title: High resolution imaging of CO outflows in OMC-2 and OMC-3

abstract:
  A large scale, high resolution map of CO(1-0) emission toward the OMC-2 and
OMC-3 star forming regions is presented. The map is a mosaic of 46 fields using
the Berkeley-Illinois-Maryland Array (BIMA) and covers $\sim 10'\times 15'$ at
$\sim 10" $ resolution. These data are combined with singledish FCRAO
observations and analyzed to identify and determine the properties of nine
protostellar outflows. The BIMA data alone almost completely resolve out the
cloud emission at central velocities and only recover 1/20 of the flux in the
high velocity gas showing that outflows are generally broadly dispersed over
$\sim 1'$ angular scales. All nine identified outflows emanate from known Class
0 or borderline Class 0/I sources, are associated with knots of shocked \h2\
emission, and have short dynamical times. It is suggested that only the
youngest, most spatially compact, and energetic outflows have been found and
that more distributed high velocity gas undetected by BIMA is due to older
outflows continuing through the Class I phase of protostellar evolution. The
mechanical energy injection rate into the cloud is estimated to be $\sim 1.5
L_\odot$ which is comparable to the turbulent energy dissipation rate.
Outf`lows appear capable, therefore, of sustaining cloud turbulence but a high
starformation rate is required implying a short cloud lifetime $\leq 5$ `Myr.


title: A High Resolution Intergalactic Explorer for the Soft X-ray/FUV

abstract:
  We present a mission concept for high resolution X-ray spectroscopy with a
resolving power, R~6000, (c.f. R=<1000 for Chandra, XMM-Newton). This
resolution is physics-driven, since it allows the thermal widths of coronal
X-ray lines to be measured, and astrophysics-driven, since 50 km/s resolves
internal galaxy motions, and galaxy motions within larger structures.
  Such a mission could be small and have a rapid response allowing us to `X-ray
the Universe' using the afterglows of Gamma-ray Bursts (GRBs) as strong
background sources of X-rays, and so illuminate the `Cosmic Web'. The Cosmic
Web is predicted to contain most of the normal matter (baryons) in the nearby
Universe.


title: Distances on Cosmological Scales with VLTI

abstract:
  We present here a new method using interferometric measurements of quasars,
that allows the determination of direct geometrical distances on cosmic scales.
Quasar Broad Emission Line Regions sizes provide a "meter rule" with which to
measure the metric of the Universe. This method is less dependent of model
assumptions, and even of variations in the fundamental constants (other than
c). We discuss the spectral and spatial requirements on the VLTI observations
needed to carry out these measurements.


title: Cepheid Limb Darkening Models for the VLTI

abstract:
  We present a new method to compute wavelength- and phase-dependent limb
darkening corrections for classical Cepheids. These corrections are derived
from hydrodynamic simulations and radiative transfer modeling with a full set
of atomic and molecular opacities. Comparison with hydrostatic models having
the same stellar parameters show a larger limb darkening for most phases in our
models, and temporal variations related to the hydrodynamics of the stellar
pulsation. We assess the implications of our results with respect to the
geometric Baade-Wesselink method, which uses interferometric measurements of
Cepheid angular diameters to determine their distances and radii. The relevance
of the hydrodynamic effects predicted by our model on the limb darkening of
pulsating Cepheids is finally discussed in terms of the predicted capabilities
of the VLTI.


title: Thermonuclear Stability of Material Accreting onto a Neutron Star

abstract:
  We present a global linear stability analysis of nuclear fuel accumulating on
the surface of an accreting neutron star and we identify the conditions under
which thermonuclear bursts are triggered. The analysis reproduces all the
recognized regimes of hydrogen and helium bursts, and in addition shows that at
high accretion rates, near the limit of stable burning, there is a regime of
``delayed mixed bursts'' which is distinct from the more usual ``prompt mixed
bursts.'' In delayed mixed bursts, a large fraction of the fuel is burned
stably before the burst is triggered. Bursts thus have longer recurrence times,
but at the same time have somewhat smaller fluences. Therefore, the parameter
alpha, which measures the ratio of the energy released via accretion to that
generated through nuclear reactions in the burst, is up to an order of
magnitude larger than for prompt bursts. This increase in alpha near the
threshold of stable burning has been seen in observations. We explore a wide
range of mass accretion rates, neutron star radii and core temperatures, and
calculate a variety of burst properties. From a preliminary comparison with
data, we suggest that bursting neutron stars may have hot cores, with T_{core}
>~ 10^{7.5} K, consistent with interior cooling via the modified URCA or
similar low-efficiency process, rather than T_{core} ~ 10^7 K, as expected for
the direct URCA process. There is also an indication that neutron star radii
are somewhat small <~ 10 km. Both of these conclusions need to be confirmed by
comparing more careful calculations with better data.


title: Soliton-Like Solutions of the Grad-Shafranov Equation

abstract:
  A new class of soliton-like solutions is derived for the Grad-Shafranov (GS)
equations. A mathematical analogy between the GS equation for MHD equilibria
and the cubic Schr\"odinger (CS) equation for non-linear wave propagation forms
the basis to derive the new class of solutions. The soliton-like solutions are
considered for their possible relevance to astrophysics and solar physics
problems. We discuss how a soliton-like solution can be generated by a
repetitive process of magnetic arcade stretching and plasmoid formation induced
by the differential rotation of the solar photosphere or of an accretion disk.


title:
Feedback From the First Supernovae in Protogalaxies:The Fate of the
  Generated Metals

abstract:
  We investigate the chemo-dynamical effects of multiple supernova explosions
in the central region of primordial galaxies using three-dimensional
hydrodynamical simulations of the inhomogenous interstellar medium down to
parsec-scales. We find that the final protogalactic structure and metal
distribution depend strongly on the number of SNe. Specifically, 1) 1000 SNe
after an instantaneous burst of star formation are sufficient to almost
completely blow away the gas in these systems, whereas 2) 100 SN explosions
trigger the collapse of the protogalactic cloud, leading to the formation of a
cold, dense clumpy disk (n > 300 cm^-3) with metallicity, Z = 4 10^-4 Z_sun.
These results imply that the metallicity of the ``second generation'' of stars
could be Z ~ 10^-4 Z_sun, and that the environment to form metal-free stars in
protogalaxies may be lost relatively quickly (< 10^7 yr) after the first burst
of Z=0 star formation. The recently discovered ultra-metal-poor star
(Christlieb et al. 2002) may represent surviving members of such
second-generation star formation.


title:
Galaxy groups in the 2dF galaxy redshift survey: Large Scale Structure
  with Groups

abstract:
  We use the 2dF Galaxy Group Catalogue constructed by Merch\'an & Zandivarez
to study the large scale structure of the Universe traced by galaxy groups. We
concentrate on the computation of the power spectrum and the two point
correlation function. The resulting group power spectrum shows a similar shape
to the galaxy power spectrum obtained from the 2dF Galaxy Redshift Survey by
Percival et al., but with a higher amplitude quantified by a relative bias in
redshift space of $b_s(k) \sim 1.5$ . The group two point correlation function
for the total sample is well described by a power law with correlation length
$s_0=8.9 \pm 0.3 \mpc$ and slope $\gamma=-1.6 \pm 0.1$ on scales $s < 20 \mpc$.
In order to study the dependence of the clustering properties on group mass we
split the catalogue in four subsamples defined by different ranges of group
virial masses. These computations allow a fair estimate of the relation
described by the correlation length $s_0$ and the mean intergroup separation
$d_c$ for galaxy systems of low mass. We also extend our study to the redshift
space distortions of galaxy groups, where we find that the anisotropies in the
clustering pattern of the 2dF group catalogue are consistent with gravitational
instability, with a flattening of the redshift-space correlation function
contours in the direction of the line of sight.


title: The SZ Effect Signature of Excess Entropy in Distant, Massive Clusters

abstract:
  Studies of cluster X-ray scaling relations have led to suggestions that
non-gravitational processes, e.g., radiative cooling and/or "preheating", have
significantly modified the entropy of the intracluster medium (ICM). For the
first time, we test this hypothesis through a comparison of predicted thermal
Sunyaev-Zeldovich (SZ) effect scaling relations with available data from the
literature. One of the relations that we explore, in principle, depends solely
on SZ effect observations, thus offering an X-ray independent probe of the ICM.
A detailed comparison of the theoretical relations with the largest compilation
of high redshift SZ effect data to date indicates that the presence of an
entropy floor is favored by the data. Furthermore, the inferred level of that
floor, 300 keV cm^2 or higher, is comparable to that found in studies of X-ray
scaling relations of nearby massive clusters. Thus, we find no evidence for
significant evolution of the entropy floor out to z = 0.7. We further
demonstrate that the high quality data to be obtained from the upcoming
Sunyaev-Zeldovich Array (SZA) and the (soon-to-be) upgraded Owens Valley Radio
Observatory (OVRO) array will open powerful new windows into the properties of
the ICM. Specifically, the new measurements will allow for accurate
measurements of the ICM entropy for even the most distant galaxy clusters.


title:
The Composition Gradient in M101 Revisited. II. Electron Temperatures
  and Implications for the Nebular Abundance Scale

abstract:
  (Abridged) We use high S/N spectra of 20 HII regions in the giant spiral
galaxy M101 to derive electron temperatures for the HII regions and robust
metal abundances over radii R = 0.19-1.25 Ro (6-41 kpc). We compare the
consistency of electron temperatures measured from the [O III]4363, [N II]5755,
[S III]6312, and [O II]7325 auroral lines. Temperatures from [O III], [S III],
and [N II] are correlated with relative offsets that are consistent with
expectations from nebular photoionization models. However, the temperatures
derived from the [O II]7325 line show a large scatter and are nearly
uncorrelated with temperatures derived from other ions. Our derived oxygen
abundances O/H are well fitted by an exponential distribution over six disk
scale lengths, from approximately 1.3 solar in the center to 1/15 solar in the
outermost region studied (for solar 12 + log (O/H)=8.7). We measure significant
radial gradients in N/O and He/H abundance ratios, but relatively constant S/O
and Ar/O. Our abundances are systematically lower by 0.2-0.5 dex than those
derived from the most widely used strong-line "empirical" abundance indicators.
We suspect that most of the disagreement with the strong-line abundances arises
from uncertainties in the nebular models that are used to calibrate the
"empirical" scale, and that strong-line abundances derived for HII regions and
emission-line galaxies are as much as a factor of two higher than the actual
oxygen abundances. However other explanations, such as the effects of
temperature fluctuations on the auroral line based abundances cannot be
completely ruled out. These results point to the need for direct abundance
determinations of a larger sample of extragalactic HII regions, especially for
objects more metal-rich than solar.


title: Finding White Dwarfs with Transit Searches

abstract:
  We make predictions for the rate of discovery of eclipsing white dwarf-main
sequence (WD-MS) binaries in terrestrial-planet transit searches, taking the
planned Kepler and Eddington missions as examples. We use a population
synthesis model to characterize the Galactic WD-MS population, and we find
that, despite increased noise due to stellar variability compared with the
typical planetary case, discovery of >100 non-accreting, eclipsing WD-MS
systems is likely using Kepler and Eddington, with periods of 2-20 days and
transit amplitudes of |delta m|~0.0003-0.00003 magnitudes. Follow-up
observations of these systems could accurately test the theoretical white dwarf
mass-radius relation or theories of binary star evolution.


title: Bulk viscosity, r-modes, and the early evolution of neutron stars

abstract:
  We discuss the effect of nonlinear bulk viscosity and the associated
reheating on the evolution of newly born, rapidly rotating neutron stars with
r-modes destabilized through the Chandrasekhar-Friedman-Schutz (CFS) mechanism.
Bulk viscosity in these stars is due to the adjustment of the relative
abundances of different particle species as the density of a fluid element is
perturbed. It becomes nonlinear when the chemical potential difference
$\delta\mu$, measuring the chemical imbalance in the fluid element, becomes
larger than the temperature $T$, which is generally much smaller than the Fermi
energy. From this scale on, the bulk viscosity increases much faster with
$\delta\mu$ than predicted by the usual, linear approximation. This provides a
potential saturation mechanism for stellar oscillation modes at a small to
moderate amplitude. In addition, bulk viscosity dissipates energy, which can
lead to neutrino emission, reheating of the star, or both. This is the first
study to explicitly consider these effects in the evolution of the r-mode
instability. For stars with little or no hyperon bulk viscosity, these effects
are not strong enough to prevent the r-modes from growing to amplitudes
$\alpha\sim 1$ or higher, so other saturation mechanisms will probably set in
earlier. The reheating effect makes spin-down occur at a higher temperature
than would otherwise be the case, in this way possibly avoiding complications
associated with a solid crust or a core superfluid. On the other hand, stars
with a substantial hyperon bulk viscosity and a moderate magnetic field
saturate their mode amplitude at a low value, which makes them gravitational
radiators for hundreds of years, while they lose angular momentum through
gravitational waves and magnetic braking.


title: Flat Central Density Profiles from Scalar Field Dark Matter Halo

abstract:
  The scalar field endowed with a cosh scalar field potential, behaves exactly
in the same way as cold dark matter (CDM) in the region where the scalar field
oscillates around its minimum. Also, in the linear regime, the scalar field
dark matter (SFDM) hypothesis predicts the same structure formation as the cold
dark matter one. This means that CDM and SFDM are equivalent from the
cosmological point of view. The free parameters of the SFDM model can be fixed
using cosmological observations. In a previous work, we showed by solving the
Einstein Klein Gordon equations, that if we use such parameters, the scalar
field collapses forming stable objects with a mass around $10^{12}M_{\odot}$.
In the present work we use analytical solutions of the flat and weak field
limit of the Einstein- Klein-Gordon equations. With this solutions we show that
its scalar field density profile corresponds to a halo with an almost flat
central density and that this halo coincides with the CDM model in a large
outer region. Such a result could solve the problem of the cusp DM halo in
galaxies without extra hypothesis, adding to the viability of the SFDM model.
Thus, the SFDM model can be seen as an alternative model to the CDM one, with a
self interacting WIMP.


title: Formation and Evolution of Compact Stellar X-ray Sources

abstract:
  In this chapter we review the formation and evolution of compact binaries
with neutron star and/or black hole components (i.e. LMXBs, HMXBs, binary
pulsars). After an introduction we discuss stellar evolution in binaries and
the processes involved in the mass-transfer phases of close binaries (RLO, CE,
ang.mom.loss) with radiative/convective hydrogen or helium donor stars. We also
describe the effects of accretion, asymmetric SN and systems merging as a
result of gravitational wave radiation.


title: Microlensing of Large Sources

abstract:
  We prove a gravitational lensing theorem: the magnification of a source of
uniform brightness by a foreground spherical lens is mu =1+pi(2R_E^2-R_L^2)/A,
where A is the area of the source and R_E and R_L are the Einstein radius and
size of the lens projected into the source plane; this provides an accurate
approximation to the exact magnification for R_L^2,R_E^2 << A. Remarkably, this
result is independent of the shape of the source or position of the lens
(except near the edges). We show that this formula can be generalized to
include limb-darkening of a circular source by simply inserting the
surface-brightness at the position of the foreground object (divided by the
average surface-brightness of the star). We also show that similar formulae
apply for a point-mass lens contained in a shear field and mass sheet, and for
an ensemble of point masses as long as the Einstein radii are much smaller than
the source size. This theorem may be used to compute transit or microlensing
lightcurves for which the foreground star or planet has a size and Einstein
radius much smaller than the background star.


title: The metallicity range of variables in M3

abstract:
  The recently published spectroscopic metallicities of RR Lyrae stars in M3
(Sandstrom, K., Pilachowski, C. A., and Saha, A. 2001, AJ 122, 3212) though
show a relatively wide range of the [Fe/H] values, the conclusion that no
metallicity spread is real has been drawn, as no dependence on either minimum
temperature or period was detected. Comparing these spectroscopic metallicities
with [Fe/H] calculated from the Fourier parameters of the light curves of the
variables a correlation between the [Fe/H] values appears. As a consequence of
the independence of the spectroscopic and photometric metallicities, this
correlation points to the reality of a metallicity spread. The absolute
magnitudes of these stars follow a similar trend along both the spectroscopic
and photometric metallicities as the general $\mathrm{M_V - [Fe/H]}$ relation
predicts, which strengthens that the detected metallicity range is real.


title:
Equilibrium Models of Galaxy Clusters with Cooling, Heating and
  Conduction

abstract:
  It is generally argued that most clusters of galaxies host cooling flows in
which radiative cooling in the centre causes a slow inflow. However, recent
observations by Chandra and XMM conflict with the predicted cooling flow rates.
Amongst other mechanisms, heating by a central active galactic nucleus and
thermal conduction have been invoked in order to account for the small mass
deposition rates. Here, we present a family of hydrostatic models for the
intra-cluster medium where radiative losses are exactly balanced by thermal
conduction and heating by a central source. We describe the features of this
simple model and fit its parameters to the density and temperature profiles of
Hydra A.


title: Non-equilibrium CO chemistry in the solar atmosphere

abstract:
  Investigating the reliability of the assumption of instantaneous chemical
equilibrium (ICE) for calculating the CO number density in the solar atmosphere
is of crucial importance for the resolution of the long-standing controversy
over the existence of `cool clouds' in the chromosphere, and for determining
whether the cool gas owes its existence to CO radiative cooling or to a
hydrodynamical process. Here we report the first results of such an
investigation in which we have carried out time-dependent gas-phase chemistry
calculations in radiation hydrodynamical simulations of solar chromospheric
dynamics. We show that while the ICE approximation turns out to be suitable for
modeling the observed infrared CO lines at the solar disk center, it may
substantially overestimate the `heights of formation' of strong CO lines
synthesized close to the edge of the solar disk, especially concerning vigorous
dynamic cases resulting from relatively strong photospheric disturbances. This
happens because during the cool phases of the hydrodynamical simulations the CO
number density in the outer atmospheric regions is smaller than what is
stipulated by the ICE approximation, resulting in decreased CO opacity in the
solar chromosphere. As a result, the cool CO-bearing gas which produces the
observed molecular lines must be located at atmospheric heights not greater
than 700 km, approximately. We conclude that taking into account the
non-equilibrium chemistry improves the agreement with the available on-disk and
off-limb observations, but that the hydrodynamical simulation model has to be
even cooler than anticipated by the ICE approximation, and this has to be the
case at the `new' (i.e. deeper) formation regions of the rovibrational CO
lines.


title:
Age Dependence of the Vertical Distribution of Young Open Clusters:
  Implications for Local Mass Density, Stellar Evolution, and Star Formation

abstract:
  The ages of 203 open clusters from the list of Dambis (1999) are computed in
terms of the evolutionary tracks of Pols et al. (1998) with and without the
allowance for convective overshooting. The vertical scaleheight of the cluster
layer at Galactocentric distances R_0-1 kpc < R_g< R_0+ 1 kpc varies
nonmonotonically with age, exhibiting a wavelike pattern similar to the one
earlier found for the Cepheid population (Joeveer 1974), with a period of P_Z =
74 +/- 2 Myr and P_Z = 92 +/- 2 Myr if cluster ages are computed in terms of
evolutionary models without and with overshooting, respectively. The period of
vertical oscillations can be reconciled with the known local mass density only
if cluster ages are computed with no or just mild overshooting: the
overshooting-based ages imply a local mass density of rho = 0.075 +/- 0.003
M_Sun/pc^3, which is incompatibe with the recent Hipparcos-based estimate of
rho = 0.102 M_Sun/pc^3 (Holmberg and Flynn 2000). Our results imply a maximum
local dark-mass density of rho_DM <= 0.027 M_Sun/pc^3. At the time of their
formation open clusters have, on the average, excess vertical kinetic energy
and as a population are not in virial equilibrium; moreover, their initial
vertical coordinates (at the time of birth) are strongly and positively
correlated with initial vertical velocities (r = 0.81 +/-0.08), thus favoring a
scenario where star formation in the disk is triggered by some massive objects
falling onto the Galactic plane.


title: The sigma Orionis substellar population

abstract:
  VLT/FORS spectroscopy and 2MASS near-infrared photometry, together with
previously known data, have been used to establish the membership and the
properties of a sample of low-mass candidate members of the sigma Orionis
cluster with masses spanning from 1 Msun down to about 0.013 Msun (i.e.,
deuterium-burning mass limit). We have observed K-band infrared excess and
remarkably intense H(alpha) emission in various cluster members, which, in
addition to the previously detected forbidden emision lines and the presence of
LiI in absorption at 6708 A, have allowed us to tentatively classify sigma
Orionis members as classical or weak-line TTauri stars and substellar analogs.
Variability of the H(alpha) line has been investigated and detected in some
objects. Based on the K-band infrared excesses and the intensity of H(alpha)
emission, we estimate that the minimum disk frequency of the sigma Orionis
low-mass population is in the range 5-12%.


title:
The Kinematics and Zero Point of the log P -- <M_K> Relation for
  Galactic Field RR Lyrae Variables via Statistical Parallax

abstract:
  The kinematical parameters of the local field RR Lyrae population and the
zero point of the log P--<M_K> relation for these variables are inferred by
applying the statistical parallax (maximum-likelihood) technique to a sample of
182 RR Lyraes with known periods, radial-velocities, metallicities, K-band
photometry, and absolute proper motions on the ICRS system. The K-band
magnitudes were adopted from the list of Fernley et al. (1998) and the 2MASS
Second Incremental Data Release. The parameters of the velocity distribution
are found to be (U_0,V_0,W_0) = (-10 +/- 10, -51 +/- 8, -14 +/- 5) km/s,
(sigma_U, sigma_V, sigma_W) = (62 +/- 10, 45 +/- 8, 28 +/- 6) km/s and
(U_0,V_0,W_0) = (-23 +/- 13, -213 +/- 12, -5 +/- 8) km/s, (sigma_U, sigma_V,
sigma_W) = (157 +/- 12, 98 +/- 8, 91 +/- 7) km/s for the thick-disk (41 stars)
and halo (141 stars) objects, respectively. The zero point of the infrared PL
relation of Jones et al. (1992) (based on the results obtained using the
Baade-Wesselink method) is confirmed: we find <M_K> = -2.33 log P_F-0.82 +/-
0.12 compared to <M_K> = -2.33 log P_F-0.88 as inferred by Jones et al. (1992).
A conversion of the resulting log P-<M_K> relation to V-band luminosities
yields the metallicity-luminosity relation <M_V> = +1.04 + 0.14 [Fe/H] +/-
0.11. Our results imply a solar Galactocentric distance of R_0 = 7.6 +/- 0.4
kpc and an LMC distance modulus of DM_LMC = 18.18 +/- 0.12 (cluster RR Lyraes)
or DM_LMC = 18.11 +/- 0.12 (field RR Lyraes), thereby favoring the so-called
short distance scale.


title:
A grid of synthetic ionizing spectra for very hot compact stars from
  NLTE model atmospheres

abstract:
  The precise analysis of properties of planetary nebulae is strongly dependent
on good models for the stellar ionizing spectrum. Observations in the UV -
X-ray wavelength range as well as NLTE model atmosphere calculations of spectra
of their exciting stars have shown that neither blackbody fluxes nor "standard"
NLTE atmosphere models which are composed out of hydrogen and helium only are
good approximations. Strong differences between synthetic spectra from these
compared to observed spectra at energies higher than 54 eV (He II ground state)
can be ascribed to the neglect of metal-line blanketing.
  Realistic modeling of the emergent fluxes of hot stars in the UV - X-ray
wavelength range requires metal-line blanketed NLTE model atmospheres which
include all elements from hydrogen up to the iron-group. For this purpose, we
present a grid (solar and halo abundance ratios) of metal-line blanketed NLTE
model atmosphere fluxes which covers the parameter range of central stars of
planetary nebulae.


title: Tomography of high-redshift clusters with OSIRIS

abstract:
  High-redshift clusters of galaxies are amongst the largest cosmic structures.
Their properties and evolution are key ingredients to our understanding of
cosmology: to study the growth of structure from the inhomogeneities of the
cosmic microwave background; the processes of galaxy formation, evolution, and
differentiation; and to measure the cosmological parameters (through their
interaction with the geometry of the universe, the age estimates of their
component galaxies, or the measurement of the amount of matter locked in their
potential wells). However, not much is yet known about the properties of
clusters at redshifts of cosmological interest. We propose here a radically new
method to study large samples of cluster galaxies using microslits to perform
spectroscopy of huge numbers of objects in single fields in a narrow spectral
range-chosen to fit an emission line at the cluster redshift. Our objective is
to obtain spectroscopy in a very restricted wavelength range (~100 A in width)
of several thousands of objects for each single 8x8 square arcmin field.
Approximately 100 of them will be identified as cluster emission-line objects
and will yield basic measurements of the dynamics and the star formation in the
cluster (that figure applies to a cluster at z~0.50, and becomes ~40 and ~20
for clusters at z~0.75 and z~1.00 respectively). This is a pioneering approach
that, once proven, will be followed in combination with photometric redshift
techniques and applied to other astrophysical problems.


title: New metallicity calibration down to [Fe/H] = -2.75 dex

abstract:
  88 dwarfs, covering the colour index interval 0.37 <(B-V)o <= 1.07 mag, with
metallicities -2.70 <= [Fe/H] <= +0.26 dex have been taken from three different
sources for new metallicity calibration. The catalogue of Cayrel de Stroble et
al. (2001) which includes 65% of the stars in our sample supplies detailed
information on abundances for stars with determination based on high resolution
spectroscopy. 77 stars which supplies at least one of the following conditions
have been used as "corner stones" for constructing the new calibration: (i) the
parallax is larger than 10 mas (distance relative to the Sun less than 100 pc)
and the galactic latitude is absolutely higher than 30 degrees, (ii) the
parallax is rather large, if the galactic latitude is absolutely low and vice
versa. Contrary to the previous investigations, a third-degree polynomial
fitted for the new calibration: [Fe/H] = 0.10-2.76d-24.04d^2+30.00d^3. The
coefficients were evaluated by the least-square method, without regarding the
metallicity of Hyades. However, the constant term is in the range of
metallicity determined for this cluster i.e.: 0.08 <= [Fe/H] <= 0.11 dex. The
mean deviation and the mean error in our work are equal to those of Carney
(1979), for [Fe/H] >= -1.75 dex where Carney's calibration is valid.


title: A new seismic analysis of Alpha Centauri

abstract:
  Models of alpha Cen A & B have been computed using the masses determined by
Pourbaix et al. (2002) and the data derived from the spectroscopic analysis of
Neuforge and Magain (1997). The seismological data obtained by Bouchy and
Carrier (2001, 2002) do help improve our knowledge of the evolutionary status
of the system. All the constraints are satisfied with a model which gives an
age of about 6 Gyr for the binary.


title: A New Metallicity Calibration for Dwarfs for the RGU-Photometry

abstract:
  We adopted the procedure of Carney to obtain a metallicity calibration for
dwarfs for the RGU-photometry. For this purpose we selected 76 dwarfs of
different metallicities from Carney, and Strobel et al., and evaluated their
\delta(U-G) ultra-violet excess relative to Hyades by transforming their UBV
magnitudes to RGU via metallicity dependent equations of Ak-Gungor. The
\delta_{0.6}/\deltaM normalized factors of Sandage transform \delta(U-G) excess
at any G-R to \delta=\delta_{1.08}, i.e.: the ultra-violet excess at G-R=1.08
mag, corresponding to B-V = 0.60 mag in the UBV-system. Finally, the (\delta,
[Fe/H]) couples were fitted by the equation [Fe/H] = 0.11-2.22d-7.95d^2. This
calibration covers the metallicity interval (-2.20, +0.20) dex.


title: Coevolution of Black Holes and Galaxies: Conference Summary

abstract:
  In the past decade, much effort was devoted to measure the masses of
supermassive black holes in galactic nuclei, to establish the relation between
black hole mass and the global/nuclear properties of the host galaxy, and to
understand the role of these objects in the formation and subsequent dynamical
evolution of galaxies. This whole area of research is an appropriate and timely
topic for the first in this series of symposia. Nearly half the contributions
were devoted to the various methods that are being used to estimate masses of
central black holes, from nearby globular clusters all the way to quasars at
redshifts z>6. This work forms the foundation of our understanding of black
hole demography, and provides constraints on scenarios for black hole formation
and growth, and on their connection to the formation and properties of the host
galaxy. I will address these topics in this same order.


title:
HETE-2 Localization and Observation of the Bright, X-Ray-Rich Gamma-Ray
  Burst GRB021211

abstract:
  A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec
2002. The WXM localization was to 14' and relayed to the GCN 22 s after the
start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m
00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse
with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number
and photon energy fluxes in the 2-400 keV band, are 34.0 +/- 1.8 ph cm^-2 s^-1
and 1.68 +/- 0.11 x 10^-6 erg cm^-2 s^-1, respectively. The energy fluences in
the 2-30 keV and 30-400 kev energy bands are S_X = 1.36 +/- 0.05 x 10^-6 erg
cm^-2 and S_gamma 2.17 +/- 0.15 x 10^-6 erg cm^-2, respectively. Thus GRB021211
is an X-ray-rich GRB (S_X/S_gamma = 0.63 > 0.32). The spectrum is well-fit by a
Band function (alpha = -0.805, beta = -2.37, E_peak = 46.8 keV). The prompt
localization allowed the detection of an optical afterglow for what would
otherwise have been an ``optically dark'' GRB. GRB 021211 demonstrates that
some fraction of burst afterglows are ``optically dark'' because their optical
afterglows at times > 1 hr after the burst are very faint, and thus have often
escaped detection. GRB 021211 shows that such ``optically dim'' bursts can have
very bright afterglows at times < 20 min after the burst.


title: Discovery of a quiescent neutron star binary in the globular cluster M13

abstract:
  We have discovered with XMM-Newton an X-ray source in the core of the
globular cluster M13, whose X-ray spectral properties suggest that it is a
quiescent neutron star X-ray binary. The spectrum can be well fitted with a
pure hydrogen atmosphere model, with T=76 +/- 3 eV, R=12.8 +/- 0.4 km and an
X-ray luminosity of 7.3 +/- 0.6 x 10^{32} erg/s. In the light of this result,
we have discovered a strong correlation between the stellar encounter rate and
the number of quiescent neutron stars found in the ten globular clusters
observed so far by either XMM-Newton or Chandra. This result lends strong
support to the idea that these systems are primarily produced by stellar
encounters in the core of globular clusters.


title:
Analytical Predictions for Statistics of Cosmic Shear: Tests Against
  Simulations

abstract:
  Weak gravitational lensing surveys are rapidly becoming important tools to
probe directly the mass density fluctuations in the universe and its background
dynamics. Earlier studies have shown that it is possible to model the
statistics of the convergence field on small angular scales by suitably
modeling the statistics of the underlying density field in the highly
non-linear regime. We extend such methods to model the complete probability
distribution function, PDF, of the shear as a function of smoothing angle. Our
model relies on a simple hierarchical Ansatz for the behaviour of the
higher-order correlations in the density field. We compare our predictions with
the results of numerical simulations and find excellent agreement for different
cosmological scenarios. Our method provides a new way to study the evolution of
non-Gaussianity in gravitational clustering and should help to break the
degeneracies in parameter estimation based on analysis of the power spectrum
alone.


title:
The Parkes multibeam pulsar survey: III. Young pulsars & the discovery
  and timing of 200 pulsars

abstract:
  The Parkes multibeam pulsar survey has unlocked vast areas of the Galactic
plane which were previously invisible to earlier low-frequency and
less-sensitive surveys. The survey has discovered more than 600 new pulsars so
far, including many that are young and exotic. In this paper we report the
discovery of 200 pulsars for which we present positional and spin-down
parameters, dispersion measures, flux densities and pulse profiles. A large
number of these new pulsars are young and energetic, and we review possible
associations of $\gamma$-ray sources with the sample of about 1300 pulsars for
which timing solutions are known. Based on a statistical analysis, we estimate
that about $19\pm6$ associations are genuine. The survey has also discovered 12
pulsars with spin properties similar to those of the Vela pulsar, nearly
doubling the known population of such neutron stars. Studying the properties of
all known `Vela-like' pulsars, we find their radio luminosities to be similar
to normal pulsars, implying that they are very inefficient radio sources.
Finally, we review the use of the newly discovered pulsars as Galactic probes
and discuss the implications of the new NE2001 Galactic electron density model
for the determination of pulsar distances and luminosities.


title: Ultrahigh Energy Neutrals from Extreme Magnetic Flares

abstract:
  It is shown that bulk acceleration during reconnection of extremely strong
magnetic fields near compact objects can accelerate ions to Lorentz factors of
$\sim 10^2 \sigma^{3/5}$ under general conditions, where $\sigma$, the magnetic
energy per current-carrying proton rest energy, can approach $10^{15}$. For
magnetar-type fields, neutrons and neutrinos can be generated at potentially
detectable levels via hadron polarization. Ultrahigh energy photons can also be
emitted and escorted from the high field region by Poynting flux.


title: Inflation at the maxima of the potentials

abstract:
  We construct a two-stage inflationary model which can accommodate early
inflation at a scale $\Lambda_1$ as well as a second stage of inflation at
$\Lambda_2$ with a single scalar field $\phi$.
  We use a symmetric potential, valid in a frictionless world, in which the two
inflationary periods have exactly the same scale, i.e. $\Lambda_1=\Lambda_2$.
However, we see today $\Lambda_1 \gg \Lambda_2$ due to the friction terms
(expansion of the universe and interaction with matter). These type of models
can be motivated from supergravity.
  Inflation occurs close to the maxima of the potential. As a consequence both
inflations are necessarily finite. This opens the interesting possibility that
the second inflation has already or is about to end. A first inflation is
produced when fluctuations displace the inflaton field from its higher maximum
rolling down the potential as in new inflation. Instead of rolling towards a
global minimum the inflaton approaches a lower maximum where a second inflation
takes place.


title: Probing the Ionization State of the Universe at z>6

abstract:
  We present high signal-to-noise ratio Keck ESI spectra of the two quasars
known to have Gunn-Peterson absorption troughs, SDSS J1030+0524 (z=6.28) and
SDSS J1148+5251 (z=6.37). The Ly alpha and Ly beta troughs for SDSS J1030+0524
are very black and show no evidence for any emission over a redshift interval
of ~0.2 starting at z=6. On the other hand, SDSS J1148+5251 shows a number of
emission peaks in the Ly beta Gunn-Peterson trough along with a single weak
peak in the Ly alpha trough. The Ly alpha emission has corresponding Ly beta
emission, suggesting that it is indeed a region of lower optical depth in the
intergalactic medium at z=6.08.
  The stronger Ly beta peaks in the spectrum of SDSS J1148+5251 could
conceivably also be the result of "leaks" in the IGM, but we suggest that they
are instead Ly alpha emission from an intervening galaxy at z=4.9. This
hypothesis gains credence from a strong complex of C IV absorption at the same
redshift and from the detection of continuum emission in the Ly alpha trough at
the expected brightness. If this proposal is correct, the quasar light has
probably been magnified through gravitational lensing by the intervening
galaxy. The Stromgren sphere observed in the absorption spectrum of SDSS
J1148+5251 is significantly smaller than expected based on its brightness,
which is consistent with the hypothesis that the quasar is lensed.
  If our argument for lensing is correct, the optical depths derived from the
troughs of SDSS J1148+5251 are only lower limits (albeit still quite strong,
with tau(LyA)>16 inferred from the Ly beta trough.) The Ly beta absorption
trough of SDSS J1030+0524 gives the single best measurement of the IGM
transmission at z>6, with an inferred optical depth tau(LyA)>22.


title:
Age and Abundance Discrimination in Old Stellar Populations Using
  Mid-Ultraviolet Colors

abstract:
  The restframe mid-ultraviolet spectral region (2000-3200 A) is important in
analyzing the stellar populations of the "red envelope" systems observed at
high redshifts. Here, we explore the usefulness of the mid-UV for determining
ages and abundances of old populations. A mid-UV to optical/IR wavelength
baseline provides good separation of population components because the main
sequence turnoff dominates the integrated light between 2500 and 4000 A. We
find a six magnitude difference in the mid-UV continuum level over the
metallicity range -1.5 < log Z/Z_o < +0.5 and a comparable difference (per unit
log t) for ages in the range 4-16 Gyr. Logarithmic derivatives of mid-UV colors
with respect to age or metal abundance are 3-10 times larger than for the UBV
region. Most of the spectral information on old populations therefore resides
below 4000 A. We investigate the capability of UBV and mid-UV broad-band colors
to separately determine age and abundance, taking into account precision in the
color measurements. We find that the mid-UV improves resolution in (log t,log
Z) space by about a factor of 3 for a given observational precision.
Contamination by hot horizontal branch phases can seriously affect mid-UV
spectra, reaching over 80% in some cases. However, this is straightforward to
remove as long as far-UV measurements are available. Finally, we show that a 4
Gyr, solar abundance model based on empirical spectra provides an excellent fit
to the mid-UV spectrum of the E galaxy M32. This indicates that the poorer
results obtained from theoretical spectra arise from limitations of the
synthesis models for individual stars. [Condensed]


title:
The case for late-time optical bumps in GRB afterglows as a supernova
  signature

abstract:
  Observations of late-time optical bumps have been reported for several GRBs.
The timescale for such bumps, and colors of such when available, find a natural
explanation as due to associated supernovae. Ground-based and HST observations
of the afterglow and bump of GRB 011121, in particular, place the strongest
constraints yet on the physical nature of the supernova and any alternative
explanations, such as supranovae or dust echoes. I summarize the search for
underlying bumps in other GRBs and make the case for the supernova hypothesis
in light of observed bumps and bump non-detections (e.g., GRB 010921).


title:
2-D Radiative Transfer in Protostellar Envelopes: I. Effects of Geometry
  on Class I Sources

abstract:
  We present 2-D radiation transfer models of Class I Protostars and show the
effect of including more realistic geometries on the resulting spectral energy
distributions and images. We begin with a rotationally flattened infalling
envelope as our comparison model, and add a flared disk and bipolar cavity. The
disk affects the spectral energy distribution most strongly at edge-on
inclinations, causing a broad dip at about 10 um (independent of the silicate
feature) due to high extinction and low scattering albedo in this wavelength
region. The bipolar cavities allow more direct stellar+disk radiation to emerge
into polar directions, and more scattering radiation to emerge into all
directions. The wavelength-integrated flux, often interpreted as luminosity,
varies with viewing angle, with pole-on viewing angles seeing 2-4 times as much
flux as edge-on, depending on geometry. Thus, observational estimates of
luminosity should take into account the inclination of a source. The envelopes
with cavities are significantly bluer in near-IR and mid-IR color-color plots
than those without cavities. Using 1-D models to interpret Class I sources with
bipolar cavities would lead to an underestimate of envelope mass and an
overestimate of the implied evolutionary state. We compute images at near-,
mid-, and far-IR wavelengths. We find that the mid-IR colors and images are
sensitive to scattering albedo, and that the flared disk shadows the midplane
on large size scales at all wavelengths plotted. Finally, our models produce
polarization spectra which can be used to diagnose dust properties, such as
albedo variations due to grain growth. Our results of polarization across the
3.1 um ice feature agree well with observations for ice mantles covering 5% of
the radius of the grains.


title:
X-ray Bursts in Neutron Star and Black Hole Binaries from USA and RXTE
  Data: Detections and Upper Limits

abstract:
  Narayan and Heyl (2002) have developed a theoretical framework to convert
suitable upper limits on type I X-ray bursts from accreting black hole
candidates (BHCs) into evidence for an event horizon. However, no appropriate
observational limit exists in the literature. In this paper we survey 2101.2 ks
of data from the Unconventional Stellar Aspect (USA) X-ray timing experiment
and 5142 ks of data from the Rossi X-ray Timing Explorer (RXTE) experiment to
obtain a formal constraint of this type. 1122 ks of neutron star data yield a
population averaged mean burst rate of 1.69 x 10-5 bursts s-1 while 6081 ks of
BHC data yield a 95% confidence level upper limit of 4.9 x 10-7 bursts s-1.
This is the first published limit of this type for Black Hole Candidates.
  Applying the theoretical framework of Narayan and Heyl (2002) we calculate
regions of unstable luminosity where the neutron stars are expected to burst
and the BHCs would be expected to burst if they had a surface. In this unstable
luminosity region 464 ks of neutron star data yield an averaged mean burst rate
of 4.1 x 10-5 bursts s-1 and 1512 ks of BHC data yield a 95% confidence level
upper limit of 2.0 x 10-6 bursts s-1, and a limit of > 10\sigma that BHCs do
not burst with a rate similar to the rate of neutron stars in these unstable
regions. This gives further evidence that BHCs do not have surfaces unless
there is some new physics occurring on their surface.


title: The Epoch of Reionization in Models with Reduced Small Scale Power

abstract:
  Reducing the power on small scales relative to the `standard' LCDM model
alleviates a number of possible discrepancies with observations, and is favored
by the recent analysis of WMAP plus galaxy and Lyman-alpha forest data. Here,
we investigate the epoch of reionization in several models normalized to WMAP
on large scales, and with sufficiently reduced power on small scales to solve
the halo concentration and substructure problems. These include a tilted model,
the WMAP running-index model, and a Warm Dark Matter model. We assume that the
Universe was reionized by stellar sources comprised of a combination of
supermassive (~200 M_sun) Pop III stars and Pop II stars with a `normal' IMF.
We find that in all of these models, structure formation and hence reionization
occurs late, certainly at redshifts below ten, and more probably at z < 6. This
is inconsistent (at 2 sigma) with the determination of z_reion ~ 17 from the
WMAP temperature-polarization data and is only marginally consistent with SDSS
quasar observations. The tension between the galactic-scale observations, which
favor low-power models, and the early reionization favored by WMAP can only be
resolved if the efficiency of Pop III star formation is dramatically higher
than any current estimate, or if there is an exotic population of ionizing
sources such as mini-quasars. Otherwise, we may have to live with the standard
LCDM power spectrum, and solve the small-scale problems in some other way.


title:
Relativistic Magnetohydrodynamics with Application to Gamma-Ray Burst
  Outflows: I. Theory and Semianalytic Trans-Alfvenic Solutions

abstract:
  We present a general formulation of special-relativistic magnetohydrodynamics
and derive exact radially self-similar solutions for axisymmetric outflows from
strongly magnetized, rotating compact objects. We generalize previous work by
including thermal effects and analyze in detail the various forces that guide,
accelerate, and collimate the flow. We demonstrate that, under the assumptions
of a quasi-steady poloidal magnetic field and of a highly relativistic poloidal
velocity, the equations become effectively time-independent and the motion can
be described as a frozen pulse. We concentrate on trans-Alfvenic solutions and
consider outflows that are super-Alfvenic throughout in the companion paper.
Our results are applicable to relativistic jets in gamma-ray burst (GRB)
sources, active galactic nuclei, and microquasars, but our discussion focuses
on GRBs. We envision the outflows in this case to initially consist of a hot
and optically thick mixture of baryons, electron-positron pairs, and photons.
We show that the flow is at first accelerated thermally but that the bulk of
the acceleration is magnetic, with the asymptotic Lorentz factor corresponding
to a rough equipartition between the Poynting and kinetic-energy fluxes (i.e.,
\~50% of the injected total energy is converted into baryonic kinetic energy).
The electromagnetic forces also strongly collimate the flow, giving rise to an
asymptotically cylindrical structure.


title:
Relativistic Magnetohydrodynamics with Application to Gamma-Ray Burst
  Outflows: II. Semianalytic Super-Alfvenic Solutions

abstract:
  We present exact radially self-similar solutions of special-relativistic
magnetohydrodynamics representing ``hot'' super-Alfvenic outflows from strongly
magnetized, rotating compact objects. We argue that such outflows can plausibly
arise in gamma-ray burst (GRB) sources and demonstrate that, just as in the
case of the trans-Alfvenic flows considered in the companion paper, they can
attain Lorentz factors that correspond to a rough equipartition between the
Poynting and kinetic-energy fluxes and become cylindrically collimated on
scales compatible with GRB observations. As in the trans-Alfvenic case, the
initial acceleration is thermal, but, in contrast to the solutions presented in
Paper I, part of the enthalpy flux is transformed into Poynting flux during
this phase. The subsequent, magnetically dominated acceleration can be
significantly less rapid than in trans-Alfvenic flows.


title:
Conceptual Design of a Cosmic Ray Detector Operating Between 10^17 and
  10^19 eV for the Study of the Galactic Center

abstract:
  For our understanding of the origin of ultra high energy cosmic rays, the
energy region between 10^17 and 10^19 eV is of crucial importance. Previous
experiments have found indirect evidence that at these energies, the origin of
cosmic rays changes from predominantly Galactic to extragalactic. In addition,
weak evidence for an excess of cosmic rays from the direction of the Galactic
center in a narrow energy band around 10^18 eV has been claimed. However, so
far there is no direct evidence supporting this scenario. Neither Galactic nor
extragalactic sources have been unambiguously established. Given the importance
of this energy range, there is a strong case for a dedicated experiment to
study the EeV energy region with high precision. We present the conceptual
design of GRaNDScan, a mobile stereo air fluorescence detector optimized to
study the spectrum, composition, and arrival direction of cosmic rays in this
important energy range. If located at a site on the southern hemisphere with
good exposure to the Galactic center, this type of experiment will provide an
accurate map of the Galactic center region, long suspected to harbor one or
several sources of ultra high energy cosmic rays.


title: Extragalactic Objects in Basle Fields

abstract:
  We discriminated the extragalactic objects (galaxies and quasars) from stars
for Basle star fields, Plaut I, SA 54, and SA 82 by comparison of Basle fields
and APS POSS I finder charts. Their numbers are 187, 70, and 93 for Plaut I, SA
54, and SA 82, respectively. Most of these objects are apparently faint in V,
and they cause an overestimated local luminosity function for absolutely faint
magnitudes, M(V) > 5. This effect is more conspicious for the field Plaut I.


title:
An XMM-Newton view of the extended "filament" near the cluster of
  galaxies Abell 85

abstract:
  We have observed with XMM-Newton the extended 4 Mpc filament detected by the
ROSAT PSPC in the neighbourhood of the cluster of galaxies Abell 85. We confirm
that there is an extended feature, aligned at the same position angle as the
major axis of the central cD, the bright cluster galaxies, and nearby groups
and clusters. We find that the X-ray emission from the filament is best
described by thermal emission with a temperature of about 2 keV, which is
significantly lower than the ambient cluster medium, but is significantly
higher than anticipated for a gas in a weakly bound extended filament. It is
not clear whether this is a filament of diffuse emission, a chain of several
groups of galaxies, or stripped gas from the infalling south blob.


title: The near-IR Ca II triplet - sigma relation for bulges of spiral galaxies

abstract:
  We present measurements of the near-infrared Calcium II triplet (CaT, CaT*),
Paschen (PaT) and Magnesium (MgI) indices for a well-studied sample of 19
bulges of early to intermediate spiral galaxies. We find that both the CaT* and
CaT indices decrease with central velocity dispersion (sigma) with small
scatter. This dependence is similar to that recently found by Cenarro (2002)
for elliptical galaxies, implying an uniform CaT* -- sigma relation that
applies to galaxies from ellipticals to intermediate-type spirals. The decrease
of CaT and CaT* with sigma contrasts with the well-known increase of another
alpha-element index, Mg_2, with sigma. We discuss the role of Ca underabundance
([Ca/Fe]<0) and IMF variations in the onset of the observed relations.


title: A New Evolutionary Channel for Type Ia Supernovae

abstract:
  We show that long-period dwarf novae offer a promising route for making Type
Ia supernovae. For typical dwarf nova duty cycles d ~ 0.1 - 0.01, mass is
accreted by the white dwarf mainly during dwarf nova outbursts at rates
allowing steady nuclear burning of most of the accreted matter. Mass gains up
to ~ 0.4 Msun are possible in this way. Although these are too small to allow a
0.7 Msun WD to reach the Chandrasekhar mass, they are sufficient if the WD grew
to ~ 1 Msun in a previous episode of thermal-timescale mass transfer, i.e. for
those long-period dwarf novae which descend from supersoft binaries. A further
advantage of this picture is that the supernova always occurs in a binary of
small secondary/primary mass ratio, with the secondary having very little
remaining hydrogen. Both features greatly reduce the possibility of hydrogen
contamination of the supernova ejecta.


title:
A new white dwarf constraint on the rate of change of the gravitational
  constant

abstract:
  In this paper we derive a bound on the rate of change of the gravitational
constant G coming from the pulsating white dwarf G117-B15A. This star is a ZZ
Ceti pulsator extensively studied with astroseismological techniques for last
three decades. The most recent determination of {\dot P} = (2.3 \pm 1.4) *
10^{-15} s/s^{-1} for the 215.2s fundamental mode agrees very well with
predictions of the best fit theoretical model. The rate of change of the
oscillation period can be explained by two effects: the cooling (dominant
factor) and change of gravitational binding energy (residual gravitational
contraction). Since the white dwarfs are pulsating in g-modes whose frequencies
are related to the Brunt-Vaisala frequency (explicitly dependent on G)
observational determination of the change of the period (more precisely the
difference between observed and calculated \dot P) can be used to set the upper
bound on the rate of change of G. In the light of the current data concerning
G117-B15A we derive the following bound: |{\frac {\dot G}{G}}| \leq 4.10 \times
10^{-10} yr^{-1}. Our result is model independent in the sense that it does not
need to invoke a concrete physical theory (such like Brans-Dicke
theory)underlying the temporal variability of G. We also demonstrate that
varying gravitational constant G does not modify cooling of white dwarfs in a
significant way. This result implies that some earlier claims present in the
literature that varying G can be reflected in the WD luminosity function are
not correct.


title: The Cepheid Instability Strip in the GAIA Era

abstract:
  We present recent results concerning distance determinations based on the two
most popular primary distance indicators, namely classical Cepheids and RR
Lyrae. We discuss the problems affecting the Cepheid distance scale, and in
particular the dependence of fundamental Period-Luminosity (PL) and
Period-Luminosity-Color (PLC) relations on the metal content. The key
advantages in using the K-band PL relation of RR Lyrae stars when compared with
the M_V vs [Fe/H] are also presented.


title:
Spherically symmetric relativistic MHD simulations of pulsar wind
  nebulae in supernova remnants

abstract:
  Pulsars, formed during supernova explosions, are known to be sources of
relativistic magnetized winds whose interaction with the expanding supernova
remnants (SNRs) gives rise to a pulsar wind nebula (PWN). We present
spherically symmetric relativistic magnetohydrodynamics (RMHD) simulations of
the interaction of a pulsar wind with the surrounding SNR, both in particle and
magnetically dominated regimes. As shown by previous simulations, the evolution
can be divided in three phases: free expansion, a transient phase characterized
by the compression and reverberation of the reverse shock, and a final Sedov
expansion. The evolution of the contact discontinuity between the PWN and the
SNR (and consequently of the SNR itself) is almost independent of the
magnetization of the nebula as long as the total (magnetic plus particle)
energy is the same. However, a different behaviour of the PWN internal
structure is observable during the compression-reverberation phase, depending
on the degree of magnetization=2E The simulations were performed using the
third order conservative scheme by Del Zanna et al. (2003).


title: Separating the X-Ray Emissions of UV Ceti A and B with Chandra

abstract:
  We present the first spatially separated X-ray observation of the active UV
Ceti binary with \textit{Chandra}, providing important new information on the
relative X-ray activity levels of its nearly identical dM5.5e components. The
two components had similar X-ray luminosities during low-level periods and
emission measure loci derived from Low Energy Transmission Grating spectra
reveal similar coronal temperatures ($3 - 6$ MK). However, the B component
showed a higher degree of variability, resulting in a higher average X-ray
luminosity than that of UV Cet A. We discuss possible causes of this enhanced
activity in UV Ceti B.


title: The Carina Project: II. Stellar Populations

abstract:
  We present a new (V,B-V) Color-Magnitude Diagram (CMD) of the Carina dwarf
spheroidal (dSph) that extends from the tip of the Red Giant Branch (RGB) down
to about V=25 mag. Data were collected with the Wide Field Imager (WFI)
available at 2.2m ESO/MPI telescope and cover an area of about 0.3 square
degrees around the center of the galaxy. We confirm the occurrence of a
substantial amount of old stars with ages around 11 Gyr, together with an
intermediate-age population around 5 Gyr. Moreover, we also detected a new
well-defined blue plume of young Main-Sequence (MS) stars with an age at most
of the order of 1 Gyr. At odds with previous results available in the
literature we found thatstars along the RGB of the old and of the
intermediate-age stellar populationindicate a mean metallicity roughly equal to
Z=0.0004 and a small dispersion around this value. We find evidence for a
smooth spatial distribution of the "intermediate-age" stellar population, which
appears more centrally concentrated than the oldest one.


title: XMM-Newton observations of High Mass X-ray Binaries in the SMC

abstract:
  Based on XMM-Newton EPIC data of four pointings towards the Small Magellanic
Cloud (SMC), results on timing and spectral analyses of 16 known high mass
X-ray binaries (HMXBs) and HMXB candidates in the SMC are presented. We confirm
the pulse periods of four sources which were known to show pulsations. In
addition, two new X-ray pulsars are discovered: XMMU J005605.2-722200 with
P_pulse = 140.1 +/- 0.3 s and RX J0057.8-7207 with P_pulse = 152.34 +/- 0.05 s.
Due to the low Galactic foreground absorption, X-ray binary systems in the
Magellanic Clouds are well suited for studies of the soft component in their
X-ray spectrum. Spectral analysis reveals soft emission besides a power law
component in the spectra of three sources. The existence of emission lines in
at least one of them corroborates the thermal nature of this emission with
temperatures of 0.2 - 0.3 keV and heavy element abundances lower than solar.
For the HMXB SMC X-2 which was in a low luminosity state, we determine a flux
upper limit of 1.5 x 10^-14 erg cm^-2 s^-1 (0.3 - 10.0 keV). Furthermore, two
new sources (XMMU J005735.7-721932 and XMMU J010030.2-722035) with hard
spectrum and emission line objects as likely optical counterparts are proposed
as new X-ray binary candidates.


title: Molecular Hydrogen in Damped Ly-alpha Systems: Spatial Distribution

abstract:
  To interpret H_2 quasar absorption line observations in Damped Ly-alpha
clouds (DLAs), we model the H_2 spatial distribution within a DLA. Based on
numerical simulations of disk structures with parameters similar to those
derived for such absorbers, we calculate the H_2 distribution as a function of
ultraviolet background (UVB) intensity and dust-to-gas ratio. For typical
values of these two quantities we find that the area in which the H_2 fraction
exceeds 10^{-6} (typical observational detection limit) only covers $\la 10$%
of the disk surface, i.e. H_2 has a very inhomogeneous, clumpy distribution
even at these low abundance levels. This explains the relative paucity of H_2
detections in DLAs. We also show the dependence of the covering fraction of H_2
on dust-to-gas ratio and UVB intensity and we comment on the physics governing
the H_2 chemical network at high redshift.


title: New radiative transfer models for obscuring tori in active galaxies

abstract:
  Two-dimensional radiative transfer is employed to obtain the broad-band
infrared spectrum of active galaxies. In the models we vary the geometry and
size of the obscuring medium, the surface density, the opacity and the grain
size distribution. Resulting spectral energy distributions are constructed for
different orientations of the toroid. Colour-colour comparisons with
observational data are consistent with previous observations that the emission
longward of 60 micron is produced by star-formation and unrelated to the
presence of an obscuring torus. We also find that the toroid cannot be flat,
but is rather conical or flaring. The density is most likely constant with
radius, and the size is relatively large with an inner radius around 10 pc. A
direct comparison with radio galaxy Cygnus A yields a best fit for a conical
disk with constant surface density, and a size from 10 to 30 pc assuming the
far-infrared emission is due to star-formation in the host galaxy.


title: Cosmological Evolution of Homogeneous Universal Extra Dimensions

abstract:
  The lightest Kaluza-Klein particle appearing in models with universal extra
dimensions has recently been proposed as a viable dark matter candidate when
the extra dimensions are compactified on a scale of the order of 1 TeV.
Underlying assumptions of this proposal are that the size of the extra
dimensions stays constant and that the evolution of the universe is given by
standard cosmology. Here we investigate, both analytically and numerically,
whether this is possible without introducing an explicit stabilization
mechanism. By analyzing Einstein's field equations for a (3+n+1)-dimensional
homogeneous, but in general anisotropic universe, we find that approximately
static extra dimensions arise naturally during radiation domination. For matter
domination, however, there are no solutions to the field equations that allow
static extra dimensions or the usual behavior of the scale factor for ordinary
three-dimensional space. We conclude that an explicit mechanism is needed in
order to stabilize the extra dimensions and reproduce standard cosmology as we
know it.


title: Unidentified EGRET sources in the Galaxy

abstract:
  Identifying gamma-ray sources in the Galaxy is hampered by their poor
localization, source confusion, and the large variety of potential emitters.
Neutron stars and their environment offer various ways to power gamma-ray
sources: pulsed emission from the open magnetosphere and unpulsed gamma rays
from the wind nebula and from the cosmic rays accelerated in the supernova
remnant. While the latter still awaits confirmation, new candidate associations
bring forward the importance of 10-kyr old pulsars as GeV sources, with a
diversity that will help constrain the acceleration mechanisms near the pulsar
and in the wind. Theoretical interest in the gamma-ray activity of X-ray
binaries and micro-quasars has also been revived by the emergence of a subset
of variable sources in the inner Galaxy and another one in the halo.


title: String Cosmology: A Review

abstract:
  The second string revolution, which begin around 1995, has led to a drastic
alteration in our perception of the universe, perhaps even more so then did the
first string revolution of 1984. That is, extending 10-dimensional string
theory to 11-dimensional M-theory has had more profound implications than did
the original extension of 4-dimensional quantum mechanics and relativity to
10-dimensional string theory. After a brief review of M-theory, I discuss some
implications of large extra dimensions. I then consider astronomical evidence
for, and constraints on, large compactified dimensions. I conclude with a
possible resolution to the apparent inconsistency between the MSSM scale and
string scale in the weak coupling limit. Talk presented at COSPAR '02, Houston,
Texas, October 2002.


title: The world according to the Hubble Space Telescope

abstract:
  The Hubble Space Telescope (HST), in its thirteen years of operation, has
allowed us to observe properties of the universe humans have been able, until
very recently, to probe only with their thoughts. This review presents a brief
summary of a few of the highlights of HST discoveries, discusses their physical
implications, and identifies unsolved problems. A broad range of topics is
covered, from our own solar system to cosmology. The topics fall into the
general categories of: planets (including both in the solar system and
extrasolar), stellar evolution, black holes (including both of stellar-mass and
supermassive), galaxy formation and evolution, the determination of
cosmological parameters, and the nature of the recently discovered ``dark
energy.''


title:
Differential Neutrino Rates and Emissivities from the Plasma Process in
  Astrophysical Systems

abstract:
  The differential rates and emissivities of neutrino pairs from an equilibrium
plasma are calculated for the wide range of density and temperature encountered
in astrophysical systems. New analytical expressions are derived for the
differential emissivities which yield total emissivities in full agreement with
those previously calculated. The photon and plasmon pair production and
absorption kernels in the source term of the Boltzmann equation for neutrino
transport are provided. The appropriate Legendre coefficients of these kernels,
in forms suitable for multi-group flux-limited diffusion schemes are also
computed.


title: VLA multifrequency observations of RS CVn binaries

abstract:
  We present multiepoch Very Large Array (VLA) observations at 1.4 GHz, 4.9
GHz, 8.5 GHz and 14.9 GHz for a sample of eight RS CVn binary systems. Circular
polarization measurements of these systems are also reported. Most of the
fluxes observed are consistent with incoherent emission from mildly
relativistic electrons. Several systems show an increase of the degree of
circular polarization with increasing frequency in the optically thin regime,
in conflict with predictions by gyrosynchrotron models. We observed a reversal
in the sense of circular polarization with increasing frequency in three
non-eclipsing systems: EI Eri, DM Uma and HD 8358. We find clear evidence for
coherent plasma emission at 1.4 GHz in the quiescent spectrum of HD 8358 during
the helicity reversal. The degrees of polarization of the other two systems
could also be accounted for by a coherent emission process. The observations of
ER Vul revealed two U-shaped flux spectra at the highest frequencies. The
U-shape of the spectra may be accounted for by an optically thin
gyrosynchrotron source for the low frequency part whereas the high frequency
part is dominated by a thermal emission component.


title: Astrometric Positions and Proper Motions of 19 Radio Stars

abstract:
  We have used the Very Large Array, linked with the Pie Town Very Long
Baseline Array antenna, to determine astrometric positions of 19 radio stars in
the International Celestial Reference Frame (ICRF). The positions of these
stars were directly linked to the positions of distant quasars through phase
referencing observations. The positions of the ICRF quasars are known to 0.25
mas, thus providing an absolute reference at the angular resolution of our
radio observations. Average values for the errors in our derived positions for
all sources were 13 mas and 16 mas in R.A. and declination respectively, with
accuracies approaching 1-2 mas for some of the stars observed. Differences
between the ICRF positions of the 38 quasars, and those measured from our
observations showed no systematic offsets, with mean values of -0.3 mas in R.A.
and -1.0 mas in declination. Standard deviations of the quasar position
differences of 17 mas and 11 mas in R.A. and declination respectively, are
consistent with the mean position errors determined for the stars. Our measured
positions were combined with previous Very Large Array measurements taken from
1978-1995 to determine the proper motions of 15 of the stars in our list. With
mean errors of approximately 1.6 mas/yr, the accuracies of our proper motions
approach those derived from Hipparcos, and for a few of the stars in our
program, are better than the Hipparcos values. Comparing the positions of our
radio stars with the Hipparcos catalog, we find that at the epoch of our
observations, the two frames are aligned to within formal errors of
approximately 3 mas. This result confirms that the Hipparcos frame is inertial
at the expected level.


title: Cosmology from Topological Defects

abstract:
  The potential role of cosmic topological defects has raised interest in the
astrophysical community for many years now. In this set of notes, we give an
introduction to the subject of cosmic topological defects and some of their
possible observable signatures. We begin with a review of the basics of general
defect formation and evolution, we briefly comment on some general features of
conducting cosmic strings and vorton formation, as well as on the possible role
of defects as dark energy, to end up with cosmic structure formation from
defects and some specific imprints in the cosmic microwave background radiation
from simulated cosmic strings. A detailed, pedagogical explanation of the
mechanism underlying the tiny level of polarization discovered in the cosmic
microwave background by the DASI collaboration (and recently confirmed by WMAP)
is also given, and a first rough comparison with some predictions from defects
is provided.


title: Neutrino Tomography of Gamma Ray Bursts and Massive Stellar Collapses

abstract:
  Neutrinos at energies above TeV can serve as probes of the stellar progenitor
and jet dynamics of gamma ray bursts arising from stellar core collapses. They
can also probe collapses which do not lead to gamma-rays, which may be much
more numerous. We calculate detailed neutrino spectra from shock accelerated
protons in jets just below the outer stellar envelope, before their emergence.
We present neutrino flux estimates from such pre-burst jets for two different
massive stellar progenitor models. These should be distinguishable by IceCube,
and we discuss the implications.


title: Keck Spectroscopy of 4 QSO Host Galaxies

abstract:
  We present optical spectroscopy of the host galaxies of 4 QSO's: PG1444+407,
PKS 2349-147, 3C 323.1, and 4C 31.63 having a redshift range (0.1 < z < 0.3).
The spectra were obtained at the Keck Observatory with the LRIS instrument
offset 2-4 arcseconds from the nucleus at several position angles in each
galaxy. The objects close to 3C 323.1 and PKS 2349-147 have the same redshifts
of their nearby QSOs and appear to be the nuclei of galaxies in the final
states of merging with the host galaxies. The spectra of the hosts show some
variety: PKS 2349-147 and 3C 323.1 show strong off-nuclear emission lines plus
stellar absorption features, while the other two show only stellar absorption.
PKS 2349-147 and PG 1444+407 have a mixture of old and moderately young stars,
while 4C 31.63 has the spectrum of a normal giant elliptical, which is very
rare in our larger sample. The spectrum of the host of 3C 323.1 appears to
dominated by older stars, though our data for it are of lower quality. The
redshifts of the off-nucleus emission lines and stellar components are very
close to those of the associated QSOs.


title:
Optimal Techniques in Two-dimensional Spectroscopy: Background
  Subtraction for the 21st Century

abstract:
  In two-dimensional spectrographs, the optical distortions in the spatial and
dispersion directions produce variations in the sub-pixel sampling of the
background spectrum. Using knowledge of the camera distortions and the
curvature of the spectral features, one can recover information regarding the
background spectrum on wavelength scales much smaller than a pixel. As a
result, one can propagate this better-sampled background spectrum through
inverses of the distortion and rectification transformations, and accurately
model the background spectrum in two-dimensional spectra for which the
distortions have not been removed (i.e. the data have not been
rebinned/rectified). The procedure, as outlined in this paper, is extremely
insensitive to cosmic rays, hot pixels, etc. Because of this insensitivity to
discrepant pixels, sky modeling and subtraction need not be performed as one of
the later steps in a reduction pipeline. Sky-subtraction can now be performed
as one of the earliest tasks, perhaps just after dividing by a flat-field.
Because subtraction of the background can be performed without having to
``clean'' cosmic rays, such bad pixel values can be trivially identified after
removal of the two-dimensional sky background.


title: Discovery of powerful millisecond flares from Cygnus X-1

abstract:
  We have found a large number of very strong flares in the available XTE PCA
data of Cyg X-1 (also seen in available HEXTE and BATSE data) with 13 flares
satisfying our chosen threshold criterion, occuring both in the hard and the
soft states. We analyze here in detail two of them. The strongest one took
place in the soft state, with the 3-30 keV energy flux increasing 30 times with
respect to the preceding 16-s average. The e-folding time is ~ 7 ms for the
main flare and ~ 1 ms for its precursor. The spectrum strongly hardens during
the flare. On the other hand, flares in the hard state have generally lower
amplitudes and longer e-folding times, and their spectra soften during the
flare, with the hardness of the spectrum at the flare peak similar for both
types of the flares. The presence of the flares shows unusually dramatic events
taking place in the accretion flow of Cyg X-1. On the other hand, the rate of
occurence of hard-state flares shows they may represent a high-flux end of the
distribution of shots present in usual lightcurves of Cyg X-1.


title: Relativistic Acceleration of Magnetically Driven Jets

abstract:
  We present an analytical model for describing highly relativistic
acceleration of magnetically driven jets, within the framework of ideal MHD for
cold, stationary and axisymmetric outflows. Our novel procedure is to treat the
wind equation as an algebraic relation between the relativistic Alfv\'{e}n
Mach-number and the poloidal electric to toroidal magnetic field amplitudes
ratio $\xi$.
  This allows us to obtain easily the wind solutions for
trans-fast-magnetosonic flows, together with the required range of
  $\xi$. Then, to determine the spatial variation of $\xi$, we solve
approximately the Grad-Shafranov equation applied to a jet flow ejected with a
very large total specific energy $E$ and confined within a very small opening
angle. Our trans-fast-magnetosonic model provides a closed-form expression for
the transition from a magnetically dominated flow to a kinetic-energy dominated
one, which occurs in the sub-asymptotic region far beyond the light cylinder of
the radius
  $R_{\rm L}$. Importantly, we find that the equipartition between magnetic and
kinetic energies is realized at a cylindrical radius of order of
  $R_{\rm L}E/c^{2}$, and confirm that the further conversion of magnetic to
kinetic energy proceeds logarithmically with distance in the asymptotic region.
Finally, we discuss briefly the astrophysical implications of our model for
jets originating from active galactic nuclei.


title:
Peculiar Velocity Limits from Measurements of the Spectrum of the
  Sunyaev-Zel'dovich Effect in Six Clusters of Galaxies

abstract:
  We have made measurements of the Sunyaev-Zel'dovich (SZ) effect in six galaxy
clusters at z > 0.2 using the Sunyaev-Zel'dovich Infrared Experiment (SuZIE II)
in three frequency bands between 150 and 350 GHz. Simultaneous multi-frequency
measurements have been used to distinguish between thermal and kinematic
components of the SZ effect, and to significantly reduce the effects of
variations in atmospheric emission which can otherwise dominate the noise. We
have set limits to the peculiar velocities of each cluster with respect to the
Hubble flow, and have used the cluster sample to set a 95% confidence limit of
< 1410 km/s to the bulk flow of the intermediate-redshift universe in the
direction of the CMB dipole. This is the first time that SZ measurements have
been used to constrain bulk flows. We show that systematic uncertainties in
peculiar velocity determinations from the SZ effect are likely to be dominated
by submillimeter point sources and we discuss the level of this contamination.


title:
GAIA: AGB stars as tracers of star formation histories in the Galaxy and
  beyond

abstract:
  We discuss the tracing of star formation histories with ESA's space
astrometry mission GAIA, emphasizing the advantages of AGB stars for this
purpose. GAIA's microarcsecond-level astrometry, multi-band photometry and
spectroscopy will provide individual distances, motions, effective
temperatures, gravities and metallicities for vast numbers of AGB stars in the
Galaxy and beyond. Reliable ages of AGB stars can be determined to distances of
\~200 kpc in a wide range of ages and metallicities, allowing star formation
histories to be studied in a diversity of astrophysical environments.


title:
Prospects for the detection of electromagnetic counterparts to
  gravitational wave events

abstract:
  Various models for electromagnetic emissions correlated with the
gravitational wave signals expected to be detectable by the current and planned
gravitational wave detectors are studied. The position error on the location of
a gravitational wave source is estimated, and is used to show that it could be
possible to observe the electromagnetic counterparts to neutron star-neutron
star or neutron star-black hole binary coalescences detected with the Advanced
LIGO and the Virgo detectors.


title: An energetic stellar outburst accompanied by circumstellar light echoes

abstract:
  Some classes of stars, including supernovae and novae, undergo explosive
outbursts that eject stellar material into space. In 2002, the previously
unknown variable star V838 Monocerotis brightened suddenly by a factor of about
10^4. Unlike a supernova or nova, V838 Mon did not explosively eject its outer
layers; rather, it simply expanded to become a cool supergiant with a
moderate-velocity stellar wind. Superluminal light echoes were discovered as
light from the outburst propagated into surrounding, pre-existing circumstellar
dust. Here we report high-resolution imaging and polarimetry of the light
echoes, which allow us to set direct geometric distance limits to the object.
At a distance of >6 kpc, V838 Mon at its maximum brightness was temporarily the
brightest star in the Milky Way. The presence of the circumstellar dust implies
that previous eruptions have occurred, and spectra show it to be a binary
system. When combined with the high luminosity and unusual outburst behavior,
these characteristics indicate that V838 Mon represents a hitherto unknown type
of stellar outburst, for which we have no completely satisfactory physical
explanation.


title: The First Two Host Galaxies of X-ray Flashes: XRF 011030 and XRF 020427

abstract:
  Given the paucity of empirical constraints, the nature of the
newly-recognized phenomena called X-Ray Flashes (XRFs) has been an open
question. However, with the recent detections of radio and X-ray afterglow it
is finally possible to study the large- and small-scale environments of XRFs.
We present Chandra, Hubble Space Telescope (HST), and Keck observations of the
fields of XRFs 011030 and 020427. Astrometric comparisons of the X-ray
transient positions and the HST images reveal the XRFs to be associated with
faint blue galaxies. Photometric evidence of these putative hosts suggests that
these two XRFs originated from redshifts less than z ~ 3.5, and thus cannot be
due to GRBs at very high redshifts. In both host-burst offsets and host
properties, these XRFs could have been drawn from distributions similar to
those measured of gamma-ray bursts (GRBs). We conclude with a discussion of the
implications of this XRF-GRB host connection for the possible progenitors of
XRFs.


title: ACBAR: The Arcminute Cosmology Bolometer Array Receiver

abstract:
  We describe the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a
multifrequency millimeter-wave receiver designed for observations of the Cosmic
Microwave Background (CMB) and the Sunyaev-Zel'dovich effect in clusters of
galaxies. The ACBAR focal plane consists of a 16-pixel, background-limited, 240
mK bolometer array that can be configured to observe simultaneously at 150,
220, 280, and 350 GHz. With 4-5' FWHM Gaussian beam sizes and a 3 degree
azimuth chop, ACBAR is sensitive to a wide range of angular scales. ACBAR was
installed on the 2 m Viper telescope at the South Pole in January 2001. We
describe the design of the instrument and its performance during the 2001 and
2002 observing seasons.


title: 3D dynamical evolution of the interstellar gas in the Gould Belt

abstract:
  The dynamical evolution of the Gould Belt has been modelled in 3D and
confronted to the spatial and velocity distributions of all HI and H2 clouds
found within a few hundred parsecs from the Sun and to the Hipparcos distances
of the nearby OB associations. The model describes the expansion of a shock
wave that sweeps momentum from the ambient medium and it includes the effects
of the Galactic differential rotation and its gravitational torque, as well as
interstellar density gradients within and away from the Galactic plane,
possible fragmentation and drag forces in the late stages, and an initial
rotation of the system. The best fit to the data yields values for the current
Belt semi-axes of 373 +- 5 pc and 233 +- 5 pc, and an inclination of 17.2 +-
0.5 degrees, in agreement with earlier results. A different Belt orientation,
however, results from new H2 data and distance information. The present Belt
rim is found to coincide with most of the nearby OB associations and H2 clouds,
but its expansion bears little relation to the average association velocities.
An initial kinetic energy of (1.0 +- 0.1) 10^(45) J and an expansion age of
26.4 +- 0.4 Myr are required, in agreement with earlier 2D estimates. The
factor of 2 discrepancy between the Belt dynamical age and its stellar nuclear
age could not be solved by adding a vertical dimension in the expansion, drag
forces, fragmentation, or an initial rotation. Allowing the Belt to cross the
Galactic disc in the early stages requires a longer age of 52 Myr, but yields a
very poor fit to the data.


title: Gamma-Ray Bursts: The Underlying Model

abstract:
  A pedagogical derivation is presented of the ``fireball'' model of gamma-ray
bursts, according to which the observable effects are due to the dissipation of
the kinetic energy of a relativistically expanding wind, a ``fireball.'' The
main open questions are emphasized, and key afterglow observations, that
provide support for this model, are briefly discussed. The relativistic outflow
is, most likely, driven by the accretion of a fraction of a solar mass onto a
newly born (few) solar mass black hole. The observed radiation is produced once
the plasma has expanded to a scale much larger than that of the underlying
``engine,'' and is therefore largely independent of the details of the
progenitor, whose gravitational collapse leads to fireball formation. Several
progenitor scenarios, and the prospects for discrimination among them using
future observations, are discussed. The production in gamma- ray burst
fireballs of high energy protons and neutrinos, and the implications of burst
neutrino detection by kilometer-scale telescopes under construction, are
briefly discussed.


title:
Hybrid stars with color superconductivity within a nonlocal chiral quark
  model

abstract:
  The equation of state for quark matter is derived for a nonlocal, chiral
quark model within the mean field approximation. Special emphasis is on the
occurrence of a diquark condensate which signals a phase transition to color
superconductivity and its effects on the equation of state. We present a fit
formula for the Bag pressure, which is density dependent in case when the quark
matter is color superconducting. We calculate the quark star configurations by
solving the Tolman- Oppenheimer- Volkoff equations and demonstrate the effects
of diquark condensation on the stability of hybrid stars for different
formfactors of the quark interaction.


title: Constraining CMB-consistent primordial voids with cluster evolution

abstract:
  Using cosmological simulations, we make predictions for the distribution of
clusters in a plausible non-gaussian model where primordial voids nucleated
during inflation act together with scale-invariant adiabatic gaussian
fluctuations as seeds for the formation of large-scale structure. This model
agrees with most recent observations of the anisotropies of the cosmic
microwave background (CMB) and can account for the excess of power measured on
cluster scales by the Cosmic Background Imager (CBI), the large empty regions
apparent in nearby galaxy redshift surveys and the number of giant arcs
measured in deep cluster lensing surveys. We show that the z=0 cluster mass
function differs from predictions for a standard LCDM cosmology with the same
sigma_8. Moreover, as massive clusters also form much earlier in the "void"
scenario, we show that integrated number counts of SZ sources and simple
statistics of strong lensing can easily falsify this model.


title: Trapped Protostellar Winds and their Breakout

abstract:
  Observations show that high-velocity jets stem from deeply embedded young
stars, which may still be experiencing infall from their parent cloud cores.
Yet theory predicts that, early in this buildup, any outgoing wind is trapped
by incoming material of low angular momentum. As collapse continues and brings
in more rapidly rotating gas, the wind can eventually break out. Here we model
this transition by following the motion of the shocked shell created by impact
of the wind and a rotating, collapsing envelope. We first demonstrate, both
analytically and numerically, that our previous, quasi-static solutions are
dynamically unstable. Our present, fully time-dependent calculations include
cases both where the wind is driven back by infall to the stellar surface, and
where it erupts as a true outflow. For the latter, we find that the time of
breakout is sim 50,000 yr for wind speeds of 200 km/s. The reason for the delay
is that the shocked material, including the swept-up infall, must be able to
climb out of the star's gravitational potential well.
  We explore the critical wind speed necessary for breakout as a function of
the mass transport rates in the wind and infall, as well as the cloud rotation
rate Omega0 and time since the start of infall. Breakout does occur for
realistic parameter choices. The actual breakout times would change if we
relaxed the assumption of perfect mixing between the wind and infall material.
Our expanding shells do not exhibit the collimation of observed jets, but
continue to expand laterally. To halt this expansion, the density in the
envelope must fall off less steeply than in our model.


title: Gasoline: An adaptable implementation of TreeSPH

abstract:
  The key algorithms and features of the Gasoline code for parallel
hydrodynamics with self-gravity are described. Gasoline is an extension of the
efficient Pkdgrav parallel N-body code using smoothed particle hydrodynamics.
Accuracy measurements, performance analysis and tests of the code are
presented. Recent successful Gasoline applications are summarized. These cover
a diverse set of areas in astrophysics including galaxy clusters, galaxy
formation and gas-giant planets. Future directions for gasdynamical simulations
in astrophysics and code development strategies for tackling cutting edge
problems are discussed.


title: Gamma ray and infrared emission from the M87 jet and torus

abstract:
  The existence of intrinsic obscuration of Fanaroff-Riley I objects is a
controversial topic. M87, the nearest such object, is puzzling in that although
it has very massive central black hole it has a relatively low luminosity,
suggesting it is in a dormant state. Despite of its proximity to us (16 Mpc) it
is not known with certainty whether or not M87 has a dusty torus.
  Infrared observations indicate that if a torus exists in M87 it must have a
rather low infrared luminosity. Using arguments from unification theory of
active galactic nuclei, we have earlier suggested that the inner parsec-scale
region of M87 could still harbour a small torus sufficiently cold such that its
infrared emission is dwarfed by the jet emission. The infrared emission from
even a small cold torus could affect through photon-photon pair production
interactions the escape of 100 GeV to TeV energy gamma rays from the central
parsec of M87.
  The TeV gamma-ray flux from the inner jet of M87 has recently been predicted
in the context of the Synchrotron Proton Blazar (SPB) model to extend up to at
least 100 GeV (Protheroe, Donea, Reimer, 2002). Subsequently, the detection of
gamma-rays above 730 GeV by the HEGRA Cherenkov telescopes has been reported.
We discuss the interactions of gamma-rays produced in the inner jet of M87 with
the weak infrared radiation expected from a possible dusty small-scale torus,
and show that the HEGRA detection shows that the temperature of any torus
surrounding the gamma-ray emission region must be cooler than about 250 K. We
suggest that if no gamma-rays are in future detected during extreme flaring
activity in M87 at other wavelength, this may be expected because of torus
heating.


title: Large Scale Magnetic Fields: Galaxy Two-Point correlation function

abstract:
  We study the effect of large scale tangled magnetic fields on the galaxy
two-point correlation function in the redshift space. We show that (a) the
magnetic field effects can be comparable the gravity-induced clustering for
present magnetic field strength $B_0 \simeq 5 \times 10^{-8}$ G, (b) the
absence of this signal from the present data gives an upper bound $B_0 \la 3
\times 10^{-8}$ G, (c) the future data can probe the magnetic fields of $\simeq
10^{-8}$ G. A comparison with other constraints on the present magnetic field
shows that they are marginally compatible.However if the magenetic fields
corresponding to $B_0 \simeq 10^{-8}$ G existed at the last scattering surface
they will cause unacceptably large CMBR anisotropies.


title:
Populating Dark Matter Haloes with Galaxies: Comparing the 2dFGRS with
  Mock Galaxy Redshift Surveys

abstract:
  In two recent papers, we developed a powerful technique to link the
distribution of galaxies to that of dark matter haloes by considering halo
occupation numbers as function of galaxy luminosity and type. In this paper we
use these distribution functions to populate dark matter haloes in
high-resolution N-body simulations of the standard LCDM cosmogony with
Omega_m=0.3 and sigma_8=0.9. Stacking simulation boxes of 100 Mpc/h and 300
Mpc/h with 512^3 CDM particles each we construct Mock Galaxy Redshift Surveys
out to a redshift of z=0.2. We use these mock surveys to investigate various
clustering statistics. The projected correlation functions for galaxies with
different luminosities and types match the observations well on scales larger
than about 3 Mpc/h. On smaller scales, however, the model overpredicts the
clustering power by about a factor two. Furthermore, the model predicts
pairwise velocity dispersions (PVD) that are about 400 km/s too high at
projected pair separations of ~1 Mpc/h. A strong velocity bias in massive
haloes can reduce the predicted PVD to the observed level, but does not help to
resolve the over-prediction of clustering power on small scales. Consistent
results can be obtained within the standard LCDM model only when the
mass-to-light ratio of clusters is almost twice the observed value.
Alternatively, a LCDM model with sigma_8=0.75 can also reproduce the
observational results.


title: The formation of the coronal flow/ADAF

abstract:
  We develop a new method to describe the accretion flow in the corona above a
thin disk around a black hole in vertical and radial extent. The model is based
on the same physics as the earlier one-zone model, but now modified including
inflow and outflow of mass, energy and angular momentum from and towards
neighboring zones. We determine the radially extended coronal flow for
different mass flow rates in the cool disk resulting in the truncation of the
thin disk at different distance from the black hole. Our computations show how
the accretion flow gradually changes to a pure vertically extended coronal or
advection-dominated accretion flow (ADAF). Different regimes of solutions are
discussed. For some cases wind loss causes an essential reduction of the mass
flow.


title: Large scale structure in non-standard cosmologies

abstract:
  We study the growth of large scale structure in two recently proposed
non-standard cosmological models: the brane induced gravity model of Dvali,
Gabadadze and Porrati (DGP) and the Cardassian models of Freese and Lewis. A
general formalism for calculating the growth of fluctuations in models with a
non-standard Friedman equation and a normal continuity equation of energy
density is discussed. Both linear and non-linear growth are studied, together
with their observational signatures on higher order statistics and abundance of
collapsed objects. In general, models which show similar cosmic acceleration at
z ~ 1, can produce quite different normalization for large scale density
fluctuations, ie sigma_8, cluster abundance or higher order statistics, such as
the normalized skewness S_3, which is independent of the linear normalization.
For example, for a flat universe with Omega_M ~ 0.22, DGP and standard
Cardassian cosmologies predict about 2 and 3 times more clusters respectively
than the standard Lambda model at z=1.5. When normalized to CMB fluctuations
the sigma_8 amplitude turns out to be lower by a few tens of a percent. We also
find that, for a limited red-shift range, the linear growth rate can be faster
in some models (eg modified polytropic Cardassian with q>1) than in the
Einstein-deSitter universe. The value of the skewness S_3 is found to have up
to ~10 percent variations (up or down) from model to model.


title: The Torino Observatory Parallax Program: White Dwarf Candidates

abstract:
  We present parallax determinations for six white dwarf candidates in the
Torino Observatory Parallax Program. The absolute parallaxes are found with
precisions at the 2-3 milliarcsecond level. For WD 1126+185 we find a distance
incompatible with being a white dwarf, implying an incorrect classification.
For WD 2216+484 we find our distance is consistent with a simple DA white dwarf
rather than a composite system as previously proposed in the literature. In
general it is found that the published photometric distance is an overestimate
of the distance found here.


title:
The low-level radial velocity variability in Barnard's star (=GJ 699).
  Secular acceleration, indications for convective redshift, and planet mass
  limits

abstract:
  We report results from 2 1/2 yr of high precision radial velocity (RV)
monitoring of Barnard's star. The high RV measurement precision of the
VLT-UT2+UVES of 2.65 m/s made the following findings possible. (1) The first
detection of the change in the RV of a star caused by its space motion (RV
secular acceleration). (2) An anti-correlation of the measured RV with the
strength of the filling-in of the Halpha line by emission. (3) Very stringent
mass upper limits to planetary companions. Using only data from the first 2
years, we obtain a best-fit value for the RV secular acceleration of
5.15+/-0.89 m/s/yr. This agrees with the predicted value of 4.50 m/s/yr based
on the Hipparcos proper motion and parallax combined with the known absolute
radial velocity of the star. When the RV data of the last half-year are added
the best-fit slope is strongly reduced to 2.97+/-0.51 m/s/yr suggesting the
presence of additional RV variability in the star. Part of it can be attributed
to stellar activity as we demonstrate by correlating the residual RVs with an
index that describes the filling-in of the Halpha line by emission. A
correlation coefficient of -0.50 indicates that the appearance of active
regions causes a blueshift of photospheric absorption lines. Assuming that
active regions basically inhibit convection we discuss the possibility that the
fundamental (inactive) convection pattern in this M4V star produces a
convective redshift. We also determine upper limits to the projected mass msini
and to the true mass m of hypothetical planetary companions in circular orbits.
For the separation range 0.017-0.98 AU we exclude any planet with msini>0.12
Mjupiter and m>0.86 Mjupiter. Throughout the habitable zone, i.e. 0.034-0.082
AU, we exclude planets with msini>7.5 Mearth and m>3.1 Mneptune.