title: Entropy and holography constraints for inhomogeneous universes

abstract:
  We calculated the entropy of a class of inhomogeneous dust universes.
Allowing spherical symmetry, we proposed a holographic principle by reflecting
all physical freedoms on the surface of the apparent horizon. In contrast to
flat homogeneous counterparts, the principle may break down in some models,
though these models are not quite realistic. We refined fractal parabolic
solutions to have a reasonable entropy value for the present observable
universe and found that the holographic principle always holds in the realistic
cases.


title: The Sloan Digital Sky Survey: Technical Summary

abstract:
  The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed
investigations of the distribution of luminous and non- luminous matter in the
Universe: a photometrically and astrometrically calibrated digital imaging
survey of pi steradians above about Galactic latitude 30 degrees in five broad
optical bands to a depth of g' about 23 magnitudes, and a spectroscopic survey
of the approximately one million brightest galaxies and 10^5 brightest quasars
found in the photometric object catalog produced by the imaging survey. This
paper summarizes the observational parameters and data products of the SDSS,
and serves as an introduction to extensive technical on-line documentation.


title: Mass-to-Light Ratios of Groups and Clusters of Galaxies

abstract:
  We constrain the mass-to-light ratios, gas mass fractions, baryon mass
fractions and the ratios of total to luminous mass for a sample of eight nearby
relaxed galaxy groups and clusters: A262, A426, A478, A1795, A2052, A2063,
A2199 and MKW4s. We use ASCA spatially resolved spectroscopic X-ray
observations and ROSAT PSPC images to constrain the total and gas masses of
these clusters. To measure cluster luminosities we use galaxy catalogs
resulting from the digitization and automated processing of the second
generation Palomar Sky Survey plates calibrated with CCD images in the
Gunn-Thuan g, r, and i bands.
  Under the assumption of hydrostatic equilibrium and spherical symmetry, we
can measure the total masses of clusters from their intra-cluster gas
temperature and density profiles. Spatially resolved ASCA spectra show that the
gas temperature decreases with increasing distance from the center. By
comparison, the assumption that the gas is isothermal results in an
underestimate of the total mass at small radii, and an overestimate at large
cluster radii.
  We have obtained luminosity functions for all clusters in our sample. After
correcting for background and foreground galaxies, we estimate the total
cluster luminosity using Schechter function fits to the galaxy catalogs. In the
three lowest redshift clusters where we can sample to fainter absolute
magnitudes, we have detected a flattening of the luminosity function at
intermediate magnitudes and a rise at the faint end. These clusters were fit
with a sum of two Schechter functions. The remaining clusters were well fit
with a single Schechter function.


title: Supernovae evidence for an accelerating expansion of the universe

abstract:
  Recent experimental results find strong indications that the universe is
flat, while other experimental results from supernovae Ia observations have
been interpreted to show that, not only that there is an accelerating expansion
of the universe, but also that the universe is strongly curved. By means of a
recently proposed metric, I am able to show that the experimental results which
had previously been analyzed to give a strong curvature are quite consistent
with a flat universe, thus resolving the apparent mismatch. The conclusion of
these latter authors which indicated an accelerating expansion of the universe
remains unchanged.


title: Spectroscopy of Blue Stragglers and Turnoff Stars in M67 (NGC 2682)

abstract:
  We have analyzed high-resolution spectra of relatively cool blue stragglers
and main sequence turnoff stars in the old open cluster M67 (NGC 2682). We
attempt to identify blue stragglers whose spectra are least contaminated by
binary effects (contamination by a binary companion or absorption by
circumstellar material). These ``best'' stragglers have metallicities ([Fe/H] =
-0.05) and abundance ratios of the blue stragglers are not significantly
different from those of the turnoff stars. Based on arguments from
hydrodynamical models of stellar collisions, we assert that the current upper
limits for the lithium abundances of all blue stragglers observed in M67 (by us
and others) are consistent with no mixing during the formation process,
assuming pre-main sequence and main sequence depletion patterns observed for
M67 main sequence stars. We discuss composition signatures that could more
definitively distinguish between blue straggler formation mechanisms in open
cluster stars.
  We confirm the spectroscopic detection of a binary companion to the straggler
S 1082. From our spectra, we measure a projected rotational speed of 90+/-20
km/sec for the secondary, and find that its radial velocity varies with a
peak-to-peak amplitude of ~ 25 km/sec. Because the radial velocities do not
vary with a period corresponding to the partial eclipses in the system, we
believe this system is currently undergoing mass transfer. In addition we
present evidence that S 984 is a true blue straggler (and not an unresolved
pair). If this can be proven, our detection of lithium may indicate a
collisional origin.


title: The evolution of disk galaxies

abstract:
  We study the evolution of disk galaxies using galaxy evolutionary models with
initial and boundary conditions linked to the hierarchical formation scenario.
Disks galaxies are modeled locally within growing cold dark matter halos and
including a physical model for star formation. We focus our attention on
predictions of the star formation history, size and surface brightness
evolution and the evolution of the H- and B-band Tully-Fisher relations.
Comparisons with available observational data are presented.


title:
Bayesian Methods for Cosmological Parameter Estimation from Cosmic
  Microwave Background Measurements

abstract:
  We present a strategy for a statistically rigorous Bayesian approach to the
problem of determining cosmological parameters from the results of observations
of anisotropies in the cosmic microwave radiation background. We propose the
application of Markov chain Monte Carlo methods, specifically the
Metropolis-Hastings algorithm, to estimate the parameters. A complete
statistical analysis is presented, with the Metropolis-Hastings algorithm
described in detail.


title:
AstroMD. A multi-dimensional data analysis tool for astrophysical
  simulations

abstract:
  Over the past few years, the role of visualization for scientific purpose has
grown up enormously. Astronomy makes an extended use of visualization
techniques to analyze data, and scientific visualization has became a
fundamental part of modern researches in Astronomy. With the evolution of high
performance computers, numerical simulations have assumed a great role in the
scientific investigation, allowing the user to run simulation with higher and
higher resolution. Data produced in these simulations are often
multi-dimensional arrays with several physical quantities. These data are very
hard to manage and to analyze efficiently. Consequently the data analysis and
visualization tools must follow the new requirements of the research. AstroMD
is a tool for data analysis and visualization of astrophysical data and can
manage different physical quantities and multi-dimensional data sets. The tool
uses virtual reality techniques by which the user has the impression of
travelling through a computer-based multi-dimensional model. AstroMD is a
freely available tool for the whole astronomical community
(http://www.cineca.it/astromd/).


title: Gas flow in barred galaxies

abstract:
  I briefly review the properties of the gas flow in and around the region of
the bar in a disc galaxy and discuss the corresponding inflow and the loci of
star formation. I then review the flow of gas in barred galaxies which have an
additional secondary bar. Finally I discuss the signatures of bars in edge-on
galaxies.


title:
Stellar Evolution with Rotation V: Changes in all the Outputs of Massive
  Star Models

abstract:
  Grids of models for rotating stars are constructed in the range of 9 to 120
M$_{\odot}$ at solar metallicity. The following effects of rotation are
included: shellular rotation, new structure equations for non-conservative
case, surface distorsions, increase of mass loss with rotation, meridional
circulation and interaction with horizontal turbulence, shear instability and
coupling with thermal effects, advection and diffusion of angular momentum
treated in the non-stationary regime, transport and diffusion of the chemical
elements.
  Globally we find that for massive stars the effects of rotation have an
importance comparable to those of mass loss. For an average rotation, the
tracks in the HR diagram are modified like a moderate overshoot would do. In
general, an average rotation may increase the MS lifetime up to about 30 %; for
the helium-burning phase the effects are smaller and amount to at most 10 %.
  Rotation also brings significant surface He- and N-enhancements, they are
higher for higher masses and rotation.


title:
Stellar evolution with rotation VI: The Eddington and Omega-limits, the
  rotational mass loss for OB and LBV stars

abstract:
  Several properties of massive stars with large effects of rotation and
radiation are studied. We show that there are 2 roots for the equation giving
the rotational velocities at break-up: 1) The usual solution, which is shown to
apply when the Eddington ratio $\Gamma$ of the star is smaller than formally
0.639. 2) Above this value of $\Gamma$, there is a second root, inferior to the
first one, for the break-up velocity. This second solution tends to zero, when
$\Gamma$ tends towards 1. This second root results from the interplay of
radiation and rotation, and in particular from the reduction by rotation of the
effective mass in the local Eddington factor. The analysis made here should
hopefully clarify a recent debate between Langer (\cite{La97,La98}) and Glatzel
(\cite{Gla98}).
  The expression for the global mass loss-rates is a function of both $\Omega$
and $\Gamma$, and this may give raise to extreme mass loss-rates ($\Omega
\Gamma $-limit). In particular, for O-type stars, LBV stars, supergiants and
Wolf-Rayet stars, even slow rotation may dramatically enhance the mass loss
rates. Numerical examples in the range of 9 to 120 M$_{\odot}$ at various
$T_\mathrm{eff}$ are given.


title: SN 1998bw at late phases

abstract:
  We present observations of the peculiar supernova SN 1998bw, which was
probably associated with GRB 980425. The photometric and spectroscopic
evolution is monitored up to 500 days past explosion. We also present modeling
based on spherically symmetric, massive progenitor models and very energetic
explosions. The models allow line identification and clearly show the
importance of mixing. From the late light curves we estimate that about 0.3-0.9
solar masses of ejected Nickel-56 is required to power the supernova.


title: Correlation Function of Galaxy Groups

abstract:
  We use the Updated Zwicky Catalog of galaxies (Falco et al. 1999) to generate
a catalog of groups, by means of a friend-of-friend algorithm. The correlation
length of the total sample is well fitted with a power law $
\xi(r)=(r/r_0)^\gamma $ with parameters $r_0=9.0 \pm 0.4 h^{-1}Mpc$ and $\gamma
= -1.67 \pm 0.09$ for values of $r<70 h^{-1} Mpc$. Three subsamples defined by
the range of group virial masses ${\cal M}$ were used to have their clustering
properties examined throughout the autocorrelation function. We find an
increase of the amplitude of the correlation function according to the group
masses which extends the results of the $ r_0-d_c$ relation for galaxy systems
at small $d_c$. For completeness we have also analyzed a sample of groups
obtained from the Southern Sky Redshift Survey (da Costa et al.1998) in the
range of virial masses $5\times10^{12}M_{\odot}<{\cal
M}<4\times10^{14}M_{\odot} $ to compare the results with those obtained from
GUZC.


title: The dusty SF history of distant galaxies and modelling tools

abstract:
  I review recent advances in the determination of the cosmic history of star
formation, and its relevance in our understanding of the formation of
structures. I emphasize the importance of dust reprocessing in the high--z
universe, as demonstrated in particular by IR and sub-mm data. This demand a
panchromatic approach to observations and suitable modelling tools. I summarize
the basic requirements for these models and to what extent they are satisfied
by models published so far.


title: New star clusters projected close to the Galactic Centre

abstract:
  We carried out a systematic search for new star clusters in a field of
5$^{\circ} \times5^{\circ}$ centred close to the Galactic Nucleus using the
infrared JHK$_s$ 2MASS Survey archive. In addition we searched for embedded
clusters in the directions of HII regions and dark clouds for
$|\ell|\le4^{\circ}$. As a result we present a list of 58 IR star clusters or
candidates. We provide positions, sizes and reddening estimated from 100 $\mu$m
dust emission. Their angular distribution together with previously catalogued
objects in the region and possible relation with star forming complexes are
also discussed.


title:
Some aspects of the chemical evolution of 4He in the Galaxy: the He/H
  abundance gradient and the Delta Y/Delta Z enrichment ratio

abstract:
  Two aspects of the chemical evolution of 4He in the Galaxy are considered on
the basis of a sample of disk planetary nebulae by the application of
corrections due to the contamination of 4He from the progenitor stars. First,
the He/H radial gradient is analyzed, and then, the helium to heavy element
enrichment ratio is determined for metallicities up to the solar value.


title:
Exploring Halo Substructure with Giant Stars: I. Survey Description and
  Calibration of the Photometric Search Technique

abstract:
  We have begun a survey of the structure of the Milky Way halo, as well as the
halos of other Local Group galaxies, as traced by their constituent giant
stars. These giant stars are identified via large area, CCD photometric
campaigns. Here we present the basis for our photometric search method, which
relies on the gravity sensitivity of the Mg I triplet + MgH features near 5150
Angstroms in F-K stars, and which is sensed by the flux in the intermediate
band DDO51 filter. To calibrate our (M-T_2, M-DDO51) diagram as a means to
discriminate field giant stars from nearby dwarfs, we utilize new photometry of
the main sequences of the open clusters NGC 3680 and NGC 2477 and the red giant
branches of the clusters NGC 3680, Melotte 66 and omega Centauri, supplemented
with data on field stars, globular clusters and open clusters by Doug Geisler
and collaborators. By combining the data on stars from different clusters, and
by taking advantage of the wide abundance spread within omega Centauri, we
verify the primary dependence of the M-DDO51 color on luminosity, and
demonstrate the secondary sensitivity to metallicity among giant stars. Our
empirical results are found to be generally consistent with those from analysis
of synthetic spectra by Paltoglou & Bell [1994, MNRAS, 268, 793].


title:
The Extraordinary `Superthin' Spiral Galaxy UGC7321. II. The Vertical
  Disk Structure

abstract:
  We explore the vertical light distribution as a function of galactocentric
radius in the edge-on (i=88) Sd `superthin' galaxy UGC7321. UGC7321 is a
low-luminosity spiral (M_B,i=-17.0) with a diffuse, low surface brightness
stellar disk and no discernible bulge component. Within 0.25' (725 pc) of the
disk center the global luminosity profile of UGC7321 can be reasonably
characterized by an exponential function with a scale height h_z=2.9" (140 pc)
in H and h_z=3.1" (150 pc) in R, making this among the thinnest galaxy disks
know. Near the disk center we derive a ratio of disk scale length to global
disk scale height h_r/h_z=14 in both H and R; near the edge of the disk,
h_r/h_z=10. At intermediate galactocentric radii (0.25'<r<1.5'), the disk of
UGC7321 becomes less peaked than an exponential near the galactic plane. At
these radii the vertical luminosity profiles can be well reproduced by a linear
combination of two isothermal disk components of differing scale heights. These
fits, together with the strong disk color gradients by Matthews, Gallagher, &
van Driel (1999), suggest that UGC7321 has multiple disk subcomponents
comprised of stellar populations with different ages and velocity dispersions.
Thus even examples of the thinnest pure disk galaxies exhibit complex structure
and signatures of dynamical heating.


title:
Physical Conditions and Spatial Structure in the Molecular Interstellar
  Medium of M33

abstract:
  In this review, I discuss recent detailed studies of individual molecular
clouds in M33 in higher rotational transitions of CO, 13CO, and the fine
structure line of atomic carbon. These data reveal that the temperature and
density of the molecular gas is correlated with the presence of nearby massive
star formation, with clouds with more intense star formation having higher
temperatures and lower densities. This effect is most likely due to post-star
formation processing of the molecular gas. A comparison of 13CO observations
for M33 and individual molecular clouds in the Milky Way suggests that a
significant fraction of the molecular interstellar medium resides in low column
density regions and accounts for 30-60% of the CO luminosity. Finally, a
detailed map of a single molecular cloud in the giant HII region NGC 604
reveals an offset between the atomic carbon and CO emission, which indicates
that the dominant source of atomic carbon in this cloud is likely
photodissociation of CO by ultraviolet photons from the massive stars. A
complete map of the CO emission in M33 would be extremely helpful to guide
further detailed studies.


title: Constraints on Type Ia Supernovae from Near Infrared Spectra

abstract:
  We describe a research program to improve the understanding of Type Ia
Supernovae (SNe Ia) by modeling and observing near infrared (NIR) spectra of
these events. The NIR between 0.9 microns and 2.5 microns is optimal for
examining certain products of the SNe Ia explosion that may be blended or
obscured in other spectral regions. NIR analysis will enable us to place
important constraints on the physical properties of SNe Ia progenitors and
their explosion dynamics. These are critical steps toward understanding the
physics of Type Ia Supernovae. We have identified features in NIR spectra of
SNe Ia that discriminate between Population I and Population II progenitors.
These features can significantly restrict the evolutionary history of SNe Ia.
We also examine certain products of the nuclear burning that enable us to place
constraints on the propagation of nuclear burning during the explosion, and on
the behavior of the burning front during the event. We will be able to
differentiate between the several explosion models for SNe Ia.


title: The Synthesis Telescope at the Dominion Radio Astrophysical Observatory

abstract:
  We describe an aperture synthesis radio telescope optimized for studies of
the Galactic interstellar medium (ISM), providing the ability to image extended
structures with high angular resolution over wide fields. The telescope
produces images of atomic hydrogen emission using the 21-cm HI spectral line,
and, simultaneously, continuum emission in two bands centred at 1420 MHz and
408 MHz, including linearly polarized emission at 1420 MHz, with synthesized
beams of 1 degree and 3.4 degrees at the respective frequencies.


title:
A spiral structure in the disk of EX Draconis on the rise to outburst
  maximum

abstract:
  We report on the R-band eclipse mapping analysis of high-speed photometry of
the dwarf nova EX Dra on the rise to the maximum of the November 1995 outburst.
The eclipse map shows a one-armed spiral structure of ~180 degrees in azimuth,
extending in radius from R ~0.2 to 0.43 R_{L1} (where R_{L1} is the distance
from the disk center to the inner Lagrangian point), that contributes about 22
per cent of the total flux of the eclipse map. The spiral structure is
stationary in a reference frame co-rotating with the binary and is stable for a
timescale of at least 5 binary orbits. The comparison of the eclipse maps on
the rise and in quiescence suggests that the outbursts of EX Dra may be driven
by episodes of enhanced mass-transfer from the secondary star. Possible
explanations for the nature of the spiral structure are discussed.


title: Dynamics of the Galaxy's Satellites

abstract:
  The Milky Way's satellites provide unique information about the density of
the Galactic halo at large radii. The inclusion of even a few rather inaccurate
proper motions resolves an ambiguity in older mass estimates in favour of
higher values. Many of the satellites are concentrated into streams. The
dynamics of the Magellanic Stream provided an early indication that the halo
reaches out to beyond 100 kpc. Tidal forces between the Clouds are currently
disturbing the Clouds' internal dynamics. One would expect this damage to
worsen rapidly as the tidal field of the MW excites the eccentricity of the
Clouds' mutual orbit. This process, which has yet to be completely modelled, is
important for understanding the degree of self-lensing in searches for
gravitational lensing events. The Sagittarius Dwarf galaxy very likely
contributes significantly to the Galactic warp. The direction of the warp's
line of nodes is incorrectly predicted by the simplest models of the Dwarf's
orbit. More sophisticated models, in which a complex distribution of stripped
dark matter is predicted, may be more successful.


title:
Probing the gravitational well: No supernova explosion in spherical
  symmetry with general relativistic Boltzmann neutrino transport

abstract:
  We report on the stellar core collapse, bounce, and postbounce evolution of a
13 solar mass star in a self-consistent general relativistic spherically
symmetric simulation based on Boltzmann neutrino transport. We conclude that
approximations to exact neutrino transport and omission of general relativistic
effects were not alone responsible for the failure of numerous preceding
attempts to model supernova explosions in spherical symmetry. Compared to
simulations in Newtonian gravity, the general relativistic simulation results
in a smaller shock radius. We however argue that the higher neutrino
luminosities and rms energies in the general relativistic case could lead to a
larger supernova explosion energy.


title: Optimal Supernova Search Strategies

abstract:
  Recent use of Type Ia supernovae to measure acceleration of the universe has
motivated questions regarding their optimal use to constrain cosmological
parameters Omega_M, Omega_{\Lambda} and w_Q. In this work we address the
question: what is the optimal distribution of supernovae in redshift in order
to best constrain the cosmological parameters? The solution to this problem is
not only of theoretical interest, but can be useful in planning supernova
searches. Using the Fisher matrix formalism we show that the error ellipsoid
corresponding to N parameters (for N=1, 2, 3) has the smallest volume if the
supernovae are located at N discrete redshifts, with equal number of supernovae
at each redshift and with one redshift always being the maximum one probed.
Including marginalization over the ``nuisance parameter'' M changes this result
only trivially.


title:
Near-infrared probing of embedded structures in starburst and Seyfert
  galaxies

abstract:
  Surface photometry in the J and K' bands of 15 southern Seyfert or starburst
galaxies is presented. The detailed central morphology and structural
properties of these objects were analyzed by fitting ellipses to isophotes. New
central peculiar structures have been identified like, for instance, three
double-barred systems (ESO 215-G031; ESO 320-G030; ESO 443-G017), one object
with a nested nuclear spiral structure at the center of a primary bar (NGC
5135), one object with a nuclear bar without evidence of a large-scale bar (NGC
4941), and one galaxy with a likely dissolved secondary bar within a primary
one (ESO 508-G005). The J-K' radial profile proved to be reasonably well linked
with the presence of a starburst, but not with the Seyfert activity. For
significant starbursts, the central J-K' value is 0.3-1.5 magnitude larger than
the disc one.


title:
Steep inflation: ending braneworld inflation by gravitational particle
  production

abstract:
  We propose a scenario for inflation based upon the braneworld picture, in
which high-energy corrections to the Friedmann equation permit inflation to
take place with potentials ordinarily too steep to sustain it. Inflation ends
when the braneworld corrections begin to lose their dominance. Reheating may
naturally be brought about via gravitational particle production, rather than
the usual inflaton decay mechanism; the reheat temperature may be low enough to
satisfy the gravitino bound and the Universe becomes radiation dominated early
enough for nucleosynthesis. We illustrate the idea by considering steep
exponential potentials, and show they can give satisfactory density
perturbations (both amplitude and slope) and reheat successfully. The scalar
field may survive to the present epoch without violating observational bounds,
and could be invoked in the quintessential inflation scenario of Peebles and
Vilenkin.


title: The Surroundings of Disturbed, Active Galaxies

abstract:
  The brightest apparent magnitude examples of ultra luminous infrared galaxies
(ULIRG's) are studied here in X-ray, optical, infrared and radio wavelengths.
It is is found that they have associated material reaching out to apparent
diameters of the order of a degree on the sky.
  Gas, dust, X-ray material and quasars appear to be ejected from the active
nuclei with all objects nearer than their redshift distances.


title: Reflections on Gravity

abstract:
  A pedagogical description of a simple ungeometrical approach to General
Relativity is given, which follows the pattern of well understood field
theories, such as electrodynamics. This leads quickly to most of the important
weak field predictions, as well as to the radiation damping of binary pulsars.
Moreover, certain consistency arguments imply that the theory has to be
generally invariant, and therefore one is bound to end up with Einstein's field
equations. Although this field theoretic approach, which has been advocated
repeatedly by a number of authors, starts with a spin-2 theory on Minkowski
spacetime, it turns out in the end that the flat metric is actually
unobservable, and that the physical metric is curved and dynamical.
  Short sections are devoted to tensor-scalar generalizations, the mystery of
the vacuum energy density, and quintessence.


title: Type Ia supernova rate at $z \sim 0.1$

abstract:
  We present the EROS nearby supernova ($z \sim 0.02 - 0.2$) search and the
analysis of the first year of data (1997). A total of 80 square degrees were
surveyed. Eight supernov{\ae} were detected, four of which were
spectroscopically identified as type Ia supernov{\ae}. The search efficiency
was determined with a Monte-Carlo simulation taking into account the
efficiencies for both supernova detection and host galaxy identification.
Assuming that for a given galaxy the supernova rate is proportional to the
galactic luminosity, we compute a type Ia supernova explosion rate of:
  ${\cal R} = 0.44 {}_{-0.21}^{+0.35} {}_{-0.07}^{+0.13} h^2: / 10^{10}
  \lbsun / 100 {\rm yrs}$ at an average redshift of $\sim 0.1$ where the errors
are respectively statistical and systematic (type misidentification included).


title: Star formation in expanding shells

abstract:
  We discuss the induced star formation in dense walls of expanding shells. The
fragmentation process is studied using the linear perturbation theory. The
influence of the energy input, the ISM distribution and the ISM speed of sound
is examined analytically and by numerical simulations. We formulate the
universal condition for the gravitational fragmentation of expanding shells: if
the total surface density of the disk is higher than a certain critical value,
shells are unstable. The value of the critical density depends on the energy of
the shell and the sound speed in the ISM.


title: On Physical Interpretation of the Poynting-Robertson Effect

abstract:
  Comments to the statements of Srikanth (1999) are presented. As for the
standard definition of the Poynting-Robertson drag, the results of Srikanth
(1999) are incorrect. Srikanth's statements about the isothermality condition
and ``red-shift'' are also discussed. Srikanth's results are generalized for
the most general case of the equation of motion when momentum loss per unit
time is proportional to -v/c (higher orders are neglected), where v is
(heliocentric) velocity of the particle, c is the speed of light.


title:
X-ray absorption and rapid variability of the dwarf Seyfert nucleus of
  NGC4395

abstract:
  We report the detection of an absorbed central X-ray source and its strong,
rapid variability in NGC4395, the least luminous Seyfert nucleus known. The
X-ray source exhibits a number of flares with factors of 3-4 flux changes
during a half day ASCA observation. Such X-ray variability is in constrast to
the behaviour of other low luminosity active galaxies. It provides further
support for an accreting black hole model rather than an extreme stellar
process in accounting for the nuclear activity of NGC4395. The soft X-ray
emission below 3 keV is strongly attenuated by absorption. The energy spectrum
in this absorption band shows a dramatic change in response to the variation in
continuum luminosity. A variable warm absorber appears to be an explanation for
the spectral change. The absorption-corrected 2-10 keV luminosity is 4e39 erg/s
for a source distance of 2.6 Mpc, and at 1 keV is one order of magnitude above
previous ROSAT estimates. Our X-ray results infer the nuclear source of NGC4395
to be a scaled-down version of higher luminosity Seyfert nuclei, with an
intermediate mass (10^4-10^5 Msun) black hole, unlike the nearby low luminosity
active galaxies in which underfed massive black holes are suspected to reside.


title: Is the Galactic center populated with young star clusters?

abstract:
  We study the evolution and observability of young and compact star clusters
near the Galactic center, such as the Arches cluster and the Quintuplet. The
star clusters are modeled with a combination of techniques; using direct
N-body, integration to calculate the motions of all stars and detailed stellar
and binary evolution to follow the evolution of the stars. The modeled star
clusters dissolve within 10 to 60 million years in the tidal field of the
Galaxy. The projected stellar density in the modeled clusters drops within 5%
to 70% of the lifetime to a level comparable to the projected background
density towards the Galactic center. And it will be very hard to distinguished
these clusters at later age among the background stars. This effect is more
severe for clusters at larger distance from the Galactic center but in
projection at the same distance. Based on these arguments we conclude that the
Galactic center easily hides 10 to 40 clusters with characteristics similar to
the Arches and the Quintuplet cluster.


title: Limits on isocurvature fluctuations from Boomerang and MAXIMA

abstract:
  We present the constraints on isocurvature fluctuations for a flat universe
implied by the Boomerang and Maxima-1 data on the anisotropy of the cosmic
microwave background. Because the new data defines the shape of the angular
power spectrum in the region of the first acoustic peaks much more clearly than
earlier data, even a tilted pure isocurvature model is now ruled out. However,
a mixed model with a sizable isocurvature contribution remains allowed. We
consider primordial fluctuations with different spectral indices for the
adiabatic and isocurvature perturbations, and find that the 95% C.L. upper
limit to the isocurvature contribution to the low multipoles is $\alpha \leq
0.63$. The upper limit to the contribution in the ${\l}\sim 200$ region is
$\alpha_{200} \leq 0.13$.


title: Extremely red galaxies: age and dust degeneracy solved ?

abstract:
  The extremely red galaxies (ERGs) are defined in terms of their very red
optical-to-near IR colours (as R-K>5 or I-K>4). Originally this selection was
aimed at selecting old (> 1 Gyr) passively evolving elliptical galaxies at
intermediate redshift (1<z<2), but it was soon discovered that young
star-forming dusty galaxies can show similar colours and therefore be selected
in the same surveys. It is crucial to distinguish between these two populations
because they have very different consequences on the models of galaxy
formation. Here we show that old ellipticals and dusty starburst are expected
to show different colours in the (I-K) vs. (J-K) diagram for redshift range
1<z<2, providing thus a useful tool to classify ERGs in large samples up to
K<20. This is mainly due to the fact that old galaxies at these redshifts have
a strong 4000 ang. break at lambda<1.2 mic. (J band), while dusty galaxies show
a smoother spectral energy distributions and therefore redder J-K colours. We
discuss this difference in detail both in the framework of the stellar
population synthesis models and by using observed spectra. The selection
criterion is also compared with the properties of ERGs of known nature. We also
show that this colour selection criterion is also useful to separate the ERGs
from brown dwarf stars showing similar optical-to-IR colours.


title:
EISily looking for distant clusters of galaxies - - a new algorithm and
  its application to the EIS-wide data

abstract:
  We present a new algorithm to search for distant clusters of galaxies on
catalogues deriving from imaging data, as those of the ESO Imaging Survey. Our
algorithm is a matched filter one, similar to that adopted by Postman et al.
(1996), aiming at identifying cluster candidates by using positional and
photometric data simultaneously. The main novelty of our approach is that
spatial and luminosity filter are run separately on the catalogue and no
assumption is made on the typical size nor on the typical M* for clusters, as
these parameters intervene in our algorithm as typical angular scale (sigma)
and typical apparent magnitude m*. Moreover we estimate the background locally
for each candidate, allowing us to overcome the hazards of inhomogeneous
datasets. As a consequence our algorithm has a lower contamination rate -
without loss of completeness - in comparison to other techniques, as tested
through extensive simulations. We provide catalogues of galaxy cluster
candidates as the result of applying our algorithm to the I-band data of the
EIS-wide patches A and B.


title: Lensing Degeneracies Revisited

abstract:
  This paper shows that the mass-sheet degeneracy and other degeneracies in
lensing have simple geometrical interpretations: they are mostly rescalings of
the arrival-time surface. Different degeneracies appear in Local Group lensing
and in cosmological lensing, because in the former the absolute magnification
is measured but the image structure is not resolved, whereas in the latter the
reverse usually applies. The most dangerous of these is a combination we may
call the `mass-disk degeneracy' in multiply-imaging galaxy lenses, which may
lead to large systematic uncertainties in estimates of cosmological parameters
from these systems.


title: Intrinsic colour calibration for F, G, K stars

abstract:
  We derive an intrinsic colour calibration for F--K stars using broad band
Johnson colours and line indices KP and HP2. Through this calibration we can
determine E(B-V) of an individual star within 0.03 mag. The E(B-V) values thus
derived are in excellent agreement with those derived from Stromgren photometry
through the Schuster & Nissen (1989) calibration. The agreement is also good
with the reddening maps of Burstein & Heiles (1982) and Schlegel et al (1998),
although in this case there exists a small offset of about 0.01 mag. This
calibration may be applied to the large body of data of the HK survey extension
which will be published in the near future.


title:
Spectroscopic Gravitational Lens Candidates in the CNOC2 Field Galaxy
  Redshift Survey

abstract:
  We present five candidate gravitational lenses discovered spectroscopically
in the Canadian Network for Observational Cosmology Field Galaxy Redshift
Survey (CNOC2), along with one found in followup observations. Each has a
secure redshift based on several features, plus a discrepant emission line
which does not match any known or plausible feature and is visible in multiple
direct spectral images. We identify these lines as Lyman-alpha or [OII]
emission from galaxies lensed by, or projected onto, the CNOC2 target galaxies.
Einstein radii estimated from the candidate deflector galaxy luminosities
indicate that for two candidates the lines are probably [OII] from projected
z<1 galaxies (consistent with the detection of H-beta as well as [OII] in one
of them), but that in the remaining four cases the lines could be Ly-alpha from
lensed z>3 galaxies. We estimate that only 1.9+-0.7 [OII]-emitting galaxies are
expected to project onto target galaxies in the original CNOC2 sample,
consistent with three or four of the six candidates being true gravitational
lenses.


title: Distribution of dust from Kuiper belt objects

abstract:
  (Abridged) Using an efficient computational approach, we have reconstructed
the structure of the dust cloud in the Solar system between 0.5 and 100 AU
produced by the Kuiper belt objects. Our simulations offer a 3-D physical model
of the `kuiperoidal' dust cloud based on the distribution of 280 dust particle
trajectories produced by 100 known Kuiper belt objects ; the resulting 3-D grid
consists of $1.9\times 10^6$ cells containing $1.2\times 10^{11}$ particle
positions. The following processes that influence the dust particle dynamics
are taken into account: 1) gravitational scattering on the eight planets
(neglecting Pluto); 2) planetary resonances; 3) radiation pressure; and 4) the
Poynting-Robertson (P-R) and solar wind drags. We find the dust distribution
highly non-uniform: there is a minimum in the kuiperoidal dust between Mars and
Jupiter, after which both the column and number densities of kuiperoidal dust
sharply increase with heliocentric distance between 5 and 10 AU, and then form
a plateau between 10 and 50 AU. Between 25 and 45 AU, there is an appreciable
concentration of kuiperoidal dust in the form of a broad belt of mostly
resonant particles associated with Neptune. In fact, each giant planet
possesses its own circumsolar dust belt consisting of both resonant and
gravitationally scattered particles. As with the cometary belts simulated in
our related papers (Ozernoy, Gorkavyi, & Taidakova 2000a,b), we reveal a
complex resonant structure of the dust belts containing rich families of
resonant peaks and gaps. An important result is that both the column and number
dust density are more or less flat between 10 and 50 AU, which might explain
the surprising data obtained by Pioneers 10 & 11 and Voyager that the dust
number density remains approximately distance-independent in this region.


title: CMB Observables and Their Cosmological Implications

abstract:
  We show that recent measurements of the power spectrum of cosmic microwave
background anisotropies by BOOMERanG and MAXIMA can be characterized by four
observables, the position of the first acoustic peak l_1= 206 pm 6, the height
of the first peak relative to COBE normalization H_1= 7.6 pm 1.4, the height of
the second peak relative to the first H_2 = 0.38 pm 0.04, and the height of the
third peak relative to the first H_3 = 0.43 pm 0.07. This phenomenological
representation of the measurements complements more detailed likelihood
analyses in multidimensional parameter space, clarifying the dependence on
prior assumptions and the specific aspects of the data leading to the
constraints. We illustrate their use in the flat LCDM family of models, where
we find Omega_m h^{3.8} > 0.079 (or nearly equivalently, the age of the
universe t_0 < 13-14 Gyr) from l_1 and a baryon density Omega_b h^2 > 0.019, a
matter density Omega_m h^2 < 0.42 and tilt n>0.85 from the peak heights (95%
CL). With the aid of several external constraints, notably nucleosynthesis, the
age of the universe and the cluster abundance and baryon fraction, we construct
the allowed region in the (Omega_m,h) plane; it points to high h (0.6< h < 0.9)
and moderate Omega_m (0.25 < Omega_m < 0.6).


title: Circular Polarization Induced by Scintillation in a Magnetized Medium

abstract:
  A new theory is presented for the development of circular polarization as
radio waves propagate through the turbulent, birefringent interstellar medium.
The fourth order moments of the wavefield are calculated and it is shown that
unpolarized incident radiation develops a nonzero variance in circular
polarization. A magnetized turbulent medium causes the Stokes parameters to
scintillate in a non-identical manner. A specific model for this effect is
developed for the case of density fluctuations in a uniform magnetic field.


title: Monte Carlo Simulations of Star Clusters

abstract:
  A revision of Stod\'o{\l}kiewicz's Monte Carlo code is used to simulate
evolution of large star clusters. The survey on the evolution of multi-mass
N-body systems influenced by the tidal field of a parent galaxy and by stellar
evolution is discussed. For the first time, the simulation on the
"star-by-star" bases of evolution of 1,000,000 body star cluster is presented.
\


title: Probing the galactic center by gravitational lensing

abstract:
  The nature of Galactic Center could be probed by lensing experiments capable
of testing the spatial and velocity distributions of stars nearby and beyond
it. Several hypotheses are possible (e.g. massive neutrino condensation, boson
star) which avoid the shortcomings of the supermassive black hole model.


title: Mixed quark-nucleon phase in neutron stars and nuclear symmetry energy

abstract:
  The influence of the nuclear symmetry energy on the formation of a mixed
quark-nucleon phase in neutron star cores is studied. We use simple
parametrizations of the nuclear matter equation of state, and the bag model for
the quark phase. The behavior of nucleon matter isobars, which is responsible
for the existence of the mixed phase, is investigated. The role of the nuclear
symmetry energy changes with the value of the bag constant B. For lower values
of B the properties of the mixed phase do not depend strongly on the symmetry
energy. For larger B we find that a critical pressure for the first quark
droplets to form is strongly dependent on the nuclear symmetry energy, but the
pressure at which last nucleons disappear is independent of it.


title: Confidence levels of evolutionary synthesis models

abstract:
  The stochastic nature of the IMF in young stellar clusters implies that
clusters of the same mass and age do not present the same unique values of
their observed parameters. Instead they follow a distribution. We address the
study of such distributions, parameterised in terms of their confidence limits,
in evolutionary synthesis models. These confidence limits can be understood as
the inherent uncertainties of the synthesis models. Here we concentrate on some
parameters such as EW(Hb) in emission. For instance, we show that for a cluster
where 10^5 Mo have been transformed into stars, the dispersion of EW(Hb) is
about 18% within the 90% confidence levels at ages between 3.5 and 5 Myrs.


title: Chemical abundances in seven red giants of NGC 2360 and NGC 2447

abstract:
  Chemical abundances of about fifteen elements from oxygen to europium are
measured in seven red giants of the two open clusters NGC 2360 and NGC 2447.
The effective temperatures of the giants are determined spectroscopically by
taking advantage of their known masses (~2 Mo in NGC 2360 and ~3 Mo in NGC
2447) and bolometric magnitudes.
  The average iron abundances we obtain for the two clusters are [Fe/H]=0.07
for NGC 2360 and [Fe/H]=0.03 for NGC 2447.
  Evolutionary stellar model calculations are performed in the mass range 1-4
Mo in order to analyze the surface Na and O abundances predicted after the
first dredge-up. The sodium abundance shows a well defined correlation with
stellar mass in the 2-3 Mo range. The agreement between our Na abundance
determinations in NGC 2360 and our model predictions at 2 Mo is very good. In
contrast, the overabundance in one of the three stars in NGC 2447 exceeds that
predicted at 3 Mo by ~0.08 dex, which is significant compared to the
observational error bars. The effects of core overshooting, convection
prescription, metallicity and nuclear reaction rates on the Na surface
predictions of our models are investigated.
  An oxygen deficiency relative to iron by 0.2 dex is measured in our stars, in
disagreement with our model predictions. Assuming that the Sun is 0.1-0.3 dex
enriched in oxygen relative to neighbor stars could explain the discrepancy.


title: Gamma-ray loud quasars: a view with BeppoSAX

abstract:
  We present BeppoSAX observations of three gamma-ray emitting quasars, namely
0836+710, 1510-089 and 2230+114. The three objects have been detected up to 100
keV showing extremely flat power-law spectra above 2 keV (energy index
alpha_{2-10}=0.3-0.5). The soft X-ray spectrum of 0836+710 implies either an
absorption column density higher than the galactic one or an intrinsically very
hard slope (alpha_{0.1-1}=-0.2) below 1 keV. 1510-089 shows a soft excess, with
the low energy spectrum steeper (alpha_{0.1-1}=1.6) than the high energy
power-law. The results are discussed in the framework of current Inverse
Compton models for the high energy emission of Flat Spectrum Radio Quasars and
are used to estimate the physical quantities in the jet emitting region and to
shed light on the energy transport mechanisms in jets. Finally we discuss the
estimates of the jet luminosity in the context of the Blandford & Znajek
mechanism for jet production.


title:
ISO deep far-infrared survey in the "Lockman Hole" II. Power spectrum
  analysis: evidence of a strong evolution in number counts

abstract:
  We investigate the characteristics of FIR brightness fluctuations at 90
micron and 170 micron in the Lockman Hole, which were surveyed with ISOPHOT
aboard the Infrared Space Observatory(ISO). We first calculated the angular
correlation function of each field and then its Fourier transform(the angular
Power Spectral Density: PSD) over the spatial frequency range of f=0.05 - 1
arcmin^-1. The PSDs are found to be rather flat at low spatial frequencies (f
<= 0.1 arcmin^-1), slowly decreasing toward higher frequencies. These spectra
are unlike the power-law ones seen in the IR cirrus fluctuations, and are well
explained by randomly distributed point sources. Furthermore, point-to-point
comparison between 90 micron and 170 micron brightness shows a linear
correlation between them, and the slope of the linear fit is much shallower
than that expected from the IR cirrus color, and is consistent with the color
of galaxies at low or moderate redshift(z < 1). We conclude that the brightness
fluctuations in the Lockman Hole are not caused by the IR cirrus, but are most
likely due to faint star-forming galaxies. We also give the constraints on the
galaxy number counts down to 35 mJy at 90 micron and 60 mJy at 170 micron,
which indicate the existence of a strong evolution down to these fluxes in the
counts. The galaxies responsible for the fluctuations also significantly
contribute to the cosmic infrared background radiation.


title: Double Inflation in Supergravity and the Boomerang Observations

abstract:
  One of the biggest mystery of the recent observation of cosmic microwave
background anisotropies by the boomerang team is insignificance of the second
acoustic peak in the angular power spectrum. It is very difficult to explain
such a low amplitude without assuming the higher baryon density than predicted
by the Big Bang Nucleosynthesis (BBN). Employing the double inflation model in
supergravity, we show that the density fluctuations produced by this inflation
model can produce a sufficient low second acoustic peak with the standard value
of the baryon density from BBN. It is shown that these density fluctuations are
also consistent with the observations of cluster abundances and galaxy
distributions.


title:
Out of Equilibrium Fields in Self-consistent Inflationary Dynamics.
  Density Fluctuations

abstract:
  The physics during the inflationary stage of the universe is of quantum
nature involving extremely high energy densities. Moreover, it is out of
equilibrium on a fastly expanding dynamical geometry.We present in these
lectures non-perturbative out of equilibrium field theoretical methods in
cosmological universes. We then study the non-linear dynamics of quantum fields
in matter and radiation dominated FRW and de Sitter universes. We investigate
the explosive particle production due to spinodal instabilities and parametric
amplification in FRW and deSitter universes with and without symmetry breaking.
We show how the particle production is sensitive to the expansion of the
universe.We present a complete renormalization scheme for the equation of
motion and the energy momentum tensor in flat cosmologies. We then consider an
O(N) inflaton model coupled self-consistently to gravity in the semiclassical
approximation, with `new inflation' type initial conditions. We study the
dynamics self-consistently and non-perturbatively with non-equilibrium field
theory methods in the large N limit. We find that spinodal instabilities drive
the growth of non-perturbatively large quantum fluctuations which shut off the
inflationary growth of the scale factor. A very specific combination of these
large quantum fluctuations plus the inflaton zero mode assemble into a new
effective field. This new field behaves classically and it is the object which
actually rolls down. The metric perturbations during inflation are computed
using this effective field and the Bardeen variable for superhorizon modes
during inflation. We compute the amplitude and index for the spectrum of scalar
density and tensorperturbations and find for these models that the spinodal
instabilities are responsible for a `red' primordial spectrum.


title: Orbital Dynamics of Triaxial Black-Hole Nuclei

abstract:
  Orbital motion in triaxial nuclei with central point masses, representing
supermassive black holes, is investigated. The stellar density is assumed to
follow a power law, rho ~ 1/r^gamma, with gamma=1 or gamma=2. At low energies
the motion is essentially regular; the major families of orbits are the tubes
and the pyramids. Pyramid orbits are similar to box orbits but have their major
elongation parallel to the short axis of the figure. A number of regular orbit
families associated with resonances also exist, most prominently the banana
orbits, which are also elongated with the short axis. At a radius where the
enclosed stellar mass is a few times the black hole mass, the pyramid orbits
become stochastic. The energy of transition to this ``zone of chaos'' is
computed as a function of gamma and of the shape of the stellar figure; it
occurs at lower energies in more elongated potentials. Our results suggest that
supermassive black holes may place tight constraints on departures from
triaxiality in galactic nuclei, both by limiting the allowed shapes of regular
orbits and by inducing chaos.


title: Antimatter Regions in the Early Universe and Big Bang Nucleosynthesis

abstract:
  We have studied big bang nucleosynthesis in the presence of regions of
antimatter. Depending on the distance scale of the antimatter region, and thus
the epoch of their annihilation, the amount of antimatter in the early universe
is constrained by the observed abundances. Small regions, which annihilate
after weak freezeout but before nucleosynthesis, lead to a reduction in the 4He
yield, because of neutron annihilation. Large regions, which annihilate after
nucleosynthesis, lead to an increased 3He yield. Deuterium production is also
affected but not as much. The three most important production mechanisms of 3He
are 1) photodisintegration of 4He by the annihilation radiation, 2) pbar-4He
annihilation, and 3) nbar-4He annihilation by "secondary" antineutrons produced
in anti-4He annihilation. Although pbar-4He annihilation produces more 3He than
the secondary nbar-4He annihilation, the products of the latter survive later
annihilation much better, since they are distributed further away from the
annihilation zone.


title:
Accurate Determination of the Mass Distribution in Spiral Galaxies: II.
  Testing the Shape of Dark Halos

abstract:
  New high resolution CFHT Fabry-Perot data, combined with published VLA 21 cm
observations are used to determine the mass distribution of NGC 3109 and IC
2574. The multi-wavelength rotation curves allow to test with confidence
different dark halo functional forms from the pseudo-isothermal sphere to some
popular halo distributions motivated by N-body simulations. It appears that
density distribution with an inner logarithmic slope <= -1 are very hard to
reconcile with rotation curves of late type spirals. Modified Newtonian
Dynamics (MOND) is also considered as a potential solution to missing mass and
tested the same way. The new higher resolution data show that MOND can
reproduce in details the rotation curve of IC 2574 but confirm its difficulty
to fit the kinematics of NGC 3109.


title: The Dependence of the Galaxy Luminosity Function on Environment

abstract:
  We present luminosity functions for galaxies in loose groups in the Las
Campanas Redshift Survey, differentiated by their environment (defined by the
line-of-sight velocity dispersion sigma of the host groups) and also by their
spectral type (emission or non-emission, defined by the equivalent width of the
3727-Angstrom [OII] line).
  We find systematic variations in the Schechter parameters alpha and M* for
non-emission line galaxies over a range of 0 < sigma < 800 km/s. Alpha varies
from 0.20 to -0.91, indicating an increase in the steepness of the faint end
slope with increasing sigma. The accompanying variation in M* appears to be
accounted for by the intrinsic correlation with alpha and does not indicate a
significant physical variation in the bright end of the luminosity function.
For emission line galaxies, we find no significant systematic variation of the
luminosity function with the environment. Our results show that emission and
non-emission galaxies generally occupy two distinct regions in the alpha-M*
parameter space. From our luminosity functions, we derive the number ratios of
emission to non-emission galaxies as a function of environment and absolute
magnitude, showing that the relative abundance of non-emission line galaxies
generally increases for all magnitudes -23 < M_R < -17.5 towards high-sigma
environments, from ~80% to >90% at M_R = -22 and from ~10% to >50% at M_R = -18
(H_0 = 100 km s^{-1} Mpc^{-1} and q_0 = 0.5).


title: Further Adventures: Oxygen Burning in a Convective Shell

abstract:
  Two dimensional hydrodynamical simulations of convective oxygen burning shell
in the presupernova evolution of a 20 solar-mass star are extended to later
times. We used the VULCAN code to simulate longer evolution times than
previously possible. Our results confirm the previous work of Bazan and Arnett
(98) over their time span of 400s. However, at 1200s, we could identify a new
steady state that is significantly different than the original one dimensional
model. There is considerable overshooting at both the top and bottom boundaries
of convection zone. Beyond the boundaries, the convective velocity falls off
exponentially, with excitation of internal modes. The resulting mixing greatly
affect the evolution of the simulations. Connections with other works of
simulation of convection, in which such behavior is found in a different
context, are discussed.


title: The Size and Shape of Voids in Three-Dimensional Galaxy Surveys

abstract:
  The sizes and shapes of voids in a galaxy survey depend not only on the
physics of structure formation, but also on the sampling density of the survey
and on the algorithm used to define voids. Using an N-body simulation with a
CDM power spectrum, we study the properties of voids in samples with different
number densities of galaxies, both in redshift space and in real space. When
voids are defined as regions totally empty of galaxies, their characteristic
volume is strongly dependent on sampling density; when they are defined as
regions whose density is 0.2 times the mean galaxy density, the dependence is
less strong. We compare two void-finding algorithms, one in which voids are
nonoverlapping spheres, and one, based on the algorithm of Aikio and Mahonen,
which does not predefine the shape of a void. Regardless of the algorithm
chosen, the characteristic void size is larger in redshift space than in real
space, and is larger for low sampling densities than for high sampling
densities. We define an elongation statistic Q which measures the tendency of
voids to be stretched or squashed along the line of sight. Using this
statistic, we find that at sufficiently high sampling densities (comparable to
the number densities of galaxies brighter than L_*), large voids tend to be
slightly elongated along the line of sight in redshift space.


title: An attempt to do without dark matter

abstract:
  The discrepancy between dynamical mass measures of objects such as galaxies
and the observed distribution of luminous matter in the universe is typically
explained by invoking an unseen ``dark matter'' component. Dark matter must
necessarily be non-baryonic. We introduce a simple hypothesis to do away with
the necessity for dark matter by introducing an additional non-gravitational
force coupled to baryon number as a charge. We compare this hypothesis to
Milgrom's Modified Newtonian Dynamics. The model ultimately fails when
confronted with observation, but it fails in an interesting way.


title:
Global Cosmological Parameters Determined Using Classical Double Radio
  Galaxies

abstract:
  A sample of 20 powerful extended radio galaxies with redshifts between zero
and two were used to determine constraints on global cosmological parameters.
Data for six radio sources were obtained from the VLA archive, analyzed, and
combined with the sample of 14 radio galaxies used previously by Guerra & Daly
to determine cosmological parameters. The results are consistent with our
previous results, and indicate that the current value of the mean mass density
of the universe is significantly less than the critical value. A universe with
$\Omega_m$ of unity is ruled out at 99.0% confidence, and the best fitting
values of $\Omega_m$ in matter are $0.10^{+0.25}_{-0.10}$ and
$-0.25^{+0.35}_{-0.25}$ assuming zero space curvature and zero cosmological
constant, respectively. Note that identical results obtain when the low
redshift bin, which includes Cygnus A, is excluded; these results are
independent of whether the radio source Cygnus A is included. The method does
not rely on a zero-redshift normalization.
  The radio properties of each source are also used to determine the density of
the gas in the vicinity of the source, and the beam power of the source. The
six new radio sources have physical characteristics similar to those found for
the original 14 sources. The density of the gas around these radio sources is
typical of gas in present day clusters of galaxies. The beam powers are
typically about $10^{45} \hbox{erg s}^{-1}$.


title:
Determinations of Key Physical Parameters Related to Classical Double
  Radio Sources

abstract:
  Multi-frequency radio observations of the radio bridge of a powerful
classical double radio source can be used to determine: the beam power of the
jets emanating from the AGN; the total time the source will actively produce
jets that power large-scale radio emission; the thermal pressure of the medium
in the vicinity of the radio source; and the total mass, including dark matter,
of the galaxy or cluster of galaxies traced by the ambient gas that surrounds
the radio source. Empirical determinations of each of these quantities are
obtained and analyzed for 22 radio sources. Typical beam powers are about
$10^{45} {erg s}^{-1}$. The characteristic or total time the AGN will actively
produce a collimated outflow is estimated. Typical total lifetimes are $\sim
(10^7$ to $10^8$) years. Total masses, and mass-density profiles, similar to
those of low-redshift clusters of galaxies are obtained. Thus, some clusters of
galaxies, or cores of clusters, exist at redshifts of one to two.
  A new method of estimating the thermal pressure of the ambient gas in the
vicinity of a powerful classical double radio source is presented. This new
estimate is independent of synchrotron and inverse Compton aging arguments, and
depends only upon the properties of the radio lobe and the shape of the radio
bridge. Thermal pressures on the order of $10^{-10} {dyne cm}^{-2}$, typical of
gas in low-redshift clusters of galaxies, are found for the environments of the
sources studied here. It is shown that appreciable amounts of cosmic microwave
background diminution (the Sunyaev-Zel'dovich effect) are expected from many of
these clusters. This could be detected at high frequency where the emission
from the radio sources is weak.


title:
Global MHD Simulation of the Inner Accretion Disk in a Pseudo-Newtonian
  Potential

abstract:
  We present a detailed three dimensional magnetohydrodynamic (MHD) simulation
describing the inner region of a disk accreting onto a black hole. To avoid the
technical complications of general relativity, the dynamics are treated in
Newtonian fashion using the pseudo-Newtonian Pacz\'ynski-Wiita potential. The
disk evolves due to angular momentum transport which is produced naturally from
MHD turbulence generated by the magnetorotational instability. We find that the
resulting stress is continuous across the marginally stable orbit, in
contradiction with the widely-held assumption that the stress should go to zero
there. As a consequence, the specific angular momentum of the matter accreted
into the hole is smaller than the specific angular momentum at the marginally
stable orbit. The disk exhibits large fluctuations in almost every quantity,
both spatially and temporally. In particular, the ratio of stress to pressure
(the local analog of the Shakura-Sunyaev $\alpha$ parameter) exhibits both
systematic gradients and large fluctuations; from $\sim 10^{-2}$ in the disk
midplane at large radius, it rises to $\sim 10$ both at a few gas density
scaleheights above the plane at large radius, and near the midplane well inside
the plunging region. Driven in part by large-amplitude waves excited near the
marginally stable orbit, both the mass accretion rate and the integrated stress
exhibit large fluctuations whose Fourier power spectra are smooth "red"
power-laws stretching over several orders of magnitude in timescale.


title:
High Resolution X-Ray Spectra of Capella: Initial Results from the
  Chandra High Energy Transmission Grating Spectrometer

abstract:
  High resolution spectra of the active binary Capella (G8 III + G1 III)
covering the energy range 0.4-8.0 keV (1.5-30 Angstroms) show a large number of
emission lines, demonstrating the performance of the HETGS. A preliminary
application of plasma diagnostics provides information on coronal temperatures
and densities. Lines arising from different elements in a range of ionization
states indicate that Capella has plasma with a broad range of temperatures,
from log T = 6.3 to 7.2, generally consistent with recent results from
observations with the Extreme Ultraviolet Explorer (EUVE) and the Advanced
Satellite for Cosmology and Astrophysics (ASCA). The electron density is
determined from He-like O VII lines, giving the value N_e=10^10 cm^-3 at
T_e=2*10^6 K; He-like lines formed at higher temperatures give only upper
limits to the electron density. The density and emission measure from O VII
lines together indicate that the coronal loops are significantly smaller than
the stellar radius.


title:
Optical Imaging of Nova Shells and the Maximum Magnitude-Rate of Decline
  Relationship

abstract:
  An optical imaging study of recent 30 novae has been undertaken using both
ground-based and space-based observations. Resolved shells have been detected
around 9 objects in the ground-based data, while another four objects have
shells detected by HST observations; for RW UMi, we fail to detect a shell
which was observed five years earlier. Images in H-alpha, and when appropriate
[O III], are shown, and finding charts for novae without shells are given if no
published chart is available. Expansion parallaxes for all systems with shells
are derived, and absolute magnitudes for a total of 28 objects are presented,
along with a discussion of the maximum magnitude-rate of decline relation. We
find that separate linear fits for fast and slow novae may be a better
representation of the data than a single, global fit. At minimum, most novae
have similar magnitudes as those of dwarf novae at maximum and novalike stars.


title:
Hubble Space Telescope Photometry of the Dwarf Spheroidal Galaxy ESO
  410-G005

abstract:
  We present HST WFPC2 imaging of the nearby low-surface-brightness dwarf
spheroidal galaxy ESO 410-G005, which has been resolved into stars for the
first time. The resulting color-magnitude diagram for about 2500 stars shows a
red giant branch branch with a tip at I=(22.4+-0.15), which yields a distance
of D=(1.9+-0.2) Mpc. ESO 410-G005 is found to be metal-poor with a mean
metallicity of (-1.8+-0.4) dex estimated from its red giant branch. Upper
asymptotic giant branch stars appear to be present near the center of the
galaxy, indicative of a substantial, centrally concentrated intermediate-age
population, unless these objects are artifacts of crowding. Previous studies
did not detect ESO 410-G005 in H alpha or in HI. ESO 410-G005 is a probable
member of the Sculptor group. Its linear separation from the nearest spiral,
NGC 55, is 230 kpc on the sky. The deprojected separation ranges from 340 to
615 kpc depending on the assumed distance of NGC 55. ESO 410 G005 appears to be
a relatively isolated dSph within the Sculptor group. Its absolute magnitude,
Mv = (-12.1+-0.2) mag, its central surface brightness, mu_V = (22.7+-0.1)
mag/arcsec^2, and its mean metallicity, [Fe/H] = (-1.8+-0.4) dex, follow the
trend observed for dwarf galaxies in the Local Group. (abridged)


title:
Stellar Populations in the Host Galaxies of Mrk 1014, IRAS 07598+6508,
  and Mrk 231

abstract:
  We present deep spectroscopic and imaging data of the host galaxies of Mrk
1014, IRAS 07598+6508, and Mrk 231. These objects form part of both the QSO and
the ultraluminous infrared galaxy (ULIG) families, and may represent a
transition stage in an evolutionary scenario. Our imaging shows that all three
objects have highly perturbed hosts with tidal tails and destroyed disks, and
appear to be in the final stages of major mergers. The host galaxies of the
three objects have spectra typical of E+A galaxies, showing simultaneously
features from an old and a young stellar component. We model spectra from
different regions of the host galaxies using Bruzual & Charlot spectral
synthesis models using two component models including an old underlying
population and recent superposed starbursts. Our results indicate a strong
connection between interactions and vigorous bursts of star formation in these
objects. We propose that the starburst ages found are indicative of young ages
for the QSO activity. The young starburst ages found are also consistent with
the intermediate position of these objects in the far infrared color-color
diagram. (abridged)


title:
Searches for astronomical neutrino sources and WIMPs with
  Super-Kamiokande

abstract:
  Searches for astronomical neutrino sources and weakly interactive massive
particles (WIMPs) using the Super-Kamiokande detector have been performed. We
select the neutrino-induced upward muon events for the first 4 years, which is
already the world largest data sample, and look for statistically significant
excesses compared to the atmospheric neutrino background. No excess has been
found so far. Limits of upward muon flux from various potential sources are
obtained. Also limits of upward muon flux due to annihilations of WIMPs in the
Earth core, the Sun and the Galactic center are obtained as a function of WIMP
masses.


title: Rotating compact strange stars

abstract:
  We compute numerical models of uniformly rotating strange stars (SS) in
general relativity for the recently proposed QCD-based equation of state (EOS)
of strange quark matter (Dey et al. 1998). Static models based on this EOS are
characterised by a larger surface redshift than strange stars within the MIT
bag model. The frequencies of the fastest rotating configurations described by
Dey model are much higher than these for neutron stars (NS) and for the
simplest SS MIT bag model. We determine a number of physical parameters for
such stars and compare them with those obtained for NS. We construct constant
baryon mass equilibrium sequences both normal and supramassive. Similarly to
the NS a supramassive SS, prior to collapse to a black hole, spins up as it
loses angular momentum. We find the upper limits on maximal masses and maximal
frequencies of the rotating configurations. We show that the maximal rotating
frequency for each of considered evolutionary sequences is never the Keplerian
one. A normal and low mass supramassive strange stars gaining angular momentum
always slows down just before reaching the Keplerian limit. For a high mass
supramassive SS sequence the Keplerian configuration is the one with the lowest
rotational frequency in the sequence. The value of $T/W$ for rapidly rotating
SS of any mass is significantly higher than those for ordinary NS. For
Keplerian configurations it increases as mass decreases. The results are robust
for all linear self-bound equations of state.


title: CO Observations of Luminous IR Galaxies at Intermediate Redshift

abstract:
  We present new measurement of $^{12}$CO($J=1-0$) emission from 16 luminous
infrared galaxies (LIGs) at intermediate redshift ($cz \sim 10,000 - 50,000
{\rm km s^{-1}}$). These new data were selected by isolated and normal
morphology. The CO observations were performed using the NRO 45-m telescope.
Comparison of the CO and dust properties of the new result with those from
other CO measurements revealed characteristics of this sample: (1) It is the
deepest CO observations of IRAS galaxies at intermediate redshift without
strong interaction features. (2) It has typical properties of normal IRAS
galaxies in terms of star-formation efficiency, color-color diagrams and
galactic nuclear activity. (3) It has smaller gas-to-dust ratio than normal
IRAS galaxies. This can be explained by two-component dust model, and our
sample consists of most of warm dust.


title: A Dwarf Galaxy Survey in the Local Volume

abstract:
  We are carrying out a comprehensive multi-wavelength study of dwarf galaxies
in the Local Volume (< 5 Mpc). After our all-sky survey more than doubled the
dwarf census we are now measuring structural parameters, integrated properties,
and velocities. Our 200-orbit HST snapshot program yields stellar content, star
formation history, and TRGB distances. We can thus study the morphology-density
relation in galaxy groups in three dimensions, the influence of environment on
galaxy evolution, and the universality of the metallicity-surface
brightness-luminosity relation.


title:
Oxygen Abundance Determination in Very Metal-Deficient Giants: Permitted
  O I Lines Versus Forbidden [O I] Lines

abstract:
  The abundance of oxygen was determined for selected very metal-poor G-K stars
(six giants and one turn-off star) based on the high S/N and high-resolution
spectra observed with Keck HIRES in the red through near-IR region comprising
the permitted O I lines (7771-5, 8446) along with the [O I] forbidden line at
6363 A. It turned out that both the abundances from the permitted line
features, O I 7771-5 and O I 8446, agree quite well with each other, while the
forbidden line yields somewhat discrepant and divergent abundances with a
tendency of being underestimated on the average. The former (7773/8446)
solution, which we believe to be more reliable, gives a fairly tight [O/Fe] vs.
[Fe/H] relation such that increasing steadily from [O/Fe] = 0.6 (at [Fe/H] =
-1.5) to [O/Fe] = 1.0 (at [Fe/H] = -3.0), in reasonable consistency with the
trend recently reported based on the analysis of the UV OH lines. We would
suspect that some kind of weakening mechanism may occasionally act on the
formation of [O I] forbidden lines in metal-poor stars. Therefore, [O I] lines
may not be so a reliable abundance indicator as has been generally believed.


title: Radiative Cooling Flows of Self-Gravitating Filamentary Clouds

abstract:
  We study the dynamics of a self-gravitating cooling filamentary cloud using a
simplified model. We concentrate on the radial distribution and restrict
ourselves to quasi-hydrostatic, cylindrically symmetric cooling flows. For a
power-law dependence of cooling function on the temperature, self-similar
solutions which describe quasi-hydrostatic cooling flows are derived. We
consider obtically thin filaments with a constant mass per unit length and the
solutions are parameterized by their line masses. There is no polytropic
relation between the density and the pressure. The filament experiences
radiative condensation, irrespective of the \gamma, the gas specific heat
ratio. So, the filament becomes denser due to the quasi-hydrostatic flows and
the density at the center increases in proportion to (t_{0}-t)^{-1}, where t
denotes the time. The term, t_{0}, denotes an epoch at which the central
density increases infinitely. We also found that the radius of the filament
decreases in proportion to (t_{0}-t)^{0.5}.


title: Magnetic propeller in symbiotic stars

abstract:
  Rapidly spinning magnetic white dwarfs in symbiotic stars may pass through
the propeller stage. It is believed that a magnetic propeller acts in two such
stars CH Cyg and
  MWC 560. We review a diversity of manifestations of the propeller there. In
these systems in a quiescent state the accretion onto a white dwarf from the
strong enough wind of a companion star is suppressed by the magnetic field, and
the hot component luminosity is low. Since the gas stored in the envelope
eventually settles to the corotation radius the star-propeller reveals itself
by long-time outbursts, short-time brightness dips, strong amplitude
flickering, ejection of a powerful wind and jets. The envelope appears to be
stratified and inhomogeneous because of the shock pumping of the propeller. At
this stage, at which catastrophic transitions to the accretion stage and back
are possible, the release of energy and angular momentum of the white dwarf is
maximum. Using this property, we estimate the magnetic field strength of the
white dwarfs in CH Cyg and MWC 560 to be of order $10^8$ G.
  The most spectacular property of these stars - jets - is inherently connected
with the propeller. This suggests hydromagnetic models of jet acceleration.


title:
Light Curve and Spectral Models for the Hypernova SN 1998bw associated
  with GRB980425

abstract:
  A refined model for the unusual Type Ic supernova 1998bw, discovered as the
optical counterpart of GRB980425, is presented, and synthetic light curves and
spectra are compared with the observations. The first 30 days of the light
curve and the broad line features of the spectra can be reproduced with the
hydrodynamical model of the explosion of a 14$M_\odot$ C+O star, the core of a
star with initial mass 40$M_\odot$, assuming that the explosion was very
energetic (kinetic energy $E_{\rm K} = 5 \times 10^{52}$ erg) and that
0.4$M_\odot$ of $^{56}$Ni were synthesized. At late times, however, the
observed light curve tail declines more slowly than this energetic model, and
is in better agreement with a less energetic ($E_{\rm K} = 7 \times 10^{51}$
erg) one. This shift to a less energetic model may imply that the inner part of
the ejecta has higher density and lower velocities than the spherically
symmetric model with $E_{\rm K} = 5 \times 10^{52}$ erg, so that $\gamma$-rays
deposit more efficiently. We suggest that an aspherical explosion can produce
such a structure of the ejecta. We also study detailed nucleosynthesis
calculations for hyper-energetic supernova explosions and compare the yields
with those of normal supernovae.


title: The Influence of Central Black Holes on Gravitational Lenses

abstract:
  Recent observations indicate that many if not all galaxies host massive
central black holes. In this paper we explore the influence of black holes on
the lensing properties. We model the lens as an isothermal ellipsoid with a
finite core radius plus a central black hole. We show that the presence of the
black hole substantially changes the critical curves and caustics. If the black
hole mass is above a critical value, then it will completely suppress the
central images for all source positions. Realistic central black holes likely
have masses below this critical value. Even in such sub-critical cases, the
black hole can suppress the central image when the source is inside a zone of
influence, which depends on the core radius and black hole mass. In the
sub-critical cases, an additional image may be created by the black hole in
some regions, which for some radio lenses may be detectable with
high-resolution and large dynamic-range VLBI maps. The presence of central
black holes should also be taken into account when one constrains the core
radius from the lack of central images in gravitational lenses.


title: Power Spectrum Analysis of the ESP Galaxy Redshift Survey

abstract:
  We measure the power spectrum of the galaxy distribution in the ESO Slice
Project (ESP) galaxy redshift survey. We develope a technique to describe the
survey window function analytically, and then deconvolve it from the measured
power spectrum using a variant of the Lucy method. We test the whole
deconvolution procedure on ESP mock catalogues drawn from large N-body
simulations, and find that it is reliable for recovering the correct amplitude
and shape of $P(k)$ at $k> 0.065 h$ Mpc$^{-1}$. In general, the technique is
applicable to any survey composed by a collection of circular fields with
arbitrary pattern on the sky, as typical of surveys based on fibre
spectrographs. The estimated power spectrum has a well-defined power-law shape
$k^n$ with $n\simeq -2.2$ for $k\ge 0.2 h$ Mpc$^{-1}$, and a smooth bend to a
flatter shape ($n\simeq -1.6$) for smaller $k$'s. The smallest wavenumber,
where a meaningful reconstruction can be performed ($k\sim 0.06 h$ Mpc$^{-1}$),
does not allow us to explore the range of scales where other power spectra seem
to show a flattening and hints for a turnover. We also find, by direct
comparison of the Fourier transforms, that the estimate of the two-point
correlation function $\xi(s)$ is much less sensitive to the effect of a
problematic window function as that of the ESP, than the power spectrum.
Comparison to other surveys shows an excellent agreement with estimates from
blue-selected surveys. In particular, the ESP power spectrum is virtually
indistinguishable from that of the Durham-UKST survey over the common range of
$k$'s, an indirect confirmation of the quality of the deconvolution technique
applied.


title: Flaring and warping of the Milky Way disk: not only in the gas

abstract:
  This paper presents an investigation of the outer disk structure by using
data from a recent release of the 2 micron sky survey (2MASS).
  This 2MASS data show unambiguously that the stellar disk thickens with
increasing distance from the Sun. In one of the field (longitude l$=$240) there
is also strong evidence of an assymetry associated with the Galactic warp. This
flaring and warping of the stellar disk is very similar to the features
observed in the HI disk. The thickening of the stellar disk explains the drop
in density observed near the Galactic plane: stars located at lower
  Galactic latitudes are re-distributed to higher latitudes. It is no longer
necessary to introduce a disk cut-off to explain the drop in density. It is
also not clear how this flaring disk is distinct from the thick disk in the
outer disk region. At least, for lines of sight in the direction of the outer
disk, the thickening of the disk is sufficient to account for the excess in
star counts attributed by some models to the thick disk.


title: Signatures of exosolar planets in dust debris disks

abstract:
  We apply our recently elaborated, powerful numerical approach to the
high-resolution modeling of the structure and emission of circumstellar dust
disks, incorporating all relevant physical processes. Specifically, we examine
the resonant structure of a dusty disk induced by the presence of one planet.
It is shown that the planet, via resonances and gravitational scattering,
produces (1) an asymmetric resonant dust belt with one or more clumps
intermittent with one or a few off-center cavities; and (2) a central cavity
void of dust. These features can serve as indicators of a planet embedded in
the circumstellar dust disk and, moreover, can be used to determine its major
orbital parameters and even the mass of the planet. The results of our study
reveal a remarkable similarity with various types of highly asymmetric
circumstellar disks observed with the James Clerk Maxwell Telescope around
Epsilon Eridani and Vega. The proposed interpretation of the clumps in those
disks as being resonant patterns is testable -- it predicts the asymmetric
design around the star to revolve, viz., by 1.2--1.6 deg/yr about Vega and
0.6--0.8 deg/yr about Epsilon Eri.


title:
GRB990712: First Indication of Polarization Variability in a Gamma-ray
  Burst Afterglow

abstract:
  We report the detection of significant polarization in the optical afterglow
of GRB990712 on three instances 0.44, 0.70 and 1.45 days after the gamma-ray
burst, with (P, theta) being (2.9% +- 0.4%, 121.1 degr +- 3.5 degr), (1.2% +-
0.4%, 116.2 degr +- 10.1 degr) and (2.2% +- 0.7%, 139.2 degr +- 10.4 degr)
respectively. The polarization is intrinsic to the afterglow. The degree of
polarization is not constant, and smallest at the second measurement. The
polarization angle does not vary significantly during these observations. We
find that none of the existing models predict such polarization variations at
constant polarization angle, and suggest ways in which these models might be
modified to accommodate the observed behavior of this afterglow.


title: Integral field spectroscopy of the radio galaxy 3C 171

abstract:
  We have performed integral field spectroscopy of the radio galaxy 3C 171
(redshift z=0.238) with the TIGER instrument at the Canada France Hawaii
telescope in the Hbeta-[OIII]4959-5007 wavelength region. We present the
reconstructed Hbeta and [OIII] images and compare them to the HST and radio
maps. We discuss the variations of the [OIII]/Hbeta line ratio throughout the
nebulosity. We also analyze the velocity field in detail, in particular the
presence of several components. We find that the kinematics derived with
emission lines in the central region (inside 1 arcsec) are compatible with a
disk-like rotation of low amplitude (50 km/s). The continuum surface brightness
profile follows an r^{1/4} law, suggesting that the underlying galaxy is an
elliptical with an effective radius of 15 kpc.
  We have fit two components in the region centered 2.7 arcsec to the West and
of extension 3 arcsec^2. We find that the blueshifted component is an extension
of the central part, whereas the second one is redshifted by 600 km/s. In both
components, line ratios and FWHM are compatible with the presence of shocks
induced by jet-cloud interactions.


title: A Kinematic Model for the Narrow-Line Region in NGC 4151

abstract:
  We present a simple kinematic model for the narrow-line region (NLR) of the
Seyfert 1 galaxy NGC 4151, based on our previous observations of extended [O
III] emission with the Space Telescope Imaging Spectrograph (STIS). The model
is similar to a biconical radial outflow model developed for the Seyfert 2
galaxy NGC 1068, except that the bicone axis is tilted much more into our line
of sight (40 degrees out of the plane of the sky instead of 5 degrees), and the
maximum space velocities are lower (750 km/s instead of 1300 km/s. We find
evidence for radial acceleration of the emission-line knots to a distance of
160 pc, followed by deceleration that approaches the systemic velocity at a
distance of 290 pc (for a distance to NGC 4151 of 13.3 Mpc). Other similarities
to the kinematics of NGC 1068 are: 1) there are a number of high-velocity
clouds that are not decelerated, suggesting that the medium responsible for the
deceleration is patchy, and 2) the bicone in NGC 4151 is at least partially
evacuated along its axis. Together, these two Seyfert galaxies provide strong
evidence for radial outflow (e.g., due to radiation and/or wind pressure) and
against gravitational motion or expansion away from the radio jets as the
principal kinematic component in the NLR.


title:
Resolved Spectra of the Narrow-Line Region in NGC 1068. III. Physical
  Conditions in the Emission-Line Gas

abstract:
  The physical conditions in the inner narrow line region (NLR) of the Seyfert
2 galaxy NGC 1068 are examined using HST/STIS ultraviolet and optical spectra
and photoionization models. 1) The emission-line gas in the blueshifted
northeast quadrant is photoionized by the hidden central source out to 100 pc,
at which point we find evidence of another source of ionizing radiation, which
may be due to fast (1000 km/s) shocks resulting from the interaction of the
emission-line knots and the interstellar medium. 2) The gas in the redshifted
northeast quadrant is photoionized by continuum radiation that has been heavily
absorbed by gas within 30 pc of the central source. We find no strong evidence
of the effects of shocks in this component. 3) The redshifted emission-line gas
in the southwest quadrant is photoionized by unabsorbed continuum from the
central source, similar to that in the inner 100 pc of the blueshifted
northeast quadrant. Finally, 4) the emission-line spectrum of the blueshifted
southwest quadrant appears to be the superposition of highly ionized, tenuous
component within the ionization cone and gas outside the cone, the latter
photoionized by scattered continuum radiation. There are several implications
of this complicated physical scenario. First, the hidden active nucleus is the
dominant source of ionizing radiation in the inner NLR. The absorption of
continuum radiation along the line-of-sight to the redshifted northeast
quadrant may result from the intersection of the ionization cone and the plane
of the host galaxy. Finally, the evidence for shock-induced continuum radiation
at the point where the emission-line knots begin to decelerate indicates that
the deceleration is due to the interaction of emission-line knots with slower
moving gas.


title: An Open Singularity-Free Cosmological Model with Inflation

abstract:
  In the light of recent observations which point to an open universe
$(\Omega_{0}<1)$, we construct an open singularity-free cosmological model by
reconsidering a model originally constructed for a closed universe. Our model
starts from a nonsingular state called prematter, governed by an inflationary
equation of state $P=(\gamma_{p}-1)\rho$ where $\gamma_{p}$ $(\simeq 10^{-3})$
is a small positive parameter representing the initial vacuum dominance of the
universe. Unlike the closed models universe cannot be initially static hence,
starts with an initial expansion rate represented by the initial value of the
Hubble constant H(0). Therefore, our model is a two-parameter universe model
$(\gamma_{p},H(0))$. Comparing the predictions of this model for the present
properties of the universe with the recent observational results, we argue that
the model constructed in this work could be used as a realistic universe model.


title: Looking for High Energy Peaked Blazars

abstract:
  Blazars can be classified on the basis of their overall Spectral Energy
Distribution (SED). BL Lac objects are usually divided in LBL or HBL (Low or
High energy peaked BL Lacs), according to the peak frequency of the synchrotron
emission, if in the optical or UV-soft-X band respectively. FSRQs instead are
characterized by synchrotron peaks mainly at IR-optical frequencies, similarly
to LBLs. Here we report on recent BeppoSAX observations which are unveiling the
high energy branch of the range of synchrotron peak frequencies. Four new
"extreme" HBLs have been discovered, one of which (1ES 1426+428) peaks near or
above 100 keV, in a quiescent state.


title: How accurately can we measure weak gravitational shear?

abstract:
  With the recent detection of cosmic shear, the most challenging effect of
weak gravitational lensing has been observed. The main difficulties for this
detection were the need for a large amount of high quality data and the control
of systematics during the gravitational shear measurement process, in
particular those coming from the Point Spread Function anisotropy. In this
paper we perform detailed simulations with the state-of-the-art algorithm
developed by Kaiser, Squires and Broadhurst (KSB) to measure gravitational
shear. We show that for realistic PSF profiles the KSB algorithm can recover
any shear amplitude in the range $0.012 < |\gammavec |<0.32$ with a relative,
systematic error of $10-15%$. We give quantitative limits on the PSF correction
method as a function of shear strength, object size, signal-to-noise and PSF
anisotropy amplitude, and we provide an automatic procedure to get a reliable
object catalog for shear measurements out of the raw images.


title:
An Early-Time Infrared and Optical Study of the Type Ia Supernova 1998bu
  in M96

abstract:
  We present first-season infrared (IR) and optical photometry and spectroscopy
of the Type Ia Supernova 1998bu in M96. We also report optical polarimetry of
this event. SN1998bu is one of the closest type Ia Supernovae of modern times
and the distance of its host galaxy is well-determined. We find that SN1998bu
is both photometrically and spectroscopically normal. However, the extinction
to this event is unusually high, with Av=1.0 +/-0.11. We find that SN1998bu
peaked at an intrinsic Mv=-19.37 +/-0.23. Adopting a distance modulus of 30.25
(Tanvir et al. 1999) and using Phillips et al.'s (1999) relations for the
Hubble constant we obtain Ho=70.4 +/-4.3 km/s/Mpc. Combination of our IR
photometry with those of Jha et al. (1999) provides one of the most complete
early-phase IR light curves for a SN Ia published so far. In particular, SN
1998bu is the first normal SN Ia for which good pre-maximum (in the B band) IR
coverage has been obtained. It reveals that the J, H and K light curves peak
about 5 days earlier than the flux in the B-band curve.


title: Numerical Simulations of Weak Lensing Measurements

abstract:
  (Abridged) Weak gravitational lensing induces distortions on the images of
background galaxies, and thus provides a direct measure of mass fluctuations in
the universe. Since the distortions induced by lensing on the images of
background galaxies are only of a few percent, a reliable measurement demands
very accurate galaxy shape estimation and a careful treatment of systematic
effects. Here, we present a study of a shear measurement method using detailed
simulations of artificial images. The images are produced using realisations of
a galaxy ensemble drawn from the HST Groth strip. We consider realistic
observational effects including atmospheric seeing, PSF anisotropy and
pixelisation, incorporated in a manner to reproduce actual observations with
the William Herschel Telescope. By applying an artificial shear to the
simulated images, we test the shear measurement method proposed by Kaiser,
Squires & Broadhurst (1995, KSB). Overall, we find the KSB method to be
reliable with several provisos. To guide future weak lensing surveys, we study
how seeing size, exposure time and pixelisation affect the sensitivity to
shear. In addition, we study the impact of overlapping isophotes of neighboring
galaxies, and find that this effect can produce spurious lensing signals on
small scales. We discuss the prospects of using the KSB method for future, more
sensitive, surveys. Numerical simulations of this kind are a required component
of present and future analyses of weak lensing surveys.


title:
Collective Modes in Neutrino `Beam' Electron-Positron Plasma
  Interactions

abstract:
  We derive semiclassical neutrino-electron transport equations in the
collisionless (Vlasov) limit from the coupled Dirac equations, incorporating
the charged and neutral weak current-current as well as electromagnetic
interactions. A corresponding linear response theory is derived. In particular,
we calculate the response functions for a variety of beam-plasma geometries,
which are of interest in a supernova scenario. We apply this to the study of
plasmons and to a new class of collective {\it pharon} resonance modes, which
are characterized by $\omega < q$. We find that the growth rates of the
unstable modes correspond to a strongly temperature ($\propto T_\nu^2T_e^3$)
and linearly momentum dependent e-folding length of about $10^{10}$ km under
typical conditions for Type II supernovae. This appears to rule out such
long-wavelength collective modes as an efficient means of depositing neutrino
energy into the plasma sphere.


title: The optical polarization of spiral galaxies

abstract:
  Scattering of starlight by dust, molecules and electrons in spiral galaxies
will produce a modification of the direct intensity and a polarization in the
observed light. We treat the case where the distribution of scatterers can be
considered to be optically thin, and derive semi-analytic expressions for the
resolved intensity and polarized intensity for Thomson, Rayleigh, and more
general scattering mechanisms. These expressions are applied to a parametric
model spiral galaxies. It is further shown that in the case of Thomson and
Rayleigh scattering, and when scatterers and stars are distributed with
rotational symmetry, the total polarized flux depends on the inclination, $i$,
of the galactic axis to the line of sight according to a simple $\sin ^2 i$
law. This generalises the well known result for pointlike and spherical light
sources. By using a method based on spherical harmonics, we generalise this law
for more general mechanisms, and show that to good approximation, the $\sin ^2
i$ law still holds for the class of models considered.


title:
HST imaging survey of sub-mJy star-forming galaxies I: morphologies at z
  ~ 0.2

abstract:
  We present the first results of our HST WFPC2 F814W snapshot imaging survey,
targeting virtually all sub-mJy decimetric radio-selected star-forming
galaxies. The radio selection at ~1 GHz is free from extinction effects and the
radio luminosities are largely unaffected by AGN contamination, making these
galaxies ideal tracers of the cosmic star formation history. A sub-sample of 4
targets is presented here, selected at 1.4 GHz from the spectroscopically
homogenous and complete samples of Benn et al. (1993) and Hopkins et al.
(1999). The redshifts are confined to a narrow range around z~0.2, to avoid
differential evolution, with a radio luminosity close to L* where the galaxies
dominate the comoving volume-averaged star formation rate. We find clearly
disturbed morphologies resembling those of ultraluminous infrared galaxies,
indicating that galaxy interactions may be the dominant mechanism for
triggering star formation at these epochs. The morphologies are also clearly
different from coeval quasars and radiogalaxies, as found in star-forming
galaxies selected at other wavelengths. This may prove challenging for models
which propose direct causal links between AGN evolution and the cosmic star
formation history at these epochs. The asymmetries are typically much larger
than seen in the CFRS at similar redshifts, optical luminosities and
Halpha-derived star formation rates, indicating the possible existence of an
obscuration-related morphological bias in such samples.


title: The frequency of nuclear star-formation in Seyfert 2 galaxies

abstract:
  We investigate the detectability of starburst signatures in the nuclear
spectrum of Seyfert 2 galaxies by constructing spectral models in the
wavelength range 3500-4100A, combining the spectrum of a bulge population (of
age ~10Gyr) with that of younger stellar populations, spanning ages from ~3 Myr
to 1 Gyr. We also construct models combining the bulge template with a
power-law (PL) continuum, which is observed in some Seyfert 2's in polarized
light, contributing with typically 10-40% of the flux at 4020A. We conclude
that such continuum cannot be distinguished from that of a very young stellar
population (age < 10 Myr), contributing with less than ~0.02% of the mass of
the bulge. The models are compared with nuclear spectra - corresponding to a
radius of 200-300 pc at the galaxy - of 20 Seyfert 2 galaxies, in which we
specifically look for the signatures above of young to intermediate age stellar
populations. We find them in ten galaxies, thus 50% of the sample. But only in
six cases (30% of the sample) they can be attributed to young stars (age < 500
Myr): Mrk 1210, ESO 362-G8, NGC 5135, NGC 5643, NGC 7130 and NGC 7582. In the
remaining four cases, the signatures are due to intermediate age stars (~1
Gyr). We find a tendency for the young stars to be found more frequently among
the late type Seyfert's. This tendency is supported by a comparison between the
equivalent widths (W) of absorption lines of the nuclear spectra of the Seyfert
2's with those of normal galaxies of the same Hubble type.