title:
The impact of bars on the mid-infrared dust emission of spiral galaxies:
  global and circumnuclear properties

abstract:
  We study the mid-infrared properties of a sample of 69 nearby spiral
galaxies, selected to avoid Seyfert activity contributing a significant
fraction of the central energetics, or strong tidal interaction, and to have
normal infrared luminosities. These observations were obtained with ISOCAM,
which provides an angular resolution of the order of 10 arcsec (half-power
diameter of the point spread function) and low-resolution spectro-imaging
information. Between 5 and 18 microns, we mainly observe two dust phases,
aromatic infrared bands and very small grains, both out of thermal equilibrium.
On this sample, we show that the global F15/F7 colors of galaxies are very
uniform, the only increase being found in early-type strongly barred galaxies,
consistent with previous IRAS studies. The F15/F7 excesses are unambiguously
due to galactic central regions where bar-induced starbursts occur. However,
the existence of strongly barred early-type galaxies with normal circumnuclear
colors indicates that the relationship between a distortion of the
gravitational potential and a central starburst is not straightforward. As the
physical processes at work in central regions are in principle identical in
barred and unbarred galaxies, and since this is where the mid-infrared activity
is mainly located, we investigate the mid-infrared circumnuclear properties of
all the galaxies in our sample. We show how surface brightnesses and colors are
related to both the available molecular gas content and the mean age of stellar
populations contributing to dust heating. Therefore, the star formation history
in galactic central regions can be constrained by their position in a
color-surface brightness mid-infrared diagram.


title:
The relationship between star formation rates and mid-infrared emission
  in galactic disks

abstract:
  The Halpha and mid-infrared mean disk surface brightnesses are compared in a
sample of nearby spirals observed by ISOCAM. This shows that, in spiral disks,
dust emission at 7 and 15 microns provides a reasonable star formation tracer.
The fact that the 15 to 7 micron flux ratio is nearly constant in various
global exciting conditions indicates a common origin, namely the aromatic
infrared band carriers, and implies that at these wavelengths, dust emission
from the disks of normal galaxies is dominated by photodissociation regions and
not by HII regions themselves. We use this newly-found correlation between the
mid-infrared and the Halpha line to investigate the nature of the link between
the far-infrared (60 and 100 microns) and Halpha. Although the separation of
the central regions from the disk is impossible to achieve in the far-infrared,
we show that a circumnuclear contribution to the dust emission, having no
equivalent counterpart in Halpha, is most likely responsible for the well-known
non-linearity between far-infrared and Halpha fluxes in spiral galaxies. We
derive a calibration of 7 and 15 micron fluxes in terms of star formation rates
from a primary calibration of Halpha in the literature, and also outline the
applicability limits of the proposed conversion, which should not be blindly
extrapolated to objects whose nature is unknown.


title:
Effects of perturbing forces on the orbital stability of planetary
  systems

abstract:
  We consider dynamical effects of additional perturbative forces due to the
non-point mass nature of stars and planets: effects such as quadrupolar
distortion and tidal friction in the systems of exo-planets. It is shown that
these forces should not be neglected while modelling the dynamics of planetary
systems, especially taking into account the undefined real masses of the
planets due to unknown orbital inclinations and the unsatisfactory application
of Keplerian fits to the radial velocity data in multiple planetary systems.


title: Plasmoid impacts on neutron stars and highest energy cosmic rays

abstract:
  Particle acceleration by electrostatic polarization fields that arise in
plasmas streaming across magnetic fields is discussed as a possible
acceleration mechanism of highest-energy cosmic rays. Specifically, plasmoids
arising in planetoid impacts onto neutron star magnetospheres are considered.
We find that such impacts at plausible rates may account for the observed flux
and energy spectrum of the highest energy cosmic rays.


title: Neutral Hydrogen and Star Formation in the Irregular Galaxy NGC 2366

abstract:
  We present UBVJHKHalpha and HI data of the irregular galaxy NGC 2366. It is a
normal boxy-shaped disk seen at high inclination angle. We do not see any
unambiguous observational signature of a bar. There is an asymmetrical
extension of stars along one end of the major axis of the galaxy, and this is
where the furthest star-forming regions are found, at 1.3R_Holmberg. The HI is
normal in many respects but shows some anomalies: 1) The integrated HI shows
two ridges running parallel to the major axis that deproject to a large ring.
2) The velocity field exhibits several large-scale anomalies superposed on a
rotating disk. 3) The inclination and position angles derived from the
kinematics differ from those dervied from the optical and HI mor- phology. 4)
There are regions in the HI of unusually high velocity dispersion that
correlate with deficits of HI emission in a manner suggestive of long-range,
turbulent pressure equilibrium. Star-forming regions are found where the gas
densities locally exceed 6 Msolar/pc^2. NGC 2366, like other irregulars, has
low gas densities relative to the critical gas densities of gravitational
instability models. Because of the lack of shear in the optical galaxy, there
is little competition to the slow gravitational contraction that follows energy
dissipation. However, the peak gas densities in the star-forming regions are
equal to the local tidal densities for gravitational self-binding of a rotating
cloud. Evidently the large scale gas concentrations are marginally bound
against background galactic tidal forces. This condition for self-binding may
be more fundamental than the instability condition because it is local,
three-dimensional, and does not involve spiral arm generation as an
intermediate step toward star formation.


title: PMN J1632-0033: A new gravitationally lensed quasar

abstract:
  We report the discovery of a gravitationally lensed quasar resulting from our
survey for lenses in the southern sky. Radio images of PMN J1632-0033 with the
VLA and ATCA exhibit two compact, flat-spectrum components with separation
1.47" and flux density ratio 13.2. Images with the HST reveal the optical
counterparts to the radio components and also the lens galaxy. An optical
spectrum of the bright component, obtained with the first Magellan telescope,
reveals quasar emission lines at redshift 3.42. Deeper radio images with MERLIN
and the VLBA reveal a faint third radio component located near the center of
the lens galaxy, which is either a third image of the background quasar or
faint emission from the lens galaxy.


title: On a mechanism of highest-energy cosmic ray acceleration

abstract:
  A recently proposed mechanism of acceleration of highest energy cosmic rays
by polarization electric fields arising in plasmoids injected into neutron star
magnetospheres is discussed.


title: Discovery of a Galaxy Cluster via Weak Lensing

abstract:
  We report the discovery of a cluster of galaxies via its weak gravitational
lensing effect on background galaxies, the first spectroscopically confirmed
cluster to be discovered through its gravitational effects rather than by its
electromagnetic radiation. This fundamentally different selection mechanism
promises to yield mass-selected, rather than baryon or photon-selected, samples
of these important cosmological probes. We have confirmed this cluster with
spectroscopic redshifts of fifteen members at z=0.276, with a velocity
dispersion of 615 km/s. We use the tangential shear as a function of source
photometric redshift to estimate the lens redshift independently and find z_l =
0.30 +- 0.08. The good agreement with the spectroscopy indicates that the
redshift evolution of the mass function may be measurable from the imaging data
alone in shear-selected surveys.


title: The 2dF QSO Redshift Survey - V. The 10k catalogue

abstract:
  We present a catalogue comprising over 10000 QSOs covering an effective area
of 289.6 sq. degrees, based on spectroscopic observations with the 2-degree
Field instrument at the Anglo-Australian Telescope. This catalogue forms the
first release of the 2-degree Field QSO Redshift Survey. QSO candidates with
18.25<b_J<20.85 were obtained from a single homogeneous colour-selected
catalogue based on APM measurements of UK Schmidt photographic material. The
final catalogue will contain approximately 25000 QSOs and will be released to
the public at the end of 2002, one year after the observational phase is
concluded.


title: Post-AGB Stars in Globular Clusters and Galactic Halos

abstract:
  We discuss three aspects of post-AGB (PAGB) stars in old populations. (1) HST
photometry of the nucleus of the planetary nebula (PN) K 648 in the globular
cluster (GC) M15 implies a mass of 0.60 Msun, in contrast to the mean masses of
white dwarfs in GCs of ~0.5 Msun. This suggests that K 648 is descended from a
merged binary, and we infer that single Pop II stars do not produce visible
PNe. (2) Yellow PAGB stars are the visually brightest stars in old populations
(Mv ~ -3.3) and are easily recognizable because of their large Balmer jumps;
thus they show great promise as a Pop II standard candle. Two yellow PAGB stars
in the GC NGC 5986 have the same V magnitudes to within +/-0.05 mag, supporting
an expected narrow luminosity function. (3) Using CCD photometry and a u filter
lying below the Balmer jump, we have detected yellow PAGB stars in the halo of
M31 and in its dwarf elliptical companion NGC 205. With the Milky Way zero
point, we reproduce the Cepheid distance to M31, and find that NGC 205 is ~100
kpc further away than M31. The star counts imply a yellow PAGB lifetime of
about 25,000 yr, and their luminosities imply masses near 0.53 Msun.


title: The Substellar Mass Function in sigma Orionis

abstract:
  We combine results from imaging searches for substellar objects in the sigma
Orionis cluster and follow-up photometric and spectroscopic observations to
derive a census of the brown dwarf population in a region of 847 arcmin^2. We
identify 64 very low-mass cluster member candidates in this region. We have
available three color (IZJ) photometry for all of them, spectra for 9 objects,
and K photometry for 27% of our sample. These data provide a well defined
sequence in the I vs I-J, I-K color magnitude diagrams, and indicate that the
cluster is affected by little reddening despite its young age (~5 Myr). Using
state-of-the-art evolutionary models, we derive a mass function from the
low-mass stars (0.2 Msol) across the complete brown dwarf domain (0.075 Msol to
0.013 Msol), and into the realm of free-floating planetary-mass objects (<0.013
Msol). We find that the mass spectrum (dN/dm ~ m^{-alpha}) increases toward
lower masses with an exponent alpha = 0.8+/-0.4. Our results suggest that
planetary-mass isolated objects could be as common as brown dwarfs; both kinds
of objects together would be as numerous as stars in the cluster. If the
distribution of stellar and substellar masses in sigma Orionis is
representative of the Galactic disk, older and much lower luminosity
free-floating planetary-mass objects with masses down to about 0.005 Msol
should be abundant in the solar vicinity, with a density similar to M-type
stars.


title:
On the Statistical Significance of the Hipparcos Astrometric Orbit of
  rho Coronae Borealis

abstract:
  Recently Gatewood, Han & Black presented an analysis of the Hipparcos stellar
positions and their own ground-based measurements of rho CrB, suggesting an
astrometric orbit of 1.5 mas with an extremely small orbital inclination of 0.5
degrees. This indicates that the planet-candidate secondary might be a late M
star. We used the Hipparcos data of rho CrB together with the individual radial
velocities of Noyes et al. to independently study the stellar orbit and to
assess its statistical significance. Our analysis yielded the same astrometric
orbit. However, a permutation test we performed on the Hipparcos measurements
indicated that the statistical significance of the astrometric orbit is only
2-sigma. Therefore, we can expect about one out of 40 systems with a similar
data set to show a false astrometric orbit.


title:
Calibration of the CH and CN Variations Among Main Sequence Stars in M71
  and in M13

abstract:
  An analysis of the CN and CH band strengths measured in a large sample of M71
and M13 main sequence stars by Cohen (1999a,b) is undertaken using synthetic
spectra to quantify the underlying C and N abundances. In the case of M71 it is
found that the observed CN and CH band strengths are best matched by the
{\it{identical}} C/N/O abundances which fit the bright giants, implying: 1)
little if any mixing is taking place during red giant branch ascent in M71, and
2) a substantial component of the C and N abundance inhomogeneities is in place
before the main sequence turn-off. The unlikelihood of mixing while on the main
sequence requires an explanation for the abundance variations which lies
outside the present stars (primordial inhomogeneities or intra-cluster self
enrichment). For M13 it is shown that the 3883\AA CN bands are too weak to be
measured in the spectra for any reasonable set of expected compositions. A
similar situation exists for CH as well. However, two of the more luminous
program stars do appear to have C abundances considerably greater than those
found among the bright giants thereby suggesting deep mixing has taken place on
the M13 red giant branch.


title:
Microlensing Constraints on the Frequency of Jupiter-Mass Companions:
  Analysis of Five Years of PLANET Photometry

abstract:
  We analyze five years of PLANET photometry of microlensing events toward the
Galactic bulge to search for the short-duration deviations from single lens
light curves that are indicative of the presence of planetary companions to the
primary microlenses. Using strict event selection criteria, we construct a well
defined sample of 43 intensively monitored events. We search for planetary
perturbations in these events over a densely sampled region of parameter space
spanning two decades in mass ratio and projected separation, but find no viable
planetary candidates. By combining the detection efficiencies of the events, we
find that, at 95% confidence, less than 25% of our primary lenses have
companions with mass ratio q=0.01 and separations in the lensing zone, 0.6-1.6
Einstein ring radii. Using a model of the mass, velocity and spatial
distribution of bulge lenses, we infer that the majority of our lenses are
likely M dwarfs in the Galactic bulge. We conclude that less than 33% of
M-dwarfs in the Galactic bulge have Jupiter-mass companions between 1.5 and 4
AU, and less than 45% have 3 Jupiter-mass companions between 1 and 7 AU, the
first significant limits on planetary companions to M-dwarfs. We consider the
effects of the finite size of the source stars and changing our detection
criterion, but find that these do not alter our conclusions substantially.


title: Spectral variability in transonic discs around black holes

abstract:
  Transonic discs with accretion rates relevant to intrinsically bright
Galactic X-ray sources ($L\approx 10^{38}$-$10^{39} {\rm erg s}^{-1}$) exhibit
a time dependent cyclic behaviour due to the onset of a thermal instability
driven by radiation pressure. In this paper we calculate radiation spectra
emitted from thermally-unstable discs to provide detailed theoretical
predictions for observationally relevant quantities. The emergent spectrum has
been obtained by solving self-consistently the vertical structure and radiative
transfer in the disc atmosphere. We focus on four particular stages of the disc
evolution, the maximal evacuation stage and three intermediate stages during
the replenishment phase. The disc is found to undergo rather dramatic spectral
changes during the evolution, emitting mainly in the 1-10 keV band during
outburst and in the 0.1-1 keV band off-outburst. Local spectra, although
different in shape from a blackbody at the disc effective temperature, may be
characterized in terms of a hardening factor $f$. We have found that $f$ is
rather constant both in radius and in time, with a typical value $\sim 1.65$.


title:
Host Galaxies of Gamma-ray Bursts: Spectral Energy Distributions and
  Internal Extinction

abstract:
  We present BVRcIc broad-band flux spectra for the host galaxies of GRB970508,
GRB980613, GRB980703, GRB990123 and GRB991208 obtained with the 6-m telescope
of SAO RAS. The BVRcIc of these hosts are best fitted by the spectral
properties of template SEDs of starburst galaxies and that there is a
significant internal extinction in these host galaxies. We derived the absolute
magnitudes of the GRB host galaxies making use of SEDs for the starburst
galaxies. We performed the population synthesis modeling of the continuum
spectral energy distribution of the host galaxies of GRB970508 and GRB980703
using different extinction laws and assuming burst and exponential scenarios of
star formation. The comparison of BVRcIc broad-band flux spectra with the local
starburst galaxies templates and theoretical templates as well as direct
estimates (using Balmer emission lines) of the internal extinction shows that
it is likely to be of great importance to take into account effects of the
internal extinction in the host galaxies. From the SED of the host galaxy of
GRB991208 and from the intensity of their spectral lines it follows that this
is a GRB galaxy with the highest massive star-formation rate of all known GRB
galaxies. The reduced luminosity of these dusty galaxies (e.g. for the host of
GRB970508 A_V\sim 2 mag, for the host of GRB980703 A_V\sim 0.6 mag and for the
host of GRB991208 A_V\sim 2 mag) could explain the observational fact: none of
the observed GRB host galaxies with known distances is brighter than the local
galaxies with the luminosity L_*.


title:
The potential of the variable DA white dwarf G117-B15A as a tool for
  Fundamental Physics

abstract:
  White dwarfs are well studied objects. The relative simplicity of their
physics allows to obtain very detailed models which can be ultimately compared
with their observed properties. Among white dwarfs there is a specific class of
stars, known as ZZ-Ceti objects, which have a hydrogen-rich envelope and show
periodic variations in their light curves. G117-B15A belongs to this particular
set of stars. The luminosity variations have been successfully explained as due
to g-mode pulsations. G117-B15A has been recently claimed to be the most stable
optical clock ever found, being the rate of change of its 215.2 s period very
small: \dot{P}= (2.3 +- 1.4)x10^{-15} s s^-1, with a stability comparable to
that of the most stable millisecond pulsars. The rate of change of the period
is closely related to its cooling timescale, which can be accurately computed.
In this paper we study the pulsational properties of G117-B15A and we use the
observed rate of change of the period to impose constraints on the axion
emissivity and, thus, to obtain a preliminary upper bound to the mass of the
axion. This upper bound turns out to be 4cos^{2}{\beta} meV at the 95%
confidence level. Although there are still several observational and
theoretical uncertainties, we conclude that G117-B15A is a very promising
stellar object to set up constraints on particle physics.


title: Properties of the Trans-Neptunian Belt: Statistics From the CFHT Survey

abstract:
  We present the results of a wide-field survey designed to measure the size,
inclination, and radial distributions of Kuiper Belt Objects (KBOs). The survey
found 86 KBOs in 73 square degrees observed to limiting red magnitude 23.7
using the Canada-France-Hawaii Telescope and the 12k x 8k CCD Mosaic camera.
For the first time, both ecliptic and off-ecliptic fields were examined to more
accurately constrain the inclination distribution of the KBOs. The survey data
were processed using an automatic moving object detection algorithm, allowing a
careful characterization of the biases involved. In this work, we quantify
fundamental parameters of the Classical KBOs (CKBOs), the most numerous objects
found in our sample, using the new data and a maximum likelihood simulation.
Deriving results from our best-fit model, we find that the size distribution
follows a differential power law with exponent q = 4.0 (+0.6)(-0.5) (1 sigma,
or 68.27% confidence). In addition, the CKBOs inhabit a very thick disk
consistent with a Gaussian distribution of inclinations with a Half-Width of
i(1/2) = 20 (+6)(-4) deg (1 sigma). We estimate that there are N = 3.8
(+2.0)(-1.5) x 10^4 (1 sigma) CKBOs larger than 100 km in diameter. We also
find compelling evidence for an outer edge to the CKBOs at heliocentric
distance R = 50 AU.


title: Brane World Astronomy

abstract:
  Unified theories suggest that space is intrinsically 10 dimensional, even
though everyday phenomena seem to take place in only 3 large dimensions. In
``Brane World'' models, matter and radiation are localized to a ``brane'' which
has a thickness less than 1/TeV in all but the usual three dimensions, while
gravity propagates in additional dimensions, some of which may extend as far as
submillimeter scales. A brief review is presented of some of these models and
their astrophysical phenomenology. One distinctive possibility is a
gravitational wave background originating in the mesoscopic early universe, at
temperatures above about 1 TeV and on scales smaller than a millimeter, during
the formation of our 3-dimensional brane within a 10-dimensional space.


title: Particle Annihilation in Cold Dark Matter Micropancakes

abstract:
  Cold primordial particle dark matter forms with a distribution in
six-dimensional phase space closely approximating a three-dimensional sheet.
Folds in the mapping of this sheet onto configuration space create ubiquitous
sheetlike caustics (``micropancakes''). A typical WIMP dark matter halo has
many micropancakes, each with a scale comparable to the halo itself, a width
about $10^{-8}$ of the halo size and a typical maximum density up to about
$10^4$ times the halo mean. It is demonstrated here that the total annihilation
rate of dark matter particles is dominated by particles close to these
micropancakes, so radiation is emitted predominantly from highly contorted
two-dimensional surfaces rather than a filled volume. The total annihilation
rate of particles is about a factor of 5 higher than predicted from N-body
simulations, which cannot resolve these features. Micropancakes also produce
sharp line discontinuities in the surface brightness of annihilation radiation.


title:
Detection of Doppler Shifted X-ray Line Profiles from the Wind of Zeta
  Puppis (O4f)

abstract:
  We report on a 67 ks HETG observation of the optically brightest early
O-star, Zeta Pup (O4 f). Many resolved X-ray lines are seen in the spectra over
a wavelength range of 5 to 25 A. Chandra has sufficient spectral resolution to
study the velocity structure of isolated X-ray line profiles, and to
distinguish the individual forbidden, intercombination, and resonance (fir)
emission lines in several He-like ions even where the individual components are
strongly Doppler broadened. In contrast with X-ray line profiles in other hot
stars, Zeta Pup shows blue-shifted and skewed line profiles, providing the
clearest and most direct evidence that the X-ray sources are embedded in the
stellar wind. The broader the line, the greater the blueward centroid shift
tends to be. The N VII line at 24.78 A is a special case, showing a flat-topped
profile. This indicates it is formed in regions beyond most of the wind
attenuation. The sensitivity of the He-like ion fir lines to a strong UV
radiation field is used to derive the radial distances at which lines of S XV,
Si XIII, Mg XI, Ne IX, and O VII originate. The formation radii correspond well
with continuum optical depth unity at the wavelength of each line complex,
indicating that the X-ray line emission is distributed throughout the stellar
wind. However, the S XV emission lines form deeper in the wind than expected
from standard wind shock models.


title: Three newly-discovered M-dwarf companions of Solar Neighbourhood stars

abstract:
  We present low-resolution spectroscopy of newly-discovered candidate
companions to three stars in the Solar Neighbourhood. All three companions are
M dwarfs, with spectral types ranging from M4 to M9.5. In two cases, G85-55`B'
(M6) and G87-9`B' (M4), we have circumstantial evidence from spectroscopy,
photometry and limited astrometry that the systems are physical binaries; in
the third, G216-7B (M9.5), comparison of POSS II IIIaF plate material and the
2MASS image indicates common proper motion. The primary star in this system,
G216-7A (M0), appears itself to be an unresolved, nearly equal-mass binary. All
three low-mass companions are highly likely to be stellar in nature, although
G216-7B lies very close to the hydrogen-burning limit.


title:
PSR J2229+6114: Discovery of an Energetic Young Pulsar in the Error Box
  of the EGRET Source 3EG J2227+6122

abstract:
  We report the detection of radio and X-ray pulsations at a period of 51.6 ms
from the X-ray source RX/AX J2229.0+6114 in the error box of the EGRET source
3EG J2227+6122. An ephemeris derived from a single ASCA observation and
multiple epochs at 1412 MHz from Jodrell Bank indicates steady spin-down with
P-dot = 7.83 x 10^(-14) s/s. From the measured P and P-dot we derive spin-down
power E-dot = 2.2 x 10^(37) erg/s, magnetic field B = 2.0 x 10^(12) G, and
characteristic age P/2P-dot = 10,460 yr. An image from the Chandra X-ray
Observatory reveals a point source surrounded by centrally peaked diffuse
emission that is contained within an incomplete radio shell. We assign the name
G106.6+2.9 to this new supernova remnant, which is evidently a pulsar wind
nebula. For a distance of 3 kpc estimated from X-ray absorption, the ratio of
X-ray luminosity to spin-down power is ~8 x 10^(-5), smaller than that of most
pulsars, but similar to the Vela pulsar. If PSR J2229+6114 is the counterpart
of 3EG J2227+6122 then its efficiency of gamma-ray production, if isotropic, is
0.016 (d/3 kpc)^2. It obeys an established trend of gamma-ray efficiency among
known gamma-ray pulsars which, in combination with the demonstrated absence of
any other plausible counterpart for 3EG J2227+6122, makes the identification
compelling. If confirmed, this identification bolsters the pulsar model for
unidentified Galactic EGRET sources.


title: High-velocity white dwarfs: thick disk, not dark matter

abstract:
  We present an alternative interpretation of the nature of the extremely cool,
high-velocity white dwarfs identified by Oppenheimer et al (2001) in a
high-latitude astrometric survey. We argue that the velocity distribution of
the majority of the sample is more consistent with the high-velocity tail of a
rotating population, probably the thick disk, rather than a pressure-supported
halo system. Indeed, the observed numbers are well matched by predictions based
on the kinematics of a complete sample of nearby M dwarfs. Analysing only stars
showing retrograde motion gives a local density close to that expected for
white dwarfs in the stellar (R^-3.5) halo. Under our interpretation, none of
the white dwarfs need be assigned to the dark-matter, heavy halo. However,
luminosity functions derived from observations of these stars can set important
constraints on the age of the oldest stars in the Galactic Disk.


title:
A K-band central disk surface-brightness correlation with scale-length
  for early-type disk galaxies, and the inclination correction

abstract:
  The K-band light-profiles from two statistically complete, diameter-limited
samples of disk galaxies have been simultaneously modelled with a
seeing-convolved Sersic r^{1/n} bulge and a seeing-convolved exponential disk.
This has enabled an accurate separation of the bulge and disk light, and hence
an estimate of the central disk surface brightness mu_{0,K} and the disk
scale-length h. There exists a bright envelope of galaxy disks in the
mu_{0,K}-log h diagram; for the early-type (<Sc) disk galaxies mu_{0,K} is
shown to increase with log h, with a slope of ~2 and a correlation coefficient
equal to 0.75. This relation exists over a range of disk scale-lengths from 0.5
to 10 kpc (H_0=75 km/s/Mpc). In general, galaxy types Scd or later are observed
to deviate from this relation; they have fainter surface brightnesses for a
given scale-length.
  With a sub-sample of 59 low-inclination (i<50 deg) and 29 high-inclination
(i>50 deg) galaxies having morphological types ranging from S0 to Sc, the need
for an inclination correction to the K-band disk surface brightness is
demonstrated. Measured central disk surface brightnesses are found to be
significantly (>5-sigma) brighter for the high-inclination disk galaxies than
for the low-inclination disk galaxies. With no surface brightness inclination
correction or allowance for the trend between mu_{0,K} and log h, the standard
deviation to the distribution of mu_{0,K} values is ~1 mag arcsec^{-2}, while
the standard deviation about the mean mu_{0,K}-log h relation decreases from
0.69 mag arcsec^{-2}, when no inclination correction is applied, to 0.47 mag
arcsec^{-2} when the inclination correction is applied.


title: The Tensor to Scalar Ratio of Phantom Dark Energy Models

abstract:
  We investigate the anisotropies in the cosmic microwave background in a class
of models which possess a positive cosmic energy density but negative pressure,
with a constant equation of state w = p/rho < -1. We calculate the temperature
and polarization anisotropy spectra for both scalar and tensor perturbations by
modifying the publicly available code CMBfast. For a constant initial curvature
perturbation or tensor normalization, we have calculated the final anisotropy
spectra as a function of the dark energy density and equation of state w and of
the scalar and tensor spectral indices. This allows us to calculate the
dependence of the tensor-to-scalar ratio on w in a model with phantom dark
energy, which may be important for interpreting any future detection of
long-wavelength gravitational waves.


title: 1/2 Law for Non-Radiative Accretion Flow

abstract:
  At low densities, when radiation of an accreting gas is dynamically
unimportant, quasi-spherical non-radiative accretion flow is formed around a
compact object. We show that the density of the flow is n\propto r^{-1/2}. The
gas compression is much weaker than the standard Bondi's, n\propto r^{-3/2},
because most of the gas does not reach the compact object. It can either
circulate indefinitely long or it can be launched to infinity.


title: A step toward the calibration of the RGB Tip as a Standard Candle

abstract:
  The absolute I magnitude of the Tip of the Red Giant Branch M_I(TRGB) is one
of the most promising Standard Candles actually used in astrophysics as a
fundamental pillar for the Cosmological Distance Scale. With the aim of
improving the observational basis of its calibration, we have obtained an
accurate estimate of the M_I(TRGB) for the globular cluster Omega Centauri,
based (a) on the largest photometric database ever assembled for a globular, by
Pancino et al.(2000), and (b) on a direct distance estimate for Omega Cen,
recently obtained by Thompson et al.(2001) from a detached eclipsing binary.
The derived value M_I(TRGB) =-4.04\pm 0.12 provides, at present, the most
accurate empirical zero-point for the calibration of the M_I(TRGB) - [Fe/H]
relation, at [Fe/H] ~ -1.7. We also derived a new empirical M_I(TRGB) - [Fe/H]
relation, based on the large IR dataset of red giants in Galactic Globular
Clusters recently presented by Ferraro et al.(2000). This database (extending
up to [Fe/H]=-0.2) covers a more appropriate metallicity range, for
extragalactic applications, than previous empirical calibrations (limited to
[Fe/H]<= -0.7). The proposed relation is in excellent agreement with the newly
determined zero-point.


title:
Statistics of the detection rates for tensor and scalar gravitational
  waves from the local galaxy universe

abstract:
  We use data on the local 3-dimensional galaxy distribution for studying the
statistics of the detection rates of gravitational waves (GW) coming from
supernova explosions. We consider both tensor and scalar gravitational waves
which are possible in a wide range of relativistic and quantum gravity
theories. We show that statistics of GW events as a function of sidereal time
can be used for distinction between scalar and tensor gravitational waves
because of the anisotropy of spatial galaxy distribution. For calculation of
the expected amplitudes of GW signals we use the values of the released GW
energy, frequency and duration of GW pulse which are consistent with existing
scenarios of SN core collapse. The amplitudes of the signals produced by Virgo
and the Great Attractor clusters of galaxies is expressed as a function of the
sidereal time for resonant bar detectors operating now (IGEC) and for
forthcoming laser interferometric detectors (VIRGO).Then, we calculate the
expected number of GW events as a function of sidereal time produced by all the
galaxies within 100 Mpc. In the case of axisymmetric rotational core collapse
which radiates a GW energy of $10^{-9}M_{\odot}c^2$, only the closest
explosions can be detected. However, in the case of nonaxisymmetric supernova
explosion, due to such phenomena as centrifugal hangup, bar and lump formation,
the GW radiation could be as strong as that from a coalescing neutron-star
binary. For radiated GW energy higher than $10^{-6}M_{\odot}c^2$ and
sensitivity of detectors at the level $h \approx 10^{-23}$ it is possible to
detect Virgo cluster and Great Attractor, and hence to use the statistics of GW
events for testing gravity theories.


title: The crust of rotating strange quark stars

abstract:
  Calculations of the properties of rotating strange stars with crusts are
performed within the framework of general relativity. We employ an equation of
state (EOS) of strange quark matter based on the MIT Bag Model with massive
strange quarks and lowest order QCD interactions. The crust is described by the
BPS equation of state. A significant increase of the stellar radius is found
close to the Keplerian (mass-shedding limit) configuration. This leads to the
disappearance of the gap between the stellar surface and the innermost stable
circular orbit (ISCO) at very high rotation rates, for a rather broad range of
stellar masses. The Keplerian configuration for the strange star with crust
corresponds to values of J, T/W which are about 20% smaller than in the case of
bare strange stars. Because the Keplerian configuration is achieved due to the
increase of the stellar oblateness, the Keplerian frequency (of the rotation)
remains almost unaltered. The lack of the gap close to the Keplerian rotation
could imply a more stringent limit on the frequency of the ISCO, if the
existence of such a gap is supported by observations, as in the source 4U
1820-30 with the upper QPO frequency 1.07 kHz. During the spin-down of a
magnetized strange quark star with crust, the crust matter is absorbed in the
equatorial region by the strange matter core. The deconfinement of absorbed
crust matter is a strongly exothermic process, which would influence the
cooling curve of this compact object.


title: The Large-Scale Structure and Environment of HoII

abstract:
  Neutral hydrogen VLA D-array observations of the dwarf irregular galaxy HoII,
a prototype galaxy for studies of shell formation and self-propagating star
formation, are presented. The large-scale HI morphology is reminiscent of ram
pressure and is unlikely caused by interactions. A case is made for intragroup
gas in poor and compact groups similar to the M81 group, to which HoII belongs.
Numerous shortcomings of the supernova explosions and stellar winds scenario to
create the shells in HoII are highlighted, and it is suggested that ram
pressure may be able to reconcile the numerous observations available.


title: Extremely red radio galaxies

abstract:
  At least half the radio galaxies at z>1 in the 7C Redshift Survey have
extremely red colours (R-K>5), consistent with stellar populations which formed
at high redshift (z>5). We discuss the implications of this for the evolution
of massive galaxies in general and for the fraction of near-IR-selected EROs
which host AGN, a result which is now being tested by deep, hard X-ray surveys.
The conclusion is that many massive galaxies undergo at least two active
phases: one at z~5 when the black hole and stellar bulge formed and another at
z~1-2 when activity is triggered by an event such as an interaction or merger.


title: Fossil Radio Plasma in Cluster Merger Shock Waves

abstract:
  In several merging clusters of galaxies so-called cluster radio relics have
been observed. These are extended radio sources which do not seem to be
associated with any radio galaxy. Two competing physical mechanisms to
accelerate the radio emitting electrons have been proposed: (i) diffusive shock
acceleration and (ii) adiabatic compression of fossil radio plasma by merger
shock waves. Here the second scenario is investigated. We present detailed
3-dimensional magneto-hydrodynamical simulations of the passage of a radio
plasma cocoon through a shock wave. Taking into account synchrotron, inverse
Compton and adiabatic energy losses and gains we evolved the relativistic
electron population to produce synthetic radio maps in Stokes I-, Q-, and
U-polarisation. In the synthetic radio maps the electric polarisation vectors
are mostly perpendicular to the filamentary radio structures.


title: Numerical Simulations of Relativistic Shock Acceleration

abstract:
  We review the present status of the cosmic ray acceleration theory in mildly
relativistic shock waves. Due to the involved substantial particle anisotropies
analytical methods can tackle only simple situations involving weakly turbulent
conditions near the shock. The numerical Monte Carlo methods are used to study
the acceleration process in more general conditions. Contrary to
non-relativistic shocks, the cosmic ray spectra at relativistic shock waves
depend substantially on the magnetic field configurations and turbulence
spectra. Depending on these conditions both very flat and very steep spectra
can be created, with the characteristic acceleration time scales changing
non-monotonously with the turbulence amplitude. Thus, the discussed theory is
not able to uniquely explain the observed synchrotron spectra of relativistic
shocks. We also mention an interesting possibility of particle acceleration at
incompressible flow discontinuities (shear layers) at boundaries of
relativistic jets.


title:
X-ray emission from the giant molecular clouds in the Galactic Center
  region and the discovery of new X-ray sources

abstract:
  We report the results of X-ray (2-10 keV) observations of the giant molecular
clouds SgrB, SgrC and SgrD in the Galactic Center region, together with the
discovery of the point-like source SAXJ1748.2-2808. The data have been obtained
with the MECS instrument on the BeppoSAX satellite. The core of SgrB2 has an
X-ray luminosity of 6x10^34 erg/s and its spectrum is characterized by a strong
Fe emission line at 6.5 keV with an equivalent width of 2 keV. Faint diffuse
X-ray emission is detected from SgrC and from the SNR G1.05-0.15 (SgrD). A new,
unresolved source with a strong Fe line has been discovered in the SgrD region.
This source, SAXJ1748.2-2808, is probably associated with a SiO and OH maser
source at the Galactic Center distance. If so, its luminosity is 10^34 erg/s.
We propose that the X-ray emission from SAX J1748.2-2808 is produced either by
protostars or by a giant molecular cloud core. Emission from sources similar to
SAX J1748.2-2808 could have an impact on the expected contribution on the
observed Fe line emission from the Galactic ridge.


title:
1.65 micron (H-band) surface photometry of galaxies. VII: dwarf galaxies
  in the Virgo cluster

abstract:
  We present near-infrared H-band (1.65micron) observations and surface
brightness profile decompositions for 75 faint (13.5 < m_p < 18.5) galaxies,
primarily taken among dwarf Ellipticals members of the Virgo cluster. We model
their surface brightness profiles with a de Vaucouleurs (D), exponential (E),
mixed (bulge+disk or M) or truncated (T) law, and we derive for each galaxy the
H band effective surface brightness (mu_e) and effective radius (r_e), the
asymptotic total magnitude H_T and the light concentration index C_31.
Combining the present data with those previously obtained by our group (1157
objects) we analyze the NIR properties of a nearly complete sample,
representative of galaxies of all morphological types, spanning 4 decades in
luminosity. We confirm our earlier claim that the presence of cusps and
extended haloes in the light profiles (C_31>5) is a strong, non-linear function
of the total luminosity. We also find that: i) among dEs and dS0s galaxies D
profiles are absent; 50% of the decompositions are of type M, the remaining
being of type E or T. ii) Less than 50% of the giant elliptical galaxies have
pure D profiles, the majority being represented by M profiles. iii) Most giant
galaxies (from elliptical to Sb) have M profiles. iv) Most of late type spirals
(Scd to BCD) have either E or T profiles. v) The type of decomposition is a
strong function of the total H band luminosity, independent of the Hubble
classification: the fraction of type E decompositions decreases with increasing
luminosity, while those of type M increase with luminosity. Pure D profiles are
absent in the low luminosity range L_H<10^10 solar and become dominant above
10^11 solar, while T profiles are present only among low luminosity galaxies.


title: Investigation of Gravitational Lens Mass Models

abstract:
  We have previously reported the discovery of strong gravitational lensing by
faint elliptical galaxies using the WFPC2 on HST and here we investigate their
potential usefulness in putting constraints on lens mass models. We compare
various ellipsoidal surface mass distributions, including those with and
without a core radius, as well as models in which the mass distributions are
assumed to have the same axis ratio and orientation as the galaxy light. We
also study models which use a spherical mass distribution having various
profiles, both empirical and following those predicted by CDM simulations.
These models also include a gravitational shear term. The model parameters and
associated errors have been derived by 2-dimensional analysis of the observed
HST WFPC2 images. The maximum likelihood procedure iteratively converges
simultaneously on the model for the lensing elliptical galaxy and the lensed
image components. The motivation for this study was to distinguish between
these mass models with this technique. However, we find that, despite using the
full image data rather than just locations and integrated magnitudes, the
lenses are fit equally well with several of the mass models. Each of the mass
models generates a similar configuration but with a different magnification and
cross-sectional area within the caustic, and both of these latter quantities
govern the discovery probability of lensing in the survey. These differences
contribute to considerable cosmic scatter in any estimate of the cosmological
constant using gravitational lenses.


title:
WFPC2 Imaging of Quasar Environments: A Comparison of LBQS and HST
  Archive Quasars

abstract:
  We present Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2)
data on the large-scale environments of 16 0.39 < z < 0.51 quasars from the
Large Bright Quasar Survey (LBQS). The LBQS quasars are representative of the
radio-quiet population, and this is the first look at their large-scale
environments. We compare the LBQS environments with the environments of 27 0.15
< z < 0.55 quasars selected from the HST Archive. The majority of the Archive
quasars are from the PG and PKS surveys, and these quasars are more luminous on
average than the LBQS. By comparing the LBQS and Archive environments, we
investigate whether previous quasar environment studies have been biased due to
studying unusually radio or optically luminous quasars. We detect a significant
excess of galaxies around the Archive quasars but find no such excess around
the LBQS quasars. We calculate the amplitude of the spatial correlation
function and find that the LBQS environments are consistent with that of the
typical galaxy while the Archive environments are slightly less rich than Abell
0 clusters. We find no difference between the environments of radio-loud and
radio-quiet quasars in either sample. However, comparison with previously
published work shows that the LBQS radio-loud quasars are in sparse
environments when compared with other radio-loud quasars, and the Archive
radio-quiet quasars are in dense environments compared to other radio-quiet
quasars. The richer environments of the Archive radio-quiet quasars can not be
explained by their higher optical luminosities.We find a positive correlation
(95%) between radio luminosity and environment for the radio-loud quasars. This
may explain why the LBQS radio-loud quasars, which are less radio luminous, are
in sparser environments.


title:
High-Resolution X-ray and Ultraviolet Spectroscopy of the Complex
  Intrinsic Absorption in NGC 4051 with Chandra and HST

abstract:
  We present the results from simultaneous observations of the Narrow-Line
Seyfert 1 galaxy NGC 4051 with the Chandra High Energy Transmission Grating
Spectrometer and the HST Space Telescope Imaging Spectrograph. The X-ray
grating spectrum reveals absorption and emission lines from hydrogen-like and
helium-like ions of O, Ne, Mg and Si. We resolve two distinct X-ray absorption
systems: a high-velocity blueshifted system at -2340+/-130 km/s and a
low-velocity blueshifted system at -600+/-130 km/s. In the UV spectrum we
detect strong absorption, mainly from C IV, N V and Si IV, that is resolved
into as many as nine different intrinsic absorption systems with velocities
between -650 km/s and 30 km/s. Although the low-velocity X-ray absorption is
consistent in velocity with many of the UV absorption systems, the
high-velocity X-ray absorption seems to have no UV counterpart. In addition to
the absorption and emission lines, we also observe rapid X-ray variability and
a state of low X-ray flux during the last ~15 ks of the observation. NGC 4051
has a soft X-ray excess which we fit in both the high and low X-ray flux
states. The high-resolution X-ray spectrum directly reveals that the soft
excess is not composed of narrow emission lines and that it has significant
spectral curvature. A power-law model fails to fit it, while a blackbody
produces a nearly acceptable fit. We compare the observed spectral variability
with the results of previous studies of NGC 4051.


title: Evolution in Binary and Triple Stars, with an application to SS Lac

abstract:
  We present equations governing the way in which both the orbit and the
intrinsic spins of stars in a close binary should evolve subject to a number of
perturbing forces, including the effect of a third body in a possibly inclined
wider orbit. We illustrate the solutions in some binary-star and triple-star
situations: tidal friction in a wide but eccentric orbit of a radio pulsar
about a B star, the Darwin and eccentricity instabilities in a more massive but
shorter-period massive X-ray binary, and the interaction of tidal friction with
Kozai cycles in a triple such as Algol (beta-Per), at an early stage in that
star's life when all 3 components were ZAMS stars. We also attempt to model in
some detail the interesting triple system SS Lac, which stopped eclipsing in
about 1950. We find that our model of SS Lac is quite constrained by the
relatively good observational data of this system, and leads to a specific
inclination (29 deg) of the outer orbit relative to the inner orbit at epoch
zero (1912). Although the intrinsic spins of the stars have little effect on
the orbit, the converse is not true: the spin axes can vary their orientation
relative to the close binary by up to 120 deg on a timescale of about a
century.


title:
The Formation of Stellar Clusters: Mass Spectra from Turbulent Molecular
  Cloud Fragmentation

abstract:
  Turbulent fragmentation determines where and when protostellar cores form,
and how they contract and grow in mass from the surrounding cloud material.
This process is investigated, using numerical models of self-gravitating
molecular cloud dynamics. Molecular cloud regions without turbulent driving
sources, or where turbulence is driven on large scales, exhibit rapid and
efficient star formation in a clustered mode, whereas interstellar turbulence
that carries most energy on small scales results in isolated star formation
with low efficiency. The clump mass spectrum of shock-generated density
fluctuations in pure hydrodynamic, supersonic turbulence is not well fit by a
power law, and it is too steep at the high-mass end to be in agreement with the
observational data. When gravity is included in the turbulence models, local
collapse occurs, and the spectrum extends towards larger masses as clumps merge
together, a power-law description dN/dM ~ M^nu becomes possible with slope nu <
-2. In the case of pure gravitational contraction, i.e. in regions without
turbulent support, the clump mass spectrum is shallower with nu = -3/2. The
mass spectrum of protostellar cores in regions without turbulent support and
where turbulence is replenished on large-scales, however, is well described by
a log-normal or by multiple power laws, similar to the stellar IMF at low and
intermediate masses. In the case of small-scale turbulence, the core mass
spectrum is too flat compared to the IMF for all masses.


title:
The Inverse Compton Emission Spectra in the Very Early Afterglows of
  Gamma-Ray Bursts

abstract:
  We calculate the spectra of inverse Compton (IC) emissions in gamma-ray burst
(GRB) shocks produced when relativistic ejecta encounters the external
interstellar medium, assuming a broken power-law approximation to the
synchrotron seed spectrum. Four IC processes, including the synchrotron
self-Compton (SSC) processes in GRB forward and reverse shocks, and two
combined-IC processes (i.e. scattering of reverse shock photons on the
electrons in forward shocks and forward shock photons on the electrons in
reverse shocks), are considered. We find that the SSC emission from reverse
shocks dominates over other emission processes in energy bands from tens of MeV
to tens of GeV, for a wide range of shock parameters. This mechanism may be
responsible for the prompt high energy gamma-rays detected by the Energetic
Gamma Ray Experiment Telescope (EGRET). At TeV energy bands, however, the
combined-IC emissions and/or the SSC emission from the forward shocks become
increasingly dominant for a moderately steep distribution of shocked electrons.


title:
Age Estimation of Extragalactic Globular Cluster Systems Using H beta
  Index

abstract:
  After taking into account, for the first time, the detailed systematic
variation of horizontal-branch (HB) morphology with age and metallicity, our
population synthesis models show that the integrated H beta index is
significantly affected by the presence of blue HB stars. Our models indicate
that the strength of the H beta index increases as much as 0.75 A due to blue
HB stars. According to our models, a systematic difference between the globular
cluster system in the Milky Way Galaxy and that in NGC 1399 in the H beta vs.
Mg2 diagram is understood if globular cluster systems in giant elliptical
galaxies are couple of billion years older, in the mean, than the Galactic
counterpart.


title:
Magnetohydrodynamic Simulations of Accretion Disks around a Weakly
  Magnetized Neutron Star in Strong Gravity

abstract:
  We carried out two dimensional high-resolution magnetohydrodynamic (MHD)
simulations of an accretion disk around a weakly magnetized neutron star.
General relativistic effects are taken into account by using pseudo-Newtonian
potential of Pacz\'{y}nski, B., P. J. Witta (1980). When magnetic loops connect
the neutron star and the accretion disk, the twist injection from the disk or
from the rotating neutron star triggers expansion of the loops. Since the
expanding magnetic loops prevent inflow toward the magnetic poles of the
neutron star, disk matter accumulates on the boundary between the magnetosphere
and the disk. Magnetic reconnection taking place in the loops creates a channel
along which the disk matter can accrete and unloads the magnetosphere. This
process produces quasi-periodic variation of the accretion flow in the
innermost region of the disk. We found two kinds of oscillations. One is the
magnetospheric oscillation regulated by magnetic reconnection. The other is the
radial disk oscillation. The typical frequency of the oscillations is 100 Hz to
2 kHz. Furthermore, we predict that QPO sources inevitably accompany X-ray
flares by magnetic reconnection and bipolar outflows of hot X-ray emitting
plasma similar to the optical jets in protostars.


title: GRB000615 in X-rays

abstract:
  GRB000615 was detected simultaneously by the BeppoSAX GRBM and WFC 1 with a
localization uncertainty of 2' (error circle radius). X-ray emission was
detected only in the 0.1-4 keV range during a NFI observation started about 10
hours after the trigger time. The positional and temporal analysis shows the
presence of two sources, one of which may be related to the GRB.


title: Smooth maps from clumpy data

abstract:
  We study an estimator for smoothing irregularly sampled data into a smooth
map. The estimator has been widely used in astronomy, owing to its low level of
noise; it involves a weight function -- or smoothing kernel -- w(\theta). We
show that this estimator is not unbiased, in the sense that the expectation
value of the smoothed map is not the underlying process convolved with $w$, but
a convolution with a modified kernel w_eff(\theta). We show how to calculate
w_eff for a given kernel w and investigate its properties. In particular, it is
found that (1) w_eff is normalized, (2) has a shape `similar' to the original
kernel w, (3) converges to w in the limit of high number density of data
points, and (4) reduces to a top-hat filter in the limit of very small number
density of data points. Hence, although the estimator is biased, the bias is
well understood analytically, and since w_eff has all the desired properties of
a smoothing kernel, the estimator is in fact very useful. We present explicit
examples for several filter functions which are commonly used, and provide a
series expression valid in the limit of large density of data points.


title: Structure and Mass of a Young Globular Cluster in NGC 6946

abstract:
  Using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope,
we have imaged a luminous young star cluster in the nearby spiral galaxy NGC
6946. The cluster has an absolute visual magnitude M(V)=-13.2, comparable to
the brightest young `super-star clusters' in the Antennae merger galaxy. UBV
colors indicate an age of about 15 Myr. The cluster has a compact core (core
radius = 1.3 pc), surrounded by an extended envelope. We estimate that the
effective radius (Reff) = 13 pc, but this number is uncertain because the outer
parts of the cluster profile gradually merge with the general field. Combined
with population synthesis models, the luminosity and age of the cluster imply a
mass of 8.2x10^5 Msun for a Salpeter IMF extending down to 0.1 Msun, or
5.5x10^5 Msun if the IMF is log-normal below 0.4 Msun. Depending on model
assumptions, the central density of the cluster is between 5300 Msun pc^-3 and
17000 Msun pc^-3, comparable to other high-density star forming regions. We
also estimate a dynamical mass for the cluster, using high-dispersion spectra
from the HIRES spectrograph on the Keck I telescope. The velocity dispersion is
10.0 +/- 2.7 km/s, implying a total cluster mass within 65 pc of (1.7 +/- 0.9)
x 10^6 Msun. Comparing the dynamical mass with the mass estimates based on the
photometry and population synthesis models, the mass-to-light ratio is at least
as high as for a Salpeter IMF extending down to 0.1 Msun, although a turn-over
in the IMF at 0.4 Msun is still possible within the errors. The cluster will
presumably remain bound, evolving into a globular cluster-like object.


title: Gamma-Ray Bursts - When Theory Meets Observations

abstract:
  Gamma-Ray Bursts (GRBs) are the brightest objects observed. They are also the
most relativistic objects known so far. GRBs occur when an ultrarelativisitic
ejecta is slowed down by internal shocks within the flow. Relativistic
particles accelerated within these shocks emit the observed gamma-rays by a
combination of synchrotron and inverse Compton emission. External shocks with
the circumstellar matter slow down further the ejecta and produce the
afterglow, which lasts for months. Comparison of the predictions of this
fireball model with observations confirm a relativistic macroscopic motion with
a Lorentz factor of $\Gamma \ge 100$. Breaks in the light curves of the
afterglow indicate that GRBs are beamed with typical opening angles of a few
degrees. The temporal variability of the gamma-rays signal provide us with the
best indirect evidence on the nature of the ``internal engine'' that powers the
GRBs and accelerates the relativistic ejecta, suggesting accretion of a massive
disk onto a newborn black hole: GRBs are the birth cries of these black holes.
Two of the most promising models: Neutron Star Mergers and Collapars lead
naturally to this scenario.


title:
NICS-TNG low-resolution 0.85-2.45um spectra of L-Dwarfs: a near-infrared
  spectral classification scheme for faint dwarfs

abstract:
  We present complete near-infrared (0.85-2.45 um), low-resolution (~100)
spectra of a sample of 26 disk L-dwarfs with reliable optical spectral type
classification. The observations have been obtained with NICS at the TNG using
a prism-based optical element (the Amici device) that provides a complete
spectrum of the source on the detector. Our observations show that
low-resolution near-infrared spectroscopy can be used to determine the spectral
classification of L-dwarfs in a fast but accurate way. We present a library of
spectra that can be used as templates for spectral classification of faint
dwarfs. We also discuss a set of near-infrared spectral indices well correlated
with the optical spectral types that can be used to accurately classify
L-dwarfs earlier than L6.


title: The Observed Trend of Boron and Oxygen in Field Stars of the Disk

abstract:
  Oxygen abundances are derived in a sample of 13 field F and G dwarfs and
subgiants with metallicities in the range of -0.75 < [Fe/H] < +0.15. This is
the same sample of stars for which boron abundances have been derived earlier
from archived spectra obtained with the Hubble Space Telescope. In a log-log
comparison of the B versus the O abundances, a slope of m(BO)=1.39 is found,
indicating that in the disk, the abundance of B relative to O is intermediate
between primary and secondary production (hybrid behavior). This relation of B
versus O for disk stars is compared to the same relation for halo stars.


title: Exploiting VSIPL and OpenMP for Parallel Image Processing

abstract:
  VSIPL and OpenMP are two open standards for portable high performance
computing. VSIPL delivers optimized single processor performance while OpenMP
provides a low overhead mechanism for executing thread based parallelism on
shared memory systems. Image processing is one of the main areas where VSIPL
and OpenMP can make a large impact. Currently, a large fraction of image
processing applications are written in the Interpreted Data Language (IDL)
environment. The aim of this work is to demonstrate that the performance
benefits of these new standards can be brought to image processing community in
a high level manner that is transparent to users. To this end, this talk
presents a fast, FFT based algorithm for performing image convolutions. This
algorithm has been implemented within the IDL environment using VSIPL (for
optimized single processor performance) with added OpenMP directives (for
parallelism). This work demonstrates that good parallel speedups are attainable
using standards and can be integrated seamlessly into existing user
environments.


title: Magneto-Fluid Coupling - Eruptive Events in the Solar Corona

abstract:
  By modelling the coronal structures by "slowly" evolving Double-Beltrami
two-fluid equilibria (created by the interaction of the magnetic and velocity
fields), the conditions for catastrophic transformations of the original state
are derived. It is shown that, at the transition, much of the magnetic energy
of the original state is converted to the the flow kinetic energy.


title:
Observational tests of the delta_c-M_vir relation in hierarchical
  clustering models

abstract:
  Observational determinations of the correlation between the characteristic
density delta_c and the virial mass M_vir of dark halos constitute a critical
test for models of hierarchical structure formation. Using the dynamical
properties of dark halos reconstructed from the galaxy distributions in massive
systems (groups/clusters) and the rotation curves in less massive systems
(dwarf, low surface brightness and spiral galaxies) drawn from the literature,
we confirm the existence of the delta_c-M_vir relation over a broad mass range
from 10**10 to 10**15 solar masses, which is in gross consistency with the
prediction of a flat cosmological model with Omega_M=0.3 and Omega_Lambda=0.7.
It is pointed out that previous analyses based on the measurements of X-ray
emitting gas and the hydrostatic equilibrium hypothesis, which claimed a
shallower scale-free spectrum of n=-1 for initial density fluctuations, may
suffer from nongravitational heating influence especially in low-mass systems.


title:
Imaging of detached shells around the carbon stars R Scl and U Ant
  through scattered stellar light

abstract:
  We present the first optical images of scattered light from large, detached
gas/dust shells around two carbon stars, R Scl and U Ant, obtained in narrow
band filters centred on the resonance lines of neutral K and Na, and in a Str.
b filter (only U Ant). They confirm results obtained in CO radio line
observations, but also reveal new and interesting structures. Towards R Scl the
scattering appears optically thick in both the K and Na filters, and both
images outline almost perfectly circular disks with essentially uniform
intensity out to a sharp outer radius of 21". These disks are larger -- by
about a factor of two -- than the radius of the detached shell which has been
marginally resolved in CO radio line data. In U Ant the scattering in the K
filter appears to be, at least partially, optically thin, and the image is
consistent with scattering in a geometrically thin (3") shell (radius 43") with
an overall spherical symmetry. The size of this shell agrees very well with
that of the detached shell seen in CO radio line emission. The scattering in
the Na filter appears more optically thick, and the image suggests the presence
of at least one, possibly two, shells inside the 43" shell. There is no
evidence for such a multiple-shell structure in the CO data, but this can be
due to considerably lower masses for these inner shells. Weak scattering
appears also in a shell which is located outside the 43" shell. The present
data do not allow us to conclusively identify the scattering agent, but we
argue that most of the emission in the K and Na filter images is to due to
resonance line scattering, and that there is also a weaker contribution from
dust scattering in the U Ant data. Awaiting new observational data, our
interpretation must be regarded as tentative.


title:
Analyses of Type Ia Supernova Data in Cosmological Models with a Local
  Void

abstract:
  The data of type Ia supernovae observed by the High-z SN Search Team and
Supernova Cosmology Project are analyzed in inhomogeneous cosmological models
with a local void on scales of about 200 Mpc, to derive the best-fit values of
model parameters and the confidence contours. The $\chi^2$ fitting is found to
be slightly better than that in homogeneous models. It is shown that (1) the
best-fit values are most sensitive to the ratio $R$ of the outer Hubble
constant ($H_0^{\rm II}$) to the inner Hubble constant ($H_0^{\rm I}$), (2) the
best-fit outer density parameter ($\Omega_0^{\rm II}$) (and cosmological
constant parameter ($\lambda_0^{\rm II}$)) increases (and decreases) with the
increase of $R$, respectively, and (3) $(\Omega_0^{\rm II}, \lambda_0^{\rm
II})$ can be $(1, 0)$ for $R \approx 0.8$. Moreover it is shown that these
models may be naturally consistent with the new supernova data (SN1997ff) for
$z = 1.7$.


title:
The distance to galactic globular clusters through RR Lyrae pulsational
  properties

abstract:
  By adopting the same approach outlined in De Santis & Cassisi (1999), we
evaluate the absolute bolometric magnitude of the Zero Age Horizontal Branch
(ZAHB) at the level of the RR Lyrae variable instability strip in selected
galactic globular clusters. This allows us to estimate the ZAHB absolute visual
magnitude for these clusters and to investigate its dependence on the cluster
metallicity. The derived $M_V(ZAHB) - [Fe/H]$ relation, corrected in order to
account for the luminosity difference between the ZAHB and the mean RR Lyrae
magnitude, has been compared with some of the most recent empirical
determinations in this field, as the one provided by Baade-Wesselink analyses,
RR Lyrae periods, Hipparcos data for field variables and Main Sequence fitting
based on Hipparcos parallaxes for field subdwarfs. As a result, our relation
provides a clear support to the "long" distance scale. We discuss also another
method for measuring the distance to galactic globular clusters. This method is
quite similar to the one adopted for estimating the absolute bolometric
magnitude of the ZAHB but it relies only on the pulsational properties of the
Lyrae variables in each cluster. The reliability and accuracy of this method
has been tested by applying it to a sample of globulars for which, due to the
morphology of their horizontal branch (HB), the use of the commonly adopted
ZAHB fitting is a risky procedure.


title:
Gamma Ray and Hadron generated \v{C}erenkov Photon Spectra at Various
  Observation Altitudes

abstract:
  We study the propagation of Cerenkov photons generated by Very High Energy
gamma-rays and hadrons in the atmosphere. The photon production height
distributions are estimated from semi-empirical methods and compared with those
derived by standard simulation techniques. Incident spectra at various
observation altitudes are then derived after applying wavelength dependent
corrections due to photon attenuation in the atmosphere during the propagation
of photons from the height of production to the height of observation. These
are generated both for gamma- and hadron primaries of various energies. The
derived production height distributions agree very well with those generated by
the simulation package `CORSIKA' at all energies and for both gamma-$ray and
proton primaries. The incident photon spectra are found to be both altitude
dependent and primary energy dependent. The peak of the incident spectrum
shifts towards the shorter wavelength with increasing altitude of observation
for a given primary. Also the peak of the photon spectrum shifts towards the
shorter wavelength with increasing energy of the primary at given altitude. The
fraction of the UV component in the incident Cerenkov spectrum is estimated
both for gamma-ray and hadronic primaries at various observation altitudes and
energies. Hadron generated Cerenkov spectra are marginally richer in UV light
and the difference increases slightly at higher altitudes. The fraction of the
UV to the visible light in the Cerenkov spectrum could be a useful parameter to
separate gamma-rays from cosmic ray background only if one can measure this
fraction very accurately.


title: The aromatic infrared bands as seen by ISO-SWS: probing the PAH model

abstract:
  We discuss the Aromatic Infrared Band (AIB) profiles observed by ISO-SWS
towards a number of bright interstellar regions where dense molecular gas is
illuminated by stellar radiation. Our sample spans a broad range of excitation
conditions (exciting radiation fields with effective temperature, Teff, ranging
from 23,000 to 45,000 K). The SWS spectra are decomposed coherently in our
sample into Lorentz profiles and a broadband continuum. We find that the
individual profiles of the main AIBs at 3.3, 6.2, 8.6 and 11.3 microns are well
represented with at most two lorentzians. Furthermore, we show that the
positions and widths of these AIBs are remarkably stable (within a few cm-1).
We then extract the profiles of individual AIBs from the data and compare them
to a model of Polycyclic Aromatic Hydrocarbon (PAH) cation emission which
includes the temperature dependence of the AIB profiles. The present similarity
of the AIB profiles requires that the PAH temperature distribution remains
roughly the same whatever the radiation field hardness. Deriving the
temperature distribution of interstellar PAHs, we show that its hot tail, which
controls the AIB spectrum, sensitively depends on Nmin (the number of C-atoms
in the smallest PAH) and Teff. Comparing the observed profiles of the
individual AIBs to our model results, we can match most of the AIB profiles if
Nmin is increased with Teff. We then discuss our results in the broader context
of ISO observations of fainter interstellar regions where PAHs are expected to
be in neutral form.


title: The O II Recombination Line Abundance Problem in Planetary Nebulae

abstract:
  We present new observations of O II recombination lines in ten bright
planetary nebulae, along with spatially-resolved measurements of O II and [O
III] in the Ring nebula NGC 6720, to study the discrepancy between abundances
derived from O II recombination lines and those derived from
collisionally-excited [O III]. We see a large range in the difference between O
II- and [O III] derived abundances, from no difference up to a factor six
difference. The size of this discrepancy is anti-correlated with nebular
surface brightness; compact, high-surface-brightness nebulae have the smallest
discrepancies. O II levels that are populated mainly by dielectronic
recombination give larger abundances than other levels. Finally, our long-slit
observation of the Ring nebula shows that the O II emission peaks interior to
the bright shell where [O III] and H-beta are strongest. Based on the observed
correlations, we propose that the strong recombination line emission in
planetary nebulae is a result of enhanced dielectronic recombination in hot gas
in the nebular interior, perhaps driven by a hot stellar wind.


title:
Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission I. Curvature
  Radiation Pair Fronts

abstract:
  We investigate the effect of pulsar polar cap (PC) heating produced by
positrons returning from the upper pair formation front. Our calculations are
based on a self-consistent treatment of the pair dynamics and the effect of
electric field screening by the returning positrons. We calculate the resultant
X-ray luminosities, and discuss the dependence of the PC heating efficiencies
on pulsar parameters, such as characteristic spin-down age, spin period, and
surface magnetic field strength. In this study we concentrate on the regime
where the pairs are produced in a magnetic field by curvature photons emitted
by accelerating electrons. Our theoretical results are not in conflict with the
available observational X-ray data and suggest that the effect of PC heating
should significantly contribute to the thermal X-ray fluxes from middle-aged
and old pulsars. The implications for current and future X-ray observations of
pulsars are briefly outlined.


title: Discovery of strong CIV absorption in the highest redshift quasar

abstract:
  We report the near-IR detection of a prominent CIV absorption in the
rest-frame UV spectrum of the most distant known QSO, SDSS J104433.04-012502.2,
at z=5.80. This QSO was recently observed with XMM-Newton and it was found to
be notably X-ray weak. The equivalent width of the CIV absorption feature (~10
A) strongly supports the idea that the X-ray faintness of this QSO is due to
heavy absorption by gas with a column density N_H > 10^{24} cm^-2. The shape of
the CIV feature suggests that this is a Broad Absorption Line QSO. Although
absorbed by a huge column of gas, the observed continuum in the 0.9-2.4um range
(~1300-3500 A rest frame) exactly matches the template of unabsorbed QSOs
without invoking any reddening (E(B-V)<0.08 mag), indicating that dust in the
absorbing gas is either absent or composed of large grains.


title: Nickel Mixing in the Outer Layers of SN 1987A

abstract:
  Supernova 1987A remains the most well-observed and well-studied supernova to
date. Observations produced excellent broad-band photometric and spectroscopic
coverage over a wide wavelength range at all epochs. Here, we focus on the very
early spectroscopic observations. Only recently have numerical models been of
sufficient detail to accurately explain the observed spectra. In SN 1987A, good
agreement has been found between observed and synthetic spectra for day one,
but by day four, the predicted Balmer lines become much weaker than the
observed lines. We present the results of work based on a
radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE
spectra generated from this model by the general radiation transfer code
PHOENIX strongly support the theory that significant mixing of nickel into the
outer envelope is required to maintain strong Balmer lines. Preliminary results
suggest a lower limit to the average nickel mass of 1.0 \times 10^{-5} solar
masses is required above 5000 \kmps by day four. PHOENIX models thus have the
potential to be a sensitive probe for nickel mixing in the outer layers of a
supernova.


title: ASCA Detection of Pulsed X-ray Emission from PSR J0631+1036

abstract:
  ASCA's long look at the 288 millisecond radio pulsar, PSR J0631+1036, reveals
coherent X-ray pulsation from this source for the first time. The source was
first detected in the serendipitous Einstein observation and later identified
as a radio pulsar. Possible pulsation in the gamma-ray band has been detected
from the CGRO EGRET data (Zepka, et al. 1996). The X-ray spectrum in the ASCA
band is characterized by a hard power-law type emission with a photon index of
about 2.3, when fitted with a single power-law function modified with
absorption. An additional blackbody component of about 0.14 keV increases the
quality of the spectral fit. The observed X-ray flux is 2.1e-13 ergs/s/cm2 in
the 1-10 keV band. We find that many characteristics of PSR J0631+1036 are
similar to those of middle-aged gamma-ray pulsars such as PSR B1055-52, PSR
B0633+17 (Geminga), and PSR B0656+14.


title:
Photoelectric effect on dust grains across the L1721 cloud in the rho
  Ophiuchi molecular complex

abstract:
  We present ISO-LWS measurements of the main gas cooling lines, C+ 158 mum and
O 63 mum towards a moderate opacity molecular cloud (Av=3), L1721, illuminated
by the B2 star nu Sco (X = 5-10). These data are combined with an extinction
map and IRAS dust emission images to test our understanding of gas heating and
cooling in photo-dissociation regions (PDRs). This nearby PDR is spatially
resolved in the IRAS images; variations in the IRAS colors across the cloud
indicate an enhanced abundance of small dust grains within the PDR. A spatial
correlation between the gas cooling lines and the infrared emission from small
dust grains illustrates the dominant role of small dust grains in the gas
heating through the photoelectric effect. The photoelectric efficiency,
determined from the observations by ratioing the power radiated by gas and
small dust grains, is in the range 2 to 3% in close agreement with recent
theoretical estimates. The brightness profiles across the PDR in the C+ 158 mum
and O 63 mum lines are compared with model calculations where the density
profile is constrained by the extinction data and where the gas chemical and
thermal balances are solved at each position. We show that abundance variations
of small dust grains across the PDR must be considered to account for the LWS
observations.


title: A spectrophotometric atlas of Narrow-Line Seyfert 1 galaxies

abstract:
  We have compiled a list of 83 objects classified as Narrow-Line Seyfert 1
galaxies (NLS1s) or known to have a broad Balmer component narrower than 2000
km/s. Out of these, 19 turned out to have been spectroscopically misidentified
in previous studies; only 64 of the selected objects are genuine NLS1s. We have
spectroscopically observed 59 of them and tried to characterize their Narrow
and Broad-Line Regions (NLR and BLR) by fitting the emission-lines with
Gaussian and/or Lorentzian profiles. In most cases, the broad Balmer components
are well fitted by a single Lorentzian profile. This has consequences
concerning their FWHMs and line ratios: when the broad Balmer components are
fitted with a Lorentzian, most narrow line regions have line ratios typical of
Seyfert 2s while, when a Gaussian profile isused for fitting the broad Balmer
components, the line ratios are widely scattered in the usual diagnostic
diagrams (Veilleux & Osterbrock 1987). We find that, in general, the [O III]
lines have a relatively narrow Gaussian profile (~ 200-500 km/s FWHM) with
often, in addition, a second broad (~ 500-1800 km/s FWHM), blueshifted Gaussian
component. We do not confirm that the [O III] lines are weak in NLS1s. As
previously suggested, there is a continuous transition of all properties
between NLS1s and classical Broad-Line Seyfert 1 Galaxies (BLS1s) and the limit
of 2000 km/s used to separate the two species is arbitrary; R_4570, the ratio
of the Fe II to the H_beta fluxes, could be a physically more meaningful
parameter to distinguish them. (abridged abstract)


title:
An efficient parallel tree-code for the simulation of self-gravitating
  systems

abstract:
  We describe a parallel version of our tree-code for the simulation of
self-gravitating systems in Astrophysics. It is based on a dynamic and adaptive
method for the domain decomposition, which exploits the hierarchical data
arrangement used by the tree-code. It shows low computational costs for the
parallelization overhead -- less than 4% of the total CPU-time in the tests
done -- because the domain decomposition is performed 'on the fly' during the
tree setting and the portion of the tree that is local to each processor
'enriches' itself of remote data only when they are actually needed.
  The performances of an implementation of the parallel code on a Cray T3E are
presented and discussed. They exhibit a very good behaviour of the speedup (=15
with 16 processors and 10^5 particles) and a rather low load unbalancing (< 10%
using up to 16 processors), achieving a high computation speed in the forces
evaluation (>10^4 particles/sec with 8 processors).


title:
A Brown Dwarf Companion for the Accreting Millisecond Pulsar SAX
  J1808.4-3658

abstract:
  BeppoSAX has revealed a population of faint neutron star X-ray transients in
the Galactic bulge. King conjectured that these neutron stars are accreting
from brown dwarfs (BD) with a time-averaged mass transfer rate <\dot M>\approx
10^{-11} M_sun/year. We show that the orbital parameters of the 401 Hz
accreting millisecond pulsar SAX J1808.4-3658 support this hypothesis. A
main-sequence mass donor requires a nearly face-on inclination and a higher
<\dot M> than observed. However, the range of allowed inclinations is
substantially relaxed and the predicted mass transfer rate is consistent with
that observed if a hot 0.05 M_sun BD is the donor. We then explain the BD
radius required (0.13 R_\sun) to fill the Roche lobe. All transiently accreting
neutron stars have a minimum luminosity in quiescence set by the time-averaged
mass transfer rate onto the neutron star. We show that the constant heating of
the BD by this emission can maintain the higher entropy implied by a 0.13
R_\sun radius. Our work bolsters the case that SAX J1808.4-3658 is a progenitor
to compact ms radio pulsar binaries (e.g. like those found in 47 Tuc). The very
low <\dot M>'s implies that the progenitors to these radio pulsars are
long-lived (Gyrs) transient systems, rather than short-lived (Myrs)
Eddington-limited accretors. Hence, the accreting progenitor population to
millisecond radio pulsars in 47 Tuc could still be present and found in
quiescence with Chandra.(abridged)


title: Late AGB Magnetic Cycles: MHD Solutions for the HST PN Rings

abstract:
  The Hubble Space Telescope has revealed the existence of multiple, regularly
spaced, and faint concentric shells around some planetary nebulae. Here we
present 2(1/2)D magnetohydrodinamic numerical simulations of the effects of a
solar-like magnetic cycle, with periodic polarity inversions, in the slow wind
of an AGB star. The stellar wind is modeled with a steady mass-loss at constant
velocity. This simple version of a solar-like cycle, without mass-loss
variations, is able to reproduce many properties of the observed concentric
rings. The shells are formed by pressure oscillations, which drive compressions
in the magnetized wind. These pressure oscillations are due to periodic
variations in the field intensity. The periodicity of the shells, then, is
simply a half of the magnetic cycle since each shell is formed when the
magnetic pressure goes to zero during the polarity inversion. As a consequence
of the steady mass-loss rate, the density of the shells scales as $r^{-2}$, and
their surface brightness has a steeper drop-off, as observed in the shells of
NGC 6543, the best documented case of these HST rings. Deviations from
sphericity can be generated by changing the strength of the magnetic field. For
sufficiently strong fields, a series of symmetric and equisdistant blobs are
formed at the polar axis, resembling the ones observed in He 2-90. These blobs
are originated by magnetic collimation within the expanding AGB wind.


title: Luminosity Evolution of Field Early-Type Galaxies to z=0.55

abstract:
  We study the Fundamental Plane of field early-type galaxies at intermediate
redshift, using HST WFPC2 observations and deep Keck spectroscopy. Structural
parameters and internal velocity dispersions are measured for eighteen galaxies
at 0.15 < z < 0.55. Rest frame M/L_B ratios are determined from the Fundamental
Plane and compared to those of cluster early-type galaxies at the same
redshifts. The systematic offset between M/L ratios of field and cluster
early-type galaxies at intermediate redshift is small, and not significant: <ln
M/L_B>(field) - <ln M/L_B>(cluster) = -0.18 +- 0.11. The M/L ratios of field
early-type galaxies evolve as \Delta (ln M/L_B) = (-1.35 +- 0.35) z, very
similar to cluster early-type galaxies. After correcting for luminosity
evolution, the FP of field early-type galaxies has a scatter 0.09 +- 0.02 in
log r_e, similar to that in local clusters. The scatter appears to be driven by
low mass S0 galaxies; for the elliptical galaxies alone we find 0.03 +- 0.03.
There is a hint that the FP has a different slope than in clusters, but more
data are needed to confirm this. The similarity of the M/L ratios of cluster
and field early-type galaxies provides a constraint on the relative ages of
their stars. At <z> = 0.43, field early-type galaxies are younger than cluster
early-type galaxies by only 21 +- 13 %, and we infer that the stars in field
early-type galaxies probably formed at z >~ 1.5. Recent semi-analytical models
for galaxy formation in a Lambda-CDM Universe predict a systematic difference
between field and cluster galaxies of \Delta (ln M/L_B) ~ -0.6, much larger
than the observed difference. This result is consistent with the hypothesis
that field early-type galaxies formed earlier than predicted by these models.


title:
SN1993J VLBI (I): The Center of the Explosion and a Limit on Anisotropic
  Expansion

abstract:
  Phase-referenced VLBI observations of supernova 1993J at 24 epochs, from 50
days after shock breakout to the present, allowed us to determine the
coordinates of the explosion center relative to the quasi-stationary core of
the host galaxy M81 with an accuracy of 45 micro-arcsec, and to determine the
nominal proper motion of the geometric center of the radio shell with an
accuracy of 9micro-arcsec/yr. The uncertainties correspond to 160 AU for the
position and 160 km/s for the proper motion at the distance of the source of
3.63 Mpc. After correcting for the expected galactic proper motion of the
supernova around the core of M81 using HI rotation curves, we obtain a peculiar
proper motion of the radio shell center of only 320 +/- 160 km/s to the south,
which limits any possible one-sided expansion of the shell. We also find that
the shell is highly circular, the outer contours in fact being circular to
within 3%. Combining our proper motion values with the degree of circular
symmetry, we find that the expansion of the shockfront from the explosion
center is isotropic to within 5.5% in the plane of the sky. This is a more
fundamental result on isotropic expansion than can be derived from the
circularity of the images alone. The brightness of the radio shell, however,
varies along the ridge and systematically changes with time. The degree of
isotropy in the expansion of the shockfront contrasts with the asymmetries and
polarization found in optical spectral lines. Asymmetric density distributions
in the ejecta or more likely in the circumstellar medium, are favored to
reconcile the radio and optical results. We see no sign of any disk-like
density distribution of the circumstellar material, with the average axis ratio
of the radio shell of SN1993J being less than 1.04.


title:
On the lack of cold dust in IRAS P09104+4109 and IRAS F15307+3252 --
  their spectral energy distributions and implications for finding dusty AGNs
  at high redshift

abstract:
  We present upper limits on the 850 micron and 450 micron fluxes of the warm
hyperluminous (bolometric luminosity L_bol > 10^13 L_sun galaxies IRAS
P09104+4109 (z=0.442) and IRAS F15307+3252 (z=0.926), derived from measurements
using the SCUBA bolometer array on the James Clerk Maxwell Telescope. Hot
luminous infrared sources like these are thought to differ from more normal
cold ultraluminous infrared (L_bol > 10^12 L_sun) galaxies in that they derive
most of their bolometric luminosities from dusty AGNs as opposed to starbursts.
Such hot, dusty AGNs at high redshift are thought to be responsible for much of
the mass accretion of the Universe that is in turn responsible for the
formation of the supermassive black holes seen in the centres of local
galaxies. The galaxy IRAS P09104+4109 is also unusual in that it is a cD galaxy
in the center of a substantial cooling-flow cluster, not an isolated
interacting galaxy like most ultraluminous infrared galaxies. Previously it was
known to have large amounts of hot (T > 50 K) dust from IRAS observations. We
now show that the contribution of cold dust to the bolometric luminosity is
less than 3 per cent. Most ultraluminous infrared galaxies possess large
amounts of cold dust, and it is now known that some cooling flow cluster cD
galaxies do as well. Yet this object, which is an extreme example of both, does
not have enough cold gas to contribute significantly to the bolometric
luminosity. We outline physical reasons why this could have happened. We then
provide a discussion of stategies for finding hot dusty AGNs, given the
limitations on submillimetre surveys implied by this work.


title: Dust to Dust: Evidence for Planet Formation?

abstract:
  We discuss the properties of several circumstellar debris disk systems imaged
with the Hubble Space Telescope's Near Infrared Camera and Multi-Object
Spectrometer in a survey of young stars with known far-IR excesses. These dusty
disks around young ($\sim$ 5--8 Myr) unembedded stars exhibit morphological
anisotropies and other characteristics which are suggestive of recent or
on-going planet formation. We consider evidence for the evolution of
populations of collisionally produced disk grains in light of the significant
presence of remnant primordial gas in the optically thick disk of the classical
T-Tauri star TW Hya; the dust-dominated and Kuiper-belt like circumstellar ring
about the young main-sequence star HR 4796A; and a possible ``intermediate''
case, the complex disk around the Herbig AeBe star HD 141569A. Only a small
number of debris disks have been imaged thus far in scattered light. Yet all
show structures that may be indicative of dust reprocessing, possibly as a
result of planet formation, and speak to the contemporary competing scenarios
of disk/planet evolution and formation time scales.


title:
Serendipitous discovery of a cluster of galaxies with a peculiar central
  galaxy

abstract:
  We report the serendipitous discovery of a cluster of galaxies at z=0.369.
Thirty-eight candidate members were identified based on rough broad-band
photometric redshifts, and three members were confirmed spectroscopically. The
brightest cluster galaxy (BCG) is exceptionally blue, with B-V=0.12 and
V-I=1.02. The surface-brightness profile of the BCG follows an r^(1/4)-law
profile out to 3" in all three bands. The effective radius is significantly
smaller in bluer bandpasses, resulting in a blue core and a color gradient
opposite to the metallicity-induced color gradient observed in typical
elliptical galaxies. Beyond 3" an extended envelope of emission in excess of
the r^(1/4)-law profile is observed, the position angle of which coincides with
the major axis of the galaxy cluster. The spectrum of the BCG contains strong
Balmer absorption, a minimal 4000 A break, and a broad Mg II emission line,
suggesting that the galaxy has undergone recent star formation and may harbor a
central AGN. The presence of numerous nearby bright stars makes this cluster an
interesting target for next-generation adaptive optics using natural guide
stars.


title: Dwarf spheroidals with tidal tails and structure formation

abstract:
  Recent N-Body simulations have shown that dIrrs evolve into dSphs owing to
the strong tidal perturbation of the Milky Way. Satellites whose dark matter
halos have a core or an NFW profile with a concentration $c < 5$ undergo severe
stripping even on low eccentricity orbits and their remnants have projected
stellar profiles that become flat at large radii as observed in some of the
dSphs. Satellites with higher central densities, as predicted by CDM models,
are more robust to tides and can reproduce the observations only on nearly
radial orbits. Accurate proper motions for LG dSphs will allow to test current
models of structure formation.


title: Chandra Detection of the Forward and Reverse Shocks in Cassiopeia-A

abstract:
  We report the localization of the forward and reversed shock fronts in the
young supernova remnant Cas-A using X-ray data obtained with the Chandra
Observatory. High resolution X-ray maps resolve a previously unseen X-ray
feature encompassing the extremity of the remnant. This feature consists of
thin, tangential wisps of emission bordering the outer edge of the thermal
X-ray and radio remnant, forming a circular rim, approx. 2.7 in radius. Radio
images show a sharp rise in brightness at this X-ray rim, along with a large
jump in the synchrotron polarization angle. These characteristics suggest that
these wisps are the previously unresolved signature of the forward, or outer,
shock. Similarly, we identify the sharp rise in emissivity of the bright shell
for both the radio and X-ray line emission associated with the reverse shock.
The derived ratio of the averaged forward and reverse shock radii of approx.
3:2 constrains the remnant to have swept up roughly the same amount of mass as
was ejected; this suggests that Cas-A is just entering the Sedov phase.
Comparison of the X-ray spectra from the two shock regions shows that the
equivalent widths of prominent emission lines are significantly lower exterior
to the bright shell, as expected if they are respectively identified with the
shocked circumstellar material and shocked ejecta. Furthermore, the spectrum of
the outer rim itself is dominated by power-law emission, likely the counterpart
of the non-thermal component previously seen at energies above 10 keV.


title: Early-universe constraints on a Primordial Scaling Field

abstract:
  In the past years 'quintessence' models have been considered which can
produce the accelerated expansion in the universe suggested by recent
astronomical observations. One of the key differences between quintessence and
a cosmological constant is that the energy density in quintessence,
$\Omega_\phi$, could be a significant fraction of the overall energy even in
the early universe, while the cosmological constant will be dynamically
relevant only at late times. We use standard Big Bang Nucleosynthesis and the
observed abundances of primordial nuclides to put constraints on $\Omega_\phi$
at temperatures near $T \sim 1MeV$. We point out that current experimental data
does not support the presence of such a field, providing the strong constraint
$\Omega_\phi(MeV) < 0.045$ at $2\sigma$ C.L. and strengthening previous
results. We also consider the effect a scaling field has on CMB anisotropies
using the recent data from Boomerang and DASI, providing the CMB constraint
$\Omega_\phi \le 0.39$ at $2\sigma$ during the radiation dominated epoch.


title:
The CFHT Open Star Cluster Survey I -- Cluster Selection and Data
  Reduction

abstract:
  We present this paper in conjuction with the following as the first results
in the CFHT Open Star Cluster Survey. This survey is a large BVR imaging data
set of 19 open star clusters in our Galaxy. This data set was taken with the
CFH12K mosaic CCD (42' X 28') and the majority of the clusters were imaged
under excellent photometric, sub-arcsecond seeing conditions. The combination
of multiple exposures extending to deep (V ~ 25) magnitudes with short (< 10
second) frames allows for many different studies. The primary aim of this
survey is to catalogue the white dwarf stars in these clusters and establish
observational constraints on the initial-final mass relationship for these
stars and the upper mass limit to white dwarf production. Additionally, we hope
to better determine the properties of the clusters, such as age and distance,
and also test evolution and dynamical theories by analyzing luminosity and mass
functions. In order to more easily incorporate this data in further studies, we
have produced a catalogue of positions, magnitudes, colors, and stellarity
confidence for all stars in each cluster of the survey. This paper is intended
both as a source for the astronomical community to obtain information on the
clusters in the survey and as a detailed reference of reduction procedures for
further publications of individual clusters. We discuss the methods employed to
reduce the data and compute the photometric catalogue. The scientific results
for each individual cluster and global results from the study of the entire
survey will be presented in further publications (results for the rich old open
cluster NGC 6819 immediately follow this paper).


title:
The CFHT Open Star Cluster Survey II -- Deep CCD Photometry of the Old
  Open Star Cluster NGC 6819

abstract:
  We present analysis of deep CCD photometry for the very rich, old open star
cluster NGC 6819. These CFH12K data results represent the first of nineteen
open star clusters which were imaged as a part of the CFHT Open Star Cluster
Survey. We find a tight, very rich, main-sequence and turn-off consisting of
over 2900 cluster stars in the V, B-V color-magnitude diagram (CMD).
Main-sequence fitting of the un-evolved cluster stars with the Hyades star
cluster yields a distance modulus of (m-M)v = 12.30 +/- 0.12, for a reddening
of E(B-V) = 0.10. These values are consistent with a newly calculated
theoretical stellar isochrone of age 2.5 Gyrs, which we take to be the age of
the cluster. Detailed star counts indicate a much larger cluster extent (R =
9.5' +/- 1.0'), by a factor of ~2 over some previous estimates. Incompleteness
tests confirm a slightly negatively sloped luminosity function extending to
faint (V ~ 23) magnitudes which is indicative of a dynamically evolved cluster.
Further luminosity function and mass segregation tests indicate that low mass
objects (M < 0.65Mo) predominate in the outer regions of the cluster, 3.5 < R <
9.5. The estimation of the number of white dwarfs in NGC 6819 are in good
agreement with the observed number. For those white dwarf candidates which pass
both a statistical and image classification tests, we show comparisons to white
dwarf isochrones and cooling models which suggest the need for spectroscopy to
confirm the white dwarf nature of the brighter objects.


title:
Bounds on the neutrino flux from cosmic sources of relativistic
  particles

abstract:
  In order to facilitate the identification of possible new physics signatures
in neutrino telescopes, such as neutrinos from the annihilation of neutralinos
or decaying relics, it is essential to gain full control over the astrophysical
inventory of neutrino sources in the Universe. The total available accretion
power, the extragalactic gamma ray background, and the cosmic ray proton
intensity can be used to constrain astrophysical models of neutrino production
in extragalactic sources. The resulting upper limit on the extragalactic muon
neutrino intensity from cosmic particle accelerators combined with a reasonable
minimum intensity of neutrinos due to cosmic rays stored in clusters of
galaxies demark a zone of opportunity for neutrino astronomy over a broad range
of energies between 100 MeV and 1 EeV. Discovery of this neutrino background
would open a new era for astronomy and provide the first un-obscured view to
the early Universe.