title:
Is the Fast Evolution Scenario for Virialized Compact Groups Really
  Compelling? The Role of a Dark Massive Group Halo

abstract:
  We report on results of N-body simulations aimed at testing the hypothesis
that galaxies in X-ray emitting (i.e., virialized) Compact Groups are not
tidally stripped when they are embedded in a common, massive, quiescent dark
matter halo. To disentangle the effects of interactions from spurious effects
due to an incorrect choice of the initial galaxy model configurations, these
have been chosen to be tidally-limited King spheres, representing systems in
quasi-equilibrium within the tidal field of the halo. The potential of the halo
has been assumed to be frozen and the braking due to dynamical friction
neglected. Our results confirm the hypothesis of low rates of tidal stripping
and suggest a scenario for virialized Compact Group evolution in their
quiescent phases with only very moderate tidally induced galaxy evolution can
be generally expected. This implies the group stability, provided that the
dynamical friction timescales in these systems are not much shorter than the
Hubble time. We discuss briefly this possibility, in particular taking account
of the similarity between the velocity dispersions of a typical virialized
Compact Groups and the internal velocity dispersion of typical member galaxies.
A number of puzzling observational data on Compact Groups can be easily
explained in this framework. Other observations would be better understood as
the result of enhanced merging activity in the proto-group environment, leading
to virialized Compact Group formation through mergers of lower mass halos, as
predicted by hierarchical scenarios of structure formation.


title: The blazar GB1428+4217: a warm absorber at z=4.72?

abstract:
  BeppoSAX observations of the high redshift (z=4.72) blazar GB 1428+4217
confirm the presence of a complex soft X-ray spectrum first seen with the ROSAT
PSPC. Flattening below a rest frame energy of 5 keV can be accounted for by
absorption from an equivalent column density of (cold) gas with N_H ~ 8 x 10^22
cm^-2. Below 2 keV a (variable) excess of a factor ~ 20 above the extrapolated
absorbed spectrum is also detected. These findings are consistent with and
extend to higher redshifts the correlation between increasing soft X-ray
flattening and increasing z, previously pointed out for large samples of
radio-loud quasars. We propose that such features, including X-ray absorption,
soft excess emission as well as absorption in the optical spectra, can be
satisfactorily accounted for by the presence of a highly-ionized nuclear
absorber with column N_H ~ 10^23 cm^-2, with properties possibly related to the
conditions in the nuclear regions of the host galaxy. High energy X-ray
emission consistent with the extrapolation of the medium energy spectrum is
detected up to ~ 300 keV (rest frame).


title:
X-rays from the environment of supermassive black holes in active
  galaxies

abstract:
  X-rays are a powerful probe of the physical conditions in the nuclei of
active galaxies. We review the X-ray properties of radio-quiet AGN, LINERs and
ultraluminous IR galaxies based on observations carried out with the X-ray
satellite ROSAT. We then summarize the observations of giant X-ray flares from
non-active galaxies, interpreted as stellar tidal disruptions by supermassive
black holes.


title:
Detection of magnetic dipole lines of Fe XII in the ultraviolet spectrum
  of the dwarf star Epsilon Eri

abstract:
  We report observations of the dwarf star Epsilon Eri (K2 V) made with the
Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope
(HST). The high sensitivity of the STIS instrument has allowed us to detect the
magnetic dipole transitions of Fe XII at 1242.00A and 1349.38A for the first
time in a star other than the Sun. The width of the stronger line at 1242.00A
has also been measured; such measurements are not possible for the permitted
lines of Fe XII in the extreme ultraviolet. To within the accurcy of the
measurements, the N V and the Fe XII lines occur at their rest wavelengths.
Electron densities and line widths have been measured from other transition
region lines. Together, these can be used to investigate the non-thermal energy
flux in the lower and upper transition region, which is useful in constraining
possible heating processes. The Fe XII lines are also present in archival STIS
spectra of other G/K-type dwarfs.


title: On the origin of Gamma Ray Burst radiation

abstract:
  In the standard internal shock model, the observed X and gamma-ray radiation
is assumed to be produced by synchrotron emission. I will show that there are
serious problems with this interpretation, calling for other radiation
mechanisms, such as quasi-thermal Comptonization and/or Compton drag processes,
or both. These new ideas can have important consequences on the more general
internal shock scenario, and can be tested by future observations.


title:
Inhomogeneous Big Bang Nucleosynthesis: Upper Limit on Omega_b and
  Production of Lithium, Beryllium, and Boron

abstract:
  We examine the Big Bang nucleosynthesis (BBN) process in the presence of
small-scale baryon inhomogeneities. Primordial abundance yields for D, He4,
Li6, Li7, Be9, and B11 are computed for wide ranges of parameters
characterizing the inhomogeneities taking account of all relevant diffusive and
hydrodynamic processes. These calculations may be of interest due to (a) recent
observations of the anisotropies in the cosmic microwave background radiation
favoring slightly larger baryonic contribution to the critical density,
Omega_b, than allowed by a standard BBN scenario and (b) new observational
determinations of Li6 and Be9 in metal-poor halo stars. We find considerable
parameter space in which production of D and He4 is in agreement with
observational constraints even for Omega_b h^2 a factor 2-3 larger than the
Omega_b inferred from standard BBN. Nevertheless, in this parameter space
synthesis of Li7 in excess of the inferred Li7 abundance on the Spite plateau
results. Production of Li6, Be9, and B11 in inhomogeneous BBN scenarios is
still typically well below the abundance of these isotopes observed in the most
metal-poor stars to date thus neither confirming nor rejecting inhomogeneous
BBN. In an appendix we summarize results of a reevaluation of baryon diffusion
constants entering inhomogeneous BBN calculations.


title:
Numerical simulations of the Accretion-Ejection Instability in
  magnetised accretion disks

abstract:
  The Accretion-Ejection Instability (AEI) described by Tagger & Pellat (1999)
is explored numerically using a global 2d model of the inner region of a
magnetised accretion disk. The disk is initially currentless but threaded by a
vertical magnetic field created by external currents, and frozen in the flow.
In agreement with the theory a spiral instability, similar in many ways to
those observed in self-gravitating disks, develops when the magnetic field is,
within a factor of a few, at equipartition with the disk thermal pressure.
Perturbations in the flow build up currents and create a perturbed magnetic
field within the disk. The present non-linear simulations give good evidence
that such an instability can occur in the inner region of accretion disks, and
generate accretion of gas and vertical magnetic flux toward the central object,
if the equilibrium radial profiles of density and magnetic flux exceed a
critical threshold.


title:
X-Ray Line Profiles from Parameterized Emission Within an Accelerating
  Stellar Wind

abstract:
  Motivated by recent detections by the XMM and Chandra satellites of X-ray
line emission from hot, luminous stars, we present synthetic line profiles for
X-rays emitted within parameterized models of a hot-star wind. The X-ray line
emission is taken to occur at a sharply defined co-moving-frame resonance
wavelength, which is Doppler-shifted by a stellar wind outflow parameterized by
a `beta' velocity law, $v(r)=v_{\infty} (1-\R_{\ast}/r)^\beta$. Above some
initial onset radius $R_o$ for X-ray emission, the radial variation of the
emission filling factor is assumed to decline as a power-law in radius, $f(r)
\sim r^{-q}$. The computed emission profiles also account for continuum
absorption within the wind, with the overall strength characterized by a
cumulative optical depth $\tau_\ast$. In terms of a wavelength shift from
line-center scaled in units of the wind terminal speed $v_{\infty}$, we present
normalized X-ray line profiles for various combinations of the parameters
$\beta$, $\tau_\ast$, $q$ and $R_o$, and including also the effect of
instrumental broadening as characterized by a Gaussian with a parameterized
width $\sigma$. We discuss the implications for interpreting observed hot-star
X-ray spectra, with emphasis on signatures for discriminating between
``coronal'' and ``wind-shock'' scenarios. In particular, we note that in
profiles observed so far the substantial amount of emission longward of line
center will be difficult to reconcile with the expected attenuation by the wind
and stellar core in either a wind-shock or coronal model.


title: The broad band X-ray/hard X-ray spectra of accreting neutron stars

abstract:
  I review the energy spectra of low mass X-ray binaries (LMXBs) containing
weakly magnetized accreting neutron stars (NS), emphasizing the most recent
broad band (0.1-200 keV) spectral and timing observations performed by
Beppo-SAX and RXTE. Drawing on the similarities between black hole candidate
(BHC) and NS accretion, I discuss the accretion geometry and emission processes
of NS LMXBs.


title: Evolution of galaxies due to self-excitation

abstract:
  These lectures will cover methods for studying the evolution of galaxies
since their formation. Because the properties of a galaxy depend on its
history, an understanding of galaxy evolution requires that we understand the
dynamical interplay between all components. The first part will emphasize
n-body simulation methods which minimize sampling noise. These techniques are
based on harmonic expansions and scale linearly with the number of bodies,
similar to Fourier transform solutions used in cosmological simulations.
Although fast, until recently they were only efficiently used for small number
of geometries and background profiles. These same techniques may be used to
study the modes and response of a galaxy to an arbitrary perturbation. In
particular, I will describe the modal spectra of stellar systems and role of
damped modes which are generic to stellar systems in interactions and appear to
play a significant role in determining the common structures that we see. The
general development leads indirectly to guidelines for the number of particles
necessary to adequately represent the gravitational field such that the modal
spectrum is resolvable. I will then apply these same excitation to
understanding the importance of noise to galaxy evolution.


title: The redshifts of bright sub-mm sources

abstract:
  One of the key goals in observational cosmology over the next few years will
be to establish the redshift distribution of the recently-discovered sub-mm
source population. In this brief review I discuss and summarize the redshift
information which has been gleaned to date for the ~ 50 bright sub-mm sources
which have been uncovered via the six main classes of survey performed with
SCUBA on the JCMT over the last 2-3 years. Despite the biases inherent in some
of these surveys, and the crudeness of the redshift information available in
others, I conclude that all current information suggests that only 10-15 % of
luminous sub-mm sources lie at z < 2, and that the median redshift of this
population is z ~ 3. I suggest that such a high median redshift is arguably not
unexpected given current theories designed to explain the correlation between
black-hole mass and spheroid mass found at low redshift. In such scenarios,
peak AGN emission is expected to correspond to, or even to cause termination of
major star-formation activity in the host spheroid. In contrast, maximum dust
emission is expected to occur roughly half-way through the star-formation
process. Given that optical emission from bright quasars peaks at z = 2.5,
dust-emission from massive ellipticals might be reasonably expected to peak at
some point in the preceding ~ 1 Gyr, at z ~ 3. Confirmation or refutation of
this picture requires significantly-improved redshift information on bright
samples of SCUBA sources.


title:
A universal law for tails of density pdf's in multi-dimensional Burgers
  turbulence

abstract:
  Extending work of E, Khanin, Mazel and Sinai (1997 PRL 78:1904-1907) on the
one-dimensional Burgers equation, we show that density pdf's have universal
power-law tails with exponent -7/2. This behavior stems from singularities,
other than shocks, whose nature is quite different in one and several
dimensions. We briefly discuss the possibility of detecting singularities of
Navier-Stokes turbulence using pdf tails.


title: Chandra Observations of the X-Ray Jet of 3C273

abstract:
  We report results from Chandra observations of the X-ray jet of 3C~273 during
the calibration phase in 2000 January. The zeroeth-order images and spectra
from two 40-ks exposures with the HETG and LETG+ACIS-S show a complex X-ray
structure. The brightest optical knots are detected and resolved in the 0.2-8
keV energy band. The X-ray morphology tracks well the optical. However, while
the X-ray brightness decreases along the jet, the outer parts of the jet tend
to be increasingly bright with increasing wavelength. The spectral energy
distributions of four selected regions can best be explained by inverse Compton
scattering of (beamed) cosmic microwave background photons. The model
parameters are compatible with equipartition and a moderate Doppler factor,
which is consistent with the one-sidedness of the jet. Alternative models
either imply implausible physical conditions and energetics (the synchrotron
self-Compton model) or are sufficiently ad hoc to be unconstrained by the
present data (synchrotron radiation from a spatially or temporally distinct
particle population).


title: Extreme Ultraviolet Emission in the Fornax Cluster of Galaxies

abstract:
  We present studies of the Extreme Ultraviolet (EUV) emission in the Fornax
cluster of galaxies; a relatively nearby well-studied cluster with X-ray
emitting cluster gas and a very large radio source. We examine both the
large-scale (~size of the X-ray emitting cluster gas), and the small-scale
(<arcmin) emission.
  We find that this cluster has large-scale diffuse EUV emission. However, at
the sensitivity level of the existing EUVE data, this emission is due entirely
to the low energy tail of the X-ray emitting gas. We have also examined
small-scale structures in raw EUVE images of this cluster. We find that
small-scale irregularities are present in all raw Deep Survey images as a
result of small-scale detector effects. These effects can be removed by
appropriate flat-fielding. After flat-fielding, the Fornax cluster still shows
a few significant regions of small-scale EUV enhancement. We find that these
are emission from stars and galaxies in the field. We find that at existing
levels of sensitivity, there is no excess EUV emission in the cluster on either
large or small scales.


title: Egret (GeV) Blazars

abstract:
  The EGRET instrument on the Compton Gamma Ray Observatory (1991-2000) has
positively detected high energy gamma-ray emission from more than 67 active
galaxies of the blazar class. The majority of the EGRET blazars are
flat-spectrum radio quasars, which are characterized by inferred isotropic
luminosities often as high as 3E49 ergs/s. The remainder are BL Lac objects,
some of which have been detected at TeV energies (> 250 GeV) by ground-based
atmospheric Cherenkov telescopes. One of the remarkable characteristics
observed in blazars is that the gamma-ray luminosity often dominates the
bolometric power in these sources. The detection of blazars by EGRET has
undoubtedly been one of the highlights of the mission, and has forever impacted
upon our understanding of the emission mechanisms in these objects. In this
article, we summarize the properties of EGRET blazars, and review the
constraints that the EGRET observations place on the various models of
gamma-ray production in these sources.


title: The temperature-mass relation in magnetized galaxy clusters

abstract:
  We use cosmological, magneto-hydrodynamic simulations of galaxy clusters to
quantify the dynamical importance of magnetic fields in these clusters. The
set-up of initial magnetic field strengths at high redshifts is chosen such
that observed Faraday-rotation measurements in low-redshift clusters are well
reproduced in the simulations. We compute the radial profiles of the
intracluster gas temperature and of the thermal and magnetic pressure in a set
of clusters simulated in the framework of an Einstein-de Sitter and a
low-density, spatially-flat CDM cosmological model. We find that, for a
realistic range of initial magnetic field strengths, the temperature of the
intracluster gas changes by less than $\approx5%$.


title: High-mass X-ray binaries and OB-runaway stars

abstract:
  High-mass X-ray binaries (HMXBs) represent an important phase in the
evolution of massive binary systems. HMXBs provide unique diagnostics to test
massive-star evolution, to probe the physics of radiation-driven winds, to
study the process of mass accretion, and to measure fundamental parameters of
compact objects. As a consequence of the supernova explosion that produced the
neutron star (or black hole) in these systems, HMXBs have high space velocities
and thus are runaways. Alternatively, OB-runaway stars can be ejected from a
cluster through dynamical interactions. Observations obtained with the
Hipparcos satellite indicate that both scenarios are at work. Only for a
minority of the OB runaways (and HMXBs) a wind bow shock has been detected.
This might be explained by the varying local conditions of the interstellar
medium.


title: A Differential Spectroscopic Analysis of 16 Cygni A and B

abstract:
  We utilize high-resolution, high signal-to-noise spectra to perform a
differential analysis of Fe abundances in the common proper-motion pair 16 Cyg
A and B. We confirm that both stars are slightly metal-rich compared to the
Sun, and we show for the first time that the primary is enhanced in Fe relative
to the secondary by a significant amount. We find Delta[Fe/H]=+0.025\pm0.009.
This tends to support the ``self-pollution'' scenario proposed by Gonzalez
(1998), though lack of a complete understanding of small primordial metallicity
variations among binaries and open cluster members prevents a definitive
conclusion.


title:
The optical emission lines as a probe of state transitions in black-hole
  candidates

abstract:
  Optical spectroscopic studies of emission lines in black-hole candidates can
help us investigate state transitions in those systems. Changes in the optical
line profiles reflect changes in the geometry of the accretion flow, usually
associated with X-ray state transitions in the inner region. We identify at
least four optical states in the black-hole candidate GRO J1655-40 in outburst,
and two optical states in GX339-4.


title: Spatially Varying X-ray Synchrotron Emission in SN 1006

abstract:
  A growing number of both galactic and extragalactic supernova remnants show
non-thermal (non-plerionic) emission in the X-ray band. New synchrotron models,
realized as SRESC and SRCUT in XSPEC 11, which use the radio spectral index and
flux as inputs and include the full single-particle emissivity, have
demonstrated that synchrotron emission is capable of producing the spectra of
dominantly non-thermal supernova remnants with interesting consequences for
residual thermal abundances and acceleration of particles. In addition, these
models deliver a much better-constrained separation between the thermal and
non-thermal components, whereas combining an unconstrained powerlaw with modern
thermal models can produce a range of acceptable fits. While synchrotron
emission can be approximated by a powerlaw over small ranges of energy, the
synchrotron spectrum is in fact steepening over the X-ray band. Having
demonstrated that the integrated spectrum of SN 1006, a remnant dominated by
non-thermal emission, is well described by synchrotron models I now turn to
spatially resolved observations of this well studied remnant. The synchrotron
models make both spectral and spatial predictions, describing how the
non-thermal emission varies across the remnant. Armed with spatially resolved
non-thermal models and new thermal models such as VPSHOCK we can now dissect
the inner workings of SN 1006.


title:
Transmission Spectra as Diagnostics of Extrasolar Giant Planet
  Atmospheres

abstract:
  Atmospheres of transiting extrasolar giant planets (EGPs) such as HD 209458 b
must impose features on the spectra of their parent stars during transits;
these features contain information about the physical conditions and chemical
composition of the atmospheres. The most convenient observational index showing
these features is the ``spectrum ratio'', defined as the wavelength-dependent
ratio of spectra taken in and out of transit. I describe a model that estimates
this ratio and its dependence upon parameters of the planetary atmosphere,
including its cloud structure, temperature, chemical composition, and wind
fields. For giant planets in close orbits, the depths of atomic and molecular
features in the spectrum ratio may be as large as 0.001. Observations in
visible and near-IR wavelengths using existing and planned spectrographs should
be adequate to detect these features, and to provide some diagnostics of the
conditions within the planetary atmosphere. I give numerous examples of such
diagnostics, and I discuss their practicality.


title:
Molecular Gas in Infrared-Excess, Optically-Selected QSOs and the
  Connection with Infrared Luminous Galaxies

abstract:
  The initial results of a millimeter (CO) survey of infrared-excess,
optically-selected quasars from the Palomar-Green (PG) Bright Quasar Survey
(BQS) with redshifts in the range 0.04 < z < 0.17 are presented. These
observations represent the first step towards establishing with a complete
sample whether or not quasi-stellar objects (QSOs) reside in molecular gas-rich
galaxies, as well as towards determining how the infrared and molecular gas
properties of QSOs compare with those of ultraluminous infrared galaxies
(ULIGs), which are a possible evolutionary precursor of QSOs. The sample
consists of QSOs having absolute blue magnitudes, M_B <~ -22.0, and infrared
excesses, L_IR (8-1000 um) /L_bbb (0.1-1.0 um) >0.36, where the contribution to
the bolometric luminosity of infrared thermal dust emission for all PG QSOs is
typically 20--40%. Six out of 10 of the QSOs observed are detected in the
CO(1-0) emission line; two detections confirm previous, less sensitive
detections of CO(1-0) in PG 1613+658 and PG 0838+770, and four additional QSOs
are detected for the first time (PG 1119+120, PG 1351+640, PG 1415+451, and PG
1440+356). These six detections, plus two previous detections of CO in IZw1 and
Mrk 1014, bring the total number of 0.04 < z < 0.17 infrared-excess PG QSOs
detected in CO to date to eight, and provide possible evidence that, in
addition to fueling star formation, molecular gas may also serve as a primary
source of fuel for QSO activity...


title: A Three Micron Survey of the Chamaeleon I Dark Cloud

abstract:
  We describe an L-band photometric survey of 0.5 square deg of the Cha I dark
cloud. The survey has a completeness limit of L < 11.0. Our survey detects 124
sources, including all known pre-main sequence stars with L < 11. The fraction
of sources with near-IR excess emission is 58% +- 4% for K = 9-11. Cha I
sources have bluer H-K and K-L colors than pre-main sequence stars in
Taurus-Auriga. These sources also have a strong correlation between EW(H-alpha)
and K-L. Stars with K-L < 0.6 have weak H-alpha emission; stars with K-L > 0.6
have strong H-alpha emission. Because many Cha I sources are heavily reddened,
this division between weak emission T Tauri stars and classical T Tauri stars
occurs at a redder K-L than in Taurus-Auriga.


title:
The spatial distribution of O-B5 stars in the solar neighborhood as
  measured by Hipparcos

abstract:
  We have developed a method to calculate the fundamental parameters of the
vertical structure of the Galaxy in the solar neighborhood from trigonometric
parallaxes alone. The method takes into account Lutz-Kelker-type biases in a
self-consistent way and has been applied to a sample of O-B5 stars obtained
from the Hipparcos catalog. We find that the Sun is located 24.2 +/- 1.7
(random) +/- 0.4 (systematic) pc above the galactic plane and that the disk
O-B5 stellar population is distributed with a scale height of 34.2 +/- 0.8
(random) +/- 2.5 (systematic) pc and an integrated surface density of (1.62 +/-
0.04 (random) +/- 0.14 (systematic)) 10^{-3} stars pc^{-2}. A halo component is
also detected in the distribution and constitutes at least ~5% of the total
O-B5 population. The O-B5 stellar population within ~100 pc of the Sun has an
anomalous spatial distribution, with a less-than-average number density. This
local disturbance is probably associated with the expansion of Gould's belt.


title: Multi-transition study and new detections of class II methanol masers

abstract:
  We have used the ATNF Mopra antenna and the SEST antenna to search in the
directions of several class II methanol maser sources for emission from six
methanol transitions in the frequency range 85-115 GHz. The transitions were
selected from excitation studies as potential maser candidates. Methanol
emission at one or more frequencies was detected from five of the maser
sources, as well as from Orion KL. Although the lines are weak, we find
evidence of maser origin for three new lines in G345.01+1.79, and possibly one
new line in G9.62+0.20.
  The observations, together with published maser observations at other
frequencies, are compared with methanol maser modelling for G345.01+1.79 and
NGC6334F. We find that the majority of observations in both sources are
consistent with a warm dust (175 K) pumping model at hydrogen density ~10^6
cm^-3 and methanol column density ~5 x 10^17 cm^-2. The substantial differences
between the maser spectra in the two sources can be attributed to the geometry
of the maser region.


title: Narrow Moving Fe K-alpha lines from magnetic flares in AGN

abstract:
  We point out that luminous magnetic flares, thought to occur in standard AGN
accretion disks, cannot be located much higher than few pressure scale heights
above the disk. Using this fact, we estimate the fraction of the disk surface
illuminated by a typical flare. This fraction turns out to be very small for
geometrically thin disks, which implies that the instantaneous Fe K-alpha
emission line from a specific magnetic flare is narrow. The line is red- or
blue-shifted depending on the position of the observer relative to the flare
and sweeps across the line band with time. We present several examples of
theoretical time-resolved line profiles from such flares for a non-rotating
black hole. The observations of such moving features with future X-ray
telescopes will present a powerful test of the accretion disk geometry and may
also test General Relativity in the strong field limit.


title:
Measuring the brightness temperature distribution of extragalactic radio
  sources with space VLBI

abstract:
  We have used VSOP space very long baseline interferometry observations to
measure the brightness temperature distribution of a well-defined sub-set of
the Pearson-Readhead sample of extragalactic radio sources. VLBI which is
restricted to Earth-diameter baselines is not generally sensitive to emitting
regions with brightness temperatures greater than approximately $10^{12}$ K,
coincidentally close to theoretical estimates of brightness temperature limits,
$10^{11} - 10^{12}$ K. We find that a significant proportion of our sample have
brightness temperatures greater than $10^{12}$ K; many have unresolved
components on the longest baselines, and some remain completely unresolved.
These observations begin to bridge the gap between the extended jets seen with
ground-based VLBI and the microarcsecond structures inferred from intraday
variability, evidenced here by the discovery of a relationship between intraday
variability and VSOP-measured brightness temperature, likely due to the effects
of relativistic beaming. Also, lower limits on jet Lorentz factors, estimated
from space VLBI observations, are starting to challenge numerical simulations
that predict low Lorentz factor jets.


title:
A study of possible temporal and latitudinal variations in the
  properties of the solar tachocline

abstract:
  Temporal variations of the structure and the rotation rate of the solar
tachocline region are studied using helioseismic data from the Global
Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI)
obtained during the period 1995--2000. We do not find any significant temporal
variation in the depth of the convection zone, the position of the tachocline
or the extent of overshoot below the convection zone. No systematic variation
in any other properties of the tachocline, like width, etc., is found either.
Possibility of periodic variations in these properties is also investigated.
Time-averaged results show that the tachocline is prolate with a variation by
about 0.02R_sun in its position. The depth of the convection zone or the extent
of overshoot does not show any significant variation with latitude.


title: Signal Characteristics from Electromagnetic Cascades in Ice

abstract:
  We investigate the development of electromagnetic cascades in ice using a
GEANT Monte Carlo simulation. We examine the Cherenkov pulse that is generated
by the charge excess that develops and propagates with the shower. This study
is important for the RICE experiment at the South Pole, as well as any test
beam experiment which seeks to measure coherent Cherenkov radiation from an
electromagnetic shower.


title:
Probability of Detecting a Planetary Companion during a Microlensing
  Event

abstract:
  The probability of detecting a planetary companion of a lensing star during a
microlensing event toward the Galactic center, averaged over all relevant event
and galactic parameters, when the planet-star mass ratio $q=0.001$ has a
maximum exceeding 10% at an orbit semimajor axis $a$ near 1.5 AU for a uniform
distribution of impact parameters. The maximum probability is raised to more
than 20% for a distribution of source-lens impact parameters that is determined
by the efficiency of event detection. The averaging procedures are carefully
defined, and they determinine the dependence of the detection probabilities on
several properties of the Galaxy. The probabilities scale approximately as
$\sqrt{q}$. A planet is assumed detectable if the perturbation of the single
lens light curve exceeds $2/(S/N)$ for at least 20 consecutive photometric
points sometime during the event. Two meter telescopes with 60 second
integrations in I-band with high time resolution photometry throughout the
duration of an ongoing event are assumed. The probabilities are derived as a
function of $a$, where they remain significant for $0.6<a<10$ AU. Dependence of
the detection probabilities on the lens mass function, luminosity function of
the source stars as modified by extinction, distribution of source-lens impact
parameters, and the line of sight to the source are also determined, and the
probabilities are averaged over the distribution of the projected planet
position, the lens mass function, the distribution of impact parameters, the
lens and source distances as weighted by their distributions along the line of
sight and over the $I$-band apparent luminosity function of the sources. The
extraction of the probabilility as a function of $a$ for a particular $q$ from
empirical data is indicated.


title: On the Energy Required to Eject Processed Matter from Galaxies

abstract:
  We evaluate the minimum energy input rate that starbursts require for
expelling their newly processed matter from their host galaxies. Special
attention is given to the pressure caused by the environment in which a galaxy
is situated, as well as to the intrinsic rotation of the gaseous component. We
account for these factors and for a massive dark matter distribution, and
develop a self-consistent solution for the interstellar matter gas
distribution. Our results are in excellent agreement with the results of Mac
Low & Ferrara (1999) for galaxies with a flattened disk-like ISM density
distribution and a low intergalactic gas pressure ($P_{IGM}/k$ $\leq $ 1
cm$^{-3}$ K). However, our solution also requires a much larger energy input
rate threshold when one takes into consideration both a larger intergalactic
pressure and the possible existence of a low-density, non-rotating, extended
gaseous halo component.


title:
Particle Identification by Multifractal Parameters in Gamma-Astronomy
  with the HEGRA-Cherenkov-Telescopes

abstract:
  Cherenkov images of air showers can also be classified using multifractal and
wavelet parameters, as compared to the conventional Hillas image parameters.
This technique was applied to the images recorded by the cameras of the
stereoscopic imaging air Cherenkov-telescopes operated by the HEGRA
collaboration. With respect to the identification of particles, the performance
of multifractal and wavelet parameters was examined using a data sample from
the observation of the active galaxy Mkn 501 that showed a high gamma-ray flux.
The multifractal parameters were also combined with the Hillas parameters using
a neural network approach in order to further improve the
gamma/hadron-separation.


title: Star Formation in Tidal Dwarf Galaxies

abstract:
  Tidal Dwarf Galaxies (TDGs) are objects presently forming from gas which has
been expelled from their parent galaxies during an interaction. We observed the
CO emission of a sample of 11 TDGs, of which 8 were detected. The CO is found
at the peak of the HI observations and has the same line velocity and width,
indicating that the molecular gas is forming in situ instead of being torn from
the parent galaxies. The presence of H$\alpha$ emission furthermore shows that
stars are forming from this molecular gas. In order to investigate star
formation in TDGs further, we compared their molecular gas content and star
formation rate (SFR), traced by H$\alpha$, to those of spiral galaxies and
classical dwarfs. The major difference between TDGs and classical dwarfs is the
lower metallicity of the latter. The star formation efficiency (SFR per
molecular gas mass) of TDGs lies in the range typical of spiral galaxies
indicating that star formation is proceeding in a normal fashion from molecular
gas.


title: Coronagraphic Survey for Companions of Stars within 8 pc

abstract:
  We present the technique and results of a survey of stars within 8 pc of the
Sun with declinations $\bf\delta > -35\arcdeg$ (J2000.00). The survey, designed
to find without color bias faint companions, consists of optical coronagraphic
images of the 1\arcmin field of view centered on each star and infrared direct
images with a 32\asc field of view. The images were obtained through the
optical Gunn $r$ and $z$ filters and the infrared J and K filters. The survey
achieves sensitivities up to four absolute magnitudes fainter than the
prototype brown dwarf, Gliese 229B. However, this sensitivity varies with the
seeing conditions, the intrinsic brightness of the star observed and the
angular distance from the star. As a result we tabulate sensitivity limits for
each star in the survey. We used the criterion of common proper motion to
distinguish companions and to determine their luminosities. In addition to the
brown dwarf Gliese 229B, we have identified 6 new stellar companions of the
sample stars. Since the survey began, accurate trigonometric parallax
measurements for most of the stars have become available. As a result some of
the stars we originally included should no longer be included in the 8 pc
sample. In addition, the 8 pc sample is incomplete at the faint end of the main
sequence complicating our calculation of the binary fraction of brown dwarfs.
We assess the sensitivity of the survey to stellar companions and to brown
dwarf companions of various masses and ages.


title: Evidence in Favour of IMF Variations

abstract:
  The stellar initial mass function (IMF) determines the relative number of
stars born at a given mass. Despite the tremendous effort to establish a
universal IMF, the astronomical literature offers a wealth of diverse evidence
for IMF variations. This review was prepared for a controversial debate at the
conference ``Starbursts -- Near and Far'' at Ringberg Castle, 2000, and gives a
one-sided portrayal in favour of IMF variations. I will summarise the empirical
evidence that the IMF varies with time, with environment, and for all stellar
masses. While I see no obvious systematic trend in most regions of our Galaxy,
there is at least an indication that the IMF is biased towards more massive
stars in the early universe and in starbursts.


title:
A radio continuum survey of the southern sky at 1420 MHz. Observations
  and data reduction

abstract:
  We describe the equipment, observational method and reduction procedure of an
absolutely calibrated radio continuum survey of the South Celestial Hemisphere
at a frequency of 1420 MHz. These observations cover the area 0h < R.A. < 24h
for declinations less than -10 degree. The sensitivity is about 50 mK T_B (full
beam brightness) and the angular resolution (HPBW) is 35.4', which matches the
existing northern sky survey at the same frequency.


title:
Lithium-Beryllium-Boron Evolution: From Meneguzzi, Audouze and Reeves
  1971 Up to Now

abstract:
  We review the main sources of LiBeB production and show that a primary
mechanism is at work in the early Galaxy involving both ejection and
acceleration of He, C and O at moderate energy, which by nuclear interaction
with
  H and He produce light isotopes. The precise measurement of the Be abundance
at [Fe/H] = -3.3 and of $^6Li$ in halo stars find an explanation in this
framework. Thus, the preservation of $^6Li$ in the atmosphere of metal poor
stars implied, points toward the fact the Spite plateau reflects the primordial
value of Li. Consequently, it can be used as a baryodensitometer.


title: On the Origin of the FeK$\alpha$ Line in the Seyfert 2 Galaxy NGC 7172

abstract:
  The Seyfert 2 Galaxy NGC 7172 was observed twice by BeppoSAX narrow field
instruments approximately one year apart. As found in previous observations,
the source is variable on short time scales (hours) by a factor of $\sim$30%,
confirming the presence of a type 1 nucleus at the center. A strong flux
variability (by a factor of 2) on a longer time scale was observed between the
two observations. Indeed, in November 1997, the lowest flux ever recorded was
detected by BeppoSAX. The broad band spectra obtained with the BeppoSAX narrow
field instruments show marginal evidence of a reflection component. This
structure could explain the very flat spectra previously observed in the 2-10
keV band. An FeK$\alpha$ line was also detected in both observations. The line
intensity appears to remain almost constant between the two observations even
if the associated large errors cannot exclude some variability. In order to
understand the problem of the origin of the line, data from previous
observations, performed with other satellites, were also used. The scenario
favored is one where the line is produced at a distance of approximatively 8
light years from the continuum source region, rather than having its origin in
the accretion disk. In the framework of the standard unified models for AGN,
this suggests that its origin is located in the molecular torus.


title: Variability and polarization in the inner jet of 3C395

abstract:
  We present new results on the parsec-scale jet of the quasar 3C395, derived
from VLBI polarization sensitive observations made in 1995.91 and 1998.50 at
8.4, 15.4 and 22.2 GHz. The observations show a complex one-sided jet extending
up to 20 mas, with a projected magnetic field essentially aligned with the
radio jet. The emission is strongly dominated, in total intensity and
polarization, by the core and the inner jet region (of ~3 mas length). We have
studied the details of this dominant region finding clear structural variations
during this ~2.5 years period, in contrast with the apparent quietness of the
jet structure inferred from lower resolution VLBI observations. We observe the
ejection of a new component from the core and variations in the degree of
polarization of the inner jet components. We estimate a high Faraday Rotation
Measure close to the core, with a strong decrease along the inner jet.


title: The VLT-VIRMOS Mask Manufacturing Unit

abstract:
  The VIRMOS Consortium has the task to design and manufacture two
spectrographs for ESO VLT, VIMOS (Visible Multi-Object Spectrograph) and NIRMOS
(Near Infrared Multi-Object Spectrograph). This paper describes how the Mask
Manufacturing Unit (MMU), which cuts the slit masks to be used with both
instruments, meets the scientific requirements and manages the storage and the
insertion of the masks into the instrument. The components and the software of
the two main parts of the MMU, the Mask Manufacturing Machine and the Mask
Handling System, are illustrated together with the mask material and with the
slit properties. Slit positioning is accurate within 15 micron, equivalent to
0.03 arcsec on the sky, while the slit edge roughness has an rms on the order
of 0.03 pixels on scales of a slit 5 arcsec long and of 0.01 pixels on the
pixel scale (0.205 arcsec). The MMU has been successfully installed during
July/August 2000 at the Paranal Observatory and is now operational for
spectroscopic mask cutting, compliant with the requested specifications.


title:
Multiwavelength Study of the Starburst Galaxy NGC 7714. II: The Balance
  between Young, Intermediate Age and Old Stars

abstract:
  We combine existing multiwavelength data (incl. an HST/GHRS UV spectrum, an
optical spectrum, far-IR, Xray and radio fluxes) with new HST/WFPC2 images,
near-IR photometry and K band spectroscopy. We use these data to constrain the
young, the intermediate age and the old stellar populations in the central 330
pc of the starburst galaxy NGC 7714. [...]
  We find that the young burst responsible for the UV light is only a small
part of an extended episode of enhanced star formation (SF) [...]. The mass of
young and intermediate age stars thus formed equals at least 10% of the mass
locked in pre-existing stars of the underlying galaxy nucleus [...]. The
spectrophotometric SF timescale is long compared to the ~110 Myr elapsed since
closest contact with NGC 7715. The trigger of the starburst remains elusive.
  NGC 7714 owes its brightness in the UV to a few low extinction lines of sight
towards young stars. [...] The different extinction estimates obtained from
different indicators result naturally from the coexistence of populations with
various ages and obscurations. The near-IR continuum image looks smoothest, as
a consequence of lower sensitivity to extinction and of a larger contribution
of old stars. We compare the nuclear properties of NGC 7714 with results from
studies in larger apertures. We emphasize that the global properties of
starburst galaxies are the result of the averaging over many lines of sight
with diverse properties in terms of obscuration and stellar ages.


title:
Limits on the cosmological abundance of supermassive compact objects
  from a search for multiple imaging in compact radio sources

abstract:
  Using Very Long Baseline Interferometry we have searched a sample of 300
compact radio sources for examples of multiple imaging produced by
gravitational lensing; no multiple images were found with separations in the
angular range 1.5--50 milliarcsec. This null result allows us to place a limit
on the cosmological abundance of intergalactic supermassive compact objects in
the mass range $\sim 10^{6}$ to $\sim 10^{8}$M$_{\odot}$; such objects cannot
make up more than $\sim 1%$ of the closure density (95% confidence). A
uniformly distributed population of supermassive black holes forming soon after
the Big Bang do not, therefore, contribute significantly to the dark matter
content of the Universe.


title: Z Cam stars: a particular response to a general phenomenon

abstract:
  We show that the disc instability model can reproduce all the observed
properties of Z Cam stars if the energy equation includes heating of the outer
disc by the mass-transfer stream impact and by tidal torques and if the
mass-transfer rate from the secondary varies by about 30% around the value
critical for stability. In particular the magnitude difference between outburst
maxima and standstills corresponds to observations, all outbursts are of the
inside-out type and can be divided into two classes: long (wide) and short
(narrow) outbursts, as observed. Mass transfer rate fluctuations should occur
in other dwarf novae but one can exclude variations similar to those observed
in magnetic systems (AM Her's and some DQ Her's) and some nova-like systems (VY
Scl's), in which \dot{M} become very small during low states; these would
produce mini-outburst which, although detectable, have never been observed.


title: Accretion Processes in the Nucleus of M31

abstract:
  The hypothesized supermassive black hole in the nucleus of M31 (which we
shall hereafter call M31*) has many features in common with Sgr A* at the
Galactic Center, yet they differ in several significant and important ways.
Though M31* is probably ten times heavier, its radio luminosity at 3.6 cm is
only one third that of Sgr A*. At the same time, M31* is apparently thousands
of times more luminous in X-rays than its Galactic Center counterpart. Thus, a
comparative study of these objects can be valuable in helping us to understand
the underlying physical basis for their activity. We show here that the
accretion model being developed for Sgr A* comprises two branches of solutions,
distinguished by the relative importance of cooling compared to compressional
heating at the radius $r_C$ where the ambient gas is captured by the black
hole. For typical conditions in the ISM, the initial temperature ($T[r_C]\sim
10^6-10^7$ K) sits on the unstable branch of the cooling function.
  Depending on the actual value of $T(r_C)$ and the accretion rate, the plasma
settles either onto a hot branch (attaining a temperature as high as $10^{10}
K$ or so at small radii) or a cold branch, in which $T$ drops to $\sim 10^4$ K.
Sgr A* is presumably a `hot' black hole. We show here that the VLA, UV and {\it
Chandra} observations of M31* reveal it to be a member of the `cold' black hole
family. We discuss several predicted features in the spectrum of M31* that may
be testable by future multi-wavelength observations, including the presence of
a prominent UV spike (from hydrogen line emission) that would be absent on the
hot branch.


title: Cosmic Rays and Particle Physics

abstract:
  The study of high energy cosmic rays is a diversified field of observational
and phenomenological physics addressing questions ranging from shock
acceleration of charged particles in various astrophysical objects, via
transport properties through galactic and extragalactic space, to questions of
dark matter, and even to those of particle physics beyond the Standard Model
including processes taking place in the earliest moments of our Universe. After
decades of mostly independent evolution of nuclear-, particle- and high energy
cosmic ray physics we find ourselves entering a symbiotic era of these fields
of research. Some examples of interrelations will be given from the perspective
of modern Particle-Astrophysics and new major experiments will briefly be
sketched.


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

abstract:
  We present new results related to the coupled evolution of a two giant planet
system embedded in a protoplanetary disk, in which a Saturn mass protoplanet is
trapped in an outer mean motion resonance with a Jupiter mass protoplanet. The
gaps opened in the disk by the two planets overlap, therefore the two planet
system exchanges angular momentum with the disk at the inner planet's Inner
Lindblad Resonances (ILRs) and at the outer planet Outer Lindblad Resonances
(OLRs). Since the torques are proportional to the square of the planet masses,
and since the inner planet is about three times more massive than the outer
one, the ILR torques are favored by a factor ~10 with respect to the one planet
case. In the case presented here, this leads to a positive differential
Lindblad torque and consequently an outwards migration. We briefly discuss the
long-term behavior of the system, which could account for the high
eccentricities of the extra-solar planets with semi-major axis a>0.2 AU.


title:
Numerical study of statistical properties of the lensing excursion
  angles

abstract:
  We present ray tracing simulations combined with sets of large N-body
simulations. Experiments were performed to explore, for the first time,
statistical properties of fluctuations in angular separations of nearby light
ray pairs (the so-called lensing excursion angle) induced by weak lensing by
large-scale structures. We found that the probability distribution function
(PDF) of the lensing excursion angles is not simply Gaussian but has an
exponential tail. It is, however, found that the tail, or more generally
non-Gaussian nature in the PDF has no significant impact on the weak lensing of
the CMB. Moreover, we found that the variance in the lensing excursion angles
predicted by the power spectrum approach is in good agreement with our
numerical results. These results demonstrate a validity of using the power
spectrum approach to compute lensing effects on the CMB.


title: Immersive 4D Interactive Visualization of Large-Scale Simulations

abstract:
  In dense clusters a bewildering variety of interactions between stars can be
observed, ranging from simple encounters to collisions and other mass-transfer
encounters. With faster and special-purpose computers like GRAPE, the amount of
data per simulation is now exceeding 1TB. Visualization of such data has now
become a complex 4D data-mining problem, combining space and time, and finding
interesting events in these large datasets. We have recently starting using the
virtual reality simulator, installed in the Hayden Planetarium in the American
Museum for Natural History, to tackle some of these problem. This work
(http://www.astro.umd.edu/nemo/amnh/) reports on our first ``observations'',
modifications needed for our specific experiments, and perhaps field ideas for
other fields in science which can benefit from such immersion. We also discuss
how our normal analysis programs can be interfaced with this kind of
visualization.


title:
A Comprehensive Statistical Analysis of the Gas Distribution in
  Lyman-limit and Damped Lyman-alpha Absorption Systems

abstract:
  In this paper we show how to use data on Lyman-limit and Damped Lyman-alpha
absorption systems to derive the hydrogen ionization fractions and the
distribution of the face-on total gas column density. We consider axially
symmetric, randomly oriented absorbers, ionized by an external background
radiation field in order to relate the face-on total gas distribution to that
of the neutral hydrogen observed along the line of sight. We devise a
statistical procedure based on the Maximum Likelihood criterion, that is able
to treat simultaneously data coming from different surveys and statistically
recovers the "true" column densities in the presence of large uncertainties:
this is especially important for Lyman-limit systems which leave an
unmeasurable residual flux at wavelengths shorter than the Lyman break. We make
use of simulated data to look for possible observational biases and extensively
test our procedure. For a large statistical sample of real data in the redshift
range [1.75,3.25] (collected from all published surveys) our Maximum Likelihood
procedure gives a power-law slope for the total hydrogen distribution of -2.7.
All together Lyman-limit systems therefore contain more gas than Damped
Lyman-alpha systems. Analysis of data at other redshifts shows that more
observations are needed to reach a compelling evidence for a cosmological
evolution of the slope of the gas distribution.


title: HST Time-Series Photometry of the Transiting Planet of HD 209458

abstract:
  We have observed 4 transits of the planet of HD 209458 using the STIS
spectrograph on HST. Summing the recorded counts over wavelength between 582 nm
and 638 nm yields a photometric time series with 80 s time sampling and
relative precision of about 1.1E-4 per sample. The folded light curve can be
fit within observational errors using a model consisting of an opaque circular
planet transiting a limb-darkened stellar disk. In this way we estimate the
planetary radius R_p = 1.347 +/- 0.060 R_Jup, the orbital inclination i = 86.68
+/- 0.14 degrees, the stellar radius R_* = 1.146 +/- 0.050 R_solar, and one
parameter describing the stellar limb darkening. Our estimated radius is
smaller than those from earlier studies, but is consistent within measurement
errors, and is also consistent with theoretical estimates of the radii of
irradiated Jupiter-like planets. Satellites or rings orbiting the planet would,
if large enough, be apparent from distortions of the light curve or from
irregularities in the transit timings. We find no evidence for either
satellites or rings, with upper limits on satellite radius and mass of 1.2
Earth radii and 3 Earth masses, respectively. Opaque rings, if present, must be
smaller than 1.8 planetary radii in radial extent. The high level of
photometric precision attained in this experiment confirms the feasibility of
photometric detection of Earth-sized planets circling Sun-like stars.


title:
Optical and Infrared Photometry of the Micro-Quasar GRO J1655-40 in
  Quiescence

abstract:
  We present BVIJK photometry of the black-hole candidate GRO J1655-40 in full
quiescence. We report a refined orbital period of 2.62191 +/- 0.00020 days. The
light curves are dominated by ellipsoidal variations from the secondary star.
We model the light curves with an upgraded code which includes a more accurate
treatment of limb darkening. Previous models containing a large cool disk are
ruled out, and indeed our data can be fit with a pure ellipsoidal light curve
without any disk contribution. In general agreement with previous results, we
derive a confidence region of the correlated quantities of inclination and mass
ratio, centered on an inclination of 70.2 +/ 1.9 degrees, and mass ratio 2.6
+/- 0.3, resulting in a primary mass M = 6.3 +/- 0.5 Mo (all 95% confidence).
The complex limits and errors on these values, and on the possible disk
contribution to the light curve, are discussed.


title: Observational Signatures of the First Stars

abstract:
  At present, there are several feasible observational probes of the first
stars in the universe. Here, we examine the constraints on early stellar
activity from the metallicity of the high-redshift Ly-$\alpha$ clouds, from the
effects of stellar ionizing photons on reionization and the cosmic microwave
background (CMB), and from the implications of gravitational microlensing
results for the presence of stellar remnants in galactic halos. We also discuss
whether the above signatures are consistent with each other, i.e., if they
reflect the same population of stars.


title: A Ray-Tracing Model of the Vela Pulsar

abstract:
  In the relativistic plasma surrounding a pulsar, a subluminal ordinary-mode
electromagnetic wave will propagate along a magnetic field line. After some
distance, it can break free of the field line and escape the magnetosphere to
reach an observer. We describe a simple model of pulsar radio emission based on
this scenario and find that applying this model to the case of the Vela pulsar
reproduces qualitative characteristics of the observed Vela pulse profile.


title:
Dust-penetrated morphology in the high-redshift universe: clues from NGC
  922

abstract:
  Results from the Hubble Deep Field (HDF) North and South show a large
percentage of high-redshift galaxies whose appearance falls outside traditional
classification systems. The nature of these objects is poorly understood, but
sub-mm observations indicate that at least some of these systems are heavily
obscured (Sanders 2000). This raises the intriguing possibility that a
physically meaningful classification system for high-redshift galaxies might be
more easily devised at rest-frame infrared wavelengths, rather than in the
optical regime. Practical realization of this idea will become possible with
the advent of the Next Generation Space Telescope (NGST). In order to explore
the capability of NGST for undertaking such science, we present NASA-IRTF and
SCUBA observations of NGC 922, a chaotic system in our local Universe which
bears a striking resemblance to objects such as HDF 2-86 (z=0.749) in the HDF
North. If objects such as NGC 922 are common at high-redshifts, then this
galaxy may serve as a local morphological `Rosetta stone' bridging low and
high-redshift populations. In this paper we demonstrate that quantitative
measures of galactic structure are recoverable in the rest-frame infrared for
NGC 922 seen at high redshifts using NGST, by simulating the appearance of this
galaxy at redshifts z=0.7 and z=1.2 in rest-frame K'. Our results suggest that
the capability of efficiently exploring the rest-wavelength IR morphology of
high-z galaxies should probably be a key factor in deciding the final choice of
instruments for the NGST.


title:
The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic
  Clouds. VI. Double-Mode Cepheids in the Large Magellanic Cloud

abstract:
  We present a sample of 76 double-mode Cepheids detected in the 4.5 square
degree area in the central part of the LMC. 19 stars from the sample pulsate in
the fundamental mode and the first overtone while 57 objects are the first and
second overtone pulsators.
  We analyze the period ratio of double-mode Cepheids and Fourier parameters of
decomposition of the light curves of these objects. We also present location of
different type Cepheids from the LMC in the color-magnitude diagram and show
the distribution of their ${V-I}$ color indices.


title: Detection of a light echo from SN1998bu

abstract:
  About 500d after explosion the light curve of the Type Ia SN1998bu suddenly
flattened and at the same time the spectrum changed from the typical nebular
emission to a blue continuum with broad absorption and emission features
reminiscent of the SN spectrum at early phases. We show that in analogy to
SN1991Tbu (Schmidt et al. 1994), this can be explained by the emergence of a
light echo from a foreground dust cloud. Based on a simple model we argue that
the amount of dust required can consistently explain the extinction which has
been estimated by completely independent methods. Because of the similar echo
luminosity but much higher optical depth of the dust in SN1998bu compared with
SN1991T, we expect that the echo ring size of SN1998bu grows faster than in
SN1991T. HST observations have indeed confirmed this prediction.


title: Nucleosynthesis in classical novae

abstract:
  A general review of the relevance of classical novae for the chemical
evolution of the Galaxy, as well as for Galactic radioactivity is presented. A
special emphasis is put on the pioneering work done by Jim Truran in this field
of research. The impact of recent developments in nuclear astrophysics on nova
nucleosynthesis, together with the prospects for observability of novae
radioactivities with the INTEGRAL satellite are discussed.


title:
The ultraviolet visibility and quantitative morphology of galactic disks
  at low and high redshift

abstract:
  We used ultraviolet (200 nm) images of the local spiral galaxies M33, M51,
M81, M100, M101 to compute morphological parameters of galactic disks at this
wavelength : half-light radius $r_{hl}$, surface brightness distributions,
asymmetries ($A$) and concentrations ($C_A$). The visibility and the evolution
of the morphological parameters are studied as a function of the redshift. The
main results are : local spiral galaxies would be hardly observed and
classified if projected at high redshifts (z $\ge$ 1) unless a strong
luminosity evolution is assumed. Consequently, the non-detection of large
galactic disks cannot be used without caution as a constraint on the evolution
of galatic disks. Spiral galaxies observed in ultraviolet appear more irregular
since the contribution from the young stellar population becomes predominent.
When these galaxies are put in a (log $A$ vs. log $C_A$) diagram, they move to
the irregul ar sector defined at visible wavelengths. Moreover, the log $A$
parameter is degenerate and cannot be used for an efficient classification of
morphological ultraviolet types. The analysis of high redshift galaxies cannot
be carried out in a reliable way so far and a multi-wavelength approach is
required if one does not want to misinterpret the data.


title:
Globular cluster systems II: On the formation of old globular clusters
  and their sites of formation

abstract:
  We studied the metal-poor globular cluster (GC) populations of a large
variety of galaxies (47 galaxies spanning about 10mag in absolute brightness)
and compared their mean [Fe/H] with the properties of the host galaxies. The
mean [Fe/H] of the systems lie in the -1.65<[Fe/H]<-1.20 range (74% of the
population). Using only GC systems with more than 6 objects detected, 85% of
the population lie within -1.65<[Fe/H]<-1.20. The relation between the mean
[Fe/H] of the metal-poor GC systems and the Mv of their host galaxies presents
a very low slope which includes zero. An analysis of the correlation of the
mean [Fe/H] with other galaxy properties also leads to the conclusion that no
strong correlation exists. The lack of correlation suggests a formation of all
metal-poor GC in similar gas fragments. A weak correlation might exist between
mean [Fe/H] of the metal-poor GC and host galaxy metallicity. This would imply
that some fragments in which metal-poor GC formed were already embedded in the
larger dark matter halo of the final galaxy (as oppose to being independent
satellites that were accreted later). Our result suggests a homogeneous
formation of metal-poor GC in all galaxies, in typical fragments of masses
around 10^9-10^10 solar masses with very similar metallicities, compatible with
hierarchical formation scenarios for galaxies. We compared the mean [Fe/H] of
the metal-poor GC populations with the typical metallicities of high-z objects.
If we add the constraint that GC need a high column density of gas to form,
DLAs are the most likely sites for the formation of metal-poor GC populations.


title: Spectral evidence for a powerful compact jet from XTE J1118+480

abstract:
  We present observations of the X-ray transient XTE J1118+480 during its
Low/Hard X-ray state outburst in 2000, at radio and sub-millimetre wavelengths
with the VLA, Ryle Telescope, MERLIN and JCMT. The high-resolution MERLIN
observations reveal all the radio emission (at 5 GHz) to come from a compact
core with physical dimensions smaller than 65*d(kpc) AU. The combined radio
data reveal a persistent and inverted radio spectrum, with spectral index
\~+0.5. The source is also detected at 350 GHz, on an extrapolation of the
radio spectrum. Flat or inverted radio spectra are now known to be typical of
the Low/Hard X-ray state, and are believed to arise in synchrotron emission
from a partially self-absorbed jet. Comparison of the radio and sub-millimetre
data with reported near-infrared observations suggest that the synchrotron
emission from the jet extends to the near-infrared, or possibly even optical
regimes. In this case the ratio of jet power to total X-ray luminosity is
likely to be P_J/L_X >> 0.01, depending on the radiative efficiency and
relativistic Doppler factor of the jet. Based on these arguments we conclude
that during the period of our observations XTE J1118+480 was producing a
powerful outflow which extracted a large fraction of the total accretion power.


title:
Rapid-Process Nucleosynthesis in Neutrino-Magneto-Centrifugally Driven
  Winds

abstract:
  We have studied whether the rotation and magnetic fields in neutrino-driven
winds can be key processes for the rapid-process (r-process) nucleosynthesis.
We have examined the features of a steady and subsonic wind solutions which
extend the model of Weber and Davis (1967), which is a representative solar
wind model. As a result, we found that the entropy per baryon becomes lower and
the dynamical timescale becomes longer as the angular velocity becomes higher.
These results are inappropriate for the production of the r-process nuclei. As
for the effects of magnetic fields, we found that a solution as a steady wind
from the surface of the proto-neutron star can not be obtained when the
strength of the magnetic field becomes $\ge$ $10^{11}$ G. Since the magnetic
field in normal pulsars is of order $10^{12}$ G, a steady wind solution might
not be realized there, which means that the models in this study may not be
adopted for normal proto-neutron stars. In this situation, we have little
choice but to conclude that it is difficult to realize a successful r-process
nucleosynthesis in the wind models in this framework.


title: Photometric and spectroscopic study of the young open cluster NGC 1893

abstract:
  We present uvby-beta CCD photometry of the field of the open cluster NGC
1893. Our photometry is deep enough to cover the complete main sequence B
spectral type. We identify ~50 very likely members of the cluster down to
spectral type B9-A0, some of which have much higher reddenings than the
average. We derive a color excess E(b-y) = 0.33+-0.03 and a dereddened distance
modulus V_0 - M_V = 13.9+-0.2. From the beta index, we identify several
candidates as emission-line stars, for which we have obtained spectroscopy.
Three of them display spectra corresponding to spectral type F, but showing
H-alpha in emission. Photometric measurements in this and previous studies
indicate strong variability. These characteristics show them to be
pre-main-sequence stars of spectral type F. We also identify two likely Herbig
Be stars. These results hint at the existence of a sizable pre-main-sequence
population in NGC 1893.


title: Self-Interacting Scalar Dark Matter and Higgs Decay

abstract:
  Self-interacting dark matter has been suggested in order to overcome the
difficulties of the Cold Dark Matter model on galactic scales. We argue that a
scalar gauge singlet coupled to the Higgs boson, leading to an invisibly
decaying Higgs, is an interesting candidate for this self-interacting dark
matter particle.


title: The Galactic Center Interstellar Medium: from ISO to FIRST

abstract:
  The Infrared Space Observatory (ISO) has shown the complexity of the Galactic
center (GC) Interstellar medium (ISM) detecting, not only large column
densities of warm molecular gas (H2), but the emission of neutral atoms and
ions of low ionization potential (CII, OI, SiII,...) that should arise in
shocked or photon-dominated regions (PDRs). In addition, ISO has also detected
emission from ions like SIII, NeII, ArII, or NII (in some clouds we have even
detected NeIII and OIII) that should arise from HII regions that were
previously unsuspected due to the non-detection of Hydrogen recombination
lines. Here we review some ISO results on the large scale study of the GC ISM
and in particular, on the heating mechanisms of the clouds. Although, shocks
should play an important role on the physics and chemistry of the GC ISM, ISO
shows that the effect of radiation on the heating of the gas cannot be ruled
out with the simple argument that the dust temperature is lower than that of
the gas.


title: Cross-Roads in Studies of Galaxy Evolution

abstract:
  Studies of galaxy evolution at optical and near-infrared wavelengths have
reached an interesting point in their historical development and the arrival of
a new millenium provides an appropriate occasion to review the overall
direction in which this subject is moving. The aim of this short essay is to
emphasize the qualitatively different datasets now arriving and the more
detailed and challenging scientific analyses needed for future progress.


title: The Hubble Constant from (CLASS) Gravitational Lenses

abstract:
  One of the main objectives of the Cosmic Lens All-Sky Survey (CLASS)
collaboration has been to find gravitational lens (GL) systems at radio
wavelengths that are suitable for the determination of time delays between
image pairs. The survey is now near completion and at least 18 GL systems have
been found. Here, I will discuss our efforts to measure time delays from
several of these systems with the ultimate aim of constraining the Hubble
Constant (H0). Thus far three CLASS GL systems (i.e. B0218+357, B1600+434 and
B1608+656) have yielded measurements of time delays, from which values of
H0=60-70 km/s/Mpc have been estimated. Although most GL systems give similar
values of H0, statistical and systematic uncertainties are still considerable.
To reduce these uncertainties, I will shortly mention two monitoring programs
that we are undertaking to (re)measure time delays in 15 CLASS GL systems and
address several important issues for the near future.


title: A Search for HI in E+A Galaxies

abstract:
  We present the results of HI line and radio continuum observations of five
nearby E+A galaxies. These galaxies have spectra that are dominated by a young
stellar component but lack the emission lines characteristic of significant,
on-going star formation. They are selected from a unique sample of 21 E+A's
identified by Zabludoff et al.(1996) in their spectroscopic search for E+A
galaxies using the Las Campanas Redshift Survey, where over 11,000 nearby
galaxies were examined. The five E+A galaxies span a range of environments:
three are in the field and two are in clusters. Only one system was detected in
HI emission, the field E+A galaxy EA1, with a total flux of 0.30 +/- 0.02 Jy
km/s and an HI mass of (3.5 +/- 0.2) 10^9 h^(-2) M_sun. The HI morphology and
kinematics of EA 1 suggest a galaxy-galaxy interaction, with a dynamical age of
about 6 x 10^8 h^(-1) yr inferred from the HI tail lengths and velocities. This
age estimate is consistent with the interpretation drawn from optical
spectroscopy that starbursts in E+A galaxies began (and subsequently ended)
within the last 10^9 yr. Our HI detection limits are such that if the other
E+A's in our sample had the HI properties of EA 1, we would have detected (or
marginally detected) them. We conclude that E+A galaxies have a range of HI
properties. None of the galaxies were detected in radio continuum emission,
with upper limits to the radio power of about 10^21 h^(-2) W/Hz. Our limits
exclude the possibility that these E+A's are dust-enshrouded massive starburst
galaxies, but are insufficient to exclude modest star formation rates of less
than a few h^(-2) M_sun per yr.


title:
Measuring the metric: a parametrized post-Friedmanian approach to the
  cosmic dark energy problem

abstract:
  We argue for a ``parametrized post-Friedmanian'' approach to linear
cosmology, where the history of expansion and perturbation growth is measured
without assuming that the Einstein Field Equations hold. As an illustration, a
model-independent analysis of 92 type Ia supernovae demonstrates that the curve
giving the expansion history has the wrong shape to be explained without some
form of dark energy or modified gravity. We discuss how upcoming lensing,
galaxy clustering, cosmic microwave background and Lyman alpha forest
observations can be combined to pursue this program, which generalizes the
quest for a dark energy equation of state, and forecast the accuracy that the
proposed SNAP satellite can attain.


title: Emissive mechanism of radio flat spectrum on X-ray binaries

abstract:
  We present that the radio emission with flat spectrum in X-ray binaries comes
from the synchrotron emission of relativistic electrons in the high energy tail
of hot electrons in continuous conical jet. The jet is assumed to be produced
by the advection-dominated accretion flow (ADAF) and maintains ion and electron
temperatures constant in the case of adiabatic steady conical expansion. The
flat spectrum is result of self-absorbed synchrotron emission by relativistic
thermal electrons. We find that the critical frequency at which the radiation
becomes optically thin declines along the jet. The emission observed at higher
frequencies originates at smaller distance, closer to the base of the jet. The
highest cut-off frequency of the flat spectrum is at the base of the jet, and
is determined by the physics of the ADAF and the position of the jet formation.
We assert that it is a characteristic of the ADAF in black hole X-ray binaries
that a continuous steady outflow is formed and causes the observed flat
spectrum in the low/hard state. The observed synchrotron emission consists of
the flat spectral component from the jet and the steep spectral component from
the ADAF. The flat spectral component extends from infrared to radio
wavelengths, while the steep spectral component with the 2/5 spectral slope
extends from infrared to shorter wavelengths, it will be dominated by the
thermal emission from companion star.


title: The Hubble Deep Field in the Far Ultraviolet

abstract:
  Results from a recent HST survey of field galaxies at wavelengths 1600
Angstroms and 2400 Angstroms are be presented. The data are used to constrain
the fraction of Lyman-continuum radiation that escapes from galaxies at
redshifts z ~ 1. The combined UV-IR photometry for HDF galaxies is also used to
investigate whether low-mass starburst galaxies dominate the field-galaxy
population at redshift z ~1. The relative lack of objects with the colors of
faded bursts suggests that star-formation is largly quiescent rather than
bursty or episodic.


title: Detectable Signals from Mergers of Compact Stars

abstract:
  Merging neutron stars and neutron star-black holes binaries are powerful
sources of gravitational waves. They have also been suggested as possible
sources of cosmic gamma-ray bursts and are discussed as sites for the formation
of r-process elements. Whereas the first aspect is undoubtable, the latter two
are very uncertain. The current status of our knowledge and of the numerical
modeling is briefly reviewed and the results of simulations are critically
discussed concerning their significance and implications for potentially
observable signals.


title: A study of the old galactic star cluster Berkeley 32

abstract:
  We present new CCD photometry of the distant old open star cluster Berkeley
32 in Johnson V and Cousins I passbands. A total of about 3200 stars have been
observed in a field of 13X13 arcmin**2. The colour-magnitude diagram in V,
(V-I) has been generated down to V = 22 mag. A broad but well defined main
sequence is clearly visible. Some blue stragglers, a well developed subgiant
branch and a Red Clump are also seen. By fitting isochrones to this CMD as well
as to other CMDs available in the literature, and using the Red Clump location,
the reddening, distance and age of the star cluster have been determined. The
cluster has a distance of 3.3 kpc, its radius is about 2.4 pc; the reddening
E(B-V) is 0.08 mag and the age is 6.3 Gyr. By comparison with theoretical
isochrones, a metallicity of [Fe/H]= -0.2 dex has been estimated. We find a
much flatter mass function than what has been found for young clusters. If the
mass function is a power law dN/dm = const.*m**alpha, then we get alpha =
-0.5+-0.3 in the mass range 0.6-1.1 solar masses. This may be seen as a
signature of the highly evolved dynamical state of the cluster.


title:
Light Propagation in Inhomogeneous Universes II. Cosmological Parameter
  Survey

abstract:
  Using a multiple-lens plane algorithm, we study light propagation in
inhomogeneous universes, for 43 different COBE-normalized Cold Dark Matter
models, with various values of the density parameter Omega_0, cosmological
constant lambda_0, Hubble constant H_0, and rms density fluctuation sigma_8.
This is the largest cosmological parameter survey ever done in this field. We
performed a total of 3,798 experiments, each experiment consisting of
propagating a square beam of angular size 21.9'' x 21.9'' composed of 116,281
light rays from the observer up to redshift z=3. These experiments provide
statistics of the magnification, shear, and multiple imaging of distant
sources. The results of these experiments can be compared with observations,
and eventually help constraining the possible values of the cosmological
parameters. Additionally, they provide insight into the gravitational lensing
process and its complex relationship with the various cosmological parameters.


title:
On an Estimation of the Coronal Magnetic Field Strength from
  Spectrographic Observations in the Microwave Range

abstract:
  Observations of the solar radio emission in the microwave frequency range
show fine structures consisting of a number of the almost parallel narrow
frequency bands. We interpret these bands as the cyclotron harmonics plasma
emission. This emission is generated by the anisotropic electron beam, which
excites longitudinal waves on the normal Doppler effect resonance. Then the
longitudinal waves convert into the radio emission on the second harmonic of
the longitudinal waves frequency and sometimes into the fundamental one.
Estimations of the magnetic field strength made on the basis of such a model
give the values of the magnetic field in the microwave burst sources as ~
100-200 G. The estimations of density variations are also given.


title:
Cosmological Density and Power Spectrum from Peculiar Velocities:
  Nonlinear Corrections and PCA

abstract:
  We allow for nonlinear effects in the likelihood analysis of galaxy peculiar
velocities, and obtain ~35%-lower values for the cosmological density parameter
Om and the amplitude of mass-density fluctuations. The power spectrum in the
linear regime is assumed to be a flat LCDM model (h=0.65, n=1, COBE) with only
Om as a free parameter. Since the likelihood is driven by the nonlinear regime,
we "break" the power spectrum at k_b=0.2 h/Mpc and fit a power law at k>k_b.
This allows for independent matching of the nonlinear behavior and an unbiased
fit in the linear regime. The analysis assumes Gaussian fluctuations and
errors, and a linear relation between velocity and density. Tests using proper
mock catalogs demonstrate a reduced bias and a better fit. We find for the
Mark3 and SFI data Om_m=0.32+-0.06 and 0.37+-0.09 respectively, with
sigma_8*Om^0.6 = 0.49+-0.06 and 0.63+-0.08, in agreement with constraints from
other data. The quoted 90% errors include cosmic variance. The improvement in
likelihood due to the nonlinear correction is very significant for Mark3 and
moderately so for SFI. When allowing deviations from LCDM, we find an
indication for a wiggle in the power spectrum: an excess near k=0.05 and a
deficiency at k=0.1 (cold flow). This may be related to the wiggle seen in the
power spectrum from redshift surveys and the second peak in the CMB anisotropy.
A chi^2 test applied to modes of a Principal Component Analysis (PCA) shows
that the nonlinear procedure improves the goodness of fit and reduces a spatial
gradient of concern in the linear analysis. The PCA allows addressing spatial
features of the data and fine-tuning the theoretical and error models. It shows
that the models used are appropriate for the cosmological parameter estimation
performed. We address the potential for optimal data compression using PCA.


title:
Gamma-ray Bursts, Type Ib/c Supernovae and Star-forming Sites in Host
  Galaxies

abstract:
  The data on the location of gamma-ray bursts (GRBs) relative to their host
galaxies are used to derive the distribution of surface density of GRBs along
the galaxy radius. It is shown that the gradient of GRB surface density changes
abruptly near the half-light radius. In the central parts of galaxies the
distribution of GRBs resembles closely the luminosity distribution, while in
the outer parts the galactic surface brightness falls much steeper than the
GRBs density. The radial distribution of type Ib/c supernovae is investigated
on the basis of enlarged statistics. It is shown that SNe Ib/c do not differ
significantly from other types of supernovae and their distribution is more
similar to the one for recent star formation sites than that of GRBs. In spite
of the poor statistics of GRBs, the difference in the distributions of active
star formation regions and GRBs appears to be significant. We get the
Kolmogorov-Smirnov probability P_ks of only 4% that GRBs and star-forming sites
belong to the same distribution. The correlation of GRBs with the distribution
of dark matter in the outer parts of galaxies is not excluded.


title: High Energy X-Ray Emission in Clusters of Galaxies

abstract:
  Observations with the RXTE and SAX satellites have recently led to the
measurement of a second component in the spectra of several clusters of
galaxies which are known to have regions of extended radio emission. This new
component is quite likely nonthermal emission resulting from Compton scattering
of relativistic electrons by the cosmic microwave background. The nonthermal
X-ray and radio measurements yield the values of the mean intracluster magnetic
field, and relativistic electron density, for the first time in extragalactic
environments. These results have important consequences on issues such as the
origin of cosmic ray electrons and protons, their propagation modes in
clusters, and the effects of these particles and magnetic fields on the
intracluster gas. The observational results are reviewed, and some of their
direct implications are discussed, along with near-future prospects for
improved spectral and spatial measurements of nonthermal emission in clusters.


title: Stellar Encounters with the Beta Pictoris Planetesimal System

abstract:
  We use data from the Hipparcos Catalog and the Barbier-Brossat & Figon (2000)
catalog of stellar radial velocities to test the hypothesis that the Beta Pic
planetesimal disk was disrupted by a close stellar encounter. We trace the
space motions of 21,497 stars and discover 18 that have passed within 5 pc of
Beta Pic in the past 1 Myr. Beta Pic's closest encounter is with the K2III star
HIP 27628 (0.6 pc), but dynamically the most important encounter is with the
F7V star HIP 23693 (0.9 pc). We calculate the velocity and eccentricity changes
induced by the 18 perturbations and conclude that they are dynamically
significant if planetesimals exist in a Beta Pic Oort cloud. We provide a
first-order estimate for the evolutionary state of a Beta Pic Oort cloud and
conclude that the primary role of these stellar perturbations would be to help
build a comet cloud rather than destroy a pre-existing structure. The stellar
sample is 20% complete and motivates future work to identify less common close
interactions that would significantly modify the observed circumstellar disk.
For future radial velocity study we identify six stars in the Hipparcos Catalog
that may have approached Beta Pic to within 0.1 pc and therefore remain as
candidate disk perturbers.


title: Gravitational Settling of 22Ne in Liquid White Dwarf Interiors

abstract:
  The nuclear reactions that occur in the stellar progenitors of white dwarfs
(WDs) lead to an internal composition of 12C, 16O, and a ``contaminant''
nucleus, 22Ne. The 22Ne is produced by helium captures on 14N left from
hydrogen burning via the CNO cycle. By virtue of its two excess neutrons
(relative to the predominant A=2Z nuclei), a downward force of 2m_pg is exerted
on 22Ne in the WD interior. This biases its diffusive equilibrium, forcing 22Ne
to settle towards the center of the WD. We discuss the physics of the
gravitational settling when the WD is in the liquid state and the luminosity
generated by it. This modifies the cooling of WD's with masses in excess of a
solar mass. The current uncertainties in the microphysics even allow for
solutions where a 1.2M_\odot WD remains mostly liquid for a few Gyrs due to the
internal heating from 22Ne sedimentation. This highlights the need for an
accurate calculation of the inter-diffusion coefficient, especially in the
quantum liquid regime relevant for high mass WD's. There is also time in old,
liquid WD's (such as those found in cataclysmic variables and possibly in
accreting Type Ia progenitors) for partial settling.


title:
Do angular momentum induced ellipticity correlations contaminate weak
  lensing measurements?

abstract:
  Alignments in the angular momentum vectors of galaxies can induce large scale
correlations in their projected orientations. Such alignments arise from the
tidal torques exerted on neighboring proto-galaxies by the smoothly varying
shear field. Weak gravitational lensing can also induce ellipticity
correlations since the images of neighboring galaxies will be distorted
coherently by the intervening mass distribution. Comparing these two sources of
shape correlations, it is found that for current weak lensing surveys with a
median redshift of 1, the intrinsic signal is a contaminant on the order of
1-10% of the measured signal. However, for shallower surveys, the intrinsic
correlations dominate over the lensing signal. The distortions induced by
lensing are curl-free, whereas those resulting from intrinsic alignments are
not. This difference can be used to disentangle these two sources of
ellipticity correlations. When the distortions are dominated by lensing, as
occurs at high redshifts, the decomposition provides a valuable tool for
understanding properties of the noise and systematic errors.


title: Radio Galaxy Spectra

abstract:
  Radio spectra of radio galaxies are often ascribed a simple power law form
($S_{\nu} \propto \nu^{\alpha}$) with the spectral index, $\alpha$, being of
order -0.7. However, all radio galaxies deviate from this simple power law
behaviour. In this paper we derive simple expressions for the average
rest-frame spectra of FRI and FRII radio galaxies. These will be used to
describe the spectral curvature of the parent (FRI and FRII) populations in
models of radio source evolution.


title:
Polarization of the Cosmic Microwave Background from Non-Uniform
  Reionization

abstract:
  We study the signal in the Cosmic Microwave Background (CMB) polarization
anisotropy resulting from patchy reionization. It is well known that the
primordial polarization of the CMB is very sensitive to the details of
reionization. Combining a semi-analytic model of galaxy formation, in which the
optical depth to the reionization epoch is in the range 0.014 to 0.048, with a
high resolution N-body simulation we find that reionization generates a peak
with amplitude 0.05~0.15 \mu K at large angular scales. The position of this
peak reveals the size of the horizon at reionization, whilst its amplitude is a
measure of the optical depth to reionization. On small scales, ionized patches
prior to full reionization create a second order polarization signal due to the
coupling of the free electron density fluctuation with the quadrupole moment of
the temperature anisotropy. Careful study reveals that the coupling generates
the same power spectra for electric and magnetic modes, whose amplitudes of
polarization anisotropies from this process are predicted to be ~10nK. The
amplitude depends strongly on the total baryon density $\Omega_b$ and on the
spatial correlations of the free electron density in the ionized regions, and
weakly on the fraction of ionizing photons able to escape their source galaxy,
$f_{esc}$. The first- and second-order signals are therefore sensitive to the
details of how the reionization occurred. Detection of these signals will place
important constraints on the reionization history of the Universe.


title:
Large scale geometry and evolution of a universe with radiation pressure
  and cosmological constant

abstract:
  In view of new experimental results that strongly suggest a non-zero
cosmological constant, it becomes interesting to revisit the Friedman-Lemaitre
model of evolution of a universe with cosmological constant and radiation
pressure. In this paper, we discuss the explicit solutions for that model and
perform numerical explorations for reasonable values of cosmological
parameters. We also analyse the behaviour of redshifts in such models and the
description of ``very large scale geometrical features'' when analysed by
distant observers.


title: The low-mass IMF - deep star counts in the dSph galaxy Ursa Minor

abstract:
  We present a new study of deep star counts in the Local Group dwarf
spheroidal (dSph) in Ursa Minor. Both the luminosity function (LF) and the
colour-magnitude diagram (CMD) of the unevolved stars are compared with the LF
and CMD of the old, metal-poor globular cluster M92. The main sequence
locations and turn-offs are identical within the errors. Since we know from the
brighter evolved stars that the metallicities for these two disparate systems
are the same this implies that they also have equal ages. A direct comparison
of faint LFs is then equivalent to comparison of the low-mass stellar Initial
Mass Functions (IMF). We find that their LFs are identical within the
mass-range covered (~0.35 - 0.8 M_sun). The Ursa Minor dSph has one of the
highest apparent M/L ratios known in the Local Group, and is an extremely low
surface brightness external galaxy. M92 is a typical high surface brightness
globular cluster, with no apparent dark matter. These results lead to the
conclusion that the low-mass stellar IMF in systems that formed at high
redshift is independent of environment. Indeed, it is consistent with the
low-mass IMF in star-forming regions today.


title: Luminosity and mass function of galactic open clusters: I. NGC 4815

abstract:
  We present deep V and I photometry for the open cluster NGC 4815 and four
surrounding Galactic fields down to a limiting magnitude $V\sim25$. These data
are used to study cluster spatial extension by means of star counts, and to
derive the luminosity (LF) and mass function (MF). The radius turns out to be
$3.6\pm0.3 arcmin$ at V=19.0 level, whereas the mass amounts at $880\pm230
m_{\odot}$ down to V=20.8. From the color-magnitude diagram, we obtain the LFs
in the V and I bands, using both the standard histogram and an adaptive kernel.
After correction for incompleteness and field star contamination, the LFs have
been transformed into the present day mass functions (PDMF). The PDMFs from the
V and I photometry can be represented as a power-law with a slope $\alpha =
3.1\pm0.3$ and $\alpha = 2.9\pm0.3$ (the \cite{salp55} MF in this notation has
a slope $\alpha = 2.35$) respectively, in the mass range $2.5 \leq
\frac{m}{m_{\odot}} \leq 0.8$. Below this mass, the MF cannot be considered as
representative of the cluster IMF, as it is the result of the combined effect
of strong irregularities in the stellar background, probable internal dynamical
evolution of the cluster and/or interaction of the cluster with the dense
Galactic field. Unresolved binaries and mass segregation can only flatten the
apparent derived IMF, so we expect that the real IMF must be steeper than the
quoted slope by an unknown amount.


title:
Surface features, rotation and atmospheric variability of ultra cool
  dwarfs

abstract:
  Photometric I band light curves of 21 ultra cool M and L dwarfs are
presented. Variability with amplitudes of 0.01 to 0.055 magnitudes (RMS) with
typical timescales of an hour to several hours are discovered in half of these
objects. Periodic variability is discovered in a few cases, but interestingly
several variable objects show no significant periods, even though the
observations were almost certainly sensitive to the expected rotation periods.
It is argued that in these cases the variability is due to the evolution of the
surface features on timescales of a few hours. This is supported in the case of
2M1145 for which no common period is found in two separate light curves. It is
speculated that these features are photospheric dust clouds, with their
evolution possibly driven by rotation and turbulence. An alternative
possibility is magnetically-induced surface features. However, chromospheric
activity undergoes a sharp decrease between M7 and L1, whereas a greater
occurrence of variability is observed in objects later than M9, lending support
to the dust interpretation.


title: Magnetically driven superluminal motion from rotating black holes

abstract:
  We have investigated magnetically driven superluminal jets originating from
rotating black holes. The stationary, general relativistic, magnetohydrodynamic
wind equation along collimating magnetic flux surfaces has been solved
numerically. In particular, we apply our results to the Galactic superluminal
sources GRS 1915+105 and GRO 1655-40. Our results show that the observed speed
of more than 0.9 c can be achieved in general by magnetohydrodynamic
acceleration. The velocity distribution along the magnetic field has a
saturating profile. Further, we find that highly relativistic speeds can be
reached also for jets not emerging from a region close to the black hole, if
the flow magnetization is sufficiently large. The plasma temperature rapidly
decreases from about 10**10 K at the foot point of the jet to about 10**6 K at
a distance of 5000 gravitational radii from the source. Temperature and the
mass density follow a power law distribution with the radius.


title:
Lithium and mass loss in massive AGB stars in the Large Magellanic
  Clouds

abstract:
  The aim of this work is to use full evolutionary models to derive
observational constraints on the mass loss rate of the upper Asymptotic Giant
Branch (AGB) stars. The observations used to constrain the models are the
relative number of luminous Lithium rich AGBs in the Magellanic Clouds and the
s-process enhancement of the same sample. We find that we can put lower and
upper limits to the mass loss rate during the AGB phase. The mass loss
calibation obtained in this work implies that massive AGBs do not contribute
significantly to the lithium enrichment of the interstellar medium.


title:
Could We Detect Molecular Oxygen in the Atmosphere of a Transiting
  Extra-Solar Earth-Like Planet?

abstract:
  Although the extra-solar planets discovered so far are of the giant, gaseous,
type, the increased sensitivity of future surveys will result in the discovery
of lower mass planets. The detection of O2 in the atmosphere of a rocky
extra-solar planet would be a potential indicator of a life. In this paper we
address the specific issue of whether we would be able to detect the O2 A-band
absorption feature in the atmosphere of a planet similar to the Earth, if it
were in orbit around a nearby star. Our method is empirical, in that we use
observations of the Earth's O2 A-band, with a simple geometric modification for
a transiting extra-solar planet, allowing for limb-darkening of the host star.
We simulate the spectrum of the host star with the superposed O2 A-band
absorption of the transiting planet, assuming a spectral resolution of 7 km/s
(typical of current echelle spectrographs), for a range of spectral
signal-to-noise ratios. The main result is that we could reliably detect the O2
A-band of the transiting planet for host stars with radii 0.3 solar or less.
However, using existing instrumentation and 8m telescopes, this requires target
M stars with m(V) of approximately 10 or brighter for integration times of
about 10 hours or less. The number of such stars over the sky is small. Larger
aperture telescopes and/or improved instrumentation efficiency would enable
surveys of M stars down to m(V) = 13 and greatly improve the chances of
discovering life elsewhere.


title:
Chemical Evolution of the Galaxy: the G-dwarf problem and radioactive
  chronology revisited taking account of the Thick Disk

abstract:
  Thin and Thick disk metallicities overlap, but alpha(Fe) relations differ;
there is also a hiatus in time before the first thin-disk stars, with a minimum
metallicity [Fe/H] = -0.6. Thus there are two `G-dwarf' problems. We fit
metallicity distribution functions (MDFs) for the two disks derived by Wyse &
Gilmore (1995) with analytical models (for O and Mg). The Thick disk fits a
simple inflow model with effective yield and final [Mg/H] about the same as for
the Thin Disk, excluding continuous mass loss from the former as a source of
prompt initial enrichment (PIE) for the latter. The Thin disk has a narrow MDF
fitted (rather poorly) with a closed model having PIE from some other source,
or more elegantly with a slow infall model similar to the `two-inflow' scenario
of Matteucci et al., but with a PIE and a severe break in the age-metallicity
relation. Implications for radio-active cosmochronology are investigated.


title:
Bisector analysis as a diagnostic of intrinsic radial-velocity
  variations

abstract:
  In this contribution we present the results of the application of the
bisector of the cross-correlation function as a diagnostic of activity-related
radial-velocity variations. The results show that the technique is very
effective. We present examples for which the application of the bisector
analysis was essential to establish the planetary nature of the candidate or to
exclude an orbital signature. An analysis of the behaviour of the bisector for
active dwarfs of different spectral types shows that the relation between the
bisector and the radial-velocity variation depends in a great extent on the v
sin(i) of the star. The results may shed a new light on the intrinsic sources
of radial-velocity variation for different types of solar-type dwarfs.