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astro-ph/0403537 | Charlotte Vastel | Detection of D2H+ in the Dense Interstellar Medium | astro-ph | The 692 GHz para ground-state line of D2H+ has been detected at the Caltech
Submillimeter Observatory towards the pre-stellar core 16293E. The derived D2H+
abundance is comparable to that of H2D+, as determined by observations of the
372 GHz line of ortho-H2D+. This is an observational verification of recent
theoretical predictions (Roberts, Herbst & Millar 2003), developed to explain
the large deuteration ratios observed in cold, high-density regions of the
interstellar medium associated with low mass pre-stellar cores and protostars.
This detection confirms expectations that the multiply deuterated forms of H3+
were missing factors of earlier models. The inclusion of D2H+ and D3+ in the
models leads to predictions of higher values of the D/H ratio in the gas phase.
| No Label | No Label |
astro-ph/0607030 | Eric Linder | Snapping Supernovae at z>1.7 | astro-ph | We examine the utility of very high redshift Type Ia supernovae for cosmology
and systematic uncertainty control. Next generation space surveys such as the
Supernova/Acceleration Probe (SNAP) will obtain thousands of supernovae at
z>1.7, beyond the design redshift for which the supernovae will be exquisitely
characterized. We find that any z\gtrsim2 standard candles' use for
cosmological parameter estimation is quite modest and subject to pitfalls; we
examine gravitational lensing, redshift calibration, and contamination effects
in some detail. The very high redshift supernovae - both thermonuclear and core
collapse - will provide copious interesting information on star formation,
environment, and evolution. However, the new observational systematics that
must be faced, as well as the limited expansion of SN-parameter space afforded,
does not point to high value for 1.7<z<3 SNe Ia in controlling evolutionary
systematics relative to what SNAP can already achieve at z<1.7. Synergy with
observations from JWST and thirty meter class telescopes afford rich
opportunities for advances throughout astrophysics.
| No Label | No Label |
0805.2844 | Samuli Kotiranta | Mapping the three-body system - decay time and reversibility | astro-ph | In this paper we carry out a quantitative analysis of the three-body systems
and map them as a function of decaying time and intial conguration, look at
this problem as an example of a simple deterministic system, and ask to what
extent the orbits are really predictable. We have investigated the behavior of
about 200 000 general Newtonian three body systems using the simplest initial
conditions. Within our resolution these cover all the possible states where the
objects are initially at rest and have no angular momentum. We have determined
the decay time-scales of the triple systems and show that the distribution of
this parameter is fractal in appearance. Some areas that appear stable on large
scales exhibit very narrow strips of instability and the overall pattern,
dominated by resonances, reminds us of a traditional Maasai warrior shield.
Also an attempt is made to recover the original starting conguration of the
three bodies by backward integration. We find there are instances where the
evolution to the future and to the past lead to different orbits, in spite of
time symmetric initial conditions. This implies that even in simple
deterministic systems there exists an Arrow of Time.
| No Label | No Label |
astro-ph/9510111 | David Merritt | The Frequency Function of Elliptical Galaxy Intrinsic Shapes | astro-ph | We present fully nonparametric estimates of the frequency function of
elliptical galaxy intrinsic shapes under the axisymmetric and triaxial
hypotheses. If elliptical galaxies are assumed to be oblate or prolate, the
frequency function of intrinsic shapes is negative for axis ratios near unity
due to the lack of apparently round galaxies. Both axisymmetric hypotheses are
found to be inconsistent at the 99 percent level with the data. Triaxial
intrinsic shapes are fully consistent with the data; a number of possible
triaxial frequency functions are presented, some of which exhibit strong
bimodality. We also compute the ``maximum entropy'' distribution of intrinsic
shapes under the triaxial hypothesis.
| No Label | No Label |
astro-ph/0009229 | Ichi Tanaka | Superclustering of Faint Galaxies in the Field of a QSO Concentration at
z~1.1 | astro-ph | We report on a wide-area (48' x 9') imaging survey of faint galaxies in R and
I bands toward the 1338+27 field where an unusual concentration of five QSOs at
z\sim1.1, embedded in a larger-scale clustering of 23 QSOs, is known to exist.
Using a quite homogeneous galaxy catalog with a detection completeness limit of
I~23.5, we detect a significant clustering signature of faint red galaxies with
I > 21 and R-I > 1.2 over a scale extending to ~20h^{-1}_{50} Mpc. Close
examination of the color-magnitude diagram, the luminosity function, and the
angular correlation function indeed suggests that those galaxies are located at
z~1.1 and trace the underlying large-scale structure at that epoch, together
with the group of 5 QSOs. Since the whole extent of the cluster of 23 QSOs
(~70h^{-1}_{50} Mpc) is roughly similar to the local ``Great Wall'', the area
may contain a high-redshift counterpart of superclusters in the local universe.
| No Label | No Label |
astro-ph/0411023 | Xiaoping Zheng | Cooling of strange stars in the color-flavor locked phase with a
rotating crust Cooling of strange stars in the color-flavor locked phase with
a rotating crust | astro-ph | The presence of the color-flavor locked (CFL) phase strongly suppresses the
neutrino emission processes and the quark specific heat. As a result the
cooling of the strange stars in the CFL phase is dominated by deconfinement
heating and surface emission. The temperature of these stars with strong
magnetic field ($B{\geq}10^{10}G$) rise significantly during the first several
ten or hundred years, which may be an effective signature of strange stars as
implicated by pulsar 0540-69. Furthermore a limit line is predicted, which
means compact stars have an upper limit temperature at any moment. We still may
search for the candidates for strange stars in the CFL phase along the limit
line.
The presence of the color-flavor locked (CFL) phase strongly suppresses the
neutrino emission processes and the quark specific heat. As a result the
cooling of the strange stars in the CFL phase is dominated by deconfinement
heating and surface emission. The temperature of these stars with strong
magnetic field ($B{\geq}10^{10}G$) rise significantly during the first several
ten or hundred years, which may be an effective signature of strange stars as
implicated by pulsar 0540-69. Furthermore a limit line is predicted, which
means compact stars have an upper limit temperature at any moment. We still may
search for the candidates for strange stars in the CFL phase along the limit
line.
| No Label | No Label |
0811.1675 | Hiroaki Nishioka | Tests of AMiBA Data Integrity | astro-ph | We describe methods used to validate data from the Y.T. Lee Array for
Microwave Background Anisotropy (AMiBA), an interferometric array designed to
measure the Sunyaev-Zel'dovich effect and the anisotropy of the Cosmic
Microwave Background (CMB). We perform several statistical tests on data from
pointed galaxy cluster observations taken in 2007 and noise data from long-term
blank sky observations and measurements with the feeds covered by the
absorbers. We apply power spectrum analysis, cross power spectrum analysis
among different outputs with different time lags in our analog correlator, and
sample variance law tests to noise data. We find that (1) there is no time
variation of electronic offsets on the time scale of our two-patch observations
(~10 minutes); (2) noise is correlated by less than 10% between different lags;
and (3) the variance of noise scales with the inverse of time. To test the
Gaussianity of the data, we apply Kolmogorov-Smirnov (K-S) tests to cluster
data, and find that a 5% significance level efficiently detects data sets with
known hardware problems without rejecting an excess of acceptable data. We also
calculate third- and fourth-order moments and cumulants for the noise residual
visibilities and find that about 95% of our data are within the 99% confidence
regions of Gaussianity.
| No Label | No Label |
astro-ph/0111278 | Anja C. Andersen | Interstellar extinction by fractal polycrystalline graphite clusters? | astro-ph | Certain dust particles in space are expected to appear as clusters of
individual grains. The morphology of these clusters could be fractal or
compact. To determine how these structural features would affect the
interpretation of the observed interstellar extinction peak at $\sim 4.6 \mu$m,
we have calculated the extinction by compact and fractal polycrystalline
graphite clusters consisting of touching identical spheres. We compare three
general methods for computing the extinction of the clusters, namely, a
rigorous solution and two different discrete-dipole approximation methods.
| No Label | No Label |
astro-ph/0011353 | Marcella Carollo | The Metallicity of 0.5<z<1 Field Galaxies | astro-ph | We have measured the emission line ratios in a sample of 34 CFRS star-forming
galaxies with redshifts between 0.5 < z < 1.0, and computed their metallicities
by means of the empirically-calibrated R_23 metallicity estimator introduced by
Pagel et al. (1979). The current analysis concentrates on the 15 galaxies with
L_Hbeta > 1.2x10^41 erg s-1. Although our results can only be regarded as
preliminary until near-IR spectroscopy of Halpha and [NII]6583 are available,
the metallicities of these galaxies appear to be remarkably similar to those of
local galaxies selected in the same way, and there appears to have been little
change in the relationship between metallicity and line- and
continuum-luminosity from z~1 to today. At this stage our results do not
support the idea that these galaxies, known to be generally small and with
late-type morphologies, are dwarf galaxies brightened by large bursts of
star-formation, as had been suggested from previous studies. Rather, our
findings are more consistent with a picture in which these systems are the
progenitors of today's massive metal-rich galaxies.
| No Label | No Label |
astro-ph/9911122 | Andrei Beloborodov | Power Density Spectra of Gamma-Ray Bursts | astro-ph | Power density spectra (PDSs) of long gamma-ray bursts provide useful
information on GRBs, indicating their self-similar temporal structure. The best
power-law PDSs are displayed by the longest bursts (T_90 > 100 s) in which the
range of self-similar time scales covers more than 2 decades. Shorter bursts
have apparent PDS slopes more strongly affected by statistical fluctuations.
The underlying power law can then be reproduced with high accuracy by averaging
the PDSs for a large sample of bursts. This power-law has a slope alpha\approx
-5/3 and a sharp break at 1 Hz.
The power-law PDS provides a new sensitive tool for studies of gamma-ray
bursts. In particular, we calculate the PDSs of bright bursts in separate
energy channels. The PDS flattens in the hard channel (h\nu > 300 keV) and
steepens in the soft channel (h\nu < 50 keV), while the PDS of bolometric light
curves approximately follows the -5/3 law.
We then study dim bursts and compare them to the bright ones. We find a
strong correlation between the burst brightness and the PDS slope. This
correlation shows that the bursts are far from being standard candles and dim
bursts should be intrinsically weak. The time dilation of dim bursts is
probably related to physical processes occurring in the burst rather than to a
cosmological redshift.
Finally, we test the internal shock model against the observed PDS. We
demonstrate how the model can reproduce the -5/3 power law.
| No Label | No Label |
0704.3229 | Tabetha Boyajian | The Long Period, Massive Binaries HD 37366 and HD 54662: Potential
Targets for Long Baseline Optical Interferometry | astro-ph | We present the results from an optical spectroscopic analysis of the massive
stars HD 37366 and HD 54662. We find that HD 37366 is a double-lined
spectroscopic binary with a period of 31.8187 +/- 0.0004 days, and HD 54662 is
also a double lined binary with a much longer period of 557.8 +/- 0.3 days. The
primary of HD 37366 is classified as O9.5 V, and it contributes approximately
two-thirds of the optical flux. The less luminous secondary is a broad-lined,
early B-type main-sequence star. Tomographic reconstruction of the individual
spectra of HD 37366 reveals absorption lines present in each component,
enabling us to constrain the nature of the secondary and physical
characteristics of both stars. Tomographic reconstruction was not possible for
HD 54662; however, we do present mean spectra from our observations that show
that the secondary component is approximately half as bright as the primary.
The observed spectral energy distributions (SEDs) were fit with model SEDs and
galactic reddening curves to determine the angular sizes of the stars. By
assuming radii appropriate for their classifications, we determine distance
ranges of 1.4 - 1.9 and 1.2 - 1.5 kpc for HD 37366 and HD 54662, respectively.
| No Label | No Label |
astro-ph/0407205 | Ken Ebisawa | A Chandra Deep X-ray Exposure on the Galactic Plane and Near Infrared
Identification | astro-ph | Using the Chandra ACIS-I instruments, we have carried out a deep X-ray
observation on the Galactic plane region at (l,b) ~ (28.5, 0.0), where no
discrete X-ray sources have been known previously. We have detected, as well as
strong diffuse emission, 274 new point X-ray sources (4 sigma confidence)
within two partially overlapping fields (~250 arcmin^2 in total) down to the
flux limit ~3 x 10^{-15} $ erg s^{-1} cm^{-2} (2 -- 10 keV) and ~ 7 x 10^{-16}
erg s^{-1} cm^{-2} (0.5 -- 2 keV). We clearly resolved point sources and the
Galactic diffuse emission, and found that ~ 90 % of the flux observed in our
field of view originates from diffuse emission. Many point sources are detected
either in the soft X-ray band (below 2 keV) or in the hard band (above 2 keV),
and only a small number of sources are detected in both energy bands.
On the other hand, most soft X-ray sources are considered to be nearby X-ray
active stars. We have carried out a follow-up near-infrared (NIR) observation
using SOFI at ESO/NTT. Most of the soft X-ray sources were identified, whereas
only a small number of hard X-ray sources had counterparts in NIR. Using both
X-ray and NIR information, we can efficiently classify the point X-ray sources
detected in the Galactic plane. We conclude that most of the hard X-ray sources
are background Active Galactic Nuclei seen through the Milky Way, whereas
majority of the soft X-ray sources are nearby X-ray active stars.
| No Label | No Label |
astro-ph/0002219 | Biswajit Paul | Changes in the long term intensity variations in Cyg X-2 and LMC X-3 | astro-ph | We report the detection of changes in the long-term intensity variations in
two X-ray binaries, Cyg X-2 and LMC X-3. In this work, we have used the
long-term light curves obtained with the All-Sky Monitors (ASMs) of the Rossi
X-Ray Timing Explorer (RXTE), Ginga, Ariel 5, and Vela 5B and the scanning
modulation collimator of HEAO 1. It is found that in the light curves of both
the sources, obtained with these instruments at various times over the last 30
years, more than one periodic or quasi-periodic component is always present.
The multiple prominent peaks in the periodograms have frequencies unrelated to
each other. In Cyg X-2, RXTE-ASM data show strong peaks at 40.4 and 68.8 days,
and Ginga-ASM data show strong peaks at 53.7 and 61.3 days. Multiple peaks are
also observed in LMC X-3. The various strong peaks in the periodograms of LMC
X-3 appear at 104, 169, and 216 days (observed with RXTE-ASM) and 105, 214, and
328 days (observed with Ginga-ASM). The present results, when compared with the
earlier observations of periodicities in these two systems, demonstrate the
absence of any stable long period. The 78 day periodicity detected earlier in
Cyg X-2 was probably due to the short time base in the RXTE data that were
used, and the periodicity of 198 days in LMC X-3 was due to a relatively short
duration of observation with HEAO 1.
| No Label | No Label |
astro-ph/0601117 | Seth Redfield | The Local Interstellar Medium | astro-ph | The Local Interstellar Medium (LISM) is a unique environment that presents an
opportunity to study general interstellar phenomena in great detail and in
three dimensions. In particular, high resolution optical and ultraviolet
spectroscopy have proven to be powerful tools for addressing fundamental
questions concerning the physical conditions and three-dimensional (3D)
morphology of this local material. After reviewing our current understanding of
the structure of gas in the solar neighborhood, I will discuss the influence
that the LISM can have on stellar and planetary systems, including LISM dust
deposition onto planetary atmospheres and the modulation of galactic cosmic
rays through the astrosphere - the balancing interface between the outward
pressure of the magnetized stellar wind and the inward pressure of the
surrounding interstellar medium. On Earth, galactic cosmic rays may play a role
as contributors to ozone layer chemistry, planetary electrical discharge
frequency, biological mutation rates, and climate. Since the LISM shares the
same volume as practically all known extrasolar planets, the prototypical
debris disks systems, and nearby low-mass star-formation sites, it will be
important to understand the structures of the LISM and how they may influence
planetary atmospheres.
| No Label | No Label |
0809.1796 | Lin Lin | Extended Emission of Short Gamma-Ray Bursts | astro-ph | Preliminary results of our analysis on the extended emission of short/medium
duration GRBs observed with Swift/BAT are presented. The Bayesian blocks
algorithm is used to analyze the burst durations and the temporal structure of
the lightcurves in different energy bands. We show here the results of three
bursts (GRBs 050724, 061006 and 070714B) that have a prominent soft extended
emission component in our sample. The extended emission of these bursts is a
continuous, flickering-liked component, lasting $\sim 100$ seconds post the GRB
trigger at 15-25 keV bands. Without considering this component, the three
bursts are classified as short GRBs, with $T_{90}=2\sim 3$ seconds. GRB 060614
has an emission component similar to the extended emission, but this component
has pulse-liked structure, possibly indicating that this emission component is
different from that observed in GRBs 050724, 061006, and 070714B. Further
analysis on the spectral evolution behavior of the extended emission component
is on going.
| No Label | No Label |
0706.2801 | Richard Edgar | Evidence for Growth of Eccentricity and Mass Clearing in a Disc Interior
to a Planet | astro-ph | We present computational results showing eccentricity growth in the inner
portions of a protoplanetary disc. We attribute this to the evolving surface
density of the disc. The planet creates a gap, which adjusts the balance
between the 3:1 (eccentricity exciting) and 2:1 (eccentricity damping)
resonances. The eccentricity of the inner disc can rise as high as 0.3, which
is sufficient to cause it to be accreted onto the star. This offers an
alternative mechanism for producing the large holes observed in the discs of
CoKu Tau/4, GM Aur and DM Tau.
| No Label | No Label |
astro-ph/0202275 | Gustavo Bruzual A. | Modeling Stellar Populations in Star Clusters and Galaxies | astro-ph | Combining population synthesis models with simple Montecarlo simulations of
stochastic effects in the number of stars occupying sparsely populated stellar
evolutionary phases in the HRD, I show that the scatter observed in the
photometric magnitudes and colors of LMC and NGC 7252 star clusters can be
understood in the framework of current stellar evolution theory. The use of a
high resolution stellar spectral atlas in population synthesis models improves
considerably the quality of the fits to observed galaxy SEDs, making the
assignment of a spectroscopic age to stellar populations more reliable than
with low spectral resolution models.
| No Label | No Label |
astro-ph/0301354 | G. Sironi | Search for distortions in the spectrum of the Cosmic Microwave Radiation | astro-ph | We present preliminary results of TRIS, an experiment dedicated to the search
of deviations from a pure planckian distribution in the spectrum of the Cosmic
Microwave Background at frequencies close to 1 GHz
| No Label | No Label |
astro-ph/0510120 | Edvard Mortsell | Strong lensing, cosmology and lensing halos | astro-ph | With future wide and deep cosmological sky surveys, a large number of
gravitationally lensed, multiply imaged systems will be found. In addition to
multiply imaged galaxies and quasars, sources will include transient events
like supernovae and gamma ray bursts in which case very accurate time delay
measurements are possible. Also, large numbers of systems with several lensed
sources behind a single lens will be observed. In this paper, we review and
compare different possibilities of using future strong lensing data to probe
lens matter distributions and to determine the Hubble parameter and the matter
density of the universe. Specifically, we investigate the possibility to break
the well-known degeneracy between dark matter halo profiles and the Hubble
parameter using observed flux ratios. We also investigate how strong lensing
can provide useful constraints on the matter density of the universe
independently of the flux ratios and other cosmological probes.
| No Label | No Label |
astro-ph/0612409 | Krzysztof Stanek | Strongly Variable z=1.48 FeII and MgII Absorption in the Spectra of
z=4.05 GRB 060206 | astro-ph | We report on the discovery of strongly variable FeII and MgII absorption
lines seen at z=1.48 in the spectra of the z=4.05 GRB 060206 obtained between
4.13 to 7.63 hours (observer frame) after the burst. In particular, the FeII
line equivalent width (EW) decayed rapidly from 1.72+-0.25 AA to 0.28+-0.21 AA,
only to increase to 0.96+-0.21 AA in a later date spectrum. The MgII doublet
shows even more complicated evolution: the weaker line of the doublet drops
from 2.05+-0.25 AA to 0.92+-0.32 AA, but then more than doubles to 2.47+-0.41
AA in later data. The ratio of the EWs for the MgII doublet is also variable,
being closer to 1:1 (saturated regime) when the lines are stronger and becoming
closer to 2:1 (unsaturated regime) when the lines are weaker, consistent with
expectations based on atomic physics. We have investigated and rejected the
possibility of any instrumental or atmospheric effects causing the observed
strong variations. Our discovery of clearly variable intervening FeII and MgII
lines lends very strong support to their scenario, in which the characteristic
size of intervening patches of MgII ``clouds'' is comparable to the GRB beam
size, i.e, about 10^16 cm. We discuss various implications of this discovery,
including the nature of the MgII absorbers, the physics of GRBs, and
measurements of chemical abundances from GRB and quasar absorption lines.
| No Label | No Label |
0810.4927 | Robert King | Epsilon Indi Ba, Bb: a spectroscopic study of the nearest known brown
dwarfs | astro-ph | The discovery of Epsilon Indi Ba and Bb, a nearby binary brown dwarf system
with a main-sequence companion, allows a concerted campaign to characterise the
physical parameters of two T dwarfs providing benchmarks against which
atmospheric and evolutionary models can be tested. Some recent observations
suggest the models at low mass and intermediate age may not reflect reality
with, however, few conclusive tests.
We are carrying out a comprehensive characterisation of these, the nearest
known brown dwarfs, to allow constraints to be placed upon models of cool field
dwarfs. We present broadband photometry from the V- to M-band and the
individual spectrum of both components from 0.6-5.1 microns at a resolution of
up to R=5000. A custom analytic profile fitting routine was implemented to
extract the blended spectra and photometry of both components separated by 0.7
arcsec. We confirm the spectral types to be T1 and T6, and notably, we do not
detect lithium at 6708A in the more massive object which may be indicative both
of the age of the system and the mass of the components.
| No Label | No Label |
astro-ph/0410667 | Giulia Rodighiero | A far infrared view of the Lockman Hole from ISO 95 micron observations
- II. Optical identifications and insights into the nature of the
far-infrared sources | astro-ph | We present the optical identifications of a 95 micron ISOPHOT sample in the
Lockman Hole over an area of about half square degree. The catalogue
(Rodighiero et al. 2003) includes 36 sources, making up a complete flux-limited
sample for fluxes > 100 mJy. Reliable sources were detected, with decreasing
but well-controlled completeness, down to 20 mJy. We have combined mid-IR and
radio catalogues in this area to identify the potential optical counterparts of
the far-IR sources. We found 14 radio and 13 15 micron associations, 10 of
which have both associations. For the 11 sources with spectroscopic redshift,
we have performed a spectrophotometric analysis of the observed Spectral Energy
Distributions. Four of these 95 micron sources have been classified as faint IR
galaxies (L_FIR<1.e11 solar luminosity), six as LIRGs and only one ULIRG. We
have discussed the redshift distribution of these objects, comparing our
results with evolutionary model predictions 95 and 175 micron. Given their
moderate distances (the bulk of the closest spectroscopically identified
objects lying at z<0.2), their luminosities and star formation rates (median
value 10 solar masses/yr), the sources unveiled by ISOPHOT at 95 micron seem to
correspond to the low redshift (z<0.3) FIRBACK 175 micron population, composed
of dusty, star-forming galaxies with moderate star formation rates. We computed
and compared different SFR estimators, and found that the SF derived from the
bolometric IR luminosity is well correlated with that computed from the radio
and mid-IR fluxes.
| No Label | No Label |
astro-ph/0601009 | Renyue Cen | Where Are the Baryons? III: Non-Equilibrium Effects and Observables | astro-ph | Numerical simulations of the intergalactic medium have shown that at the
present epoch a significant fraction (40-50%) of the baryonic component should
be found in the (T~10^6K) Warm-Hot Intergalactic Medium (WHIM) - with several
recent observational lines of evidence indicating the validity of the
prediction. We here recompute the evolution of the WHIM with the following
major improvements: (1) galactic superwind feedback processes from galaxy/star
formation are explicitly included; (2) major metal species (O V to O IX) are
computed explicitly in a non-equilibrium way; (3) mass and spatial dynamic
ranges are larger by a factor of 8 and 2, respectively, than in our previous
simulations. We find: (1) non-equilibrium calculations produce significantly
different results from ionization equilibrium calculations. (2) The abundance
of O VI absorption lines based on non-equilibrium simulations with galactic
superwinds is in remarkably good agreement with latest observations, implying
the validity of our model, while the predicted abundances for O VII and O VIII
absorption lines appear to be lower than observed but the observational
errorbars are currently very large. The expected abundances for O VI (as well
as Lyman alpha), O VII and O VIII absorption systems are in the range 50-100
per unit redshift at EW=1km/s decreasing to 10-20 per unit redshift at
EW=10km/s. The number of O VI absorption lines with EW>100km/s is very small,
while there are about 1-3 lines per unit redshift for O VII and O VIII
absorption lines at EW=100km/s. (3) Emission lines, primarily O VI and \lya in
the UV and O VII and O VIII in the soft X-rays are potentially observable by
future missions. The number of emission lines per unit redshift that may be
detectable by planned UV and soft X-ray missions are in the order of 0.1-1.
| No Label | No Label |
0811.3441 | Andr\'es Mu\~noz-Jaramillo | Helioseismic data inclusion in solar dynamo models | astro-ph | An essential ingredient in kinematic dynamo models is the velocity field
within the solar convection zone. In particular, the differential rotation is
now well constrained by helioseismic observations. Helioseismology also gives
us information about the depth-dependence of the meridional circulation in the
near-surface layers. The typical velocity inputs used in solar dynamo models,
however, continue to be an analytic fit to the observed differential rotation
and a theoretically constructed meridional flow profile that matches only the
peak flow speed at the surface. Here we take the first steps towards realistic
helioseismic data assimilation, by presenting methodologies for constructing
differential rotation and meridional circulation profiles that more closely
conform to the observational constraints currently available. We also present
simulations driven by the assimilated rotation and four plausible profiles for
the internal meridional circulation -- all of which match the helioseismically
inferred near-surface depth-dependence, but whose magnitudes are made to vary.
We discuss how the results compare with those that are driven by purely
analytic fits. Our results indicate that the latitudinal shear of the rotation
in the bulk of the solar convection zone plays a more important role, than
either the tachocline or surface radial shear, in the induction of toroidal
field. We also find that it is the speed of the equatorward counter-flow in the
meridional flow at the base of the convection zone, and not how far into the
radiative interior it penetrates, that primarily determines the dynamo cycle
period. Given that improved helioseismic constraints are expected to be
available in the future, our analysis lays the basis for assimilating these
data within dynamo models.
| No Label | No Label |
astro-ph/9804213 | James N. Fry | Large-scale structure and the redshift-distance relation | astro-ph | In efforts to demonstrate the linear Hubble law v = Hr from galaxy
observations, the underlying simplicity is often obscured by complexities
arising from magnitude-limited data. In this paper we point out a simple but
previously unremarked fact: that the shapes and orientations of structures in
redshift space contain in themselves independent information about the
cosmological redshift-distance relation.
The orientations of voids in the CfA slice support the Hubble law, giving a
redshift-distance power index p = 0.83 +/- 0.36 (void data from Slezak, de
Lapparent, & Bijoui 1993) or p = 0.99 +/- 0.38 (void data from Malik &
Subramanian 1997).
| No Label | No Label |
0810.0281 | Damian Fabbian | The C/O ratio at low metallicity: constraints on early chemical
evolution from observations of Galactic halo stars | astro-ph | We present new measurements of the abundances of carbon and oxygen derived
from high-excitation C I and O I absorption lines in metal-poor halo stars,
with the aim of clarifying the main sources of these two elements in the early
stages of the chemical enrichment of the Galaxy. We target 15 new stars
compared to our previous study, with an emphasis on additional C/O
determinations in the crucial metallicity range -3<[Fe/H]<-2. Departures from
local thermodynamic equilibrium were accounted for in the line formation for
both carbon and oxygen. The non-LTE effects are very strong at the lowest
metallicities but, contrary to what has sometimes been assumed in the past due
to a simplified assessment, of different degrees for the two elements. In
addition, for the 28 stars with [Fe/H]<-1 previously analysed, stellar
parameters were re-derived and non-LTE corrections applied in the same fashion
as for the rest of our sample, giving consistent abundances for 43 halo stars
in total. The new observations and non-LTE calculations strengthen previous
suggestions of an upturn in C/O towards lower metallicity (particularly for
[O/H]<-2). Adopting the H collisional cross-sections estimated from the
classical Drawin formula leads to [C/O]~0 at [O/H]~-3. To remove the upturn in
C/O, near-LTE formation for O I lines would be required, which could only
happen if the H collisional efficiency with the Drawin recipe is underestimated
by factors of up to several tens of times, which we consider unlikely. The high
C/O values derived at the lowest metallicities may be revealing the
fingerprints of Population III stars or may signal rotationally-aided
nucleosynthesis in more normal Population II stars.
| No Label | No Label |
astro-ph/0302061 | Neal A. Miller | Abell 2255: Increased Star Formation and AGN Activity in a
Cluster-Cluster Merger | astro-ph | Deep VLA 1.4 GHz radio continuum imaging of Abell 2255 is presented. This
cluster is among the better nearby candidates for rich cluster-cluster merger
systems, with evidence including an elongated X-ray morphology, the presence of
a radio halo, and substructure present in its galaxy distribution. Our radio
observations reach an rms sensitivity of ~40 uJy/beam, enabling us to detect
(at 5 sigma) star formation rates as low as 1.4 M(sun)/year from the center of
the cluster out to a radial distance of 3 Mpc. The radio data are complemented
by optical imaging and a large spectroscopic database, allowing us to separate
all galaxies with M_R < -20 into cluster members and foreground/background
galaxies. The spectra are also used to associate the galaxies' radio emission
with either star formation or AGN. We compare the resulting cluster radio
galaxy population with those of nineteen other nearby Abell clusters, and find
strong evidence for an increase in the frequency of radio galaxies in Abell
2255. This increase is seen in two separate types of galaxies: powerful radio
AGN and optically-faint star forming galaxies. The optical spectra of the
latter often indicate current or recent starbursts, and these galaxies appear
to be distributed along an axis perpendicular to the probable merger axis. We
assess these factors in light of models of galaxy evolution, and suggest that
the cluster-cluster merger is responsible for triggering galaxy activity in
Abell 2255.
| No Label | No Label |
astro-ph/0603648 | Jong-Hak Woo | Cosmic Evolution of Black Holes and Spheroids. I: The M_BH-sigma
Relation at z=0.36 | astro-ph | We test the evolution of the correlation between black hole mass and bulge
velocity dispersion (M$_{\rm BH}-\sigma$), using a carefully selected sample of
14 Seyfert 1 galaxies at $z=0.36\pm0.01$. We measure velocity dispersion from
stellar absorption lines around Mgb (5175\AA) and Fe (5270\AA) using high S/N
Keck spectra, and estimate black hole mass from the H$\beta$ line width and the
optical luminosity at 5100\AA, based on the empirically calibrated
photo-ionization method. We find a significant offset from the local relation,
in the sense that velocity dispersions were smaller for given black hole masses
at $z=0.36$ than locally. We investigate various sources of systematic
uncertainties and find that those cannot account for the observed offset. The
measured offset is $\Delta \log M_{\rm BH}=0.62 \pm 0.10 \pm 0.25$, i.e.
$\Delta \log \sigma=0.15 \pm 0.03 \pm 0.06$, where the error bars include a
random component and an upper limit to the systematics. At face value, this
result implies a substantial growth of bulges in the last 4 Gyr, assuming that
the local M$_{\rm BH}-\sigma$ relation is the universal evolutionary end-point.
Along with two samples of active galaxies with consistently determined black
hole mass and stellar velocity dispersion taken from the literature, we
quantify the observed evolution with the best fit linear relation, $\Delta \log
M_{\rm BH} = (1.66\pm0.43)z + (0.04\pm0.09)$ with respect to the local
relationship of Tremaine et al. (2002), and $\Delta \log M_{\rm BH} =
(1.55\pm0.46)z + (0.01\pm0.12)$ with respect to that of Ferrarese (2002). This
result is consistent with the growth of black holes predating the final growth
of bulges at these mass scales ($<\sigma>$=170 km s$^{-1}$).
| No Label | No Label |
astro-ph/0609252 | Anatoly A. Suchkov | SDSS AGNs with X-ray Emission from ROSAT PSPC Pointed Observations | astro-ph | We present a sample of 1744 type 1 active galactic nuclei (AGNs) from the
Sloan Digital Sky Survey (SDSS DR4) spectroscopic catalog with X-ray
counterparts in the White-Giommi-Angelini Catalog (WGACAT) of ROSAT PSPC
pointed observations. Of 1744 X-ray sources, 1410 (80.9%) are new AGN
identifications. Of 4574 SDSS DR4 AGNs for which we found radio matches in the
catalog of radio sources from the FIRST catalog, 224 turned up in our sample of
SDSS X-ray AGNs. The sample objects are given in a catalog that contains
optical and X-ray parameters along with radio emission parameters where
available. We illustrate the content of our catalog and its potential for AGN
science by providing statistical relationships for the catalog data. The
potential of the morphological information is emphasized by confronting the
statistics of optically resolved and unresolved AGNs. The immediate properties
of the catalog objects include significant correlation of X-ray and optical
fluxes, which is consistent with expectations. Also expected is the decrease of
X-ray flux toward higher redshifts. The X-ray to optical flux ratio for the
unresolved AGNs exhibits a decline toward higher redshifts, in agreement with
previous results. The resolved AGNs, however, display the opposite trend. At a
given optical brightness, X-ray fluxes of radio-quiet AGNs by a factor of 2. We
caution, however, that because of the variety of selection effects present in
both the WGACAT and the SDSS, the interpretation of any relationships based on
our sample of X-ray AGNs requires a careful analysis of these effects.
| No Label | No Label |
0705.2962 | Vanessa McBride | On the cyclotron line in Cep X-4 | astro-ph | Accreting X-ray pulsars provide us with laboratories for the study of extreme
gravitational and magnetic fields, hence accurate descriptions of their
observational properties contribute to our understanding of this group of
objects. We aim to detect a cyclotron resonance scattering feature in the
Be/X-ray binary Cep X-4 and to investigate pulse profile and spectral changes
through the outburst. Spectral fitting and timing analysis are employed to
probe the properties of Cep X-4 during an outburst in 2002 June. A previously
announced cyclotron feature at 30.7 keV is confirmed, while the source shows
spectral behaviour and luminosity related changes similar to those observed in
previous outbursts. The long-term X-ray lightcurve shows a periodicity at 20.85
d, which could be attributed to the orbit in this Be system.
| No Label | No Label |
astro-ph/9810446 | Douglas Scott | What have we already learned from the CMB? | astro-ph | The COBE satellite, and the DMR experiment in particular, was extraordinarily
successful. However, the DMR results were announced about 7 years ago, during
which time a great deal more has been learned about anisotropies in the Cosmic
Microwave Background (CMB). The CMB experiments currently being designed and
built, including long-duration balloons, interferometers, and two space
missions, promise to address several fundamental cosmological issues. We
present our evaluation of what we already know, what we are beginning to learn
now, and what the future may bring.
| No Label | No Label |
astro-ph/9803107 | Creidhe O'Sullivan | Time-Resolved Optical Observations of PSR 1509-58 | astro-ph | Using time resolved 2-dimensional aperture photometry we have established
that the optical candidate for PSR 1509-58 does not pulse. Our pulsed upper
limits (m_V = 24.3 and m_B = 25.7) put severe constraints on this being the
optical counterpart. Furthermore the colours of the candidate star are
consistent with a main sequence star at a distance of 2-4 kpc. The probability
of a chance coincidence with a normal star and the difficulty of explaining the
lack of pulsed emission leads us to conclude that this object is an
intermediate field star.
| No Label | No Label |
astro-ph/0101479 | Gerhardt Meurer | How to Correct for Dust Absorption in Starbursts | astro-ph | We review new and published results to examine how well the bolometric flux
of starbursts can be recovered from ultraviolet (UV) and optical observations.
We show that the effective absorption of starbursts can be substantial, up to
\~10 mag in the far UV, and ~5 mag in H-alpha, but apparently not as high as
some claims in the literature (several tens to a thousand mag). The bolometric
fluxes of an IUE sample of starbursts can be recovered to 0.14 dex accuracy
using the UV flux and spectral slope. However, this relationship breaks down
for Ultra Luminous Infrared Galaxies (ULIGs). The H-alpha flux combined with
the Balmer decrement can be used to predict the bolometric flux to 0.5 dex
accuracy for starbursts including most ULIGs. These results imply a foreground
screen component to the dust distribution.
| No Label | No Label |
0801.2108 | Cathie Clarke | Eccentricity growth of planetesimals in a self-gravitating
protoplanetary disc | astro-ph | We investigate the orbital evolution of planetesimals in a self-gravitating
circumstellar disc in the size regime ($\sim 1-5000$ km) where the
planetesimals behave approximately as test particles in the disc's
non-axisymmetric potential. We find that the particles respond to the
stochastic, regenerative spiral features in the disc by executing large random
excursions (up to a factor of two in radius in $\sim 1000$ years), although
typical random orbital velocities are of order one tenth of the Keplerian
speed. The limited time frame and small number of planetesimals modeled does
not permit us to discern any {\it net} direction of planetesimal migration. Our
chief conclusion is that the high eccentricities ($\sim 0.1$) induced by
interaction with spiral features in the disc is likely to be highly
unfavourable to the collisional growth of planetesimals in this size range
while the disc is in the self-gravitating regi me. Thus {\it if}, as recently
argued by Rice et al 2004, 2006, the production of planetesimals gets under way
when the disc is in the self-gravitating regime (either at smaller planetesimal
size scales, where gas drag is important, or via gravitational fragmentation of
the solid component), then the planetesimals thus produced would not be able to
grow collisionally until the disc ceased to be self-gravitating. It is unclear,
however,given the large amplitude excursions undergone by planetesimals in the
self-gravitating disc, whether they would be retained in the disc throughout
this period, or whether they would instead be lost to the central star.
| No Label | No Label |
astro-ph/0102429 | Giovanni Pinzon | Low order p-modes in a bipolytropic model of the Sun | astro-ph | Based on the Solar Standard Model we developed a solar model in hydrostatic
equilibrium using two polytropes that describes both the "radiative" and
"convective" zones of the solar interior. Then we apply small periodic and
adiabatic perturbations on this bipolytropic model in order to obtain proper
frequencies and proper functions. The frequencies obtained are in the "p-modes"
range of low order l<20 which agrees with the observational data, particularly
with the so called five minutes solar oscillations.
Key Words: Solar Standard Model, Lane-Emden, Non Radial Oscillations,
p-modes.
| No Label | No Label |
astro-ph/9907071 | Bernd Pfeiffer | Nuclear Structure Studies at ISOLDE and their Impact on the
Astrophysical r-Process | astro-ph | The focus of the present review is the production of the heaviest elements in
nature via the r-process. A correct understanding and modeling requires the
knowledge of nuclear properties far from stability and a detailed prescription
of the astrophysical environment. Experiments at CERN/ISOLDE have played a
pioneering role in exploring the characteristics of nuclear structure in terms
of masses and beta-decay properties. Initial examinations paid attention to far
unstable nuclei with magic neutron numbers related to r-process peaks, while
present activities are centered on the evolution of shell effects with the
distance from the valley of stability. We first show in site-independent
applications the effect of both types of nuclear properties on r-process
abundances. Then, we explore the results of calculations related to two
different `realistic' astrophysical sites, (i) the supernova neutrino wind and
(ii) neutron star mergers. We close with a list of remaining theoretical and
experimental challenges needed to overcome for a full understanding of the
nature of the r-process, and the role CERN/ISOLDE can play in this process.
| No Label | No Label |
astro-ph/0010361 | Chris Carilli | Astronomical Constraints on the Cosmic Evolution of the Fine Structure
Constant and Possible Quantum Dimensions | astro-ph | We present measurements of absorption by the 21cm hyperfine transition of
neutral hydrogen toward radio sources at substantial look-back times. These
data are used in combination with observations of rotational transitions of
common interstellar molecules, to set limits on the evolution of the fine
structure constant: (dot alpha)/alpha < 3.5e-15/yr to a look-back time of 4.8
Gyr. The neutral hydrogen observations employed Very Long Baseline
Interferometry in order to mitigate the substantial uncertainty arising from
the fact that observations at very different wavelengths may probe different
lines-of-site due to frequency dependent structure of the background source. We
discuss the implication of these results on theories unifying natural forces
based on compact quantum dimensions. In the context of string theory, the limit
on the secular evolution of the scale factor of these compact dimensions, R, is
(dot R)/R < 1e-15/yr. Including terrestrial and other astronomical measurements
places limits (2sigma) on slow oscillations of R from the present to the epoch
of cosmic nucleosynthesis, just seconds after the big bang, of (Delta R)/R <
1e-5.
| No Label | No Label |
astro-ph/9707318 | Sergei B. Popov | RX J0720.4--3125 as a Possible Example of the Magnetic Field Decay of
Neutron Stars | astro-ph | We studied possible evolution of the rotational period and the magnetic field
of the X-ray source RX J0720.4-3125 assuming this source to be an isolated
neutron star accreting interstellar medium. Magnetic field of the source is
estimated to be $10^6 - 10^9$ G, and it is difficult to explain observed
rotational period 8.38 s without invoking hypothesis of the magnetic field
decay. We used the model of ohmic decay of the crustal magnetic field. The
estimates of accretion rate ($10^{-14} - 10^{-16} M_\odot/yr$), velocity of the
source relative to interstellar medium ($10 - 50 $ km/s), neutron star age
($2\cdot 10^9 - 10^{10}$ yrs) are obtained.
| No Label | No Label |
astro-ph/0010355 | Rita M. Sambruna | X-ray imaging of the Seyfert 2 galaxy Circinus with Chandra | astro-ph | We present results from the zeroth-order imaging of a Chandra HETGS
observation of the nearby Seyfert 2 galaxy Circinus. Twelve X-ray sources were
detected in the ACIS-S image of the galaxy, embedded in diffuse X-ray emission.
The latter shows a prominent (~18arcsec) soft ``plume'' in the N-W direction,
coincident with the [OIII] ionization cone. The radial profiles of the
brightest X-ray source at various energies are consistent with an unresolved
(FWHM ~0.8arcsec) component, which we identify as the active nucleus, plus two
extended components with FWHMs ~ 2.3arcsec and 18arcsec, respectively. In a
radius of 3arcsec, the nucleus contributes roughly the same flux as the
extended components at the softest energies (< 2 keV). However, at harder
energies (> 2 keV), the contribution of the nucleus is dominant. The
zeroth-order ACIS spectrum of the nucleus exhibits emission lines at both soft
and hard X-rays, including a prominent Fe Kalpha line at 6.4 keV, showing that
most of the X-ray lines previously detected with ASCA originate in a compact
region (<15 pc). Based on its X-ray spectrum, we argue that the 2.3arcsec
extended component is scattered nuclear radiation from nearby ionized gas. The
large-scale extended component includes the emission from the N-W plume and
possibly from the outer starburst ring.
| No Label | No Label |
astro-ph/9912384 | August A. Muench | Modeling the Near-Infrared Luminosity Functions of Young Stellar
Clusters | astro-ph | We present the results of numerical experiments designed to evaluate the
usefulness of near-infrared luminosity functions for constraining the Initial
Mass Function (IMF) of young stellar populations. From this numerical modeling,
we find that the luminosity function of a young stellar population is
considerably more sensitive to variations in the underlying initial mass
function than to either variations in the star forming history or assumed
pre-main-sequence (PMS) mass-to-luminosity relation. To illustrate the
potential effectiveness of using the KLF of a young cluster to constrain its
IMF, we model the observed K band luminosity function of the nearby Trapezium
cluster. Our derived mass function for the Trapezium spans two orders of
magnitude in stellar mass (5 Msun to 0.02 Msun), has a peak near the hydrogen
burning limit, and has an IMF for Brown Dwarfs which steadily decreases with
decreasing mass.
| No Label | No Label |
astro-ph/0205492 | Eliot Quataert | The Magnetorotational Instability in a Collisionless Plasma | astro-ph | We consider the linear axisymmetric stability of a differentially rotating
collisionless plasma in the presence of a weak magnetic field; we restrict our
analysis to wavelengths much larger than the proton Larmor radius. This is the
kinetic version of the magnetorotational instability explored extensively as
mechanism for magnetic field amplification and angular momentum transport in
accretion disks. The kinetic calculation is appropriate for hot accretion flows
onto compact objects and for the growth of very weak magnetic fields, where the
collisional mean free path is larger than the wavelength of the unstable modes.
We show that the kinetic instability criterion is the same as in MHD, namely
that the angular velocity decrease outwards. However, nearly every mode has a
linear kinetic growth rate that differs from its MHD counterpart. The kinetic
growth rates also depend explicitly on beta, i.e., on the ratio of the gas
pressure to the pressure of the seed magnetic field. For beta ~ 1 the kinetic
growth rates are similar to the MHD growth rates while for beta >> 1 they
differ significantly. For beta >> 1, the fastest growing mode has a growth rate
of sqrt{3} Omega for a Keplerian disk, larger than its MHD counterpart; there
are also many modes whose growth rates are negligible, < beta^{-1/2} Omega <<
Omega. We provide a detailed physical interpretation of these results and show
that gas pressure forces, rather than just magnetic forces, are central to the
behavior of the magnetorotational instability in a collisionless plasma. We
also discuss the astrophysical implications of our analysis.
| No Label | No Label |
astro-ph/9911137 | Soo-Chang Rey | Multiple Stellar Populations in the Globular Cluster omega Centauri as
Tracers of a Merger Event | astro-ph | The discovery of the Sagittarius dwarf galaxy, which is being tidally
disrupted by and merging with the Milky Way, supports the view that the halo of
the Galaxy has been built up at least partially by the accretion of similar
dwarf systems. The Sagittarius dwarf contains several distinct populations of
stars, and includes M54 as its nucleus, which is the second most massive
globular cluster associated with the Milky Way. The most massive globular
cluster is omega Centauri, and here we report that omega Centauri also has
several distinct stellar populations, as traced by red-giant-branch stars. The
most metal-rich red-giant-branch stars are about 2 Gyr younger than the
dominant metal-poor component, indicating that omega Centauri was enriched over
this timescale. The presence of more than one epoch of star formation in a
globular cluster is quite surprising, and suggests that omega Centauri was once
part of a more massive system that merged with the Milky Way, as the
Sagittarius dwarf galaxy is in the process of doing now. Mergers probably were
much more frequent in the early history of the Galaxy and omega Centauri
appears to be a relict of this era.
| No Label | No Label |
0812.0546 | Martin Schroedter | Search for Primordial Black Holes with SGARFACE | astro-ph | The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) uses the
Whipple 10 m telescope to search for bursts of $\gamma$ rays. SGARFACE is
sensitive to bursts with duration from a few ns to $\sim$20 $\mu$s and with
$\gamma$-ray energy above 100 MeV. SGARFACE began operating in March 2003 and
has collected 2.2 million events during an exposure time of 2267 hours. A
search for bursts of $\gamma$ rays from explosions of primordial black holes
(PBH) was carried out. A Hagedorn-type PBH explosion is predicted to be visible
within 60 pc of Earth. Background events were caused by cosmic rays and by
atmospheric phenomena and their rejection was accomplished to a large extent
using the time-resolved images. No unambiguous detection of bursts of $\gamma$
rays could be made as the remaining background events mimic the expected shape
and time development of bursts. Upper limits on the PBH explosion rate were
derived from the SGARFACE data and are compared to previous and future
experiments. We note that a future array of large wide-field air-Cherenkov
telescopes equipped with a SGARFACE-like trigger would be able to operate
background-free with a 20 to 30 times higher sensitivity for PBH explosions.
| No Label | No Label |
astro-ph/0106509 | Mordecai-Mark Mac Low | The Distribution of Pressures in a Supernova-Driven Interstellar Medium | astro-ph | Observations have suggested substantial departures from pressure equilibrium
in the interstellar medium (ISM) in the plane of the Galaxy, even on scales
under 50 pc. Nevertheless, multi-phase models of the ISM assume at least
locally isobaric gas. The pressure then determines the density reached by gas
cooling to stable thermal equilibrium. We use two different sets of numerical
models of the ISM to examine the consequences of supernova driving for
interstellar pressures. The first set of models is hydrodynamical, and uses
adaptive mesh refinement to allow computation of a 1 x 1 x 20 kpc section of a
stratified galactic disk. The second set of models is magnetohydrodynamical,
using an independent code framework, and examines a 200 pc cubed periodic
domain threaded by magnetic fields. Both of these models show broad pressure
distributions with roughly log-normal functional forms produced by both shocks
and rarefaction waves, rather than the power-law distributions predicted by
previous work, with rather sharp thermal pressure gradients. The width of the
distribution of the logs of pressure in gas with log T < 3.9 is proportional to
the rms Mach number in that gas, while the distribution in hotter gas is
broader, but not so broad as would be predicted by the Mach numbers in that
gas. Individual parcels of gas reach widely varying points on the thermal
equilibrium curve: no unique set of phases is found, but rather a
dynamically-determined continuum of densities and temperatures. Furthermore, a
substantial fraction of the gas remains entirely out of thermal equilibrium.
Our results appear consistent with observations of interstellar pressures, and
suggest that the pressures observed in molecular clouds may be due to ram
pressure rather than gravitational confinement.
| No Label | No Label |
astro-ph/9908324 | Hiroyuki Hirashita | Cyclic Changes of Dust-to-Gas Ratio | astro-ph | We discuss the time variation of dust-to-gas mass ratio in spiral galaxies
using the multi-phase model of interstellar medium. The typical timescale of
the phase change of an interstellar gas is $\sim 10^7$--$10^8$ yr in spiral
galaxies. Since the phase transition changes the filling factor of the cold gas
where the dust growth occurs, the dust growth rate varies on that timescale. In
order to examine the response of the dust-to-gas ratio to the phase transition,
we construct a model of the time evolution of the dust-to-gas ratio. We adopt
the three phase model for the interstellar gas and the Ikeuchi-Tomita model for
the mass exchange among the phases. According to the model, three types of
solutions are possible: [1] all the gas is transformed to a hot gas; [2] a
stable stationary state of three phases is realized; [3] the filling factor of
each phase cyclically changes. For each of the three types of solutions, the
dust-to-gas ratio behaves as follows: [1] almost all the dust is destroyed (the
dust-to-gas ratio becomes $\sim 0$); [2] the dust-to-gas ratio converges to a
stationary state; [3] the dust-to-gas ratio varies cyclically in response to
the phase transition. In the case of [3], the amplitude of the variation of the
dust-to-gas ratio is large (nearly an order of magnitude) if the dust growth
timescale is shorter than the phase transition timescale. This condition is
easily satisfied in spiral galaxies. However, it is difficult for dwarf
galaxies to realize the condition because their small metallicity makes the
dust growth timescale long.
| No Label | No Label |
astro-ph/0107358 | L. V. E. Koopmans | The Kinematics of High Proper Motion Halo White Dwarfs | astro-ph | We analyse the kinematics of the entire spectroscopic sample of 99 recently
discovered high proper-motion white dwarfs by Oppenheimer et al. using a
maximum-likelihood analysis, and discuss the claim that the high-velocity white
dwarfs are members of a halo population with a local density at least ten times
greater than traditionally assumed. We argue that the observations, as
reported, are consistent with the presence of an almost undetected thin disc
plus a thick disc, with densities as conventionally assumed. In addition, there
is a kinematically distinct, flattened, halo population at the more than 99%
confidence level. Surprisingly, the thick disc and halo populations are
indistinguishable in terms of luminosity, color and apparent age (1-10 Gyr).
Adopting a bimodal, Schwarzschild model for the local velocity ellipsoid, with
the ratios sigma_U:sigma_V:sigma_W=1:2/3:1/2, we infer radial velocity
dispersions of sigma_U=62(+8/-10) km/s and 150(+80/-40) km/s (90% C.L.) for the
local thick disc and halo populations, respectively. The thick disc result
agrees with the empirical relation between asymmetric drift and radial velocity
dispersion, inferred from local stellar populations. The local thick-disc plus
halo density of white dwarfs is n^{td+h}=(1.9+-0.5)x10^-3 pc^-3 (90% C.L.), of
which n^{h}=1.1(+2.1/-0.7)x10^-4 pc^-3 (90% C.L.) belongs to the halo, a
density about five times higher than previously thought. (Abridged)
| No Label | No Label |
astro-ph/9906400 | Dong Lai | Growth of Perturbation in Gravitational Collapse and Accretion | astro-ph | When a self-gravitating spherical gas cloud collapses or accretes onto a
central mass, the inner region of the cloud develops a density profile
$\rho\propto r^{-3/2}$ and the velocity approaches free-fall. We show that in
this region, nonspherical perturbations grow with decreasing radius. In the
linear regime, the tangential velocity perturbation increases as $r^{-1}$,
while the Lagrangian density perturbation, $\Delta\rho/\rho$, grows as
$r^{-1/2}$. Faster growth occurs if the central collapsed object maintains a
finite multiple moment, in which case $\Delta\rho/\rho$ increases as $r^{-l}$,
where $l$ specifies the angular degree of the perturbation. These scaling
relations are different from those obtained for the collapse of a homogeneous
cloud. Our numerical calculations indicate that nonspherical perturbations are
damped in the subsonic region, and that they grow and approach the asymptotic
scalings in the supersonic region. The implications of our results to
asymmetric supernova collapse and to black hole accretion are briefly
discussed.
| No Label | No Label |
astro-ph/0103078 | Laurent Cambresy | The Cosmic Infrared Background at 1.25 microns and 2.2 microns using
DIRBE and 2MASS: a contribution not due to galaxies ? | astro-ph | Using the 2MASS 2nd Incremental Data Release and the Zodiacal-Subtracted
Mission Average maps of COBE/DIRBE, we estimate the cosmic background in the J
(1.25 micron) and K (2.2 microns) bands using selected areas representing 550
square degrees of sky. We find a J background of 22.9 \pm 7.0 kJy/sr (54.0 \pm
16.8 nW/m2/sr) and a K background of 20.4 \pm 4.9 kJy/sr (27.8 \pm 6.7
nW/m2/sr). This large scale study shows that the main uncertainty comes from
the residual zodiacal emission. The cosmic background we obtain is
significantly higher than integrated galaxy counts (3.6 \pm 0.8 kJy/sr and 5.3
\pm 1.2 kJy/sr for J and K, respectively), suggesting either an increase of the
galaxy luminosity function for magnitudes fainter than 30 or the existence of
another contribution to the cosmic background from primeval stars, black holes,
or relic particle decay.
| No Label | No Label |
astro-ph/9807304 | David Kornreich | A Photometric Method for Quantifying Asymmetries in Disk Galaxies | astro-ph | A photometric method for quantifying deviations from axisymmetry in optical
images of disk galaxies is applied to a sample of 32 face-on and nearly face-on
spirals. The method involves comparing the relative fluxes contained within
trapezoidal sectors arranged symmetrically about the galaxy center of light,
excluding the bulge and/or barred regions. Such a method has several advantages
over others, especially when quantifying asymmetry in flocculent galaxies.
Specifically, the averaging of large regions improves the signal-to-noise in
the measurements; the method is not strongly affected by the presence of spiral
arms; and it identifies the kinds of asymmetry that are likely to be
dynamically important. Application of this "method of sectors" to R-band images
of 32 disk galaxies indicates that about 30% of spirals show deviations from
axisymmetry at the 5-sigma level.
| No Label | No Label |
astro-ph/0109212 | Stefan Immler | X-Ray Detection of a Pre-Supernova Evolution for the SN 1993J Progenitor | astro-ph | We report on the first detection of a pre-supernova (SN) evolution in the
X-ray regime. The results are based on ROSAT observations of SN 1993J ranging
from six days to five years after the outburst. The X-ray observations are used
to probe the SN shell interaction with the ambient circumstellar matter (CSM).
After exploring various scenarios that might explain the observed X-ray
lightcurve with a t^-0.27 rate of decline, we present a coherent picture in
terms of the interaction of the SN shock front with the CSM deposited by the
progenitor's stellar wind. During the observed period, the SN shell has reached
a radius of 3x10^17 cm from the site of the explosion, corresponding to ~10^4
years in the progenitors stellar wind history. Our analysis shows that the
mass-loss rate of the progenitor has decreased constantly from \dot{M} =
4x10^-4 to 4x10^-5 M_sun/yr (v_w/10 km/s) during the late stage of the
evolution. Assuming a spherically symmetric expansion, the circumstellar matter
density profile is found to be significantly flatter (\rho_csm \propto r^-1.63)
than expected for a constant mass-loss rate and constant wind velocity profile
(r^-2). The observed evolution either reflects a decrease in the mass-loss
rate, an increase in the wind speed or a combination of both, indicating that
the progenitor likely was making a transition from the red to the blue
supergiant phase during the late stage of its evolution.
| No Label | No Label |
astro-ph/0309569 | Adam Krawiec | Constraints on a Cardassian model from SNIa data - revisited | astro-ph | We discuss some observational constraints resulting only from SNIa
observations, imposed on the behavior of the original flat Cardassian model,
and its extension with the curvature term included. We test the models using
the Perlmutter SN Ia data as well as the new Knop and Tonry samples. We
estimate the Cardassian model parameters using the best-fitting procedure and
the likelihood method. In the fitting procedure we use the density variables
for matter, Cardassian fluid and curvature, and include the errors in redshift
measurements. For the Perlmutter sample in the non-flat Cardassian model we
obtain the high or normal matter density universe ($\Omega_{m,0} \ge 0.3$),
while for the flat Cardassian model we have the high density universe. For
sample A in the high density universe we also find the negative values of
estimates of $n$ which can be interpreted as the phantom fluid effect. For the
likelihood method we get that a nearly flat universe is preferred. We show
that, if we assume that the matter density is 0.3, then $n \approx 0$ in the
flat Cardassian model, which corresponds to the Perlmutter model with the
cosmological constant. Testing with the Knop and Tonry SN Ia samples show no
significant differences.
| No Label | No Label |
astro-ph/0302223 | Janet L. Weiland | First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations:
Tests of Gaussianity | astro-ph | We present limits to the amplitude of non-Gaussian primordial fluctuations in
the WMAP 1-year cosmic microwave background sky maps. A non-linear coupling
parameter, f_NL, characterizes the amplitude of a quadratic term in the
primordial potential. We use two statistics: one is a cubic statistic which
measures phase correlations of temperature fluctuations after combining all
configurations of the angular bispectrum. The other uses the Minkowski
functionals to measure the morphology of the sky maps. Both methods find the
WMAP data consistent with Gaussian primordial fluctuations and establish
limits, -58<f_NL<134, at 95% confidence. There is no significant frequency or
scale dependence of f_NL. The WMAP limit is 30 times better than COBE, and
validates that the power spectrum can fully characterize statistical properties
of CMB anisotropy in the WMAP data to high degree of accuracy. Our results also
validate the use of a Gaussian theory for predicting the abundance of clusters
in the local universe. We detect a point-source contribution to the bispectrum
at 41 GHz, b_src = (9.5+-4.4) X 1e-5 uK^3 sr^2, which gives a power spectrum
from point sources of c_src = (15+-6) X 1e-3 uK^2 sr in thermodynamic
temperature units. This value agrees well with independent estimates of source
number counts and the power spectrum at 41 GHz, indicating that b_src directly
measures residual source contributions.
| No Label | No Label |
0810.1676 | Filippo D'Ammando | AGILE detection of intense gamma-ray emission from the blazar PKS
1510-089 | astro-ph | We report the detection by the AGILE (Astro-rivelatore Gamma a Immagini
LEggero) satellite of an intense gamma-ray flare from the source AGL
J1511-0909, associated with the powerful quasar PKS 1510-089, during ten days
of observations from 23 August to 1 September 2007. During the observation
period, the source was in optical decrease following a flaring event monitored
by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope
(WEBT). The simultaneous gamma-ray, optical, and radio coverage allows us to
study the spectral energy distribution and the theoretical models based on the
synchrotron and inverse Compton (IC) emission mechanisms. AGILE observed the
source with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the
hard X-ray imager Super-AGILE sensitive in the 30 MeV - 50 GeV and 18 - 60 keV
bands, respectively. Between 23 and 27 August 2007, AGILE detected gamma-ray
emission from PKS 1510-089 when this source was located about 50 degrees
off-axis, with an average flux of (270 +/- 65) x 10^{-8} photons cm^{-2} s^{-1}
for photon energy above 100 MeV. In the following period, 28 August - 1
September, after a satellite re-pointing, AGILE detected the source at about 35
degrees off-axis, with an average flux (E > 100 MeV) of (195 +/- 30) x 10^{-8}
photons cm^{-2} s^{-1}. No emission was detected by Super-AGILE, with a 3-sigma
upper limit of 45 mCrab in 200 ksec. The spectral energy distribution is
modelled with a homogeneous one-zone synchrotron self Compton (SSC) emission
plus contributions by external photons: the SSC emission contributes primarily
to the X-ray band, whereas the contribution of the IC from the external disc
and the broad line region match the hard gamma-ray spectrum observed.
| No Label | No Label |
astro-ph/0507195 | Peng Wang | Virialization in Dark Energy Cosmology | astro-ph | We discuss the issue of energy nonconservation in the virialzation process of
spherical collapse model with homogeneous dark energy. We propose an
approximation scheme to find the virialization radius. By comparing various
schemes and estimating the parameter characterizing the ratio of dark energy to
dark matter at the turn-around time, we conclude that the problem of energy
nonconservation may have sizable effects in fitting models to observations.
| No Label | No Label |
astro-ph/0302583 | Andrew Willes | Electron-cyclotron maser emission from white-dwarf pairs and white-dwarf
planetary systems | astro-ph | By analogy to Jovian radio emissions powered by the electromagnetic
interaction between Jupiter and its moons, we propose that close
magnetic-nonmagnetic white-dwarf pairs and white-dwarf planetary systems are
strong radio sources. A simple model is developed to predict the flux densities
of radio emission generated by a loss-cone-driven electron-cyclotron maser. The
radio emission from these systems has high brightness temperatures, is highly
polarized, and varies on a periodic cycle following the orbital rotation.
Masers from magnetic-nonmagnetic white-dwarf pairs, with orbital periods <10
min, are expected to be detectable over a wide range of radio frequencies.
Terrestrial planets in close orbits about magnetic white dwarfs, with orbital
periods $\la 30$ hr, can also produce detectable radio emission, thus providing
a means to identify Earth-sized extrasolar planets.
| No Label | No Label |
astro-ph/0507237 | Hu Zhan | Optimal Softening for N-Body Halo Simulations | astro-ph | We propose to determine the optimal softening length in N-body halo
simulations by minimizing the ensemble-average acceleration error at a small
radius r0. This strategy ensures that the error never exceeds the optimal value
beyond r0. Furthermore, we derive semi-analytic formulae for calculating the
acceleration error due to the discreteness of particles and softened gravity,
which are validated by direct N-body force calculations. We estimate that
current state-of-the-art halo simulations suffer >~6% acceleration error at 1%
of the halo virial radius. The error grows rapidly toward the center and could
contribute significantly to the uncertainties of inner halo properties.
| No Label | No Label |
0802.2509 | Ilaria Biscardi | Optical Surface Brightness Fluctuations of shell galaxies towards 100
Mpc | astro-ph | We measure F814W Surface Brightness Fluctuations (SBF) for a sample of
distant shell galaxies with radial velocities ranging from 4000 to 8000 km/s.
The distance at galaxies is then evaluated by using the SBF method. For this
purpose, theoretical SBF magnitudes for the ACS@HST filters are computed for
single burst stellar populations covering a wide range of ages (t=1.5-14 Gyr)
and metallicities (Z=0.008-0.04). Using these stellar population models we
provide the first $\bar{M}_{F814W}$ versus $(F475W-F814W)_0$ calibration and we
extend the previous I-band versus $(B-I)_0$ color relation to colors
$(B-I)_{0}\leq 2.0$ mag. Coupling our SBF measurements with the theoretical
calibration we derive distances with a statistical uncertainty of $\sim 8%$,
and systematic error of $\sim 6 %$. The procedure developed to analyze data
ensures that the indetermination due to possible unmasked residual shells is
well below $\sim 12 %$. The results suggest that \emph{optical} SBFs can be
measured at $d \geq 100 Mpc$ with ACS@HST imaging. SBF-based distances coupled
with recession velocities corrected for peculiar motion, allow us obtain $H_{0}
= 76 \pm 6$ (statistical) $\pm 5$ (systematic) km/s/Mpc.
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astro-ph/9908107 | Scott T. Kay | Parameter Tests Within Cosmological Simulations of Galaxy Formation | astro-ph | Numerical simulations of galaxy formation require a number of parameters.
Some of these are intrinsic to the numerical integration scheme (eg the
timestep), while others describe the physical model (eg the gas metallicity).
In this paper, we present results of a systematic exploration of the effects of
varying a subset of these parameters on simulations of galaxy formation. We use
N-body and ``Smoothed Particle Hydrodynamics'' techniques to follow the
evolution of cold dark matter and gas in a small volume. We compare a fiducial
model to 24 different simulations, in which one parameter at a time is varied,
focussing on properties such as the relative fraction of hot and cold gas, and
the abundance and masses of galaxies. We find that for reasonable choices of
numerical values, many parameters have relatively little effect on the
galaxies, with the notable exception of the parameters that control the
resolution of the simulation and the efficiency with which gas cools.
| No Label | No Label |
astro-ph/0203345 | Roberto Soria | XMM-Newton observations of the spiral galaxy M74 (NGC 628) | astro-ph | The face-on spiral galaxy M74 (NGC 628) was observed by XMM on 2002 February
2. In total, 21 sources are found in the inner 5' from the nucleus (after
rejection of a few sources associated to foreground stars). Hardness ratios
suggest that about half of them belong to the galaxy. The higher-luminosity end
of the luminosity function is fitted by a power-law of slope -0.8. This can be
interpreted as evidence of ongoing star formation, in analogy with the
distributions found in disks of other late-type galaxies. A comparison with
previous Chandra observations reveals a new ultraluminous X-ray transient (L_x
\~ 1.5 x 10^39 erg/s in the 0.3--8 keV band) about 4' North of the nucleus. We
find another transient black-hole candidate (L_x ~ 5 x 10^38 erg/s) about 5'
North-West of the nucleus. The UV and X-ray counterparts of SN 2002ap are also
found in this XMM observation.
| No Label | No Label |
astro-ph/0108231 | Edward M. Drobyshevski | Detection of several daemon populations in Earth-crossing orbits | astro-ph | Detection of negative daemons, DArk Electric Matter Objects, viz. Planckian
supermassive (~2*10^-5 g) particles, whose population has been detected in
March 2000 to populate near-Earth, almost circular, heliocentric orbits
(NEACHOs), is being continued. The NEACHO objects hit the Earth with a velocity
~10-15 km/s. The results of these and new experiments (April-June, 2001) are
now processed taking into account the scintillation shape depending on the
magnitude and sign of the velocity of the daemons crossing our detector. The
data accumulated during the time of the experiment and processed in this way
reveal also the presence of (1) a high-velocity (~35-50 km/s) daemon population
whose objects can be related to a population in the Galactic disk and/or that
in strongly elongated, Earth-crossing heliocentric orbits (SEECHOs), as well as
(2) a low-velocity (~3-10 km/s) population in geocentric Earth-surface-crossing
orbits (GESCOs), whose objects traverse repeatedly the Earth to suffer a
decrease in velocity by ~30-40% in a month in the process. An evolutionary
relation between all these three (four?) populations is discussed. Assumptions
concerning their manifestations in further observations are put forward. An
analysis of possible interaction processes of daemons, which may have different
velocities and directions of motion, with the detector components [ZnS(Ag)
layers, 0.3-mm thick tinned-iron sheets etc.] on the atomic (emission of Auger
electrons) and nuclear (nucleon evaporation from a nucleus excited in the
capture and, subsequently, the decay of its protons) levels has permitted
estimation of some characteristic times. In particular, the decay time of a
daemon-containing proton is ~10^-6 s.
| No Label | No Label |
astro-ph/0404139 | Charles Dermer | Nonthermal Radiation Processes in X-ray Jets | astro-ph | Analytic approximations for synchrotron, synchrotron self-Compton (SSC), and
external Compton (EC) processes are used to constrain model parameters for knot
and hot-spot emission in extended jets of radio galaxies. Equipartition
formulas are derived that relate the Doppler factor $\delta$ and comoving
magnetic field $B$ assuming a nonthermal synchrotron origin of the radio
emission, and synchrotron, SSC and EC origins of the X-ray emission.
Expressions are also derived for $\delta$ and $B$ that minimize the total jet
powers of the emitting region in synchrotron, SSC and EC models for the X-ray
emission. The results are applied to knot WK7.8 of PKS 0637-752. Predictions to
test two-component synchrotron and EC models are made for {\it Chandra} and
{\it GLAST}.
| No Label | No Label |
0706.0193 | Joachim Moortgat | Particle-in-cell simulations of fast collisionless reconnection in
gamma-ray burst outflows | astro-ph | We present preliminary results of particle-in-cell simulations of
collisionless magnetic reconnection for conditions that apply to magnetically
dominated pair plasma jets such as those in gamma-ray bursts. We find similar
behaviour to previous authors but with reduced reconnection efficiency. This
results because we include the full electromagnetic field dynamically and allow
electric field fluctuations to grow. Although weak, these fluctuations impede
early x-point formation by periodically decelerating and even reversing the
inflow.
| No Label | No Label |
0708.2158 | Olivier Mousis | Clathrate hydrates as a sink of noble gases in Titan's atmosphere | astro-ph | We use a statistical thermodynamic approach to determine the composition of
clathrate hydrates which may form from a multiple compound gas whose
composition is similar to that of Titan's atmosphere. Assuming that noble gases
are initially present in this gas phase, we calculate the ratios of xenon,
krypton and argon to species trapped in clathrate hydrates. We find that these
ratios calculated for xenon and krypton are several orders of magnitude higher
than in the coexisting gas at temperature and pressure conditions close to
those of Titan's present atmosphere at ground level. Furthermore we show that,
by contrast, argon is poorly trapped in these ices. This trapping mechanism
implies that the gas-phase is progressively depleted in xenon and krypton when
the coexisting clathrate hydrates form whereas the initial abundance of argon
remains almost constant. Our results are thus compatible with the deficiency of
Titan's atmosphere in xenon and krypton measured by the {\it Huygens} probe
during its descent on January 14, 2005. However, in order to interpret the
subsolar abundance of primordial Ar also revealed by {\it Huygens}, other
processes that occurred either during the formation of Titan or during its
evolution must be also invoked.
| No Label | No Label |
astro-ph/0310027 | Dirk Grupe | A Complete Sample of Soft X-ray Selected AGN: I. The Data | astro-ph | We present the optical spectra and simple statistical analysis for a complete
sample of 110 soft X-ray selected AGN. About half of the sources are
Narrow-Line Seyfert 1 galaxies (NLS1s), which have the steepest X-ray spectra,
strongest FeII emission and slightly weaker [OIII]5007 emission than broad line
Seyfert 1s (BLS1s).
Kolmogorov Smirnov tests show that NLS1s and BLS1s have clearly different
distributions of the X-ray spectral slope, X-ray short-term variability, and
FeII equivalent widths and luminosity and FeII/H-beta ratios. The differences
in the [OIII]/H-beta and [OIII] equivalent widths are only marginal. We found
no significant differences between NLS1s and BLS1s in their rest frame 0.2-2.0
X-ray luminosities, rest frame 5100A monochromatic luminosities, bolometric
luminosities, redshifts, and their H$\beta$ equivalent widths.
| No Label | No Label |
astro-ph/0308353 | Tod E. Strohmayer | X-ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338 | astro-ph | Since the discovery of the accreting millisecond pulsar XTE J1814-338 a total
of 27 thermonuclear bursts have been observed from the source with the
Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer
(RXTE). Spectroscopy of the bursts, as well as the presence of continuous burst
oscillations, suggests that all but one of the bursts are sub-Eddington. The
remaining burst has the largest peak bolometric flux of 2.64 x E^-8
erg/sec/cm^2, as well as a gap in the burst oscillations, similar to that seen
in Eddington limited bursts from other sources. Assuming this burst was
Eddington limited we obtain a source distance of about 8 kpc. All the bursts
show coherent oscillations at the 314.4 Hz spin frequency. The burst
oscillations are strongly frequency and phase locked to the persistent
pulsations. Only two bursts show evidence for frequency drift in the first few
seconds following burst onset. In both cases the initial drift corresponds to a
spin down of a few tenths of a Hz. The large oscillation amplitude during the
bursts confirms that the burst flux is modulated at the spin frequency. We
detect, for the first time, a significant first harmonic component in burst
oscillations. The ratio of countrate in the first harmonic to that in the
fundamental can be > 0.25 and is, on average, less than that of the persistent
pulsations. If the pulsations result from a single bright region on the
surface, the harmonic strength suggests the burst emission is beamed, perhaps
due to a stronger magnetic field than in non-pulsing LMXBs. Alternatively, the
harmonic content could result from a geometry with two bright regions.
| No Label | No Label |
astro-ph/0612286 | Sherri Honza | Structural Phases of Bounded Three-Dimensional Screened Coulomb Clusters
(Finite Yukawa System) | astro-ph | The formation of three-dimensional (3D) dust clusters within a complex plasma
modeled as a spatially confined Yukawa system is simulated using the box_tree
code. Similar to unscreened Coulomb clusters, the occurrence of concentric
shells with characteristic occupation numbers was observed. Both the occupation
numbers and radii were found to depend on the Debye length. Ground and low
energy meta-stable states of the shielded 3D Coulomb clusters were determined
for 4<N<20. The structure and energy of the clusters in different states was
analyzed for various Debye lengths. Structural phase transitions, including
inter-shell structural phase transitions and intra-shell structural phase
transitions, were observed for varying Debye length and the critical value for
transitions calculated.
| No Label | No Label |
astro-ph/0103376 | C. R. Kerton | A Submillimeter View of Star Formation Near the HII Region KR 140 | astro-ph | We present the results of 450 and 850 micron continuum mapping of the HII
region KR 140 using the SCUBA instrument on the JCMT. KR 140 is a small (5.7 pc
diameter) HII region at a distance of 2.3+/-0.3 kpc. Five of the six IRAS point
sources near KR 140 were mapped in this study. Our analysis shows that two of
these IRAS sources are embedded late B type stars lying well outside the HII
region, two are a part of the dust shell surrounding the HII region, and one is
the combined emission from an ensemble of smaller sources unresolved by IRAS.
We have discovered a number of relatively cold submillimeter sources not
visible in the IRAS data, ranging in size from 0.2 to 0.7 pc and in mass from
0.5 to 130 Msun. The distribution of masses for all sources is well
characterized by a power law N(>M) ~ M^{-alpha} with alpha = 0.5 +/- 0.04, in
agreement with the typical mass function for clumped structures of this scale
in molecular clouds. Several of the submillimeter sources are found at the
HII-molecular gas interface and have probably been formed as the result of the
expansion of the HII region. Many of the submillimeter sources we detect are
gravitationally bound and most of these follow a mass-size relationship
expected for objects in virial equilibrium with non-thermal pressure support.
Upon the loss of non-thermal support they could be sites of star formation.
Along with the two B stars that we have identified as possible cluster members
along with VES 735, we argue that five nearby highly-reddened stars are in a
pre-main-sequence stage of evolution.
| No Label | No Label |
0802.3978 | Elisabetta Semboloni | Sources of contamination to weak lensing three-point statistics:
constraints from N-body simulations | astro-ph | We investigate the impact of the observed correlation between a galaxies
shape and its surrounding density field on the measurement of third order weak
lensing shear statistics. Using numerical simulations, we estimate the
systematic error contribution to a measurement of the third order moment of the
aperture mass statistic (GGG) from three-point intrinsic ellipticity
correlations (III), and the three-point coupling between the weak lensing shear
experienced by distant galaxies and the shape of foreground galaxies (GGI and
GII). We find that third-order weak lensing statistics are typically more
strongly contaminated by these physical systematics compared to second-order
shear measurements, contaminating the measured three-point signal for
moderately deep surveys with a median redshift z_m ~ 0.7 by ~ 15%. It has been
shown that accurate photometric redshifts will be crucial to correct for this
effect, once a model and the redshift dependence of the effect can be
accurately constrained. To this end we provide redshift-dependent fitting
functions to our results and propose a new tool for the observational study of
intrinsic galaxy alignments. For a shallow survey with z_m ~ 0.4 we find III to
be an order of magnitude larger than the expected cosmological GGG shear
signal. Compared to the two-point intrinsic ellipticity correlation which is
similar in amplitude to the two-point shear signal at these survey depths,
third order statistics therefore offer a promising new way to constrain models
of intrinsic galaxy alignments. Early shallow data from the next generation of
very wide weak lensing surveys will be optimal for this type of study.
| No Label | No Label |
astro-ph/0007223 | R. J. Wilman | Molecular hydrogen emission in Cygnus A | astro-ph | We present J, H and K-band spectroscopy of Cygnus A, spanning 1.0-2.4 micron
in the rest-frame and hence several rovibrational H2, H recombination and
[FeII] emission lines. The lines are spatially extended by up to 6kpc from the
nucleus, but their distinct kinematics indicate that the three groups (H, H2
and [FeII]) are not wholly produced in the same gas. The broadest line,
[FeII]1.644, exhibits a non-gaussian profile with a broad base (FWHM=1040
km/s), perhaps due to interaction with the radio source. Extinctions to the
line-emitting regions substantially exceed earlier measurements based on
optical H recombination lines.
Hard X-rays from the quasar nucleus are likely to dominate the excitation of
the H2 emission. The results of Maloney, Hollenbach and Tielens (1996) are thus
used to infer the total mass of gas in H2 v=1-0 S(1)-emitting clouds as a
function of radius, for gas densities of 10^3 and 10^5 cm^-3, and stopping
column densities N_H=10^22-10^24 cm^-2. Assuming azimuthal symmetry, at least
2.3E8 Msun of such material is present within 5kpc of the nucleus, if the
line-emitting clouds see an unobscured quasar spectrum. Alternatively, if the
bulk of the X-ray absorption to the nucleus inferred by Ueno et al. (1994)
arises in a circumnuclear torus, the implied gas mass rises to 10^10 Msun. The
latter plausibly accounts for 10^9 yr of mass deposition from the cluster
cooling flow, for which Mdot \simeq 10 Msun/yr within this radius.
| No Label | No Label |
astro-ph/0703070 | Stuart Wyithe | Biased Reionisation and Non-Gaussianity in Redshifted 21cm Intensity
Maps of the Reionisation Epoch | astro-ph | Spatial dependence in the statistics of redshifted 21cm fluctuations promises
to provide the most powerful probe of the reionisation epoch. In this paper we
consider the second and third moments of the redshifted 21cm intensity
distribution using a simple model that accounts for galaxy bias during the
reionisation process. We demonstrate that skewness in redshifted 21cm maps
should be substantial throughout the reionisation epoch and on all angular
scales, owing to the effects of galaxy bias which leads to early reionisation
in over-dense regions of the IGM. The variance (or power-spectrum) of 21cm
fluctuations will exhibit a minimum in redshift part way through the
reionisation process, when the global ionisation fraction is around 50%. This
minimum is generic, and is due to the transition from 21cm intensity being
dominated by over-dense too under-dense regions as reionisation progresses. We
show that the details of the reionisation history, including the presence of
radiative feedback are encoded in the evolution of the auto-correlation and
skewness functions with redshift and mean IGM neutral fraction. We discuss the
detection of skewness by first generation instruments, and conclude that the
Mileura Widefield Array - Low Frequency Demonstrator will have sufficient
sensitivity to detect skewness on a range of angular scales at redshifts near
the end of reionisation, while a subsequent instrument of 10 times the
collecting area could map out the evolution of skewness in detail. The
observation of a minimum in variance during the reionisation history, and the
detection of skewness would both provide important confirmation of the
cosmological origin of redshifted 21cm intensity fluctuations.
| No Label | No Label |
astro-ph/0005085 | Martin White | The redshift space power spectrum in the halo model | astro-ph | Recently there has been a lot of attention focussed on a virialized
halo-based approach to understanding the properties of the matter and galaxy
power spectrum. We show that this model allows a natural treatment of the large
and small scale redshift space distortions, which we develop here, which
extends the pedagogical value of the approach.
| No Label | No Label |
astro-ph/0402127 | Sachindra Naik | Timing and spectral studies of the transient X-ray pulsar EXO
053109-6609.2 with ASCA and Beppo-SAX | astro-ph | We report timing and spectral properties of the transient Be X-ray pulsar EXO
053109--6609.2 studied using observations made with the ASCA and BeppoSAX
observatories. Though there must have been at least one spin-down episode of
the pulsar since its discovery, the new pulse period measurements show a
monotonic spin-up trend since 1996. The pulse profile is found to have marginal
energy dependence. There is also evidence for strong luminosity dependence of
the pulse profile, a single peaked profile at low luminosity that changes to a
double peaked profile at high luminosity. This suggests a change in the
accretion pattern at certain luminosity level. The X-ray spectrum is found to
consist of a simple power-law with photon index in the range of 0.4--0.8. At
high intensity level the spectrum also shows presence of weak iron emission
line.
| No Label | No Label |
astro-ph/0308238 | A. J. Barger | The Changing AGN Population | astro-ph | We investigate how the fraction of broad-line sources in the AGN population
changes with X-ray luminosity and redshift. We first construct the rest-frame
hard-energy (2-8 keV) X-ray luminosity function (HXLF) at z=0.1-1 using Chandra
Lockman Hole-Northwest wide-area data, Chandra Deep Field-North 2 Ms data,
other Chandra deep field data, and the ASCA Large Sky Survey data. We find that
broad-line AGNs dominate above 3e43 ergs/s and have a mean luminosity of 1.3e44
ergs/s. Type II AGNs can only become an important component of the X-ray
population at Seyfert-like X-ray luminosities. We then construct z=0.1-0.5 and
z=0.5-1 HXLFs and compare them with both the local HXLF measured from HEAO-1 A2
survey data and the z=1.5-3 HXLF measured from soft-energy (0.5-2 keV) Chandra
and ROSAT data. We find that the number density of >1e44 ergs/s sources
(quasars) steadily declines with decreasing redshift, while the number density
of 1e43-1e44 ergs/s sources peaks at z=0.5-1. Strikingly, however, the number
density of broad-line AGNs remains roughly constant with redshift while their
average luminosities decline at the lower redshifts, showing another example of
cosmic downsizing.
| No Label | No Label |
0809.5054 | Joshua Eisner | Spatially Resolved Spectroscopy of Sub-AU-Sized Regions of T Tauri and
Herbig Ae/Be Disks | astro-ph | We present spatially resolved near-IR spectroscopic observations of 15 young
stars. Using a grism spectrometer behind the Keck Interferometer, we obtained
an angular resolution of a few milli-arcseconds and a spectral resolution of
230, enabling probes of both gas and dust in the inner disks surrounding the
target stars. We find that the angular size of the near-IR emission typically
increases with wavelength, indicating hot, presumably gaseous material within
the dust sublimation radius. Our data also clearly indicate Brackett-gamma
emission arising from hot hydrogen gas, and suggest the presence of water vapor
and carbon monoxide gas in the inner disks of several objects. This gaseous
emission is more compact than the dust continuum emission in all cases. We
construct simple physical models of the inner disk and fit them to our data to
constrain the spatial distribution and temperature of dust and gas emission
components.
| No Label | No Label |
astro-ph/0409122 | Robin Barnard | Black hole hunting in the Andromeda Galaxy | astro-ph | We present a new technique for identifying stellar mass black holes in low
mass X-ray binaries (LMXBs), and apply it to XMM-Newton observations of M31. We
examine X-ray time series variability seeking power density spectra (PDS)
typical of LMXBs accreting at a low accretion rate (which we refer to as Type A
PDS); these are very similar for black hole and neutron star LMXBs. Galactic
neutron star LMXBs exhibit Type A PDS at low luminosities (~10^36--10^37 erg/s)
while black hole LMXBs can exhibit them at luminosities >10^38 erg/s. We
propose that Type A PDS are confined to luminosities below a critical fraction
of the Eddington limit, $l_c$ that is constant for all LMXBs; we have examined
asample of black hole and neutron star LMXBs and find they are all consistent
with $l_c$ = 0.10+/-0.04 in the 0.3--10 keV band. We present luminosity and PDS
data from 167 observations of X-ray binaries in M31 that provide strong support
for our hypothesis. Since the theoretical maximum mass for a neutron star is
\~3.1 M_Sun, we therefore assert that any LMXB that exhibits a Type A PDS at a
0.3--10 keV luminosity greater than 4 x 10^37 erg/s is likely to contain a
black hole primary. We have found eleven new black hole candidates in M31 using
this method. We focus on XMM-Newton observations of RX J0042.4+4112, an X-ray
source in M31 and find the mass of the primary to be 7+/-2 M_Sun, if our
assumptions are correct. Furthermore, RX J0042.4+4112 is consistently bright in
\~40 observations made over 23 years, and is likely to be a persistently bright
LMXB; by contrast all known Galactic black hole LMXBs are transient. Hence our
method may be used to find black holes in known, persistently bright Galactic
LMXBs and also in LMXBs in other galaxies.
| No Label | No Label |
astro-ph/0701639 | Silvia Pellegrini dr. | A deep Chandra look at the low L_B elliptical NGC821: X-ray binaries, a
galactic wind and emission at the nucleus | astro-ph | The relatively nearby (distance=24.1 Mpc) elliptical galaxy NGC821, hosting a
central massive black hole but inactive at all wavelengths, was observed with
Chandra for a total exposure of 230 ksec, to search for nuclear emission and
gas available for accretion. Within its optical image, 41 sources were
detected, with spectral properties typical of low mass X-ray binaries (LMXBs).
The fractions of LMXBs in the field and in globular clusters were determined,
together with their X-ray luminosity function (XLF) down to L(0.3-8
keV)=2\times 10^{37} erg/s. At the galactic center a source of L(0.3-8
keV)=6\times 10^{38} erg/s was detected for the first time, slightly extended.
Its spectral shape is quite hard (\Gamma=1.49^{+0.14}_{-0.13}), without
intrinsic absorption. It is surrounded by three sources with spectral shape
typical of LMXBs and luminosities on the brightest end of the XLF. One is
consistent with being pointlike; the others could be the superposition of few
point sources and/or truly diffuse emission, with one resembling a jet-like
feature. Diffuse emission was detected out to R\sim 30'', and comes mostly from
unresolved LMXBs, with a minor contribution from other types of stellar
sources. Different lines of investigation consistently provide no evidence for
hot gas. Hydrodynamical simulations show that stellar mass losses are driven
out of NGC821 in a wind sustained by type Ia supernovae, but also hot accreting
gas within a very small inner region. A companion paper presents further
observational results from $Spitzer$ and the VLA, and possible accretion
modalities for this central massive black hole.
| No Label | No Label |
astro-ph/0308128 | J. M. Barr | The cluster environments of radio-loud quasars at 0.6 < z < 1.1 | astro-ph | We have carried out multicolour imaging of a complete sample of radio-loud
quasars at 0.6 < z < 1.1 and find groups or clusters of galaxies in the fields
of at least 8 and possibly 13 of the 21 sources. There is no evidence for an
evolution in the richness of the environments of radio-loud quasars from other
low-redshift studies to z >~ 0.9. The quasars associated with groups and
clusters in our sample do not necessarily reside in the centre of the galaxy
distribution which rarely displays a spherical geometry. Clustering is
preferentially associated with small or asymmetric steep-spectrum radio
sources. The quasars with the largest projected angular size are, in nearly all
cases, found in non-clustered environments. Radio-based selection (including
source size) of high-redshift groups and clusters can be a very efficient
method of detecting rich environments at these redshifts.
We find that in optical searches for galaxy overdensities above z ~ 0.6
multiple filters must be used. If the single-filter counting statistics used by
groups at lower redshift are applied to our data, uncertainties are too large
to make accurate quantifications of cluster richness. This means that genuine
clustering of galaxies about quasars will be missed and, in ~10% of cases,
putative clusters turn out to be false detections. The statistics are further
diluted by the fact that galaxy overdensities are generally not centred on the
quasar.
| No Label | No Label |
astro-ph/9606158 | Eric J. Hooper | The Radio Properties of Optically Selected Quasars. III. Comparison
Between Optical and X-Ray Selected Samples | astro-ph | A sample of 103 quasars from the Large Bright Quasar Survey (LBQS) has been
observed with the VLA at 8.4 GHz to study the evolution of the radio luminosity
distribution and its dependence on absolute magnitude. Radio data from pointed
observations are now available for 359 of the 1055 LBQS quasars. The radio-loud
fraction is constant at ~10% over the absolute magnitude range -28 <= MB <=
-23, and it rises to ~20% (log R > 1) or ~35% (log L > 25) at the brightest
absolute magnitudes in the sample. This nearly flat distribution differs
markedly from those of the optically selected Palomar-Green (PG) Bright Quasar
Survey and the X-ray selected Extended Medium Sensitivity Survey (EMSS), both
of which have lower radio-loud fractions for absolute magnitudes fainter than
MB = -24 and higher fractions at brighter magnitudes. The reason for the high
radio-loud fraction at bright absolute magnitudes in the PG, compared to the
LBQS and other optically selected quasar surveys, is unknown. The trend of
increasing radio-loud fraction with absolute magnitude in the EMSS is due at
least in part to a correlation between X-ray and radio luminosity. Combining
the LBQS data with radio studies of high-redshift quasars leads to the
conclusion that the radio-loud fraction in optically selected quasars does not
appear to evolve significantly, aside from a modest increase at z ~1, from z =
0.2 to redshifts approaching 5, a result that is contrary to previous studies
which found a decrease in radio-loud fraction with increasing redshift by
comparing the low-z fraction in the PG to higher redshift samples.
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astro-ph/9710327 | Marc Davis | Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR
Foregrounds | astro-ph | We present a full sky 100 micron map that is a reprocessed composite of the
COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point
sources removed. Before using the ISSA maps, we remove the remaining artifacts
from the IRAS scan pattern. Using the DIRBE 100 micron and 240 micron data, we
have constructed a map of the dust temperature, so that the 100 micron map can
be converted to a map proportional to dust column density. The result of these
manipulations is a map with DIRBE-quality calibration and IRAS resolution.
To generate the full sky dust maps, we must first remove zodiacal light
contamination as well as a possible cosmic infrared background (CIB). This is
done via a regression analysis of the 100 micron DIRBE map against the Leiden-
Dwingeloo map of H_I emission, with corrections for the zodiacal light via a
suitable expansion of the DIRBE 25 micron flux. For the 100 micron map, no
significant CIB is detected. In the 140 micron and 240 micron maps, where the
zodiacal contamination is weaker, we detect the CIB at surprisingly high flux
levels of 32 \pm 13 nW/m^2/sr at 140 micron, and 17 \pm 4 nW/m^2/sr at 240
micron (95% confidence). This integrated flux is ~2 times that extrapolated
from optical galaxies in the Hubble Deep Field.
The primary use of these maps is likely to be as a new estimator of Galactic
extinction. We demonstrate that the new maps are twice as accurate as the older
Burstein-Heiles estimates in regions of low and moderate reddening. These dust
maps will also be useful for estimating millimeter emission that contaminates
CMBR experiments and for estimating soft X-ray absorption.
| No Label | No Label |
0804.1640 | Peter den Hartog | Detailed high-energy characteristics of AXP 4U 0142+61 - Multi-year
observations with INTEGRAL, RXTE, XMM-Newton and ASCA | astro-ph | We present detailed spectral and temporal characteristics both in the hard
X-ray (>10 keV) and soft X-ray (<10 keV) domains, obtained using data from
INTEGRAL, XMM-Newton, ASCA and RXTE. The INTEGRAL time-averaged total spectrum
shows a power-law like shape with photon index Gamma = 0.93 +/- 0.06. 4U
0142+61 is detected up to 229 keV and the flux between 20 keV and 229 keV is
(15.01 +/- 0.82) x 10^(-11) erg/cm^2/s. Using simultaneously collected data
with the spectrometer SPI of INTEGRAL the combined total spectrum yields the
first evidence for a spectral break with a peak energy of 228 +65/-41 keV.
There is no evidence for significant long-term time variability of the total
emission. Pulsed emission is measured with ISGRI up to 160 keV. The 20-160 keV
profile shows a broad double-peaked pulse with a 6.2 sigma detection
significance. The total pulsed spectrum can be described with a very hard
power-law shape with a photon index \Gamma = 0.40 +/- 0.15. We performed
phase-resolved spectroscopy over the total high-energy band (2.8-300 keV) and
identify at least three genuinely different pulse components with different
spectra. The high level of consistency between the detailed results from the
four missions is indicative for a remarkable stable geometry underlying the
emission scenario.
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astro-ph/9606169 | Paul Nandra | ASCA observations of Seyfert 1 galaxies: II. Relativistic Iron K-alpha
emission | astro-ph | We present evidence for widespread relativistic effects in the central
regions of active galactic nuclei. In a sample of 18 Seyfert 1 galaxies
observed by \asca, 14 show an iron K$\alpha$ line which is is resolved, with
mean width $\sigma_{\rm K\alpha}=0.43\pm 0.12$~keV for a gaussian profile (Full
Width at Half Maximum, FWHM$\sim 50,000$~km s$^{-1}$). However, many of the
line profiles are asymmetric. A strong red wing is indicative of gravitational
redshifts close to a central black hole and accretion disk models provide an
excellent description of the data. The peak energy of the line is 6.4~keV,
indicating that it arises by fluorescence in near-neutral material. Our fits
imply a low inclination for the disk in these Seyfert 1 galaxies, with a mean
of 30\deg, consistent with orientation-dependent unification schemes.
Differences in the line profiles from source-to-source imply slight variations
in geometry, which cannot be accounted for solely by inclination. In most
cases, we require that the line emission arises from a range of radii. Although
a small contribution to the emission from a region other than the disk is not
ruled out, it is not generally required and has little effect on our
conclusions regarding the disk line. Our data are fit equally well with
rotating (Kerr) and non-rotating (Schwarzschild) black hole models. We find a
mean spectral index in the 3-10 keV range of $<\Gamma_{3-10}>=1.91\pm 0.07$
after accounting for the effects of reflection. Such observations probe the
innermost regions of AGN, and arguably provide the best evidence yet obtained
for the existence of super-massive black holes in the centers of active
galaxies.
| No Label | No Label |
0709.1192 | Derek Homeier | K-H_2 Quasi-molecular absorption detected in the T-dwarf epsilon Indi Ba | astro-ph | T-type dwarfs present a broad and shallow absorption feature centred around
6950 A in the blue wing of the K doublet at 0.77 micron which resembles in
depth and shape the satellite absorption predicted by detailed collisional
broadening profiles. In our previous work, the predicted line satellite
position was however somewhat too blue compared to the observed feature. In
this paper we investigate whether new calculations of the energy surfaces of
the potentials in the K-H_2 system, including spin-orbit coupling, result in a
closer coincidence of the satellite with the observed position. We also
investigate the extent to which CaH absorption bands contribute to the feature.
We present model atmospheres and synthetic spectra, including gravitational
settling for an improved description of depth-dependent abundances of
refractory elements, and based on new K-H_2 line profiles using improved
interaction potentials. By comparison with a high signal-to-noise optical
spectrum of the T1 dwarf epsilon Indi Ba, we find that these new models do
reproduce the observed feature, while CaH does not contribute for the
atmospheric parameters considered. We also find that CaH is settled out so deep
into the atmosphere that even turbulent vertical mixing would appear
insufficient to bring significant amounts of CaH to the photosphere in dwarfs
later than ~L5. We conclude that previous identification of the feature at this
location in T and late L dwarf spectra with CaH was erroneous, as expected on
physical grounds: calcium condenses onto grains in early L dwarfs and thus
should have settled out of the photosphere in cooler brown dwarfs. This finding
revokes one observational verification for the cloud-clearing theory: a gradual
clearing of the cloud cover in early T dwarfs.
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astro-ph/0610455 | John Stephen | INTEGRAL/IBIS 20-100 keV Extragalactic survey: an update | astro-ph | Analysis of INTEGRAL Core Program and public Open Time observations has
recently provided a sample of 60 extragalactic sources selected in the 20-100
keV band above a flux of 1.5 10^-11 erg/cm2/s. As this band probes heavily
obscured regions/objects, i.e. those that could be missed in optical, UV, and
even X-ray surveys, our sample offers the opportunity to study the
extragalactic sky from a different point of view with respect to surveys at
lower energies. We present an update of our analysis, including the first
sample of AGNs detected above 100 keV. We also discuss the results of follow up
observations performed at optical and X-ray frequencies with the aim of
classifying our objects and studying the effects of intrinsic absorption in
gamma-ray selected AGNs. The average redshift of our sample is 0.134 while the
mean 20-100 keV luminosity in Log is 43.84; if blazars are excluded these
numbers become 0.022 and 43.48 respectively. Defining an absorbed object as one
with NH above 10^22 atoms/cm2, we find that absorption is present in 60% of the
objects with at most 14% of the total sample due to Compton thick active
galaxies. Almost all Seyfert 2s in our sample are absorbed as are 24% of
Seyfert 1s. We also present broad-band spectral information on a sub-sample of
the brightest objects: our observations indicate a mean photon index of 1.8
spanning from 30-50 keV to greater than 200 keV. Finally, we discuss the
LogN/LogS distribution in the 20-100 and 100-150 keV bands derived from our
sample. The present data highlight the capability of INTEGRAL to probe the
extragalactic gamma-ray sky, to discover new AGNs and to find absorbed objects.
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astro-ph/0604302 | Artem Tuntsov | Microlensing in phase space I: Continuous propagation of variability
moments | astro-ph | A method to calculate the statistical properties of microlensing light curves
is developed. The approach follows works by Deguchi & Watson, Seitz & Schneider
and Neindorf, attempting to clarify the ideas involved and techniques used in
the calculations. The method is then modified to include scattering by multiple
lensing planes along the line of sight and transition to a continuous limit of
this treatment for average quantities is performed leading to a Fokker-Planck
type equation. The equation is solved for a particular model of the random star
field and microlensing effect on the flux temporal variability is extracted.
Applications in astrophysically relevant situations are discussed.
| No Label | No Label |
astro-ph/0107385 | Bahram Mobasher | A photometric and spectroscopic study of dwarf and giant galaxies in the
Coma cluster - II. Spectroscopic observations | astro-ph | This is the second paper in a series studying the photometric and
spectroscopic properties of galaxies of different luminosities in the Coma
cluster. The sample selection, spectroscopic observations and completeness
functions are presented here. To study the spectral properties of galaxies as a
function of their local environment, two fields were selected for spectroscopic
observations to cover both the core (Coma1) and outskirts (ie. south-west of
the core and centered on NGC4839)- (Coma3) of the cluster. Medium resolution
spectroscopy (6-9 \AA) was carried out for a total of 490 galaxies in both
fields (302 in Coma1 and 188 in Coma3), using the WYFFOS multi-fiber
spectrograph on the William Herschel Telescope. The galaxies cover a range of
$12 < R < 20$, corresponding to -23 < M_R < -15 (H0=65 km/sec/Mpc). The
redshifts are measured with an accuracy of 100 km/sec. The spectral line
strengths and equivalent widths are also measured for the same galaxies and
analysed in Poggianti et al (2001- paper III). A total of 189 (Coma1) and 90
(Coma3) galaxies are identified as members of the Coma cluster. An analysis of
the colors show that only two members of the Coma cluster in our sample have
B-R > 2. The completeness functions for the spectroscopic sample is presented.
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astro-ph/9905221 | Adrian Melott | Massive Cooling Flow Clusters Inhabit Crowded Environments | astro-ph | With the availability of large-scale redshift survey data, it is now becoming
possible to explore correlations between large-scale structure and the
properties and morphologies of galaxy clusters. We investigate the spatial
distributions of a 98% complete, volume-limited sample of nearby (z<0.1) Abell
clusters with well-determined redshifts and find that cooling flow clusters
with high mass-accretion rates have nearest neighbors which are much closer
than those of other clusters in the sample (at the 99.8% confidence level), and
reside in more crowded environments out to 30/h Mpc. Several possible
explanations of this effect are discussed.
| No Label | No Label |
astro-ph/0208224 | Jon Paul Willis | Luminous early-type field galaxies at z ~ 0.4 - II. Star-formation
history and space density | astro-ph | We present a combined photometric and spectroscopic analysis of the star
formation history and space density of a sample of 485 luminous, M_V - 5 log h
< -20.5, field early-type galaxies at redshifts 0.3 < z < 0.6. The observed
b_Jori colours as a function of redshift, mean absorption line strengths and
[OII] 3727 emission properties are used to constrain the star formation history
of the galaxies. The mean star formation history of the early-type galaxy
sample is consistent with an old (z_f>1), passively evolving
luminosity-weighted stellar population. Twenty-one percent of the sample
possess detectable [OII] 3727 emission consistent with a low level (<1
M_solar/yr) of on-going star formation. Parametric and non-parametric estimates
of the space density of the sample are derived. The integrated luminosity
density at z ~ 0.4, allowing only for passive luminosity evolution, is in
excellent agreement with the local, (<z> = 0.1), luminosity density of
early-type galaxies. Overall, the sample properties are consistent with a
galaxy formation scenario in which the majority of luminous field early-type
galaxies formed at redshifts z>1 and have largely evolved passively since the
formation epoch.
| No Label | No Label |
0801.0451 | Shanil N. Virani | A cgi synthetic CMD calculator for the YY Isochrones | astro-ph | We describe a web-based cgi calculator for constructing synthetic
color-magnitude diagrams for a simple stellar population (SSP) using the
Yonsei-Yale (YY) isochrone data base. This calculator is designed to be used
interactively. It creates quick look CMD displays in (B-V) and (V-I) colors.
Stochastic effects on the CMDs are included. Output in tabular form is also
provided for special purpose displays, or for combining the CMDs of different
stellar populations. This research tool has applications in studies of the
stellar content of our Galaxy and external systems. It provides an easy way to
interpret the CMDs in resolved stellar populations. It offers the means to
explore the dependence of the integrated properties of unresolved stellar
systems on stellar parameters (ages, chemical composition, binarity) and on the
characteristics of their parent population (IMF slope and mass range).
| No Label | No Label |
astro-ph/0601252 | Emeric Le Floc'h | Missing GRB host galaxies in deep mid-infrared observations:
implications on the use of GRBs as star formation tracers | astro-ph | We report on the first mid-infrared observations of 16 GRB host galaxies
performed with the Spitzer Space Telescope, and investigate the presence of
evolved stellar populations and dust-enshrouded star-forming activity
associated with GRBs. Only a very small fraction of our sample is detected by
Spitzer, which is not consistent with recent works suggesting the presence of a
GRB host population dominated by massive and strongly-starbursting galaxies
(SFR > ~100 Msol/yr). Should the GRB hosts be representative of star-forming
galaxies at high redshift, models of galaxy evolution indicate that >~50% of
GRB hosts would be easily detected at the depth of our mid-infrared
observations. Unless our sample suffers from a strong observational bias which
remains to be understood, we infer in this context that the GRBs identified
with the current techniques can not be directly used as unbiased probes of the
global and integrated star formation history of the Universe.
| No Label | No Label |
0809.4242 | Nozomu Tominaga | Supernova Nucleosynthesis in the Early Universe | astro-ph | The first metal enrichment in the universe was made by supernova (SN)
explosions of population (Pop) III stars. The trace remains in abundance
patterns of extremely metal-poor (EMP) stars. We investigate the properties of
nucleosynthesis in Pop III SNe by means of comparing their yields with the
abundance patterns of the EMP stars. We focus on (1) jet-induced SNe with
various energy deposition rates [$\dot{E}_{\rm dep}=(0.3-1500)\times10^{51}{\rm
ergs s^{-1}}$], and (2) SNe of stars with various main-sequence masses ($M_{\rm
ms}=13-50M_\odot$) and explosion energies [$E=(1-40)\times10^{51}$ergs]. The
varieties of Pop III SNe can explain varieties of the EMP stars: (1) higher
[C/Fe] for lower [Fe/H] and (2) trends of abundance ratios [X/Fe] against
[Fe/H].
| No Label | No Label |
astro-ph/0001377 | Abdul I. Asvarov | Diffusive Shock Acceleration of Electrons and Radio Emission from Large
Diameter Shell-Type Supernova Remnants | astro-ph | In present study I examine the capability of diffusive shock acceleration
mechanism to explain existing data on radio emission from evolved large
diameter shell-type adiabatic supernova remnants (SNRs). Time-dependent
''onion-shell'' model for the radio emission of SNRs is developed, which is
based on the assumptions: a) acceleration takes place from thermal energies and
test-particle approximation is valid; b) the problem of injection is avoided by
introducing, like Bell (1978), two injection parameters; c) to take into
consideration very late stages of SNR evolution the analytic approximation of
Cox and Andersen (1982) for the shell structure is used; c)no radiative
cooling. Constructed Surface Brightness - Diameter $(\Sigma -D)$ tracks are
compared with the empirical $\Sigma -D$ diagram. The main conclusion of the
study is that the DSA mechanism is capable of explaining all the statistics of
radio SNRs including very large diameter remnants and giant galactic loops.
| No Label | No Label |
astro-ph/0701138 | Monica Tosi | Star formation histories of resolved stellar populations: in and beyond
the Local Group | astro-ph | The exploitation of the power and the spatial resolution of HST and new
generation ground-based telescopes allows to measure with good precision the
individual stars of galaxies in and beyond the Local Group. This leads to very
successful studies of the star formation histories of galaxies of different
morphological types. Our current knowledge of the star formation history of
galaxies within 10-20 Mpc, as derived from the colour-magnitude diagrams of
their resolved stellar populations, is reviewed here.
| No Label | No Label |
astro-ph/0603325 | Vitaly Neustroev | Simultaneous photometry and echelle-spectroscopy of the dwarf nova BZ
Ursae Majoris during the 2005 January Outburst | astro-ph | We report simultaneous photometric and echelle-spectroscopic observations of
the dwarf nova BZ UMa during which we were lucky to catch the system at the
onset of an outburst, the development of which we traced in detail from
quiescence to early decline. The outburst had a precursor, and was of a short
duration (~5 days) with a highly asymmetrical light curve. On the rise we
observed a `jump' during which the brightness almost doubled over the course of
half an hour. Power spectra analysis revealed well-defined oscillations with
period of ~42 minutes. Using Doppler tomography we found that the unusual
emission distribution detected in quiescence held during the outburst. After
the maximum a new emission source arose, from the inner hemisphere of the
secondary star, which became the brightest at that time. We analyse this
outburst in terms of `inside-out' and `outside-in' types, in order to determine
which of these types occured in BZ UMa.
| No Label | No Label |
astro-ph/0304207 | Svetlana V. Starikova | Globular Clusters as Candidates for Gravitational Lenses to Explain
Quasar-Galaxy Associations | astro-ph | We argue that globular clusters (GCs) are good candidates for gravitational
lenses in explaining quasar-galaxy associations. The catalog of associations
(Bukhmastova 2001) compiled from the LEDA catalog of galaxies (Paturel 1997)
and from the catalog of quasars (Veron-Cetty and Veron 1998) is used. Based on
the new catalog containing 8382 pairs, we show that one might expect an
increased number of GCs around irregular galaxies of types 9 and 10 from the
hypothesis that distant compact sources are gravitationally lensed by GCs in
the halos of foreground galaxies. The King model is used to determine the
central surface densities of 135 GCs in the Milky Way. The distribution of GCs
in central surface density was found to be lognormal.
| No Label | No Label |
astro-ph/9907031 | Fabien Malbet | Integrated optics for astronomical interferometry. I. Concept and
astronomical applications | astro-ph | We propose a new instrumental concept for long-baseline optical single-mode
interferometry using integrated optics which were developed for
telecommunication. Visible and infrared multi-aperture interferometry requires
many optical functions (spatial filtering, beam combination, photometric
calibration, polarization control) to detect astronomical signals at very high
angular resolution. Since the 80's, integrated optics on planar substrate have
become available for telecommunication applications with multiple optical
functions like power dividing, coupling, multiplexing, etc. We present the
concept of an optical / infrared interferometric instrument based on this new
technology. The main advantage is to provide an interferometric combination
unit on a single optical chip. Integrated optics are compact, provide
stability, low sensitivity to external constrains like temperature, pressure or
mechanical stresses, no optical alignment except for coupling, simplicity and
intrinsic polarization control. The integrated optics devices are inexpensive
compared to devices that have the same functionalities in bulk optics. We think
integrated optics will fundamentally change single-mode interferometry.
Integrated optics devices are in particular well-suited for interferometric
combination of numerous beams to achieve aperture synthesis imaging or for
space-based interferometers where stability and a minimum of optical alignments
are wished.
| No Label | No Label |
0801.3237 | Thomas Wiegelmann | Nonlinear force-free magnetic field extrapolations: comparison of the
Grad-Rubin and Wheatland-Sturrock-Roumeliotis algorithm | astro-ph | We compare the performance of two alternative algorithms which aim to
construct a force-free magnetic field given suitable boundary conditions. For
this comparison, we have implemented both algorithms on the same finite element
grid which uses Whitney forms to describe the fields within the grid cells. The
additional use of conjugate gradient and multigrid iterations result in quite
effective codes. The Grad-Rubin and Wheatland-Sturrock-Roumeliotis algorithms
both perform well for the reconstruction of a known analytic force-free field.
For more arbitrary boundary conditions the Wheatland-Sturrock-Roumeliotis
approach has some difficulties because it requires overdetermined boundary
information which may include inconsistencies. The Grad-Rubin code on the other
hand loses convergence for strong current densities. For the example we have
investigated, however, the maximum possible current density seems to be not far
from the limit beyond which a force free field cannot exist anymore for a given
normal magnetic field intensity on the boundary.
| No Label | No Label |
astro-ph/9811423 | Jaan Einasto | Structure and Evolution of Stellar Populations in Local Group Galaxies | astro-ph | We use detailed modeling of stellar populations of nearby galaxies to
calculate population parameters. Our sample of galaxies includes most galaxies
of the Local Group and several more distant giant galaxies. Available data are
sufficient to decompose galaxies into the nucleus, the metal rich core, the
bulge, the halo, the young and old disks, and the dark halo. We compare
mass-to-luminosity ratios and colors of bulges, disks and halos with results of
models of galactic chemical evolution. The luminosity weighted mean of the
mass-to-luminosity ratio of visible stellar population is M/L_B = 4 +- 1.4 in
solar units. This ratio is surprisingly constant for galaxies of very different
absolute magnitude.
| No Label | No Label |
astro-ph/0602017 | Angela Bragaglia | The old anticentre open cluster Berkeley 32: membership and fundamental
parameters | astro-ph | We have obtained medium-low resolution spectroscopy and BVI CCD imaging of
Berkeley 32, an old open cluster which lies in the anticentre direction. From
the radial velocities of 48 stars in the cluster direction we found that 31 of
them, in crucial evolutionary phases, are probable cluster members, with an
average radial velocity of +106.7 (sigma = 8.5) km/s. From isochrone fitting to
the colour magnitude diagrams of Berkeley 32 we have obtained an age of 6.3
Gyr, (m-M)0 = 12.48 and E(B-V) = 0.10. The best fit is obtained with Z=0.008. A
consistent distance, (m-M)0 ~= 12.6 +/- 0.1, has been derived from the mean
magnitude of red clump stars with confirmed membership; we may assume (m-M)0 ~=
12.55 +/- 0.1. The colour magnitude diagram of the nearby field observed to
check for field stars contamination looks intriguingly similar to that of the
Canis Major overdensity.
| No Label | No Label |
astro-ph/9810103 | Srdjan Samurovic | Ly$\alpha$ forest and the total absorption cross-section of galaxies --
an example of the NTT SUSI Deep Field | astro-ph | By extrapolating the accumulated low-redshift data on the absorption radius
of galaxies and its luminosity scaling, it is possible to predict the total
absorption cross-section of the gas associated with collapsed structures in the
universe at any given epoch. This prediction can be verified observationally
through comparison with the well-known spatial distribution of the QSO
absorption systems. In this way, it is shown that HDF, NTT SUSI Deep Field and
other such data give further evidence for the plausibility of origin of the
significant fraction of the Ly$\alpha$ forest in haloes of normal galaxies.
| No Label | No Label |
astro-ph/0405570 | Adrian Turner | The soft X-ray absorption lines of the Seyfert 1 galaxy MCG--6-30-15 | astro-ph | The absorption lines in the soft X-ray spectrum of MCG--6-30-15 are studied
using the Reflection Grating Spectrometer data from the 2001 XMM-Newton 320 ks
observation. A line search of the full time-averaged spectrum reveals 51
absorption lines and one emission line. The equivalent widths of the lines are
measured and the majority of the lines identified. We find lines produced by a
broad range of charge states for several elements, including almost all the
charge states oxygen and iron, suggesting a broad range of ionization
parameters is present in the warm absorber. The equivalent widths of the lines
are broadly consistent with the best fitting warm absorber models from Turner
et al (2003). The equivalent widths of the absorption lines allow confidence
limits on the column density of the species to be determined. For OVII a column
density of 10^18.36-10^18.86 cm^-2 is found. This column density of OVII, when
combined with the inferred FeI absorption, is sufficient to explain the drop in
flux at 0.7 keV as being due to absorption from the warm absorber. Fitting OI
K-edge absorption to the spectrum reveals a column of 10^17.51-10^17.67 cm^-2
of OI, suggesting an Fe:O ratio of ~1:2, consistent with the neutral iron being
in the form of iron oxide dust. Variability is seen in a few absorption lines,
but the majority of the absorption features, including the prominent absorption
edges, stay constant throughout the observation despite variability in the
continuum flux.
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