title:
Evidence for Evolving Spheroidals in the Hubble Deep Fields North and
  South

abstract:
  We investigate the dispersion in the internal colours of faint spheroidals in
the HDFs North and South. We find that a remarkably large fraction ~30% of the
morphologically classified spheroidals with I<24 mag show strong variations in
internal colour, which we take as evidence for recent episodes of
star-formation. In most cases these colour variations manifest themselves via
the presence of blue cores, an effect of opposite sign to that expected from
metallicity gradients. Examining similarly-selected ellipticals in five rich
clusters with 0.37<z<0.83 we find a significant lower dispersion in their
internal colours. This suggests that the colour inhomogeneities have a strong
environmental dependence being weakest in dense environments where spheroidal
formation was presumably accelerated at early times. We use the trends defined
by the cluster sample to define an empirical model based on a high-redshift of
formation and estimate that at z~1 about half the field spheroidals must be
undergoing recent episodes of star-formation. Using spectral synthesis models,
we construct the time dependence of the density of star-formation. Although the
samples are currently small, we find evidence for an increase in $\rho_{SFR}$
between z=0 to z=1. We discuss the implications of this rise in the context of
that observed in the similar rise in the abundance of galaxies with irregular
morphology. Regardless of whether there is a connection our results provide
strong evidence for the continued formation of field spheroidals over 0<z<1.


title: Are "Bondi-Hoyle Wakes" detectable in clusters of galaxies?

abstract:
  In clusters of galaxies, the reaction of the intracluster medium (ICM) to the
motion of the co-existing galaxies in the cluster triggers the formation of
unique features, which trace their position and motion. Galactic wakes, for
example, are an apparent result of the ICM/galaxy interactions, and they
constitute an important tool for deciphering the motion of the cluster
galaxies. In this paper we investigate whether Bondi-Hoyle accretion can create
galactic wakes by focusing the ICM behind moving galaxies. The solution of the
equations that describe this physical problem provide us with observable
quantities along the wake at any time of its lifetime. We also investigate
which are the best environmental conditions for the detectability of such
structures in the X-ray images of clusters of galaxies. We find that
significant Bondi-Hoyle wakes can only be formed in low temperature clusters,
and that they are more pronounced behind slow-moving, relatively massive
galaxies. The scale length of these elongated structures is not very large: in
the most favourable conditions a Bondi-Hoyle wake in a cluster at the redshift
of z=0.05 is 12 arcsec long. However, the wake's X-ray emission is noticeably
strong: the X-ray flux can reach ~30 times the flux of the surrounding medium.
Such features will be easily detectable in Chandra's and XMM-Newton's X-ray
images of nearby, relatively poor clusters of galaxies.


title: Rotation, Statistical Dynamics and Kinematics of Globular Clusters

abstract:
  Evolution with mass segregation and the evolution of the rotation of cores
are both discussed for self-similar core collapse. Evolution with angular
velocity proportional to the square root of the density is predicted. On the
Dynamical Main Sequence of globular clusters the energy emission from binaries
balances the energy expended in expanding the halo.
  Newton's exactly solved N-body problem is then given, along with recent
generalisations, all of which have no violent relaxation, but a new type of
statistical equilibrium is discussed.
  Finally, we set the creation of streams in the Galaxy's halo in the
historical context of their discovery.


title: Photometric Redshifts and Gravitational Telescopes

abstract:
  We review the use of photometric redshifts in the particular context of
Gravitational Telescopes. We discuss on the possible application of such a
technique to the study of both the faint population of distant sources and the
properties of cluster lenses. Photometric reshifts could be used to derive the
redshift distribution and properties of a very faint subsample of high-z lensed
galaxies, otherwise out of reach. Concerning the mass distribution in lensing
clusters, photometric reshifts are strongly needed to scale the mass in weak
lensing analysis, and to characterize the lensing structure.


title:
The BeppoSAX HELLAS survey: on the nature of faint hard X-ray selected
  sources

abstract:
  The BeppoSAX 4.5-10 keV High Energy Large Area Survey has covered about 80
square degrees of sky down to a flux of F(5-10keV)~5E-14 cgs. Optical
spectroscopic identification of about half of the sources in the sample (62)
shows that many (~50%) are highly obscured AGN, in line with the predictions of
AGN synthesis models for the hard X-ray background (XRB, see e.g. Comastri et
al. 1995). The X-ray data, complemented by optical, near-IR and radio
follow-up, indicate that the majority of these AGN are ``intermediate''
objects, i.e. type 1.8-1.9 AGN,`red' quasars, and even a few broad line, blue
continuum quasars, obscured in X-rays by columns of the order of
logNH=22.5-23.5 cm-2, but showing a wide dispersion in optical extinction. The
optical and near-IR photometry of the obscured objects are dominated by galaxy
starlight, indicating that a sizeable fraction of the accretion power in the
Universe may actually have been missed in optical color surveys. This also
implies that multicolor photometry techniques may be efficiently used to assess
the redshift of the hard X-ray selected sources.


title:
N-body simulations of self-gravitating gas in stationary fragmented
  state

abstract:
  The interstellar medium is observed in a hierarchical fractal structure over
several orders of magnitude in scale. Aiming to understand the origin of this
structure, we carry out numerical simulations of molecular cloud fragmentation,
taking into account self-gravity, dissipation and energy input. Self-gravity is
computed through a tree code, with fully or quasi periodic boundary conditions.
Energy dissipation is introduced through cloud-cloud ineslatic collisions.
Several schemes are tested for the energy input. It appears that energy input
from galactic shear allows to achieve a stationary clumped state for the gas,
avoiding final collapse. When a stationary turbulent cascade is established, it
is possible to derive meaningful statistical studies on the data such as the
fractal dimension of the mass distribution.


title: Shallow cores in the dark matter halos: self-interaction in action?

abstract:
  Using observational data for a sample of dark matter dominated galaxies and
two cluster of galaxies, we have found that the central halo density does not
depend on its mass, and the core radius is roughly proportional to the maximum
rotation velocity. A good agreement with these scaling laws is obtained for CDM
halos whose dense inner parts were expanded by gravothermal instabilities if
the particles efficiently self-interact only in these parts. We find that the
particle cross-section is inversely proportional to the velocity dispersion.


title:
Disk Galaxies as Cosmological Benchmarks: Cold Dark Matter versus
  Modified Newtonian Dynamics

abstract:
  We discuss a comparison of models for the formation of disk galaxies both in
a Universe dominated by cold dark matter (CDM) and one in which the force law
is given by modified Newtonian dynamics (MOND). Our main aim is to address the
claim made by McGaugh & de Blok that CDM suffers from severe fine-tuning
problems, which are circumvented under MOND. As we show, CDM indeed requires
some amount of tuning of the feedback efficiencies to obtain a Tully-Fisher
relation (TFR) as steep as observed. However, that same model is in excellent
agreement with a wide variety of additional observations. Therefore, the modest
amount of feedback needed should not be regarded a fine-tuning problem.
Instead, its requirement should be considered a generic prediction for CDM,
which might be tested with future observations and with detailed modeling of
feedback processes. We also show that galaxy formation in a MOND universe can
not simultaneously reproduce the TFR and the lack of high surface brightness
dwarf galaxies. We thus conclude that CDM is a more viable theory for the
formation of disk galaxies than MOND.


title: Comment on "On physical interpretation of the Poynting-Robertson effect"

abstract:
  In response to the comments of astro-ph/0006426 on Srikanth (Icarus 1999), we
clarify, and thereby justify, the definition of Poynting-Robertson drag adopted
in the latter. We confirm that dust absorption is a necessary condition while
re-emission is neither necessary nor sufficient for the inspiralling of a
rest-isotropically emitting dust.


title:
Black Hole Mass Estimates from Reverberation Mapping and from Spatially
  Resolved Kinematics

abstract:
  Black hole (BH) masses that have been measured by reverberation mapping in
active galaxies fall significantly below the correlation between bulge
luminosity and BH mass determined from spatially resolved kinematics of nearby
normal galaxies. This discrepancy has created concern that one or both
techniques suffer from systematic errors. We show that BH masses from
reverberation mapping are consistent with the recently discovered relationship
between BH mass and galaxy velocity dispersion. Therefore the bulge
luminosities are the probable source of the disagreement, not problems with
either method of mass measurement. This result underscores the utility of the
BH mass -- velocity dispersion relationship. Reverberation mapping can now be
applied with increased confidence to galaxies whose active nuclei are too
bright or whose distances are too large for BH searches based on spatially
resolved kinematics.


title:
Proper Motions of Pre-Main Sequence Stars in Southern Star-Forming
  Regions

abstract:
  We present proper motion measurements of pre-main sequence (PMS) stars
associated with major star-forming regions of the southern hemisphere
(Chamaeleon, Lupus, Upper Scorpius - Ophiuchus, Corona Australis), situated in
the galactic longitude range l = 290\degr to l = 360\degr. A list of PMS stars
as complete as possible was established based on the Herbig and Bell catalogue
and many new catalogues like the PDS survey, the catalogue of Herbig Ae/Be
stars by Th\'e et al. (1994), X-rays surveys, etc. The measurements made use of
public material (mainly AC2000 and USNO--A2.0 catalogues) as well as scans of
SERC-J Schmidt plates with the MAMA measuring machine (Paris) and Valinhos CCD
meridian circle observations (Brazil). We derived proper motions for 214 stars,
with an accuracy of 5 to 10 mas/yr depending mainly on the difference of epochs
between the position sources. The main characteristics of the sample are
discussed. We show that systematic motions of groups of stars exist, which are
not explained by the reflex solar motion.


title: Topology of the Las Campanas Redshift Survey

abstract:
  The topology of the Las Campanas Redshift Survey is analyzed using Minkowski
functional statistics, taking into account the selection effects of the survey.
The results are compared with the predictions of some toy models of structure
formation, including the Standard Cold Dark Matter Model and topological
defect-based models. All of the toy models have a scale invariant primordial
spectrum of perturbations, but quite different topologies. The statistics can
discriminate between the predictions of the models with high significance.
Amongst the four Minkowski functionals, the integrated mean curvature statistic
appears to be the most powerful discriminant, followed by the genus statistic.
None of the models considered gives an acceptable fit to the data.


title: The Infall Region of Abell 576: Independent Mass and Light Profiles

abstract:
  We describe observations of the nearby cluster of galaxies A576 beyond the
virial radius and into the infall region. Using 1057 redshifts, we use the
infall pattern in redshift space to determine the mass profile of A576 to a
radius of ~4 Mpc/h. This mass estimation technique makes no assumptions about
the equilibrium state of the cluster. Within 1 Mpc/h, the mass profile we
derive exceeds that determined from X-ray observations by a factor of 2.5. At
\~2.5 Mpc/h, however, the mass profile agrees with virial mass estimates. Our
mass profile is consistent with a NFW or Hernquist profile, but it is
inconsistent with an isothermal sphere. R-band images of a $3^\circ x 3^\circ$
region centered on the cluster allow an independent determination of the
cluster light profile. We calculate the integrated mass-to-light ratio as a
function of cluster radius; it decreases smoothly from the core to ~4 Mpc/h.
The differential dM/dL_R profile decreases more steeply; we find M/L_R ~100 h
at ~4 Mpc/h, in good agreement with the mass-to-light ratios of individual
galaxies. This value implies $\Omega_m \lesssim 0.4$ at 95% confidence. For a
Hernquist model, the best-fit mass profiles differ from the observed surface
number density of galaxies; the galaxies have a larger scale radius than the
mass. This result is consistent with the centrally peaked $M/L_R$ profile.
Similarly, the scale radius of the light profile is larger than that of the
mass profile. We discuss some potential systematic effects; none can easily
reconcile our results with a constant mass-to-light ratio. (abstract edited)


title: Optical spectroscopy of galaxies in the direction of the Virgo cluster

abstract:
  Optical spectroscopy of 76 galaxies, 48 of which are projected in the
direction of the Virgo cluster and 28 onto the Coma-A1367 supercluster, is
reported. Adding these new measurements to those found in the literature, the
redshift completeness in the Virgo region becomes 92% at B_T<=16.0 and 68% at
B_T<=18.0. The one of CGCG galaxies in the direction of the Coma-A1367
supercluster becomes 98%. The Virgo cluster membership estimates obtained on
morphological grounds by Binggeli et al. (1985) are confirmed in all cases.
However, several "possible members" classified as BCD (if in the cluster) are
found instead to be giant emission-line galaxies in the background of the Virgo
cluster


title: Effective cosmological "constant " and quintessence

abstract:
  In this paper we present exactly solved extended quintessence models;
furthermore, through a dynamical effective Q-cosmological "constant", we
recover some of the L decaying cases found in the literature. Finally we
introduce a sort of complementarity between the Q-dominated or L-dominated
expansions of the Universe.


title: Radial velocity measurements of white dwarfs

abstract:
  We present 594 radial velocity measurements for 71 white dwarfs obtained
during our search for binary white dwarfs and not reported elsewhere. We
identify three excellent candidate binaries, which require further observations
to confirm our preliminary estimates for their orbital periods, and one other
good candidate. We investigate whether our data support the existence of a
population of single, low mass (<~0.5 solar masses) white dwarfs (LMWDs). These
stars are difficult to explain in standard models of stellar evolution. We find
that a model with a mixed single/binary population is at least ~20 times more
likely to explain our data than a pure binary population. This result depends
on assumed period distributions for binary LMWDs, assumed companion masses and
several other factors. Therefore, the evidence in favour of the existence of a
population of single LMWDs is not sufficient, in our opinion, to firmly
establish the existence of such a population, but does suggest that extended
observations of LMWDs to obtain a more convincing result would be worthwhile .


title:
The Cometary Blue Compact Dwarf Galaxies Mkn 59 and Mkn 71: Clues to
  Dwarf Galaxy Evolution?

abstract:
  "Cometary" Blue Compact Dwarf Galaxies (iI,C BCDs) are characterized by
off-center starbursts close to the end of an elongated dwarf irregular
(dI)-like host galaxy. This may either represent randomly enhanced star-forming
activity of a dI, or may be caused by a set of special properties of such
systems or their environment. For a first investigation of this issue, we
analyse the nearby iI,C BCDs Markarian 59 and Markarian 71. Using deep
ground-based spectrophotometric data and HST images, we derive physical
properties, structure and ages of the starburst regions and the underlying
stellar host galaxies. The metallicities show small scatter in the vicinity of
the star-forming regions and along the major axis of Mrk 59 which suggests
effective mixing of heavy elements on kpc scales. The surface brightness
profiles of the underlying host galaxies in either iI,C BCD show an exponential
decay with a central surface brightness and scale length that are intermediate
between typical iE/nE BCDs and dIs. Spectral population synthesis models in
combination with colour magnitude diagrams and colour profiles yield most
likely formation ages of ~2 Gyr for the host galaxies in both iI,C BCDs, with
upper limits of ~4 Gyr for Mrk 59 and ~3 Gyr for Mrk 71, i.e. significantly
lower than the typical age of several Gyr derived for the host galaxies of
iE/nE BCDs. These findings raise the question whether iI,C systems form a
distinct class within BCDs with respect to the age and structure of their
hosts, or whether they represent an evolutionary stage connecting young i0 BCDs
and "classical" iE/nE BCDs. Properties of analogous objects studied in the
local universe and at medium redshifts provide some support for this
evolutionary hypothesis.


title:
A combined HST/CFH12k/XMM survey of X-ray luminous clusters of galaxies
  at z~0.2

abstract:
  We describe a project to study a sample of X-ray luminous clusters of
galaxies at redshift z~0.2 at several scales (with HST/WFPC2 and CFHT/CFH12k)
and wavebands (optical and X-ray). The main aims of the project are (i) to
determine the mass profiles of the clusters on scales ranging from ~10 kpc/h to
>1.5 Mpc/h using weak and strong lensing, thereby testing theoretical
predictions of a ``universal mass profile'', and (ii) to calibrate the M_tot -
T_X relation in view of future application in the study of the evolution of the
cluster mass function at higher redshift.


title: The Newton Wonder in Mechanics

abstract:
  Application of Newton's ideas from "Principia" gives many new results in
mechanics. Here we explore the question ``What form of extra force will
maintain the magnitude of a vector constant of the motion while changing its
direction?''


title: Amplitude-Phase Analysis of Cosmic Microwave Background maps

abstract:
  We propose a novel method for the extraction of unresolved point sources from
CMB maps. This method is based on the analysis of the phase distribution of the
Fourier components for the observed signal and unlike most other methods of
denoising does not require any significant assumptions about the expected CMB
signal. The aim of our paper is to show how, using our algorithm, the
contribution from point sources can be separated from the resulting signal on
all scales. We believe that this technique is potentially a very powerful tool
for extracting this type of noise from future high resolution maps.


title: Wandering Among Newton Wonders

abstract:
  In the electromagnetic fields t^2 B = b(r/t), E = r x B/t trajectories of
non-relativistic charged particles conserve (r-vt)^2. The transformation r'=r/t
t'=1/t maps such trajectories into orbits in the constant magnetic field all of
which conserve kinetic energy. The transformation may also be used to transform
any fields obeying Curl E = B/dt, div B = 0 into others and relates the
particle trajectories in them.


title: The Optical Velocity of the Antlia Dwarf Galaxy

abstract:
  We present the results of a VLT observing program carried out in service mode
using FORS1 on ANTU in Long Slit mode to determine the optical velocities of
nearby low surface brightness galaxies. Outlying Local Group galaxies are of
paramount importance in placing constraints the dynamics and thus on both the
age and the total mass of the Local Group. Optical velocities are also
necessary to determine if the observations of HI gas in and around these
systems are the result of gas associated with these galaxies or a chance
superposition with high velocity HI clouds or the Magellanic Stream. The data
were of sufficient signal-to-noise to obtain a reliable result in one of the
galaxies we observed - Antlia - for which we have found an optical
helio-centric radial velocity of 351 $\pm$ 15 km/s.


title:
An optical time-delay estimate for the double gravitational lens system
  B1600+434

abstract:
  We present optical I-band light curves of the gravitationally lensed double
QSO B1600+434 from observations obtained at the Nordic Optical Telescope (NOT)
between April 1998 and November 1999. The photometry has been performed by
simultaneous deconvolution of all the data frames, involving a numerical lens
galaxy model. Four methods have been applied to determine the time delay
between the two QSO components, giving a mean estimate of \Delta_t = 51+/-4
days (95% confidence level). This is the fourth optical time delay ever
measured. Adopting a Omega=0.3, Lambda=0 Universe and using the mass model of
Maller et al. (2000), this time-delay estimate yields a Hubble parameter of
H_0=52 (+14, -8) km s^-1 Mpc^-1 (95% confidence level) where the errors include
time-delay as well as model uncertainties. There are time-dependent offsets
between the two (appropriately shifted) light curves that indicate the presence
of external variations due to microlensing.


title: MACHOs and the clouds of uncertainty

abstract:
  I review proposals for explaining the current gravitational microlensing
results from the EROS and MACHO surveys towards the Magellanic Clouds.
Solutions involving massive compact halo objects (MACHOs), both baryonic and
non-baryonic, as well as solutions that do not require MACHOs, are discussed.
Whilst the existence and nature of MACHOs remains to be established, the
prospects for achieving this over the next few years are good.


title:
Properties of PACE-I HgCdTe Detectors in Space - the NICMOS Warm-up
  Monitoring Program

abstract:
  We summarize the results of a monitoring program which was executed following
the cryogen exhaustion of the Near Infrared Camera and Multi-Object
Spectrometer (NICMOS) onboard the Hubble Space Telescope. During the subsequent
warm-up, detector parameters such as detective quantum efficiency, dark
current, bias offsets, and saturation levels have been measured over the
temperature range 62K to about 100K. The measurements provide a unique database
of the characteristics of PACE-I HgCdTe detector arrays in the space
environment. A surprising result of the analysis is the fact that all three
NICMOS detectors showed an enhanced dark current in the temperature range
between 77K and 85K. However, a subsequent laboratory experiment designed to
replicate the on-orbit warm-up did not reproduce the anomaly, despite the fact
that it employed a flight-spare detector of the same pedigree. The mechanism
behind the on-orbit dark current anomaly is therefore believed to be unique to
the space environment. We discuss possible explanations for these unexpected
observational results, as well as their implications for future NICMOS
operations.


title: The evolution of AGB stars with convective overshoot

abstract:
  The influence of extended convective mixing (overshoot) on asymptotic giant
branch stellar evolution is investigated in detail. The extended mixing is
treated time-dependently, and the efficiency declines exponentially with the
geometric distance from the convective boundary. It has been considered at all
convective boundaries, including the He-flash convection zone in the intershell
region which forms during the thermal pulses. Both the structural and the
chemical evolution are affected by the inclusion of overshoot. The main results
include a very efficient third dredge-up which leads to the formation of carbon
stars of low mass and luminosity. A C13 pocket which may serve as a neutron
source for the s-process can form after the third dredge-up has reached into
the C12 rich intershell. Overshoot applied to the pulse-driven convective zone
during the He-flash leads to a deeper penetration of the bottom of this
convective zone into the C/O core below the He-burning shell. This in turn
causes He4 to be less abundant in the intershell while C12 and O16 are more
abundant compared to calculations without overshoot. We show that overshoot at
the He-flash convection zone as well as at the base of the envelope convection
enhance the efficiency of the third dredge-up. Characteristic properties of the
structural and chemical evolution of AGB stars are presented.


title:
A Counterexample to Claimed COBE Constraints on Compact Toroidal
  Universe Models

abstract:
  It has been suggested that if the Universe satisfies a flat, multiply
connected, perturbed Friedmann-Lema^itre model, then cosmic microwave
background data from the COBE satellite implies that the minimum size of the
injectivity diameter (shortest closed spatial geodesic) must be larger than
about two fifths of the horizon diameter. To show that this claim is
misleading, a simple $T^2 \times R$ universe model of injectivity diameter a
quarter of this size, i.e. a tenth of the horizon diameter, is shown to be
consistent with COBE four year observational maps of the cosmic microwave
background. This is done using the identified circles principle.


title: Double lenses

abstract:
  The analysis of the shear induced by a single cluster on the images of a
large number of background galaxies is all centered around the curl-free
character of a well-known vector field that can be derived from the data. Such
basic property breaks down when the source galaxies happen to be observed
through two clusters at different redshifts, partially aligned along the line
of sight. In this paper we address the study of double lenses and obtain five
main results. (i) First we generalize the procedure to extract the available
information, contained in the observed shear field, from the case of a single
lens to that of a double lens. (ii) Then we evaluate the possibility of
detecting the signature of double lensing given the known properties of the
distribution of clusters of galaxies. (iii) As a different astrophysical
application, we demonstrate how the method can be used to detect the presence
of a dark cluster that might happen to be partially aligned with a bright
cluster studied in terms of statistical lensing. (iv) In addition, we show that
the redshift distribution of the source galaxies, which in principle might also
contribute to break the curl-free character of the shear field, actually
produces systematic effects typically two orders of magnitude smaller than the
double lensing effects we are focusing on. (v) Remarkably, a discussion of
relevant contributions to the noise of the shear measurement has brought up an
intrinsic limitation of weak lensing analyses, since one specific contribution,
associated with the presence of a non-vanishing two-galaxy correlation
function, turns out not to decrease with the density of source galaxies (and
thus with the depth of the observations).


title: Can gravitational waves be detected in quasar microlensing?

abstract:
  Studies of the lensed quasar ${\rm Q}0957+561 {\rm A,B}$ have shown evidence
for microlensing in the brightness history of the quasar images. It had been
suggested that a frequency offset between the brightness fluctuations in each
of the two images might possibly be caused by gravitational radiation generated
by a massive black hole binary at the center of the lensing galaxy. This paper
demonstrates that the fluctuations produced by such a source of gravitational
waves will be too small to account for the observed frequency offsets.


title:
Dust Emission Features in NGC 7023 between 0.35 and 2.5 micron: Extended
  Red Emission (0.7 micron) and Two New Emission Features (1.15 and 1.5 micron)

abstract:
  We present 0.35 to 2.5 micron spectra of the south and northwest filaments in
the reflection nebula NGC 7023. These spectra were used to test the theory of
Seahra & Duley that carbon nanoparticles are responsible for Extended Red
Emission (ERE). Our spectra fail to show their predicted second emission band
at 1.0 micron even though both filaments exhibit strong emission in the
familiar 0.7 micron ERE band. The northwest filament spectrum does show one,
and possibly two, new dust emission features in the near-infrared. We clearly
detect a strong emission band at 1.5 micron which we tentatively attribute to
beta-FeSi_2 grains. We tentatively detect a weaker emission band at 1.15 micron
which coincides with the location expected for transitions from the conduction
band to mid-gap defect states of silicon nanoparticles. This is added evidence
that silicon nanoparticles are responsible for ERE as they already can explain
the observed behavior of the main visible ERE band.


title: How to Form (Twin) Globular Clusters?

abstract:
  Though it is generally assumed that massive molecular clouds are the
progenitors of globular clusters, their detailed formation mechanism is still
unclear. Standard scenarios based on the collapse of a smooth matter
distribution suffer from strong requirements with respect to cluster formation
time scale, binding energy and star formation efficiency. An alternative model
assuming cluster formation due to the recollapse of a supernova-induced,
fragmented shell can relax these difficulties.
  In this paper the final collapse stages of the different scenarios are
compared by N-body simulations for shells and spheres. It is shown that
fragmentation is much more pronounced for shells. Taking a galactic tidal field
into account shells preferably form twin (or multiple) systems, whereas spheres
end up as single clusters. The twins are characterized by identical
metallicities, and stellar mass functions; some of them show counter-rotating
cores. Their orbital evolution can result in both, a final merger or well
separated twins sharing a common galactic orbit.


title: Molecular Clouds Around a Run-away O Star, zeta Oph

abstract:
  Molecular clouds around a run-away O star z Oph have been surveyed with
NANTEN telescope and their streaming motion caused by z Oph has been detected.
z Oph is the earliest member of the Sco OB2 association and is a runaway star
rapidly moving with an HII region, S27. We detected 2 major filamentary cloud
complexes; one including L156 (L156 complex) is lying across nearly the center
of S27, and the other one (L204 complex) is located near the eastern edge of
S27. Total masses of them traced by the 12CO are 520 Mo and 1110 Mo,
respectively. Denser cloud cores detected in C18O are locally distributed on
the near side of the L204 complex to z Oph, and lower density gas traced by
12CO spreads toward the opposite side. Both complexes have radial velocity
shifts that are correlated with the gas density. These spatial and velocity
structures can be interpreted as follows; (1) the L156 complex is stuck on the
expanding Stromgrem sphere and has been accelerated, (2) the gas in L204
complex was compressed and has also been accelerated outward by z Oph,
resulting the radial velocity shifts of diffuse low-density gas relative to the
dense cores embedded in the clouds. These density and velocity structures
indicate dynamical interaction between the HII region and the molecular clouds.
The cloud complexes are divided into 7 clouds by intensity distributions. In
order to investigate the acceleration mechanism, we calculated momentum and
kinetic energy for each cloud. They range from 60 to 800 Mo km/s and from 0.9
to 21 times 10^45 erg, respectively. We examined the effects of the stellar
wind and photo evaporation by UV field of z Oph and found that the stellar wind
can hardly input the momentum during the crossing time of the movement of z
Oph. UV radiation seems to be a more likely origin of the streaming gas motion.


title: The formation of Encke meteoroids and dust trail

abstract:
  We observed comet 2P/Encke with the Infrared Space Observatory ISOCAM on July
14, 1997 from a particularly favorable viewing geometry above the comet's
orbital plane and at a distance of 0.25 AU. A structured coma was observed,
along with a long, straight dust trail. For the first time, we are able to
observe the path of particles as they evolve from the nucleus to the trail. The
particles that produce the infrared coma are large, with a radiation to
gravitational force ratio beta<0.001 (corresponding to >mm-sized particles).
The dust trail follows the orbit of the comet across our image, with a central
core that is 20,000 km wide, composed of particles with beta<1e-5 (size $\sim
5$ cm) from previous apparitions. The abundant large particles near the comet
pose a significant hazard to spacecraft. There is no evidence of a classical
cometary dust tail due to small particles with beta>0.001, in marked contrast
to other comets like P/Halley or C/Hale-Bopp. The structure of the coma
requires anisotropic emission and that the spin axis of the nucleus to be
nearly parallel to the orbital plane, resulting in strong seasonal variations
of the particle emission. While most of the infrared coma emission is due to
dust produced during the 1997 apparition, the core of the dust trail requires
emissions from previous apparitions. The total mass lost during the 1997
apparition is estimated to be
  2-6e13 g. Comparing to the gas mass loss from ultraviolet observations, the
dust-to-gas mass ratio is 10-30, much higher than has ever been suggested from
visual light observations. Using the recently-measured nuclear diameter, we
find that Encke can only last 3000-10,000 rhoN yr (where rhoN is the nuclear
density in g/cc) at its present mass loss rate.


title:
Evidence for Supermassive Black Holes in Active Galactic Nuclei from
  Emission-Line Reverberation

abstract:
  Emission-line variability data for Seyfert 1 galaxies provide strong evidence
for the existence of supermassive black holes in the nuclei of these galaxies,
and that the line-emitting gas is moving in the gravitational potential of that
black hole. The time-delayed response of the emission lines to continuum
variations is used to infer the size of the line-emitting region, which is then
combined with measurements of the Doppler widths of the variable line
components to estimate a virial mass. In the case of the best-studied galaxy,
NGC 5548, various emission lines spanning an order of magnitude in distance
from the central source show the expected velocity proportional to inverse
square root of the distance correlation between distance and line width, and
are thus consistent with a single value for the mass. Two other Seyfert
galaxies, NGC 7469 and 3C 390.3, show a similar relationship. We compute the
ratio of luminosity to mass for these three objects and the narrow-line Seyfert
1 galaxy NGC 4051 and find that that the gravitational force on the
line-emitting gas is much stronger than radiation pressure. These results
strongly support the paradigm of gravitationally bound broad emission-line
region clouds.


title: Infrared Spectroscopy of Molecular Supernova Remnants

abstract:
  We present Infrared Space Observatory spectroscopy of sites in the supernova
remnants W28, W44, and 3C391, where blast waves are impacting molecular clouds.
Atomic fine-structure lines were detected from C, N, O, Si, P, and Fe. The S(3)
and S(9) lines of H2 were detected for all three remnants. The observations
require both shocks into gas with moderate (~ 100 /cm3) and high (~10,000 /cm3)
pre-shock densities, with the moderate density shocks producing the ionic lines
and the high density shock producing the molecular lines. No single shock model
can account for all of the observed lines, even at the order of magnitude
level. We find that the principal coolants of radiative supernova shocks in
moderate-density gas are the far-infrared continuum from dust grains surviving
the shock, followed by collisionally-excited [O I] 63.2 and [Si II] 34.8 micron
lines. The principal coolant of the high-density shocks is
collisionally-excited H2 rotational and ro-vibrational line emission. We
systematically examine the ground-state fine structure of all cosmically
abundant elements, to explain the presence or lack of all atomic fine lines in
our spectra in terms of the atomic structure, interstellar abundances, and a
moderate-density, partially-ionized plasma. The [P II] line at 60.6 microns is
the first known astronomical detection. There is one bright unidentified line
in our spectra, at 74.26 microns. The presence of bright [Si II] and [Fe II]
lines requires partial destruction of the dust. The required gas-phase
abundance of Fe suggests 15-30% of the Fe-bearing grains were destroyed. The
infrared continuum brightness requires ~1 Msun of dust survives the shock,
suggesting about 1/3 of the dust mass was destroyed, in agreement with the
depletion estimate and with theoretical models for dust destruction.


title: Carbon in the N159/N160 Complex of the Large Magellanic Cloud

abstract:
  We present a study of carbon in N159/N160, an HII region complex in the low
metallicity Large Magellanic Cloud. We have mapped this region, which comprises
four distinct molecular clouds spanning a wide range of star-formation
activity, in four transitions: 13CO (1-0) CO (2-1) and (4-3), and [CI] (1-0).
Combining these data with existing [CII] observations provides a complete
picture of the predominant forms of carbon in the gas phase of the ISM. The new
CO (2-1) data show that the complex is immersed in an envelope of extended, low
level emission, undetected by previous (1-0) mapping efforts. The CO
(2-1)/(1-0) ratio in this envelope is >~3, a value consistent with optically
thin CO emission. The envelope is also relatively bright in [CI] and [CII], and
calculations show that it is mostly photodissociated: it appears to be
translucent (Av<1). Neutral carbon emission in the complex unexpectedly peaks
at the quiescent southern cloud (N159S). In the northern portion of the map
(the N160 nebula), the HII regions prominent in [CII] correspond to holes in
the [CI] distribution. Overall we find that, while the [CII]/CO ratio is
enhanced with respect to similar complexes in the Milky Way, the [CI]/CO ratio
appears to be similar or reduced.


title:
HST/WFPC2 and VLA Observations of the Ionized Gas in the Dwarf Starburst
  Galaxy NGC 4214

abstract:
  We present new H alpha and [O III] 5007 narrow band images of the
starbursting dwarf galaxy NGC 4214, obtained with the WFPC2 onboard HST,
together with VLA observations of the same galaxy. The HST images resolve
features down to physical scales of 2-5 pc, revealing several young (<10 Myr)
star forming complexes of various ionized gas morphologies (compact knots,
complete or fragmentary shells) and sizes (10-200 pc). Our results are
consistent with a uniform set of evolutionary trends: The youngest, smaller,
filled regions that presumably are those just emerging from dense star forming
clouds, tend to be of high excitation and are highly obscured. Evolved, larger
shell-like regions have lower excitation and are less extincted due of the
action of stellar winds and supernovae. In at least one case we find evidence
for induced star formation which has led to a two-stage starburst. Age
estimates based on W(H alpha) measurements do not agree with those inferred
from wind-driven shell models of expanding H II regions. The most likely
explanation for this effect is the existence of a 2 Myr delay in the formation
of superbubbles caused by the pressure exerted by the high density medium in
which massive stars are born. We report the detection of a supernova remnant
embedded in one of the two large H II complexes of NGC 4214. The dust in NGC
4214 is not located in a foreground screen but is physically associated with
the warm ionized gas.


title: Stellar contributors to the hard X-ray background?

abstract:
  We use simple energetic arguments to estimate the contribution of massive
X-ray binaries and supernova remnants to the cosmic X-ray background (XRB) at
energies in excess of 2 keV. Recent surveys have shown that AGN probably
account for most of the hard XRB (E > 2 keV), but there have been many
suggestions that star-forming galaxies could emerge at fainter fluxes and
perhaps account for a significant fraction of the soft and hard X-ray energy
density. Assuming that the formation rate of massive X-ray binaries (MXRBs)
traces the global star-formation rate, we find that their integrated
contribution to the hard XRB can be estimated and is shown to be small (at less
than the 1% level). Similarly, the integrated flux of SN is also shown to be
insignificant, or at most comparable to MXRBs. AGN therefore remain the most
viable candidates for producing the hard XRB, unless additional processes can
be shown to dominate the global hard X-ray emission in distant starburst
galaxies.


title:
On the "failure" of the standard model for Soft X-ray Transients in
  quiescence

abstract:
  It is currently believed that the ``standard'' accretion disk theory
under-predicts the observed X-ray luminosity from Soft X-ray Transients (SXT)
in quiescence by as much as 4 to 6 orders of magnitude. This failure of the
standard model is considered to be an important argument for the existence of
the alternative mode of accretion -- Advection Dominated Accretion Flows (ADAF)
in astrophysics, since these flows allow a much higher level of X-ray emission
in quiescence, in agreement with the observations. Here we point out that, in
stark contrast to steady-state standard disks, such disks in quiescence (being
non-steady) produce most of the X-ray emission very far from the last stable
orbit. Taking this into account, these disks can accommodate the observed X-ray
luminosities of SXTs rather naturally. Our theory predicts that Fe K-alpha
lines from standard accretion disks in quiescence should be narrow even though
the cold disk goes all the way down to the last stable orbit.


title: Constraining (\Omega_m,\Omega_\lambda) from strong lensing

abstract:
  The knowledge of the redshift of multiple images in cluster-lenses allows to
determine precisely the total projected mass within the Einstein radius. The
observation of various multiple images in a same cluster is opening new
possibilities to constrain the curvature of the universe. Indeed, although the
influence of $\Omega_m$ and $\Omega_\lambda$ on the images formation is of the
second order, observations of many multiple images at different redshifts
formed by a regular cluster-lens should allow to constrain very accurately the
mass distribution of the cluster and to start to be sensitive to the
cosmological parameters entering the diameter angular distances. We present,
analytical expressions and numerical simulations that allow us to compute the
expected error bars on the cosmological parameters provided an HST/WFPC2
resolution image and spectroscopic redshifts for the multiple images. Numerical
tests on simulated data confirm the rather small uncertainties we could obtain
this way for the two popular cosmological world models: $\Omega_m=0.3{\pm
0.24}$, $\Omega_\lambda=0.7{\pm 0.5}$ or $\Omega_m=1.{\pm 0.33}$,
$\Omega_\lambda=0.{\pm 1.2}$.


title: Spectroscopic follow up of arclets in AC114 with the VLT

abstract:
  We present the first results on the VLT/FORS-1 spectroscopic survey of
amplified sources and multiple images in the lensing cluster AC114. Background
sources were selected in the cluster core, close to the critical lines, using
photometric redshifts combined with lensing inversion criteria. Spectroscopic
results are given, together with a brief summary of the properties of some of
these high-z galaxies.


title: PSCz Superclusters: Detection, Shapes & Cosmological Implications

abstract:
  We study the possibility of correctly identifying superclusters, from the
smooth galaxy density field of the PSCz redshift catalogue, and of recovering
their true shapes in the presence of a bias introduced by the coupling between
the selection function and the constant radius smoothing. Using simulations we
quantify such systematic biases in the smoothed PSCz density field and after
applying the necessary corrections we study the PSCz supercluster multiplicity
and morphologies using a differential geometry definition of shape. Our results
strongly suggest that filamentariness is the dominant morphological feature of
PSCz superclusters. Finally, we compare our results with those expected in
three different cosmological models and find that the LCDM model performs
better than Omega_m=1 CDM models.


title: The Outflow-Disc Interaction in Young Stellar Objects

abstract:
  In this work the most spectacular phenomena occurring during the formation of
a star are briefly reviewed: accretion through a rotating disc of matter and
outflow through the poles of the new stellar object. Magnetic fields have been
proposed to be principally responsible for the coexistence of these opposed
mechanisms of accretion and outflowing. According to different models, the
magnetic fields are either twisted or stretched by the accretion disc, allowing
the formation of polar channels through which part of the accreting matter can
escape. The high degree of coupling between the physical parameters describing
the young stellar object (e.g. circular velocity of the disc and the central
object, viscosity, strength and freezing of magnetic fields, etc.) makes
detailed understanding of the interaction between accretion discs and outflows
very difficult. The models presented here provide only a partial answer to this
difficult problem.


title: Pre-Main Sequence models for low-mass stars and brown dwarfs

abstract:
  We present evolutionary models for low mass stars and brown dwarfs ($m \le
1.2 \msol$) based on recent improvement of the theory: equation of state,
atmosphere models, ... We concentrate on early evolutionary phases from the
initial deuterium burning phase to the zero-age Main Sequence. Evolutionary
models for young brown dwarfs are also presented. We discuss the uncertainties
of the present models. We analyse the difficulties arising when comparing
models with observations for very young objects, in particular concerning the
problem of reddening.


title: The complex X-ray absorbers of NGC 3516 observed by BeppoSAX

abstract:
  In this paper we present the analysis of two broad band (0.1-150 keV)
BeppoSAX observations of the Seyfert 1 galaxy NGC 3516. The two observations
were taken 4 months apart, on 1996 November 8 and 1997 March 12 respectively.
We report a dramatic change in the degree of obscuration of the central source
between the two observations, and propose, as possible explanations transient
absorption by either a stationary-state cloud of cold gas crossing the line of
sight, or a varying-state, initially neutral and dense amount of expanding gas
with decreasing density and therefore decreasing opacity. We also report the
detection of a second highly ionized absorber/emitter, which causes deep
FeXVII-XXII K edges at about 7.8 keV to appear in both BeppoSAX spectra of NGC
3516, and possibly produces the soft X-ray continuum emission and the 1 keV
blend of Fe L recombination lines detected during the epoch of heavy nuclear
obscuration.


title: X-ray Emission From Nearby M-dwarfs: the Super-saturation Phenomenon

abstract:
  A rotation rate and X-ray luminosity analysis is presented for rapidly
rotating single and binary M-dwarf systems. X-ray luminosities for the majority
of both single & binary M-dwarf systems with periods below $\simeq 5-6$ days
(equatorial velocities, V$_{eq}>$ 6 km~s$^{-1}$) are consistent with the
current rotation-activity paradigm, and appear to saturate at about $10^{-3}$
of the stellar bolometric luminosity. The single M-dwarf data show tentative
evidence for the super-saturation phenomenon observed in some ultra-fast
rotating ($>$ 100 km~s$^{-1}$) G & K-dwarfs in the IC 2391, IC 2602 and Alpha
Persei clusters. The IC 2391 M star VXR60b is the least X-ray active and most
rapidly rotating of the short period (P$_{rot}<$ 2 days) stars considered
herein, with a period of 0.212 days and an X-ray activity level about 1.5 sigma
below the mean X-ray emission level for most of the single M-dwarf sample. For
this star, and possibly one other, we cautiously believe that we have
identified the first evidence of super-saturation in M-dwarfs. If we are wrong,
we demonstrate that only M-dwarfs rotating close to their break up velocities
are likely to exhibit the super-saturation effect at X-ray wavelengths.


title:
Measurements of Tidal Tail Populations Designed to Optimize Their Use as
  Potential Probes

abstract:
  The launching of up to four astrometric missions in the next decade will
enable us to make measurements of stars in tidal streamers from Galactic
satellites of sufficient accuracy to place strong constraints on the mass
distribution in the Milky Way. In this paper we simulate observations of debris
populations in order to assess the required properties of any data set chosen
to implement this experiment. We apply our results to find the desired target
properties of stars (e.g., accuracy of velocity and proper motion measurements)
associated with the dwarf spheroidal satellites of the Milky Way.


title: Spectral Variability of QSOs in the Optical Band

abstract:
  A new analysis of the variability of the spectral slope of PG QSOs has been
performed, on the basis of recent literature data in the B and R photometric
bands. Preliminary results confirm our previous findings concerning the
increase of variability with the rest-frame observing frequency. We also find a
correlation of the spectral slope with luminosity, consistent with temperature
changes of an emitting black body.


title:
Shedding light on the dark side of galaxy formation: submillimetre
  surveys through lensing clusters

abstract:
  Most new sub-mm/mm surveys, both deep and shallow, are being targeted at rich
cluster fields. I explain why, comparing surveys that have exploited weak
lensing by massive foreground clusters with those done in blank fields.


title: ASCA view on High-Redshift Radio-Quiet Quasars

abstract:
  We briefly discuss the latest ASCA results on the X-ray spectral properties
of high-redshift radio-quiet quasars.


title: Abundance gradients and their evolution in the Milky Way disk

abstract:
  Based on a simple, but fairly successful, model of the chemical evolution of
the Milky Way disk, we study the evolution of the abundances of the elements
He, C, N, O, Ne, Mg, Al, Si, S, Ar and Fe. We use metallicity dependent yields
for massive stars with and without mass loss. We find that most observed
abundance profiles are correctly reproduced by massive star yields, but C and N
require supplementary sources. We argue that massive, mass losing stars can
totally account for the abundance profile of C, while intermediate mass stars
are the main source of N; in both cases, some conflict with corresponding data
on extragalactic HII regions arises, at least if current observations in the
Galaxy are taken at face value. The observed behaviour of Al is marginally
compatible with current massive star yields, which probably overestimate the
``odd-even'' effect. We also find that the adopted ``inside-out'' formation
scheme for the Milky Way disk produce abundance profiles steeper in the past.
The corresponding abundance scatter is smaller in the inner disk than in the
outer regions for a given interval of Galactic age.


title: Hot Dark Matter in Cosmology

abstract:
  Cosmological dark matter in the form of neutrinos with masses of up to a few
electron volts is known as hot dark matter. After an historical review of the
subject, this article considers constraints on hot dark matter from current
data on neutrino oscillations and on cosmology. The atmospheric neutrino
oscillation data imply a lower limit on the HDM contribution to the
cosmological density $\Omega_\nu \gsim 0.001$. The possible improvement of
low-$\Omega_m$ flat ($\Lambda$CDM) cosmological models with the addition of
light neutrinos appears to be rather limited, but$\Lambda$CDM models with
$\Omega_\nu \lsim 0.1$ may be consistent with presently available data. Data
expected soon may permit detection of such a hot dark matter contribution, or
alternatively provide stronger upper limits on $\Omega_\nu$ and neutrino
masses.


title:
Mapping the substructure in the Galactic halo with the next generation
  of astrometric satellites

abstract:
  We run numerical simulations of the disruption of satellite galaxies in a
Galactic potential to build up the entire stellar halo, in order to investigate
what the next generation of astrometric satellites will reveal by observing the
halo of the Milky Way. We generate artificial DIVA, FAME and GAIA halo
catalogues, in which we look for the signatures left by the accreted
satellites. We develop a method based on the standard Friends-of-Friends
algorithm applied to the space of integrals of motion. We find this simple
method can recover about 50% of the different accretion events, when the
observational uncertainties expected for GAIA are taken into account, even when
the exact form of the Galactic potential is unknown. The recovery rate for DIVA
and FAME is much smaller, but these missions, like GAIA, should be able to test
the hierarchical formation paradigm on our Galaxy by measuring the amount of
halo substructure in the form of nearby kinematically cold streams with for
example, a two-point correlation function in velocity space.


title: Active Galactic Nuclei in the CNOC2 Field Galaxy Redshift Survey

abstract:
  We present a sample of 47 confirmed and 14 candidate Active Galactic Nuclei
(AGN) discovered in the Canadian Network for Observational Cosmology field
galaxy redshift survey (CNOC2). The sample consists of 38 objects identified
from broad emission lines, 8 from narrow [NeV] emission, and 15 candidates from
FeII or MgII absorption lines, one of which has been confirmed as a broad-line
AGN via infrared spectroscopy. Redshifts of these AGN range from z=0.27 to
z=4.67, and the average absolute magnitude is M_B=-22.25. No color selection
criteria were involved in selecting this spectroscopically discovered sample.
The sample is also unbiased against objects with luminous host galaxies since
the spectroscopy preferentially targeted extended objects. Simple color-color
diagram selection criteria can recover 81+-6% of the CNOC2 AGN, but several of
the most unusual objects would be missing from such a color-selected sample. In
the subsample with broad emission lines, the average equivalent widths for MgII
and CIII] agree with the predictions of previous studies of the Baldwin effect.
However, the average equivalent widths for CIV and Ly-alpha are smaller than
predicted by previous studies of the Baldwin effect at lower redshift. This may
imply that the slopes of the CIV and Ly-alpha Baldwin effects evolve with
redshift, steepening with cosmic time. The broad emission line AGN also show a
higher incidence of associated MgII and CIV absorption than in most previous
surveys. This may arise from strong absorption being anti-correlated with
optical luminosity or becoming less frequent with cosmic time, or possibly
because our selection method is not biased against objects with resolved
spatial structure or reddened by dust associated with the absorbing gas.
(Abridged)


title: The Baryon Content of Groups and Clusters of Galaxies

abstract:
  We have analyzed the properties of a sample of 33 groups and clusters of
galaxies and examine the baryon content to check for trends over a decade in
temperature down to 1 keV. We examine the relative contribution of galaxies and
ICM to baryons in clusters through the gas-to-stellar mass ratio and find that
the typical stellar contribution to the baryonic mass is between 5 and 20%.
This ratio is found to be roughly independent of temperature. Therefore, we do
not confirm the trend of increasing gas-to-stellar mass ratio with increasing
temperature as previously claimed. We also determine distribution of the baryon
fraction with the density contrast. Virial masses are estimated from two
different mass estimators: one based on the isothermal hydrostatic equation
(IHE), the other based on scaling law models (SLM). Comparing the two methods,
we find that SLM lead to less dispersed baryon fractions over all density
contrasts and that the derived mean absolute valuesare significantly lower than
IHE mean values. We show that this is not due to the uncertainties on the outer
slope $\beta$ of the gas density profile but is rather indicating that IHE
masses are less reliable. Examining the shape of the baryon fraction profiles
we find that cluster baryon fractions estimated from SLM follow a scaling law.
Moreover, we do not find any strong evidence of increasing baryon (gas)
fraction with temperature, neither do we find the slope $\beta$ to increase
with temperature. The absence of clear trends between $f_{b}$ and
$M_{gas}/M_{*}$ with temperature is consistent with the similarity of baryon
fraction profiles and suggests that non-gravitational processes such as galaxy
feedback, do not play a dominant r\^ole in heating the intra-cluster gas on the
virial scale.


title: Properties of the Molecular Clouds in NGC 205

abstract:
  The nearby dwarf elliptical galaxy NGC 205 offers a unique opportunity for
high resolution studies of the interstellar medium in an elliptical galaxy.
This paper investigates the distribution of molecular gas, molecular line
ratios, and the relationships between atomic gas, molecular gas, and dust in
NGC 205. The line ratios 12CO(2-1)/(1-0) and 12CO(1-0)/13CO(1-0) in one of the
molecular clouds in NGC 205 are consistent with the ratios found in other
elliptical galaxies and in Galactic giant molecular clouds; they suggest that
the CO in this cloud is probably subthermally excited. Atomic gas, molecular
gas, and dust are very closely associated on scales of 100 pc; the atomic gas
can be understood as photodissociated envelopes around the molecular clouds.
The atomic column densities in this galaxy are quite low (10^20 cm^-2) because
the interstellar UV field is relatively low. The total gas-to-dust column
density ratios are consistent with Galactic gas-to-dust ratios. In short, the
molecular gas in NGC 205 seems to have very similar properties to the familiar
molecular clouds in our own Galaxy, except for the low atomic column densities.


title: Stellar Companions and the Age of HD 141569 and its Circumstellar Disk

abstract:
  We investigate the stellar environment of the Beta Pictoris-like star HD
141569 with optical spectroscopy and near infrared imaging. The B9.5Ve primary,
and an M2 and an M4 type star both located in projection less than nine
arseconds away have the same radial velocity and proper motion and therefore
almost certainly form a triple star system. From their x-ray flux, lithium
absorption and location on pre-main-sequence evolutionary tracks, the
companions appear to be 5 Myr old. HD 141569 A is now one of the few stars with
a circumstellar disk that has a well-determined age. The circumstellar disk is
composed of secondary debris material (Fisher et al. 2000), thus placing an
upper limit on the time needed for disk processing. These three stars may be
part of an association of young stars.


title:
Hydrogen Lyman-alpha Absorption Predictions by Boltzmann Models of the
  Heliosphere

abstract:
  We use self-consistent kinetic/hydrodynamic models of the heliosphere to
predict H I Lyman-alpha absorption profiles for various lines of sight through
the heliosphere. These results are compared with Lyman-alpha absorption lines
of six nearby stars observed by the Hubble Space Telescope. The directions of
these lines of sight range from nearly upwind (36 Oph) to nearly downwind
(Epsilon Eri). Only three of the Lyman-alpha spectra (36 Oph, Alpha Cen, and
Sirius) actually show evidence for the presence of heliospheric absorption,
which is blended with the ubiquitous interstellar absorption, but the other
three spectra still provide useful upper limits for the amount of heliospheric
absorption for those lines of sight. Most of our models use a Boltzmann
particle code for the neutrals, allowing us to estimate neutral velocity
distributions throughout the heliosphere, from which we compute model
Lyman-alpha absorption profiles. In comparing these models with the data, we
find they predict too much absorption in sidewind and downwind directions,
especially when higher Mach numbers are assumed for the interstellar wind.
Models created assuming different values of the interstellar temperature and
proton density fail to improve the agreement. Somewhat surprisingly, a model
that uses a multi-fluid treatment of the neutrals rather than the Boltzmann
particle code is more consistent with the data, and we speculate as to why this
may be the case.


title:
The Mg II and Lyman-alpha Lines of Nearby K Dwarfs: ISM Components and
  Flux Measurements

abstract:
  We analyze local ISM absorption observed in the Lyman-alpha and Mg II h & k
lines of six nearby K dwarf stars, using UV spectra of these stars obtained
with the Goddard High Resolution Spectrograph on the Hubble Space Telescope.
For four of the six stars, we detect an absorption component with a velocity
and column density consistent with the Local Interstellar Cloud (LIC). For HD
197890, there is no observed component at the expected LIC velocity, or at the
projected velocity of the G cloud, which is a nearby cloud in the general
direction of the Galactic Center. It also seems doubtful that either of the two
components seen toward HD 82558 are LIC or G cloud absorption. The total H I
column density toward HD 82558 (d=18.3 pc) is extremely high (log N(H)=19.05
+/- 0.15), representing the largest average H I density detected for any line
of sight through the nearby LISM (n(H)=0.2 cm^-3). This is particularly
remarkable considering that this star is only 39 degrees from the "interstellar
tunnel" toward Epsilon CMa, where column densities are an order of magnitude
lower than this toward stars which are an order of magnitude farther away.


title: The Evolved Red Stellar Content of M32

abstract:
  Near-infrared images obtained with the CFHT AOB are used to investigate the
stellar content of the Local Group elliptical galaxy M32. Observations of a
field 2.3 arcmin from the galaxy center reveal a large population of AGB stars,
and comparisons with models indicate that these objects have an age log(t_Gyr)
< 9.3. It is concluded that intermediate age stars account for roughly 25% of
the total K light and 10% +/- 5% of the mass in this field.
  The K LF of bright sources between 20 and 30 arcsec from the nucleus is well
matched by the LF of the outer regions of the galaxy after accounting for
differences in surface brightness and correcting for crowding. It is concluded
that the relative size of the intermediate age component with respect to other
populations does not change with radius over most of the galaxy. However, the
integrated J-K color and 2.3 micron CO index change with radius within a few
tenths of an arcsec of the galaxy center indicating that, contrary to what
might be inferred from observations at visible wavelengths, the integrated
photometric properties of the central regions of M32 differ from those of the
surrounding galaxy.


title: Interpreting the Mg II h and k Line Profiles of Mira Variables

abstract:
  We use radiative transfer calculations to reproduce the basic appearance of
Mg II lines observed from Mira variables. These lines have centroids that are
blueshifted by at least 30 km/s from the stellar rest frame. It is unlikely
that flow velocities in the stellar atmospheres are this fast, so radiative
transfer effects must be responsible for this behavior. Published hydrodynamic
models predict the existence of cool, downflowing material above the shocked
material responsible for the Mg II emission, and we demonstrate that scattering
in this layer can result in Mg II profiles as highly blueshifted as those that
are observed. However, our models also show that scattering within the shock
plays an equally strong role in shaping the Mg II profiles, and our
calculations illustrate the importance of partial redistribution and the
effects of being out of ionization equilibrium.


title:
The Nature of the Hard X-ray Background Sources: Optical, Near-infrared,
  Submillimeter, and Radio Properties

abstract:
  With recent Chandra observations, at least 60% of the 2-10 keV background is
now resolved into discrete sources. Here we present deep optical, NIR, submm,
and 20 cm (radio) images, as well as high-quality optical spectra, of a
complete sample of 20 hard X-ray sources in a deep Chandra observation of the
SSA13 field. The thirteen I<23.5 galaxies have redshifts in the range 0.1 to
2.6. Two are quasars, five show AGN signatures, and six are z<1.5 luminous
bulge-dominated galaxies whose spectra show no obvious optical AGN signatures.
The seven spectroscopically unidentified sources have colors that are
consistent with evolved early galaxies at z=1.5-3. Only one hard X-ray source
is significantly detected in an ultradeep submm map; its millimetric redshift
is in the range z=1.2-2.4. None of the remaining 19 sources is detected in the
submm. These results probably reflect the fact that the 850-micron flux limits
obtainable with SCUBA are quite close to the expected fluxes from obscured AGN.
The hard X-ray sources have an average L(FIR)/L(2-10 keV)~60, similar to that
of local obscured AGN. The same ratio for a sample of submm selected sources is
in excess of 1100, suggesting that their FIR light is primarily produced by
star formation. Our data show that luminous hard X-ray sources are common in
bulge-dominated optically luminous galaxies. We use our measured bolometric
corrections with the 2-10 keV EBL to infer the growth of supermassive black
holes. Even with a high radiative efficiency of accretion (e=0.1), the black
hole mass density required to account for the observed light is comparable to
the local black hole mass density. (Abridged)


title: Pair-Instability Supernovae, Gravity Waves, and Gamma-Ray Transients

abstract:
  Growing theoretical evidence suggests that the first generation of stars may
have been quite massive (~100-300 solar masses). If they retain their high mass
until death, such stars will, after about 3Myr, make pair-instability
supernovae. We consider the complete evolution of two zero-metallicity stars of
250 and 300 solar masses. Explosive oxygen and silicon burning cause the 130
solar mass helium core to explode, but explosive burning is unable to drive an
explosion in the 300 solar mass star and it collapses to a black hole. For this
star, the calculated angular momentum in the presupernova model is sufficient
to delay black hole formation and the star initially forms a 50 solar mass,
1000km core within which neutrinos are trapped. Although the star does not
become dynamically unstable, the calculated growth time of secular rotational
instabilities is shorter than the black hole formation time, and such
instabilities may develop. We estimate the energy and amplitude of the
gravitational waves emitted during this collapse. After the black hole forms,
accretion continues through a disk. Although the disk is far too large and cool
to transport energy efficiently to the rotational axis by neutrino
annihilation, it has ample potential energy to produce a 1e54erg jet driven by
magnetic fields. The interaction of this jet with surrounding circumstellar gas
may produce an energetic gamma-ray transient, but given the redshift and time
scale, this is probably not a model for typical gamma-ray bursts.


title: Testing the AGN-Starburst Connection in Seyfert Galaxies

abstract:
  We use the CO band at 2.3 micron to constrain the populations of young stars
in the central regions of Seyfert galaxies. We report new CO band spectroscopy
of 46 Seyfert galaxies. In most cases, the observed CO indices appear diluted
by the presence of a non-stellar component (most likely, warm dust surrounding
the active nucleus). We used JHKL aperture photometry to estimate the
non-stellar contribution at 2.3 micron. We successfully corrected the CO band
for the dilution for 16 galaxies which were not dominated by the non-stellar
component. Comparing with CO indices measured in elliptical and purely
starbursting galaxies, we find no evidence for strong starbursts in the
majority of these galaxies.


title: Stellar production rates of carbon and its abundance in the universe

abstract:
  The bulk of the carbon in our universe is produced in the triple-alpha
process in helium-burning red giant stars. We calculated the change of the
triple-alpha reaction rate in a microscopic 12-nucleon model of the C-12
nucleus and looked for the effects of minimal variations of the strengths of
the underlying interactions. Stellar model calculations were performed with the
alternative reaction rates. Here, we show that outside a narrow window of 0.5
and 4% of the values of the strong and Coulomb forces, respectively, the
stellar production of carbon or oxygen is reduced by factors of 30 to 1000.


title: Physical Processes at Cosmic Dawn

abstract:
  In this summary paper I will focus on the four main topics discussed at this
Conference: (i) First luminous sources in the universe, (ii) Reionization,
(iii) Intergalactic medium and (iv) Galaxy formation. In addition to provide a
necessarily sketchy summary of the various talks on these subjects, I will also
outline some of potentially important issues that still need to be fully
addressed.


title: Can we really rule out the existence of antistars?

abstract:
  The existence of large domains of antimatter is still an open question. Some
space mission and experiments in the near future are expected to give
reasonable answer to that question. Meanwhile, we can try to search for other
signatures of the presence of antimatter. This paper presents a discussion
about possible effects of the close encounter of stars and antistars. It is
known that the accretion power can be higher in presence of antimatter, because
of high-energy photons generated in annihilation, which result in a smaller
radiation pressure. Therefore, the Eddington luminosity can reach higher
values. Calculations of the gamma-ray flux above 100 MeV, and comparison with
recent data from satellites, show a good agreement for certain sources. So,
let's play some science-fiction!


title:
Statistical properties of visual binaries as tracers of the formation of
  young stellar clusters

abstract:
  In this review, we summarize the observed statistical properties of visual
binaries in various young stellar clusters. The binary frequency, orbital
period distribution and mass ratio distribution are considered for populations
of both low-mass and high-mass stars. These properties are then compared to
numerical models of the dynamical evolution of stellar clusters and to the
predictions of binary formation mechanisms.


title: Bulk Viscosity of Magnetized Neutron Star Matter

abstract:
  We study the effect of magnetic field on the bulk viscosity of nuclear matter
in neutron stars. We employ the framework of relativistic mean field theory to
observe the dense nuclear matter in neutron stars. The effects are first
studied for the case when the magnetic field does not exceed the critical value
to confine the electrons to the lowest Landau levels. We then consider the case
of intense magnetic field to evaluate viscosity for the URCA processes and show
that the inequality $p_{F}(e)+p_{F}(p)\geq p_{F}(n)$ is no longer required to
be satisfied for the URCA processes to proceed.


title: Escape of VHE gamma-rays from close massive binary Cen X-3

abstract:
  We consider propagation of very high energy (VHE) gamma-rays in the radiation
field of a massive star in the binary system Cen X-3, which has been reported
as a source of gamma-ray photons in the GeV and TeV energies. VHE gamma-rays or
electrons, injected by the compact object, should develop inverse Compton pair
cascades. We predict the gamma-ray spectra and light curves for the parameters
of Cen X-3 system. It is found that the gamma-ray spectra, observed at
different directions, have different shape and intensity. The gamma-ray light
curves, produced in the case of electron injection by the compact object in the
Cen X-3 system, should have opposite tendencies for photons with energies above
100 MeV and above 300 GeV, i.e. the photon intensities increases with phase in
the first case and decreases with phase in the second case. However the model
with injection of primary electrons seems to be in contrary with the reported
modulation of the GeV gamma-ray flux with the pulsar's period. The model with
injection of primary photons allows such modulation with the pulsar's period,
but predicts strong modulation of the TeV flux with the orbital period of the
binary. Modulation of TeV emission with the orbital period has been reported by
the early Cherenkov observations, but was not confirmed by the recent, more
sensitive observations by the Durham Mark 6 telescope.


title:
The 2-point angular correlation function of 20,000 galaxies to V<23.5
  and I<22

abstract:
  The UH8K wide field camera of the CFHT was used to image 0.68 deg^2 of sky.
  From these images, ~20,000 galaxies were detected to completeness magnitudes
V<23.5 and I<22.5. The angular correlation function of these galaxies is well
represented by the parameterization omega(theta) = A_W*theta^-delta. The slope
delta=-0.8 shows no significant variation over the range of magnitude. The
amplitude A_W decreases with increasing magnitude in a way that is most
compatible with a Lambda-CDM model (Omega_0 = 0.2, Lambda=0.8) with a
hierarchical clustering evolution parameter epsilon>0. We infer a best-fit
spatial correlation length of r_00= 5.85+/-0.5 h^-1 Mpc at z=0. The peak
redshift of the survey (I<22.5) is estimated to be z_peak~0.58, using the
blue-evolving luminosity function from the CFRS and the flat Lambda cosmology,
and r_0(z_peak)=3.5+/-0.5 h^-1 Mpc. We also detect a significant difference in
clustering amplitude for the red and blue galaxies, quantitatively measured by
correlation lengths of r_00=5.3+/-0.5 h^-1 Mpc and r_00=1.9+/-0.9 h^-1 Mpc
respectively, at z=0.


title: Advection-Dominated Accretion Onto Weakly-Magnetized White Dwarfs

abstract:
  The boundary layers of weakly-magnetized white dwarfs (WDs) accreting at
rates <=10^16 g/s are radially extended, hot, optically-thin, and they advect
some of their internally-dissipated energy (Narayan & Popham 1993). Motivated
by this, I construct here idealized spectral models of an Advection-Dominated
Accretion Flow (ADAF) around a WD, for application to quiescent Dwarf Novae
(DN). The Bremsstrahlung cooling of the gas in the ADAF, with temperatures
ranging from a few keV to a few tens of keV, can account for the X-ray emission
properties of quiescent DN. If the energy advected by the flow is thermalized
in the WD atmosphere, the resulting emission from the entire stellar surface
(blackbody of temperature T_eff ~ 5 eV) outshines the X-ray luminosity
substantially. This extreme-UV component provides a flux in the 0.055-0.28 keV
band which is sufficient to power the strong HeII lambda4686 emission lines of
quiescent DN by photoionization of the disk material. Reprocessing of the ADAF
X-ray emission by a cold outer thin disk could also lead to an observable iron
Kalpha fluorescence emission line, which can be used to probe the geometry of
the accretion flow. Existing observational data indicate that the presence of
ADAFs in quiescent DN is not ubiquitous, while future observations, in
particular with the X-ray satellites Chandra and XMM-Newton, have the potential
to detect signatures of the hot flow in promising candidates.


title: The Outbursts of Dwarf Novae

abstract:
  We present a numerical scheme for the evolution of an accretion disc through
a dwarf nova outburst. We introduce a time-varying artificial viscosity into an
existing smoothed particle hydrodynamics code optimised for two and
three-dimensional simulations of accretion discs. The technique gives rise to
coherent outbursts and can easily be adapted to include a complete treatment of
thermodynamics. We apply a two-dimensional isothermal scheme to the system SS
Cygni and present a wide range of observationally testable results.


title: Cosmological Parameters 2000

abstract:
  The cosmological parameters that I emphasize are the age of the universe
$t_0$, the Hubble parameter $H_0 \equiv 100 h$ km s$^{-1}$ Mpc$^{-1}$, the
average matter density $\Omega_m$, the baryonic matter density $\Omega_b$, the
neutrino density $\Omega_\nu$, and the cosmological constant $\Omega_\Lambda$.
The evidence currently favors $t_0 \approx 13$ Gyr, $h \approx 0.65$, $\Omega_m
\approx 0.4\pm0.1$, $\Omega_b = 0.02h^{-2}$, $0.001 < \Omega_\nu < 0.1$, and
$\Omega_\Lambda \approx 0.7$.


title: The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies

abstract:
  We investigate trends of the cold and hot gas content of early-type galaxies
with the presence of optical morphological peculiarities, as measured by the
fine-structure index (Sigma). HI mapping observations from the literature are
used to track the cold-gas content, and archival ROSAT PSPC data are used to
quantify the hot-gas content. We find that E and S0 galaxies with a high
incidence of optical peculiarities are exclusively X-ray underluminous and,
therefore, deficient in hot gas. In contrast, more relaxed galaxies with little
or no signs of optical peculiarities span a wide range of X-ray luminosities.
That is, the X-ray excess anticorrelates with Sigma. There appears to be no
similar trend of cold-gas content with either fine-structure index or X-ray
content. The fact that only apparently relaxed E and S0 galaxies are strong
X-ray emitters is consistent with the hypothesis that after strong disturbances
such as a merger hot-gas halos build up over a time scale of several gigayears.
This is consistent with the expected mass loss from stars.


title:
Three Dimensional Magneto-Hydrodynamical Modeling of Planetary Nebuale ~
  II: The Formation of Bipolar and Elliptical Nebulae with Point-Symmetric
  Structures and Collimated Outflows

abstract:
  This work presents three dimensional, magneto-hydrodynamical simulations of
the formation and early evolution of a subgroup of planetary nebulae that
exhibit a variety of point-symmetric structures. For bipolar nebulae, the
formation of point-symmetric nebular shapes along the inner borders of their
opposing lobes and/or collimated outflows or jets internal or external to their
cavities, is reproduced by considering a steady misalignment of the magnetic
collimation axis with respect to the symmetry axis of the bipolar wind outflow,
defined perpendicular to the equatorial density enhancement. Elliptical
planetary nebulae with ansae displaced from the symmetry axis in
point-symmetric fashion are reproduced through the same process by reducing the
equatorial density enhancement. This mechanism represents an alternative
explanation to some cases where morphological appearances give the impression
of the action of a symmetric, rotating or precessing jet from the central
source. The computational survey reveals that jet formation is detected only
for dense enough winds with mass loss rates $\gtrsim 10^{-7}$ \Moy. For lower
mass loss rates the jets tend to vanish leaving behind only ansae-like
structures at the tips of the lobes, as observed in some cases. The results are
rather independent of the wind terminal velocity, since magnetized bubbles
behave adiabatically for low wind velocities ($\simeq$ $100 \kms$), which in
the absence of a magnetic field would behave as momentum driven.


title:
Hubble Space Telescope Observations of the Planetary Nebula K648 in the
  Globular Cluster M15

abstract:
  We have obtained observations of the planetary nebula K648 in the Galactic
globular cluster M15 with the Hubble Space Telescope's WFPC2 camera, covering
an interval of 7 days. The frames provide both time-sampled broad-band
photometry of the central star and high-resolution images of the nebula in the
light of H-alpha, [OIII], and [NII]. In the deep narrow-band images, K648 is a
fairly typical double-shelled elliptical, but with a bright arc at one end of
the major axis that is especially prominent in [NII]; this feature is probably
a collection of FLIERs. The nebula is surrounded by a faint, smooth elliptical
halo, which appears undisturbed by any interaction with the interstellar
medium. Adopting Teff = 40,000 +- 3,000 K based upon published spectral-line
analyses, and employing our new broad-band optical flux data along with the
known cluster distance, we find log L/L_sun = 3.78 +- 0.08 for the K648 central
star. Theoretical post-asymptotic-giant-branch evolutionary tracks imply a mass
of 0.60 +- 0.02 M_sun for this luminosity, which is significantly higher than
the mean mass of white dwarfs in globular clusters and the halo field (0.50 +-
0.02). The K648 central star exhibits no significant photometric variability in
our data; thus we find no direct evidence of a close binary companion. We
suggest that the progenitor of K648 experienced mass augmentation in a
close-binary merger, allowing it to evolve to a remnant of higher mass than
those of the single stars in the cluster.


title:
Cyclotron Line Features from Near-Critical Fields II: on the Effect of
  Anisotropic Radiation Fields

abstract:
  We assess the impact of radiation anisotropy on the line shapes that result
from relativistic magnetic Compton scattering in the low-density/high-field
regime. A Monte Carlo implementation of radiation transport allows for spatial
diffusion of photons in arbitrary geometries and accounts for relativistic
angular redistribution. The cross section includes natural line widths and
photon "spawning" from up to fourth harmonic photons. In our first paper we
noted that even if the photon injection is isotropic a strongly anisotropic
radiation field rapidly ensues. We now investigate the angular distribution of
cyclotron spectra emerging from an internally irradiated magnetized plasma with
a prescribed global geometry (either cylindrical or plane parallel) and the
effects of anisotropic photon injection on the line shapes. Varying the input
angular distribution permits a better understanding of the line formation
process in more realistic scenarios where the radiative mechanisms are
influenced by the intrinsic anisotropy of the field and by moderate
relativistic beaming. In general, the line features are most pronounced along
the directions of the anisotropic continuum injection and tend to be weakened
in other directions, relative to the line features resulting from an isotropic
continuum injection. We find that the enhancements at the line wings of the
fundamental, which appear prominantly in the case of isotropic continuum
injection, are strongly suppressed along the direction of anisotropy in the
case of beamed continuum injection, regardless of geometry or beaming pattern.


title: Feedback from Protostellar Outflows in Star and Star Cluster Formation

abstract:
  Magnetic stresses collimate protostellar winds into a common distribution of
force with angle. Sweeping into the ambient medium, such winds drive bipolar
molecular outflows whose properties are insensitive to the distribution of
ambient gas and to the details of how the wind is launched, and how its
intensity varies over time. Moreover, these properties are in accord with the
commonly observed features of outflows.
  This model is simple enough to permit a quantitative study of the feedback
effects from low-mass star formation. It predicts the rate at which
star-forming gas is ejected by winds, and hence the efficiency with which stars
form. Applied to individual star formation, it relates the stellar initial mass
function to the distribution of pre-stellar cores. Applied to cluster
formation, it indicates whether the resulting stellar system will remain
gravitationally bound.
  Using the energy injection and mass ejection implied by this model, we
investigate the dynamical evolution of a molecular clump as a stellar cluster
forms within it. This depends critically on the rate at which turbulence
decays: it may involve equilibrium star formation (slow decay), overstable
oscillations, or collapse (fast decay).


title: The Relative Age of the Thin and Thick Galactic Disks

abstract:
  We determine the relative ages of the open cluster NGC 188 and selected
Hipparcos field stars by isochrone fitting, and compare them to the age of the
thick disk globular cluster 47 Tuc. The best fit age for NGC 188 was determined
to be $6.5 \pm 1.0$ Gyr. The solar metallicity Hipparcos field stars yielded a
slightly older thin disk age, $7.5 \pm 0.7$ Gyr. Two slightly metal-poor ($\feh
= -0.22$) field stars whose kinematic and orbital parameters indicate that they
are members of the thin disk were found to have an age of $9.7\pm 0.6$ Gyr. The
age for 47 Tuc was determined to be $12.5 \pm 1.5$ Gyr. All errors are internal
errors due to the uncertainty in the values of metallicity and reddening. Thus,
the oldest stars dated in the thin disk are found to be $2.8\pm 1.6$ Gyr
younger than 47 Tuc. Furthermore, as discussed by \citet{Chb99} 47 Tuc has a
similar age to three globular clusters located in the inner part of the
Galactic halo, implying that star formation in the thin disk started within
$2.8\pm 1.6$ Gyr of star formation in the halo.


title:
The optical reflector system for the CANGAROO-II imaging atmospheric
  Cherenkov telescope

abstract:
  A new imaging atmospheric Cherenkov telescope (CANGAROO-II) with a
light-weight reflector has been constructed. Light, robust, and durable mirror
facets of containing CFRP (Carbon Fiber Reinforced Plastic) laminates were
developed for the telescope. The attitude of each facet can be adjusted by
stepping motors. In this paper, we describe the design, manufacturing,
alignment procedure, and the performance of the CANGAROO-II optical reflector
system.


title: Observations of Spectral and Time Variabilities from MCG-2-58-22

abstract:
  We present results from analysis of the X-ray archive data of MCG-2-58-22,
acquired with ROSAT from 1991 to 1993 and with ASCA from 1993 to 1997. By
analyzing light curves, we find that MCG-2-58-22 shows a clear time variability
in X-ray flux. The time scales of the variations range widely from about 1000 s
to more than years. Among the variations, a flare-like event overlaid on the
gradual flux decrease from 1979 to 1993 is detected. We also find clear time
variability of the spectra in the energy range of 0.1 - 2.0 keV. However, the
flux variation does not influences on their spectra in the energy range of 2 -
10 keV. The implications of these observational results are discussed in terms
of a supermassive black hole model and accretion flow dynamics near the central
black hole.


title: A gravitational lens survey with Planck Surveyor

abstract:
  The Planck Surveyor cosmic microwave background (CMB) imaging mission will
make very sensitive maps of the whole sky at microwave, millimetre (mm) and
sub-mm wavelengths. The steep source counts expected in the highest frequency
Planck bands are likely to be associated with a strong magnification bias, and
so the fraction of galaxies magnified by a factor of two or more could be
greater than 10%. In this paper, previous predictions of the significance of
the Planck survey for studies of lensing statistics are updated, to reflect our
expanded knowledge of the properties of high-redshift dusty galaxies, obtained
from far-infrared and sub-mm surveys. A catalogue of probably about 10000
galaxies, but perhaps as many as 100000 or as few as 1000, is expected to be
generated from the final Planck all-sky maps. Of order 1000 galaxies, a better
determined number, might reasonably be expected to be strongly lensed.
Co-ordinated sub-mm and far-infrared follow-up observations made using the
SPIRE and PACS instruments aboard the ESA cornerstone mission FIRST - Planck's
travelling companion to its L2 orbit - and the ground-based ALMA interferometer
array will provide accurate positions and very valuable information about the
spectral energy distributions (SEDs), redshifts and astrophysical properties of
the galaxies in the Planck catalogue. ALMA and radio images will also reveal
their morphology, and the characteristic arc and multiple image structures
produced by gravitational lensing. Studies of these bright sub-mm-selected
galaxies will allow new insight into the process of galaxy formation and
evolution.


title: Magnetic Activity in Stars, Discs and Quasars

abstract:
  Although magnetic fields in interstellar matter were postulated almost fifty
years ago, magnetohydrodynamic theory was then much hampered by our inability
to see what the magnetic field configurations were like and, after a decade of
innovative development, cynics, not without some justification, began to claim
that anything can happen when magnetism and an imaginative theorist get
together. Thus cosmic lightning in particular received a bad press. More
recently great advances in observational techniques that we shall hear of from
Title, Beck, Moran and Mirabel have enabled us to see not only the sun's
magnetic field with unprecedented clarity but the fields in galaxies, quasars
and microquasars are now measured and not merely figments of fertile
imaginations.


title: Simulations of Pregalactic Structure Formation with Radiative Feedback

abstract:
  We present results from three-dimensional hydrodynamic simulations of the
high redshift collapse of pregalactic clouds including feedback effects from a
soft H2 photodissociating UV radiation field. The simulations use an Eulerian
adaptive mesh refinement technique to follow the nonequilibrium chemistry of
nine chemical species with cosmological initial conditions drawn from a popular
Lambda-dominated cold dark matter model. The results confirm that the soft UV
background can delay the cooling and collapse of small halos (~10^6 Msun). For
reasonable values of the photo-dissociating flux, the H2 fraction is in
equilibrium throughout most of the objects we simulate. We determine the mass
threshold for collapse for a range of soft-UV fluxes and also derive a simple
analytic expression. Continuing the simulations beyond the point of initial
collapse demonstrates that the fraction of gas which can cool depends mostly on
the virial mass of the halo and the amount of soft-UV flux, with remarkably
little scatter. We parameterize this relation, for use in semi-analytic models.


title:
Dilaton-derived quintessence scenario leading naturally to the late-time
  acceleration of the Universe

abstract:
  Quintessence scenarios provide a simple explanation for the observed
acceleration of the Universe. Yet, explaining why acceleration did not start a
long time ago remains a challenge. The idea that the transition from radiation
to matter domination played a dynamical role in triggering acceleration has
been put forward in various guises. We propose a simple dilaton-derived
quintessence model in which temporary vacuum domination is naturally triggered
by the radiation to matter transition. In this model Einstein's gravity is
preserved but quintessence couples non-minimally to the cold dark matter, but
not to ``visible'' matter. Such couplings have been attributed to the dilaton
in the low-energy limit of string theory beyond tree level. We also show how a
cosmological constant in the string frame translates into a quintessence-type
of potential in the atomic frame.


title: HST Observations of the Interacting Galaxies NGC 2207 and IC 2163

abstract:
  Hubble Space Telescope images of the galaxies NGC 2207 and IC 2163 show star
formation and dust structures in a system that has experienced a recent grazing
encounter. Tidal forces from NGC 2207 compressed and elongated the disk of IC
2163, forming an oval ridge of star formation. Gas flowing away from this ridge
has thin parallel dust filaments transverse to the direction of motion.
Numerical models suggest that the filaments come from flocculent spiral arms
that were present before the interaction. A dust lane at the outer edge of the
tidal tail is a shock front where the flow abruptly changes direction. A spiral
arm of NGC 2207 that is backlit by IC 2163 is seen to contain several parallel,
knotty filaments that are probably shock fronts in a density wave. Blue
clusters of star formation inside these dust lanes show density wave triggering
by local gravitational collapse. Spiral arms inside the oval of IC 2163 could
be the result of ILR-related orbits in the tidal potential that formed the
oval. Their presence suggests that tidal forces alone may initiate a temporary
nuclear gas flow and eventual starburst without first forming a stellar bar.
Several emission structures resembling jets 100-1000 pc long appear. There is a
dense dark cloud with a conical shape 400 pc long and a bright compact cluster
at the tip, and with a conical emission nebula of the same length that points
away from the cluster in the other direction. This region coincides with a
non-thermal radio continuum source that is 1000 times the luminosity of Cas A
at 20 cm.


title:
The very red afterglow of GRB 000418 - further evidence for dust
  extinction in a GRB host galaxy

abstract:
  We report near-infrared and optical follow-up observations of the afterglow
of the Gamma-Ray Burst 000418 starting 2.5 days after the occurrence of the
burst and extending over nearly seven weeks. GRB 000418 represents the second
case for which the afterglow was initially identified by observations in the
near-infrared. During the first 10 days its R-band afterglow was well
characterized by a single power-law decay with a slope of 0.86. However, at
later times the temporal evolution of the afterglow flattens with respect to a
simple power-law decay. Attributing this to an underlying host galaxy we find
its magnitude to be R=23.9 and an intrinsic afterglow decay slope of 1.22. The
afterglow was very red with R-K=4 mag. The observations can be explained by an
adiabatic, spherical fireball solution and a heavy reddening due to dust
extinction in the host galaxy. This supports the picture that (long) bursts are
associated with events in star-forming regions.


title:
HST/STIS observations of GRB000301C: CCD imaging and NUV MAMA
  spectroscopy

abstract:
  We present HST/STIS observations of the optical counterpart (OT) of the
gamma-ray burster GRB 000301C obtained on 2000 March 6, five days after the
burst. CCD clear aperture imaging reveals a R ~ 21.50+/-0.15 source with no
apparent host galaxy. An 8000 s, 1150 < lambda/A < 3300 NUV-MAMA prism spectrum
shows a relatively flat continuum (in f_lambda) between 2800 and 3300 A, with a
mean flux 8.7 (+0.8,-1.6)+/- 2.6 10^(-18) ergs/s/cm^2/A, and a sharp break
centered at 2797+/-25 A. We interpret it as HI Lyman break at z = 2.067+/-0.025
indicating the presence of a cloud with a HI column density log(HI) > 18 on the
line-of-sight to the OT. This value is conservatively a lower limit to the GRB
redshift. However, the facts that large N(HI) system are usually considered as
progenitors of present day galaxies and that other OTs are found associated
with star forming galaxies strongly suggest that it is the GRB redshift. In any
case, this represents the largest direct redshift determination of a gamma-ray
burster to date. Our data are compatible with an OT spectrum represented by a
power-law with an intrinsic index \alpha = 1.2((f_nu \propto nu^-alpha) and no
extinction in the host galaxy or with alpha = 0.5 and extinction by a SMC-like
dust in the OT rest-frame with A_V = 0.15. The large N(HI) and the lack of
detected host is similar to the situation for damped Ly-alpha absorbers at z >
2.


title:
Measurements of solar irradiance and effective temperature as a probe of
  solar interior magnetic fields

abstract:
  We argue that a variety of solar data suggest that the activity-cycle
timescale variability of the total irradiance, is produced by structural
adjustments of the solar interior. Assuming these adjustments are induced by
variations of internal magnetic fields, we use measurements of the total
irradiance and effective temperature over the period from 1978 to 1992, to
infer the magnitude and location of the magnetic field. Using an updated
stellar evolution model, which includes magnetic fields, we find that the
observations can be explained by fields whose peak values range from 120k to
2.3k gauss, located in the convection zone between $0.959R_{\sun}$ and
$0.997R_{\sun}$, respectively. The corresponding maximal radius changes, are 17
km when the magnetic field is located at $0.959R_{\sun}$ and 3 km when it is
located at $0.997R_{\sun}$. At these depths, the $W$ parameter(defined by
$\Delta \ln R / \Delta \ln L$, where $R$ and $L$ are the radius and luminosity)
ranges from 0.02 to 0.006. All these predictions are consistent with
helioseismology and recent measurements carried out by the MDI experiment on
SOHO.


title:
Placing limits on the spin-torsion fluctuation from the stability of
  Friedmann solution and COBE data

abstract:
  The gravitational stability of Friedmann metric with respect to homogeneous
and isotropic perturbations in Einstein-Cartan cosmology is used together with
the COBE data to place a limit on the spin-torsion primordial density
fluctuation.Cosmological perturbations in Bianchi type III models are shown to
have no contributions from torsion at the early stages of the Universe.