title: Magnetic pressure support and accretion disk spectra

abstract:
  Stellar atmosphere models of ionized accretion disks have generally neglected
the contribution of magnetic fields to the vertical hydrostatic support,
although magnetic fields are widely believed to play a critical role in the
transport of angular momentum. Simulations of magnetorotational turbulence in a
vertically stratified shearing box geometry show that magnetic pressure support
can be dominant in the upper layers of the disk. We present calculations of
accretion disk spectra that include this magnetic pressure support, as well as
a vertical dissipation profile based on simulation. Magnetic pressure support
generically produces a more vertically extended disk atmosphere with a larger
density scale height. This acts to harden the spectrum compared to models that
neglect magnetic pressure support. We estimate the significance of this effect
on disk-integrated spectra by calculating an illustrative disk model for a
stellar mass black hole, assuming that similar magnetic pressure support exists
at all radii.


title: Chemistry of Low Mass Substellar Objects

abstract:
  "Brown dwarfs" is the collective name for objects more massive than giant
planets such as Jupiter but less massive than M dwarf stars. This review gives
a brief description of the classification and chemistry of low mass dwarfs. The
current spectral classification of stars includes L and T dwarfs that encompass
the coolest known stars and substellar objects. The relatively low atmospheric
temperatures and high total pressures in substellar dwarfs lead to molecular
gas and condensate chemistry. The chemistry of elements such as C, N, O, Ti, V,
Fe, Cr, and the alkali elements play a dominant role in shaping the optical and
infrared spectra of the "failed" stars. Chemical diagnostics for the
subclassifications are described.


title:
XMM-Newton observations of Abell 2255 : a test case of a merger after
  `core-crossing'

abstract:
  It has been known that Abell 2255 is not a relaxed cluster, but it is
undergoing a merger. Here, we report on the analysis of the XMM-Newton
observations of this cluster. The X-ray data give us the opportunity to reveal
the complexity of the cluster, especially its temperature distribution. The
integrated spectrum is well fitted by a single temperature thermal model,
indicating a mean temperature of ~7 keV. However, the cluster is not isothermal
at this temperature: its eastern regions are significantly cooler, at ~5.5 keV,
whilst towards the West the temperature reaches ~8.5 keV.
  These temperature asymmetries can be explained if Abell 2255 has been
assembled recently by the merging of smaller subunits. It is now in the phase
after the cores of these subunits have collided (the `core-crossing' phase)
some 0.1-0.2 Gyr ago. A comparison with numerical simulations suggests that it
will settle down into a single relaxed cluster in ~(2-3) Gyr.


title:
Observable Effects of Dust Formation in Dynamic Atmospheres of M-type
  Mira Variables

abstract:
  The formation of dust with temperature-dependent non-grey opacity is
considered in a series of self-consistent model atmospheres at different phases
of an O-rich Mira variable of mass 1.2 $M_\odot$. Photometric and
interferometric properties of these models are predicted under different
physical assumptions regarding the dust formation. The iron content of the
initial silicate that forms and the availability of grain nuclei are found to
be critical parameters that affect the observable properties. In particular,
parameters were found where dust would form at 2-3 times the average continuum
photospheric radius. This work provides a consistent physical explanation for
the larger apparent size of Mira variables at wavelengths shorter than 1 $\mu$m
than that predicted by dust free fundamental-mode pulsation models.


title:
Improved low-temperature rate constants for rotational excitation of CO
  by H_2

abstract:
  Cross sections for the rotational (de)excitation of CO by ground state para-
and ortho-H_2 are obtained using quantum scattering calculations for collision
energies between 1 and 520 cm^{-1}. A new CO-H_2 potential energy surface is
employed and its quality is assessed by comparison with explicitly correlated
CCSD(T)-R12 calculations. Rate constants for rotational levels of CO up to 5
and temperatures in the range 5-70 K are deduced. The new potential is found to
have a strong influence on the resonance structure of the cross sections at
very low collision energies. As a result, the present rates at 10 K differ by
up to 50% with those obtained by \citet{flower01} on a previous, less accurate,
potential energy surface.


title: The Environment of Active Galaxies in the SDSS-DR4

abstract:
  We study the environment of active galaxies and compare it with that of star
forming and normal galaxies. We extracted from the Fourth Data Release (DR4) of
the Sloan Digitaly Sky Survey (SDSS) the galaxies in the redshift range 0.05
\le z \le 0.095 and with M(r) \le -20.0 (that is M* + 1.45). Emission line
ratios and/or widths are used to separate Active Galactic Nuclei (AGN) from
Star-Forming Galaxies (SFGs); AGN are classified as Seyfert-1 and Seyfert-2
galaxies according to emission line widths. The environmental properties, as
defined by a density parameter and the number of companions, are compared for
the different types of galaxies, taking into account the morphological type of
the host galaxies. We find no difference in the large-scale environment of
Seyfert-1 and Seyfert-2 galaxies; however, a larger fraction of Seyfert-2 (~2%)
than Seyfert-1 (~1%) is found in systems which are smaller than r_{max} \le 100
kpc, mainly in low-density environments (pairs or triplets); for comparison,
this fraction is ~2% for star forming galaxies and ~1% for normal galaxies. We
find no evidence for a relation between large-scale environment properties and
activity. If activity and environment are related, this more likely occurs on
small scales (e.g. galaxy interaction, merging).


title:
Near-IR Spectroscopy of a Young Super-Star Cluster in NGC 6946: Chemical
  Abundances and Abundance Patterns

abstract:
  Using the NIRSPEC spectrograph at Keck II, we have obtained H and K-band
echelle spectra for a young (10-15 Myr), luminous (MV=-13.2) super-star cluster
in the nearby spiral galaxy NGC 6946. From spectral synthesis and equivalent
width measurements we obtain for the first time accurate abundances and
abundance patterns in an extragalactic super-star cluster. We find
[Fe/H]=-0.45+/-0.08 dex, an average alpha-enhancement of +0.22+/-0.1 dex, and a
relatively low 12C/13C~ 8+/-2 isotopic ratio. We also measure a velocity
dispersion of ~9.1 km/s, in agreement with previous estimates. We conclude that
integrated high-dispersion spectroscopy of massive star clusters is a promising
alternative to other methods for abundance analysis in extragalactic young
stellar populations.


title:
First results from the VIMOS-IFU survey of gravitationally lensing
  clusters at z~0.2

abstract:
  We present the on-going observational program of a VIMOS Integral Field Unit
survey of the central regions of massive, gravitational lensing galaxy clusters
at redshift z~0.2. We have observed six clusters using the low-resolution blue
grism (R about 200), and the spectroscopic survey is complemented by a wealth
of photometric data, including Hubble Space Telescope optical data and near
infrared VLT data. The principal scientific aims of this project are: the study
of the high-z lensed galaxies, the transformation and evolution of galaxies in
cluster cores and the use of multiple images to constrain cosmography. We
briefly report here on the first results from this project on the clusters
Abell 2667 and Abell 68.


title: FUV Scattering by Dust in Orion

abstract:
  We have modelled diffuse far-ultraviolet spectrum observed by FUSE near M42
as scattering of starlight from the Trapezium stars by dust in front of the
nebula. The dust grains are known to be anomalous in Orion with Rv = 5.5 and
these are the first measurements of the FUV optical properties of the grains
outside of ``normal'' Milky Way dust. We find an albedo varying from 0.3 $\pm$
0.1 at 912 \AA to 0.5 $\pm$ 0.2 at 1020 \AA which is consistent with
theoretical predictions.


title: Understanding the origin of CMB constraints on Dark Energy

abstract:
  We study the observational constraints of CMB temperature and polarization
anisotropies on models of dark energy, with special focus on models with
variation in properties of dark energy with time. We demonstrate that the key
constraint from CMB observations arises from the location of acoustic peaks. An
additional constraint arises from the limits on Omega_nr from the relative
amplitudes of acoustic peaks. Further, we show that the distance to the last
scattering surface is not how the CMB observations constrain the combination of
parameters for models of dark energy. We also use constraints from Supernova
observations and show that unlike the Gold and Silver samples, the SNLS sample
prefers a region of parameter space that has a significant overlap with the
region preferred by the CMB observations. This is a verification of a
conjecture made by us in an earlier work. We discuss combined constraints from
WMAP5 and SNLS observations. We find that models with w ~ -1 are preferred for
models with a constant equation of state parameters. In case of models with a
time varying dark energy, we show that constraints on evolution of dark energy
density are almost independent of the type of variation assumed for the
equation of state parameter. This makes it easy to get approximate constraints
from CMB observations on arbitrary models of dark energy. Constraints on models
with a time varying dark energy are predominantly due to CMB observations, with
Supernova constraints playing only a marginal role.


title: Thermodynamics and dynamics of a 1-D gravitational system

abstract:
  We describe a one-dimensional self-gravitating system derived from the
problem of large-scale structure formation in cosmology. Considering small
times so that the expansion can be neglected we present a thermodynamical
analysis of this system. We find a second-order phase transition at $T_{c1}$
from an homogeneous equilibrium at high temperature to a clustered phase (with
a density peak at one of the boundaries of the system) at low temperature.
There also exists an infinite series of unstable equilibria which appear at
lower temperatures $T_{cn}$, reflecting the scale-free nature of the
gravitational interaction and the usual Jeans instability. We find that, as for
the similar HMF (Hamiltonian mean field) model, all three micro-canonical,
canonical and grand-canonical ensembles agree with each other, as well as with
the stability properties associated with a hydrodynamical approach. On the
other hand, the collisionless dynamics governed by the Vlasov equation yields
the same results except that at low $T$ the equilibrium associated with two
density peaks (one at each boundary) becomes stable.


title: Lensed Quasar Hosts

abstract:
  Gravitational lensing assists in the detection of quasar hosts by amplifying
and distorting the host light away from the unresolved quasar core images. We
present the results of HST observations of 30 quasar hosts at redshifts 1 < z <
4.5. The hosts are small in size (r_e <~ 6 kpc), and span a range of
morphologies consistent with early-types (though smaller in mass) to
disky/late-type. The ratio of the black hole mass (MBH, from the virial
technique) to the bulge mass (M_bulge, from the stellar luminosity) at 1<z<1.7
is broadly consistent with the local value; while MBH/M_bulge at z>1.7 is a
factor of 3--6 higher than the local value. But, depending on the stellar
content the ratio may decline at z>4 (if E/S0-like), flatten off to 6--10 times
the local value (if Sbc-like), or continue to rise (if Im-like). We infer that
galaxy bulge masses must have grown by a factor of 3--6 over the redshift range
3>z>1, and then changed little since z~1. This suggests that the peak epoch of
galaxy formation for massive galaxies is above z~1. We also estimate the duty
cycle of luminous AGNs at z>1 to be ~1%, or 10^7 yrs, with sizable scatter.


title:
Can gas dynamics in centres of galaxies reveal orbiting massive black
  holes?

abstract:
  If supermassive black holes in centres of galaxies form by merging of
black-hole remnants of massive Population III stars, then there should be a few
black holes of mass one or two orders of magnitude smaller than that of the
central ones, orbiting around the centre of a typical galaxy. These black holes
constitute a weak perturbation in the gravitational potential, which can
generate wave phenomena in gas within a disc close to the centre of the galaxy.
Here we show that a single orbiting black hole generates a three-arm spiral
pattern in the central gaseous disc. The density excess in the spiral arms in
the disc reaches values of 3-12% when the orbiting black hole is about ten
times less massive than the central black hole. Therefore the observed density
pattern in gas can be used as a signature in detecting the most massive
orbiting black holes.


title: Pseudobulges in the Disk Galaxies NGC 7690 and NGC 4593

abstract:
  We present Ks-band surface photometry of NGC 7690 (Hubble type Sab) and NGC
4593 (SBb). We find that, in both galaxies, a major part of the "bulge" is as
flat as the disk and has approximately the same color as the inner disk. In
other words, the "bulges" of these galaxies have disk-like properties. We
conclude that these are examples of "pseudobulges" -- that is, products of
secular dynamical evolution. Nonaxisymmetries such as bars and oval disks
transport disk gas toward the center. There, star formation builds dense
stellar components that look like -- and often are mistaken for -- merger-built
bulges but that were constructed slowly out of disk material. These
pseudobulges can most easily be recognized when, as in the present galaxies,
they retain disk-like properties. NGC 7690 and NGC 4593 therefore contribute to
the growing evidence that secular processes help to shape galaxies.
  NGC 4593 contains a nuclear ring of dust that is morphologically similar to
nuclear rings of star formation that are seen in many barred and oval galaxies.
The nuclear dust ring is connected to nearly radial dust lanes in the galaxy's
bar. Such dust lanes are a signature of gas inflow. We suggest that gas is
currently accumulating in the dust ring and hypothesize that the gas ring will
starburst in the future. The observations of NGC 4593 therefore suggest that
major starburst events that contribute to pseudobulge growth can be episodic.


title: Bulge evolution in face-on spirals and low surface brightness galaxies

abstract:
  It is an observational fact that bulges of spiral galaxies contain a high
fraction of old and metal-rich stars. Following this observational fact, we
have investigated colors of 21 bulges hosted by a selected sample of high
surface brightness spirals and low surface brightness galaxies observed in B
and R optical bands and in J and Ks near-IR bands. Using structural parameters
derived from these observations we obtain evidence that bulges could be formed
by pure disk evolution (secular evolution), in agreement with the suggestion by
some authors. The color profiles, especially the near-IR ones show null or
almost null color gradients, supporting the hypothesis that the disk stellar
populations are similar to those present in the bulge, and/or some bulges can
be understood as disks with enhanced stellar density (or pseudobulges). In the
optical, half of the galaxies present an inverse color gradient, giving
additional evidence in favor of secular evolution for the sample investigated.
The comparison of the observed colors with those obtained from
spectrophotometric models of galaxy evolution suggests that bulges of the
selected sample have solar and subsolar metallicity, and are independent of the
current stellar formation rate. Also, we obtain evidence suggesting that
galaxies hosting small bulges tend to be systematically metal poor compared to
those with larger bulges. These results are being checked more carefully with
high S/N spectroscopy.


title:
The Araucaria Project. Bright Variable Stars in NGC 6822 from a
  Wide-Field Imaging Survey

abstract:
  We have performed a search for variable stars in the dwarf irregular galaxy
NGC 6822 using wide-field multi-epoch VI photometry down to a limiting
magnitude $V$ $\sim$ 22. Apart from the Cepheid variables in this galaxy
already reported in an earlier paper by Pietrzynski et al. (2004), we have
found 1019 "non-periodic" variable stars, 50 periodically variable stars with
periods ranging from 0.12 to 66 days and 146 probably periodic variables.
Twelve of these stars are eclipsing binaries and fifteen are likely new,
low-amplitude Cepheids. Interestingly, seven of these Cepheid candidates have
periods longer than 100 days, have very low amplitudes (less than 0.2 mag in
$I$), and are very red. They could be young, massive Cepheids still embedded in
dusty envelopes. The other objects span a huge range in colours and represent a
mixture of different types of luminous variables. Many of the variables
classified as non-periodic in the present study may turn out to be {\it
periodic} variables once a much longer time baseline will be available to study
them.
  We provide the catalogue of photometric parameters and show the atlas of
light curves for the new variable stars. Our present catalogue is complementary
to the one of Baldacci et al. (2005) which has focussed on very short-period
and fainter variables in a subfield in NGC 6822.


title: Physical parameters of the O6.5V+B1V eclipsing binary system LS 1135

abstract:
  ASAS photometric observations of LS 1135, an O-type SB1 binary system with an
orbital period of 2.7 days, show that the system is also eclipsing. This
prompted us to re-examine the spectra used in the previously published
spectroscopic orbit. Our new analysis of the spectra obtained near quadratures,
reveal the presence of faint lines of the secondary component. We present for
the first time a double-lined radial velocity orbit and values of physical
parameters of this binary system. These values were obtained by analyzing ASAS
photometry jointly with the radial velocities of both components performing a
numerical model of this binary based on the Wilson-Devinney method. We obtained
an orbital inclination i ~ 68.5 deg. With this value of the inclination we
deduced masses M1 ~ 30 +/- 1 Mo and M2 ~ 9 +/- 1 Mo; and radii R1 ~ 12 +/- 1 Ro
and R2 ~ 5 +/- 1 Ro for primary and secondary components, respectively. Both
components are well inside their respective Roche lobes. Fixing the Teff of the
primary to the value corresponding to its spectral type (O6.5V), the Teff
obtained for the secondary component corresponds approximately to a spectral
type of B1V. The mass ratio M2/M1 ~ 0.3 is among the lowest known values for
spectroscopic binaries with O-type components.


title: The ICECUBE prototype string in AMANDA

abstract:
  The Antarctic Muon And Neutrino Detector Array (Amanda) is a high-energy
neutrino telescope. It is a lattice of optical modules (OM) installed in the
clear ice below the South Pole Station. Each OM contains a photomultiplier tube
(PMT) that detects photons of Cherenkov light generated in the ice by muons and
electrons. IceCube is a cubic-kilometer-sized expansion of Amanda currently
being built at the South Pole. In IceCube the PMT signals are digitized already
in the optical modules and transmitted to the surface. A prototype string of 41
OMs equipped with this new all-digital technology was deployed in the Amanda
array in the year 2000. In this paper we describe the technology and
demonstrate that this string serves as a proof of concept for the IceCube
array. Our investigations show that the OM timing accuracy is 5 ns. Atmospheric
muons are detected in excellent agreement with expectations with respect to
both angular distribution and absolute rate.


title:
Black Hole Masses of Active Galaxies with Double-Peaked Balmer Emission
  Lines

abstract:
  We have obtained near-IR spectra of five Active Galactic Nuclei that exhibit
double-peaked Balmer Emission Lines (NGC 1097, Pictor A, PKS 0921-213, 1E
0450.30-1817, and IRAS 0236.6-3101). The stellar velocity dispersions of the
host galaxies were measured from the Ca II 8494,8542,8662 Angstrom absorption
lines and were found to range from 140 to 200 km/s. Using the well-known
correlation between the black hole mass and the stellar velocity dispersion,
the black hole masses in these galaxies were estimated to range from 4x10^7 to
1.2x10^8 solar masses. We supplement the observations presented here with
estimates of the black holes masses for five additional double-peaked emitters
(Arp 102B, 3C 390.3, NGC 4579, NGC 4203, and M81) obtained by other authors
using similar methods. Using these black hole masses, we infer the ratio of the
bolometric luminosity to the Eddington luminosity, L_bol/L_Edd. We find that
two objects (Pictor A and PKS 0921--213) have L_bol/L_Edd ~ 0.2, whereas the
other objects have L_bol/L_Edd <~ 10^-2 (nearby, low-luminosity double-peaked
emitters are the most extreme, with L_bol/L_Edd <~ 10^-4). The physical time
scales in the outer regions of the accretion disks (at r ~ 10^3 GM/c^2) in
these objects were also estimated and range from a few months, for the
dynamical time scale, to several decades for the sound crossing time scale. The
profile variability in these objects are typically an order of magnitude longer
than the dynamical time, but we note that variability occurring on the
dynamical time scale has not been ruled out by the observations.


title: Prebiotic Homochirality as a Critical Phenomenon

abstract:
  The development of prebiotic homochirality on early-Earth or another
planetary platform may be viewed as a critical phenomenon. It is shown, in the
context of spatio-temporal polymerization reaction networks, that environmental
effects -- be them temperature surges or other external disruptions -- may
destroy any net chirality previously produced. In order to understand the
emergence of prebiotic homochirality it is important to model the coupling of
polymerization reaction networks to different planetary environments.


title:
Red Mergers and the Assembly of Massive Elliptical Galaxies: the
  Fundamental Plane and its Projections

abstract:
  Several recent observations suggest that gas-poor (dissipationless) mergers
of elliptical galaxies contribute significantly to the build-up of the massive
end of the red sequence. We perform a series of major merger simulations to
investigate the spatial and velocity structure of the remnants of such mergers.
Regardless of orbital energy or angular momentum, we find that the stellar
remnants lie on the fundamental plane defined by their progenitors, a result of
virial equilibrium with a small tilt due to an increasing central dark matter
fraction. However, the locations of merger remnants in the projections of the
fundamental plane -- the Faber-Jackson and R_e-M_* relations -- depend strongly
on the merger orbit, and the relations steepen significantly from the canonical
scalings (L sigma^4 and R_e M_*^0.6) for mergers on radial orbits. Our results
imply that the projections of the fundamental plane -- but not necessarily the
plane itself -- provide a powerful way of investigating the assembly history of
massive elliptical galaxies, including the brightest cluster galaxies at or
near the centers of galaxy clusters. We argue that most massive ellipticals are
formed by anisotropic merging and that their fundamental plane projections
should thus differ noticeably from those of lower mass ellipticals even though
they should lie on the same fundamental plane. Current observations are
consistent with this conclusion. The steepening in the L-sigma relation for
luminous ellipticals may also be reflected in a corresponding steepening in the
M_BH-sigma relation for massive black holes.


title: Fossils of Reionization in the Local Group

abstract:
  We use a combination of high-resolution gasdynamics simulations of
high-redshift dwarf galaxies and dissipationless simulations of a Milky Way
sized halo to estimate the expected abundance and spatial distribution of the
dwarf satellite galaxies that formed most of their stars around z~8 and evolved
only little since then. Such galaxies can be considered as fossils of the
reionization era, and studying their properties could provide a direct window
into the early, pre-reionization stages of galaxy formation. We show that 5-15%
of the objects existing at z~8 do indeed survive until the present in the MW
like environment without significant evolution. This implies that it is
plausible that the fossil dwarf galaxies do exist in the Local Group. Because
such galaxies form their stellar systems early during the period of active
merging and accretion, they should have spheroidal morphology regardless of
their current distance from the host galaxy. We show that both the expected
luminosity function and spatial distribution of dark matter halos which are
likely to host fossil galaxies agree reasonably well with the observed
distributions of the luminous (L_V>10^6 Lsun) Local Group fossil candidates
near the host galaxy (d<200 kpc). However, the predicted abundance is
substantially larger (by a factor of 2-3) for fainter galaxies (L_V<10^6 Lsun)
at larger distances (d>300 kpc). We discuss several possible explanations for
this discrepancy.


title: The baryon mass function for galaxy clusters

abstract:
  Context: The evolution of the cluster abundance with redshift is known to be
a powerful cosmological constraint when applied to X-ray clusters. Recently,
the evolution of the baryon mass function has been proposed as a new variant
that is free of the uncertainties present in the temperature-mass relation. A
flat model with Omega_matter ~ 0.3 was shown to be preferred in the case of a
standard cold dark matter scenario.
  Aims: We compared the high redshift predictions of the baryon mass in
clusters with data for a more general class of spectra with a varying shape
factor Gamma without any restriction to the standard cold dark matter scenario
in models normalized to reproduce the local baryon mass function.
  Methods: Using various halo mass functions existing in the literature we
evaluated the corresponding baryon mass functions for the case of the
non-standard power spectra mentioned previously.
  Results: We found that models with Omega_matter ~ 1 and Gamma ~ 0.12
reproduce high redshift cluster data just as well as the concordance model
does.
  Conclusions: Finally, we conclude that the baryon mass function evolution
alone does not efficiently discriminate between the more general family of flat
cosmological models with non-standard power spectra.


title: The Fundamental Plane for z=0.8-0.9 cluster galaxies

abstract:
  We present the Fundamental Plane (FP) for 38 early-type galaxies in the two
rich galaxy clusters RXJ0152.7-1357 (z=0.83) and RXJ1226.9+3332 (z=0.89),
reaching a limiting magnitude of M_B =-19.8 mag in the rest frame of the
clusters. While the zero point offset of the FP for these high redshift
clusters relative to our low redshift sample is consistent with passive
evolution with a formation redshift of z_form ~ 3.2, the FP for the high
redshift clusters is not only shifted as expected for a mass-independent
z_form, but rotated relative to the low redshift sample. Expressed as a
relation between the galaxy masses and the mass-to-light ratios the FP is
significantly steeper for the high redshift clusters than found at low
redshift. We interpret this as a mass dependency of the star formation history,
as has been suggested by other recent studies. The low mass galaxies (10^10.3
M_sun) have experienced star formation as recently as z ~ 1.35 (1.5 Gyr prior
to their look back time), while galaxies with masses larger than 10^11.3 M_sun
had their last major star formation episode at z > 4.5.


title: Does the Fornax dwarf spheroidal have a central cusp or core?

abstract:
  The dark matter dominated Fornax dwarf spheroidal has five globular clusters
orbiting at ~1 kpc from its centre. In a cuspy CDM halo the globulars would
sink to the centre from their current positions within a few Gyrs, presenting a
puzzle as to why they survive undigested at the present epoch. We show that a
solution to this timing problem is to adopt a cored dark matter halo. We use
numerical simulations and analytic calculations to show that, under these
conditions, the sinking time becomes many Hubble times; the globulars
effectively stall at the dark matter core radius. We conclude that the Fornax
dwarf spheroidal has a shallow inner density profile with a core radius
constrained by the observed positions of its globular clusters. If the phase
space density of the core is primordial then it implies a warm dark matter
particle and gives an upper limit to its mass of ~0.5 keV, consistent with that
required to significantly alleviate the substructure problem.


title:
Chandra Study of the Cepheus B Star Forming Region: Stellar Populations
  and the Initial Mass Function

abstract:
  Cepheus B (Cep B) molecular cloud and a portion of the nearby Cep OB3b OB
association, one of the most active regions of star formation within 1 kpc, has
been observed with the ACIS detector on board the Chandra X-ray Observatory. We
detect 431 X-ray sources, of which 89% are confidently identified as clustered
pre-main sequence stars. Two main results are obtained. First, we provide the
best census to date for the stellar population of the region. We identify many
members of two rich stellar clusters: the lightly obscured Cep OB3b
association, and the deeply embedded cluster in Cep B whose existence was
previously traced only by a handful of radio sources and T Tauri stars. Second,
we find a discrepancy between the X-ray Luminosity Functions of the Cep OB3b
and the Orion Nebula Cluster. This may be due to different Initial Mass
Functions of two regions (excess of ~0.3 solar mass stars), or different age
distributions. Several other results are obtained. A diffuse X-ray component
seen in the field is attributed to the integrated emission of unresolved low
mass PMS stars. The X-ray emission from HD 217086 (O7n), the principle ionizing
source of the region, follows the standard model involving many small shocks in
an unmagnetized radiatively accelerated wind. The X-ray source #294 joins a
number of similar superflare PMS stars where long magnetic structures may
connect the protoplanetary disk to the stellar surface.


title: Radiation Transport Around Kerr Black Holes

abstract:
  This Thesis describes the basic framework and applications of a relativistic
ray-tracing code for analyzing accretion processes around Kerr black holes. We
begin in Chapter 1 with a brief historical summary of the major advances in
black hole astrophysics over the past few decades. In Chapter 2 we present a
detailed description of the ray-tracing code, which is used to calculate the
transfer function between the accretion disk and the detector. In Chapter 3, we
employ a simple ``hot spot'' model to explain the frequencies and amplitudes of
quasi-periodic oscillations (QPOs). In Chapter 4, we introduce additional
features to the hot spot model to explain the broadening of the QPO peaks as
well as the damping of higher-frequency harmonics in the power spectrum. In
Chapter 5 we present a description of the structure of a relativistic
alpha-disk around a Kerr black hole, and the observed spectrum from such a
disk. The features of this modified thermal spectrum may be used to infer the
physical properties of the accretion disk and the central black hole. In
Chapter 6 we develop a Monte Carlo code to calculate the detailed propagation
of photons from a hot spot emitter scattering through a corona surrounding the
black hole. The coronal scattering has two major observable effects: the
inverse-Compton process alters the photon spectrum by adding a high energy
power-law tail, and the random scattering of each photon effectively damps out
the highest frequency modulations in the X-ray light curve.


title:
The environmental dependence of galaxy clustering in the Sloan Digital
  Sky Survey

abstract:
  A generic prediction of hierarchical clustering models is that the mass
function of dark haloes in dense regions in the Universe should be top-heavy.
We provide a novel test of this prediction using a sample of galaxies drawn
from the Sloan Digital Sky Survey. To perform the test, we compare measurements
of galaxy clustering in dense and underdense regions. We find that galaxies in
dense regions cluster significantly more strongly than those in less dense
regions. This is true over the entire 0.1--30 Mpc pair separation range for
which we can make accurate measurements. We make similar measurements in
realistic mock catalogs in which the only environmental effects are those which
arise from the predicted correlation between halo mass and environment. We also
provide an analytic halo-model based calculation of the effect. Both the mock
catalogs and the analytic calculation provide rather good descriptions of the
SDSS measurements. Thus, our results provide strong support for hierarchical
models. They suggest that, unless care is taken to study galaxies at fixed
mass, correlations between galaxy properties and the surrounding environment
are almost entirely due to more fundamental correlations between galaxy
properties and host halo mass, and between halo mass and environment.


title: A Spitzer View of Massive Galaxies at z~1-3

abstract:
  I discuss constraints on star--formation and AGN activity in massive galaxies
at z~1-3 using observations from the Spitzer Space Telescope. In particular I
focus on a sample of distant red galaxies (DRGs) with J-K>2.3 in GOODS-S. Based
on their ACS, ISAAC, and IRAC photometry, the DRGs have typical stellar masses
>10^11 Msol. Interestingly, the majority (>50%) of these objects have 24 micron
detections. If attributed to star formation, this implies SFRs of ~100-1000
Msol/yr. Thus, massive galaxies at z~1.5-3 have specific SFRs equal to or
exceeding the global average value at that epoch. In contrast, galaxies with
>10^11 Msol at z~0.3-0.75 have specific SFRs less than the global average, and
more than an order of magnitude lower than that at z~1.5-3. Thus, the bulk of
assembly of massive galaxies is largely complete by z~1.5. At the same time,
based on the X-ray luminosities and near-IR colors, as many as 25% of the
massive galaxies at z>1.5 host AGN, implying that the growth of supermassive
black holes coincides with massive-galaxy assembly. The analysis of
high-redshift galaxies depends on bolometric corrections between the observed
24 micron data and total IR luminosity. I review some of the sources of the
(significant) uncertainties on these corrections, and discuss improvements for
the future.


title: The Inclination Angle of and Mass of the Black Hole in XTE J1118+480

abstract:
  We have obtained optical and infrared photometry of the quiescent soft X-ray
transient XTE J1118+480. In addition to optical and J-band variations, we
present the first observed H- and K_s-band ellipsoidal variations for this
system. We model the variations in all bands simultaneously with the WD98 light
curve modeling code. The infrared colors of the secondary star in this system
are consistent with a K7V, while there is evidence for light from the accretion
disk in the optical. Combining the models with the observed spectral energy
distribution of the system, the most likely value for the orbital inclination
angle is 68 +/- 2 deg. This inclination angle corresponds to a primary black
hole mass of 8.53 +/- 0.60 M_sun. Based on the derived physical parameters and
infrared colors of the system, we determine a distance of 1.72 +/- 0.10 kpc to
XTE J1118+480.


title:
General Relativistic Force-Free Electrodynamics: A New Code and
  Applications to Black Hole Magnetospheres

abstract:
  The force-free limit of magnetohydrodynamics (MHD) is often a reasonable
approximation to model black hole and neutron star magnetospheres. We describe
a general relativistic force-free (GRFFE) formulation that allows general
relativistic magnetohydrodynamic (GRMHD) codes to directly evolve the GRFFE
equations of motion. Established, accurate, and well-tested conservative GRMHD
codes can simply add a new inversion piece of code to their existing code,
while continuing to use all the already-developed facilities present in their
GRMHD code. We show how to enforce the $\mathbf{E}\cdot\mathbf{B}=0$ constraint
and energy conservation, and we introduce a simplified general model of the
dissipation of the electric field to enforce the $B^2-E^2>0$ constraint. We
also introduce a simplified yet general method to resolve current sheets,
without much reconnection, over many dynamical times. This formulation is
incorporated into an existing GRMHD code (HARM), which is demonstrated to give
accurate and robust GRFFE results for Minkowski and black hole space-times.


title:
Relativistic Force-Free Electrodynamic Simulations of Neutron Star
  Magnetospheres

abstract:
  The luminosity and structure of neutron star magnetospheres are crucial to
our understanding of pulsar and plerion emission. A solution found using the
force-free approximation would be an interesting standard with which any model
with more physics could be compared. Prior quasi-analytic force-free solutions
may not be stable, while prior time-dependent magnetohydrodynamic models used
unphysical model parameters. We use a time-dependent relativistic force-free
electrodynamics code with no free parameters to find a unique stationary
solution for the axisymmetric rotating pulsar magnetosphere in a Minkowski
space-time in the case of no surface currents on the star. The solution is
similar to the force-free quasi-analytic solution of \citet{cont99} and the
numerical magnetohydrodynamic solution of \citet{kom05}. The magnetosphere
structure and the usefulness of the classical y-point in the general
dissipative regime are discussed. The pulsar luminosity is found to be $L
\approx 0.99\pm 0.01 \mu^2\Omega_\star^4/c^3$ for a dipole moment $\mu$ and
stellar angular frequency $\Omega_\star$.


title: Sersic Properties of Disc Galaxy Mergers

abstract:
  Sersic parameters characterising the density profiles of remnants formed in
collision-less disc galaxy mergers are obtained; no bulge is included in our
simulations. For the luminous component we find that the Sersic index is n ~
(1.5,5.3) with <n> ~ 3 +/- 1 and an effective radius of R_e ~ (1.6,12.9) kpc
with <R_e> ~ 5 +/- 3 kpc. A strong correlation of n with the central projected
density I_0 is found [n ~ I_0^(-0.14)] which is consistent with observations.
No positive linear correlation between the size (R_e) and structure (n) of our
remnants is found; we do not advocate the existence of this. The photometric
plane (PHP) of the luminous component [n ~ R_e^(0.05) I_0^(0.15)] agrees well,
within the uncertainties and the assumption of a constant mass-to-light ratio,
with those observationally determined for ellipticals. We found that the
surface defined by Sersic parameters (n, R_e, mu_0) in log-space is not a true
plane, but a pseudo-plane with a small curvature at low values of n owed to
intrinsic properties of the Sersic model. The dark haloes of the remnants have
a 3-dimensional Sersic index of <n> ~ 4 +/- 0.5 that are smaller than the ones
obtained for dark haloes in LCDM cosmologies <n> ~ 6 +/- 1. A tight dark Sersic
``plane'' (DSP) is also defined by the parameters of the remnants haloes with n
\~ r_e^(0.07) rho_0^(0.10). We conclude that collision-less merger remnants of
pure disc galaxies have Sersic properties and correlations consistent with
those of observed in early-type galaxies and local remnants. It seems that a
``primordial'' bulge in spirals is not a necessary condition to form bona fide
ellipticals on grounds of the Sersic properties of remnants.


title:
Spitzer Observations of Centaurus A: Infrared Synchrotron Emission from
  the Northern Lobe

abstract:
  We present measurements obtained with the Spitzer Space Telescope in five
bands from 3.6-24 microns of the northern inner radio lobe of Centaurus A, the
nearest powerful radio galaxy. We show that this emission is synchrotron in
origin. Comparison with ultraviolet observations from GALEX shows that diffuse
ultraviolet emission exists in a smaller region than the infrared but also
coincides with the radio jet. We discuss the possibility, that synchrotron
emission is responsible for the ultraviolet emission and conclude that further
data are required to confirm this.


title:
Exploring the surface properties of Transneptunian Objects and Centaurs
  with polarimetric FORS1/VLT observations

abstract:
  Polarization is a powerful remote-sensing method to investigate solar system
bodies. It is an especially sensitive diagnostic tool to reveal physical
properties of the bodies whose observational characteristics are governed by
small scatterers (dust, regolith surfaces). For these objects, at small phase
angles, a negative polarization is observed, i.e., the electric vector E
oscillates predominantly in the scattering plane, contrary to what is typical
for rather smooth homogeneous surfaces. The behavior of negative polarization
with phase angle depends on the size, composition and packing of the
scatterers. These characteristics can be unveiled by modelling the light
scattering by the dust or regolith in terms of the coherent backscattering
mechanism.
  We have investigated the surface properties of TNOs and Centaurs by means of
polarimetric observations with FORS1 of the ESO VLT.
  TNOs Ixion and Quaoar, and Centaur Chiron show a negative polarization surge.
The Centaur Chiron has the deepest polarization minimum (-1.5 - 1.4%). The two
TNOs show differing polarization curves: for Ixion, the negative polarization
increases rapidly with phase; for Quaoar, the polarization is relatively small
(~ -0.6%), and nearly constant at the observed phase angles. For all three
objects, modelling results suggest that the surface contains an areal mixture
of at least two components with different single-scatterer albedos and photon
mean-free paths.


title:
Light Element Production in the Circumstellar Matter of Energetic Type
  Ic Supernovae

abstract:
  We investigate energetic type Ic supernovae as production sites for Li6 and
Be in the early stages of the Milky Way. Recent observations have revealed that
some very metal-poor stars with [Fe/H]<-2.5 possess unexpectedly high
abundances of Li6. Some also exbihit enhanced abundances of Be as well as N.
  From a theoretical point of view, recent studies of the evolution of
metal-poor massive stars show that rotation-induced mixing can enrich the outer
H and He layers with C, N, and O (CNO) elements, particularly N, and at the
same time cause intense mass loss of these layers. Here we consider energetic
supernova explosions occurring after the progeniter star has lost all but a
small fraction of the He layer. The fastest portion of the supernova ejecta can
interact directly with the circumstellar matter (CSM), both composed of He and
CNO, and induce light element production through spallation and He-He fusion
reactions. The CSM should be sufficiently thick to energetic particles so that
the interactions terminate within its innermost regions. We calculate the
resulting Li6/O and Be9/O ratios in the ejecta+CSM material out of which the
very metal-poor stars may form. We find that they are consistent with the
observed values if the mass of the He layer remaining on the pre-explosion core
is 0.01-0.1 solar mass, and the mass fraction of N mixed in the He layer is
about 0.01. Further observations of Li6, Be and N at low metallicity should
provide critical tests of this production scenario.


title: Rotating compact star with superconducting quark matter

abstract:
  A compact star with superconducting quark core, the hadron crust and the
mixed phase between the two is considered. The quark meson coupling model for
hadron matter and the color flavor locked quark model for quark matter is used
in order to construct the equation of state for the compact star. The effect of
pairing of quarks in the color flavor locked phase and the mixed phase on the
mass, radius, and period of the rotating star is studied.


title:
SINFONI's take on Star Formation, Molecular Gas, and Black Hole Masses
  in AGN

abstract:
  We present some preliminary (half-way) results on our adaptive optics
spectroscopic survey of AGN at spatial scales down to 0.085arcsec. Most of the
data were obtained with SINFONI which provides integral field capability at a
spectral resolution of R~4000. The themes on which we focus in this
contribution are: star formation around the AGN, the properties of the
molecular gas and its relation to the torus, and the mass of the black hole.


title:
Analysis of the circumstellar environment of the B[e] star HD 45677 (FS
  CMa)

abstract:
  We studied the circumstellar environment of the B[e] star HD 45677 through
the analysis of the emission lines from ionized metals. We used the statistical
approach of the self absorption curve method (SAC) to derive physical
parameters of the line emitting region. The Fe II and Cr II double-peaked
emission line structure is explained by the presence of a thin absorption
component red shifted by ~3 km/s. This absorption component can be interpreted
geometricaly as being due to infalling material perpendicularly to the disk
seen nearly pole-on, as indicated by the emission line structure. The Cr II and
Fe II emission lines have a complex structure with two (narrow and broad)
components, of 45 and 180 km/s FWHM for the permitted lines and 25 and 100 km/s
FWHM for the forbidden ones, respectively. We argue that the narrow components
are principaly emitted by an optically thin disk seen nearly pole-on, in a
region whose minimum radius is estimated to be 4 10^12 cm, while the broad ones
are formed in a disk-linked wind.


title: Discovery of two new methanol masers in NGC 7538

abstract:
  Context: NGC7538 is known to host a 6.7 and 12.2GHz methanol maser cospatial
with a Ultra Compact (UC) HII region, IRS1.
  Aims: We report on the serendipitous discovery of two additional 6.7GHz
methanol masers in the same region, not associated with IRS1.
  Methods: Interferometry maser positions are compared with recent single-dish
and interferometry continuum observations.
  Results: The positions of the masers agree to high accuracy with the 1.2mm
continuum peak emission in NGC7538 IRS9 and NGC7538 S. This clear association
is also confirmed by the positional agreement of the masers with existing high
resolution continuum observations at cm and/or mm wavelengths.
  Conclusions: Making use of the established strong relation between methanol
masers and high-mass star formation, we claim that we have accurately
positioned the high-mass protostars within the regions where they are detected.
The variety of objects hosting a 6.7GHz methanol maser in NGC7538 shows that
this emission probably traces different evolutionary stages within the
protostellar phase.


title: Motion toward the Great Attractor from an ether-drift experiment

abstract:
  Since the end of 80's, the region of sky of galactic coordinates (l\sim
309^o, b\sim 18^o), corresponding to a declination \gamma\sim -44^o and right
ascension \alpha\sim 202^o, usually denoted as the "Great Attractor", is known
to control the overall galaxy flow in our local Universe. In this sense, this
direction might represent a natural candidate to characterize a hypothetical
Earth's "absolute motion". Our analysis of the extensive ether-drift
observations recently reported by an experimental group in Berlin provides
values of \alpha and \gamma that coincide almost exactly with those of the
Great Attractor and not with the values \gamma\sim -6^o and \alpha\sim 168^o
obtained from a dipole fit to the anisotropy of the CMB. This supports in a new
fashion the existence of a discrepancy between the observed motion of the Local
Group and the direction obtained from the CMB dipole.


title:
The infrared jet in Centaurus A: multiwavelength constraints on emission
  mechanisms and particle acceleration

abstract:
  We report on Spitzer and Gemini observations of the jet of Centaurus A in the
infrared, which we combine with radio, ultraviolet and X-ray data. Spitzer
detects jet emission from about 2 arcmin from the nucleus, becoming
particularly bright after the jet flare point at ~3.4 arcmin. Where X-ray and
infrared emission are seen together the broad-band data strongly support a
synchrotron origin for the X-rays. The jet flare point is marked by a broad,
diffuse region of X-rays which may be associated with a shock: we discuss
possible physical mechanisms for this. The infrared jet persists after the
flare point region although X-ray emission is absent; it is plausible that here
we are seeing the effects of particle acceleration followed by downstream
advection with synchrotron losses. Gemini data probe the inner regions of the
jet, putting limits on the mid-infrared flux of jet knots.


title: Upper limits on density of dark matter in Solar system

abstract:
  The analysis of the observational data for the secular perihelion precession
of Mercury, Earth, and Mars, based on the EPM2004 ephemerides, results in new
upper limits on density of dark matter in the Solar system.


title:
Two-dimensional spectroscopy of a sunspot. III Thermal and kinematic
  structure of the penumbra at 0.5"

abstract:
  We investigate the thermal and kinematic configuration of a sunspot penumbra
using very high spectral and spatial resolution intensity profiles of the
non-magnetic Fe I 557.6 nm line. The dataset was acquired with the 2D solar
spectrometer TESOS. The profiles are inverted using a one-component model
atmosphere with gradients of the physical quantities. From this inversion we
obtain the stratification with depth of temperature, line-of-sight velocity,
and microturbulence across the penumbra. Our results suggest that the physical
mechanism(s) responsible for the penumbral filaments operate preferentially in
the lower photosphere. We confirm the existence of a thermal asymmetry between
the center and limb-side penumbra, the former being hotter by 100-150 K on
average. We also investigate the nature of the bright ring that appears in the
inner penumbra when sunspots are observed in the wing of spectral lines. The
line-of-sight velocities retrieved from the inversion are used to determine the
flow speed and flow angle at different heights in the photosphere. Both the
flow speed and flow angle increase with optical depth and radial distance.
Downflows are detected in the mid and outer penumbra, but only in deep layers
(log tau_{500} < -1.4). We demonstrate that the velocity stratifications
retrieved from the inversion are consistent with the idea of penumbral flux
tubes channeling the Evershed flow. Finally, we show that larger Evershed flows
are associated with brighter continuum intensities in the inner center-side
penumbra. Dark structures, however, are also associated with significant
Evershed flows. This leads us to suggest that the bright and dark filaments
seen at 0.5" resolution are not individual flow channels, but a collection of
them.


title:
The Contribution of the Intergalactic Medium to Cosmic Microwave
  Background Anisotropies

abstract:
  We compute the power spectrum of the Cosmic Microwave Background temperature
anisotropies generated by the Intergalactic Medium. To estimate the electron
pressure along the line of sight and its contribution to the Sunyaev-Zeldovich
component of the CMB anisotropies, we assume the non-linear baryonic density
contrast is well described by a log-normal distribution. For model parameters
in agreement with observations and for an experiment operating in the
Rayleigh-Jeans regime, the largest IGM contribution is expected at scales
corresponding to multipole numbers of about 2000. The amplitude is rather
uncertain and could be as large as 100-200 [mikroK]^2, comparable to the
contribution of galaxy clusters. The actual value is strongly dependent on the
gas polytropic index and the amplitude of the matter power spectrum sigma_8. At
all redshifts, the largest contribution comes from scales very close to the
comoving baryon Jeans length. This scale is not yet resolved in numerical
simulations that follow the evolution of gas on cosmological scales. The
anisotropy generated by the Intergalactic Medium could make compatible the
excess of power measured by Cosmic Background Imager (CBI) on scales of l >
2000 with sigma_8=0.9. Taking the CBI result as an upper limit, the polytropic
index can be constrained to < 1.5 at 2-sigma level at redshifts z ~ 0.1-0.4.
With its large frequency coverage, the PLANCK satellite will be able to measure
the secondary anisotropies coming from hot gas. Cluster and Intergalactic
Medium contributions could be separated by cross correlating galaxy/cluster
catalogs with CMB maps. This measurement will determine the state of the gas at
low and intermediate redshifts.


title: On the Origin of the High Helium Sequence in $\omega$ Centauri

abstract:
  The blue Main Sequence (bMS) of $\omega$ Cen implies a ratio of helium to
metal enrichment $\Delta Y/\Delta Z \approx 70$, which is a major enigma.
  We show that rotating models of low metallicity stars, which account for the
anomalous abundance ratios of extremely metal poor stars, are also useful for
understanding the very high $\Delta Y/\Delta Z$ ratio in $\omega$ Cen. Models
of massive stars with moderate initial rotation velocities produce stellar
winds with large He-- and N--excesses, but without the large C-- (and O--)
excesses made by very fast rotation, in agreement with the observed chemical
abundance ratios in $\omega$ Cen. It is still uncertain whether the abundance
peculiarities of $\omega$ Cen result from the fact that the high velocity
contributions of supernovae escaped the globular cluster, usually considered as
a tidally stripped core of a dwarf galaxy. Another possibility is a general
dominance of wind ejecta at very low $Z$, due to the formation of black holes.
Some abundance and isotopic ratios like $Mg/Al$, $Na/Mg$, $Ne/N$,
$^{12}C/^{13}C$, $^{16}O/^{18}O$ and $^{17}O/^{18}O$ may allow us to further
discriminate between these scenarios and between the AGB and massive star
contributions.


title:
Comment on "PIC simulations of circularly polarised Alfv\'en wave phase
  mixing: A new mechanism for electron acceleration in collisionless plasmas"
  by Tsiklauri et al

abstract:
  Tsiklauri et al. recently published a theoretical model of electron
acceleration by Alfv\'en waves in a nonuniform collisionless plasmas. We
compare their work with a series of results published earlier by an another
team, of which Tsiklauri et al. were probably unaware. We show that these two
series of works, apparently conducted independently, lead to the same
conclusions. This reinforces the theoretical consistency of the model.


title:
The non-Gaussian Cold Spot in WMAP: significance, morphology and
  foreground contribution

abstract:
  The non--Gaussian cold spot in the 1-year WMAP data, described in Vielva et
al. and Cruz et al., is analysed in detail in the present paper. First of all,
we perform a more rigorous calculation of the significance of the non-zero
kurtosis detected in WMAP maps by Vielva et al. in wavelet space, mainly
generated by the Spot. We confirm the robustness of that detection, since the
probability of obtaining this deviation by chance is 0.69%. Afterwards, the
morphology of the Spot is studied by applying Spherical Mexican Hat Wavelets
with different ellipticities. The shape of the Spot is found to be almost
circular. Finally, we discuss if the observed non-Gaussianity in wavelet space
can arise from bad subtracted foreground residues in the WMAP maps. We show
that the flat frequency dependence of the Spot cannot be explained by a thermal
Sunyaev-Zeldovich effect. Based on our present knowledge of Galactic foreground
emissions, we conclude that the significance of our detection is not affected
by Galactic residues in the region of the Spot. Considering different Galactic
foreground estimates, the probability of finding such a big cold spot in
Gaussian simulations is always below 1%.


title: Deuterium at High Redshifts: Recent Advances and Open Issues

abstract:
  Among the light elements created in the Big Bang, deuterium is one of the
most difficult to detect but is also the one whose abundance depends most
sensitively on the density of baryons. Thus, although we still have only a few
positive identifications of D at high redshifts--when the D/H ratio was close
to its primordial value--they give us the most reliable determination of the
baryon density, in excellent agreement with measures obtained from entirely
different probes, such as the anisotropy of the cosmic microwave background
temperature and the average absorption of the UV light of quasars by the
intergalactic medium. In this review, I relate observations of D/H in distant
gas clouds to the large body of data on the local abundance of D obtained in
the last few years with the FUSE satellite. I also discuss some of the
outstanding problems in light element abundances and consider future prospects
for advances in this area.


title:
The importance of the ortho:para H2 ratio for the deuteration of
  molecules during pre-protostellar collapse

abstract:
  We have studied the evolution of molecular gas during the early stages of
protostellar collapse. In addition to allowing for the freeze out of `heavy'
species on to grains, we have computed the variation of population densities of
the different nuclear spin states of ``tracer'' molecular ions such as H2D+ and
D2H+. Processes which determine the relative populations of the nuclear spin
states of molecules and molecular ions have received much less attention in the
literature than those involved in their deuteration; but in fact the former
processes are as significant as the latter and often involve the same
reactants. We find that the ortho:para ratio of some species, e.g. H2D+, vary
considerably as the density increases. Because the dynamical timescale is much
shorter than some of the chemical timescales, there can be large departures of
the predictions of the free--fall model from the steady state solution at the
same density and temperature. In the case of H2, it seems unlikely that the
steady state value of the ortho:para ratio is attained before protostellar
collapse from the progenitor molecular cloud commences. Values of the
ortho:para H2 ratio much higher than in steady state, which would prevail in
``young'' molecular clouds, are found to be inconsistent with high levels of
deuteration of the gas. The internal energy of ortho--H2 acts as a reservoir of
chemical energy which inhibits the deuteration of H3+ and hence of other
species, such as N2H+ and NH3. In essence, the deuteration of molecular ions
and molecules is sensitive to the ortho:para H2 ratio and hence to the chemical
and thermal history of the parent molecular cloud.


title: Extreme superstarclusters

abstract:
  The presence of superstarclusters is a characteristic feature of starburst
galaxies. We examine the properties of star forming regions and young star
clusters in various environments, ranging from common to extreme. We then
discuss new high spatial resolution mid-infrared imaging and spectroscopy of
extreme superstarclusters in the obscured region of the Antennae
(NGC4038-4039). We find that the PAH emission in this region is not dominated
by the superstarclusters but is mostly diffuse. Emission line ratios found in
our high spatial resolution data differ significantly from those in larger
apertures, strongly affecting the derived results.


title: Modified gravity without dark matter

abstract:
  On an empirical level, the most successful alternative to dark matter in
bound gravitational systems is the modified Newtonian dynamics, or MOND,
proposed by Milgrom. Here I discuss the attempts to formulate MOND as a
modification of General Relativity. I begin with a summary of the
phenomenological successes of MOND and then discuss the various covariant
theories that have been proposed as a basis for the idea. I show why these
proposals have led inevitably to a multi-field theory. I describe in some
detail TeVeS, the tensor-vector-scalar theory proposed by Bekenstein, and
discuss its successes and shortcomings. This lecture is primarily pedagogical
and directed to those with some, but not a deep, background in General
Relativity


title: A Catalogue of RR Lyrae Stars from the Northern Sky Variability Survey

abstract:
  A search for RR Lyrae stars has been conducted in the publicly available data
of the Northern Sky Variability Survey (NSVS). Candidates have been selected by
the statistical properties of their variation; the standard deviation, skewness
and kurtosis with appropriate limits determined from a sample 314 known RRab
and RRc stars listed in the GCVS. From the period analysis and light curve
shape of over 3000 candidates 785 RR Lyrae have been identified of which 188
are previously unknown. The light curves were examined for the Blazhko effect
and several new stars showing this were found. Six double-mode RR Lyrae stars
were also found of which two are new discoveries. Some previously known
variables have been reclassified as RR Lyrae stars and similarly some RR Lyrae
stars have been found to be other types of variable, or not variable at all.


title: Constraining Cosmic Topology with CMB Polarization

abstract:
  Multiply connected space sections of the universe on a scale smaller than the
horizon size can leave an imprint on cosmic microwave background polarization
maps, in such a way that the so-called ``circles-in-the-sky'' method can be
used to detect or constrain the topology. We investigate some specific cases,
namely toroidal and sixth-turn spaces, in order to show the influence of
topology on CMB polarization. The correlation between matched points happens to
be always positive and higher than 75% regardless of the angular scale and of
the cosmological parameters, except for reionization. This figure is better
than what occurs in temperature maps, but is achieved only in the absence of
noise. It is only slightly reduced by the filtering scheme.


title:
The SDSS Quasar Survey: Quasar Luminosity Function from Data Release
  Three

abstract:
  We determine the number counts and z=0-5 luminosity function for a
well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey
(SDSS). We conservatively define the most uniform statistical sample possible,
consisting of 15,343 quasars within an effective area of 1622 deg^2 that was
derived from a parent sample of 46,420 spectroscopically confirmed broad-line
quasars in the 5282 deg^2 of imaging data from SDSS Data Release Three. The
sample extends from i=15 to i=19.1 at z<3 and to i=20.2 for z>3. The number
counts and luminosity function agree well with the results of the 2dF QSO
Survey, but the SDSS data probe to much higher redshifts than does the 2dF
sample. The number density of luminous quasars peaks between redshifts 2 and 3,
although uncertainties in the selection function in this range do not allow us
to determine the peak redshift more precisely. Our best fit model has a flatter
bright end slope at high redshift than at low redshift. For z<2.4 the data are
best fit by a redshift-independent slope of beta = -3.1 (Phi(L) propto L^beta).
Above z=2.4 the slope flattens with redshift to beta=-2.37 at z=5. This slope
change, which is significant at a >5-sigma level, must be accounted for in
models of the evolution of accretion onto supermassive black holes.


title: Dusty Sources at the Galactic Center: The N- and Q-band view with VISIR

abstract:
  We present mid-infrared N- and Q-band photometry of the Galactic Center from
images obtained with the mid-infrared camera VISIR at the ESO VLT in May 2004.
The high resolution and sensitivity possible with VISIR enables us to
investigate a total of over 60 point-like sources, an unprecedented number for
the Galactic Center at these wavelengths. Combining these data with previous
results at shorter wavelengths (Viehmann et al. 2005) enables us to construct
SEDs covering the H- to Q-band regions of the spectrum, i.e. 1.6 to 19.5
$\mu$m. We find that the SEDs of certain types of Galactic Center sources show
characteristic features. We can clearly distinguish between luminous Northern
Arm bow-shock sources, lower luminosity bow-shock sources, hot stars, and cool
stars. This characterization may help clarify the status of presently
unclassified sources.


title: Burst Detector Sensitivity: Past, Present & Future

abstract:
  I compare the burst detection sensitivity of CGRO's BATSE, Swift's BAT, the
GLAST Burst Monitor (GBM) and EXIST as a function of a burst's spectrum and
duration. A detector's overall burst sensitivity depends on its energy
sensitivity and set of accumulations times Delta t; these two factors shape the
detected burst population. For example, relative to BATSE, the BAT's softer
energy band decreases the detection rate of short, hard bursts, while the BAT's
longer accumulation times increase the detection rate of long, soft bursts.
Consequently, Swift is detecting long, low fluence bursts (2-3x fainter than
BATSE).


title:
Colliding Clouds: The Star Formation Trigger of the Stellar Cluster
  Around BD+40 4124

abstract:
  We present BIMA and SCUBA observations of the young cluster associated with
BD +40 4124 in the dense molecular gas tracer CS J=2-1 and the continuum dust
continuum at 3.1 mm and 850 micron. The dense gas and dust in the system is
aligned into a long ridge morphology extending ~0.4 pc with 16 gas clumps of
estimated masses ranging from 0.14 - 1.8 Solar masses. A north-south variation
in the CS center line velocity can be explained with a two cloud model. We
posit that the BD +40 4124 stellar cluster formed from a cloud-cloud collision.
The largest linewidths occur near V1318 Cyg-S, a massive star affecting its
natal environment. In contrast, the dense gas near the other, more evolved,
massive stars displays no evidence for disruption; the material must either be
processed into the star, dissipate, or relax, fairly quickly. The more evolved
low-mass protostars are more likely to be found near the massive stars. If the
majority of low-mass stars are coeval, the seemingly evolved low-mass
protostars are not older: the massive stars have eroded their structures.
Finally, at the highest resolution, the 3.1 mm dust emission is resolved into a
flattened structure 3100 by 1500 AU with an estimated mass of 3.4 Solar masses.
The continuum and CS emission are offset by 1.1 arcsec from the southern binary
source. A simple estimate of the extinction due to the continuum emission
structure is AV = 700 mag. From the offset and as the southern source is
detected in the optical, the continuum emission is from a previously unknown
very young, intermediate-mass, embedded stellar object. (see high resolution
figures at http://eeyore.astro.uiuc.edu/~lwl/recent/bd40.pdf).


title: Large dust grains in the inner region of circumstellar disks

abstract:
  CONTEXT: Simple geometrical ring models account well for near-infrared
interferometric observations of dusty disks surrounding pre-main sequence stars
of intermediate mass. Such models demonstrate that the dust distribution in
these disks has an inner hole and puffed-up inner edge consistent with
theoretical expectations. AIMS: In this paper, we reanalyze the available
interferometric observations of six intermediate mass pre-main sequence stars
(CQ Tau, VV Ser, MWC 480, MWC 758, V1295 Aql and AB Aur) in the framework of a
more detailed physical model of the inner region of the dusty disk. Our aim is
to verify whether the model will allow us to constrain the disk and dust
properties. METHODS: Observed visibilities from the literature are compared
with theoretical visibilities from our model. With the assumption that
silicates are the most refractory dust species, our model computes
self-consistently the shape and emission of the inner edge of the dusty disk
(and hence its visibilities for given interferometer con gurations). The only
free parameters in our model are the inner disk orientation and the size of the
dust grains. RESULTS: In all objects with the exception of AB Aur, our
self-consistent models reproduce both the interferometric results and the
near-infrared spectral energy distribution. In four cases, grains larger than
1.2 micron, and possibly much larger are either required by or consistent with
the observations. The inclination of the inner disk is found to be always
larger than 30 deg, and in at least two objects much larger.


title: Planetary nebulae with emission-line central stars

abstract:
  The kinematic structure of a sample of planetary nebulae, consisting of 23
[WR] central stars, 21 weak emission line stars (wels) and 57 non-emission line
central stars, is studied. The [WR] stars are shown to be surrounded by
turbulent nebulae, a characteristic shared by some wels but almost completely
absent from the non-emission line stars. The fraction of objects showing
turbulence for non-emission-line stars, wels and [WR] stars is 7%, 24% and 91%,
respectively. The [WR] stars show a distinct IRAS 12-micron excess, indicative
of small dust grains, which is not found for wels. The [WR]-star nebulae are on
average more centrally condensed than those of other stars. On the
age-temperature diagram, the wels are located on tracks of both high and low
stellar mass, while [WR] stars trace a narrow range of intermediate masses.
Emission-line stars are not found on the cooling track. One group of wels may
form a sequence wels--[WO] stars with increasing temperature. For the other
groups both the wels and the [WR] stars appear to represent several,
independent evolutionary tracks. We find a discontinuity in the [WR] stellar
temperature distribution and suggest different evolutionary sequences above and
below the temperature gap. One group of cool [WR] stars has no counterpart
among any other group of PNe and may represent binary evolution. A prime factor
distinguishing wels and [WR] stars appears to be stellar luminosity. We find no
evidence for an increase of nebular expansion velocity with time.


title:
Discovery of a Very Nearby Brown Dwarf to the Sun: A Methane Rich Brown
  Dwarf Companion to the Low Mass Star SCR 1845-6357

abstract:
  We present VLT/NACO SDI images of the very nearby star SCR 1845-6357
(hereafter SCR 1845). SCR 1845 is a recently discovered (Hambly et al. 2004)
M8.5 star just 3.85 pc from the sun (Henry et al. 2006). Using the capabilities
of the unique SDI device, we discovered a substellar companion to SCR 1845 at a
separation of 4.5 AU (1.170''+-0.003'' on the sky) and fainter by 3.57+-0.057
mag in the 1.575 um SDI filter. This substellar companion has an H magnitude of
13.16+0.31-0.26 (absolute H magnitude of 15.30+0.31-0.26), making it likely the
brightest mid-T dwarf known. The unique Simultaneous Differential Imager (SDI)
consists of 3 narrowband filters placed around the 1.6 um methane absorption
feature characteristic of T-dwarfs (Teff < 1200 K). The flux of the substellar
companion drops by a factor of 2.7+-0.1 between the SDI F1(1.575 um) filter and
the SDI F3(1.625 um) filter, consistent with strong methane absorption in a
substellar companion. We estimate a spectral type of T5.5+-1 for the companion
based on the strength of this methane break. The chances that this object is a
background T dwarf are vanishing small -- and there is no isolated background
T-dwarf in this part of the sky according to 2MASS. Thus, it is a bound
companion, hereafter SCR 1845-6357B. For an age range of 100 Myr - 10 Gyr and
spectral type range of T4.5-T6.5, we find a mass range of 9 - 65 MJup for SCR
1845B from the Baraffe et al. 2003 COND models. SCR 1845AB is the 24th closest
stellar system to the Sun (at 3.85 pc); the only brown dwarf system closer to
the Sun is Eps Indi Ba-Bb (at 3.626 pc). In addition, this is the first T-dwarf
companion discovered around a low mass star.


title:
Discovery of the Closest Brown Dwarf to the Sun? A Methane Rich Brown
  Dwarf around the Nearby M8.5 Star SCR 1845-6357

abstract:
  This paper was accidentally submitted twice to astro-ph. This version has
been withdrawn -- please see astro-ph/0601440 instead.


title: Smear fitting: a new deconvolution method for interferometric data

abstract:
  A new technique is presented for producing images from interferometric data.
The method, ``smear fitting'', makes the constraints necessary for
interferometric imaging double as a model, with uncertainties, of the sky
brightness distribution. It does this by modelling the sky with a set of
functions and then convolving each component with its own elliptical gaussian
to account for the uncertainty in its shape and location that arises from
noise. This yields much sharper resolution than CLEAN for significantly
detected features, without sacrificing any sensitivity. Using appropriate
functional forms for the components provides both a scientifically interesting
model and imaging constraints that tend to be better than those used by
traditional deconvolution methods. This allows it to avoid the most serious
problems that limit the imaging quality of those methods. Comparisons of smear
fitting to CLEAN and maximum entropy are given, using both real and simulated
observations. It is also shown that the famous Rayleigh criterion (resolution =
wavelength / baseline) is inappropriate for interferometers as it does not
consider the reliability of the measurements.


title: The C-flash and the ignition conditions of type Ia supernovae

abstract:
  Thanks to a stellar evolution code able to compute through the
  C-flash we link the binary population synthesis of single degenerate
progenitors of type Ia supernovae (SNe Ia) to their physical condition at the
time of ignition. We show that there is a large range of possible ignition
densities and we detail how their probability distribution depends on the
accretion properties. The low density peak of this distribution qualitatively
reminds of the clustering of the luminosities of Branch-normal SNe Ia. We
tighten the possible range of initial physical conditions for explosion models:
they form a one-parameter family, independent of the metallicity. We discuss
how these results may be modified if we were to relax our hypothesis of a
permanent Hachisu wind or if we were to include electron captures.


title: The OGLE-II event sc5_2859 : a Classical Nova outburst?

abstract:
  The OGLE-II event sc5_2859 was previously identified as the third longest
microlensing event ever observed. Additional photometric observations from the
EROS (Experience de Recherche d'Objets Sombres) survey and spectroscopic
observations of the candidate star are used to test the microlensing
hypothesis.The combined OGLE and EROS data provide a high quality coverage of
the light curve. The colour of the sc5_2859 event is seen to change with time.
A spectrum taken in 2003 exhibits a strong Halpha emission line. The
additionnal data show that the OGLE-II sc5_2859 event is actually a classical
nova outburst.


title: Microwave sky and the local Rees-Sciama effect

abstract:
  The microwave sky shows unexpected features at the largest angular scales,
among them the alignments of the dipole, quadrupole and octopole. Motivated by
recent X-ray cluster studies, we investigate the possibility that local
structures at the 100 h^(-1) Mpc scale could be responsible for such
correlations. These structures give rise to a local Rees-Sciama contribution to
the microwave sky that may amount to Delta T/T ~ 10^(-5) at the largest angular
scales. We model local structures by a spherical overdensity
(Lemaitre-Tolman-Bondi model) and assume that the Local Group is falling toward
the centre. We superimpose the local Rees-Sciama effect on a statistically
isotropic, gaussian sky. As expected we find alignments among low multipoles,
but a closer look reveals that they do not agree with the type of correlations
revealed by the data.


title:
Period-color and amplitude-color relations in classical Cepheid
  variables III: The Large Magellanic Cloud Cepheid models

abstract:
  Period-colour (PC) and amplitude-colour (AC) relations are studied for the
Large Magellanic Cloud (LMC) Cepheids under the theoretical framework of the
hydrogen ionization front (HIF) - photosphere interaction. LMC models are
constructed with pulsation codes that include turbulent convection, and the
properties of these models are studied at maximum, mean and minimum light. As
with Galactic models, at maximum light the photosphere is located next to the
HIF for the LMC models. However very different behavior is found at minimum
light. The long period (P>10days) LMC models imply that the photosphere is
disengaged from the HIF at minimum light, similar to the Galactic models, but
there are some indications that the photosphere is located near the HIF for the
short period (P<10 days) LMC models. We also use the updated LMC data to derive
empirical PC and AC relations at these phases. Our numerical models are broadly
consistent with our theory and the observed data, though we discuss some
caveats in the paper. We apply the idea of the HIF-photosphere interaction to
explain recent suggestions that the LMC period-luminosity (PL) and PC relations
are non-linear with a break at a period close to 10 days. Our empirical PC and
PL relations are also found to be non-linear with the F-test. Our explanation
relies on the properties of the Saha ionization equation, the HIF-photosphere
interaction and the way this interaction changes with the phase of pulsation
and metallicity to produce the observed changes in the Cepheid PC and PL
relations.


title:
Period-colour and amplitude-colour relations in classical Cepheid
  variables IV: The multi-phase relations

abstract:
  The superb phase resolution and quality of the OGLE data on LMC and SMC
Cepheids, together with existing data on Galactic Cepheids, are combined to
study the period-colour (PC) and amplitude-colour (AC) relations as a function
of pulsation phase. Our results confirm earlier work that the LMC PC relation
(at mean light) is more consistent with two lines of differing slopes,
separated at a period of 10 days. However, our multi-phase PC relations reveal
much new structure which can potentially increase our understanding of Cepheid
variables. These multi-phase PC relations provide insight into why the Galactic
PC relation is linear but the LMC PC relation is non-linear. This is because
the LMC PC relation is shallower for short (log P < 1) and steeper for long
(log P > 1) period Cepheids than the corresponding Galactic PC relation. Both
of the short and long period Cepheids in all three galaxies exhibit the
steepest and shallowest slopes at phases around 0.75-0.85, respectively. A
consequence is that the PC relation at phase ~0.8 is highly non-linear.
Further, the Galactic and LMC Cepheids with log P > 1 display a flat slope in
the PC plane at phases close to the maximum light. When the LMC
period-luminosity (PL) relation is studied as a function of phase, we confirm
that it changes with the PC relation. The LMC PL relation in V- and I-band near
the phase of 0.8 provides compelling evidence that this relation is also
consistent with two lines of differing slopes joined at a period close to 10
days.


title:
Discovery and application of Frequency Ratio Method to the new
  multiperiodic gamma Dor star HD 218427

abstract:
  gamma Dor-type oscillations have been discovered in the star HD218427 through
simultaneous uvby photometric observations carried out in the year 2003. A few
Hbeta-Crawford measurements were also collected for calibration purposes which
place this star well-located inside the gamma Dor instability region.
Deficiency in metal content, similar to other well-defined gamma Dor stars, is
found in HD218427 and the possibility of a lambda Boo nature is discussed.
Frequency analysis was carried out for different filters, the combined "vby"
filter was also used and five frequencies were found as significant with
periods ranging between 0.3 and 0.8 days. The recently developed Frequency
Ratio Method is used in order to perform an identification of the excited
modes. The results are consistent with an l=2 identification for all the modes
and high radial quantum numbers (n~40) for the three main observed
periodicities. The possibility of multiplet structures is also discussed.
However, no consistency is found when the Time-Dependent Convection treatment
is used for modes discrimination. The disagreement can be due to the large
rotation velocity taking place in HD218427 and, consequently, the significant
coupling between the modes.


title:
Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk
  data

abstract:
  We present the interpretation of the muon and scintillation signals of
ultra-high-energy air showers observed by AGASA and Yakutsk extensive air
shower array experiments. We consider case-by-case ten highest energy events
with known muon content and conclude that at the 95% confidence level (C.L.)
none of them was induced by a primary photon. Taking into account statistical
fluctuations and differences in the energy estimation of proton and photon
primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of
primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors
the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.


title: Upper limits on the central black hole masses of 47Tuc and NGC6397

abstract:
  We present upper-limits on the masses of the putative central
intermediate-mass black holes in two nearby Galactic globular clusters: 47Tuc
(NGC104), the second brightest Galactic globular cluster, and NGC6397, a
core-collapse globular cluster and, with a distance of 2.7 kpc, quite possibly
the nearest globular cluster, using a technique suggested by T. Maccarone.
These mass estimates have been derived from 3sigma upper limits on the radio
continuum flux at 1.4 GHz, assuming that the putative central black hole
accretes the surrounding matter at a rate between 0.1% and 1% of the Bondi
accretion rate. For 47Tuc, we find a 3sigma upper limit of 2060 - 670 solar
masses, depending on the actual accretion rate of the black hole and the
distance to 47Tuc. For NGC6397, which is closer to us, we derive a 3sigma upper
limit of 1290 - 390 solar masses. While estimating mass upper-limits based on
radio continuum observations requires making assumptions about the gas density
and the accretion rate of the black hole, their derivation does not require
complex and time consuming dynamical modeling. Thus, this method offers an
independent way of estimating black hole masses in nearby globular clusters.
If, generally, central black holes in stellar systems accrete matter faster
than 0.1% of the Bondi accretion rate, then these results indicate the absence
of black holes in these globular clusters with masses as predicted by the
extrapolated M-sigma relation.


title: Discovery of 35 New Supernova Remnants in the Inner Galaxy

abstract:
  We report the discovery of up to 35 new supernova remnants (SNRs) from a 42
arcsec resolution 90cm multi-configuration Very Large Array survey of the
Galactic plane covering 4.5 deg< l <22.0 deg and |b| < 1.25 deg. Archival 20cm,
11cm, and 8 micron data have also been used to identify the SNRs and constrain
their properties. The 90cm image is sensitive to SNRs with diameters 2.5 arcmin
to 50 arcmin and down to a surface brightness limit of about 10^{-21} W m^{-2}
Hz^{-1} sr^{-1}. This survey has nearly tripled the number of SNRs known in
this part of the Galaxy, and represents an overall 15% increase in the total
number of Galactic SNRs. These results suggest that further deep low frequency
surveys of the inner Galaxy will solve the discrepancy between the expected
number of Galactic SNRs and the significantly smaller number of currently known
SNRs.


title: AGN and Galaxy evolution from Deep X-ray surveys

abstract:
  Deep X-ray surveys are providing crucial information on the evolution of AGN
and galaxies. We review some of the latest results based on the X-ray spectral
analysis of the sources detected in the Chandra Deep Field South, namely: i)
constraints on obscured accretion; ii) constraints on the missing fraction of
the X-ray background; iii) the redshift distribution of Compton-thick sources
and TypeII QSO; iv) the detection of star formation activity in high-z galaxies
through stacking techniques; v) the detection of large scale structure in the
AGN distribution and its effect on nuclear activity. Such observational
findings are consistent with a scenario where nuclear activity and star
formation processes develop together in an anti-hierarchical fashion.


title: Observational constraints on the acceleration of the Universe

abstract:
  We propose a new parametrization of the deceleration parameter to study its
time-variation behavior. The advantage of parameterizing the deceleration
parameter is that we do not need to assume any underlying theory of gravity. By
fitting the model to the 157 gold sample supernova Ia data, we find strong
evidence that the Universe is currently accelerating and it accelerated in the
past. By fitting the model to the 115 nearby and Supernova Legacy Survey
supernova Ia data, the evidence that the Universe is currently accelerating is
weak, although there is still a strong evidence that the Universe once
accelerated in the past. The results obtained from the 157 gold sample
supernova Ia data and those from the 115 supernova Ia data are not directly
comparable because the two different data sets measure the luminosity distance
up to different redshifts.
  We then use the Friedmann equation and a dark energy parametrization to
discuss the same problem. When we fit the model to the supernova Ia data alone,
we find weak evidence that the Universe is accelerating and the current matter
density is higher than that measured from other experiments. After we add the
Sloan Digital Sky Survey data to constrain the dark energy model, we find that
the behavior of the deceleration parameter is almost the same as that obtained
from parameterizing the deceleration parameter.


title:
Constraints on SN Ia progenitor time delays from high-z SNe and the star
  formation history

abstract:
  We re-assess the question of a systematic time delay between the formation of
the progenitor and its explosion in a type Ia supernova (SN Ia) using the
Hubble Higher-z Supernova Search sample (Strolger et al. 2004). While the
previous analysis indicated a significant time delay, with a most likely value
of 3.4 Gyr, effectively ruling out all previously proposed progenitor models,
our analysis shows that the time-delay estimate is dominated by systematic
errors, in particular due to uncertainties in the star-formation history. We
find that none of the popular progenitor models under consideration can be
ruled out with any significant degree of confidence. The inferred time delay is
mainly determined by the peak in the assumed star-formation history. We show
that, even with a much larger Supernova sample, the time delay distribution
cannot be reliably reconstructed without better constraints on the
star-formation history.


title:
The Afterglow, Energetics and Host Galaxy of the Short-Hard Gamma-Ray
  Burst 051221a

abstract:
  We present detailed optical, X-ray and radio observations of the bright
afterglow of the short gamma-ray burst 051221a obtained with Gemini, Swift/XRT,
and the Very Large Array, as well as optical spectra from which we measure the
redshift of the burst, z=0.5464. At this redshift the isotropic-equivalent
prompt energy release was about 1.5 x 10^51 erg, and using the standard
afterglow synchrotron model we find that the blastwave kinetic energy is
similar, E_K,iso ~ 8.4 x 10^51 erg. An observed jet break at t ~ 5 days
indicates that the opening angle is ~ 7 degrees and the total beaming-corrected
energy is therefore ~ 2.5 x 10^49 erg, comparable to the values inferred for
previous short GRBs. We further show that the burst experienced an episode of
energy injection by a factor of 3.4 between t=1.4 and 3.4 hours, which was
accompanied by reverse shock emission in the radio band. This result provides
continued evidence that the central engines of short GRBs may be active
significantly longer than the duration of the burst and/or produce a wide range
of Lorentz factors. Finally, we show that the host galaxy of GRB051221a is
actively forming stars at a rate of about 1.6 M_solar/yr, but at the same time
exhibits evidence for an appreciable population of old stars (~ 1 Gyr) and near
solar metallicity. The lack of bright supernova emission and the low
circumburst density (n ~ 10^-3 cm^-3) continue to support the idea that short
bursts are not related to the death of massive stars and are instead consistent
with a compact object merger. Given that the total energy release is a factor
of ~ 10 larger than the predicted yield for a neutrino annihilation mechanism,
this suggests that magnetohydrodynamic processes may be required to power the
burst.


title:
The M_BH - T relation for a black hole in thermodynamic equilibrium with
  the surrounding intergalactic medium

abstract:
  I consider a toy model of self-regulated black hole accretion. The black hole
grows through Bondi accretion and a fraction of the accretion power is
distributed as thermal feedback into the surrounding gas. The gas expands or
contracts until AGN heating and radiative cooling balance each other. The
balance of heating and cooling is used to determine a quasi-equilibrium
temperature at which the black hole accretes in self-regulated equilibrium with
the surrounding intergalactic medium. This temperature grows with the black
hole mass. The temperature increase is very steep around a critical black hole
mass due to the shape of the cooling function. The quasi-equilibrium
temperature cannot exceed the virial temperature or the AGN will drive a
thermal wind. This limits the black hole mass to a maximum value determined by
the depth of the potential well. In the regime in which cooling is dominated by
bremsstrahlung, this model determines a relation between black hole mass and
halo characteristic velocity of the form M_BH ~ v^4. The predictions of the
model are consistent with the observed black hole mass -- bulge velocity
dispersion relation.


title: The Chang-Refsdal Lens Revisited

abstract:
  This paper provides a complete theoretical treatment of the point-mass lens
perturbed by constant external shear, often called the Chang-Refsdal lens. We
show that simple invariants exist for the products of the (complex) positions
of the four images, as well as moment sums of their signed magnifications. The
image topographies and equations of the caustics and critical curves are also
studied. We derive the fully analytic expressions for precaustics, which are
the loci of non-critical points that map to the caustics under the lens
mapping. They constitute boundaries of the region in the image domain that maps
onto the interior of the caustics. The areas under the critical curves,
caustics and precaustics are all evaluated, which enables us to calculate the
mean magnification of the source within the caustics. Additionally, the exact
analytic expression for the magnification distribution for the source in the
triangular caustics is derived, as well as a useful approximate expression.
Finally, we find that the Chang-Refsdal lens with the convergence greater than
unity can exhibit third-order critical behaviour, if the reduced shear is
exactly equal to \sqrt{3}/2, and that the number of images for N-point masses
with non-zero constant shear cannot be greater than 5N-1.


title: A Study of Compact Object Mergers as Short Gamma-ray Burst Progenitors

abstract:
  We present a theoretical study of double compact objects as potential
short/hard gamma-ray burst (GRB) progenitors. An updated population synthesis
code StarTrack is used to calculate properties of double neutron stars and
black-hole neutron star binaries. We obtain their formation rates, estimate
merger times and finally predict their most likely merger locations and
afterglow properties for different types of host galaxies. Our results serve
for a direct comparison with the recent HETE-II and SWIFT observations of
several short bursts, for which afterglows and host galaxies were detected. We
also discuss the possible constraints these observations put on the
evolutionary models of double compact object formation. We emphasize that our
double compact object models can successfully reproduce at the same time short
GRBs within both young, star-forming galaxies (e.g., GRB 050709 and GRB
051221A), as well as within old, elliptical hosts (e.g., GRB 050724 and
probably GRB 050509B)


title: Thermalisation of electrons in a stellar atmosphere

abstract:
  We are interested in electrons kinetics in a stellar atmosphere to validate
or invalidate the usually accepted hypothesis of thermalisation of electrons.
For this purpose, we calculate the velocity distribution function of electrons
by solving the kinetic equation of these particles together with the equations
of radiative transfer and statistical equilibrium. We note that this
distribution can deviate strongly from a Maxwell-Boltzmann distribution if
non-LTE effects are important. Some results and astrophysical consequences are
examined.


title:
The accuracy of the ALI method for solving the radiative transfer
  equation in stellar atmospheres

abstract:
  We test the accuracy of the ALI method, widely used in stellar atmosphere
modelling, by solving exactly a standard radiative transfer problem in
plane-parallel geometry. Some recommendations are given for a practical use of
this method.


title: Evolutionary state of magnetic chemically peculiar stars

abstract:
  We present a comprehensive statistical investigation of the evolution of
magnetic CP stars, aimed at providing constraints to the theories that deal
with the origin of the magnetic field in these stars. We have collected from
the literature data for 150 magnetic CP stars with accurate Hipparcos
parallaxes. We have retrieved from the ESO archive 142 FORS1 observations of
circularly polarized spectra for 100 stars. From these spectra we have measured
the mean longitudinal magnetic field, and discovered 48 new magnetic CP stars
(five of which belonging to the rare class of rapidly oscillating Ap stars). We
have determined effective temperature and luminosity, then mass and position in
the H-R diagram for a final sample of 194 magnetic CP stars. We found that
magnetic stars with M>3Msun are homogeneously distributed along the main
sequence. Instead, there are statistical indications that lower mass stars
(especially those with M<=2Msun) tend to concentrate in the centre of the main
sequence band. We show that this inhomogeneous age distribution cannot be
attributed to the effects of random errors and small number statistics. Our
data suggest also that the surface magnetic flux of CP stars increases with
stellar age and mass, and correlates with the rotation period. For stars with
M>3Msun, rotation periods decrease with age in a way consistent with the
conservation of the angular momentum, while for less massive magnetic CP stars
an angular momentum loss cannot be ruled out. The mechanism that originates and
sustains the magnetic field in the upper main sequence stars may be different
in CP stars of different mass.


title: Exact vs. Gauss-Seidel non-LTE radiation transfer solutions

abstract:
  Although published in 1995, the Gauss-Seidel method for solving the non-LTE
radiative transfer problem has deserved too little attention in the
astrophysical community yet. Further tests of the performances and of the
accuracy of the numerical scheme are provided.


title: On the normalisation of the cosmic star formation history

abstract:
  Strong constraints on the cosmic star formation history (SFH) have recently
been established using ultraviolet and far-infrared measurements, refining the
results of numerous measurements over the past decade. Taken together, the most
recent and robust data indicate a compellingly consistent picture of the SFH
out to redshift z~6, with especially tight constraints for z<~1. We fit these
data with simple analytical forms, and derive conservative bands to indicate
possible variations from the best fits. Since the z<~1 SFH data are quite
precise, we investigate the sequence of assumptions and corrections that
together affect the SFH normalisation, to test their accuracy, both in this
redshift range and beyond. As lower limits on this normalisation, we consider
the evolution in stellar mass density, metal mass density, and supernova rate
density, finding it unlikely that the SFH normalisation is much lower than
indicated by our direct fit. Additionally, predictions from the SFH for
supernova type Ia rate densities tentatively suggests delay times of ~3 Gyr. As
a corresponding upper limit on the SFH normalisation, we consider the
Super-Kamiokande (SK) limit on the electron antineutrino flux from past
core-collapse supernovae, which applies primarily to z<~1. We find consistency
with the SFH only if the neutrino temperatures from SN events are relatively
modest. Constraints on the assumed initial mass function (IMF) also become
apparent. The traditional Salpeter IMF, assumed for convenience by many
authors, is known to be a poor representation at low stellar masses (<~ 1 solar
mass), and we show that recently favoured IMFs are also constrained. In
particular, somewhat shallow, or top-heavy, IMFs may be preferred, although
they cannot be too top-heavy. (Abridged)


title: The puzzle of the soft X-ray excess in AGN: absorption or reflection?

abstract:
  The 2-10 keV continuum of AGN is generally well represented by a single power
law. However, at smaller energies the continuum displays an excess with respect
to the extrapolation of this power law, called the ''soft X-ray excess''. Until
now this soft X-ray excess was attributed, either to reflection of the hard
X-ray source by the accretion disk, or to the presence of an additional
comptonizing medium, giving a steep spectrum. An alternative solution proposed
by Gierlinski and Done (2004) is that a single power law well represents both
the soft and the hard X-ray emission and the impression of the soft X-ray
excess is due to absorption of a primary power law by a relativistic wind. We
examine the advantages and drawbacks of reflection versus absorption models,
and we conclude that the observed spectra can be well modeled, either by
absorption (for a strong excess), or by reflection (for a weak excess). However
the physical conditions required by the absorption models do not seem very
realistic: we would prefer an ''hybrid model''.