title:
Widespread atomic gas emission reveals the rotation of the beta Pictoris
  disk

abstract:
  We present high resolution Na I D spectroscopy of the beta Pic disk, and the
resonantly scattered sodium emission can be traced from less than 30 AU to at
least 140 AU from the central star. This atomic gas is co-existent with the
dust particles, suggestive of a common origin or source. The disk rotates
towards us in the south-west and away from us in the north-east. The velocity
pattern of the gas finally provides direct evidence that the faint linear
feature seen in images of the star is a circumstellar disk in Keplerian
rotation. From modelling the spatial distribution of the Na I line profiles we
determine the effective dynamical mass to be 1.40 +/- 0.05 M_sun, which is
smaller than the stellar mass, 1.75 M_sun. We ascribe this difference to the
gravity opposing radiation pressure in the Na I lines. We argue that this is
consistent with the fact that Na is nearly completely ionised throughout the
disk (Na I/Na < 10^-4). The total column density of sodium gas is N(Na) = 10^15
cm^-2.


title:
Dim galaxies and outer halos of galaxies missed by 2MASS ? The
  near-infrared luminosity function and density

abstract:
  By using high-resolution and deep Ks band observations of early-type galaxies
of the nearby Universe and of a cluster at z=0.3 we show that the two
luminosity functions (LFs) of the local universe derived from 2MASS data miss a
fair fraction of the flux of the galaxies (more than 20 to 30%) and a whole
population of galaxies of central brightness fainter than the isophote used for
detection, but bright enough to be included in the published LFs. In
particular, the fraction of lost flux increases as the galaxy surface
brightness become fainter. Therefore, the so far derived LF slopes and
characteristic luminosity as well as luminosity density are underestimated.
Other published near-infrared LFs miss flux in general, including the LF of the
distant field computed in a 3 arcsec aperture.


title:
Features in the primordial power spectrum: constraints from the CMB and
  the limitation of the 2dF and SDSS redshift surveys to detect them

abstract:
  We allow a more general (step-function) form of the primordial power spectrum
than the usual featureless power-law Harrison--Zeldovich (with spectral index
n=1) power spectrum, and fit it to the latest Cosmic Microwave Background data
sets. Although the best-fitting initial power spectrum can differ significantly
from the power-law shape, and contains a bump at scales k ~ 0.003 h/Mpc, we
find Omega_m to be approximately 0.24, consistent with previous analyses that
assume power-law initial fluctuations. We also explore the feasibility of the
2dF and SDSS galaxy redshifts surveys to observe these features, and we find
that even if features exist in the primoridal power spectrum, they are washed
out by the window functions of the redshift surveys on scales k< 0.03 h/Mpc.


title: The Mass Distribution of Black Holes in BL Lacertae Objects

abstract:
  In this {\it Letter}, we make an attempt to estimate the masses of black
holes and their distributions in BL Lac objects. We find there is a bimodal
population of black hole masses in BL Lacs: the first has a lower-mass peak
centred at $\sim 7.0 \times 10^6\sunm$ composed of high frequency-peaked BL
Lacs (HBLs) and the second is a higher-mass ($>10^9\sunm$) population composed
of low frequency-peaked BL Lacs (LBLs). The low mass family of black holes in
HBLs does not satisfy the Magorrian et al. relation whereas the high mass
family in LBLs does this relation and is in agreement with Laor's limit. The
origination of the bimodal distribution of black hole mass remains open.


title:
Collisions of Free Floating Planets with Evolved Stars in Globular
  Clusters

abstract:
  We estimate the rate of collisions between stars and free-floating planets
(FFPs) in globular clusters, in particular the collision of FFPs with red giant
branch (RGB) stars. Recent dynamical simulations imply that the density of such
objects could exceed million per cubic parsec near the cores of rich globular
clusters. We show that in these clusters 5-10 per cents of all RGB stars near
the core would suffer a collision with a FFP, and that such a collision can
spin up the RGB star's envelope by an order of magnitude. In turn, the higher
rotation rates may lead to enhanced mass-loss rates on the RGB, which could
result in bluer horizontal branch (HB) stars. Hence, it is plausible that the
presence of a large population of FFPs in a globular cluster can influence the
distribution of stars on the HB of that cluster to a detectable degree.


title: Searching and studying clusters with the SZ effect

abstract:
  I discuss galaxy cluster surveys based on the Sunyaev--Zel'dovich effect and
their relevance for cosmological studies. The unique aspects of cluster
selection by this method are emphasized and certain issues of surveying are
addressed. Finally, I briefly present prospects for upcoming surveys.


title:
Chandra Observation of the Globular Cluster NGC 6440 and the Nature of
  Cluster X-ray Luminosity Functions

abstract:
  As part of our campaign to determine the nature of the various source
populations of the low-luminosity globular cluster X-ray sources, we have
obtained a Chandra X-ray Observatory ACIS-S3 image of the globular cluster NGC
6440. We detect 24 sources to a limiting luminosity of ~2 times 10^31 erg/s
(0.5-2.5keV) inside the cluster's half-mass radius, all of which lie within ~2
core radii of the cluster center. We also find excess emission in and around
the core which could be due to unresolved point sources. Based upon X-ray
luminosities and colors, we conclude that there are 4-5 likely quiescent
low-mass X-ray binaries and that most of the other sources are cataclysmic
variables. We compare these results to Chandra results from other globular
clusters and find the X-ray luminosity functions differ among the clusters.


title:
Identification of the optical and quiescent counterparts to the bright
  X-ray transient in NGC 6440

abstract:
  After 3 years of quiescence, the globular cluster NGC 6440 exhibited a bright
transient X-ray source turning on in August 2001, as noted with the RXTE
All-Sky Monitor. We carried out a short target of opportunity observation with
the Chandra X-ray Observatory and are able to associate the transient with the
brightest of 24 X-ray sources detected during quiescence in July 2000 with
Chandra. Furthermore, we securely identify the optical counterpart and
determine that the 1998 X-ray outburst in NGC 6440 was from the same object.
This is the first time that an optical counterpart to a transient in a globular
cluster is securely identified. Since the transient is a type I X-ray burster,
it is established that the compact accretor is a neutron star. Thus, this
transient provides an ideal case to study the quiescent emission in the optical
and X-ray of a transiently accreting neutron star while knowing the distance
and reddening accurately. One model that fits the quiescent spectrum is an
absorbed power law plus neutron star hydrogen atmosphere model. We find an
intrinsic neutron star radius of 17_{-12}^{+31} km and an unabsorbed bolometric
luminosity for the neutron star atmosphere of (2.1+/-0.8)E33 erg/s which is
consistent with predictions for a cooling neutron star.


title: Polarized Microwave Emission from Dust

abstract:
  Polarized emission from dust is an important foreground that can hinder the
progress in polarized CMB studies unless carefully accounted for. We discuss
potential difficulties associated with the dust foreground, namely, the
existence of different grain populations with very different
emission/polarization properties and variations of the polarization yield with
grain temperature. In this context we appeal for systematic studies of
polarized dust emission as the means of dealing with this foreground.


title:
The search for possible mesolensing of cosmic gamma-ray bursts. Double
  and triple bursts in BATSE catalogue

abstract:
  The work is devoted to the search for possible effect of gravitational
lensing on the objects like globular stellar clusters (mesolensing) on the
lightcurves and spectra of large number of gamma-ray bursts from BATSE
catalogue. The general properties and different types of such event were
considered. As the result 11 possibly mesolensed gamma-ray bursts were found.
The properties of possible mesolensed are investigated.


title:
Far-infrared and molecular line observations of Lynds 183 - studies of
  cold gas and dust

abstract:
  We have mapped the dark cloud L183 in the far-infrared at 100um and 200um
with the ISOPHOT photometer aboard the ISO satellite. The observations make it
possible for the first time to study the properties of the large dust grains in
L183 without confusion from smaller grains. The observations show clear colour
temperature variations which are likely to be caused by changes in the emission
properties of the dust particles. In the cloud core the far-infrared colour
temperature drops below 12K. The data allow a new determination of the cloud
mass and the mass distribution. The mass within a radius of 10 arcmin from the
cloud centre is 25 Msun. We have mapped the cloud in several molecular lines
including DCO+(2-1) and H13CO+(1-0). These species are believed to be tracers
of cold and dense molecular material and we detect a strong anticorrelation
between the DCO+ emission and the dust colour temperatures. In particular, the
DCO+(2-1) emission is not detected towards the maximum of the 100um emission
where the colour temperature rises above 15K. The H13CO+ emission follows the
DCO+ distribution but CO isotopes show strong emission even towards the 100um
peak. A comparison of the DCO+ and C18O maps shows sharp variations in the
relative intensities of the species. Morphologically the 200um dust emission
traces the distribution of dense molecular material as seen e.g. in C18O lines.
A comparison with dust column density shows that C18O is depleted by a factor
of 1.5 in the cloud core. We present results of R- and B-band starcounts. The
extinction is much better correlated with the 200um than with the 100um
emission. Based on the 200um correlation at low extinction values we deduce a
value of ~17mag for the visual extinction towards the cloud centre.


title: Helical structures in Seyfert galaxies

abstract:
  The Seyfert galaxies with Z-shaped emission filaments in the Narrow Line
Region (NLR) are considered. We assume that observable Z-shaped structures and
velocity pattern of NLR may be explained as tridimensional helical waves in the
ionization cone.


title: Halpha Flares from V404 Cyg in Quiescence

abstract:
  We present a spectrophotometric study of short-term optical variability in
the quiescent black hole X-ray transient V404 Cyg. This includes two nights of
high time-resolution Halpha spectroscopy with which we resolve much of the
time-variability, and a further six nights of archival spectroscopy with lower
time-resolution but higher spectral-resolution. We find significant variability
in most of the data considered, with both the Halpha line and the continuum
often varying in a correlated way. This includes both dramatic flares lasting a
few hours in which the line flux nearly doubles and lower-level flickering. The
strongest flares involve development of asymmetry in the line profile, with the
red wing usually strongest independent of orbital phase. It is unclear why this
is the case, but we discuss several possible explanations. We consider the
energetics of the flares and compare with plausible models including
chromospheric activity on the companion star, local magnetic reconnection
events within the disc and a varying irradiation from close to the black hole.
Based on the line profile changes during the flares, we conclude that the most
likely origin for the variability is variable photoionisation by the central
source, although local flares within the disc cannot be ruled out.


title:
Measurement of radial velocities and velocity dispersion of stars in
  circumnuclear regions of galaxies using the 2D spectrosopy technique

abstract:
  A procedure is described of construction of velocity fields and velocity
dispersion of the stellar component in the central regions of galaxies on the
basis of data obtained with the integral field spectrograph MPFS.
Cross-correlation and Fourier quotients techniques adapted for 2D spectra
reduction are used. A detailed discussion is given of the problems of providing
for the instrumental profile in measuring the velocity dispersion. Using the
existing version of the spectrograph, one can measure radial velocities and the
dispersion of velocities to an accuracy of 5-10 km/s and 10-15 km/s,
respectively. As an example the double-barred galaxy NGC2950 is considered.


title: Velocity dispersion of stars and gas motion in double-barred galaxies

abstract:
  The current state of the problem of double-barred galaxies investigation is
reviewed. The necessity for application of the panoramic spectroscopy methods
to a detailed study of kinematics of these objects is being proved. The first
results of observing double-barred galaxies at the 6m telescope using the
multipupil spectrograph MPFS and the scanning interferometer Fabry-Perot are
described.


title:
A search for radio supernovae and supernova remnants in the region of
  NGC1569's super star clusters

abstract:
  We have used MERLIN, at 1.4 and 5 GHz, to search for radio supernovae (RSNe)
and supernova remnants (SNRs) in the unobscured irregular dwarf galaxy NGC1569,
and in particular in the region of its super star clusters (SSCs) A and B.
Throughout NGC1569 we find some 5 RSNe and SNRs but the SSCs and their
immediate surroundings are largely devoid of non-thermal radio sources. Even
though many massive stars in the SSCs are expected to have exploded already,
when compared with M82 and its many SSCs the absence of RSNe and SNRs in and
near A and B may seem plausible on statistical arguments. The absence of RSNe
and SNRs in and near A and B may, however, also be due to a violent and
turbulent outflow of stellar winds and supernova ejected material, which does
not provide a quiescent environment for the development of SNRs within and near
the SSCs.


title:
Overall Temporal Synchrotron Emissions from Relativistic Jets: Adiabatic
  and Radiative Breaks

abstract:
  We discuss the GRB afterglow emission from a relativistic jet that is
initially in the radiative regime in which the accelerated electrons are fast
cooling. We note that such a ``semiradiative'' jet decelerates faster than an
adiabatic jet does. We also take into account the effect of strong
inverse-Compton scattering on the cooling frequency in the synchrotron
component and therefore on the light curve decay index. We find that there are
two kinds of light-curve break for the jet effect. The first is an ``adiabatic
break'' if the electrons become slow cooling before the jet enters a spreading
phase, and the second is a ``radiative break'' which appears on the contrary
case. We then show how a relativistic jet evolves dynamically and derive the
overall temporal synchrotron emission in both cases, focusing on the change in
light curve decay index around the break time. Finally, in view of our results,
we rule out two cases for relativistic jets to account for the observed light
curve breaks in a few afterglows: (i) an adiabatic jet with strong Compton
cooling (Y>1) and with the cooling frequency nu_c locating in the observed
energy range; (ii) a radiative jet with a significant fraction of total energy
occupied by electrons (epsilon_e 1).


title: Lithium Depletion in Pre-Mainsequence Solar-Like Stars

abstract:
  We examine the internal structure of solar-like stars in detail between 0.8
and 1.4M Sun and during pre-main sequence phase. Recent opacity computations of
OPAL along with a new hydrodynamical mixing process have been considered. We
also introduce up-to-date nuclear reaction rates and explore the impact of
accretion, mixing-length parameter, non-solar distributions among metals and
realistic rotation history. We compare models predictions of lithium depletion
to the $^7Li$ content observations of the Sun and to 4 young clusters of
different metallicities and ages. We show that we can distinguish two phases in
lithium depletion: 1- a rapid nuclear destruction in the T-Tauri phase before
20 Myrs : this is independent of the mass used within our range but largely
dependent on the extension and temperature of the convective zone, 2- a second
phase where the destruction is slow and moderate and which is largely dependent
on the (magneto)hydrodynamic instability located at the base of the convective
zone.
  In terms of composition, we show the interest on considering helium and
especially the mixture of heavy elements : carbon, oxygen, silicium and iron.
We outline the importance of O/Fe ratio. We note a reasonable agreement on
lithium depletion for the two best known cases, the Sun and the Hyades cluster
for solar-like stars. Other clusters suggest that processes which may partly
inhibit the predicted premainsequence depletion cannot be excluded, in
particular for stars below ~ 0.9M Sun. Finally we suggest different research
areas such as initial stellar models and more realistic atmospheres which could
contribute to a better understanding of this early phase of evolution and which
should become the object of subsequent research.


title:
Detailed Analysis of Nearby Bulge-like Dwarf Stars I. Stellar
  Parameters, Kinematics and Oxygen Abundances

abstract:
  High resolution \'echelle spectra were obtained with the FEROS spectrograph
at the 1.5m ESO telescope for 35 nearby bulge-like stars with metallicities in
the range -0.8 $\leq$ [Fe/H] $\leq$ +0.4. Geneva photometry, astrometric data
from Hipparcos and radial velocities from Coravel are available for these
stars. From Hipparcos data it appears that the turnoff of this population
indicates an age of 10-11 Gyr (Grenon 1999).
  Detailed analysis of the sample stars is carried out and atmospheric
parameters derived from spectroscopic and photometric determinations are
presented. Oxygen abundances are derived based on the forbidden [O I] $\lambda$
6300.3 {\rm \AA} line. The results show an oxygen overabundance pattern for
most of the sample stars when compared to their disk counterparts.


title: Radial velocity variations of the pulsating subdwarf B star PG 1605+072

abstract:
  We present an analysis of high-speed spectroscopy of the pulsating subdwarf B
star PG 1605+072. Periodic radial motions are detected at frequencies similar
to those reported for photometric variations in the star, with amplitudes of up
to 6 km/s. Differences between relative strengths for given frequency peaks for
our velocity data and previously measured photometry are probably a result of
shifting of power between modes over time. Small differences in the detected
frequencies may also indicate mode-shifting. We report the detection of
line-shape variations using the moments of the cross correlation function
profiles. It may be possible to use the moments to identify the star's
pulsation modes.


title: FUSE Observations of O VI Overlying the Scutum Supershell

abstract:
  We present Far Ultraviolet Spectroscopic Explorer observations of the B0 III
star HD 177989 ($l = 17.8^{rm \o}, b = -11.9^{\rm o}, d$ = 4.9 kpc). This line
of sight passes through the high latitude outflow from the Scutum Supershell
(GS 018-04+44), a structure that lies at a kinematic distance of ~ 3.5 kpc, and
spans ~ 5$^{\rm o}$ in diameter. The O VI $\lambda$1031.93 line is compared
with STIS observations of Si IV, C IV, and N V to examine the ionizing
mechanisms responsible for producing the high ion absorption, as well as to
study the processes by which gas is expelled into the halo. The O VI profile
spans a similar velocity range as the other highly ionized atoms, from -70 to
+80 km/s. Component fits reveal very broad absorption at the kinematic velocity
of the Scutum shell, which differs from the narrow Si IV, C IV, and N V
components, suggesting that these other species occupy a more confined region.
It is possible that the O VI is present in hot gas from the shell interior that
is diffusing into the high latitude region above it. The column density ratios
show that while the C IV and Si IV columns are amplified in this region, the
enhancement is not reflected in N V or O VI. We suggest that the ionic ratios
and column densities could be produced by ~ 150-200 turbulent mixing layers
lying in a fragmented medium above the polar cap of the superbubble. We note
through a sight line comparison that although these absorption characteristics
are similar to those near the center of Radio Loops I and IV, they differ
considerably from those near the edges of the loops. It is apparent that the
traits of high ion absorption in a supershell, as well as the ionizing
mechanisms responsible, can vary among sight lines through the shell.


title: Error analysis of the photometric redshift tecnique

abstract:
  We present a calculation of the systematic component of the error budget in
the photometric redshift technique. We make use of it to describe a simple
technique that allows for the assignation of confidence limits to redshift
measurements obtained through photometric methods. We show that our technique,
through the calculation of a redshift probability function, gives complete
information on the probable redshift of an object and its associated confidence
intervals. This information can and must be used in the calculation of any
observable quantity which makes use of the redshift.


title:
An Eulerian Perturbation Approach to Large Scale Structures: Extending
  the Adhesion Approximation

abstract:
  A description of the dynamics of a collisionless, self-gravitating fluid is
developed and applied to follow the development of Large Scale Structures in
the Universe. Such description takes on one of the assumptions of the Adhesion
Approximation (AA) model, i.e., the introduction of an artificial viscosity
$\nu$ in the Euler equation, but extends it to deeper non-linear stages, where
the extrapolation of the linear relation $\psi=-\phi$ between the velocity and
the gravitational potentials -- at the basis of both the Zel'dovich and the
Adhesion models -- is no longer valid. This is achieved by expanding the
relation bewteen the gravitational potential $\phi$ and the velocity potential
$\psi$, in powers of the small viscosity $\nu$. When the results are compared
to the outcomes of an N-body simulation, the proposed extension of the Adhesion
approach provides a better description of small-scale, deeply non-linear
regions, as it is quantitatively shown by the computation of some statistical
indicators. At larger scales, the satisfactory description of the large scale
texture and of the voids given by the canonical Adhesion Approximation is
preserved in the extended model.


title: Formation of Planetary Nebula Lobes by Jets

abstract:
  I conduct an analytical study of the interaction of jets, or a collimated
fast wind (CFW), with a previously blown asymptotic giant branch (AGB) slow
wind. Such jets (or CFWs) are supposedly formed when a compact companion, a
main sequence star or a white dwarf, accretes mass from the AGB star, forms an
accretion disk, and blows two jets. This type of flow, which is thought to
shape bipolar planetary nebulae (PNe), requires 3-dimensional gas dynamical
simulations, which are limited in the parameter space they can cover. By
imposing several simplifying assumptions, I derive simple expressions which
reproduce some basic properties of lobes in bipolar PNe, and which can be used
to guide future numerical simulations. I quantitatively apply the results to
two proto-PNe. I show that the jet interaction with the slow wind can form
lobes which are narrow close to, and far away from, the central binary system,
and which are wider somewhere in between. Jets that are recollimated and have
constant cross section can form cylindrical lobes with constant diameter, as
observed in several bipolar PNe. Close to their source, jets blown by main
sequence companions are radiative; only further out they become adiabatic,
i.e., they form high-temperature low-density bubbles that inflate the lobes.
This implies that radiative cooling must be incorporated in numerical codes
intended to study the formation of lobes in PNe.


title: Inferring the Linear Power Spectrum from the Lyman-alpha Forest

abstract:
  We discuss the determination of the linear power spectrum of dark matter
fluctuations from measurements of the transmitted flux Ly-alpha Forest power
spectrum. We show that at most scales probed by current measurements, the flux
power spectrum is significantly affected by non-linear corrections to the
linear dark matter power spectrum due to gravitational clustering. Inferring
the linear dark matter power spectrum shape is therefore difficult due to
non-linear corrections driving the non-linear power spectrum to a k^{-1.4}
shape nearly independent of initial conditions. We argue that some methods used
in previous estimates underestimate the uncertainties in the shape of the
linear dark matter power spectrum.


title: Searching for Pulsars in Close Binary Systems

abstract:
  We present a detailed mathematical analysis of the Fourier response of binary
pulsar signals whose frequencies are modulated by circular orbital motion. The
fluctuation power spectrum of such signals is found to be \nu_orb-periodic over
a compact frequency range, where \nu_orb denotes orbital frequency.
Subsequently, we consider a wide range of binary systems with circular orbits
and short orbital periods, and present a Partial Coherence Recovery Technique
for searching for binary millisecond X-ray and radio pulsars. We use numerical
simulations to investigate the detectability of pulsars in such systems with
P_orb ~ 6 hours, using this technique and three widely used pulsar search
methods. These simulations demonstrate that the Partial Coherence Recovery
Technique is on average several times more sensitive at detecting pulsars in
close binary systems when the data span is more than 2 orbital periods. The
systems one may find using such a method can be used to improve the constraints
on the coalescence rate of compact objects and they also represent those
systems most likely to be detected with gravitational wave detectors such as
LISA.


title: Intraday Variability in Northern Hemisphere Radio Sources

abstract:
  We summarize results from flux density monitoring campaigns performed with
the 100 meter radio-telescope at Effelsberg and the VLA during the past 15 yrs.
We briefly discuss some of the statistical properties of the rapid variability
from now more than 40 high declination sources, which show Intraday Variability
(IDV). In general, IDV is more pronounced for sources with flat radio spectra
and compact VLBI structures. The frequency dependence of the variability
pattern varies with source and observing time. For 0917+62, we present new VLBI
images, which suggest that the variability pattern is modified by the
occurrence of new jet components. For 0716+71, we show the first detection of
IDV at millimeter wavelengths (32 GHz). For the physical interpretation of the
IDV phenomenon, a complex source and frequency dependent superposition of
interstellar scintillation and source intrinsic variability should be
considered.


title: On the effective temperature scale of O stars

abstract:
  We rediscuss the temperature of O dwarfs based on new non-LTE line blanketed
atmosphere models including stellar winds computed with the CMFGEN code of
Hillier & Miller (1998). Compared to the latest calibration of Vacca et al.
(1996), the inclusion of line blanketing leads to lower effective temperatures,
typically by 4000 to 1500 K for O3 to O9.5 dwarf stars. The dependence of the
Teff-scale on stellar and model parameters - such as mass loss,
microturbulence, and metallicity - is explored, and model predictions are
compared to optical observations of O stars. Even for an SMC metallicity we
find a non-negligible effect of line blanketing on the Teff-scale. The
temperature reduction implies downward revisions of luminosities by 0.1 dex and
Lyman continuum fluxes Q0 by approximately 40% for dwarfs of a given spectral
type.


title: Boundary Corrections in Fractal Analysis of Galaxy Surveys

abstract:
  The analysis of redshift surveys with fractal tools requires one to apply
some form of statistical correction for galaxies lying near the geometric
boundary of the sample. In this paper we compare three different methods of
performing such a correction upon estimates of the correlation integral in
order to assess the extent to which estimates may be biased by boundary terms.
We apply the corrections illustrative examples, including a simple fractal set
(L\'{e}vy flight), a random $\beta$-model, and a subset of the CfA2 Southern
Cap survey. This study shows that the new ``angular'' correction method we
present is more generally applicable than the other methods used to date: the
conventional ``capacity'' correction imposes a bias towards homogeneity, and
the ``deflation'' method discards large-scale information, and consequently
reduces the statistical usefulness of data sets. The ``angular'' correction
method is effective at recovering true fractal dimensions, although the extent
to which boundary corrections are important depends on the form of fractal
distribution assumed as well as the details of the survey geometry. We also
show that the CfA2 Southern sample does not show any real evidence of a
transition to homogeneity. We then revisit the IRAS PSCz survey and ``mock''
PSCz catalogues made using N-body simulations of two different cosmologies. The
results we obtain from the PSCz survey are not significantly affected by the
form of boundary correction used, confirming that the transition from fractal
to homogeneous behaviour reported by Pan & Coles (2000) is real.


title:
Doin' the twist: Secular changes in the surface differential rotation on
  AB Doradus

abstract:
  We present measurements of the rotation rates of individual starspots on the
rapidly rotating young K0 dwarf AB Doradus, at six epochs between 1988 December
and 1996 December. The equatorial rotation period of the star decreased from
0.5137 to 0.5129 days between 1988 December and 1992 January. It then increased
steadily, attaining a value of 0.5133 days by 1996 December. The latitude
dependence of the rotation rate mirrored the changes in the equatorial rotation
rate. The beat period between the equatorial and polar rotation periods dropped
from 140 days to 70 days initially, then rose steadily. The most rigid
rotation, in 1988 December, occurred when the starspot coverage was at a
maximum. The time-dependent part of the differential rotation is found to have
Delta Omega / Omega ~ 0.004, which should alter the oblateness of the star
enough to explain the period changes observed in several close binaries via the
mechanism of Applegate (1992).


title: Stationary equatorial MHD flows in general relativity

abstract:
  We derive a new formulation of the fully general relativistic equations
describing a stationary equatorial MHD outflow from a rotating central object.
The wind solution appears as a level contour of a `Bernoulli' function fixed by
the requirements that it must pass through the slow and fast critical points.
This approach is the general relativistic extension to the classical treatment
of Sakurai (1985). We discuss in details how the efficiency of the magnetic to
kinetic energy conversion depends mainly on the geometry of the flux tubes and
show that the magnetic acceleration can work very well under some conditions.
We show how this tool can be used for the study of several astrophysical
phenomena, among which gamma-ray bursts.


title:
Radial B-V/V-K color gradients, extinction-free Q_BVK combined color
  indices, and the history of star formation in the Cartwheel ring galaxy

abstract:
  In this paper we model and analyse the B-V/V-K radial color gradients
observed in the Cartwheel ring galaxy. Along with the color-color diagrams, we
use the Q_BVK combined color indices, which minimise the uncertainties in the
observed B-V and V-K colors introduced by dust extinction. To model the optical
and near-infrared color properties of the Cartwheel galaxy, we assume that an
intruder galaxy generates an expanding ring density wave in the Cartwheel's
disk, which in its turn triggers massive star formation along the wave's
perimeter according to the Schmidt law. We use the population synthesis to
calculate the color properties of stellar populations formed in the expanding
density wave. The results of color modelling suggest that the pre-collision
Cartwheel was a late-type spiral, embedded in an extensive gaseous disk of
sub-critical surface density. The properties of the old stellar disk are
typical for the late-type Freeman disks, with the central surface brightness in
V-band and the scale length being 21.0 mag arcsec^-2 and 2 kpc respectively.
The pre-collision gaseous disk has a metallicity gradient ranging from
z=z_sun/5 at the outer regions to z=z_sun in the central regions. At present,
the wave of star formation has passed the initial extent of the pre-collision,
old stellar disk and is currently moving in the predominantly gaseous,
low-metallicity disk at the radius of 16 kpc. Neither young stellar populations
formed in an expanding density wave, nor their mixture with the old,
pre-collision stellar populations can reproduce the B-V and V-K colors of the
Cartwheel's nucleus+inner ring. We find that an additional 10-Myr-old burst of
star formation in the nuclear regions, along with the visual extinction of 1.3
mag, might be responsible for the peculiar colors of the Cartwheel's nucleus.


title:
An HI survey of the Centaurus and Sculptor Groups - Constraints on the
  space density of low mass galaxies

abstract:
  We present results of two 21-cm HI surveys performed with the Australia
Telescope Compact Array in the nearby Centaurus A and Sculptor galaxy groups.
These surveys are sensitive to compact HI clouds and galaxies with HI masses as
low as 3E+06 Msun, and are therefore among the most sensitive extragalactic HI
surveys to date. The surveys consist of sparsely spaced pointings that sample
approximately 2% of the groups' area on the sky. We detected previously known
group members, but we found no new HI clouds or galaxies down to the
sensitivity limit of the surveys. If the HI mass function had a faint end slope
of alpha = 1.5 below M_{HI} = 10^{7.5} Msun in these groups, we would have
expected ~3 new objects. Cold dark matter theories of galaxy formation predict
the existence of a large number low mass DM sub-halos that might appear as tiny
satellites in galaxy groups. Our results support and extend similar conclusions
derived from previous HI surveys that a HI rich population of these satellites
does not exist.


title:
Clustering properties and gravitational lensing of forming spheroidal
  galaxies

abstract:
  We show that the predictions of the recent physical model by Granato et al.
(2001) are fully consistent with the available estimates of the clustering
properties of galaxies at (sub)-mm wavelengths. The model is then exploited to
compute the expected power spectrum of fluctuations due to clustering at the
frequencies of the High Frequency Instrument (HFI) of ESA's {\sc Planck}
satellite. The clustering signal is found to be detectable in regions of low
interstellar dust emission. A further distinctive prediction of the adopted
model is a remarkably high fraction of gravitationally lensed sources at bright
mm/sub-mm fluxes. In fact, according to the adopted model, only thanks to
gravitational lensing, a significant number of high-$z$ forming spheroidal
galaxies will be detectable by large area, shallow surveys at mm/sub-mm
wavelengths, such as those carried out by P{\sc lanck}/HFI. Allowing for other
source populations, we find that the fraction of gravitationally lensed sources
at bright mm/sub-mm fluxes is expected to be up to $\simeq 40%$.


title: CO Observations of the Interacting Galaxy Pair NGC 5394/95

abstract:
  BIMA CO 1-0 observations are presented of the spiral galaxies NGC 5394 and
NGC 5395 that have undergone a recent, grazing encounter. In NGC 5394, 80% of
the CO emission detected by BIMA is concentrated in the central 800 pc (FWHM)
starburst region.In an encounter simulation that reproduces some of the main
features of this galaxy pair, a considerable amount of gas in NGC 5394 falls
into the central region early in the collision. The observed total gas
distribution in the disk of NGC 5394 is lopsided, with more HI, CO, and H-alpha
emission coming from the western or southwestern side. The innermost western
arm of NGC 5394 is seen in CO and H-alpha emission, but the eastern inner-disk
arm, which is very bright in the optical continuum, is not detected in CO or
H-alpha emission. From a comparison of the radio continuum, H-alpha, 60 micron,
and CO luminosities, we estimate that the average visual extinction of the
starburst is 3 - 4 mag and the conversion factor N(H2)/I(CO) in the starburst
is a factor of 3 - 4 below the standard value. Comparison of NGC 5394 with two
other systems previously studied suggests that in prograde grazing encounters a
central starburst may not develop until near the end of the ocular phase. Very
little of the CO emission from NGC 5395 found in previous single-dish
observations is detected by BIMA.


title: The Color-Magnitude Diagram of composite stellar populations

abstract:
  The theoretical relation between the number of post main sequence stars from
stellar populations and their total mass in investigated. This is used to
derive some basic relations between the stellar number counts of stellar
populations with an age spread and the star formation history which produced
them. The main purpose of this investigation is to offer a guideline for the
construction of simulations aimed at reproducing color- magnitude diagrams.


title:
The XMM-LSS Survey: Mapping hot, luminous, obscured and dark material
  out to z~1-2

abstract:
  We review the unique cosmological implications of the XMM-LSS survey in
association with its multi-WL follow-up: (1) Large Scale Structures traced by
X-ray clusters and AGNs, optical galaxies, weak lensing as well as
Sunyaev-Zel'dovich effect; (2) location of IR star forming galaxies and IR
(obscured) AGNs within the cosmic web. The XMM/MegaCam/VIRMOS/SIRTF data base
will provide the first comprehensive study of structure formation - from
hundreds of Mpc to galaxy scale - in close connection with environmental
processes.


title:
ISOCAM Mid-InfraRed Detection of HR 10: A Distant Clone of Arp 220 at
  z=1.44

abstract:
  We report the detection of the extremely red object (ERO), HR 10 (I-K= 6.5,
z=1.44), at 4.9 and 6.1 microns (rest-frame) with ISOCAM, the mid-infrared
(MIR) camera onboard the Infrared Space Observatory (ISO). HR 10 is the first
ERO spectroscopically identified to be associated with an ultra-luminous IR
galaxy (ULIG) detected in the radio, MIR and sub-millimeter. The rest-frame
spectral energy distribution (SED) of HR 10 is amazingly similar to the one of
Arp 220, scaled by a factor 3.8+/-1.3. The corresponding 8-1000 microns
luminosity (~ 7x10^12 h70^{-2} Lsol) translates into a star formation rate of
about 1200 h70^{-2} Msol/yr if HR 10 is mostly powered by star formation. We
address the key issue of the origin of the powerful luminosity of HR 10, i.e.
starburst versus active galactic nucleus (AGN), by using the similarity with
its closeby clone, Arp 220.


title: Galactic Structure and Radioactivity Source Distributions

abstract:
  A probable sky map of the emission from a short-lived isotrope produced by
massive stars is presented. The model is based on the nonaxisymmetric component
of a dust distribution model developed to reproduce Galactic FIR emission.
Features seen in COMPTEL observations are qualitatively reproduced.


title:
Equilibrium abundances in hot DA white dwarfs as derived from
  self-consistent diffusion models I. Analysis of spectroscopic EUVE data

abstract:
  We present the first analysis of an EUV selected sample of hot DA white
dwarfs using a new type of atmospheric models. These models take into account
the interplay between gravitational settling and radiative acceleration to
predict the chemical stratification from an equilibrium between the two forces
while self-consistently solving for the atmospheric structure. In contrast to
atmospheric models with the assumption of chemical homogeneity, the number of
free parameters in the new models is reduced to the effective temperature and
surface gravity alone. The overall good reproduction of observed EUV spectra
reveals that these models are able to describe the physical conditions in hot
DA white dwarf atmospheres correctly. A comparison with previous analyses
highlights the improvements as well as the limits of our new models.


title: X-ray flashes and X-ray rich Gamma Ray Bursts

abstract:
  X-ray flashes are detected in the Wide Field Cameras on BeppoSAX in the
energy range 2-25 keV as bright X-ray sources lasting of the order of minutes,
but remaining undetected in the Gamma Ray Bursts Monitor on BeppoSAX. They have
properties very similar to the x-ray counterparts of GRBs and account for some
of the Fast X-ray Transient events seen in almost every x-ray satellite. We
review their X-ray properties and show that x-ray flashes are in fact very
soft, x-ray rich, untriggered gamma ray bursts, in which the peak energy in
2-10 keV x-rays could be up to a factor of 100 larger than the peak energy in
the 50-300 keV gamma ray range. The frequency is ~100 per year.


title: Multi-wavelength Surveys for Distant Clusters

abstract:
  Given the importance of clusters to the fields of cosmology and galaxy
evolution, it is critical to understand how the cluster detection process
affects (biases) ones scientific conclusions derived from a given cluster
sample. I review the astrophysics, algorithms, and observational constraints
that must be considered when attempting to assess cluster selection biases and
their impact on the scientific constraints derived from multi-wavelength
cluster surveys. In particular, one can more accurately quantify and understand
the selection biases and assess cluster evolution when using joint
optical/NIR/x-ray surveys than can be achieved when employing any single
cluster survey.


title: The Star Formation History of the Blue Compact Dwarf Galaxy UGCA 290

abstract:
  We present the star formation history of UGCA 290, a galaxy with properties
intermediate between Blue Compact Dwarfs and Dwarf Irregulars. This galaxy is
particularly interesting because its young stellar population is extremely
similar to that of the well-studied type iE Blue Compact Dwarf VII Zw 403,
despite its different spatial morphology and old stellar content. Our Hubble
Space Telescope/Wide Field Planetary Camera 2 single-star photometry for UGCA
290 extends over nine magnitudes in I, and allows a detailed study of its star
formation history. Using synthetic color-magnitude diagrams, we show that the
recent "burst" which gives this galaxy its BCD status is a moderate enhancement
in star formation which lasted for approximately 20 Myr, at a rate about ten
times above its previous rate. The star formation history for most of the
previous billion years is consistent with a constant rate, although
enhancements as large as the current one are possible at times ealier than 400
Myr ago. We estimate that the total mass converted into stars in UGCA 290 more
than one billion years ago is about three times the astrated mass since that
time. The initial mass function is consistent with a Salpeter slope, and the
stellar metallicity is bracketed by Z_sun/50 and Z_sun/5, with evidence for
metallicity evolution. Similar results for the star formation history over the
past 600 Myr apply to VII Zw 403. Our main result is that despite the
traditional picture of BCDs, the current bursts in these two galaxies are
neither remarkably intense nor short-lived, and that most of their star
formation occured more than a billion years ago.


title:
A spectroscopic survey of stars brighter than B=16.6 magnitude in omega
  Centauri

abstract:
  Using the 2dF multi-fibre instrument at the AAT, we have carried out a
spectroscopic survey of over 1500 stars brighter than B=16.6 mag, which have
been confirmed by the proper motion study of van Leeuwen et al. (2000) to be
members of the massive galactic globular cluster, omega Centauri. The survey
aimed at sampling the Hertzsprung-Russell Diagram in a uniform way, thus
avoiding a bias towards the dominant stellar population and allowing the study
of stars with less common properties such as particularly metal-rich or
metal-poor stars. Exceptionally, though, emphasis has been given to include as
many RR Lyrae variables as possible in order to address the question why these
variables are distributed over such a wide observed range in colours --
coinciding with many non-variable stars of similar colours. The potential of
the data and analysis are presented together with the first preliminary
results.


title: The Trispectrum of the 4 Year COBE-DMR data

abstract:
  We propose an estimator for the trispectrum of a scalar random field on a
sphere, discuss its geometrical and statistical properties, and outline its
implementation. By estimating the trispectrum of the 4 year COBE-DMR data (in
HEALPix pixelization) we find new evidence of a non-Gaussian signal associated
with a known systematic effect. We find that by removing data from the sky maps
for those periods of time perturbed by this effect, the amplitudes of the
trispectrum coefficients become completely consistent with predictions for a
Gaussian sky. These results reinforce the importance of statistical methods
based in harmonic space for quantifying non-Gaussianity.


title:
A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. I. Evidence for an
  Evolutionary Relationship Between Quasars and Radio Galaxies

abstract:
  Deep optical images have been gathered for a nearly complete sample of radio
galaxies from the Revised 3rd Cambridge (3CR) Catalog in the redshift range
0.15 < z < 0.65. Total and nuclear magnitudes and colors have been extracted.
The richness of the galaxy clustering environment has also been quantified by
calculating the amplitude of the galaxy-galaxy spatial covariance function
(B_gg), showing overdensities ranging up to Abell class 0-1 clusters. These
optical data are compared to similar data from an existing sample of radio-loud
quasars in the same redshift range for the purpose of determining the
relationship between radio galaxies and quasars. In the range 0.15 < z < 0.4,
we find that quasars and radio galaxies have significantly different
environments in that only radio galaxies are found in rich cluster
environments. This comparison appears to rule out the hypothesis that all
quasars are radio galaxies viewed from a particular angle at the 97% confidence
level (99.6% confidence level if N-galaxies are considered quasars). The
existence of quasars in clusters at z > 0.4 supports the hypothesis that some
radio-loud quasars may dim with time and evolve into radio galaxies with an
e-folding time of ~0.9 Gyr. A compatible scenario is presented for this
evolution in which the quasar dims due to the absence of low velocity
interactions between the quasar host and companion galaxies which trigger
quasar activity and/or a diminishing fuel supply caused by the more effective
gas ``sweeping'' of a growing intracluster medium.


title: Understanding the LMXB X2127+119 in M15 I. X-ray eclipses and dips

abstract:
  We present X-ray observations of the high-inclination low-mass X-ray binary
system X2127+119 (AC211) in the globular cluster M15 (NGC 7078). The
observations consist of data acquired in 1996 with the RXTE satellite and in
1995 with the ASCA satellite. Also, the MPC1 data from the 1988 GINGA
observations were de-archived and re-analysed. The phase-folded 2-10 keV
hardness ratios from all three missions differ significantly indicating that
the system can exhibit different spectral behaviours. We find that the X-ray
eclipse profiles can be described relatively well using a simple model where
the secondary star passes in front of a large X-ray emitting region. For this
we require a mass ratio (q=M1/M2) of about one. The radius of this X-ray
emitting region is ~0.8 RL1 and its vertical extent 60 degrees above the
orbital plane. We suggest that if this X-ray emitting region were an optically
thick corona, it would explain various puzzling aspects of this system. We also
show that the X-ray dip observed at phases around 0.65 does not conform with
the idea that the dip is caused by vertically extended material associated with
the stream/disc impact region, but that it could be due to structure in the
inner parts of the disc.


title: Dust Polarization From Starlight Data

abstract:
  We present a statistical analysis of the interstellar medium (ISM)
polarization from the largest compilation available of starlight data, which
comprises ~ 5500 stars. The measured correlation between the mean polarization
degree and extinction indicates that ISM dust grains are not fully aligned with
the uniform component of the large-scale Galactic magnetic field. Moreover, we
estimate the ratio of the uniform to the random plane-of-the-sky components of
the magnetic field to be B_u/B_r = 0.8. From the analysis of starlight
polarization degree and position angle we find that the magnetic field broadly
follows Galactic structures on large-scales. On the other hand, the angular
power spectrum C_l of the polarization degree for Galactic plane data is found
to be consistent with a power-law, C_l ~ l^{-1.5} (where l = 180 deg/\theta is
the multipole order), for angular scales \theta > 10 arcmin. We argue that this
data set can be used to estimate diffuse polarized emission at microwave
frequencies.


title: Radio AGN Surveys

abstract:
  We present a short overview of radio surveys for AGN, including the
`complete' flux limited surveys and `filtered' surveys. We also describe our
ultra-steep spectrum search for the highest redshift radio galaxies, and our
follow-up VLA and ATCA observations of the most distant (z=5.19) and the most
luminous z<2 radio galaxy known.


title: Two extra-solar planets from the Anglo-Australian Planet Search

abstract:
  We report the detection of two new extra-solar planets from the
Anglo-Australian Planet Search around the stars HD142 and HD23079. The planet
orbiting HD142 has an orbital period of just under one year, while that
orbiting HD23079 has a period of just under two years. HD142 falls into the
class of "eccentric" gas giants. HD23079 lies in the recently uncovered class
of "epsilon Ret-like" planets - extra-solar gas giant planets with
near-circular orbits outside 0.1 a.u. The recent discovery of several more
members of this class provides new impetus for the extension of existing planet
searches to longer periods, in the search for Jupiter-like planets in
Jupiter-like orbits.


title: Identifying modes in a pulsating sdB (EC14026) star

abstract:
  We present a preliminary analysis of time series photometry on the pulsating
subdwarf B star PG1336-018 acquired as part of two Whole Earth Telescope runs.
PG1336-018 is a multi-mode pulsator with at least 15 periods centered around
175 seconds. It is also an HW~Vir-type eclipsing binary with a period of 2.4
hours.
  Though over 20 pulsating subdwarf B stars have been discovered, only a few
have resolved temporal spectra and still fewer have identified pulsation modes.
We analyze features unique to the eclipsing binary system of PG1336-018 as a
means of identifying pulsation modes.


title: Magnetohydrodynamics of Gamma-Ray Burst Outflows

abstract:
  Using relativistic, axisymmetric, ideal MHD, we examine the outflow from a
disk around a compact object, taking into account the baryonic matter, the
electron-positron/photon fluid, and the large-scale electromagnetic field.
Focussing on the parameter regime appropriate to gamma-ray burst outflows, we
demonstrate, through exact self-similar solutions, that the thermal force
(which dominates the initial acceleration) and the Lorentz force (which
dominates further out and contributes most of the acceleration) can convert up
to ~50% of the initial total energy into asymptotic baryon kinetic energy. We
examine how baryon loading and magnetic collimation affect the structure of the
flow, including the regime where emission due to internal shocks could take
place.


title:
The Thermal Sunyaev Zel'dovich effect : a powerful probe for missing
  baryons

abstract:
  About 90% of baryons in the universe have thus far escaped direct
observation. This is known as the {\it missing baryon problem}. The Sunyaev
Zel'dovich effect (SZ effect) has the potential to directly measure the state
of the majority of these missing baryons. The next generation CMB experiments
such as AMIBA will provide an unbiased sample of the intergalactic medium
through the SZ effect. The existing and upcoming simulations and analytical
studies provide a quantitative understanding of the SZ effect. All these make
the SZ effect a powerful baryon probe. We present an overview of this probe
from both phenomelogical and theoretical aspects.


title: Accelerating Universe, Cosmological Constant and Dark Energy

abstract:
  We present a space-velocity theory of gravitation in a 4-dimensional curved
space. The solutions of the field equations yield 3 possibilities for the
universe expansion but only the accelerating one is possible. Although the
theory has no cosmological constant, we exract from it its equivalent value
which is shown to be in agreement with measurements. No pressure is used in the
theory.


title:
Velocity, Acceleration and Cosmic Distances in Cosmological Special
  Relativity

abstract:
  In this paper we present the fundamentals of the cosmological special
relativity (CSR) by discussing the dynamical concepts of velocity, acceleration
and cosmic distances in spacevelocity. These concepts occur in CSR just as
those of mass, linear momentum and energy appear in Einstein's special
relativity (ESR) in spacetime.


title: A half-a-day long thermonuclear X-ray burst from KS 1731-260

abstract:
  We report on an approximately twelve hour long X-ray flare from the low-mass
X-ray binary KS 1731-260. The flare has a rise time of less than 13 min and
declines exponentially with a decay time of 2.7 hours. The flare emission is
well described by black-body radiation with peak temperature of 2.4 keV. The
total energy release from the event is 10^{42} erg (for an assumed distance of
7 kpc). The flare has all the characteristics of thermo-nuclear X-ray bursts
(so-called type I X-ray bursts), except for its very long duration and
therefore large energy release (factor of 1500-4000 longer and 250-425 more
energy than normal type I X-ray bursts from this source). The flare is preceded
by a short and weak X-ray burst, possibly of type I. Days to weeks before the
flare, type I X-ray bursts were seen at a rate of ~3 per day. However, after
the flare type I X-ray bursting ceased for at least a month, suggesting that
the superburst affected the type I bursting behaviour. The persistent emission
is not significantly different during the non-bursting period. We compare the
characteristics of this event with similar long X-ray flares, so-called
superbursts, seen in other sources (4U 1735-44, 4U 1820-30, 4U 1636-53, Ser
X-1, GX 3+1). The event seen from KS 1731-260 is the longest reported so far.
We discuss two possible mechanisms that might cause these superbursts, unstable
carbon burning (as proposed recently) and electron capture by protons with
subsequent capture of the resulting neutrons by heavy nuclei.


title: Tidally distorted accretion discs in binary stars

abstract:
  The non-axisymmetric features observed in the discs of dwarf novae in
outburst are usually considered to be spiral shocks, which are the non-linear
relatives of tidally excited waves. This interpretation suffers from a number
of problems. For example, the natural site of wave excitation lies outside the
Roche lobe, the disc must be especially hot, and most treatments of wave
propagation do not take into account the vertical structure of the disc.
  In this paper I construct a detailed semi-analytical model of the non-linear
tidal distortion of a thin, three-dimensional accretion disc by a binary
companion on a circular orbit. The analysis presented here allows for vertical
motion and radiative energy transport, and introduces a simple model for the
turbulent magnetic stress. The m=2 inner vertical resonance has an important
influence on the amplitude and phase of the tidal distortion. I show that the
observed patterns find a natural explanation if the emission is associated with
the tidally thickened sectors of the outer disc, which may be irradiated from
the centre. According to this hypothesis, it may be possible to constrain the
physical parameters of the disc through future observations.


title: A four-hours long burst from Serpens X-1

abstract:
  During a serendipitous observation of the BeppoSAX Wide Field Cameras, a very
long Type I X-ray burst was observed from the low mass X-ray binary Serpens
X-1. The burst lasted for approximately 4 hours and had an exponential decay
time of 69+/-2 min (2-28 keV). The bolometric peak-luminosity is
(1.6+/-0.2)x10^38 erg/s and the fluence (7.3+/-1.4)x10^41 erg. The first
'normal' Type I burst was observed 34 days after the superburst. This is in
rough agreement with recent predictions for unstable carbon burning in a heavy
element ocean.


title: Cosmic Background Anisotropy due to Neutrino Oscillations Revisited

abstract:
  This paper has been withdrawn by the author due to a crucial error in several
equations.


title: On the wake generated by a planet in a disc

abstract:
  A planet of low mass orbiting in a two-dimensional gaseous disc generates a
one-armed spiral wake. We explain this phenomenon as the result of constructive
interference between wave modes in the disc, somewhat similar to the Kelvin
wedge produced in the wake of a ship. The same feature is not expected in a
three-dimensional disc with thermal stratification.


title: X-Ray Emission from Central Binary Systems of Planetary Nebulae

abstract:
  We study the conditions under which a main sequence binary companion to the
central ionizing star of a planetary nebula (PN) might become magnetically
active and thereby display strong X-ray luminosity. Since most PNe are older
than few billion years, any main sequence companion will rotate too slowly to
have magnetic activity and hence bright X-ray emission, unless it is spun-up.
We demonstrate that if the orbital separation during the AGB phase of the PN
progenitor is less than 30-60 AU, main sequence companions in the spectral type
range F7 to M4 will accrete enough angular momentum from the AGB wind to rotate
rapidly, become magnetically active, and exhibit strong X-ray luminosities.
Lower mass M stars and brown dwarfs can also become magnetically active, but
they should have small orbital separations and hence are less likely to survive
the AGB phase of the progenitor. We estimate that 20-30 per cent of elliptical
PNe and 30-50 per cent of bipolar PN are likely to have magnetically active
companions which will reveal themselves in X-ray observations. Re-analysis of
Chandra X-ray Observatory spectroscopy of the compact central source of NGC
7293 indicates that the emitting region of this object possesses abundance
anomalies similar to those of coronally active main-sequence stars.


title:
Implications of the HST/FGS parallax of SS Cygni on the disc instability
  model

abstract:
  We analyse the consequences of the recently measured parallax of SS Cygni
(Harrison et al. 1999) on the accretion disc limit cycle model. Using the
observed long term light curve of SS Cyg and d=166 pc, we obtain for the mean
mass transfer rate 4.2*10^(17)g/s. In addition, we calculate the vertical
structure of the accretion disc taking into account heating of the outer disc
by the stream impact. Comparing the mean accretion rate derived from the
observations with the calculated critical mass transfer rate, we find that the
disc instability model disagrees with the observed long term light curve of SS
Cyg as the mean mass transfer rate is greater or similar to the critical mass
transfer rate. The failure of the model indicated by this result can be
confirmed by considering that the accretion rate at the onset of the decline
should be exactly equal to the value critical for stability. In contrast to
this prediction of the model, we find that the accretion rate required to
explain the observed visual magnitude at the onset of the decline must be
significantly higher than the critical mass transfer rate. Our results strongly
suggest that either the usually assumed temperature dependence of the viscosity
parameter alpha is not a realistic description of the disc viscosity, that the
mass transfer rate in SS Cyg noticeably increases during the outbursts or,
finally, that the HST distance of 166 pc, is too high.


title: VLA detection of OH absorption from the elliptical galaxy NGC 1052

abstract:
  VLA observations of OH absorption towards the elliptical galaxy NGC 1052 are
presented. Both OH lines, at 1665 and 1667 MHz, were detected in absorption
towards the center of NGC 1052. The hyperfine ratio of the two OH lines
($\tau$$_{1667}$/$\tau$$_{1665}$) is 2.6$\pm$0.8 as compared to 1.8 expected
for the excitation under LTE conditions for an optically thin cloud. The column
density of OH is estimated to be $2.73(\pm0.26)\times10^{14} cm^{-2}$ assuming
$T_{ex} \sim$10 K. The centers of both the OH lines are redshifted from the
systemic velocity of the galaxy by $\sim$173 km s$^{-1}$. The velocity of OH
line coincides with the velocity corresponding to the strongest HI absorption.
We suggest that OH absorption is arising from a molecular cloud falling towards
the nucleus. The OH line, though narrower, is found to be within the much
broader and smoother H$_2$O megamaser emission. The possible link between OH/HI
and $H_2O$ emission is discussed.


title: The origin of the high velocity circumstellar gas around SN 1998S

abstract:
  Modelling of high resolution Balmer line profiles in the early-time spectra
of SN 1998S shows that the inferred fast (roughly 400 km/s) circumstellar (CS)
gas on days 23 and 42 post-explosion is confined to a narrow, negative velocity
gradient shell just above the photosphere. This gas may be identified with a
slow (v < 40 km/s) progenitor wind accelerated at the ejecta-wind interface. In
this scenario, the photosphere coincides with a cool dense shell formed in the
reverse shock. Acceleration by radiation from the supernova or by a
shock-accelerated relativistic particle precursor are both possible
explanations for the observed fast CS gas. An alternative, equally plausible
scenario is that the fast CS gas is accelerated within shocked clouds engulfed
by the outer shock, as it propagates through the intercloud wind.


title: ISO-LWS two colour diagram of young stellar objects

abstract:
  We present a [60--100] vs. [100--170] $\mu$m two colour diagram for a sample
of 61 young stellar objects (YSOs) observed with the Long Wavelength
Spectrometer (LWS) on-board the Infrared Space Observatory (ISO). The sample
consists of 17 Class 0 sources, 15 Class I, 9 Bright Class I ($L_{\rm bol}>10^4
L_\odot$), 20 Class II (14 Herbig Ae/Be stars and 6 T Tauri stars). We find
that each class occupies a well defined region in our diagram with colour
temperatures increasing from Class 0 to Class II. Therefore the [60--100] vs.
[100--170] two colours diagram is a powerful and simple tool to derive from
future (e.g. with the Herschel Space Observatory) photometric surveys the
evolutionary status of YSOs. The advantage over other tools already developed
is that photometry at other wavelengths is not required: three flux
measurements are enough to derive the evolutionary status of a source. As an
example we use the colours of the YSO IRAS 18148$-$0440 to classify it as Class
I. The main limitation of this work is the low spatial resolution of the LWS
which, for some objects, causes a high uncertainty in the measured fluxes due
to the background emission or to the source confusion inside the LWS beam.


title: X-rays from Star-Forming Regions in the VLT Era

abstract:
  The association between star-forming regions and X-ray emission was
discovered over 30 years ago. We now know that essentially all young stellar
objects, T Tauri stars and protostars, are X-ray emitters, although the case of
the youngest, Class~0 protostars, is less clear. The paper highlights X-ray
emission and absorption mechanisms, and summarizes X-ray observations of young
stellar objects. The impact of the VLT on the characterization of the new X-ray
sources is also briefly discussed.


title:
Observational Signatures of Black Holes: Spectral and Temporal Features
  of XTE J1550-564

abstract:
  The theoretical predictions of the converging inflow, or Bulk-Motion
Comptonization model are discussed and some predictions are compared to X- and
gamma-ray observations of the high/soft state of Galactic black hole candidate
XTE J1550+564. The 100 Hz QPO phenomenon tends to be detected in the high-state
at times when the bolometric luminosity surges and the hard-power-law spectral
component is dominant. Furthermore, the power in these features increases with
energy. We offer interpretation of this phenomenon, as oscillations of the
innermost part of the accretion disk, which in turn supplies the seed photons
for the converging inflow where the hard power-law is formed through Bulk
Motion Comptonization (BMC). We further argue that the noted lack of coherence
between intensity variations of the high-soft-state low and high energy bands
is a natural consequence of our model, and that a natural explanation for the
observed hard and soft lag phenomenon is offered. In addition, we address some
criticisms of the BMC model supporting our claims with observational results.


title: N=1 Supergravity Chaotic Inflation in the Braneworld Scenario

abstract:
  We study a N=1 Supergravity chaotic inflationary model, in the context of the
braneworld scenario. It is shown that successful inflation and reheating
consistent with phenomenological constraints can be achieved via the new terms
in the Friedmann equation arising from brane physics. Interestingly, the model
satisfies observational bounds with sub-Planckian field values, implying that
chaotic inflation on the brane is free from the well known difficulties
associated with the presence of higher order non-renormalizable terms in the
superpotential. A bound on the mass scale of the fifth dimension, $M_5 \gsim
1.3 \times 10^{-6} M_P$, is obtained from the requirement that the reheating
temperature be higher than the temperature of the electroweak phase transition.


title:
Extinction calculations of multi-sphere polycrystalline graphitic
  clusters - A comparison with the 2175 AA peak and between a rigorous solution
  and discrete-dipole approximations

abstract:
  Certain dust particles in space are expected to appear as clusters of
individual grains. The morphology of these clusters could be fractal or
compact. In this paper we study the light scattering by compact and fractal
polycrystalline graphitic clusters consisting of touching identical spheres. We
compare three general methods for computing the extinction of the clusters in
the wavelength range 0.1 - 100 micron, namely, a rigorous solution (Gerardy &
Ausloos 1982) and two different discrete-dipole approximation methods --
MarCODES (Markel 1998) and DDSCAT (Draine & Flatau 1994). We consider clusters
of N = 4, 7, 8, 27,32, 49, 108 and 343 particles of radii either 10 nm or 50
nm, arranged in three different geometries: open fractal (dimension D = 1.77),
simple cubic and face-centred cubic. The rigorous solution shows that the
extinction of the fractal clusters, with N < 50 and particle radii 10 nm,
displays a peak within 2% of the location of the observed interstellar
extinction peak at ~4.6 inverse micron; the smaller the cluster, the closer its
peak gets to this value. By contrast, the peak in the extinction of the more
compact clusters lie more than 4% from 4.6 inverse micron. At short wavelengths
(0.1 - 0.5 micron), all the methods show that fractal clusters have markedly
different extinction from those of non-fractal clusters. At wavelengths > 5
micron, the rigorous solution indicates that the extinction from fractal and
compact clusters are of the same order of magnitude. It was only possible to
compute fully converged results of the rigorous solution for the smaller
clusters, due to computational limitations, however, we find that both
discrete-dipole approximation methods overestimate the computed extinction of
the smaller fractal clusters.


title: The Formation of Massive Stars through Stellar Collisions

abstract:
  In this review, I present the case for how massive stars may form through
stellar collisions. This mechanism requires very high stellar densities, up to
4 orders of magnitude higher than are observed in the cores of dense young
clusters. In this model, the required stellar densities arise due to gas
accretion onto stars in the cluster core, including the precursers of the
massive stars. This forces the core to contract until the stellar densities are
sufficiently high for collisions to occur. Gas accretion is also likely to play
a major role in determining the distribution of stellar masses in the cluster
as well as the observed mass segregation. One of the main advantages of this
mechanism is that it explicitly relies on the cluster environment in order to
produce the massive stars. It is thus in a position to explain the relation
between clustered and massive star formation which is not an obvious outcome of
an isolated accretion mechanism. A recent numerical simulation supports this
model as the cluster core increases its density by $10^5$ during gas accretion.
Approximately 15 stellar collisions occur (with $R_{coll}=1$ au) in the cluster
core, making a significant contribution to the mass of the most massive star.


title:
An Instrument for Investigating the Large Angular Scale Polarization of
  the Cosmic Microwave Background

abstract:
  We describe the design and performance of a microwave polarimeter used to
make precision measurements of polarized astrophysical radiation in three
microwave frequency bands spanning 26-36 GHz. The instrument uses cooled HEMT
amplifiers in a correlation polarimeter configuration to achieve high
sensitivity and long-term stability. The instrument demonstrates long term
stability and has produced the most restrictive upper limits to date on the
large angular scale polarization of the 2.7 K cosmic microwave background
radiation.


title: The influence of dust properties on the mass loss in pulsating AGB stars

abstract:
  We are currently studying carbon based dust types of relevance for
carbon-rich AGB stars, to obtain a better understanding of the influence of the
optical and chemical properties of the grains on the mass loss of the star. An
investigation of the complex interplay between hydrodynamics,radiative transfer
and chemistry has to be based on a better knowledge of the micro-physics of the
relevant dust species.


title: Interstellar extinction by fractal polycrystalline graphite clusters?

abstract:
  Certain dust particles in space are expected to appear as clusters of
individual grains. The morphology of these clusters could be fractal or
compact. To determine how these structural features would affect the
interpretation of the observed interstellar extinction peak at $\sim 4.6 \mu$m,
we have calculated the extinction by compact and fractal polycrystalline
graphite clusters consisting of touching identical spheres. We compare three
general methods for computing the extinction of the clusters, namely, a
rigorous solution and two different discrete-dipole approximation methods.


title:
Bendings of radio jets in BL Lacertae objects I: EVN and MERLIN
  observations

abstract:
  Several blazars, and BL Lac objects in particular, show a misalignment
between the jet orientation on parsec and kiloparsec scales. Some authors (i.e.
Conway & Murphy, 1993) have attempted to explain this behaviour invoking
helical jets for misalignment angles around 90$\degr$, showing how in this case
there are interesting implications for the understanding of the medium into
which the jet is expanding. By comparing sensitive VLA observations (Cassaro et
al., 1999) with images available in the literature for the BL Lac objects from
the 1-Jy Sample (Stickel et al., 1991), it is clear that there is a wide range
of misalignments between the initial jet direction and the kpc-scale jet, when
detected. We have carried out VLBI observations of these BL Lac objects, in
order to investigate the spatial evolution of the radio jets from few tens to
hundreds of mas, and to search for helical jets in this class of sources. We
present here the first dataset obtained from EVN+MERLIN observations at 5 GHz
for seven objects. From these observations we never have a clear detection of
helical jets, we only have a possible signature of their presence in 2 objects.
In only one of the sources with a misalignment angle around 90$\degr$ the
presence of helical jets can be ruled out. This implies that it is not possible
to invoke helical jets to explain the morphology of all the sources showing a
misalignment of about 90$\degr$ between the parsec and the kiloparsec scale
jets.


title: Carbon Star Dust from Meteorites

abstract:
  Inside carbonaceous chondrite meteorites are tiny dust particles which, when
heated, release noble gases with an isotopic composition different from what is
found anywhere else in the solar system. For this reason it is believed that
these grains are (inter)stellar dust which survived the collapse of the
interstellar cloud that became the solar system. We will describe here why we
believe that the most abundant of these grains, nano-diamonds, were formed in
the atmospheres of carbon stars, and explain how this theory can be tested
observationally.


title:
Cross-Correlation of the Cosmic Microwave Background with Radio Sources:
  Constraints on an Accelerating Universe

abstract:
  We present a new limit on the cosmological constant based on the absence of
correlations between the cosmic microwave background (CMB) and the distribution
of distant radio sources. In the cosmological constant-cold dark matter models
currently favored, such correlations should have been produced via the
integrated Sachs-Wolfe effect, assuming that radio sources trace the local
(z=1) matter density. We find no evidence of correlations between the COBE 53Hz
microwave map and the NVSS 1.4 GHz radio survey. The implied 95% CL limit on
the cosmological constant is Lambda < 0.74, in marginal agreement with the
values suggested by recent measurements of the CMB anisotropy and type-IA
supernovae observations, 0.6 < Lambda < 0.7. If the cosmological model does lie
in this range, then the integrated Sachs-Wolfe effect should be detectable with
upcoming CMB maps and radio surveys.


title: Non-thermal X-ray Emission: An Alternative to Cluster Cooling Flows?

abstract:
  We report the results of experiments aimed at reducing the major problem with
cooling flow models of rich cluster X-ray sources: the fact that most of the
cooled gas or its products have not been found. Here we show that much of the
X-ray emission usually attributed to cooling flows can, in fact, be modeled by
a power-law component which is indicative of a source(s) other than thermal
bremsstrahlung from the intracluster medium. We find that adequate simultaneous
fits to ROSAT PSPCB and ASCA GIS/SIS spectra of the central regions of ten
clusters are obtained for two-component models that include a thermal plasma
component that is attributable to hot intracluster gas and a power-law
component that is likely generated by compact sources and/or extended
non-thermal emission. For five of the clusters that purportedly have massive
cooling flows, the best-fit models have power-law components that contribute
$\sim$ 30 % of the total flux (0.14 - 10.0 keV) within the central 3
arcminutes. Because cooling flow mass deposition rates are inferred from X-ray
fluxes, our finding opens the possibility of significantly reducing cooling
rates.


title: Infrared Signatures of Protoplanetary Disk Evolution

abstract:
  We investigate the observational signatures of a straightforward evolutionary
scenario for protoplanetary disks in which the disk mass of small (50 micron)
particles decreases homologously with time, but the disk structure and stellar
parameters do not change. Our goal is to identify optimal infrared spectral
indicators of the existence of disks, their structure, and mass evolution that
may be tested with the upcoming SIRTF mission. We present simulated spectral
energy distributions and colors over a wide range of masses. The SED is most
sensitive to disk mass in the far-IR and longer wavelengths, which is already
known from millimeter and radio observations. As the disk mass decreases, the
excess emission of the disk over the stellar photosphere diminishes more
rapidly at the longest rather than at short wavelengths. At near-infrared
wavelengths, the disk remains optically thick to stellar radiation over a wide
range of disk mass, resulting in a slower decline in the SED in this spectral
regime. Therefore, near-IR excesses (K-L) provide a robust means of detecting
disks in star clusters down to 1E-7 solar masses, while the far-IR excess
probes the disk mass. Reducing the disk mass results in a clear progression in
color-color diagrams with low mass disks displaying the bluest colors. We
interpret color-color diagrams for Taurus-Auriga sources in the context of
decreasing disk mass.


title:
The performance of spherical wavelets to detect non-Gaussianity in the
  CMB sky

abstract:
  We investigate the performance of spherical wavelets in discriminating
between standard inflationary models (Gaussian) and non-Gaussian models. For
the later we consider small perturbations of the Gaussian model in which an
artificially specified skewness or kurtosis is introduced through the Edgeworth
expansion. By combining all the information present in all the wavelet scales
with the Fisher discriminant, we find that the spherical Mexican Hat wavelets
are clearly superior to the spherical Haar wavelets. The former can detect
levels of the skewness and kurtosis of ~1% for 33' resolution, an order of
magnitude smaller than the later. Also, as expected, both wavelets are better
for discriminating between the models than the direct consideration of moments
of the temperature maps. The introduction of instrumental white noise in the
maps, S/N=1, does not change the main results of this paper.


title: The Mass Function of an X-Ray Flux-Limited Sample of Galaxy Clusters

abstract:
  A new X-ray selected and X-ray flux-limited galaxy cluster sample is
presented. Based on the ROSAT All-Sky Survey the 63 brightest clusters with
galactic latitude |bII| >= 20 deg and flux fx(0.1-2.4 keV) >= 2 * 10^{-11}
ergs/s/cm^2 have been compiled. Gravitational masses have been determined
utilizing intracluster gas density profiles, derived mainly from ROSAT PSPC
pointed observations, and gas temperatures, as published mainly from ASCA
observations, assuming hydrostatic equilibrium. This sample and an extended
sample of 106 galaxy clusters is used to establish the X-ray
luminosity--gravitational mass relation. From the complete sample the galaxy
cluster mass function is determined and used to constrain the mean cosmic
matter density and the amplitude of mass fluctuations. Comparison to
Press--Schechter type model mass functions in the framework of Cold Dark Matter
cosmological models and a Harrison--Zeldovich initial density fluctuation
spectrum yields the constraints OmegaM = 0.12^{+0.06}_{-0.04} and sigma8 =
0.96^{+0.15}_{-0.12} (90% c.l.). Various possible systematic uncertainties are
quantified. Adding all identified systematic uncertainties to the statistical
uncertainty in a worst case fashion results in an upper limit OmegaM < 0.31.
For comparison to previous results a relation sigma8 = 0.43 OmegaM^{-0.38} is
derived. The mass function is integrated to show that the contribution of mass
bound within virialized cluster regions to the total matter density is small,
i.e., OmegaCluster = 0.012^{+0.003}_{-0.004} for cluster masses larger than
6.4^{+0.7}_{-0.6} * 10^{13} h_{50}^{-1} Msun.


title: Is Thermal Expansion Driving the Initial Gas Ejection in NGC 6251?

abstract:
  In this paper, we explore the possibility that the radiative properties of
the most compact region in NGC 6251* may be understood in the same sense as Sgr
A*, though with some telling differences that may hint at the nature of jet
formation. We show that observations of this object with ASCA, ROSAT, HST and
VLBI together may be hinting at a picture in which Bondi-Hoyle accretion from
an ambient ionized medium feeds a standard disk accreting at ~ 4.0*10^{22} g
s^{-1}. Somewhere near the event horizon, this plasma is heated to >10^{11} K,
where it radiates via thermal synchrotron (producing a radio component) and
self-Comptonization (accounting for a nonthermal X-ray flux). This temperature
is much greater than its virial value and the hot cloud expands at roughly the
sound speed (~0.1c), after which it begins to accelerate on a parsec scale to
relativistic velocities. In earlier work, the emission from the extended jet
has been modeled successfully using nonthermal synchrotron self-Compton
processes, with a self-absorbed inner core. In the picture we are developing
here, the initial ejection of matter is associated with a self-absorbed thermal
radio component that dominates the core emission on the smallest scales. The
nonthermal particle distributions responsible for the emission in the extended
jet are then presumably energized, e.g., via shock acceleration, within the
expanding, hot gas. The power associated with this plasma represents an
accretion efficiency of about 0.54, requiring dissipation in a prograde disk
around a rapidly spinning black hole (with spin parameter a~1).


title:
On Casimir Energy Contribution to Observable Value of the Cosmological
  Constant

abstract:
  The contribution of the ground state energy of quantum fields to the
cosmological constant is estimated from the point of view of the standard
Casimir energy calculation scheme. It is shown that the requirement of the
renormalization group invariance leads to the value of the effective $\L$-term
which is of 11 orders higher than the result extracted from the experimental
data.


title:
Probing the distribution of dark matter in the Abell 901/902
  supercluster with weak lensing

abstract:
  We present a weak shear analysis of the Abell 901/902 supercluster, composed
of three rich clusters at z=0.16. Using a deep R-band image from the 0.5 x 0.5
degree MPG/ESO Wide Field Imager together with supplementary B-band
observations, we build up a comprehensive picture of the light and mass
distributions in this region. We find that, on average, the light from the
early-type galaxies traces the dark matter fairly well, although one cluster is
a notable exception to this rule. The clusters themselves exhibit a range of
mass-to-light (M/L) ratios, X-ray properties, and galaxy populations. We
attempt to model the relation between the total mass and the light from the
early-type galaxies with a simple scale-independent linear biasing model. We
find M/L_B=130h for the early type galaxies with zero stochasticity, which, if
taken at face value, would imply Omega_m < 0.1. However, this linear relation
breaks down on small scales and on scales equivalent to the average cluster
separation (approximately 1 Mpc), demonstrating that a single M/L ratio is not
adequate to fully describe the mass-light relation in the supercluster. Rather,
the scatter in M/L ratios observed for the clusters supports a model
incorporating non-linear biasing or stochastic processes. Finally, there is a
clear detection of filamentary structure connecting two of the clusters, seen
in both the galaxy and dark matter distributions, and we discuss the effects of
cluster-cluster and cluster-filament interactions as a means to reconcile the
disparate descriptions of the supercluster.


title:
Star Formation, Metallicity and Dust Properties Derived from the SAPM
  Galaxy Survey Spectra

abstract:
  We have derived star formation rates (SFRs), gas-phase oxygen abundances and
effective dust absorption optical depths for a sample of galaxies drawn from
the Stromlo-APM redshift survey using the new Charlot and Longhetti (2001;
CL01) models, which provide a physically consistent description of the effects
of stars, gas and dust on the integrated spectra of galaxies. Our sample
consists of 705 galaxies with measurements of the fluxes and equivalent widths
of Halpha, [OII], and one or both of [NII] and [SII]. For a subset of the
galaxies, 60 and 100 micron IRAS fluxes are available. We compare the star
formation rates derived using the models with those derived using standard
estimators based on the Halpha, the [OII] and the far-infrared luminosities of
the galaxies. The CL01 SFR estimates agree well with those derived from the
IRAS fluxes, but are typically a factor of ~3 higher than those derived from
the Halpha or the [OII] fluxes, even after the usual mean attenuation
correction of A_Halpha=1 mag is applied to the data. We show that the reason
for this discrepancy is that the standard Halpha estimator neglects the
absorption of ionizing photons by dust in HII regions and the contamination of
Halpha emission by stellar absorption. We also use our sample to study
variations in star formation and metallicity as a function of galaxy absolute
bJ magnitude. For this sample, the star formation rate per unit bJ luminosity
is independent of magnitude. The gas-phase oxygen abundance does increase with
bJ luminosity, although the scatter in metallicity at fixed magnitude is large.


title: The formation of Uranus and Neptune among Jupiter and Saturn

abstract:
  The outer giant planets, Uranus and Neptune, pose a challenge to theories of
planet formation. They exist in a region of the Solar System where long
dynamical timescales and a low primordial density of material would have
conspired to make the formation of such large bodies ($\sim$ 15 and 17 times as
massive as the Earth, respectively) very difficult. Previously, we proposed a
model which addresses this problem: Instead of forming in the trans-Saturnian
region, Uranus and Neptune underwent most of their growth among proto-Jupiter
and -Saturn, were scattered outward when Jupiter acquired its massive gas
envelope, and subsequently evolved toward their present orbits. We present the
results of additional numerical simulations, which further demonstrate that the
model readily produces analogues to our Solar System for a wide range of
initial conditions. We also find that this mechanism may partly account for the
high orbital inclinations observed in the Kuiper belt.


title: Gamma-ray emission from rotation-powered pulsars

abstract:
  Using a simplified model of cascade pair creation over pulsar polar caps
presented in two previous papers, we investigate the expected gamma-ray output
from pulsars' low altitude particle acceleration and pair creation regions. We
divide pulsars into several categories, based on which mechanism truncates the
particle acceleration off the polar cap, and give estimates for the expected
luminosity of each category.
  We find that inverse Compton scattering above the pulsar polar cap provides
the primary gamma rays which initiate the pair cascades in most pulsars. This
reduces the expected $\gamma$-ray luminosity below previous estimates which
assumed curvature gamma ray emission was the dominant initiator of pair
creation in all pulsars.


title:
The Inflaton Field as Self-Interacting Dark Matter in the Braneworld
  Scenario

abstract:
  A unified model is developed within the context of the braneworld paradigm,
where a single scalar field can act as both the inflaton field in the very
early universe and also as strong, self-interacting dark matter in the
post-inflationary universe. Reheating proceeds due to the overproduction and
subsequent evaporation of primordial black holes. Observational constraints,
most notably from gravitational waves, are satisfied if the probability of PBH
formation is sufficiently high.


title: Stellar X-ray Binary Populations in Elliptical Galaxies

abstract:
  Chandra's high angular resolution can resolve emission from stellar X-ray
binaries out of the diffuse X-ray emission from gaseous atmospheres within
elliptical galaxies. Variations in the X-ray binary populations (per unit
galaxian optical luminosity) are correlated with variations in the specific
frequency of globular clusters in ellipticals. This indicates that X-ray
binaries are largely formed in globular clusters, rather than being a
primordial field population.


title:
Losing Weight: A KECK Spectroscopic Survey of the Massive Cluster of
  Galaxies RX J1347-1145

abstract:
  We present a sample of 47 spectroscopically confirmed members of RX
J1347-1145, the most luminous X-ray cluster of galaxies discovered to date.
With two exceptions, all the galaxies in this sample have red B-R colors and
red spectral indices, with spectra similar to old local ellipticals. Using all
47 cluster members, we derive a mean redshift of 0.4509\pm 0.003, and a
velocity dispersion of 910\pm130 km/sec, which corresponds to a virial mass of
4.4 x 10^{14} h^{-1} Solar masses with an harmonic radius of 380 h^{-1} kpc.
The derived total dynamical mass is marginally consistent with that deduced
from the cluster's X-ray emission based on the analysis of ROSAT/ASCA images
(Schindler et al. 1997), but not consistent with the more recent X-ray analyses
of Allen (2000), Ettori, Allen & Fabian (2001) and Allen, Schmidt & Fabian
(2002). Furthermore, the dynamical mass is significantly smaller than that
derived from weak lensing (Fischer & Tyson 1997) and from strong lensing (Sahu
et al. 1998). We propose that these various discrepant mass estimates may be
understood if RX J1347-1145 is the product of two clusters caught in the act of
merging in a direction perpendicular to the line of sight, although there is no
evidence from the galaxy redshift distribution supporting this hypothesis. Even
with this hypothesis, a significant part of the extremely high X-ray luminosity
must still arise from non-virialized, presumably shocked, gas. Finally, we
report the serendipitous discovery of a lensed background galaxy at z=4.083
which will put strong constraints on the lensing mass determination once its
counter-image is securely identified.


title: A Superwind from Early Post-Red Giant Stars?

abstract:
  We suggest that the gap observed at 20,000 K in the horizontal branches of
several Galactic globular clusters is caused by a small amount of extra mass
loss which occurs when stars start to "peel off" the red giant branch (RGB),
i.e., when their effective temperature starts to increase, even though they may
still be on the RGB. We show that the envelope structure of RGB stars which
start to peel off is similar to that of late asymptotic giant branch stars
known to have a super-wind phase. An analogous super-wind in the RGB peel-off
stars could easily lead to the observed gap in the distribution of the hottest
HB stars.


title:
Intrinsic Variability of the Vela Pulsar: Lognormal Statistics and
  Theoretical Implications

abstract:
  Individual pulses from pulsars have intensity-phase profiles that differ
widely from pulse to pulse, from the average profile, and from phase to phase
within a pulse. Widely accepted explanations for pulsar radio emission and its
time variability do not exist. Here, by analysing data near the peak of the
Vela pulsar's average profile, we show that Vela's variability corresponds to
lognormal field statistics, consistent with the prediction of stochastic growth
theory (SGT) for a purely linear system close to marginal stability. Vela's
variability is therefore a direct manifestation of an SGT state and the field
statistics constrain the emission mechanism to be linear (either direct or
indirect), ruling out nonlinear mechanisms like wave collapse. Field statistics
are thus a powerful, potentially widely applicable tool for understanding
variability and constraining mechanisms and source characteristics of coherent
astrophysical and space emissions.


title:
The Chemical Composition of Carbon-Rich, Very Metal-Poor Stars: A New
  Class of Mildly Carbon-Rich Objects Without Excess of Neutron-Capture
  Elements

abstract:
  We report on an analysis of the chemical composition of five carbon-rich,
very metal-poor stars based on high-resolution spectra. One star, CS22948-027,
exhibits very large overabundances of carbon, nitrogen, and the neutron-capture
elements, as found in the previous study of Hill et al.. This result may be
interpreted as a consequence of mass transfer from a binary companion that
previously evolved through the asymptotic giant branch stage. By way of
contrast, the other four stars we investigate exhibit no overabundances of
barium ([Ba/Fe]<0), while three of them have mildly enhanced carbon and/or
nitrogen ([C+N]+1). We have been unable to determine accurate carbon and
nitrogen abundances for the remaining star (CS30312-100). These stars are
rather similar to the carbon-rich, neutron-capture-element-poor star
CS22957-027 discussed previously by Norris et al., though the carbon
overabundance in this object is significantly larger ([C/Fe]=+2.2). Our results
imply that these carbon-rich objects with ``normal'' neutron-capture element
abundances are not rare among very metal-deficient stars. One possible process
to explain this phenomenon is as a result of helium shell flashes near the base
of the AGB in very low-metallicity, low-mass (M~< 1M_sun) stars, as recently
proposed by Fujimoto et al..
  The moderate carbon enhancements reported herein ([C/Fe]+1) are similar to
those reported in the famous r-process-enhanced star CS22892-052. We discuss
the possibility that the same process might be responsible for this similarity,
as well as the implication that a completely independent phenomenon was
responsible for the large r-process enhancement in CS22892-052.


title: Thermal Radio Emission as Incoherent Induced Radiation

abstract:
  The synchrotron interpretation of radio emission from various astrophysical
objects encounters the essential difficulties . These difficulties may be
overcome in a new theory of thermal radio emission of non-uniform gas which is
based on a stimulated character of thermal radio emission following from the
relations between Einstein?s coefficients for spontaneous and induced emission
of radiation .


title:
The effects of an ionizing background on the HI column density
  distribution in the local Universe

abstract:
  Using data on the HI column density distribution in the local Universe,
f(N_{HI}), we show how to determine g(N_{H}), the distribution of the total gas
(HI+HII) column density. A simple power law fit to f(N_{HI}) fails due to
bendings in the distributions when N_{HI}<10^{20} cm^{-2} and H is no longer
fully neutral. If an ultraviolet background is responsible for the gas
ionization, and g(N_{H}) is proportional N_{H}^{-alpha}, we find the values of
alpha and of the intensity of the background radiation which are compatible
with the present data. These best fitting values, however, depend upon the
scaling law of the the gas volume densities with N_{H} and cannot be determined
unambiguously. We examine in detail two models: one in which the average gas
volume density decreases steadily with N_H, while in the other it stays
constant at low column densities. The former model leads to a steep power law
fit for g(N_{H}), with alpha of order 3.3 +- 0.4 and requires an ultraviolet
flux larger than what the QSOs alone produce at z=0. For the latter alpha is
1.5 +- 0.1 and a lower ionizing flux is required. The ambiguities about the
modelling and the resulting steep or shallow N_{H} distribution can be resolved
only if new 21-cm observations and QSOs Lyman limit absorbers searches will
provide more data in the HI-HII transition region at low redshifts. Using the
best fit obtained for higher redshift data we outline two possible scenarios
for the evolution of gaseous structures, compatible with the available data at
z=0.


title: Actinides: How well do we know their stellar production?

abstract:
  The reliable evaluation of the r-process production of the actinides and
careful estimates of the uncertainties affecting these predictions are key
ingredients especially in nucleo-cosmochronology studies based on the analysis
of very metal-poor stars or on the composition of meteorites. This type of
information is also required in order to make the best possible use of future
high precision data on the actinide composition of galactic cosmic rays, of the
local interstellar medium, or of meteoritic grains of presumed circumstellar
origin. This paper provides the practitioners in these various fields with the
most detailed and careful analysis of the r-process actinide production
available to-date. In total, thirty-two different multi-event canonical
calculations using different nuclear ingredients or astrophysics conditions are
presented, and are considered to give a fair picture of the level of
reliability of the predictions of the actinide production, at least in the
framework of a simple r-process model. This simplicity is imposed by our
inability to identify the proper astrophysical sites for the r-process.
Constraints on the actinide yield predictions and associated uncertainties are
suggested on grounds of the measured abundances of r-nuclides, including Th and
U, in the star CS 31082-001, and under the critical and questionable assumption
of the `universality' of the r-process. We also define alternative constraints
based on the nucleo-cosmochronological results derived from the present
actinide content of meteorites. Implications to the different above-cited
fields, and in particular nucleo-cosmochronometry are discussed.