title: Evolution, Explosion and Nucleosynthesis of Core Collapse Supernovae

abstract:
  We present a new set of presupernova evolutions and explosive yields of
massive stars of initial solar composition (Y=0.285, Z=0.02) in the mass range
13-35 Msun. All the models have been computed with the latest version (4.97) of
the FRANEC code that now includes a nuclear network extending from neutrons to
Mo98. The explosive nucleosynthesis has been computed twice: a first one with
an hydro code and a second one following the simpler radiation dominated shock
approximation (RDA).


title:
Discovery, identification, and study of variability in gamma-ray point
  sources

abstract:
  We present preliminary results of a statistical analysis obtained with a
sample of blazars observed at the Perugia Astronomical Observatory since 1992.
We briefly show how these statistical results can be useful to discriminate
faint variable sources against the background noise. This technique, together
with the more traditional ones, may be used to discover and identify
high-energy point sources.


title:
Challenges in generating density perturbations from a fluctuating
  inflaton coupling

abstract:
  We discuss the possibility of generating adiabatic density perturbations from
spatial fluctuations in the inflaton decay rate which are due to quantum
fluctuations of light moduli fields coupling to the inflaton. We point out that
non-renormalizable operators, which lift the flatness of the moduli potential,
play an important role for the density perturbations. In particular, the
non-renormalizable terms give rise to a considerable damping of the
fluctuations and thereby pose an obstruction to the construction of possible
models.


title:
Distance and mass of pulsating stars from multicolour photometry and
  atmospheric models

abstract:
  For determining distance and mass of pulsating stars a new, purely
photometric method is described in which radial velocity observations are not
needed. The method is compared with the Baade-Wesselink method. As an example
the RR Lyrae variable SU Dra is given.


title: The Growth of Supermassive Black Holes and QSO Formation

abstract:
  A novel mechanism to build up a supermassive black hole (SMBH) is proposed.
Here, relativistic radiation-hydrodynamic processes are considered from a
galactic scale to a horizon scale. In the present scenario, the mass of a SMBH
is predicted to be in proportion to the bulge mass, and it turns out that the
SMBH-to-bulge mass ratio is basically determined by the nuclear energy
conversion efficiency from hydrogen to helium, $\epsilon=0.007$. The BH
hierarchy is also addressed in relation to the BH formation in globular
clusters. Futhermore, a new picture for QSO formation is proposed based on the
present SMBH formation scenario. It is predicted that a host
luminosity-dominant ``proto-QSO phase'' exists before the QSO phase, and the
proto-QSO phase is preceded by an optically-thick ultraluminous infrared galaxy
(ULIRG) phase.


title:
Host galaxies and black hole masses of low and high luminosity radio
  loud active nuclei

abstract:
  We investigate the host galaxy luminosities of BL Lac Objects (BLLs) and
Radio Loud Quasars (RLQs) at z<0.5 imaged with the Hubble Space Telescope
(HST). From a homogeneous treatment of the data we construct the host galaxy
luminosity functions (HGLFs) and find that RLQ hosts are ~0.5 mag brighter than
those of BLL: <M[R]_RLQ = -24.0, <M[R]>_BLL= -23.5. For both classes the HGLFs
exhibit a remarkably different distribution with respect to that of normal
(inactive) ellipticals, with clear preference for more luminous galaxies to
show nuclear activity. We make use of the black hole mass -- bulge luminosity
(M[BH] -L[bulge]) relation, derived for nearby inactive ellipticals, to
estimate the central black hole mass in our sample of radio loud active
galaxies. In spite of a ~2 order of magnitude difference of intrinsic nuclear
luminosity BLL and RLQ have BH of similar mass <M[BH]/M[sun]>_BLL= 5.6x10^{8},
<M[BH]/M[sun]_RLQ = 1.0 10^{9}). This implies that the two types of objects are
radiating at very different rates with respect to their Eddington luminosity.


title: Motion Statistics in the CJ Survey -- The Status in October 2002

abstract:
  In the Caltech-Jodrell Survey of bright flat-spectrum radio sources, 3-5
epochs have now been observed for nearly all 293 sources; a uniquely large
sample. The derivation of component motions has not yet been completed; it is
complicated by, for example, variability and jet curvature. Nevertheless, some
basic results are clear. The average apparent velocity in CJF quasars is near
3c, while for radio galaxies and BL Lacs it is around 1c. The distribution of
velocities is broad, indicating a broad distribution of jet Lorentz factors,
with many low values, and/or a decoupling of the Lorentz factors between the
cores and the moving jet components, due to bending, speed changes, or due to
pattern motions (shocks). A hint has emerged at this workshop that the average
apparent velocities might be lower at lower radio frequencies; this will need
careful verification.


title: Search for Fractional Charges in Cosmic Rays with Ams

abstract:
  Preliminary results on the flux of non strongly-interacting, fractionally
charged particles in primary cosmic rays at 400 Km above sea level are given.
Cosmic ray data collected by AMS-01 in June 1998 have been analysed on the
hypotheses of 2/3 charged leptons. The search is carried on by looking at the
energy deposition measurements by the time of flight system scintillator
counters. A preliminary flux limit is given.


title: Ionised, Atomic, and Molecular Gas around the Twin Radio Jets of NGC1052

abstract:
  The bright radio structure of the LINER elliptical galaxy NGC1052 is
dominated by bi-symmetric jets on parsec scales. Features move outward on both
sides of the core at v_{app}~0.26c. We have established the occurrence of
free-free absorption, and suggest the presence of a patchy, geometrically
region oriented roughly orthogonal to the jets; components have a wide range of
spectral shapes and brightness temperatures. We distinguish three velocity
systems in HI absorption. The ``high velocity'' system is the most prominent of
these; it is redshifted from systemic by about 150 km/s. In HI VLBI it is seen
towards both jets, but appears to be restricted to a shell 1 to 2 pc away from
the core. The central hole might be largely ionised, and could be connected to
the free-free absorption. WSRT spectroscopy shows 1667 and 1665 MHz OH main
line absorption over at least the full ~250 km/s velocity range seen in HI. In
the ``high velocity'' system, the profiles of the OH main lines and HI are
similar, which suggests co-location of molecular and atomic gas. The OH
satellite lines are also detected in the ``high velocity'' system: 1612 MHz in
absorption and 1720 MHz in emission, with complementary strength. But we have
no satisfactory model to explain all properties; the connection to H_2O masing
gas at the same velocity but apparently a different location is also unclear.


title:
The Outer Regions of the Nearby Sc Galaxies NGC 2403 and M33: Evidence
  for an Intermediate Age Population at Large Radii

abstract:
  Deep g'r'i'z' images obtained with the Gemini Multi-Object Spectrograph are
used to investigate the stellar content in the outer regions of the nearby Sc
galaxies NGC 2403 and M33. The red giant branch tip occurs at i' = 23.6 +/- 0.1
in NGC 2403, and the Cepheid and RGB-tip distance scales for this galaxy are in
good agreement. While very young stars are restricted to radii < 10 kpc along
the plane of the disk, a population of bright asymptotic giant branch (AGB)
stars is present out to r = 20 kpc, indicating that star formation occured
outside of the present-day star-forming disk of NGC 2403 during intermediate
epochs. The AGB stars are not in a tidal stream; in fact, the ratio of AGB
stars above the RGB-tip to those below the RGB-tip does not change with radius,
indicating that the bright AGB stars are uniformly mixed with the fainter
stellar content throughout the field. A similar population of bright AGB stars
is detected in the outer regions of M33, and the ratio of bright AGB stars to
stars on the upper RGB is at least as large as that measured in the outer
regions of NGC 2403; thus, an intermediate-age population occurs well outside
of the young star-forming disk of M33.


title:
Hubble Space Telescope observations of globular cluster systems along
  the Hubble sequence of spiral galaxies

abstract:
  We have studied the globular cluster (GC) systems of 7 giant, edge-on spiral
galaxies using Hubble Space Telescope imaging in V and I. The galaxy sample
covers the Hubble types Sa to Sc, allowing us to study the variation of the
properties of GC systems along the Hubble sequence. The photometry reaches ~1.5
mag beyond the turn-over magnitude of the GC luminosity function for each
galaxy. Specific frequencies (S_N values) of GCs were evaluated by comparing
the numbers of GCs found in our WFPC2 pointings with those in the Milky Way
which would be detected in the same metric area. The S_N values of spirals with
B/T <= 0.3 (i.e., spirals with a Hubble type later than about Sb) are
consistent with a value of S_N = 0.55 +- 0.25. We suggest that this population
of GCs represents a `universal', old halo population that is present around
each galaxy. Most galaxies in our sample have S_N values that are consistent
with a scenario in which GC systems are made up of (i) the aforementioned halo
population plus (ii) a population that is associated with bulges, which grows
linearly with the mass of the bulge. Such scenarios include the `merger
scenario' for the formation of elliptical galaxies as well as the `multi-phase
collapse' scenario, but it seems inconsistent with the `secular evolution'
scenario of Pfenniger & Norman (1990), in which bulges are formed from disc
stars by means of the redistribution of angular momentum through bar
instabilities and/or minor perturbations. However, there is one bulge-dominated
spiral galaxy in our sample (NGC 7814) with a low S_N value that is consistent
with those of the latest-type spirals. Thus, our results suggest that the
formation histories of galaxy bulges of early-type spirals can be significantly
different from one galaxy to another. (abridged)


title:
On the Origin of the High-Ionization Intermediate-Velocity Gas Toward HD
  14434

abstract:
  We present Far Ultraviolet Spectroscopic Explorer and Space Telescope Imaging
Spectrograph observations of high-ionization interstellar absorption toward HD
14434 [(l, b) = (135.1, -3.8); d ~ 2.3 kpc], an O5.5 V star in the Perseus OB1
Association. Intermediate-velocity interstellar Si IV and C IV absorption is
present at V_LSR = -67 km/s, while low-ionization gas associated with the
Perseus arm is detected at ~ -50 km/s. Neither N V nor O VI is detected at
V_LSR = -67 km/s; although Al III and Fe III, tracers of warm ionized gas, are
seen. The high-ion column densities in the -67 km/s component are log[N(C IV)]
= 13.92 +/- 0.02 cm^-2, log[N(Si IV)] = 13.34 +/- 0.02 cm^-2, log[N(N V)] <
12.65 cm^-2, and log[N(O VI)] < 13.73 cm^-2 (3-sigma limits). The observed C
IV/Si IV ratio of 3.8 +/- 0.3 in this intermediate-velocity cloud (IVC) is
similar to the Galactic average (4.3 +/- 1.9). Our analysis of the Si IV andC
IV line widths yields a temperature of T = 10,450 +/- 3,400 K for this
component. At this low temperature, neither Si IV nor C IV can be produced via
collisions. We investigate several photoionization models to explain the
intermediate-velocity Si IV and C IV absorption toward HD 14434.
Photoionization models employing cooling of a hot (T ~ 10^6 K) diffuse plasma
as the source of ionizing radiation reproduces the observed properties of the
IVC toward HD 14434 quite well. The hot plasma responsible for the ionizing
radiation in these models may be attributed to hot gas contained in a
supershell in or near the Perseus Arm or from a more generally distributed hot
ionized medium.


title: The Galactic Center stellar cluster: The central arcsecond

abstract:
  With 10 years of high-resolution imaging data now available on the stellar
cluster in the Galactic Center, we analyze the dynamics of the stars at
projected distances $\leq1.2''$ from the central black hole candidate
Sagittarius A* (Sgr A*). We find evidence for radial anisotropy of the cluster
of stars surrounding Sgr A*. We confirm/find accelerated motion for 6 stars,
with 4 stars having passed the pericenter of their orbits during the observed
time span. We calculated/constrained the orbital parameters of these stars. All
orbits have moderate to high eccentricities. The center of acceleration
coincides with the radio position of Sgr A*. From the orbit of the star S2, the
currently most tightly constrained one, we determine the mass of Sgr A* to
$3.3\pm0.7\times10^{6}$M$_{\odot}$ and its position to $2.0\pm2.4$ mas East and
$2.7\pm4.5$ mas South of the nominal radio position. The data provide
compelling evidence that Sgr A* is a single supermassive black hole.


title:
A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of
  the Sagittarius Core and Tidal Arms

abstract:
  We present the first all-sky view of the Sagittarius (Sgr) dwarf galaxy
mapped by M giant star tracers detected in the complete Two Micron All-Sky
Survey (2MASS). The main body is fit with a King profile of 30 deg limiting
radius, but with a break in the density profile from stars in tidal tails. We
argue that much of the observed structure beyond the 224' core radius may be
unbound as the satellite undergoes catastrophic disruption. A striking, >150
deg trailing tidal tail extends from the Sgr center and arcs across the South
Galactic Hemisphere. A prominent leading debris arm extends from the Sgr center
northward of the Galactic plane to an ~40 kpc apoGalacticon, loops towards the
North Galactic Cap (NGC) and descends back towards the Galactic plane,
foreshortened and covering the NGC. The Sgr tails lie along a well-defined
orbital plane that shows little precession, which supports the notion of a
nearly spherical Galactic potential. The Sun lies near the path of leading Sgr
debris; thus, former Sgr stars may be near or in the solar neighborhood. The
number of M giants in the Sgr tails is >15% that within the King limiting
radius of the Sgr center. That several gigayear old M giants are so widespread
along the Sgr tidal arms not only places limits on the dynamical age of these
arms but poses a timing problem that bears on the recent binding energy of the
Sgr core and that is naturally explained by recent and catastrophic mass loss.
Sgr appears to contribute >75% of the high latitude, halo M giants; no evidence
for M giant tidal debris from the Magellanic Clouds is found. Generally good
correspondence is found between the M giant, all-sky map of the Sgr system and
all previously published detections of potential Sgr debris with the exception
of Sgr carbon stars -- which must be subluminous to resolve the discrepancy.


title: The Metallicity of the Red Giant Branch in the Disk of NGC 6822

abstract:
  Deep J, H, and K' images obtained with the Canada-France-Hawaii Telescope
adaptive optics system are used to investigate the metallicity of red giant
branch (RGB) stars in three fields in the disk of the Local Group dwarf
irregular galaxy NGC 6822. The slope of the RGB on the (K, J-K) color-magnitude
diagrams indicates that <[Fe/H]> = -1.0 +/- 0.3. The locus of the RGB is bluer
than that of globular clusters with the same RGB slope, by an amount that is
consistent with the majority of RGB stars in these fields having an age near 3
Gyr. It is demonstrated that if RGB stars in NGC 6822 are this young then the
metallicity computed from the RGB slope may be ~ 0.05 dex too low.


title:
Assessment of the Fluorescence and Auger Data Base used in Plasma
  Modeling

abstract:
  We have investigated the accuracy of the 1s-vacancy fluorescence data base of
Kaastra & Mewe (1993, A&AS, 97, 443) resulting from the initial atomic physics
calculations and the subsequent scaling along isoelectronic sequences. In
particular, we have focused on the relatively simple Be-like and F-like
1s-vacancy sequences. We find that the earlier atomic physics calculations for
the oscillator strengths and autoionization rates of singly-charged B II and Ne
II are in sufficient agreement with our present calculations. However, the
substantial charge dependence of these quantities along each isoelectronic
sequence, the incorrect configuration averaging used for B II, and the neglect
of spin-orbit effects (which become important at high-Z) all cast doubt on the
reliability of the Kaastra & Mewe data for application to plasma modeling.


title: The dynamical evolution of Taurus--Auriga-type aggregates

abstract:
  (abridged) Star formation in the Taurus--Auriga (TA) molecular clouds is
producing binary-rich aggregates containing at most a few dozen systems within
a region spanning one pc without massive stars. This environment is very
different to another well-studied star-forming event which produced the Orion
Nebula cluster (ONC). Differences between these two environments have been
found. Notably, the ONC has a significantly smaller binary proportion but a
significantly larger number of isolated brown dwarfs per star than TA. This
paper focusses on the dynamical evolution of the TA aggregates and the changes
in their binary populations with an emphasis on the brown-dwarf properties.


title: Formation of Supermassive Black Holes: Simulations in General Relativity

abstract:
  There is compelling evidence that supermassive black holes exist. Yet the
origin of these objects, or their seeds, is still unknown. We discuss several
plausible scenarios for forming the seeds of supermassive black holes. These
include the catastrophic collapse of supermassive stars, the collapse of
relativistic clusters of collisionless particles or stars, the gravothermal
evolution of dense clusters of ordinary stars or stellar-mass compact objects,
and the gravothermal evolution of self-interacting dark matter halos.
Einstein's equations of general relativity are required to describe key facets
of these scenarios, and large-scale numerical simulations are performed to
solve them.


title:
Quasar-Galaxy and Galaxy-Galaxy Cross-Correlations: Model Predictions
  with Realistic Galaxies

abstract:
  Several measurements of QSO-galaxy correlations have reported signals much
larger than predictions of magnification by large-scale structure. We find that
the expected signal depends stronly on the properties of the foreground galaxy
population. On arcminute scales it can be either larger or smaller by a factor
of two for different galaxy types in comparison with a linearly biased version
of the mass distribution. Thus the resolution of some of the excess
measurements may lie in examining the halo occupation properties of the galaxy
population sampled by a given survey; this is also the primary information such
measurements will provide.
  We use the halo model of clustering and simulations to predict the
magnification induced cross-correlations and errors for forthcoming surveys.
With the full Sloan Digital Sky Survey the statistical errors will be below 1
percent for the galaxy-galaxy correlations and significantly larger for
QSO-galaxy correlations. Thus accurate constraints on parameters of the galaxy
halo occupation distribution can be obtained from small scale measurements and
on the bias parameter from large scales. Since the lensing induced
cross-correlation measures the first moment of the halo occupation number of
galaxies, these measurements can provide the basis for interpreting galaxy
clustering measurements which measure the second and higher order moments.


title:
Electron-Ion Recombination Rate Coefficients and Photoionization Cross
  Sections for Astrophysically Abundant Elements. VII. Relativistic
  calculations for O VI and O VII for UV and X-ray modeling

abstract:
  Aimed at ionization balance and spectral analysis of UV and X-ray sources, we
present self-consistent sets of photoionization cross sections, recombination
cross sections, and rate coefficients for Li-like O VI and He-like O VII.
Relativistic fine structure is considered through the Breit-Pauli R-matrix
(BPRM) method in the close coupling approximation, implementing the unified
treatment for total electron-ion recombination subsuming both radiative and
di-electronic recombination processes. Self-consistency is ensured by using an
identical wavefunction expansion for the inverse processes of photoionization
and photo-recombination. Radiation damping of resonances, important for H-like
and He-like core ions, is included. Compared to previous LS coupling results
without radiative decay of low-n (<= 10) resonances, the presents results show
significant reduction in O VI recombination rates at high temperatures. In
addition to the total rates, level-specific photoionization cross sections and
recombination rates are presented for all fine structure levels n (lSLJ) up to
n <= 10, to enable accurate computation of recombination-cascade matrices and
spectral formation of prominent UV and X-ray lines such as the 1032,1038 A
doublet of O VI, and the `triplet' forbidden, intercombination, and resonance
X-ray lines of O VII at 22.1, 21.8, and 21.6 \ang respectively. Altogether,
atomic parameters for 98 levels of O VI and 116 fine structure levels of O VII
are theoretically computed. These data should provide a reasonably complete set
of photoionization and recombination rates in collisional or radiative
equilibrium.


title:
A Major SGR-like Outburst and Rotation Glitch in the
  No-Longer-So-Anomalous X-ray Pulsar 1E 2259+586

abstract:
  We report a major outburst from the Anomalous X-ray Pulsar 1E 2259+586, in
which over 80 X-ray bursts were detected in four hours using the Rossi X-ray
Timing Explorer. The bursts range in duration from 2 ms to 3 s and have
fluences in the 2-10 keV band that range from 3 x 10^{-11} to 5 x 10^{-9} erg
cm^{-2}. We simultaneously observed increases of the pulsed and persistent
X-ray emission by over an order of magnitude relative to quiescent levels. Both
decayed significantly during the course of our 14 ks observation. Correlated
spectral hardening was also observed, with the spectrum softening during the
observation. In addition, we observed a pulse profile change, in which the
amplitudes of the two peaks in the pulse profile were swapped. The profile
relaxed back to its pre-outburst morphology after ~6 days. The pulsar also
underwent a sudden spin-up (df/f = 4 x 10^{-6}), followed by a large (factor of
\~2) increase in spin-down rate which persisted for >18 days. We also observed,
using the Gemini-North telescope, an infrared enhancement, in which the K_s
(2.15 um) flux increased, relative to that measured in a observation made in
2000, by a factor of ~3, three days post-outburst. The IR counterpart then
faded by a factor of ~2 one week later. In addition, we report an upper limit
of 50 uJy on radio emission at 1.4 GHz two days post-outburst. The X-ray
properties of this outburst are like those seen only in Soft Gamma Repeaters.
This conclusively unifies Anomalous X-ray Pulsars and Soft Gamma Repeaters, as
predicted uniquely by the magnetar model.


title: Theoretical Aspects of Ultra-High Energy Cosmic Rays

abstract:
  We review the basic ideas on the origin of cosmic rays with energy in excess
of $\sim 10^{19}$ eV, in the light of the most recent observational findings.
The limited statistics of events detected by the two largest experiments
currently operating does not allow as yet to claim the detection of the GZK
feature in the cosmic ray spectrum or the lack of it. Although extragalactic
point sources seem to be preferred on the basis of the small scale anisotropies
detected by AGASA, the possibility that UHECRs with energy in excess of
$10^{20}$ eV may be the result of the decay of supermassive particles is not
ruled out by present data. It seems clear that if we want to have a clear idea
of the origin of UHECRs, we have to auspicate the realization of larger, better
experiments, such as the ongoing Auger project and the space-borne EUSO
experiment.


title:
Globular Clusters as Candidates for Gravitational Lenses to Explain
  Quasar-Galaxy Associations

abstract:
  We argue that globular clusters (GCs) are good candidates for gravitational
lenses in explaining quasar-galaxy associations. The catalog of associations
(Bukhmastova 2001) compiled from the LEDA catalog of galaxies (Paturel 1997)
and from the catalog of quasars (Veron-Cetty and Veron 1998) is used. Based on
the new catalog containing 8382 pairs, we show that one might expect an
increased number of GCs around irregular galaxies of types 9 and 10 from the
hypothesis that distant compact sources are gravitationally lensed by GCs in
the halos of foreground galaxies. The King model is used to determine the
central surface densities of 135 GCs in the Milky Way. The distribution of GCs
in central surface density was found to be lognormal.


title: Galaxy-galaxy lensing results from COMBO-17

abstract:
  We use galaxy-galaxy lensing to study the statistical properties of the dark
matter halos of galaxies. Our data is taken from the COMBO-17 survey which has
imaged 1 square degree in 17 optical filters giving accurate photometric
redshifts and spectral classification down to R=24. This allows us to study
lens galaxies at $z=0.2-0.7$. Shapes are measured from deep $R$-band images
taken at the best seeing conditions ($0\farcs 8$ PSF). We model the lens
galaxies as singular isothermal spheres (SIS). Investigating the dependence of
the velocity dispersion on the luminosities of the lens galaxies we are able to
reproduce the Tully-Fisher/Faber-Jackson relation. Further we find a larger
lensing signal for early-type galaxies than for the late-types. However, when
testing the dependence of the velocity dispersion on radius we see clear
deviations from the SIS model. The velocity dispersion is first rising and then
declining again. This is exactly what is expected for lens galaxies that can be
modeled by Navarro-Frenk-White (NFW) profiles.


title: The Primordial Binary Population in OB Associations

abstract:
  For understanding the process of star formation it is essential to know how
many stars are formed as singles or in multiple systems, as a function of
environment and binary parameters. This requires a characterization of the
primordial binary population, which we define as the population of binaries
that is present just after star formation has ceased, but before dynamical and
stellar evolution have significantly altered its characteristics. In this
article we present the first results of our adaptive optics survey of 200
(mainly) A-type stars in the nearby OB association Sco OB2. We report the
discovery of 47 new candidate companions of Sco OB2 members. The next step will
be to combine these observations with detailed simulations of young star
clusters, in order to find the primordial binary population.


title: The warm absorber of the Seyfert 1 galaxy H1419+480

abstract:
  The bright Seyfert 1 galaxy H1419+480 (z~0.072), whose X-ray colours from
earlier HEAO-1 and ROSAT missions suggested a complex X-ray spectrum, has been
observed with XMM-Newton. The EPIC spectrum above 2 keV is well fit by a
power-law with photon index \Gamma=1.84\pm 0.01 and an Fe Ka line of equivalent
width ~250 eV. At softer energies, a decrement with respect to this model
extending from 0.5 to 1 keV is clearly detected. After trying a number of
models, we find that the best fit corresponds to OVII absorption at the
emission redshift, plus a 2-sigma detection of OVIII absorption. A photoionised
gas model fit yields log xi~ 1.15-1.30 (xi in erg cm/s) with N_H~ 5 10^{21}
cm^{-2} for solar abundances. We find that the ionized absorber was weaker or
absent in an earlier ROSAT observation. An IUE spectrum of this source obtained
two decades before shows a variable (within a year) CIV absorber outflowing
with a velocity ~1800 km/s. We show that both X-ray and UV absorptions are
consistent with arising in the same gas, with varying ionisation.


title: Dispersion of the Break Energy in the GRB Internal Shock Model

abstract:
  In order to investigate the dispersion of the spectral break energy in
gamma-ray bursts, we simulate internal shocks, including effects of
shell-splitting after shell collisions and the Thomson optical depth due to
electron--positron pairs produced by synchrotron photons. We produce pseudo
observational data and estimate the break energy. If the distribution of
initial Lorentz factors of shells has only one peak, many pulses with a break
energy much lower than the typical observed value should be detected, while the
effect of the Thomson optical depth reduces pulses with a break energy of $>1$
MeV. If the Lorentz factor distribution has multiple peaks, the distribution of
the break energy can be consistent with observations.


title:
Gauge-Invariant Initial Conditions and Early Time Perturbations in
  Quintessence Universes

abstract:
  We present a systematic treatment of the initial conditions and evolution of
cosmological perturbations in a universe containing photons, baryons,
neutrinos, cold dark matter, and a scalar quintessence field. By formulating
the evolution in terms of a differential equation involving a matrix acting on
a vector comprised of the perturbation variables, we can use the familiar
language of eigenvalues and eigenvectors. As the largest eigenvalue of the
evolution matrix is fourfold degenerate, it follows that there are four
dominant modes with non-diverging gravitational potential at early times,
corresponding to adiabatic, cold dark matter isocurvature, baryon isocurvature
and neutrino isocurvature perturbations. We conclude that quintessence does not
lead to an additional independent mode.


title: Stellar Evolutionary Models for Magellanic Clouds

abstract:
  We supplement current evolutionary computations concerning Magellanic Cloud
stars by exploring the evolutionary behavior of canonical stellar models
(i.e.,with inefficient core overshooting) with metallicities suitable for stars
in the Clouds. After discussing the adequacy of the adopted evolutionary
scenario, we present evolutionary sequences as computed following a selected
sample of stellar models in the mass range 0.8-8 Mo from the Main Sequence till
the C ignition or the onset of thermal pulses in the advanced Asymptotic Giant
Branch phase. On this basis, cluster isochrones covering the range of ages from
100 Myr to 15 Gyr are presented and discussed. To allow a comparison with
evolutionary investigations appeared in the recent literature, we computed
additional sets of models which take into account moderate core overshooting
during the H burning phase, discussing the comparison in terms of current
uncertainties in the stellar evolutionary models. Selected predictions
constraining the cluster ages are finally discussed, presenting a calibration
of the difference in magnitude between the luminous MS termination and the He
burning giants in terms of cluster age. Both evolutionary tracks and isochrones
have been made available at the node http://gipsy.cjb.net as a first step of a
planned ``Pisa Evolutionary Library''.


title: Reconstruction of the early Universe as a convex optimization problem

abstract:
  We show that the deterministic past history of the Universe can be uniquely
reconstructed from the knowledge of the present mass density field, the latter
being inferred from the 3D distribution of luminous matter, assumed to be
tracing the distribution of dark matter up to a known bias. Reconstruction
ceases to be unique below those scales -- a few Mpc -- where multi-streaming
becomes significant. Above 6 Mpc/h we propose and implement an effective
Monge-Ampere-Kantorovich method of unique reconstruction. At such scales the
Zel'dovich approximation is well satisfied and reconstruction becomes an
instance of optimal mass transportation, a problem which goes back to Monge
(1781). After discretization into N point masses one obtains an assignment
problem that can be handled by effective algorithms with not more than cubic
time complexity in N and reasonable CPU time requirements. Testing against
N-body cosmological simulations gives over 60% of exactly reconstructed points.
  We apply several interrelated tools from optimization theory that were not
used in cosmological reconstruction before, such as the Monge-Ampere equation,
its relation to the mass transportation problem, the Kantorovich duality and
the auction algorithm for optimal assignment. Self-contained discussion of
relevant notions and techniques is provided.

categories: astro-ph cond-mat math-ph math.MP math.OC nlin.PS


title: Mechanisms of the Vertical Secular Heating of a Stellar Disk

abstract:
  We investigate the nonlinear growth stages of bending instability in stellar
disks with exponential radial density profiles.We found that the unstable modes
are global (the wavelengths are larger than the disk scale lengths) and that
the instability saturation level is much higher than that following from a
linear criterion. The instability saturation time scales are of the order of
one billion years or more. For this reason, the bending instability can play an
important role in the secular heating of a stellar disk in the $z$ direction.
In an extensive series of numerical $N$-body simulations with a high spatial
resolution, we were able to scan in detail the space of key parameters (the
initial disk thickness $z_0$, the Toomre parameter $Q$, and the ratio of dark
halo mass to disk mass $M_{\rm h} / M_{\rm d}$). We revealed three distinct
mechanisms of disk heating in the $z$ direction: bending instability of the
entire disk, bending instability of the bar, and heating on vertical
inhomogeneities in the distribution of stellar matter.


title:
Ionization structure in the winds of B[e] supergiants: I. Ionization
  equilibrium calculations in a H plus He wind

abstract:
  The non-spherically symmetric winds of B[e] supergiants are investigated. An
empirical density distribution is chosen that accounts for the density
concentrations and ratios derived from observations, and our model winds are
assumed to contain only hydrogen and helium. We first calculate the approximate
ionization radii for H and He and compare the results with the ionization
fractions calculated from the more accurate ionization balance equations. We
find that winds with a r^-2 density distribution turn out to reach a constant
ionization fraction as long as the wind density is low, i.e. in polar
direction. For the high density equatorial regions, however, we find that the
winds become neutral just above the stellar surface of the hot and massive B[e]
supergiants forming a disk-like neutral region. In such a disk molecules and
dust can form even very near the hot central star.


title: Resistive MHD simulations of the Parker instability in galactic disks

abstract:
  Parker instability leads to the formation of tangential discontinuities in a
magnetic field and subsequent magnetic reconnection due to a numerical and/or
an explicit resistivity. In this paper we investigate the role of the uniform,
localized and numerical resistivity on the diffusion of magnetic field lines
during the growth phase of Parker instability modes. We propose a new method to
quantify the diffusion of magnetic field lines which is attributed to the
presence of resistivity in ideal and non-ideal MHD codes. The method relies (1)
on integration of magnetic lines in between periodic boundaries, (2) on
measurements of the dispersion of magnetic field lines with the left and the
right periodic boundaries and (3) on a statistical analysis of shifts of a
large set of magnetic lines. The proposed method makes it possible to detect
topological evolution of magnetic field. We perform a series of resistive MHD
simulations of the Parker instability in uniformly rotating galactic disks. We
follow the topological evolution of the magnetic field evolving due to the
Parker instability and relate it to the ratio of total to uniform magnetic
field in galactic disks. We find that after the onset of the Parker
instability, the magnetic field becomes first tangled and later on it evolves
toward a uniform state due to the presence of resistivity. A similar effect of
a varying contribution of a turbulent magnetic field is observed in arms and
inter-arm regions of galaxies.


title:
The Contribution of Particle Impact to the Production of Fe K Emission
  from Accreting Black Holes

abstract:
  The iron K line is perhaps the most important spectral diagnostic available
in the study of accreting black holes. The line is thought to result from the
reprocessing of external X-rays by the surface of the accretion disk. However,
as is observed in the solar corona, illumination by energetic particles may
also produce line emission. In principle, such a process may be uncorrelated
with the observed X-rays and could explain some of the unexpected variability
behavior of the Fe line. This paper compares predictions of iron K flux
generated by impacting electrons and protons to that from photoionization.
Non-thermal power-laws of electrons are considered as well as thermal
distributions of electrons and virialized protons. The electrons are thought to
originate in a magnetically dominated accretion disk corona, while the protons
are considered in the context of a two phase (hot/cold) accretion scenario. In
each case, the Fe K flux from particle impact is found to be < 1% of that
produced by photoionization by a hard X-ray power-law (normalized to the same
energy flux as the particles). Thus, the electrons or protons must strike the
disk with 100--10,000 times more energy flux than radiation for particle impact
to be a significant producer of Fe K flux. This situation is difficult to
reconcile with the observations of hard X-ray spectra, or the proposed particle
acceleration mechanisms in the accretion disk corona. Truncated accretion flows
must be externally illuminated by hard X-rays in order to produce the Fe line,
as proton impact is very inefficient in generating line emission. In contrast
to the Sun, our conclusion is that, with the possible exception for localized
regions around magnetic footpoints, particle impact will not be an important
contributor to the X-ray emission in accreting black holes.


title:
X-Ray Flares and Oscillations from the Black Hole Candidate X-Ray
  Transient XTE J1650-500 at Low Luminosity

abstract:
  We report on X-ray observations made with the Rossi X-ray Timing Explorer of
the black hole candidate (BHC) transient XTE J1650-500 at the end of its first,
and currently only, outburst. By monitoring the source at low luminosities over
several months, we found 6 bright ~100 second X-ray flares and long time scale
oscillations of the X-ray flux. The oscillations are aperiodic with a
characteristic time scale of 14.2 days and an order of magnitude variation in
the 2.8-20 keV flux. The oscillations may be related to optical
"mini-outbursts" that have been observed at the ends of outbursts for other
short orbital period BHC transients. The X-ray flares have durations between 62
and 215 seconds and peak fluxes that are 5-24 times higher than the persistent
flux. The flares have non-thermal energy spectra and occur when the persistent
luminosity is near 3E34 (d/4 kpc)^2 erg/s (2.8-20 keV). The rise time for the
brightest flare demonstrates that physical models for BHC systems must be able
to account for the situation where the X-ray flux increases by a factor of up
to 24 on a time scale of seconds. We discuss the flares in the context of
observations and theory of Galactic BHCs and compare the flares to those
detected from Sgr A*, the super-massive black hole at the Galactic center. We
also compare the flares to X-ray bursts that are seen in neutron star systems.
While some of the flare light curves are similar to those of neutron star
bursts, the flares have non-thermal energy spectra in contrast to the blackbody
spectra exhibited in bursts. This indicates that X-ray bursts should not be
taken as evidence that a given system contains a neutron star unless the
presence of a blackbody component in the burst spectrum can be demonstrated.


title:
The envelope of IRC+10216 reflecting the galactic light: UBV surface
  brightness photometry and interpretation

abstract:
  We present and analyse new optical images of the dust envelope surrounding
the high mass-loss carbon star IRC+10216. This envelope is seen due to external
illumination by galactic light. Intensity profiles and colors of the nebula
were obtained in the UBV bandpasses. The data are compared with the results of
a radiative transfer model calculating multiple scattering of interstellar
field photons by dust grains with a single radius. The data show that the
observed radial shape of the nebula, especially its half maximum radius, does
not depend on wavelength (within experimental errors), suggesting that grains
scatter in the grey regime, etc, etc (this abstract has been shortened)


title:
Optimization with numerical simulations of the conjugate altitudes of
  deformable mirrors in an MCAO system

abstract:
  This article reports on the results of simulations conducted to assess the
performance of a modal Multi-Conjugate Adaptive Optics (MCAO) system on a 10m
telescope with one Deformable Mirror (DM) conjugated to the telescope pupil and
a second DM conjugated at a certain altitude above the pupil. The main goal of
these simulations is to study the dependence of MCAO performance upon the
altitude of the high-altitude conjugated DM and thereby determine its optimal
conjugation. The performance is also studied with respect to the geometry of
the Guide Star constellation when using constellations of Natural Guide Stars
(NGS), which are rare, or constellations of Laser Guide Stars (LGS) which would
allow large sky coverage.


title:
A Chandra Survey of the Nearest ULIRGs: Obscured AGN or
  Super-Starbursts?

abstract:
  We present initial results from a Chandra survey of a complete sample of the
8 nearest (z <= 0.04) ultraluminous IR galaxies (ULIRGs), and also include the
IR-luminous galaxy NGC 6240 for comparison. In this paper we use the hard
X-rays (2-8 kev) to search for the possible presence of an obscured AGN. In
every case, a hard X-ray source is detected in the nuclear region. If we divide
the sample according to the optical/IR spectroscopic classification (starburst
vs. AGN), we find that the 5 ``starburst'' ULIRGs have hard X-ray luminosities
about an order-of-magnitude smaller than the 3 ``AGN'' ULIRGs. NGC 6240 has an
anomalously high hard X-ray luminosity compared to the ``starburst'' ULIRGs.
The Fe Kalpha line is convincingly detected in only two ULIRGs. The weakness of
the Fe-K emission in these ULIRGs generally suggests that the hard X-ray
spectrum is not dominated by reflection from high N_H neutral material. The
hard X-ray continuum flux ranges from a few X 10^3 to a few X 10^-5 of the
far-IR flux, similar to values in pure starbursts, and several
orders-of-magnitude smaller than in Compton-thin AGN. The upper limits on the
ratio of the Fe Kalpha to far-IR flux are below the values measured in
Compton-thick type 2 Seyfert galaxies. While very large column densities of
molecular gas are observed in the nuclei of these galaxies, we find no evidence
that the observed X-ray sources are obscured by Compton-thick material. Thus,
our new hard X-ray data do not provide direct evidence that powerful ``buried
quasars'' dominate the overall energetics of most ultraluminous infrared
galaxies.


title:
Forward Symplectic Integrators for Solving Gravitational Few-Body
  Problems

abstract:
  We introduce a class of fourth order symplectic algorithms that are ideal for
doing long time integration of gravitational few-body problems. These
algorithms have only positive time steps, but require computing the force
gradient in additional to the force. We demonstrate the efficiency of these
Forward Symplectic Integrators by solving the circularly restricted three-body
problem in the space-fixed frame where the force on the third body is
explicitly time-dependent. These algorithms can achieve accuracy of
Runge-Kutta, backward time step and corrector symplectic algorithms at step
sizes five to ten times as large.


title:
Kinetic simulations of collisionless magnetic reconnection in presence
  of a guide field

abstract:
  The results of kinetic simulations of magnetic reconnection in Harris current
sheets are analyzed. A range of guide fields is considered to study
reconnection in plasmas characterized by different $\beta$ values, $\beta >
m_e/m_i$. Both an implicit Particle-in-Cell (PIC) simulation method and a
parallel explicit PIC code are used. Simulations with mass ratios up to the
physical value are performed. The simulations show that the reconnection rate
decreases with the guide field and depends weakly on the mass ratio. The
off-diagonal components of the electron pressure tensor break the frozen-in
condition, even in low $\beta$ plasmas. In high $\beta$ plasmas, evidence is
presented that whistler waves play a key role in the enhanced reconnection,
while in low $\beta$ plasmas the kinetic Alfv\'en waves are important. The
in-plane and the out-of-plane ion and electron motion are also considered,
showing that they are influenced by the mass ratio and the plasma $\beta$.


title: Proceedings of the Davis Meeting on Cosmic Inflation

abstract:
  The Davis Meeting on Cosmic Inflation marked an exciting milestone on the
road to precision cosmology. This is the index page for the proceedings of the
conference. Individual proceedings contributions, when they appear on this
archive, are linked from this page.


title:
Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of
  the Coolest Brown Dwarfs

abstract:
  We explore the spectral and atmospheric properties of brown dwarfs cooler
than the latest known T dwarfs. Our focus is on the yet-to-be-discovered
free-floating brown dwarfs in the \teff range from $\sim$800 K to $\sim$130 K
and with masses from 25 to 1 \mj. This study is in anticipation of the new
characterization capabilities enabled by the launch of SIRTF and the eventual
launch of JWST. We provide spectra from $\sim$0.4 \mic to 30 \mic, highlight
the evolution and mass dependence of the dominant H$_2$O, CH$_4$, and NH$_3$
molecular bands, consider the formation and effects of water-ice clouds, and
compare our theoretical flux densities with the sensitivities of the
instruments on board SIRTF and JWST. The latter can be used to determine the
detection ranges from space of cool brown dwarfs. In the process, we determine
the reversal point of the blueward trend in the near-infrared colors with
decreasing \teff, the \teffs at which water and ammonia clouds appear, the
strengths of gas-phase ammonia and methane bands, the masses and ages of the
objects for which the neutral alkali metal lines are muted, and the increasing
role as \teff decreases of the mid-infrared fluxes longward of 4 \mic. These
changes suggest physical reasons to expect the emergence of at least one new
stellar class beyond the T dwarfs. Our spectral models populate, with cooler
brown dwarfs having progressively more planet-like features, the theoretical
gap between the known T dwarfs and the known giant planets. Such objects likely
inhabit the galaxy, but their numbers are as yet unknown.


title:
The Fate of Non-Radiative Magnetized Accretion Flows:
  Magnetically-Frustrated Convection

abstract:
  We present a scenario for non-radiative accretion onto the supermassive black
hole at the galactic center. Conducting MHD simulations with 1400^3 grid zones
that break the axial and reflection symmetries of earlier investigations and
extend inward from the Bondi radius, we find a quasi-hydrostatic radial density
profile rho propto r^{-0.72} with superadiabatic gradient corresponding to an
n~0.72 polytrope. Buoyancy generated by magnetic dissipation is resisted by the
same fields so effectively that energy is advected inward: a state of
magnetically-frustrated convection. This scenario is consistent with
observational constraints on energetics andouter boundary conditions.


title:
Swift Pointing and the Association Between Gamma-Ray Bursts and
  Gravitational-Wave Bursts

abstract:
  The currently accepted model for gamma-ray burst phenomena involves the
violent formation of a rapidly rotating solar mass black hole. Gravitational
waves should be associated with the black-hole formation, and their detection
would permit this model to be tested, the black hole progenitor (e.g.,
coalescing binary or collapsing stellar core) identified, and the origin of the
gamma rays (within the expanding relativistic fireball or at the point of
impact on the interstellar medium) located. Even upper limits on the
gravitational-wave strength associated with gamma-ray bursts could constrain
the gamma-ray burst model. To do any of these requires joint observations of
gamma-ray burst events with gravitational and gamma-ray detectors. Here we
examine how the quality of an upper limit on the gravitational-wave strength
associated with gamma-ray burst observations depends on the relative
orientation of the gamma-ray-burst and gravitational-wave detectors, and apply
our results to the particular case of the Swift Burst-Alert Telescope (BAT) and
the LIGO gravitational-wave detectors. A result of this investigation is a
science-based ``figure of merit'' that can be used, together with other mission
constraints, to optimize the pointing of the Swift telescope for the detection
of gravitational waves associated with gamma-ray bursts.


title: Optical Seeing at Sierra Negra

abstract:
  Optical seeing measurements carried out at Sierra Negra, the site of the
Large Millimeter Telescope, are reported. The site, one of the highest peaks of
Central Mexico, offers good coverage of Northern and Southern hemispheres and
we have undertaken several campaigns to investigate the astronomical potential
of the site in the optical. Here we report on our campaign aimed at
establishing the seeing quality of the site. We present data of the first three
campaigns of optical seeing monitoring covering from February 2000 to May 2002,
carried out with a Differential Image Motion Monitor. The results clearly
indicate a sub-arcsec seeing, better statistics during the dry season and no
dependence with the time of night. We find no dependence of our results with
the integration time used.


title: High resolution imaging by employing passive and active approaches

abstract:
  This article begins with the discussions on the formation of speckles in the
case of non-coherent quasi monochromatic source and of ways to detect them.
Prior to this, a brief introduction on the behavior of the atmosphere and its
effect on the plane wavefront from a stellar source is presented. The benefit
of short-exposure images over long exposure is highlighted with emphasis set on
their comparison as well. The data processing methods that are implemented in
our institute in order to decipher both Fourier modulus and Fourier phase are
described. The salient features of the adaptive optics system that compensates
the atmospheric effects on the image in real time are discussed. The article
concludes after a brief discussion on certain astrophysical problems that can
be targeted using moderate sized telescopes available in India, such as 2.34
meter Vainu Bappu Telescope (VBT), Kavalur, 2 meter Himalayan Chandra Telescope
(HCT), Hanley.


title: Coronal X-ray emission from an intermediate-age brown dwarf

abstract:
  We report the X-ray detection of the brown dwarf (BD) companion TWA 5B in a
$\simeq 12$ Myr old pre-main sequence binary system. We clearly resolve the
faint companion (35 photons) separated from the X-ray luminous primary by 2
arcsec in a {\it Chandra} ACIS image. TWA 5B shows a soft X-ray spectrum with a
low plasma temperature of only 0.3 keV and a constant flux during the 3 hour
observation, of which the characteristics are commonly seen in the solar
corona. The X-ray luminosity is 4$\times10^{27}$ erg s$^{-1}$ (0.1--10 keV
band) or $\log L_X/L_{bol} = -3.4$.
  Comparing these properties to both younger and older BDs, we discuss the
evolution of the X-ray emission in BDs. During their first few Myr, they
exhibit high levels of X-ray activity as seen in higher mass pre-main sequence
stars. The level in TWA 5B is still high at $t \simeq 12$ Myr in $\log
L_X/L_{bol}$ while $kT$ has already substantially cooled.


title:
Magnetic Helicity Evolution During the Solar Activity Cycle:
  Observations and Dynamo Theory

abstract:
  We study a simple model for the solar dynamo in the framework of the Parker
migratory dynamo, with a nonlinear dynamo saturation mechanism based on
magnetic helicity conservation arguments. We find a parameter range in which
the model demonstrates a cyclic behaviour with properties similar to that of
Parker dynamo with the simplest form of algebraic alpha-quenching. We compare
the nonlinear current helicity evolution in this model with data for the
current helicity evolution obtained during 10 years of observations at the
Huairou Solar Station of China. On one hand, our simulated data demonstrate
behaviour comparable with the observed phenomenology, provided that a suitable
set of governing dynamo parameters is chosen. On the other hand, the
observational data are shown to be rich enough to reject some other sets of
governing parameters. We conclude that, in spite of the very preliminary state
of the observations and the crude nature of the model, the idea of using
observational data to constrain our ideas concerning magnetic field generation
in the framework of the solar dynamo appears promising.


title: The IR counterpart to the Anomalouos X-ray Pulsar 1RXS J1708-4009

abstract:
  We report the discovery of the likely IR counterpart to the Anomalous X-ray
Pulsar (AXP) 1RXS J1708-4009, based on the combination of Chandra HRC-I X-ray
position, and deep optical/IR observations carried out from ESO telescopes and
the Canada France Hawaii Telescope (CFHT) during 1999-2002. Within the narrow
uncertainty region we found two relatively faint (K'=20.0 and K'=17.53) IR
objects. Based on their color and position in the J-K' versus J-H diagram only
the brighter object is consistent with the known IR properties of the
counterparts to other AXPs. No variability was detected for this source,
similarly to what is observed in the case of 4U 0142+614. Like in other AXPs,
we found that the IR flux of 1RXSJ1708-4009 is higher then expected for a
simple blackbody component extrapolated from the X-ray data. If confirmed, this
object would be the fourth IR counterpart to a source of the AXP class, and
would make the IR excess a likely new characteristic of AXPs.


title:
Combining WMAP and SDSS Quasar Data on Reionization Constrains
  Cosmological Parameters and the Star Formation Efficiency

abstract:
  We present constraints on cosmological and star formation parameters based on
combining observations of the Wilkinson Microwave Anisotropy Probe (WMAP) and
high-redshift quasars from the Sloan Digital Sky Survey (SDSS). We use a
semi-analytic model for reionization (Chiu and Ostriker 2000) that takes into
account a number of important physical processes both within collapsing halos
and in the intergalactic medium. Assuming that the efficiency of producing UV
photons per baryon is constant, we derive a constraint of the form sigma_8
Omega_0^0.5~0.33 in a flat, Lambda-dominated universe with h=0.72, n=0.99, and
Omega_b h^2=0.024. However, the calculated optical depth to electron scattering
of tau_es~0.06 is well below the value found by WMAP of 0.17+/-(0.04~0.07)
(Spergel et al 2003). Since the WMAP constraints on tau_es are somewhat
degenerate with the value of the spectral index n, we then permit the
primordial spectral index n to float and fix Omega_0 h^2=0.14, while
normalizing the power spectrum using WMAP. In addition, we allow the
UV-efficiency to have time-dependence. Combining the WMAP constraints with the
quasar transmission data, our analysis then favors a model with
tau_es=0.11^{+0.02}_{-0.03}, n=0.96^{+0.02}_{-0.03}$, implying
sigma_8=0.83^{+0.03}_{-0.05} (95% confidence), and an effective UV-efficiency
that was at least ~10x greater at z >> 6. These results indicate that the
quasar and WMAP observations are consistent. If future observations confirm an
optical depth to electron scattering tau_es~0.1, then it would appear that no
more "exotic" sources of UV-photons, such as mini-quasars or AGNs, are
necessary; but our analysis indicates that a determination of tau_es>~0.17
would require a more radical solution.


title:
A median redshift of 2.4 for galaxies bright at submillimetre
  wavelengths

abstract:
  A significant fraction of the energy emitted in the early Universe came from
very luminous galaxies that are largely hidden at optical wavelengths (because
of interstellar dust grains); this energy now forms part of the cosmic
background radiation at wavelengths near 1mm. These submillimetre (submm)
galaxies were resolved from the background in 1997 but have been difficult to
identify and study due to the poor spatial resolution of submm instruments.
This has impeded the determination of their distances (or redshifts, z), a
crucial element in understanding their nature and evolution. Here we report
spectroscopic redshifts for ten representative submm galaxies that we
identified reliably using high resolution radio observations. The median
redshift for our sample is 2.4, with a quartile range of z = 1.9-2.8. The submm
population therefore coexists with the peak activity of quasars, which are
thought to be massive black holes in the process of accreting matter,
suggesting a close relationship between the growth of massive black holes and
luminous dusty galaxies. The space density of submm galaxies at z>2 is about
1000 times greater than that of similarly luminous galaxies in the present-day
Universe, so they represent an important component of star formation at high
redshifts.


title:
The spectroscopic redshifts of SCUBA galaxies: implications for spheroid
  formation

abstract:
  We present spectroscopic identifications for a sample of 55
submillimeter(submm)-selected `SCUBA' galaxies, lying at redshifts z=0.7 to
3.7, that were pinpointed in deep 1.4-GHz VLA radio maps. We describe their
properties, especially the presence of active galactic nuclei (AGN) in the
sample, and discuss the connection of the SCUBA galaxies and the formation of
spheroidal components of galaxies, which requires knowledge of their masses and
the timescales of their very luminous activity. For a subset of the galaxies,
we show their disturbed and diverse Hubble Space Telescope (HST) optical
morphologies.


title: An alternative to the cosmological 'concordance model'

abstract:
  Precision measurements of the cosmic microwave background by WMAP are
believed to have established a flat $\Lambda$-dominated universe, seeded by
nearly scale-invariant adiabatic primordial fluctuations. However by relaxing
the hypothesis that the fluctuation spectrum can be described by a single power
law, we demonstrate that an Einstein-de Sitter universe with {\em zero}
cosmological constant can fit the data as well as the best concordance model.
Moreover unlike a $\Lambda$-dominated universe, such an universe has no strong
integrated Sachs-Wolfe effect, so is in better agreement with the low
quadrupole seen by WMAP. The main problem is that the Hubble constant is
required to be rather low: $H_0 \simeq 46$ km/s/Mpc; we discuss whether this
can be consistent with observations. Furthermore for universes consisting only
of baryons and cold dark matter, the amplitude of matter fluctuations on
cluster scales is too high, a problem which seems generic. However, an
additional small contribution ($\Omega_X \sim 0.1$) of matter which does not
cluster on small scales, e.g. relic neutrinos with mass of order eV or a
`quintessence' with $w \sim 0$, can alleviate this problem. Such models provide
a satisfying description of the power spectrum derived from the 2dF galaxy
redshift survey and from observations of the Ly-$\alpha$ forest. We conclude
that Einstein-de Sitter models can indeed accommodate all data on the large
scale structure of the Universe, hence the Hubble diagram of distant Type Ia
supernovae remains the only {\em direct} evidence for a non-zero cosmological
constant.


title:
Two-dimensional hydrodynamic simulation of an accretion flow with
  radiative cooling in a close binary system

abstract:
  Two-dimensional numerical simulations of an accretion flow in a close binary
system are performed by solving the Euler equations with radiative transfer. In
the present study, the specific heat ratio is assumed to be constant while
radiative cooling effect is included as a non-adiabatic process. The cooling
effect of the disc is considered by discharging energy in the vertical
directions from the top and bottom surfaces of the disc. We use the
flux-limited diffusion approximation to calculate the radiative heat flux
values. Our calculations show that a disc structure appears and the spiral
shocks are formed on the disc. These features are similar to that observed in
the case of an adiabatic gas with a lower specific heat ratio, $\gamma=1.01$.
It is found that when radiative cooling effect is accounted for, the mass of
the disc becomes larger than that assuming $\gamma=5/3$, and smaller than that
assuming $\gamma=1.01$. It is concluded that employing an adiabatic gas with a
lower specific heat ratio is almost a valid assumption for simulating accretion
disc with radiative cooling effect.


title: The Host Galaxies of AGN

abstract:
  We examine the properties of the host galaxies of 22,623 narrow-line AGN with
0.02<z<0.3 selected from a complete sample of 122,808 galaxies from the Sloan
Digital Sky Survey. We focus on the luminosity of the [OIII]$\lambda$5007
emission line as a tracer of the strength of activity in the nucleus. We study
how AGN host properties compare to those of normal galaxies and how they depend
on L[OIII]. We find that AGN of all luminosities reside almost exclusively in
massive galaxies and have distributions of sizes, stellar surface mass
densities and concentrations that are similar to those of ordinary early-type
galaxies in our sample. The host galaxies of low-luminosity AGN have stellar
populations similar to normal early-types. The hosts of high- luminosity AGN
have much younger mean stellar ages. The young stars are not preferentially
located near the nucleus of the galaxy, but are spread out over scales of at
least several kiloparsecs. A significant fraction of high- luminosity AGN have
strong H$\delta$ absorption-line equivalent widths, indicating that they
experienced a burst of star formation in the recent past. We have also examined
the stellar populations of the host galaxies of a sample of broad-line AGN. We
conclude that there is no significant difference in stellar content between
type 2 Seyfert hosts and QSOs with the same [OIII] luminosity and redshift.
This establishes that a young stellar population is a general property of AGN
with high [OIII] luminosities.


title: The intrinsic colour dispersion in Type Ia supernovae

abstract:
  The properties of low-redshift Type Ia supernovae are investigated using
published multi-band optical broadband data from the Calan/Tololo and CfA
surveys. The average time evolution of B-V, V-R, R-I, B-I and V-I, the
intrinsic dispersion and time correlations are studied. This information is
required to deduce the extinction of such explosions from the measured colours.
We find that extinction corrections on individual SNe based on their colours up
to 40 days past the B-band lightcurve maximum are generaly limited to
\sigma_{A_V} \gsim 0.1, due to intrinsic variations, as far as it can be
conservatively deduced with the current sample of data. However, we find that
the V-R colour, especially at late times, is consistent with a negligible
intrinsic spread, and may be the most accurate estimator for extinction.


title:
Multi-TeV Gamma-Ray Flares from Markarian 421 in 2000 and 2001 Observed
  with the Tibet Air Shower Array

abstract:
  Several strong TeV gamma-ray flares were detected from Markarian 421 in the
years 2000 and 2001 by the Tibet III air shower array at a level of statistical
significance of 5.1 sigma. Markarian 421 was unprecedentedly active at X-ray
and TeV gamma-ray energies during this period, and a positive correlation was
found between the change of the ASM/RXTE X-ray flux and the Tibet TeV gamma-ray
flux. When a power-law energy spectrum for gamma-rays from this source is
assumed, the spectral index is calculated to be -3.24+-0.69 at the most active
phase in 2001. The spectral index observed by the Tibet air shower array is
consistent with those obtained via imaging air Cerenkov telescopes.


title: Mapping of Large Scale 158 micron [CII] Line Emission: Orion A

abstract:
  We present the first results of an observational programme undertaken to map
the fine structure line emission of singly ionized carbon ([CII] 157.7409
micron) over extended regions using a Fabry Perot spectrometer newly installed
at the focal plane of a 100cm balloon-borne far-infrared telescope. This new
combination of instruments has a velocity resolution of ~200 km/s and an
angular resolution of 1.5'. During the first flight, an area of 30'x15' in
Orion A was mapped. The observed [CII] intensity distribution has been compared
with the velocity-integrated intensity distributions of 13CO(1-0), CI(1-0) and
CO(3-2) from the literature. The observed line intensities and ratios have been
analyzed using the PDR models by Kaufman et al. 1999 to derive the incident UV
flux and volume density at a few selected positions.


title: The wavelength dependence of polarization in active galactic nuclei

abstract:
  Using the gaseous disk model and the condition for emission based on a
stimulated origin of thermal radio emission (Prigara 2003), we received the
wavelength dependence of polarization for radio emission from active galactic
nuclei consistent with available observational data. The strength of magnetic
field required to produce an observable degree of polarization in active
galactic nuclei is discussed.


title:
BeppoSAX Observations of Centaurus A: the Hard Continuum and the Iron
  Line Feature

abstract:
  The radio galaxy Centaurus A was observed by the BeppoSAX satellite five
times from 1997 to 2000. From July 6 1999 to August 17 1999, the source was
also simultaneously pointed by COMPTEL on-board of the satellite CGRO.
Centaurus A has a complex spectrum with multiple extended components and a
strongly absorbed (N_H\sim 10^{23}$ cm${-2}) nucleus well fitted by a power law
(\Gamma \sim 1.8) which bends at high energies. When the BeppoSAX and COMPTEL
observations are combined together, an exponential cutoff with e-folding energy
\sim 1000 keV gives an adequate description of the spectral steepening. A
complex feature in emission at 6-7 keV is resolved into two Fe components, one
narrow cold line and an ionized line centred at 6.8 keV. Significant variations
have been observed in the iron feature, with the less prominent ionized line
seemingly being the only one responsible for them: its variations do not appear
to correlate with the strength of the continuum. The high energy cutoff and the
Fe feature suggest the presence of an accretion flow in the Centaurus A
nucleus. However the absence of a significant reflection, the narrowness of the
cold line as well as the lack of correlation between the continuum and 6.8 keV
line variations disfavour a standard cold/ionized thin disk (at least in the
inner regions). A more plausible configuration might be a hot thick optically
thin accretion flow surrounded by material with different opacities.
  Finally, we note that high energy break observed by BeppoSAX and COMPTEL
could be also reasonably explained by Inverse Compton radiation from a jet. If
this is the case, a structured jet with outer slow layers surrounding a beamed
inner region is necessary to explain the strong Fe feature observed by
BeppoSAX.


title: Radio Observations of the Magnetic Fields in Galaxies

abstract:
  After a short introduction on how we get information of the magnetic fields
from radio observations I discuss the results concerning the magnetic field
structure in galaxies: Large-scale regular magnetic field pattern of spiral
structure exist in grand-design spirals, flocculent and even irregular
galaxies. The regular field in spirals is aligned along the optical spiral arms
but strongest in the interarm region, sometimes forming 'magnetic arms'. The
strongest total field is found in the optical arms, but mainly irregular. The
large-scale regular field is best explained by some kind of dynamo action. Only
a few galaxies show a dominant axisymmetric field pattern, most field
structures seem to be a superposition of different dynamo modes or rather
reveal more local effects related to density waves, bars or shocks.
Observations of edge-on galaxies show that the magnetic fields are mainly
parallel to the disk except in some galaxies with strong star formation and
strong galactic winds as e.g. NGC 4631.


title: Density Profile Asymptotes at the Centre of Dark Matter Halos

abstract:
  For the spherical symmetric case, all quantities describing the relaxed dark
matter halo can be expressed as functions of the gravitational potential
$\Phi$. Decomposing the radial velocity dispersion $\sigma_r$ with respect to
$\Phi$ at very large and very small radial distances the possible asymptotic
behavior for the density and velocity profiles can be obtained. If reasonable
boundary conditions are posed such as a finite halo mass and force-free halo
centre the asymptotic density profiles at the centre should be much less steep
than the profiles obtained within numerical simulations. In particular cases
profiles like Plummer's model are obtained. The reasons of that seeming
discrepancy with respect to the results of N-body simulations are discussed.


title:
A far infrared view of the Lockman Hole from ISO 95 $\mu$m observations
  - I. A new data reduction method

abstract:
  We report results of a new analysis of a deep 95 mu imaging survey with the
photo-polarimeter ISOPHOT on board the Infrared Space Observatory, over a half
square degree area within the Lockman Hole. To this end we exploit a newly
developed parametric algorithm able to identify and clean spurious signals
induced by cosmic-rays impacts and by transient effects and non-linearities in
the detectors. These results provide us with the currently deepest -- to our
knowledge -- far-IR image of the extragalactic sky. Within the survey area we
detect thirty-six sources with S/N>3 (corresponding to a flux of 16 mJy),
making up a complete flux-limited sample around 100$ mJy. Reliable sources are
detected, with decreasing but well-controlled completeness, down to 20 mJy. The
source extraction process and the completeness, the photometric and astrometric
accuracies of this catalogue have been tested by us with extensive simulations
accounting for all the details of the procedure. We estimate source counts down
to a flux of ~30 mJy, at which limit we evaluate that from 10% to 20% of the
cosmic IR background has been resolved into sources. The 95mu galaxy counts
reveal a steep slope at fluxes lower than 100 mJy (alpha~1.6), in excess of
that expected for a non-evolving source population. The shape of these counts
agrees with those determined by ISO at 15 and 175 mu, and starts setting strong
constraints on the evolution models for the far-IR galaxy populations.


title:
The CORALIE survey for southern extra-solar planets. X. A Hot Jupiter
  orbiting HD73256

abstract:
  Recent radial-velocity measurements obtained with the CORALIE spectrograph on
the 1.2-m Euler Swiss telescope at La Silla unveil the presence of a new
Jovian-mass Hot Jupiter around HD 73256. The 1.85-M_Jup planet moves on an
extremely short-period (P=2.5486 d), quasi-circular orbit. The best Keplerian
orbital solution is presented together with an unsuccessful photometric
planetary-transit search performed with the SAT Danish telescope at La Silla.
Over the time span of the observations, the photometric follow-up of the
candidate has nevertheless revealed a P=14-d photometric periodicity
corresponding to the rotational period of the star. This variation as well as
the radial-velocity jitter around the Keplerian solution are shown to be
related to the fair activity level known for HD 73256.


title: Radiative acceleration and transient, radiation-induced electric fields

abstract:
  The radiative acceleration of particles and the electrostatic potential
fields that arise in low density plasmas hit by radiation produced by a
transient, compact source are investigated. We calculate the dynamical
evolution and asymptotic energy of the charged particles accelerated by the
photons and the radiation-induced electric double layer in the full
relativistic, Klein-Nishina regime. For fluxes in excess of $10^{27}$ ${\rm
erg} {\rm cm}^{-2} {\rm s}^{-1}$, the radiative force on a diluted plasma
($n\la 10^{11}$ cm$^{-3}$) is so strong that electrons are accelerated rapidly
to relativistic speeds while ions lag behind owing to their larger inertia. The
ions are later effectively accelerated by the strong radiation-induced double
layer electric field up to Lorentz factors $\approx 100$, attainable in the
case of negligible Compton drag. The asymptotic energies achieved by both ions
and electrons are larger by a factor 2--4 with respect to what one could
naively expect assuming that the electron-ion assembly is a rigidly coupled
system. The regime we investigate may be relevant within the framework of giant
flares from soft gamma-repeaters.


title:
The Hubble Flow Why Does the Cosmological Expansion Preserve its
  Kinematical Identity from a Few MPC Distance to the Observation Horizon?

abstract:
  The problem of the physical nature of the Hubble flow in the Local Volume ($D
< 10$ Mpc) stated by Sandage(1986, 1999) is studied. New observational data on
galaxy motions and matter distribution around the Local Group and nearby
similar systems are described. Dynamical models are discussed on the basis of
the recent data on cosmic vacuum or dark energy.


title: Loss cone: past, present and future

abstract:
  The capture and subsequent in--spiral of compact stellar remnants by central
massive black holes, is one of the more interesting likely sources of
gravitational radiation detectable by LISA. The relevant stellar population
includes stellar mass black holes, and possibly intermediate mass black holes,
generally on initially eccentric orbits. Predicted detectable rates of capture
are highly uncertain, but may be high enough that source confusion is an issue.
Foreground events with relatively high signal-to-noise ratio may provide
important tests of general relativity. I review the rate estimates in the
literature, and the apparent discrepancy between different authors' estimates,
and discuss some of the relevant uncertainties and physical processes. The
white dwarf mergers rate are uncertain by a factor of few; the neutron star
merger rate is completely uncertain and likely to be small; the black hole
merger rate is likely to be dominant for detectable mergers and is uncertain by
at least two orders of magnitude, largely due to unknown physical conditions
and processes. The primary difference in rate estimates is due to different
initial conditions and less directly due to different estimates of key physical
processes, assumed in different model scenarios for in-spiral and capture.


title: The First Heroic Decade of Microlensing

abstract:
  We review the fundamentals of vanilla and exotic microlensing. Deviations
from the standard form of an achromatic, time-symmetric lightcurve can be
caused by the parallax and xallarap effects, finite source size effects and
binarity. The pioneering experiments of MACHO, EROS and OGLE reported first
candidate events exactly ten years ago, so now is an opportune moment to
summarise the achievements of the First Heroic Decade. Three applications are
reviewed in detail -- namely (i) searches for compact dark objects in the
Galactic halo, (ii) probes of the baryonic mass distribution in the inner
Galaxy and the Andromeda Galaxy and (iii) studies of the limb darkening of
source stars. Finally, we suggest four projects for the Second Heroic Decade --
(i) K band microlensing towards the Bulge, (ii) pixel lensing towards the low
luminosity spiral galaxy M33, (iii) polarimetry of on-going microlensing events
and (iv) astrometric microlensing with the GAIA satellite.


title: Inverse temperature dependence of the dust submillimeter spectral index

abstract:
  We present a compilation of PRONAOS-based results concerning the temperature
dependence of the dust submillimeter spectral index, including data from
Galactic cirrus, star-forming regions, dust associated to a young stellar
object, and a spiral galaxy. We observe large variations of the spectral index
(from 0.8 to 2.4) in a wide range of temperatures (11 to 80 K). These spectral
index variations follow a hyperbolic-shaped function of the temperature, high
spectral indices (1.6-2.4) being observed in cold regions (11-20 K) while low
indices (0.8-1.6) are observed in warm regions (35-80 K). Three distinct
effects may play a role in this temperature dependence: one is that the grain
sizes change in dense environments, another is that the chemical composition of
the grains is not the same in different environments, a third one is that there
is an intrinsic dependence of the dust spectral index on the temperature due to
quantum processes. This last effect is backed up by laboratory measurements and
could be the dominant one.


title: Low-Mass Relics of Early Star Formation

abstract:
  The earliest stars to form in the Universe were the first sources of light,
heat and metals after the Big Bang. The products of their evolution will have
had a profound impact on subsequent generations of stars. Recent studies of
primordial star formation have shown that, in the absence of metals (elements
heavier than helium), the formation of stars with masses 100 times that of the
Sun would have been strongly favoured, and that low-mass stars could not have
formed before a minimum level of metal enrichment had been reached. The value
of this minimum level is very uncertain, but is likely to be between 10^{-6}
and 10^{-4} that of the Sun. Here we show that the recent discovery of the most
iron-poor star known indicates the presence of dust in extremely
low-metallicity gas, and that this dust is crucial for the formation of
lower-mass second-generation stars that could survive until today. The dust
provides a pathway for cooling the gas that leads to fragmentation of the
precursor molecular cloud into smaller clumps, which become the lower-mass
stars.


title:
Matching the Cosmic Star Formation History to the Local Galaxy
  Population

abstract:
  In this review I will describe a number of recent advances in extragalactic
astronomy. First of all I will describe our current best estimates of the star
formation history of the Universe. Then I will describe measurements of local
galaxies and their stellar populations, concentrating on measurements of the
luminosity functions and stellar population compositions of the different kinds
of galaxies. Finally, I will investigate the relationship between these two
sets of results. The ultimate aim is to tell at what stage in the history of
the Universe the different stars seen in the local galaxies formed. At present
much is known but there are significant uncertainties and I will highlight some
prospects for the future.


title:
Relativistic and slowing down: the flow in the hotspots of powerful
  radio galaxies and quasars

abstract:
  Pairs of radio emitting jets with lengths up to several hundred kiloparsecs
emanate from the central region (the `core') of radio loud active galaxies.
  In the most powerful of them, these jets terminate in the `hotspots', compact
high brightness regions, where the jet flow collides with the intergalactic
medium (IGM). Although it has long been established that in their inner
($\sim$parsec) regions these jet flows are relativistic, it is still not clear
if they remain so at their largest (hundreds of kiloparsec) scales. We argue
that the X-ray, optical and radio data of the hotspots, despite their
at-first-sight disparate properties, can be unified in a scheme involving a
relativistic flow upstream of the hotspot that decelerates to the
sub-relativistic speed of its inferred advance through the IGM and viewed at
different angles to its direction of motion. This scheme, besides providing an
account of the hotspot spectral properties with jet orientation, it also
suggests that the large-scale jets remain relativistic all the way to the
hotspots.


title: The nature and space density of fossil groups of galaxies

abstract:
  We describe the properties of a sample of galaxy groups with very unusual
distributions of galaxy luminosities. The most extreme example has an X-ray
luminosity similar to that of the Virgo cluster but has a very low richness,
with only one galaxy brighter than L*, compared with six in Virgo. That one
galaxy, however, is optically more luminous than any galaxy in Virgo and has an
optical luminosity as bright as many of the central cD galaxies in rich Abell
clusters. The characteristic feature of the fossil groups we study is that most
of the light arises from one dominant, central galaxy. We define a fossil
system and, based on this definition, construct a small X-ray selected,
flux-limited sample of fossil groups with well known selection criteria. We
confirm that these systems are indeed groups of galaxies, but dominated by one
central luminous giant elliptical galaxy and with few, or no, L* galaxies. We
find that fossil systems represent 8%-20% of all systems of the same X-ray
luminosity. Fossil groups are at least as numerous as all poor and rich
clusters combined, and are thus a possible site for the formation of luminous
central cluster galaxies before infall into clusters occurs. The fossil systems
in our sample have significantly higher X-ray luminosities than normal groups
of similar total optical luminosities (or similar X-ray temperature, where the
latter can be measured). These enhanced X-ray luminosities may be due to
relatively cool gas in the innermost regions or due to a low central gas
entropy. We interpret fossil groups as old, undisturbed systems which have
avoided infall into clusters, but where galaxy merging of most of the L*
galaxies has occurred. An early formation epoch, before that of most groups,
could explain low central gas entropies and high X-ray luminosities.


title:
High Spectral Resolution H2 Measurements of Herbig-Haro Objects 38,
  46/47, and HH 120

abstract:
  We report high spectral resolution (R=20,000) measurements of the H2 1-0 S(1)
line in Herbig-Haro Objects 38, 46/47, and 120. The long-slit spectra reveal
complex velocity structure with evidence for bow-shock structures as well as
prompt entrainment and shock heating of ambient molecular gas. Individual knots
within HH 38 show distinct double peaked velocity stucture, consistent with
that expected from spatially unresolved bow shocks. A portion of the HH 47A bow
shock is resolved in our measurements, and the kinematics of the H2 trace
closely that found for H-alpha emission. The evidence indicates that the
preshock medium for HH 47A that formed in the wake of a previous ejection
contains molecular clumps. The HH 46CjetA feature in the HH 46/47 counterflow
is suggestive of a bow shock emerging from near the base of the flow, with H2
emission arising from ambient cloud material excited in the oblique flanks of
the bow shock. HH 46F is situated downstream at the boundary between an ovoid
cavity and the ambient could material, and represents either entrainment by a
stellar wind that fills the cavity or entrainment in the far wing of a giant
bow shock. For HH 120, the H2 velocity results also corroborate those found
from atomic emission, and there is substantial evidence that the preshock
medium is inhomogeneous, producing clumps of H2 emission on the wings of a bow
shock that has an apex at HH 120A.


title: On marginally resolved objects in optical interferometry

abstract:
  With the present and soon-to-be breakthrough of optical interferometry,
countless objects shall be within reach of interferometers; yet, most of them
are expected to remain only marginally resolved with hectometric baselines.
  In this paper, we tackle the problem of deriving the properties of a
marginally resolved object from its optical visibilities. We show that they
depend on the moments of flux distribution of the object: centre, mean angular
size, asymmetry, and curtosis. We also point out that the visibility amplitude
is a second-order phenomenon, whereas the phase is a combination of a
first-order term, giving the location of the photocentre, and a third-order
term, more difficult to detect than the visibility amplitude, giving an
asymmetry coefficient of the object. We then demonstrate that optical
visibilities are not a good model constraint while the object stays marginally
resolved, unless observations are carried out at different wavelengths.
Finally, we show an application of this formalism to circumstellar discs.


title: A Survey for Transient Astronomical Radio Emission at 611 MHz

abstract:
  We have constructed and operated the Survey for Transient Astronomical Radio
Emission (STARE) to detect transient astronomical radio emission at 611 MHz
originating from the sky over the northeastern United States. The system is
sensitive to transient events on timescales of 0.125 s to a few minutes, with a
typical zenith flux density detection threshold of approximately 27 kJy. During
18 months of around-the-clock observing with three geographically separated
instruments, we detected a total of 4,318,486 radio bursts. 99.9% of these
events were rejected as locally generated interference, determined by requiring
the simultaneous observation of an event at all three sites for it to be
identified as having an astronomical origin. The remaining 3,898 events have
been found to be associated with 99 solar radio bursts. These results
demonstrate the remarkably effective RFI rejection achieved by a coincidence
technique using precision timing (such as GPS clocks) at geographically
separated sites. The non-detection of extra-solar bursting or flaring radio
sources has improved the flux density sensitivity and timescale sensitivity
limits set by several similar experiments in the 1970s. We discuss the
consequences of these limits for the immediate solar neighborhood and the
discovery of previously unknown classes of sources. We also discuss other
possible uses for the large collection of 611 MHz monitoring data assembled by
STARE.


title:
Spectral and Temporal Behavior of the Black Hole Candidate XTE J1118+480
  as Observed with BeppoSAX

abstract:
  XTE J1118+480 is a well established black hole candidate with a mass estimate
in the range from 7 to 10 solar masses. With BeppoSAX we observed the source 4
times, from April to December 2000. Results of the firs t observation were
already reported (Frontera et al. 2001). Here we report spectral results of the
later observations, performed in May, June and December 2000 and compare them
with the results obtained from the 2000 April observation. We observe a
decrease of the column density from a value consistent with the Galactic N_H
obtained from radio measurement s to a value a factor 2 lower. The spectra are
well fit with a thermal Comptonization plus a blackbody model. The blackbody
luminosity decreases with time, while the electron temperature of the
Comptonizing electron s does not show significant changes. A Compton reflection
component is apparent and stable, although weak (mean value of Omega/2pi =
0.21[-0.04,+0.05]). The reflector shows a low metallicity (mean value of Z/Zsun
= 0.13[-0.04,+0.06]). On the basis of the spectral results, a hot central disk
appears the best scenar io for the high energy photons, while the temporal
properties point to a non therma l origin of a fraction of the soft X-ray
photons, likely synchrotron emission internal to the hot disk.


title: A Capture Scenario for Globular Cluster Omega Centauri

abstract:
  We explore an accretion origin for Omega Cen by N-body modeling of the
orbital decay and disruption of a Milky-Way dwarf satellite. This work is
focused on studying a particular satellite model that aims to reproduce the
present orbit of Omega Cen, as recently determined from absolute proper
motions. The model satellite is launched from 58 kpc from the Galactic Center,
on a radial, low-inclination orbit. We find that a capture scenario can produce
an Omega Cen-like object with the current low-energy orbit of the cluster. Our
best model is a nucleated galaxy with a Hernquist density profile that has a
mass of 8 10**8 Msun, and a half-mass radius of 1.4 kpc.


title: Review of low-mass X-ray binaries near the Galactic center

abstract:
  Results of observations of several LMXBs in the Galactic center region
carried out with the ART-P telescope on board \Granat observatory are briefly
reviewed. More than dozen sources were revealed in this region during five
series of observations which were performed with the ART-P telescope in
1990-1992. The investigation of the spectral evolution of persistent emission
of two X-ray bursters GX3+1 and KS1731-260, discussion of QPO and spectral
variations detected from the very bright Z-source GX5-1 and studying the pulse
profile changes of the pulsar GX1+4 were carried out.


title: An XMM and Chandra view of massive clusters of galaxies to z=1

abstract:
  The X-ray properties of a sample of high redshift (z>0.6), massive clusters
observed with XMM-Newton and Chandra are described, including two exceptional
systems. One, at z=0.89, has an X-ray temperature of T=11.5 (+1.1, -0.9) keV
(the highest temperature of any cluster known at z>0.6), an estimated mass of
(1.4+/-0.2)x10^15 solar masses and appears relaxed. The other, at z=0.83, has
at least three sub-clumps, probably in the process of merging, and may also
show signs of faint filamentary structure at large radii,observed in X-rays. In
general there is a mix of X-ray morphologies, from those clusters which appear
relaxed and containing little substructure to some highly non-virialized and
probably merging systems. The X-ray gas metallicities and gas mass fractions of
the relaxed systems are similar to those of low redshift clusters of the same
temperature, suggesting that the gas was in place, and containing its metals,
by z=0.8. The evolution of the mass-temperature relation may be consistent with
no evolution or with the ``late formation'' assumption. The effect of point
source contamination in the ROSAT survey from which these clusters were
selected is estimated, and the implications for the ROSAT X-ray luminosity
function discussed.


title: New results on GP Com

abstract:
  We present high resolution optical and UV spectra of the 46 min orbital
period, helium binary, GP Com. Our data contains simultaneous photometric
correction which confirms the flaring behaviour observed in previous optical
and UV data. In this system all lines show a triple peaked structure where the
outer two peaks are associated with the accretion disc around the compact
object. The main aim of this paper is to constrain the origin of the central
peak, also called ``central spike''. We find that the central spike contributes
to the flare spectra indicating that its origin is probably the compact object.
We also detect that the central spike moves with orbital phase following an
S-wave pattern. The radial velocity semiamplitude of the S-wave is ~10 km/s
indicating that its origin is near the centre of mass of the system, which in
this case lies very close to the white dwarf. Our resolution is higher than
that of previous data which allows us to resolve structure in the central peak
of the line. The central spike in three of the HeI lines shows another peak
blueshifted with respect to the main peak. We propose that one of the peaks is
a neutral helium forbidden transition excited in a high electron density
region. This forbidden transition is associated with the permitted one (the
stronger peak in two of the lines). The presence of a high electron density
region again favours the white dwarf as their origin.


title: Star Formation and the ISM in Four Dwarf Irregular Galaxies

abstract:
  We present new, high sensitivity VLA observations of HI in four dwarf
galaxies (UGCA 292, GR8, DDO 210, and DDO 216) and we use these data to study
interactions between star formation and the interstellar medium. HI velocity
dispersions and line shapes in UGCA 292, GR8, and DDO 210 show that these three
galaxies contain both warm and cool or cold HI phases. The presence of the cold
neutral medium is indicated by a low-dispersion (3--6 km/s) HI component or by
the Gauss-Hermite shape parameter h_4 > 0. Contrary to expectations, we find no
trend between the incidence of the low-dispersion (colder) phase and the star
formation rate in five dwarf galaxies. The colder HI phase may be a necessary
ingredient for star formation, but it is clearly not sufficient. However, there
is a global trend between the star formation rate of a galaxy and the incidence
of asymmetric HI profiles. This trend probably reflects kinetic energy input
from young massive stars. Numerical simulations show that the effects of
rotational broadening (finite angular resolution) are minimal for these
galaxies. Simulations are also used to estimate the errors in the column
densities of the high-dispersion and the low-dispersion HI phases.


title: An Upper Limit on the Granularity of the Local Stellar Halo

abstract:
  I use the statistical properties of 4588 nearby halo stars to show that if
the local stellar halo is composed of cold streams from disrupted dwarf
satellites as is predicted by popular cosmologies, then at 95% confidence there
are at least 1350 such streams. Moreover, no stream can contain more than 2.3%
of the local stars, while average streams must contain less than 0.08%.


title: Growth Rate of Large Scale Structure as a Powerful Probe of Dark Energy

abstract:
  The redshift evolution of the growth rate of the gravitational potential,
d(D/a)/dz, is an excellent discriminator of dark energy parameters and, in
principle, more powerful than standard classical tests of cosmology. This
evolution is directly observable through the integrated Sachs-Wolfe effect in
cosmic microwave background (CMB) anisotropies. We consider the prospects of
measuring the growth rate via a novel method employed through measurements of
CMB polarization towards galaxy clusters. The potentially achievable errors on
dark energy parameters are comparable and fully complementary to those expected
from other upcoming tests of dark energy, making this test a highly promising
tool of precision cosmology.


title: Does the Sun shrink with increasing magnetic activity?

abstract:
  It has been demonstrated that frequencies of f-modes can be used to estimate
the solar radius to a good accuracy. These frequencies have been used to study
temporal variations in the solar radius with conflicting results. The variation
in f-mode frequencies is more complicated than what is assumed in these
studies. If a careful analysis is performed then it turns out that there is no
evidence for any variation in the solar radius.


title:
Perturbation configurations in a two-fluid system of singular isothermal
  disks

abstract:
  We investigate properties of stationary aligned and unaligned spiral
perturbation configurations in a composite system of gravitationally coupled
stellar and gaseous singular isothermal disks (SIDs) using the two-fluid
formalism. We obtain stationary perturbation solutions for aligned and
unaligned spiral logarithmic configurations in such a composite SID system and
derive analytically existence criteria for these solutions. In comparison with
the similar problem of a single SID studied by Shu et al. (2000), there are now
two possible sets of solutions owing to an additional SID.


title:
VLT/NACO adaptive optics imaging of the TY CrA system - A fourth stellar
  component candidate detected

abstract:
  We report the detection of a possible subsolar mass companion to the triple
young system TY CrA using the NACO instrument at the VLT UT4 during its
commissioning. Assuming for TY CrA a distance similar to that of the close
binary system HD 176386, the photometric spectral type of this fourth stellar
component candidate is consistent with an ~M4 star. We discuss the dynamical
stability of this possible quadruple system as well as the possible location of
dusty particles inside or outside the system.


title:
Gravitomagnetic corrections to the lensing deflection angle for spiral
  galaxy models

abstract:
  We investigate the effects of the gravitomagnetic corrections to the usual
gravitational lens quantities for a specific lensing mass distribution modelled
after spiral galaxies. An exponential disk is embedded into two different
spherical halo models where disk and haloes parameters are fixed according to
the observed mass to light ratios, galaxy magnitudes and rotation curves. The
general expressions for the lensing deflection angle are given also taking into
account the orientation of the galaxy disk plane with respect to the lens
plane. It is found that the gravitomagnetic term changes the deflection angle
by a typical amount of the order of ten microarcseconds.