title:
The Infrared Counterparts of the Optically Unidentified CDF-S 1Ms
  Sources

abstract:
  The Chandra Deep Field South (CDF-S) 1Ms exposure produced a catalog of 346
X-ray sources, of which 59 were not visible on the VLT/FORS1 and the
ESO-MPI/WFI deep R-band images to a limit of R_{vega}=26.1--26.7 mag. Using the
first release of the ESO VLT/ISAAC JHK_s data on the CDF-S, we identified six
of the twelve such objects that were within the coverage of these IR
observations. The VLT/FORS1 I-band data further confirms that five of these six
objects are undetected in the optical. The photometric properties of these six
counterparts are compared against those of the optically brighter counterparts
of Chandra sources in the same field. We found that the location of these
optically brighter Chandra sources in the near-IR color space was bifurcated,
with the color of one branch being consistent with that of E/S0 galaxies at 0
<= z <= 1.5 and the other branch being consistent with that of unreddened
AGN/QSOs at 0 <= z <= 3.5. The six counterparts that we identified seemed to
lie on the E/S0 branch and its extension, suggesting that these X-ray source
hosts are mostly luminous E/S0 galaxies (M_V ~ -20 mag in AB system) at 1 <= z
<= 2.5. On the other hand, some of them can also be explained by AGN/QSOs over
a wide redshift range (0 <= z <= 5) if a range of internal extinction (A_V=0--1
mag) is allowed. However, the later interpretation requires fine-tuning
extinction together with redshift for these objects individually. If they are
indeed AGN/QSOs, the most luminous of them is just barely qualified for being a
QSO. Finally, we point out that neither high-redshift (z > 5) star-forming
galaxies nor irregular galaxies at lower redshift can be a viable explanation
to the nature of these six counterparts.


title:
Astrometric authentication of RX J2309.8+2135 as a nearby dwarf nova
  candidate

abstract:
  RX J2309.8+2135 = 1RXS J230949.6+213523 is an X-ray source discovered through
the ROSAT all-sky survey. The object was later identified with a star showing a
spectrum resembling a cataclysmic variable (CV). Schwope et al. (2002,
astro-ph/0210059) recently proposed the spectral type of M3, which would
indicate a small distance. We have detected a large proper motion (~69 mas/yr)
of this object. This detection authenticates RX J2309.8+2135 as a nearby dwarf
nova candidate. Even at a reasonable distance of ~100 pc, which is inferred
from the measured proper motion, the outburst maxima of RX J2309.8+2135 would
reach V~9. RX J2309.8+2135 may belong to a hitherto unidentified class of
long-period CVs with the lowest mass-transfer rates.


title: Protoplanetary Disk Mass Distribution in Young Binaries

abstract:
  We present millimeter-wave continuum images of four wide (separations 210-800
AU) young stellar binary systems in the Taurus-Auriga star-forming region. For
all four sources, the resolution of our observations is sufficient to determine
the mm emission from each of the components. In all four systems, the primary
star's disk has stronger millimeter emission than the secondary and in three of
the four, the secondary is undetected; this is consistent with predictions of
recent models of binary formation by fragmentation. The primaries'
circumstellar disk masses inferred from these observations are comparable to
those found for young single stars, confirming that the presence of a wide
binary companion does not prevent the formation of a protoplanetary disk. Some
of the secondaries show signatures of accretion (H-alpha emission and K - L
excesses), yet their mm fluxes suggest that very little disk mass is present.


title:
Stability of the Submillimeter Brightness of the Atmosphere Above Mauna
  Kea, Chajnantor and the South Pole

abstract:
  The summit of Mauna Kea in Hawaii, the area near Cerro Chajnantor in Chile,
and the South Pole are sites of large millimeter or submillimeter wavelength
telescopes. We have placed 860 GHz sky brightness monitors at all three sites
and present a comparative study of the measured submillimeter brightness due to
atmospheric thermal emission. We report the stability of that quantity at each
site.


title:
The Spectral Correlation Function of Molecular Clouds: A Statistical
  Test for Theoretical Models

abstract:
  We compute the spectral correlation function (SCF) of 13CO J=1--0 maps of
molecular cloud complexes. The SCF is a power law over approximately an order
of magnitude in spatial separation in every map. The power law slope of the
SCF, alpha, its normalization, S_0(1pc), and the spectral line width averaged
over the whole map, sigma_v, are computed for all the observational maps. The
values of alpha, S_0(1pc) and sigma_v are combined to obtain empirical
correlations to be used as tests for theoretical models of molecular clouds.
Synthetic spectral maps are computed from different theoretical models,
including solutions of the magneto-hydrodynamic (MHD) equations with different
values of the rms Mach number of the flow and stochastic models with different
power spectra of the velocity field. In order to compute the radiative transfer
from the MHD models it is necessary to assign the models a physical scale and a
physical density. When these assignments are made according to Larson type
relations the best fit to the observational correlations is obtained.
Unphysical stochastic models are instead ruled out by the empirical
correlations. MHD models with equipartition of magnetic and kinetic energy of
turbulence do not reproduce the observational data when their average magnetic
field is oriented approximately parallel to the line of sight.


title: Gamma-Ray Bursts in Pulsar Wind Bubbles: Putting the Pieces Together

abstract:
  We present the main observational features expected for GRBs that occur
inside pulsar wind bubbles (PWBs). This is the most natural outcome of
supranova model where initially a supernova explosion takes place, leaving a
supra-massive NS, which loses its rotational energy over a time t_sd and
collapses to a BH, triggering a GRB explosion. We find that the time delay t_sd
between the supernova and GRB events is the most important parameter that
determines the behavior of the system. We consider the afterglow, prompt GRB
and direct emission from the PWB. The observational signatures for different
t_sd are described and joined together into one coherent framework. Constraints
on the model are derived for a spherical PWB, from the lack of detection of the
PWB emission and afterglow observations. For very low values of t_sd<1 hr the
supranova model reduces to the collapsar model; 0.4<t_sd/1yr<1 is required to
produce the iron lines seen in some X-ray afterglows. However, we find that for
a spherical PWB, this implies no detectable radio afterglow, a small jet break
time and non-relativistic transition time, in disagreement with observations
for some of these GRBs. These discrepancies with the observations may be
reconciled by resorting to a non-spherical geometry. We find that light element
lines, recently detected in a few X-ray afterglows, are expected to dominate
over iron lines for small t_sd, while for large t_sd the situation is reversed.
Finally, we predict that external Compton scattering of the PWB photons by the
afterglow relativistic electrons, should lead to high energy emission during
the early afterglow that may explain the GeV photons detected by EGRET in some
GRBs, and should be detectable by future missions (GLAST).


title:
Dipole anisotropies of IRAS galaxies and the contribution of a
  large-scale local void

abstract:
  Recent observations of dipole anisotropies show that the velocity of the
Local Group ($\Vec v_{\rm G}$) induced by the clustering of IRAS galax ies has
an amplitude and direction similar to those of the velocity of Cosmic Microwave
Background dipole anisotropy ($\Vec v_{\rm CMB}$), but the difference $| \Vec
v_{\rm G} - \Vec v_{\rm CMB} |$ is still $\sim 170$ km/s, which is about 28% of
$|\Vec v_{\rm CMB} |$. Here we consider the possibility that the origin of this
difference comes from a hypothetical large-scale local void, with which we can
account for the accelerating behavior of type Ia supernovae due to the spatial
inhomogeneity of the Hubble constant without dark energies and derive the
constraint to the model parameters of the local void. It is found as a result
that the distance between the Local Group and the center of the void must be
$(10 -- 20) h^{-1}$ Mpc, whose accurate value depends on the background model
parameters.


title: Particle Acceleration and Cosmic-Ray Origin in the Galaxy

abstract:
  In 1990's Very High Energy Gamma-ray Astrophysics has dramatically advanced
due to the Imaging Air \v{C}erenkov Telescopes(IACTs). After the first
detection of TeV gamma-ray emission from the Crab nebula in 1989, several type
of TeV gamma-ray sources, Active Galactic Nuclei(AGN), young pulsar, and
SuperNova Remnant(SNR), have been detected. In those discoveries, recent
detections of both synchrotron X-rays and TeV gamma-ray emissions from several
SNRs are very significant. SNR has been widely believed to be an unique
candidate of galactic cosmic-ray origin since the beginning of cosmic-ray
physics, whereas little observational evidences have been reported so far.
Those are expected to be a clue of not only the galactic cosmic-ray origin but
also the understanding of the particle acceleration due to a diffusive shock.
Here I present the recent results obtained by our group, CANGAROO, about the
evidences of electron and proton acceleration in SNRs.


title:
The nature of the ultraluminous X-ray sources inside galaxies and their
  relation to local QSOs

abstract:
  It is suggested that many of the ultraluminous compact x-ray sources now
being found in the main bodies of galaxies, particularly those that are active,
like M82, NGC 3628 and others, are "local" QSOs, or BL Lac objects, with high
intrinsic redshifts in the process of being ejected from those galaxies.
Evidence in support of this hypothesis is summarized.


title: The Speed of Gravity: What a Theory Says

abstract:
  Following a quantum-gravity approach we use a gravitational quantum defined
elsewhere as well as an effective gravitational "cross section" in conjunction
with Mach's Principle and the de Broglie wavelength concept. We find the speed
of gravity v_g related to a gravitational mass m as given by v_g of order c
(M_u/m)^(1/2), where c is the speed of light and M_u the mass of the seeable
Universe. For the solar system we get v_g of order 10^(11) c, which agrees very
well with experimental results. For the Universe v_g is of the order of c.


title: On the nature of the Blandford-Znajek mechanism

abstract:
  It is widely accepted in the astrophysical community that the event horizon
plays crucial role in the Blandford-Znajek mechanism of extraction of
rotational energy of black holes. In fact, this view is a quintessence of the
Membrane Paradigm of black holes which suggests that the event horizon, or
rather the so-called stretched horizon, is similar to a rotating conducting
sphere of finite resistivity. In this paper we argue that this interpretation
is rather misleading and the proper explanation of the Blandford-Znajek
mechanism has to be sought in the properties of the ergospheric region of black
holes.


title:
The photospheric abundances of active binaries I Detailed analysis of HD
  113816 (IS Vir) and HD 119285 (V851 Cen)

abstract:
  The high-resolution optical spectra of the two X-ray active binaries RS CVn
stars HD 113816 (IS Vir) and HD 119285 (V851 Cen) are analysed and their Na,
Mg, Al, Si, Ca, Sc, Ti, Co and Ni contents determined. The analysis of IS Vir
and V851 Cen is performed with three different LTE methods. In the first one,
abundances are derived using measured equivalent widths and Kurucz LTE model
atmospheres as input for the MOOG software package. The input atmospheric
parameters and abundances are iteratively modified until (i) the Fe I
abundances exhibit no trend with excitation potential or equivalent width, (ii)
Fe I and Fe II average abundances are the same and (iii) Fe and Alpha elements
average abundances are consistent with the input values. The second method
follows a similar approach, but relies on the B-V and V-I colour indices to
determine the temperature. The third method relies on fitting the 6162 A Ca I
line wing profiles to derive the surface gravity. The reliability of these
methods is investigated in the context of single line RS CVn stars. It is shown
that the V-I photometric index gives, on a broader sample of stars,
significantly cooler estimates of the effective temperature than the B-V index.
All other approaches give results in good agreement with each other. The
analysis of IS Vir and V851 Cen results in both cases in their primaries being
giant stars of near-solar metallicity. Their parameters as derived with the
first method are respectively Teff = 4720 K, log g = 2.65, [Fe/H] = +0.04 and
Teff = 4700 K, log g = 3.0 and [Fe/H] = -0.13. In the case of V851 Cen the
derived iron content is significantly higher than a previous determination in
the literature. Both stars exhibit relative overabundances of several elements
(e.g. Ca) with respect to the solar mix.


title:
Spectrophotometry of the comets C/2000 WM1 (LINEAR) and C/2002 C1
  (Ikeya-Zhang)

abstract:
  Spectrophotometric observations of the coma of the comets C/2000 WM1 (LINEAR)
and C/2002 C1 (Ikeya-Zhang) were taken during Nov, Dec 2001 and Mar, Apr 2002
respectively with 104-cm telescope of the State Observatory, Nainital. CN
($\lambda$ 3883 \AA) and C$_{2}$ swan bands ($\lambda$ 4695, $\lambda$ 5165 and
$\lambda$ 5538 \AA) have been identified in both the comets. Na I emission was
detected in comet Ikeya-Zhang. An estimate of CN and C$_{2}$ abundances and
their production rates have been derived. Dust production rates have also been
determined.


title: The dusty type IIn Supernova 1998S

abstract:
  The type IIn SN 1998S is one of the most remarkable core-collapse supernovae
ever observed. It underwent a complex interaction with a substantial
circumstellar medium, resulting in radiation at wavelengths from radio to
X-rays. IR and optical observations have revealed a wide variety of broad and
narrow emission lines. Examination of the SN/CSM interaction and of the ejecta
spectra has allowed us to deduce that the supernova probably arose from a
massive, RSG progenitor having a large (>3200 AU radius), dusty circumstellar
disk. SN 1998S also developed one of the strongest, most persistent infrared
excesses ever seen in a supernova. IR/optical monitoring of SN 1998S has been
carried out to nearly 1200 days post-explosion. This includes coverage to
wavelengths as long as 4.7 microns, making SN 1998S only the second supernova
(after SN 1987A) to be observed in this spectral region. Fading of the central
and redshifted components of the late-time H I and He I line profiles suggests
strongly that dust condensed in the ejecta. However, it is less clear whether
the strong late-time IR emission arose from this dust, or from an IR echo in
the dusty CSM. One interesting possibility is that dust condensed in the cool
dense shell between the outer and reverse shocks, thus simultaneously producing
both the line obscuration and the IR emission.


title:
Constraints on the Cluster Environments and Hot Spot Magnetic Field
  Strengths of the Radio Sources 3C254 and 3C280

abstract:
  We present new Chandra Observatory observations with archival HST and radio
observations of 3C254, a radio quasara at z=0.734, and 3C280, a radio galaxy at
z=0.996. We report the detection of X-ray and possible HST optical counterparts
to the radio hot spots in 3C280 and of an X-ray counterpart to the radio hot
spot in 3C254. We present constraints on the presence of X-ray clusters and on
the magnetic field strengths in and around the radio hot spots. The spatial
resolution of Chandra allows us to show that these sources are not in hot,
massive clusters. The extended emission seen in ROSAT observations is resolved
into point sources. The IGM around these sources is demonstrably not dense and
hot. We conclude that radio sources are not reliable signposts of massive
clusters at moderate redshifts. X-ray synchrotron emission could explain the
radio, optical, and X-ray hot spot fluxes in 3C280, but it would require
continuous acceleration of electrons to high Lorentz factors, since the
synchrotron lifetime required to produce the X-ray emission is of order a human
lifetime. SSC with or without IC scattering of the CMB can also explain the
X-ray emission, but not the optical. We review all of the physical mechanisms
and summarize our current constraints on the magnetic field strengths in
andaround the hot spots of 3C254 and 3C280.


title: Discovery of an M8.5 Dwarf With Proper Motion mu=2.38 arcsec/yr

abstract:
  We report the discovery of LSR1826+3014, a very faint (V=19.36) star with a
very large proper motion (mu=2.38 arcsec/yr). A low resolution red spectrum
reveals that LSR1826+3014 is an ultra-cool red dwarf with spectral type M8.5 V
and with a radial velocity v_rad=+77+/-10 km/s. LSR1826+3014 is thus the
faintest red dwarf ever discovered with a proper motion larger than 2
arcsec/yr. Optical and infrared photometry suggest that the star is at a
distance d=13.9+/-3.5 pc from the Sun, which implies it is moving relative to
the local standard of rest with a total velocity of 175+/-25 km/s. Numerical
integration of its orbit suggests that LSR1826+3014 is on a halo-like galactic
orbit.


title: The Disc-Jet Relation in Strong-Lined Blazars

abstract:
  The relation between accretion disc (thermal emission) and jet (non-thermal
emission) in blazars is still a mystery as, typically, the beamed jet emission
swamps the disc even in the ultraviolet band where disc emission peaks. In this
paper we estimate the accretion disc component for 136 flat-spectrum radio
quasars selected from the Deep X-ray Radio Blazar Survey. We do this by
deriving the accretion disc spectrum from the mass and accretion rate onto the
central black hole for each object, estimated using the emission line widths
and the power emitted from the broad line region. We find that non-thermal
emission dominates the optical/UV band of our sources. The thermal component,
in fact, is, on average, ~ 15 per cent of the total and > 90 per cent of the
objects in the sample have a thermal component < 0.5 of the total luminosity.
We then estimate the integrated disc and kinetic jet powers and find that, on
average, the disc luminosity is ~ 1 to 20 times the jet power (depending on the
uncertainties in the estimation of the latter quantity). A comparison with
previous, independent results favours a scenario in which jet and disk powers
are of the same order of magnitude. Extraction of energy from a rotating black
hole via the ``Blandford-Znajek'' mechanism fails to explain the estimated jet
power in the majority of our sources. Finally, we find that the typical masses
for our sources are ~ 5 10^8 solar masses and that, contrary to previous
claims, about one quarter of our radio quasars have relatively small (< 3 10^8
solar masses) black hole mass.


title: Element Abundances in Nearby Galaxies

abstract:
  In these lectures I present a highly opinionated review of the observed
patterns of metallicity and element abundance ratios in nearby spiral,
irregular, and dwarf elliptical galaxies, with connection to a number of
astrophysical issues associated with chemical evolution. I also discuss some of
the observational and theoretical issues associated with measuring abundances
in H II regions and gas and stellar surface densities in disk galaxies.
Finally, I will outline a few open questions that deserve attention in future
investigations.


title: On the origin of irregular structure in Saturn's rings

abstract:
  We suggest that the irregular structure in Saturn's B ring arises from the
formation of shear-free ring-particle assemblies of up to ~100 km in radial
extent. The characteristic scale of the irregular structure is set by the
competition between tidal forces and the yield stress of these assemblies; the
required tensile strength of ~10^5 dyn/cm^2 is consistent with the sticking
forces observed in laboratory simulations of frosted ice particles. These
assemblies could be the nonlinear outcome of a linear instability that occurs
in a rotating fluid disk in which the shear stress is a decreasing function of
the shear. We show that a simple model of an incompressible, non-Newtonian
fluid in shear flow leads to the Cahn-Hilliard equation, which is widely used
to model the formation of structure in binary alloys and other systems.


title:
Wide-field Imaging Interferometry Testbed II: Implementation,
  Performance, and Plans

abstract:
  The Wide-Field Imaging Interferometry Testbed (WIIT) will provide valuable
information for the development of space-based interferometers. This laboratory
instrument operates at optical wavelengths and provides the ability to test
operational algorithms and techniques for data reduction of interferometric
data. Here we present some details of the system design and implementation,
discuss the overall performance of the system to date, and present our plans
for future development of WIIT. In order to make best use of the
interferometric data obtained with this system, it is critical to limit
uncertainties within the system and to accurately understand possible sources
of error. The WIIT design addresses these criteria through a number of
ancillary systems. The use of redundant metrology systems is one of the most
important features of WIIT, and provides knowledge of the delay line position
to better than 10 nm. A light power detector is used to monitor the brightness
of our light sources to ensure that small fluctuations in brightness do not
affect overall performance. We have placed temperature sensors on critical
components of the instrument, and on the optical table, in order to assess
environmental effects on the system. The use of these systems provides us with
estimates of the overall system uncertainty, and allows an overall
characterization of the results to date. These estimates allow us to proceed
forward with WIIT, adding rotation stages for 2-D interferometry. In addition,
they suggest possible avenues for system improvement. Funding for WIIT is
provided by NASA Headquarters through the ROSS/SARA Program and by the Goddard
Space Flight Center through the IR&D Program.


title: The superfluid two-stream instability and pulsar glitches

abstract:
  This paper provides the first study of a new dynamical instability in
superfluids. This instability is similar to the two-stream instability known to
operate in plasmas. It is analogous to the Kelvin-Helmholtz instability, but
has the distinguishing feature that the two fluids are interpenetrating. The
instability sets in once the relative flow between the two components of the
system reaches a critical level. Our analysis is based on the two-fluid
equations that have been used to model the dynamics of the outer core of a
neutron star, where superfluid neutrons are expected to coexist with
superconducting protons and relativistic electrons. These equations are
analogous to the standard Landau model for superfluid Helium. We study this
instability for two different model problems. First we analyze a local
dispersion relation for waves in a system where one fluid is at rest while the
other flows at a constant rate. This provides a proof of principle of the
existence of the two-stream instability for superfluids. Our second model
problem concerns two rotating fluids confined within an infinitesimally thin
spherical shell. The aim of this model is to assess whether the two-stream
instability may be relevant (perhaps as a trigger mechanism) for pulsar
glitches. Our results for this problem show that the entrainment effect could
provide a sufficiently strong coupling for the instability to set in at a
relative flow small enough to be astrophysically plausible.


title:
The spectroscopic orbits and other parameters of the symbiotic binary FN
  Sgr

abstract:
  We present an analysis of optical and near infrared spectra of the eclipsing
symbiotic system FN Sgr. In particular, we have determined for the first time
spectroscopic orbits based of the radial velocity curves for both components. A
set of blue absorption lines resembling an A-F type star is present in all our
spectra. They seem to be associated with the hot component but the best orbital
fitting corresponds to a larger eccentricity. We have also studied spectral
changes and photometric variations in function of both the hot component
activity and the orbital motion.


title: Chemical evolution and nature of Damped Lyman-Alpha systems

abstract:
  We study the nature of Damped Lyman -Alpha systems (DLAs) by means of a
comparison between observed abundances and models of chemical evolution of
galaxies of different morphological type. In particular, we compare for the
first time the abundance ratios as functions of metallicity and redshift with
dust-corrected data. We have developed detailed models following the evolution
of several chemical elements (H, D, He, C, N, O, Ne, Mg, Si, S, Fe, Ni and Zn)
for elliptical, spiral and irregular galaxies. Each of the models is calibrated
to reproduce the main features of a massive elliptical, the Milky Way and the
LMC, respectively. In addition, we run some models also for dwarf irregular
starburst galaxies. All the models share the same uptodate nucleosynthesis
prescriptions but differ in their star formation histories. The role of SNe of
different type (II, Ia) is studied in each galaxy model together with detailed
and up to date nucleosynthesis prescriptions. Our main conclusions are: 1) when
dust depletion is taken into account most of the claimed alpha/Fe
overabundances disappear and DLAs show solar or subsolar abundance ratios. 2)
The majority of DLAs can be explained either by disks of spirals observed at
large galactocentric distances or by irregular galaxies like the LMC or by
starburst dwarf irregulars observed at different times after the last burst of
star formation. 3) Elliptical galaxies cannot be DLA systems since they reach a
too high metallicity at early times and their abundance ratios show
overabundances of $\alpha$-elements relative to Fe over a large range of
[Fe/H]. 4) The observed neutral gas cosmic evolution is compared with our
predictions but no firm conclusions can be drawn in the light of the available
data.


title:
The optical light curves of XTE J2123--058: the mass of the binary
  components and the structure of the quiescent accretion disk

abstract:
  We present optical photometry of XTE J2123-058 during its quiescent state
taken in 1999 and 2000. The dominant feature of our R-band light curve is the
ellipsoidal modulation of the secondary star, however, in order to fit this
satisfactorily we require additional components which comprise an X-ray heated
Roche-lobe filling secondary star, and an accretion disk bulge, i.e. where the
gas stream impacts the accretion disk. The observed dip near phase 0.8 is
interpreted as the eclipse of inner parts of the accretion disk by the bulge.
This scenario is highly plausible given the high binary inclination. Our fits
allow us to constrain the size of the quiescent accretion disk to lie in the
range 0.26-0.56R_L1 (68% confidence). Using the distance of 9.6 kpc and the
X-ray flux inferred from the heated hemisphere of the companion, we obtain an
unabsorbed X-ray luminosity of 1.2x10^33 erg/s for XTE J2123-058 in quiescence.
  From the observed quiescent optical/IR colors we find that the power-law
index (-1.4) for the spectral distribution of the accretion disk compares well
with other quiescent X-ray transients. We also re-analyse the optical light
curves of the soft X-ray transient XTE J2123-058 taken during its outburst and
decay in 1998. We use a robust method to fit the data using a refined X-ray
binary model. The model computes the light arising from a Roche-lobe filling
star and flared accretion disk irradiated by X-rays, and calculates the effects
of shadowing and mutual star/disk eclipses. We obtain relatively accurate
values for the binary inclination and mass ratio, which when combined with
spectroscopic results obtained in paper II gives a neutron star mass in the
range 1.04-1.56Mo (68% confidence).


title: Structure of the Mid-Infrared Emitting Disk Around WL16

abstract:
  WL16 is a unique member of the embedded young stellar population in the
nearby rho Ophiuchi cloud core: its extended (900 AU diameter), high surface
brightness disk is visible only at mid-infrared wavelengths. We present
diffraction-limited (~ 0.3 arcsec) images, from 7.9 to 24.5 microns, of WL16
acquired at the Keck II telescope. We find the central star to be a 250 Lsun, 4
Msun, Herbig Ae star, seen through foreground material of the rho Oph cloud
core that provides an extinction of Av=31+/-1 magnitudes. WL16's disk is
detected through all nine observed passbands. We confirm, therefore, that the
emitting particles are composed of both polycyclic aromatic hydrocarbons (PAHs)
and very small (5--100 Angstroms) graphitic grains (VSGs). We confirm a
resolved (1.5" diameter) core component at 7.9 and 8.8 microns, due to emission
from positively charged PAHs. An enhancement in the emission at 12.5 microns at
the disk's edges is found for the first time, and signals the presence of
larger (>= 50-80 carbon atoms) PAHs and/or more hydrogenated PAHs than those
found in the bulk of the disk. We find a disk asymmetry, observed at all nine
mid-infrared wavelengths, at projected radii 1"-2.5" (corresponding to 125 AU
<= r <= 300 AU) from the central source.


title: Keck Spectroscopy of Globular Clusters in the Elliptical Galaxy NGC 3610

abstract:
  We present moderate-resolution Keck spectra of nine candidate globular
clusters in the possible merger-remnant elliptical galaxy NGC 3610. Eight of
the objects appear to be bona fide globular clusters of NGC 3610. We find that
two of the clusters belong to an old metal-poor population, five to an old
metal-rich population, and only one to an intermediate-age metal-rich
population. The estimated age of the intermediate-age cluster is 1-5 Gyr, which
is in agreement with earlier estimates of the merger age, and suggests that
this cluster was formed during the merger. However, the presence of five old
metal-rich clusters indicates that a substantial number of the metal-rich
clusters in NGC 3610 likely came from the progenitor galaxies, although the
global ratio of old to intermediate-age metal-rich clusters remains very
uncertain.


title:
Radial-velocity survey of members and candidate members of the TW Hydrae
  association

abstract:
  We report our spectroscopic observations of stars belonging to the young
nearby group known as the TW Hydrae association, as well as of a number of
potential members of the association identified in kinematic and X-ray surveys.
Multiple radial velocity measurements were obtained for each object, several of
which turn out to be multiple systems. Orbital solutions are presented for 3
double-lined binaries, one single-lined binary, and a double-lined triple
system, all with short periods. Effective temperatures and projected rotational
velocities are presented for each visible object. None of the candidate members
of the association in our sample is confirmed as a true member. The large
fraction of close binaries among the candidate members has to do with their
selection based on X-ray emission from ROSAT, which tends to favor the
inclusion of tidally-locked systems that are active but not necessarily young.


title:
A Search for Period Changes in Delta Scuti Stars with the Super-LOTIS
  Sky Patrol System

abstract:
  We have observed a sample of Delta Scuti stars discovered by the ROTSE
collaboration in 1999 with Super-LOTIS in order to characterize changes in
their pulsation periods over a time baseline of roughly three years. Achieving
these goals required the creation of an automated astrometric and photometric
data reduction pipeline for the Super-LOTIS camera. Applying this pipeline to
data from a June 2002 observing campaign, we detect pulsations in 18 objects,
and find that in two cases the periods have changed significantly over the
three years between the ROTSE and Super-LOTIS observations. Since theory
predicts that evolutionary period changes should be quite small, sources of
non-evolutionary period changes due to the interactions of pulsations modes are
discussed.


title:
One-point Statistics of the Cosmic Density Field in Real and Redshift
  Spaces with A Multiresolutional Decomposition

abstract:
  In this paper, we develop a method of performing the one-point statistics of
a perturbed density field with a multiresolutional decomposition based on the
discrete wavelet transform (DWT). We establish the algorithm of the one-point
variable and its moments in considering the effects of Poisson sampling and
selection function. We also establish the mapping between the DWT one-point
statistics in redshift space and real space, i.e. the algorithm for recovering
the DWT one-point statistics from the redshift distortion of bulk velocity,
velocity dispersion, and selection function. Numerical tests on N-body
simulation samples show that this algorithm works well on scales from a few
hundreds to a few Mpc/h for four popular cold dark matter models.
  Taking the advantage that the DWT one-point variable is dependent on both the
scale and the shape (configuration) of decomposition modes, one can design
estimators of the redshift distortion parameter (beta) from combinations of DWT
modes. When the non-linear redshift distortion is not negligible, the beta
estimator from quadrupole-to-monopole ratio is a function of scale. This
estimator would not work without adding information about the scale-dependence,
such as the power-spectrum index or the real-space correlation function of the
random field. The DWT beta estimators, however, do not need such extra
information. Numerical tests show that the proposed DWT estimators are able to
determine beta robustly with less than 15% uncertainty in the redshift range 0
< z < 3.


title:
Recent Globular Cluster Searches with Arecibo and the Green Bank
  Telescope

abstract:
  We report the discovery of seven new millisecond pulsars during 20 cm
searches of 19 globular clusters using the recently upgraded Arecibo Telescope
and the new Green Bank Telescope (GBT). Five of the pulsars are in compact
binaries, three of which are eclipsing. One of the systems is in an eccentric
orbit which is almost certainly highly relativistic. Additional searches and
timing observations are underway.


title: Starburst-AGN Connection from High Redshift to the Present Day

abstract:
  We give a review on possible starburst-AGN (active galactic nuclei)
connections from high redshift to the present day. First, we give a historical
review on some basic ideas related to the starburst-AGN connection published in
the literature. Second, we focus our attention to the so-called Magorrian
relation which is the close relationship between the nuclear black hole mass
and the bulge mass, established in nearby galaxies. If the Magorrian relation
is universal, we obtain an important implication that any supermassive black
holes were made through successive merging processes of starburst remnants
(i.e., neutron stars and stellar-sized black holes), providing a channel of the
starburst-AGN connection. Third, we briefly discuss a possible new scenario for
the formation of quasar nuclei at very high redshift based on an idea that the
successive mergers of starburst remnants formed in subgalactic gaseous clouds.


title:
Violation of the Pauli principle and dimension of the Universe at very
  large distances

abstract:
  We discuss a Modified Field theory (MOFT) in which the number of fields can
vary. It is shown that in MOFT fermions obey the so-called parastatistics in
which the order of the parastatistics depends on scales. In particular, at very
large distances $r>r_{\min}$ fermions violate the Pauli principle. It is also
shown that in MOFT in some range of scales $r_{\max}>r>r_{\min}$ the Universe
acquires features of a two-dimensional space whose distribution in the observed
3-dimensional volume has an irregular character. This provides a natural
explanation to the observed fractal distribution of galaxies and the
logarithmic behavior of the Newton's potential for a point source.


title: The evolution of cosmic star formation, metals and gas

abstract:
  We reconstruct the history of the cosmic star formation as well as the cosmic
production of metals in the universe by means of detailed chemical evolution
models for galaxies of different morphological types. We consider a picture of
coeval, non-interacting evolving galaxies where ellipticals experience intense
and rapid starbursts within the first Gyr after their formation, and spirals
and irregulars continue to form stars at lower rates up to the present time. We
show that spirals are the main contributors to the decline of the luminosity
density in all bands between z=1 and z=0.


title:
Spectroscopy of Dwarf HII Galaxies in the Virgo Cluster. I. Data,
  Chemical Abundances and Ionization Structure

abstract:
  Long-slit spectroscopy has been obtained for a sample of 22 blue dwarf
galaxies selected in the direction of the Virgo Cluster as part of a larger
sample of Virgo blue dwarf galaxies for which deep Halpha imaging has been
collected. Most of the galaxies in the present sample appear classified as BCDs
or dwarf Irregulars in the Virgo Cluster Catalog. Line fluxes, Hbeta equivalent
width and extinction coefficients, spatial emission profiles, ionization
structure and physical conditions are presented for the galaxies of the sample.
Chemical abundances have been derived either using a direct determination of
the electron temperature or after detailed examination of the predictions of
different empirical calibrations. The oxygen abundance derived for the sample
of Virgo dwarf galaxies span in the range 7.6 < 12 + log O/H < 8.9, and the
corresponding nitrogen to oxygen abundance ratio cover from values typical of
low metallicity field BCD galaxies up to near solar.


title:
Detectability of Prompt TeV Gamma Rays of Proton Synchrotron Origin from
  Gamma Ray Bursts by AMANDA/ICECUBE Detectors

abstract:
  The detectability of a possible ``high'' energy ($>100\gev$) component of
Gamma-Ray Bursts (GRBs) using AMANDA/ICECUBE large area muon detectors is
examined within the context of a specific model of such high energy gamma ray
production within GRBs, namely, the proton-synchrotron model, which requires
protons to be accelerated to ultrahigh energies $\gsim10^{20}\ev$ within GRBs.
In this model, the high energy component is distinct from, but may well be
emitted in coincidence with, the usual ``low'' (keV--MeV) energy component
observed by satellite-borne detectors. The AMANDA/ICECUBE detectors can detect
TeV photons by detecting the secondary muons created by the TeV photons in the
Earth's atmosphere. We calculate the muon signal to noise ratio in these
detectors due to TeV gamma-rays from individual GRBs for various assumptions on
their luminosity, distance (redshift), Lorentz Gamma factor of the underlying
fireball model, and various spectral characteristics of the GRBs, including the
effect of the absorption of TeV photons within the GRB as well as in the
intergalactic infrared radiation background. The intergalactic absorption
effect essentially precludes detection of TeV photons in the AMANDA detector
for reasonable values of the luminosity in the high energy component, but they
may well be detectable in the proposed ICECUBE detector which may have an
effective area for downward-going muons a factor of 100 larger than that in
AMANDA. However, even in ICECUBE, only relatively close-by GRBs at redshifts $<
0.05$ or so can be expected to be detectable with any reasonable degree of
confidence. We discuss the requirement on the luminosity of the GRB in the high
energy component for its detectability in ICECUBE.


title:
XMM-Newton observations of two hyperluminous IRAS galaxies:
  Compton-thick quasars with obscuring starbursts

abstract:
  We present XMM-Newton observations of two hyperluminous IRAS galaxies
(L_Bol>1E13 L_sun), neither of which was previously detected by ROSAT.
Published models of the infrared SEDs imply that a starburst and obscured
quasar contribute equally to the power of each source.
  IRAS F12514+1027 (z=0.30) is detected in 18.6 ks with 130 EPIC-pn counts over
0.2-12 keV. The soft X-ray spectrum exhibits thermal emission from the
starburst, with T=0.3 keV and L(0.5-2.0keV)=2.1E42 erg/s. With its Fe K-edge,
the flat continuum above 2 keV is interpreted as cold reflection from a hidden
AGN with an intrinsic L(2-10keV) of at least 1.8E44 erg/s. Comparison with the
infrared power requires that the X-ray reflector subtend ~2pi/5 sr at the
central engine. IRAS F00235+1024 (z=0.575) is not detected by the EPIC-pn in
15.9 ks; the limits imply that the starburst is X-ray weak, and (for the AGN)
that any hard X-ray reflector subtend <2pi/5 sr. The direct lines of sight to
the AGN in both objects are Compton-thick, and the presence of a reflection
component in F12514+1027, but not in F00235+1024, suggests that the AGN in the
latter object is more completely obscured. This is consistent with their
Seyfert-2 and starburst optical spectra, respectively.


title:
VLT/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies: I.
  Nucleosynthesis and Abundance Ratios

abstract:
  We have used UVES on VLT-UT2 to take spectra of 15 red giants in the
Sculptor, Fornax, Carina and Leo I dwarf spheroidal galaxies. We measure the
abundances of alpha, iron peak, s and r-process elements. No dSph giants in our
sample show the deep mixing abundance pattern seen in nearly all globular
clusters. At a given metallicity, the dSph giants exhibit lower [el/Fe]
abundance ratios for the alpha elements than stars in the Galactic halo. This
can be caused by a slow star formation rate and contribution from Type Ia SN,
and/or a small star formation event (low total mass) and mass dependent Type II
SN yields. Differences in the even-Z [el/Fe] ratios between these galaxies, as
well as differences in the evolution of the s&r-process elements are
interpreted in terms of their star formation histories. Comparison of the dSph
abundances with those of the Galactic halo reveals some consistencies. In
particular, we find stars that mimic the abundance pattern found by Nissen &
Shuster (1997) for metal-rich, high R_max, high z_max halo stars, supporting
their suggestion that disrupted dSph's may explain up to 50% of the metal-rich
halo. A comparison with the metal-poor Galactic halo reveal no consistencies
suggesting that the majority of the metal-poor Galactic halo could not have
been formed from objects similar to these dSph. Finally, we use the dSph
abundances to place new constraints on the nucleosynthetic origins, including
Cu and Mn which are more consistent with metallicity dependent SN yields than
the more commonly assumed SN Ia production.


title:
VLT/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies: II.
  Implications for Understanding Galaxy Evolution

abstract:
  We have used UVES on VLT-UT2 to take spectra of 15 individual red giant stars
in the centers of four nearby dwarf spheroidal galaxies: Sculptor, Fornax,
Carina and Leo I. We measure the abundance variations of numerous elements in
these low mass stars with a range of ages (1-15Gyr old). This means that we can
effectively measure the chemical evolution of these galaxies WITH TIME. Our
results show a significant spread in metallicity with age, but an overall trend
consistent with what might be expected from a closed (or perhaps leaky) box
chemical evolution scenario over the last 10-15Gyr. We notice that each of
these galaxies show broadly similar abundance patterns for all elements
measured. This suggests a fairly uniform progression of chemical evolution with
time, despite quite a large range of star formation histories. It seems likely
that these galaxies had similar initial conditions, and evolve in a similar
manner with star formation occurring at a uniformly low rate, even if at
different times. With our accurate measurements we find evidence for small
variations in abundances which are correlated to variations in star formation
histories. The alpha-elements suggest that dSph chemical evolution has not been
affected by very high mass stars (>15-20 Msun). The abundance patterns we
measure for stars in dwarf spheroidal galaxies are significantly different from
those typically observed in the disk, bulge and inner-halo of our Galaxy. This
suggests that it is NOT possible to construct a significant fraction of our
Galaxy from STARS formed in these dwarf spheroidal galaxies which subsequently
merged into our own. Any merger scenario involving dSph has to occur in the
very early Universe whilst they are still gas rich, so the majority of mass
transfer is gas, and few stars.


title:
Testing intermediate-age stellar evolution models with VLT photometry of
  LMC clusters. III. Padova results

abstract:
  The color-magnitude diagrams (CMDs) of three intermediate-age LMC clusters,
NGC 2173, SL556 and NGC2155 are analyzed to determine their age and metallicity
basing on Padova stellar models. Synthetic CMDs are compared with cluster data.
The best match is obtained using two fitting functions based on star counts in
the different bins of the cluster CMD. Two different criteria are used. One of
them takes into account the uncertainties in the color of the red clump stars.
Given the uncertainties on the experimental values of the clusters metallicity,
we provide a set of acceptable solutions. They define the correspondent values
of metallicity, age, reddening and distance modulus (for the assumed IMF). The
comparison with Padova models suggests for NGC 2173 a prolonged star formation
(spanning a period of about 0.3 Gyr), beginning 1.7 Gyr and ending 1.4 Gyr ago.
The metallicity Z is in the range 0.0016 $-$ 0.003. Contrary to what suggested
for NGC 2173 a period of extended star formation was not required to fit the SL
556 and the NGC 2155 observations. For SL 556 an age of 2.0 Gyr is obtained.
The metallicity value is in the range 0.002 $-$ 0.004, depending on the adopted
comparison criterium. The derived age for NGC 2155 is 2.8 Gyr and its
metallicity Z is in the range 0.002 $-$ 0.003. The CMD features of this cluster
suggest that a more efficient overshoot should be adopted in the evolutionary
models.


title: On the Primordial Magnetic Field from Domain Walls

abstract:
  In this paper we discuss once more the zero mode contribution to the vacuum
energy density. We show that a careful treatment of the zero modes leads to the
conclusion that domain walls may be ferromagnetic, and could generate a
magnetic field of cosmological interest.


title:
P-Process Nucleosynthesis inside Supernova-Driven Supercritical
  Accretion Disks

abstract:
  We investigate p-process nucleosynthesis in a supercritical accretion disk
around a compact object of 1.4 M_solar, using the self-similar solution of an
optically thick advection dominated flow. Supercritical accretion is expected
to occur in a supernova with fallback material accreting onto a new-born
compact object. It is found that appreciable amounts of p-nuclei are
synthesized via the p-process in supernova-driven supercritical accretion disks
(SSADs) when the accretion rate m_dot = M_dot c^2/(16 L_Edd) >10^5, where L_Edd
is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs
have similar feature to those of the oxygen/neon layers in Type II supernovae
when the abundance of the fallback gas far from the compact object is that of
the oxygen/neon layers in the progenitor. The overall abundance profile is in
agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and
La, are underproduced in the SSADs as in Type II supernovae. If the fallback
gas is mixed with a small fraction of proton through Rayleigh-Taylor
instability during the explosion, significant amounts of Mo92 are produced
inside the SSADs. Ru96 and La138 are also produced when the fallback gas
contains abundant proton though the overall abundance profile of p-nuclei is
rather different from that of the solar system. The p-process nucleosynthesis
in SSADs contributes to chemical evolution of p-nuclei, in particular Mo92, if
several percents of fallback matter are ejected via jets and/or winds.


title: ISM Abundances in Sculptor Group Dwarf Irregular Galaxies

abstract:
  Using the CTIO 4-m telescope, we have obtained optical spectra of HII regions
in five Sculptor Group dwarf irregular galaxies. We derive oxygen, nitrogen,
and sulfur abundances from the HII region spectra. Oxygen abundances are
derived via three different methods (the ``direct'' method, the empirical
method guided by photoionization modeling of McGaugh (1991), and the purely
empirical method of Pilyugin (2000)) and are compared. Significant systematic
differences are found between the three methods, and we suggest that a
recalibration of the empirical abundance scale is required. The N/O ratio for
the metal-poor dI ESO 473-G24 of log (N/O) = -1.43 +/- 0.03 lies well above the
plateau of log (N/O) = -1.60 +/- 0.02 found by Izotov & Thuan (1999) for a
collection of metal-poor blue compact galaxies. This shows that not all
galaxies with 12 + log (O/H) < 7.6 have identical elemental abundance ratios,
and this implies that the Izotov & Thuan scenario for low metallicity galaxies
is not universal. Measurements of the HII regions in NGC 625 yield log (N/O) =
-1.25. Assuming N production by intermediate mass stars, this relatively high
N/O ratio may be indicative of a long quiescent period prior to the recent
active burst of star formation. The oxygen abundances in the Sculptor Group dIs
are in good agreement with the relationship between metallicity and luminosity
observed in the Local Group dIs. The Sculptor Group dIs, in general, lie closer
to the simple closed box model evolutionary path than the Local Group dIs. The
higher gas contents, lower average star formation rates, and closer resemblance
to closed box evolution could all be indicative of evolution in a relatively
low density environment.


title: Revisiting the Blazar Main Sequence

abstract:
  A discussion of the FSRQ -- BL Lac unification. All distinctive features
marking these two Blazar subclasses find an unifying explanation if the sources
are powered by central engines constituted by similar Kerr holes, but fueled at
high and low accretion rates, respectively. The connection need not be a
genetic one, but evidence toward some FSRQs switching into BL Lacs at lower z
will be provided by moderately negative BL Lac evolution. Then an extrapolation
will be warranted toward ultra-high energy particle accelerators operating at
very low accretion rates.


title: X-ray lines, progenitor and beaming of Gamma-Ray Bursts

abstract:
  X-ray emission features have been detected in at least five GRB afterglows.
Their detection and properties are of great importance in our understanding of
the nature of the GRB progenitor. Moreover, they provide us with an
un-collimated source of photons, allowing us to put firm constraints on the
total energy produced in GRBs, and therefore on their degree of collimation. I
will review the radiation mechanisms and geometries proposed as sources of the
line emission, and discuss the energy budget of the lines and their implication
for the overall energetics of the phenomenon.


title: Polarization of photospheric lines from turbulent dynamo simulations

abstract:
  We employ the magnetic and velocity fields from turbulent dynamo simulations
to synthesize the polarization of a typical photospheric line. The synthetic
Stokes profiles have properties in common with those observed in the quiet Sun.
The simulated magnetograms present a level of signal similar to that of the
Inter-Network regions. Asymmetric Stokes V profiles with two, three and more
lobes appear in a natural way. The intensity profiles are broadened by the
magnetic fields in fair agreement with observational limits. Furthermore, the
Hanle depolarization signals of the Sr I 4607 A line turn out to be within the
solar values. Differences between synthetic and observed polarized spectra can
also be found. There is a shortage of Stokes V asymmetries, that we attribute
to a deficit of structuring in the magnetic and velocity fields from the
simulations as compared to the Sun This deficit may reflect the fact that the
Reynolds numbers of the numerical data are still far from solar values. We
consider the possibility that intense and tangled magnetic fields, like those
in the simulations, exist in the Sun. This scenario has several important
consequences. For example, less than 10% of the existing unsigned magnetic flux
would be detected in present magnetograms. The existing flux would exceed by
far that carried by active regions during the maximum of the solar cycle.
Detecting these magnetic fields would involve improving the angular resolution,
the techniques to interpret the polarization signals, and to a less extent, the
polarimetric sensitivity.


title: Intermediate-Age Globular Clusters in Merger Remnants

abstract:
  Recent observations of globular clusters in intermediate-age (2-4 Gyr old)
merger remnants have provided the hitherto `missing link' between between young
merger remnants and normal elliptical galaxies. The luminosity functions (LFs)
of the `blue' globular clusters exhibit a Gaussian shape centered on M_V ~ -7.2
as found for giant ellipticals, while the `red' clusters exhibit LFs that are
more extended towards both the bright and faint ends, as expected for a cluster
population of intermediate age. Specific frequencies for these systems have
been calculated by evolving both the LF of the `red' clusters and the parent
galaxy luminosity to an age of 10 Gyr. They are found to be consistent with the
values found for giant ellipticals in poor clusters. These findings support the
viability of the `merger scenario' for forming the `red' GCs in giant
early-type galaxies.


title:
Probing The Cosmological Constant Through The Alcock-Paczynski Test
  Based on The Lyman-Alpha Forest

abstract:
  In recent years, the possibility of measuring the cosmological constant
$\Omega_\Lambda$ through the application of the Alcock-Paczynski test to the
Lyman Alpha (Ly$\alpha$) forest has been suggested (McDonald et al. 1999; Hui
et al. 1999). Despite the theoretical uncertainties due to a few other
cosmological parameters, some of the greatest difficulties we encounter concern
the huge uncertainties due to cosmic variance and noise. In this paper, we
propose a maximum likelihood estimation (MLE) method to deal with cosmic
variance and noise using synthetic spectra of quasistellar objects (QSOs) from
our cosmological hydrodynamic simulations. We demonstrate that the MLE method
can overcome the cosmic variance problem. Applying the MLE method, we find that
we have more than 90% probability to determine $\Omega_\Lambda$ within 20%
error and approximately of 66% probability to determine $\Omega_\Lambda$ within
10% error by using 30 pairs QSO spectra when other cosmological parameters are
assumed. Another important source of error is from noise in the flux spectra,
and we have modeled the corresponding effect by studying artificial spectra
with different kinds of noise added. We discover that the noise distribution
does not have significant effect on the final cross-correlation functions as
long as the signal-to-noise ratio (S/N) is fixed. Finally, a preliminary test
and discussion about the sensitivities to other cosmological parameters are
included in this paper as well.


title:
X-ray Spectroscopic Evidence for Intermediate Mass Black Holes: Cool
  Accretion Disks in Two Ultra--Luminous X-ray Sources

abstract:
  We have analyzed an XMM-Newton observation of the nearby spiral galaxy NGC
1313, which contains two "ultra-luminous" X-ray (ULX) sources. We measure
isotropic luminosities of L_X = 2.0 * 10^(40) erg/s and L_X = 6.6 * 10^(39)
erg/s for NGC 1313 X-1 and X-2 (0.2-10.0 keV, assuming a distance of 3.7 Mpc).
The spectra statistically require soft and hard spectral components to describe
the continuum emission; some prior studies of ULXs have claimed cool soft
components with lower statistics. The improvement over several single-component
models exceeds the 8 sigma level of confidence for X-1; the improvement for X-2
is significant at the 3 sigma level. The soft components in these ULX spectra
are well-fit by multi-color disk blackbody models with color temperatures of kT
= 150 eV. This temperature differs markedly from those commonly measured in the
spectra of stellar-mass (10 M_sun) black holes in their brightest states (kT ~
1 keV). It is expected that the temperature of an accretion disk orbiting a
black hole should decrease with increasing black hole mass. If the soft
components we measure are due to emission from the inner region of an accretion
disk, and disks extend close to the innermost stable circular orbit at the
accretion rates being probed, the low color temperatures may be interpreted as
spectroscopic evidence of black holes with intermediate masses: M_BH ~ 10^(3)
M_sun. Simple Eddington scaling arguments suggest a mimum mass of M_BH ~ 10^(2)
M_sun. NGC 1313 X-1 and X-2 are found in optical nebulae (Pakull and Mirioni
2002), which may indicate that anisotropic emission geometries are unlikely to
account for the fluxes observed.


title:
Two-Dimensional Axisymmetric Collapse of Thermally Unstable Primordial
  Clouds

abstract:
  We have performed two-dimensional hydrodynamic simulations of the collapse of
isolated axisymmetric clouds condensing via radiative cooling in a primordial
background gas. In order to study the development of the so-called
``shape-instability'', we have considered two types of axisymmetric clouds,
oblate and prolate clouds of various sizes and with axial ratios of $0.5 \leq
{R_{\rm c,R}} /{R_{\rm c,z}} \leq 2$. We find that the degree of oblateness or
prolateness is enhanced during the initial cooling phase. But it can be
reversed later, if the initial contrast in cooling times between the cloud gas
and the background gas is much greater than one. In such cases an oblate cloud
collapses to a structure composed of an outer thin disk and a central prolate
component. A prolate cloud, on the other hand, becomes a thin cigar-shape
structure with a central dense oblate component. The reversal of shape in the
central part of the cooled clouds is due to supersonic motions either along the
disk plane in the case of oblate clouds or along the symmetry axis in the case
of prolate clouds. For a background gas of $T_h=1.7\times 10^6$K and $n_h=0.1
\cm3$ in a protogalactic halo environment, the mean density of the cloud gas
that has cooled to $10^4$K increases to $100 n_h$ or so, in our simulations
where nonequilibrium cooling is adopted and the background gas cools too. The
spherical Jeans mass of such gas is estimated to be about $M_J \sim
5\times10^{7}\Msun$. In order for cloud mass to exceed the Jeans mass and at
the same time in order for the thermal instability to operate, the initial
cloud size should be around $1 - 1.5 l_{\rm cool}$ where $l_{\rm cool}$ is the
cooling length.


title:
Probing the structure of a birthplace of intermediate-mass stars:
  Ammonia cores in Lynds 1340

abstract:
  Lynds 1340, a molecular cloud forming intermediate-mass stars, has been
mapped in the NH_3(1,1) and (2,2) transitions with the Effelsberg 100m
telescope. We observed the whole area of the cloud where C18O emission was
detected earlier, at a 40 arcsec grid, with additional positions towards the
C18O peaks and optically invisible IRAS point sources. Our observations covered
an area of 170 arcmin^2, corresponding to about 5.15 pc^2 at a distance of 600
pc, and revealed 10 ammonia cores. The cores, occupying some 7% of the mapped
area, probably represent the highest density regions of L1340. Their total mass
is 80 solar mass, about 6% of the mass traced by C18O. Six cores are associated
with optically invisible IRAS point sources. Their average nonthermal line
width is 0.78 kms^{-1}, while the same quantity for the four starless cores is
0.28 kms^{-1}. We suggest that the narrow-line cores are destined to form
low-mass stars, whereas small groups of intermediate-mass stars are being
formed in the turbulent cores. The features traced by NH_3, 13CO, C18O and HI
obey the line width-size relation log Delta v_{NT} = 0.41(0.06)log R_{1/2}+
0.12(0.06). Comparison of sizes, densities and nonthermal line widths of
ammonia cores with those of C18O and 13CO structures supports the scenario in
which core formation has been induced by turbulent fragmentation. The typical
physical properties of the ammonia cores of L1340, R_{1/2} =0.08 pc,
T_{kin}=13.8 K, Delta v_{total}=0.64 kms^{-1}, and M =9 solar mass are close to
those of the high-mass star forming Perseus and Orion B clouds.


title:
Non-confirmation of reported HI clouds without optical counterparts in
  the Hercules Cluster

abstract:
  21 cm HI line observations were made with the Arecibo Gregorian telescope of
9 HI clouds in the Hercules Cluster which were reported as tenative detections
in a VLA HI study of the cluster (Dickey 1997) and for which our deep CCD
imaging failed to find any optical counterparts. No sensitive observations
could be made of one of these (sw-174) due to the presence of a close-by strong
continuum source. The other 8 tentative HI detections were not reconfirmed by
the Arecibo HI measurements. The CCD images did reveal faint, low surface
brightness counterparts near the centres of two other VLA HI sources invisible
on the Palomar Sky Survey, sw-103 and sw-194.


title: Precession of Isolated Neutron Stars

abstract:
  I summarize the evidence for precession of isolated neutron stars and
theoretical effort to understand the observations. I discuss factors that might
set the precession period, describe constraints on the material properties of
the crust, and conclude with a brief discussion of possible sources of stress
that would deform a neutron star to the extent required.


title: Probing the Circular Polarization of Relativistic Jets on VLBI Scales

abstract:
  High resolution studies of circular polarization allow us see where it arises
in a jet, study its local fractional level and spectrum, and compare these
results to local measures of linear polarization and Faraday rotation. Here we
not only review past results from Very Long Baseline Array (VLBA) circular
polarization studies, but we also present preliminary new results on two
quasars. In the core of PKS 0607-157, we find strong circular polarization at 8
GHz and much weaker levels at 15 GHz. Combined with the linear polarization
data, we favor a simple model where the circular is produced by Faraday
conversion driven by a small amount of Faraday rotation. In the core of 3C345,
we find strong circular polarization at 15 GHz in a component with distinct
linear polarization. This core component is optically thick at 8 GHz, where we
detect no circular polarization. With opposite trends in frequency for PKS
0607-157 and 3C345, it seems clear that local conditions in a jet can have a
strong effect on circular polarization and need to be taken into account when
studying inhomogeneous objects with multi-frequency observations.


title:
An Empirical Decomposition of Near-IR Emission into Galactic and
  Extragalactic Components

abstract:
  We decompose the COBE/DIRBE observations of the near-IR sky brightness (minus
zodiacal light) into Galactic stellar and interstellar medium (ISM) components
and an extragalactic background. This empirical procedure allows us to estimate
the 4.9 micron cosmic infrared background (CIB) as a function of the CIB
intensity at shorter wavelengths. A weak indication of a rising CIB intensity
at wavelengths > 3.5 micron hints at interesting astrophysics in the CIB
spectrum, or warns that the foreground zodiacal emission may be incompletely
subtracted. Subtraction of only the stellar component from the
zodiacal-light-subtracted all-sky map reveals the clearest 3.5 micron ISM
emission map, which is found to be tightly correlated with the ISM emission at
far-IR wavelengths.


title:
An Extreme Ultraviolet Explorer Atlas of Seyfert Galaxy Light Curves:
  Search for Periodicity

abstract:
  The Deep Survey instrument on the Extreme Ultraviolet Explorer satellite
(EUVE) obtained long, nearly continuous soft X-ray light curves of 5-33 days
duration for 14 Seyfert galaxies and QSOs. We present a uniform reduction of
these data, which account for a total of 231 days of observation. Several of
these light curves are well suited to a search for periodicity or QPOs in the
range of hours to days that might be expected from dynamical processes in the
inner accretion disk around ~10^8 M_sun black holes. Light curves and
periodograms of the three longest observations show features that could be
transient periods: 0.89 days in RX J0437.4-4711, 2.08 days in Ton S180, and 5.8
days in 1H 0419-577. The statistical significance of these signals is estimated
using the method of Timmer & Konig (1995), which carefully takes into account
the red-noise properties of Seyfert light curves. The result is that the
signals in RX J0437.4-4711 and Ton S180 exceed 95% confidence with respect to
red noise, while 1H 0419-577 is only 64% significant. These period values
appear unrelated to the length of the observation, which is similar in the
three cases, but they do scale roughly as the luminosity of the object, which
would be expected in a dynamical scenario if luminosity scales with black hole
mass.


title: Measuring Sigma8 with Cluster Lensing : Biases from Unrelaxed Clusters

abstract:
  We use gravitational lens models and X-ray spectral analysis of ten X-ray
luminous galaxy clusters at z~0.2 to study the impact of cluster substructure
on attempts to normalize the matter power spectrum. We estimate that unrelaxed
clusters are 30% hotter than relaxed clusters causing sigma8 to be
over-estimated by 20% if the cluster selection function is not accounted for
correctly. This helps to explain the wide range in sigma8 derived from
different techniques, sigma8~0.6-1, and offers a physically motivated
explanation for some of the discrepancy. We also identify two further
systematics in our analysis: (i) extrapolation of small field-of-view mass
measurements to the cluster virial radius and (ii) projection of 3-dimensional
masses contained in numerical simulations to the 2-dimensional information that
is available from observations. We combine quantitative estimates of these two
effects with our model fitting to estimate from the current data that
sigma8=0.75+/-0.05(statistical)+/-0.15(systematic), where the systematic error
reflects the extrapolation and projection uncertainties. All three systematics
(substructure, extrapolation and projection) are fundamental to future
cluster-based measurements of sigma8 regardless of the techniques employed.
However, we identify gravitational lensing as the tool of choice for such
studies, because a combination of strong- and weak-lensing offers the most
direct route to control the systematics and thus achieve an unbiased comparison
between observation and theory.


title: On Magnetic Field Amplification in Gamma-Ray Burst Sources

abstract:
  Magnetic fields play a dual role in gamma-ray bursts (GRBs). First, GRB and
afterglow spectra (the latter interpreted as emission from external shocks)
imply synchrotron radiation in a magnetic field that is a significant fraction
of equipartition with the particle energy density. Second, magnetized rotators
with $\sim 10^{15}$ Gauss field may power GRB by transporting Poynting flux to
large distances where it dissipates and also drives an external shock. The
field amplification at external shocks and in the engine involve separate
processes. External shock fields are likely either seeded by a pre-GRB wind, or
are amplified by two-stream plasma instabilities with MHD turbulence playing a
subsequent role. In the engine, the large scale fields are likely produced by
MHD helical dynamos, since flux accretion cannot easily compete with turbulent
diffusion, and because structures must be large enough to rise to coronae
before diffusing. Why helical dynamos are feasible, and their relation to the
magnetorotational instability are among the points discussed.


title: Statistical Identification of XMM-Newton Sources Using XID Database

abstract:
  The XMM identification programme (XID) is accumulating Optical/IR images and
spectra to identify thousands of XMM sources. The XID Database is the main
repository of this data and permits easy selection and correlation of XMM X-ray
and UV (from Optical Monitor) data with Optical/IR observations. Here we
discuss the methodology and some preliminary results of statistical
classification and identification of X-ray sources using the data from XID
Database. We show that in the medium range of X-ray fluxes and optical/UV
magnitudes most of XMM sources are AGNs in agreement with previous
observations. Moreover, AGNs are mostly concentrated in a small area of
(U/g-r)-HR2/HR3 plane. At present the confirmed identifications are too scarce
to permit statistical identification of individual sources without taking their
spectra. Nonetheless, these types of investigation help to better understand
general characteristics of classes of astronomical objects in X-ray and its
relation with optical/IR ones.


title: GRB 021004: a Massive Progenitor Star Surrounded by Shells

abstract:
  We present spectra of the optical transient of GRB021004 obtained with the
Hobby-Eberly telescope starting 15.48, 20.31 hours, and 4.84 days after the
burst and a spectrum obtained with the H. J. Smith 2.7 m Telescope starting
14.31 hours after the burst. GRB021004 is the first afterglow whose spectrum is
dominated by absorption lines from high ionization species with multiple
velocity components separated by up to 3000 km/s. We argue that these lines are
likely to come from shells around a massive progenitor star. The high
velocities and high ionizations arise from a combination of acceleration and
flash-ionization by the burst photons and the wind velocity and steady
ionization by the progenitor. We also analyze the broad-band spectrum and the
light curve. We distinguish six components along the line of sight: (1) The
z~2.293 absorption lines arise from the wind of a massive star. For a mass loss
rate of ~6 x 10^{-5} solar masses per year, this component also provides the
external medium to create the afterglow light. (2) A second shell produces
absorption lines with a relative velocity of 560 km/s, and this is associated
with the shell created by the fast massive star wind blowing a bubble in the
preceding slow wind at a radial distance of order 10 pc. (3) More distant
clouds within the host galaxy lie between 30-2500 pc, where they have been
ionized by the burst. (4-6) The massive star wind has clumps with radii and
over-densities of 0.022, 0.063, and 0.12 parsecs and 50%, 10%, and 10%
respectively. The immediate progenitor of the burster could either be a WC-type
Wolf-Rayet star or a highly evolved star whose original mass was just too small
for it to become a WN-type Wolf-Rayet star.


title: The Nature of 3EG J1746-2851 in the Nucleus of the Galaxy

abstract:
  There are a number of candidate sources that are considered to be responsible
for the origin of the EGRET source 3EG J1746--2851 (Hartman et al. 1999). The
lack of clear identification of this source with any known sources in this
region is due to the complexity and the richness of the environment of the
Galactic center as well as the low spatial resolution of the EGRET
observations. Four hypotheses, which include the interaction of something with
something else, are described to account for the energetics and the spectrum of
the $\gamma$-ray emission from the enigmatic EGRET source which lies within
0.2$^0$ of the Galactic center. The possible interaction sites result from the
following: i) the nonthermal filaments of the radio Arc & G0.13-0.13 molecular
cloud, ii) the supernova remnant Sgr A East & the 50 km s$^{-1}$ molecular
cloud, iii) the magnetized filaments of the Arc & M0.20-0.033 molecular cloud
and iv) the relativistic particles of the Arches cluster & its own stellar
radiations field.


title: OH (1720 MHz) Masers and Mixed-Morphology Supernova Remnants

abstract:
  Radio surveys of supernova remnants (SNRs) in the Galaxy have uncovered 19
SNRs accompanied by OH maser emission at 1720 MHz. This unusual class of maser
sources is suggested to be produced behind a shock front from the expansion of
a supernova remnant running into a molecular cloud. An important ingredient of
this model is that X-ray emission from the remnant enhances the production of
OH molecule. The role of X-ray emission from maser emitting (ME) SNRs is
investigated by comparing the X-ray induced ionization rate with theory. One
aspect of this model is verified: there is a strong association between maser
emitting and mixed-morphology (MM) or thermal composite SNRs --center-filled
thermal X-ray emission surrounded by shell-like radio morphology. We also
present ROSAT and ASCA observations of two maser emitting SNRs: G21.8--0.6 (Kes
69) and G357.7--0.1 (Tornado).


title: X-ray Source Population in the Elliptical Galaxy NGC 720 with Chandra

abstract:
  With a Chandra ACIS-S3 observation, we detect 42 X-ray point sources in the
elliptical galaxy NGC 720, including a possible central source. Most of these
sources will be low-mass X-ray binaries (LMXBs), and 12 are located within 2"
of globular cluster candidates. We investigate both the hardness ratios and
combined spectra of the sources. They exhibit a distribution of X-ray colors
similar to those seen in other early-type galaxies. We find that there is a
population of highly absorbed sources located at large distances from the
center of the galaxy. The overall spatial distribution of sources is consistent
with the ellipticity and position angle of the galaxy, but the sources appear
to form several arcs. NGC 720 contains nine ultraluminous sources (L_x >= 10^39
ergs/s). This number is more than have previously been detected in an
early-type galaxy but similar to the number seen in the Antennae merger system.
The ratio L_ULX/L_B for NGC 720 is more than double the ratio for the S0 galaxy
NGC 1553 and a factor of seven higher than for the elliptical galaxy NGC 4697,
although uncertainties in the distance and the source spectral properties could
bring these ratios into agreement. The X-ray source luminosity function is also
nearly as flat as those seen in disk and merger systems. The large number of
ULXs in NGC 720 and its relatively flat XLF may provide evidence against the
association of all ULXs with young stars. We also see a possible high
luminosity break in the luminosity function at 2x10^39 h_50^-2 ergs/s.


title: The Birth of the HST Snapshot Programs

abstract:
  This article describes the unconventional and occassionally stormy birth and
early history of the HST Snapshot Program.


title: Shock Breakout in Core-Collapse Supernovae and its Neutrino Signature

abstract:
  (Abridged) We present results from dynamical models of core-collapse
supernovae in one spatial dimension, employing a newly-developed Boltzmann
neutrino radiation transport algorithm, coupled to Lagrangean hydrodynamics and
a consistent high-density nuclear equation of state. We focus on shock breakout
and its neutrino signature and follow the dynamical evolution of the cores of
11 M_sun, 15 M_sun, and 20 M_sun progenitors through collapse and the first 250
milliseconds after bounce. We examine the effects on the emergent neutrino
spectra, light curves, and mix of species of artificial opacity changes, the
number of energy groups, the weak magnetism/recoil corrections, nucleon-nucleon
bremsstrahlung, neutrino-electron scattering, and the compressibility of
nuclear matter. Furthermore, we present the first high-resolution look at the
angular distribution of the neutrino radiation field both in the
semi-transparent regime and at large radii and explore the accuracy with which
our tangent-ray method tracks the free propagation of a pulse of radiation in a
near vacuum. Finally, we fold the emergent neutrino spectra with the
efficiencies and detection processes for a selection of modern underground
neutrino observatories and argue that the prompt electron-neutrino breakout
burst from the next galactic supernova is in principle observable and usefully
diagnostic of fundamental collapse/supernova behavior. Though we are not in
this study focusing on the supernova mechanism per se, our simulations support
the theoretical conclusion (already reached by others) that spherical (1D)
supernovae do not explode when good physics and transport methods are employed.


title: Pointing Refinement of SIRTF Images

abstract:
  The soon-to-be-launched Space Infrared Telescope Facility (SIRTF) shall
produce image data with an a-posteriori pointing knowledge of 1.4 arcsec (1
sigma radial) with a goal of 1.2 arcsec in the International Celestial
Reference System (ICRS). To perform robust image coaddition, mosaic generation,
extraction and position determination of faint sources, the pointing will need
to be refined to better than a few-tenths of an arcsecond. We use a
linear-sparse matrix solver to find a "global-minimization" of all relative
image offsets in a mosaic from which refined pointings and orientations can be
computed. This paper summarizes the pointing-refinement algorithm and presents
the results of testing on simulated data.


title: How many arcminute-separation lenses are expected in the 2dF QSO survey?

abstract:
  Wide separation lensing statistics offer information about the density
profile and abundance of dark halos. Recently a possible discovery of six
quasar pairs, which may be lensed multiple images, was reported by Miller et
al. (2003, astro-ph/0210644). These pairs are selected from a catalog of the
2dF quasar (QSO) survey comprising 22163 quasars. We calculate expected numbers
of lensed quasars taking account of the redshift and magnitude distributions of
the quasar catalog. Given some of the six pairs are genuine lensed systems, we
put interesting constraints on the inner slope of dark halos, \Omega_0, and
\sigma_8. We show that the detection of even one lens with separation >30'' is
marginally consistent with models that have cuspy inner density profile, \rho
\propto r^{-1.5}, and very large \sigma_8, \sigma_8>~1.2 for \Omega_0=0.3. To
reconcile with constraints from X-ray clusters or cosmic shear, much lower
\Omega_0 and much higher \sigma_8 are needed, although such high \sigma_8 seems
too extreme. The shallower inner density profile \rho \propto r^{-1} is hardly
acceptable. In particular, the expected number of lenses with separation >200''
is too small to explain the discovery of such anomalously wide separation lens
systems. These results imply that we miss some important systematic effects,
there is a problem in the cold dark matter scenario, or none of these six
quasar pairs is likely to be lensed images.


title:
The large-scale Galactic magnetic field structure and pulsar rotation
  measures

abstract:
  Pulsars provide unique probes for the {\it large-scale} interstellar magnetic
field in the Galactic disk. The Parkes multibeam pulsar survey has discovered
many distant pulsars which enables us for the first time to explore the
magnetic field in most of the nearby half of the Galactic disk. The fields are
found to be {\it coherent in direction} over a linear scale of $\sim 10$ kpc
between the Carina-Sagittarius and Crux-Scutum arms from $l\sim45\degr$ to
$l\sim305\degr$. The coherent spiral structures and field direction reversals,
including the newly determined counterclockwise field near the Norma arm, are
consistent with bi-symmetric spiral model for the disk field. However, the
antisymmetric rotation measure sky from the Galactic halo and the dipole field
in the Galactic center suggest that the A0 dynamo is operating there.


title:
Nonadiabatic resonant dynamic tides and orbital evolution in close
  binaries

abstract:
  This investigation is devoted to the effects of nonadiabatic resonant dynamic
tides generated in a uniformly rotating stellar component of a close binary.
The companion is considered to move in a fixed Keplerian orbit, and the effects
of the centrifugal force and the Coriolis force are neglected. Semi-analytical
solutions for the linear, nonadiabatic resonant dynamic tides are derived by
means of a two-time variable expansion procedure. The solution at the lowest
order of approximation consists of the resonantly excited oscillation mode and
displays a phase shift with respect to the tide-generating potential.
Expressions are established for the secular variations of the semi-major axis,
the orbital eccentricity, and the star's angular velocity of rotation caused by
the phase shift. The orders of magnitude of these secular variations are
considerably larger than those derived earlier by Zahn (1977) for the limiting
case of dynamic tides with small frequencies. For a 5 solar mass ZAMS star, an
orbital eccentricity e = 0.5, and orbital periods in the range from 2 to 5
days, numerous resonances of dynamic tides with second-degree lower-order
gravity modes are seen to induce secular variations of the semi-major axis, the
orbital eccentricity, and the star's angular velocity of rotation with time
scales shorter than the star's nuclear life time.


title:
The VLBA 2cm Survey: Kinematics of pc-Scale Structures in Active
  Galactic Nuclei

abstract:
  The kinematics of jets in active galactic nuclei (QSOs, BL Lacs, Radio
Galaxies and Empty Field objects) on parsec scales is being studied with Very
Long Baseline Array observations at 15 GHz of a sample of more than 170 radio
sources. More than 1000 images have been taken since 1994. Here we present an
overview of the results of our study, including the proper motions of
components in the jets, and their relationship with other source properties.


title: A Multi-Frequency Study of 3C309.1

abstract:
  Here we summarize our results from a detailed multi-frequency study of the
QSO 3C309.1 based on the Very Long Baseline Array (VLBA) observations made in
mid 1998. From our images, we find a curved jet extending up to 100
milliarcseconds (mas) to the east at low frequencies with two main components,
A and B. A preliminary astrometric analysis (Ros and Lobanov 2001) provides a
determination of the core position at different frequencies by
phase-referencing to a nearby radio source, QSO S5 1448+76. The changes of the
core position with frequency suggest high opacity close to the core caused by
synchrotron self-absorption. Due to the large astrometric uncertainties we
cannot draw any conclusions about the values of the opacity gradients at high
frequencies. We believe that a detailed analysis of the frequency depedence of
the core position will reveal the profile of the matter distribution in the
broad line region, as was initially suggested by Lobanov (1998).


title: The Brera Multi-scale Wavelet ROSAT HRI source catalogue (BMW-HRI)

abstract:
  We present the Brera Multi-scale Wavelet ROSAT HRI source catalogue (BMW-HRI)
derived from all ROSAT HRI pointed observations with exposure time longer than
100 s available in the ROSAT public archives. The data were analyzed
automatically using a wavelet detection algorithm suited to the detection and
characterization of both point-like and extended sources. This algorithm is
able to detect and disentangle sources in very crowded fields and/or in
presence of extended or bright sources. Images have been also visually
inspected after the analysis to ensure verification. The final catalogue,
derived from 4,303 observations, consists of 29,089 sources detected with a
detection probability of greater or equal 4.2 sigma. For each source, the
primary catalogue entries provide name, position, count rate, flux and
extension along with the relative errors. In addition, results of
cross-correlations with existing catalogues at different wavelengths (FIRST,
IRAS, 2MASS and GSC2) are also reported. All these information are available on
the web via the DIANA Interface. As an external check, we compared our
catalogue with the previously available ROSHRICAT catalogue (both in its short
and long versions) and we were able to recover, for the short version, \~90% of
the entries. We computed the sky coverage of the entire HRI data set by means
of simulations. The complete BMW-HRI catalogue provides a sky coverage of 732
square degrees down to a limiting flux of ~1E-12 erg/s/cm2 and of 10 square
degrees down to ~1E-14 erg/s/cm2. We were able to compute the cosmological
log(N)-log(S) distribution down to a flux of about 1.2x1E-14 erg/s/cm2.


title:
On the small-scale stability of thermonuclear flames in Type Ia
  supernovae

abstract:
  We present a numerical model which allows us to investigate thermonuclear
flames in Type Ia supernova explosions. The model is based on a finite-volume
explicit hydrodynamics solver employing PPM. Using the level-set technique
combined with in-cell reconstruction and flux-splitting schemes we are able to
describe the flame in the discontinuity approximation. We apply our
implementation to flame propagation in Chandrasekhar-mass Type Ia supernova
models. In particular we concentrate on intermediate scales between the flame
width and the Gibson-scale, where the burning front is subject to the
Landau-Darrieus instability. We are able to reproduce the theoretical
prediction on the growth rates of perturbations in the linear regime and
observe the stabilization of the flame in a cellular shape. The increase of the
mean burning velocity due to the enlarged flame surface is measured. Results of
our simulation are in agreement with semianalytical studies.


title: Global Electrophonic Fireball Survey: a review of witness reports - I

abstract:
  Despite more than 300 years since its first scientific description, the
phenomenon of electrophonic sounds from meteors are still eluding complete
physical explanation. According to the accepted knowledge, the sound itself is
created by strong electric fields on the ground induced by the meteor.
Nonetheless, there is no convincing theory that can fully explain how a meteor
can generate such a strong electric field. Extreme rareness of the phenomenon
has prevented a substantial experimental work so far; thus, consequently, it
remains on the margins of scientific interest. This is quite unfortunate since
these electric fields suggest existence of a highly complex electromagnetic
coupling and charge dynamics between the meteors and the ionosphere. Therefore,
the existing theoretical work relies mostly on the witness reports. The Global
Electrophonic Fireball Survey (GEFS) is the first systematic survey of witness
reports of these sounds with a standardized questionnaire designed exclusively
for this phenomenon. Here we present the overall picture of the phenomenon that
emerged after almost 100 reports collected by GEFS. It becomes clear now that
the lover meteor brightness limit is about -2$^m$, suggesting a bias in the
existing electrophonic sounds catalogues toward brighter meteors. In contrast
to the current belief that such low brightness electrophonic meteors produce
transient sounds, we find that they can also produce sustained sounds. The
current theories can not accommodate these results. We revive the old idea that
the electrophonic sounds can be created by the corona discharge mechanism, in
addition to the existing prevalent suggestion of resonant vibration of objects
on the ground.


title: On metal abundances in QSO absorbers

abstract:
  I review our recent results concerning the metal abundances in quasar
absorption-line spectra obtained with the UVES/VLT, HIRES/ KECK, and STIS/HST
spectrographs. The analysis is based on the Monte Carlo inversion procedure
aimed at the restoring the physical parameters and the 1D distributions of the
velocity and density fields in quasar absorbers. A functional dependence of the
line-of-sight velocity dispersion, sigma_v, on the absorber linear size, L, was
found which may indicate that the metal absorbers are associated with
virialized systems like galaxies or their halos. A metal content enhancement
(up to Z = 4Z_solar) was observed in small-size absorbers (L < 0.4 kpc),
whereas decreasing metal abundances were found in systems with increasing L.The
lowest metallicity ([C/H] = -3.0) was detected in the z = 2.917 Lymna-limit
system (LLS) with N(HI) = 3.2 10^{17} cm^{-2} and L = 140 kpc. The relative
abundance ratio of [Si/C] = 0.35, measured in this LLS, seems to indicate that
the initial mass function for the stellar population, produced the observed
metallicity pattern, was constrained to intermediate masses, M_up < 25M_solar.


title: BeppoSAX observation of the composite remnant G327.1-1.1

abstract:
  We report an X-ray study of the composite supernova remnant G327.1-1.1, with
particular emphasis on its thermal emission. By virtue of a combined spatial
and spectral analysis, we have been able to model the X-ray emission of the
remnant as a sum of two components: a non-thermal component, due to the pulsar
nebula and the pulsar itself, and a thermal component, of which we have
analysed spectrum and morphology, after proper subtraction of the plerion. We
discuss three possible interpretations of the thermal emission of \src: pure
Sedov expansion, expansion through a inhomogeneous medium with evaporation from
ISM clouds, and radiative expansion. On the light of our new data and
interpretation, we have re-derived all the physical parameters of this SNR. In
the framework of Sedov or radiative expansion we derive a longer age than
previously estimated ($1.1\times 10^4$), thus not requiring a high velocity for
the pulsar.


title: Observing the effects of the event horizon in black holes

abstract:
  The key difference between neutron stars and black holes is the
presence/absence of a solid surface. Recent attempts to detect this difference
have concentrated on the quiescent luminosity, but here these sources are faint
and difficult to observe. Instead we look at these sources when they are
bright, and show that there is a clear difference between black holes and
neutron stars in the evolution of their X-ray spectra which is due to the
presence of a surface in the neutron stars. We also show that there is a type
of X-ray spectrum which is only seen from black holes, making it a good
diagnostic for the nature of new transient sources.


title: Spectropolarimetry and the Geometry of Type 1 Seyfert Nuclei

abstract:
  We describe the results of a detailed study of the polarization properties of
the broad H-alpha emission line in Type 1 Seyfert nuclei. Our analysis of these
data points to a model in which the broad Balmer lines are emitted by a
rotating disk, and are scattered in two main regions - one co-planar with the
disk and within the circum-nuclear torus, the other, the polar scattering
region, outside the torus but aligned with its axis. The relative importance of
the two sources of polarized light is largely determined by the inclination of
the system axis to the line-of-sight.


title:
Latest results from the POINT-AGAPE pixel-lensing survey of the
  Andromeda Galaxy

abstract:
  I report on recent results from the POINT-AGAPE pixel-lensing experiment,
which is engaged in a search towards the Andromeda galaxy (M31) for
gravitational microlensing signatures from massive compact halo objects
(Machos). An analysis of two years of data reveals over 360 light-curves
compatible with microlensing. The third year of data, currently being analysed,
will be crucial in determining how many of these candidates are long-period
variables rather than microlensing. Within the dataset we have isolated a
subset of four high signal-to-noise ratio, short duration events which are
compelling microlensing candidates. The properties and possible origins of
these events are discussed.


title: Gravitational waves from stars orbiting the Sagittarius A* black hole

abstract:
  One of the main astrophysical processes leading to strong emission of
gravitational waves to be detected by the future space-borne interferometer
LISA is the capture of a compact star by a black hole with a mass of a few
million solar masses in the center of a galaxy. In previous studies, main
sequence stars were thought not to contribute because they suffer from early
tidal disruption. Here we show that, according to our simulations of the
stellar dynamics of the Sgr A* cluster, there must be one to a few low-mass
main sequence stars sufficiently bound to the central Galactic black hole to be
conspicuous sources in LISA observations. The probability that a white dwarf
may be detectable is lower than 0.5 and, in spite of mass segregation,
detection of a captured neutron star or stellar black hole in the center of the
Milky Way is highly unlikely.


title:
Stellar Abundances in Giant Stars in the Metal-Rich Globular Cluster
  NGC6528

abstract:
  We present the first results of a detailed abundance analysis, based on VLT
observations, of giant stars in the very metal-rich globular cluster NGC 6528.
We will be able to tie the horizontal branch abundances (see e.g. Carretta et
al. 2001) to those of the more luminous giants (see CMDs). For the very similar
cluster NGC 6553 studies of different types of stars have yielded very
disparate results. Our first analysis of three of our stars seem to indicate
that indeed the different sorts of stars do show similar abundances if one
homogeneous set of models and parameters are being used.


title:
Statistical properties of exoplanets II. Metallicity, orbital
  parameters, and space velocities

abstract:
  In this article we present a detailed spectroscopic analysis of more than 50
extra-solar planet host stars. Stellar atmospheric parameters and metallicities
are derived using high resolution and high S/N spectra. The spectroscopy
results, added to the previous studies, imply that we have access to a large
and uniform sample of metallicities for about 80 planet hosts stars. We make
use of this sample to confirm the metal-rich nature of stars with planets, and
to show that the planetary frequency is rising as a function of the [Fe/H].
Furthermore, the source of this high metallicity is shown to have most probably
an ``primordial'' source, confirming previous results. The comparison of the
orbital properties (period and eccentricity) and minimum masses of the planets
with the stellar properties also reveal some emerging but still not significant
trends. These are discussed and some explanations are proposed. Finally, we
show that the planet host stars included in the CORALIE survey have similar
kinematical properties as the whole CORALIE volume-limited planet search
sample. Planet hosts simply seem to occupy the metal-rich envelope of this
latter population.


title: A window to the Galactic X-ray halo: The ISM towards the Lockman hole

abstract:
  We present a combined X-ray/HI-analysis of the ISM towards the Lockman hole.
This sky region is considered as the "window to the distant universe" because
of its absolute lowest HI column density on the whole sky. The Lockman hole
appears to be not as transparent as the HI data suggest. We propose that about
half of the ISM towards the Lockman hole is in form of ionized hydrogen rather
than HI.


title: The Ghost in the Machine

abstract:
  I examine simple tests for the presence of accretion disks in AGN - changes
of surface brightness with viewing angle, changes of colour temperature with
luminosity, and behaviour during variability. AGN observations pass the first
two tests but fail the third, unless there is some previously unobserved source
of heating - the ``ghost in the machine''.


title: What can the redshift observed in EXO 0748-676 tell us?

abstract:
  The mass-radius relations for bare and crusted strange stars are calculated
with the bag model. Comparing these relations with the observed one derived
from redshift, we address that the conclusion, that EXO 0748-676 can not be a
strange star, is incorrect. Various strange star models can show that EXO
0748-676 could have a mass of (1.3 ~ 1.7) M_sun and a radius of (8.4 ~ 11.4)
km. It is proposed that some nascent strange stars could be bare and have mass
\~ 0.1 M_sun, whereas their masses increase during a long accretion history.


title: Discovery of X-rays from Mars with Chandra

abstract:
  On 4 July 2001, X-rays from Mars were detected for the first time. The
observation was performed with the ACIS-I detector onboard Chandra and yielded
data of high spatial and temporal resolution, together with spectral
information. Mars is clearly detected as an almost fully illuminated disk, with
an indication of limb brightening at the sunward side, accompanied by some
fading on the opposite side. The morphology and the X-ray luminosity of ~4 MW
are fully consistent with fluorescent scattering of solar X-rays in the upper
Mars atmosphere. The X-ray spectrum is dominated by a single narrow emission
line, which is most likely caused by O-K_alpha fluorescence. No evidence for
temporal variability is found. This is in agreement with the solar X-ray flux,
which was almost constant during the observation. In addition to the X-ray
fluorescence, there is evidence for an additional source of X-ray emission,
indicated by a faint X-ray halo which can be traced to about three Mars radii,
and by an additional component in the X-ray spectrum of Mars, which has a
similar spectral shape as the halo. Within the available limited statistics,
the spectrum of this component can be characterized by 0.2 keV thermal
bremsstrahlung emission. This is indicative of charge exchange interactions
between highly charged heavy ions in the solar wind and exospheric hydrogen and
oxygen around Mars. Although the observation was performed at the onset of a
global dust storm, no evidence for dust-related X-ray emission was found.