title:
Membership, lithium, and metallicity in the young open clusters IC 2602
  and IC 2391: enlarging the sample

abstract:
  We present lithium abundances for ~50 X-ray selected candidate members of the
30-50 Myr old open clusters IC 2602 and IC 2391. These data enlarge and extend
to cooler temperatures previous Li surveys of these clusters by Stauffer et al.
(1989) and Randich et al. (1997). We also give for the first time an estimate
of the metallicity of the two clusters which turns out to be close to solar.
Radial velocity measurements together with Halpha chromospheric emission and
the presence/absence of other spectroscopic features are used to ascertain the
membership status for the sample stars not yet confirmed as cluster members;
rotational velocities have also been determined for all sample stars. Stars
more massive than ~1 Mo in both clusters show no sign of significant Li
depletion, while lower mass stars are all lithium depleted, with the amount of
Li depletion increasing to cooler temperatures. We confirm that the late G and
early K stars in IC 2602 present a star-to-star scatter in Li abundances
similar to, but not as large as the one in the Pleiades. A scatter is also seen
among late-K and M dwarfs. Unlike in the Pleiades and Alpha Per clusters, the
scatter among early-K stars in IC 2602 shows only marginal correlation with
rotation. Our data suggest that the drop-off of lithium towards lower masses
may start at an earlier color in IC 2391 than in IC 2602, but larger cluster
samples are needed to confirm this result. In addition, whereas G and early K
stars in the two clusters are, on average, more Li rich than their counterparts
in the Pleiades, a fraction of the coolest stars, in particular in IC 2391, are
as depleted as as the lowest-Li Pleiades stars of the same mass. If they
continue depleting Li on their way to the main sequence, they are expected to
be more Li depleted than the Pleiades at the age of the latter cluster.


title: FUSE Observations of Capella

abstract:
  Far Ultraviolet Spectroscopic Explorer FUSE observations of the bright binary
system Capella (Alpha Aurigae; G1 III + G8 III) reveal a rich emission line
spectrum containing neutral and ionic species, among them H I, O I, C III, O
VI, S VI, Ne V and Ne VI. In addition the Fe XVIII 974.85 A line, formed at
temperatures of approx. 6 x 10^6 K, is detected. Whereas the chromospheric and
transition region emission is dominated by that from the G1 giant, consistent
with results from previous ultraviolet observations, Fe XVIII is formed largely
in the G8 giant atmosphere. Line ratios from C III suggest densities of 2-8 x
10^10 cm^-3, although anomalous line profiles of the 1176 transition may signal
optical depth effects. The hydrogen Lyman series, detected for the first time,
displays asymmetric emission consistent with an expanding atmosphere.


title:
The SZ Effect as a Probe of Non-Gravitational Entropy in Groups and
  Clusters of Galaxies

abstract:
  We investigate how strongly and at what scales the Sunyaev- Zel'dovich effect
reflects the shifting balance between the two processes that compete for
governing the density and the thermodynamic state of the hot intra-cluster
medium pervading clusters and groups of galaxies: the hierarchical clustering
of the DM; the non-gravitational energy and momentum fed back into the ICM by
the condensing baryons. We base on a SAM of galaxy formation and clustering to
describe how the baryons are partitioned among the hot, the cool and the
stellar phase; the partition shifts as the galaxies cluster hierarchically, and
as the feedback by stellar winds and SN explosions follows the star formation.
Their impact is amplified by the same large scale accretion shocks that
thermalize the gravitational energy of gas falling into the growing potential
wells. We compute the Compton parameter $y$, and find a relation of $y$ with
the ICM temperature, the $y-T$ relation, which departs from the self-similar
scaling and bends down at temperatures typical of galaxy groups. We
model-independently relate this with the analogous behaviour of the L_x - T
relation, and discuss to what extent our results are generic of the
hierarchical models of galaxy formation and clustering.


title:
Testing the Unified Model with an Infrared Selected Sample of Seyfert
  Galaxies

abstract:
  We present a series of statistical tests done to a sample of 29 Seyfert 1 and
59 Seyfert 2 galaxies selected from mostly isotropic properties, their far
infrared fluxes and warm infrared colors. Such selection criteria provide a
profound advantage over the criteria used by most investigators in the past,
such as ultraviolet excess. These tests were done using ground based high
resolution VLA A-configuration 3.6 cm radio and optical B and I imaging data.
  From the relative number of Seyfert 1's and Seyfert 2's we calculate that the
torus half opening angle is 48deg. We show that, as seen in previous papers,
there is a lack of edge-on Seyfert 1 galaxies, suggesting dust and gas along
the host galaxy disk probably play an important role in hiding some nuclei from
direct view. We find that there is no statistically significant difference in
the distribution of host galaxy morphological types and radio luminosities of
Seyfert 1's and Seyfert 2's, suggesting that previous results showing the
opposite may have been due to selection effects. The average extension of the
radio emission of Seyfert 1's is smaller than that of Seyfert 2's by a factor
of ~2-3, as predicted by the Unified Model. A search for galaxies around our
Seyferts allows us to put a lower and an upper limit on the possible number of
companions around these galaxies of 19% and 28%, respectively, with no
significant difference in the number of companion galaxies between Seyfert 1's
and Seyfert 2's. We also show that there is no preference for the radio jets to
be aligned closer to the host galaxy disk axis in late type Seyferts, unlike
results claimed by previous papers. These results, taken together, provide
strong support for a Unified Model in which type 2 Seyferts contain a torus
seen more edge-on than the torus in type 1 Seyferts.


title: Deuterated Ammonia in Galactic Protostellar Cores

abstract:
  We report on a survey of \nh2d towards protostellar cores in low-mass star
formation and quiescent regions in the Galaxy. Twenty-three out of thirty-two
observed sources have significant ($\gsim 5\sigma$) \nh2d emission.
Ion-molecule chemistry, which preferentially enhances deuterium in molecules
above its cosmological value of \scnot{1.6}{-5} sufficiently explains these
abundances. NH2D/NH3 ratios towards Class 0 sources yields information about
the ``fossil remnants'' from the era prior to the onset of core collapse and
star formation. We compare our observations with predictions of gas-phase
chemical networks.


title: Extragalactic neutrino background from PBHs evaporation

abstract:
  We calculated the energy spectra and the fluxes of electron neutrinos in
extragalactic space emitted in the process of the evaporation of primordial
black holes (PBHs) in the early universe. It was assumed that PBHs are formed
by a blue power-law spectrum of primordial density fluctuations. In the
calculations of neutrino spectra the spectral index of density fluctuations and
the reheating temperature were used as free parameters. The absorption of
neutrinos during propagation in the space was taken into account. We obtained
the bounds on the spectral index assuming validity of the standard picture of
gravitational collapse and using the available data of several experiments with
atmospheric and solar neutrinos. The comparison of our results with the
previous constraints (which had been obtained using diffuse photon background
data) shows that such bounds are quite sensitive to an assumed form of the
initial PBH mass function.


title:
High-resolution radio observations of Seyfert galaxies in the extended
  12-micron sample - II. The properties of compact radio components

abstract:
  We discuss the properties of compact nuclear radio components in Seyfert
galaxies from the extended 12-micron AGN sample of Rush et al.(1993). Our main
results can be summarised as follows. Type 1 and type 2 Seyferts produce
compact radio components which are indistinguishable in strength and aspect,
indicating that their central engines are alike as proposed by the unification
model. Infrared IRAS fluxes are more closely correlated with low-resolution
radio fluxes than high-resolution radio fluxes, suggesting that they are
dominated by kiloparsec-scale, extra-nuclear emission regions; extra-nuclear
emission may be stronger in type 2 Seyferts. Early-type Seyfert galaxies tend
to have stronger nuclear radio emission than late-type Seyfert galaxies.
V-shaped extended emission-line regions, indicative of `ionisation cones', are
usually found in sources with large, collimated radio outflows. Hidden broad
lines are most likely to be found in sources with powerful nuclear radio
sources. Type 1 and type 2 Seyferts selected by their IRAS 12-micron flux
densities have well matched properties.


title:
Luminous early-type field galaxies at $z \sim 0.4$ - I. Observations and
  redshift catalogue of 581 galaxies

abstract:
  We have compiled a sample of $\sim 9600$ bright, $i\le 18.95$, red,
$b_j-r>2$, candidate galaxies in an area of 220 deg$^2$. These are luminous, $L
> L^*$, field early-type galaxies with redshifts $0.3 \la z \la 0.6$. We
present a redshift catalogue of a sub-sample of 581 targets. The galaxies were
selected according to their broadband $b_jri$ colours from United Kingdom
Schmidt Telescope plates, and have a surface density on the sky of only $\sim
50 $deg$^{-2}$. Such luminous field galaxies are virtually absent from
published redshift surveys and the catalogue provides a large sample of the
most luminous normal galaxies, at cosmological distances. The statistical
properties of the galaxy spectra, including absorption line and emission line
measures, are presented and a composite spectrum constructed. The nature of the
sample, combined with the relatively bright apparent magnitudes make the
galaxies suitable targets for several key investigations in galaxy evolution
and cosmology.


title:
A Bow Shock Nebula Around a Compact X-Ray Source in the Supernova
  Remnant IC443

abstract:
  We present spectra and high resolution images of the hard X-ray feature along
the southern edge of the supernova remnant IC443. Data from the Chandra X-ray
Observatory reveal a comet-shaped nebula of hard emission, which contains a
softer point source at its apex. We also present 20cm, 6cm, and 3.5cm images
from the Very Large Array that clearly show the cometary nebula. Based on the
radio and X-ray morphology and spectrum, and the radio polarization properties,
we argue that this object is a synchrotron nebula powered by the compact source
that is physically associated with IC443. The spectrum of the soft point source
is adequately but not uniquely fit by a black body model (kT=0.71 +/- 0.08 keV,
L=(6.5 +/- 0.9) * 10^31 erg/s). The cometary morphology of the nebula is the
result of the supersonic motion of the neutron star (V_NS=250 +/- 50 km/s),
which causes the relativistic wind of the pulsar to terminate in a bow shock
and trail behind as a synchrotron tail. This velocity is consistent with an age
of 30,000 years for the SNR and its associated neutron star.


title:
The Role of Clouds in Brown Dwarf and Extrasolar Giant Planet
  Atmospheres

abstract:
  Clouds and hazes are important throughout our solar system and in the
atmospheres of brown dwarfs and extrasolar giant planets. Among the brown
dwarfs, clouds control the colors and spectra of the L-dwarfs; the
disappearance of clouds helps herald the arrival of the T-dwarfs. The structure
and composition of clouds will be among the first remote-sensing results from
the direct detection of extrasolar giant planets.


title: The Clustering of AGN and Galaxies at Intermediate Redshift

abstract:
  Galaxies in the environments of 69 0.2<z<0.7 UBR selected AGN have been
imaged to Bj~23.5. By applying photometric redshifts and color selection
criteria to the galaxy catalogue, the AGN-galaxy cross-correlation function has
been measured as a function of galaxy type. The spatial cross-correlation of
AGN with red (early-type) galaxies is comparable to the autocorrelation
function of elliptical galaxies at low redshift. In contrast, the
cross-correlation of AGN with blue (late-type) galaxies is weak and has been
detected with low significance. As blue galaxies dominate Bj~23.5 galaxy
catalogues, the cross-correlation of UBR selected AGN with all galaxies is weak
at intermediate redshifts.


title:
Observational Evidence for Two Cosmological Predictions Made by
  Bit-String Physics

abstract:
  A decade ago bit-string physics predicted that the baryon/photon ratio at the
time of nucleogenesis $\eta= 1/256^4$ and that the dark matter/baryonic matter
ratio $\Omega_{DM}/\Omega_B= 12.7$. Accepting that the normalized Hubble
constant is constrained observationally to lie in the range $0.6 < h_0 < 0.8$,
this translates into a prediction that $0.325 > \Omega_M > 0.183 $. This and a
prediction by E.D.Jones, using a model-independent argument and ideas with
which bit-string physics is not inconsistent, that the cosmological constant
$\Omega_{\Lambda}=0.6\pm 0.1$ are in reasonable agreement with recent
cosmological observations, including the BOOMERANG data.


title: GEST

abstract:
  Galactic Exoplanet Survey Telescope (GEST) was proposed for a discovery
mission to search for microlensing terrestrial planets toward the Galactic
bulge and also Kuiper Belt Objects (KBOs) that are believed to hold vital
information of the early history of the solar system. Earth mass planets
require massive survey, angular resolution, temporal resolution, and continuous
monitoring capability in a statistically stable observing condition. A 2m scale
wide FOV space telescope with a large focal plane such as the GSET meets the
needs. During the non-bulge time, the GEST will be ideal for high resolution
mapping of the large scale structures which will include weak lensing by dark
matter, quasar lensing and host galaxies, strong lensing by clusters, and a
large volume of galaxies, which with selective follow-up measurements of whose
redshifts and IR images will shed light on the dark stuff (matter, energy,
essesnce, extra dimenstions, topological defects, ...). The data base can be
mined for foreground objects such as high proper motion white dwarfs. We
discuss microlensing, planets, and the necessity for a space imager.


title:
Anomalous X-ray Pulsars and Soft gamma-ray Repeaters: Spectral Fits and
  the Magnetar Model

abstract:
  The energy source powering the X-ray emission from anomalous X-ray pulsars
(AXPs) and soft gamma-ray repeaters (SGRs) is still uncertain. In one scenario,
the presence of an ultramagnetized neutron star, or ``magnetar'', with B on the
order of 10^{14} - 10^{15} G is invoked. To investigate this hypothesis, we
have analyzed archival ASCA data for several known AXPs and SGRs, and fitted
them with a model in which all or part of the X-ray flux originates as thermal
emission from a magnetar. Our magnetar spectral model includes the effects of
the anisotropy of the heat flow through an ultramagnetized neutron star
envelope, reprocessing by a light element atmosphere, and general relativistic
corrections to the observed spectrum. We obtain good fits to the data with
radii for the emitting areas which are generally consistent with those expected
for neutron stars, in contrast to blackbody (BB) fits, which imply much smaller
radii. Furthermore, the inclusion of atmospheric effects results in inferred
temperatures which are lower than those implied by BB fits, but however still
too high to be accounted by thermal cooling alone. An extra source of heating
(possibly due to magnetic field decay) is needed. Despite the harder tail in
the spectrum produced by reprocessing of the outgoing flux through the
atmosphere, spectral fits still require a considerable fraction of the flux to
be in a power-law component.


title: New solution to viscous evolution of accretion disks in binary systems

abstract:
  Analytical investigation of time-dependent accretion in disks is carried out.
We consider a time-dependent disk in a binary system at outburst which has a
fixed tidally-truncated outer radius. The standard Shakura-Sunyaev model of the
disk is considered. The vertical structure of the disk is accurately described
in two regimes of opacity: Thomson and free-free. Fully analytical solutions
are obtained, characterized by power-law variations of accretion rate with
time. The solutions supply asymptotic description of disk evolution in flaring
sources in the periods after outbursts while the disk is fully ionized. The
X-ray flux of multicolor (black-body) alpha-disk is obtained as varying
quasi-exponentially. Application to X-ray novae is briefly discussed concerning
the observed faster-than-power decays of X-ray light curves. The case of
time-dependent advective disk when the exponential variations of accretion rate
can occur is discussed.


title: TeV Neutrinos from Successful and Choked Gamma-Ray Bursts

abstract:
  Core collapse of massive stars resulting in a relativistic fireball jet which
breaks through the stellar envelope is a widely discussed scenario for
gamma-ray burst production. For very extended or slow rotating stars, the
fireball may be unable to break through the envelope. Both penetrating and
choked jets will produce, by photo-meson interactions of accelerated protons, a
burst of neutrinos with energies in excess of 5 TeV while propagating in the
envelope. The predicted flux, from both penetrating and chocked fireballs,
should be easily detectable by planned cubic kilometer neutrino telescopes.


title: GRBs and the Ghost of the Fireball

abstract:
  Gamma Ray Burst has been widely believed in last decade to be
super-explosions: the Fireball. We are argue on the contrary that GRBs (as well
as Soft Gamma Repeaters SGR) are precessing Gamma Jets. We remind the list of
contradiction that Fireball and its smaller galactic version, the Magnetar,
have to face. In particular the existence of weak isolated X-ray precursor
signal before the main Gamma Ray Burst and (rare SGR) events disagree with any
explosive, one shoot, scenarios either isotropic or wide-beamed. We interpret
them as earlier marginal blazing of outlying X conical Jet tails of precessing,
spinning gamma Jet.


title: The Unique Signature of Shell Curvature in Gamma-Ray Bursts

abstract:
  As a result of spherical kinematics, temporal evolution of received gamma-ray
emission should demonstrate signatures of curvature from the emitting shell.
Specifically, the shape of the pulse decay must bear a strict dependence on the
degree of curvature of the gamma-ray emitting surface. We compare the spectral
evolution of the decay of individual GRB pulses to the evolution as expected
from curvature. In particular, we examine the relationship between photon flux
intensity (I) and the peak of the \nu F\nu distribution (E_{peak}) as predicted
by colliding shells. Kinematics necessitate that E_{peak} demonstrate a
power-law relationship with I described roughly as: I=E_{peak}^{(1-\zeta)}
where \zeta represents a weighted average of the low and high energy spectral
indices. Data analyses of 24 BATSE gamma-ray burst pulses provide evidence that
there exists a robust relationship between E_{peak} and I in the decay phase.
Simulation results, however, show that a sizable fraction of observed pulses
evolve faster than kinematics allow. Regardless of kinematic parameters, we
found that the existence of curvature demands that the I - E_{peak} function
decay be defined by \sim (1-\zeta). Efforts were employed to break this
curvature dependency within simulations through a number of scenarios such as
anisotropic emission (jets) with angular dependencies, thickness values for the
colliding shells, and various cooling mechanisms. Of these, the only method
successful in dominating curvature effects was a slow cooling model. As a
result, GRB models must confront the fact that observed pulses do not evolve in
the manner which curvature demands.


title:
GMRT Observations of Interstellar Clouds in the 21cm line of Atomic
  Hydrogen

abstract:
  Nearby interstellar clouds with high (|v| >/= 10 km/s) random velocities
although easily detected in NaI and CaII lines have hitherto not been detected
(in emission or absorption) in the HI 21cm line. We describe here deep Giant
Metrewave Radio Telescope (GMRT) HI absorption observations toward radio
sources with small angular separation from bright O and B stars whose spectra
reveal the presence of intervening high random velocity CaII absorbing clouds.
In 5 out of the 14 directions searched we detect HI 21cm absorption features
from these clouds. The mean optical depth of these detections is ~ 0.09 and
FWHM is ~ 10 km/s, consistent with absorption arising from CNM clouds.


title:
Fluctuations in the Cosmic Microwave Background I: Form Factors and
  their Calculation in Synchronous Gauge

abstract:
  It is shown that the fluctuation in the temperature of the cosmic microwave
background in any direction may be evaluated as an integral involving scalar
and dipole form factors, which incorporate all relevant information about
acoustic oscillations before the time of last scattering. A companion paper
gives asymptotic expressions for the multipole coefficient $C_\ell$ in terms of
these form factors. Explicit expressions are given here for the form factors in
a simplified hydrodynamic model for the evolution of perturbations.


title:
Gas Distribution and Starburst Activity in the Widely Separated
  Interacting Galaxies NGC 6670

abstract:
  We present high resolution H I 21 cm line, 20 cm radio continuum, and CO(1-0)
line observations of the luminous infrared galaxy NGC 6670. NGC 6670 consists
of two edge-on disk galaxies (NGC 6670E and NGC 6670W) with a projected nuclear
separation of ~16 kpc. While there are no optically identified tidal features
and the molecular disks are not distorted much, we have detected a 90 kpc long
H I tail which suggests that the galaxies are interacting and have already
experienced at least one close encounter. Our observations suggest that the
previous encounter between the galaxies had a large impact parameter and that
the system is still in an early stage of interaction.
  Even though NGC 6670 is in an early stage of interaction, we find evidence of
starburst. The CO(1-0) observations show large molecular gas reservoirs in the
central regions and the 20 cm radio continuum observations reveal enhanced star
formation activity in the nuclear regions of both galaxies. We estimate the
ratio L_IR/M_H2, which is often used as an indicator of star formation
efficiency, in the nuclear regions of NGC 6670E and NGC 6670W to be 18 and 11
L_sun/M_sun, respectively. The nuclear star formation efficiency of these two
galaxies has been elevated to the level observed in other nearby starburst
galaxies (L_IR/M_H2 > 10 L_sun/M_sun). Other indicators of starburst activity
such as CO brightness temperature and infrared surface brightness are also
observed.


title:
Fluctuations in the Cosmic Microwave Background II: $C_\ell$ at Large
  and Small $\ell$

abstract:
  General asymptotic formulas are given for the coefficient $C_\ell$ of the
term of multipole number $\ell$ in the temperature correlation function of the
cosmic microwave background, in terms of scalar and dipole form factors
introduced in a companion paper. The formulas apply in two overlapping limits:
for $\ell\gg 1$ and for $\ell d/d_A\ll 1$ (where $d_A$ is the angular diameter
distance of the surface of last scattering, and $d$ is a length, of the order
of the acoustic horizon at the time of last scattering, that characterizes
acoustic oscillations before this time.) The frequently used approximation that
$C_\ell$ receives its main contribution from wave numbers of order $\ell/d_A$
is found to be less accurate for the contribution of the Doppler effect than
for the Sachs--Wolfe effect and intrinsic temperature fluctuations. For $\ell
d/d_A\ll 1$ and $\ell\geq 2$, the growth of $C_\ell$ with $\ell$ is shown to be
affected by acoustic oscillation wave numbers of all scales. The asymptotic
formulas are applied to a model of acoustic oscillations before the time of
last scattering, with results in reasonable agreement with more elaborate
computer calculations.


title: What next for the Likely Pre-Supernova, HD 179821?

abstract:
  We have used the Owens Valley Radio Observatory Millimeter Array to obtain a
map of the J = (1-0) CO emission from the circumstellar shell around HD 179821,
a highly evolved G-type star which will probably explode as a supernova in the
next 100,000 yr. Very approximately, the gas presents as a circular ring with
azimuthal variations in the CO brightness by about a factor of 2. Until about
1600 years ago, the star was a red hypergiant losing about 0.0003 M(Sun)/yr at
an average outflow speed of 32 km/s. We propose that when HD 179821 explodes as
a supernova, it may resemble Kepler's supernova remnant and thus some of the
anisotropies in supernova remnants may be intrinsic. If the factors which cause
the anisotropic mass loss in HD 179821 persist to the moment when the star
explodes as a supernova, the newly-born pulsar may receive a momentum "kick"
leading to a space motion near 700 km/s. Independent of the angular
asymmetries, the radially detached shell around HD 179821 may be representative
of environments which produce dust echoes from gamma-ray bursts.


title:
Incompatibility of a comoving Ly-alpha forest with supernova-Ia
  luminosity distances

abstract:
  Recently Perlmutter et al. suggested a positive value of Einstein's
cosmological constant Lambda on the basis of luminosity distances from type-Ia
supernovae. However, Lambda world models had earlier been proposed by Hoell &
Priester and Liebscher et al. on the basis of quasar absorption-line data.
Employing more general repulsive fluids ("dark energy") encompassing the Lambda
component we quantitatively compare both approaches with each other.
  Fitting the SN-data by a minimum-component model consisting of dark energy +
dust yields a closed universe with a large amount of dust exceeding the
baryonic content constrained by big-bang nucleosynthesis. The nature of the
dark energy is hardly constrained. Only when enforcing a flat universe there is
a clear tendency to a dark-energy Lambda fluid and the `canonical' value
Omega_M = 0.3 for dust.
  Conversely, fitting the quasar-data by a minimum-component model yields a
sharply defined, slightly closed model with a low dust density ruling out
significant pressureless dark matter. The dark-energy component obtains an
equation-of-state P = -0.96 epsilon close to that of a Lambda-fluid. Omega_M =
0.3 or a precisely flat spatial geometry are inconsistent with
minimum-component models.
  It is found that quasar and supernova data sets cannot be reconciled with
each other via (repulsive ideal fluid+dust+radiation)-world models.
Compatibility could be reached by drastic expansion of the parameter space with
at least two exotic fluids added to dust and radiation as world constituents.
If considering such solutions as far-fetched one has to conclude that the
quasar absorption line and the SN-Ia constraints are incompatible.


title:
Gamma-Ray Burst Afterglows with Energy Injection: Homogeneous Versus
  Wind External Media

abstract:
  Assuming an adiabatic evolution of a gamma-ray burst (GRB) fireball
interacting with an external medium, we calculate the hydrodynamics of the
fireball with energy injection from a strongly magnetic millisecond pulsar
through magnetic dipole radiation, and obtain the light curve of the optical
afterglow from the fireball by synchrotron radiation. Results are given both
for a homogeneous external medium and for a wind ejected by GRB progenitor. Our
calculations are also available in both ultra-relativistic and non-relativistic
phases. Furthermore, the observed R-band light curve of GRB{000301C} can be
well fitted in our model, which might provide a probe of the properties of GRB
progenitors.


title: Nature of widely separated ultraluminous infrared galaxies

abstract:
  In the complete sample of ultraluminous infrared galaxies (ULIRGs) compiled
by Kim (1995) about 5% consists of widely separated galaxies which are
presumably in the early phase of interaction. This fact is contrary to the
conventional view that ULIRGs are in the final stages of the merger of two
gas-rich disk galaxies. We have undertaken high resolution CO(J=1-0)
observations for the ultraluminous infrared galaxies that have nuclear
separations larger than 20 kpc. We have detected the CO emission in 5 out of 6
systems, but only in one component of the ULIRG pairs. 4 of them have LINER
spectral type and 1 galaxy has Seyfert II spectral type. In K'-band images
these components are also brighter than the other components which have either
HII-region spectra or no detectable emission lines. Using the standard
conversion factor, the molecular gas content is estimated to be a few times 10
$^{10}$ M$_\odot$, similar to that of the other ultraluminous galaxies. The
result indicates that the galaxy containing the molecular gas is also the
source of most, if not all, of the huge far-infrared luminosity of the system.
The optical and K'-band imaging observations and optical spectra suggest
multiple merger scenario for 1 system. If the remaining systems are in an early
stage of a binary tidal interaction, the commonly accepted interpretation of
the ULIRG phenomenon as the final merger stage of two disk galaxies may need to
be re-examined.


title:
Magnetic Field Diagnostics Based on Far-Infrared Polarimetry: Tests
  Using Numerical Simulations

abstract:
  The dynamical state of star-forming molecular clouds cannot be understood
without determining the structure and strength of their magnetic fields.
Measurements of polarized far-infrared radiation from thermally aligned dust
grains are used to map the orientation of the field and estimate its strength,
but the accuracy of the results has remained in doubt. In order to assess the
reliability of this method, we apply it to simulated far-infrared polarization
maps derived from three-dimensional simulations of supersonic
magnetohydrodynamical turbulence, and compare the estimated values to the known
magnetic field strengths in the simulations. We investigate the effects of
limited telescope resolution and self-gravity on the structure of the maps.
Limited observational resolution affects the field structure such that small
scale variations can be completely suppressed, thus giving the impression of a
very homogeneous field. The Chandrasekhar-Fermi method of estimating the mean
magnetic field in a turbulent medium is tested, and we suggest an extension to
measure the rms field. Both methods yield results within a factor of 2 for
field strengths typical of molecular clouds, with the modified version
returning more reliable estimates for slightly weaker fields. However, neither
method alone works well for very weak fields, missing them by a factor of up to
150. Taking the geometric mean of both methods estimates even the weakest
fields accurately within a factor of 2.5. Limited telescope resolution leads to
a systematic overestimation of the field strengths for all methods. We discuss
the effects responsible for this overestimation and show how to extract
information on the underlying (turbulent) power spectrum.


title: A Chandra Observation of M51: Active Nucleus and Nuclear Outflows

abstract:
  We present a Chandra ACIS-S observation of the nuclear region of the nearby
spiral galaxy M51 (NGC 5194), which has a low-luminosity Seyfert 2 nucleus. The
X-ray image shows the nucleus, southern extranuclear cloud, and northern loop,
the morphology of the extended emission being very similar to those seen in
radio continuum and optical emission line images. The X-ray spectrum of the
nucleus is well represented by a model consisting of soft thermal plasma with
kT ~0.5 keV, a very hard continuum, and an Fe Kalpha emission line at 6.45 keV
with an equivalent width of >2 keV. The very strong Fe line and the flat
continuum indicate that the nucleus is obscured by a column density in excess
of 10^24 cm^-2 and the spectrum is dominated by reflected emission from cold
matter near the nucleus. The X-ray spectra of the extranuclear clouds are well
fitted by a thermal plasma model with kT ~0.5 keV. This spectral shape and
morphology strongly suggest that the clouds are shock heated by the bi-polar
outflow from the nucleus. The shock velocities of the extranuclear cloud and
northern loop inferred from the temperatures of the X-ray gas are 690 km/s and
660 km/s, respectively. By assuming a steady-state situation in which the
emission of the extranuclear clouds is powered by the jets, the mechanical
energy in the jets is found to be comparable to the bolometric luminosity of
the nucleus.


title: IRSI-DARWIN: How to see through the interplanetary dust cloud

abstract:
  ESA has identified interferometry as one of the major goals of the Horizon
2000+ programme. Infrared interferometers are a highly sensitive astronomical
instruments that enable us to observe terrestrial planets around nearby stars.
In this context the Infrared Space Interferometry Mission (IRSI)/ DARWIN is
studied. The current design calls for a constellation of 6 free flying
telescopes using 1.5m mirrors, plus one hub and one master spacecraft. As the
baseline trajectory an orbit about the second collinear libration point of the
Earth-Sun system has been selected. The thermal radiation from the
interplanetary dust cloud that surrounds the Sun, the so-called zodiacal
infrared foreground, is a major concern for any high-sensitivity infrared
mission. The most reliable information about this radiation comes from the
measurements by NASA's Cosmic Background Explorer (COBE) mission. There are
various ways to detect faint terrestrial planets despite the bright foreground.
We find that, using integration times in the order of 30h, the baseline mission
scenario is capable of detecting earth-sized exo-planets out to 14pc. We seize
the suggestion that increasing the heliocentric distance of the instrument
would make the observing conditions even better. A dust model that was fitted
to the COBE measurements shows that an observing location of DARWIN in the
outer solar system would potentially reduce the zodiacal foreground by a factor
of 100, effectively increasing the number of potential target stars by almost a
factor of 30.


title:
An analytical MHD wind model with latitudinal dependences obtained using
  separation of the variables

abstract:
  A new class of analytical 2-D solutions of the full set of the steady
magnetohydrodynamic (MHD) equations, describing an axisymmetric helicoidal
magnetized outflow originating from a rotating central object, is presented.
The solutions are systematically obtained via a nonlinear separation of the
variables in the momentum equation. The analysis yields three parameters which
measure the anisotropy in the latitudinal distribution of various flow
quantities. Topologically, the wind speed is controlled by an X-type critical
point that acts to filter out a single wind-type branch and the Alfven
singularity. The solutions can be regarded as an extension outside the
equatorial plane of the Weber & Davis (1967) model of magnetized winds but with
a variable polytropic index.


title:
Bulk viscosity in superfluid neutron star cores. II. Modified Urca
  processes in $npe\mu$ matter

abstract:
  We study the bulk viscosity in neutron star cores due to modified Urca
processes involving nucleons, electrons and muons and analize its reduction by
singlet-state or triplet-state superfluidity of nucleons. In combination with
the results of our previous paper on the bulk viscosity due to direct Urca
processes, a realistic description of the bulk viscosity in superfluid neutron
star cores is obtained. Switching off direct Urca processes with decreasing
density in a nonsuperfluid matter lowers the bulk viscosity by 3-5 orders of
magnitude. The presense of muons opens additional source of bulk viscosity due
to muon Urca processes and lowers the threshold density of the electron direct
Urca process. The superfluidity may strongly reduce the bulk viscosity and
affect thus damping of neutron star vibrations.


title:
A search for distant radio-loud quasars in the CLASS survey: three new
  radio-selected quasars at z>4

abstract:
  We report on the search for distant radio-loud quasars in the Cosmic Lens All
Sky Survey (CLASS) of flat spectrum radio sources with S_5GHz>30 mJy.
Unresolved optical counterparts were selected from APM scans of POSS-I plates,
with e<19.0 and red o-e>2.0 colours, in an effective area of ~6400 deg^2. Four
sources were found to be quasars with z>4, of which one was previously known.
This sample bridges the gap between the strong radio surveys with S_5GHz>200
mJy and the samples of radio-weak quasars that can be generated via radio
observations of optically selected quasars.
  In addition, 4 new quasars at z>3 have been found. The selection criteria
result in a success-rate of ~1:7 for radio-loud quasars at z>4, which is a
significant improvement over previous studies. This search yields a surface
density of 1 per 1600 deg^2, which is about a factor of ~15 lower than that
found in a similar search for radio-quiet quasars at z>4. The study presented
here is strongly biased against quasars beyond z>4.5, since the e-passband of
the POSS-I only samples the spectra shortward of 1200 Angstrom at these
redshifts.


title:
A New Method for ISOCAM Data Reduction - I. Application to the European
  Large Area ISO Survey Southern Field: Method and Results

abstract:
  We have developed a new data reduction technique for ISOCAM LW data and have
applied it to the European Large Area ISO Survey (ELAIS) LW3 (15 micron)
observations in the southern hemisphere (S1). This method, known as LARI
technique and based on the assumption of the existence of two different time
scales in ISOCAM transients (accounting either for fast or slow detector
response), was particularly designed for the detection of faint sources. In the
ELAIS S1 field we obtained a catalogue of 462 15 micron sources with
signal-to-noise ratio >= 5 and flux densities in the range 0.45 - 150 mJy
(filling the whole flux range between the Deep ISOCAM Surveys and the IRAS
Faint Source Survey). The completeness at different flux levels and the
photometric accuracy of this catalogue have been tested with simulations. Here
we present a detailed description of the method and discuss the results
obtained by its application to the S1 LW3 data.


title: X-ray luminosities of galaxies in groups

abstract:
  We have derived the X-ray luminosities of a sample of galaxies in groups,
making careful allowance for contaminating intragroup emission. The L_X:L_B and
L_X:L_{FIR} relations of spiral galaxies in groups appear to be
indistinguishable from those in other environments, however the elliptical
galaxies fall into two distinct classes. The first class is central-dominant
group galaxies which are very X-ray luminous, and may be the focus of group
cooling flows. All other early-type galaxies in groups belong to the second
class, which populates an almost constant band of L_X/L_B over the range 9.8 <
log L_B < 11.3. The X-ray emission from these galaxies can be explained by a
superposition of discrete galactic X-ray sources together with a contribution
from hot gas lost by stars, which varies a great deal from galaxy to galaxy. In
the region where the optical luminosity of the non-central group galaxies
overlaps with the dominant galaxies, the dominant galaxies are over an order of
magnitude more luminous in X-rays.
  We also compared these group galaxies with a sample of isolated early-type
galaxies, and used previously published work to derive L_X:L_B relations as a
function of environment. The non-dominant group galaxies have mean L_X/L_B
ratios very similar to that of isolated galaxies, and we see no significant
correlation between L_X/L_B and environment. We suggest that previous findings
of a steep L_X:L_B relation for early-type galaxies result largely from the
inclusion of group-dominant galaxies in samples.


title: Dust-enshrouded Asymptotic Giant Branch Stars in the Solar Neighbourhood

abstract:
  A study is made of a sample of 58 dust-enshrouded Asymptotic Giant Branch
(AGB) stars (including 2 possible post AGB stars), of which 27 are carbon-rich
and 31 are oxygen-rich. These objects were originally identified by Jura &
Kleinmann as nearby (within about 1 kpc of the sun) AGB stars with high
mass-loss rates, greater than 1E-6 solar masses per year. Ground-based
near-infrared photometry, data obtained by IRAS and kinematic data from the
literature are combined to investigate the properties of these stars. The light
amplitude in the near-infrared is found to be correlated with period, and this
amplitude decreases with increasing wavelength. Statistical tests show that
there is no reason to suspect any difference in the period distributions of the
carbon- and oxygen-rich stars for periods less than 1000 days, and no
carbon-rich star has a period longer than 1000 days. The colours are consistent
with those of cool stars with evolved circumstellar dust-shells. Luminosities
and distances are estimated using a period-luminosity relation. Mass-loss
rates, estimated from the 60 micron fluxes, show a correlation with pulsation
period and is tightly correlated with the K-[12] colour. The kinematics and
scale-height of the sample shows that the sources with periods less than 1000
days must have low mass main-sequence progenitors. It is argued that the three
oxygen-rich stars with periods over 1000 days probably had intermediate mass
main-sequence progenitors with remaining stars having an average progenitor
mass of about 1.3 solar masses. The average lifetime of stars in this phase is
estimated to be about 4.0E4 years, indicating they will undergo at most one
more thermal pulse before leaving the AGB.


title:
Line-of-sight velocity distributions of low-luminosity elliptical
  galaxies

abstract:
  The shape of the line-of-sight velocity distribution (LOSVD) is measured for
a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals.
The sample is dominated by galaxies in the Virgo cluster but also contains
ellipticals in nearby groups and low density environments. The parameterization
of the LOSVD due to Gerhard and van der Marel and Franx is adopted, which
measures the asymmetrical and symmetrical deviations of the LOSVD from a
Gaussian by the amplitudes h3 and h4 of the Gauss-Hermite series. Rotation,
velocity dispersion, h3 and h4 are determined as a function of radius for both
major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the
major axes. Deviations from a Gaussian LOSVD along the minor axis are of much
lower amplitude if present at all. Central decreases in velocity dispersion are
found for three galaxies. Two galaxies have kinematically-decoupled cores: NGC
4458 and the well-known case of NGC 3608.


title: GRB010222: afterglow emission from a rapidly decelerating shock

abstract:
  The GRB010222 optical and near-infrared (NIR) afterglow was monitored at the
TNG and other Italian telescopes starting ~1 day after the high-energy prompt
event. The optical BVR light curves, which are the best sampled, are
continuously steepening, and can be described by two power laws, f(t) =
t^(-alpha), of indices alpha_1 ~ 0.7 and alpha_2 ~ 1.3 before and after a break
occurring at about 0.5 days after the GRB start time, respectively. This model
accounts well also for the flux in the U, I and J bands, which are less well
monitored. The temporal break appears to be achromatic. The two K-band points
are not consistent with the above behaviour, and rather suggest a constant
trend. A low-resolution optical spectrum has also been taken with TNG. In the
optical spectrum we found three absorption systems at different redshifts
(0.927, 1.155 and 1.475), the highest of which represents a lower limit to, and
probably coincides with, the redshift of this GRB. The broad-band optical
spectral energy distributions do not appear to vary with time, consistently
with the achromatic behaviour of the light curves. We compare our measurements
with different afterglow evolution scenarios and we find that they favor a
transition from relativistic to non-relativistic conditions in the shock
propagation.


title:
Temperature effects on the 15-85-micron spectra of olivines and
  pyroxenes

abstract:
  Far-infrared spectra of laboratory silicates are normally obtained at room
temperature even though the grains responsible for astronomical silicate
emission bands seen at wavelengths >20 micron are likely to be at temperatures
below ~150 K. In order to investigate the effect of temperature on silicate
spectra, we have obtained absorption spectra of powdered forsterite and
olivine, along with two orthoenstatites and diopside clinopyroxene, at 3.5+-0.5
K and at room temperature (295+-2K). To determine the changes in the spectra
the resolution must be increased from 1 to 0.25 cm^-1 at both temperatures
since a reduction in temperature reduces the phonon density, thereby reducing
the width of the infrared peaks. Several bands observed at 295 K split at 3.5
K. At 3.5 K the widths of isolated single bands in olivine, enstatites and
diopside are ~ 90% of their 295 K-widths. However, in forsterite the
3.5-K-widths of the 31-, 49- and 69-micron bands are, respectively, 90%, 45%
and 31% of their 295 K widths. Due to an increase in phonon energy as the
lattice contracts, 3.5-K-singlet peaks occur at shorter wavelengths than do the
corresponding 295-K peaks; the magnitude of the wavelength shift increases from
\~ 0-0.2 micron at 25 micron to ~0.9 micron at 80 micron. Changes in the
relative absorbances of spectral peaks are also observed. The temperature
dependence of lambda_pk and bandwidth shows promise as a means to deduce
characteristic temperatures of mineralogically distinct grain populations. In
addition, the observed changes in band strength with temperature will affect
estimates of grain masses and relative mineral abundances inferred using
room-temperature laboratory data.


title: The mean surface density of companions in a stellar-dynamical context

abstract:
  Applying the mean surface density of companions, Sigma(r), to the dynamical
evolution of star clusters is an interesting approach to quantifying structural
changes in a cluster. It has the advantage that the entire density structure,
ranging from the closest binary separations, over the core-halo structure
through to the density distribution in moving groups that originate from
clusters, can be analysed coherently as one function of the stellar separations
r.
  This contribution assesses the evolution of Sigma(r) for clusters with
different initial densities and binary populations. The changes in the binary,
cluster and halo branches as the clusters evolve are documented using direct
N-body calculations, and are correlated with the cluster core and half-mass
radius. The location of breaks in the slope of Sigma(r) and the possible
occurrence of a binary gap can be used to infer dynamical cluster properties.


title: Th Ages for Metal-Poor Stars

abstract:
  With a sample of 22 metal-poor stars, we demonstrate that the heavy element
abundance pattern (Z > 55) is the same as the r-process contributions to the
solar nebula. This bolsters the results of previous studies that there is a
universal r-process production pattern. We use the abundance of thorium in five
metal-poor stars, along with an estimate of the initial Th abundance based on
the abundances of stable r-process elements, to measure their ages. We have
four field red giants with errors of 4.2 Gyr in their ages and one M92 giant
with an error of 5.6 Gyr, based on considering the sources of observational
error only. We obtain an average age of 11.4 Gyr, which depends critically on
the assumption of an initial production ratio of Th/Eu of 0.496. If the
Universe is 15 Gyr old, then the initial Th/Eu value should be 0.590, in
agreement with some theoretical models of the r-process.


title: In ice radio detection of GZK neutrinos

abstract:
  Models for the source and propagation of cosmic rays are stressed by
observations of cosmic rays with energies $E>10^{20}$ eV. A key discriminant
between different models may be complementary observations of neutrinos with
energies $E>10^{18}$ eV. Independent of the source of the cosmic rays,
neutrinos are produced during propagation via the GZK mechanism. Event rates
for GZK neutrinos are expected to be in the range of $0.01-0.1$ per km$^3$ yr,
suggesting a detector mass in excess of 1 Eg. Detection of radio cherenkov
emission from showers produced in Antarctic ice may be an economical way to
instrument such a large mass. It is suggested that a 100 km$^2$ array of
antennas centered on Icecube may allow confirmation of the radio technique and
also increase the science achievable with Icecube by providing vertex
information for events with throughgoing muons.


title: Multiscale Gaussian Random Fields for Cosmological Simulations

abstract:
  This paper describes the generation of initial conditions for numerical
simulations in cosmology with multiple levels of resolution, or multiscale
simulations. We present the theory of adaptive mesh refinement of Gaussian
random fields followed by the implementation and testing of a computer code
package performing this refinement called GRAFIC2. This package is available to
the computational cosmology community at http://arcturus.mit.edu/grafic/ or by
email from the author.


title: Mechanical Feedback: From stellar wind bubbles to starbursts

abstract:
  The current understanding of mechanical feedback is reviewed by evaluating
the standard, adiabatic model for shell formation and evolution. This model is
relevant to phenomena ranging from individual stellar-wind bubbles to galactic
superwinds, forming the basis for our understanding of the multiphase ISM, IGM,
and galactic evolutionary processes. Although significant discrepancies between
the model and observation have been identified, to date there are none that
require a fundamental revision. A variety of evidence, ranging over three
orders of magnitude in spatial scale, is broadly consistent with the standard
model. This includes kinematics of individual objects, observations of hot gas,
the size distribution of HI shells, and outflow rates from starburst galaxies.
However, some of the most pressing issues relating to shell evolution are still
outstanding and obstruct efforts to resolve key questions like the fate of the
hot gas.


title: Size-Mass-luminosity relations in AGN and the role of the accretion disc

abstract:
  We address the question of the relations between the black hole's mass, the
accretion rate, the bolometric luminosity, the optical luminosity and the size
of the Broad Line Region (BLR) in Active Galactic Nuclei, using recent
observational data obtained from monitoring campaigns. We show that a standard
accretion disc cannot account for the observed optical luminosity, unless it
radiates at super-Eddington rates. This implies the existence of another,
dominant emission mechanism in the optical range, or a non standard disc (non
stationary, ADAF and/or strong outflows). Narrow Line Seyfert 1 galaxies
(NLS1s) are most extreme in this context: they have larger bolometric to
Eddington luminosity ratios than Broad Line Seyfert 1 (BLS1s), and most likely
a larger "non disc" component in the optical range. From realistic simulations
of self-gravitating $\alpha$-discs, we have systematically localized the
gravitationally unstable disc and shown that, given uncertainties on both the
model and observations, it coincides quite well with the size of the BLR. We
therefore suggest that the gravitationally unstable disc is the source which
releases BLR clouds in the medium. However the influence of the ionization
parameter is also required to explain the correlation found between the size of
the BLR and the luminosity. In this picture the size of the BLR in NLS1s
(relative to the black hole size) is larger (and the emission line width
smaller) than in BLS1s simply because their Eddington ratio is larger.


title:
Two Different Long-term Behaviors in Black-Hole Candidates: Evidence for
  Two Accretion Flows?

abstract:
  We discuss the results of long-term hard x-ray monitoring of Galactic
black-hole candidates 1E 1740.7-2942, GRS 1758-258, Cyg X-1, GX 339-4, and Cyg
X-3 with the Rossi X-Ray Timing Explorer (RXTE). The objects divide into two
classes. In the first class, exemplified by Cyg X-1, luminosity and spectral
hardness evolve simultaneously. In the second class, the relation is more
complicated: the softest spectra occur while the count rate is dropping. Most
models of accretion, tailored to Cyg X-1, do not predict the second sort of
behavior. One interpretation is a simple model with two simultaneous,
independent accretion flows: a thin disk and a hot halo. A drop in the
accretion rate affecting both flows would propagate through the halo
immediately but might take up to several weeks to propagate through the disk.
While the inner halo is thus temporarily depleted compared to the disk, a
temporary soft state is expected. This picture is supported by the observation
that those sources which show delays (1E 1740.7-2942, GRS 1758-258, and GX
339-4) are expected to have low-mass companions, and those which do not (Cyg
X-1, Cyg X-3) are known or thought to have high-mass companions. Low-mass
companions imply accretion by Roche-lobe overflow, with a high specific angular
momentum in the accreting material, and therefore a large disk with a long
viscous timescale. Wind accretion from massive companions is expected to result
in a much smaller disk, and thus little viscous delay.


title:
New HST spectra indicate the QSO PG1718+4807 will not give the
  primordial deuterium abundance

abstract:
  The z ~ 0.701 absorption system towards the QSO PG1718+4807 is the only
example of a QSO absorption system which might have a deuterium/hydrogen ratio
approximately ten times the value found towards other QSOs. We have obtained
new STIS spectra from the Hubble Space Telescope of the Lyman alpha and Lyman
limit regions of the system. These spectra give the redshift and velocity
dispersion of the neutral hydrogen which produces most of the observed
absorption. The Lyman alpha line is too narrow to account for all of the
observed absorption. It was previously known that extra absorption is needed on
the blue side of the main H I near to the expected position of deuterium. The
current data suggests with a 98% confidence level that the extra absorption is
not deuterium. Some uncertainty persists because we have a low signal to noise
ratio and the extra absorption - be it deuterium or hydrogen - is heavily
blended with the Lyman alpha absorption from the main hydrogen component.


title:
The X-ray afterglow of GRB000926 observed by BeppoSAX and Chandra: a
  mildly collimated fireball in a dense medium ?

abstract:
  We present X-ray observations of the afterglow of GRB000926 performed around
and after the break observed in the optical light curve two days after the
burst. The steep X-ray light curve observed around the break confirms the
presence of this feature in X-rays. However, the spectral and temporal
properties are not consistent with a standard jet scenario based on synchrotron
emission, requiring a more complicated model. We find that X-ray and optical
data are compatible with a moderately collimated fireball (with opening angle
$\theta\approx25 \deg$) expanding in a dense medium ($n\approx 4\times 10^4$
cm$^{-3}$). This produces two breaks in the light curve. The first, at
$t\approx$ 2 days, is due to jet behavior. The second, around 5 days, is
attributed to the transition of the fireball to a non-relativistic expansion.
This transition predicts a{\it flattening} of the light curve, that explains
the late X-ray measurement in excess above the extrapolation of the simple jet
scenario, and is also consistent with optical data.


title: Early afterglows as probes for the reionization epoch

abstract:
  The nature of Gamma-Ray Burst progenitors is still a debated issue, but
consensus is growing on the association of GRBs with massive stars.
Furthermore, current models for the reionization of the universe consider
massive Pop--III stars as the sources of the ionizing photons. There could then
be a natural link between GRBs and reionization. The reionization epoch can be
measured through prompt IR spectral observations of high redshift GRBs. For
this, GRBs are better than quasars: they produce a smaller HII region even if
they are much brighter than quasars (but for a much shorter time) and then,
contrary to quasars, they do not modify the absorption properties of the
surrounding IGM.


title: Relativistic approach to positronium levels in a strong magnetic field

abstract:
  We have investigated the bound states of an electron and positron in
superstrong magnetic fields typical for neutron stars. The complete
relativistic problem of positronium in a strong magnetic field has not been
succesfully solved up to now. In particular, we have studied the positronium
when it moves relativistically across the magnetic field. A number of problems
which deal with the pulsar magnetosphere, as well as the evolution of
protoneutron stars, could be considered as a field for application.


title: Neutrino-pair radiation form neutron star crusts: Collective effects

abstract:
  We present a method to calculate $\nu \bar{\nu}$ energy losses from neutron
star crusts, which automatically takes into account for collective effects, and
allows to calculate the total emissivity without a separate consideration of
particular processes. We show that the formula we obtain describe the known
results for the emissivity due to plasmon decay and Bremsstrahlung from
degenerate electrons, when one of this processes dominates. In the case of low
temperatures, our formula gives a suppression of the electron vector
weak-current contribution to $\nu \bar{\nu}$ Bremsstrahlung, due to the
collective effects discussed in this paper.


title:
Period - magnitude relationships in BVIJHK-Bands for fundamental mode
  and first overtone Cepheids

abstract:
  We present theoretical period - magnitude relationships for Cepheids in
different filters for fundamental and first overtone pulsators, completing the
work by Alibert et al. (1999). The results are provided for different
metallicities characteristic of the Magellanic Clouds and the Milky Way. In
contrast to the fundamental mode, we find a small metallicity effect on the
period - luminosity relationship for the first overtone, due to the sensitivity
of the period ratio $P_1$/$P_0$ with metallicity. Comparison is made with
observations from OGLE and EROS in the Small and Large Magellanic Clouds. We
emphasize the constraint on theoretical predictions provided by the combination
of both fundamental and first overtone observed sequences. We obtain excellent
agreement between models and data in a $\log P$ - $\wi$ (Wesenheit index)
diagram for a distance modulus for the LMC $\mu_0$ = 18.60 - 18.70. We analyse
the uncertainties of the fundamental period - magnitude relationships and the
consequences on distance determination. We show that an arbitrary shift of the
instability strip by 350 K in $\te$ yields up to 0.45 mag effect on $\mv$ at a
given period, whereas the effect is less than 0.1 mag in the $K$-band. Using
recent near-IR observations in the Large Magellanic Cloud and our $P$ - $\mk$
relationship, we derive a distance modulus for the LMC in agreement with the
value based on $\wi$ data.


title: Circumstellar structure of RU Lupi down to au scales

abstract:
  We have used the technique of spectro-astrometry to study the milli-arcsecond
scale structure of the emission lines in the T Tauri star RU Lupi. The wings of
the H-alpha emission are found to be displaced from the star towards the
south-west (blue wing) and north-east (red wing) with angular scales of 20-30
milli-arcsecs. This structure is consistent with a bipolar outflow from the
star. From a study of the variability of the intensity and position spectra we
argue that a combination of magnetically-driven bipolar outflow and accreting
gas contribute to the H-alpha emission. On the other hand, the [OI] and [SII]
emission are displaced from the star to the south-west but at much larger
distances than the H-alpha, hundreds of milli-arcsecs for the high-velocity
component (HVC) and down to 30 milli-arcsecs for the low-velocity components
(LVC). The presence of both red-shifted and blue-shifted outflows in H-alpha
but only a blue-shifted outflow in the forbidden lines can be explained if the
disc obscures the red-shifted forbidden line outflow, but a disc gap with outer
radius 3-4 au allows the red-shifted H-alpha to be seen. This gap could be
induced by an unseen companion.


title:
Interstellar Medium Surrounding the WO Star in the Galaxy IC 1613: New
  Optical and Radio Observations

abstract:
  Observations of the nebula S3 associated with the WO star in the galaxy IC
1613 and of an extended region surrounding S3 are reported. The star and bright
core of the nebula were observed with a multipupil fiber spectrograph mounted
on the 6-m telescope of the Special Astrophysical Observatory of the Russian
Academy of Sciences. Images in the principle spectral lines and integrated
spectra of the star and three compact clumps were obtained, and the
radial-velocity field constructed. An extended region of the galaxy was
observed with the Very Large Array at 21 cm. A giant ring or HI shell enclosing
a large fraction of the stellar population in IC 1613 was discovered. The WO
star and associated bipolar nebula, which we discovered earlier, lies at the
inner edge of the H ring. A local HI deficiency and two arc-like HI ridges were
also detected for the first time, and probably represent the neutral component
of the bipolar shell surrounding the WO star. The two arc-like ridges may also
have been produced by the collective stellar wind (and supernova explosions?)
in OB association No. 9 from the list of Hodge. A scenario for the formation of
the extended bipolar feature is discussed, based on the new data.


title: Velocity dispersion in N-body simulations of CDM models

abstract:
  This work reports on a study of the spatially coarse-grained velocity
dispersion in cosmological N-body simulations (OCDM and Lambda-CDM models) as a
function of time (redshifts z=0-4) and of the coarsening length (0.6-20 Mpc/h).
The main result is the discovery of a polytropic relationship I_1 ~ rho^{2-eta}
between the velocity-dispersion kinetic energy density of the coarsening cells,
I_1, and their mass density, rho. The exponent eta, dependent on time and
coarsening scale, is a compact measure of the deviations from the naive virial
prediction eta_virial=0. This relationship supports the ``polytropic
assumption'' which has been employed in theoretical models for the growth of
cosmological structure by gravitational instability.


title: Local Constraints on the Oscillating G Model

abstract:
  We analyze the observational constraints on the effective Brans-Dicke
parameter and on the temporal variation of the effective gravitational constant
within the context of the oscillating G model, a cosmological model based on a
massive scalar field non-minimally coupled to gravity. We show that these local
constraints cannot be satisfied simultaneously once the values of the free
parameters entering the model become fixed by the global attributes of our
Universe. In particular, we show that the lower observational bound for the
effective Brans-Dicke parameter and the upper bound of the variation of the
effective gravitational constant lead to a specific value of the oscillation
amplitude which lies well below the value required to explain the periodicity
of 128 Mpc h^{-1} in the galaxy distribution observed in the pencil beam
surveys.


title: On the White Dwarf distances to Galactic Globular Clusters

abstract:
  We analyze in detail various possible sources of systematic errors on the
distances of globular clusters derived by fitting a local template DA white
dwarf sequence to the cluster counterpart (the so-called WD-fitting technique).
We find that the unknown thickness of the hydrogen layer of white dwarfs in
clusters plays a non negligible role. For reasonable assumptions - supported by
the few sparse available observational constraints - about the unknown mass and
thickness of the hydrogen layer for the cluster white dwarfs, a realistic
estimate of the systematic error on the distance is within +-0.10 mag. However,
particular combinations of white dwarf masses and envelope thicknesses - which
at present cannot be excluded a priori - could produce larger errors.
Contamination of the cluster DA sequence by non-DA white dwarfs introduces a
very small systematic error of about -0.03 mag in the Mv/(V-I) plane, but in
the Mv/(B-V) plane the systematic error amounts to ~ +0.20 mag. Contamination
by white dwarfs with helium cores should not influence appreciably the
WD-fitting distances. Finally, we obtain a derivative D((m-M)v)/D(E(B-V))~ -5.5
for the WD-fitting distances, which is very similar to the dependence found
when using the Main Sequence fitting technique.


title:
Proton Cyclotron Features in Thermal Spectra of Ultra-magnetized Neutron
  Stars

abstract:
  A great deal of interest has been recently raised in connection with the
possibility that soft $\gamma$-ray repeaters (SGRs) and anomalous X-ray pulsars
(AXPs) contain {\em magnetars}, young neutron stars endowed with magnetic
fields $\gtrsim 10^{14}$ G. In this paper we calculate thermal spectra from
ultra-magnetized neutron stars for values of the luminosity and magnetic field
believed to be relevant to SGRs and AXPs. Emergent spectra are found to be very
close to a blackbody at the star effective temperature and exhibit a
distinctive absorption feature at the proton cyclotron energy $E_{c,p}\simeq
0.63 (B/10^{14} {\rm G})$ keV. The proton cyclotron features (PCFs) are
conspicuous (equivalent width of up to many hundreds eV) and relatively broad
($\Delta E/E \sim 0.05-0.2$). The detection of the PCFs is well within the
capabilities of present X-ray spectrometers, like the HETGS and METGS on board
Chandra. Their observation might provide decisive evidence in favor of the
existence of magnetars.


title:
Codes for optically thick and hot photoionized media - Radiative
  transfer and new developments

abstract:
  We describe a code designed for hot media {(T $\ge$} a few 10$^4$ K),
optically thick to Compton scattering. It computes the structure of a
plane-parallel slab of gas in thermal and ionization equilibrium, illuminated
on one side or on both sides by a given spectrum. This code has been presented
in a previous paper (Dumont, Abrassart & Collin 2000), where several aspects
were already discussed. So we focus here mainly on the recent developments.
Presently the code solves the transfer of the continuum with the Accelerated
Lambda Iteration method (ALI) and that of the lines in a two stream Eddington
approximation, without using the local escape probability formalism to
approximate the line transfer. This transfer code is coupled with a Monte Carlo
code which allows to take into account direct and inverse Compton diffusions,
and to compute the spectrum emitted up to MeV energies, in any geometry. The
influence of a few physical parameters is shown, and the importance of the
density and pressure distribution (constant density, pressure equilibrium, or
hydrostatic equilibrium) is stressed. Recent improvements in the treatment of
the atomic data are described, and foreseen developments are mentioned.


title:
Limits Due to Instrumental Polarisation in CMB Experiments at Microwave
  Wavelengths

abstract:
  An extended analysis of some instrumental polarisation sources has been done,
as a consequence of the renewed interest in extremely sensitive polarisation
measurements stimulated by Cosmic Microwave Background experiments. The case of
correlation polarimeters, being them more suitable than other configurations,
has been studied in detail and the algorithm has been derived to calculate
their intrinsic sensitivity limit due to device characteristics as well as to
the operating environment. The atmosphere emission, even though totally
unpolarised, has been recognized to be the most important source of sensitivity
degradation for ground based experiments. This happens through receiver
component losses (mainly in the OMT), which generate instrumental polarisation
in genuinely uncorrelated signals. The relevant result is that, also in best
conditions (cfr. Antarctica), integration times longer than ~40s are not
allowed on ground without modulation techniques. Finally, basic rules to
estimate the maximum modulation period for each instrumental configuration have
been provided.


title:
Gamma Ray Bursts statistical properties and limitations on the physical
  model

abstract:
  The present common view about GRB origin is related to cosmology. There are
two evidences in favour of this interpretation. The first is connected with
statistics, the second is based on measurements of the redshifts in the GRB
optical afterglows. Red shifts in optical afterglows had been observed only in
long GRB. Statistical errors, and possibility of galactic origin of short GRB
is discussed; their connection with Soft Gamma Repeaters (SGR) is analyzed.


title: Accretion Disk Models of Luminous Black Holes

abstract:
  Models of X-ray production in black-hole sources are reviewed and compared
with recent observations. Possible diagnostics of the hot-disk and disk-corona
models are discussed in the light of spectral and temporal data. A new model of
a small-scale inviscid accretion disk is presented.


title: Radiation Front Sweeping the Ambient Medium of Gamma-Ray Bursts

abstract:
  Gamma-ray bursts (GRBs) are emitted by relativistic ejecta from powerful
cosmic explosions. Their light curves suggest that the gamma-ray emission
occurs at early stages of the ejecta expansion, well before it decelerates in
the ambient medium. If so, the launched gamma-ray front must overtake the
ejecta and sweep the ambient medium outward. As a result a gap is opened
between the ejecta and the medium that surfs the radiation front ahead.
Effectively, the ejecta moves in a cavity until it reaches a radius
R_{gap}=10^{16}E_{54}^{1/2} cm where E is the isotropic energy of the GRB. At
R=R_{gap} the gap is closed, a blast wave forms and collects the medium swept
by radiation. Further development of the blast wave is strongly affected by the
leading radiation front: the front plays the role of a precursor where the
medium is loaded with e+- pairs and preaccelerated just ahead of the blast. It
impacts the emission from the blast at R < R_{load}=5R_{gap} (the early
afterglow). A spectacular observational effect results: GRB afterglows should
start in optical/UV and evolve fast (< min) to a normal X-ray afterglow. The
early optical emission observed in GRB 990123 may be explained in this way. The
impact of the front is especially strong if the ambient medium is a wind from a
massive progenitor of the GRB. In this case three phenomena are predicted: (1)
The ejecta decelerates at R<R_{load} producing a lot of soft radiation. (2) The
light curve of soft emission peaks at
t_{peak}=40(1+z)E_{54}^{1/2}(Gamma_{ej}/100)^{-2} s where Gamma_{ej} is the
Lorentz factor of the ejecta. Given measured redshift z and t_{peak}, one finds
Gamma_{ej}. (3) The GRB acquires a spectral break at 5 - 50 MeV because harder
photons are absorbed by radiation scattered in the wind.


title: X-Ray and UV Orbital Phase Dependence in LMC X-3

abstract:
  The black-hole binary LMC X-3 is known to be variable on time scales of days
to years. We investigate X-ray and ultraviolet variability in the system as a
function of the 1.7 day binary phase using a 6.4 day observation with the Rossi
X-ray Timing Explorer (RXTE) from December 1998. An abrupt 14% flux decrease,
lasting nearly an entire orbit, is followed by a return to previous flux
levels. This behavior occurs twice, at nearly the same binary phase, but it is
not present in consecutive orbits. When the X-ray flux is at lower intensity, a
periodic amplitude modulation of 7% is evident in data folded modulo the
orbital period. The higher intensity data show weaker correlation with phase.
This is the first report of X-ray variability at the orbital period of LMC X-3.
Archival RXTE observations of LMC X--3 during a high flux state in December
1996 show similar phase dependence. An ultraviolet light curve obtained with
the High Speed Photometer aboard the Hubble Space Telescope shows orbital
modulation consistent with that in the optical, caused by the ellipsoidal
variation of the spatially deformed companion.
  The X-ray spectrum of LMC X-3 can be acceptably represented by a
phenomenological disk-black-body plus a power law. Changes in the spectrum of
LMC X-3 during our observations are compatible with earlier observations during
which variations in the 2-10 keV flux are tracked closely by the disk geometry
spectral model parameter.


title:
Ultra-High Energy Cosmic Rays and Neutron-Decay Halos from Gamma Ray
  Bursts

abstract:
  Simple arguments concerning power and acceleration efficiency show that
ultra-high energy cosmic rays (UHECRS) with energies >~ 10^{19} eV could
originate from GRBs. Neutrons formed through photo-pion production processes in
GRB blast waves leave the acceleration site and travel through intergalactic
space, where they decay and inject a very energetic proton and electron
component into intergalactic space. The neutron-decay protons form a component
of the UHECRs, whereas the neutron-decay electrons produce optical/X-ray
synchrotron and gamma radiation from Compton-scattered background radiation. A
significant fraction of galaxies with GRB activity should be surrounded by
neutron-decay halos of characteristic size ~ 100 kpc.


title: SNO and Supernovae

abstract:
  The Sudbury Neutrino Observatory (SNO) has unique capabilities as a supernova
detector. In the event of a galactic supernova there are opportunities, with
the data that SNO would collect, to constrain certain intrinsic neutrino
properties significantly, to test details of the various models of supernova
dynamics, and to provide prompt notification to the astronomical community
through the Supernova Early Warning System (SNEWS). This paper consists of a
discussion of these opportunities illustrated by some preliminary Monte Carlo
results.


title:
Chaos and the continuum limit in the gravitational N-body problem. I.
  Integrable potentials

abstract:
  This paper summarises a numerical investigation of the statistical properties
of orbits evolved in `frozen,' time-independent N-body realisations of smooth,
time-independent density distributions, allowing for 10^(2.5)<N<10^(5.5). Two
principal conclusions were reached: (1) In the limit of a nearly `unsoftened'
two-body kernel, the value of the largest Lyapunov exponent does NOT appear to
decrease systematically with increasing N. (2) Nevertheless, there is a clear
quantifiable sense in which, on the average, as N increases chaotic orbits in
the frozen-N systems come to more closely approximate characteristics in the
smooth potential. When viewed in configuration or velocity space, or as probed
by collisionless invariants like angular momentum, frozen-N orbits typically
diverge from smooth potential characteristics as a power law in time on a time
scale proportional to N^(1/2)t_D, with t_D a characteristic dynamical, or
crossing, time.


title: Accretion-Assisted Spindown of Young Radio Pulsars

abstract:
  We present a model for the spindown of young radio pulsars in which the
neutron star loses rotational energy not only by emitting magnetic dipole
radiation but also by torquing a surrounding accretion disk produced by
supernova fallback. The braking index predicted in our model is in general less
than n=3 (the value for pure dipole magnetic radiation), in agreement with the
reported values of n<3 for five young radio pulsars. With an accuracy of 30% or
better, our model reproduces the age, braking index and third frequency
derivative of the Crab pulsar for a disk accretion rate in the range 3 x 10^16
- 10^17 g/s.


title: Migration of giant planets in planetesimal discs

abstract:
  Planets orbiting a planetesimal circumstellar disc can migrate inward from
their initial positions because of dynamical friction between planets and
planetesimals. The migration rate depends on the disc mass and on its time
evolution. Planets that are embedded in long-lived planetesimal discs, having
total mass of $10^{-4}-0.01 M_{\odot}$, can migrate inward a large distance and
can survive only if the inner disc is truncated or because of tidal interaction
with the star. In this case the semi-major axis, a, of the planetary orbit is
less than 0.1 AU. Orbits with larger $a$ are obtained for smaller value of the
disc mass or for a rapid evolution (depletion) of the disc. This model may
explain several of the orbital features of the giant planets that were
discovered in last years orbiting nearby stars as well as the metallicity
enhancement found in several stars associated with short-period planets.


title: A Targeted Survey for HI Clouds in Galaxy Groups

abstract:
  Five galaxy groups with properties similar to those of the Local Group have
been surveyed for HI clouds with the Arecibo Telescope. In total 300 pointings
have been observed on grids of approximately 2.5 x 1.5 Mpc centred on the
groups. The 4.5 sigma detection limit on the minimal detectable HI masses is
approximately 7 x 10^6 M_sun (H_0=65). All detections could be attributed to
optical galaxies; no significant detections of HI clouds have been made. This
null result leads to the conclusion that the total HI mass of intragroup clouds
must be less than 10 per cent of the total HI mass of galaxy groups and less
than 0.05 per cent of the dynamical mass. The recent hypothesis that Galactic
high velocity clouds are Local Group satellite galaxies is highly inconsistent
with these observations.


title:
Atmospheric Lensing and Oblateness Effects During an Extrasolar
  Planetary Transit

abstract:
  Future high precision photometric measurements of transiting extrasolar
planets promise to tell us much about the nature of these systems. We examine
how atmospheric lensing and (projected) planet oblateness/ellipticity modify
transit light curves. The large density gradients expected in planet
atmospheres can offset the unfavorably large observer-lens to source-lens
distance ratio, and allow the existence of caustics. Under such conditions,
starlight from all points in the planet's shadow is refracted into view
producing a characteristic slowing down of the dimming at ingress (vice versa
for egress). A search over several parameters, the planet radius etc., cannot
produce a nonlensed transit light curve that can mimic a lensed light curve.
The fractional change in the diminution of starlight is approximately the ratio
of atmospheric scale height to planet radius, expected to be 1 % or less.
Planet oblateness induces an asymmetry to the transit light curve about the
point of minimum flux, depending on the planet orientation. The fractional
asymmetry is around 0.5 % for a projected ellipticity of 10 %, independent of
lensing. For favorable ratios of planet to star radius, the above effects are
potentially observable with future space-based missions. This will allow us to
constrain the planet shape, and its atmospheric scale height, density and
refractive coefficient, providing information on its rotation, temperature and
composition. For HD 209458b, the only currently known transiting extrasolar
planet, caustics are absent because of the very small lens-source separation.
Finally, we provide estimates of other variations to transit light curves that
could be of comparable importance, including rings, satellites, stellar
oscillations, star spots, and weather.


title: Poynting Jets from Accretion Disks

abstract:
  The powerful narrow jets observed to emanate from many compact accreting
objects may arise from the twisting of a magnetic field threading a
differentially rotating accretion disk which acts to magnetically extract
angular momentum and energy from the disk. Two main regimes have been
discussed, {\it hydromagnetic outflows}, which have a significant mass flux and
have energy and angular momentum carried by both the matter and the
electromagnetic field and, Poynting outflows, where the mass flux is negligible
and energy and angular momentum are carried predominantly by the
electromagnetic field. Here we consider a Keplerian disk initially threaded by
a dipole-like magnetic field and we present solutions of the force-free
Grad-Shafranov equation for the coronal plasma. We find solutions with Poynting
jets where there is a continuous outflow of energy and toroidal magnetic flux
from the disk into the external space. This behavior contradicts the commonly
accepted ``theorem'' of Solar plasma physics that the motion of the footpoints
of a magnetic loop structure leads to a stationary magnetic field configuration
with zero power and flux outflows.
  In addition we discuss recent magnetohydrodynamic (MHD) simulations which
establish that quasi-stationary collimated Poynting jets similar to our
Grad-Shafranov solutions arise from the inner part of a disk threaded by a
dipole-like magnetic field. At the same time we find that there is a steady
uncollimated hydromagnetic outflow from the outer part of the disk. The
Poynting jets represent a likely model for the jets from active galactic
nuclei, microquasars, and gamma ray burst sources.


title:
ROSAT and BeppoSAX evidence of soft X-ray excess emission in the Shapley
  supercluster: A3571, A3558, A3560 and A3562

abstract:
  Excess soft X-ray emission in clusters of galaxies has so far been detected
for sources that lie along lines-of-sight to very low Galactic HI column
density (such as Coma, A1795, A2199 and Virgo, N_H 0.9-2.0 10^{20} cm-2). We
show that the cluster soft excess emission can be investigated even at higher
N_H, which provides an opportunity for investigating soft X-ray emission
characteristics among a large number of clusters.
  The ROSAT PSPC analysis of some members of the Shapley concentration (A3571,
A3558, A3560 and A3562, at N_H 4-4.5 10^{20} cm-2) bears evidence for excess
emission in the 1/4 keV band. We were able to confirm the finding for the case
of A3571 by a pointed SAX observation. Within the current sample the soft X-ray
flux is again found to be consistently above the level expected from a hot
virialized plasma. The data quality is however insufficient to enable a
discrimination between alternative models of the excess low energy flux.


title: Quasi-Stellar Objects, Ultraluminous IR Galaxies, and Mergers

abstract:
  We test the hypothesis that QSOs are formed via strong tidal interactions or
mergers, initially going through an ultraluminous infrared phase, by looking
for traces to this phase in the host galaxies of QSOs. We present a systematic
spectroscopic and imaging study of a sample of QSOs that may be in a
transitionary stage. By modeling the spectra, we obtain ages for the recent
starburst events in the host galaxies and interacting companions. We have
discussed in detail the first 5 objects in the sample in previous publications;
here we present results for the remaining 4 objects, and discuss the sample as
a whole. We find that all 9 transition QSOs are undergoing tidal interactions
and that 8 are major mergers. Every object also shows strong recent
star-forming activity, and in at least eight cases this activity is directly
related to the tidal interaction. The ages we derive for the starburst
populations range from currently active star formation in some objects, to
post-starburst ages < 300 Myr in others. There is also a clear connection
between interactions, starbursts, and QSO activity. Seven of the QSOs in the
sample are also ULIGs; statistical considerations show that the two phenomena
are necessarily physically related in these objects. Our results imply one of
two scenarios: (1) at least some ULIGs evolve to become classical QSOs, and the
transition stage lasts < 300 Myr, or (2) at least some QSOs are born under the
same conditions as ULIGs, and their lifetime as QSOs lasts < 300 Myr. We
discuss other properties and trends found in the sample, and propose a model
that accounts for all of them, as well as the youth of these systems.
(abridged)


title:
Spectra and Growth Rates of Fluctuating Magnetic Fields in the Kinematic
  Dynamo Theory with Large Magnetic Prandtl Numbers

abstract:
  The existence of a weak galactic magnetic field has been repeatedly confirmed
by observational data. The origin of this field has not as yet been explained
in a fully satisfactory way and represents one of the main challenges of the
astrophysical dynamo theory. In both the galactic dynamo theory and the
primordial-origin theory, a major influence is exerted by the small-scale
magnetic fluctuations. This article is devoted to constructing a systematic
second-order statistical theory of such small-scale fields. The statistics of
these fields are studied in the kinematic approximation and for the case of
large Prandtl numbers, which is relevant for the galactic and protogalactic
plasma. The advecting velocity field is assumed to be Gaussian and short-time
correlated. Theoretical understanding of this kinematic dynamo model is a
necessary prerequisite for any prospective nonlinear dynamo theory. The theory
is developed for an arbitrary degree of compressibility and formally in d
dimensions, which generalizes the previously known results, elicits the
structure of the solutions, and uncovers a number of new effects. The magnetic
energy spectra are studied as they grow and spread over scales during the
initial stage of the field amplification. Exact Green's-function solutions are
obtained. The spectral theory is supplemented by the study of magnetic-field
correlation functions in the configuration space, where the dynamo problem can
be mapped onto a particular one-dimensional quantum-mechanical problem. The
latter approach is most suitable for the description of the kinematic dynamo in
the long-time limit, i.e. when the magnetic excitation has spread over all
scales present in the system. A simple way of calculating the growth rates of
the magnetic fields in this long-time limit is proposed.

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


title: Submillimeter Imaging Polarimetry of the NGC 7538 Region

abstract:
  Imaging polarimetry of the 0.85mm continuum emission in the NGC 7538 region,
obtained with the SCUBA Polarimeter, is presented. The polarization map is
interpreted in terms of thermal radiation by magnetically aligned dust grains.
Two prominent cores associated with IRS 1 and IRS 11, IRS 1(SMM) and IRS
11(SMM), are found in the surface brightness map. Although these cores look
similar in surface brightness, their polarization shows striking differences.
In IRS 11(SMM), the polarization vectors are extremely well ordered, and the
degrees of polarization are quite high with an average of ~3.9 %. In IRS
1(SMM), on the other hand, the directions of polarization vectors are locally
disturbed, and the degrees of polarization are much lower than those of IRS
11(SMM). These differences suggest that small scale fluctuations of the
magnetic field are more prominent in IRS 1(SMM). This can be interpreted in
terms of the difference in evolutionary stage of the cores. Inside IRS 1(SMM),
which seems to be at a later evolutionary stage than IRS 11(SMM), substructures
such as subclumps or a cluster of infrared sources have already formed. Small
scale fluctuations in the magnetic field could have developed during the
formation of these substructures. The distribution of magnetic field directions
derived from our polarization map agrees well with those of molecular outflows
associated with IRS 1(SMM) and IRS 11(SMM). Comparisons of energy densities
between the magnetic field and the outflows show that the magnetic field
probably plays an important role in guiding the directions of the outflows.


title:
On Some Exponential Potentials for a Cosmological Scalar Field as
  Quintessence

abstract:
  We present general exact solutions for two classes of exponential potentials
in scalar field models for quintessence. The coupling is minimal and we
consider only dust and scalar field. To some extent, it is possible to
reproduce experimental results from supernovae.


title:
The Mbh-sigma relation as a constraint on the formation of elliptical
  galaxies

abstract:
  Most elliptical galaxies contain central black holes, whose masses scale
proportionally to the observed central velocity dispersions of the host
galaxies according to the so-called Mbh-sigma relation. Here we discuss some
consequences that can be derived by combining the Mbh-sigma relation with the
scaling relation describing the Fundamental Plane of elliptical galaxies. In
particular, the possibility of substantial dissipationless merging in the
formation and evolution of elliptical galaxies is discussed. Enforcing the
merger end-products to satisfy the two scaling relations mentioned above, a
major role of dissipation in galaxy formation is strongly suggested by our
analysis. Moreover, we show that existing observational data may shed some
light on the complex process of black hole merging.


title: Predictions for self-pollution in globular cluster stars

abstract:
  Full evolutionary models have been built to follow the phases of asymptotic
giant branch evolution with mass loss for metal mass fractions from Z=0.0002 to
Z=0.004. For the first time, we find that temperatures close to or even larger
than 10^8 K are achieved at low Z; the full CNO cycle operates at the base of
the envelope, the Oxygen abundance for the most metal-poor models of 4 and 5
solar masses is drastically reduced, and sodium and aluminum production by by
proton capture on neon and magnesium can occur. These results may be relevant
for the evolution of primordial massive globular clusters: we suggest that the
low-mass stars may have been polluted at the surface by accretion from the gas
that was lost from the evolving intermediate-mass stars at early ages.


title: An iterative technique for solving equations of statistical equilibrium

abstract:
  Superlevel partitioning is combined with a simple relaxation procedure to
construct an iterative technique for solving equations of statistical
equilibrium. In treating an $N$-level model atom, the technique avoids the
$N^{3}$ scaling in computer time for direct solutions with standard linear
equation routines and also does not fail at large $N$ due to the accumulation
of round-off errors. In consequence, the technique allows detailed model atoms
with $N \ga 10^{3}$, such as those required for iron peak elements, to be
incorporated into diagnostic codes for analysing astronomical spectra. Tests
are reported for a 394-level Fe II ion and a 1266-level Ni I--IV atom.


title: Massive zero-metal stars: Energy production and mixing

abstract:
  Time-dependent nuclear network calculations at constant temperature show that
for zero-metal stars >= 20 Msun (i) beta-decay reactions and (ii) the
13N(p,gamma)14O reaction must be included. It is also shown that the nuclear
timescale in these zero-metal stars is shorter than the mixing timescale and
therefore the assumption of instantaneous mixing across convective regions is
not fulfilled. We conclude that proper modeling of these processes may alter
the evolution of massive zero-metal stars.


title: Star-Forming AGN Host Galaxies

abstract:
  The symbiosis of nuclear activity and star-formation in galaxies, as
manifested in their spectral energy distributions (SEDs) is reviewed. Attention
is drawn to an Hertzsprung-Russell diagram-equivalent for such objects, as well
as to the importance of the SEDs in cosmological context.


title: Resonance accretion on the magnetized rotating neutron star

abstract:
  It is suggested that the accretion disk excites the eigen modes of Alfven
oscillations of the magnetic field tubes the ends of which are frozen to the
neutron star surface. The resonance takes place when the eigen Alfven frequency
coincides with the difference of the Keplerian disk rotation frequency and the
frequency of rotation of a neutron star. This model explains the two narrow
lines of QPO oscillations in kHz band and permits to calculate the masses and
radii of the neutron stars in X-ray binaries.


title: The binary fraction of extreme horizontal branch stars

abstract:
  (Abbreviated) We have used precise radial velocity measurements of subdwarf-B
stars from the Palomar-Green catalogue to look for binary extreme horizontal
branch (EHB) stars. We identify 36 EHB stars in our sample and find that at
least 21 of these stars are binaries. All but one or two of these are new
identifications. The minimum binary fraction for EHB stars implied by our
survey is 60+-8%. Our survey is sensitive to binaries with orbital periods P
less than about 10d. For reasonable assumptions concerning the period
distribution and the mass ratio distribution of the binaries, we find that the
mean detection efficiency of our survey over this range of orbital periods is
87%. Allowing for this estimated detection efficiency, the fraction of EHB
stars which are short-period binaries ($0.03 < P <10d, approximately) is
69+-9%. The value is not strongly dependent on the period distribution below
P=10d or the mean companion mass for these short-period binaries. The orbital
separation of the stars in these binaries is much less than the size of the red
giant from which the EHB star has formed. This is strong evidence that binary
star evolution is fundamental to the formation of the majority of EHB stars. If
there are also binary EHB stars whose orbital periods are more than about 10d,
the fraction of EHB stars whose evolution has been affected by the presence of
a companion may be much higher.


title: Extreme synchrotron BL Lac objects

abstract:
  We performed an observational program with the X-ray satellite BeppoSAX to
study objects with extreme synchrotron peak frequencies (nu_peak > 1 keV). Of
the seven sources observed, four showed peak frequencies in the range 1-5 keV,
while one (1ES 1426+428) displayed a flat power law spectrum (alpha= 0.92),
locating its synchrotron peak at or above 100 keV. This is the third source of
this type ever found, after Mkn 501 and 1ES 2344+514. Our data confirm the
large nu_peak variability of this class of sources, compared with lower peaked
objects. The high synchrotron peak energies, flagging the presence of high
energy electrons, make the extreme BL Lacs also good candidates for TeV
emission, and therefore good probes for the IR background.


title: Near infrared spectroscopy of starburst galaxies

abstract:
  (Abridged) We present new K-band spectroscopy for a sample of 48 starburst
galaxies, obtained using UKIRT in Hawaii. This constitutes a fair sample of the
most common types of starburst galaxies found in the nearby Universe. The
variety of near infrared spectral features shown by these galaxies implies
different bursts characteristics, which suggests that we survey galaxies with
different star formation histories or at different stages of their burst
evolution.
  Using synthetic starburst models, we conclude that the best ensemble of
parameters which describe starburst galaxies in the nearby universe are a
constant rate of star formation, a Salpeter IMF with an upper mass cutoff equal
to 30 solar mass and bursts ages between 10 Myr and 1 Gyr. The model is fully
consistent with the differences observed in the optical and FIR between the
different types of starbursts. It suggests that HII galaxies have younger
bursts and lower metallicities than SBNGs, while LIRGs have younger bursts but
higher metallicities.
  Our observations suggest that the starburst phenomenon must be a sustained or
self--sustained phenomenon: either star formation is continuous in time or
multiple bursts happen in sequence over a relatively long period of time. The
generality of our observations implies that this is a characteristic of
starburst galaxies in the nearby Universe.


title:
The Optical/Infrared Astronomical Quality of High Atacama Sites. I.
  Preliminary Results of Optical Seeing

abstract:
  The region surrounding the Llano de Chajnantor, a high altitude plateau in
the Atacama Desert in northern Chile, has caught the attention of the
astronomical community for its potential as an observatory site. Combining high
elevation and extremely low atmospheric water content, the Llano has been
chosen as the future site of the Atacama Large Millimeter Array. We have
initiated a campaign to investigate the astronomical potential of the region in
the optical/infrared. Here, we report on an aspect of our campaign aimed at
establishing a seeing benchmark to be used as a reference for future activities
in the region. After a brief description of the region and its climate, we
describe the results of an astronomical seeing campaign, carried out with a
Differential Image Motion Monitor that operates at 0.5 micron wavelength. The
seeing at the Llano level of 5000 m, measured over 7 nights in May 1998,
yielded a median FWHM of 1.1". However, the seeing decreased to 0.7" at a
modest 100 m gain above the plateau (Cerro Chico), as measured over 38 nights
spread between July 1998 and October 2000. Neither of these represents the best
seeing expected in the region; the set of measurements provides a reference
base for simultaneous dual runs at Cerro Chico and at other sites of interest
in the region, currently underway. A comparison between simultaneous
measurements at Cerro Chico and Cerro Paranal indicates that seeing at Cerro
Chico is about 12% better than at Paranal. The percentage of optically
photometric nights in the Chajnantor region is about 60%, while that of nights
useful for astronomical work is near 80%.