title: Long-term Scintillation Observations of Five Pulsars at 1540 MHz

abstract:
  From 2001 January to 2002 June, we monitored PSRs B0329+54, B0823+26,
B1929+10, B2020+28 and B2021+51 using the Nanshan 25-m radio telescope of
Urumqi Observatory to study their diffractive interstellar scintillation
(DISS). The average interval between observations was about 9 days and the
observation duration ranged between 2 and 6 hours depending on the pulsar. Wide
variations in the DISS parameters were observed over the 18-month data span.
Despite this, the average scintillation velocities are in excellent agreement
with the proper motion velocities. The average two-dimensional autocorrelation
function for PSR B0329+54 is well described by a thin-screen Kolmogorov model,
at least along the time and frequency axes. Observed modulation indices for the
DISS time scale and bandwidth and the pulsar flux density are greater than
values predicted for a Kolmogorov spectrum of electron density fluctuations.
Correlated variations over times long compared to the nominal refractive
scintillation time are observed, suggesting that larger-scale density
fluctuations are important. For these pulsars, the scintillation bandwidth as a
function of frequency has a power-law index (~3.6) much less than expected for
Kolmogorov turbulence (~4.4). Sloping fringes are commonly observed in the
dynamic spectra, especially for PSR B0329+54. The detected range of fringe
slopes are limited by our observing resolution. Our observations are sensitive
to larger-scale fringes and hence smaller refractive angles, corresponding to
the central part of the scattering disk.


title: FORS spectroscopy of galaxies in the Hubble Deep Field South

abstract:
  We present low resolution multi-object spectroscopy of an I-band magnitude
limited (I_{AB} ~ 23--23.5) sample of galaxies located in an area centered on
the Hubble Deep Field-South (HDFS). The observations were obtained using the
Focal Reducer low dispersion Spectrograph (FORS) on the ESO Very Large
Telescope. Thirty-two primary spectroscopic targets in the HST-WFPC2 HDFS were
supplemented with galaxies detected in the Infrared Space Observatory's survey
of the HDFS and the ESO Imaging Deep Survey to comprise a sample of 100
galaxies for spectroscopic observations. Based on detections of several
emission lines, such as [OII]3727, H_beta and [OIII]5007, or other
spectroscopic features, we have measured accurate redshifts for 50 objects in
the central HDFS and flanking fields. The redshift range of the current sample
of galaxies is 0.6--1.2, with a median redshift of 1.13 (at I ~ 23.5 not
corrected for completeness). The sample is dominated by starburst galaxies with
only a small fraction of ellipticals (~10%). For the emission line objects, the
extinction corrected [OII]3727 line strengths yield estimates of star formation
rates in the range 0.5--30 M_solar/yr. We have used the present data to derive
the [OII]3727 luminosity function up to redshift of 1.2. When combined with
[OII]3727 luminosity densities for the local and high redshift Universe, our
results confirm the steep rise in the star formation rate (SFR) to z ~ 1.3.


title: Origins of Brown Dwarfs

abstract:
  The formation of objects below or close to the hydrogen burning limit is
currently vividly discussed and is one of the main open issues in the field of
the origins of stars and planets. Applying various observational techniques, we
explored a sample of brown dwarfs and very low-mass stars in the ChaI star
forming cloud at an age of only a few million years and determined fundamental
parameters for their formation and early evolution. Tracking the question of
how frequent are brown dwarf binaries and if brown dwarfs have planets, one of
the first radial velocity (RV) surveys of brown dwarfs sensitive down to
planetary masses is carried out based on high-resolution spectra taken with
UVES at the VLT. The results hint at a low multiplicity fraction, which is in
contrast to the situation for young low-mass stars. Testing recent formation
scenarios, which propose an ejection out of the birth place in the early
accretion phase, we carried out a precise kinematic analysis of the brown
dwarfs in our sample in comparison with T Tauri stars in the same field. This
yielded the first empirical upper limit for possible ejection velocities of a
homogeneous group of brown dwarfs. Rotation is a fundamental parameter for
objects in this early evolutionary phase. By means of studying the line
broadening of spectral features in the UVES spectra as well as by tracing
rotational modulation of their lightcurves due to surface spots in photometric
monitoring data, one of the first rotation rates of very young brown dwarfs
have been determined. In the light of the presented observational results, the
current scenarios for the formation of brown dwarfs are discussed.


title:
The Dependence of Galaxy Shape on Luminosity and Surface Brightness
  Profile

abstract:
  For a sample of 96,951 galaxies from the Sloan Digital Sky Survey Data
Release 3, we study the distribution of apparent axis ratios as a function of
r-band absolute magnitude and surface brightness profile type. We use the
parameter fracDeV to quantify the profile type (fracDeV = 1 for a de
Vaucouleurs profile; fracDeV = 0 for an exponential profile). When the apparent
axis ratio q_{am} is estimated from the moments of the light distribution, the
roundest galaxies are very bright (M_r \sim -23) de Vaucouleurs galaxies and
the flattest are modestly bright (M_r \sim -18) exponential galaxies. When the
apparent axis ratio q_{25} is estimated from the axis ratio of the 25
mag/arcsec^2 isophote, we find that de Vaucouleurs galaxies are flatter than
exponential galaxies of the same absolute magnitude. For a given surface
brightness profile type, very bright galaxies are rounder, on average, than
fainter galaxies. We deconvolve the distributions of apparent axis ratios to
find the distribution of the intrinsic short-to-long axis ratio gamma, assuming
constant triaxiality T. For all profile types and luminosities, the
distribution of apparent axis ratios is inconsistent with a population of
oblate spheroids, but is usually consistent with a population of prolate
spheroids. Bright galaxies with a de Vaucouleurs profile (M_r < -21.84, fracDeV
> 0.9) have a distribution of q_{am} that is consistent with triaxiality in the
range 0.4 < T < 0.8, with mean intrinsic axis ratio 0.66 < gamma < 0.69. The
fainter de Vaucouleurs galaxies are best fit with prolate spheroids (T = 1)
with mean axis ratio gamma = 0.51.


title: On viscosity, conduction and sound waves in the intracluster medium

abstract:
  Recent X-ray and optical observations of the Perseus cluster indicate that
the viscous and conductive dissipation of sound waves is the mechanism
responsible for heating the intracluster medium and thus balancing radiative
cooling of cluster cores. We discuss this mechanism more generally and show how
the specific heating and cooling rates vary with temperature and radius. It
appears that the heating mechanism is most effective above 10^7K, which allows
for radiative cooling to proceed within normal galaxy formation but will stifle
the growth of very massive galaxies. The scaling of the wavelength of sound
waves with cluster temperature and feedback in the system are investigated.


title: X-rays, pre-main sequence stars and planet formation

abstract:
  The study of magnetic activity of pre-main sequence (PMS) stars through their
X-ray emission is entering a mature phase. We review here two recent
developments. First, we present some early findings from the Chandra Orion
Ultradeep Project (COUP) relating to the age-activity-rotation relations of PMS
stars. COUP is a nearly continuous exposure of the Orion Nebula Cluster over 13
days and gives the most comprehensive view to date of X-ray emission from the
PMS population. We find that the activity-rotation connection that dominates
main sequence activity behavior is absent in PMS stars, although the
activity-age relation is present as well as links to stellar mass and volume.
  Second, we discuss investigations of effects of PMS X-rays on their cold
protoplanetary disks. It is possible that the the ionization, heating and
spallogenic effects of high energy photons and particles produced in PMS
stellar flares have significant effects on disk dynamics, heating and
chemistry. X-ray ionization may induce MHD turbulence in the disk which, in
turn, may regulate disk evolution and planet formation processes such as Jovian
planet migration.


title: The Morphology - Density Relation in z ~ 1 Clusters

abstract:
  We measure the morphology--density relation (MDR) and morphology-radius
relation (MRR) for galaxies in seven z ~ 1 clusters that have been observed
with the Advanced Camera for Surveys on board the Hubble Space Telescope.
Simulations and independent comparisons of ourvisually derived morphologies
indicate that ACS allows one to distinguish between E, S0, and spiral
morphologies down to zmag = 24, corresponding to L/L* = 0.21 and 0.30 at z =
0.83 and z = 1.24, respectively. We adopt density and radius estimation methods
that match those used at lower redshift in order to study the evolution of the
MDR and MRR. We detect a change in the MDR between 0.8 < z < 1.2 and that
observed at z ~ 0, consistent with recent work -- specifically, the growth in
the bulge-dominated galaxy fraction, f_E+SO, with increasing density proceeds
less rapidly at z ~ 1 than it does at z ~ 0. At z ~ 1 and density <= 500
galaxies/Mpc^2, we find <f_E+S0> = 0.72 +/- 0.10. At z ~ 0, an E+S0 population
fraction of this magnitude occurs at densities about 5 times smaller. The
evolution in the MDR is confined to densities >= 40 galaxies/Mpc^2 and appears
to be primarily due to a deficit of S0 galaxies and an excess of Spiral+Irr
galaxies relative to the local galaxy population. The Elliptical fraction -
density relation exhibits no significant evolution between z = 1 and z = 0. We
find mild evidence to suggest that the MDR is dependent on the bolometric X-ray
luminosity of the intracluster medium. Implications for the evolution of the
disk galaxy population in dense regions are discussed in the context of these
observations.


title: A High-Resolution Stellar Library for Evolutionary Population Synthesis

abstract:
  We present a library of 1654 high-resolution stellar spectra, with a sampling
of 0.3 A and covering the wavelength range from 3000 A ~ to 7000 A The library
was computed with the latest improvements in stellar atmospheres, incorporating
non-LTE line-blanketed models for hot, massive (Teff >= 27500 K) and
line-blanketed models for cool (3000 K =< Teff =< 4500 K) stars. The total
coverage of the grid is 3000 K =< Teff =< 55000 K and -0.5 =< log g =< 5.5, for
four chemical abundance values: twice solar, solar, half solar and 1/10 solar.
Evolutionary synthesis models using this library are presented in a companion
paper. We tested the general behavior of the library by calculating and
comparing equivalent widths of numerous H and HeI lines, and some of the
commonly used metallic indices. We also compared the library with the empirical
libraries STELIB and Indo-US. The full set of the synthetic stellar spectra is
available from our websites (http://www.iaa.csic.es/~rosa and
http://www.astro.iag.usp.br/~lucimara/library.html).


title: Pulsars in Globular Clusters

abstract:
  More than 100 radio pulsars have been detected in 24 globular clusters. The
largest observed samples are in Terzan 5 and 47 Tucanae, which together contain
45 pulsars. Accurate timing solutions, including positions in the cluster, are
known for many of these pulsars. Here we provide an observational overview of
some properties of pulsars in globular clusters, as well as properties of the
globular clusters with detected pulsars. The many recent detections also
provide a new opportunity to re-examine theoretically the formation and
evolution of recycled pulsars in globular clusters. Our brief review considers
the most important dynamical interaction and binary evolution processes:
collisions, exchange interactions, mass transfer, and common-envelope phases.


title:
Effects of cooling and star formation on the baryon fractions in
  clusters

abstract:
  We study the effects of dissipation on the baryon fractions in clusters using
high-resolution cosmological simulations of nine clusters that resolve
formation of cluster galaxies. The simulations of each cluster are performed
with the shock-capturing eulerian adaptive mesh refinement N-body+gasdynamics
ART code with and without radiative cooling. We show that dissipation and
associated galaxy formation increase the total baryon fractions within radii as
large as the virial radius. The effect is the strongest within cluster cores,
where the simulations with cooling have baryon fractions larger than the
universal value, while the fraction of baryons in adiabatic simulations are
smaller than universal. At larger radii (r >~ r_500) the cumulative baryon
fractions in simulations with cooling are close to, while those in the
adiabatic runs remain below than, the universal value. The gas fractions in
simulations with dissipation are reduced by ~20-40% at r<0.3r_vir and ~10% at
larger radii compared to the adiabatic runs, because a fraction of gas is
converted into stars. There is an indication that gas fractions within
different radii increase with increasing cluster mass as f_gas ~ M_vir^0.2. We
find that the total baryon fraction within the virial radius does not evolve
with time in both adiabatic simulations and in simulations with cooling.
Finally, to evaluate systematic uncertainties in the baryon fraction in
cosmological simulations we present a comparison of gas fractions in our
adiabatic simulations to re-simulations of the same objects with the
entropy-conserving SPH code Gadget. The cumulative gas fraction profiles in the
two sets of simulations on average agree to <~3% at r/r_vir>0.2, but differ
systematically by up to 10% at small radii.


title:
Understanding B-type supergiants in the low metallicity environment of
  the SMC II

abstract:
  Despite a resurgence of effort over the last decade in the area of massive
stars there is still ambiguity over their evolutionary path, contamination of
their surface abundances and the behaviour of their stellar winds. Here 10 SMC
B-type supergiants are analysed applying a unified model atmosphere code
FASTWIND to intermediate resolution spectra from the ESO Multi Mode Instrument
(EMMI) on the NTT telescope. Combined with the 8 targets analysed in paper 1,
this work provides observational results on the properties of the winds and
chemical compositions of B-type supergiants in the SMC. This paper emphasizes
and substantiates the implications for stellar evolution from paper 1; that
current theoretical models need to produce larger degrees of surface nitrogen
enhancements at lower rotational velocities. In addition a significant
discrepancy between theoretical and observed mass-loss rates is discussed which
will have important implications for the rotational velocities obtained from
stellar evolution calculations. Furthermore, an initial calibration of the
wind-momentum luminosity relationship for B-type supergiants in a low
metallicity environment (Z = 0.004) is presented.


title: Aperture effects on Star Formation Rate, Metallicity and Reddening

abstract:
  (Abridged) We use 101 galaxies selected from the Nearby Field Galaxy Survey
(NFGS) to investigate the effect of aperture size on the star formation rate,
metallicity and reddening determinations for galaxies. We compare the star
formation rate, metallicity and reddening derived from nuclear spectra to those
derived from integrated spectra. For apertures capturing <20% of the B(26)
light, the differences between nuclear and global metallicity, extinction and
star formation rate are substantial. We calculate an `expected' star formation
rate using our nuclear spectra and apply the commonly-used aperture correction
method. The expected star formation rate overestimates the global value for
early type spirals, with large scatter for all Hubble types, particularly late
types. The differences between the expected and global star formation rates
probably result from the assumption that the distributions of the emission-line
gas and the continuum are identical. We discuss the implications of these
results for metallicity-luminosity relations and star formation history studies
based on fiber spectra. To reduce systematic and random errors from aperture
effects, we recommend selecting samples with fibers that capture >20% of the
galaxy light. For the Sloan Digital Sky Survey and the 2dFGRS, redshifts z>0.04
and z>0.06 are required, respectively, to ensure a covering fraction >20% for
galaxies similar to the average size, type, and luminosity observed in our
sample. Higher luminosity samples and samples containing many late-type
galaxies require a larger minimum redshift to ensure that >20% of the galaxy
light is enclosed by the fiber.


title:
Twenty-One Millisecond Pulsars in Terzan 5 Using the Green Bank
  Telescope

abstract:
  We have discovered 21 millisecond pulsars (MSPs) in the globular cluster
Terzan 5 using the Green Bank Telescope, bringing the total of known MSPs in
Terzan 5 to 24. These discoveries confirm fundamental predictions of globular
cluster and binary system evolution. Thirteen of the new MSPs are in binaries,
of which two show eclipses and two have highly eccentric orbits. The
relativistic periastron advance for the two eccentric systems indicates that at
least one of these pulsars has a mass >1.68 Msun at 95% confidence. Such large
neutron star masses constrain the equation of state of matter at or beyond the
nuclear equilibrium density.


title: Prospects of Non-Riemannian Cosmology

abstract:
  In this work we provide the motivation for considering non-Riemannian models
in cosmology. Non-Riemannian extensions of general relativity theory have been
studied for a long time. In such theories the spacetime continuum is no longer
described by the metric alone but endowed with additional geometric quantities.
These new quantities can be coupled to the intrinsic properties of matter in a
very natural way and therefore provide a richer gravitational theory, which
might be necessary in view of the recent cosmological evidence for dark matter
and dark energy. In this work we mainly focus on the concepts in metric-affine
gravity and point out their possible significance in the process of
cosmological model building.


title: Sources for Metals in the Intergalactic Medium

abstract:
  We present a discussion of possible sources of C, O, and Si in the IGM using
the yields of VMSs and SNe II. The chemical evolution of the IGM is considered
based on analytical phenomenological models of hierarchical structure
formation. Two regimes are considered: one for gas expulsion by VMSs and SNe II
in low-mass halos prior to dissociation of H2 molecules and reionization, and
the other for later SN II-driven outflows from intermediate-mass halos. We use
recent data on the abundances of C, O, and Si in the IGM inferred from two UVB
models. We show that the results from a UVB model including quasars only cannot
be explained by existing stellar models. To account for the results, in
particular [Si/C], from a softer UVB model requires VMSs to provide more than
15% of the C in the IGM. The preferred scenario is that VMSs in low-mass halos
provided between 15% and 60% of the C in the regime of very high redshift
(z>15) and that galactic outflows provided the remainder during later epochs
(4<z<6). Thus, there is a large gap in z between metal production by VMSs very
early in the chemical evolution of the IGM and subsequent contributions from
galactic outflows. (Abridged)


title:
Constraints on the small-scale power spectrum of density fluctuations
  from high-redshift gamma-ray bursts

abstract:
  Cosmological models that include suppression of the power spectrum of density
fluctuations on small scales exhibit an exponential reduction of high-redshift,
non-linear structures, including a reduction in the rate of gamma ray bursts
(GRBs). Here we quantify the constraints that the detection of distant GRBs
would place on structure formation models with reduced small-scale power. We
compute the number of GRBs that could be detectable by the Swift satellite at
high redshifts (z > 6), assuming that the GRBs trace the cosmic star formation
history, which itself traces the formation of non-linear structures. We
calibrate simple models of the intrinsic luminosity function of the bursts to
the number and flux distribution of GRBs observed by the Burst And Transient
Source Experiment (BATSE). We find that a discovery of high-z GRBs would imply
strong constraints on models with reduced small-scale power. For example, a
single GRB at z > 10, or 10 GRBs at z > 5, discovered by Swift during its
scheduled two-year mission, would rule out an exponential suppression of the
power spectrum on scales below R_c=0.09 Mpc (exemplified by warm dark matter
models with a particle mass of m_x=2 keV). Models with a less sharp suppression
of small-scale power, such as those with a red tilt or a running scalar index,
n_s, are more difficult to constrain, because they are more degenerate with an
increase in the power spectrum normalization, sigma_8, and with models in which
star-formation is allowed in low-mass minihalos. We find that a tilt of \delta
n_s ~ 0.1 is difficult to detect; however, an observed rate of 1 GRB/yr at z >
12 would yield an upper limit on the running of the spectral index, alpha =
d(n_s)/d(ln k) > -0.05.


title:
Constraining Brans-Dicke Gravity with Millisecond Pulsars in
  Ultracompact Binaries

abstract:
  The five accreting, millisecond X-ray pulsars in ultracompact binaries that
were recently discovered with the Rossi X-ray Timing Explorer provide excellent
candidates for constraining the deviations from general relativity described by
the Brans-Dicke parameter omega_BD. I calculate the expected rate of change of
the orbital periods of these binaries and discuss the prospects of constraining
omega_BD to values that are an order of magnitude larger than current
constraints. Finally, I show how measurements of the orbital period derivative
in ultracompact binaries can be used to place lower bounds on their orbital
inclination.


title: The r-Process: Current Understanding and Future Tests

abstract:
  Current understanding of the r-process is summarized in terms of the
astrophysical sites, the yield patterns, and the role of neutrinos. The
importance of observational and experimental tests is emphasized. A number of
future tests regarding the above three aspects of the r-process are discussed.


title: A JavaScript Passive Evolution Calculator

abstract:
  We present a JavaScript calculator which provides the redshift evolution of
the luminosities and colors of passively evolving galaxies for a range of
rest-frame filters. In its simplest form it gives the evolution of a single age
stellar population formed at a given redshift. However, it can also incorporate
morphological evolution in the galaxy population ("progenitor bias") and
complex star formation histories of individual galaxies. The calculator is
based on the models of van Dokkum & Franx (2001), with small updates.


title: Nuclear physics and astrophysics of the r-process

abstract:
  Some nuclear and astrophysical aspects of the r-process are discussed.
Particular attention is paid to observations of abundances in metal-poor stars
and their implications for the astrophysical site and yield patterns of the
r-process. The effects of supernova neutrinos and related nuclear processes on
the yield patterns are explored. The uncertainties in the theoretical nuclear
input for the r-process are discussed and the need for experimental data is
emphasized.


title:
Gravitational Waves from binary black holes in the extreme mass ratio
  regime: Self-force calculations

abstract:
  We present a report on the progress made in the development of computational
techniques to evaluate the gravitational radiation generated by a particle
orbiting a massive black hole to second pertrubative order.


title: Coherence Constraint on the Existence of Cosmic Defects

abstract:
  We devise a measure n(r) to quantify a robust feature in the coherent cosmic
perturbations, namely the narrowness of the first peak in the power spectrum of
the Cosmic Microwave Background (CMB) anisotropy. A maximum-likelihood analysis
using the WMAP data shows that the power fraction of any defect models at the
first peak is persistently less than 4.5% at the 68% confidence. Our approach
and results are insensitive to the uncertainties in the theoretical predictions
for defect models, and thus the most robust to date. We show that to convert
these results into realistic constraints on theories such as inflation, string
cosmology, and SUSY GUTs, a more robust study for the cosmic-string-induced CMB
around the degree scale is required.


title:
Investigating the Andromeda Stream: I. Simple Analytic Bulge-Disk-Halo
  Model for M31

abstract:
  This paper is the first in a series which studies interactions between M31
and its satellites, including the origin of the giant southern stream. We
construct accurate yet simple analytic models for the potential of the M31
galaxy to provide an easy basis for calculation of orbits in M31's halo. We use
an NFW dark halo, an exponential disk, a Hernquist bulge, and a central black
hole point mass to describe the galaxy potential. We constrain the parameters
of these functions by comparing to existing surface brightness, velocity
dispersion, and rotation curve measurements of M31. Our description provides a
good fit to the observations, and agrees well with more sophisticated modeling
of M31. While in many respects the parameter set is well constrained, there is
substantial uncertainty in the outer halo potential and a near-degeneracy
between the disk and halo components, producing a large, nearly two-dimensional
allowed region in parameter space. We limit the allowed region using
theoretical expectations for the halo concentration, baryonic content, and
stellar $M/L$ ratio, finding a smaller region where the parameters are
physically plausible. Our proposed mass model for M31 has $M_{bulge} = 3.2
\times 10^{10} \Msun$, $M_{disk} = 7.2 \times 10^{10} \Msun$, and $M_{200} =
7.1\times 10^{11} \Msun$, with uncorrected (for internal and foreground
extinction) mass-to-light ratios of $M/L_R = 3.9$ and 3.3 for the bulge and
disk, respectively. We present some illustrative test particle orbits for the
progenitor of the stellar stream in our galaxy potential, highlighting the
effects of the remaining uncertainty in the disk and halo masses.


title:
Investigating the Andromeda Stream: II. Orbital Fits and Properties of
  the Progenitor

abstract:
  We construct test-particle orbits and simple N-body models that match the
properties of the giant stellar stream observed to the south of M31, using the
model of M31's potential derived in the companion paper by Geehan et al.
(2006). We introduce a simple approximation to account for the difference in
position between the stream and the orbit of the progenitor; this significantly
affects the best-fitting orbits. The progenitor orbits we derive have orbital
apocenter $\sim 60 \kpc$ and pericenter $\sim 3 \kpc$, though these quantities
vary somewhat with the current orbital phase of the progenitor which is as yet
unknown. Our best combined fit to the stream and galaxy properties implies a
mass within 125 kpc of M31 of $(7.4 \pm 1.2) \times 10^{11} \Msun$. Based on
its length, width, luminosity, and velocity dispersion, we conclude that the
stream originates from a progenitor satellite with mass $M_s \sim 10^9 \Msun$,
and at most modest amounts of dark matter; the estimate of $M_s$ is again
correlated with the phase of the progenitor. M31 displays a large number of
faint features in its inner halo which may be progenitors or continuations of
the stream. While the orbital fits are not constrained enough for us to
conclusively identify the progenitor, we can identify several plausible
candidates, of which a feature in the planetary nebula distribution found by
Merrett et al. is the most plausible, and rule out several others. We make
predictions for the kinematic properties of the successful candidates. These
may aid in observational identification of the progenitor object, which would
greatly constrain the allowed models of the stream.


title:
Ultra-Luminous X-ray Sources: Evidence for Very Efficient Formation of
  Population III Stars Contributing to the Cosmic Near-Infrared Background
  Excess?

abstract:
  Accumulating evidence indicates that some of ultra-luminous X-ray sources
(ULXs) are intermediate mass black holes (IMBHs), but the formation process of
IMBHs is unknown. One possibility is that they were formed as remnants of
population III (Pop III) stars, but it has been thought that the probability of
being an ULX is too low for IMBHs distributed in galactic haloes to account for
the observed number of ULXs. Here we show that the number of ULXs can be
explained by such halo IMBHs passing through a dense molecular cloud, if Pop
III star formation is very efficient as recently suggested by the excess of the
cosmic near-infrared background radiation that cannot be accounted for by
normal galaxy populations. We calculate the luminosity function of X-ray
sources in our scenario and find that it is consistent with observed data. Our
scenario can explain that ULXs are preferentially found at outskirts of large
gas concentrations in star forming regions. A few important physical effects
are pointed out and discussed, including gas dynamical friction, radiative
efficiency of accretion flow, and radiative feedback to ambient medium. ULXs
could last for ~10^{5-6} yr to emit a total energy of ~10^{53} erg, which is
sufficient to power the ionized expanding nebulae found by optical
observations.


title:
Quasilinear Drift Of Cosmic Rays In Weak Turbulent Electromagnetic
  Fields

abstract:
  A general quasilinear transport parameter for particle drift in arbitrary
turbulence geometry is presented. The new drift coefficient is solely
characterized by a nonresonant term and is evaluated for slab and
two-dimensional turbulence geometry. The calculations presented here
demonstrate that fluctuating electric fields are a key quantity for
understanding quasilinear particle drift in slab geometry. It is shown that
particle drift does not exist in unpolarized and purely magnetic slab
fluctuations. This is in stark contrast to previous models, which are
restricted to slab geometry and the field line random walk limit. The
evaluation of the general transport parameter for two-dimensional turbulence
geometry, presented here for the first time for dynamical magnetic turbulence,
results in a drift coefficient valid for a magnetic power spectrum and
turbulence decay rate varying arbitrarily in wavenumber. For a two-component,
slab/two-dimensional turbulence model, numerical calculations are presented.
The new quasilinear drift, induced by the magnetic perturbations, is compared
with a standard drift expression related to the curvature and gradient of an
unperturbed heliospheric background magnetic field. The considerations
presented here offer a solid ground and natural explanation for the hitherto
puzzling observation that drift models often describe observations much better
when drift effects are reduced.


title: Circumstellar and Circumbinary Disks in Eccentric Stellar Binaries

abstract:
  We explore test particle orbits in the orbital plane of eccentric stellar
binary systems, searching for ``invariant loops'': closed curves that change
shape periodically as a function of binary orbital phase as the test particles
in them move under the stars' gravity. Stable invariant loops play the same
role in this periodically-varying potential as stable periodic orbits do in
stationary potentials; in particular, when dissipation is weak, gas will most
likely follow the non-intersecting loops, while nearby particle orbits librate
around them. We use this method to set bounds on the sizes of disks around the
stars, and on the gap between those and the inner edge of a possible
circumbinary disk. Gas dynamics may impose further restrictions, but our study
sets upper bounds for the size of circumstellar disks, and a lower bound for
the inner radius of a circumbinary disk. We find that circumstellar disks are
sharply reduced as the binary's eccentricity grows. Disks change in size and
shape only marginally with the binary phase, with no strong preference to
increase or decrease at any particular phase. The circumstellar disks in
particular can be quite asymmetric. We compare our results with other numerical
and theoretical results and with observations of the $\alpha$ Centauri and
L1551 systems, finding very good agreement. The calculated changes in the
shapes and crowding of the circumstellar orbits can be used to predict how the
disk luminosity and mass inflow should vary with binary phase.


title:
Contribution to diffuse gamma-rays in the Galactic center region from
  unresolved millisecond pulsars

abstract:
  The diffuse gamma-rays in the Galactic center region have been studied. We
propose that there exists a population of millisecond pulsars (MSPs) in the
Galactic Center, which will emit GeV gamma-rays through the
synchrotron-curvature radiation as predicted by outer gap models. These GeV
gamma-rays from unresolved millisecond pulsars probably contribute to the
diffuse gamma-ray spectrum detected by EGRET which displays a break at a few
GeV. We have used the Monte Carlo method to obtain the simulated samples of
millisecond pulsars in the Galactic center region covered by EGRET ($\sim
1.5^\circ$) according to the different period and magnetic field distributions
from the observed millisecond pulsars in the Galactic field and globular
clusters, and superposed their synchrotron-curvature spectra to derive the
total GeV flux. Our simulated results suggest that there probably exist about
6000 unresolved millisecond pulsars in the region of the angular resolution for
EGRET, whose emissions could contribute significantly to the observed diffuse
gamma-rays in the Galactic center.


title:
Possibility of Measuring the Width of Narrow Fe II Astrophysical Laser
  Lines in the Vicinity of Eta Carinae by means of Brown-Twiss-Townes
  Heterodyne Correlation Interferometry

abstract:
  We consider the possibility of measuring the true width of the narrow Fe II
optical lines observed in spectra of the Weigelt blobs in the vicinity of Eta
Carinae. The lines originate as a result of stimulated amplification of
spontaneous emission of radiation in quantum transitions between energy levels
showing inverted population (Johansson & Letokhov, 2002, 2003, 2004). The lines
should have a subDoppler spectral width of 30-100 MHz, depending on the
geometry of the lasing volume. To make measurements with a spectral resolution
of R>10^7 and an angular resolution better than 0.1 arcsec, we suggest the use
of the Brown-Twiss-Townes optical heterodyne intensity correlation
interferometry. The estimates made of the S/N ratio for the optical heterodyne
astrophysical laser experiment imply that it is feasible.


title: Three-micron spectra of AGB stars and supergiants in nearby galaxies

abstract:
  The dependence of stellar molecular bands on the metallicity is studied using
infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and
M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and
in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for
oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB
stars. The equivalent width of acetylene is found to be high even at low
metallicity. The high C2H2 abundance can be explained with a high
carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast,
the HCN equivalent width is low: fewer than half of the extra-galactic carbon
stars show the 3.5micron HCN band, and only a few LMC stars show high HCN
equivalent width. HCN abundances are limited by both nitrogen and carbon
elemental abundances. The amount of synthesized nitrogen depends on the initial
mass, and stars with high luminosity (i.e. high initial mass) could have a high
HCN abundance. CH bands are found in both the extra-galactic and Galactic
carbon stars. None of the oxygen-rich LMC stars show SiO bands, except one
possible detection in a low quality spectrum. The limits on the equivalent
widths of the SiO bands are below the expectation of up to 30angstrom for LMC
metallicity. Several possible explanations are discussed. The observations
imply that LMC and SMC carbon stars could reach mass-loss rates as high as
their Galactic counterparts, because there are more carbon atoms available and
more carbonaceous dust can be formed. On the other hand, the lack of SiO
suggests less dust and lower mass-loss rates in low-metallicity oxygen-rich
stars. The effect on the ISM dust enrichment is discussed.


title:
Line identification in soft X-ray spectra of stellar coronae by
  comparison with the hottest white dwarf's photosphere: Procyon, alpha Cen
  A+B, and H1504+65

abstract:
  H1504+65 is a young white dwarf with an effective temperature of 200,000 K
and is the hottest post-AGB star ever analysed with detailed model atmospheres.
Chandra LETG+HRC-S spectra have revealed the richest X-ray absorption line
spectrum recorded from a stellar photosphere to date. The line forming regions
in this extremely hot photosphere produce many transitions in absorption that
are also observed in emission in cool star coronae. We have performed a
detailed comparison of Chandra spectra of H1504+65 with those of Procyon and
alpha Cen A and B. State of the art non-LTE model spectra for the hot white
dwarf have enabled us to identify a wealth of absorption lines from highly
ionized O, Ne and Mg. In turn, these features have allowed us to identify
coronal lines whose origins were hitherto unknown.


title: ABELL 43 a second pulsating "hybrid PG 1159 star"

abstract:
  We report observations of the planetary nebula nucleus Abell 43, obtained at
the 2.5m Nordic Optical Telescope, which shows that it is a pulsator. Abell 43,
a "hybrid-PG 1159" type star, is the second pulsator of this class, after HS
2324+3944. From the limited data set aquired, we find that Abell 43 exhibits at
least two periods of 2600s and 3035s, the longest ones observed up to now in PG
1159 and "hybrid-PG 1159" pulsators. This strongly suggests that the variations
are due to non-radial g-mode pulsations and cannot be a consequence of
binarity. This discovery raises puzzling questions regarding the exitation
mechanism in this H rich, C and O poor "hybrid-PG 1159" since the C and O
abundances are too low to trigger the instability through the
$\kappa$-mechanism invoked to explain the instability in the PG 1159 stars and
in the previously known "hybrid-PG 1159" pulsator HS 2324+3944.


title: A search for CI J=2--1 emission in IRAS F10214+4724

abstract:
  Sensitive new observations of the fine structure line $^3$P$_2$$\to $
$^3$P$_1$ (J=2--1) of the neutral atomic carbon CI ($\nu_{rest}\sim 809$ GHz)
in the strongly lensed Ultra Luminous Infrared Galaxy (ULIRG) IRAS F10214+4724
at z=2.3 with the mm/sub-mm telescope James Clerk Maxwel (JCMT) are presented.
These do not confirm the presence of emission from this line at the flux levels
or angular extent previously reported in the literature. The new 2$\sigma $
upper limits are: $\rm S_{CI}\la 7 Jy km s^{-1}$ (central position), and $\rm <
S_{CI} > \la 8.5 Jy km s^{-1}$ (average over the two $\rm [\delta (RA), \delta
(Dec)]=[0'',\pm 10'']$ positions). A CI emission assumed fully concomitant with
the bulk of H$_2$ and confined entirely within the strongly lensed object
yields an upper limit of $\rm M_{CI}(H_2)\la 1.5 \times 10^{10} M_{\odot}$,
compatible with the reported CO-derived H$_2$ gas mass, within the
uncertainties of the two methods. A comparison with the recent detection of the
$^3$P$_1$$\to $ $^3$P$_0$ (J=1--0) line in this galaxy by Weiss et al. (2004)
is made and the large discrepancy with the previous CI measurements is briefly
discussed.


title:
Overview on direct and indirect measurements of cosmic rays - Some
  thoughts on galactic cosmic rays and the knee

abstract:
  An overview is given on results from direct and indirect measurements of
galactic cosmic rays. Their implications on the contemporary understanding of
the origin of cosmic rays and the knee in their energy spectrum are discussed.


title:
Spectral Analyses of DO White Dwarfs and PG1159 Stars from the Sloan
  Digital Sky Survey

abstract:
  SDSS (DR1 and DR2) has recently proposed 7 new DO white dwarfs as well as 6
new PG1159 stars. This is a significant increase in the known number of DOs and
PG1159 stars. Our spectral analyses provide stellar parameters which can then
be used to derive constraints for the evolution of H-deficient white dwarfs. A
comprehensive understanding of these objects is still severely hampered by
low-number statistics.


title:
IR mergers and IR QSOs with galactic winds. III. Mrk 231: composite
  outflow with multiple expanding bubbles and BALs (an exploding young QSO?)

abstract:
  A study of outflow (OF) and BAL systems in Mrk 231 (and in similar IR QSOs)
is presented. This study is based mainly on 1D and 2D spectroscopy (obtained at
La Palma/WHT, HST, IUE, ESO/NTT, KPNO, APO and CASLEO observatories) plus HST
images. For Mrk 231 we report evidence that the extreme nuclear OF process has
at least 3 main components, which are probably associated with: (i) the radio
jet, at pc scale, and (ii(the extreme starburst at pc and kpc scale. This OF
has generate 4 or more concentric expanding bubbles and the BAL systems. The
variability of the short lived BAL-III system was studied. Finally, the IR
colour diagram and the UV BAL system of IR+OF+FeII QSOs are analysed. We
propose that the phase of young QSO is associated with:accretion of large
amount of gas (by the SMBH)+extreme starburst+extreme composite OFs/BALs.


title: Lattice QCD Constraints on Hybrid and Quark Stars

abstract:
  A QCD-motivated dynamical-quasiparticle model with parameters adjusted to
reproduce the lattice-QCD equation of state is extrapolated from region of high
temperatures and moderate baryonic densities to the domain of high baryonic
densities and zero temperature. The resulting equation of state matched with
realistic hadronic equations of state predicts a phase transition into the
quark phase at higher densities than those reachable in neutron star interiors.
This excludes the possibility of the existence of hybrid (hadron-quark) stars.
Pure quark stars are possible and have low masses, small radii and very high
central densities. Similar results are obtained for a simple bag model with
massive quarks, fitted to reproduce the same lattice results. Self-bound quark
matter is also excluded within these models. Uncertainties in the present
extrapolation re discussed. Comparison with standard bag models is made.


title:
NLTE Analysis of the Ultra-short Period White-dwarf Binary RX
  J0806.3+1527

abstract:
  RX J0806.3+1527 is suspected to be a double-degenerate white dwarf binary. We
present first results of our NLTE analysis of its optical spectrum. The
VLT/FORS1 data show a composite spectrum consisting of a blue continuum and
superimposed emission lines of the HeII Pickering series and, possibly, the H
Balmer series. Our models are based on hot white dwarf atmospheres and include
illumination effects onto the secondary star. The physical parameters and
chemical abundances derived from the comparison of the observed spectrum with a
grid of model atmospheres provide constraints on the true nature of this
enigmatic binary and on the models proposed so far.


title:
Origin of the Joint Distribution of Structural Parameters in Disc
  Galaxies

abstract:
  We use a simple model of disc-galaxy formation in the LCDM cosmology to
simultaneously reproduce the slopes, zero-points, scatter and uncorrelated
residuals in the observed velocity-luminosity (VL) and radius-luminosity (RL)
relations. Observed I-band luminosities are converted to stellar masses using
the IMF-dependent relation between stellar mass-to-light ratio, M/L, and color.
The model treats halo concentration, spin parameter, and disc mass fraction as
independent log-normal random variables. Our main conclusion is that the VL and
RL zero-points and the uncorrelated residuals can only be reproduced
simultaneously if adiabatic contraction is avoided. One or the other could be
fixed by appealing to unrealistic values for M/L, halo concentration c, and
spin parameter lambda, but not all together. The small VL scatter is naturally
determined by the predicted scatter in c and in M/L, quite independent of the
large scatter in lambda. However, the RL scatter, driven by the scatter in
lambda, can be as low as observed only if sigma_lambda simeq 0.25, about half
the value predicted for CDM haloes. This may indicate that discs form in a
special subset of haloes. The VL slope is reproduced once star formation occurs
only above a threshold surface density, and the RL slope implies that the disc
mass fraction is increasing with halo mass, consistent with feedback effects. A
model that incorporates the above ingredients provides a simultaneous fit to
all the observed features. In particular, the elimination of adiabatic
contraction allows 80% disc contribution to the observed rotation velocity of
bright discs at 2.2 disc scale lengths. The lack of halo contraction may
indicate that disc formation is not as smooth as typically envisioned, but
instead may involve clumpy, cold streams.


title:
The Connection between the Narrow-Line Region and the UV Absorbers in
  Seyfert Galaxies

abstract:
  We present evidence that the outflowing UV absorbers in Seyfert 1 galaxies
arise primarily in their inner narrow (emission) line regions (NLRs), based on
similarities in their locations, kinematics, and physical conditions. 1) Hubble
Space Telescope observations show that nearly all Seyfert galaxies have bright,
central knots of [O III] emission in their NLRs with radii of tens of parsecs.
These sizes are consistent with most previous estimates of the distances of UV
(and X-ray) absorbers from their central continuum sources, and a recently
obtained reliable distance of ~25 pc for a UV absorber in the Seyfert 1 galaxy
NGC 3783. 2) The nuclear emission-line knots in a sample of 10 Seyfert galaxies
have velocity widths of 300 - 1100 km/s (half-width at zero intensity), similar
to the radial velocities of most UV absorbers. The highest radial velocity for
a Seyfert UV absorber to date is only -2100 km/s, which is much lower than
typical broad-line region (BLR) velocities. There is also mounting evidence
that the NLR clouds are outflowing from the nucleus, like the UV absorbers. 3)
If our hypothesis is correct, then the NLR must have a component with a high
global covering factor (Cg) of the continuum source and BLR, to match that
found from previous surveys of UV absorbers (Cg = 0.5 - 1.0). Using STIS
spectra of NGC 4151, obtained when the continuum and BLR fluxes were low, we
find evidence for optically thin gas in its nuclear emission-line knot. We are
able to match the line ratios from this gas with photoionization models that
include a component with Cg ~ 1 and an ionization parameter and hydrogen column
density that are typical of UV absorbers.


title: Competitive Accretion and the IMF

abstract:
  Competitive accretion occurs when stars in a cluster accrete from a shared
reservoir of gas. The competition arises due to the relative attraction of
stars as a function of their mass and location in the cluster.
  The low relative motions of the stars and gas in young, gas dominated
clusters results in a tidal limit to the accretion whereas in the stellar
dominated cluster cores, the high relative velocities results in Bondi-Hoyle
accretion.
  The combination of these two accretion processes produces a two power-law IMF
with $\gamma \approx -1.5$, for low-mass stars which accrue their mass in the
gas dominated regime, and a steeper, $\gamma\approx -2.5$, IMF for higher-mass
stars that form in the core of a cluster. Simulations of the fragmentation and
formation of a stellar cluster show that the final stellar masses, and IMF, are
due to competitive accretion. Competitive accretion also naturally results in a
mass segregated cluster and in a direct correlation between the richness of a
cluster and the mass of the most massive star therein. The {\sl knee} where the
IMF slope changes occurs near the Jeans mass of the system.


title: Properties of Ly-alpha emitters around the radio galaxy MRC 0316-257

abstract:
  Observations of the radio galaxy MRC 0316-257 at z=3.13 and the surrounding
field are presented. Using narrow- and broad-band imaging obtained with the
VLT, 77 candidate Ly-alpha emitters with a rest-frame equivalent width of > 15
A were selected in a ~7'x7' field around the radio galaxy. Spectroscopy of 40
candidate emitters resulted in the discovery of 33 emission line galaxies of
which 31 are Ly-alpha emitters with redshifts similar to that of the radio
galaxy, while the remaining two galaxies turned out to be [OII] emitters. The
Ly-alpha profiles have widths (FWHM) in the range of 120-800 km/s, with a
median of 260 km/s. Where the signal-to-noise was large enough, the Ly-alpha
profiles were found to be asymmetric, with apparent absorption troughs blueward
of the profile peaks, indicative of absorption along the line of sight of an HI
mass of at least 2x10^2 - 5x10^4 M_sun. The properties of the Ly-alpha galaxies
(faint, blue and small) are consistent with young star forming galaxies which
are still nearly dust free. The volume density of Ly-alpha emitting galaxies in
the field around MRC 0316-257 is a factor of 3.3+0.5-0.4 larger compared with
the density of field Ly-alpha emitters at that redshift. The velocity
distribution of the spectroscopically confirmed emitters has a FWHM of 1510
km/s, which is substantially smaller than the width of the narrow-band filter
(FWHM ~ 3500 km/s). The peak of the velocity distribution is located within 200
km/s of the redshift of the radio galaxy. We conclude that the confirmed
Ly-alpha emitters are members of a protocluster of galaxies at z~3.13. The size
of the protocluster is larger than 3.3x3.3 Mpc^2. The mass of this structure is
estimated to be > 3-6x10^14 M_sun and could be the progenitor of a cluster of
galaxies similar to e.g. the Virgo cluster. (Abridged)


title: The Formation of Massive Binary Stars

abstract:
  The formation of massive stars in close binary systems is complicated due to
their high radiation pressure, the crowded environment and the expected minimum
separation for fragmentation being many times greater than the orbital
separation. I discuss how massive star formation can be understood as being due
to competitive accretion in stellar clusters. Massive binary systems are then
formed due to accretion onto wider low-mass systems. The combination of
accretion and dynamical interactions with other stars in the cluster then
result in producing a close binary system. Tidal and 3-body captures in dense
stellar cores can also play a role in forming massive binary systems while
stellar mergers of such close binary systems due to interactions may play an
important role in overcoming the radiation pressure.


title:
First Results from the CHARA Array. I. An Interferometric and
  Spectroscopic Study of the Fast Rotator alpha Leonis (Regulus)

abstract:
  We report on K-band interferometric observations of the bright, rapidly
rotating star Regulus (type B7 V) made with the CHARA Array on Mount Wilson,
California. Through a combination of interferometric and spectroscopic
measurements, we have determined for Regulus the equatorial and polar diameters
and temperatures, the rotational velocity and period, the inclination and
position angle of the spin axis, and the gravity darkening coefficient. These
first results from the CHARA Array provide the first interferometric
measurement of gravity darkening in a rapidly rotating star and represent the
first detection of gravity darkening in a star that is not a member of an
eclipsing binary system.


title: New seismological results on the G0 IV eta Bootis

abstract:
  Several attempts have been made to detect solar-like oscillations in the G0
IV star eta Boo. We present here new observations on this star simultaneously
conducted with two spectrographs: Coralie mounted on the 1.2-m Swiss telescope
at the ESO La Silla Observatory (Chile) and Elodie based on the 1.93-m
telescope at the Observatoire de Haute Provence (France). In total, 1239
spectra were collected over 13 nights. The power spectrum of the high precision
velocity time series clearly presents several identifiable peaks between 0.4
and 1.0 mHz showing regularity with a large and small separations of Delta_nu =
39.9 uHz and delta_nu02 = 3.95 uHz respectively. Twenty-two individual
frequencies have been identified. Detailed models based on these measurements
and non-asteroseismic observables were computed using the Geneva evolution code
including shellular rotation and atomic diffusion. By combining these
seismological data with non-asteroseismic observations, we determine the
following global parameters for eta Boo: a mass of 1.57 +- 0.07 M_sol, an age
t=2.67 +- 0.10 Gyr and an initial metallicity Z/X_i=0.0391 +- 0.0070. We also
show that the mass of eta Boo is very sensitive to the choice of the observed
metallicity, while the age of eta Boo depends on the input physics used.
Indeed, a higher metallicity favours a higher mass, while non-rotating models
without overshooting predict a smaller age.


title:
Asteroseismology of the Beta Cephei star Nu Eridani: photometric
  observations and pulsational frequency analysis

abstract:
  We undertook a multisite photometric campaign for the Beta Cephei star Nu
Eridani. More than 600 hours of differential photoelectric uvyV photometry were
obtained with 11 telescopes during 148 clear nights. The frequency analysis of
our measurements shows that the variability of Nu Eri can be decomposed into 23
sinusoidal components, eight of which correspond to independent pulsation
frequencies between 5 - 8 c/d. Some of these are arranged in multiplets, which
suggests rotational m-mode splitting of nonradial pulsation modes as the cause.
If so, the rotation period of the star must be between 30 - 60 d. One of the
signals in the light curves of Nu Eri has a very low frequency of 0.432 c/d. It
can be a high-order combination frequency or, more likely, an independent
pulsation mode. In the latter case Nu Eri would be both a Beta Cephei star and
a slowly pulsating B (SPB) star. The photometric amplitudes of the individual
pulsation modes of Nu Eri appear to have increased by about 20 per cent over
the last 40 years. So do the amplitudes of the dominant combination frequencies
of the star. Among the latter, we only could identify sum frequencies with
certainty, not difference frequencies, which suggests that neither light-curve
distortion in its simplest form nor resonant mode coupling are their single
cause. One of our comparison stars, Mu Eridani, turned out to be variable with
a dominant time scale of 1.62 d. We believe that it is either an SPB star just
leaving its instability strip or that its variations are of rotational origin.


title: Accretion-driven millisecond X-ray pulsars

abstract:
  I present an overview of our current observational knowledge of the six known
accretion-driven millisecond X-ray pulsars. A prominent place in this review is
given to SAX J1808.4-3658; it was the first such system discovered and
currently four outbursts have been observed from this source, three of which
have been studied in detail using the Rossi X-ray Timing Explorer satellite.
This makes SAX J1808.4-3658 the best studied example of an accretion-driven
millisecond pulsar. Its most recent outburst in October 2002 is of particular
interest because of the discovery of two simultaneous kilohertz quasi-periodic
oscillations and nearly coherent oscillations during type-I X-ray bursts. This
is the first (and so far only) time that such phenomena are observed in a
system for which the neutron star spin frequency is exactly known. The other
five systems were discovered within the last three years (with IGR J00291+5934
only discovered in December 2004) and only limited results have been published.


title: Very high energy gamma rays from the composite SNR G0.9+0.1

abstract:
  Very high energy (> 100 GeV) gamma-ray emission has been detected for the
first time from the composite supernova remnant G0.9+0.1 using the H.E.S.S.
instrument. The source is detected with a significance of 13 sigma, and a
photon flux above 200 GeV of (5.7+/-0.7 stat +/- 1.2 sys) * 10^-12 cm^-2 s^-1,
making it one of the weakest sources ever detected at TeV energies. The photon
spectrum is compatible with a power law (dN/dE \propto E^-Gamma) with photon
index Gamma = 2.40 +/- 0.11 stat +/- 0.20 sys. The gamma-ray emission appears
to originate in the plerionic core of the remnant, rather than the shell, and
can be plausibly explained as inverse Compton scattering of relativistic
electrons.


title:
New High Proper Motion Stars from the Digitized Sky Survey. III. Stars
  with proper motions 0.45<mu<2.0''/yr south of Decl.=-30

abstract:
  We report the discovery of 182 new southern stars with proper motion larger
than 0.45''/yr. The stars were found in an expansion of the SUPERBLINK proper
motion survey to 8,980 square degrees south of Decl.=-30. The new high proper
motion stars include 123 objects with mu>0.5''/yr, and 5 with mu>1.0''/yr.
These new stars consist in a variety of nearby red dwarfs and white dwarfs, and
(slightly more distant) red halo subdwarf, and are all prime targets for
follow-up spectroscopic and astrometric (parallax) observations. Comparison
with previous proper motion surveys in the southern sky suggests that
SUPERBLINK has a recovery rate between 80% and 90% at southern declinations for
stars with red magnitude 10<R<19 and proper motion in the range
0.5<mu<2.0''/yr. This survey makes a significant addition to the census of high
proper motion stars at southern declinations.


title: Three-Dimensional Vortices in Stratified Protoplanetary Disks

abstract:
  We present the results of high-resolution, three-dimensional (3D)
hydrodynamic simulations of the dynamics and formation of coherent, long-lived
vortices in stably-stratified protoplanetary disks. Tall, columnar vortices
that extend vertically through many scale heights in the disk are unstable to
small perturbations; such vortices cannot maintain vertical alignment over more
than a couple scale heights and are ripped apart by the Keplerian shear. Short,
finite-height vortices that extend only one scale height above and below the
midplane are also unstable, but for a different reason: we have isolated an
antisymmetric (with respect to the midplane) eigenmode that grows with an
e-folding time of only a few orbital periods; the nonlinear evolution of this
instability leads to the destruction of the vortex. Serendipitously, we observe
the formation of 3D vortices that are centered not in the midplane, but at one
to three scale heights above and below. Breaking internal gravity waves create
vorticity; anticyclonic regions of vorticity roll-up and coalesce into new
vortices, whereas cyclonic regions shear into thin azimuthal bands. Unlike the
midplane-centered vortices that were placed ad hoc in the disk and turned out
to be linearly unstable, the off-midplane vortices form naturally out of
perturbations in the disk, and are stable and robust for many hundreds of
orbits.


title: Probing the origins of voids with the CMB

abstract:
  In this talk presented at the 5th Rencontres du Vietnam 2004, we discuss our
preliminary investigations into voids of primordial origin. We show that if
voids in the cold dark matter distribution existed at the epoch of decoupling,
they could contribute significantly to the apparent rise in cosmic microwave
background (CMB) power on small scales detected by the Cosmic Background Imager
(CBI) Deep Field. Here we present the preliminary results of our improved
method for predicting the effects of primordial voids on the CMB in which we
treat the voids as an external source in the cold dark matter (CDM)
distribution, employing a Boltzmann solver. Our improved predictions include
the effects of a cosmological constant (Lambda) and acoustic oscillations
generated by voids at early times. We find that models with relatively large
voids on the last scattering surface predict too much CMB power in an
Einstein-de Sitter background cosmology but could be consistent with the
current CMB observations in a Lambda CDM universe.


title:
The UNSW Extrasolar Planet Search: Methods and First Results from a
  Field Centred on NGC 6633

abstract:
  We report on the current status of the University of New South Wales
Extrasolar Planet Search project, giving details of the methods we use to
obtain millimagnitude precision photometry using the 0.5m Automated Patrol
Telescope. We use a novel observing technique to optimally broaden the PSF and
thus largely eliminate photometric noise due to intra-pixel sensitivity
variations on the CCD. We have observed 8 crowded Galactic fields using this
technique during 2003 and 2004. Our analysis of the first of these fields
(centred on the open cluster NGC 6633) has yielded 49 variable stars and 4
shallow transit candidates. Follow-up observations of these candidates have
identified them as eclipsing binary systems. We use a detailed simulation of
our observations to estimate our sensitivity to short-period planets, and to
select a new observing strategy to maximise the number of planets detected.


title: Models of Procyon A including seismic constraints

abstract:
  Detailed models of Procyon A based on new asteroseismic measurements by
Eggenberger et al (2004) have been computed using the Geneva evolution code
including shellular rotation and atomic diffusion. By combining all
non-asteroseismic observables now available for Procyon A with these
seismological data, we find that the observed mean large spacing of 55.5 +- 0.5
uHz favours a mass of 1.497 M_sol for Procyon A. We also determine the
following global parameters of Procyon A: an age of t=1.72 +- 0.30 Gyr, an
initial helium mass fraction Y_i=0.290 +- 0.010, a nearly solar initial
metallicity (Z/X)_i=0.0234 +- 0.0015 and a mixing-length parameter alpha=1.75
+- 0.40. Moreover, we show that the effects of rotation on the inner structure
of the star may be revealed by asteroseismic observations if frequencies can be
determined with a high precision. Existing seismological data of Procyon A are
unfortunately not accurate enough to really test these differences in the input
physics of our models.


title: Solar-like oscillations in Procyon A

abstract:
  The F5 subgiant Procyon A (alpha CMi, HR 2943) was observed with the Coralie
fiber-fed echelle spectrograph on the 1.2-m Swiss telescope at La Silla in
February 1999. The resulting 908 high-accuracy radial velocities exhibit a mean
noise level in the amplitude spectrum of 0.11 m s^-1 at high frequency. These
measurements show significant excess in the power spectrum between 0.6-1.6 mHz
with 0.60 m s^-1 peak amplitude. An average large spacing of 55.5 uHz has been
determined and twenty-three individual frequencies have been identified.


title: Using distant globular clusters as a test for gravitational theories

abstract:
  We propose to determine the stellar velocity dispersions of globular clusters
in the outer halo of the Milky Way in order to decide whether the dynamics of
the universe on large scales is governed by dark matter or modified Newtonian
dynamics (MOND). We show that for a number of galactic globular clusters, both
the internal and the external accelerations are significantly below the
critical acceleration parameter $a_0$ of MOND. This leads to velocity
dispersions in case of MOND which exceed their Newtonian counterparts by up to
a factor of 3, providing a stringent test for MOND. Alternatively, in case high
velocity dispersions are found, these would provide the first evidence that
globular clusters are dark matter dominated.


title: Tidal streams in a MOND potential: constraints from Sagittarius

abstract:
  We compare orbits in a thin axisymmetric disc potential in MOND to those in a
thin disc plus near-spherical dark matter halo predicted by a $\Lambda$CDM
cosmology. Remarkably, the amount of orbital precession in MOND is nearly
identical to that which occurs in a mildly oblate CDM Galactic halo (potential
flattening q=0.9), consistent with recent constraints from the Sagittarius
stream. Since very flattened mass distributions in MOND produce rounder
potentials than in standard Newtonian mechanics, we show that it will be very
difficult to use the tidal debris from streams to distinguish between a MOND
galaxy and a standard CDM galaxy with a mildly oblate halo.
  If a galaxy can be found with either a prolate halo, or one which is more
oblate than $q \sim 0.9$ this would rule out MOND as a viable theory. Improved
data from the leading arm of the Sagittarius dwarf - which samples the Galactic
potential at large radii - could rule out MOND if the orbital pole precession
can be determined to an accuracy of the order of $\pm 1^o$.


title: Cosmic-rays: an unsolved mystery at all energies!

abstract:
  We consider the phenomenology of cosmic-rays (CRs) and stress the interest of
jointly studying their properties over the whole energy spectrum. While UHECRs
are known to raise important physical and astrophysical problems, we recall
that low-energy CRs also remain poorly understood, and we indicate the possibly
important role of superbubbles in accelerating CRs up to a few EeV. We also
investigate the viability of holistic models, and show that a unique type of
sources producing CRs with a spectrum in E^{-2.3} could in principle account
for all the CRs in the universe.


title: Signs of WHIM in the soft X-ray background

abstract:
  Small angular scale structure of the soft X-ray background correlated with
the galaxy distribution is investigated. An extensive data sample from the
ROSAT and XMM-Newton archives are used. Excess emission below 1 keV extending
up to at least 1.5 Mpc around galaxies is detected. The relative amplitude of
the excess emission in the 0.3-0.5 keV band amounts to 1.3+/-0.2 % of the total
background flux. A steep spectrum of the emission at higher energies is
indicated by a conspicuous decline of the signal above 1 keV. The XMM-Newton
EPIC/MOS data covering wider energy range than the ROSAT PSPC are consistent
with a thermal bremsstrahlung spectrum with k}T < 0.5 keV. This value is
consistent with temperatures of the Warm-Hot Intergalactic Medium derived by
several groups from hydrodynamic simulations. Correlation analysis allows for
estimate of the average excess emission associated with galaxies but the data
are insufficient to constrain physical parameters of the WHIM and to determine
the contribution of WHIM to the total baryonic mass density.


title: Dark Energy and Non-linear Perturbations

abstract:
  Dark energy might have an influence on the formation of non--linear
structures during the cosmic history. For example, in models in which dark
energy couples to dark matter, it will be non--homogeneous and will influence
the collapse of a dark matter overdensity. We use the spherical collapse model
to estimate how much influence dark energy might have.


title: Class Transitions and Two Component Accretion Flow in GRS 1915+105

abstract:
  The light curve of the galactic micro-quasar GRS 1915+105 changes in at least
thirteen different ways which are called classes. We present examples of the
transitions from one class to another as observed by the IXAE instrument aboard
the Indian Satellite IRS-P3. We find that the transitions are associated with
changes in photon counts over a time-scale of only a few hours and they take
place through unknown classes. Assuming that the transitions are caused by
variation of the accretion rates, this implies that a significant fraction of
the matter must be nearly freely falling in order to have such dramatic changes
in such a short time.


title: Modelling and interpreting optical spectra of galaxies at R=10000

abstract:
  One way to extract more information from the integrated light of galaxies is
to improve the spectral resolution at which observations and analysis are
carried out. The population synthesis code currently providing the highest
spectral resolution is Pegase-HR, which was made available by D. Le Borgne et
al. in 2004. Based on an empirical stellar library, it provides synthetic
spectra between 4000 and 6800 A at lambda/d(lambda)=10000 for any star
formation history, with or without chemical evolution. Such a resolution is
particularly useful for the study of low mass galaxies, massive star clusters,
or other galaxy regions with low internal velocity dispersions.
  After a summary of the main features of Pegase-HR and comparisons with other
population synthesis codes, this paper focuses on the inversion of optical
galaxy spectra. We explore the limits of what information can or can not be
recovered, based on theoretical principles and extensive simulations. First
applications to extragalactic objects are shown.


title:
Signatures of Accretion Shocks in Broadband Spectrum of Advective Flows
  Around Black Holes

abstract:
  We compute the effects of the centrifugal pressure supported shock waves on
the emitted spectrum from an accretion disk primarily consisting of low angular
momentum matter. Electrons are very efficiently accelerated by the accretion
shock and acquire power-law distribution. The accelerated particles in turn
emit synchrotron radiation in presence of a stochastic magnetic field in
equipartition with the gas. Efficient cooling of the electrons by these soft
photons reduces its temperature in comparison to the protons. We explore the
nature of the broadband spectra by using Comptonization, bremsstrahlung and
synchrotron emission. We then show that there could be two crossing points in a
broadband spectrum, one near $\sim 10 keV$ and the other $\sim 300-400$KeV.


title: Spectral Properties of Black Holes in Gamma Rays

abstract:
  Black holes are the most compact objects in the universe. Therefore, matter
accreting onto is likely to radiate photons of energy comparable to very high
gravitational potential energy. We discuss the nature of the emitted radiation
in X-rays and gamma-rays from black hole candidates. We present theoretical
solutions which comprise both Keplerian and sub-Keplerian components and
suggest that shocks in accretion and outflows


title: Identification of Shocks in the Spectra from Black Holes

abstract:
  We study the spectral properties of a low angular momentum flow as a function
of the shock strength, compression ratio, accretion rate and flow geometry. In
the absence of a satisfactory description of magnetic fields inside the
advective disk, we consider the presence of only stochastic fields and use the
ratio of the field energy to the gravitational energy density as a parameter.
We not only include `conventional' synchrotron emission and Comptonization by
Maxwell-Bolzmann electrons in the gas, but we also compute these effects due to
power-law electrons. For strong shocks, a bump is produced due to the
post-shock flow. A power-law spectral components due to the thermal and
non-thermal electrons appear after this bump.


title: Evidence of Class Transitions in GRS 1915+105 from IXAE Data

abstract:
  GRS 1915+105 shows at least twelve distinct classes of light curves. By
analysing the data obtained from Indian X-ray Astronomy Experiment (IXAE)
instrument aboard IRS-P3 satellite, we show that in at least two days,
transitions between one class to another were observed. In these days the
so-called $\kappa$ class went to $\rho$ class and $\chi$ class went to $\rho$
class. In the frequency-time plane such transitions exhibited change in
quasi-periodic oscillation (QPO) frequency. We could detect that low-frequency
QPOs can occur in anticipation of a class transition several hundred minutes
before the actual transition


title: Molecular Hydrogen Formation During Dense Interstellar Cloud Collapse

abstract:
  We study the evolution of molecular hydrogen on the grain surfaces and in the
gas phase using both the rate equation (which tracks the average number of
molecules) and the master equation (which tracks the expectation values of
molecules). We show that above a certain critical accretion rate of $H$ on the
grains, the results from these two methods become identical. We used this
result to follow the collapse of a dense interstellar cloud and studied the
formation of molecular hydrogen for two different temperatures (T=10K and 12K)
and two different masses ($1M_\odot$ and $10M_\odot$) of the cloud when olivine
grains were used. Since at higher temperatures, the recombination is very small
for these grains, we also studied a similar hydrodynamic processes at higher
temperatures (T=20K and 25K) when amorphous carbon grains were used. We find
that generally, for olivine grains, more than 90% $H$ is converted to $H_2$
within $\sim 10^{5-7}$yr whereas for amorphous grains it takes $\sim
10^{6-7}$yr. $H_2$ formed in this manner can be adequate to produce the
observed complex molecules.


title:
Signature of Accretion Shocks in Emitted Radiation From a Two
  Temperature Advective Flows Around Black Holes

abstract:
  Centrifugal barrier supported boundary layer (CENBOL) of a black hole affects
the spectrum exactly in the same way the boundary layer of a neutron star does.
The CENBOL is produced due to standing or oscillating shock waves and these
shocks accelerate electrons very efficiently and produce a power-law
distribution. The accelerated particles in turn emit synchrotron radiation in
presence of the magnetic field. We study the spectral properties of an
accretion disk as a function of the shock strength, compression ratio, flow
accretion rate and flow geometry. In the absence of a satisfactory description
of magnetic fields inside the advective disk, we consider the presence of only
stochastic fields and use the ratio of the field energy density to the
gravitational energy density to be a parameter. Not surprisingly, stronger
fields produce stronger humps due to synchrotron radiation. We not only include
`conventional' synchrotron emission and Comptonization due to Maxwell-Bolzmann
electrons in the gas, we also compute these effects due to power-law electrons.
For strong shocks, a bump is produced at a frequency just above the synchrotron
self-absorption frequency at $\nu_{bump} \sim \nu_{inj} [1+{4/3}\frac{R-1}
{R}\frac{1}{x_s^{1/2}}]^{x_s^{1/2}}$, where, $\nu_{inj}$ is the frequency of
the dominant photons from the pre-shock flow, $R$ is the compression ratio of
the shock located at $x_s$. For strong shocks, a bump at a higher frequency
appears predominantly due to the power-law electrons formed at the shock front.


title: SS 433: Results of a Recent Multi-wavelength Campaign

abstract:
  We conducted a multi-wavelength campaign in September-October, 2002, to
observe SS 433. We used 45 meter sized 30 dishes of Giant Meter Radio Telescope
(GMRT) for radio observation, 1.2 meter Physical Research Laboratory Infra-red
telescope at Mt Abu for IR, 1 meter Telescope at the State Observatory,
Nainital for Optical photometry, 2.3 meter optical telescope at the Vainu Bappu
observatory for spectrum and Rossi X-ray Timing Explorer (RXTE) Target of
Opportunity (TOO) observation for X-ray observations. We find sharp variations
in intensity in time-scales of a few minutes in X-rays, IR and radio
wavelengths. Differential photometry at the IR observation clearly indicated
significant intrinsic variations in short time scales of minutes throughout the
campaign. Combining results of these wavelengths, we find a signature of delay
of about two days between IR and Radio. The X-ray spectrum yielded double Fe
line profiles which corresponded to red and blue components of the relativistic
jet. We also present the broadband spectrum averaged over the campaign
duration.


title:
Analytical studies of particle dynamics in bending waves in planetary
  rings

abstract:
  Particles inside a planetary ring are subject to forcing due to the central
planet, moons in inclined orbits, self-gravity of the ring and other forces due
to radiation drag, collisional effects and Lorentz force due to magnetic field
of the planet. We write down the equations of motion of a single particle
inside the ring and solve them analytically. We find that the importance of the
shear caused by variation of the radial velocity component with local vertical
direction cannot be ignored and it may be responsible for damping of the
bending waves in planetary rings as observed by the Voyager data. We present
the wave profile resulting from the dissipation. We estimate that the surface
mass density of the C ring to be of the order of $\sigma \sim 1.2-1.6$gm
cm$^{-2}$, and the height $h \sim 2.2-2.4$m. These theoretical results are in
agreement with observations.


title:
Mass accretion rate of the galactic black hole A0620-00 in its quiescent
  state

abstract:
  Our recent radio observation using the Giant Meter Radio Telescope (GMRT) of
the galactic black hole transient A0620-00 at 1.280GHz revealed a micro-flare
of a few milli-Jansky. Assuming an equipartition of magnetic energy and the
gravitational potential energy of accreting matter, it is possible to estimate
the upper limit of the accretion rate. Assuming a black hole mass of
$10M_\odot$ residing at the center, we find this to be at the most ${\dot M} =
(8.5 \pm 1.4) \times 10^{-11} M_\odot$ yr$^{-1}$. This is consistent with
earlier estimates of accretion rates based on optical and X-ray observations.


title: VLF observation during Leonid Meteor Shower-2002 from Kolkata

abstract:
  Using a Gyrator-II Loop antenna tuned at 19.0Khz, we monitored the meteor
shower during 17-24th November, 2002. We observe the primary peak at 3h58m (UT)
on the 19th of November, 2002. We distinctly observed several `beadlike' and
`exponentially dropping' signals. The `beadlike' signals were more in abundance
on the 18th of November, 2002, one day prior to the actual encounter.


title: Monitoring of Sudden Ionospheric Disturbances (SID) from Kolkata (INDIA)

abstract:
  We report our first results of monitoring sudden ionospheric disturbances
(SID). We present data taken continuously for two weeks during 20th Sept. 2002
and 4th Oct. 2002. We compare the effects of solar flares of the VLF signal
with those obtained by GOES Satellite of NASA monitoring in X-rays and found
excellent agreement.


title: Role of Disk models in Indentifying Astrophysical Black Holes

abstract:
  We discuss how disk models may limit the scope of identifying astrophysical
black holes. We show that the standard Keplerian thin disk model, the thick
disk model, slim disks, ADAFs etc. are fundamentally limited. We present the
most complete solution to date called the advective accretion disk and discuss
how it has the scope to address every observational aspects of a black hole.
Though the magnetic field is not fully self-consistently taken care of yet, the
details with which the present model can handle various issues successfully are
astounding. We present some of the examples.


title: Precessions in Relativity

abstract:
  From Mercury's perihelion precession (open question from 1845 to 1915) to
Gravity Probe-B satellite (first proposal in 1959, launch in 2004), General
Relativity had to deal with precession phenomena. Perihelion advancement
precession (Einstein), geodetic (de Sitter), gravitomagnetic (Lense-Thirring)
and spin-spin (Pugh-Schiff) precession are compared with all Newtonian terms in
cases of weak and strong gravitational fields. Qualitative models and order of
magnitude estimates from classical papers are presented.


title:
Spectral Properties of a Two Component and Two Temperature Advective
  Flow

abstract:
  Low angular momentum accretion flows very often have centrifugal pressure
supported standing shock waves which can accelerate flow particles. The
accelerated particles in turn emit synchrotron radiation in presence of
magnetic fields. Efficient cooling of the electrons reduces its temperature in
comparison to the protons. In this paper, we assume two temperature flows to
explore this property of shocks and present an example of the emitted radiation
spectrum.


title:
QPOs from Radial and Vertical Oscillation of Shocks in Advective
  Accretion Flows

abstract:
  We present results of several numerical simulations of two dimensional
advective flows which include cooling processes. We show that the computed
light curve is similar to the $\chi$ state in GRS 1915+105. The power density
spectrum (PDS) also shows presence of QPOs near the break frequency.


title: Spectral Signatures of Winds from Accretion Disks Around Black Holes

abstract:
  We show that with the wind/jet activity, the spectral index of hard X-ray is
changed in galactic microquasars. When mass loss takes place, the spectrum
becomes softer and when mass gain takes place, the spectrum becomes harder. We
present examples of such changes in GRS1915+105.


title: Photometric Evidence of Bullets in SS433 Jet

abstract:
  We report the photometric evidence of bullet like features in SS433 in
X-rays, Infra-red and Radio bands through a multi-wavelength campaign.


title:
A GHz Flare in a Quiescent Black Hole and A Determination of the Mass
  Accretion Rate

abstract:
  If the total energy of a radio flare is known, one can estimate the mass
accretion rate of the disk by assuming equipartition of magnetic energy and the
gravitational potential energy of accreting matter. We present here an example
of how such an estimate could be done. Our recent radio observation using the
Giant Meter Radio Telescope (GMRT) of the galactic black hole transient
A0620-00 at 1.280 GHz revealed a micro-flare of a few milli-Jansky. Assuming a
black hole mass of $10 M_\odot$ for the compact object, we find the accretion
rate to be at the most ${\dot M} = (8.5 \pm 1.4) \times 10^{-11}
(\frac{x}{3})^{5/2} M_\odot$ yr$^{-1}$, where, $x$ is the distance from the
hole in units of Schwarzschild radius. This is consistent with the earlier
estimate of the accretion rate based on optical and X-ray observations. We
claim that this procedure is general enough to be used for any black hole
candidate.


title: Results of Recent Multi-wavelength Campaign of SS433

abstract:
  We conducted multi wavelength campaign on SS433 in Sept. 2002 using X-ray, B,
Infra-Red and radio telescopes. We observed variabilities on a time-scale of
few minutes in all the wavelengths. We interpret them to be due to bullet-like
features from the accretion disk. We also present X-ray properties as obtained
by RXTE.


title: Class Transitions in Black Holes

abstract:
  A black hole spectrum is known to change from the hard state to the soft
state when the energy spectral index $\alpha$ ($F_E \propto E^{-\alpha}$) in,
say, 2-20 keV range changes from $\alpha \sim 0.5$ to $\sim 1.5$. However, this
`classical' definition which characterizes black holes like Cyg X-1, becomes
less useful for many objects such as GRS 1915+105 in which the spectral slope
is seen to vary from one to the other in a matter of seconds and depending on
whether or not winds form, the spectral slope also changes. The light curves
and the colour-colour diagrams may look completely different on different days
depending on the frequency and mode of switching from one spectral state to the
other. Though RXTE observations have yielded wealth of information on such
`variability classes' in GRS 1915+105, very rarely one has been able to observe
how the object goes from one class to the other. In the present review, we
discuss possible origins of the class transition and present several examples
of such transitions. In this context, we use mostly the results of the Indian
X-ray Astronomy Experiment (IXAE) which observed GRS 1915+105 more regularly.


title: Numerical Simulations Reveal the Origin of QPOs in Black Hole Candidates

abstract:
  We present results of various types of numerical simulations of black hole
accretion disks and find that those flows which are relatively non-dissipative
and which contain accretion shocks are the best candidates so far. The power
density spectra (PDS) reveal the aspects which are similar to what are observed
in black hole candidates.


title:
A Model Grid for the Spectral Analysis of X-ray Emission in Young Type
  Ia Supernova Remnants

abstract:
  We address a new set of models for the spectral analysis of the X-ray
emission from young, ejecta-dominated Type Ia supernova remnants. These models
are based on hydrodynamic simulations of the interaction between Type Ia
supernova explosion models and the surrounding ambient medium, coupled to
self-consistent ionization and electron heating calculations in the shocked
supernova ejecta, and the generation of synthetic spectra with an appropriate
spectral code. The details are provided elsewhere, but in this paper we
concentrate on a specific class of Type Ia explosion models (delayed
detonations), commenting on the differences that arise between their synthetic
X-ray spectra under a variety of conditions.


title:
Thermal X-Ray Emission from Shocked Ejecta in Type Ia Supernova Remnants
  II: Parameters Affecting the Spectrum

abstract:
  The supernova remnants left behind by Type Ia supernovae provide an excellent
opportunity for the study of these enigmatic objects. In a previous work, we
showed that it is possible to use the X-ray spectra of young Type Ia supernova
remnants to explore the physics of Type Ia supernovae and identify the relevant
mechanism underlying these explosions. Our simulation technique is based on
hydrodynamic and nonequilibrium ionization calculations of the interaction of a
grid of Type Ia explosion models with the surrounding ambient medium, coupled
to an X-ray spectral code. In this work we explore the influence of two key
parameters on the shape of the X-ray spectrum of the ejecta: the density of the
ambient medium around the supernova progenitor and the efficiency of
collisionless electron heating at the reverse shock. We also discuss the
performance of recent 3D simulations of Type Ia SN explosions in the context of
the X-ray spectra of young SNRs. We find a better agreement with the
observations for Type Ia supernova models with stratified ejecta than for 3D
deflagration models with well mixed ejecta. We conclude that our grid of Type
Ia supernova remnant models can improve our understanding of these objects and
their relationship to the supernovae that originated them.


title:
Nearby early-type galaxies with ionized gas. Characterization of the
  underlying stellar population

abstract:
  We present a preliminary analysis of the sample of early type galaxies of
Rampazzo et al. (2005), selected to build a data-set of spectral properties of
well studied early-type galaxies showing emission lines. Because of the
presence of emission lines, the sample is biased toward objects that might be
expected to have ongoing and recent star formation. We have compared the
line-strength indices presented in Rampazzo et al. (2005) with Simple Stellar
Populations (SSPs) in order to characterize the underlying stellar population
of the galaxies. We have derived ages, metallicities and [alpha/Fe] ratios. The
positive trend of the sigma-metallicity and sigma-[alpha/Fe] relations is
reproduced. The bulk of the galaxies span a range in metallicity from ~ solar
to ~ twice solar and a range in [alpha/Fe] from ~0.2 to ~0.4. Furthermore the
comparison of the derived parameters at different galactocentric distances
shows the presence of negative metallicity gradients from the center outwards.


title:
Indirect manifestation of GRBs in the Galaxy: Compton trails and
  positrons

abstract:
  Two independent indirect manifestations of Galactic gamma-ray bursts (GRBs)
are considered, whose importance for gamma-ray astronomy will depend on a still
poorly known -- though astrophysically important -- parameter, namely the GRB
repetition timescale in a Galaxy like ours. Both phenomena are expected to lead
to observational constrains about this timescale. The first one relates to the
Compton scattering of the GRB gamma-rays in the disk of the Galaxy, and the
second one to the long-term annihilation pattern of positrons produced just
ahead of the ultra-relativistic plasma, by photo-pair production.


title: Dwarf galaxies in voids: Suppressing star formation with photo-heating

abstract:
  We study structure formation in cosmological void regions using
high-resolution hydrodynamical simulations. Despite being significantly
underdense, voids are populated abundantly with small dark matter halos which
should appear as dwarf galaxies if their star formation is not suppressed
significantly. We here investigate to which extent the cosmological
UV-background photo-evaporates baryons out of halos of dwarf galaxies, and
thereby limits their cooling and star formation rates. Assuming a Haardt &
Madau UV-background with reionisation at redshift z=6, our samples of simulated
galaxies show that halos with masses below a characteristic mass of M_c(z=0) =
6.5 x 10^9 h^{-1} M_sun are baryon-poor, but in general not completely empty,
because baryons that are in the condensed cold phase or are already locked up
in stars resist evaporation. In halos with mass M < M_c, we find that
photo-heating suppresses further cooling of gas. The redshift and UV-background
dependent characteristic mass M_c(z) can be understood from the equilibrium
temperature between heating and cooling at a characteristic overdensity of
\delta ~ 1000. If a halo is massive enough to compress gas to this density
despite the presence of the UV background, gas is free to `enter' the condensed
phase and cooling continues in the halo, otherwise it stalls. By analysing the
mass accretion histories of dwarf galaxies in voids, we show that they can
build up a significant amount of condensed mass at early times before the epoch
of reionisation. Later on, the amount of mass in this phase remains roughly
constant, but the masses of the dark matter halos continue to increase.
(abridged)


title: The optical counterpart of an Ultra-luminous X-Ray Source in NGC 5204

abstract:
  Ultra-luminous X-Ray sources are extra-nuclear point sources in external
galaxies with $L_X=10^{39}$--$10^{41}$ erg/s and are among the most poorly
understood X-ray sources. To help understand their nature, we are trying to
identify their optical counterparts by combining images from the Hubble Space
Telescope and the Chandra Observatory. Here we report upon the optical
counterpart for the ULX in NGC 5204, which has average X-ray luminosity of
$\sim3\times10^{39}$ erg/s and has varied by a factor of 50% over the last 10
years. A unique optical counterpart to this ULX is found by carefully comparing
the Chandra ACIS images and HST WFPC2 and ACS/HRC images. The spectral energy
distribution and the HST/STIS FUV spectrum of this object show that it is a B0
Ib supergiant star with peculiarities, including the $\lambda$1240 N V emission
line that is uncommon in B stellar spectra but has been predicted for X-ray
illuminated accretion disks and seen in some X-ray binaries. Study of its FUV
spectrum leads to a binary model for this ULX in which the B0 Ib supergiant is
overflowing its Roche Lobe and accreting onto the compact primary, probably a
black hole. This picture predicts an orbital period of $\sim10$ days for
different black hole mass, which can be tested by future observations.


title: A Two Hour Quasi-Period in an Ultra-luminous X-Ray source in NGC628

abstract:
  Quasi-periodic oscillations and X-ray spectroscopy are powerful probes of
black hole masses and accretion disks, and here we apply these diagnostics to
an ultraluminous X-ray source (ULX) in the spiral galaxy NGC628 (M74). This
object was observed four times over two years with the Chandra X-ray
Observatory and XMM-Newton, with three long observations showing dramatic
variability, distinguished by a series of outbursts with a quasi-period (QPO)
of 4,000-7,000 seconds. This is unique behavior among both ULXs and Galactic
X-ray binaries due to the combination of its burst-like peaks and deep troughs,
its long quasi-periods, its high variation amplitudes of $>90$%, and its
substantial variability between observations. The X-ray spectra is fitted by an
absorbed accretion disk plus a power-law component, suggesting the ULX was in a
spectral state analogous to the Low Hard state or the Very High state of
Galactic black hole X-ray binaries. A black hole mass of $\sim2$--$20\times10^3
M_\odot$ is estimated from the $f_b$--$M_\bullet$ scaling relation found in the
Galactic X-ray binaries and active galactic nuclei.


title:
A Long-Lived Accretion Disk Around a Lithium-Depleted Binary T Tauri
  Star

abstract:
  We present a high dispersion optical spectrum of St 34 and identify the
system as a spectroscopic binary with components of similar luminosity and
temperature (both M3+/-0.5). Based on kinematics, signatures of accretion, and
location on an H-R diagram, we conclude that St 34 is a classical T Tauri star
belonging to the Taurus-Auriga T Association. Surprisingly, however, neither
component of the binary shows LiI 6708 A, absorption, the most universally
accepted criterion for establishing stellar youth. In this uniquely known
instance, the accretion disk appears to have survived longer than the lithium
depletion timescale. We speculate that the long-lived accretion disk is a
consequence of the sub-AU separation companion tidally inhibiting, though not
preventing, circumstellar accretion. Comparisons with pre-main sequence
evolutionary models imply, for each component of St 34, a mass of 0.37+/-0.08
Msun and an isochronal age of 8+/-3 Myr, which is much younger than the
predicted lithium depletion timescale of ~ 25 Myr. Although a distance 38%
closer than that of Taurus-Auriga or a hotter temperature scale could reconcile
this discrepancy at 21-25 Myr, similar discrepancies in other systems and the
implications of an extremely old accreting Taurus-Auriga member suggest instead
a possible problem with evolutionary models. Regardless, the older age implied
by St 34's depleted lithium abundance is the first compelling evidence for a
substantial age spread in this region. Additionally, since St 34's coeval
co-members with early M spectral types would likewise fail the lithium test for
youth, current membership lists may be incomplete.


title:
Observations of T Tauri Disks at Sub-AU Radii: Implications for
  Magnetospheric Accretion and Planet Formation

abstract:
  We determine inner disk sizes and temperatures for four solar-type (1-2
M$_{\odot}$) classical T Tauri stars (AS 207A, V2508 Oph, AS 205A, and PX Vul)
using 2.2 $\mu$m observations from the Keck Interferometer. Nearly
contemporaneous near-IR adaptive optics imaging photometry, optical photometry,
and high-dispersion optical spectroscopy are used to distinguish contributions
from the inner disks and central stars in the interferometric observations. In
addition, the spectroscopic and photometric data provide estimates of stellar
properties, mass accretion rates, and disk co-rotation radii. We model our
interferometric and photometric data in the context of geometrically flat
accretion disk models with inner holes, and flared disks with puffed-up inner
walls. Models incorporating puffed-up inner disk walls generally provide better
fits to the data, similar to previous results for higher-mass Herbig Ae stars.
Our measured inner disk sizes are larger than disk truncation radii predicted
by magnetospheric accretion models, with larger discrepancies for sources with
higher mass accretion rates. We suggest that our measured sizes correspond to
dust sublimation radii, and that optically-thin gaseous material may extend
further inward to the magnetospheric truncation radii. Finally, our inner disk
measurements constrain the location of terrestrial planet formation as well as
potential mechanisms for halting giant planet migration.


title:
Ultra-luminous X-ray Sources in nearby galaxies from ROSAT HRI
  observations I. data analysis

abstract:
  X-ray observations have revealed in other galaxies a class of extra-nuclear
X-ray point sources with X-ray luminosities of $10^{39}$--$10^{41}$ erg/sec,
exceeding the Eddington luminosity for stellar mass X-ray binaries. These
ultra-luminous X-ray sources (ULXs) may be powered by intermediate mass black
hole of a few thousand $M_\odot$ or stellar mass black holes with special
radiation processes. In this paper, we present a survey of ULXs in 313 nearby
galaxies with $D_{25}$$>$$1^\prime$ within 40 Mpc with 467 ROSAT HRI archival
observations. The HRI observations are reduced with uniform procedures, refined
by simulations that help define the point source detection algorithm employed
in this survey. A sample of 562 extragalactic X-ray point sources with $L_X =
10^{38}$--$10^{43}$ erg/sec is extracted from 173 survey galaxies, including
106 ULX candidates within the $D_{25}$ isophotes of 63 galaxies and 110 ULX
candidates between 1--2$\times D_{25}$ of 64 galaxies, from which a clean
sample of 109 ULXs is constructed to minimize the contamination from foreground
or background objects. In a subsequent paper, the statistic properties of the
survey will be studied to calculate the occurrence frequencies and luminosity
functions for ULXs in different types of galaxies to shed light on the nature
of these enigmatic sources.