title:
A search for extragalactic H2O maser emission towards IRAS galaxies -
  Detection of a maser from an infrared-luminous merger, NGC6240

abstract:
  We report the result of an on-going survey for 22 GHz H2O maser emission
towards infrared luminous galaxies. The observed galaxies were selected
primarily from the IRAS bright galaxy sample. The survey has resulted in the
detection of one new maser. The new maser was discovered towards the
[U]LIRG/merger galaxy NGC6240, which contains a LINER nucleus. This is the
first detection of an H2O maser towards this class of galaxy, they are
traditionally associated with OH megamaser sources. The detected maser emission
is highly redshifted (~ 260-300 km/s) with respect to the adopted systemic
velocity of the galaxy, and we identified no other significant emission at
velocities < +- 500 km/s relative to the systemic velocity. The presence of
high-velocity maser emission implies the possible existence of a rotating maser
disk formed in the merging process. The large maser luminosity (~ 40 Lo)
suggests that an active galactic nucleus could be the energy source that gives
rise to the water emission. Alternatively, the maser emission could be
associated with the previously observed double radio source in the centre of
the galaxy. Interferometric observations with high angular resolution will be
able to clarify the origin of the new maser.


title: On the Merit of Observations Beyond the Cluster Core

abstract:
  I discuss recent seminal work on the LARCS dataset: a panoramic study of rich
clusters of galaxies at z~0.12. The importance of observing beyond the cluster
core is illustrated by exploiting these data to examine colour gradients across
the clusters.


title: Far-Infrared Emission from Intracluster Dust in Abell Clusters

abstract:
  The ISOPHOT instrument aboard ISO has been used to observe extended FIR
emission of six Abell clusters. The raw profiles of the I_(120 um) / I_(180 um)
surface brightness ratio including zodiacal light show a bump towards Abell
1656 (Coma), dips towards Abell 262 and Abell 2670, and are without clear
structure towards Abell 400, Abell 496, and Abell 4038. After subtraction of
the zodiacal light, the bump towards Abell 1656 is still present, while the
dips towards Abell 262 and Abell 2670 are no longer noticable. This indicates a
localized excess of emitting material outside the Galaxy towards Abell 1656,
while the behavior in Abell 262 and Abell 2670 can be reconciled with galactic
cirrus structures localized on the line-of-sight to these clusters. The excess
towards Abell 1656 (Coma) is interpreted as thermal emission from intracluster
dust distributed in the hot X-ray emitting intracluster medium. The absence of
any signature for intracluster dust in five clusters and the rather low
inferred dust mass in Abell 1656 indicates that intracluster dust is likely not
responsible for the excess X-ray absorption seen in cooling flow clusters.
These observations thereby represent a further unsuccessful attempt in
detecting the presumed final stage of the cooling flow material, in accord with
quite a number of previous studies in other wavelengths regions. Finally, the
observed dimming of the high-redshift supernovae is unlikely be attributable to
extinction caused by dust in the intracluster or even a presumed intercluster
medium.


title: On the primordial helium content: CMB and stellar constraints

abstract:
  We present the results of a joint investigation aimed at constraining the
primordial He content ($Y_P$) on the basis of both the Cosmic Microwave
Background (CMB) anisotropy and two stellar observables, namely the tip of the
Red Giant Branch (TRGB) and the luminosity of the Zero Age Horizontal Branch
(ZAHB). Current baryon density estimates based on CMB measurements cover a wide
range values $0.009\la \Omega_bh^2 \la 0.045$, that according to Big Bang
Nucleosynthesis (BBN) models would imply $0.24\la Y_P \la 0.26$. We constructed
several sets of evolutionary tracks and HB models by adopting $Y_P=0.26$ and
several metal contents. The comparison between theory and observations suggests
that ZAHB magnitudes based on He-enhanced models are 1.5$\sigma$ brighter than
the empirical ones. The same outcome applies for the TRGB bolometric
magnitudes. This finding somewhat supports a $Y_P$ abundance close to the
canonical 0.23-0.24 value. More quantitative constraints on this parameter are
hampered by the fact that the CMB pattern shows a sizable dependence on both
$Y_P$ and the baryon density only at small angular scales, i.e. at high l in
the power spectrum ($l\ga 100$). However, this region of the power spectrum
could be still affected by deceptive systematic uncertainties. Finally, we
suggest to use the {\em UV-upturn} to estimate the He content on Gpc scales. In
fact, we find that a strong increase in $Y_P$ causes in metal-poor, hot HB
structures a decrease in the UV emission.


title:
Potentials and distribution functions to be used for dynamical modeling
  with GAIA-like data

abstract:
  We present new tools to establish axisymmetric equilibrium models of the
Milky Way. The models we wish to establish are pairs (V,F) where V is the
gravitational potential generated by the whole mass distribution including the
dark matter, and F is the distribution function in phase space for late-type
tracer stars. We present a set of Stackel potentials that fit some fundamental
parameters of the Milky Way (mass density in the solar neighbourhood and Oort
constants). Then we define new component distribution functions that can be
combined with these potentials in order to reproduce kinematical data like
those that will be provided by GAIA.


title:
The host galaxy of GRB010222: The strongest damped Lyman-alpha system
  known

abstract:
  Analysis of the absorption lines in the afterglow spectrum of the gamma-ray
burst GRB010222 indicates that its host galaxy (at a redshift of z=1.476) is
the strongest damped Lyman-alpha (DLA) system known, having a very low
metallicity and modest dust content. This conclusion is based on the detection
of the red wing of Lyman-alpha plus a comparison of the equivalent widths of
ultraviolet Mg I, Mg II, and Fe II lines with those in other DLAs. The column
density of H I, deduced from a fit to the wing of Lyman-alpha, is (5 +/- 2)
10^22 cm^-2. The ratio of the column densities of Zn and Cr lines suggests that
the dust content in our line of sight through the galaxy is low. This could be
due to either dust destruction by the ultraviolet emission of the afterglow or
to an initial dust composition different to that of the diffuse interstellar
material, or a combination of both.


title:
The circumstellar material around SN IIn 1997eg: Another detection of
  Very Narrow P Cygni profile

abstract:
  We report the detection of a very narrow P Cygni profile on top of the broad
emission Ha and Hb lines of the Type IIn Supernova 1997eg. A similar feature
has been detected in SN 1997ab (Salamanca et al. 1998), SN 1998S (Meikle &
Geballe 1998, Fassia et al. 2001) and SN 1995G (Filippenko & Schlegel 1995).
The detection of the narrow P Cygni profile indicates the existence of a dense
circumstellar material (CSM) into which the ejecta of the supernova is
expanding. From the analysis of the spectra of SN 1997eg we deduce (a) that
such CSM is very dense (n ~ 5x10^7 cm^-3), (b) that has a low expanding
velocity of about 160 \kms. The origin of such dense CSM can be either a very
dense progenitor wind (dotM ~ 10^-2 solar masses per year) or a circumstellar
shell product of the progenitor wind expanding into a high pressure
environment.


title: Astronomical Seeing from the Summits of the Antarctic Plateau

abstract:
  From the South Pole, microthermal turbulence within a narrow surface boundary
layer some 200m thick provides the dominant contribution to the astronomical
seeing. We present results for the seeing at a wavelength of 2.4um. The narrow
turbulence layer above the site, confined close to the surface, provides
greatly superior conditions for adaptive optics correction than do temperate
latitude sites. An analysis of the available meteorological data for the
Antarctic plateau suggests that sites on its summit, such as Domes A and C,
probably experience significantly better boundary layer seeing than does the
South Pole. In addition, the inversion layers may be significantly narrower,
lending the sites even further to adaptive optics correction than does the
Pole.


title: MOND--a pedagogical review

abstract:
  An account is given of the development, and the status, of the modified
dynamics (MOND)--a proposed alternative to dark matter, which posits a
breakdown of Newtonian dynamics in the limit of small accelerations.


title: X-ray and optical periodicities in X-ray binaries. I.A0535+26

abstract:
  A homogeneous set of UBV photometry (354 data points obtained between 1983
and 1998) for the Be/X-ray binary A0535+26 = V725Tau is analysed, aiming to
look for possible periodic component(s). After subtraction of the long-term
variation it was found that only a 103-day periodic component remains in the
power spectra in both the V and B colour bands. The probability of chance
occurrence of such a peak is less than 0.1%. There are no signs of optical
variability at the X-ray period (111 d). We discuss possible reasons for a
103-day modulation and suggest that it corresponds to a beat frequency of the
orbital period of the neutron star and the precession period (~1400 d) either
of an accretion disc around the neutron star or a warped decretion disc around
the Be star.


title:
A new approach to inferring the mass composition of cosmic rays at
  energies above 10^18 eV

abstract:
  We describe a new approach to establishing the mass composition at high
energies. Based on measuring both the vertical and inclined shower rates, it
has the potential to distinguish heavy nuclei from light nuclei. We apply the
method to Haverah Park data above 10^18 eV to show that, under the assumption
that the Quark Gluon String Jet Model correctly describes the high energy
interactions, the inclined shower measurements favour a light composition at
energies above 10^19 eV. The same conclusion is obtained using a variety of
assumptions about the cosmic ray spectrum. To the extent that precise spectral
measurements will be possible by forthcoming experiments such as the Auger
observatories, the method will further constrain data on composition of the
ultra high energy cosmic rays.


title: The Big Flow

abstract:
  The late infall of cold dark matter onto an isolated galaxy, such as our own,
produces streams and caustics in its halo. The outer caustics are topological
spheres whereas the inner caustics are rings. The self-similar model of
galactic halo formation predicts that the caustic ring radii $a_n$ follow the
approximate law $a_n \sim 1/n$. In a study of 32 extended and well-measured
external galactic rotation curves evidence was found for this law. In the case
of the Milky Way, the locations of eight sharp rises in the rotation curve fit
the prediction of the self-similar model at the 3% level. Moreover, a
triangular feature in the IRAS map of the galactic plane is consistent with the
imprint of a ring caustic upon the baryonic matter. These observations imply
that the dark matter in our neighborhood is dominated by a single flow.
Estimates of that flow's density and velocity vector are given.


title: The high-field magnetic white dwarf LP 790-29: not a fast rotator

abstract:
  We have investigated the nature of the magnetic white dwarf LP 790-29 = LHS
2293 by polarimetric monitoring, searching for short-term variability. No
periodicity was found and we can exclude rotation periods between 4 sec and 1.5
hour with a high confidence. Maximum amplitudes of sinusoidal variations are
Delta R < 0.009 mag and Delta V_R < 0.7% for a mean value of the R-band
circular polarization of V_R = +9.1+/-0.3%. Combined with earlier results by
other authors, our observation suggests that LP 790-29 is, in fact, an
extremely slowly rotating single white dwarf and not an unrecognized fast
rotator and/or disguised cataclysmic variable.


title:
Radio-to-FIR Spectral Energy Distribution and Photometric Redshifts for
  Dusty Starburst Galaxies

abstract:
  As a logical next step in improving the radio-to-submm spectral index as a
redshift indicator (Carilli & Yun 1999), we have investigated a technique of
using the entire radio-to-FIR spectral energy distribution (SED) for deriving
photometric redshifts for dusty starburst galaxies at high redshift. A dusty
starburst SED template is developed from theoretical understanding on various
emission mechanisms related to massive star formation process, and the template
parameters are selected by examining the observed properties of 23 IR selected
starburst galaxies: $T_d=58$ K, $\beta=1.35$, and $f_{nth}=1$. The major
improvement in using this template SED for deriving photometric redshifts is
the significant reduction in redshift uncertainty over the spectral index
technique, particularly at higher redshifts. Intrinsic dispersion in the radio
and FIR SEDs as well as absolute calibration and measurement errors contribute
to the overall uncertainty of the technique. The derived photometric redshifts
for five submm galaxies with known redshifts agree well with their
spectroscopic redshifts within the estimated uncertainty. Photometric redshifts
for seven submm galaxies without known spectroscopic redshifts (HDF850.1,
CUDSS14.1, Lockman850.1, SMM J00266+1708, SMM J09429+4658, SMM J14009+0252,
FIRBACK J1608+5418) are derived.


title: VLT observations of the z=6.28 quasar SDSS 1030+0524

abstract:
  We present new VLT spectroscopic observations of the most distant quasar
known, SDSS J1030+0524 at z=6.28 which was recently discovered by the Sloan
Digital Sky Survey. We confirm the presence of a complete Gunn-Peterson trough
caused by neutral hydrogen in the intergalactic medium. There is no detectable
flux over the wavelength range from 8450 to 8710 A. We set an improved limit on
the drop of the flux level blueward of the Ly alpha line: a factor of
  > 200. Below 8450 A the spectrum shows a rise in flux, with a large fraction
(> 60 %) of the total emission produced by few narrow features of transmitted
flux. We discuss the obvious proximity effect around this quasar, with the
presence of transmitted flux with many absorption features in a region of about
23h^{-1} comoving Mpc. If assuming the surrounding medium were completely
neutral, the size of this region would imply a quasar lifetime of \~1.3x10^7
years.
  We also present near-IR spectroscopy of both SDSS J1030+0524 and of SDSS
J1306+05, the second most distant quasar known at redshift 6.0. We combine
measurements of the CIV line and limits on the HeII emission with the NV line
measurements from the optical spectra to derive line ratios, and by implication
the abundances of these early quasar environments. The results are
indistinguishable from those of lower redshift quasars and indicate little or
no evolution in the abundances from z ~ 6 to z ~ 2. The line ratios suggest
supersolar metallicities, implying that the first stars around the quasars must
have formed at least a few hundreds of Myrs prior to the observation, i.e. at
redshift higher than 8.


title: Isolated and Interacting Galaxies : Simulations with GRAPE

abstract:
  I present N-body simulations of isolated and interacting galaxies, made on
GRAPE machines. In particular I discuss the formation and evolution of N-body
bars and compare their properties to those of bars in early-type and late-type
galactic discs. I argue that the halo can help the bar grow, contrary to
previous beliefs, by taking positive angular momentum from it via its resonant
stars. I then focus on the interaction and subsequent merging of a barred disc
galaxy with a spheroidal satellite. The evolution depends strongly on the mass
(density) of the satellite and may lead to its destruction or to the
destruction of the bar.


title: New Results on Bar-Halo Interactions

abstract:
  In this paper I argue that, far from necessarily hindering bar formation in
disc galaxies, inner haloes may stimulate it. This constitutes a new
instability mechanism by which bars can grow. To show this I use a number of
N-body simulations whose initial conditions have identical discs and more or
less concentrated haloes. They show that the bar that grows in the more
halo-dominated environment is considerably stronger than the bar that grows in
the more disc-dominated environment. This result is obtained from simulations
with live haloes, i.e. composed of particles which respond to the disc and take
part in the evolution. On the other hand, if the halo is rigid, it hinders or
quenches bar formation, as expected. Comparison of two simulations which are
identical in everything, except that the halo is live in the first one and
rigid in the second one, leads me to suggest that the halo response can help
the bar grow. Following the orbits of the stars in the halo, I find that a
considerable fraction of the halo particles are in resonance with the bar. The
halo may thus take angular momentum from the bar and stimulate its growth. I
finally discuss whether and how the results of the N-body simulations can be
applied to real galaxies.


title: On a Formation Scenario of Star Clusters

abstract:
  Most formation scenarios of globular clusters assume a molecular cloud as the
progenitor of the stellar system. However, it is still unclear, how this cloud
is transformed into a star cluster, i.e. how the destructive processes related
to gas removal or low star formation efficiency can be avoided. Here a scheme
of supernova (SN) induced cluster formation is studied. According to this
scenario an expanding SN shell accumulates the mass of the cloud. This is
accompanied by fragmentation resulting in star formation in the shell. Provided
the stellar shell expands sufficiently slow, its self-gravity stops the
expansion and the shell recollapses, by this forming a stellar system.
  I present N-body simulations of collapsing shells which move in a galactic
potential on circular and elliptic orbits. It is shown that typical shells
(10^5 Msun, 30 pc) evolve to twin clusters over a large range of galactocentric
distances. Outside this range single stellar systems are formed, whereas at
small galactocentric distances the shells are tidally disrupted. In that case
many small fragments formed during the collapse survive as single bound
entities. About 1/3 of the twin cluster systems formed on circular orbits merge
within 400 Myr. On elliptic orbits the merger rate reduces to less than 4%.
Thus, there could be a significant number of twin clusters even in our Galaxy,
which, however, might be undetected as twins due to a large phase shift on
their common orbit.


title: Non-singular big-bounces and evolution of linear fluctuations

abstract:
  We consider evolutions of linear fluctuations as the background Friedmann
world model goes from contracting to expanding phases through smooth and
non-singular bouncing phases. As long as the gravity dominates over the
pressure gradient in the perturbation equation the growing-mode in the
expanding phase is characterized by a conserved amplitude, we call it a C-mode.
In the spherical geometry with a pressureless medium, we show that there exists
a special gauge-invariant combination \Phi which stays constant throughout the
evolution from the big-bang to the big-crunch with the same value even after
the bounce: it characterizes the coefficient of the C-mode. We show this result
by using a bounce model where the pressure gradient term is negligible during
the bounce; this requires additional presence of an exotic matter. In such a
bounce, even in more general situations of the equation of states before and
after the bounce, the C-mode in the expanding phase is affected only by the
C-mode in the contracting phase, thus the growing mode in the contracting phase
decays away as the world model enters expanding phase. In the case the
background curvature has significant role during the bounce, the pressure
gradient term becomes important and we cannot trace C-mode in the expanding
phase to the one before the bounce. In such situations, perturbations in a
fluid bounce model show exponential instability, whereas the ones in a scalar
field bounce model show oscillatory behaviors.


title: HI and dark matter in spiral galaxies

abstract:
  We still do not have a "standard" model for the mass distribution of spiral
galaxies. I review various methods used to delimit the range of values of the
mass-to-light ratio of the disk, such as spiral structure criteria, the
influence of bars, warped and flaring HI layers, velocity dispersions, and
features in the rotation curve occuring just beyond the optical radius. It is
not yet clear whether disks are maximal or not.


title: Exchange Processes in a Multi-Phase ISM

abstract:
  We present a new particle based code with a multi-phase description of the
ISM implemented in order to follow the chemo-dynamical evolution of galaxies.
The multi-phase ISM consists of clouds (sticky particles) and diffuse gas
(SPH): Exchange of matter, energy and momentum is achieved by drag (due to ram
pressure) and condensation or evaporation. Based on time scales we show that in
Milky-Way-like galaxies the drag force is for molecular clouds only important,
if their relative velocities exceed 100 km/s. For the mass exchange we find
that clouds evaporate only if the temperature of the ambient gas is higher than
one million Kelvin. At lower temperatures condensation takes place at time
scales of the order of 1-10 Gyr.


title: The dynamics of S0 galaxies and their Tully-Fisher relation

abstract:
  This paper investigates the detailed dynamical properties of a relatively
homogeneous sample of disc-dominated S0 galaxies, with a view to understanding
their formation, evolution and structure. By using high signal-to-noise ratio
long-slit spectra of edge-on systems, we have been able to reconstruct the
complete line-of-sight velocity distributions of stars along the galaxies'
major axes. From these data, we have derived both model distribution functions
(the phase density of their stars) and the approximate form of their
gravitational potentials. The derived distribution functions are all consistent
with these galaxies being simple disc systems, with no evidence for a complex
formation history. Essentially no correlation is found between the
characteristic mass scale-lengths and the photometric scale-lengths in these
galaxies, suggesting that they are dark-matter dominated even in their inner
parts. Similarly, no correlation is found between the mass scale-lengths and
asymptotic rotation speed, implying a wide range of dark matter halo
properties. By comparing their asymptotic rotation speeds with their absolute
magnitudes, we find that these S0 galaxies are systematically offset from the
Tully-Fisher relation for later-type galaxies. The offset in luminosity is what
one would expect if star formation had been suddenly switched off a few Gyrs
ago, consistent with a simple picture in which these S0s were created from
ordinary later-type spirals which were stripped of their star-forming ISM when
they encountered a dense cluster environment.


title:
Afterglow lightcurves, viewing angle and the jet structure of gamma-ray
  bursts

abstract:
  Gamma ray bursts are often modelled as jet-like outflows directed towards the
observer; the cone angle of the jet is then commonly inferred from the time at
which there is a steepening in the power-law decay of the afterglow. We
consider an alternative model in which the jet has a beam pattern where the
luminosity per unit solid angle (and perhaps also the initial Lorentz factor)
decreases smoothly away from the axis, rather than having a well-defined cone
angle within which the flow is uniform. We show that the break in the afterglow
light curve then occurs at a time that depends on the viewing angle. Instead of
implying a range of intrinsically different jets - some very narrow, and others
with similar power spread over a wider cone - the data on afterglow breaks
could be consistent with a standardized jet, viewed from different angles. We
discuss the implication of this model for the luminosity function.


title:
A probable planetary companion to HD 39091 from the Anglo-Australian
  Planet Search

abstract:
  We report the detection of a extrasolar planet candidate orbiting the G1 V
star HD 39091. The orbital period is 2083 d and the eccentricity is 0.62. With
a minimum (M sin $i$) mass of 10.3 M$_{\rm JUP}$ this object falls near the
high mass end of the observed planet mass function, and may plausibly be a
brown dwarf. Other characteristics of this system, including orbital
eccentricity and metallicity, are typical of the well populated class of radial
velocity planets in eccentric orbits around metal-rich stars.


title:
On the effects of the stellar magnetic field on the structure of T Tauri
  accretion discs

abstract:
  The structure of accretion discs around magnetic T Tauri stars is numerically
calculated using a particle hydrodynamical code, in which magnetic interaction
is included in the framework of King's diamagnetic blob accretion model.
Setting up the calculation so as to simulate the density structure of a
quasi-steady disc in the equatorial plane of a T Tauri star, we find that the
central star's magnetic field typically produces a central hole in the disc and
spreads out the surface density distribution. We argue that this result
suggests a promising mechanism for explaining the unusual flatness (IR excess)
of T Tauri accretion disc spectra.


title:
An HST Census of Nuclear Star Clusters in Late-Type Spiral Galaxies: I.
  Observations and Image Analysis

abstract:
  We present new HST I-band images of a sample of 77 nearby, late-type spiral
galaxies with low inclination. The main purpose of this catalog is to study the
frequency and properties of nuclear star clusters. In 59 galaxies of our
sample, we have identified a distinct, compact (but resolved), and dominant
source at or very close to their photocenter. In many cases, these clusters are
the only prominent source within a few kpc from the galaxy nucleus. We present
surface brightness profiles, derived from elliptical isophote fits, of all
galaxies for which the fit was successful. We use the fitted isophotes at radii
larger than 2" to check whether the location of the cluster coincides with the
photocenter of the galaxy, and confirm that in nearly all cases, we are truly
dealing with ``nuclear'' star clusters. From analytical fits to the surface
brightness profiles, we derive the cluster luminosities after subtraction of
the light contribution from the underlying galaxy disk and/or bulge.


title: Gamma-Ray Burst Afterglows in Pulsar-Wind Bubbles

abstract:
  We propose to identify pulsar-wind bubbles (PWBs) as the environment in which
the afterglow emission in at least some gamma-ray bursts (GRBs) originates.
Such bubbles could naturally account for the high fraction of the internal
energy residing in relativistic electrons/positrons ($\epsilon_e$) and the high
magnetic-to-internal energy ratio ($\epsilon_B$) that have been inferred in a
number of sources. GRBs might occur within PWBs under a number of scenarios: in
particular, in the supranova model of GRB formation a prolonged (months to
years) period of intense pulsar-type wind from the GRB progenitor precedes the
burst. Focusing on this scenario, we construct a simple model of the early-time
structure of a plerionic supernova remnant. The model is based on the
assumption of an ``equipartition'' upper bound on the electromagnetic-
to-thermal pressure ratio in the bubble and takes into account synchrotron-
radiation cooling. We derive an expression for the effective hydrogen number
density $n_{H,equiv}$ of the shocked pulsar wind in terms of the comoving
particle pressure and electromagnetic fields. We show that, for plausible
parameter values, $n_{H,equiv}$ spans the range inferred from spectral fits to
GRB afterglows and that its radial profile varies within the bubble and may
resemble a uniform interstellar medium or a stellar wind. We consider how the
standard expressions for the characteristic synchrotron spectrum are modified
when the afterglow-emitting shock propagates inside a PWB and demonstrate that
the predictions for the empirically inferred values of $\epsilon_e$ and
$\epsilon_B$ are compatible with the observations. Finally, we outline a
self-consistent interpretation of the X-ray emission features detected in
sources like GRB 991216 in the context of the supranova/PWB picture.


title: The Formation of the First Star in the Universe

abstract:
  We describe results from a fully self-consistent three dimensional
hydrodynamical simulation of the formation of one of the first stars in the
Universe. Dark matter dominated pre-galactic objects form because of
gravitational instability from small initidal density perturbations. As they
assemble via hierarchical merging, primordial gas cools through ro-vibrational
lines of hydrogen molecules and sinks to the center of the dark matter
potential well. The high redshift analog of a molecular cloud is formed. When
the dense, central parts of the cold gas cloud become self-gravitating, a dense
core of approximately 100 solar mass undergoes rapid contraction. At densities
n>10^9 cm^-3 a one solar mass proto-stellar core becomes fully molecular due to
three-body H_2 formation. Contrary to analytical expectations this process does
not lead to renewed fragmentation and only one star is formed. The calculation
is stopped when optical depth effects become important, leaving the final mass
of the fully formed star somewhat uncertain. At this stage the protostar is
acreting material very rapidly (~0.01 solar masses per year). Radiative
feedback from the star will not only halt its growth but also inhibit the
formation of other stars in the same pre-galactic object (at least until the
first star ends its life, presumably as a supernova). We conclude that at most
one massive (M >> 1 solar mass) metal free star forms per pre-galactic halo,
consistent with recent abundance measurements of metal poor galactic halo
stars.


title:
Achieving Extreme Resolution in Numerical Cosmology Using Adaptive Mesh
  Refinement: Resolving Primordial Star Formation

abstract:
  As an entry for the 2001 Gordon Bell Award in the "special" category, we
describe our 3-d, hybrid, adaptive mesh refinement (AMR) code, Enzo, designed
for high-resolution, multiphysics, cosmological structure formation
simulations. Our parallel implementation places no limit on the depth or
complexity of the adaptive grid hierarchy, allowing us to achieve unprecedented
spatial and temporal dynamic range. We report on a simulation of primordial
star formation which develops over 8000 subgrids at 34 levels of refinement to
achieve a local refinement of a factor of 10^12 in space and time. This allows
us to resolve the properties of the first stars which form in the universe
assuming standard physics and a standard cosmological model. Achieving extreme
resolution requires the use of 128-bit extended precision arithmetic (EPA) to
accurately specify the subgrid positions. We describe our EPA AMR
implementation on the IBM SP2 Blue Horizon system at the San Diego
Supercomputer Center.


title: Circular polarization from stochastic synchrotron sources

abstract:
  The transfer of polarized radiation in stochastic synchrotron sources is
explored by means of analytic treatment and Monte Carlo simulations. We argue
that the main mechanism responsible for the circular polarization properties of
compact synchrotron sources is likely to be Faraday conversion and that,
contrary to common expectation, a significant rate of Faraday rotation does not
necessarily imply strong depolarization. The long-term persistence of the sign
of circular polarization, observed in many sources, is most likely due to a
small net magnetic flux generated in the central engine, carried along the jet
axis and superimposed on a highly turbulent magnetic field. We show that the
mean levels of circular and linear polarizations depend on the number of field
reversals along the line of sight and that the gradient in Faraday rotation
across turbulent regions can lead to ``correlation depolarization''. Our model
is potentially applicable to a wide range of synchrotron sources. In
particular, we demonstrate how our model can naturally explain the excess of
circular over linear polarization in the Galactic Center and the nearby spiral
galaxy M81 and discuss its application to the quasar 3C 279, the intraday
variable blazar PKS 1519-273 and the X-ray binary SS 433.


title: Scalar field description of decaying-$\Lambda$ cosmologies

abstract:
  The conditions under which cosmologies driven by time varying cosmological
terms can be described by a scalar field coupled to a perfect fluid are
discussed. An algorithm to reconstruct potentials dynamically and
thermodynamically analogue to given phenomenological $\Lambda$ models is
presented. As a worked example, the deflationary cosmology, which evolves from
a pure de Sitter vacuum state to a slightly modified FRW cosmology is
considered. It is found that this is an example of nonsingular warm inflation
with an asymptotic exponential potential. Differences with respect to other
scalar field descriptions of decaying vacuum cosmologies are addressed and
possible extensions are indicated.


title:
Systolic and Hyper-Systolic Algorithms for the Gravitational N-Body
  Problem, with an Application to Brownian Motion

abstract:
  A systolic algorithm rhythmically computes and passes data through a network
of processors. We investigate the performance of systolic algorithms for
implementing the gravitational N-body problem on distributed-memory computers.
Systolic algorithms minimize memory requirements by distributing the particles
between processors. We show that the performance of systolic routines can be
greatly enhanced by the use of non-blocking communication, which allows
particle coordinates to be communicated at the same time that force
calculations are being carried out. Hyper-systolic algorithms reduce the
communication complexity at the expense of increased memory demands. As an
example of an application requiring large N, we use the systolic algorithm to
carry out direct-summation simulations using 10^6 particles of the Brownian
motion of the supermassive black hole at the center of the Milky Way galaxy. We
predict a 3D random velocity of 0.4 km/s for the black hole.


title: Outflow 20--2000 AU from a High-Mass Protostar in W51-IRS2

abstract:
  We present the results of the first high angular resolution observations of
SiO maser emission towards the star forming region W51-IRS2 made with the Very
Large Array (VLA) and Very Long Baseline Array (VLBA). Our images of the water
maser emission in W51-IRS2 reveal two maser complexes bracketing the SiO maser
source. One of these water maser complexes appears to trace a bow shock whose
opening angle is consistent with the opening angle observed in the distribution
of SiO maser emission. A comparison of our water maser image with an image
constructed from data acquired 19 years earlier clearly shows the persistence
and motion of this bow shock. The proper motions correspond to an outflow
velocity of 80 km/s, which is consistent with the data of 19 years ago (that
spanned 2 years). We have discovered a two-armed linear structure in the SiO
maser emission on scales of ~25 AU, and we find a velocity gradient on the
order of 0.1 km/s/AU along the arms. We propose that the SiO maser source
traces the limbs of an accelerating bipolar outflow close to an obscured
protostar. We estimate that the outflow makes an angle of <20 degrees with
respect to the plane of the sky. Our measurement of the acceleration is
consistent with a reported drift in the line-of-sight velocity of the W51 SiO
maser source.


title:
Are Omega Centauri and G1 like massive globular clusters the remnant
  cores of infalling dwarf galaxies? -- Dynamical constraints

abstract:
  We simulate the result of orbital decay for a dwarf satellite galaxy in a
disk galaxy potential. The peeling-off of the satellite by the strong tidal
field within the disk of the host galaxy quickly reduces the satellite's mass,
and drastically slows down the decaying of the orbit. The result is generally a
cluster on a large halo orbit, like the M54 cluster of the Sagittarius galaxy
in the Milky Way and the massive G1 cluster in outer halo of M31. It is
generally challenging for this mechanism to deliver globular cluster-mass
objects to the observed very close-in orbit of Omega Cen unless the dwarf
galaxy was born within a few scale lengths of the Galactic disk.


title: Spectral Evidence for Widespread Galaxy Outflows at z>4

abstract:
  We present discovery spectra of a sample of eight lensed galaxies at high
redshift, 3.7<z<5.2, selected by their red colors in the fields of four massive
clusters: A1689, A2219, A2390, and AC114. Metal absorption lines are detected
and observed to be blueshifted by 300-800 km/s with respect to the centroid of
Ly-alpha emission. A correlation is found between this blueshift and the
equivalent width of the metal lines, which we interpret as a broadening of
saturated absorption lines caused by a dispersion in the outflow velocity of
interstellar gas. Local starburst galaxies show similar behavior, associated
with obvious gas outflows. We also find a trend of increasing equivalent width
of Ly-alpha emission with redshift, which may be a genuine evolutionary effect
towards younger stellar populations at high redshift with less developed
stellar continua. No obvious emission is detected below the Lyman limit in any
of our spectra, nor in deep U or B-band images. The UV continua are reproduced
well by early B-stars, although some dust absorption would allow a fit to
hotter stars. After correcting for the lensing, we derive small physical sizes
for our objects, ~0.5-5 kpc/h for a flat cosmology with Omega_m=0.3,
Omega_Lambda=0.7. The lensed images are only marginally resolved in good seeing
despite their close proximity to the critical curve, where large arcs are
visible and hence high magnifications of up to ~20x are inferred. Two objects
show a clear spatial extension of the Ly-alpha emission relative to the
continuum starlight, indicating a ``breakout'' of the gas. The sizes of our
galaxies together with their large gas motion suggests that outflows of gas are
common at high redshift and associated with galaxy formation.


title: Feeding black holes at galactic centres by capture from isothermal cusps

abstract:
  We estimate the rate at which stars are captured by supermassive black holes
(BHs) in the centres of bulges and elliptical galaxies assuming that these
initially had an isothermal cusp (rho ~ r^{-2} with velocity dispersion
sigma_*). If radial orbits can be adequately replenished a BH can grow
significantly by capturing stars and particles of the dark halo; the latter
could be up to 20--40 percent of the total mass captured. A tight relation M_bh
10^8 (sigma_*/200\kms)^5 between BH hole mass and stellar velocity dispersion
arises at the high mass end M_bh >= 10^8 M_sun if these giant BHs grow
primarily by swallowing stars. For smaller masses a gradual flattening of the
relation and an increase of the scatter are expected due to tidal disruption of
stars. At moderate redshifts when bright galaxies may still possess isothermal
cusps tidal disruption flares may be as frequent as 10^{-4} -- 10^{-2} yr^{-1}
per galaxy, a few percent of the supernovae rate. Efficient randomization of
the orbits can occur when the dense cores of infalling satellites sink to the
sphere of influence of the BH by dynamical friction. Efficient replenishment of
the loss cone of radial orbits can also explain why the supermassive binary BHs
expected in hierarchically merging galaxies do generally coalesce, as suggested
by the observed relation between BH mass and the inferred mass of stars ejected
from an isothermal cusp.


title: Chandra X-ray Imaging and Spectroscopy of the M87 Jet and Nucleus

abstract:
  We report X-ray imaging - spectroscopy of the jet of M87 at sub arc second
resolution with the Chandra X-ray Observatory. The galaxy nucleus and all the
knots seen at radio and optical wavelengths, as far from the nucleus as knot C,
are detected in the X-ray observations. There is a strong trend for the ratio
of X-ray to radio, or optical, flux to decline with increasing distance from
the nucleus. At least three knots are displaced from their radio/optical
counterparts, being tens of pc closer to the nucleus at X-ray than at radio or
optical wavelengths. The X-ray spectra of the nucleus and knots are well
described by power laws absorbed by cold gas, with only the unresolved nucleus
exhibiting intrinsic absorption. In view of the similar spectra of the nucleus
and jet knots, and the high X-ray flux of the knots closest to the nucleus, we
suggest that the X-ray emission coincident with the nucleus may actually
originate from the pc - or sub-pc - scale jet rather than the accretion disk.
  Arguments are given that the X-ray emission process is unlikely to be inverse
Compton scattering. Instead, we favor synchrotron radiation. Plotted as
$\nu$S$_{\rm \nu}$, the spectra of the knots generally peak in or just above
the optical - near infrared band. However, the overall spectra of at least
three knots cannot be described by simple models in which the spectral index
monotonically increases with frequency, as would result from synchrotron losses
or a high energy cut-off to the injected electron spectrum. Instead, these
spectra must turn down just above the optical band and then flatten in the
X-ray band. (Abstract truncated)


title: Structure and Instabilities of an Irradiated Viscous Protoplanetary Disk

abstract:
  We investigate the structure and the stabilities of a protoplanetary disk,
which is heated by viscous process in itself and by its central star. The disk
is set to rotate with the Keplerian velocity and has the surface density
distribution of the minimum mass solar nebula. We assume the vertical
hydrostatic equilibrium and the radiative equilibrium at each point, and solve
the two-dimensional radiative transfer equation by means of the Short
Characteristic method in the spherical coordinate in order to determine the
disk structure. Our calculation shows that at the outer region of the disk with
a distance from the central star of x>1AU the radiative heating from the inner
disk dominates the viscous heating even near the midplane. It is because of the
high temperature distribution in the optically thin surface layer and the
relatively high disk height as a consequence of the irradiation from the inner
hot region of the disk. In addition, we examine the convective and the
magnetorotational instabilities of the disk. As a result, the whole disk is
convectively stable since the dusty region is not heated by the viscous
dissipation from the midplane but by the radial radiative heating. On the other
hand, almost all the disk is magnetorotationally unstable except for the region
near the equatorial plane of from 2AU to 10AU. Finally we discuss the growth
and the size distribution of dust particles in the disk, which suggests that
there exist cm-sized particles in the surface layer, namely, in the exposed
region of the disk.


title: Principal component analysis for spectral indices of stellar populations

abstract:
  We apply the method of principal component analysis to a sample of simple
stellar populations to select some age-sensitive spectral indices. Besides the
well-known age-sensitive index, H B, we find that some other spectral indices
have great potential to determine the age of stellar populations, such as
G4300, Fe4383, C24668, and Mgb. In addition, we find that the sensitivity to
age of these spectral indices depends on the metallicity of the simple stellar
population (SSP): H B and G4300 are more suited to determine the age of the
low-metallicity stellar population, C24668 and Mgb are more suited to the
high-metallicity stellar population. The results suggest that the principal
component analysis method provides a more objective and informative alternative
to diagnostics by individual spectral lines.


title: The nature of faint submm-selected galaxies

abstract:
  We present the source catalogue for the SCUBA Lens Survey. We summarise the
results of extensive multi-wavelength observations of the 15
submillimetre-selected galaxies in the catalogue, from X-rays to radio. We
discuss the main observational characteristics of faint submillimetre galaxies
as a population, and consider their interpretation within the framework of our
understanding of galaxy formation and evolution.


title: Dynamical Evidence for a Black Hole in the Microquasar XTE J1550-564

abstract:
  Optical spectroscopic observations of the companion star (type G8IV to K4III)
in the microquasar system XTE J1550-564 reveal a radial velocity curve with a
best fitting spectroscopic period of P_sp = 1.552 +/- 0.010 days and a
semiamplitude of K_2 = 349 +/- 12 km/s. The optical mass function is f(M) =
6.86 +/- 0.71 solar masses (1 sigma). We tentatively measure the rotational
velocity of the companion star to be V_rot*sin(i) = 90 +/- 10 km/s, which when
taken at face value implies a mass ratio of Q = M_1/M_2 = 6.6 (+2.5 / -1.6) (1
sigma), using the above value of K_2. We derive constraints on the binary
parameters from simultaneous modelling of the ellipsoidal light and radial
velocity curves. We find the most likely value of the mass of the compact
object is 9.41 solar masses with a 1 sigma range of 8.36 < M_1 < 10.76 solar
masses. If we apply our tentative value of V_rot*sin(i) = 90 +/- 10 km/s as an
additional constraint in the ellipsoidal modelling, we find the most likely
value of the mass of the compact object is 10.56 solar masses with a 1 sigma
range of 9.68 < M_1 < 11.58 solar masses. In either case the mass of the
compact object is well above the maximum mass of a stable neutron star, and we
therefore conclude XTE J1550-564 contains a black hole.


title: Transients from Zel'dovich initial conditions

abstract:
  We investigate the error implied by the use of the Zel'dovich approximation
to set up the initial conditions at a finite redshift zi in numerical
simulations. Using a steepest-descent method developed in a previous work we
derive the probability distribution P(delta_R) of the density contrast in the
quasi-linear regime. This also provides its dependence on the redshift zi at
which the simulation is started. Thus, we find that the discrepancy with the
exact pdf (defined by the limit zi->infinity) is negligible after the scale
factor has grown by a factor a/a_i>5, for scales which were initially within
the linear regime with sigma_i>0.1. This shows that the use of the Zel'dovich
approximation to implement the initial conditions is sufficient for practical
purposes since these are not very severe constraints.


title:
Resolved Near-Infrared Spectroscopy of the Mysterious Pre-Main Sequence
  Binary Systems T Tau S

abstract:
  We obtained new near-infrared images of the prototypical pre-main sequence
triple system T Tau, as well as the first resolved medium-resolution spectra of
the close pair T Tau S. At the time of our observations, the tight binary had a
13 AU projected separation and showed significant motion since its discovery,
three years before. The orbit cannot be strongly constrained yet, but the
observed motion of T Tau Sb with respect to T Tau Sa suggests that the system
is at least as massive as T Tau N itself. This may indicate that T Tau N is not
the most massive star in the system. The spectrum of T Tau Sa, which is totally
featureless except for a strong Br gamma emission line, identifies this
component with the ``infrared companion'', whose exact nature remains obscure
but may be the consequence of it being the most massive component of the
system. Contrasting sharply with T Tau Sa, the spectrum of T Tau Sb shows
numerous photospheric features consistent with an early-M spectral type. The
presence of a strong Br gamma emission line and of a significant veiling
continuum classifies this object as a deeply embedded T Tauri star. From these
observations, we conclude that both components of T Tau S are embedded in their
own dense circumstellar cocoon of material, which are probably fed by a much
more extended structure.


title:
High resolution infrared spectra of bulge globular clusters: Liller~1
  and NGC 6553

abstract:
  Using the NIRSPEC spectrograph at Keck II, we have obtained echelle spectra
covering the range 1.5-1.8um for 2 of the brightest giants in Liller 1 and NGC
6553, old metal rich globular clusters in the Galactic bulge. We use spectrum
synthesis for the abundance analysis, and find [Fe/H]=-0.3 +/- 0.2 and
[O/H]=+0.3 +/- 0.2 dex. The composition of the clusters is similar to that of
field stars in the bulge and is consistent with a sceanrio in which the
clusters formed early, with rapid enrichment. We have dificulty achieveing a
good fit to the spectrum of NGC 6553 using either the low or the high values
recently reported in the literature, unless unusually large, or no
alpha-element enhancements are adopted, respectively.


title: The baryon fraction in X-Rays galaxy clusters revisited

abstract:
  One of the most direct way to constrain the matter density of the universe
$\Omega_M$ is to measure the baryon content in X-Rays clusters of galaxies.
Typical value of the mean gas mass fraction is $\fg \sim 0.15h^{-3/2}$ which
leads to $\omM <0.4$. In this talk I will discuss the issue of the gas fraction
radial distribution inside a cluster and foccus on the apparent discrepancy
between the theoretical shape predicted by numerical simulations and the
observations. I will show that a significant part of this discrepancy is due to
several systematics in both the gas mass and total mass determinations.
Revising the gas as well as the binding masses removes such a discrepancy and
results in a lower baryon mass fraction of $\fb(r_{500}) \sim 10 %$ (Sadat &
Blanchard 2001). Finally, I will discuss the cosmological constraints we obtain
when we combine the revised baryon fraction with primordial fluctuations.


title: Arecibo timing observations of 17 pulsars along the Galactic plane

abstract:
  We present phase-coherent timing solutions obtained for the first time for 17
pulsars discovered at Arecibo by Hulse & Taylor (1975ab) in a 430-MHz survey of
the Galactic plane. This survey remains the most sensitive of the Galactic
plane at 430 MHz and has comparable equivalent sensitivity to the 1400-MHz
Parkes multibeam survey. Comparing both surveys we find that, as expected, the
one at 430 MHz is limited in depth by interstellar dispersion and scattering
effects; and that the detection rate of pulsars with high spin-down luminosity
($\dot E>10^{34}$ erg s$^{-1}$) at the low frequency is a factor of 5 smaller
than at high frequency. We also present scatter-broadening measurements for two
pulsars and pulse nulling and mode-changing properties for two others.


title: Surface Electric Field of Bare Strange Stars

abstract:
  The surface electric characteristics of bare strange stars are investigated
with the inclusion of boundary effects. The thickness of the electron layer
where pairs can be spontaneously created is calculated as a function of the bag
parameters. We find that previous estimates are representative for bag
parameters within a rather wide range, and therefore our results favor the
thermal radiation mechanism of bare strange stars advanced by V. V. Usov.


title: Galaxy Formation in Preheated Intergalactic Media

abstract:
  We outline a scenario of galaxy formation in which the gas in galaxy-forming
regions was preheated to high entropy by vigorous energy feedback associated
with the formation of stars in old ellipticals and bulges and with AGN
activity. Such preheating likely occurred at redshifts z ~ 2-3, and can produce
the entropy excess observed today in low-mass clusters of galaxies without
destroying the bulk of the Lyman alpha forest. Subsequent galaxy formation is
affected by the preheating, because the gas no longer follows the dark matter
on galaxy scales. The hot gas around galaxy haloes has very shallow profiles
and emits only weakly in the X-ray. Cooling in a preheated halo is not
inside-out, because the cooling efficiency does not change significantly with
radius. Only part of the gas in a protogalaxy region can cool and be accreted
into the final galaxy halo. The accreted gas is likely in diffuse clouds and so
does not lose angular momentum to the dark matter. Cluster ellipticals are
produced by mergers of stellar systems formed prior to the preheating, while
large galaxy disks form in low-density environments where gas accretion can
continue to the present time.


title: Merging Massive Star Clusters as Building Blocks of Dwarf Galaxies ?

abstract:
  Recent spectroscopic observations of galaxies in the Fornax-Cluster reveal
nearly unresolved `star-like' objects with red-shifts appropriate to the
Fornax-Cluster. These objects have intrinsic sizes of about 100 pc and absolute
B-band magnitudes in the range -14 < M_B < -11.5 mag and lower limits for the
central surface brightness mu_B >= 23 mag/arcsec^2 (Phillipps et al. 2001,
Hilker et al. 1999), and so appear to constitute a new population of
ultra-compact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form
from the amalgamation of stellar super-clusters (= clusters of star clusters;
not to confuse with super stellar clusters (SSC)) by P. Kroupa (1998), which
are rich aggregates of young massive star clusters (YMCs) that can form in
collisions between gas-rich galaxies. Here we present the evolution of
super-clusters in a tidal field. The YMCs merge on a few super-cluster crossing
times. Super-clusters that are initially as concentrated and massive as Knot S
in the interacting Antennae galaxies (Whitmore et al. 1999) evolve to merger
objects that are long-lived and show properties comparable to the newly
discovered UCDs.


title:
Infrared Emission from Interstellar Dust. III. The Small Magellanic
  Cloud

abstract:
  The infrared (IR) emission from interstellar dust in the Small Magellanic
Cloud (SMC) is modelled using a mixture of amorphous silicate and carbonaceous
grains, including a population of polycyclic aromatic hydrocarbon (PAH)
molecules. (1) It is shown that this dust model is able to reproduce the
spectral energy distribution from near-IR to far-IR for the entire SMC Bar
region, provided the PAH abundance in the SMC Bar region is very low. (2) The
IR spectrum of the SMCB1#1 molecular cloud can also be reproduced by our dust
model provided the PAH abundance is increased relative to the overall SMC Bar.
The PAHs in SMCB1#1 incorporate ~3% of the SMC C abundance, compared to <0.4%
in the SMC Bar. (3) The spectrum of SMCB1#1 is best reproduced if the PAH
mixture has intrinsic IR band strengths which differ from the band strengths
which best fit Milky Way PAH mixtures. The variation in the PAH IR band
strengths would imply different PAH mixtures, presumably a consequence of
differing metallicity or environmental conditions. Other possibilities such as
super-hydrogenation of PAHs and softening of the starlight spectrum are also
discussed.


title: Asymptotic Giant Branch predictions: theoretical uncertainties

abstract:
  In this paper we investigate the level of agreement between observations and
"new" Asymptotic Giant Branch (AGB) models, as produced by updating the
physical inputs adopted in previous stellar computations. One finds that the
new physics increases the predicted luminosity of Horizontal Branch (HB) and
AGB stellar structures by a similar amount, keeping unchanged the predictions
about the difference in luminosity between these two evolutionary phases. The
best fit of selected globular clusters appears rather satisfactory, disclosing
the relevance of the assumption on the mass of the Red Giant Branch (RGB)
progenitor in assessing the distance modulus of moderately metal rich clusters.
The still existing uncertainties related either to the input physics or to the
efficiency of some macroscopic mechanisms, like convection or microscopic
diffusion, are critically discussed, ruling out the occurrence of the so called
"breathing pulses" during the central He exhaustion, in agreement with earlier
suggestions.


title:
Caught in the Act; Chandra Observations of Microlensing of the
  Radio-Loud Quasar MG J0414+0534

abstract:
  We present results from monitoring of the distant (z = 2.64), gravitationally
lensed quasar MG J0414+0534 with the Chandra X-ray Observatory. An Fe Ka line
at 6.49 +/- 0.09 keV (rest-frame) with an equivalent width of ~ 190eV
consistent with fluorescence from a cold medium is detected at the 99 percent
confidence level in the spectrum of the brightest image A. During the last two
observations of our monitoring program we detected a five-fold increase of the
equivalent width of a narrow Fe Ka line in the spectrum of image B but not in
the brighter image A whereas image C is too faint to resolve the line. The
continuum emission component of image B did not follow the sudden enhancement
of the iron line in the last two observations. We propose that the sudden
increase in the iron line strength from ~ 190eV to 900eV only in image B can be
explained with a caustic crossing due to microlensing that selectively enhances
a strip of the line emission region of the accretion disk. The non-enhancement
of the continuum emission in the spectrum of image B suggests that the
continuum emission region is concentrated closer to the center of the accretion
disk than the iron line emission region and the magnification caustic has not
reached close enough to the former region to amplify it. A model of a caustic
crossing event predicts discontinuities in the light-curve of the magnification
and provides an upper limit of ~ 5 x 10^(-4) pc on the outer radius of the Fe
Ka emission region. The non-detection of any relativistic or Doppler shifts of
the iron line in the spectrum of image B implies that the magnification caustic
for the last two observations was located at a radius greater than ~ 100
gravitational radii.


title:
Models of Metal Poor Stars with Gravitational Settling and Radiative
  Accelerations: I. Evolution and Abundance Anomalies

abstract:
  Evolutionary models have been calculated for Pop II stars of 0.5 to
1.0$M_\odot$ from the pre-main-sequence to the lower part of the giant branch.
Rosseland opacities and radiative accelerations were calculated taking into
account the concentration variations of 28 chemical species, including all
species contributing to Rosseland opacities in the OPAL tables. The effects of
radiative accelerations, thermal diffusion and gravitational settling are
included. While models were calculated both for Z=0.00017 and 0.0017, we
concentrate on models with Z=0.00017 in this paper. These are the first Pop II
models calculated taking radiative acceleration into account. It is shown that,
at least in a 0.8$M_\odot$ star, it is a better approximation not to let Fe
diffuse than to calculate its gravitational settling without including the
effects of $g_{rad}(Fe)$. In the absence of any turbulence outside of
convection zones, the effects of atomic diffusion are large mainly for stars
more massive than 0.7$M_\odot$. Overabundances are expected in some stars with
$\teff \ge 6000K$. Most chemical species heavier than CNO are affected. At 12
Gyr, overabundance factors may reach 10 in some cases (e.g. for Al or Ni) while
others are limited to 3 (e.g. for Fe). The calculated surface abundances are
compared to recent observations of abundances in globular clusters as well as
to observations of Li in halo stars. It is shown that, as in the case of Pop I
stars, additional turbulence appears to be present.


title: Analytic marginalization over CMB calibration and beam uncertainty

abstract:
  With the increased accuracy and angular scale coverage of the recent CMB
experiments it has become important to include calibration and beam
uncertainties when estimating cosmological parameters. This requires an
integration over possible values of the calibration and beam size, which can be
done numerically but increases computation times. We present a fast and simple
algorithm for marginalization over beam and calibration errors by analytical
integration. We also illustrate the effect of incorporating these uncertainties
by calculating the constraints on various cosmological and inflationary
parameters including the spectral index n_s and the physical baryon density
Omega_b h^2, using the latest CMB data. We find that parameter constraints are
significantly changed when calibration/beam uncertainties are taken into
account. Typically the best fit parameters are shifted and the errors bars are
increased by up to fifty per cent for e.g. n_s and Omega_b h^2, although as
expected there is no change for Omega_K, because it is constrained by the
positions of the peaks.


title:
Determination of masses and other properties of extra-solar planetary
  systems with more than one planet

abstract:
  Recent analysis of the Doppler shift oscillations of the light from
extra-solar planetary systems indicate that some of these systems have more
than one large planet. In this case it has been shown that the masses of these
planets can be determined without the familiar ambiguity due to the unknown
inclination angle of the plane of the orbit of the central star provided,
however, that its mass is known. A method is presented here which determines
also a lower limit to the mass of this star from these observations. As an
illustration, our method is applied to the Keck and Lick data for GJ876.


title:
Solar Magnetic Field Studies Using the 12-Micron Emission Lines. IV.
  Observations of a Delta-Region Solar Flare

abstract:
  We have recently developed the capability to make solar vector (Stokes IQUV)
magnetograms using the infrared line of MgI at 12.32 microns. On 24 April 2001,
we obtained a vector magnetic map of solar active region NOAA 9433,
fortuitously just prior to the occurrence of an M2 flare. Examination of a
sequence of SOHO/MDI magnetograms, and comparison with ground-based H-alpha
images, shows that the flare was produced by the cancellation of newly emergent
magnetic flux outside of the main sunspot. The very high Zeeman-sensitivity of
the 12-micron data allowed us to measure field strengths on a spatial scale
which was not directly resolvable. At the flare trigger site, opposite polarity
fields of 2700 and 1000 Gauss occurred within a single 2 arc-sec resolution
element, as revealed by two resolved Zeeman splittings in a single spectrum.
Our results imply an extremely high horizontal field strength gradient (5 G/km)
prior to the flare, significantly greater than seen in previous studies. We
also find that the magnetic energy of the cancelling fields was more than
sufficient to account for the flare's X-ray luminosity.


title: Solar Convection and Magneto-Convection Simulations

abstract:
  Magneto-convection simulations with two scenarios have been performed: In
one, horizontal magnetic field is advected into the computational domain by
fluid entering at the bottom. In the other, an initially uniform vertical
magnetic field is imposed on a snapshot of non-magnetic convection and allowed
to evolve. In both cases, the field is swept into the intergranular lanes and
the boundaries of the underlying mesogranules. The largest field concentrations
at the surface reach pressure balance with the surrounding gas. They suppress
both horizontal and vertical flows, which reduces the heat transport. They
cool, become evacuated and their optical depth unity surface is depressed by
several hundred kilometers. Micropores form, typically where a small granule
disappears and surrounding flux tubes squeeze into its previous location.


title:
Gamma-ray burst beaming: a universal configuration with a standard
  energy reservoir?

abstract:
  We consider a gamma-ray burst (GRB) model based on an anisotropic fireball
with an axisymmetric power-law distribution of the energy per solid angle with
index -k, and allow for the observer's viewing direction being at an arbitrary
angle with respect to the jet axis. This model can reproduce the key features
expected from the conventional on-axis uniform jet models, with the novelty
that the achromatic break time in the broadband afterglow lightcurves
corresponds to the epoch when the relativistic beaming angle is equal to the
viewing angle rather than to the jet half opening angle. If all the GRB
fireballs have such a similar energy distribution form with 1.5 < k < (or \sim)
2, GRBs may be modeled by a quasi-universal beaming configuration, and an
approximately standard energy reservoir. The conclusion also holds for some
other forms of angular energy distributions, such as the Gaussian function.


title:
Strong Gravitational Lensing Time Delay Statistics and the Density
  Profile of Dark Halos

abstract:
  The distribution of differential time delays \Delta t between images produced
by strong gravitational lensing contains information on the mass distributions
in the lensing objects as well as on cosmological parameters such as H_0. We
derive an explicit expression for the conditional probability distribution
function of time delays P(\Delta t|\theta), given an image separation between
multiple images \theta, and related statistics. We consider lensing halos
described by the singular isothermal sphere (SIS) approximation and by its
generalization as proposed by Navarro, Frenk, & White (NFW) which has a density
profile \rho \propto r^{-\alpha} in the innermost region. The time delay
distribution is very sensitive to these profiles; steeper inner slopes tend to
produce larger time delays. For example, if H_0=70 km/s/Mpc, a
\Lambda-dominated cosmology and a source redshift z_S=1.27 are assumed, lenses
with \theta=5'' produce a time delay of \Delta t[yr]=1.5^{+1.7}_{-0.9},
0.39^{+0.37}_{-0.22}, 0.15^{+0.11}_{-0.09}, and 0.071^{+0.054}_{-0.038} (50%
confidence interval), for SIS, generalized NFW with \alpha=1.5, \alpha=1.0, and
\alpha=0.5, respectively. At a fixed image separation, the time delay is
determined by the difference in the lensing potential between the position of
the two images, which typically occur at different impact parameters. Although
the values of \Delta t are proportional to the inverse of H_0, P(\Delta
t|\theta) is rather insensitive to all other cosmological model parameters,
source redshifts, magnification biases and so on. A knowledge of P(\Delta
t|\theta) will also be useful in designing the observing program of future
large scale synoptic variability surveys and for evaluating possible selection
biases operating against large splitting lens systems.


title: Planet Formation in the Outer Solar System

abstract:
  This paper reviews coagulation models for planet formation in the Kuiper
Belt, emphasizing links to recent observations of our and other solar systems.
At heliocentric distances of 35-50 AU, single annulus and multiannulus
planetesimal accretion calculations produce several 1000 km or larger planets
and many 50-500 km objects on timescales of 10-30 Myr in a Minimum Mass Solar
Nebula. Planets form more rapidly in more massive nebulae. All models yield two
power law cumulative size distributions, N_C propto r^{-q} with q = 3.0-3.5 for
radii larger than 10 km and N_C propto r^{-2.5} for radii less than 1 km. These
size distributions are consistent with observations of Kuiper Belt objects
acquired during the past decade. Once large objects form at 35-50 AU,
gravitational stirring leads to a collisional cascade where 0.1-10 km objects
are ground to dust. The collisional cascade removes 80% to 90% of the initial
mass in the nebula in roughly 1 Gyr. This dust production rate is comparable to
rates inferred for alpha Lyr, beta Pic, and other extrasolar debris disk
systems.


title: Propeller vs. Magnetar Concepts for SGR/AXPs

abstract:
  Two lines of thought exist as to the nature of Soft Gamma-ray Repeaters
(SGRs) and Anomalous X-ray Pulsars (AXPs). On the one hand,we have neutron
stars with super-critical magnetic fields, which spin-down the stars and power
the gamma-ray bursts. On the other hand, are neutron stars with typical pulsar
magnetic fields, which are spun-down by magnetospheric ``propeller'' torques
from fallback or fossil disks in addition to magnetic dipole radiation. Many
observational facts are available for comparing and contrasting these two
concepts. The facts are described and whether or not each is compatible with
these concepts is presented.


title: Study of Gamma Ray Burst Binary Progenitors

abstract:
  Recently much work in studying Gamma-Ray Burst has been devoted to revealing
the nature of outburst mechanism and studies of GRB afterglows. These issues
have also been closely followed by the quest for identifying GRB progenitors.
In this paper we consider the proposed binary star progenitors of GRBs: white
dwarf neutron star binaries, white dwarf black hole binaries, helium core
neutron star mergers, helium core black hole mergers, double neutron stars and
neutron star black hole binaries. Using population synthesis methods we
calculate merger rates of these binary progenitors and we compare them to the
observed BATSE GRB rate. We also calculate the distribution of merger sites
around host galaxies and compare them to the observed locations of GRB
afterglows with respect to their hosts. We find that the rates of binary GRB
progenitors in our standard model are lower than the observed GRB rates if GRBs
are highly collimated. However, the uncertainty in the population synthesis
results is too large to make this a firm conclusion. Although some
observational signatures seem to point to collapsars as progenitors of long
GRBs, we find that mergers of WD-NS, He-NS, He-BH, and NS-NS systems also trace
the star formation regions of their host galaxies, as it is observed for long
GRBs. We also speculate about possible progenitors of short-duration GRBs. For
these, the most likely candidates are still mergers of compact objects. We find
that the locations NS-NS and NS-BH mergers with respect to their hosts are
significantly different. This may allow to distinguish between these two
progenitor models, once current and near future missions, such as HETE-II or
SWIFT, measure the locations of short GRBs.


title: Strong and Weak Lensing Constraints on Galaxy Mass Distribution

abstract:
  Gravitational Lensing is a UNIQUE tool to constrain the mass distribution of
collapsed structures, this is particularly true for galaxies, either on a case
by case basis using multiple images of background sources (such as quasars), or
statistically using the so called galaxy-galaxy lensing technique. First, I
will present the lensing theory, and then discuss the various methods applied
to current observations. Finally, I will review the bright future prospects of
galaxy lensing that will benefit of the development of high resolution, large,
wide and deep (lensing) surveys.


title: Astrometric Detection of Double Gravitational Microlensing Events

abstract:
  If a gravitational microlensing event is caused by a widely separated binary
lens and the source approaches both lens components, the source flux is
successively magnified by the individual lenses: double microlensing events. If
events are observed astrometrically, double lensing events are expected to
occur with an increased frequency due to the long range astrometric effect of
the companion. We find that although the trajectory of the source star image
centroid shifts of an astrometric double lensing event has a distorted shape
from both of the elliptical ones induced by the individual single lens
components, event duplication can be readily identified by the characteristic
loop in the trajectory formed during the source's passage close to the
companion. We determine and compare the probabilities of detecting double
lensing events from both photometric and astrometric lensing observations by
deriving analytic expressions for the relations between binary lensing
parameters to become double lensing events. From this determination, we find
that for a given set of the binary separation and the mass ratio the
astrometric probability is roughly an order higher than the photometric
probability. Therefore, we predict that a significant fraction of events that
will be followed up by using future high precision interferometeric instruments
will be identified as double lensing events.


title:
Search for the Optical Counterparts of Southern Anomalous X-Ray Pulsars
  and Radio-Quiet Neutron Stars in Young Supernova Remnants

abstract:
  We report on our search for the optical counterparts of the Southern
Hemisphere anomalous X-ray pulsar 1E1048.1-5937 and the radio-quiet neutron
stars in supernova remnants Puppis A, RCW 103, and PKS 1209-52. The
observations were carried out with the new MIT/CfA MagIC camera on the
Magellan-I 6.5 m telescope in Chile. We present deep multiband optical images
of the X-ray error circles for each of these targets and discuss the resulting
candidates and limits.


title: Infrared Spectra of the Subluminous Type Ia Supernova 1999by

abstract:
  Near-infrared spectra of the subluminous Type Ia SN1999by are presented which
cover the time evolution from about 4 days before to 2 weeks after maximum.
Analysis of these data was accomplished through the construction of an extended
set of delayed detonation (DD) models. The explosion, light curves and spectra
including their evolution with time are calculated consistently leaving the
initial WD and the description of the nuclear burning front the free
parameters. We cover the entire range of normal to subluminous SNeIa. From this
model set, one was selected for SN99by by matching properties of the synthetic
& observed optical light curves. We find DD models require a certain amount of
burning during the deflagration phase setting a lower limit for the absolute
brightness. For SN1999by, a model close to the minimum 56Ni production is
required. Without tuning,good agreement has been found between synthetic and
observed IR spectra. In contrast to 'normal' SNeIa and prior to maximum, the
NIR spectra of SN1999by are dominated by products of explosive carbon burning.
Spectra taken after maximum are dominated by products of incomplete Si burning.
Pure deflagration scenarios or mergers are unlikely. However,problems for DD
models still remain, as the data seem to be at odds with recent predictions
from 3-D models which find significant mixing of the inner layers. Possible
solutions include the effects of rapid rotation on the propagation of nuclear
flames, or extensive burning of carbon just prior to the runaway.


title: Variability and Spectra of Two Neutron Stars in 47 Tucanae

abstract:
  We report spectral and variability analysis of two quiescent low mass x-ray
binaries (previously identified with ROSAT HRI as X5 and X7) in the globular
cluster 47 Tuc, from a Chandra ACIS-I observation. X5 demonstrates sharp
eclipses with an 8.666+-0.008 hr period, as well as dips showing an increased
N_H column. Their thermal spectra are well-modelled by unmagnetized hydrogen
atmospheres of hot neutron stars, most likely heated by transient accretion,
with little to no hard power law component.


title:
An X-ray, Optical and Radio Search for Supernova Remnants in the Nearby
  Sculptor Group Sd Galaxy NGC 7793

abstract:
  We present a multi-wavelength study of the properties of supernova remnants
(SNRs) in the nearby Sculptor Group Sd galaxy NGC 7793. Using our own Very
Large Array radio observations at 6 and 20 cm, as well as archived ROSAT X-ray
data, previously published optical results and our own H-alpha image, we have
searched for X-ray and radio counterparts to previously known
optically-identified SNRs and for new previously unidentified SNRs at these two
wavelength regimes. Only two of the 28 optically-identified SNRs are detected
at another wavelength. The most noteworthy source in our study is N7793-S26,
which is the only SNR that is detected at all three wavelengths. It features a
long (approximately 450 pc) filamentary morphology that is clearly seen in both
the optical and radio images. N7793-S26's radio luminosity exceeds that of the
Galactic SNR Cas A, and based on equipartition calculations we determine that
an energy of at least 10^52 ergs is required to maintain this source. A second
optically identified SNR, N7793-S11, has detectable radio emission but is not
detected in the X-ray. Complementary X-ray and radio searches for SNRs have
yielded five new candidate radio SNRs, to be added to the 28 SNRs in this
galaxy that have already been detected by optical methods. We find that the
density of the ambient interstellar medium (ISM) surrounding these SNRs
significantly impacts the spectral characteristics of SNRs in this galaxy,
consistent with surveys of the SNR populations in other galaxies.


title: Searching for Clusters of Galaxies with SUMSS

abstract:
  Statistical overdensities of radio sources in the NRAO VLA Sky Survey (NVSS)
catalogue have proven to be signposts to high-redshift clusters of galaxies. A
similar search for overdensities has been carried out in the Sydney University
Molonglo Sky Survey (SUMSS), which is closely matched in resolution and
frequency to the NVSS. Sixty potential southern-hemisphere clusters have been
found in SUMSS.


title: RR Lyrae variables in Omega Centauri: a theoretical route

abstract:
  We present a theoretical approach to infer information about RR Lyrae
variables from the morphology of their light curves. The method, already
successfully applied to the field first overtone variable U Comae, is now
tested on a RR$_{\mathrm ab}$ variable in the globular cluster $\omega$ Cen. We
show that, with this method, it could be possible to give an estimate of the
distance modulus of the cluster with an uncertainty not larger than $\pm$0.1
mag. The predicted variable luminosity and mass are well within the range of
theoretical evolutionary expectations giving the ``feeling'' of a full
compatibility between pulsational and evolutionary theory. However, before
completely relying on the method, further tests are needed; the goal is that a
well tested and well calibrated pulsational theory could provide reliable
distance moduli from just one (or few) RR Lyrae stars.


title:
What does the local black hole mass distribution tell us about the
  evolution of the quasar luminosity function?

abstract:
  We present a robust method to derive the duty cycle of QSO activity based on
the empirical QSO luminosity function and on the present-day linear relation
between the masses of supermassive black holes and those of their spheroidal
host stellar systems. It is found that the duty cycle is substantially less
than unity, with characteristic values in the range $3-6\times 10^{-3}$.
Finally, we tested the expectation that the QSO luminosity evolution and the
star formation history should be roughly parallel, as a consequence of the
above--mentioned relation between BH and galaxy masses.


title:
X-ray Statistical Properties of the Central Cool Component in Clusters
  of Galaxies

abstract:
  Central cool gas component that is often observed from a well-relaxed cluster
system has long been interpreted as a consequence of ``Cooling Flow'' (CF),
radiative cooling followed by inflow of Intra-Cluster Medium (ICM). However,
recent XMM-Newton spectroscopy has shown no signatures of cooler gas phases
below certain temperatures in typical CF clusters (A1795, Tamura et al. 2001;
A1835, Peterson et al. 2001). This contradicts the conventional CF model or at
least requires a major revision of the model. In order to investigate
statistical properties of the central cool component, we performed systematic
analysis of ASCA data on 85 clusters. We found that 1) temperature of the
central cool component strongly depends on the temperature of the main ICM, 2)
the cool component is selectively found around a brightest cluster galaxy (BCG)
that coincide with the X-ray peak position, and 3) the luminosity-temperature
(L-T) relation of the cool component shows nice agreement with the L-T relation
of the main ICM. Together with the previous observational fact that, in some of
the ``CF'' clusters, the total gravitating mass is clustering in two distinct
spatial scales, a main cluster component and a second small-scale system, we
conclude that the central cool component is associated with the second
small-scale self-gravitating system that is immersed in the host cluster, and
the cool component temperature reflects the gravitational potential depth.


title: Galaxy merging and the Fundamental Plane of elliptical galaxies

abstract:
  We present preliminary results of numerical simulations of dissipationless
merging of stellar systems, aimed at exploring the consequences of merging
between gas free, spheroidal systems. In particular, we study the dynamical and
structural characteristics of hierarchical merging between equal mass stellar
systems, and we compare the properties of the end-products with the most
important structural and dynamical scaling relations obeyed by spheroids. In
the explored hierarchy of four successive mergings we find that the FP tilt is
marginally conserved, but both the Faber-Jackson and Kormendy relations are not
conserved.


title: Cosmic ray propagation and acceleration

abstract:
  This report covers the studies of energetic particle propagation and
acceleration presented during the 27th ICRC in sessions OG 1.3 and 1.4, plus a
few selected papers from neighbouring OG sections. We list problems discussed
within these sections and we shortly describe selected interesting achievements
and/or novel approaches.


title:
The CORALS Survey II: Clues to Galaxy Clustering Around QSOs from z_abs
  ~ z_em Damped Lyman Alpha Systems

abstract:
  We present a list of z_abs ~ z_em (Delta v < 3000 km/s) DLAs discovered
during the CORALS survey for absorbers in a radio-selected QSO sample. On the
assumption that z_abs ~ z_em DLAs are neither ejecta from the QSO, nor part of
the host galaxy itself, we use the number density statistics of these DLAs to
investigate galaxy clustering near the QSO redshift. We find that n(z) of z_abs
\~z_em DLAs in our radio-selected QSO sample is ~4 times larger than the number
density of intervening DLAs, implying an excess of galaxies near the QSO. This
result is further supported with the inclusion of the radio-loud QSOs in the
FIRST survey, although the total number of DLAs is still small (4) and the
result is currently only significant at approximately the 2 sigma level. Since
all of the z_abs ~ z_em DLAs we identify in CORALS are found towards optically
bright (B < 20) QSOs, there is no strong evidence (based on these limited
statistics) that this population suffers from a severe dust bias. We compare
our results with those from an optically-selected, radio-quiet QSO sample in
order to determine whether there is evidence for an excess of galaxies around
radio-loud versus radio-quiet QSOs. We find that the n(z) of z_abs ~ z_em DLAs
towards radio-quiet QSOs is in agreement with the number density of intervening
absorbers. This result, although currently limited by the small number
statistics of our survey, supports the conclusion that radio-loud quasars are
found preferentially in rich galaxy environments at high redshift. Finally, we
report that one of the new z_abs ~ z_em DLAs discovered by CORALS has some
residual flux in the base of the Lya trough which may be due to Lya emission,
either from star formation in the DLA galaxy or from gas photoionised by the
QSO.


title:
General Relativistic Spectra from Accretion Disks around Rapidly
  Rotating Neutron Stars

abstract:
  We compute spectra from accretion disks around rapidly rotating neutron
stars. The full effect of general relativity is considered for the structure
calculation of the stars. We take into account the Doppler shift, gravitational
redshift and light-bending effects in order to compute the observed spectra. To
facilitate direct comparison with observations, a simple empirical function is
presented which describes the numerically computed spectra well. This function
can in principle be used to distinguish between the Newtonian spectra and the
relativistic spectra. We also discuss the possibility of constraining neutron
star's equation of state using our spectral models.


title:
Initial low/hard state, multiple jet ejections and X-ray/radio
  correlations during the outburst of XTE J1859+226

abstract:
  We have studied the 1999 soft X-ray transient outburst of XTE J1859+226 at
radio and X-ray wavelengths. The event was characterised by strong variability
in the disc, corona and jet - in particular, a number of radio flares
(ejections) took place and seemed well-correlated with hard X-ray events.
Apparently unusual for the `canonical soft' X-ray transient, there was an
initial period of low/hard state behaviour during the rise from quiescence but
prior to the peak of the main outburst - we show that not only could this
initial low/hard state be an ubiquitous feature of soft X-ray transient
outbursts but that it could also be extremely important in our study of
outburst mechanisms.


title:
Pseudo Elliptical Lensing Mass Model: Application to the NFW Mass
  Distribution

abstract:
  We introduce analytical expressions for a pseudo fully analytical elliptical
projected Navarro, Frenk & White (NFW) mass profile to be used in lensing
equations. We propose a formalism that incorporates the ellipticity into the
expression for the lens potential, producing a pseudo-elliptical mass
distribution. This approach can be implemented to any circular mass profile for
which the projected mass profile Sigma(r) and the deflection angle profile
alpha(r) both have analytical expressions; however the potential does not
necessarily need to take an analytical form. We apply this new formalism to the
NFW mass distribution and study how well this pseudo-elliptical NFW model
describes an elliptical mass distribution. We conclude that the
pseudo-elliptical NFW model is a good description of elliptical mass
distributions provided that the ellipticity of the projected mass distribution
is <~ 0.4, although with a slightly boxy distribution.


title: The Ermakov-Pinney Equation in Scalar Field Cosmologies

abstract:
  It is shown that the dynamics of cosmologies sourced by a mixture of perfect
fluids and self-interacting scalar fields are described by the non-linear,
Ermakov-Pinney equation. The general solution of this equation can be expressed
in terms of particular solutions to a related, linear differential equation.
This characteristic is employed to derive exact cosmologies in the inflationary
and quintessential scenarios. The relevance of the Ermakov-Pinney equation to
the braneworld scenario is discussed.


title: IRAS F02044+0957: radio source in interacting system of galaxies

abstract:
  The steep spectrum of IRAS F02044+0957 was obtained with the RATAN-600 radio
telescope at four frequencies. Optical spectroscopy of the system components,
was carried out with the 2.1m telescope of the Guillermo Haro Observatory.
Observational data allow us to conclude that this object is a pair of
interacting galaxies, a LINER and a HII galaxy, at $z=0.093$.


title:
Associated absorption in radio quasars. I. C IV absorption and the
  growth of radio sources

abstract:
  We assess the global properties of associated C IV 1548,1550 absorption lines
measured in the spectra of radio-loud quasars drawn from a near-complete,
low-frequency selected sample. The observations span restframe C IV in two
redshift ranges -- 0.7<z<1.0 and 1.5<z<3.0 -- which were targetted in the UV
with HST/STIS and in the optical with ground-based telescopes, respectively.
First, we corroborate trends for C IV associated absorption to be found
preferentially in steep-spectrum and lobe-dominated quasars, implying the
absorbing material tends to lie away from the radio-jet axis. Furthermore, we
find a clear anticorrelation between C IV absorption strength and the projected
linear size of steep-spectrum quasars, indicative of an evolutionary sequence.
We also find that heavily-absorbed quasars are systematically redder, implying
dust is mixed in with the C IV-absorbing gas. No redshift dependence was found
in any of the trends considered. These new results show that radio sources are
triggered in galaxies which are exceptionally rich in gas and dust, which then
dissipates on a timescale comparable with, but less than, that of the radio
source. This observational sequence, together with the lack of
redshift-dependence, points to a direct causal link between the event which
triggered the radio source and the build-up of absorbing gas and dust, whose
make-up is tantalisingly similar to the products of a post-merger starburst.
Thus, these new results provide direct evidence for the clearing of absorbing
material around quasars with time, as well as the probable association of
starburst activity with the onset of the radio activity in AGN.


title: System to estimate ages and redshifts for radio galaxies

abstract:
  The system allowing a user to operate with simulated curves of spectral
energy distribution (SED) and to estimate ages and redshifts by photometric
data at server {\bf sed.sao.ru} is described.


title: Decametric AGNs: FIRST and NVSS maps and radio spectra

abstract:
  Radio sources from the decametric UTR--2 catalog were cross-identified with
other radio catalogs at higher frequencies. We used the CATS database to
extract all sources within the UTR beam size ($\sim40'$) to find candidate
radio identifications. Using the least squares method we fitted the spectrum of
each source with one of a set of curves. We extracted NVSS and FIRST radio
images for the radio-identified sources, and looked for a possible relation
between size and spectral index.


title: Photometric study of radio galaxies in RATAN--600 "Cold" survey

abstract:
  About 100 steep spectrum radio sources from the RATAN--600 RC catalog were
mapped by the VLA and identified with optical objects down to 24$^m$--25$^m$ in
the R band using the 6 m telescope. An updated list of calibrators with known
redshifts of the same class RGs was compiled to evaluate the accuracy of
photometric redshifts estimates. BVRI photometry for 60 RC objects was
performed with the 6 m telescope, and by standard model fitting we have
estimated colour redshifts and ages of stellar population of host gE galaxies.
The mean redshift of FRII RGs from the RC list happened to be $\approx$1.
Several objects were found in which active star formation began in the first
billion years after the Big Bang.


title: Cosmic String Signatures in the Cosmic Microwave Background Anisotropies

abstract:
  We briefly review certain aspects of cosmic microwave background anisotropies
as generated in passive and active models of structure formation. We then focus
on cosmic strings based models and discuss their status in the light of current
high-resolution observations from the BOOMERanG, MAXIMA and DASI
collaborations. Upcoming megapixel experiments will have the potential to look
for non-Gaussian features in the CMB temperature maps with unprecedented
accuracy. We therefore devote the last part of this review to treat the
non-Gaussianity of the microwave background and present a method for
computation of the bispectrum from simulated string realizations.


title:
Indirect imaging of the accretion stream in eclipsing polars IV: V895
  Cen

abstract:
  We present spectroscopic and high speed photometric data of the eclipsing
polar V895 Cen. We find that the eclipsed component is consistent with it being
the accretion regions on the white dwarf. This is in contrast to Stobie et al
who concluded that the eclipsed component was not the white dwarf. Further, we
find no evidence for an accretion disc in our data. From our Doppler tomography
results, we find that the white dwarf has M geq 0.7 Msun. Our indirect imaging
of the accretion stream suggests that the stream is brightest close to the
white dwarf. When we observed V895 Cen in its highest accretion state, emission
is concentrated along field lines leading to the upper pole. There is no
evidence for enhanced emission at the magnetic coupling region.


title:
Exact solutions for the spatial de Vaucouleurs and Sersic laws and
  related quantities

abstract:
  Using the Mathematica package, we find exact analytical expressions for the
so-called de-projected De Vaucouleurs and Sersic laws as well as for related
spatial (3D) quantities, such the mass, gravitational potential, the total
energy and the central velocity dispersion, generally involved in astronomical
calculations expressed in terms of the Meijer G functions.


title:
Adaptive Mesh Refinement in Computational Astrophysics -- Methods and
  Applications

abstract:
  The advent of robust, reliable and accurate higher order Godunov schemes for
many of the systems of equations of interest in computational astrophysics has
made it important to understand how to solve them in multi-scale fashion. This
is so because the physics associated with astrophysical phenomena evolves in
multi-scale fashion and we wish to arrive at a multi-scale simulational
capability to represent the physics. Because astrophysical systems have
magnetic fields, multi-scale magnetohydrodynamics (MHD) is of especial
interest. In this paper we first discuss general issues in adaptive mesh
refinement (AMR). We then focus on the important issues in carrying out
divergence-free AMR-MHD and catalogue the progress we have made in that area.
We show that AMR methods lend themselves to easy parallelization. We then
discuss applications of the RIEMANN framework for AMR-MHD to problems in
computational astophysics.


title:
What's Behind Acoustic Peaks in the Cosmic Microwave Background
  Anisotropies

abstract:
  We give a brief review of the physics of acoustic oscillations in Cosmic
Microwave Background (CMB) anisotropies. As an example of the impact of their
detection in cosmology, we show how the present data on CMB angular power
spectrum on sub-degree scales can be used to constrain dark energy cosmological
models.


title: Divergence-Free Adaptive Mesh Refinement for Magnetohydrodynamics

abstract:
  In this paper we present a full-fledged scheme for the second order accurate,
divergence-free evolution of vector fields on an adaptive mesh refinement (AMR)
hierarchy. We focus here on adaptive mesh MHD. The scheme is based on making a
significant advance in the divergence-free reconstruction of vector fields. In
that sense, it complements the earlier work of Balsara and Spicer (1999) where
we discussed the divergence-free time-update of vector fields which satisfy
Stoke's law type evolution equations. Our advance in divergence-free
reconstruction of vector fields is such that it reduces to the total variation
diminishing (TVD) property for one-dimensional evolution and yet goes beyond it
in multiple dimensions. Divergence-free restriction is also discussed. An
electric field correction strategy is presented for use on AMR meshes. The
electric field correction strategy helps preserve the divergence-free evolution
of the magnetic field even when the time steps are sub-cycled on refined
meshes. The above-mentioned innovations have been implemented in Balsara's
RIEMANN framework for parallel, self-adaptive computational astrophysics which
supports both non-relativistic and relativistic MHD. Several rigorous, three
dimensional AMR-MHD test problems with strong discontinuities have been run
with the RIEMANN framework showing that the strategy works very well.


title:
The HST survey of the B2 sample of radio-galaxies: optical nuclei and
  the FRI/BL Lac unified scheme

abstract:
  We examine the optical properties of the nuclei of low luminosity
radio-galaxies using snapshot HST images of the B2 sample. In agreement with
the results obtained from the analysis of the brighter 3C/FRI sample, we find a
correlation between fluxes (and luminosities) of the optical and radio cores.
This provides further support for the interpretation that the optical nuclear
emission in FRI is dominated by synchrotron emission and that accretion in
these sources takes place in a low efficiency radiative regime. In the
framework of the FRI/BL Lacs unified scheme, we find that the luminosity
difference between FRI and BL Lac nuclei can be reproduced with a common
beaming factor in both the radio and the optical band, independent of the
extended radio luminosity, thus supporting such a scenario. The corresponding
bulk Lorentz factor is significantly smaller than is expected from
observational and theoretical considerations in BL Lacs: this can be
interpreted as due to a velocity structure in the jet, with a fast spine
surrounded by a slower layer.


title: The X-ray sources at the center of G266.1-1.2

abstract:
  We present optical observations of the fields of two X-ray sources located
near the center of the shell-like supernova remnant G266.1-1.2. No objects
brighter than R~22.5 and B~23 are present within the small Chandra error region
of AX J0851.9-4617.4, besides a R~17 star that has already been excluded as a
possible counterpart. A bright diffuse H_alpha nebula is present close to the
position of the candidate neutron star.


title:
The First Detections of the Extragalactic Background Light at 3000,
  5500, and 8000A (I): Results

abstract:
  (Abridged) We present the first detections of the mean flux of the optical
extragalactic background light (EBL) at 3000, 5500, and 8000A. Diffuse
foreground flux at these wavelengths comes from terrestrial airglow,
dust-scattered sunlight (zodiacal light), and dust-scattered Galactic starlight
(diffuse Galactic light). We have avoided the brightest of these, terrestrial
airglow, by measuring the absolute surface brightness of the night sky from
above the Earth's atmosphere using the Wide Field Planetary Camera2 (WFPC2) and
Faint Object Spectrograph (FOS), both aboard the Hubble Space Telescope (HST).
On the ground, we have used the duPont 2.5 m Telescope at Las Campanas
Observatory (LCO) to obtain contemporaneous spectrophotometry of ``blank'' sky
in the HST field of view to measure and then subtract foreground zodiacal light
from the HST observations. We have minimized the diffuse Galactic light in
advance by selecting the HST target field along a line of sight with low
Galactic dust column density, and then estimated the low--level Galactic
foreground using a simple scattering model and the observed correlation between
thermal, 100 micron emission and optical scattered flux from the same dust. In
this paper, we describe the coordinated LCO/HST program and the HST
observations and data reduction, and present the resulting measurements of the
EBL.