title:
Angular Momentum Transport by MHD Turbulence in Accretion Disks: Gas
  Pressure Dependence of the Saturation Level of the Magnetorotational
  Instability

abstract:
  The saturation level of the magnetorotational instability (MRI) is
investigated using three-dimensional MHD simulations. The shearing box
approximation is adopted and the vertical component of gravity is ignored, so
that the evolution of the MRI is followed in a small local part of the disk. We
focus on the dependence of the saturation level of the stress on the gas
pressure, which is a key assumption in the standard alpha disk model. From our
numerical experiments it is found that there is a weak power-law relation
between the saturation level of the Maxwell stress and the gas pressure in the
nonlinear regime; the higher the gas pressure, the larger the stress. Although
the power-law index depends slightly on the initial field geometry, the
relationship between stress and gas pressure is independent of the initial
field strength, and is unaffected by Ohmic dissipation if the magnetic Reynolds
number is at least 10. The relationship is the same in adiabatic calculations,
where pressure increases over time, and nearly-isothermal calculations, where
pressure varies little with time. Our numerical results are qualitatively
consistent with an idea that the saturation level of the MRI is determined by a
balance between the growth of the MRI and the dissipation of the field through
reconnection. The quantitative interpretation of the pressure-stress relation,
however, may require advances in the theoretical understanding of non-steady
magnetic reconnection.


title:
Low-mass supernovae in the early Galactic halo: source of the double
  r/s-process enriched halo stars?

abstract:
  Several stars at the low-metallicity extreme of the Galactic halo
([Fe/H]=-2.5) show strong enhancements of both s-process and r-process
elements. The presence of s-process elements in main-sequence stars is
explained via mass transfer from an AGB companion star in a binary system.
r-Process elements originate in type-II supernovae and also require mass
transfer. It is however unclear how pollution by both an AGB star and a
supernova could have occured. Here I show that the initial--final-mass relation
steepens at low metallicity, due to low mass-loss efficiency. This may cause
the degenerate cores of low-Z, high-mass AGB stars to reach the Chandresekhar
mass, leading to an Iben & Renzini-type-1.5 supernova. Such supernovae can
explain both the enhancement patterns and the metallicity dependence of the
double-enhanced halo stars. Reduced mass loss efficiency predicts more massive
remnants in metal-poor globular clusters. The evidence for a high M/L
population in the cores of globular clusters is briefly discussed.


title:
Alfvenic reacceleration of relativistic particles in galaxy clusters:
  MHD waves, leptons and hadrons

abstract:
  There is a growing evidence that extended radio halos are most likely
generated by electrons reaccelerated via some kind of turbulence generated in
the cluster volume during major mergers. It is well known that Alfv\'en waves
channel most of their energy flux in the acceleration of relativistic
particles. Much work has been done recently to study this phenomenon and its
consequences for the explanation of the observed non-thermal phenomena in
clusters of galaxies. We investigate here the problem of particle-wave
interactions in the most general situation in which relativistic electrons,
thermal protons and relativistic protons exist within the cluster volume. The
interaction of all these components with the waves, as well as the turbulent
cascading and damping processes of Alfv\'en waves, are treated in a fully
time-dependent way. This allows us to calculate the spectra of electrons,
protons and waves at any fixed time. The {\it Lighthill} mechanism is invoked
to couple the fluid turbulence, supposedly injected during cluster mergers, to
MHD turbulence. We find that present observations of non-thermal radiation from
clusters of galaxies are well described within this approach, provided the
fraction of relativistic hadrons in the intracluster medium (ICM) is smaller
than 5-10 %.


title: Preparing Red-Green-Blue (RGB) Images from CCD Data

abstract:
  We present a new, and we believe arguably correct, algorithm for producing
Red-Green-Blue (RBG) composites from 3-band astronomical images. Our method
ensures that an object with a specified astronomical color (e.g. g-r and r-i)
has a unique color in the RGB image, as opposed to the burnt-out white stars to
which we are accustomed. A natural consequence of this is that we can use the
same colors to code color-magnitude diagrams, providing a natural `index' to
our images. We also introduce the use of an asinh stretch, which allows us to
show faint objects while simultaneously preserving the structure of brighter
objects in the field, such as the spiral arms of large galaxies. We believe
that, in addition to their aesthetic value, our images convey far more
information than do the traditional ones, and provide examples from Sloan
Digital Sky Survey (SDSS) imaging, the Hubble Deep Field (HDF), and Chandra to
support our claims. More examples are available at
http://www.astro.princeton.edu/~rhl/PrettyPictures


title: Phantom appearance of non-phantom matter

abstract:
  Two cosmological models with non-phantom matter having the same expansion of
the universe as phantom cosmologies are constructed. The first model is
characterized by the evolving gravitational "constant" $G$ and a dark energy
component with a non-conserved energy-momentum tensor. The second model
includes two interacting components, the dark energy component and the matter
component. Closed form solutions are obtained for the constant values of model
parameters and constraints on the parameters of each model from cosmological
observations are outlined. For both models it is explicitly shown how the
components of each model produce the expansion of the universe characteristic
of phantom cosmologies, despite the absence of phantom energy. These findings
stress the interpretation of phantom energy as an effective description of the
more complex dynamics of non-phantom matter.


title:
On the highly reddened members in 6 young galactic star clusters - a
  multiwavelength study

abstract:
  The spectral and reddening properties of 211 highly reddened proper motion
members with $V < 15$ mag in 6 young galactic star clusters are investigated
using low resolution spectroscopic, broad-band $UBVRIJHK$ and mid-IR data. We
report emission features in CaII HK and HI lines for a sample of 29 stars
including 11 stars reported for the first time and also provide either a new or
more reliable spectral class for a sample of 24 stars. CaII triplet width
measurements are used to indicate the presence of an accretion disk for a dozen
stars and to hint luminosity for a couple of stars. On the basis of spectral
features, near-IR excesses, dereddened color-color diagrams and mid-IR spectral
indices we identify a group of 28 pre-main sequence cluster members including 5
highly probable Herbig Ae/Be and 6 classical T Tauri star. A total of 25
non-emission MS stars, amounting to $\sim$ 10 % early type MS members, appears
to show Vega-like characteristics or are precursors to such a phenomenon. The
various membership indicators suggest that $\sim$ 16% of the PM members are
non-members. A significant fraction ($>$70%) of program stars in NGC 1976, NGC
2244, NGC 6530 and NGC 6611 show anomalous reddening with $R_{V}$ =
$5.11\pm0.11$, $3.60\pm0.05$, $3.87\pm0.05$ and $3.56\pm 0.02$, respectively,
indicating the presence of grain size dust larger than that typical to the
diffuse medium. A small number of stars in NGC 1976, NGC 2244 and NGC 6611 also
show normal behavior while the cluster NGC 6823 appears to have a normal
reddening. Three highly luminous late type giants, one in NGC 2244 and two in
NGC 6530, appears to be member and are in post-hydrogen-core-burning stages
suggesting a prolonged duration ($\sim$ 25 Myrs) of star formation.


title:
Atomic and Molecular Data for Stellar Physics: Former Successes and
  Future Challenges

abstract:
  This review highlights current (and future) hot topics in astrophysics where
atomic or molecular input data are (or will be) essential, with special
emphasis on topics relating to nucleosynthesis and cosmochemistry.
  We first discuss issues (like the abundances of oxygen and iron in the Sun,
and that of lithium in post-AGB stars) where the use of poor-quality atomic or
molecular data have led to spurious astrophysical puzzles which sparked fancy
astrophysical models or theories. We then address issues where the advent of
new instruments (like the ultraviolet high-resolution spectrographs--GHRS
onboard HST, Keck-HRS or VLT-UVES--or future infrared satellites) calls for new
and accurate atomic or molecular data.


title: Early optical and millimeter observations of GRB 030226 afterglow

abstract:
  The CCD magnitudes in Johnson $UBV$ and Cousins $RI$ photometric passbands
for the afterglow of the long duration GRB 030226 are presented. Upper limits
of a few mJy to millimeter wave emission at the location of optical are
obtained over the first two weeks. The optical data presented here, in
combination with other published data on this afterglow, show an early $R$ band
flux decay slope of 0.77$\pm$0.04, steepening to 2.05$\pm$0.04 about
0.65$\pm$0.03 day after the burst. Interpreted as the ``jet break'', this
indicates a half opening angle of $\sim 3.2$ degree for the initial ejection,
for an assumed ambient density of $\sim 1 {\rm cm}^{-3}$. Broadband spectra
show no appreciable evolution during the observations, and indicate the
presence of synchrotron cooling frequency $\nu_c$ near the upper edge of the
optical band. From the broadband spectra we derive an electron energy
distribution index $p = 2.07\pm0.06$ and an intrinsic extinction $E(B -
V)\sim0.17$. Millimeter upper limits are consistent with these derived
parameters.


title: On the "Causality Argument" in Bouncing Cosmologies

abstract:
  We exhibit a situation in which cosmological perturbations of astrophysical
relevance propagating through a bounce are affected in a scale-dependent way.
Involving only the evolution of a scalar field in a closed universe described
by general relativity, the model is consistent with causality. Such a specific
counter-example leads to the conclusion that imposing causality is not
sufficient to determine the spectrum of perturbations after a bounce provided
it is known before. We discuss consequences of this result for string motivated
scenarios.


title: Self-consistent stellar dynamical tori

abstract:
  We present preliminary results on a new family of distribution functions that
are able to generate axisymmetric, truncated (i.e., finite size) stellar
dynamical models characterized by toroidal shapes. The relevant distribution
functions generalize those that are known to describe polytropic spheres, for
which all the dynamical and structural properties of the system can be
expressed in explicit form as elementary functions of the system gravitational
potential. The model construction is then completed by a numerical study of the
associated Poisson equation. We note that our axisymmetric models can also
include the presence of an external gravitational field, such as that produced
by a massive disk or by a central mass concentration (e.g., a supermassive
black hole).


title: Free-free absorption effects on Eddington luminosity

abstract:
  In standard treatments the Eddington luminosity is calculated by assuming
that the electron-photon cross section is well described by the Thomson cross
section which is gray (frequency independent). Here we discuss some consequence
of the introduction of free-free opacity in the Eddington luminosity
computation: in particular, due to the dependence of free-free emission on the
square of the gas density, it follows that the associated absorption cross
section increases linearly with the gas density, so that in high density
environments Eddington luminosity is correspondingly reduced. We present a
summary of an ongoing exploration of the parameter space of the problem, and we
conclude that Eddington luminosity in high density environments can be lowered
by a factor of ten or more, making it considerably easier for black holes to
accelerate and eject ambient gas.


title: The role of Compton heating in cluster cooling flows

abstract:
  Recent observations by Chandra and XMM-Newton demonstrate that the central
gas in "cooling flow" galaxy clusters has a mass cooling rate that decreases
rapidly with decreasing temperature. This contrasts the predictions of a steady
state cooling flow model. On the basis of these observational results, the gas
can be in a steady state only if a steady temperature dependent heating
mechanism is present; alternatively the gas could be in an unsteady state,
i.e., heated intermittently. Intermittent heating can be produced by accretion
on the supermassive black hole residing in the central cluster galaxy, via
Compton heating. This mechanism can be effective provided that the radiation
temperature of the emitted spectrum is higher than the gas temperature. Here we
explore whether this heating mechanism can be at the origin of the enigmatic
behavior of the hot gas in the central regions of ``cooling flow'' clusters.
Although several characteristics of Compton heating appear attractive in this
respect, we find that the fraction of absorbed heating for realistic gas and
radiation temperatures falls short by two orders of magnitude of the required
heating.


title: Inflation and Precision Cosmology

abstract:
  A brief review of inflation is presented. After having demonstrated the
generality of the inflationary mechanism, the emphasize is put on its simplest
realization, namely the single field slow-roll inflationary scenario. Then, it
is shown how, concretely, one can calculate the predictions of a given model of
inflation. Finally, a short overview of the most popular models is given and
the implications of the recently released WMAP data are briefly (and partially)
discussed.


title:
The very high state accretion disk structure from the galactic black
  hole transient XTE J1550-564

abstract:
  The 1998 outburst of the bright Galactic black hole binary system XTE
J1550-564 was used to constrain the accretion disc structure in the strongly
Comptonised very high state spectra. These data show that the disc emission is
not easily compatible with the constant area L ~ T^4 behaviour seen during the
thermal dominated high/soft state and weakly comptonised very high state. Even
after correcting for the effects of the scattering geometry, the disc
temperature is always much lower than expected for its derived luminosity in
the very high state. The simplest interpretation is that this indicates that
the optically thick disc is truncated in the strongly Comptonised very high
state, so trivially giving the observed continuity of properties between the
low/hard and very high states of Galactic black holes.


title:
FUSE observations of G226-29: First detection of the H_2 quasi-molecular
  satellite at 1150A

abstract:
  We present new FUV observations of the pulsating DA white dwarf G226-29
obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This ZZ Ceti
star is the brightest one of its class and the coolest white dwarf observed by
FUSE. We report the first detection of the broad quasi-molecular
collision-induced satellite of Ly-beta at 1150 A, an absorption feature that is
due to transitions which take place during close collisions of hydrogen atoms.
The physical interpretation of this feature is based on recent progress of the
line broadening theory of the far wing of Ly-beta. This predicted feature had
never been observed before, even in laboratory spectra.


title: Rotating disks in high-mass young stellar objects

abstract:
  We report on the detection of four rotating massive disks in two regions of
high-mass star formation. The disks are perpendicular to known bipolar outflows
and turn out to be unstable but long lived. We infer that accretion onto the
embedded (proto)stars must proceed through the disks with rates of ~10E-2
Msun/yr.


title: GRB Redshift Evolution Within the Unified Jet Model

abstract:
  HETE-2 has provided new evidence that gamma-ray bursts may evolve with
redshift. We investigate the consequences of this possibility for the unified
jet model of XRFs and GRBs. We find that burst evolution with redshift can be
naturally explained within the unified jet model, and the resulting model
provides excellent agreement with existing HETE-2 and BeppoSAX data sets. In
addition, this evolution model produces reasonable fits to the BATSE peak
photon number flux distribution -- something that cannot be easily done without
redshift evolution.


title: On the Maximum Binary Fraction in Globular Cluster Cores

abstract:
  We study the evolution of binary stars in globular clusters using a novel
approach combining a state-of-the-art population synthesis code with a simple
treatment of dynamical interactions in the dense cluster core. We find that the
combination of stellar evolution and dynamical interactions (binary-single and
binary-binary) leads to a rapid depletion of the binary population in the
cluster core. The maximum binary fraction today in the core of a typical dense
cluster like 47 Tuc, assuming an initial binary fraction of 100%, is only about
5%. We show that this is in good agreement with recent HST observations of
close binaries in the core of 47 Tuc, provided that a realistic distribution of
binary periods is used to interpret the results. Our findings also have
important consequences for the dynamical modeling of globular clusters,
suggesting that ``realistic models'' should incorporate much larger initial
binary fractions than has usually been done in the past.


title: Evidence From HETE-2 For GRB Evolution With Redshift

abstract:
  After taking into account threshold effects, we find that the
isotropic-equivalent energies E_iso and luminosities L_iso of gamma-ray bursts
(GRBs) are correlated with redshift at the 5% and 0.9% signficance levels,
respectively. Our results are based on 10 BeppoSAX GRBs and 11 HETE-2 GRBs with
known redshifts. Our results suggest that the isotropic-equivalent energies and
luminosities of GRBs increase with redshift. They strengthen earlier clues to
this effect from analyses of the BATSE catalog of GRBs, using the variability
of burst time histories as an estimator of burst luminosities (and therefore
redshifts), and from an analysis of BeppoSAX bursts only. If the
isotropic-equivalent energies and luminosities of GRBs really do increase with
redshift, it suggests that GRB jets at high redshifts may be narrower and thus
the cores of GRB progenitor stars at high redshifts may be rotating more
rapidly. It also suggests that GRBs at very high redshifts may be more luminous
-- and therefore easier to detect -- than has been thought, which would make
GRBs a more powerful probe of cosmology and the early universe than has been
thought.


title: Early Formation and Late Merging of the Giant Galaxies

abstract:
  The most luminous galaxies in the present Universe are found at the centers
of the most massive dark matter haloes, rich galaxy clusters. In the LCDM
cosmology, such massive halo cores are present at redshift z=6 with a comoving
number density (as a function of mass interior to ~10 kpc) that is comparable
to today's value. The identity of the matter in these central regions is,
however, predicted to change as major mergers bring together stars and dark
matter from initially well separated sub-units. We use N-body simulations to
investigate how these mergers push pre-existing matter outwards in the dominant
galaxy while preserving the inner density profile of collisionless matter. It
appears that the central regions of large galaxies end up dominated by stars
formed in a number of dense cores, well before the last major mergers. The
density profile of collisionless matter (stars and dark matter combined) in
these central regions appears to be stable and to have attractor-like behavior
under merging. This suggests that the baryon loading associated with
dissipative contraction and star formation may be erased as subsequent mergers
drive the mass distribution back to a universal profile. Such suppression of
the effects of baryon loading, along with the early assembly of mass
concentrations, may help resolve some apparent challenges to the CDM model for
structure formation.


title: Spectropolarimetric Observations of Supernovae

abstract:
  We briefly review the existing database of supernova spectropolarimetry,
concentrating on recent data and on results from our group's research.
Spectropolarimetry provides the only direct known probe of early-time supernova
geometry. To obtain reliable conclusions, however, it is very important to
correctly account for interstellar polarization. We find that Type IIn
supernovae (SNe IIn) tend to be highly polarized, perhaps in part because of
the interaction of the ejecta with an asymmetric circumstellar medium. In
contrast, SNe II-P are not polarized much, at least shortly after the
explosion. At later times, however, there is evidence for increasing
polarization, as one views deeper into the expanding ejecta. Moreover,
core-collapse SNe that have lost part (SN IIb) or all (SN Ib) of their hydrogen
(or even helium; SN Ic) layers prior to the explosion tend to show substantial
polarization; thus, the deeper we probe into core-collapse events, the greater
the asphericity. There is now conclusive evidence that at least some SNe Ia are
intrinsically polarized, although only by a small amount. Finally, SN
spectropolarimetry provides the opportunity to study the fundamental properties
of the interstellar dust in external galaxies. For example, we have found
evidence for extremely high polarization efficiency for the dust along the
line-of-sight to SN 1999gi in NGC 3184.


title: Application of the Variability -> Luminosity Indicator to X-Ray Flashes

abstract:
  We have applied the proposed variability -> luminosity indicator to ten
"X-Ray Flashes" (XRFs) observed by the Wide-Field Cameras on BeppoSAX for which
BATSE survey data exists. Our results suggest that the variability ->
luminosity indicator probably works for XRFs. Assuming this to be so, we find
that the luminosity and redshift distributions of XRFs are consistent with
those of long-duration gamma-ray bursts (GRBs), and therefore most XRFs are
probably not very high redshift GRBs. The fact that XRFs and GRBs have similar
luminosity and redshift distributions suggests that XRFs and long-duration GRBs
are produced by a similar mechanism.


title: Gamma-Ray Bursts as a Probe of the Epoch of Reionization

abstract:
  GRBs are expected to occur at redshifts far higher than the highest quasar
redshifts so far detected. And unlike quasars, GRB afterglows may provide
"clean" probes of the epoch of reionization because no complications (such as
the presence of a strong Ly-alpha emission line) or "proximity effects" (such
as the Stromgren sphere produced by ionizing photons from the quasar) are
expected. Thus NIR and optical observations of GRB afterglows may provide
unique information about the epoch of reionization. In particular, the flux at
wavelengths shortward of Ly-alpha provides a direct measure of the density
fluctuations of the IGM at the GRB redshift, while the flux at wavelengths
longward of Ly-alpha provides an integrated measure of the number of ionizing
photons produced by stars in the host galaxy of the GRB up until the burst
occurs. A comparison of the sizes of the Stromgren spheres produced by stars in
the host galaxies of GRBs and by quasars then provides an estimate of the
relative contributions of star formation and quasars to reionization. We use
detailed calculations of the expected shape of the GRB afterglow spectrum in
the vicinity of Ly-alpha for GRBs at a variety of redshifts to illustrate these
points.


title:
GRB 020531: A Short, Hard Gamma-Ray Burst Localized and Observed by
  HETE-2

abstract:
  The HETE-2 FREGATE and WXM instruments detected a short, hard GRB at
00:26:18.72 UT on 31 May 2002. A preliminary localization was reported as a GCN
Position Notice 88 min after the burst, and a refined localization was
disseminated 123 minutes later. An IPN localization of the burst was reported
18 hours after the GRB, and a refined IPN localization was disseminated ~5 days
after the burst. The final IPN localization, disseminated on 25 July 2002, is a
diamond-shaped region centered on RA=15h 15m 11.18s, Dec=-19o 24' 27.08"
(J2000), and has an area of ~9 square arcminutes (99.7% confidence region). The
prompt localization of the burst by HETE-2, coupled with the refinement of the
localization by the IPN, made possible the most sensitive follow-up
observations to date of a short, hard GRB at radio, optical, and X-ray
wavelengths. The time history of GRB020531 at high (>30 keV) energies consists
of a short, intense spike followed by a much less intense secondary peak, which
is characteristic of many short, hard bursts. The duration of the burst
increases with decreasing energy and the spectrum of the burst evolves from
hard to soft, behaviors which are similar to those of long GRBs. This suggests
that short, hard GRBs are closely related to long GRBs.


title: A Unified Jet Model of X-Ray Flashes, X-ray Rich GRBs and GRBs

abstract:
  HETE-2 has provided strong evidence that the properties of X-Ray Flashes
(XRFs) and GRBs form a continuum, and therefore that these two types of bursts
are the same phenomenon. We show that both the structured jet and the uniform
jet models can explain the observed properties of GRBs reasonably well.
However, if one tries to account for the properties of both XRFs and GRBs in a
unified picture, the uniform jet model works reasonably well while the
structured jet model fails utterly. The uniform jet model of XRFs and GRBs
implies that most GRBs have very small jet opening angles (~ half a degree).
This suggests that magnetic fields play a crucial role in GRB jets. The model
also implies that the energy radiated in gamma rays is ~100 times smaller than
has been thought. Most importantly, the model implies that there are ~10^4
-10^5 more bursts with very small jet opening angles for every such burst we
see. Thus the rate of GRBs could be comparable to the rate of Type Ic core
collapse supernovae. Accurate, rapid localizations of many XRFs, leading to
identification of their X-ray and optical afterglows and the determination of
their redshifts, will be required in order to confirm or rule out these
profound implications.


title: Self-similar scaling in decaying numerical turbulence

abstract:
  Decaying turbulence is studied numerically using as initial condition a
random flow whose shell-integrated energy spectrum increases with wavenumber k
like k^q. Alternatively, initial conditions are generated from a driven
turbulence simulation by simply stopping the driving. It is known that the
dependence of the decaying energy spectrum on wavenumber, time, and viscosity
can be collapsed onto a unique scaling function that depends only on two
parameters. This is confirmed using three-dimensional simulations and the
dependence of the scaling function on its two arguments is determined.


title: Eclipsing binaries in open clusters

abstract:
  Accurate physical parameters have been determined for two early-type detached
eclipsing binaries in the open cluster h Persei (NGC 869). Masses accurate to
1.5% are derived from high-resolution spectroscopy and radii accurate to 4--6%
have been obtained from fitting the existing light curves. The four stars are
placed in the mass radius plane and compared to the theoretical stellar models
of the Granada Group. The best-fitting models have a low metallicity of
approximately Z=0.01 and a high helium abundance of Y=0.34. This is the first
determination of the bulk metallicity of the Perseus Double Cluster. Recent
studies have assumed a solar metallicity so their results should be reviewed.


title:
Nonlinear Outcome of Gravitational Instability in Disks with Realistic
  Cooling

abstract:
  We consider the nonlinear outcome of gravitational instability in optically
thick disks with a realistic cooling function. We use a numerical model that is
local, razor-thin, and unmagnetized. External illumination is ignored. Cooling
is calculated from a one-zone model using analytic fits to low temperature
Rosseland mean opacities. The model has two parameters: the initial surface
density Sigma_0 and the rotation frequency Omega. We survey the parameter space
and find: (1) The disk fragments when t_c,eff Omega = 1, where t_c,eff is an
effective cooling time defined as the average internal energy of the model
divided by the average cooling rate. This is consistent with earlier results
that used a simplified cooling function. (2) The initial cooling time t_c0 or a
uniform disk with Q = 1 can differ by orders of magnitude from t_c,eff in the
nonlinear outcome. The difference is caused by sharp variations in the opacity
with temperature. The condition t_c0 Omega = 1 therefore does not necessarily
indicate where fragmentation will occur. (3) The largest difference between
t_c,eff and t_c0 is near the opacity gap, where dust is absent and hydrogen is
largely molecular. (4) In the limit of strong illumination the disk is
isothermal; we find that an isothermal version of our model fragments for Q <
1.4. Finally, we discuss some physical processes not included in our model, and
find that most are likely to make disks more susceptible to fragmentation. We
conclude that disks with t_c,eff Omega < 1 do not exist.


title: On The Hydrogen Emission From The Type Ia Supernova 2002ic

abstract:
  The discovery of SN 2002ic and subsequent spectroscopic studies have led to
the surprising finding that SN 2002ic is a Type Ia supernova with strong
ejecta-circumstellar interaction. Here we show that nearly 1 year after the
explosion the supernova has become fainter overall, but the H$\alpha$ emission
has brightened and broadened dramatically compared to earlier observations. We
have obtained spectropolarimetry data which show that the hydrogen-rich matter
is highly aspherically distributed. These observations suggest that the
supernova exploded inside a dense, clumpy, disk-like circumstellar environment.


title:
Chandra High-Resolution X-Ray Spectrum of Supernova Remnant
  1E0102.2-7219

abstract:
  Chandra High Energy Transmission Grating Spectrometer observations of the
supernova remnant 1E0102.2-7219 in the Small Magellanic Cloud reveal a spectrum
dominated by X-ray emission lines from hydrogen-like and helium-like ions of
oxygen, neon, magnesium and silicon, with little iron. The dispersed spectrum
shows a series of monochromatic images of the source in the light of individual
spectral lines. Detailed examination of these dispersed images reveals Doppler
shifts within the supernova remnant, indicating bulk matter velocities on the
order of 1000 km/s. These bulk velocities suggest an expanding ring-like
structure with additional substructure, inclined to the line of sight. A
two-dimensional spatial/velocity map of the SNR shows a striking spatial
separation of redshifted and blueshifted regions, and indicates a need for
further investigation before an adequate 3D model can be found. The radii of
the ring-like images of the dispersed spectrum vary with ionization stage,
supporting an interpretation of progressive ionization due to passage of the
reverse shock through the ejecta. Plasma diagnostics with individual emission
lines of oxygen are consistent with an ionizing plasma in the low density
limit, and provide temperature and ionization constraints on the plasma.
Assuming a pure metal plasma, the mass of oxygen is estimated at ~6 solar
masses, consistent with a massive progenitor.


title: Violation of the Equivalence Principle in String Dilaton Theories

abstract: This paper has been withdrawn


title: ACS Observations of a Strongly Lensed Arc in a Field Elliptical

abstract:
  We report the discovery of a strongly lensed arc system around a field
elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys
(ACS) images of a parallel field observed during NICMOS observations of the HST
Ultra-Deep Field. The ACS parallel data comprise deep imaging in the F435W,
F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 1.6 arcsec
from the galaxy center and subtends about 120 deg. Spectroscopic follow-up at
Magellan Observatory yields a redshift z=0.6174 for the lensing galaxy, and we
photometrically estimate z_phot = 2.4\pm0.3 for the arc. We also identify a
likely counter-arc at a radius of 0.6 arcsec, which shows structure similar to
that seen in the main arc. We model this system and find a good fit to an
elliptical isothermal potential of velocity dispersion $\sigma \approx 300$
\kms, the value expected from the fundamental plane, and some external shear.
Several other galaxies in the field have colors similar to the lensing galaxy
and likely make up a small group.


title: Infrared Spectroscopic Study of 8 Galactic Globular Clusters

abstract:
  We have obtained medium-resolution infrared K band spectra of 44 giants in
seven heavily reddened clusters in the Galactic bulge, as well as 12 giants in
omega Centauri. We measure the equivalent widths of the Na doublet, the Ca
triplet, and the CO band head, and then apply the new technique of Frogel et al
to determine the metallicity of each star. Averaging these values, we estimate
the metallicity for each cluster, and compare our new [Fe/H] values with
previous determinations from the literature. Our estimates for each cluster
are: NGC 6256 (-1.35), NGC 6539 (-0.79), HP 1 (-1.30), Liller 1 (-0.36),
Palomar 6 (-0.52), Terzan 2 (-0.87), and Terzan 4 (-1.62). We briefly discuss
differences between the various [Fe/H] scales on which it was possible to base
our calibration, which is found to be the largest uncertainty in using this
technique to determine metallicities.


title: Turbulent Magnetohydrodynamic Jet Collimation and Thermal Driving

abstract:
  We have argued that magnetohydrodynamic (MHD) turbulence in an accretion disk
naturally produces hoop-stresses, and that in a geometrically-thick flow these
stresses could both drive and collimate an outflow. We based this argument on
an analogy of turbulent MHD fluids to viscoelastic fluids, in which azimuthal
shear flow creates hoop-stresses that cause a variety of flow phenomena,
including the Weissenberg effect in which a fluid climbs a spinning rod. One of
the more important differences between the Weissenberg effect and astrophysical
jets is the source of power. In our previous analysis, we only considered the
power due to the spin-down torque on the central object, and thus found that we
could only drive an outflow if the central object were maximally rotating. Here
we take into account the energy that is liberated by the accreting matter, and
describe a scenario in which this energy couples to the outflow to create a
thermodynamic engine.


title: Optimal Moments for Velocity Fields Analysis

abstract:
  We describe a new method of overcoming problems inherent in peculiar velocity
surveys by using data compression as a filter with which to separate
large-scale, linear flows from small-scale noise that biases the results
systematically. We demonstrate the effectiveness of our method using realistic
catalogs of galaxy velocities drawn from N--body simulations. Our tests show
that a likelihood analysis of simulated catalogs that uses all of the
information contained in the peculiar velocities results in a bias in the
estimation of the power spectrum shape parameter $\Gamma$ and amplitude
$\beta$, and that our method of analysis effectively removes this bias. We
expect that this new method will cause peculiar velocity surveys to re--emerge
as a useful tool to determine cosmological parameters.


title: The Circumbinary Ring of KH 15D

abstract:
  The light curves of the pre-main-sequence star KH 15D from the years
1913--2003 can be understood if the star is a member of an eccentric binary
that is encircled by a vertically thin, inclined ring of dusty gas. Eclipses
occur whenever the reflex motion of a star carries it behind the circumbinary
ring; the eclipses occur with period equal to the binary orbital period of 48.4
days. Features of the light curve--including the amplitude of central reversals
during mid-eclipse, the phase of eclipse with respect to the binary orbit
phase, the level of brightness out-of-eclipse, the depth of eclipse, and the
eclipse duty cycle--are all modulated on the timescale of nodal regression of
the obscuring ring, in accord with the historical data. The ring has a mean
radius near 3 AU and a radial width that is likely less than this value. While
the inner boundary could be shepherded by the central binary, the outer
boundary may require an exterior planet to confine it against viscous
spreading. The ring must be vertically warped to maintain a non-zero
inclination. Thermal pressure gradients and/or ring self-gravity can readily
enforce rigid precession. In coming years, as the node of the ring regresses
out of our line-of-sight toward the binary, the light curve from the system
should cycle approximately back through its previous behavior. Near-term
observations should seek to detect a mid-infrared excess from this system; we
estimate the flux densities from the ring to be 3 mJy at wavelengths of 10--100
microns.


title:
Status of a self-bound equations of state and analytic solutions in
  general relativity

abstract:
  We have obtained a criterion for spherically symmetric and static structures
under hydrostatic equilibrium in general relativity (GR), which states that for
a given value of $\sigma \equiv (P_0/E_0) \equiv $ the ratio of central
pressure to central energy-density], the compaction parameter $u \equiv (M/a)$,
where $M$ is the total mass and $a$ is the radius of the configuration] or the
surface redshift of any regular configuration cannot exceed that of the
corresponding homogeneous density sphere, that is, $u \leq u_h$, where $u_h$ is
the compaction parameter of the homogeneous density sphere. By examining
various exact solutions and surface). On the other hand, configurations having
a finite density on the surface (that is, the self-bound structures) do not
fulfill this criterion. This criterion puts a severe restriction on the static
structures based upon the general relativistic field equations and consequently
on the upper limit of mass, surface and central redshift and other physical
parameters of spherically symmetric and static configurations.


title: Cosmic Matter Distribution: Cosmic Baryon Budget Revisited

abstract:
  The cosmic baryon budget is revisited using modern observations that have
become available since our first publication. I also present an estimate for
the heavy element abundance. An increased accuracy in the accounting of the
baryon budget reveals `missing baryons', which amount to $\approx 35$% of the
total. This would provide an interesting test for models of the cosmic
structure formation.


title:
Actively Star Forming Elliptical Galaxies at Low Redshifts in the Sloan
  Digital Sky Survey

abstract:
  We report discovery of actively star forming elliptical galaxies in a
morphologically classified sample of bright galaxies at a low redshift obtained
from the Sloan Digital Sky Survey. The emission lines of these galaxies do not
show the characteristics of active galactic nuclei, and thus their strong
H$\alpha$ emission is ascribed to star formation with a rate nearly as high as
that is seen in typical late spiral galaxies. This is taken as evidence against
the traditional view that all elliptical galaxies formed early and now evolve
only passively. The frequency of such star forming elliptical galaxies is a few
tenths of a percent in the sample, but increases to 3% if we include active S0
galaxies. We may identify these galaxies as probable progenitors of so-called
E+A galaxies that show the strong Balmer absorption feature of A stars
superimposed on an old star population. The approximate match of the abundance
of active elliptical plus S0 galaxies with that of E+A galaxies indicates that
the duration of such late star formation episodes is of the order of $\gsim 1$
Gyr. If we interpret these galaxies as new additions to the early-type galaxy
population, and if we assume a power law for their number evolution, the
abundance of early-type galaxies at $z=1$ is about 30% less than that at $z=0$.


title:
The H alpha Luminosity Function of Morphologically Classified Galaxies
  in the Sloan Digital Sky Survey

abstract:
  We present a study of the H$\alpha$ line emission from a sample of 1482
optically-selected, morphologically-classified bright galaxies (median redshift
of 0.05) derived from the Sloan Digital Sky Survey. The luminosity function is
calculated for each morphological class and for the total sample. The
luminosity function fitted with the Schechter form gives a slope
$\alpha=-1.43\pm 0.10$ for the total sample and the H$\alpha$ luminosity
density is $10^{39.31\pm 0.04{+0.10\atop-0.07}}h$ erg s$^{-1}$Mpc$^{-3}$, where
the first error is statistical and the second is systematic. This value is
consistent with that derived by Gallego et al. (1995), but this agreement is
caused by a fortuitous cancellation of their neglect of stellar absorption that
affects the estimate of extinction corrections and a significant sample
incompleteness of emission line galaxies. The fraction of H$\alpha$ emitters
monotonically increases from early (a few % for ellipticals) to late types
(100% for irregular galaxies), whereas strong emitters exist in all classes of
morphological types. We find that 83% of the luminosity density comes from
spiral galaxies, 5% from irregular galaxies, and 9% from early type galaxies; a
small number of morphologically disturbed galaxies contribute by 3%.


title:
Spatial Variations of Galaxy Number Counts in the SDSS I.: Extinction,
  Large-Scale Structure and Photometric Homogeneity

abstract:
  We study the spatial variation of galaxy number counts using five band
photometric images from the Sloan Digital Sky Survey. The spatial variation of
this sample of 46 million galaxies collected from 2200 sq. degrees can be
understood as the combination of Galactic extinction and large-scale
clustering. With the use of the reddening map of Schlegel, Finkbeiner & Davis
(1998), the standard extinction law is verified for the colour bands from u to
z within 5% in the region of small extinction values, E(B-V)<0.15. The residual
spatial variations of the number counts suggests that the error of global
calibration for SDSS photometry is smaller than 0.02 mag.


title:
Search for Galaxy Clustering around a Quasar Pair at z=4.25 found in the
  Sloan Digital Sky Survey

abstract:
  We present an investigation of the environment (\approx 600 kpc radius) of a
pair of luminous z=4.25 quasars, SDSS J1439-0034 A,B, separated by 33''. An
analysis of high-quality Subaru spectra of the quasars suggests that this
configuration is indeed a physical pair and not a gravitational lens; the
redshifts are slightly different (although marginally consistent with being the
same), and the two spectra have strikingly different features. We search for
bright galaxies (L\gsim 0.4 L^*) having similar redshifts using the V dropout
technique and semi-narrow band imaging looking for strong Ly alpha emission. We
find no enhancement in the galaxy density around the quasar pair; its
environment differs very little from a general field, with the upper limit of
the density enhancement being about 3 at a 90% confidence. We infer that bright
quasars happened to appear in two normal galaxies in a general field.


title:
The evolution of habitable zones during stellar lifetimes and its
  implications on the search for extraterrestrial life

abstract:
  A stellar evolution computer model has been used to determine changes in the
luminosity L and effective temperature T(e) of single stars during their time
on the main sequence. The range of stellar masses investigated was from 0.5 to
1.5 times that of the Sun, each with a mass fraction of metals (metallicity, Z)
from 0.008 to 0.05. The extent of each star's habitable zone (HZ) has been
determined from its values of L and T(e). These stars form a reference
framework for other main sequence stars. All of the 104 main sequence stars
known to have one or more giant planets have been matched to their nearest
stellar counterpart in the framework, in terms of mass and metallicity, hence
closely approximating their HZ limits. The limits of HZ, for each of these
stars, have been compared to its giant planet(s)'s range of strong
gravitational influence. This allows a quick assessment as to whether
Earth-mass planets could exist in stable orbits within the HZ of such systems,
both presently and at any time during the star's main sequence lifetime. A
determination can also be made as to the possible existence of life-bearing
satellites of giant planets, which orbit within HZs. Results show that about
half of the 104 known extrasolar planetary systems could possibly have been
housing an Earth-mass planet in HZs during at least the past billion years, and
about three-quarters of the 104 could do so for at least a billion years at
some time during their main sequence lives. Whether such Earth-mass planets
could have formed is an urgent question now being investigated by others, with
encouraging results.


title: Kolmogorov Complexity, Cosmic Background Radiation and Irreversibility

abstract:
  We discuss the algorithmic information approach to the analysis of the
observational data on the Universe. Kolmogorov complexity is proposed as a
descriptor of the Cosmic Microwave Background (CMB) radiation maps. An
algorithm of computation of the complexity is described, applied, first, to toy
models and then, to the data of the Boomerang experiment. The sky maps obtained
via the summing of two independent Boomerang channels reveal threshold
independent behavior of the mean ellipticity of the anisotropies, thus
indicating correlations present in the sky signal and possibly carrying crucial
information on the curvature and the non-Friedmannian, i.e. accelerated
expansion of the Universe. Similar effect has been detected for COBE-DMR 4 year
maps. Finally, as another application of these concepts, we consider the
possible link between the CMB properties, curvature of the Universe and arrows
of time.


title: Radiative transfer through the Intergalactic Medium

abstract:
  We use a probabilistic method to compute the propagation of an ionization
front corresponding to the re-ionization of the intergalactic medium in a LCDM
cosmology, including both hydrogen and helium. The effects of radiative
transfer substantially boost the temperature of the ionized gas over the case
of uniform re-ionization. The resulting temperature-density relation of the
ionized gas is both non-monotonic and multiple-valued, reflecting the non-local
character of radiative transfer and suggesting that a single polytropic
relation between local gas density and temperatue is a poor description of the
thermodynamic state of baryons in the post-reionization universe.


title:
A study of the s-process in the carbon-rich post-AGB stars
  IRAS06530-0213 and IRAS08143-4406 on the basis of VLT-UVES spectra

abstract:
  In an effort to extend the still limited sample of s-process enriched
post-AGB stars, high-resolution, high signal-to-noise VLT+UVES spectra of the
optical counterparts of the infrared sources IRAS06530-0213 and IRAS08143-4406
were analysed. The objects are moderately metal deficient by [Fe/H]=-0.5 and
-0.4 respectively, carbon-rich and, above all, heavily s-process enhanced with
a [ls/Fe] of 1.8 and 1.5 respectively. Especially the spectrum of
IRAS06530-0213 is dominated by transitions of s-process species, and therefore
resembling the spectrum of IRAS05341+0852, the most s-process enriched object
known so far. The two objects are chemically very similar to the 21micron
objects discussed in Van Winckel & Reyniers (2000). A homogeneous comparison
with the results of these objects reveals that the relation between the third
dredge-up efficiency and the neutron nucleosynthesis efficiency found for the
21micron objects, is further strengthened. On the other hand, a detailed
comparison with the predictions of the latest AGB models indicates that the
observed spread in nucleosynthesis efficiency is certainly intrinsic, and
proves that different C-13 pockets are needed for stars with comparable mass
and metallicity to explain their abundances.


title: Star Formation in High Redshift Radio Galaxies

abstract:
  We present evidence for star formation in distant radio galaxies based on
deep FORS1/VLT spectropolarimetry and SCUBA/JCMT 850 micron photometry.


title: Characterizing Low-Ionization Structures in PNe

abstract:
  Fifty five planetary nebulae containing micro-structures of low-ionization
(LIS) are analyzed in this review in terms of LIS morphology, kinematics, and
physical and excitation properties. We attempt to address the issue of their
origin through the comparison of LIS properties with the main shells of the
nebulae, as well as the contrast with the theoretical model predictions. We
finally conclude that, while LIS morphology and kinematics can be reasonably
accounted for by the available theoretical models, they cannot explain the LIS
physical/excitation properties, unless we agree that evolved PNe are expected
to show neither shock-excited LIS nor significant density contrasts relatively
to their environments. Some evidence for the latter ideas is actually presented
in this paper.


title: The Physical Parameters and Excitation of Jets and Knots in PNe

abstract:
  We are carrying out a study of the physical parameters and excitation of
low-ionization structures (LIS) in planetary nebulae (PNe). Since the optical
morphology and kinematics of the LIS and the main components (rims, shells and
haloes) of our sample were studied previously, our main goal now is to search
for: i) the density contrasts between jets/knots and the main nebular
components; ii) their main excitation processes; and iii) their chemical
abundances. The first results of this survey -- based on the analysis of
NGC7009, NGC6543, NGC6891 and K4-47 -- are that there is no significant density
contrast between LIS and their surroundings, and that most of the LIS studied
(but not all) are mainly photoionized, rather than shock excited.


title:
Rotation curves of galactic disks for arbitrary surface density
  profiles: a simple and efficient recipe

abstract:
  There is apparently a widespread belief that the gravitational field (and
subsequently the rotation curve) ``inside'' razor-thin, axially symmetric disks
can not be determined accurately from elliptic integrals because of the
singular kernel in the Poisson integral. Here, we report a simple and powerful
method to achieve this task numerically using the technique of ``density
splitting''.


title:
Constraints on the energetics and plasma composition of relativistic
  jets in FR II sources

abstract:
  We explore the energetics and plasma composition in FR II sources using a new
simple method of combining shock dynamics and radiation spectrum. The hot spots
are identified with the reverse shocked region of jets. With the
one-dimensional shock jump conditions taking account of the finite pressure of
hot ICM, we estimate the rest mass and energy densities of the sum of thermal
and non-thermal particles in hot spots. Independently, based on the Synchrotron
Self-Compton (SSC) model, we estimate the number and energy densities of {\it
non-thermal} electrons using the multi-frequency radiation spectrum of hot
spots. We impose the condition that the obtained rest mass, internal energy,
and number densities of non-thermal electrons should be lower than those of the
total particles determined by shock dynamics. We apply this method to Cygnus A.
We examine three extreme cases of pure electron-positron pair plasma (Case I),
pure electron-proton plasma with separate thermalization (Case II), and pure
electron-proton plasma in thermal-equilibrium (Case III). By detailed SSC
analysis for Cygnus A and 3C123, we find that the energy density of non-thermal
electrons is about 10 times larger than that of magnetic field. We find that
the Case III is not acceptable because predicted photon spectra do not give a
good fit to the observed one. We find that Case II can also be ruled out since
the number density of non-thermal electrons exceeds that of the total number
density. Hence, we find that only pure $e^{\pm}$ plasma (Case I) is acceptable
among the three cases. Total kinetic power of jet and electron acceleration
efficiency are also constrained by internal energy densities of non-thermal and
total particles.


title: A multi-beam HI survey of the Virgo Cluster - two isolated HI clouds ?

abstract:
  We have carried out a fully sampled large area ($4^{\circ} \times 8^{\circ}$)
21cm \HI line survey of part of the Virgo cluster using the Jodrell Bank
multi-beam instrument. The survey has a sensitivity some 3 times better than
the standard HIJASS and HIPASS surveys. We detect 31 galaxies, 27 of which are
well known cluster members. The four new detections have been confirmed in the
HIPASS data and by follow up Jodrell Bank pointed observations. One object lies
behind M86, but the other 3 have no obvious optical counter parts upon
inspection of the digital sky survey fields. These 3 objects were mapped at
Arecibo with a smaller \am{3}{6} HPBW and a 4 times better sensitivity than the
Jodrell Bank data, which allow an improved determination of the dimensions and
location of two of the objects, but surprisingly failed to detect the third.
The two objects are resolved by the Arecibo beam giving them a size far larger
than any optical images in the nearby field. To our mass limit of $5 \times
10^{7}$ $\frac{\Delta v}{50 km s^{-1}}$ $M_{\odot}$ and column density limit of
$3 \times 10^{18}$ $\frac{\Delta v}{50 km s^{-1}}$ atoms cm$^{-2}$ these new
detections represent only about 2% of the cluster atomic hydrogen mass. Our
observations indicate that the \HI mass function of the cluster turns down at
the low mass end making it very different to the field galaxy \HI mass
function. This is quite different to the Virgo cluster optical luminosity
function which is much steeper than that in the general field. Many of the
sample galaxies are relatively gas poor compared to \HI selected samples of
field galaxies, confirming the 'anaemic spirals' view of Virgo cluster late
type galaxies.


title:
Thermodynamic evolution of cosmological baryonic gas: I. Influence of
  non-equipartition processes

abstract:
  Using N-body/hydrodynamic simulations, the influence of non-equipartition
processes on the thermal and dynamical properties of cosmological baryonic gas
is investigated. We focus on a possible departure from equilibrium between
electrons, ions and neutral atoms in low temperature (10^4-10^6 K) and weakly
ionized regions of the intergalactic medium. The simulations compute the energy
exchanges between ions, neutrals and electrons, without assuming thermal
equilibrium. They include gravitation, shock heating and cooling processes, and
follow self-consistently the chemical evolution of a primordial composition
hydrogen-helium plasma without assuming collisional ionization equilibrium. At
high redshift, a significant fraction of the intergalactic medium is found to
be warmer and weakly ionized in simulations with non-equipartition processes
than in simulations in which the cosmological plasma is considered to be in
thermodynamic equilibrium. With a semi-analytical study of the out of
equilibrium regions we show that, during the formation of cosmic structures,
departure from equilibrium in accreted plasma results from the competition
between the atomic cooling processes and the elastic processes between heavy
particles and electrons. Our numerical results are in agreement with this
semi-analytical model. Therefore, since baryonic matter with temperatures
around 10^4 K is a reservoir for galaxy formation, non-equipartition processes
are expected to modify the properties of the objects formed.


title: Voids in the 2dF Galaxy Redshift Survey

abstract:
  We present an analysis of voids in the 2dF Galaxy Redshift Survey (2dFGRS).
This analysis includes identification of void regions and measurement of void
statistics. The 2dFGRS is the largest completed redshift survey to date,
including a total of 245,591 galaxies covering 1500 deg$^2$ to a median depth
of z~0.11. We use the voidfinder algorithm to identify a total of 289 voids in
the 2dFGRS with radius larger than 10h^{-1}Mpc. These voids have an average
effective radius of 14.89+- 2.65 h^{-1}Mpc in the North Galactic Pole region
(NGP) and 15.61+- 2.84h^{-1}Mpc in the South Galactic Pole region (SGP). These
voids are extremely underdense, with average density contrast of delta rho/rho=
-0.94+-0.02. The centers of voids are even emptier, because the few galaxies
within the voids typically lie close to the edges. The total volume of the
universe filled by these void regions is approximately 40%. We measure the Void
Probability Function (VPF) of the 2dFGRS for volume-limited samples with
limiting absolute magnitudes from -16 to -21 in b_J. We measure the
Underdensity Probability Function for samples with limiting absolute magnitudes
from -18 to -21. We find that the SGP is more underdense than the NGP for all
but the brightest sample under consideration. There is good agreement between
the VPF's of the Center for Astrophysics Survey and the 2dFGRS. Comparison of
VPF's measured for the 2dFGRS with the distribution of simulated dark-matter
halos of similar number density indicates that voids in the matter distribution
in LCDM simulations are not empty enough. However, semi-analytic models of
galaxy formation that include feedback effects yield VPF's that show excellent
agreement with the data.


title:
The Integrated Sachs-Wolfe effect as a probe of non-standard
  cosmological evolution

abstract:
  The Integrated Sachs-Wolfe effect is studied in non-standard cosmologies. By
considering flat universes with a non-fluctuating dark energy component, it is
shown how the quadrupole power can be suppressed by atypical evolution of the
scale factor. For example, a brief period of non-standard evolution at a high
redshift can suppress the quadrupole significantly. The effect on the overall
normalization of the CMB power spectrum is also discussed. Non-standard
cosmologies can affect the overall normalization significantly and enhance the
primordial fluctuations. The possibility of constraining such non-standard
models with CMB and independent measures of $\sigma_8$, is considered.


title: The isolated interacting galaxy pair NGC 5426/27 (Arp 271)

abstract:
  We present H alpha observations of the isolated interacting galaxy pair NGC
5426/27 using the scanning Fabry-Perot interferometer PUMA. The velocity field,
various kinematical parameters and rotation curve for each galaxy were derived.
The FWHM map and the residual velocities map were also computed to study the
role of non-circular motions of the gas. Most of these motions can be
associated with the presence of spiral arms and structure such as central bars.
We found a small bar-like structure in NGC 5426, a distorted velocity field for
NGC 5427 and a bridge-like feature between both galaxies which seems to be
associated with NGC 5426. Using the observed rotation curves, a range of
possible masses was computed for each galaxy. These were compared with the
orbital mass of the pair derived from the relative motion of the participants.
The rotation curve of each galaxy was also used to fit different mass
distribution models considering the most common theoretical dark halo models.
An analysis of the interaction process is presented and a possible 3D scenario
for this encounter is also suggested.


title: Mapping the cold molecular gas in a cooling flow cluster: Abell 1795

abstract:
  Cold molecular gas is found in several clusters of galaxies (Edge, 2001,
Salome' & Combes, 2003): single dish telescope observations in CO(1-0) and
CO(2-1) emission lines have revealed the existence of large amounts of cold gas
(up to ~10^11 Msol) in the central region of cooling flow clusters. We present
here interferometric observations performed with the IRAM Plateau de Bure
interferometer in Abell 1795. Comparison with IRAM 30m data shows the cold gas
detected is extended suggesting a cooling flow origin. The CO features
identified are very similar to the structures observed in Halpha and with the
star forming regions observed through UV continuum excess. A large fraction of
the cold gas is not centered on the central cD, but located near brightest
X-ray emitting regions along the North-West orientated radio lobe. The cold gas
kinematics is consistent with the optical nebulosity behaviour in the very
central region. It is not in rotation around the central cD : a velocity
gradient shows the cold gas might be cooled gas from the intra-cluster medium
being accreted by the central galaxy. The optical filaments, aligned with the
cD orbit, are intimately related to the radio jets and lobes. The material
fueling the star formation certainly comes from the deposited gas, cooling more
efficiently along the edge of the radio lobes. Even if some heating mechanisms
are present, these millimetric observations show that an effective cooling to
very low temperatures indeed occurs and is probably accelerated by the presence
of the radio source.


title: The diagnostic power of X-ray emission lines in GRBs

abstract:
  Absorption and reprocessing of Gamma-ray burst radiation in the environment
of cosmological GRBs can be used as a powerful probe of the elusive nature of
their progenitors. Although it is widely accepted that long-duration GRBs are
associated with the deaths of massive stars, at least two fundamentally
different scenarios concerning the final collapse are currently being
considered. Delayed reddened excesses in the optical afterglows of several GRBs
indicate that a supernova, possibly of Type Ic, takes place within a few days
of a GRB. This supports the collapsar model, where the core of a massive star
collapses promptly to a black hole. Variable X-ray features observed in the
prompt and afterglow spectra of several GRBs, suggest that a highly metal
enriched and dense shell of material surrounds the sources of GRBs. In some
cases, evidence for expansion of these shells with velocities of a substantial
fraction of the speed of light has been claimed. These observations have been
interpreted as support for the supranova model, where a massive star collapses
first to a supramassive neutron star, which later collapses to a black hole
following loss of rotational support. In this review paper, I will present a
brief overview of the current status of the observational evidence for X-ray
spectral features in GRBs, and discuss their implications for both the
collapsar and the supranova model.


title: A ULX in NGC 4559: a "mini-cartwheel" scenario?

abstract:
  We have studied an ultraluminous X-ray source (ULX) in NGC 4559 with
XMM-Newton, and its peculiar star-forming environment with HST/WFPC2. The X-ray
source is one of the brightest in its class (L_x ~ 2 x 10^{40} erg/s).
Luminosity and timing arguments suggest a mass >~ 50 M_sun for the accreting
black hole. The ULX is located near the rim of a young (age < 30 Myr), large
(diameter ~ 700 pc) ring-like star forming complex possibly triggered by the
impact of a dwarf satellite galaxy through the gas-rich outer disk of NGC 4559.
We speculate that galaxy interactions (including the infall of high-velocity
clouds and satellites on a galactic disk) and low-metallicity environments
offer favourable conditions for the formation of compact remnants more massive
than "standard" X-ray binaries, and accreting from a massive Roche-lobe filling
companion.


title:
Statistical properties of the combined emission of a population of
  discrete sources: astrophysical implications

abstract:
  We study the statistical properties of the combined emission of a population
of discrete sources (e.g. X-ray emission of a galaxy due to its X-ray binaries
population). Namely, we consider the dependence of their total luminosity
L_tot=SUM(L_k) and of fractional rms_tot of their variability on the number of
sources N or, equivalently, on the normalization of the luminosity function. We
show that due to small number statistics a regime exists, in which L_tot grows
non-linearly with N, in an apparent contradiction with the seemingly obvious
prediction <L_tot>=integral(dN/dL*L*dL) ~ N. In this non-linear regime, the
rms_tot decreases with N significantly more slowly than expected from the rms ~
1/sqrt(N) averaging law. For example, for a power law luminosity function with
a slope of a=3/2, in the non-linear regime, L_tot ~ N^2 and the rms_tot does
not depend at all on the number of sources N. Only in the limit of N>>1 do
these quantities behave as intuitively expected, L_tot ~ N and rms_tot ~
1/sqrt(N). We give exact solutions and derive convenient analytical
approximations for L_tot and rms_tot.
  Using the total X-ray luminosity of a galaxy due to its X-ray binary
population as an example, we show that the Lx-SFR and Lx-M* relations predicted
from the respective ``universal'' luminosity functions of high and low mass
X-ray binaries are in a good agreement with observations. Although caused by
small number statistics the non-linear regime in these examples extends as far
as SFR<4-5 Msun/yr and log(M*/Msun)<10.0-10.5, respectively.


title: XMM-Newton observations of Sagittarius A East

abstract:
  We present an analysis of a recent XMM-Newton observation of Sgr A East, a
supernova remnant located close to the Galactic Centre. Very high quality X-ray
spectra reveal many emission lines from highly ionized atoms consistent with a
multi-temperature thin thermal plasma in ionization equilibrium. We use a
two-temperature model to fit the spectra and derive temperatures of 1 keV and 4
keV. There is significant concentration of iron towards the centre of the X-ray
source such that the iron abundance varies from ~4 times solar in the core down
to ~0.5 solar in the outer regions, which contrasts with the rather uniform
distribution of other metals such as sulfur, argon and calcium, which have
abundances in the range 1--3. The derived total energy, mass, and the abundance
pattern are consistent with a single supernova event, either of type-Ia or
type-II origin, involving a relatively low-mass progenitor star. A weak 6.4-keV
neutral iron fluorescence line is also detected, the illumination source most
likely being Sgr A East itself. The morphology and spectral characteristics of
Sgr A East show no clear linkage to putative past activity in Sgr A*.


title: Neutron Star Kicks and Supernova Asymmetry

abstract:
  Observations over the last decade have shown that neutron stars receive a
large kick velocity (of order a hundred to a thousand km/s) at birth. The
physical origin of the kicks and the related supernova asymmetry is one of the
central unsolved mysteries of supernova research. We review the physics of
different kick mechanisms, including hydrodynamically driven, neutrino --
magnetic field driven, and electromagnetically driven kicks. The viabilities of
the different kick mechanisms are directly related to the other key parameters
characterizing nascent neutron stars, such as the initial magnetic field and
the initial spin. Recent observational constraints on kick mechanisms are also
discussed.


title: Ejection of bi-helical fields from the sun

abstract:
  It is argued that much of the observed magnetic helicity losses at the solar
surface may represent a reduction of an otherwise more dominant nonlinearity of
solar and stellar dynamos. This nonlinearity is proportional to the internal
twist (as opposed to writhe) of helical and sigmoidal surface structures.


title: Evolution of the Density Profiles of Dark Matter Haloes

abstract:
  We use numerical simulations in a Lambda CDM cosmology to model density
profiles in a set of 16 dark matter haloes with resolutions of up to 7 million
particles within the virial radius. These simulations allow us to follow
robustly the formation and evolution of the central cusp over a large mass
range of 10^11 to 10^14 M_sun, down to approximately 0.5% of the virial radius,
and from redshift 5 to the present. The cusp of the density profile is set at
redshifts of 2 or greater and remains remarkably stable to the present time,
when considered in non-comoving coordinates. We fit our haloes to a 2 parameter
profile where the steepness of the asymptotic cusp is given by gamma, and its
radial extent is described by the concentration, c_gamma. In our simulations,
we find gamma = 1.4 - 0.08Log(M/M_*) for haloes of 0.01M_* to 1000M_*, with a
large scatter of gamma ~ +/-0.3$; and c_gamma = 8*M/M_*^{-0.15}, with a large
M/M_* dependent scatter roughly equal to +/- c_gamma. Our redshift zero haloes
have inner slope parameters ranging approximately from r^{-1} to r^{-1.5}, with
a median of roughly r^{-1.3}. This 2 parameter profile fit works well for all
our halo types, whether or not they show evidence of a steep asymptotic cusp.
We also model a cluster in power law cosmologies of P ~ k^n (n=0,-1,-2,-2.7).
We find larger concentration radii and shallower cusps for steeper n. The
minimum resolved radius is well described by the mean interparticle separation.
The trend of steeper and more concentrated cusps for smaller $M/M_*$ haloes
clearly shows that dwarf sized Lambda CDM haloes have, on average,
significantly steeper density profiles within the inner few percent of the
virial radius than inferred from recent observations. Code to reproduce this
profile can be downloaded from http://www.icc.dur.ac.uk/~reed/profile.html


title: AGN Unification: An Update

abstract:
  The paradigm for AGN unification is reviewed, in terms of its optical
manifestation as obscuration in the equatorial plane and its radio
manifestation as relativistic beaming of the jet emission. Within this
paradigm, observed AGN properties depend strongly on orientation angle. The
predictions of unification are commensurate with the local numbers of AGN of
various types. The outstanding question concerns a possible population of
obscured AGN at high redshift, which are thought to produce the X-ray
background, although few are observed directly. We describe early results from
GOODS, an HST-SIRTF-Chandra multiwavelength survey, which has as one of its
principal goals the search for such obscured AGN.


title: The 2dF Galaxy Redshift Survey: Wiener Reconstruction of the Cosmic Web

abstract:
  We reconstruct the underlying density field of the 2 degree Field Galaxy
Redshift Survey (2dFGRS) for the redshift range 0.035<z<0.200 using the Wiener
Filtering method. The Wiener Filter suppresses shot noise and accounts for
selection and incompleteness effects. The method relies on prior knowledge of
the 2dF power spectrum of fluctuations and the combination of matter density
and bias parameters however the results are only slightly affected by changes
to these parameters. We present maps of the density field in two different
resolutions: 5 Mpc/h and 10 Mpc/h. We identify all major superclusters and
voids in the survey. In particular, we find two large superclusters and two
large local voids. A version of this paper with full set of colour maps can be
found at http://www.ast.cam.ac.uk/~pirin.


title: The Origin and Distribution of Angular Momemtum in Galaxies

abstract:
  Cold Dark Matter with a large cosmological constant (LambdaCDM) appears to
fit large scale structure observations well. Of the possible small scale
problems, the Central Cusps and Too Many Satellites problems now appear to be
at least partly solved, so Angular Momentum has become the most serious
remaining CDM problem. There are actually at least two different angular
momentum problems: A. Too much transfer of angular momentum to the dark halo to
make big disks, and B. Wrong distribution of spedific angular momentum to make
spiral galaxies, if the baryonic material has the same angular momentum
distribution as the dark matter. The angular momentum of dark matter halos, and
presumably that of the galaxies they host, appears to arise largely from the
orbital angular momentum of the satellites that they accrete. Since the dark
and baryonic matter behave very differently in such accretion events, it is
possible that the resulting angular momentum distribution of the baryons is
different from that of the dark matter, as required to make the sort of
galactic disks that are observed. The latest hydrodynamical simulations give
some grounds for hope on this score, but much higher resolution simulations are
needed.


title: Behaviour of matter close to the event horizon

abstract:
  Investigation of the behaviour of accreting matter close to the black hole
event horizon is of fundamental importance in relativistic and high energy
astrophysics because they provide the key features of the diagnostic spectra of
the stellar mass and super-massive black holes. In this paper, we examine the
terminal behaviour of general relativistic matter in multi-transonic, advective
black hole accretion discs. We compute, for the first time we believe, the
values of various dynamical and thermodynamic multi-transonic flow variables
{\it extremely close} ($\le$ 0.01 $r_g$) to the event horizon and study the
dependence of these variables on fundamental accretion parameters. Our
calculation is useful for a better understanding of Hawking radiation from
acoustic black holes.


title:
Summary talk: How serious are the problems faced by CDM: cusps, thin
  disks, and halo substructure

abstract:
  This is a summary of the discussion in Panel I of IAU Symposium 220 on Dark
Matter in Galaxies. The panel topics and panellists were as follows -- Cusps
Theory: Julio Navarro; Cusps Observations: Erwin de Blok, Rob Swaters;
Substructure Observations: Mario Mateo; Substructure Theory: James Taylor,
Shude Mao. In addition to the talks by the panellists and the discussion among
them, there was a good deal of discussion with the audience. Despite the
differences of opinion expressed I think a consensus emerged, and I try to
summarize it here.


title: A Disk Galaxy of Old Stars at z ~ 2.5

abstract:
  We describe observations of a galaxy in the field of the $z=2.483$ radio
galaxy 4C 23.56, photometrically selected to have a spectral-energy
distribution consistent with an old stellar population at the redshift of the
radio galaxy. Exploration of redshift--stellar-population-reddening constraints
from the photometry indicates that the galaxy is indeed at a redshift close to
that of 4C23.56, that the age of the most recent significant star formation is
roughly >~2 Gyr, and that reddening is fairly modest, with more reddening
required for the younger end of stellar age range. From analysis of a deep
adaptive-optics image of the galaxy, we find that an r^1/4-law profile, common
for local spheroidal galaxies, can be excluded quite strongly. On the other
hand, a pure exponential profile fits remarkably well, while the best fit is
given by a Sersic profile with index n=1.49. Reconstruction of the
two-dimensional form of the galaxy from the best-fit model is consistent with a
disk galaxy with neither a significant bulge component nor gross azimuthal
structure. The assembly of roughly 2L* of old stars into such a configuration
this early in the history of the universe is not easily explainable by any of
the currently popular scenarios for galaxy formation. A galaxy with these
properties would seem to require smooth but rapid infall of the large mass of
gas involved, followed by a burst of extremely vigorous and efficient star
formation in the resulting disk.


title: The three-body problem and the Hannay angle

abstract:
  The Hannay angle has been previously studied for a celestial circular
restricted three-body system by means of an adiabatic approach. In the present
work, three main results are obtained. Firstly, a formal connection between
perturbation theory and the Hamiltonian adiabatic approach shows that both lead
to the Hannay angle; it is thus emphasised that this effect is already
contained in classical celestial mechanics, although not yet defined nor
evaluated separately. Secondly, a more general expression of the Hannay angle,
valid for an action-dependent potential is given; such a generalised expression
takes into account that the restricted three-body problem is a time-dependent,
two degrees of freedom problem even when restricted to the circular motion of
the test body. Consequently, (some of) the eccentricity terms cannot be
neglected {\it a priori}. Thirdly, we present a new numerical estimate for the
Earth adiabatically driven by Jupiter. We also point out errors in a previous
derivation of the Hannay angle for the circular restricted three-body problem,
with an action-independent potential.

categories: astro-ph gr-qc math-ph math.MP nlin.SI physics.class-ph quant-ph


title: Klio: A 5 micron camera for the detection of giant exoplanets

abstract:
  We plan to take advantage of the unprecedented combination of low thermal
background and high resolution provided by the 6.5m MMT's adaptive secondary
mirror, to target the 3-5 micron atmospheric window where giant planets are
expected to be anomalously bright. We are in the process of building a 3-5
micron coronograph that is predicted to be sensitive to planets as close as 0.4
arcsec to the parent star. We expect to be able to detect giant planets down to
5 times Jupiter's mass for a 1 Gyr old system at 10 pc. We plan to carry out a
survey which is complementary to the radial velocity detections of planets and
constructed to characterize the prevalence and distribution of giant planets
around nearby, Sun-like stars.


title: A Catalog of Compact Groups of Galaxies in the SDSS Commissioning Data

abstract:
  Compact groups (CGs) of galaxies -- relatively poor groups of galaxies in
which the typical separations between members is of the order of a galaxy
diameter -- offer an exceptional laboratory for the study of dense galaxian
environments with short (<1Gyr) dynamical time-scales. In this paper, we
present an objectively defined catalog of CGs in 153 sq deg of the Sloan
Digital Sky Survey Early Data Release (SDSS EDR). To identify CGs, we applied a
modified version of Hickson's (1982) criteria aimed at finding the highest
density CGs and thus reducing the number of chance alignments. Our catalog
contains 175 CGs down to a limiting galaxy magnitude of r* = 21. The resulting
catalog has a median depth of approximately z = 0.13, substantially deeper than
previous CG catalogs. Since the SDSS will eventually image up to one quarter of
the celestial sphere, we expect our final catalog, based upon the completed
SDSS, will contain on the order of 5,000 - 10,000 CGs. This catalog will be
useful for conducting studies of the general characteristics of CGs, their
environments, and their component galaxies.


title:
A Preliminary Seismic Analysis of 51 Peg: Large and Small Spacings from
  Standard Models

abstract:
  We present a preliminary theoretical seismic study of the astronomically
famous star 51 Peg. This is done by first performing a detailed analysis within
the Hertzsprung-Russell diagram (HRD). Using the Yale stellar evolution code
(YREC), a grid of stellar evolutionary tracks has been constructed for the
masses 1.00 M_sun, 1.05 M_sun and 1.10 M_sun, in the metallicity range
Z=0.024-0.044, and for values of the Galactic helium enrichment ratio DY/DZ in
the range 0-2.5. Along these evolutionary tracks, we select 75 stellar model
candidates that fall within the 51 Peg observational error box in the HRD (all
turn out to have masses of 1.05 M_sun and 1.10 M_sun. The corresponding
allowable age range for these models, which depends sensitively on the
parameters of the model, is relatively large and is ~2.5 - 5.5 Gyr. For each of
the 75 models, a non-radial pulsation analysis is carried out, and the large
and small frequency spacings are calculated. The results show that just
measuring the large and small frequency spacings will greatly reduce the
present uncertainties in the derived physical parameters and in the age of 51
Peg. Finally we discuss briefly refinements in the physics of the models and in
the method of analysis which will have to be included in future models to make
the best of the precise frequency determinations expected from space
observations.


title:
A Survey of Open Clusters in the u'g'r'i'z' Filter System: I. Results
  for NGC2548 (M48)

abstract:
  We present initial results of a photometric survey of open star clusters,
primarily in the southern hemisphere, taken in the u'g'r'i'z' filter system.
While our entire observed sample covers more than 100 clusters, here we present
data for NGC2548 (M48) which is a cluster characterized in the UBV and DDO
photometric systems. We compare our results to the published values from other
observers and to the Padova theoretical isochrones and metallicity curves.
These observations demonstrate that the u'g'r'i'z' filters can play an
important role in determining the metallicity of stars and clusters. We begin
this series of papers with a study of NGC2548 because we have obtained data of
this cluster not only with our main program telescope, the CTIO Curtis-Schmidt,
but also with the US Naval Observatory (USNO) 1.0m telescope (the telescope
used to define the u'g'r'i'z' system), and the Sloan Digital Sky Survey (SDSS)
0.5m Photometric Telescope (the photometric monitoring telescope used to
calibrate the SDSS 2.5m telescope imaging data). We have used the data from
this study to validate our ability to transform measurements obtained on other
telescopes to the standard USNO 1.0m u'g'r'i'z' system. This validation is
particularly important for very red stars, for which the original u'g'r'i'z'
standard star network is poorly constrained.


title:
Subaru Spectroscopy of the Giant Ly$\alpha$ Nebula Associated with the
  High-$z$ Powerful Radio Galaxy 1243+036

abstract:
  We report results of our new spatially-resolved, optical spectroscopy of the
giant Ly$\alpha$ nebula around a powerful radio galaxy 1243+036 (4C+03.24) at
$z=3.57$. The nebula is extended over $\sim 30$ kpc from the nucleus, and forms
a pair of cones or elongated bubbles. The high-velocity ($\sim -1000$ km
s$^{-1}$; blueshifted with respect to the systemic velocity)
Ly$\alpha$-emitting components are detected at both sides of the nucleus along
its major axis. The northwestern nebula is more spectacular in its velocity
shift (blueshifted by -1000 km s$^{-1}$ to -1400 km s$^{-1}$) and in its width
($\simeq 1900$ km s$^{-1}$ FWHM) over $\simeq 30$ kpc scale. We discuss
possible origin of the nebula; 1) the shock-heated expanding bubble or
outflowing cone associated with the superwind activity of the host galaxy, 2)
halo gas photoionized by the anisotropic radiation from the active galactic
nuclei (AGN), and 3) the jet-induced star-formation or shock. The last
possibility may not be likely because Ly$\alpha$ emission is distributed out of
the narrow channel of the radio jet. We show that the superwind model is most
plausible since it can explain both the characteristics of the morphology (size
and shape) and the kinematical structures (velocity shift and line width) of
the nebula although the photoionization by AGN may contribute to the excitation
to some extent.


title:
A Study of the Reionization History of Intergalactic Helium with FUSE
  and VLT

abstract:
  We obtained high-resolution VLT and FUSE spectra of the quasar HE2347-4342 to
study the properties of the intergalactic medium between redshifts z=2.0-2.9.
The high-quality optical spectrum allows us to identify approximately 850 HeII
absorption components with column densities between N~5X10^11 and $ 10^18
cm^-2. The reprocessed FUSE spectrum extends the wavelength coverage of the
HeII absorption down to an observed wavelength of 920 A. Approximately 1400
HeII absorption components are identified, including 917 HeII Ly-alpha systems
and some of their HeII Ly-beta, Ly-gamma, and Ly-delta counterparts. The
ionization structure of HeII is complex, with approximately 90 components that
are not detected in the hydrogen spectrum. These components may represent the
effect of soft ionizing sources. The ratio Eta=N(HeII)/N(HI) varies
approximately from unity to more than a thousand, with a median value of 62 and
a distribution consistent with the intrinsic spectral indices of quasars. This
suggests that the dominant ionizing field is from the accumulated quasar
radiation, with contributions from other soft sources such as star-forming
regions and obscured AGN, which do not ionize helium. We find an evolution in
Eta toward smaller values at lower redshift, with the gradual disappearance of
soft components. At redshifts z>2.7, the large but finite increase in the HeII
opacity, Tau=5+/-1, suggests that we are viewing the end stages of a
reionization process that began at an earlier epoch. Fits of the absorption
profiles of unblended lines indicate comparable velocities between hydrogen and
He^+ ions. At hydrogen column densities N<3X10^12 cm^-2 the number of forest
lines shows a significant deficit relative to a power law, and becomes
negligible below N=10^11 cm^-2.


title: High Energy Neutrino Astrophysics

abstract:
  Astroparticle physics is a field rich of perspectives in investigating the
ultra-high energy region which will never be accessible to man made machines.
Many efforts are underway in order to detect the first cosmic neutrinos,
messengers of the unobserved universe. The motivations of this field of
research, the current and next future experimental status are reviewed.


title:
The $^{14}N(p, \gamma)^{15}O$ reaction, solar neutrinos and the age of
  the globular clusters

abstract:
  We discuss implications of a new measurement of $^{14}N(p, \gamma)^{15}O$
concerning solar neutrinos, solar models and globular cluster dating.
Predictions for the gallium and chlorine experiments are reduced by 2 and 0.1
SNU respectively. Predictions for helioseismic observables are unchanged within
uncertainties. The age of globular clusters as deduced from the Turn-Off
luminosity is increased by about 0.7 Gyr.


title: Comparing Geometrical and Delay Radio Emission Heights in Pulsars

abstract:
  We use a set of carefully selected published average multifrequency
polarimetric observations for six bright cone dominated pulsars and devise a
method to combine the multifrequency polarization position angle (PPA) sweep
traverses. We demonstrate that the PPA traverse is in excellent agreement with
the rotating vector model over this broad frequency range confirming that radio
emission emanates from perfectly dipolar field lines.
  For pulsars with central core emission in our sample, we find the peak of
central core component to lag the steepest gradient of the PPA traverse at
several frequencies. Also significant frequency evolution of the core width is
observed over this frequency range. The above facts strongly suggest: (a) the
peak core emission does not lie on the fiducial plane containing the dipole
magnetic axis and the rotation axis, and (b) the core emission does not
originate from the polar cap surface.


title:
Modeling of Oxygen-Neon Dominated Accretion Disks in Ultracompact X-ray
  Binaries: 4U1626-67

abstract:
  We report on first results of computing synthetic spectra from H/He-poor
accretion disks in ultracompact LMXBs. We aim at the determination of the
chemical composition of the very low-mass donor star, which is the core of a
former C/O white dwarf. The abundance analysis allows to draw conclusions on
gravitational settling in WDs which is an important process affecting cooling
times and pulsational g-mode periods.


title: Constraining corotation from shocks in tightly-wound spiral galaxies

abstract:
  We present a new method for estimating the corotation radius in tightly wound
spiral galaxies, through analysis of the radial variation of the offset between
arms traced by the potential (P-arms) and those traced by dust (D-arms). We
have verified the predictions of semi-analytical theory through hydrodynamical
simulations and have examined the uniqueness of the galactic parameters that
can be deduced by this method. We find that if the range of angular offsets
measured at different radii in a galaxy is greater than around pi/4, it is
possible to locate the radius of corotation to within ~ 25%. We argue that the
relative location of the P- and D-arms provides more robust constraints on the
galactic parameters than can be inferred from regions of enhanced star
formation (SF-arms), since interpretation of the latter involves uncertainties
due to reddening and the assumed star formation law. We thus stress the
importance of K-band studies of spiral galaxies.


title: Ultra High Energy Cosmic Rays

abstract:
  The detection of cosmic rays with energy around and in excess of $10^{20}$ eV
raises many questions that future experiments will help answering to. I address
here my view of some of these open issues, as they are now and as they might be
affected by future observations.


title:
The phenomenon of the galaxy NGC 6286: a forming polar ring or a
  superwind?

abstract:
  (abridged)We present the observations of the pair of interacting galaxies
NGC6285/86 carried out with the 6m SAO RAS telescope by using 1D and 2D
spectroscopy. The observations of NGC6286 with a long-slit spectrograph (UAGS)
near the H-alpha line revealed the rotation of the gaseous disk around an axis
offset by 5''-7'' from the photometric center and a luminous gas at a distance
up to 9 kpc in a direction perpendicular to the galactic plane. Using a
multipupil fiber spectrograph (MPFS), we constructed the velocity fields of the
stellar and gaseous components in the central region of this galaxy, which
proved to be similar. The similar line-of-sight velocities of the pair and the
wide (5'x 5') field of view of the scanning Fabry-Perot interferometer (IFP)
allowed us to obtain images in the H-alpha and [NII]6583 emission lines and in
the continuum as well as to construct the line-of-sight velocity fields and to
map the distribution of the [NII]6583/H-alpha ratio for both galaxies
simultaneously. Based on these data, we studied the gas kinematics in the
galaxies, constructed their rotation curves, and estimated their masses. We
found no evidence of gas rotation around the major axis of NGC6286, which
argues against the assumption that this galaxy has a forming polar ring. The
IFP observations revealed an emission nebula around this galaxy with a
structure characteristic for superwind galaxies. The large [NII]6583/H-alpha
ratio, which suggests the collisional excitation of its emission, and the high
infrared luminosity are additional arguments for the hypothesis of a superwind
in the galaxy NGC 6286. A close encounter of the two galaxies was probably
responsible for the starburst and the bipolar outflow of hot gas from the
central region of the disk.


title:
The role of beam geometry in population statistics and pulse profiles of
  radio and gamma-ray pulsars

abstract:
  We present results of a pulsar population synthesis study that incorporates a
number of recent developments and some significant improvements over our
previous study. We have included the results of the Parkes multi-beam pulsar
survey in our select group of nine radio surveys, doubling our sample of radio
pulsars. We adopted with some modifications the radio beam geometry of
Arzoumanian, Chernoff & Cordes (2002). For the $\gamma$-ray beam, we have
assumed the slot gap geometry described in the work of Muslimov & Harding
(2003). To account for the shape of the distribution of radio pulsars in the
$\dot P-P$ diagram, we continue to find that decay of the magnetic field on a
timescale of 2.8 Myr is needed. With all nine surveys, our model predicts that
EGRET should have seen 7 radio-quiet (below the sensitivity of these radio
surveys) and 19 radio-loud $\gamma$-ray pulsars. AGILE (nominal sensitivity
map) is expected to detect 13 radio-quiet and 37 radio-loud $\gamma$-ray
pulsars, while GLAST, with greater sensitivity is expected to detect 276
radio-quiet and 344 radio-loud $\gamma$-ray pulsars. When the Parkes multi-beam
pulsar survey is excluded, the ratio of radio-loud to radio-quiet $\gamma$-ray
pulsars decreases, especially for GLAST. The decrease for EGRET is 45%,
implying that some fraction of EGRET unidentified sources are radio-loud
$\gamma$-ray pulsars. In the radio geometry adopted, short period pulsars are
core dominated. Unlike the EGRET $\gamma$-ray pulsars, our model predicts that
when two $\gamma$-ray peaks appear in the pulse profile, a dominant radio core
peak appears in between the $\gamma$-ray peaks. Our findings suggest that
further improvements are required in describing both the radio and $\gamma$-ray
geometries.


title:
The Stellar Content of the Polar Rings in the Galaxies NGC 2685 and NGC
  4650A

abstract:
  We present the results of stellar photometry of polar-ring galaxies NGC 2685
and NGC 4650A, using the archival data obtained with the Hubble Space
Telescope's Wide Field Planetary Camera 2. Polar rings of these galaxies were
resolved into ~800 and ~430 stellar objects in the B, V and Ic bands,
considerable part of which are blue supergiants located in the young stellar
complexes. The stellar features in the CM-diagrams are best represented by
isochrones with metallicity Z = 0.008. The process of star formation in the
polar rings of both galaxies was continuous and the age of the youngest
detected stars is about 9 Myr for NGC 2685 and 6.5 Myr for NGC 4650A.


title:
Large-scale magnetic field generation by alpha-effect driven by
  collective neutrino-plasma interaction

abstract:
  We suggest a new mechanism for generation of large-scale magnetic field in
the hot plasma of early universe which is based on the parity violation in weak
interactions and depends neither on helicity of matter turbulence resulting in
the standard alpha-effect nor on general rotation. The mechanism can result in
a self-excitation of an (almost) uniform cosmological magnetic field.


title: Displacement of X-Ray Sources from Star Clusters in Starburst Galaxies

abstract:
  We examine the spatial offsets between X-ray point sources and star clusters
in three starburst galaxies. We find that the X-ray sources are preferentially
located near the star clusters. Because the star clusters are very good tracers
of the star formation activity in the galaxies, this indicates that the X-ray
sources are young objects associated with current star formation. We find
significant displacements of the X-ray sources from the clusters. These
displacements are likely due to motion of the X-ray sources and indicates that
they are X-ray binaries. We find that brighter X-ray sources preferentially
occur closer to clusters. The absence of very bright sources at large
displacements from clusters may help constrain models of the sources.


title: Neutrino Oscillations and the Early Universe

abstract:
  The observational and theoretical status of neutrino oscillations in
connection with solar and atmospheric neutrino anomalies is presented in brief.
The effect of neutrino oscillations on the early Universe evolution is
discussed in detail. A short review is given of the standard Big Bang
Nucleosynthesis and the influence of resonant and nonresonant neutrino
oscillations on active neutrinos and on primordial nucleosynthesis of He-4. BBN
cosmological constraints on neutrino oscillation parameters are discussed.


title: Confrontation of MOND Predictions with WMAP First Year Data

abstract:
  I present a model devoid of non-baryonic cold dark matter (CDM) which
provides an acceptable fit to the WMAP data for the power spectrum of
temperature fluctuations in the cosmic background radiation (CBR). An a priori
prediction of such no-CDM models was a first-to-second peak amplitude ratio
A1:2 = 2.4. WMAP measures A1:2 = 2.34 +/- 0.09. The baryon content is the
dominant factor in fixing this ratio; no-CDM models which are consistent with
the WMAP data are also consistent with constraints on the baryon density from
the primordial abundances of 2H, 4He, and 7Li. However, in order to match the
modest width of the acoustic peaks observed by WMAP, a substantial neutrino
mass is implied: m(nu) ~ 1 eV. Even with such a heavy neutrino, structure is
expected to form rapidly under the influence of MOND. Consequently, the epoch
of reionization should occur earlier than is nominally expected in LCDM. This
prediction is realized in the polarization signal measured by WMAP. An
outstanding test is in the amplitude of the third acoustic peak. Experiments
which probe high-L appear to favor a third peak which is larger than predicted
by the no-CDM model.


title: Near-Infrared Photometry of Irregular Satellites of Jupiter and Saturn

abstract:
  We present JHKs photometry of 10 Jovian and 4 Saturnian irregular satellites,
taken with the Near-InfraRed Imager (NIRI) at the 8-m Gemini North Observatory
on Mauna Kea, Hawaii. The observed objects have near-infrared colors consistent
with C, P and D-type asteroids, although J XII Ananke and S IX Phoebe show weak
indications of possible water features in the H filter. The four members of the
Himalia-family have similar near-infrared colors, as do the two members of the
Gallic family, S XX Paaliaq and S XXIX Siarnaq. From low resolution normalized
reflectance spectra based on the broadband colors and covering 0.4 to 2.2
microns, the irregular satellites are identified as C-type (J VII Pasiphae, J
VI Himalia and S IX Phoebe), P-type (J XII Ananke and J XVIII Themisto) and
D-type (J IX Carme and J X Sinope), showing a diversity of origins of these
objects.