title: Radio emission and the optical isophotal twist of radio-loud ellipticals

abstract:
  Using the surface photometric analysis data for a well defined sample of 79
nearby radio galaxies (z < 0.12), it is shown that the level of radio emission
associated with an elliptical galaxy during the radio-loud phase is related to
the presence of large amounts of isophotal twist in its optical image. In
particular, radio galaxies with P_408 > 3 x 10^{25} W/Hz appear to show a
preference to be associated with elliptical hosts exhibiting an isophotal twist
in excess of ~20 degrees.


title: Searches for high redshift galaxies using gravitational lensing

abstract:
  We present different methods used to identify high redshift (z>5) objects in
the high-magnification regions of lensing galaxy clusters, taking advantage of
very well constrained lensing models. The research procedures are explained and
discussed. The detection of emission lines in the optical/NIR spectra, such as
Lyman-alpha, allows us to determine the redshift of these sources. Thanks to
the lensing magnification, it is possible to identify and to study more distant
or intrinsically fainter objects with respect to standard field surveys.


title:
Photorecombination and Photoionization Experiments at Heavy-Ion
  Storage-Rings and Synchrotron-Light Sources

abstract:
  Recent experimental work on the photorecombination and the photoionization of
astrophysically relevant atomic ions employing the merged-beams technique at
heavy-ion storage-rings and synchrotron-light sources, respectively, is
summarized. The resulting absolute photoionization cross sections and
recombination rate coefficients benchmark corresponding theoretical
calculations and are needed for the accurate determination of ionization
equilibria in astrophysical plasmas.


title:
The Mass Function of Super Giant Molecular Complexes and Implications
  for Forming Young Massive Star Clusters in the Antennae (NGC 4038/39)

abstract:
  We have used previously published observations of the CO emission from the
Antennae (NGC 4038/39) to study the detailed properties of the super giant
molecular complexes with the goal of understanding the formation of young
massive star clusters. Over a mass range from 5E6 to 9E8 solar masses, the
molecular complexes follow a power-law mass function with a slope of -1.4 +/-
0.1, which is very similar to the slope seen at lower masses in molecular
clouds and cloud cores in the Galaxy. Compared to the spiral galaxy M51, which
has a similar surface density and total mass of molecular gas, the Antennae
contain clouds that are an order of magnitude more massive. Many of the
youngest star clusters lie in the gas-rich overlap region, where extinctions as
high as Av~100 imply that the clusters must lie in front of the gas. Combining
data on the young clusters, thermal and nonthermal radio sources, and the
molecular gas suggests that young massive clusters could have formed at a
constant rate in the Antennae over the last 160 Myr and that sufficient gas
exists to sustain this cluster formation rate well into the future. However,
this conclusion requires that a very high fraction of the massive clusters that
form initially in the Antennae do not survive as long as 100 Myr. Finally, we
compare our data with two models for massive star cluster formation and
conclude that the model where young massive star clusters form from dense cores
within the observed super giant molecular complexes is most consistent with our
current understanding of this merging system. (abbreviated)


title: Blue Horizontal Branch Stars in the Sagittarius dwarf spheroidal galaxy

abstract:
  We report on the recovery of a Blue Horizontal Branch (BHB) population
belonging to the Sagittarius Dwarf Spheroidal Galaxy (Sgr). The sequence is
clearly identified in the (V, V-I) Color Magnitude Diagram (CMD) obtained for
about 500,000 stars in the region of the globular cluster M~54. The BHB
morphology is similar to the analogous sequence in M~54, but it is
unambiguously associated with Sgr since {\it(i)} it is detected well outside
the main body of the cluster, up to more than 5 tidal radii from the cluster
center and {\it(ii)} the BHB stars follow the radial distribution of the other
stellar populations of Sgr. This finding finally demonstrates that the Sgr
galaxy hosts a significant (of the order of $\sim$10%) old and metal-poor
stellar population ([Fe/H]\ltsima -1.3; age \gtsima 10 Gyr), similar to that of
its oldest clusters (M~54, Ter~8). We also show that the Sgr BHB sequence found
here is the counterpart of the analogous feature observed by Newberg et al.
(2002) in the Sgr Stream, in a field more than 80$\degr$ away from the center
of the galaxy.


title: A High Relative-Precision Color-Magnitude Diagram of M67

abstract:
  We have calibrated an extensive set of BVI observations of M67. We have
selected stars that are most likely to be single-star members of the cluster
using proper motion, radial velocity, and variability information from the
literature, and an examination of the most probable color-magnitude diagram
locations of unresolved stellar blends. Observations of M67 turnoff stars are a
severe test of algorithms attempting to describe convective cores in the limit
of small extent, and we find strong evidence of a ``hook'' just fainter than
the turnoff gap. The stars in M67 support assertions that the degree of
convective core overshooting decreases to zero for stars with masses in the
range 1.0 < (M / M_sun) < 1.5, but that the degree of overshoot is smaller than
currently used in published isochrones. We also verify that all current
theoretical models for the lower main sequence (with the exception of Baraffe
et al. 1998) are too blue for M_V >~ 6 even when the sequences are shifted to
match M67 near the M_V of the Sun, probably due to a combination of problems
with color-T_eff transformations and realistic surface boundary conditions for
models. Finally, we identify a subset of cluster members with unusual
photometry (candidate red giant binaries, blue straggler stars, and triple
systems) deserving of further study.


title: The Last Hurrah: PPN Formation by a Magnetic Explosion

abstract:
  We discuss a mechanism by which a giant star can expel its envelope in an
outburst, leaving its core exposed. The outburst is powered by rotational
kinetic energy of the core, transferred to the envelope via the twisting of
magnetic fields. We show that, if the core is magnetized, and if it has
sufficient angular momentum, this mechanism may be triggered at the end of the
asymptotic giant branch phase, and drive a proto-planetary nebula (pPN)
outflow. This explosion of magnetic energy self-consistently explains some of
the asymmetries and dynamics of pPNe.


title: New Hipparcos-based Parallaxes for 424 Dim Stars

abstract:
  We present a catalog of 424 common proper motion companions to Hipparcos
stars with good (>3 sigma) parallaxes, thereby effectively providing new
parallaxes for these companions. Compared to stars in the Hipparcos catalog,
these stars are substantially dimmer. The catalog includes 20 WDs and an
additional 29 stars with M_V>14, the great majority of the latter being M
dwarfs.


title: High altitude wind velocity at San Pedro Martir and Mauna Kea

abstract:
  We analyze the monthly average wind velocity at about 12 km above sea level,
between 1980 to 1995, for San Pedro Martir, Mauna Kea, another existing
observatorie and some sites of interest. We compare the results obtained from
two different data sets, the GGUAS and NCEP. Our results show that San Pedro
Martir and Mauna Kea are comparable and are amongst the most suitable sites to
apply slow wavefront corrugation correction techniques


title:
High Resolution Images of Orbital Motion in the Trapezium Cluster: First
  Scientific Results from the MMT Deformable Secondary Mirror Adaptive Optics
  System

abstract:
  We present the first scientific images obtained with a deformable secondary
mirror adaptive optics system. We utilized the 6.5m MMT AO system to produce
high-resolution (FWHM=0.07'') near infrared (1.6 um) images of the young (~1
Myr) Orion Trapezium theta 1 Ori cluster members. A combination of high spatial
resolution and high signal to noise allowed the positions of these stars to be
measured to within ~0.003'' accuracies. Including previous speckle data
(Weigelt et al. 1999), we analyze a six year baseline of high-resolution
observations of this cluster. Over this baseline we are sensitive to relative
proper motions of only ~0.002''/yr (4.2 km/s at 450 pc). At such sensitivities
we detect orbital motion in the very tight theta 1 Ori B2B3 (52 AU separation)
and theta 1 Ori A1A2 (94 AU separation) systems. Such motions are consistent
with those independently observed by Schertl et al. (2003) with speckle
interferometry, giving us confidence that these very small (~0.002''/yr)
orbital motions are real. All five members of the theta 1 Ori B system appear
likely gravitationally bound. The very lowest mass member of the theta 1 Ori B
system (B4) has K' ~11.66 and an estimated mass of ~0.2 Msun. There was very
little motion (4+/-15 km/s) detected of B4 w.r.t B1 or B2, hence B4 is possibly
part of the theta 1 Ori B group. We suspect that if this very low mass member
is physically associated it most likely is in an unstable (non-hierarchical)
orbital position and will soon be ejected from the group. The theta 1 Ori B
system appears to be a good example of a star formation ``mini-cluster'' which
may eject the lowest mass members of the cluster in the near future. This
``ejection'' process could play a major role in the formation of low mass stars
and brown dwarfs.


title: The AST/RO Survey of the Galactic Center Region

abstract:
  AST/RO is a 1.7m diameter submillimeter-wave telescope at the geographic
South Pole. A key AST/RO project is the mapping of C I and CO J=4-3 and J=7-6
emission from the inner Milky Way (Martin et al. 2003). These data are released
for general use.


title:
The Case for a 30m Diameter Submillimeter Telescope on the Antarctic
  Plateau

abstract:
  A large single-dish submillimeter-wave telescope equipped with a focal plane
array containing ~10^4 bolometers and costing about $120M could locate most
protogalaxies in the southern sky within a year of operation.


title: High-resolution optical studies of nearby Type Ia supernovae

abstract:
  Since April 2000, a program using the ESO/VLT/UVES to search for early
circumstellar signatures from nearby supernovae has been conducted. Until now,
two Type Ia supernovae have been observed, SNe 2000cx and 2001el. Here we
report on preliminary results for SNe 2001el, and we discuss how the
observations can be used together with detailed modeling to derive an upper
limit on the putative wind from the progenitor system. For a hydrogen-rich wind
with velocity 10 km/s, the mass loss rate for the progenitor system of SN
2001el is less than 1O^{-5} solar masses per year.


title:
2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary
  Sequence

abstract:
  We present model spectral energy distributions, colors, polarization, and
images for an evolutionary sequence of a low-mass protostar from the early
collapse stage (Class 0) to the remnant disk stage (Class III). We find a
substantial overlap in colors and SEDs between protostars embedded in envelopes
(Class 0-I) and T Tauri disks (Class II), especially at mid-IR wavelengths.
Edge-on Class I-II sources show double-peaked spectral energy distributions,
with a short-wavelength hump due to scattered light and the long-wavelength
hump due to thermal emission. These are the bluest sources in mid-IR
color-color diagrams.
  Since Class 0 and I sources are diffuse, the size of the aperture over which
fluxes are integrated has a substantial effect on the computed colors, with
larger aperture results showing significantly bluer colors. This causes overlap
in color-color diagrams between all evolutionary states, especially in the
mid-IR. However the near-IR polarization of the Class 0 sources is much higher
than the Class I-II sources, providing a means to separate these evolutionary
states.
  We varied the grain properties in the circumstellar envelope, allowing for
larger grains in the disk midplane and smaller in the envelope. We find that
grain growth in disks of Class I sources can be detected at wavelengths greater
than 100 $\mu$m.
  Our image calculations predict that the diffuse emission from edge-on Class I
and II sources should be detectable in the mid-IR with the Space Infrared
Telescope Facility (SIRTF) in nearby star forming regions (out to several
hundred parsecs).


title: The Race to Build Supermassive Black Holes

abstract:
  The high redshifts of the most distant known quasars, and the best estimates
of their black hole masses, require that supermassive black holes (SMBHs) must
have formed very early in history. Several mechanisms for creating and growing
these holes have been proposed. Here we present an evaluation of the timescales
needed for various critical processes in order to discriminate between the
proposed scenarios. We find in particular that mergers alone are not able to
grow the black holes at a sufficient rate. Accretion models offer a solution
and we use accretion timescales to constrain the manner in which the black hole
was first formed. This analysis implies, but does not require, the action of
some unconventional process.


title: Tycho Brahe's supernova: light from centuries past

abstract:
  The light curve of SN 1572 is described in the terms used nowadays to
characterize SNeIa. By assembling the records of the observations done in
1572--74 and evaluating their uncertainties, it is possible to recover the
light curve and the color evolution of this supernova. It is found that, within
the SNe Ia family, the event should have been a SNIa with a normal rate of
decline, its stretch factor being {\it s} $\sim$ 0.9. Visual light curve near
maximum, late--time decline and the color evolution sustain this conclusion.
After correcting for extinction, the luminosity of this supernova is found to
be M$_{V}$ $=$ --19.58 --5 log (D/3.5 kpc) $\pm$ 0.42.


title:
On total inelastic cross-sections and the average depth of the maximum
  of extensive air showers

abstract:
  The model dependence of the development of extensive air showers generated by
high-energy cosmic-ray particles in the atmosphere is studied. The increase of
proton-proton and proton-air inelastic cross-sections and values for the
elasticity are varied in the hadronic interaction model QGSJET. Using the
CORSIKA simulation program, the impact of these changes is investigated on air
shower observables like the average depth of the shower maximum X_max and the
number of muons and electrons at ground level. Calculating the mean logarithmic
mass from experimental X_max values, it is found that a moderate logarithmic
increase of the proton-proton inelastic cross-section from sigma_pp^inel=51 mb
at E_0=10^6 GeV to sigma_pp^inel=64 mb at E_0=10^8 GeV and an elasticity,
additionally increased by 10% to 15%, describes the data best. Using these
parameters, the mean logarithmic mass lna derived from X_max measurements is
compatible with the extrapolations of the results of direct measurements to
high energies using the poly-gonato model.


title: Mass loss predictions for Subdwarf B stars

abstract:
  We present the results of Monte Carlo mass-loss predictions for hot low-mass
stars, specifically for Subdwarf B (SdB) stars. It is shown that the mass-loss
rates on the Horizontal Branch (HB) computed from radiative line-driven wind
models are not high enough to create SdB stars. We argue, however, that the
mass loss plays a role in the chemical abundance patterns observed both in
field SdB stars, as well as in cluster HB stars. The derived mass loss recipe
for these (extremely) hot HB stars may also be applied to other groups of hot
low-mass stars, such as post-HB (AGB-manque, UV-bright) stars, over a range in
effective temperatures between 10000 and 50000 Kelvin. Finally, we present
preliminary spectral synthesis on the more luminous SdB stars for which
emission cores in Halpha have been detected (Heber et al. 2002). We find that
these line profiles can indeed be interpreted as the presence for a stellar
wind with mass loss of the order of log(Mdot) = -11 (Msun/year).


title: Kinematically quiet halos around z~2.5 radio galaxies. Keck spectroscopy

abstract:
  We present the results of the kinematic study of the extended gas in a sample
of 10 high redshift radio galaxies (z~2.5) based on high signal to noise Keck
II and VLT long slit spectroscopy. In addition to the typical high surface
brightness kinematically perturbed regions (FWHM and velocity shifts >1000
km/s), we find in all objects giant low surface brightness halos which show
quieter kinematics with typical emission line FWHM and velocity shifts of
\~several hundred km/s. The giant halos often extend for more than 100 kpc and
sometimes beyond the radio structures. Their emission line specta are typical
of high redshift active galaxies. Continuum is also often detected. The halos
are enriched with heavy elements at tens of kpc from the active nucleus. The
quasar continuum is the dominant source of ionization of the quiescent halos
along the radio axis. The detection of giant quiescent halos in all objects
suggests that they could be a common ingredient of high redshift radio
galaxies. The radio galaxies seem to be embedded within the halos. The nature,
origin of the halos and the cosmological implications are also discussed.


title: Thermonuclear supernova explosions and their remnants: the case of Tycho

abstract:
  We propose to use the thermal X-ray emission from young supernova remnants
(SNRs) originated in Type Ia supernovae (SNe) to extract relevant information
concerning the explosion mechanism. We focus on the differences between
numerical 1D and 3D explosion calculations, and the impact that these
differences could have on young SNRs. We use the remnant of the Tycho supernova
(SN 1572) as a test case to compare with our predictions, discussing the
observational features that allow to accept or discard a given model.


title:
Structure of pair winds from compact objects with application to
  emission from hot bare strange stars

abstract:
  We consider a stationary, spherically outflowing wind consisting of
electron-positron pairs and photons. We do not assume thermal equilibrium, and
include the two-body processes that occur in such a wind: Moller and Bhaba
scattering of pairs, Compton scattering, two-photon pair annihilation, and
two-photon pair production, together with their radiative three-body variants:
bremsstrahlung, double Compton scattering, and three-photon pair annihilation,
with their inverse processes. In the concrete example described here, the wind
injection source is a hot, bare, strange star. Such stars are thought to be
powerful sources of pairs created by the Coulomb barrier at the quark surface.
We present a new, finite-difference scheme for solving the relativistic kinetic
Boltzmann equations for pairs and photons. Using this method we study the
kinetics of the wind particles and the emerging emission for total luminosities
of L=10^{34}-10^{42} ergs/s. We find the rates of particle number and energy
outflows, outflow velocities, number densities, energy spectra, and other
parameters for both photons and pairs as functions of the distance. We find
that for L>2x10^{35} ergs/s, photons dominate the emerging emission. As L
increases from ~ 10^{34} to 10^{42} ergs/s, the mean energy of emergent photons
decreases from ~400-500 keV to 40 keV, as the spectrum changes in shape from
that of a wide annihilation line to nearly a blackbody spectrum with a high
energy (> 100 keV) tail. These results are pertinent to the deduction of the
outside appearance of hot bare strange stars, which might help discern them
from neutron stars.


title: Time-dependent thermal effects in GRB afterglows

abstract:
  Time-dependent thermal effects should accompany standard non-thermal
afterglows of GRB when gamma-rays pass through inhomogeneous surroundings of
the GRB site. Thermal relaxation of an optically thin plasma is calculated
using time-dependent collisional ionization of the plasma ion species. X-ray
emission lines are similar to those found in the fading X-ray afterglow of GRB
011211. Thermal relaxation of clouds or shells around the GRB site could also
contribute to the varying late optical GRB afterglows, such as in GRB021004 and
GRB030329.


title:
Increase of the Hawking radiation for spinor particles from
  Schwarzschild black holes by Dirac monopoles

abstract:
  An algorithm for numerical computation of the barrier transparency for the
potentials surrounding Schwarzschild black holes is described for massless
spinor particles. It is then applied to calculate the all configurations
(including the contributions of twisted field configurations connected with
Dirac monopoles) luminosity for the Hawking radiation from a Schwarzschild
black hole. It is found that the contribution due to monopoles can be of order
22 % of the all configurations luminosity.


title:
Probing the presence of a single or binary black hole in the globular
  cluster NGC 6752 with pulsar dynamics

abstract:
  The five millisecond pulsars that inhabit NGC 6752 display locations or
accelerations that are quite unusual compared to all other pulsars known in
globular clusters. In particular PSR-A, a binary pulsar, lives in the cluster
halo, while PSR-B and PSR-E, located in the core, show remarkably high negative
spin derivatives. This is suggestive that some uncommon dynamical process is at
play in the cluster core that we attribute to the presence of a massive
perturber. We here investigate whether a single intermediate-mass black hole,
lying on the extrapolation of the Mass versus Sigma relation observed in galaxy
spheroids, or a less massive binary consisting of two black holes could play
the requested role. To this purpose we simulated binary-binary encounters
involving PSR-A, its companion star, and the black hole(s). Various scenarios
are discussed in detail. In our close 4-body encounters, a black hole-black
hole binary may attract on a long-term stable orbit a millisecond pulsar.
Timing measurements on the captured satellite-pulsar, member of a hierarchical
triplet, could unambiguously unveil the presence of a black hole(s) in the core
of a globular cluster.


title: Triggered massive-star formation at the border of the HII region Sh 104

abstract:
  We present millimetre-line imaging of the Galactic HII region Sh 104. We show
that it is surrounded by a ring of molecular gas and dust. Four large molecular
condensations are regularly spaced around the ring. These condensations are
themselves fragmented and contain several massive dense cores. A deeply
embedded cluster is observed in the near IR towards the largest condensation.
It contains at least one massive star ionizing an ultra-compact HII region. The
Sh 104 region is a good illustration of the `collect and collapse' model for
star formation triggered by the expansion of an HII region.


title: XMM-Newton discovery of an X-ray filament in Coma

abstract:
  XMM-Newton observations of the outskirts of the Coma cluster of galaxies
confirm the existence of a soft X-ray excess claimed previously and show it
comes from warm thermal emission. Our data provide a robust estimate of its
temperature (~0.2 keV) and oxygen abundance (~0.1 solar). Using a combination
of XMM-Newton and ROSAT All-Sky Survey data, we rule out a Galactic origin of
the soft X-ray emission. Associating this emission with a 20 Mpc region in
front of Coma, seen in the skewness of its galaxy velocity distribution, yields
an estimate of the density of the warm gas of ~50 f_baryon rho_critical, where
f_baryon is the baryon fraction of the gas and rho_critical is the critical
density needed to halt the expansion of the universe. Our measurement of the
gas mass associated with the warm emission strongly support its nonvirialized
nature, suggesting that we are observing the warm-hot intergalactic medium
(WHIM). Our measurements provide a direct estimate of the O, Ne and Fe
abundance of the WHIM. Differences with the reported Ne/O ratio for some OVI
absorbers hints at a different origin of the OVI absorbers and the Coma
filament. We argue that the Coma filament has likely been preheated, but at a
substantially lower level compared to what is seen in the outskirts of groups.
The thermodynamic state of the gas in the Coma filament reduces the
star-formation rate in the embedded spiral galaxies, providing an explanation
for the presence of passive spirals observed in this and other clusters.


title: Galaxy Disruption in a Halo of Dark Matter

abstract:
  The relics of disrupted satellite galaxies around the Milky Way and Andromeda
have been found, but direct evidence of a satellite galaxy in the early stages
of being disrupted has remained elusive. We have discovered a dwarf satellite
galaxy in the process of being torn apart by gravitational tidal forces as it
merges with a larger galaxy's dark matter halo. Our results illustrate the
morphological transformation of dwarf galaxies by tidal interaction and the
continued build-up of galaxy halos.


title:
Proton capture elements in the globular cluster NGC 2808 I. First
  detection of large variations in Sodium abundances along the Red Giant Branch

abstract:
  We have used spectra obtained as part of the Science Verification program of
the FLAMES multi-object spectrograph mounted on Kueyen (VLT-UT2) to perform an
abundance analysis of stars along the giant branch (RGB) in the globular
cluster NGC 2808. Sodium abundances are derived from Na D lines for a sample of
81 cluster stars spanning a range of about 2 magnitudes from the tip of the
RGB. Our results show that a large star-to-star scatter does exist at all
positions along the RGB, suggesting large variations in the abundance of proton
capture elements down to luminosities comparable to the red horizontal branch
(HB). The distribution of Na abundances along the RGB seems to point out that
in this cluster most of the observed spread has a primordial origin.
Overimposed evolutionary effects, if any, must be only at ``noise'' level, at
odds with results from a similar analysis in M 13 (Pilachowski et al. 1996).
This study is a first step towards ascertaining if a link exists between the
distribution of chemical anomalies in light elements along the RGB and the
global properties of globular clusters, in particular the HB morphology.


title:
On a Separatrix in the Gravitational Collapse to an Overcritical
  Electromagnetic Black Hole

abstract:
  The dynamical properties of an electron--positron--photon plasma created by
the vacuum polarization process occurring around a charged gravitationally
collapsing core of an initially neutral star are examined within the framework
of General Relativity and Quantum Field Theory. The Reissner--Nordstr\"{o}m
geometry is assumed to apply between the collapsing core and the oppositely
charged remnant of the star. The appearance of a separatrix at radius
$\bar{R}$, well outside the asymptotic approach to the horizon, is evidenced.
The neutral electron--positron--photon plasma created at radii $r>\bar{R}$
self-propels outwards to infinity, following the classical PEM--pulse analysis.
The plasma created at $r<\bar{R}$ remains trapped and follows the gravitational
collapse of the core only contributing to the reduction of the electromagnetic
energy of the black hole and to the increase of its irreducible mass. This
phenomenon has consequences for the observational properties of gamma--ray
bursts and is especially relevant for the theoretical prediction of the
temporal and spectral structure of the short bursts.


title: Fe II lifetimes and transition probabilities

abstract:
  Fe II radiative lifetimes were measured applying the time-resolved nonlinear
laser-induced fluoresence technique. We investigated 21 levels of up to 47000
1/cm. The uncertainties are typically 2-3%. The lifetimes provide an improved
absolute scale to our branching fractions which were measured with a Fourier
transform spectrometer and a high-resolution grating spectrometer and which
have been published earlier. We report absolute transition probabilities of 140
Fe II lines in the wavelength range 220-780 nm. The overall uncertainties are
estimated to be 6% for the strong and up to 26% for the weak transitions. The
results are compared with recent experimental data from the literature. Our
large set of accurate data can be used for a reliability check of theoretical
data calculated for iron abundances in astrophysical plasmas.


title: Jovian Dust Streams: A monitor of Io's volcanic plume activity

abstract:
  Streams of high speed dust particles originate from Jupiter's innermost
Galilean moon Io. After release from Io, the particles collect electric charges
in the Io plasma torus, gain energy from the co-rotating electric field of
Jupiter's magnetosphere, and leave the Jovian system into interplanetary space
with escape speeds over $\rm 200 km s^{-1}$. Galileo, which was the first
orbiter spacecraft of Jupiter, has continuously monitored the dust streams
during 34 revolutions about the planet between 1996 and 2002. The observed dust
fluxes exhibit large orbit-to-orbit variability due to systematic and
stochastic changes. After removal of the systematic variations, the total dust
emission rate of Io has been calculated. It varies between $10^{-3}$ and
$\mathrm{10} \rm kg s^{-1}$, and is typically in the range of 0.1 to $\rm 1 kg
s^{-1}$. We compare the dust emission rate with other markers of volcanic
activity on Io like large-area surface changes caused by volcanic deposits and
sightings of volcanic plumes.


title:
A study of Complexity in Gamma Ray Burst using the Diffusion Entropy
  Approach

abstract:
  The Diffusion Entropy algorithm is a method that allows the study of
correlated non stationary time series and allows the discrimination between
signal and uncorrelated noise. DE provides a quantitative measure of the
complexity by means of a scaling index delta. The aim of this paper is to apply
this method to study and statistically characterize Gamma-Ray Burst light
curves and to introduce a method to constrain and test GRB models.


title:
Three-dimensional simulations of the interstellar medium in dwarf
  galaxies - I. Ram pressure stripping

abstract:
  We present 3D hydrodynamic simulations of ram pressure stripping in dwarf
galaxies. Analogous studies on this subject usually deal with much higher ram
pressures, typical of galaxy clusters, or mild ram pressure due to the gas halo
of the massive galactic companions. We extend over previous investigations by
considering flattened, rotating dwarf galaxies subject to ram pressures typical
of poor galaxy groups.
  We study the ram pressure effects as a function of several parameters such as
galactic mass and velocity, ambient gas density, and angle between the galactic
plane and the direction of motion. It turns out that this latter parameter
plays a role only when the gas pressure in the galactic centre is comparable to
the ram pressure. Despite the low values of the ram pressure, some dwarf
galaxies can be completely stripped after 1-2 hundred of million years. This
pose an interesting question on the aspect of the descents and, more in
general, on the morphological evolution of dwarf galaxies. In cases in which
the gas is not completely stripped, the propagation of possible galactic wind
may be influenced by the disturbed distribution of the interstellar matter.
  We also consider the modification of the ISM surface density induced by the
ram pessure and find that the resulting compression may trigger star formation
over long time spans.


title: Cosmic Physics: The High Energy Frontier

abstract:
  Cosmic rays have been observed up to energies $10^8$ times larger than those
of the best particle accelerators. Studies of astrophysical particles (hadrons,
neutrinos and photons) at their highest observed energies have implications for
fundamental physics as well as astrophysics. Thus, the cosmic high energy
frontier is the nexus to new particle physics. This overview discusses recent
advances being made in the physics and astrophysics of cosmic rays and cosmic
gamma-rays at the highest observed energies as well as the related physics and
astrophysics of very high energy cosmic neutrinos. These topics touch on
questions of grand unification, violation of Lorentz invariance, as well as
Planck scale physics and quantum gravity.


title: High-Energy Spectra from Black-Hole Candidates

abstract:
  Our knowledge of the high-energy emission spectra from black-hole candidates
has increased enormously with missions like BeppoSAX and RossiXTE, thanks to
their broad-band window. I present the main and most solid points of this
current knowledge, both in terms of detailed spectral modeling of X-ray
broad-band spectra, and more generally in relation to the "black-hole state
paradigm", which links spectral and timing properties of accretion disks.
Finally, through the discussion of recent results on two systems, XTE J1650-500
and GX 339-4, I present evidence for a new view of the state paradigm.


title: Thin Disk Models of Anomalous X-ray Pulsars

abstract:
  We discuss the options of the fall-back disk model of Anomalous X-Ray Pulsars
(AXPs). We argue that the power-law index of the mass inflow rate during the
propeller stage can be lower than those employed in earlier models. We take
into account the effect of the super-critical mass inflow at the earliest
stages on the inner radius of the disk and argue that the system starts as a
propeller. Our results show that, assuming a fraction of the mass inflow is
accreted onto the neutron star, the fall-back disk scenario can produce AXPs
for acceptable parameters.


title: Synoptic study of the SMC SNRs using XMM-Newton

abstract:
  We present a detailed X-ray spectral analysis of 13 supernova remnants (SNR)
in the Small Magellanic Cloud (SMC). We apply both single-temperature
non-equilibrium ionisation models and models based on the Sedov similarity
solution, where applicable. We also present detailed X-ray images of individual
SNRs, which reveal a range of different morphological features. Eight remnants,
viz DEM S 32, IKT 2, HFPK 419, IKT 6, IKT 16, IKT 18 and IKT 23, are consistent
with being in their Sedov evolutionary phase. IKT 6 and IKT 23 both have a
clear shell like morphology with oxygen-rich X-ray emitting material in the
centre. We draw attention to similarities between these two remnants and the
well studied, oxygen-rich remnant IKT 22 (SNR 0102-72.3) and propose that they
are more evolved versions of IKT 22. IKT 4, IKT 5, DEM S 128 and IKT 5 are
evolved remnants which are in, or in the process of entering, the radiative
cooling stage. We argue that the X-ray emission from these four remnants is
most likely from the ejecta remains of type Ia SNe. Our modeling allow us to
derive estimates for physical parameters, such as densities, ages, masses and
initial explosion energies. Our results indicate that the average SMC hydrogen
density is a factor of ~6 lower as compared to the Large Magellanic Cloud. This
has obvious implications for the evolution and luminosities of the SMC SNRs. We
also estimate the average SMC gas phase abundances for the elements O, Ne, Mg,
Si and Fe.


title:
Excitation of oscillation modes by tides in close binaries: constraints
  on stellar and orbital parameters

abstract:
  The parameter space favourable for the resonant excitation of free
oscillation modes by dynamic tides in close binary components is explored using
qualitative considerations to estimate the order of magnitude of the tidal
force and the frequency range covered by the tidally induced oscillations. The
investigation is valid for slowly rotating stars with masses in the interval
between 2 and 20 solar masses, and an evolutionary stage ranging from the
beginning to the end of the main sequence. Oscillation modes with
eigenfrequencies of the order of five times the inverse of the star's dynamical
time scale - i.e. the lowest-order p-modes, the f-mode, and the lowest-order
g-modes - are found to be outside the favourable parameter space since their
resonant excitation requires orbital eccentricities that are too high for the
binary to stay detached when the components pass through the periastron of
their relative orbit. Resonances between dynamic tides and g-modes with
frequencies of the order of half of the inverse of the star's dynamical time
scale on the other hand are found to be favourable for orbital periods up to
200 times the star's dynamical time scale, provided that the binary mass ratio
q is larger than 1/3 and the orbital eccentricity e is larger than
approximately 0.25. This favourable range comes down to orbital periods of up
to 5-12 days in the case of 2-20 solar mass zero-age main-sequence binary
components, and orbital periods of up to 21-70 days in the case of terminal
main-sequence binary components.


title:
The covariance of cosmic shear correlation functions and cosmological
  parameter estimates using redshift information

abstract:
  Cosmological weak lensing by the large scale structure of the Universe,
cosmic shear, is coming of age as a powerful probe of the parameters describing
the cosmological model and matter power spectrum. It complements CMB studies,
by breaking degeneracies and providing a cross-check. An important measure of
the cosmic shear signal are the shear correlation functions; these can be
directly calculated from data, and compared with theoretical expectations for
different cosmological models and matter power spectra. We present a Monte
Carlo method to quickly simulate mock cosmic shear surveys. One application of
this method is in the determination of the full covariance matrix for the
correlation functions; this includes redshift binning and is applicable to
arbitrary survey geometries. Terms arising from shot noise and cosmic variance
(dominant on small and large scales respectively) are accounted for naturally.
As an illustration of the use of such covariance matrices, we consider to what
degree confidence regions on parameters are tightened when redshift binning is
employed. The parameters considered are those commonly discussed in cosmic
shear analyses - the matter density parameter, dark energy density parameter
(classical cosmological constant), power spectrum normalisation and shape
parameter. We incorporate our covariance matrices into a likelihood treatment,
and also use the Fisher formalism to explore a larger region of parameter space
(abridged).


title:
Numerical Examination of the Stability of an Exact Two-dimensional
  Solution for Flux Pile-up Magnetic Reconnection

abstract:
  The Kelvin--Helmholtz (KH) and tearing instabilities are likely to be
important for the process of fast magnetic reconnection that is believed to
explain the observed explosive energy release in solar flares. Theoretical
studies of the instabilities, however, typically invoke simplified initial
magnetic and velocity fields that are not solutions of the governing
magnetohydrodynamic (MHD) equations. In the present study, the stability of a
reconnecting current sheet is examined using a class of exact global MHD
solutions for steady state incompressible magnetic reconnection, discovered by
Craig & Henton. Numerical simulation indicates that the outflow solutions where
the current sheet is formed by strong shearing flows are subject to the KH
instability. The inflow solutions where the current sheet is formed by a fast
and weakly sheared inflow are shown to be tearing unstable. Although the
observed instability of the solutions can be interpreted qualitatively by
applying standard linear results for the KH and tearing instabilities, the
magnetic field and plasma flow, specified by the Craig--Henton solution, lead
to the stabilization of the current sheet in some cases. The sensitivity of the
instability growth rate to the global geometry of magnetic reconnection may
help in solving the trigger problem in solar flare research.


title: The Grandeur of Massive Star Formation Revealed with ISAAC

abstract:
  We present selected results from our ongoing investigation of high-mass
star-forming regions which are based on infrared observations with ESO's ISAAC
camera at the 8.2-m ANTU VLT telescope. Although these young stellar objects
comprise a high degree of complexity, our data enable us to disentangle these
crowded regions. By means of broad- and narrow-band imaging between 1 - 5
micron we performed a thorough characterisation of the embedded population.
Special emphasis was put on the importance of an accurate astrometry which has
a major impact on the interpretation of the data. In the case of G9.62+0.19, we
clarified the true nature of the infrared emission in the immediate vicinity of
an hot molecular core (HMC). We unveil the counterpart of this HMC in the
thermal infrared. For GGD27 IRS2, we found thermal emission at 3.8 and 4.7
micron caused by a deeply embedded object that is powering a large radio jet
and has counterparts in our mid-infrared and VLA 7-mm data. The presented
results mark a further step on the way to disclose the mechanisms of massive
star formation. They demonstrate the value of sensitive infrared imaging with
the current generation of IR cameras on 8-m-class telescopes.


title: An Observational Diagnostic for Ultraluminous X-Ray Sources

abstract:
  We consider observational tests for the nature of Ultraluminous X-ray sources
(ULXs). These must distinguish between thermal-timescale mass transfer on to
stellar-mass black holes leading to anisotropic X-ray emission, and accretion
on to intermediate-mass black holes. We suggest that long-term transient
behavior via the thermal-viscous disk instability could discriminate between
these two possibilities for ULXs in regions of young stellar populations.
Thermal-timescale mass transfer generally produces stable disks and persistent
X-ray emission. In contrast, mass transfer from massive stars to black holes
produces unstable disks and thus transient behavior, provided that the black
hole mass exceeds some minimum value. This minimum mass depends primarily on
the donor mass and evolutionary state. We show that it exceeds 50 solar masses
for a large fraction (greater than 90%) of the mass-transfer lifetime for the
most likely donors in young clusters. Thus if long-term monitoring reveals a
large transient fraction among ULXs in a young stellar population, these
systems would be good candidates for intermediate-mass black holes in a
statistical sense; information about the donor star is needed to make this
identification secure in any individual case. A transient ULX population would
imply a much larger population of quiescent systems of the same type.


title:
Advanced Camera for Surveys Photometry of the Cluster RDCS1252.9-2927:
  The Color-Magnitude Relation at z=1.24

abstract:
  We investigate the color-magnitude (CM) relation of galaxies in the distant
X-ray selected cluster RDCS1252.9-2927 at z=1.24 using images obtained with the
Advanced Camera for Surveys (ACS) on the Hubble Space Telescope in the F775W
and F850LP bandpasses. We select galaxies based on morphological
classifications extending about 3.5 mag down the galaxy luminosity function,
augmented by spectroscopic membership information. At the core of the cluster
is an extensive early-type galaxy population surrounding a central pair of
galaxies that show signs of dynamical interaction. The early-type population
defines a tight sequence in the CM diagram, with an intrinsic scatter in
observed (i-z) of $0.029\pm0.007$ mag based on 52 galaxies, or $0.024\pm0.008$
mag for $\sim30$ ellipticals. Simulations using the latest stellar population
models indicate an age scatter for the ellipticals of about 34%, with a mean
age $\taul\gta2.6$ Gyr (corresponding to $z_L\gta2.7$), and the last star
formation occurring at $z_{end}\gta1.5$. Transforming to rest-frame $(U-B)$, we
conclude that the slope and scatter in the CM relation for morphologically
selected early-type galaxies show little or no evidence for evolution out to
$z\approx1.2$. Thus, elliptical galaxies were already well established in X-ray
luminous clusters when the universe was a third of its present age.


title: Disks and Halos in Pre-Main-Sequence Stars

abstract:
  We study the IR emission from flared disks with and without additional
optically thin halos. Flux calculations of a flared disk in vacuum can be
considered a special case of the more general family of models in which the
disk is imbedded in an optically thin halo. In the absence of such halo, flux
measurements can never rule out its existence because the disk flaring surface
defines a mathematically equivalent halo that produces the exact same flux at
all IR wavelengths. When a flared disk with height H at its outer radius R is
imbedded in a halo whose optical depth at visual wavelengths is \tau\sub{halo},
the system IR flux is dominated by the halo whenever \tau\sub{halo} > (1/4)H/R.
Even when its optical depth is much smaller, the halo can still have a
significant effect on the disk temperature profile. Imaging is the only way to
rule out the existence of a potential halo, and we identify a decisive test
that extracts a signature unique to flared disks from imaging observations.


title:
Compton drag as a mechanism for very high linear polarization in
  Gamma-Ray Bursts

abstract:
  The recent claim by Coburn & Boggs to have detected a very high degree of
linear polarization in the prompt emission of GRB 021206 has stimulated
interest in how much polarization could arise in gamma-ray bursts from
synchrotron emission. Alternatively, as Shaviv & Dar have shown, GRB
polarization could be produced by inverse Compton scattering in the
point-source limit. We discuss polarization from a fireball that upscatters a
soft radiation field. We show that, after the proper angular integration, the
residual polarization can be large, in some cases approaching the point-source
limit. We discuss the probability of realizing the geometrical conditions in
which a large polarization is obtained showing that, for a particularly bright
burst as GRB 021206, the detection of polarization at the first attempt in the
Compton drag scenario is not unlikely.


title:
Observing the Formation of the Hubble Sequence in the Great
  Observatories Origins Deep Survey

abstract:
  Understanding the physical formation of the Hubble sequence remains one of
the most important unsolved astrophysical problems. Searches for proto-disks
and proto-ellipticals can now be effectively done using deep wide-field Hubble
Space Telescope images taken with the new Advanced Camera for Surveys. Through
an analysis of concentrations (C), asymmetries (A) and clumpiness values (S)
(CAS) of galaxies found in the GOODS Field South, we are able to identify
objects possibly forming onto the Hubble sequence. Using this approach, we
detect a sizeable population of star forming luminous diffuse objects and star
forming luminous asymmetric objects between redshifts 0.5 < z < 2. These
galaxies have extremely low light concentrations, or high asymmetries, with
absolute magnitudes M_B < -19. The luminous diffuse objects are found in
abundance between z = 1 - 2, with fewer objects at z > 2 and z < 1. The
luminous asymmetric objects are found at a similar abundance, with a peak at
z~1. We argue that these galaxies are a subset of modern disks and ellipticals
in formation. The co-moving volume density of the luminous diffuse objects
between z = 1 - 2 is similar to the local density of bright disk galaxies, with
values ~5*10^{5} Gpc^{-3}. The SEDs of these objects are mostly consistent with
starbursts, or star-forming normal galaxies, with average uncorrected for
extinction star formation rates of ~4 M_0 yr^{-1}. These galaxies also host
35-40% of the star formation activity at 1 < z < 2. We briefly discuss the
implications of these objects for understanding the origin of the Hubble
sequence.


title: IR emission from AGNs

abstract:
  Unified schemes of active galactic nuclei (AGN) require an obscuring dusty
torus around the central source, giving rise to type 1 line spectrum for
pole-on viewing and type 2 characteristics in edge-on sources. Infrared
radiation at its different wavelengths is the best probe of the dust
distribution, whether the torus orientation is edge-on or pole-on. The observed
IR is in broad agreement with the unified scheme but serious problems remained
in all early modeling efforts. In spite of a general awareness that the dust
must be concentrated in clouds, clumpiness remained the one major ingredient
missing in those radiative transfer studies because of the inherent
difficulties it presents. We have recently developed the formalism to handle
dust clumpiness and our results indicate that its inclusion may resolve the
difficulties encountered by the previous theoretical efforts. We show that
these problems find a natural explanation if the dust is contained in \about\
5--10 clouds along radial rays through the torus. The spectral energy
distributions (SED) of both type 1 and type 2 sources are properly reproduced
from different viewpoints of the same object if the optical depth of each cloud
is \ga 40 at visual wavelengths and the clouds' mean free path increases
roughly in proportion to radial distance.


title:
Hubble Space Telescope Imaging in the Chandra Deep Field South: III.
  Quantitative Morphology of the 1Ms Chandra Counterparts and Comparison with
  the Field Population

abstract:
  We present quantitative morphological analyses of 37 HST/WFPC2 counterparts
of X-ray sources in the 1 Ms Chandra Deep Field-South (CDFS). We investigate:
1) 1-D surface brightness profiles via isophotal ellipse fitting; 2) 2-D, PSF-
convolved, bulge+disk+nucleus profile-fitting; 3) asymmetry and concentration
indices compared with all ~3000 sources in our three WFPC2 fields; and 4) near-
neighbor analyses comparing local environments of X-ray sources versus the
field control sample. Significant nuclear point-source optical components
appear in roughly half of the resolved HST/WFPC2 counterparts, showing a narrow
range of F_X/F_{opt,nuc} consistent with the several HST-unresolved X-ray
sources (putative type-1 AGN) in our fields. We infer roughly half of the
HST/WFPC2 counterparts host unobscured AGN, which suggests no steep decline in
the type-1/type-2 ratio out to the redshifts z~0.5-1 typical of our sources.
The concentration indices of the CDFS counterparts are clearly larger on
average than those of the field distribution, at 5-sigma, suggesting that the
strong correlation between central black hole mass and host galaxy properties
(including concentration index) observed in nearby galaxies is already evident
by z~0.5-1. By contrast, the asymmetry index distribution of the 21 resolved
CDFS sources at I<23 is indistinguishable from the I<23 field. Moreover, the
frequency of I<23 near neighbors around the CDFS counterparts is not
significantly different from the field sample. These results, combined with
previous similar findings for local samples, suggest that recent merger/
interaction history is not a good indicator of AGN activity over a substantial
range of look-back time.


title:
Simultaneous radio and X-ray observations of the low-mass X-ray binary
  GX 13+1

abstract:
  We present the results of two simultaneous X-ray/radio observations of the
low-mass X-ray binary GX 13+1, performed in July/August 1999 with the Rossi
X-ray Timing Explorer and the Very Large Array. In X-rays the source was
observed in two distinct spectral states; a soft state, which had a
corresponding 6 cm flux density of ~0.25 mJy, and a hard state, which was much
brighter at 1.3-7.2 mJy. For the radio bright observation we measured a delay
between changes in the X-ray spectral hardness and the radio brightness of ~40
minutes, similar to what has been found in the micro-quasar GRS 1915+105. We
compare our results with those of GRS 1915+105 and the atoll/Z-type neutron
star X-ray binaries. Although it has some properties that do not match with
either atoll or Z sources, GX 13+1 seems more similar to the Z sources.


title: WR 7a: a V Sagittae or a qWR star?

abstract:
  The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V
Sagittae stars although no O VI emission has been reported. The Temporal
Variance Spectrum - TVS - analysis of our data shows weak but strongly variable
emission of O VI lines which is below the noise level in the intensity
spectrum. Contrary to what is seen in V Sagittae stars, optical photometric
monitoring shows very little, if any, flickering. We found evidence of periodic
variability. The most likely photometric period is P(phot) = 0.227(14) d, while
radial velocities suggest a period of P(spec) = 0.204(13) d. One-day aliases of
these periods can not be ruled out. We call attention to similarities with HD
45166 and DI Cru (= WR 46), where multiple periods are present. They may be
associated to the binary motion or to non-radial oscillations. In contrast to a
previous conclusion by Pereira et al. (1998), we show that WR 7a contains
hydrogen. The spectrum of the primary star seems to be detectable as the N V
4604A absorption line is visible. If so, it means that the wind is optically
thin in the continuum and that it is likely to be a helium main sequence star.
Given the similarity to HD 45166, we suggests that WR 7a may be a qWR - quasi
Wolf-Rayet - star. Its classification is WN4h/CE in the Smith et al. (1996)
three dimensional classification system.


title: The Nuclear Structure of the Sagittarius Dwarf Spheroidal Galaxy

abstract:
  We present a study of the central parts of the Sagittarius dwarf spheroidal
galaxy (Sgr). We found a clear overdensity of Sgr's stars around M~54
(hereafter NS). NS is well represented by a King model and it has the
characteristics of a typical dwarf elliptical nucleus. Whether this means that
M~54 has spiraled into the potential well of NS or that M~54 is the real
nucleus and NS has formed into its potential wells, remains an open question to
be addressed.


title:
The last Gift of BeppoSAX: PDS Observations of the two Blazars 1ES
  0507-040 and PKS 1229-021

abstract:
  Towards the end of the BeppoSAX mission, the only operated Narrow Field
Instrument was the PDS, which covers the energy range 13-300 keV. Two blazars,
1ES 0507-040 (z=0.304) and PKS 1229-021 (z= 1.045), suitably located in the sky
for BeppoSAX pointing, were observed for about 2 days each in Spring 2002 with
the PDS and detected up to 50 keV. 1ES0507-040 had been already observed by the
BeppoSAX NFIs at an earlier epoch for a much shorter time. We have re-analysed
those data as well, and identified a possible contamination problem in the PDS
spectrum. We present our recent PDS data on both sources, combined with the
previous BeppoSAX data and with non-simultaneous observations at other
frequencies. The derived Spectral Energy Distributions allow us to discuss the
origin of the high energy component.


title:
GLITP Optical Monitoring of QSO 0957+561: VR Light Curves and
  Variability

abstract:
  The GLITP collaboration observed the first gravitational lens system (QSO
0957+561) from 2000 February 3 to 2000 March 31. The daily VR observations were
made with the 2.56-m Nordic Optical Telescope at Roque de los Muchachos
Observatory, La Palma (Spain). We have derived detailed and robust VR light
curves of the two components Q0957+561A and Q0957+561B. In spite of the
excellent sampling rate, we have not found evidence in favor of true daily
variability. With respect to variability on time-scales of several weeks, we
measure VR gradients of about -0.8 mmag/day in Q0957+561A and + 0.3 mmag/day in
Q0957+561B. The gradients are very probably originated in the far source, thus
adopting this reasonable hypothesis (intrinsic variability), we compare them to
the expected gradients during the evolution of a compact supernova remnant at
the redshift of the source quasar. The starburst scenario is roughly consistent
with some former events, but the new gradients do not seem to be caused by
supernova remnant activity.


title:
Multiwavelength observations revealing the evolution of the outburst of
  the black hole XTE J1118+480

abstract:
  We report multiwavelength observations of the soft X-ray transient (SXT) XTE
J1118+480, which we observed with UKIRT, HST, RXTE, EUVE and many other
instruments and facilities. Adding radio (Ryle Telescope, VLA), sub-millimeter
(JCMT) and X-ray (Chandra and SAX) data from the literature, we assembled the
most complete spectral energy distribution (SED) of this source yet published.
We followed the evolution of this source for 1 year, including 6 observations
performed during the outburst, and one observation at the end of the outburst.
Because of XTE J1118+480's unusually high galactic latitude, it suffers from
very low extinction, and its SED is near-complete, including EUV (Extreme
Ultraviolet) observations. XTE J1118+480 exhibits an unusually low low-hard
state (estimated inner radius 350Rs) and a strong non-thermal contribution in
the radio to optical domain, which is likely to be due to synchrotron emission.
We discuss the interstellar column density and show that it is low, between
0.80 and 1.30 x 10^20 cm-2. We analyse the evolution of the SED during the
outburst, including the contributions from the companion star, the accretion
disc, the outflow, and relating irradiation and variability of the source in
different bands to the SED. We find no significant spectral variability during
the outburst evolution, consistent with the presence of a steady outflow.
Analysis of its outflow to accretion energy ratio suggests that the microquasar
XTE J1118+480 is analogous to radio-quiet quasars. This, combined with the
inverted spectrum from radio to optical, makes XTE J1118+480 very similar to
other microquasar sources, e.g. GRS 1915+105 and GX 339-4 in their low/hard
state. We model the high-energy emission with a hot disc model, and discuss
different accretion models for XTE J1118+480's broad band spectrum.


title: Gas and Dust in the Cloverleaf Quasar at Redshift 2.5

abstract:
  We observed the upper fine structure line of neutral carbon, CI(2-1), the
CO(3-2) line and the 1.2mm continuum emission from H1413+117 (Cloverleaf
quasar, z=2.5) using the IRAM interferometer. Together with the detection of
the lower fine structure line (Barvainis etal. 1997), the Cloverleaf quasar is
now only the second extragalactic system, besides M82, where both carbon lines
have convincingly been detected. Our analysis shows that the carbon lines are
optically thin and have an excitation temperature of ~30 K. CO is subthermally
excited and the observed line luminosity ratios are consistent with
n(H2)=10^(3-4) cm^(-3) at Tkin=30-50 K. Using three independent methods (CI,
dust, CO) we derive a total molecular gas mass (corrected for magnification) of
M(H2)=1.2+/-0.3*10^(10) SM. Our observations suggest that the molecular disk
extends beyond the region seen in CO(7-6) to a zone of more moderately excited
molecular gas that dominates the global emission in CI and the low J CO lines.


title: The Space Density of High-Redshift QSOs in the GOODS Survey

abstract:
  We present a sample of 17 high-redshift (3.5<z<5.2) QSO candidates in the 320
sq.arcmin area of the Great Observatories Origins Deep Survey, selected in the
magnitude range 22.45<z_{850}<25.25 using deep imaging with the Advanced Camera
for Surveys onboard the Hubble Space Telescope and the Advanced CCD Imaging
Spectrometer onboard the Chandra X-ray Observatory. On the basis of seven
spectroscopic and ten photometric redshifts we estimate that the final sample
will contain between two and four QSOs with 4<z<5.2. A dearth of high-redshift,
moderate-luminosity (M_{145}=~-23) QSOs is observed with respect to predictions
based on a) the extrapolation of the z~2.7 luminosity function (LF), according
to a pure luminosity evolution calibrated by the results of the Sloan Digital
Sky Survey; and b) a constant universal efficiency in the formation of
super-massive black holes (SMBHs) in dark-matter halos. Evidence is gathered in
favor of a density evolution of the LF at high redshift and of a suppression of
the formation or feeding of SMBHs in low-mass halos.


title: Properties of three gas-rich dwarfs in the Centaurus A group

abstract:
  We present HST/WFPC2 observations (F555W, F814W) and ATCA high resolution HI
maps of three gas-rich dwarf galaxies in the Centaurus A group discovered in
two blind 21-cm surveys (HIPASS, HIDEEP). We compare their individual
properties and discuss their star formation history. Although we can not
constrain the age of the oldest population from the diagrams very well, the
presence of an extended population of red giant stars suggests that these
systems were not formed recently. The presence of asymptotic giant branch (AGB)
stars in two out of three dwarfs, sets a lower limit on the age of about 6 Gyr.


title: Statistical Interpretation of LMC Microlensing Candidates

abstract:
  After a decade of gravitational microlensing experiments, a dozen of
microlensing candidates in the direction of the stars of the Large Magellanic
Cloud (LMC) have been detected by the EROS and MACHO groups. Recently it was
shown that the distribution of the duration of the observed LMC microlensing
events is significantly narrower than what is expected from the standard halo
model. In this article we make the same comparison, using non-standard halo
models and considering the contribution of non-halo components of the Milky Way
such as the disc, spheroid and LMC itself in the microlensing events. Comparing
the theoretical and experimental widths of distributions of the duration of
events shows that neither standard nor non-standard halo models are compatible
with the microlensing data at least with 95 per cent of confidence. This
results maybe explained if (i) the MACHOs in the Galactic halo reside in clumpy
structures or (ii) the durations of events have been underestimated due to the
blending effect.


title: Type Ia Supernovae in semi-detached binary systems

abstract:
  We have considered scenarios for the evolution of close binaries resulting in
the formation of semi-detached systems in which a white dwarf can accumulate
Chandrasekhar mass by accretion from a main-sequence or subgiant companion with
$M\sim 2 M_\odot$. These white dwarfs, probably, explode as type Ia supernovae
or collapse with formation of neutron stars. We have carried out a population
synthesis study for these systems and have estimated the occurrence rate of
such events in the Galaxy, depending on the parameter of common envelopes,
mass-exchange rate in the binary, reaction of the main-sequence component on
accretion of helium in the intervening phase of evolution. We have found that
the model occurrence rate of SNe Ia in semi-detached systems is $\simeq 0.2
\times 10^{-3}$ yr$^{-1}$, i. e., it does not exceed $\sim 10%$ of the
observational estimate of the Galactic occurrence rate of SNe Ia.


title: Neutral Hydrogen Mapping of Virgo Cluster Blue Compact Dwarf Galaxies

abstract:
  A new installment of neutral hydrogen mappings of Blue Compact Dwarf
galaxies, as defined by optical morphology, in and near the Virgo cluster is
presented. The primary motivation was to search for outlying clouds of HI as
potential interactive triggers of the enhanced star formation, and therefore
the mapped galaxies were selected for large HI} mass, large optical diameter,
and large velocity profile width. Approximately half the sample proved to have
one or more small, low column density star-free companion clouds, either
detached or appearing as an appendage in our maps, at resolution of order 4
kpc. Comparison is made to a sample of similarly mapped field BCD galaxies
drawn from the literature; however, the Virgo cluster sample of mapped BCDs is
still too small for conclusive comparisons to be made.
  We found, on the one hand, little or no evidence for ram pressure stripping
nor, on the other, for extremely extended low column density HI envelopes. The
HI rotation curves in most cases rise approximately linearly, and slowly, as
far out as we can trace the gas.


title:
Measuring the matter distribution within z=0.2 cluster lenses with
  XMM-Newton

abstract:
  We present an analysis of 7 clusters observed by XMM as part of our survey of
17 most X-ray luminous clusters of galaxies at z=0.2 selected for a
comprehensive and unbiased study of the mass distribution in massive clusters.
Using public software, we have set up an automated pipeline to reduce the EPIC
MOS & pn spectro-imaging data, optimized for extended sources analysis. We also
developped a code to perform intensive spectral and imaging analysis
particularly focussing on proper background estimate and removal. XMM deep
spectro-imaging of these clusters allowed us to fit a standard beta-model to
their gas emission profiles as well as a standard MEKAL emission model to their
extracted spectra, and test their inferred characteristics against already
calibrated relations.


title:
Near-infrared spectroscopy of powerful compact steep-spectrum radio
  sources

abstract:
  We have obtained near-infrared spectroscopy of a small sample of powerful
Compact Steep-Spectrum (CSS) radio sources mainly, but not exclusively, from
the 3CR sample. We find no differences between the distributions in the
equivalent width and luminosity of the [OIII] 5007A line for our sample and
other larger, presumably older, high-redshift 3C objects, suggesting that the
underlying quasar luminosity remains roughly constant as quasars age. We also
find a possible broad line in 3C241, adding to recent evidence for broad lines
in some radio galaxies.


title: On the Possibility of V4444 Sgr as a Recurrent Nova

abstract:
  V4444 Sgr (Nova Sgr 1999) has been recently suggested to be a possible
recurrent nova based on the detection of the preexisting dust, which may have
been formed in a previous outburst. We examined this possibility using the
available outburst observations, including the VSNET observations. We also
noticed that this nova was recorded in the OGLE II public photometric database,
which covered both preoutburst and late decline phases. The outburst light
curve constructed from these observations showed a plateau phase, particularly
in the OGLE II I-band light curve, which was followed by a more rapid decline.
The light curve resembled those of "fast" recurrent novae and candidates in the
presence of the distinct plateau phase. The outburst spectrum and the
preoutburst magnitude more resembled those of classical novae, but they do not
exclude the possibility of a recurrent nova.


title: Line temperatures and elemental abundances in HII galaxies

abstract:
  We present long-slit spectrophotometric observations in the red and near
infrared of 12 HII galaxies. The spectral range includes the sulphur lines
[SII] at wavelengths 6716, 6731 angstroms and [SIII] at 6312 angstroms and
9069, 9532 angstroms. For all of the observed galaxies, at least three
ion-weighted temperatures from forbidden auroral to nebular line ratios have
been obtained and the relations between the different line temperatures have
been discussed. It is found that, for some objects, the [OII] temperatures
derived from those of [OIII] through the use of photo-ionisation models,
without taking into account the effect of density, can lead to a significant
underestimate of the O+/H+ ionic abundance and hence of the total oxygen
abundance.


title: The Size Evolution of High Redshift Galaxies

abstract:
  Hubble Space Telescope images of high-redshift galaxies selected via color
and photometric redshifts are used to examine the size and axial-ratio
distribution of galaxies as a function of redshift at lookback times t > 8 Gyr.
These parameters are measured at rest-frame UV wavelengths (1200-2000
Angstroms) on images with a rest-frame resolution of less than 0.8 kpc. Galaxy
radii are found to scale with redshift approximately as the inverse of the
Hubble parameter H(z). This is in accord with the theoretical expectation that
the typical sizes of the luminous parts of galaxies should track the expected
evolution in the virial radius of dark-matter halos. The mean ratio of
semi-major to semi-minor axis for a bright well-resolved sample of galaxies at
z ~ 4 is b/a = 0.65, suggesting that these Lyman break galaxies are not drawn
from a spheroidal population. However the median concentration index of this
sample is C = 3.5, which is closer to the typical concentration indices, C ~ 4,
of nearby elliptical galaxies than to the values, C<2 for local disk galaxies
of type Sb and later.


title:
The epsilon Chamaeleontis young stellar group and the characterization
  of sparse stellar clusters

abstract:
  We present the outcomes of a Chandra X-ray Observatory snapshot study of five
nearby Herbig Ae/Be (HAeBe) stars which are kinematically linked with the
Oph-Sco-Cen Association (OSCA). Optical photometric and spectroscopic followup
was conducted for the HD 104237 field. The principal result is the discovery of
a compact group of pre-main sequence (PMS) stars associated with HD 104237 and
its codistant, comoving B9 neighbor epsilon Chamaeleontis AB. We name the group
after the most massive member. The group has five confirmed stellar systems
ranging from spectral type B9-M5, including a remarkably high degree of
multiplicity for HD 104237 itself. The HD 104237 system is at least a quintet
with four low mass PMS companions in nonhierarchical orbits within a projected
separation of 1500 AU of the HAeBe primary. Two of the low-mass members of the
group are actively accreting classical T Tauri stars. The Chandra observations
also increase the census of companions for two of the other four HAeBe stars,
HD 141569 and HD 150193, and identify several additional new members of the
OSCA.
  We discuss this work in light of several theoretical issues: the origin of
X-rays from HAeBe stars; the uneventful dynamical history of the
high-multiplicity HD 104237 system; and the origin of the epsilon Cha group and
other OSCA outlying groups in the context of turbulent giant molecular clouds.
Together with the similar eta Cha cluster, we paint a portrait of sparse
stellar clusters dominated by intermediate-mass stars 5-10 Myr after their
formation.


title: Strong Gravitational Lens Candidates in the GOODS ACS Fields

abstract:
  We present results from a systematic search for strong gravitational lenses
in the GOODS ACS data. The search technique involves creating a sample of
likely lensing galaxies, which we define as massive early-type galaxies in a
redshift range 0.3 < z <1.3. The target galaxies are selected by color and
magnitude, giving a sample of 1092 galaxies. For each galaxy in the sample, we
subtract a smooth description of the galaxy light from the z_{850}-band data.
The residuals are examined, along with true-color images created from the
B_{435}V_{606}i_{775} data, for morphologies indicative of strong lensing. We
present our six most promising lens candidates, as well as our full list of
candidates.


title: MSST observations of the pulsating sdB star PG1605+072

abstract:
  We present the first results from the MultiSite Spectroscopic Telescope
(MSST) observations of the sdBV star PG1605+072. Pulsating sdB stars (also
known as EC14026 stars) offer the chance to gain new insights into the
formation and evolution of extreme Horizontal Branch stars using the tools of
asteroseismology. PG1605+072 is an outstanding object in its class, with the
richest frequency spectrum, the longest periods, and the largest variations.
The MSST campaign took place in May/June 2002 immediately following the Whole
Earth Telescope Xcov22 run, which observed PG1605+072 as an alternate target.
We will first give an overview of the project and its feasibility, after which
we will present the massive data set, made up of 399 hours of photometry and
151 hours of spectroscopy. The overall aims of the project are to examine
light/velocity amplitude ratios and phase differences, changes in equivalent
width/line index, and wavelength-dependence of photometric amplitudes, and to
use these properties for mode identification.


title:
HST/STIS observations of sdBV stars: testing diffusion and pulsation
  theory

abstract:
  We present the initial results of an abundance analysis of echelle UV spectra
of 5 hot subdwarf B (sdB) stars. These stars have been identified as core
helium burning objects on the extreme Horizontal Branch. Around 5% of sdBs show
short-period acoustic mode oscillations. Models predict that these oscillations
are due to an opacity bump caused by the ionisation of iron group elements. The
necessary metal abundance has to be maintained by diffusive equilibrium between
gravitational settling and radiative levitation. However, analyses of high
resolution optical spectra has revealed that we cannot discriminate between
pulsating and non-pulsating sdBs on the basis of the surface iron abundance. We
have therefore obtained HST/STIS observations of 3 pulsators and 2
non-pulsators in the near and far UV to measure the surface abundance of
elements that are unobservable from the ground. The overall aim of our study is
to test diffusion and pulsation calculations by searching for significant
differences between these surface abundances.


title: Search for High Energy Gamma Rays from an X-ray Selected Blazar Sample

abstract:
  Our understanding of blazars has been greatly increased in recent years by
extensive multi-wavelength observations, particularly in the radio, X-ray and
gamma-ray regions. Over the past decade the Whipple 10m telescope has
contributed to this with the detection of 5 BL Lacertae objects at very high
gamma-ray energies. The combination of multi-wavelength data has shown that
blazars follow a well-defined sequence in terms of their broadband spectral
properties. Together with providing constraints on emission models, this
information has yielded a means by which potential sources of TeV emission may
be identified and predictions made as to their possible gamma-ray flux. We have
used the Whipple telescope to search for TeV gamma-ray emission from eight
objects selected from a list of such candidates. No evidence has been found for
VHE emission from the objects in our sample, and upper limits have been derived
for the mean gamma-ray flux above 390GeV. These flux upper limits are compared
with the model predictions and the implications of our results for future
observations are discussed.


title:
A light bending model for the X-ray temporal and spectral properties of
  accreting black holes

abstract:
  Uncorrelated variability between direct X-ray continuum and reflection
components (including the Fe line, if present) has been reported in many
accreting black hole systems, challenging theoretical models of disc
reflection. We explore a model based on gravitational light bending in the near
vicinity of the central black hole in which the X-ray variability is controlled
by the height of the primary source of X-rays above the accretion disc. The
relationship between the direct power law component (PLC) and the
reflection-dominated component (RDC) is not trivial and allows to identify
three different regimes in which the RDC (and the Fe line) is correlated,
anti-correlated or almost independent with respect to the PLC. X-ray
observations of the active galaxy MCG-6-30-15 and the black hole candidate XTE
J1650-500 (and possibly other sources, e.g. NGC 4051) reveal that a series of
predictions are actually observed: the behaviour of the Fe line flux, profile,
and EW and of the reflection fraction with respect to the continuum supports
our model which may explain what are otherwise puzzling properties of these
sources.


title:
The Rest-Frame UV Luminosity Density of Star-Forming Galaxies at
  Redshifts z>3.5

abstract:
  We have measured the rest--frame lambda~1500 Ang comoving specific luminosity
density of star--forming galaxies at redshift 3.5<z<6.5 from deep images taken
with the Hubble Space Telescope (HST)and the Advanced Camera for Surveys (ACS),
obtained as part of the Great Observatories Origins Deep Survey (GOODS). We
used color selection criteria to construct samples of star--forming galaxies at
redshifts z~4, 5 and 6, identified by the signature of the 912 Ang Lyman
continuum discontinuity and Lyman-alpha forest blanketing in their rest--frame
UV colors (Lyman--break galaxies). The ACS samples cover ~0.09 square degree,
and are also relatively deep, reaching between 0.2 and 0.5 L_3^*, depending on
the redshift, where $L_3^*$ is the characteristic UV luminosity of Lyman--break
galaxies at z~3. The specific luminosity density of Lyman--break galaxies
appears to be nearly constant with redshift from z~3 to z~6, although the
measure at z~6 remains relatively uncertain, because it depends on the accurate
estimate of the faint counts of the z~6 sample. If Lyman--break galaxies are
fair tracers of the cosmic star formation activity, our results suggest that at
z~6 the universe was already producing stars as vigorously as it did near its
maximum several Gyr later, at 1<~z<~3. Thus, the onset of large--scale star
formation in the universe is to be sought at around z~6 or higher, namely at
less than ~7% of the current cosmic age.


title: Structure and Evolution of Starburst and Normal Galaxies

abstract:
  We study the rest-frame morphology and structural properties of optically
selected starburst galaxies at redshift z < 1, using multi-waveband (BViz) high
resolution images taken by the Advanced Camera for Surveys (ACS) as part of the
Great Observatories Origins Deep Survey (GOODS). We classify galaxies into
starburst, early and late types by comparing their observed spectral energy
distributions (SEDs) with local templates. We find that early-type systems have
significantly higher rest-frame B -band concentration indices and AGN fraction
(> 25%) than late-type spirals and optically-selected starbursts. These results
are consistent with the scenario in which early-epoch (z > 1) gas-rich
dissipative processes (e.g., major mergers) have played an important role in
developing large central concentrations in early-type E/Sa galaxies, leading to
concurrent growth of central black holes and bulge formation in some of these
early merger events. The starbursts have, on average, larger asymmetries than
our control sample of normal galaxies, suggesting that a significant fraction
of the starburst activity is tidally triggered.


title:
The Redshift Distribution of Near-IR Selected Galaxies in the Great
  Observatories Origins Deep Survey as a Test of Galaxy Formation Scenarios

abstract:
  The redshift distribution of near-IR selected galaxies is often used to
attempt to discriminate between the classical view of galaxy formation, in
which present-day luminous galaxies were assembled at early times and evolve
due to the passive aging of their stellar populations, and that of hierarchical
structure formation, in which galaxies were assembled more recently via the
merging of smaller objects. We carry out such a test here, by computing the
distribution of photometric redshifts of K_AB<22 galaxies in the Great
Observatories Origins Deep Field Survey GOODS Southern Field, and comparing the
results with predictions from a semi-analytic model based on hierarchical
structure formation, and a classical `passive evolution' model. We find that
the redshift distributions at z <~ 1.5 of both the hierarchical and passive
models are very similar to the observed one. At z>~1.5, the hierarchical model
shows a deficit of galaxies, while the passive model predicts an excess. We
investigate the nature of the observed galaxies in the redshift range where the
models diverge, and find that the majority have highly disturbed morphologies,
suggesting that they may be merger-induced starbursts. While the hierarchical
model used here does not produce these objects in great enough numbers, the
appearance of this population is clearly in better qualitative agreement with
the hierarchical picture than with the classical passive evolution scenario. We
conclude that the observations support the general framework of hierarchical
formation, but suggest the need for new or modified physics in the models.


title: Photometric Redshifts for Galaxies in the GOODS Southern Field

abstract:
  We use extensive multi-wavelength photometric data from the Great
Observatories Origins Deep Survey (GOODS) to estimate photometric redshifts for
a sample of 434 galaxies with spectroscopic redshifts in the Chandra Deep Field
South. Using the Bayesian method, which incorporates redshift/magnitude priors,
we estimate photometric redshifts for galaxies in the range 18 < R (AB) < 25.5,
giving an rms scatter of 0.11. The outlier fraction is < 10%, with the
outlier-clipped rms being 0.047. We examine the accuracy of photometric
redshifts for several, special sub--classes of objects. The results for
extremely red objects are more accurate than those for the sample as a whole,
with rms of 0.051 and very few outliers (3%). Photometric redshifts for active
galaxies, identified from their X-ray emission, have a dispersion of 0.104,
with 10% outlier fraction, similar to that for normal galaxies. Employing a
redshift/magnitude prior in this process seems to be crucial in improving the
agreement between photometric and spectroscopic redshifts.


title: User Guide for the Discrete Dipole Approximation Code DDSCAT.6.0

abstract:
  DDSCAT.6.0 is a freely available software package
(http://www.astro.princeton.edu/~draine/DDSCAT.6.0.html) which applies the
"discrete dipole approximation" (DDA) to calculate scattering and absorption of
electromagnetic waves by targets with arbitrary geometries and complex
refractive index.
  DDSCAT.6.0 allows accurate calculations of electromagnetic scattering from
targets with ``size parameters'' 2*pi*a/lambda < 15 provided the refractive
index m is not large compared to unity (|m-1| < 1). DDSCAT.6.0 includes the
option of using the FFTW (Fastest Fourier Transform in the West) package.
DDSCAT.6.0 also includes MPI support, permitting parallel calculations on
multiprocessor systems.
  DDSCAT package is written in Fortran and is highly portable. The program
supports calculations for a variety of target geometries (e.g., ellipsoids,
regular tetrahedra, rectangular solids, finite cylinders, hexagonal prisms,
etc.). Target materials may be both inhomogeneous and anisotropic. It is
straightforward for the user to ``import'' arbitrary target geometries into the
code, and relatively straightforward to add new target generation capability to
the package. DDSCAT automatically calculates total cross sections for
absorption and scattering and selected elements of the Mueller scattering
intensity matrix for specified orientation of the target relative to the
incident wave, and for specified scattering directions.
  This User Guide explains how to use DDSCAT.6.0 to carry out electromagnetic
scattering calculations. CPU and memory requirements are described.


title:
Color-selected galaxies at z~6 in the Great Observatories Origins Deep
  Survey

abstract:
  We report early results on galaxies at z~6, selected from Hubble Space
Telescope imaging for the Great Observatories Origins Deep Survey. Spectroscopy
of one object with the Advanced Camera for Surveys grism and from the Keck and
VLT observatories a shows a strong continuum break and asymmetric line
emission, identified as Lya at z=5.83. We detect only five spatially extended,
z~6 candidates with signal-to-noise ratios > 10, two of which have
spectroscopic confirmation. This is many fewer than would be expected if
galaxies at z=6 had the same luminosity function as those at z=3. There are
many fainter candidates, but we expect substantial contamination from
foreground interlopers and spurious detections. Our best estimates favor a z=6
galaxy population with fainter luminosities, higher space density, and similar
co-moving ultraviolet emissivity to that at z=3, but this depends critically on
counts at fluxes fainter than those reliably probed by the current data.


title: Cosmic Variance in the Great Observatories Origins Deep Survey

abstract:
  Cosmic variance is the uncertainty in observational estimates of the volume
density of extragalactic objects such as galaxies or quasars arising from the
underlying large-scale density fluctuations. This is often a significant source
of uncertainty, especially in deep galaxy surveys, which tend to cover
relatively small areas. We present estimates of the relative cosmic variance
for one-point statistics (i.e. number densities) for typical scales and volumes
sampled by the Great Observatories Origins Deep Survey (GOODS). We use two
approaches: for objects with a known two-point correlation function that is
well-approximated by a power law, one can use the standard analytic formalism
to calculate the cosmic variance (in excess of shot noise). We use this
approach to estimate the cosmic variance for several populations that are being
studied in the GOODS program: Extremely Red Objects (ERO) at z~1, and Lyman
Break Galaxies (LBG) at z~3 and z~4, using clustering information for similar
populations in the literature. For populations with unknown clustering, one can
use predictions from Cold Dark Matter theory to obtain a rough estimate of the
variance as a function of number density. We present a convenient plot which
allows one to use this approach to read off the cosmic variance for a
population with a known mean redshift and estimated number density. We conclude
that for the volumes sampled by GOODS, cosmic variance is a significant source
of uncertainty for strongly clustered objects (~40-60% for EROs) and less
serious for less clustered objects, ~10-20% for LBGs.


title:
Rotational modulation of the photospheric and chromospheric activity in
  the young, single K2-dwarf PW And

abstract:
  High resolution echelle spectra of PW And (HD~1405) have been taken during
eight observing runs from 1999 to 2002. The detailed analysis of the spectra
allow us to determine its spectral type (K2V), mean heliocentric radial
velocity (V_hel = -11.15 km/s) rotational velocity (vsin{i} = 22.6 km/s), and
equivalent width of the lithium line 6707.8 AA (EW(LiI) = 273 mAA). The
kinematic (Galactic Velocity (U, V, W)) confirms its membership of the Local
Association moving group, in agreement with the age (30 to 80 Myrs) inferred
from the color magnitude diagram and the lithium equivalent width. Photospheric
activity (presence of cool spots that disturb the profiles of the photospheric
lines) has been detected as changes in the the bisectors of the cross
correlation function (CCF) resulting of cross-correlate the spectra of PW And
with the spectrum of a non active star of similar spectral type. These
variations of the CCF bisectors are related to the variations in the measured
radial velocities and are modulated with a period similar to the photometric
period of the star. At the same time, chromospheric activity has been analyzed,
using the spectral subtraction technique and simultaneous spectroscopic
observations of the H_alpha, H_beta, NaI D_1 and D_2$, HeI D_3, MgI b triplet,
CaII H&K, and CaII infrared triplet lines. A flare was observed during the last
observing run of 2001, showing an enhancement in the observed chromospheric
lines. A less powerful flare was observed on 2002 August 23. The variations of
the chromospheric activity indicators seem to be related to the photospheric
activity. A correlation between radial velocity, changes in the CCF bisectors
and equivalent width of different chromospheric lines is observed with a
different behaviour between epochs 1999, 2001 and 2002.


title: Sweeping and shaking dwarf satellites

abstract:
  We present the first high-resolution N-Body/SPH simulations that follow the
evolution of low surface brightness disk satellites in a primary halo
containing both dark matter and a hot gas component. Tidal shocks turn the
stellar disk into a spheroid with low $v/\sigma$ and remove most of the outer
dark and baryonic mass. In addition, by weakening the potential well of the
dwarf, tides enhance the effect of ram pressure, and the gas is stripped down
to radius three times smaller than the stellar component A very low gas/stars
ratio results after several Gyr, similarly to what seen in dwarf spheroidal
satellites of the Milky Way and M31.


title: Reaching to the Edge of the Milky Way Halo with SDSS

abstract:
  We discuss a sample of over 3000 candidate RR Lyrae stars selected by various
methods using Sloan Digital Sky Survey data for about 1000 deg^2 of sky. These
stars probe the halo structure out to ~100 kpc from the Galactic center. Their
spatial and radial velocity distributions are very inhomogeneous, with the most
prominent features tracing the Sgr dwarf tidal stream. Outside the Sgr dwarf
tidal stream, the spatial distribution in the 5-60 kpc range of Galactocentric
radius R is well described by an R^{-3} power law.


title: Halo Structure Traced by SDSS RR Lyrae

abstract:
  We discuss the density and radial velocity distributions of over 3000
candidate RR Lyrae stars selected by various methods using Sloan Digital Sky
Survey data for about 1000 deg^2 of sky. This is more than 20 times larger
sample than previously reported by SDSS (Ivezic et al. 2000), and includes
candidate RR Lyrae stars out to the sample limit of 100 kpc. A cutoff in the
radial distribution of halo RR Lyrae at ~50-60 kpc that was suggested by the
early SDSS data appears to be a statistical anomaly confined to a small region
(~100 deg^2). Despite the large increase in observed area, the most prominent
features remain to be those associated with the Sgr dwarf tidal stream. We find
multiple number density peaks along three lines of sight in the Sgr dwarf tidal
stream plane, that may indicate several perigalactic passages of the Sgr dwarf
galaxy.


title:
Variable Infrared Emission from the Supermassive Black Hole at the
  Center of the Milky Way

abstract:
  We report the detection of a variable point source, imaged at L'(3.8 microns)
with the W. M. Keck II 10-meter telescope's adaptive optics system, that is
coincident to within 18 mas of the Galaxy's central supermassive black hole and
the unique radio source Sgr A*. While in 2002 this source (SgrA*-IR) was
confused with the stellar source S0-2, in 2003 these two sources are separated
by 87 mas allowing the new source's properties to be determined directly. On
four separate nights, its observed L' magnitude ranges from 12.2 to 13.8, which
corresponds to a flux density of 0.7 - 3 mJy, observed, and 4 - 17 mJy,
dereddened; no other source in this region shows such large variations in flux
density - a factor of 4 over a week and a factor of 2 over 40 min. In addition,
it has a K-L' color greater than 2.1, which is at least 1 mag redder than any
other source detected at L' in its vicinity. Based on this source's coincidence
with the Galaxy's dynamical center, its lack of motion, its variability, and
its red color, we conclude that it is associated with the central supermassive
black hole. The short timescale for the 3.8 micron flux density variations
implies that the emission arises in the accretion flow on physical size scales
smaller than 5 AU, or 80 R_s for a 4x10^6 Mo black hole. We suggest that the
3.8 micron emission and the X-ray flares arise from the same underlying
physical process, possibly the acceleration of a small populations of electrons
to ultrarelativistic energies. In contrast to the X-ray flares which are only
detectable 2% of the time, the 3.8 micron emission provides a new, constantly
accessible, window into the physical conditions of the plasma in close
proximity to the central black hole.


title: Faint Galaxies in deep ACS observations

abstract:
  We present the analysis of the faint galaxy population in the Advanced Camera
for Surveys (ACS) Early Release Observation fields VV 29 (UGC 10214) and NGC
4676. Here we attempt to thoroughly consider all aspects relevant for faint
galaxy counting and photometry, developing methods which are based on public
software and that are easily reproducible by other astronomers. Using
simulations we determine the best SExtractor parameters for the detection of
faint galaxies in deep HST observations, paying special attention to the issue
of deblending, which significantly affects the normalization and shape of the
number count distribution. We confirm, as claimed by Bernstein, Freedman and
Madore (2002), that Kron-like magnitudes, such as the ones generated by
SExtractor, can miss more than half of the light of faint galaxies, what
dramatically affects the slope of the number counts. We present catalogs for
the VV 29 and NGC 4676 fields with photometry in the g,V and I bands. We also
show that combining the bayesian software BPZ with superb ACS data and new
spectral templates enables us to estimate reliable photometric redshifts for a
significant fraction of galaxies with as few as three filters. After correcting
for selection effects, we measure slopes of 0.32+- 0.01 for 22 < g < 28,
0.34+-0.01 for 22< V <27.5 and 0.33+-0.01 for 22 < I < 27. The counts do not
flatten (except perhaps in the g-band), up to the depth of our observations. We
find that the faint counts m_{AB}> 25.5 can be well approximated in all our
filters by a passive luminosity evolution model based on the COMBO-17
luminosity function (\alpha=-1.5), with a strong merging rate following the
prescription of Glazebrook et al. (1994), \phi^*\propto (1+Qz), with Q=4.


title: Phase-Referenced VLBA Observations of OH Masers at 4765 MHz

abstract:
  We report VLBA observations of maser emission from the rotationally excited
doublet Pi 1/2, J=1/2 state of OH at 4765 MHz. We made phase-referenced
observations of W3(OH) at both 4765 MHz and 1720 MHz and found emission in
three fields within a about 2000 AU diameter region and verified that in two of
the three fields, 4765 MHz and 1720 MHz emission arise from the same position
to within about 4 mas (about 5 AU diameter emission regions along an
approximately N-S arc with linear extent about 500 AU. In addition, we carried
out phase-referenced observations of 4765 MHz emission from K3-50. We searched
for the 4765 MHz line in W49 (without phase referencing) and W75N
(phase-referenced to the strongest 4765 MHz maser feature in DR21EX); we were
unable to detect these sources with the VLBA. For 2 1/2 years (including the
dates of the VLBA observations), we carried out monitoring observations of 4765
MHz emission with the VLA. Constraints on models for maser emission at 1720 MHz
and 4765 MHz are derived from the observations. These observations are then
briefly compared with existing models.


title: Magnesium isotopic abundance ratios in cool stars

abstract:
  From high resolution spectra of 61 cool dwarfs and giants, Mg isotopic
abundance ratios 24Mg:25Mg:26Mg are derived from spectral synthesis of the MgH
A-X lines near 5140A. Our sample spans the range -2.5 < [Fe/H] < 0.1, including
the first measurements of Mg isotope ratios in stars with metallicities below
[Fe/H]=-2.0. We confirm the decrease in 25,26Mg/24Mg with decreasing [Fe/H] as
predicted by recent models of Galactic chemical evolution where the Mg isotopes
are produced in massive stars. A subset of kinematically identified thin disk
stars have Mg isotope ratios in excellent agreement with the predictions.
Within the measurement uncertainties, these thin disk stars show no scatter
about the predictions. Several of our stars are likely members of the thick
disk and their high Mg isotopic ratios may reflect the nucleosynthetic history
of the thick disk which is distinct from the predictions for, and observations
of, the thin disk. For thick disk and halo stars we find a scatter in
25,26Mg/24Mg exceeding our measurement uncertainties and increasing with
increasing metallicity. Our data suggest that an additional source of 25Mg and
26Mg is required. Intermediate mass asymptotic giant branch stars are likely
candidates.


title:
Magnetorotationally-Driven Galactic Turbulence and the Formation of
  Giant Molecular Clouds

abstract:
  Using local 3D MHD simulations, we investigate ways in which galactic
turbulence associated with the magnetorotational instability (MRI) may
influence the formation and properties of GMCs. Our disk models are vertically
stratified and subject to uniform shear. Initial magnetic fields are weak and
purely vertical. For simplicity, we adopt an isothermal equation of state. We
find that MRI-driven turbulence develops rapidly, with the saturated-state
Shakura & Sunyaev parameter alpha~(0.15-0.3) dominated by Maxwell stresses.
Many of the dimensionless characteristics of the turbulence (e.g. the ratio of
the Maxwell to Reynolds stresses) are similar to results from previous MRI
studies of accretion disks, hence insensitive to the degree of vertical disk
compression, shear rate, and the presence of self-gravity. The density-weighted
velocity dispersions in non- or weakly self-gravitating disks are sigma_x ~
sigma_y ~ (0.4-0.6)c_s and sigma_z~(0.2-0.3)c_s, suggesting that MRI can
contribute significantly to the observed level of galactic turbulence. The
saturated-state magnetic field strength B ~ 2 \mu G is similar to typical
galactic values. When self-gravity is strong enough, MRI-driven high-amplitude
density perturbations are swing-amplified to form Jeans-mass (~10^7 Msun) bound
clouds. Compared to previous unmagnetized or strongly-magnetized disk models,
the threshold for nonlinear instability in the present models occurs for
surface densities at least 50% lower, corresponding to the Toomre parameter
Q_th~1.6. We present evidence that self-gravitating clouds like GMCs formed
under conditions similar to our models can lose much of their original spin
angular momenta by magnetic braking, preferentially via fields threading
near-perpendicularly to their spin axes.


title: The final two redshifts for radio sources from the equatorial BRL sample

abstract:
  Best, Rottgering and Lehnert (1999, 2000a) defined a new sample of powerful
radio sources from the Molonglo Reference Catalogue, for which redshifts were
compiled or measured for 177 of the 178 objects. For the final object,
MRC1059-010 (3C249), the host galaxy is here identified using near-infrared
imaging, and the redshift is determined from VLT spectroscopy. For one other
object in the sample, MRC0320+053 (4C05.14), the literature redshift has been
questioned: new spectroscopic observations of this object are presented,
deriving a corrected redshift. With these two results, the spectroscopic
completeness of this sample is now 100%.
  New redshifts are also presented for PKS0742+10 from the Wall & Peacock 2.7
GHz catalogue, and PKS1336+003 from the Parkes Selected Regions. PKS0742+10
shows a strong neutral hydrogen absorption feature in its Lyman-alpha emission
profile.