title: The endpoint of the rp process on accreting neutron stars

abstract:
  We calculate the rapid proton (rp) capture process of hydrogen burning on the
surface of an accreting neutron star with an updated reaction network that
extends up to Xe, far beyond previous work. In both steady-state nuclear
burning appropriate for rapidly accreting neutron stars (such as the magnetic
polar caps of accreting X-ray pulsars) and unstable burning of Type I X-ray
bursts, we find that the rp process ends in a closed SnSbTe cycle. This
prevents the synthesis of elements heavier than Te and has important
consequences for X-ray burst profiles, the composition of accreting neutron
stars, and potentially galactic nucleosynthesis of light p nuclei.


title: Scalar Field Dark Matter

abstract:
  This work is a review of the last results of research on the Scalar Field
Dark Matter model of the Universe at cosmological and at galactic level. We
present the complete solution to the scalar field cosmological scenario in
which the dark matter is modeled by a scalar field $\Phi$ with the scalar
potential $V(\Phi)=V_{0}(cosh {(\lambda \sqrt{\kappa_{0}}\Phi)}-1)$ and the
dark energy is modeled by a scalar field $\Psi$, endowed with the scalar
potential $\tilde{V}(\Psi)= \tilde{V_{0}}(\sinh{(\alpha
\sqrt{\kappa_{0}}\Psi)})^{\beta}$, which together compose the 95% of the total
matter energy in the Universe. The model presents successfully deals with the
up to date cosmological observations, and is a good candidate to treat the dark
matter problem at the galactic level.


title:
Kinematics of Molecular Gas in the Nucleus of NGC1068, from H2 line
  emission observed with VLT

abstract:
  We present results about the distribution and kinematics of the molecular
environment of the AGN in NGC1068, over a 1.5'' x 3.5'' region around the
central engine in NGC1068, derived from H2 line emission detected with ISAAC at
VLT/ANTU on ESO/Paranal. The H2 emitting molecular gas is found to be
distributed along the East-West direction and with two main peak emission
(knots) located at a distance of about 70 pc from the central engine. The
eastern H2 knot is more intense than the western one. The line profiles mapped
across the entire 1.5'' x 3.5'' region, at a spatial resolution of 0.3'' x
0.45'', appear to be quite complex with either a blue or red wing. At first
order, we find a velocity difference of 140 km/s between the two knots; if
interpreted as quasi-keplerian velocity, this implies a central enclosed mass
of 10^8 solar masses.


title:
Bounds on Compactness for LMXB Neutron Stars from X-ray Burst
  Oscillations

abstract:
  We have modelled X-ray burst oscillations observed with the Rossi X-ray
Timing Explorer (RXTE) from two low mass X-ray binaries (LMXB): 4U 1636-53 with
a frequency of 580 Hz, and 4U 1728-34 at a frequency of 363 Hz. We have
computed least squares fits to the oscillations observed during the rising
phase of bursts using a model which includes emission from either a single
circular hot spot or a pair of circular antipodal hot spots on the surface of a
neutron star. We model the spreading of the thermonuclear hot spots by assuming
that the hot spot angular size grows linearly with time. We calculate the flux
as a function of rotational phase from the hot spots and take into account
photon deflection in the relativistic gravitational field of the neutron star
assuming the exterior spacetime is the Schwarzschild metric. We find acceptable
fits with our model and we use these to place constraints on the compactness of
the neutron stars in these sources. For 4U 1636-53, in which detection of a 290
Hz sub-harmonic supports the two spot model, we find that the compactness
(i.e., mass/radius ratio) is constrained to be M/R < 0.163 at 90% confidence (G
= c = 1). This requires a relatively stiff equation of state (EOS) for the
stellar interior. For example, if the neutron star has a mass of 1.4 Msun then
its radius must be > 12.8 km. Fits using a single hot spot model are not as
highly constraining. We discuss the implications of our findings for recent
efforts to calculate the EOS of dense nucleon matter and the structure of
neutron stars.


title: Ultralight Scalars and Spiral Galaxies

abstract:
  We study some possible astrophysical implications of a very weakly coupled
ultralight dilaton-type scalar field. Such a field may develop an
(approximately stable) network of domain walls. The domain wall thickness is
assumed to be comparable with the thickness of the luminous part of the spiral
galaxies. The walls provide trapping for galactic matter. This is used to
motivate the very existence of the spiral galaxies. A zero mode existing on the
domain wall is a massless scalar particle confined to 1+2 dimensions. At
distances much larger than the galaxy/wall thickness, the zero-mode exchange
generates a logarithmic potential, acting as an additional term with respect to
Newton's gravity. The logarithmic term naturally leads to constant rotational
velocities at the periphery. We estimate the scalar field coupling to the
matter energy-momentum tensor needed to fit the observable flat rotational
curves of the spiral galaxies. The value of this coupling turns out to be
reasonable -- we find no contradiction with the existing data.


title: f(R) gravity theory and CMBR constraints

abstract:
  We consider the large-scale cosmic structure generation by an inflation based
on a pure f(R)-type gravity theory. Comparison with recent CMBR observations
gives the following results: (1) The near Zel'dovich spectral conditions
uniquely choose R^2-type gravity. (2) The R^2 gravity predicts specific nearly
scale-invariant Zel'dovich spectra for both the scalar- and tensor-type
perturbations. Thus, (3) the considered model survives current observational
data. The COBE-DMR quadrupole data (4) give constraints on the coupling
constant and the energy scale during inflation, and (5) require the
gravitational wave contribution to be suppressed. (6) Therefore, future
observations of (2) and (5) can provide strong tests of the inflation scenario
based on R^2 gravity. Parallel analyses made in the conformally transformed
Einstein frame give the observationally identical results.


title: Variable 21cm absorption at z=0.3127

abstract:
  We report multi-epoch GMRT HI observations of the z = 0.3127 damped absorber
towards the quasar PKS 1127-145, which reveal variability in both the
absorption profile and the flux of the background source, over a time-scale of
a few days.
  The observed variations cannot be explained by simple inter-stellar
scintillation (ISS) models where there are only one or two scintillating
components and all of the ISS occurs in the Galaxy. More complicated models
where there are either more scintillating components or some of the ISS occurs
in the ISM of the z=0.3127 absorber may be acceptable. However, the variability
can probably best be explained in models incorporating motion (on sub-VLBI
scales) of a component of the background continuum source, with or without some
ISS.
  All models for producing the variable 21cm absorption profile require small
scale variations in the 21cm optical depth of the absorber. The length scale
for the opacity variations is $\sim 0.1$ pc in pure super-luminal motion
models, and $\sim$ 10 pc in pure ISS models. Models involving sub-luminal
motion, combined with scintillation of the moving component, require opacity
variations on far smaller scales, $\sim$ 10 - 100 AU.


title:
Chemo-spectrophotometric evolution of spiral galaxies: V. Properties of
  galactic discs at high redshift

abstract:
  We explore the implications for the high redshift universe of
``state-of-the-art'' models for the chemical and spectrophotometric evolution
of spiral galaxies. The models are based on simple ``scaling relations'' for
discs, obtained in the framework of Cold Dark Matter models for galaxy
formation, and were ``calibrated'' as to reproduce the properties of the Milky
Way and of nearby discs (at redshift z~0). In this paper, we compare the
predictions of our ``hybrid'' approach to galaxy evolution to observations at
moderate and high redshift. We find that the models are in fairly good
agreement with observations up to z~1, while some problems appear at higher
redshift (provided there is no selection bias in the data); these discrepancies
may suggest that galaxy mergers (not considered in this work) played a non
negligible role at z>1. We also predict the existence of a ``universal''
correlation between abundance gradients and disc scalelengths, independent of
redshift.


title:
Shadows of Relic Neutrino Masses and Spectra on Highest Energy GZK
  Cosmic Rays

abstract:
  The Ultra High Energy (UHE) neutrino scattering onto relic cosmic neutrinos
in galactic and local halos offers an unique way to overcome GZK cut-off. The
UHE nu secondary of UHE photo-pion decays may escape the GZK cut-off and travel
on cosmic distances hitting local light relic neutrinos clustered in dark
halos. The Z resonant production and the competitive W^+W^-, ZZ pair production
define a characteristic imprint on hadronic consequent UHECR spectra. This
imprint keeps memory both of the primary UHE nu spectra as well as of the
possible relic neutrino masses values, energy spectra and relic densities. Such
an hadronic showering imprint should reflect into spectra morphology of cosmic
rays near and above GZK 10^{19}-10^{21}eV cut-off energies. A possible neutrino
degenerate masses at eVs or a more complex and significant neutrino mass split
below or near Super-Kamiokande \triangle m_{\nu_{SK}}= 0.1 eV masses might be
reflected after each corresponding Z peak showering, into new twin unexpected
UHECR flux modulation behind GZK energies: E_{p} sim 3(frac{triangle
m_{\nu_{SK}}}/m_{\nu}10^{21}),eV.
  Other shadowsof lightest, nearly massless, neutrinos m_{nu_{2K} simeq 0.001eV
simeq kT_{\nu}, their lowest relic temperatures, energies and densities might
be also reflected at even higher energies edges near Grand Unification: E_{p}
\sim 2.2(m_{\nu_{2K}/E_{\nu}})10^{23}, eV .


title: A new population of soft X-ray weak quasars

abstract:
  Quasars selected in optical surveys by means of their blue or UV excess are
known to be strong emitters in the X-rays, except for Broad Absorption Line
(BAL) objects. In this paper we study the X-ray emission of quasars selected
through their emission line spectrum rather than their blue excess. X-ray data
are obtained by cross-correlating two optical samples (the Hamburg Survey
Catalogue and the Palomar Transit Catalogue) with the WGA catalogue of ROSAT
observations. We find that a significant fraction of objects are strongly
underluminous in the X-rays. We discuss the physical nature of these sources
and we propose an interpretation for their optical and X-ray properties based
on a dust-poor and gas-rich absorber. Our results suggest the existence of a
population of AGNs having a type 1 optical spectrum and a type 2 X-ray emission


title:
The BeppoSAX High Energy Large Area Survey. IV. On the soft X-ray
  properties of the hard X-ray-selected HELLAS sources

abstract:
  We present a comprehensive study of the soft X-ray properties of the BeppoSAX
High-Energy Large Area Survey (HELLAS) sources. A large fraction (about 2/3) of
the hard X-ray selected sources is detected by ROSAT. The soft X-ray colors for
many of these objects, along with the 0.5-2 keV flux upper limits for those
undetected in the ROSAT band, do imply the presence of absorption. The
comparison with the ROSAT Deep Survey sources indicates that a larger fraction
of absorbed objects among the HELLAS sources is present, in agreement with
their hard X-ray selection and the predictions of the X-ray background
synthesis models. Another striking result is the presence of a soft
(additional) X-ray component in a significant fraction of absorbed objects.


title: Low order p-modes in a bipolytropic model of the Sun

abstract:
  Based on the Solar Standard Model we developed a solar model in hydrostatic
equilibrium using two polytropes that describes both the "radiative" and
"convective" zones of the solar interior. Then we apply small periodic and
adiabatic perturbations on this bipolytropic model in order to obtain proper
frequencies and proper functions. The frequencies obtained are in the "p-modes"
range of low order l<20 which agrees with the observational data, particularly
with the so called five minutes solar oscillations.
  Key Words: Solar Standard Model, Lane-Emden, Non Radial Oscillations,
p-modes.


title:
Probing the Evolution of Gas Mass Fraction with Sunyaev-Zel'dovich
  Effect

abstract:
  Study of the primary anisotropies of the Cosmic Microwave Background (CMB)
can be used to determine the cosmological parameters to a very high precision.
The power spectrum of the secondary CMB anisotropies due to the thermal
Sunyaev-Zel'dovich Effect (SZE) by clusters of galaxies, can then be studied,
to constrain more cluster specific properties (like gas mass). We show the SZE
power spectrum from clusters to be a sensitive probe of any possible evolution
(or constancy) of the gas mass fraction. The position of the peak of the SZE
power spectrum is a strong discriminatory signature of different gas mass
fraction evolution models. For example, for a flat universe, there can be a
difference in the $l$ values (of the peak) of {\it as much as 3000} between a
constant gas mass fraction model and an evolutionary one. Moreover,
observational determination of power spectrum, from blank sky surveys, is
devoid of any selection effects that can possibly affect targeted X-ray or
radio studies of gas mass fractions in galaxy clusters.


title: On the age of PSR B1509-58

abstract:
  It is generally accepted that the PSR B1509-58 is associated with the
supernova remnant (SNR) MSH 15-52 (G 320.4-01.2). The spin-down age of the
pulsar is \simeq 1700 years, while the size and the general appearance of the
SNR suggest that this system is much older. A few possible explanations of this
discrepancy have been put forward. We offer an alternative one and suggest that
the high spin-down rate of the pulsar characterizes only a relatively short
period of its (present) spin history, and that the enhanced braking torque is
connected with the interaction between the pulsar's magnetosphere and the dense
matter of a circumstellar clump (created during the late evolutionary stages of
the supernova (SN) progenitor star). Our suggestion implies that the "true" age
of PSR B1509-58 could be much larger than the spin-down age, and therefore the
SNR MSH 15-52 is a middle-aged remnant similar to the Vela SNR (G 263.9-3.3).
We also suggest that the dense (neutral) gas of the circumstellar clump could
be responsible for the enhanced neutral hydrogen absorption towards PSR
B1509-58, and that the optical emission of an optical counterpart for PSR
B1509-58 should rather be attributed to a bow shock around this pulsar than to
the pulsar itself.


title: Astronomical Research with Liquid Mirror Telescopes

abstract:
  Liquid mirror telescopes are of interest to Astronomy because of their very
low capital and operating costs. Low cost has a potentially revolutionary
impact since it allows one to dedicate a large telescope to a narrowly focused
project that needs a large quantity of observations. The technology is now well
proven in the laboratory as well as in observatory settings and is stepping
into the mainstream of astronomical research. This paper has two main purposes.
a) To acquaint the astronomical community with LMT zenith observing and to
illustrate the LMT advantage with specific examples of research topics of
current interest that could be carried out only with LMTs because of their low
costs. I argue that LMTs are more versatile than generally thought and that the
challenge is to use LMTs in such ways as to maximize their advantages and
minimize their disadvantages. I briefly review specific issues regarding zenith
telescopes. I then illustrate the LMT advantage with specific examples of
astronomical research. b) I show that the large number of objects observed with
a surveying LMT allows one to carry out cosmological projects at low redshifts.
I show that a variability survey would obtain light curves for several
thousands of type Ia supernovae per year up to z=1 and easily discriminate
among competing cosmological models. The same survey would find large numbers
of MACHOs in clusters of galaxies and in background faint galaxies. Finally, I
discuss a spectrophotometric survey carried out with interference filters,
showing its power to discriminate among cosmological models and to study the
large-scale distribution of galaxies in the Universe.


title:
Optical Tests of a 3.7-m diameter Liquid Mirror: Behavior under External
  Perturbations

abstract:
  We have built and tested a 3.7-m diameter liquid mirror that rotates on a
ball bearing. We have carried out extensive optical tests. We find that
although the ball bearing has a poor quality, the quality of the mirror, with
mercury layers 1-mm thick, is surprisingly good. Taken at face values the
instantaneous Strehl ratios indicate a mirror, that is not quite diffraction
limited but usable for astronomical applications. However, the large coning
error of the bearing (1.5 arcseconds P-V) induces an excessive wobble,
considerably worsening the time averaged PSF. The most interesting result of
the interferometry is that we do not see any evidence of the strong astigmatism
that may have been expected from Coriolis forces.


title:
Stability analyses of two-temperature radiative shocks: formulation,
  eigenfunctions, luminosity response and boundary conditions

abstract:
  We present a general formulation for stability analyses of radiative shocks
with multiple cooling processes, longitudinal and transverse perturbations, and
unequal electron and ion temperatures. Using the accretion shocks of magnetic
cataclysmic variables as an illustrative application, we investigate the shock
instabilities by examining the eigenfunctions of the perturbed hydrodynamic
variables. We also investigate the effects of varying the condition at the
lower boundary of the post-shock flow from a zero-velocity fixed wall to
several alternative type of boundaries involving the perturbed hydrodynamic
variables, and the variations of the emission from the post-shock flow under
different modes of oscillations. We found that the stability properties for
flow with a stationary-wall lower boundary are not significantly affected by
perturbing the lower boundary condition, and they are determined mainly by the
energy-transport processes. Moreover, there is no obvious correlation between
the amplitude or phase of the luminosity response and the stability properties
of the system. Stability of the system can, however, be modified in the
presence of transverse perturbation. The luminosity responses are also altered
by transverse perturbation.


title: Radio limits on an isotropic flux of >100 EeV cosmic neutrinos

abstract:
  We report on results from about 30 hours of livetime with the Goldstone Lunar
Ultra-high energy neutrino Experiment (GLUE). The experiment searches for <10
ns microwave pulses from the lunar regolith, appearing in coincidence at two
large radio telescopes separated by about 22 km and linked by optical fiber.
The pulses can arise from subsurface electromagnetic cascades induced by
interactions of up-coming ~100 EeV neutrinos in the lunar regolith. A new
triggering method implemented after the first 12 hours of livetime has
significantly reduced the terrestrial interference background, and we now
operate at the thermal noise level. No strong candidates are yet seen. We
report on limits implied by this non-detection, based on new Monte Carlo
estimates of the efficiency. We also report on preliminary analysis of smaller
pulses, where some indications of non-statistical excess may be present.


title: The Host Haloes of Lyman Break Galaxies and Sub-millimeter Sources

abstract:
  We use the observed sizes and star formation rates of Lyman-break galaxies
(LBGs) to understand their properties expected in the hierarchical scenario of
galaxy formation. The observed size distribution constrains the masses of the
host haloes of LBGs from below, while the observed star-formation distribution
constrains the masses from above. Assuming a flat CDM model with a cosmological
constant ($\Omega_\Lambda=0.7$), we find that consistency with observations
requires the circular velocities of LBG host haloes to be in the range
100--$300 {\rm km s^{-1}}$. The predicted comoving correlation length of these
objects is $\sim 3 h^{-1}{\rm Mpc}$, and the predicted velocity dispersion of
their stellar contents is typically $70 {\rm km s^{-1}}$. The same prescription
applied to larger haloes in the CDM cosmogony predicts the existence of
galaxies with star formation rates $\sim 1000 {\rm M_\odot yr^{-1}}$ at
redshift $z\sim 3$. We explore the possibility of identifying these galaxies to
be the bright sub-millimeter (sub-mm) sources detected by SCUBA. The model
predicts that the host haloes of these sub-mm sources are massive. These
galaxies are predicted to be strongly correlated, with a comoving correlation
length of $\sim 7 h^{-1}{\rm Mpc}$. The descendants of the bright sub-mm
sources should reside in clusters of galaxies at the present time, and it is
likely that these objects are the progenitors of giant ellipticals. The model
predicts the existence of a relatively bright and red population of galaxies at
$z\sim 3$, which may be observed in the K-band.


title:
The X-ray emission from Nova V382 Velorum: I. The hard component
  observed with BeppoSAX

abstract:
  We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), done in a
broad X-ray band covering 0.1-300 keV only 15 days after the discovery and
again after 6 months. The nova was detected at day 15 with the BeppoSAX
instruments in the energy range 1.8-10 keV and we attribute the emission to
shocks in the ejecta. The plasma temperature was kT~6 keV and the unabsorbed
flux was F(x)~4.3 x 10(-11) erg/cm**2/s. The nebular material was affected by
high intrinsic absorption of the ejecta. 6 months after after the outburst, the
intrinsic absorption did not play a role, the nova had turned into a bright
supersoft source, and the hot nebular component previously detected had cooled
to a plasma temperature kT<=1 keV. No emission was detected in either
observation above 20 keV.


title: The BeppoSAX view of the X-ray active nucleus of NGC4258

abstract:
  BeppoSAX observed NGC4258 on December 1998, when its 2-10 keV luminosity was
\~1E41 erg/s. 100% variability is observed in the 3-10 keV band on timescales
of a half a day while 20% variability is observed on timescales of one hour.
The nuclear component is visible above 2 keV only, being obscured by a column
density of (9.5+/-1.2)E22 cm-2; this component is detected up to 70 keV with
S/N>=3 and with the steep power law energy index of 1.11+/-0.14. Bremsstrahlung
emission for the 2-70 keV X-ray luminosity, as expected in ADAF models with
strong winds, is ruled out by the data. The ratio between the nuclear radio and
the X-ray luminosities is <=1E-5, similar to that of radio quiet AGN. X-ray
variability and spectral shape, radio to X-ray and NIR to X-ray luminosity
ratios suggest that the nucleus of NGC4258 could be a scaled-down version of a
Seyfert nucleus. The soft (E<=2keV) X-ray emission is complex. There are at
least two thermal-like components, with T1=0.6+/-0.1 keV and T2>=1.3 keV. The
cooler (L(0.1-2.4keV)=1E40 erg/s) component is probably associated with the
jet, resolved in X-rays by the ROSAT HRI. The second component, which can be
modeled equally well by an unobscured power law model, has L(0.1-2.4keV)~7E39
erg/s, consistent with that expected from discrete X-ray sources in the host
galaxy. NGC4258 and other maser AGNs show strong nuclear X-ray absorption. We
propose that this large column of gas might be responsible for shielding the
regions of maser emission from X-ray illumination. So a large column density
gas may be a necessary property of masing AGNs.


title: Cosmic Mass Functions from Gaussian Stochastic Diffusion Processes

abstract:
  Gaussian stochastic diffusion processes are used to derive cosmic mass
functions. To get analytic relations previous studies exploited the sharp
$k$-space filter assumption yielding zero drift terms in the corresponding
Fokker-Planck (Kolmogorov's forward) equation and thus simplifying analytic
treatments significantly (excursion set formalism). In the present paper
methods are described to derive for given diffusion processes and Gaussian
random fields the corresponding mass and filter functions by solving the
Kolmogorov's forward and backward equations including nonzero drift terms. This
formalism can also be used in cases with non-sharp $k$-space filters and for
diffusion processes exhibiting correlations between different mass scales.


title: V382 Vel: a "shocking" supersoft x-ray source?

abstract:
  Nova Vel 1999 (V382 Vel) was observed with BeppoSAX twice, 15 days and 6
months after the optical maximum. A hard X-ray source was detected in the first
observation, while the second time also a very luminous supersoft X-ray source
was detected.
  The continuum observed in the supersoft range with the BeppoSAX LECS cannot
be fitted with atmospheric models of hot hydrogen burning while dwarfs. We
suggest that we are observing instead mainly a ``pseudocontinuum'', namely a
blend of very strong emission lines in the supersoft X-ray range.


title: Optical identification of supersoft X-ray sources in M31

abstract:
  We report on initial progress in a program of optical identification of
supersoft X-ray sources in M31, pursued mainly with the WIYN telescope. We
propose the identification of one supersoft X-ray source with a variable star,
which we believe to have been a classical or recurrent nova in outburst in
September 1990. The nova remnant must have been still a supersoft X-ray sources
5 years after this observation, when it was observed with ROSAT.


title: M Dwarfs from Hubble Space Telescope Star Counts. IV

abstract:
  We study a sample of about 1400 disk M dwarfs that are found in 148 fields
observed with the Wide Field Camera 2 (WFC2) on the Hubble Space Telescope and
162 fields observed with pre-repair Planetary Camera 1 (PC1), of which 95 of
the WFC2 fields are newly analyzed. The method of maximum likelihood is applied
to derive the luminosity function and the Galactic disk parameters. At first,
we use a local color-magnitude relation and a locally determined
mass-luminosity relation in our analysis. The results are consistent with those
of previous work but with considerably reduced statistical errors. These small
statistical errors motivate us to investigate the systematic uncertainties.
Considering the metallicity gradient above the Galactic plane, we introduce a
modified color-magnitude relation that is a function of Galactic height. The
resultant M dwarf luminosity function has a shape similar to that derived using
the local color-magnitude relation but with a higher peak value. The peak
occurs at $M_V \sim 12$ and the luminosity function drops sharply toward $M_V
\sim 14$. We then apply a height-dependent mass-luminosity function
interpolated from theoretical models with different metallicities to calculate
the mass function. Unlike the mass function obtained using local relations,
which has a power-law index $\alpha = 0.47$, the one derived from the
height-dependent relations tends to be flat ($\alpha = -0.10$). The resultant
local surface density of disk M dwarfs (12.2 +/- 1.6 M_sun pc^{-2}) is somewhat
smaller than the one obtained using local relations (14.3 +/- 1.3 M_sun
pc^{-2}). Our measurement favors a short disk scale length, H = 2.75 +/- 0.16
(statistical) +/- 0.25 (systematic) kpc.


title:
A Non-Parametric Approach to Infer the Energy Spectrum and the Mass
  Composition of Cosmic Rays

abstract:
  The experiment KASCADE observes simultaneously the electron-photon, muon, and
hadron components of high-energy extensive air showers (EAS). The analysis of
EAS observables for an estimate of energy and mass of the primary particle
invokes extensive Monte Carlo simulations of the EAS development for preparing
reference patterns. The present studies utilize the air shower simulation code
CORSIKA with the hadronic interaction models VENUS, QGSJet and Sibyll,
including simulations of the detector response and efficiency. By applying
non-parametric techniques the measured data have been analyzed in an
event-by-event mode and the mass and energy of the EAS inducing particles are
reconstructed. Special emphasis is given to methodical limitations and the
dependence of the results on the hadronic interaction model used. The results
obtained from KASCADE data reproduce the knee in the primary spectrum, but
reveal a strong model dependence. Owing to the systematic uncertainties
introduced by the hadronic interaction models no strong change of chemical
composition can be claimed in the energy range around the knee.


title: A Comprehensive Look at LH72 in the Context of Supergiant Shell LMC-4

abstract:
  Stellar spectroscopy, UBV photometry, H$\alpha$ imaging, and analysis of data
from the ATCA \ion{H}{1} survey of the LMC are combined in a study of the LMC
OB association LH 72 and its surroundings. LH 72 lies on the rim of a
previously identified \ion{H}{1} shell, SGS-14, and in the interior of LMC-4,
one of the LMC's largest known supergiant shells. Our analysis of the
\ion{H}{1} data finds that SGS-14 is expanding with velocity $v_{exp}\sim15$ km
s$^{-1}$, giving it an expansion age of $\sim$15 Myr. Through the stellar
spectroscopy and photometry, we find similar ages for the oldest stars of LH
72, $\sim15-$30 Myr. We confirm that LH 72 contains an age spread of
$\sim15-$30 Myr, similar to the range in ages of stars derived for the entire
surrounding supergiant shell. Combining analysis of the O and B stars with
H$\alpha$ imaging of the \ion{H}{2} region DEM 228, we find that DEM 228
accounts for only 60% of the available ionizing Lyman continuum photons.
Comparing the distribution of ionized gas with that of the \ion{H}{1}, we find
that DEM 228 and LH 72 are offset by $\sim1-2\arcmin$ from the peak 21-cm
emission, towards the interior of SGS-14. Taken together, these results imply
that SGS-14 has cleared its interior of gas and triggered the formation of LH
72. On the basis of our results, we suggest that LMC-4 was not formed as unit
but by overlapping shells such as SGS-14, and that LH 72 will evolve to produce
a stellar arc similar to others seen within LMC-4.


title: Optical Structure and Physics of the M87 Jet

abstract:
  We summarize HST observations of the M87 jet, concentrating on polarimetry
and spectral index maps, and compare its optical and radio structures. The
evidence now supports a stratified model for the structure of the jet, whereby
high-energy, optical synchrotron emitting particles occupy physically different
regions of the jet, closer to the jet axis, with different magnetic field
configurations. It is in these regions where the shocks that produce the knots
in the inner jet appear to originate. Knot regions have optical spectra which
are much flatter than average for the jet, with the flattest-spectrum regions
coinciding with flux maxima of knots. These same regions are preceded by
regions where perpendicular magnetic fields are seen. Thus not only do we see
all the necessary ingredients for {\it in situ} particle acceleration in the
knots, but there is now fairly direct evidence for it as well. By tracking the
changes in radio-optical and optical spectral index in the knot regions, we can
comment on acceleration and cooling timescales in each knot.


title:
Near-Infrared Photometric Variability of Stars Toward the Orion A
  Molecular Cloud

abstract:
  We present an analysis of J, H, and K time series photometry obtained with
the southern 2MASS telescope over a 0.84 x 6 deg^2 region centered near the
Orion Nebula Cluster. These data are used to establish the near-infrared
variability properties of pre-main-sequence stars in Orion on time scales of
1-36 days, 2 months, and 2 years. A total of 1235 variable stars are
identified, ~93% of which are associated with the Orion A molecular cloud. The
variable stars exhibit a diversity of photometric behavior with time, including
cyclic fluctuations, aperiodic day-to-day fluctuations, eclipses, slow drifts
in brightness over one month, colorless variability, stars that become redder
as they fade, and stars that become bluer as they fade. We examine rotational
modulation of cool and hot star spots, variable obscuration from an inner
circumstellar disk, and changes in the mass accretion rate and other properties
in a circumstellar disk as possible origins of the variability. Cool spots can
explain the variability characteristics in 56-77% of the stars, while the
properties of the photometric fluctuations are more consistent with hot spots
or extinction changes in at least 23% of the stars, and with variations in the
disk mass accretion rate or inner disk radius in 1% of our sample. However,
differences between the details of the observations and the details of
variability predicted these models suggest either that another variability
mechanism not considered here may be operative, or that the observed
variability represents the net results of several of these phenomena. Analysis
of the star count data indicates that the ONC is part of a larger area of
enhanced stellar surface density which extends over a 0.4 x 2.4 deg^2 (3.4 x 20
pc^2) region containing 2700 stars brighter than K=14. (abridged version)


title:
The Effects of Metallicity on the Cepheid P-L Relation and the
  Consequences for the Extragalactic Distance Scale

abstract:
  Using published HST Cepheid data from 25 galaxies, we have found a
correlation between the P-L dispersion and host galaxy metallicity which is
significant at the ~3sigma level in the V band. This result supports the
suggestion that the metallicity dependence of the Cepheid P-L relation may be
stronger than expected. The high observed dispersions in the HST Cepheid P-L
relations have the further consequence that the bias due to incompleteness in
the P-L relation at faint magnitudes is more significant than previously
thought. In the HST sample, galaxies at higher distance tend to have higher
metallicity. This means that when a full metallicity/incompleteness correction
is made, a scale error in the published Cepheid distances is seen in the sense
that the published distance moduli are increasingly underestimates at larger
distances. This results in the average distance modulus to the four galaxies in
the Virgo cluster core increasing from (m-M)_0=31.2+-0.19 to (m-M)_0=31.8+-0.17
with similar increases for the Fornax and Ursa Major clusters. For the 18 HST
galaxies with good Tully-Fisher distances and (m-M)_0>29.5 the Cepheid-TF
distance modulus average residual increases from 0.44+-0.09 mag to 0.82+-0.1mag
indicating a significant scale error in TF distances and resulting in the
previous Pierce & Tully TF estimate of H_0=85 reducing to H_0=58+-7. Finally,
for the 8 HST galaxies with SNIa, the metallicity corrected Cepheid distances
now imply a metallicity dependence of SNIa peak luminosity in the sense that
metal-poor hosts have lower luminosity SNIa. Thus SNIa Hubble diagram estimates
of both H_0 and q_0 may also require significant metallicity corrections.


title:
Gauge Invariant Perturbation Analysis for Quintessence with an
  Exponential Potential

abstract:
  Adiabatic perturbations in the cosmology of a quintessential scalar field
with exponential potential gravitationally coupled to radiation/matter are
investigated in a gauge invariant formalism. The main question addressed in
this paper is if the inhomogenous fluctuations can be ignored as often argued
and the result is that this is not always the case. Consequences for microwave
background radiation and structure formation in the matter dominated era are
considered.


title: Detection of C$_{3}$ in Diffuse Interstellar Clouds

abstract:
  The smallest polyatomic carbon chain, C$_{3}$, has been identified in
interstellar clouds (A$_{v}\sim$1 mag) towards $\zeta$ Ophiuchi, 20 Aquilae,
and $\zeta$ Persei by detection of the origin band in its
$A^{1}\Pi_{u}-X^{1}\Sigma^{+}_{g}$ electronic transition, near 4052\AA.
Individual rotational lines were resolved up to $J$=30 enabling the rotational
level column densities and temperature distributions to be determined. The
inferred limits for the total column densities ($\sim$1 to 2$\times10^{12}$
cm$^{-2}$) offer a strong incentive to laboratory and astrophysical searches
for the longer carbon chains. Concurrent searches for C$_2^{+}$, C$_2^{-}$ and
C$_3^{-}$ were negative but provide sensitive estimates for their maximum
column densities.


title: Cepheid and SNIa Distance Scales

abstract:
  We first discuss why there remains continuing, strong motivation to
investigate Hubble's Constant. Then we review new evidence from an
investigation of the Galactic Open Clusters containing Cepheids by Hoyle et al.
that the metallicity dependence of the Cepheid P-L relation is stronger than
expected. This result is supported by a new analysis of mainly HST Distance
Scale Key Project data which shows a correlation between host galaxy
metallicity and the rms scatter around the Cepheid P-L relation. If Cepheids do
have a significant metallicity dependence then an already existing scale error
for Tully-Fisher distances becomes worse and the distances of the Virgo and
Fornax clusters extend to more than 20Mpc, decreasing the value of H_0.
Finally, if the Cepheids have a metallicity dependence then so do Type Ia
Supernovae since the metallicity corrected Cepheid distances to eight galaxies
with SNIa now suggests that the SNIa peak luminosity is fainter in metal poor
galaxies. As well as having important implications for H_0, this would also
imply that the evidence for a non-zero cosmological constant from the SNIa
Hubble Diagram may be subject to corrections for metallicity which are as big
as the effects of cosmology.


title:
Studies of multiple stellar systems - IV. The triple-lined spectroscopic
  system Gliese 644

abstract:
  We present a radial-velocity study of the triple-lined system Gliese 644 and
derive spectroscopic elements for the inner and outer orbits with periods of
2.9655 and 627 days. We also utilize old visual data, as well as modern speckle
and adaptive optics observations, to derive a new astrometric solution for the
outer orbit. These two orbits together allow us to derive masses for each of
the three components in the system: M_A = 0.410 +/- 0.028 (6.9%), M_Ba = 0.336
+/- 0.016 (4.7%), and $M_Bb = 0.304 +/- 0.014 (4.7%) M_solar. We suggest that
the relative inclination of the two orbits is very small. Our individual masses
and spectroscopic light ratios for the three M stars in the Gliese 644 system
provide three points for the mass-luminosity relation near the bottom of the
Main Sequence, where the relation is poorly determined. These three points
agree well with theoretical models for solar metallicity and an age of 5 Gyr.
Our radial velocities for Gliese 643 and vB 8, two common-proper-motion
companions of Gliese 644, support the interpretation that all five M stars are
moving together in a physically bound group. We discuss possible scenarios for
the formation and evolution of this configuration, such as the formation of all
five stars in a sequence of fragmentation events leading directly to the
hierarchical configuration now observed, versus formation in a small N cluster
with subsequent dynamical evolution into the present hierarchical
configuration.


title:
The Stellar Content of NGC 6789, A Blue Compact Dwarf Galaxy in the
  Local Void

abstract:
  We find that NGC6789 is the most nearby example of a Blue Compact Dwarf
galaxy known to date. With the help of WFPC2 aboard the Hubble Space Telescope,
we resolve NGC6789 into over 15,000 point sources in the V and I bands. The
young stars of NGC6789 are found exclusively near the center of the galaxy. The
red giant population identified at large galacticentric radii yields a distance
of about 3.6 Mpc, a stellar metallicity [Fe/H] of about -2, and a minimum age
of about 1 Gyr. Despite its isolated location in the Local Void,its low
metallicity, and its active star formation, the properties of NGC6789 are
clearly not those of a galaxy in formation.


title: A Cepheid is No More: Hubble's Variable 19 in M33

abstract:
  We report on the remarkable evolution in the light curve of a variable star
discovered by Hubble (1926) in M33 and classified by him as a Cepheid. Early in
the 20th century, the variable, designated as V19, exhibited a 54.7 day period,
an intensity-weighted mean B magnitude of 19.59+/-0.23 mag, and a B amplitude
of 1.1 mag. Its position in the P-L plane was consistent with the relation
derived by Hubble from a total of 35 variables. Modern observations by the
DIRECT project show a dramatic change in the properties of V19: its mean B
magnitude has risen to 19.08 +/- 0.05 mag and its B amplitude has decreased to
less than 0.1 mag. V19 does not appear to be a classical (Population I) Cepheid
variable at present, and its nature remains a mystery. It is not clear how
frequent such objects are nor how often they could be mistaken for classical
Cepheids.


title:
Bursts of gravitational radiation from superconducting cosmic strings
  and the neutrino mass spectrum

abstract:
  Berezinsky, Hnatyk and Vilenkin showed that superconducting cosmic strings
could be central engines for cosmological gamma-ray bursts and for producing
the neutrino component of ultra-high energy cosmic rays. A consequence of this
mechanism would be that a detectable cusp-triggered gravitational wave burst
should be released simultaneously with the $\gamma$-ray surge. If contemporary
measurements of both $\gamma$ and $\nu$ radiation could be made for any
particular source, then the cosmological time-delay between them might be
useful for putting unprecedently tight bounds on the neutrino mass spectrum.
Such measurements could consistently verify or rule out the model, since
strictly correlated behaviour is expected for the duration of the event and for
the time variability of the spectra.


title: The Chandra High Resolution Spectra of Mkn 421

abstract:
  Mkn 421 was observed by Chandra twice, on November 5, 1999 as part of the
Chandra calibration program, with the ACIS-HETG configuration, and on May 29,
2000 following our Target Of Opportunity request aimed to catch the source in
an ultra-high state, with both the ACIS-HETG and the HRC-LETG configurations.
In this contribution we present and compare the two Chandra-MEG observations of
Mkn 421, which lasted 26 and 19.6 ks respectively.


title:
The Rest Frame Optical Spectra of Lyman Break Galaxies: Star Formation,
  Extinction, Abundances, and Kinematics

abstract:
  We present the first results of a spectroscopic survey of Lyman break
galaxies in the near-infrared aimed at detecting the emission lines of [O II],
[O III], and Hbeta from the H II regions of star forming galaxies at z = 3.
  From observations of 19 objects with the Keck and VLT telescopes, we reach
the following main conclusions. Contrary to expectations, the star formation
rates deduced from the Hbeta luminosity are on average no larger than those
implied by the stellar continuum at 1500 A; presumably any differential
extinction between rest-frame optical and UV is small compared with the
relative uncertainties in the calibrations of these two star formation tracers.
For the galaxies in our sample, the abundance of O can only be determined to
within one order of magnitude. Even so, it seems well established that LBGs are
the most metal-enriched structures at z = 3, apart from QSOs, with abundances
greater than about 1/10 solar. They are also significantly overluminous for
their metallicities; this is probably an indication that their mass-to-light
ratios are small compared with present-day galaxies. At face value their
velocity dispersions, sigma = 50 - 115 km/s imply virial masses of about
10^{10} solar masses within half-light radii of 2.5 kpc. However, we are unable
to establish if the widths of the emission lines do reflect the motions of the
H II regions within the gravitational potential of the galaxies, even though in
two cases we see hints of rotation curves. All 19 LBGs observed show evidence
for galactic-scale superwinds; such outflows are important for regulating star
formation, distributing metals over large volumes, and allowing Lyman continuum
photons to escape and ionize the IGM.


title: Imaging of a Complete Sample of IR-Excess PG QSOs

abstract:
  Ground-based high spatial-resolution optical and near-IR imaging at BIHK' is
presented for a complete sample of optically selected Palomar-Green QSOs which
have infrared excesses at least as great as those of "warm" AGN-like
ultraluminous infrared galaxies. In all cases, the host galaxies of the QSOs
were detected and most have considerable two-dimensional structure. One-half of
the QSOs occur in spiral hosts while an additional one-quarter show extended
merger-induced tidal tails suggestive of mergers between similar-sized disk
galaxies. Eleven percent more are in elliptical hosts, and the remainder are
indeterminate. Slightly more than half of the spiral hosts have strong nuclear
bars or other nuclear disturbances consistent with (but not necessarily
implying) very advanced minor merger systems, bringing the possible merger
fraction to as high as 50%. Several of the host galaxies have knots of star
formation similar to those seen in other merger systems and in the ULIGs.
H-band luminosities of the hosts have a mean of 2.2 L*, and are also consistent
with those found in ultraluminous infrared galaxies. This result suggests that
some, but not all, optically-selected QSOs may have evolved from an
infrared-active state.


title: High Temporal Resolution XMM Monitoring of PKS 2155-304

abstract:
  The bright, strongly variable BL Lac object PKS 2155-304 was observed by XMM
for two essentially uninterrupted periods of ~11 and 16 hr on 30-31 May 2000.
The strongest variations occurred in the highest energy bands. After scaling
for this effect, the three softest bands (0.1-1.7 keV) showed strong
correlation with no measurable lag to reliable limits of $\tau \ls 0.3$ hr.
However, the hardest band (~3 keV) was less well-correlated with the other
three, especially on short time scales, showing deviations of ~10-20% in ~1 hr
although, again, no significant interband lag was detected. This result and
examination of previous ASCA and BeppoSAX cross-correlation functions suggest
that previous claims of soft lags on time scales of 0.3-4 hr could well be an
artifact of periodic interruptions due to Earth-occultation every 1.6 hr.
Previous determinations of the magnetic field/bulk Lorentz factor were
therefore premature, as these data provide only a lower limit of $B
\gamma^{1/3} \gs 2.5$ G. The hardest band encompasses the spectral region above
the high-energy break; its enhanced variability could be indicating that the
break energy of the synchrotron spectrum, and therefore of the underlying
electron energy distribution, changes independently of the lower energies.


title: ASCA Identification of SMC X-2 with the 2.37-s Pulsar Discovered by RXTE

abstract: This paper has been withdrawn because the class file must not be uploaded.


title:
Variable line profiles due to non-axisymmetric patterns in an accretion
  disc around a rotating black hole

abstract:
  We have explored spectral line profiles due to spiral patterns in accretion
discs around black holes. A parametrization was employed for the shape and
emissivity of spiral waves, which can be produced by non-axisymmetric
perturbations affecting the disc density and ionization structure. The effects
of the light-travel time, energy shift, and gravitational focusing near to a
rotating black hole were taken into account. A high-resolution ray-tracing code
was used to follow the time variations of the synthetic line profile. A variety
of expected spectral features were examined and the scheme applied to a broad
iron line observed in MCG-6-30-15.


title:
The intermittent behavior and hierarchical clustering of the cosmic mass
  field

abstract:
  The hierarchical clustering model of the cosmic mass field is examined in the
context of intermittency. We show that the mass field satisfying the
correlation hierarchy $\xi_n\simeq Q_n(\xi_2)^{n-1}$ is intermittent if $\kappa
< d$, where $d$ is the dimension of the field, and $\kappa$ is the power-law
index of the non-linear power spectrum in the discrete wavelet transform (DWT)
representation. We also find that a field with singular clustering can be
described by hierarchical clustering models with scale-dependent coefficients
$Q_n$ and that this scale-dependence is completely determined by the
intermittent exponent and $\kappa$. Moreover, the singular exponents of a field
can be calculated by the asymptotic behavior of $Q_n$ when $n$ is large.
Applying this result to the transmitted flux of HS1700 Ly$\alpha$ forests, we
find that the underlying mass field of the Ly$\alpha$ forests is significantly
intermittent. On physical scales less than about 2.0 h$^{-1}$ Mpc, the observed
intermittent behavior is qualitatively different from the prediction of the
hierarchical clustering with constant $Q_n$. The observations, however, do show
the existence of an asymptotic value for the singular exponents. Therefore, the
mass field can be described by the hierarchical clustering model with
scale-dependent $Q_n$. The singular exponent indicates that the cosmic mass
field at redshift $\sim 2$ is weakly singular at least on physical scales as
small as 10 h$^{-1}$ kpc.


title: Einstein, Eddington and the 1919 Eclipse

abstract:
  The modern era of cosmology began with the publication of Einstein's general
theory of relativity in 1915. The first experimental test of this theory was
Eddington's famous expedition to measure the bending of light at a total solar
eclipse in 1919. So famous is this experiment, and so dramatic was the impact
on Einstein himself, that history tends not to recognize the controversy that
surrounded the results at the time. In this paper I discuss the experiment in
its historical and sociological context and show that it provides valuable
lessons for modern astronomy and cosmology.


title: Gamma-ray bursts: afterglows from cylindrical jets

abstract:
  Nearly all previous discussion on beaming effects in GRBs have assumed a
conical geometry. However, more and more observations on relativistic jets in
radio galaxies, active galactic nuclei, and "microquasars" in the Galaxy have
shown that many of these outflows are not conical, but cylindrical, i.e., they
maintain constant cross sections at large scales. Thus it is necessary to
discuss the possibility that GRBs may be due to highly collimated cylindrical
jets, not conical ones. Here we study the dynamical evolution of cylindrical
jets and discuss their afterglows. Both analytical and numerical results are
presented. It is shown that when the lateral expansion is not taken into
account, a cylindrical jet typically remains to be highly relativistic for \sim
10^8 - 10^9 s. During this relativistic phase, the optical afterglow decays as
\propto t^{-p/2} at first, where p is the index characterizing the power-law
energy distribution of electrons. Then the light curve steepens to be \propto
t^{-(p+1)/2} due to cooling of electrons. After entering the non-relativistic
phase (i.e., t > 10^{11} s), the afterglow is \propto t^{-(5p-4)/6}. But if the
cylindrical jet expands laterally at co-moving sound speed, then the decay
becomes \propto t^{-p} and \propto t^{-(15p-21)/10} - t^{-(15p-20)/10} in the
ultra-relativistic and non-relativistic phase respectively. Note that in both
cases, the light curve turns flatter after the relativistic-Newtonian
transition point, which differs markedly from the behaviour of a conical jet.
It is suggested that some GRBs with afterglows decaying as t^{-1.1} - t^{-1.3}
may be due to cylindrical jets, not necessarily isotropic fireballs.


title:
Theoretical predictions on the clustering of SCUBA galaxies and
  implications for small-scale fluctuations at sub-mm wavelengths

abstract:
  This paper investigates the clustering properties of SCUBA-selected galaxies
in the framework of a unifying scheme relating the formation of QSOs and
spheroids (Granato et al. 2000). The theoretical angular correlation function
is derived for different bias functions, corresponding to different values of
the ratio $M_{\rm halo}/M_{\rm sph}$ between the mass of the dark halo and the
final mass in stars. SCUBA sources are predicted to be strongly clustered, with
a clustering strength increasing with mass. We show that the model accounts for
the clustering of Lyman-break Galaxies, seen as the optical counterpart of low-
to intermediate-mass primeval spheroidal galaxies and is also consistent with
the observed angular correlation function of Extremely Red Objects. Best
agreement is obtained for $M_{\rm halo}/M_{\rm sph}=100$. We also consider the
implications for small scale fluctuations observed at sub-mm wavelengths by
current or forthcoming experiments aimed at mapping the Cosmic Microwave
Background (CMB). The predicted amplitude of the clustering signal in the 350
GHz channel of the Planck mission strongly depends on the halo-to-bulge mass
ratio and may be of comparable amplitude to primary CMB anisotropies for
multipole numbers $l\simgt 50$.


title:
General relativistic spectra of accretion discs around rapidly rotating
  neutron stars: Effect of light bending

abstract:
  We present computed spectra, as seen by a distant observer, from the
accretion disc around a rapidly rotating neutron star. Our calculations are
carried out in a fully general relativistic framework, with exact treatment of
rotation. We take into account the Doppler shift, gravitational redshift and
light bending effects in order to compute the observed spectrum. We find that
light bending significantly modifies the high-energy part of the spectrum.
Computed spectra for slowly rotating neutron stars are also presented. These
results would be important for modelling the observed X-ray spectra of Low Mass
X-ray Binaries containing fast spinning neutron stars.


title: Primordial Feature at the Scale of Superclusters of Galaxies

abstract:
  We investigate a spatially-flat cold dark matter model (with the matter
density parameter $\Omega_m=0.3$) with a primordial feature in the initial
power spectrum. We assume that there is a bump in the power spectrum of density
fluctuations at wavelengths $\lambda \sim 30-60h^{-1}$Mpc, which correspond to
the scale of superclusters of galaxies. There are indications for such a
feature in the power spectra derived from redshift surveys and also in the
power spectra derived from peculiar velocities of galaxies. We study the mass
function of clusters of galaxies, the power spectrum of the CMB temperature
fluctuations, the rms bulk velocity and the rms peculiar velocity of clusters
of galaxies. The baryon density is assumed to be consistent with the BBN value.
We show that with an appropriately chosen feature in the power spectrum of
density fluctuations at the scale of superclusters, the mass function of
clusters, the CMB power spectrum and peculiar velocities are in good agreement
with the observed data.


title:
Rotational Viscosity in Linear Irreversible Thermodynamics and its
  Application to Neutron Stars

abstract:
  A generalized analysis of the local entropy production of a simple fluid is
used to show that, if intrinsic angular momentum is taken into account,
rotational viscosity must arise in the linear non-equilibrium regime. As a
consequence, the stress tensor of dense rotating matter, such as the one
present in neutron stars, posseses a significant non-vansishing antisymmetrical
part. A simple argument suggests that, due to the extreme magnetic fields
present in neutron stars, the relaxation time associated to rotational
viscosity is large (approx 10^{21} s). The formalism leads to generalized
Navier-Stokes equations useful in neutron star physics which involve vorticity
in the linear regime.


title:
Discovery of Extended X-ray Emission from the Planetary Nebula NGC 7027
  by the Chandra X-ray Observatory

abstract:
  We report the discovery of X-ray emission from NGC 7027, a prototypical
object for the study of the formation and evolution of planetary nebulae (PNs).
Observations with the Advanced CCD Imaging Spectrometer (ACIS) aboard the
Chandra X-ray Observatory show that the X-ray emission from NGC 7027 is
extended and is bipolar in morphology. The ACIS spectrum displays strong
emission from highly ionized Ne and weaker emission features which we attribute
to O, Mg, and Si. Model fits to this spectrum suggest a characteristic
temperature T_x ~ 3x10^6 K and an intrinsic (unabsorbed) X-ray luminosity of
L_x ~ 1.3x10^32 ergs/s. The intranebular absorption of X-ray emission is highly
nonuniform, but the modeling indicates an average column density N_H ~ 6x10^21
cm^-2, consistent with previous measurements of relatively large visual
extinction within the nebula. We suggest that the X-ray emission from NGC 7027
is or was generated by a hitherto undetected fast wind from the central star of
NGC 7027, or from a companion to this star. Chandra's detection of extended,
high-temperature X-ray emission from BD +30 3639, NGC 6543, and now NGC 7027
suggests that such emission is a common feature of young planetary nebulae.


title:
New OH Zeeman measurements of magnetic field strengths in molecular
  clouds

abstract:
  We present the results of a new survey of 23 molecular clouds for the Zeeman
effect in OH undertaken with the ATNF Parkes 64-m radio telescope and the NRAO
Green Bank 43-m radio telescope. The Zeeman effect was clearly detected in the
cloud associated with the HII region RCW 38, with a field strength of 38+/-3
micro-Gauss, and possibly detected in a cloud associated with the HII region
RCW 57, with a field strength of -203+/-24 micro-Gauss. The remaining 21
measurements give formal upper limits to the magnetic field strength, with
typical 1-sigma sensitivities <20 micro-Gauss. For 22 of the molecular clouds
we are also able to determine thecolumn density of the gas in which we have
made a sensitive search for the Zeeman effect. We combine these results with
previous Zeeman studies of 29 molecular clouds, most of which were compiled by
Crutcher (1999), for a comparsion of theoretical models with the data. This
comparison implies that if the clouds can be modeled as initially spherical
with uniform magnetic fields and densities that evolve to their final
equilibrium state assuming flux-freezing then the typical cloud is magnetically
supercritical, as was found by Crutcher (1999). If the clouds can be modeled as
highly flattened sheets threaded by uniform perpendicular fields, then the
typical cloud is approximately magnetically critical, in agreement with Shu et
al. (1999), but only if the true values of the field for the non-detections are
close to the 3-sigma upper limits. If instead these values are significantly
lower (for example, similar to the 1-sigma limits), then the typical cloud is
generally magnetically supercritical.


title:
The redshift-space two-point correlation functions of galaxies and
  groups in the Nearby Optical Galaxy sample

abstract:
  We use the two-point correlation function in redshift space, $\xi(s)$, to
study the clustering of the galaxies and groups of the Nearby Optical Galaxy
(NOG) sample, which is a nearly all-sky, complete, magnitude-limited sample of
$\sim$7000 bright and nearby optical galaxies. The correlation function of
galaxies is well described by a power law, $\xi(s)=(s/s_0)^{-\gamma}$, with
slope $\gamma\sim1.5$ and $s_0\sim6.4 h^{-1}$Mpc (on scales $2.7 - 12
h^{-1}$Mpc), in agreement with previous results of several redshift surveys of
optical galaxies. We confirm the existence of morphological segregation between
early- and late-type galaxies and, in particular, we find a gradual decreasing
of the strength of clustering from the S0 galaxies to the late-type spirals, on
intermediate scales. Furthermore, luminous galaxies turn out to be more
clustered than dim galaxies. The luminosity segregation, which is significant
for both early- and late-type objects, starts to become appreciable only for
galaxies brighter than $M_B\sim -19.5 + 5 \log h$ ($\sim 0.6 L^*$) and is
independent on scale. The NOG group correlation functions are characterized by
$s_0$-values ranging from $\sim 8 h^{-1}$ Mpc (for groups with at least three
members) to $\sim10 h^{-1}$ Mpc (for groups with at least five members). The
degree of group clustering depends on the physical properties of groups.
Specifically, groups with greater velocity dispersions, sizes and masses tend
to be more clustered than those with lower values of these quantities.


title: X-Ray and Radio Observations of Bright GeV Sources

abstract:
  We present X-ray and radio studies of sources which are brightabove 1 GeV
(F_{>1GeV} > 4e-8 ph/cm^2/s. Only 11 out of ~30 of these gamma-ray sources have
been identified with lower energy counterparts: 5 blazars and 6 pulsars. Three
of these pulsars are surrounded by radio pulsar wind nebulae (PWN), two of
which are also seen as bright, extended X-ray synchrotron nebulae. The ASCA
X-ray telescope has observed 28 of the bright GeV sources, revealing an excess
of F_{2-10keV} > 10e-12 ergs/cm^2/s sources within the {\it EGRET} error
contours of the unidentified sources. Although several supernova remnants are
positionally coincident with these sources, we find no X-ray evidence of high
energy particle production in SNR shell shocks consistent with the GeV
positions. We also present initial results from follow on radio imaging studies
of several fields containing unidentified sources. We have discovered new
X-ray/radio nebulae in three of these fields which are strong candidates for
PWN. These sources, along with a similar nebula in CTA 1 and the PWN around PSR
B1853+01 in W44, are all positionally coincident with variable EGRET sources.
This suggests a class of variable gamma-ray sources associated with synchrotron
emitting regions powered by the winds of young pulsars.


title:
The Clustering of Hot and Cold IRAS Galaxies: The Redshift Space
  Correlation Function

abstract:
  We measure the autocorrelation function of galaxies in the IRAS Point Source
Catalogue galaxy redshift (PSCz) survey and investigate its dependence on the
far-infrared colour and absolute luminosity of the galaxies. We find that the
PSCz survey correlation function can be modelled out to a scale of 10 h^{-1}Mpc
as a power law of slope 1.30 +/- 0.04 and correlation length 4.77 +/- 0.20. At
a scale of 75 h^{-1}Mpc we find the value of J_3 to be 1500 +/- 400.
  We also find that galaxies with cooler dust temperatures, are more strongly
clustered than warmer galaxies. Splitting the survey into three colour
subsamples, we find that, between 1 and 10 h^{-1}Mpc, the ratio of the
correlation function is factor of 1.5 higher for the cooler galaxies compared
to the hotter galaxies. This is consistent with the suggestion that hotter
galaxies have higher star-formation rates, and correspond to later-type
galaxies which are less clustered than earlier types.
  Using volume limited sub-samples, we find a weak variation of the correlation
function as a function of absolute luminosity, in the sense that more luminous
galaxies are less clustered than fainter galaxies. The trend is consistent with
the colour dependence of the correlation function and the observed
colour-luminosity correlation, but the large uncertainties mean that it has a
low statistical significance.


title:
Constraints on properties of the protoplanetary disks around UX Ori and
  CQ Tau

abstract:
  We present Very Large Array observations of the intermediate mass
pre-main-sequence stars UX Ori and CQ Tau at 7mm, 3.6cm, and 6cm. These stars
are members of the UX Ori variability class, where the origin of optical
variability is thought to derive from inhomogeneities in circumstellar disks.
Both stars are detected at 7mm but not at longer wavelengths, which confirms
that the millimeter emission is dominated by dust.
  The UX Ori system exhibits a remarkably flat spectral index in the millimeter
range, with alpha_mm 2 (F_nu nu^alpha_mm). Two different disk models can
reproduce this property: i) a physically small disk with optically thick
emission, truncated at a radius about 30 AU, or ii) a massive (~0.3-1 Msun)
disk mainly composed of dust particles grown to radii of 10cm (``pebbles'').
The observations do not spatially resolve the 7mm emission. We discuss
implications of these two models and suggest observational tests that will
discriminate between them.
  The CQ Tau system exhibits a spectral index in the millimeter range of
alpha_mm 2.6, consistent with values commonly found for disks around
pre-main-sequence stars. The observations marginally resolve the 7mm emission
as an elongated structure with full width at half maximum of 2.4"x1.1" (240x110
AU at 100pc distance). The size and inclination of ~63 degrees (implied by
circular symmetry) are consistent with flared disk models previously suggested
to explain the optical colors and polarization properties.


title: Inflation from Tsunami-waves

abstract:
  We investigate inflation driven by the evolution of highly excited quantum
states within the framework of out of equilibrium field dynamics. These states
are characterized by a non-perturbatively large number of quanta in a band of
momenta but with vanishing expectation value of the scalar field.They represent
the situation in which initially a non-perturbatively large energy density is
localized in a band of high energy quantum modes and are coined tsunami-waves.
The self-consistent evolution of this quantum state and the scale factor is
studied analytically and numerically. It is shown that the time evolution of
these quantum states lead to two consecutive stages of inflation under
conditions that are the quantum analogue of slow-roll. The evolution of the
scale factor during the first stage has new features that are characteristic of
the quantum state. During this initial stage the quantum fluctuations in the
highly excited band build up an effective homogeneous condensate with a non-
perturbatively large amplitude as a consequence of the large number of quanta.
The second stage of inflation is similar to the usual classical chaotic
scenario but driven by this effective condensate.The excited quantum modes are
already superhorizon in the first stage and do not affect the power spectrum of
scalar perturbations. Thus, this tsunami quantum state provides a field
theoretical justification for chaotic scenarios driven by a classical
homogeneous scalar field of large amplitude.


title:
Mushroom-Shaped Structures as Tracers of Buoyant Flow in the Galactic
  Disk

abstract:
  Recent HI emission observations of the Southern Galactic hemisphere have
revealed a mushroom-like structure extending from z=-70 to -450 pc, composed of
a stem and a cap. Similar structures occur in three-dimensional simulations of
a dynamic galactic disk driven by isolated and clustered supernovae. Using
these simulations, we show that hot gas in the Galactic disk that is not
evacuated through chimneys expands into the cooler gas of the thick disk,
forming mushroom-shaped structures. This new class of objects traces buoyant
flow of hot gas into the thick disk.


title:
BL Lacertae are probable sources of the observed ultra-high energy
  cosmic rays

abstract:
  We calculate angular correlation function between ultra-high energy cosmic
rays (UHECR) observed by Yakutsk and AGASA experiments, and most powerful BL
Lacertae objects. We find significant correlations which correspond to the
probability of statistical fluctuation less than $10^{-4}$, including penatly
for selecting the subset of brightest BL Lacs. We conclude that some of BL Lacs
are sources of the observed UHECR and present a list of most probable
candidates.


title:
The Structure and Evolution of Magnetized Cloud Cores in a Zero--Density
  Background

abstract:
  Molecular-line observations of star-forming cloud cores indicate that they
are not the flattened structures traditionally considered by theory. Rather,
they are elongated, perhaps in the direction of their internal magnetic field.
We are thus motivated to consider the structure and evolution of axisymmetric,
magnetized clouds that start from a variety of initial states, both flattened
(oblate) and elongated (prolate). We devise a new technique, dubbed the
$q$-method, that allows us to construct magnetostatic equilibria of any
specified shape. We find, in agreement with previous authors, that the field
lines in oblate clouds bend inward. However, those in prolate clouds bow
outward, confining the structures through magnetic tension.
  We next follow the quasi-static evolution of these clouds via ambipolar
diffusion, under the assumption of constant core mass. An oblate cloud either
relaxes to a magnetically force-free sphere or, if sufficiently massive,
flattens along its polar axis as its central density runs away. A prolate cloud
always relaxes to a sphere of modest central density. We finally consider the
evolution of an initially spherical cloud subject to the tidal gravity of
neighboring bodies. Although the structure constricts equatorially, it also
shortens along the pole, so that it ultimately flattens on the way to collapse.
In summary, none of our initial states can evolve to the point of collapse
while maintaining an elongated shape. We speculate that this situation will
change once we allow the cloud to gain mass from its environment.


title: Stability and Evolution of Supernova Fallback Disks

abstract:
  We show that thin accretion disks made of Carbon or Oxygen are subject to the
same thermal ionization instability as Hydrogen and Helium disks. We argue that
the instability applies to disks of any metal content. The relevance of the
instability to supernova fallback disks probably means that their power-law
evolution breaks down when they first become neutral. We construct simple
analytical models for the viscous evolution of fallback disks to show that it
is possible for these disks to become neutral when they are still young (ages
of a few 10^3 to 10^4 years), compact in size (a few 10^9 cm to 10^11 cm) and
generally accreting at sub-Eddington rates (Mdot ~ a few 10^14 - 10^18 g/s).
Based on recent results on the nature of viscosity in the disks of close
binaries, we argue that this time may also correspond to the end of the disk
activity period. Indeed, in the absence of a significant source of viscosity in
the neutral phase, the entire disk will likely turn to dust and become passive.
We discuss various applications of the evolutionary model, including anomalous
X-ray pulsars and young radio pulsars. Our analysis indicates that metal-rich
fallback disks around newly-born neutron stars and black holes become neutral
generally inside the tidal truncation radius (Roche limit) for planets, at
\~10^11 cm. Consequently, the efficiency of the planetary formation process in
this context will mostly depend on the ability of the resulting disk of rocks
to spread via collisions beyond the Roche limit. It appears easier for the
merger product of a doubly degenerate binary, whether it is a massive white
dwarf or a neutron star, to harbor planets because it can spread beyond the
Roche limit before becoming neutral.[Abridged]


title: On the metallicities of UM 133, UM 283 and UM 382

abstract:
  The study of group properties of the extremely metal-deficient gas-rich local
dwarfs is very promising for the understanding the galaxy formation process at
high redshifts. About 20 such objects have been picked up from the literature
in the recent review by Kunth & Ostlin(2000). However part of these galaxies
got low metallicity as a result of earlier observations, and can have rather
large uncertainties in their cited element abundances. Before to perform the
detailed studies of such galaxies as of some extreme group, it is useful to
revise their metallicities. We present the results of the SAO 6m telescope
spectrophotometry of two Blue Compact Galaxies (BCG) reported from earlier
studies as very metal-poor objects. Well measured [O III] line 4363 A allows to
deduce the temperature in HII regions and get reliable abundances of chemical
elements. For UM 133 we derive 12+log(O/H) = 7.63+/-0.02, coincident with the
published value. UM 382, according to our data, is significantly more
metal-rich: its 12+log(O/H) = 7.82+/-0.03 in comparison to the published value
7.45. The third galaxy, UM 283 seems have got its very low 12+log(O/H) = 7.59
due to a misprint. We used its published emission line intensities and derived
instead the value of 7.95. Thus the latter two galaxies should NOT be
considered as the extremely metal-poor BCGs.


title:
Models for Old, Metal-Poor Stars with Enhanced alpha-Element Abundances.
  III. Isochrones and Isochrone Population Functions

abstract:
  An improved algorithm for interpolating isochrones and isochrone population
functions (IPFs), based on the scheme introduced by Bergbusch & VandenBerg
(1992, APJS, 81, 163), is described. The computer programs (FORTRAN 77) and the
grids of evolutionary tracks, for 17 [Fe/H] values between -2.31 and and -0.3,
with three choices of [alpha/Fe] (0.0, 0.3, and 0.6) at each iron abundance,
are freely available to users interested in producing isochrones and IPFs. We
add to the evidence presented in previous papers in this series in support of
the Teff and color scales of our models. The temperatures derived by Gratton et
al. (1996, A&A, 314, 191) for local Population II subdwarfs with accurate
{Hipparcos} parallaxes are in excellent agreement with those predicted for
them, when the Gratton et al. [Fe/H] scale is also assumed. The locus defined
by local subdwarfs and subgiants on the [M_V, log Teff] plane and the
morphologies of globular cluster C-M diagrams are well matched by the present
models, despite the neglect of diffusion. The three field halo subgiants in our
sample all have ages >15 Gyr, which is also favored for the Galaxy's most
metal-poor globular clusters (GCs). Our isochrones accurately reproduce the Da
Costa & Armandroff (1990, AJ, 100, 162) red-giant branch fiducials for M15, NGC
6752, NGC 1851, and 47 Tuc on the [M_I, (V-I)_0]-diagram. However, our models
fail to predict the observed luminosities of the red-giant bump by ~0.25 mag:
this may indicate inward overshooting of convective envelopes in red giants.
The Zinn & West (1984, ApJS, 55, 45) metallicities for intermediate metal-poor
GCs (-1.8 > [Fe/H] > -1.1) are preferred over recent spectroscopic results,
suggesting an inconsistency between current subdwarf and GC [Fe/H] scales.


title: Microlensing by Stellar Black Holes Around Sgr A*

abstract:
  We show that at any given time, the Galactocentric black hole Sgr A* is
expected to be microlensing N(lens)=1.7 bulge stars if the threshold of
detectability of the fainter image is K(thr)=21, and about N(lens)=8 sources if
K(thr)=23. The lensed images then provide a unique way to detect stellar-mass
black holes predicted to cluster around Sgr A*. If a black hole passes close to
a microlensed image, it will give rise to a short (weeks long) microlensing
event. We show that the mass and projected velocity of the stellar-mass black
hole can both be measured unambiguously from such an event, provided that
either a caustic crossing is observed or the astrometric displacement is
measured. For K(thr)=23 and moderate magnifications by Sgr A*, the microlensing
event rate from a cluster of 20000 black holes within a radius of 0.7 pc is
only 0.06 events per year; however, if highly magnified images of a star were
found, the rate of events by the stellar black holes would be much higher. In
addition, the N(lens) sources lensed by Sgr A* provide a unique probe of
extinction behind the Galactic center along 2N(lens) lines of sight.


title: Convection in radiatively inefficient black hole accretion flows

abstract:
  Recent numerical simulations of radiatively inefficient accretion flows onto
compact objects have shown that convection is a general feature in such flows.
Dissipation of rotational and gravitational energies in the accretion flows
results in inward increase of entropy and development of efficient convective
motions. Convection-dominated accretion flows (CDAFs) have a structure that is
modified significantly in comparison with the canonical advection-dominated and
Bondi-like accretion flows. The flows are characterized by the flattened radial
density profiles, ~R^{-1/2}, and have reduced mass accretion rates. Convection
transports outward a significant amount of the released binding energy of the
accretion flow. We discuss basic dynamical and observational properties of
ADAFs using numerical models and self-similar analytical solutions.


title:
Zooming in on the Coma Cluster with Chandra: Compressed Warm Gas in the
  Brightest Cluster Galaxies

abstract:
  The Chandra image of the central region of the Coma cluster reveals that both
its dominant galaxies, NGC4874 and NGC4889, retain the central parts of their
X-ray gas coronae. The interstellar gas with a temperature of 1-2 keV is
confined by the hot intergalactic medium of the Coma cluster into compact
clouds (only 3 kpc in radius) containing 10^8 M_sun of gas. The physical state
of the gas in these clouds appears to be determined by a delicate balance
between radiative cooling and suppressed (by a factor of 30-100) heat
conduction through the interface between these clouds and the hot cluster gas.


title: Is Angular Momentum in an Accretion Disk Transported Inwards?

abstract:
  The derivation of the viscosity formula of accretion disks appearing in a
number of textbooks is based on a mean free path theory of gas particles.
However, this procedure, when followed precisely, leads to the incorrect
conclusion that the angular momentum of an accretion disk flows from the outer
part to the inner part.


title: Optical Observations of Core-Collapse Supernovae

abstract:
  I present an overview of optical observations (mostly spectra) of Type II,
Ib, and Ic supernovae (SNe). SNe II are defined by the presence of hydrogen,
and exhibit a very wide variety of properties. SNe II-L tend to show evidence
of late-time interaction with circumstellar material. SNe IIn are distinguished
by relatively narrow emission lines with little or no P-Cygni absorption
component and (quite often) slowly declining light curves; they probably have
unusually dense circumstellar gas with which the ejecta interact. Some SNe IIn,
however, might not be genuine SNe, but rather are ``impostors'' ---
specifically, super-outbursts of luminous blue variables. SNe Ib do not exhibit
the deep 6150 Angstrom absorption characteristic of ``classical'' SNe Ia;
instead, their early-time spectra have He I absorption lines. SNe Ic appear
similar to SNe Ib, but lack the helium lines as well. Spectra of SNe IIb
initially exhibit hydrogen, yet gradually evolve to resemble those of SNe Ib;
their progenitors seem to contain only a low-mass skin of hydrogen.
Spectropolarimetry thus far indicates large asymmetries in the ejecta of SNe
IIn, but much smaller ones in SNe II-P. As one peers deeper into the ejecta of
core-collapse SNe, the asymmetry (indicated by the amount of polarization)
seems to increase. There is intriguing, but inconclusive, evidence that some
peculiar SNe IIn might be associated with gamma-ray bursts. The rates of
different kinds of SNe as a function of Hubble type are still relatively poorly
known, although there are good prospects for future improvement.


title: Distances in inhomogeneous quintessence cosmology

abstract:
  We investigate the properties of cosmological distances in locally
inhomogeneous universes with pressureless matter and dark energy
(quintessence), with constant equation of state. We give exact solutions for
angular diameter distances in theempty beam approximation. In this hypothesis,
the distance-redshift equation is derived fron the multiple lens-plane theory.
The case of a flat universe is considered with particular attention. We show
how this general scheme makes distances degenerate with respect to w_X and the
smoothness parameters, alpha, accounting for the homogeneously distributed
fraction of energy of the i-components. We analyse how this degeneracy
influences the critical redshift where the angular diameter distance takes its
maximum, and put in evidence future prospects for measuring the smoothness
parameter of the pressureless matter, alpha_M.


title: On the Neutrino Flux from Gamma-Ray Bursts

abstract:
  Observations imply that gamma-ray bursts (GRBs) are produced by the
dissipation of the kinetic energy of a highly relativistic fireball.
Photo-meson interactions of protons with gamma-rays within the fireball
dissipation region are expected to convert a significant fraction of fireball
energy to >10^14 eV neutrinos. We present an analysis of the internal shock
model of GRBs, where production of synchrotron photons and photo-meson
neutrinos are self-consistently calculated, and show that the fraction of
fireball energy converted to high energy neutrinos is not sensitive to
uncertainties in fireball model parameters, such as the expansion Lorentz
factor and characteristic variability time. This is due in part to the
constraints imposed on fireball parameters by observed GRB characteristics, and
in part to the fact that for parameter values for which the photo-meson optical
depth is high (implying high proton energy loss to pion production) neutrino
production is suppressed by pion and muon synchrotron losses. The neutrino flux
is therefore expected to be correlated mainly with the observed gamma-ray flux.
The time averaged neutrino intensity predicted by the model, ~10^-8.5 GeV/cm^2
s sr, is consistent with the flux predicted by the assumption that GRBs are the
sources of >10^19 eV cosmic-rays.


title:
Galactic Center: Implications of Recent Chandra Observations for
  Spherical Accretion Models of Sgr A*

abstract:
  At the center of the Milky Way lurks a unique compact nonthermal radio
source, Sgr A*. It is thought to be powered by a 2.6 million solar mass black
hole that is accreting the stellar winds from the numerous early-type stars
that exist in the central parsec. However, until recent high resolution Chandra
observations, Sgr A* had never been unequivocably detected at wavelengths
shorter than the sub-millimeter. We present a spherical accretion model which
is consistent with both the flux and steep spectral shape of the X-ray emission
from Sgr A*.


title:
A maximum-likelihood approach to removing radio sources from SZ
  observations, with application to Abell 611

abstract:
  We describe a maximum-likelihood technique for the removal of contaminating
radio sources from interferometric observations of the Sunyaev-Zel'dovich (SZ)
effect. This technique, based on a simultaneous fit for the radio sources and
extended SZ emission, is also compared to techniques previously applied to Ryle
Telescope observations and is found to be robust. The technique is then applied
to new observations of the cluster Abell 611, and a decrement of -540 +/- 125
microJy/beam is found. This is combined with a ROSAT HRI image and a published
ASCA temperature to give an Hubble constant estimate of 52+24-16 km/s/Mpc.


title: X-ray spectra of accretion discs with dynamic coronae

abstract:
  We compute the X-ray spectra produced by non-static coronae atop accretion
discs around black holes and neutron stars. The hot corona is radiatively
coupled to the underlying disc (the reflector) and generates an X-ray spectrum
which is sensitive to the bulk velocity of the coronal plasma, beta=v/c. We
show that an outflowing corona reproduces the hard-state spectrum of Cyg X-1
and similar objects. The dynamic model predicts a correlation between the
observed amplitude of reflection R and the X-ray spectrum slope Gamma since
both strongly depend on beta. A similar correlation was observed and its shape
is well fitted by the dynamic model. The scattering of soft radiation in an
outflowing corona can also account for the observed optical-UV polarization
pattern in active galactic nuclei.


title:
Inhomogeneous metal enrichment at z \sim 1.9: the Lyman limit systems in
  the spectrum of the HDF-S quasar

abstract:
  We present a detailed analysis of three metal absorption systems observed in
the spectrum of the HDF-South quasar J2233-606 (z_em = 2.238), taking advantage
of new VLT-UVES high resolution data (R=45000, S/N = 40-60, \lambda\lambda
3050-10000 \AA). Three main components, spanning about 300 km/s, can be
individuated in the Lyman limit system at z~1.92. They show a surprisingly
large variation in metallicities, respectively ~1/500, 1/8 and 1/100 solar. The
large value found for the second component at z=1.9259, suggests that the line
of sight crosses a star-forming region. In addition, there is a definite
correlation between velocity position and ionisation state in this component,
which we interpret as a possible signature of an expanding H II region. The
systems at z~1.94 and z~1.87 have also high metallicity, ~1/4 and 1/3 solar. We
find that photoionisation and collisional ionisation are equal alternatives to
explain the high excitation phase revealed by O VI absorption, seen in these
two systems. From the width of the Si IV, C IV, Si III and C III lines in the
system at z~1.87, we can estimate the temperature of the gas to be log T ~ 4.7,
excluding collisional ionisation. Finally, we compute the Si IV/C IV ratio for
all Voigt profile components in a sample of log N(C IV) > 14 systems at z < 2.
The values show a dispersion of more than an order of magnitude and most of
them are much larger than what is observed for weaker systems. This is probably
an indication that high column density systems preferably originate in galactic
halos and are mostly influenced by local ionising sources.


title:
Evidence for a Supernova in the Ic Band Light Curve of the Optical
  Transient of GRB 970508

abstract:
  Unique data on $BVRI$ brightness curves of the OT of GRB 970508 obtained with
the 6-m telescope have been interpreted in the framework of the GRB-SN
(supernovae) connection. The effect must be maximal in the I_c band as OT GRB
970228. The peak absolute (M_B) magnitude of the suggested SN must be around
-19.5 for the OT of GRB 970508. If all or the main part of long GRBs are
associated with SNe, the GRB host galaxies (for ground-based observations, at
least) must be dimmer than the peak magnitude of the SN.


title:
The Multiband Photometry of GRB Host Galaxies: Comparison with the
  Spectral Energy Distributions of Nearby and Theoretical Modeling Galaxies

abstract:
  We present one of the results of $BVRI$ photometry of the hosts of GRB for
the host galaxy of GRB 970508 and the theoretical modeling of its continuum
spectral energy distribution (SED) to show that it is important to take into
account internal extinction in the host galaxies. We compared the BVRI
broad-band flux spectrum of the host to template SEDs of local starburst
galaxies and found that there is a significant internal extintion in this host.
Moreover, this comparison allows us to derive the absolute magnitude
(M_{B_{rest}}) and rouhgly estimate reddening (A_V). Population synthesis
modeling of the continuum SED for different reddening laws demostrates that the
observational data of the host galaxy of GRB 970508 are best fitted by the
spectral properties of a model SED with extinction of A_V\approx 2.


title:
Constraints on thick disc and halo parameters from HST photometry of
  field stars in the Galaxy

abstract:
  We analyse a sample of over 1000 stars from 32 fields imaged in the V and I
bands with the Wide Field and Planetary Camera, on board of the Hubble Space
Telescope. The fields are located at Galactic latitudes | b | >= 15deg and in
various directions on the sky. We consider models for the structure of the
Galaxy with different choices for the main parameters governing the shape and
luminosity function of the thick disk and stellar halo. Comparing model
predictions with the observed colour-magnitude diagram we are able to rule out
an increasing or flat stellar luminosity function at the low-luminosity end. We
also rule out large values of the vertical scale height of the thick disc, z_0,
finding it to be in the range 800 <= z_0 <= 1200 pc. As for the local density
normalization, values within the range 4 % <= n_0 <= 8 % seem to better
reproduce the data. Our data essentially rule out a flattened stellar halo (c/a
<~ 0.5) or models with both large local normalization and effective radii.


title: The Gamma-Ray Properties of Unidentified EGRET Sources

abstract:
  Although the majority of gamma-ray sources still remain unidentified, we have
various kinds of information to characterize the observational properties of
unidentified EGRET sources. Despite astronomical properties like locations of
individual sources or the collective arrangement of the class as such, the nine
years of CGRO observations provide the ability to investigate flux variability
at different timescales, enable us to perform periodicity searches, determine
gamma-ray source spectra between 30 MeV and 10 GeV and even investigate
spectral variability. The basic observational properties of unidentified
high-energy gamma-ray sources discovered by EGRET are reviewed. Various
instrumental and observational peculiarities affecting the interpretation of
the EGRET data are pointed out, also describing the way such biases might
affect scientific conclusions drawn from the EGRET data.


title:
Mapping of the SZ effect in the cluster Cl 0016+16 with the Ryle
  Telescope

abstract:
  We have mapped the high-redshift (z = 0.546) cluster Cl 0016+16 with the Ryle
Telescope at 15 GHz. The Sunyaev-Zel'dovich decrement is clearly detected, and
resolved. We combine our data with an X-ray image from ROSAT, and a gas
temperature from ASCA to estimate the Hubble Constant H0 = 69 +21/-16 km/s/Mpc
for an Omega_M=1.0 cosmology or H0 = 84 +25/-19 km/s/Mpc for Omega_M=0.3 and
Omega_Lambda=0.7.


title:
The radio source counts at 15 GHz and their implications for cm-wave CMB
  imaging

abstract:
  We present the preliminary results of a new survey of radio sources using the
Ryle telescope at 15.2 GHz. This is the highest frequency at which a survey has
been done that is relevant to the issue of radio source contamination in CMB
experiments. The differential source count of the 66 sources found in 63 sqdeg
is 80(S/Jy)^-2 /Jy/sr from about 20 to 500 mJy. Extrapolating this to 34 GHz
(where many cm-wave CMB experiments operate) gives an estimated temperature
contribution from sources of 9 microK in a CMB image, with a beam corresponding
to multipole l=500. A means of source subtraction is evidently necessary,
otherwise the signal-to-noise ratio in CMB images will be limited to 4 or 5,
becoming worse at higher resolution. We compare the population of sources
observed in this new survey to that predicted by extrapolation from lower
frequency surveys, finding that source fluxes, and indeed the existence of many
sources, cannot be determined by extrapolation.


title: An Extremely Slow Nova?

abstract:
  The binary companion to the peculiar F supergiant HD 172481 is shown to be a
Mira variable with a pulsation period of 312 days. Its characteristics are
within the normal range found for solitary Miras of that period, although its
pulsation amplitude and mass-loss rate (M(dot) ~ 3 x 10^{-6} solar masses per
year) are higher than average. Reasons are given for suspecting that the F
supergiant, which has L ~ 10^4 solar luminosities, is a white dwarf burning
hydrogen accreted from its companion.


title:
The Environments of a Complete, Moderate-Redshift Sample of FIRST
  Bent-Double Radio Sources

abstract:
  We present an optical spectroscopic and imaging study of the environments of
a complete sample of moderate-redshift, bent-double radio sources. More than
half of the forty radio galaxies in the sample are associated with Abell
richness class 0 or greater clusters at z<0.4. Most of the remaining objects
are associated with groups, although a few appear to be hosted by nearly
isolated elliptical galaxies. For the bent doubles appearing in poor
environments, either dense gas must be associated with the systems to provide
the ram pressure to bend the lobes, or alternative bending mechanisms will have
to be invoked to explain the radio morphologies. Correlation with the ROSAT All
Sky Survey Bright and Faint Source Catalogs reveals the majority of the z<0.2
objects in our sample that we classify optically as clusters are also X-ray
sources.


title:
Multiple Components of the Luminous Compact X-ray Source at the Edge of
  Holmberg II observed by ASCA and ROSAT

abstract:
  We report the results of the analysis of ASCA/ROSAT observations of the
compact luminous X-ray source found at the edge of the nearby star-forming
dwarf galaxy Holmberg II (UGC 4305).Our ASCA spectrum revealed that the X-ray
emission extends to the hard band and can be best described by a power-law with
a photon spectral index of 1.9. The ASCA spectrum does not fit with a
multi-color disk blackbody. The joint ASCA-ROSAT spectrum suggests two
components to the spectrum: the hard power-law component and a warm thermal
plasma kT~0.3[keV]. An additional absorption over that of our galaxy is
required. The wobble correction of the ROSAT HRI image has clearly unveiled the
existence of an extended component which amounts to 27+/-5% of the total X-ray
emission.
  These observations indicate that there are more than one component in the
X-ray emission. The properties of the point-like component is indicative of an
accretion onto an intermediate mass blackhole, unless a beaming is taking
place. We argue that the extended component does not come from electron
scattering and/or reflection by scattered optically-thick clouds of the central
radiation. Possible explanations of this X-ray source include multiple
supernova remnants feeding an intermediate-mass blackhole. (abridged)


title: LBQS 0103-2753: A 0.3 Arcsec Binary Quasar

abstract:
  Imaging and spectroscopy with HST show that LBQS 0103-2753 (V = 17.8, z =
0.848) is a binary quasar with a separation of 0.3 arcsec or 2.3 kpc. This is
by far the smallest separation binary quasar reported to date. The two
components have very different spectra, including the presence of strong broad
absorption lines (BALs) in component A only. The emission-line redshifts, based
on the broad high ionization C IV lines, are z_A = 0.834 and z_B = 0.858; their
difference is 3900 km/s in velocity units. The broad C IV lines, however, are
probably not a good indicator of systemic redshift; and LBQS 0103-2753 A and B
could have a much smaller systemic redshift difference, like the other known
binary quasars. If the systemic redshift difference is small, then LBQS
0103-2753 would most likely be a galaxy merger that has led to a binary
supermassive black hole. There is now one known 0.3 arcsec binary among roughly
500 QSOs that have been observed in a way that would reveal such a close
binary. This suggests that QSO activity is substantially more likely for black
hole binaries at spacings ~2 kpc than at ~15 to 60 kpc. Between 1987 and 1998,
the observed Mg II BAL disappeared.


title: Nuclear Luminosities and Radio Loudness of Seyfert Nuclei

abstract:
  Historically, Seyfert nuclei have been considered to be radio-quiet active
galactic nuclei (AGNs). We question this widely held assumption by showing that
the distribution of the radio-to-optical luminosity ratio R, when properly
measured for the {\it nuclear} component, places the majority of type 1 Seyfert
nuclei in the category of radio-loud AGNs, defined here as objects with R
greater than or equal to 10. This result is further strengthened by strong
correlations found between radio power and optical continuum and emission-line
luminosities, as has been established previously for more powerful AGNs. We
also present a new calibration of the relation between optical continuum and
Balmer emission-line luminosities valid in the regime of low-luminosity AGNs.


title: The Formation of the First Stars. I. The Primordial Star Forming Cloud

abstract:
  To constrain the nature of the very first stars, we investigate the collapse
and fragmentation of primordial, metal-free gas clouds. We explore the physics
of primordial star formation by means of three-dimensional simulations of the
dark matter and gas components, using smoothed particle hydrodynamics, under a
wide range of initial conditions, including the initial spin, the total mass of
the halo, the redshift of virialization, the power spectrum of the DM
fluctuations, the presence of HD cooling, and the number of particles employed
in the simulation. We find characteristic values for the temperature, T ~ a few
100 K, and the density, n ~ 10^3-10^4 cm^-3, characterising the gas at the end
of the initial free-fall phase. These values are rather insensitive to the
initial conditions. The corresponding Jeans mass is M_J ~ 10^3 M_sun. The
existence of these characteristic values has a robust explanation in the
microphysics of H2 cooling, connected to the minimum temperature that can be
reached with the H2 coolant, and to the critical density at which the
transition takes place betweeb levels being populated according to NLTE, and
according to LTE.
  In all cases, the gas dissipatively settles into an irregular, central
configuration which has a filamentary and knotty appearance. The fluid regions
with the highest densities are the first to undergo runaway collapse due to
gravitational instability, and to form clumps with initial masses ~ 10^3 M_sun,
close to the characteristic Jeans scale. These results suggest that the first
stars might have been quite massive, possibly even very massive with M_star >
100 M_sun.