title:
Improvement of the Spatial Resolution of the ACIS Using Split Pixel
  Events

abstract:
  The position accuracy of X-ray photons on a CCD detector is generally
believed to be limited by the CCD pixel size. While this is true in general,
the position accuracy for X-ray events which deposit charge in more than one
pixel can be better than that of the CCD pixel size. Since the position
uncertainty for corner events is much better than the pixel size, we can
improve the Chandra ACIS spatial resolution by selecting only these events.
  We have analyzed X-ray images obtained with the Chandra ACIS for six
point-like sources observed near the optical axis. The image quality near the
optical axis is characterized by a half power diameter (HPD) of $0.^{\!\!\prime
\prime}66$ that is a convolution of the PSF of the HRMA and the CCD pixel shape
($24\,\mu$m square). By considering only corner events the image quality is
improved to $0.^{\!\!\prime \prime}56$ (HPD), which is very close to the image
quality of the HRMA alone. We estimated the degradation of the image quality
obtained by using all events, compared to that obtained using only corner
events, to be $0.^{\!\!\prime \prime}33$, which coincides with that expected
from the pixel size. Since the fraction of the corner events is relatively
small, this technique requires correspondingly longer exposure time to achieve
good statistics.


title: Reflection Shocked Gas in the Cygnus Loop Supernova Remnant

abstract:
  We performed spectroscopic X-ray observations of the eastern and northern
regions of the Cygnus Loop with the ASCA observatory. The
  X-ray surface brightness of these regions shows a complex structure in the
ROSAT all-sky survey image. We carried out a spatially-resolved analysis for
both regions and found that $kT_{\rm e}$ did not increase toward the center
region, but showed inhomogeneous structures. Such variation cannot be explained
by a blast wave model propagating into a homogeneous interstellar medium. We
thus investigated the interaction between a blast wave and an interstellar
cloud. Two major emission mechanisms are plausible: a cloud evaporation model
and a reflection shock model. In both regions, only a reflection shock model
qualitatively explains our results. Our results suggest the existence of a
large-scale interstellar cloud. We suppose that such a large-scale structure
would be produced by a precursor.


title:
The fluxes of sub--cutoff particles detected by AMS, the cosmic ray
  albedo and atmospheric neutrinos

abstract:
  New measurements of the cosmic ray fluxes (p, e+, e- and Helium) performed by
the Alpha Magnetic Spectrometer (AMS) during a ten days flight of space shuttle
have revealed the existence of significant fluxes of particles below the
geomagnetic cutoff. These fluxes exhibit a number of remarkable properties,
such as a He-3/He-4 ratio of order ~10, an e+/e- ratio of order ~4 and
production from well defined regions of the Earth that are distinct for
positively and negatively charged particles. In this work we show that the
natural hypothesis, that these subcutoff particles are generated as secondary
products of primary cosmic ray interactions in the atmosphere can reproduce all
the observed properties. We also discuss the implications of the subcutoff
fluxes for the estimate of the atmospheric neutrino fluxes, and find that they
represent a negligibly small correction. On the other hand the AMS results give
important confirmations about the assumption of isotropy for the interplanetary
cosmic ray fluxes also on large angular scales, and on the validity of the
geomagnetic effects that are important elements for the prediction of the
atmospheric neutrino fluxes.


title:
Disk-locking and the presence of slow rotators among solar-type stars in
  young star clusters

abstract:
  The simultaneous presence of both the so-called `ultra-fast rotators' and
slowly rotating stars among the solar-type stars ($\sim 0.6-1.2 M_{\odot}$) in
the same young star clusters has been a puzzle in the field of stellar
rotation. No model to date has been able to explain both by a single mechanism
intrinsic to the star and questions about the appropriate initial conditions
for models often complicate the problem.
  In this paper, using the same starting conditions for the models that we used
in examining the origin of the ultra-fast rotators in young star clusters, we
show that the slowest rotators demand an extrinsic mechanism. Assuming that
this mechanism is a disk-star interaction, we determine that a disk-locking
timescale of a few Myr must operate for this type of star. If, instead of
allowing (radial) differential rotation, we enforce solid-body rotation, the
models require timescales about two to three times as long.


title:
Galactic Chemical Evolution and the abundances of lithium, beryllium and
  boron

abstract:
  A LiBeB evolution model including Galactic Cosmic Ray nucleosynthesis, the
$\nu$-process, novae, AGB and C-stars is presented. We have included Galactic
Cosmic Ray Nucleosynthesis (GCRN) in a complete Chemical Evolution Model that
takes into account 76 stable isotopes from hydrogen to zinc. Any successful
LiBeB evolution model should also be compatible with other observational
constraints like the age-metallicity relation, the G-dwarf distribution or the
evolution of other elements. At the same time, we have checked how different
would be a model that took into account the last observations by Wakker et al.
(1999) of metal-enriched clouds falling onto the disk, from a primordial infall
model.


title: The effects of anti-correlation on gravitational clustering

abstract:
  We use non-linear scaling relations (NSRs) to investigate the effects arising
from the existence of negative correlations on the evolution of gravitational
clustering in an expanding universe. It turns out that such anti-correlated
regions have important dynamical effects on {\it all} scales. In particular,
the mere existence of negative values for the linear two-point correlation
function $\xib_L$ over some range of scales starting from $l = L_o$, implies
that the non-linear correlation function is bounded from above at {\it all}
scales $x < L_o$. This also results in the relation $\xib \propto x^{-3}$, at
these scales, at late times, independent of the original form of the
correlation function. Current observations do not rule out the existence of
negative $\xib$ for $ 200 h^{-1}$ Mpc $\la \xib \la 1000 h^{-1}$ Mpc; the
present work may thus have relevance for the real Universe. The only assumption
made in the analysis is the {\it existence} of the NSR; the results are
independent of the form of the NSR as well as of the stable clustering
hypothesis.


title: Cosmological Perturbations in an Inflationary Universe

abstract:
  After introducing gauge-invariant cosmological perturbation theory we give an
improved set of governing equations for multiple fluids including energy
transfer. Having defined adiabatic and entropic perturbations we derive the
``conservation law'' for the curvature perturbation on large scales using only
the energy conservation equation. We then investigate the dynamics of assisted
inflation. By choosing an appropriate rotation in field space we can write down
explicitly the potential for the weighted mean field along the scaling solution
and for fields orthogonal to it. This allows us to present analytic solutions
describing homogeneous and inhomogeneous perturbations about the attractor
solution without resorting to slow-roll approximations. Finally we analyze the
simplest model of preheating analytically, and show that in linear perturbation
theory the effect of preheating on the amplitude of the curvature perturbation
on large scales is negligible. We end with some concluding remarks, possible
extensions and an outlook to future work.


title: The Mass-Temperature Relation of 22 Nearby Clusters

abstract:
  We present a new investigation of the mass-temperature (\MTrelation) relation
of 22 nearby clusters based on the analysis of their ROSAT X-ray surface
brightness profiles ($S_{X}(r)$) and their ASCA emission weighted temperatures.
Two methods of the cluster mass estimations are employed and their results are
compared: (1) the conventional $\beta$ model for gas distribution along with
the isothermal and hydrostatic equilibrium assumptions, and (2) the NFW profile
for dark matter distribution whose characteristic density and length are
determined by the observed $S_{X}(r)$. These two models yield essentially the
same goodness of fits for $S_{X}(r)$ and the similar \MTrelation relations,
with the latter demonstrating a significant departure from the simple
gravitational scaling of $M_{tot}\propto T_X^{3/2}$. It is also shown that the
best-fit \MTrelation relations could be reconciled with the theoretical
expectation if the low-temperature clusters ($T_X<3.5$ keV) are excluded from
the list, which lends support to the scenario that the intra-cluster medium is
preheated in the early phase of cluster formation. Together with the
entropy-temperature distribution, the existence of a similarity break at
$T_X=3-4$ keV in the dynamical scaling relations for galaxy clusters has been
confirmed.


title: Tau Air-Showers Signature of Ultra High Energy Neutrinos

abstract:
  The discover of Ultra High Energy Neutrino of astrophysical nature may be
already reached. Indeed upward and horizontal tau Air-showers emerging from the
Earth crust or mountain chains offer the best and most powerful signal of Ultra
High Energy UHE neutrinos nu_tau}, bar\nu_tau and bar{\nu}_e at PeV and higher
energy. The multiplicity in tau Air-showers secondary particles,N_{opt}
=10^{12}, (E_tau}/ PeV, N_{\gamma}= 10^8 E_tau/ PeV, N_{e^- e^+}= 2 10^7
E_tau/PeV, N_mu =3 10^5 (E_tau/PeV)^{0.85}, make easy its over-amplified
discover. Indeed UHE nu_tau, following Super Kamiokande evidence of neutrino
flavour mixing, should be as abundant as nu_mu. Also anti-neutrino electrons,
bar{\nu}_e, near the Glashow W resonance peak, E_{\bar{\nu_e}} = M^2_W / 2m_e,
may generate tau Air-showers. Such horizontal tau air-showers by nu_{\tau}-N
and UHE bar\nu_{e}-e at PeVs emerging from mountain high chain is one of the
most power-full UHE neutrino imprint. Upward UHE nu_{\tau}- N interaction on
Earth crust at horizontal edge and from below, their consequent UHE tau
air-showers beaming toward high mountains should flash gamma,mu,X and Cherenkov
lights toward detectors located on the top of the mountains or on balloons.
Such upward tau air-shower may hit also nearby satellite flashing them by
short, hard, diluted gamma-burst at the edge of most sensitive Gamma Ray
Observatory BATSE threshold. We identify already these rarest gamma events with
recent (1994) discovered upward Terrestrial Gamma Flashes (TGF); we show their
very probable UHE tau-UHE \nu_\tau origin. Partial TGF Galactic signature and
known galactic and extra-galactic source location are discovered within known
47 TGF events at low, 2 10^{-3}, probability threshold.


title: Diffusion of Neutrinos in Proto-Neutron Star Matter with Quarks

abstract:
  Neutrino opacities important in the evolution of a proto-neutron star
containing quark matter are studied. The results for pure quark matter are
compared with limiting expressions previously derived, and are generalized to
the temperatures, neutrino degeneracies and lepton contents encountered in a
proto-neutron star's evolution. We find that the appearance of quarks in
baryonic matter drastically reduces the neutrino opacity for a given entropy,
the reduction being sensitive to the thermodynamic conditions in the mixed
quark-hadron phase.


title:
Statistical Mechanics of the Self-Gravitating Gas: II. Local Physical
  Magnitudes and Fractal Structures

abstract:
  We complete our study of the selfgravitating gas by computing the
fluctuations around the saddle point solution for the three statistical
ensembles. Although the saddle point is the same for the three ensembles, the
fluctuations change from one ensemble to another. The zeroes of the
fluctuations determinant determine the position of the critical points for each
ensemble.This yields the domains of validity of the mean field approach. Only
the S wave determinant exhibits critical points.Closed formulae for the S and P
wave determinants are derived.The local properties of the selfgravitating gas
in thermodynamic equilibrium are studied in detail. The pressure, energy
density, particle density and speed of sound are computed and analyzed as
functions of the position. The equation of state turns out to be locally p(r) =
T rho(r) as for the ideal gas. Starting from the partition function of the
selfgravitating gas, we prove in this microscopic calculation that the
hydrostatic description yielding locally the ideal gas equation of state is
exact in the N = infinity limit. The dilute nature of the thermodynamic
limit(N, L -> infinity with N/L fixed) together with the long range nature of
the gravitational forces play a crucial role in the obtention of such ideal gas
equation. The self-gravitating gas being inhomogeneous, we have PV/[NT] =
f(eta) leq 1 for any finite volume V. The inhomogeneous particle distribution
in the ground state suggests a fractal distribution with Haussdorf dimension D,
D is slowly decreasing with increasing density, 1 lesssim D < 3. The average
distance between particles is computed in Monte Carlo simulations
andanalytically in the mean field approach. A dramatic drop at the phase
transition is exhibited, clearly illustrating the properties of the collapse.


title:
Statistical Mechanics of the Self-Gravitating Gas: I. Thermodynamic
  Limit and Phase Diagram

abstract:
  We provide a complete picture to the selfgravitating non-relativistic gas at
thermal equilibrium using Monte Carlo simulations, analytic mean field methods
(MF) and low density expansions. The system is shown to possess an infinite
volume limit in the grand canonical (GCE), canonical (CE) and microcanonical
(MCE) ensembles when(N, V) --> infinity, keeping N/ V^{1/3} fixed. We compute
the equation of state (we do not assume it as is customary), as well as the
energy, free energy, entropy, chemical potential, specific heats, compressibi-
lities and speed of sound;we analyze their properties, signs and singularities.
All physical quantities turn out to depend on a single variable eta = G m^2 N/
[V^{1/3} T] that is kept fixed in the N--> infinity and V --> infinity limit.
The system is in a gaseous phase for eta < eta_T and collapses into a dense
objet for eta > \eta_T in the CE with the pressure becoming large and negative.
At eta simeq eta_T the isothermal compressibility diverges. Our Monte Carlo
simulations yield eta_T simeq 1.515. PV/[NT] = f(eta) and all physical magni-
tudes exhibit a square root branch point at eta = eta_C > eta_T. The MF for
spherical symmetry yields eta_C = 1.561764.. while Monte Carlo on a cube yields
eta_C simeq 1.540.The function f(eta) has a second Riemann sheet which is only
physically realized in the MCE.In the MCE, the collapse phase transition takes
place in this second sheet near eta_MC = 1.26 and the pressure and temperature
are larger in the collapsed phase than in the gas phase.Both collapse phase
transitions (CE and MCE) are of zeroth order since the Gibbs free energy jumps
at the transitions. f(eta), obeys in MF a first order non-linear differential
equation of first kind Abel's type.The MF gives an extremely accurate picture
in agreement with Monte Carlo both in the CE and MCE.


title:
From infall to rotation around young stellar objects: A transitional
  phase with a 2000 AU radius contracting disk?

abstract:
  Evidence for a transitional stage in the formation of a low-mass star is
reported, intermediate between the fully embedded and the T Tauri phases.
Millimeter aperture synthesis observations in the HCO+ J=1-0 and 3-2, HCN 1-0,
13CO 1-0, and C18O 1-0 transitions reveal distinctly different velocity fields
around two embedded, low-mass young stellar objects. The 0.6 M(sun) of material
around TMC 1 (IRAS 04381+2517) closely follows inside-out collapse in the
presence of a small amount of rotation (~3 km/s/pc), while L1489 IRS (IRAS
04016+2610) is surrounded by a 2000 AU radius, flared disk containing 0.02
M(sun). This disk shows Keplerian rotation around a ~0.65 M(sun) star and
infall at 1.3 (r/100 AU)^-0.5 km/s, or, equivalently, sub-Keplerian motions
around a central object between 0.65 and 1.4 M(sun). Its density is
characterized by a radial power law and an exponential vertical scale height.
The different relative importance of infall and rotation around these two
objects suggests that rotationally supported structures grow from collapsing
envelopes over a few times 10^5 yr to sizes of a few thousand AU, and then
decrease over a few times 10^4 yr to several hundred AU typical for T Tauri
disks. In this scenario, L1489 IRS represents a transitional phase between
embedded YSOs and T Tauri stars with disks. The expected duration of this phase
of ~5% of the embedded stage is consistent with the current lack of other known
objects like L1489 IRS. Alternative explanations cannot explain L1489 IRS's
large disk, such as formation from a cloud core with an unusually large
velocity gradient or a binary companion that prevents mass accretion onto small
scales. It follows that the transfer and dissipation of angular momentum is key
to understanding the formation of disks from infalling envelopes.


title:
Multi-Epoch VLBA Observations of EGRET-Detected Quasars and BL Lac
  Objects: Superluminal Motion of Gamma-Ray Bright Blazars

abstract:
  We present the results of a program to monitor the structure of the radio
emission in 42 $\gamma$-ray bright blazars (31 quasars and 11 BL Lac objects)
with the VLBA at 43, 22, and occasionally 15 and 8.4 GHz, over the period from
November 1993 to July 1997. We determine proper motions in 33 sources and find
that the apparent superluminal motions in $\gamma$-ray sources are much faster
than for the general population of bright compact radio sources. This follows
the strong dependence of the $\gamma$-ray flux on the level of relativistic
beaming for both external-radiation Compton and synchrotron self-Compton
emission. There is a positive correlation (correlation coefficient $r$=0.45)
between the flux density of the VLBI core and the $\gamma$-ray flux and a
moderate correlation (partial correlation coefficient $r$=0.31) between
$\gamma$-ray apparent luminosity and superluminal velocities of jet components,
as expected if the $\gamma$-ray emission originates in a very compact region of
the relativistic jet and is highly beamed. In 43% of the sources the jet bends
by more than 20$^\circ$ on parsec scales, which is consistent with
amplification by projection effects of modest actual changes in position angle.
  In 27 of the sources in the sample there is at least one non-core component
that appears to be stationary during our observations. Different
characteristics of stationary features close to and farther from the core lead
us to suggest two different classes of stationary components: those within
about 2 milliarcseconds (mas) of the core, probably associated with standing
hydrodynamical compressions, and those farther down the jet, which tend to be
associated with bends in the jet.


title: Near-Infrared Light Curves of the Black Hole Binary A0620-00

abstract:
  We measured the near-infrared orbital light curve of the black hole binary
A0620-00 in 1995 and 1996. The light curves show an asymmetric, double-humped
modulation with extra emission in the peak at orbital phase 0.75. There were no
significant changes in the shape of the light curve over the one-year
observation period. There were no sharp dips in the light curves nor reversals
of the asymmetry between the two peaks as seen in earlier observations. The
light curves are well fit by models incorporating ellipsoidal variations from
the mass-losing K-type star plus a beamed bright spot on the accretion disk
around the compact star. The long-term stability of the light curve shape rules
out superhumps and star spots as sources of asymmetry when we observed
A0620-00. The ellipsoidal variations yield a lower limit i >= 38 deg on the
orbital inclination. The light curves show no eclipse features, which places an
upper limit i <= 75 deg. This range of inclinations constrains the mass of the
compact object to 3.3 < M_1 < 13.6 Msun. The light curves do not further
constrain the orbital inclination because the contribution of the accretion
disk to the observed flux is unknown. We argue that a previous attempt to
measure the near-infrared flux from the accretion disk using the dilution of
the 12CO(2,0) bandhead in the spectrum of the K star is not reliable because
the band strength depends strongly on surface gravity.


title:
Spectroscopic Discovery of Brown Dwarf-like Secondary Stars in the
  Cataclysmic Variables LL And and EF Eri

abstract:
  Infrared spectroscopic observations of LL Andromedae and EF Eridani are
presented. Our K band spectrum of LL Andromedae reveals the presence of methane
absorption in the secondary star indicating an effective temperature less than
1300K, similar to a "T" type methane brown dwarf. The secondary star in EF
Eridani is seen to be warmer with an effective temperature of ~1650K and a
spectroscopic classification consistent with an L4-5 star. Both secondaries
have theoretical mass estimates of 0.04-0.055 solar masses (40-55 Jupiter
masses). Our IR spectroscopic observations of LL And and EF Eri provide the
first direct proof of the theoretical prediction that post-period minimum
cataclysmic variables contain brown dwarf-like secondary stars.


title: Superflares and Giant Planets

abstract:
  Stellar flares 100-10^7 times more energetic than the most powerful solar
flares have been detected from 9 normal F and G main sequence stars (Schaefer,
King & Deliyannis 2000). Although these stars are not in close binary systems,
their superflares show a remarkable similarity to the large stellar flares
observed on RS Canum Venaticorum binary systems. Such flares are caused by
magnetic reconnection events associated with the tangling of magnetic fields
between the two stars. The superflare stars are certainly not of this class,
although the mechanism may be similar. The superflares may be caused by
magnetic reconnection between fields of the primary star and a close-in Jovian
planet. This scenario explains the energies, durations, and spectra of
superflares, as well as explain why our Sun does not have such events. Only
known planetary properties and reconnection scenarios are required by this
mechanism.


title: Formation and Evolution of Black Hole X-ray Transient Systems

abstract:
  We study the formation of low-mass black hole X-ray binaries with main
sequence companions that have formed through case C mass transfer (mass
transfer following the helium core burning phase of the black hole progenitor).
We identify these objects with the observed soft X-ray transients. Although
this scenario requires a set of fine tuned conditions, we are able to produce a
current Galactic population of about 2000 objects, in agreement with estimates
based on observations.
  The narrow interval in initial separations leading to case C mass transfer,
combined with the allowed narrow range of separations after the common envelope
evolution, constrains the common envelope efficiency in this scenario: $\lambda
\alpha_{ce} \approx 0.2-0.5$.


title: Signature Studies of Cosmic Magnetic Monopoles

abstract:
  This talk explores the possibility that the Universe may be populated with
relic magnetic monopoles. Observations of galactic and extragalactic magnetic
fields, lead to the conclusion that monopoles of mass < 10^{14} GeV are
accelerated in these fields to relativistic velocities. The relativistic
monopole signatures and features we derive are (i) the protracted shower
development, (ii) the Cherenkov signals, (iii) the tomography of the Earth with
monopoles, and (iv) a model for monopole airshowers above the GZK cutoff.


title:
Resolving the Image of Gamma-Ray Burst Afterglows with Gravitational
  Microlensing

abstract:
  Microlensing of a gamma-ray burst afterglow by an intervening star can be
used to infer the radial structure of the afterglow image. Near the peak of the
microlensing event, the outer edge of the image is more highly magnified than
its central region, whereas the situation is reversed at later times due to the
rapid radial expansion of the image on the sky. Thus, the microlensed afterglow
light curve can be inverted to recover the self-similar radial intensity
profile of the afterglow image. We calculate the expected errors in the
recovered intensity profile as a function of the number of resolution elements,
under the assumption that the afterglow and microlensing event parameters are
known. For a point-mass lens and uniform source, we derive a simple scaling
relation between these parameters and the resultant errors. The afterglow need
not be monitored for its entire duration; rather, observations from the peak
magnification time t_p of the microlensing event until 7 t_p are sufficient to
resolve the majority of the image. Thus, microlensing events can be alerted by
relatively infrequent observations of afterglows and then monitored
intensively, without significant loss of information about the afterglow
intensity profile. The relative intensity profile of about 1% of all afterglows
can be measured with 10 resolution elements to an accuracy of 1% in the optical
and 10% in the infrared, using 4m-class telescopes. Weak microlensing events
with large impact parameters are more common; we estimate that for about 10% of
afterglows the image profile may be inverted to a fractional accuracy 20%
through frequent optical observations. We also calculate the effects of
external shear due to the host galaxy or a binary companion, and contamination
by background light from the host galaxy.


title:
The proper motion of the neutron star RXJ1856.5-3754 as measured by
  optical and X-ray imaging

abstract:
  The proper motion of the faint (V=25.6 mag) neutron star RXJ1856.5-3754 as
measured consistently with both the FORS1 optical imager on the ESO Very Large
Telescope (VLT) as well as with the ROSAT High Resolution Imager is presented.
With two VLT images obtained with a 0.95 year epoch difference in Apr 1999 and
Apr 2000, a proper motion of mu_alpha = 0.326 \pm 0.064" per year to the east
and no detectable motion in declination is found, consistent with simultaneous
findings by Walter (2001) using three HST observations. Also, by comparing the
positional differences between the strong X-ray source RXJ1856.5-3754 and other
X-ray sources detected in the same ROSAT High Resolution Imager field (observed
in Oct 1994 and Oct 1997), a proper motion of 0.34 \pm 0.12" to the east is
detected. This may be the first star, where a proper motion is clearly detected
in X-ray images. Additional VLT images taken in half-year intervalls give an
upper limit to the parallax of about 51 mas. Furthermore, in archived VLT
observations, the first B-band detection of this object is found with B=25.14
\pm 0.41 mag.


title:
Gauge-ready formulation of the cosmological kinetic theory in
  generalized gravity theories

abstract:
  We present cosmological perturbations of kinetic components based on
relativistic Boltzmann equations in the context of generalized gravity
theories. Our general theory considers an arbitrary number of scalar fields
generally coupled with the gravity, an arbitrary number of mutually interacting
hydrodynamic fluids, and components described by the relativistic Boltzmann
equations like massive/massless collisionless particles and the photon with the
accompanying polarizations. We also include direct interactions among fluids
and fields. The background FLRW model includes the general spatial curvature
and the cosmological constant. We consider three different types of
perturbations, and all the scalar-type perturbation equations are arranged in a
gauge-ready form so that one can implement easily the convenient gauge
conditions depending on the situation. In the numerical calculation of the
Boltzmann equations we have implemented four different gauge conditions in a
gauge-ready manner where two of them are new. By comparing solutions solved
separately in different gauge conditions we can naturally check the numerical
accuracy.


title: Identification of the 4486,4504A emission lines in O-type spectra

abstract:
  Inspired by an appeal to the community from Walborn (these proceedings) we
decided to solve the long-standing problem concerning the nature of the
4486,4504A emission lines, which are frequently observed in O-type spectra and
which are particularly prominent in supergiants. We claim that these lines
emerge from sulfur, namely by de-excitation of a highly excited S IV doublet
state. We prove this by an exploratory NLTE calculation with a detailed model
atom.


title: The INTEGRAL Core Observing Programme

abstract:
  The Core Programme (CP) of the INTEGRAL mission is defined as the portion of
the scientific observing programme covering the guaranteed time observations
for the PI collaborations and other members of the INTEGRAL Science Working
Team. During the first two years of the mission, the guaranteed observing time
uses 35% (year 1) and 30% (year 2) of the total annual observing time
(~26.6x10^{6}s per year). The Core Programme consists of three elements: a deep
exposure of the Galactic central radian, regular (weekly) scans of the Galactic
plane and pointed observations. This paper describes the current status of the
INTEGRAL Core Programme and summarizes the key elements.


title: Seismic detection of stellar tachoclines

abstract:
  Helioseismic inversions for the rotation rate have established the presence
of a tachocline near the base of the solar convection zone. We show that the
tachocline produces a characteristic oscillatory signature in the splitting
coefficients of low degree modes, which could be observed on distant stars.
Using this signature it may be possible to determine the characteristics of the
tachocline using only low degree modes. The limitations of this technique in
terms of observational uncertainties are discussed, to assess the possibility
of detecting tachoclines on distant stars.


title: Enigmatic low-velocity jet-like features in planetary nebulae

abstract:
  We are developing a project aimed at studying the physical properties, origin
and evolution of low-ionization structures in planetary nebulae. Within this
project we have identified a number of pairs of highly collimated
low-ionization jet-like features (Goncalves et al. 2001). In spite of being
very similar to real jets, they have the intriguing property of possessing
expansion velocities which are very low, or at least not significantly
different from, that of the shells in which they are embedded. In this
contribution we discuss our data on these fake jets (Corradi et al. 1997, 1999)
and compare them with existing theoretical models for the formation of
collimated structures in PNe. These enigmatic jet-like systems are not easily
accounted for within the theoretical scenarios that deal with collimated
features in PNe.


title: New Light on the Baryon Fraction in Galaxy Clusters

abstract:
  Baryon fraction in clusters, combined with constraints from primordial
nucleosynthesis is currently used to provide a robust upper limit on the
cosmological density parameter $\Omega_0$. Current analyses lead to gas
fractions at virial radius which are typically of the order of
0.20$h^{-3/2}_{50}$, favoring a low density universe. In this work, we examine
critically this issue through the analysis of the baryon distribution in
clusters. We find that the currently derived gas fraction profile, increases
regularly from the inner part to the outer part, up to the virial radius, and
beyond. Such a shape contrasts with what is expected from numerical
hydro-dynamical simulations, in which the gas fraction is more or less constant
in the outer region, reaching a plateau when the contrast density falls off
below $10^4$. We argue that such a difference is hardly explained by reheating
effects, while taking into account various factors entering into the
determination of clusters gas fraction may erase such a difference. Indeed,
using recent estimates on gas content in the outer part of clusters (Vikhlinin
et al., 1999) and applying the correction factor due to the effect of gas
clumping, we find that the gas fraction shape over the range $ 200< \delta<
10^5$ is roughly consistent with hydro-dynamical simulations for an universal
gas fraction in the range 8-11% (for $h_{50} =1.$), the mass estimators being
calibrated from numerical simulations. In contrast, values of the order of 20%
do not give acceptable fit to the data on any scale. We conclude, that high
values of $\Omega_0$ can not be ruled out on the basis of the baryon fraction
argument.


title:
Disc-like Objects in Hierarchical Hydrodynamical Simulations: Comparison
  with Observations

abstract:
  We present results from a careful and detailed analysis of the structural and
dynamical properties of a sample of 29 disc-like objects identified at z=0 in
three AP3M-SPH fully consistent cosmological simulations. These simulations are
realizations of a CDM hierarchical model, where an inefficient Schmidt law-like
algorithm to model the stellar formation process has been implemented. We focus
on properties that can be constrained with available data from observations of
spiral galaxies, namely, the bulge and disc structural parameters and the
rotation curves. Comparisons with data from Broeils (1992), de Jong (1996) and
Courteau (1996, 1997) give satisfactory agreement, in contrast with previous
findings using other codes. This suggests that the stellar formation
implementation we have used has succeded in forming compact bulges that
stabilize disc-like structures in the violent phases of their assembly, while
in the quiescent phases the gas has cooled and collapsed according with the
Fall & Efstathiou standard model of disc formation.


title:
Multi-Epoch VLBA Observations of EGRET-Detected Quasars and BL Lac
  Objects: Connection between Superluminal Ejections and Gamma-Ray Flares in
  Blazars

abstract:
  We examine the coincidence of times of high $\gamma$-ray flux and ejections
of superluminal components from the core in EGRET blazars based on a VLBA
monitoring program at 22 and 43 GHz from November 1993 to July 1997. In 23
cases of $\gamma$-ray flares for which sufficient VLBA data exist, 10 of the
flares (in 8 objects) fall within 1$\sigma$ uncertainties of the extrapolated
epoch of zero separation from the core of a superluminal radio component. In
each of two sources (0528+134 and 1730-130) two successive $\gamma$-ray flares
were followed by the appearance of new superluminal components. We carried out
statistical simulations which show that if the number of coincidences $\ge$ 10
the radio and $\gamma$-ray events are associated with each other at >99.999%
confidence. Our analysis of the observed behavior, including variability of the
polarized radio flux, of the sources before, during, and after the $\gamma$-ray
flares suggests that the $\gamma$-ray events occur in the superluminal radio
knots. This implies that the $\gamma$-ray flares are caused by inverse Compton
scattering by relativistic electrons in the parsec-scale regions of the jet
rather than closer to the central engine.


title: The Sagittarius dwarf galaxy as a microlensing target

abstract:
  We estimate the optical depth, time-scale distribution and fraction of
microlensing events originating from sources in the Sagittarius dwarf galaxy
(Sgr) lensed by deflectors in the Milky Way. These events have a time-scale
longer by a factor ~1.3 than the MW/MW events and occur mainly on sources
fainter than V~21 mag below Sgr's turn off. The fraction of events involving a
source in Sgr depends on the location and extinction of the field and on the
limiting magnitude of the survey. The contribution of the MW/Sgr events is
negligible (<1%) at very low latitudes (|b|<2 deg.) but increases continuously
towards higher |b| and becomes dominant near the highest density region of the
dwarf galaxy. Sgr is present within the fields of current microlensing surveys
and any optical depth map inferred from observations will become biased by the
presence of Sgr towards higher |b| where the contribution of MW/Sgr events is
significant. Systematic spectroscopic measurements on the sources of all the
microlensing events may allow detection of this kind of event for which the
degeneracy on the lens mass can be significantly reduced.


title:
An abundance analysis for four Red Horizontal Branch Stars in the
  extremely metal rich globular cluster NGC 6528

abstract:
  We present the results of the first analysis of high dispersion spectra of
four red HB stars in the metal rich globular cluster NGC 6528, located in
Baade's Window. We find that the mean [Fe/H] for NGC 6528 is +0.07+-0.01 dex
(error of the mean), with a star-to-star scatter of sigma = 0.02 dex (4 stars),
although the total error is likely to be larger (~0.1 dex) due to systematic
errors related to the effective temperature scale and to model atmospheres.
This metallicity is somewhat larger than both the mean abundance in the
galactic bulge found by McWilliam & Rich (1994) and that found in our previous
paper for NGC 6553. However, we find that the spectra of clump stars in NGC
6528 and NGC 6553 are very similar each other, the slightly different metal
abundances found being possibly due to the different atmospheric parameters
adopted in the two analyses. For NGC 6528 we find excesses for the
alpha-process elements Si and Ca ([Si/Fe]=+0.4 and [Ca/Fe]=+0.2), whereas Mn is
found to be underabundant ([Mn/Fe]=-0.4). We find a solar abundance of O;
however this is somewhat uncertain due to the dependence of the O abundance on
the adopted atmospheric parameters and to coupling between C and O abundances
in these cool, metal-rich stars. Finally, we find large Na excesses ([Na/Fe]~
+0.4) in all stars examined. Since the present analysis is based on higher
quality material, we propose to revise our previous published metal abundance
for NGC 6553 to [Fe/H]=$0.06+-0.15.


title: Evolution of Proto-Neutron Stars with Quarks

abstract:
  Neutrino fluxes from proto-neutron stars with and without quarks are studied.
Observable differences become apparent after 10--20 s of evolution.
Sufficiently massive stars containing negatively-charged, strongly interacting,
particles collapse to black holes during the first minute of evolution. Since
the neutrino flux vanishes when a black hole forms, this is the most obvious
signal that quarks (or other types of strange matter) have appeared. The
metastability timescales for stars with quarks are intermediate between those
containing hyperons and kaon condensates.


title:
The ATESP Radio Survey IV. Optical Identifications and Spectroscopy in
  the EIS-A Region

abstract:
  (Abridged) This paper is the fourth of a series reporting the results of the
ATESP 1.4 GHz radio survey. The survey covers a region of ~26 sq. degrees at
decl. -40 degr. and has produced a catalogue of 2967 radio sources down to ~0.5
mJy (6sigma). In this paper we present the optical identifications over a 3 sq.
degr. region of the public ESO Imaging Survey. In this region deep photometry
and 95% complete object catalogues in the I band are available down to I~22.5.
These data allowed us to identify 57% of the ATESP sources present in the
region (219/386). For a magnitude limited sample of 70 identified sources with
I<19.0 we have obtained spectroscopy at the ESO 3.6 m telescope. This data
allowed us to get redshifts and spectral classification for all sources (except
one). From the analysis of the spectroscopic sample we find that the
composition of the faint radio population abruptly changes going from mJy to
sub-mJy fluxes: the early type galaxies largely dominate the mJy population
(60%), while star forming processes become important in the sub-mJy regime.
Starburst and post-starburst galaxies go from 13% at S>1 mJy to 39% at S<1 mJy.
Nevertheless, at sub-mJy fluxes, early type galaxies still constitute a
significant fraction (25%) of the whole population. We also show that, due to
the distribution of radio to optical ratios, sub-mJy samples with fainter
spectroscopic follow-ups should be increasingly sensitive to the population of
early type galaxies, while a larger fraction of star-forming galaxies would be
expected in microJy samples. We compare our results with others obtained from
studies of sub-mJy samples and we show how the existing discrepancies can be
explained in terms of selection effects.


title: The Zoo of X-ray Pulsars

abstract:
  I review some recent developments in the field of X-ray pulsars: the
discovery of millisecond pulsations in the Low Mass Binary System SAX
J1808.4-3658, the large number of transient Be systems discovered in the
Magellanic Clouds and the enigmatic class of objects known as Anomalous X-ray
Pulsars.


title: A One-sided, Highly Relativistic Jet from Cygnus X-3

abstract:
  Very Long Baseline Array images of the X-ray binary, Cygnus X-3, were
obtained 2, 4 and 7 days after the peak of a 10 Jy flare on 4 February 1997.
The first two images show a curved one-sided jet, the third a scatter-broadened
disc, presumably at the position of the core. The jet curvature changes from
the first to the second epoch, which strongly suggests a precessing jet. The
ratio of the flux density in the approaching to that in the (undetected)
receding jet is > 330; if this asymmetry is due to Doppler boosting, the
implied jet speed is > 0.81c. Precessing jet model fits, together with the
assumptions that the jet is intrinsically symmetric and was ejected during or
after the major flare, yield the following constraints: the jet inclination to
the line of sight must be < 14 degrees; the cone opening angle must be < 12
degrees; and the precession period must be > 60 days.


title:
Results of a LMXB survey: variation in the height of the neutron star
  blackbody emission region

abstract:
  We present results of a survey of the spectra of Low Mass X-ray Binaries
using ASCA. It is shown that all sources in the survey are well-fitted by the
same two-component emission model that we have previously shown is able to
describe both the non-dip and dip spectra of the dipping class of LMXB. This
model consists of point-like blackbody emission from the neutron star plus
Comptonized emission from a disk-like accretion disk corona of radius typically
50,000 km. Additional data from results published elsewhere by us from BeppoSAX
and ASCA are added to the survey. The large variation in blackbody luminosity
of survey sources is shown to be due primarily to major changes in blackbody
emitting area. Fitting a multi-temperature disk blackbody plus Comptonization
model to the survey spectra requires values of inner disk radius substantially
less than the neutron star radius in many cases, making disk origin of the
blackbody highly unlikely. Assuming that the emission is from an equatorial
strip on the neutron star, it is shown that the half-height of the strip h
agrees well with the half-height H of the radiatively-supported inner accretion
disk, this agreement spanning three orders of magnitude in each parameter.
Possible mechanisms for the agreement are discussed, including radial accretion
flow between inner disk and star, and accretion flow ``creep' on the surface of
the neutron star.


title: Romano's star in M33 - LBV candidate or LBV?

abstract:
  We present the light curve of Luminous Blue Variable candidate star GR290
(Romano's star) in M33. The photographic photometry was made in photographic
plates taken in B band of the M33 galaxy and cover an eight year period, 1982 -
1990. Twenty five plates, separated in seven groups, have been used. CCD B
magnitude of the star is also presented. The analysis of our data together with
the Romano's magnitudes (1978) shows "normal" eruptions with amplitude of more
than 1 mag and timescale of about 20 years and smaller oscillations with
amplitude 0.5 mag and a period of about 320 days. This is a typical
photometrical behavior for LBVs.


title: ROSAT X-Ray Observations of the Spiral Galaxy M81

abstract:
  We present results from the analysis of deep ROSAT HRI and PSPC observations
of the spiral galaxy M81. The inferred total (0.5-2 keV band) luminosity of M81
is ~3x10^40 ergs/s, excluding the contribution from identified interlopers
found within the D_25 ellipse. The nucleus of the galaxy alone accounts for
about 65% of this luminosity. The rest is due to 26 other X-ray sources
(contributing ~10%) and to apparently diffuse emission, which is seen across
much of the galactic disk and is particularly bright in the bulge region around
the nucleus. Spectral analysis further gives evidence for a soft component,
which can be characterized by a two-temperature optically thin plasma with
temperature at ~0.15 keV and 0.60 keV and an absorption of the Galactic
foreground only. These components, accounting for ~13% of the X-ray emission
from the region, apparently arise in a combination of hot gas and faint
discrete sources. We find interesting spatial coincidences of luminous
(10^37-10^40 ergs/s) and variable X-ray sources with shock-heated optical
nebulae. Three of them are previously classified as supernova remnant
candidates. The other one is far off the main body of M81, but is apparently
associated with a dense HI concentration produced most likely by the tidal
interactions of the galaxy with its companions. These associations suggest that
such optical nebulae may be powered by outflows from luminous X-ray binaries,
which are comparable to, or more luminous than Galactic `micro-quasars'.


title: Radiative Bulk Viscosity

abstract:
  Viscous resistance to changes in the volume of a gas arises when different
degrees of freedom have different relaxation times. Collisions tend to oppose
the resulting departures from equilibrium and, in so doing, generate entropy.
Even for a classical gas of hard spheres, when the mean free paths or mean
flight times of constituent particles are long, we find a nonvanishing bulk
viscosity. Here we apply a method recently used to uncover this result for a
classical rarefied gas to radiative transfer theory and derive an expression
for the radiative stress tensor for a gray medium with absorption and Thomson
scattering. We determine the transport coefficients through the calculation of
the comoving entropy generation. When scattering dominates absorption, the bulk
viscosity becomes much larger than either the shear viscosity or the thermal
conductivity.


title: NICMOS Imaging of the Cores of M 31 and M 32

abstract:
  We present 1.1, 1.6, and 2.2 micron images of the cores of the Local Group
galaxies M 31 and M 32 obtained with the Near Infrared Camera and Multi-Object
Spectrometer (NICMOS) instrument of the Hubble Space Telescope. These images
are also compared to optical images of the galaxies obtained with the HST Wide
Field Planetary Camera 2 (WFPC2). In M 31 the nucleus remains distinctly
asymmetric in all of the infrared bands, with no evidence of concentrated dust,
although the distinction between the two nuclei, P1 and P2, is not as strong as
in the WFPC and WFPC2 images. This result is nonetheless consistent with the
model of the nucleus as an eccentric stellar disk produced by the dynamical
influence of a central supermassive black hole. Several individual M-giant
stars are detected within ~ 3" of the nuclei, and may represent stars that have
escaped from the disk and phase-mixed around the nuclear center of mass. In M
32 we also do not find strong evidence of dust, and the brightness profiles
within the central ~ 1" of the infrared images can be fitted by a power law of
the same form as that fitted to the optical images. The infrared color profiles
of the central few arcseconds of M 32 show no strong gradients, and indicate a
population dominated by K-giant stars. This is consistent with recent
groud-based spectroscopy and photometry of the core region, which similarly
show no strong gradients in age or metallicity within its stellar population.


title: Impact of Gas Removal on the Evolution of Embedded Clusters

abstract:
  We study both analytically and numerically the disruptive effect of
instantaneous gas removal from an embedded cluster. We setup a calculation
based on the stellar velocity distribution function, to compute the fraction of
stars that remain bound once the cluster has ejected the gas and is out of
equilibrium. We find tracks of bound mass-fraction vs star formation efficiency
similar to those obtained with N-body calculations. We use these to argue that
embedded clusters must develop high-binding energy cores if they are to survive
as bound clusters despite a star formation rate as low as 20 per cent or lower
suggested by observations.


title: Galactosynthesis Predictions at High Redshift

abstract:
  We predict the Tully-Fisher (TF) and surface-brightness--magnitude relation
for disk galaxies at z=3 and discuss the origin of these scaling relations and
their scatter. We show that the variation of the TF relation with redshift can
be a potentially powerful discriminator of galaxy-formation models. In
particular, the TF relation at high redshift might be used to break parameter
degeneracies among galactosynthesis models at z=0, as well as to constrain the
redshift distribution of collapsing dark-matter halos, the star-formation
history and baryon fraction in the disk, and the distribution of halo spins.


title: Recycled Pulsars Discovered at High Radio Frequency

abstract:
  We present the timing parameters of nine pulsars discovered in a survey of
intermediate Galactic latitudes at 1400 MHz with the Parkes radio telescope.
Eight of these pulsars possess small pulse periods and period derivatives
thought to be indicative of ``recycling''. Six of the pulsars are in circular
binary systems, including two with relatively massive white dwarf companions.
We discuss the implications of these new systems for theories of binary
formation and evolution. One long-period pulsar (J1410-7404) has a moderately
weak magnetic field and an exceedingly narrow average pulse profile, similar to
other recycled pulsars.


title:
Photometric detection of high proper motions in dense stellar fields
  using Difference Image Analysis

abstract:
  The Difference Image Analysis (DIA) of the images obtained by the Optical
Gravitational Lensing Experiment (OGLE-II) revealed a peculiar artifact in the
sample of stars proposed as variable by Wozniak (2000) in one of the Galactic
bulge fields: the occurrence of pairs of candidate variables showing
anti-correlated light curves monotonic over a period of 3 years. This effect
can be understood, quantified and related to the stellar proper motions. DIA
photometry supplemented with a simple model offers an effective and easy way to
detect high proper motion stars (HPM stars) in very dense stellar fields, where
conventional astrometric searches are extremely inefficient.


title: Microlensing of collimated Gamma-Ray Burst afterglows

abstract:
  We investigate stellar microlensing of the collimated gamma-ray burst
afterglows. A spherical afterglow appears on the sky as a superluminally
expanding thin ring (``ring-like'' image), which is maximally amplified as it
crosses the lens. We find that the image of the collimated afterglow becomes
quite uniform (``disk-like'' image) after the jet break time (after the Lorentz
factor of the jet drops below the inverse of the jet opening angle).
Consequently, the amplification peak in the light curve after the break time is
lower and broader. Therefore detailed monitoring of the amplification history
will be able to test whether the afterglows are jets or not, i.e.,
``disk-like'' or not, if the lensing occurs after the break time. We also show
that some proper motion and polarization is expected, peaking around the
maximum amplification. The simultaneous detection of the proper motion and the
polarization will strengthen that the brightening of the light curve is due to
microlensing.


title: Linear nonadiabatic properties of SX Phoenicis variables

abstract:
  We present a detailed linear, nonadiabatic pulsational scenario for
oscillating Blue Stragglers (BSs)/SX Phoenicis (SX Phe) in Galactic Globular
Clusters (GGCs) and in Local Group (LG) dwarf galaxies. The sequences of models
were constructed by adopting a wide range of input parameters and properly
cover the region of the HR diagram in which these objects are expected to be
pulsationally unstable. Current calculations together with more metal-rich
models already presented by Gilliland et al. suggest that the pulsation
properties of SX Phe are partially affected by metal content. Our calculations
also suggest that the secular period change seems to be a good observable to
identify the pulsation mode of cooler SX Phe variables. The dependence of
pulsation properties on the helium envelope content is discussed and we find
that the secular period change for He-enhanced models is approximately a factor
of two larger than for canonical ones. According to this evidence we suggest
that the pulsation properties of SX Phe can be soundly adopted to constrain the
evolutionary history of BSs, and in turn to single out the physical mechanisms
which trigger their formation.


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

abstract:
  We present computer simulations of interferometric imaging with the Very
Large Telescope Interferometer (VLTI) of the European Southern Observatory
(ESO) and the Astronomical MultiBEam Recombiner (AMBER) phase-closure
instrument. These simulations include both the astrophysical modelling of a
stellar object by radiative transfer calculations and the simulation of light
propagation from the object to the detector (through atmosphere, telescopes,
and the AMBER instrument), simulation of photon noise and detector read-out
noise, and finally data processing of the interferograms. The results show the
dependence of the visibility error bars on the following observational
parameters: different seeing during the observation of object and reference
star (Fried parameters r_0,object and r_0,ref ranging between 0.9m and 1.2m),
different residual tip-tilt error (delta_tt,object and delta_tt,ref ranging
between 0.1% and 20% of the Airy disk diameter), and object brightness
(K_object=0.7mag to 10.2mag, K_ref=0.7mag). Exemplarily, we focus on stars in
late stages of stellar evolution and study one of its key objects, the dusty
supergiant IRC+10420 that is rapidly evolving on human timescales. We show
computer simulations of VLT interferometry (visibility and phase closure
measurements) of IRC+10420 with two and three Auxiliary Telescopes (ATs; AMBER
wide-field mode, i.e. without fiber optics spatial filters) and discuss whether
the visibility accuracy is sufficient to distinguish between different
theoretical model predictions.


title: On calculation of microlensing light curve by gravitational lens caustic

abstract:
  For an analysis of microlensing observational data in case of binary
gravitational lenses as well as for an interpretation of observations of high
magnification events in multiple images of a lensed quasar it is necessary to
calculate for a given source the microlensing light curve by a fold caustic.
This problem comes to the numerical calculation of a singular integral. We
formulated the sufficient condition of a convergence of the integral sum for
this singular integral. The strictly approach to the problem of a comparison of
model results with the unequally sampled observational data consists in
calculation of the model light curve in equidistant points of the canonical
dissection of the integration segment and a following interpolation of its
values at the moments of observations.


title: In Support of Inflation

abstract:
  The cosmic microwave background (CMB) provides a snapshot of the early
Universe when matter began to become structured and has been the focus of
several recent observational campaigns. In this Perspective, we discuss the
results from these campaigns, which provide support for inflationary models of
the Universe.

categories: astro-ph gr-qc hep-ph hep-th physics.pop-ph


title: Value of the Cosmological Constant: Theory versus Experiment

abstract:
  The numerical value of the cosmological constant is calculated using a
recently suggested cosmological model and found to be 2.036 x 10^(-35) s^(-2).
This value of the cosmological constant is in excellent agreement with the
measurements recently obtained by the High-Z Supernova Team and the Supernova
Cosmology Project.


title: A new sample of large angular size radio galaxies. I. The radio data

abstract:
  We present a new sample of 84 large angular size radio galaxies selected from
the NRAO VLA Sky Survey. Radio sources with declination above +60 degrees,
total flux density greater than 100 mJy at 1.4 GHz and angular size larger than
4 arcmin have been selected and observed with the VLA at 1.4 and 4.9 GHz. The
radio observations attempt to confirm the large angular size sources and to
isolate the core emission for optical identification. In this paper, the first
of a series of three, we present radio maps of 79 sources from the sample and
discuss the effects of the selection criteria in the final sample. 37 radio
galaxies belong to the class of giants, of which 22 are reported in this paper
for the first time.


title:
Effects of non-thermal tails in Maxwellian electron distributions on
  synchrotron and Compton processes

abstract:
  We investigate how the presence of a non-thermal tail beyond a Maxwellian
electron distribution affects the synchrotron process as well as Comptonization
in plasmas with parameters typical for accretion flows onto black holes. We
find that the presence of the tail can significantly increase the net (after
accounting for self-absorption) cyclo-synchrotron emission of the plasma, which
emission then provides seed photons for Compton upscattering. Thus, the
luminosity in the thermally-Comptonized spectrum is enhanced as well. The
importance of these effects increases with both increasing Eddington ratio and
the black hole mass. The enhancement of the Comptonized synchrotron luminosity
can be as large as by factors of $\sim 10^3$ and $\sim 10^5$ for stellar and
supermassive black holes, respectively, when the energy content in the
non-thermal tail is 1 per cent.
  The presence of the tail only weakly hardens the thermal Comptonization
spectrum but it leads to formation of a high-energy tail beyond the thermal
cut-off, which two effects are independent of the nature of the seed photons.
Since observations of high-energy tails in Comptonization spectra can constrain
the non-thermal tails in the electron distribution and thus the Comptonized
synchrotron luminosity, they provide upper limits on the strength of magnetic
fields in accretion flows. In particular, the measurement of an MeV tail in the
hard state of Cyg X-1 by McConnell et al. implies the magnetic field strength
in this source to be at most an order of magnitude below equipartition.


title:
A wide field survey at the Northern Ecliptic Pole: II. Number counts and
  galaxy colours in B_j, R, and K

abstract:
  We present a medium deep survey carried out in the three filters B_j, R and
K. The survey covers homogeneously the central square degree around the
Northern Ecliptic Pole (NEP) down to a completeness limit of 24.25, 23.0 and
17.5mag in B_j, R and K, respectively. While the near infrared data have been
presented in the first paper of this series, here we concentrate on the optical
data and the results based on the combined B_jRK-data. The unique combination
of area and depth in our survey allows to perform a variety of investigations
based on homogeneous material covering more than ten magnitudes in apparent
brightness. We analyze the number counts for point-like and extended sources in
B_j and R to determine the slopes in dlogN/dm and to test for possible breaks
therein. While we can confirm the slopes found in previous works with a higher
statistical significance, the largest uncertainty remaining for the amplitudes
is galactic extinction. We determine the colour distributions of galaxies in
B_j-R and R-K down to B_j=24.0 and K=18.0mag, respectively. The distributions
in both colours are modeled using galaxy spectral evolution synthesis. We
demonstrate that the standard models of galaxy evolution are unable to
reproduce the steady reddening trend in R-K despite flawless fits to the colour
distributions in the optical (B_j-R). The B_jRK data collected over a large
area provides the opportunity to select rare objects like candidates for
high-redshift galaxies and extremely red objects (EROs, R-K>5.0) and to
determine their surface density. Our EROs are selected at an intermediate
magnitude range and contain contribution from both galactic as well as
extragalactic sources. At K<16.5mag, where a morphological classification is
possible, the stellar component dominates the sample.


title:
AGN and starbursts at high redshift: High resolution EVN radio
  observations of the Hubble Deep Field

abstract:
  VLBI now has the capability of imaging relatively large fields-of-view (~ 5
arcmin sq) with sub-mJy detection limits. In principle such observations can
distinguish between starburst and AGN activity in cosmologically distant
sources. We present the first deep, wide-field European VLBI Network (EVN) 1.6
GHz observations of faint radio sources in the Hubble Deep Field (HDF) region.
The EVN clearly (> 5sigma) detects 2 radio sources in a field that encompasses
the HDF and part of the Hubble Flanking Fields (HFF). The sources detected are:
VLA J123644+621133 (a z=1.01, low-luminosity FR-I radio source located within
the HDF itself) and VLA J123642+621331 (a dust enshrouded, optically faint,
z=4.424 starburst system). A third radio source, J123646+621404, is detected at
the 4sigma level. The observations presented here, suggest that the radio
emission in the dusty starburst, VLA J123642+621331, arises mainly from AGN
activity, suggesting that in this system, both AGN and starburst activity
co-exist. The prospects for future VLBI deep fields are briefly discussed.


title: H3+ Between the Stars

abstract:
  The presence of H3+ in the interstellar medium was forecast almost four
decades ago. Almost three decades ago it was asserted that its reactions with
neutral molecular and atomic species directly lead to the production of many of
the interstellar molecules that have been discovered by radio and infrared
astronomers. With the recent detection of H3+ in interstellar space,
astronomers finally have direct confirmation of H3+ as the foundation of
ion-molecule interstellar chemistry. Although many questions remain to be
answered, it is clear that H3+is a unique tool for understanding the properties
of interstellar clouds.


title: Modes of Multiple Star Formation

abstract:
  This paper argues that star forming environments should be classified into
finer divisions than the traditional isolated and clustered modes. Using the
observed set of galactic open clusters and theoretical considerations regarding
cluster formation, we estimate the fraction of star formation that takes place
within clusters. We find that less than 10% of the stellar population
originates from star forming regions destined to become open clusters,
confirming earlier estimates. The smallest clusters included in the
observational surveys (having at least N=100 members) roughly coincide with the
smallest stellar systems that are expected to evolve as clusters in a dynamical
sense. We show that stellar systems with too few members N < N_\star have
dynamical relaxation times that are shorter than their formation times (1-2
Myr), where the critical number of stars N_\star \approx 100. Our results
suggest that star formation can be characterized by (at least) three principal
modes: I. isolated singles and binaries, II. groups (N<N_\star), and III.
clusters (N>N_\star). Many -- if not most -- stars form through the
intermediate mode in stellar groups with 10<N<100. Such groups evolve and
disperse much more rapidly than open clusters; groups also have a low
probability of containing massive stars and are unaffected by supernovae and
intense ultraviolet radiation fields. Because of their short lifetimes and
small stellar membership, groups have relatively little effect on the star
formation process (on average) compared to larger open clusters.


title: X-ray Reflection By Photoionized Accretion Discs

abstract:
  We present the results of reflection calculations that treat the relevant
physics with a minimum of assumptions. The temperature and ionization structure
of the top five Thomson depths of an illuminated disc are calculated while also
demanding that the atmosphere is in hydrostatic equilibrium. In agreement with
Nayakshin, Kazanas & Kallman, we find that there is a rapid transition from hot
to cold material in the illuminated layer. However, the transition is usually
not sharp so that often we find a small but finite region in Thomson depth
where there is a stable temperature zone at T \sim 2 x 10^{6} K due to
photoelectric heating from recombining ions. As a result, the reflection
spectra often exhibit strong features from partially-ionized material,
including helium-like Fe K lines and edges. We find that due to the highly
ionized features in the spectra these models have difficulty correctly
parameterizing the new reflection spectra. There is evidence for a spurious
$R-\Gamma$ correlation in the ASCA energy range, where $R$ is the reflection
fraction for a power-law continuum of index $\Gamma$, confirming the suggestion
of Done & Nayakshin that at least part of the R-Gamma correlation reported by
Zdziarski, Lubinski & Smith for Seyfert galaxies and X-ray binaries might be
due to ionization effects. Although many of the reflection spectra show strong
ionized features, these are not typically observed in most Seyfert and quasar
X-ray spectra.


title: High Energy Large Area Surveys: from BeppoSAX to Chandra and XMM

abstract:
  Optical identification of hard X-ray selected BeppoSAX and Chandra sources
indicates that a large fraction of the sources are ``intermediate'' AGN, i.e.
type 1.8-1.9 AGN, broad-line quasars and even X-ray loud but optically dull
(apparently normal) galaxies, all obscured in X-rays by columns of the order of
logNH=22-23.5 cm-2. Because of this obscuring matter, these sources are more
difficult to detect or select at other wavelengths, implying that a fraction of
the accretion power in the Universe may have been missed so far.


title: The near-infrared and ice-band variability of Haro 6-10

abstract:
  We have monitored the angularly resolved near infrared and 3.1 micron
ice-band flux of the components of the young binary Haro 6-10 on 23 occasions
during the years 1988 to 2000. Our observations reveal that both the visible
star Haro 6-10 (Haro 6-10S) and its infrared companion (Haro 6-10N) show
significant variation in flux on time scales as short as a month. The
substantial flux decrease of Haro 6-10S over the last four years carries the
reddening signature of increased extinction. However, a comparable K-band flux
increase observed in the IRC is associated with a dimming in the H-band and
cannot be explained by lower extinction. Absorption in the 3.1 micron water-ice
feature was always greater towards the IRC during our observations, indicating
a larger amount of obscuring material along its line of sight. We detect
variability in the ice-band absorption towards Haro 6-10S and Haro 6-10N,
significant at the 3.5 sigma and 2.0 sigma levels, respectively.


title: The Infrared Evolution of Sakurai's Object

abstract:
  Infrared spectroscopy and photometry have revealed the remarkable evolution
of Sakurai's Object from 1996 to the present. A cooling, carbon-rich
photospheric spectrum was observable from 1996 to 1998. Considerable changes
occured in 1998 as the continuum reddened due to absorption and emission by
newly formed dust located outside the photosphere. In addition, a strong and
broad helium 1.083 $\mu$m P Cygni line developed, signifying the acceleration
of an outer envelope of material to speeds as high as 1000 km s$^{-1}$. At the
same time the photosphere of the central star remained quiescent. By 1999 the
photosphere was virtually completely obscured by the dust and the helium
emission line was the only detectable spectral feature remaining in the 1-5
$\mu$m band. In 2000 emission by dust has become even more dominant, as the
envelope continues to expand and cool and the helium line weakens.


title: Morphology and Galactic Distribution of PNs: a New Scenario

abstract:
  We review recent studies on the morphology and distribution with respect to
the galactic plane of planetary nebulae (PNs), as well as recent advances in
MHD modeling of PNs. We discuss a tentative explanation for the connection
between morphological classes and their galactic distribution


title: Magnetohydrodynamic simulations of black hole accretion

abstract:
  We discuss the results of three-dimensional magnetohydrodynamic simulations,
using a pseudo-Newtonian potential, of thin disk (h/r ~ 0.1) accretion onto
black holes. We find (i) that magnetic stresses persist within the marginally
stable orbit, and (ii) that the importance of those stresses for the dynamics
of the flow depends upon the strength of magnetic fields in the disk outside
the last stable orbit. Strong disk magnetic fields (alpha > 0.1) lead to a
gross violation of the zero-torque boundary condition at the last stable orbit,
while weaker fields (alpha ~ 0.01) produce results more akin to traditional
models for thin disk accretion onto black holes. Fluctuations in the magnetic
field strength in the disk could lead to changes in the radiative efficiency of
the flow on short timescales.


title: QSO environments at intermediate redshifts

abstract:
  We have made a survey of quasar environments at 0.5 < z < 0.8, using a sample
of both radio-loud and radio-quiet quasars matched in B-band luminosity. Our
observations include images of background control fields to provide a good
determination of the field galaxy counts. About 10 per cent of the quasars
appear to live in rich clusters, whereas approximately 45 per cent live in
environments similar to that of field galaxies.
  The richness of galaxies within a 0.5 Mpc radius around the radio-quiet
quasars is found to be indistinguishable from the richness around the
radio-loud quasars, corresponding on average to groups or poorer clusters of
galaxies. Comparing the galaxy richness in the radio-loud quasar fields with
quasar fields in the literature, we find no evidence of an evolution in the
environment with epoch. Instead, a weak, but significant correlation between
quasar radio luminosity and environmental richness is present. It is thus
possible that the environments of quasars, at least the powerful ones, do not
evolve much between the present epoch and z \approx 0.8.


title:
Neutron star cooling in transiently accreting low mass binaries: a new
  tool for probing nuclear matter

abstract:
  We explore, using an exact cooling code, the thermal evolution of a neutron
star undergoing episodes of intense accretion, alternated by long periods of
quiescence (e.g. Soft X-Ray Transients). We find that the soft component of the
quiescent luminosity of Aql X-1, 4U 1608-522 and of SAX J1808.4-3658 can be
understood as thermal emission from a cooling neutron star with negligible
neutrino emission. In the case of Cen X-4 strong neutrino emission from the
inner core is necessary to explain the observation: this may indicate that the
neutron star of Cen X-4 is heavier than 1.4 Msun. This study opens the
possibility of using the quiescent emission of Soft X-Ray Transients as a tool
for probing the core superfluidity in relation to the mass of the neutron star.


title:
The effect of radiative cooling on scaling laws of X-ray groups and
  clusters

abstract:
  We have performed cosmological simulations in a $\Lambda$CDM cosmology with
and without radiative cooling, in order to study the effect of cooling on the
cluster scaling relations. Our simulations consist of 4.1 million particles
each of gas and dark matter within a box-size of 100 $h^{-1}$ Mpc and the run
with cooling is the largest of its kind to have been evolved to $z=0$. Our
cluster catalogues both consist of over 400 objects and are complete in mass
down to $\sim 10^{13} h^{-1} {\rm M_{\odot}}$. We contrast the
emission-weighted temperature-mass ($T_{\rm ew}-M$) and bolometric
luminosity-temperature ($L_{\rm bol}-T_{\rm ew}$) relations for the simulations
at $z=0$. We find that radiative cooling \emph{increases} the temperature of
intracluster gas and \emph{decreases} its total luminosity, in agreement with
the results of Pearce et al. Furthermore, the temperature dependence of these
effects flattens the slope of the $T_{\rm ew}-M$ relation and steepens the
slope of the $L_{\rm bol}-T_{\rm ew}$ relation. Inclusion of radiative cooling
in the simulations is sufficient to reproduce the observed X-ray scaling
relations without requiring excessive non-gravitational energy injection.


title: Resolution of the Age Discrepancies in Pulsar/SNR Associations

abstract:
  Pulsars associated with supernova remnants (SNRs) are valuable because they
provide constraints on the mechanism(s) of pulsar spin-down. Here we discuss
two SNR/pulsar associations in which the SNR age is much greater than the age
of the pulsar obtained by assuming pure magnetic dipole radiation (MDR)
spin-down. The PSR B1757-24/SNR G5.4-1.2 association has a minimum age of ~40
kyr from proper motion upper limits, yet the MDR timing age of the pulsar is
only 16 kyr, and the newly discovered pulsar PSR J1846-0258 in the >2 kyr old
SNR Kes 75 has an MDR timing age of just 0.7 kyr. These and other pulsar/SNR
age discrepancies imply that the pulsar spin-down torque is not due to pure
MDR, and we discuss a model for the spin-down of the pulsars similar to the
ones recently proposed to explain the spin-down of soft gamma-ray repeaters and
anomalous x-ray pulsars.


title:
Annual modulation in IDV of quasar 0917+624 due to Interstellar
  Scintillation

abstract:
  The quasar 0917+624 has been one of the best studied intraday variable (IDV)
radio sources. However, debate continues as to whether the underlying cause is
intrinsic or extrinsic. Much previous work has assumed the IDV to be intrinsic
and which implies an extraordinarily compact source for the radio emission; in
contrast, an extrinsic variation due to interstellar scintillation (ISS)
implies a relatively larger source diameter, though at the smaller end of the
range expected for relativistic jet models. Kraus et al. (1999) reported a
marked slowing of the IDV at 6cm wavelength in September 1998, and suggested a
change in the source was responsible. However, here we show that the slowing is
consistent with the annual modulation in scintillation time-scale expected for
ISS, under the assumption that the scattering medium moves with the local
standard of rest (LSR). The ISS time scale is governed by the ISS spatial scale
divided by the Earth's velocity relative to the scattering plasma. It happens
that in the direction of 0917+624 the transverse velocity of the Earth with
respect to the LSR varies widely with a deep minimum in the months of September
to November. Hence the slowing of the IDV in September 1998 strongly suggests
that ISS, rather than intrinsic variation of the source is the dominant cause
of the IDV.


title: An atlas of mid-infrared dust emission in spiral galaxies

abstract:
  We present maps of dust emission at 7 microns and 15 microns/7 microns
intensity ratios of selected regions in 43 spiral galaxies observed with
ISOCAM. This atlas is a complement to studies based on these observations,
dealing with star formation in centers of barred galaxies and in spiral disks.
It is accompanied by a detailed description of data reduction and an inventory
of generic morphological properties in groups defined according to bar strength
and HI gas content.


title:
Atmospheric Turbulence Measurements with the Palomar Testbed
  Interferometer

abstract:
  Data from the Palomar Testbed Interferometer, with a baseline length of 110 m
and an observing wavelength of $2.2 \mu{\rm m}$, were used to derive
information on atmospheric turbulence on 64 nights in 1999. The measured
two-aperture variance coherence times at $2.2 \mu{\rm m}$ ranged from 25 msec
to 415 msec (the lower value was set by instrumental limitations---the
interferometer could not operate when the coherence time was lower than this).
On all nights, the spectrum of the short time scale ($<600$ msec) delay
fluctuations had a shallower spectrum than the theoretical Kolmogorov value of
5/3. On most nights, the mean value of the power law slope was between 1.40 and
1.50. Such a sub-Kolmogorov slope will result in the seeing improving as the
$\approx 0.4$ power of wavelength, rather than the slower 0.2 power predicted
by Kolmogorov theory.
  On four nights, the combination of delay and angle tracking measurements
allowed a derivation of the (multiple) wind velocities of the turbulent layers,
for a frozen-flow model. The derived wind velocities were all $\le 4 {\rm m\
s^{-1}}$, except for a small $10 {\rm m s^{-1}}$ component on one night.
  The combination of measured coherence time, turbulence spectral slope, and
wind velocity for the turbulent layer(s) allowed a robust solution for the
outer scale size (beyond which the fluctuations do not increase). On the four
nights with angle tracking data, the outer scale varied from 6 to 54 m, with
most values in the 10-25 m range. Such small outer scale values cause some
components of visibility and astrometric errors to average down rapidly.


title: Comparing Optical and Near Infrared Luminosity Functions

abstract:
  The Sloan Digital Sky Survey [SDSS] has measured an optical luminosity
function for galaxies in 5 bands, finding 1.5 to 2.1 times more luminosity
density than previous work. This note compares the SDSS luminosity density to
two recent determinations of the near infrared luminosity function based on
2MASS data, and finds that an extrapolation of the SDSS results gives a 2.3
times greater near infrared luminosity density.


title: Search for an Near-IR Counterpart to the Cas A X-ray Point Source

abstract:
  We report deep near-infrared and optical observations of the X-ray point
source in the Cassiopeia A supernova remnant, CXO J232327.9+584842. We have
identified a J=21.4 +/- 0.3 mag and Ks=20.5 +/- 0.3 mag source within the
1-sigma error circle, but we believe this source is a foreground Pop II star
with Teff=2600-2800 K at a distance of ~2 kpc, which could not be the X-ray
point source. We do not detect any sources in this direction at the distance of
Cas A, and therefore place 3-sigma limits of R >~ 25 mag, F675W >~ 27.3 mag, J
>~ 22.5 mag and Ks >~ 21.2 mag (and roughly H >~ 20 mag) on emission from the
X-ray point source, corresponding to M_{R} >~ 8.2 mag, M_{F675W} >~ 10.7 mag,
M_{J} >~ 8.5 mag, M_{H} >~ 6.5 mag, and M_{Ks} >~ 8.0 mag, assuming a distance
of 3.4 kpc and an extinction A_{V}=5 mag.


title:
Pinpointing the massive black hole in the Galactic Center with
  gravitationally lensed stars

abstract:
  A new statistical method for pinpointing the massive black hole (BH) in the
Galactic Center on the IR grid is presented and applied to astrometric IR
observations of stars close to the BH. This is of interest for measuring the IR
emission from the BH, in order to constrain accretion models; for solving the
orbits of stars near the BH, in order to measure the BH mass and to search for
general relativistic effects; and for detecting the fluctuations of the BH away
from the dynamical center of the stellar cluster, in order to study the stellar
potential. The BH lies on the line connecting the two images of any background
source it gravitationally lenses, and so the intersection of these lines fixes
its position. A combined search for a lensing signal and for the BH shows that
the most likely point of intersection coincides with the center of acceleration
of stars orbiting the BH. This statistical detection of lensing by the BH has a
random probability of ~0.01. It can be verified by deep IR stellar
spectroscopy, which will determine whether the most likely lensed image pair
candidates (listed here) have identical spectra.


title: Galaxy Formation and Evolution: Recent Progress

abstract:
  In this series of lectures I review recent observational progress in
constraining models of galaxy formation and evolution highlighting the
importance advances in addressing questions of the assembly history and origin
of the Hubble sequence in the context of modern pictures of structure
formation.


title: A Sober Assessment of Cosmology at the New Millennium

abstract:
  Cosmology is the dot com of the sciences. Boom or bust. It is about nothing
less than the origin and evolution of the Universe, the all of everything. It
is the boldest of enterprises and not for the fainthearted. Cosmologists are
the flyboys of astrophysics, and they often live up to all that image conjures
up. It is hardly surprising then that words written about cosmology are rarely
balanced. They verve to one extreme or the other. .... Once or twice, I have
probably been guilty of irrational exuberance when it comes to cosmology.


title: Gravitational Memory ? - a Perturbative Approach

abstract:
  It has been pointed out that the value of the gravitational ``constant'' in
the early universe may be different from that at present. In that case, it was
conjectured that primordial black holes may ``remember'' the value of the
gravitational constant in the early universe. The present analysis shows that
this is not the case, at least in certain contexts.


title:
Infrared Spectroscopy of Brown Dwarfs: the onset of methane absorption
  in L dwarfs and the L/T transition

abstract:
  We present infrared spectra of brown dwarfs with spectral types from mid-L to
T. The 0.9-2.5 $\mu$m spectra of three dwarfs found by the Sloan Digital Sky
Survey contain absorption bands of both methane and carbon monoxide and bridge
the gap between late L and previously observed T dwarfs. These dwarfs form a
clear spectral sequence, with CH$_{4}$ absorption increasing as the CO
absorption decreases. Water vapor band strengths increase in parallel with the
methane bands and thus also link the L and T types. We suggest that objects
with detectable CO and CH$_{4}$ in the H and K bands should define the earliest
T subclasses. From observations of bright (K~$\leq$~13 mag) L dwarfs found by
2MASS, we find that the onset of detectable amounts of CH$_{4}$ occurs near
spectral type L5. For this spectral type methane is observable in the
3.3~$\mu$m $\nu$$_{3}$ band only, and not in the overtone and combination bands
at H and K.


title:
The elementary spike produced by a pure $e^+e^-$ pair-electromagnetic
  pulse from a Black Hole: The PEM Pulse

abstract:
  In the framework of the model that uses black holes endowed with
electromagnetic structure (EMBH) as the energy source, we study how an
elementary spike appears to the detectors. We consider the simplest possible
case of a pulse produced by a pure $e^+e^-$ pair-electro-magnetic plasma, the
PEM pulse, in the absence of any baryonic matter. The resulting time profiles
show a {\em Fast-Rise-Exponential-Decay} shape, followed by a power-law tail.
This is obtained without any special fitting procedure, but only by fixing the
energetics of the process taking place in a given EMBH of selected mass,
varying in the range from 10 to $10^3$ $M_\odot$ and considering the
relativistic effects to be expected in an electron-positron plasma gradually
reaching transparency. Special attention is given to the contributions from all
regimes with Lorentz $\gamma$ factor varying from $\gamma=1$ to $\gamma=10^4$
in a few hundreds of the PEM pulse travel time. Although the main goal of this
paper is to obtain the elementary spike intensity as a function of the arrival
time, and its observed duration, some qualitative considerations are also
presented regarding the expected spectrum and on its departure from the thermal
one. The results of this paper will be comparable, when data will become
available, with a subfamily of particularly short GRBs not followed by any
afterglow. They can also be propedeutical to the study of longer bursts in
presence of baryonic matter currently observed in GRBs.


title:
A probabilistic formulation for Empirical Population Synthesis: Sampling
  methods and tests

abstract:
  We present a probabilistic formulation of the classical problem of
synthesizing spectral properties of a galaxy using a base of star clusters. The
problem consists of estimating the population vector x, composed by the
contributions of n_star base elements to the integrated spectrum of a galaxy,
and the extinction A_V, given a set of absorption line equivalent widths and
continuum colors. The formalism is applied to the n_star = 12 base defined by
Schmidt etal and subsequently used in several studies. The 13-D parameter space
is explored with a Markov chain Monte Carlo sampling scheme based on the
Metropolis algorithm, which produces a smooth and efficient mapping of the
P(x,A_V) probability distribution.
  This version of Empirical Population Synthesis is used to investigate the
ability to recover the detailed history of star-formation and chemical
evolution using this spectral base. This is studied as a function of (1) the
magnitude of the measurement errors and (2) the set of observables used in the
synthesis. Only for extremely high S/N all 12 base proportions can be
accurately recovered, though the observables are very precisely reproduced for
any S/N. Furthermore, the individual mean x components are biased in the sense
that components which carry a large fraction of the light tend to share their
contribution preferably among components of same age. This compensation effect
is linked to noise-induced linear dependences in the base, which very
effectively redistribute the likelihood in x-space. The age distribution,
however, can be satisfactorily recovered for realistic data quality. (abridged)


title:
Clustering in the Universe: from Highly Nonlinear Structures to
  Homogeneity

abstract:
  These lecture notes concentrate on a few specific topics concerning the
distribution of galaxies on scales from 0.1 to nearly 1000/h Mpc. The main aim
is to provide the students with the information and tools to familiarize with a
few basic questions: 1) What are the scaling laws followed by the clustering of
luminous objects over almost four decades of scales; 2) How galaxy motions
distort the observed maps in redshift space, and how we can correct and use
them to our benefit; 3) Is the observed clustering of galaxies suggestive of a
fractal Universe; and consequently, 4) Is our faith in the Cosmological
Principle still well placed, i.e. do we see evidence for a homogeneous
distribution of matter on the largest explorable scales, in terms of the
correlation function and power spectrum of the distribution of luminous
objects. For some of these questions we have a well--defined answer, but for
some others the goal is to indicate the path along which there is still a good
deal of exciting work to be done.


title:
The likelihood of GODs' existence: Improving the SN1987a constraint on
  the size of large compact dimensions

abstract:
  The existence of compact dimensions which are accessible only to gravity
represents an intriguing possible solution to the hierarchy problem. At present
the strongest constraint on the existence of such compact Gravity-Only
Dimensions (GODs) comes from SN1987a. Here we report on the first
self-consistent simulations of the early, neutrino-emitting phase of a
proto-neutron star which include energy losses due to the coupling of the
Kaluza-Klein modes of the graviton which arise in a world with GODs. We compare
the neutrino signals from these simulations to that from SN1987a and use a
rigorous probabilistic analysis to derive improved bounds for the radii of such
GODs. We find that the possibility that there are two compact extra dimensions
with radii larger than 0.66 $\mu$m is excluded at the 95% confidence level---as
is the possibility that there are three compact extra dimensions larger than
0.8 nm.


title: Strip Searching for Supernovae

abstract:
  The survey of a strip of sky carried out with a zenith-observing 4-m liquid
mirror can discover and observe several thousand supernovae/year to z = 1,
making it quite competitive with other proposed surveys. Because LMs are
inexpensive, and easy to build, a SNeIa survey can begin rapidly. As documented
in the published literature, the present technology, and its cost, has been
proven in both the laboratory and in observatory settings and is ready, at a
very modest cost, for a 4-m class telescope.
  As a bonus, the coadded data would survey 150 square degrees of sky to
magnitudes > 27, as deep as the deepest optical surveys but in a far larger
area of sky. There presently is a window of opportunity to make fundamental
discoveries by exploiting the cost advantage of this powerful novel technology.


title:
Spectral variability of Ultra Luminous Compact X-ray Sources in Nearby
  Spiral Galaxies

abstract:
  Using the X-ray data taken with ASCA, a detailed analysis was made of
intensity and spectral variations of three ultra-luminous extra-galactic
compact X-ray sources (ULXs); IC 342 source 1, M81 X-6, and NGC 1313 source B,
all exhibiting X-ray luminosity in the range 10^{39}-1.5x10^{40} erg s^{-1}. As
already reported, IC 342 source 1 showed short-term X-ray intensity variability
by a factor of 2.0 on a typical time scale of 10 ks. M81 X-6 varied by a factor
of 1.6 across seven observations spanning 3 years, while NGC 1313 source B
varied by a factor of 2.5 between two observations conducted in 1993 July and
1995 November. The ASCA spectra of these sources, acquired on these occasions,
were all described successfully as optically-thick emission from standard
accretion disks around black holes. This confirms previous ASCA works which
explained ULXs as mass-accreting massive black-hole binaries. In all three
sources, the disk color temperature was uncomfortably high at T_{in}=1.0-2.0
keV, and was found to vary in proportion to the square-root of the source flux.
The apparent accretion-disk radius is hence inferred to change as inversely
proportional to T_{in}. This suggests a significant effect of advection in the
accretion disk. However, even taking this effect fully into account, the too
high values of T_{in} of ULXs cannot be explained. Further invoking the rapid
black-hole rotation may give a solution to this issue.


title: A `superoutburst' in XTE J1118+480

abstract:
  I propose that the properties of the two outbursts observed in the X-ray
transient XTE J1118+480 in 2000 are akin to superoutbursts of SU UMa stars. In
these systems a `normal' outburst immediately precedes a 5-10 times longer
(`super')outburst. The optical light curve of the outbursts of XTE J1118+480 is
remarkably similar to that seen in some SU UMa stars, such as UV Per and T Leo,
where the precursor outburst is distinct from the superoutburst, but the time
scales are a factor of ~15 different. The first outburst of XTE J1118+480 was
relatively short (~1 month) while the second outburst was ~5 times longer.
During the second outburst superhumps were seen, a feature characteristic for
superoutbursts. The gap of about a month between the two outbursts is longer in
X-rays with respect to the optical, a feature not previously recognized for
X-ray transients. Also in SU UMa stars the precursor outburst becomes more
distinct at shorter wavelengths. Finally, I show that the time of appearance of
the superhumps in XTE J1118+480 is consistent with the expected superhump
growth time, if the superhump mechanism was triggered during the first
outburst. I conclude that the similarity in outburst behaviour in the two types
of systems provides further support that a common mechanism is at work to start
the long (`super')outbursts.


title: On the Covariance of the Mixmaster Chaoticity

abstract:
  We analyze the dynamics of the Mixmaster Universe on the base of a standard
Arnowitt-Deser-Misner Hamiltonian approach showing how its asymptotic evolution
to the cosmological singularity is isomorphic to a billiard on the Lobachevsky
plane. The key result of our study consists in the temporary gauge invariance
of the billiard representation, once provided the use of very general
Misner-Chitre'-like variables.


title:
A 3D MHD model of astrophysical flows: algorithms, tests and
  parallelisation

abstract:
  In this paper we describe a numerical method designed for modelling different
kinds of astrophysical flows in three dimensions. Our method is a standard
explicit finite difference method employing the local shearing-box technique.
  To model the features of astrophysical systems, which are usually
compressible, magnetised and turbulent, it is desirable to have high spatial
resolution and large domain size to model as many features as possible, on
various scales, within a particular system. In addition, the time-scales
involved are usually wide-ranging also requiring significant amounts of CPU
time.
  These two limits (resolution and time-scales) enforce huge limits on
computational capabilities. The model we have developed therefore uses parallel
algorithms to increase the performance of standard serial methods. The aim of
this paper is to report the numerical methods we use and the techniques invoked
for parallelising the code. The justification of these methods is given by the
extensive tests presented herein.


title:
Dynamical modeling of large scale asymmetries in the beta Pictoris dust
  disk

abstract:
  We report a new and complete model of the beta Pictoris disk, which succeeds
in accounting for both the surface brightness distribution, warp
characteristics, the outer ``butterfly'' asymmetry as observed by HST/STIS in
scattered light, as well as the infrared emission. Our model includes the
presence of a disk of planetesimals extending out to 120-150 AU, perturbed
gravitationally by a giant planet on an inclined orbit, following the approach
of Mouillet et al. (1997b). At any time, the planetesimal disk is assumed to be
the source of a distribution of grains produced through collisional evolution,
with the same initial orbital parameter distribution. The steady state spatial
grain distribution is found incorporating the effects of radiation pressure
which can cause the distribution of the smallest particles to become very
distended. With realistic assumptions about the grains' chemical properties,
the modeling confirms the previously evident need for an additional population
of hot grains close to the star, to account for the 12 microns fluxes at short
distances from the star. It also indicates that this population cannot explain
the outer 12 microns flux distribution when the effects of gravity and
radiation pressure determine the distribution. Very small grains, produced by
collisions among aggregates, are tentatively proposed to account for this 12
microns outer emission.


title: Radio Emission from the X-ray transient XTE J1550-564

abstract:
  We report multifrequency radio observations of XTE J1550-564 obtained with
the Molonglo Observatory Synthesis Telescope and the Australia Telescope
Compact Array at the time of its discovery and subsequent hard and soft X-ray
outburst in 1998 September. A large radio flare was observed, peaking about 1.8
days after the X-ray flare. In addition, we present Australian Long Baseline
Array images obtained shortly after the maximum of the radio flare which show
evolving structure. The apparent separation velocity of the two outermost
components is v>2c.


title: Supernova Ia Predicted without the Cosmological Constant

abstract:
  The current big-bang cosmological model requires re-introduction of
Einstein's "regretted" old cosmological constant to fit the astronomical
measurements of supernova Ia magnitude versus redshift. The physical basis of
the cosmological constant and the resulting acceleration of the universe are
not supported by any other physical evidence and some advise caution in rushing
to its acceptance. An altogether new cosmological model with only one
adjustable parameter, the present age of the universe, does provide an
excellent prediction of the supernova measurements without the cosmological
constant. With a minimum description of the new model, a full set of equations
is presented here sufficient to calculate the peak effective magnitude of a
type Ia supernova for an input value of redshift Z and age t0. A full
description of the model, together with many more falsifiable predictions, are
presented elsewhere.


title:
The disc instability model of dwarf-novae and low-mass X-ray binary
  transients

abstract:
  The disc instability model which is supposed to describe outbursts of dwarf
nova and low-mass X-ray binary transient systems is presented and reviewed in
detail. Various deficiencies of the model are pointed out and various remedies
and generalizations are presented and discussed.


title: Ultraviolet and visible spectropolarimetric variability in P Cygni

abstract:
  We report on new data, including four vacuum ultraviolet spectropolarimetric
observations by the Wisconsin Ultraviolet Photo-Polarimeter Experiment
("WUPPE") on the Astro-1 (one observation) and Astro-2 (three observations)
shuttle missions, and 15 new visible-wavelength observations obtained by the
HPOL CCD spectropolarimeter at the Pine Bluff Observatory of the University of
Wisconsin. This includes three HPOL observations made within 12 hours of each
of the three Astro-2 WUPPE observations, giving essentially simultaneous
observations extending from 1500 to 10500 Angstroms. An analysis of these data
yields estimates on the properties of wind "clumps" when they are detectable by
the polarization of their scattered light. We find that the clumps must be
detected near the base of the wind, r/R* = 1.3 - 2.5. At this time the clump
density is at least 10^13 cm^-3, 20 times the mean wind, and the temperature is
roughly 10,000 K, about 20% cooler than the mean wind. The clumps leading to
the largest observed polarization must have electron optical depth of 0.1 - 1
and an angular extent of 0.1 - 1 ster, and account for at most 2% of the wind
mass loss. The H and HeI emission lines from the wind are unpolarized, but
their P Cygni absorption is enhanced by a factor of 4 in the scattered light.
We speculate on the possible relationship of the clumps detected
polarimetrically to those seen as Discrete Absorption Features (DACs) and in
interferometry.