title: Gamma-Hadron Separation using Cerenkov Photon Density Fluctuations

abstract:
  In the atmospheric Cerenkov technique gamma rays are detected against the
abundant background produced by hadronic showers. In order to improve the
signal to noise ratio of the experiment, it is necessary to reject a
significant fraction of hadronic showers. Traditional background rejection
methods based on image shape parameters have been extensively used for the data
from imaging telescopes. However, non-imaging Cerenkov telescopes have to
develop very different means of statistically identifying and removing cosmic
ray events. Some of the parameters which could be potentially important for
non-imaging arrays are the temporal and spectral differences, the lateral
distributions and density fluctuations of Cerenkov photons generated by gamma
ray and hadron primaries. Here we study the differences in fluctuations of
Cerenkov photon density in the light pool at the observation level from showers
initiated by photons and those initiated by protons or heavier nuclei. The
database of simulated events for the PACT array has been used to evaluate the
efficiency of the new technique. Various types of density fluctuations like the
short range and medium range fluctuations as well as flatness parameter are
studied. The estimated quality factors reflect the efficiencies with which the
hadrons can be rejected from the data. Since some of these parameters are
independent, the cuts may be applied in tandem and we demonstrate that the
proton rejection efficiency of about 90% can be achieved. Use of density
fluctuations is particularly suited for wavefront sampling observations and it
seems to be a good technique to improve the signal to noise ratio.


title:
High speed photometry of faint Cataclysmic Variables: III. V842 Cen, BY
  Cir, DD Cir, TV Crv, V655 CrA, CP Cru, V794 Oph, V992 Sco, EU Sct and V373
  Sct

abstract:
  We present further results from a high speed photometric survey of faint
cataclysmic variables. We find that V842 Cen (Nova Cen 1986 No. 2) is highly
active, but with no evident orbital modulation. BY Cir (Nova Cir 1995) is an
eclipsing system with an orbital period P(orb) of 6.76 h. TV Crv, an SU UMa
type dwarf nova, is found to have P(orb) = 1.509 h from photometry at
quiescence. DD Cir (Nova Cir 1999) is an eclipsing system with P(orb) = 2.339
h, a possible secondary eclipse, and a ~670 s photometric modulation. V655 CrA
is highly active but shows no orbital modulation. The identification of V794
Oph is probably incorrect as we find no photometric variability. CP Cru (Nova
Cru 1996) is an eclipsing system with P(orb) = 22.7 h. V992 Sco has P(orb) =
3.686 h from its periodic modulation. The supposed identification of EU Sct is
probably incorrect. And finally, during one run V373 Sct (Nova Sct 1975) had a
258.3 s coherent periodicity, making it a candidate DQ Herculis star.


title:
Dark Matter Profiles in Clusters of Galaxies: a Phenomenological
  Approach

abstract:
  There are some basic differences between the observed properties of galaxies
and clusters and the predictions from current hydrodynamical simulations. These
are particularly pronounced in the central regions of galaxies and clusters.
The popular NFW (Navarro, Frenk, and White) profile, for example, predicts a
density cusp at the center, a behavior that (unsurprisingly) has not been
observed. While it is not fully clear what are the reasons for this
discrepancy, it perhaps reflects (at least partly) insufficient spatial
resolution of the simulations. In this paper we explore a purely
phenomenological approach to determine dark matter density profiles that are
more consistent with observational results. Specifically, we deduce the gas
density distribution from measured X-ray brightness profiles, and substitute it
in the hydrostatic equilibrium equation in order to derive the form of dark
matter profiles. Given some basic theoretical requirements from a dark matter
profile, we then consider a number of simple profiles that have the desired
asymptotic form. We conclude that a dark matter density profile of the form
1/(1+r/r_a)^3 is most consistent with current observational results.


title:
The mass of the neutron star in Vela X-1 and tidally induced non-radial
  oscillations in GP Vel

abstract:
  We report new radial velocity observations of GP Vel/HD77581, the optical
companion to the eclipsing X-ray pulsar Vela X-1. Using data spanning more than
two complete orbits of the system, we detect evidence for tidally induced
non-radial oscillations on the surface of GP Vel, apparent as peaks in the
power spectrum of the residuals to the radial velocity curve fit. By removing
the effect of these oscillations (to first order) and binning the radial
velocities, we have determined the semi-amplitude of the radial velocity curve
of GP Vel to be K_o=22.6+/-1.5 km/s. Given the accurately measured
semi-amplitude of the pulsar's orbit, the mass ratio of the system is
0.081+/-0.005. We are able to set upper and lower limits on the masses of the
component stars as follows. Assuming GP Vel fills its Roche lobe then the
inclination angle of the system, i=70.1+/-2.6 deg. In this case we obtain the
masses of the two stars as M_x=2.27 +/-0.17 M_sun for the neutron star and
M_o=27.9+/-1.3 M_sun for GP Vel. Conversely, assuming the inclination angle is
i=90 deg, the ratio of the radius of GP Vel to the radius of its Roche lobe is
beta=0.89+/-0.03 and the masses of the two stars are M_x=1.88+/-0.13 M_sun and
M_o=23.1+/-0.2 M_sun. A range of solutions between these two sets of limits is
also possible, corresponding to other combinations of i and beta. In addition,
we note that if the zero phase of the radial velocity curve is allowed as a
free parameter, rather than constrained by the X-ray ephemeris, a significantly
improved fit is obtained with an amplitude of 21.2+/-0.7 km/s and a phase shift
of 0.033+/-0.007 in true anomaly. The apparent shift in the zero phase of the
radial velocity curve may indicate the presence of an additional radial
velocity component at the orbital period.


title:
Accurate mass ratio and heating effects in the dual-line millisecond
  binary pulsar in NGC 6397

abstract:
  By means of high-resolution spectra we have measured radial velocities of the
companion (hereafter COM J1740-5340) to the eclipsing millisecond pulsar PSR
J1740-5340 in the Galactic globular cluster NGC 6397. The radial-velocity curve
fully confirms that COM J1740-5340 is orbiting the pulsar and enables us to
derive the most accurate mass ratio (M_ PSR/M_COM=5.85+/-0.13) for any
non-relativistic binary system containing a neutron star. Assuming a pulsar
mass in the range 1.3-1.9 Msun, the mass of COM J1740-5340 spans the interval
0.22-0.32 Msun, the inclination of the system is constrained within 56 deg <= i
<= 47 deg and the Roche lobe radius is r_RL ~ 1.5-1.7 Rsun. A preliminary
chemical abundance analysis confirms that COM J1740-5340 has a metallicity
compatible with that measured for other stars in this metal-poor globular, but
the unexpected detection of strong He I absorption lines implies the existence
of regions at T>10,000 K, significantly warmer than the rest of the star. The
intensity of this line correlates with the orbital phase, suggesting the
presence of a region on the companion surface, heated by the millisecond pulsar
flux.


title: Burst-properties as a function of mass accretion rate in GX 3+1

abstract:
  GX 3+1 is a low-mass X-ray binary that is persistently bright since its
discovery in 1964. It was found to be an X-ray burster twenty years ago proving
that the compact object in this system is a neutron star. The burst rate is so
low that only 18 bursts were reported prior to 1996. The Wide Field Cameras on
BeppoSAX have, through a dedicated monitoring program on the Galactic center
region, increased the number of X-ray bursts from GX 3+1 by 61. Since GX 3+1
exhibits a slow (order of years) modulation in the persistent flux of about
50%, these observations opens up the unique possibility to study burst
properties as a function of mass accretion rate for very low burst rates. This
is the first time that bursts are detected from GX 3+1 in the high state. From
the analysis we learn that all bursts are short with e-folding decay times
smaller than 10 s. Therefore, all bursts are due to unstable helium burning.
Furthermore, the burst rate drops sixfold in a fairly narrow range of 2-20 keV
flux; we discuss possible origins for this.


title:
On the coupling between helium settling and rotation-induced mixing in
  stellar radiative zones : II- Numerical approach

abstract:
  In the first paper of this series, we discussed analytically, in an
approximate way, the mixing processes which occur in slowly rotating stars when
the feed-back effects due to the diffusion-induced $\mu$-gradients are
introduced in the computations. We found that the classical scheme of
meridional circulation was dramatically modified, with important possible
consequences. Here we present a complete 2D numerical simulation of these
processes in a static stellar model. The helium microscopic diffusion and the
meridional advection are computed simultaneously, so that we can follow the
evolution of the abundances and mixing processes in the radiative zone. Most of
the effects discussed in paper I are confirmed. Some consequences will be
discussed in a forthcoming paper (Th\'eado and Vauclair 2002, paper III).


title: Mass of clusters in simulations

abstract:
  We show that DM halos, in n--body simulations, have a boundary layer (BL),
separating bound from unbound mass. Let T(r) and W(r) be the kinetic and
potential energies in shells of halos. We find that, in almost all halos: (i)
The virial ratio R=-2T/W has at least one persistent (i.e. resolution
independent) minimum r_c, such that, close to it, (ii) the function w=-d log
W/d log r has a maximum and (iii) the relation R(r_c)=w(r_c) is almost exactly
fulfilled. The radius r_c is the position of BL's, in halos found in
simulations of TCDM and LCDM models, run using ART and GADGET codes at various
resolutions. We find that 97% of the ~300 halos (per model) with M>4.2 10^14
M_s h^-1 owns a BL. Those with no BL are undergoing major mergings. The mass
M_c enclosed in r_c almost coincides with the mass evaluated from velocities,
according to virial theorem. Particles at r>r_c are not in virial equilibrium.
Using r_c we have a density contrast \Delta_c for each halo. For each mass
scale, \Delta_v=178 Omega_m^0.45 is within the range of \Delta_c's, but the
spread in \Delta_c is wide and the average \Delta_c is ~25% smaller than the
corresponding \Delta_v. The matching of properties derived under the assumption
of spherical symmetry is a consequence of violent relaxation destroying
features related to previous ellipsoidal non-linear growth. In turn, the spread
of final \Delta_c's is an imprint of the different 3-D geometries and of the
variable environment during collapses, as suggested by a comparison with Sheth
& Tormen analysis.


title: Formation and Cosmic Evolution of Elliptical Galaxies

abstract:
  A review of the present observational and theoretical status of elliptical
galaxies is presented with the aim to clarify whether the monolithic or the
hierarchical, is a more viable scenario for the origin of these structures. We
describe the dynamical structure of elliptical galaxies using photometric and
spectroscopic data, in particular 3D observations from integral field
spectrographs, with emphasis on properties such as brightness distribution,
velocity profiles, central structures like "cuspy" profiles and "cores", as
well as central supermassive black holes.
  We also report on the main relations between these quantities like the
fundamental plane and colour-luminosity diagram. We present observational
evidences for the presence of dark matter in the elliptical galaxies and
examine the theories of galaxy formation within the framework of a cold dark
matter cosmological model. We discuss the formation of large-scale structure,
Press-Schechter theory and universal density profile of dark matter halos.
Subsequently, gas dynamics, star formation, feedback, angular momentum,
morphology and the epoch of galaxy formation are studied and comparison between
disks and spheroids are made. Valuable insights into the formation epoch of
elliptical galaxies are provided by deriving the mean metallicities and ages at
different redshifts through the study of different population synthesis models
(single-burst and evolutionary models) in particular the magnesium to iron
ratio.


title: Status and Prospects of Planetary Transit Searches: Hot Jupiters Galore

abstract:
  The first transiting extrasolar planet, orbiting HD209458, was a Doppler
wobble planet before its transits were discovered with a 10 cm CCD camera.
Wide-angle CCD cameras, by monitoring in parallel the light curves of tens of
thousands of stars, should find hot Jupiter transits much faster than the
Doppler wobble method. The discovery rate could easily rise by a factor 10. The
sky holds perhaps 1000 hot Jupiters transiting stars brighter than V=13. These
are bright enough for follow-up radial velocity studies to measure planet
masses to go along with the radii from the transit light curves. I derive
scaling laws for the discovery potential of ground-based transit searches, and
use these to assess over two dozen planetary transit surveys currently
underway. The main challenge lies in calibrating small systematic errors that
limit the accuracy of CCD photometry at milli-magnitude levels. Promising
transit candidates have been reported by several groups, and many more are sure
to follow.


title: Echo Tomography of Black Hole Accretion Flows

abstract:
  We discuss technologies for micro-arcsec echo mapping of black hole accretion
flows in Active Galactic Nuclei (AGN). Echo mapping employs time delays,
Doppler shifts, and photoionisation physics to map the geometry, kinematics,
and physical conditions in the reprocessing region close to a compact
time-variable source of ionizing radiation. Time delay maps are derived from
detailed analysis of variations in lightcurves at different wavelengths. Echo
mapping is a maturing technology at a stage of development similar to that of
radio interferometry just before the VLA. The first important results are in,
confirming the basic assumptions of the method, measuring the sizes of AGN
emission line regions, delivering dozens of black hole masses, and showing the
promise of the technique. Resolution limits with existing AGN monitoring
datasets are typically ~5-10 light days. This should improve down to 1-2 light
days in the next-generation echo mapping experiments, using facilities like
Kronos and Robonet that are designed for and dedicated to sustained
spectroscopic monitoring. A light day is 0.4 micro-arcsec at redshift 0.1, thus
echo mapping probes regions 10^3 times smaller than VLBI, and 10^5 times
smaller than HST.


title:
About the connection between the $C_{\ell}$ power spectrum of the Cosmic
  Microwave Background and the $\Gamma_{m}$ Fourier spectrum of rings on the
  sky

abstract:
  In this article we present and study a scaling law of the $m\Gamma_m$ CMB
Fourier spectrum on rings which allows us (i) to combine spectra corresponding
to different colatitude angles (e.g. several detectors at the focal plane of a
telescope), and (ii) to recover the $C_l$ power spectrum once the $\Gamma_m$
coefficients have been measured. This recovery is performed numerically below
the 1% level for colatitudes $\Theta> 80^\circ$ degrees. In addition, taking
advantage of the smoothness of the $C_l$ and of the $\Gamma_m$, we provide
analytical expressions which allow to recover one of the spectrum at the 1%
level, the other one being known.


title: Evolution of Migrating Planet Pairs in Resonance

abstract:
  In this paper we present numerical simulations of the evolution of planets or
massive satellites captured in the 2/1 and 3/1 resonances, under the action of
an anti-dissipative tidal force. The evolution of resonant trapped bodies show
a richness of solutions: librations around stationary symmetric solutions with
aligned periapses (w1-w2=0) or anti-aligned periapses (w1-w2=180 deg), and
librations around stationary solutions in which the periapses configuration is
fixed, but with w1-w2 taking values in a wide range of angles. Many of these
solutions exist for large values of the eccentricities and, during the
semimajor axis drift, the solutions show turnabouts from one configuration to
another. These results are valid for other non-conservative forces leading to
adiabatic covergent migration and capture into one of these resonances.


title: HST and VLT observations of Isolated Neutron Stars

abstract:
  New results of HST and VLT observations of isolated pulsars and their
environments are presented. We present the first deep optical observations of
the nearby pulsar PSR J0108-1431, the identification evidence of PSR 1929+10
based on the proper motion measurement of its optical counterpart and a deep
investigation at optical wavelengths of the X-ray PWN around the Vela pulsar.


title:
The origin of crystalline silicates in the Herbig Be star HD100546 and
  in comet Hale-Bopp

abstract:
  We have investigated the spatial distribution, and the properties and
chemical composition of the dust orbiting HD 100546. This system is remarkably
different from other isolated Herbig Ae/Be stars in both the strength of the
mid-IR excess and the composition of the circumstellar dust. We speculate that
the formation and spatial distribution of the crystalline dust observed in the
HD 100546 system may be linked to the formation of a proto-Jupiter in the disk
around HD 100546. Such a proto-Jupiter could gravitationally stir the disk
leading to a collisional cascade of asteroidal sized objects producing small
crystalline grains, or it could cause shocks by tidal interaction with the disk
which might produce crystalline dust grains through flash heating. As shown by
Malfait et al. (1998), the infrared spectrum of HD 100546 is very similar to
that of C/1995 O1 Hale-Bopp (Crovisier et al. 1997). Using an identical
methodology, we have therefore also studied this solar system comet. Both
objects have an almost identical grain composition, but with the important
difference that the individual dust species in Hale-Bopp are in thermal contact
with each other, while this is not the case in HD 100546. This suggests that if
similar processes leading to the dust composition as seen in HD 100546 also
occurred in our own solar system, that Hale-Bopp formed after the formation of
one or more proto-gas giants.


title:
New Light on the Stellar Populations in IZw18: Deep Near-Infrared
  Imaging

abstract:
  We present deep JHK images of IZw18, the most metal-deficient Blue Compact
Dwarf galaxy known, and analyze them in conjunction with archival HST/WFPC2
optical images. To investigate the stellar populations, we have divided the
main body of IZw18 into eight regions, and fit the optical, near-infrared
(NIR), and hybrid optical-NIR colors of these and the C component with
evolutionary synthesis models. The composite best fit is obtained for an age
for evolved stellar populations of <= 200Myr; fits with an older age of <=
500Myr are less likely but possible. Our data show no evidence for stellar
populations in IZw18 older than this, although as much as 22% of the stellar
mass in older stars (4% in J light) could remain undetected. The colors of the
young and intermediate-age stellar populations are significantly affected by
widespread and inhomogeneously distributed ionized gas and dust. Ionized gas
emission is important in every region examined except the NW star cluster.
Extinction is significant in both the NW and SE clusters. Red H-K, B-H, and V-K
colors are not reliable indicators of old stellar populations because ionized
gas emission is also red in these colors. V-I, on the other hand, reliably
separates stars from gas because the former are red (V-I >= 0.4) while the
latter is blue (V-I ~ -0.4).


title: Gamma Ray Bursts: open problems

abstract:
  The internal/external synchrotron shock scenario has proved very successful
in interpreting the key observations about gamma ray bursts. There still
remains, however, some big uncertainties. The hottest issue concerns the nature
of the progenitor, but there are also other problems concerning the global
energetics, coupled with the issue of the degree of the collimation of the
fireball. To be efficient, internal shocks within the relativistic wind must
occur with large contrasts of their bulk Lorentz factors, and it is not clear
yet the role of the Compton drag process in limiting the velocity differences.
The fireball itself can be "hot" or "cold" according to what accelerates it to
ultrarelativistic bulk speeds. In this respect the recent observations of a
black body shape of the early phases of a few bursts shed new light on this
issue. The most popular radiation process thought to explain the prompt
emission is synchrotron, but it faces severe problems when comparing the
expected spectrum with observations. Alternatives are called for. Emission
features in the X-ray afterglow and absorption features in the prompt spectra
are a powerful diagnostical tool. Besides shedding light on the nature of the
progenitor, they can constrain the total energy release in a
beaming-independent way.


title: Single and Binary Black Holes and their Influence on Nuclear Structure

abstract:
  Massive central objects affect both the structure and evolution of galactic
nuclei. Adiabatic growth of black holes generates power-law central density
profiles with logarithmic slopes in the range from ~1.5 to ~2.5, in good
agreement with the profiles observed in the nuclei of galaxies fainter than
visual magnitude -20. However the shallow nuclear profiles of bright galaxies
require a different explanation. Binary black holes are an inevitable result of
galactic mergers, and the ejection of stars by a massive binary displaces a
mass of order the binary's own mass, creating a core or shallow power-law cusp.
This model is at least crudely consistent with core sizes in bright galaxies.
Uncertainties remain about the effectiveness of stellar- and gas-dynamical
processes at inducing coalescence of binary black holes, and uncoalesced
binaries may be common in low-density nuclei.


title:
Stellar rotation: Evidence for a large horizontal turbulence and its
  effects on evolution

abstract:
  We derive a new expression for the coefficient $D_{\mathrm{h}}$ of diffusion
by horizontal turbulence in rotating stars. This new estimate can be up to two
orders of magnitude larger than given by a previous expression. As a
consequence the differential rotation on an equipotential is found to be very
small, which reinforces Zahn's hypothesis of shellular rotation. The role of
the so--called $\mu$--currents, as well as the driving of circulation, are
reduced by the large horizontal turbulence. Stellar evolutionary models for a
20 M${\odot}$ star are calculated with the new coefficient. The new and large
$D_{\mathrm{h}}$ tends to limit the size of the convective core and at the same
time it largely favours the diffusion of helium and nitrogen to the surface of
rotating OB stars, a feature supported by recent observations.


title: Evolution of massive stars with rotation and mass loss

abstract:
  Rotation appears as a dominant effect in massive star evolution. It largely
affects all the model outputs: inner structure, tracks, lifetimes, isochrones,
surface compositions, blue to red supergiant ratios, etc. At lower
metallicities, the effects of rotational mixing are larger; also, more stars
may reach critical velocity, even if the initial distribution of rotational
velocities is the same.


title:
Lowering Inferred Cluster Magnetic Field Strengths - the radio galaxy
  contributions

abstract:
  We present a detailed examination of the relationship between the magnetic
field structures and the variations in Faraday Rotation across PKS1246-410, a
radio source in the Centaurus cluster of galaxies, using data from Taylor,
Fabian and Allen. We find a significant relationship between the intrinsic
position angle of the polarization and the local amount of Faraday Rotation.
The most plausible explanation is that most or all of the rotation is local to
the source. We suggest that the rotations local to cluster radio galaxies may
result from either thermal material mixed with the radio plasma, or from thin
skins of warm, ionized gas in pressure balance with the observed galaxy or hot
cluster atmospheres. We find that the contribution of any unrelated cluster
Rotation Measure variations on scales of 2 - 10 arcsec are less than 25
rad/m^2; the standard, although model dependent, derivation of cluster fields
would then lead to an upper limit of approximately 0.4 microGauss on these
scales. Inspection of the distributions of Rotation Measure, polarisation angle
and total intensity in 3C75, 3C465 and Cygnus A also shows source-related
Faraday effects in some locations. Many effects can mask the signatures of
locally-dominated RMs, so the detection of even isolated correlations can be
important, although difficult to quantify statistically. In order to use radio
sources such as shown here to derive {\it cluster-wide} magnetic fields, as is
commonly done, one must first remove the local contributions; this is not
possible at present.


title:
Blue Straggler Stars: a direct comparison of Star counts and population
  ratios in six Galactic Globular Clusters

abstract:
  The central regions of six Galactic Globular Clusters (GGCs) (M3, M80, M10,
M13, M92 and NGC 288) have been imaged using HST-WFPC2 and the ultraviolet (UV)
filters (F255W, F336W). The selected sample covers a large range in both
central density and metallicity ([Fe/H]). In this paper, we present a direct
cluster-to-cluster comparison of the Blue Stragglers Stars (BSS) population as
selected from (m_{255},m_{255}-m_{336}) Color Magnitude Diagrams (CMDs). We
have found:(a) BSS in three of the clusters (M3, M80, M92) are much more
concentrated toward the center of the cluster than the red giants; because of
the smaller BSS samples for the other clusters we can only note that the BSS
radial distributions are consistent with central concentration; (b) the
specific frequency of BSS varies greatly from cluster to cluster.
  The most interesting result is that the two clusters with largest BSS
specific frequency are at the central density extremes of our sample: NGC 288
(lowest central density) and M80 (highest). This evidence together with the
comparison with theoretical collisional models suggests that both stellar
interactions in high density cluster cores and at least one other alternate
channel operating low density GGCs play an important role in the production of
BSS. We also note a possible connection between HB morphology and blue
straggler luminosity functions in these six clusters.


title: 'On the difference between the short and long gamma-ray bursts'

abstract:
  We argue that the distributions of both the intrinsic fluence and the
intrinsic duration of the gamma-ray emission in gamma-ray bursts from the BATSE
sample are well represented by log-normal distributions, in which the intrinsic
dispersion is much larger than the cosmological time dilatation and redshift
effects. We perform separate bivariate log-normal distribution fits to the
BATSE short and long burst samples. The bivariate log-normal behaviour results
in an ellipsoidal distribution, whose major axis determines an overall
statistical relation between the fluence and the duration. We show that this
fit provides evidence for a power-law dependence between the fluence and the
duration, with a statistically significant different index for the long and
short groups. We discuss possible biases, which might affect this result, and
argue that the effect is probably real. This may provide a potentially useful
constraint for models of long and short bursts.


title:
Particle Acceleration through Multiple Conversions from Charged into
  Neutral State and Back

abstract:
  We propose a new way of quick and very efficient acceleration of protons
and/or electrons in relativistic bulk flows. The new mechanism takes advantage
of conversion of particles from the charged state (protons or
electrons/positrons) into neutral state (neutrons or photons) and back. In most
cases, the conversion is photon-induced and requires presence of intense
radiation fields, but the converter acceleration mechanism may also operate via
inelastic nucleon-nucleon collisions.
  Like in the traditional model -- ``stochastic'' (or diffusive) acceleration,
-- the acceleration cycle in our scenario consists of escape of particles from
the relativistic flow followed by their return back after deflection from the
ambient magnetic field. The difference is that the charge-changing reactions,
which occur during the cycle, allow accelerated particles to increase their
energies in each cycle by a factor roughly equal to the bulk Lorentz factor
squared.
  The emerging spectra of accelerated particles can be very hard and their
cut-off energy in some cases is larger than in the standard mechanism. This
drastically reduces the required energy budget of the sources of the
highest-energy particles observed in cosmic rays. Also, the proposed
acceleration mechanism may serve as an efficient means of transferring the
energy of bulk motion to gamma-radiation and, if the accelerated particles are
nucleons, routinely produces high-energy neutrinos at $\sim 50 %$ relative
efficiency.


title:
Generation of Large-Scale Vorticity in a Homogeneous Turbulence with a
  Mean Velocity Shear

abstract:
  An effect of a mean velocity shear on a turbulence and on the effective force
which is determined by the gradient of Reynolds stresses is studied. Generation
of a mean vorticity in a homogeneous incompressible turbulent flow with an
imposed mean velocity shear due to an excitation of a large-scale instability
is found. The instability is caused by a combined effect of the large-scale
shear motions (''skew-induced" deflection of equilibrium mean vorticity) and
''Reynolds stress-induced" generation of perturbations of mean vorticity.
Spatial characteristics, such as the minimum size of the growing perturbations
and the size of perturbations with the maximum growth rate, are determined.
This instability and the dynamics of the mean vorticity are associated with the
Prandtl's turbulent secondary flows. This instability is similar to the
mean-field magnetic dynamo instability. Astrophysical applications of the
obtained results are discussed.


title:
Rotation curves in spiral galaxies due to intergalactic accretion flows
  onto the disc

abstract: The above mentioned paper is withdrawn.


title:
Spectropolarimetry of GRB 021004 - Evidence for High Velocity
  Lyman-alpha Absorptions

abstract:
  We present spectropolarimetry observations of GRB 021004 obtained at the ESO
VLT. We detect a remarkable increase of the degree of polarization blueward of
the host galaxy rest frame Ly-alpha to about 5-10% that corresponds to a
decrease in the continuum flux below the extrapolation of a power law. An
increase of the degree of polarization is perhaps also recorded in some narrow
lines, but of lower statistical significance. The broad polarization feature
blueward of the Ly-alpha absorption line at 4040 \AA is at least partially
produced by hydrogen-rich material with velocities approaching 40,000 \kms\
located beyond the front of the afterglow shock, rather than due entirely to
intergalactic Ly-alpha absorption systems on the line of sight to the GRB. The
presence of the broad Ly-alpha absorption provides evidence that the GRB
occurred inside the ejecta from a hydrogen-rich supernova that exploded before
the GRB.


title: The z<=0.1 Surface Brightness Distribution

abstract:
  The surface brightness distribution (SBD) function describes the number
density of galaxies as measured against their central surface brightness.
Because detecting galaxies with low central surface brightnesses is both
time-consuming and complicated, determining the shape of this distribution
function can be difficult. In a recent paper Cross, et al. suggested a
bell-shaped SBD disk-galaxy function which peaks near the canonical Freeman
value of 21.7 and then falls off significantly by 23.5 B mag arcsec-2. This is
in contradiction to previous studies which have typically found flat (slope=0)
SBD functions out to 24 - 25 B mag arcsec^-2 (the survey limits). Here we take
advantage of a recent surface-brightness limited survey by Andreon & Cuillandre
which reaches considerably fainter magnitudes than the Cross, et.al sample (M_B
reaches fainter than -12 for Andreon & Cuillandre while the Cross, et.al sample
is limited to M_B < -16) to re-evaluate both the SBD function as found by their
data and the SBD for a wide variety of galaxy surveys, including the Cross, et
al. data. The result is a SBD function with a flat slope out through the survey
limits of 24.5 B mag arcsec^-2, with high confidence limits.


title: A Standard Kinetic Energy Reservoir in Gamma-Ray Burst Afterglows

abstract:
  We present a comprehensive sample of X-ray observations of 41 gamma-ray burst
(GRB) afterglows, as well as jet opening angles, \theta_j for a subset with
measured jet breaks. We show that there is a significant dispersion in the
X-ray fluxes, and hence isotropic X-ray luminosities (L_{X,iso}), normalized to
10 hr. However, there is a strong correlation between L_{X,iso} and the beaming
fractions, f_b=[1-cos(\theta_j)]. As a result, the true X-ray luminosity of GRB
afterglows, L_X=f_b L_{X,iso}, is approximately constant, with a dispersion of
only a factor of two. Since \epsilon_e E_b \propto L_X, the strong clustering
of L_X directly implies that the adiabatic blastwave kinetic energy in the
afterglow phase, E_b, is tightly clustered. The narrow distribution of L_X also
suggests that p\approx 2, that inverse Compton emission does not in general
dominate the observed X-ray luminosity, and that radiative losses at t<10 hr
are relatively small. Thus, despite the large diversity in the observed
properties of GRBs and their afterglows the energy imparted by the GRB central
engine to the relativistic ejecta is approximately constant.


title: Near-Infrared Interferometric Measurements of Herbig Ae/Be Stars

abstract:
  We have observed the Herbig Ae/Be sources AB Aur, VV Ser, V1685 Cyg (BD+40
4124), AS 442, and MWC 1080 with the Palomar Testbed Interferometer, obtaining
the longest baseline near-IR interferometric observations of this class of
objects. All of the sources are resolved at 2.2 microns with angular size
scales generally <5 mas, consistent with the only previous near-IR
interferometric measurements of Herbig Ae/Be stars by Millan-Gabet and
collaborators. We determine the angular size scales and orientations predicted
by uniform disk, Gaussian, ring, and accretion disk models. Although it is
difficult to distinguish different radial distributions, we are able to place
firm constraints on the inclinations of these models, and our measurements are
the first that show evidence for significantly inclined morphologies. In
addition, the derived angular sizes for the early type Herbig Be stars in our
sample, V1685 Cyg and MWC 1080, agree reasonably well with those predicted by
the face-on accretion disk models used by Hillenbrand and collaborators to
explain observed spectral energy distributions. In contrast, our data for the
later-type sources AB Aur, VV Ser, and AS 442 are somewhat inconsistent with
these models, and may be explained better through the puffed-up inner disk
models of Dullemond and collaborators.


title: Evolution of the Mass Function of Dark Matter Haloes

abstract:
  We use a high resolution $\Lambda$CDM numerical simulation to calculate the
mass function of dark matter haloes down to the scale of dwarf galaxies, back
to a redshift of fifteen, in a 50 $h^{-1}$Mpc volume containing 80 million
particles. Our low redshift results allow us to probe low $\sigma$ density
fluctuations significantly beyond the range of previous cosmological
simulations. The Sheth and Tormen mass function provides an excellent match to
all of our data except for redshifts of ten and higher, where it overpredicts
halo numbers increasingly with redshift, reaching roughly 50 percent for the
$10^{10}-10^{11} \msun$ haloes sampled at redshift 15. Our results confirm
previous findings that the simulated halo mass function can be described solely
by the variance of the mass distribution, and thus has no explicit redshift
dependence. We provide an empirical fit to our data that corrects for the
overprediction of extremely rare objects by the Sheth and Tormen mass function.
This overprediction has implications for studies that use the number densities
of similarly rare objects as cosmological probes. For example, the number
density of high redshift (z $\simeq$ 6) QSOs, which are thought to be hosted by
haloes at 5$\sigma$ peaks in the fluctuation field, are likely to be
overpredicted by at least a factor of 50%. We test the sensitivity of our
results to force accuracy, starting redshift, and halo finding algorithm.


title: On the Life and Death of Satellite Haloes

abstract:
  We study the evolution of dark matter satellites orbiting inside more massive
haloes using semi-analytical tools coupled with high-resolution N-Body
simulations. We select initial satellite sizes, masses, orbital energies, and
eccentricities as predicted by hierarchical models of structure formation. Both
the satellite and the main halo are described by a Navarro, Frenk & White
density profile with various concentrations.


title:
Multi-wavelength observations of stellar populations in Galactic
  globular clusters

abstract:
  I report on some recent results in the framework of a complex project aimed
to characterize the photometric properties of stellar populations in Galactic
Globular Clusters.


title: Can the dark energy equation-of-state parameter w be less than -1?

abstract:
  Models of dark energy are conveniently characterized by the equation-of-state
parameter w=p/\rho, where \rho is the energy density and p is the pressure.
Imposing the Dominant Energy Condition, which guarantees stability of the
theory, implies that w \geq -1. Nevertheless, it is conceivable that a
well-defined model could (perhaps temporarily) have w<-1, and indeed such
models have been proposed. We study the stability of dynamical models
exhibiting w<-1 by virtue of a negative kinetic term. Although naively
unstable, we explore the possibility that these models might be
phenomenologically viable if thought of as effective field theories valid only
up to a certain momentum cutoff. Under our most optimistic assumptions, we
argue that the instability timescale can be greater than the age of the
universe, but only if the cutoff is at or below 100 MeV. We conclude that it is
difficult, although not necessarily impossible, to construct viable models of
dark energy with w<-1; observers should keep an open mind, but the burden is on
theorists to demonstrate that any proposed new models are not ruled out by
rapid vacuum decay.


title:
The Northern Sky Optical Cluster Survey II: An Objective Cluster Catalog
  for 5800 Square Degrees

abstract:
  We present a new, objectively defined catalog of candidate galaxy clusters
based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky
Survey (DPOSS). This cluster catalog, derived from the best calibrated plates
in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square
degrees, and contains 8,155 candidate clusters. A simple adaptive kernel
density mapping technique, combined with the SExtractor object detection
algorithm, is used to detect galaxy overdensities, which we identify as
clusters. Simulations of the background galaxy distribution and clusters of
varying richnesses and redshifts allow us to optimize detection parameters, and
measure the completeness and contamination rates for our catalog. Cluster
richnesses and photometric redshifts are measured, using integrated colors and
magnitudes for each cluster. An extensive spectroscopic survey is used to
confirm the photometric results.
  This catalog, with well-characterized sample properties, provides a sound
basis for future studies of cluster physics and large scale structure.


title: Hard X-ray Emission Associated with White Dwarfs

abstract:
  We have used the WGACAT to search for hard X-ray sources associated with
white dwarfs (WDs) from the catalog of McCook & Sion (1999). We find 17 X-ray
sources coincident with WDs showing significant hard X-ray emission at energies
>0.5 keV. Twelve of these WDs are in known binary systems, in two of which the
accretion of the close companion's material onto the white dwarf produces the
hard X-ray emission, and in the other ten of which the late-type companions'
coronal activity emits hard X-rays. One WD is projected near an AGN which is
responsible for the hard X-ray emission. The remaining four WDs and two
additional white dwarfs with hard X-ray emission appear single. The lack of
near-IR excess from the apparently single WDs suggests that either X-ray
observations are more effective than near-IR photometry in diagnosing faint
companions or a different emission mechanism is needed. It is intriguing that
50% of the six apparently single WDs with hard X-ray emission are among the
hottest WDs. We have compared X-ray properties of 11 hot WDs with different
spectral types, and conclude that stellar pulsation and fast stellar winds are
not likely the origin of the hard X-ray emission, but a leakage of the
high-energy Wien tail of emission from deep in the stellar atmosphere remains a
tantalizing source of hard X-ray emission from hot DO and DQZO WDs. (This
abstract is an abridged version.)


title:
A Study of the Luminosity and Mass Functions of the Young IC 348 Cluster
  using FLAMINGOS Wide-Field Near-Infrared Images

abstract:
  We present wide-field near-infrared (JHK) images of the young, 2 Myr IC 348
cluster taken with FLAMINGOS. We use these new data to construct an infrared
census of sources, which is sensitive enough to detect a 10 Mjup brown dwarf
seen through an extinction of Av=7mag. We examine the cluster's structure and
relationship to the molecular cloud and construct the cluster's K band
luminosity function. Using our model luminosity function algorithm, we derive
the cluster's initial mass function throughout the stellar and substellar
regimes and find that the IC 348 IMF is very similar to that found for the
Trapezium Cluster with both cluster IMFs having a mode between 0.2 - 0.08 Msun.
In particular we find that, similar to our results for the Trapezium, brown
dwarfs constitute only 1 in 4 of the sources in the IC 348 cluster. We show
that a modest secondary peak forms in the substellar IC 348 KLF, corresponding
to the same mass range responsible for a similar KLF peak found in the
Trapezium. We interpret this KLF peak as either evidence for a corresponding
secondary IMF peak at the deuterium burning limit, or as arising from a feature
in the substellar mass-luminosity relation that is not predicted by current
theoretical models. Lastly, we find that IC 348 displays radial variations of
its sub-solar (0.5 - 0.08 Msun) IMF on a parsec scale. Whatever mechanism that
is breaking the universality of the IMF on small spatial scales in IC 348 does
not appear to be acting upon the brown dwarf population, whose relative size
does not vary with distance from the cluster center.


title: Gamma-Ray Burst Luminosity Functions Based on Luminosity Criteria

abstract:
  We review five studies of the gamma-ray burst (GRB) luminosity function that
are based on one or more of the proposed luminosity criteria, i.e.,
variability, spectral lag and spectral hardness. A comparison between the
resulting luminosity functions at redshift zero shows considerable divergence.
We derive for each of the luminosity functions the expected source counts and
the Euclidean value of <V/Vmax>. The source counts exhibit large differences
from the observed counts. In most cases the value of <V/Vmax> differs
substantially from the observed value of 0.34 for BATSE-based samples, with
offsets ranging from 6-24 sigmas. Given that the value of <V/Vmax> is well
established and that it is a cosmological distance indicator, we recommend that
any study of the GRB luminosity function take its value into account.


title:
Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and
  Related Systems

abstract:
  We present an analysis of over 2200 V images taken on 14 nights at the Mt.
Laguna 1 m telescope of the open cluster M67. Our observations overlap but
extend beyond the field analyzed by Gilliland et al. (1991), and complement
data recently published by van den Berg et al. (2002) and Stassun et al.
(2002). We show variability in the light curves of all 4 of the known W UMa
variables on timescales ranging from a day to decades (for AH Cnc). We have
modeled the light curve of AH Cnc, and the total eclipses allow us to determine
q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near
the turnoff of M67 makes it useful for constraining the turnoff mass for the
cluster. We have also detected two unusual features in the light curve of AH
Cnc that may be caused by prominences. We have also monitored cluster blue
stragglers for variability, and we present evidence hinting at low level
variations in the stragglers S752, S968, and S1263, and we place limits on the
variability of a number of other cluster blue stragglers. Finally, we provide
photometry of the sub-subgiant branch star S1063 showing variability on
timescales similar to the orbital period, while the ``red straggler'' S1040
shows evidence of an unexplained drop in brightness at phases corresponding to
the passage of the white dwarf in front of the giant.


title: Distances from Planetary Nebulae

abstract:
  The [O III] 5007 planetary nebula luminosity function (PNLF) occupies an
important place on the extragalactic distance ladder. Since it is the only
method that is applicable to all the large galaxies of the Local Supercluster,
it is uniquely useful for cross-checking results and linking the Population I
and Population II distance scales. We review the physics underlying the method,
demonstrate its precision, and illustrate its value by comparing its distances
to distances obtained from Cepheids and the Surface Brightness Fluctuation
(SBF) method. We use the Cepheid and PNLF distances to 13 galaxies to show that
the metallicity dependence of the PNLF cutoff is in excellent agreement with
that predicted from theory, and that no additional systematic corrections are
needed for either method. However, when we compare the Cepheid-calibrated PNLF
distance scale with the Cepheid-calibrated SBF distance scale, we find a
significant offset: although the relative distances of both methods are in
excellent agreement, the PNLF method produces results that are systematically
shorter by about 15%. We trace this discrepancy back to the calibration
galaxies and show how a small amount of internal reddening can lead to a very
large systematic error. Finally, we demonstrate how the PNLF and Cepheid
distances to NGC 4258 argue for a short distance to the Large Magellanic Cloud,
and a Hubble Constant that is about 8% larger than that derived by the HST Key
Project.


title: On Departures From a Power Law in the Galaxy Correlation Function

abstract:
  We measure the projected correlation function w_p(r_p) from the Sloan Digital
Sky Survey for a flux-limited sample of 118,000 galaxies and for a volume
limited subset of 22,000 galaxies with absolute magnitude M_r<-21. Both
correlation functions show subtle but systematic departures from the best-fit
power law, in particular a change in slope at r_p~1-2 Mpc/h. These departures
are stronger for the volume-limited sample, which is restricted to relatively
luminous galaxies. We show that the inflection point in w_p(r_p) can be
naturally explained by contemporary models of galaxy clustering, according to
which it marks the transition from a large scale regime dominated by galaxy
pairs in separate dark matter halos to a small scale regime dominated by galaxy
pairs in the same dark matter halo. For example, given the dark halo population
predicted by an inflationary cold dark matter scenario, the projected
correlation function of the volume-limited sample can be well reproduced by a
model in which the mean number of M_r<-21 galaxies in a halo of mass M>M_1=4.74
X 10^{13}\msun/h is <N>_M=(M/M_1)^{0.89}, with 75% of the galaxies residing in
less massive, single-galaxy halos. This physically motivated model has the same
number of free parameters as a power law, and it fits the w_p(r_p) data better,
with a \chi^2/d.o.f.=0.93 compared to 6.12 (for 10 degrees of freedom,
incorporating the covariance of the correlation function errors). Departures
from a power-law correlation function encode information about the relation
between galaxies and dark matter halos. Higher precision measurements of these
departures for multiple classes of galaxies will constrain galaxy bias and
provide new tests of the theory of galaxy formation.


title:
The Latest Version of the Standardized Candle Method for Type II
  Supernovae

abstract:
  I use the largest available sample of Type II plateau supernovae to examine
the previously reported luminosity-velocity relation. This study confirms such
relation which permits one to standardize the luminosities of these objects
from a spectroscopic measurement of their envelope velocities, and use them as
extragalactic distance indicators. The "standard candle method" (SCM) yields a
Hubble diagram with a dispersion of 0.3 mag, which implies that the SCM
produces distances with a precision of 15%. Using two nearby supernovae with
Cepheid distances I find Ho=81+/-10 km/s/Mpc, which compares with Ho=74 derived
from Type Ia supernovae.


title: LSR0602+3910 - Discovery of a Bright Nearby L-type Brown Dwarf

abstract:
  We report the discovery of LSR0602+3910, an L dwarf of class L1. The object
was initially identified by Lepine et al. (2002) as a new high proper motion
star lying close to the Galactic plane. Its 2MASS J-K_s=1.43 is consistent with
an L dwarf, which we now confirm spectroscopically. In addition, we see a
signature of Li I absorption, making LSR0602+3910 a brown dwarf, one of the
brightest known (K_s=10.86). Among L dwarfs it is second in brightness to the
combined light of 2MASS 0746+20, a close binary system. We see no indication
that LSR0602+3910 is a binary, although high-resolution imaging will be
required to confirm this. Spectroscopic and photometric distance estimates
agree very well, placing LSR0602+3910 at d=10.6+-0.8 pc. LSR0602+3910 was most
likely missed in previous searches because of its proximity to the plane, the
region that most searches avoided. We estimate that some 40% of bright L dwarfs
are missed because of this selection effect.


title: Feedback Heating in Cluster and Galactic Cooling Flows

abstract:
  Cluster cooling flow models that include both thermal conduction and AGN
heating have lower overall mass cooling rates and simultaneously sustain
density and temperature profiles similar to those observed with no ad hoc mass
dropout. To achieve this agreement, the thermal conductivity must be about 0.35
+/- 0.10 of the Spitzer value, similar to that advocated by Narayan & Medvedev.
However, when applied to galaxy/group scales the synergistic combination of AGN
heating and conduction is less satisfactory. When the computed density profile
and the global cooling rate are lowered by AGN heating to match observations of
these smaller scale flows, the gas temperatures within about 10 kpc are too
large. In addition, best-fitting flows in galaxy/groups with AGN heating and
thermal conduction require larger conductivities, about 0.5 - 1.0 of the
Spitzer value. When the gas density in galaxy/group flows is lowered by
heating, the iron enrichment by Type Ia supernovae is more effective and the
hot gas iron abundance greatly exceeds observed values. Consequently,
galactic/group flows with central heating and conduction require an additional
process that removes the iron: failure of Type Ia ejecta to go into the hot
phase, selective cooling, etc.


title:
Effects of the Sound Speed of Quintessence on the Microwave Background
  and Large Scale Structure

abstract:
  We consider how quintessence models in which the sound speed differs from the
speed of light and varies with time affect the cosmic microwave background and
the fluctuation power spectrum. Significant modifications occur on length
scales related to the Hubble radius during epochs in which the sound speed is
near zero and the quintessence contributes a non-negligible fraction of the
total energy density. For the microwave background, we find that the usual
enhancement of the lowest multipole moments by the integrated Sachs-Wolfe
effect can be modified, resulting in suppression or bumps instead. Also, the
sound speed can produce oscillations and other effects at wavenumbers $k >
10^{-2}$ h/Mpc in the fluctuation power spectrum.


title: Improved approximations of Poissonian errors for high confidence levels

abstract:
  We present improved numerical approximations to the exact Poissonian
confidence limits for small numbers n of observed events following the approach
of Gehrels (1986). Analytic descriptions of all parameters used in the
approximations are provided to allow their straightforward inclusion in
computer algorithms for processing of large data sets. Our estimates of the
upper (lower) Poisson confidence limits are accurate to better than 1% for
n<100 and values of S, the derived significance in units of Gaussian standard
deviations, of up to 7 (5). In view of the slow convergence of the commonly
used Gaussian approximations toward the correct Poissonian values, in
particular for higher values of S, we argue that, for n<40, Poissonian
statistics should be used in most applications, unless errors of the order of,
or exceeding, 10% are acceptable.


title: Near-Infrared Photometric Survey of Proto-Planetary Nebula Candidates

abstract:
  We present JHK' photometric measurements of 78 objects mostly consisting of
proto-planetary nebula candidates. Photometric magnitudes are determined by
means of imaging and aperture photometry. Unlike the observations with a
photometer with a fixed-sized beam, the method of imaging photometry permits
accurate derivation of photometric values because the target sources can be
correctly identified and confusion with neighboring sources can be easily
avoided. Of the 78 sources observed, we report 10 cases in which the source
seems to have been misidentified or confused by nearby bright sources. We also
present nearly two dozen cases in which the source seems to have indicated a
variability which prompts a follow-up monitoring. There are also a few sources
that show previously unreported extendedness. In addition, we present H band
finding charts of the target sources.


title:
The effects of rotation on Wolf--Rayet stars and on the production of
  primary nitrogen by intermediate mass stars

abstract:
  We use the rotating stellar models described in the paper by A. Maeder & G.
Meynet in this volume to consider the effects of rotation on the evolution of
the most massive stars into and during the Wolf--Rayet phase, and on the
post-Main Sequence evolution of intermediate mass stars. The two main results
of this discussion are the following. First, we show that rotating models are
able to account for the observed properties of the Wolf--Rayet stellar
populations at solar metallicity. Second, at low metallicities, the inclusion
of stellar rotation in the calculation of chemical yields can lead to a longer
time delay between the release of oxygen and nitrogen into the interstellar
medium following an episode of star formation, since stars of lower masses
(compared to non-rotating models) can synthesize primary N. Qualitatively, such
an effect may be required to explain the relative abundances of N and O in
extragalactic metal--poor environments, particularly at high redshifts.


title: Stellar yields in CNO from rotating stellar models

abstract:
  For $^{12}$C and $^{16}$O, rotating models predict in general enhanced
yields. At high metallicity, the carbon and oxygen yields from the very high
mass stars, which go through a WR phase, are little affected by rotation. For
$^{14}$N, rotation allows the production of important amounts of primary
nitrogen in {\it intermediate mass stars} at very low metallicity. The process
invoked for this production is different, from the classically accepted
scenario {\it i.e.} the Hot Bottom Burning (HBB) in Asymptotic Giant Branch
(AGB) stars. Rotating models also predict important productions of primary
$^{13}$C, $^{17}$O and $^{22}$Ne at very low metallicity.


title: Parameters for Very Light Jets of cD Galaxies

abstract:
  Recent Chandra X-ray observations of jets in central cluster galaxies show
interesting features around the symmetry plane. We have carried out simulations
involving bipolar jets, removing the artificial boundary condition at the
symmetry plane. We use a very low jet density (IGM/jet roughly 10000) and take
into account a decreasing density profile. We find that the jet bow shock
undergoes two phases: First a nearly spherical one and second the well-known
cigar-shaped one. We propose Cygnus A to be in a transition phase, clear signs
from both phases. Due to inward growing of Kelvin Helmholtz instabilities (KHI)
between cocoon and shocked IGM, mass entrainment is observed predominantly in
the symmetry plane. We propose this mechanism to produce some of the so far
enigmatic X-ray features in the symmetry plane in Cygnus A.


abstract:
  Gravitational lensing in metric theories of gravity is discussed. I introduce
a generalized approximate metric element, inclusive of both post-post-Newtonian
(ppN) contributions and gravito-magnetic field. Following Fermat's principle
and standard hyphoteses, I derive the time delay function and deflection angle
caused by an isolated mass distribution. Several astrophysical systems are
considered. In most of the cases, the gravito-magnetic correction offers the
best perspectives for an observational detection. Actual measurements
distinguish only marginally different metric theories one from another.


title: Calibration of the Distance Scale from Cepheids

abstract:
  We have used the infrared surface brightness technique to obtain a new
absolute calibration of the Cepheid PL relation in optical and near-infrared
bands from improved data on Galactic stars. The infrared surface brightness
distances to the Galactic variables are consistent with direct interferometric
Cepheid distance measurements, and with the PL calibration coming from
Hipparcos parallaxes of nearby Cepheids, but are more accurate than these
determinations. We find that in all bands, the Galactic Cepheid PL relation
appears to be slightly, but significantly steeper than the corresponding
relation defined by the LMC Cepheids. Since the slope of our LMC Cepheid sample
is clearly better defined than the one of the much smaller Galactic sample, we
fit the LMC slopes to our Galactic calibrating Cepheid sample (which introduces
only a small uncertainty) to obtain our final, adopted and improved absolute
calibrations of the Cepheid PL relations in the VIWJHK bands. Comparing the
absolute magnitudes of 10-day period Cepheids in both galaxies which are only
slightly affected by the different Galactic and LMC slopes of the PL relation,
we derive values for the LMC distance modulus in all these bands which can be
made to agree extremely well under reasonable assumptions for both, the
reddening law, and the adopted reddenings of the LMC Cepheids. This yields, as
our current best estimate from Cepheid variables, a LMC distance modulus of
18.55 +- 0.06.


title: Upper Limits on the X-ray Emission of "Uranium" Stars

abstract:
  A paper by Qian & Wasserburg suggests the optical absorption lines of uranium
observed in the spectra of ultra-metal-poor stars (defined as [Fe/H] $<$-3)
arise from contamination from a supernova in a binary star system. Assuming the
binary survived the explosion, a collapsed compact object may be present and
implying potential accretion processes with accompanying X-ray emission. Upper
limits on X-ray emission from an accreting compact object are described here.


title: Simulating IGM Reionization

abstract:
  We have studied the IGM reionization process in its full cosmological context
including structure evolution and a realistic galaxy population. We have used a
combination of high-resolution N-body simulations (to describe the dark matter
and diffuse gas component), a semi-analytic model of galaxy formation (to track
the evolution of the sources of ionizing radiation) and the Monte Carlo
radiative transfer code CRASH (to follow the propagation of ionizing photons
into the IGM). The process has been followed in the largest volume ever used
for this kind of study, a field region of the universe with a comoving length
of L~20/h Mpc, embedded in a much larger cosmological simulation. To assess the
effect of environment on the reionization process, the same radiative transfer
simulations have been performed on a 10/h Mpc comoving box, centered on a
clustered region. We find that, to account for the all ionizing radiation,
objects with total masses of M~10^9 Msun must be resolved. In this case, the
simulated stellar population produces a volume averaged ionization fraction
x_v=0.999 by z~8, consistent with observations without requiring any additional
sources of ionization. We also find that environment substantially affects the
reionization process. In fact, although the simulated proto-cluster occupies a
smaller volume and produces a higher number of ionizing photons, it gets
totally ionized later. This is because high density regions, which are more
common in the proto-cluster, are difficult to ionize because of their high
recombination rates.


title:
The trispectrum of the Cosmic Microwave Background on sub-degree angular
  scales: an analysis of the BOOMERanG data

abstract:
  The trispectrum of the cosmic microwave background can be used to assess the
level of non-Gaussianity on cosmological scales. It probes the fourth order
moment, as a function of angular scale, of the probability distribution
function of fluctuations and has been shown to be sensitive to primordial
non-gaussianity, secondary anisotropies (such as the Ostriker-Vishniac effect)
and systematic effects (such as astrophysical foregrounds). In this paper we
develop a formalism for estimating the trispectrum from high resolution sky
maps which incorporates the impact of finite sky coverage. This leads to a
series of operations applied to the data set to minimize the effects of
contamination due to the Gaussian component and correlations between estimates
at different scales. To illustrate the effect of the estimation process, we
apply our procedure to the BOOMERanG data set and show that it is consistent
with Gaussianity. This work presents the first estimation of the CMB
trispectrum on sub-degree scales.


title: On the Selection of Photometric Planetary Transits

abstract:
  We present a new method for differentiating between planetary transits and
eclipsing binaries based on the presence of the ellipsoidal light variations.
These variations can be used to detect stellar secondaries with masses ~0.2
M_sun orbiting sun-like stars at a photometric accuracy level which has already
been achieved in transit surveys. By removing candidates exhibiting this effect
it is possible to greatly reduce the number of objects requiring spectroscopic
follow up with large telescopes. Unlike the usual candidate selection method,
which are primarily based on the estimated radius of the orbiting object, this
technique is not biased against bona-fide planets and brown dwarfs with large
radii, because the amplitude of the effect depends on the transiting object's
mass and orbital distance. In many binary systems, where a candidate planetary
transit is actually due to the partial eclipse of two normal stars, the
presence of flux variations due to the gravity darkening effect will show the
true nature of these systems. We show that many of the recent OGLE-III
photometric transit candidates exhibit the presence of significant variations
in their light curves and are likely to be due to stellar secondaries. We find
that the light curves of white dwarf transits will generally not mimic those of
small planets because of significant gravitationally induced flux variations.
We discuss the relative merits of methods used to detect transit candidates
which are due to stellar blends rather than planets. We outline how photometric
observations taken in two bands can be used to detect the presence of stellar
blends.


title:
Fundamental Properties and Distances of LMC Eclipsing Binaries: IV. HV
  5936

abstract:
  We have determined the fundamental properties and distance of a fourth
eclipsing binary system (EB) in the Large Magellanic Cloud, HV5936 (B0.5 V + B2
III). As in our previous studies, we combine "classical" EB light curve and
radial velocity curve analyses with modeling of the UV-through-optical spectral
energy distribution of HV5936 to produce a detailed characterization of the
system. In this paper, we also include an analysis of the high-resolution
optical absorption line spectra of the binary components. We find HV5936 to be
an Algol-class system, in which the masses of the primary and secondary stars
have evolved via mass transfer to their current values of 11.6 Mo and 4.7 Mo,
respectively. The properties of the primary star are indistinguishable from
those of a "normal" star of the same current mass. The secondary is found to be
overluminous for its current mass and exhibits a factor-of-2 enhancement in its
surface He abundance. These results are compatible with "Case A" mass exchange
occurring during the core hydrogen burning phase of the current secondary. The
distance derived to the system, 43.2 +/- 1.8 kpc, implies a distance of ~44.3
kpc to the optical center of the LMC. This is several kpc closer than found in
our analyses of other systems and we suggest that HV5936 lies "above" the LMC
disk. This is supported by the very low interstellar H I column density and low
E(B-V) found for the system - both of which are consistent with expected Milky
Way foreground material - and may be associated with HV5936's location near the
LMC supergiant shell LMC4.


title:
The X-ray-faint Emission of the Supermassive Nuclear Black Hole of
  IC1459

abstract:
  Chandra observations of the supermassive black hole in the nucleus of IC1459
show a weak [L_X=8x10(40)erg s(-1), 0.3-8keV], unabsorbed nuclear X-ray source,
with a slope Gamma=1.88+/-0.09, and no strong Fe-K line at 6.4keV (EW$<382 eV).
This describes a normal AGN X-ray spectrum, but lies at 3x10(-7) below the
Eddington limit. The SED of the IC1459 nucleus is extremely radio loud compared
to normal radio-loud quasars. The nucleus is surrounded by hot ISM (kT~0.5-0.6
keV) with an average density of 0.3cm(-3), within the central ~180 pc radius,
which is comparable to the gravitational capture radius, r_A~140 pc. We
estimate that for a standard AGN efficiency of 10%, the Bondi accretion would
correspond to a luminosity of ~6x10(44)erg s(-1), nearly four orders of
magnitude higher than L_X. ADAF solutions can explain the X-ray spectrum, but
not the high radio/X-ray ratio. A jet model fits the radio-100micron and X-ray
spectra well. The total power in this jet is ~10% of L(Bondi), implying that
accretion close to the Bondi rate is needed.


title: Tight LMC massive star clusters R 127 and R 128

abstract:
  We study the Large Magellanic Cloud (LMC) star clusters R 127 and R 128 using
imaging and spectroscopy obtained at the ESO NTT telescope. An advanced image
restoration technique allows us to resolve these two clusters into at least 14
and 33 stars respectively and obtain their photometry. In particular, we show
that the core of R 127 is composed of at least four stars and identify the
Luminous Blue Variable (LBV) component. The closest neighbor of the LBV (star
#8) is 1".5 away. Moreover, from medium dispersion spectroscopy we determine
the spectral types for 19 stars in and near both clusters, and in particular
present the first spatially resolved observation of the second brightest
component of the R 127 cluster (star #3) situated 3".3 from the LBV. By
comparing with evolutionary models we also look into the stellar ages. The
oldest stars of the cluster are ~ 6-8 Myr old, whereas the most massive star of
the region (#7), formed ~ 3 Myr ago as an 80 solar mass star, has turned into
an LBV, the ``R 127'' star.


title: Ultra high energy cosmic ray sources & experimental results

abstract:
  Here we discuss the latest developments in the debate, where the ultrahigh
energy cosmic ray particles come from. In this brief review, we emphasize the
predictions that necessarily follow from the various concepts proposed. We
discuss both sources and propagation, and spend some space on the by now most
conservative model, giant radio galaxies and their hot spots and jets, because
it allows more steps in the reasoning to be checked, and is more tightly
constrained than any other model. It has survived about forty years of debate
already. We summarize the task ahead of us at the end, including the
development of new technologies to observe ultra high energy cosmic rays, e.g.,
with the radio emission of air showers, which may lead to an alternative to the
fluorescence detectors with their small duty cycle. Due to HiRes, AUGER, and
the plans for EUSO, the future is bright, and the ultra high energy cosmic ray
particles may yet allow us to explore new physics.


title:
Numerical simulations of interacting gas-rich barred galaxies. Vertical
  impact of small companions

abstract:
  We investigate the dynamical effects of an interaction between an initially
barred galaxy and a small spherical companion using an N-body/SPH algorithm. In
the models described here the small companion passes through the disc of the
larger galaxy near-perpendicular to its plane. The impact positions and times
are varied with respect to the phase of the bar and the dynamical evolution of
the disc.
  The interactions produce expanding ring structures, offset bars, spokes,and
other asymmetries in the stars and gas. These characteristic signatures of the
interaction are present in the disc for about 1 Gyr. We find that in some cases
it is possible to destroy the bar while keeping the disc structure. In general
the central impacts cause larger damage to the bar and the disc than the
peripheral ones. The interaction tends to accelerate the transition from a
strongly barred galaxy to a weakly or non-barred galaxy. The final disc
morphology is determined more by the impact position relative to the bar rather
than the impact time.


title:
Fine Structure of Dark Matter Halos and its Effect on Terrestrial
  Detection Experiments

abstract:
  Terrestrial dark matter detection experiments probe the velocity-space
distribution of dark matter particles in the vicinity of the Earth. We present
a novel method, to be used in conjunction with standard cosmological
simulations of hierarchical clustering, that allows one to extract a truly
local velocity-space distribution in exquisite detail. Preliminary results
suggest a new picture for this distribution which is decidedly non-Maxwellian
but instead is characterized by randomly positioned peaks in velocity space. We
discuss the implications of these results for both WIMP and axion detection
experiments.


title:
The Morphological Butcher-Oemler effect in the SDSS Cut&Enhance Galaxy
  Cluster Catalog

abstract:
  We investigate the evolution of the fractions of late type cluster galaxies
as a function of redshift, using one of the largest, most uniform cluster
samples available. The sample consists of 514 clusters of galaxies in the range
0.02<z<0.3 from the Sloan Digital Sky Survey Cut & Enhance galaxy cluster
catalog. This catalog was created using a single automated cluster finding
algorithm on uniform data from a single telescope, with accurate CCD
photometry, thus, minimizing selection biases. We use four independent methods
to analyze the evolution of the late type galaxy fraction. Specifically, we
select late type galaxies based on: restframe g-r color, u-r color, galaxy
profile fitting and concentration index. The first criterion corresponds to the
one used in the classical Butcher-Oemler analyses. The last three criteria are
more sensitive to the morphological type of the galaxies. In all four cases, we
find an increase in the fraction of late type galaxies with increasing
redshift, significant at the 99.9% level. The results confirm that cluster
galaxies do change colors with redshift (the Butcher-Oemler effect) and, in
addition, they change their morphology to later-type toward higher redshift --
indicating a morphological equivalent of the Butcher-Oemler effect. We also
find a tendency of richer clusters to have lower fractions of late type
galaxies. The trend is consistent with a ram pressure stripping model, where
richer clusters have more effective ram pressure due to their higher
temperature.


title: The Environment of Passive Spiral Galaxies in the SDSS

abstract:
  In previous work on galaxy clusters, several authors reported a discovery of
an unusual population of galaxies, which have spiral morphologies, but do not
show any star formation activity. These galaxies are called ``passive
spirals'', and have been interesting since it has been difficult to understand
the existence of such galaxies. Using a volume limited sample (0.05<z<0.1 and
Mr<-20.5; 25813 galaxies) of the Sloan Digital Sky Survey data, we have found
73 (0.28$\pm$0.03%) passive spiral galaxies and studied their environments. It
is found that passive spiral galaxies live in local galaxy density 1-2
Mpc$^{-2}$ and 1-10 cluster-centric virial radius. Thus the origins of passive
spiral galaxies are likely to be cluster related. These characteristic
environments coincide with the previously reported environment where galaxy
star formation rate suddenly declines and the so-called morphology-density
relation turns. It is likely that the same physical mechanism is responsible
for all of these observational results. The existence of passive spiral
galaxies suggests that a physical mechanism that works calmly is preferred to
dynamical origins such as major merger/interaction since such a mechanism can
destroy spiral arm structures. Compared with observed cluster galaxy evolution
such as the Butcher-Oemler effect and the morphological Butcher-Oemler effect,
passive spiral galaxies are likely to be a galaxy population in transition
between red, elliptical/S0 galaxies in low redshift clusters and blue, spiral
galaxies more numerous in higher redshift clusters.


title: Global Dynamics in the Singular Logarithmic Potential

abstract:
  We present an analytical description of the motion in the singular
logarithmic potential. This potential plays an important role in the modeling
of triaxial systems (like elliptical galaxies) or bars in the centers of galaxy
disks. In order to obtain information about the motion near the singularity, we
resort to McGehee -type transformations and regularize the vector field. In the
axis-symmetric case (b=1), we offer a complete description of the global
dynamics. In the non axis-symmetric case (b<1), we prove that all orbits, with
the exception of a negligible set, are centrophobic and retrieve numerically
partial aspects of the orbital structure.


title: Hdelta-Selected Galaxies in the Sloan Digital Sky Survey I: The Catalog

abstract:
  [Abridged] We present here a new and homogeneous sample of 3340 galaxies
selected from the Sloan Digital Sky Survey (SDSS) based solely on the observed
strength of their Hdelta absorption line. These galaxies are commonly known as
``post-starburst'' or ``E+A'' galaxies, and the study of these galaxies has
been severely hampered by the lack of a large, statistical sample of such
galaxies. In this paper, we rectify this problem by selecting a sample of
galaxies which possess an absorption Hdelta equivalent width of EW(Hdelta_max)
- Delta EW(Hdelta_max) > 4A from 106682 galaxies in the SDSS. We have performed
extensive tests on our catalog including comparing different methodologies of
measuring the Hdelta absorption and studying the effects of stellar absorption,
dust extinction, emission-filling and measurement error. The measured abundance
of our Hdelta-selected (HDS) galaxies is 2.6 +/- 0.1% of all galaxies within a
volume-limited sample of 0.05<z<0.1 and M(r*)<-20.5, which is consistent with
previous studies of such galaxies in the literature. We find that only 25 of
our HDS galaxies in this volume-limited sample (3.5+/-0.7%) show no evidence
for OII and Halpha emission, thus indicating that true E+A (or k+a) galaxies
are extremely rare objects at low redshift, i.e., only 0.09+/-0.02% of all
galaxies in this volume-limited sample are true E+A galaxies. In contrast,
89+/-5% of our HDS galaxies in the volume-limited sample have significant
detections of the OII and Halpha emission lines. We find 27 galaxies in our
volume-limited HDS sample that possess no detectable OII emission, but do
however possess detectable Halpha emission. These galaxies may be dusty
star-forming galaxies. We provide the community with this new catalog of
Hdelta-selected galaxies to aid in the understanding of these galaxies.


title: The Interplay of Cluster and Galaxy Evolution

abstract:
  We review here the interplay of cluster and galaxy evolution. As a case
study, we consider the Butcher-Oemler effect and propose that it is the result
of the changing rate of cluster merger events in a hierarchical universe. This
case study highlights the need for new catalogs of clusters and groups that
possess quantified morphologies. We present such a sample here, namely the
Sloan Digital Sky Survey (SDSS) C4 Catalog, which has been objectively-selected
from the SDSS spectroscopic galaxy sample. We outline here the C4 algorithm and
present first results based on the SDSS Early Data Release, including an X-ray
luminosity-velocity dispersion (L_x-sigma) scaling relationship (as a function
of cluster morphology), and the density-SFR relation of galaxies within C4
clusters (Gomez et al. 2003). We also discuss the merger of Coma and the
NGC4839 group, and its effect on the galaxy populations in these systems. We
finish with a brief discussion of a new sample of Hdelta-selected galaxies
(i.e., k+a, post--starburst galaxies) obtained from the SDSS spectroscopic
survey.


title: Ram pressure stripping in Planetary Nebulae

abstract:
  We present two-dimensional numerical simulations of the evolution of a
low-mass star moving supersonically through its surrounding interstellar medium
(ISM). We show that the ejecta of a moving star with a systemic velocity of 20
km/s will interact with the ISM and will form bow-shock structures
qualitatively similar to what is observed. We find that, due to ram-pressure
stripping, most of the mass ejected during the AGB phase is left downstream of
the moving star. As a consequence, the formation of the PN is highly
influenced, even at the low relative velocity of the star. The models are based
on the predictions of stellar evolution calculations. Therefore, the density
and velocity of the AGB and post-AGB winds are time dependent and give rise to
the formation of shock regions inside the cavity formed by the previous winds.
As a result, the stand-off distance is also time dependent and cannot be
determined by simple analytical arguments.


title: Are Chaplygin gases serious contenders to the dark energy throne?

abstract:
  We study the implications on both background and perturbation evolution of
introducing a Chaplygin gas component in the universe's ingredients. We perform
likelihood analyses using wide-ranging, SN1a, CMB and large scale structure
observations to assess whether such a component could be a genuine alternative
to a cosmological constant. We find that current data favors an adiabatic
Chaplygin gas with behavior akin to a cosmological constant.


title: The AGN Paradigm for Radio-Loud Objects

abstract:
  Radio-loud AGN are characterized by relativistic jets originating near the
central supermassive black hole and forming large-scale radio sources at parsec
to kiloparsec to Megaparsec distances. The jets are energetically significant,
in many cases representing the bulk of the energy extracted from the accretion
process. Host galaxies are apparently normal luminous ellipticals, supporting
the "Grand Unification" scenario wherein AGN are a transient phase in the
evolution of every galaxy. Black hole mass appears to be largely uncorrelated
with bolometric luminosity, Eddington ratio, radio luminosity, or radio
loudness.


title:
Limits on the Dark Energy Parameters from Cosmic Microwave Background
  experiments

abstract:
  Full suite of the present day Cosmic Microwave background (CMB) data, when
combined with weak prior information on the Hubble constant and the age of the
Universe, or the Large-Scale structure, provides strong indication for a
non-zero density of the vacuum-like dark energy in our universe. This result
independently supports the conclusions from Supernovae Ia (SN1a) data. When the
model parameter space is extended to allow for the range of the equation of
state parameter w_Q for the dynamical field Q which gives rise to dark energy,
the CMB data is found to give a weak upper bound w_Q < -0.4 at 95% CL, however
combined with SN1a data it strongly favours w_Q < -0.8, consistent with
Lambda-term like behaviour.


title:
Spatially Resolved 3 um Spectroscopy of IRAS 22272+5435: Formation and
  Evolution of Aliphatic Hydrocarbon Dust in Proto-Planetary Nebula

abstract:
  We present medium-resolution 3 um spectroscopy of the carbon-rich
proto-planetary nebula IRAS 22272+5435. Spectroscopy with the Subaru Telescope
adaptive optics system revealed a spatial variation of hydrocarbon molecules
and dust surrounding the star. The ro-vibrational bands of acetylene (C2H2) and
hydrogen cyanide (HCN) at 3.0 um are evident in the central star spectra. The
molecules are concentrated in the compact region near the center. The 3.3 and
3.4 um emission of aromatic and aliphatic hydrocarbons is detected at 600--1300
AU from the central star. The separation of spatial distribution between gas
and dust suggests that the small hydrocarbon molecules are indeed the source of
solid material, and that the gas leftover from the grain formation is being
observed near the central star. The intensity of aliphatic hydrocarbon emission
relative to the aromatic hydrocarbon emission decreases with distance from the
central star. The spectral variation is well matched to that of a laboratory
analog thermally annealed with different temperatures. We suggest that either
the thermal process after the formation of a grain or the variation in the
temperature in the dust-forming region over time determines the chemical
composition of the hydrocarbon dust around the proto-planetary nebula.


title:
Analysis of the Flux and Polarization Spectra of the Type Ia Supernova
  SN 2001el: Exploring the Geometry of the High-velocity Ejecta

abstract:
  SN 2001el is the first normal Type Ia supernova to show a strong, intrinsic
polarization signal. In addition, during the epochs prior to maximum light, the
CaII IR triplet absorption is seen distinctly and separately at both normal
photospheric velocities and at very high velocities. The high-velocity triplet
absorption is highly polarized, with a different polarization angle than the
rest of the spectrum. The unique observation allows us to construct a
relatively detailed picture of the layered geometrical structure of the
supernova ejecta: in our interpretation, the ejecta layers near the photosphere
(v \approx 10,000 km/s) obey a near axial symmetry, while a detached,
high-velocity structure (v \approx 18,000-25,000 km/s) with high CaII line
opacity deviates from the photospheric axisymmetry. By partially obscuring the
underlying photosphere, the high-velocity structure causes a more incomplete
cancellation of the polarization of the photospheric light, and so gives rise
to the polarization peak and rotated polarization angle of the high-velocity IR
triplet feature. In an effort to constrain the ejecta geometry, we develop a
technique for calculating 3-D synthetic polarization spectra and use it to
generate polarization profiles for several parameterized configurations. In
particular, we examine the case where the inner ejecta layers are ellipsoidal
and the outer, high-velocity structure is one of four possibilities: a
spherical shell, an ellipsoidal shell, a clumped shell, or a toroid. The
synthetic spectra rule out the spherical shell model, disfavor a toroid, and
find a best fit with the clumped shell. We show further that different
geometries can be more clearly discriminated if observations are obtained from
several different lines of sight.


title:
Line versus Flux Statistics -- Considerations for the Low Redshift
  Lyman-alpha Forest

abstract:
  The flux/transmission power spectrum has become a popular statistical tool in
studies of the high redshift ($z > 2$) Lyman-alpha forest. At low redshifts,
where the forest has thinned out into a series of well-isolated absorption
lines, the motivation for flux statistics is less obvious. Here, we study the
relative merits of flux versus line correlations, and derive a simple condition
under which one is favored over the other on purely statistical grounds.
Systematic errors probably play an important role in this discussion, and they
are outlined as well.


title:
A Search for 6.7 GHz Methanol Masers in OH Megamaser Galaxies at
  0.11<z<0.27

abstract:
  We report the results of a search for 6.7 GHz methanol (CH3OH) maser emission
in OH megamaser galaxies at 0.11<z<0.27. No detections were made in the 25
objects observed down to rms noise levels of roughly 0.6 mJy in 150 kHz
channels. The OH megamaser sample includes OH emission of all observed types:
narrow and broad, physically compact and extended, variable and quiescent, and
from simple single lines to multi-component complexes to lines with high
velocity wings. Our null result indicates, for the widest possible range of OH
megamaser environments, that methanol masing does not scale with OH from
Galactic masers to megamasers. These observations, however, are not sensitive
enough to rule out methanol masing that scales with star formation from
Galactic compact HII regions to starbursts associated with major mergers. This
and previous work suggest that OH megamasers do not represent large ensembles
of individual masers associated with star forming regions. Maser models
combined with observational constraints on the physical settings of OH
megamasers indicate that 6.7 GHz methanol megamasers will not be detected by
this survey if T(dust) < 100 K or if n(CH3OH) < n(OH).


title:
First-generation black-hole-forming supernovae and the metal abundance
  pattern of a very iron-poor star

abstract:
  It has been proposed theoretically that the first generation of stars in the
Universe (population III) would be as massive as 100 solar masses (100Mo),
because of inefficient cooling of the precursor gas clouds. Recently, the most
iron-deficient (but still carbon-rich) low-mass star -- HE0107-5240 -- was
discovered. If this is a population III that gained its metals (elements
heavier than helium) after its formation, it would challenge the theoretical
picture of the formation of the first stars. Here we report that the patterns
of elemental abundance in HE0107-5240 (and other extremely metal-poor stars)
are in good accord with the nucleosynthesis that occurs in stars with masses of
20-130Mo when they become supernovae if, during the explosions, the ejecta
undergo substantial mixing and fall-back to form massive black holes. Such
supernovae have been observed. The abundance patterns are not, however,
consistent with enrichment by supernovae from stars in the range 130-300 Mo. We
accordingly infer that the first-generation supernovae came mostly from
explosions of ~ 20-130Mo stars; some of these produced iron-poor but carbon-
and oxygen-rich ejecta. Low-mass second-generation stars, like HE0107-5240,
could form because the carbon and oxygen provided pathways for gas to cool.


title: Observation of coronal loop torsional oscillation

abstract:
  We suggest that the global torsional oscillation of solar coronal loop may be
observed by the periodical variation of a spectral line width. The amplitude of
the variation must be maximal at the velocity antinodes and minimal at the
nodes of the torsional oscillation. Then the spectroscopic observation as a
time series at different heights above the active region at the solar limb may
allow to determine the period and wavelength of global torsional oscillation
and consequently the Alfv{\'e}n speed in corona. From the analysis of early
observation (Egan & Schneeberger \cite{egan}) we suggest the value of coronal
Alfv{\'e}n speed as $\sim 500 {\rm km}{\cdot}{\rm s}^{-1}$.


title: Gamma-Ray Bursts environment and progenitors

abstract:
  The properties of the ambient medium in which GRBs go off are an important
piece of the puzzle, not only as an issue in itself, but because of their link
with the nature of the progenitor. In this review, I describe and critically
comment the various experiments proposed to study the burst environment. I
discuss emission and absorption features techniques and compare their results
to afterglow modelling. A consistent picture cannot be drawn, and I suggest
that the evaporation of the soft X-ray absorbing column is the more promising
of the tools, even though the fast reaction of Swift is required in order to
obtain data of sufficiently high quality.


title: Early Hard X-ray Afterglows of Short GRBs with Konus Experiments

abstract:
  For a ten of 125 short GRBs observed by Konus-Wind and the Konus-A the
existance of statistically significant flux of hard photons accompanying
initial event for a time of tens to hundred seconds after the trigger was
revealed. Temporal, spectral, and energetic characteristics of these events are
presented. The statistical analysis of the whole burst sample reveals that the
afterglow is a more common feature of short GRBs.


title: Chandra Observation of the X-Ray Source Population of NGC 6946

abstract:
  We present the results of a study of discrete X-ray sources in NGC 6946 using
a deep Chandra ACIS observation. Based on the slope of the log N-log S
distribution and the general correlation of sources with the spiral arms, we
infer that the overall discrete source sample in NGC 6946 is dominated by high
mass X-ray binaries, in contrast to the source distributions in M31 and the
Milky Way. This is consistent with the higher star formation rate in NGC 6946
than in those galaxies. We find that the strong X-ray sources in the region of
the galactic center do not correlate in detail with images of the region in the
near-IR, although one of them may be coincident with the galactic center. The
non-central ultra-luminous X-ray source in NGC 6946, previously identified with
a supernova remnant, has an X-ray spectrum and luminosity that is inconsistent
with either a traditional pulsar wind nebula or a blast wave remnant.


title:
Optical spectroscopy and the UV luminosity function of galaxies in the
  Abell 1367, Coma and Virgo clusters

abstract:
  Optical spectroscopy of 93 galaxies, 60 projected in the direction of Abell
1367, 21 onto the Coma cluster and 12 on Virgo, is reported. The targets were
selected either because they were detected in previous H\alpha, UV or r'
surveys. The present observations bring to 100% the redshift completeness of
H\alpha selected galaxies in the Coma region and to 75% in Abell 1367. All
observed galaxies except one show H\alpha emission and belong to the clusters.
This confirms previous determinations of the H\alpha luminosity function of the
two clusters that were based on the assumption that all H\alpha detected
galaxies were cluster members. Using the newly obtained data we re-determine
the UV luminosity function of Coma and we compute for the first time the UV
luminosity function of A1367. Their faint end slopes remain uncertain (-2.00 <
\alpha < -1.35) due to insufficient knowledge of the background counts. If 90%
of the UV selected galaxies without redshift will be found in the background
(as our survey indicates), the slope of UV luminosity function will be \alpha ~
-1.35, in agreement with the UV luminosity function of the field (Sullivan et
al. 2000) and with the H$\alpha$ luminosity functions of the two clusters
(Iglesias-Paramo et al. 2002). We discover a point like H\alpha source in the
Virgo cluster, associated with the giant galaxy VCC873, possibly an
extragalactic HII region similar to the one recently observed in Virgo by
Gerhard et al. (2002).


title: The Integral Equation Method for a Steady Kinematic Dynamo Problem

abstract:
  With only a few exceptions, the numerical simulation of cosmic and laboratory
hydromagnetic dynamos has been carried out in the framework of the differential
equation method. However, the integral equation method is known to provide
robust and accurate tools for the numerical solution of many problems in other
fields of physics. The paper is intended to facilitate the use of integral
equation solvers in dynamo theory. In concrete, the integral equation method is
employed to solve the eigenvalue problem for a hydromagnetic dynamo model with
a spherically symmetric, isotropic helical turbulence parameter alpha. Three
examples of the function alpha(r) with steady and oscillatory solutions are
considered. A convergence rate proportional to the inverse squared of the
number of grid points is achieved. Based on this method, a convergence
accelerating strategy is developed and the convergence rate is improved
remarkably. Typically, quite accurate results can be obtained with a few tens
of grid points. In order to demonstrate its suitability for the treatment of
dynamos in other than spherical domains, the method is also applied to alpha^2
dynamos in rectangular boxes. The magnetic fields and the electric potentials
for the first eigenvalues are visualized.


title: A Brown Dwarf Microlens Candidate in the OGLE-II Database

abstract:
  We describe a unique mass determination for a microlensing event from the
second phase of the Optical Gravitational Microlensing Experiment (OGLE-II).
The event, sc26_2218, which is very bright (baseline magnitude I=15.10),
appears to exhibit both parallax and finite source effects. The parallax effect
allows us to determine the projected Einstein radius on the observer plane
(approx. 3.8 AU), while the finite source effect allows us to determine the
ratio of the angular source size and the angular Einstein radius. As the
angular size of the star can be estimated using its color and magnitude, we can
hence determine the angular Einstein radius (approx. 0.1 mas). By combining
both the projected and angular Einstein radius we can determine the lens mass M
= 0.050^{+0.016}_{-0.011} solar masses, independent of the source distance. The
lens is therefore a brown dwarf candidate. However, the `parallax' signature is
weak and so we cannot completely discount the possibility that these signatures
originate from binary rotation of the source (which would prevent any estimate
of the lens mass), rather than parallax. However, this can be tested by future
spectroscopic observations. This event highlights the scientific returns for
intense monitoring of bright microlensing events, since the parallax and finite
source effects can be more easily identified due to their high signal-to-noise
ratios.


title: Testing general relativity by micro-arcsecond global astrometry

abstract:
  The global astrometric observations of a GAIA-like satellite were modeled
within the PPN formulation of Post-Newtonian gravitation. An extensive
experimental campaign based on realistic end-to-end simulations was conducted
to establish the sensitivity of global astrometry to the PPN parameter \gamma,
which measures the amount of space curvature produced by unit rest mass. The
results show that, with just a few thousands of relatively bright,
photometrically stable, and astrometrically well behaved single stars, among
the ~10^9 objects that will be observed by GAIA, \gamma can be estimated after
1 year of continuous observations with an accuracy of ~10^{-5} at the 3\sigma
level. Extrapolation to the full 5-year mission of these results based on the
scaling properties of the adjustment procedure utilized suggests that the
accuracy of \simeq 2x10^{-7}, at the same 3\sigma level, can be reached with
\~10^6 single stars, again chosen as the most astrometrically stable among the
millions available in the magnitude range V=12-13. These accuracies compare
quite favorably with recent findings of scalar-tensor cosmological models,
which predict for \gamma a present-time deviation, |1-\gamma|, from the General
Relativity value between 10^{-5} and 10^{-7}.


title:
Mass limits for the progenitor star of supernova 2001du and other type
  II-P supernovae

abstract:
  The supernova SN2001du in the galaxy NGC1365 (19+/-2Mpc), is a core-collapse
event of type II-P. Images of this galaxy, have been taken with HST
approximately 6.6 years before discovery and include the supernova position on
the WFPC2 field of view. We have observed the supernova with the WFPC2 to allow
accurate differential astrometry of SN2001du on the pre-explosion frames. There
is a marginal detection (3-sigma) of a source close to the supernova position
on the prediscovery V-band frame, however it is not precisely coincident and we
do not believe it to be a robust detection of a point source. We conclude that
there is no stellar progenitor at the supernova position and derive sensitivity
limits of the prediscovery images which provide an upper mass limit for the
progenitor star. We estimate that the progenitor had a mass of less than
15M_sol. We revisit two other nearby SNe II-P which have high quality
pre-explosion images, and refine the upper mass limits for the progenitor
stars. Finally we compile all the direct information available for the
progenitors of eight nearby core-collapse supernovae and compare their mass
estimates. These are compared with the latest stellar evolutionary models of
pre-supernova evolution which have attempted to relate metallicity and mass to
the supernovae type. Reasonable agreement is found for the lower mass events
(generally the II-P), but some discrepancies appear at higher masses.
(abridged).