title: Does life's rapid appearance imply a Martian origin?

abstract:
  The hypothesis that the rapid appearance of life on Earth justifies the
belief that life is widespread in the universe has been investigated
statistically by Lineweaver and Davis. However, a rapid appearance could also
be interpreted as evidence for a nonterrestrial origin. I attempt to quantify
the relative probabilities for a nonindigenous versus an indigenous origin of
life on Earth, on the assumption that biogenesis involved one or more highly
improbable steps, using a generalization of the well known observer selection
argument of Carter. The analysis is specifically applied to a Martian origin of
life, with subsequent transfer to Earth within impact ejecta.


title: How bio-friendly is the universe

abstract:
  The oft-repeated claim that life is written into the laws of nature are
examined and criticized. Arguments are given in favour of life spreading
between near-neighbour planets in rocky impact ejecta (transpermia), but
against panspermia, leading to the conclusion that if life is indeed found to
be widespread in the universe, some form of life principle or biological
determinism must be at work in the process of biogenesis. Criteria for what
would constitute a credible life principle are elucidated. I argue that the key
property of life is its information content, and speculate that the emergence
of the requisite information-processing machinery might require quantum
information theory for a satisfactory explanation. Some clues about how
decoherence might be evaded are discussed. The implications of some of these
ideas for fine tuning are discussed.


title: Abundance differences between components of wide binaries

abstract:
  In this paper we present iron abundance analysis for 23 wide binaries with
main sequence components in the temperture range 4900-6300 K, taken from the
sample of the pairs currently included in the radial velocity planet search on
going at the TNG. The use of a line-by-line differential analysis technique
between the components of each pair allows to reach errors of about 0.02 dex in
the iron content difference. Most of the pairs have abundance differences lower
than 0.02 dex and there are no pairs with differences larger than 0.07 dex. The
four cases of differences larger than 0.02 dex may be spouriuos because of the
larger error bars affecting pairs with large temperature difference, cold stars
and rotating stars. The pair HD 219542, previously reported by us to have
different composition, results instead normal. For non-rotating stars warmer
than 5500 K, we are able to exclude in most cases the ingestion of more than 1
Earth Mass of iron (about 5 Earth masses of meteoritic material) during the
main sequence lifetime of the stars, placing more stringent limits (about 0.4
Earth masses of iron) in five cases of warm stars. This latter limit is similar
to the estimates of rocky material accreted by the Sun during its main sequence
lifetime. Combining the results of the present analysis with those for the
Hyades and Pleiades, we conclude that the hypothesis that pollution by
planetary material is the only responsible for the highest metallicity of the
stars with planets may be rejected at more than 99% level of confidence if the
incidence of planets in these samples is as high as 8% and similar to the field
stars included in current radial velocity surveys. However, the significance of
this result drops considerably if the incidence of planets around stars in
binary systems and clusters is less than a half than around normal field stars.


title: The Status of the H.E.S.S. Project

abstract:
  The High Energy Stereoscopic System (H.E.S.S.) - is a system of four, 107 m^2
mirror area, imaging Cherenkov telescopes under construction in the Khomas
Highland of Namibia (1800 m asl). The H.E.S.S. system is characterised by a low
threshold (~ 100 GeV) and a ~1 % Crab flux sensitivity resulting from the good
angular resolution and background rejection provided by the stereoscopic
technique.
  The first two telescopes are operational and first results are reported here.
The remaining two telescopes (of H.E.S.S. Phase-I) will be commissioned early
in 2004.


title: The structure of cool accretion disc in semidetached binaries

abstract:
  We present the results of qualitative consideration of possible changes
occurring during the transition from the hot accretion disc to the cool one. We
argue the possible existence of one more type of spiral density waves in the
inner part of the disc where gasdynamical perturbations are negligible. The
mechanism of formation of such a wave as well as its parameters are considered.
We also present the results of 3D gasdynamical simulation of cool accretion
discs. These results confirm the hypothesis of possible formation of the spiral
wave of a new, "precessional" type in the inner regions of the disc. Possible
observational manifestations of this wave are discussed.


title:
Radio continuum observations of the Virgo cluster spiral NGC 4522 The
  signature of ram pressure

abstract:
  Radio continuum observations at 20 and 6 cm of the highly inclined Virgo
spiral galaxy NGC 4522 are presented. Both, 20 and 6 cm total emission
distributions are asymmetric with an extended component to the west where
extraplanar atomic gas and Halpha emission are found. The 6 cm polarized
emission is located at the eastern edge of the galactic disk. Its peak is
located about 1 kpc to the east of the total emission peak. We argue that this
phenomena is a characteristic feature for cluster galaxies which are
experiencing significant pressure from the intracluster medium. The degree of
polarization decreases from the east to the west. The flattest spectral index
between 20 and 6 cm coincides with the peak of the 6 cm polarized emission.
These findings are consistent with a picture of a large scale shock due to ram
pressure located at the east of the galaxy where cosmic rays are accelerated.
We conclude that it is likely that the galaxy experiences active ram pressure.


title:
Running spectral index and mode-mode correlation of inflationary
  perturbations from off-equilibrium effects

abstract:
  We study the off-equilibrium effects of inflaton on the dynamics of
primordial perturbations in the O(N) model. A self-consistent off-equilibrium
formalism is employed to investigate the evolution of the inflationary
background field and its fluctuations with the back-reaction effects. We find
two observable remains left behind the off-equilibrium processes: the running
spectral index of primordial density perturbations and the correlations between
perturbation modes in phase space, which would serve as the imprints to probe
the epoch of inflation, even beyond.


title:
Extragalactic Globular Clusters in the Near Infrared: IV. Quantifying
  the Age Structure using Monte-Carlo Simulations

abstract:
  In previous papers of the series we used a combination of optical and
near-infrared colours to derive constraints on the relative age structure in
globular cluster systems. Here, we present the details, strength and
limitations of our method based on Monte-Carlo simulations of colour-colour
diagrams and cumulative age distributions. The simulations are based on general
informations about the globular cluster systems (e.g. colour-ranges, the number
ratios between sub-populations) and the different single stellar population
models (SSP's) which are used to derive relative ages. For both the modeled
systems and the observed globular cluster systems we derive the cumulative age
distribution and introduce two parameters to define it, the so-called 50 % age
and the result of the reduced $\chi$$^2$test of the comparison between models
and observations. The method was tested successfully on several systems and
allowed to reveal significant intermediate age populations in two of them.


title: A model of superoutbursts in binaries of SU UMa type

abstract:
  A new mechanism explaining superoutbursts in binaries of SU UMa type is
proposed. In the framework of this mechanism the accretion rate increase
leading to the superoutburst is associated with formation of a spiral wave of a
new "precessional" type in inner gasdynamically unperturbed parts of the
accretion disc. The possibility of existence of this type of waves was
suggested in our previous work (astro-ph/0403053). The features of the
"precessional" spiral wave allow explaining both the energy release during the
outburst and all its observational manifestations. The distinctive
characteristic of a superoutburst in a SU UMa type star is the appearance of
the superhump on the light curve. The proposed model reproduces well the
formation of the superhump as well as its observational features, such as the
period that is 3-7% longer than the orbital one and the detectability of
superhumps regardless of the binary inclination.


title:
The elemental abundances in the intracluster medium as observed with
  XMM-Newton

abstract:
  XMM-Newton observations of 19 galaxy clusters are used to measure the
elemental abundances and their spatial distributions in the intracluster
medium. The sample mainly consists of X-ray bright and relaxed clusters with a
cD galaxy. Along with detailed Si, S and Fe radial abundance distributions
within 300-700 kpc in radius, the O abundances are accurately derived in the
central region of the clusters. The Fe abundance maxima towards the cluster
center, possibly due to the metals from the cD galaxy,are spatially resolved.
The Si and S abundances also exhibit central increases in general, resulting in
uniform Fe-Si-S ratios within the cluster. In contrast, the O abundances are in
general uniform over the cluster. The mean O to Fe ratio within the cluster
core is sub-solar, while that of the cluster scale is larger than the solar
ratio. These measurements indicate that most of the Fe-Si-S and O in the
intracluster medium have different origins, presumably in supernovae Ia and II,
respectively. The obtained Fe and O mass are also used to discuss the past star
formation history in clusters.


title:
Hyperfine Structure in H^{13}CO^{+} and ^{13}CO: measurement, analysis,
  and consequences for the study of dark clouds

abstract:
  The magnetic moment of the ^{13}C nucleus is shown to provide a potentially
useful tool for analysing quiescent cold molecular clouds. We report discovery
of hyperfine structure in the H^{13}CO^{+}(1-0) transition. The doublet
splitting is observed to be 38.5 +/- 5.2 kHz, and is confirmed by calculations
which give 39.8 kHz and a line strength ratio of 3:1. We improve the
spectroscopic constants of H^{13}CO^{+} and determine the frequencies of its
low-J spectrum to better precision by analysing the dark cloud L1512.
Potentially high optical depths (3 to 5 in L1512) in quiescent clouds require
to consider the line's doublet nature when comparing to other molecular
species, possibly reversing previous conclusions from single-component
interpretations. We further confirm the hyperfine splitting in the ^{13}CO(1-0)
transition that had been predicted, and measured in the laboratory, to be about
46 kHz. By applying hyperfine analysis to the data set of the first IRAM
key-project we show that ^{13}CO optical depths can be estimated in narrow
linewidth regions without recourse to other transitions nor to assumptions on
beam filling factors, and linewidth and velocity determinations can be
improved. For the core of L1512 we find an inverse proportionality between
linewidth and column density resp. square root of optical depth, and a
systematic inside-out increase of excitation temperature and of the
^{13}CO:C^{18}O abundance ratio. Overall motion toward the innermost region is
suggested.


title: The second US Naval Observatory CCD Astrograph Catalog (UCAC2)

abstract:
  The second USNO CCD Astrograph Catalog, UCAC2 was released in July 2003.
Positions and proper motions for 48,330,571 sources (mostly stars) are
available on 3 CDs, supplemented with 2MASS photometry for 99.5% of the
sources. The catalog covers the sky area from -90 to +40 degrees declination,
going up to +52 in some areas; this completely supersedes the UCAC1 released in
2001. Current epoch positions are obtained from observations with the USNO
8-inch Twin Astrograph equipped with a 4k CCD camera. The precision of the
positions are 15 to 70 mas, depending on magnitude, with estimated systematic
errors of 10 mas or below. Proper motions are derived by utilizing over 140
ground-and space-based catalogs, including Hipparcos/Tycho, the AC2000.2, as
well as yet unpublished re-measures of the AGK2 plates and scans from the NPM
and SPM plates. Proper motion errors are about 1 to 3 mas/yr for stars to 12th
magnitude, and about 4 to 7 mas/yr for fainter stars to 16th magnitude. The
observational data, astrometric reductions, results, and important information
for the users of this catalog are presented.


title:
ISO spectroscopy of gas and dust: from molecular clouds to
  protoplanetary disks

abstract:
  Observations of interstellar gas-phase and solid-state species in the 2.4-200
micron range obtained with the spectrometers on board the Infrared Space
Observatory are reviewed. Lines and bands due to ices, polycyclic aromatic
hydrocarbons, silicates and gas-phase atoms and molecules (in particular H2,
CO, H2O, OH and CO2) are summarized and their diagnostic capabilities
illustrated. The results are discussed in the context of the physical and
chemical evolution of star-forming regions, including photon-dominated regions,
shocks, protostellar envelopes and disks around young stars.


title:
The Coronal X-ray Spectrum of the Multiple Weak-Lined T Tauri Star
  System HD 98800

abstract:
  We present high-resolution X-ray spectra of the multiple (hierarchical
quadruple) weak-lined T Tauri star system HD 98800, obtained with the High
Energy Transmission Gratings Spectrograph (HETGS) aboard the Chandra X-ray
Observatory (CXO). In the zeroth-order CXO/HETGS X-ray image, both principle
binary components of HD 98800 (A and B, separation 0.8'') are detected;
component A was observed to flare during the observation. The infrared excess
(dust disk) component, HD 98800B, is a factor ~4 fainter in X-rays than the
apparently ``diskless'' HD 98800A, in quiescence. The line ratios of He-like
species (e.g., Ne IX, O VII) in the HD 98800A spectrum indicate that the
X-ray-emitting plasma around HD 98800 is in a typical coronal density regime
(log n <~ 11). We conclude that the dominant X-ray-emitting component(s) of HD
98800 is (are) coronally active. The sharp spectral differences between HD
98800 and the classical T Tauri star TW Hya demonstrate the potential utility
of high-resolution X-ray spectroscopy in providing diagnostics of pre-main
sequence accretion processes.


title:
Constraining the X-ray Luminosities of Asymptotic Giant Branch Stars: TX
  Cam and T Cas

abstract:
  To probe the magnetic activity levels of asymptotic giant branch (AGB) stars,
we used XMM-Newton to search for X-ray emission from two well-studied objects,
TX Cam and T Cas. The former star displays polarized maser emission indicating
magnetic field strengths of B ~ 5 G; the latter is one of the nearest known AGB
stars. Neither star was detected by XMM-Newton. We use the upper limits on EPIC
(CCD detector) count rates to constrain the X-ray luminosities of these stars,
and derive L_X < 10^{31} erg s^{-1} (<10^{30} erg s^{-1}) for an assumed X-ray
emission temperature T_X = 3x10^6 K (10^7 K). These limits represent <~ 10% (<~
1%) of the X-ray luminosity expected under models in which AGB magnetic fields
are global and potentially play an important role in collimating and/or
launching AGB winds. We suggest, instead, that the B field strengths inferred
from maser observations are representative of localized, magnetic clouds.


title: Introduction to Non-Baryonic Dark Matter

abstract:
  These lectures on non-baryonic dark matter matter are divided into two parts.
In the first part, I discuss the need for non-baryonic dark matter in light of
recent results in cosmology, and I present some of the most popular candidates
for non-baryonic dark matter. These include neutrinos, axions, neutralinos,
WIMPZILLAs, etc. In the second part, I overview several observational
techniques that can be employed to search for WIMPs (weakly interacting massive
particles) as non-baryonic dark matter. Among these techniques, I discuss the
direct detection of WIMP dark matter, and its indirect detection through
high-energy neutrinos, gamma-rays, positrons, etc.


title: 200 Mpc Sized Structure in the 2dF QSO Redshift Survey

abstract:
  The completed 2dF QSO Redshift (2QZ) Survey has been used to search for
extreme large-scale cosmological structure (around 200 Mpc) over the redshift
range 0<z<2.5. We demonstrate that statistically significant overdensities and
underdensities do exist and hence represent the detection of cosmological
fluctuations on comoving scales that correspond to those presently detected in
the cosmic microwave background. However, the fractional overdensities on
scales >100Mpc are in the linear or only weakly non-linear regime and do not
represent collapsed non-linear structures. We compare the measurements with the
expectation of a standard LCDM model by measuring the variance of counts in
cells and find that, provided the distribution of QSOs on large scales exhibits
a mild bias with respect to the distribution of dark matter, the observed
fluctuations are found to be in good agreement with the model. There is no
evidence on such scales for any extreme structures that might require, for
example, departures from the assumption of Gaussian initial perturbations. Thus
the power-spectrum derived from the 2QZ Survey appears to provide a complete
description of the distribution of QSOs. The amount of bias and its redshift
dependence that is required is consistent with that found from studying the
clustering of 2QZ QSOs on 10 Mpc scales, and may be adequately described by an
approximately redshift-invariant power spectrum with normalisation sigma_8=1.0
corresponding to a bias at z=0 of b=1.1 rising to b=2 at the survey's mean
redshift z=1.5.


title:
Multiresolution approach for period determination on unevenly sampled
  data

abstract:
  In this paper we present a multiresolution-based method for period
determination that is able to deal with unevenly sampled data. This method
allows us to detect superimposed periodic signals with lower signal-to-noise
ratios than in classical methods. This multiresolution-based method is a
generalization of the wavelet-based method for period detection that is unable
to deal with unevenly sampled data, presented by the authors in Otazu et al.
(2002). This new method is a useful tool for the analysis of real data and, in
particular, for the analysis of astronomical data.


title: The Nuclei of Late-type Spiral Galaxies

abstract:
  We summarize some recent results from our observational campaign to study the
central regions of spiral galaxies of late Hubble type (Scd - Sm). These
disk-dominated, bulgeless galaxies have an apparently uneventful merger
history. The evolution of their nuclei thus holds important constraints on the
mechanisms that are responsible for bulge formation and nuclear activity in
spiral galaxies. We discuss the structural properties, stellar populations, and
dynamical masses of the compact, luminous star cluster that is found in the
nuclei of most late-type spiral galaxies. Although preliminary, our results
strongly indicate that many galaxies of our sample experience repeated periods
of nuclear star formation. While the exact mechanism that leads to the required
high gas densities in the galaxy nucleus remains unclear, results from our
recent CO survey of late-type spirals demonstrate that in most cases, the
central kpc contains enough molecular gas to support repetitive nuclear
starbursts.


title:
Taking measure of the Andromeda halo: a kinematic analysis of the giant
  stream surrounding M31

abstract:
  We present a spectroscopic survey of the giant stellar stream found in the
halo of the Andromeda galaxy. Taken with the DEIMOS multi-object spectrograph
on the Keck2 telescope, these data display a narrow velocity dispersion of
11+/-3 km/s, with a steady radial velocity gradient of 245 km/s over the 125
kpc radial extent of the stream studied so far. This implies that the Andromeda
galaxy possesses a substantial dark matter halo. We fit the orbit of the stream
in different galaxy potential models. In a simple model with a composite bulge,
disk and halo, where the halo follows a ``universal'' profile that is
compressed by the formation of the baryonic components, we find that the
kinematics of the stream require a total mass inside 125 kpc of
7.5^(+2.5)_(-1.3) x 10^{11} M_Sun, or more than 5.4 x 10^{11} M_Sun at the 99%
confidence level. This is the first galaxy in which it has been possible to
measure the halo mass distribution by such direct dynamical means over such a
large distance range. The resulting orbit shows that if M32 or NGC 205 are
connected with the stream, they must either trail or lag the densest region of
the stream by more than 100 kpc. Furthermore, according to the best-fit orbit,
the stream passes very close to M31, causing its demise as a coherent structure
and producing a fan of stars that will pollute the inner halo, thereby
confusing efforts to measure the properties of genuine halo populations. Our
data show that several recently identified planetary nebulae, which have been
proposed as evidence for the existence of a new companion of M31, are likely
members of the Andromeda Stream.


title:
Two Years of Observations of the X-ray Pulsar SMC X-1 with the ART-P
  Telescope onboard the Granat Observatory

abstract:
  We present the observations of the pulsar SMC X-1 with the ART-P telescope
onboard the Granat observatory. We investigate the variability of the flux from
the source on time scales of several tens of days. The intensity variation of
the pulsar are shown to be consistent with the presence of a periodicity in the
system with a characteristic time scale of $\sim61$ days. The precession of an
inclined accretion disk, as indirectly confirmed by the absence of low-state
pulsations, may be responsible for the observed variability. The spectrum of
the source is well described by a power-law energy dependence of the photon
flux density with a slope of $\sim1.5$ and an exponential cutoff at energies
above $\sim14-18$ keV. We estimated the inclinations between the planes of the
orbit and the accretion disk and the magnetic field of the neutron star.


title: Different kinds of long-term variability from Cygnus X-1

abstract:
  We present a study of the long-term variability of Cyg X-1 using data from
the RXTE/ASM and the RXTE/PCA during the time between the two soft states of
1996 and 2001/2002. This period has been characterized by many short ASM
flaring episodes which we have identified as "failed state transitions". The
150 d period which has been seen before and shortly after the 1996 soft state
is not obviously present in the ASM rate during most of this time. Applying
selection criteria from our pointed RXTE/PCA observations to exclude the
flaring episodes we show that the 150 d period can indeed still be
significantly detected in the hard state. Furthermore, while the ~420 d
timescale associated with the flaring is reduced in the selected hard state
count rate, it is still pronounced in the temporal evolution of the
corresponding hardness ratios. The Ryle radio flux is also consistent with the
150 d period being present but distorted during this time.


title: The bottleneck of the CNO burning and the age of the Globular Clusters

abstract:
  The transition between the Main Sequence and the Red Giant Branch in low mass
stars is powered by the onset of the CNO burning, whose bottleneck is the
$^{14}$N(p,$\gamma)^{15}$O. The LUNA collaboration has recently improved the
low energy measurements of the cross section of this key reaction. We analyse
the impact of the revised reaction rate on the estimate of the Globular
Clusters ages, as derived from the turnoff luminosity. We found that the age of
the oldest Globulars should be increased by about 0.7-1 Gyr with respect to the
current estimates.


title: On the Geometry of Dark Energy

abstract:
  Experimental evidence suggests that we live in a spatially flat, accelerating
universe composed of roughly one-third of matter (baryonic + dark) and
two-thirds of a negative-pressure dark component, generically called dark
energy. The presence of such energy not only explains the observed accelerating
expansion of the Universe but also provides the remaining piece of information
connecting the inflationary flatness prediction with astronomical observations.
However, despite of its good observational indications, the nature of the dark
energy still remains an open question. In this paper we explore a geometrical
explanation for such a component within the context of brane-world theory
without mirror symmetry, leading to a geometrical interpretation for dark
energy as warp in the universe given by the extrinsic curvature. In particular,
we study the phenomenological implications of the extrinsic curvature of a
Friedman-Robertson-Walker universe in a five-dimensional constant curvature
bulk, with signatures (4,1) or (3,2), as compared with the X-matter (XCDM)
model. From the analysis of the geometrically modified Friedman's equations,
the deceleration parameter and the Weak Energy Condition, we find a consistent
agreement with the presently known observational data on inflation for the
deSitter bulk, but not for the anti-deSitter case.


title:
Exact likelihood evaluations and foreground marginalization in low
  resolution WMAP data

abstract:
  The existing analysis of WMAP data is based on approximations for the
likelihood function, which is likely to be inaccurate on large scales. Here we
present exact evaluations of the likelihood of the low multipoles by direct
inversion of the theoretical covariance matrix for low resolution WMAP maps. We
project out the unwanted galactic contaminants rather than subtract them, which
can remove some of the cosmological signal and may lead to a suppression of
power. We find an increase in power at low multipoles. For the quadrupole the
maximum likelihood values are rather uncertain and vary between 140-220\muK^2.
On the other hand, the probability distribution away from the peak is robust
and, assuming a uniform prior between 0 an 2000\muK^2, the probability of
having the true value above 1200\muK^2 (as predicted by the simplest Lambda CDM
model) is 10%, a factor of 2.5 higher than predicted by WMAP likelihood code.
We develop a fast likelihood evaluation routine that can be used instead of
WMAP routines for low l values. We apply it to the MCMC analysis to compare the
cosmological parameters between the two cases. The new analysis of WMAP either
alone or jointly with SDSS and VSA reduces the reported 2-sigma evidence for
running to less than 1-sigma, giving \alpha_s=-0.022\pm 0.033 for the combined
case. The new analysis prefers about 1-sigma lower value of Omega_m, a
consequence of an increased ISW contribution required by the increase in the
spectrum at low l. These results suggest that the details of foreground removal
and full likelihood analysis are important for the parameter estimation from
WMAP data and these methods should be particularly useful in the analysis of
polarisation, where foreground contamination may be much more severe.


title: Relativistic Calculations of Coalescing Binary Neutron Stars

abstract:
  We have designed and tested a new relativistic Lagrangian hydrodynamics code,
which treats gravity in the conformally flat approximation to general
relativity. We have tested the resulting code extensively, finding that it
performs well for calculations of equilibrium single-star models, collapsing
relativistic dust clouds, and quasi-circular orbits of equilibrium solutions.
By adding in a radiation reaction treatment, we compute the full evolution of a
coalescing binary neutron star system. We find that the amount of mass ejected
from the system, much less than a percent, is greatly reduced by the inclusion
of relativistic gravitation. The gravity wave energy spectrum shows a clear
divergence away from the Newtonian point-mass form, consistent with the form
derived from relativistic quasi-equilibrium fluid sequences.


title: Weak Lensing of the CMB by Large-Scale Structure

abstract:
  Several recent papers have studied lensing of the CMB by large-scale
structures, which probes the projected matter distribution from $z=10^3$ to
$z\simeq 0$. This interest is motivated in part by upcoming high resolution,
high sensitivity CMB experiments, such as APEX/SZ, ACT, SPT or Planck, which
should be sensitive to lensing. In this paper we examine the reconstruction of
the large-scale dark matter distribution from lensed CMB temperature
anisotropies. We go beyond previous work in using numerical simulations to
include higher order, non-Gaussian effects and study how well the quadratic
estimator of \cite{Hu01a} is able to recover the input field. We also study
contamination by kinetic Sunyaev-Zel'dovich signals, which is spectrally
indistinguishable from lensed CMB anisotropies. We finish by estimating the
sensitivity of the previously cited experiments.


title: On the nature of eclipses in binary pulsar J0737-3039

abstract:
  We consider magnetohydrodynamical interaction between relativistic pulsar
wind and static magnetosphere in binary pulsar system PSR J0737-3039. We
construct semi-analytical model describing the form of the interface separating
the two pulsars.
  An assumption of vacuum dipole spin down for Pulsar B leads to eclipse
duration ten times longer than observed. We discuss possible Pulsar B torque
modification and magnetic field estimates due to the interaction with
  Pulsar A wind.
  Unless the orbital inclination is $\leq 86 ^\circ$, the duration of eclipses
is typically shorter than the one implied by the size of the eclipsing region.
We propose that eclipses occur due to synchrotron absorption by mildly
relativistic particles in the shocked Pulsar A wind. The corresponding optical
depth may be high enough if Pulsar A wind density is at the upper allowed
limits. We derive jump conditions at oblique, relativistic,
magnetohydrodynamical shocks and discuss the structure of the shocked Pulsar A
wind. Finally, we speculate on a possible mechanism of orbital modulation of
Pulsar B radio emission.


title: Circular velocity profiles of dark matter haloes

abstract:
  We use a high-resolution simulation of a galaxy-sized dark matter halo,
published simulated data as well as four cluster-sized haloes from Fukushige,
Kawai & Makino to study the inner halo structure in a Lambda cold dark matter
cosmology. We find that the circular velocity curves are substantially better
described by Stoehr et al. (SWTS) profiles than by Navarro, Frenk & White (NFW)
or Moore et al. profiles. Our findings confirm that no asymptotic slope is
reached and that the profiles are nearly universal, but not perfectly. The
velocity profiles curve at a_constant_ rate in log(r) over the full converged
range in radii and the corresponding extrapolated density profiles reach a
finite maximum density. We find, that the claim of a strong discrepancy between
the observed inner slopes of the density profiles of low surface brightness
galaxies (LSB) and their simulated counterparts on the grounds of currently
available observations and simulations is unfounded. In addition, if the SWTS
profile turns out to be a good description of the halo profile for the regions
that cannot be probed with simulations of today, then even in these regions the
agreeement between simulations and observations is very reasonable.


title:
A Limit from the X-ray Background on the Contribution of Quasars to
  Reionization

abstract:
  A population of black holes (BHs) at high redshifts (z>6) that contributes
significantly to the ionization of the intergalactic medium (IGM) would be
accompanied by the copious production of hard (>10keV) X-ray photons. The
resulting hard X-ray background would redshift and be observed as a present-day
soft X-ray background (SXB). Under the hypothesis that BHs are the main
producers of reionizing photons in the high-redshift universe, we calculate
their contribution to the present-day SXB. Our results, when compared to the
unresolved component of the SXB in the range 0.5-2 keV, suggest that accreting
BHs (be it luminous quasars or their lower-mass ``miniquasar'' counterparts)
did not dominate reionization. Distant miniquasars that produce enough X-rays
to only partially ionize the IGM to a level of at most 50% are still allowed,
but could be severely constrained by improved determinations of the unresolved
component of the SXB.


title:
Cosmological Simulations of X-ray Clusters: The Quest for Higher
  Resolution and Essential Physics

abstract:
  I review cosmological simulations of X-ray clusters. Simulations have
increased in resolution dramatically and the effects of radiative cooling, star
formation feedback, and chemical enrichment on the ICM are being simulated. The
structure and evolution of non-radiative X-ray clusters is now well
characterized. Such models fail to reproduce the observed L_x-T relation,
implying the need for additional physics. Simulations adding radiative cooling
produce too much cool gas and unreasonably high X-ray luminosities. Simulations
including star formation and feedback appear more promising, but need further
refinement. New observations should help in this regard.


title:
The host of GRB 030323 at z=3.372: a very high column density DLA system
  with a low metallicity

abstract:
  We present photometry and spectroscopy of the afterglow of GRB 030323. VLT
spectra of the afterglow show damped Lya (DLA) absorption and low- and
high-ionization lines at a redshift z=3.3718+-0.0005. The inferred neutral
hydrogen column density, log N(HI)=21.90+-0.07, is larger than any (GRB- or
QSO-) DLA HI column density inferred directly from Lya in absorption. From the
afterglow photometry, we derive a conservative upper limit to the host-galaxy
extinction: A(V)<0.5 mag. The iron abundance is [Fe/H]=-1.47+-0.11, while the
metallicity of the gas as measured from sulphur is [S/H]=-1.26+-0.20. We derive
an upper limit on the H2 molecular fraction of 2N(H2)/(2N(H2)+N(HI))<~10^-6. In
the Lya trough, a Lya emission line is detected, which corresponds to a
star-formation rate (not corrected for dust extinction) of roughly 1 Msun per
year. All these results are consistent with the host galaxy of GRB 030323
consisting of a low metallicity gas with a low dust content. We detect
fine-structure lines of silicon, SiII*, which have never been clearly detected
in QSO-DLAs; this suggests that these lines are produced in the vicinity of the
GRB explosion site. Under the assumption that these fine-structure levels are
populated by particle collisions, we estimate the HI volume density to be
n_HI=100-10000 cm^-3. HST/ACS imaging 4 months after the burst shows an
extended AB(F606W)=28.0+-0.3 mag object at a distance of 0.14" (1kpc) from the
early afterglow location, which presumably is the host galaxy of GRB 030323.


title:
The EUV Emission in the Coma Cluster of Galaxies and the Underlying
  Source of this Radiation

abstract:
  Observations with the Extreme Ultraviolet Explorer (EUVE) have shown the Coma
Cluster to be a source of EUV emission in excess of that produced by X-ray gas
in the cluster. We have re-examined the EUVE data on this cluster in an attempt
to obtain clues as to the origin of this emission. We find two important new
results. First, the ratio between the azimuthally averaged EUV excess emission
and the ROSAT hard X-ray flux is constant as a function of distance from the
cluster center outward. Second, a correlation analysis between the EUV excess
emission and the X-ray emission shows that on a detailed level the EUV excess
is spatially closely related to the X-ray emission. These findings contradict
previous suggestions as to the underlying source of the diffuse EUV emission in
Coma and provide important information in regards to the true source of this
emission. We propose a new explanation for the source of this emission: inverse
Compton scattering of microwave background photons by secondary electrons and
positrons. We explore this possibility in some detail and show that it is
consistent with all of the available observational evidence. The parent cosmic
ray protons may have been produced by any of a number of sources, including
supernovae, active galaxies, galactic winds, and cluster formation shocks, but
we believe that the most likely source is cluster formation shocks. If the EUV
emission in the Coma Cluster is, in fact, the result of secondary electrons,
this may be the only direct evidence for secondary electrons in the
intracluster medium of a cluster of galaxies, since recent work suggests that
secondary electrons may not be the cause of radio halos.


title:
Propagation of Electromagnetic Waves on a Rectangular Lattice of
  Polarizable Points

abstract:
  We discuss the propagation of electromagnetic waves on a rectangular lattice
of polarizable point dipoles. For wavelengths long compared to the lattice
spacing, we obtain the dispersion relation in terms of the lattice spacing and
the dipole polarizabilities. We also obtain the polarizabilities required for
the lattice to have the same dispersion relation as a continuum medium of given
refractive index m.; our result differs slightly from previous work by Draine &
Goodman (1993). Our new prescription can be used to assign dipole
polarizabilities when the discrete dipole approximation is used to study
scattering by finite targets. Results are shown for selected cases.


title:
The Internal Structural Adjustment due to Tidal Heating of Short-Period
  Inflated Giant Planets

abstract:
  Several short-period Jupiter-mass planets have been discovered around nearby
solar-type stars. During the circularization of their orbits, the dissipation
of tidal disturbance by their host stars heats the interior and inflates the
sizes of these planets. Based on a series of internal structure calculations
for giant planets, we examine the physical processes which determine their
luminosity-radius relation. In order for young or intensely heated gas giant
planets to attain quasi-hydrostatic equilibria, with sizes comparable to or
larger than two Jupiter radii, their interiors must have sufficiently high
temperature and low density such that degeneracy effects are relatively weak
compared to those in a mature and compact Jupiter. Consequently, the polytropic
index monotonically increases whereas the central temperature increases and
then decreases with the planets' size. These effects, along with a
temperature-sensitive opacity for the radiative surface layers of giant
planets, cause the power index of the luminosity's dependence on radius to
decrease with increasing radius. For planets larger than twice Jupiter's
radius, this index is sufficiently small that they become unstable to tidal
inflation. We make comparisons between cases of uniform heating and cases in
which the heating is concentrated in various locations within the giant planet.
Based on these results we suggest that accurate measurement of the sizes of
close-in young Jupiters can be used to probe their internal structure under the
influence of tidal heating.


title:
Wide-Area Mapping of 155 Micron Continuum Emission from the Orion
  Molecular Cloud Complex

abstract:
  We present the results of a wide-area mapping of the far-infrared continuum
emission toward the Orion complex by using a Japanese balloon-borne telescope.
The 155-um continuum emission was detected over a region of 1.5 deg^2 around
the KL nebula with 3' resolution similar to that of the IRAS 100-um map.
Assuming a single-temperature model of the thermal equilibrium dust, maps of
the temperature and the optical depth were derived from the 155 um intensity
and the IRAS 100 um intensity. The derived dust temperature is 5 - 15 K lower
and the derived dust optical thickness were derived from the 155-um intensity
and the IRAS 100-um intensity. The derived dust temperature is 5 - 15 K lower
and the derived dust optical depth is 5 - 300 times larger than those derived
from the IRAS 60 and 100-um intensities due to the significant contribution of
the statistically heated very small grains to the IRAS 60-um intensity. The
optical-thickness distribution shows a filamentary dust ridge that has a 1.5
degrees extent in the north - south direction and well resembles the
Integral-Shaped Filament (ISF) molecular gas distribution. The gas-to-dust
ratio derived from the CO molecular gas distribution along the ISF is in the
range 30 - 200, which may be interpreted as being an effect of CO depletion due
to the photodissociation and/or the freezing on dust grains.


title:
Chandra X-ray Observatory High-resolution X-ray Spectroscopy of Stars:
  Modeling and Interpretation

abstract:
  The Chandra X-ray Observatory grating spectrometers allow study of stellar
spectra at resolutions on the order of 1000. Prior x-ray observatories' low
resolution data have shown that nearly all classes of stars emit x-rays.
Chandra reveals details of line and continuum contributions to the spectra
which can be interpreted through application of plasma models based on atomic
databases. For cool stars with hot coronae interpreted in the Solar paradigm,
assumption of collisional ionization equilibrium allows derivation of
temperature distributions and elemental abundances. Densities can be derived
from He-like ion's metastable transition lines. Abundance trends are unlike the
Sun, as are the very hot temperature distributions. For young stars, there is
evidence of accretion driven x-ray emission, rather than magnetically confined
plasma emission. For some hot stars, the expected emission mechanism of shocked
winds has been challenged; there is now evidence for magnetically confined
thermal plasmas. The helium-like line emission in hot stars is susceptible to
photoexcitation, which can also be exploited to derive wind structure.


title:
Multicolor Photometric Observations of Optical Candidates to Faint ROSAT
  X-ray Sources in a 1 deg$^2$ field of the BATC Survey

abstract:
  We present optical candidates for 75 X-ray sources in a $\sim 1$ deg$^2$
overlapping region with the medium deep ROSAT survey. These candidates are
selected using the multi-color CCD imaging observations made for the T329 field
of the Beijing-Arizona-Taipei-Connecticut (BATC) Sky Survey. These X-ray
sources are relatively faint (CR $<< 0.2 s^{-1}$) and thus mostly are not
included in the RBS catalog, they also remain as X-ray sources without optical
candidates in a previous identification program carried out by the Hamburg
Quasar Survey. Within their position-error circles, almost all the X-ray
sources are observed to have one or more spatially associated optical
candidates within them down to the magnitude $m_V \sim 23.1$. We have
classified 149 of 156 detected optical candidates with 73 of the 75 X-ray
sources with a SED-based Object Classification Approach (SOCA). These optical
candidates include: 31 QSOs, 39 stars, 37 starburst galaxies, 42 galaxies, and
7 "just" visible objects. We have also cross-correlated the positions of these
optical objects with NED, the FIRST radio source catalog and the 2MASS catalog.
Separately, we have also SED-classified the remaining 6011 objects in our field
of view. Optical objects are found at the $6.5\sigma$ level above what one
would expect from a random distribution, only QSOs are over-represented in
these error circles at greater than 4$\sigma$ frequency. We estimate redshifts
for all extragalactic objects, and find a good correspondence of our predicted
redshift with the measured redshift (a mean error of 0.04 in $\Delta z$. There
appears to be a supercluster at z $\sim$ 0.3-0.35 in this direction, including
many of the galaxies in the X-ray error circles are found in this redshift
range.


title: A molecular gas phase in the Cold Neutral Medium?

abstract:
  I examine the possibility that the Cold Neutral Medium of the interstellar
medium in galaxies contains a molecular gas phase that may represent a
significant and even the dominant amount of its mass in metal-poor regions. In
spiral galaxies such regions are found at large galactocentric distances where
diffuse H$_2$ gas will be untraceable through its feeble $ ^{12}$CO J=1--0
emission, the very lack of it being also responsible its higher kinetic
temperatures ($\rm T_k\sim 60-100$ K). Sensitive sub-mm imaging of spiral
galaxies has demonstrated the existence of dust well inside their HI gas
distribution while recent observational work suggests a high H$_2$ formation
rate from HI association onto grains. The latter is indeed a critical unknown
and a high value can easily compensate for the reduction of the available grain
surface in the metal-poor environments giving rise to a CO-poor, diffuse H$_2$
phase that may then contribute significantly to the mass and pressure of the
interstellar medium in such environments.


title: Young Massive Clusters in the Galactic Center

abstract:
  The three young clusters in the Galactic Center represent the closest
examples of massive starbursts and they define the upper mass limit of the
Galactic cluster mass functions. In this review, I describe the characteristics
and content of the Arches, Quintuplet, and Central clusters. They each are more
massive than any other cluster in the Galaxy, and the Arches cluster, in
particular, has a mass and age that make it ideal for studies of massive
stellar evolution and dense stellar systems. A preliminary measurement
indicates that the initial mass function in the Galactic center is top-heavy,
suggesting an environmental effect that has otherwise been absent in similar
observations for Galactic clusters. Given the relatively more evolved nature of
the Quintuplet and Central clusters, these clusters contain stars in a wide
range of evolutionary states, including Luminous Blue Variables and Wolf-Rayet
stars. The Quintuplet cluster provides a particularly interesting view of the
most massive stars that are known, the Pistol Star and FMM362. An analysis of
the mass spectrum in the Arches cluster suggests an upper mass cutoff of
\~150-200 Msun.


title:
Comments on the Redshift Distribution of 44,200 SDSS Quasars: Evidence
  for Predicted Preferred Redshifts?

abstract:
  A Sloan Digital Sky Survey (SDSS) source sample containing 44,200 quasar
redshifts is examined. Although arguments have been put forth to explain some
of the structure observed in the redshift distribution, it is argued here that
this structure may just as easily be explained by the presence of previously
predicted preferred redshifts.


title: Detached white dwarf main-sequence star binaries

abstract:
  We considered the formation of detached white dwarf main-sequence star (WDMS)
binaries through seven evolutionary channels subdivided according to the
evolutionary process that gives rise to the formation of the white dwarf or its
helium-star progenitor: dynamically stable Roche-lobe overflow (Algol-type
evolution), dynamically unstable Roche-lobe overflow (common-envelope
evolution), or stellar winds (single star evolution). We examine the
sensitivity of the population to changes in the amount of mass lost from the
system during stable Roche-lobe overflow, the common-envelope ejection
efficiency, and the initial mass ratio or initial secondary mass distribution.
In the case of a flat initial mass ratio distribution, the local space density
of WDMS binaries is of the order of 10^{-3}/pc^3. This number decreases to
10^{-4}/pc^3 when the initial mass ratio distribution is approximately
proportional to the inverse of the initial mass ratio. More than 75% of the
WDMS binary population stems from wide systems in which both components evolve
as if they were single stars. The remaining part of the population is dominated
by systems in which the white dwarf is formed in a common-envelope phase. The
birthrate of WDMS binaries forming through a common-envelope phase is about 10
times larger than the birthrate of WDMS binaries forming through a stable
Roche-lobe overflow phase. The ratio of the number of helium white dwarf
systems to the number of carbon/oxygen or oxygen/neon/magnesium white dwarf
systems derived from large samples of observed WDMS binaries by, e.g., future
planet-search missions such as SuperWASP, COROT, and Kepler may furthermore
constrain the common-envelope ejection efficiency.


title: The Gamma-ray bright BL Lac object RX J1211+2242

abstract:
  RX J1211+2242 is an optically faint (B = 19.2 mag) but X-ray bright (2 - 10
keV flux fx = 5e-12 erg/cm**2/sec) AGN, which has been shown to be a BL Lac
object at redshift z = 0.455. The ROSAT X-ray, Calar Alto optical, and NVSS
radio data suggest that the peak of the synchrotron emission of this object is
at energies as high as several keV. BeppoSAX observations have been carried out
simultaneously with optical observations in order to extend the coverage to
higher energies. The new data indeed indicate a turn-over in the 2 - 10 keV
energy region. We propose that RX J1211+2242 is the counterpart of the
unidentified EGRET source 3EG J1212+2304, making it a gamma-ray emitter with
properties similar to, for example, Markarian 501 in its bright state, though
being at a much larger distance.


title:
The CI lines as tracers of molecular gas, and their prospects at high
  redshifts

abstract:
  We examine the fine structure lines $^{3}P_{1}\to $$^{3}P_{0}$ (492 GHz) and
$ ^{3}P_2\to $$^{3}P_1$ (809 GHz) of neutral atomic carbon as bulk molecular
gas mass tracers and find that they can be good and on many occasions better
than $ ^{12}$CO transitions, especially at high redshifts. The notion of CI
emission as an H$_2$ gas mass tracer challenges the long-held view of its
distribution over only a relatively narrow layer in the CII/CI/CO transition
zone in FUV-illuminated molecular clouds. Past observations have indeed
consistently pointed towards a more extended CI distribution but it was only
recently, with the advent of large scale imaging of its $^{3}P_{1}\to
$$^{3}P_{0}$ transition, that its surprising ubiquity in molecular clouds has
been fully revealed. In the present work we show that under {\it typical} ISM
conditions such an ubiquity is inevitable because of well known dynamic and
non-equilibrium chemistry processes maintaining a significant [C]/[$ ^{12}$CO]
abundance throughout Giant Molecular Clouds during their lifetime. These
processes are more intense in star-forming environments where a larger ambient
cosmic ray flux will also play an important role in boosting [C]/[$ ^{12}$CO].
The resulting CI lines can be bright and effective H$_2$ mass tracers
especially for diffuse ($\sim 10^2-10^3\rm cm^{-3}$) gas while in UV-intense
and/or metal-poor environments their H$_2$-tracing capability diminishes
because of large scale CII production but nevertheless remains superior to that
of $ ^{12}$CO. The best place to take full advantage of CI's capacity to trace
H$_2$ is not in the low-$z$ Universe, where large atmospheric absorption at 492
and 809 GHz precludes routine observations, but at high redshifts ($\rm z\ga
1$).


title:
Stochastic excitation of gravity waves by overshooting convection in
  solar-type stars

abstract:
  The excitation of gravity waves by penetrative convective plumes is
investigated using 2D direct simulations of compressible convection. The
oscillation field is measured by a new technique based on the projection of our
simulation data onto the theoretical g-modes solutions of the associated linear
eigenvalue problem. This allows us to determine both the excited modes and
their corresponding amplitudes accurately.


title: On the properties of young multiple stars

abstract:
  Abridged/ We present numerical results on the properties of young binary and
multiple stellar systems. Our analysis is based on a series of SPH + Nbody
simulations of the fragmentation of small molecular clouds, that fully resolve
the opacity limit for fragmentation. We have produced a statistically
significant number of stable multiple systems, with components separations in
the range 1-1000 AU. At the end of the hydrodynamical evolution (0.5 Myr) we
find that ~60% of stars and brown dwarfs are members of multiples systems, with
about a third of these being low mass, weakly bound outliers in wide eccentric
orbits. Our results imply that in the stellar regime most stars are in
multiples (~80%) and that this fraction is an increasing function of primary
mass. After Nbody integration to 10.5 Myr, the percentage of bound objects has
dropped to ~40%, as most very low mass stars and brown dwarfs have been
released to the field. Brown dwarfs are never found to be very close companions
to stars (brown dwarf desert at very small separations), but one case exists of
a brown dwarf companion at intermediate separations (10 AU). Our simulations
can accommodate the existence of brown dwarf companions at large separations,
but only if the primaries of these systems are themselves multiples. We have
compared the outcome of our simulations with the properties of real stellar
systems as deduced from the IR CM diagram of the Praesepe cluster and from
spectroscopic and high-resolution imaging surveys of young clusters and the
field.


title: Diffusive propagation of UHECR and the propagation theorem

abstract:
  We present a detailed analytical study of the propagation of ultra high
energy (UHE) particles in extragalactic magnetic fields. The crucial parameter
which affects the diffuse spectrum is the separation between sources. In the
case of a uniform distribution of sources with a separation between them much
smaller than all characteristic propagation lengths, the diffuse spectrum of
UHE particles has a {\em universal} form, independent of the mode of
propagation. This statement has a status of theorem. The proof is obtained
using the particle number conservation during propagation, and also using the
kinetic equation for the propagation of UHE particles. This theorem can be also
proved with the help of the diffusion equation. In particular, it is shown
numerically, how the diffuse fluxes converge to this universal spectrum, when
the separation between sources diminishes. We study also the analytic solution
of the diffusion equation in weak and strong magnetic fields with energy losses
taken into account. In the case of strong magnetic fields and for a separation
between sources large enough, the GZK cutoff can practically disappear, as it
has been found early in numerical simulations. In practice, however, the source
luminosities required are too large for this possibility.


title: HAWC: A Next Generation All-Sky VHE Gamma-Ray Telescope

abstract:
  The study of the universe at energies above 100 GeV is a relatively new and
exciting field. The current generation of pointed instruments have detected TeV
gamma rays from at least 10 sources and the next generation of detectors
promises a large increase in sensitivity. We have also seen the development of
a new type of all-sky monitor in this energy regime based on water Cherenkov
technology (Milagro). To fully understand the universe at these extreme
energies requires a highly sensitive detector capable of continuously
monitoring the entire overhead sky. Such an instrument could observe prompt
emission from gamma-ray bursts and probe the limits of Lorentz invariance at
high energies. With sufficient sensitivity it could detect short transients
($\sim$15 minutes) from active galaxies and study the time structure of flares
at energies unattainable to space-based instruments. Unlike pointed instruments
a wide-field instrument can make an unbiased study of all active galaxies and
enable many multi-wavelength campaigns to study these objects. This paper
describes the design and performance of a next generation water Cherenkov
detector. To attain a low energy threshold and have high sensitivity the
detector should be located at high altitude ($>$ 4km) and have a large area
($\sim$40,000 m$^2$). Such an instrument could detect gamma ray bursts out to a
redshift of 1, observe flares from active galaxies as short as 15 minutes in
duration, and survey the overhead sky at a level of 50 mCrab in one year.


title:
TeV Gamma-Ray Survey of the Northern Hemisphere Sky Using the Milagro
  Observatory

abstract:
  Milagro is a water Cherenkov extensive air shower array that continuously
monitors the entire overhead sky in the TeV energy band. The results from an
analysis of $\sim$3 years of data (December 2000 through November 2003) are
presented. The data has been searched for steady point sources of TeV gamma
rays between declinations of 1.1 degrees and 80 degrees. Two sources are
detected, the Crab Nebula and the active galaxy Mrk 421. For the remainder of
the Northern hemisphere we set 95% C.L. upper limits between 275 and 600 mCrab
(4.8-10.5$\times 10^{-12}$ cm$^{-2}$ s$^{-1}$) above 1 TeV for source
declinations between 5 degrees and 70 degrees. Since the sensitivity of Milagro
depends upon the spectrum of the source at the top of the atmosphere, the
dependence of the limits on the spectrum of a candidate source is presented.
Because high-energy gamma rays from extragalactic sources are absorbed by
interactions with the extragalactic background light the dependence of the flux
limits on the redshift of a candidate source are given. The upper limits
presented here are over an order of magnitude more stringent than previously
published limits from TeV gamma-ray all-sky surveys.


title:
On Foreground Removal from the Wilkinson Microwave Anisotropy Probe Data
  by an Internal Linear Combination Method: Limitations and Implications

abstract:
  We study the Internal Linear Combination (ILC) method presented by the
Wilkinson Microwave Anisotropy Probe (WMAP) science team, with the goal of
determining whether it may be used for cosmological purposes, as a
template-free alternative to existing foreground correction methods. We
conclude that the method does have the potential to do just that, but great
care must be taken both in implementation, and in a detailed understanding of
limitations caused by residual foregrounds which can still affect cosmological
results. As a first step we demonstrate how to compute the ILC weights both
accurately and efficiently by means of Lagrange multipliers, and apply this
method to the observed data to produce a new version of the ILC map. Next we
describe how to generate Monte Carlo simulations of the ILC map, and find that
these agree well with the observed map on angular scales up to l~200. Finally
we make two comments to the on-going debates concerning the large-scale
properties of the WMAP data. First, we note that the Galactic south-eastern
quadrant is associated with notably different ILC weights than the other three
quadrants, possibly indicating a foreground related anisotropy. Second, we
study the properties of the quadrupole and octopole (amplitude, alignment and
planarity), and confirm the previously reported anomalies. Even more
interestingly, we find that the l=5 mode is spherically symmetric at about 3
sigma, and that the l=6 mode is planar at the 2 sigma level. However, we also
assess the impact of residual foregrounds on these statistics, and find that
the ILC map is not clean enough to allow for cosmological conclusions.
Alternative methods must be developed to study these issues further.


title: KH 15D: A Spectroscopic Binary

abstract:
  We present the results of a high-resolution spectroscopic monitoring program
of the eclipsing pre-main-sequence star KH 15D that reveal it to be a
single-line spectroscopic binary. We find that the best-fit Keplerian model has
a period P = 48.38 days, which is nearly identical to the photometric period.
Thus, we find the best explanation for the periodic dimming of KH 15D is that
the binary motion carries the currently visible star alternately above and
below the edge of an obscuring cloud. The data are consistent with the models
involving an inclined circumstellar disk, as recently proposed by Winn et al.
(2004) and Chiang & Murray-Clay (2004). We show that the mass ratio expected
from models of PMS evolution, together with the mass constraints for the
visible star, restrict the orbital eccentricity to 0.68 < e < 0.80 and the mass
function to 0.125 < Fm < 0.5 Msun.


title:
The HELLAS2XMM 1dF Survey: a window on exotic hard X-ray selected
  sources

abstract:
  Recent Chandra and XMM-Newton surveys have confirmed that the cosmic X-ray
background is mostly due to accretion onto super-massive black holes,
integrated over cosmic time. Here we review the results obtained from the
photometric and spectroscopic follow-up observations of the 122 X-ray sources
detected by the HELLAS2XMM 1dF Survey down to a 2-10 keV flux of ~10^{-14} erg
cm^-2 s^-1. In particular, we focus on the multiwavelength properties of a few
intriguing classes of X-ray sources: high X-ray-to-optical flux ratio sources,
Type 2 quasars, and XBONGs.


title:
A new powerful method for probing the atmospheres of transiting
  exoplanets

abstract:
  Although atmospheric transmission spectroscopy of HD209458b with the Hubble
Space Telescope has been very successful, attempts to detect its atmospheric
absorption features using ground-based telescopes have so far been fruitless.
Here we present a new method for probing the atmospheres of transiting
exoplanets which may be more suitable for ground-based observations, making use
of the Rossiter effect. During a transit, an exoplanet sequentially blocks off
light from the approaching and receding parts of the rotating star, causing an
artificial radial velocity wobble. The amplitude of this signal is directly
proportional to the effective size of the transiting object, and the wavelength
dependence of this effect can reveal atmospheric absorption features, in a
similar way as with transmission spectroscopy. The advantage of this method
over conventional atmospheric transmission spectroscopy is that it does not
rely on accurate photometric comparisons of observations on and off transit,
but instead depends on the relative velocity shifts of individual stellar
absorption lines within the same on-transit spectra. We used an archival
VLT/UVES data set to apply this method to HD209458. The amplitude of the
Rossiter effect is shown to be 1.7+-1.2 m/sec higher in the Sodium D lines than
in the weighted average of all other absorption lines in the observed
wavelength range, corresponding to an increment of 4.3+-3% (1.4 sigma). The
uncertainty in this measurement compares to a photometric accuracy of 5e-4 for
conventional atmospheric transmission spectroscopy, more than an order of
magnitude higher than previous attempts using ground-based telescopes.
Observations specifically designed for this method could increase the accuracy
further by a factor 2-3.


title: Are Halos of Collisionless Cold Dark Matter Collisionless?

abstract:
  Much recent discussion about dark matter has been centered on two seemingly
independent problems: the abundance of substructure in dark matter halos, and
the cuspiness of the halos' inner density profile. We explore possible
connections between the two problems by studying the gravitational scattering
effects due to subhalos on the phase-space distribution of dark matter
particles in the main halos. Our series of controlled numerical experiments
indicates that the number and mass density of subhalos can be high enough to
cause the collisionless dark matter particles in the inner part of a main halo
to diffuse, flattening the main halo's inner cusp within a few dynamical times.
Depending on the masses and concentration of the subhalos, the inner density
profile of the whole system (main plus sub halos) can either steepen or
flatten. Subhalo accretion can therefore introduce significant scatter in the
inner density profiles of dark matter halos, offering a possible explanation
for the range of profiles seen in both observations and cosmological
simulations.


title:
VLA HI Observations of Gas Stripping in the Virgo Cluster Spiral NGC
  4522

abstract:
  We present VLA HI observations at ~20"=1.5 kpc resolution of the highly
inclined, HI-deficient Virgo cluster spiral galaxy NGC 4522, which is one of
the clearest and nearest cases of ongoing ICM-ISM stripping. HI is abundant and
spatially coincident with the stellar disk in the center, but beyond R = 3 kpc
the HI distribution in the disk is sharply truncated and the only HI is
extraplanar, and all on the northwest side. The kinematics and the morphology
of the HI appear more consistent with ongoing stripping, and less consistent
with gas fall-back which may occur long after peak pressure. Much of the
extraplanar gas exhibits a modest net blueshift with respect to the galaxy's
disk rotational velocities, consistent with gas accelerated toward the mean
cluster velocity. The SW side of the galaxy has less HI in the disk but more HI
in the halo, suggesting more effective gas removal on the side of the galaxy
which is rotating into the ICM wind. The galaxy is 3.3 degrees ~800 kpc from
M87, somewhat outside the region of strongest cluster X-ray emission. The ram
pressure may be significantly stronger than standard values, due to large bulk
motions and local density enhancements of the ICM gas, which may occur in a
dynamic, shock-filled ICM experiencing subcluster merging. The HI and H-alpha
distributions are similar, implying that the star-forming molecular ISM has
been effectively stripped from the outer disk of the galaxy along with the HI.


title:
Modeling the Counts of Faint Radio Loud Quasars: Constraints on the
  Supermassive Black Hole Population and Predictions for High Redshift

abstract:
  We use a physically motivated semi-analytic model, based on the mass function
of dark matter halos, to predict the number of radio-loud quasars as a function
of redshift and luminosity. Simple models in which the central BH mass scales
with the velocity dispersion of its host halo as M(bh) sigma(halo)^5 have been
previously found to be consistent with a number of observations, including the
optical and X-ray quasar luminosity functions. We find that similar models,
when augmented with an empirical prescription for radio emission, overpredict
the number of faint (10 micro-Jy) radio sources by 1-2 orders of magnitude.
This translates into a more stringent constraint on the low-mass end of the
quasar black hole mass function than is available from the Hubble and Chandra
Deep Fields. We interpret this discrepancy as evidence that black holes with
masses below 10^7 Msun are either rare or are not as radio-loud as their more
massive counterparts. Models that exclude BHs with masses below 10^7 Msun are
in agreement with the deepest existing radio observations, but still produce a
significant tail of high-redshift objects. In the 1-10GHz bands, at the
sensitivity of 10 micro-Jy, we find surface densities of 100, 10, and 0.3
deg^-2 for sources located at z>6, 10, and 15, respectively. The discovery of
these sources with instruments such as the Allen Telescope Array (ATA),
Extended Very Large Array (EVLA), and the Square Kilometer Array (SKA) would
open a new window for the study of supermassive BHs at high redshift. We also
find surface densities of 0.1 deg^-2 at z > 6 for mJy sources that can be used
to study 21 cm absorption from the epoch of reionization. We suggest that,
although not yet optically identified, the FIRST survey may have already
detected 10^3-10^4 such sources.


title:
XMM-Newton Observations of NGC 507: Super-solar Metal Abundances in the
  Hot ISM

abstract:
  We present the results of the X-ray XMM-Newton observations of NGC 507, a
dominant elliptical galaxy in a small group of galaxies, and report
'super-solar' metal abundances of both Fe and a-elements in the hot ISM of this
galaxy. We find Z_Fe = 2-3 times solar inside the D25 ellipse of NGC 507. This
is the highest Z_Fe reported so far for the hot halo of an elliptical galaxy;
this high Iron abundance is fully consistent with the predictions of stellar
evolution models, which include the yield of both type II and Ia supernovae.
The spatially resolved, high quality XMM spectra provide enough statistics to
formally require at least three emission components: two soft thermal
components indicating a range of temperatures in the hot ISM, plus a harder
component, consistent with the integrated output of low mass X-ray binaries
(LMXBs). The abundance of a-elements (most accurately determined by Si) is also
found to be super-solar. The a-elements to Fe abundance ratio is close to the
solar ratio, suggesting that ~70% of the Iron mass in the hot ISM was
originated from SNe Type Ia. The a-element to Fe abundance ratio remains
constant out to at least 100 kpc, indicating that SNe Type II and Ia ejecta are
well mixed in a scale much larger than the extent of the stellar body.


title:
A sample of radio galaxies spanning three decades in radio luminosity -
  I. The host-galaxy properties and black-hole masses

abstract:
  The results of analysis of HST I-band imaging of a sample of 41 radio
galaxies spanning three orders of magnitude in radio luminosity at redshift
z~0.5 are presented. The full sample is drawn from four complete, low-frequency
selected radio samples with progressively fainter flux-density limits (3CRR,
6CE, 7CRS and the new TexOx-1000 sample). Modelling of the HST imaging data
shows that the host galaxies have surface-brightness distributions consistent
with those expected for classic ellipticals (Sersic parameter, beta~0.25), with
beta in the range 0.17<beta<0.30, and a mean of <beta>=0.23\pm0.01. The
host-galaxy luminosities are comparable with those of galaxies drawn from the
bright end of the local cluster galaxy luminosity function, spanning the range
0.7L^{\star}<L<10L^{\star}, with a mean of 3.2\pm0.3 L^{\star}. In addition,
the radio galaxies are shown to follow a Kormendy relation indistinguishable
from that of powerful low-redshift radio galaxies. Combining our new results
with those in the literature it is found that the scalelengths and Kormendy
relations of 3C-class radio galaxies do not vary significantly over the
redshift range 0.0<z<0.8, providing no evidence for dynamical evolution of this
class of host galaxy within this redshift interval. Converting the host-galaxy
luminosities into black-hole mass estimates predicts that the radio galaxies
harbour central black holes with masses in the range 10^{8.1}\Msun <M_{bh}<
10^{9.5}\Msun, with a geometric mean of <M_{bh}>=10^{8.87\pm 0.04}\Msun.
Finally, a significant (~3 sigma) correlation is found between black-hole mass
and 151-MHz radio luminosity for those objects in the sample with either
high-excitation nuclear spectra or classical double radio structures.
(abridged)


title:
Application of fast CCD drift scanning to speckle imaging of binary
  stars

abstract:
  A new application of a fast CCD drift scanning technique that allows us to
perform speckle imaging of binary stars is presented. For each observation, an
arbitrary number of speckle frames is periodically stored on a computer disk,
each with an appropriate exposure time given both atmospheric and instrumental
considerations. The CCD charge is shifted towards the serial register and read
out sufficiently rapidly to avoid an excessive amount of interframe dead time.
Four well-known binary systems (ADS 755, ADS 2616, ADS 3711 and ADS 16836) are
observed in to show the feasibility of the proposed technique.
  Bispectral data analysis and power spectrum fitting is carried out for each
observation, yielding relative astrometry and photometry. A new approach for
self-calibrating this analysis is also presented and validated.
  The proposed scheme does not require any additional electronic or optical
hardware, so it should allow most small professional observatories and advanced
amateurs to enjoy the benefits of diffraction-limited imaging.


title: S4N: A Spectroscopic Survey of Stars in the Solar Neighborhood

abstract:
  [ABRIDGED] We report the results of a high-resolution spectroscopic survey of
all the stars more luminous than Mv = 6.5 mag within 14.5 pc from the Sun. We
derive stellar parameters and perform a preliminary abundance and kinematic
analysis of the F-G-K stars in the sample. The inferred metallicity ([Fe/H])
distribution is centered at about -0.1 dex, and shows a standard deviation of
0.2 dex.
  We identify a number of metal-rich K-type stars which appear to be very old,
confirming the claims for the existence of such stars in the solar
neighborhood. With atmospheric effective temperatures and gravities derived
independently of the spectra, we find that our classical LTE model-atmosphere
analysis of metal-rich (and mainly K-type) stars provides discrepant abundances
from neutral and ionized lines of several metals. Based on transitions of
majority species, we discuss abundances of 16 chemical elements.
  In agreement with earlier studies we find that the abundance ratios to iron
of Si, Sc, Ti, Co, and Zn become smaller as the iron abundance increases until
approaching the solar values, but the trends reverse for higher iron
abundances. At any given metallicity, stars with a `low' galactic rotational
velocity tend to have high abundances of Mg, Si, Ca, Sc, Ti, Co, Zn, and Eu,
but low abundances of Ba, Ce, and Nd. The Sun appears deficient by roughly 0.1
dex in O, Si, Ca, Sc, Ti, Y, Ce, Nd, and Eu, compared to its immediate
neighbors with similar iron abundances.


title: Simulation of Vortex--Dominated Flows Using the FLASH Code

abstract:
  We compare the results of two--dimensional simulations to experimental data
obtained at Los Alamos National Laboratory in order to validate the FLASH code.
FLASH is a multi--physics, block--structured adaptive mesh refinement code for
studying compressible, reactive flows in various astrophysical environments.
The experiment involves the lateral interaction between a planar Ma=1.2 shock
wave with a cylinder of gaseous sulfur hexafluoride (SF$_6$) in air. The
development of primary and secondary flow instabilities after the passage of
the shock, as observed in the experiments and numerical simulations, are
reviewed and compared. The sensitivity of numerical results to several
simulation parameters are examined. Computed and experimentally measured
velocity fields are compared. Motivation for experimental data in planes
parallel to the cylinder axis is provided by a speculative three--dimensional
simulation.


title:
Consequences of Observational Uncertainties on the Detection of Cosmic
  Topology

abstract:
  The observed values of density parameters inevitably involve uncertainties.
We study the conditions for detectability and undetectability of cosmic
topology in presence of such uncertainties. We present closed analytical forms
of (un)detectability conditions for infinite redshift, which are important
because: (i) they allow the examine of the detectability of cosmic topology not
only for individual manifolds (topologies), but also in whole classes of
manifolds; (ii) they are, to a very good approximation, (un)detectibility
conditions for z=1100.


title:
Problems with studying topology of the universe via circles from cosmic
  microwave background data

abstract: This paper has been withdrawn by the authors for future revision.


title: Omega Centauri: The Population Puzzle Goes Deeper

abstract:
  We present HST observations that show a bifurcation of colors in the middle
main sequence of the globular cluster Omega Centauri. We see this in three
different fields, observed with different cameras and filters. We also present
high precision photometry of a central ACS field which shows a number of
main-sequence turnoffs and subgiant branches. The double main sequence, the
multiple turnoffs and subgiant branches, and other population sequences
discovered in the past along the red giant branch of this cluster add up to a
fascinating but frustrating puzzle. We suggest various explanations, none of
them very conclusive.


title: SiO Maser Survey of the Large-Amplitude Variables in the Galactic Center

abstract:
  We have surveyed ~400 known large-amplitude variables within 15' of the
galactic center in the SiO J=1--0 v=1 and 2 maser lines at 43 GHz, resulting in
179 detections. SiO lines were also detected from 16 other resulting in 180
detections. SiO lines were also detected from 16 other sources, which are
located within 20" (the telescope half beamwidth) of the program objects. The
detection rate of 48 percent is comparable to that obtained in Bulge IRAS
source surveys. Among the SiO detections, five stars have radial velocities
greater than 200 km/s. The SiO detection rate increases steeply with the period
of light variation, particularly for stars with P>500 d, where it exceeds 80%.
We found that, at a given period, the SiO detection rate is approximately three
times that for OH. These facts suggest that the large-amplitude variables in
the Nuclear Disk region are AGB stars similar in their overall properties to
the inner and outer Bulge IRAS/SiO sources. From the set of radial velocity
data, the mass distribution within 30 pc of the galactic center is derived by a
new method which is based on the collisionless Boltzmann equation integrated
along the line of sight. The mass within 30 pc is about 6.4 [\pm 0.7] \times
10^7 M_{\odot} and the mass of the central black hole is 2.7 [\pm 1.3] \times
10^6 M_{\odot}. Consideration of the line-of-sight velocity of each star and
its potential energy leads to the conclusion that the five high-velocity stars
come from galactocentric distances as high as 300 pc. The high-velocity
subsample of stars with negative radial velocities exhibits a tendency to have
brighter K magnitudes than the subsample of stars with positive velocities. The
origin of these high-velocity stars is discussed.


title: High-Energy Gamma-Ray Observations of W Comae with STACEE

abstract:
  We report on observations of the blazar W Comae (ON+231) with the Solar Tower
Atmospheric Cherenkov Effect Experiment (STACEE), a wavefront-sampling
atmospheric Cherenkov telescope, in the spring of 2003. In a data set
comprising 10.5 hours of ON-source observing time, we detect no significant
emission from W Comae. We discuss the implications of our results in the
context of the composition of the relativistic jet in W Comae, examining both
leptonic and hadronic models for the jet. We derive 95% confidence level upper
limits on the flux at the level of 1.5--3.5 x 10^{-10} cm^{-2} s^{-1} above 100
GeV for the leptonic models, or 0.5--1.1 x 10^{-10} cm^{-2} s^{-1} above 150
GeV for the hadronic models.


title: Radiative Shocks in Rotating Accretion Flows around Black Holes

abstract:
  It is well known that the rotating inviscid accretion flows with adequate
injection parameters around black holes could form shock waves close to the
black holes, after the flow passes through the outer sonic point and can be
virtually stopped by the centrifugal force.
  We examine numerically such shock waves in 1D and 2D accretion flows, taking
account of cooling and heating of the gas and radiation transport.
  The numerical results show that the shock location shifts outward compared
with that in the adiabatic solutions and that the more rarefied ambient density
leads to the more outward shock location.
  In the 2D-flow, we find an intermediate frequency QPO behavior of the shock
location as is observed in the black hole candidate
  GRS 1915+105.


title:
Detection of X-ray Clusters of Galaxies by Matching RASS Photons and
  SDSS Galaxies within GAVO

abstract:
  A new method for a simultaneous search for clusters of galaxies in X-ray
photon maps and optical galaxy maps is described. The merging of X-ray and
optical data improves the source identification so that a large amount of
telescope time for spectroscopic follow-up can be saved. The method appears
thus ideally suited for the analysis of the recently proposed wide-angle X-ray
missions like DUO and ROSITA. As a first application, clusters are extracted
from the 3rd version of the ROSAT All-Sky Survey and the Early Date Release of
the Sloan Digital Sky Survey (SDSS). The time-consuming computations are
performed within the German Astrophysical Virtual Observatory (GAVO). On a test
area of 140 square degrees, 75 X-ray clusters are detected down to an X-ray
flux limit of $3-5\times 10^{-13} {\rm erg} {\rm s}^{-1} {\rm cm}^{-2}$ in the
ROSAT energy band 0.1-2.4 keV. The clusters have redshifts $z\le 0.5$. The
survey thus fills the gap between traditional large-area X-ray surveys and
serendipitous X-ray cluster searches based on pointed observations, and has the
potential to yield about 4,000 X-ray clusters after completion of SDSS.


title: The crust cooling curve of the neutron star in MXB 1659-29

abstract:
  We have monitored the quasi-persistent neutron-star X-ray transient MXB
1659-29 in quiescence using Chandra. The purpose of our observations was to
monitor the quiescent behavior of the source after its last prolonged outburst
episode and to study the cooling curve of the neutron star in this system. We
discuss the results obtained and how they constrain the properties of the
neutron star in MXB 1659-29


title: Stellar polarimetry with ESPaDOnS

abstract:
  ESPaDOnS is a new-generation cross-dispersed echelle spectropolarimeter, the
commissioning phase of which is scheduled at the Canada-France-Hawaii Telescope
(CFHT) for spring 2004. This instrument will provide full coverage of the
optical domain (370 nm to 1,000 nm) in all polarization states (circular and
linear) at a resolving power of about 70,000, with a peak efficiency of 20%
(telescope and detector included). It includes a bench-mounted spectrograph,
fiber-fed from a Cassegrain-mounted module including all polarimetric and
calibration facilities.
  ESPaDOnS should be the most powerful tool dedicated to stellar
spectropolarimetry, therefore opening unprecedented perspectives for major
issues of stellar physics, from studies of stellar interiors to investigations
of stellar atmospheres, stellar surfaces, stellar magnetic fields, and to
observations of circumstellar environments and extra-solar planets.


title: Radio spectra of a sample of X-ray selected BL Lacs

abstract:
  We present simultaneous multifrequency radio observations for a complete
subsample of 26 XBLs from the Einstein Extended Medium-Sensitivity Survey,
obtained with the Very Large Array (VLA). Spectra are computed using fluxes at
20, 6 and 3.6 cm. Unlike many radio selected samples, the EMSS did not impose
any criterion on the radio spectrum to identify BL Lac objects. It is therefore
possible to investigate the intrinsic radio spectral slope distribution and to
determine the effect produced by this selection criterion. We find that 15% of
the observed objects do not meet the flat-spectrum criterion imposed on some
other BL Lac samples. A dataset that includes non-simultaneous data (that are
also taken with different VLA configurations) shows an even higher percentage
of steep spectrum sources. This effect can be ascribed to a larger fraction of
extended flux detected with the more compact VLA configuration.Possible biases
introduced by the flat--radio-spectrum criterion in the radio-selected BL Lac
samples cannot explain the discrepancies observed in the evolutionary
properties of Radio and X-ray selected samples of BL Lacs.


title: BeppoSAX-WFC monitoring of the Galactic Center region

abstract:
  We review the results obtained with the Galactic center campaigns of the
BeppoSAX Wide Field X-ray Cameras (WFCs). This pertains to the study of
luminous low-mass X-ray binaries (LMXBs). When pointed at the Galactic center,
the WFC field of view contains more than half of the Galactic LMXB population.
The results exemplify the excellent WFC capability to detect brief X-ray
transients. Firstly, the WFCs expanded the known population of Galactic
thermonuclear X-ray bursters by 50%. At least half of all LMXBs are now
established to burst and, thus, to contain a neutron star as compact accretor
rather than a black hole candidate. We provide a complete list of all 76
currently known bursters, including the new case 1RXS J170854.4-321857.
Secondly, the WFCs have uncovered a population of weak transients with peak
luminosities up to ~10^37 erg/s and durations from days to weeks. One is the
first accretion-powered millisecond pulsar SAX J1808.4-3658. Thirdly, the WFCs
contributed considerably towards establishing that nearly all (12 out of 13)
luminous low-mass X-ray binaries in Galactic globular clusters contain neutron
stars rather than black holes. Thus, the neutron star to black hole ratio in
clusters differs from that in the Galactic disk at a marginal confidence level
of 97%.


title:
The Absorption Signatures of Dwarf Galaxies: The z=1.04 Multicloud Weak
  MgII Absorber toward PG 1634+706

abstract:
  We analyze high resolution spectra of a multi--cloud weak [defined as
W_r(MgII) < 0.3 A] absorbing system along the line of sight to PG 1634+706.
This system gives rise to a partial Lyman limit break and absorption in MgII,
SiII, CII, SiIII, SiIV, CIV, and OVI. The lower ionization transitions arise in
two kinematic subsystems with a separation of ~150 km/s. Each subsystem is
resolved into several narrow components, having Doppler widths of 3-10 kms. For
both subsystems, the OVI absorption arises in a separate higher ionization
phase, in regions dominated by bulk motions in the range of 30-40 km/s. The two
OVI absorption profiles are kinematically offset by ~50 km/s with respect to
each of the two lower ionization subsystem. In the stronger subsystem, the
SiIII absorption is strong with a distinctive, smooth profile shape and may
partially arise in shock heated gas. Moreover, the kinematic substructure of
SiIV traces that of the lower ionization MgII, but may be offset by ~3 km/s.
Based upon photoionization models, constrained by the partial Lyman limit
break, we infer a low metallicity of ~0.03 solar for the low ionization gas in
both subsystems. The broader OVI phases have a somewhat higher metallicity, and
they are consistent with photoionization; the profiles are not broad enough to
imply production of OVI through collisional ionization. Various models,
including outer disks, dwarf galaxies, and superwinds, are discussed to account
for the phase structure, metallicity, and kinematics of this absorption system.
We favor an interpretation in which the two subsystems are produced by
condensed clouds far out in the opposite extremes of a multi-layer dwarf galaxy
superwind.


title:
Three-dimensional magnetohydrodynamic simulations of in situ shock
  formation in the coronal streamer belt

abstract:
  We present a numerical study of an idealized magnetohydrodynamic (MHD)
configuration consisting of a planar wake flow embedded into a
three-dimensional (3D) sheared magnetic field. Our simulations investigate the
possibility for in-situ development of large-scale compressive disturbances at
cospatial current sheet -- velocity shear regions in the heliosphere. Using a
linear MHD solver, we first systematically chart the destabilized wavenumbers,
corresponding growth rates, and physical parameter ranges for dominant 3D
sinuous-type instabilities in an equilibrium wake--current sheet system. Wakes
bounded by sufficiently supersonic (Mach number $M_s > 2.6$) flow streams are
found to support dominant fully 3D sinuous instabilities when the plasma beta
is of order unity. Fully nonlinear, compressible 2.5D and 3D MHD simulations
show the self-consistent formation of shock fronts of fast magnetosonic type.
They carry density perturbations far away from the wake's center. Shock
formation conditions are identified in sonic and Alfv\'enic Mach number
parameter space. Depending on the wake velocity contrast and magnetic field
magnitude, as well as on the initial perturbation, the emerging shock patterns
can be plane-parallel as well as fully three-dimensionally structured. Similar
large-scale transients could therefore originate at distances far above coronal
helmet streamers or at the location of the ecliptic current sheet.


title: A Dense-Cloud Model for Gamma-Ray Bursts to Explain Bimodality

abstract:
  In this model a collimated ultra-relativistic ejecta collides with an
amorphous dense cloud surrounding the central engine, producing gamma-rays via
synchrotron process. The ejecta is taken as a standard candle, while assuming a
gaussian distribution in thickness and density of the surrounding cloud. Due to
the cloud high density, the synchrotron emission would be an instantaneous
phenomenon (fast cooling synchrotron radiation), so a GRB duration corresponds
to the time that the ejecta takes to pass through the cloud. Fitting the model
with the observed bimodal distribution of GRBs' durations, the ejecta's initial
Lorentz factor, and its initial opening angle are obtained as
$\Gamma_{0}\lesssim 10^{3}$, and $\zeta_{0} \approx 10^{-2}$, and the mean
density and mean thickness of the surrounding cloud as $\bar{n} \sim 3 \times
10^{17} cm^{-3}$ and $\bar{L} \sim 2 \times 10^{13} cm$. The clouds maybe
interpreted as the extremely amorphous envelops of Thorne-Zytkow objects. In
this model the two classes of long and short duration GRBs are explained in a
unique frame.


title:
Adaptive mesh refinement for conservative systems: multi-dimensional
  efficiency evaluation

abstract:
  Obtainable computational efficiency is evaluated when using an Adaptive Mesh
Refinement (AMR) strategy in time accurate simulations governed by sets of
conservation laws. For a variety of 1D, 2D, and 3D hydro- and
magnetohydrodynamic simulations, AMR is used in combination with several
shock-capturing, conservative discretization schemes. Solution accuracy and
execution times are compared with static grid simulations at the corresponding
high resolution and time spent on AMR overhead is reported. Our examples reach
corresponding efficiencies of 5 to 20 in multidimensional calculations and only
1.5 -- 8 % overhead is observed. For AMR calculations of multi-dimensional
magnetohydrodynamic problems, several strategies for controlling the $\nabla
\cdot \BB =0$ constraint are examined. Three source term approaches suitable
for cell-centered $\BB$ representations are shown to be effective. For 2D and
3D calculations where a transition to a more globally turbulent state takes
place, it is advocated to use an approximate Riemann solver based
discretization at the highest allowed level(s), in combination with the robust
Total Variation Diminishing Lax-Friedrichs method on the coarser levels. This
level-dependent use of the spatial discretization acts as a computationally
efficient, hybrid scheme.


title:
The two-dimensional magnetohydrodynamic Kelvin-Helmholtz instability:
  compressibility and large-scale coalescence effects

abstract:
  The Kelvin-Helmholtz (KH) instability occurring in a single shear flow
configuration that is embedded in a uniform flow-aligned magnetic field, is
revisited by means of high resolution two-dimensional (2D) magnetohydrodynamic
(MHD) simulations. First, the calculations extend previous studies of
magnetized shear flows to a higher compressibility regime. The nonlinear
evolution of an isolated KH billow emerging from the fastest growing linear
mode for a convective sonic Mach number $M_{cs}=0.7$ layer is in many respects
similar to its less compressible counterpart (Mach $M_{cs}=0.5$). In
particular, the disruptive regime where locally amplified, initially weak
magnetic fields, control the nonlinear saturation process is found for Alfv\'en
Mach numbers $4\simlt M_A \simlt 30$. The most notable difference between
$M_{cs}=0.7$ versus $M_{cs}=0.5$ layers is that higher density contrasts and
fast magnetosonic shocklet structures are observed. Second, the use of adaptive
mesh refinement allows to parametrically explore much larger computational
domains, including up to 22 wavelengths of the linearly dominant mode. A strong
process of large-scale coalescence is found, whatever the magnetic field
regime. It proceeds through continuous pairing/merging events between adjacent
vortices up to the point where the final large-scale vortical structure reaches
the domain dimensions. This pairing/merging process is attributed to the growth
of subharmonic modes and is mainly controlled by relative phase differences
between them. These grid-adaptive simulations demonstrate that even in very
weak magnetic field regimes ($M_A \simeq 30$), the large-scale KH coalescence
process can trigger tearing-type reconnection events previously identified in
cospatial current-vortex sheets.


title: Time-dependent ejection velocity model for the outflow of Hen 3--1475

abstract:
  We present 2D axisymmetric and 3D numerical simulations of the
proto-planetary nebula Hen 3-1475, which is characterized by a remarkably
highly collimated optical jet, formed by a string of shock-excited knots along
the axis of the nebula. It has recently been suggested that the kinematical and
morphological properties of the Hen 3-1475 jet could be the result of an
ejection variability of the central source (Riera et al. 2003). The
observations suggest a periodic variability of the ejection velocity
superimposed on a smoothly increasing ejection velocity ramp. From our
numerical simulations, we have obtained intensity maps (for different optical
emission lines) and position-velocity diagrams, in order to make a direct
comparison with the HST observations of this object. Our numerical study allows
us to conclude that a model of a precessing jet with a time-dependent ejection
velocity, which is propagating into an ISM previously perturbed by an AGB wind,
can succesfully explain both the morphological and the kinematical
characteristics of this proto-planetary nebula.


title: HI absorption at the center of NGC2146

abstract:
  We present 1.4 GHz HI absorption line observations towards the starburst in
NGC2146, made with the VLA and MERLIN. The HI gas has a rotating disk/ring
structure with column densities between 6 and 18 x 10(21) atoms cm(-2). The HI
absorption has a uniform spatial and velocity distribution, and does not reveal
any anomalous material concentration or velocity in the central region of the
galaxy which might indicate an encounter with another galaxy or a far-evolved
merger. We conclude that the signs of an encounter causing the starburst should
be searched for in the outer regions of the galaxy.


title: Mechanical heating by active galaxies

abstract:
  Jets and winds are significant channels for energy loss from accreting black
holes. These outflows mechanically heat their surroundings, through shocks as
well as gentler forms of heating. We discuss recent efforts to understand the
nature and distribution of mechanical heating by central AGNs in clusters of
galaxies, using numerical simulations and analytic models. Specifically, we
will discuss whether the relatively gentle `effervescent heating' mechanism can
compensate for radiative losses in the central regions of clusters, and account
for the excess entropy observed at larger radii.


title: Spiral Galaxy - ICM Interactions in the Virgo Cluster

abstract:
  We discuss HI and optical evidence for ongoing ICM-ISM interactions in 6
HI-deficient Virgo cluster spiral galaxies. One of the clearest cases is the
highly inclined Virgo galaxy NGC 4522, which has a normal stellar disk but a
truncated gas disk, and lots of extraplanar gas right next to the gas
truncation radius in the disk. Unusually strong HI, H-alpha and radio continuum
emission are all detected from the extraplanar gas. The radio continuum
polarized flux and spectral index peak on the side opposite the extraplanar
gas, suggesting ongoing pressure by the ICM. Four other HI-deficient edge-on
Virgo spirals show evidence of extraplanar ISM gas or exhibit asymmetries in
their disk HI distributions, but contain much less extraplanar HI than NGC
4522. Comparison with recent simulations suggests this difference may be
evolutionary, with large surface densities of extraplanar gas observed only in
early phases of an ICM-ISM interaction. In NGC 4569, the H-alpha image shows 2
effects of ICM pressure on the galaxy ISM. An anomalous arm of HII regions,
possibly extraplanar, emerges from the edge of a truncated H-alpha disk. This
resembles the arms seen in simulations which are formed by the combined effects
of wind pressure plus rotation. An extended nebulosity near the minor axis,
also in the NW, is interpreted as a starburst outflow bubble disturbed by ICM
wind pressure.


title:
Another possible interpretation of SN 1a data - without kinematics:
  Comments on the paper astro-ph/0402512 by A. Riess et al

abstract:
  It is shown here that for redshifts $z < 0.5$ the luminosity distance, which
is predicted in author's model astro-ph/0005084 v2, fits well supernova
observational data of astro-ph/0402512 by A.Riess et al. Discrepancies for
higher $z$ would be explained in the model as a result of specific deformation
of SN spectra due to a discrete character of photon energy losses. The model
does not require any dark energy; it is based on the conjecture that gravitons
are super-strong interacting particles fulfilling a flat non-expanding
universe.


title:
A Sub-Millimeter Search of Nearby Young Stars for Cold Dust: Discovery
  of Debris Disks around Two Low-Mass Stars

abstract:
  (Abridged) We present results from a JCMT/SCUBA 850 um search for cold dust
around nearby young stars belonging to the beta Pic (t~12 Myr) and the Local
Association (t~50 Myr) moving groups. Unlike most past sub-mm studies, our
sample was chosen on the basis of stellar age. Our observations achieve about
an order of magnitude greater sensitivity in dust mass compared to previous
work in this age range. We detected two of the three M dwarfs in our sample at
850 um, GJ 182 and GJ 803. GJ 182 may also possess a 25 um excess, indicative
of warm dust in the inner few AU of its disk. For GJ 803 (AU Mic), sub-mm
mapping finds that the 850 um emission is unresolved. A non-detection of the CO
3-2 line indicates the system is gas-poor, and the SED suggests the presence of
a large inner disk hole (~17 AU = 1.7 arcsec in radius). These are possible
indications that planets at large separations can form around M dwarfs within
\~10 Myr. In a companion paper (Kalas, Liu & Matthews 2004), we confirm the
existence of a dust disk around GJ 803 using optical coronagraphic imaging.
Given its youthfulness, proximity, and detectability, the GJ 803 disk will be a
valuable system for studying disk, and perhaps planet, formation in great
detail. Overall, sub-mm measurements of debris disks point to a drop in dust
mass by a factor of about 10^3 within the first ~10 Myr, with the subsequent
decline in the masses of sub-mm detected disks consistent with t^{-0.5} to
t^{-1}.