title:
M2000 : an astrometric catalog in the Bordeaux Carte du Ciel zone +11
  degrees < {delta} < +18 degrees

abstract:
  During four years, systematic observations have been conducted in drift scan
mode with the Bordeaux automated meridian circle in the declination band [+11 ;
+18]. The resulting astrometric catalog includes about 2 300 000 stars down to
the magnitude limit V_M=16.3. Nearly all stars (96%) have been observed at
least 6 times, the catalog being complete down to V_M=15.4. The median internal
standard error in position is about 35 mas in the V_M magnitude range [11 ;
15], which degrades to about 50 mas when the faintest stars are considered.
M2000 provides also one band photometry with a median internal standard error
of 0.04 mag. Comparisons with the Hipparcos and bright part of Tycho-2 catalogs
have enabled to estimate external errors in position to be lower than 40 mas.
In this zone and at epoch 1998, the faint part of Tycho-2 is found to have an
accuracy of 116 mas in alpha instead of 82 mas deduced from the model-based
standard errors given in the catalog.


title:
The CORALS Survey I: New Estimates of the Number Density and Gas Content
  of Damped Lyman Alpha Systems Free from Dust Bias

abstract:
  (Abridged) We present the first results from the Complete Optical and Radio
Absorption Line System (CORALS) survey. We have compiled a homogeneous sample
of radio-selected QSOs from the Parkes Catalogue and searched for damped Lyman
alpha systems (DLAs) towards every target, irrespective of its optical
magnitude. This approach circumvents selection effects -- particularly from
intervening dust -- which have long been suspected to affect DLA surveys in
optically-selected, magnitude-limited QSO samples. The CORALS data set consists
of 66 z_em > 2.2 QSOs in which 22 DLAs with absorption redshifts 1.8 < z_abs <
z_em have been identified over a total redshift interval Delta z = 55.46. In
this first paper of the CORALS series we describe the sample, present
intermediate resolution spectroscopy and determine the population statistics of
DLAs. We deduce a value of the neutral gas mass density traced by DLAs
(expressed as a fraction of the closure density) log Omega_DLA h =
-2.59^{+0.17}_{-0.24}, and a number density of DLAs per unit redshift n(z) =
0.31^{+0.09}_{-0.08}, both at a mean redshift <z> = 2.37. Taking into account
the errors, we conclude that dust-induced bias in previous surveys may have led
to an underestimate of these quantities by at most a factor of two and we have
not uncovered a previously unrecognised population of high column density DLAs
in front of faint QSOs.


title: Insights from Pulsating Nova Envelopes

abstract:
  Based on a linear and non-linear study of radial pulsations in the envelopes
of classical novae (Schenker 1999), I discuss the results both from the point
of view of pulsation theory as well as their consequences for current nova
models.
  Starting from initially static envelope structures at various stages during
the decline of a nova outburst, strong `running wave' instabilities have been
found that rapidly grow into shocks. Improved analytical concepts give a new
direction to the interpretation of such highly non-adiabatic radial pulsations.
  For direct observational confirmation a search for short period variability
in the UV and soft X-ray is suggested during the very late decline phase.
Speculative consequences for mass loss scenarios in novae due to these
instabilities will need some more work in the future.


title: A RICH prototype for the AMS experiment

abstract:
  The AMS spectrometer will be installed on the International Space Station at
the end of 2003. Among other improvements over the first version of the
instrument, a ring imaging Cherenkov detector (RICH) will be added which latter
should open a new window for cosmic-ray physics, allowing isotope separation up
to A~25 between 1 and 10 GeV/c and elements identification up to Z~25 between
threshold and 1 TeV/c/nucleon. It should also contribute to the high level of
redundancy required for AMS and reject efficiency albedo particles. The results
of the first generation prototype and the expected results of the new one are
discussed.


title: High Redshift Quasars and Star Formation in the Early Universe

abstract:
  In order to derive information on the star formation history in the early
universe we observed 6 high-redshift (z=3.4) quasars in the near-infrared to
measure the relative iron and \mgii emission strengths. A detailed comparison
of the resulting spectra with those of low-redshift quasars show essentially
the same FeII/MgII emission ratios and very similar continuum and line spectral
properties, indicating a lack of evolution of the relative iron to magnesium
abundance of the gas since z=3.4 in bright quasars. On the basis of current
chemical evolution scenarios of galaxies, where magnesium is produced in
massive stars ending in type II SNe, while iron is formed predominantly in SNe
of type Ia with a delay of ~1 Gyr and assuming as cosmological parameters H_o =
72 km/s Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7$, we conclude that major
star formation activity in the host galaxies of our z=3.4 quasars must have
started already at an epoch corresponding to z_f ~= 10, when the age of the
universe was less than 0.5 Gyrs.


title: Weak magnetism for antineutrinos in supernovae

abstract:
  Weak magnetism increases antineutrino mean free paths in core collapse
supernovae. The parity violating interference between axial and vector currents
makes antineutrino-nucleon cross sections smaller then those for neutrinos. We
calculate simple, exact correction factors to include recoil and weak magnetism
in supernova simulations. Weak magnetism may significantly increase the
neutrino energy flux. We calculate, in a diffusion approximation, an increase
of order 15% in the total energy flux for temperatures near 10 MeV. This should
raise the neutrino luminosity. Weak magnetism also changes the emitted spectrum
of $ \bar\nu_x$ (with $x=\mu$ or $\tau$) and $\bar\nu_e$. We estimate that
$\bar\nu_x$ will be emitted about 7% hotter than $\nu_x$ because $\bar\nu_x$
have longer mean free paths. Likewise weak magnetism may increase the
$\bar\nu_e$ temperature by of order 10%. This increase in temperature coupled
with the increase in neutrino luminosity should increase the heating in the low
density region outside of the neutrino sphere. This, in turn, could be
important for the success of an explosion. It is important to check our results
with a full simulation that includes Boltzmann neutrino transport and weak
magnetism corrections.


title: High-velocity clouds: a diverse phenomenon

abstract:
  In this contribution the current state of knowledge about the high-velocity
clouds (HVCs) is summarized. Recent progress has shown that the HVCs are a
diverse phenomenon. The intermediate-velocity clouds (IVCs) are likely to be
part of a Galactic Fountain. The Magellanic Stream is a tidal remnant. HVC
complex C (possibly complexes A and GCN) are low-metallicity clouds near the
Galaxy; they could be remnants of the formation of the Galaxy or old tidal
streams extracted from nearby dwarf galaxies. Having a substantial number of HI
HVCs dispersed throughout the Local Group seems incompatible with the observed
HI mass function of galaxies. Finally, FUSE finds high-velocity OVI, some of
which is clearly associated with HI HVCs, but some which is not.


title: The small-scale structure of the Magellanic Stream

abstract:
  We have mapped in neutral hydrogen (HI) two regions at the northern tip of
the Magellanic Stream, known as MS V and MS VI, using the Arecibo telescope.
The small-scale structure of the MS shows clumpy and head-tail morphology. The
spatial power spectrum of this star-free intergalactic medium has a power-law
behavior with the density slope of -3.8. A gradual steepening of the power-law
slope is seen when increasing the thickness of velocity slices.


title: X-Ray Detection of a Pre-Supernova Evolution for the SN 1993J Progenitor

abstract:
  We report on the first detection of a pre-supernova (SN) evolution in the
X-ray regime. The results are based on ROSAT observations of SN 1993J ranging
from six days to five years after the outburst. The X-ray observations are used
to probe the SN shell interaction with the ambient circumstellar matter (CSM).
After exploring various scenarios that might explain the observed X-ray
lightcurve with a t^-0.27 rate of decline, we present a coherent picture in
terms of the interaction of the SN shock front with the CSM deposited by the
progenitor's stellar wind. During the observed period, the SN shell has reached
a radius of 3x10^17 cm from the site of the explosion, corresponding to ~10^4
years in the progenitors stellar wind history. Our analysis shows that the
mass-loss rate of the progenitor has decreased constantly from \dot{M} =
4x10^-4 to 4x10^-5 M_sun/yr (v_w/10 km/s) during the late stage of the
evolution. Assuming a spherically symmetric expansion, the circumstellar matter
density profile is found to be significantly flatter (\rho_csm \propto r^-1.63)
than expected for a constant mass-loss rate and constant wind velocity profile
(r^-2). The observed evolution either reflects a decrease in the mass-loss
rate, an increase in the wind speed or a combination of both, indicating that
the progenitor likely was making a transition from the red to the blue
supergiant phase during the late stage of its evolution.


title:
FUSE and STIS Observations of Intervening OVI Absorption Line Systems in
  the Spectrum of PG0953+415

abstract:
  We present FUSE and STIS observations of the IGM toward PG 0953+415 (z_em =
0.239). An O VI system at z = 0.06807 is detected in H I Lya, Lyb, Lyg, O VI N
V, C IV, and C III. The observations are modeled as a low density intervening
gas with a metallicity of 0.4 (+0.6, -0.2) times solar in photoionization
equilibrium with the ionizing extragalactic radiation. The best fit is achieved
with an ionization parameter, logU = -1.35, which implies nH ~ 10-5 cm-3 and a
path length of ~ 80 kpc through the absorbing gas. H I Lya absorption at z =
0.14232 spans a velocity range of 410 km s-1 with the strongest components near
0 and 80 km s-1 in the z = 0.14232 rest frame. In this system O VI absorption
is strong near 0 km s-1 and not detected at 80 km s-1. The new observations
place constraints on the properties of the z = 0.14232 system but do not
discriminate between collisional ionization in hot gas versus photoionization
in a very low density medium with an ionization parameter logU > -0.74. The two
O VI systems occur at redshifts where there are peaks in the number density of
intervening galaxies along the line of sight. We update the estimate of the low
redshift number density of intervening O VI systems. Over a total deltaz =
0.43, we detect six O VI systems with restframe equivalent widths of the O VI
1031.93 line exceeding 50 mA yielding dN/dz = 14 (+9, -6) for <z> = 0.09. This
implies a low redshift value of the baryonic contribution to the closure
density of the O VI systems of WB(O VI) > 0.002h75-1 assuming the average
metallicity in the O VI systems is 0.1 solar.


title:
Atomic calculation for the atmospheres of strongly-magnetized neutron
  stars

abstract:
  Complete modeling of radiative transfer in neutron star atmospheres is in
progress, taking into account the anisotropy induced by magnetic fields,
non-ideal effects and general relativity. As part of our modeling, we present a
novel atomic calculation method producing an extensive atomic data set
including energy values and oscillator strengths in the so-called Landau regime
($B > 4.7\times10^9Z^2$ G). Conventional atmosphere models for B=0 are not
applicable to typical field strengths of cooling neutron stars ($B
\sim10^{12}-10^{13}$ G), since an atom no longer keeps its spherical shape. The
elemental composition and the configuration of the magnetic field in the
atmosphere are presently unknown, so that atomic data must be produced for
ground and excited states of several ions as a function of magnetic field. To
accomplish this efficiently, we minimized the iterations in the Hartree
equation and treated exchange terms and higher Landau states by perturbation
methods. This method has the effect of reducing the computation time
significantly. Inclusion of higher Landau states gives us much more accurate
data for inner orbitals unlike other methods based on the adiabatic
approximation. While existing atomic data in the Landau regime are available
only for low $Z$ atoms, our method can be used in elements up to Fe with
sufficient accuracy to be of use for spectroscopic missions such as {\it
Chandra}, {\it XMM-Newton} and next-generation X-ray telescopes.


title: Note on Solving for the Dynamics of the Universe

abstract:
  In a recent article, Faraoni proposed an alternative procedure to solve the
Friedman-Lemaitre-Robertson-Walker (FLRW) cosmological equations. The basic
result of that paper was obtained long ago through a different approach, which
seems to be little known and deserves closer attention due to its pedagogical
interest. The broad importance of this method is readily recognized by
examining some additional cases not considered by Faraoni. Its instructive
potential for introductory courses on cosmology has been positively verified by
the author in many lectures during the last decade.


title: A Possible Massive Asteroid Belt Around zeta Lep

abstract:
  We have used the Keck I telescope to image at 11.7 microns and 17.9 microns
the dust emission around zeta Lep, a main sequence A-type star at 21.5 pc from
the Sun with an infrared excess. The excess is at most marginally resolved at
17.9 microns. The dust distance from the star is probably less than or equal to
6 AU, although some dust may extend to 9 AU. The mass of observed dust is
\~10^22 g. Since the lifetime of dust particles is about 10,000 years because
of the Poytning-Robertson effect, we robustly estimate at least 4 10^26 g must
reside in parent bodies which may be asteroids if the system is in a steady
state and has an age of ~300 Myr. This mass is approximately 200 times that
contained within the main asteroid belt in our solar system.


title: Washington Photometry of New Globular Clusters in M31

abstract:
  We present a progress report on Washington photometry of several hundred new
globular cluster (GC) candidates in M31 which were recently found from our new
CCD survey of GCs. Washington CMT1 filters we used are very efficient to survey
extragalactic GCs and to estimate the metallicity of GCs. Preliminary
color-magnitude diagrams and color-color diagrams of the new GC candidates and
known GCs in M31 are obtained.


title:
Surface Photometry of Star Clusters in the Dwarf Elliptical Galaxies NGC
  185 and NGC 205

abstract:
  We present the surface photometry of star clusters in the nearby dwarf
elliptical galaxies NGC 185 and NGC 205, obtained from deep HST WFPC2 F555W (V)
and F814W (I) images. We have obtained surface brightness and color profiles of
six star clusters in NGC 185, seven star clusters in NGC 205, and one recently
discovered non-stellar object in NGC 205. The surface brightness profiles of
ten star clusters are fitted well by the King model, and those of four star
clusters are fitted well by the power-law. Three out of ten star clusters
fitted well with King model show signs of tidal tails.


title: New CCD Survey of Globular Clusters in M31

abstract:
  We present a progress report of our wide field CCD survey of globular
clusters in M31. We have covered 3 deg X 3 deg area centered on M31, using the
KPNO 0.9m and Washington CMT1 filters. Our survey is much deeper and more
sensitive than previous surveys. We have found several hundred new globular
cluster candidates in M31 in addition to confirming previously known globular
clusters, and also have found a number of interlopers among previous globular
cluster catalogs. We have also obtained spectra of about 500 objects among
these candidates using the HYDRA at the WIYN 3.5m telescope, which are used for
classification and measuring the radial velocity of the candidate objects. When
completed, a new master catalog of globular clusters in M31 will be made,
combining the new globular clusters with the known globular clusters.


title: High-Velocity Cloud Complex C: Galactic Fuel or galactic Waste?

abstract:
  We present HST GHRS and STIS observations of five QSOs that probe the
prominent high-velocity cloud (HVC) Complex C, covering 10% of the northern
sky. Based upon a single sightline measurement (Mrk 290), a metallicity
[S/H]=-1.05+/-0.12 has been associated with Complex C by Wakker et al.
(1999a,b). When coupled with its inferred distance (5<d<30 kpc) and
line-of-sight velocity (v=-100 to -200 km/s), Complex C appeared to represent
the first direct evidence for infalling low-metallicity gas onto the Milky Way,
which could provide the bulk of the fuel for star formation in the Galaxy. We
have extended the abundance analysis of Complex C to encompass five sightlines.
We detect SII absorption in three targets (Mrk 290, Mrk 817, and Mrk 279); the
resulting [SII/HI] values range from -0.36 (Mrk 279) to -0.48 (Mrk 817) to
-1.10 (Mrk 290). Our preliminary OI FUSE analysis of the Mrk 817 sightline also
supports the conclusion that metallicities as high as 0.3 times solar are
encountered within Complex C. These results complicate an interpretation of
Complex C as infalling low-metallicity Galactic fuel. Ionization corrections
for HII and SIII cannot easily reconcile the higher apparent metallicities
along the Mrk 817 and Mrk 279 sightlines with that seen toward Mrk 290, since
H-alpha emission measures preclude the existence of sufficient HII. If gas
along the other lines of sight has a similar pressure and temperature to that
sampled toward Mrk 290, the predicted H-alpha emission measures would be 900
mR. It may be necessary to reclassify Complex C as mildly enriched Galactic
waste from the Milky Way or processed gas torn from a disrupted neighboring
dwarf, as opposed to low-metallicity Galactic fuel.


title:
Study of the neutron star structure in strong magnetic fields including
  the anomalous magnetic moments

abstract:
  We study the effects of strong magnetic fields on the neutron star structure.
If the interior field of a star is on the same order of the surface field
currently observed, the influences of the magnetic field on the star mass and
radius are negligible. If one assumes that the internal magnetic field can be
as large as that estimated from the scalar virial theorem, considerable effects
can be induced. The maximum mass of stars is arisen substantially while the
central density is largely suppressed. For two equal-mass stars the radius of
the magnetic star can be larger by about 10% $\sim$ 20% than the nonmagnetic
star.


title:
The 1998 outburst of XTE J1550-564: a model based on multiwavelength
  observations

abstract:
  The 1998 September outburst of the black-hole X-ray binary XTE J1550-564 was
monitored at X-ray, optical and radio wavelengths. We divide the outburst
sequence into five phases and discuss their multiwavelength properties. The
outburst starts with a hard X-ray spike, while the soft X-ray flux rises with a
longer timescale. We suggest that the onset of the outburst is determined by an
increased mass transfer rate from the companion star, but the outburst
morphology is determined by the distribution of specific angular momentum in
the accreting matter. The companion in XTE J1550-564 is likely to be an active
magnetic star, with a surface field strong enough to influence the dynamics of
mass transfer. We suggest that its magnetic field can create a magnetic bag
capable of confining gas inside the Roche lobe of the primary. The impulsive
rise in the hard X-rays is explained by the inflow of material with low angular
momentum onto the black hole, on a free-fall timescale, when the magnetic
confinement breaks down. At the same time, high angular momentum matter,
transferred via ordinary Roche-lobe overflow, is responsible for the formation
of a disk.


title: Transport of Cosmic Rays in Chaotic Magnetic Fields

abstract:
  The transport of charged particles in disorganised magnetic fields is an
important issue which concerns the propagation of cosmic rays of all energies
in a variety of astrophysical environments, such as the interplanetary,
interstellar and even extra-galactic media, as well as the efficiency of Fermi
acceleration processes. We have performed detailed numerical experiments using
Monte-Carlo simulations of particle propagation in stochastic magnetic fields
in order to measure the parallel and transverse spatial diffusion coefficients
and the pitch angle scattering time as a function of rigidity and strength of
the turbulent magnetic component. We confirm the extrapolation to high
turbulence levels of the scaling predicted by the quasi-linear approximation
for the scattering frequency and parallel diffusion coefficient at low
rigidity. We show that the widely used Bohm diffusion coefficient does not
provide a satisfactory approximation to diffusion even in the extreme case
where the mean field vanishes. We find that diffusion also takes place for
particles with Larmor radii larger than the coherence length of the turbulence.
We argue that transverse diffusion is much more effective than predicted by the
quasi-linear approximation, and appears compatible with chaotic magnetic
diffusion of the field lines. We provide numerical estimates of the Kolmogorov
length and magnetic line diffusion coefficient as a function of the level of
turbulence. Finally we comment on applications of our results to astrophysical
turbulence and the acceleration of high energy cosmic rays in supernovae
remnants, in super-bubbles, and in jets and hot spots of powerful
radio-galaxies.


title: Interstellar O VI in the Large Magellanic Cloud

abstract:
  I summarize Far Ultraviolet Spectroscopic Explorer (FUSE) observations of
interstellar O VI absorption towards 12 early-type stars in the Large
Magellanic Cloud (LMC), the closest disk galaxy to the Milky Way. LMC O VI is
seen towards all 12 stars with properties (average column densities,
kinematics) very similar to those of the Milky Way halo, even though O/H in the
LMC is lower by a factor of ~2.5. Sight lines projected onto known LMC
superbubbles show little enhancement in O VI column density compared to sight
lines towards quiescent regions of the LMC. The O VI absorption is displaced by
\~-30 km/sec from the corresponding low-ionization absorption associated with
the bulk of the LMC gas. The LMC O VI most likely arises in a
vertically-extended distribution, and I discuss the measurements in the context
of a halo composed of radiatively-cooling hot gas. In this case, the mass-flow
rate from one side of the LMC disk is of the order 1 solar mass/yr.


title:
Extragalactic neutrino background from very young pulsars surrounded by
  supernova envelopes

abstract:
  We estimate the extragalactic muon neutrino background which is produced by
hadrons injected by very young pulsars at an early phase after supernova
explosion. It is assumed that hadrons are accelerated in the pulsar wind zone
which is filled with thermal photons captured below the expanding supernova
envelope. In collisions with those thermal photons hadrons produce pions which
decay into muon neutrinos. At a later time, muon neutrinos are also produced by
the hadrons in collisions with matter of the expanding envelope. We show that
extragalactic neutrino background predicted by such a model should be
detectable by the planned 1 km$^2$ neutrino detector if a significant part of
pulsars is born with periods shorter than $\sim 10$ ms. Since such population
of pulsars is postulated by the recent models of production of extremely high
energy cosmic rays, detection of neutrinos with predicted fluxes can be used as
their observational test.


title: High Redshift Galaxy Clusters as Probes of Cosmology

abstract:
  A few, simple and qualitative examples of the potential of galaxy clusters as
diagnostics of cosmology are presented. In relation to these we discuss briefly
three ongoing or forthcoming cluster surveys in the optical/NIR, X-rays and the
cosmic microwave radiation background.


title:
Theoretical Spectral Models of T Dwarfs at Short Wavelengths and Their
  Comparison with Data

abstract:
  We have generated new, self-consistent spectral and atmosphere models for the
effective temperature range 600 K to 1300 K thought to encompass the known T
dwarfs. For the first time, theoretical models are compared with a {\it family}
of measured T dwarf spectra at wavelengths shortward of $\sim$1.0 micron. By
defining spectral indices and standard colors in the optical and very
near-infrared, we explore the theoretical systematics with \teff, gravity, and
metallicity. We conclude that the short- wavelength range is rich in
diagnostics that complement those in the near-infrared now used for spectral
subtyping. We also conclude that the wings of the Na D and K I (7700\AA)
resonance lines and aggressive rainout of heavy metals (with the resulting
enhancement of the sodium and potassium abundances at altitude) are required to
fit the new data shortward of 1.0 \mic. Furthermore, we find that the water
bands weaken with increasing gravity, that modest decreases in metallicity
enhance the effect in the optical of the sodium and potassium lines, and that
at low \teffs, in a reversal of the normal pattern, optical spectra become
bluer with further decreases in \teff. Moreover, we conclude that T dwarf
subtype is not a function of \teff alone, but that it is a non-trivial function
of gravity and metallicity as well. As do Marley et al. (2001), we see evidence
in early T dwarf atmospheres of a residual effect of clouds. With cloudless
models, we obtain spectral fits to the two late T dwarfs with known parallaxes,
but a residual effect of clouds on the emergent spectra of even late T dwarfs
can not yet be discounted.


title: Recently discovered pulsars and unidentified EGRET sources

abstract:
  We present a correlative study between all unidentified EGRET sources at low
Galactic latitudes and the newly discovered pulsars in the released portion of
the Parkes multibeam radio survey. We note 14 positional coincidences: eight of
these are ``Vela-like'' pulsars, with relatively small periods, small
characteristic ages, and high spin-down luminosities. Three of these
coincidences have been investigated by D'Amico et al. (2001) and Camilo et al.
(2001). Among the others, we argue that PSR J1015-5719 may plausibly generate
part of the high energy radiation observed from 3EG J1014-5705. Three
additional interesting cases are: 3EG J1410-6147 and either of PSRs J1412-6145
or J1413-6141, if the pulsars are at the estimated distance of the coincident
SNR G312.4-0.4; and 3EG J1639-4702/PSR J1637-4642. The remaining positional
coincidences between the EGRET sources and the newly discovered pulsars are
almost certainly spurious.


title: Millimeter and Submillimeter Observations from the South Pole

abstract:
  During the past decade, a year-round observatory has been established at the
geographic South Pole by the Center for Astrophysical Research in Antarctica
(CARA). CARA has fielded several millimeter- and submillimeter-wave
instruments: AST/RO (the Antarctic Submillimeter Telescope and Remote
Observatory, a 1.7-m telescope outfitted with a variety of receivers at
frequencies from 230 GHz to 810 GHz, including PoleSTAR, a heterodyne
spectrometer array), Python (a degree-scale CMB telescope), Viper (a 2-m
telescope which has been outfitted with SPARO, a submillimeter-wave bolometric
array polarimeter, ACBAR, a multi-channel CMB instrument, and Dos Equis, a HEMT
polarimeter), and DASI (the Degree-Angular Scale Interferometer). These
instruments have obtained significant results in studies of the interstellar
medium and observational cosmology, including detections of the 1 degree
acoustic peak in the CMB and the Sunyaev-Zel'dovich effect. The South Pole
environment is unique among observatory sites for unusually low wind speeds,
low absolute humidity, and the consistent clarity of the submillimeter sky. The
atmosphere is dessicated by cold: at the South Pole's average annual
temperature of -49 C, the partial pressure of saturated water vapor is only
1.2% of what it is at 0 C. The low water vapor levels result in exceptionally
low values of sky noise. This is crucial for large-scale observations of faint
cosmological sources---for such observations the South Pole is unsurpassed.


title:
Stability of the Forward/Reverse Shock System Formed by the Impact of a
  Relativistic Fireball on an Ambient Medium

abstract:
  We analyze the stability of a relativistic double (forward/reverse) shock
system which forms when the fireball of a Gamma-Ray Burst (GRB) impacts on the
surrounding medium. We find this shock system to be stable to linear global
perturbations for either a uniform or a wind (r^{-2}) density profile of the
ambient medium. For the wind case, we calculate analytically the frequencies of
the normal modes which could modulate the early short-term variability of GRB
afterglows. We find that perturbations in the double shock system could induce
oscillatory fluctuations in the observed flux on short (down to seconds) time
scales during the early phase of an afterglow.


title: BVRI Surface Photometry of (S+S) Binary Galaxies. I. The data

abstract:
  We present multicolour broad band ($BVRI$) photometry for a sample of 33
spiral-spiral (S+S) binary galaxies drawn from the Karachentsev Catalogue of
Isolated Pairs of Galaxies (KPG). The data is part of a joint observational
programme devoted to systematic photometric study of one of the most complete
and homogeneous pair samples available in the literature. We present
azimuthally averaged colour and surface brightness profiles, colour index (B-I)
maps, B band and sharp/filtered B band images as well as integrated magnitudes,
magnitudes at different circular apertures and integrated colours for each
pair. Internal and external data comparisons show consistency within the
estimated errors. Two thirds of the sample have total aperture parameters
homogeneously derived for the first time. After reevaluating morphology for all
the pairs, we find a change in Hubble type for 24 galaxies compared to the
original POSS classifications. More than half of our pairs show morphological
concordance which could explain, in part, the strong correlation in the (B-V)
colour indices (Holmberg Effect) between pair components. We find a tendency
for barred galaxies to show grand design morphologies and flat colour profiles.
The measurements will be used in a series of forthcoming papers where we try to
identify and isolate the main structural and photometric properties of disk
galaxies at different stages of interaction.


title:
The Age of the Universe and the Cosmological Constant Determined from
  Cosmic Microwave Background Anisotropy Measurements

abstract:
  If Omega_tot = 1 and structure formed from adiabatic initial conditions then
the age of the Universe, as constrained by measurements of the cosmic microwave
background (CMB), is t_0=14.0 +/- 0.5 Gyr. The uncertainty is surprisingly
small given that CMB data alone constrain neither h nor Omega_Lambda
significantly. It is due to the tight (and accidental) correlation, in these
models, of the age with the angle subtended by the sound horizon on the
last--scattering surface and thus with the well-determined acoustic peak
locations. If we assume either the HST Key Project result h = 0.72 \pm .08 or
simply that h > 0.55, we find Omega_Lambda > 0.4 at 95% confidence--another
argument for dark energy, independent of supernovae observations. Our analysis
is greatly simplified by the Monte Carlo Markov chain approach to Bayesian
inference combined with a fast method for calculating angular power spectra.


title: Unbiased Estimate of Dark Energy Density from Type Ia Supernova Data

abstract:
  Type Ia supernovae (SNe Ia) are currently the best probes of the dark energy
in the universe. To constrain the nature of dark energy in a model-independent
manner, we allow the density of dark energy, $\rho_X(z)$, to be an arbitrary
function of redshift. Using simulated data from a space-based supernova pencil
beam survey, we find that by optimizing the number of parameters used to
parametrize the dimensionless dark energy density,
$f(z)=\rho_X(z)/\rho_X(z=0)$, we can obtain an unbiased estimate of both f(z)
and $\Omega_m$ (assuming a flat universe and that the weak energy condition is
satisfied). A plausible supernova pencil beam survey (with a square degree
field of view and for an observational duration of one year) can yield about
2000 SNe Ia with $0\le z \le 2$. Such a survey in space would yield SN peak
luminosities with a combined intrinsic and observational dispersion of $\sigma
(m_{int})=0.16$ mag. We find that for such an idealized survey, $\Omega_m$ can
be measured to 10% accuracy, and f(z) can be estimated to $\sim$ 20% to $z \sim
1.5$, and $\sim$ 20-40% to $z \sim 2$, depending on the time dependence of the
true dark energy density. Dark energy densities which vary more slowly can be
more accurately measured. For the anticipated SNAP mission, $\Omega_m$ can be
measured to 14% accuracy, and f(z) can be estimated to $\sim$ 20% to $z \sim
1.2$. Our results suggest that SNAP may gain much sensitivity to the
time-dependence of f(z) and $\Omega_m$ by devoting more observational time to
the central pencil beam fields to obtain more SNe Ia at z>1.2. We also find
that Monte Carlo analysis gives a more accurate estimate of the dark energy
density than the maximum likelihood analysis. (abridged)


title: The First Known Mira-type Variable Star in IC 1613

abstract:
  King, Modjaz, & Li (1999) discovered Nova 1999 in IC1613 at Lick Observatory.
Both Fugazza et al. (2000) and Borissova et al. (2000) questioned this
classification, because they were able to detect the star on images obtained in
previous years. In infrared frames taken on Oct. 15, 1998, the Nova 1999 has
(J-K) = 1.14 and K = 14.69 mag. Our light curve study, based primarily on 92
unfiltered Lick images, suggested that the object could be a Mira-type variable
with a period of 640.7 days. This period is very close to that obtained by
Fugazza et al. (2000) - 631 days. The star is overluminous with respect to the
period-luminosity (PL) relation derived by Feast et al. (1989) for Mira
variables in the LMC. At longer periods (P > 400 ~ days), many LMC Miras show
such behavior and the PL relation appears to break down. It is possible that
the situation in IC1613 is similar. An optical spectrum obtained with the
Keck-II telescope shows features typical of M3Ie or M3IIIe stars. We conclude
that the star is a normal long-period M-type Mira variable, the first such star
confirmed in IC1613.


title:
MUSICOS 1998: Observations of Rotational Modulation and Flares on the RS
  CVn Binary HR 1099

abstract:
  We present simultaneous and continuous observations of H_alpha, H_beta, NaI
D_1, D_2, HeI D_3 and CaII H & K lines of the chromospherically active binary
HR 1099. We have observed HR 1099 for more than 3 weeks almost continuously and
monitored two flares. An increase in H_alpha and CaII H & K, H_beta and HeI D_3
and a strong filling-in of the NaI D_1, D_2 during the flares are observed. We
have found that the flares took place at the same phase (0.85) of the binary
orbit, and both of them seems to occur near the limb.


title:
The First High Resolution X-ray Spectrum of Cyg X-1: Soft X-Ray
  Ionization and Absorption

abstract:
  We observed the black hole candidate Cyg X-1 for 15 ks with the High-Energy
Transmission Grating Spectrometer aboard the CHANDRA X-ray Observatory. The
source was observed during a period of intense flaring activity, so it was
about a factor of 2.5 brighter than usual, with a 0.5-10 keV (1-24 A)
luminosity of 1.6x10^37 erg/s (at a distance of 2.5 kpc). The spectrum of the
source shows prominent absorption edges, some of which have complicated
substructure. We use the most recent results from laboratory measurements and
and calculations to model the observed substructure of the edges. From the
model, we derive a total absorption column of 6.21+/-0.22 10^21 cm^-2.
Furthermore, the results indicate that there are ~ 10 - 25% abundance
variations relative to solar values for neon, oxygen and iron. The X-ray
continuuum is described well by a two-component model that is often adopted for
black hole candidates: a soft multicolor disk component (with kT = 203 eV) and
a hard power law component (with a photon index of ~2). Comparing the fit
results to those of the hard and soft states, we conclude that the source was
in a transitional state. Finally, the spectrum also shows the presence of faint
emission lines which could be attributed to highly ionized species.


title:
Tidal scattering of stars on supermassive black holes in galactic
  centers

abstract:
  Some of the mass that feeds the growth of a massive black hole (BH) in a
galactic center is supplied by tidal disruption of stars that approach it on
unbound, low angular momentum orbits. For each star that is disrupted, others
narrowly escape after being subjected to extreme tidal distortion, spin-up,
mixing and mass-loss, which may affect their evolution and appearance. We show
that it is likely that a significant fraction of the stars around massive BHs
in galactic centers have undergone such extreme tidal interactions and survived
subsequent total disruption, either by being deflected off their orbit or by
missing the BH due to its Brownian motion. We discuss possible long-term
observable consequences of this process, which may be relevant for
understanding the nature of stars in galactic centers, and may provide a
signature of the existence of massive BHs there.


title:
Numerical Simulation of Interaction between an L1 Stream and an
  Accretion Disk in a Close Binary System

abstract:
  The hydrodynamic behavior of an accretion disk in a close binary system is
numerically simulated. Calculation is made for a region including the compact
star and the gas-supplying companion. The equation of state is that of an ideal
gas characterized by the specific heat ratio $\gamma$. Two cases with $\gamma$
of 1.01 and 1.2 are studied. Our calculations show that the gas, flowing from
the companion via a Lagrangian L1 point towards the accretion disk, forms a
fine gas beam (L1 stream), which penetrates into the disk. No hot spot
therefore forms in these calculations. Another fact discovered is that the gas
rotating with the disk forms, on collision with the L1 stream, a bow shock
wave, which may be called an L1 shock. The disk becomes hot because the L1
shock heats the disk gas in the outer parts of the disk, so that the spiral
shocks wind loosely even with $\gamma=1.01$. The L1 shock enhances the
non-axisymmetry of the density distribution in the disk, and therefore the
angular momentum transfer by the tidal torque works more effectively. The
maximum of the effective $\alpha$ becomes $\sim 0.3$. The 'hot spot' is not
formed in our simulations, but our results suggest the formation of the 'hot
line', which is the L1 shock elongated along the penetrating L1 stream.


title:
The Milky Way in X-rays for an outside observer: Log(N)-Log(S) and
  Luminosity Function of X-ray binaries from RXTE/ASM data

abstract:
  We study the Log(N)-Log(S) and X-ray luminosity function in the 2-10 keV
energy band, and the spatial (3-D) distribution of bright, log(L_X) > 34-35
erg/s, X-ray binaries in the Milky Way. In agreement with theoretical
expectations and earlier results we found significant differences between the
spatial distributions of low (LMXB) and high (HMXB) mass X-ray binaries. The
volume density of LMXB sources peaks strongly at the Galactic Bulge. HMXBs tend
to avoid the inner 3-4 kpc of the Galaxy, HMXBs are more concentrated towards
the Galactic Plane and show clear signatures of the spiral structure in their
spatial distribution. LMXB sources have a flatter Log(N)-Log(S) distribution
and luminosity function than HMXBs. The integrated 2-10 keV luminosities of
X-ray binaries, averaged over 1996--2000, are 2-3 * 10^39 (LMXB) and 2-3 *
10^38 (HMXB) erg/s. Normalised to the stellar mass and the star formation rate,
respectively, these correspond to 5 * 10^28 erg/s/M_sol for LMXBs and 5 * 10^37
erg/s/(M_sol/yr) for HMXBs. Due to the shallow slopes of the luminosity
functions the integrated emission of X-ray binaries is dominated by the 5-10
most luminous sources which determine the appearance of the Milky Way in the
standard X-ray band for an outside observer. In particular variability of
individual sources or an outburst of a bright transient source can increase the
integrated luminosity of the Milky Way by as much as a factor of ~2. Although
the average LMXB luminosity function shows a break near the Eddington
luminosity for a 1.4 M_sol neutron star, at least 11 sources showed episodes of
super-Eddington luminosity during ASM observations. We provide the maps of
distribution of X-ray binaries in the Milky Way in various projections, which
can be compared to images of nearby galaxies taken by CHANDRA and XMM-Newton.


title: Populations of Transient Galactic Bulge X-Ray Sources

abstract:
  Starting in 1999, the Rossi X-ray Timing Explorer (RXTE) has monitored the
central bulge region of the Galaxy with the Proportional Counter Array (PCA),
resolving about 50 binary X-ray sources, including 18 sources discovered by
RXTE and BeppoSAX. The accretion rates that RXTE observed from these sources
ranged from highs approaching Eddington limits to lows that may correspond to
mass exchange for a binary period near the minimum of 80 minutes. Several
neutron star binaries with low peak luminosity have outburst or cycle
time-scales which are shorter than those of brighter and better known
counterparts. We compare the characteristics of the binaries with low rates of
mass exchange to predictions of their evolution.


title:
Radio Foregrounds for the 21cm Tomography of the Neutral Intergalactic
  Medium at High Redshifts

abstract:
  Absorption or emission against the cosmic microwave background radiation
(CMB) may be observed in the redshifted 21cm line if the spin temperature of
the neutral intergalactic medium prior to reionization differs from the CMB
temperature. This so-called 21cm tomography should reveal important information
on the physical state of the intergalactic medium at high redshifts. The
fluctuations in the redshifted 21 cm, due to gas density inhomogeneities at
early times, should be observed at meter wavelengths by the next generation
radio telescopes such as the proposed {\it Square Kilometer Array (SKA)}. Here
we show that the extra-galactic radio sources provide a serious contamination
to the brightness temperature fluctuations expected in the redshifted 21 cm
emission from the IGM at high redshifts. Unless the radio source population
cuts off at flux levels above the planned sensitivity of SKA, its clustering
noise component will dominate the angular fluctuations in the 21 cm signal. The
integrated foreground signal is smooth in frequency space and it should
nonetheless be possible to identify the sharp spectral feature arising from the
non-uniformities in the neutral hydrogen density during the epoch when the
first UV sources reionize the intergalactic medium.


title: The Metallicity of the Local IGM from the HST/STIS Spectrum of 3C273

abstract:
  We present a preliminary study of the metallicity of low-redshift Lyman alpha
absorbers from the HST/STIS spectrum of 3C273. Using a pixel-based
shift-and-coadd technique, we compare observations to carefully-constructed
mock quasar spectra from a cosmological hydrodynamic simulation. We place an
upper limit of [C/H]<-1.5 at >90% confidence using two Ly-alpha absorbers with
N_HI>10^14 cm^-2, from the fact that we see little absorption near the expected
CIV positions, whereas the artificial spectra predict significant absorption.
We assume a Haardt & Madau (quasar-based) ionizing background spectrum, but a
softer spectrum results in a stronger constraint on the metallicity. With only
two absorbers and various modeling uncertainties, it is too early to make a
definitive determination of the diffuse IGM metallicity, but upcoming
observations should improve constraints.


title:
Iron line profiles from black hole accretion discs with spiral velocity
  structure

abstract:
  We calculate the iron line profiles from accretion discs with spiral velocity
structures around Schwarzschild black holes. We find that quasi-periodic bumps
appear in the the profiles, thereby providing a test for spiral wave patterns.
This study is motivated by recent work showing that spiral density waves can
result from MHD instabilities even in non-self-gravitating discs, and by
improved spectral resolution of forthcoming X-ray missions.


title: Formation of the Black Hole in Nova Scorpii

abstract:
  Israelian et al. (1999) showed that the stellar companion of the black-hole
binary Nova Sco is polluted with material ejected in the supernova that
accompanied the formation of the black-hole primary. Here we systematically
investigate the implications of these observations for the black-hole formation
process. Using a variety of supernova models, including both standard as well
as hypernova models (for different helium-star masses, explosion energies, and
explosion geometries) and a simple model for the evolution of the binary and
the pollution of the secondary, we show that most of the observed abundance
anomalies can be explained for a large range of model parameters (apart from
the abundance of Ti). The best models are obtained for He star masses of 10 to
16 Msun, where spherical hypernova models are generally favoured over standard
supernova ones. Aspherical hypernova models also produce acceptable fits,
provided there is extensive lateral mixing. All models require substantial
fallback and that the fallback material either reached the orbit of the
secondary or was mixed efficiently with material that escaped. The black hole
therefore formed in a two-step process, where the initial mass of the collapsed
remnant was increased substantially by matter that fell back after the initial
collapse. This may help to explain the high observed space velocity of Nova Sco
either because of a neutrino-induced kick (if a neutron star was formed first)
or by asymmetric mass ejection in an asymmetric supernova explosion.


title:
Photospheric Abundances of Volatile and Refractory Elements in
  Planet-Harboring Stars

abstract:
  By using the high-dispersion spectra of 14 bright planet-harboring stars
(along with 4 reference stars) observed with the new coude echelle spectrograph
at Okayama Astrophysical Observatory, we investigated the abundances of
volatile elements (C, N, O, S, Zn; low condensation temperature Tc) in order to
examine whether these show any significant difference compared to the
abundances of other refractory elements (Si, Ti, V, Fe, Co, Ni; high Tc) which
are known to be generally overabundant in those stars with planets, since a
Tc-dependence is expected if the cause of such a metal-richness is due to the
accretion of solid planetesimals onto the host star. We found, however, that
all elements we studied behave themselves quite similarly to Fe (i.e.,
[X/Fe]~0) even for the case of volatile elements, which may suggest that the
enhanced metallicity in those planet-bearing stars is not so much an acquired
character (by accretion of rocky material) as rather primordial.


title: Three LINERs Under the Chandra X-Ray Microscope

abstract:
  We use X-ray observations of three galaxies hosting LINERs (NGC 404, NGC
4736, NGC 4579) with Chandra to study their power sources. We find very diverse
properties within this small group: NGC 404 has an X-ray-faint nucleus with a
soft, thermal spectrum, NGC 4736 harbors a plethora of discrete X-ray sources
in and around its nucleus, and NGC 4579 has a dominant nuclear point source
embedded in a very extended, diffuse nebulosity. From their multi- wavelength
properties we conclude the following: the nucleus of NGC 404 is the site of a
weak, compact starburst, whose X-ray emission is due to gas heated by stellar
winds and supernovae, NGC 4736 is in a recent or aging starburst phase, where
the X-ray emission is dominated by a dense cluster of X-ray binaries, and NGC
4579 is powered by accretion onto a supermassive black hole. We detect 39
discrete sources in NGC 4736 and 21 in NGC 4579, most with L_X > 10^37 erg/s.
One source in the disk of NGC 4579 could be an ultraluminous X-ray binary with
L_X (2-10 keV) = 9x10^39 erg/s, but it could also be a background quasar. The
most luminous discrete sources have simple power-law spectra, which along with
their luminosities suggest that these are X-ray binaries accreting near or
above the Eddington rate for a neutron star. By comparing the luminosity
functions of discrete X-ray sources in these and other galaxies we find a
potential connection between the age of the stellar population and the slope of
the cumulative X-ray source luminosity function: galaxies with primarily old
stellar populations have steeper luminosity functions than starburst galaxies.
We suggest that this difference results from the contribution of high-mass
X-ray binaries from the young stellar population to the upper end of the
luminosity function.


title: The Wide Field Imaging Interferometry Testbed

abstract:
  We are developing a Wide-Field Imaging Interferometry Testbed (WIIT) in
support of design studies for NASA's future space interferometry missions, in
particular the SPIRIT and SPECS far-infrared/submillimeter interferometers.
WIIT operates at optical wavelengths and uses Michelson beam combination to
achieve both wide-field imaging and high-resolution spectroscopy. It will be
used chiefly to test the feasibility of using a large-format detector array at
the image plane of the sky to obtain wide-field interferometry images through
mosaicing techniques. In this setup each detector pixel records interferograms
corresponding to averaging a particular pointing range on the sky as the
optical path length is scanned and as the baseline separation and orientation
is varied. The final image is constructed through spatial and spectral Fourier
transforms of the recorded interferograms for each pixel, followed by a
mosaic/joint-deconvolution procedure of all the pixels. In this manner the
image within the pointing range of each detector pixel is further resolved to
an angular resolution corresponding to the maximum baseline separation for
fringe measurements.
  We present the motivation for building the testbed, show the optical,
mechanical, control, and data system design, and describe the image processing
requirements and algorithms. WIIT is presently under construction at NASA's
Goddard Space Flight Center.


title: A Comparative Study of Globular Cluster Systems in UGC 9799 and NGC 1129

abstract:
  We present a preliminary analysis of HST-WFPC2 observations of globular
cluster systems in the two brightest galaxies, UGC 9799 (cD) and NGC 1129
(non-cD), located in the center of rich clusters.


title:
A Faint Star-Forming System Viewed Through the Lensing Cluster Abell
  2218: First Light at z~5.6?

abstract:
  We discuss the physical nature of a remarkably faint pair of Lyman
alpha-emitting images discovered close to the giant cD galaxy in the lensing
cluster Abell 2218 (z=0.18) during a systematic survey for highly-magnified
star-forming galaxies beyond z=5. A well-constrained mass model suggests the
pair arises via a gravitationally-lensed source viewed at high magnification.
Keck spectroscopy confirms the lensing hypothesis and implies the unlensed
source is a very faint (I~30) compact (<150 pc) and isolated object at z=5.576
whose optical emission is substantially contained within the Lyman alpha
emission line; no stellar continuum is detectable. The available data suggest
the source is a promising candidate for an isolated ~10^6 solar mass system
seen producing its first generation of stars close to the epoch of
reionization.


title:
Constraining cosmological models using arc statistics in future SZ
  cluster surveys

abstract:
  Upcoming wide-area surveys in the submillimetre regime will allow the
construction of complete galaxy cluster samples through their thermal
Sunyaev-Zel'dovich effect. We propose an analytic method to predict the number
of gravitationally lensed giant arcs produced by the cluster sample expected to
be detectable for the Planck satellite. The statistics of lensed arcs can be
used to constrain cosmological parameters. This computation implies the choice
of an analytic cluster model which has to reproduce the lensing properties of
realistic galaxy clusters. Comparing the results of analytic computations and
numerical ray-tracing simulations, we show that spherical models with the
Navarro-Frenk-White density profile fail by far to produce as many giant arcs
as realistic galaxy clusters. This confirms the great importance of asymmetries
and substructures in the lensing matter distribution. By elliptically
distorting the lensing potential of spherical NFW density profiles, we show
that the discrepancy between analytic and numerical computations can almost
completely be removed.


title: Envelope tomography of long-period variable stars II. Method

abstract:
  A tomographic method is described that makes it possible to follow the
propagation of shock waves across the photosphere of long-period variable
stars. The method relies on the correlation of the observed spectrum with
numerical masks probing layers of different atmospheric depths. The formation
depth of spectral lines is derived from synthetic spectra of non-variable red
giant stars. When applied to Mira stars around maximum light, the tomographic
masks reveal that the deepest photospheric layers are generally characterized
by blueshifted absorption lines (attesting their upward motion), whereas the
uppermost layers generally exhibit redshifted absorption lines (indicating
their infalling motion). Double absorption lines are found in intermediate
layers, where the shock front is located. At later phases, the shock front is
seen moving towards upper layers, until it leaves the photosphere.


title: Statistical Properties of Lyman Break Galaxies at z~4

abstract:
  We study the luminosity function and the correlation function of about 1200
z~4 Lyman break galaxies (LBGs) with i'<26 that are photometrically selected
from deep BRi' imaging data of a 618 arcmin^2 area in the Subaru/XMM-Newton
Deep Field taken with Subaru Prime Focus Camera. The contamination and
completeness of our LBG sample are evaluated, on the basis of the Hubble Deep
Field-North (HDF-N) objects, to be 17% and 45%, respectively. We derive the UV
(rest 1700A) luminosity functions (LFs) and find a large population of
UV-luminous galaxies at z~4. The LFs of the red and blue subsamples imply that
the bright LBGs are redder in the UV continuum than the average color of the
LBGs. Then we calculate the correlation function over theta = 2''-1000'' and
find that it is fitted fairly well by a power law, omega(theta)=A_omega
theta^(-0.8), with A_omega=0.71 +/- 0.26. We estimate the correlation length
r_0 (in comoving units) of the two-point spatial correlation function xi(r) =
(r/r_0)^(-1.8) to be r_0=2.7 +0.5/-0.6 h^(-1) Mpc (Omega_m=0.3 and
Omega_Lambda=0.7). The correlation function shows an excess of omega (theta) on
small scales (theta < 5''), departing from the power-law fit at > 3 sigma
significance level. Interpreting this as being due to galaxy mergers, we
evaluate the fraction of galaxies undergoing mergers to be 3.0 +/- 0.9%, which
is significantly smaller than those of galaxies at intermediate redshifts.


title:
Collisional excitation of hydrogen and the determination of the
  primordial helium abundance from H II regions

abstract:
  This paper investigates the effect of collisional enhancement of the hydrogen
lines on the derivation of the helium abundances in low metallicity H II
regions. For this, we have constructed a grid of photoionization models
relevant for the analysis of giant \hii regions in blue compact galaxies. We
show that the effect of collisional excitation on the Halpha/Hbeta ratio can be
quite important (up to 8% or more). The impact of this effect on the
determination of the helium mass fraction has been tracked on four
low-metallicity blue compact galaxies for which Keck spectra are available and
which are among the best objects for the quest of the pregalactic helium
abundance. We find that taking into account the effects of collisional
excitation of hydrogen results in an upward correction of the helium mass
fraction Y by up to 5%. However, combining with other systematic effects
usually not considered in the determination of the helium abundance in
low-metallicity galaxies, the resulting uncertainty should be much less.


title:
Deep spectroscopy of the low-metallicity blue compact dwarf galaxy SBS
  0335-052

abstract:
  The results of deep long-slit spectroscopy of the extremely low-metallicity
blue compact dwarf (BCD) galaxy SBS 0335-052 are presented. Down to intensity
levels of 10^{-3 ... -4} of Hbeta, unprecedented for spectroscopy of
extra-galactic giant H II regions, we detect numerous weak permitted and
forbidden nebular lines in the brightest part of the galaxy. With varying
degrees of confidence, the detections include lines of high-ionization ions
like Fe^{4+} -Fe^{6+}, implying very hard ionizing radiation. Two broad
emission features, possibly from Wolf-Rayet stars, and stellar He II 4200
absorption are seen in the same region. The large spatial extent of He II 4686
emission (implying the presence of sufficient ionizing photons with energies
above 54 eV) and the spatial distribution of the electron temperature suggest
that at least some part of the hard radiation is associated with shocks.
Extended Halpha emission is detected over ~ 6 - 8 kpc, a much larger area than
in previous studies, suggesting that hot ionized gas is spread out far away
from the central ionizing clusters. This shows that nebular line and continuous
emission can significantly modify the colours of these extended regions and
must be taken into account in studies of the underlying stellar population.


title:
The He abundance in the metal-deficient blue compact dwarf galaxies Tol
  1214-277 and Tol 65

abstract:
  We present high-quality Keck telescope spectroscopic observations of the two
metal-deficient blue compact dwarf (BCD) galaxies Tol 1214-277 and Tol 65.
These data are used to derive the heavy-element and helium abundances. We find
that the oxygen abundances in Tol 1214-277 and Tol 65 are the same,
12+logO/H=7.54+/-0.01, or Zsun/24, despite the different ionization conditions
in these galaxies. The nitrogen-to-oxygen abundance ratio in both galaxies is
logN/O=-1.64+/-0.02 and lies in the narrow range found for the other most
metal-deficient BCDs. We use the five strongest HeI emission lines 3889, 4471,
5876, 6678 and 7065, to correct self-consistently their intensities for
collisional and fluorescent enhancement mechanisms and to derive the He
abundance. Underlying stellar absorption is found to be important for the HeI
4471 emission line in both galaxies, being larger in Tol 65. The weighted He
mass fractions in Tol 1214-277 and Tol 65 are respectively Y=0.2458+/-0.0039
and 0.2410+/-0.0050 when the three HeI emission lines, 4471, 5876 and 6678, are
used, and are, respectively, 0.2466+/-0.0043 and 0.2463+/-0.0057 when the HeI
4471 emission line is excluded. These values are in very good agreement with
recent measurements of the He mass fraction in others of the most
metal-deficient BCDs by Izotov and coworkers. We find that the combined effect
of the systematic uncertainties due to the underlying HeI stellar absorption
lines, ionization and temperature structure of the HII region and collisional
excitation of the hydrogen emission lines is likely small, not exceeding ~2%
(the error is 2sigma). Our results support the validity of the standard big
bang model of nucleosynthesis.


title:
The evolutionary status of the low-metallicity blue compact dwarf galaxy
  SBS 0940+544

abstract:
  We present the results of spectrophotometry and V,R,I, Halpha CCD photometry
of the blue compact dwarf (BCD) galaxy SBS 0940+544. Broad-band images taken
with the 2.1m KPNO and 1.23m Calar Alto telescopes reveal a compact
high-surface-brightness H II region with ongoing star formation, located at the
northwestern tip of the elongated low surface brightness (LSB) main body of the
BCD. High signal-to-noise 4.5m Multiple Mirror Telescope (MMT) and 10m Keck II
telescope long-slit spectroscopy of SBS 0940+544 is used to derive element
abundances of the ionized gas in the brightest H II region and to study the
stellar population in the host galaxy. The oxygen abundance in the brightest
region with strong emission lines is 12+log(O/H) = 7.46-7.50, or 1/29-1/26
solar, in agreement with earlier determinations and among the lowest for BCDs.
Hbeta and Halpha emission lines and Hdelta and Hgamma absorption lines are
detected in a large part of the main body. Three methods are used to put
constraints on the age of the stellar population at different positions along
the major axis. They are based on (a) the equivalent widths of the emission
lines, (b) the equivalent widths of the absorption lines and (c) the spectral
energy distributions (SED). Several scenarios of star formation have been
considered. The observed properties in the main body can be reproduced by a
continuous star formation process which started not earlier than 100 Myr ago,
if a small extinction is assumed. However, the observations can be reproduced
equally well by a stellar population forming continuously since 10 Gyr ago, if
the star formation rate has increased during the last 100 Myr in the main body
of SBS 0940+544 by at least a factor of five. In summary, we find no compelling
evidence which favors either a young or an old age of SBS 0940+544.


title:
A spectroscopic study of component C and the extended emission around I
  Zw 18

abstract:
  Long-slit Keck II, 4m Kitt Peak, and 4.5m MMT spectrophotometric data are
used to investigate the stellar population and the evolutionary status of I Zw
18C, the faint C component of the nearby blue compact dwarf galaxy I Zw 18.
Hydrogen H$\alpha$ and H$\beta$ emission lines are detected in the spectra of I
Zw 18C, implying that ionizing massive stars are present. High signal-to-noise
Keck II spectra of different regions in I Zw 18C reveal H$\gamma$, H$\delta$
and higher order hydrogen lines in absorption. Several techniques are used to
constrain the age of the stellar population in I Zw 18C. Ages derived from two
different methods, one based on the equivalent widths of the H$\alpha$,
H$\beta$ emission lines and the other on H$\gamma$, H$\delta$ absorption lines
are consistent with a 15 Myr instantaneous burst model. We find that a small
extinction in the range $A_V$ = 0.20 -- 0.65 mag is needed to fit the observed
spectral energy distribution of I Zw 18C with that model. In the case of
constant star formation, all observed properties are consistent with stars
forming continuously between ~ 10 Myr and < 100 Myr ago. We use all available
observational constraints for I Zw 18C, including those obtained from Hubble
Space Telescope color-magnitude diagrams, to argue that the distance to I Zw 18
should be as high as ~ 15 Mpc. The deep spectra also reveal extended ionized
gas emission around I Zw 18. H$\alpha$ emission is detected as far as 30" from
it. To a B surface brightness limit of ~ 27 mag arcsec$^{-2}$ we find no
observational evidence for extended stellar emission in the outermost regions,
at distances > 15" from I Zw 18.


title:
HST-WFPC2 Observations of the Star Clusters in the Giant HII Regions of
  M33

abstract:
  We present a photometric study of the stars in ionizing star clusters
embedded in several giant HII regions of M33 (CC93, IC 142, NGC 595, MA2, NGC
604 and NGC 588). Our photometry are based on the HST-WFPC2 images of these
clusters. Color-magnitude diagrams and color-color diagrams of these clusters
are obtained and are used for estimating the reddenings and ages of the
clusters. The luminosity functions (LFs) and initial mass functions (IMFs) of
the massive stars in these clusters are also derived. The slopes of the IMFs
range from Gamma = -0.5 to -2.1. It is found interestingly that the IMFs get
steeper with increasing galactocentric distance and with decreasing [O/H]
abundance.


title:
Envelope tomography of long-period variable stars III. Line-doubling
  frequency among Mira stars

abstract:
  This paper presents statistics of the line-doubling phenomenon in a sample of
81 long-period variable (LPV) stars of various periods, spectral types and
brightness ranges. When correlated with a mask mimicking a K0III spectrum, 54%
of the sample stars clearly showed a double-peaked cross-correlation profile
around maximum light, reflecting double absorption lines. Several pieces of
evidence are presented that point towards the double absorption lines as being
caused by the propagation of a shock wave through the photosphere. The
observation of the Balmer lines appearing in emission around maximum light in
these stars corroborates the presence of a shock wave. The observed velocity
discontinuities, ranging between 10 and 25 km/s, are not correlated with the
brightness ranges. A comparison with the center-of-mass (COM) velocity obtained
from submm CO lines originating in the circumstellar envelope reveals that the
median velocity between the red and blue peaks is blueshifted with respect to
the COM velocity, as expected if the shock moves upwards.


title: Mass Profiles of Clusters at Large Radii from Weak Gravitational Lensing

abstract:
  We present the weak lensing mass reconstructions of three clusters of
galaxies from data taken on the ESO Wide Field Imager. We detect a lensing
signal in all three clusters over a range of 1' < r < 17' (~0.1 h^-1 Mpc < r <
2 h^-1 Mpc). We measure the best fitting SIS and NFW profiles for each cluster
and show that in two of the three clusters the NFW profile is preferred to the
SIS with marginal significance (~95%).


title: Delaunay recovery of cosmic density and velocity probes

abstract:
  Optimally resolved one-dimensional density and velocity profiles through
cosmological N-body simulations are constructed by means of the
Voronoi-Delaunay tessellation reconstruction technique. In a fully
self-adaptive fashion a strikingly detailed view of the density features and
the corresponding cosmic motions is recovered.


title: Unusual magnetic fields in the interacting spiral NGC 3627

abstract:
  By observing the interacting galaxy NGC 3627 in radio polarization we try to
answer the question to which degree the magnetic field follows the galactic gas
flows. We obtained total power and polarized intensity maps at 8.46 GHz and
4.85 GHz using the VLA in its compact D-configuration. In order to overcome the
zero-spacing problems, the interferometric data were combined with single-dish
measurements obtained with the Effelsberg 100-m radio telescope. The observed
magnetic field structure in NGC 3627 suggests that two field components are
superposed. One component smoothly fills the interarm space and shows up also
in the outermost disk regions, the other component follows a symmetric S-shaped
structure. In the western disk the latter component is well aligned with an
optical dust lane, following a bend which is possibly caused by external
interactions. However, in the SE disk the magnetic field crosses a heavy dust
lane segment, apparently being insensitive to strong density-wave effects. We
suggest that the magnetic field is decoupled from the gas by high turbulent
diffusion, in agreement with the large \ion{H}{i} line width in this region. We
discuss in detail the possible influence of compression effects and
non-axisymmetric gas flows on the general magnetic field asymmetries in NGC
3627. On the basis of the Faraday rotation distribution we also suggest the
existence of a large ionized halo around this galaxy.


title: Chandra Observations of Galaxy Cluster Abell 2218

abstract:
  We present results from two observations (combined exposure of ~17 ks) of
galaxy cluster A2218 using the Advanced CCD Imaging Spectrometer on board the
Chandra X-ray Observatory that were taken on October 19, 1999. Using a
Raymond-Smith single temperature plasma model corrected for galactic absorption
we find a mean cluster temperature of kT = 6.9+/-0.5 keV, metallicity of
0.20+/-0.13 (errors are 90 % CL) and rest-frame luminosity in the 2-10 keV
energy band of 6.2x10^{44} erg/s in a LambdaCDM cosmology with H_0=65 km/s/Mpc.
The brightness distribution within 4'.2 of the cluster center is well fit by a
simple spherical beta model with core radius 66".4 and beta = 0.705 . High
resolution Chandra data of the inner 2' of the cluster show the x-ray
brightness centroid displaced ~22" from the dominant cD galaxy and the presence
of azimuthally asymmetric temperature variations along the direction of the
cluster mass elongation. X-ray and weak lensing mass estimates are in good
agreement for the outer parts (r > 200h^{-1}) of the cluster; however, in the
core the observed temperature distribution cannot reconcile the x-ray and
strong lensing mass estimates in any model in which the intracluster gas is in
thermal hydrostatic equilibrium. Our x-ray data are consistent with a scenario
in which recent merger activity in A2218 has produced both significant
non-thermal pressure in the core and substructure along the line of sight; each
of these phenomena probably contributes to the difference between lensing and
x-ray core mass estimates.


title: A Study of the Coronal Plasma in RS CVn binary systems: HR 1099 and co

abstract:
  XMM-Newton has been performing comprehensive studies of X-ray luminous RS CVn
binary systems in its calibration and guaranteed time programs. We present
results from ongoing investigations in the context of a systematic study of
coronal emission from RS CVns. We concentrate here on coronal abundances and
investigate the abundance pattern in RS CVn binaries as a function of activity
and average temperature. We find a transition from an Inverse First Ionization
Potential (FIP) effect towards an absence of a clear trend (no FIP) in
intermediately active RS CVn systems. This scheme fits well into the long-term
evolution from an IFIP to a FIP effect found in solar analogs. We further study
variations in the elemental abundances during a large flare.


title:
XMM-Newton Probes the Solar Past: Coronal Abundances of Solar Analogs at
  Different Ages

abstract:
  We present an X-ray spectral analysis of four solar analogs with different
ages and magnetic activity levels. We find largely different coronal
compositions. The most active stars tend to show an ``Inverse First Ionization
Potential'' (IFIP) effect, i.e., elements with low FIP are underabundant. Less
active stars tend to the opposite effect, with relative overabundances of
low-FIP elements. Equivalent Chandra results are presented that support these
results.


title: Multiwavelength Aspects of Stellar Coronae

abstract:
  Coronae express different facets of their energy release processes in
different wavelength regions. While soft X-ray and EUV emission dominates the
radiative losses of the thermal plasma, hard X-ray emission (>10 keV) can be
produced from non-thermal high-energy particles accelerated as a consequence of
flare processes, and radio emission is often emitted from mildly relativistic
electrons trapped in magnetic fields. Combined measurements of all emissions
are important to understand the ultimate mechanisms responsible for coronal
energy release and heating. This presentation will summarize a number of
aspects for which multi-wavelength studies are important, both for quiescent
and flare emission.


title:
A Systematic Spectroscopic X-Ray Study of Stellar Coronae with
  XMM-Newton: Early Results

abstract:
  We have been conducting a comprehensive survey of stellar coronae with the
XMM-Newton Reflection Grating Spectrometers during the commissioning,
calibration, verification, and guaranteed time phases of the mission,
accompanied by simultaneous observations with the EPIC cameras and, for several
targets, with the radio VLA and/or the VLBA. The principal aim of this project
is threefold: i) To understand stellar coronal structure and composition by
studying systematics in the coronae of stars with widely different levels of
magnetic activity; ii) to investigate heating and particle acceleration physics
during flares, their role in the overall coronal energy budget, and their
possible role in the quiescent stellar emission; iii) to probe stellar coronal
evolution by studying solar analogs of different ages. We report early results
from this project.


title: A Study of the Coronal Plasma in RS CVn binary systems

abstract:
  XMM-Newton has been performing comprehensive studies of X-ray bright RS CVn
binaries in its Calibration and Guaranteed Time programs. We present results
from ongoing investigations in the context of a systematic study of coronal
emission from RS CVns. We concentrate in this paper on coronal abundances and
investigate the abundance pattern in RS CVn binaries as a function of activity
and average temperature. A transition from an Inverse First Ionization
Potential (FIP) effect towards an absence of a clear trend is found in
intermediately active RS CVn systems. This scheme corresponds well into the
long-term evolution from an IFIP to a FIP effect found in solar analogs. We
further study variations in the elemental abundances during a large flare.


title: V4641Sgr - Super-Eddington source enshrouded by an extended envelope

abstract:
  An optical spectroscopy of an unusual fast transient V4641 Sgr constrains its
mass to 8.7-11.7M_sun (9.6M_sun is the best fit value) and the distance to
7.4--12.3 kpc (Orosz et al. 2001). At this distance the peak flux of 12 Crab in
the 2--12 keV energy band, measured by ASM/RXTE, implies the X-ray luminosity
exceeding 2-3e39 erg/s, i.e. near or above the Eddington limit for a 9.6M_sun
black hole. An optical photometry shows that at the peak of the optical
outburst the visual magnitude increased by Delta m_V > 4.7^m relative to the
quiescent level and reached m_V < 8.8^m. An assumption that this optical
emission is due to irradiated surface of an accretion disk or a companion star
with the the black body shape of the spectrum would mean that the bolometric
luminosity of the system exceeds L>3e41 erg/s > 300 L_Edd.
  We argue that the optical data strongly suggest presence of an extended
envelope surrounding the source which absorbs primary X-rays flux and reemits
it in optical and UV. The data also suggests that this envelope should be
optically thin in UV, EUV and soft X-rays. The observed properties of V4641 Sgr
at the peak of an optical flare are very similar to those of SS433. This
envelope is likely the result of near or super Eddington rate of mass accretion
onto the black hole and it vanishes during subsequent evolution of the source
when apparent luminosity drops well below the Eddington value. Thus this
transient source provides us direct proof of the dramatic change in the
character of an accretion flow at the mass accretion rate near or above the
critical Eddington value as predicted long time ago by the theoretical models.


title: A burst from the direction of UZ Fornacis with XMM-Newton

abstract:
  The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For
finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT
observations. The source was not detected for the majority of a 22 ksec
exposure with the EPIC cameras, suggesting that the accretion rate either
decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ
For during the observation. Spectral fits favour optically thin, kT = 4.4 keV
thermal emission. Detection of the burst by the on-board Optical Monitor
indicates that this was most probably an accretion event. The 0.1-10 keV
luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from
high state polars and would result from the potential energy release of ~ 10^16
g of gas. There is no significant soft excess due to reprocessing in the white
dwarf atmosphere.


title: A Scalar Measure Of The Local Expansion Rate

abstract:
  We define a scalar measure of the local expansion rate based on how
astronomers determine the Hubble constant. Our observable is the inverse
conformal d'Alembertian acting on a unit ``standard candle.'' Because this
quantity is an integral over the past lightcone of the observation point it
provides a manifestly causal and covariant technique for averaging over small
fluctuations. For an exactly homogeneous and isotropic spacetime our scalar
gives minus one half times the inverse square of the Hubble parameter. Our
proposal is that it be assigned this meaning generally and that it be employed
to decide the issue of whether or not there is a significant quantum
gravitational back-reaction on inflation. Several techniques are discussed for
promoting the scalar to a full invariant by giving a geometrical description
for the point of observation. We work out an explicit formalism for evaluating
the invariant in perturbation theory. The results for two simple models are
presented in subsequent papers.


title: No One Loop Back_Reaction In Chaotic Inflation

abstract:
  We use an invariant operator to study the quantum gravitational back-reaction
to scalar perturbations during chaotic inflation. Our operator is the inverse
covariant d'Alembertian expressed as a function of the local value of the
inflaton. In the slow roll approximation this observable gives $-1/(2 H^2)$ for
an arbitrary homogeneous and isotropic geometry, hence it is a good candidate
for measuring the local expansion rate even when the spacetime is not perfectly
homogeneous and isotropic. Corrections quadratic in the scalar creation and
annihilation operators of the initial value surface are included using the
slow-roll and long wavelength approximations. The result is that all terms
which could produce a significant secular back-reaction cancel from the
operator, before one even takes its expectation value. Although it is not
relevant to the current study, we also develop a formalism for using stochastic
samples to study back-reaction.


title: Back-Reaction Is For Real

abstract:
  We demonstrate the existence of a secular back-reaction on inflation using a
simple scalar model. The model consists of a massless, minimally coupled scalar
with a quartic self-interaction which is a spectator to $\Lambda$-driven
inflation. To avoid problems with coincident propagators, and to make the
scalars interact more like gravitons, we impose a covariant normal ordering
prescription which has the effect of removing tadpole graphs. This version of
the theory exhibits a secular slowing at three loop order due to interactions
between virtual infrared scalars which are ripped apart by the inflating
background. The effect is quantified using an invariant observable and all
orders bounds are given. We also argue that, although stochastic effects can
have either sign, the slowing mechanism is superimposed upon them.


title:
Physics of Cosmic Microwave Background anisotropies and primordial
  fluctuations

abstract:
  The physics of the origin and evolution of CMB anisotropies is described. I
explain the idea and status of cosmic parameter estimation and follow it up
with critical comments on its dependence on model assumptions and initial
conditions.


title: Interoperability tools for the Virtual Observatory

abstract:
  Interoperability is one of the key issues in the current efforts to build the
Virtual Observatory. We present here some of the tools which already contribute
to the efficient exchange of information between archives, databases, and
journals.


title: Probing the Intergalactic Medium with the OVI Forest

abstract:
  Recent STIS and FUSE observations have detected OVI absorption lines at low
redshift that are not clearly associated with any galactic system. In this
paper, we argue that these lines are due to metal enriched hot gas in the
intergalactic medium. Using numerical simulations of a cosmological-constant
dominated cosmology, combined with reasonable assumptions about the metallicity
distribution, we show that the number density and internal characteristics of
these lines are correctly predicted. We find that the OVI is primarily produced
by collisional ionization from gas at a few times 10^5 K for lines with
equivalent widths larger than 40 mA, while weaker lines can also be produced by
photo-ionization. The absorption occurs in diffuse gas in filaments at moderate
overdensity (delta ~ 5-100).


title:
The Local Lya Forest. III. Relationship between Lya Absorbers and
  Galaxies, Voids and Superclusters

abstract:
  In this paper, we use large-angle, nearby galaxy redshift surveys to
investigate the relationship between the 81 low-redshift Lya absorbers in our
HST/GHRS survey and galaxies, superclusters, and voids. In a subsample of 46
Lya absorbers located in regions where the February 8, 2000 CfA catalog is
complete down to at least L* galaxies, the nearest galaxy neighbors range from
100kpc to >10 Mpc. Of these 46 absorbers, 8 are found in galaxy voids. After
correcting for pathlength and sensitivity, we find that 22+-8% of the Lya
absorbers lie in voids, which requires that at least some low-column density
absorbers are not extended halos of individual bright galaxies. The number
density of these clouds yields a baryon fraction of 4.5+-1.5% in voids.
  The stronger Lya absorbers (10^{13.2-15.4} cm^-2) cluster with galaxies more
weakly than galaxies cluster with each other, while the weaker absorbers
(10^{12.4-13.2} cm^-2) are more randomly distributed. The median distance from
a low-z Lya absorber in our sample to its nearest galaxy neighbor (~500 kpc) is
twice the median distance between bright galaxies in the same survey volume.
This makes any purposed "association" between these Lya absorbers and
individual galaxies problematic. The suggested correlation between Lya absorber
equivalent width (W) and nearest-galaxy impact parameter does not extend to
W<200mA, or to impact parameters >200kpc. Instead, we find statistical support
for the contention that absorbers align with large-scale filaments of galaxies.
While some strong (W>400mA) Lya absorbers may be gas in the extended gaseous
halos of individual galaxies, much of the local Lya "forest" appears to be
associated with the large-scale structures of galaxies and some with voids.


title: Enrichment of the High-Redshift IGM by Galactic Winds

abstract:
  This paper discusses a semi-numerical method of investigating the enrichment
of the intergalactic medium by galactic winds. We find that most galaxies at z
>~ 3 should be driving winds, and that (if these winds are similar to those at
low-z) these winds should escape to large distances. Our calculations -- which
permit exploration of a large region of model parameter space -- indicate that
the wind velocity, the mass of the wind-driving galaxies, the fraction of
ambient material entrained, and the available time (between wind launch and the
observed redshift) all affect wind propagation significantly; other physical
effects can be important but are sub-dominant. We find that under reasonable
assumptions, the enrichment by 3 <~ z <~ 6 galaxies could account for the
quantity of metals seen in the Ly-alpha forest, though it is presently unclear
whether this enrichment is compatible with the intergalactic medium's detailed
metal distribution or relative quiescence.


title:
Discovery of close companions to the nearby young stars HD 199143 and HD
  358623

abstract:
  Young stellar systems in the solar neighborhood provide valuable laboratories
for detailed studies of star and planet formation. The bright F8V star HD
199143 and the Li-rich late-type emission line star HD 358623 are among the
nearest young stars identified to date, and may be members of a young
association in Capricornus. We present high-resolution near-infrared images of
these two sources, obtained using the adaptive optics system on the 3.6-meter
telescope at the European Southern Observatory in La Silla, Chile. Our
observations reveal that both are in fact close binary systems. The newly
discovered companion at a separation of $\sim$1'' may account for the unusual
characteristics of HD 199143 --rapid rotation, emission lines, ultraviolet
variability, and excess infrared emission-- recently discussed by van den
Ancker and co-workers. HD 199143 may be a rare example of a close binary with
only a circum{\it secondary} disk. With the detection of a $\sim$2'' companion,
HD 358623 is now possibly one of the closest known T Tauri binaries. Both
binary systems are prime targets for follow-up spectroscopic and astrometric
observations.


title: A physical upper limit on the HI column density of gas clouds

abstract:
  An intriguing fact about cosmic gas clouds is that they all appear to have
neutral (atomic) hydrogen column densities smaller than 10^{22} cm^{-2}.
Observations of damped Ly-alpha (DLA) absorption systems further indicate that
the maximum N(HI) decreases with increasing metallicity. It is generally
assumed that this trend is due to a dust-induced selection bias: DLA systems
with high N(HI) and high metallicity contain so much dust that the background
QSO becomes too dim to be included in optically selected surveys. Here, it is
argued that this explanation may not be viable. Instead, it is proposed that
conversion to molecular hydrogen determines the maximum HI column density.
Molecular hydrogen forms on the surface of dust grains and is destroyed by
photodissociation. Therefore, the molecular fraction correlates with both the
dust content and, because of self-shielding, the total hydrogen column density,
and anticorrelates with the intensity of the incident UV radiation. It is shown
that the first relation can account for the observed anticorrelation between
the maximum N(HI) and metallicity.


title: Comparison of subclustering frequency determined from 2D and 3D data

abstract:
  Frequencies of substructure within Abell clusters determined for the same
objects using the wavelet analysis for 2-D and 3-D data are similar.


title:
Hydrodynamic Interaction of Strong Shocks with Inhomogeneous Media - I:
  Adiabatic Case

abstract:
  Many astrophysical flows occur in inhomogeneous (clumpy) media. We present
results of a numerical study of steady, planar shocks interacting with a system
of embedded cylindrical clouds. Our study uses a two-dimensional geometry. Our
numerical code uses an adaptive mesh refinement allowing us to achieve
sufficiently high resolution both at the largest and the smallest scales. We
neglect any radiative losses, heat conduction, and gravitational forces.
Detailed analysis of the simulations shows that interaction of embedded
inhomogeneities with the shock/postshock wind depends primarily on the
thickness of the cloud layer and arrangement of the clouds in the layer. The
total cloud mass and the total number of individual clouds is not a significant
factor. We define two classes of cloud distributions: thin and thick layers. We
define the critical cloud separation along the direction of the flow and
perpendicular to it distinguishing between the interacting and noninteracting
regimes of cloud evolution. Finally we discuss mass-loading and mixing in such
systems.


title: Inclinations and black hole masses of Seyfert 1 galaxies

abstract:
  A tight correlation of black hole mass and central velocity dispersion has
been found recently for both active and quiescent galaxies. By applying this
correlation, we develop a simple method to derive the inclination angles for a
sample of 11 Seyfert 1 galaxies that have both measured central velocity
dispersions and black hole masses estimated by reverberation mapping. These
angles, with a mean value of 36 degree that agrees well with the result
obtained by fitting the iron K$\alpha$ lines of Seyfert 1s observed with ASCA,
provide further support to the orientation-dependent unification scheme of AGN.
A positive correlation of the inclinations with observed FWHMs of H$\beta$ line
and a possible anti-correlation with the nuclear radio-loudness have been
found. We conclude that more accurate knowledge on inclinations and broad line
region dynamics is needed to improve the black hole mass determination of AGN
with the reverberation mapping technique.


title: Beryllium in the Hyades F and G Dwarfs from Keck/HIRES Spectra

abstract:
  Beryllium is not destroyed as easily as Li, so the abundances of Li and Be
together can tell us more about the internal physical processes in stars than
either element can alone. We have obtained high-resolution (45,000) and high
signal-to-noise (typically 90 per pixel) spectra of the Be II resonance lines
in 34 Hyades F and G dwarfs with the Keck I telescope and HIRES. The Be
abundances have been derived with the spectrum synthesis method. We find that
Be is depleted in the Li gap in the F stars reaching down to values of A(Be) =
0.60, or a factor of nearly seven below the meteoritic Be abundance. There is
little or no depletion of Be in stars cooler than 6000 K, in spite of the large
depletions (0.5 - 2.5 dex) in Li. The mean value of A(Be) for the ten coolest
stars is 1.33 +/- 0.06, not far from the meteoritic value of 1.42. The pattern
in the Be abundances - a Be dip in the F stars and undepleted Be in the cool
stars - is well matched by the predictions of slow mixing due to stellar
rotation (e.g. Deliyannis and Pinsonneault). The depletions of Li and Be
probably occur simultaneously. The Li and Be abundances are correlated for
stars in the temperature range of 5850 - 6680 K, similar to results from
earlier work on Li and Be in F and G field stars. The Hyades G dwarfs have more
Be than the sun; their initial Be may have been larger or they may not be old
enough to have depleted Be. For those Hyades stars which appear to have little
or no depletion of Li or Be, the Li/Be ratio is found to be 75 +/- 30.
(abridged)


title:
Scientific Potential of Enhancing the Integral-Field Spectrometer SPIFFI
  with a Large Detector and High Spectral Resolution

abstract:
  SPIFFI is the near-infrared integral-field spectrometer for the VLT. Assisted
by the SINFONI adaptive optics module, the instrument will be offered to the
astronomical community in 2004. We outline the scientific rationale for
infrared integral-field spectroscopy at the VLT, and specifically for the
enhancement of SPIFFI with a larger detector and higher spectral resolution
gratings. We give examples of a broad variety of astronomical research which
will gain specifically from the high angular and spectral resolution provided
by SPIFFI, including studies of high red-shift galaxies, merging galaxies,
starburst galaxies, superstar clusters, galactic nuclei, extra-solar planets,
and circum-stellar discs.


title: TeV blazars as seen by the CAT telescope

abstract:
  To date, only two extragalactic objects have been firmly established as very
high-energy gamma-ray sources in the Northern sky: these are the two blazars
Markarian 501 and Markarian 421. This paper reviews the most striking results
obtained from these sources by the CAT atmospheric Cherenkov imaging telescope,
with a particular emphasis on the 1999-2000 and 2000-2001 observation campaigns
of Markarian 421.


title:
The optical afterglow of GRB 000911: evidence for an associated
  supernova?

abstract:
  We present photometric and spectroscopic observations of the late afterglow
of GRB 000911, starting ~1 day after the burst event and lasting ~8 weeks. We
detect a moderately significant re-brightening in the R, I and J lightcurves,
associated with a sizable reddening of the spectrum. This can be explained
through the presence of an underlying supernova, outshining the afterglow ~30
days after the burst event. Alternative explanations are discussed.


title: Dark Energy in a Hyperbolic Universe

abstract:
  Dark energy models due to a slowly evolving scalar (quintessence) field
$\phi$ are studied for various potentials $V(\phi)$ in a universe with negative
curvature. The potentials differ in whether they possess a minimum at $\phi=0$
or are monotonically declining, i.e. have a minimum at infinity. The angular
power spectrum $C_l$ of the cosmic microwave background (CMB) as well as the
magnitude-redshift relation $m_B(z)$ of the type Ia supernovae are compared
with the quintessence models. It is demonstrated that some of the models with
$\Omega_tot \simeq 0.85...0.9$ are in agreement with the observations, i.e.
possess acoustic peaks in the angular power spectrum of the CMB anisotropy as
observed experimentally, and yield a magnitude-redshift relation in agreement
with the data. Furthermore, it is found that the power spectrum $P(k)$ of the
large-scale structure (LSS) agrees with the observations too.


title:
The FALCON concept: multi-object spectroscopy combined with MCAO in
  near-IR

abstract:
  A large fraction of the present-day stellar mass was formed between z=0.5 and
z~3 and our understanding of the formation mechanisms at work at these epochs
requires both high spatial and high spectral resolution: one shall
simultaneously} obtain images of objects with typical sizes as small as
1-2kpc(~0''.1), while achieving 20-50 km/s (R >= 5000) spectral resolution. The
obvious instrumental solution to adopt in order to tackle the science goal is
therefore a combination of multi-object 3D spectrograph with multi-conjugate
adaptive optics in large fields. A partial, but still competitive correction
shall be prefered, over a much wider field of view. This can be done by
estimating the turbulent volume from sets of natural guide stars, by optimizing
the correction to several and discrete small areas of few arcsec2 selected in a
large field (Nasmyth field of 25 arcmin) and by correcting up to the 6th, and
eventually, up to the 60th Zernike modes. Simulations on real extragalactic
fields, show that for most sources (>80%), the recovered resolution could reach
0".15-0".25 in the J and H bands. Detection of point-like objects is improved
by factors from 3 to >10, when compared with an instrument without adaptive
correction. The proposed instrument concept, FALCON, is equiped with deployable
mini-integral field units (IFUs), achieving spectral resolutions between R=5000
and 20000. Its multiplex capability, combined with high spatial and spectral
resolution characteristics, is a natural ground based complement to the next
generation of space telescopes.


title: Gravitationally lensed high redshift galaxies in the field of 1E0657-56

abstract:
  We present images and long-slit spectra obtained with FORS1 at UT1 of the VLT
centered on the gravitational arc of the galaxy cluster 1E0657-56 (z = 0.296).
The cluster is one of the hottest, most massive clusters known so far and acts
as a powerful gravitational telescope, amplifying the flux of background
sources by up to a factor of 17.
  We present photometric results together with the spectra of the gravitational
arc (z = 3.24) and four additional amplified high redshift objects (z = 2.34 to
3.08) that were also included in the slit by chance coincidence. A
magnification map has been obtained from a lens model derived from the multiple
image systems. We compare our observed spectra with models and briefly discuss
the stellar contents of these galaxies.
  Furthermore we measured the equivalent widths of the CIV 1550 and SiIV 1400
absorption lines for the objects behind 1E0657-56 studied here, as well as for
some additional starburst galaxies (nearby and at high z). For CIV we find an
increasing absorption equivalent width with decreasing redshift. We discuss
whether this correlation could be related to the increase of metallicity with
the age of the universe.


title: Local Group velocity versus gravity: the coherence function

abstract:
  In maximum-likelihood analyses of the Local Group (LG) acceleration, the
object describing nonlinear effects is the coherence function (CF), i.e. the
cross-correlation coefficient of the Fourier modes of the velocity and gravity
fields. We study the CF both analytically, using perturbation theory, and
numerically, using a hydrodynamic code. The dependence of the function on
Omega_m and the shape of the power spectrum is very weak. The only cosmological
parameter that the CF is strongly sensitive to is the normalization sigma_8 of
the underlying density field. Perturbative approximation for the function turns
out to be accurate as long as sigma_8 is smaller than about 0.3. For higher
normalizations we provide an analytical fit for the CF as a function of sigma_8
and the wavevector. The characteristic decoherence scale which our formula
predicts is an order of magnitude smaller than that determined by Strauss et
al. This implies that present likelihood constraints on cosmological parameters
from analyses of the LG acceleration are significantly tighter than hitherto
reported.


title:
Is the Supernova Remnant RX J1713.7-3946 a Hadronic Cosmic Ray
  Accelerator ?

abstract:
  The non-thermal supernova remnant RX J1713.7-3946 (G347.3-0.5) has recently
been shown to be a site of cosmic ray (CR) electron acceleration to TeV
energies (Muraishi et al. 2000). Here we present evidence that this remnant is
also accelerating CR nuclei. Such nuclei can interact with ambient interstellar
gas to produce high energy gamma-rays via the decay of neutral pions. We
associate the unidentified EGRET GeV gamma- ray source 3EG J1714-3857 with a
massive (~3*10 5 Mo) and dense (~500 nucleons cm -3) molecular cloud
interacting with RX J1713.7-3946. Direct evidence for such interaction is
provided by observations of the lowest two rotational transitions of CO in the
cloud; as in other clear cases of interaction, the CO(J=2-1)/CO(J=1-0) ratio is
significantly enhanced. Since the cloud is of low radio and X-ray brightness,
CR electrons cannot be responsible for the bulk of its GeV emission there. A
picture thus emerges where both electrons and nuclei are being accelerated by
the SNR: whereas the CR electrons dominate the local non-thermal radio, X-ray
and TeV emission, the shock accelerated CR protons and ions (hadrons) are
revealed through their interactions in the adjacent massive cloud. Such a
scenario had been anticipated by Aharonian, Drury and Volk (1994).