PhysBERT
Collection
9 items
•
Updated
•
1
text
stringlengths 73
2.82k
| category
stringclasses 21
values |
|---|---|
Imprints of deviations from the gravitational inverse-square law on the
power spectrum of mass fluctuations: Deviations from the gravitational inverse-square law would imprint
scale-dependent features on the power spectrum of mass density fluctuations. We
model such deviations as a Yukawa-like contribution to the gravitational
potential and discuss the growth function in a mixed dark matter model with
adiabatic initial conditions. Evolution of perturbations is considered in
general non-flat cosmological models with a cosmological constant, and an
analytical approximation for the growth function is provided. The coupling
between baryons and cold dark matter across recombination is negligibly
affected by modified gravity physics if the proper cutoff length of the
long-range Yukawa-like force is > 10 h^{-1} Mpc. Enhancement of gravity affects
the subsequent evolution, boosting large-scale power in a way that resembles
the effect of a lower matter density. This phenomenon is almost perfectly
degenerate in power-spectrum shape with the effect of a background of massive
neutrinos. Back-reaction on density growth from a modified cosmic expansion
rate should however also affect the normalization of the power spectrum, with a
shape distortion similar to the case of a non-modified background. | astro-ph |
A New Weak Lensing Analysis of MS1224.7+2007: Galaxy cluster mass distributions are useful probes of Omega_0 and the nature
of the dark matter. Large clusters will distort the observed shapes of
background galaxies through gravitational lensing allowing the measurement of
the cluster mass distributions. For most cases, the agreement between weak
lensing and radial velocity mass measurements of clusters is reasonably good.
There is, however, one significant exception, the z=0.32 cluster MS1224.7+2007,
which has a lensing mass substantially larger than the virial mass and also a
very high mass-to-light ratio. Since this controversial object might be an
unusually dark mass a follow-up study is definitely warranted. In this paper we
study the mass and light distributions of MS1224+2007 out to a projected radius
of 800/h kpc by measuring the gravitationally-induced distortions of background
galaxies. We detect a shear signal in the background galaxies in the radial
range 27.5 arcsec < r < 275 arcsec at the 5.5 sigma level. The resultant mass
map exhibits a peak centered on the dominant cluster galaxy and strong evidence
for substructure which is even more strongly seen in the galaxy distribution.
Assuming all the detected shear is due to mass at z=0.32 we find cluster
mass-to-light ratio of M/L_R = 640 +/- 150. The mass profile is quite flat
compared to other clusters, disagreeing with a pseudo-singular isothermal
sphere at the 95% confidence level. Our mass and M/L estimates are consistent
with the previous weak lensing result. The discrepancy between the lensing and
virial mass remains although it might be partially explained by subclustering
and infall perpendicular to the line-of-site. This cluster remains a candidate
dark object deficient in baryons and as such severely tests cosmological
models. | astro-ph |
Spherical Gravitational Collapse of Annihilating Dark Matter and the
Minimum Mass of CDM Black Holes: Spherical gravitational collapse of a cold gas of annihilating particles
involves a competition between the free-fall rate $\propto\sqrt{\rho}$ and the
(s-wave) annihilation rate $\propto\rho$. Thus, there is a critical density
$\rhoann$ above which annihilation proceeds faster than free fall.
Gravitational collapse of a cloud of (initial) mass $M$ to a black hole is only
possible if $3/32\pi G^3M^2\lesssim\rhoann$, or $M\gtrsim\Mann\equiv (3/32\pi
G^3\rhoann)^{1/2}$. For a particle mass $m$ and freeze-out temperature
$T_f=m/x_f$, the minimum black hole mass is $\Mann\approx 10^{10}\msun
\times(x_f\sqrt{g_\star}/100\omcdm g_{\star S}m({\rm Gev}))$, where $g_{\star
S}$ and $g_\star$ are degeneracy factors. The formation of a black hole of
initial mass $M_{BH}$ is accompanied by the annihilation of about $M_{ann}$
released in a burst lasting a time $\sim GM_{BH}$ that could reach a total
annihilation luminosity $\sim 10^{59} {\rm erg s^{-1}}$. The absence of
astronomical observations of such spectacular events suggests either: (i) the
branching ratio for CDM annihilation to $e^{+}e^{-}$ pairs or quarks $\lesssim
10^{-10}$, while the branching ratio to $\nu{\bar{\nu}}$ is $\lesssim 10^{-5}$;
or (ii) CDM is not made of annihilating particles, but may be in some
non-annihilating form, such as axions; or (iii) CDM black holes never form. | astro-ph |
An outflow powers the optical rise of the nearby, fast-evolving tidal
disruption event AT2019qiz: At 66 Mpc, AT2019qiz is the closest optical tidal disruption event (TDE) to
date, with a luminosity intermediate between the bulk of the population and
iPTF16fnl. Its proximity allowed a very early detection and triggering of
multiwavelength and spectroscopic follow-up well before maximum light. The
velocity dispersion of the host galaxy and fits to the TDE light curve indicate
a black hole mass $\approx 10^6$ M$_\odot$, disrupting a star of $\approx 1$
M$_\odot$. Comprehensive UV, optical and X-ray data shows that the early
optical emission is dominated by an outflow, with a luminosity evolution $L
\propto t^2$, consistent with a photosphere expanding at constant velocity
($\gtrsim 2000$ km s$^{-1}$), and a line-forming region producing initially
blueshifted H and He II profiles with $v=3000-10000$ km s$^{-1}$. The fastest
optical ejecta approach the velocity inferred from radio detections (modelled
in a forthcoming companion paper from K.~D.~Alexander et al.), thus the same
outflow may be responsible for both the fast optical rise and the radio
emission -- the first time this connection has been observed in a TDE. The
light curve rise begins $29 \pm 2$ days before maximum light, peaking when the
photosphere reaches the radius where optical photons can escape. The
photosphere then undergoes a sudden transition, first cooling at constant
radius then contracting at constant temperature. At the same time, the
blueshifts disappear from the spectrum and Bowen fluorescence lines (N III)
become prominent, implying a source of far-UV photons, while the X-ray light
curve peaks at $\approx 10^{41}$ erg s$^{-1}$. Assuming that these X-rays are
from prompt accretion, the size and mass of the outflow are consistent with the
reprocessing layer needed to explain the large optical to X-ray ratio in this
and other optical TDEs, possibly favouring accretion-powered over
collision-powered outflow models. | astro-ph |
PyTransit: Fast and Easy Exoplanet Transit Modelling in Python: We present a fast and user friendly exoplanet transit light curve modelling
package PyTransit, implementing optimised versions of the Gimen\'ez and the
Mandel & Agol transit models. The package offers an object-oriented Python
interface to access the two models implemented natively in Fortran with OpenMP
parallelisation. A partial OpenCL version of the quadratic Mandel-Agol model is
also included for GPU-accelerated computations. The aim of PyTransit is to
facilitate the analysis of photometric time series of exoplanet transits
consisting of hundreds of thousands of datapoints, and of multi-passband
transit light curves from spectrophotometric observations, as a part of a
researcher's programming toolkit for building complex, problem-specific,
analyses. | astro-ph |
Formation of spiral structure from the violent relaxation of
self-gravitating disks: We present the numerical study of the formation of spiral structure in the
context of violent relaxation. Initial conditions are the out-of-equilibrium
disks of self-gravitating particles in rigid rotation. By that mechanism,
robust and non-stationary spiral arms can be formed within a few free-fall
times by the shearing of the mass ejection following the collapse. With a
closer look, we find different properties of the arms in connection with the
initial configuration. The winding degree tends to increase with initial
angular speed provided that a disk is thin. If disk surface is circular, both
number and position of arms are governed by the Poissonian density fluctuations
that produce more arms as more particles are introduced. On the contrary, if
the surface ellipticity is imposed, the number of arms and their placement are
effectively controlled. Otherwise, the increase of thickness leads to a
complicated outcome since the number of arms and winding degree are less
effectively controlled. We speculate that this complexity is caused by a strong
non-axisymmetric field during the violent relaxation that disorganizes the
pre-collapse motion and the concentration of particles. | astro-ph |
The Nature of Nearby Counterparts to Intermediate Redshift Luminous
Compact Blue Galaxies II. CO Observations: We present the results of a single-dish beam-matched survey of the three
lowest rotational transitions of CO in a sample of 20 local (D < 70 Mpc)
Luminous Compact Blue Galaxies (LCBGs). These ~L*, blue, high surface
brightness, starbursting galaxies were selected with the same criteria used to
define LCBGs at higher redshifts. Our detection rate was 70%, with those
galaxies having Lblue<7e9 Lsun no detected. We find the H2 masses of local
LCBGs range from 6.6e6 to 2.7e9 Msun, assuming a Galactic CO-to-H2 conversion
factor. Combining these results with our earlier HI survey of the same sample,
we find that the ratio of molecular to atomic gas mass is low, typically 5-10%.
Using a Large Velocity Gradient model, we find that the average gas conditions
of the entire ISM in local LCBGs are similar to those found in the centers of
star forming regions in our Galaxy, and nuclear regions of other galaxies. Star
formation rates, determined from IRAS fluxes, are a few solar masses per year,
much higher per unit dynamical mass than normal spirals. If this rate remains
constant, the molecular hydrogen depletion time scales are short, 10-200 Myr. | astro-ph |
Short gamma-ray burst jet propagation in binary neutron star merger
environments: The multimessenger event GW170817/GRB 170817A confirmed that binary neutron
star (BNS) mergers can produce short gamma-ray burst (SGRB) jets. This evidence
promoted new investigations on the mechanisms through which a BNS merger
remnant can launch such a powerful relativistic outflow and on the propagation
of the latter across the surrounding post-merger environment. In particular,
great strides have been made in jet propagation models, establishing
connections between the initial jet launching conditions, including the
incipient jet launching time (with respect to merger) and the injection
parameters, and the observable SGRB prompt and afterglow emission. However,
present semi-analytical models and numerical simulations (with one notable
exception) adopt simple hand-made prescriptions to account for the post-merger
environment, lacking a direct association with any specific merging BNS system.
Here, we present the first three-dimensional relativistic hydrodynamics
simulations of incipient SGRB jets propagating through a post-merger
environment that is directly imported from the outcome of a previous general
relativistic BNS merger simulation. Our results show that the evolution and
final properties of the jet can be largely affected by the anisotropies and the
deviations from axisymmetry and homologous expansion characterizing more
realistic BNS merger environments. In addition, we find that the inclusion of
the gravitational pull from the central compact object, often overlooked, can
have a major impact. Finally, we consider different jet launching times
referred to the same BNS merger model and discuss the consequences for the
ultimate jet properties. | astro-ph |
Long-term gamma-ray observations of the binary HESS J0632+057 with
H.E.S.S., MAGIC and VERITAS: The gamma-ray binary HESS J0632+057 has been observed at very-high energies
(E $>$ 100 GeV) for more than ten years by the major systems of imaging
atmospheric Cherenkov telescopes. We present a summary of results obtained with
the H.E.S.S., MAGIC, and VERITAS experiments based on roughly 440 h of
observations in total. This includes a discussion of an unusually bright TeV
outburst of HESS J0632+057 in January 2018. The updated gamma-ray light curve
now covers all phases of the orbital period with significant detections in
almost all orbital phases. Results are discussed in context with simultaneous
observations with the X-ray Telescope onboard the Neil Gehrels Swift
Observatory. | astro-ph |
The growth rate of cosmic structures in the local Universe with the
ALFALFA survey: We investigate the growth rate of structures in the local Universe. For this,
we use as a cosmological tracer the HI line extra-galactic sources from the
Arecibo Legacy Fast ALFA (ALFALFA) survey to obtain a measurement of the
normalized growth rate parameter, $f \sigma_{8}$, considered a powerful tool to
constrain alternative models of gravity. For these analyses, we calculate the
Local Group velocity due to the matter structures distribution in the ALFALFA
catalogue and compare it with the Local Group velocity relative to the Cosmic
Microwave Background frame to obtain the velocity scale parameter, $\beta$.
Using Monte Carlo realizations and log-normal simulations, our methodology
quantifies the errors introduced by shot-noise and partial sky coverage of the
analysed data. The measurement of the velocity scale parameter $\beta$, and the
calculation of the matter fluctuation of the cosmological tracer,
$\sigma_{8}^{\text{tr}}$, lead us to $f \sigma_{8} = 0.46 \pm 0.06$ at $\bar{z}
= 0.013$, in good agreement (at $1 \sigma$ level) with the value expected in
the $\Lambda$CDM concordance model. In addition, our analyses of the ALFALFA
sample also provide a measurement of the growth rate of structures $f \,=\,
0.56 \pm 0.07$, at $\bar{z} = 0.013$. | astro-ph |
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, 13CO, and C18O 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} free-fall 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 C18O emission suggests that
material in the spiral-like structure is infalling at a speed that is 20% of
the local Keplerian speed. | astro-ph |
Baseline correction for FAST radio recombination lines: a modified
penalized least squares smoothing technique: A pilot project has been proceeded to map 1 deg$^2$ on the Galactic plane for
radio recombination lines (RRLs) using the Five hundred meter Aperture
Spherical Telescope (FAST). The motivation is to verify the techniques and
reliabilities for a large-scale Galactic plane RRL survey with FAST aiming to
investigate the ionized environment in the Galaxy. The data shows that the
bandpass of the FAST 19 beam L-band is severely affected by radio frequency
interferences (RFIs) and standing wave ripples, which can hardly be corrected
by traditional low order polynomials. In this paper, we investigate a series of
penalized least square (PLS) based baseline correction methods for radio
astronomical spectra that usually contain weak signals with high level of
noise. Three promising penalized least squares based methods, AsLS, arPLS, and
asPLS are evaluated. Adopting their advantages, a modified method named rrlPLS
is developed to optimize the baseline fitting to our RRL spectra. To check
their effectiveness, the four methods are tested by simulations and further
verified using observed data sets. It turns out that the rrlPLS method, with
optimized parameter $\lambda = 2 \times 10^8$ , reveals the most sensitive and
reliable emission features in the RRL map. By injecting artificial line
profiles into the real data cube, a further evaluation of profile distortion is
conducted for rrlPLS. Comparing to simulated signals, the processed lines with
low signal-to-noise ratio are less affected, of which the uncertainties are
mainly caused by the rms noise. The rrlPLS method will be applied for baseline
correction in future data processing pipeline of FAST RRL survey. Configured
with proper parameters, the rrlPLS technique verified in this work may also be
used for other spectroscopy projects. | astro-ph |
Outflowing disk formation in B[e] supergiants due to rotation and
bi--stability in radiation driven winds: The effects of rapid rotation and bi-stability upon the density contrast
between the equatorial and polar directions of a B[e] supergiant are
re-investigated. Based upon a new slow solution for different high rotational
radiation driven winds (Cur\'e 2004) and the fact that bi--stability allows a
change in the line--force parameters ($\alpha$, $k$, and $\delta$), the
equatorial densities are about $10^2$--$10^4$ times higher than the polar ones.
These values are in qualitative agreement with the observations. | astro-ph |
The ESO Nearby Abell Cluster Survey IX. The morphology-radius and
morphology-density relations in rich galaxy clusters: We study the morphology-radius (MR-) and morphology-density (MD-) relations
for a sample of about 850 galaxies (with M <= -19.5) in 23 clusters from the
ENACS (ESO Nearby Abell Cluster Survey). On the basis of their radial
distributions we must distinguish: 1. brightest ellipticals (with M < -22), 2.
late spirals, and 3. the ensemble of less bright ellipticals, S0 galaxies and
early spirals. The latter have indistinguishable distributions of projected
radial distance R. The brightest ellipticals are most centrally concentrated,
the late spirals are almost absent from the central regions and the other
classes are intermediate. Radial segregation of the ellipticals is due to the
brightest ellipticals only, that of the spirals to the late spirals only. We
derive the MD-relation with two measures of projected density: one using the 10
nearest neighbours (Sigma10) and another using only the nearest neighbour
(Sigma1). The Sigma10 MD-relation only shows a significant difference between
early- and late-type galaxies, but the different galaxy types within those
classes are indistinguishable. However, The Sigma1 MD-relation shows that the
normal 'ellipticals' (with M >= -22), the S0 galaxies and the early spirals
have different Sigma1-distributions. The reason for this is that Sigma1 is much
less correlated with R than is Sigma10, and thus has much less cross-talk from
the (MR-) relation. On average, the 'normal' ellipticals populate environments
with higher projected density than do the S0 galaxies while the early spirals
populate even less dense environments. The segregation of the brightest
ellipticals and the late spirals is driven mostly by global factors, while the
segregation between 'normal' ellipticals, S0 galaxies and early spirals is
driven primarily by local factors. | astro-ph |
Distances of Quasars and Quasar-Like Galaxies: Further Evidence that
QSOs may be Ejected from Active Galaxies: If high-redshift QSOs are ejected from the nuclei of low-redshift galaxies,
as some have claimed, a large portion of their redshift must be intrinsic
(non-Doppler). If these intrinsic components have preferred values, redshifts
will tend to cluster around these preferred values and produce peaks in the
redshift distribution. Doppler ejection and Hubble flow components will broaden
each peak. Because ejection velocities are randomly directed and Hubble flow
components are always positive, in this model all peaks are expected to show an
asymmetry, extending further out in the red wing. If peaks are present showing
this predicted asymmetry, it can lead directly to an estimate of quasar
distances. Using two quasar samples, one with high redshifts and one with low,
it is shown here that not only do all peaks in these two redshift distributions
occur at previously predicted preferred values, they also all show the
predicted extra extension in the red wing. For the low and high redshift
samples the mean cosmological components are found to be z$_{c} \sim 0.024$ and
$\sim 0.066$, respectively. The difference can be explained by the improved
detection limit of the high redshift sample. These results offer further
evidence in favor of the model proposing that QSOs are ejected from active
galaxies. | astro-ph |
Probing the dynamical state of galaxy clusters: We show how hydrostatic equilibrium in galaxy clusters can be quantitatively
probed combining X-ray, SZ, and gravitational-lensing data. Our previously
published method for recovering three-dimensional cluster gas distributions
avoids the assumption of hydrostatic equilibrium. Independent reconstructions
of cumulative total-mass profiles can then be obtained from the gas
distribution, assuming hydrostatic equilibrium, and from gravitational lensing,
neglecting it. Hydrostatic equilibrium can then be quantified comparing the
two. We describe this procedure in detail and show that it performs well on
progressively realistic synthetic data. An application to a cluster merger
demonstrates how hydrostatic equilibrium is violated and restored as the merger
proceeds. | astro-ph |
Kilonova Light-Curve Interpolation with Neural Networks: Kilonovae are the electromagnetic transients created by the radioactive decay
of freshly synthesized elements in the environment surrounding a neutron star
merger. To study the fundamental physics in these complex environments,
kilonova modeling requires, in part, the use of radiative transfer simulations.
The microphysics involved in these simulations results in high computational
cost, prompting the use of emulators for parameter inference applications.
Utilizing a training set of 22248 high-fidelity simulations, we use a neural
network to efficiently train on existing radiative transfer simulations and
predict light curves for new parameters in a fast and computationally efficient
manner. Our neural network can generate millions of new light curves in under a
minute. We discuss our emulator's degree of off-sample reliability and
parameter inference of the AT2017gfo observational data. Finally, we discuss
tension introduced by multi-band inference in the parameter inference results,
particularly with regard to the neural network's recovery of viewing angle. | astro-ph |
Optical technologies for the observation of low Earth orbit objects: In order to avoid collisions with space debris, the near Earth orbit must be
continuously scanned by either ground- or spaced-based facilities. For the low
Earth orbit, radar telescopes are the workhorse for this task, especially due
to their continuous availability. However, optical observation methods can
deliver complementary information, especially towards high accuracy
measurements. Passive-optical observations are inexpensive and can yield very
precise information about the apparent position of the object in the sky via
comparison with background stars. However, the object's distance from the
observer is not readily accessible, which constitutes a major drawback of this
approach for the precise calculation of the orbital elements. Two experimental
methods have been devised to overcome this problem: Using two observatories a
few kilometres apart, strictly simultaneous observations of the same object
yield an accurate, instantaneous 3D position determination through measurement
of the parallax. If only one observatory is available, a pulsed laser can be
used in addition to the passive-optical channel to measure the distance to the
object, in a similar fashion as used by the satellite laser ranging community.
However, compared to conventional laser ranging, a stronger laser and more
elaborate tracking algorithms are necessary. The two approaches can also be
combined by illuminating the object with a pulsed laser from one observatory
and measuring the return times at both observatories. These techniques are
explored by German Aerospace Center in Stuttgart using its orbital debris
research observatory, in cooperation with the Satellite Laser Ranging station
in Graz and the Geodetic Observatory in Wettzell. This contribution will
present some of the results and plans for further measurement campaigns. | astro-ph |
Hector - a new massively multiplexed IFS instrument for the
Anglo-Australian Telescope: Hector will be the new massively-multiplexed integral field spectroscopy
(IFS) instrument for the Anglo-Australian Telescope (AAT) in Australia and the
next main dark-time instrument for the observatory. Based on the success of the
SAMI instrument, which is undertaking a 3400-galaxy survey, the integral field
unit (IFU) imaging fibre bundle (hexabundle) technology under-pinning SAMI is
being improved to a new innovative design for Hector. The distribution of
hexabundle angular sizes is matched to the galaxy survey properties in order to
image 90% of galaxies out to 2 effective radii. 50-100 of these IFU imaging
bundles will be positioned by 'starbug' robots across a new 3-degree field
corrector top end to be purpose-built for the AAT. Many thousand fibres will
then be fed into new replicable spectrographs. Fundamentally new science will
be achieved compared to existing instruments due to Hector's wider field of
view (3 degrees), high positioning efficiency using starbugs, higher
spectroscopic resolution (R~3000-5500 from 3727-7761A, with a possible redder
extension later) and large IFUs (up to 30 arcsec diameter with 61-217 fibre
cores). A 100,000 galaxy IFS survey with Hector will decrypt how the accretion
and merger history and large-scale environment made every galaxy different in
its morphology and star formation history. The high resolution, particularly in
the blue, will make Hector the only instrument to be able to measure
higher-order kinematics for galaxies down to much lower velocity dispersion
than in current large IFS galaxy surveys, opening up a wealth of new nearby
galaxy science. | astro-ph |
NBFTP: A Dedicated Data Transfer System for Remote Astronomical
Observation at Dome A: Dome A, Antarctica has been thought to be one of the best astronomical sites
on the earth since decades ago. From it was first visited by astronomers in
2008, dozens of facilities for astronomical observation and site testing were
deployed. Due to its special geographical location, the data and message
exchange between Dome A and the domestic control center could only depend on
Iridium. Because the link bandwidth of Iridium is extremely limited, meanwhile
the network traffic cost is quite expensive and the network is rather unstable,
the commonly used data transfer tools, such as rsync and scp, are not suitable
in this case. In this paper, we design and implement a data transfer tool
called NBFTP (narrow bandwidth file transfer protocol) for the astronomical
observation of Dome A. NBFTP uses a uniform interface to arrange all types of
data and matches specific transmission schemes for different data types
according to rules. Break-point resuming and extensibility functions are also
implemented. Our experimental results show that NBFTP consumes 60% less network
traffic than rsync when detecting the data pending to be transferred. And when
transferring small files of 1KB, the network traffic consumption of NBFTP is
40% less than rsync. However, as the file size increases, the network traffic
consumption of NBFTP tends to approach rsync, but it is still smaller than
rsync. | astro-ph |
Rapid Dissipation of Protoplanetary Disks in Ophiuchus: We present the results of an age determination study for pre-main sequence
stars in the Ophiuchus molecular cloud. The ages of eight pre-main sequence
stars were estimated from surface gravities derived from high-resolution
spectroscopy. The average age of the target stars was 0.7 Myr. By comparing the
individual age and the near-infrared color excess, we found that color excess
decreases gradually with a constant rate and the lifetime of the inner disk was
determined to be 1.2 Myr. The estimated lifetime is nearly a half of the time
compared to that of the pre-main sequence stars in the Taurus molecular cloud
estimated with the same method. This result indicates that the disk evolution
timescale depends on the environment of the star-forming region. | astro-ph |
Kinematics of OB Stars with Data from the LAMOST and Gaia Catalogues: We have analyzed the kinematics of OB stars from the list by Xiang et al.
(2021) that contains $\sim$13 000 single OB stars. For these stars there are
photometric distance estimates and proper motions from the Gaia catalogue and
line-of-sight velocities from the LAMOST catalogue. Based on a sample of single
OB stars and using the photometric distances and proper motions of stars from
the Gaia EDR3 catalogue, we have found the group velocity components
$(U_\odot,V_\odot,W_\odot)=(9.63,9.93,7.45)\pm(0.27,0.34,0.10)$ km s$^{-1}$,
and the following parameters of the angular velocity of Galactic rotation:
$\Omega_0=29.20\pm0.18$ km s$^{-1}$ kpc$^{-1}$, $\Omega^{'}_0=-4.150\pm0.046$
km s$^{-1}$ kpc$^{-2}$ and $\Omega^{''}_0=0.795\pm0.018$ km s$^{-1}$
kpc$^{-3}$, where the error per unit weight $\sigma_0$ is 9.56 km s$^{-1}$ and
$V_0=236.5\pm3.3$ km s$^{-1}$ (for the adopted $R_0=8.1\pm0.1$ kpc). Based on
the same OB stars, we have found the residual velocity dispersions
$(\sigma_1,\sigma_2,\sigma_3)=(15.13,9.69,7.98)\pm(0.07,0.05,0.04)$ km
s$^{-1}$. We show that using the line-of-sight velocities increases
significantly the space velocity dispersion and leads to a biased estimate of
the velocity $U_\odot$. A comparison of the distances scales used has shown
that the photometric distances from Xiang et al. (2021) should be lengthened
approximately by 10%. | astro-ph |
Accretion-disc model spectra for dwarf-nova stars: Radiation from accretion discs in cataclysmic variable stars (CVs) provides
fundamental information about the properties of these close binary systems and
about the physics of accretion in general. The detailed diagnostics of
accretion disc structure can be achieved by including in its description all
the relevant heating and cooling physical mechanism, in particular the
convective energy transport that, although dominant at temperatures less than
about 10 000 K, is usually not taken into account when calculating spectra of
accretion discs. We constructed a radiative transfer code coupled with a code
determining the disc's hydrostatic vertical structure. We have obtained for the
first time model spectra of cold, convective accretion discs. As expected,
these spectra are mostly flat in the optical wavelengths with no contribution
from the UV, which in quiescence must be emitted by the white dwarf. The disc
structures obtained with our radiative-transfer code compare well with the
solutions of equations used to describe the dwarf-nova outburst cycle according
to the thermal-viscous disc instability model thus allowing the two to be
combined. Our code allows calculating the spectral evolution of dwarf nova
stars through their whole outburst cycle, providing a new tool for testing
models of accretion discs in cataclysmic variables. We show that convection
plays an important role in determining the vertical disc structure and
substantially affects emitted spectra when, as often the case, it is effective
at optical depths tau ~ 1. The emergent spectrum is independent of the
parameters of the convection model.(Abstract shortened) | astro-ph |
Time-Variable Jet Ejections from RW Aur A, RY Tau and DG Tau: We present Gemini-NIFS, VLT-SINFONI and Keck-OSIRIS observations of
near-infrared [Fe II] emission associated with the well-studied jets from three
active T Tauri stars; RW Aur A, RY Tau and DG Tau taken from 2012-2021. We
primarily covered the redshifted jet from RW Aur A, and the blueshifted jets
from RY Tau and DG Tau, to investigate long-term time variabilities potentially
related to the activities of mass accretion and/or the stellar magnetic fields.
All of these jets consist of several moving knots with tangential velocities of
70-240 km s-1, ejected from the star with different velocities and at irregular
time intervals. Via comparison with literature, we identify significant
differences in tangential velocities for the DG Tau jet between 1985-2008 and
2008-2021. The sizes of the individual knots appear to increase with time, and
in turn, their peak brightnesses in the 1.644-micron emission decreased up to a
factor of ~30 during the epochs of our observations. A variety of the decay
timescales measured in the [Fe II] 1.644 micron emission can be attributed to
different pre-shock conditions if the moving knots are unresolved shocks.
However, our data do not exclude the possibility that these knots are due to
non-uniform density/temperature distributions with another heating mechanism,
or in some cases due to stationary shocks without proper motions. Spatially
resolved observations of these knots with significantly higher angular
resolutions are necessary to better understand their physical nature. | astro-ph |
Monte Carlo simulations of alternative sky observation modes with the
Cherenkov Telescope Array: We investigate possible sky survey modes with the Middle Sized Telescopes
(MST, aimed at covering the energy range from $\sim$100 GeV to 10 TeV)
subsystem of the Cherenkov Telescope Array (CTA). We use the standard CTA
tools, CORSIKA and sim_telarray, to simulate the development of gamma-ray
showers, proton background and the telescope response. We perform simulations
for the H.E.S.S.-site in Namibia, which is one of the candidate sites for the
CTA experiment. We study two previously considered modes, parallel and
divergent, and we propose a new, convergent mode with telescopes tilted toward
the array center. For each mode we provide performance parameters crucial for
choosing the most efficient survey strategy. For the non-parallel modes we
study the dependence on the telescope offset angle. We show that use of both
the divergent and convergent modes results in potential advantages in
comparison with use of the parallel mode. The fastest source detection can be
achieved in the divergent mode with larger offset angles ($\sim 6^{\circ}$ from
the Field of View centre for the outermost telescopes), for which the time
needed to perform a scan at a given sensitivity level is shorter by a factor of
$\sim$2.3 than for the parallel mode. We note, however, the direction and
energy reconstruction accuracy for the divergent mode is even by a factor of
$\sim 2$ worse than for other modes. Furthermore, we find that at high energies
and for observation directions close to the center of the array field of view,
the best performance parameters are achieved with the convergent mode, which
favors this mode for deep observations of sources with hard energy spectra. | astro-ph |
Radio Polarimetry Results for Young Southern Pulsars: We present radio polarimetry results for nine Southern pulsars. Six of the
nine are young, with characteristic ages less than 100 kyr and high spin-down
luminosities. All six show significant linear polarization, and we confirm a
previously noticed trend in which the degree of linear polarization increases
with spin-down luminosity. We have used the rotating vector model to fit the
observed position angle data for PSR J1513-5908 (B1509-58). We find that a
magnetic inclination angle alpha > 60 degrees is excluded at the 3-sigma level
in the fit, and that the geometry suggested by the morphology of an apparent
bipolar X-ray outflow is marginally inconsistent with a recent model of the
pulsar magnetosphere. | astro-ph |
Raytracing simulations of coupled dark energy models: Dark matter and dark energy are usually assumed to couple only
gravitationally. An extension to this picture is to model dark energy as a
scalar field coupled directly to cold dark matter. This coupling leads to new
physical effects, such as a fifth-force and a time-dependent dark matter
particle mass. In this work we examine the impact that coupling has on weak
lensing statistics by constructing realistic simulated weak-lensing maps using
raytracing techniques through N-body cosmological simulations. We construct
maps for different lensing quantities, covering a range of scales from a few
arcminutes to several degrees. The concordance $\Lambda$CDM model is compared
to different coupled dark energy models, described either by an exponential
scalar field potential (standard coupled dark energy scenario) or by a SUGRA
potential (bouncing model). We analyse several statistical quantities and our
results, with sources at low redshifts are largely consistent with previous
work on CMB lensing by Carbone et al., 2013. The most significant differences
from the $\Lambda$CDM model are due to the enhanced growth of the perturbations
and to the effective friction term in non-linear dynamics. For the most extreme
models, we see differences in the power spectra up to 40% compared to the
$\Lambda$CDM model. The different time evolution of the linear matter
overdensity can account for most of the differences, but when controlling for
this using a $\Lambda$CDM model having the same normalization, the overall
signal is smaller due to the effect of the friction term appearing in the
equation of motion for dark matter particles. | astro-ph |
Discovery of a bright microlensing event with planetary features towards
the Taurus region: a super Earth planet: The transient event labeled as TCP J05074264+2447555 recently discovered
towards the Taurus region was quickly recognized to be an ongoing microlensing
event on a source located at distance of only $700-800$ pc from Earth. Here, we
show that observations with high sampling rate close to the time of maximum
magnification revealed features that imply the presence of a binary lens system
with very low mass ratio components. We present a complete description of the
binary lens system which hosts an Earth-like planet with most likely mass of
$9.2\pm 6.6$ M$_{\oplus}$. Furthermore, the source estimated location and
detailed Monte Carlo simulations allowed us to classify the event as due to the
closest lens system, being at a distance of $\simeq 380$ pc and mass $\simeq
0.25$ M$_{\odot}$. | astro-ph |
Cold dark matter heats up: One of the principal discoveries in modern cosmology is that standard model
particles (including baryons, leptons and photons) together comprise only 5% of
the mass-energy budget of the Universe. The remaining 95% consists of dark
energy and dark matter (DM). Consequently our picture of the universe is known
as {\Lambda}CDM, with {\Lambda} denoting dark energy and CDM cold dark matter.
{\Lambda}CDM is being challenged by its apparent inability to explain the low
density of DM measured at the centre of cosmological systems, ranging from
faint dwarf galaxies to massive clusters containing tens of galaxies the size
of the Milky Way. But before making conclusions one should carefully include
the effect of gas and stars, which were historically seen as merely a passive
component during the assembly of galaxies. We now understand that these can in
fact significantly alter the DM component, through a coupling based on rapid
gravitational potential fluctuations. | astro-ph |
Estimating the impact of recombination uncertainties on the cosmological
parameter constraints from cosmic microwave background experiments: [Abridged] We use our most recent training set for the RICO code to estimate
the impact of recombination uncertainties on the posterior probability
distributions which will be obtained from future CMB experiments, and in
particular the Planck satellite. Using a MCMC analysis to sample the posterior
distribution of the cosmological parameters, we find that Planck will have
biases of -0.7, -0.3 and -0.4 sigmas for n_S, Omega_b h2 and log(As),
respectively, in the minimal 6-parameter LCDM model, if the description of the
recombination history given by RICO is not used. The remaining parameters are
not significantly affected. We also show, that the cosmology dependence of the
corrections to the recombination history modeled with RICO has a negligible
impact on the posterior distributions obtained for the case of the Planck
satellite. In practice, this implies that the inclusion of additional
corrections to existing recombination codes can be achieved using simple
cosmology-independent `fudge functions'. Finally, we also investigated the
impact of some recent improvements in the treatment of hydrogen recombination
which are still not included in the current version of our training set for
Rico, by assuming that the cosmology dependence of those corrections can be
neglected. In summary, with our current understanding of the complete
recombination process, the expected biases in the cosmological parameters
inferred from Planck might be as large as -2.3, -1.7 and -1 sigmas for n_S,
Omega_b h2 and log(As) respectively, if all those corrections are not taken
into account. We note that although the list of physical processes that could
be of importance for Planck seems to be nearly complete, still some effort has
to be put in the validation of the results obtained by the different groups. | astro-ph |
The Robo-AO-2 facility for rapid visible/near-infrared AO imaging and
the demonstration of hybrid techniques: We are building a next-generation laser adaptive optics system, Robo-AO-2,
for the UH 2.2-m telescope that will deliver robotic, diffraction-limited
observations at visible and near-infrared wavelengths in unprecedented numbers.
The superior Maunakea observing site, expanded spectral range and rapid
response to high-priority events represent a significant advance over the
prototype. Robo-AO-2 will include a new reconfigurable natural guide star
sensor for exquisite wavefront correction on bright targets and the
demonstration of potentially transformative hybrid AO techniques that promise
to extend the faintness limit on current and future exoplanet adaptive optics
systems. | astro-ph |
Towards a multi-scale understanding of the gas-star formation cycle in
the Central Molecular Zone: The Central Molecular Zone (CMZ, the central 500 pc of the Milky Way)
contains the largest reservoir of high-density molecular gas in the Galaxy, but
forms stars at a rate 10-100 times below commonly-used star formation
relations. We discuss recent efforts in understanding how the nearest galactic
nucleus forms its stars. The latest models of the gas inflow, star formation,
and feedback duty cycle reproduce the main observable features of the CMZ,
showing that star formation is episodic and that the CMZ currently resides at a
star formation minimum. Using orbital modelling, we derive the
three-dimensional geometry of the CMZ and show how the orbital dynamics and the
star formation potential of the gas are closely coupled. We discuss how this
coupling reveals the physics of star formation and feedback under the
conditions seen in high-redshift galaxies, and promotes the formation of the
densest stellar clusters in the Galaxy. | astro-ph |
Variability of VHE $γ$-ray emission from the binary PSR B1259-63/LS
2883: We examine changes of the $\gamma$-ray intensity observed from the direction
of the binary system PSR B1259-63/LS 2883 during campaigns around its three
periastron passages. A simple and straightforward method is applied to the
published data obtained with the Imaging Atmospheric Cherenkov Technique.
Regardless of many issues of the detection process, the method works only with
numbers of very high energetic photons registered in the specified regions.
Within the realm of this scheme, we recognized changes attributable to the
variations of the intrinsic source activity at high levels of significance. | astro-ph |
EMPRESS. IV. Extremely Metal-Poor Galaxies (EMPGs) Including Very
Low-Mass Primordial Systems with M*=10^4--10^5 M_sun and 2--3% (O/H)_sun:
High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-Instability
Supernovae: We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of
extremely metal poor galaxies (EMPGs) selected by a machine-learning technique
applied to the deep (~26 AB mag) optical and wide-area (~500 deg^2) Subaru
imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs
with an oxygen abundance (O/H) less than ~10% solar value (O/H)_sun, and four
sources are contaminants of moderately metal-rich galaxies or no emission-line
objects. Notably, two out of the nine EMPGs have extremely-low stellar masses
and oxygen abundances of 5*10^4--7*10^5 M_sun and 2--3% (O/H)_sun,
respectively. With a sample of five EMPGs with (Fe/O) measurements, two (three)
of which are taken from this study (the literature), we confirm that two EMPGs
with the lowest (O/H) ratios of ~2% (O/H)_sun show high (Fe/O) ratios of ~0.1,
close to the solar abundance ratio. Comparing galaxy chemical enrichment
models, we find that the two EMPGs cannot be explained by a scenario of
metal-poor gas accretion/episodic star-formation history due to their low (N/O)
ratios. We conclude that the two EMPGs can be reproduced by an inclusion of
bright hypernovae and/or hypothetical pair-instability supernovae (SNe)
preferentially produced in a metal-poor environment. This conclusion implies
that primordial galaxies at z~10 could have a high abundance of Fe that is not
originated from Type Ia SNe with delays, and that Fe may not serve as a cosmic
clock for primordial galaxies. | astro-ph |
The dust effects on galaxy scaling relations: Accurate galaxy scaling relations are essential for a successful model of
galaxy formation and evolution as they provide direct information about the
physical mechanisms of galaxy assembly over cosmic time. We present here a
detailed analysis of a sample of nearby spiral galaxies taken from the KINGFISH
survey. The photometric parameters of the morphological components are obtained
from bulge-disk decompositions using GALFIT data analysis algorithm, with
surface photometry of the sample done beforehand. Dust opacities are determined
using a previously discovered correlation between the central face-on dust
opacity of the disk and the stellar mass surface density. The method and the
library of numerical results previously obtained are used to correct the
measured photometric and structural parameteres for projection (inclination),
dust and decomposition effects in order to derive their intrinsic values.
Galaxy disk scaling relations are then presented, both the measured (observed)
and the intrinsic (corrected) ones, in the optical regime, to show the scale of
the biases introduced by the aforementioned effects. The slopes of the
size-luminosity relations and the dust vs stellar mass are in agreement with
values found in other works. We derive mean dust optical depth and dust/stellar
mass ratios of the sample, which we find to be consistent with previous studies
of nearby spiral galaxies. While our sample is rather small, it is sufficient
to quantify the influence of galaxy environment (dust, in this case) when
deriving scaling relations. | astro-ph |
Predicted Colors and Flux Densities of Protostars in the Herschel PACS
and SPIRE Filters: Upcoming surveys with the Herschel Space Observatory will yield far-IR
photometry of large samples of young stellar objects, which will require
careful interpretation. We investigate the color and luminosity diagnostics
based on Herschel broad-band filters to identify and discern the properties of
low-mass protostars. We compute a grid of 2,016 protostars in various physical
congurations, present the expected flux densities and flux density ratios for
this grid of protostars, and compare Herschel observations of three protostars
to the model results. These provide useful constraints on the range of colors
and fluxes of protostar in the Herschel filters. We find that Herschel data
alone is likely a useful diagnostic of the envelope properties of young stars | astro-ph |
Evidence for an X-ray Emitting Galactic Bulge: Shadows Cast by Distant
Molecular Gas: A mosaic of 7 ROSAT PSPC pointed observations in the direction of (l,b ~ 10,0
deg) reveals deep X-ray shadows in the 0.5-2.0 keV band cast by dense molecular
gas. The comparison between the observed on-cloud and off-cloud X-ray fluxes
indicates that ~43% of the diffuse X-ray background in this direction in both
the 3/4 keV and 1.5 keV bands originates behind the molecular gas, which is
located at 2-4 kpc from the Sun. Given the short mean free path of X-rays in
the 3/4 keV band in the Galactic plane (~1 kpc assuming an average space
density of 1 cm^-3), this large percentage of the observed flux which
originates beyond the molecular gas most likely indicates a strong enhancement
in the distribution of X-ray emitting gas in the Galactic center region,
possibly associated with a Galactic X-ray bulge. | astro-ph |
Deep Learning for Gamma-Ray Bursts: A data driven event framework for
X/Gamma-Ray analysis in space telescopes: This thesis comprises the first three chapters dedicated to providing an
overview of Gamma Ray-Bursts (GRBs), their properties, the instrumentation used
to detect them, and Artificial Intelligence (AI) applications in the context of
GRBs, including a literature review and future prospects. Considering both the
current and the next generation of high X-ray monitors, such as Fermi-GBM and
HERMES Pathfinder (an in-orbit demonstration of six 3U nano-satellites), the
research question revolves around the detection of long and faint high-energy
transients, potentially GRBs, that might have been missed by previous detection
algorithms. To address this, two chapters introduce a new data-driven
framework, DeepGRB.
In Chapter 4, a Neural Network (NN) is described for background count rate
estimation for X/gamma-ray detectors, providing a performance evaluation in
different periods, including both solar maxima, solar minima periods, and one
containing an ultra-long GRB. The application of eXplainable Artificial
Intelligence (XAI) is performed for global and local feature importance
analysis to better understand the behavior of the NN.
Chapter 5 employs FOCuS-Poisson for anomaly detection in count rate
observations and estimation from the NN. DeepGRB demonstrates its capability to
process Fermi-GBM data, confirming cataloged events and identifying new ones,
providing further analysis with estimates for localization, duration, and
classification. The chapter concludes with an automated classification method
using Machine Learning techniques that incorporates XAI for eventual bias
identification. | astro-ph |
Making the unmodulated Pyramid wavefront sensor smart. Closed-loop
demonstration of neural network wavefront reconstruction with MagAO-X: Almost all current and future high-contrast imaging instruments will use a
Pyramid wavefront sensor (PWFS) as a primary or secondary wavefront sensor. The
main issue with the PWFS is its nonlinear response to large phase aberrations,
especially under strong atmospheric turbulence. Most instruments try to
increase its linearity range by using dynamic modulation, but this leads to
decreased sensitivity, most prominently for low-order modes, and makes it blind
to petal-piston modes. In the push toward high-contrast imaging of fainter
stars and deeper contrasts, there is a strong interest in using the PWFS in its
unmodulated form. Here, we present closed-loop lab results of a nonlinear
reconstructor for the unmodulated PWFS of the Magellan Adaptive Optics eXtreme
(MagAO-X) system based on convolutional neural networks (CNNs). We show that
our nonlinear reconstructor has a dynamic range of >600 nm root-mean-square
(RMS), significantly outperforming the linear reconstructor that only has a 50
nm RMS dynamic range. The reconstructor behaves well in closed loop and can
obtain >80% Strehl at 875 nm under a large variety of conditions and reaches
higher Strehl ratios than the linear reconstructor under all simulated
conditions. The CNN reconstructor also achieves the theoretical sensitivity
limit of a PWFS, showing that it does not lose its sensitivity in exchange for
dynamic range. The current CNN's computational time is 690 microseconds, which
enables loop speeds of >1 kHz. On-sky tests are foreseen soon and will be
important for pushing future high-contrast imaging instruments toward their
limits. | astro-ph |
Relationship between the moment of inertia and the $k_2$ Love number of
fluid extra-solar planets: Context: Tidal and rotational deformation of fluid giant extra-solar planets
may impact their transit light curves, making the $k_2$ Love number observable
in the upcoming years. Studying the sensitivity of $k_2$ to mass concentration
at depth is thus expected to provide new constraints on the internal structure
of gaseous extra-solar planets. Aims: We investigate the link between the mean
polar moment of inertia $N$ of a fluid, stably layered extra-solar planet and
its $k_2$ Love number, aiming at obtaining analytical relationships valid, at
least, for some particular ranges of the model parameters. We also seek a
general, approximate relationship useful to constrain $N$ once observations of
$k_2$ will become available. Methods: For two-layer fluid extra-solar planets,
we explore the relationship between $N$ and $k_2$ by analytical methods, for
particular values of the model parameters. We also explore approximate
relationships valid over all the possible range of two-layer models. More
complex planetary structures are investigated by the semi-analytical propagator
technique. Results: A unique relationship between $N$ and $k_2$ cannot be
established. However, our numerical experiments show that a `rule of thumb' can
be inferred, valid for complex, randomly layered stable planetary structures.
The rule robustly defines the upper limit to the values of $N$ for a given
$k_2$, and agrees with analytical results for a polytrope of index one and with
a realistic non-rotating model of the tidal equilibrium of Jupiter. | astro-ph |
The Completed SDSS-IV Extended Baryon Oscillation Spectroscopic Survey:
N-body Mock Challenge for the Quasar Sample: The growth rate and expansion history of the Universe can be measured from
large galaxy redshift surveys using the Alcock-Paczynski effect. We validate
the Redshift Space Distortion models used in the final analysis of the Sloan
Digital Sky Survey (SDSS) extended Baryon Oscillation Spectroscopic Survey
(eBOSS) Data Release 16 quasar clustering sample, in configuration and Fourier
space, using a series of HOD mock catalogues generated using the OuterRim
N-body simulation. We test three models on a series of non-blind mocks, in the
OuterRim cosmology, and blind mocks, which have been rescaled to new
cosmologies, and investigate the effects of redshift smearing and catastrophic
redshifts. We find that for the non-blind mocks, the models are able to recover
$f\sigma_8$ to within 3% and $\alpha_\parallel$ and $\alpha_\bot$ to within 1%.
The scatter in the measurements is larger for the blind mocks, due to the
assumption of an incorrect fiducial cosmology. From this mock challenge, we
find that all three models perform well, with similar systematic errors on
$f\sigma_8$, $\alpha_\parallel$ and $\alpha_\bot$ at the level of
$\sigma_{f\sigma_8}=0.013$, $\sigma_{\alpha_\parallel}=0.012$ and
$\sigma_{\alpha_\bot}=0.008$. The systematic error on the combined consensus is
$\sigma_{f\sigma_8}=0.011$, $\sigma_{\alpha_\parallel}=0.008$ and
$\sigma_{\alpha_\bot}=0.005$, which is used in the final DR16 analysis. For BAO
fits in configuration and Fourier space, we take conservative systematic errors
of $\sigma_{\alpha_\parallel}=0.010$ and $\sigma_{\alpha_\bot}=0.007$. | astro-ph |
A Massive Millisecond Pulsar in an Eccentric Binary: The recent discovery of a population of eccentric (e ~ 0.1) millisecond
pulsar (MSP) binaries with low-mass white dwarf companions in the Galactic
field represents a challenge to evolutionary models that explain MSP formation
as recycling: all such models predict that the orbits become highly
circularised during a long period of accretion. The members of this new
population exhibit remarkably similar properties (orbital periods,
eccentricities, companion masses, spin periods) and several models have been
put forward that suggest a common formation channel. In this work we present
the results of an extensive timing campaign focusing on one member of this new
population, PSR J1946+3417. Through measurement of the both the advance of
periastron and Shapiro delay for this system, we determine the mass of the
pulsar, companion and the inclination of the orbit to be 1.828(22) Msun,
0.2656(19) Msun and 76.4(6) , under the assumption that general relativity is
the true description of gravity. Notably, this is the third highest mass
measured for any pulsar. Using these masses and the astrometric properties of
PSR J1946+3417 we examine three proposed formation channels for eccentric MSP
binaries. While our results are consistent with eccentricity growth driven by a
circumbinary disk or neutron star to strange star phase transition, we rule out
rotationally delayed accretion-induced collapse as the mechanism responsible
for the configuration of the PSR J1946+3417 system. | astro-ph |
Spatially Resolved Stellar Populations of $0.3<z<6.0$ Galaxies in
WHL0137-08 and MACS0647+70 Clusters as Revealed by JWST: How do Galaxies Grow
and Quench Over Cosmic Time?: We study the spatially resolved stellar populations of 444 galaxies at
$0.3<z<6.0$ in two clusters (WHL0137-08 and MACS0647+70) and a blank field,
combining imaging data from HST and JWST to perform spatially resolved spectral
energy distribution (SED) modeling using pixedfit. The high spatial resolution
of the imaging data combined with magnification from gravitational lensing in
the cluster fields allows us to resolve some galaxies to sub-kpc scales (for
109 of our galaxies). At redshifts around cosmic noon and higher ($2.5\lesssim
z\lesssim 6.0$), we find mass doubling times to be independent of radius,
inferred from flat specific star formation rate (sSFR) radial profiles and
similarities between the half-mass and half-SFR radii. At lower redshifts
($1.5\lesssim z\lesssim 2.5$), a significant fraction of our star-forming
galaxies show evidence for nuclear starbursts, inferred from centrally elevated
sSFR, and a much smaller half-SFR radius compared to the half-mass radius. At
later epochs, we find more galaxies suppress star formation in their center but
are still actively forming stars in the disk. Overall, these trends point
toward a picture of inside-out galaxy growth consistent with theoretical models
and simulations. We also observe a tight relationship between the central mass
surface density and global stellar mass with $\sim 0.38$ dex scatter. Our
analysis demonstrates the potential of spatially resolved SED analysis with
JWST data. Future analysis with larger samples will be able to further explore
the assembly of galaxy mass and the growth of their structures | astro-ph |
Pulse profiles from thermally emitting neutron stars: The problem of computing the pulse profiles from thermally emitting spots on
the surface of a neutron star in general relativity is reconsidered. We show
that it is possible to extend Beloborodov (2002) approach to include (multiple)
spots of finite size in different positions on the star surface. Results for
the pulse profiles are expressed by comparatively simple analytical formulas
which involve only elementary functions. | astro-ph |
Prevailing dust-transport directions on comet 67P/Churyumov-Gerasimenko: Dust transport and deposition behind larger boulders on the comet
67P/Churyumov-Gerasimenko (67P/C-G) have been observed by the Rosetta mission.
We present a mechanism for dust transport vectors based on a homogenous surface
activity model incorporating in detail the topography of 67P/C-G. The
combination of gravitation, gas drag, and Coriolis force leads to specific dust
transfer pathways, which for higher dust velocities fuel the near nucleus coma.
By distributing dust sources homogeneously across the whole cometary surface,
we derive a global dust-transport map of 67P/C-G. The transport vectors are in
agreement with the reported wind-tail directions in the Philae descent area. | astro-ph |
How many low-mass stars do destroy 3He?: We recall the current status of the long-standing 3He problem, and its
possible connection with chemical anomalies on the red giant branch. In this
context, we collect in the literature all the available observations of the
carbon isotopic ratio in field and cluster giant stars. Using the HIPPARCOS
parallaxes, we get constraints on the evolutionary status of the field stars of
the sample. This allows us to identify the stars that have passed the
luminosity function bump and present 12C/13C ratios in disagreement with the
standard predictions of stellar evolutionary models. We determine statistically
what fraction of low mass stars experience an extra-mixing process on the red
giant branch, and are then expected to destroy their 3He at this evolutionary
phase. The high number we get satisfies the galactic requirements for the
evolution of the 3He abundance. | astro-ph |
Spitzer Observations of V838 Monocerotis: Detection of a Rare Infrared
Light Echo: We present Spitzer observations of the unusual variable V838 Monocerotis.
Extended emission is detected around the object at 24, 70 and 160um. The
extended infrared emission is strongly correlated spatially with the HST
optical light echo images taken at a similar epoch. We attribute this diffuse
nebulosity to be from an infrared light echo caused by reprocessed thermal
emission from dust heated by the outward-propagating radiation from the 2002
eruption. The detection of an IR light echo provides an opportunity to estimate
the mass in dust of the echo material and hence constrain its origin. We
estimate the dust mass of the light echo to be on the order of a solar mass -
thereby implying the total gas plus dust mass to be considerably more - too
massive for the echo material to be the ejecta from previous
outburst/mass-losing events. This is therefore suggestive that a significant
fraction of the matter seen through the light echo is interstellar in origin.
Unresolved emission at 24 and 70um is also seen at the position of the central
star possibly indicating the presence of hot dust freshly condensed in the
outburst ejecta. | astro-ph |
How to make maps from CMB data without losing information: The next generation of CMB experiments can measure cosmological parameters
with unprecedented accuracy - in principle. To achieve this in practice when
faced with such gigantic data sets, elaborate data analysis methods are needed
to make it computationally feasible. An important step in the data pipeline is
to make a map, which typically reduces the size of the data set my orders of
magnitude. We compare ten map-making methods, and find that for the Gaussian
case, both the method used by the COBE DMR team and various variants of Wiener
filtering are optimal in the sense that the map retains all cosmological
information that was present in the time-ordered data (TOD). Specifically, one
obtains just as small error bars on cosmological parameters when estimating
them from the map as one could have obtained by estimating them directly from
the TOD. The method of simply averaging the observations of each pixel (for
total-power detectors), on the contrary, is found to generally destroy
information, as does the maximum entropy method and most other non-linear
map-making techniques.
Since it is also numerically feasible, the COBE method is the natural choice
for large data sets. Other lossless (e.g. Wiener-filtered) maps can then be
computed directly from the COBE method map. | astro-ph |
Molecular Gas in the Inner 3.2 Kiloparsecs of NGC 2403: Star Formation
at Subcritical Gas Surface Densities: We present a fully sampled map of the inner 3.2 kpc of the nearby spiral
galaxy NGC 2403 in the CO J=1-0 line. These data emphasize the relatively small
contribution of molecular hydrogen to the cold gas content of this galaxy, and
confirm that the gas surface densities in the inner 2.8 kpc of NGC 2403 lie
below the critical surface density for star formation under the theory proposed
by Kennicutt (1989). Since star formation is occurring throughout the inner
disk, the simple dynamical model used by Kennicutt cannot be the only important
process regulating star formation in galaxies. We suggest that stochastic star
formation processes are responsible for the star formation seen in these
regions, and thus that supercritical gas densities may not be a necessary
condition for star formation in the inner regions of galactic disks. | astro-ph |
Interaction of massive black hole binaries with their stellar
environment: III. Scattering of bound stars: We develop a formalism for studying the dynamics of massive black hole
binaries embedded in gravitationally-bound stellar cusps, and study the binary
orbital decay by three-body interactions, the impact of stellar slingshots on
the density profile of the inner cusp, and the properties of the ejected
hypervelocity stars (HVSs). We find that the scattering of bound stars shrinks
the binary orbit and increases its eccentricity more effectively than that of
unbound ambient stars. Binaries with initial eccentricities e>0.3 and/or
unequal-mass companions (M_2/M_1<0.1) can decay by three-body interactions to
the gravitational wave emission regime in less than a Hubble time. The stellar
cusp is significantly eroded, and cores as shallow as \rho\propto r^-0.7 may
develop from a pre-existing singular isothermal density profile. A population
of HVSs is ejected in the host galaxy halo, with a total mass ~M_2. We scale
our results to the scattering of stars bound to Sgr A*, the massive black hole
in the Galactic Center, by an inspiraling companion of intermediate mass.
Depending on binary mass ratio, eccentricity, and initial slope of the stellar
cusp, a core of radius ~0.1 pc typically forms in 1-10 Myr. On this timescale
about 500-2500 HVSs are expelled with speeds sufficiently large to escape the
gravitational potential of the Milky Way. | astro-ph |
Wavelet analysis of MCG-6-30-15 and NGC 4051: a possible discovery of
QPOs in 2:1 and 3:2 resonance: Following our previous work of Lachowicz & Czerny (2005), we explore further
the application of the continuous wavelet transform to X-ray astronomical
signals. Using the public archive of the XMM-Newton satellite, we analyze all
available EPIC-pn observations for nearby Seyfert 1 galaxies MCG-6-30-15 and
NGC 4051. We confine our analysis to 0.002-0.007 Hz frequency band in which, on
the way of theoretically motivated premises, some quasi-periodic oscillations
(QPOs) are expected to be found. We find that indeed wavelet power histogram
analysis reveals such QPOs centered at two frequencies of ~2.5E-3 Hz and 4-6E-3
Hz, respectively. We show that these quasi-periodic features can be
disentangled from the Poisson noise contamination level what is hardly to
achieve with the standard Fourier analysis. Interestingly, we find some of them
to be in 2:1 or 3:2 ratio. If real, our finding may be considered as a link
between QPOs observed in AGN and kHz QPOs seen in X-ray binary systems. | astro-ph |
Alternating Direction Implicit Method for Two-Dimensional Fokker-Planck
Equation of Dense Spherical Stellar Systems: The Fokker-Planck (FP) model is one of the commonly used methods for studies
of the dynamical evolution of dense spherical stellar systems such as globular
clusters and galactic nuclei. The FP model is numerically stable in most cases,
but we find that it encounters numerical difficulties rather often when the
effects of tidal shocks are included in two-dimensional (energy and angular
momentum space) version of the FP model or when the initial condition is
extreme (e.g., a very large cluster mass and a small cluster radius). To avoid
such a problem, we have developed a new integration scheme for a
two-dimensional FP equation by adopting an Alternating Direction Implicit (ADI)
method given in the Douglas-Rachford split form. We find that our ADI method
reduces the computing time by a factor of ~2 compared to the fully implicit
method, and resolves problems of numerical instability. | astro-ph |
Optimal limits on f_{NL}^{local} from WMAP 5-year data: We have applied the optimal estimator for f_{NL}^{local} to the 5 year WMAP
data. Marginalizing over the amplitude of foreground templates we get -4 <
f_{NL}^{local} < 80 at 95% CL. Error bars of previous (sub-optimal) analyses
are roughly 40% larger than these. The probability that a Gaussian simulation,
analyzed using our estimator, gives a result larger in magnitude than the one
we find is 7%. Our pipeline gives consistent results when applied to the three
and five year WMAP data releases and agrees well with the results from our own
sub-optimal pipeline. We find no evidence of any residual foreground
contamination. | astro-ph |
Solution to the conflict between the resolved and unresolved galaxy
stellar mass estimation from the perspective of JWST: By utilizing the spatially-resolved photometry of galaxies at $0.2<z<3.0$ in
the CEERS field, we estimate the resolved and unresolved stellar mass via
spectral energy distribution (SED) fitting to study the discrepancy between
them. We first compare $M_{\ast}$ derived from photometry with and without the
JWST wavelength coverage and find that $M_{\ast}$ can be overestimated by up to
0.2 dex when lacking rest-frame NIR data. The SED fitting process tends to
overestimate both stellar age and dust attenuation in the absence of rest-frame
NIR data, consequently leading to a larger observed mass-to-light ratio and
hence an elevated $M_{\ast}$. With the inclusion of the JWST NIR photometry, we
find no significant disparity between the resolved and unresolved stellar mass
estimates, providing a plausible solution to the conflict between them out to
$z\sim 3$. Further investigation demonstrates that reliable $M_{\ast}$
estimates can be obtained, regardless of whether they are derived from
spatially resolved or spatially unresolved photometry, so long as the reddest
filter included in the SED fitting has a rest-frame wavelength larger than
10000 \AA. | astro-ph |
3-D simulations of shells around massive stars: As massive stars evolve, their winds change. This causes a series of
hydrodynamical interactions in the surrounding medium. Whenever a fast wind
follows a slow wind phase, the fast wind sweeps up the slow wind in a shell,
which can be observed as a circumstellar nebula.
One of the most striking examples of such an interaction is when a massive
star changes from a red supergiant into a Wolf-Rayet star. Nebulae resulting
from such a transition have been observed around many Wolf-Rayet stars and show
detailed, complicated structures owing to local instabilities in the swept-up
shells.
Shells also form in the case of massive binary stars, where the winds of two
stars collide with one another. Along the collision front gas piles up, forming
a shell that rotates along with the orbital motion of the binary stars. In this
case the shell follows the surface along which the ram pressure of the two
colliding winds is in balance.
Using the MPI-AMRVAC hydrodynamics code we have made multi-dimensional
simulations of these interactions in order to model the formation and evolution
of these circumstellar nebulae and explore whether full 3D simulations are
necessary to obtain accurate models of such nebulae. | astro-ph |
Determination of dark matter type by X-ray sources statistics: The current cosmological model includes cold dark matter, which consists of
massive nonrelativistic particles. There are also some observational and
theoretical evidences for warm dark matter. The existence of warm DM can be
examined by measuring of the galaxy clusters density profiles and accurate
counting of dwarf galaxies. In this work I suppose that DM haloes are well
traced by X-ray gas in clusters, groups, pairs and even single galaxies. The
type of DM is inspected with the Xgal sample of 5021 X-ray emitting galaxies
observed by XMM-Newton. The selection bias of this sample is also analyzed. | astro-ph |
UVES observations of QSO 0000-2620: oxygen and zinc abundances in the
Damped Ly-alpha galaxy at z_abs=3.3901: Observations of the QSO 0000-2620 with UVES spectrograph at the 8.2m ESO
KUEYEN telescope are used for abundance analysis of the damped Ly-alpha system
at z_{abs}=3.3901. Several Oxygen lines are identified in the Ly_alpha forest
and a measure for the oxygen abundance is obtained at [O/H]=-1.85 +/- 0.1 by
means of the unsaturated OI 925 A and OI 950 A lines. This represents the most
accurate O measurement in a damped Ly_alpha galaxy so far. We have also
detected ZnII 2026 A and CrII 2056, 2062 A redshifted at about 8900 A and found
abundances [Zn/H] = -2.07 +/- 0.1 and [Cr/H]=-1.99 +/- 0.1. Furthermore,
previous measurements of Fe, Si, Ni and N have been refined yielding
[Fe/H]=-2.04 +/- 0.1, [Si/H]=-1.90 +/- 0.1, [Ni/H]=-2.27 +/- 0.1, and
[N/H]=-2.68 +/- 0.1. The abundance of the non-refractory element zinc is the
lowest among the damped Ly-alpha systems showing that the associated
intervening galaxy is indeed in the early stages of its chemical evolution. The
fact that the Zn abundance is identical to that of the refractory elements Fe
and Cr suggests that dust grains have not formed yet. In this Damped Ly-alpha
system the observed [O,S,Si/Zn,Fe,Cr] ratios, in whatever combination are
taken, are close to solar (i.e 0.1-0.2 dex) and do not show the
[alpha-element/Fe] enhancement observed in Milky Way stars of comparable
metallicity. The observed behavior supports a galaxy evolution model
characterized by either episodic or low star formation rate rather than a
Milky-Way-type evolutionary model. | astro-ph |
3D mapping of the neutral X-ray absorption in the local interstellar
medium: The Gaia and XMM-Newton synergy: We present a three-dimensional map of the hydrogen density distribution in
the Galactic interstellar medium. The hydrogen equivalent column densities were
obtained from the Exploring the X-ray Transient and variable Sky project ({\sc
EXTraS}) which provides equivalent $N_{\rm H}$ values from X-ray spectral fits
of observations within the {\it XMM-Newton} Data Release. {\sc EXTraS} include
multiple fits for each source, allowing an accurate determination of the
equivalent column densities, which depends on the continuum modeling of the
spectra. A cross-correlation between the {\sc EXTraS} catalogue and the first
{\it Gaia} Data Release was performed in order to obtain accurate parallax and
distance measurements. We use a Bayesian method explained in \citet{rez17} in
order to predict the most probable distribution of the density at any arbitrary
point, even for lines of sight along which there are no initial observation.
The resulting map shows small-scale density structures which can not been
modeled by using analytic density profiles. In this paper we present a proof of
concept of the kind of science possible with the synergy of these catalogs.
However, given the systematic uncertainties connected to the source
identification and to the dependence of $N_{\rm H}$ on the spectral model, the
present maps should be considered qualitatively at this point. | astro-ph |
CMB Polarization in Einstein-Aether Theory: We study the impact of modifying the vector sector of gravity on the CMB
polarization. We employ the Einstein-aether theory as a concrete example. The
Einstein-aether theory admits dynamical vector perturbations generated during
inflation, leaving imprints on the CMB polarization. We derive the perturbation
equations of the aether vector field in covariant formalism and compute the CMB
B-mode polarization using the modified CAMB code. It is found that the
amplitude of the B-mode signal from the aether field can surpass the one from
the inflationary gravitational waves. The shape of the spectrum is clearly
understood in an analytic way using the tight coupling approximation. | astro-ph |
A Disc Reflection Model for Ultra-Soft Narrow-Line Seyfert 1 Galaxies: We present a detailed analysis of the XMM-Newton observations of five
narrow-line Seyfert 1 galaxies (NLS1s). They all show very soft continuum
emission in the X-ray band with a photon index of $\Gamma\gtrsim 2.5$.
Therefore, they are referred to as `ultra-soft' NLS1s in this paper. By
modeling their optical/UV-X-ray spectral energy distribution (SED) with a
reflection-based model, we find indications that the disc surface in these
ultra-soft NLS1s is in a higher ionisation state than other typical Seyfert 1
AGN. Our best-fit SED models suggest that these five ultra-soft NLS1s have an
Eddington ratio of $\lambda_{\rm Edd}=1-20$ assuming available black hole mass
measurements. In addition, our models infer that a significant fraction of the
disc energy in these ultra-soft NLS1s is radiated away in the form of
non-thermal emission instead of the thermal emission from the disc. Due to
their extreme properties, X-ray observations of these sources in the iron band
are particularly challenging. Future observations, e.g. from Athena, will
enable us to have a clearer view of the spectral shape in the iron band and
thus distinguish the reflection model from other interpretations of their
broadband spectra. | astro-ph |
Radio Polarimetry of the ELAIS N1 Field: Polarized Compact Sources: We present deep polarimetric observations at 1420 MHz of the European Large
Area ISO Survey North 1 region (ELAIS N1) as part of the Dominion Radio
Astrophysical Observatory Planck Deep Fields project. By combining closely
spaced aperture synthesis fields, we image a region of 7.43 square degrees to a
maximum sensitivity in Stokes Q and U of 78 microJy/beam, and detect 786
compact sources in Stokes I. Of these, 83 exhibit polarized emission. We find
that the differential source counts (log N - log p) for polarized sources are
nearly constant down to p > 500 microJy, and that these faint polarized radio
sources are more highly polarized than the strong source population. The median
fractional polarization is (4.8 +/- 0.7)% for polarized sources with Stokes I
flux density between 1 and 30 mJy; approximately three times larger than
sources with I > 100 mJy. The majority of the polarized sources have been
identified with galaxies in the Spitzer Wide Area Infrared Extragalactic Survey
(SWIRE) image of ELAIS N1. Most of the galaxies occupy regions in the IRAC
5.8/3.6 micron vs. 8.0/4.5 micron color-color diagram associated with dusty
AGNs, or with ellipticals with an aging stellar population. A few host galaxies
have colors that suggests significant PAH emission in the near-infrared. A
small fraction, 12%, of the polarized sources are not detected in the SWIRE
data. None of the polarized sources in our sample appears to be associated with
an actively star-forming galaxy. | astro-ph |
A Stellar Flare during the Transit of the Extrasolar Planet OGLE-TR-10b: We report a stellar flare occurring during a transit of the exoplanet
OGLE-TR-10b, an event not previously reported in the literature. This reduces
the observed transit depth, particularly in the u'-band, but flaring could also
be significant in other bands and could lead to incorrect planetary parameters.
We suggest that OGLE-TR-10a is an active planet-hosting star and has an
unusually high X-ray luminosity. | astro-ph |
Evidence for Black Hole Growth in Local Analogs to Lyman Break Galaxies: We have used XMM-Newton to observe six Lyman Break Analogs (LBAs): members of
the rare population of local galaxies that have properties that are very
similar to distant Lyman Break Galaxies. Our six targets were specifically
selected because they have optical emission-line properties that are
intermediate between starbursts and Type 2 (obscured) AGN. Our new X-ray data
provide an important diagnostic of the presence of an AGN. We find X-ray
luminosities of order 10^{42} erg/s and ratios of X-ray to far-IR luminosities
that are higher than values in pure starburst galaxies by factors ranging from
~ 3 to 30. This strongly suggests the presence of an AGN in at least some of
the galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O
III]\lambda 5007 emission-line are low by about an order-of-magnitude compared
to Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN.
Either the AGN hard X-rays are significantly obscured or the [O III] emission
is dominated by the starburst. We searched for an iron emission line at ~ 6.4
keV, which is a key feature of obscured AGN, but only detected emission at the
~ 2\sigma level. Finally, we find that the ratios of the mid-infrared (24\mu m)
continuum to [O III]\lambda 5007 luminosities in these LBAs are higher than the
values for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we
conclude that an AGN is likely to be present, but that the bolometric
luminosity is produced primarily by an intense starburst. If these black holes
are radiating at the Eddington limit, their masses would lie in the range of
10^5 to 10^6 M_{sun}. These objects may offer ideal local laboratories to
investigate the processes by which black holes grew in the early universe. | astro-ph |
Non-parametric Reconstruction of Photon Escape Fraction from
Reionization: One of the most crucial yet poorly constrained parameters in modelling the
ionizing emissivity is the escape fraction of photons from star-forming
galaxies. Several theoretical and observational studies have been conducted
over the past few years, but consensus regarding its redshift evolution has yet
to be achieved. We present here the first non-parametric reconstruction of this
parameter as a function of redshift from a data-driven reionization model using
a Gaussian Process Regression method. Our finding suggests a mild redshift
evolution of escape fraction with a mean value of $4\%,7\%,\sim10\%$ at
$z=2,6,12$. However, a constant escape fraction of $6-10\%$ at $z\gtrsim 6$ is
still allowed by current data and also matches other reionization-related
observations. With the detection of fainter high redshift galaxies from
upcoming observations of JWST, the approach presented here will be a robust
tool to put the most stringent constraint on escape fraction as well as
reionization histories. | astro-ph |
Magnetized, Relativistic Jets: Extragalactic relativistic jets are composed by charged particles and
magnetic fields, as inferred from the synchrotron emission that we receive from
them. The Larmor radii of the particles propagating along the magnetic field
are much smaller than the scales of the problem, providing the necessary
coherence to the system to treat is as a flow. We can thus study them using
relativistic magnetohydrodynamics. As a first step, we have studied the
structure of steady-state configurations of jets by using numerical
simulations. We have used a helical field configuration and have changed
different relevant parameters that control the way in which the energy flux is
distributed in jets (namely, the proportion of the energy flux carried by
internal, kinetic or magnetic energy). Our results show significant differences
among the different kinds of jets. Finally, we also report on results based on
synthetic maps of our simulated jets. | astro-ph |
Thermal Convection in Stars and in Their Atmosphere: Thermal convection is one of the main mechanisms of heat transport and mixing
in stars in general and also in the photospheric layers which emit the
radiation that we observe with astronomical instruments. The present lecture
notes first introduce the role of convection in astrophysics and explain the
basic physics of convection. This is followed by an overview on the modelling
of convection. Challenges and pitfalls in numerical simulation based modelling
are discussed subsequently. Finally, a particular application for the
previously introduced concepts is described in more detail: the study of
convective overshooting into stably stratified layers around convection zones
in stars. | astro-ph |
A Lagrangian Dynamical Theory for the Mass Function of Cosmic
Structures: I Dynamics: A new theory for determining the mass function of cosmic structures is
presented. It relies on a realistic treatment of collapse dynamics.
Gravitational collapse is analyzed in the Lagrangian perturbative framework.
Lagrangian perturbations provide an approximation of truncated type, i.e.
small-scale structure is filtered out. The collapse time is suitably defined as
the instant at which orbit crossing takes place. The convergence of the
Lagrangian series in predicting the collapse time of a homogeneous ellipsoid is
demonstrated; it is also shown that third-order calculations are necessary in
predicting collapse. Then, the Lagrangian prediction, with a correction for
quasi-spherical perturbations, can be used to determine the collapse time of a
homogeneous ellipsoid in a fast and precise way. Furthermore, ellipsoidal
collapse can be considered as a particular truncation of the Lagrangian series.
Gaussian fields with scale-free power spectra are then considered. The
Lagrangian series for the collapse time is found to converge when the collapse
time is not large. In this case, ellipsoidal collapse gives a fast and accurate
approximation of the collapse time; spherical collapse is found to poorly
reproduce the collapse time, even in a statistical sense. Analytical fits of
the distribution functions of the inverse collapse times, as predicted by the
ellipsoid model and by third-order Lagrangian theory, are given. These will be
necessary for a determination of the mass function, which will be given in
paper II. | astro-ph |
Equation of state description of the dark energy transition between
quintessence and phantom regimes: The dark energy crossing of the cosmological constant boundary (the
transition between the quintessence and phantom regimes) is described in terms
of the implicitly defined dark energy equation of state. The generalizations of
the models explicitly constructed to exhibit the crossing provide the insight
into the cancellation mechanism which makes the transition possible. | astro-ph |
Asteroids and Comets: Asteroids and comets are remnants from the era of Solar System formation over
4.5 billion years ago, and therefore allow us to address two fundamental
questions in astronomy: what was the nature of our protoplanetary disk, and how
did the process of planetary accretion occur? The objects we see today have
suffered many geophysically-relevant processes in the intervening eons that
have altered their surfaces, interiors, and compositions. In this chapter we
review our understanding of the origins and evolution of these bodies, discuss
the wealth of science returned from spacecraft missions, and motivate important
questions to be addressed in the future. | astro-ph |
Radio continuum and far-infrared emission from the galaxies in the
Eridanus group: The Eridanus galaxies follow the well-known radio-FIR correlation. Majority
(70%) of these galaxies have their star formation rates below that of the Milky
Way. The galaxies having a significant excess of radio emission are identified
as low luminosity AGNs based on their radio morphologies obtained from the GMRT
observations. There are no powerful AGNs (L{20cm} > 10^{23} W Hz^{-1}) in the
group. The two most far-infrared and radio luminous galaxies in the group have
optical and HI morphologies suggestive of recent tidal interactions. The
Eridanus group also has two far-infrared luminous but radio-deficient galaxies.
It is believed that these galaxies are observed within a few Myr of the onset
of an intense star formation episode after being quiescent for at least a 100
Myr. The upper end of the radio luminosity distribution of the Eridanus
galaxies (L_{20cm} ~ 10^{22} W Hz^{-1}) is consistent with that of the field
galaxies, other groups, and late-type galaxies in nearby clusters. | astro-ph |
AEGIS: The Morphologies of Green Galaxies at 0.4<z<1.2: We present quantitative morphologies of ~300 galaxies in the
optically-defined green valley at 0.4<z<1.2, in order to constrain the
mechanism(s) responsible for quenching star formation in the bulk of this
population. The sample is selected from galaxies in the All-Wavelength Extended
Groth Strip International Survey (AEGIS). While the green valley is defined
using optical U-B colors, we find that using a green valley sample defined
using NUV-R colors does not change the results. Using HST/ACS imaging, we study
several quantitative morphological parameters including CAS, B/T from GIM2D,
and Gini/M_20. We find that the green galaxy population is intermediate between
the red and blue galaxy populations in terms of concentration, asymmetry, and
morphological type and merger fraction estimated using Gini/M_20. We find that
most green galaxies are not classified as mergers; in fact, the merger fraction
in the green valley is lower than in the blue cloud. We show that at a given
stellar mass, green galaxies have higher concentration values than blue
galaxies and lower concentration values than red galaxies. Additionally, we
find that 12% of green galaxies have B/T = 0 and 21% with B/T \leq 0.05. Our
results show that green galaxies are generally massive (M\ast ~ 10^10.5 M_sun)
disk galaxies with high concentrations. We conclude that major mergers are
likely not the sole mechanism responsible for quenching star formation in this
population and that either other external processes or internal secular
processes play an important role both in driving gas towards the center of
these galaxies and in quenching star formation. | astro-ph |
Finding Planets Around White Dwarf Remnants of Massive Stars: Planet frequency shows a strong positive correlation with host mass from the
hydrogen-burning limit to M ~ 2Msun. No search has yet been conducted for
planets of higher-mass hosts because all existing techniques are insensitive to
these planets. We show that infrared observations of the white-dwarf (WD)
remnants of massive stars 3Msun < M < 7Msun would be sensitive to these planets
for reasons that are closely connected to the insensitivity of other methods.
We identify 49 reasonably bright, young, massive WDs from the Palomar-Green
survey and discuss methods for detecting planets and for distinguishing between
planet and disk explanations for any excess flux observed. The young, bright,
massive WD sample could be expanded by a factor 4-5 by surveying the remainder
of the sky for bright UV-excess objects. | astro-ph |
Variability in X-ray line ratios in helium-like ions of massive stars:
the radiation-driven case: Line ratios in "fir" triplets of helium-like ions have proven to be a
powerful diagnostic of conditions in X-ray emitting gas surrounding massive
stars. Recent observations indicate that these ratios can be variable with
time.
The possible causes of variation in line ratios are limited: changes in the
radiation field or changes in density, and changes in mass-loss or geometry. In
this paper, we investigate the ability of changes in the radiation field to
induce variability in the ratio R=f/i.
To isolate the radiative effect, we use a heuristic model of temperature and
radius changes in variable stars in the B and O range with low-density,
steady-state winds. We model the changes in emissivity of X-ray emitting gas
close to the star due to differences in level-pumping from available UV photons
at the location of the gas.
We find that under these conditions, variability in R is dominated by the
stellar temperature. Although the relative amplitude of variability is roughly
comparable for most lines at most temperatures, detectable variations are
limited to a few lines for each spectral type. We predict that variable values
in R due to stellar variability must follow predictable trends found in our
simulations.
Our model uses radial pulsations as a mode of stellar variability that
maximizes the amplitude of variation in R. This model is robust enough to show
which ions will provide the best opportunity for observing variability in the
f/i ratio at different stellar temperatures, and the correlation of that
variability with other observable parameters. In real systems, the effects
would be more complex than in our model, with differences in phase and
suppressed amplitude in the presence of non-radial pulsations. This suggests
that changes in R across many lines concurrently are not likely to be produced
by a variable radiation field. | astro-ph |
Charge-sign dependent solar modulation for everyone: We present a tool to compute the influence of charge-sign dependent solar
modulation for cosmic ray spectra. The code is publicly available, easy to use
and offers an extended view on solar modulation compared to the force-field
approximation. We present some examples for proton and antiproton fluxes in the
light of recent experimental data. | astro-ph |
Analyzing X-ray pulsar profiles: geometry and beam pattern of A 0535+26: We applied a decomposition method to the energy dependent pulse profiles of
the accreting binary pulsar A 0535+26, in order to identify the contribution of
the two magnetic poles of the neutron star and to obtain constraints on the
geometry of the system and on the beam pattern. We analyzed pulse profiles
obtained from RXTE observations in the X-ray regime. Basic assumptions of the
method are that the asymmetry observed in the pulse profiles is caused by
non-antipodal magnetic poles and that the emission regions have axisymmetric
beam patterns. Constraints on the geometry of the pulsar and a possible
solution of the beam pattern are given. We interpreted the reconstructed beam
pattern in terms of a geometrical model of a hollow column plus a halo of
scattered radiation on the neutron star surface, which includes relativistic
light deflection. | astro-ph |
The 5 - 10 keV AGN luminosity function at 0.01<z<4.0: The active galactic nuclei X-ray luminosity function traces actively
accreting supermassive black holes and is essential for the study of the
properties of the active galactic nuclei (AGN) population, black hole
evolution, and galaxy-black hole coevolution. Up to now, the AGN luminosity
function has been estimated several times in soft (0.5-2 keV) and hard X-rays
(2-10 keV). AGN selection in these energy ranges often suffers from
identification and redshift incompleteness and, at the same time, photoelectric
absorption can obscure a significant amount of the X-ray radiation. We estimate
the evolution of the luminosity function in the 5-10 keV band, where we
effectively avoid the absorbed part of the spectrum, rendering absorption
corrections unnecessary up to NH=10^23 cm^-2. Our dataset is a compilation of
six wide, and deep fields: MAXI, HBSS, XMM-COSMOS, Lockman Hole, XMM-CDFS,
AEGIS-XD, Chandra-COSMOS, and Chandra-CDFS. This extensive sample of ~1110 AGN
(0.01<z<4.0, 41<log L_x<46) is 98% redshift complete with 68% spectroscopic
redshifts. We use Bayesian analysis to select the best parametric model from
simple pure luminosity and pure density evolution to more complicated
luminosity and density evolution and luminosity-dependent density evolution. We
estimate the model parameters that describe best our dataset separately for
each survey and for the combined sample. We show that, according to Bayesian
model selection, the preferred model for our dataset is the
luminosity-dependent density evolution (LDDE). Our estimation of the AGN
luminosity function does not require any assumption on the AGN absorption and
is in good agreement with previous works in the 2-10 keV energy band based on
X-ray hardness ratios to model the absorption in AGN up to redshift three. Our
sample does not show evidence of a rapid decline of the AGN luminosity function
up to redshift four. [abridged] | astro-ph |
Non-thermal X-ray and Gamma-ray Emission from the Colliding Wind Binary
WR140: WR140 is the archetype long-period colliding wind binary (CWB) system, and is
well known for dramatic variations in its synchrotron emission during its
7.9-yr, highly eccentric orbit. This emission is thought to arise from
relativistic electrons accelerated at the global shocks bounding the
wind-collision region (WCR). The presence of non-thermal electrons and ions
should also give rise to X-ray and gamma-ray emission from several separate
mechanisms, including inverse-Compton cooling, relativistic bremsstrahlung, and
pion decay. We describe new calculations of this emission and make some
preliminary predictions for the new generation of gamma-ray observatories. We
determine that WR140 will likely require several Megaseconds of observation
before detection with INTEGRAL, but should be a reasonably strong source for
GLAST. | astro-ph |
The ICECUBE prototype string in AMANDA: The Antarctic Muon And Neutrino Detector Array (Amanda) is a high-energy
neutrino telescope. It is a lattice of optical modules (OM) installed in the
clear ice below the South Pole Station. Each OM contains a photomultiplier tube
(PMT) that detects photons of Cherenkov light generated in the ice by muons and
electrons. IceCube is a cubic-kilometer-sized expansion of Amanda currently
being built at the South Pole. In IceCube the PMT signals are digitized already
in the optical modules and transmitted to the surface. A prototype string of 41
OMs equipped with this new all-digital technology was deployed in the Amanda
array in the year 2000. In this paper we describe the technology and
demonstrate that this string serves as a proof of concept for the IceCube
array. Our investigations show that the OM timing accuracy is 5 ns. Atmospheric
muons are detected in excellent agreement with expectations with respect to
both angular distribution and absolute rate. | astro-ph |
Updated Proper Motion of the Neutron Star in the Supernova Remnant
Cassiopeia~A: In this paper, we present updated estimates of the velocity of the neutron
star (NS) in the supernova remnant (SNR) Cassiopeia A using over two decades of
Chandra observations. We use two methods: 1.) recording NS positions from
dozens of Chandra observations, including the astrometric uncertainty estimates
on the data points but not correcting the astrometry of the observations, and
2.) correcting the astrometry of the 13 Chandra observations that have a
sufficient number of point sources with identified Gaia counterparts. For
method #1, we find velocity of 280 $\pm$ 123 km s$^{-1}$, with an angle of 87
$\pm$ 22 degrees south of east. For method #2, we find a velocity of 445 $\pm$
90 km s$^{-1}$ at an angle of 68 $\pm$ 12 degrees south of east. Both of these
results match with the explosion-center-estimated velocity of $\sim$350 km
s$^{-1}$ and the previous 10 year baseline proper motion measurement of 570
$\pm$ 260 km s$^{-1}$, but our use of additional data over a longer baseline
has led to a smaller uncertainty by a factor of 2$\unicode{x2013}$3. Our
estimates rule out velocities $\gtrsim$600 km s$^{-1}$ and better match with
simulations of Cassiopeia A that include NS kick mechanisms. | astro-ph |
The Core Mass Function Across Galactic Environments. III. Massive
Protoclusters: The stellar initial mass function (IMF) is fundamental for many areas of
astrophysics, but its origin remains poorly understood. It may be inherited
from the core mass function (CMF) or arise as a result of more chaotic,
competitive accretion. Dense, gravitationally bound cores are seen in molecular
clouds and some observations have suggested that the CMF is similar in shape to
the IMF, though translated to higher masses by a factor of $\sim3$. Here we
measure the CMF in 28 dense clumps within 3.5 kpc that are likely to be central
regions of massive protoclusters, observed via $1.3\:{\rm{mm}}$ dust continuum
emission by the ALMAGAL project. We identify 222 cores using the dendrogram
algorithm with masses ranging from 0.04 to $252\:M_{\odot}$. We apply
completeness corrections for flux and number recovery, estimated from core
insertion and recovery experiments. At higher masses, the final derived CMF is
well described by a single power law of the form
$dN/d\:{\textrm{log}}\:M\propto\:M^{-\alpha}$ with $\alpha\simeq0.94\pm0.08$.
However, we find evidence of a break in this power-law behavior between $\sim5$
and $15\:M_{\odot}$, which is, to our knowledge, the first time such a break
has been found in distant ($\gtrsim 1$ kpc) regions by ALMA. We compare this
massive protocluster CMF with those derived using the same methods in the G286
protocluster and a sample of Infrared Dark Clouds. The massive protocluster CMF
is significantly different, i.e., containing more massive cores, which is a
potential indication of the role of environment on the CMF and IMF. | astro-ph |
Solar Energetic Particles and Associated EIT Disturbances in Solar Cycle
23: We explore the link between solar energetic particles (SEPs) observed at 1 AU
and large-scale disturbances propagating in the solar corona, named after the
Extreme ultraviolet Imaging Telescope (EIT) as EIT waves, which trace the
lateral expansion of a coronal mass ejection (CME). A comprehensive search for
SOHO/EIT waves was carried out for 179 SEP events during Solar Cycle 23
(1997-2006). 87% of the SEP events were found to be accompanied by EIT waves.
In order to test if the EIT waves play a role in the SEP acceleration, we
compared their extrapolated arrival time at the footpoint of the Parker spiral
with the particle onset in the 26 eastern SEP events that had no direct
magnetic connection to the Earth. We find that the onset of proton events was
generally consistent with this scenario. However, in a number of cases the
first near-relativistic electrons were detected too early. Furthermore, the
electrons had in general only weakly anisotropic pitch-angle distributions.
This poses a problem for the idea that the SEPs were accelerated by the EIT
wave or in any other spatially confined region in the low corona. The presence
of weak electron anisotropies in SEP events from the eastern hemisphere
suggests that transport processes in interplanetary space, including
cross-field diffusion, play a role in giving the SEPs access to a broad range
of helio-longitudes. | astro-ph |
The Dynamics of Tightly-packed Planetary Systems in the Presence of an
Outer Planet: case studies using Kepler-11 and Kepler-90: We explore the effects of an undetected outer giant planet on the dynamics,
observability, and stability of Systems with Tightly-packed Inner Planets
(STIPs). We use direct numerical simulations along with secular theory and
synthetic secular frequency spectra to analyze how analogues of Kepler-11 and
Kepler-90 behave in the presence of a nearly co-planar, Jupiter-like outer
perturber with semi-major axes between 1 and 5.2 au. Most locations of the
outer perturber do not affect the evolution of the inner planetary systems,
apart from altering precession frequencies. However, there are locations at
which an outer planet causes system instability due to, in part, secular
eccentricity resonances. In Kepler-90, there is a range of orbital distances
for which the outer perturber drives planets b and c, through secular
interactions, onto orbits with inclinations that are $\sim16^\circ$ away from
the rest of the planets. Kepler-90 is stable in this configuration. Such
secular resonances can thus affect the observed multiplicity of transiting
systems. We also compare the synthetic apsidal and nodal precession frequencies
with the secular theory and find some misalignment between principal
frequencies, indicative of strong interactions between the planets (consistent
with the system showing TTVs). First-order libration angles are calculated to
identify MMRs in the systems, for which two near-MMRs are shown in Kepler-90,
with a 5:4 between b and c, as well as a 3:2 between g and h. | astro-ph |
Phase-space mixing and the merging of cusps: Collisionless stellar systems are driven towards equilibrium by mixing of
phase-space elements. I show that the excess-mass function D(f)= int_{F(x,v)>f}
(F(x,v)-f) d^3x d^3v (with F(x,v) the coarse-grained distribution function)
always decreases on mixing. D(f) gives the excess mass from values of
F(x,v))>f. This novel form of the mixing theorem extends the maximum
phase-space density argument to all values of f. The excess-mass function can
be computed from N-body simulations and is additive: the excess mass of a
combination of non-overlapping systems is the sum of their individual D(f). I
propose a novel interpretation for the coarse-grained distribution function,
which avoids conceptual problems with the mixing theorem.
As an example application, I show that for self-gravitating cusps (rho propto
r^{-gamma} as r->0) the excess mass D propto f^{-2(3-gamma)/(6-gamma)} as
f->oo, i.e. steeper cusps are less mixed than shallower ones, independent of
the shape of surfaces of constant density or details of the distribution
function (e.g. anisotropy). This property, together with the additivity of D(f)
and the mixing theorem, implies that a merger remnant cannot have a cusp
steeper than the steepest of its progenitors. Furthermore, I argue that the
remnant's cusp should not be shallower either, implying that the steepest cusp
always survives. | astro-ph |
Multiple stellar populations in Schwarzschild modeling and the
application to the Fornax dwarf: Dwarf spheroidal (dSph) galaxies are believed to be strongly dark matter
dominated and thus are considered perfect objects to study dark matter
distribution and test theories of structure formation. They possess resolved,
multiple stellar populations that offer new possibilities for modeling. A
promising tool for the dynamical modeling of these objects is the Schwarzschild
orbit superposition method. In this work we extend our previous implementation
of the scheme to include more than one population of stars and a more general
form of the mass-to-light ratio function. We tested the improved approach on a
nearly spherical, gas-free galaxy formed in the cosmological context from the
Illustris simulation. We modeled the binned velocity moments for stars split
into two populations by metallicity and demonstrate that in spite of larger
sampling errors the increased number of constraints leads to significantly
tighter confidence regions on the recovered density and velocity anisotropy
profiles. We then applied the method to the Fornax dSph galaxy with stars
similarly divided into two populations. In comparison with our earlier work, we
find the anisotropy parameter to be slightly increasing, rather than
decreasing, with radius and more strongly constrained. We are also able to
infer anisotropy for each stellar population separately and find them to be
significantly different. | astro-ph |
Sources of X-rays from galaxies: Galactic X-ray emission is a manifestation of various high-energy phenomena
and processes. The brightest X-ray sources are typically accretion-powered
objects: active galactic nuclei and low- or high-mass X-ray binaries. Such
objects with X-ray luminosities of > 10^{37} ergs/s can now be detected
individually in nearby galaxies. The contributions from fainter discrete
sources (including cataclysmic variables, active binaries, young stellar
objects, and supernova remnants) are well correlated with the star formation
rate or stellar mass of galaxies. The study of discrete X-ray sources is
essential to our understanding of stellar evolution, dynamics, and end-products
as well as accretion physics. With the subtraction of the discrete source
contributions, one can further map out truly diffuse X-ray emission, which can
be used to trace the feedback from active galactic nuclei, as well as from
stars, both young and old, in the form of stellar winds and supernovae. The
X-ray emission efficiency, however, is only about 1% of the energy input rate
of the stellar feedback alone. The bulk of the feedback energy is most likely
gone with outflows into large-scale galactic halos. Much is yet to be
investigated to comprehend the role of such outflows in regulating the
ecosystem, hence the evolution of galaxies. Even the mechanism of the diffuse
X-ray emission remains quite uncertain. A substantial fraction of the emission
cannot arise directly from optically-thin thermal plasma, as commonly assumed,
and most likely originates in its charge exchange with neutral gas. These
uncertainties underscore our poor understanding of the feedback and its
interplay with the galaxy evolution. | astro-ph |
Massive black holes at high redshifts from superconducting cosmic
strings: The observation of quasars at high redshifts presents a mystery in the theory
of black hole formation. In order to source such objects, one often relies on
the presence of heavy seeds ($M \approx 10^{4-6} \, M_{\odot}$) in place at
early times. Unfortunately, the formation of these heavy seeds are difficult to
realize within the standard astrophysical context. Here, we investigate whether
superconducting cosmic string loops can source sufficiently strong
overdensities in the early universe to address this mystery. We review a set of
direct collapse conditions under which a primordial gas cloud will undergo
monolithic collapse into a massive black hole (forming with a mass of $M_{BH}
\approx 10^5 \, M_{\odot}$ at $z \approx 300$ in our scenario), and
systematically show how superconducting cosmic string loops can satisfy such
conditions in regions of the $G\mu-I$ parameter space. | astro-ph |
Bridging the Gap Between Simply Parametrized and Free-Form Pixelated
Models of Galaxy Lenses: The Case of WFI 2033-4723 Quad: We study the radial and azimuthal mass distribution of the lensing galaxy in
WFI2033-4723. Mindful of the fact that modeling results depend on modeling
assumptions, we examine two very different recent models: simply parametrized
(SP) models from the H0LiCOW collaboration, and pixelated free-form (FF) GLASS
models. In addition, we fit our own models which are a compromise between the
astrophysical grounding of SP, and the flexibility of FF approaches. Our models
consist of two offset parametric mass components, and generate many solutions,
all fitting the quasar point image data. Among other results, we show that to
reproduce point image properties the lensing mass must be lopsided, but the
origin of this asymmetry can reside in the main lens plane or along the line of
sight. We also show that there is a degeneracy between the slope of the density
profile and the magnitude of external shear, and that the models from various
modeling approaches are connected not by the mass sheet degeneracy, but by a
more generalized transformation. Finally, we discuss interpretation degeneracy
which afflicts all mass modeling: inability to correctly assign mass to the
main lensing galaxy vs. nearby galaxies or line of sight structures. While this
may not be a problem for the determination of $H_0$, interpretation degeneracy
may become a major issue for the detailed study of galaxy structure. | astro-ph |
Synchrotron radiation from the fast tail of dynamical ejecta of neutron
star mergers: We find, using high resolution numerical relativistic simulations, that the
tail of the dynamical ejecta of neutron star mergers extends to mildly
relativistic velocities faster than $0.7c$. The kinetic energy of this fast
tail is $\sim 10^{47}$--$10^{49}$ erg, depending on the neutron star equation
of state and on the binary masses. The synchrotron flare arising from the
interaction of this fast tail with the surrounding ISM can power the observed
non-thermal emission that followed GW170817, provided that the ISM density is
$\sim 10^{-2}\,{\rm cm^{-3}}$, the two neutron stars had roughly equal masses
and the neutron star equation of state is soft (small neutron star radii). One
of the generic predictions of this scenario is that the cooling frequency
crosses the X-ray band on a time scale of a few months to a year, leading to a
cooling break in the X-ray light curve. If this dynamical ejecta scenario is
correct, we expect that the synchrotron radio flare from the ejecta that have
produced the macronova/kilonova emission will be observable on time scales of
$10^3$ to $10^5$ days. Further multi-frequency observations will confirm or
rule out this dynamical ejecta scenario. | astro-ph |
Kinematics of Black Hole X-ray Binary GRS 1915+105: The space velocity of a stellar black hole encodes the history of its
formation and evolution. Here we measure the 3-dimensional motion of the
microquasar GRS 1915+105, using a decade of astrometry with the NRAO Very Long
Baseline Array, together with the published radial velocity. The velocity in
the Galactic Plane deviates from circular rotation by 53-80 +_ 8 km/s, where
the range covers any specific distance from 6-12 kpc. Perpendicular to the
plane, the velocity is only 10 +_ 4 km/s. The peculiar velocity is minimized at
a distance 9-10 kpc, and is then nearly in the radial direction towards the
Galactic Center. We discuss mechanisms for the origin of the peculiar velocity,
and conclude that it is most likely a consequence of Galactic velocity
diffusion on this old binary, rather than the result of a supernova kick during
the formation of the 14 Mo black hole. Finally, a brief comparison is made with
4 other BH binaries whose kinematics are well determined. | astro-ph |
Inhomogeneous Big Bang Nucleosynthesis: Upper Limit on Omega_b and
Production of Lithium, Beryllium, and Boron: We examine the Big Bang nucleosynthesis (BBN) process in the presence of
small-scale baryon inhomogeneities. Primordial abundance yields for D, He4,
Li6, Li7, Be9, and B11 are computed for wide ranges of parameters
characterizing the inhomogeneities taking account of all relevant diffusive and
hydrodynamic processes. These calculations may be of interest due to (a) recent
observations of the anisotropies in the cosmic microwave background radiation
favoring slightly larger baryonic contribution to the critical density,
Omega_b, than allowed by a standard BBN scenario and (b) new observational
determinations of Li6 and Be9 in metal-poor halo stars. We find considerable
parameter space in which production of D and He4 is in agreement with
observational constraints even for Omega_b h^2 a factor 2-3 larger than the
Omega_b inferred from standard BBN. Nevertheless, in this parameter space
synthesis of Li7 in excess of the inferred Li7 abundance on the Spite plateau
results. Production of Li6, Be9, and B11 in inhomogeneous BBN scenarios is
still typically well below the abundance of these isotopes observed in the most
metal-poor stars to date thus neither confirming nor rejecting inhomogeneous
BBN. In an appendix we summarize results of a reevaluation of baryon diffusion
constants entering inhomogeneous BBN calculations. | astro-ph |
BST1047+1156: A (Failing) Ultradiffuse Tidal Dwarf in the Leo I Group: We use deep Hubble Space Telescope imaging to study the resolved stellar
populations in BST1047+1156, a gas-rich, ultradiffuse dwarf galaxy found in the
intragroup environment of the Leo I galaxy group. While our imaging reaches
approximately two magnitudes below the tip of the red giant branch at the Leo I
distance of 11 Mpc, we find no evidence for an old red giant sequence that
would signal an extended star formation history for the object. Instead, we
clearly detect the red and blue helium burning sequences of its stellar
populations, as well as the fainter blue main sequence, all indicative of a
recent burst of star formation having taken place over the past 50--250 Myr.
Comparing to isochrones for young metal-poor stellar populations, we infer this
post-starburst population to be moderately metal poor, with metallicity [M/H]
in the range -1 to -1.5. The combination of a young, moderately metal-poor post
starburst population and no old stars motivates a scenario in which BST1047 was
recently formed during a weak burst of star formation in gas that was tidally
stripped from the outskirts of the neighboring massive spiral M96. BST1047's
extremely diffuse nature, lack of ongoing star formation, and disturbed HI
morphology all argue that it is a transitory object, a "failing tidal dwarf" in
the process of being disrupted by interactions within the Leo I group. Finally,
in the environment surrounding BST1047, our imaging also reveals the old,
metal-poor ([M/H]=-1.3 +/- 0.2) stellar halo of M96 at a projected radius of 50
kpc. | astro-ph |
Interstellar extinction in twenty open star clusters: The interstellar extinction law in twenty open star clusters namely Berkeley
7, Collinder 69, Hogg 10, NGC 2362, Czernik 43, NGC 6530, NGC 6871, Bochum 10,
Haffner 18, IC 4996, NGC 2384, NGC 6193, NGC 6618, NGC 7160, Collinder 232,
Haffner 19, NGC 2401, NGC 6231, NGC 6823 and NGC 7380 have been studied in the
optical and near-IR wavelength ranges. The difference between maximum and
minimum values of E(B-V) indicates the presence of non-uniform extinction in
all the clusters except Collinder 69, NGC 2362 and NGC 2384. The colour excess
ratios are consistent with a normal extinction law for the clusters NGC 6823,
Haffner 18, Haffner 19, NGC 7160, NGC 6193, NGC 2401, NGC 2384, NGC 6871, NGC
7380, Berkeley 7, Collinder 69 and IC 4996. We found that differential
colour-excess which may be due to the occurrence of dust and gas inside the
clusters, decreases with age of the clusters. A spatial variation of colour
excess is found in NGC 6193 in sense that it decreases from east to west in
cluster region. For cluster Berkeley 7, NGC 7380 and NGC 6871, a dependence of
colour excess with spectral class and luminosity is observed. Eight stars in
Collinder 232, four stars in NGC 6530 and one star in NGC 6231 have colour
excess flux in near-IR. This indicates that these stars may have circumstellar
material around them. | astro-ph |
Dependence of the He/H8 emission ratio on brightness, temperature, and
structuring of prominences: We investigate the dependence of the He/H8 emission ratio on kinetic
temperature and total Balmer brightness. The line pair He\,{\sc i}\,3888\,\AA{}
and H$_8$\,3889 has been observed simultaneously with the Ca II 8498 line in a
number of quiescent prominences. The He/H8 emission ratio R is found to cover
defined parts of a general anti-relation with the total H8 emission, depending
on the kinetic temperature, T_kin, of the individual prominence: High H8
brightness is related to small R and T_kin values, and preferably occurs in
prominences with a less significant fine-structure. | astro-ph |
Clustered Massive Star Formation in Molecular Clouds: I review some important questions in the field of massive star formation:
What are the initial conditions for proto star clusters and how do they arise?
What are the initial conditions for individual massive star formation within
star clusters? How do massive protostars accumulate their mass? I compare the
Turbulent Core Model (McKee & Tan 2003) to several nearby regions, including
Orion KL. Here I also discuss the origin of BN's high proper motion. | astro-ph |
Prompt emission of GRB 121217A from gamma-rays to the NIR: The mechanism that causes the prompt-emission episode of gamma-ray bursts
(GRBs) is still widely debated despite there being thousands of prompt
detections. The favoured internal shock model relates this emission to
synchrotron radiation. However, it does not always explain the spectral indices
of the shape of the spectrum, often fit with empirical functions.
Multi-wavelength observations are therefore required to help investigate the
possible underlying mechanisms that causes the prompt emission. We present GRB
121217A, for which we were able to observe its near-infrared (NIR) emission
during a secondary prompt-emission episode with the Gamma-Ray Burst Optical
Near-infrared Detector (GROND) in combination with the Swift and Fermi
satellites, covering an energy range of 0.001 keV to 100 keV. We determine a
photometric redshift of z=3.1+/-0.1 with a line-of-sight extinction of A_V~0
mag, utilising the optical/NIR SED. From the afterglow, we determine a bulk
Lorentz factor of Gamma~250 and an emission radius of R<10^18 cm. The
prompt-emission broadband spectral energy distribution is well fit with a
broken power law with b1=-0.3+/-0.1, b2=0.6+/-0.1 that has a break at
E=6.6+/-0.9 keV, which can be interpreted as the maximum injection frequency.
Self-absorption by the electron population below energies of E_a<6 keV suggest
a magnetic field strength of B~10^5 G. However, all the best fit models
underpredict the flux observed in the NIR wavelengths, which also only
rebrightens by a factor of ~2 during the second prompt emission episode, in
stark contrast to the X-ray emission, which rebrightens by a factor of ~100,
suggesting an afterglow component is dominating the emission. We present GRB
121217A one of the few GRBs for which there are multi-wavelength observations
of the prompt-emission period and show that it can be understood with a
synchrotron radiation model. | astro-ph |
Fast-varying time lags in the Quasi-periodic Oscillation in GRS 1915+105: The properties of sub-second time variability of the X-ray emission of the
black-hole binary GRS 1915+105 are very complex and strictly connected to its
patterns of variability observed on long time scales. A key aspect for
determining the geometry of the accretion flow is the study of time lags
between emission at different energies, as they are associated to key time
scales of the system. In particular, it is important to examine the lags
associated to the strong low-frequency Quasi-periodic Oscillations (QPOs), as
the QPOs provide unambiguous special frequencies to sample the variability. We
have analyzed data from an observation with the AstroSat satellite, in which
the frequency of the low-frequency QPO varies smoothly between 2.5 and 6.6 Hz
on a time scale of ~10 hours. The derived phase lags show the same properties
and evolution of those observed on time scales of a few hundred days,
indicating that changes in the system geometry can take place on times below
one day. We fit selected energy spectra of the source and rms and phase-lag
spectra of the QPO with a time-variable Comptonization model, as done
previously to RossiXTE data of the same source, and find that indeed the
derived parameters match those obtained for variations on much longer time
scales. | astro-ph |
On the origin of X-ray spectra in luminous blazars: Gamma-ray luminosities of some quasar-associated blazars imply jet powers
reaching values comparable to the accretion power even if assuming very strong
Doppler boosting and very high efficiency of gamma-ray production. With much
lower radiative efficiencies of protons than of electrons, and the recent
reports of very strong coupling of electrons with shock-heated protons
indicated by Particle-in-Cell (PIC) simulations, the leptonic models seem to be
strongly favored over the hadronic ones. However, the electron-proton coupling
combined with the ERC (External-Radiation-Compton) models of gamma-ray
production in leptonic models predict extremely hard X-ray spectra, with energy
indices about 0. This is inconsistent with the observed 2-10 keV slopes of
blazars, which cluster around an index value of 0.6. This problem can be
resolved by assuming that electrons can be cooled down radiatively to
non-relativistic energies, or that blazar spectra are entirely dominated by the
SSC (Synchrotron-Self Compton) component up to at least 10 keV. Here, we show
that the required cooling can be sufficiently efficient only at distances r <
0.03pc. SSC spectra, on the other hand, can be produced roughly co-spatially
with the observed synchrotron and ERC components, which are most likely located
roughly at a parsec scale. We show that the dominant SSC component can also be
produced much further than the dominant synchrotron and ERC components, at
distances larger than 10 parsecs. Hence, depending on the spatial distribution
of the energy dissipation along the jet, one may expect to see
gamma-ray/optical events with either correlated or uncorrelated X-rays. In all
cases the number of electron-positron pairs per proton is predicted to be very
low. The direct verification of the proposed SSC scenario requires sensitive
observations in the hard X-ray band which is now possible with the NuSTAR
satellite. | astro-ph |
The Radiative Efficiency of Hot Accretion Flows: Two significant progresses have been made in the past years on our
understanding of hot accretion flows. One is that only a small fraction of
accretion flow available at the outer boundary can finally falls onto the black
hole while most of them is lost in outflow. Another one is that electrons may
directly receive a large fraction of the viscously dissipated energy in the
accretion flow, i.e, $\delta\sim 0.1-0.5$. The radiative efficiency of hot
accretion flow when these two progresses are taken into account has not been
systematically studied and is the subject of the present paper. We consider two
regimes of hot accretion model. One is the advection dominated accretion flows
(ADAFs) which lie on low accretion rate regime, $\la 10\alpha^2\ledd/c^2$;
another being the luminous hot accretion flows (LHAFs) which lie above this
accretion rate. For the latter, we assume that the accretion flow will has a
two-phase structure above a certain accretion rate, and a simplification is
adopted in our calculation of the dynamics. Our results indicate that the
radiative efficiency of hot accretion flow increases with the accretion rate
and is highly enhanced by the direct viscous heating to electrons compared to
the previous case of $\delta\ll 1$. When the accretion rate is high, the
radiative efficiency of hot accretion flow is comparable to that of the
standard thin disk. Fitting formulae of radiative efficiency as a function of
accretion rate for various $\delta$ values are presented. | astro-ph |
JWST high-z galaxy constraints on warm and cold dark matter models: We compare properties of high-redshift galaxies observed by JWST with
hydrodynamical simulations, in the standard cold dark matter model and in warm
dark matter models with a suppressed linear matter power spectrum. We find that
current data are not in tension with cold dark matter nor with warm dark matter
models with mWDM > 2 keV, since they probe bright and rare objects whose
physical properties are similar in the different scenarios. We also show how
two observables, the galaxy luminosity functions and the galaxy correlation
function at small scales of faint objects, can be promising tools for
discriminating between the different dark matter models. Further hints may come
from early stellar-mass statistics and galaxy CO emission. | astro-ph |
A Fourier method for the determination of focus for telescopes with
stars: We introduce a Fourier method (Fm) for the determination of best focus for
telescopes with stars. Our method fits a power function, that we will derive in
this paper, to a set of images taken as a function of focuser position. The
best focus position is where the power is maximum. Fm was first tested with
small refractor and Schmidt-Cassegrain (SCT) telescopes. After the successful
small telescope tests, we then tested Fm with a 2 m Ritchey-Chr\'etien-Coud\'e
(RCC). Our tests show that Fm is immune to the problems inherent in the popular
half-flux diameter method. | astro-ph |
End of preview. Expand
in Dataset Viewer.
README.md exists but content is empty.
- Downloads last month
- 40
Size of downloaded dataset files:
23.4 MB
Size of the auto-converted Parquet files:
12.5 MB
Number of rows:
21,000