title: Resolving the extragalactic hard X-ray background

abstract:
  The origin of the hard (2-10 keV) X-ray background has remained mysterious
for over 35 years. Most of the soft (0.5-2 keV) X-ray background has been
resolved into discrete sources, which are primarily quasars; however, these
sources do not have the flat spectral shape required to match the X-ray
background spectrum. Here we report the results of an X-ray survey 30 times
more sensitive than previous studies in the hard band and four times more
sensitive in the soft band. The sources detected in our survey account for at
least 75 per cent of the hard X-ray background. The mean X-ray spectrum of
these sources is in good agreement with that of the background. The X-ray
emission from the majority of the detected sources is unambiguously associated
with either the nuclei of otherwise normal bright galaxies or optically faint
sources, which could either be active nuclei of dust enshrouded galaxies or the
first quasars at very high redshifts.


title:
Detection of Multi-TeV Gamma Rays from Markarian 501 during an
  Unforeseen Flaring State in 1997 with the Tibet Air Shower Array

abstract:
  In 1997, the BL Lac Object Mrk 501 entered a very active phase and was the
brightest source in the sky at TeV energies, showing strong and frequent
flaring. Using the data obtained with a high density air shower array that has
been operating successfully at Yangbajing in Tibet since 1996, we searched for
gamma-ray signals from this source during the period from February through
August in 1997. Our observation detected multi-TeV $\gamma$-ray signals at the
3.7-Sigma level during this period. The most rapid increase of the excess
counts was observed between April 7 and June 16 and the statistical
significance of the excess counts in this period was 4.7-Sigma. Among several
observations of flaring TeV gamma-rays from Mrk 501 in 1997, this is the only
observation using a conventional air shower array. We present the energy
spectrum of gamma-rays which will be worthy to compare with those obtained by
imaging atmospheric Cerenkov telescopes.


title:
Perturbative Analysis of Adaptive Smoothing Methods in Quantifying
  Large-Scale Structure

abstract:
  Smoothing operation to make continuous density field from observed point-like
distribution of galaxies is crucially important for topological or
morphological analysis of the large-scale structure, such as, the genus
statistics or the area statistics (equivalently the level crossing statistics).
It has been pointed out that the adaptive smoothing filters are more efficient
tools to resolve cosmic structures than the traditional spatially fixed
filters. We study weakly nonlinear effects caused by two representative
adaptive methods often used in smoothed hydrodynamical particle (SPH)
simulations. Using framework of second-order perturbation theory, we calculate
the generalized skewness parameters for the adaptive methods in the case of
initially power-law fluctuations.
  Then we apply the multidimensional Edgeworth expansion method and investigate
weakly nonlinear evolution of the genus statistics and the area statistics.
Isodensity contour surfaces are often parameterized by the volume fraction of
the regions above a given density threshold. We also discuss this
parameterization method in perturbative manner.


title: Performance Results of the AMS-01 Aerogel Threshold Cherenkov

abstract:
  The Alpha Magnetic Spectrometer (AMS) was flown in june 1998 on board of the
space shuttle Discovery (flight STS-91) at an altitude ranging between 320 and
390 km. This preliminary version of AMS included an Aerogel Threshold Cherenkov
detector (ATC) to separate antiprotons from electron background, for momenta
less than 3.5 GeV/c. In this paper, the design and physical principles of ATC
will be discussed briefly, then the performance results of the ATC will be
presented.


title: Analytic solutions for coupled linear perturbations

abstract:
  Analytic solutions for the evolution of cosmological linear density
perturbations in the baryonic gas and collisionless dark matter are derived.
The solutions are expressed in a closed form in terms of elementary functions,
for arbitrary baryonic mass fraction. They are obtained assuming $\Omega=1$ and
a time independent comoving Jeans wavenumber, $k_J$. By working with a time
variable $\tau\equiv \ln(t^{2/3})$, the evolution of the perturbations is
described by linear differential equations with constant coefficients. The new
equations are then solved by means of Laplace transformation assuming that the
gas and dark matter trace the same density field before a sudden heating epoch.
In a dark matter dominated Universe, the ratio of baryonic to dark matter
density perturbation decays with time roughly like $\exp(-5\tau/4)\propto
t^{-5/6}$ to the limiting value $1/[1+(k/k_J)^2]$. For wavenumbers
$k>k_J/\sqrt{24}$, the decay is accompanied with oscillations of a period $
8\pi/\sqrt{24 (k/k_J)^2 -1}$ in $\tau$. In comparison, as $\tau $ increases in
a baryonic matter dominated Universe, the ratio approaches $1-(k/k_J)^2$ for
$k\le k_J$, and zero otherwise.


title: ROSAT HRI catalogue of X-ray sources in the LMC region

abstract:
  All 543 pointed observations of the ROSAT High Resolution Imager (HRI) with
exposure times higher than 50 sec in a field of 10 deg x 10 deg covering the
Large Magellanic Cloud (LMC) were analyzed. A catalogue was produced containing
397 X-ray sources with their properties measured by the HRI. The list was
cross-correlated with the ROSAT Position Sensitive Propotional Counter (PSPC)
source catalogue presented by Haberl & Pietsch (1999), the SIMBAD data base,
and the TYCHO catalogue. 138 HRI sources are contained in the PSPC catalogue.
The spatial resolution of the HRI was higher than that of the PSPC and the
source position could be determined with errors mostly smaller than 15 arcsec
which are dominated by systematic attitude errors. 94 HRI sources were
identified with known objects based on their positional coincidence and X-ray
properties. The catalogue contains 39 foreground stars, 24 supernova remnants
(SNRs), five supersoft sources (SSSs), nine X-ray binaries (XBs), and nine AGN
well known from literature. Another eight sources were identified with known
candidates for these source classes. Additional 21 HRI sources are suggested in
the present work as candidates for SNR, X-ray binary in the LMC, or background
AGN because of their extent, hardness ratios, X-ray to optical flux ratio, or
flux variability.


title:
X-ray photoionized plasma diagnostics with Helium-like ions. Application
  to Warm Absorber-Emitter in Active Galactic Nuclei

abstract:
  We present He-like line ratios (resonance, intercombination and forbidden
lines) for totally and partially photoionized media. For solar plasmas, these
line ratios are already widely used for density and temperature diagnostics of
coronal (collisional) plasmas. In the case of totally and partially
photoionized plasmas, He-like line ratios allow for the determination of the
ionization processes involved in the plasma (photoionization with or without an
additional collisional ionization process), as well as the density and the
electronic temperature. With the new generation of X-ray satellites,
Chandra/AXAF, XMM and Astro-E, it will be feasible to obtain both high spectral
resolution and high sensitivity observations. Thus in the coming years, the
ratios of these three components will be measurable for a large number of
non-solar objects. In particular, these ratios could be applied to the Warm
Absorber-Emitter, commonly present in Active Galactic Nuclei (AGN). A better
understanding of the Warm Absorber connection to other regions (Broad Line
Region, Narrow Line Region) in AGN (Seyferts type-1 and type-2, low- and
high-redshift quasars...) will be an important key to obtaining strong
constraints on unified schemes.
  We have calculated He-like line ratios, for Z=6, 7, 8, 10, 12 and 14, taking
into account the upper level radiative cascades which we have computed for
radiative and dielectronic recombinations and collisional excitation. The
atomic data are tabulated over a wide range of temperatures in order to be used
for interpreting a large variety of astrophysical plasmas.


title: CHVCs: Galactic Building Blocks at z = 0

abstract:
  A distinct sub-class of anomalous velocity HI emission features has emerged
from recent high quality surveys of the Local Group environment, namely the
compact high velocity clouds (CHVCs). A program of high-resolution imaging with
the Westerbork array and the Arecibo telescope has begun to provide many
insights into the nature of these objects. Elongated core components with a
velocity gradient consistent with rotation (V_Rot ~ 15 km/s) are seen in many
objects. Comparison of volume and column densities has allowed the first
distance estimates to be made (600+/-300 kpc). The objects appear to be
strongly dark-matter dominated with dark-to-gas mass ratios of 30-50 implied if
the typical distance is 700 kpc.


title: Evidence for a Young Stellar Population in NGC 5018

abstract:
  Two absorption line indices, Ca II and Hdelta/FeI4045, measured from high
resolution spectra are used with evolutionary synthesis models to verify the
presence of a young stellar population in NGC 5018. The derived age of this
population is about ~2.8 Gyr with a metallicity roughly solar and it completely
dominates the integrated light of the galaxy near 4000 A.


title:
Testing the connection between the X-ray and submillimetre source
  populations using Chandra

abstract:
  The powerful combination of the Chandra X-ray telescope, the SCUBA
submillimetre-wave camera and the gravitational lensing effect of the massive
galaxy clusters A2390 and A1835 has been used to place stringent X-ray flux
limits on six faint submillimetre SCUBA sources and deep submillimetre limits
on three Chandra sources which lie in fields common to both instruments. One
further source is marginally detected in both the X-ray and submillimetre
bands. For all the SCUBA sources our results are consistent with
starburst-dominated emission. For two objects, including SMMJ14011+0252 at
z=2.55, the constraints are strong enough that they can only host powerful
active galactic nuclei if they are both Compton-thick and any scattered X-ray
flux is weak or itself absorbed. The lensing amplification for the sources is
in the range 1.5-7, assuming that they lie at z>1. The brightest detected X-ray
source has a faint extended optical counterpart (I~22) with colours consistent
with a galaxy at z~1. The X-ray spectrum of this galaxy is hard, implying
strong intrinsic absorption with a column density of about 1e23 cm-2 and an
intrinsic (unabsorbed) 2-10 keV luminosity of 3e44 erg/s. This source is
therefore a Type-II quasar. The weakest detected X-ray sources are not detected
in HST images down to I~26.


title: Ages of late spectral type Vega-like stars

abstract:
  We have estimated the ages of eight late-type Vega-like stars by using
standard age dating methods for single late-type stars, e.g., location on the
color magnitude diagram, Li 6708 angstrom absorption, CaII H&K emission, X-ray
luminosity, and stellar kinematic population. With the exception of the very
unusual pre-main sequence star system HD 98800, all the late-type Vega-like
stars are the same age as the Hyades cluster (600-800 Myr) or older.


title:
High Resolution Spectroscopy of the X-ray Photoionized Wind in Cygnus
  X-3 with the Chandra High Energy Transmission Grating Spectrometer

abstract:
  We present a preliminary analysis of the 1--10 keV spectrum of the massive
X-ray binary Cyg X-3, obtained with the High Energy Transmission Grating
Spectrometer on the Chandra X-ray Observatory. The source reveals a richly
detailed discrete emission spectrum, with clear signatures of
photoionization-driven excitation.
  Among the spectroscopic novelties in the data are the first astrophysical
detections of a number of He-like 'triplets' (Si, S, Ar) with emission line
ratios characteristic of photoionization equilibrium, fully resolved narrow
radiative recombination continua of Mg, Si, and S, the presence of the H-like
Fe Balmer series, and a clear detection of a ~ 800 km/s large scale velocity
field, as well as a ~1500 km/s FWHM Doppler broadening in the source. We
briefly touch on the implications of these findings for the structure of the
Wolf-Rayet wind.


title:
Multi-colour PL-relations of Cepheids in the Hipparcos catalogue and the
  distance to the LMC

abstract:
  We analyse a sample of 236 Cepheids from the Hipparcos catalog, using the
method of ``reduced parallaxes'' in V, I, K and the reddening-free
``Wesenheit-index''. We compare our sample to those considered by Feast &
Catchpole (1997) and Lanoix et al. (1999).
  We stress the importance of two systematic effects which influence the
distance to the LMC: the slopes of the Galactic PL-relations and metallicity
corrections. In order to assess the influence of these various effects, we
present 27 distance moduli (DM) to the LMC, based on three different colours
(V,I,K), three different slopes, and three different metallicity corrections.
  The DM to the LMC based on the parallax data can be summarised as follows.
Based on the PL-relation in V and I, and the Wesenheit-index, the DM is 18.60
\pm 0.11 (\pm 0.08 slope)(^{+0.08}_{-0.15} metallicity), which is our current
best estimate.
  Based on the PL-relation in K the DM is 18.52 \pm 0.18$ (\pm 0.03 slope) (\pm
0.06 metallicity)(^{+0.10}_{-0} sampling bias}).
  The random error is mostly due to the given accuracy of the Hipparcos
parallaxes and the number of Cepheids in the respective samples. The terms
between parentheses indicate the possible systematic uncertainties due to the
slope of the Galactic PL-relations, the metallicity corrections, and in the
K-band, due to the limited number of stars. Recent work by Sandage et al.
(1999) indicates that the effect of metallicity towards shorter distances may
be smaller in V and I than indicated here.


title:
Study of Multi-muon Events from EAS with the L3 Detector at Shallow
  Depth Underground

abstract:
  We present first preliminary data from the L3+Cosmics experiment and results
from Monte Carlo simulations of multi-muon events as observed 30 m underground.


title:
The 35-Day Evolution of the Hercules X-1 Pulse Profile: Evidence For A
  Resolved Inner Disk Occultation of the Neutron Star

abstract:
  Ginga and Rossi X-ray Timing Explorer (RXTE) observations have allowed an
unprecedented view of the recurrent systematic pulse shape changes associated
with the 35-day cycle of Hercules X-1, a phenomenon currently unique among the
known accretion-powered pulsars. We present observations of the pulse shape
evolution. An explanation for the pulse evolution in terms of a freely
precessing neutron star is reviewed and shown to have several major
difficulties in explaining the observed pulse evolution pattern. Instead, we
propose a phenomenological model for the pulse evolution based upon an
occultation of the pulse emitting region by the tilted, inner edge of a
precessing accretion disk. The systematic and repeating pulse shape changes
require a resolved occultation of the pulse emission region. The observed pulse
profile motivates the need for a pulsar beam consisting of a composite coaxial
pencil and fan beam but the observed evolution pattern requires the fan beam to
be focused around the neutron star and beamed in the antipodal direction. The
spectral hardness of the pencil beam component suggests an origin at the
magnetic polar cap, with the relatively softer fan beam emission produced by
backscattering from within the accretion column, qualitatively consistent with
several theoretical models for X-ray emission from the accretion column of an
accreting neutron star.


title: An analytic model for the epoch of halo creation

abstract:
  In this paper we describe the Bayesian link between the cosmological mass
function and the distribution of times at which isolated halos of a given mass
exist. By assuming that clumps of dark matter undergo monotonic growth on the
time-scales of interest, this distribution of times is also the distribution of
`creation' times of the halos. This monotonic growth is an inevitable aspect of
gravitational instability. The spherical top-hat collapse model is used to
estimate the rate at which clumps of dark matter collapse. This gives the prior
for the creation time given no information about halo mass. Applying Bayes'
theorem then allows any mass function to be converted into a distribution of
times at which halos of a given mass are created. This general result covers
both Gaussian and non-Gaussian models. We also demonstrate how the mass
function and the creation time distribution can be combined to give a joint
density function, and discuss the relation between the time distribution of
major merger events and the formula calculated. Finally, we determine the
creation time of halos within three N-body simulations, and compare the link
between the mass function and creation rate with the analytic theory.


title:
Emission-Line Properties of 3CR Radio Galaxies III: Origins and
  Implications of the Velocity Fields

abstract:
  We present the results of an analysis of the large scale velocity fields of
the ionized gas associated with powerful radio galaxies. Long-slit spectra of
52 objects provide a sample of resolved velocities that span a wide range of
redshifts, radio and emission-line luminosities. Line widths reaching 1000 km/s
and resolved velocity fields with amplitudes of up 1500 km/ s are found on
scales from 10 to 100 kpc in the environments of radio galaxies at redshifts
larger than 0.5. The global velocities and FWHM are of comparable amplitudes in
the FRII sources, while the FRI sources have FWHM values that are larger than
their resolved velocity fields. We find evidence for systematically larger line
widths and velocity field amplitudes at z > 0.6. Several of the largest
amplitude systems contain two galaxies with small projected separations. All of
the > 1000 km/s systems occur in objects at z > 0.6 and all have comparable
radio and [OII] sizes. There is a weak correlation of off-nuclear line widths
and velocity field with the ratio of the radio and emission-line sizes, but it
is of low statistical significance and there is a very large dispersion. The
change in properties at redshifts above z ~ 0.6 could reflect a difference in
environments of the host galaxies, with the hosts inhabiting higher density
regions with increasing redshift. The mass of ionized gas and the apparent
enclosed dynamical mass are correllated and both increase steeply with redshift
and/or radio power.


title: New Dark Matter Physics: Clues from Halo Structure

abstract:
  We examine the effect of primordial dark matter velocity dispersion and/or
particle self-interactions on the structure and stability of galaxy halos,
especially with respect to the formation of substructure and central density
cusps. Primordial velocity dispersion is characterised by a ``phase density''
$Q\equiv \rho/<v^2>^{3/2}$, which for relativistically-decoupled relics is
determined by particle mass and spin and is insensitive to cosmological
parameters. Finite $Q$ leads to small-scale filtering of the primordial power
spectrum, which reduces substructure, and limits the maximum central density of
halos, which eliminates central cusps. The relationship between $Q$ and halo
observables is estimated. The primordial $Q$ may be preserved in the cores of
halos and if so leads to a predicted relation, closely analogous to that in
degenerate dwarf stars, between the central density and velocity dispersion.
Classical polytrope solutions are used to model the structure of halos of
collisional dark matter, and to show that self-interactions in halos today are
probably not significant because they destabilize halo cores via heat
conduction. Constraints on masses and self-interactions of dark matter
particles are estimated from halo stability and other considerations.


title: CO on Titan: More Evidence for a Well-Mixed Vertical Profile

abstract:
  We report new interferometric observations of the CO (2-1) rotational
transition on Titan. We find that the spectrum is best fit by a uniform profile
of 52 ppm, with estimated errors of 6 ppm (40 to 200 km) and 12 ppm (200 to 300
km).


title: Probing black hole X-ray binaries with the Keck telescopes

abstract:
  The advent of the large effective apertures of the Keck telescopes has
resulted in the determination with unprecedented accuracy of the mass functions
and mass ratios of faint (R ~ 21 mag) X-ray transients (GS 2000+25, GRO
J0422+32, Nova Oph 1977, Nova Vel 1993), as well as constraining the
main-sequence companion star parameters and producing images of the accretion
disks around the black holes.


title: A Close Separation Double Quasar Lensed by a Gas-Rich Galaxy

abstract:
  In the course of a Cycle 8 snapshot survey, we have discovered that the
z=1.565 quasar HE 0512-3329 is a double with image separation 0.644", almost
certainly due to gravitational lensing. The two components differ in brightness
by only 0.4 magnitudes and a high signal-to-noise ground-based composite
optical spectrum shows no trace of any stellar features at zero redshift,
essentially ruling out the possibility that one of the two components is an
ordinary Galactic star. The optical spectrum shows strong absorption features
of MgII, MgI, FeII, FeI, and CaI, all at an identical intervening redshift of
z=0.9313, probably due to the lensing object. The strength of the MgII and the
presence of the other low ionization absorption features is strong evidence for
a damped Lyman alpha system, likely the disk of a spiral galaxy. Point spread
function fitting to remove the two quasar components from the STIS image leads
to a tentative detection of a third object which may be the nucleus of the
lensing galaxy. The brighter component is significantly redder than the
fainter, due to either differential extinction or microlensing.


title: Distance-Redshift in Inhomogeneous FLRW

abstract:
  We give distance--redshift relations in terms of elliptic integrals for three
different mass distributions of the Friedmann-Lema\^\i tre-Robertson-Walker
(FLRW) cosmology. These models are dynamically pressure free FLRW on large
scales but, due to mass inhomogeneities, differ in their optical properties.
They are the filled-beam model (standard FLRW), the empty-beam model (no mass
density exists in the observing beams) and the 2/3 filled-beam model. For
special $\OM$-- $\OL$ values the elliptic integrals reduce to more familiar
functions. These new expressions for distance-redshift significantly reduce
computer evaluation times.


title:
Discovery of an Obscured Broad Line Region in the High Redshift Radio
  Galaxy MRC 2025-218

abstract:
  This paper presents infrared spectra taken with the newly commissioned
NIRSPEC spectrograph on the Keck II Telescope of the High Redshift Radio Galaxy
MRC 2025-218 (z=2.63) These observations represent the deepest infrared spectra
of a radio galaxy to date and have allowed for the detection of Hbeta, [OIII]
(4959/5007), [OI] (6300), Halpha, [NII] (6548/6583) and [SII] (6716/6713). The
Halpha emission is very broad (FWHM = 9300 km/s) and luminous (2.6x10^44
ergs/s) and it is very comparable to the line widths and strengths of radio
loud quasars at the same redshift. This strongly supports AGN unification
models linking radio galaxies and quasars, although we discuss some of the
outstanding differences. The [OIII] (5007) line is extremely strong and has
extended emission with large relative velocities to the nucleus. We also derive
that if the extended emission is due to star formation, each knot has a star
formation rate comparable to a Lyman Break Galaxy at the same redshift.


title:
Constraints on Cosmological Parameters from Future Galaxy Cluster
  Surveys

abstract:
  We study the expected redshift evolution of galaxy cluster abundance between
0 < z < 3 in different cosmologies, including the effects of the cosmic
equation of state parameter w=p/rho. Using the halo mass function obtained in
recent large scale numerical simulations, we model the expected cluster yields
in a 12 deg^2 Sunyaev-Zeldovich Effect (SZE) survey and a deep 10^4 deg^2 X-ray
survey over a wide range of cosmological parameters. We quantify the
statistical differences among cosmologies using both the total number and
redshift distribution of clusters. Provided that the local cluster abundance is
known to a few percent accuracy, we find only mild degeneracies between w and
either Omega_m or h. As a result, both surveys will provide improved
constraints on Omega_m and w. The Omega_m-w degeneracy from both surveys is
complementary to those found either in studies of CMB anisotropies or of
high-redshift Supernovae (SNe). As a result, combining these surveys together
with either CMB or SNe studies can reduce the statistical uncertainty on both w
and Omega_m to levels below what could be obtained by combining only the latter
two data sets. Our results indicate a formal statistical uncertainty of about
3% (68% confidence) on both Omega_m and w when the SZE survey is combined with
either the CMB or SN data; the large number of clusters in the X-ray survey
further suppresses the degeneracy between w and both Omega_m and h. Systematics
and internal evolution of cluster structure at the present pose uncertainties
above these levels. We briefly discuss and quantify the relevant systematic
errors. By focusing on clusters with measured temperatures in the X-ray survey,
we reduce our sensitivity to systematics such as non-standard evolution of
internal cluster structure.


title:
Nucleosynthesis in Chandrasekhar Mass Models for Type Ia Supernovae and
  Constraints on Progenitor Systems and Burning-Front Propagation

abstract:
  We calculate explosive nucleosynthesis in Chandrasekhar mass models for Type
Ia Supernovae(SNe Ia) to obtain new constraints on the rate of matter accretion
onto the progenitor white dwarf and on the ignition density of central carbon
deflagration. The calculated abundance of the Fe-group neutron-rich nuclei is
highly sensitive to the electron captures taking place in the central layers.
The yields obtained from a slow central deflagration, and from a fast
deflagration or delayed detonation in the outer layers, are combined and put to
comparison with solar isotopic abundances. We found that (1) to avoid too large
ratios of $^{54}$Cr/$^{56}$Fe and $^{50}$Ti/$^{56}$Fe, the ignition density
should be as low as \ltsim 2 \e9 \gmc, and that (2) to avoid the overproduction
of $^{58}$Ni and $^{54}$Fe, either the flame speed should not exceed a few % of
the sound speed in the central low $Y_e$ layers, or the progenitor star has to
be metal-poor compared with solar. Such low central densities can be realized
by a rapid accretion as fast as $\dot M$ \gtsim 1 $\times$ 10$^{-7}$M$_\odot$
yr$^{-1}$. In order to reproduce the solar abundance of $^{48}$Ca, one also
needs progenitor systems that undergo ignition at higher densities. We also
found that the total amount of $^{56}$Ni, the Si-Ca/Fe ratio, and the abundance
of elements like Mn and Cr (incomplete Si-burning ashes), depend on the density
of the deflagration-detonation transition in delayed detonations. Our
nucleosynthesis results favor transition densities slightly below 2.2$\times
10^7$ g cm$^{-3}$.


title: Discovery of a Color-Selected Quasar at z=5.50

abstract:
  We present observations of RD J030117+002025, a quasar at z=5.50 discovered
from deep, multi-color, ground-based observations covering 74 square arcmin.
This is the most distant quasar or AGN currently known. The object was targeted
as an R-band dropout, with R(AB)>26.3 (3-sigma limit in a 3 arcsec diameter
region), I(AB)=23.8, and z(AB)=23.4. The Keck/LRIS spectrum shows broad
Lyman-alpha/NV emission and sharp absorption decrements from the
highly-redshifted hydrogen forests. The fractional continuum depression due to
the Lyman-alpha forest is D(A)=0.90. RD J030117+002025 is the least luminous,
high-redshift quasar known (M(B)~-22.7).


title: Runaway of Line-Driven Winds Towards Critical and Overloaded solutions

abstract:
  Line-driven winds from hot stars and accretion disks are thought to adopt a
unique, critical solution which corresponds to maximum mass loss rate and a
particular velocity law. We show that in the presence of negative velocity
gradients, radiative-acoustic (Abbott) waves can drive shallow wind solutions
towards larger velocities and mass loss rates. Perturbations introduced
downstream from the wind critical point lead to convergence towards the
critical solution. By contrast, low-lying perturbations cause evolution towards
a mass-overloaded solution, developing a broad deceleration region in the wind.
Such a wind differs fundamentally from the critical solution. For sufficiently
deep-seated perturbations, overloaded solutions become time-dependent and
develop shocks and shells.


title: The Toronto Red-Sequence Cluster Survey: First Results

abstract:
  The Toronto Red-Sequence Cluster Survey (TRCS) is a new galaxy cluster survey
designed to provide a large sample of optically selected 0.1 < z < 1.4
clusters. The planned survey data is 100 square degrees of two color (R and z')
imaging, with a 5-sigma depth ~2 mag past M* at z=1. The primary scientific
drivers of the survey are a derivation of Omega_m and sigma_8 (from N(M,z) for
clusters) and a study of cluster galaxy evolution with a complete sample. This
paper gives a brief outline of the TRCS survey parameters and sketches the
methods by which we intend to pursue the main scientific goals, including an
explicit calculation of the expected survey completeness limits. Some
preliminary results from the first set of data (~6 deg^2) are also given. These
preliminary results provide new examples of rich z~1 clusters, strong cluster
lensing, and a possible filament at z~1.


title: Variable stars in the field of the globular cluster E3

abstract:
  We present the results of a search for variable stars in the faint sparse
globular cluster E3. We have found two variable stars: an SX Phe variable (V1)
and a W UMa eclipsing binary (V2). We have applied period-luminosity and
period-color-luminosity relations to the variables to obtain their distance
moduli. V1 seems to be a blue straggler belonging to E3, based on its distance
modulus and location on the CMD. V2 is probably located behind the cluster, in
the Milky Way halo. We also present V/B-V and V/V-I color magnitude diagrams of
E3.


title:
The discovery of a low mass, pre-main-sequence stellar association
  around gamma Velorum

abstract:
  We report the serendipitous discovery of a population of low mass, pre-main
sequence stars (PMS) in the direction of the Wolf-Rayet/O-star binary system
gamma^{2} Vel and the Vela OB2 association. We argue that gamma^{2} Vel and the
low mass stars are truly associated, are approximately coeval and that both are
at distances between 360-490 pc, disagreeing at the 2 sigma level with the
recent Hipparcos parallax of gamma^{2} Vel, but consistent with older distance
estimates. Our results clearly have implications for the physical parameters of
the gamma^{2} Vel system, but also offer an exciting opportunity to investigate
the influence of high mass stars on the mass function and circumstellar disc
lifetimes of their lower mass PMS siblings.


title:
Subaru Observations for the K-band Luminosity Distribution of Galaxies
  in Clusters near to 3C 324 at z$\sim$1.2

abstract:
  We investigate the $K$-band luminosity distribution of galaxies in the region
of clusters at $z\sim1.2$ near to the radio galaxy 3C 324. The imaging data
were obtained during the commissioning period of the Subaru telescope. There is
a significant excess of the surface number density of the galaxies with $K =$
17--20 mag in the region within $\sim$ 40'' from 3C 324. At this bright end,
the measured luminosity distribution shows a drop, which can be represented by
the exponential cut off of the Schechter-function formula; the best-fitted
value of the characteristic magnitude, $K^{*}$, is $\sim 18.4\pm0.8$. This
measurement follows the evolutionary trend of the $K^*$ of the rich clusters
observed at an intermediate redshift, which is consistent with passive
evolution models with a formation redshift $z_f \gtsim 2$. At $K \gtsim 20$
mag, however, the excess of the galaxy surface density in the region of the
clusters decreases abruptly, which may imply that the luminosity function of
the cluster galaxies has a negative slope at the faint end. This may imply
strong luminosity segregation between the inner and outer parts of the
clusters, or some deficit of faint galaxies in the cluster central region of
the cluster.


title:
Color-Magnitude Sequence in the Clusters at z$\sim$1.2 near the Radio
  Galaxy 3C 324

abstract:
  We have investigated the optical and near-infrared colors of K'-selected
galaxies in clusters at z ~ 1.2 near to the radio galaxy 3C 324 using images
obtained with the Subaru telescope and archival HST data. The distribution of
colors of the galaxies in the cluster region is found to be fairly broad, and
it may imply significant scatter in their star-formation histories, although
the effect of contamination of field galaxies is uncertain. The red sequence of
galaxies whose R-K colors are consistent with passive evolution models for old
galaxies is found to be truncated at K' ~ 20 mag, and there are few fainter
galaxies with similar red colors in the cluster region. We find that the
bulge-dominated galaxies selected by quantitative morphological classification
form a broad sequence in the color-magnitude diagram, whose slope is much
steeper than that expected from metallicity variations within a passively
evolving coeval galaxy population. We argue that the observed color-magnitude
sequence can be explained by metallicity and age variations, and the fainter
galaxies with K' > 20 mag may be 1-2 Gyr younger than the brighter galaxies.
Some spatial segregation of the color and K'-band luminosity is seen in the sky
distribution; the redder and the brighter objects tend to be located near 3C
324.


title:
X-ray absorption lines in the Seyfert 1 galaxy NGC 5548 discovered with
  Chandra-LETGS

abstract:
  We present for the first time a high-resolution X-ray spectrum of a Seyfert
galaxy. The Chandra-LETGS spectrum of NGC 5548 shows strong, narrow absorption
lines from highly ionised species (the H-like and He-like ions of C, N, O, Ne,
Na, Mg, Si, as well as Fe XIV--XXI). The lines are blueshifted by a few hundred
km/s. The corresponding continuum absorption edges are weak or absent. The
absorbing medium can be modelled by an outflowing, thin and warm shell in
photoionization equilibrium. The absorption lines are similar to lower
ionization absorption lines observed in the UV, although these UV lines
originate from a different location or phase of the absorbing medium.
Redshifted with respect to the absorption lines, emission from the O VIII Lyman
alpha line as well as the O VII triplet is visible. The flux of these lines is
consistent with emission from the absorbing medium. The O VII triplet intensity
ratios demonstrate that photoionization dominates and yield an upper limit to
the electron density.


title:
Cyclotron lines in X-ray pulsars as a probe of relativistic plasmas in
  superstrong magnetic fields

abstract:
  The systematic search for the presence of cyclotron lines in the spectra of
accreting X-ray pulsars is being carried on with the BeppoSAX satellite since
the beginning of the mission. These highly successful observations allowed the
detection of cyclotron lines in many of the accreting X-ray pulsars observed.
Some correlations between the different measured parameters were found. We
present these correlations and discuss them in the framework of the current
theoretical scenario for the X-ray emission from these sources.


title:
Electron acceleration due to high frequency instabilities at supernova
  remnant shocks

abstract:
  Observations of synchrotron radiation across a wide range of wavelengths
provide clear evidence that electrons are accelerated to relativistic energies
in supernova remnants (SNRs). However, a viable mechanism for the
pre-acceleration of such electrons to mildly relativistic energies has not yet
been established. In this paper an electromagnetic particle-in-cell (PIC) code
is used to simulate acceleration of electrons from background energies to tens
of keV at perpendicular collisionless shocks associated with SNRs. Free energy
for electron energization is provided by ions reflected from the shock front,
with speeds greater than the upstream electron thermal speed. The PIC
simulation results contain several new features, including: the acceleration,
rather than heating, of electrons via the Buneman instability; the acceleration
of electrons to speeds exceeding those of the shock-reflected ions producing
the instability; and strong acceleration of electrons perpendicular to the
magnetic field. Electron energization takes place through a variety of resonant
and non-resonant processes, of which the strongest involves stochastic
wave-particle interactions. In SNRs the diffusive shock process could then
supply the final step required for the production of fully relativistic
electrons. The mechanisms identified in this paper thus provide a possible
solution to the electron pre-acceleration problem.


title:
ASCA and BeppoSAX observations of the peculiar X-ray source
  4U1700+24/HD154791

abstract:
  The X-ray source 4U1700+24/HD154791 is one of the few galactic sources whose
counterpart is an evolved M star. In X-rays the source shows extreme erratic
variability and a complex and variable spectrum. While this strongly suggests
accretion onto a compact object, no clear diagnosis of binarity was done up to
now. We report on ASCA and BeppoSAX X-ray broad band observations of this
source and on ground optical observations from the Loiano 1.5 m telescope.


title: Mode identification from line-profile variations

abstract:
  We review the current status of different mode-identification techniques
based on observed line-profile variations. Three basic methods are currently
available to identify the non-radial pulsation modes. These three methods are
described, together with their different variants. We further present
applications to real data, focusing especially on delta Scuti stars. After
having discussed all the methods and their applications, we present an
inventory in which we compare the properties of the different methods. Finally,
we end with future prospects, both on the theoretical and observational side.


title: The Black Hole Mass - Galaxy Age Relation

abstract:
  We present evidence that there is a significant correlation between the
fraction of a galaxy's mass that lies in its central black hole and the age of
the galaxy's stellar population. Since the absorption line indices that are
used to estimate the age are luminosity weighted, they essentially measure the
time since the last significant episode of star formation in the galaxy. The
existence of this correlation is consistent with several theories of galaxy
formation, including the currently-favoured hierarchical picture of galaxy
evolution, which predicts just such a relation between black hole mass and the
time since the last burst of merger-induced star formation. It is not
consistent with models in which the massive black hole is primordial, and hence
uncoupled from the stellar properties of the galaxy.


title:
Transport Phenomena and Light Element Abundances in the Sun and Solar
  Type Stars

abstract:
  The observations of light elements in the Sun and Solar type stars give
special clues for understanding the hydrodynamical processes at work in stellar
interiors. In the Sun 7Li is depleted by 140 while 3He has not increased by
more than 10% in 3 Gyrs. Meanwhile the inversion of helioseismic modes lead to
a precision on the sound velocity of about .1%. The mixing processes below the
solar convection zone are constrained by these observations. Lithium is
depleted in most Pop I solar type stars. In halo stars however, the lithium
abundance seems constant in the "spite plateau" with no observed dispersion,
which is difficult to reconcile with the theory of diffusion processes. In the
present paper, the various relevant observations will be discussed. It will be
shown that the mu-gradients induced by element settling may help solving the
"lithium paradox".


title:
Self-regulated hydrodynamical process in halo stars : a possible
  explanation of the lithium plateau

abstract:
  It has been known for a long time (Mestel~1953) that the meridional
circulation velocity in stars, in the presence of mu-gradients, is the sum of
two terms, one due to the classical thermal imbalance (Omega-currents) and the
other one due to the induced horizontal mu-gradients (mu-induced currents, or
mu-currents in short). In the most general cases, mu-currents are opposite to
Omega-currents. Vauclair (1999) has shown that such processes can, in specific
cases, lead to a quasi-equilibrium stage in which both the circulation and the
helium settling is frozen. Here we present computations of the circulation
currents in halo star models, along the whole evolutionary sequences for four
stellar masses with a metallicity of [Fe/H] = -2. We show that such a
self-regulated process can account for the constancy of the lithium abundances
and the small dispersion in the Spite plateau.


title: Lithium abundances in main-sequence F stars and sub-giants

abstract:
  The application to main-sequence stars of the rotation-induced mixing theory
in the presence of mu-gradients leads to partial mixing in the lithium
destruction region, not visible in the atmosphere. The induced lithium
depletion becomes visible in the sub-giant phase as soon as the convective zone
deepens enough. This may explain why the observed " lithium dilution " is
smoother and the final dilution factor larger than obtained in standard models,
while the lithium abundance variations are very small on the main sequence.


title:
X-ray flares on zero-age- and pre-main sequence stars in
  Taurus-Auriga-Perseus

abstract:
  We present results of a systematic search for X-ray flares on young stars
observed during ROSAT PSPC observations of the Taurus-Auriga-Perseus region.
All pointed PSPC observations currently available from the ROSAT Public Data
Archive with known T Tauri stars, Pleiads, or Hyads in the field are analyzed
in order to study the evolution of coronal activity. 38 large flares can be
attributed to late-type stars. A flare rate is derived for the different
stellar samples making use of the flare duration and the observing time. We
investigate the influence of stellar parameters such as age, rotation and
multiplicity on individual flare parameters and the flare frequency.


title: Relativistic flows in blazars

abstract:
  The radiation we observe from blazars is most likely the product of the
transformation of bulk kinetic energy into random energy. This process must
have a relatively small efficiency (e.g. 10%) if jets are to power the extended
radio-structures. Recent results suggest that the average power reaching the
extended radio regions and lobes is of the same order of that produced by
accretion and illuminating the emission line clouds. Most of the radiative
power is produced in a well localized region of the jet, and, at least during
flares, is mainly emitted in the gamma-ray band. A possible scenario
qualitatively accounting for these facts is the internal shock model, in which
the central engine produces a relativistic plasma flow in an intermittent way.


title: The Iron Project

abstract:
  Recent advances in theoretical atomic physics have enabled large-scale
calculation of atomic parameters for a variety of atomic processes with high
degree of precision. The development and application of these methods is the
aim of the Iron Project. At present the primary focus is on collisional
processes for all ions of iron, Fe I- FeXXVI, and other iron-peak elements; new
work on radiative processes has also been initiated. Varied applications of the
Iron Project work to X-ray astronomy are discussed, and more general
applications to other spectral ranges are pointed out. The IP work forms the
basis for more specialized projects such as the RMaX Project, and the work on
photoionization/recombination, and aims to provide a comprehensive and
self-consistent set of accurate collsional and radiative cross sections, and
transition probabilities, within the framework of relativistic close coupling
formulation using the Breit-Pauli R-Matrix method. An illustrative example is
presented of how the IP data may be utilised in the formation of X-ray spectra
of the K$\alpha$ complex at 6.7 keV from He-like Fe XXV.


title:
K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the
  Antennae Galaxies (NGC 4038/4039) with NIRSPEC

abstract:
  We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039)
with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the
vicinity of the southern nucleus (NGC 4039) in 0.39" seeing in K-band using
NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the
near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the
highest surface brightness peak in the mid-IR (12-18 um) ISO image presented by
Mirabel et al (1998). We obtained high signal-to-noise 2.03-2.45 um spectra of
the nucleus and the obscured star cluster at R = 1900.
  The cluster is very young (age ~ 4 Myr), massive (M ~ 16E6 M_sun), and
compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius),
assuming a Salpeter IMF (0.1-100 M_sun). Its hot stars have a radiation field
characterized by T_eff ~ 39,000 K, and they ionize a compact HII region with
n_e ~ 10^4 cm^(-3). The stars are deeply embedded in gas and dust (A_V = 9-10
mag), and their strong FUV field powers a clumpy photodissociation region with
densities n_H > 10^5 cm^(-3) on scales of ~ 200 pc, radiating L{H_2 1-0 S(1)}=
9600 L_sun.


title: Photometric Properties of Low Redshift Galaxy Clusters

abstract:
  We have recently completed a comprehensive photometric survey of 27 Abell
clusters with the 8k mosaic camera on the KPNO 0.9m telescope. Preliminary
luminosity functions and dwarf-to-giant galaxy ratios have been calculated for
five galaxy clusters (A1185, A1656, A2151, A2152, and A2197). A significant
increase in the faint end slope between the inner (0.0-0.75 Mpc) and outer
(0.75-1.50 Mpc) luminosity function is measured for A2151 (H_o = 50 km/s/Mpc).
All five clusters show a significant dip in the luminosity function at M_R =
-19.5.


title: Testing the SOC hypothesis for the magnetosphere

abstract:
  As noted by Chang, the hypothesis of Self-Organised Criticality provides a
theoretical framework in which the low dimensionality seen in magnetospheric
indices can be combined with the scaling seen in their power spectra and the
recently-observed plasma bursty bulk flows. As such, it has considerable
appeal, describing the aspects of the magnetospheric fuelling:storage:release
cycle which are generic to slowly-driven, interaction-dominated, thresholded
systems rather than unique to the magnetosphere. In consequence, several recent
numerical "sandpile" algorithms have been used with a view to comparison with
magnetospheric observables. However, demonstration of SOC in the magnetosphere
will require further work in the definition of a set of observable properties
which are the unique "fingerprint" of SOC. This is because, for example, a
scale-free power spectrum admits several possible explanations other than SOC.
  A more subtle problem is important for both simulations and data analysis
when dealing with multiscale and hence broadband phenomena such as SOC. This is
that finite length systems such as the magnetosphere or magnetotail will by
definition give information over a small range of orders of magnitude, and so
scaling will tend to be narrowband. Here we develop a simple framework in which
previous descriptions of magnetospheric dynamics can be described and
contrasted. We then review existing observations which are indicative of SOC,
and ask if they are sufficient to demonstrate it unambiguously, and if not,
what new observations need to be made?


title: Solving the Coincidence Problem: Tracking Oscillating Energy

abstract:
  Recent cosmological observations strongly suggest that the universe is
dominated by an unknown form of energy with negative pressure. Why is this dark
energy density of order the critical density today? We propose that the dark
energy has periodically dominated in the past so that its preponderance today
is natural. We illustrate this paradigm with a model potential and show that
its predictions are consistent with all observations.


title: Effect of Beam-Plasma Instabilities on Accretion Disk Flares

abstract:
  We show that a certain class of flare models for variability from accretion
disk coronae are subject to beam-plasma instabilities. These instabilities can
prevent significant direct acceleration and greatly reduce the variable X-ray
emission argued to arise via inverse Compton scattering involving relativistic
electrons in beams and soft photons from the disk.


title: Collisional dark matter and the structure of dark halos

abstract:
  We study how the internal structure of dark halos is affected if Cold Dark
Matter particles are assumed to have a large cross-section for elastic
collisions. We identify a cluster halo in a large cosmological N-body
simulation and resimulate its formation with progressively increasing
resolution. We compare the structure found in the two cases where dark matter
is treated as collisionless or as a fluid. For the collisionless case our
results agree with those of other workers. Collisional dark matter results in a
cluster which is more nearly spherical and has a more singular central density
profile. Substructure within the cluster is only weakly suppressed relative to
the collisionless case. The observed structure of dwarf galaxies argues against
self-interacting dark matter if, as seems likely, intermediate cross-sections
produce structure lying between the extremes we have simulated.


title: A Review of Mass Estimates for Galactic Dark Matter Objects

abstract:
  Empirical mass estimates for galactic dark matter objects, published between
December 1991 and May 1999, are presented in tabular and graphical forms.
Trends in the data are identified and uncertainties are discussed. Similarities
among various stellar and dark matter mass functions are noted, and a possible
identification of the galactic dark matter objects is suggested.


title:
Nonlinear Velocity-Density Coupling: Analysis by Second-Order
  Perturbation Theory

abstract:
  Cosmological linear perturbation theory predicts that the peculiar velocity
$V(x)$ and the matter overdensity $\delta(x)$ at a same point $x$ are
statistically independent quantities, as log as the initial density
fluctuations are random Gaussian distributed. However nonlinear gravitational
effects might change the situation. Using framework of second-order
perturbation theory and the Edgeworth expansion method, we study local density
dependence of bulk velocity dispersion that is coarse-grained at a weakly
nonlinear scale. For a typical CDM model, the first nonlinear correction of
this constrained bulk velocity dispersion amounts to $\sim 0.3\delta$ (Gaussian
smoothing) at a weakly nonlinear scale with a very weak dependence on
cosmological parameters. We also compare our analytical prediction with
published numerical results given at nonlinear regimes.


title:
Measuring Cosmological Parameters from the Evolution of Cluster X-ray
  Temperatures

abstract:
  We have determined the cluster X-ray temperature function from two flux- and
redshift-limited samples of clusters. The first sample is comprised of 25
clusters with average redshift 0.05. The local temperature function derived
from it supercedes the one we previously published. Fourteen clusters with
average redshift 0.38 comprise the second sample. We perform maximum likelihood
fits of cluster evolution models to these data in order to constrain
cosmological parameters. For an open model with zero cosmological constant we
find that the density parameter is Omega_0 = 0.49+/-0.12, the rms mass density
fluctuation averaged over 8 h-1 Mpc spheres is sigma_8 = 0.72+/-0.10, and the
effective index of the mass density fluctuation spectrum on cluster scales is n
= -(1.72+/-0.34) where all errors are symmetrized at 68% confidence. The
corresponding results for the case where a cosmological constant produces a
flat universe are : 0.44+/-0.12, 0.77+/-0.15, and -(1.68+/-0.38). These results
agree with those determined from a variety of different independent methods,
including supernovae, galaxy-galaxy correlations, fluctuations in the microwave
background, gravitational lens statistics, and cluster peculiar velocities.


title: The first COMPTEL Source Catalogue

abstract:
  The imaging Compton telescope COMPTEL aboard NASA's Compton Gamma-Ray
Observatory has opened the MeV gamma-ray band as a new window to astronomy.
COMPTEL provided the first complete all-sky survey in the energy range 0.75 to
30 MeV. The catalogue, presented here, is largely restricted to published
results. It contains firm as well as marginal detections of continuum and line
emitting sources and presents upper limits for various types of objects. The
numbers of the most significant detections are 32 for steady sources and 31 for
gamma-ray bursters. Among the continuum sources, detected so far, are spin-down
pulsars, stellar black-hole candidates, supernova remnants, interstellar
clouds, nuclei of active galaxies, gamma-ray bursters, and the Sun during solar
flares. Line detections have been made in the light of the 1.809 MeV 26Al line,
the 1.157 MeV 44Ti line, the 847 and 1238 keV 56Co lines, and the neutron
capture line at 2.223 MeV. For the identification of galactic sources, a
modelling of the diffuse galactic emission is essential. Such a modelling at
this time does not yet exist at the required degree of accuracy. Therefore, a
second COMPTEL source catalogue will be produced after a detailed and accurate
modelling of the diffuse interstellar emission has become possible.


title:
5cm OH masers as diagnostics of physical conditions in star-forming
  regions

abstract:
  We demonstrate that the observed characteristics of the 5 cm OH masers in
star-forming regions can be explained with the same model and the same
parameters as the 18 cm and the 6 cm OH masers. In our already published study
of the 18 cm and the 6 cm OH masers in star-forming regions we had examined the
pumping of the 5 cm masers, but did not report the results we had found because
of some missing collision rate coefficients, which in principle could be
important. The recently published observations on the 5 cm masers of OH
encourage us to report our old calculations along with some new ones that we
have performed. These calculations, in agreement with the observations, reveal
the main lines at 5 cm as strong masers, the 6049 MHz satellite line as a weak
maser, and the 6017 MHz satellite line as never inverted for reasonable values
of the parameters


title: Quasar variability: correlations with amplitude

abstract:
  The relation between quasar variability and parameters such as luminosity and
redshift has been a matter of hot debate over the last few years with many
papers on the subject. Any correlations which can be established will have a
profound effect on models of quasar structure and evolution. The sample of
quasars in ESO/SERC field 287 contains over 600 quasars in the range 0 < z <
3.5 and is now large enough to bin in luminosity and redshift, and give
definitive measures of the correlations. We find no significant correlation
between amplitude and redshift, except perhaps at very low redshift, but an
inverse correlation between amplitude and luminosity. This is examined in the
context of various models for quasar variability.


title:
Breaking the degeneracy of cosmological parameters in galaxy redshift
  surveys

abstract:
  The measurement of cosmological parameters is investigated in a
representation of the least-action method that uses a redshift-space dataset to
simultaneously constrain the real-space fields $\delta$,$\b v$. This method is
robust in recovering the entire evolution of the matter density contrast and
peculiar velocities of galaxies in real space from current galaxy redshift
surveys. The main strength of the method is that it permits us to break the
degeneracy of the parameters $b$ and $\Omegam$ (customarily measured in the
ratio $\beta\equiv \Omegam^{0.6}/b$ from redshift-space distortions), and these
are evaluated in the current context separately. The procedure provides a
simple numerical means to extract as much information as possible from a given
sample, in the simplest linear bias model, before resorting to cosmic
complementarity to resolve the degeneracy in the measurement of $\Omegam$. The
same premise applies to more sophisticated choices of bias models. We construct
a likelihood parameter $\lambda(b,\Omegam)$ to evaluate the relative likelihood
of different values of $b$ and $\Omegam$. The method is applied to the \iras
redshift survey with a low-resolution Gaussian smoothing length of 1200 \km
within a spherical region $x_{\rm max} \sim 15,000$ \km and the reconstructed
velocity field is then compared with POTENT-reconstructed velocities from the
Mark III radial-velocity dataset within a radius $\sim 5000$ \km, which have
been suitably prepared to account for Malmquist bias and other systematic
errors. The analysis yields a likelihood for the parameters that is overall
consistent with $\Omegam\approx 0.3$ and $b\approx 1.1$, thus lending support
to a non-vanishing cosmological constant $\Omega_{\Lambda}\approx 0.7$ in a
flat universe.


title: Dynamical and chemical evolution of gas-rich dwarf galaxies

abstract:
  We study the effect of a single, instantaneous starburst on the dynamical and
chemical evolution of a gas-rich dwarf galaxy, whose potential well is
dominated by a dark matter halo. We follow the dynamical and chemical evolution
of the ISM by means of an improved 2-D hydrodynamical code coupled with
detailed chemical yields originating from type II SNe, type Ia SNe and single
low and intermediate mass stars (IMS). In particular we follow the evolution of
the abundances of H, He, C, N, O, Mg, Si and Fe. We find that for a galaxy
resembling IZw18, a galactic wind develops as a consequence of the starburst
and it carries out of the galaxy mostly the metal-enriched gas. In addition, we
find that different metals are lost differentially in the sense that the
elements produced by type Ia SNe are more efficiently lost than others. As a
consequence of that we predict larger [$\alpha$/Fe] ratios for the gas inside
the galaxy than for the gas leaving the galaxy. A comparison of our predicted
abundances of C, N, O and Si in the case of a burst occurring in a primordial
gas shows a very good agreement with the observed abundances in IZw18 as long
as the burst has an age of $\sim 31$ Myr and IMS produce some primary nitrogen.
However, we cannot exclude that a previous burst of star formation had occurred
in IZw18 especially if the preenrichment produced by the older burst was lower
than $Z=0.01$ Z$_{\odot}$. Finally, at variance with previous studies, we find
that most of the metals reside in the cold gas phase already after few Myr.
This result is mainly due to the assumed low SNII heating efficiency, and
justifies the generally adopted homogeneous and instantaneous mixing of gas in
chemical evolution models.


title: Chemical and dynamical evolution in gas-rich dwarf galaxies

abstract:
  We study the effect of a single, instantaneous starburst in a gas-rich dwarf
galaxy on the dynamical and chemical evolution of its interstellar medium. We
consider the energetic input and the chemical yields originating from SNeII,
SNeIa and intermediate-mass stars. We find that a galaxy resembling IZw18
develops a galactic wind carrying out mostly the metal-rich gas. The various
metals are lost differentially and the metals produced by the SNeIa are lost
more efficiently than the others. As a consequence, we find larger
[$\alpha$/Fe] ratios for the gas inside the galaxy than for the gas leaving the
galaxy. Finally we find that a single burst occurring in primordial gas
(without pre-enrichment), gives chemical abundances and dynamical structures in
good agreement with what observed in IZw18 after $\sim$ 29 Myr from the
beginning of star formation.


title: The Luminosity Function of MS2255.7+2039 at z=0.288

abstract:
  The luminosity function of MS2255.7+2039 at z=0.288 is determined down to a
total magnitude of R ~ 24, corresponding to M_R ~ -17 (H_0 = 50 km/s/Mpc). The
data are corrected for incompleteness and crowding using detailed simulations.
We find that the luminosity function is steeper than a standard Schechter
function at faint magnitudes, and shows an excess of galaxies below M_R ~ -19.
After corrections for light loss and crowding, the data can be described by a
sum of two Schechter functions, one with M_R = -22.8 and alpha = -1.0, and one
steeper with M_R = -18.9 and alpha = -1.5, representing the dwarf population. A
straight-line fit to the faint part yields a slope similar to the Schechter
alpha = -1.5 of the dwarf population. The luminosity function of MS2255.7+2039
is compared to other clusters at lower redshifts, and does not show any
significant difference. The redshift range for clusters in which increased
number of dwarf galaxies have been found is therefore extended to higher
redshifts.


title: Properties of Proto--Planetary Nebulae

abstract:
  This review describes some general properites of proto-planetary nebulae with
particular emphasis on the recent work of morpholgical studies. The weight of
observational evidence shows that proto-planetary nebulae (PPNe) are most
certainly axisymmetric like planetary nebulae. Recent work suggests two
subclasses of PPNe optical morphology, DUst-Prominent Longitudinally-EXtended
(DUPLEX) and Star-Obvious Low-level Elongated (SOLE). Radiative transfer models
of an example DUPLEX PPN and SOLE PPN, presented here, support the
interpretation that DUPLEX and SOLE are two physically distinct types of PPNe.
The DUPLEX PPNe and SOLE PPNe may well be the precursors to bipolar and
elliptical PNe, respectively.


title:
Observations of the Crab Nebula and its pulsar in the far-ultraviolet
  and in the optical

abstract:
  We present HST/STIS far-UV observations of the Crab nebula and its pulsar.
Broad, blueshifted absorption arising in the nebula is seen in C IV 1550,
reaching about 2500 km/s. This can be interpreted as evidence for a fast outer
shell, and we adopt a spherically symmetric model to constrain the properties
of this. We find that the density appears to decrease outward in the shell. A
lower limit to the mass is 0.3 solar masses with an accompanying kinetic energy
of 1.5EE{49} ergs. A massive 10^{51} erg shell cannot be excluded, but is less
likely if the density profile is much steeper than R^{-4} and the velocity is
<6000 km/s. The observations cover the region 1140-1720 A. With the time-tag
mode of the spectrograph we obtain the pulse profile. It is similar to that in
the near-UV, although the primary peak is marginally narrower. Together with
the near-UV data, and new optical data from NOT, our spectrum of the pulsar
covers the entire region from 1140-9250 A. Dereddening the spectrum gives a
flat spectrum for E(B-V)=0.52, R=3.1. This dereddened spectrum of the Crab
pulsar can be fitted by a power law with spectral index alpha_{\nu} = 0.11 +/-
0.04. The main uncertainty is the amount and characteristics of the interstel-
lar reddening, and we have investigated the dependence of \alpha_{\nu} on
E(B-V) and R. In the extended emission covered by our 25" x 0.5" slit in the
far-UV, we detect C IV 1550 and He II 1640 emission lines from the Crab nebula.
Several interstellar absorption lines are detected toward the pulsar. The Ly
alpha absorption indicates a column density of 3.0+/-0.5\EE{21} cm^{-2} of
neutral hydrogen, which agrees well with our estimate of E(B-V)=0.52 mag. Other
lines show no evidence of severe depletion of metals in atomic gas.


title: Asymmetric, arc minute scale structures around NGC 1275

abstract:
  ROSAT HRI observations show complicated substructure in the X-ray surface
brightness within $\sim$5 arcminutes around NGC 1275 -- the dominant galaxy of
the Perseus cluster. The typical amplitude of the variations is of the order of
30% of the azimuthally averaged surface brightness at a given distance from NGC
1275. We argue that this substructure could be related to the activity of NGC
1275 in the past. Bubbles of relativistic plasma, inflated by jets, be forced
to rise by buoyancy forces, mix with the ambient intracluster medium (ICM), and
then spread. Overall evolution of the bubble may resemble the evolution of a
hot bubble during a powerful atmospheric explosion. From a comparison of the
time scale of the bubble inflation to the rise time of the bubbles and from the
observed size of the radio lobes which displace the thermal gas, the energy
release in the relativistic plasma by the active nucleus of NGC 1275 can be
inferred. Approximate modeling implies a nuclear power output of the order of
$10^{45}$ erg s$^{-1}$ averaged over the last $\sim 3~10^7$ years. This is
comparable with the energy radiated in X-rays during the same epoch. Detailed
measurements of the morphology of the X-ray structure, the temperature and
abundance distributions with Chandra and XMM may test this hypothesis.


title:
Evidence of self-interacting cold dark matter from galactic to galaxy
  cluster scales

abstract:
  Within the framework of the cold dark matter (CDM) cosmogony, a central cusp
in the density profiles of virialized dark haloes is predicted. This prediction
disagrees with the soft inner halo mass distribution inferred from observations
of dwarf and low surface brightness galaxies, and some clusters of galaxies. By
analysing data for some of these objects, we find that the halo central density
is nearly independent of the mass from galactic to galaxy cluster scales with
an average value of around 0.02 M_sun/pc^3. We show that soft cores can be
produced in the CDM haloes by introducing a lower cut-off in the power spectra
of fluctuations and assuming high orbital thermal energies during halo
formation. However, the scale invariance of the halo central density is not
reproduced in these cases. The introduction of self-interaction in the CDM
particles offers the most attractive alternative to the core problem. We
propose gravothermal expansion as a possible mechanism to produce soft cores in
the CDM haloes with self-interacting particles. A global thermodynamical
equilibrium can explain the central density scale invariance. We find a minimum
cross section capable of establishing isothermal cores in agreement with the
observed shallow cores. If \sigma and m_x are the cross section and mass of the
dark matter particle, and v is the halo velocity dispersion, then (\sigma/m_x)
\~ 4 10^{-25} (100 km s^{-1}/v) cm^2/GeV.


title:
Quantum corrections to the ground state energy of inhomogeneous neutron
  matter

abstract:
  We estimate the quantum corrections to the ground state energy in neutron
matter (which could be termed as well either shell correction energy or Casimir
energy) at subnuclear densities, where various types of inhomogeneities
(bubbles, rods, plates) are energetically favorable. We show that the magnitude
of these energy corrections are comparable to the energy differences between
various types of inhomogeneous phases. We discuss the dependence of these
corrections on a number of physical parameters (density, filling factor,
temperature, lattice distortions).


title:
The Least-Action Principle: Theory of Cosmological Solutions and the
  Radial-Velocity Action

abstract:
  Formulating the equations of motion for cosmological bodies (such as
galaxies) in an integral, rather than differential, form has several
advantages. Using an integral the mathematical instability at early times is
avoided and the boundary conditions of the integral correspond closely with
available data. Here it is shown that such a least-action calculation for a
number of bodies interacting by gravity has a finite number of solutions,
possibly only one. Characteristics of the different possible solutions are
explored. The results are extended to cover the motion of a continuous fluid. A
method to generalize an action to use velocities, instead of positions, in
boundary conditions, is given, which reduces in particular cases to those given
by Giavalisco et al. (1993) and Schmoldt & Saha (1998). The velocity boundary
condition is shown to have no effect on the number of solutions.


title: HV Ursae Majoris, a new contact binary with early-type components

abstract:
  We present the first UBV and uvby photometric observations for the short
period variable star HV Ursae Majoris classified as a field RRc variable. The
observed differences between the consecutive minima and the lack of colour
variations disagree with the RRc-classification and suggest the possible binary
nature of HV UMa. In order to reveal the real physical status of this star, we
took medium resolution spectra in the red spectral region centered at 6600 A.
Spectra obtained around the assumed quadratures clearly showed the presence of
the secondary component.
  An improved ephemeris calculated using our and Hipparcos epoch photometry is
Hel. JD_min=2451346.743+/-0.001, P=0.7107523(3) d. A radial velocity curve was
determined by modelling the cores of Halpha profiles with two Gaussian
components. This approximative approach gave a spectroscopic mass ratio of
q_sp=0.19+/-0.03. A modified Lucy model containing a temperature excess of the
secondary was fitted to the V light curve. The obtained set of physical
parameters together with the parallax measurement indicate that this binary
lies far from the galactic plane, and the primary component is an evolved
object, probably a subgiant or giant star. The large temperature excess of the
secondary may suggest a poor thermal contact between the components due to a
relatively recent formation of this contact system.


title: The Dependence of Tidally-Induced Star Formation on Cluster Density

abstract:
  A survey of H alpha emission in 320 spiral galaxies in 8 nearby clusters
shows an enhancement of circumnuclear starburst emission with increasingly rich
clusters. These observations provide convincing evidence that spirals have been
transformed into S0s in clusters predominantly by tidal forces, a picture fully
in accord with the most recent numerical simulations of clusters. For the
richest clusters, the enhancement of starburst emission is greater than would
be expected on the basis of increasing galaxy surface density alone, which may
explain the anomalous result for the type-galaxy surface density relation found
for low richness clusters at intermediate redshift.


title:
Fossils of turbulence and non-turbulence in the primordial universe: the
  fluid mechanics of dark matter

abstract:
  Was the primordial universe turbulent or non-turbulent soon after the Big
Bang? How did the hydrodynamic state of the early universe affect the formation
of structure from gravitational forces, and how did the formation of structure
by gravity affect the hydrodynamic state of the flow? What can be said about
the dark matter that comprises 99.9 % of the mass of the universe according to
most cosmological models? Space telescope measurements show answers to these
questions persist literally frozen as fossils of the primordial turbulence and
nonturbulence that controlled structure formation, contrary to standard
cosmology which relies on the erroneous Jeans 1902 linear-inviscid-acoustic
theory and a variety of associated misconceptions (e. g., cold dark matter).
When effects of viscosity, turbulence, and diffusion are included, vastly
different structure scenarios and a clear explanation for the dark matter
emerge. From Gibson's 1996 theory the baryonic (ordinary) dark matter is
comprised of proto-globular-star-cluster (PGC) clumps of hydrogenous planetoids
termed ``primordial fog particles''(PFPs), observed by Schild 1996 as ``rogue
planets ... likely to be the missing mass'' of a quasar lensing galaxy. The
weakly collisional non-baryonic dark matter diffuses to form outer halos of
galaxies and galaxy clusters.


title: Eclipse studies of the dwarf-nova Ex Draconis

abstract:
  We report on high speed photometry of EX Dra in quiescence and in outburst.
The analysis of the lightcurves indicates that the outbursts do not start in
the outer disc regions. The disc expands during rise to maximum and shrinks
during decline and along the quiescent period. At the end of two outbursts the
system was seen to go through a phase of lower brightness, characterized by an
out-of-eclipse level ~15 per cent lower than the typical quiescent level and by
the fairly symmetric eclipse of a compact source at disc centre with little
evidence of a bright spot at disc rim. New eclipse timings were measured and a
revised ephemeris was derived. The residuals with respect to the linear
ephemeris are well described by a sinusoid of amplitude 1.2 minutes and period
\~4 years and are possibly related to a solar-like magnetic activity cycle in
the secondary star. Eclipse phases of the compact central source and of the
bright spot were used to derive the geometry of the binary. By constraining the
gas stream trajectory to pass through the observed position of the bright spot
we find q=0.72+/-0.06 and i= 85 +3/-2 degrees. The binary parameters were
estimated by combining the measured mass ratio with the assumption that the
secondary star obeys an empirical main sequence mass-radius relation. We find
M_1= 0.75+/-0.15 M_sun and M_2= 0.54+/-0.10 M_sun. The white dwarf at disc
centre is surrounded by an extended and variable atmosphere or boundary layer
of at least 3 times its radius and a temperature of T ~28000 K. The fluxes at
mid-eclipse yield an upper limit to the contribution of the secondary star and
lead to a lower limit photometric parallax distance of D= 290+/-80 pc. The
fluxes of the secondary star are well matched by those of a M0+/-2 main
sequence star.


title:
Predictions on the number of variable stars for the GAIA space mission
  and for surveys as the ground-based International Liquid Mirror Telescope

abstract:
  Future space and ground-based survey programmes will produce an impressive
amount of photometric data. The GAIA space mission will map the complete sky
down to mag V=20 and produce time series for about 1 billion stars. Survey
instruments as the International Liquid Mirror Telescope will observe slices of
the sky down to magnitude V=23. In both experiments, the opportunity exists to
discover a huge amount of variable stars. A prediction of the expected total
number of variable stars and the number of variables in specific subgroups is
given.


title: Quasar Clustering and the Lifetime of Quasars

abstract:
  Although the population of luminous quasars rises and falls over a period of
10^9 years, the typical lifetime of individual quasars is uncertain by several
orders of magnitude. We show that quasar clustering measurements can
substantially narrow the range of possible lifetimes with the assumption that
luminous quasars reside in the most massive host halos. If quasars are
long-lived, then they are rare phenomena that are highly biased with respect to
the underlying dark matter, while if they are short-lived they reside in more
typical halos that are less strongly clustered. For a given quasar lifetime, we
calculate the minimum host halo mass by matching the observed space density of
quasars, using the Press-Schechter approximation. We use the results of Mo &
White to calculate the clustering of these halos, and hence of the quasars they
contain, as a function of quasar lifetime. A lifetime of t_Q = 4 x 10^7 years,
the e-folding timescale of an Eddington luminosity black hole with accretion
efficiency eps=0.1, corresponds to a quasar correlation length r_0 ~ 10 Mpc/h
in low-density cosmological models at z=2-3; this value is consistent with
current clustering measurements, but these have large uncertainties.
High-precision clustering measurements from the 2dF and Sloan quasar surveys
will test our key assumption of a tight correlation between quasar luminosity
and host halo mass, and if this assumption holds then they should determine t_Q
to a factor of three or better. An accurate determination of the quasar
lifetime will show whether supermassive black holes acquire most of their mass
during high-luminosity accretion, and it will show whether the black holes in
the nuclei of typical nearby galaxies were once the central engines of
high-luminosity quasars.


title: Where Do Cooling Flows Cool?

abstract:
  Although only about 5 percent of the total baryonic mass in luminous
elliptical galaxies is in the form of cooled interstellar gas, it is
concentrated within the optical effective radius r_e where it influences the
local dynamical mass. The mass of cooled gas must be spatially distributed
since it greatly exceeds the masses of central black holes. We explore here the
proposition that a population of low mass, optically dark stars is created from
the cooled gas. We consider a wide variety of radial distributions for the
interstellar cooling, but only a few are consistent with observed X-ray surface
brightness profiles. In a region of concentrated interstellar cooling, the
X-ray emission can exceed that observed, suggesting the presence of additional
support by magnetic stresses or non-thermal pressure. In general we find that
the mass of cooled gas contributes significantly to stellar dynamical mass to
light ratios which vary with galactic radius. If the stars formed from cooled
interstellar gas are optically luminous, their influence on the the mass to
light ratio would be reduced. The mass of cooled gas inside r_e is sensitive to
the rate that old stars lose mass, which is nearly independent of the initial
mass function of the old stellar population.


title: Dust Emission from High Redshift QSOs

abstract:
  We present detections of emission at 250 GHz (1.2 mm) from two high redshift
QSOs from the Sloan Digital Sky Survey sample using the bolometer array at the
IRAM 30m telescope. The sources are SDSSp 015048.83+004126.2 at z = 3.7, and
SDSSp J033829.31+002156.3 at z = 5.0, which is the third highest redshift QSO
known, and the highest redshift mm emitting source yet identified. We also
present deep radio continuum imaging of these two sources at 1.4 GHz using the
Very Large Array. The combination of cm and mm observations indicate that the
250 GHz emission is most likely thermal dust emission, with implied dust masses
of 1e8 M_solar. We consider possible dust heating mechanisms, including UV
emission from the active nucleus (AGN), and a massive starburst concurrent with
the AGN, with implied star formation rates > 1e3 M_solar/year.


title: A Priori Probability Distribution of the Cosmological Constant

abstract:
  In calculations of the probability distribution for the cosmological
constant, it has been previously assumed that the a priori probability
distribution is essentially constant in the very narrow range that is
anthropically allowed. This assumption has recently been challenged. Here we
identify large classes of theories in which this assumption is justified.


title: Star Formation and Chemical Evolution of Lyman-Break Galaxies

abstract:
  The number density and clustering properties of Lyman-break galaxies (LBGs)
observed at redshift $z\sim 3$ are best explained by assuming that they are
associated with the most massive haloes at $z\sim 3$ predicted in hierarchical
models of structure formation. In this paper we study, under the same
assumption, how star formation and chemical enrichment may have proceeded in
the LBG population. A consistent model, in which the amount of cold gas
available for star formation must be regulated, is suggested. It is found that
gas cooling in dark haloes provides a natural regulation process. In this
model, the star formation rate in an LBG host halo is roughly constant over
about 1 Gyr. The predicted star formation rates and effective radii are
consistent with observations. The metallicity of the gas associated with an LBG
is roughly equal to the chemical yield, or about the order of $1 Z_{\odot}$ for
a Salpeter IMF. The contribution to the total metals of LBGs is roughly
consistent with that obtained from the observed cosmic star formation history.
The model predicts a marked radial metallicity gradient in a galaxy, with the
gas in the outer region having much lower metallicity. As a result, the
metallicities for the damped Lyman-alpha absorption systems expected from the
LBG population are low. Since LBG halos are filled with hot gas in this model,
their contributions to the soft X-ray background and to the UV ionization
background are calculated and discussed.


title:
Formation of intermediate-mass black holes in circumnuclear regions of
  galaxies

abstract:
  Recent high-resolution X-ray imaging studies have discovered possible
candidates of intermediate-mass black holes with masses of $M_\bullet \sim
10^{2-4} \MO$ in circumnuclear regions of many (disk) galaxies. It is known
that a large number of massive stars are formed in a circumnuclear giant H {\sc
ii} region. Therefore, we propose that continual merger of compact remnants
left from these massive stars is responsible for the formation of such an
intermediate-mass black hole within a timescale of $\sim 10^9$ years. A
necessary condition is that several hundreds of massive stars are formed in a
compact region with a radius of a few pc.


title:
High-Resolution Near-Infrared Imaging of the Powerful Radio Galaxy 3C
  324 at z = 1.21 with the Subaru Telescope

abstract:
  We have obtained high-resolution K'-band images of the powerful z=1.206 radio
galaxy 3C 324 with the Subaru telescope under seeing conditions of 0.3--0.4
arcsec. We clearly resolved the galaxy and directly compared it to the optical
images obtained with the Hubble Space Telescope. The host galaxy of 3C 324 is
revealed to be a moderately luminous elliptical galaxy with a smooth light
profile. The effective radius of the galaxy, as determined by profile fitting,
is 1.3+-0.1 arcsec (1.2 kpc), which is significantly smaller than the value of
2.2 arcsec, published in Best et al. (1998, MNRAS, 292, 758). The peak of the
K'-band light coincides with the position of the radio core, which implies that
the powerful AGN lies at the nucleus of the host galaxy. The peak also
coincides with the gap in the optical knotty structures which may be a dust
lane hiding the UV-optical emission of the AGN from our line of sight; it is
very likely that we are seeing the obscuring structure almost edge-on. We
clearly detected the `aligned component' in the K'-band image by subtracting a
model elliptical galaxy from the observed image. The red R_F702W-K color of the
outer region of the galaxy avoiding the aligned component indicates that the
near infrared light of the host galaxy is dominated by an old stellar
population.


title: A New Dark Matter Model for Galaxies

abstract:
  In this paper a new theory of Dark Matter is proposed. Experimental analysis
of several Galaxies show how the non-gravitational contribution to galactic
Velocity Rotation Curves can be interpreted as that due to the Cosmological
Constant $\Lambda$. The experimentally determined values for $\Lambda$ are
found to be consistent with those expected from Cosmological Constraints. The
Cosmological Constant is interpreted as leading to a constant energy density
which in turn can be used to partly address the energy deficit problem (Dark
Energy) of the Universe. The work presented here leads to the conclusion that
the Cosmological Constant is negative and that the universe is de-accelerating.
This is in clear contradiction to the Type Ia Supernovae results which support
an accelerating universe.


title:
The role of outflows and star formation efficiency in the evolution of
  early-type cluster galaxies

abstract:
  A phenomenological model for chemical enrichment in early-type galaxies is
presented, in which the process of star formation is reduced to a set of four
parameters: star formation efficiency (Ceff), fraction of ejected gas in
outflows (Bout), formation redshift (zF) and infall timescale (Tf). Out of
these four parameters, only variations of Bout or Ceff can account for the
color-magnitude relation. A range of outflows results in a metallicity
sequence, whereas a range of star formation efficiencies will yield a mixed age
+ metallicity sequence. The age-metallicity degeneracy complicates the issue of
determining which mechanism contributes the most (i.e. outflows versus
efficiency). However, the determination of the slope of the correlation between
mass-to-light ratio and mass in clusters at moderate or high redshift will
allow us to disentangle age and metallicity.


title: A study of young radio-loud AGN using space-VLBI

abstract:
  Gigahertz Peaked Spectrum (GPS) sources form a key element in the study of
the onset and evolution of radio-loud AGN, since they are most likely the young
counterparts of extended radio sources. Here we discuss space-VLBI observations
of GPS sources, which enable us to obtain unprecedented angular resolution at
frequencies near their spectral turnovers. Observed peak brightness
temperatures of Log[T]=10.5-11 Kelvin indicate that synchrotron self absorption
is responsible for their spectral turnovers. This is in close agreement with
previous size - spectral turnover statistics for GPS sources. The combination
of these new space-VLBI observations with ground-based VLBI observations taken
at an earlier epoch, confirm the young ages for the most compact GPS galaxies
of several hundred years.


title:
Innermost stable circular orbits around strange stars and kHz QPOs in
  low-mass X-ray binaries

abstract:
  Exact calculations of innermost stable circular orbit (ISCO) around rotating
strange stars are performed within the framework of general relativity.
Equations of state (EOS) of strange quark matter based on the MIT Bag Model
with massive strange quarks and lowest order QCD interactions, are used. The
presence of a solid crust of normal matter on rotating, mass accreting strange
stars in LMXBs is taken into account. It is found that, contrary to neutron
stars, above some minimum mass a gap always separates the ISCO and stellar
surface, independently of the strange star rotation rate. For a given baryon
mass of strange star, we calculate the ISCO frequency as function of stellar
rotation frequency, from static to Keplerian configuration. For masses close to
the maximum mass of static configurations the ISCO frequencies for static and
Keplerian configurations are similar. However, for masses significantly lower
than the maximum mass of static configurations, the minimum value of the ISCO
frequency is reached in the Keplerian limit. Presence of a solid crust
increases the ISCO frequency for the Keplerian configuration by about ten
percent compared to that for a bare strange star of the same mass.


title:
Properties of spherical galaxies and clusters with an NFW density
  profile

abstract:
  Using the standard dynamical theory of spherical systems, we calculate the
properties of spherical galaxies and clusters whose density profiles obey the
universal form first obtained in high resolution cosmological N-body
simulations by Navarro, Frenk & White. We adopt three models for the internal
kinematics: isotropic velocities, constant anisotropy and increasingly radial
Osipkov-Merritt anisotropy. Analytical solutions are found for the radial
dependence of the mass, gravitational potential, velocity dispersion, energy
and virial ratio and we test their variability with the concentration parameter
describing the density profile and amount of velocity anisotropy. We also
compute structural parameters, such as half-mass radius, effective radius and
various measures of concentration. Finally, we derive projected quantities, the
surface mass density and line-of-sight as well as aperture velocity dispersion,
all of which can be directly applied in observational tests of current
scenarios of structure formation. On the mass scales of galaxies, if constant
mass-to-light is assumed, the NFW surface density profile is found to fit well
Hubble-Reynolds laws. It is also well fitted by Sersic R^(1/m) laws, for m ~ 3,
but in a much narrower range of m and with much larger effective radii than are
observed. Assuming in turn reasonable values of the effective radius, the mass
density profiles imply a mass-to-light ratio that increases outwards at all
radii.


title: The spectral variations of the O-type runaway supergiant HD 188209

abstract:
  We report spectral time series of the late O-type runaway supergiant HD
188209. Radial velocity variations of photospheric absorption lines with a
possible quasi-period ~ 6.4 days have been detected in high-resolution echelle
spectra. Night-to-night variations in the position and strength of the central
emission reversal of the Ha profile occuring over ill-defined time-scales have
been observed. The fundamental parameters of the star have been derived using
state-of-the-art plane--parallel and unified non-LTE model atmospheres, these
last including the mass-loss rate. The derived helium abundance is moderately
enhanced with respect to solar, and the stellar masses are lower than those
predicted by the evolutionary models. The binary nature of this star is not
suggested either from Hipparcos photometry or from radial velocity curves.


title:
Observational constraints on the spectral index of the cosmological
  curvature perturbation

abstract:
  We evaluate the observational constraints on the spectral index $n$, in the
context of the $\Lambda$CDM hypothesis which represents the simplest viable
cosmology. We first take $n$ to be practically scale-independent. Ignoring
reionization, we find at a nominal 2-$\sigma$ level $n\simeq 1.0 \pm 0.1$. If
we make the more realisitic assumption that reionization occurs when a fraction
$f\sim 10^{-5}$ to 1 of the matter has collapsed, the 2-$\sigma$ lower bound is
unchanged while the 1-$\sigma$ bound rises slightly. These constraints are
compared with the prediction of various inflation models. Then we investigate
the two-parameter scale-dependent spectral index, predicted by running-mass
inflation models, and find that present data allow significant scale-dependence
of $n$, which occurs in a physically reasonable regime of parameter space.


title:
OH Zeeman Magnetic Field Detections Toward Five Supernova Remnants Using
  the VLA

abstract:
  We have observed the OH (1720 MHz) line in five galactic SNRs with the VLA to
measure their magnetic field strengths using the Zeeman effect. We detected all
12 of the bright ($S_{\nu} > 200$ mJy) OH (1720 MHz) masers previously detected
by Frail et al. (1996) and Green et al. (1997) and measured significant
magnetic fields (i.e. $ > 3\sigma$) in ten of them. Assuming that the
``thermal'' Zeeman equation can be used to estimate $\mid\vec{B}\mid$ for OH
masers, our estimated fields range from 0.2 to 2 mG. These magnetic field
strengths are consistent with the hypothesis that ambient molecular cloud
magnetic fields are compressed via the SNR shock to the observed values.
Magnetic fields of this magnitude exert a considerable influence on the
properties of the cloud with the magnetic pressures ($10^{-7} - 10^{-9}$ erg
cm$^{-3}$) exceeding the pressure in the ISM or even the thermal pressure of
the hot gas interior to the remnant. This study brings the number of galactic
SNRs with OH (1720 MHz) Zeeman detections to ten.


title:
The Detection of the Diffuse Interstellar Bands in Dusty Starburst
  Galaxies

abstract:
  We report the detection of the Diffuse Interstellar Bands (``$DIBs$'') in the
optical spectra of seven far-infrared-selected starburst galaxies. The
$\lambda$6283.9 \AA and $\lambda$ 5780.5 \AA features are detected with
equivalent widths of $\sim$ 0.4 to 1 \AA and 0.1 to 0.6 \AA respectively. In
the two starbursts with the highest quality spectra (M82 and NGC2146), four
other weaker $DIBs$ at $\lambda$ 5797.0 \AA, 6010.1 \AA, 6203.1 \AA, and 6613.6
\AA are detected with equivalent widths of $\sim$ 0.1 \AA. The region over
which the $DIBs$ can be detected ranges from $\sim$ 1 kpc in the less powerful
starbursts, to several kpc in the more powerful ones. The gas producing the
$DIBs$ is more kinematically quiescent on-average than the gas producing the
strongly-blueshifted $NaI\lambda\lambda$5890,5896 absorption in the same
starbursts. We show that the $DIBs$ in these intense starbursts are remarkably
similar to those in our Galaxy: the relative strengths of the features detected
are similar, and the equivalent widths follow the same dependence as Galactic
$DIBs$ on $E(B-V)$ and $NaI$ column density. While the ISM in starbursts is
heated by a photon and cosmic ray bath that is $\sim$ 10$^3$ times more intense
than in the diffuse ISM of the Milky Way, the gas densities and pressures are
also correspondingly larger in starbursts. This ``homology'' may help explain
the strikingly similar $DIB$ properties.


title: Cosmic Equation of State, Quintessence and Decaying Dark Matter

abstract:
  If CDM particles decay and their lifetime is comparable to the age of the
Universe, they can modify its equation of state. By comparing the results of
numerical simulations with high redshift SN-Ia observations we show that this
hypothesis is consistent with present data. Fitting the simplest quintessence
models with constant $w_q$ to data leads to $w_q \lesssim -1$. We show that a
universe with a cosmological constant or quintessence matter with $w_q \sim -1$
and a decaying Dark Matter has an effective $w_q < -1$ and fits SN data better
than stable CDM or quintessence models with $w_q > -1$.


title:
Gravitational Lenses With More Than Four Images: I. Classification of
  Caustics

abstract:
  We study the problem of gravitational lensing by an isothermal elliptical
density galaxy in the presence of a tidal perturbation. When the perturbation
is fairly strong and oriented near the galaxy's minor axis, the lens can
produce image configurations with six or even eight highly magnified images
lying approximately on a circle. We classify the caustic structures in the
model and identify the range of models that can produce such lenses. Sextuple
and octuple lenses are likely to be rare because they require special lens
configurations, but a full calculation of the likelihood will have to include
both the existence of lenses with multiple lens galaxies and the strong
magnification bias that affects sextuple and octuple lenses. At optical
wavelengths these lenses would probably appear as partial or complete Einstein
rings, but at radio wavelengths the individual images could probably be
resolved.


title:
Intrinsic constraints on very high energy emission in gamma-ray loud
  blazars

abstract:
  Photons with very high energy up to TeV (VHE) emitted from active galactic
nuclei (AGNs) provide some invaluable information of the origin of $\gam$-ray
emission. Although 66 blazars have been detected by {\it EGRET}, only three low
redshift X-ray selected BL Lacs (Mrk 421, Mrk 501, and 1ES 2344+514) are
conclusive TeV emitters (PKS 2155-304 is a potential TeV emitter) since VHE
photons may be absorbed by cosmological background infrared photons ({\it
external} absorption). Based on the ``mirror'' effect of clouds in broad line
region, we argue that there is an {\it intrinsic} mechanism for the deficiency
of TeV emission in blazars. Employing the observable quantities we derive the
pair production optical depth $\tgg(\eps_{\rm obs})$ due to the interaction of
VHE photons with the reflected synchrotron photons by electron Thomson
scattering in broad line region. This sets a more strong constraints on very
high energy emission, and provides a sensitive upper limit of Doppler factor of
the relativistic bulk motion. It has been suggested to distinguish the {\it
intrinsic} absorption from the {\it external} by the observation on variation
of multiwavelegenth continuum.


title: ISO far-infrared observations of rich galaxy clusters II. Sersic 159-03

abstract:
  The far-infrared emission from rich galaxy clusters is investigated. Maps
have been obtained by ISO at 60, 100, 135, and 200 microns using the PHT-C
camera. Ground based imaging and spectroscopy were also acquired. Here we
present the results for the cooling flow cluster Sersic 159-03. An infrared
source coincident with the dominant cD galaxy is found. Some off-center sources
are also present, but without any obvious counterparts.


title:
The Nature of Composite LINER/HII Galaxies, As Revealed from
  High-Resolution VLA Observations

abstract:
  A sample of 37 nearby galaxies displaying composite LINER/HII and pure HII
spectra was observed with the VLA in an investigation of the nature of their
weak radio emission. The resulting radio contour maps overlaid on optical
galaxy images are presented here, together with an extensive literature list
and discussion of the individual galaxies. Radio morphological data permit
assessment of the ``classical AGN'' contribution to the global activity
observed in these ``transition'' LINER galaxies. One in five of the latter
objects display clear AGN characteristics: these occur exclusively in
bulge-dominated hosts.


title:
Recovering the Topology of the Initial Density Fluctuations Using the
  IRAS Point Source Catalogue Redshift Survey

abstract:
  We apply the reconstruction technique of Nusser & Dekel (1992) to the
recently available Point Source Catalogue Redshift Survey (PSCz) in order to
subtract the phase correlations that are expected to develop in the mild
non-linear regime of gravitational evolution. We study the evolution of
isodensity contours defined using an adaptive smoothing algorithm in order to
minimize the problems derived from the non-comutivity of operators. We study
the genus curves of the fields thus obtained and concentrate on the evolution
of the amplitude drops, a meta-statistic able to quantify the level of
phase-correlation present in the field. In order to test the method and to
quantify the level of statistical uncertainty, we apply the method to a set of
mock PSCz catalogues derived from the N-body simulations of two 'standard' CDM
models, kindly granted to us by the Virgo consortium. We find the method to be
reliable in recovering the right amplitude drops. When applied to PSCz, the
level of phase correlations observed is very low on all scales ranging from
5h-1Mpc to 60 h-1Mpc, providing support to the theory that structure originated
from gaussian initial conditions.