title: Magnetically warped discs in close binaries

abstract:
  We demonstrate that measurable vertical structure can be excited in the
accretion disc of a close binary system by a dipolar magnetic field centred on
the secondary star. We present the first high resolution hydrodynamic
simulations to show the initial development of a uniform warp in a tidally
truncated accretion disc. The warp precesses retrogradely with respect to the
inertial frame. The amplitude depends on the phase of the warp with respect to
the binary frame. A warped disc is the best available explanation for negative
superhumps.


title:
SCUBA observations of galaxies with metallicity measurements: a new
  method for determining the relation between submm luminosity and dust mass

abstract:
  Using a new technique we have determined a value for the constant of
proportionality between submillimetre emission and dust mass, the dust mass
absorption coefficient at 850 microns. Our method has an advantage over
previous methods in that we avoid assumptions about the properties of dust in
the interstellar medium. Our only assumption is that the fraction of metals
incorporated in the dust is a universal constant. To implement our method we
require objects that have submillimetre and far-infrared flux measurements as
well as gas mass and metallicity estimates. We present data for all the
galaxies with suitable measurements, including new submillimetre maps for five
galaxies. We find kappa(850 microns)=0.07 m^2/kg


title: Adiabatic oscillations of non-rotating superfluid neutron stars

abstract:
  We present results concerning the linear (radial and non-radial) oscillations
of non-rotating superfluid neutron stars in Newtonian physics. We use a simple
two-fluid model to describe the superfluid neutron star, where one fluid
consists of the superfluid neutrons,while the second fluid contains all the
comoving constituents (protons, electrons). The two fluids are assumed to be
"free" in the sense of absence of vortex-mediated forces like mutual friction
or pinning, but they can be coupled by the equation of state, in particular by
entrainment.We calculate numerically the eigen-frequencies and -modes of
adiabatic oscillations, neglecting beta-reactions that would lead to
dissipation.We find a doubling of all acoustic-type modes (f-modes, p-modes),
and confirm the absence of g-modes in these superfluid models. We show
analytically and numerically that only in the case of non-stratified background
models (i.e. with no composition gradient) can these doublets of acoustic modes
be separated into two distinct families, which are characterised by either co-
or counter-moving fluids respectively, and which are sometimes referred to as
"ordinary" and "superfluid" modes. In the general, stratified case, however,
this separation is not possible, and these acoustic modes can not be classified
as being either purely "ordinary" or "superfluid". We show how the properties
of the two-fluid modes change as functions of the coupling by entrainment. We
find avoided mode-crossings for the stratified models, while the crossings are
not avoided in the non-stratified, separable case. The oscillations of
normal-fluid neutron stars are recovered as a special case simply by locking
the two fluids together.In this effective one-fluid case we find the usual
singlet f- and p-modes, and we also find the expected g-modes.


title: Modified Newtonian Dynamics as an Alternative to Dark Matter

abstract:
  Modified Newtonian dynamics (MOND) is an empirically motivated modification
of Newtonian gravity or inertia suggested by Milgrom as an alternative to
cosmic dark matter. The basic idea is that at accelerations below a0 ~ 10^{-8}
cm/s^2 ~ cH0/6 the effective gravitational attraction approaches sqrt{gN*a0}
where gN is the usual Newtonian acceleration. This simple algorithm yields flat
rotation curves for spiral galaxies and a mass-rotation velocity relation of
the form M ~ V^4 that forms the basis for the observed luminosity-rotation
velocity relation-- the Tully-Fisher law. We review the phenomenological
success of MOND on scales ranging from dwarf spheroidal galaxies to
superclusters, and demonstrate that the evidence for dark matter can be equally
well interpreted as evidence for MOND. We discuss the possible physical basis
for an acceleration-based modification of Newtonian dynamics as well as the
extension of MOND to cosmology and structure formation.


title: The clustering of dark energy

abstract:
  A cosmological model with pressurelless matter and a fluid of negative
pressure is studied. At perturbative level, fluctuations of both fluids are
considered. It is shown that at least at very large scales, the fluid of
negative pressure, which represents the dark energy content of the universe,
clusters like the dust fluid. Numerical integration reveals that this behaviour
may also occur at scales smaller than the Hubble radius.


title: Spiral Structure and Galaxy Environment

abstract:
  Among 330 normal spirals of types Sa-Sc the fraction of objects exhibiting
``ring'', ``intermediate'' and ``spiral'' arm varieties does not correlated
with environment. A similar conclusion appears to apply to the arm varieties of
123 barred spirals of types SBa-SBc. It is concluded that, among the northern
Shapley-Ames galaxies, the distinction between the spiral and ring varieties of
spiral arms is, within the accuracy of presently available data, independent of
galaxy environment. This result suggests that the detailed morphology of spiral
arms depends primarily on parent galaxy characteristics, rather than on the
galactic environment.


title:
Observations of Hyperluminous Infrared Galaxies with the Infrared Space
  Observatory: Implications for the origin of their extreme luminosities

abstract:
  We present 7-180micron photometry of a sample of hyperluminous infrared
galaxies (HyLIGs) obtained with the photometer and camera mounted on the
Infrared Space Observatory. We have used radiative transfer models of obscured
starbursts and dusty torii to model their spectral energy distributions (SEDs).
We find that F00235+1024, F14218+3845 and F15307+3252 require a combination of
starburst and AGN components to explain their mid to far-infrared emission,
while for TXS0052+471 a dust torus AGN model alone is sufficient. For
F00235+1024 and F14218+3845 the starburst component is the predominant
contributor whereas for F15307+3252 the dust torus component dominates. The
implied star formation rates (SFR) for these three sources estimated from their
infrared luminosities are $\dot{M}_{*,all} > 3000M_{\odot}yr^{-1}h_{50}^{-2}$
and are amongst the highest SFRs estimated to date. We also demonstrate that
the well-known radio-FIR correlation extends into both higher radio and
infrared power than previously investigated. The relation for HyLIGs has a mean
q value of ~1.94. The results of this study imply that better sampling of the
IR spectral energy distributions of HyLIgs may reveal that both AGN and
starburst components are required to explain all the emission from the NIR to
the sub-millimetre.


title:
The Westerbork HI Survey of Spiral and Irregular Galaxies I. HI Imaging
  of Late-type Dwarf Galaxies

abstract:
  Neutral hydrogen observations with the Westerbork Synthesis Radio Telescope
are presented for a sample of 73 late-type dwarf galaxies. These observations
are part of the WHISP project (Westerbork HI Survey of Spiral and Irregular
Galaxies). Here we present HI maps, velocity fields, global profiles and radial
surface density profiles of HI, as well as HI masses, HI radii and line widths.
For the late-type galaxies in our sample, we find that the ratio of HI extent
to optical diameter, defined as 6.4 disk scale lengths, is on average 1.8+-0.8,
similar to that seen in spiral galaxies. Most of the dwarf galaxies in this
sample are rich in HI, with a typical M_HI/L_B of 1.5. The relative HI content
M_HI/L_R increases towards fainter absolute magnitudes and towards fainter
surface brightnesses. Dwarf galaxies with lower average HI column densities
also have lower average optical surface brightnesses. We find that lopsidedness
is as common among dwarf galaxies as it is in spiral galaxies. About half of
the dwarf galaxies in our sample have asymmetric global profiles, a third has a
lopsided HI distribution, and about half shows signs of kinematic lopsidedness.


title:
The Westerbork HI Survey of Spiral and Irregular Galaxies II. R-Band
  Surface Photometry of Late-type Dwarf Galaxies

abstract:
  R-band surface photometry is presented for 171 late-type dwarf and irregular
galaxies. For a subsample of 46 galaxies B-band photometry is presented as
well. We present surface brightness profiles as well as isophotal and
photometric parameters including magnitudes, diameters and central surface
brightnesses. Absolute photometry is accurate to 0.1 mag or better for 77% of
the sample. For over 85% of the galaxies the radial surface brightness profiles
are consistent with published data within the measured photometric uncertainty.
For most of the galaxies in the sample HI data have been obtained with the
Westerbork Synthesis Radio Telescope. The galaxies in our sample are part of
the WHISP project (Westerbork HI Survey of Spiral and Irregular Galaxies),
which aims at mapping about 500 nearby spiral and irregular galaxies in HI. The
availability of HI data makes this data set useful for a wide range of studies
of the structure, dark matter content and kinematics of late-type dwarf
galaxies.


title: High-energy Neutrino Astronomy: The Cosmic Ray Connection

abstract:
  This is a review of neutrino astronomy anchored to the observational fact
that Nature accelerates protons and photons to energies in excess of $10^{20}$
and $10^{13}$ eV, respectively.
  Although the discovery of cosmic rays dates back close to a century, we do
not know how and where they are accelerated. Basic elementary-particle physics
dictates a universal upper limit on their energy of $5\times10^{19}$ eV, the
so-called Greisen-Kuzmin-Zatsepin cutoff; however, particles in excess of this
energy have been observed by all experiments, adding one more puzzle to the
cosmic ray mystery. Mystery is fertile ground for progress: we will review the
facts as well as the speculations about the sources including gamma ray bursts,
blazars and top-down scenarios.
  The important conclusion is that, independently of the specific blueprint of
the source, it takes a kilometer-scale neutrino observatory to detect the
neutrino beam associated with the highest energy cosmic rays and gamma rays. We
also briefly review the ongoing efforts to commission such instrumentation.


title:
Star-Formation Rates of Local Blue Compact Dwarf Galaxies I: 1.4 GHz and
  60 um luminosities

abstract:
  We determine and examine the star-formation rates of 50 well known, local
Blue Compact Dwarf (BCD) galaxies based on their 1.4 GHz and 60 $\mu$m
luminosities. We find that in cases for which both radio and far-infrared
luminosities are available, the resulting star-formation rates agree extremely
well with one another. We determine that the star-formation rates of the BCD
galaxies in our sample span nearly five orders of magnitude, from approximately
a few times 10$^{-3}$ to several times 10$^{1}$ M$_\odot$ yr$^{-1}$, with a
median SFR of about 0.3$ $M$_\odot$ yr$^{-1}$. We discuss trends of metallicity
(primarily oxygen abundance) with star-formation rate, and explore the
connections between SFR and galaxy mass estimates.


title:
Measuring the Size of Quasar Broad-Line Clouds Through Time Delay
  Light-Curve Anomalies of Gravitational Lenses

abstract:
  Intensive monitoring campaigns have recently attempted to measure the time
delays between multiple images of gravitational lenses. Some of the resulting
light-curves show puzzling low-level, rapid variability which is unique to
individual images, superimposed on top of (and concurrent with) longer
time-scale intrinsic quasar variations which repeat in all images. We
demonstrate that both the amplitude and variability time-scale of the rapid
light-curve anomalies, as well as the correlation observed between intrinsic
and microlensed variability, are naturally explained by stellar microlensing of
a smooth accretion disk which is occulted by optically-thick broad-line clouds.
The rapid time-scale is caused by the high velocities of the clouds (~5x10^3
km/s), and the low amplitude results from the large number of clouds covering
the magnified or demagnified parts of the disk. The observed amplitudes of
variations in specific lenses implies that the number of broad-line clouds that
cover ~10% of the quasar sky is ~10^5 per 4 pi steradian. This is comparable to
the expected number of broad line clouds in models where the clouds originate
from bloated stars.


title:
The Luminosity Functions of Old and Intermediate-Age Globular Clusters
  in NGC 3610

abstract:
  The WFPC2 Camera on board HST has been used to obtain high-resolution images
of NGC 3610, a dynamically young elliptical galaxy. These observations
supersede shorter, undithered HST observations where an intermediate-age
population of globular clusters was first discovered. The new observations show
the bimodal color distribution of globular clusters more clearly, with peaks at
(V-I)o = 0.95 and 1.17. The luminosity function (LF) of the blue, metal-poor
population of clusters in NGC 3610 turns over, consistent with a Gaussian
distribution with a peak Mv ~= -7.0, similar to old globular-cluster
populations in ellipticals. The red, metal-rich population of clusters has a LF
that is more extended toward both the bright and faint ends, as expected for a
cluster population of inter-mediate age. It is well fit by a power law with an
exponent of alpha = -1.78 +-0.05, or -1.90+-0.07 when corrected for
observational scatter. A Kolmogorov-Smirnov test confirms the significant
difference between the LFs of the red and blue clusters, with a probability of
less than 0.1% that they come from the same population. A comparison with the
Fall & Zhang cluster disruption models shows marginal agreement with the
observed LF, although there are differences in detail. In particular, there is
no clear evidence of the predicted turnover at the faint end. A by-product of
the analysis is the demonstration that, at any given metallicity, the peak of
the LF should remain nearly constant from 1.5 Gyr to 12 Gyr, since the effect
of the disruption of faint clusters is almost perfectly balanced by the fading
of the clusters. This may help explain the apparent universality of the peak of
the globular cluster luminosity function. (Abridged)


title: Recent Developments in Magnetic Dynamo Theory

abstract:
  Some recent results and open issues in magnetic dynamo theory are addressed.
The distinction between small-scale and mean-field dynamo (MFD) action in
forced turbulent flows is emphasized. Though useful, the MFD has been
controversial. This is partly due to concerns about its need for helically
forced turbulence, but mainly because simple "textbook" treatments are
kinematic and linear. The non-linear backreaction of the growing magnetic field
has been suspected to prematurely quench MFD action. To resolve the
controversy, we must first understand those non-linear MFDs which can be
numerically simulated. Recently, there has been progress on this front. For
simple MFDs in closed systems, dynamical quenching models that incorporate a
transfer of magnetic helicity between small and large scales agree reasonably
well with fully 3-D numerical periodic box simulations. Unresolved issues such
as the quenching of turbulent diffusion and the additional physics needed to
apply these results to real systems are also discussed herein. The following
summarizes conceptual progress in describing mean-field magnetic energy growth
in the simplest MFDs:
  For a closed turbulent flow, the non-linear mean-field dynamo, is first fast
and kinematic, then slow and dynamic, and magnetic helicity transfer makes it
so.


title:
On the Formation of Binary Stars and Small Stellar Groups in
  Magnetically Subcritical Clouds

abstract:
  In the standard scenario of isolated low-mass star formation, strongly
magnetized molecular clouds are envisioned to condense gradually into cores,
driven by ambipolar diffusion. Once the cores become magnetically
supercritical, they collapse to form stars. Most previous studies based on this
scenario are limited to axisymmetric calculations leading to single
supercritical core formation. The assumption of axisymmetry has precluded a
detailed investigation of cloud fragmentation, generally thought to be a
necessary step in the formation of binary and multiple stars. In this
contribution, we describe the non-axisymmetric evolution of initially
magnetically subcritical clouds using a newly-developed MHD code. It is shown
that non-axisymmetric perturbations of modest fractional amplitude ($\sim 5%$)
can grow nonlinearly in such clouds during the supercritical phase of cloud
evolution, leading to the production of either a highly elongated bar or a set
of multiple dense cores.


title: Further Study of the Gamma-Ray Bursts Duration Distribution

abstract:
  Two classes of gamma-ray bursts have been identified so far, characterized by
durations shorter and longer than approximately 2 seconds. In 1998 two
independent papers indicated the existence of the third class of the bursts
roughly duration between 2 and 10 seconds. In this paper, using the full BATSE
Catalog, the maximum likelihood estimation is presented, which gives a 0.5%
probability to having only two subclasses. The Monte-Carlo simulation confirms
this probability, too.


title:
Optimal photometry for colour-magnitude diagrams and its application to
  NGC 2547

abstract:
  We have developed the techniques required to use the optimal photometry
algorithm of Naylor (1998) to create colour-magnitude diagrams with well
defined completeness functions. To achieve this we first demonstrate that the
optimal extraction is insensitive to uncertainties in the star's measured
position. We then show how to correct the optimally extracted fluxes such that
they correspond to those measured in a large aperture, so aperture photometry
of standard stars can be used to place the measurements on a standard system.
The technique simultaneously removes the effects of a position dependent
point-spread function. Finally we develop a method called "ghosting", which
calculates the completeness corrections in the absence of an accurate
description of the point spread function.
  We apply these techniques to the young cluster NGC 2547 (=C0809-491), and use
an X-ray selected sample to find an age of 20-35Myr and an intrinsic distance
modulus of 8.00-8.15 magnitudes. We use these isochrones to select members from
our photometric surveys. Our derived luminosity function shows a well defined
Wielen dip, making NGC 2547 the youngest cluster in which such a feature has
been observed. Our derived mass function spans the range 0.1-6Mo and is similar
to that for the field and the older, more massive clusters M35 and the
Pleiades, supporting the idea of a universal initial mass function.


title:
Electron Neutrino Pair Annihilation: A New Source for Muon and Tau
  Neutrinos in Supernovae

abstract:
  We show that in a supernova core the annihilation process nu_e nu_e-bar ->
nu_{mu,tau} nu_{mu,tau}-bar is always more important than the traditional
reaction e^+ e^- -> nu_{mu,tau} nu_{mu,tau}-bar as a source for muon and tau
neutrino pairs. We study the impact of the new process by means of a Monte
Carlo transport code with a static stellar background model and by means of a
self-consistent hydrodynamical simulation with Boltzmann neutrino transport.
Nucleon bremsstrahlung NN -> NN nu_{mu,tau} nu_{mu,tau}-bar is also included as
another important source term. Taking into account nu_e nu_e-bar -> nu_{mu,tau}
nu_{mu,tau}-bar increases the nu_mu and nu_tau luminosities by as much as 20%
while the spectra remain almost unaffected. In our hydrodynamical simulation
the shock was somewhat weakened. Elastic nu_{mu,tau} nu_e and nu_{mu,tau} nu_e
scattering is not negligible but less important than nu_{mu,tau} e^+ or e^-
scattering. Its influence on the nu_{mu,tau} fluxes and spectra is small after
all other processes have been included.


title:
Cosmological constraints from the X-ray gas mass fraction in relaxed
  lensing clusters observed with Chandra

abstract:
  We present precise measurements of the X-ray gas mass fraction for a sample
of luminous, relatively relaxed clusters of galaxies observed with the Chandra
Observatory, for which independent confirmation of the mass results is
available from gravitational lensing studies. Parameterizing the total
(luminous plus dark matter) mass profiles using the model of Navarro, Frenk &
White (1997), we show that the X-ray gas mass fractions in the clusters
asymptote towards an approximately constant value at a radius r_2500, where the
mean interior density is 2500 times the critical density of the Universe at the
redshifts of the clusters. Combining the Chandra results on the X-ray gas mass
fraction and its apparent redshift dependence with recent measurements of the
mean baryonic matter density in the Universe and the Hubble Constant determined
from the Hubble Key Project, we obtain a tight constraint on the mean total
matter density of the Universe, Omega_m = 0.30^{+0.04}_{-0.03}, and measure a
positive cosmological constant, Omega_Lambda = 0.95^{+0.48}_{-0.72}. Our
results are in good agreement with recent, independent findings based on
analyses of anisotropies in the cosmic microwave background radiation, the
properties of distant supernovae, and the large-scale distribution of galaxies.


title: An Untriggered Search for Optical Bursts

abstract:
  We present an untriggered search for optical bursts with the ROTSE-I
telephoto array. Observations were taken which monitor an effective 256 square
degree field continuously over 125 hours to m_{ROTSE}=15.7. The uniquely large
field, moderate limiting magnitude and fast cadence of $\sim$10 minutes permits
transient searches in a new region of sensitivity. Our search reveals no
candidate events. To quantify this result, we simulate potential optical bursts
with peak magnitude, m_{p}, at t=10 s, which fade as f=(\frac{t}{t_{0}})
^{\alpha_{t}}, where \alpha_t < 0. Simple estimates based on observational
evidence indicate that a search of this sensitivity begins to probe the
possible region occupied by GRB orphan afterglows. Our observing protocol and
image sensitivity result in a broad region of high detection efficiency for
light curves to the bright and slowly varying side of a boundary running from
[\alpha_{t},m_{p}]=[-2.0,6.0] to [-0.3,13.2]. Within this region, the
integrated rate of brief optical bursts is less than 1.1\times 10^{-8} {\rm
s}^{-1} {\rm deg}^{-2}. At $\sim$22 times the observed GRB rate from BATSE,
this suggests a limit on \frac{\theta_{opt}}{\theta_{\gamma}}\lesssim 5 where
\theta_{opt} and \theta_{\gamma} are the optical and gamma-ray collimation
angles, respectively. Several effects might explain the absence of optical
bursts, and a search of the kind described here but more sensitive by about 4
magnitudes should offer a more definitive probe.


title: Discovery of an optical bow-shock around pulsar B0740-28

abstract:
  We report the discovery of a faint H-alpha pulsar wind nebula (PWN) powered
by the radio pulsar B0740-28. The characteristic bow-shock morphology of the
PWN implies a direction of motion consistent with the previously measured
velocity vector for the pulsar. The PWN has a flux density more than an order
of magnitude lower than for the PWNe seen around other pulsars, but, for a
distance 2 kpc, it is consistent with propagation through a medium of atomic
density n_H ~ 0.25 cm^{-3}, and neutral fraction of 1%. The morphology of the
PWN in the area close to the pulsar is distinct from that in downstream
regions, as is also seen for the PWN powered by PSR B2224+65. In particular,
the PWN associated with PSR B0740-28 appears to close at its rear, suggesting
that the pulsar has recently passed through a transition from low density to
high density ambient gas. The faintness of this source underscores that deep
searches are needed to find further examples of optical pulsar nebulae.


title: Ionization freeze-out and barium problem in supernova 1987A

abstract:
  We have shown that in the atmosphere of SN 1987A level populations of
hydrogen are mostly controlled by an ionization freeze-out and ion-molecular
processes up to 40 days. The ionization freeze-out effects are important for
normal SNe II-P as well. The time dependent effects and the mutual
neutralization between H^- and H^+ may result in a non-monotonic radial
dependence of the Sobolev optical depth for H-alpha and then in a blue emission
satellite of H-alpha observed in SN 1987A spectra at Bochum event phase. The
relative abundance of molecular hydrogen about 0.0001-0.001 is high enough for
the photospheric phase of SN 1987A. We emphasize that the poor knowledge of the
far UV radiation field in the envelope of SN 1987A still forbids a truly
reliable estimate of the Ba abundance but well-constructed and tested models
may improve this situation.


title:
The Dwarf Irregular/Wolf-Rayet Galaxy NGC4214: I. A New Distance,
  Stellar Content, and Global Parameters

abstract:
  We present the results of a detailed optical and near-IR study of the nearby
star-forming dwarf galaxy NGC4214. We discuss the stellar content, drawing
particular attention to the intermediate-age and/or old field stars, which are
used as a distance indicator. On images obtained with the Hubble Space
Telescope WFPC2 and NICMOS instruments in the equivalents of the V, R, I, J and
H bands, the galaxy is well resolved into stars. We achieve limiting magnitudes
of F814W ~27 in the WF chips and F110W ~25 in the NIC2. The optical and
near-infrared color-magnitude diagrams confirm a core-halo galaxy morphology:
an inner high surface-brightness young population within ~1.5' (~1 kpc) from
the center of the galaxy, where the stars are concentrated in bright complexes
along a bar-like structure; and a relatively low-surface-brightness, field-star
population extending out to at least 8' (7 kpc). The color-magnitude diagrams
of the core region show evidence of blue and red supergiants, main-sequence
stars, asymptotic giant branch stars and blue loop stars. We identify some
candidate carbon stars from their extreme near-IR color. The field-star
population is dominated by the "red tangle", which contains the red giant
branch. We use the I-band luminosity function to determine the distance based
on the tip-of-the-red-giant-branch method: 2.7\pm0.3 Mpc. This is much closer
than the values usually assumed in the literature, and we provide revised
distance dependent parameters such as physical size, luminosity, HI mass and
star-formation rate.


title:
A High Spectral Resolution Observation of the Soft X-ray Diffuse
  Background with Thermal Detectors

abstract:
  A high spectral resolution observation of the diffuse X-ray background in the
60 - 1000 eV energy range has been made using an array of thirty-six 1 mm^2
micro-calorimeters flown on a sounding rocket. Detector energy resolution
ranged from 5-12 eV FWHM, and a composite spectrum of ~ 1 steradian of the
background centered at l = 90, b = +60 was obtained with a net resolution of ~
9 eV. The target area includes bright 1/4 keV regions, but avoids Loop I and
the North Polar Spur. Lines of C VI, O VII, and O VIII are clearly detected
with intensities of 5.4 +/- 2.3, 4.8 +/- 0.8, and 1.6 +/- 0.4 photons cm^-2
s^-1 sr^-1, respectively. The oxygen lines alone account for a majority of the
diffuse background observed in the ROSAT R4 band that is not due to resolved
extragalactic discrete sources. We also have a positive detection of the Fe-M
line complex near 70 eV at an intensity consistent with previous upper limits
that indicate substantial gas phase depletion of iron. We include a detailed
description of the instrument and its detectors.


title:
History of Milky Way Dwarf Spheroidal Galaxies Imprinted on Abundance
  Patterns of Neutron-Capture Elements

abstract:
  Stellar abundance pattern of neutron-capture elements such as barium is used
as a powerful tool to infer how star formation proceeded in dwarf spheroidal
(dSph) galaxies. It is found that the abundance correlation of barium with iron
in stars belonging to dSph galaxies orbiting the Milky Way, i.e., Draco,
Sextans, and Ursa Minor have a feature similar to the barium-iron correlation
in Galactic metal-poor stars. The common feature of these two correlations can
be realized by our inhomogeneous chemical evolution model based on the
supernova-driven star formation scenario if dSph stars formed from gas with a
velocity dispersion of ~26 km/s. This velocity dispersion together with the
stellar luminosities strongly suggest that dark matter dominated dSph galaxies.
The tidal force of the Milky Way links this velocity dispersion with the
currently observed value <10 km/s by stripping the dark matter in dSph
galaxies. As a result, the total mass of each dSph galaxy is found to have been
originally ~25 times larger than at present. Our inhomogeneous chemical
evolution model succeeds in reproducing the stellar [Fe/H] distribution
function observed in Sextans. In this model, supernovae immediately after the
end of the star formation epoch can expel the remaining gas over the
gravitational potential of the dSph galaxy.


title:
Does the rapid appearance of life on Earth suggest that life is common
  in the Universe?

abstract:
  It is sometimes assumed that the rapidity of biogenesis on Earth suggests
that life is common in the Universe. Here we critically examine the assumptions
inherent in this if-life-evolved-rapidly-life-must-be-common argument. We use
the observational constraints on the rapidity of biogenesis on Earth to infer
the probability of biogenesis on terrestrial planets with the same unknown
probability of biogenesis as the Earth. We find that on such planets, older
than ~ 1 Gyr, the probability of biogenesis is > 13% at the 95% confidence
level. This quantifies an important term in the Drake Equation but does not
necessarily mean that life is common in the Universe.


title: Cherenkov Images : Why Multifractal ?

abstract:
  Cherenkov images are multifractal in nature. We show that multifractal
behaviour of cherenkov images arises due to binomial multiplicative nature of
pair production and bremsstahlung processes in the longitudinal shower passage.


title:
Modeling Pairwise Peculiar Velocity Distribution Function of Dark Matter
  from Halo Density Profiles

abstract:
  We derive the pairwise peculiar velocity distribution function of dark matter
particles applying the dark matter halo approach. Unlike the previous work, we
do not assume a Gaussian velocity distribution function of dark matter in a
single halo, but compute it self-consistently with the assumed density profile
for dark matter halo. The resulting distribution function is well approximated
by an exponential distribution which is consistent with the previous
observational, numerical and theoretical results. We also compute the pairwise
peculiar velocity dispersion for different density profiles, and provide a
practical fitting formula. We apply an empirical biasing scheme into our model
and present prediction for pairwise peculiar velocity dispersion of {\it
galaxies}, and reproduce the previous results of simulations using our
semi-analytical method.


title:
Perturbation theory in Lagrangian hydrodynamics for a cosmological fluid
  with velocity dispersion

abstract:
  We extensively develop a perturbation theory for nonlinear cosmological
dynamics, based on the Lagrangian description of hydrodynamics. We solve
hydrodynamic equations for a self-gravitating fluid with pressure, given by a
polytropic equation of state, using a perturbation method up to second order.
This perturbative approach is an extension of the usual Lagrangian perturbation
theory for a pressureless fluid, in view of inclusion of the pressure effect,
which should be taken into account on the occurrence of velocity dispersion. We
obtain the first-order solutions in generic background universes and the
second-order solutions in wider range of a polytropic index, whereas our
previous work gives the first-order solutions only in the Einstein-de Sitter
background and the second-order solutions for the polytropic index 4/3. Using
the perturbation solutions, we present illustrative examples of our formulation
in one- and two-dimensional systems, and discuss how the evolution of
inhomogeneities changes for the variation of the polytropic index.


title: Photon Splitting in the Superstrong Magnetic Fields of Pulsars

abstract:
  We discuss the polarization selection rules for splitting of the two
principal electromagnetic modes that propagate in a vacuum polarized by a
superstrong magnetic field (B>0.1B_{cr} ~ 4x10^{12} G). We show that below the
threshold of free pair creation the selection rules found by Adler in the limit
of weak dispersion remain unaffected by taking the resonant effects into
consideration, i.e., splitting of one mode is strictly forbidden, while
splitting of the other is allowed.


title: The "Mysterious" Origin of Brown Dwarfs

abstract:
  Hundreds of brown dwarfs (BDs) have been discovered in the last few years in
stellar clusters and among field stars. BDs are almost as numerous as hydrogen
burning stars and so a theory of star formation should also explain their
origin. The ``mystery'' of the origin of BDs is that their mass is two orders
of magnitude smaller than the average Jeans' mass in star--forming clouds, and
yet they are so common. In this work we investigate the possibility that
gravitationally unstable protostellar cores of BD mass are formed directly by
the process of turbulent fragmentation. Supersonic turbulence in molecular
clouds generates a complex density field with a very large density contrast. As
a result, a fraction of BD mass cores formed by the turbulent flow are dense
enough to be gravitationally unstable. We find that with density, temperature
and rms Mach number typical of cluster--forming regions, turbulent
fragmentation can account for the observed BD abundance.


title:
Distortion of secondaries in semi-detached binaries and the cataclysmic
  variable period minimum

abstract:
  Based on SPH simulations, we quantify the geometrical distortion effect due
to tidal and rotational forces on polytropic secondaries in semi-detached
binaries. The main effect is an expansion of the polytropic star, with an
effect on the radius of $\sim$ 5%-12%, depending on the polytropic index and
the mass ratio. We apply such distortion effects to the secular evolution of
secondaries in cataclysmic variable systems. We focus on systems below the 2-3h
period gap and that approach the minimum period. We find a significant increase
of the predicted minimum period ($\sim$ 4% if changes in the secondary's
thermal relaxation are approximately taken into account). Though an
improvement, the effect is not big enough to solve the mismatch between
predicted and observed minimum period at 80 min.


title:
Chemical Abundances of NGC 5461 and NGC 5471 derived from Echelle
  Spectrophotometry

abstract:
  We present high resolution spectroscopic data of the two giant extragalactic
H II regions NGC 5461 and NGC 5471 in M101, which have been obtained with the
2.1-m telescope of the Observatorio Astron\'omico Nacional in San Pedro
M\'artir, Baja California. We measured the intensities of several H and He
recombination lines, and of forbidden lines of a large number of ions. We
calculate the physical conditions in the two nebulae with a large number of
diagnostics and determine their chemical abundances by applying ionization
correction factors icf's to the observed ionic abundances. For NGC 5461, the
icf's are based on a tailored photoionization model of the region (Luridiana &
Peimbert 2001), while for NGC 5471 they are computed from those predicted by a
photoionization model of NGC 2363 (Luridiana, Peimbert, & Leitherer 1999), a
region which is similar to NGC 5471 in the ionization structure. For both
regions, the icf's are compared to those computed following the prescriptions
by Mathis & Rosa (1991). Such comparison shows large discrepancies for several
elements, including nitrogen, neon, and chlorine.


title: An unusual iron Lo-BAL quasar detected by ISOCAM

abstract:
  We report the discovery of an unusual low--ionization broad absorption line
quasar at z=1.776 which exhibits absorption lines from many excited states of
Feii. This member of the rare class of 'FeLoBAL' quasars was serendipitously
found in a mid-infrared (MIR) survey of distant clusters carried out with the
ISOCAM camera. ISO J005645.1-273816 has a high MIR to UV luminosity ratio,
suggesting a strong dust obscuration plus emission from very hot dust. This
characteristic makes MIR surveys particularly efficient at detecting LoBAL
quasars.


title:
320g Ionization-Heat Cryogenic Detector for Dark Matter Search in the
  EDELWEISS Experiment

abstract:
  The EDELWEISS experiment used in 2001 a 320g heat-and-ionization cryogenic Ge
detector operated in a low-background environment in the Laboratoire Souterrain
de Modane for direct WIMP detection. This detector presents an increase of more
than 4 times the mass of previous detectors. Calibrations of this detector are
used to determine its energy resolution and fiducial volume, and to optimize
the detector design for the 1kg phase of the EDELWEISS-I experiment. Analysis
of the calibrations and characteristics of a first series of 320g-detectors are
presented.


title:
Kinematics of elliptical galaxies with a diffuse dust component - III. A
  Monte Carlo approach to include the effects of scattering

abstract:
  This paper is the third one in a series, intended to investigate how the
observed kinematics of elliptical galaxies are affected by dust attenuation. In
Paper I and Paper II, we investigated the effects of dust absorption; here we
extend our modelling in order to include the effects of scattering. We describe
how kinematical information can be combined with the radiative transfer
equation, and present a Monte Carlo code that can handle kinematical
information in an elegant way.
  Compared to the case where only absorption is taken into account, we find
that dust attenuation considerably affects the observed kinematics when
scattering is included. For the central lines of sight, dust can either
decrease or increase the central observed velocity dispersion. The most
important effect of dust attenuation, however, is found at large projected
radii. The kinematics at these lines of sight are strongly affected by photons
scattered into these lines of sight, which were emitted by high-velocity stars
in the central regions of the galaxy. These photons bias the LOSVDs towards
high line-of-sight velocities, and significantly increase the observed velocity
dispersion and LOSVD shape parameters. These effects are similar to the
expected kinematical signature of a dark matter halo, such that dust
attenuation may form an alternative explanation for the usual stellar
kinematical evidence for dark matter halos around elliptical galaxies.
  We apply our results to discuss several other topics in galactic dynamics,
where we feel dust attenuation should be taken into account. In particular, we
argue that the kinematics observed at various wavelengths can help to constrain
the spatial distribution of dust in elliptical galaxies.


title:
The DEEP Groth Strip Survey II. Hubble Space Telescope Structural
  Parameters of Galaxies in the Groth Strip

abstract:
  The quantitative morphological classification of distant galaxies is
essential to the understanding of the evolution of galaxies over the history of
the Universe. This paper presents Hubble Space Telescope WFPC2 F606W and F814W
photometric structural parameters for 7450 galaxies in the ``Groth Strip.''
These parameters are based on a two-dimensional bulge+disk surface brightness
model and were obtained using an automated reduction and analysis pipeline
described in detail here. A first set of fits was performed separately in each
bandpass, and a second set of fits was performed simultaneously on both
bandpasses. The information produced by these two types of fits can be used to
explore different science goals. Systematic and random fitting errors in all
structural parameters as well as bulge and disk colors are carefully
characterized through extensive sets of simulations. The results of these
simulations are given in catalogs similar to the real science catalogs so that
both real and simulated measurements can be sampled according to the same
selection criteria to show biases and errors in the science data subset of
interest. The effects of asymmetric structures on the recovered bulge+disk
fitting parameters are also explored through simulations. The full
multidimensional photometric survey selection function of the Groth Strip is
also computed. This selection function, coupled to bias maps from simulations,
provides a complete and objective reproduction of the observational limits, and
these limits can be applied to theoretical predictions from galaxy evolution
models for direct comparisons with the data.


title: The Kinematics and Metallicity of the M31 Globular Cluster System

abstract:
  With the ultimate aim of distinguishing between various models describing the
formation of galaxy halos (e.g. radial or multi-phase collapse, random
mergers), we have completed a spectroscopic study of the globular cluster
system of M31. We present the results of deep, intermediate-resolution,
fibre-optic spectroscopy of several hundred of the M31 globular clusters using
the Wide Field Fibre Optic Spectrograph (WYFFOS) at the William Herschel
Telescope in La Palma, Canary Islands. These observations have yielded precise
radial velocities (+/-12 km/s) and metallicities (+/-0.26 dex) for over 200
members of the M31 globular cluster population out to a radius of 1.5 degrees
from the galaxy center. Many of these clusters have no previous published
radial velocity or [Fe/H] estimates, and the remainder typically represent
significant improvements over earlier determinations. We present analyses of
the spatial, kinematic and metal abundance properties of the M31 globular
clusters. We find that the abundance distribution of the cluster system is
consistent with a bimodal distribution with peaks at [Fe/H] = -1.4 and -0.5.
The metal-rich clusters demonstrate a centrally concentrated spatial
distribution with a high rotation amplitude, although this population does not
appear significantly flattened and is consistent with a bulge population. The
metal-poor clusters tend to be less spatially concentrated and are also found
to have a strong rotation signature.


title:
Galaxy groups in the 2dF redshift survey: Galaxy Spectral Type
  Segregation in Groups

abstract:
  The behaviour of the relative fraction of galaxies with different spectral
types in groups is analysed as a function of projected local galaxy density and
the group-centric distance. The group sample was taken from the 2dF Group
Galaxy Calatogue constructed by Merch\'an & Zandivarez. Our group sample was
constrained to have a homogeneous virial mass distribution with redshift.
Galaxies belonging to this group sample were selected in order to minimize
possible biases such as preferential selection of high luminosity objects. We
find a clear distinction between high virial mass groups ($M_V\gsim 10^{13.5}
M_{\odot}$) and the less massive ones. While the massive groups show a
significant dependence of the relative fraction of low star formation galaxies
on local galaxy density and group-centric radius,groups with lower masses show
no significant trends. We also cross-correlate our group subsample with the
previously identified clusters finding that this sample shows a very similar
behaviour as observed in the high virial mass group subsample.


title:
A very massive spectroscopic binary in the LH 54 OB association in the
  LMC

abstract:
  We announce the discovery of a new early-type, double-lined spectroscopic
binary in the LH 54 OB association in the LMC. We present a V light curve and
radial velocities. We investigate the possible configurations of the system,
concluding that it probably contains the most massive star measured at the
present, with a mass (in solar units) of the order of 100, while its companion
has approximately 50.


title: X-ray Timing of the Enigmatic Neutron Star RX J0720.4-3125

abstract:
  RX J0720.4-3125 is the third brightest neutron star in the soft X-ray sky and
has been a source of mystery since its discovery, as its long 8-s period
separates it from the population of typical radio pulsars. Three models were
proposed for this source: a neutron star accreting from the interstellar
medium, an off-beam radio pulsar, or an old, cooling magnetar. Using data from
Chandra, ROSAT, and BeppoSAX we are able to place an upper limit to the period
derivative, $|\dot{P}| < 3.6\times10^{-13}{s s}^{-1}$ (3-$\sigma$). While our
upper limit on $\dot P$ allows for the accretion model, this model is
increasingly untenable for another similar but better studied neutron star, RX
J1856.5-3754, and we therefore consider the accretion model unlikely for RX
J0720.4-3125. We constrain the initial magnetic field of RX J0720.4-3125 to be
$\lsim 10^{14}$ G based on cooling models, suggesting that it is not and never
was a magnetar, but is instead middle-aged neutron star. We propose that it is
either a long-period high-magnetic field pulsar with $\dot P\sim 10^{-13}{s
s}^{-1}$ similar to PSR J1814-1744, or a neutron star born with an initial
period of $\approx 8.3$ s and $\dot P\sim 10^{-15}{s s}^{-1}$. The proximity of
RX J0720.4-3125 is strongly suggestive of a large population of such objects;
if so, radio pulsar surveys must have missed many of these sources.


title:
Eclipse Timings of the Low Mass X-ray Binary EXO0748-676 III. An
  Apparent Orbital Period Glitch Observed with USA and RXTE

abstract:
  We present 7 eclipse timings of the low mass X-ray binary EXO0748-676
obtained with the USA experiment during 1999-2000 as well as 122 eclipse
timings obtained with RXTE during 1996-2000. According to our analysis, the
mean orbital period has increased by ~8 ms between the pre-RXTE era (1985-1990)
and the RXTE/USA era (1996-2000). This corresponds to an orbital period
derivative of P(orb)/(dP(orb)/dt)~2x10^7 years. However, neither a constant
orbital period derivative nor any other simple ephemeris provides an acceptable
fit to the data: individual timings of eclipse centers have residuals of up to
15 or more seconds away from our derived smooth ephemerides. When we consider
all published eclipse timing data including those presented here, a model that
includes observational measurement error, cumulative period jitter, and
underlying period evolution is found to be consistent with the timing data. We
discuss several physical mechanisms for LMXB orbital evolution in an effort to
account for the change in orbital period and the observed intrinsic jitter in
the mid-eclipse times.


title:
Westphal-MMD11: An interacting, submillimeter luminous Lyman break
  galaxy

abstract:
  We present new Hubble Space Telescope, high-resolution optical imaging of the
submm luminous Lyman-break galaxy, Westphal-MMD11, an interacting starburst at
z=2.979. The new imaging data, in conjunction with re-analysis of Keck optical
and near-IR spectra, demonstrate MMD11 to be an interacting system of at least
three components: a luminous blue source, a fainter blue source, and an
extremely red object (ERO) with R-K>6. The separations between components are
\~8 kpc (Lambda=0.7, Omega_M=0.3, h=0.65), similar to some of the local
ultra-luminous infrared galaxies (ULIGs). The lack of obvious AGN in MMD11,
along with the fragmented, early stage merger morphology, suggest a young
forming environment. While we cannot unambiguously identify the location of the
far-IR emission within the system, analogy to similar ULIGs suggests the ERO as
the likely far-IR source. The >10^{12} L_sun bolometric luminosity of MMD11 can
be predicted reasonably from its rest frame UV properties once all components
are taken into account, however this is not typically the case for local
galaxies of similar luminosities. While LBGs as red in g-R and R-K as MMD11 are
rare, they can only be found over the restricted 2.7 < z < 3.0 range. Therefore
a substantial number of MMD11-like galaxies (~<0.62 arcmin^{-2}) may exist when
integrated over the likely redshift range of SCUBA sources (z=1 -5), suggesting
that SCUBA sources should not necessarily be seen as completely orthogonal to
optically selected galaxies.


title: Expanding shells of shocked neutral hydrogen around compact HII regions

abstract:
  By comparing radial velocities of radio bright compact HII regions with their
HI absorption profiles, we discovered expanding shells of neutral hydrogen
around them. These shells are revealed by absorption of the radio continuum
emission from the HII regions at velocities indicating greater distances than
the observed radial velocity. We believe that these shells are shock zones at
the outer edge of the expanding ionized region. Additionally we found evidence
for a velocity inversion inside the Perseus arm caused by a spiral shock, which
results in a deep absorption line in the spectra of compact HII regions behind
it.


title: AAT/WFI observations of the Extragalactic H I Cloud HIPASS J1712-64

abstract:
  AAT/WFI optical images of a candidate extragalactic HI cloud, HIPASS
J1712-64, are presented. The g and r-band CCD mosaic camera frames were
processed using a new data pipeline recently installed at the AAO. The
resultant stacked images reach significantly deeper levels than those of
previous published optical imaging of this candidate, providing a detection
limit M_g -7 at a distance of 3Mpc, the inferred distance to HIPASS J1712-64.
However, detailed analysis of the images fails to uncover any stellar
population associated with the HI emission. If this system is a member of the
Local Group then it is pathologically different to other members. Hence, our
observations reinforce earlier suggestions that this HI cloud is most likely
Galactic in origin and not a Local Volume dwarf galaxy.


title: The distance to the SNR CTB109 deduced from its environment

abstract:
  We conducted a study of the environment around the supernova remnant CTB109.
We found that the SNR is part of a large complex of HII regions extending over
an area of 400 pc along the Galactic plane at a distance of about 3 kpc at the
closer edge of the Perseus spiral arm. At this distance CTB109 has a diameter
of about 24 pc. We demonstrated that including spiral shocks in the distance
estimation is an ultimate requirement to determine reliable distances to
objects located in the Perseus arm. The most likely explanation for the high
concentration of HII regions and SNRs is that the star formation in this part
of the Perseus arm is triggered by the spiral shock.


title: Stability of Satellites Around Close-in Extrasolar Giant Planets

abstract:
  We investigate the long-term dynamical stability of hypothetical moons
orbiting extrasolar giant planets. Stellar tides brake a planet's rotation and,
together with tidal migration, act to remove satellites; this process limits
the lifetimes of larger moons in extrasolar planetary systems. Because more
massive satellites are removed more quickly than less massive ones, we are able
to derive an upper mass limit for those satellites that might have survived to
the present day. For example, we estimate that no primordial satellites with
masses greater than 7 x 10^{-7} M_Earth$ (~ \70km radius for rho=3 g cm^{-3})
could have survived around the transiting planet HD209458b for the age of the
system. No meaningful mass limits can be placed on moons orbiting Jovian
planets more than ~0.6 AU from their parent stars. Earth-like moons of Jovian
planets could exist for 5 Gyr in systems where the stellar mass is greater than
0.15 M_Sun. Transits show the most promise for the discovery of extrasolar
moons -- we discuss prospects for satellite detection via transits using
space-based photometric surveys and the limits on the planetary tidal
dissipation factor Q that a discovery would imply.


title:
The 2dF QSO Redshift Survey - IX. A measurement of the luminosity
  dependence of QSO clustering

abstract:
  In this Paper we present a clustering analysis of QSOs as a function of
luminosity over the redshift range z=0.3-2.9. We use a sample of 10566 QSOs
taken from the preliminary data release catalogue of the 2dF QSO Redshift
Survey (2QZ). We analyse QSO clustering as a function of apparent magnitude.
The strong luminosity evolution of QSOs means that this is approximately
equivalent to analysing the data as a function of absolute magnitude relative
to M* over the redshift range that the 2QZ probes. Over the relatively narrow
range in apparent magnitude of the 2QZ we find no significant (>2sigma)
variation in the strength of clustering, however, there is marginal evidence
for QSOs with brighter apparent magnitudes having a stronger clustering
amplitude. QSOs with 18.25<bj<19.80 show a correlation scale length
s_0=5.50+-0.79h-1Mpc in an Einstein-de Sitter (EdS) universe and
s_0=8.37+-1.17h-1Mpc in a universe with omega_0=0.3 and lambda_0=0.7 (Lambda),
while the best fit values for the full magnitude interval (18.25<bj<20.85) over
the same spatial scales are s_0=4.29+-0.30h-1Mpc (EdS) and s_0=6.35+-0.45h-1Mpc
(Lambda). We can therefore determine that the bias of the brightest sub-sample
is a factor 1.22+-0.15 (EdS) or 1.24+-0.15 (Lambda) larger than that of the
full data set. An increase in clustering with luminosity, if confirmed, would
be in qualitative agreement with models in which the luminosity of a QSO is
correlated to the mass of the dark halo in which it resides, implying that the
mass of the host plays at least some part in determining a QSO's formation and
evolution. These models predict that the clustering in brighter QSO data sets,
such as Sloan Digital Sky Survey QSO sample or the bright extension of the 2QZ
should show a higher clustering amplitude than the 2QZ.


title:
X-Ray Scaling Relations of Galaxy Groups in a Hydrodynamic Cosmological
  Simulation

abstract:
  We examine the scalings of X-ray luminosity, temperature, and dark matter or
galaxy velocity dispersion for galaxy groups in an LCDM cosmological
simulation, which incorporates gravity, gas dynamics, radiative cooling, and
star formation, but no substantial non-gravitational heating. In agreement with
observations, the simulated L_X-sigma and L_X-T_X relations are steeper than
those predicted by adiabatic simulations or self-similar models, with
L_X\propto sigma^{4.4} and L_X\propto T_X^{2.6} for massive groups and
significantly steeper relations below a break at sigma~180 km/s (T_X~0.7 keV),
but T_X-sigma is fairly close to self-similar, with T_X\propto sigma^{1.75}.
The entropy of hot gas in low mass groups is higher than predicted by
self-similar scaling, and agrees with observations that suggest an "entropy
floor". The steeper scalings of the luminosity relations are driven by
radiative cooling, which reduces the hot gas fraction from 50% of the total
baryons at sigma \approx 500 km/s to 20% at sigma \approx 100 km/s. A secondary
effect is that hot gas in smaller systems is less clumpy, further driving down
L_X. A smaller volume simulation with eight times higher mass resolution
predicts nearly identical X-ray luminosities at a given group mass,
demonstrating the insensitivity of the predicted scaling relations to numerical
resolution. There remain some quantitative discrepancies: the predicted mass
scale of the L_X-T_X and L_X-sigma breaks is somewhat too low, and the
luminosity-weighted temperatures are too high at a given sigma. We conclude
that radiative cooling has an important quantitative impact on group X-ray
properties and can account for many of the observed trends that have been
interpreted as evidence for non-gravitational heating. (abridged)


title: Single Dish Polarization Calibration

abstract:
  Using the formalism of Hamaker et al. (1996), I derive a method for the
polarization calibration of observations made with a single radio telescope.
This method is particularly appropriate for observations of pulsars, where the
sign and magnitude of the circular polarization are useful for understanding
the emission processes at work. I apply the method to observations of PSR
J1359-6038 made using the multibeam receiver on the Parkes radio telescope.


title: Clustering in the 2dF QSO Redshift Survey

abstract:
  We present clustering results from the 2dF QSO Redshift Survey (2QZ) which
currently contains over 20,000 QSOs at z<3. The two-point correlation function
of QSOs averaged over the entire survey (<z>~1.5) is found to be similar to
that of local galaxies. When sub-dividing the sample as a function of redshift,
we find that for an Einstein-de Sitter universe QSO clustering is constant (in
comoving coordinates) over the entire redshift range probed by the 2QZ, while
in a universe with Omega_0=0.3 and Lambda_0=0.7 there is a marginal increase in
clustering with redshift. Sub-dividing the 2QZ on the basis of apparent
magnitude we find only a slight difference between the clustering of QSOs of
different apparent brightness, with the brightest QSOs having marginally
stronger clustering. We have made a first measurement of the redshift space
distortion of QSO clustering, with the goal of determining the value of
cosmological parameters (in partcular Lambda_0) from geometric distortions. The
current data do not allow us to discriminate between models, however, in
combination with constraints from the evolution of mass clustering we find
Omega_0=1-Lambda_0=0.23 +0.44-0.13 and beta(z~1.4)=0.39 +0.18-0.17. The full
2QZ data set will provide further cosmological constraints.


title: The Extended Emission-Line Region of 4C 37.43

abstract:
  We have explored the nature of the extended emission-line region around the
z=0.37 quasar 4C 37.43, using extensive ground-based and HST imaging and
spectroscopy. The velocity field of the ionized gas shows gradual gradients
within components but large jumps between components, with no obvious global
organization. The HST [O III] image shows radial linear features on the east
side of the QSO that appear to mark the edges of an ionization cone.
Concentrating on the bright emission peaks ~4\arcsec$ east of the quasar, we
find through modeling that we require at least two density regimes contributing
significantly to the observed emission-line spectrum: one with a density of ~2
cm^-3, having essentially unity filling factor, and one with a density of ~500
cm^-3, having a very small (~10^-5) filling factor. Because the temperatures of
these two components are similar, they cannot be in pressure equilibrium, and
there is no obvious source of confinement for the dense regions. We estimate
that the dense regions will dissipate on timescales <~10^4 years and therefore
need to be continuously regenerated, most likely by shocks. Because we know
that some QSOs, at least, begin their lives in conjunction with merger-driven
massive starbursts in their host galaxies, an attractive interpretation is that
the extended emission region comprises gas that has been expelled as a result
of tidal forces during the merger and is now being shocked by the galactic
superwind from the starburst. This picture is supported by the observed
distribution of the ionized gas, the presence of velocities ranging up to ~700
km s^{-1}, and the existence of at least two QSOs having similarly luminous and
complex extended emission regions that are known to have ultra-luminous IR
galaxy hosts with current or recent starbursts.


title: Self-similar Collapse of Rotating Magnetic Molecular Cloud Cores

abstract:
  We present self-similar solutions that describe the gravitational collapse of
rotating, isothermal, magnetic molecular-cloud cores, relevant to the formation
of rotationally supported protostellar disks. This work focuses on the
evolution after a point mass first forms at the center and generalizes previous
results by Contopoulos, Ciolek, & Konigl that did not include rotation. Our
model includes ambipolar diffusion and magnetic braking and allows us to
examine the full range of expected behaviors and their dependence on the
physical parameters. For typical parameter values, the inflow first passes
through an ambipolar-diffusion shock (at a radius r_a, where the magnetic flux
decouples from the matter), and later through a centrifugal shock at r=r_c, the
outer edge of a rotationally supported disk of mass M_d. By the time (~10^5 yr)
that the central mass M_c grows to ~1 M_\sun, r_a may be larger than 1000 AU,
r_c larger than 100 AU, and M_d/M_c smaller than 10%. Disk properties are
consistent with data on T Tauri systems, and our results imply that
protostellar disks may well be Keplerian also during earlier phases. We show
that the disk is likely to drive centrifugal outflows transporting angular
momentum and mass, and we incorporate these effects into the model. We verify
that gravitational torques and magnetorotational instability-induced turbulence
typically do not play an important role in the angular momentum transport. We
also present solutions for the limiting cases of fast rotation (where collapse
results in a massive disk with such a large outer radius that it traps the
ambipolar diffusion front) and strong braking (where no disk is formed and the
collapse resembles that of a nonrotating core at small radii), as well as
solutions for the rotational collapse of ideal-MHD and nonmagnetic model cores.


title: Jet triggered Type Ia supernovae in radio-galaxies?

abstract:
  We report the serendipitous discovery of a supernova (SN) in the nearby
radio-galaxy 3C 78. Observations obtained with the STIS spectrograph on board
the Hubble Space Telescope show, at a distance of 0.54 arcsec (300 pc) from the
galaxy nucleus, a second bright source, not present in previous images. As this
source was fortuitously covered by the spectrograph slit its spectrum was
obtained and it is characteristic of a Type Ia SN. This SN is closely aligned
with the radio-jet of 3C 78. Analysis of historical records shows that such a
close association between jet and supernova occurred in 6 of the 14 reported
SNe in radio-galaxies. The probability that this results from a random
distribution of SN in the host galaxy is less than 0.05%. We then argue that
jets might trigger supernova explosions.


title: The Dynamical Simulations of the Planets Orbiting GJ 876

abstract:
  We have performed simulations to investigate the dynamics of the M dwarf star
GJ 876 in an attempt to reveal any stabilizing mechanism for sustaining the
system.We simulated different coplanar and noncoplanar configurations of
two-planet systems and other cases.From the simulations,we found that the 2 :1
mean-motion resonance between two planets can act as an effective mechanism for
maintaining the stability of the system.This result is explained by a proposed
analytical model.Using this model,we studied the region of motion of the inner
planet by varying the parameters of the system,and we detected that the
analytical results are well consistent with the numerical simulations.


title: Low Microlensing Optical Depth Toward the Galactic Bar

abstract:
  I make a new evaluation of the microlensing optical depth toward the Galactic
bar from Difference Image Analysis (DIA) of the MACHO Collaboration. First, I
present supplementary evidence that MACHO field 104 located at (l,b) =
(3.11,-3.01) is anomalous in terms of the event duration distribution. I argue
that both the event durations and the very high optical depth of field 104 are
not representative and, therefore, exclude this field as an outlier. In
addition, I eliminate field 159 at (l,b) = (6.35,-4.40) based mainly on its
separate location, but also on unexplained statistical properties of the event
durations. The remaining six DIA fields form a very homogeneous and spatially
compact set that is very suitable for averaging. The weighting of the optical
depth values for these six DIA fields results in a total optical depth
tau_{tot} = 2.01^{+0.34}_{-0.32} x 10^{-6} at (l,b) = (2.22,-3.18). If a
fraction of all sources, f_{disk}, assumed to be in the disk, does not
contribute to microlensing, then the optical depth toward the sources in the
bar is tau_{bar} = 2.23^{+0.38}_{-0.35} x 10^{-6} 0.9/(1-f_{disk}). Both
tau_{tot} and tau_{bar} are substantially lower than the original estimates of
Alcock et al. Most of the change in the DIA-based optical depths comes from a
more appropriate statistical treatment of the results in individual fields and
not from the removal of fields 104 and 159. When taken together with tau_{bar}
= (1.4 +/- 0.3) x 10^{-6} at (l,b) = (3.9,-3.8) as derived from clump giants,
this new result suggests that the conclusions from microlensing experiments are
in reasonable agreement with the expectations from infrared-based Galactic
models.


title:
Compton reflection and iron fluorescence in BeppoSAX observations of
  Seyfert type 1 galaxies

abstract:
  A sample of nine bright Seyfert 1 and NELG type galaxies, observed with
BeppoSAX, is analyzed to assess on a truly broad band basis (0.1-200 keV) the
issue of the spectral contributions of Compton reflection and iron line
fluorescence from circumnuclear gas. The empirical description adopted for the
direct continuum is the commonly used power law with an exponential cut-off.
The most direct test of the theoretical predictions, namely that the equivalent
width of the line, Walpha, and the strength R of the reflection relative to the
direct continuum are closely related to each other, gives a substantially
positive result, that is their mean ratio is very close to expectation, and
only a modest spread in the iron abundance seems implied. The existence of a
steep correlation between R and the slope Gamma of the power law is not
confirmed. A weak evidence is found that the existence of a very shallow trend
to increase on average with Gamma cannot be altogether excluded in both R and
Walpha, but needs to be tested with a larger sample. The energy Ef in the
exponential cut-off spans a range from about 80 to more than 300 keV. A
possible correlation is found, with Ef increasing on average with Gamma: if
ignored, for instance by keeping Ef at a fixed value in a sample study, it
could be cause of artificial steepening in a correlation between R and Gamma.


title:
A prototype system for detecting the radio-frequency pulse associated
  with cosmic ray air showers

abstract:
  The development of a system to detect the radio-frequency (RF) pulse
associated with extensive air showers of cosmic rays is described. This work
was performed at the CASA/MIA array in Utah, with the intention of designing
equipment that can be used in conjunction with the Auger Giant Array. A small
subset of data (less than 40 out of a total of 600 hours of running time),
taken under low-noise conditions, permitted upper limits to be placed on the
rate for pulses accompanying showers of energies around $10^{17}$ eV.


title: WIMP Search by DAMA at Gran Sasso

abstract:
  DAMA is searching for rare processes by developing and using several kinds of
radiopure scintillators: in particular, NaI(Tl), liquid Xenon and CaF$_2$(Eu).
Here only the results released so far on the WIMP annual modulation signature
are summarized and compared with results from other experiments, including the
recent re-analysis of CDMS-I data. Next perspectives are also shortly
addressed.


title: IBIS/PICsIT Data and Analysis

abstract:
  The imager IBIS on board INTEGRAL is composed of two detector planes: ISGRI
(15 keV - 1 MeV) and PICsIT (170 keV - 10 MeV). Here we describe the data
structure of PICsIT and the instrument specific software, including the
standard scientific analysis. Some examples of shadowgrams and spectra are
shown, by using data collected during the End-to-End Tests of January 2002.


title:
What does helioseismology tell us about solar cycle related structural
  changes in the Sun?

abstract:
  Solar oscillations frequencies show a distinct change with solar activity.
The changes in frequencies can be used to study the time variation of solar
structure. We discuss constraints on the changes in solar structure with time
as obtained with helioseismic data covering the last six years. The frequency
variations appear to be dominated by changes in the near-surface layers rather
than by changes in the structure of the deeper layers.


title: Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs

abstract:
  Trigonometric parallax determinations are presented for 28 late type dwarfs
and brown dwarfs, including eight M dwarfs with spectral types between M7 and
M9.5, 17 L dwarfs with spectral types between L0 and L8, and three T dwarfs.
Broadband photometry at CCD wavelengths (VRIz) and/or near-IR wavelengths (JHK)
are presented for these objects and for 24 additional late-type dwarfs.
Supplemented with astrometry and photometry from the literature, including ten
L and two T dwarfs with parallaxes established by association with bright,
usually HIPPARCOS primaries, this material forms the basis for studying various
color-color and color-absolute magnitude relations. The I-J color is a good
predictor of absolute magnitude for late-M and L dwarfs. M_J becomes
monotonically fainter with I-J color and with spectral type through late-L
dwarfs, then brightens for early-T dwarfs. The combination of zJK colors alone
can be used to classify late-M, early-L, and T dwarfs accurately, and to
predict their absolute magnitudes, but is less effective at untangling the
scatter among mid- and late-L dwarfs. The mean tangential velocity of these
objects is found to be slightly less than that for dM stars in the solar
neighborhood, consistent with a sample with a mean age of several Gyr. Using
colors to estimate bolometric corrections, and models to estimate stellar
radii, effective temperatures are derived. The latest L dwarfs are found to
have T_eff ~ 1360 K.


title: Evidence for Cloud Disruption in the L/T Dwarf Transition

abstract:
  Clouds of metal-bearing condensates play a critical role in shaping the
emergent spectral energy distributions of the coolest classes of low-mass stars
and brown dwarfs, L and T dwarfs. Because condensate clouds in planetary
atmospheres show distinct horizontal structure, we have explored a model for
partly cloudy atmospheres in brown dwarfs. Our model successfully reproduces
the colors and magnitudes of both L and T dwarfs for the first time, including
the unexpected brightning of the early- and mid-type T dwarfs at J-band,
provided that clouds are rapidly removed from the photosphere at T_eff ~ 1200
K. The clearing of cloud layers also explains the surprising persistence and
strengthening of gaseous FeH bands in early- and mid-type T dwarfs. The breakup
of cloud layers is likely driven by convection in the troposphere, analogous to
phenomena observed on Jupiter. Our results demonstrate that planetary-like
atmospheric dynamics must be considered when examining the evolution of
free-floating brown dwarfs.


title:
The Oldest Stars of the Extremely Metal-Poor Local Group Dwarf Irregular
  Galaxy Leo A

abstract:
  We present deep Hubble Space Telescope single-star photometry of Leo A in B,
V, and I. Our new field of view is offset from the centrally located field
observed by Tolstoy et al. (1998) in order to expose the halo population of
this galaxy. We report the detection of metal-poor red horizontal branch stars,
which demonstrate that Leo A is not a young galaxy. In fact, Leo A is as least
as old as metal-poor Galactic Globular Clusters which exhibit red horizontal
branches, and are considered to have a minimum age of about 9 Gyr. We discuss
the distance to Leo A, and perform an extensive comparison of the data with
stellar isochrones. For a distance modulus of 24.5, the data are better than
50% complete down to absolute magnitudes of 2 or more. We can easily identify
stars with metallicities between 0.0001 and 0.0004, and ages between about 5
and 10 Gyr, in their post-main-sequence phases, but lack the detection of
main-sequence turnoffs which would provide unambiguous proof of ancient (>10
Gyr) stellar generations. Blue horizontal branch stars are above the detection
limits, but difficult to distinguish from young stars with similar colors and
magnitudes. Synthetic color-magnitude diagrams show it is possible to populate
the blue horizontal branch in the halo of Leo A. The models also suggest ~50%
of the total astrated mass in our pointing to be attributed to an ancient (>10
Gyr) stellar population. We conclude that Leo A started to form stars at least
about 9 Gyr ago. Leo A exhibits an extremely low oxygen abundance, of only 3%
of Solar, in its ionized interstellar medium. The existence of old stars in
this very oxygen-deficient galaxy illustrates that a low oxygen abundance does
not preclude a history of early star formation.


title: On mode trapping in pulsating DA white dwarf stars

abstract:
  The present work is designed to explore the effects of the time-dependent
element diffusion on the mode trapping properties of DA white dwarf models with
various thickness of the hydrogen envelope. Our predictions are compared with
the standard assumption of diffusive equilibrium in the trace element
approximation. We find that element diffusion markedly weakens the presence of
mode trapping originated in the outer layers of the models, even for the case
of thin hydrogen envelopes.


title: Violence in the Dark Ages

abstract:
  A wide range of observational and theoretical arguments suggest that the
universe experienced a period of heating and metal enrichment, most likely from
starbursting dwarf galaxies. Using a hydrodynamic simulation we have conducted
a uniquely detailed theoretical investigation of this epoch at the end of the
cosmological ``dark ages''. Outflows strip baryons from pre-viralized halos
with total masses $\lesssim10{}^{10}$ M${}_\odot$, reducing their number
density and the overall star formation rate, while pushing these quantities
toward their observed values. We show that the metallicity of
$\lesssim10{}^{10}$ M${}_\odot$ objects increases with size, but with a large
scatter, reproducing the metallicity-luminosity relation of dwarf galaxies.
Galaxies $\gtrsim10{}^{10}$ M${}_\odot$ form with a roughly constant initial
metallicity of 10% solar, explaining the observed lack of metal-poor disk stars
in these objects. Outflows enrich roughly 20% of the simulation volume,
yielding a mean metallicity of 0.3% solar, in agreement with observations of
CIV in QSO absorption-line systems.


title: The Kurtosis of the Cosmic Shear Field

abstract:
  We study the fourth-order moment of the cosmic shear field using the dark
matter halo approach to describe the nonlinear gravitational evolution of
structure in the universe. Since the third-order moment of the shear field
vanishes because of symmetry, non-Gaussian signatures in its one-point
statistics emerge at the fourth-order level. We argue that the shear kurtosis
parameter S_4 = <gamma^4>/<gamma^2>^3 may be more directly applicable to
realistic data than the well-studied higher-order statistics of the convergence
field, since obtaining the convergence requires a non-local reconstruction from
the measured shear field.
  We compare our halo model predictions for the variance, skewness and kurtosis
of lensing fields with ray-tracing simulations of cold dark matter models and
find good agreement. The shear kurtosis calculation is made tractable by
developing approximations for fast and accurate evaluations of the
8-dimensional integrals needed to obtain the kurtosis. We show that on small
scales it is dominated by correlations within halos more massive than 10^14
solar masses. The shear kurtosis is sensitive to the mass density parameter of
the universe, Omega, and has relatively weak dependences on other parameters.
The approximations we develop for the third- and fourth-order moments allow for
accurate halo model predictions for the 3-dimensional mass distribution as
well. We demonstrate their accuracy in the small scale regime, below 2 Mpc,
where analytical approaches used in the literature so far cease to be accurate.


title:
Light Element Synthesis in High Entropy Relativistic Flows Associated
  with Gamma Ray Bursts

abstract:
  We calculate and discuss the light element freeze-out nucleosynthesis in high
entropy winds and fireballs for broad ranges of entropy-per-baryon, dynamic
timescales characterizing relativistic expansion, and neutron-to-proton ratios.
With conditions characteristic of Gamma Ray Bursts (GRBs) we find that
deuterium production can be prodigious, with final abundance values 2H/H
approximately 2%, depending on the fireball isospin, late time dynamics, and
the effects of neutron decoupling- induced high energy non-thermal nuclear
reactions. This implies that there potentially could be detectable local
enhancements in the deuterium abundance associated with GRB events.


title:
The Effect of radiative cooling on the scale-dependence of global
  stellar and gas contents of groups and clusters of galaxies

abstract:
  It is widely believed that the global baryon content and mass-to-light ratio
of groups and clusters of galaxies are a fair representative of the matter mix
of the universe and therefore, can be used to reliably determine the cosmic
mass density parameter Omega_M. However, this fundamental assumption is
challenged by growing evidence from optical and X-ray observations that the
average gas mass fraction and mass-to-light ratio increase mildly with scale
from poor groups to rich clusters. Although a number of time-consuming
hydrodynamical simulations combined with semi-analytic approaches have been
carried out, which permit a sophisticated treatment of some complicated
processes in the formation and evolution of cosmic structures, the essential
physics behind the phenomenon still remains a subject of intense debate. In
this Letter, using a simple analytic model, we show that radiative cooling of
the hot intragroup/intracluster gas may allow one to reproduce the observed
scale-dependence of the global stellar and gas mass fractions and mass-to-light
ratio of groups and clusters, provided that about half of the cooled gas is
converted into stars. Together with the recent success in the recovery of the
entropy excess and the steepening of the X-ray luminosity-temperature relations
detected in groups and clusters, radiative cooling provides a simple, unified
scheme for the evolution of hot gas and the formation of stars in the largest
virialized systems of the universe.


title:
Iron abundance in hot hydrogen-deficient central stars and white dwarfs
  from FUSE, HST, and IUE spectroscopy

abstract:
  We present a first systematic investigation of the iron abundance in very hot
(Teff>50,000K) hydrogen-deficient post-AGB stars. Our sample comprises 16
PG1159 stars and four DO white dwarfs. We use recent FUSE observations as well
as HST and IUE archival data to perform spectral analyses with line blanketed
NLTE model atmospheres. Iron is not detected in any PG1159 star. In most cases
this is compatible with a solar iron abundance due to limited quality of HST
and IUE data, although the tendency to an iron underabundance may be
recognized. However, the absence of iron lines in excellent FUSE spectra
suggests an underabundance by at least 1 dex in two objects (K1-16 NGC 7094). A
similar result has been reported recently in the [WC]-PG1159 transition object
Abell 78 (Werner et al. 2002). We discuss dust fractionation and s-process
neutron-captures as possible origins. We also announce the first identification
of sulfur in PG1159 stars.


title: Improved limits on photon velocity oscillations

abstract:
  The mixing of the photon with a hypothetical sterile paraphotonic state would
have consequences on the cosmological propagation of photons. The absence of
distortions in the optical spectrum of distant Type Ia supernov\ae allows to
extend by two orders of magnitude the previous limit on the Lorentz-violating
parameter $\delta$ associated to the photon-paraphoton transition, extracted
from the abscence of distortions in the spectrum of the cosmic microwave
background. The new limit is consistent with the interpretation of the dimming
of distant Type Ia supernov\ae as a consequence of a nonzero cosmological
constant. Observations of gamma-rays from active galactic nuclei allow to
further extend the limit on $\delta$ by ten orders of magnitude.


title: The faint end of the galaxy luminosity function

abstract:
  We present and discuss optical measurements of the faint end of the galaxy
luminosity function down to M_R = -10 in five different local environments of
varying galaxy density and morphological content. The environments we studied,
in order of decreasing galaxy density, are the Virgo Cluster, the NGC 1407
Group, the Coma I Group, the Leo Group and the NGC 1023 Group. Our results come
from a deep wide-angle survey with the NAOJ Subaru 8 m Telescope on Mauna Kea
and are sensitive down to very faint surface-brightness levels. Galaxies were
identified as group or cluster members on the basis of their surface brightness
and morphology. The faintest galaxies in our sample have R ~ 22.5. There were
thousands of fainter galaxies but we cannot distinguish cluster members from
background galaxies at these faint limits so do not attempt to determine a
luminosity function fainter than M_R = -10.
  In all cases, there are far fewer dwarfs than the numbers of low mass halos
anticipated by cold dark matter theory. The mean logarithmic slope of the
luminosity function between M_R = -18 and M_R = -10 is alpha ~ -1.2, far
shallower than the cold dark matter mass function slope of alpha ~ -1.8. We
would therefore need to be missing about 90 per cent of the dwarfs at the faint
end of our sample in all the environments we study to achieve consistency with
CDM theory.


title:
The electron temperatures of HII regions S 201, S 206, and S 209 :
  Multi-frequency GMRT observations

abstract:
  Three Galactic HII regions, viz., S 201, S 206, and S 209 have been imaged at
three frequencies, viz., 232, 327, and 610 MHz using the GMRT. The resolutions
of these images are typically 15" at 232, 10" at 327, and 6" at 610 MHz. These
are the highest resolution low frequency images of these HII regions. We found
that all three HII regions have core--envelope morphologies. We use the high
resolution afforded by the data to estimate the electron temperatures of the
compact cores of these HII regions. These estimates of the electron
temperatures are consistent with an increase in the temperature with
Galacto-centric distance; an effect attributed to a decrease in the heavy
elements abundances at large Galacto-centric distances.


title: GMRT HI imaging survey of ERIDANUS group of galaxies

abstract:
  This project aims to image a subset of galaxies in the nearby group Eridanus
in HI emission and in radio continuum using the GMRT. The typical resolution of
HI images will be $\sim$1 kpc with a 3$\sigma$ sensitivity to HI mass of a few
times 10$^{7}$ M$_\odot$. The rotation curves obtained using the HI velocity
field together with the 2MASS magnitudes in the near infrared will be used to
construct the Tully-Fisher relation for this group. High resolution (sub-kpc)
multi-frequency radio continuum images will be used to study star-formation
rates, radio morphologies and spectral indices of Eridanus galaxies. About half
of the galaxies have already been observed and further observations on some
late type galaxies are proposed with the GMRT. We present here the HI image and
the rotation curve for a member of this group viz. NGC 1385.


title: Deep I-band Imaging of z=5.99 Quasar

abstract:
  Deep I-band imaging was carried out to search for the optical counterpart of
the X-ray jet candidate near SDSS 1306+0356, reported by Schwartz (2002,
astro-ph/0202190). The data suggest that the extended X-ray source may be a
jet, related to a galaxy rather than to the quasar itself.


title: Interpretations of the Accelerating Universe

abstract:
  It is generally argued that the present cosmological observations support the
accelerating models of the universe, as driven by the cosmological constant or
`dark energy'. We argue here that an alternative model of the universe is
possible which explains the current observations of the universe. We
demonstrate this with a reinterpretation of the magnitude-redshift relation for
Type Ia supernovae, since this was the test that gave a spurt to the current
trend in favour of the cosmological constant.


title:
The new model of a tidally disrupted star: further development and
  relativistic calculations

abstract:
  In this paper we develop the new semi-analitical model of a tidally perturbed
or tidally disrupted star proposed recently by two of us. This model is
effectively a one dimensional Lagrangian model and it can be evolved
numerically much faster that the conventional 3D models. A self-consistent
derivation of the dynamical equations of the model is performed and several
important theorems about the dynamics of the model are proved without any
particular assumption about the equation of state of the stellar gas. The
dynamical equations are solved numerically for the case of $n=1.5$ polytropic
star evolving in the relativistic field of a $10^7M_{\odot}$ Kerr black hole.
Some results of these calculations are compared with the results of
calculations based on finite-difference 3D simulations. The comparison shows a
very good agreement between both approaches to the problem. Then we show that
the strength of the tidal encounter depends significantly on the relative
orientation of the orbital angular momentum of the star and the spin of the
black hole.


title: Solar Seismic Model as a New Constraint on Supersymmetric Dark Matter

abstract:
  If the Milky Way is populated by WIMPs as predicted by cosmological models of
the large-scale structure of the universe and as motivated by SUSY, the capture
of high-mass WIMPs by the Sun would affect the temperature, density and
chemical composition of the solar core. We use the sound speed and the density
profiles inferred from the helioseismic instruments on the Solar and
Heliospheric Observatory (SOHO) to discuss the effect of WIMP accretion and
annihilation on the evolution of the Sun. The WIMP transport of energy inside
the Sun is not negligible for WIMPs with a mass smaller than 60 GeV and
annihilating WIMPs with <sigma_a v>~ 10^{-27}cm^3/sec. WIMP-accreting models
with WIMP masses smaller than 30 GeV are in conflict with the most recent
seismic data. We combine our new constraints with the analysis of predicted
neutrino fluxes from annihilating WIMPs in the solar core. Working in the
framework of the Minimal Supersymmetric Standard Model and considering the
neutralino as the best dark matter particle candidate, we find that
supersymmetric models, consistent with solar seismic data and with recent
measurements of dark matter relic density, lead to a measured muon flux on
Earth in the range of 1 to 10^4 km^{-2} yr^{-1}, for neutralino masses between
30 and 400 GeV.


title:
Line Caustic Revisted: Which distance is $\delta$ in $J^{-1}\propto
  \sqrt{\delta^{-1}}$?

abstract:
  The line caustic behavior has been discussed since Chang and Refsdal (1979)
mentioned inverse-square-root-of-the-distance dependence of the amplification
of the images near the critical curve in a study of a single point mass under
the influence of a constant shear due to a larger mass. A quarter century
later, Gaudi and Petters (2001) interprets that the distance is {\it a vertical
distance to the caustic}. It is an erroneous misinterpretation.
  We rehash Rhie and Bennett (1999) where the caustic behavior of the binary
lenses was derived to study the feasibility of limb darkening measurements in
caustic crossing microlensing events. ~({\it 1}) $J = \pm
\sqrt{4\delta\omega_{2-} J_-}$ where ~$\delta\omega\parallel\bar\partial J$,
and $\delta\omega_{2-}$ and $J_-$ are $E_-$-components of $\delta\omega$ (the
source position shift from the caustic curve) and $2\bar\partial J$ (the
gradient of the Jacobian determinant) respectively; ~({\it 2}) The critical
eigenvector $\pm E_-$ is normal to the caustic curve and easily determined from
the analytic function $\kappa$-field; ~({\it 3}) Near a cusp ($J_- = 0$) is of
a behavior of the third order, and the direction of $\bar\partial J$ with
respect to the caustic curve changes rapidly because a cusp is an accumulation
point; ~({\it 4}) On a planetary caustic, $|\partial J|\sim
\sqrt{1/\epsilon_{pl}}$ is large and power expansion does not necessarily
converge over the size of the lensed star. In practice, direct numerical
summation is inevitable.
  We also note that a lens equation with constant shear is intrinsically
incomplete and requires supplementary physical assumptions and interpretations
in order to be a viable model for a lensing system.


title: Physical structure and CO abundance of low-mass protostellar envelopes

abstract:
  We present 1D radiative transfer modelling of the envelopes of a sample of 18
low-mass protostars and pre-stellar cores with the aim of setting up realistic
physical models, for use in a chemical description of the sources. The density
and temperature profiles of the envelopes are constrained from their radial
profiles obtained from SCUBA maps at 450 and 850 micron and from measurements
of the source fluxes ranging from 60 micron to 1.3 mm. The densities of the
envelopes within ~10000 AU can be described by single power-laws r^{-p} for the
class 0 and I sources with p ranging from 1.3 to 1.9, with typical
uncertainties of +/- 0.2. Four sources have flatter profiles, either due to
asymmetries or to the presence of an outer constant density region. No
significant difference is found between class 0 and I sources. The power-law
fits fail for the pre-stellar cores, supporting recent results that such cores
do not have a central source of heating. The derived physical models are used
as input for Monte Carlo modelling of submillimeter C18O and C17O emission. It
is found that class I objects typically show CO abundances close to those found
in local molecular clouds, but that class 0 sources and pre-stellar cores show
lower abundances by almost an order of magnitude implying that significant
depletion occurs for the early phases of star formation. While the 2-1 and 3-2
isotopic lines can be fitted using a constant fractional CO abundance
throughout the envelope, the 1-0 lines are significantly underestimated,
possibly due to contribution of ambient molecular cloud material to the
observed emission. The difference between the class 0 and I objects may be
related to the properties of the CO ices.


title: New mechanism of pulsar radio emission

abstract:
  It is shown that pulsar radio emission can be generated effectively through a
streaming motion in the polar-cap regions of a pulsar magnetosphere causing
nonresonant growth of waves that can escape directly. As in other beam models,
a relatively low-energy high-density beam is required. The instability
generates quasi-transverse waves in a beam mode at frequencies that can be well
below the resonant frequency. As the waves propagate outward growth continues
until the height at which the wave frequency is equal to the resonant
frequency. Beyond this point the waves escape in a natural plasma mode (L-O
mode). This one-step mechanism is much more efficient than previously widely
considered multi-step mechanisms.


title:
The Dependence of Star Formation History and Internal Structure on
  Stellar Mass for 10^5 Low-Redshift Galaxies

abstract:
  We study the relations between stellar mass, star formation history, size and
internal structure for a complete sample of 122,808 galaxies drawn from the
Sloan Digital Sky Survey. We show that low-redshift galaxies divide into two
distinct families at a stellar mass of 3 \times 10^10 M_sol. Lower mass
galaxies have young stellar populations, low surface mass densities and the low
concentrations typical of disks. A significant fraction of the lowest mass
galaxies in our sample have experienced recent starbursts. At given stellar
mass, the sizes of low mass galaxies are log- normally distributed with
dispersion sigma(ln R_50) \sim 0.5, in excellent agreement with the idea that
they form with little angular momentum loss through cooling and condensation in
a gravitationally dominant dark matter halo. Their median stellar surface mass
density scales with stellar mass as mu* propto M_*^0.54, suggesting that the
stellar mass of a disk galaxy is proprtional to the three halves power of its
halo mass. This suggests that the efficiency of the conversion of baryons into
stars in low mass galaxies increases in propor- tion to halo mass, perhaps as a
result of supernova feedback processes. At stellar masses above 3 \times 10^10
M_sol, there is a rapidly increasing frac- tion of galaxies with old stellar
populations, high surface mass densities and high concentrations typical of
bulges. In this regime, the size distribution is log-normal, but its dispersion
decreases rapidly with increasing stellar mass and the median mass surface
density is approximately constant. This suggests that the star formation
efficiency decreases in the highest mass halos, and that little star formation
occurs in massive galaxies once they have assembled.


title: Observation of Gamma-ray Bursts with INTEGRAL

abstract:
  We expect that at least one Gamma-Ray Burst per month will be detected in the
field of view of INTEGRAL instruments and localized with an accuracy of a few
arcminutes. IBIS (the Imager on board INTEGRAL) will be the most sensitive
instrument in the soft $\gamma$-ray band during the next few years. This will
allow INTEGRAL to detect the faintest (and hence the most distant) $\gamma$-ray
bursts, thus surely contributing to the study of the physics of GRBs and to the
comprehension of the early stages of the Universe. GRBs will be detected and
localized in (near) real time with the IBAS (INTEGRAL Burst Alert System)
software, and their coordinates will be immediately distributed to the
scientific community, allowing for prompt follow-up observations at other
wavelengths. The flexibility of the IBAS software, running on ground at the
ISDC, will allow us to possibly reveal new classes of bursts, such as
ultra-short bursts ($\sim$ ms) or very long (t $>$ 50 s) but slowly rising
bursts, that could not be detected by previous experiments.


title:
New nearby stars selected in a high proper motion survey by DENIS
  photometry

abstract:
  We present new nearby stars extracted from a proper motion catalogue and
having a DENIS counterpart. Their distances and spectral type are estimated
using the DENIS colours. 107 stars are within 50 pc. 31 stars among them have
previously measured distances. In addition, 40 stars may enter within the 50 pc
limit depending on which population they belong to. 6 stars among them have
already measured distances. 5 objects, LHS5045, LP225-57, LP831-45, LHS1767,
and WT792, are probably closer than 15 pc, with LP225-57 at 9.5 pc. Most of
these stars are M-type while 4 stars are white dwarfs. 88 M-dwarfs are disc
stars, 14 belong to the thick disc and 1 to the spheroid.


title: Optical and near IR spectroscopy of low excitation HII regions with GTC

abstract:
  The determination of chemical abundances in ionized gas nebulae is based on
the detection of auroral emission lines, from which it is possible to deduce
the line temperatures of several ions. These lines are weak in low excitation
objects, so its measurement is only possible in great aperture telescopes. The
GTC would allow to plan a comprehenssive study of chemical abundances in such
objects from mid-high resolution spectra, what would give more accurate
observational restrictions to models of chemical evolution.


title: Spectro-photometry of galaxies in the Virgo cluster

abstract:
  As a result of an extensive observational campaign targeting the Virgo
cluster, we obtained integrated (drift-scan mode) optical spectra and
multiwavelength (UV,U,B,V,H) photometry for 124 and 330 galaxies, respectively,
spanning the whole Hubble sequence, and with m_p<=16 (M_p<=-15). These data
were combined to obtain galaxy SEDs extending from 2000 to 22000 A. By fitting
these SEDs with synthetic ones derived using Bruzual & Charlot population
synthesis models we try to constrain observationally the SFH of these galaxies.
Assuming a Salpeter IMF and an analytical form for the SFH, the fit free
parameters are: the age (T) of the star formation event, its characteristic
time-scale (tau) and the initial metallicity (Z). We test the (simplistic) case
where all galaxies have a common age T=13 Gyr, exploring a SFH with "delayed"
exponential form, thus allowing for an increasing SFR with time. This SFH is
consistent with the full range of observed SEDs, provided that the
characteristic time-scale tau is let free to vary between 0.1 and 25 Gyr and Z
between 1/5 and 2.5 Z solar. Elliptical galaxies (including dEs) are best
fitted with short time scales (tau~3 Gyr) and Z varying between 1/5 and 1 Z
solar. The model metallicity is found to increase with H band luminosity.
Spiral galaxies require that both tau and Z correlate with H band luminosity:
low mass Im+BCD have sub-solar Z and tau>=10 Gyr, whereas giant spirals have
solar metallicities and tau~3 Gyr, consistent with ellipticals. Moreover we
find that the SFH of spirals depends upon the presence at their interior of
fresh gas capable of sustaining the star formation. In fact the residuals of
the tau vs. L_H relation depend significantly on the HI content. HI deficient
galaxies have shorter tau than spirals with normal HI content.


title:
H1504+65 - The Naked Stellar C/O Core of a Former Red Giant Observed
  with FUSE and Chandra

abstract:
  H1504+65 is an extremely hot hydrogen-deficient white dwarf with an effective
temperature close to 200,000 K. We present new FUV and soft X-ray spectra
obtained with FUSE and Chandra, which confirm that H1504+65 has an atmosphere
primarily composed of carbon and oxygen. The Chandra spectra show a wealth of
absorption lines from highly ionized oxygen, neon and magnesium and suggest
relatively high Ne and Mg abundances. This corroborates an earlier suggestion
that H1504+65 represents a naked C/O stellar core or even the C/O envelope of a
O-Ne-Mg white dwarf.