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The Fourth VLBA Calibrator Survey - VCS4: This paper presents the fourth extension to the Very Long Baseline Array
(VLBA) Calibrator Survey, containing 258 new sources not previously observed
with very long baseline interferometry (VLBI). This survey, based on three 24
hour VLBA observing sessions, fills remaining areas on the sky above
declination -40 degrees where the calibrator density is less than one source
within a 4 degree radius disk at any given direction. The share of these area
was reduced from 4.6% to 1.9%. Source positions were derived from astrometric
analysis of group delays determined at 2.3 and 8.6 GHz frequency bands using
the Calc/Solve software package. The VCS4 catalogue of source positions, plots
of correlated flux density versus projected baseline length, contour plots and
fits files of naturally weighted CLEAN images, as well as calibrated visibility
function files are available on the Web at http://gemini.gsfc.nasa.gov/vcs4 . | astro-ph |
Compact Galaxies at Intermediate Redshifts Quench Faster than
Normal-sized Galaxies: Massive quiescent compact galaxies have been discovered at high redshifts,
associated with rapid compaction and cessation of star formation (SF). In this
work we set out to quantify the time-scales in which SF is quenched in compact
galaxies at intermediate redshifts. For this, we select a sample of green
valley galaxies within the COSMOS field in the midst of quenching their SF at
$0.5<z<1.0$ that exhibit varying degrees of compactness. Based on the H$\delta$
absorption line and the 4000 \AA \ break of coadded zCOSMOS spectra for
sub-samples of normal-sized and compact galaxies we determine quenching
time-scales as a function of compactness. We find that the SF quenching
time-scales in green valley compact galaxies are much shorter than in
normal-sized ones. In an effort to understand this trend, we use the Illustris
simulation to trace the evolution of the SF history, the growth rate of the
central super massive black hole (SMBH) {\bf and the AGN-feedback in compact
and normal-sized galaxies. We find that the key difference between their SF
quenching time-scales is linked to the mode of the AGN-feedback. In the compact
galaxies predominates the kinematic-mode, which is highly efficient at
quenching the SF by depleting the internal gas. On the normal-sized galaxies,
the prevailing thermal-mode injects energy in the circumgalactic gas, impeding
the cold gas supply and quenching the SF via the slower strangulation
mechanism.} These results are consistent with the violent disk instability and
gas-rich mergers scenarios, followed by strong AGN and stellar feedback.
Although this kind of event is most expected to occur at $z=2-3$, we find
evidences that the formation of compact quiescent galaxies can occur at $z<1$. | astro-ph |
QU Carinae: a SNeIa progenitor?: Optical spectra obtained in 2006-07 of the nova-like cataclysmic variable QU
Car are studied for radial velocities, line profiles, and line identifications.
We are not able to confirm the reported 10.9 hr orbital period from 1982,partly
because our sampling is not ideal for this purpose and also, we suspect,
because our radial velocities are distorted by line profile changes due to an
erratic wind. P-Cygni profiles are found in several of the emission lines,
including those of C IV. Carbon lines are abundant in the spectra, suggesting a
carbon enrichment in the doner star. The presence of [O III] 5007\AA and [N II]
6584\AA is likely due to a diffuse nebula in the vicinity of the system.
The wind signatures in the spectra and the presence of nebular lines are in
agreement with the accretion wind evolution scenario that has been suggested to
lead to SNeIa. We argue that QU Car is a member of the V Sge subclass of CVs,
and a possible SNeIa progenitor. It is shown that the recent light curve of QU
Car has ~1 mag low states, similar to the light curve of V Sge, strengthening
the connection of QU Car with V Sge stars, supersoft x-ray sources, and SNeIa
progenitors. | astro-ph |
Star Formation Signatures in the Condensation Downstream of HH 80N: HH80N is one of the Herbig-Haro objects that have associated quiescent dense
clumps. We report CO and CS BIMA observations that reveal star formation within
the HH80N dense clump. The CO emission reveals clearly a bipolar molecular
outflow centered on the dense clump. The CS emission traces a ring-like
structure of radius ~0.24 pc. The CS kinematics shows that the ring is
collapsing with an infall speed of ~0.6 km/s. The required mass to produce the
collapse is in agreement with previous ammonia observations of the 20 solar
mass core, which is embedded within the CS structure. However, we cannot
discard that the ring structure is expanding driven by protostellar winds, if
the CS abundance if unusually high and the CO momentum rate is much higher than
that measured, due to inclination and optical depth effects. The properties of
the molecular outflow and of the dense core suggest that it harbors a Class 0
object. There are also signatures of interaction of the HH 80/81/80N outflow
with the dense gas. In particular it is possible that the HH 80/81/80N outflow
has triggered or at least speed up the star formation in this region. | astro-ph |
On the (non-)enhancement of the Lyman α equivalent width by a
multiphase interstellar medium: It has been suggested that radiative transfer effects may explain the
unusually high equivalent widths (EWs) of the Lya line, observed occasionally
from starburst galaxies, especially at high redshifts. If the dust is locked up
inside high-density clouds dispersed in an empty intercloud medium, the Lya
photons could scatter off of the surfaces of the clouds, effectively having
their journey confined to the dustless medium. The continuum radiation, on the
other hand, does not scatter, and would thus be subject to absorption inside
the clouds. This scenario is routinely invoked when Lya EWs higher than what is
expected theoretically are observed, although the ideal conditions under which
the results are derived usually are not considered. Here we systematically
examine the relevant physical parameters in this idealized framework, testing
whether any astrophysically realistic scenarios may lead to such an effect. It
is found that although clumpiness indeed facilitates the escape of Lya, it is
highly unlikely that any real interstellar media should result in a
preferential escape of Lya over continuum radiation. Other possible causes are
discussed, and it is concluded that the observed high EWs are more likely to be
caused by cooling radiation from cold accretion and/or anisotropic escape of
the Lya radiation. | astro-ph |
NICER Discovery of Millisecond X-ray Pulsations and an Ultracompact
Orbit in IGR J17494-3030: We report the detection of 376.05 Hz (2.66 ms) coherent X-ray pulsations in
NICER observations of a transient outburst of the low-mass X-ray binary IGR
J17494-3030 in 2020 October/November. The system is an accreting millisecond
X-ray pulsar in a 75 minute ultracompact binary. The mass donor is most likely
a $\simeq 0.02 M_\odot$ finite-entropy white dwarf composed of He or C/O. The
fractional rms pulsed amplitude is 7.4%, and the soft (1-3 keV) X-ray pulse
profile contains a significant second harmonic. The pulsed amplitude and pulse
phase lag (relative to our mean timing model) are energy-dependent, each having
a local maximum at 4 keV and 1.5 keV, respectively. We also recovered the X-ray
pulsations in archival 2012 XMM-Newton observations, allowing us to measure a
long-term pulsar spin-down rate of $\dot\nu = -2.1(7)\times10^{-14}$ Hz/s and
to infer a pulsar surface dipole magnetic field strength of $\simeq 10^9$ G. We
show that the mass transfer in the binary is likely non-conservative, and we
discuss various scenarios for mass loss from the system. | astro-ph |
Multi-Scale CLEAN: A comparison of its performance against classical
CLEAN in galaxies using THINGS: A practical evaluation of the Multi-Scale CLEAN algorithm is presented. The
data used in the comparisons are taken from The HI Nearby Galaxy Survey
(THINGS). The implementation of Multi-Scale CLEAN in the CASA software package
is used, although comparisons are made against the very similar
Multi-Resolution CLEAN algorithm implemented in AIPS. Both are compared against
the classical CLEAN algorithm (as implemented in AIPS). The results of this
comparison show that several of the well-known characteristics and issues of
using classical CLEAN are significantly lessened (or eliminated completely)
when using the Multi-Scale CLEAN algorithm. Importantly, Multi-Scale CLEAN
reduces significantly the effects of the clean `bowl' caused by missing
short-spacings, and the `pedestal' of low-level un-cleaned flux (which affects
flux scales and resolution). Multi-Scale CLEAN can clean down to the noise
level without the divergence suffered by classical CLEAN. We discuss practical
applications of the added contrast provided by Multi-Scale CLEAN using two
selected astronomical examples: HI holes in the interstellar medium and
anomalous gas structures outside the main galactic disk. | astro-ph |
Why do only some Radio Galaxies acquire giant Sizes?: We study the morphology of the radio emission of giant radio galaxies (GRGs),
a rare type of active galaxies, in order to find new clues for the reasons of
their large size. Using radio images from two sky surveys at 1.4 GHz we
quantified their radio morphology by measuring the geometry (armlength, bending
angle, etc.) and flux symmetry for 58 such objects. Preliminary analysis
suggests that radio source symmetry does not differ between galaxies and
quasars, that there is no evidence for a decrease in linear size with redshift,
and only a marginal trend for increasing symmetry with larger size. A merging
with data available for other such objects is expected to yield new clues on
the possible reasons for their large size. We also searched radio survey images
around the positions of 1059 galaxies and quasars for further giant radio
sources, and present a preliminary sample of six of these. | astro-ph |
Photometric and spectroscopic variability of 53 Per: A new investigation of the variability of the SPB-type star 53 Per is
presented. The analysis of the BRITE photometry allowed us to determine eight
independent frequencies and the combination one. Five of these frequencies and
the combination one were not known before. In addition, we gathered more than
1800 new moderate and high-resolution spectra of 53 Per spread over
approximately six months. Their frequency analysis revealed four independent
frequencies and the combination one, all consistent with the BRITE results. | astro-ph |
The full spectral radiative properties of Proxima Centauri: The discovery of Proxima b, a terrestrial temperate planet, presents the
opportunity of studying a potentially habitable world in optimal conditions. A
key aspect to model its habitability is to understand the radiation environment
of the planet in the full spectral domain. We characterize the X-rays to mid-IR
radiative properties of Proxima with the goal of providing the
top-of-atmosphere fluxes on the planet. We also aim at constraining the
fundamental properties of the star. We employ observations from a large number
of facilities and make use of different methodologies to piece together the
full spectral energy distribution of Proxima. In the high-energy domain, we pay
particular attention to the contribution by rotational modulation, activity
cycle, and flares so that the data provided are representative of the overall
radiation dose received by the atmosphere of the planet. We present the full
spectrum of Proxima covering 0.7 to 30000 nm. The integration of the data shows
that the top-of-atmosphere average XUV irradiance on Proxima b is 0.293 W m^-2,
i.e., nearly 60 times higher than Earth, and that the total irradiance is
877+/-44 W m^-2, or 64+/-3% of the solar constant but with a significantly
redder spectrum. We also provide laws for the XUV evolution of Proxima
corresponding to two scenarios. Regarding the fundamental properties of
Proxima, we find M=0.120+/-0.003 Msun, R=0.146+/-0.007 Rsun, Teff=2980+/-80 K,
and L=0.00151+/-0.00008 Lsun. In addition, our analysis reveals a ~20% excess
in the 3-30 micron flux of the star that is best interpreted as arising from
warm dust in the system. The data provided here should be useful to further
investigate the current atmospheric properties of Proxima b as well as its past
history, with the overall aim of firmly establishing the habitability of the
planet. | astro-ph |
Empirical models for Dark Matter Halos. I. Nonparametric Construction of
Density Profiles and Comparison with Parametric Models: We use techniques from nonparametric function estimation theory to extract
the density profiles, and their derivatives, from a set of N-body dark matter
halos. We consider halos generated from LCDM simulations of gravitational
clustering, as well as isolated, spherical collapses. The logarithmic density
slopes gamma = d(log rho)/d(log r) of the LCDM halos are found to vary as
power-laws in radius, reaching values of gamma ~ -1 at the innermost resolved
radii (~0.01 r_virial). This behavior is significantly different from that of
broken power-law models like the NFW profile, but similar to that of models
like de Vaucouleurs'. Accordingly, we compare the N-body density profiles with
various parametric models to find which provide the best fit. We consider an
NFW-like model with arbitrary inner slope; Dehnen & McLaughlin's anisotropic
model; Einasto's model (identical in functional form to Sersic's model but fit
to the space density); and the density model of Prugniel & Simien that was
designed to match the deprojected form of Sersic's R^{1/n} law. Overall, the
best-fitting model to the LCDM halos is Einasto's, although the Prugniel-Simien
and Dehnen-McLaughlin models also perform well. With regard to the spherical
collapse halos, both the Prugniel-Simien and Einasto models describe the
density profiles well, with an rms scatter some four times smaller than that
obtained with either the NFW-like model or the 3-parameter Dehnen-McLaughlin
model. Finally, we confirm recent claims of a systematic variation in profile
shape with halo mass. | astro-ph |
Evidence for a New Class of Extreme UV Sources: Most of the sources detected in the extreme ultraviolet (EUV; 100 Ang to 600
Ang) by the Rosat WFC and EUVE all-sky surveys have been identified with active
late-type stars and hot white dwarfs that are near enough to escape absorption
by interstellar gas. However, about 15% of EUV sources are as of yet
unidentified with any optical counterparts. We examine whether the unidentified
EUV sources may consist of the same population of late-type stars and white
dwarfs. We present B and R photometry of stars in the fields of seven of the
unidentified EUV sources. We detect in the optical the entire main-sequence and
white-dwarf population out to the greatest distances where they could still
avoid absorption. We use colour-magnitude diagrams to demonstrate that, in most
of the fields, none of the observed stars have the colours and magnitudes of
late-type dwarfs at distances less than 100 pc. Similarly, none are white
dwarfs within 500 pc that are hot enough to be EUV-emitters. The unidentified
EUV sources we study are not detected in X-rays, while cataclysmic variables,
X-ray binaries, and active galactic nuclei generally are. We conclude that some
of the EUV sources may be a new class of nearby objects, that are either very
faint at optical bands or which mimic the colours and magnitudes of distant
late-type stars or cool white dwarfs. One candidate for optically faint objects
is isolated old neutron stars, slowly accreting interstellar matter. Such
neutron stars are expected to be abundant in the Galaxy, and have not been
unambiguously detected. | astro-ph |
SPI data analysis: the CESR/Toulouse approach: In order to allow for an efficient and flexible scientific analysis of data
from the SPI imaging spectrometer aboard INTEGRAL, I developed a set of
analysis executables that are publicly available through the internet. The
software is fully compatible with the ISDC data format. It complements software
that is actually available through ISDC, and will be included in the next ISDC
software release. This paper describes the design of my software system and
provides a brief introduction to the executables. | astro-ph |
The radial gradient of the near-surface shear layer of the Sun: Helioseismology has provided unprecedented information about the internal
rotation of the Sun. One of the important achievements was the discovery of two
radial shear layers: one near the bottom of the convection zone (the
tachocline) and one near the surface. These shear layers may be important
ingredients for explaining the magnetic cycle of the Sun. We measure the
logarithmic radial gradient of the rotation rate ($\rm d\ln\Omega/\rm d\ln r$)
near the surface of the Sun using 15 years of f mode rotational frequency
splittings from the Michelson Doppler Imager (MDI) and four years of data from
the Helioseismic and Magnetic Imager (HMI). We model the angular velocity of
the Sun in the upper $\sim 10$ Mm as changing linearly with depth and use a
multiplicative optimally localized averaging inversion to infer the gradient of
the rotation rate as a function of latitude. Both the MDI and HMI data show
that $\rm d\ln\Omega/\rm d\ln r$ is close to $-1$ from the equator to
60$^{\circ}$ latitude and stays negative up to 75$^{\circ}$ latitude. However,
the value of the gradient is different for MDI and HMI for latitudes above
$60^{\circ}$. Additionally, there is a significant difference between the value
of $d\ln\Omega/d\ln r$ using an older and recently reprocessed MDI data for
latitudes above $30^\circ$. We could reliably infer the value of $\rm
d\ln\Omega/\rm d\ln r$ up to 60$^{\circ}$, but not above this latitude, which
will hopefully constrain theories of the near-surface shear layer and dynamo.
Furthermore, the recently reprocessed MDI splitting data are more reliable than
the older versions which contained clear systematic errors in the high degree f
modes. | astro-ph |
High Energy Observations of XRF 030723: Evidence for an Off-axis
Gamma-Ray Burst?: We report High Energy Transient Explorer 2 (HETE-2) Wide Field X-ray
Monitor/French Gamma Telescope observations of XRF030723 along with
observations of the XRF afterglow made using the 6.5m Magellan Clay telescope
and the Chandra X-ray Observatory. The observed peak energy E_pk_obs of the nu
F_nu burst spectrum is found to lie within (or below) the WXM 2-25 keV passband
at 98.5% confidence, and no counts are detected above 30 keV. Our best fit
value is E_pk_obs=8.4+3.5/-3.4 keV. The ratio of X-ray to Gamma-ray flux for
the burst follows a correlation found for GRBs observed with HETE-2, and the
duration of the burst is similar to that typical of long-duration GRBs. If we
require that the burst isotropic equivalent energy E_iso and E_pk_rest satisfy
the relation discovered by Amati et al. (2002), a redshift of z=0.38+0.36/-0.18
can be determined, in agreement with constraints determined from optical
observations. We are able to fit the X-ray afterglow spectrum and to measure
its temporal fade. Although the best-fit fade is shallower than the concurrent
fade in the optical, the spectral similarity between the two bands indicates
that the X-ray fade may actually trace the optical fade. If this is the case,
the late time rebrightening observed in the optical cannot be due to a
supernova bump. We interpret the prompt and afterglow X-ray emission as arising
from a jetted GRB observed off-axis and possibly viewed through a complex
circumburst medium due to a progenitor wind. | astro-ph |
Gas Giant Simulations of Eddy-Driven Jets Accompanied by Deep Meridional
Circulation: Jupiter's atmosphere comprises several dynamical regimes: the equatorial
eastward flows and surrounding retrograde jets; the midlatitudes, with the
eddy-driven, alternating jet-streams and meridional circulation cells; and the
jet-free turbulent polar region. Despite intensive research conducted on each
of these dynamical regimes over the past decades, they remain only partially
understood. Saturn's atmosphere also encompasses similar distinguishable
regimes, but observational evidence for midlatitude deep meridional cells is
lacking. Models offer a variety of explanations for each of these regions, but
only a few are capable of simulating more than one of the regimes at once. This
study presents new numerical simulations using a 3D deep anelastic model that
can reproduce the equatorial flows as well as the midlatitudinal pattern of the
mostly barotropic, alternating eddy-driven jets and the meridional circulation
cells accompanying them. These simulations are consistent with recent Juno
mission gravity and microwave data. We find that the vertical eddy momentum
fluxes are as important as the meridional eddy momentum fluxes, which drive the
midlatitudinal circulation on Earth. In addition, we discuss the parameters
controlling the number of midlatitudinal jets/cells, their extent, strength,
and location. We identify the strong relationship between meridional
circulation and the zonal jets in a deep convection setup, and analyze the
mechanism responsible for their generation and maintenance. The analysis
presented here provides another step in the ongoing pursuit of understanding
the deep atmospheres of gas giants. | astro-ph |
An Empirical Correlation of $T_{\rm max}$ - $M_{\rm WD}$ of Dwarf Novae
and The Average White Dwarf Mass in Cataclysmic Variables in the Galactic
Bulge: The mean white dwarf (WD) mass in the Galactic bulge cataclysmic variables
(CVs) was measured by applying the the shock temperature-WD mass correlation of
magnetic cataclysmic variables (mCVs) to the Galactic Bulge X-ray Emission
(GBXE) spectra. However, the resulting mean WD mass is lower than that of the
local CVs. This discrepancy could be explained by the dominating sources in the
GBXE are non-mCVs instead of mCVs. In this work, we conduct an thorough
investigation on the X-ray spectra of local DNe from \suzaku\ archives, and
derive semi-empirical correlations between the shock temperature $T_{\rm max}$,
the flux ratio of \fec\ to \feb\ lines, and WD mass for quiescent, non-magnetic
CVs. By applying these correlations to the GBXE, we derive the average WD mass
of CVs in the Galactic bulge to be $0.81\pm 0.07M_\odot$. This value is
consistent with previous optical measurements of WD mass in local CVs. | astro-ph |
The Galactic Sky seen by H.E.S.S: The H.E.S.S. experiment is an array of four imaging Cherenkov telescopes
located in the Khomas Highlands of Namibia. It has been operating in its full
configuration since December 2003 and detects very-high-energy (VHE) gamma rays
ranging from 100 GeV to 50 TeV. Since 2004, the continuous observation of the
Galactic Plane by the H.E.S.S. array of telescopes has yielded the discovery of
more than 50 sources, belonging to the classes of pulsar wind nebulae (PWN),
supernova remnants (SNR), gamma ray binaries and, more recently, a stellar
cluster and molecular clouds in the vicinity of shell-type SNRs. Galactic
emission seen by H.E.S.S. and its implications for particle acceleration in our
Galaxy are discussed. | astro-ph |
Toward a direct measurement of the cosmic acceleration: roadmap and
forecast on FAST: HI absorption systems are great targets for direct measurement of the
Sandage-Loeb (SL) effect throughout a wide range of redshift for ground-based
radio telescopes. We demonstrate the significance of improving the accuracy of
SL effect measurement in cosmological model selection. With its wide sky
coverage and high sensitivity, we forecast that for 1 year of the upcoming
commensal survey (CRAFTS) the FAST telescope is capable of discovering about
800 HI absorption systems thereby improving the SL measurement accuracy. Aiming
to measurement the cosmic redshift drift rate at the precision of $\dot{z} \sim
10^{-10} \mathrm{decade^{-1}}$, we propose combined observation mode with
blind-searching and targeted observation. For a decade of consecutive targeted
spectroscopic observation with the frequency resolution at a level of sub-$0.1\
\rm Hz$, we could detect the first-order derivative of the cosmological
redshift with the expected precision. | astro-ph |
Clumpy Streams from Clumpy Halos: Detecting Missing Satellites with Cold
Stellar Structures: Dynamically cold stellar streams are ideal probes of the gravitational field
of the Milky Way. This paper re-examines the question of how such streams might
be used to test for the presence of "missing satellites" -the many thousands of
dark-matter subhalos with masses 10^5-10^7Msolar which are seen to orbit within
Galactic-scale dark-matter halos in simulations of structure formation in LCDM
cosmologies. Analytical estimates of the frequency and energy scales of stream
encounters indicate that these missing satellites should have a negligible
effect on hot debris structures, such as the tails from the Sagittarius dwarf
galaxy. However, long cold streams, such as the structure known as GD-1 or
those from the globular cluster Palomar 5 (Pal 5) are expected to suffer many
tens of direct impacts from missing satellites during their lifetimes.
Numerical experiments confirm that these impacts create gaps in the debris'
orbital energy distribution, which will evolve into degree- and sub-degree-
scale fluctuations in surface density over the age of the debris. Maps of Pal
5's own stream contain surface density fluctuations on these scales. The
presence and frequency of these inhomogeneities suggests the existence of a
population of missing satellites in numbers predicted in the standard LCDM
cosmologies. | astro-ph |
Geysers in the Lagoon: new Herbig-Haro objects in M8: Aims: We search for direct evidence of ongoing star formation by accretion in
the Lagoon Nebula (M8), using optical wide-field narrow-band imaging obtained
at La Silla Observatory.
Methods: We examine [SII] and Halpha images for line-emission features that
could be interpreted as signatures of outflow activity of the exciting sources.
Results: We discover five new Herbig-Haro objects, study in detail their
morphology and attempt to identify their potential driving sources among the
population of T Tauri stars and embedded sources in the surroundings.
Conclusions: The results reported here conclusively demonstrate the existence
of very young stars going through the accreting phase in the M8 region. | astro-ph |
Resolving the Disc-Halo Degeneracy II: NGC 6946: The mass-to-light ratio (M/L) is a key parameter in decomposing galactic
rotation curves into contributions from the baryonic components and the dark
halo of a galaxy. One direct observational method to determine the disc M/L is
by calculating the surface mass density of the disc from the stellar vertical
velocity dispersion and the scale height of the disc. Usually, the scale height
is obtained from near-IR studies of edge-on galaxies and pertains to the older,
kinematically hotter stars in the disc, while the vertical velocity dispersion
of stars is measured in the optical band and refers to stars of all ages (up to
~10 Gyr) and velocity dispersions. This mismatch between the scale height and
the velocity dispersion can lead to underestimates of the disc surface density
and a misleading conclusion of the sub-maximality of galaxy discs. In this
paper we present the study of the stellar velocity dispersion of the disc
galaxy NGC 6946 using integrated star light and individual planetary nebulae as
dynamical tracers. We demonstrate the presence of two kinematically distinct
populations of tracers which contribute to the total stellar velocity
dispersion. Thus, we are able to use the dispersion and the scale height of the
same dynamical population to derive the surface mass density of the disc over a
radial extent. We find the disc of NGC 6946 to be closer to maximal with the
baryonic component contributing most of the radial gravitational field in the
inner parts of the galaxy (Vmax(bar) = 0.76($\pm$0.14)Vmax). | astro-ph |
Global Simulations of Magnetorotational Instability in The Collapsed
Core of A Massive Star: We performed the first numerical simulations of magnetorotational instability
from a sub-magnetar-class seed magnetic field in core collapse supernovae. As a
result of axisymmetric ideal MHD simulations, we found that the magnetic field
is greatly amplified to magnetar-class strength. In saturation phase, a
substantial part of the core is dominated by turbulence, and the magnetic field
possesses dominant large scale components, comparable to the size of the
proto-neutron star. A pattern of coherent chanel flows, which generally appears
during exponential growth phase in previous local simulations, is not observed
in our global simulations. While the approximate convergence in the exponential
growth rate is attained by increasing spatial resolution, that of the
saturation magnetic field is not achieved due to still large numerical
diffusion. Although the effect of magnetic field on the dynamics is found to be
mild, a simulation with a high-enough resolution might result in a larger
impact. | astro-ph |
Effect of an external mass distribution on the magnetized accretion disk: In this paper, we constructed the magnetized thick disk model analytically
around the static black hole in the presence of an external distribution of
matter up to the quadrupole moment. This space-time is a solution to Einstein's
field equation describing the exterior of a static and axially symmetric object
locally. This work aims to study this space-time and the effects of quadrupole
moments via studying the properties of the equilibrium sequences of magnetized,
non-self-gravitating disks in this space-time. We discussed a procedure to
build the thick disk model based on a combination of two approaches previously
considered in the literature. We have examined different angular momentum
distributions, and We have shown the properties of this relativistic accretion
disc model in this background. | astro-ph |
The cold circumgalactic environment of MAMMOTH-I: dynamically cold gas
in the core of an Enormous Ly-alpha Nebula: The MAMMOTH-I Nebula at redshift 2.3 is one of the largest known Ly-alpha
nebulae in the Universe, spanning ~440 kpc. Enormous Ly-alpha nebulae like
MAMMOTH-I typically trace the densest and most active regions of galaxy
formation. Using sensitive low-surface-brightness observations of CO(1-0) with
the Very Large Array, we trace the cold molecular gas in the inner 150 kpc of
the MAMMOTH-I Nebula. CO is found in four regions that are associated with
either galaxies or groups of galaxies that lie inside the nebula. In three of
the regions, the CO stretches up to ~30 kpc into the circum-galactic medium
(CGM). In the centermost region, the CO has a very low velocity dispersion
(FWHM$_{\rm CO}$ ~ 85 km/s), indicating that this gas is dynamically cold. This
dynamically cold gas coincides with diffuse restframe optical light in the CGM
around a central group of galaxies, as discovered with the Hubble Space
Telescope. We argue that this likely represents cooling of settled and enriched
gas in the center of MAMMOTH-I. This implies that the dynamically cold gas in
the CGM, rather than the obscured AGN, marks the core of the potential well of
this Ly-alpha nebula. In total, the CO in the MAMMOTH-I Nebula traces a
molecular gas mass of M$_{\rm H2}$ ~ 1.4 ($\alpha_{\rm CO}$/3.6) $\times$
10$^{11}$ M$_{\odot}$, with roughly 50% of the CO(1-0) emission found in the
CGM. Our results add to the increasing evidence that extended reservoirs of
molecular gas exist in the CGM of massive high-z galaxies and proto-clusters. | astro-ph |
A Dynamic Galaxy: Stellar Age Patterns Across the Disk of M101: Using deep, narrowband imaging of the nearby spiral galaxy M101, we present
stellar age information across the full extent of the disk of M101. Our
narrowband filters measure age-sensitive absorption features such as the Balmer
lines and the slope of the continuum between the Balmer break and 4000 \r{A}
break. We interpret these features in the context of inside-out galaxy
formation theories and dynamical models of spiral structure. We confirm the
galaxy's radial age gradient, with the mean stellar age decreasing with radius.
In the relatively undisturbed main disk, we find that stellar ages get
progressively older with distance across a spiral arm, consistent with the
large-scale shock scenario in a quasi-steady spiral wave pattern. Unexpectedly,
we find the same pattern across spiral arms in the outer disk as well, beyond
the corotation radius of the main spiral pattern. We suggest that M101 has a
dynamic, or transient, spiral pattern with multiple pattern speeds joined
together via mode coupling to form coherent spiral structure. This scenario
connects together the radial age gradient inherent to inside-out galaxy
formation with the across-arm age gradients predicted by dynamic spiral arm
theories across the full radial extent of the galaxy. | astro-ph |
Fluid Dynamics of Stellar Jets in Real Time: Third Epoch HST Images of
HH 1, HH 34, and HH 47: We present new, third-epoch HST H-alpha and [S II] images of three HH jets
(HH 1 and 2, HH 34, and HH 47) and compare these images with those from the
previous epochs. The high-spatial resolution, coupled with a time-series whose
cadence is of order both the hydrodynamical and radiative cooling timescales of
the flow allows us to follow the hydrodynamical/magnetohydrodynamical evolution
of an astrophysical plasma system in which ionization and radiative cooling
play significant roles. Cooling zones behind the shocks are resolved, so it is
possible to identify which way material flows through a given shock wave. The
images show that heterogeneity is paramount in these jets, with clumps
dominating the morphologies of both bow shocks and their Mach disks. This
clumpiness exists on scales smaller than the jet widths and determines the
behavior of many of the features in the jets. Evidence also exists for
considerable shear as jets interact with their surrounding molecular clouds,
and in several cases we observe shock waves as they form and fade where
material emerges from the source and as it proceeds along the beam of the jet.
Fine-structure within two extended bow shocks may result from Mach stems that
form at the intersection points of oblique shocks within these clumpy objects.
Taken together, these observations represent the most significant foray thus
far into the time domain for stellar jets, and comprise one of the richest data
sets in existence for comparing the behavior of a complex astrophysical plasma
flows with numerical simulations and laboratory experiments. | astro-ph |
X-ray emission from black-hole binaries: The properties of X-ray emission from accreting black holes are reviewed. The
contemporary observational picture and current status of theoretical
understanding of accretion and formation of X-ray radiation in the vicinity of
the compact object are equally in the focus of this chapter. The emphasis is
made primarily on common properties and trends rather than on peculiarities of
individual objects and details of particular theoretical models. The chapter
starts with discussion of the geometry of the accretion flow, spectral
components in X-ray emission and black hole spectral states. The prospects and
diagnostic potential of X-ray polarimetry are emphasized. Significant attention
is paid to the discussion of variability of X-ray emission in general and of
different spectral components -- emission of the accretion disk, Comptonized
radiation and reflected component. Correlations between spectral and timing
characteristics of X-ray emission are reviewed and discussed in the context of
theoretical models. Finally, a comparison with accreting neutron stars is made. | astro-ph |
K-band spectroscopy of pre-cataclysmic variables: We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to
examine them for anomalous chemical abundances. In particular, we study the
strength of the 12CO and 13CO absorption bands that have been found diminished
and enhanced, respectively, in similar studies of CVs.
All our systems show CO abundances that are within the range observed for
single stars. The weakest 12CO bands with respect to the spectral type are
found in the pre-CV BPM 71214, although on a much smaller scale than observed
in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account
that our sample is subject to the present observational bias that favours the
discovery of young pre-CVs with secondary stars of late spectral types, we can
conclude the following: 1) our study provides observational proof that the CO
anomalies discovered in certain CVs are not due to any material acquired during
the common envelope phase, and 2) if the CO anomalies in certain CVs are not
due to accretion of processed material during nova outburst, then the
progenitors of these CVs are of a significantly different type than the
currently known sample of pre-CVs. | astro-ph |
Structure and Evolution of Internally Heated Hot Jupiters: Hot Jupiters receive strong stellar irradiation, producing equilibrium
temperatures of $1000 - 2500 \ \mathrm{Kelvin}$. Incoming irradiation directly
heats just their thin outer layer, down to pressures of $\sim 0.1 \
\mathrm{bars}$. In standard irradiated evolution models of hot Jupiters,
predicted transit radii are too small. Previous studies have shown that deeper
heating -- at a small fraction of the heating rate from irradiation -- can
explain observed radii. Here we present a suite of evolution models for HD
209458b where we systematically vary both the depth and intensity of internal
heating, without specifying the uncertain heating mechanism(s). Our models
start with a hot, high entropy planet whose radius decreases as the convective
interior cools. The applied heating suppresses this cooling. We find that very
shallow heating -- at pressures of $1 - 10 \ \mathrm{bars}$ -- does not
significantly suppress cooling, unless the total heating rate is $\gtrsim 10\%$
of the incident stellar power. Deeper heating, at $100 \ \mathrm{bars}$,
requires heating at only $1\%$ of the stellar irradiation to explain the
observed transit radius of $1.4 R_{\rm Jup}$ after 5 Gyr of cooling. In
general, more intense and deeper heating results in larger hot Jupiter radii.
Surprisingly, we find that heat deposited at $10^4 \ \mathrm{bars}$ -- which is
exterior to $\approx 99\%$ of the planet's mass -- suppresses planetary cooling
as effectively as heating at the center. In summary, we find that relatively
shallow heating is required to explain the radii of most hot Jupiters, provided
that this heat is applied early and persists throughout their evolution. | astro-ph |
NG7538 IRS1 N: modeling a circumstellar maser disk: We present an edge-on Keplerian disk model to explain the main component of
the 12.2 and 6.7 GHz methanol maser emission detected toward NGC7538-IRS1 N.
The brightness distribution and spectrum of the line of bright masers are
successfully modeled with high amplification of background radio continuum
emission along velocity coherent paths through a maser disk. The bend seen in
the position-velocity diagram is a characteristic signature of differentially
rotating disks. For a central mass of 30 solar masses, suggested by other
observations, our model fixes the masing disk to have inner and outer radii of
about 270 AU and 750 AU. | astro-ph |
Evidence for dark matter interactions in cosmological precision data?: We study a two-parameter extension of the cosmological standard model
$\Lambda$CDM in which cold dark matter interacts with a new form of dark
radiation. The two parameters correspond to the energy density in the dark
radiation fluid $\Delta N_\mathrm{fluid}$ and the interaction strength between
dark matter and dark radiation. The interactions give rise to a very weak "dark
matter drag" which damps the growth of matter density perturbations throughout
radiation domination, allowing to reconcile the tension between predictions of
large scale structure from the CMB and direct measurements of $\sigma_8$. We
perform a precision fit to Planck CMB data, BAO, large scale structure, and
direct measurements of the expansion rate of the universe today. Our model
lowers the $\chi$-squared relative to $\Lambda$CDM by about 12, corresponding
to a preference for non-zero dark matter drag by more than $3 \sigma$. Particle
physics models which naturally produce a dark matter drag of the required form
include the recently proposed non-Abelian dark matter model in which the dark
radiation corresponds to massless dark gluons. | astro-ph |
Planetary Nebulae towards the Galactic bulge. I. [OIII] fluxes: We present [OIII]{\lambda}5007 fluxes and angular diameters for 435 Planetary
Nebulae (PN) in the central 10' x 10' region towards the Galactic bulge. Our
sample is taken from the new discoveries of the MASH PN surveys as well as
previously known PN. This sample accounts for 80% of known PN in this region.
Fluxes and diameters are measured from narrow-band imaging with the MOSAIC-II
camera on the 4-m Blanco telescope at the Cerro-Tololo Inter-American
Observatory. This is the largest (~60 square degrees), uniform
[OIII]{\lambda}5007 survey of the inner Galactic bulge ever undertaken. 104 of
the objects have measured [OIII]{\lambda}5007, [OIII]{\lambda}4959, H{\alpha}
or H{\beta} fluxes from the literature, which we use to undertake a detailed
comparison to demonstrate the integrity of our new fluxes. Our independent
measurements are in excellent agreement with the very best literature sources
over two orders of magnitude, while maintaining good consistency over five
orders of magnitude. The excellent resolution and sensitivity of our data
allows not only for a robust set of homogenous PN fluxes, but provides greater
detail into their intricate, otherwise undetermined [OIII]{\lambda}5007
morphologies. These new, extensive measurements significantly increase the
sample of reliable [OIII]{\lambda}5007 fluxes for Galactic bulge PN making it a
valuable resource and a prelude to the construction of our new Galactic bulge
Planetary Nebula luminosity function (Paper II). | astro-ph |
The effect of photometric redshift uncertainties on galaxy clustering
and baryonic acoustic oscillations: In the upcoming era of high-precision galaxy surveys, it becomes necessary to
understand the impact of redshift uncertainties on cosmological observables. In
this paper we explore the effect of sub-percent photometric redshift errors
(photo-$z$ errors) on galaxy clustering and baryonic acoustic oscillations
(BAO). Using analytic expressions and results from $1\,000$ $N$-body
simulations, we show how photo-$z$ errors modify the amplitude of moments of
the 2D power spectrum, their variances, the amplitude of BAO, and the
cosmological information in them. We find that: a) photo-$z$ errors suppress
the clustering on small scales, increasing the relative importance of shot
noise, and thus reducing the interval of scales available for BAO analyses; b)
photo-$z$ errors decrease the smearing of BAO due to non-linear redshift-space
distortions (RSD) by giving less weight to line-of-sight modes; and c)
photo-$z$ errors (and small-scale RSD) induce a scale dependence on the
information encoded in the BAO scale, and that reduces the constraining power
on the Hubble parameter. Using these findings, we propose a template that
extracts unbiased cosmological information from samples with photo-$z$ errors
with respect to cases without them. Finally, we provide analytic expressions to
forecast the precision in measuring the BAO scale, showing that
spectro-photometric surveys will measure the expansion history of the Universe
with a precision competitive to that of spectroscopic surveys. | astro-ph |
All Quiet in Globular Clusters: Cataclysmic Variables (CVs) should be present in large numbers in Globular
Clusters (GCs). Numerous low-luminosity X-ray sources identified over the past
few years as candidate CVs in GCs support this notion. Yet, very few
"cataclysms," the characteristic feature of this class of objects in the field,
have been observed in GCs. We address this discrepancy here, within the
framework of the standard Disk Instability Model for CV outbursts. We argue
that the paucity of outbursts in GCs is probably not a direct consequence of
the donors' low metallicities. We present diagnostics based on outburst
properties allowing tests of the hypothesis that rare cataclysms are entirely
due to lower mass transfer rates in GCs relative to the field, and we argue
against this explanation. Instead, we propose that a combination of low mass
transfer rates (>~ 10^14-15 g/s) and moderately strong white dwarf magnetic
moments (>~ 10^30 G cm^3) stabilize CV disks in GCs and thus prevent most of
them from experiencing frequent outbursts. If it is so, rare cataclysms in GCs
would signal important evolutionary differences between field and cluster CVs. | astro-ph |
Universal protoplanetary disk size under complete non-ideal
magnetohydrodynamics: The interplay between ion-neutral friction, Hall
effect, and the Ohmic dissipation: The role of non-ideal magnetohydrodynamics has been proven critical during
the formation of the protoplanetary disk, particularly in regulating its size.
We provide a simple model to predict the disk size under the interplay among
the ambipolar diffusion, the Hall effect, and the Ohmic dissipation. The model
predicts a small disk size of around 20 AU, that depends only sub-linearly on
disk parameters, for a wide range of initial conditions of sub-Solar mass and
moderate magnetization. It is able to explain phenomena manifested in existing
numerical simulations, including the bimodal disk behavior under parallel and
anti-parallel alignment between the rotation and magnetic field. In the
parallel configuration, the disk size decreases and eventually disappears. In
the anti-parallel configuration, and the disk has an outer partition (or
pseudo-disk) that is flat, shrinking , and short-lived, as well as a inner
partition that grows slowly with mass and is long-lived. Even with significant
initial magnetization, the vertical field in the disk can only dominate at the
early stage when the mass is low, and the toroidal field eventually dominates
in all disks. | astro-ph |
A Novel Estimator for the Equation of State of the IGM by Ly$α$
Forest Tomography: We present a novel procedure to estimate the Equation of State of the
intergalactic medium in the quasi-linear regime of structure formation based on
Ly$\alpha$ forest tomography and apply it to 21 high quality quasar spectra
from the UVES\_SQUAD survey at redshift $z=2.5$. Our estimation is based on a
full tomographic inversion of the line of sight. We invert the data with two
different inversion algorithms, the iterative Gauss-Newton method and the
regularized probability conservation approach, which depend on different priors
and compare the inversion results in flux space and in density space. In this
way our method combines fitting of absorption profiles in flux space with an
analysis of the recovered density distributions featuring prior knowledge of
the matter distribution. Our estimates are more precise than existing
estimates, in particular on small redshift bins. In particular, we model the
temperature-density relation with a power law and observe for the temperature
at mean density $T_0 = 13400^{+1700}_{-1300}\,\mathrm{K}$ and for the slope of
the power-law (polytropic index) $\gamma = 1.42 \pm 0.11$ for the power-law
parameters describing the temperature-density relation. Moreover, we measure an
photoionization rate $\Gamma_{-12} = 1.1^{+0.16}_{-0.17}$. An implementation of
the inversion techniques used will be made publicly available. | astro-ph |
C$^+$ detection of warm dark gas in diffuse clouds: We present the first results of the Herschel open time key program, Galactic
Observations of Terahertz C$^+$ (GOT C+) survey of the [CII] fine-structure
line at 1.9 THz (158 microns) using the HIFI instrument on Herschel. We
detected 146 interstellar clouds along sixteen lines-of-sight towards the inner
Galaxy. We also acquired HI and CO isotopologue data along each line-of-sight
for analysis of the physical conditions in these clouds. Here we analyze 29
diffuse clouds (A$_{V}$ < 1.3 mag.) in this sample characterized by having
[CII] and HI emission, but no detectable CO. We find that [CII] emission is
generally stronger than expected for diffuse atomic clouds, and in a number of
sources is much stronger than anticipated based on their HI column density. We
show that excess [CII] emission in these clouds is best explained by the
presence of a significant diffuse warm H$_2$, dark gas, component. This first
[CII] 158 micron detection of warm dark gas demonstrates the value of this
tracer for mapping this gas throughout the Milky Way and in galaxies. | astro-ph |
Dynamical neutrino masses in the generalized Chaplygin gas scenario with
mass varying CDM: Neutrinos coupled to an underlying scalar field in the scenario for
unification of mass varying dark matter and cosmon-{\em like} dark energy is
examined. In the presence of a tiny component of mass varying neutrinos, the
conditions for the present cosmic acceleration and for the stability issue are
reproduced. It is assumed that {\em sterile} neutrinos behave like mass varying
dark matter coupled to mass varying {\em active} neutrinos through the {\em
seesaw} mechanism, in a kind of {\em mixed} dark matter sector. The crucial
point is that the dark matter mass may also exhibit a dynamical behavior driven
by the scalar field. The scalar field mediates the nontrivial coupling between
the mixed dark matter and the dark energy responsible for the accelerated
expansion of the universe. The equation of state of perturbations reproduce the
generalized Chaplygin gas (GCG) cosmology so that all the effective results
from the GCG paradigm are maintained, being perturbatively modified by
neutrinos. | astro-ph |
VERITAS follow-up observation of the blazar TXS 0506+056: The gamma-ray blazar TXS 0506+056 was found with an enhanced gamma-ray
emission state in spatial and temporal coincidence with the IceCube high energy
neutrino event IC170922A. This is the most significant association by far
between a high-energy neutrino event and a blazar in a flaring state. Studying
the time evolution and spectral behavior of the blazar emission may help in
identifying the sources of the diffuse neutrino flux observed by IceCube and
the origin of energetic cosmic rays. TXS 0506+056 was detected by the VERITAS
gamma-ray observatory with a significance of 5.8 standard deviations above 110
GeV in a 35 hour data set collected between September 23, 2017 and February 6,
2018. Here we will present results from recent VERITAS observations and an
associated multiwavelength campaign, collected between October 10, 2018 to
March 1, 2021. A relatively quiet very high energy gamma-ray emission state was
observed during this time period, and flux upper limits are used to constrain
the potential variability of this blazar. | astro-ph |
The molecular cloud S242: physical environment and star formation
activities: We present a multi-wavelength study to probe the star formation (SF)
processes on a larger scale (~1.05 deg x 0.56 deg) around the S242 site. The
S242 molecular cloud is depicted in a velocity range from -3.25 to 4.55 km/s
and has spatially elongated appearance. Based on the virial analysis, the cloud
is prone to gravitational collapse. The cloud harbors an elongated filamentary
structure (EFS; length ~25 pc) evident in the Herschel column density map and
the EFS has an observed mass per unit length of ~200 M_sun/pc exceeding the
critical value of ~16 M_sun/pc (at T = 10 K). The EFS contains a chain of
Herschel clumps (M_clump ~150 to 1020 M_sun), revealing the evidence of
fragmentation along its length. The most massive clumps are observed at both
the EFS ends, while the S242 HII region is located at one EFS end. Based on the
radio continuum maps at 1.28 and 1.4 GHz, the S242 HII region is ionized by a
B0.5V - B0V type star and has a dynamical age of ~0.5 Myr. The photometric 1 -
5 microns data analysis of point-like sources traces young stellar objects
(YSOs) toward the EFS and the clusters of YSOs are exclusively found at both
the EFS ends, revealing the SF activities. Considering the spatial presence of
massive clumps and YSO clusters at both the EFS ends, the observed results are
consistent with the prediction of a SF scenario of the end-dominated collapse
driven by the higher accelerations of gas. | astro-ph |
Cosmology with the shear-peak statistics: Weak-lensing searches for galaxy clusters are plagued by low completeness and
purity, severely limiting their usefulness for constraining cosmological
parameters with the cluster mass function. A significant fraction of `false
positives' are due to projection of large-scale structure and as such carry
information about the matter distribution. We demonstrate that by constructing
a "peak function", in analogy to the cluster mass function, cosmological
parameters can be constrained. To this end we carried out a large number of
cosmological N-body simulations in the \Omega_m-\sigma_8 plane to study the
variation of this peak function. We demonstrate that the peak statistics is
able to provide constraints competitive with those obtained from cosmic-shear
tomography from the same data set. By taking the full cross-covariance between
the peak statistics and cosmic shear into account, we show that the combination
of both methods leads to tighter constraints than either method alone can
provide. | astro-ph |
Optimising Spectroscopic and Photometric Galaxy Surveys: Efficient
Target Selection and Survey Strategy: The next generation of spectroscopic surveys will have a wealth of
photometric data available for use in target selection. Selecting the best
targets is likely to be one of the most important hurdles in making these
spectroscopic campaigns as successful as possible. Our ability to measure dark
energy depends strongly on the types of targets that we are able to select with
a given photometric data set. We show in this paper that we will be able to
successfully select the targets needed for the next generation of spectroscopic
surveys. We also investigate the details of this selection, including
optimisation of instrument design and survey strategy in order to measure dark
energy. We use color-color selection as well as neural networks to select the
best possible emission line galaxies and luminous red galaxies for a
cosmological survey. Using the Fisher matrix formalism we forecast the
efficiency of each target selection scenario. We show how the dark energy
figures of merit change in each target selection regime as a function of target
type, survey time, survey density and other survey parameters. We outline the
optimal target selection scenarios and survey strategy choices which will be
available to the next generation of spectroscopic surveys. | astro-ph |
A Frequency Comb calibrated Solar Atlas: The solar spectrum is a primary reference for the study of physical processes
in stars and their variation during activity cycles. In Nov 2010 an experiment
with a prototype of a Laser Frequency Comb (LFC) calibration system was
performed with the HARPS spectrograph of the 3.6m ESO telescope at La Silla
during which high signal-to-noise spectra of the Moon were obtained. We exploit
those Echelle spectra to study the optical integrated solar spectrum . The
DAOSPEC program is used to measure solar line positions through gaussian
fitting in an automatic way. We first apply the LFC solar spectrum to
characterize the CCDs of the HARPS spectrograph. The comparison of the LFC and
Th-Ar calibrated spectra reveals S-type distortions on each order along the
whole spectral range with an amplitude of +/-40 m/s. This confirms the pattern
found by Wilken et al. (2010) on a single order and extends the detection of
the distortions to the whole analyzed region revealing that the precise shape
varies with wavelength. A new data reduction is implemented to deal with CCD
pixel inequalities to obtain a wavelength corrected solar spectrum. By using
this spectrum we provide a new LFC calibrated solar atlas with 400 line
positions in the range of 476-530, and 175 lines in the 534-585 nm range. The
new LFC atlas improves the accuracy of individual lines by a significant factor
reaching a mean value of about 10 m/s. The LFC--based solar line wavelengths
are essentially free of major instrumental effects and provide a reference for
absolute solar line positions. We suggest that future LFC observations could be
used to trace small radial velocity changes of the whole solar photospheric
spectrum in connection with the solar cycle and for direct comparison with the
predicted line positions of 3D radiative hydrodynamical models of the solar
photosphere. | astro-ph |
Numerical Analysis of Relativistic Boltzmann-kinetic Equations to Solve
Relativistic Shock Layer Problems: The relativistic shock layer problem was numerically analyzed by using two
relativistic Boltzmann-kinetic equations. One is Marle model, and the other is
Anderson-Witting model. As with Marle model, the temperature of the gain term
was determined from its relation with the dynamic pressure in the framework of
14-moments theory. From numerical results of the relativistic shock layer
problem, behaviors of projected moments in the nonequilibrium region were
clarified. Profiles of the heat flux given by Marle model and Anderson-Witting
model were quite adverse to the profile of the heat flux approximated by
Navier-Stokes-Fourier law. On the other hand, profiles of the heat flux given
by Marle model and Anderson-Witting model were similar to the profile
approximated by Navier-Stokes-Fourier law. Additionally we discuss the
differences between Anderson-Witting model and Marle model by focusing on the
fact that the relaxational rate of the distribution function depends on both
flow velocity and molecular velocity for Anderson-Witting model, while it
depends only on the molecular velocity for Marle model. | astro-ph |
A comparison between Fast Multipole Algorithm and Tree-Code to evaluate
gravitational forces in 3-D: We present tests of comparison between our versions of the Fast Multipole
Algorithm (FMA) and ``classic'' tree-code to evaluate gravitational forces in
particle systems. We have optimized the Greengard's original version of FMA
allowing for a more efficient criterion of well-separation between boxes, to
improve the adaptivity of the method (which is very important in highly
inhomogeneous situations) and to permit the smoothing of gravitational
interactions. The results of our tests indicate that the tree-code is almost
three times faster than FMA for both a homogeneous and a clumped distribution,
at least in the interval of N (N< 10^5) here investigated and at the same level
of accuracy (error ~ 10^{-3)). This order of accuracy is generally considered
as the best compromise between CPU-time consumption and precision for
astrophysical simulation. Moreover, the claimed linear dependence on N of the
CPU-time of FMA is not confirmed and we give a ``theoretical'' explanation for
that. | astro-ph |
A new insight into neutrino energy loss by electron capture of iron
group nuclei in magnetars surface: Based on the relativistic mean-field effective interactions theory, and Lai
dong model \citep{b37, b38, b39}, we discuss the influences of superstrong
magnetic fields (SMFs) on electron Fermi energy, nuclear blinding energy, and
single-particle level structure in magnetars surface. By using the method of
Shell-Model Monte Carlo (SMMC), and the Random Phase Approximation (RPA)
theory, we detailed analyze the neutrino energy loss rates(NELRs) by electron
capture (EC) for iron group nuclei in SMFs. | astro-ph |
Ultraviolet Imaging Telescope (UVIT) observation of the Galactic
Globular Cluster NGC 7492: We present detailed photometric observations of the Galactic globular cluster
NGC 7492 using the data obtained with two far-ultraviolet (FUV: 1300 - 1800
\AA) and three near-ultraviolet (NUV: 2000 - 3000 \AA) filters of Ultraviolet
Imaging Telescope (UVIT) on-board the \textit{AstroSat} satellite. We confirmed
the cluster membership of the extracted sources using GAIA data release 2 (Gaia
DR2) proper motion data. We have used color-magnitude diagrams (CMDs) using
UVIT and GAIA filters to separate out different evolutionary stages of the
stars present in the cluster. We have identified a new extreme horizontal
branch (EHB) star at the core of the cluster using UV and UV-optical CMDs. The
estimated distance-modulus of the cluster is $16.95\pm0.05$ obtained by fitting
BaSTI isochrones with cluster parameters, $[Fe/H] = -1.8$ dex and age $= 12.0$
Gyr on the V $-$ I vs V CMD. Interestingly, only the EHB star and blue
horizontal branch stars (BHBs) among the UV-bright hot sources are detected in
FUV filters of UVIT. We have derived the effective temperature of BHBs using
color-temperature relation and spectral energy distributions (SEDs) of
multi-band filters, which are in the range from 8,000 K to 10,500 K. We find a
variation of He abundance of BHBs by fitting the BaSTI ZAHB. The range in the
He abundance of the BHBs corresponding to the best fit isochrones is 0.247 to
0.350. We have estimated various physical parameters of the newly identified
EHB star in the cluster using SED fit and post-HB evolutionary tracks. We have
studied the radial distribution of all the sources of the cluster detected in
UVIT. The sources detected in FUV filters extend beyond the half light radius
(1.15$'$) of the cluster, whereas the sources detected in NUV filters extend
beyond the tidal radius (9.2$'$) of the cluster. | astro-ph |
High resolution CMB power spectrum from the complete ACBAR data set: In this paper, we present results from the complete set of cosmic microwave
background (CMB) radiation temperature anisotropy observations made with the
Arcminute Cosmology Bolometer Array Receiver (ACBAR) operating at 150 GHz. We
include new data from the final 2005 observing season, expanding the number of
detector-hours by 210% and the sky coverage by 490% over that used for the
previous ACBAR release. As a result, the band-power uncertainties have been
reduced by more than a factor of two on angular scales encompassing the third
to fifth acoustic peaks as well as the damping tail of the CMB power spectrum.
The calibration uncertainty has been reduced from 6% to 2.1% in temperature
through a direct comparison of the CMB anisotropy measured by ACBAR with that
of the dipole-calibrated WMAP5 experiment. The measured power spectrum is
consistent with a spatially flat, LambdaCDM cosmological model. We include the
effects of weak lensing in the power spectrum model computations and find that
this significantly improves the fits of the models to the combined ACBAR+WMAP5
power spectrum. The preferred strength of the lensing is consistent with
theoretical expectations. On fine angular scales, there is weak evidence (1.1
sigma) for excess power above the level expected from primary anisotropies. We
expect any excess power to be dominated by the combination of emission from
dusty protogalaxies and the Sunyaev-Zel'dovich effect (SZE). However, the
excess observed by ACBAR is significantly smaller than the excess power at ell
> 2000 reported by the CBI experiment operating at 30 GHz. Therefore, while it
is unlikely that the CBI excess has a primordial origin; the combined ACBAR and
CBI results are consistent with the source of the CBI excess being either the
SZE or radio source contamination. | astro-ph |
Optical Observations of the Type Ic Supernova 2007gr in NGC 1058 and
Implications for the Properties of its Progenitor: We present extensive optical observations of the normal Type Ic supernova
(SN) 2007gr, spanning from about one week before maximum light to more than one
year thereafter. The optical light and color curves of SN 2007gr are very
similar to those of the broad-lined Type Ic SN 2002ap, but the spectra show
remarkable differences. The optical spectra of SN 2007gr are characterized by
unusually narrow lines, prominent carbon lines, and slow evolution of the line
velocity after maximum light. The earliest spectrum (taken at t=-8 days) shows
a possible signature of helium (He~I 5876 at a velocity of ~19,000 km s{-1}).
Moreover, the larger intensity ratio of the [O I] 6300 and 6364 lines inferred
from the early nebular spectra implies a lower opacity of the ejecta shortly
after the explosion. These results indicate that SN 2007gr perhaps underwent a
less energetic explosion of a smaller-mass Wolf-Rayet star (~ 8--9 Msun) in a
binary system, as favored by an analysis of the progenitor environment through
pre-explosion and post-explosion Hubble Space Telescope images. In the nebular
spectra, asymmetric double-peaked profiles can be seen in the [O~I] 6300 and
Mg~I] 4571 lines. We suggest that the two peaks are contributed by the
blueshifted and rest-frame components. The similarity in velocity structure and
the different evolution of the strength of the two components favor an
aspherical explosion with the ejecta distributed in a torus or disk-like
geometry, but inside the ejecta the O and Mg have different distributions. | astro-ph |
New X-ray Clusters in the EMSS I: Modifications to the XLF: The complete ensemble of Einstein Imaging Proportional Counter (IPC) X-ray
images has been re-processed and re-analyzed using a multi-aperture source
detection algorithm. A catalog of 772 new source candidates detected within the
central regions of the 1435 IPC fields comprising the Extended Medium
Sensitivity Survey (EMSS) has been compiled. By comparison, 478 EMSS sources
fall within the same area of sky. A randomly-selected subsample of 133 fields
was first examined. We found that most of these sources are either the
summation of two or more lower count rate point sources that fall within the
larger detection apertures or are single point sources, while \leq 2.3% of the
full catalog of sources are extrapolated to be actual distant (z > 0.14)
clusters whose extended X-ray structure kept them from being detected in the
EMSS despite having sufficient total flux.
We then constructed other subsamples specifically selected to contain those
X-ray sources most likely to be clusters. Both a database search and an optical
imaging campaign have found several new distant clusters, setting a firm lower
limit on the number of new clusters in the entire catalog. We estimate that the
original EMSS cluster sample is 72-83% complete. We update the Henry et al.
1992 EMSS distant cluster sample with more recent information, and use the
redshifts and X-ray luminosities for these new EMSS clusters to compute a
revised X-ray Luminosity Function (XLF). The addition of these new high-z,
high-L_X clusters to the EMSS is sufficient to remove the requirement for
``negative'' evolution at high-L_X out to z~0.5. We conclude that the EMSS has
systematically missed clusters of low surface brightness. | astro-ph |
Near-IR observations of UCHII regions: We present adaptive-optics (AO) assisted J, H and K/K' images of 8 UCHII
regions taken with the ALFA and ADONIS AO systems at Calar Alto and La Silla
observatories. The images show details of the stellar population and the
near-IR morphology of UCHIIs with unprecedented resolution. We have searched
for the ionizing sources of the regions using near-IR photometry. The spectral
type of the ionizing and most luminous stars inferred from our photometry has
been compared with spectral type estimates from IRAS and published
radio-continuum measurements. We find that the photometric near-IR spectral
types are earlier than estimates from radio and IRAS data. This difference is
alleviated when stellar spherical models including line blanketing and stellar
winds instead of non-LTE plane-parallel models are used to derive the radio-
and IRAS-based spectral types. We also made an attempt to correlate the
properties of the near-IR ionizing population with MSX data and published CS
measurements. No correlation was found. We note that in two of the regions
(G309.92+0.48 and G61.48+0.09B1), the best candidate to ionize the region is
possibly a super-giant. | astro-ph |
CMB anisotropy power spectrum statistics: Much attention has been given to the problem of estimating cosmological
parameters from the $C_l$ measured by future experiments. Many of the
approaches which are being used either invoke poorly controlled approximations
or are computationally expensive. We derive exact results as well as fast and
highly accurate approximations for mapping a theoretical model onto the
observed power spectrum coefficients and computing their statistical
properties. These results obtain from an analytic framework which applies for
any azimuthally symmetric sky coverage regardless of the fraction of the sky
observed by the experiment. | astro-ph |
WALLABY Pilot Survey: HI in the host galaxy of a Fast Radio Burst: We report on the commensal ASKAP detection of a fast radio burst (FRB),
FRB20211127I, and the detection of neutral hydrogen (HI) emission in the FRB
host galaxy, WALLABYJ131913-185018 (hereafter W13-18). This collaboration
between the CRAFT and WALLABY survey teams marks the fifth, and most distant,
FRB host galaxy detected in HI, not including the Milky Way. We find that
W13-18 has a HI mass of $M_{\rm HI}$ = 6.5 $\times$ 10$^{9}$ M$_{\odot}$, a
HI-to-stellar mass ratio of 2.17, and coincides with a continuum radio source
of flux density at 1.4 GHz of 1.3 mJy. The HI global spectrum of W13-18 appears
to be asymmetric, albeit the HI observation has a low S/N, and the galaxy
itself appears modestly undisturbed. These properties are compared to the early
literature of HI emission detected in other FRB hosts to date, where either the
HI global spectra were strongly asymmetric, or there were clearly disrupted HI
intensity map distributions. W13-18 lacks sufficient S/N to determine whether
it is significantly less asymmetric in its HI distribution than previous
examples of FRB host galaxies. However, there are no strong signs of a major
interaction in the HI or optical image of the host galaxy that would stimulate
a burst of star formation and hence the production of putative FRB progenitors
related to massive stars and their compact remnants. | astro-ph |
A comprehensive comparison of cosmological models from latest
observational data: We investigate in detail some popular cosmological models in light of the
latest observational data, including the Union2.1 supernovae compilation, the
baryon acoustic oscillation measurements from the WiggleZ Dark Energy Survey,
the cosmic microwave background information from the WMAP 7-year observations
along with the observational Hubble parameter data. Based on the model
selection statistics such as the Akaike and the Bayesian information criterias,
we compare different models to assess the worth of them. We do not assume a
flat universe in the fitting. Our results show that the concordance
$\Lambda$CDM model remains the best one to explain the data, while the DGP
model is clearly disfavored by the data. Among these models, those whose
parameters can reduce themselves to the $\Lambda$CDM model provide good fits to
the data. These results indicate that for the current data, there is no obvious
evidence supporting any more complex models over the simplest $\Lambda$CDM
model. | astro-ph |
Search for Continuous Gravitational Waves from Scorpius X-1 in LIGO O2
Data: We present the results of a search in LIGO O2 public data for continuous
gravitational waves from the neutron star in the low-mass X-ray binary Scorpius
X-1. We search for signals with $\approx$ constant frequency in the range
40-180 Hz. Thanks to the efficiency of our search pipeline we can use a long
coherence time and achieve unprecedented sensitivity, significantly improving
on existing results. This is the first search that has been able to probe
gravitational wave amplitudes that could balance the accretion torque at the
neutron star radius. Our search excludes emission at this level between 67.5 Hz
and 131.5 Hz, for an inclination angle $44^\circ \pm 6^\circ$ derived from
radio observations (Fomalont et al. 2001), and assuming that the spin axis is
perpendicular to the orbital plane. If the torque arm is $\approx $ 26 km -- a
conservative estimate of the \alfven\ radius -- our results are more
constraining than the indirect limit across the band. This allows us to exclude
certain mass-radius combinations and to place upper limits on the strength of
the star's magnetic field. We also correct a mistake that appears in the
literature in the equation that gives the gravitational wave amplitude at the
torque balance (Abbott et al. 2017b, 2019a) and we re-interpret the associated
latest LIGO/Virgo results in light of this. | astro-ph |
Magneto-Rotational Transport in the Early Sun: Angular momentum transport must have occurred in the Sun's radiative zone to
explain its current solid body rotation. We survey the stability of the early
Sun's radiative zone with respect to diffusive rotational instabilities, for a
variety of plausible past configurations. We find that the (faster rotating)
early Sun was prone to rotational instabilities even if only weak levels of
radial differential rotation were present, while the current Sun is not.
Stability domains are determined by approximate balance between dynamical and
diffusive timescales, allowing generalizations to other stellar contexts.
Depending on the strength and geometry of the weak magnetic field present, the
fastest growing unstable mode can be hydrodynamic or magneto-hydrodynamic (MHD)
in nature. Our results suggest that diffusive MHD modes may be more efficient
at transporting angular momentum than their hydrodynamic
(``Goldreich-Schubert-Fricke'') counterparts because the minimum spatial scale
required for magnetic tension to be destabilizing limits the otherwise very
small scales favored by double-diffusive instabilities. Diffusive
magneto-rotational instabilities are thus attractive candidates for angular
momentum transport in the early Sun's radiative zone. | astro-ph |
The Very Small Array: The Very Small Array (VSA) is a fourteen-element interferometer designed to
study the cosmic microwave background on angular scales of 2.4 to 0.2 degrees
(angular multipoles l = 150 to 1800). It operates at frequencies between 26 and
36 GHz, with a bandwidth of 1.5 GHz, and is situated at the Teide Observatory,
Tenerife. The instrument also incorporates a single-baseline interferometer,
with larger collecting area, operating simultaneously with and at the same
frequency as the VSA main array. This provides accurate flux measurements of
contaminating radio sources in the VSA observations. Since September 2000, the
VSA has been making observations of primordial CMB fluctuations. We describe
the instrument, observing strategy and current status of the first year of
observations. | astro-ph |
Optical and near-infrared photometric monitoring of the transient X-ray
binary A0538-66 with REM: The transient Be/X-ray binary A0538-66 shows peculiar X-ray and optical
variability. Despite numerous studies, the intrinsic properties underlying its
anomalous behaviour remain poorly understood. Since 2014 September we are
conducting the first quasi-simultaneous optical and near-infrared photometric
monitoring of A0538-66 in seven filters with the Rapid Eye Mount (REM)
telescope, aiming to understand the properties of this binary system. We found
that the REM lightcurves show fast flares lasting one or two days that repeat
almost regularly every ~16.6 days, the orbital period of the neutron star. If
the optical flares are powered by X-ray outbursts through photon reprocessing,
the REM lightcurves indicate that A0538-66 is still active in X-rays: bright
X-ray flares (L_x > 1E37 erg/s) could be observable during the periastron
passages. The REM lightcurves show a long-term variability that is especially
pronounced in the g band and decreases with increasing wavelength, until it no
longer appears in the near-infrared lightcurves. In addition, A0538-66 is
fainter with respect to previous optical observations most likely due to the
higher absorption of the stellar radiation of a denser circumstellar disc. On
the basis of the current models, we interpret these observational results with
a circumstellar disc around the Be star observed nearly edge-on during a
partial depletion phase. The REM lightcurves also show short-term variability
on timescales of ~1 day possibly indicative of perturbations in the density
distribution of the circumstellar disc caused by the tidal interaction with the
neutron star. | astro-ph |
A Radio Observatory on the Lunar Surface for Solar studies (ROLSS): By volume, more than 99% of the solar system has not been imaged at radio
frequencies. Almost all of this space (the solar wind) can be traversed by fast
electrons producing radio emissions at frequencies lower than the terrestrial
ionospheric cutoff, which prevents observation from the ground. To date, radio
astronomy-capable space missions consist of one or a few satellites, typically
far from each other, which measure total power from the radio sources, but
cannot produce images with useful angular resolution. To produce such images,
we require arrays of antennas distributed over many wavelengths (hundreds of
meters to kilometers) to permit aperture synthesis imaging. Such arrays could
be free-flying arrays of microsatellites or antennas laid out on the lunar
surface. In this white paper, we present the lunar option. If such an array
were in place by 2020, it would provide context for observations during Solar
Probe Plus perihelion passes. Studies of the lunar ionosphere's density and
time variability are also important goals. This white paper applies to the
Solar and Heliospheric Physics study panel. | astro-ph |
CAOS spectroscopy of Am stars Kepler targets: The {\it Kepler} space mission and its {\it K2} extension provide photometric
time series data with unprecedented accuracy. These data challenge our current
understanding of the metallic-lined A stars (Am stars) for what concerns the
onset of pulsations in their atmospheres. It turns out that the predictions of
current diffusion models do not agree with observations. To understand this
discrepancy, it is of crucial importance to obtain ground-based spectroscopic
observations of Am stars in the {\it Kepler} and {\it K2} fields in order to
determine the best estimates of the stellar parameters.
In this paper, we present a detailed analysis of high-resolution
spectroscopic data for seven stars previously classified as Am stars. We
determine the effective temperatures, surface gravities, projected rotational
velocities, microturbulent velocities and chemical abundances of these stars
using spectral synthesis. These spectra were obtained with {\it CAOS}, a new
instrument recently installed at the observing station of the Catania
Astrophysical Observatory on Mt. Etna. Three stars have already been observed
during quarters Q0-Q17, namely: HD\,180347, HD\,181206, and HD\,185658, while
HD\,43509 was already observed during {\it K2} C0 campaign.
We confirm that HD\,43509 and HD\,180347 are Am stars, while HD 52403,
HD\,50766, HD\,58246, HD\,181206 and HD\,185658 are marginal Am stars. By means
of non-LTE analysis, we derived oxygen abundances from O{\sc
I}$\lambda$7771--5{\AA} triplet and we also discussed the results obtained with
both non-LTE and LTE approaches. | astro-ph |
Multi-wavelength spectral modelling of the candidate neutrino blazar PKS
0735+178: The BL Lac object PKS 0735+178 was in its historic $\gamma$-ray brightness
state during December 2021. This period also coincides with the detection of a
neutrino event IC211208A, which was localized close to the vicinity of PKS
0735+178. We carried out detailed $\gamma$-ray timing and spectral analysis of
the source in three epochs (a) quiescent state ($E_{1}$), (b) moderate activity
state ($E_{2}$) and (c) high activity state ($E_{3}$) coincident with the epoch
of neutrino detection. During the epoch of neutrino detection ($E_{3}$), we
found the largest variability amplitude of 95%. The $\gamma$-ray spectra
corresponding to these three epochs are well fit by the power law model and the
source is found to show spectral variations with a softer when brighter trend.
In the epoch $E_{3}$, we found the shortest flux doubling/halving time of 5.75
hrs. Even though the spectral energy distribution in the moderate activity
state and in the high activity state could be modeled by the one-zone leptonic
emission model, the spectral energy distribution in the quiescent state
required an additional component of radiation over and above the leptonic
component. Here we show that a photo-meson process was needed to explain the
excess $\gamma$-ray emission in the hundreds of GeV which could not be
accounted for by the synchrotron self-Compton process. | astro-ph |
What can BeppoSAX tell us about short GRBs: An update from the Subsecond
GRB Project: We present some statistical considerations on the BeppoSAX hunt for subsecond
GRBs at the Scientific Operation Center. Archive analysis of a BATSE/SAX
sub-sample of bursts indicates that the GRB Monitor is sensitive to short (< 2
sec) events, that are in fact about 22% of the total. The non-detection of
corresponding prompt X-ray counterparts to short bursts in the Wide Field
Cameras, in about 3 years of operations, is discussed: with present data no
implications on the X-to-gamma-ray spectra of short vs long GRBs may be
inferred. Finally, the status of searching procedures at SOC is reviewed. | astro-ph |
The aromatic infrared bands as seen by ISO-SWS: probing the PAH model: We discuss the Aromatic Infrared Band (AIB) profiles observed by ISO-SWS
towards a number of bright interstellar regions where dense molecular gas is
illuminated by stellar radiation. Our sample spans a broad range of excitation
conditions (exciting radiation fields with effective temperature, Teff, ranging
from 23,000 to 45,000 K). The SWS spectra are decomposed coherently in our
sample into Lorentz profiles and a broadband continuum. We find that the
individual profiles of the main AIBs at 3.3, 6.2, 8.6 and 11.3 microns are well
represented with at most two lorentzians. Furthermore, we show that the
positions and widths of these AIBs are remarkably stable (within a few cm-1).
We then extract the profiles of individual AIBs from the data and compare them
to a model of Polycyclic Aromatic Hydrocarbon (PAH) cation emission which
includes the temperature dependence of the AIB profiles. The present similarity
of the AIB profiles requires that the PAH temperature distribution remains
roughly the same whatever the radiation field hardness. Deriving the
temperature distribution of interstellar PAHs, we show that its hot tail, which
controls the AIB spectrum, sensitively depends on Nmin (the number of C-atoms
in the smallest PAH) and Teff. Comparing the observed profiles of the
individual AIBs to our model results, we can match most of the AIB profiles if
Nmin is increased with Teff. We then discuss our results in the broader context
of ISO observations of fainter interstellar regions where PAHs are expected to
be in neutral form. | astro-ph |
Application of Deep Learning Methods for Distinguishing Gamma-Ray Bursts
from Fermi/GBM TTE Data: To investigate GRBs in depth, it is crucial to develop an effective method
for identifying GRBs accurately. Current criteria, e.g., onboard blind search,
ground blind search, and target search, are limited by manually set thresholds
and perhaps miss GRBs, especially for sub-threshold events. We propose a novel
approach that utilizes convolutional neural networks (CNNs) to distinguish GRBs
and non-GRBs directly. We structured three CNN models, plain-CNN, ResNet, and
ResNet-CBAM, and endeavored to exercise fusing strategy models. Count maps of
NaI detectors onboard Fermi/GBM were employed as the input samples of datasets
and models were implemented to evaluate their performance on different time
scale data. The ResNet-CBAM model trained on 64 ms dataset achieves high
accuracy overall, which includes residual and attention mechanism modules. The
visualization methods of Grad-CAM and t-SNE explicitly displayed that the
optimal model focuses on the key features of GRBs precisely. The model was
applied to analyze one-year data, accurately identifying approximately 98% of
GRBs listed in the Fermi burst catalog, 8 out of 9 sub-threshold GRBs, and 5
GRBs triggered by other satellites, which demonstrated the deep learning
methods could effectively distinguish GRBs from observational data. Besides,
thousands of unknown candidates were retrieved and compared with the bursts of
SGR J1935+2154 for instance, which exemplified the potential scientific value
of these candidates indeed. Detailed studies on integrating our model into
real-time analysis pipelines thus may improve their accuracy of inspection, and
provide valuable guidance for rapid follow-up observations of multi-band
telescopes. | astro-ph |
Development of a cosmic ray oriented trigger for the fluorescence
telescope on EUSO-SPB2: The Extreme Universe Space Observatory on a Super Pressure Balloon 2
(EUSO-SPB2), in preparation, aims to make the first observations of Ultra-High
Energy Cosmic Rays (UHECRs) from near space using optical techniques. EUSO-SPB2
will prototype instrumentation for future satellite-based missions, including
the Probe of Extreme Multi-Messenger Astrophysics (POEMMA) and K-EUSO. The
payload will consist of two telescopes. The first is a Cherenkov telescope (CT)
being developed to quantify the background for future below-the-limb very high
energy (E>10 PeV) astrophysical neutrino observations, and the second is a
fluorescence telescope (FT) being developed for detection of UHECRs. The FT
will consist of a Schmidt telescope, and a 6192 pixel ultraviolet camera with
an integration time of 1.05 microseconds. The first step in the data
acquisition process for the FT is a hardware level trigger in order to decide
which data to record. In order to maximize the number of UHECR induced
extensive air showers (EASs) which can be detected, a novel trigger algorithm
has been developed based on the intricacies and limitations of the detector.
The expected performance of the trigger has been characterized by simulations
and, pending hardware verification, shows that EUSO-SPB2 is well positioned to
attempt the first near-space observation of UHECRs via optical techniques. | astro-ph |
Shock Waves and Cosmic Ray Acceleration in the Outskirts of Galaxy
Clusters: The outskirts of galaxy clusters are continuously disturbed by mergers and
gas infall along filaments, which in turn induce turbulent flow motions and
shock waves. We examine the properties of shocks that form within $r_{200}$ in
sample galaxy clusters from structure formation simulations. While most of
these shocks are weak and inefficient accelerators of cosmic rays (CRs), there
are a number of strong, energetic shocks which can produce large amounts of CR
protons via diffusive shock acceleration. We show that the energetic shocks
reside mostly in the outskirts and a substantial fraction of them are induced
by infall of the warm-hot intergalactic medium from filaments. As a result, the
radial profile of the CR pressure in the intracluster medium is expected to be
broad, dropping off more slowly than that of the gas pressure, and might be
even temporarily inverted, peaking in the outskirts. The volume-integrated
momentum spectrum of CR protons inside $r_{200}$ has the power-law slope of
$4.25 - 4.5$, indicating that the average Mach number of the shocks of main CR
production is in the range of $\left< M_s \right>_{\rm CR} \approx 3 - 4$. We
suggest that some radio relics with relatively flat radio spectrum could be
explained by primary electrons accelerated by energetic infall shocks with $M_s
>~ 3$ induced in the cluster outskirts. | astro-ph |
The Role of a Massive Central Singularity in Galactic Mergers on the
Survival of the Core Fundamental Plane: In order for the core Fundamental Plane (cFP) to endure, small ellipticals
must not survive mergers with giant ellipticals, despite the fact the small
secondary galaxy can be as much as a million times more dense than the primary.
However, our previous set of experiments has shown that, for purely stellar
galaxies, the secondary does in fact survive mergers with primaries up to 100
times more massive. In this paper, we demonstrate the effect that a massive
central black hole has on mergers of cFP galaxies. Our results indicate that
the addition of a massive central singularity inside the primary galaxy
provides strong enough tidal forces to destroy dense cFP companions when the
secondary's orbital decay is sufficiently elongated. The destruction of the
secondary acts to preserve the original low central density profile of the
primary in the giant merger remnant, which allows the remnant to remain on the
cFP. On more circular orbits, though, the secondary is only disrupted near the
end of the merger, and the degree to which the secondary particles disperse
depends on the amount of orbital energy left in the merger. Hence, there are
some mergers for which the cFP is not preserved in our experiments. We find
that if the secondary is not dispersed, it forms a spinning stellar disk with a
central density that forces the merger remnant off the cFP. | astro-ph |
Hot One-Temperature Accretion Flows Around Black Holes: We describe hot, optically-thin solutions for one-temperature accretion disks
around black holes. We include cooling by synchrotron, bremsstrahlung, and
Comptonization. Our solutions are thermally and viscously stable, with gas
temperatures on the order of $T \sim 10^9-10^{10.7}$K. The thermal stability is
a direct result of the inclusion of synchrotron cooling.
The new solution branch is related to the advection-dominated solution for a
two-temperature gas described by Narayan \& Yi (1995b). It is present only for
mass accretion rates less than some critical $\dot{M}_{crit}$ which depends on
the radius $R$ and viscosity parameter $\alpha$. The solutions are
advection-dominated for extremely low values of $\dot{M}$. However, for a range
of intermediate accretion rates, the new solutions are both hot ($T \sim
10^{10}$K) and cooling-dominated. Because of this new feature, one-temperature
solutions are significantly more luminous than the corresponding two
temperature solutions.
The radial profile of the new solutions is unusual. The inner parts of the
flow are cooling-dominated and have a disk-like geometry, while the outer parts
are fully advection-dominated and nearly quasi-spherical. | astro-ph |
Multi-messenger astronomy with Centaurus A: We calculated for the nearest active galactic nucleus (AGN), Centaurus A (Cen
A), the flux of high energy cosmic rays and of accompanying secondary photons
and neutrinos expected from hadronic interactions in the source. We used as two
basic models for the generation of ultrahigh energy cosmic rays (UHECR) shock
acceleration in the radio jet and acceleration in the regular electromagnetic
field close to the core of the AGN, normalizing the UHECR flux to the
observations of the Auger experiment. Here we compare the previously obtained
photon fluxes with the recent data reported by the Fermi LAT and H.E.S.S.
collaborations. In the case of the core model, we find good agreement both for
the predicted spectral shape and the overall normalization between our earlier
results and the H.E.S.S. observations for a primary proton energy $dN/dE\propto
E^{-\alpha}$ with $\alpha\sim 2$ or smaller. A broken-power law with
high-energy part $\alpha=-2.7$ leads to photon fluxes in excess of the Fermi
measurements. The energy spectrum of the photon fluxes obtained by us for the
jet scenario is in all cases at variance with the H.E.S.S. and Fermi
observations. | astro-ph |
Binning is Sinning: Redemption for Hubble Diagram using Photometrically
Classified Type Ia Supernovae: Bayesian Estimation Applied to Multiple Species (BEAMS) is implemented in the
BEAMS with Bias Corrections (BBC) framework to produce a redshift-binned Hubble
diagram (HD) for Type Ia supernovae (SNe Ia). BBC corrects for selection
effects and non-SNIa contamination, and systematic uncertainties are described
by a covariance matrix with dimension matching the number of BBC redshift bins.
For spectroscopically confirmed SN Ia samples, a recent "Binning is Sinning"
article (BHS21, arxiv:2012.05900) showed that an unbinned HD and covariance
matrix reduces the systematic uncertainty by a factor of ~1.5 compared to the
binned approach. Here we extend their analysis to obtain an unbinned HD for a
photometrically identified sample processed with BBC. To test this new method,
we simulate and analyze 50 samples corresponding to the Dark Energy Survey
(DES) witha low-redshift anchor; the simulation includes SNe Ia, and
contaminants from core-collapse SNe and peculiar SNe Ia. The analysis includes
systematic uncertainties for calibration, and measures the dark energy equation
of state parameter (w). Compared to a redshift-binned HD, the unbinned HD with
nearly 2000 events results in a smaller systematic uncertainty, in qualitative
agreement with BHS21, and averaging results among the 50 samples we find no
evidence for a w-bias. To reduce computation time for fitting an unbinned HD
with large samples, we propose an HD-rebinning method that defines the HD in
bins of redshift, color, and stretch; the rebinned HD results in similar
uncertainty as the unbinned case, and shows no evidence for a w-bias. | astro-ph |
Gaia view of primitive inner-belt asteroid families: Searching for the
origins of asteroids Bennu and Ryugu: Near-Earth asteroids Ryugu and Bennu, were visited, characterised, and
sampled by the Hayabusa2 and OSIRIS-REx missions: remote sensing data and
sample return analysis showed that both asteroids have primitive, hydrated and
organic-rich compositions. The dark families of the inner main belt (IMB) that
belong to the spectroscopic C-complex have been claimed to be the sources of
both Ryugu and Bennu. Hence, there has been large effort to characterise them.
Here we used the Gaia Data Release 3 (DR3) asteroid reflectance spectra to
investigate the 11 known IMB C-complex families (Chaldaea, Chimaera, Clarissa,
Erigone, Eulalia, Klio, Polana, Primordial, Sulamitis, Svea, Tamara). For each
family, we extracted the family members that have known geometric visible
albedo values and Gaia DR3 data and we created an average reflectance spectrum
per family between 370 and 950 nm. The average DR3 reflectance spectra of each
family were compared with the previous literature data and to Bennu's and
Ryugu's spectra. We found that DR3 reflectance spectra of the IMB C-complex
families are in general consistent with previous findings with the only
exception of the Svea family. We also showed that the Polana and the Eulalia
families can be distinguished in the wavelength region 370 - 500 nm. Among all
the IMB C-complex families, we determined that the average reflectance spectra
of the Eulalia and Polana families are the most similar to those of Bennu and
Ryugu, respectively. In particular, Eulalia family's average spectrum is a good
match to Bennu's in the wavelength range 450 - 800 nm, while beyond 800 nm the
spectrum of Bennu is bluer than that of Eulalia. Moreover, the spectrum of the
Polana family has the smallest discrepancy against the spectrum of Ryugu,
although this match is formally unsatisfactory (reduced chi^2 ~ 1.9). | astro-ph |
A Comparison of Weak Lensing Measurements From Ground- and Space-Based
Facilities: We assess the relative merits of weak lensing surveys, using overlapping
imaging data from the ground-based Subaru telescope and the Hubble Space
Telescope (HST). Our tests complement similar studies undertaken with simulated
data. From observations of 230,000 matched objects in the 2 square degree
COSMOS field, we identify the limit at which faint galaxy shapes can be
reliably measured from the ground. Our ground-based shear catalog achieves
sub-percent calibration bias compared to high resolution space-based data, for
galaxies brighter than i'~24.5 and with half-light radii larger than 1.8". This
selection corresponds to a surface density of ~15 galaxies per sq arcmin
compared to ~71 per sq arcmin from space. On the other hand the survey speed of
current ground-based facilities is much faster than that of HST, although this
gain is mitigated by the increased depth of space-based imaging desirable for
tomographic (3D) analyses. As an independent experiment, we also reconstruct
the projected mass distribution in the COSMOS field using both data sets, and
compare the derived cluster catalogs with those from X-ray observations. The
ground-based catalog achieves a reasonable degree of completeness, with minimal
contamination and no detected bias, for massive clusters at redshifts
0.2<z<0.5. The space-based data provide improved precision and a greater
sensitivity to clusters of lower mass or at higher redshift. | astro-ph |
Black hole spin and size of the X-ray emitting region(s) in the Seyfert
1.5 galaxy ESO 362-G18: We report results from multi-epoch X-ray observations of the Seyfert 1.5
galaxy ESO 362-G18 performed between November 2005 and June 2010. ESO 362-G18
generally exhibits the typical X-ray spectrum of type 1 Active Galactic Nuclei
(AGN). A disc-reflection component accounts for broad residuals in the iron K
band and above 10~keV, as well as for a significant soft excess. From our
best-fitting reflection model, we measure a black hole spin greater or equal to
0.92 at the 99.99 per cent confidence level. ESO 362-G18 is also (typically)
mildly absorbed by a column of neutral gas. The absorber is variable and one
observation, performed ~2 months after a typical mildly absorbed one, is
heavily absorbed by a cold column density two orders of magnitude higher than
that during any other observation. UV variability between the heavily absorbed
observation and the others suggests that the absorber can be identified with a
dusty, clumpy torus. The absorption variability timescale enables us to locate
the X-ray emitting region within the innermost ~50 gravitational radii. Such
result holds not only for the X-ray continuum, but also for the soft excess. | astro-ph |
Multiplicity among solar-type stars IV. The CORAVEL radial velocities
and the spectroscopic orbits of nearby K dwarfs: Context. The statistical properties of binary stars are clues for
understanding their formation process. A radial velocity survey was carried on
amongst nearby G-type stars and the results were published in 1991. Aims. The
survey of radial velocity measurements was extended towards K-type stars.
Methods. A sample of 261 K-type stars was observed with the spectrovelocimeter
CORAVEL (COrrelation RAdial VELocities). Those stars with a variable radial
velocity were detected on the basis of the P(chi^2) test. The orbital elements
of the spectroscopic binaries were then derived. Results. The statistical
properties of binary stars were derived from these observations and published
in 2003. We present the catalogue of the radial velocity measurements obtained
with CORAVEL for all the K stars of the survey and the orbital elements derived
for 34 spectroscopic systems. In addition, the catalogue contains eight G-type
spectroscopic binaries that have received additional measurements since 1991
and for which the orbital elements are revised or derived for the first time. | astro-ph |
Characterizing the Conditional Galaxy Property Distribution using
Gaussian Mixture Models: Line-intensity mapping (LIM) is a promising technique to constrain the global
distribution of galaxy properties. To combine LIM experiments probing different
tracers with traditional galaxy surveys and fully exploit the scientific
potential of these observations, it is necessary to have a physically motivated
modeling framework. As part of developing such a framework, in this work we
introduce and model the conditional galaxy property distribution (CGPD), i.e.
the distribution of galaxy properties conditioned on the host halo mass and
redshift. We consider five galaxy properties, including the galaxy stellar
mass, molecular gas mass, galaxy radius, gas phase metallicity and star
formation rate (SFR), which are important for predicting the emission lines of
interest. The CGPD represents the full distribution of galaxies in the five
dimensional property space; many important galaxy distribution functions and
scaling relations, such as the stellar mass function and SFR main sequence, can
be derived from integrating and projecting it. We utilize two different kinds
of cosmological galaxy simulations, a semi-analytic model and the IllustrisTNG
hydrodynamic simulation, to characterize the CGPD and explore how well it can
be represented using a Gaussian mixture model (GMM). We find that with just a
few ($\sim 3$) Gaussian components, a GMM can describe the CGPD of the
simulated galaxies to high accuracy for both simulations. The CGPD can be
mapped to LIM or other observables by constructing the appropriate relationship
between galaxy properties and the relevant observable tracers. | astro-ph |
Observational Consequences of the Recently Proposed Super-Earth Orbiting
GJ436: Ribas and collaborators have recently proposed that an additional, ~5 M_earth
planet orbits the transiting planet host star GJ436. Long-term dynamical
interactions between the two planets leading to eccentricity excitation might
provide an explanation for the transiting planet's unexpectedly large orbital
eccentricity. In this paper we examine whether the existence of such a second
planet is supported by the available observational data when the short-term
interactions that would result from its presence are accounted for. We find
that the model for the system suggested by Ribas and collaborators lead to
predictions that are strongly inconsistent with the measured host star radial
velocities, transiting planet primary and secondary eclipse times, and
transiting planet orbital inclinations. A search for an alternative two planet
model that is consistent with the data yields a number of plausible solutions,
although no single one stands out as particularly unique by giving a
significantly better fit to the data than the nominal single planet model. We
conclude from this study that Ribas and collaborator's general hypothesis of an
additional short-period planet in the GJ436 system is still plausible, but that
there is not sufficient evidence to support their claim of a planet detection. | astro-ph |
Indirect dark matter searches in Gamma- and Cosmic Rays: Dark matter candidates such as weakly-interacting massive particles are
predicted to annihilate or decay into Standard Model particles leaving behind
distinctive signatures in gamma rays, neutrinos, positrons, antiprotons, or
even anti-nuclei. Indirect dark matter searches, and in particular those based
on gamma-ray observations and cosmic ray measurements could detect such
signatures. Here we review the strengths and limitations of this approach and
look into the future of indirect dark matter searches. | astro-ph |
A Comparative Study of Convolutional Neural Networks for the Detection
of Strong Gravitational Lensing: As we enter the era of large-scale imaging surveys with the up-coming
telescopes such as LSST and SKA, it is envisaged that the number of known
strong gravitational lensing systems will increase dramatically. However, these
events are still very rare and require the efficient processing of millions of
images. In order to tackle this image processing problem, we present Machine
Learning techniques and apply them to the Gravitational Lens Finding Challenge.
The Convolutional Neural Networks (CNNs) presented have been re-implemented
within a new modular, and extendable framework, LEXACTUM. We report an Area
Under the Curve (AUC) of 0.9343 and 0.9870, and an execution time of 0.0061s
and 0.0594s per image, for the Space and Ground datasets respectively, showing
that the results obtained by CNNs are very competitive with conventional
methods (such as visual inspection and arc finders) for detecting gravitational
lenses. | astro-ph |
Density, Velocity, and Magnetic Field Structure in Turbulent Molecular
Cloud Models: We use 3D numerical MHD simulations to follow the evolution of cold,
turbulent, gaseous systems with parameters representing GMC conditions. We
study three cloud simulations with varying mean magnetic fields, but identical
initial velocity fields. We show that turbulent energy is reduced by a factor
two after 0.4-0.8 flow crossing times (2-4 Myr), and that the magnetically
supercritical cloud models collapse after ~6 Myr, while the subcritical cloud
does not collapse. We compare density, velocity, and magnetic field structure
in three sets of snapshots with matched Mach numbers. The volume and column
densities are both log-normally distributed, with mean volume density a factor
3-6 times the unperturbed value, but mean column density only a factor 1.1-1.4
times the unperturbed value. We use a binning algorithm to investigate the
dependence of kinetic quantities on spatial scale for regions of column density
contrast (ROCs). The average velocity dispersion for the ROCs is only weakly
correlated with scale, similar to the mean size-linewidth relation for clumps
within GMCs. ROCs are often superpositions of spatially unconnected regions
that cannot easily be separated using velocity information; the same difficulty
may affect observed GMC clumps. We analyze magnetic field structure, and show
that in the high density regime, total magnetic field strengths increase with
density with logarithmic slope 1/3 -2/3. Mean line-of-sight magnetic field
strengths vary widely across a projected cloud, and do not correlate with
column density. We compute simulated interstellar polarization maps at varying
orientations, and determine that the Chandrasekhar-Fermi formula multiplied by
a factor ~0.5 yields a good estimate of the plane-of sky magnetic field
strength provided the dispersion in polarization angles is < 25 degrees. | astro-ph |
Generating realistic synthetic meteoroid orbits: Context. Generating a synthetic dataset of meteoroid orbits is a crucial step
in analysing the probabilities of random grouping of meteoroid orbits in
automated meteor shower surveys. Recent works have shown the importance of
choosing a low similarity threshold value of meteoroid orbits, some pointing
out that the recent meteor shower surveys produced false positives due to
similarity thresholds which were too high. On the other hand, the methods of
synthetic meteoroid orbit generation introduce additional biases into the data,
thus making the final decision on an appropriate threshold value uncertain.
Aims. As a part of the ongoing effort to determine the nature of meteor
showers and improve automated methods, it was decided to tackle the problem of
synthetic meteoroid orbit generation, the main goal being to reproduce the
underlying structure and the statistics of the observed data in the synthetic
orbits.
Methods. A new method of generating synthetic meteoroid orbits using the
Kernel Density Estimation method is presented. Several types of approaches are
recommended, depending on whether one strives to preserve the data structure,
the data statistics or to have a compromise between the two.
Results. The improvements over the existing methods of synthetic orbit
generation are demonstrated. The comparison between the previous and newly
developed methods are given, as well as the visualization tools one can use to
estimate the influence of different input parameters on the final data. | astro-ph |
The Properties of Long-Period Variables in the Large Magellanic Cloud
from MACHO: We present a new analysis of the long-period variables in the Large
Magellanic Cloud (LMC) from the MACHO Variable Star Catalog. Three-quarters of
our sample of evolved, variable stars have periodic light curves. We
characterize the stars in our sample using the multiple periods found in their
frequency spectra. Additionally, we use single-epoch Two Micron All Sky Survey
measurements to construct the average infrared light curves for different
groups of these stars. Comparison with evolutionary models shows that stars on
the red giant branch (RGB) or the early asymptotic giant branch (AGB) often
show non-periodic variability, but begin to pulsate with periods on the two
shortest period-luminosity sequences (3 & 4) when they brighten to K_s ~ 13.
The stars on the thermally pulsing AGB are more likely to pulsate with longer
periods that lie on the next two P-L sequences (1 & 2), including the sequence
associated with the Miras in the LMC. The Petersen diagram and its variants
show that multi-periodic stars on each pair of these sequences (3 & 4, and 1 &
2) typically pulsate with periods associated only with that pair. The periods
in these multi-periodic stars become longer and stronger as the star evolves.
We further constrain the mechanism behind the long secondary periods (LSPs)
seen in half of our sample, and find that there is a close match between the
luminosity functions of the LSP stars and all of the stars in our sample, and
that these star's pulsation amplitudes are relatively wavelength independent.
Although this is characteristic of stellar multiplicity, the large number of
these variables is problematic for that explanation. | astro-ph |
Light pollution is skyrocketing: Artificial light at night is a pollutant that is rising fast, as demonstrated
by Kyba et al. (1) work by analyzing ten of thousands observations by citizen
scientists in the last 12 years. The study found that the dimmest stars are
vanishing, progressively hidden by a 10 percent yearly increase of the sky
background due to artificial lights. This increase is difficult to be detected
by the global coverage satellites now in operation, due to detector's blindness
to the blue peak of white LEDs that are progressively replacing older
technology lamps. This shows the need for a satellite with nighttime multi band
capability in the visible light to study and control future evolution. More
importantly, a call for a strong reverse in the light pollution rising trend is
extremely urgent to avoid all the cultural, scientific, energetic, ecological
and health negative effects of artificial nightlights. | astro-ph |
Precessing Warped Be Disk Triggering the Giant Outbursts in 2009 and
2011 in A 0535+262/V725 Tau: We carried out optical high-dispersion spectroscopic monitoring of the Be
disk in a Be/X-ray binary A 0535+262/V725 Tau from 2009 to 2012, covering two
giant outbursts and several normal outbursts. This monitoring was performed in
order to investigate variabilities of the Be disk due to the interaction with
the neutron star in recent X-ray active phase from 2008 to 2011. Such
variabilities give a clue to uncleared detailed mechanism for very bright X-ray
outbursts, which are unique to some Be/X-ray binaries with relatively wide and
eccentric orbit. In the previous letter (Moritani et al. 2011), a brief
overview of line profile variabilities around the 2009 giant outburst was given
and the possibility of a warped Be disk was discussed. In this paper, a full
analysis of the Halpha line profiles as well as other line profiles is carried
out. A bright blue component, or blue "shoulder", showing up after periastron
indicates the presence of a dense gas stream toward the neutron star, which is
associated with observed outbursts. We re-analyze the Halpha line profiles
before 2009 (down to 2005) in order to investigate the variability of the the
disk structure in the innermost region, which seems to have detached from the
Be star surface by 2008. A redshifted enhanced component is remarkable in all
emission lines observed around the 2009 giant outburst, occasionally forming a
triple peak. These features indicate that the Be disk was warped in X-ray
active phase. We estimate the position of the warped region from fitting the
radial velocity of the redshifted enhanced component of Halpha, and find that
it was very close to the periastron when two giant outbursts in 2009 and 2011
and a bright normal outburst in 2010 March occurred. These facts strongly
suggest that the warped Be disk triggered these giant outbursts. | astro-ph |
Turbulence in the Molecular Interstellar Medium: The observational record of turbulence within the molecular gas phase of the
interstellar medium is summarized. We briefly review the analysis methods used
to recover the velocity structure function from spectroscopic imaging and the
application of these tools on sets of cloud data. These studies identify a
near-invariant velocity structure function that is independent of local the
environment and star formation activity. Such universality accounts for the
cloud-to-cloud scaling law between the global line-width and size of molecular
clouds found by Larson (1981) and constrains the degree to which supersonic
turbulence can regulate star formation. In addition, the evidence for large
scale driving sources necessary to sustain supersonic flows is summarized. | astro-ph |
Cosmology with cosmic web environments II. Redshift-space auto and cross
power spectra: Degeneracies among parameters of the cosmological model are known to
drastically limit the information contained in the matter distribution. In the
first paper of this series, we shown that the cosmic web environments; namely
the voids, walls, filaments and nodes; can be used as a leverage to improve the
real-space constraints on a set of six cosmological parameters, including the
summed neutrino mass.
Following-upon these results, we propose to study the achievable constraints
of environment-dependent power spectra in redshift space where the velocities
add up information to the standard two-point statistics by breaking the
isotropy of the matter density field. A Fisher analysis based on a set of
thousands of Quijote simulations allows us to conclude that the combination of
power spectra computed in the several cosmic web environments is able to break
some degeneracies. Compared to the matter monopole and quadrupole information
alone, the combination of environment-dependent spectra tightens down the
constraints on key parameters like the matter density or the summed neutrino
mass by up to a factor of $5.5$. Additionally, while the information contained
in the matter statistic quickly saturates at mildly non-linear scales in
redshift space, the combination of power spectra in the environments appears as
a goldmine of information able to improve the constraints at all the studied
scales from $0.1$ to $0.5$ $h$/Mpc and suggests that further improvements are
reachable at even finer scales. | astro-ph |
Interstellar Deuterium, Nitrogen, and Oxygen Abundances Toward GD 246,
WD 2331$-$475, HZ 21, and Lan 23: Results from the FUSE Mission: The interstellar abundances of D I, N I, and O I in the local ISM are studied
us ing high-resolution spectra of four hot white dwarfs. The spectra of GD 246,
WD 2331$-$475, HZ 21, and Lan 23 were obtained with the {\it Far Ultraviolet
Spectroscopic Explorer} FUSE in the wavelength range 905-1187 A. The line of
sight to GD 246 probes the Local Interstellar Cloud and at least one other H I
cloud inside the Local Bubble, which contains most of the gas seen al ong this
line of sight. The column densities of H I, C II*, S II, and Si II are measured
using archival STIS echelle-mode observations. The H I column density is
determined by fitting the strong damping wings of inte rstellar Lyman alpha
using a model atmosphere to account for the stellar continuum. We combine the
different abundance ratios computed here with previous published values to
produce revised FUSE abundance ratios for DI/HI, OI/HI, NI/HI, DI/NI, DI/OI,
and OI/NI. | astro-ph |
A Chi-Squared Analysis of the Measurements of Two Cosmological
Parameters Over Time: The aim of this analysis was to determine whether or not the given error bars
truly represented the dispersion of values in a historical compilation of two
cosmological parameters: the amplitude of mass fluctuations ($\sigma_8$) and
Hubble's constant ($H_0$) parameters in the standard cosmological model. For
this analysis, a chi-squared test was executed on a compiled list of past
measurements. It was found through analysis of the chi-squared ($\chi^2$)
values of the data that for $\sigma_8$ (60 data points measured between 1993
and 2019 and $\chi^2$ between 182.4 and 189.0) the associated probability Q is
extremely low, with $Q = 1.6 \times 10^{-15}$ for the weighted average and $Q =
8.8 \times 10^{-15}$ for the best linear fit of the data. This was also the
case for the $\chi^2$ values of $H_0$ (163 data points measured between 1976
and 2019 and $\chi^2$ between 480.1 and 575.7), where $Q = 1.8 \times 10^{-33}$
for the linear fit of the data and $Q = 1.0 \times 10^{-47}$ for the weighted
average of the data. The general conclusion was that the statistical error bars
associated with the observed parameter measurements have been underestimated or
the systematic errors were not properly taken into account in at least 20\% of
the measurements. The~fact that the underestimation of error bars for $H_0$ is
so common might explain the apparent 4.4$\sigma$ discrepancy formally known
today as the Hubble tension. | astro-ph |
The accretion of galaxies into groups and clusters: We use the galaxy stellar mass and halo merger tree information from the
semi-analytic model galaxy catalogue of Font et al. (2009) to examine the
accretion of galaxies into a large sample of groups and clusters, covering a
wide range in halo mass (10E12.9 to 10E15.3 Msun/h), and selected from each of
four redshift epochs (z=0, 0.5, 1.0 and 1.5). We find that clusters at all
examined redshifts have accreted a significant fraction of their final galaxy
populations through galaxy groups. A 10E14.5 Msun/h mass cluster at z=0 has, on
average, accreted ~ 40% of its galaxies (Mstellar > 10E9 Msun/h) from halos
with masses greater than 10E13 Msun/h. Further, the galaxies which are accreted
through groups are more massive, on average, than galaxies accreted through
smaller halos or from the field population. We find that at a given epoch, the
fraction of galaxies accreted from isolated environments is independent of the
final cluster or group mass. In contrast, we find that observing a cluster of
the same halo mass at each redshift epoch implies different accretion rates of
isolated galaxies, from 5-6 % per Gyr at z=0 to 15% per Gyr at z=1.5. We find
that combining the existence of a Butcher Oemler effect at z=0.5 and the
observations that galaxies within groups display significant environmental
effects with galaxy accretion histories justifies striking conclusions. Namely,
that the dominant environmental process must begin to occur in halos of 10E12
-- 10E13 Msun/h, and act over timescales of > 2 Gyrs. This argues in favor of a
mechanism like "strangulation", in which the hot halo of a galaxy is stripped
upon infalling into a more massive halo . This simple model predicts that by
z=1.5 galaxy groups and clusters will display little to no environmental
effects. | astro-ph |
A Multiwavelength Investigation of Unidentified EGRET Sources: Statistical studies indicate that the 271 point sources of high-energy gamma
rays belong to two groups: a Galactic population and an isotropic extragalactic
population. Many unidentified extragalactic sources are certainly blazars, and
it is the intention of this work to uncover gamma-ray blazars missed by
previous attempts. Until recently, searches for blazar counterparts to
unidentified EGRET sources have focused on finding AGN that have 5-GHz radio
flux densities S_5 near or above 1 Jy. However, the recent blazar
identification of 3EG J2006-2321 (S_5 = 260 mJy) and other work suggest that
careful studies of weaker flat-spectrum sources may be fruitful. In this
spirit, error circles of 4 high-latitude unidentified EGRET sources have been
searched for 5-GHz sources. The gamma-ray sources are 3EG J1133+0033, 3EG
J1212+2304, 3EG J1222+2315, and 3EG J1227+4302. Within the error contours of
each of the four sources are found 6 radio candidates; by observing the
positions of the radio sources with the 0.81-m Tenagra II telescope it is
determined that 14 of these 24 radio sources have optical counterparts with R <
22. Eight of these from two different EGRET sources have been observed in the
B, V, and R bands in more than one epoch and the analysis of these data is
ongoing. Any sources that are found to be variable will be the objects of
multi-epoch polarimetry studies. | astro-ph |
Starless Cores: Dense low mass cores in nearby clouds like Taurus and Auriga are some of the
simplest sites currently forming stars like our Sun. Because of their
simplicity and proximity, dense cores offer the clearest view of the different
phases of star formation, in particular the conditions prior to the onset of
gravitational collapse. Thanks to the combined analysis of the emission from
molecular lines and the emission/absorption from dust grains, the last several
years have seen a very rapid progress in our understanding of the structure and
chemical composition of starless cores. Previous contradictions between
molecular tracers are now understood to arise from core chemical
inhomogeneities, which are caused by the selective freeze out of molecules onto
cold dust grains. The analysis of the dust emission and absorption, in
addition, has allowed us to derive accurate density profiles, and has made
finally possible to carry out self consistent modeling of the internal
structure of starless cores. In this paper I briefly review the evolution of
core studies previous to the current golden age, and show how multi-tracer
emission can now be modeled in a systematic manner. Finally I show how we can
start to reconstruct the early history of core formation taking advantage of
the chemical changes in the gas. | astro-ph |
Magnetic Accretion and Photopolarimetric Variability in Classical T
Tauri Stars: We employ a Monte Carlo radiation transfer code to investigate the multi-
wavelength photopolarimetric variability arising from a spotted T Tauri star
surrounded by a dusty circumstellar disk. Our aim is to assess the ability of
the magnetic accretion model to explain the observed photopolarimetric
variability of classical T Tauri stars, and to identify potentially useful
observational diagnostics of T Tauri star/disk/spot parameters. We model a
range of spot sizes, spot latitudes, inner disk truncation radii, and system
inclination angles, as well as multiple disk and spot geometries. We find that
the amplitude, morphology, and wavelength dependence of the photopolarimetric
variability predicted by our models are generally consistent with existing
observations; a flared disk geometry is required to reproduce the largest
observed polarization levels and variations. Our models can further explain
stochastic polarimetric variability if unsteady accretion is invoked, in which
case irregular -- but correlated -- photometric variability is predicted, in
agreement with observations.
Potentially useful observational diagnostics of system parameters of interest
are discussed. We also investigate the reliability of modeling spot parameters
via analytic fits to multi-band photometric variations. | astro-ph |
The data acquisition system for the ANTARES neutrino telescope: The ANTARES neutrino telescope is being constructed in the Mediterranean Sea.
It consists of a large three-dimensional array of photo-multiplier tubes. The
data acquisition system of the detector takes care of the digitisation of the
photo-multiplier tube signals, data transport, data filtering, and data
storage. The detector is operated using a control program interfaced with all
elements. The design and the implementation of the data acquisition system are
described. | astro-ph |
Disk Evolution and Bar Triggering Driven by Interactions with Dark
Matter Substructure: We study formation and evolution of bar-disk systems in fully self-consistent
cosmological simulations of galaxy formation in the LCDM WMAP3 Universe. In a
representative model we find that the first generation of bars form in response
to the asymmetric dark matter (DM) distribution (i.e., DM filament) and quickly
decay. Subsequent bar generations form and are destroyed during the major
merger epoch permeated by interactions with a DM substructure (subhalos). A
long-lived bar is triggered by a tide from a subhalo and survives for ~10 Gyr.
The evolution of this bar is followed during the subsequent numerous minor
mergers and interactions with the substructure. Together with intrinsic
factors, these interactions largely determine the stellar bar evolution. The
bar strength and its pattern speed anticorrelate, except during interactions
and when the secondary (nuclear) bar is present. For about 5 Gyr bar pattern
speed increases substantially despite the loss of angular momentum to stars and
cuspy DM halo. We analyze the evolution of stellar populations in the bar-disk
and relate them to the underlying dynamics. While the bar is made mainly of an
intermediate age, ~5-6 Gyr, disk stars at z=0, a secondary nuclear bar which
surfaces at z~0.1 is made of younger, ~1-3 Gyr stars. | astro-ph |
Did the 2000 November 8 solar flare accelerate protons to >=40 GeV?: It has been reported that a 5.7sigma directional muon excess coincident with
the 2000 July 14 solar flare was registered by the L3 precision muon
spectrometer [Ruiguang Wang, Astroparticle Phys., 31(2009) 149]. Using a same
analysis method and similar criteria of event selection, we have analyzed the
L3 precision muon spectrometer data during November 2000. The result shows that
a 4.7sigma muon excess appeared at a time coincident with the solar flare of 8
of November 2000. This muon excess corresponds to above 40 GeV primary protons
which came from a sky cell of solid angle 0.048 sr. The probability of being a
background fluctuation is estimated to be about 0.1%. It has been convinced
that solar protons could be accelerated to tens of GeV in those Class X solar
flares which usually arose solar cosmic ray ground level enhancement (GLE)
events. However, whether a Class M solar flare like the non-GLE event of 8
November 2000 may also accelerate solar protons to such high energies? It is
interesting and noteworthy. | astro-ph |
The 2dF-SDSS LRG and QSO survey: evolution of the clustering of luminous
red galaxies since z = 0.6: We present an analysis of the small-to-intermediate scale clustering of
samples of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey and
the 2dF-SDSS LRG and QSO (2SLAQ) survey carefully matched to have the same
rest-frame colours and luminosity. We study the spatial two-point
auto-correlation function in both redshift-space and real-space of a combined
sample of over 10,000 LRGs, which represent the most massive galaxies in the
universe with stellar masses > 10^11 h^-1 M_sun and space densities 10^-4 h^-3
Mpc^-3. We find no significant evolution in the amplitude r_0 of the
correlation function with redshift, but do see a slight decrease in the slope
with increasing redshift over 0.19 < z < 0.55 and scales of 0.32 < r < 32 h^-1
Mpc. We compare our measurements with the predicted evolution of dark matter
clustering and use the halo model to interpret our results. We find that our
clustering measurements are inconsistent (>99.9% significance) with a passive
model whereby the LRGs do not merge with one another; a model with a merger
rate of 7.5 +/- 2.3% from z = 0.55 to z = 0.19 (i.e. an average rate of 2.4%
Gyr^-1) provides a better fit to our observations. Our clustering and number
density measurements are consistent with the hypothesis that the merged LRGs
were originally central galaxies in different haloes which, following the
merger of these haloes, merged to create a single Brightest Cluster Galaxy. In
addition, we show that the small-scale clustering signal constrains the scatter
in halo merger histories. When combined with measurements of the luminosity
function, our results suggest that this scatter is sub-Poisson. While this is a
generic prediction of hierarchical models, it has not been tested before. | astro-ph |
Abundance stratification in Type Ia supernovae - V. SN 1986G bridging
the gap between normal and subluminous SNe Ia: A detailed spectroscopic analysis of SN 1986G has been performed. SN 1986G
`bridges the gap' between normal and sub luminous type Ia supernova (SNe Ia).
The abundance tomography technique is used to determine the abundance
distribution of the elements in the ejecta. SN 1986G was found to be a low
energy Chandrasekhar mass explosion. Its kinetic energy was 70% of the standard
W7 model (0.9x10$^{51}$erg). Oxygen dominates the ejecta from the outermost
layers down to $\sim$9000kms$^{-1}$ , intermediate mass elements (IME) dominate
from $\sim$ 9000kms$^{-1}$ to $\sim$ 3500kms$^{-1}$ with Ni and Fe dominating
the inner layers $<\sim$ 3500kms$^{-1}$. The final masses of the main elements
in the ejecta were found to be, O=0.33M, IME=0.69M, stable NSE=0.21M,
$^{56}$Ni=0.14M. An upper limit of the carbon mass is set at C=0.02M. The
spectra of SN1986G consist of almost exclusively singly ionised species.
SN1986G can be thought of as a low luminosity extension of the main population
of SN Ia, with a large deflagration phase that produced more IMEs than a
standard SN Ia. | astro-ph |
Rayleigh scattering: blue sky thinking for future CMB observations: Rayleigh scattering from neutral hydrogen during and shortly after
recombination causes the CMB anisotropies to be significantly frequency
dependent at high frequencies. This may be detectable with Planck, and would be
a strong signal in any future space-based CMB missions. The later peak of the
Rayleigh visibility compared to Thomson scattering gives an increased
large-scale CMB polarization signal that is a greater than 4% effect for
observed frequencies greater than 500GHz. There is a similar magnitude
suppression on small scales from additional damping. Due to strong correlation
between the Rayleigh and primary signal, measurement of the Rayleigh component
is limited by noise and foregrounds, not cosmic variance of the primary CMB,
and should observable over a wide range of angular scales at frequencies
between roughly 200GHz and 800GHz. I give new numerical calculations of the
temperature and polarization power spectra, and show that future CMB missions
could measure the temperature Rayleigh cross-spectrum at high precision, detect
the polarization from Rayleigh scattering, and also accurately determine the
cross-spectra between the Rayleigh temperature signal and primary polarization.
The Rayleigh scattering signal may provide a powerful consistency check on
recombination physics. In principle it can be used to measure additional
horizon-scale primordial perturbation modes at recombination, and distinguish a
significant tensor mode B-polarization signal from gravitational lensing at the
power spectrum level. | astro-ph |
Echelle Spectroscopy of a GRB Afterglow at z=3.969: A New Probe of the
Interstellar and Intergalactic Media in the Young Universe: We present an echelle spectrum of the Swift GRB 050730, obtained four hours
after the burst using the MIKE spectrograph on the Magellan Clay Telescope when
the afterglow was at R=17.7. The spectrum reveals a forest of absorption
features superimposed on a simple power-law shaped continuum, best described as
f_nu(lambda)\propto lambda^{alpha} with alpha =1.88\pm 0.01 over
lambda=7000-9000 A. We identify the GRB host at z_GRB=3.96855 based on the
hydrogen Lyman absorption series, narrow absorption lines due to heavy ions
such as OI, CII, SiII, SII, NiII, FeII, CIV, SiIV, and NV, and fine structure
transitions such as OI*, OI**, SiII*, CII*, and FeII*. Together these
transitions allow us to study the the properties of the interstellar medium
(ISM) in the GRB host. The principal results are as follows. (1) We estimate a
neutral hydrogen column density of log N(HI)=22.15\pm 0.05 in the host. (2) The
associated metal lines exhibit multiple components over a velocity range of ~80
km/s, with >90% of the neutral gas confined in 20 km/s. (3) Comparisons between
different ionic transitions show that the host has little/no dust depletion and
has 1/100 solar metallicity. (4) The absorbing gas has much higher density than
that of intervening damped Lya absorption (DLA) systems. In addition, we report
the identification of an intervening DLA system at z_DLA=3.56439 with log
N(HI)=20.3\pm 0.1 and < 5% solar metallicity, a Lyman limit system at
z_LLS=3.02209 with log N(HI)=19.9\pm 0.1, a strong MgII absorber at
z_MgII=2.25313, and a pair of MgII absorbers at z_MgII=1.7731, 57 km/s apart.
We demonstrate that rapid echelle spectroscopy of GRB afterglows helps to
reveal a wealth of information in the ISM and the intergalactic medium along
the sightline (abridged). | astro-ph |
The Penn State - Toruń Centre for Astronomy Planet Search stars. III.
The evolved stars sample: We present basic atmospheric parameters ($T_{eff}$, $log g$, $v_{t}$ and
[Fe/H]), rotation velocities and absolute radial velocities as well as
luminosities, masses, ages and radii for 402 stars (including 11 single-lined
spectroscopic binaries), mostly subgiants and giants. For 272 of them we
present parameters for the first time. For another 53 stars we present
estimates of $T_{eff}$ and $log g$ based on photometric calibrations. More than
half objects were found to be subgiants, there is also a large group of giants
and a few stars appeard to be dwarfs. The results show that the presented
sample is composed of stars with masses ranging from 0.52 to $3.21 M_{\odot}$
of which 17 have masses $\geq$ $2.0 M_{\odot}$. The radii of stars studied in
this paper range from 0.66 to $36.04 R_{\odot}$ with vast majority having radii
between 2.0 and $4.0 R_{\odot}$. They are generally less metal abundant than
the Sun with median [Fe/H]$=-0.07$. For 62 stars in common with other planet
searches we found a very good agreement in obtained stellar atmospheric
parameters. We also present basic properties of the complete list of 744 stars
that form the PTPS evolved stars sample. We examined stellar masses for 1255
stars in five other planet searches and found some of them likely to be
significantly overestimated. Applying our uniformly determined stellar masses
we confirm the apparent increase of companions masses for evolved stars, and we
explain it, as well as lack of close-in planets with limited effective radial
velocity precision for those stars due to activity. | astro-ph |
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