title:
VIMOS-IFU survey of z~0.2 massive galaxy clusters. I. Observations of
  the strong lensing cluster Abell 2667

abstract:
  (abridged) We present extensive multi-color imaging and low resolution VIMOS
Integral Field Unit spectroscopic observations of the X-ray luminous cluster
Abell 2667 (z=0.233). An extremely bright giant gravitational arc (z=1.0334) is
easily identified as part of a triple image system and other fainter multiple
images are also revealed by the HST-WFPC2 images. The VIMOS-IFU observations
cover a field of view of 54'' x 54'' and enable us to determine the redshift of
all galaxies down to V=22.5. Furthermore, redshifts could be identified for
some sources down to V=23.2. In particular we identify 21 cluster members in
the cluster inner region, from which we derive a velocity dispersion of
\sigma=960 km/s, corresponding to a total mass of 7.1 x 10^{13} solar masses
within a 110 kpc radius. Using the multiple images constraints and priors on
the mass distribution of cluster galaxy halos we construct a detailed lensing
mass model leading to a total mass of 2.9 x 10^{13} solar masses within the
Einstein radius (16 arcsec). The lensing mass and dynamical mass are in good
agreement although the dynamical one is much less accurate. Comparing these
measurements with published X-ray analysis, is however less conclusive.
Although the X-ray temperature matches the dynamical and lensing estimates, the
published NFW mass model derived from the X-ray measurement with its small
concentration of c ~3 can not account for the large Einstein radius observed in
this cluster. A larger concentration of ~6 would however match the strong
lensing measurements. These results are likely reflecting the complex structure
of the cluster mass distribution, underlying the importance of panchromatic
studies from small to large scale in order to better understand cluster
physics.


title:
The Observed Galactic Annihilation Line. Possible Signature of the
  Cluster for Accreting Small Mass Black Holes

abstract:
  Compton Gamma Ray Observatory, OSSE, SMM, TGRS, balloon and recent INTEGRAL
data reveal a feature of the 0.511 MeV annihilation radiation of the Galactic
Center with a flux of approximately 5x 10^{-4}~0.511 MeV photons cm^{-2}
s^{-1}. We argue that e+e- pairs can be generated when the X-ray radiation
photons and ~10-30 MeV photons interact with each other in the compact region
in the proximity of the Galactic Center black hole. In fact, disks formed near
black holes of 10^{17} g mass should emit the ~ 10 MeV temperature blackbody
radiation. If positron e+ sources are producing about 10^{42} e+ s^{-1} near
the Galactic Center they would annihilate on the way out and result in 0.511
MeV emission. We suggest that the annihilation radiation can be an
observational consequence of the interaction of the accretion disk radiation of
the SMall Mass Black Holes (SMMBHs) with X-ray radiation in the Galactic
Center. This is probably the only way to identify and observe these SMMBHs.


title: A Dynamical Model for the Extra-planar Gas in Spiral Galaxies

abstract:
  Recent HI observations reveal that the discs of spiral galaxies are
surrounded by extended gaseous haloes. This extra-planar gas reaches large
distances (several kpc) from the disc and shows peculiar kinematics (low
rotation and inflow). We have modelled the extra-planar gas as a continuous
flow of material from the disc of a spiral galaxy into its halo region. The
output of our models are pseudo-data cubes that can be directly compared to the
HI data. We have applied these models to two spiral galaxies (NGC891 and
NGC2403) known to have a substantial amount of extra-planar gas. Our models are
able to reproduce accurately the vertical distribution of extra-planar gas for
an energy input corresponding to a small fraction (<4%) of the energy released
by supernovae. However they fail in two important aspects: 1) they do not
reproduce the right gradient in rotation velocity; 2) they predict a general
outflow of the extra-planar gas, contrary to what is observed. We show that
neither of these difficulties can be removed if clouds are ionized and
invisible at 21cm as they leave the disc but become visible at some point on
their orbits. We speculate that these failures indicate the need for accreted
material from the IGM that could provide the low angular momentum and inflow
required.


title: Galaxy Collisions - Dawn of a New Era

abstract:
  The study of colliding galaxies has progressed rapidly in the last few years,
driven by observations with powerful new ground and space-based instruments.
These instruments have used for detailed studies of specific nearby systems,
statistical studies of large samples of relatively nearby systems, and
increasingly large samples of high redshift systems. Following a brief summary
of the historical context, this review attempts to integrate these studies to
address the following key issues. What role do collisions play in galaxy
evolution, and how can recently discovered processes like downsizing resolve
some apparently contradictory results of high redshift studies? What is the
role of environment in galaxy collisions? How is star formation and nuclear
activity orchestrated by the large scale dynamics, before and during merger?
Are novel modes of star formation involved? What are we to make of the
association of ultraluminous X-ray sources with colliding galaxies? To what do
degree do mergers and feedback trigger long-term secular effects? How far can
we push the archaeology of individual systems to determine the nature of
precursor systems and the precise effect of the interaction? Tentative answers
to many of these questions have been suggested, and the prospects for answering
most of them in the next few decades are good.


title: Infrared Radiation from Hot Jupiters

abstract:
  Recent Spitzer infrared (IR) observations of two transiting hot Jupiters
during their secondary eclipses have provided the first direct detection of
planets orbiting other stars (Charbonneau et al. 2005; Deming et al. 2005). We
here elaborate on some aspects of our detection of HD209458b at 24 microns, and
we compare to the detection of TrES-1 by Charbonneau et al. Spitzer will
eventually determine the IR spectral energy distribution of these and similar
hot Jupiters, opening the new field of comparative exoplanetology. For now, we
have only three Spitzer data points, augmented by upper limits from the ground.
We here interpret the available measurements from a purely observational
perspective, and we point out that a blackbody spectrum having T=1100K can
account for all current IR measurements, within the errors. This will surely
not remain true for long, since ongoing Spitzer observations will be very
sensitive to the IR characteristics of hot Jupiters.


title: 10,000 Standard Solar Models: a Monte Carlo Simulation

abstract:
  We have evolved 10,000 solar models using 21 input parameters that are
randomly drawn for each model from separate probability distributions for every
parameter. We use the results of these models to determine the theoretical
uncertainties in the predicted surface helium abundance, the profile of the
sound speed versus radius, the profile of the density versus radius, the depth
of the solar convective zone, the eight principal solar neutrino fluxes, and
the fractions of nuclear reactions that occur in the CNO cycle or in the three
branches of the p-p chains. We also determine the correlation coefficients of
the neutrino fluxes for use in analysis of solar neutrino oscillations. Our
calculations include the most accurate available input parameters, including
radiative opacity, equation of state, and nuclear cross sections. We
incorporate both the recently determined heavy element abundances recommended
by Asplund, Grevesse & Sauval (2005) and the older (higher) heavy element
abundances recommended by Grevesse & Sauval (1998). We present best-estimates
of many characteristics of the standard solar model for both sets of
recommended heavy element compositions.


title: The broken hierarchy of galaxy formation

abstract:
  Recent observations of the distant Universe suggest that much of the stellar
mass of bright galaxies was already in place at $z>1$. This presents a
challenge for models of galaxy formation because massive halos are assembled
late in hierarchical cosmologies such as cold dark matter (CDM). In this paper,
we discuss a new implementation of the Durham semi-analytic model in which
feedback due to active galactic nuclei (AGN) is assumed to quench cooling flows
in massive halos. This mechanism naturally creates a break in the local galaxy
luminosity function at bright magnitudes. The model is implemented within the
Millennium N-body simulation; the accurate dark matter merger trees and large
number of realizations of the galaxy formation process that the simulation
provides results in highly accurate statistics. After adjusting the values of
the physical parameters in the model by reference to the properties of local
galaxies, we use it to investigate the evolution of the K-band luminosity and
galaxy stellar mass functions. We also calculate the volume averaged star
formation rate density of the Universe as a function of redshift and the way in
which this is apportioned amongst galaxies of different mass. The model
robustly predicts a substantial population of massive galaxies out to redshift
$z\sim 5$ and a star formation rate density which rises with increasing
redshift in objects of all masses. Although observational data on these
properties have been cited as evidence for ``anti-hierarchical'' galaxy
formation, we find that when AGN feedback is taken into account, the
fundamentally hierachical CDM model provides a very good match to these
observations.


title:
A method to search for topological signatures in the angular
  distribution of cosmic objects

abstract:
  We present a method to search for large angular-scale correlations, termed
topological signatures, in the angular distribution of cosmic objects, which
does not depend on cosmological models or parameters and is based only on the
angular coordinates of the objects. In order to explore Cosmic Microwave
Background temperature fluctuations data, we applied this method to simulated
distributions of objects in thin spherical shells located in three different
multiply-connected Euclidean 3-spaces ($T^3$, $T_{\pi}$, and $G_6$), and found
that the topological signatures due to these topologies can be revealed even if
their intensities are small. We show how to detect such signatures for the
cases of full-sky and partial-sky distributions of objects. This method can
also be applied to other ensembles of cosmic objects, like galaxies or quasars,
in order to reveal possible angular-scale correlations in their distributions.


title:
A Lower Bound on Neutrino Mass and Its Implication on The Z-burst
  Scenario

abstract:
  We show that the cascade limit on ultra high energy cosmic neutrino
(UHEC$\nu$) flux imposes a lower bound on the neutrino mass provided that
super-GZK events of ultra high energy cosmic rays (UHECRs) are produced from
Z-bursts. Based on the data from HiRes and AGASA, the obtained neutrino mass
lower bound violates its existing cosmological upper bound. We conclude that
the Z-bursts cannot be the dominant source for the observed super-GZK UHECR
events. This is consistent with the recent ANITA-lite data.


title:
Accretion and nuclear activity of quiescent supermassive black holes.
  II: optical study and interpretation

abstract:
  Our X-ray study of the nuclear activity in a new sample of six quiescent
early-type galaxies, and in a larger sample from the literature, confirmed
(Soria et al., Paper I) that the Bondi accretion rate of diffuse hot gas is not
a good indicator of the supermassive black hole (SMBH) X-ray luminosity. Here
we suggest that a more reliable estimate of the accretion rate must include the
gas released by the stellar population inside the sphere of influence of the
SMBH, in addition to the Bondi inflow of hot gas across that surface. We use
optical surface-brightness profiles to estimate the mass-loss rate from stars
in the nuclear region: we show that for our sample of galaxies it is an order
of magnitude higher (~ 10^{-4} - 10^{-3} M_sun/yr) than the Bondi inflow rate
of hot gas, as estimated from Chandra (Paper I). Only by taking into account
both sources of fuel can we constrain the true accretion rate, the accretion
efficiency, and the power budget. Radiatively efficient accretion is ruled out,
for quiescent SMBHs. For typical radiatively inefficient flows, the observed
X-ray luminosities of the SMBHs imply accretion fractions ~ 1 - 10% (ie, ~ 90 -
99% of the available gas does not reach the SMBH) for at least five of our six
target galaxies, and most of the other galaxies with known SMBH masses. We
discuss the conditions for mass conservation inside the sphere of influence, so
that the total gas injection is balanced by accretion plus outflows. We show
that a fraction of the total accretion power (mechanical plus radiative) would
be sufficient to sustain a self-regulating, slow outflow which removes from the
nuclear region all the gas that does not sink into the BH (``BH feedback'').
The rest of the accretion power may be carried out in a jet, or advected. We
also discuss scenarios that would lead to an intermittent nuclear activity.


title: High Energy All Sky Transient Radiation Observatory

abstract:
  The scientific discoveries made by H.E.S.S. during its first year of
operation encourage a reexamination of the open problems in high energy
astrophysics and of the capabilities of the atmospheric Cherenkov technique,
which could be employed to address them. We report on an initial Monte Carlo
exploration of a ground-based instrument for observing cosmologically distant
high energy transient phenomena. Such observations would require combining an
order of magnitude increase in collecting area over existing instruments, with
a similarly large increase in field of view for routine sky monitoring, and a
factor of five decrease in energy threshold to extend the visibility range to
redshifts exceeding one. A large array of moderately sized Imaging Atmospheric
Cherenkov Telescopes (IACTs) through which the total array collecting area,
array field of view and array data rates can be distributed, appears to be able
to meet these requirements. To be practically feasible for construction,
however, a cost effective imaging solution, with resolution of ~1 minute of arc
within ~15 degrees field of view needs to be found. If image intensifier based
technology provides such a solution in future, then, combined with super-fast
parallel data processing, it may become a technological foundation for the next
breakthrough in ground-based gamma-ray astronomy.


title:
Computation of Fluid Flows in Non-inertial Contracting, Expanding, and
  Rotating Reference Frames

abstract:
  We present the method for computation of fluid flows that are characterized
by the large degree of expansion/contraction and in which the fluid velocity is
dominated by the bulk component associated with the expansion/contraction
and/or rotation of the flow. We consider the formulation of Euler equations of
fluid dynamics in a homologously expanding/contracting and/or rotating
reference frame. The frame motion is adjusted to minimize local fluid
velocities. Such approach allows to accommodate very efficiently large degrees
of change in the flow extent. Moreover, by excluding the contribution of the
bulk flow to the total energy the method eliminates the high Mach number
problem in the flows of interest. An important practical advantage of the
method is that it can be easily implemented with virtually any implicit or
explicit Eulerian hydrodynamic scheme and adaptive mesh refinement (AMR)
strategy.
  We also consider in detail equation invariance and existence of conservative
formulation of equations for special classes of expanding/contracting reference
frames. Special emphasis is placed on extensive numerical testing of the method
for a variety of reference frame motions, which are representative of the
realistic applications of the method. We study accuracy, conservativity, and
convergence properties of the method both in problems which are not its optimal
applications as well as in systems in which the use of this method is maximally
beneficial. Such detailed investigation of the numerical solution behavior is
used to define the requirements that need to be considered in devising
problem-specific fluid motion feedback mechanisms.


title:
Oscillation mode lifetimes in ksi Hydrae: Will strong mode damping limit
  asteroseismology of red giant stars?

abstract:
  We introduce a new method to measure frequency separations and mode lifetimes
of stochastically excited and damped oscillations, so-called solar-like
oscillations. Our method shows that velocity data of the red giant star ksi Hya
(Frandsen et al. 2002) support a large frequency separation between modes of
roughly 7 microHz. We also conclude that the data are consistent with a mode
lifetime of 2 days, which is so short relative to its pulsation period that
none of the observed frequencies are unambiguous. Hence, we argue that the
maximum asteroseismic output that can be obtained from these data is an average
large frequency separation, the oscillation amplitude and the average mode
lifetime. However, the significant discrepancy between the theoretical
calculations of the mode lifetime (Houdek & Gough 2002) and our result based on
the observations of ksi Hya, implies that red giant stars can help us better
understand the damping and driving mechanisms of solar-like p-modes by
convection.


title: Chandra observation of the most interesting cluster in the Universe

abstract:
  Chandra has recently observed 1E0657-56, a hot merging system at z=0.3 (the
``bullet'' cluster), for 500 ks. I present some of the findings from this
dataset. The cluster exhibits a prominent bow shock with M=3.0+-0.4 (one of
only two known M>>1 shock fronts), which we use for a first test of the
electron-ion equilibrium in an intergalactic plasma. The temperatures across
the shock are consistent with instant shock-heating of the electrons; at 95%
confidence, the equilibration timescale is much shorter than the collisional
Spitzer value. Global properties of 1E0657-56 are also remarkable. Despite
being extremely unrelaxed, the cluster fits well on the Lx-T relation, yet its
total mass estimated from the M-T relation is more than twice the value
measured from lensing. This is consistent with simulations predicting that in
the middle of a merger, global temperature and X-ray luminosity may be
temporarily boosted by a large factor.


title:
Automatic classification of eclipsing binaries light curves using neural
  networks

abstract:
  In this work we present a system for the automatic classification of the
light curves of eclipsing binaries. This system is based on a classification
scheme that aims to separate eclipsing binary sistems according to their
geometrical configuration in a modified version of the traditional
classification scheme. The classification is performed by a Bayesian ensemble
of neural networks trained with {\em Hipparcos} data of seven different
categories including eccentric binary systems and two types of pulsating light
curve morphologies.


title: Infrared Extinction by Aggregates of SiC Particles

abstract:
  Particle shape and aggregation have a strong influence on the spectral
profiles of infrared phonon bands of solid dust grains. In this paper, we use a
discrete dipole approximation, a cluster-of-spheres code following the
Gerardy-Ausloos approach and a T-matrix method for calculating IR extinction
spectra of aggregates of spherical silicon carbide (SiC) particles. We compare
the results obtained with the three different methods and discuss differences
in the band profiles.


title:
Axisymmetric stability criteria for a composite system of stellar and
  magnetized gaseous singular isothermal discs

abstract:
  Using the fluid-magnetofluid formalism, we obtain axisymmetric stability
criteria for a composite disc system consisting of stellar and gaseous
magnetized singular isothermal discs (MSIDs). Lou & Zou recently constructed
exact global stationary configurations for both axisymmetric and
nonaxisymmetric coplanar MHD perturbations in such a composite MSID system and
proposed the MHD $D_s-$criteria for axisymmetric stability by the hydrodynamic
analogy. In a different perspective, we derive and analyze here the
time-dependent WKBJ dispersion relation in the low-frequency and tight-winding
regime to examine axisymmetric stability properties. By introducing a
rotational Mach number $D_s$ for the ratio of the stellar rotation speed $V_s$
to the stellar velocity dispersion $a_s$, one readily determines the stable
range of $D_s^2$ numerically to establish the $D_s-$criteria for axisymmetric
MSID stability. Those MSID systems rotating either too fast (ring ragmentation)
or too slow (Jeans collapse) are unstable. Our WKBJ results of (M)SID
instability provide physically compelling explanations for the stationary
analysis of Lou & Zou. We further introduce an effective MHD $Q$ parameter for
a composite MSID system and compare with the earlier work of Elmegreen, Jog and
Shen & Lou. As expected, an axisymmetric dark matter halo enhances the
stability against axisymmetric disturbances in a composite partial MSID system.


title:
Double stage Lyot coronagraph with the apodized reticulated stop for
  extremely large telescope

abstract:
  One of the science drivers for the extremely large telescope (ELT) is imaging
and spectroscopy of exo-solar planets located as close as 20mas to their parent
star. The application requires a well thought-out design of the high contrast
imaging instrumentation. Several working coronagraphic concepts have already
been developed for the monolithic telescope with the diameter up to 8 meter.
Nevertheless the conclusions made about the performance of these systems cannot
be applied directly to the telescope of the diameter 30-100m. The existing
schemes are needed to be reconsidered taking into account the specific
characteristics of a segmented surface. We start this work with the classical
system ? Lyot coronagraph. We show that while the increase in telescope
diameter is an advantage for the high contrast range science, the segmentation
sets a limit on the performance of the coronagraph. Diffraction from
intersegment gaps sets a floor to the achievable extinction of the starlight.
Masking out the bright segment gaps in the Lyot plane although helps increasing
the contrast, does not solve completely the problem: the high spatial frequency
component of the diffractive light remains. We suggest using the Lyot stop
which acts on the light within gaps in order to produce the uniform
illumination in the Lyot plane. We show that for the diffraction limit regime
and a perfect phasing this type of coronagraph achieves a sufficient star light
extinction.


title: The possible orbital period of the nova V1493 Aquilae

abstract:
  Period analysis of CCD photometry of V1493 Aql (Nova Aql 1999 no. 1)
performed during 12 nights through I and R filters a few weeks after maximum is
presented. The PDM method for period analysis (Stellingwerf 1978) is used. The
photometric data is modulated with a period of 0.156 +- 0.001 d. Following the
sinusoidal shape of the phased light curve, we interpret this periodicity as
possibly orbital in nature which is consistent with a cataclysmic variable
above the period gap.


title: The dust-scattered X-ray halo around Swift GRB 050724

abstract:
  This paper discusses the X-ray halo around the Swift gamma-ray burst GRB
050724 (z=0.258), detected by the Swift X-Ray Telescope. The halo, which forms
a ring around the fading X-ray source, expands to a radius of 200" within 8 ks
of the burst exactly as expected for small-angle X-ray scattering by Galactic
dust along the line of sight to a cosmologically distant GRB. The expansion
curve and radial profile of the halo constrain the scattering dust to be
concentrated at a distance of D = 139 +/- 9 pc (from Earth) in a cloud/sheet of
thickness delta-D < 22 pc. The halo was observed only out to scattering angles
of 200", for which the scattering is dominated by the largest grains, with a
maximum size estimated to be a_max ~ 0.4-0.5 um. The scattering-to-extinction
ratio was estimated to be tau_scat/A_V > 0.022; this is a lower limit to the
true value because contribution from smaller grains, which scatter to larger
angles, was not directly observed. The line-of-sight to the GRB passes close to
the Ophiuchus molecular cloud complex, which provides a plausible site for the
scattering dust.


title:
Optical Observations and Multiband Modelling of the Afterglow of GRB
  041006: Evidence of A Hard Electron Energy Spectrum

abstract:
  We present the CCD Cousins R band photometric observations of the afterglow
of GRB 041006. The multiband afterglow evolution is modelled using an
underlying `hard' electron energy spectrum with a $p_1 \sim 1.3$. The burst
appears to be of very low energy ($E \sim 10^{48}$ ergs) confined to a narrow
cone of opening angle $\theta \sim 2.3^{\circ}$. The associated supernova is
compared with SN1998bw and is found to be brighter.


title: Diffusive synchrotron radiation from extragalactic jets

abstract:
  Flattenings of nonthermal radiation spectra observed from knots and interknot
locations of the jets of 3C273 and M87 in UV and X-ray bands are discussed
within modern models of magnetic field generation in the relativistic jets.
Specifically, we explicitly take into account the effect of the small-scale
random magnetic field, probably present in such jets, which gives rise to
emission of Diffusive Synchrotron Radiation, whose spectrum deviates
substantially from the standard synchrotron spectrum, especially at high
frequencies. The calculated spectra agree well with the observed ones if the
energy densities contained in small-scale and large-scale magnetic fields are
comparable. The implications of this finding for magnetic field generation,
particle acceleration, and jet composition are discussed.


title: Observing campaign of Eta Carinae from La Plata. Period 2003-2004

abstract:
  After the Observing Campaign of Eta Carinae carried out during 2003, we have
continued the CCD observations using the 0.8 m Reflector telescope at La Plata
Observatory, in the BVRI bands. Here, we present the results obtained since
November 2003 until August 2004. In addition, we present differential
photometry of other objects included in the Eta Car's frames, belonging to the
open cluster Trumpler 16.


title:
Supernova Remnant 1987A: High Resolution Images and Spectrum from
  Chandra Observations

abstract:
  We report on the morphological and spectral evolution of SNR 1987A from the
monitoring observations with the Chandra/ACIS. As of 2005, the X-ray-bright
lobes are continuously brightening and expanding all around the ring. The
softening of the overall X-ray spectrum also continues. The X-ray lightcurve is
particularly remarkable: i.e., the recent soft X-ray flux increase rate is
significantly deviating from the model which successfully fits the earlier
data, indicating even faster flux increase rate since early 2004 (day ~6200).
We also report results from high resolution spectral analysis with deep
Chandra/LETG observations. The high resolution X-ray line emission features
unambiguously reveal that the X-ray emission of SNR 1987A is originating
primarily from a "disk" along the inner ring rather than from a spherical
shell. We present the ionization structures, elemental abundances, and the
shock velocities of the X-ray emitting plasma.


title: Common envelope evolution through planetary nebula eyes

abstract:
  The common envelope interaction is responsible for evolved close binaries.
Among them are a minority of central stars of planetary nebula (PN). Recent
observational results, however, point to most PN actually being in binary
systems. We therefore ask the question if it is feasible that most, or even all
Galactic PN derive from a common envelope interaction. Our recent calculation
finds that if all single and binary primary stars with mass between ~1-8 Mo
eject a PN, there would be many more PN in the galaxy than observed. On the
other hand, the predicted number of post-common envelope PN is more in
agreement with the total number of PN in the Galaxy. This is a new indication
that binary interactions play a functional role in the creation of PN and an
encouragement to intensify efforts to detect binary companions.


title:
Simulating the physical properties of dark matter and gas inside the
  cosmic web

abstract:
  Using the results of a high-resolution, cosmological hydrodynamical
re-simulation of a supercluster-like region we investigate the physical
properties of the gas located along the filaments and bridges which constitute
the so-called cosmic web. First we analyze the main characteristics of the
density, temperature and velocity fields, which have quite different
distributions, reflecting the complex dynamics of the structure formation
process. Then we quantify the signals which originate from the matter in the
filaments by considering different observables. Inside the cosmic web, we find
that the halo density is about 4-6 times larger than in the neighbouring
region; the bremsstrahlung X-ray surface brightness reaches at most 10e-16
erg/s/cm^2/armin^2; the Compton-y parameter due to the thermal
Sunyaev-Zel'dovich effect is about 10e-6; the reduced shear produced by the
weak lensing effect is ~ 0.01-0.02. These results confirm the difficulty of an
observational detection of the cosmic web. Finally we find that projection
effects of the filamentary network can affect the estimates of the properties
of single clusters, increasing their X-ray luminosity by less than 10% and
their central Compton-y parameter by up to 30% cent.


title: The Dust cloud around the White Dwarf G 29-38

abstract:
  We present new observations of the white dwarf G 29-38 with the camera (4.5
and 8 microns), photometer (24 microns), and spectrograph (5.5-14 microns) of
the Spitzer Space Telescope. This star has an exceptionally large infrared
excess amounting to 3% of the bolometric luminosity. The spectral energy
distribution has a continuum peak around 4.5 micros and a 9-11 micron emission
feature 1.25 times brighter than the continuum. A mixture of amorphous olivine
and a small amount of forsterite in an emitting region 1-5 Rsun from the star
can reproduce the shape of the 9-11 micron feature. The spectral energy
distribution also appears to require amorphous carbon to explain the hot
continuum. Our new measurements support the idea that a relatively recent
disruption of a comet or asteroid created the cloud.


title:
Statistical constraints on the IR galaxy number counts and cosmic IR
  background from the Spitzer GOODS survey

abstract:
  We perform fluctuation analyses on the data from the Spitzer GOODS survey
(epoch one) in the Hubble Deep Field North (HDF-N). We fit a parameterised
power-law number count model of the form dN/dS = N_o S^{-\delta} to data from
each of the four Spitzer IRAC bands, using Markov Chain Monte Carlo (MCMC)
sampling to explore the posterior probability distribution in each case. We
obtain best-fit reduced chi-squared values of (3.43 0.86 1.14 1.13) in the four
IRAC bands. From this analysis we determine the likely differential faint
source counts down to $10^{-8} Jy$, over two orders of magnitude in flux
fainter than has been previously determined.
  From these constrained number count models, we estimate a lower bound on the
contribution to the Infra-Red (IR) background light arising from faint
galaxies. We estimate the total integrated background IR light in the Spitzer
GOODS HDF-N field due to faint sources. By adding the estimates of integrated
light given by Fazio et al (2004), we calculate the total integrated background
light in the four IRAC bands. We compare our 3.6 micron results with previous
background estimates in similar bands and conclude that, subject to our
assumptions about the noise characteristics, our analyses are able to account
for the vast majority of the 3.6 micron background. Our analyses are sensitive
to a number of potential systematic effects; we discuss our assumptions with
regards to noise characteristics, flux calibration and flat-fielding artifacts.


title:
The rapidly oscillating Ap star HD 99563 and its distorted dipole
  pulsation mode

abstract:
  We undertook a time-series photometric multi-site campaign for the rapidly
oscillating Ap star HD 99563 and also acquired mean light observations over two
seasons. The pulsations of the star, that show flatter light maxima than
minima, can be described with a frequency quintuplet centred on 1557.653
microHertz and some first harmonics of these. The amplitude of the pulsation is
modulated with the rotation period of the star that we determine with 2.91179
+/- 0.00007 d from the analysis of the stellar pulsation spectrum and of the
mean light data. We break the distorted oscillation mode up into its pure
spherical harmonic components and find it is dominated by the l=1 pulsation,
and also has a notable l=3 contribution, with weak l=0 and 2 components. The
geometrical configuration of the star allows one to see both pulsation poles
for about the same amount of time; HD 99563 is only the fourth roAp star for
which both pulsation poles are seen and only the third where the distortion of
the pulsation modes was modelled. We point out that HD 99563 is very similar to
the well-studied roAp star HR 3831. Finally, we note that the visual companion
of HD 99563 is located in the Delta Scuti instability strip and may thus show
pulsation. We show that if the companion was physical, the roAp star would be a
2.03 solar mass object, seen at a rotational inclination of 44 degrees, which
then predicts a magnetic obliquity of 86.4 degrees.


title: Formation of mini-galaxies in defunct cosmological HII regions

abstract:
  Using a large set of high resolution numerical simulations incorporating
non-equilibrium molecular hydrogen chemistry and a constant source of external
radiation, we study gas collapse in previously photo-ionized mini-galaxies with
virial temperatures less than 10^4 K in the early universe (redshifts z=10-20).
We confirm that the mechanism of positive feedback of ionizing radiation on
star formation in mini-galaxies proposed by Ricotti, Gnedin, & Shull (2002) can
be efficient despite a significant flux of metagalactic photo-dissociating
radiation. We derive critical fluxes for the Lyman-Werner background radiation
sufficient to prevent the collapse of gas in mini-galaxies as a function of the
virial mass of the halo and redshift. In our model, the formation of
mini-galaxies in defunct HII regions is most efficient at large redshifts
(z>15) and/or for large local gas overdensity delta>10. We show that
non-equilibrium chemistry plays an important dynamical role not only during the
initial evolutionary phase leading to the gas becoming gravitationally unstable
inside the mini-halo, but also at the advanced stages of the core collapse,
resulting in efficient gas accretion in the core region. We speculate on a
possible connection between our objects and metal-poor globular clusters and
dwarf spheroidal galaxies.


title: Effects of galaxy interactions in different environments

abstract:
  We analyse star formation rates derived from photometric and spectroscopic
data of galaxies in pairs in different environments using the 2dF Galaxy
Redshift Survey (2dFGRS) and the Sloan Digital Sky Survey (SDSS). The two
samples comprise several thousand pairs, suitable to explore into detail the
dependence of star formation activity in pairs on orbital parameters and global
environment. We use the projected galaxy density derived from the fifth nearest
neighbour of each galaxy, with convenient luminosity thresholds to characterise
environment in both surveys in a consistent way. Star formation activity is
derived through the $\eta$ parameter in 2dFGRS and through the star formation
rate normalised to the total mass in stars, $SFR/M^*$, given by Brinchmann et
al. (2004) in the second data release SDSS-DR2. For both galaxy pair catalogs,
the star formation birth rate parameter is a strong function of the global
environment and orbital parameters. Our analysis on SDSS pairs confirms
previous results found with the 2dFGRS where suitable thresholds for the star
formation activity induced by interactions are estimated at a projected
distance $r_{\rm p} = 100 \kpc$ and a relative velocity $\Delta V = 350$ km
$s^{-1}$. We observe that galaxy interactions are more effective at triggering
important star formation activity in low and moderate density environments with
respect to the control sample of galaxies without a close companion. Although
close pairs have a larger fraction of actively star-forming galaxies, they also
exhibit a greater fraction of red galaxies with respect to those systems
without a close companion, an effect that may indicate that dust stirred up
during encounters could be affecting colours and, partially, obscuring
tidally-induced star formation.


title: On the Reionization of the Universe

abstract:
  I present first principle model calculations for the reionization of the
Universe, which provide simple diagnostics to identify the reionization
sources. Within this frame, I also discuss the results derived from the Hubble
Ultra-Deep Field observations, and the possible need for future observations
with JWST to provide the final answer.


title: The pulsar wind nebula of the Geminga pulsar

abstract:
  The superb spatial resolution of Chandra has allowed us to detect a 20''-long
tail behind the Geminga pulsar, with a hard spectrum (photon index 1.0+/-0.2)
and a luminosity (1.3+/-0.2) 10^{29} ergs/s in the 0.5 - 8 keV band, for an
assumed distance of 200 pc. The tail could be either a pulsar jet, confined by
a toroidal magnetic field of about 100 microGauss, or it can be associated with
the shocked relativistic wind behind the supersonically moving pulsar confined
by the ram pressure of the oncoming interstellar medium. We also detected an
arc-like structure 5'' - 7'' ahead of the pulsar, extended perpendicular to the
tail, with a factor of 3 lower luminosity. We see a 3-sigma enhancement in the
Chandra image apparently connecting the arc with the southern outer tail that
has been possibly detected with XMM-Newton. The observed structures imply that
the Geminga's pulsar wind is intrinsically anisotropic.


title:
An excursion set model of the cosmic web: The abundance of sheets,
  filaments and halos

abstract:
  We discuss an analytic approach for modeling structure formation in sheets,
filaments and knots. This is accomplished by combining models of triaxial
collapse with the excursion set approach: sheets are defined as objects which
have collapsed along only one axis, filaments have collapsed along two axes,
and halos are objects in which triaxial collapse is complete. In the simplest
version of this approach, which we develop here, large scale structure shows a
clear hierarchy of morphologies: the mass in large-scale sheets is partitioned
up among lower mass filaments, which themselves are made-up of still lower mass
halos. Our approach provides analytic estimates of the mass fraction in sheets,
filaments and halos, and its evolution, for any background cosmological model
and any initial fluctuation spectrum. In the currently popular $\Lambda$CDM
model, our analysis suggests that more than 99% of the cosmic mass is in
sheets, and 72% in filaments, with mass larger than $10^{10} M_{\odot}$ at the
present time. For halos, this number is only 46%. Our approach also provides
analytic estimates of how halo abundances at any given time correlate with the
morphology of the surrounding large-scale structure, and how halo evolution
correlates with the morphology of large scale structure.


title:
The Dynamical Evolution of Black Hole-Neutron Star Binaries in General
  Relativity: Simulations of Tidal Disruption

abstract:
  We calculate the first dynamical evolutions of merging black hole-neutron
star binaries that construct the combined black hole-neutron star spacetime in
a general relativistic framework. We treat the metric in the conformal flatness
approximation, and assume that the black hole mass is sufficiently large
compared to that of the neutron star so that the black hole remains fixed in
space. Using a spheroidal spectral methods solver, we solve the resulting field
equations for a neutron star orbiting a Schwarzschild black hole. The matter is
evolved using a relativistic, Lagrangian, smoothed particle hydrodynamics (SPH)
treatment. We take as our initial data recent quasiequilibrium models for
synchronized neutron star polytropes generated as solutions of the conformal
thin-sandwich (CTS) decomposition of the Einstein field equations. We are able
to construct from these models relaxed SPH configurations whose profiles show
good agreement with CTS solutions. Our adiabatic evolution calculations for
neutron stars with low compactness show that mass transfer, when it begins
while the neutron star orbit is still outside the innermost stable circular
orbit, is more unstable than is typically predicted by analytical formalisms.
This dynamical mass loss is found to be the driving force in determining the
subsequent evolution of the binary orbit and the neutron star, which typically
disrupts completely within a few orbital periods. The majority of the mass
transferred onto the black hole is accreted promptly; a significant fraction
(~30%) of the mass is shed outward as well, some of which will become
gravitationally unbound and ejected completely from the system. The remaining
portion forms an accretion disk around the black hole, and could provide the
energy source for short-duration gamma ray bursts.


title: FITDisk: A Cataclysmic Variable Accretion Disk Demonstration Tool

abstract:
  We present the software tool FITDisk, a precompiled-binary Windows GUI
version of our smoothed particle hydrodynamics cataclysmic variable accretion
disk research code. Cataclysmic variables are binary star systems in which a
compact stellar remnant, typically a white dwarf star, is stripping mass from a
lower-main-sequence companion star by way of an accretion disk. Typically the
disk is the brightest component of the system, because the plasma is heated
dramatically as it spirals down in the gravitational well of the primary white
dwarf star. The shortest-period systems can display disk "superhump"
oscillations driven by the rotating tidal field of the secondary star. FITDisk
models these accretion disk phenomena using a fully three-dimensional
hydrodynamics calculation, and data can be visualized as they are computed or
stored to hard drive for later playback at a fast frame rate. Simulations are
visualized using OpenGL graphics and the viewing angle can be changed
interactively. Pseudo light curves of simulated systems can be plotted along
with the associated Fourier amplitude spectrum. FITDisk is available for free
download at www.astro.fit.edu/cv/fitdisk.html.


title: The Absence of the Fundamental Plane of Black Hole Activity

abstract:
  An analysis of the radio and X-ray luminosities, along with black hole masses
has led to a relationship, the fundamental plane of black hole activity, where
logL_R = 0.60logL_X + 0.78logM_BH. We show that this same relationship can be
obtained by using upper limit data or by randomizing the radio fluxes. In those
cases, the relationship arises because one is effectively plotting distance vs
distance in a flux-limited sample of objects. To correctly establish a
relationship between L_R, L_X, and M_BH, one would need to analyze a
volume-limited sample of objects. The distance effect can be removed from the
sample, where a relationship between L_R/L_X and M_BH is found, showing that
the L_R rises more quickly than L_X with increasing M_BH. However, until a
well-define sample is used, it is unclear the degree to which this relationship
is influenced by the sample-selection.


title:
Non-Spherical Core-Collapse Supernovae II. Late-Time Evolution of
  Globally Anisotropic Neutrino-Driven Explosions and Implications for SN 1987A

abstract:
  Two-dimensional simulations of strongly anisotropic supernova explosions of a
nonrotating 15 solar mass blue supergiant progenitor are presented, which
follow the hydrodynamic evolution from times shortly after shock formation
until hours later. It is shown that explosions which around the time of shock
revival are dominated by low-order unstable modes (i.e. by a superposition of
the l=2 and l=1 modes, in which the former is strongest), are consistent with
all major observational features of SN 1987A, in contrast to models which show
high-order mode perturbations only and were published in earlier work. Among
other items, the low-mode models exhibit final iron-group velocities of up to
3300 km/s, strong mixing at the He/H composition interface, with hydrogen being
mixed downward in velocity space to only 500 km/s, and a final prolate
anisotropy of the ejecta with a major to minor axis ratio of about 1.6. The
success of low-mode explosions with an energy of about 2x10**51 erg to
reproduce these observed features is based on two effects: the (by 40%) larger
initial maximum velocities of metal-rich clumps compared to our high-mode
models, and the initial global deformation of the shock. The latter triggers
the growth of a strong Richtmyer-Meshkov instability at the He/H interface that
results in a global anisotropy of the inner ejecta at late times (i.e. t >
10000 s), although the shock itself has long become spherical by then. The
simulations suggest a coherent picture, which explains the observational data
of SN 1987A within the framework of the neutrino-driven explosion mechanism
using a minimal set of assumptions. It is therefore argued that other
paradigms, which are based on (more) controversial physics, may not be required
to explain this event. (abbreviated)


title: The Origin and Evolution of the Asteroid Main Belt

abstract:
  Using a fully autonomous spacecraft - Bering - we propose to detect and study
sub-km asteroids from an orbit within the asteroid Main Belt. The main purpose
of the proposed Bering mission is to detect a statistically significant sample
of an expected population of approximately 10^(10) main belt asteroids in the
size range 1 m to 1 km. These asteroids are too faint to be observed using
Earth-based telescopes. Sub-km asteroids can be detected from spacecraft at
close range but due to the high relative velocities and the long communication
times this requires a fully autonomous spacecraft. Using theoretical estimates
of the distribution and abundance of sub-km asteroids we find that the Bering
mission would detect approximately 6 new sub-km asteroids per day. With an
expected lifetime for the mission of a few years we expect to detect and study
several thousand sub-km asteroids. Results from the Bering mission would allow
us to: 1) Provide further links between groups of meteorites and their parent
asteroids. 2) Constrain the cratering rate at planetary surfaces and thus allow
significantly improved cratering ages for terrains on Mars and other planets.
3) Constrain processes that transfer small asteroids from orbits in the main
belt to the inner Solar System.


title:
Infrared extinction by homogeneous particle aggregates of SiC, FeO and
  SiO2: comparison of different theoretical approaches

abstract:
  Particle shape and aggregation have a strong influence on the spectral
profiles of infrared phonon bands of solid dust grains. Calculating these
effects is difficult due to the often extreme refractive index values in these
bands. In this paper, we use the Discrete Dipole Approximation (DDA) and the
T-matrix method to compute the absorption band profiles for simple clusters of
touching spherical grains. We invest reasonable amounts of computation time in
order to reach high dipole grid resolutions and take high multi-polar orders
into account, respectively. The infrared phonon bands of three different
refractory materials of astrophysical relevance are considered - Silicon
Carbide (SiC), Wustite (FeO) and Silicon Dioxide (SiO2). We demonstrate that
even though these materials display a range of material properties and
therefore different strengths of the surface resonances, a complete convergence
is obtained with none of the approaches. For the DDA, we find a strong
dependence of the calculated band profiles on the exact dipole distribution
within the aggregates, especially in the vicinity of the contact points between
their spherical constituents. By applying a recently developed method to
separate the material optical constants from the geometrical parameters in the
DDA approach, we are able to demonstrate that the most critical material
properties are those where the real part of the refractive index is much
smaller than unity.


title: The Evolution of the Water Distribution in a Viscous Protoplanetary Disk

abstract:
  (Abridged) Astronomical observations have shown that protoplanetary disks are
dynamic objects through which mass is transported and accreted by the central
star. Age dating of meteorite constituents shows that their creation,
evolution, and accumulation occupied several Myr, and over this time disk
properties would evolve significantly. Moreover, on this timescale, solid
particles decouple from the gas in the disk and their evolution follows a
different path. Here we present a model which tracks how the distribution of
water changes in an evolving disk as the water-bearing species experience
condensation, accretion, transport, collisional destruction, and vaporization.
Because solids are transported in a disk at different rates depending on their
sizes, the motions will lead to water being concentrated in some regions of a
disk and depleted in others. These enhancements and depletions are consistent
with the conditions needed to explain some aspects of the chemistry of
chondritic meteorites and formation of giant planets. The levels of
concentration and depletion, as well as their locations, depend strongly on the
combined effects of the gaseous disk evolution, the formation of rapidly
migrating rubble, and the growth of immobile planetesimals. We present examples
of evolution under a range of plausible assumptions and demonstrate how the
chemical evolution of the inner region of a protoplanetary disk is intimately
connected to the physical processes which occur in the outer regions.


title: On the Detection of Magnetic Helicity

abstract:
  Magnetic fields in various astrophysical settings may be helical and, in the
cosmological context, may provide a measure of primordial CP violation during
baryogenesis. Yet it is difficult, even in principle, to devise a scheme by
which magnetic helicity may be detected, except in some very special systems.
We propose that charged cosmic rays originating from known sources may be
useful for this purpose. We show that the correlator of the arrival momenta of
the cosmic rays is sensitive to the helicity of an intervening magnetic field.
If the sources themselves are not known, the method may still be useful
provided we have some knowledge of their spatial distribution.


title: Flame-capturing technique. 1: Adaptation to gas expansion

abstract:
  Various flame tracking techniques are often used in hydrodynamic simulations.
Their use is indispensable when resolving actual scale of the flame is
impossible. We show that parameters defining "artificial flame" propagation
found from model systems may yield flame velocities several times distinct from
the required ones, due to matter expansion being ignored in the models.
  Integral effect of material expansion due to burning is incorporated into
flame capturing technique (FCT) [Khokhlov(1995)]. Interpolation formula is
proposed for the parameters governing flame propagation yielding 0.2% accurate
speed and width for any expansion (and at least 0.01% accurate for expansions
typical in type Ia supernova explosions.) Several models with simple burning
rates are studied with gas expansion included. Plausible performance of the
technique in simulations is discussed. Its modification ensuring finite flame
width is found. Implementation suggestions are summarized, main criterion being
the scheme performance being insensitive to expansion parameter (thus absence
of systematic errors when the burning progresses from inner to outer layers);
in this direction promising realizations are found, leading to flame structure
not changing while flame evolves through the whole range of densities in the
white dwarf.


title: Epicyclic oscillations of fluid bodies Paper II. Strong gravity

abstract:
  Fluids in external gravity may oscillate with frequencies characteristic of
the epicyclic motions of test particles. We explicitly demonstrate that global
oscillations of a slender, perfect fluid torus around a Kerr black hole admit
incompressible vertical and radial epicyclic modes. Our results may be directly
relevant to one of the most puzzling astrophysical phenomena -- high (hundreds
of hertz) frequency quasiperiodic oscillations (QPOs) detected in X-ray fluxes
from several black hole sources. Such QPOs are pairs of stable frequencies in
the 3/2 ratio. It seems that they originate a few gravitational radii away from
the black hole and thus observations of them have the potential to become an
accurate probe of super-strong gravity.


title: Neutrino-induced nucleosynthesis of A>64 nuclei: The nu p-process

abstract:
  We present a new nucleosynthesis process, that we denote nu p-process, which
occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino
fluxes create proton-rich ejecta. In this process, antineutrino absorptions in
the proton-rich environment produce neutrons that are immediately captured by
neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with
mass numbers A >64. Making this process a possible candidate to explain the
origin of the solar abundances of 92,94Mo and 96,98Ru. This process also offers
a natural explanation for the large abundance of Sr seen in an hyper-metal-poor
star.


title: Photometric Identification of Type Ia Supernovae at Moderate Redshift

abstract:
  Large photometric surveys with the aim of identifying many Type Ia supernovae
(SNe) at moderate redshift are challenged in separating these SNe from other SN
types. We are motivated to identify Type Ia SNe based only on broadband
photometric information, since spectroscopic determination of the SN type, the
traditional method, requires significant amounts of time on large telescopes.
We consider the possible observables provided by a large synoptic photometry
survey. We examine the optical colors and magnitudes of many SN types from
z=0.1 to z=1.0, using space-based ultraviolet spectra and ground-based optical
spectra to simulate the photometry. We also discuss the evolution of colors
over the SN outburst and the use of host galaxy characteristics to aid in the
identification of Type Ia SNe. We consider magnitudes in both the SDSS
photometric system and in a proposed filter system with logarithmically spaced
bandpasses. We find that photometric information in four bands covering the
entire optical spectrum appears capable of providing identification of Type Ia
SNe based on their colors at a single observed epoch soon after maximum light,
even without independent estimates of the SN redshift. Very blue filters are
extremely helpful, as at moderate redshift they sample the restframe
ultraviolet spectrum where the SN types are very different. We emphasize the
need for further observations of SNe in the restframe ultraviolet to fully
characterize, refine, and improve this method of SN type identification.


title: The influence of the Mach number on the stability of radiative shocks

abstract:
  We study the stability properties of hydrodynamic shocks with finite Mach
numbers. The linear analysis supplements previous analyses which took the
strong shock limit. We derive the linearised equations for a general specific
heat ratio as well as temperature and density power-law cooling functions,
corresponding to a range of conditions relevant to interstellar atomic and
molecular cooling processes. Boundary conditions corresponding to a return to
the upstream temperature ($R$ = 1) and to a cold wall ($R$ = 0) are
investigated. We find that for Mach number $M > 5$, the strong shock
overstability limits are not significantly modified. For $M < 3$, however,
shocks are considerably more stable for most cases. In general, as the shock
weakens, the critical values of the temperature power-law index (below which
shocks are overstable) are reduced for the overtones more than for the
fundamental, which signifies a change in basic behaviour. In the $R$ = 0
scenario, however, we find that the overstability regime and growth rate of the
fundamental mode are increased when cooling is under local thermodynamic
equilibrium. We provide a possible explanation for the results in terms of a
stabilising influence provided downstream but a destabilising effect associated
with the shock front. We conclude that the regime of overstability for
interstellar atomic shocks is well represented by the strong shock limit unless
the upstream gas is hot. Although molecular shocks can be overstable to
overtones, the magnetic field provides a significant stabilising influence.


title:
The Nuclear Cycle that Powers the Stars: Fusion, Gravitational Collapse
  and Dissociation

abstract:
  The finding of an unexpectedly large source of energy from repulsive
interactions between neutrons in the 2,850 known nuclides has challenged the
assumption that H-fusion is the main source of energy that powers the Sun and
other stars. Neutron repulsion in compact objects produced by the collapse of
stars and collisions between galaxies may power more energetic cosmological
events (quasars, gamma ray bursts, and active galactic centers) that had been
attributed to black holes before neutron repulsion was recognized. On a
cosmological scale, nuclear matter cycles between fusion, gravitational
collapse, and dissociation (including neutron emission) rather than evolve in
one direction by fusion. The similarity Bohr noted between atomic and planetary
structures may extend to a similarity nuclear and stellar structures.


title:
Eddington-limited X-ray Bursts as Distance Indicators. II. Possible
  Compositional Effects in Bursts from 4U 1636-536

abstract:
  We analyzed 123 thermonuclear (type-I) X-ray bursts observed by the Rossi
X-ray Timing Explorer from the low-mass X-ray binary 4U 1636-536. All but two
of the 40 radius-exansion bursts in this sample reached peak fluxes which were
normally distributed about a mean of 6.4e-8 ergs/cm^2/s, with a standard
deviation of 7.6%. The remaining two radius-expansion bursts reached peak
fluxes a factor of 1.69+/-0.13 lower than this mean value; as a consequence,
the overall variation in the peak flux of the radius-expansion bursts was a
factor of ~2. This variation is comparable to the range of the Eddington limit
between material with solar H-fraction (X=0.7) and pure He. Such a variation
may arise if, for the bright radius-expansion bursts, most of the accreted H is
eliminated either by steady hot CNO burning or expelled in a radiatively-driven
wind. However, steady burning cannot exhaust the accreted H for solar
composition material within the typical ~2 hr burst recurrence time, nor can it
result in sufficient elemental stratification to allow selective ejection of
the H only. An additional stratification mechanism appears to be required to
separate the accreted elements and thus allow preferential ejection of the
hydrogen. We found no evidence for a gap in the peak flux distribution between
the radius-expansion and non-radius expansion bursts, previously observed in
smaller samples. Assuming that the faint radius-expansion bursts reached the
Eddington limit for H-rich material (X~0.7), and the brighter bursts the limit
for pure He (X=0), we estimate the distance to 4U 1636-536 (for a canonical
neutron star with M_NS=1.4M_sun, R_NS=10 km) to be 6.0+/-0.5 kpc, or for
M_NS=2M_sun at most 7.1 kpc. (Abstract abridged)


title:
Detection of the Buried AGN in NGC 6240 with the Infrared Spectrograph
  on The Spitzer Space Telescope

abstract:
  We present mid-infrared spectra of the nearby, Ultraluminous Infrared Galaxy
NGC 6240 taken with the IRS on Spitzer. The spectrum of NGC 6240 is dominated
by strong fine-structure lines, rotational H2 lines, and PAH emission features.
The H2 line fluxes suggest molecular gas at a variety of temperatures. A simple
two-temperature fit to the S(0) through S(7) lines implies a mass of 6.7E6
solar masses at T=957K and 1.6E9 solar masses at T=164K, or about 15% of the
total molecular gas mass in this system. Noteably, we have detected the [NeV]
14.3 micron emission line, with a flux of 5E-14 erg/cm^2/s, providing the first
direct detection of the buried AGN in the mid-infrared. Modelling of the total
SED from near to far-infrared wavelengths requires the presence of a hot dust
(T=700K) component, which we also associate with the buried AGN. The small
[NeV]/[NeII] and [NeV]/IR flux ratios, the relative fraction of hot dust
emission, as well as the large 6.2 micron PAH EQW, are all consistent with an
apparent AGN contribution of only 3-5% to the bolometric luminosity. However,
correcting the measured [NeV] flux by the extinction implied by the silicate
optical depth and our SED fitting, suggests an intrinsic fractional AGN
contribution to the bolometric luminosity of about 20-24% in NGC 6240, which
lies within the range implied by fits to the hard X-ray spectrum.


title: QPO as the Rosetta Stone for understanding black hole accretion

abstract:
  Quasi periodic oscillations (QPO) seen in the X-ray fluxes of individual
neutron stars and black hole sources are one of most intriguing phenomena in
today's astrophysics. The QPO nature is visibly determined by super-strong
Einstein's gravity. I argue here that it also profoundly depends on the MRI
turbulence in accretion flows. Understanding the QPO physics may therefore
guide accretion theory out of its present state of confusion.


title: Milli-arcsecond--scale Spectral Properties and Jet Motions in M87

abstract:
  We have combined high resolution VLBI Space Observatory Programme (VSOP) data
at 1.6 and 4.8 GHz with Very Long Baseline Array (VLBA) data at higher
frequencies and with similar resolutions to study the spectral properties of
the core of M87 with milliarcsecond resolution. The VSOP data allow a more
accurate measurement of the turn-over frequency, and hence more reliable
determination of associated physical parameters of the source. Comparison of
the images with previously published images yields no evidence for significant
motion of components in the parsec-scale jet. In addition, the brightness
temperatures obtained from model-fits to the core are well below the inverse
Compton limit, suggesting the radio emission we are observing is not strongly
Doppler boosted.
  Colour version on http://www.vsop.isas.jaxa.jp/survey/publications/m87.ps.gz


title: A determination of the Spectra of Galactic components observed by WMAP

abstract:
  WMAP data when combined with ancillary data on free-free, synchrotron and
dust allow an improved understanding of the spectrum of emission from each of
these components. Here we examine the sky variation at intermediate latitudes
using a cross-correlation technique. In particular, we compare the observed
emission in 15 selected sky regions to three ``standard'' templates.
  The free-free emission of the diffuse ionised gas is fitted by a well-known
spectrum at K and Ka band, but the derived emissivity corresponds to a mean
electron temperature of ~4000-5000K. This is inconsistent with estimates from
galactic HII regions. The origin of the discrepancy is unclear.
  The anomalous emission associated with dust is clearly detected in most of
the 15 fields studied; it correlates well with the Finkbeiner et al. model 8
predictions (FDS8) at 94 GHz, with an effective spectral index between 20 and
60GHz of -2.85. Furthermore, the emissivity varies by a factor of ~2 from cloud
to cloud. A modestly improved fit to the anomalous dust at K-band is provided
by modulating the template by an estimate of the dust colour temperature,
specifically FDS8*T^n. We find a preferred value n~1.6.
  The synchrotron emission steepens between GHz frequencies and the WMAP bands.
There are indications of spectral index variations across the sky but the
current data are not precise enough to accurately quantify this from region to
region. Our analysis of the WMAP data indicates strongly that the
dust-correlated emission at the low WMAP frequencies has a spectrum which is
compatible with spinning dust; we find no evidence for a synchrotron component
correlated with dust (abridged).


title: Morphology Segregation of Galaxies in the Color-Color Gradient Space

abstract:
  We have found the u -r color versus g -i color gradient space can be used for
highly successful morphology classification of galaxies in the Sloan Digital
Sky Survey. In this space galaxies form early and late type branches
well-separated from each other. The location of galaxies along the branches
reflects the degree and locality of star formation activity, and monotonically
corresponds to the sequence of morphological subclasses. When the concentration
index is used together, the completeness and reliability of classification
reaches about 91% for a training set of SDSS galaxies brighter than r~15.9. At
faintest magnitudes (r~17.5) of the SDSS spectroscopic sample, the performance
still remains at about 88%. The new classification scheme will help us find
accurate relations of galaxy morphology with spatial and temporal environments,
and help one understand the origin of morphology of galaxies.


title:
Nuclear Reaction Rate Uncertainties and Astrophysical Modeling. II.
  Carbon Yields from Low-mass Giants

abstract:
  Calculations that demonstrate the influence of three key nuclear reaction
rates on the evolution of Asymptotic Giant Branch stars have been carried out.
We study the case of a star with an initial mass of 2Msun and a metallicity of
Z=0.01, somewhat less than the solar metallicity. The dredge-up of nuclear
processed material from the interior of the star, and the yield predictions for
carbon, are sensitive to the rate of the N14(p,gamma)O15 and triple-alpha
reactions. These reactions dominate the H- and He-burning shells of stars in
this late evolutionary phase. Published uncertainty estimates for each of these
two rates propagated through stellar evolution calculations cause uncertainties
in carbon enrichment and yield predictions of about a factor of two. The other
important He-burning reaction C12(alpha,gamma)O16, although associated with the
largest uncertainty in our study, does not have a significant influence on the
abundance evolution compared to other modelling uncertainties. This finding
remains valid when the entire evolution from the main-sequence to the tip of
the AGB is considered. We discuss the experimental sources of the rate
uncertainties addressed here, and give some outlook for future work.


title: A prominent relativistic iron line in the Seyfert 1 MCG-02-14-009

abstract:
  I report the discovery of a prominent broad and asymmetrical feature near 6.4
keV in the Seyfert 1 MCG-02-14-009 (z=0.028) with XMM-Newton/EPIC. The present
short X-ray observation (PN net exposure time ~5 ks) is the first one above 2
keV for MCG-02-14-009. The feature can be explained by either a relativistic
iron line around either a Schwarzschild (non-rotating) or a Kerr (rotating)
black hole. If the feature is a relativistic iron line around a Schwarzschild
black hole, the line energy is 6.51 (+0.21,-0.12) keV with an equivalent width
of 631 (+259,-243) eV and that the inclination angle of the accretion disc
should be less than 43 degrees. A relativistically blurred photoionized disc
model gives a very good spectral fit over the broad band 0.2-12keV energy
range. The spectrum is reflection dominated and this would indicate that the
primary source in MCG-02-14-009 is located very close to the black hole, where
gravitational light bending effect is important (about 3-4 Rg), and that the
black hole may rapidly rotate.


title: INTEGRAL high energy behaviour of 4U 1812-12

abstract:
  The low mass X-ray binary system 4U 1812-12 was monitored with the INTEGRAL
observatory in the period 2003-2004 and with BeppoSAX on April 20, 2000. We
report here on the spectral and temporal analysis of both persistent and burst
emission. The full data set confirms the persistent nature of this burster, and
reveals the presence of emission up to 200 keV. The persistent spectrum is well
described by a comptonization (CompTT) model plus a soft blackbody component.
The source was observed in a hard spectral state with a 1-200 keV luminosity of
2*10^(36) ergs/s and L/LEdd~1% and no meaningful flux variation has been
revealed, as also confirmed by a 2004 RXTE observation. We have also detected 4
bursts showing double peaked profiles and blackbody spectra with temperatures
ranging from 1.9 to 3.1 keV.


title: Optical Emission from Aspherical Supernovae and the Hypernova SN 1998bw

abstract:
  A fully 3D Monte Carlo scheme is applied to compute optical bolometric light
curves for aspherical (jet-like) supernova explosion models. Density and
abundance distributions are taken from hydrodynamic explosion models, with the
energy varied as a parameter to explore the dependence. Our models show
initially a very large degree ($\sim 4$ depending on model parameters) of
boosting luminosity toward the polar ($z$) direction relative to the equatorial
($r$) plane, which decreases as the time of peak is approached. After the peak,
the factor of the luminosity boost remains almost constant ($\sim 1.2$) until
the supernova enters the nebular phase. This behavior is due mostly to the
aspherical $^{56}$Ni distribution in the earlier phase and to the disk-like
inner low-velocity structure in the later phase. Also the aspherical models
yield an earlier peak date than the spherical models, especially if viewed from
near the z-axis. Aspherical models with ejecta mass $\sim 10\Msun$ are
examined, and one with the kinetic energy of the expansion $\sim 2 \pm 0.5
\times 10^{52}$ ergs and a mass of $^{56}$Ni $\sim 0.4\Msun$ yields a light
curve in agreement with the observed light curve of SN 1998bw (the prototypical
hyper-energetic supernova). The aspherical model is also at least qualitatively
consistent with evolution of photospheric velocities, showing large velocities
near the z-axis, and with a late-phase nebular spectrum. The viewing angle is
close to the z-axis, strengthening the case for the association of SN 1998bw
with the gamma ray burst GRB980425.


title: The X-ray Telescope of the CAST Experiment

abstract:
  The CERN Axion Solar Telescope (CAST) searches for solar axions employing a 9
Tesla superconducting dipole magnet equipped with 3 independent detection
systems for X-rays from axion-photon conversions inside the 10 m long magnetic
field. Results of the first 6 months of data taking in 2003 imply a 95 % CL
upper limit on the axion-photon coupling constant of 1.16x10(-10) GeV(-1) for
axion masses < 0.02 eV. The most sensitive detector of CAST is a X-ray
telescope consisting of a Wolter I type mirror system and a fully depleted
pn-CCD as focal plane detector. Exploiting the full potential of background
suppression by focussing X-rays emerging from the magnet bore, the axion
sensitivity obtained with telescope data taken in 2004, for the first time in a
controlled laboratory experiment, will supersede axion constraints derived from
stellar energy loss arguments.


title:
Evolution of Massive Blackhole Triples I -- Equal-mass binary-single
  systems

abstract:
  We present the result of $N$-body simulations of dynamical evolution of
triple massive blackhole (BH) systems in galactic nuclei. We found that in most
cases two of the three BHs merge through gravitational wave (GW) radiation in
the timescale much shorter than the Hubble time, before ejecting one BH through
a slingshot. In order for a binary BH to merge before ejecting out the third
one, it has to become highly eccentric since the gravitational wave timescale
would be much longer than the Hubble time unless the eccentricity is very high.
We found that two mechanisms drive the increase of the eccentricity of the
binary. One is the strong binary-single BH interaction resulting in the
thermalization of the eccentricity. The second is the Kozai mechanism which
drives the cyclic change of the inclination and eccentricity of the inner
binary of a stable hierarchical triple system. Our result implies that many of
supermassive blackholes are binaries.


title: Saturn's internal structure and carbon enrichment

abstract:
  We use the clathrate hydrate trapping theory to calculate the enrichments in
O, N, S, Xe, Ar and Kr compared to solar in Saturn's atmosphere. For this, we
calibrate our calculations using two different carbon abundance determinations
that cover the domain of measurements published in the last decades: one
derived from the NASA $Kuiper$ Airborne Observatory measurements and the other
obtained from the Cassini spacecraft observations. We show that these two
different carbon abundances imply quite a different minimum heavy element
content for Saturn. Using the Kuiper Airborne Observatory measurement for
calibration, the amount of ices accreted by Saturn is found to be consistent
with current interior models of this planet. On the other hand, using the
Cassini measurement for calibration leads to an ice content in the planet's
envelope which is higher than the one derived from the interior models. In this
latter case, reconciling the interior models with the amount of C measured by
the Cassini spacecraft requires that significant differential sedimentation of
water and volatile species have taken place in Saturn's interior during its
lifetime.


title: Models of Ultraluminous X-Ray Sources with Intermediate-Mass Black Holes

abstract:
  We have computed models for ultraluminous X-ray sources ("ULXs") consisting
of a black-hole accretor of intermediate mass ("IMBH"; e.g., ~1000 Msun) and a
captured donor star. For each of four different sets of initial donor masses
and orbital separations, we computed 30,000 binary evolution models using a
full Henyey stellar evolution code. To our knowledge this is the first time
that a population of X-ray binaries this large has been carried out with other
than approximation methods, and it serves to demonstrate the feasibility of
this approach to large-scale population studies of mass-transfer binaries. In
the present study, we find that in order to have a plausible efficiency for
producing active ULX systems with IMBHs having luminosities > 10^{40} ergs/sec,
there are two basic requirements for the capture of companion/donor stars.
First, the donor stars should be massive, i.e., > 8 Msun. Second, the initial
orbital separations, after circularization, should be close, i.e., < 6-30 times
the radius of the donor star when on the main sequence. Even under these
optimistic conditions, we show that the production rate of IMBH-ULX systems may
fall short of the observed values by factors of 10-100.


title:
Non-linear axisymmetric pulsations of rotating relativistic stars in the
  conformal flatness approximation

abstract:
  We study non-linear axisymmetric pulsations of rotating relativistic stars
using a general relativistic hydrodynamics code under the assumption of a
conformal flatness. We compare our results to previous simulations where the
spacetime dynamics was neglected. The pulsations are studied along various
sequences of both uniformly and differentially rotating relativistic polytropes
with index N = 1. We identify several modes, including the lowest-order l = 0,
2, and 4 axisymmetric modes, as well as several axisymmetric inertial modes.
Differential rotation significantly lowers mode frequencies, increasing
prospects for detection by current gravitational wave interferometers. We
observe an extended avoided crossing between the l = 0 and l = 4 first
overtones, which is important for correctly identifying mode frequencies in
case of detection. For uniformly rotating stars near the mass-shedding limit,
we confirm the existence of the mass-shedding-induced damping of pulsations,
though the effect is not as strong as in the Cowling approximation. We also
investigate non-linear harmonics of the linear modes and notice that rotation
changes the pulsation frequencies in a way that would allow for various
parametric instabilities between two or three modes to take place. We assess
the detectability of each obtained mode by current gravitational wave detectors
and outline how the empirical relations that have been constructed for
gravitational wave asteroseismology could be extended to include the effects of
rotation.


title: Status of the XMM-Newton cross-calibration with SASv6.5.0

abstract:
  Further achievements of the XMM-Newton cross-calibration - XMM internal as
well as with other X-ray missions - are presented. We explain the major changes
in the new version SASv6.5 of the XMM-Newton science analysis system. The
current status of the cross-calibration of the three EPIC cameras is shown.
Using a large sample of blazars, the pn energy redistribution at low energy
could be further calibrated, correcting the overestimation of fluxes in the
lowest energy regime. In the central CCDs of the MOSs, patches were identified
at the bore-sight positions, leading to an underestimation of the low energy
fluxes. The further improvement in the understanding of the cameras resulted in
a good agreement of the EPIC instruments down to lowest energies. The latest
release of the SAS software package already includes corrections for both
effects as shown in several examples of different types of sources. Finally the
XMM internal cross-calibration is completed by the presentation of the current
cross-calibration status between EPIC and RGS instruments. Major efforts have
been made in cross-calibrations with other X-ray missions, most importantly
with Chandra, of course, but also with currently observing satellites like
Swift.


title: "Graceful" Old Inflation

abstract:
  We show that Inflation in a False Vacuum becomes viable in the presence of a
spectator scalar field non minimally coupled to gravity. The field is unstable
in this background, it grows exponentially and slows down the pure de Sitter
phase itself, allowing then fast tunneling to a true vacuum. We compute the
constraint from graceful exit through bubble nucleation and the spectrum of
cosmological perturbations.


title:
The ecology of star clusters and intermediate mass black holes in the
  Galactic bulge

abstract:
  We simulate the inner 100pc of the Milky-Way Galaxy to study the formation
and evolution of the population of star clusters and intermediate mass black
holes. For this study we perform extensive direct N-body simulations of the
star clusters which reside in the bulge, and of the inner few tenth of parsecs
of the super massive black hole in the Galactic center. In our N-body
simulations the dynamical friction of the star cluster in the tidal field of
the bulge are taken into account via (semi)analytic soluations. The N-body
calculations are used to calibrate a (semi)analytic model of the formation and
evolution of the bulge. We find that about 10% of the clusters born within
100pc of the Galactic center undergo core collapse during their inward
migration and form intermediate-mass black holes (IMBHs) via runaway stellar
merging. After the clusters dissolve, these IMBHs continue their inward drift,
carrying a few of the most massive stars with them. We predict that region
within about 10 parsec of the SMBH is populated by about 50IMBHs of some
1000Msun. Several of these are expected to be accompanied still by some of the
most massive stars from the star cluster. We also find that within a few
milliparsec of the SMBH there is a steady population of several IMBHs. This
population drives the merger rate between IMBHs and the SMBH at a rate of about
one per 10Myr, sufficient to build the accumulate majority of mass of the SMBH.
Mergers of IMBHs with SMBHs throughout the universe are detectable by LISA, at
a rate of about two per week.


title: The Schizophrenic Spectrum of LSR 1610-0040: a Peculiar M Dwarf/Subdwarf

abstract:
  We present a moderate resolution (R=2000), 0.8-4.1 micron spectrum of LSR
1610-0040, a high proper motion star classified as an early-type L subdwarf by
Lepine and collaborators based on its red-optical spectrum. The near-infrared
spectrum of LSR 1610-0040 does not fit into the (tentative) M/L subdwarf
sequence but rather exhibits a mix of characteristics found in the spectra of
both M dwarfs and M subdwarfs. In particular, the near-infrared spectrum
exhibits a Na I doublet and CO overtone bandheads in the K band, and Al I and K
I lines and an FeH bandhead in the H band, all of which have strengths more
typical of field M dwarfs. Furthermore the spectrum of Gl 406 (M6 V) provides a
reasonably good match to the 0.6-4.1 micron spectral energy distribution of LSR
1610. Nevertheless the near-infrared spectrum of LSR 1610 also exhibits
features common to the spectra of M subdwarfs including a strong Ti I multiplet
centered at ~0.97 microns, a weak VO band at ~1.06 microns, and possible
collision-induced H_2 absorption in the H and K bands. We discuss a number of
possible explanations for the appearance of the red-optical and near-infrared
spectrum of LSR 1610-0040. Although we are unable to definitively classify LSR
1610-0040, the preponderance of evidence suggests that it is a mildly
metal-poor M dwarf. Finally, we tentatively identify a new band of TiO at ~0.93
microns in the spectra of M dwarfs.


title:
Discovery and disentangling of multi-mode delta-Sct pulsations in the
  eclipsing binary V994 Her

abstract:
  Accurate and extensive photoelectric photometry has been obtained of V994 Her
which was discovered as an eclipsing binary by Hipparcos satellite. A marked
pulsation activity is evident in the light-curve, with periods 0.152100488,
0.116836079 and 0.09466580 day that appears to be the contemporanous presence
of fundamental, first and second overtone periods of a multi-mode delta-Sct
pulsation. The latter is observed to remain stable in amplitude and phase over
the whole observaing campaign that lasted between June 10, 2002 and July 15,
2004.


title:
Star formation at very low metallicity. II: On the insignificance of
  metal-line cooling during the early stages of gravitational collapse

abstract:
  We study the influence of low levels of metal enrichment on the cooling and
collapse of ionized gas in small protogalactic halos using three-dimensional,
smoothed particle hydrodynamics simulations. Our initial conditions represent
protogalaxies forming within a fossil HII region -- a previously ionized HII
region which has not yet had time to cool and recombine. Prior to cosmological
reionization, such regions should be relatively common, since the
characteristic lifetimes of the likely ionizing sources are significantly
shorter than a Hubble time. We show that in these regions, H_2 is the dominant
and most effective coolant, and that it is the amount of H_2 formed that
determines whether or not the gas can collapse and form stars.
  At the low metallicities (Z < 10^{-3} Z_sun) thought to be associated with
the transition from population III to early population II star formation, metal
line cooling has an almost negligible effect on the evolution of low density
gas, altering the density and temperature evolution of the gas by less than 1%
compared to the metal-free case at densities below 1 cm^{-3} and temperatures
above 2000 K. Although there is evidence that metal line cooling becomes more
effective at higher density, we find no significant differences in behaviour
from the metal-free case at any density below our sink particle creation
threshold at n = 500 cm^{-3}. Increasing the metallicity also increases the
importance of metal line cooling, but it does not significantly affect the
dynamical evolution of the low density gas until Z = 0.1 Z_sun. This result
holds regardless of whether or not an ultraviolet background is present.


title: Entropy Profiles in the Cores of Cooling Flow Clusters of Galaxies

abstract:
  The X-ray properties of a relaxed cluster of galaxies are determined
primarily by its gravitational potential well and the entropy distribution of
its intracluster gas. That entropy distribution reflects both the accretion
history of the cluster and the feedback processes which limit the condensation
of intracluster gas. Here we present Chandra observations of the core entropy
profiles of nine classic "cooling-flow" clusters that appear relaxed and
contain intracluster gas with a cooling time less than a Hubble time. We show
that those entropy profiles are remarkably similar, despite the fact that the
clusters range over a factor of three in temperature. They typically have an
entropy level of ~ 130 keV cm^2 at 100 kpc that declines to a plateau ~10 keV
cm^2 at \lesssim 10 kpc. Between these radii, the entropy profiles are \propto
r^alpha with alpha ~ 1.0 - 1.3. The non-zero central entropy levels in these
clusters correspond to a cooling time ~10^8 yr, suggesting that episodic
heating on this timescale maintains the central entropy profile in a
quasi-steady state.


title: Lithium isotopes in population II dwarfs

abstract:
  We investigate the history of $^6$Li and $^7$Li in population II dwarfs
during the pre main sequence and main sequence. The evolution is followed using
the CESAM code and taking into account the most recent physics. The effective
temperature ranges from $\approx$ 4700 K to $\approx$ 6400 K and therefore
concerns objects on the so-called Spite plateau and cooler. We find the $^7$Li
pre main sequence depletion is unable to account for the observations in the
halo whatever the effective temperature. This supports microscopic diffusion
and an additional non standard mixing process both acting during the main
sequence. On the contrary the models $^6$Li pre main sequence depletion appears
too strong and is marginally compatible with recent detections.
  During the main sequence we introduce the effects of tachocline diffusion.
This process is a rotationnally induced mixing acting at the top of the
radiative core. We show that the differences in the early rotation history
cannot result in scattered lithium abundances on the Spite plateau. Moreover
the tachocline mixing process predicts $^7$Li abundances in good agreement with
the observations. We briefly address the question of turn off $^7$Li poor
stars. A modest accretion of lithium free matter would be enough to explain
their low abundance in this element.
  We expect the scatter in $^7$Li abundances is correlated to variations in
[Fe/O] ratio for dwarfs cooler than 5500 K. Finally the tachocline mixing is
robust with respect to the recent $^6$Li observations around the turn-off. We
similarly suggest the [Fe/O] should be higher in objects with $^6$Li and
effective temperature below 6000 K.


title: Searching for the "Missing" PG Hot Subdwarfs in SDSS and GALEX Data

abstract:
  Many EHB stars have been found in short-period binaries, where the companions
in these post-common envelope systems are either white dwarfs or dM stars;
these systems are catalogued as hot subdwarfs because the subdwarf is the more
luminous component. Hypothesized Roche-lobe overflow systems (with more massive
companions) may largely be uncatalogued, since the G band or Ca II K-line from
the companion may have caused them to be overlooked or discarded. In
particular, many candidate objects were excluded from the PG catalog because of
such spectroscopic indicators. Could these rejects include large numbers of
"missing" hot subdwarfs? We have examined 2MASS, SDSS, and GALEX archival data
for large subsets of these rejected stars, and conclude that only a handful
(about 3%) show indications of binarity; most are consistent with (single)
metal-poor F stars, as was originally supposed.


title:
The Nature of the Late-Type Companions in Hot Subdwarf
  Composite-Spectrum Binaries

abstract:
  We present the results of a study of the late-type companions in hot subdwarf
composite spectrum binaries. The exact nature of these late-type companions has
been disputed in the literature -- some argue that they are main sequence
stars, and others have claimed they are subgiants. To determine the properties
of the late-type companions, we first conducted a survey utilizing the Two
Micron All Sky Survey (2MASS) All-Sky Data Release Catalog to identify
composite-colored binaries in the "Catalogue of Spectroscopically Identified
Hot Subdwarfs" (Kilkenny, Heber, & Drilling 1988, 1992). We then conducted a
spectroscopic study of a sub-sample of the 2MASS composite-colored hot
subdwarfs. The sample consists of photometrically and spectroscopically single
and composite hot subdwarfs (14 single and 51 composite). We also obtained
spectra of 59 single late-type stars with Hipparcos parallaxes for calibration.
We used measured equivalent width (EW) indices from the composite systems to
estimate the temperature and gravity of the late-type star, taking into account
the dilution of its spectral features by light from the hot subdwarf. Results
from combining the spectroscopic data with model energy distributions indicate
that the late-type companions in composite-spectrum systems are best described
by main sequence companions overall.


title: New nearby AGNs from all sky surveys of INTEGRAL and RXTE observatories

abstract:
  We present first results of a campaign of optical identifications of X-ray
sources discovered by RXTE and INTEGRAL observatories during their sky surveys.
In this work we study six newly discovered nearby active galactic nuclei at
z<0.1. The optical spectrophotometric data were obtained with Russian-Turkish
1.5-m telescope (RTT150). We present their redshifts and main parameters of
brightest emission lines.


title: New evolutionary calculations for the Born Again scenario

abstract:
  We present evolutionary calculations aimed at describing the born-again
scenario for post-AGB remnant stars of 0.5842 and 0.5885 \msun. Results are
based on a detailed treatment of the physical processes responsible for the
chemical abundance changes. We considered two theories of convection: the
standard mixing length theory (MLT) and the double-diffusive GNA convection
developed by Grossman et al. The latter accounts for the effect of the chemical
gradient ($\nabla\mu$) in the mixing processes and in the transport of energy.
We also explore the dependence of the born-again evolution on some physical
hypothesis, such as the effect of the existence of non-zero chemical gradients,
the prescription for the velocity of the convective elements and the size of
the overshooting zones. Attention is given to the behavior of the born-again
times and to the chemical evolution during the ingestion of protons. We find
that in our calculations born again times are dependent on time resolution. In
particular when the minimum allowed time step is below $5 \times 10^{-5}$ yr we
obtain, with the standard mixing length theory, born again times of 5-10 yr.
This is true without altering the prescription for the efficiency of convective
mixing during the proton ingestion. On the other hand we find that the
inclusion of the chemical gradients in the calculation of the mixing velocity
tend to increase the born again times by about a factor of two. In addition we
find that proton ingestion can be seriously altered if the occurrence of
overshooting is modified by the $\nabla\mu$-barrier at the H-He interface,
strongly altering born again times.


title: Magnetic fields in the Southern Galactic Plane Survey

abstract:
  The Southern Galactic Plane Survey (SGPS) is a 1.4 GHz radio polarization and
HI survey in a large part of the inner Galactic plane at a resolution of about
an arcmin. Depolarization and Faraday rotation of polarized radiation from
diffuse Galactic synchrotron emission, pulsars, and extragalactic sources can
be used to infer information about the strength and structure of the Galactic
magnetic field. Here, we discuss science results of the polarization data from
the SGPS. We show from statistical analysis of rotation measures of polarized
extragalactic sources that fluctuations in the magneto-ionized medium of the
spiral arms are probably mainly caused by HII regions, while the rotation
measure fluctuations in the interarm regions may be connected to the
interstellar turbulent cascade. Furthermore, the variations of rotation measure
with Galactic longitude enable modeling of the large-scale component of the
Galactic magnetic field, including determination of the number and location of
magnetic field reversals. Finally, the SGPS is an excellent way to study
subparsec-scale structure in the ionized ISM by way of depolarization studies
in HII regions.


title:
Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow
  wind and a moderately eccentric orbit

abstract:
  Massive X-ray binaries are usually classified depending on the properties of
the donor star in classical, supergiant and Be X-ray binaries. The massive
X-ray binary 4U 2206+54 does not fit in any of these groups, and deserves a
detailed study to understand how the transfer of matter and the accretion on to
the compact object take place. To this end we study an IUE spectrum of the
donor and obtain a wind terminal velocity (v_inf) of ~350 km/s, which is
abnormally slow for its spectral type. We also analyse here more than 9 years
of available RXTE/ASM data. We study the long-term X-ray variability of the
source and find it to be similar to that observed in the wind-fed supergiant
system Vela X-1, reinforcing the idea that 4U 2206+54 is also a wind-fed
system. We find a quasi-period decreasing from ~270 to ~130 d, noticed in
previous works but never studied in detail. We discuss possible scenarios and
conclude that long-term quasi-periodic variations in the mass-loss rate of the
primary are probably driving such variability in the measured X-ray flux. We
obtain an improved orbital period of 9.5591 d with maximum X-ray flux at MJD
51856.6. Our study of the orbital X-ray variability in the context of wind
accretion suggests a moderate eccentricity around 0.15. Moreover, the low value
of v_inf solves the long-standing problem of the relatively high X-ray
luminosity for the unevolved nature of the donor, BD +53 2790, which is
probably an O9.5 V star. We note that changes in v_inf and/or the mass-loss
rate of the primary alone cannot explain the diferent patterns displayed by the
orbital X-ray variability. We finally emphasize that 4U 2206+54, together with
LS 5039, could be part of a new population of wind-fed HMXBs with main sequence
donors, the natural progenitors of supergiant X-ray binaries. (Abridged)


title: A counter-rotating core in the dwarf elliptical galaxy VCC 510

abstract:
  We present optical long-slit spectra of the Virgo dwarf elliptical galaxy VCC
510 at high spectral and spatial resolution. Heliocentric velocities and
velocity dispersions as functions of galaxy radius are derived by deconvolving
line-of-sight velocity distributions. A maximum rotation v_rot=8 km/s inside
half the effective radius (re~20 arcsec) and a mean, radially flat velocity
dispersion sigma=44 km/s are measured. The core extending over the inner 2
arcsec (~140 pc) is found to rotate in the opposite sense with v_rot(core) ~
-1/2 v_rot. VCC 510 (M_B ~ -15.7) is therefore by far the faintest and smallest
galaxy with a counter-rotating core known. From the main body rotation and the
velocity dispersion profile we deduce that VCC 510 is anisotropic and clearly
not entirely supported by rotation. By comparison of Lick absorption-line
indices with stellar population models we derive an old luminosity-weighted age
(10 Gyr) and sub-solar metallicity ([Z/H]=-0.4) inside the effective radius.
There is tentative evidence that the counter-rotating core might be younger and
less alpha/Fe enhanced. From the stellar population parameters we obtain a
total stellar mass-to-light ratio of ~3.6 (M/L_B)_sun which is significantly
lower than a rough dynamical estimate obtained from the kinematics through the
virial theorem (~15). This discrepancy hints toward the possible presence of
dark matter in the centre of VCC 510. We discuss the origin of the
counter-rotating core and exclude fly-by encounters as a viable possibility.
Gas accretion or galaxy merging provide more likely explanations. VCC 510 is
therefore the direct observational evidence that such processes do occur in
cluster satellite galaxies on dwarf galaxy scales.


title: Cosmological Signatures of Interacting Neutrinos

abstract:
  We investigate signatures of neutrino scattering in the Cosmic Microwave
Background (CMB) and matter power spectra, and the extent to which present
cosmological data can distinguish between a free streaming or tightly coupled
fluid of neutrinos. If neutrinos have strong non-standard interactions, for
example, through the coupling of neutrinos to a light boson, they may be kept
in equilibrium until late times. We show how the power spectra for these models
differ from more conventional neutrino scenarios, and use CMB and large scale
structure data to constrain these models. CMB polarization data improves the
constraints on the number of massless neutrinos, while the Lyman--$\alpha$
power spectrum improves the limits on the neutrino mass. Neutrino mass limits
depend strongly on whether some or all of the neutrino species interact and
annihilate. The present data can accommodate a number of tightly-coupled
relativistic degrees of freedom, and none of the interacting-neutrino scenarios
considered are ruled out by current data -- although considerations regarding
the age of the Universe disfavor a model with three annihilating neutrinos with
very large neutrino masses.


title:
Dark-matter particles and baryons from inflation and spontaneous CP
  violation in the early universe

abstract:
  We present aspects of a model which attempts to unify the creation of cold
dark matter, a CP-violating baryon asymmetry, and also a small, residual vacuum
energy density, in the early universe. The model contains a primary scalar
(inflaton) field and a primary pseudoscalar field, which are initially related
by a cosmological, chiral symmetry. The nonzero vacuum expectation value of the
pseudoscalar field spontaneously breaks CP invariance.