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astro-ph/0112357
|
Stacy McGaugh
|
Galaxy Masses: Disks and Their Halos
|
astro-ph
|
I review what we currently do and do not know about the masses of disk
galaxies and their dark matter halos. The prognosis for disks is good: the
asymptotic rotation velocity provides a good indicator of total disk mass. The
prognosis for halos is bad: cuspy halos provide a poor description of the data,
and the total mass of individual dark matter halos remains ill-constrained.
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No Label
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No Label
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astro-ph/0509596
|
Pavel Ivanov
|
Oscillations of rotating bodies: A self-adjoint formalism applied to
dynamic tides and tidal capture
|
astro-ph
|
We consider the excitation of the inertial modes of a uniformly rotating
fully convective body due to a close encounter with another object. This could
lead to a tidal capture or orbital circularisation depending on whether the
initial orbit is unbound or highly eccentric. We develop a general self-adjoint
formalism for the response problem and thus solve it taking into account the
inertial modes with $m=2$ for a full polytrope with $n=1.5.$ We are accordingly
able to show in this case that the excitation of inertial modes dominates the
response for large impact parameters and thus cannot be neglected in
calculations of tidal energy and angular momentum exchange or orbital
circularisation from large eccentricity.
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No Label
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No Label
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0809.0568
|
Jeremy Mould
|
The Extragalactic Distance Scale without Cepheids
|
astro-ph
|
Distances of galaxies in the Hubble Space Telescope Key Project are based on
the Cepheid period-luminosity relation. An alternative basis is the tip of the
red giant branch. Using archival HST data, we calibrate the infrared
Tully-Fisher relation using 14 galaxies with tip of the red giant branch
measurements. Compared with the Key Project, a higher value of the Hubble
Constant by 10% +/- 7% is inferred. Within the errors the two distance scales
are therefore consistent. We describe the additional data required for a
conclusive tip of the red giant branch measurement of H_0.
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No Label
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No Label
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astro-ph/9910530
|
Duncan K. Galloway
|
X-ray Beaming in the High Magnetic Field Pulsar GX 1+4
|
astro-ph
|
Pulse profiles from X-ray pulsars often exhibit strong energy dependence and
both periodic and aperiodic variations with time. The great variety of profiles
observed in various sources, and even from individual sources, makes it
difficult to separate the numerous factors influencing the phase-dependence of
the X-ray emission. These factors include the system geometry and particularly
the photon energy and angle dependence of emission about the neutron star
poles.
Comptonisation may play an important role in determining beam patterns and
hence pulse profiles in X-ray pulsars. A Monte Carlo simulation is used to
investigate the beaming due to Comptonisation in a simple accretion column
geometry. We apply the model to the extremely variable pulse profiles of the
high-magnetic field pulsar GX 1+4.
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No Label
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astro-ph/9704163
|
Chris Willott
|
A complete sample of quasars from the 7C redshift survey
|
astro-ph
|
We present details of a new sample of radio-loud quasars drawn from 0.013 sr
of the 7C Redshift Survey. This sample is small (21 quasars) but complete in
that every object with an unresolved nucleus and/or broad emission lines with
S(151MHz) > 0.5 Jy has been discovered. The dependence of the quasar fraction
with redshift and radio luminosity is investigated, providing new evidence
supporting the unification of radio-loud quasars and powerful radio galaxies.
This 7C sample is compared with optically-selected quasars, in order to
determine whether there are systematic biases in the different selection
techniques. There are no lightly reddened (Av approx. 1) quasars in our sample
amongst the 14 with z < 2. The discovery of a reddened quasar at z = 2.034 and
its implications are discussed. A tight correlation between radio luminosity
and optical/near infrared continuum luminosity for a subset of the sample is
also found.
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No Label
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astro-ph/9910114
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Sergei B. Popov
|
The Neutron Stars Census
|
astro-ph
|
The paucity of old isolated accreting neutron stars in ROSAT observations is
used to derive a lower limit on the mean velocity of neutron stars at birth.
The secular evolution of the population is simulated following the paths of a
statistical sample of stars for different values of the initial kick velocity,
drawn from an isotropic Gaussian distribution with mean velocity $0\leq <
V>\leq 550$ ${\rm km s^{-1}}$. The spin--down, induced by dipole losses and the
interaction with the ambient medium, is tracked together with the dynamical
evolution in the Galactic potential, allowing for the determination of the
fraction of stars which are, at present, in each of the four possible stages:
Ejector, Propeller, Accretor, and Georotator. Taking from the ROSAT All Sky
Survey an upper limit of $\sim 10$ accreting neutron stars within $\sim 140$ pc
from the Sun, we infer a lower bound for the mean kick velocity, $ < V>\gtrsim
200-300$ ${\rm km s^{-1}},$ corresponding to a velocity dispersion
$\sigma_V\gtrsim 125-190$ km s$^{-1}$. The same conclusion is reached for both
a constant magnetic field ($B\sim 10^{12}$ G) and a magnetic field decaying
exponentially with a timescale $\sim 10^9$ yr. Such high velocities are
consistent with those derived from radio pulsar observations. Present results,
moreover, constrain the fraction of low velocity stars, which could have
escaped pulsar statistics, to less than 1%.
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astro-ph/0301603
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David A. Green
|
The Historical Supernovae
|
astro-ph
|
The available historical records of supernovae occurring in our own Galaxy
over the past two thousand years are reviewed. These accounts include the
well-recorded supernovae of AD 1604 (Kepler's SN), 1572 (Tycho's SN), 1181,
1054 (which produced the Crab Nebula) and 1006, together with less certain
events dating back to AD 185. In the case of the supernovae of AD 1604 and 1572
it is European records that provide the most accurate information available,
whereas for earlier supernovae records are principally from East Asian sources.
Also discussed briefly are several spurious supernova candidates, and the
future prospects for studies of historical supernovae.
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No Label
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astro-ph/0209059
|
Roman Rafikov
|
The growth of planetary embryos: orderly, runaway, or oligarchic?
|
astro-ph
|
We consider the growth of a protoplanetary embryo embedded in a planetesimal
disk. We take into account the dynamical evolution of the disk caused by (1)
planetesimal-planetesimal interactions, which increase random motions and
smooth gradients in the disk, and (2) gravitational scattering of planetesimals
by the embryo, which tends to heat up the disk locally and repels planetesimals
away. The embryo's growth is self-consistently coupled to the planetesimal disk
dynamics. We demonstrate that details of the evolution depend on only two
dimensionless parameters incorporating all the physical characteristics of the
problem: the ratio of the physical radius to the Hill radius of any solid body
in the disk and the number of planetesimals inside the annulus of the disk with
width equal to the planetesimal Hill radius. The results of exploration in the
framework of our model of several situations typical for protosolar nebula can
be summarized as follows: initially, the planetesimal disk dynamics is not
affected by the presence of the embryo and the growth of the embryo's mass
proceeds very rapidly in the runaway regime. Later on, when the embryo starts
being dynamically important, its accretion slows down similar to the
``oligarchic'' growth picture. The scenario of orderly growth suggested by
Safronov (1972) is never realized in our calculations; scenario of runaway
growth suggested by Wetherill & Stewart (1989) is only realized for a limited
range in mass. Slow character of the planetesimal accretion on the oligarchic
stage of the embryo's accumulation leads to a considerable increase of the
protoplanetary formation timescale compared to that following from a simple
runaway accretion picture valid in the homogeneous planetesimal disks.
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0810.5617
|
Shardha Jogee Dr
|
Galaxy Interactions, Star Formation History, and Bulgeless Galaxies
|
astro-ph
|
Hierarchical Lambda CDM models provide a successful paradigm for the growth
of dark matter on large scales, but they face important challenges in
predicting how the baryonic components of galaxies evolve. I present
constraints on two aspects of this evolution: (1) The interaction history of
galaxies over the last 7 Gyr and the impact of interactions on their star
formation properties, based on Jogee et al. (2008a,b); (2) Constraints on the
origin of bulges in hierarchical models and the challenge posed in accounting
for galaxies with low bulge-to-total ratios, based on Weinzirl, Jogee, Khochar,
Burkert, and Kormendy (2008, hereafter WJKBK08)
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astro-ph/0103513
|
Mirko Boezio
|
The Cosmic-Ray antiproton flux between 3 and 49 GeV
|
astro-ph
|
We report on a new measurement of the cosmic ray antiproton spectrum. The
data were collected by the balloon-borne experiment CAPRICE98 which was flown
on 28-29 May 1998 from Fort Sumner, New Mexico, USA. The experiment used the
NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas
Ring Imaging Cherenkov (RICH) detector, a time-of-flight system, a tracking
device consisting of drift chambers and a superconducting magnet and a
silicon-tungsten calorimeter. The RICH detector was the first ever flown
capable of mass-resolving charge-one particles at energies above 5 GeV.
A total of 31 antiprotons with rigidities between 4 and 50 GV at the
spectrometer were identified with small backgrounds from other particles. The
absolute antiproton energy spectrum was determined in the kinetic energy region
at the top of the atmosphere between 3.2 and 49.1 GeV. We found that the
observed antiproton spectrum and the antiproton-to-proton ratio are consistent
with a pure secondary origin. However, a primary component may not be excluded.
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astro-ph/0505145
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Crystal L. Brogan
|
Discovery of a Radio Supernova Remnant and Non-thermal X-rays Coincident
with the TeV Source HESS J1813-178
|
astro-ph
|
We present the discovery of non-thermal radio and X-ray emission positionally
coincident with the TeV $\gamma$-ray source HESS J1813--178. We demonstrate
that the non-thermal radio emission is due to a young shell-type supernova
remnant (SNR) G12.8--0.0, and constrain its distance to be greater than 4 kpc.
The X-ray emission is primarily non-thermal and is consistent with either an
SNR shell or unidentified pulsar/pulsar wind nebula origin; pulsed emission is
not detected in archival ASCA data. A simple synchrotron+inverse Compton model
for the broadband emission assuming that all of the emission arises from the
SNR shell implies maximum energies of $(30-450)(B/10 microG)^{-0.5}$ TeV.
Further observations are needed to confirm that the broadband emission has a
common origin and better constrain the X-ray spectrum.
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astro-ph/0209392
|
Laura Pentericci
|
A Chandra study of X-ray sources in the field of the z=2.16 radio galaxy
MRC 1138-262
|
astro-ph
|
We present results from a Chandra X-ray Observatory study of the field X-ray
source population in the vicinity of the radio galaxy MRC 1138-262. Many
serendipitous X-ray sources are detected in an area of 8'x8' around the radio
source and 90% are identified in our deep VLT images. The space density of such
sources is higher than expected on the basis of the statistics of ROSAT and
Chandra deep surveys. The most likely explanation is in terms of a
concentration of AGN associated with the protocluster at z=2.16 which was found
around the radio galaxy in previous studies. Two sources have a confirmed
spectroscopic redshift close to that of the radio galaxy, and for three more
sources other observations suggest that they are associated with the
protocluster. Four of these five X-ray sources form, together with the radio
galaxy, a filament in the plane of the sky. The direction of the filament is
similar to that of the radio source axis, the large scale distribution of the
other protocluster members, the 150 kpc-sized emission-line halo and the
extended X-ray emission associated with the radio galaxy.
The majority of optically identified X-ray sources in this field have
properties consistent with type I AGN, a few could be soft, low luminosity
galaxies, one is probably an obscured (type II) AGN and one is a star. These
statistics are consistent with the results of deep X-ray surveys.
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astro-ph/0611517
|
Jan Pflamm-Altenburg
|
Captured older stars as the reason for apparently prolonged star
formation in young star clusters
|
astro-ph
|
The existence of older stars within a young star cluster can be interpreted
to imply that star formation occurs on time scales longer than a free-fall time
of a pre-cluster cloud core. Here the idea is explored that these older stars
are not related to the star formation process forming the young star cluster
but rather that the orbits of older field stars are focused by the collapsing
pre-cluster cloud core. Two effects appear: The focussing of stellar orbits
leads to an enhancement of the density of field stars in the vicinity of the
centre of the young star cluster. And due to the time-dependent potential of
the forming cluster some of these stars can get bound gravitationally to the
cluster. These stars exhibit similar kinematical properties as the newly formed
stars and can not be distinguished from them on the basis of radial-velocity or
proper-motion surveys. Such contaminations may lead to a wrong apparent
star-formation history of a young cluster. In the case of the ONC the
theoretical number of gravitationally bound older low-mass field stars agrees
with the number of observed older low-mass stars.
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astro-ph/0205018
|
Vladimir V. Usov
|
Photon Splitting in the Superstrong Magnetic Fields of Pulsars
|
astro-ph
|
We discuss the polarization selection rules for splitting of the two
principal electromagnetic modes that propagate in a vacuum polarized by a
superstrong magnetic field (B>0.1B_{cr} ~ 4x10^{12} G). We show that below the
threshold of free pair creation the selection rules found by Adler in the limit
of weak dispersion remain unaffected by taking the resonant effects into
consideration, i.e., splitting of one mode is strictly forbidden, while
splitting of the other is allowed.
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0802.2236
|
Jean-Pierre Luminet
|
The Shape and Topology of the Universe
|
astro-ph
|
What is the shape of the Universe? Is it curved or flat, finite or infinite ?
Is space "wrapped around" to create ghost images of faraway cosmic sources? We
review how tessellations allow to build multiply-connected 3D Riemannian spaces
useful for cosmology. We discuss more particularly the proposal of a finite,
positively curved, dodecahedral space for explaining some puzzling features of
the cosmic microwave background radiation, as revealed by the 2003-2006 WMAP
data releases.
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No Label
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0802.1050
|
Kalliopi Maria Dasyra
|
HST NICMOS imaging of z~2, 24 micron-selected Ultraluminous Infrared
Galaxies
|
astro-ph
|
We present Hubble Space Telescope NICMOS H-band imaging of 33 Ultraluminous
Infrared Galaxies (ULIRGs) at z~2 that were selected from the 24 micron catalog
of the Spitzer Extragalactic First Look Survey. The images reveal that at least
17 of the 33 objects are associated with interactions. Up to one fifth of the
sources in our sample could be minor mergers whereas only 2 systems are merging
binaries with luminosity ratio <=3:1, which is characteristic of local ULIRGs.
The rest-frame optical luminosities of the sources are of the order 10^10-10^11
L_sun and their effective radii range from 1.4 to 4.9 kpc. The most compact
sources are either those with a strong active nucleus continuum or those with a
heavy obscuration in the mid-infrared regime, as determined from Spitzer
Infra-Red Spectrograph data. The luminosity of the 7.7 micron feature produced
by polycyclic aromatic hydrocarbon molecules varies significantly among compact
systems whereas it is typically large for extended systems. A bulge-to-disk
decomposition performed for the 6 brightest (m_H<20) sources in our sample
indicates that they are best fit by disk-like profiles with small or negligible
bulges, unlike the bulge-dominated remnants of local ULIRGs. Our results
provide evidence that the interactions associated with ultraluminous infrared
activity at z~2 can differ from those at z~0.
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0801.1505
|
Aaron Dutton
|
The Tully-Fisher Zero Point Problem
|
astro-ph
|
A long standing problem for hierarchical disk galaxy formation models has
been the simultaneous matching of the zero point of the Tully-Fisher relation
and the galaxy luminosity function (LF). We illustrate this problem for a
typical disk galaxy and discuss three solutions: low stellar mass-to-light
ratios, low initial dark halo concentrations, and no halo contraction. We
speculate that halo contraction may be reversed through a combination of mass
ejection through feedback and angular momentum exchange brought about by
dynamical friction between baryons and dark matter during the disk formation
process.
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No Label
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No Label
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0709.1236
|
Guillermo Hagele
|
The metal abundance of circumnuclear star forming regions in early type
spirals. Spectrophotometric observations
|
astro-ph
|
We have obtained long-slit observations in the optical and near infrared of
12 circumnuclear HII regions (CNSFR) in the early type spiral galaxies NGC
2903, NGC 3351 and NGC 3504 with the aim of deriving their chemical abundances.
Only for one of the regions, the [SIII] $\lambda$ 6312 \AA was detected
providing, together with the nebular [SIII] lines at $\lambda\lambda$ 9069,
9532 \AA, a value of the electron temperature of T$_e$([SIII])= 8400$^{+
4650}_{-1250}$K. A semi-empirical method for the derivation of abundances in
the high metallicity regime is presented.
We obtain abundances which are comparable to those found in high metallicity
disc HII regions from direct measurements of electron temperatures and
consistent with solar values within the errors. The region with the highest
oxygen abundance is R3+R4 in NGC 3504, 12+log(O/H) = 8.85, about 1.5 solar if
the solar oxygen abundance is set at the value derived by Asplund et al.
(2005), 12+log(O/H)$_{\odot}$ = 8.66$\pm$0.05. Region R7 in NGC 3351 has the
lowest oxygen abundance of the sample, about 0.6 times solar. In all the
observed CNSFR the O/H abundance is dominated by the O$^+$/H$^+$ contribution,
as is also the case for high metallicity disc HII regions. For our observed
regions, however, also the S$^+$/S$^{2+}$ ratio is larger than one, contrary to
what is found in high metallicity disc HII regions for which, in general, the
sulphur abundances are dominated by S$^{2+}$/H$^+$...
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astro-ph/9703094
|
Frank P. Pijpers
|
The residence time of dust grains in turbulent molecular clouds
|
astro-ph
|
The residence time of dust grains inside turbulent molecular clouds is
calculated. Earlier estimates of this time by Boland & de Jong (1982) have been
criticized by Prasad et al. (1987) for not taking into account properly the
turbulent character of the velocity field in molecular clouds which implies
that the trajectory of a dust grain should be treated as a random walk. Taking
some minimal assumptions regarding the turbulent velocity field a time scale is
derived that depends on the Reynolds number of the flow. The near
proportionality with Reynolds number of this time scale results in a much
longer time scale over which dust grains will remain inside a molecular cloud.
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astro-ph/0207484
|
Taichi Kato
|
Unusually Increased Activity of GZ Cnc
|
astro-ph
|
GZ Cnc was discovered as a variable star by Takamizawa (Tmz V34), which
turned out to a cataclysmic variable (CV). Past studies have shown that this
object is a good candidate for a rarely outbursting, long-period dwarf nova.
Only three outbursts were recorded between 1999 and 2001. In 2002 March-May,
the object suddenly showed a dramatic increase of the outburst frequency. The
shortest observed interval was only 11 d. We suggest that the present behavior
may be interpreted as a clustering of short outbursts occasionally seen in
intermediate polars (magnetic CVs). The present activity can also be comparable
to V426 Oph, another dwarf nova which is known to show occasionally increased
activities. The resemblances in the X-ray properties and the outburst behavior
suggests that GZ Cnc and V426 Oph may comprise a new class of (weakly magnetic)
cataclysmic variables.
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astro-ph/0212175
|
Eiichi Egami
|
Near-Infrared Observations of Powerful High-Redshift Radio Galaxies: 4C
40.36 and 4C 39.37
|
astro-ph
|
We present near-infrared imaging and spectroscopic observations of two FR II
high-redshift radio galaxies (HzRGs), 4C 40.36 (z=2.3) and 4C 39.37 (z=3.2),
obtained with the Hubble, Keck, and Hale Telescopes. High resolution images
were taken with filters both in and out of strong emission lines, and together
with the spectroscopic data, the properties of the line and continuum emissions
were carefully analyzed. Our analysis of 4C 40.36 and 4C 39.37 shows that
strong emission lines (e.g., [O III] 5007 A and H alpha+[N II]) contribute to
the broad-band fluxes much more significantly than previously estimated (80%
vs. 20-40%), and that when the continuum sources are imaged through line-free
filters, they show an extremely compact morphology with a high surface
brightness. If we use the R^1/4-law parametrization, their effective radii
(r(e)) are only 2-3 kpc while their restframe B-band surface brightnesses at
r(e) are I(B) ~ 18 mag/arcsec^2. Compared with z ~ 1 3CR radio galaxies, the
former is x3-5 smaller, while the latter is 1-1.5 mag brighter than what is
predicted from the I(B)-r(e) correlation. Although exponential profiles produce
equally good fits for 4C 40.36 and 4C 39.37, this clearly indicates that with
respect to the z~1 3CR radio galaxies, the light distribution of these two
HzRGs is much more centrally concentrated. Spectroscopically, 4C 40.36 shows a
flat (fnu=const) continuum while 4C 39.37 shows a spectrum as red as that of a
local giant elliptical galaxy. Although this difference may be explained in
terms of a varying degree of star formation, the similarities of their surface
brightness profiles and the submillimeter detection of 4C 39.37 might suggest
that the intrinsic spectra is equally blue (young stars or an AGN), and that
the difference is the amount of reddening.
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astro-ph/0305377
|
Wayne Coburn
|
Polarization of the prompt gamma-ray emission from the gamma-ray burst
of 6 December 2002
|
astro-ph
|
Observations of the afterglows of gamma-ray bursts (GRBs) have revealed that
they lie at cosmological distances, and so correspond to the release of an
enormous amount of energy. The nature of the central engine that powers these
events and the prompt gamma-ray emission mechanism itself remain enigmatic
because, once a relativistic fireball is created, the physics of the afterglow
is insensitive to the nature of the progenitor. Here we report the discovery of
linear polarization in the prompt gamma-ray emission from GRB021206, which
indicates that it is synchrotron emission from relativistic electrons in a
strong magnetic field. The polarization is at the theoretical maximum, which
requires a uniform, large-scale magnetic field over the gamma-ray emission
region. A large-scale magnetic field constrains possible progenitors to those
either having or producing organized fields. We suggest that the large magnetic
energy densities in the progenitor environment (comparable to the kinetic
energy densities of the fireball), combined with the large-scale structure of
the field, indicate that magnetic fields drive the GRB explosion.
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0802.3985
|
Olga Merkulova
|
2D Spectroscopy of Candidate Polar-Ring Galaxies: I. The Pair of
Galaxies UGC 5600/09
|
astro-ph
|
Observations of the pair of galaxies VV 330 with the SCORPIO multimode
instrument on the 6-m Special Astrophysical Observatory telescope are
presented. Large-scale velocity fields of the ionized gas in H-alfa and
brightness distributions in continuum and H-alfa have been constructed for both
galaxies with the help of a scanning Fabry Perot interferometer. Long-slit
spectroscopy is used to study the stellar kinematics. Analysis of the data
obtained has revealed a complex structure in each of the pair components. Three
kinematic subsystems have been identified in UGC 5600: a stellar disk, an inner
gas ring turned with respect to the disk through ~80degrees, and an outer gas
disk. The stellar and outer gas disks are noncoplanar. Possible scenarios for
the formation of the observed multicomponent kinematic galactic structure are
considered, including the case where the large-scale velocity field of the gas
is represented by the kinematic model of a disk with a warp. The velocity field
in the second galaxy of the pair, UGC 5609, is more regular. A joint analysis
of the data on the photometric structure and the velocity field has shown that
this is probably a late-type spiral galaxy whose shape is distorted by the
gravitational interaction, possibly, with UGC 5600.
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0711.0782
|
Nader Haghighipour
|
Extreme Habitability: Formation of Habitable Planets in Systems with
Close-in Giant Planets and/or Stellar Companions
|
astro-ph
|
With more than 260 extrasolar planetary systems discovered to-date, the
search for habitable planets has found new grounds. Unlike our solar system,
the stars of many of these planets are hosts to eccentric or close-in giant
bodies. Several of these stars are also members of moderately close ($<$40 AU)
binary or multi-star systems. The formation of terrestrial objects in these
"extreme" environments is strongly affected by the dynamics of their giant
planets and/or their stellar companions. These objects have profound effects on
the chemical structure of the disk of planetesimals and the radial mixing of
these bodies in the terrestrial regions of their host stars. For many years, it
was believed that such effects would be so destructive that binary stars and
also systems with close-in giant planets would not be able to form and harbor
habitable bodies. Recent simulations have, however, proven otherwise. I will
review the results of the simulations of the formation and long-term stability
of Earth-like objects in the habitable zones of such "extreme" planetary
systems, and discuss the possibility of the formation of terrestrial planets,
with significant amounts of water, in systems with hot Jupiters, and also
around the primaries of moderately eccentric close binary stars.
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astro-ph/9709106
|
David Merritt
|
Dynamical Evolution of Elliptical Galaxies with Central Singularities
|
astro-ph
|
We study the effect of a massive central singularity on the structure of a
triaxial galaxy using N-body simulations. Starting from a single initial model,
we grow black holes with various final masses Mh and at various rates, ranging
from impulsive to adiabatic. In all cases, the galaxy achieves a final shape
that is nearly spherical at the center and close to axisymmetric throughout.
However, the rate of change of the galaxy's shape depends strongly on the ratio
Mh/Mg of black hole mass to galaxy mass. When Mh/Mg < 0.3%, the galaxy evolves
in shape on a timescale that exceeds 100 orbital periods, or roughly a galaxy
lifetime. When Mh/Mg > 2%, the galaxy becomes axisymmetric in little more than
a crossing time. We propose that the rapid evolution toward axisymmetric shapes
that occurs when Mh/Mg > 2% provides a negative feedback mechanism which limits
the mass of central black holes by cutting off their supply of fuel.
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astro-ph/0203242
|
Craig Tyler
|
Particle Dark Matter Constraints from the Draco Dwarf Galaxy
|
astro-ph
|
It is widely thought that neutralinos, the lightest supersymmetric particles,
could comprise most of the dark matter. If so, then dark halos will emit radio
and gamma ray signals initiated by neutralino annihilation. A particularly
promising place to look for these indicators is at the center of the local
group dwarf spheroidal galaxy Draco, and recent measurements of the motion of
its stars have revealed it to be an even better target for dark matter
detection than previously thought. We compute limits on WIMP properties for
various models of Draco's dark matter halo. We find that if the halo is nearly
isothermal, as the new measurements indicate, then current gamma ray flux
limits prohibit much of the neutralino parameter space. If Draco has a moderate
magnetic field, then current radio limits can rule out more of it. These
results are appreciably stronger than other current constraints, and so
acquiring more detailed data on Draco's density profile becomes one of the most
promising avenues for identifying dark matter.
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astro-ph/0303542
|
John J. Cowan
|
The Extremely Metal-Poor, Neutron-Capture-Rich Star CS 22892-052: A
Comprehensive Abundance Analysis
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astro-ph
|
High-resolution spectra obtained with three ground-based facilities and the
Hubble Space Telescope (HST) have been combined to produce a new abundance
analysis of CS 22892-052, an extremely metal-poor giant with large relative
enhancements of neutron-capture elements. A revised model stellar atmosphere
has been derived with the aid of a large number of Fe-peak transitions,
including both neutral and ionized species of six elements.Several elements,
including Mo, Lu, Au, Pt and Pb, have been detected for the first time in CS
22892-052, and significant upper limits have been placed on the abundances of
Ga, Ge, Cd, Sn, and U in this star. In total, abundance measurements or upper
limits have been determined for 57 elements, far more than previously possible.
New Be and Li detections in CS 22892-052 indicate that the abundances of both
these elements are significantly depleted compared to unevolved main-sequence
turnoff stars of similar metallicity. Abundance comparisons show an excellent
agreement between the heaviest n-capture elements (Z >= 56) and scaled solar
system r-process abundances, confirming earlier results for CS 22892-052 and
other metal-poor stars. New theoretical r-process calculations also show good
agreement with CS 22892-052 abundances as well as the solar r-process abundance
components.The abundances of lighter elements (40<= Z <= 50), however, deviate
from the same scaled abundance curves that match the heavier elements,
suggesting different synthesis conditions or sites for the low-mass and
high-mass ends of the abundance distribution. The detection of Th and the upper
limit on the U abundance together imply a lower limit of 10.4 Gyr on the age of
CS 22892-052, quite consistent with the Th/Eu age estimate of 12.8 +/- ~= 3
Gyr. An average of several chronometric ratios yields an age 14.2 +/- ~= 3 Gyr.
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astro-ph/0608615
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Coralie Doucet Mrs
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Mid-InfraRed imaging of the circumstellar dust around three Herbig Ae
stars : HD135344, CQTau, HD163296
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astro-ph
|
Planet formation has been known for many years to be tied to the spatial
distribution of gas and dust in disks around young stars. To constrain planet
formation models, imaging observations of protoplanetary disks are required. In
this framework, we have undertaken a mid-infrared imaging survey of Herbig Ae
stars, which are pre-main sequence stars of intermediate mass still surrounded
by a large amount of circumstellar material. The observations were made at a
wavelength of 20.5 $\mu$m with the CAMIRAS camera mounted at the Cassegrain
focus of the Canada France Hawaii Telescope.
We report the observations of three stars, HD135344, CQTau and HD163296. The
circumstellar material around the three objects is spatially resolved. The
extensions feature a disk like shape. The images provide direct information on
two key parameters of the disk : its inclination and its outer radius. The
outer radius is found to be quite different from the one deduced from disk
models only constrained by fitting the Spectral Energy Distribution of the
object. Other parameters of the disk, such as flaring, dust mass have been
deduced from fitting both the observed extension and the spectral energy
distribution with sophisticated disk models.
Our results show how important imaging data are to tighten constraints on the
disk model parameters.
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0704.2059
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Joannah L. Hinz
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Spitzer Observations of Low Luminosity Isolated and Low Surface
Brightness Galaxies
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astro-ph
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We examine the infrared properties of five low surface brightness galaxies
(LSBGs) and compare them with related but higher surface brightness galaxies,
using Spitzer Space Telescope images and spectra. All the LSBGs are detected in
the 3.6 and 4.5um bands, representing the stellar population. All but one are
detected at 5.8 and 8.0um, revealing emission from hot dust and aromatic
molecules, though many are faint or point-like at these wavelengths. Detections
of LSBGs at the far-infrared wavelengths, 24, 70, and 160um, are varied in
morphology and brightness, with only two detections at 160um, resulting in
highly varied spectral energy distributions. Consistent with previous
expectations for these galaxies, we find that detectable dust components exist
for only some LSBGs, with the strength of dust emission dependent on the
existence of bright star forming regions. However, the far-infrared emission
may be relatively weak compared with normal star-forming galaxies.
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astro-ph/0509296
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Bartosz Pindor
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SDSSJ102111.02+491330.4: A Newly Discovered Gravitationally Lensed
Quasar
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astro-ph
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We report follow-up observations of two gravitational lens candidates
identified in the Sloan Digital Sky Survey (SDSS) dataset. We have confirmed
that SDSS J102111.02+491330.4 is a previously unknown gravitationally lensed
quasar. This lens system exhibits two images of a $z = 1.72$ quasar, with an
image separation of $1{\farcs}14 \pm 0.04$. Optical and near-IR imaging of the
system reveals the presence of the lensing galaxy between the two quasar
images. Observations of SDSS J112012.12+671116.0 indicate that it is more
likely a binary quasar than a gravitational lens. This system has two quasars
at a redshift of $z = 1.49$, with an angular separation of $1{\farcs}49 \pm
0.02$. However, the two quasars have markedly different SEDs and no lens galaxy
is apparent in optical and near-IR images of this system. We also present a
list of 31 SDSS lens candidates which follow-up observations have confirmed are
\textit{not} gravitational lenses.
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0707.1027
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George Seabroke
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Re-visiting the relations: Galactic thin disc age-velocity dispersion
relation
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astro-ph
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The velocity dispersion of stars in the solar neighbourhood thin disc
increases with time after star formation. Nordstrom et al. (2004) is the most
recent observational attempt to constrain the age-velocity dispersion relation.
They fitted the age-velocity dispersion relations of each Galactic cardinal
direction space velocity component, U (towards the Galactic centre), V (in the
direction of Galactic rotation) and W (towards the North Galactic Pole), with
power laws and interpreted these as evidence for continuous heating of the disc
in all directions throughout its lifetime. We re-visit these relations with
their data and use Famaey et al. (2005) to show that structure in the local
velocity distribution function distorts the in-plane (U and V) velocity
distributions away from Gaussian so that a dispersion is not an adequate
parametrization of their functions. The age-sigma(W) relation can however be
constrained because the sample is well phase-mixed vertically. We do not find
any local signature of the stellar warp in the Galactic disc. Vertical disc
heating does not saturate at an early stage. Our new result is that a power law
is not required by the data: disc heating models that saturate after ~ 4.5 Gyr
are equally consistent with observations.
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astro-ph/9902171
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Martin Zwaan
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The HI Column Density Distribution Function at z=0: the Connection to
Damped Ly alpha Statistics
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astro-ph
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We present a measurement of the HI column density distribution function,
f(N), at the present epoch for column densities log N > 20 cm^-2. These high
column densities compare to those measured in damped Ly alpha lines seen in
absorption against background quasars. Although observationally rare, it
appears that the bulk of the neutral gas in the Universe is associated with
these damped Ly alpha systems. In order to obtain a good anchor point at z=0 we
determine f(N) in the local Universe by using 21cm synthesis observations of a
complete sample of spiral galaxies. We show that f(N) for damped Ly alpha
systems has changed significantly from high z to the present and that change is
greatest for the highest column densities. The measurements indicate that low
surface brightness galaxies make a minor contribution to the cross section for
HI, especially for log N > 21^-2.
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astro-ph/9805174
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Sally D. Hunsberger
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The Luminosity Function of Galaxies in Compact Groups
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astro-ph
|
From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts
to determine a luminosity function extending to M_R=-14.0, approximately two
magnitudes deeper than previous compact group luminosity functions. We find
that a single Schechter function is a poor fit to the data, so we fit a
composite function consisting of separate Schechter functions for the bright
and faint galaxies. The bright end is best fit with M^*=-21.6 and alpha=-0.52
and the faint end with M^*=-16.1 and alpha=-1.17. The decreasing bright end
slope implies a deficit of intermediate luminosity galaxies in our sample of
HCGs and the faint end slope is slightly steeper than that reported for earlier
HCG luminosity functions. Furthermore, luminosity functions of subsets of our
sample reveal more substantial dwarf populations for groups with x-ray halos,
groups with tidal dwarf candidates, and groups with a dominant elliptical or
lenticular galaxy. Collectively, these results support the hypothesis that
within compact groups, the initial dwarf galaxy population is replenished by
"subsequent generations" formed in the tidal debris of giant galaxy
interactions.
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astro-ph/0207394
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Axel Brandenburg
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The helicity issue in large scale dynamos
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astro-ph
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The connection between helically isotropic MHD turbulence and mean-field
dynamo theory is reviewed. The nonlinearity in the mean-field theory is not yet
well established, but detailed comparison with simulations begin to help select
viable forms of the nonlinearity. The crucial discriminant is the magnetic
helicity, which is known to evolve only on a slow resistive time scale in the
limit of large magnetic Reynolds number. Particular emphasis is put on the
possibility of memory effects, which means that an additional explicitly
time-dependent equation for the nonlinearity is solved simultaneously with the
mean-field equations. This approach leads to better agreement with the
simulations, while it would also produce more favorable agreement between
models and stellar dynamos.
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astro-ph/0305190
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Alexis Finoguenov
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Role of clusters of galaxies in the evolution of the metal budget in the
Universe
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astro-ph
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Using the guidelines on SN element production provided by XMM-Newton, we
summarize the results of ASCA observations on the element abundance in groups
and clusters of galaxies. We show that while the metal production in groups
could be described by a stellar population with a standard local IMF, clusters
of galaxies require a more top-heavy IMF. We attribute an excess heavy element
production to an IMF evolution with redshift. Dating the galaxy formation in
clusters by observations of the star-formation rate, we conclude that the IMF
variations have occurred preferentially at z>~4. We further combine our
metallicity measurements with the mass function of clusters to estimate the
role of clusters in the evolution of the metal content of the Universe. We
argue that at no epoch stars are a major container of metals, unless groups of
galaxies are not representative for the star-formation. This lends further
support for the reduced (0.6 solar) mass-averaged oxygen abundance in the
stellar population.
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astro-ph/0601375
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Charles J. Lada
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Stellar Multiplicity and the IMF: Most Stars Are Single
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astro-ph
|
In this short communication I compare recent findings suggesting a low binary
star fraction for late type stars with knowledge concerning the forms of the
stellar initial and present day mass functions for masses down to the hydrogen
burning limit. This comparison indicates that most stellar systems formed in
the galaxy are likely single and not binary as has been often asserted. Indeed,
in the current epoch two-thirds of all main sequence stellar systems in the
Galactic disk are composed of single stars. Some implications of this
realization for understanding the star and planet formation process are briefly
mentioned.
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astro-ph/0601549
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William Wall
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Comparison of 13CO Line and Far-Infrared Continuum Emission as a
Diagnostic of Dust and Molecular Gas Physical Conditions: III. Systematic
Effects and Scientific Implications
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astro-ph
|
Far-infrared continuum data from the {\it COBE}/{\it DIRBE} instrument were
combined with Nagoya 4-m $\cOone$ spectral line data to infer the
multiparsec-scale physical conditions in the Orion$ $A and B molecular clouds,
using 140$\um$/240$\um$ dust color temperatures and the 240$\um$/$\cOone$
intensity ratios. In theory, the ratio of far-IR, submillimeter, or millimeter
continuum to that of a $\cO$ (or $\Co$) rotational line can place reliable
upper limits on the temperature of the dust and molecular gas on multi-parsec
scales; on such scales, both the line and continuum emission are optically
thin, resulting in a continuum-to-line ratio that suffers no loss of
temperature sensitivity in the high-temperature limit as occurs for ratios of
CO rotational lines or ratios of continuum emission in different wavelength
bands. Two-component models fit the Orion data best, where one has a
fixed-temperature and the other has a spatially varying temperature. The former
represents gas and dust towards the surface of the clouds that are heated
primarily by a very large-scale (i.e. $\sim 1 $kpc) interstellar radiation
field. The latter represents gas and dust at greater depths into the clouds and
are shielded from this interstellar radiation field and heated by local stars.
The inferred physical conditions are consistent with those determined from
previously observed maps of $\COone$ and $\Jtwo$ that cover the entire Orion$
$A and B molecular clouds. The models require that the dust-gas temperature
difference is 0$\pm 2 $K. If this surprising result applies to much of the
Galactic ISM, except in unusual regions such as the Galactic Center, then there
are a number implications.
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astro-ph/0303137
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Devendra Ojha
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Stellar sources in the ISOGAL intermediate bulge fields
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astro-ph
|
We present a study of ISOGAL sources in the "intermediate" galactic bulge
($|$$l$$|$ $<$ 2$^\circ$, $|$$b$$|$ $\sim$ 1$^\circ$--4$^\circ$), observed by
ISOCAM at 7 and 15 $\mu m$. In combination with near-infrared (I, J, K$_{\rm
s}$) data of DENIS survey, complemented by 2MASS data, we discuss the nature of
the ISOGAL sources, their luminosities, the interstellar extinction and the
mass-loss rates. A large fraction of the 1464 detected sources at 15 $\mu m$
are AGB stars above the RGB tip, a number of them show an excess in
([7]-[15])$_{\rm 0}$ and (K$_{\rm s}$-[15])$_{\rm 0}$ colours, characteristic
of mass-loss. The latter, especially (K$_{\rm s}$-[15])$_{\rm 0}$, provide
estimates of the mass-loss rates and show their distribution in the range
10$^{-8}$ to 10$^{-5}$ M$_{\rm \odot}$/yr.
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astro-ph/0205229
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Xu Kong
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Spectroscopic study of blue compact galaxies: I. The spectra
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astro-ph
|
Blue compact galaxies are compact objects that are dominated by intense star
formation. Most of them have dramatically different properties compared to the
Milky Way and many other nearby galaxies. Using the IRAS, HI data, and optical
spectra, we wanted to measure the current star formation rates, stellar
components, metallicities, and star formation histories and evolution of a
large blue compact galaxy sample. We anticipate that our study will be useful
as a benchmark for studies of emission line galaxies at high redshift.
In the first paper of this series, we describe the selection, spectroscopic
observation, data reduction and calibration, and spectrophotometric accuracy of
a sample of 97 luminous blue compact galaxies.
We present a spectrophotometric atlas of rest-frame spectra, as well as
tables of the recession velocities and the signal-to-noise ratios. The
recession velocities of these galaxies are measured with an accuracy of
$\delta$V $<$ 67 km s$^{-1}$. The average signal-to-noise ratio of sample
spectra is $\sim$ 51. The spectral line strengths, equivalent widths and
continuum fluxes are also measured for the same galaxies and will be analyzed
in the next paper of this series. The atlas and tables of measurements will be
made available electronically.
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astro-ph/0404020
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Orkan Umurhan
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Hydrodynamic stability of rotationally supported flows: Linear and
nonlinear 2D shearing box results
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astro-ph
|
We present here both analytical and numerical results of hydrodynamic
stability investigations of rotationally supported circumstellar flows using
the shearing box formalism. Asymptotic scaling arguments justifying the
shearing box approximation are systematically derived, showing that there exist
two limits which we call small shearing box (SSB) and large shearing box (LSB).
The physical meaning of these two limits and their relationship to model
equations implemented by previous investigators are discussed briefly. Two
dimensional (2D) dynamics of the SSB are explored and shown to contain
transiently growing (TG) linear modes, whose nature is first discussed within
the context of linear theory. The fully nonlinear regime in 2D is investigated
numerically for very high Reynolds (Re) numbers. Solutions exhibiting sustained
dynamics are found and manifest episodic but recurrent TG behavior and these
are associated with the formation and long-term survival of coherent vortices.
The life-time of this spatio-temporal complexity depends on the Re number and
the strength and nature of the initial disturbance. We show results for a case
in which the dynamical activity persists for the entire duration of the
simulation (hundreds of box orbits). Some combinations of the Re number and the
initial perturbation spectrum (and strength) show the transiently growing
phenomenon to ultimately fade away or, in some instances, to be absent
altogether. Because the SSB approximation used here is equivalent to a 2D
incompressible flow, the dynamics can not depend on the Coriolis force.
Therefore, three dimensional (3D) simulations are needed in order to decide if
this force indeed suppresses nonlinear hydrodynamical instability in
rotationally supported disks in the shearing box.
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astro-ph/0303254
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Luigi Bedin
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V, J, H and K Imaging of the Metal Rich Globular Cluster NGC 6528
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astro-ph
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New near-infrared observations of NGC6528 are presented. The JHK observations
complement a previous HST/NICMOS data set by Ortolani et al. (2001), in that
they sample a larger area, contain a more numerous sample of red giant stars,
and include the K band. Also, archival HST data sets (separated by 6.093 years)
were used to proper-motion decontaminate the near-infrared sample and extract a
clean VJHK catalogue. Using the present wide colour baseline, we compared the
cleaned colour-magnitude diagrams of NGC6528 with those of NGC 6553 and NGC104
and derived new estimates of reddening and distance, E(B-V)=0.55 and
(m-M)o=14.44 (7.7 kpc). Moreover, the morphology and location of the cleaned
red giant branch were used to derive a photometric estimate of the cluster
metallicity. The average of 10 metallicity indicators yields a mean value of
[M/H] ~ 0.0, and [Fe/H] ~-0.20 and +0.08 on the Zinn & West (1984) and Carretta
& Gratton (1997) revised metallicity scale, respectively. The best isochrone
fit to the cleaned K,V-K diagram is obtained for a 12.6 Gyr and Z=0.02
isochrone, i.e. the derived metallicity of NGC6528 turns out to be very close
to the mean of stars in the Baade's Window. Five AGB variable star candidates,
whose membership has to be confirmed spectroscopically, are bolometrically as
bright as the known long period variable stars in NGC6553. As discussed in
Guarnieri et al. (1997) for NGC6553, this may indicate that an `intermediate
age' population is not needed to account for the brightest stars in external
galaxies such as M32.
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astro-ph/0505421
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Asantha R. Cooray
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A Divided Universe: Red and Blue Galaxies and their Preferred
Environments
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astro-ph
|
(Summary) Making use of scaling relations between the central and the total
galaxy luminosity of a dark matter halo as a function of the halo mass, and the
scatter in these relations, we present an empirical model to describe the
luminosity function (LF) of galaxies. We extend this model to describe relative
statistics of early-type, or red, and late-type, or blue, galaxies, with the
fraction of early type galaxies at halo centers, relative to the total sample,
determined only by the halo mass and the same fraction in the case of
satellites is taken to be dependent on both the halo mass and the satellite
galaxy luminosity. This simple model describes the conditional luminosity
functions, LF of galaxies as a function of the halo mass, measured with the 2dF
galaxy group catalog from cluster to group mass scales. Using 2dF measurements,
we extract information related to conditional mass function for halos from
extreme voids to dense regions in terms of the galaxy overdensity. We also
calculate the probability distribution function of halo mass, as a function of
the galaxy overdensity, and use these probabilities to address preferred
environments of red and blue galaxies. Our model also allow us to make
predictions, for example, galaxy bias as a function of the galaxy type and
luminosity, the void mass function, and the average galaxy luminosity as a
function of the density environment.
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astro-ph/0602520
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Witold Maciejewski
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Response of the integrals in the Tremaine-Weinberg method to multiple
pattern speeds: a counter-rotating inner bar in NGC 2950?
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astro-ph
|
When integrals in the standard Tremaine-Weinberg method are evaluated for the
case of a realistic model of a doubly barred galaxy, their modifications
introduced by the second rotating pattern are in accord with what can be
derived from a simple extension of that method, based on separation of tracer's
density. This extension yields a qualitative argument that discriminates
between prograde and retrograde inner bars. However, the estimate of the value
of inner bar's pattern speed requires further assumptions. When this extension
of the Tremaine-Weinberg method is applied to the recent observation of the
doubly barred galaxy NGC 2950, it indicates that the inner bar there is
counter-rotating, possibly with the pattern speed of -140 +/- 50 km/s/arcsec.
The occurrence of counter-rotating inner bars can constrain theories of galaxy
formation.
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astro-ph/0501039
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Anatoli Iyudin
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New Gamma-Ray Probe of the Baryonic Dark Matter
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astro-ph
|
We expand on the recently reported detections of the gamma-ray resonant
absorption along the line of sight toward gamma-ray bright quasars (QSOs), like
3C279. We propose to use this novel gamma-ray absorption method to study the
Dark Matter distribution in the Milky Way, as well as in the Local Group.
Properties of the absorber that was detected on the sight lines towards
gamma-ray bright QSOs at zero redshift are discussed. We compare our results
with the expected Dark Matter distributions in the halo of Milky Way, that were
simulated in boundaries of different CDM models. Application of this new method
to study evolution of CDM in the QSO host galaxies, and of baryons distribution
in the halo of galaxies in the Local Universe is proposed.
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astro-ph/0112133
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Luca Ciotti
|
Galaxy merging and the Fundamental Plane of elliptical galaxies
|
astro-ph
|
We present preliminary results of numerical simulations of dissipationless
merging of stellar systems, aimed at exploring the consequences of merging
between gas free, spheroidal systems. In particular, we study the dynamical and
structural characteristics of hierarchical merging between equal mass stellar
systems, and we compare the properties of the end-products with the most
important structural and dynamical scaling relations obeyed by spheroids. In
the explored hierarchy of four successive mergings we find that the FP tilt is
marginally conserved, but both the Faber-Jackson and Kormendy relations are not
conserved.
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astro-ph/0309267
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Bodo Ziegler
|
Internal kinematics of spiral galaxies in distant clusters Part I
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astro-ph
|
We introduce our project on galaxy evolution in the environment of rich
clusters aiming at disentangling the importance of specific interaction and
galaxy transformation processes from the hierarchical evolution of galaxies in
the field. Emphasis is laid on the examination of the internal kinematics of
disk galaxies through spatially resolved MOS spectroscopy with FORS at the VLT.
First results are presented for the clusters MS1008.1-1224 (z=0.30),
Cl0303+1706 (z=0.42), and Cl0413-6559 (F1557.19TC) (z=0.51). Out of 30 cluster
members with emission-lines, 13 galaxies exhibit a rotation curve of the
universal form rising in the inner region and passing over into a flat part.
The other members have either intrinsically peculiar kinematics (4), or too
strong geometric distortions (9) or too low S/N (4 galaxies) for a reliable
classification of their velocity profiles. The 13 cluster galaxies for which a
maximum rotation velocity could be derived are distributed in the Tully--Fisher
diagram very similar to field galaxies from the FORS Deep Field that have
corresponding redshifts and do not show any significant luminosity evolution
with respect to local samples. The same is true for seven galaxies observed in
the cluster fields that turned out not to be members. The mass-to-light ratios
of the 13 TF cluster spirals cover the same range as the distant field
population indicating that their stellar populations were not dramatically
changed by possible clusterspecific interaction phenomena. The cluster members
with distorted kinematics may be subject to interaction processes but it is
impossible to determine whether these processes also lead to changes in the
overall luminosity of their stellar populations.
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astro-ph/9908293
|
Krzysztof Stanek
|
The DIRECT Project: Influence of Blending on the Cepheid Distance Scale.
I. Cepheids in M31
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astro-ph
|
We investigate the influence of blending on the Cepheid distance scale.
Blending is the close association of a Cepheid with one or more intrinsically
luminous stars. High-resolution HST images are compared to our ground-based
data, obtained as part of the DIRECT project, for a sample of 22 Cepheids in
the M31 galaxy. The average (median) V-band flux contribution from luminous
companions which are not resolved on the ground-based images is about 19% (12%)
of the flux of the Cepheid. This is a large effect - at the 10% level for
distances. The current Cepheid distance estimates to M31 are all ground-based,
and are thus affected (underestimated). We discuss indirect methods to find
which Cepheids are blended, e.g. by the use of well-sampled light curves in at
least two optical bands. More generally, our ground-based resolution in M31
corresponds to the HST resolution at about 10 Mpc. Blending leads to
systematically low distances in the observed galaxies, and therefore to
systematically high estimates of H_0; we discuss the issue and the
implications.
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0810.2995
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Christoffer Karoff
|
On Flare Driven Global Waves
|
astro-ph
|
We recently presented evidence of a strong correlation between the energy in
the high-frequency part of the acoustic spectrum of the Sun and the solar X-ray
flux Karoff & Kjeldsen (2008). The discovery indicates that flares drive global
oscillations in the Sun in the same way that the entire Earth is set ringing
for several weeks after a major earthquake, such as the 2004 December
Sumatra-Andaman one. If this indication turns out to be true we might be able
to use the relation between flares and the energy in the high-frequency part of
the acoustic spectrum to detect e.g. flares on the far side of the Sun and
flares on other solar-like stars. But, the discovery also opens many new
questions such as why is it only the high-frequency part of the acoustic
spectrum that is correlated with the X-ray flux? And, are there energy enough
in solar flares do drive global oscillations?
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astro-ph/0609332
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James R. Graham
|
The Signature of Primordial Grain Growth in the Polarized Light of the
AU Mic Debris Disk
|
astro-ph
|
We have used the Hubble Space Telescope/ACS coronagraph to make polarization
maps of the AU Mic debris disk. The fractional linear polarization rises
monotonically from about 0.05 to 0.4 between 20 and 80 AU. The polarization is
perpendicular to the disk, indicating that the scattered light originates from
micron sized grains in an optically thin disk. Disk models, which
simultaneously fit the surface brightness and polarization, show that the inner
disk (< 40-50 AU) is depleted of micron-sized dust by a factor of more than
300, which means that the disk is collision dominated. The grains have high
maximum linear polarization and strong forward scattering. Spherical grains
composed of conventional materials cannot reproduce these optical properties. A
Mie/Maxwell-Garnett analysis implicates highly porous (91-94%) particles. In
the inner Solar System, porous particles form in cometary dust, where the
sublimation of ices leaves a "bird's nest" of refractory organic and silicate
material. In AU Mic, the grain porosity may be primordial, because the dust
"birth ring" lies beyond the ice sublimation point. The observed porosities
span the range of values implied by laboratory studies of particle coagulation
by ballistic cluster-cluster aggregation. To avoid compactification, the upper
size limit for the parent bodies is in the decimeter range, in agreement with
theoretical predictions based on collisional lifetime arguments. Consequently,
AU Mic may exhibit the signature of the primordial agglomeration process
whereby interstellar grains first assembled to form macroscopic objects.
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astro-ph/0208158
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Edward J. M. Colbert
|
The X-ray Reflectors in the Nucleus of the Seyfert Galaxy NGC 1068
|
astro-ph
|
(abridged) Based on observations of the Seyfert nucleus in NGC1068 with ASCA,
RXTE and BeppoSAX, we report the discovery of a flare (increase in flux by a
factor of ~1.6) in the 6.7 keV Fe K line component between observations
obtained 4 months apart, with no significant change in the other (6.21, 6.4,
and 6.97 keV) Fe K_alpha line components. During this time, the continuum flux
decreased by ~20%. The RXTE spectrum requires an Fe K absorption edge near 8.6
keV (Fe XXIII - XXV). The spectral data indicate that the 2-10 keV continuum
emission is dominated (~2/3 of the luminosity) by reflection from a previously
unidentified region of warm, ionized gas located <~ 0.2 pc from the AGN. The
remaining ~1/3 of the observed X-ray emission is reflected from optically
thick, neutral gas. The inferred properties of the warm reflector (WR) are:
size (diameter) <~0.2 pc, gas density n >~ 10^{5.5} /cm3, ionization parameter
xi approx 10^{3.5} erg cm/s, and covering fraction 0.003 (L_0/10^{43.5}
erg/s)^{-1} < (Omega/4 pi) < 0.024 (L_0/10^{43.5})^{-1}, where L_0 is the
intrinsic 2-10 keV X-ray luminosity of the AGN. We suggest that the WR gas is
the source of the (variable) 6.7 keV Fe line emission, and the 6.97 keV Fe line
emission. The 6.7 keV line flare is assumed to be due to an increase in the
emissivity of the WR gas from a decrease (by 20-30%) in L_0. The properties of
the WR are most consistent with an intrinsically X-ray weak AGN with L_0 approx
10^{43.0} erg/s. The optical and UV emission that scatters from the WR into our
line of sight is required to suffer strong extinction, which can be reconciled
if the line-of-sight skims the outer surface of the torus. Thermal
bremsstrahlung radio emission from the WR may be detectable in VLBA radio maps
of the NGC 1068 nucleus.
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astro-ph/0002070
|
Markus Kissler-Patig
|
Extragalactic Globular Cluster Systems: A new Perspective on Galaxy
Formation and Evolution
|
astro-ph
|
We present an overview of observational progress in the study of
extragalactic globular cluster systems. Globular clusters turn out to be
excellent tracers not only for the star-formation histories in galaxies, but
also for kinematics at large galactocentric radii. Their properties can be used
to efficiently constrain galaxy formation and evolution. After a brief
introduction of the current methods and futures perspectives, we summarize the
knowledge gained in various areas of galaxy research through the study of
globular clusters. In particular, we address the star-formation histories of
early-type galaxies; globular cluster population in late-type galaxies and
their link to early-type galaxies; star and cluster formation during mergers
and violent interactions; and the kinematics at large radii in early-type
galaxies. The different points are reviewed within the context of galaxy
formation and evolution.
Finally, we revisit the globular cluster luminosity function as a distance
indicator. Despite its low popularity in the literature, we demonstrate that it
ranks among one of the most precise distance indicators to early-type galaxies,
provided that it is applied properly.
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No Label
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astro-ph/0508508
|
Zuhui Fan
|
Effects of the complex mass distribution of dark matter halos on weak
lensing cluster surveys
|
astro-ph
|
Gravitational lensing effects arise from the light ray deflection by all of
the mass distribution along the line of sight. It is then expected that weak
lensing cluster surveys can provide us true mass-selected cluster samples. With
numerical simulations, we analyze the correspondence between peaks in the
lensing convergence $\kappa$-map and dark matter halos. Particularly we
emphasize the difference between the peak $\kappa$ value expected from a dark
matter halo modeled as an isolated and spherical one, which exhibits a
one-to-one correspondence with the halo mass at a given redshift, and that of
the associated $\kappa$-peak from simulations. For halos with the same expected
$\kappa$, their corresponding peak signals in the $\kappa$-map present a wide
dispersion. At an angular smoothing scale of $\theta_G=1\hbox{arcmin}$, our
study shows that for relatively large clusters, the complex mass distribution
of individual clusters is the main reason for the dispersion. The projection
effect of uncorrelated structures does not play significant roles. The
triaxiality of dark matter halos accounts for a large part of the dispersion,
especially for the tail at high $\kappa$ side. Thus lensing-selected clusters
are not really mass-selected. (abridged)
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No Label
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astro-ph/0410189
|
Michael Shull
|
He II Reionization and Sources of Metagalactic Ionization
|
astro-ph
|
Intergalactic Ly-alpha opacity suggests that H I was reionized at z ~ 6,
while He II reionization was delayed to z ~ 3. Both epochs are in conflict with
inferences from CMB optical depth (WMAP) which suggest early reionization at z
= 10-20. One of the major contributions of FUSE to cosmological studies has
been the detection of He II Ly-alpha (Gunn-Peterson) absorption in the spectra
of AGN at redshifts z > 2.03. Spectra of He II absorbers, taken in concert with
corresponding H I (Ly-alpha) lines, allow us to fix the epoch of helium
reionization at z(HeII) ~ 2.8 +/- 0.2. Here, I review FUSE observations of He
II absorption, together with their implications for the sources and transport
of ionizing radiation over 30-50 Mpc distances through the IGM. FUSE
observations of He II absorption toward HE 2347-4342, combined with Keck and
VLT observations of H I, are consistent with photoionization by QSOs, with a
wide range of intrinsic spectral indices, and modified by filtering and
reprocessing in the IGM. The He II/H I ratio (eta) exhibits variations over 1
Mpc distance scales (Delta z ~ 0.001). Intriguingly, this eta-ratio is also
correlated with Ly-alpha filaments and voids. The ionizing radiation field
appears to be softer (higher He II/H I) in the voids. These void regions may be
ionized by local soft sources (dwarf starburst galaxies), or the QSO radiation
may softened by escape from AGN cores and transport through denser regions in
the cosmic web. The differences in ionizing spectra may explain the 1.4 Gyr lag
between H I and He II reionization epochs.
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No Label
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0809.2266
|
Aaron Parsons
|
A Scalable Correlator Architecture Based on Modular FPGA Hardware,
Reuseable Gateware, and Data Packetization
|
astro-ph
|
A new generation of radio telescopes is achieving unprecedented levels of
sensitivity and resolution, as well as increased agility and field-of-view, by
employing high-performance digital signal processing hardware to phase and
correlate large numbers of antennas. The computational demands of these imaging
systems scale in proportion to BMN^2, where B is the signal bandwidth, M is the
number of independent beams, and N is the number of antennas. The
specifications of many new arrays lead to demands in excess of tens of PetaOps
per second.
To meet this challenge, we have developed a general purpose correlator
architecture using standard 10-Gbit Ethernet switches to pass data between
flexible hardware modules containing Field Programmable Gate Array (FPGA)
chips. These chips are programmed using open-source signal processing libraries
we have developed to be flexible, scalable, and chip-independent. This work
reduces the time and cost of implementing a wide range of signal processing
systems, with correlators foremost among them,and facilitates upgrading to new
generations of processing technology. We present several correlator
deployments, including a 16-antenna, 200-MHz bandwidth, 4-bit, full Stokes
parameter application deployed on the Precision Array for Probing the Epoch of
Reionization.
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No Label
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astro-ph/0508426
|
Alin Panaitescu
|
Jets, Structured Outflows, and Energy Injection in GRB Afterglows:
Numerical Modelling
|
astro-ph
|
We investigate numerically the ability of three models (jet, structured
outflow, energy injection) to accommodate the optical light-curve breaks
observed in 10 GRB afterglows (980519, 990123, 990510, 991216, 000301c, 000926,
010222, 011211, 020813, and 030226), and the relative intensities of the radio,
optical, and X-ray emissions of these afterglows. We find that the jet and
structured outflow models fare much better than the energy injection model in
accommodating the multiwavelength data of the above 10 afterglows. For the
first two models, a uniform circumburst medium provides a better fit to the
optical light-curve break than a wind-like medium with a r^{-2} stratification.
However, in the only two cases where the energy injection model may be at work,
a wind medium is favoured (an energy injection is also possible in a third
case, the afterglow 970508, whose optical emission exhibited a sharp rise but
not a steepening decay). The best fit parameters obtained with the jet model
indicate an outflow energy of 2-6 E50 ergs and a jet opening of 2-3 degrees.
Structured outflows with a quasi-uniform core have a core angular size of
0.7-1.0 degrees and an energy per solid angle of 0.5-3 E53 erg/sr, surrounded
by an envelope where this energy falls-off roughly as theta^{-2} with angle
from the outflow axis, requiring thus the same energy budget as jets.
Circumburst densities are found to be typically in the range 0.1-1 per cc, for
either model. We also find that the reverse shock emission resulting from the
injection of ejecta into the decelerating blast wave at about 1 day after the
burst can explain the slowly decaying radio light-curves observed for the
afterglows 990123, 991216, and 010222.
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No Label
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astro-ph/0010163
|
Lachieze-Rey
|
The Friedmann-Lemaitre models in perspective
|
astro-ph
|
I show that all FRW models (four dimensional pseudo-Riemannian manifolds with
maximally symmetric space) can be embedded in a flat Minkowski manifold with 5
dimensions. The pseudo Riemannian metric of space-time is induced by the flat
metric. This generalizes the usual embedding widely used for the \dS ~models. I
give the coordinate transformations for the embedding. Taking into account the
spatial isotropy, one can reduce space-time to a two-dimensional surface,
embedded in a three-dimensional Minkowski space. This allows to give exact
graphic representations of the FRW models, and in particular of their
curvature.
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No Label
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astro-ph/0702590
|
David Rabinowitz
|
The QUEST Large Area CCD Camera
|
astro-ph
|
We have designed, constructed and put into operation a very large area CCD
camera that covers the field of view of the 1.2 m Samuel Oschin Schmidt
Telescope at the Palomar Observatory. The camera consists of 112 CCDs arranged
in a mosaic of four rows with 28 CCDs each. The CCDs are 600 x 2400 pixel
Sarnoff thinned, back illuminated devices with 13 um x 13 um pixels. The camera
covers an area of 4.6 deg x 3.6 deg on the sky with an active area of 9.6
square degrees. This camera has been installed at the prime focus of the
telescope, commissioned, and scientific quality observations on the
Palomar-QUEST Variability Sky Survey were started in September of 2003. The
design considerations, construction features, and performance parameters of
this camera are described in this paper.
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No Label
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astro-ph/0306550
|
Delphine Porquet
|
An intense and broad FeKalpha line observed in the X-ray luminous quasar
Q0056-363 with XMM-Newton
|
astro-ph
|
We present an XMM-Newton observation of the radio-quiet quasar Q0056-363
(z=0.162). This is the first time that this quasar is observed in the hard
X-ray range (above 2 keV). We find that Q0056-363 is a powerful X-ray quasar,
with a 0.3-12 keV unabsorbed luminosity of about 1.2 x 10^45 erg s-1 with the
largest part (~67%) emitted below 2 keV. The spectrum reveals a large
featureless soft X-ray excess below 2 keV and a strong broad FeKalpha line at
6.4 keV (in the quasar frame). The FeK alpha line is due to low to moderate
ionization states of iron (i.e., < Fe XVII), with an equivalent width of about
250 eV and a velocity width of about 25,000 km s-1. Q0056-363 is presently the
most luminous AGN known to exhibit such a broad and intense FeKalpha line
profile from near neutral iron. The line can be fitted with a relativistic
profile from an accretion disc around either a Schwarzschild (non-rotating) or
a Kerr (rotating) black hole. A combination of two thermal Comptonization
components and a disc reflection model is favored to explain both the continuum
over the energy range 0.3-12 keV and the FeK alpha line. A patchy corona
covering a large part of the inner disc surface is needed in order to be
compatible with the accretion rate inferred from the spectral energy
distribution of Q0056-363, unless the mass of the black hole is much higher
than about 5 x 10^8 M_odot.
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No Label
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0712.2326
|
Dominique Eckert M.
|
INTEGRAL discovery of non-thermal hard X-ray emission from the Ophiuchus
cluster
|
astro-ph
|
We present the results of deep observations of the Ophiuchus cluster of
galaxies with INTEGRAL in the 3-80 keV band. We analyse 3 Ms of INTEGRAL data
on the Ophiuchus cluster with the IBIS/ISGRI hard X-ray imager and the JEM-X
X-ray monitor. In the X-ray band using JEM-X, we show that the source is
extended, and that the morphology is compatible with the results found by
previous missions. Above 20 keV, we show that the size of the source is
slightly larger than the PSF of the instrument, and is consistent with the soft
X-ray morphology found with JEM-X and ASCA. Thanks to the constraints on the
temperature provided by JEM-X, we show that the spectrum of the cluster is not
well fitted by a single-temperature thermal Bremsstrahlung model, and that
another spectral component is needed to explain the high energy data. We detect
the high energy tail with a higher detection significance (6.4 sigma) than the
BeppoSAX claim (2 sigma). Because of the imaging capabilities of JEM-X and
ISGRI, we are able to exclude the possibility that the excess emission comes
from very hot regions or absorbed AGN, which proves that the excess emission is
indeed of non-thermal origin. Using the available radio data together with the
non-thermal hard X-ray flux, we estimate a magnetic field B ~ 0.1-0.2 mu G.
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astro-ph/9611102
|
Albrecht Karle
|
Analog Optical Transmission of Fast Photomultiplier Pulses Over
Distances of 2 km
|
astro-ph
|
New LED-transmitters have been used to develop a new method of fast analog
transmission of PMT pulses over large distances. The transmitters, consisting
basically of InGaAsP LEDs with the maximum emission of light at 1300 nm, allow
the transmission of fast photomultiplier pulses over distances of more than 2
km. The shape of the photomultiplier pulses is maintained, with an attenuation
less than 1 dB/km. Typical applications of analog optical signal transmission
are surface air shower detectors and underwater/ice neutrino experiments, which
measure fast Cherenkov or scintillator pulses at large detector distances to
the central DAQ system.
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No Label
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astro-ph/0011315
|
Felix Mirabel
|
Microquasars: Open Questions and Future Perspectives
|
astro-ph
|
The discovery and subsequent study of microquasars lead to major progress in
our understanding of: 1) the nature of relativistic jets seen elsewhere in the
universe, and 2) the connection between the accretion onto compact objects and
the formation of collimated jets. A detailed account of the major progress
accomplished until present was published in Annual Review of Astronomy &
Astrophysics (Mirabel & Rodr\'\i guez, 1999). Here I review the questions that
remain unanswered, as well as the future perspectives that this new field of
research is opening.
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No Label
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0704.2085
|
Y. M. Pihlstr\"om
|
Stirring the Embers: High Sensitivity VLBI Observations of GRB030329
|
astro-ph
|
We present high sensitivity Very Long Baseline Interferometry (VLBI)
observations 806 days after the gamma-ray burst of 2003 March 29 (GRB030329).
The angular diameter of the radio afterglow is measured to be 0.347 +- 0.09
mas, corresponding to 0.99 +- 0.26 pc at the redshift of GRB030329 (z =
0.1685). The evolution of the image size favors a uniform external density over
an R^-2 wind-like density profile (at distances of R >~10^18 cm from the
source), although the latter cannot be ruled out yet. The current apparent
expansion velocity of the image size is only mildly relativistic, suggesting a
non-relativistic transition time of t_NR ~ 1 yr. A rebrightening, or at least a
significant flattening in the flux decay, is expected within the next several
years as the counter-jet becomes visible (this has not yet been observed). An
upper limit of <1.9c is set on the proper motion of the flux centroid.
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No Label
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astro-ph/0506366
|
Su Min Tang
|
Critical Examinations of QSO Redshift Periodicities and Associations
with Galaxies in Sloan Digital Sky Survey Data
|
astro-ph
|
We have used the publicly available data from the Sloan Digital Sky Survey
and 2dF QSO Redshift Survey to test the hypothesis that QSOs are ejected from
active galaxies with periodic non-cosmological redshifts. For two different
intrinsic redshift models, namely the Karlsson $\log(1+z)$ model and Bell's
decreasing intrinsic redshift (DIR) model, we do two tests respectively. First,
using different criteria, we generate four sets of QSO-galaxy pairs and find
there is no evidence for a periodicity at the predicted frequency in
$\log(1+z)$, or at any other frequency. We then check the relationship between
high redshift QSOs and nearby active galaxies, and we find the distribution of
projected distance between high redshift QSOs and nearby active galaxies and
the distribution of redshifts of those active galaxies are consistent with a
distribution of simulated random pairs, completely different from Bell's
previous conclusion. We also analyze the periodicity in redshifts of QSOs, and
no periodicity is found in high completeness samples, contrary to the DIR
model. These results support that QSOs are not ejected from active galaxies.
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No Label
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0805.1219
|
Raphael Lamon
|
GLAST and Lorentz violation
|
astro-ph
|
We study possible Lorentz violations by means of gamma-ray bursts (GRB) with
special focus on the Large Array Telescope (LAT) of GLAST. We simulate bursts
with gtobssim and introduce a Lorentz violating term in the arrival times of
the photons. We further perturb these arrival times and energies with a
Gaussian distribution corresponding to the time resp. energy resolution of
GLAST. We then vary the photon flux in gtobssim in order to derive a relation
between the photon number and the standard deviation of the Lorentz violating
term. We conclude with the fact that our maximum likelihood method as first
developed in [1] is able to make a statement whether Nature breaks the Lorentz
symmetry if the number of bursts with known redshifts is of the order of 100.
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No Label
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astro-ph/0004062
|
Tatsumi
|
Ferromagnetism of quark liquid and magnetars
|
astro-ph
|
Spontaneous magnetization of quark liquid is examined on the analogy with
that in electron gas. It is pointed out that quark liquid has potential to be
ferromagnetic at rather low densities, around nuclear saturation density. Somme
comments are given as for implications on magnetars.
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No Label
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0711.3858
|
Motohiko Kusakabe
|
The X^- Solution to the ^6Li and ^7Li Big Bang Nucleosynthesis Problems
|
astro-ph
|
The $^6$Li abundance observed in metal poor halo stars appears to exhibit a
plateau as a function of metallicity similar to that for $^7$Li, suggesting a
big bang origin. However, the inferred primordial abundance of $^6$Li is
$\sim$1000 times larger than that predicted by standard big bang
nucleosynthesis for the baryon-to-photon ratio inferred from the WMAP data.
Also, the inferred $^7$Li primordial abundance is 3 times smaller than the big
bang prediction. We here describe in detail a possible simultaneous solution to
both the problems of underproduction of $^6$Li and overproduction of $^7$Li in
big bang nucleosynthesis. This solution involves a hypothetical massive,
negatively-charged leptonic particle that would bind to the light nuclei
produced in big bang nucleosynthesis, but would decay long before it could be
detected. We consider only the $X$-nuclear reactions and assume that the effect
of decay products is negligible, as would be the case if lifetime were large or
the mass difference between the charged particle and its daughter were small.
An interesting feature of this paradigm is that, because the particle remains
bound to the existing nuclei after the cessation of the usual big bang nuclear
reactions, a second longer epoch of nucleosynthesis can occur among $X$-nuclei.
We confirm that reactions in which the hypothetical particle is transferred can
occur that greatly enhance the production of $^6$Li while depleting $^7$Li. We
also identify a new reaction that destroys large amounts of $^7$Be, and hence
reduces the ultimate $^7$Li abundance. Thus, big-bang nucleosynthesis in the
presence of these hypothetical particles, together with or without an event of
stellar processing, can simultaneously solve the two Li abundance problems.
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No Label
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astro-ph/0110040
|
Kai Noeske
|
Optical & NIR Surface Photometry of I Zw 18
|
astro-ph
|
Using HST and ground-based optical and NIR data, we investigate whether the
blue compact dwarf (BCD) galaxy I Zw 18 has an extended low-surface-brightness
(LSB) older stellar population underlying the star-forming regions, as is the
case in evolved iE/nE BCDs. Subtraction of narrow band H_alpha and [O III]
exposures from R and V images shows that the filamentary LSB envelope extending
out to ~2 kpc away from the starburst region, and hence the optical broad-band
colors observed therein, are due mainly to ionized gas emission. Ionized gas
accounts already at a galactocentric distance of 0.7 kpc for more than 80% of
the R band line-of-sight intensity and contributes more than 40% of the
integrated R band light of I Zw 18. The structural properties (such as the
exponential scale length) of the stellar LSB component underlying the extended
ionized gas emission place I Zw 18 among the most compact BCDs studied so far.
Contrary to evolved nE/iE BCDs, the stellar component in I Zw 18 shows no
appreciable color gradients over a range of ~8 mag in surface brightness.
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No Label
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astro-ph/9708154
|
Takahiko Matsubara
|
Beyond Zel'dovich-Type Approximations in Gravitational Instability
Theory --- Pad\'e Prescription in Spheroidal Collapse ---
|
astro-ph
|
Among several analytic approximations for the growth of density fluctuations
in the expanding Universe, Zel'dovich approximation in Lagrangian coordinate
scheme is known to be unusually accurate even in mildly non-linear regime. This
approximation is very similar to the Pad\'e approximation in appearance. We
first establish, however, that these two are actually different and independent
approximations with each other by using a model of spheroidal mass collapse.
Then we propose Pad\'e-prescribed Zel'dovich-type approximations and
demonstrate, within this model, that they are much accurate than any other
known nonlinear approximations.
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No Label
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astro-ph/0309629
|
Stephen Serjeant
|
The local sub-mm luminosity functions and predictions from ASTRO-F/SIRTF
to Herschel
|
astro-ph
|
We present new determinations of the local sub-mm luminosity functions. We
find the local sub-mm luminosity density converging to 7.3+/-0.2 x 10^19
W/Hz/Mpc^3 /h_65 at 850um solving the ``sub-mm Olbers' Paradox.'' Using the
sub-mm colour temperature relations from the SCUBA Local Universe Galaxy
Survey, and the discovery of excess 450um excess emission in these galaxies, we
interpolate and extrapolate the IRAS detections to make predictions of the SEDs
of all 15411 PSC-z galaxies from 50-3000um. Despite the long extrapolations we
find excellent agreement with (a) the 90um luminosity function of Serjeant et
al. (2001), (b) the 850um luminosity function of Dunne et al. (2000), (c) the
mm-wave photometry of Andreani & Franceschini (1996); (d) the asymptotic
differential and integral source count predictions at 50-3000um by
Rowan-Robinson (2001). Remarkably, the local luminosity density and the
extragalactic background light together strongly constrain the cosmic star
formation history for a wide class of evolutionary assumptions. We find that
the extragalactic background light, the 850um 8mJy source counts, and the
Omega_* constraints all independently point to a decline in the comoving star
formation rate at z>1.
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No Label
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astro-ph/0411287
|
Luka C. Popovic
|
The influence of gravitational lensing on the spectra of lensed QSOs
|
astro-ph
|
We consider the influence of (milli/micro)lensing on the spectra of lensed
QSOs. We propose a method for the observational detection of microlensing in
the spectra of lensed QSOs and apply it to the spectra of the three lensed QSOs
(PG 1115+080, QSO 1413+117 and QSO 0957+561) observed with Hubble Space
Telescope (HST). We find that the flux ratio between images A1 and A2 of PG
1115+080 is wavelength-dependent and shows differential magnification between
the emission lines and the continuum. We interpret this magnification as
arising from millilensing. We also find that the temporal variations in the
continuum of image C of QSO 1413+117 may be caused by microlensing, while the
temporal variation observed in QSO 0957+561 was probably an intrinsic one.
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No Label
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0801.0859
|
Masaki Iwasawa
|
Evolution of Massive Blackhole Triples II -- The effect of the BH
triples dynamics on the structure of the galactic nuclear
|
astro-ph
|
In this paper, we investigate the structures of galaxies which either have or
have had three BHs using $N$-body simulations, and compare them with those of
galaxies with binary BHs. We found that the cusp region of a galaxy which have
(or had) triple BHs is significantly larger and less dense than that of a
galaxy with binary BHs of the same mass. Moreover, the size of the cusp region
depends strongly on the evolution history of triple BHs, while in the case of
binary BHs, the size of the cusp is determined by the mass of the BHs. In
galaxies which have (or had) three BHs, there is a region with significant
radial velocity anisotropy, while such a region is not observed in galaxies
with binary BH. These differences come from the fact that with triple BHs the
energy deposit to the central region of the galaxy can be much larger due to
multiple binary-single BH scatterings. Our result suggests that we can
discriminate between galaxies which experienced triple BH interactions with
those which did not, through the observable signatures such as the cusp size
and velocity anisotropy.
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No Label
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0811.0158
|
Augustin Skopal
|
Transient jets in the symbiotic prototype Z Andromedae
|
astro-ph
|
We present development of the collimated bipolar jets from the symbiotic
prototype Z And that appeared and disappeared during its 2006 outburst. In 2006
July Z And reached its historical maximum at U ~ 8.0. During this period, rapid
photometric variations with Dm ~ 0.06 mag on the timescale of hours developed.
Simultaneously, high-velocity satellite components appeared on both sides of
the H-alpha and H-beta emission line profiles. They were launched
asymmetrically with the red/blue velocity ratio of 1.2 - 1.3. From about
mid-August they became symmetric. Their spectral properties indicated ejection
of bipolar jets collimated within an average opening angle of 6.1 degrees. We
estimated average outflow rate via jets to dM(jet)/dt ~
2xE10-6(R(jet)/1AU)**(1/2) M(Sun)/year, during their August - September
maximum, which corresponds to the emitting mass in jets, M(jet, emitting) ~
6xE-10(Rjet)/1AU)^{3/2} M(Sun). During their lifetime, the jets released the
total mass of M(jet, total) approx 7.4x1E-7 M(Sun). Evolution in the rapid
photometric variability and asymmetric ejection of jets around the optical
maximum can be explained by a disruption of the inner parts of the disk caused
by radiation-induced warping of the disk.
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No Label
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astro-ph/0309499
|
Markus Aschwanden
|
On the Photometric Accuracy of RHESSI Imaging and Spectrosocopy
|
astro-ph
|
We compare the photometric accuracy of spectra and images in flares observed
with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)}spacecraft. We
test the accuracy of the photometry by comparing the photon fluxes obtained in
different energy ranges from the spectral-fitting software SPEX with those
fluxes contained in the images reconstructed with the Clean, MEM, MEM-Vis,
Pixon, and Forward-fit algorithms. We quantify also the background fluxes, the
fidelity of source geometries, and spatial spectra reconstructed with the five
image reconstruction algorithms. We investigate the effects of grid selection,
pixel size, field-of-view, and time intervals on the quality of image
reconstruction. The detailed parameters and statistics are provided in an
accompanying CD-ROM and web page. We find that Forward-fit, Pixon, and Clean
have a robust convergence behavior and a photometric accuracy in the order of a
few percents, while MEM does not converge optimally for large degrees of
freedom (for large field-of-views and/or small pixel sizes), and MEM-Vis
suffers in the case of time-variable sources. This comparative study documents
the current status of the RHESSI spectral and imaging software, one year after
launch.
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No Label
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No Label
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0710.4065
|
Monika Balucinska-Church
|
The periodic bursters XB1323-619 and GS1826-24: longterm evolution of
the nuclear burning regime and comparison with theory
|
astro-ph
|
The majority of X-ray burst sources do not display a burst rate that
increases with luminosity as expected, but this is seen in the two clocked
bursters XB1323-619 and GS1826-24. We present a detailed investigation of these
two sources which in the case of the first source, spans 18 years. Based on
measurements of the burst rate, X-ray luminosity, the alpha-parameter and the
two time constants generally present in the burst decays, we demonstrate the
importance of the rp nuclear burning process. A detailed comparison with theory
shows that although the burst rate in each source agrees well with the
theoretical value, there is a difference of more than a factor of 5 in the
burst rate at a given luminosity between the sources. We show that the main
reason for this is that the two sources have substantially different emitting
areas on the neutron star in non-burst emission, a factor often neglected.
Variation of this area may explain the inverse relation of burst rate with
luminosity in the majority of burst sources.
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No Label
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No Label
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astro-ph/0306327
|
Vladimir Avila-Reese
|
The structure of halos in Self-Interacting Cold Dark Matter models
|
astro-ph
|
High-resolution numerical simulations were performed to study the structure
and substructure of Milky Way- and cluster-sized halos in a LCDM cosmology with
self-interacting (SI) dark particles, where the particle cross section,
+AFw-sig, is assumed constant or inversely proportional to the relative
velocity. We conclude that the cuspy halo problem at galaxy scales of the LCDM
cosmogony can be solved in the latter case. In this case, the inner density of
galaxy-cluster halos is only slightly affected by the SI, resulting in
agreement with observational constraints. At the same time, the subhalo
population in galaxy and cluster SI-CDM halos remains roughly similar to that
seen on collisionless CDM halos.
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No Label
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No Label
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astro-ph/0310316
|
Stephane Udry
|
The CORALIE survey for southern extra-solar planets. XII. Orbital
solutions for 16 extra-solar planets discovered with CORALIE
|
astro-ph
|
This paper summarizes the information gathered for 16 still unpublished
exoplanet candidates discovered with the CORALIE echelle spectrograph mounted
on the Euler Swiss telescope at La Silla Observatory. Amongst these new
candidates, 10 are typical extrasolar Jupiter-like planets on intermediate- or
long-period (100<P<1350d) and fairly eccentric (0.2<e<0.5) orbits (HD19994,
HD65216, HD92788, HD111232, HD114386, HD142415, HD147513, HD196050, HD216437,
HD216770). Two of these stars are in binary systems. The next 3 candidates are
shorter-period planets (HD6434, HD121504) with lower eccentricities among which
a hot Jupiter (HD83443). More interesting cases are finally given by the
multiple-planet systems HD82943 and HD169830. The former is a resonant
P_2/P_1=2/1 system in which planet-planet interactions are influencing the
system evolution. The latter is more hierarchically structured.
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No Label
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astro-ph/0301297
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Martin Elvis
|
The X-ray-faint Emission of the Supermassive Nuclear Black Hole of
IC1459
|
astro-ph
|
Chandra observations of the supermassive black hole in the nucleus of IC1459
show a weak [L_X=8x10(40)erg s(-1), 0.3-8keV], unabsorbed nuclear X-ray source,
with a slope Gamma=1.88+/-0.09, and no strong Fe-K line at 6.4keV (EW$<382 eV).
This describes a normal AGN X-ray spectrum, but lies at 3x10(-7) below the
Eddington limit. The SED of the IC1459 nucleus is extremely radio loud compared
to normal radio-loud quasars. The nucleus is surrounded by hot ISM (kT~0.5-0.6
keV) with an average density of 0.3cm(-3), within the central ~180 pc radius,
which is comparable to the gravitational capture radius, r_A~140 pc. We
estimate that for a standard AGN efficiency of 10%, the Bondi accretion would
correspond to a luminosity of ~6x10(44)erg s(-1), nearly four orders of
magnitude higher than L_X. ADAF solutions can explain the X-ray spectrum, but
not the high radio/X-ray ratio. A jet model fits the radio-100micron and X-ray
spectra well. The total power in this jet is ~10% of L(Bondi), implying that
accretion close to the Bondi rate is needed.
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No Label
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0802.1650
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Roberto Aloisio
|
Detection of GRB signals with Fluorescence Detectors
|
astro-ph
|
Gamma Ray Bursts are being searched in many ground based experiments
detecting the high energy component (GeV $\div$ TeV energy range) of the photon
bursts. In this paper, Fluorescence Detectors are considered as possible
candidate devices for these searches. It is shown that the GRB photons induce
fluorescence emission of UV photons on a wide range of their spectrum. The
induced fluorescence flux is dominated by GRB photons from 0.1 to about 100 MeV
and, once the extinction through the atmosphere is taken into account, it is
distributed over a wide angular region. This flux can be detected through a
monitor of the diffuse photon flux, provided that its maximum value exceeds a
threshold value, that is primarily determined by the sky brightness above the
detector. The feasibility of this search and the expected rates are discussed
on the basis of the current GRB observations and the existing fluorescence
detectors.
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No Label
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0707.2702
|
Martin Haas F.
|
VISIR/VLT mid-infrared imaging of Seyfert nuclei: Nuclear dust emission
and the Seyfert-2 dichotomy
|
astro-ph
|
Half of the Seyfert-2 galaxies escaped detection of broad lines in their
polarised spectra observed so far. Some authors have suspected that these
non-HBLRs contain real Sy2 nuclei without intrinsic broad line region hidden
behind a dust torus. If this were true, then their nuclear structure would
fundamentally differ from that of Sy2s with polarised broad lines: in
particular, they would not be explained by orientation-based AGN unification.
Further arguments for two physically different Sy2 populations have been
derived from the warm and cool IRAS F25/F60 ratios. These ratios, however,
refer to the entire host galaxies and are unsuitable to conclusively establish
the absence of a nuclear dust torus. Instead, a study of the Seyfert-2
dichotomy should be performed on the basis of nuclear properties only. Here we
present the first comparison between [OIII] 5007A and mid-infrared imaging at
matching spatial resolution. Exploring the Seyfert-2 dichotomy we find that the
distributions of nuclear mid-infrared/[OIII] luminosity ratios are
indistinguishable for Sy1s and Sy2s with and without detected polarised broad
lines and irrespective of having warm or cool IRAS F25/F60 ratios. We find no
evidence for the existence of a population of real Sy2s with a deficit of
nuclear dust emission. Our results suggest 1) that all Seyfert nuclei possess
the same physical structure including the putative dust torus and 2) that the
cool IRAS colours are caused by a low contrast of AGN to host galaxy. Then the
Seyfert-2 dichotomy is explained in part by unification of non-HBLRs with
narrow-line Sy1s and to a larger rate by observational biases caused by a low
AGN/host contrast and/or an unfavourable scattering geometry.
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No Label
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astro-ph/9712158
|
Soojong Pak
|
Molecular Cloud Structure in the Magellanic Clouds: Effect of
Metallicity
|
astro-ph
|
The chemical structure of neutral clouds in low metallicity environments is
examined with particular emphasis on the H to H_2 and C+ to CO transitions. We
observed near-IR H_2 lines and the CO J=1-0 line from 30 Doradus and N159/N160
in the Large Magellanic Cloud and from DEM S 16, DEM S 37, and LI-SMC 36 in the
Small Magellanic Cloud. We find that the H_2 emission is UV-excited and that
(weak) CO emission always exists (in our surveyed regions) toward positions
where H_2 and [CII] emission have been detected. Using a PDR code and a
radiative transfer code, we simulate the emission of line radiation from
spherical clouds and from large planar clouds. Because the [CII] emission and
H_2 emission arise on the surface of the cloud and the lines are optically
thin, these lines are not affected by changes in the relative sizes of the
neutral cloud and the CO bearing core, while the optically thick CO emission
can be strongly affected. The sizes of clouds are estimated by measuring the
deviation of CO emission strength from that predicted by a planar cloud model
of a given size. The average cloud column density and therefore size increases
as the metallicity decreases. Our result agrees with the photoionization
regulated star formation theory by Mc Kee (1989).
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No Label
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astro-ph/0505547
|
Wlodek Bednarek
|
TeV neutrinos from microquasars in compact massive binaries
|
astro-ph
|
We consider a compact binary system in which a Wolf-Rayet star supplies
matter onto a stellar mass black hole or a neutron star. This matter forms an
accretion disk which ejects a jet as observed in Galactic microquasars. A part
of the jet kinetic energy, typically 10%, can be transfered to relativistic
nuclei. These nuclei lose nucleons as a result of photo-disintegration process
in collisions with thermal photons from the accretion disk and the massive
star. Due to the head on photon-nucleus collisions most of neutrons released
from nuclei move towards the surface of the accretion disk and/or the massive
star producing neutrinos in collisions with the matter. We calculate the
spectra of muon neutrinos and expected neutrino event rates in a 1 km^2
neutrino detector of the IceCube type from a microquasar inside our Galaxy
applying, as an example, the parameters of the Cyg X-3 binary system, provided
that nuclei are accelerated to the Lorentz factors above 10^6 with the power
law spectrum with an index close to 2.
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No Label
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0705.3009
|
Travis S. Metcalfe
|
Asteroseismic Signatures of Small Convective Cores
|
astro-ph
|
We present an analytical study of the effect of small convective cores on the
oscillations of solar-like pulsators. Based on an asymptotic analysis of the
wave equation near the center of the star, we derive an expression for the
perturbations to the frequencies of radial modes generated by a convective core
and discuss how these perturbations depend on the properties of the core.
Moreover, we propose a diagnostic tool to isolate the predicted signature of
the core, constructed from a particular combination of the oscillation
frequencies, and we validate this tool with simulated data. We also show that
the proposed tool can be applied to the pulsation data soon expected from
satellite missions such as CoRoT and Kepler to constrain the amplitude of the
discontinuity in the sound speed at the edge of the convective core, the ratio
between the sound speed and the radius at this same location, and the stellar
age.
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No Label
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astro-ph/0506235
|
Yuji Urata
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Kiso observations for 20 GRBs in HETE-2 era
|
astro-ph
|
We have established a GRB follow-up observation system at Kiso observatory
(Japan) in 2001. Since the east Asian area had been blank for the GRB follow-up
observational network, this observational system is very important in studying
the temporal and spectral evolution of early afterglows. Using this system, we
have performed quick observations for optical afterglows from early phase based
on HETE-2 and INTEGRAL alerts. Thanks to the quick follow-up observation
system, we have been able to use the Kiso observatory in 20 events, and conduct
their follow-up observations in optical and near infrared wavelengths.
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No Label
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astro-ph/9907343
|
Renato A. Dupke
|
Constraints on Type Ia Supernova Models from X-ray Spectra of Galaxy
Clusters
|
astro-ph
|
We present constraints on theoretical models of Type Ia supernovae using
spatially resolved ASCA X-ray spectroscopy of three galaxy clusters: Abell 496,
Abell 2199 and Abell 3571. All three clusters have central iron abundance
enhancements; an ensemble of abundance ratios are used to show that most of the
iron in the central regions of the clusters comes from SN Ia. These
observations are consistent with the suppressed galactic wind scenario proposed
by Dupke and White (1999). At the center of each cluster, simultaneous analysis
of spectra from all ASCA instruments shows that the nickel to iron abundance
ratio (normalized by the solar ratio) is Ni/Fe ~ 4. We use the nickel to iron
ratio as a discriminator between SN Ia explosion models: the Ni/Fe ratio of
ejecta from the "Convective Deflagration" model W7 is consistent with the
observations, while those of "delayed detonation" models are not consistent at
the 90% confidence level.
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No Label
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astro-ph/9807190
|
Lam Hui
|
A Geometrical Test of the Cosmological Energy Contents Using the
Lyman-alpha Forest
|
astro-ph
|
In this Letter we explore a version of the test of cosmological geometry
proposed by Alcock and Paczynski (1979), using observations of the Lyman-alpha
forest in the spectra of close quasar pairs. By comparing the correlations in
absorption in one quasar spectrum with correlations between the spectra of
neighboring quasars one can determine the relation of the redshift distance
scale to the angle distance scale at the redshift of the absorbers, $z \sim 2 -
4$. Since this relationship depends on the parameters of the cosmological
model, these parameters may be determined using the Lyman-alpha forest. While
this test is relatively insensitive to the density parameter $\Omega_m$ in a
dust-dominated universe, it is more sensitive to the presence of a matter
component with large negative pressure (such as a cosmological constant
$\Lambda$) and its equation of state. With only 25 pairs of quasar spectra at
angular separations $0.5' - 2'$, one can discriminate between an $\Omega_m =
0.3$ open universe ($\Lambda=0$) and an $\Omega_m = 0.3$ flat
($\Lambda$-dominated) universe at the $4-\sigma$ level. The S/N can be enhanced
by considering quasar pairs at smaller angular separations, but requires proper
modeling of nonlinear redshift space distortions. Here the correlations and
redshift space distortions are modeled using linear theory.
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No Label
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astro-ph/9807246
|
Mike Shull
|
A Cluster of Low-Redshift Lyman-alpha Clouds toward PKS 2155-304. I.
Limits on Metals and D/H
|
astro-ph
|
We report observations from the Hubble Space Telescope (HST) and the VLA on
the galactic environment, metallicity, and D/H in strong low-redshift Lya
absorption systems toward the bright BL Lac object PKS 2155-304. GHRS/G160M
spectra at 20 km/s resolution show 14 Lya absorbers, 6 clustered at cz =
16,100-18,500 km/s. ORFEUS claimed LyC absorption at z = 0.056 with N(HI) =
(2-5)x10^16 cm^-2, while our Lya data suggest N(HI) = (3-10)x10^14 cm^-2.
Higher columns are possible if the Lya line core at 17,000 +/- 50 km/s contains
narrow HI components. We identify the Lya cluster with a group of five HI
galaxies offset by 400-800 kpc from the sightline. The two strongest absorption
features cover the same velocity range as the HI emission in the two galaxies
closest to the line of sight. If the Lya is associated with these galaxies,
they must have huge halos of highly turbulent, mostly ionized gas. The Lya
absorption could also arise from an extended sheet of intragroup gas, or from
smaller primordial clouds and halos of dwarf galaxies. We see no absorption
from SiIII 1206, CIV 1548, or DI Lya. Photoionization models yield limits of
(Si/H) < 0.003 solar, (C/H) < 0.005 solar, (D/H) < 2.8x10^-4 (4 sigma) if N(HI)
= 2x10^16 cm^-2. The limits increase to 0.023 solar and D/H < 2.8x10^-3 if
N(HI) = 2x10^15 cm^-2. The data suggest that the IGM in this group has not been
enriched to the levels suggested by X-ray studies of intracluster gas and that
these absorbers could be primordial gas clouds.
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No Label
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astro-ph/0701142
|
Sven Van Loo
|
Dense core compression and fragmentation induced by the scattering of
hydromagnetic waves
|
astro-ph
|
We have performed 2D hydromagnetic simulations with an adaptive mesh
refinement code to examine the response of a pre-existing initially spherical
dense core to a non-linear fast-mode wave. One key parameter is the ratio of
the wavelength to the initial core radius. If that ratio is large and the wave
amplitude is sufficient, significant compression of the core occurs, as
envisaged by Myers & Lazarian (1998) in their "turbulent cooling flow" picture.
For smaller values of that ratio, an initial value of the ratio of the thermal
pressure to magnetic pressure of 0.2, and sufficiently large wave amplitude,
the scattering induces the production of dense substructure in the core. This
substructure may be related to that detected in the dense core associated with
the cyanopolyyne peak in TMC-1. Our simulations also show that short-wavelength
waves, contrary to large-wavelength waves, do not confine dense cores.
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No Label
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astro-ph/0511617
|
Valentin Niess
|
Underwater Acoustic Detection of Ultra High Energy Neutrinos
|
astro-ph
|
We investigate the acoustic detection method of 10^18-20 eV neutrinos in a
Mediterranean Sea environment. The acoustic signal is re-evaluated according to
dedicated cascade simulations and a complex phase dependant absorption model,
and compared to previous studies. We detail the evolution of the acoustic
signal as function of the primary shower characteristics and of the acoustic
propagation range. The effective volume of detection for a single hydrophone is
given taking into account the limitations due to sea bed and surface boundaries
as well as refraction effects. For this 'benchmark detector' we present
sensitivity limits to astrophysical neutrino fluxes, from which sensitivity
bounds for a larger acoustic detector can be derived. Results suggest that with
a limited instrumentation the acoustic method would be more efficient at
extreme energies, above 10^20 eV.
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No Label
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No Label
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0810.5279
|
Lara Silvers
|
Three-Layer Magnetoconvection
|
astro-ph
|
It is believed that some stars have two or more convection zones in close
proximity near to the stellar photosphere. These zones are separated by
convectively stable regions that are relatively narrow. Due to the close
proximity of these regions it is important to construct mathematical models to
understand the transport and mixing of passive and dynamic quantities. One key
quantity of interest is a magnetic field, a dynamic vector quantity, that can
drastically alter the convectively driven flows, and have an important role in
coupling the different layers. In this paper we present the first investigation
into the effect of an imposed magnetic field in such a geometry. We focus our
attention on the effect of field strength and show that, while there are some
similarities with results for magnetic field evolution in a single layer, new
and interesting phenomena are also present in a three layer system.
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No Label
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astro-ph/0012400
|
Robert Rutledge
|
The Quiescent X-Ray Spectrum of the Neutron Star in Cen X-4 Observed
with Chandra/ACIS-S
|
astro-ph
|
We report on spectral and intensity variability analysis from a
Chandra/ACIS-S observation of the transient, type-I X-ray bursting low-mass
X-ray binary Cen X-4. The quiescent X-ray spectrum during this observation is
statistically identical to one observed previously with Beppo/SAX, and close,
but not identical, to one observed previously with ASCA. The X-ray spectrum is
best described as a pure Hydrogen atmosphere thermal spectrum plus a power-law
component that dominates the spectrum above 2 keV. The best-fit radius of the
neutron star is r=12.9+/-2.6 (d/1.2 kpc) km if the interstellar absorption is
fixed at the value implied by the optical reddening. Allowing the interstellar
absorption to be a free parameter yields r=19+45-10 (d/1.2 kpc) km (90%
confidence). The thermal spectrum from the neutron star surface is inconsistent
with a solar metallicity. We find a 3sigma upper-limit of root-mean-square
variability <18% (0.2-2.0 keV; 0.0001-1 Hz) during the observation. On the
other hand, the 0.5-10.0 keV luminosity decreased by 40+/-8% in the 4.9 years
between the Asca and Chandra observations. This variability can be attributed
to the power-law component. Moreover, we limit the variation in thermal
temperature to <10% over these 4.9 years. The stability of the thermal
temperature and emission area radius supports the interpretation that the
quiescent thermal emission is due to the hot neutron star core.
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No Label
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astro-ph/9601018
|
Salucci Paolo
|
Dark Baryons in the Universe: the Quest Goes On
|
astro-ph
|
We show that the high local baryonic fraction, M(bar) ~ 1/3 M(tot), found in
groups and clusters of galaxies does not reconcile the observed cosmological
baryon density with the standard Big-Bang prediction. Taking into account
recent measurements on the hot-gas content and temperature functions of
clusters and groups, we get Omega(gas) = 0.0023 h_{50}^{-1.5} ~ 4% Omega(BBN).
Including the contributions of galaxies and of (local) Ly-alpha clouds we
estimate Omega(bar) ~ 0.004-0.006 < 10% Omega(BBN) as the amount of detected
baryons. Most of the synthesised atoms are still to be discovered. We propose
to relate the impressive presence of the hot gas component in clusters with the
very low, mass-dependent efficiency of the process of galaxy formation in
making stars from the primordial gas.
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No Label
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No Label
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astro-ph/0607393
|
Katia Cunha
|
Chemical Evolution of the Galactic Bulge as Derived from High-Resolution
Infrared Spectroscopy of K and M Red Giants
|
astro-ph
|
We present chemical abundances in K and M red-giant members of the Galactic
bulge derived from high-resolution infrared spectra obtained with the Phoenix
spectrograph on Gemini-South. The elements studied are carbon, nitrogen,
oxygen, sodium, titanium, and iron. The evolution of C and N abundances in the
studied red-giants show that their oxygen abundances represent the original
values with which the stars were born. Oxygen is a superior element for probing
the timescale of bulge chemical enrichment via [O/Fe] versus [Fe/H]. The
[O/Fe]-[Fe/H] relation in the bulge does not follow the disk relation, with
[O/Fe] values falling above those of the disk. Titanium also behaves similarly
to oxygen with respect to iron. Based on these elevated values of [O/Fe] and
[Ti/Fe] extending to large Fe abundances, it is suggested that the bulge
underwent a more rapid chemical enrichment than the halo. In addition, there
are declines in both [O/Fe] and [Ti/Fe] in those bulge targets with the largest
Fe abundances, signifying another source affecting chemical evolution: perhaps
Supernovae of Type Ia. Sodium abundances increase dramatically in the bulge
with increasing metallicity, possibly reflecting the metallicity dependant
yields from supernovae of Type II, although Na contamination from H-burning in
intermediate mass stars cannot be ruled out.
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astro-ph/0010618
|
L. Matthew Haffner
|
Mapping the Galactic Free-Free Foreground via Interstellar H-Alpha
Emission
|
astro-ph
|
Recently completed H-Alpha surveys of large portions of the sky can be used
to create maps of the free-free intensity distribution at high Galactic
latitude that are independent of the spectral fits to the CMB data. This
provides an opportunity to test the accuracy of the spectral fitting procedures
and to search for other sources of Galactic forground contamination that could
be confused spectrally with the free-free, such as spinning dust grains. The
Wisconsin H-Alpha Mapper (WHAM) survey has sampled the sky north of declination
-30 deg at about one degree angular resolution and has revealed that, except
for a few isolated regions of enhanced emission, \Delta T_{ff} (30 GHz) < 30
micro-K at Galactic latitudes near 15 deg, decreasing to \Delta T_{ff} (30 GHz)
< 4 mircro-K at latitudes above 50 deg. Also in progress are H-Alpha surveys
that sample the sky at higher angular resolution.
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No Label
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astro-ph/0305540
|
Andrea De Luca
|
Search for the Optical Counterpart of the Vela Pulsar X-ray Nebula
|
astro-ph
|
Observations of the Vela pulsar region with the Chandra X-ray observatory
have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN),
which showed an overall similarity with the Crab PWN. However, contrary to the
Crab, no firm detection of the Vela PWN in optical has been reported yet. To
search for the optical counterpart of the X-ray PWN, we analyzed deep optical
observations performed with different telescopes. We compared the optical
images with those obtained with the Chandra ACIS to search for extended
emission patterns which could be identified as counterparts of the X-ray nebula
elements. Although some features are seen in the optical images, we find no
correlation with the X-ray structure. Thus, we conclude that the diffuse
optical emission is more likely associated with filaments in the host Vela SNR.
The derived upper limits on the optical flux from the PWN are compatibile,
within the uncertainties, with the values expected on the basis of the
extrapolations of the X-ray data.
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No Label
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astro-ph/0606496
|
Michael Zingale
|
Low Mach Number Modeling of Type Ia Supernovae. II. Energy Evolution
|
astro-ph
|
The convective period leading up to a Type Ia supernova (SN Ia) explosion is
characterized by very low Mach number flows, requiring hydrodynamical methods
well-suited to long-time integration. We continue the development of the low
Mach number equation set for stellar scale flows by incorporating the effects
of heat release due to external sources. Low Mach number hydrodynamics
equations with a time-dependent background state are derived, and a numerical
method based on the approximate projection formalism is presented. We
demonstrate through validation with a fully compressible hydrodynamics code
that this low Mach number model accurately captures the expansion of the
stellar atmosphere as well as the local dynamics due to external heat sources.
This algorithm provides the basis for an efficient simulation tool for studying
the ignition of SNe Ia.
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No Label
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No Label
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astro-ph/0412204
|
Marcello Giroletti
|
The two sided parsec scale structure of the Low Luminosity Active
Galactic Nucleus in NGC 4278
|
astro-ph
|
We present new Very Long Baseline Interferometry observations of the LINER
galaxy NGC 4278. The observations were taken with the Very Long Baseline Array
(VLBA) and a single antenna of the Very Large Array (VLA) at 5 GHz and 8.4 GHz
and have a linear resolution of <0.1 pc. Our radio data reveal a two sided
structure, with symmetric S-shaped jets emerging from a flat spectrum core. We
fit the jet brightness with gaussian components, which we identify from a
previous observation taken five years before. By comparing the positions of the
components in the two epochs, we measure motions between 0.45 +/- 0.14 and 3.76
+/- 0.65 mas, corresponding to apparent velocities < 0.2c, and to ages in the
range 8.3 - 65.8 years. Assuming that the radio morphology is intrinsically
symmetric and its appearance is governed by Doppler beaming effects, we find
that NGC4278 has mildly relativistic jets (beta ~ 0.75), closely aligned to the
line-of-sight (2 degrees < theta < 4 degrees). Alternatively, the source could
be oriented at a larger angle and asymmetries could be related to the jet
interaction with the surrounding medium. We also present new simultaneous VLA
observations between 1.4 and 43 GHz, and a 5 GHz light curve between 1972 and
2003. The radio spectrum can be fit by a relatively steep power-law (alpha =
0.54). We find significant variability at 5 GHz. All these arguments indicate
that the radiation from NGC 4278 is emitted via the synchrotron process by
relativistic particles accelerated by a supermassive black hole. Despite a much
lower power, this is the same process that takes place in ordinary radio loud
AGNs.
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No Label
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astro-ph/0607649
|
Arjen van der Wel
|
Comparing Dynamical and Photometric Mass Estimates of Low- and
High-Redshift Galaxies: Random and Systematic Uncertainties
|
astro-ph
|
We determine the importance of redshift-dependent systematic effects in the
determination of stellar masses from broad band spectral energy distributions
(SEDs), using high quality kinematic and photometric data of early-type
galaxies at z~1 and z~0. We find that photometric masses of z~1 galaxies can be
systematically different, by up to a factor of 2, from photometric masses of
z~0 galaxies with the same dynamical mass. The magnitude of this bias depends
on the choice of stellar population synthesis model and the rest-frame
wavelength range used in the fits. The best result, i.e., without significant
bias, is obtained when rest-frame optical SEDs are fitted with models from
Bruzual&Charlot (2003). When the SEDs are extended to the rest-frame near-IR, a
bias is introduced: photometric masses of the z~1 galaxies increase by a factor
of 2 relative to the photometric masses of the z~0 galaxies. When we use the
Maraston (2005) models, the photometric masses of the z~1 galaxies are low
relative to the photometric masses of the z~0 galaxies by a factor of ~1.8.
This offset occurs both for fits based on rest-frame optical SEDs, and fits
based on rest-frame optical+near-IR SEDs. The results indicate that model
uncertainties produce uncertainties as high as a factor of 2.5 in mass
estimates from rest-frame near-IR photometry, independent of uncertainties due
to unknown star formation histories.
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0804.2436
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Orsola De Marco
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Binary central stars of PN discovered through photometric variability.
I. What we know and what we would like to find out
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astro-ph
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Shaping axi-symmetric planetary nebulae is easier if a companion interacts
with a primary at the top of the asymptotic giant branch. To determine the
impact of binarity on planetary nebula formation and shaping, we need to
determine the central star of planetary nebula binary fraction and period
distribution. The short-period binary fraction has been known to be 10-15% from
a survey of ~100 central stars for photometric variability indicative of
irradiation effects, ellipsoidal variability or eclipses. This survey technique
is known to be biased against binaries with long periods and this fact is used
to explain why the periods of all the binaries discovered by this survey are
smaller than 3 days. In this paper we assess the status of knowledge of binary
central stars discovered because of irradiation effects. We determine that, for
average parameters, this technique should be biased against periods longer than
1-2 weeks, so it is surprising that no binaries were found with periods longer
than 3 days. Even more puzzling is the fact that 9 out of 12 of the irradiated
binaries, have periods smaller than one day, a fact that is starkly at odds
with post-common envelope predictions. We suggest that either all common
envelope models tend to overestimate post-common envelope periods or that this
binary survey might have suffered from additional, unquantified biases. If the
latter hypothesis is true, the currently-known short-period binary fraction is
put in serious doubt. We also introduce a new survey for binary-related
variability, which will enable us to better quantify biases and determine an
independent value for the short period binary fraction.
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astro-ph/0506107
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Friedrich Konrad Roepke
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Type Ia supernova diversity in three-dimensional models
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astro-ph
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The use of type Ia supernovae as distance indicators for cosmology has
initiated a search for theoretical arguments supporting the empirical
calibration methods applied. To this end, as a first step, a sound
understanding of the origin of the observed diversity in type Ia supernova
properties is needed. Here we present a first systematic study of effects
resulting from changing some physical parameters of three-dimensional
deflagration models of thermonuclear supernovae. In our study we vary the
progenitor's carbon-to-oxygen ratio and its central density prior to ignition
because both properties are not well determined by stellar evolution theory and
they may change from supernova to supernova. Next we compute for these
explosion models the nucleosynthesis yields in a post-processing step. This, in
addition, allows us to study variations in the progenitor's metallicity by
means of different $^{22}$Ne mass fractions in the initial composition. We find
that the progenitor's carbon-to-oxygen ratio and its central density affect the
energy release of the models and thus the expansion velocity of the supernova.
Moreover, we find that changing the metallicity and the central density changes
the production of radioactive $^{56}$Ni and thus affects the luminosity. In
contrast, the carbon-to-oxygen ratio has little effect on the $^{56}$Ni
production. Implications of the found variations of the explosion energy and
the produced $^{56}$Ni mass for the type Ia supernova diversity are discussed.
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astro-ph/0603379
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Elia Stefano Battistelli Dr
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Polarization Observations of the Anomalous Microwave Emission in the
Perseus Molecular Complex with the Cosmosomas Experiment
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astro-ph
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The anomalous microwave emission detected in the Perseus molecular complex by
Watson \ea has been observed at 11 GHz through dual orthogonal polarizations
with the COSMOSOMAS experiment. Stokes U and Q maps were obtained at a
resolution of \sim 0.9deg. for a 30deg. X 30deg. region including the Perseus
molecular complex. A faint polarized emission has been measured; we find Q=-0.2
% \pm1.0%, while U=-3.4^{+1.8}_{-1.4}% both at the 95% confidence level with a
systematic uncertainty estimated to be lower than 1% determined from tests of
the instrumental performance using unpolarized sources in our map as null
hypothesis. The resulting total polarization level is \Pi = 3.4^{+1.5}_{-1.9}%.
These are the first constraints on the polarization properties of an anomalous
microwave emission source. The low level of polarization seems to indicate that
the particles responsible for this emission in the Perseus molecular complex
are not significantly aligned in a common direction over the whole region, as a
consequence of either a high structural symmetry in the emitting particle or a
low-intensity magnetic field. Our weak detection is fully consistent with
predictions from electric dipole emission and resonance relaxation at this
frequency.
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