title: Cosmological Surveys at Submillimetre Wavelengths

abstract:
  One of the major goals of observational cosmology is to acquire empirical
data that has the diagnostic power to develop the theoretical modelling of the
high-redshift universe, ultimately leading to an accurate understanding of the
processes by which galaxies and clusters form and subsequently evolve. New
bolometer arrays operating on the world's largest submillimetre telescopes now
offer a unique view of the high-redshift universe through unbiassed surveys
with unprecedented sensitivity. For brevity, except when there is a need to be
more specific, the FIR to millimetre wavelength regime (100um < lambda <
6000um) will be referred to as the ``submillimetre'' (submm). One of the major
challenges in this field is to accurately quantify the star-formation history
of submm-selected galaxies, particularly those at redshifts > 1, and determine
their contribution to the submm extragalactic background. The field of
observational cosmology will be revolutionized during the course of the next 10
years due to the variety of powerful new ground-based, airborne and satellite
facilities, particularly those operating at FIR to millimetre wavelengths. This
review summarises the results from the recent blank-field submm surveys, and
describes the future observations that will provide accurate source-counts over
wider ranges of wavelength and flux-density, constrain the spectral energy
distributions of the submm-selected galaxies and accurately constrain the
redshift distribution and submm luminosity function by removing the current
ambiguities in the optical, IR and radio counterparts.


title: Dust Echos from Gamma Ray Bursts

abstract:
  The deviation from the power-law decline of the optical flux observed in GRB
970228 and GRB 980326 has been used recently to argue in favor of the
connection between GRBs and supernovae. We consider an alternative explanation
for this phenomenon, based on the scattering of a prompt optical burst by 0.1
solar masses of dust located beyond its sublimation radius 0.1-1 pc from the
burst. In both cases, the optical energy observed at the time of the first
detection of the afterglow suffices to produce an echo after 20-30 days, as
observed. Prompt optical monitoring of future bursts and multiband photometry
of the afterglows will enable quantitative tests of simple models of dust
reprocessing and a prediction of the source redshift.


title: The Evolution of Galaxies on Cosmological Timescales

abstract:
  I discuss the chemical and spectrophotometric evolution of galaxies over
cosmological timescales and present a first attempt to treat both aspects in a
chemically consistent way. In our evolutionary synthesis approach, we account
for the increasing metallicity of successive generations of stars and use sets
of stellar evolutionary tracks, stellar yields, spectra, etc. for various
metallicities. This gives a more realistic description of nearby galaxies,
which are observed to have broad stellar metalllicty distributions, as well as
of young galaxies at high redshift. Selected results are presented for the
chemo-cosmological evolution of galaxies as compared to QSO absorption line
observations and for the spectrophotometric evolution of galaxies to very high
redshifts. On cosmological timescales, intercations are important drivers of
galaxy evolution. Neglecting dynamical aspects we study the effects of
interaction-induced starbursts on the spectrophotometric and chemical evolution
of galaxies and briefly discuss the formation of star clusters and Tidal Dwarf
Galaxies in this context.


title: Young Star Clusters: Metallicities, Ages, and Masses

abstract:
  Observations of Young Star Cluster ({\bf YSC}) systems in interacting
galaxies are reviewed with particular emphasis on their Luminosity Functions
({\bf LF}) and colour distributions. A few spectroscopic abundance measurements
are available. They will be compared to YSC abundance predictions from spiral
galaxy models. Evolutionary synthesis models allow to derive ages for
individual YSCs on the basis of their broad band colours. With individual YSC
ages, models predict the future colour and luminosity evolution of the YSC
systems that will be compared - after a Hubble time - to observations of old
Globular Cluster ({\bf GC}) systems. Using model M/L ratios as a function of
age, YSC masses can be estimated. Age spread effects in young systems can cause
the shape of the LF to substantially differ from the shape of the underlying
mass function. Major sources of uncertainty are the metallicity, dust
reddening, and observational colour uncertainties.


title:
Radiation Spectra of Advection Dominated Accretion Flows around Kerr
  Black Holes

abstract:
  We study the formation of the spectra in advection dominated accretion flows
(ADAFs) around Kerr black holes. We use a Monte Carlo approach and fully
general relativistic treatment to follow the paths of individual photons and
model their scattering with mildly relativistic, thermal electrons of the two
temperature plasma present in the flow. We study the influence of the accretion
rate, black hole mass, black hole angular momentum, and the strength of the
small scale magnetic field present in the plasma on the resulting spectra. The
impact of the black hole angular momentum on the spectra is present and can be
distinguished from the influence of changes in other parameters. This property
of the models should be taken into account when modeling the individual sources
and the population of inefficiently accreting black holes in the Universe.


title:
On breaking the age-metallicity degeneracy in early-type galaxies:
  Outflows versus Star Formation Efficiency

abstract:
  A simple model of chemical enrichment in cluster early-type galaxies is
presented where the main parameters driving the formation of the stellar
component are reduced to four: infall timescale (tf), formation epoch (zF),
star formation efficiency (Ceff) and fraction of gas ejected in outflows
(Bout). We find that only variations in Bout or Ceff can account for the
colour-magnitude relation, so that the most luminous galaxies had low values of
ejected gas and high efficiencies. The combination of chemical enrichment
tracks with population synthesis models is used to explore the correlation
between mass-to-light ratios and masses. A significant slope mismatch is found
between stellar and total M/L ratios, which cannot be explained by an age
spread and implies a non-linear correlation between total and stellar mass. The
sequences driven by star formation efficiency and outflows are shown to predict
different trends at high redshift. Measurement of the dependence of the tilt of
the fundamental plane on redshift will break the degeneracy between outflows
and star formation efficiency, which will enable us to determine whether the
colour-magnitude relation is controlled by age or metallicity.


title: Statistical Study of Short Quiescent Times Between Flares

abstract:
  The study of the statistical distribution of short quiescent times ($\le$ 30
minutes) between solar flares has been investigated on a 1D MHD model. A power
law behaviour is found which indicates the existence of sympathetic flaring.
This prediction is supported by recent observations.


title:
Reversing type II migration: resonance trapping of a lighter giant
  protoplanet

abstract:
  We present a mechanism related to the migration of giant protoplanets
embedded in a protoplanetary disc whereby a giant protoplanet is caught up,
before having migrated all the way to the central star, by a lighter outer
giant protoplanet. This outer protoplanet may get captured into the 2:3
resonance with the more massive one, in which case the gaps that the two
planets open in the disc overlap. Two effects arise, namely a squared mass
weighted torque imbalance and an increased mass flow through the overlapping
gaps from the outer disc to the inner disc, which both play in favour of an
outwards migration. Indeed under the conditions presented here, which describe
the evolution of a pair of protoplanets respectively Jupiter and Saturn sized,
the migration is reversed, while the planets semi-major axis ratio is constant
and the eccentricities are confined to small values by the disc material. The
long-term behaviour of the system is briefly discussed, and could account for
the high eccentricities observed for the extrasolar planets with semi-major
axis a>0.2 AU.


title: A microlensing search for cold molecular clouds in Virgo

abstract:
  We report preliminary results from a first season of photometric monitoring
of 600 quasars behind the Virgo galaxy cluster with the aim of detecting
microlensing by the cluster dark matter. Our project is sensitive to dark
objects of surface mass densities down to ~20 g/cm^2. We are thus capable of
detecting diffuse objects, such as cold molecular clouds, unlike all Galactic
microlensing surveys whose surface mass density limits are > 10^4 g/cm^2. The
average optical depth to microlensing of quasars through the central 30 sq.
deg. of Virgo is ~1x10^-3. We report a null detection which implies that less
than half the dark matter in Virgo is in objects of mass ~10^-5 solar masses,
of surface mass density > 20 g/cm^2, at 90% confidence.


title: The Ratio of Total to Selective Extinction Toward Baade's Window

abstract:
  We measure the ratio of total to selective extinction, R_{VI}=A_V/E(V-I),
toward Baade's Window by comparing the VIK colors of 132 Baade's Window G and K
giants from Tiede, Frogel, & Terndrup with the solar-neighborhood (V-I),(V-K)
relation from Bessell & Brett. We find R_{VI}=2.283 +/- 0.016, and show that
our measurement has no significant dependence on stellar type from G0 to K4.
Adjusting the Paczynski et al. determination of the centroid of the dereddened
Baade's Window clump for this revised value of $R_{VI}$, we find I_{0,RC}=14.43
and (V-I)_{0,RC}=1.058. This implies a distance to the Baade's Window clump of
d_{BW} = 8.63 +/- 0.16 kpc, where the error bar takes account of statistical
but not systematic uncertainties.


title: Superhumps in V348 Pup

abstract:
  The eclipsing novalike cataclysmic variable star V348 Pup exhibits a
persistent luminosity modulation with a period 6 per cent longer than its 2.44
hour orbital-period (Porb). This has been interpreted as a `positive superhump'
resulting from a slowly precessing non-axisymmetric accretion disc
gravitationally interacting with the secondary. We find a clear modulation of
mid-eclipse times on the superhump period, which agrees well with the
predictions of a simple precessing eccentric disc model. Our modelling shows
that the disc light centre is on the far side of the disc from the donor star
when the superhump reaches maximum light. This phasing suggests a link between
superhumps in V348 Pup and late superhumps in SU UMa systems. Modelling of the
full lightcurve and maximum entropy eclipse mapping both show that the disc
emission is concentrated closer to the white dwarf at superhump maximum than at
superhump minimum. We detect additional signals consistent with the beat
periods between the implied disc precession period and both (1/2)Porb and
(1/3)Porb.


title: Mass Loss On the Horizontal Branch: an Application to NGC6791

abstract:
  The presence of a substantial number of hot stars in the extremely
metal-rich} open cluster NGC6791 has been a mystery. If these hot stars are in
their core helium burning phase, they are significantly bluer (hotter) than
predicted by canonical stellar evolution theory. No obvious explanation is
available yet. We consider the effects of mass loss during the evolution of
horizontal branch (HB) stars as their possible origin. We find that the
addition of mass loss causes HB stars to evolve to be hotter and fainter. Mass
loss has a more pronounced effect for less massive stars and thus naturally
widens the temperature (and color) distribution on the HB. If mass loss rates
are higher for more metal-rich stars, this phenomenon would be even more
pronounced in the metal-rich populations, such as NGC6791. We find that mass
loss on the HB may be a viable method of forming subdwarf B (sdB) stars both in
the field and in clusters, especially when the metallicity is high.


title: Possible evidence of quark matter in neutron star X-ray binaries

abstract:
  We study the spin evolution of X-ray neutron stars in binary systems, which
are being spun up by mass transfer from accretion disks. Our investigation
reveals that a quark phase transition resulting from the changing central
density induced by the changing spin, can lead to a pronounced peak in the
frequency distribution of X-ray neutron stars. This finding provides one of
several possible explanations available in the literature, or at least a
contributor to part of the observed anomalous frequency distribution of neutron
stars in low-mass X-ray binaries (LMXBs), which lie in a narrow band centered
at about 300 Hz, as found by the Rossi Explorer (RXTE).


title: HST spectroscopy of the double QSO HS 1216+5032 AB

abstract:
  (Abridged) We report on HST FOS observations of the double QSO HS 1216+5032
AB (z(A)=1.455; z(B)=1.451, and angular separation theta=9 arcsec). An unusual
broad-absorption-line (BAL) system is observed only in the B component: maximum
outflow velocity of ~5000 km/s; probably a mixture of broad and narrow
components. Observed ions are: HI, CII, CIII, NIII, NV, OVI, and possibly SIV
and SVI. We also discuss two outstanding intervening systems: (1) a complex CIV
system at z=0.72 of similar strength in A and B, with a velocity span of 1500
km/s; and (2) a possible strong MgII system at z=0.04 observed in B only.
  Assuming HS 1216+5032 is a binary QSO, the size of Ly-alpha forest clouds is
constrained using S~ 80 /h_50 kpc at redshifts between z=1.15 and 1.45. Four
Ly-alpha systems not associated with metal lines and producing lines with
W_0>0.17 AA are observed in both spectra, while five appear in only one
spectrum. This sample, although scarce due to the redshift path blocked out by
the BALs in B, allows us to place upper limits on the transverse cloud sizes.
Modelling the absorbers as non-evolving spheres, a maximum-likelihood analysis
yields a most probable cloud diameter D=256 /h_50 kpc and 2 sigma bounds of
172<D<896 /h_50 kpc. If the clouds are modelled as filamentary structures, the
same analysis yields lower transverse dimensions by a factor of two.
Independently of the maximum-likelihood approach, the equivalent width
differences provide evidence for coherent structures. The suggestion that the
size of Ly-alpha forest clouds increases with decreasing redshift is not
confirmed.


title:
The Equilibrium Structure of Cosmological Halos: From Dwarf Galaxies to
  X-ray Clusters

abstract:
  A new model for the postcollapse equilibrium structure of virialized objects
which condense out of the cosmological background universe is described and
compared with observations and simulations of cosmological halos from dwarf
galaxies to X-ray clusters. The model is based upon the assumption that
virialized halos are isothermal, which leads to a prediction of a unique
nonsingular isothermal sphere for the equilibrium structure, with a core radius
which is approximately 1/30 times the size and a core density which is
proportional to the mean background density at the epoch of collapse. These
predicted nonsingular isothermal spheres are in good agreement with the
observations of the internal structure of dark-matter-dominated halos from
dwarf galaxies to X-ray clusters.


title: RJK Observations of the Optical Afterglow of GRB 991216

abstract:
  We present near-infrared and optical observations of the afterglow to the
Gamma-Ray Burst (GRB) 991216 obtained with the F. L. Whipple Observatory 1.2-m
telescope and the University of Hawaii 2.2-m telescope. The observations range
from 15 hours to 3.8 days after the burst. The temporal behavior of the data is
well described by a single power-law decay with index -1.36 +/-0.04,
independent of wavelength. The optical spectral energy distribution, corrected
for significant Galactic reddening of E(B-V)=0.626, is well fitted by a single
power-law with index -0.58 +/- 0.08. Combining the IR/optical observations with
a Chandra X-ray measurement gives a spectral index of -0.8 +/- 0.1 in the
synchrotron cooling regime. A comparison between the spectral and temporal
power-law indices suggest that a jet is a better match to the observations than
a simple spherical shock.


title: Rotation, mass loss and pulsations of the star: an analytical model

abstract:
  The characteristics of the star with the "prescribed" density distribution
$\rho=\rho_c[1-(r/R)^\alpha]$ are analytically studied.


title:
The Central Gas Systems of Early-Type Galaxies Traced by Dust Feature:
  Based on the HST WFPC2 Archival Images

abstract:
  We investigated the central gas systems of E/S0 galaxies by making use of the
WFPC2 images of the Hubble Space Telescope archive. We searched the gas systems
that were traced by the dust with a new method of making color excess images in
F555W - F814W (V-I). Out of 25 sample galaxies, we detected gas system in 14
galaxies. The dust was newly detected in two galaxies that were thought to
contain no dust based on single band, pre-refurbishment data. The full extents
of the gas systems are 0.1 to 3.5 kpc, and the masses of the gas, log M(gas)
[M(solar)], are 4.2 to 7.2. The AGN activity is well correlated with existence
of the gas systems. None of galaxies without the gas systems show the AGN
activity. On the other hand, some galaxies with the gas systems show the AGN
activity; optical AGN activities are shown in 5 out of 11 galaxies of which
AGNs are optically studied, and radio activities are shown in 6 out of 14
galaxies. This shows that the AGN activity is driven with the gas system.


title: Estimation of steady-state basic parameters of stars

abstract:
  From a minimum of total energy of celestial bodies, their basic parameters
are obtained. The steady-state values of the mass, radius, and temperature of
stars and white dwarfs, as well as masses of pulsars are calculated. The
luminosity and giromagnetic ratio of celestial bodies are estimated. All the
obtained values are in a satisfactory agreement with observation data.


title: The black hole in IC 1459 from HST observations of the ionized gas disk

abstract:
  The peculiar elliptical galaxy IC 1459 (M_V = -21.19, D = 16.5 Mpc) has a
fast counterrotating stellar core, stellar shells and ripples, a blue nuclear
point source and strong radio core emission. We present results of a detailed
HST study of IC 1459, and in particular its central gas disk, aimed a
constraining the central mass distribution. We obtained WFPC2 narrow-band
imaging centered on the Halpha+[NII] emission lines to determine the flux
distribution of the gas emission at small radii, and we obtained FOS spectra at
six aperture positions along the major axis to sample the gas kinematics. We
construct different dynamical models for the Halpha+[NII] and Hbeta kinematics
that include a supermassive black hole, and in which the stellar mass
distribution is constrained by the observed surface brightness distribution and
ground-based stellar kinematics. All models are consistent with a black hole
mass in the range Mbh=1-4 x 10^8 Msun, and models without a black hole are
always ruled out at high confidence.


title: Direct Detection of Nonbaryonic Dark Matter

abstract:
  Weakly Interacting Massive Particles (WIMPs) are leading candidates for the
dominant part of the mass density of the Universe. Here we will review direct
WIMP detection techniques by giving examples of currently running experiments,
and present the status of the most promising future projects.


title: GENIUS: the first real-time detector for solar pp-neutrinos?

abstract:
  The GENIUS project is a proposal for a large supersensitive Germanium
detector system for WIMP and double beta decay searches with a much increased
sensitivity relative to existing and other future experiments. In this paper,
the possibility to detect low energy solar neutrinos with GENIUS in real-time
through elastic neutrino-electron scattering is studied.


title:
Large Magellanic Cloud Planetary Nebula Morphology: Probing Stellar
  Populations and Evolution

abstract:
  Planetary Nebulae (PNe) in the Large Magellanic Cloud (LMC) offer the unique
opportunity to study both the Population and evolution of low- and
intermediate-mass stars, by means of the morphological type of the nebula.
Using observations from our LMC PN morphological survey, and including images
available in the HST Data Archive, and published chemical abundances, we find
that asymmetry in PNe is strongly correlated with a younger stellar Population,
as indicated by the abundance of elements that are unaltered by stellar
evolution (Ne, Ar, S). While similar results have been obtained for Galactic
PNe, this is the first demonstration of the relationship for extra-galactic
PNe. We also examine the relation between morphology and abundance of the
products of stellar evolution. We found that asymmetric PNe have higher
nitrogen and lower carbon abundances than symmetric PNe. Our two main results
are broadly consistent with the predictions of stellar evolution if the
progenitors of asymmetric PNe have on average larger masses than the
progenitors of symmetric PNe. The results bear on the question of formation
mechanisms for asymmetric PNe, specifically, that the genesis of PNe structure
should relate strongly to the Population type, and by inference the mass, of
the progenitor star, and less strongly on whether the central star is a member
of a close binary system.


title: What's wrong with AGN models for the X-ray background ?

abstract:
  The origin of the hard X-ray background (XRB) as a superposition of
unabsorbed and absorbed Active Galactic Nuclei is now widely accepted as the
standard model. The identification of faint X-ray sources in ROSAT, ASCA, and
BeppoSAX medium-deep surveys and their average spectral properties are in broad
agreement with the model predictions. However, AGN models, at least in their
simplified version, seem to be at odds with some of the most recent findings
calling for substantial revisions. I will review the recent XRB "best fit"
models and discuss how the foreseen XMM and Chandra surveys will be able to
constrain the allowed parameter space.


title: X-ray Transients Monitored by the All-Sky Monitor on RXTE: A Tabulation

abstract:
  We present a tabulation of 46 transient x-ray sources monitored with the
All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE). They fall into
four broad categories: short (~d), intermediate, and long (>500 d) duration of
outbursts, and long period binary systems that flare up at periastron (e.g., Be
systems). The mixture of outburst/quiescent cycles and low-level persistent
emission in a few systems could indicate conditions are near the limit for
stable mass flow in the accretion disk. The two short-time-scale systems, CI
Cam and V4641 Sgr, are within 1 kpc of the sun, and hence many more such
systems may await discovery.


title: The Structure of IR Luminous Galaxies at 100 Microns

abstract:
  We have observed twenty two galaxies at 100 microns with the Kuiper Airborne
Observatory in order to determine the size of their FIR emitting regions. Most
of these galaxies are luminous far-infrared sources, with L_FIR > 10^11 L_sun.
This data constitutes the highest spatial resolution ever achieved on luminous
galaxies in the far infrared. Our data includes direct measurements of the
spatial structure of the sources, in which we look for departures from point
source profiles. Additionally, comparison of our small beam 100 micron fluxes
with the large beam IRAS fluxes shows how much flux falls beyond our detectors
but within the IRAS beam. Several sources with point- like cores show evidence
for such a net flux deficit. We clearly resolved six of these galaxies at 100
microns and have some evidence for extension in seven others. Those galaxies
which we have resolved can have little of their 100 micron flux directly
emitted by a point-like active galactic nucleus (AGN). Dust heated to ~40 K by
recent bursts of non-nuclear star formation provides the best explanation for
their extreme FIR luminosity. In a few cases, heating of an extended region by
a compact central source is also a plausible option. Assuming the FIR emission
we see is from dust, we also use the sizes we derive to find the dust
temperatures and optical depths at 100 microns which we translate into an
effective visual extinction through the galaxy. Our work shows that studies of
the far infrared structure of luminous infrared galaxies is clearly within the
capabilities of new generation far infrared instrumentation, such as SOFIA and
SIRTF.


title:
Proper motion and membership determination in the young open cluster
  NGC1662

abstract:
  Relative proper motions and cluster membership probabilities of 30 stars
within an area of 14' of diameter centered in the open cluster NGC1662
(\alpha=04^{\rm h}48^{\rm m}, \delta=+10^{\rm o}56') are determined by
combining positions of stars observed by the Valinhos CCD meridian circle with
those from other astrometric catalogues. Our basic source for first epoch of
stars brighter than B=13 magnitudes is the AC2000 Catalogue, which provides a
time baseline of about 90 years, whereas the USNO-A2.0 Catalogue is used for
fainter stars, providing a time baseline of about 40 years in this region.
Average accuracies in proper motion of 2 mas/yr and 7 mas/yr are achieved,
respectively, when the AC2000 or the USNO-A2.0 is used. Membership
determination is obtained by applying the Zhao & He (1990) method. The cluster
proper motion was found to be (-3.2\pm 0.6) mas/yr in right ascension and
(-1.6\pm 0.6) mas/yr in declination.


title: The violent past of Cygnus X-2

abstract:
  Cygnus X-2 appears to be the descendant of an intermediate-mass X-ray binary
(IMXB). Using Mazzitelli's (1989) stellar code we compute detailed evolutionary
sequences for the system and find that its prehistory is sensitive to stellar
input parameters, in particular the amount of core overshooting during the
main-sequence phase. With standard assumptions for convective overshooting a
case B mass transfer starting with a 3.5 M_sun donor star is the most likely
evolutionary solution for Cygnus X-2. This makes the currently observed state
rather short-lived, of order 3 Myr, and requires a formation rate > 1e-7 - 1e-6
per yr of such systems in the Galaxy. Our calculations show that neutron star
IMXBs with initially more massive donors (> 4 M_sun) encounter a delayed
dynamical instability; they are unlikely to survive this rapid mass transfer
phase. We determine limits for the age and initial parameters of Cygnus X-2 and
calculate possible dynamical orbits of the system in a realistic Galactic
potential, given its observed radial velocity. We find trajectories which are
consistent with a progenitor binary on a circular orbit in the Galactic plane
inside the solar circle that received a kick velocity < 200 km/s at the birth
of the neutron star. The simulations suggests that about 7% of IMXBs receiving
an arbitrary kick velocity from a standard kick velocity spectrum would end up
in an orbit similar to Cygnus X-2, while about 10% of them reach yet larger
Galactocentric distances.


title:
A Comparative Study of the Depth of Maximum of Simulated Air Shower
  Longitudinal Profiles

abstract:
  A comparative study of simulated air shower longitudinal profiles is
presented. An appropriate thinning level for the calculations is first
determined empirically. High statistics results are then provided, over a wide
energy range, (10^14.0 to 10^20.5 eV), for proton & iron primaries, using four
combinations of the MOCCA & CORSIKA program frameworks, and the SIBYLL & QGSJET
high energy hadronic interaction models. These results are compared to existing
experimental data. The way in which the first interaction controls Xmax is
investigated, as is the distribution of Xmax.


title: High Resolution Near-Infrared Spectra of Protostars

abstract:
  We present new high resolution (R = 21,000) near-infrared (2 microns)
spectroscopic observations of a sample of Class I and flat-spectrum
protostellar objects in the rho Ophiuchi dark cloud. None of the five Class I
spectra show CO v = 0 -- 2 absorption features, consistent with high K-band
continuum veilings, 4 <= r_k <= 20 and fast stellar rotation, assuming that the
underlying protostellar photospheres are of late spectral type, as is suggested
by the low luminosities of most of these objects. Two of the flat-spectrum
protostellar objects also show no absorption features and are likely to be
highly veiled. The remaining two flat-spectrum sources show weak, broad
absorptions which are consistent with an origin in quickly rotating (v sin i ~
50 km / s) late-type stellar photospheres which are also strongly veiled, r_k =
3 - 4. These observations provide further evidence that: 1)-Class I sources are
highly veiled at near-infrared wavelengths, confirming previous findings of
lower resolution spectroscopic studies; and 2)- flat-spectrum protostars rotate
more rapidly than classical T Tauri stars (Class II sources), supporting
findings from a recent high resolution spectroscopic study of other
flat-spectrum sources in this cloud. In addition our observations are
consistent with the high rotation rates derived for two of the Class I
protostellar objects in our sample from observations of variable hard X-ray
emission obtained with the ASCA satellite. These observations suggest that
certain Class I sources can rotate even more rapidly than flat-spectrum
protostars, near breakup velocity.


title: New Developments in Cosmology

abstract:
  A brief review is given of the present observational data in cosmology. A
review of a new bimetric gravity theory with multiple light cones is presented.
The physical consequences of this gravity theory for the early universe are
analyzed.


title:
Neutrino and axion emissivities of neutron stars from nucleon-nucleon
  scattering data

abstract:
  Neutrino and axion production in neutron stars occurs mainly as
bremsstrahlung from nucleon-nucleon (NN) scattering. The energy radiated via
neutrinos or axions is typically very small compared to other scales in the
two-nucleon system. The rate of emission of such "soft" radiation is directly
related to the on-shell NN amplitude, and thereby to the NN experimental data.
This facilitates the model-independent calculation of the neutrino and axion
radiation rates which is presented here. We find that the resultant rates are a
factor of four below earlier estimates based on a one-pion-exchange NN
amplitude.


title:
High Resolution HST-STIS Spectra of CI and CO in the Beta Pictoris
  Circumstellar Disk

abstract:
  High resolution FUV echelle spectra showing absorption features arising from
CI and CO gas in the Beta Pictoris circumstellar (CS) disk were obtained on
1997 December 6 and 19 using the Space Telescope Imaging Spectrograph (STIS).
An unsaturated spin-forbidden line of CI at 1613.376 A not previously seen in
spectra of Beta Pictoris was detected, allowing for an improved determination
of the column density of CI at zero velocity relative to the star (the stable
component), N = (2-4) x 10^{16} cm^{-2}. Variable components with multiple
velocities, which are the signatures of infalling bodies in the Beta Pictoris
CS disk, are observed in the CI 1561 A and 1657 A multiplets. Also seen for the
first time were two lines arising from the metastable singlet D level of
carbon, at 1931 A and 1463 A The results of analysis of the CO A-X (0-0),
(1-0), and (2-0) bands are presented, including the bands arising from {13}^CO,
with much better precision than has previously been possible, due to the very
high resolution provided by the STIS echelle gratings. Only stable CO gas is
observed, with a column density N(CO) = (6.3 +/- 0.3) x 10^{14} cm{-2}. An
unusual ratio of the column densities of {12}^CO to {13}^CO is found (R = 15
+/- 2). The large difference between the column densities of CI and CO
indicates that photodissociation of CO is not the primary source of CI gas in
the disk, contrary to previous suggestion.


title:
Gamma-Ray Background from Structure Formation in the Intergalactic
  Medium

abstract:
  The universe is filled with a diffuse and isotropic extragalactic background
of gamma-ray radiation, containing roughly equal energy flux per decade in
photon energy between 3 MeV-100 GeV. The origin of this background is one of
the unsolved puzzles in cosmology. Less than a quarter of the gamma-ray flux
can be attributed to unresolved discrete sources, but the remainder appears to
constitute a truly diffuse background whose origin has hitherto been
mysterious. Here we show that the shock waves induced by gravity during the
formation of large-scale structure in the intergalactic medium, produce a
population of highly-relativistic electrons with a maximum Lorentz factor above
10^7. These electrons scatter a small fraction of the microwave background
photons in the present-day universe up to gamma-ray energies, thereby providing
the gamma-ray background. The predicted diffuse flux agrees with the observed
background over more than four decades in photon energy, and implies a mean
cosmological density of baryons which is consistent with Big-Bang
nucleosynthesis.


title:
Discovery of a new pulsating X-ray source with a 1549.1-s period, AX
  J183220-0840

abstract:
  A new pulsating X-ray source, AX J183220-0840, with a 1549.1-s period was
discovered at R.A.= 18h32m20s and Dec.=-8d40'30'' (J2000,
uncertainty=0.6degree) during an ASCA observation on the Galactic plane. The
source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux
of 1.1E-11 ergs cm-2 s-1 and pulsation period of 1549.1+/-0.4 s were
consistently obtained from these two observations. The X-ray spectrum was
represented by a flat absorbed power-law with a photon-index of =~0.8 and an
absorption column density of =~1.3E22 cm-2. Also, a signature of iron K-shell
line emission with a centroid of 6.7 keV and an equivalent width of
approximately 450 eV was detected. From the pulsation period and the iron-line
feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a
complexly absorbed thermal spectrum with a temperature of about 10 keV.


title:
Limits on magnetic field strength of the extended nebula of PSR B1706-44
  from optical, X-ray and TeV observations

abstract:
  The detection of unpulsed TeV emission from PSR B1706-44 raised the question
if this VHE emission results from inverse Compton scattering of multi-TeV
electrons on the CMBR and other soft photon fields. This hints at the existence
of an unseen synchrotron nebula, which is larger than the observed 1 arcminute
compact X-ray nebula. In a search for synchrotron counterpart of the TeV
nebula, we have taken V-band CCD images of the region around the PSR B1706-44
pulsar position. By rejecting all point source contributions down to the
diffuse sky limit, we were able to search for such extended plerionic
synchrotron emission on scale sizes limited by the angular resolution of the
CANGAROO imaging TeV observations. By combining the V-band flux limits with the
observed TeV flux, we were able to obtain upper limits for the magnetic field
strength as a function of the radius of the assumed TeV nebula. Assuming that
the 2 arcminute radio plerion also defines the size of the TeV nebula, we
constrain the steady state particle spectral index to the values between 4 and
5.5, with a field strength limit of about 3x10^-6 G. This compares with an
index of 3.6+/-0.6 inside the 1 arcminute compact X-ray nebula.


title: Asymptotic Giant Branch Stars in Interacting Galaxy Globular Clusters

abstract:
  We present new modelling of the spectrophotometric properties of intermediate
age stellar populations in the near-infrared (NIR). We take into account the
evolutionary and spectroscopic properties of the Asymptotic Giant Branch (AGB)
stars which dominate the integrated NIR emission of those populations. The
predictions of spectrophotometric narrow-band molecular indices require the use
of an effective temperature -- colour (or spectrum) calibration for AGB stars;
synthetic indices show a strong dependence upon this calibration. Preliminary
results of NIR observations of a supermassive 500 Myr old stellar cluster in
the prototypical merger remnant NGC 7252 are presented. The spectra are indeed
consistent with intermediate age models dominated by light from AGB stars, a
significant fraction of which may be carbon rich. Implications for the stellar
inputs used in the modelling of intermediate age stellar populations and their
NIR emission are discussed.


title:
Stochastic Fluctuations in the Spectrophotometric Properties of Star
  Clusters

abstract:
  Integrated spectrophotometric properties of stellar systems are intrinsically
dispersed due to the stochastic nature of the small numbers of bright stars
they contain. Among clusters, only the most massive ones can be used
individually for comparison with the mean properties predicted by population
synthesis calculations. The appropriate minimal masses depend, among others, on
the waveband or colour index studied and on age. Selected indices (near-IR CO
and H2O, EW(Halpha)) are used to illustrate the asymmetric nature of the
probability distribution of observable properties and their dependence on
cluster mass.


title: Non-conservative Evolution of Cataclysmic Variables

abstract:
  We suggest a new mechanism to account for the loss of angular momentum in
binaries with non-conservative mass exchange. It is shown that in some cases
the loss of matter can result in increase of the orbital angular momentum of a
binary. If included into consideration in evolutionary calculations, this
mechanism appreciably extends the range of mass ratios of components for which
mass exchange in binaries is stable. It becomes possible to explain the
existence of some observed cataclysmic binaries with high donor/accretor mass
ratio, which was prohibited in conservative evolution models.


title:
Possibly interacting Vorontsov-Velyaminov galaxies. I. Observations of
  VV432, VV543 and VV747

abstract:
  Among the galaxies which were included in the Atlas and Catalogue of
Interacting galaxies by Vorontsov-Velyaminov (hereafter VV) as multiple systems
("nests", "chains" and similarly looking systems), there are many objects,
where the interaction is not evident. Some of them are single objects,
including low-mass galaxies with active star formation (SF). In this work we
present the description of observations and results of the long-slit
spectrophotometry with the Russian 6-m telescope of three VV-galaxies looking
like double or multiple systems, and HI-observations of one of them in order to
elucidate their nature, determine their metallicity, kinematic properties and
the evolution status. Galaxies VV432 and VV747 are found to be dwarf systems
with low oxygen abundance (O/H = 1/22 and 1/12 of the solar value,
respectively). Their velocity curves indicate quite slow rotation with
respective maximum velocities of about 60 and 80 km/s, in agreement with their
low luminosities. The distance to VV432 is rather uncertain. If it is a member
of Virgo Cluster, this is the most metal-deficient known galaxy of this
aggregate. For galaxy VV543 the measured emission-line redshift 0.047 appeared
ten times larger than it was given in the original paper and is cited in
databases. This "system" evidently represents an optical pair of two galaxies
with large velocity difference. The fainter western component is an HII-galaxy,
while the brighter one is an absorption-line early-type galaxy with the radial
velocity being 1600 km/s lower.


title:
The longest thermonuclear X-ray burst ever observed? (A BeppoSAX Wide
  Field Camera observation of 4U 1735-44)

abstract:
  A long flux enhancement, with an exponential decay time of 86 min, is
detected in 4U 1735-44 with the BeppoSAX Wide Field Cameras. We argue that this
is a type-I X-ray burst, making it the longest such burst ever observed.
Current theories for thermonuclear bursts predict shorter and more frequent
bursts for the observed persistent accretion rate.


abstract:
  We investigate the properties of clusters of galaxies in the $\Lambda$CDM
models with a steplike initial power spectrum. We examine the mass function,
the peculiar velocities and the power spectrum of clusters in models with
different values of the density parameter $\Omega_0$, the normalized Hubble
constant h and the spectral parameter p, which describes the shape of the
initial power spectrum. The results are compared with observations. We also
investigate the rms bulk velocity in the models, where the properties of
clusters are consistent with the observed data. We find that the power spectrum
of clusters is in good agreement with the observed power spectrum of the
Abell-ACO clusters, if the spectral parameter p is in the range p=0.6-0.8. The
power spectrum and the rms peculiar velocity of clusters are consistent with
observations only if $\Omega_0<0.4$. The $\Omega_0=0.3$ models are consistent
with the observed properties of clusters, if h=0.50-0.63. For h=0.65, we find
that $\Omega_0=0.20 -0.27$.


title:
An efficient algorithm for two-dimensional radiative transfer in
  axisymmetric circumstellar envelopes and disks

abstract:
  We present an algorithm for two-dimensional radiative transfer in
axisymmetric, circumstellar media. The formal integration of the transfer
equation is performed by a generalization of the short characteristics (SC)
method to spherical coordinates. Accelerated Lambda Iteration (ALI) and Ng's
algorithm are used to converge towards a solution. By taking a logarithmically
spaced radial coordinate grid, the method has the natural capability of
treating problems that span several decades in radius, in the most extreme case
from the stellar radius up to parsec scale. Flux conservation is guaranteed in
spherical coordinates by a particular choice of discrete photon directions and
a special treatment of nearly-radially outward propagating radiation. The
algorithm works well from zero up to very high optical depth, and can be used
for a wide variety of transfer problems, including non-LTE line formation, dust
continuum transfer and high temperature processes such as compton scattering.
In this paper we focus on multiple scattering off dust grains and on non-LTE
transfer in molecular and atomic lines. Line transfer is treated according to
an ALI scheme for multi-level atoms/molecules, and includes both random and
systematic velocity fields. The algorithms are implemented in a multi-purpose
user-friendly radiative transfer program named RADICAL. We present two example
computations: one of dust scattering in the Egg Nebula, and one of non-LTE line
formation in rotational transitions of HCO$^{+}$ in a flattened protostellar
collapsing cloud.


title: Mid-infrared ISO spectroscopy of NGC 4945

abstract:
  We have observed the central region of the nearby starburst galaxy NGC4945
with the mid-infrared spectrometers SWS and PHT-S aboard ISO. We do not find
any evidence for the existence of the powerful AGN, inferred from hard X-ray
observations. The upper limits on our AGN tracers [NeV] 14.32um & 24.32um and
[NeVI] 7.65um imply an A(V)>160 towards the NLR, assuming the NLR to be of
equal strength as in the Circinus galaxy. Other possibilities are discussed.
The starburst excitation indicators [NeIII]15.56um/[NeII]12.81um and
L(bol)/L(lyc) suggest that the starburst in the central region is at least
5x10^6 yrs old, and that it accounts for at least half of the nuclear
bolometric luminosity. The starburst might well power the entire bolometric
luminosity, but the available constraints are also consistent with an up to 50%
contribution of the embedded AGN. With PHT-S, at a resolution of approximately
90, we detect strong absorption features of water ice, and, for the first time
in an external galaxy, of CO_2 and CO. The same PHT-S spectrum also reveals
strong emission from the family of PAH features. Finally, we have observed and
detected several pure rotational and ro-vibrational H_2 lines, two of which,
the (0-0) S(0) & S(1) lines, allow us to determine the excitation temperature
(160K) and warm H_2 mass (2.4x10^7 Msun). The low excitation temperature shows
Orion-like shocks not to be representative for the entire emission of the
central region of the galaxy and fairly normal PDRs to be perhaps more typical.


title: Inflation models, spectral index and observational constraints

abstract:
  We have evaluated the observational constraints on the spectral index $n$, in
the context of a $\Lambda$CDM model. For $n$ scale-independent, as predicted by
most models of inflation, present data require $n\simeq 1.0 \pm 0.1$ at the
2-$\sigma$ level. We have also studied the two-parameter scale-dependent
spectral index, predicted by running-mass inflation models. Present data allow
significant variation of $n$ in this case, within the theoretically preferred
region of parameter space.


title: Exploring the Ultrahigh Energy Neutrino Universe

abstract:
  Astronomy at the highest energies observed must be performed by studying
neutrinos rather than photons because the universe is opaque to photons of
these energies. By making observations of neutrinos with energies above 10 EeV
one can deduce information about the distribution and cosmological history of
cosmic rays which may have been accelerated to energies above 100 EeV. Very
large fluxes of neutrinos at these energies which exhibit a hard spectrum would
be evidence of a GUT phase transition or superheavy dark matter particles.
Neutrinos at energies around a PeV may be produced in observable quantities in
active galaxies from the acceleration and interactions of cosmic rays in the
vicinity of massive black holes or in relativistic jets produced by these black
holes. Cosmological gamma-ray bursts may also produce PeV neutrinos. Neutrinos
at these energies may oscillate into tau neutrinos which can travel through the
Earth by the process of regeneration and produce upward moving air-showers.
Neutrinos of energies above of 1000 EeV can produce ultrahigh energy cosmic
rays thorugh interactions with big-bang neutrinos, producing Z bosons. This
"Z-burst" phenomenon can be used to study the mass and distribution of big-bang
neutrinos.


title:
Coupling of the X-ray and radio emission in the black hole candidate a
  nd compact jet source GX 339-4

abstract:
  We report the results of a long-term campaign of radio, soft- and hard- X-ray
observations of the galactic black hole candidate GX 339-4. In the Low-Hard
X-ray state the system displays a strong 3-way linear correlation between soft-
and hard-X-rays and radio emission, implying a coupling between the
Comptonising corona and a radio-emitting compact jet. In this state the radio
emission is linearly polarised at a level of around 2 %, with an almost
constant polarisation angle, indicative of a favored axis in this system
probably related to the compact jet and/or black hole spin axis. In the Off
X-ray state the radio emission declines with the X-ray emission to below
detectable levels, suggesting that it is simply a lower-luminosity version of
the Low-Hard state. In the High-Soft state both the hard-X-ray and radio
emission are suppressed. We also note that the transitions from the Low-Hard
state to the High-Soft state (and the reverse) are possibly associated with
discrete ejection(s) of expanding relativistic plasma.


title:
The quasar fraction in low-frequency selected complete samples and
  implications for unified schemes

abstract:
  Low-frequency radio surveys are ideal for selecting orientation-independent
samples of extragalactic sources because the sample members are selected by
virtue of their isotropic steep-spectrum extended emission. We use the new 7C
Redshift Survey along with the brighter 3CRR and 6C samples to investigate the
fraction of objects with observed broad emission lines - the `quasar fraction'
- as a function of redshift and of radio and narrow emission line luminosity.
We find that the quasar fraction is more strongly dependent upon luminosity
(both narrow line and radio) than it is on redshift. Above a narrow [OII]
emission line luminosity of log L_[OII] > 35 W (or radio luminosity log L_151 >
26.5 W/Hz/sr), the quasar fraction is virtually independent of redshift and
luminosity; this is consistent with a simple unified scheme with an obscuring
torus with a half-opening angle theta_trans approx 53 degrees. For objects with
less luminous narrow lines, the quasar fraction is lower. We show that this is
not due to the difficulty of detecting lower-luminosity broad emission lines in
a less luminous, but otherwise similar, quasar population. We discuss evidence
which supports at least two probable physical causes for the drop in quasar
fraction at low luminosity: (i) a gradual decrease in theta_trans and/or a
gradual increase in the fraction of lightly-reddened (0 < A(V) < 5)
lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a
distinct second population of low luminosity radio sources which, like M87,
lack a well-fed quasar nucleus and may well lack a thick obscuring torus.


title: A Central Engine for Cosmic Gamma-Ray Burst Sources

abstract:
  One of a family previously proposed ``central engines'' for cosmic gamma-ray
burst sources (Klu\'zniak & Ruderman 1998) is considered in some detail. A
steadily accreting $10^6$ Gauss magnetic white dwarf should ultimately collapse
to a strongly differentially rotating, millisecond-rotation-period neutron star
for a wide range of steady accretion rates and initial masses if the accreting
white dwarf has an evolved O-Ne-Mg composition. A similar neutron star could
also result from an initial C-O white dwarf but only for more constrained
accretion rates. Because the collapsing white dwarf begins as a $\gamma=4/3$
polytrope, the final neutron star's spin-rate increases strongly with
cylindrical radius. A stable wind-up of the neutron star's poloidal magnetic
field then produces buoyant magnetic toroids which grow, break loose, rise, and
partly penetrate the neutron star surface to form a transient, $B\approx
10^{17}$ G millisecond spin-period pulsar with a powerful pulsar wind (Usov
1992). This pulsar wind emission is then rapidly suppressed by the surface
shear motion from the strong stellar differential rotation. This wind-up and
transient pulsar formation can occur at other times on different cylinders
and/or repeat on the same one, with (re-)wind up and surface penetration time
scales hugely longer han the neutron star's millisecond spin period. In this
way, differential rotation both opens and closes the doors which allow neutron
star spin-energy to be emitted in powerful bursts of pulsar wind. Predictions
of this model compare favorably to needed central engine properties of
gamma-ray burst sources (total energy, duration, sub-burst fluctuations and
time scales, variability among burst events, and baryon loading).


title: The Age-Redshift Relation for Standard Cosmology

abstract:
  We present compact, analytic expressions for the age-redshift relation
$\tau(z)$ for standard Friedmann-Lema\^ \itre-Robertson-Walker (FLRW)
cosmology. The new expressions are given in terms of incomplete Legendre
elliptic integrals and evaluate much faster than by direct numerical
integration.


title: Is Cold Dark Matter Baryonic? Alternative Opinion

abstract:
  Minutes into the big bang, nucleosynthesis finds 96 percent of matter
nonreactive. Massive pure disk protogalaxies must be formed in the early
universe as their galaxies are found at high redshift. Surrounded by hot gas,
they made little imprint on the CBR. The LHC has not found the Higgs or dark
matter candidates. These phenomena can be explained by a cold baryonic shell.


title: First Results from the Large Area Lyman Alpha Survey

abstract:
  We report on a new survey for z=4.5 Lyman alpha sources, the Large Area Lyman
Alpha (LALA) survey. Our survey achieves an unprecedented combination of volume
and sensitivity by using narrow-band filters on the new 8192x8192 pixel CCD
Mosaic Camera at the 4 meter Mayall telescope of Kitt Peak National
Observatory.
  Well-detected sources with flux and equivalent width matching known high
redshift Lyman alpha galaxies (i.e., observed equivalent width above 80
Angstroms and line+continuum flux between 2.6e-17 and 5.2e-17 erg/cm^2/sec in
an 80 Angstrom filter) have an observed surface density corresponding to 11000
+- 700 per square degree per unit redshift at z=4.5. Spatial variation in this
surface density is apparent on comparison between counts in 6561 and 6730
Angstrom filters.
  Early spectroscopic followup results from the Keck telescope included three
sources meeting our criteria for good Lyman alpha candidates. Of these, one is
confirmed as a z=4.52 source, while another remains consistent with either
z=4.55 or z=0.81. We infer that 30 to 50% of our good candidates are bona fide
Lyman alpha emitters, implying a net density of about 4000 Lyman alpha galaxies
per square degree per unit redshift.


title: Radio Emission from GRO J1655-40 during the 1994 Jet Ejection Episodes

abstract:
  We report multifrequency radio observations of GRO J1655-40 obtained with the
Australia Telescope Compact Array, the Molonglo Observatory Synthesis Telescope
and the Hartebeesthoek Radio Astronomy Observatory at the time of the major
hard X-ray and radio outbursts in 1994 August-September. The radio emission
reached levels of the order of a few Jy and was found to be linearly polarized
by up to 10%, indicating a synchrotron origin. The light curves are in good
agreement with those measured with the VLA, but our closer time sampling has
revealed two new short-lived events and significant deviations from a simple
exponential decay. The polarization data show that the magnetic field is well
ordered and aligned at right angles to the radio jets for most of the
monitoring period. The time evolution of the polarization cannot be explained
solely in terms of a simple synchrotron bubble model, and we invoke a hybrid
`core-lobe' model with a core which contributes both synchrotron and free-free
emission and `lobes' which are classical synchrotron emitters.


title:
Studies of multiple stellar systems - III. Modulation of orbital
  elements in the triple-lined system HD 109648

abstract:
  The triple-lined spectroscopic triple system HD 109648 has one of the
shortest periods known for the outer orbit in a late-type triple, 120.5 days,
and the ratio between the periods of the outer and inner orbits is small, 22:1.
With such extreme values, this system should show orbital element variations
over a timescale of about a decade. We have monitored the radial velocities of
HD 109648 with the CfA Digital Speedometers for eight years, and have found
evidence for modulation of some orbital elements. While we see no definite
evidence for modulation of the inner binary eccentricity, we clearly observe
variations in the inner and outer longitudes of periastron, as well as in the
radial velocity amplitudes of the three components. The observational results,
combined with numerical simulations, allow us to put constraints on the
orientation of the orbits.


title: The Intrinsic Shape Distribution of a Sample of Elliptical Galaxies

abstract:
  We apply the dynamical modeling approach of Statler (1994b) to 13 elliptical
galaxies from the Davies and Birkinshaw (1988) sample of radio galaxies to
derive constraints on their intrinsic shapes and orientations. We develop an
iterative Bayesian algorithm to combine these results to estimate the parent
shape distribution from which the sample was drawn, under the assumption that
this parent distribution has no preferred orientation. In the process we obtain
improved estimates for the shapes of individual objects. The parent shape
distribution shows a tendency toward bimodality, with peaks at the oblate and
prolate limits. Under minimal assumptions about the galaxies' internal
dynamics, 35% of the objects would be strongly triaxial (0.2 < T < 0.8).
However, the parent distribution is sensitive to the assumed orbit populations
in the galaxies. Dynamical configurations in which all galaxies rotate purely
about either their long or short axes can be ruled out because they would
require the sample to have a strong orientation bias. Configurations in which
the mean motion about the short or long axis is either ``disklike''---dropping
off away from the symmetry planes---or ``spheroidlike''---remaining roughly
constant at a given radius---are equally viable. Spheroidlike rotation in the
long-axis or short-axis tube orbits significantly lowers the abundance of
prolate or oblate galaxies, respectively. If rotation in ellipticals is
generally disklike, then triaxiality is rare; if spheroidlike, triaxiality is
common.


title: The Radiative Stress Tensor

abstract:
  We use the transfer equation in relativistic form to develop an expansion of
the one-photon distribution for a medium with constant photon mean free path,
$\epsilon$. The resulting radiative viscosity tensor may be expressed either as
a simple integral operator acting on the Thomas stress tensor or as the
solution of an inhomogenous, linear partial differential equation. The
expression obtained for the radiative viscosity tensor applies for media with
long, as well as short, photon mean free paths. We also develop results
applicable for relatively smooth flows by using the form of the Thomas stress
tensor with generalized transport coefficients derived by the application of a
suitable operator to the bare Thomas coefficients.


title:
Why Are Rotating Elliptical Galaxies Less Elliptical at X-ray
  Frequencies?

abstract:
  If mass and angular momentum were conserved in cooling flows associated with
luminous, slowly rotating elliptical galaxies, the inflowing hot gas would spin
up, resulting in disks of cold gas and X-ray images that are highly flattened
along the equatorial plane out to several effective radii. Such X-ray
flattening is not observed at the spatial resolution currently available to
X-ray observations. Evidently mass and angular momentum are not in fact
conserved. If cooling flows are depleted by localized radiative cooling at
numerous sites distributed throughout the flows, then disks of cooled gas do
not form and the X-ray images appear nearly circular. However, the distribution
of young stars formed from the cooled gas is still somewhat flattened relative
to the stellar light. X-ray images of galactic cooling flows can also be
circularized by the turbulent diffusion of angular momentum away from the axis
of rotation, but the effective viscosity of known processes -- stellar mass
loss, supernovae, cooling site evolution, etc. -- is insufficient to
appreciably circularize the X-ray images. Radial gradients in the interstellar
iron abundance are unaffected by the expected level of interstellar turbulence
since these gradients are continuously re-established by Type Ia supernovae.


title:
A Theoretical Light-Curve Model for the Recurrent Nova V394 Coronae
  Austrinae

abstract:
  A theoretical light curve for the 1987 outburst of V394 Coronae Austrinae
(V394 CrA) is modeled to obtain various physical parameters of this recurrent
nova. We then apply the same set of parametersto a quiescent phase and confirm
that these parameters give a unified picture of the binary. The early visual
light curve (1-10 days after the optical maximum) is well reproduced by a
thermonuclear runaway model on a very massive WD close to the Chandrasekhar
limit (1.37 +- 0.01 M_sun). The ensuing plateau phase (10-30 days) is also
reproduced by the combination of a slightly irradiated MS and a fully
irradiated flaring-up disk with a radius ~1.4 times the Roche lobe size. The
best fit parameters are the WD mass 1.37 M_sun, the companion mass 1.5 M_sun
(0.8-2.0 M_sun is acceptable), the inclination angle of the orbit i~65-68
degree, and the flaring-up rim ~0.30 times the disk radius. The envelope mass
at the optical peak is estimated to be ~6 x 10^{-6} M_sun, which indicates an
average mass accretion rate of 1.5 x 10^{-7} M_sun yr^{-1} during the quiescent
phase between the 1949 and 1987 outbursts. In the quiescent phase, the observed
light curve can be reproduced with a disk size of 0.7 times the Roche lobe size
and a rather slim thickness of 0.05 times the accretion disk size at the rim.
About 0.5 mag sinusoidal variation of the light curve requires the mass
accretion rate higher than ~1.0 x 10^{-7} M_sun yr^{-1}, which is consistent
with the above estimation from the 1987 outburst. These newly obtained
quantities are exactly the same as those predicted in a new progenitor model of
Type Ia supernovae.


title: Entropy & equation of state (EOS) for hot bare strange stars

abstract:
  Compactness of some stars is explained if they are strange stars (SS) as
shown by Dey et al. (1998) (D98) and Li et al. (1999a). One of these compact
star candidates is the SAX J1808.4-3658 (SAX in short) believed to be an
important link in the genesis of radio pulsars. SS have also been suggested for
bursting X-ray pulsars (GRO J1744-28, Cheng et al. 1998), from quasi-periodic
oscillations (QPO) of X-ray binaries (4U 1728-34, Li et al. 1999b) and from
peculiarity of properties of radio pulsars (PSR 0943+10, Xu et al.1999; Kapoor
et al. 2000). We now extend the calculation to include high temperatures upto T
= 70 MeV ~ 8 times 10^{11} ^oK and find that the nature of the mass (M) and
radius (R), derived from astrophysical data, is still retained. The entropy is
calculated and matches onto that calculated from hadronic models thus
supporting the idea that the quark-hadron transition may be continuous.


title:
Pulsational M_V versus [Fe/H] relation(s) for globular cluster RR Lyrae
  variables

abstract:
  We use the results from recent computations of updated non-linear convective
pulsating models to constrain the distance modulus of Galactic globular
clusters through the observed periods of first overtone RRc pulsators. The
resulting relation between the mean absolute magnitude of RR Lyrae stars
<M_V(RR)> and the heavy element content [Fe/H] appears well in the range of
several previous empirical calibrations, but with a non linear dependence on
[Fe/H] so that the slope of the relation increases when moving towards larger
metallicities. On this ground, our results suggest that metal-poor
([Fe/H]<-1.5) and metal-rich ([Fe/H]>-1.5) variables follow two different
linear <M_V(RR)>-[Fe/H] relations. Application to RR Lyrae stars in the
metal-poor globular clusters of the Large Magellanic Cloud provides a LMC
distance modulus of the order of 18.6 mag, thus supporting the "long" distance
scale. The comparison with recent predictions based on updated stellar
evolution theory is shortly presented and discussed.


title:
Computer simulations of interferometric imaging with the VLT
  interferometer and the AMBER instrument

abstract:
  We present computer simulations of interferometric imaging with the VLT
interferometer and the AMBER instrument. These simulations include both the
astrophysical modelling of a stellar object by radiative transfer calculations
and the simulation of light propagation from the object to the detector
(through atmosphere, telescopes, and the AMBER instrument), simulation of
photon noise and detector read-out noise, and finally data processing of the
interferograms. The results show the dependence of the visibility error bars on
the following observational parameters: different seeing during the observation
of object and reference star (Fried parameters r_0,object=2.4m, r_0,ref.=2.5m,
different residual tip-tilt error (delta_tt,object=2% of the Airy disk
diameter, delta_tt,ref.=0.1%), and object brightness (K_object=3.5 mag and 11
mag, K_ref.=3.5 mag). Exemplarily, we focus on stars in late stages of stellar
evolution and study one of its key objects, the dusty supergiant IRC+10420 that
is rapidly evolving on human timescales. We show computer simulations of VLTI
interferometry of IRC+10420 with two ATs (wide-field mode, i.e. without fiber
optics spatial filters) and discuss whether the visibility accuracy is
sufficient to distinguish between different theoretical model predictions.


title: Mode identification of Pulsating White Dwarfs using the HST

abstract:
  We have obtained time-resolved ultraviolet spectroscopy for the pulsating DAV
stars G226-29 and G185-32, and for the pulsating DBV star PG1351+489 with the
Hubble Space Telescope Faint Object Spectrograph, to compare the ultraviolet to
the optical pulsation amplitude and determine the pulsation indices. We find
that for essentially all observed pulsation modes, the amplitude rises to the
ultraviolet as the theoretical models predict for l=1 non-radial g-modes. We do
not find any pulsation mode visible only in the ultraviolet, nor any modes
whose phase flips by 180 degrees; in the ultraviolet, as would be expected if
high l pulsations were excited. We find one periodicity in the light curve of
G185-32, at 141 s, which does not fit theoretical models for the change of
amplitude with wavelength of g-mode pulsations.


title: Cicrumnuclear Supernova Remnants and HII Regions in NGC 253

abstract:
  Archival VLA data has been used to produce arcsecond-resolution 6- and 20-cm
images of the region surrounding the nuclear 200-pc (~15") starburst in NGC
253. Twenty-two discrete sources stronger than 0.4 mJy have been detected
within ~2 kpc (~3') of the galaxy nucleus; almost all these sources must be
associated with the galaxy. None of the radio sources coincides with a detected
X-ray binary, so they appear to be due to supernova remnants and H II regions.
The region outside the central starburst has a derived radio supernova rate of
<~0.1/yr, and may account for at least 20% of the recent star formation in NGC
253. Most of the newly identified sources have steep, nonthermal radio spectra,
but several relatively strong thermal sources also exist, containing the
equivalent of tens of O5 stars. These stars are spread over tens of parsecs,
and are embedded in regions having average ionized gas densities of
20-200/cm^3, much lower than in the most active nuclear star-forming regions in
NGC 253 or in the super star clusters seen in other galaxies. The strongest
region of thermal emission coincides with a highly reddened area seen at
near-infrared wavelengths, possibly containing optically obscured H II regions.


title:
An internet server for update pre-main sequence tracks of low- and
  intermediate-mass stars

abstract:
  We present new grids of pre-main sequence (PMS) tracks for stars in the mass
range 0.1 to 7.0 Msun. The computations were performed for four different
metallicities (Z=0.01, 0.02, 0.03 and 0.04). A fifth table has been computed
for the solar composition (Z=0.02), including a moderate overshooting. We
describe the update in the physics of the Grenoble stellar evolution code which
concerns mostly changes in the equation of state (EOS) adopting the formalism
proposed by Pols et al. (1995) and in the treatment of the boundary condition.
Comparisons of our models with other grids demonstrate the validity of this EOS
in the domain of very low-mass stars. Finally, we present a new server
dedicated to PMS stellar evolution which allows the determination of stellar
parameters from observational data, the calculation of isochrones, the
retrieval of evolutionary files and the possibility to generate graphic
outputs.
  WWW site : http://www-laog.obs.ujf-grenoble.fr/activites/starevol/evol.html


title:
Evolutionary Timescale of the DAV G117-B15A: The Most Stable Optical
  Clock Known

abstract:
  We observe G117-B15A, the most precise optical clock known, to measure the
rate of change of the main pulsation period of this blue-edge DAV white dwarf.
Even though the obtained value is only within 1 sigma, Pdot = (2.3 +/- 1.4) x
10^{-15} s/s, it is already constraining the evolutionary timescale of this
cooling white dwarf star.


title: The Age of the Solar Neighbourhood

abstract:
  High-quality Hipparcos data for a complete sample of nearly 12000
main-sequence and subgiant stars, together with Padua isochrones, are used to
constrain the star-formation history of the solar neigbourhood and the
processes that stochastically accelerate disk stars. The velocity dispersion of
a coeval group of stars is found to increase with time from ~8 kms at birth as
t^{0.33}. In the fits, the slope of the IMF near 1 Msun proves to be degenerate
with the rate at which the star-formation rate declines. If the slope of the
IMF is to lie near Salpeter's value, -2.35, the star-formation rate has to be
very nearly constant. The age of the solar neighbourhood is found to be
11.2+/-0.75 Gyr with remarkably little sensitivity to variations in the assumed
metallicity distribution of old disk stars. This age is only a Gyr younger than
the age of the oldest globular clusters when the same isochrones and distance
scale are employed. It is compatible with current indications of the redshift
of luminous galaxy formation only if there is a large cosmological constant. A
younger age is formally excluded because it provides a poor fit to the number
density of red stars. Since this density is subject to a significantly
uncertain selection function, ages as low as 9 Gyr are plausible even though
they lie outside our formal error bars.


title: Hotspot Emission from a Freely Precessing Neutron Star

abstract:
  Recent observations of 1E~161348-5055, the neutron-star candidate at the
center of the supernova remnant RCW 103, show that a component of its emission
varies sinusoidally with a period of approximately six hours. We argue that
this period is what one would expect for a freely precessing neutron star with
a spin period of about one second. We produce light curves for a freely
precessing neutron star with a hotspot. By a suitable choice of parameters, we
obtain light curves which are constant with rotational phase when the flux from
the star reaches a maximum. At other phases of the precession, the flux varies
as the star rotates but the total flux decreases by a factor of several. These
models can explain the behavior observed from 1E~161348-5055 and predict that
the spin period should be detectable at minimum flux from sufficiently
sensitive measurements.


title: Error Estimates for Measurements of Cosmic Shear

abstract:
  In the very near future, weak lensing surveys will map the projected density
of the universe in an unbiased way over large regions of the sky. In order to
interpret the results of studies it is helpful to develop an understanding of
the errors associated with quantities extracted from the observations. In a
generalization of one of our earlier works, we present estimators of the
cumulants and cumulant correlators of the weak lensing convergence field, and
compute the variance associated with these estimators. By restricting ourselves
to so-called compensated filters we are able to derive quite simple expressions
for the errors on these estimates. We also separate contributions from cosmic
variance, shot noise and intrinsic ellipticity of the source galaxies.


title: Complete Zeldovich approximation

abstract:
  We have developed a generalization of the Zeldovich approximation (ZA) that
is exact in a wide variety of situations, including plannar, spherical and
cilyndrical symmetries. We have shown that this generalization, that we call
complete Zeldovich approximation (CZA), is exact to second order at an
arbitrary point within any field. For gaussian fields, the third order error
have been obtained and shown to be very small. For statistical purposes, the
CZA leads to results exact to the third order.


title: A Quantitative Study of Interacting Dark Matter in Halos

abstract:
  We study the evolution of Hernquist profile ``galaxies'' in the presence of
self-interacting dark matter (SIDM), where the properties of the dark matter
can be parameterized by one number, sigma-hat = sigma M/a^2 for a halo of mass
M and break radius a. While the halos form constant density cores of size a/2
on the core radius relaxation time scale core collapse begins shortly
thereafter and a steeper 1/r^2 central density cusp starts forming faster than
predicted by 2-body relaxation. The formation of the steeper central cusp is
accelerated if the cooling baryons adiabatically compress the dark matter. The
natural consequence of SIDM is to exacerbate rather than to mitigate
astrophysical problems created by dark matter density cusps.


title: Propagation of ultra-high energy protons in the nearby universe

abstract:
  We present a new calculation of the propagation of protons with energies
above $10^{19}$ eV over distances of up to several hundred Mpc. The calculation
is based on a Monte Carlo approach using the event generator
  SOPHIA for the simulation of hadronic nucleon-photon interactions and a
realistic integration of the particle trajectories in a random extragalactic
magnetic field. Accounting for the proton scattering in the magnetic field
affects noticeably the nucleon energy as a function of the distance to their
source and allows us to give realistic predictions on arrival energy, time
delay, and arrival angle distributions and correlations as well as secondary
particle production spectra.


title: Cosmic Ray Antiprotons

abstract:
  Cosmic ray antiprotons have been detected for over 20 years and are now
measured reliably. Standard particle and astrophysics predict a conventional
spectrum and abundance of secondary antiprotons consistent with all current
measurements. These measurements place limits on exotic Galactic antiproton
sources and non-standard antiproton properties. Complications arise,
particularly at low energies, with heliospheric modulation of cosmic ray fluxes
and production of standard secondaries from A > 1 nuclear targets. Future
experiments and theoretical developments are discussed.


title: HST/STIS Ultraviolet Imaging of Polar Aurora on Ganymede

abstract:
  We report new observations of the spectrum of Ganymede in the spectral range
1160 - 1720 A made with the Space Telescope Imaging Spectrograph (STIS) on HST
on 1998 October 30. The observations were undertaken to locate the regions of
the atomic oxygen emissions at 1304 and 1356 A, previously observed with the
GHRS on HST, that Hall et al. (1998) claimed indicated the presence of polar
aurorae on Ganymede. The use of the 2" wide STIS slit, slightly wider than the
disk diameter of Ganymede, produced objective spectra with images of the two
oxygen emissions clearly separated. The OI emissions appear in both
hemispheres, at latitudes above 40 degrees, in accordance with recent Galileo
magnetometer data that indicate the presence of an intrinsic magnetic field
such that Jovian magnetic field lines are linked to the surface of Ganymede
only at high latitudes. Both the brightness and relative north-south intensity
of the emissions varied considerably over the four contiguous orbits (5.5
hours) of observation, presumably due to the changing Jovian plasma environment
at Ganymede. However, the observed longitudinal non-uniformity in the emission
brightness at high latitudes, particularly in the southern hemisphere, and the
lack of pronounced limb brightening near the poles are difficult to understand
with current models. In addition to observed solar HI Lyman-alpha reflected
from the disk, extended Lyman-alpha emission resonantly scattered from a
hydrogen exosphere is detected out to beyond two Ganymede radii from the limb,
and its brightness is consistent with the Galileo UVS measurements of Barth et
al. (1997).


title:
Photometric Light Curves and Polarization of Close-in Extrasolar Giant
  Planets

abstract:
  The close-in extrasolar giant planets [CEGPs], $\ltorder$ 0.05 AU from their
parent stars, may have a large component of optically reflected light. We
present theoretical optical photometric light curves and polarization curves
for the CEGP systems, from reflected planetary light. Different particle sizes
of three condensates are considered. In the most reflective case, the
variability is $\approx 100$ micromagnitudes, which will be easily detectable
by the upcoming satellite missions MOST, COROT, and MONS, and possibly from the
ground in the near future. The least reflective case is caused by small, highly
absorbing grains such as solid Fe, with variation of much less than one
micromagnitude. Polarization for all cases is lower than current detectability
limits. We also discuss the temperature-pressure profiles and resulting
emergent spectra of the CEGP atmospheres. We discuss the observational results
of Tau Boo b by Cameron et al. (1999) and Charbonneau et al. (1999) in context
of our model results. The predictions - the shape and magnitude of the light
curves and polarization curves - are highly dependent on the size and type of
condensates present in the planetary atmosphere.


title: Simulated Submillimetre Galaxy Surveys

abstract:
  Current submillimetre surveys are hindered in their ability to reveal
detailed information on the epoch of galaxy formation and the evolutionary
history of a high-redshift starburst galaxy population. The difficulties are
due to the small primary apertures (D < 15 m) of existing submillimetre
telescopes and the limited sensitivities of their first generation of bolometer
cameras. This situation is changing rapidly due to a variety of powerful new
ground-based, airborne and satellite FIR to millimetre wavelength facilities.
Improving our understanding of the luminosity and clustering evolution provides
the motivation for conducting cosmological submillimetre and millimetre
surveys. It is therefore important that we quantify the limitations of the
future surveys and the significance of the results that can be drawn from them.
In this paper we present simulated surveys which are made as realistic as
possible in order to address some key issues confronting existing and
forthcoming surveys. We discuss the results from simulations with a range of
wavelengths (200 um - 1.1 mm), spatial resolutions (6 arcsec - 27 arcsec) and
flux densities (0.01-310 mJy). We address how the measured source-counts could
be affected by resolution and confusion, by the survey sensitivity and noise,
and by the sampling variance due to clustering and shot-noise.


title: Still flat after all these years

abstract:
  The Universe could be spatially flat, positively curved or negatively curved.
Each option has been popular at various times, partly affected by an
understanding that models tend to evolve away from flatness. The curvature of
the Universe is amenable to measurement, through tests such as the
determination of the angles of sufficiently large triangles. The angle
subtended by the characteristic scale on the Cosmic Microwave sky provides a
direct test, which has now been realised through a combination of exquisite
results from a number of CMB experiments.
  After a long and detailed investigation, with many false clues, it seems that
the mystery of the curvature of the Universe is now solved. It's an open and
shut case: the Universe is flat.


title: Galaxy Distributions and Tsallis Statistical Mechanics

abstract:
  Large-scale astrophysical systems are non-extensive due to their long-range
force of gravity. Here we show an approach toward the statistical mechanics of
such self-gravitating systems (SGS). This is a generalization of the standard
statistical mechanics based on the new definition of entropy; Tsallis
statistical mechanics. Developing the composition of entropy and the
generalized Euler relation, we investigate the galaxy distributions in
count-in-cell method. This is applied to the data of CfA II South redshift
survey.


title: 3C radio sources as they've never been seen before

abstract:
  Low-radio-frequency observations played a remarkable role in the early days
of radio astronomy; however, in the subsequent three or four decades their
usefulness has largely been in terms of the finding-frequency of surveys.
Recent technical innovation at the VLA has meant that spatially well-resolved
imaging at low frequencies is now possible. Such imaging is essential to
understanding the relationship between the hotspot and lobe emission in
classical double radio sources, for example. We here present new images of 3C
radio sources at 74 MHz and 330 MHz and discuss their implications.


title: Numerical Simulations of Convective Accretion Flows in Three Dimensions

abstract:
  Advection-dominated accretion flows (ADAFs) are known to be convectively
unstable for low values of the viscosity parameter alpha. Two-dimensional
axisymmetric hydrodynamic simulations of such flows reveal a radial density
profile which is significantly flatter than the rho~r^{-3/2} expected for a
canonical ADAF. The modified density profile is the result of inward transport
of angular momentum by axisymmetric convective eddies. We present
three-dimensional hydrodynamic simulations of convective ADAFs which are free
of the assumption of axisymmetry. We find that the results are qualitatively
and quantitatively similar to those obtained with two-dimensional simulations.
In particular, the convective eddies are nearly axisymmetric and transport
angular momentum inward.


title: The Absolute Abundance of Iron in the Solar Corona

abstract:
  We present a measurement of the abundance of Fe relative to H in the solar
corona using a technique which differs from previous spectroscopic and solar
wind measurements. Our method combines EUV line data from the CDS spectrometer
on SOHO with thermal bremsstrahlung radio data from the VLA. The coronal Fe
abundance is derived by equating the thermal bremsstrahlung radio emission
calculated from the EUV Fe line data to that observed with the VLA, treating
the Fe/H abundance as the sole unknown. We apply this technique to a compact
cool active region and find Fe/H
  = 1.56 x 10^{-4}, or about 4 times its value in the solar photosphere.
Uncertainties in the CDS radiometric calibration, the VLA intensity
measurements, the atomic parameters, and the assumptions made in the spectral
analysis yield net uncertainties of order 20%. This result implies that low
first ionization potential elements such as Fe are enhanced in the solar corona
relative to photospheric values.


title:
Multiple Sub-Jet Model of Gamma Ray Bursts and Possible Origin of X-ray
  Precursors and Post-cursors

abstract:
  We assume that internal shocks of Gamma Ray Bursts (GRBs) consist of multiple
sub-jets with a collimation half-angle $\sim {\rm several
}\times\gamma_i^{-1}$, where $\gamma_i$ is the Lorenz factor of each sub-jet.
If by chance a sub-jet is first emitted off-axis from the line of sight, the
observed peak energy can be in the X-ray region. Next if by chance a subsequent
sub-jet is emitted along the line of sight, then the peak energy will be in the
gamma ray region and the gamma ray may arrive after the X-ray precursor from
the former sub-jet depending on parameters. This model predicts a new class of
GRBs with extremely weak and short gamma ray emission but X-ray precursor
and/or post-cursor as well as an afterglow.


title:
Age and metallicity for six LMC clusters and their surrounding field
  population

abstract:
  We investigate, on the basis of CCD Stroemgren photometry, the ages and
metallicities of six LMC clusters together with their surrounding field
population. The clusters and metallicities are: NGC1651 (in the range
[Fe/H]=-0.65 dex to -0.41 dex), NGC1711 (-0.57+/-0.17 dex), NGC 1806
(-0.71+/-0.23 dex), NGC2031 (-0.52+/-0.21 dex) and NGC2136/37 (-0.55+/-0.23
dex) and NGC2257 (-1.63+/-0.21 dex). In the cluster surroundings, we found
about 650 field stars that were suitable to be used for a determination of an
age-metallicity relation (AMR). Our method is to estimate ages for individual
stars on the basis of Stroemgren isochrones with individually measured
metallicities. With this method we are able to sample the AMR of the field
population up to 8 Gyr. Our metallicity data are incompatible with models
predicting many metal-poor stars (G-dwarf problem). The metallicity of the
field population increased by a factor of six, starting around 2 Gyr ago. The
proposed AMR is consistent with the AMR of the LMC cluster system (including
ESO 121 SC03 and three clusters with an age of 4 Gyr).


title:
Equilibrium sequences of irrotational binary polytropic stars : The case
  of double polytropic stars

abstract:
  Solutions to equilibrium sequences of irrotational binary polytropic stars in
Newtonian gravity are expanded in a power of $\epsilon=a_0/R$, where R and
$a_0$ are the orbital separation of the binary system and the radius of each
star for $R=\infty$. For each order of $\epsilon$, we should solve ordinary
differential equations for arbitrary polytropic indices n. We show solutions
for polytropic indices n= 0.5, 1, 1.5 and 2 up to $\epsilon^6$ orders. Our
semi-analytic solutions can be used to check the validity of numerical
solutions.


title:
Great Circle tidal streams: evidence for a nearly spherical massive dark
  halo around the Milky Way

abstract:
  An all high-latitude sky survey for cool carbon giant stars in the Galactic
halo has revealed 75 such stars, of which the majority are new detections. Of
these, more than half are clustered on a Great Circle on the sky which
intersects the center of Sagittarius dwarf galaxy (Sgr) and is parallel to its
proper motion vector, while many of the remainder are outlying Magellanic Cloud
C-stars. A pole-count analysis of the carbon star distribution clearly
indicates that the Great Circle stream we have isolated is statistically
significant, being a 5-6 sigma over-density. These two arguments strongly
support our conclusion that a large fraction of the Halo carbon stars
originated in Sgr. The stream orbits the Galaxy between the present location of
Sgr, 16 kpc from the Galactic center, and the most distant stream carbon star,
at ~60 kpc. It follows neither a polar nor a Galactic plane orbit, so that a
large range in both Galactic R and z distances are probed. That the stream is
observed as a Great Circle indicates that the Galaxy does not exert a
significant torque upon the stream, so the Galactic potential must be nearly
spherical in the regions probed by the stream. We present N-body experiments
simulating this disruption process as a function of the distribution of mass in
the Galactic halo. A likelihood analysis shows that, in the Galactocentric
distance range 16 kpc < R < 60 kpc, the dark halo is most likely almost
spherical. We rule out, at high confidence levels, the possibility that the
Halo is significantly oblate, with isodensity contours of aspect q_m < 0.7.
This result is quite unexpected and contests currently popular galaxy formation
models. (Abridged)


title: Spectroscopy and BVI photometry of the young open cluster NGC 6604

abstract:
  BVI photometry (from South Africa Astron. Obs.), Echelle high resolution
spectroscopy and AFOSC integral field spectroscopy (from Asiago, Italy) of the
young open cluster NGC 6604 are presented. Age, distance, reddening,
membership, radial and rotational velocities are derived and discussed. An age
of 5 million years, a distance of 1.7 kpc and a reddening E(B-V)=1.02 are
found. The cluster radial velocity is in agreement with the Hron (1987) model
for the Galaxy disk rotation. Pre-ZAMS objects are not present down to M_V =
+1.5 mag.


title:
Observations of Mira stars with the IOTA/FLUOR interferometer and
  comparison with Mira star models

abstract:
  We present K-band observations of five Mira stars with the IOTA
interferometer. The interferograms were obtained with the FLUOR fiber optics
beam combiner which provides high-accuracy visibility measurements in spite of
time-variable atmospheric conditions. For the Mira stars X Oph, R Aql, RU Her,
R Ser, and V CrB we derived the uniform-disk diameters 11.7 mas, 10.9 mas, 8.4
mas, 8.1 mas, and 7.9 mas (+/-0.3 mas), respectively. Simultaneous photometric
observations yielded the bolometric fluxes. The derived angular Rosseland radii
and the bolometric fluxes allowed the determination of effective temperatures.
For instance, the effective temperature of R Aql was determined to be 3072 K
+/- 161 K. A Rosseland radius for R Aql of 250 Rsun +/- 63 Rsun was derived
from the angular Rosseland radius of 5.5 mas +/- 0.2 mas and the HIPPARCOS
parallax of 4.73 mas +/- 1.19 mas. The observations were compared with
theoretical Mira star models of Bessel, Scholz and Wood (1996) and Hofmann,
Scholz and Wood (1998).


title: BeppoSAX observations of AM Herculis in intermediate and high states

abstract:
  Temporal and spectral analyses from BeppoSAX observations of AM Her performed
during both an intermediate and a high state are presented and discussed.
Optical observations taken a few days after the X-ray ones are also presented.
  During the intermediate state observation, the source was in its "normal",
one-pole accretion mode. In the high state it switched to an hitherto
unobserved atypical "two-pole" accretion mode, with significant soft and hard
X-ray emission from both poles. The emission from the second pole is much
softer than that from the primary pole, while the soft X-ray excess of the
primary pole is fairly modest in this accretion mode. These facts suggest that
accretion onto the secondary is mainly due to blobs penetrating deeply in the
photosphere, while that on the primary pole is mostly via a more homogeneous
column, giving rise to the classical standing shock. A strong X-ray flaring
activity is also observed in the soft X-ray band, but not the hard X-ray and
optical emissions indicating that flares are due to inhomogeneous
blobby-accretion events.


title: ROSAT Observations of the Vela Pulsar

abstract:
  The ROSAT HRI was used to monitor X-ray emission from the Vela Pulsar. Six
observations span 2-1/2 years and 3 glitches. The summed data yield a
determination of the pulse shape, and X-ray emission from the pulsar is found
to be 12 % pulsed with one broad and two narrow peaks. One observation occurred
15 days after a large glitch. No change in pulse structure was observed and any
change in X-ray luminosity, if present, was less than 3 %. Implications for
neutron star structure are discussed.


title: Cosmic Ray Anisotropy Analysis with a Full-Sky Observatory

abstract:
  A cosmic ray observatory with full-sky coverage can exploit standard
anisotropy analysis methods that do not work if part of the celestial sphere is
never seen. In particular, the distribution of arrival directions can be fully
characterized by a list of spherical harmonic coefficients. The dipole vector
and quadrupole tensor are of special interest, but the full set of harmonic
coefficients constitutes the anisotropy fingerprint that may be needed to
reveal the identity of the cosmic ray sources. The angular power spectrum is a
coordinate-independent synopsis of that fingerprint. The true cosmic ray
anisotropy can be measured despite non-uniformity in celestial exposure,
provided the observatory is not blind to any region of the sky. This paper
examines quantitatively how the accuracy of anisotropy measurement depends on
the number of arrival directions in a data set.


title:
Accretion Disk Boundary Layers Around Neutron Stars: X-ray Production in
  Low-Mass X-ray Binaries

abstract:
  We present solutions for the structure of the boundary layer where the
accretion disk meets the neutron star, which is expected to be the dominant
source of high-energy radiation in low-mass X-ray binaries which contain weakly
magnetized accreting neutron stars.
  We find that the main portion of the boundary layer gas is hot (> ~10^8 K),
low in density, radially and vertically extended, and optically thick to
scattering but optically thin to absorption. It will produce large X-ray
luminosity by Comptonization. Energy is transported inward by viscosity,
concentrating the energy dissipation in the dense, optically thick zone close
to the stellar surface. We explore the dependence of the boundary layer
structure on the mass accretion rate, the rotation rate of the star, the alpha
viscosity parameter and the viscosity prescription.
  Radiation pressure is the dominant source of pressure in the boundary layer;
the flux is close to the Eddington limiting flux even for luminosities well
below (~0.01 times) L(Edd). At luminosities near L(Edd), the boundary layer
expands radially, and has a radial extent larger than one stellar radius.
  Based on the temperatures and optical depths which characterize the boundary
layer, we expect that Comptonization will produce a power-law spectrum at low
source luminosities. At high luminosities, a Planckian spectrum will be
produced in the dense region where most of the energy is released, and modified
by Comptonization as the radiation propagates outward.


title: Temporal Evolution of X-ray Lags in Cygnus X-1

abstract:
  We present the long term evolution of the frequency-dependent X-ray time lags
of the black hole candidate Cygnus X-1 as measured in 1996 and 1998 with the
Rossi X-ray Timing Explorer (RXTE). Lag spectra measured during the 1996 June
soft state are very similar to those seen during 1996 December and most of 1998
while Cyg~X-1 was in its hard state. During state transitions, however, the
shape and magnitude of the X-ray lag is highly variable and tends to be much
larger than outside of the state transitions. This behavior is most obvious in
the 1--10 Hz band. The increase of the X-ray lag during the state transitions
might be related to the formation and destruction of the synchrotron radiation
emitting outflows present during the hard state.


title: Imaging of the protoelliptical NGC 1700 and its globular cluster system

abstract:
  An excellent candidate for a young elliptical, or `protoelliptical' galaxy is
NGC 1700. Here we present new B, V and I band imaging using the Keck telescope
and reanalyse existing V and I band images from the Hubble Space Telescope.
After subtracting a model of the galaxy from the Keck images NGC 1700 reveals
two symmetric tidal tail-like structures. If this interpretation is correct, it
suggests a past merger event involving two spiral galaxies. These tails are
largely responsible for the `boxiness' of the galaxy isophotes observed at a
radius of about 13 kpc. We also show that the B-I colour distribution of the
globular cluster system is bimodal. The mean colour of the blue population is
consistent with those of old Galactic globular clusters. Relative to this old,
metal poor population, we find that the red population is younger and more
metal rich. This young population has a similar age and metallicity as that
inferred for the central stars, suggesting that they are both associated with
an episode of star formation triggered by the merger that may have formed the
galaxy. Although possessing large errors, we find that the majority of the age
estimates of NGC 1700 are reasonably consistent and we adopt a `best estimate'
for the age of 3.0 +/-1.0 Gyr. This relatively young age places NGC 1700 within
the age range where there is a notable lack of obvious candidates for
protoellipticals. The total globular cluster specific frequency is rather low
for a typical elliptical, even after taking into account fading of the galaxy
over the next 10 Gyr. We speculate that NGC 1700 will eventually form a
relatively `globular cluster poor' elliptical galaxy.


title: VLT observations of GRS 1915+105

abstract:
  We present near infrared spectroscopy of the superluminal microquasar \grs\
obtained with the first unit of the VLT (Based on observations collected at the
European Southern Observatory, Chile (ESO No 63.H-0261).) and the ISAAC
spectro-imager. The emission features detected in the VLT data have been
identified as He I, Br $\gamma$, He II and Na I. The detection of Na I is
reported here for the first time, while our confirmation of weak He II emission
provides support to previous marginal detections of this feature. By comparing
the observed spectra with those of massive stars, we find that our results are
very consistent with \grs being a high mass X-ray system with an early type
primary, as previously proposed by Chaty et al. (1996) and Mirabel et al.
(1997). The VLT spectra also provide evidence of P Cygni profiles, that turn
into blue emission wings when the system is in outburst. This observed line
profile evolution implies that \grs must be surrounded by an expanding
envelope, that is partially blown out during the X-ray outbursts. The presence
of such circumstellar gaseous material around \grs is more naturally understood
in the context of a massive luminous star than if the system was a low-mass
X-ray binary.


title:
On the Blandford - Znajek mechanism of the energy loss of a rotating
  black hole

abstract:
  The Grad--Shafranov approach to the problem of the structure of the black
hole magnetosphere is discussed. For the double transonic flow, the number of
boundary conditions in the pair creation region is shown to be sufficient to
determine not only the longitudinal electric current, but also the angular
velocity of a flow as a solution to a problem. As a result, the energy loss is
determined by the physical parameters at the particle creation region rather
than the "boundary conditions" at the event horizon.


title: Gamma-Ray Bursts as a Cosmic Window for Galaxy Evolution

abstract:
  Present knowledge indicates that gamma-ray bursts are linked with massive
stars. They will become invaluable probes of the early universe and galaxy
formation. In the future, it will be possible to use gamma-ray bursts for two
purposes: 1) to probe the history of massive star formation in the Universe by
the rate of occurence of gamma-ray bursts, and 2) for the study of galaxy
evolution at all lookback times by determining the nature of the galaxy hosts.
Because gamma-rays are not attenuated by intervening dust and gas, the
selection of the cosmic sites of massive star formation by this method is less
affected by the biases associated with optical-uv surveys (e.g. UV-dropout
techniques). Infrared and sub-millimeter follow up studies of the hosts of
gamma-ray bursts may: 1) reveal a putative population of reddened ($R-K \geq
4$) galaxies at high redshifts, and 2) detect very massive stars (population
III) formed at $z \geq$ 5.