively target simulations to run, resulting in a custom, high-performance training set. We test psy-cris on a toy problem and find the resulting training sets require fewer simulations for accurate classification and regression than either regular or randomly sampled grids. We further apply psy-cris to the target problem of building a dynamic grid of MESA simulations, and we demonstrate that, even without fine tuning, a simulation set of only ~1/4 the size of a rectilinear grid is sufficient to achieve the same classification accuracy. We anticipate further gains when algorithmic parameters are optimized for the targeted application. We find that optimizing for classification only may lead to performance losses in regression, and vice versa. Lowering the computational cost of producing grids will enable new population synthesis codes such as POSYDON to cover more input parameters while preserving interpolation accuracies.
|
[
1857,
1907,
1914,
2153
] |
[
"astronomical simulations",
"classification",
"regression",
"multiple star evolution"
] |
2022ApJ...936...21Z
|
A Reliable Calibration of H II Galaxies Hubble Diagram with Cosmic Chronometers and Artificial Neural Network
|
The L-σ relation of H II galaxies (HIIGx) calibrated by a distance indicator is a reliable standard candle for measuring the Hubble constant H <SUB>0</SUB>. The most straightforward calibration technique anchors them with the first tier of distance ladders from the same galaxies. Recently another promising method that uses the cosmological model-independent cosmic chronometers as a calibrator has been proposed. We promote this technique by removing the assumptions about the cosmic flatness and using a nonparametric artificial neural network for the data reconstruction process. We observe a correlation between the cosmic curvature density parameter and the slope of the L-σ relation, thereby improving the reliability of the calibration. Using the calibrated HIIGx Hubble diagram, we obtain a Type Ia supernovae Hubble diagram free of the conventional assumption about H <SUB>0</SUB>. Finally we get a value of ${H}_{0}={65.9}_{-2.9}^{+3.0}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , which is compatible with the latest Planck 18 measurement.
|
[
759,
694,
1563,
758,
1858,
1933,
1728
] |
[
"hubble diagram",
"h ii regions",
"standard candles",
"hubble constant",
"astronomy data analysis",
"neural networks",
"type ia supernovae"
] |
2024ApJ...965....3Z
|
A Study of the Merging Dwarf Galaxy VCC322
|
Galaxy interactions and mergers can enhance or reduce star formation, but a complete understanding of the involved processes is still lacking. The effect of dwarf galaxy mergers is even less clear than their massive counterpart. We present a study on a dwarf merger remnant in the Virgo cluster, VCC322, which might form a triple system with VCC334 and VCC319. We identify a prominent long and straight tail-like substructure that has a size comparable to its host galaxy VCC322. By comparing the color–color (g ‑ r versus r ‑ H) distribution with simple stellar population models, we infer that the metallicity and stellar age of this tail are Z <SUB>⋆</SUB> ∼ 0.02 Z <SUB>⊙</SUB> and t <SUB>⋆</SUB> ∼ 10 Gyr, respectively. In VCC319, we find a sign of isophotal twisting. This suggests that VCC319 may be subject to tidal interaction. An analysis of the Sloan Digital Sky Survey optical spectra of VCC322 indicates mass- and light-weighted ages of about 10<SUP>9.8</SUP> yr and 10<SUP>7.5</SUP> yr, respectively, indicating an ongoing star formation activity. However, the star formation in VCC322 seems suppressed when compared to other star-forming dwarfs of comparable stellar masses. Our finding of shock excitation of optical emission lines indicates that interaction-induced shock may contribute to the heating of cold gas and suppression of star formation.
|
[
594,
611,
2125,
1569,
608
] |
[
"galaxy evolution",
"galaxy photometry",
"galaxy tails",
"star formation",
"galaxy mergers"
] |
2021ApJ...915...65M
|
Resolving the Emission Regions of the Crab Pulsar's Giant Pulses
|
The Crab pulsar has striking radio emission properties, with the two dominant pulse components-the main pulse and the interpulse-consisting entirely of giant pulses. The emission is scattered in both the Crab Nebula and the interstellar medium, causing multipath propagation and thus scintillation. We study the scintillation of the Crab's giant pulses using phased Westerbork Synthesis Radio Telescope data at 1668 MHz. We find that giant pulse spectra correlate at only ~2%, much lower than the one-third correlation expected from a randomized signal imparted with the same impulse response function. In addition, we find that the main pulse and the interpulse appear to scintillate differently; the 2D cross-correlation of scintillation between the interpulse and main pulse has a lower amplitude and is wider in time and frequency delay than the 2D autocorrelation of the main pulses. These lines of evidence suggest that the giant pulse emission regions are extended, and that the main pulse and interpulse arise in physically distinct regions that are resolved by the scattering screen. Assuming the scattering takes place in the nebular filaments, the emission regions are of order a light-cylinder radius, as projected on the sky. With further very long baseline interferometry and multifrequency data, it may be possible to measure the distance to the scattering screens, the size of giant pulse emission regions, and the physical separation between the pulse components.
|
[
1353,
855
] |
[
"radio pulsars",
"interstellar scintillation"
] |
2022AJ....163..261M
|
Confirmation of Water Absorption in the Thermal Emission Spectrum of the Hot Jupiter WASP-77Ab with HST/WFC3
|
Secondary eclipse observations of hot Jupiters can reveal both their compositions and thermal structures. Previous observations have shown a diversity of hot Jupiter eclipse spectra, including absorption features, emission features, and featureless blackbody-like spectra. We present a secondary eclipse spectrum of the hot Jupiter WASP-77Ab observed between 1 and 5 μm with the Hubble Space Telescope (HST) and the Spitzer Space Telescope. The HST observations show signs of water absorption indicative of a noninverted thermal structure. We fit the data with both a one-dimensional free retrieval and a grid of one-dimensional self-consistent forward models to confirm this noninverted structure. The free retrieval places a 3σ lower limit on the atmospheric water abundance of $\mathrm{log}({n}_{{{\rm{H}}}_{2}{\rm{O}}})\gt -4.78$ and cannot constrain the CO abundance. The grid fit produces a slightly superstellar metallicity and constrains the carbon-to-oxygen ratio to less than or equal to the solar value. We also compare our data to recent high-resolution observations of WASP-77Ab taken with the IGRINS/IGRINS spectrograph. We find that the best-fit model to the IGRINS data gives a reduced chi squared of χ<SUP>2</SUP> <SUB>ν</SUB> = 1.32 when compared to the WFC3 data. However, the metallicity derived from the IGRINS data is significantly lower than that derived from our self-consistent model fit. We find that this difference may be due to disequilibrium chemistry, and the varying results between the models applied here demonstrate the model dependence of derived metallicities when comparing to low-resolution, low-wavelength coverage data alone. Future work to combine observations from IGRINS, HST, and the James Webb Space Telescope will improve our estimate of the atmospheric composition of WASP-77Ab.
|
[
753,
509,
2021
] |
[
"hot jupiters",
"extrasolar gaseous giant planets",
"exoplanet atmospheric composition"
] |
2021ApJ...920..133H
|
Turbulent Magnetic Dynamos with Halo Lags, Winds, and Jets
|
This paper presents scale-invariant/self-similar galactic magnetic dynamo models based on the classic equations and compares them qualitatively to recently observed magnetic fields in edge-on spiral galaxies. We classify the axially symmetric dynamo magnetic field by its separate sources, advected flux, and subscale turbulence. We ignore the diffusion term under plausible physical conditions. There is a time dependence determined by globally conserved quantities. We show that magnetic scale heights increase with radius and wind velocity. We suggest that active galactic nucleus (AGN) outflow is an important element of the large-scale galactic dynamo, based on the dynamo action of increasing subscale vorticity. This leads us to predict a correlation between the morphology of coherent galactic magnetic field (i.e., extended polarized flux) and the presence of an AGN.
|
[
391,
507,
321
] |
[
"disk galaxies",
"extragalactic magnetic fields",
"cosmic magnetic fields theory"
] |
2022ApJ...927..127S
|
Another Look at Erupting Minifilaments at the Base of Solar X-Ray Polar Coronal "Standard" and "Blowout" Jets
|
We examine 21 solar polar coronal jets that we identify in soft X-ray images obtained from the Hinode/X-ray telescope (XRT). We identify 11 of these as blowout jets and four as standard jets (with six uncertain), based on their X-ray-spire widths being respectively wide or narrow (compared to the jet's base) in the XRT images. From corresponding extreme ultraviolet (EUV) images from the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA), essentially all (at least 20 of 21) of the jets are made by minifilament eruptions, consistent with other recent studies. Here, we examine the detailed nature of the erupting minifilaments (EMFs) in the jet bases. Wide-spire ("blowout") jets often have ejective EMFs, but sometimes they instead have an EMF that is mostly confined to the jet's base rather than ejected. We also demonstrate that narrow-spire ("standard") jets can have either a confined EMF, or a partially confined EMF where some of the cool minifilament leaks into the jet's spire. Regarding EMF visibility: we find that in some cases the minifilament is apparent in as few as one of the four EUV channels we examined, being essentially invisible in the other channels; thus, it is necessary to examine images from multiple EUV channels before concluding that a jet does not have an EMF at its base. The sizes of the EMFs, measured projected against the sky and early in their eruption, is 14″ ± 7″, which is within a factor of 2 of other measured sizes of coronal-jet EMFs.
|
[
1981,
1536,
1483,
1493
] |
[
"solar filament eruptions",
"solar x-ray emission",
"solar corona",
"solar extreme ultraviolet emission"
] |
2022ApJ...941...27L
|
Standard GRB Spectral Models "Misused"?
|
The standard model characterizing the gamma-ray burst (GRB) spectrum invokes a four-parameter empirical function, the so-called the BAND model. An alternative model named cutoff power law (COMP) implements a power law with an exponential cutoff. These functions achieve almost equally good fits on observed spectra, and are adopted in nearly all of the GRB literature. Here, we reanalyze the sample defined in Li et al. (39 bursts including 944 spectra). We classify the spectra by two methods: (1) checking their corner-corner plots of the posteriors to determine well-constrained β (BAND-better) and unconstrained β (COMP-better) categories; and (2) defining the four groups by difference of the deviance information criterion (DIC). We find inconsistent peaks of the parameter distributions between the BAND-better spectra (α = -0.64 ± 0.28 and ${\mathrm{log}}_{10}({{E}}_{{\rm{p}}})={\mathrm{log}}_{10}(191)\pm 0.41$ ) and the COMP-better spectra (α = -0.96 ± 0.33 and ${\mathrm{log}}_{10}({{E}}_{{\rm{p}}})={\mathrm{log}}_{10}(249)\pm 0.40$ ). With the statistically preferred model and vice versa the misused model defined based on DIC statistics, we also find that the fitted parameters obtained by the misused model (COMP) significantly deviate from those obtained by the statistically preferred model (BAND). This means that if a spectrum is statistically preferred, described as the BAND, applying COMP to derive the spectral parameters will prominently deviate from their intrinsic shape, therefore affecting the physical interpretation. Our analysis indicates that the better or statistically preferred model should be duly examined during GRB spectral analysis. In addition, the β distribution exhibits a bimodal structure containing the BAND-better and COMP-better spectra, respectively, implying that BAND and COMP both may have physical origin.
|
[
629,
1390,
1858
] |
[
"gamma-ray bursts",
"relativistic jets",
"astronomy data analysis"
] |
2022ApJ...940L..45H
|
CME-related Large Decreases in the Differential Phase Delay of Tianwen-1 DOR Signals
|
Differential phase delay is calculated for the differential one-way range (DOR) signals transmitted by Tianwen-1, the first Chinese Mars spacecraft that entered into the Mars orbit on 2021 February 10. Large decreases in the differential phase delay are identified in the DOR signals received by ground stations on 2021 March 23 and June 18. The decreases indicate sizable increases of the total electron content (TEC) along the DOR signal path between Tianwen-1 and the ground stations. The TEC increases are estimated to be 85 and 175 TEC units on 2021 March 23 and June 18, respectively. Evidence shows that they are caused by the sheath regions ahead of the coronal mass ejections (CMEs) that traversed the signal path on both days. The results represent the first observations of CME-related structures by the DOR signals and demonstrate the potential of DOR signals in remote sensing the interplanetary plasma structures in the solar wind.
|
[
1534,
310,
366,
1338,
2191
] |
[
"solar wind",
"solar coronal mass ejections",
"deep space probes",
"radio astronomy",
"remote sensing"
] |
2021PSJ.....2...69I
|
Dynamical Tides in Jupiter as Revealed by Juno
|
The Juno orbiter has continued to collect data on Jupiter's gravity field with unprecedented precision since 2016, recently reporting a nonhydrostatic component in the tidal response of the planet. At the mid-mission perijove 17, Juno registered a Love number k<SUB>2</SUB> = 0.565 ± 0.006 that is -4% ± 1% (1σ) from the theoretical hydrostatic ${k}_{2}^{(\mathrm{hs})}=0.590$ . Here we assess whether the aforementioned departure of tides from hydrostatic equilibrium represents the neglected gravitational contribution of dynamical tides. We employ perturbation theory and simple tidal models to calculate a fractional dynamical correction Δk<SUB>2</SUB> to the well-known hydrostatic k<SUB>2</SUB>. Exploiting the analytical simplicity of a toy uniform-density model, we show how the Coriolis acceleration motivates the negative sign in the Δk<SUB>2</SUB> observed by Juno. By simplifying Jupiter's interior into a coreless, fully convective, and chemically homogeneous body, we calculate Δk<SUB>2</SUB> in a model following an n = 1 polytrope equation of state. Our numerical results for the n = 1 polytrope qualitatively follow the behavior of the uniform-density model, mostly because the main component of the tidal flow is similar in each case. Our results indicate that the gravitational effect of the Io-induced dynamical tide leads to Δk<SUB>2</SUB> = - 4% ± 1%, in agreement with the nonhydrostatic component reported by Juno. Consequently, our results suggest that Juno obtained the first unambiguous detection of the gravitational effect of dynamical tides in a gas giant planet. These results facilitate a future interpretation of Juno tidal gravity data with the purpose of elucidating the existence of a dilute core in Jupiter.
|
[
1702,
873,
667,
627,
1248
] |
[
"tides",
"jupiter",
"gravitational fields",
"galilean satellites",
"planetary interior"
] |
2024ApJ...966..196M
|
Variability of Blue Supergiants in the LMC with TESS
|
The blue supergiant (BSG) problem, namely, the overabundance of BSGs inconsistent with classical stellar evolution theory, remains an open question in stellar astrophysics. Several theoretical explanations have been proposed, which may be tested by their predictions for the characteristic time variability. In this work, we analyze the light curves of a sample of 20 BSGs obtained from the Transiting Exoplanet Survey Satellite (TESS) mission. We report a characteristic signal in the low-frequency (f ≲ 2 day<SUP>‑1</SUP>) range for all our targets. The amplitude spectrum has a peak frequency of ∼0.2 day<SUP>‑1</SUP>, and we are able to fit it by a modified Lorentzian profile. The signal itself shows strong stochasticity across different TESS sectors, suggesting its driving mechanism happens on short (≲months) timescales. Our signals resemble those obtained for a limited sample of hotter OB stars and yellow supergiants, suggesting their possible common origins. We discuss three possible physical explanations: stellar winds launched by rotation, convection motions that reach the stellar surface, and waves from the deep stellar interior. The peak frequency of the signal favors processes related to the convective zone caused by the iron opacity peak, and the shape of the spectra might be explained by the propagation of high-order, damped gravity waves excited from that zone. We discuss the uncertainties and limitations of all these scenarios.
|
[
1580,
1916,
130
] |
[
"stellar activity",
"time series analysis",
"b supergiant stars"
] |
2023RNAAS...7..127S
|
Extratidal Members of Segue 3 are Rare and Difficult to Confirm
|
We simulate extratidal members of Segue 3, a sparse, faint, and small, ~2.6 Gyr halo cluster, and investigate their observational detectability. Using the Gala package to simulate Segue 3's potential tidal tails, we find that the tails are narrow, linear, and around 4°-6° in length: the tails' position angles and width are most sensitive to the uncertainties in the cluster's distance and mean proper motion. Post-processing the synthetic tail particles to assign realistic observational properties, we infer that Segue 3 would have close to 25 extra-tidal members with G ≤ 23, concentrated ≲1.°33 from the center of the cluster. The 11 candidate extratidal members identified by Fadely and collaborators are comparable in number, but significantly closer to the cluster center (d ~ 4') than these simulations predict. This analysis demonstrates the difficulty of identifying extratidal stars in the Milky Way's halo clusters, even in deep photometric surveys.
|
[
1567,
656,
1160
] |
[
"star clusters",
"globular star clusters",
"open star clusters"
] |
2021ApJS..254...29X
|
A New Fast Monte Carlo Code for Solving Radiative Transfer Equations Based on the Neumann Solution
|
In this paper, we propose a new Monte Carlo radiative transport (MCRT) scheme, which is based completely on the Neumann series solution of the Fredholm integral equation. This scheme indicates that the essence of MCRT is the calculation of infinite terms of multiple integrals in the Neumann solution simultaneously. Under this perspective, we redescribe the MCRT procedure systematically, in which the main work amounts to choosing an associated probability distribution function for a set of random variables and the corresponding unbiased estimation functions. We select a relatively optimal estimation procedure that has a lower variance from an infinite number of possible choices, such as term-by-term estimation. In this scheme, MCRT can be regarded as a pure problem of integral evaluation, rather than as the tracing of random-walking photons. Keeping this in mind, one can avert some subtle intuitive mistakes. In addition, the δ functions in these integrals can be eliminated in advance by integrating them out directly. This fact, together with the optimal chosen random variables, can remarkably improve the Monte Carlo (MC) computational efficiency and accuracy, especially in systems with axial or spherical symmetry. An MCRT code, Lemon (Linear integral Equations' Monte carlo solver based On the Neumann solution; the code is available on the GitHub codebase at https://github.com/yangxiaolinyn/Lemon, and version 2.0 is archived on Zenodo at https://doi.org/10.5281/zenodo.4686355), has been developed completely based on this scheme. Finally, we intend to verify the validation of Lemon; a suite of test problems mainly restricted to a flat spacetime has been reproduced, and the corresponding results are illustrated in detail.
|
[
293,
1336,
1335,
1967
] |
[
"computational astronomy",
"radiative transfer equation",
"radiative transfer",
"radiative transfer simulations"
] |
2023ApJ...955...93A
|
GRB-SN Association within the Binary-driven Hypernova Model
|
Observations of supernovae (SNe) Ic occurring after the prompt emission of long gamma-ray bursts (GRBs) are addressed within the binary-driven hypernova (BdHN) model where GRBs originate from a binary composed of a ~10M <SUB>⊙</SUB> carbon-oxygen (CO) star and a neutron star (NS). The CO core collapse gives the trigger, leading to a hypernova with a fast-spinning newborn NS (νNS) at its center. The evolution depends strongly on the binary period, P <SUB>bin</SUB>. For P <SUB>bin</SUB> ~ 5 min, BdHNe I occur with energies 10<SUP>52</SUP>-10<SUP>54</SUP> erg. The accretion of SN ejecta onto the NS leads to its collapse, forming a black hole (BH) originating the MeV/GeV radiation. For P <SUB>bin</SUB> ~ 10 min, BdHNe II occur with energies 10<SUP>50</SUP>-10<SUP>52</SUP> erg and for P <SUB>bin</SUB> ~ hours, BdHNe III occur with energies below 10<SUP>50</SUP> erg. In BdHNe II and III, no BH is formed. The 1-1000 ms νNS originates, in all BdHNe, the X-ray-optical-radio afterglows by synchrotron emission. The hypernova follows an independent evolution, becoming an SN Ic, powered by nickel decay, observable after the GRB prompt emission. We report 24 SNe Ic associated with BdHNe. Their optical peak luminosity and time of occurrence are similar and independent of the associated GRBs. From previously identified 380 BdHN I comprising redshifts up to z = 8.2, we analyze four examples with their associated hypernovae. By multiwavelength extragalactic observations, we identify seven new episodes, theoretically explained, fortunately not yet detected in Galactic sources, opening new research areas. Refinement of population synthesis simulations is needed to map the progenitors of such short-lived binary systems inside our galaxy.
|
[
629
] |
[
"gamma-ray bursts"
] |
2022ApJ...928..113K
|
CALLIOPE: Pseudospectral Shearing Magnetohydrodynamics Code with a Pencil Decomposition
|
The pseudospectral method is a highly accurate numerical scheme suitable for turbulence simulations. We have developed an open-source pseudospectral code, CALLIOPE, which adopts the P3DFFT library to perform a fast Fourier transform with the two-dimensional (pencil) decomposition of numerical grids. CALLIOPE can solve incompressible magnetohydrodynamics (MHD), isothermal compressible MHD, and rotational reduced MHD with parallel computation using very large numbers of cores (>10<SUP>5</SUP> cores for 2048<SUP>3</SUP> grids). The code can also solve for local magnetorotational turbulence in a shearing frame using the remapping method. CALLIOPE is currently the only pseudospectral code that can compute magnetorotational turbulence using pencil-domain decomposition. This paper presents the numerical scheme of CALLIOPE and the results of linear and nonlinear numerical tests, including compressible local magnetorotational turbulence with the largest grid number reported to date.
|
[
1261,
1966
] |
[
"plasma astrophysics",
"magnetohydrodynamical simulations"
] |
2024AJ....167..159L
|
In This Day and Age: An Empirical Gyrochronology Relation for Partially and Fully Convective Single Field Stars
|
Gyrochronology, the field of age dating stars using mainly their rotation periods and masses, is ideal for inferring the ages of individual main-sequence stars. However, due to the lack of physical understanding of the complex magnetic fields in stars, gyrochronology relies heavily on empirical calibrations that require consistent and reliable stellar age measurements across a wide range of periods and masses. In this paper, we obtain a sample of consistent ages using the gyro-kinematic age-dating method, a technique to calculate the kinematics ages of stars. Using a Gaussian process model conditioned on ages from this sample (∼1–14 Gyr) and known clusters (0.67–3.8 Gyr), we calibrate the first empirical gyrochronology relation that is capable of inferring ages for single, main-sequence stars between 0.67 and 14 Gyr. Cross-validating and testing results suggest our model can infer cluster and asteroseismic ages with an average uncertainty of just over 1 Gyr, and the inferred ages for wide binaries agree within 0.83 Gyr. With this model, we obtain gyrochronology ages for ∼100,000 stars within 1.5 kpc of the Sun with period measurements from Kepler and Zwicky Transient Facility and 384 unique planet host stars. A simple code is provided to infer gyrochronology ages of stars with temperature and period measurements.
|
[
1581,
1629,
205,
1930,
1000
] |
[
"stellar ages",
"stellar rotation",
"catalogs",
"gaussian processes regression",
"main sequence stars"
] |
2024ApJ...965..113I
|
Bell Instability–mediated Diffusive Shock Acceleration at Supernova Blast Wave Shock Propagating in the Interstellar Medium
|
Supernova blast wave shock is a very important site of cosmic-ray acceleration. However, the detailed physical process of acceleration, in particular, nonlinear interplay between cosmic-ray streaming and magnetic field amplification, has not been studied under a realistic environment. In this paper, using a unique and novel numerical method, we study cosmic-ray acceleration at supernova blast wave shock propagating in the interstellar medium with well-resolved magnetic field amplification by nonresonant hybrid instability (or Bell instability). We find that the magnetic field is mildly amplified under typical interstellar medium conditions that leads to maximum cosmic-ray energy ≃30 TeV for supernova remnants with age ≃1000 yr consistent with gamma-ray observations. The strength of the amplified magnetic field does not reach the so-called saturation level because the cosmic-ray electric current toward the shock upstream has a finite spatial extent, by which Bell instability cannot experience many e-folding times.
|
[
1667,
329
] |
[
"supernova remnants",
"cosmic rays"
] |
2022PSJ.....3..189L
|
Physical Characterization of 2015 JD<SUB>1</SUB>: A Possibly Inhomogeneous Near-Earth Asteroid
|
The surfaces of airless bodies such as asteroids are exposed to many phenomena that can alter their physical properties. Bennu, the target of the OSIRIS-REx mission, has demonstrated how complex the surface of a small body can be. In 2019 November, the potentially hazardous asteroid 2015 JD<SUB>1</SUB> experienced a close approach of 0.033 1 au from the Earth. We present results of the physical characterization of 2015 JD<SUB>1</SUB> based on ground-based radar, spectroscopy, and photometric observations acquired during 2019 November. Radar polarimetry measurements from the Arecibo Observatory indicate a morphologically complex surface. The delay-Doppler images reveal a contact binary asteroid with an estimated visible extent of ~150 m. Our observations suggest that 2015 JD<SUB>1</SUB> is an E-type asteroid with a surface composition similar to aubrites, a class of differentiated enstatite meteorites. The dynamical properties of 2015 JD<SUB>1</SUB> suggest that it came from the ν <SUB>6</SUB> resonance with Jupiter, and spectral comparison with major E-type bodies suggests that it may have been derived from a parental body similar to the progenitor of the E-type (64) Angelina. Significantly, we find rotational spectral variation across the surface of 2015 JD<SUB>1</SUB> from the red to blue spectral slope. Our compositional analysis suggests that the spectral slope variation could be due to the lack of iron and sulfides in one area of the surface of 2015 JD<SUB>1</SUB> and/or differences in grain sizes.
|
[
2209,
1092,
72,
1558,
1234,
1329
] |
[
"asteroid surfaces",
"near-earth objects",
"asteroids",
"spectroscopy",
"photometry",
"radar astronomy"
] |
2024ApJ...966..122Z
|
Spectroscopic Observations of the Solar Corona during the 2017 August 21 Total Solar Eclipse: Comparison of Spectral Line Widths and Doppler Shifts between Open and Closed Magnetic Structures
|
The spectroscopic observations presented here were acquired during the 2017 August 21 total solar eclipse (TSE) with a three-channel partially multiplexed imaging spectrometer operating at extremely high orders (>50). The 4 R <SUB>⊙</SUB> extent of the slit in the north–south direction scanned the corona starting from the central meridian out to approximately 1.0 R <SUB>⊙</SUB> off the east limb throughout totality. The line widths and Doppler shifts of the Fe X (637.4 nm) and Fe XIV (530.3 nm) emission lines, characteristic of 1.1 × 10<SUP>6</SUP> K and 1.8 × 10<SUP>6</SUP> K electron temperatures, respectively, varied across the different coronal structures intercepted by the slit. Fe XIV was the dominant emission in the closed fields of an active region and the base of a streamer, with relatively constant 20–30 km s<SUP>‑1</SUP> line widths independent of the height. In contrast, Fe X emission exhibited broader (>40 km s<SUP>‑1</SUP>) line widths in open fields, which increased with height, in particular in the polar coronal hole. Inferences of line widths and Doppler shifts were consistent with extreme ultraviolet (EUV) observations from the Hinode/EUV Imaging Spectrograph, as well as with the near-infrared Fe XIII 1074 nm line observed by Coronal Multichannel Polarimeter. The differences in the spectral line widths between distinct coronal structures are interpreted as an indication of the predominance of wave heating in open structures versus localized heating in closed structures. This study underscores the unparalleled advantages and the enormous potential of TSE spectroscopy in measuring line widths simultaneously in open and closed fields at high altitudes, with minimal exposure times, stray light levels, and instrumental widths.
|
[
1704,
1558,
2038,
1486,
1992,
1484
] |
[
"total eclipses",
"spectroscopy",
"solar coronal lines",
"solar coronal streamers",
"quiet solar corona",
"solar coronal holes"
] |
2020ApJ...899..126S
|
The Erratic Path to Coalescence of LISA Massive Black Hole Binaries in Subparsec-resolution Simulations of Smooth Circumnuclear Gas Disks
|
We perform high-resolution simulations to follow the orbital decay of 5 × 10<SUP>5</SUP> and 10<SUP>7</SUP> M<SUB>⊙</SUB> massive black hole (MBH) pairs embedded in a circumnuclear gas disk (CND), from the CND scale (100 pc) down to 0.1-0.01 pc, the scale at which a circumbinary disk (CBD) could form. The MBHs' erratic orbital evolution is characterized by three stages: (i) a slow initial decay that leads to some circularization; (ii) a fast-migration phase, analogous to type III migration for massive planets in protoplanetary disks, in which angular momentum is efficiently drained by disk-driven torques arising from the co-orbital region of the secondary MBH, at a distance of 1-3 Hill radii; and (iii) a very slow decay phase, in which orbital angular momentum can even increase. In this last stage, a CBD forms when the parsec-scale decay rate becomes small enough to allow sufficient time for a cavity to be carved. When this happens, the MBH separation nearly stalls in our higher-resolution run. We suggest an empirically modified gap-opening criterion that takes into account such timescale effects, as well as other deviations from standard assumptions. Interestingly, a CBD does not form in the lower-resolution runs, resulting in a faster subparsec decay. Our findings show that the subparsec MBH pairing in gaseous disks is a stochastic and fragile process. Additional mechanisms, such as the stellar-driven hardening, may be necessary to guarantee that the gravitational wave emission phase is entered and the MBHs become accessible to future detectors such as the Laser Interferometer Space Antenna.
|
[
1663,
581,
609
] |
[
"supermassive black holes",
"galaxy circumnuclear disk",
"galaxy nuclei"
] |
2021ApJ...921...51I
|
A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). IV. Rapidly Growing (Super)Massive Black Holes in Extremely Radio-loud Galaxies
|
We present the optical and infrared properties of 39 extremely radio-loud galaxies discovered by cross-matching the Subaru/Hyper Suprime-Cam (HSC) deep optical imaging survey and VLA/FIRST 1.4 GHz radio survey. The recent Subaru/HSC strategic survey revealed optically faint radio galaxies (RG) down to g<SUB>AB</SUB> ~ 26, opening a new parameter space of extremely radio-loud galaxies (ERGs) with radio-loudness parameter of $\mathrm{log}{{ \mathcal R }}_{\mathrm{rest}}\,=\mathrm{log}({f}_{1.4\mathrm{GHz},\mathrm{rest}}/{f}_{g,\mathrm{rest}})\gt 4$ . Because of their optical faintness and small number density of ~1 deg<SUP>-2</SUP>, such ERGs were difficult to find in the previous wide but shallow or deep but small area optical surveys. ERGs show intriguing properties that are different from the conventional RGs: (1) most ERGs reside above or on the star-forming main-sequence and some of them might be low-mass galaxies with $\mathrm{log}({M}_{\star }/{M}_{\odot })\lt 10$ . (2) ERGs exhibit a high specific black hole accretion rate, reaching the order of the Eddington limit. The intrinsic radio loudness ( ${{ \mathcal R }}_{\mathrm{int}}$ ), defined by the ratio of jet power over bolometric radiation luminosity, is one order of magnitude higher than that of radio quasars. This suggests that ERGs harbor a unique type of active galactic nuclei (AGN) that show both powerful radiations and jets. Therefore, ERGs are prominent candidates of very rapidly growing black holes reaching Eddington-limited accretion just before the onset of intensive AGN feedback.
|
[
1663,
16,
2134
] |
[
"supermassive black holes",
"active galactic nuclei",
"radio active galactic nuclei"
] |
2021ApJ...920...71A
|
Multi-scale Dust Polarization and Spiral-like Stokes-I Residual in the Class I Protostellar System TMC-1A
|
We have observed the Class I protostar TMC-1A in the Taurus molecular cloud using the Submillimeter Array (SMA) and the Atacama Large Millimeter/submillimeter Array (ALMA) in the linearly polarized 1.3 mm continuum emission at angular resolutions of ~3″ and ~0.3″, respectively. The ALMA observations also include CO, <SUP>13</SUP>CO, and C<SUP>18</SUP>O J = 2-1 spectral lines. The SMA observations trace magnetic fields on the 1000 au scale, the directions of which are neither parallel nor perpendicular to the outflow direction. Applying the Davis-Chandrasekhar-Fermi method to the SMA polarization angle dispersion, we estimate a field strength in the TMC-1A envelope of 1-5 mG. It is consistent with the field strength needed to reduce the radial infall velocity to the observed value, which is substantially less than the local freefall velocity. The ALMA polarization observations consist of two distinct components-a central component and a north/south component. The central component shows polarization directions in the disk minor axis to be azimuthal, suggesting dust self-scattering in the TMC-1A disk. The north/south component is located along the outflow axis and the polarization directions are aligned with the outflow direction. We discuss possible origins of this polarization structure, including grain alignment by a toroidal magnetic field and mechanical alignment by the gaseous outflow. In addition, we discover a spiral-like residual in the total intensity (Stokes I) for the first time. The C<SUP>18</SUP>O emission suggests that material in the spiral-like structure is infalling at a speed that is 20% of the local Keplerian speed.
|
[
235,
1278,
1302,
2050
] |
[
"circumstellar disks",
"polarimetry",
"protostars",
"low mass stars"
] |
2022ApJ...931...21V
|
Possible In Situ Formation of Uranus and Neptune via Pebble Accretion
|
The origin of Uranus and Neptune is still unknown. In particular, it has been challenging for planet formation models to form the planets in their current radial distances within the expected lifetime of the solar nebula. In this paper, we simulate the in situ formation of Uranus and Neptune via pebble accretion and show that both planets can form within ~3 Myr at their current locations, and have final compositions that are consistent with the heavy element to H-He ratios predicted by structure models. We find that Uranus and Neptune could have been formed at their current locations. In several cases a few earth masses (M <SUB>⊕</SUB> ) of heavy elements are missing, suggesting that Uranus and/or Neptune may have accreted ~1-3 M<SUB>⊕</SUB> of heavy elements after their formation via planetesimal accretion and/or giant impacts.
|
[
492,
2024,
2172,
509,
1241
] |
[
"exoplanet formation",
"extrasolar ice giants",
"extrasolar gaseous planets",
"extrasolar gaseous giant planets",
"planet formation"
] |
2023ApJ...943..109P
|
NuSTAR Observes Two Bulgeless Galaxies: No Hard X-Ray AGN Detected in NGC 4178 or J0851+3926
|
The discovery over the last several decades of low- and moderate-luminosity active galactic nuclei (AGNs) in disk-dominated galaxies-which show no "classical" bulges-suggests that secular mechanisms represent an important growth pathway for supermassive black holes in these systems. We present new follow-up NuSTAR observations of the optically elusive AGNs in two bulgeless galaxies, NGC 4178 and J0851+3926. Galaxy NGC 4178 was originally reported as hosting an AGN based on the detection of [Ne V] mid-infrared emission detected by Spitzer, and based on Chandra X-ray imaging, it has since been argued to host either a heavily obscured AGN or a supernova remnant. Galaxy J0851+3926 was originally identified as an AGN based on its Wide-Field Infrared Survey Explorer mid-IR colors, and follow-up near-infrared spectroscopy previously revealed a hidden broad-line region, offering compelling evidence for an optically elusive AGN. Neither AGN is detected within the new NuSTAR imaging, and we derive upper limits on the hard X-ray 10-24 keV fluxes of <7.41 × 10<SUP>-14</SUP> and <9.40 × 10<SUP>-14</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP> for the AGNs in NGC 4178 and J0851+3926, respectively. If these nondetections are due to large absorbing columns along the line of sight, the nondetections in NGC 4178 and J0851+3926 could be explained with column densities of log(N <SUB>H</SUB>/cm<SUP>2</SUP>) > 24.2 and 24.1, respectively. The nature of the nuclear activity in NGC 4178 remains inconclusive; it is plausible that the [Ne V] traces a period of higher activity in the past, but that the AGN is relatively quiescent now. The nondetection in J0851+3926 and multiwavelength properties are consistent with the AGN being heavily obscured.
|
[
16,
2017,
2033
] |
[
"active galactic nuclei",
"agn host galaxies",
"low-luminosity active galactic nuclei"
] |
2023ApJ...942...81C
|
Afterglow Polarization from Off-axis Gamma-Ray Burst Jets
|
As we further our studies on gamma-ray bursts (GRBs), via both theoretical models and observational tools, more and more options begin to open for exploration of its physical properties. As GRBs are transient events primarily dominated by synchrotron radiation, it is expected that the synchrotron photons emitted by GRBs should present some degree of polarization throughout the evolution of the burst. Whereas observing this polarization can still be challenging due to the constraints on observational tools, especially for short GRBs, it is paramount that the groundwork is laid for the day we have abundant data. In this work, we present a polarization model linked with an off-axis spreading top-hat jet synchrotron scenario in a stratified environment with a density profile n(r) ∝ r <SUP>-k </SUP>. We present this model's expected temporal polarization evolution for a realistic set of afterglow parameters constrained within the values observed in the GRB literature for four degrees of stratification k = 0, 1, 1.5, and 2 and two magnetic field configurations with high extreme anisotropy. We apply this model and predict polarization from a set of GRBs exhibiting off-axis afterglow emission. In particular, for GRB 170817A, we use the available polarimetric upper limits to rule out the possibility of an extremely anisotropic configuration for the magnetic field.
|
[
629
] |
[
"gamma-ray bursts"
] |
2020ApJ...892..123T
|
Constraints on the Intergalactic Magnetic Field from Bow Ties in the Gamma-Ray Sky
|
Pair creation on the cosmic infrared background and subsequent inverse-Compton scattering on the cosmic microwave background potentially reprocesses the TeV emission of blazars into faint GeV halos with structures sensitive to intergalactic magnetic fields (IGMF). Previous work has shown that these halos are then highly anisotropic and extended. If the coherence length of the IGMF is greater than the inverse-Compton cooling length of the pairs, then the orientation of the gamma-ray halo will be correlated with the direction of the magnetic field which is unknown and expected to change for each source. In order to constructively add each source we then use angular power spectra which are insensitive to the jet orientation. By looking at known GeV blazars detected by Fermi, we exclude the existence of an IGMF with coherence lengths >100 Mpc at greater than 3.9σ with current-day strengths in the range 10<SUP>-16</SUP> to 10<SUP>-15</SUP> G, and at 2σ from 10<SUP>-17</SUP> to 10<SUP>-14</SUP> G. This provides a direct measurement of the nonexistence of gamma-ray halos, providing an important check on previous results.
|
[
158,
637,
739
] |
[
"bl lacertae objects",
"gamma-rays",
"high energy astrophysics"
] |
2021ApJ...909..175Y
|
Effects of Forcing Mechanisms on the Multiscale Properties of Magnetohydrodynamics
|
We performed numerical simulations to study the response of magnetohydrodynamics (MHD) to large-scale stochastic forcing mechanisms parameterized by one parameter, 0 ≤ a ≤ 1, going from direct injection on the velocity field (a = 1) to stirring acts on the magnetic field only (a = 0). We study the multiscale properties of the energy transfer by splitting the total flux in channels mediated by (i) the kinetic nonlinear advection, (ii) the Lorentz force, (iii) the magnetic advection, and (iv) the magnetic stretching term. We further decompose the fluxes into two subchannels given by heterochiral and homochiral components in order to distinguish forward, inverse, and flux-loop cascades. We show that there exists a quasi-singular role of the magnetic forcing mechanism for a ∼ 1: a small injection on the magnetic field a < 1 can strongly deplete the mean flux of kinetic energy transfer throughout the kinetic nonlinear advection channel. We also show that this negligible mean flux is the result of a flux-loop balance between heterochiral (direct) and homochiral (inverse) transfers. Conversely, both homochiral and heterochiral channels transfer energy forward for the other three channels. Cross-exchange between velocity and the magnetic field is reversed around a = 0.4, and except when a ∼ 1, we always observe that heterochiral mixed velocity-magnetic energy triads tend to move energy from magnetic to velocity fields. Our study is an attempt to further characterize the multiscale nature of MHD dynamics by disentangling different properties of the total energy transfer mechanisms, which can be useful for improving subgrid modeling.
|
[
1964,
1966,
830
] |
[
"magnetohydrodynamics",
"magnetohydrodynamical simulations",
"interplanetary turbulence"
] |
2024ApJ...961...15N
|
Efficiency of Turbulent Reacceleration by Solenoidal Turbulence and Its Application to the Origin of Radio Megahalos in Cluster Outskirts
|
Recent radio observations with the Low Frequency Array (LOFAR) discovered diffuse emission extending beyond the scale of classical radio halos. The presence of such megahalos indicates that the amplification of the magnetic field and acceleration of relativistic particles are working in the cluster outskirts, presumably due to the combination of shocks and turbulence that dissipate energy in these regions. Cosmological magnetohydrodynamical (MHD) simulations of galaxy clusters suggest that solenoidal turbulence has a significant energy budget in the outskirts of galaxy clusters. In this paper, we explore the possibility that this turbulence contributes to the emission observed in megahalos through second-order Fermi acceleration of relativistic particles and magnetic field amplification by the dynamo. We focus on the case of A2255 and find that this scenario can explain the basic properties of the diffuse emission component that is observed under assumptions that are used in previous literature. More specifically, we conduct a numerical follow-up, solving the Fokker-Planck equation by using a snapshot of an MHD simulation and deducing the synchrotron brightness integrated along the lines of sight. We find that a volume-filling emission, ranging between 30% and almost 100% of the projected area, depending on our assumptions on the particle diffusion and transport, can be detected at LOFAR sensitivities. Assuming a magnetic field B ~ 0.2 μG, as derived from a dynamo model applied to the emitting region, we find that the observed brightness can be matched when ~1% of the solenoidal turbulent energy flux is channeled into particle acceleration.
|
[
584
] |
[
"galaxy clusters"
] |
2024RNAAS...8...36V
|
Dynamical Classifications of Multi-opposition TNOs as of 2023 December
|
We report the dynamical classifications of 3357 observed outer solar system objects listed as transneptunian objects (TNOs) or Centaurs by the Minor Planet Center. We use the Gladman et al. classification scheme to identify 28 Jupiter-coupled objects (all secure), 168 Centaurs (all secure), 234 scattering TNOs (70 secure/164 insecure), 204 detached TNOs (118 secure/86 insecure), 1650 classical TNOs (1494 secure/156 insecure), and 1073 resonant TNOs (907 secure, 166 insecure). Among the resonant TNOs, the most observationally populated resonance is the close-in 3:2 MMR with 452 objects, followed by the 2:1 with 105 objects, the 7:4 with 103 objects, the 5:3 with 68 objects, and the 5:2 with 56 objects. We discuss a few notable objects here, but all classifications and plots of the 10 Myr integrations are available in a linked GitHub repository.
|
[
1705,
893,
250,
376,
1396
] |
[
"trans-neptunian objects",
"kuiper belt",
"classical kuiper belt objects",
"detached objects",
"resonant kuiper belt objects"
] |
2021ApJ...911...17G
|
Jet-Accretion System in the Nearby mJy Radio Galaxies
|
It is generally thought that FRII radio galaxies host thin optically thick disks, while FRIs are powered by advection-dominated accretion flows. Sources with an efficient engine are optically classified as high-excitation radio galaxies (HERGs) and those with an inefficient motor as low-excitation radio galaxies (LERGs). Recently, the study of radio galaxies down to mJy fluxes has cast serious doubts on the LERG-FRI and HERG-FRII correspondence, revealing that many LERGs show FRII radio morphologies. The FR catalogs recently compiled by Capetti et al. and Baldi et al. have allowed us to explore this issue in the local (z ≤ 0.15) mJy universe. Our statistical study shows that the majority of nearby mJy objects are in a late stage of their life. FRII-LERGs appear more similar to the old FRI-LERGs than to the young FRII-HERGs. FRII-LERGs may be aged HERGs that, having exhausted their cold fuel, have changed their accretion regime or are a separate LERG class particularly efficient in launching jets. Exploiting the empirical relations that convert L<SUB>[O III]</SUB> and L<SUB>1.4 GHz</SUB> into accretion power and jet kinetic power, respectively, we observed that LERGs with similar masses and accretion rates seem to expel jets of different powers. We speculate that intrinsic differences related to the black hole properties (spin and magnetic field at its horizon) can determine the observed spread in jet luminosity. In this view, FRII-LERGs should have the fastest spinning black holes and/or the most intense magnetic fluxes. On the contrary, compact LERGs (i.e., FR0s) should host extremely slow black holes and/or weak magnetic fields.
|
[
2134
] |
[
"radio active galactic nuclei"
] |
2024ApJ...966L..38T
|
Expected Impact of Glints from Space Debris in the LSST
|
We examine the simple model put forth in a recent note by Loeb regarding the brightness of space debris in the size range of 1–10 cm and their impact on the Rubin Observatory Legacy Survey of Space and Time (LSST) transient object searches. Their main conclusion was that "image contamination by untracked space debris might pose a bigger challenge [than large commercial satellite constellations in Low-Earth orbit]." Following corrections and improvements to this model, we calculate the apparent brightness of tumbling low-Earth orbit (LEO) debris of various sizes, and we briefly discuss the likely impact and potential mitigations of glints from space debris in LSST. We find the majority of the difference in predicted signal-to-noise ratio (S/N), about a factor of 6, arises from the defocus of LEO objects due to the large Simonyi Survey Telescope primary mirror and finite range of the debris. The largest change from the Loeb estimates is that 1–10 cm debris in LEO pose no threat to LSST transient object alert generation because their S/N for detection will be much lower than estimated by Loeb due to defocus. We find that only tumbling LEO debris larger than 10 cm or with significantly greater reflectivity, which give 1 ms glints, might be detected with high confidence (S/N > 5). We estimate that only one in five LSST exposures low on the sky during twilight might be affected. More slowly tumbling objects of larger size can give flares in brightness that are easily detected; however, these will not be cataloged by the LSST Science Pipelines because of the resulting long streak.
|
[
1851,
2318,
1464,
686,
68
] |
[
"transient sources",
"light pollution",
"sky surveys",
"ground-based astronomy",
"artificial satellites"
] |
2024ApJ...968...27V
|
The SN 2023ixf Progenitor in M101. II. Properties
|
We follow our first paper with an analysis of the ensemble of the extensive preexplosion ground- and space-based infrared observations of the red supergiant (RSG) progenitor candidate for the nearby core-collapse supernova SN 2023ixf in Messier 101, together with optical data prior to the explosion obtained with the Hubble Space Telescope (HST). We have confirmed the association of the progenitor candidate with the supernova (SN), as well as constrained the metallicity at the SN site, based on SN observations with instruments at Gemini-North. The internal host extinction to the SN has also been confirmed from a high-resolution Keck spectrum. We fit the observed spectral energy distribution (SED) for the star, accounting for its intrinsic variability, with dust radiative-transfer modeling, which assumes a silicate-rich dust shell ahead of the underlying stellar photosphere. The star is heavily dust obscured, likely the dustiest progenitor candidate yet encountered. We found median estimates of the star's effective temperature and luminosity of 2770 K and 9.0 × 10<SUP>4</SUP> L <SUB>⊙</SUB>, with 68% credible intervals of 2340–3150 K and (7.5–10.9) × 10<SUP>4</SUP> L <SUB>⊙</SUB>, respectively. The candidate may have a Galactic RSG analog, IRC ‑10414, with a strikingly similar SED and luminosity. Via comparison with single-star evolutionary models we have constrained the initial mass of the progenitor candidate from 12 M <SUB>⊙</SUB> to as high as 14 M <SUB>⊙</SUB>. We have had available to us an extraordinary view of the SN 2023ixf progenitor candidate, which should be further followed up in future years with HST and the James Webb Space Telescope.
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[
1731,
732,
909,
988,
1599
] |
[
"type ii supernovae",
"massive stars",
"late-type stars",
"m supergiant stars",
"stellar evolution"
] |
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