title: Stereo Imaging of the VHE Gamma-Rays with HEGRA and H.E.S.S

abstract:
  At present, the ground-based astronomy of very high energy (VHE) (E>100 GeV)
gamma-rays experiences the challenging transition phase caused by the
substantial upgrading of its observational instrumentation. Recently the HEGRA
collaboration has evidently demonstrated the power of arrays of imaging
atmospheric Cherenkov telescopes and initiated a number of complementary
projects, such as H.E.S.S., CANGAROO IV, VERITAS. The common philosophy of
those projects is based on the stereoscopic observations of air showers with a
number of imaging telescopes simultaneously. Such observations allow to reduce
substantially the effective energy threshold of detected gamma-ray showers; to
improve the angular and energy resolution for individual gamma-rays; to gain in
suppression of the cosmic ray background. In my talk I have summarized the
general advantages and achieved sensitivity of the stereoscopic observations
using the HEGRA data taken with an array of 5 imaging telescopes having the
energy threshold of 500 GeV. These results completed with the relevant
simulations may be extrapolated on a firm ground towards the future H.E.S.S.
(phase I) array of four 12 m imaging telescopes with the estimated energy
threshold below 100 GeV. Here I discuss in short the anticipated performance of
such an array.


title:
New Results on the Helium Stars in the Galactic Center Using BEAR
  Spectro-Imagery

abstract:
  Integral field spectroscopy of the central parsec of the Galactic Center was
obtained at 2.06 microns using BEAR, an imaging Fourier Transform Spectrometer,
at a spectral resolution of 74 km/s. Sixteen stars were confirmed as helium
stars by detecting the He I 2.058 microns line in emission, providing a
homogeneous set of fully resolved line profiles.
  These observations allow us to discard some of the earlier detections of such
stars in the central cluster and to add three new stars. The sources detected
in the BEAR data were compared with adaptive optics images in the K band to
determine whether the emission was due to single stars. Two sub-classes of
almost equal number are clearly identified from the width of their line
profiles, and from the brightness of their continuum.
  Most of the emission lines show a P Cygni profile. From these results, we
propose that the latter group is formed of stars in or near the LBV phase, and
the other one of stars at the WR stage. The division into two groups is also
shown by their spatial distribution, with the narrow-line stars in a compact
central cluster (IRS 16) and the other group distributed at the periphery of
the central cluster of hot stars. In the same data cube, streamers of
interstellar helium gas are also detected.
  The helium emission traces the densest parts of the SgrA West Mini-Spiral.
Several helium stars have a radial velocity comparable to the velocity of the
interstellar gas in which they are embedded. In the final discussion, all these
findings are examined to present a possible scenario for the formation of very
massive stars in the exceptional conditions of the vicinity of the central
Black Hole.


title: The XMM-Newton Optical/UV Monitor Telescope

abstract:
  The XMM-OM instrument extends the spectral coverage of the XMM-Newton
observatory into the ultraviolet and optical range. It provides imaging and
time-resolved data on targets simultaneously with observations in the EPIC and
RGS. It also has the ability to track stars in its field of view, thus
providing an improved post-facto aspect solution for the spacecraft. An
overview of the XMM-OM and its operation is given, together with current
information on the performance of the instrument.


title:
Lessons from lensed Lyman break galaxies: can dusty Lyman break galaxies
  produce the submillimetre counts and background?

abstract:
  Can the submillimetre counts and background be produced by applying a locally
derived extinction correction to the population of Lyman break galaxies? We
investigate the submillimetre emission of two strongly lensed Lyman break
galaxies (MS1512+36-cB58 and MS1358+62-G1) and find that the procedure that is
used to predict the submillimetre emission of the Lyman break galaxy population
overpredicts the observed 850 micron fluxes by a factor of up to 14. This
result calls for caution in applying local correlations to distant galaxies. It
also shows that large extinction corrections on Lyman break galaxies should be
viewed with skepticism. It is concluded that the Lyman break galaxies may
contribute to the submillimetre background at the 25 to 50% level. The brighter
submillimetre galaxies making up the rest of the background are either not
detected in optical surveys, or if they are detected, their submillimetre
emission cannot be reliably estimated from their rest-frame ultraviolet
properties.


title:
Luminous compact galaxies at intermediate redshifts: progenitors of
  bulges of massive spirals ?

abstract:
  VLT spectra of 14 luminous compact galaxies (LCGs) reveal strong metallic
absorption line sytems as well as narrow and intense emission lines. Their gas
extinction is found to be large (Av ~ 1.5 mag) leading to an upward revision of
their star formation rate (SFR) to an average value of ~ 40 Mo/yr. Large
extinction values are also supported by the large rate of detection in one
field observed by ISO. Gas metal abundances in LCGs have about half the solar
value. We argue that LCGs are the progenitors of present-day spiral bulges.
LCGs have masses and light concentrations similar to those of present-day
bulges. As in present-day galactic bulges, LCG stars show a wide range of
abundances. Thus, observing LCGs allows us to directly witness an important
stage in the formation of a massive galaxy, the building of the bulge prior to
that of the disk. The gas needed to feed the observed star formation is likely
to be falling in from the outskirts of the galaxy, being tidally pulled out
from interacting companion galaxies. Some LCGs also show evidence for the
beginning of a disk formation. If the above scenario holds for most LCGs, we
estimate that at least 20% of present-day spiral galaxies have formed the bulk
of their stars at relatively recent epochs, during the last 8-9 Gyr, at
redshifts less than ~ 1. Since they are heavily extincted, we predict their IR
luminosities to be relatively large, around Lir = 10^11 Lsun, i.e. near or
slightly below the luminosities of the galaxies detected by ISO in the same
redshift range. Taking into account the integrated IR luminosity of the LCG
galaxy population can lead to a significant upward revision of the cosmic SFR
density in the redshift range from 0.5 to 1.


title: Steps to the Planck Function : A Centenary Reflection

abstract:
  The year 2000 marks the centenary of the Planck function for the blackbody
spectral distribution. Here are traced the steps, over 100 years, along the
path leading to this important formula.


title: Palomar 13's Last Stand

abstract:
  We present a proper motion and CCD photometric study of stars in the distant
halo globular cluster Palomar 13. The absolute proper motion of Pal 13 with
respect to the background galaxies, derived from moderate scale photographic
plates separated by a 40-year baseline, is $(\mu_{\alpha cos \delta},
\mu_{\delta}) = (+2.30, +0.27) \pm (0.26, 0.25)$ milliarc-seconds per year. The
resultant total space velocity (315 km s$^{-1}$) implies that Pal 13 is in the
inner part of its orbit near perigalacticon. Orbital integration reveals the
cluster to possess an inclined, very eccentric, retrograde orbit. These data
confirm that Pal 13 is a paradigm "young halo" globular cluster.
  The derived proper motions for cluster stars are used to produce membership
probabilities and a cleaned CCD UBV catalogue for Pal 13. With this data set we
have made small revisions to Pal 13's distance, metallicity, position and light
profile. The membership of four previously reported RR Lyrae variables and a
proportionally large group of blue straggler stars are confirmed. As expected,
the blue stragglers are centrally concentrated.
  The small size of this cluster, combined with the shape of its light profile,
which shows a clear departure from a classical King function beyond the tidal
radius, suggests that Pal 13 is in the final throes of destruction. This could
explain the large blue straggler specific frequency, as destructive processes
would preferentially strip less massive stars.


title:
Cosmic ray composition and energy spectrum above 1 TeV: direct and EAS
  measurements

abstract:
  The most recent experimental results on the cosmic ray composition and energy
spectrum above 1 TeV are reviewed and discussed. All data agree on the presence
of the so-called ``knee'' at an energy E(knee) = 3-4 PeV; the knee is seen in
all the components of the Extensive Air Showers. These results support the
hypothesis of an astrophysical origin of the knee, while no new features in the
hadronic interactions at high energies are envisaged. The cosmic ray
composition below and above the knee region is still an open question.
According to most experiments, the knee seems to be due to the light component
of the primary beam, with a composition getting heavier above the knee.
However, results contradicting this conclusion have to be considered and
understood.


title: The Digital Sky Project: Prototyping Virtual Observatory Technologies

abstract:
  Astronomy is entering a new era as multiple, large area, digital sky surveys
are in production. The resulting datasets are truly remarkable in their own
right; however, a revolutionary step arises in the aggregation of complimentary
multi-wavelength surveys (i.e., the cross-identification of a billion sources).
The federation of these large datasets is already underway, and is producing a
major paradigm shift as Astronomy has suddenly become an immensely data-rich
field. This new paradigm will enable quantitatively and qualitatively new
science, from statistical studies of our Galaxy and the large-scale structure
in the universe, to discoveries of rare, unusual, or even completely new types
of astronomical objects and phenomena. Federating and then exploring these
large datasets, however, is an extremely challenging task. The Digital Sky
project was initiated with this task in mind and is working to develop the
techniques and technologies necessary to solve the problems inherent in
federating these large databases, as well as the mining of the resultant
aggregate data.


title:
The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and
  Distances

abstract:
  We report data for $I$ band Surface Brightness Fluctuation (SBF) magnitudes,
V-I colors, and distance moduli for 300 galaxies. The Survey contains E, S0 and
early-type spiral galaxies in the proportions of 49:42:9, and is essentially
complete for E galaxies to Hubble velocities of 2000 km/s, with a substantial
sampling of E galaxies out to 4000 km/s. The median error in distance modulus
is 0.22 mag.
  We also present two new results from the Survey. (1) We compare the mean
peculiar flow velocity (bulk flow) implied by our distances with predictions of
typical cold dark matter transfer functions as a function of scale, and find
very good agreement with cold, dark matter cosmologies if the transfer function
scale parameter $\Gamma$, and the power spectrum normalization $\sigma_8$ are
related by $\sigma_8 \Gamma^{-0.5} \approx 2\pm0.5$. Derived directly from
velocities, this result is independent of the distribution of galaxies or
models for biasing. The modest bulk flow contradicts reports of large-scale,
large-amplitude flows in the $\sim200$ Mpc diameter volume surrounding our
Survey volume. (2) We present a distance-independent measure of absolute galaxy
luminosity, \Nbar, and show how it correlates with galaxy properties such as
color and velocity dispersion, demonstrating its utility for measuring galaxy
distances through large and unknown extinction.


title: Star Formation from Turbulent Fragmentation

abstract:
  Star formation is intimately linked to the dynamical evolution of molecular
clouds. Turbulent fragmentation determines where and when protostellar cores
form, and how they contract and grow in mass via accretion from the surrounding
cloud material. Efficiency, spatial distribution and timescale of star
formation in turbulent clouds are estimated by comparing numerical models of
self-gravitating isothermal gas where turbulence is assumed to have decayed or
is driven at supersonic speed on various wavelengths. Turbulence that is not
continuously replenished or that is driven on large scales leads to a rapid
formation of stars in a clustered mode, whereas interstellar turbulence that
carries most energy on small scales results in isolated star formation with low
efficiency. Protostellar accretion rates strongly vary in time and peak at a
few 10^-5 M_sun/year. The clump mass spectrum for models of pure hydrodynamic
turbulence is steeper than the observed one, but becomes comparable when
including gravity. The mass spectrum of dense cores, on the other hand, is
log-normal for decaying and large-wavelength turbulence, similar to the IMF,
but is to flat in the case of small-scale turbulence.


title:
The effect of projection on the observed gas velocity fields in barred
  galaxies

abstract:
  The problem of determining the pattern of gas motions in the central cases --
noncircular motions in the triaxial bar potential and motions in circular
orbits but with orientation parameters different from those of the main disk --
are shown to have similar observational manifestations in the line-of-sight
velocity field of the gas. A reliable criterion is needed fo the observational
data to be properly interpreted. To find such a criterion, we analyze
two-dimensional nonlinear hydrodynamics models of gas motions in barred disk
galaxies. The gas line-of-sight velocity and surface brightness distributions
in the plane of the sky are constructed for various inclinations of the
galactic plane to the line-of-sight and bar orientation angles. We show that
using models of circular motions for inclinations $i > 60^\circ$ to analyze the
velocity field can lead to the erroneous conclusions of a ``tilted (polar)
disk'' at the circumnuclear region. However, it is possible to distinguish bars
from tilted disks by comparing the mutual orientations of the photometric and
dynamical axes. As an example, we consider the velocity field of the ionized
gas in the galaxy NGC 972.


title:
Millimetric Ground Based Observation of CMBR Anisotropy at $\delta
  =+28^{\lowercase{o}}$

abstract:
  Results from the third campaign of a ground-based multi-band observation of
the millimeter emission of the sky from Tenerife (Canary Islands) are
presented. The instrument consists of a 0.45 meter diameter off-axis telescope
equipped with a 4-band multi-mode $^3He$ cooled photometer working at 1.1, 1.3,
2.1 and 3.1{\notetoeditor{These are effective wavelengths}} mm wavelengths. The
beam is well approximated by a Gaussian with 1$% ^{o}$.35 Full Width Half
Maximum (FWHM) at all wavelengths. The wide wavelength coverage of our
instrument allows us to characterize and reduce both the atmospheric and
galactic contamination in our data. The CMBR data is analyzed in 6 multipole
bands whose centers span the range $\ell=39$ to $\ell =134$ at the two longest
wavelengths (2.1 and 3.1 mm). A likelihood analysis indicates that we have
detected fluctuations in all bands at the two wavelengths. We have evidence of
a rise in the angular power spectrum from low $\ell $ to high $\ell $. Our
measured spectrum is consistent with current popular theories of large scale
structure formation, COBE, and other recent balloon-borne experiments with
similar wavelength coverage.


title:
An imaging and spectroscopic study of the very metal-deficient blue
  compact dwarf galaxy Tol 1214--277

abstract:
  We present a spectrophotometric study based on VLT/FORS I observations of one
of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol
1214-277 (Z ~ Zsun/25). The data show that roughly half of the total luminosity
of the BCD originates from a bright and compact starburst region located at the
northeastern tip of a faint dwarf galaxy with cometary appearance. The
starburst has ignited less than 4 Myr ago and its emission is powered by
several thousands O7V stars and ~ 170 late-type nitrogen Wolf-Rayet stars
located within a compact region with < 500 pc in diameter. For the first time
in a BCD, a relatively strong [Fe V] 4227 emission line is seen which together
with intense He II 4686 emission indicates the presence of a very hard
radiation field in Tol 1214-277. We argue that this extraordinarily hard
radiation originates from both Wolf--Rayet stars and radiative shocks in the
starburst region. The structural properties of the low-surface-brightness (LSB)
component underlying the starburst have been investigated by means of surface
photometry down to 28 B mag/sq.arcsec. We find that, for a surface brightness
level fainter than ~ 24.5 B mag/sq.arcsec, an exponential fitting law provides
an adequate approximation to its radial intensity distribution. The broad-band
colors in the outskirts of the LSB component of Tol 1214-277 are nearly
constant and are consistent with an age below one Gyr. This conclusion is
supported by the comparison of the observed spectral energy distribution (SED)
of the LSB host with theoretical SEDs.


title:
Histogram Analysis of Gallex, GNO and Sage Neutrino Data: Further
  Evidence for Variability of the Solar Neutrino Flux

abstract:
  If the solar neutrino flux were constant, as is widely assumed, the histogram
of flux measurements would be unimodal. On the other hand, sinusoidal or
square-wave modulation (either periodic or stochastic) may lead to a bimodal
histogram. We here present evidence that the neutrino flux histogram is in fact
bimodal. We analyze all available data from gallium experiments, coordinating
results from the GALLEX and GNO experiments into one data set, and adopting
results from the SAGE experiment as another data set. The two histograms, from
the two data sets, are consistent in showing peaks in the range 45-75 SNU and
90-120 SNU, with a valley in between. By combining the data into one data set,
we may form more detailed histograms; these strengthen the case that the flux
is bimodal. A preliminary statistical analysis indicates that the bimodal
character of the solar neutrino flux is highly significant. Since the upper
peak is close to the expected flux (120-140 SNU), we may infer that the
neutrino deficit is due to time-varying attenuation of the flux produced in the
core. We estimate the time scale of this variation to be in the range 10-60
days. Attenuation that varies on such a time scale is suggestive of the
influence of solar rotation, and points towards a process involving the solar
magnetic field in conjunction with a nonzero neutrino magnetic moment.


title: Turbulent Fragmentation and the Initial Conditions for Star Formation

abstract:
  Super-sonic turbulence fragments molecular clouds (MC) into a very complex
density field with density contrasts of several orders of magnitude. A fraction
of the gas is locked into dense and gravitationally bound cores, which collapse
as proto-stars. This process can be studied with numerical simulations of
super-sonic self-gravitating turbulence.
  In this work, we use numerical simulations of magneto-hydrodynamic (MHD),
super-sonic, super-Alfv\'{e}nic and self-gravitating turbulence to compute the
mass distribution of collapsing proto-stellar cores, which are selected as
local density maxima. We find that the mass distribution of collapsing cores is
consistent with the stellar initial mass function (IMF), suggesting that
super-sonic turbulence may be responsible for the generation of the IMF.
  To support this conclusion we also show that the physical properties of the
numerically selected cores are in agreement with the properties of observed
NH$_3$ cores and that their magnetic field strength is consistent with Zeeman
splitting measurements.
  In turbulent MCs, star formation occurs via the gravitational collapse of
super-critical cores, formed by the turbulent flow, sub-critical cores being
irrelevant for the process of star formation.


title:
Three modes of long wavelength flaring from GRS 1915+105: implications
  for jet formation

abstract:
  GRS 1915+105 has exhibited at least three modes of long-wavelength (infrared
to radio) flares. Class A flares are the bright ($\sim 1$ Jy) radio events
whose apparent superluminal motion in many ways defines the microquasars. Class
B flares have intermediate ($\sim 50-300$ mJy) flux densities in the IR and
radio, and are associated with hard X-ray dipping behaviors. Class C flares are
faint ($\sim 5-50$ mJy) IR/radio events associated with soft X-ray dips. We
discuss each of these classes and their inter-relationships.


title: Ultrahigh energy cosmic rays and new particle physics

abstract:
  The current status of the ultrahigh energy cosmic ray (UHE CR) enigma and
several proposed solutions involving particle physics beyond the standard model
are discussed. Emphasis is given to top--down models, and as a main example,
supermassive dark matter as galactic source for UHE CR and the status of its
experimental signatures (galactic anisotropy, chemical composition and
clustering) is reviewed. Then different approaches to calculate fragmentation
spectra of supermassive particles are discussed. Finally, it is argued that UHE
neutrinos cannot be - neither directly or indirectly - responsible for the
observed vertical air showers.


title:
Discovery of Spectral Transitions from Two Ultra-Luminous Compact X-Ray
  Sources in Ic342

abstract:
  Two {\it ASCA} observations were made of two ultra-luminous compact X-ray
sources (ULXs), Source 1 and Source 2, in the spiral galaxy IC 342. In the 1993
observation, Source 2 showed a 0.5--10 keV luminosity of $6 \times 10^{39}$
ergs s$^{-1}$ (assuming a distance of 4.0 Mpc), and a hard power-law spectrum
of photon index $\sim 1.4$. As already reported, Source 1 was $\sim 3$ times
brighter on that occasion, and exhibited a soft spectrum represented by a
multi-color disk model of inner-disk temperature $ \sim 1.8$ keV. The second
observation made in February 2000 revealed that Source 1 had made a transition
into a hard spectral state, while Source 2 into a soft spectral state. The ULXs
are therefore inferred to exhibit two distinct spectral states, and sometimes
make transitions between them. These results significantly reinforce the
scenario which describes ULXs as mass-accreting black holes.


title:
Self-intersections and gravitational properties of chiral cosmic strings
  in Minkowski space

abstract:
  Chiral cosmic strings are naturally produced at the end of D-term inflation
and they may have interesting cosmological consequences. As was first proved by
Carter and Peter, the equations of motion for chiral cosmic strings in
Minkowski space are integrable (just as for Nambu-Goto strings). Their
solutions are labeled by a function $k(\sigma - t)$ where $t$ is time and
$\sigma$ is the invariant length along the string, and the constraints on $k$,
which determines the charge on the string, are that $0 \leq k^2 \leq 1$. We
review the origin of this parameter and also discuss some general properties of
such strings which can be deduced from the equations of motion. The metric
around infinite chiral strings is then constructed in the weak field limit, and
studied as a function of $k$. We also consider the angular momentum of circular
chiral loops, and extend previous work to consider the evolution and
self-intersection properties of a more general family of chiral cosmic string
loops for which $k^2(\sigma-t)$ is not constant.


title:
On the dependence of spectroscopic indices of early-type galaxies on
  age, metallicity and velocity dispersion

abstract:
  We investigate the Mg-sigma and <Fe>-sigma relations in a sample of 72
early-type galaxies drawn mostly from cluster and group environments using a
homogeneous data-set which is well-calibrated onto the Lick/IDS system. The
small intrinsic scatter in Mg at a given sigma gives upper limits on the spread
in age and metallicity of 49% and 32% respectively, if the spread is attributed
to one quantity only and if the variations in age and metallicity are
uncorrelated. The age/metallicity distribution as inferred from the Hbeta vs
<Fe> diagnostic diagram reinforces this conclusion, as we find mostly galaxies
with large luminosity weighted ages spanning a range in metallicity. In our
sample we do not find significant evidence for an anti-correlation of ages and
metallicities which would keep the index-sigma relations tight while hiding a
large spread in age and metallicity. As a result of correlated errors in the
age-metallicity plane, a mild age-metallicity anti-correlation cannot be
completely ruled out given the current data. Correcting the line-strengths
indices for non-solar abundance ratios following the recent paper by Trager et
al., leads to higher mean metallicity and slightly younger age estimates while
preserving the metallicity sequence. The [Mg/Fe] ratio is mildly correlated
with the central velocity dispersion and ranges from [Mg/Fe]=0.05 to 0.3 for
galaxies with sigma > 100 km/s. Under the assumption that there is no age
gradient along the index-sigma relations, the abundance-ratio corrected
Mg-sigma, <Fe>-sigma and Hbeta-sigma relations give consistent estimates of
Delta [M/H]/ Delta log sigma = 0.9 (+- 0.1). The slope of the Hbeta-sigma
relation limits a potential age trend as a function of sigma to 2-3 Gyrs along
the sequence.(abriged)


title: Gravitational lensing and elliptical galaxies

abstract:
  If the statistics of quasar lensing are to be used to constrain the
cosmological model, the various potential systematic uncertainties in the
deflector population must be accounted for. One ambiguity in the lensing
properties of the dominant deflectors - elliptical galaxies - is their
dynamical normalisation. Assuming they can be modelled as isothermal spheres,
it is shown that their mass normalisation is sufficiently high that current
upper limits on the cosmological constant remain valid, and in fact probably
strengthened, even if ellipticals have significant core radii.


title: The Merger of a Helium Star and a Black Hole: Gamma-Ray Bursts

abstract:
  There is growing observational evidence that gamma-ray bursts (GRBs) are
powered by black holes accreting rapidly through a disk. The supernova-like
outburst that accompanies some gamma-ray bursts suggest that some long-duration
GRBs may be driven by the accretion of a rotating stellar core onto a central
black hole. Such a system can be produced when a compact remnant spirals into
the helium core of its binary companion. During the inspiral, orbital angular
momentum is injected into the core. By the time the compact remnant reaches the
center of the helium core, it too has gained angular momentum as well as mass,
producing a rapidly accreting black hole (or neutron star) at the center of a
rotating stellar core. In this paper, we use a 3-dimensional smooth particle
hydrodynamics (SPH) code to follow such a merger process and make quantitative
estimates of the initial mass and spin of the central compact remnant, as well
as the angular momentum in the accreting helium core. From these results, we
estimate GRB explosion energies. In all mergers, magnetically driven jets are
expected to produce GRB explosions with energies above 10^{51} ergs. For
neutrino-annihilation-driven explosions, the GRB energy increases dramatically
with helium star mass: the merger of a 2 M_sun compact remnant with a 4 M_sun
helium star only produces a 10^{47} ergs explosion in \sim 500 s whereas the
merger of a 2 M_sun compact remnant with a 16 M_sun helium star produces a
>10^{52} ergs explosion in \sim 65 s. (Abridged)


title: Emission from Dust in Galaxies: Metallicity Dependence

abstract:
  Infrared (IR) dust emission from galaxies is frequently used as an indicator
of star formation rate (SFR). However, the effect of the dust-to-gas ratio
(i.e., amount of the dust) on the conversion law from IR luminosity to SFR has
not so far been considered. Then, in this paper, we present a convenient
analytical formula including this effect. In order to obtain the dependence on
the dust-to-gas ratio, we extend the formula derived in our previous paper, in
which a theoretical formula converting IR luminosity to SFR was derived. That
formula was expressed as ${\rm SFR}/(M_\odot~{\rm yr}^{-1})=\{3.3\times
10^{-10}(1- \eta)/(0.4-0.2f+0.6\epsilon)\} (L_{\rm IR}/L_\odot)$, where f is
the fraction of ionizing photons absorbed by hydrogen, $\epsilon$ is the
efficiency of dust absorption for nonionizing photons, $\eta$ is the cirrus
fraction of observed dust luminosity, and $L_{\rm IR}$ is the observed
luminosity of dust emission in the 8-1000-$\mu$m range. Our formula explains
the IR excess of the Galaxy and the Large Magellanic Cloud. In the current
paper, especially, we present the metallicity dependence of our conversion law
between SFR and $L_{\rm IR}$. This is possible since both f and $\epsilon$ can
be estimated via the dust-to-gas ratio, which is related to metallicity. We
have confirmed that the relation between the metallicity and the dust-to-gas
ratio is applied to both giant and dwarf galaxies. Finally, we apply the result
to the cosmic star formation history. We find that the comoving SFR at z=3
calculated from previous empirical formulae is underestimated by a factor of
4-5.


title: Mapping potential fields on the surfaces of rapidly rotating stars

abstract:
  We present a technique that combines Zeeman Doppler imaging (ZDI) principles
with a potential field mapping prescription in order to gain more information
about the surface field topology of rapid rotators. This technique is an
improvement on standard ZDI, which can sometimes suffer from the suppression of
one vector component due to the effects of stellar inclination, poor phase
coverage or lack of flux from dark areas on the surface. Defining a
relationship beween the different vector components allows information from one
component to compensate for reduced information in another. We present
simulations demonstrating the capability of this technique and discuss its
prospects.


title: The Gravitational Lens Candidate FBQ 1633+3134

abstract:
  We present our ground-based optical imaging, spectral analysis, and high
resolution radio mapping of the gravitational lens candidate FBQ 1633+3134.
This z=1.52, B=17.7 quasar appears double on CCD images with an image
separation of 0.66 arcseconds and a flux ratio of ~3:1 across BVRI filters. A
single 0.27 mJy radio source is detected at 8.46 GHz, coincident to within an
arcsecond of both optical components, but no companion at radio wavelengths is
detected down to a flux level of 0.1 mJy (3 sigma). Spectral observations
reveal a rich metal-line absorption system consisting of a strong Mg II doublet
and associated Fe I and Fe II absorption features, all at an intervening
redshift of z=0.684, suggestive of a lensing galaxy. Point spread function
subtraction however shows no obvious signs of a third object between the two
quasar images, and places a detection limit of I > 23.0 if such an object
exists. Although the possibility that FBQ 1633+3134 is a binary quasar cannot
be ruled out, the evidence is consistent with it being a single quasar lensed
by a faint, metal-rich galaxy.


title: General Relativistic Modification of a Pulsar Electromagnetic Field

abstract:
  We consider an exterior electromagnetic field surrounding a rotating star
endowed with a dipole magnetic field in the context of general relativity.
  The analytic solution for a stationary configuration is obtained, and the
general relativistic modifications and the implications for pulsar radiation
are investigated in detail. We find that the general relativistic corrections
of both the electric field strength and the curvature radii of magnetic field
lines tend to enhance the curvature radiation photon energy.


title: Search for Gamma Ray Bursts at Chacaltaya

abstract:
  A search for Gamma Ray Bursts in the GeV-TeV energy range has been performed
by INCA, an air shower array working at 5200 m of altitude at the Chacaltaya
Laboratory (Bolivia). The altitude of the detector and the use of the "single
particle technique" allows to lower the energy threshold up to few GeVs. No
significant signals are observed during the occurrence of 125 GRBs detected by
BATSE, and the obtained upper limits on the energy fluence in the interval
1-1000(100) GeV range from 3.2(8.6) 10^-5 to 2.6(7.0) 10^-2 erg/cm^2 depending
on the zenith angle of the events. These limits, thanks to the extreme altitude
of INCA, are the lowest ever obtained in the sub-TeV energy region by a ground
based esperiment.


title: The variable XMM-Newton spectrum of Markarian 766

abstract:
  The narrow-line Seyfert 1 galaxy Markarian 766 was observed for 60 ks with
the XMM-Newton observatory. The source shows a complex X-ray spectrum. The 2-10
keV spectrum can be adequately represented by a power law and broad Fe Ka
emission. Between 0.7 and 2 keV the spectrum is harder and exhibits a flux
deficit with respect to the extrapolated medium energy slope. Below 0.7 keV,
however, there is a strong excess of emission. The RGS spectrum shows an
edge-like feature at 0.7 keV; the energy of this feature is inconsistent with
that expected for an OVII edge from a warm absorber. Markarian 766 varies by a
factor of ~ 2 in overall count rate in the EPIC and RGS instruments on a
timescale of a few thousand seconds, while no significant flux changes are
observed in the ultraviolet with the OM. The X-ray variability is spectrally
dependent with the largest amplitude variability occurring in the 0.4-2 keV
band. The spectral variability can be explained by a change in flux and slope
of the medium energy continuum emission, superimposed on a less variable (or
constant) low energy emission component.


title: Stationary dark energy: the present universe as a global attractor

abstract:
  We propose a cosmological model that makes a significant step toward solving
the coincidence problem of the near similarity at the present of the dark
energy and dark matter components. Our cosmology has the following properties:
a) among flat and homogeneous spaces, the present universe is a global
attractor: all the possible initial conditions lead to the observed proportion
of dark energy and dark matter; once reached, it remains fixed forever; b) the
expansion is accelerated at the present, as requested by the supernovae
observations; c) the model is consistent with the large-scale structure and
microwave background data; d) the dark energy and the dark matter densities
always scale similarly after equivalence and are close to within two orders of
magnitude. The model makes use of a non-linear coupling of the dark energy to
the dark matter that switches on after structure formation.


title:
The central region of M31 observed with XMM-Newton (I. Group properties
  and diffuse emission)

abstract:
  We present the results of a study based on an XMM-Newton Performance
Verification observation of the central 30 arcmin of the nearby spiral galaxy
M31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116
sources down to a limiting luminosity of 6 x 10^35 erg/s (0.3--12 keV, d = 760
kpc). The luminosity distribution of the sources detected with XMM-Newton
flattens at luminosities below ~ 2.5 x 10^37 erg/s. We make use of hardness
ratios for the detected sources in order to distinguish between classes of
objects such as super-soft sources and intrinsically hard or highly absorbed
sources. We demonstrate that the spectrum of the unresolved emission in the
bulge of M31 contains a soft excess which can be fitted with a ~ 0.35-keV
optically-thin thermal-plasma component clearly distinct from the composite
point-source spectrum. We suggest that this may represent diffuse gas in the
centre of M31, and we illustrate its extent in a wavelet-deconvolved image.


title: The Extended X-ray Halo of the Crab-like SNR G21.5-0.9

abstract:
  Recent XMM-Newton observations reveal an extended (150") low-surface
brightness X-ray halo in the supernova remnant G21.5-0.9. The near circular
symmetry, the lack of any limb brightening and the non-thermal spectral form,
all favour an interpretation of this outer halo as an extension of the central
synchrotron nebula rather than as a shell formed by the supernova blast wave
and ejecta. The X-ray spectrum of the nebula exhibits a marked spectral
softening with radius, with the power-law spectral index varying from Gamma =
1.63 +/- 0.04 in the core to Gamma = 2.45 +/- 0.06 at the edge of the halo.
Similar spectral trends are seen in other Crab-like remnants and reflect the
impact of the synchrotron radiation losses on very high energy electrons as
they diffuse out from the inner nebula. A preliminary timing analysis provides
no evidence for any pulsed X-ray emission from the core of G21.5-0.9.


title: Supersonic water masers in 30 Doradus

abstract:
  We report on extremely high velocity molecular gas, up to -80 km/s relative
to the ambient medium, in the giant star-formation complex 30 Doradus in the
Large Magellanic Cloud (LMC), as observed in new 22 GHz H2O maser emission
spectra obtained with the Mopra radio telescope. The masers may trace the
velocities of protostars, and the observed morphology and kinematics indicate
that current star formation occurs near the interfaces of colliding
stellar-wind blown bubbles. The large space velocities of the protostars and
associated gas could result in efficient mixing of the LMC. A similar mechanism
in the Milky Way could seed the galactic halo with relatively young stars and
gas.


title: The Accretion-Ejection Instability in X-ray Binaries

abstract:
  The Accretion-Ejection Instability (AEI), which can occur in magnetized disks
near equipartition, is a good candidate to explain the low-frequency QPO in
black-hole binaries. Here we present analytical work concerning the behavior of
QPO frequency and the emission of Alfv\'en waves from the disk to the corona.


title: The population of close double white dwarfs in the Galaxy

abstract:
  We present a new model for the Galactic population of close double white
dwarfs. The model accounts for the suggestion of the avoidance of a substantial
spiral-in during mass transfer between a giant and a main-sequence star of
comparable mass and for detailed cooling models. It agrees well with the
observations of the local sample of white dwarfs if the initial binary fraction
is close to 50% and an ad hoc assumption is made that white dwarfs with mass
less than about 0.3 solar mass cool faster than the models suggest. About 1000
white dwarfs brighter than V=15 have to be surveyed for detection of a pair
which has total mass greater than the Chandrasekhar mass and will merge within
10 Gyr.


title: Upper limits to low energy antineutrino flux from GRB990705

abstract:
  The detection of Gamma Ray Burst GRB990705 on 1999, July 5.66765 UT, pointing
to the Large Magellanic Clouds, suggested the search for a possible neutrino
counterpart, both in coincidence with and slightly before (or after) the photon
burst. We exploited such a possibility by means of the LVD neutrino telescope
(National Gran Sasso Laboratory, Italy), which has the capability to study
low-energy cosmic neutrinos. No evidence for any neutrino signal, over a wide
range of time durations, has been found, at the occurrence of GRB990705. Due to
the lack of information about both the source distance and its emission
spectrum, the results of the search are expressed in terms of upper limits, at
the Earth, to the antineutrino flux $\cdot$ cross-section, integrated over
different time durations. Moreover, assuming thermal antineutrino spectra at
the source, upper limits to the antineutrino flux, integrated over time
duration, for different spectral temperatures, are obtained. Based on these
limits and on the expectations for neutrino emission from collapsing
astrophysical objects, the occurrence of a gravitational stellar collapse can
be excluded up to a distance r approximately 50 kpc, in the case of time
coincidence with GRB990705, and r approximately 20 kpc, for the 24 hours
preceding it.


title: Measuring Stellar and Dark Mass Fractions in Spiral Galaxies

abstract:
  We explore the relative importance of the stellar mass density as compared to
the inner dark halo, for the observed gas kinematics thoughout the disks of
spiral galaxies. We perform hydrodynamical simulations of the gas flow in a
sequence of potentials with varying the stellar contribution to the total
potential. The stellar portion of the potential was derived empirically from
K-band photometry. The output of the simulations - namely the gas density and
the gas velocity field - are then compared to the observed spiral arm
morphology and the H-alpha gas kinematics. We solve for the best matching
spiral pattern speed and draw conclusions on how massive the stellar disk can
be at most. For the case of the galaxy NGC 4254 (Messier 99) we demonstrate
that the prominent spiral arms of the stellar component would overpredict the
non-circular gas motions unless an axisymmetric dark halo component adds
significantly in the radial range R_exp < R < 3*R_exp.


title:
Cosmic Shear Analysis in 50 Uncorrelated VLT Fields. Implications for
  Omega_0, sigma_8

abstract:
  We observed with the camera FORS1 on the VLT (UT1, ANTU) 50 randomly selected
fields and analyzed the cosmic shear inside circular apertures with diameter
ranging from 0.5 to 5.0 arc-minutes. The images were obtained in optimal
conditions by using the Service Observing proposed by ESO on the VLT, which
enabled us to get a well-defined and homogeneous set of data. The 50 fields
cover a 0.65 square-degrees area spread over more than 1000 square-degrees
which provides a sample ideal for minimizing the cosmic variance. Using the
same techniques as in Van Waerbeke et al. 2000, we measured the cosmic shear
signal and investigated the systematics of the VLT sample. We find a
significant excess of correlations between galaxy ellipticities on those
angular scales. The amplitude and the shape of the correlation as function of
angular scale are remarkably similar to those reported so far. Using our
combined VLT and CFHT data and adding the results published by other teams we
put the first joint constraints on Omega_0 and sigma_8 using cosmic shear
surveys. From a deduced average of the redshift of the sources the combined
data are consistent with sigma_8\simeq (0.59 \pm 0.03) Omega_0^{-0.47} (for a
CDM power spectrum and $\Gamma=0.21$), in excellent agreement with the
cosmological constraints obtained from the local cluster abundance.


title:
Concluding Remarks on New Cosmological Data and the Values of the
  Fundamental Parameters

abstract:
  I review the reason for considering the prime purpose of the program of
measurements of the fundamental parameters of cosmology to be the tests of
cosmological models. I comment on the philosophy by which we are approaching
this goal, offer an assessment of where we stand, and present some thoughts on
where the tests may be headed.


title:
Energy Release During Disk Accretion onto a Rapidly Rotating Neutron
  Star

abstract:
  The energy release L_s on the surface of a neutron star (NS) with a weak
magnetic field and the energy release L_d in the surrounding accretion disk
depend on two independent parameters that determine its state (for example,
mass M and cyclic rotation frequency f) and is proportional to the accretion
rate. We derive simple approximation formulas illustrating the dependence of
the efficiency of energy release in an extended disk and in a boundary layer
near the NS surface on the frequency and sense of rotation for various NS
equations of state. Such formulas are obtained for the quadrupole moment of a
NS, for a gap between its surface and a marginally stable orbit, for the
rotation frequency in an equatorial Keplerian orbit and in the marginally
stable circular orbit, and for the rate of NS spinup via disk accretion. In the
case of NS and disk counterrotation, the energy release during accretion can
reach $0.67\dot{M}c^2$. The sense of NS rotation is a factor that strongly
affects the observed ratio of nuclear energy release during bursts to
gravitational energy release between bursts in X-ray bursters. The possible
existence of binary systems with NS and disk counterrotation in the Galaxy is
discussed. Based on the static criterion for stability, we present a method of
constructing the dependence of gravitational mass M on Kerr rotation parameter
j and on total baryon mass (rest mass) m for a rigidly rotating neutron star.
We show that all global NS characteristics can be expressed in terms of the
function M(j, m) and its derivatives.


title:
Galaxy mapping with the SAURON integral-field spectrograph: The star
  formation history of NGC 4365

abstract:
  We report the first wide-field mapping of the kinematics and stellar
populations in the E3 galaxy NGC 4365. The velocity maps extend previous
long-slit work. They show two independent kinematic subsystems: the central 300
x 700 pc rotates about the projected minor axis, and the main body of the
galaxy, 3 x 4 kpc, rotates almost at right angles to this. The line-strength
maps show that the metallicity of the stellar population decreases from a
central value greater than solar, to one-half solar at a radius of 2 kpc. The
decoupled core and main body of the galaxy have the same luminosity-weighted
age, of ~14 Gyr, and the same elevated magnesium-to-iron ratio. The two
kinematically distinct components have thus shared a common star formation
history. We infer that the galaxy underwent a sequence of mergers associated
with dissipative star formation that ended >12 Gyr ago. The misalignment
between the photometric and kinematic axes of the main body is unambiguous
evidence of triaxiality. The similarity of the stellar populations in the two
components suggests that the observed kinematic structure has not changed
substantially in 12 Gyr.


title: The Luminosity Function of QSO Host Galaxies

abstract:
  We present some results from our HST archival image study of 71 QSO host
galaxies. The objects are selected to have z < 0.46 and total absolute
magnitude M_V < -23 (H_0=50 km/s/Mpc). This initial study investigates host
morphology and radio loudness, and it derives the QSO host galaxy luminosity
function. We have analyzed available WFPC2 broad band images, using a uniform
set of procedures. The host galaxies span a narrow range of luminosities and
are exceptionally bright, much more so than normal galaxies, usually L > L*_V.
The QSOs are almost equally divided among radio-loud QSOs with elliptical
hosts, radio-quiet QSOs with elliptical hosts, and radio-quiet QSOs with spiral
hosts. Using a weighting procedure, we derive the combined luminosity function
of QSO host galaxies. We find that the luminosity function of QSO hosts differs
in shape from that of normal galaxies but that they coincide at the highest
luminosities. The ratio of the number of quasar hosts to the number of normal
galaxies at a luminosity L_V is R = [L_V/(11.48 L*_V)]^2.46, where L*_V
corresponds to M*_V = -22.35, and a QSO is defined to be an object with total
nuclear plus host light M_V < -23. This ratio can be interpreted as the
probability that a galaxy with luminosity L_V will host a QSO at redshift z ~
0.26. (Abridged)


title: An investigation into the prominence of spiral galaxy bulges

abstract:
  From a diameter-limited sample of 86 `face-on' spiral galaxies, the
bulge-to-disk size and luminosity ratios, and other quantitative measurements
for the prominence of the bulge are derived. The bulge and disk parameters have
been estimated using a seeing convolved Sersic r^(1/n) bulge and a seeing
convolved exponential disk. In general, early-type spiral galaxy bulges have
Sersic values of n>1, and late-type spiral galaxy bulges have values of n<1. In
the B-band, only 8 galaxies have a bulge shape parameter n consistent with the
exponential value of 1, and only 5 galaxies do in the K-band. Application of
the r^(1/n) bulge models results in a larger mean r_e/h ratio for the
early-type spiral galaxies than the late-type spiral galaxies. Although, this
result is shown not to be statistically significant. The mean B/D luminosity
ratio is, however, significantly larger (> 3-sigma) for the early-type spirals
than the late-type spirals. This apparent contradiction with the r_e/h values
can be explained with an iceberg-like scenario, in which the bulges in
late-type spiral galaxies are relatively submerged in their disk. This can be
achieved by varying the relative bulge/disk stellar density while maintaining
the same effective bulge-to-disk size ratio.
  The absolute bulge magnitude - log(n) diagram is used as a diagnostic tool
for comparative studies with dwarf elliptical and ordinary elliptical galaxies.
At least in the B-band, these objects occupy distinctly different regions of
this parameter space. While the dwarf ellipticals appear to be the faint
extension to the brighter elliptical galaxies, the bulges of spiral galaxies
are not.


title: Detection of Excess Hard X-ray Emission from the Group of Galaxies HCG62

abstract:
  From the group of galaxies HCG62, we detected an excess hard X-ray emission
in energies above $\sim 4$ keV with \A SCA. The excess emission is spatially
extended up to $\sim10'$ from the group center, and somewhat enhanced toward
north. Its spectrum can be represented by either a power-law of photon index
0.8-2.7, or a Bremsstrahlung of temperature $>6.3$ keV. In the 2-10 keV range,
the observed hard X-ray flux, $(1.0\pm0.3)\times10^{-12}$ erg cm$^{-2}$
s$^{-1}$, implies a luminosity of $(8.0\pm2.0)\times10^{41}$ erg s$^{-1}$ for a
Hubble constant of 50 km s$^{-1}$ Mpc$^{-1}$. The emission is thus too luminous
to be attributed to X-ray binaries in the memb er galaxies. We discuss possible
origin of the hard X-ray emission.


title: High-Redshift Galaxy Outflows and the Formation of Dwarf Galaxies

abstract:
  We examine the effects of galaxy outflows on the formation of dwarf galaxies
in numerical simulations of the high-redshift Universe. Using a Smoothed
Particle Hydrodynamic code, we conduct two detailed simulations of a (5.2
Mpc/h)^3 comoving volume of the Universe. In both simulations we implement
simple, well-motivated models of galaxy identification and star formation,
while our second simulation also includes a simple ``blow-out'' model of galaxy
outflows in which supernova driven winds from newly formed disk galaxies
punch-out and shock the intergalactic medium while leaving the host galaxies
intact. A direct comparison between these simulations suggests that there are
two major mechanisms by which outflows affect dwarf formation. Firstly, the
formation of an outflow slows down the further accretion of gas onto a galaxy,
causing an overall decrease of approximately 50% in the total gas mass accreted
by the objects in our simulations. Additionally, our simulations uncover a
significant population of approximately 10^9 solar mass objects whose formation
is suppressed by the mechanism of ``baryonic stripping,'' in which outflows
from early galaxies strip the gas out of nearby overdense regions that would
have otherwise later formed into dwarf galaxies. This mechanism may be
important in explaining the observed discrepancy between the number of dwarf
galaxies predicted and observed in the local group and provide a natural
explanation for the formation of empty halos which may be required by the
existence of the extremely gas-poor extra-galactic High-Velocity Clouds.


title: The ATCA/VLA OH 1612 MHz survey. III. Northern Galactic Plane

abstract:
  We present observations of the region between 5deg < l < 45deg and |b| <
3deg, in the OH 1612 MHz line, taken from 1993 to 1995 with the VLA. These
observations are the last part of a larger survey, covering |l| < 45deg and |b|
< 3deg, with the ATCA and the VLA. The region was systematically observed on a
30'x30' grid in (l,b) and the resulting coverage was 92%, with 965 pointings.
We found 286 OH--masing objects, 161 of which are new detections and 207 have
reliable IRAS point-source identifications. The outflow velocity was determined
for 276 sources. A total of 766 sources were detected in the combined ATCA/VLA
survey, of which 29 were detected in two regions of the survey. The source
tables and spectra may be downloaded from
http://msowww.anu.edu.au/~msevenst/pubs.html In this article we analyse the
data statistically and give identifications with known sources where possible.
The efficiency of this VLA survey is 75% of that of the ATCA Bulge survey. This
efficiency was determined by comparing the detections in the region where the
two surveys overlap. The completeness- and error characteristics are similar,
though less homogeneous, except for the much larger errors in the flux
densities. The relatively large surface number density found in the northern
disk, suggests that we can see the Bar extending to higher longitudes on this
side of the galactic Centre.


title:
Discovery of the Slowest X-Ray Pulsar in the SMC, AX J0049.5-7323, with
  ASCA

abstract:
  The discovery of coherent pulsations with ASCA from an X-ray source, AX
J0049.5-7323, is reported. The barycentric period was determined to be 755.5
+/- 0.6 s, which is the longest among X-ray pulsators in the SMC. The X-ray
spectrum has been found to be unchanged through ASCA observations, with a
photon index of ~0.8 and a luminosity of ~5e35 erg s^-1 (0.7-10 keV). Archival
data of the Einstein and the ROSAT satellites indicate that the flux has been <
1e-12 erg s^-1 cm^-2 (< 5e35 erg s^-1) for over 20 years and exhibits a
variability with a factor of >10. We argue that AX J0049.5-7323 is an X-ray
pulsar with a Be star companion.


title: Galaxy Formation at z~3: Constraints from Spatial Clustering

abstract:
  We use N-body simulations combined with semi-analytic models to compute the
clustering properties of modeled galaxies at z~3, and confront these
predictions with the clustering properties of the observed population of
Lyman-break galaxies (LBGs). Several scenarios for the nature of LBGs are
explored, which may be broadly categorized into models in which high-redshift
star formation is driven by collisional starbursts and those in which quiescent
star formation dominates. For each model, we make predictions for the LBG
overdensity distribution, the variance of counts-in-cells, the correlation
length, and close pair statistics. Models which assume a one-to-one
relationship between massive dark-matter halos and galaxies are disfavored by
close pair statistics, as are models in which colliding halos are associated
with galaxies in a simplified way. However, when modeling of gas consumption
and star formation is included using a semi-analytic treatment, the quiescent
and collisional starburst models predict similar clustering properties and none
of these models can be ruled out based on the available clustering data. None
of the ``realistic'' models predict a strong dependence of clustering amplitude
on the luminosity threshold of the sample, in apparent conflict with some
observational results.


title:
Emissive Mechanism on Spectral Variability of Blazars in High
  Frequencies

abstract:
  The new results of the evolution of the synchrotron peak for Mrk 421 are
mostly likely related to the particle acceleration process. In order to account
for the above results, we present a model of blazar variability during the
flare in which the emission comes from accelerating electrons. A diffusion
advection equation of the electron energy distribution is derived to calculate
the spectrum and light curve of synchrotron radiation. We present that the
observed shifts of the synchrotron peak moving to higher energies during the
flare are caused by shock acceleration. The observed relation between changes
in the fluxes at specified frequency ranges and shifts of the peak position is
fitted to constrain the physical parameters of the dissipation region.


title: Detection of a Corrugated Velocity Pattern in the Spiral Galaxy NGC 5427

abstract:
  Here we report the detection, in Halpha emission, of a radial corrugation in
the velocity field of the spiral galaxy NGC 5427. The central velocity of the
Halpha line displays coherent, wavy-like variations in the vicinity of the
spiral arms. The spectra along three different arm segments show that the
maximum amplitude of the sinusoidal line variations are displaced some 500 pc
from the central part of the spiral arms. The peak blueshifted velocities
appear some 500 pc upstream the arm, whereas the peak redshifted velocities are
located some 500 pc downstream the arm. This kinematical behavior is similar to
the one expected in a galactic bore generated by the interaction of a spiral
density wave with a thick gaseous disk, as recently modeled by Martos & Cox
(1998).


title: MHD jets around galactic objects

abstract:
  We present a self-similar, steady-state model describing both a magnetized
accretion disc and a magnetohydrodynamic jet. We focus on the role of a hot
corona in such a structure. This corona enables the disc to launch various
types of jets. By considering the energy conservation, we also present a
diagnostic of the luminosity of the magnetized disc, which could explain some
observational signatures of galactic objects.


title: Cosmological Evolution of Linear Bias

abstract:
  Using linear perturbation theory and the Friedmann-Lemaitre solutions of the
cosmological field equations, we derive analytically a second-order
differential equation for the evolution of the linear bias factor, b(z),
between the background matter and a mass-tracer fluctuation field. We find b(z)
to be a strongly dependent function of redshift in all cosmological models.
Comparing our analytical solution with the semi-analytic model of Mo & White,
which utilises the Press-Schechter formalism and the gravitationally induced
evolution of clustering, we find an extremely good agreement even at large
redshifts, once we normalize to the same bias value at two different epochs,
one of which is the present. Furthermore, our analytic b(z) function agrees
well with the outcome of N-body simulations even up to large redshifts.


title: Classification and Redshift Estimation in Multi-Color Surveys

abstract:
  We present a photometric method for identifying stars, galaxies and quasars
in multi-color surveys and estimating multi-color redshifts for the
extragalactic objects. We use a library of >65000 color templates for
comparison with observed objects. The method was originally developed for the
Calar Alto Deep Imaging Survey (CADIS), but is now used in a variety of survey
projects. We checked its performance by spectroscopy of CADIS objects, where it
provides high reliability (6 mistakes among 151 objects with R<24), especially
for the quasar selection, and redshifts accurate within sigma_z = 0.03 for
galaxies and sigma_z = 0.1 for quasars. For an optimization of future surveys,
a few model surveys are compared, which use the same amount of telescope time
but different filter sets. In summary, medium-band surveys perform superior to
broad-band surveys although they collect less photons. A full account of this
work is already in print.


title: Efficiency of Medium-Band Surveys

abstract:
  We simulate multi-color surveys, which use the same telescope time on
different filter sets of broad-band and medium-band filters. We use a
photometric classification method for identifying stars, galaxies and quasars
and for estimating multi-color redshifts of extragalactic objects. A library of
>65000 color templates is used for comparison with observed objects.
Spectroscopy from the CADIS survey has proven the performance of the method. We
learned, that medium-band surveys perform superior to broad-band surveys in
terms of classification and redshift estimation although they collect less
photons. A full account of this work is already in print.


title:
Sharp HI edges at high z: the gas distribution from Damped Lyman-alpha
  to Lyman-limit absorption systems

abstract:
  We derive the distribution of neutral and ionized gas in high redshift clouds
which are optically thick to hydrogen ionizing radiation, using published data
on Lyman-limit and Damped Lyman-alpha absorption systems in the redshift range
1.75 < z < 3.25. We assume that the distribution of the hydrogen total (HI+HII)
column density in the absorbers follows a power law K N_H^{-alpha}, whereas the
observed HI column density distribution deviates from a pure power law as a
result of ionization from a background radiation field. Comparison of the
models and observations give Maximum Likelihood solutions for the exponent
alpha and for X, the value of log(N_H/N_HI) when the Lyman-limit optical depth
is unity: alpha=2.7^{+1.0}_{-0.7} and X=2.75\pm0.35. X is much lower than what
would be obtained for a gaseous distribution in equilibrium under its own
gravity but the ratio of dark matter to gas density is not well constrained
being log(eta_0)=1.1\pm 0.8. An extrapolation of our derived power law
distribution towards systems of lower column density, the Lyman-alpha forest,
favours models with log(eta_0) < 1.1 and alpha=2.7-3.3. With alpha appreciably
larger than 2, Lyman-limit systems contain more gas than Damped Lyman-alpha
systems and Lyman-alpha forest clouds even more. Estimates of the cosmological
gas and dark matter density due to absorbers of different column density around
z=2.5 are also given.


title: The boron absorption line at 2089.6 AA in HD 140283 ?

abstract:
  We have observed the B I line at 2089.6 AA in the metal poor star HD 140283
with HST/STIS. The observation was an attempt to confirm the B abundances
derived from the 2497 AA B I line in earlier works in general, and for for this
star in particular (Edvardsson et al. 1994 A&A 290, 176; Kiselman & Carlsson
1996, A&A 311, 680). The resulting spectrum gained from 8 orbits of
observations is hardly consistent with the boron abundance derived in the
earlier works. A pure 10^B line could produce the feature observed but no
reasonable process can produce such a ratio between 10^B and 11^B. More likely
the analysed feature is affected by a statistical fluctuation. A conservative
upper limit estimate of the NLTE corrected boron abundance gives a value
marginally consistent with that derived from the 2497 AA line. We are proposing
further observations to derive a more definite abundance from the line.


title: The 2000 outburst of the recurrent nova CI Aquilae: optical spectroscopy

abstract:
  We present low- and medium resolution spectra of the recurrent nova CI
Aquilae taken at 14 epochs in May and June, 2000. The overall appearance is
similar to other U Sco-type recurrent novae (U Sco, V394 CrA). Medium
resolution (R=7000-10000) hydrogen and iron profiles suggest an early expansion
velocity of 2000-2500 km/s. The H\alpha evolution is followed from Dt = -0.6 d
to +53 d, starting from a nearly Gaussian shape to a double peaked profile
through strong P-Cyg profiles. The interstellar component of the sodium D line
and two diffuse interstellar bands put constraints on the interstellar
reddening which is estimated to be E(B-V)=0.85\pm0.3. The available visual and
CCD-V observations are used to determine t0,t2 and t3. The resulting parameters
are: t0=2451669.5\pm0.1, t2=30\pm1 d, t3=36\pm1 d. The recent lightcurve is
found to be generally similar to that observed in 1917 with departures as large
as 1-2 mag in certain phases. This behaviour is also typical for the U Sco
subclass.


title: XMM-Newton observation of the Lockman Hole; I. The X-ray Data

abstract:
  We report on the first deep X-ray survey with the XMM-Newton observatory
during the performance verification phase. The field of the Lockman Hole, one
of the best studied sky areas over a very wide range of wavelengths, has been
observed. A total of ~100 ksec good exposure time has been accumulated.
Combining the images of the European Photon Imaging Camera (EPIC) detectors we
reach a flux limit of 0.31, 1.4 and 2.4 X 10^{-15} erg cm^{-2} s^{-1},
respectively in the 0.5-2, 2-10, and 5-10 keV band. Within an off-axis angle of
10 arcmin we detect 148, 112 and 61 sources, respectively. The log(N)-log(S)
relation in the three bands is compared with previous results. In particular in
the 5-10 keV band these observations present the deepest X-ray survey ever,
about a factor 20 more sensitive than the previous BeppoSAX observations. Using
X-ray spectral diagnostics and the set of previously known, spectroscopically
identified ROSAT sources in the field, the new sources can be classified.
XMM-Newton detects a significant number (~40%) of X-ray sources with hard,
probably intrinsically absorbed X-ray spectra, confirming a prediction of the
population synthesis models for the X-ray background.


title:
The detection of a 1.4-h period in RW Ursa Minoris - candidate for
  shortest recorded orbital period nova

abstract:
  CCD photometry of the classical nova RW UMi during 10 nights in 1995 through
an R filter and 14 nights in 1997 through a `clear' filter, with the 1-m Wise
telescope yields a periodic modulation in the light curve with the period
0.05912+/-0.00015 d and a semi amplitude of 0.025 mag. We discuss several
explanations for the periodicity, and suggest that it is likely to be the
orbital period of the binary system or a superhump period. RW UMi is thus a
candidate for the classical nova with the shortest known orbital period.


title:
A comparison of the anelastic and subseismic approximations for
  low-frequency gravity modes in stars

abstract:
  A comparative study of the properties of the anelastic and subseismic
approximations is presented. The anelastic approximation is commonly used in
astrophysics in compressible convection studies whereas the subseismic
approximation comes from geophysics where it is used to describe long-period
seismic oscillations propagating in the Earth's outer fluid core. Both
approximations aim at filtering out the acoutic waves while retaining the
density variations of the equilibrium configuration. However, they disagree on
the form of the equation of mass conservation. We show here that the anelastic
approximation is in fact the only consistent approximation as far as stellar
low-frequency oscillations are concerned. We also show that this approximation
implies Cowling's approximation which neglects perturbations of the gravity
field. Examples are given to assert the efficiency of the anelastic
approximation.


title: Extreme Ultraviolet Emission from Abell 4059

abstract:
  We present the results of a search for Extreme Ultraviolet emission in A4059,
a cluster with an X-ray emitting cluster gas. Our analysis of Extreme
Ultraviolet Explorer (EUVE) Deep Survey observations of this cluster shows that
it is associated with diffuse EUV emission. Outside the central 2 arcmin radius
the entire EUV emission detected is explained by the low energy tail of the
X-ray emitting gas. Within the central 2 arcmin region of the cluster we find a
deficit of EUV emission compared to that expected from the X-ray gas. This flux
deficit is discussed in the context of the cluster's cooling flow. The results
derived for A4059 are compared to EUVE results obtained for other clusters such
as Coma, Virgo, A1795, and A2199. As part of the study we have carried out a
detailed investigation of the stability of the EUVE Deep Survey detector
background. Based on long integrations of blank sky over 27 months we disprove
claims of substantial time dependent changes in the detector background by R.
Lieu and coworkers. We also show, contrary to the claim of R. Lieu and
coworkers, that the images obtained with the detector are independent of the
pulse height threshold of the detector over a substantial range of threshold
settings.


title: The globular cluster system of the young elliptical NGC 6702

abstract:
  We study the globular cluster (GC) system of the dust-lane elliptical galaxy
NGC 6702, using B, V and I-band photometric observations carried out at the
Keck telescope. This galaxy has a spectroscopic age of ~2Gyrs suggesting recent
star-formation. We find strong evidence for a bimodal GC colour distribution,
with the blue peak having a colour similar to that of the Galactic halo GCs.
Assuming that the blue GCs are indeed old and metal-poor, we estimate an age of
2-5Gyrs and supersolar metallicity for the red GC subpopulation. Despite the
large uncertainties, this is in reasonable agreement with the spectroscopic
galaxy age. Additionally, we estimate a specific frequency of S_{N}=2.3\pm1.1
for NGC 6702. We predict that passive evolution of NGC 6702 will further
increase its specific frequency to S_{N}~2.7 within 10Gyrs, in closer agreement
to that of typical present-day ellipticals. We also discuss evidence that the
merger/accretion event that took place a few Gyrs ago involved a high gas
fraction.


title: Anomalous Surface Brightness Fluctuations in NGC 4489

abstract:
  Anomalously high K-band surface brightness fluctuations (SBF) have been
reported in NGC 4489 by Pahre & Mould (1994), Jensen et al. (1996) and Jensen
et al. (1998). However, these conclusions were uncertain because of relatively
low signal-to-noise data. New high signal-to-noise data for NGC 4489 have been
obtained at the NOAO/KPNO 2.1m and the ESO/La Silla 3.5m NTT telescopes.
Adopting the I-band SBF distance modulus determined by Tonry et al. (1990) and
the M_I versus (V-I) calibration of Tonry et al. (2000), a value of M_K =-6.18
+/-0.09 mag was derived. Relative to the average empirical M_K derived for
giant ellipticals by Jensen et al. (1998) (M_K=-5.61 +/- 0.12 mag), the
detection of an anomalous K-band SBF in NGC 4489 is confirmed at the two sigma
level. Such anomalous fluctuations could be caused by an extended giant branch,
consisting of either intermediate-age AGB stars above the tip of the
first-ascent giant branch or high-metallicity first-ascent giants, or by lack
of a full understanding of the K-band SBF calibration. This result raises
questions about the accuracy of K-band SBF distance measurements for elliptical
galaxies with unknown stellar composition and underscores the need for M_K
measurements over a larger range of color and luminosity.


title: VLT Deep I-band Surface Brightness Fluctuations of IC 4296

abstract:
  From theoretical predictions, the introduction of 8-m class telescopes
permits one to extend Surface Brightness Fluctuations measurements from the
ground to ~7000 km/s, with a precision that is comparable to current
space-based measurements. We have measured I--band SBF in IC 4296 in Abell 3565
cz~3630 km/s with the ESO Very Large Telescope. Adopting the Tonry et al.
(2000) calibration for I-band SBF we determined a distance modulus of (I_o,k -
M_I)=33.44 +/- 0.17 mag corresponding to a galaxy distance of 49 +/- 4 Mpc.
This result is consistent with the HST observation from Lauer et al. (1998):
(I_F814 - M_F814) = 33.47 +/- 0.13 mag.


title: Large-Scale Primordial Magnetic Fields from Inflation and Preheating

abstract:
  We consider models in which the (transverse) photon mass is non-zero during
inflation and drops to zero non-adiabatically at the end of inflation. Through
this process, vacuum fluctuations of the photon field are converted into
physical, long-wavelength modes with high amplitude. The resulting spectrum of
the field strength is approximately B_l ~ 1/l, where l is the relevant
coherence scale. With a reasonable model of field evolution we obtain, on
comoving galactic scales, a magnetic field strong enough to seed a dynamo
mechanism and generate the observed galactic magnetic fields.


title:
Close stellar encounters with planetesimal discs: The dynamics of
  asymmetry in the Beta Pictoris system

abstract:
  We numerically investigate the dynamics of how a close stellar fly-by
encounter of a symmetrical circumstellar planetesimal disc can give rise to the
many kinds of asymmetries and substructures attributed to the edge-on dusty
disc of Beta Pic. In addition we present new optical coronagraphic observations
of the outer parts of Beta Pic's disc, and report that the radial extent is
significantly greater than was found in previous measurements. The
northeasterly extension of the disc's midplane is now measured out to 1835au
from the star; the southwesterly component is measured out to 1450au. Hence we
use the length asymmetry induced in a distribution of simulation test particles
as the principal diagnostic feature when modelling the disc response, in order
to constrain fly-by parameters. In particular we favour a low inclination
prograde and near-parabolic orbit perturber of mass approximately 0.5 Solar
masses. These initial conditions suggest that the perturber could have been
physically associated with Beta Pic prior to the encounter. Thus we also
consider the possibility that the perturber could be bound to Beta Pic: a
consideration also of general interest where dust discs are known to exist in
binary star systems. In some of our models, we can relate groupings of
perturbed particles to the large-scale structure of the Beta Pic disc. The
groupings correspond to: high eccentricity and inclination particles that reach
apocentre and maximum height in the southwest, moderately eccentric and low
inclination particles that reach apocentre in the northeast, and relatively
unperturbed particles inside approximately 200au radius.


title: Dissolving star cluster candidates

abstract:
  We present a list of 34 neglected entries from star cluster catalogues
located at relatively high galactic latitudes ($|b| >$ 15$^{\circ}$) which
appear to be candidate late stages of star cluster dynamical evolution.
Although underpopulated with respect to usual open clusters, they still present
a high number density contrast as compared to the galactic field. This was
verified by means of (i) predicted model counts from different galactic
subsystems in the same direction, and (ii) Guide Star Catalog equal solid angle
counts for the object and surrounding fields. This suggests that the objects
are physical systems, possibly star clusters in the process of disruption or
their fossil remains. The sample will be useful for followup studies in view of
verifying their physi cal nature.


title: A New Radio - X-Ray Probe of Galaxy Cluster Magnetic Fields

abstract:
  Results are presented of a new VLA-ROSAT study that probes the magnetic field
strength and distribution over a sample of 16 ``normal'' low redshift (z < 0.1)
galaxy clusters. The clusters span two orders of magnitude in X-ray luminosity,
and were selected to be free of (unusual) strong radio cluster halos, and
widespread cooling flows. Consistent with these criteria, most clusters show a
relaxed X-ray morphology and little or no evidence for recent merger activity.
  Analysis of the rotation measure (RM) data shows cluster-generated Faraday RM
excess out to ~0.5 Mpc from cluster centers. The results, combined with RM
imaging of cluster-embedded sources and ROSAT X-ray profiles indicates that the
hot intergalactic gas within these ``normal'' clusters is permeated with a high
filling factor by magnetic fields at levels of <|B|> = 5-10 (l/10 kpc)^{-1/2}
microGauss, where l is the field correlation length. These results lead to a
global estimate of the total magnetic energy in clusters, and give new insight
into the ultimate energy origin, which is likely gravitational. These results
also shed some light on the cluster evolutionary conditions that existed at the
onset of cooling flows.


title: Timescales of Disk Evolution and Planet Formation

abstract:
  It has been suggested that circumstellar disks evolve from dense, actively
accreting structures to low-mass, replenished remnants. During this transition,
grains may assemble into planetesimals, or the disk may be cleared by newborn
planets. Recently identified nearby groups of young stars provide valuable
laboratories for probing disk evolution. I discuss the properties of dust disks
in the TW Hydrae Association and the MBM 12 cloud, and compare the results to
other studies of disk evolution and planet formation timescales.


title: Force-Free Models of Magnetically Linked Star-Disk Systems

abstract:
  Disk accretion onto a magnetized star occurs in a variety of astrophysical
contexts, from young stars to X-ray pulsars. The magnetohydrodynamic
interaction between the stellar field and the accreting matter can have a
strong effect on the disk structure, the transfer of mass and angular momentum
between the disk and the star, and the production of bipolar outflows, e.g.,
plasma jets. We study a key element of this interaction - the time evolution of
the magnetic field configuration brought about by the relative rotation between
the disk and the star - using simplified, largely semianalytic, models. We
first discuss the rapid inflation and opening up of the magnetic field lines in
the corona above the accretion disk, which is caused by the differential
rotation twisting. Then we consider additional physical effects that tend to
limit this expansion, such as the effect of plasma inertia and the possibility
of reconnection in the disk's corona, the latter possibly leading to repeated
cycles in the evolution. We also derive the condition for the existence of a
steady state for a resistive disk and conclude that a steady state
configuration is not realistically possible. Finally, we generalize our
analysis of the opening of magnetic field lines by using a non-self-similar
numerical model that applies to an arbitrarily rotating (e.g. keplerian) disk.


title: Electron-Positron Pair Cascades and Precursors in Gamma-Ray Bursts

abstract:
  Gamma-ray burst sources with a high luminosity can produce electron-positron
pair cascades in their environment as a result of back-scattering of a seed
fraction of their original hard spectrum. The resulting spectral modifications
offer the possibility of diagnosing not only the compactness parameter of the
gamma-ray emitting region but also the baryonic density of the environment
external to the burst.


title: Young Clusters in the Magellanic Clouds II

abstract:
  We present the results of a quantitative study of the degree of extension to
the boundary of the classical convective core within intermediate mass stars.
The basis of our empirical study is the stellar population of four young
populous clusters in the Magellanic Clouds which has been detailed in Keller,
Bessell & Da Costa (2000). The sample affords a meaningful comparison with
theoretical scenarios with varying degrees of convective core overshoot and
binary star fraction. Two critical properties of the population, the
main-sequence luminosity function and the number of evolved stars, form the
basis of our comparison between the observed data set and that simulated from
the stellar evolutionary models. On the basis of this comparison we conclude
that the case of no convective core overshoot is excluded at a 2 sigma level.


title:
Photometric and Spectroscopic Analysis of Cool White Dwarfs with
  Trigonometric Parallax Measurements

abstract:
  A photometric and spectroscopic analysis of 152 cool white dwarf stars is
presented. The discovery of 7 new DA white dwarfs, 2 new DQ white dwarfs, 1 new
magnetic white dwarf, and 3 weak magnetic white dwarf candidates, is reported,
as well as 19 known or suspected double degenerates. The photometric energy
distributions, the Halpha line profiles, and the trigonometric parallax
measurements are combined and compared to model atmosphere calculations to
determine the effective temperature and the radius of each object, and also to
constrain the atmospheric composition. New evolutionary sequences with C/O
cores with thin and thick hydrogen layers are used to derive masses and ages.
We confirm the existence of a range in Teff between 5000 and 6000K where almost
all white dwarfs have H-rich atmospheres. There is little evidence for mixed
H/He dwarfs, with the exception of 2 He-rich DA stars, and 5 C2H white dwarfs
which possibly have mixed H/He/C atmospheres. The DQ sequence terminates near
6500K, below which they are believed to turn into C2H stars. True DC stars
slightly above this temperature are found to exhibit H-like energy
distributions despite the lack of Halpha absorption. Attempts to interpret the
chemical evolution show the problem to be complex. Convective mixing is
necessary to account for the non-DA to DA ratio as a function of temperature.
The presence of helium in cool DA stars, the existence of the non-DA gap, and
the peculiar DC stars are also explained in terms of convective mixing,
although our understanding of how this mechanism works needs to be revised. The
oldest object in our sample is about 7.9 Gyr or 9.7 Gyr old depending on
whether thin or thick hydrogen layer models are used. The mean mass of our
sample is 0.65 +/- 0.20 Msun.


title:
The global structure of thin, stratified "alpha"-discs and the
  reliability of the one layer approximation

abstract:
  We report the results of a systematic comparison between the vertically
averaged model and the vertically explicit model of steady state, Keplerian,
optically thick "alpha"-discs. The simulations have concerned discs currently
found in three different systems: dwarf novae, young stellar objects and active
galactic nuclei. In each case, we have explored four decades of accretion rates
and almost the whole disc area
  (except the narrow region where the vertically averaged model has degenerate
solutions). We find that the one layer approach gives a remarkably good
estimate of the main physical quantities in the disc, and specially the
temperature at the equatorial plane which is accurate to within 30% for cases
considered. The major deviations (by a factor < 4) are observed on the disc
half-thickness. The sensitivity of the results to the "alpha"-parameter value
has been tested for 0.001 < alpha < 0.1 and appears to be weak. This study
suggests that the ``precision'' of the vertically averaged model which is easy
to implement should be sufficient in practice for many astrophysical
applications.


title: The Infrared Surface Brightness Fluctuation Hubble Constant

abstract:
  We measured infrared surface brightness fluctuation (SBF) distances to an
isotropically-distributed sample of 16 distant galaxies with redshifts reaching
10,000 km/s using the near-IR camera and multi-object spectrometer (NICMOS) on
the Hubble Space Telescope (HST). The excellent spatial resolution, very low
background, and brightness of the IR fluctuations yielded the most distant SBF
measurements to date. Twelve nearby galaxies were also observed and used to
calibrate the F160W (1.6 micron) SBF distance scale. Of these, three have
Cepheid variable star distances measured with HST and eleven have optical
I-band SBF distance measurements. A distance modulus of 18.5 mag to the Large
Magellanic Cloud was adopted for this calibration. We present the F160W SBF
Hubble diagram and find a Hubble constant Ho=76 +/- 1.3 (1-sigma statistical)
+/- 6 (systematic) km/s/Mpc. This result is insensitive to the velocity model
used to correct for local bulk motions. Restricting the fit to the six most
distant galaxies yields the smallest value of Ho=72 +/- 2.3 km/s/Mpc consistent
with the data. This 6% decrease in the Hubble constant is consistent with the
hypothesis that the Local Group inhabits an under-dense region of the universe,
but is also consistent with the best-fit value of Ho=76 km/s/Mpc at the
1.5-sigma level.


title: Non-LTE analysis of neutral magnesium in cool stars

abstract:
  Calculations of the statistical equilibrium of magnesium in the solar
photosphere have shown that NLTE populations hardly affect Mg line formation in
the Sun. However, in metal-poor dwarfs and giants the influence of electron
collisions is reduced, and the ultraviolet radiation field, enhanced due to
reduced background line opacity, results in more pronounced NLTE effects. In
thephotosphere of a cool star excitation and ionization due to collisions with
neutral hydrogen can outweigh electron collisions. Analyses based on NLTE
populations lead to significantly higher Mg abundances than those calculated
from LTE. We calculate magnesium abundances in 10 cool dwarfs and subgiants
with metallicities from -2.29 to 0.0. The results are based on spectra of
high-resolution and high signal-to-noise ratio. Stellar effective temperatures
are derived from Balmer line profiles,surface gravities from Hipparcos
parallaxes and the wings of the MgIb triplet, and metal abundances and
microturbulence velocities are obtained from LTE analyses of FeII line
profiles. For stars with metallicities between -2.0 < [Fe/H] < -1.0 abundance
corrections Delta{[Mg/H]_{NLTE-LTE}} ~ 0.05 - 0.11 are found. As expected the
corrections increase with decreasing metal abundance, and they increase
slightly with decreasing surface gravity. We also calculate the statistical
equilibrium of magnesium for series of model atmospheres with different stellar
parameters and find that $\Delta{\rm [Mg/H]_{NLTE-LTE}}$ increases with
effective temperature between 5200 and 6500 K. For extremely metal-poor stars
the abundance corrections approach Delta{[Mg/H]_{NLTE-LTE}} ~ 0.23 at [Fe/H] ~
-3.0.


title: Physical parameters in relativistic jets from Compact Symmetric Objects

abstract:
  Compact symmetric objects conform a class of sources characterized by high
luminosity radio emission located symmetrically on both sides of the active
galactic nucleus on linear scales of less than 1 kpc. Given their small size,
the hot spots of the jets in CSOs provide a unique laboratory for the study of
the physics of relativistic jets and their environment close to the central
engine.
  We present a simple model for the hot spots in CSOs assuming synchrotron
emission, minimum energy and ram pressure equilibrium with the external medium.
Further comparison of our model with observational data allows us to constrain
the physical parameters in the hot spots and the jets feeding them, and the
density profile of the external medium.


title:
VLA HI Line Observations of the Extremely Metal-Poor Blue Compact Dwarf
  Galaxy SBS 0335-052

abstract:
  We present the results of HI mapping with the NRAO VLA of one of the most
metal-deficient blue compact dwarf (BCD) galaxies known, SBS 0335-052, with an
oxygen abundance of only 1/40 that of the Sun. We study the structure and
dynamics of the neutral gas in this chemically young object with a spatial
resolution of 20.5"x15" (~ 5.4 x 3.9 kpc at an assumed distance of 54.3 Mpc), a
sensitivity at the 2sigma detection level of ~2.0K or 7.5x10^19 cm^-2 and a
velocity resolution of 21.2 km s^-1. We detected a large HI complex associated
with this object with an overall size of about 66 by 22 kpc and elongated in
the East-West direction. There are two prominent, slightly resolved peaks
visible in the integrated HI map, separated in the East-West direction by 22
kpc (84"). The eastern peak is nearly coincident with the position of the
optical galaxy SBS 0335-052. The western peak is about a factor of 1.3 brighter
in the HI line and is identified with a faint blue compact dwarf galaxy, SBS
0335-052W, with m_B = 19.4, and a metallicity close to the lowest values known
for BCDs, about 1/50 that of the Sun. The radial velocities of both systems are
similar, suggesting that the two BCDs SBS 0335-052 and SBS 0335-052W constitute
a pair of dwarf galaxies embedded in a common HI envelope. Alternatively, the
BCDs can be the nuclei of two distinct interacting primordial HI clouds. The
estimated total dynamical mass, assuming the BCDs form a bound system, is
larger than 6x10^9 Msun. This is to be compared to a total gaseous mass M_gas =
2.1x10^9 Msun, and a total stellar mass Mstar < 10^8 Msun. Hence, the mass of
the SBS 0335-052 system is dominated by dark matter (abridged).


title: A superfluid He3 detector for direct dark matter search

abstract:
  MACHe3 (MAtrix of Cells of superfluid He3) is a project of a new detector for
direct Dark Matter Search. The idea is to use superfluid He3 as a sensitive
medium. The existing device, the superfluid He3 cell, will be briefly
introduced. Then a description of the MACHe3 project will be presented, in
particular the background rejection and the neutralino event rate that may be
achieved with such a device.


title: Tree structure of the percolating Universe

abstract:
  We present a numerical study of topological descriptors of initially Gaussian
and scale-free density perturbations evolving via gravitational instability in
an expanding universe. We carefully evaluate and avoid numerical contamination
in making accurate measurements on simulated fields on a grid in a finite box.
Independent of extent of non linearity, the measured Euler number of the
excursion set at the percolation threshold, $\delta_c$, is positive and nearly
equal to the number of isolated components, suggesting that these structures
are trees. Our study of critical point counts reconciles the clumpy appearance
of the density field at $\delta_c$ with measured filamentary local curvature.
In the Gaussian limit, we measure $|\delta_c|> \sigma$ in contrast to widely
held belief that $|\delta_c| \sim \sigma$, where $\sigma^2$ is the variance of
the density field.


title: Escape in Hill's Problem

abstract:
  This didactic paper is motivated by the problem of understanding how stars
escape from globular star clusters. One formulation of this problem is known,
in dynamical astronomy, as Hill's problem. Originally intended as a model for
the motion of the moon around the earth with perturbations by the sun, with
simple modifications it also serves as a model for the motion of a star in a
star cluster with perturbations by the galaxy.
  The paper includes introductory sections on the derivation of the equations
of motion of Hill's problem, their elementary properties, and extensions to
deal with non-point masses and non-circular orbits. We then show how the rate
of escape may be calculated numerically and estimated theoretically, and
discuss how this simple picture is modified if the stars in a cluster are also
undergoing two-body relaxation. Finally we introduce some established ideas for
obtaining the distribution of escape times.


title: The spherical collapse model in a universe with cosmological constant

abstract:
  We generalize the spherical collapse model for the formation of dark matter
halos to apply in a universe with arbitrary positive cosmological constant. We
calculate the critical condition for collapse of an overdense region and give
exact values of the characteristic densities and redshifts of its evolution.


title:
Evidence of magnetic accretion in an SW Sex star: discovery of variable
  circular polarization in LS Pegasi

abstract:
  We report on the discovery of variable circular polarization in the SW Sex
star LS Pegasi. The observed modulation has an amplitude of ~0.3 % and a period
of 29.6 minutes, which we assume as the spin period of the magnetic white
dwarf. We also detected periodic flaring in the blue wing of Hbeta, with a
period of 33.5 minutes. The difference between both frequencies is just the
orbital frequency, so we relate the 33.5-min modulation to the beat between the
orbital and spin period. We propose a new accretion scenario in SW Sex stars,
based on the shock of the disk-overflown gas stream against the white dwarf's
magnetosphere, which extends to the corotation radius. From this geometry, we
estimate a magnetic field strength of B(1) ~ 5-15 MG. Our results indicate that
magnetic accretion plays an important role in SW Sex stars and we suggest that
these systems are probably Intermediate Polars with the highest mass accretion
rates.


title:
A search for possible interactions between ejections from GRS 1915+105
  and the surrounding interstellar medium

abstract:
  We have observed an extended region surrounding the first discovered galactic
superluminal source GRS 1915+105, seeking evidence of interaction between the
relativistic ejecta of that object and the interstellar medium. We find two
radio sources axisymmetrically aligned along the sub-arcsecond relativistic
ejecta of GRS 1915+105 and roughly 17' distant from it, which coincide with the
luminous IRAS sources 19124+1106 and 19132+1035. We have observed these sources
at centimeter (VLA), millimeter (IRAM 30m), and infrared (ISO, UKIRT, ESO/MPI
2.2m) wavelengths in both line and continuum emission. At centimeter
wavelengths a non-thermal jet-like feature aligned along the outflow axis is
located adjacent to the inner edge of the southern source. Strong density
enhancements are found in the millimeter tracers CO and H13CO+ at the positions
of both sources and some of the morphology is reminiscent of shock-like
interactions; however, linewidths are narrow. At infrared wavelengths strong
hydrogen recombination lines and weak lines of molecular hydrogen are observed
at the southern source. We discuss these results as possible evidence of the
sought-after interaction, both in terms of the regions undergoing ongoing
shock-heating and in terms of them being locations of shock-induced star
formation. The evidence for each of these is inconclusive. Millimeter line
mapping of a portion of W 50 where the relativistic jets of the X-ray binary SS
433 interact with the interstellar medium shows roughly similar morphology as
GRS 1915+105, suggesting that the phenomena observed at the IRAS sources may
not be unusual for such a long distance interaction.


title:
Gamma-ray sources as relics of recent supernovae in the nearby Gould
  Belt

abstract:
  The nearby, 30 to 40 Myr old, starburst region of the Gould Belt has formed
numerous massive stars. Within its 300 pc radius, it produces core-collapse
supernovae at an enhanced rate which is shown to be 75 to 95 Myr{-1} kpc{-2},
i.e. 3 to 5 times higher than the local Galactic rate, over the past and future
few million years. A population of persistent, but unidentified, gamma-ray
sources has been recently singled out at medium latitudes above 100 MeV. Their
distribution across the sky is shown to be quite significantly and better
correlated with the tilted Gould Belt than with other Galactic structures. As
many as 40 +- 5 sources are statistically associated with the Belt at |b|> 5
deg. It is therefore proposed that these sources are part of the Belt and are
relics of the Belt supernovae in the form of million-year old pulsars. Their
presence stresses how active the local medium is, heated, enriched and shaped
by multiple recent explosions.


title: The LMC eclipsing binary HV 2274 revisited

abstract:
  We reanalyse the UV/optical spectrum and optical broad-band data of the
eclipsing binary HV 2274 in the LMC, and derive its distance following the
method given by Guinan et al. (1998a,b) of fitting theoretical spectra to the
stars' UV/optical spectrum plus optical photometry. We describe the method in
detail, pointing out the various assumptions that have to be made; moreover, we
discuss the systematic effects of using different sets of model atmospheres and
different sets of optical photometric data. It turns out that different
selections of the photometric data, the set of model atmospheres and the
constraints on the value of the ratio of selective to total extinction in the
$V$-band, result in a 25% range in distances (although some of these models
have a large ${\chi}^2$). For our best choice of these quantities the derived
value for the reddening to HV 2274 is E(B-V) = 0.103 $\pm$ 0.007, and the
de-reddened distance modulus is DM = 18.46 $\pm$ 0.06; the DM to the center of
the LMC is found to be 18.42 $\pm$ 0.07. This is significantly larger than the
DM of 18.30 $\pm$ 0.07 derived by Guinan et al. (1998a).


title:
The Accretion-Ejection Instability and a "Magnetic Flood" scenario for
  GRS 1915+105

abstract:
  I present a global view of recent results on the Accretion-Ejection
Instability (AEI), described in more details in other contributions to this
workshop. These results address essentially the characteristics of the AEI as a
good candidate to explain the low-frequency QPO of X-ray binaries, in
particular (at $\sim 1-10$ Hz) of micro-quasars. I then discuss how, if the AEI
is considered as the source of the QPO, a possible scenario can be considered
where the $\sim 30$ mn. cycles of GRS 1915+105 are controlled by the evolution
of magnetic flux in the disk.


title:
Particle injection and reacceleration in clusters of galaxies and the
  EUV excess: the case of Coma

abstract:
  We calculate the energy distribution of the relativistic particles injected
in the ICM during a phase of reacceleration of the relativistic particles in
the cluster volume. We apply our results to the case of the Coma cluster in
which recent merging activity and the presence of the radio halo may suggest
that reacceleration processes are efficient. We find that the electron
population injected in the central part of the cluster by the head-tail radio
galaxy NGC 4869 may account for a large fraction, if not all, of the detected
EUV excess via inverse Compton scattering of the cosmic microwave background
(CMB) photons. If radio haloes are powered by reacceleration mechanisms active
in the cluster volume, moderate non-thermal EUV excesses (of order of $\sim 1-5
\cdot 10^{42}$erg s^{-1}) should be a common feature of clusters containing
powerful head-tail radio galaxies and/or AGNs.


title: Should Elliptical Galaxies Be Idealised as Collisionless Equilibria?

abstract:
  This talk summarises several different lines of argument suggesting that one
should not expect cuspy nonaxisymmetric galaxies to exist as robust, long-lived
collisionless equilibria, i.e., that such objects should not be idealised as
time-independent solutions to the collisionless Boltzmann equation.