title:
The difficulty in using orphan afterglows to measure gamma-ray burst
  beaming

abstract:
  If gamma-ray burst (GRB) emission is strongly collimated then GRBs occur
throughout the Universe at a rate much higher than is detected. Since the
emission from the optical afterglow is thought to be more isotropic than the
gamma-ray emission, it has been hypothesized that a search for orphan
afterglows (those without the triggering GRB) would allow strong constraints to
be placed on the degree of GRB collimation. We show here that, within the
context of leading models of GRB jet evolution, measurement of the GRB beaming
angle using optical orphan searches is extremely difficult, perhaps impossible
in practice. This is because in the leading model of GRB jets, the effective
afterglow beaming angle scales with the jet angle for small angles, and so the
ratio of detected orphan afterglows to GRBs is independent of the jet opening
angle. Thus, the number of expected afterglow detections is the same for
moderate jet angles (e.g. 20 deg) as for arbitrarily small jet angles (<< 0.1
deg). For nearly isotropic GRB geometry, or for radio afterglow searches in
which the jet has become non-relativistic, the ratio of afterglows to GRBs may
give information on collimation. However, using a simple model we estimate the
expected number of orphan detections in current supernova surveys, and find
this number to be less than one, for all jet opening angles. Even for future
supernova surveys, the small detection rate and lack of dependence on
collimation angle appear to ruin the prospects of determining GRB beaming by
this method. Radio searches may provide the best hope to find the missing
orphans.


title:
Matching the observed cosmological constant with vacuum energy density
  in AdS

abstract:
  We calculate the vacuum energy density by taking account of different massive
scalar fields in AdS spacetime. It is found that the mass spectrum of a scalar
field in AdS spacetime is discrete because of a natural boundary condition. The
results match well with the observed cosmological constant.


title:
X-rays and accretion discs as probes of the strong gravity of black
  holes

abstract:
  The observations and interpretation of broad iron lines in the X-ray spectra
of Seyfert 1 galaxies are reviewed. The line profiles observed from
MCG--6-30-15 and NGC 3516 show extended red wings to the line explained by
large gravitational redshifts. The results are consistent with the emission
expected from an X-ray irradiated flat accretion disc orbiting very close to a
black hole. Results from XMM-Newton and Chandra are presented and the
possibility of broad oxygen lines discussed.


title: Deep Sky Objects and the X-ray Background

abstract:
  Deep observations of the X-ray Sky have now resolved most of the X-ray
Background. Obscured active galaxies are a key component. The obscured objects
which dominate at fluxes above $10^{-15}\ergpcmsqps$ are discussed and models
in which the growth of wind-blowing active nuclei determine both black hole and
galaxy mass are presented. The power from accretion is large and can easily
influence the gas in a host galaxy, as well as heat the intergalactic medium.


title:
The DIRECT Project: Influence of Blending on the Cepheid Distance Scale.
  II. Cepheids in M33

abstract:
  We investigate the influence of blending on the Cepheid distance scale.
Blending is the close association of a Cepheid with one or more intrinsically
luminous stars. High-resolution HST images are compared to our ground-based
data, obtained as part of the DIRECT project, for a sample of 102 Cepheids in
the M33 galaxy. The average (median) flux contribution from luminous companions
not resolved on the ground-based images in the B, V and I bands (S_B, S_V, S_I)
is about 29% (15%), 24% (14%), 30% (21%) of the flux of the Cepheid. For 64
Cepheids with periods in excess of 10 days the average (median) values of S_B,
S_V, S_I are 20% (10%), 16% (7%), 23% (14%). This shows that, depending on the
sample of objects chosen, the distance derived from our ground-based V-band
magnitudes for the M33 Cepheids would be systematically underestimated by about
8%-11% (3%-6%). Using artificial star tests we study crowding and blending as
separate phenomena. These tests indicate that the effect of blending could be
more significant than crowding in regions of lower surface brightness, below
21.6 mag/arcsec^2. We also find indications that in the case of long period
Cepheids (P>10^d) companions from blending are on average bluer than companions
introduced by crowding. Our ground-based resolution in M33 corresponds to the
HST resolution at about 11 Mpc. We estimate the effect of blending at
resolutions corresponding to a range of distances as observed with the HST
using the HST M33 data as the template unblended population. We compare our
results to those obtained by other groups.


title:
The DIRECT project: Catalogs of stellar objects in nearby galaxies. II.
  Eastern arm and NGC 206 in M31

abstract:
  DIRECT is a project to directly obtain the distances to two important
galaxies in the cosmological distance ladder, M31 and M33, using detached
eclipsing binaries and Cepheids. As part of our search for these variables, we
have obtained photometry and positions for thousands of stellar objects within
the monitored fields, covering an area of 557.8 arcmin^2. In this research note
we present the equatorial coordinates and BVI photometry for 26712 stars in the
M31 galaxy, along the eastern arm and in the vicinity of the star forming
region NGC206.


title:
On faint companions in the close environment of star-forming dwarf
  galaxies. Possible external star formation triggers ?

abstract:
  We have searched for companion galaxies in the close environment of 98
star-forming dwarf galaxies (SFDGs) from field and low density environments,
using the NASA Extragalactic Database. Most of the companions are dwarf
galaxies which due to observational selection effects were previously
disregarded in environmental studies of SFDGs. A subsample at low redshift,
cz<2000 km/s, was chosen to partially eliminate the observational bias against
distant dwarf companions. We find companion candidates for approximately 30% of
the objects within a projected linear separation s_p<100 kpc and a redshift
difference (Delta cz)<500 km/s. The limited completeness of the available data
sets, together with the non-negligible frequency of HI clouds in the vicinity
of SFDGs indicated by recent radio surveys, suggest that a considerably larger
fraction of these galaxies may be accompanied by low-mass systems. This casts
doubt on the hypothesis that the majority of them can be considered truly
isolated. The velocity differences between companion candidates and sample
SFDGs amount typically to (Delta cz)<250 km/s, and show a rising distribution
towards lower (Delta cz). This is similarly found for dwarf satellites of
spiral galaxies, suggesting a physical association between the companion
candidates and the sample SFDGs. SFDGs with a close companion do not show
significant differences in their Hbeta equivalent widths and B-V colours as
compared to isolated ones. However, the available data do not allow us to rule
out that interactions with close dwarf companions can influence the star
formation activity in SFDGs.


title: A High-Frequency and Multi-Epoch VLBI Study of 3C 273

abstract:
  We show results from a 7 year VLBI monitoring programme of 3C273 at
millimeter wavelengths. We find evidence for component acceleration, motion or
rotation of fluid dynamical patterns in the VLBI jet, and evidence for an
outburst-ejection relation between Gamma-ray flares and the appearance of new
jet components.


title:
From Centimeter to Millimeter Wavelengths: A High Angular Resolution
  Study of 3C273

abstract:
  We monitored 3C273 with VLBI at 15-86 GHz since 1990. We discuss component
trajectories, opacity effects at the jet base, a rotating and perhaps
precessing jet, and outburst-ejection relations from Gamma-ray to radio bands.


title: A one-dimensional toy model of globular clusters

abstract:
  We introduce a one-dimensional toy model of globular clusters. The model is a
version of the well-known gravitational sheets system, where we take
additionally into account mass and energy loss by evaporation of stars at the
boundaries. Numerical integration by the "exact" event-driven dynamics is
performed, for initial uniform density and Gaussian random velocities. Two
distinct quasi-stationary asymptotic regimes are attained, depending on the
initial energy of the system. We guess the forms of the density and velocity
profiles which fit numerical data extremely well and allow to perform an
independent calculation of the self-consistent gravitational potential. Some
power-laws for the asymptotic number of stars and for the collision times are
suggested.


title:
Path integral Monte Carlo simulations and analytical approximations for
  high-temperature plasmas

abstract:
  The results of analytical approximations and extensive calculations based on
a path integral Monte Carlo (PIMC) scheme are presented. A new (direct) PIMC
method allows for a correct determination of thermodynamic properties such as
energy and equation of state of dense degenerate Coulomb systems. In this
paper, we present results for dense partially ionized hydrogen at intermediate
and high temperature. We give a quantitative comparison with the available
results of alternative (restricted) PIMC simulations and with analytical
expressions based on iterpolation formulas meeting the exact limits at low and
high densities. Good agreement between the two simulations is found up to
densities of the order of $10^{24}cm^{-3}$. The agreement with the analytical
results is satisfactory up to densities in the range $10^{22}...
10^{23}cm^{-3}$.


title:
RE J2248-511 - Not all variable, ultrasoft, X-ray AGN have narrow Balmer
  lines

abstract:
  We present ASCA data on RE J2248-511, extending existing optical and soft
X-ray coverage to 10 keV, and monitoring the soft component. These data show
that, despite a very strong ultrasoft X-ray excess below 0.3 keV and a soft
0.3--2 keV spectral index in earlier ROSAT data, the hard X-ray spectrum
(alpha~ -0.8; 0.6-10 keV) is typical of type 1 AGN, and the soft component has
since disappeared. Optical data taken at two different epochs show that the big
blue bump is also highly variable. The strength of the ultrasoft X-ray
component and the extreme variability in RE J2248-511 are reminiscent of the
behaviour observed in many narrow line Seyfert 1s (NLS1s). However, the high
energy end of the ROSAT spectrum, the ASCA spectrum and the Balmer line full
widths at half maximum of ~3000 km/s in RE J2248-511, are typical of normal
Seyfert 1 AGN.
  The change in the soft X-ray spectrum as observed in the ROSAT and ASCA data
is consistent with the behaviour of Galactic Black Hole Candidates (GBHCs) as
they move from a high to a low state, ie. a fall in the ultrasoft component and
a hardening of the X-ray continuum. This GBHC analogy has also been proposed
for NLS1s. Alternatively, the variability may be caused by opacity changes in a
hot, optically-thin corona which surrounds a cold, dense accretion disc; this
was first suggested by Guainazzi et al. for 1H0419-577, an object which shows
remarkably similar properties to RE J2248-511.


title: Parsec-Scale Circular Polarization Observations of 40 Blazars

abstract:
  We present circular polarization results from a 5 GHz survey of the
parsec-scale polarization properties of 40 AGN made with the VLBA. We find 11
circular polarization detections at the 3 sigma level or higher. This nearly
quadruples the number of sources detected in circular polarization at VLBI
resolution. We find no correlation between fractional linear and circular
polarization across our sample. A likely explanation is external Faraday
depolarization in the cores of AGN which reduces linear polarization but leaves
circular polarization unchanged. In comparing ours and other recent results to
observations made 20 years ago, we find that, in five of six cases, sources
have the same sign of circular polarization today as they did 20 years ago.
This suggests the presence of a long term property of the jets, such as the
polarity of a net magnetic flux, which is stable on time-scales much longer
than those of individual outbursts.


title: On The Nature Of Superoutbursts In Dwarf Novae

abstract:
  We present the first detailed hydrodynamic simulation of a superoutburst to
incorporate the full tidal potential of a binary system. A two-dimensional
smoothed particle hydrodynamics code is used to simulate a superoutburst in a
binary with the parameters of the SU UMa system Z Chamaeleontis. The simulated
light curves shows all the features observed in such systems. Analysis of the
mass flux through the disc and the growth rate of the superhumps and disc
eccentricity show that the superoutburst-superhump phenomenon is a direct
result of tidal instability. No enhanced mass transfer from the secondary is
required to initiate or sustain these phenomena. Comparisons of superoutbursts
with normal outbursts are made and we show that the model can be reconciled
with the behavior of U Geminorum type dwarf novae, which show no
superoutbursts.


title: F stars, metallicity, and the ages of red galaxies at z > 1

abstract:
  We explore whether the rest-frame near-UV spectral region, observable in
high-redshift galaxies via optical spectroscopy, contains sufficient
information to allow the degeneracy between age and metallicity to be lifted.
We do this by testing the ability of evolutionary synthesis models to reclaim
the correct metallicity when fitted to the near-UV spectra of F stars of known
(sub-solar and super-solar) metallicity. F stars are of particular interest
because the rest-frame near-UV spectra of the oldest known elliptical galaxies
at z > 1 appear to be dominated by F stars near to the main-sequence turnoff.
  We find that, in the case of the F stars, where the HST ultraviolet spectra
have high signal:noise, model-fitting with metallicity allowed to vary as a
free parameter is rather successful at deriving the correct metallicity. As a
result, the estimated turnoff ages of these stars yielded by the model fitting
are well constrained. Encouraged by this we have fitted these same variable-
metallicity models to the deep, optical spectra of the z \simeq 1.5 mJy radio
galaxies 53W091 and 53W069 obtained with the Keck telescope. While the
age-metallicity degeneracy is not so easily lifted for these galaxies, we find
that even when metallicity is allowed as a free parameter, the best estimates
of their ages are still \geq 3 Gyr, with ages younger than 2 Gyr now strongly
excluded. Furthermore, we find that a search of the entire parameter space of
metallicity and star formation history using MOPED (Heavens et al., 2000) leads
to the same conclusion. Our results therefore continue to argue strongly
against an Einstein-de Sitter universe, and favour a lambda-dominated universe
in which star formation in at least these particular elliptical galaxies was
completed somewhere in the redshift range z = 3 - 5.


title: The SAURON project. I. The panoramic integral-field spectrograph

abstract:
  A new integral-field spectrograph, SAURON, is described. It is based on the
Tiger principle, and uses a lenslet array. SAURON has a large field of view and
high throughput, and allows simultaneous sky subtraction. Its design is
optimized for studies of the stellar kinematics, gas kinematics, and
line-strength distributions of nearby early-type galaxies. The instrument
design and specifications are described, as well as the extensive analysis
software which was developed to obtain fully calibrated spectra, and the
associated kinematic and line-strength measurements. A companion paper reports
on the first results obtained with SAURON on the William Herschel Telescope.


title: Kinetic decoupling of neutralino dark matter

abstract:
  After neutralinos cease annihilating in the early Universe, they may still
scatter elastically from other particles in the primordial plasma. At some
point in time, however, they will eventually stop scattering. We calculate the
cross sections for neutralino elastic scattering from standard-model particles
to determine the time at which this kinetic decoupling occurs. We show that
kinetic decoupling occurs above a temperature $T\sim$ MeV. Thereafter,
neutralinos act as collisionless cold dark matter.


title: The ISM Interactions of a Runaway LBV Nebula in the LMC

abstract:
  New observations of the Magellanic Cloud Luminous Blue Variable candidate
S119 (HD269687) show the relationship of the star to its environs. Echelle
spectroscopy and high-resolution HST imagery reveal an expanding bubble
centered on the star. This bubble appears in both Halpha and [NII] and is
noticeably brighter on the near (blue-shifted) side. The systemic velocity of
both the expanding bubble and the star itself (as seen by the very broad Halpha
emission feature in the stellar spectrum) is V_hel=160 km/s whereas the
velocity of the superposed LMC ISM is 250-300 km/s. ISM absorption features
seen in FUSE spectra reveal components at both stellar and LMC velocities. Thus
we conclude that S119 is located within the LMC ISM and that the bubble is
interacting strongly with the ISM in a bow shock.


title:
Kinematic Constraints on Evolutionary Scenarios for Blue Compact Dwarf
  Galaxies : I. Neutral Gas Dynamics

abstract:
  We present the results of high spatial resolution HI synthesis observations
of six blue compact dwarf (BCD) galaxies. Optically, the selected galaxies have
smooth, symmetric isophotes, and thus are the most likely of the BCD class to
fade into an object morphologically similar to a dwarf elliptical when the
current starburst ends. The neutral gas in all six galaxies appears to be
rotationally supported, however, indicating that true morphological
transformation from a BCD to a dE will require significant loss of angular
momentum. Based on the observed neutral gas dynamics of these and other BCDs,
it is unlikely that present-day BCDs will evolve directly into dwarf
ellipticals after a starburst phase. We discuss alternative evolutionary
scenarios for BCDs and place them within the larger context of galaxy formation
and evolution models.


title:
On Steady State Neutrino Heated Ultra-Relativistic Winds from Compact
  Objects

abstract:
  We study steady state winds from compact objects in the regime where the wind
velocity at infinity is ultra-relativistic. This may have relevance to some
models of Gamma-Ray-Bursts (GRB's). Particular attention is paid to the case
where neutrinos provide the heating. Unless the neutrino luminosity is very
large, L>10^{54} erg/s, the only allowed steady state solutions are those where
energy deposition is dominated by neutrino-antineutrino annihilation at the
sonic point. In this case, the matter temperature near the neutron star surface
is low, less than 1MeV for typical neutrino luminosities. This is in contrast
to the case for sub-relativistic winds discussed in the context of supernovae
where the matter temperature near the neutron star approximates the temperature
characterizing the neutrinos. We also investigate the setting of the neutron to
proton ratio (n/p) in these winds and find that only for large (>10 MeV)
electron neutrino or electron anti-neutrino temperatures is n/p entirely
determined by neutrino capture. Otherwise, n/p retains an imprint of conditions
in the neutron star.


title: Unified Description of Plausible Cause and Effect of the Big Bang

abstract:
  Plausible cause and effect of the big bang model are presented without
violating conventional laws of physics. The initial cosmological singularity is
resolved by introducing the uncertainty principle of quantum theory. We
postulate that, preceding the big bang at the end of the gravitational
collapse, the total observed mass including all forms of energy of the universe
condensed into the primordial black hole (PBH) in a state of isotropic and
minimal chaos (i.e., nearest to the absolute zero temperature). The frozen
energy of the collapsed state is quantized such that each quantum of frozen
energy (the cosmic particle) is characterized by the fundamental constants of
the general theory of relativity and of quantum theory. The minimum size and
minimum lifetime of the cosmic particle are estimated within the framework of
the uncertainty principle. It is considered that these cosmic particles are
bosons with intrinsic spin zero. The minimum size and thermodynamic properties
of the PBH are estimated within the framework of the Bose-Einstein statistics
by taking into account the total observed mass of the universe. The mechanism
of the big bang is given and the currently accepted Planck temperature at the
beginning of the big bang is predicted. The critical mass density, the mean
mass density, and the missing mass are calculated as a function of the Hubble
time of expansion. Our calculations show that the universe is closed but
expanding. However, the universe remains inside the event horizon of the
primordial black hole.
  Subj-class: cosmology: theory - pre-big bang physics; post-big bang effect.


title: A New Cosmological Model

abstract:
  It is only human nature to be reluctant to accept something new and
different. This feeling is exacerbated given the success of the Big Bang model.
However, there are cogent reasons for considering this new model. Some of the
advantages of this new model over the existing Big Bang model are as follows:
(1) It does not violate any known laws of physics. This contrasts with the Big
Bang model where all known laws of physics break down in the consideration of
the universe beginning as a singular point of infinite density. (2) The cause
behind the initial explosion is provided in this new model. The Big Bang model
does not explain what caused the initial explosion. (3) The homogenous nature
of the universe is intrinsically explained in this new model. Whereas, the Big
Bang model relies on an "extraneous" concept like inflation to explain the
homogeneity of the universe. (4) This new model eliminates the mystery of why
there is a preponderance of matter over anti-matter. These are some of the
advantages of this new model. There are others. Given these qualitative
advantages, this new model is worthy of serious consideration even though it is
new and different.


title:
Near-infrared coronagraphic imaging of the circumstellar disk around TW
  Hydrae

abstract:
  We present ground-based near-infrared (H-band) imaging of the circumstellar
disk around the nearby classical T Tauri star TW Hydrae. The scattered light
image shows a face-on disk with radius 4 arcseconds (corresponding to 225 AU)
and a morphology which agrees with recent images from the Hubble Space
Telescope and the Very Large Array. The best fit power-law for the disk's
radial surface brightness profile obeys the law r^{-3.3\pm0.3}. We use our
image and published continuum flux densities to derive properties of the disk
with a simple model of emission from an optically thick, flat disk. The
best-fit values for disk mass and inner radius are 0.03 M_{\odot} and 0.3 AU;
best-fit values for temperature, density, and grain opacity power law exponents
(q, p, and \beta) are 0.7, 1.3, and 0.9, respectively. These properties are
similar to those of disks around classical T Tauri stars located in more
distant molecular clouds. Because of TW Hydrae's nearby location and pole-on
orientation, it is a uniquely favorable object for future studies of radial
disk structure at the classical T Tauri stage.


title: High Resolution Mid-IR Images of the Nucleus of M81

abstract:
  We observed two nearby galaxies with potential or weak indications of nuclear
activity, M32 and M81, with the MIRLIN mid-IR camera at N band (10.79 microns).
M32 is not detected, but we give detailed measurements of the nucleus of M81.
Our observations of M81 show a bright nuclear point source at N, and comparison
to measurements made in the early 1970's gives an increase in nuclear flux of
nearly a factor of two. If the comparison is accurate, the nuclear mid-IR
emission must ultimately be powered by a variable, compact source, similar to
that in Seyferts and quasars. M81 has been classified in the literature as a
low-luminosity LINER, not a pure Seyfert galaxy. Further, it has been suggested
that this and other low-luminosity AGN may have intrinsically different spectra
than Seyferts and quasars. However, we find that the relative fluxes in the
X-ray, MIR, and radio bands, all essentially unaffected by extinction and
galaxy pollution, show a nuclear continuum remarkably like that of a bona fide
Seyfert or quasar.


title: Galactic Bulge Pixel Lensing Events

abstract:
  Gould & DePoy proposed a pixel lensing survey towards the Galactic bulge
using a small aperture (~65 mm) camera with a large pixel size (10") detector
and deliberately degraded optics achieving 30" PSF. In this paper, we estimate
the event rate of this pixel lensing survey expected under various detection
criteria, which are characterized by the threshold signal-to-noise ratio,
(S/N)_{th}, and event duration, t_{dur,th}, and investigate the characteristics
of the detectable events. From this investigation, we find that the event rate
varies significantly in the range ~6/yr - 120/yr depending strongly on the
imposed detection criteria, implying that to maximize event detections it will
be essential to identify events by diligently inspecting light variations and
to promptly conduct followup observations for the identified events. Compared
to events detectable from classic lensing surveys, the events detectable from
the pixel lensing survey will generally involve brighter source stars and have
higher amplifications. For the pixel lensing events detectable under the
criteria of (S/N)_{th}=10 and t_{dur,th}=6 hr, we find that the baseline
brightness of source stars will be in average ~2 mag brighter than those of
classic lensing events and ~90% will have amplifications A> 20 and ~40% will be
extreme EMEs with A>200. Therefore, followup observations of the pixel lensing
events will provide high quality data, which enable one to precisely determine
the lensing parameters and obtain extra-information about the lenses and source
stars. Especially, high amplifications events with A>20 will be important
targets for high-efficiency planet detections and one can uniquely determine
the mass, distance, and transverse speed of individual lenses for EMEs.


title: Observations of Circumstellar Disks

abstract:
  The imaging of disks around young stars presents extreme challenges in high
dynamic range, angular resolution, and sensitivity. Recent instrumental
advances have met these challenges admirably, leading to a marked increase in
imaging discoveries. These have opened up a new era in studies of the origin of
planetary systems. Questions about our own solar system's formation, and of the
prevalence of extra-solar planets, are now addressed with complementary
techniques at different wavelengths. Optical and near-infrared images detail
scattered light from disks at the highest possible resolution. Mid-infrared,
sub-millimeter, and millimeter-wave techniques probe thermal dust continuum
radiation. Millimeter-wave interferometry details the small-scale structure of
the molecular gas. Kinematic imaging studies affirm the disk interpretation of
mm-wave continuum surveys, and the high incidence rate for solar nebula
analogs. Inner holes, azimuthal asymmetries, and gaps suggest the presence of
underlying planetary bodies. The combined techniques provide a
multi-dimensional picture of disks in time and have strengthened our
understanding of the connection between disks and planets. Future progress is
assured by the presence of much-improved imaging capability looming on the
horizon.


title:
Spatially resolved spectroscopy of emission-line gas in QSO Host
  galaxies

abstract:
  We present off-nuclear spectra of 3 radio loud QSO's, 3C249.1, 3C273 and
3C323.1., taken with the echellette spectrograph and imager (ESI) at Keck
observatory. From these spectra we have extracted the spatial profile along the
slit of the [OIII], $\lambda= \textsf{5007}$ line. Fitted Gaussian
distributions to each of these profiles show emission-line gas out to several
tens of kiloparsecs from the galaxy nucleus. Most observations show several gas
components at distinct velocities and velocity dispersions, much of which is
above the escape velocity for any resonable mass galaxy. In addition, we show
slitless spectroscopy images for one other object, 3C48. From the slitless
spectroscopy images we can extract 2-dimensional spatial as well as velocity
information on the emission line gas.


title: Can A Gravitational Quadruple Lens Produce 17 images?

abstract:
  Gravitational lensing can be by a faint star, a trillion stars of a galaxy,
or a cluster of galaxies, and this poses a familiar struggle between particle
method and mean field method. In a bottom-up approach, a puzzle has been laid
on whether a quadruple lens can produce 17 images. The number of images is
governed by the gravitational lens equation, and the equation for $n$-tuple
lenses suggests that the maximum number of images of a point source potentially
increases as $n^2+1$. Indeed, the classes of $n=1, 2, 3$ lenses produce up to
$n^2+1 = 2, 5, 10$ images. We discuss the $n$-point lens system as a
two-dimensional harmonic flow of an inviscid fluid, count the caustics
topologically, recognize the significance of the limit points and discuss the
notion of image domains. We conjecture that the total number of positive images
is bounded by the number of finite limit points $2(n-1): n>1$ (1 limit point at
$\infty$ if $n=1$). A corollary is that the total number of images of a point
source produced by an $n$-tuple lens can not exceed $5(n-1):n>1$. We construct
quadruple lenses with distinct finite limit points that can produce up to 15
images and argue why there can not be more than 15 images. We show that the
maximum number of images is bounded from below by $3(n+1): n \ge 3$. We also
comment on "thick Einstein rings" that can have one or more holes.


title:
Keck Imaging of the Globular Cluster Systems in the Early--type Galaxies
  NGC 1052 and NGC 7332

abstract:
  The presence of two globular cluster subpopulations in early-type galaxies is
now the norm rather than the exception. Here we present two more examples for
which the host galaxy appears to have undergone a recent merger. Using
multi-colour Keck imaging of NGC 1052 and NGC 7332 we find evidence for a
bimodal globular cluster colour distribution in both galaxies, with roughly
equal numbers of blue and red globular clusters. The blue ones have similar
colours to those in the Milky Way halo and are thus probably very old and
metal-poor. If the red GC subpopulations are at least solar metallicity, then
stellar population models indicate young ages. We discuss the origin of
globular clusters within the framework of formation models. We conclude that
recent merger events in these two galaxies have had little effect on their
overall GC systems. We also derive globular cluster density profiles, global
specific frequencies and in the case of NGC 1052, radial colour gradients and
azimuthal distribution. In general these globular cluster properties are normal
for early-type galaxies.


title: Weak-Lensing Halo Numbers and Dark-Matter Profiles

abstract:
  Integral measures of weak gravitational lensing by dark-matter haloes, like
the aperture mass, are sensitive to different physical halo properties
dependent on the halo mass density profile. For isothermal profiles, the
relation between aperture mass and virial mass is steeper than for haloes with
the universal NFW profile. Consequently, the halo mass range probed by the
aperture mass is much wider for NFW than for isothermal haloes. We use recent
modifications to the Press-Schechter mass function in CDM models normalised to
the local abundance of rich clusters, to predict the properties of the halo
sample expected to be accessible with the aperture mass technique. While ~10
haloes should be detected per square degree if the haloes have NFW profiles,
their number density is lower by approximately an order of magnitude if they
have isothermal profiles. These results depend only very mildly on the
cosmological background model. We conclude that counts of haloes with a
significant weak-lensing signal are a powerful discriminator between different
dark-matter profiles.


title:
The motion of stars near the Galactic center: A comparison of the black
  hole and fermion ball scenarios

abstract:
  After a discussion of the properties of degenerate fermion balls, we analyze
the orbits of the stars S0-1 and S0-2, which have the smallest projected
distances to Sgr A*, in the supermassive black hole as well as in the fermion
ball scenarios of the Galactic center. It is shown that both scenarios are
consistent with the data, as measured during the last six years by Genzel et
al. and Ghez et al. The free parameters of the projected orbit of a star are
the unknown components of its velocity v_z and distance z to Sgr A* in 1995.4,
with the z-axis being in the line of sight. We show, in the case of S0-1 and
S0-2, that the z-v_z phase-space which fits the data, is much larger for the
fermion ball than for the black hole scenario. Future measurements of the
positions or radial velocities of S0-1 and S0-2 could reduce this allowed
phase-space and eventually rule out one of the currently acceptable scenarios.
This may shed some light into the nature of the supermassive compact dark
object, or dark matter in general at the center of our Galaxy.


title:
A Non-Parametric Estimate of the Mass of the Central Black Hole in the
  Galaxy

abstract:
  We estimate the mass of the central black hole in our Galaxy from stellar
kinematical data published by Ghez et al. (1998) and Genzel et al. (2000). For
this we develop a method, related to Merritt (1993), for non-parametrically
reconstructing the mass profile and the stellar distribution function in the
central region of the Galaxy from discrete kinematic data, including velocity
errors. Models are searched using the Metropolis algorithm. We assume that the
mass distribution is spherical and the stellar velocity distribution is
isotropic, and devise a test of this assumption. From proper motions we obtain
an enclosed mass of $2.0\pm{0.7}\times10^6{\rm M}_{\odot}$ within the inner
$0.0044\rm pc$, from radial velocities we obtain a mass of
$2.2^{+1.6}_{-1.0}\times10^6{\rm M}_{\odot}$ within 0.046pc and from
three-dimensional velocities we obtain $1.8^{+0.4}_{-0.3}\times10^6{\rm
M}_{\odot}$ within 0.046pc.


title: Failed optical afterglows

abstract:
  While all but one Gamma-Ray Bursts observed in the X-ray band showed an X-ray
afterglow, about 60 per cent of them have not been detected in the optical
band. We show that this is not due to adverse observing conditions. We then
investigate the hypothesis that the failure of detecting the optical afterglow
is due to absorption at the source location. We find that this is a marginally
viable interpretation, but only if the X-ray burst and afterglow emission and
the possible optical/UV flash do not destroy the dust responsible for
absorption in the optical band. If dust is efficiently destroyed, we are led to
conclude that bursts with no detected optical afterglow are intrinsically
different.


title:
Accretion onto Black Holes and Neutron Stars: Differences and
  Similarities

abstract:
  Accreting black holes and neutron stars at luminosities above 0.01 of the
critical Eddington luminosity have a lot of similarities, but also drastic
differences in their radiation and power density spectra. The efficiency of
energy release due to accretion onto a rotating neutron star usually is higher
than in the case of a black hole. The theory of the spreading layer on the
surface of an accreting neutron star is discussed. It predicts the appearance
of two bright belts equidistant from the equator. This layer is unstable and
its radiation flux must vary with high frequencies.


title: Constraints on high energy phenomena from low energy nuclear physics

abstract:
  A procedure to derive bounds on coupling strengths of exotic particles to
nucleons from the neutrino signal of supernovae is outlined. The analysis is
based on a model independent calculation for the emissivities for the exotic,
detailed simulation for the evolution of the early proto-neutron star as well
as a Likelihood analysis. As an example we derive confidence levels for the
upper bound of the size of gravity only extra dimensions.


title:
Chemical composition and origin of nebulae around Luminous Blue
  Variables

abstract:
  We use the analysis of the heavy element abundances (C, N, O, S) in
circumstellar nebulae around Luminous Blue Variables to infer the evolutionary
phase in which the material has been ejected.
  (1) We discuss the different effects that may have changed the gas
composition of the nebula since it was ejected
  (2) We calculate the expected abundance changes at the stellar surface due to
envelope convection in the red supergiant phase. If the observed LBV nebulae
are ejected during the RSG phase, the abundances of the LBV nebulae require a
significantly smaller amount of mass to be lost than assumed in evolutionary
models.
  (3) We calculate the changes in the surface composition during the main
sequence phase by rotation induced mixing. If the nebulae are ejected at the
end of the MS-phase, the abundances in LBV nebulae are compatible with mixing
times between 5 x 10^6 and 1 x 10^7 years. The existence of ON stars supports
this scenario.
  (4) The predicted He/H ratio in the nebulae are significantly smaller than
the current observed photospheric values of their central stars.
  Combining various arguments we show that the LBV nebulae are ejected during
the blue SG phase and that the stars have not gone through a RSG phase. The
chemical enhancements are due to rotation induced mixing, and the ejection is
possibly triggered by near-critical rotation. During the ejection, the outflow
was optically thick, which resulted in a large effective radius and a low
effective temperature. This also explains the observed properties of LBV dust.


title: Response of a Spaceborn Gravitational Wave Antenna to Solar Oscillations

abstract:
  We investigate the possibility of observing very small amplitude low
frequency solar oscillations with the proposed laser interferometer space
antenna LISA. For frequencies below $\sim 2\times 10^{-4}$ Hz the dominant
contribution is from the near zone time dependent gravitational quadrupole
moments associated with the normal modes of oscillation. For frequencies $\nu$
above $\sim 3\times 10^{-4}$ Hz the dominant contribution is from gravitational
radiation generated by the quadrupole oscillations which is larger than the
Newtonian signal by a factor $\sim (2 \pi r \nu/ c)^4$, where $r$ is the
distance to the Sun, and $c$ is the velocity of light.
  The low order solar quadrupole pressure and gravity oscillation modes have
not yet been detected above the solar background by helioseismic velocity and
intensity measurements. Our estimates of the amplitudes needed to give a
detectable signal on a LISA type space laser interferometer imply surface
velocity amplitudes on the sun of the order of 1-10 mm/sec in the frequency
range $1 - 5~10^{-4}$Hz. Such surface velocities are below the current
sensitivity limits on helioseismic measurements. If modes exist with
frequencies and amplitudes in this range they could be detected with a LISA
type laser interferometer.


title:
Quiescent and flare analysis for the chromospherically active star Gl355
  (LQHya)

abstract:
  We discuss ROSAT and ASCA observations of the young active star Gl355}.
During the ROSAT observation a strong flare was detected with a peak flux more
than an order of magnitude larger than the quiescent level. Spectral analysis
of the data allows us to study the temperature and emission measure
distribution, and the coronal metal abundance, for the quiescent phase and, in
the case of ROSAT, also during the evolution of the flare. The global coronal
metallicity $Z/Z_{\odot} \sim 0.1$ derived from both ROSAT and ASCA data is
much lower than solar and presumably also much lower than the photospheric
abundance expected for this very young star. The temperature structure of the
quiescent corona was about the same during the various observations, with a
cooler component at $T_1 \sim 7$ MK and a hotter component (to which only ASCA
was sensitive) at $T_2 \sim 20$ MK. During the flare, the low temperature
component remained approximately constant and equal to the quiescent value,
while the high-temperature component was the only one that varied. We have
modeled the flare with the hydrodynamic-decay sustained-heating approach of
Reale at al. (1997) and we have derived a loop semi--length of the order of
$\sim 1.5$ stellar radii, i.e. much larger than the dimensions of flares on the
Sun, but comparable with the typical dimensions inferred for other stellar
flares. We have compared the derived loop size with that estimated with a
simpler (but physically inconsistent) approach, finding that for this, as well
for several other stellar flares, the two methods give comparable loop sizes.
Possible causes and consequences of this result are discussed.


title: Secondary electrons and positrons in near earth orbit

abstract:
  The secondary e+ and e- populations in near earth's orbit have been
calculated by simulation. The results are in very good agreement with the
recent AMS measurements. The e$^+$ over e$^-$ flux ratio for particles below
the geomagnetic cutoff appears to be due to the geomagnetic East-West effect.


title: The early-type galaxy population in Abell 2218

abstract:
  (Abridged) We present morphological, photometric, kinematic and line-strength
data of 48 early-type members of the rich cluster Abell 2218 at z=0.18. This
sample is both larger and spans a wider galaxy luminosity range, down to
M*_B+1, than previous studies. We compare A2218 with similar samples drawn from
local clusters to identify evolutionary changes between the samples which have
occured over the last 3Gyrs. The overall picture is one of little or no
evolution in nearly all galaxy parameters. Zeropoint offsets in the
Faber--Jackson, Mg_b-sigma and Fundamental Plane relations are all consistent
with passively evolving stellar populations. The slopes of these relations have
not changed significantly. We do however find a significant spread in the
estimated luminosity-weighted ages of the stellar populations in the galaxies,
based on line diagnostic diagrams. This age spread is seen in both the disky
early-type galaxies (S0) and also the ellipticals. We observe both ellipticals
with a strong contribution from a young stellar population and lenticulars
dominated by old stellar populations. On average, we find no evidence for
systematic differences between the populations of ellipticals and lenticulars.
This points to a common formation epoch for the bulk of the stars in most of
the early-type galaxies in A2218. This result can be reconciled with the claims
of rapid morphological evolution in distant clusters if the suggested
transformation from spirals to lenticulars does not involve significant new
star formation.


title: The Formation of Disks in Elliptical Galaxies

abstract:
  We investigate detailed kinematical properties of simulated collisionless
merger remnants of disk galaxies with mass ratios of 1:1 and 3:1. The
simulations were performed by direct summation using the new special hardware
device GRAPE-5. In agreement with observations, the shape of the line-of-sight
velocity distribution (LOSVD) is Gaussian with small deviations. For most cases
we find that the retrograde wings of the LOSVD are steeper than the prograde
ones. This is in contradiction with observations which show broad retrograde
and steep prograde wings. This serious problem in the collisionless formation
scenario of massive elliptical galaxies can be solved if all rotating
ellipticals, even boxy ones, contain an additional stellar disk component with
$\propto 15%$ of the total stellar mass and a scale length of order the
effective radius of the spheroid. We propose that the progenitor galaxies of
massive ellipticals must have contained a significant amount of gas that did
not condense into stars during the merger process itself but formed an extended
gaseous disk before the star formation epoch. The heating source that prevented
the gas from forming stars early and the origin of the large specific angular
momentum required for the gas component to form an extended disk are still
unsolved problems.


title: The Origin of the Knee in the Cosmic-Ray Energy Spectrum

abstract:
  A sudden steepening of the cosmic-ray energy spectrum (the knee) is observed
at an energy of about 3 PeV (1 PeV = 10$^{15}$eV). The recent results on
extensive air showers allow us to conclude that: a) the knee has an
astrophysical origin; b) the 'sharpness' and the fine structure of the knee
rule out 'Galactic Modulation' as the origin of the knee; c) most likely the
knee is the result of the explosion of a single, recent, nearby supernova.


title:
Determining cosmic microwave background structure from its peak
  distribution

abstract:
  We present a new method for time-efficient and accurate extraction of the
power spectrum from future cosmic microwave background (CMB) maps based on
properties of peaks and troughs of the Gaussian CMB sky. We construct a
statistic describing their angular clustering - analogously to galaxies, the
2-point angular correlation function, $\xi_\nu(\theta)$. We show that for
increasing peak threshold, $\nu$, the $\xi_\nu(\theta)$ is strongly amplified
and becomes measurable for $\nu\geq$1 on angular scales $\leq 10^\circ$. Its
amplitude at every scale depends uniquely on the CMB temperature correlation
function, $C(\theta)$, and thus the measured $\xi_\nu$ can be uniquely inverted
to obtain $C(\theta)$ and its Legendre transform, the power spectrum of the CMB
field. Because in this method the CMB power spectrum is deduced from high
peaks/troughs of the CMB field, the procedure takes only $[f(\nu)]^2N^2$
operations where $f(\nu)$ is the fraction of pixels with $|\delta T|\geq\nu$
standard deviations in the map of $N$ pixels and is e.g. 0.045 and 0.01 for
$\nu$=2 and 2.5 respectively. We develop theoretical formalism for the method
and show with detailed simulations, using MAP mission parameters, that this
method allows to determine very accurately the CMB power spectrum from the
upcoming CMB maps in only $\sim(10^{-4}-10^{-3})\times N^2$ operations.


title:
Dwarf Galaxies in the Leo I Group: the Group Luminosity Function beyond
  the Local Group

abstract:
  We present first results of a survey of the Leo I group at 10 Mpc for M_R <
-10 dwarf galaxies. This is part of a larger program to measure the faint end
of the galaxy luminosity function in nearby poor groups. Our method is
optimized to find Local-Group-like dwarfs down to dwarf spheroidal surface
brightnesses, but we also find very large LSB dwarfs in Leo I with no Local
Group counterpart. A preliminary measurement of the luminosity function yields
a slope consistent with that measured in the Local Group.


title: The Sunyaev-Zel'dovich Effect: Results and Future Prospects

abstract:
  The Sunyaev-Zel'dovich effect (SZE) provides a powerful tool for cosmological
studies. Through recent advances in instrumentation and observational
techniques it is now possible to obtain high quality measurements of the effect
toward galaxy clusters. The analysis of the SZE toward a few tens of clusters
has already led to interesting constraints on the Hubble constant and the mass
density of the universe. In the near future, instruments exploiting the
redshift independence of the SZE will be used to conduct deep surveys for
galaxy clusters providing detailed information on the growth of large scale
structure, tests of cosmological models and tight constraints on the
cosmological parameters that describe our universe. In this review we provide
an overview of the SZE and its use for cosmological studies. We summarize the
current state of observations and the constraints on cosmological parameters
already obtained and we discuss the power of using the SZE for future deep
cluster surveys.


title: Behavior of Sulfur Abundances in Metal-Poor Giants and Dwarfs

abstract:
  LTE and NLTE abundances of sulfur in 6 metal-poor giants and 61 dwarfs (62
dwarfs, including the Sun) were explored in the range of -3 \lsim [Fe/H] \lsim
$+0.5$ using high-resolution, high signal-to-noise ratio spectra of the \SI
8693.9 \AA and 8694.6 \AA lines observed by us and measured by \Francois (1987,
1988) and Clegg et al. (1981). NLTE effects in S abundances are found to be
small and practically negligible. The behavior of [S/Fe] vs. [Fe/H] exhibits a
linear increasing trend without plateau with decreasing [Fe/H]. Combining our
results with those available in the literature, we find that the slope of the
increasing trend is -0.25 in the NLTE behavior of [S/Fe], which is comparable
to that observed in [O/Fe]. The observed behavior of S may require chemical
evolution models of the Galaxy, in which scenarios of hypernovae
nucleosynthesis and/or time-delayed deposition into interstellar medium are
incorporated.


title:
The Episodic, Precessing Giant Molecular Outflow from IRAS 04239+2436
  (HH 300)

abstract:
  We present the first set of detailed molecular line maps of the region
associated with the giant Herbig-Haro flow HH 300, from the young star IRAS
04239+2436. Our results indicate that the red lobe of the HH 300 flow is
depositing a fair amount of momentum and kinetic energy over a notable volume
of its host dark cloud. This makes HH 300 a key player in the evolution and
fate of its parent cloud. The redshifted molecular outflow lobe of HH 300 is
1.1 pc long and 0.3 pc wide, and has a very clumpy structure. The density,
velocity, and momentum distributions in the outflow indicate that the observed
clumps arise from the prompt entrainment of ambient gas. Bow shock-shaped
structures are associated with the clumps, and we hypothesize that the shocks
are produced by different mass ejection episodes. Lines drawn from IRAS
04239+2436 to each of these clumps have different orientations on the plane of
the sky, and we conclude that HH 300 is a precessing and episodic outflow. The
observations include a map of the red lobe in the 12CO(2-1) line, with a beam
size of 27'', and more extended maps of the outflow region in the 12CO(1-0) and
13CO(1-0) lines, with 45'' and 47'' beam sizes, respectively. We obtain a steep
power-law mass spectrum for HH 300, which we believe is best explained by the
evolution of the outflow mass kinematics. In addition, our 13CO observations
show that the HH 300 flow has been able to redistribute (in space and velocity)
considerable amounts of its surrounding medium-density gas.


title: The Mass-Velocity and Position-Velocity Relations in Episodic Outflows

abstract:
  While observational evidence for the episodic nature of young stellar
outflows continues to mount, existing numerical and theoretical models of
molecular outflows assume they are formed by the interaction of a non-episodic
wind from a young stellar object with an ambient cloud. In this Letter we
estimate and discuss the effects of episodicity on the mass-velocity and
position-velocity relations observed in molecular outflows. We explain how many
recent observational results disagree with the predictions of non-episodic
outflow models, and we offer simple explanations for the discrepancies. In
particular, we discuss how an episodic stellar outflow can steepen the
power-law slope of the mass-velocity relation in a molecular outflow. And, we
illustrate how an episodic outflow can produce multiple "Hubble-wedges'' in the
position-velocity distribution of a molecular outflow. With a little more
information than we have now, it may be possible to use the "fossil record"
embedded in a molecular outflow's mass-velocity and position-velocity relations
to reconstruct the history of a young stellar object's mass ejection episodes.


title:
The Hard X-ray Luminosity of OB Star Populations: Implications for the
  Contribution of Star Formation to the Cosmic X-ray Background

abstract:
  We present an empirical analysis of the integrated X-ray luminosity arising
from populations of OB stars. In particular, we utilize results from the
All-Sky Monitor on RXTE, along with archival data from previous missions, to
assess the mean integrated output of X-rays in the 2-10 keV band from accreting
early-type binaries within 3 kpc of the Sun. Using a recent OB star census of
the Solar neighborhood, we then calculate the specific X-ray luminosity per O
star from accretion-powered systems. We also assess the contribution to the
total X-ray luminosity of an OB population from associated T Tauri stars,
stellar winds, and supernovae. We repeat this exercise for the major Local
Group galaxies, concluding that the total X-ray luminosity per O star spans a
broad range from 2 to 20e34 erg/s. Contrary to previous results, we do not find
a consistent trend with metallicity; in fact, the specific luminosities for M31
and the SMC are equal, despite having metallicities which differ by an order of
magnitude. In light of these results, we assess the fraction of the observed
2-10 keV emission from starburst galaxies that arises directly from their OB
star populations, concluding that, while binaries can explain most of the hard
X-ray emission in many local starbursts, a significant additional component or
components must be present in some systems. A discussion of the nature of this
additional emission, along with its implications for the contribution of
starbursts to the cosmic X-ray background, concludes our report.


title: Star formation and chemical evolution of damped Lyman $\alpha$ systems

abstract:
  In this paper, we investigate the star formation and chemical evolution of
damped Lyman-$\alpha$ systems (DLAs) based on the disc galaxy formation model
which is developed by Mo, Mao & White. We propose that the DLAs are the central
galaxies of less massive dark haloes present at redshifts $z\sim 3$, and they
should inhabit haloes of moderately low circular velocity. The empirical
Schmidt law of star formation rates, and closed box model of chemical evolution
that an approximation known as instantaneous recycling is assumed, are adopted.
In our models, when the predicted distribution of metallicity for DLAs is
calculated, two cases are considered. One is that, using the closed box model,
empirical Schmidt law and star formation time, the distribution of metallicity
can be directly calculated. The other is that, when the simple gravitational
instability of a thin isothermal gas disc as first discussed by Toomre is
considered, the star formation occurs only in the region where the surface
density of gas satisfies the critical value, not everywhere of a gas disc. We
assume that star formation in each DLA lasts for a period of 1 Gyr from
redshifts $z=3$. There is only one output parameter in our models, i.e. the
stellar yield, which relates to the time of star formation history and is
obtained by normalizing the predicted distribution of metallicity to the mean
value of 1/13 $Z_{\odot}$ as presented by Pettini et al. The predicted
metallicity distribution is consistent with the current (rather limited)
observational data. A random distribution of galactic discs is taken into
account.


title:
Extended radio emission after the soft X-ray maximum of the NOAA 9077 AR
  solar flare on July 10, 2000

abstract:
  An extended radio emission after a soft X-ray (SXR) maximum was detected in
the active region NOAA 9077 by several observatories for the solar flare after
21:42 UT on July 10, 2000. Also some radio fine structures before the enduring
radio emission were observed with the 1.0-2.0 GHz spectrometer of Beijing
Astronomical Observatory (BAO) in the same time. We apply a shear-driven
quadrupolar reconnection model (SQR) to analyze the fine structures and the
related radio emission. We find that the footpoint shear motion of the flux
loop is accompanied with the emerging up of the loop during the reconnection
process. We tentatively interpret the extended radio emission as the nonthermal
radiation caused by a new reconnection process between emerging flux loop and
pre-existing overarching loop after the soft X-ray maximum.


title:
ROSAT X-ray sources in the field of the LMC I.Total LMC gas from the
  background AGN spectral fits

abstract:
  We analyzed a sample of 26 background X-ray sources in a ~60 square degree
field of the Large Magellanic Cloud observed with the ROSAT PSPC. The sample
has been selected from previously classified and optically identified X-ray
sources. In addition pointlike and spectrally hard sources with at least 100 to
200 observed counts have been used for the analysis. We performed X-ray
spectral fitting and derived total hydrogen absorbing column densities due to
LMC gas in the range 10^20 - 2. 10^21 cm^-2. We compared these columns with the
HI columns derived from a 21-cm Parkes survey of the LMC. For 7 optically
identified sources we find, within the uncertainties derived from the X-ray
spectral fit, agreement for both columns. For further 19 sources we constrain
the LMC columns from the X-ray spectral fit assuming that the powerlaw photon
index is that of AGN type spectra. We derive for 20 sources gas columns which
are within the uncertainties in agreement with the HI columns. We derive for
two background sources (RX J0536.9-6913 and RX J0547.0-7040) hydrogen absorbing
column densities due to LMC gas, which are in excess to the HI columns. These
sources - located in regions of large (~3. 10^21 cm^-2) LMC HI column densities
- could be seen through additional gas which may be warm and diffuse, cold or
molecular. For 10 sources we derive upper limits for the gas columns additional
to HI and constrain the molecular mass fraction to <(30-140)%.


title:
Truncation of geometrically thin disks around massive black holes in
  galactic nuclei

abstract:
  The concept of an advection-dominated accretion flow (ADAF), with or without
wind loss, was used to describe the spectra of the galactic center source Sgr
A*, low-luminosity AGN and nuclei of elliptical galaxies (including M87). The
spectral fits of various authors show that the transition from the
geometrically thin disk to the hot flow occurs at quite different distances,
apparently not uniquely related to the mass flow rate in the disk. We compare
these results with the results of theoretical modeling where we determine the
truncation of the thin outer disk from the efficiency of mass evaporation. The
physics is the same as in the case of galactic black holes systems (Meyer et
al. 2000b). For the observationally indicated mass flow rates our model
predicts a truncation at 10^3 to 10^4 Schwarzschild radii. We discuss whether
far inside this truncation an innermost cool thin disk could exist and affect
the spectrum.


title:
Determining the fraction of compact objects in the Universe using
  supernova observations

abstract:
  We investigate the possibility to determine the fraction of compact objects
in the Universe by studying gravitational lensing effects on Type Ia supernova
observations. Using simulated data sets from one year of operation of the
proposed dedicated supernova detection satellite SNAP, we find that it should
be possible to determine the fraction of compact objects to an accuracy of < 5
%.


title:
Ages and metallicities of five intermediate-age star clusters projected
  towards the Small Magellanic Cloud

abstract:
  Colour-magnitude diagrams are presented for the first time for L32, L38, K28
(L43), K44 (L68) and L116, which are clusters projected onto the outer parts of
the Small Magellanic Cloud (SMC). The photometry was carried out in the
Washington system $C$ and $T_1$ filters allowing the determination of ages by
means of the magnitude difference between the red giant clump and the main
sequence turnoff, and metallicities from the red giant branch locus. The
clusters have ages in the range 2-6 Gyr, and metallicities between $-1.65<$
[Fe/H] $<-1.10$, increasing the sample of intermediate-age clusters in the SMC.
L116, the outermost cluster projected onto the SMC, is a foreground cluster,
and somewhat closer to us than the Large Magellanic Cloud. Our results,
combined with those for other clusters in the literature, show epochs of sudden
chemical enrichment in the age-metallicity plane, which favour a bursting star
formation history as opposede to a continuous one for the SMC.


title:
Spatial analysis of solar type III events associated with narrow band
  spikes at metric wavelengths

abstract:
  The spatial association of narrow band metric radio spikes with type III
bursts is analyzed. The analysis addresses the question of a possible causal
relation between the spike emission and the acceleration of the energetic
electrons causing the type III burst. The spikes are identified by the
Phoenix-2 spectrometer (ETH Zurich) from survey solar observations in the
frequency range from 220 MHz to 530 MHz. Simultaneous spatial information was
provided by the Nancay Radioheliograph (NRH) at several frequencies. Five
events were selected showing spikes at one or two and type III bursts at two or
more Nancay frequencies. The 3-dimensional geometry of the single events has
been reconstructed by applying different coronal density models. As a working
hypothesis it is assumed that emission at the plasma frequency or its harmonic
is the responsible radiation process for the spikes as well as for the type III
bursts. It has been found that the spike source location is consistent with the
backward extrapolation of the trajectory of the type III bursts, tracing a
magnetic field line. In one of the analyzed events, type III bursts with two
different trajectories originating from the same spike source could be
identified. These findings support the hypothesis that narrow band metric
spikes are closely related to the acceleration region.


title:
Low Frequency VLA Observations of Abell 754: Evidence for a Cluster
  Radio Halo and Possible Radio Relics

abstract:
  We present 74 MHz and 330 MHz VLA observations of Abell 754. Diffuse,
halo-like emission is detected from the center of the cluster at both
frequencies. At 330 MHz the resolution of 90'' distinguishes this extended
emission from previously known point sources. In addition to the halo and at a
much lower level, outlying steep-spectrum emission regions straddle the cluster
center and are seen only at 74 MHz. The location, morphology and spectrum of
this emission are all highly suggestive of at least one, and possibly two
cluster radio relics. Easily obtained higher resolution, higher sensitivity VLA
observations at both frequencies are required to confirm the extended nature of
the halo-like emission and the 74 MHz relic detections. However, since there is
prior evidence that this cluster is or has recently been in the process of a
major merger event, the possible discovery of relics in this system is of great
interest in light of recent observational and theoretical evidence in favor of
a merger-relic connection. We discuss the possible role the merger shock waves,
which are seen in the X-ray emission, may have played in the formation of the
halo and radio relics in A754.


title: AMS : A particle observatory in space

abstract:
  The expected physics and astrophysics capabilities of the AMS experiment on
board the International Space Station are briefly reviewed : high statistics
study of cosmic rays in a wide range of energies, search for primordial
antimatter, search for non-baryonic dark matter and, to some extent, gamma-ray
astronomy.


title:
Abundances in Stars from the Red Giant Branch Tip to the Near Main
  Sequence in M71: II. Iron Abundance

abstract:
  We present [Ffe/H] abundance results that involve a sample of stars with a
wide range in luminosity from luminous giants to stars near the turnoff in a
globular cluster. Our sample of 25 stars in M71 includes 10 giant stars more
luminous than the RHB, 3 horizontal branch stars, 9 giant stars less luminous
than the RHB, and 3 stars near the turnoff. We analyzed both Fe I and Fe II
lines in high dispersion spectra observed with HIRES at the W. M. Keck
Observatory. We find that the [Fe/H] abundances from both Fe I and Fe II lines
agree with each other and with earlier determinations. Also the [Fe/H] obtained
from Fe I and Fe II lines is constant within the rather small uncertainties for
this group of stars over the full range in Teff and luminosity, suggesting that
NLTE effects are negligible in our iron abundance determination. In this
globular cluster, there is no difference among the mean [Fe/H] of giant stars
located at or above the RHB, RHB stars, giant stars located below the RHB and
stars near the turnoff.


title: Circumstellar environment of RX Puppis

abstract:
  The symbiotic Mira, RX Pup, shows long-term variations in its mean light
level due to variable obscuration by circumstellar dust. The last increase in
extinction towards the Mira, between 1995 and 2000, has been accompanied by
large changes in the degree of polarization in the optical and red spectral
range. The lack of any obvious associated changes in the position angle may
indicate the polarization variations are driven by changes in the properties of
the dust grains (e.g. variable quantity of dust and variable particle size
distribution, due to dust grain formation and growth) rather than changes in
the viewing geometry of the scattering region(s), e.g. due to the binary
rotation.


title: Optical and Near-IR Monitoring of Symbiotic Binary Systems

abstract:
  Symbiotic stars are long-period interacting binary systems in which an
evolved red giant star transfers material to its much hotter compact companion.
Such a composition places them among the most variable stars. In addition to
periodic variations due to the binary motion they often show irregular changes
due to nova-like eruptions of the hot component. In some systems the cool giant
is a pulsating Mira-type star usually surrounded by a variable dust shell.
Here, I present results of optical and IR monitoring of symbiotic systems as
well as future prospects for such studies.


title: On the pulsation mode identification of short-period Galactic Cepheids

abstract:
  We present new theoretical Period-Radius (PR) relations for first overtone
Galactic Cepheids. Current predictions are based on several sequences of
nonlinear, convective pulsation models at solar chemical composition (Y=0.28,
Z=0.02) and stellar masses ranging from 3.0 to 5.5 Mo. The comparison between
predicted and empirical radii of four short-period Galactic Cepheids suggests
that QZ Nor and EV Sct are pulsating in the fundamental mode, whereas Polaris
and SZ Tau pulsate in the first overtone. This finding supports the mode
identifications that rely on the comparison between direct and
Period-Luminosity (PL) based distance determinations but it is somewhat at
variance with the mode identification based on Fourier parameters. In fact, we
find from our models that fundamental and first overtone pulsators attain, for
periods ranging from 2.7 to 4 d, quite similar phi_21 values, making mode
discrimination from this parameter difficult. The present mode identifications
for our sample of Cepheids are strengthened by the accuracy of their empirical
radius estimates, as well as by the evidence that predicted fundamental and
first overtone radii do not show, within the current uncertainty on the
Mass-Luminosity (ML) relation, any degeneracy in the same period range.
Accurate radius determinations are therefore an excellent tool to unambiguously
determine the pulsation modes of short-period Cepheids.


title:
Fourier decomposition and frequency analysis of the pulsating stars with
  P<1 d in the OGLE database. I. Monoperiodic Delta Scuti, RRc and RRab
  variables. Separation criteria and particularities

abstract:
  The OGLE database is revisited to investigate in more detail the properties
of the Fourier parameters. Methodological improvements led us to identify a
clear separation among High-Amplitude Delta Scuti (HADS), RRc and RRab stars.
The bimodal distribution of the R21 parameter in HADS stars is explained as a
contamination effect from RRc stars: there is evidence that all stars with
0.20<P<0.25 d are RRc variables. The previously claimed existence of a subclass
of unusual HADS is demonstrated to be a spurious result. Candidate overtone
pulsators are found among HADS and RRc variables. The properties of the Fourier
parameters are discussed as a function of the physical conditions in the stars
involved. Among the field RRab stars we detected different light-curve groups
producing distinct "tails" in the Fourier plots for P>0.55 d; evolutionary
phases or the combination of different physical conditions (not only
metallicity) are suggested to explain this separation, observed also in the
cluster RRab stars. The stellar parameters of RRc stars in a given globular
cluster show different tendencies than those of RRc stars from different
clusters.


title: High Energy Neutrino Fluxes from Cosmic Accelerators

abstract:
  We constrain high-energy neutrino fluxes with the observed cosmic ray and
gamma ray fluxes, include flavor oscillations and propagation through Earth,
and show that blazars could possibly be detected by cubic-kilometer neutrino
telescopes.


title: Constraining the Cosmological Parameters using Strong Lensing

abstract:
  We investigate the potentiality of using strong lensing clusters to constrain
the cosmological parameters Omega_m and Omega_lambda. The existence of a
multiple image system with known redshift allows, for a given (Omega_m,
Omega_lambda) cosmology, absolute calibration of the total mass deduced from
lens modelling. Recent Hubble Space Telescope (HST) observations of galaxy
clusters reveal a large number of multiple images, which are predicted to be at
different redshifts. If it is possible to measure spectroscopically the
redshifts of many multiple images then one can in principle constrain
(Omega_m,Omega_lambda) through ratios of angular diameter distances,
independently of any external assumptions. For a regular/relaxed cluster
observed by HST with 3 multiple image systems, each with different
spectroscopic redshifts, we show by analytic calculation that the following
uncertainties can be expected: Omega_m=0.30 +/- 0.11, Omega_lambda=0.70 +/-
0.23 or Omega_m=1.00 +/- 0.17, Omega_lambda=0.00 +/- 0.48 for the two most
popular world models. Numerical tests on simulated data confirm these good
constraints, even in the case of more realistic cluster potentials, such as
bimodal clusters, or when including perturbations by galaxies. To investigate
the sensitivity of the method to different mass profiles, we also use an
analytic ``pseudo-elliptical'' Navarro, Frenk & White profile in the
simulations. These constraints can be improved if more than 3 multiple images
with spectroscopic redshifts are observed, or by combining the results from
different clusters. Some prospects on the determination of the cosmological
parameters with gravitational lensing are given.


title: The Globular Cluster System of NGC 1316 (Fornax A)

abstract:
  We have studied the Globular Cluster System of the merger galaxy NGC 1316 in
Fornax, using CCD BVI photometry. A clear bimodality is not detected from the
broadband colours. However, dividing the sample into red (presumably metal-
rich) and blue (metal-poor) subpopulations at B-I=1.75, we find that they
follow strikingly different angular distributions. The red clusters show a
strong correlation with the galaxy elongation, but the blue ones are circularly
distributed. No systematic difference is seen in their radial profile and both
are equally concentrated.
  We derive an astonishingly low Specific Frequency for NGC 1316 of only
Sn=0.9, which confirms with a larger field a previous finding by Grillmair et
al. (1999). Assuming a "normal" Sn of ~4 for early-type galaxies, we use
stellar population synthesis models to estimate in 2 Gyr the age of this
galaxy, if an intermediate-age population were to explain the low Sn we
observe. This value agrees with the luminosity-weighted mean age of NGC 1316
derived by Kuntschner & Davies (1998) and Mackie & Fabbiano (1998).
  By fitting t5 functions to the Globular Cluster Luminosity Function (GCLF),
we derived the following turnover magnitudes: B=24.69 +/- 0.15, V=23.87 +/-
0.20 and I=22.72 +/- 0.14. They confirm that NGC 1316, in spite of its outlying
location, is at the same distance as the core of the Fornax cluster.


title:
Abundances in Stars from the Red Giant Branch Tip to the Near the Main
  Sequence in M71: I. Sample Selection, Observing Strategy and Stellar
  Parameters

abstract:
  We present the sample for an abundance analysis of 25 members of M71 with
luminosities ranging from the red giant branch tip to the upper main sequence.
The spectra are of high dispersion and of high precision. We describe the
observing strategy and determine the stellar parameters for the sample stars
using both broad band colors and fits of H$\alpha$ profiles. The derived
stellar parameters agree with those from the Yale$^2$ stellar evolutionary
tracks to within 50 -- 100K for a fixed log g, which is within the level of the
uncertainties.


title: MLAPM - a C code for cosmological simulations

abstract:
  We present a computer code written in C that is designed to simulate
structure formation from collisionless matter. The code is purely grid-based
and uses a recursively refined Cartesian grid to solve Poisson's equation for
the potential, rather than obtaining the potential from a Green's function.
Refinements can have arbitrary shapes and in practice closely follow the
complex morphology of the density field that evolves. The timestep shortens by
a factor two with each successive refinement. It is argued that an appropriate
choice of softening length is of great importance and that the softening should
be at all points an appropriate multiple of the local inter-particle
separation. Unlike tree and P3M codes, multigrid codes automatically satisfy
this requirement. We show that at early times and low densities in cosmological
simulations, the softening needs to be significantly smaller relative to the
inter-particle separation than in virialized regions. Tests of the ability of
the code's Poisson solver to recover the gravitational fields of both
virialized halos and Zel'dovich waves are presented, as are tests of the code's
ability to reproduce analytic solutions for plane-wave evolution. The times
required to conduct a LCDM cosmological simulation for various configurations
are compared with the times required to complete the same simulation with the
ART, AP3M and GADGET codes. The power spectra, halo mass functions and
halo-halo correlation functions of simulations conducted with different codes
are compared.


title: The complete ISO spectrum of NGC 6302

abstract:
  We present the combined Infrared Space Observatory Short-Wavelength
Spectrometer and Long-Wavelength Spectrometer 2.4--197 micron spectrum of the
Planetary Nebula NGC 6302 which contains in addition to strong atomic lines, a
series of emission features due to solid state components. The broad wavelength
coverage enables us to more accurately identify and determine the properties of
both oxygen- and carbon-rich circumstellar dust. A simple model fit was made to
determine the abundance and typical temperature of the amorphous silicates,
enstatite and forsterite. Forsterite and enstatite do have roughly the same
abundance and temperature. The origin and location of the dust in a toroidal
disk around the central star are discussed.


title:
Probing the Universe After Cosmological Recombination Through the Effect
  of Neutral Lithium on the Microwave Background Anisotropies

abstract:
  I show that neutral lithium couples strongly to the cosmic microwave
background (CMB) through its 6708A resonant transition after it recombines at
z~500. At observed wavelengths of <335 micron, the CMB anisotropies are
significantly altered since the optical depth for resonant scattering by
neutral lithium is substantial, of order 0.5. The scattering would suppress the
original anisotropies, but will generate strong new anisotropies in the CMB
temperature and polarization on sub-degree scales (l>100). Observations at
different wavelengths in this spectral regime can probe different thin slices
of the early universe. The anisotropy noise contributed by continuum radiation
from foreground far--infrared sources could be taken out by subtracting maps at
slightly different wavelengths. Detection of the above effects can be used to
study structure at z<500 and to constrain the primordial abundance and
recombination history of lithium.


title: The ATCA Intraday Variability Survey of Extragalactic Radio Sources

abstract:
  We present the results of an Australia Telescope Compact Array (ATCA) survey
for intra-day variability (IDV) of the total and polarized flux densities of
118 compact, flat spectrum, extragalactic radio sources from the Parkes 2.7 GHz
Survey. A total of 22 total flux density IDV sources were discovered and 15
sources were found to show IDV of their polarized flux density. We discuss the
statistical properties of the IDV sources, including the distribution of source
modulation indices, and the dependence of the variability amplitude on source
spectral index and on Galactic position. We suggest interstellar scintillation
(ISS) in the Galactic interstellar medium as the most likely mechanism for IDV.
Even so, the inferred high brightness temperatures cannot be easily explained.


title:
Restoring the full velocity field in the gaseous disk ofthe spiral
  galaxy NGC 157

abstract:
  We analyse the line-of-sight velocity field of ionized gas in the spiral
galaxy NGC 157 which has been obtained in the H\alpha emission at the 6m
telescope of SAO RAS. The existence of systematic deviations of the observed
gas velocities from pure circular motion is shown. A detailed investigation of
these deviations is undertaken by applying a Fourier analysis of the azimuthal
distributions of the line-of-sight velocities at different distances from the
galactic center. As a result of the analysis, all the main parameters of the
wave spiral pattern are determined: the corotation radius, the amplitudes and
phases of the gas velocity perturbations at different radii, and the velocity
of circular rotation of the disk corrected for the velocity perturbations due
to spiral arms. At a high confidence level, the presence of the two giant
anticyclones in the reference frame rotating with the spiral pattern is shown;
their sizes and the localization of their centers are consistent with the
results of the analytic theory and of numerical simulations. Besides the
anticyclones, the existence of cyclones in residual velocity fields of spiral
galaxies is predicted. In the reference frame rotating with the spiral pattern
these cyclones have to reveal themselves in galaxies where a radial gradient of
azimuthal residual velocity is steeper than that of the rotation velocity
(abridged).


title: A Doppler-like strong light-matter interaction

abstract:
  While complicated, unreliable alternatives to Doppler effect were proposed,
an elementary optical light- matter interaction provides one which is commonly
observed in the labs, but with a distortion due to the use of short, powerful
laser pulses. It is generally assumed that Raman scattering in gases is
incoherent. This assumption fails if the pressure is lowered enough to increase
the relaxation times over the length of light pulses; the ''Impulsive
Stimulated Raman Scattering'' (ISRS), generally used to study dense matter with
ultrashort laser pulses, is adapted to the low energy pulses making the
incoherent light beams; the usual light is redshifted by some very low pressure
gases while it propagates.
  To produce this adapted ISRS called ''Incoherent Light Spatially Coherent
Raman Scattering" (ILSCRS), a molecule must have an hyperfine structure:
polyatomic molecules must be heavy or have odd numbers of electrons; light
atoms and the other molecules must be perturbed by a Stark or Zeeman effect.
  ILSCRS redshifts may be distinguished from Doppler redshifts using a very
difficult to observe dispersion of ILSCRS redshifts. This dispersion may
explain the discrepancies of the fine structures in the spectra of the quasars,
presently attributed to a variation of the fine structure constant.
  While the present interpretation of the Lyman forest in the spectra of
quasars requires clouds stressed, for instance, by sheets of dark matter,
ILSCRS interpretation requires only usual physical concepts. It produces
thermal radiations from short wavelengths, just as dust.


title: A self-regulating braking mechanism in black hole X-ray binaries

abstract:
  The outbursts of black hole X-ray transients can be understood as caused by a
limit cycle instability in the accretion disk, similar to dwarf nova outbursts.
For adequately low mass overflow rates from the companion star long outburst
recurrence times are expected. But the fact that we find predominantly long
recurrence times or that only one X-ray nova outburst was detected at all poses
a problem. The question arises whether any braking mechanism could act in a way
that long recurrence times are favored. We suggest that a circumbinary disk
exists and brakes the orbital motion of the binary stars by tidal interaction.
The irradiation during an outburst leads to mass loss by winds from the
circumbinary disk, releaving the braking force until the removed matter is
refilled by diffusion from outer parts. We show that this reduction of braking
will self-adjust the mass transfer to the marginal rate that gives long
recurrence times.


title:
Host galaxies and nuclear structure of AGN with H_2O megamasers as seen
  with HST

abstract:
  We present results of an HST survey in Halpha and continuum filters of a
sample of H_2O megamaser galaxies compiled by Braatz et al., all of which
contain AGN. These observations allow us to study the AGN/host-galaxy
connection, e.g. study the relation between the parsec scale masing disk/torus,
bipolar outflows, and large scale properties of the galaxies such as dust
lanes, signs for interaction, and galaxy types. A number of galaxies indeed
show large-scale bi-polar Halpha structures which, however, are more
reminiscent of outflows then excitation cones. Most megamaser galaxies are
found in spiral galaxies. Only one galaxy in the original sample is known to be
an elliptical and one galaxy imaged by us shows clear signs of interactions. In
all cases we see evidence for obscuration of the nucleus (e.g. dust-lanes) in
our color maps and the disk galaxies are preferentially edge on. This suggests
that the nuclear masing disk has some relation to the large scale properties of
the galaxy and the dust distribution.


title: Detached Eclipsing Binaries for Parallax Measurement

abstract:
  A list of 50 bright Detached Eclipsing Binaries proposed for precise parallax
measurements for the FAME is presented. The eclipsing binaries, with precise
distances and with photometric and double-line spectroscopic orbits determined,
are essential for a full calibration of relations that could be used for very
precise distance determination of globular clusters, LMC, SMC, and perhaps also
M31 and M33.


title: The SZ effect as a cosmological discriminator

abstract:
  We show how future measurements of the SZ effect (SZE) can be used to
constrain the cosmological parameters. We combine the SZ information expected
from the Planck full-sky survey, N(S), where no redshift information is
included, with the N(z) obtained from an optically-identified SZ-selected
survey covering less than 1% of the sky. We demonstrate how with a small
subsample (approx. 300 clusters) of the whole SZ catalogue observed optically
it is possible to drastically reduce the degeneracy among the cosmological
parameters. We have studied the requirements for performing the optical
follow-up and we show the feasibility of such a project. Finally we have
compared the cluster expectations for Planck with those expected for Newton-XMM
during their lifetimes. It is shown that, due to its larger sky coverage,
Planck will detect a factor approx. 5 times more clusters than Newton-XMM and
also with a larger redshift coverage.


title: The Cosmic-Ray antiproton flux between 3 and 49 GeV

abstract:
  We report on a new measurement of the cosmic ray antiproton spectrum. The
data were collected by the balloon-borne experiment CAPRICE98 which was flown
on 28-29 May 1998 from Fort Sumner, New Mexico, USA. The experiment used the
NMSU-WIZARD/CAPRICE98 balloon-borne magnet spectrometer equipped with a gas
Ring Imaging Cherenkov (RICH) detector, a time-of-flight system, a tracking
device consisting of drift chambers and a superconducting magnet and a
silicon-tungsten calorimeter. The RICH detector was the first ever flown
capable of mass-resolving charge-one particles at energies above 5 GeV.
  A total of 31 antiprotons with rigidities between 4 and 50 GV at the
spectrometer were identified with small backgrounds from other particles. The
absolute antiproton energy spectrum was determined in the kinetic energy region
at the top of the atmosphere between 3.2 and 49.1 GeV. We found that the
observed antiproton spectrum and the antiproton-to-proton ratio are consistent
with a pure secondary origin. However, a primary component may not be excluded.


title: Observations with the HEGRA stereoscopic system

abstract:
  The HEGRA system of imaging air Cherenkov telescopes has successfully
pioneered the stereoscopic observation technique of extensive air showers. The
observational method is briefly described and important results of recent
observations of sources of photons with TeV($=10^{12}$ eV)-energies are
summarized: The first detection of a TeV $\gamma$-ray signal from the
shell-type supernova remnant Cassiopeia A and preliminary results obtained from
the observation of strong variability of the extragalactic source Mkn 421
during observations carried out from February to May 2000.


title: Metallicities for Double Mode RR Lyrae in the Large Magellanic Cloud

abstract:
  Metallicities for six double mode RR Lyrae's (RRd's) in the Large Magellanic
Cloud have been estimated using the DeltaS method. The derived [Fe/H] values
are in the range [Fe/H] = -1.09 to -1.78 (or -0.95 to -1.58, adopting a
different calibration of [Fe/H] vs DeltaS). Two stars in our sample are at the
very metal rich limit of all RRd's for which metal abundance has been
estimated, either by direct measure (for field objects) or on the basis of the
hosting system (for objects in globular clusters or external galaxies). These
metal abundances, coupled with mass determinations from pulsational models and
the Petersen diagram, are used to compare the mass-metallicity distribution of
field and cluster RR Lyrae variables. We find that field and cluster RRd's seem
to follow the same mass-metallicity distribution, within the observational
errors, strengthening the case for uniformity of properties between field and
cluster variables At odds to what is usually assumed, we find no significative
difference in mass for RR Lyrae's in globular clusters of different metallicity
and Oosterhoff types, or there may even be a difference contrary to the
commonly accepted one, depending on the metallicity scale adopted to derive
masses. This ``unusual'' result for the mass-metallicity relation is probably
due, at least in part, to the inclusion of updated opacity tables in the
computation of metal-dependent pulsation models.


title: Applications of Microlensing to Stellar Astrophysics

abstract:
  Over the past decade, microlensing has developed into a powerful tool to
study stellar astrophysics, especially stellar atmospheres, stellar masses, and
binarity. I review this progress. Stellar atmospheres can be probed whenever
the source in a microlensing event passes over the caustic (contour of infinite
magnification) induced by the lens because the caustic effectively resolves the
source. Broad-band observations of four events have yielded limb-darkening
measurements, which in essence map the atmospheric temperature as a function of
depth. And now, for the first time, spectroscopic observations of one event
promise much richer diagnostics of the source atmosphere. In the past two
years, a practical method has finally been developed to systematically measure
the lens masses in microlensing events. This will permit a census of all
massive objects, both dark and luminous, in the Galactic bulge, including
low-mass stars, brown dwarfs, white dwarfs, neutron stars, and black holes. The
method combines traditional ground-based photometry with astrometric and
photometric measurements by the Space Interferometry Mission (SIM) in solar
orbit. Using a related technique SIM can also obtain accurate (>~ 1%) mass
measurement of a dozen or so nearby stars, thus enabling precision tests of
stellar models. Binary lenses can give rise to dramatic and easily detectable
microlensing signatures, even for large mass ratios. This makes microlensing a
potentially powerful probe of the companion mass distribution, especially in
the Galactic bulge where this function is difficult to probe by other
techniques.


title:
Can Jupiters be found by monitoring Galactic Bulge microlensing events
  from northern sites?

abstract:
  In 1998 the EXPORT team monitored microlensing event lightcurves using a CCD
camera on the IAC 0.8m telescope on Tenerife to evaluate the prospect of using
northern telescopes to find microlens anomalies that reveal planets orbiting
the lens stars. The high airmass and more limited time available for
observations of Galactic Bulge sources makes a northern site less favourable
for microlensing planet searches. However, there are potentially a large number
of northern 1m class telescopes that could devote a few hours per night to
monitor ongoing microlensing events. Our IAC observations indicate that
accuracies sufficient to detect planets can be achieved despite the higher
airmass.


title: Background galaxies as reddening probes throughout the Magellanic Clouds

abstract:
  We study the spectral properties in the range 3600 \AA - 6800 \AA of the
nuclear region of galaxies behind the Magellanic Clouds. The radial velocities
clarified the nature of the objects as background galaxies or extended objects
belonging to the Clouds. For most galaxies behind the main bodies of the LMC
and SMC, radial velocities were measured for the first time. In the present
sample typical LMC background galaxies are nearby (4000 < V(km/s) < 6000),
while SMC's are considerably more distant (10000 < V(km/s) < 20000). We
determine the reddening in each line of sight by matching a reddening-free
galaxy template with comparable stellar population. For the LMC main body we
derive a combined Milky Way and internal reddening value E(B-V)$_{MW+i}$ =
0.12$\pm$0.10, while for the SMC E(B-V)$_{MW+i}$ = 0.05$\pm$0.05. By
subtracting Milky Way reddening values for galaxies projected onto the
surroundings of each Cloud, we estimate average internal reddening values
$\Delta$E(B-V)$_i$ = 0.06 and 0.04, respectively for the main bodies of the LMC
and SMC. The Clouds are optically thin, at least in the directions of the
studied background galaxies which are often difficult to be identified as such
on ESO/SERC sky survey images. Nevertheless, more reddened zones may occur
where it is difficult to identify galaxies.


title:
Discovery of circular polarization in the Intermediate Polar 1WGA
  J1958.2+3232

abstract:
  We report on UBVRI polarimetry of the recently identified Intermediate Polar
1WGA J1958.2+3232, carried out on 2000 August, 4-6 at the Nordic Optical
Telescope. Circular polarization was detected in R and I bands with an
increasing absolute mean value with wavelength. There is evidence of possible
modulation of the circular polarization at twice the previously reported white
dwarf spin period, suggesting that it is the true period and that the
modulation in optical and X-ray is dominated by the first harmonic. Indication
of modulation at the orbital period is also present.


title: On the nature of the hard X-ray source 4U2206+54

abstract:
  The recent discovery of a ~9.5-d period in the X-ray lightcurve of the
massive X-ray binary 4U2206+54 has opened the possibility that it is a Be/X-ray
binary with an unusually close orbit, which, together with its low intrinsic
luminosity, suggests that the system is actually a Be + WD binary, in which a
white dwarf accretes material from the dense circumstellar disc surrounding a
classical Be star. In this paper we present new X-ray observations and for the
first time high-resolution optical spectroscopy of the source. We show that
both the X-ray behaviour and the characteristics of the optical counterpart, BD
+53 2790, are more consistent with a neutron star accreting from the wind of an
early-type star. The X-ray lightcurve shows irregular flaring and no
indications of pulsations, while the very high hydrogen column density supports
accretion from a dense wind. BD +53 2790 is shown not to be a classical Be
star, as believed until now, but rather a very peculiar late O-type active
star, exhibiting emission components in the HeII lines, complex spectral
variability and strong wind resonance lines in the ultraviolet. Though many of
the characteristics of the spectrum resemble those of the He-rich stars, the
absence of HeI variability makes a connection unlikely. The spectrum is
compatible with a composite of two stars of similar spectral type, though
circumstantial evidence points to a single very peculiar active early-type
star. This adds weight to the growing evidence that the traditional
subdivisions of supergiant and Be/X-ray binaries fail to cover the whole
phenomenology of massive X-ray binaries.


title:
Molecular Excitation and Differential Gas-Phase Depletions in the IC
  5146 Dark Cloud

abstract:
  We present a combined near-infrared and molecular-line study of 25' x 8' area
in the Northern streamer of the IC 5146 cloud. Using the technique pioneered by
Lada et al 1994, we construct a Gaussian smoothed map of the infrared
extinction with the same resolution as the molecular line observations in order
to examine correlations of integrated intensities and molecular abundances with
extinction for C17O, C34S, and N2H+. We find that over a visual extinction
range of 0 to 40 magnitudes, there is good evidence for the presence of
differential gas-phase depletions in the densest portions of IC 5146. Both CO
and CS exhibit a statistically significant (factor of ~3) abundance reduction
near Av ~ 12 magnitudes while, in direct contrast, at the highest extinctions,
Av > 10 magnitudes, N2H+ appears relatively undepleted. Moreover, for Av < 4
magnitudes there exists little or no N2H+. This pattern of depletions is
consistent with the predictions of chemical theory.


title: A Magnetohydrodynamic Nonradiative Accretion Flow in Three Dimensions

abstract:
  We present a global magnetohydrodynamic (MHD) three dimensional simulation of
a nonradiative accretion flow originating in a pressure supported torus. The
evolution is controlled by the magnetorotational instability which produces
turbulence. The flow forms a nearly Keplerian disk. The total pressure scale
height in this disk is comparable to the vertical size of the initial torus.
Gas pressure dominates only near the equator; magnetic pressure is more
important in the surrounding atmosphere. A magnetically dominated bound outflow
is driven from the disk. The accretion rate through the disk exceeds the final
rate into the hole, and a hot torus forms inside 10 r_g. Hot gas, pushed up
against the centrifugal barrier and confined by magnetic pressure, is ejected
in a narrow, unbound, conical outflow. The dynamics are controlled by magnetic
turbulence, not thermal convection, and a hydrodynamic alpha model is
inadequate to describe the flow. The limitations of two dimensional MHD
simulations are also discussed.


title:
Double Bars in Disk Galaxies: Dynamical Decoupling of
  Non-Self-Gravitating Gaseous Bars

abstract:
  We find that nuclear rings in barred galaxies can be subject to a new type of
non-self-gravitational dynamical instability. The instability leads to the
formation of gaseous molecular bars with pattern speeds which are substantially
slower than speeds of the primary stellar bars. This spectacular decoupling of
nuclear bars from the underlying gravitational potential is triggered but is
not driven by the gas viscosity. We find that low-viscosity systems can spend a
substantial period of time in a fully decoupled state, with the nuclear bar
slowly tumbling in the gravitational field of the primary bar. Higher viscosity
systems form nuclear bars which librate about the primary bar. The shape of a
nuclear bar, i.e., its eccentricity, correlates strongly with the angle between
the bars. We also find that such decoupling, partial or full, most probably
will be associated with bursts of star formation and with gas inflow across the
inner (Lindblad) resonance zone towards smaller radii.


title: The Phase-Space Density Profiles of Cold Dark Matter Halos

abstract:
  We examine the coarse-grained phase-space density profiles of a set of
recent, high-resolution simulations of galaxy-sized Cold Dark Matter (CDM)
halos. Over two and a half decades in radius the phase-space density closely
follows a power-law, $\rho/\sigma^3 \propto r^{-\alpha}$, with $\alpha =
1.875$. This behaviour matches the self-similar solution obtained by
Bertschinger for secondary infall in a uniformly expanding universe. On the
other hand, the density profile corresponding to Bertschinger's solution (a
power-law of slope $r^{2\alpha-6}$) differs significantly from the density
profiles of CDM halos. We show that isotropic mass distributions with power-law
phase-space density profiles form a one-parameter family of structures
controlled by $\kappa$, the ratio of the velocity dispersion to the peak
circular velocity. For $\kappa=\alpha=1.875$ one recovers the power-law
solution $\rho \propto r^{2\alpha-6}$. For $\kappa$ larger than some critical
value, $\kappa_{cr}$, solutions become non-physical, leading to negative
densities near the center. The critical solution, $\kappa =\kappa_{cr}$, has
the narrowest phase-space density distribution compatible with the power-law
phase-space density stratification constraint. Over three decades in radius the
critical solution is indistinguishable from an NFW profile. Our results thus
suggest that the NFW profile is the result of a hierarchical assembly process
that preserves the phase-space stratification of Bertschinger's infall model
but which ``mixes'' the system maximally, perhaps as a result of repeated
merging.