title:
Cosmological constraints from the correlation function of galaxy
  clusters

abstract:
  I compare various semi-analytic models for the bias of dark matter halos with
halo clustering properties observed in recent numerical simulations. The best
fitting model is one based on the collapse of ellipsoidal perturbations
proposed by Sheth, Mo & Tormen (1999), which fits the halo correlation length
to better than 8 per cent accuracy. Using this model, I confirm that the
correlation length of clusters of a given separation depends primarily on the
shape and amplitude of mass fluctuations in the universe, and is almost
independent of other cosmological parameters. Current observational
uncertainties make it difficult to draw robust conclusions, but for
illustrative purposes I discuss the constraints on the mass power spectrum
which are implied by recent analyses of the APM cluster sample. I also discuss
the prospects for improving these constraints using future surveys such as the
Sloan Digital Sky Survey. Finally, I show how these constraints can be combined
with observations of the cluster number abundance to place strong limits on the
matter density of the universe.


title:
Far-ultraviolet Spectroscopy of Venus and Mars at 4 A Resolution with
  the Hopkins Ultraviolet Telescope on Astro-2

abstract:
  Far-ultraviolet spectra of Venus and Mars in the range 820-1840 A at 4 A
resolution were obtained on 13 and 12 March 1995, respectively, by the Hopkins
Ultraviolet Telescope (HUT), which was part of the Astro-2 observatory on the
Space Shuttle Endeavour. Longward of 1250 A, the spectra of both planets are
dominated by emission of the CO Fourth Positive band system and strong OI and
CI multiplets. In addition, CO Hopfield-Birge bands, B - X (0,0) at 1151 A and
C - X (0,0) at 1088 A, are detected for the first time, and there is a weak
indication of the E - X (0,0) band at 1076 A in the spectrum of Venus. The B -
X band is blended with emission from OI 1152. Modeling the relative intensities
of these bands suggests that resonance fluorescence of CO is the dominant
source of the emission, as it is for the Fourth Positive system. Shortward of
Lyman-alpha, other emission features detected include OII 834, OI lambda 989,
HI Lyman-beta, and NI 1134 and 1200. For Venus, the derived disk brightnesses
of the OI, OII, and HI features are about one-half of those reported by Hord et
al. (1991) from Galileo EUV measurements made in February 1990. This result is
consistent with the expected variation from solar maximum to solar minimum. The
ArI 1048, 1066 doublet is detected only in the spectrum of Mars and the derived
mixing ratio of Ar is of the order of 2%, consistent with previous
determinations.


title: Abundance of Terrestrial Planets by Microlensing

abstract:
  Terrestrial planets may be detected using the gravitational microlensing
technique. This was demonstrated in the high magnification event
MACHO-98-BLG-35. Observing strategies aimed at measuring the abundance of
terrestrial planets are discussed, using both existing telescopes and planned
telescopes.


title:
The CNOC2 Field Galaxy Redshift Survey I: The Survey and the Catalog for
  the Patch CNOC 0223+00

abstract:
  The Canadian Network for Observational Cosmology (CNOC2) Field Galaxy
Redshift Survey is a spectroscopic/photometric survey of faint galaxies over
1.5 square degrees of sky with a nominal spectroscopic limit of R_c=21.5 mag.
The primary goals of the survey are to investigate the evolution of galaxy
clustering and galaxy populations over the redshift range of approximately 0.1
to 0.6. The survey area contains four widely separated patches on the sky with
a total spectroscopic sample of over 6000 redshifts and a photometric sample of
over 40,000 galaxies with 5-color photometry. We describe the survey and
observational strategies, multi-object spectroscopy mask design procedure, and
data reduction techniques for creating the spectroscopic-photometric catalogs.
We also discuss the derivations of various statistical weights for the redshift
sample which allow it to be used as a complete sample. As the initial release
of the survey data, we present the data set and some statistics for the Patch
CNOC0223+00.


title: Galaxy Evolution at 0 < z < 2 from the NICMOS HDF-North

abstract:
  We have carried out a deep infrared imaging survey (1.1um and 1.6um) of the
Hubble Deep Field North (HDF-N) using NICMOS on board the Hubble Space
Telescope. The combined WFPC2+NICMOS data set lets us study galaxy
morphologies, colors and luminosities at common rest frame wavelengths over a
broad range of redshifts, e.g., in the V-band out to z=2. Here, I illustrate
some applications of this data set for studying the evolution of giant
galaxies, on and off the Hubble Sequence. Large, relatively ordinary spiral
galaxies are found out to at least z=~1.25. Morphological irregularities seen
in many distant HDF galaxies tend to persist from ultraviolet through optical
rest frame wavelengths, suggesting that these are genuinely peculiar,
structurally disturbed systems. Red giant ellipticals are found out to
(photometric) redshifts z=~1.8, implying that some such galaxies probably
formed the bulk of their stars at z_f>~4. However, there are also bluer early
type galaxies at z>0.5, which may have experienced extended star formation
histories. Finally, there appears to be a substantial deficit of high
luminosity galaxies of all types at 1.4<~z<2 compared to lower redshifts.
However, this result must be considered with caution given the small volume of
the HDF, its susceptibility to line-of-sight clustering variations, and the
heavy reliance on photometric redshifts at z>~1.4.


title: The first galaxies: structure and stellar populations

abstract:
  The Hubble Deep Fields continue to be a valuable resource for studying the
distant universe, particularly at z>2 where their comoving volume becomes large
enough to encompass several hundred L* galaxies or their progenitors. Here I
present recent results from a near-infrared imaging survey of the HDF-North
with NICMOS, which provides structural and photometric information in the
optical rest frame (4000-5500A) for hundreds of ordinary galaxies at 2<z<3, and
which offers the means to search for still more distant objects at z>>5. Lyman
break galaxies at 2<z<3 are compact and often irregular in the NICMOS images;
ordinary Hubble sequence spirals and ellipticals seem to be largely absent at
these redshifts, and apparently reached maturity at 1<z<2. The Lyman break
galaxies have UV-optical spectral energy distributions like those of local
starburst galaxies. Population synthesis models suggest typical ages ~few x
10^8 years and moderate UV extinction (~1.2 mag at 1700A), but the constraints
are fairly weak and there may be considerable variety. Considering a near-IR
selected galaxy sample, there is little evidence for a significant number of
galaxies at z~3 that have been missed by UV-based Lyman break selection. Using
the well-characterized z~3 galaxy population as a point of reference, I
consider Lyman break galaxy candidates at 4.5<z<9, as well as one remarkable
object which might (or might not) be at z>12. The space density of UV-bright
galaxies in the HDF appears to thin out toward larger redshifts, although
surface brightness selection effects may play an important role.


title: The effects of a Variable IMF on the Chemical Evolution of the Galaxy

abstract:
  In this work we explore the effects of adopting an initial mass function
(IMF) variable in time on the chemical evolution of the Galaxy. In order to do
that we adopt a chemical evolution model which assumes two main infall episodes
for the formation of the Galaxy. We study the effects on such a model of
different IMFs. First, we use a theoretical one based on the statistical
description of the density field arising from random motions in the gas. This
IMF is a function of time as it depends on physical conditions of the site of
star formation. We also investigate the behaviour of the model predictions
using other variable IMFs, parameterized as a function of metallicity. Our
results show that the theoretical IMF when applied to our model depends on time
but such time variation is important only in the early phases of the Galactic
evolution, when the IMF is biased towards massive stars. We also show that the
use of an IMF which is a stronger function of time does not lead to a good
agreement with the observational constraints suggesting that if the IMF varied
this variation should have been small. Our main conclusion is that the G-dwarf
metallicity distribution is best explained by infall with a large timescale and
a constant IMF, since it is possible to find variable IMFs of the kind studied
here, reproducing the G-dwarf metallicity but this worsens the agreement with
other observational constraints.


title: The Evolution of 3He, 4He and D in the Galaxy

abstract:
  In this work we present the predictions of a modified version of the
``two-infall model'' (Chiappini et al. 1997) for the evolution of 3He, 4He and
D in the solar vicinity, as well as their distributions along the Galactic
disk. In particular, we show that when allowing for extra-mixing process in low
mass stars, as predicted by Charbonnel and do Nascimento (1998), a long
standing problem in chemical evolution is solved, namely: the overproduction of
3He by the chemical evolution models as compared to the observed values in the
sun and in the interstellar medium. Moreover, we show that chemical evolution
models can constrain the primordial value of the deuterium abundance and that a
value of primordial D/H < 3 x 10(-5) is suggested by the present model.
Finally, adopting the primordial 4He abundance suggested by Viegas et al.
(1999), we obtain a value for dY/dZ around 2 and a better agreement with the
solar He abundance.


title:
The Three-dimensional Evolution of Rising, Twisted Magnetic Flux Tubes
  in a Gravitationally Stratified Model Convection Zone

abstract:
  We present three-dimensional numerical simulations of the rise and
fragmentation of twisted, initially horizontal magnetic flux tubes which evolve
into emerging Omega-loops. The flux tubes rise buoyantly through an
adiabatically stratified plasma that represents the solar convection zone. The
MHD equations are solved in the anelastic approximation, and the results are
compared with studies of flux tube fragmentation in two dimensions. We find
that if the initial amount of field line twist is below a critical value, the
degree of fragmentation at the apex of a rising Omega-loop depends on its
three-dimensional geometry: the greater the apex curvature of a given
Omega-loop, the lesser the degree of fragmentation of the loop as it approaches
the photosphere. Thus, the amount of initial twist necessary for the loop to
retain its cohesion can be reduced substantially from the two-dimensional
limit. The simulations also suggest that as a fragmented flux tube emerges
through a relatively quiet portion of the solar disk, extended crescent-shaped
magnetic features of opposite polarity should form and steadily recede from one
another. These features eventually coalesce after the fragmented portion of the
Omega-loop emerges through the photosphere.


title:
On the oxygen abundance determination in HII regions: the problem of the
  line intensities -- oxygen abundance calibration

abstract:
  The problem of the line intensities -- oxygen abundance calibration has been
considered. We confirm the idea of McGaugh (1991) that the strong oxygen lines
([OII] 3727, 3729 and [OIII] 4959, 5007) contain the necessary information for
determination of accurate abundances in low-metallicity (and may be also in
high-metallicity) HII regions. It has been found that the excitation parameters
p3 or p2 (which are defined here as contributions of the radiation in [OIII]
4959, 5007 lines and in [OII] 3727, 3729 lines to the "total" oxygen radiation
respectively) allow to take into account the variations in R23 values among HII
regions with a given oxygen abundance. Based on this fact a new way of the
oxygen abundance determination in HII regions has been constructed and
corresponding relations between line intensities and the oxygen abundance have
been derived empirically using the available oxygen abundances determined via
measurement of temperature-sensitive line ratios.
  In parallel a new R23 calibration has been derived on the base of recent data
and compared to previous calibrations. For oxygen-rich HII regions the present
R23 calibration is close to that of Edmunds and Pagel (1984): their calibration
has the same slope but is shifted towards higher oxygen abundances by around
0.07 dex as compared to the present calibration.


title: Status of HI searches for CHVCs beyond the Local Group

abstract:
  Growing evidence supports the suggestion that the compact high-velocity
clouds of HI (CHVCs) are located throughout the Local Group and continue to
fuel galactic evolution. Recent distance estimates to individual objects lie in
the range 150-850 kpc, implying an HI mass range of 10^5.7 to 10^7.2 M_Sun
together with sizes ranging from 2-12 kpc, while the average linewidth is 30
km/s FWHM. It is natural to ask whether objects of this type would not already
have been seen by current blind HI surveys of the extragalactic sky. We
consider the properties of the deepest published surveys of this type and
conclude that the sensitivity and coverage have now begun to reveal the high
mass end of the distribution (M_HI >10^7 M_Sun). Achieving detection limits an
order of magnitude deeper should finally enable direct study of these systems
beyond the Local Group, or definitively rule out their existence.


title: Current status of cosmological MDM model

abstract:
  An analysis of cosmological models in spatially flat Friedmann Universe with
cosmic gravitational wave background and zero $\Lambda$-term is presented. The
number of free parameters is equal to 5, they are $\sigma_8$, $n$,
$\Omega_\nu$, $\Omega_b$, and $h$. The normalization of the spectrum of density
perturbations on galaxy cluster abundance ($\sigma_8 = 0.52\pm 0.04$) has been
used to calculate numerically the value of the large scale CMB anisotropy
($\ell\simeq 10$) and the relative contribution of cosmological gravitational
waves T/S. Increasing $\Omega_\nu$ weaken the requirements to the value of T/S,
however even for $\Omega_\nu\le 0.4$ the models with $h+n\ge 1.5$ suggest
considerable abundance of gravitational waves: T/S${}^>_\sim 0.3$. In models
with $\Omega_\nu\le 0.4$ and scale-invariant spectrum of density perturbations
($n=1$): T/S${}^>_\sim 10(h-0.47)$. Minimization of the value T/S is possible
only in the range of the red spectra ($n<1$) and small $h$ ($<0.6$). It is
shown that the models with T/S$\in [0, 3]$ admit both moderate red and blue
spectra of density perturbations, $n\in[0.9,1.2]$, with rather high abundance
hot dark matter, $\Omega_\nu\in [0.2,0.4]$. Any condition, $n<0.9$ or
$\Omega_\nu<0.2$, decreases the relative amplitude of the first acoustic peak
for more than 30% in comparison with its hight in the standard CDM normalized
by COBE data.


title: Radiative Precession of an Isolated Neutron Star

abstract:
  Euler's equations of motion are derived exactly for a rigid, triaxial,
internally frictionless neutron star spinning down electromagnetically in
vacuo. It is shown that the star precesses, but not freely: its regular
precession relative to the principal axes of inertia couples to the component
of the radiation torque associated with the near-zone radiation fields and is
modified into an anharmonic wobble. The wobble period \tau_1 typically
satisfies \tau_1 < 10^{-2}\tau_0, where \tau_0 is the braking time-scale; the
wobble amplitude evolves towards a constant non-zero value, oscillates, or
decreases to zero, depending on the degree of oblateness or prolateness of the
star and its initial spin state; and the (negative) angular frequency
derivative d{\omega}/dt oscillates as well, exhibiting quasi-periodic spikes
for triaxial stars of a particular figure. In light of these properties, a
young, Crab-like pulsar ought to display fractional changes of order unity in
the space of a few years in its pulse profile, magnetic inclination angle, and
d{\omega}/dt. Such changes are not observed, implying that the wobble is damped
rapidly by internal friction, if its amplitude is initially large upon
crystallization of the stellar crust. If the friction is localized in the inner
and outer crusts, the thermal luminosity of the neutron star increases by a
minimum amount \Delta L = 3*10^{31} (\epsilon / 10^{-12}) (\omega / 10^3 rad
s^{-1})^2 (\tau_d / 1 yr)^{-1} erg s^{-1}, where epsilon is the ellipticity and
\tau_d is the damping time-scale, with the actual value of \Delta L determined
in part by the thermal conduction time \tau_cond. The increased luminosity is
potentially detectable as thermal X-rays lasting for a time max(tau_d,tau_cond)
following crystallization of the crust.


title:
Multiple and variable X-ray sources in the globular clusters omega Cen,
  NGC6397, NGC6752, and Liller 1

abstract:
  We detect stars from the Hipparcos and Tycho Catalogues in the field of view
of observations with the ROSAT HRI of three globular clusters. We use the
positions of these stars to reduce the systematic error in the positions of
X-ray sources in the clusters to ~2'' for omega Cen and NGC6752, and 1'' for
NGC6397. We detect three X-ray sources in the core of omega Cen, and four in
the core of NGC6752; the data for the center of NGC6397 may be fitted with five
or six sources. Outside the cores, but within the half-mass radius of the
clusters, we detect two sources in omega Cen, one in NGC6397 and two in
NGC6752; these may or may not be cluster members. A ROSAT HRI observation of
Liller 1 does not detect a low-luminosity source, at a limit below a detection
with ASCA. We discuss the nature of the low-luminosity X-ray sources in
globular clusters in the light of these new results.


title:
The Search for Cosmological Black Holes: A Surface Brightness
  Variability Test

abstract:
  Recently it has been suggested that the majority of dark matter in the
universe resides in the form of Jupiter mass black holes distributed
cosmologically. This population makes itself apparent by microlensing high
redshift quasars and introducing pronounced variability into their observed
light curves. While several arguments dismissing this hypothesis have been
presented, a conclusive observational test is, alas, sadly lacking. In this
paper we investigate the effect of a cosmologically distributed population of
microlensing masses on galaxies at low to intermediate redshift. The
magnification of bright stars in these galaxies leads to small, but observable,
fluctuations in their surface brightness. The variability time scale for
Jupiter-mass lensing objects is of the order of a few months and this
population may be detected through a future space-based monitoring campaign of
a field containing $z \sim 0.5$ galaxies. The monitoring of galactic surface
brightness will provide an effective test of the nature of dark matter on
cosmological scales.


title:
Emission Line AGNs from the REX survey: Results from optical
  spectroscopy

abstract:
  We present 71 Emission Line objects selected from the REX survey. Except for
3 of them, for which the presence of an active nucleus is dubious, all these
sources are Active Galactic Nuclei (QSOs, Seyfert galaxies, emission line
radiogalaxies). In addition, we present the spectra of other 19 AGNs included
in a preliminary version of the REX catalog but not in the final one. The
majority (80) of the 90 sources presented in this paper is newly discovered.
Finally, we present the general properties in the radio and in the X-ray band
of all the AGNs discovered so far in the REX survey.


title: Non-pulsed emission from the binary system PSR B1259-63

abstract:
  PSR B1259-63 is the only known binary system with a radio pulsar from which
the non-pulsed radio and X-ray emission was detected. The companion star in
this system is a Be star SS 2883. A rapidly rotating radio pulsar is expected
to produce a wind of relativistic particles. Be stars are known to produce
highly asymmetric mass loss. Due to the interaction of the pulsar wind and the
Be star wind the system of two shocks between the pulsar and the Be star forms.
In this paper we show that the observed non-pulsed radio emission from the
system is a result of the synchrotron emission of the relativistic particles in
the outflow beyond the shock wave and that the non-pulsed X-ray emission is due
to the inverse Compton scattering of the Be star photons on this particles.


title: Optical imaging and spectroscopy of BL Lac objects

abstract:
  We present optical images and spectroscopy for a dozen of BL Lac objects.
Most of these objects were not previously studied and we give for the first
time the properties of their host galaxies. The properties of the new host
galaxies are generally consistent with those derived in previous optical
studies. We found a case (1101-23) where the external isophotes of the galaxy
are clearly boxy.
  In addition we gathered spectroscopy for several BL Lac objects with unknown
redshift and for companion galaxies. This allowed us to derive a tentative
redshift for two new BL Lacs and to investigate the environment around PKS
0829+04. These data complement existing data available in the literature on
host galaxies of BL Lacs and their (close) environments.


title: Far Infrared Study of IRAS 00494+5617 & IRAS 05327-0457

abstract:
  High angular resolution far-infrared observations at 143 & 185 \micron, using
the TIFR 1-m balloon borne telescope, are presented for two Galactic star
forming complexes associated with IRAS 00494+5617 and 05327-0457. The latter
map also reveals the cold dust in OMC-3. The HIRES processed IRAS maps at 12,
25, 60 & 100 micron have also been presented for comparison. Both these regions
are illuminated at the edges by high mass stars with substantial UV flux.The
present study is aimed at quantifying the role of the nearby stars vis-a-vis
embedded young stellar objects in the overall heating of these sources. Based
on the FIR observations at 143 & 185 micron carried out simultaneously with
almost identical angular resolution, reliable dust temperature and optical
depth maps have been generated for the brighter regions of these sources.
Radiative transfer modeling in spherical geometry has been carried out to
extract physical parameters of these sources by considering the observational
constraints like : spectral energy distribution, angular size at different
wavelengths, dust temperature distribution etc. It has been concluded that for
both IRAS 00494+5617 and IRAS 05327-0457, the embedded energy sources play the
major role in heating them with finite contribution from the nearby stars. The
best fit model for IRAS 00494+5617 is consistent with a simple two phase
clump-interclump picture with $\sim$ 5% volume filling factor (of clumps) and a
density contrast of $\approx$ 80.


title: Theory of Microlensing

abstract:
  I present a somewhat selective review of microlensing theory, covering five
major areas: 1) the derivation of the basic formulae, 2) the relation between
the observables and the fundamental physical parameters, 3) binaries, 4)
astrometric microlensing, and 5) femtolensing.


title: Disks and Planets in Binary Systems

abstract:
  The star formation process in molecular clouds usually leads to the formation
of multiple stellar systems, mostly binaries. Remaining disks around those
stars may be located around individual stars (circumstellar disks) or around
the entire binary system (circumbinary disk). We shall briefly review the
present observational evidence for both types of disks in binary stars, in
particular the properties of circumbinary disks.
  We then present recent results of the theoretical modeling of the collapse
and fragmentation of gravitationally unstable molecular cloud cores and their
implications for binary and disk formation, and discuss the dynamical influence
of the binary companions on disk truncation and gap formation. The presence of
binaries may have profound influence on the process of planet formation as
well. We present results on the stability and evolution of orbits of planets in
disks around binaries.


title: Three-dimensional modelling of edge-on disk galaxies

abstract:
  We present detailed three-dimensional modelling of the stellar luminosity
distribution for the disks of 31 relatively nearby (<= 110 Mpc) edge-on spiral
galaxies. In contrast to most of the standard methods available in the
literature we take into account the full three-dimensional information of the
disk. We minimize the difference between the observed 2D-image and an image of
our 3D-disk model integrated along the line of sight. Thereby we specify the
inclination, the fitting function for the z-distribution of the disk, and the
best values for the structural parameters such as scalelength, scaleheight,
central surface brightness, and a disk cut-off radius. From a comparison of two
independently developed methods we conclude, that the discrepancies e.g. for
the scaleheights and scalelengths are of the order of ~10%. These differences
are not due to the individual method itself, but rather to the selected fitting
region, which masks the bulge component, the dust lane, or present foreground
stars. Other serious limitations are small but appreciable intrinsic deviations
of real disks compared to the simple input model. In this paper we describe the
methods and present contour plots as well as radial profiles for all galaxies
without previously published surface photometry. Resulting parameters are given
for the complete sample.


title: The orbital evolution of planets in disks

abstract:
  The orbital parameters of the observed extrasolar planets differ strongly
from those of our own solar system. The differences include planets with high
masses, small semi-major axis and large eccentricities. We performed numerical
computations of embedded planets in disks and follow their mass growth and
orbital evolution over several thousand periods.
  We find that planets do migrate inwards on timescales of about $10^5$ years
on nearly circular orbits, during which they may grow up to about 5 Jupiter
masses. The interaction of the disk with several planets may halt the migration
process and lead to a system similar to the solar planetary system.


title: Mirror Dark Matter

abstract:
  There appear to be three challenges that any theory of dark matter must face:
(i) why is $\Omega_{DM}$ of the same order as $\Omega_{Baryons}$ ? (ii) what
are the near solar mass objects ($\sim 0.5 M_{\odot}$) observed by the MACHO
microlensing project ? and (iii) understanding the shallow core density profile
of the halos of dwarf as well as low surface brightness galaxies. The popular
cold dark matter candidates, the SUSY LSP and the axion fail to meet these
challenges. We argue that in the mirror model suggested recently to explain the
neutrino anomalies, the mirror baryons being 15-20 times heavier than familiar
baryons, can play the role of the cold dark matter and provide reasonable
explanation of all three above properties without extra assumptions.


title: Evidence for a Black Hole and Accretion Disk in the LINER NGC 4203

abstract:
  We present spectroscopic observations from the Hubble Space Telescope that
reveal for the first time the presence of a broad pedestal of Balmer-line
emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive
of a relativistic accretion disk, and is reminiscent of double-peaked transient
Balmer emission observed in a handful of other LINERs. The very broad line
emission thus constitutes clear qualitative evidence for a black hole, and
spatially resolved narrow-line emission in NGC 4203 can be used to constrain
its mass, with M_BH less than 6 x 10^6 solar masses at 99.7% confidence. This
value implies a ratio of black-hole mass to bulge mass of less than
approximately 7 x 10^-4 in NGC 4203, which is less by a factor of ~3 - 9 than
the mean ratio obtained for other galaxies. The availability of an independent
constraint on central black-hole mass makes NGC4203 an important testbed for
probing the physics of weak active galactic nuclei. Assuming M_BH near the
detection limit, the ratio of observed luminosity to the Eddington luminosity
is approximately 10^-4. This value is consistent with advection-dominated
accretion, and hence with scenarios in which an ion torus irradiates an outer
accretion disk that produces the observed double-peaked line emission.
Follow-up observations will make it possible to improve the black-hole mass
estimate and study variability in the nuclear emission.


title:
Mitigating Charge Transfer Inefficiency in the Chandra X-ray
  Observatory's ACIS Instrument

abstract:
  The ACIS front-illuminated CCDs onboard the Chandra X-ray Observatory were
damaged in the extreme environment of the Earth's radiation belts, resulting in
enhanced charge transfer inefficiency (CTI). This produces a row dependence in
gain, event grade, and energy resolution. We model the CTI as a function of
input photon energy, including the effects of de-trapping (charge trailing),
shielding within an event (charge in the leading pixels of the 3X3 event island
protect the rest of the island by filling traps), and non-uniform spatial
distribution of traps. This technique cannot fully recover the degraded energy
resolution, but it reduces the position dependence of gain and grade
distributions. By correcting the grade distributions as well as the event
amplitudes, we can improve the instrument's quantum efficiency. We outline our
model for CTI correction and discuss how the corrector can improve
astrophysical results derived from ACIS data.


title: Galaxy surface photometry

abstract:
  We describe galaxy surface photometry based on fitting ellipses to the
isophotes of the galaxies. Example galaxies with different isophotal shapes are
used to illustrate the process, including how the deviations from elliptical
isophotes are quantified using Fourier expansions. We show how the definitions
of the Fourier coefficients employed by different authors are linked. As
examples of applications of surface photometry we discuss the determination of
the relative disk luminosities and the inclinations for E and S0 galaxies. We
also describe the color-magnitude and color-color relations. When using both
near-infrared and optical photometry, the age-metallicity degeneracy may be
broken. Finally we discuss the Fundamental Plane where surface photometry is
combined with spectroscopy. It is shown how the FP can be used as a sensitive
tool to study galaxy evolution.


title:
Discovery of Narrow X-ray Absorption Lines from NGC 3783 with the
  Chandra HETGS

abstract:
  We present the first grating-resolution X-ray spectra of the Seyfert 1 galaxy
NGC 3783, obtained with the High Energy Transmission Grating Spectrometer on
the Chandra X-ray Observatory. These spectra reveal many narrow absorption
lines from the H-like and He-like ions of O, Ne, Mg, Si, S and Ar, as well as
FeXVII-FeXXI L-shell lines. We have also identified several weak emission
lines, mainly from O and Ne. The absorption lines are blueshifted by a mean
velocity of approximately 440\pm200 km/s and are not resolved, indicating a
velocity dispersion within the absorbing gas of a few hundred km/s or less. We
measure the lines' equivalent widths and compare them with the predictions of
photoionization models. The best-fitting model has a microturbulence velocity
of 150 km/s and a hydrogen column density of 1.3\times10^22 cm^-2. The measured
blueshifts and inferred velocity dispersions of the X-ray absorption lines are
consistent with those of the strongest UV absorption lines observed in this
object. However, simple models that propose to strictly unify the X-ray and UV
absorbers have difficulty explaining simultaneously the X-ray and UV absorption
line strengths.


title: Quasars: a supermassive rotating toroidal black hole interpretation

abstract:
  A supermassive rotating toroidal black hole (TBH) is proposed as the
fundamental structure of quasars and other jet-producing active galactic
nuclei. Rotating protogalaxies gather matter from the central gaseous region
leading to the birth of massive toroidal stars whose internal nuclear reactions
proceed very rapidly. Once the nuclear fuel is spent, gravitational collapse
produces a slender ring-shaped TBH remnant. These events are typically the
first supernovae of the host galaxies. Given time the TBH mass increases
through continued accretion by several orders of magnitude, the event horizon
swells whilst the central aperture shrinks. The difference in angular
velocities between the accreting matter and the TBH induces a magnetic field
that is strongest in the region of the central aperture and innermost
ergoregion. Due to the presence of negative energy states when such a
gravitational vortex is immersed in an electromagnetic field, circumstances are
near ideal for energy extraction via non-thermal radiation including the
Penrose process and superradiant scattering. This establishes a self-sustaining
mechanism whereby the transport of angular momentum away from the quasar by
relativistic bi-directional jets reinforces both the modulating magnetic field
and the TBH/accretion disk angular velocity differential. Quasar behaviour is
extinguished once the BH topology becomes spheroidal. Similar mechanisms may be
operating in microquasars, SNe and GRBs when neutron density or BH tori arise.
In certain circumstances, long-term TBH stability can be maintained by a
negative cosmological constant, otherwise the classical topology theorems must
somehow be circumvented. Preliminary evidence is presented that Planck-scale
quantum effects may be responsible.


title: A Proton Synchrotron Blazar Model for Flaring in Markarian~501

abstract:
  (abr.) The spectral energy distribution (SED) of blazars typically has a
double-humped appearance usually interpreted in terms of synchrotron
self-Compton models. In proton blazar models, the SED is instead explained in
terms of acceleration of protons and subsequent cascading. We discuss a
variation of the Synchrotron Proton Blazar model, first proposed by M\"ucke &
Protheroe (1999), in which the low energy part of the SED is mainly synchrotron
radiation by electrons co-accelerated with protons which produce the high
energy part of the SED mainly asproton synchrotron radiation. Using a Monte
Carlo/numerical technique to simulate the interactions and subsequent cascading
of the accelerated protons, we are able to fit the observed SED of Markarian
501 during the April 1997 flare. We find that the emerging cascade spectra
initiated by gamma-rays from $\pi^0$ decay and by $e^\pm$ from $\mu^\pm$ decay
turn out to be relatively featureless. Synchrotron radiation produced by
$\mu^\pm$ from $\pi^\pm$ decay, and even more importantly by protons, and
subsequent synchrotron-pair cascading, is able to reproduce well the high
energy part of the SED. For this fit we find that synchrotron radiation by
protons dominates the TeV emission, pion photoproduction being less important
with the consequence that we predict a lower neutrino flux than in other proton
blazar models.


title:
XID: Cross-Association of ROSAT/Bright Source Catalog X-ray Sources with
  USNO A2 Optical Point Sources

abstract:
  We quantitatively cross-associate the 18811 ROSAT Bright Source Catalog
(RASS/BSC) X-ray sources with optical sources in the USNO-A2 catalog,
calculating the the probability of unique association (Pid) between each
candidate within 75 arcsec of the X-ray source position, on the basis of
optical magnitude and proximity. We present catalogs of RASS/BSC sources for
which the probability of association is >98%, >90%, and >50%, which contain
2705, 5492, and 11301 unique USNO-A2 optical counterparts respectively down to
the stated level of significance. We include in this catalog a list of objects
in the SIMBAD database within 10 arcsec of the USNO position, as an aid to
identification and source classification. The catalog is more useful than
previous catalogs which either rely on plausibility arguments for association,
or do not aid in selecting a counterpart between multiple off-band sources in
the field. We find that a fraction ~65.8% of RASS/BSC sources have an
identifiable optical counterpart, down to the magnitude limit of the USNO
catalog which could be identified by their spatial proximity and high optical
brightness.


title: Confusion errors in astrometry and counterpart association

abstract:
  In very crowded fields, the modulation of the background by the sea of
unresolved faint sources induces centroid shifts. The errors increase with the
number of sources per beam. Even the most optimistic simulations of imaging
data show that position errors can become severe (on the order of the beam
size) at flux levels at which images contain 1/50 to 1/15 sources per beam,
depending on the slope of the number-flux relation $d\log N/d\log S$. These
problems are expected to be significant for recent observations of faint
submillimeter sources and may be the reason that some sources appear to lack
optical counterparts.


title: On the Two-Phase Structure of Protogalactic Clouds

abstract:
  Within protogalaxies, thermal instability leads to the formation of a
population of cool fragments, confined by the pressure of residual hot gas. The
hot gas remains in quasi-hydrostatic equilibrium, at approximately the virial
temperature of the dark matter halo. It is heated by compression and shock
dissipation and is cooled by bremsstrahlung emission and conductive losses into
the cool clouds. The cool fragments are photoionized and heated by the
extragalactic UV background and nearby massive stars. The smallest clouds are
evaporated due to conductive heat transfer from the hot gas. All are subject to
disruption due to hydrodynamic instabilities. They also gain mass due to
collisions and mergers and condensation from the hot gas due to conduction. The
size distribution of the fragments in turn determines the rate and efficiency
of star formation during the early phase of galactic evolution. We have
performed one-dimensional hydrodynamic simulations of the evolution of the hot
and cool gas. The cool clouds are assumed to follow a power-law size
distribution, and fall into the galactic potential, subject to drag from the
hot gas. The relative amounts of the hot and cool gas is determined by the
processes discussed above, and star formation occurs at a rate sufficient to
maintain the cool clouds at 10$^4$ K. We present density distributions for the
two phases and also for the stars for several cases, parametrized by the
circular speeds of the potentials. Under some conditions, primarily low
densities of the hot gas, conduction is more efficient than radiative processes
at cooling the hot gas, limiting the x-ray radiation from the halo gas.


title: The Near Infrared and Multiwavelength Afterglow of GRB 000301c

abstract:
  We present near-infrared observations of the counterpart of GRB 000301c. The
K' filter (2.1 micron) light curve shows a well-sampled break in the decay
slope at t=3.5 days post-burst. The early time slope is very shallow (~ -0.1),
while the late time slope is steep (-2.2). Comparison with the optical (R band)
light curve shows marginally significant differences, especially in the early
time decay slope (which is steeper in the optical) and the break time (which
occurs later in the optical). This is contrary to the general expectation that
light curve breaks should either be achromatic (e.g., for breaks due to
collimation effects) or should occur later at longer wavelengths (for most
other breaks). The observed color variations might be intrinsic to the
afterglow, or might indicate systematic errors of > 0.08 magnitude in all
fluxes. Even if the break is achromatic, we argue that its sharpness poses
difficulties for explanations that depend on collimated ejecta. The R light
curve shows further signs of fairly rapid variability (a bump, steep drop, and
plateau) that are not apparent in the K' light curve. In addition, by combining
the IR-optical-UV data with millimeter and radio fluxes, we are able to
constrain the locations of the self-absorption break and cooling break and to
infer the location of the spectral peak at t=3 days: f_nu = 3.4 mJy at nu=1e12
Hz. Using the multiwavelength spectral energy distribution, we are able to
constrain the blast wave energy, which was E > 3e53 erg if the explosion was
isotropic. This implies a maximum gamma ray production efficiency of ~ 0.15 for
GRB 000301C.


title: Failed Oort Clouds and Planetary Migration

abstract:
  Planet formation is accompanied by the formation of comet clouds. In systems
where planets migrate on rapid timescales, the diffusive evolution of comet
orbits may stall, resulting in a comet cloud intermediate between a flattened
Kuiper Belt and a spherical Oort cloud. These `failed Oort clouds' may provide
a `smoking gun', indicating that planetary migration has taken place. If some
fraction of the scattered component consists of planetary embryos, it may be
possible to observe transits of such bodies even when the planetary system is
not edge-on to the line of sight.


title: Astrophysical Reaction Rates From Statistical Model Calculations

abstract:
  Theoretical reaction rates in the temperature range 0.01*10^9<=T[K]<=10.*10^9
are calculated in the statistical model (Hauser-Feshbach formalism) for targets
with 10<=Z<=83 (Ne to Bi) and for a mass range reaching the neutron and proton
driplines. Reactions considered are (n,gamma), (n,p), (n,alpha), (p,gamma),
(p,alpha),(alpha,gamma), and their inverse reactions. Reaction rates as a
function of temperature for thermally populated targets are given by analytic
seven parameter fits. To facilitate comparison with experimental rates, the
stellar enhancement factors are also tabulated. Two complete sets of rates have
been calculated, one of which includes a phenomenological treatment of shell
quenching for neutron-rich nuclei. These extensive datasets are provided
on-line as electronic files, while a selected subset from one calculation is
given as printed tables. A summary of the theoretical inputs and advice on the
use of the provided tabulations is included.


title:
Radiation-Hydrodynamical Collapse of Pregalactic Clouds in the
  Ultraviolet Background

abstract:
  To elucidate the effects of the UV background radiation on the collapse of
pregalactic clouds, we implement a radiation-hydrodynamical calculation,
combining one-dimensional spherical hydrodynamics with an accurate treatment of
the radiative transfer of ionizing photons. Both absorption and scattering of
UV photons are explicitly taken into account. It turns out that a gas cloud
contracting within the dark matter potential does not settle into hydrostatic
equilibrium, but undergoes run-away collapse even under the presence of the
external UV field. The cloud center is shown to become self-shielded against
ionizing photons by radiative transfer effects before shrinking to the rotation
barrier. Based on our simulation results, we further discuss the possibility of
H2 cooling and subsequent star formation in a run-away collapsing core. The
present results are closely relevant to the survival of subgalactic Population
III objects as well as to metal injection into intergalactic space.


title:
Multifrequency Observations of the Virgo Blazars 3C 273 and 3C 279 in
  CGRO Cycle 8

abstract:
  We report first observational results of multifrequency campaigns on the
prominent Virgo blazars 3C 273 and 3C 279 which were carried out in January and
February 1999. Both blazars are detected from radio to gamma-ray energies. We
present the measured X- to gamma-ray spectra of both sources, and for 3C 279 we
compare the 1999 broad-band (radio to gamma-ray) spectrum to measured previous
ones.


title: Ferromagnetism of quark liquid and magnetars

abstract:
  Spontaneous magnetization of quark liquid is examined on the analogy with
that in electron gas. It is pointed out that quark liquid has potential to be
ferromagnetic at rather low densities, around nuclear saturation density. Somme
comments are given as for implications on magnetars.


title:
Supernova type Ia luminosities, their dependence on second parameters,
  and the value of H_0

abstract:
  A sample of 35 SNe Ia with good to excellent photometry in B and V, minimum
internal absorption, and 1200 < v < \approx 30000 km/s is compiled from the
literature. As far as their spectra are known they are all Branch-normal. For
29 of the SNe Ia also peak magnitudes in I are known. The SNe Ia have uniform
colors at maximum, i.e. <B-V>=-0.012 mag (sigma=0.051) and <V-I>=-0.276 mag
(sigma=0.078). In the Hubble diagram they define a Hubble line with a scatter
of $\sigma_M$=0.21-0.16 mag, decreasing with wavelength. The scatter is further
reduced if the SNe Ia are corrected for differences in decline rate Delta_m_15
or color (B-V). A combined correction reduces the scatter to sigma<=0.13 mag.
After the correction no significant dependence remains on Hubble type or
galactocentric distance. The Hubble line suggests some curvature which can be
differently interpreted. A consistent solution is obtained for a cosmological
model with Omega_M=0.3, Omega_Lambda=0.7, which is indicated also by much more
distant SNe Ia. Absolute magnitudes are available for eight equally blue
(Branch-normal) SNe Ia in spirals, whose Cepheid distances are known. If their
well defined mean values of M_B, M_V, and M_I are used to fit the Hubble line
to the above sample of SNe Ia one obtains H_0=58.3 km/s/Mpc, or, after
adjusting all SNe Ia to the average values of Delta_m_15 and (B-V), H_0=60.9
km/s/Mpc. Various systematic errors are discussed whose elimination tends to
decrease H_0. The finally adopted value at the 90-percent level, including
random and systematic errors, is H_0=58.5 +/- 6.3 km/s/Mpc. Several higher
values of H_0 from SNe Ia, as suggested in the literature, are found to depend
on large corrections for variations of the light curve parameter and/or on an
unwarranted reduction of the Cepheid distances of the calibrating SNe Ia.


title: A supermassive boson star at the galactic center?

abstract:
  We explore whether supermassive non-baryonic stars (in particular boson,
mini-boson and non-topological soliton stars) might be at the center of some
galaxies, with special attention to the Milky Way. We analyze, from a dynamical
point of view, what current observational data show, concluding that they are
compatible with a single supermassive object without requiring it to be a black
hole. Particularly, we show that scalar stars fit very well into these
dynamical requirements. The parameters of different models of scalar stars
necessary to reproduce the inferred central mass are derived, and the possible
existence of boson particles with the adequate range of masses is commented.
Accretion to boson stars is also analyzed, and a comparison with another
non-baryonic candidate, a massive neutrino ball, which is also claimed as an
alternative to the central black hole, is given. Both models are capable to
explain the nature of the object in Sgr A$^*$ without invoking the presence of
a singularity. One difficult issue is why the accreted materials will not
finally produce, in a sufficiently long time, a black hole. We provide an
answer based on stellar disruption in the case of boson stars, and comment
several suggestions for its possible solution in neutrino ball scenarios.
Finally, we discuss the prospects for the observational detection of these
supermassive scalar objects, using the new generation of X-ray and radio
interferometry satellites.


title: New challenges for Adaptive Optics: Extremely Large Telescopes

abstract:
  The performance of an adaptive optics (AO) system on a 100m diameter ground
based telescope working in the visible range of the spectrum is computed using
an analytical approach. The target Strehl ratio of 60% is achieved at 0.5um
with a limiting magnitude of the AO guide source near R~10, at the cost of an
extremely low sky coverage. To alleviate this problem, the concept of
tomographic wavefront sensing in a wider field of view using either natural
guide stars (NGS) or laser guide stars (LGS) is investigated. These methods use
3 or 4 reference sources and up to 3 deformable mirrors, which increase up to
8-fold the corrected field size (up to 60\arcsec at 0.5 um). Operation with
multiple NGS is limited to the infrared (in the J band this approach yields a
sky coverage of 50% with a Strehl ratio of 0.2). The option of open-loop
wavefront correction in the visible using several bright NGS is discussed. The
LGS approach involves the use of a faint (R ~22) NGS for low-order correction,
which results in a sky coverage of 40% at the Galactic poles in the visible.


title: Global Nonradial Instabilities of Dynamically Collapsing Gas Spheres

abstract:
  Self-similar solutions provide good descriptions for the gravitational
collapse of spherical clouds or stars when the gas obeys a polytropic equation
of state, $p=K\rho^\gamma$ (with $\gamma\le 4/3$). We study the behaviors of
nonradial perturbations in the similarity solutions of Larson, Penston and
Yahil, which describe the evolution of the collapsing cloud prior to core
formation. Our global stability analysis reveals the existence of unstable
bar-modes ($l=2$) when $\gamma\le 1.09$. In particular, for the collapse of
isothermal spheres, which applies to the early stages of star formation, the
$l=2$ density perturbation relative to the background, $\delta\rho({\bf
r},t)/\rho(r,t)$, increases as $(t_0-t)^{-0.352}\propto \rho_c(t)^{0.176}$,
where $t_0$ denotes the epoch of core formation, and $\rho_c(t)$ is the cloud
central density. Thus, the isothermal cloud tends to evolve into an ellipsoidal
shape (prolate bar or oblate disk, depending on initial conditions) as the
collapse proceeds. In the context of Type II supernovae, core collapse is
described by the $\gamma\simeq 1.3$ equation of state, and our analysis
indicates that there is no growing mode (with density perturbation) in the
collapsing core before the proto-neutron star forms, although nonradial
perturbations can grow during the subsequent accretion of the outer core and
envelope onto the neutron star. We also carry out a global stability analysis
for the self-similar expansion-wave solution found by Shu, which describes the
post-collapse accretion (``inside-out'' collapse) of isothermal gas onto a
protostar. We show that this solution is unstable to perturbations of all
$l$'s, although the growth rates are unknown.


title: High magnetic field pulsars and magnetars: a unified picture

abstract:
  We propose a unified picture of high magnetic field radio pulsars and
magnetars by arguing that they are all rotating high-field neutron stars, but
have different orientations of their magnetic axes with respective to their
rotation axes. In strong magnetic fields where photon splitting suppresses pair
creation near the surface, the high-field pulsars can have active inner
accelerators while the anomalous X-ray pulsars cannot. This can account for the
very different observed emission characteristics of the anomalous X-ray pulsar
1E 2259+586 and the high field radio pulsar PSR J1814-1744. A predicted
consequence of this picture is that radio pulsars having surface magnetic field
greater than about $2\times 10^{14}$ G should not exist.


title: A deep X-ray observation of NGC 4258 and its surrounding field

abstract:
  We present a deep X-ray observation of the low-luminosity active galactic
nucleus in NGC4258 (M106) using ASCA. The soft X-ray spectrum <2keV is
dominated by thermal emission from optically-thin plasma with kT~0.5keV. The
hard X-ray emission is clearly due to a power-law component with photon index
Gamma=1.8 absorbed by a column density of N_H=8x10^22/cm^2. The power-law is
readily identified with primary X-ray emission from the AGN central engine. We
also clearly detect a narrow iron K-alpha emission line at 6.4keV. No broad
component is detected. We suggest that the bulk of this narrow line comes from
the accretion disk and, furthermore, that the power-law X-ray source which
excites this line emission (which is typically identified with a disk corona)
must be at least 100GM/c^2 in extent. This is in stark contrast to many
higher-luminosity Seyfert galaxies which display a broad iron line indicating a
small 10 GM/c^2 X-ray emitting region. It must be stressed that this study
constrains the size of the X-ray emitting corona rather than the
presence/absence of a radiatively efficient accretion disk in the innermost
regions. If, instead, a substantial fraction of the observed narrow line
originates from material not associated with the accretion disk, limits can be
placed on the parameter space of possible allowed relativistically broad iron
lines. By comparing our data with previous ASCA observations, we find marginal
evidence for a change in absorbing column density through to the central
engine, and good evidence for a change in the AGN flux.


title: Analytic Time Delays and H_0 Estimates for Gravitational Lenses

abstract:
  We study gravitational lens time delays for a general family of lensing
potentials, which includes the popular singular isothermal elliptical potential
and singular isothermal elliptical density distribution but allows general
angular structure. Using a novel approach, we show that the time delay can be
cast in a very simple form, depending only on the observed image positions.
Including an external shear changes the time delay proportional to the shear
strength, and varying the radial profile of the potential changes the time
delay approximately linearly. These analytic results can be used to obtain
simple estimates of the time delay and the Hubble constant in observed
gravitational lenses. The naive estimates for four of five time delay lenses
show surprising agreement with each other and with local measurements of H_0;
the complicated Q 0957+561 system is the only outlier. The agreement suggests
that it is reasonable to use simple isothermal lens models to infer H_0,
although it is still important to check this conclusion by examining detailed
models and by measuring more lensing time delays.


title: Stochastic Coagulation and the Timescale for Runaway Growth

abstract:
  We study the stochastic coagulation equation using simplified models and
efficient Monte Carlo simulations. It is known that (i) runaway growth occurs
if the two-body coalescence kernel rises faster than linearly in the mass of
the heavier particle; and (ii) for such kernels, runaway is instantaneous in
the limit that the number of particles tends to infinity at fixed collision
time per particle. Superlinear kernels arise in astrophysical systems where
gravitational focusing is important, such as the coalescence of planetesimals
to form planets or of stars to form supermassive black holes. We find that the
time required for runaway decreases as a power of the logarithm of the the
initial number of particles. Astrophysical implications are briefly discussed.


title:
Unbiased reconstruction of the mass function using microlensing survey
  data

abstract:
  The large number of microlensing events discovered towards the Galactic Bulge
bears the promise to reconstruct the stellar mass function. The more
interesting issue concerning the mass function is certainly to probe its low
mass end. However due to the source confusion, even if the distribution and the
kinematics of the lenses are known, the estimation of the mass function is
extremely biased at low masses. The blending due to the source confusion biases
the duration of the event, which in turn dramatically biases the estimation of
the mass of the lens. To overcome this problem we propose to use differential
photometry of the microlensing events obtained using the image subtraction
method. Differential photometry is free of any bias due to blending, however
the drawback of differential photometry is that the baseline flux is unknown.
In this paper we will show that even without knowing the baseline flux, purely
differential photometry allow to estimate the mass function without any biases.
The basis of the method is that taking the scalar product of the microlensing
light curves with a given function and taking its sum over all the microlensing
events is equivalent to project the mass function on another function. This
method demonstrates that there is a direct correspondancy between the space of
the observations and the space of the mass function. Concerning the function to
use in order to project the observations, we show that the principal components
of the light curves are an optimal set. To illustrate the method we simulate
sets consistent with the microlensing experiments. By using 1000 of these
simulations, we show that for instance the exponent of the mass function can be
reconstructed without any biases.


title: Star Formation and Galaxy Environment

abstract:
  The dependence of star formation rate on galaxian environment is a key issue
in the understanding of galaxy formation and evolution. However, the study of
this subject is complex and observationally challenging. This paper reviews
some of the current results, drawing mostly from recent large redshift surveys
such the LCRS, the MORPH collaboration, and the CNOC1 and CNOC2 redshift
surveys.


title: The UV spectrum of nebulae

abstract:
  This paper presents an analysis of the UV spectrum of some nebulae with
clearly identified illuminating stars, all observed by the IUE satellite.
  The data show remarkable properties of the UV spectrum of the nebulae. Each
spectrum is the product of the star spectrum and a linear function of 1/lambda.
There is no peculiar behaviour in the spectrums at 2200A: no bump created in
the spectrum of a nebula and no excess of scattering. When moving away from the
star, the surface brightness of a nebula decreases as the inverse of the square
of the angular distance to the star.
  These results can logically be interpreted in terms of scattering of
starlight. They imply constant properties of the interstellar grains in the UV
and in the directions of space sampled by the nebulae, and probably a strong
forward scattering phase function. There is no evidence for any particular type
of grain which would specifically extinguish starlight at 2200A.
  Concerning the UV spectrum of a star, this may imply a revisal of the
traditional interpretation of the 2200A bump.


title:
The KPNO International Spectroscopic Survey. I. Description of the
  Survey

abstract:
  The KPNO International Spectroscopic Survey (KISS) is a new objective-prism
survey for extragalactic emission-line objects. It combines many of the
features of previous slitless spectroscopic surveys that were carried out with
Schmidt telescopes using photographic plates with the advantages of modern CCD
detectors. It is the first purely digital objective-prism survey, and extends
previous photographic surveys to substantially fainter flux limits. In this,
the first paper in the series, we give an overview of the survey technique,
describe our data processing procedures, and present examples of the types of
objects found by KISS. Our first H-alpha-selected survey list detects objects
at the rate of 18.1 per square degree, which is 181 times higher than the
surface density of the Markarian survey.Since the sample is line-selected,
there is an imposed redshift limit of z ~ 0.095 due to the filter employed for
the objective-prism observations. We evaluate the quality of the observed
parameters derived from the survey data, which include accurate astrometry,
photometry, redshifts, and line fluxes. Finally, we describe some of the many
applications the KISS database will have for addressing specific questions in
extragalactic astronomy. Subsequent papers in this series will present our
survey lists of emission-line galaxy candidates.


title: The Cosmological Constant

abstract:
  This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.


title: A Note on Hydrodynamic Viscosity and Selfgravitation in Accretion Disks

abstract:
  We propose a generalized accretion disk viscosity prescription based on
hydrodynamically driven turbulence at the critical effective Reynolds number.
This approach is consistent with recent re-analysis by Richard & Zahn (1999) of
experimental results on turbulent Couette-Taylor flows. This new
$\beta$-viscosity formulation is applied to both selfgravitating and
non-selfgravitating disks and is shown to yield the standard $\alpha$-disk
prescription in the case of shock dissipation limited, non-selfgravitating
disks. A specific case of fully selfgravitating $\beta$-disks is analyzed. We
suggest that such disks may explain the observed spectra of protoplanetary
disks and yield a natural explanation for the radial motions inferred from the
observed metallicity gradients in disk galaxies. The $\beta$-mechanism may also
account for the rapid mass transport required to power ultra luminous infrared
galaxies.


title: Interpretation of the UV spectrum of some stars with little reddening

abstract:
  The spectrum of five stars is analysed and explained by the superimposition
of two components. One is the extinction of the direct starlight, with an
extinction coefficient A which varies as the inverse of the wavelength across
all the UV. This linear dependence of extinction upon the inverse of wavelength
prolongs to the UV the well known relation which exist in the optical between
extinction and wavelength.
  The second component is an additional feature, superimposed on the extincted
direct starlight. This feature is interpreted as starlight scattered by dust at
close angular distance to the star, into the beam of the observation.


title: The Origin of Star Formation Gradients in Rich Galaxy Clusters

abstract:
  We examine the origin of clustercentric gradients in the star formation rates
and colors of rich cluster galaxies within the context of a simple model where
clusters are built through the ongoing accretion of field galaxies. The model
assumes that after galaxies enter the cluster their star formation rates
decline on a timescale of a few Gyrs, the typical gas consumption timescale of
disk galaxies in the field. Such behaviour might be expected if tides and ram
pressure strip off the gaseous envelopes that normally fuel star formation in
spirals over a Hubble time. Combining these timescales with mass accretion
histories derived from N-body simulations of cluster formation in a Lambda-CDM
universe, we reproduce the systematic differences observed in the color
distribution of cluster and field galaxies, as well as the strong suppression
of star formation in cluster galaxies and its dependence on clustercentric
radius. The simulations also indicate that a significant fraction of galaxies
beyond the virial radius of the cluster may have been within the main body of
the cluster in the past, a result that explains naturally why star formation in
the outskirts of clusters (and as far out as two virial radii) is
systematically suppressed relative to the field. The agreement with the data
beyond the cluster virial radius is also improved if we assume that stripping
happens within lower mass systems, before the galaxy is accreted into the main
body of the cluster. We conclude that the star formation rates of cluster
galaxies depend primarily on the time elapsed since their accretion onto
massive virialized systems, and that the cessation of star formation may have
taken place gradually over a few Gyrs.


title:
The sources of extended continuum emission towards Q0151+048A : The host
  galaxy and the Damped Ly-alpha Absorber

abstract:
  We present deep imaging in the U, B and I bands obtained under excellent
seeing conditions of the double quasar Q0151+048A,B and of the Damped Ly-alpha
(DLA) absorbing galaxy at z(abs) = 1.9342 named S4.
  We analyse the data employing two separate and independent methods. First we
deconvolve the images using the MCS algorithm, secondly we decompose the images
via an object based iteration process where we fit models to objects without
any attempt to improve the resolution of the data. Our detailed analysis of the
images reveals, somewhat surprisingly, that extended objects centred on the
quasars themselves are much brighter continuum sources than the DLA galaxy.
  Due to the complexity caused by the many superimposed objects, we are unable
to certify whether or not continuum emission from the DLA galaxy is detected.
Continuum emission from the extended objects centred on the positions of the
quasars is clearly seen, and the objects are tentatively identified as the
``host galaxies'' of the quasars. The flux of those host galaxies is of order
2--6% of the quasar flux, and the light profile of the brighter of the two is
clearly best fit with a de Vaucouleurs profile. We discuss two alternative
interpretations of the origin of the extended flux: i) the early stage of a
massive elliptical galaxy in the process of forming the bulk of its stars, and
ii) quasar light scattered by dust.


title: Some Dynamical Effects of the Cosmological Constant

abstract:
  Newton's law gets modified in the presence of a cosmological constant by a
small repulsive term (antigarvity) that is proportional to the distance.
Assuming a value of the cosmological constant consistent with the recent SnIa
data ($\Lambda \simeq 10^{-52} m^{-2}$) we investigate the significance of this
term on various astrophysical scales. We find that on galactic scales or
smaller (less than a few tens of kpc) the dynamical effects of the vacuum
energy are negligible by several orders of magnitude. On scales of 1Mpc or
larger however we find that vacuum energy can significantly affect the
dynamics. For example we show that the velocity data in the Local Group of
galaxies correspond to galactic masses increased by 35% in the presence of
vacuum energy. The effect is even more important on larger low density systems
like clusters of galaxies or superclusters.


title:
The gamma Velorum binary system. II. WR stellar parameters and the
  photon loss mechanism

abstract:
  In this paper we derive stellar parameters for the Wolf-Rayet star in the
gamma Velorum binary system (WR11), from a detailed non-LTE model of its
optical and infrared spectra. Compared to the study of Schaerer et al., the
parameters of the WC8 star are revised to a hotter effective temperature
(Teff~57kK),a higher luminosity (log(L/Lsun = 5.00), and a lower mass loss rate
(log(Mdot / Msun/yr) = -5.0 - using a 10% clumping filling factor). These
changes lead to a significant decrease in wind efficiency number, from 144 to
7, so that the driving mechanism of the wind of this WR star may be simply
radiation pressure on lines. The derived spectroscopic luminosity is found to
be 40% lower than that derived by De Marco & Schmutz through the
mass-luminosity relationship for WR stars (log(L/Lsun = 5.2). The paper
furthermore presents a comparison of the independently-developed modelling
programs, CMFGEN and ISA-Wind . Overall, there seems to be very reasonable
agreement between the derived parameters for WR11, except for the carbon
content, which is 2 times higher for CMFGEN (C/He=0.15 vs. 0.06, by number).The
comparison also confirms a disparity in the predicted flux at lambda<$400A,
found by Crowther et al., which will have effects on several nebular line
strengths.
  The paper also presents the first independent check of the photon loss
mechanism proposed by Schmutz. We conclude that, not only is it important to
include very many lines to realistically model line blanketing, but in
particular those ones that critically interact with strong resonance lines
(e.g. HeII lambda303.78). The inclusion of these latter lines may significantly
alter the wind ionization structure.


title: Network and Internetwork: a compared Multiwavelength Analysis

abstract:
  We analyze the temporal behavior of Network Bright Points (NBPs), present in
the solar atmosphere, using a set of data acquired during coordinated
observations between ground-based observatories (mainly at the NSO/Sacramento
Peak) and the Michelson Doppler Interferometer onboard SOHO. We find that, at
any time during the observational sequence, all the NBPs visible in the NaD2
images are co-spatial within 1 arcsec with locations of enhanced magnetic
field. In analogy with the Ca II K line, the NaD2 line center emission can be
used as a proxy for magnetic structures. We also compare the oscillation
properties of NBPs and internetwork areas. At photospheric levels no
differences between the two structures are found in power spectra, but analysis
of phase and coherence spectra suggests the presence of downward propagating
waves in the internetwork. At chromospheric levels some differences are evident
in the power spectrum between NBPs and internetwork. The power spectrum of NBPs
at the Halpha core wavelength shows an important peak at 2.2 mHz (7 minutes),
not present in the internetwork areas. Its coherence spectrum with Halpha wings
shows very low coherence at this frequency, implying that the oscillations at
these chromospheric levels are not directly coupled with those present in lower
layers.


title:
Radio supernovae, supernova remnants and HII regions in NGC 2146
  observed with MERLIN and the VLA

abstract:
  We present a high-resolution 5-GHz radio continuum map of the starburst
galaxy NGC 2146 made with MERLIN and the VLA, in a search of radio supernovae
and supernova remnants expected to be already produced by the most massive
stars in the starburst. At 5 GHz, about 20 point sources were detected earlier
by Glendenning & Kronberg (1986) in the central 800 pc of NGC 2146. Our
observations with higher sensitivity and resolution made with MERLIN and the
VLA confirms the detection of 18 sources, and resolves 7 of them. Additional
1.6-GHz MERLIN observations disclose 9 sources coincident in position with
those detected at 5 GHz, which allows us to derive their spectral indices. Only
3 sources have indices consistent with synchrotron emission from supernova
remnants or radio supernovae, while the others have very steep inverted
spectra. We suggest that the sources with positive spectral index are optically
thick ultra-compact and/or ultra-dense HII regions with high electron densities
and high emission measures (EM > 10^(7) cm^(-6) pc). Minimum energy
requirements indicate that these regions may contain up to 1000 equivalent
stars of type O6. When compared with M 82, the galaxy NGC 2146 lacks however a
large number of supernova remnants. We suggest that NGC 2146 is experiencing a
burst of star formation stronger than that in M 82, but being in a younger
phase. We may, however, not exclude an alternative scenario in which strong
free-free absorption at 1.6 GHz in foreground ionized gas with very high
emission measures (EM > 10^(8) cm^(-6) pc) hides a certain number of supernova
remnants, thus rendering for some sources the observed inverted spectra.


title:
Magnetic Flux Expulsion in the Powerful Superbubble Explosions and the
  Alpha-Omega Dynamo

abstract:
  The possibility of the magnetic flux expulsion from the Galaxy in the
superbubble (SB) explosions, important for the Alpha-Omega dynamo, is
considered. Special emphasis is put on the investigation of the downsliding of
the matter from the top of the shell formed by the SB explosion which is able
to influence the kinematics of the shell. It is shown that either Galactic
gravity or the development of the Rayleigh-Taylor instabilities in the shell
limit the SB expansion, thus, making impossible magnetic flux expulsion. The
effect of the cosmic rays in the shell on the sliding is considered and it is
shown that it is negligible compared to Galactic gravity. Thus, the question of
possible mechanism of flux expulsion in the Alpha-Omega dynamo remains open.


title:
Preliminary design of a NIR prime focus corrector for the Galileo
  Telescope

abstract:
  In this paper a preliminary design for a prime focus corrector to be mounted
at the Telescopio Nazionale Galileo (TNG) is presented. The telescope is
located on La Palma (Canary Islands) and has a primary mirror of 3.5 m with a
hyperbolic sag. Two optical designs have been considered in order to exploit
detectors with 1k x 1k and 2k x 2k pixels. Each design makes use of four
lenses, two of which are aspherical. The first lens diameters are,
respectively, of 140 mm and 320 mm for the two kind of detectors. For both
designs the telescope pupil is deliberately not re-imaged, and therefore it
will not be possible to insert a cold stop. For such a reason particular care
has been dedicated to the telescope thermal background study, in order to
optimise the baffling system. The optics is able to correct fields of 11' x 11'
and of 60'x60', depending on the design. It should be considered that the
particular geometry of the focal plane array mosaic does not permit a full
exploitation of the entire field, being based on a combination of four
detectors. The selected chips are HgCdTe manufactured by Rockwell, i.e. Hawaii
I in the 1k x 1k case and Hawaii II in the 2k x 2k case.


title: The Bispectrum: From Theory to Observations

abstract:
  The bispectrum is the lowest-order statistic sensitive to the shape of
structures generated by gravitational instability and is a potentially powerful
probe of galaxy biasing and the Gaussianity of primordial fluctuations.
Although the evolution of the bispectrum is well understood theoretically from
non-linear perturbation theory and numerical simulations, applications to
galaxy surveys require a number of issues to be addressed. In this paper we
consider the effect on the bispectrum of stochastic non-linear biasing, radial
redshift distortions, non-Gaussian initial conditions, survey geometry and
sampling.
  We find that: 1) bias stochasticity does not affect the use of the bispectrum
to recover the mean biasing relation between galaxies and mass, at least for
models in which the scatter is uncorrelated at large scales. 2) radial redshift
distortions do not change significantly the monopole power spectrum and
bispectrum compared to their plane-parallel values. 3) survey geometry leads to
finite volume effects which must be taken into account in current surveys
before comparison with theoretical predictions can be made. 4) sparse sampling
and survey geometry correlate different triangles leading to a breakdown of the
Gaussian likelihood approximation.
  We develop a likelihood analysis using bispectrum eigenmodes, calculated by
Monte Carlo realizations of mock surveys generated with second-order Lagrangian
perturbation theory and checked against N-body simulations. In a companion
paper we apply these results to the analysis of the bispectrum of IRAS
galaxies.


title: The Bispectrum of IRAS Galaxies

abstract:
  We compute the bispectrum for the galaxy distribution in the IRAS QDOT, 2Jy,
and 1.2Jy redshift catalogs for wavenumbers 0.05<k<0.2 h/Mpc and compare the
results with predictions from gravitational instability in perturbation theory.
Taking into account redshift space distortions, nonlinear evolution, the survey
selection function, and discreteness and finite volume effects, all three
catalogs show evidence for the dependence of the bispectrum on configuration
shape predicted by gravitational instability. Assuming Gaussian initial
conditions and local biasing parametrized by linear and non-linear bias
parameters b_1 and b_2, a likelihood analysis yields 1/b_1 =
1.32^{+0.36}_{-0.58}, 1.15^{+0.39}_{-0.39} and b_2/b_1^2=-0.57^{+0.45}_{-0.30},
-0.50^{+0.31}_{-0.51}, for the for the 2Jy and 1.2Jy samples, respectively.
This implies that IRAS galaxies trace dark matter increasingly weakly as the
density contrast increases, consistent with their being under-represented in
clusters. In a model with chi^2 non-Gaussian initial conditions, the bispectrum
displays an amplitude and scale dependence different than that found in the
Gaussian case; if IRAS galaxies do not have bias b_1> 1 at large scales, \chi^2
non-Gaussian initial conditions are ruled out at the 95% confidence level. The
IRAS data do not distinguish between Lagrangian or Eulerian local bias.


title:
A kinematic and morphological investigation of the asymmetric nebula
  around the LBV candidate WRA 751

abstract:
  WRA 751 is an evolved massive star in our Galaxy closely resembling Luminous
Blue Variable stars (LBVs). It is surrounded by a nitrogen enriched nebula of
ab out 23" diameter. A comparative study of the nebula's morphology and
kinematics is presented, it supports - together with spectroscopical evidence -
the classification of WRA 751 as a LBV. Images show that the nebula consists of
a nearly spherical shell as well as a bipolar-like structure north and south of
its main body, the Northern and Southern Caps. In contrast to the almost
spherical appearance of the main body of the nebula, the kinematics shows a
deviation even of this part from a classical spherical expansion pattern. From
the present data it can be concluded that the main body expands asymmetrically
(central expansion velocity ~26 km/s), with a thicker shell at the back side. A
bump-like structure can be found to the west of the central star. In addition
to the main body, bipolar kinematic components can be identified with the
morphologically classified Caps. These results put WRA 751 into the class of
LBVs which are surrounded by a nebula with bipolar components, albeit
considerably less pronounced than, for instance, in the classical bipolar LBVs
Eta Car and HR Car.


title:
Direct Detection of Giant Close-In Planets Around the Source Stars of
  Caustic-Crossing Microlensing Events

abstract:
  We propose a direct method to detect close-in giant planets orbiting stars in
the Galactic bulge. This method uses caustic-crossing binary microlensing
events discovered by survey teams monitoring the bulge to measure light from a
planet orbiting the source star. When the planet crosses the caustic, it is
more magnified than the source star; its light is magnified by two orders of
magnitude for Jupiter size planets. If the planet is a giant close to the star,
it may be bright enough to make a significant deviation in the light curve of
the star. Detection of this deviation requires intensive monitoring of the
microlensing light curve using a 10-meter class telescope for a few hours after
the caustic. This is the only method yet proposed to directly detect close-in
planets around stars outside the solar neighborhood.


title:
The "Swiss cheese" cosmological model has no extrinsic curvature
  discontinuity: A comment on the paper by G.A. Baker, Jr. (astro-ph/0003152)

abstract:
  Contrary to a claim, the Schwarzschild solution insertion in an expanding
universe model, the so called "Swiss cheese" model, does not possess an
extrinsic curvature discontinuity. We show that both the intrinsic metric and
the extrinsic curvature are continuous, and point out the error that led to the
claim.


title:
CFHT Optical PDCS Survey II: Evolution in the Space Density of Clusters
  of Galaxies

abstract:
  We present the first dynamical study of the optically selected Palomar
Distant Cluster Survey (PDCS). We show that eleven out of twelve PDCS clusters
we observed are real over-densities of galaxies. Most clusters have velocity
dispersions appropriate for clusters of galaxies. However, we find a fraction
(1/3) of objects in the PDCS which have velocity dispersions in the range of
groups of galaxies (200 +/- 100 km/s) but have richnesses appropriate for
clusters of galaxies.
  We measure the richness function, X-ray luminosity function (using both the
detections and upper limits), and the mass function derived from our velocity
dispersions. We confirm that the space density, as a function of richness, of
clusters of galaxies in the PDCS is ~5 times that of the Abell catalog.
Excluding the above fraction of 1/3 of objects with low velocity dispersions,
we measure a space density ~3 times that of the Abell catalog for equivalent
mass clusters of galaxies. Our space density estimates are in agreement with
other low-redshift, optically-selected cluster surveys such as the EDCC, APM
and EDCC2, which raises the possibility that the Abell catalog is incomplete.
Our X-ray luminosity function agrees with other measurements based on both
X-ray and optically selected samples, so we find that the PDCS does not miss
clusters of galaxies that would be found in an X-ray selected survey. Our
resulting mass function, centered around 10e14 Msun/h, agrees with the
expectations from such surveys as the Canadian Network for Observational
Cosmology cluster survey, though errors on our mass measurements are too large
to constrain cosmological parameters.


title: A New Method For Galaxy Cluster Detection I: The Algorithm

abstract:
  Numerous methods for finding clusters at moderate to high redshifts have been
proposed in recent years, at wavelengths ranging from radio to X-rays. In this
paper we describe a new method for detecting clusters in two-band
optical/near-IR imaging data. The method relies upon the observation that all
rich clusters, at all redshifts observed so far, appear to have a red sequence
of early-type galaxies. The emerging picture is that all rich clusters contain
a core population of passively evolving elliptical galaxies which are coeval
and formed at high redshifts. The proposed search method exploits this strong
empirical fact by using the red sequence as a direct indicator of overdensity.
The fundamental advantage of this approach is that with appropriate filters,
cluster elliptical galaxies at a given redshift are redder than all normal
galaxies at lower redshifts. A simple color cut thus virtually eliminates all
foreground contamination, even at significant redshifts. In this paper, one of
a series of two, we describe the underlying assumptions and basic techniques of
the method in detail, and contrast the method with those used by other authors.
We provide a brief demonstration of the effectiveness of the technique using
real redshift data, and from this conclude that the method offers a powerful
yet simple way of identify galaxy clusters. We find that the method can
reliably detect structures to masses as small as groups with velocity
dispersions of only ~300 km/sec, with redshifts for all detected structures
estimated to an accuracy of ~10%.


title:
The Effect of Hydrostatic Weighting on the Vertical Temperature
  Structure of the Solar Corona

abstract:
  We investigate the effect of hydrostatic scale heights ${\lambda}(T)$ in
coronal loops on the determination of the vertical temperature structure $T(h)$
of the solar corona. Every method that determines an average temperature at a
particular line-of-sight from optically thin emission (e.g. in EUV or soft
X-ray wavelengths) of a mutli-temperature plasma, is subject to the emission
measure-weighted contributions $dEM(T)/dT$ from different temperatures. Because
most of the coronal structures (along open or closed field lines) are close to
hydrostatic equilibrium, the hydrostatic temperature scale height introduces a
height-dependent weighting function that causes a systematic bias in the
determination of the temperature structure $T(h)$ as function of altitude $h$.
The net effect is that the averaged temperature seems to increase with
altitude, $dT(h)/dh > 0$, even if every coronal loop (of a multi-temperature
ensemble) is isothermal in itself. We simulate this effect with differential
emission measure distributions observed by {\sl SERTS} for an instrument with a
broadband temperature filter such as {\sl Yohkoh/SXT} and find that the
apparent temperature increase due to hydrostatic weighting is of order $\Delta
T \approx T_0 \times h/r_{\sun}$. We suggest that this effect largely explains
the systematic temperature increase in the upper corona reported in recent
studies (e.g. by Sturrock et al., Wheatland et al., or Priest et al.), rather
than being an intrinsic signature of a coronal heating mechanism.


title:
Magnetohydrodynamic Instabilities in Shearing, Rotating, Stratified
  Winds and Disks

abstract:
  We investigate shear and buoyancy instabilities in radially stratified,
magnetized, cylindrical flows, for application to magnetocentrifugally driven
winds and to magnetized accretion disks. We identify and study nine principal
types of instabilities/overstabilities. When magnetic fields are predominantly
toroidal, as in protostellar winds, the system exhibits axisymmetric
fundamental (FM) and toroidal resonance modes, axisymmetric and
non-axisymmetric toroidal buoyancy (TB) modes, and non-axisymmetric
magnetorotational instability (MRI) modes. Winds with sufficiently steep field
gradients are unstable to the FM, which promotes narrow dense jets in the
centers of wider winds. The TB modes promote small-scale radial mixing. The
MRIs have very low growth rates under low-temperature wind conditions. The
stabilization of buoyancy modes by shear, and of MRIs by compressibility, may
be important in allowing protostellar winds to propagate over vast distances in
space. When magnetic fields are predominantly poloidal, as in winds close to
their source or in astrophysical disks, the system exhibits axisymmetric
Balbus-Hawley (BH), poloidal buoyancy (PB), non-axisymmetric geometric buoyancy
(GPB), and poloidal resonance modes. The BH mode has the fastest growth rate.
The PB mode promotes radial mixing on small scales. The GPB mode at high m is
readily stabilized by shear. We extend previous MRI analyses to focus on
compressibility. We introduce a ``coherent wavelet'' technique to derive
closed-form expressions for instantaneous instability criteria, growth rates,
and net amplification factors for non-axisymmetric MRIs in compressible flows
with both poloidal and toroidal fields. We confirm that these are in excellent
agreement with the results of shearing-sheet temporal integrations.


title:
The Stellar Population Histories of Early-Type Galaxies. II. Controlling
  Parameters of the Stellar Populations

abstract:
  We analyze single-stellar-population (SSP) equivalent parameters for 50 local
elliptical galaxies as a function of their structural parameters. These
galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H],
log t, log $\sigma$, and [E/Fe]. SSP age and velocity dispersion can be taken
as the two independent parameters that specify a galaxy's location in this
``hyperplane.'' The hyperplane can be decomposed into two sub-relations: (1) a
``Z-plane,'' in which [Z/H] is a linear function of log $\sigma$ and log t; and
(2) a relation between [E/Fe] and $\sigma$ in which [E/Fe] is larger in
high-$\sigma$ galaxies. Cluster and field ellipticals follow the same
hyperplane, but their ($\sigma$,t) distributions within it differ. Nearly all
cluster galaxies are old; the field ellipticals span a large range in SSP age.
The tight Mg--$\sigma$ relations of these ellipticals can be understood as
two-dimensional projections of the metallicity hyperplane showing it edge-on;
the tightness of these relations does not necessarily imply a narrow range of
ages at fixed $\sigma$. The relation between [E/Fe] and $\sigma$ is consistent
with a higher effective yield of Type II SNe elements at higher $\sigma$. The
Z-plane is harder to explain and may be a powerful clue to star formation in
elliptical galaxies if it proves to be general. Present data favor a
``frosting'' model in which low apparent SSP ages are produced by adding a
small frosting of younger stars to an older base population. If the frosting
abundances are close to or slightly greater than the base population, simple
two-component models run along lines of constant $\sigma$ in the Z-plane, as
required. This favors star formation from well-mixed pre-enriched gas rather
than unmixed low-metallicity gas from an accreted object. (Abridged)


title: Bubbles from dark energy ?

abstract:
  In a model recently proposed by Albrecht and Skordis it was suggested that
the observed accelerated expansion of the universe could be caused by a scalar
field which is trapped in a local minimum of an exponential potential modified
by a polynomial prefactor. We show that scalar field cosmologies with this kind
of local minimum in the potential are stable and do not decay to the true
vacuum if they fulfill the observational constraints from the Type Ia
Supernovae experiments. Further we briefly sketch how this potential could be
related to a potential of interacting D-branes.


title:
Formation of the Galactic stellar halo. Origin of the
  metallicity-eccentricity relation

abstract:
  Motivated by the recently improved knowledge on the kinematic and chemical
properties of the Galactic metal-poor stars, we present the numerical
simulation for the formation of the Galactic stellar halo to interpret the
observational results. As a model for the Galaxy contraction, we adopt the
currently standard theory of galaxy formation based on the hierarchical
assembly of the cold dark matter fluctuations. We find, for the simulated stars
with [Fe/H]$\le-1.0$, that there is no strong correlation between metal
abundances and orbital eccentricities, in good agreement with the observations.
Moreover, the observed fraction of the low eccentricity stars is reproduced
correctly for [Fe/H]$\le-1.6$ and approximately for the intermediate abundance
range of $-1.6<$[Fe/H]$\le-1.0$. We show that this successful reproduction of
the kinematics of the Galactic halo is a natural consequence of the
hierarchical evolution of the subgalactic clumps seeded from the cold dark
matter density fluctuations.


title: Cosmic Magnetic Fields from Particle Physics

abstract:
  I review a number of particle-physics models that lead to the creation of
magnetic fields in the early universe and address the complex problem of
evolving such primordial magnetic fields into the fields observed today.
Implications for future observations of the Cosmic Microwave Background (CMB)
are briefly discussed.


title: Exploring the Leo II dSph I.: The Variable Star Content

abstract:
  We present the first comprehensive catalogue of variable stars in the Leo II
dwarf spheroidal galaxy. We have identified 148 RR Lyrae type variables, of
which 140 were amenable to derivation of variability parameters with our data.
We have also confirmed the existence of four anomalous Cepheids as identified
in previous studies.
  The average period of the RR Lyrae ab variables (0.62 days), the fraction of
c variables (0.24) and the minimum period of the RR Lyrae ab variables (0.51
days) all define Leo II as an "Oosterhoff intermediate" galaxy. We have used
the properties of these variables to derive a metallicity for Leo II of
approximately [Fe/H]=-1.9. The presence of longer period, higher amplitude RR
Lyrae variable implies a metallicity distribution that extends to as poor as
[Fe/H]=-2.3.
  Leo II's location on the period-metallicity relation of clusters, like that
of other ``Ootershoff intermediate'' objects, falls between the Oosterhoff
Class I and Oosterhoff Class II clusters. The properties of the variable
populations of these objects are consistent with the idea that the Oosterhoff
"dichotomy" is a continuum. The gap between the classes seems to be explained
by the horizontal branch of Galactic globular clusters shifting away from the
instability strip at at intermediate metallicities. However, Leo II, as well as
other Oosterhoff intermediate objects, has a second parameter effect strong
enough to leave horizontal branch stars in the instability strip.


title:
ISO-SWS observations of pure rotational water absorption lines toward
  Orion-IRc2

abstract:
  First detections of thermal water vapor absorption lines have been made
toward Orion IRc2 using the Short Wavelength Spectrometer (SWS) on board the
Infrared Space Observatory (ISO). Grating spectra covering wavelengths 25-45
micron yield 19 pure rotational lines, originating from energy levels 200-750 K
above ground. Fabry-Perot spectra of 5 transitions resolve the line profiles
and reveal the water gas kinematics. The fact that all lines are seen in
absorption is in striking contrast with data from the ISO Long Wavelength
Spectrometer (LWS), where the water lines appear in emission. At least one line
displays a P-Cygni type profile, which suggests that the water is located in an
expanding shell centered on or near IRc2. The expansion velocity is 18 km per
second, in agreement with the value inferred from water maser observations by
Genzel et al. (1981). Because the continuum is intense and likely formed in or
near the water-containing gas, the excitation of the observed transitions is
dominated by radiative processes. A simple, generalised curve-of-growth method
is presented and used to analyze the data. A mean excitation temperature of 72
K and a total water column density of 1.5e18 molecules per cm squared are
inferred, each with an estimated maximum uncertainty of 20%. Combined with the
molecular hydrogen column density derived from ISO observations of the pure
rotational lines, and an assumed temperature of 200-350 K, the inferred water
abundance is 2e-4 to 5e-4 in the warm shocked gas. This abundance is similar to
that found recently by Harwit et al. (1998) toward Orion using data from the
LWS, but higher than that found for most other shocked regions by, for example,
Liseau et al. (1996).


title:
StarFinder: an IDL GUI based code to analyze crowded fields with
  isoplanatic correcting PSF fitting

abstract:
  StarFinder is a new code for the deep analysis of stellar fields, designed
for well-sampled images with high and low Strehl ratio. It is organized in the
form of a self-contained IDL widget-based application, with a 'user-friendly'
graphic interface. We give here a general description of the code along with
some applications to real data with space-invariant Point Spread Function
(PSF). We present also some methods to handle anisoplanatic effects in
wide-field Adaptive Optics (AO)observations.


title: Cosmic Strings Lens Phenomenology: Model of Poisson Energy Distribution

abstract:
  We present a novel approach for investigating lens phenomenology of cosmic
strings in order to elaborate detection strategies in galaxy deep field images.
To account for the complexity of the projected energy distribution of string
networks we assume their lens effects to be similar to those of a straight
string carrying a {\em random} lineic energy distribution. In such a model we
show that, unlike the case of uniform strings, critical phenomena naturally
appear. We explore the properties of the critical lines and caustics. In
particular, assuming that the energy coherence length along the string is much
smaller than the observation scale, we succeeded in computing the total length
of critical lines per unit string length and found it to be $4/\sqrt{3} {\bf
E}(3/4)$. The length of the associated caustic lines can also be computed to be
$16/(\pi \sqrt{3}) {\bf E}(3/4)$. The picture we obtain here for the
phenomenology of cosmic string detection is clearly at variance with common
lore.


title:
High resolution Ks polarization mapping of OH 231.8+4.2 (OH 0739-14)
  with SOFI

abstract:
  The bipolar reflection nebula OH 231.8+4.2 (OH 0739-14), centred on the Mira
variable star QX Pup, has been mapped at Ks in linear polarization using the
ESO SOFI near-infrared multi-mode instrument. The large scale linear
polarization features agree with previous studies, validating the polarimetric
mode of the instrument. However the high spatial resolution of the polarization
map reveals considerable structure, some of which finds correspondence in the
surface brightness images. The core is crossed by low polarization filaments;
the northern lobe reveals an axial finger and a rim of very high linear
polarization (upto 80%) whilst the southern lobe shows less polarization
contrast. There is a trend in polarization perpendicular to the bipolar axis in
both lobes. The individual linear polarization features most probably arise
from localised dust structures with distinct orientations leading to differing
polarization through single scattering. A single scattering geometric model,
consisting of two lobes of ellipsoidal section and a central dense disk, is
considered which can explain the general features of the intensity and
polarization images.


title: X-ray observation of radio supernova SN1979C by ASCA

abstract:
  We report on the X-ray observation of the radio selected supernova SN1979C
carried out with ASCA in December 1997. The supernova of type II$_{L}$ was
first observed in the optical and occurred in the weakly barred, almost face on
spiral galaxy NGC 4321 (M100) which is at a distance of 17.1 Mpc, and contains
at least three other supernovae discovered in this century. No point source was
detected at the radio position of SN1979C in a 3' diameter half power response
circle in a 27.3 ks SIS exposure. The background and galaxy subtracted SN
signal had a 3$\sigma$ upper limit to the count rate of 1.2$\times 10^{-3}$ cps
in the full ASCA SIS band (0.4-10.0 keV). These measurements give the first
ever x-ray flux limit of a Type II$_{L}$ SN in the higher energy band ($\geq$ 2
keV) which is an important diagnostic of the {\it outgoing} shock wave
ploughing through the circumstellar medium.


title:
Cosmic Strings Lens Phenomenology: General Properties of Distortion
  Fields

abstract:
  We reconsider the general properties of gravitational lensing effects induced
by cosmic string systems, taking into account their equation of state and
motion equations. We explicitly show that the deflection patterns induced by a
string is equivalent to the one of a lineic and static distribution of matter.
We then rigorously show that the convergence part of the deformation field is
always zero, except on the intersection of the string worldsheet and the
observer past light cone, extending previous results obtained in peculiar
cases. Phenomenological consequences of this result on multiple image systems
are investigated.


title: Accretion Disks Phase Transitions: 2-D or not 2-D?

abstract:
  We argue that the proper way to treat thin-thick accretion-disk transitions
should take into account the 2-D nature of the problem. We illustrate the
physical inconsistency of the 1-D vertically integrated approach by discussing
a particular example of the convective transport of energy.