title:
FUSE and HST STIS Observations of Hot and Cold Gas in the AB Aurigae
  System

abstract:
  We present the first observations of a Herbig Ae star with a circumstellar
disk by the Far Ultraviolet Spectroscopic Explorer (FUSE), as well as a
simultaneous observation of the star obtained with the Hubble Space Telescope
Space Telescope Imaging Spectrograph (STIS). The spectra of AB Aurigae show
emission and absorption features arising from gasses that have a wide range in
temperature, from hot OVI emission to cold molecular hydrogen and CO
absorption. Emissions from the highly ionized species OVI and CIII present in
the FUSE spectrum are redshifted, while absorption features arising from
low-ionization species like OI, NI, and SiII are blueshifted and show
characteristic stellar wind line-profiles. We find the total column density of
molecular hydrogen toward AB Aur from the FUSE apectrum, N(H_2) = (6.8 +/- 0.5)
x 10^19 cm^-2. The gas kinetic temperature of the molecular hydrogen derived
from the ratio N(J=1)/N(J=0) is 65 +/- 4 K. The column density of the CO
observed in the STIS spectrum is N(CO) = (7.1 +/- 0.5) x 10^13 cm^-2, giving a
CO/H_2 ratio of (1.04 +/- 0.11) x 10^-6. We also use the STIS spectrum to find
the column density of HI, permitting us to calculate the total column density
of hydrogen atoms, the fractional abundance of H_2, and the gas-to-dust ratio.


title: The Anisotropy of the Ultra-High Energy Cosmic Rays

abstract:
  Ultra-high energy cosmic rays (UHECRs) may originate from the decay of
massive relic particles in the dark halo of the Galaxy, or they may be produced
by supermassive black holes in the nuclei of nearby galaxies. The anisotropy in
the arrival directions is studied in four dark halo models (cusped, isothermal,
triaxial and tilted) and in four galaxy samples (galaxies intrinsically
brighter than Centaurus A within 50 and 100 Mpc, and brighter than M32 within
50 and 100 Mpc). In decaying dark matter models, the amplitude of the
anisotropy is controlled by the size of the Galactic halo, while the phase is
controlled by the shape. In the northern hemisphere, the amplitude is about 0.5
for cusped haloes, but falls to roughly 0.3 for isothermal haloes. The phase
points in the direction of the Galactic Centre, with deviations of up to 30
degrees possible for triaxial and tilted haloes. The effect of the halo of M31
is too weak to provide conclusive evidence for the decaying dark matter origin
of UHECRs. In extragalactic models, samples of galaxies brighter than Centaurus
A produce substantial anisotropies (roughly 1.8), much larger than the limits
set by the available data. If all galaxies brighter than M32 contribute, then
the anisotropy is more modest (roughly 0.5) and is directed toward mass
concentrations in the supergalactic plane, like the Virgo cluster. Predictions
are made for the southern hemisphere station of the Pierre Auger Observatory.
If the UHECRs have a Galactic origin, then the phase points towards the
Galactic Centre. If they have an extragalactic origin, then it points in the
rough direction of the Fornax cluster. This provides an unambiguous
discriminant and requires about 350-500 events at South Auger.


title: The mysterious HI deficiency of NGC 3175

abstract:
  Australia Telescope Compact Array HI observations reveal the existence of
5.8x10^8 M_sun of HI gas in the central 7 kpc of the edge-on spiral galaxy NGC
3175. The detected HI and CO gas can explain why star formation, as traced by
other emission processes, is going on in the inner part of its disk. On the
other hand, the entire outer disk, beyond 3.5 kpc radius, shows no HI emission,
has a very red colour and exhibits neither radio continuum nor H-alpha
emission. This indicates that the outer part of NGC 3175 is quiescent, i.e. not
forming stars at a measurable rate. Its HI deficiency and the small extent of
the HI layer, which is confined to the boundaries of the optically visible
disk, make NGC 3175 a peculiar spiral galaxy. No intergalactic HI gas in the
NGC 3175 group was detected in our interferometric observations. Earlier Parkes
telescope single dish HI observations put an upper limit on the amount of
diffuse gas that might have been missed by the interferometer at 2x10^8 M_sun.
On DSS plates no galaxy in the NGC 3175 group of galaxies (Garcia 1993) is
close enough to it and none exhibits disturbances that could indicate a close
interaction which might have led to the stripping of large parts of its HI gas.
Thus, despite an extensive multi-wavelength investigation, the reason for the
unusual absence of HI and star formation activity in the outer disk of NGC 3175
remains an intriguing mystery.


title:
The radio-luminosity - black hole mass correlation for quasars from the
  FIRST Bright Quasar Survey, and a ``unification scheme'' for radio-loud and
  radio-quiet quasars

abstract:
  Several independent lines of evidence now point to a correlation between
black hole mass, M_bh, and radio-luminosity. In this paper we discuss the
correlation for quasars from the FIRST Bright Quasar Survey (FBQS), using black
hole mass estimates from Hbeta linewidths. The FBQS objects fill in the gap
between the radio-loud and radio-quiet quasars in the radio-luminosity -
optical-luminosity plane, and we find that they fill the corresponding gap in
the M_bh - radio luminosity correlation. There is thus a continuous variation
of radio luminosity with M_bh, and no evidence for a ``switch'' at some set of
critical parameter values which turns on powerful radio jets. By combining the
FBQS data with that for quasars from the Palomar-Green survey we find evidence
for a dependence of radio-luminosity on accretion rate relative to the
Eddington limit, L/L_Edd, as well as on M_bh, consistent with the well-known
radio-optical correlation for radio-loud quasars. We therefore suggest a new
scheme to ``unify'' radio-loud and radio-quiet objects in which radio
luminosity scales proportional to M_bh^{1.9+/-0.2}(L/L_Edd)^{1.0} for
L/L_Edd~0.1, with an apparently weaker accretion rate dependence at low
L/L_Edd. The scatter about this relation is +/-1.1 dex, and may well hide
significant contributions from other physical effects, such as black hole spin
and radio source environment.


title: Gravitational waves from relativistic rotational core collapse

abstract:
  We present results from simulations of axisymmetric relativistic rotational
core collapse. The general relativistic hydrodynamic equations are formulated
in flux-conservative form and solved using a high-resolution shock-capturing
scheme. The Einstein equations are approximated with a conformally flat
3-metric. We use the quadrupole formula to extract waveforms of the
gravitational radiation emitted during the collapse. A comparison of our
results with those of Newtonian simulations shows that the wave amplitudes
agree within 30%. Surprisingly, in some cases, relativistic effects actually
diminish the amplitude of the gravitational wave signal. We further find that
the parameter range of models suffering multiple coherent bounces due to
centrifugal forces is considerably smaller than in Newtonian simulations.


title:
Pulsar wind nebulae around the southern pulsars PSR B1643-43 and PSR
  B1706-44

abstract:
  We present high resolution VLA images taken at the wavelengths of lambda 20
cm, lambda 6 cm, and lambda 3.6 cm in the vicinity of the pulsars PSR B1706-44
(PSR J1709-4428) and PSR B1643-43 (PSR J1646-4346). Both of these pulsars are
young (<30,000 yrs) and have large spin-down luminosities (e+35 erg/sec) and
hence are good candidates to search for extended synchrotron nebula excited by
the relativistic pulsar wind. For PSR B1643-43 we found evidences of a
4'comet-shaped nebula, suggestive of a synchrotron ``wake'' left by a fast
moving pulsar. PSR B1706-44 appears surrounded by a spherical nebula
approximately 3 ' in diameter. Based on their morphology, the detection of
significant linear polarization (>20%), and their flat radio spectra
(alpha=0.25-0.3, where S_nu aprox nu^-alpha) we argue that these are wind
nebulae powered by the rotational energy loss of the respective pulsars.


title: On the quiescence of the Hubble flow in the vicinity of the Local Group

abstract:
  Cepheid distances of local galaxies (<7 Mpc) are used to study the very
nearby velocity field, as pioneered by Sandage (Sandage 1986) who also pointed
out its remarkable properties: linearity and quietness. The new data show that
the velocity dispersion in the distance range as seen from the barycentre of
the Local Group 1-8 Mpc is as low as 38 km/sec. The local rate of expansion
coincides with the global Hubble constant. Down to 1.5 Mpc we cannot detect a
deviation from the linear Hubble flow. This puts an upper limit for the mass of
the Local Group, for a wide class of Friedman models, including those with the
cosmological constant.


title: A new approach to the problem of modes in the Mestel disk

abstract:
  We examine the modes admitted by the Mestel disk, a disk with a globally flat
rotation curve. In contrast to previous analyses of this problem by Zang
(\cite{1976PhDT........26Z}) and Evans & Read (\cite{1998MNRAS.300...83E},
\cite{1998MNRAS.300..106E}), we approximate the orbits to obtain almost closed
expressions for the kernel of the integral equation governing the behaviour of
the modes. Otherwise we, like them, follow Kalnajs' programme to simultaneously
solve the Boltzmann and Poisson equations.
  We investigate the modes admitted by both the self-consistent and a cut-out
Mestel disk, the difference being that in the latter, a part of the matter in
the disk is immobilised. This breaks the self-similarity and produces a
pronouncedly different picture, both technically and in terms of the disk
properties. The self-consistent disk is governed by a Cauchy integral equation,
the cut-out disk by an integral equation that can be treated as a Fredholm
equation of the second kind.
  In general, our approximation reproduces the results of the previous works
remarkably well, yielding quantities mostly within 5% of the values reported by
Zang and Evans & Read and thus also the basic result that in a ``standard''
cut-out disk, only one-armed modes are unstable at the limit of axisymmetric
stability. In the self-consistent disk, relatively compact expressions for the
kernel allow an intuitive understanding of most of the properties of neutral
(non-rotating, non-growing) modes there. We finally show that self-consistent
Mestel disks do not admit growing or rotating modes in this sort of
stellar-dynamical analysis.


title: The evolution of the galaxy distribution

abstract:
  We follow the evolution of the galaxy population in a Lambda-CDM cosmology by
means of high-resolution N-body simulations in which the formation of galaxies
and their observable properties are calculated using a semi-analytic model. We
display images of the spatial distribution of galaxies in the simulations that
illustrate its evolution and provide a qualitative understanding of the
processes responsible for various biases that develop. We consider three
specific statistical measures of clustering at z=1 and z=0: the correlation
length (in real- and redshift-space) of galaxies of different luminosity, the
morphology-density relation and the genus curve of the topology of galaxy
isodensity surfaces. For galaxies with luminosity below L*, the z=0 correlation
length depends very little on the luminosity of the sample, but for brighter
galaxies it increases very rapidly, reaching values in excess of 10Mpc/h. The
"accelerated" dynamical evolution experienced by galaxies in rich clusters,
which is partly responsible for this effect, also results in a strong
morphology-density relation. Remarkably, this relation is already
well-established at z=1. The genus curves of the galaxies are significantly
different from the genus curves of the dark matter but this is not due to
genuine topological differences but rather to the sparse sampling of the
density field provided by galaxies. The predictions of our model at z=0 will be
tested by forthcoming data from the 2dF and Sloan galaxy surveys, and those at
z=1 by the DEEP and VIRMOS surveys.


title: Strong gravitational lensing by multiple galaxies

abstract:
  We discuss strong gravitational lensing by multiple objects along any line of
sight. The probability for strong gravitational lensing by more than one lens
is small, but a number of strong lens systems in which more than one separate
lens contribute significantly to the lensing potential will be detected in the
large sample of lens systems compiled with new instruments. Using multi-lens
ray-tracing, we estimate the likelihood for gravitational lensing by two lenses
at different redshifts and investigate typical image geometries and
magnification cross sections. We find that, for a cosmology with Omega_M=0.3
and Omega_Lambda=0.7, about one in twenty lens systems consist of two lenses
with merging caustics. Multiple lens systems differ from single lenses. They
have a larger multiple imaging cross section and significantly differ in the
image configuration. The external shear induced by a nearby galaxy, group or
cluster can affect image positions even for more widely separated lens pairs.
Both of these effects must be accounted for in lens modelling. We also show how
the presence of aligned discs in the pair of lensing galaxies can lead to very
large high-magnification cross sections. Multiple lens systems will be
important in future, both for constraining lens models of individual systems
and for statistical lensing.


title: Caustic Rings and Cold Dark Matter

abstract:
  The hierarchical cold dark matter (CDM) model for structure formation is a
well defined and testable model. Direct detection is the best technique for
confirming the model yet predictions for the energy and density distribution of
particles on earth remain inadequate. Axially symmetric collapse of
collisionless dark matter can leave observable caustic rings in phase space and
this model is frequently used to make experimental predictions (Sikivie 1999).
Such cold collapses inevitably suffer from radial orbit instabilities that
produce unrealistic bar-like halos. Moreover, this model bears no relation to
the hierarchical growth of CDM galactic halos which form via a complicated
sequence of mergers and violent relaxation. This process destroys any symmetry
and phase wraps existing caustics on a scale comparable to the first objects to
collapse. Since axions can cluster on microscopic scales and free streaming of
neutralinos only erases structure smaller than \sim 100 (GeV/m_{CDM}) A.U., the
dynamical effects of caustics in the Galactic halo are expected to be
negligible.


title: Neutrino Propagation in Dense Astrophysical Systems

abstract:
  Even the elusive neutrinos are trapped in matter, albeit transiently, in
several astrophysical circumstances. Their interactions with the ambient matter
not only reveal the properties of such exotic matter itself, but also shed
light on the fundamental properties of the neutrinos themselves. The physical
sites of interest include the early universe, supernovae, and newly-born
neutron stars. Detection of neutrinos from these vastly different eras using
the new generation of neutrino detectors holds great promise for enhancing our
understanding of neutrino-matter interactions and astrophysical phenomena.


title: Magnetic Collimation in PNe

abstract:
  Recent studies have focused on the the role of initially weak toroidal
magnetic fields embedded in a stellar wind as the agent for collimation in
planetary nebulae. In these models the wind is assumed to be permeated by a
helical magnetic field in which the poloidal component falls off faster than
the toroidal component. The collimation only occurs after the wind is shocked
at large distances from the stellar source. In this paper we re-examine
assumptions built into this ``Magnetized Wind Blown Bubble'' (MWBB) model. We
show that a self-consistent study of the model leads to a large parameter
regime where the wind is self-collimated before the shock wave is encountered.
We also explore the relation between winds in the MWBB model and those which
are produced via magneto-centrifugal processes. We conclude that a more
detailed examination of the role of self-collimation is needed in the context
of PNe studies.


title:
Investigation of charge sharing among electrode strips for a CdZnTe
  detector

abstract:
  We have investigated charge sharing among the anode strips of a CdZnTe (CZT)
detector using a 30 micrometer collimated gamma-ray beam. We compared the
laboratory measurements with the predictions from our modeling of the charge
transport within the detector. The results indicate that charge sharing is a
function of the interaction depth and the energy of the incoming photon. Also,
depending on depth, a fraction of the electrons might drift to the inter-anode
region causing incomplete charge collection. Here, we show that photoelectron
range and diffusion of the charge cloud are the principal causes of charge
sharing and obtain limits on the size of the electron cloud as a function of
position in the detector.


title: Observational Constraints on the Formation and Evolution of Binary Stars

abstract:
  We present a high spatial resolution UV to NIR survey of 44 young binary
stars in Taurus with separations of 10-1000 AU. The primary results include:
(1) The relative ages of binary star components are more similar than the
relative ages of randomly paired single stars, supporting coeval formation. (2)
Only one of the companion masses is substellar, and hence the apparent
overabundance of T Tauri star companions relative to main-sequence star
companions can not be explained by a wealth of substellar secondaries that
would have been missed in main-sequence surveys. (3) Roughly 10% of T Tauri
binary star components have very red NIR colors (K-L > 1.4) and unusually high
mass accretion rates. This phenomenon does not appear to be restricted to
binary systems, however, since a comparable fraction of single T Tauri stars
exhibit the same properties. (4) Although the disk lifetimes of single stars
are roughly equal to their stellar ages, the disk lifetimes of binary stars are
an order of magnitude less than their ages. (5) The accretion rates for both
single and binary T Tauri stars appear to be moderately mass dependent. (6)
Although most classical T Tauri star binaries retain both a circumprimary and a
circumsecondary disk, there are several systems with only a circumprimary disk.
Together with the relative accretion rates, this suggests that circumprimary
disks survive longer, on average, than circumsecondary disks. (7) The disk
lifetimes, mass ratios, and relative accretion signatures of the closest
binaries (10-100 AU) suggest that they are being replenished from a
circumbinary reservoir with low angular momentum. Overall, these results
support fragmentation as the dominant binary star formation mechanism.


title: HIPASS Detection of an Intergalactic Gas Cloud in the NGC 2442 Group

abstract:
  We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of a gas
cloud associated with the asymmetric spiral galaxy NGC 2442. This object,
designated HIPASS J0731-69, contains ~10^9 M_sun of HI, or nearly one-third as
much atomic gas as NGC 2442 itself. No optical counterpart to any part of
HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse,
and with its stream-like kinematics. If the gas in HIPASS J0731-69 was once
part of NGC 2442, then it was most likely a fairly recent tidal encounter with
a moderately massive companion which tore it loose, although the possibility of
ram-pressure stripping cannot be ruled out. This discovery highlights the
potential of the HIPASS data for yielding new clues to the nature of some of
the best-known galaxies in the local universe.


title: The dark matter crisis

abstract:
  I explore several possible solutions to the ``missing satellites'' problem
that challenges the collisionless cold dark matter model.


title:
Infrared Emission from the Radio Supernebula in NGC 5253: A
  Proto-Globular Cluster?

abstract:
  Hidden from optical view in the starburst region of the dwarf galaxy NGC 5253
lies an intense radio source with an unusual spectrum which could be
interpreted variously as nebular gas ionized by a young stellar cluster or
nonthermal emission from a radio supernova or an AGN. We have obtained 11.7 and
18.7 micron images of this region at the Keck Telescope and find that it is an
extremely strong mid-infrared emitter. The infrared to radio flux ratio rules
out a supernova and is consistent with an HII region excited by a dense cluster
of young stars. This "super nebula" provides at least 15% of the total
bolometric luminosity of the galaxy. Its excitation requires 10^5-10^6 stars,
giving it the total mass and size (1-2 pc diameter) of a globular cluster.
However, its high obscuration, small size, and high gas density all argue that
it is very young, no more than a few hundred thousand years old. This may be
the youngest globular cluster yet observed.


title: Mass Density Profiles of LSB Galaxies

abstract:
  We derive the mass density profiles of dark matter halos that are implied by
high spatial resolution rotation curves of low surface brightness galaxies. We
find that at small radii, the mass density distribution is dominated by a
nearly constant density core with a core radius of a few kpc. For rho(r) ~ r^a,
the distribution of inner slopes a is strongly peaked around a = -0.2. This is
significantly shallower than the cuspy a < -1 halos found in CDM simulations.
While the observed distribution of alpha does have a tail towards such extreme
values, the derived value of alpha is found to depend on the spatial resolution
of the rotation curves: a ~ -1 is found only for the least well resolved
galaxies. Even for these galaxies, our data are also consistent with constant
density cores (a = 0) of modest (~ 1 kpc) core radius, which can give the
illusion of steep cusps when insufficiently resolved. Consequently, there is no
clear evidence for a cuspy halo in any of the low surface brightness galaxies
observed.


title: Chandra observtaion of A2256 - a cluster at the early stage of merging

abstract:
  We present here \chandra observations of the rich cluster of galaxies A2256.
In addition to the known cool subcluster, a new structure was resolved 2$'$
east of the peak of the main cluster. Its position is roughtly at the center of
a low-brightness radio halo. Spectral analysis shows that the "shoulder" has
high iron abundance ($\sim$ 1). We suggest that this structure is either
another merging component or an internal structure of the main cluster. The
X-ray redshifts of several regions were measured. The results agree with the
optical ones and suggest that the main cluster, the subcluster and the
"shoulder" are physically associated and interacting. The subcluster has low
temperature ($\sim$ 4.5 keV) and high iron abundance ($\sim$ 0.6) in the
central 150 kpc. The \chandra image shows a relatively sharp brightness
gradient at the south of the subcluster peak running south-south-east (SSE). A
temperature jump was found across the edge, with higher temperature ahead of
the edge in the low density region. This phenomenon is qualitatively similar to
the "cold fronts" found in A2142 and A3667. If the "shoulder" is ignored, the
temperature map resembles those simulations at the early stage of merging while
the subcluster approached the main cluster from somewhere west. This fact and
the observed edge, in combination with the clear iron abundance contrast
between the center of the subcluster ($\sim$ 0.6) and the main cluster ($\sim$
0.2), all imply that the ongoing merger is still at the early stage. At least
three member galaxies, including a radio head-tail galaxy, were found to have
corresponding X-ray emission.


title: Evolution and Nucleosynthesis of Zero Metal Intermediate Mass Stars

abstract:
  New stellar models with mass ranging between 4 and 8 Mo, Z=0 and Y=0.23 are
presented. The models have been evolved from the pre Main Sequence up to the
Asymptotic Giant Branch (AGB). At variance with previous claims, we find that
these updated stellar models do experience thermal pulses in the AGB phase. In
particular we show that: a) in models with mass larger than 6 Mo, the second
dredge up is able to raise the CNO abundance in the envelope enough to allow a
"normal" AGB evolution, in the sense that the thermal pulses and the third
dredge up settle on; b) in models of lower mass, the efficiency of the CNO
cycle in the H-burning shell is controlled by the carbon produced locally via
the 3alpha reactions. Nevertheless the He-burning shell becomes thermally
unstable after the early AGB. The expansion of the overlying layers induced by
these weak He-shell flashes is not sufficient by itself to allow a deep
penetration of the convective envelope. However, immediately after that, the
maximum luminosity of the He flash is attained and a convective shell
systematically forms at the base of the H-rich envelope. The innermost part of
this convective shell probably overlaps the underlying C-rich region left by
the inter-shell convection during the thermal pulse, so that fresh carbon is
dredged up in a "hot" H-rich environment and a H flash occurs. This flash
favours the expansion of the outermost layers already started by the weak
thermal pulse and a deeper penetration of the convective envelope takes place.
Then, the carbon abundance in the envelope rises to a level high enough that
the further evolution of these models closely resembles that of more metal rich
AGB stars. These stars provide an important source of primary carbon and
nitrogen.


title: Backflow in Post-Asymptotic Giant Branch Stars

abstract:
  We derive the conditions for a backflow toward the central star(s) of
circumstellar material to occur during the post-asymptotic giant branch (AGB)
phase. The backflowing material may be accreted by the post-AGB star and/or its
companion, if such exists. Such a backflow may play a significant role in
shaping the descendant planetary nebula, by, among other things, slowing down
the post-AGB evolution, and by forming an accretion disk which may blow two
jets. We consider three forces acting on a slowly moving mass element: the
gravity of the central system, radiation pressure, and fast wind ram pressure.
We find that for a significant backflow to occur, a slow dense flow should
exsist, such that the relation between the total mass in the slow flow, M, and
the solid angle it covers, Omega, is given by (4*pi*M/Omega)>0.1Mo. The
requirement for both high mass loss rate per unit solid angle and a very slow
wind, such that it can be decelerated and flow back, probably requires close
binary interaction.


title:
Measurement of the (gamma,n) reaction rates of the nuclides 190Pt,
  192Pt, and 198Pt in the astrophysical gamma-process

abstract:
  The nucleosynthesis of heavy neutron-deficient nuclei in a stellar photon
bath at the temperatures relevant for the astrophysical gamma process was
investigated. In order to derive (gamma,n) cross sections and reaction rates,
the stellar photon bath was simulated by the superposition of several
bremsstrahlung spectra with different endpoint energies. As a first test for
this method, the (gamma,n) reaction rates of the platinum isotopes 190Pt,
192Pt, and 198Pt were derived. The results are compared to other experimental
data and theoretical calculations.


title: On the second overtone stability among SMC Cepheids

abstract:
  We present a new set of Cepheid, full amplitude, nonlinear, convective models
which are pulsationally unstable in the second overtone (SO). Hydrodynamical
models were constructed by adopting a chemical composition typical for Cepheids
in the Small Magellanic Cloud (SMC) and stellar masses ranging from 3.25 to 4
solar masses. Predicted phi{21} Fourier parameters agree, within current
uncertainties, with empirical data for pure first and second overtone variables
as well as for first/second overtone (FO/SO) double-mode Cepheids collected by
Udalski et al. (1999a,b) in the SMC. On the other hand, predicted I band
amplitudes are systematically larger than the observed ones in the short period
range. We also find, in agreement with empirical evidence, that the region
within which both second and first overtones attain a stable limit cycle widens
when moving toward lower luminosities. Moreover, predicted P{SO}/P{FO} and
P{FO}/P{F} period ratios agree quite well with empirical period ratios for
FO/SO and F/FO double-mode SMC Cepheids. Finnaly, current models support the
evidence that pure SO Cepheids and SO components in FO/SO Cepheids are good
distance indicators.


title: Radiative Hydromagnetic Shocks in Relativistic Outflow Sources

abstract:
  We calculate the structure of a relativistic shock wave in which the internal
energy of the shocked fluid is radiated away on a time scale much shorter than
the characteristic shock propagation time. The shock is assumed to move through
a uniformly magnetized, neutral plasma consisting of protons, electrons, and
positrons, and allowance is made for the possible production of
electron/positron pairs in the shock itself. The radiation mechanism is taken
to be synchrotron and inverse-Compton emission (the latter involving both
synchrotron-produced and externally supplied seed photons) by the electrons and
positrons. We simplify the discussion by considering a shock in which the
magnetic field is transverse to the direction of propagation and focus
attention on the properties of the radiative zone that forms behind the shock
transition. In particular, we investigate the possibility that the compression
induced by the cooling of the gas amplifies the magnetic pressure until it
reaches (and ultimately exceeds) equipartition with the thermal pressure
(which, in turn, limits the overall compression). We show that, if a
significant fraction of the postshock thermal energy is deposited in the
electron/positron component, then a considerable portion of the emitted
radiation will come from regions of strong magnetic field even if the field
immediately behind the shock transition is well below equipartition. This field
amplification mechanism may be relevant to the production of synchrotron flares
in blazars, miniquasars, and gamma-ray burst sources. We consider the latter
application in some detail and show that this process may play a role in the
prompt $\gamma$-ray and possibly also the optical ``flash'' and radio ``flare''
emission, but probably not in the afterglow.


title: Understanding the radio emission geometry of PSR B0329+54

abstract:
  We have analyzed high-quality single pulse data of PSR B0329+54 at 325 MHz
and 606 MHz to study the structure of the emission beam. Using the
window-threshold technique, which is suitable for detecting weak emission
components, we have detected 4 additional emission components in the pulse
window. Three of these are new components and the fourth is a confirmation of a
recently proposed component. Hence PSR B0329+54 is now known to have 9 emission
components - the highest among all known pulsars. The distribution of the pulse
components around the central core component indicates that the emission beam
consists of four nested cones. The asymmetry in the location of the conal
components in the leading versus trailing parts of the profile is interpreted
as being due to aberration and retardation in the pulsar magnetosphere. These
measurements allow us to determine the precise location of the 4 conal rings of
emission. We find that the successive outer cones are emitted at higher
altitudes in the magnetosphere. Further, for any given cone, the emission
height at the lower frequency is found to be more than that at the higher
frequency. The inferred heights range from ~160 km to ~1150 km. The set of
``active'' field lines, from which most of the conal radiation appears to
originate, are found to be confined to a region located within ~0.5 to ~0.6 of
the polar cap radius. We discuss the implications of our new findings on our
understanding of the pulsar emission geometry and its impact on the emission
mechanisms.


title:
Quantitative Analysis of the Void Size Distribution in the LCRS and in
  CDM Models

abstract:
  We have analyzed the size distribution of voids in 2D slices of the Las
Campanas Redshift Survey (LCRS). The characteristic sizes show a scaling $D =
D_0 + \nu\lambda$ with the mean galaxy separation $\lambda$. Comparison with
mock samples of the LCRS in 2D and 3D, using various simulations, cosmologies
and galaxy identification schemes, gives a similar scaling, but with steeper
slope and a lack of large voids. Best results are obtained for dark matter
halos in a $\Lambda$CDM model.


title: The metamorphosis of SN1998bw

abstract:
  We present and discuss the photometric and spectroscopic evolution of the
peculiar SN1998bw, associated with GRB980425, through an analysis of optical
and near IR data collected at ESO-La Silla. The spectroscopic data, spanning
the period from day -9 to day +376 (relative to B maximum), have shown that
this SN was unprecedented, although somewhat similar to SN1997ef. Maximum
expansion velocities as high as 3x10^4 km/s to some extent mask its resemblance
to other Type Ic SNe. At intermediate phases, between photospheric and fully
nebular, the expansion velocities (~10^4 km/s) remained exceptionally high
compared to those of other recorded core-collapse SNe at a similar phase. The
mild linear polarization detected at early epochs suggests the presence of
asymmetry in the emitting material. The degree of asymmetry, however, cannot be
decoded from these measurements alone. The HeI 1.083 mu and 2.058 mu lines are
identified and He is suggested to lie in an outer region of the envelope. The
temporal behavior of the fluxes and profiles of emission lines of MgI]4571A,
[OI]6300,6364A and a feature ascribed to Fe are traced to stimulate future
modeling work.


title: The luminosity function of QSO host galaxies

abstract:
  We report on results from H band imaging observations of a complete sample of
high-luminosity low-redshift QSOs. The luminosity function of QSO hosts is
similar in shape to that of normal galaxies, although offset in normalisation
by a factor of 10^(-4). This supports the hypothesis that the parent population
of quasars is identical to the general population of early-type field galaxies.


title:
The Evolution of the Luminosity Function in Deep Fields: A Comparison
  with CDM Models

abstract:
  The galaxy Luminosity Function (LF) has been estimated in the rest frame B
luminosity at 0<z<1.25 and at 1700 {\AA} for 2.5<z<4.5 from deep multicolor
surveys in the HDF-N, HDF-S, NTT-DF. The results have been compared with a
recent version of galaxy formation models in the framework of hierarchical
clustering in a flat Cold Dark Matter Universe with cosmological constant. The
results show a general agreement for z<= 1, although the model LF has a steeper
average slope at the faint end; at z~3 such feature results in an
overprediction of the number of faint (I_{AB}~ 27) galaxies, while the
agreement at the bright end becomes critically sensitive to the details of dust
absorption at such redshifts. The discrepancies at the faint end show that a
refined treatement of the physical processes involving smaller galaxies is to
be pursued in the models, in terms of aggregation processes and/or stellar
feedback heavily affecting the luminosity of the low luminosity objects. The
implications of our results on the evolution of the cosmological star formation
rate are discussed.


title: Unusual Radio Properties of the BL Lac Object 0820+225

abstract:
  We present the results of simultaneous VLBA polarisation observations of the
BL Lacertae object 0820+225 at 5, 8, and 15 GHz, together with earlier images
at 5 GHz. This source has an unusually rich total intensity and polarisation
structure compared to other objects with comparable redshifts. The magnetic
field in the inner part of the complex and highly twisted VLBI jet is
transverse, as is typical of BL Lacertae objects, but becomes roughly
longitudinal further from the core, possibly due to shear. Although the
integrated rotation measure of 0820+225 is modest, the rotation-measure
distribution on parsec scales is non-uniform, and clearly shows regions where
the rotation measure is substantially higher than the integrated value.


title: On the X-ray time lags in the black hole candidates

abstract:
  It is shown that the energy dependence of the time lags in Cygnus X-1
excludes any significant contribution of the standard reflected component to
the observed lags. The conclusion is valid in the 0.1--10 Hz frequency range
where time lags have been detected with high enough significance. In fact the
data hint that reflected component is working in opposite direction, reducing
the lags at energies where contribution of the reflected component is
significant.
  We argue that the observed logarithmic dependence of time lags on energy can
be understood as due to the small variations of the spectrum power law index in
a very simple phenomenological model. We assume that an optically thin
flow/corona, emitting a power law like spectrum, is present at a range of
distances from the compact object. The slope of the locally emitted spectrum is
a function of distance with the hardest spectrum emitted in the innermost
region. If perturbations with different time scales are introduced to the
accretion flow at different radii the observed X-ray lags naturally appear due
to the inward propagation of perturbations on the diffusion time scales.


title: Asymmetric Beam Combination for Optical Interferometry

abstract:
  Optical interferometers increasingly use single-mode fibers as spatial
filters to convert varying wavefront distortion into intensity fluctuations
which can be monitored for accurate calibration of fringe amplitudes. Here I
propose using an asymmetric coupler to allow the photometric intensities of
each telescope beam to be measured at the same time as the fringe visibility,
but without the need for dedicated photometric outputs, which reduce the light
throughput in the interferometric channels. In the read-noise limited case
often encountered in the infrared, I show that a 53% improvement in
signal-to-noise ratio for the visibility amplitude measurement is achievable,
when compared to a balanced coupler setup with 50% photometric taps (e.g., the
FLUOR experiment). In the Poisson-noise limit appropriate for visible light,
the improvement is reduced to only ~8%. This scheme also reduces the cost and
complexity of the beam combination since fewer components and detectors are
required, and can be extended to more than two telescopes for "all-in-one" or
pair-wise beam combination. Asymmetric beam combination can also be employed
for monitoring scintillation and throughput variations in systems without
spatial filtering.


title: Exotic Matter research in Space

abstract:
  The direct detection of annihilation products in cosmic rays offer an
alternative way to search for dark matter particles candidates. Here we will
see in particular that the study of the spectrum of antiproton and positrons
offer good possibilities to perform this search and we will review our
experimental effort in this direction.


title:
The kinematics of molecular clumps surrounding hot cores in G29.96-0.02
  and G31.41+0.31

abstract:
  We present high angular resolution interferometric observations of the 3 and
1.3mm continuum emission, and HCO+(1-0) and SiO(2-1)v=0 lines, obtained with
the Owens Valley Radio Observatory millimeter-wave array, toward two hot cores
(HCs) associated with two well known ultracompact (UC) HII regions: G29.96-0.02
and G31.41+0.31. These HCs are believed to host young forming massive stars
which have been suggested to be surrounded by massive rotating accretion disks.
The aim of these new observations is to study the structure and kinematics of
the molecular clumps surrounding the HCs and nearby UCHII regions at moderately
high angular resolution. Our observations reveal that the clumps within which
the HCs and UCHII regions are embedded have a complex kinematical structure.
The total mass of the clumps is estimated to be in the range 1000-3000 Msun,
consistent with previous findings. Our observations also show compelling
evidence that the clump in G29.96-0.02 is contracting onto the HC position,
suggesting that the accretion process onto the massive young stellar object
embedded in the HC is still ongoing. In these objects the kinematical structure
that we observe is also compatible with the presence of a massive rotating disk
within the HC, even though we cannot prove this suggestion with our data. The
case of G31.41+0.31 is more complicated, and our data, although consistent with
the presence of an inner disk and an infalling envelope around it, do not have
the required spatial resolution to resolve the different structures.


title: Deep H I observations of the compact high-velocity cloud HVC125+41-207

abstract:
  We present deep HI observations of the compact high-velocity cloud
HVC125+41-207 using the 100-m Effelsberg telescope. Our goal was in particular
to study the warm neutral medium (WNM) in detail. The Effelsberg data reveal a
two phase core/halo structure - one component with a velocity width of FWHM
approx 5 km/s (Westerbork data show FWHM approx 2 km/s, Braun & Burton 2000)
and one with FWHM approx 18 km/s. The column density distribution of the warmer
component is highly asymmetric and shows a head-tail structure. We performed a
Gaussian decomposition of the cloud and found that 52% of the HI mass of the
cloud is in the WNM. 24% of the WNM is located in the tail. The overall
structure and the systematic variation of the observational parameters radial
velocity, velocity dispersion and column density indicate that this cloud is
currently interacting with the ambient medium.
  The Westerbork HI data of this HVC (Braun & Burton 2000) reveal an
interesting dense condensation. Assuming that this condensation is virialized
and in pressure equilibrium with the ambient medium, we derive a distance of
130 kpc for HVC125+41-207. Following these considerations, it is possible to
constrain the parameters n_IGM < 7.8 10^-6 cm^-3 and T_IGM > 1.1 10^5 K of the
intergalactic medium of the Local Group.


title: Near-infrared polarimetric observations of the afterglow of GRB 000301C

abstract:
  Based on near-infrared polarimetric observations we constrain the degree of
linear polarization of the afterglow light of GRB 000301C to less than 30% 1.8
days after the burst.


title:
Observation of the Halo of NGC 3077 Near the "Garland" Region Using the
  Hubble Space Telescope

abstract:
  We report the detection of upper main sequence stars and red giant branch
stars in the halo of an amorphous galaxy, NGC3077. The observations were made
using Wide Field Planetary Camera~2 on board the Hubble Space Telescope. The
red giant branch luminosity function in I-band shows a sudden discontinuity at
I = 24.0 +- 0.1 mag. Identifying this with the tip of the red giant branch
(TRGB), and adopting the calibration provided by Lee, Freedman, & Madore (1993)
and the foreground extinction of A_B = 0.21 mag, we obtain a distance modulus
of (m-M)_0 = 27.93 +- 0.14(random) +- 0.16(sys). This value agrees well with
the distance estimates of four other galaxies in the M81 Group. In addition to
the RGB stars, we observe a concentration of upper main sequence stars in the
halo of NGC3077, which coincides partially with a feature known as the
``Garland''. Using Padua isochrones, these stars are estimated to be <150 Myrs
old. Assuming that the nearest encounter between NGC3077 and M81 occurred 280
Myrs ago as predicted by the numerical simulations (Yun 1997), the observed
upper main sequence stars are likely the results of the star formation
triggered by the M81-NGC3077 tidal interaction.


title: Small Second Acoustic Peak from Interacting Cold Dark Matter?

abstract:
  We consider a possibility to explain the observed suppression of the second
acoustic peak in the anisotropy spectrum of the Cosmic Microwave Background
(CMB) by interaction between a fraction of non-baryonic Cold Dark Matter (CDM)
and normal baryonic matter. This scenario does not require any modifications in
the standard Big Bang Nucleosynthesis (BBN). We estimate the required values of
the cross-section-to-mass ratio for elastic scattering of CDM particles off
baryons. In case of velocity-independent elastic scattering (in the velocity
interval 10^{-5}--10^{-3}) we find that such particles do not contradict
observational limits if they are heavier than \sim 10^5 GeV or lighter than
\sim 0.5 GeV. Another candidate, which may appear in the models with infinite
extra dimensions, is a quasistable charged particle decaying through tunneling
into extra dimensions. Finally a millicharged particle with the electric charge
ranging from \sim 10^{-4} to \sim 10^{-1} and with mass M\sim 0.1 GeV--1 TeV
also may be responsible for the suppression of the second acoustic peak. As a
byproduct we point out that CMB measurements set new limits on the allowed
parameter space for the millicharged particles.


title:
A wide-field spectroscopic survey of the cluster of galaxies
  Cl0024+1654: I. The catalogue

abstract:
  We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the
lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new
spectra, of which 581 have identified redshifts. Adding redshifts available
from the literature, the final catalogue contains data for 687 objects with
redshifts identified for 650 of them. 295 galaxies have redshifts in the range
0.37<z<0.41, i. e. are cluster members or lie in the immediate neighbourhood of
the cluster. The area covered by the survey is 21x25 arcmin2 in size,
corresponding to 4x4.8 h^-2 Mpc2 at the cluster redshift. The survey is 45%
complete down to V=22 over the whole field covered; within 3 arcmin of the
cluster centre the completeness exceeds 80% at the same magnitude. A detailed
completeness analysis is presented. The catalogue gives astrometric position,
redshift, V magnitude and V-I colour, as well as the equivalent widths for a
number of lines. Apart from the cluster Cl0024+1654 itself, three other
structures are identified in redshift space: a group of galaxies at z=0.38,
just in front of Cl0024+1654 and probably interacting with it, a close pair of
groups of galaxies at z~0.495 and an overdensity of galaxies at z~0.18 with no
obvious centre. The spectroscopic catalogue will be used to trace the
three-dimensional structure of the cluster Cl0024+1654 as well as study the
physical properties of the galaxies in the cluster and in its environment.


title:
VLA Detection of the Ionized Stellar Winds Arising from Massive Stars in
  the Galactic Center Arches Cluster

abstract:
  The Galactic center Arches stellar cluster, detected and studied until now
only in the near-infrared, is comprised of at least one hundred massive (M>20
Msun) stars. Here we report the detection at centimeter wavelengths of radio
continuum emission from eight radio sources associated with the cluster. Seven
of these radio sources have rising spectral indices between 4.9 and 8.5 GHz and
coincide spatially with the brightest stars in the cluster, as determine from
JHK photometry and Brackett alpha and Brackett Gamma spectroscopy. Our results
confirm the presence of powerful ionized winds in these stars. The eighth radio
source has a nonthermal spectrum and its nature is yet unclear, but it could be
associated with a lower mass young star in the cluster.


title:
Recurrent very-long type-I X-ray bursts in the low-mass X-ray binary 4U
  1636-53

abstract:
  Two flares with a duration of several hours are reported for the low-mass
X-ray binary 4U 1636-53. The characteristics of these flares (i.e., decay time
scales, spectral softening, fluences) are very similar to the very long type-I
X-ray bursts recently found in several other low-mass X-ray binaries,
suggesting that the flares in 4U 1636-53 are also very long type-I X-ray
bursts. This would make this source the fifth to exhibit this phenomenon and
the first one for which multiple bursts have been found. Interestingly, all
five sources accrete at approximately 10% of the Eddington mass accretion rate.
Although a chance coincidence or a selection effect cannot be ruled-out at
present, this correlation is suggestive and might indicate that only at a
narrow range of mass accretion rate such very long type-I X-ray bursts can
occur.


title: New Temperatures of Diffuse Interstellar Gas: Thermally Unstable Gas

abstract:
  We present new Arecibo 21-cm line measurements of the temperatures of
interstellar gas. Our temperatures for the Cold Neutral Medium (CNM) are
significantly lower than previous single-dish results and in very good accord
with theoretical models. For warm gas at T > 500 K, we find a significant
fraction of gas (>47%) to lie in the thermally unstable region 500 ---> 5000 K;
moreover, about 60% of all the neutral atomic gas has T > 500 K. Large amounts
of thermally unstable gas are not allowed in theoretical models of the global
interstellar medium.


title: Clustering in Deep (Submillimeter) Surveys

abstract:
  Hughes & Gaztanaga (2001, see article in these proceedings) have presented
realistic simulations to address key issues confronting existing and
forthcoming submm surveys. An important aspect illustrated by the simulations
is the effect induced on the counts by the sampling variance of the large-scale
galaxy clustering. We find factors of up to 2-4 variation (from the mean) in
the extracted counts from deep surveys identical in area (6 sqr arcmin) to the
SCUBA surveys of the Hubble Deep Fields (HDF). Here we present a recipe to
model the expected degree of clustering as a function of sample area and
redshift.


title: Disk/corona model of the mean spectra of radio-quiet and radio-loud QSO

abstract:
  We test the disk/corona model of Janiuk et al. (2000) against the composite
mean optical/UV/soft X-ray spectrum of radio loud and radio quiet quasars from
Laor et al. (1997) which applies to faint quasars. The model well represents
the optical/UV continuum if the hardening of the locally emitted spectrum is
included, with the color to effective temperature ratio $f \sim 2$ in the inner
20-30 Schwarzschild radii. Comptonization seen in the soft X-ray band is well
explained by the adopted corona model in the case of radio loud objects.
However, this Comptonization is much stronger in radio quiet objects and
additional ad hoc assumed Comptonizing medium must be present. We speculate
that perhaps in both types of quasars there is a strong outflow of the hot
plasma; this plasma is collimated in radio loud objects but not collimated in
the radio quiet objects so it is present along the line of sight, serving as
the required Comptonizing medium. Hard X-ray power law is not explained by the
model and it may come from non-thermal component of electron plasma, as it is
the case for galactic black holes in their soft states.


title:
Analysis of hysteresis effect in p mode frequency shifts and solar
  activity indices

abstract:
  Using intermediate degree p mode frequency data sets for solar cycle 22, we
find that the frequency shifts and magnetic indices show a `hysteresis'
phenomenon. It is observed that the magnetic indices follow different paths for
the ascending and descending phases of the solar cycle, the descending path
always seems to follow a higher track than the ascending one. However, for the
radiative indices, the paths cross each other indicating phase reversal.


title:
The Star Formation Histories of Local Galaxies: Continuous or
  Intermittent?

abstract:
  We explore a model in which efficient star formation in galaxies is triggered
by merging satellites. We show that the merger/interaction rates predicted by
hierarchical galaxy formation models depend strongly on galaxy mass. If a
merger of a satellite larger than 1% the mass of the primary triggers efficient
star formation, low-mass dwarf galaxies experience strong bursts separated by
quiescent periods lasting several Gyr. Massive galaxies, such as our own Milky
Way, are perturbed by a 1% satellite every few hundred million years, and thus
have fluctuating, but relatively continuous star formation histories. We study
the spectral signatures of a population of galaxies undergoing intermittent
star formation by combining the models with the latest version of the Bruzual &
Charlot spectral synthesis code. We concentrate on spectral indicators that are
sensitive primarily to stellar age, rather than to metallicity and extinction.
We show that if a population undergoes intermittent rather than continuous star
formation, the signatures of the bursts should be evident from the observed
dispersion in the star formation rates, H-delta equivalent widths and gas mass
fractions of galaxies with 4000 Angstrom break strengths indicative of recent
or ongoing star formation.


title:
Phase-resolved HST/STIS spectroscopy of the exposed white dwarf in the
  high-field polar AR UMa

abstract:
  Phase-resolved HST/STIS ultraviolet spectroscopy of the high-field polar AR
UMa confirms that the WD photospheric Ly alpha Zeeman features are formed in a
magnetic field of ~200 MG. In addition to the Ly alpha pi and sigma+
components, we detect the forbidden hydrogen 1s0->2s0 transition, which becomes
``enabled'' in the presence of both strong magnetic and electric fields. Our
attempt in fitting the overall optical+UV low state spectrum with single
temperature magnetic WD models remains rather unsatisfactory, indicating either
a shortcoming in the present models or a new physical process acting in AR UMa.
As a result, our estimate of the WD temperature remains somewhat uncertain,
Twd=20000+-5000K. We detect a broad emission bump centered at ~1445A and
present throughout the entire binary orbit, and a second bump near ~1650A,
which appears only near the inferior conjunction of the secondary star. These
are suggestive of low harmonic cyclotron emission produced by low-level
(M-dot~1e-13 Msun/yr) accretion onto both magnetic poles. However, there is no
evidence in the power spectrum of light variations for accretion in gas blobs.
The observed Ly alpha emission line shows a strong phase dependence with
maximum flux and redshift near orbital phase phi~0.3, strongly indicating an
origin on the trailing hemisphere of the secondary star. An additional Ly alpha
absorption feature with similar phasing as the Ly alpha emission, but a
\~700km/s blueshift could tentatively be ascribed to absorption of WD emission
in a moderately fast wind. We derive a column density of neutral hydrogen of
NH=(1.1+-1.0)1e18 cm**-2, the lowest of any known polar.


title: Lithium in the Coma Berenices open cluster

abstract:
  Lithium abundances, radial velocities and rotational velocities are reported
for 20 candidate F, G and K stars of the sparse Coma Berenices open cluster.
All the stars are proper-motion selected, and our radial velocities support the
membership credentials of at least 12 of the candidates. Combining our data
with that in the literature, we have a close-to-complete census of Li
abundances for late-type stars with Mv < 5.8. These data show that the
Li-depletion pattern in Coma Ber is similar, but not identical, to that in the
Hyades cluster, which has a similar age but higher metallicity. Several Coma
Ber F stars have suffered significantly more Li depletion than their
counterparts in the Hyades. The G and early-K stars of Coma Ber have undergone
less Li depletion than those of the Hyades, but much more than that predicted
by standard evolutionary models featuring only convective mixing. This provides
strong evidence for additional mixing and Li depletion operating in these stars
during their first 400Myr on the main sequence, amounting to 0.3 dex at 6000K
and rising to 0.8-1.2 dex at 5400K. We find that 4 of the radial-velocity
non-members are among a small number of low-mass stars which were previously
reported as part of an extra-tidal moving group associated with the Coma Ber
cluster. As a result we now find that the luminosity function of this moving
group is indistinguishable from that of the central cluster. It is uncertain
whether there may be a significant number of stars with even lower masses among
the moving group.


title: Horizontal Branch Models as a Test of Mixing on the RGB

abstract:
  We discuss the impact of mixing and rotation along the red-giant branch (RGB)
on the properties of horizontal-branch (HB) stars with emphasis on two
problems: the nature of the unexpected blue HB population in the metal-rich
globular clusters (GCs) NGC 6388 and NGC 6441 and the cause of the low
gravities in the blue HB stars. New stellar models indicate that the sloped HBs
in NGC 6388 and NGC 6441 might arise from a spread in metallicity, implying
that these GCs may be metal-rich analogues of omega Cen. The low gravity
problem can be largely explained by the radiative levitation of Fe in the
atmospheres of the blue HB stars. We show that the onset of radiative
levitation and the drop in HB rotation velocities at Teff ~ 11,000 K coincide
with the disappearance of surface convection. The low rotation velocities of
the hotter HB stars may be due to the spin down of the surface layers by a weak
stellar wind induced by the radiative levitation of Fe. We conclude that the
impact of mixing and rotation on the HB remains to be clearly established.


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

abstract:
  We present a strategy for a statistically rigorous Bayesian approach to the
problem of determining cosmological parameters from the results of observations
of anisotropies in the cosmic microwave background. Our strategy relies on
Markov chain Monte Carlo methods, specifically the Metropolis-Hastings
algorithm, to perform the necessary high-dimensional integrals. We describe the
Metropolis-Hastings algorithm in detail and discuss the results of our test on
simulated data.


title: Resonance Line Scattering in Supernova Remnant Shocks

abstract:
  We present a three dimensional radiative transfer model to examine the
effects of resonance line scattering in the post-shock flow behind a
non-radiative supernova remnant shock. For a rippled shock front viewed
edge-on, line scattering significantly reduces the observed flux of CIV 1549
and NV 1240, two important diagnostic lines in the ultraviolet spectra of
supernova remnants. The correction factor (defined to be the ratio of the line
flux that would be observed neglecting scattering, to the actual observed line
flux) is a function of position within the filament. For sufficiently large
regions that include crisp edges as well as more diffuse regions of the
filament structure, the CIV and NV correction factors are between about 1.5 and
3.5 (and the CIV correction factor is invariably larger than the NV correction
factor). The correction factors have a larger range when smaller regions are
considered. The CIV correction factor is about 6 at the filament edges, while
the NV correction factor is about 4. These simulations of resonance line
scattering will be useful for the analysis of supernova remnant shock spectra.


title:
FUSE Observations of Molecular Hydrogen in Translucent Interstellar
  Clouds: II. The Line of Sight Toward HD 110432

abstract:
  We report the second study from the FUSE survey of molecular hydrogen in
translucent clouds, for the line of sight toward HD 110432. This star lies
beyond the Coalsack dark nebula, and with E(B-V) = 0.40, and A_V = 1.32 this
line of sight bridges the gap between less extinguished diffuse cloud lines of
sight with A_V \sim 1, such as Zeta Oph, and the translucent clouds with A_V
\gtrsim 2 such as HD 73882. Through profile fitting and a curve-of-growth
analysis, we have derived rotational populations for H2 for J = 0--7. The line
of sight has a total molecular hydrogen column density, log N(H2) = 20.68 \pm
0.05 cm^{-2}, nearly identical to that toward Zeta Oph, but a factor of three
less than HD 73882. The ratio of N(J=1) to N(J=0) yields a kinetic temperature
T_{kin} = 63 \pm 7 K, similar to other lines of sight with A_V \gtrsim 1. The
high-J lines show considerable excitation above this temperature. The high-J
excitation is similar to that toward Zeta Oph, but much smaller than that
toward HD 73882. Chemical modeling indicates that the physical conditions in
the cloud(s) are very similar to those in the cloud(s) toward Zeta Oph. An
analysis of IUE spectra of the Lyman-alpha line gives log N(H I) = 20.85 \pm
0.15 cm^{-2}. Combined with N(H2), we derive a hydrogen molecular fraction,
f_{H2} = 0.58 pm 0.12, statistically identical to that found for the lines of
sight toward Zeta Oph and HD 73882. We also report column densities for the HD
and CO molecules. From the combined measurements of hydrogen and carbon-
containing molecules, the line of sight toward HD 110432 appears quite similar
to the diffuse cloud line of sight toward Zeta Oph, and quite dissimilar to the
translucent cloud line of sight toward HD 73882.


title:
Primordial Black Holes and the Asymmetrical Distribution of Short GRB
  Events

abstract:
  We review some of the expectations for Primordial Black Hole evaporation and
we review the properties of short Gamma Ray Bursts. It is plausible that these
GRB come from PBH evaporation. We then show that the angular distribution
asymmetry recently observed by us could be due to a concentration of PBH in the
Galactic Arms like the Orion arm.


title: Supernova II Neutrino Bursts and Neutrino Massive Mixing

abstract:
  We describe the Neutrino Spectrum and detection for SN II sources. We discuss
the effects of neutrino mixing in the SN II. A new analysis of SN1987A is
described. We discuss the possible detection of the diffuse relic SN II flux.
Finally we discuss a new detection concept, OMNIS, for Nu sub mu and Nu sub tau
and detection and compare with other present and future SN detectors.


title:
Diffusion of the scalar field energy due to the backscattering off
  Schwarzschild geometry

abstract:
  This note tackles the problem of the backscattering of a mass-less scalar
field in the case of Schwarzschildean space-time. It shows that the effect
depends both on a distance from the horizon and on the wave length. The
obtained estimates significantly improve former results.


title: Phase Dependent Spectral Variability of 4U1907+09

abstract:
  We report on ASCA, RXTE, and archival observations of the high mass X-ray
binary pulsar 4U1907+09. Spectral measurements of the absorption and flux were
made at all phases of the X-ray pulsar orbit, including the first spectral
measurements of an extended period of low flux during two of the ASCA
observations. We find that a simple spherical wind model can fit the time
averaged light curve as measured by the RXTE ASM, but does not fit the observed
changes in the absorption column or account for the existence of the
phase-locked secondary flare. An additional model component consisting of a
trailing stream can account for the variations in column depth. However, these
models favor a high inclination angle for the system, suggesting a companion
mass more consistent with an identification as a Be-star. In this case an
equatorially enhanced wind and inclined neutron star orbit may be a more
appropriate interpretation of the data.


title:
Reprocessing the Hipparcos data for evolved giant stars II. Absolute
  magnitudes for the R-type carbon stars

abstract:
  The Hipparcos Intermediate Astrometric Data for carbon stars have been
reprocessed using an algorithm which provides an objective criterion for
rejecting anomalous data points and constrains the parallax to be positive. New
parallax solutions have been derived for 317 cool carbon stars, mostly of types
R and N. In this paper we discuss the results for the R stars. The most
important result is that the early R stars (i.e., R0 - R3) have absolute
magnitudes and V-K colors locating them among red clump giants in the
Hertzsprung-Russell diagram. Stars with subtypes R4 - R9 tend to be cooler and
have similar luminosity to the N-type carbon stars, as confirmed by their
position in the (J-H, H-K) color-color diagram. The sample of early R-type
stars selected from the Hipparcos Catalogue appears to be approximately
complete to magnitude K_0 ~ 7, translating into a completeness distance of 600
pc if all R stars had M_K= -2 (400 pc if M_K= -1). With about 30 early R-type
stars in that volume, they comprise about 0.04% (0.14% for M_K= -1) of the red
clump stars in the solar neighborhood. Identification with the red clump
locates these stars at the helium core burning stage of stellar evolution,
while the N stars are on the asymptotic giant branch, where helium shell
burning occurs. The present analysis suggests that for a small fraction of the
helium core burning stars (far lower than the fraction of helium shell-burning
stars), carbon produced in the interior is mixed to the atmosphere in
sufficient quantities to form a carbon star.


title: Cosmological Constraints on Terrestrial Planet Formation

abstract:
  I attempt to piece together a consistent scenario based on current estimates
of the evolution of the star formation rate of the Universe, the metallicity
evolution of the star-forming regions of the Universe and the most recent
observations of extrasolar planets. The precision of all of these data sets is
improving rapidly, but they can already be combined to yield an estimate of the
age distribution of earth-like planets in the Universe (Lineweaver 2001,
astro-ph/0012399).


title:
A measurement of the cosmological mass density from clustering in the
  2dF Galaxy Redshift Survey

abstract:
  The large-scale structure in the distribution of galaxies is thought to arise
from the gravitational instability of small fluctuations in the initial density
field of the universe. A key test of this hypothesis is that superclusters of
galaxies in the process of formation should generate systematic infall of other
galaxies. This would be evident in the pattern of recessional velocities,
causing an anisotropy in the inferred spatial clustering of galaxies. Here we
report a precise measurement of this clustering, using the redshifts of more
than 141,000 galaxies from the two-degree-field galaxy redshift survey. We
determine the parameter beta = Omega^{0.6}/b = 0.43 +- 0.07, where Omega is the
total mass-density parameter and b is a measure of the `bias' of the luminous
galaxies in the survey. Combined with the anisotropy of the cosmic microwave
background, our results favour a low-density universe with Omega approximately
0.3.


title:
Spherical collapse of supermassive stars: neutrino emission and
  gamma-ray bursts

abstract:
  We present the results of numerical simulations of the spherically symmetric
gravitational collapse of supermassive stars (SMS). The collapse is studied
using a general relativistic hydrodynamics code. The coupled system of Einstein
and fluid equations is solved employing observer time coordinates, by foliating
the spacetime by means of outgoing null hypersurfaces. The code contains an
equation of state which includes effects due to radiation, electrons and
baryons, and detailed microphysics to account for electron-positron pairs. In
addition energy losses by thermal neutrino emission are included. We are able
to follow the collapse of SMS from the onset of instability up to the point of
black hole formation. Several SMS with masses in the range $5\times 10^5
M_{\odot}- 10^9 M_{\odot}$ are simulated. In all models an apparent horizon
forms initially, enclosing the innermost 25% of the stellar mass. From the
computed neutrino luminosities, estimates of the energy deposition by
$\nu\bar{\nu}$-annihilation are obtained. Only a small fraction of this energy
is deposited near the surface of the star, where, as proposed recently by
Fuller & Shi (1998), it could cause the ultrarelativistic flow believed to be
responsible for $\gamma$-ray bursts. Our simulations show that for collapsing
SMS with masses larger than $5\times 10^5 M_{\odot}$ the energy deposition is
at least two orders of magnitude too small to explain the energetics of
observed long-duration bursts at cosmological redshifts. In addition, in the
absence of rotational effects the energy is deposited in a region containing
most of the stellar mass. Therefore relativistic ejection of matter is
impossible.


title: On The Parent Population of Radio Galaxies and the FR I--II Dichotomy

abstract:
  The possibility of radio galaxies being random sample of otherwise normal
elliptical galaxies is tested. Starting with the observed optical luminosity
functions for elliptical galaxies, it is shown that the probability of an
elliptical forming a radio source is a continuous, increasing function of
optical luminosity, precisely proportional to square of the optical luminosity
of the galaxy. Once the probability function is fixed, the luminosity function
of normal elliptical galaxies is used as input for Monte Carlo simulations that
reproduce the distribution of radio galaxies in the radio-optical luminosity
plane. Our results show that radio galaxies are luminosity biased, but
otherwise random sample of elliptical galaxies. This unified view of radio and
non-radio ellipticals also explains the well known difference of 0.5 mag in
average optical luminosity between FRI and FRII radio galaxies as a simple
selection effect. Specifically, FRII appear preferentially in smaller galaxies
because both radio and optical luminosity functions are steep, so there is a
negligible probability of observing a powerful radio source associated with a
bright galaxy; no intrinsic physical differences between FRI and FRII host
galaxies is required.


title:
'Round the Clock Observations of the Q0957+561 A,B Gravitationally
  Lensed Quasar

abstract:
  An observing campaign with 10 participating observatories has undertaken to
monitor the optical brightness of the Q0957 gravitationally lensed quasar for
10 consecutive nights in January 2000. The resulting A image brightness curve
has significant brightness fluctuations and makes a photometric prediction for
the B image light curve for a second campaign planned for 12-21 March 2001. The
ultimate purpose is to determine the gravitational lens time delay to a
fraction of an hour, and to seek evidence for rapid microlensing.


title: Cosmic Ray "Knee": A Herald of New Physics?

abstract:
  We propose that the knee in the cosmic ray spectrum at energies E ~ 10^{15.5}
eV is due to "new physics", namely to a channel in the high energy (~ TeV in
the CM) proton interactions hitherto unaccounted for in estimating the energies
of the air shower cosmic rays. The new interaction transfers part of the
primary particle's energy to modes which do not trigger the experimental
arragement (neutrinos, lightest supersymmetric particle, gravitons) thus
underestimating its true energy. We show that this underestimate leads
naturally to the observed break (the "knee") in the inferred cosmic ray
spectrum. The suggestion we advance fits nicely to current theoretical
extensions of the Standard Model (supersymmetry, technicolor, low scale
gravity) where new physics at the TeV scale manifests with the distinct
signature of missing energy. We present a simple model where the new physics
proceeds via gluon fusion and assuming a single power law for the galactic (E ~
10^{18.5} eV) cosmic ray spectrum, we produce a good fit to the data in the
10^{14}-10^{18.5} eV range. Our proposal should be testable in laboratory
experiments (LHC) in the near future and, should it be proven correct, it would
signal besides the presence of new physics in high energy interactions, a
drastically different interpretation of the sources and acceleration of cosmic
rays.


title: FIR and Radio emission in star forming galaxies

abstract:
  We examine the tight correlation observed between the far infrared (FIR) and
radio emission in normal and star burst galaxies. We show that significant
deviations from the average relation are to be expected in young star burst or
post star burst galaxies, due to the different fading times of FIR and Radio
power.


title: Rayleigh Scattering and Microwave Background Fluctuations

abstract:
  During the recombination epoch, cosmic background photons couple not only to
free electrons through Thompson scattering, but also to the neutral hydrogen
through Rayleigh scattering. This latter is ~2% effect for photons near the
peak of the photon energy distribution at z=800 and a ~0.2% effect at z=1100.
Including Rayleigh scattering in the calculation reduces Silk damping at fixed
redshift, alters the position of the surface of last scattering and alters the
propagation of acoustic waves. We estimate the amplitude of these effects. For
the Microwave Anisotropy Probe (MAP), Rayleigh scattering increases the
anisotropy spectrum by 0.1% at the most. For the highest frequencies of the
Planck Surveyor, the effects of Rayleigh scattering are much more dramatic
(decreasing the anisotropy spectrum by 3% at \nu~550GHz and l~1000). The
relative difference between the spectra of low and high frequencies is imposed
by an oscillation with a function of multipole l and the oscillation amplitude
is up to 0.5% between 100 and 550GHz. Rayleigh scattering also slows the
decoupling between radiation and matter, but the effect is undetectably small.


title: Antiprotons from spallations of cosmic rays on interstellar matter

abstract:
  Cosmic ray antiprotons provide an important probe for the study of the
galactic Dark Matter, as they could be produced by exotic sources. On the other
hand, antiprotons are anyway produced by standard nuclear reactions of cosmic
ray nuclei on interstellar matter. This process is responsible for a background
flux that must be carefully determined to estimate the detectability of an
hypothetical exotic signal. Estimates of this background suffer from potential
uncertainties of various origins. The propagation of cosmic antiprotons depends
on several physical characteristics of the Galaxy which are poorly known.
Antiprotons are created from cosmic protons and helium nuclei whose fluxes were
not measured with great accuracy until very recently. Calculations of
antiproton fluxes make use of nuclear physics models with their own
shortcomings and uncertainties. The goal of this paper is to give a new
evaluation of the cosmic antiproton flux along with the associated
uncertainties. The propagation parameters were tightly constrained in Maurin et
al. 2001 by an analysis of cosmic ray nuclei data in the framework of a
two-zone diffusion model and we apply these parameters to the propagation of
antiprotons. We use the recently published data on proton and helion fluxes,
and we find that this particular source of uncertainty has become negligible.
The Monte Carlo program DTUNUC was used to carefully examine nuclear reactions.
We find that all the cosmic antiproton fluxes naturally coming out of the
calculation are fully compatible with experimental data. Uncertainties in this
flux have been strongly reduced. Those related to propagation are less than
25%. All other possible sources of uncertainty have also been studied.


title:
Physical Conditions in the Foreground Gas of Reflection Nebulae: NGC
  2023, vdB 102, and NGC 7023

abstract:
  High resolution optical spectra of HD 37903 and HD 147009, which illuminate
the reflection nebulae, NGC 2023 and vdB 102, were obtained for comparison with
our results for HD 200775 and NGC 7023. Ground-based measurements of the
molecules, CH, C$_2$, and CN, and the atoms, Na I and K I, were analyzed to
extract physical conditions in the foreground cloud. Estimates of the gas
density, gas temperature and flux of ultraviolet radiation were derived and
were compared with the results from infrared and radio studies of the main
molecular cloud. The conditions are similar to those found in studies of
diffuse clouds. The foreground material is less dense than the gas in the
molecular cloud behind the star(s). The gas temperature was set at 40 K, the
temperature determined for the foreground gas in NGC 7023. The flux of
ultraviolet radiation was found to be less intense than in the molecular
material behind the star(s). The column densities of Na I and K I were
reproduced reasonably well when the extinction curve for the specific line of
sight was adopted. We obtained NEWSIPS data from the IUE archive for HD 37903
and HD 200775. The ultraviolet data on C I and CO allow extraction of the
physical conditions by alternate methods. General agreement among the various
diagnostics was found, leading to self-consistent pictures of the foreground
photodissociation regions. An Appendix describes checks on the usefulness of
IUE NEWSIPS data for interstellar studies. (Abridged)


title: Ultra-high-energy cosmic rays from relic topological defects

abstract:
  It is difficult for conventional sources to accelerate cosmic ray particles
to the highest energies that have been observed. Topological defects such as
monopoles and strings overcome this difficulty, because their natural energy
scale is at or above the observed energies. Monopoles connected by strings are
a particularly attractive source, because they would cluster in the galactic
halo and thus explain the absence of the GZK cutoff. Heavy monopoles connected
by light strings could last for the age of the universe as required. Further
observations might support this model by detection of the anisotropy due to the
halo, or might refute such models if strong clustering of arrival directions or
correlations with known astrophysical objects are confirmed. All top-down
models must contend with recent claims that the percentage of photons among the
cosmic rays is smaller than such models predict.


title: PN-Carbon Yields and the Chemical Evolution of the Galaxy

abstract:
  Two sets of observational carbon stellar yields for low-and-intermediate mass
stars are computed from planetary nebulae abundances derived from C II
$\lambda4267$ and C III $\lambda\lambda1906+1909$ lines, respectively. By
comparing C/O values observed in stars of the solar vicinity and Galactic HII
regions with those predicted by chemical evolution models for the Galaxy, which
assume these observational yields, I conclude that the C abundances derived
from permitted lines are better than those derived from forbidden lines.


title:
Comparative Analysis of GALLEX-GNO Solar Neutrino Data and SOHO/MDI
  Helioseismology Data; Further Evidence for Rotational Modulation of the Solar
  Neutrino Flux

abstract:
  We carry out a comparative analysis of the GALLEX-GNO solar neutrino data and
estimates of the solar internal rotation rate derived from the MDI
helioseismology experiment on the SOHO spacecraft. We introduce a statistic,
which we evaluate as a function of radius and latitude, that is a measure of
the degree of "resonance" of oscillations in the neutrino flux and the synodic
solar rotation rate at that radius and latitude. A map of this statistic
indicates that the probable location is deep in the convection zone near the
equator.
  We also examine the integral of this statistic over the equatorial section of
the convection zone. This provides a measure of the likelihood that the
variability of the solar neutrino flux, as measured by the GALLEX-GNO data, has
its origin in the equatorial section of the convection zone. We apply the
shuffle test, randomly reassigning measurements among runs, to estimate the
significance of the value of the statistic computed from the actual data. This
test implies that the result is significant at the 0.2% level. When, for
comparison, we repeat this analysis for the radiative zone, we find that the
integral resonance statistic is not significant.
  These results support earlier evidence for rotational modulation of the solar
neutrino flux.


title:
The new sample of Giant radio sources: I. Radio imaging, optical
  identification and spectroscopy of selected candidates

abstract:
  A new sample of very large angular size radio sources has been selected from
the 1.4 GHz VLA surveys: FIRST and NVSS. This sample will be very useful for an
observational constraint on the time evolution of double radio sources,
especially their size, predicted by numerous analytical models of such
evolution (cf. Introduction). In this paper we present radio and optical data
for a large fraction of the sample sources. They are: high-frequency VLA maps
with very weak radio cores detected, deep optical images showing the identified
faint host galaxies not visible on the DSS images, and optical spectra of the
identified galaxies brighter than about R ~ 18.5 mag taken with the McDonald
Observatory 2.1m telescope. For 15 galaxies (of which 4 do not belong to the
complete sample) the redshift has been determined. In the result, 44 per cent
of galaxies in the complete sample have redshift data (with one exception all
redshifts are less than 0.33), of which 70 per cent have a linear size
exceeding 1 Mpc. The photometric redshift estimates for other 11 galaxies with
19 mag<R<21.7 mag (0.3<z<0.5) predict their sizes much over 1 Mpc.


title: Semi-analytic galaxy formation: understanding the high redshift universe

abstract:
  There is now compelling evidence in favour of the hierarchical structure
formation paradigm. Semi-analytic modelling is a powerful tool which allows the
formation and evolution of galaxies to be followed in a hierarchical framework.
We review some of the latest developments in this area before discussing how
such models can help us to interpret observations of the high redshift
Universe.


title:
Populations of X-ray binaries and the dynamical history of their host
  galaxies

abstract:
  The observed luminosity distributions of X-ray sources indicate the presence
of several populations of X-ray binaries in the nearby galaxies. Each
population has its formation and evolutionary history, depending on the host
environment. The features seen in the log N($>$S) -- log S curves for different
types of galaxies and for different galactic components can be reproduced by a
birth-death model, in which the lifespans of the binaries are inversely
proportional to their X-ray brightness. Conversely, the dynamical history of a
galaxy can be inferred from the luminosity distributions of its X-ray binary
populations.


title: Exploring Topology of the Universe in the Cosmic Microwave Background

abstract:
  We study the effect of global topology of the spatial geometry on the cosmic
microwave background (CMB) for closed flat and closed hyperbolic models in
which the spatial hypersurface is multiply connected. If the CMB temperature
fluctuations were entirely produced at the last scattering, then the
large-angle fluctuations would be much suppressed in comparison with the simply
connected counterparts which is at variance with the observational data.
However, as we shall show in this thesis, for low matter density models the
observational constraints are less stringent since a large amount of
large-angle fluctuations could be produced at late times. On the other hand, a
slight suppression in large-angle temperature correlations in such models
explains rather naturally the observed anomalously low quadrupole which is
incompatible with the prediction of the "standard"
Friedmann-Robertson-Walker-Lemaitre models. Interestingly, moreover, the
development in the astronomical observation technology has made it possible to
directly explore the imprint of the non-trivial topology by looking for
identical objects so called "ghosts" in wide separated directions. For the CMB
temperature fluctuations identical patterns would appear on a pair of circles
in the sky. Another interesting feature is the non-Gaussianity in the
temperature fluctuations. Inhomogeneous and anisotropic Gaussian fluctuations
for a particular choice of position and orientation are regarded as
non-Gaussian fluctuations for a homogeneous and isotropic ensemble.


title: Gravitational instability of finite isothermal spheres

abstract:
  We investigate the stability of bounded self-gravitating systems in the
canonical ensemble by using a thermodynamical approach. Our study extends the
earlier work of Padmanabhan [Astrophys. J. Supp. 71, 651 (1989)] in the
microcanonical ensemble. By studying the second variations of the free energy,
we find that instability sets in precisely at the point of minimum temperature
in agreement with the theorem of Katz [ Mon. Not. R. astr. Soc. 183, 765
(1978)]. The perturbation that induces instability at this point is calculated
explicitly; it has not a ``core-halo'' structure contrary to what happens in
the microcanonical ensemble. We also study Jeans type gravitational instability
of isothermal gaseous spheres described by Navier-Stokes equations. We show
analytically the equivalence between dynamical stability and thermodynamical
stability and the fact that the stability of isothermal gas spheres does not
depend on the viscosity. This confirms the findings of Semelin et al.
[astro-ph/9908073] who used numerical methods. We also give a simpler
derivation of the geometric hierarchy of scales inducing instability discovered
by these authors. The density profiles that trigger these instabilities are
calculated analytically; they present more and more oscillations that also
follow a geometric progression. This suggests that the system will fragmentate
in a series of `clumps' and that these `clumps' will themselves fragmentate in
substructures. The fact that both the domain sizes leading to instability and
the `clumps' sizes within a box follow a geometric progression with the same
ratio suggests a fractal-like behaviour. This gives further support to the
interpretation of de Vega et al. [Nature, 383, 56 (1996)].

categories: astro-ph cond-mat.stat-mech nlin.CD physics.flu-dyn


title:
Contribution of nuclei accelerated by gamma-ray pulsars to cosmic rays
  in the Galaxy

abstract:
  We consider the galactic population of gamma-ray pulsars as possible sources
of cosmic rays at and just above the ``knee'' in the observed cosmic ray
spectrum at $10^{15}$--$10^{16}$ eV. We suggest that iron nuclei may be
accelerated in the outer gaps of pulsars, and then suffer partial
photo-disintegration in the non-thermal radiation fields of the outer gaps. As
a result, protons, neutrons, and surviving heavier nuclei are injected into the
expanding supernova remnant. We compute the spectra of nuclei escaping from
supernova remnants into the interstellar medium, taking into account the
observed population of radio pulsars.
  Our calculations, which include a realistic model for acceleration and
propagation of nuclei in pulsar magnetospheres and supernova remnants, predict
that heavy nuclei accelerated directly by gamma-ray pulsars could contribute
about 20% of the observed cosmic rays in the knee region. Such a contribution
of heavy nuclei to the cosmic ray spectrum at the knee can significantly
increase the average value of $<\ln A>$ with increasing energy as is suggested
by recent observations.


title: The Vacuum Energy from a New Perspective

abstract:
  It is commonly believed that the vacuum energy problem points to the need for
(1) a radically new formulation of gravitational physics and (2) a new
principle which forces the vacuum stress-energy tensor (as measured by gravity)
to be nearly zero. Here we point out that a new fundamental theory contains
both features: (1) In this theory the vierbein is interpreted as the
"superfluid velocity" associated with the order parameter for a GUT-scale Higgs
condensate. (2) The vacuum stress-energy tensor is exactly zero in the vacuum
state, because the action is extremalized with respect to variations in the
order parameter. With inhomogeneously-distributed matter present, the vacuum
stress-energy tensor is shifted away from zero.


title: Nucleosynthesis in Advective Accretion Disk around Compact Object

abstract:
  We study the nucleosynthesis in accretion disk around compact object. When
matter falls towards the compact object, due to interactions in nuclear species
nuclear energy is released in the high temperature. In some region of parameter
space nuclear energy becomes comparable or higher to the energy release due to
the viscous effect of the disk. In those regions disk may become unstable. Also
the changes of nuclear abundance in the disk are significant.


title: Temporal evolution of f-mode frequencies and radius

abstract:
  We have analysed temporal evolution in centroid frequencies and splitting
coefficients of solar f-modes obtained from MDI/SOHO. The data were divided
into 20 sets covering a period from May 1, 1996 to August 31, 2000. The
variation in frequencies is estimated to be 68 nHz over the period of four
years which includes the rapidly rising phase of the solar cycle 23. This
change is much smaller than that observed for p-mode frequencies. It is also
noticed that the f-mode frequencies appear to be weakly correlated with solar
activity indices as compared to the p-mode frequencies. We have also inferred
the relative change in the solar radii and notice a 1 year periodicity which
may be associated with the solar cycle variation.


title: On the solar rotation rate in the upper convection zone

abstract:
  We present results on variation in rotation rate in the upper convection zone
using data from GONG and MDI/SOHO covering a period of more than four years. We
find that the first few odd-order splitting coefficients vary systematically
with the solar cycle. The rotation rate near the solar surface calculated from
analytical methods agrees well with that of inversion techniques. The residual
rotation rate in the outer layers seem to be correlated with the solar
activity.


title: The Galactic Habitable Zone I. Galactic Chemical Evolution

abstract:
  We propose the concept of a "Galactic Habitable Zone" (GHZ). Analogous to the
Circumstellar Habitable Zone (CHZ), the GHZ is that region in the Milky Way
where an Earth-like planet can retain liquid water on its surface and provide a
long-term habitat for animal-like aerobic life. In this paper we examine the
dependence of the GHZ on Galactic chemical evolution. The single most important
factor is likely the dependence of terrestrial planet mass on the metallicity
of its birth cloud. We estimate, very approximately, that a metallicity at
least half that of the Sun is required to build a habitable terrestrial planet.
The mass of a terrestrial planet has important consequences for interior heat
loss, volatile inventory, and loss of atmosphere. A key issue is the production
of planets that sustain plate tectonics, a critical recycling process that
provides feedback to stabilize atmospheric temperatures on planets with oceans
and atmospheres. Due to the more recent decline from the early intense star
formation activity in the Milky Way, the concentration in the interstellar
medium of the geophysically important radioisotopes, $^{40}$K, $^{235, 238}$U,
$^{232}$Th, has been declining relative to Fe, an abundant element in the
Earth. Also likely important are the relative abundances of Si and Mg to Fe,
which affects the mass of the core relative to the mantle in a terrestrial
planet. All these elements and isotopes vary with time and location in the
Milky Way; thus, planetary systems forming in other locations and times in the
Milky Way with the same metallicity as the Sun will not necessarily form
habitable Earth-like planets.


title:
Black hole X-ray transients: mass accumulation in the disk - constraints
  for the viscosity

abstract:
  The outburst cycles of black hole X-ray transients are now generally
understood as caused by a thermal instability in the accretion disk, the same
mechanism as in dwarf novae outbursts. During quiescence the accretion occurs
via a cool disk in the outer region but changes to a coronal flow/ADAF in the
inner region. The transition to the coronal flow is caused by evaporation of
matter from the cool disk. This process is an important feature for the disk
evolution. We point out that if the disk is depleted during the outburst, e.g.
by irradiation, its evolution during quiescence is independent of the detailed
outburst luminosity decline. The mass accumulation during quiescence has to
meet several constraints as the accretion rate, the recurrence time and the
total outburst energy. We present a critical discussion of different ways to
model X-ray transient outburst cycles and compare with the requirements from
observations. For the case of only little mass left over after the outburst the
observations indicate a frictional parameter in the cool disk of order
alpha(cold) =0.05, similar to that in dwarf nova disks during quiescence, with
no need to resort to much lower alpha values of order 0.005.


title: Recent star formation in very luminous infrared galaxies

abstract:
  Among star forming galaxies, a spectral combination of a strong Hdelta line
in absorption and a moderate [OII] emission has been suggested to be a useful
method to identify dusty starburst galaxies at any redshift, on the basis of
optical data alone. On one side it has been shown that such a spectral
particularity is indeed suggestive of obscured starburst galaxies but, on the
other, the degeneracy of the optical spectrum has hindered any quantitative
estimate of the star formation and extinction during the burst. The optical
spectrum by itself, even complemented with the information on the far-IR flux,
is not enough to identify univocal evolutionary patterns. We discuss in the
following whether it is possible to reduce these uncertainties by extending the
spectral analyses to the near infrared spectral region.


title:
Pressure imbalance of FRII radio source lobes: a role of energetic
  proton population

abstract:
  Recently Hardcastle & Worrall (MNRAS, 319, 562) analyzed 63 FRII radio
galaxies imbedded in the X-ray radiating gas in galaxy clusters and concluded,
that pressures inside its lobes seem to be a factor of a few lower than in the
surrounding gas. One of explanations of the existing `blown up' radio lobes is
the existence of invisible internal pressure component due to energetic cosmic
ray nuclei (protons). Here we discuss a possible mechanism providing these
particles in the acceleration processes acting at side boundaries of
relativistic jets. The process can accelerate particles to ultra high energies
with possibly a very hard spectrum. Its action provides also an additional
viscous jet breaking mechanism. The work is still in progress.


title: INTEGRAL and Nuclear Astrophysics

abstract:
  We briefly review the fundamentals of nuclear gamma-ray line astronomy
(radioactive astronomy), focusing on its role to decipher the intimate physics
of supernovae, either immediatly (via $^{56}Co)$ or after a time delay (via
$^{44}Ti$). All kinds of supernovae can be in principle tested through their
radioactivities and their associated gamma-ray lines.
  Dedicated to the spectroscopy and imaging of celestial sources in the 15 keV
to 10 MeV band, the ESA scientific observatory INTEGRAL will open a golden age
of nuclear astrophysics in Europe


title: D/H Measurements

abstract:
  Primordial evaluations of the deuterium abundance should provide one of the
best tests of Big Bang nucleosynthesis models. Space as well as ground based
observations seem however to result in different values. This asks for more
observations in different astrophysical sites in order to link present day
interstellar medium D/H evaluations to primordial ones. New investigations,
made with FUSE (the Far Ultraviolet Spectroscopic Explorer launched in June
1999), are presented and in the case of the white dwarf G191-B2B line of sight
a low D/H evaluation of 1.16 (+/-0.24) x 10^-5 (2 sigma) is confirmed. This
seems to indicate that D/H variations are probably present in the nearby
interstellar medium. The FUSE observations should help us reach in a near
future a better global view of the evolution of that key element.


title: The X-ray Spectrum of the Vela Pulsar Resolved with Chandra

abstract:
  We report the results of the spectral analysis of two observations of the
Vela pulsar with the Chandra X-ray observatory. The spectrum of the pulsar does
not show statistically significant spectral lines in the observed 0.25-8.0 keV
band. Similar to middle-aged pulsars with detected thermal emission, the
spectrum consists of two distinct components. The softer component can be
modeled as a magnetic hydrogen atmosphere spectrum - for the pulsar magnetic
field $B=3\times 10^{12}$ G and neutron star mass $M=1.4 M_\odot$ and radius
$R^\infty =13$ km, we obtain $\tef^\infty =0.68\pm 0.03$ MK, $L_{\rm
bol}^\infty = (2.6\pm 0.2)\times 10^{32}$ erg s$^{-1}$, $d=210\pm 20$ pc (the
effective temperature, bolometric luminosity, and radius are as measured by a
distant observer). The effective temperature is lower than that predicted by
standard neutron star cooling models. A standard blackbody fit gives $T^\infty
=1.49\pm 0.04$ MK, $L_{\rm bol}^\infty=(1.5\pm 0.4)\times 10^{32} d_{250}^2$
erg s$^{-1}$ ($d_{250}$ is the distance in units of 250 pc); the blackbody
temperature corresponds to a radius, $R^\infty =(2.1\pm 0.2) d_{250}$ km, much
smaller than realistic neutron star radii. The harder component can be modeled
as a power-law spectrum, with parameters depending on the model adopted for the
soft component - $\gamma=1.5\pm 0.3$, $L_x=(1.5\pm 0.4)\times 10^{31}
d_{250}^2$ erg s$^{-1}$ and $\gamma=2.7\pm 0.4$, $L_x=(4.2\pm 0.6)\times
10^{31} d_{250}^2$ erg s$^{-1}$ for the hydrogen atmosphere and blackbody soft
component, respectively ($\gamma$ is the photon index, $L_x$ is the luminosity
in the 0.2--8 keV band). The extrapolation of the power-law component of the
former fit towards lower energies matches the optical flux at $\gamma\simeq
1.35$--1.45.


title:
Variable Interstellar Absorption toward the Halo Star HD 219188 -
  Implications for Small-Scale Interstellar Structure

abstract:
  Within the last 10 years, strong, narrow Na I absorption has appeared at
v_sun ~ -38 km/s toward the halo star HD 219188; that absorption has continued
to strengthen, by a factor 2-3, over the past three years. The line of sight
appears to be moving into/through a relatively cold, quiescent intermediate
velocity (IV) cloud, due to the 13 mas/yr proper motion of HD 219188; the
variations in Na I probe length scales of 2-38 AU/yr. UV spectra obtained with
the HST GHRS in 1994-1995 suggest N(H_tot) ~ 4.8 X 10^{17} cm^{-2}, ``halo
cloud'' depletions, n_H ~ 25 cm^{-3}, and n_e ~ 0.85-6.2 cm^{-3} (if T ~ 100 K)
for the portion of the IV cloud sampled at that time. The relatively high
fractional ionization, n_e/n_H >~ 0.034, implies that hydrogen must be
partially ionized. The N(Na I)/N(H_tot) ratio is very high; in this case, the
variations in Na I do not imply large local pressures or densities.