title:
A Hubble Space Telescope Survey of Extended [OIII]5007A Emission in a
  Far-Infrared Selected Sample of Seyfert Galaxies: Results

abstract:
  We present the results of a Hubble Space Telescope (HST) survey of extended
[OIII] emission in a sample of 60 nearby Seyfert galaxies (22 Seyfert 1's and
38 Seyfert 2's), selected by mostly isotropic properties. The comparison
between the semi major axis size of their [OIII] emitting regions (R_Maj) shows
that Seyfert 1's and Seyfert 2's have similar distributions, which seems to
contradict Unified Model predictions. We discuss possible ways to explain this
result, which could be due either to observational limitations or the models
used for the comparison with our data. We show that Seyfert 1 Narrow Line
Regions (NLR's) are more circular and concentrated than Seyfert 2's, which can
be attributed to foreshortening in the former. We find a good correlation
between the NLR size and luminosity, following the relation R_Maj propto
L([OIII])^0.33, which is flatter than a previous one found for QSO's and
Seyfert 2's. We discuss possible reasons for the different results, and their
implications to photoionization models. We confirm previous results which show
that the [OIII] and radio emission are well aligned, and also find no
correlation between the orientation of the extended [OIII] emission and the
host galaxy major axis. This agrees with results showing that the torus axis
and radio jet are not aligned with the host galaxy rotation axis, indicating
that the orientation of the gas in the torus, and not the spin of the black
hole, determine the orientation of the accretion disk, and consequently the
orientation of the radio jet.


title: Expected Detection and False Alarm Rates for Transiting Jovian Planets

abstract:
  Ground-based searches for transiting Jupiter-sized planets have so far
produced few detections of planets, but many of stellar systems with eclipse
depths, durations, and orbital periods that resemble those expected from
planets. I show that these detection rates are consistent with our present
knowledge of binary and multiple-star systems, and of Jovian-mass extrasolar
planets. Upcoming space-based searches for transiting Earth-sized planets will
be largely unaffected by the sources of false alarms that afflict current
ground-based searches, with one exception, namely distant eclipsing binaries
whose light is strongly diluted by that of a foreground star. A byproduct of
the rate estimation is evidence that the period distribution of extrasolar
planets is depressed for periods between 5 and 200 days.


title:
The Physical Conditions and Metal Enrichment of Low-Redshift
  Interstellar and Intergalactic Media: The Benefits of High-Resolution
  Ultraviolet Spectra

abstract:
  To underscore the value of high spectral resolution for the study of low-z
QSO absorption lines, we briefly present Space Telescope Imaging Spectrograph
echelle data that demonstrate how increased resolution leads to dramatic
improvement in line measurements. We show that even R = lambda/Delta lambda =
20,000 is insufficient for some measurements. The higher the resolution the
better, but R ~ 50,000 is adequate for many outstanding questions about the IGM
and the ISM of galaxies that can be probed using QSO absorption lines.


title: The Galactic Anticenter Stellar Stream

abstract:
  The recently discovered, ring-like structure just outside the Galactic disk
in Monoceros is detected and traced among 2MASS M giant stars. We have
developed a method to recover the signature of this structure from the distance
probability density function of stars along a given line of sight. Its
detection is possible even when the metallicity is unknown, provided that the
structure is not too embedded in the disk. Application of this method reveals
the presence of a large group of M giant stars at a Galactocentric distance of
18$\pm 2$ kpc, over $+36\degr<b<+12\degr$ and $100\degr < l <270\degr$.
Evidence that the stream extends to high negative latitudes is also found. That
the structure contains M giants shows that it contains populations of at least
an order of magnitude higher abundance than the [Fe/H] = -1.6 mean metallicity
previously reported for this system. The structural characteristics of the
stellar stream as traced by M giants do not support the interpretation of this
structure as a homogeneously dense ring that surrounds the Galaxy, but as a
more localized structure, possibly a merging dwarf galaxy with tidal arms, like
the Sagittarius dwarf galaxy.


title: Origin of Chaos in the Prometheus-Pandora System

abstract:
  We demonstrate that the chaotic orbits of Prometheus and Pandora are due to
interactions associated with the 121:118 mean motion resonance. Differential
precession splits this resonance into a quartet of components equally spaced in
frequency. Libration widths of the individual components exceed the splitting
resulting in resonance overlap which causes the chaos. A single degree of
freedom model captures the essential features of the chaotic dynamics. Mean
motions of Prometheus and Pandora wander chaotically in zones of width 1.8
deg/yr and 3.1 deg/yr, respectively.


title:
Magnetically Driven Accretion Flows in the Kerr Metric I: Models and
  Overall Structure

abstract:
  This is the first in a series of papers that investigate the properties of
accretion flows in the Kerr metric through three-dimensional, general
relativistic magnetohydrodynamic simulations of tori with a near-Keplerian
initial angular velocity profile. We study four models with increasing black
hole spin, from a/M=0 to 0.998, for which the structural parameters of the
initial tori are maintained nearly constant. The subsequent accretion flows
arise self-consistently from stresses and turbulence created by the
magnetorotational instability. We investigate the overall evolution and the
late-time global structure in the resulting non-radiative accretion flows,
including the magnetic fields within the disks, the properties of the flow in
the plunging region, and the flux of conserved quantities into the black hole.
Independent of black hole spin, the global structure is described in terms of
five regions: the main disk body, the coronal envelope, the inner disk,
consisting of an inner torus and plunging region, an evacuated axial funnel,
and a bi-conical outflow confined to the corona-funnel boundary. We find
evidence for lower accretion rates, stronger funnel-wall outflows, and
increased stress in the near hole region with increasing black hole spin.


title:
The Effect of Multiple Scattering on the Polarization from Binary Star
  Envelopes. I. Self- and Externally Illuminated Disks

abstract:
  We present the results of a Monte Carlo radiative transfer code that
calculates the polarization produced by multiple Thomson scattering and
variable absorptive opacity in a circumstellar disk around one component of a
close detached binary system. We consider in detail the polarization variations
over the binary cycle that result from the disk's illumination by the external
star and by its own volume emission. We identify key features of these
polarization phase curves and investigate their behavior as functions of
optical depth, albedo, and inclination for geometrically thin and thick disks.
The polarization due to disk self-illumination is sensitive to the internal
optical characteristics of the disk, while the polarization arising from
external illumination is mainly sensitive to the disk's geometrical thickness.
With appropriate flux weighting, these results, combined with those for an
internally illuminated disk, allow simulation of the polarization signature
from an arbitrary binary-disk system.


title: Electrically charged compact stars and formation of charged black holes

abstract:
  We study the effect of electric charge in compact stars assuming that the
charge distribution is proportional to the mass density. The pressure and the
density of the matter inside the stars are large, and the gravitational field
is intense. This indicates that electric charge and a strong electric field can
also be present. The relativistic hydrostatic equilibrium equation, i.e., the
Tolman-Oppenheimer-Volkoff equation, is modified in order to include electric
charge. We perform a detailed numerical study of the effect of electric charge
using a polytropic equation of state. We conclude that in order to see any
appreciable effect on the phenomenology of the compact stars, the electric
fields have to be huge (~ 10^{21} V/m), which implies that the total charge is
Q ~ 10^{20} Coulomb. From the local effect of the forces experienced on a
single charged particle, it is expected that each individual charged particle
is quickly ejected from the star. This in turn produces a huge force imbalance,
and the gravitational force overwhelms the repulsive Coulomb and fluid pressure
forces. The star can then collapse to form a charged black hole before all the
charge leaves the system.


title:
Time-variability of the fine-structure constant expected from the Oklo
  constraint and the QSO absorption lines

abstract:
  The data from the QSO absorption lines indicating a nonzero time-variability
of the fine-structure constant has been re-analyzed on the basis of a
"damped-oscillator" fit, as motivated by the same type of behavior of a scalar
field, dilaton, which mimics a cosmological constant to understand the
accelerating universe. We find nearly as good fit to the latest data as the
simple weighted mean. In this way, we offer a way to fit the more stringent
result from the Oklo phenomenon, as well.


title: Early star formation traced by the highest redshift quasars

abstract:
  The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.


title:
The physical parameters, excitation and chemistry of the rim, jets and
  knots of the planetary nebula NGC 7009

abstract:
  We present long-slit optical spectra along the major axis of the planetary
nebula NGC 7009. These data allow us to discuss the physical, excitation and
chemical properties of all the morphological components of the nebula,
including its remarkable systems of knots and jets. The main results of this
analysis are the following: i) the electron temperature throughout the nebula
is remarkably constant, T_e[OIII] = 10200K; ii) the bright inner rim and inner
pair of knots have similar densities of N_e = 6000cm^{-3}, whereas a much lower
density of N_e = 1500cm^{-3} is derived for the outer knots as well as for the
jets; iii) all the regions (rim, inner knots, jets and outer knots) are mainly
radiatively excited; and iv) there are no clear abundance changes across the
nebula for He, O, Ne, or S. There is a marginal evidence for an overabundance
of nitrogen in the outer knots (ansae), but the inner ones (caps) and the rim
have similar N/H values that are at variance with previous results. Our data
are compared to the predictions of theoretical models, from which we conclude
that the knots at the head of the jets are not matter accumulated during the
jet expansion through the circumstellar medium, neither can their origin be
explained by the proposed HD or MHD interacting-wind models for the formation
of jets/ansae, since the densities as well as the main excitation mechanisms of
the knots, disagree with model predictions.


title: Photoevaporation of Cosmological Minihalos during Reionization

abstract:
  We present the first gas dynamical simulations of the photoevaporation of
cosmological minihalos overtaken by the ionization fronts which swept through
the IGM during reionization in a LCDM universe, including the effects of
radiative transfer. We demonstrate the phenomenon of I-front trapping inside
minihalos, in which the weak, R-type fronts which traveled supersonically
across the IGM decelerated when they encountered the dense, neutral gas inside
minihalos, becoming D-type I-fronts, preceded by shock waves. For a minihalo
with virial temperature T_vir < 10^4 K, the I-front gradually burned its way
through the minihalo which trapped it, removing all of its baryonic gas by
causing a supersonic, evaporative wind to blow backwards into the IGM, away
from the exposed layers of minihalo gas just behind the advancing I-front. Such
hitherto neglected feedback effects were widespread during reionization. N-body
simulations and analytical estimates of halo formation suggest that sub-kpc
minihalos such as these, with T_vir < 10^4 K, were so common as to cover the
sky around larger-mass source halos and possibly dominate the absorption of
ionizing photons. This means that previous estimates of the number of ionizing
photons per H atom required to complete reionization which neglected this
effect may be too low. Regardless of their effect on the progress of
reionization, however, the minihalos were so abundant that random lines of
sight thru the high-z universe should encounter many of them, which suggests
that it may be possible to observe the processes described here in the
absorption spectra of distant sources.


title: Pulsar kicks from a dark-matter sterile neutrino

abstract:
  We show that a sterile neutrino with mass in the 1-20 keV range and a small
mixing with the electron neutrino can simultaneously explain the origin of the
pulsar motions and the dark matter in the universe. An asymmetric neutrino
emission from a hot nascent neutron star can be the explanation of the observed
pulsar velocities. In addition to the pulsar kick mechanism based on resonant
neutrino transitions, we point out a new possibility: an asymmetric
off-resonant emission of sterile neutrinos. The two cases correspond to
different values of the masses and mixing angles. In both cases we identify the
ranges of parameters consistent with the pulsar kick, as well as cosmological
constraints.


title:
Spectroscopic estimate of surface gravity for a planetary member in the
  Sigma Ori cluster

abstract:
  We present intermediate-resolution (R=1500) near-infrared spectroscopy from
1.17 $\mu$m to 1.37 $\mu$m of the spectral type T planetary candidate member in
the \sigori cluster S Ori 70 reported by Zapatero Osorio et al. (2002). The new
data have been obtained with NIRSPEC at the Keck II telescope. The best fit of
our mid-resolution spectrum of S Ori 70 with theoretical spectra gives log
g=3.5$\pm$0.5 cm s$^{-2}$ and T$_{\rm eff}$=1,100$^{+200}_{-100}$ K. The low
gravity of this object derived from spectral synthesis supports its youth and
membership to the young \sigori cluster. Using evolutionary models for an age
of 3 Myr, we obtain a mass of 3 \mjup and a radius of 0.16 $R_{\odot}$,
independent of the distance to the object. Our analysis confirms that S Ori 70
is the lowest mass cluster planet so far identified in the galaxy.


title: Fermion Self-Energy during Inflation

abstract:
  I report on work done with Tomislav Prokopec (Heidelberg, CERN). We computed
the one loop self-energy of a massless fermion during inflation. When the
fermion is free it experiences only a small amount of inflationary particle
production owing to the conformal invariance of its classical action. However,
when the fermion is Yukawa coupled to a massless, minimally coupled scalar,
there is copious production of fermions. In a more complicated model this
effect might generate baryon asymmetry during inflation.


title:
Angular momentum distribution of hot gas and implications for disk
  galaxy formation

abstract:
  We study the angular momentum profiles both for dark matter and for gas
within virialized halos, using a statistical sample of halos drawn from
cosmological hydrodynamics simulations. Three simulations have been analyzed,
one is the ``non-radiative'' simulation, and the other two have radiative
cooling. We find that the gas component on average has a larger spin and
contains a smaller fraction of mass with negative angular momentum than its
dark matter counterpart in the non-radiative model. As to the cooling models,
the gas component shares approximately the same spin parameter as its dark
matter counterpart, but the hot gas has a higher spin and is more aligned in
angular momentum than dark matter, while the opposite holds for the cold gas.
After the mass of negative angular momentum is excluded, the angular momentum
profile of the hot gas component approximately follows the universal function
originally proposed by Bullock et al. for dark matter, though the shape
parameter $\mu$ is much larger for hot gas and is comfortably in the range
required by observations of disk galaxies. Since disk formation is related to
the distribution of hot gas that will cool, our study may explain the fact that
the disk component of observed galaxies contains a smaller fraction of low
angular momentum material than dark matter in halos.


title: Dynamical Friction on Star Clusters near the Galactic Center

abstract:
  Numerical simulations of the dynamical friction suffered by a star cluster
near the Galactic center have been performed with a parallelized tree code.
Gerhard (2001) has suggested that dynamical friction, which causes a cluster to
lose orbital energy and spiral in towards the galactic center, may explain the
presence of a cluster of very young stars in the central parsec, where star
formation might be prohibitively difficult owing to strong tidal forces. The
clusters modeled in our simulations have an initial total mass of 10^5-10^6
Msun and initial galactocentric radii of 2.5-30 pc. We have identified a few
simulations in which dynamical friction indeed brings a cluster to the central
parsec, although this is only possible if the cluster is either very massive
(~10^6 Msun), or is formed near the central parsec (<~ 5 pc). In both cases,
the cluster should have an initially very dense core (> 10^6 Msun pc-3). The
initial core collapse and segregation of massive stars into the cluster core,
which typically happens on a much shorter time scale than that characterizing
the dynamical inspiral of the cluster toward the Galactic center, can provide
the requisite high density. Furthermore, because it is the cluster core which
is most likely to survive the cluster disintegration during its journey
inwards, this can help account for the observed distribution of presumably
massive HeI stars in the central parsec.


title:
Magnetorotational instability in stratified, weakly ionised accretion
  discs

abstract:
  We present a linear analysis of the vertical structure and growth of the
magnetorotational instability in stratified, weakly ionised accretion discs,
such as protostellar and quiescent dwarf novae systems. The method includes the
effects of the magnetic coupling, the conductivity regime of the fluid and the
strength of the magnetic field, which is initially vertical. The conductivity
is treated as a tensor and assumed constant with height. We obtained solutions
for the structure and growth rate of global unstable modes for different
conductivity regimes, strengths of the initial magnetic field and coupling
between ionised and neutral components of the fluid. The envelopes of
short-wavelenght perturbations are determined by the action of competing local
growth rates at different heights, driven by the vertical stratification of the
disc. Ambipolar diffusion perturbations peak consistently higher above the
midplane than modes including Hall conductivity. For weak coupling,
perturbations including the Hall effect grow faster and act over a more
extended cross-section of the disc than those obtained using the ambipolar
diffusion approximation. Finally, we derived an approximate criterion for when
Hall diffusion determines the growth of the magnetorotational instability. This
is satisfied over a wide range of radii in protostellar discs, reducing the
extent of the magnetic `dead zone'. Even if the magnetic coupling is weak,
significant accretion may occur close to the midplane, rather than in the
surface regions of weakly-ionised discs.


title: A three-dimensional Galactic extinction model

abstract:
  A large-scale three-dimensional model of Galactic extinction is presented
based on the Galactic dust distribution model of Drimmel and Spergel (2001).
The extinction A_V to any point within the Galactic disk can be quickly deduced
using a set of three-dimensional cartesian grids. Extinctions from the model
are compared to empirical extinction measures, including lines-of-sight in and
near the Galactic plane using optical and NIR extinction measures; in
particular we show how extinction can be derived from NIR color-magnitude
diagrams in the Galactic plane to a distance of 8 kiloparsec.


title: Photometric Properties of Void Galaxies in the Sloan Digital Sky Survey

abstract:
  Using a nearest neighbor analysis, we construct a sample of void galaxies
from the Sloan Digital Sky Survey (SDSS) and compare the photometric properties
of these galaxies to the population of non-void (wall) galaxies. We trace the
density field of galaxies using a volume-limited sample with z_{max}=0.089.
Galaxies from the flux-limited SDSS with z\leq z_{max} and fewer than three
volume-limited neighbors within 7h^{-1}Mpc are classified as void galaxies.
This criterion implies a density contrast \delta \rho/ \rho < -0.6 around void
galaxies. From 155,000 galaxies, we obtain a sub-sample of 13,742 galaxies with
z\leq z_{max}, from which we identify 1,010 galaxies as void galaxies. To
identify an additional 194 faint void galaxies from the SDSS in the nearby
universe, r~ 72 h^{-1}Mpc, we employ volume-limited samples extracted from the
Updated Zwicky Catalog and the Southern Sky Redshift Survey with z_{max}=0.025
to trace the galaxy distribution. Our void galaxies span a range of absolute
magnitude from M_r=-13.5 to M_r=-22.5. Using SDSS photometry, we compare the
colors, concentration indices, and Sersic indices of the void and wall samples.
Void galaxies are significantly bluer than galaxies lying at higher density.
The population of void galaxies with M_r ~ M* +1 and brighter is on average
bluer and more concentrated (later type) than galaxies outside of voids. The
latter behavior is only partly explained by the paucity of luminous red
galaxies in voids. These results generally agree with the predictions of
semi-analytic models for galaxy formation in cold dark matter models, which
indicate that void galaxies should be relatively bluer, more disklike, and have
higher specific star formation rates.


title: RR Lyrae stars in four globular clusters in the Fornax dwarf galaxy

abstract:
  (Abridged) We have surveyed four globular clusters in the Fornax dwarf galaxy
for RR Lyrae stars, using archival HST observations. We identify 197 new RR
Lyrae stars in these four clusters. Despite the short observational baseline,
we derive periods, light-curves, and photometric parameters for each. The
Fornax clusters have exceptionally large RR Lyrae specific frequencies compared
with the Galactic globular clusters. Furthermore, the Fornax cluster RR Lyrae
stars are unusual in that their characteristics are intermediate between the
two Galactic Oosterhoff groups. In this respect the Fornax clusters are similar
to the field populations in several dwarf galaxies. We revise previous
measurements of the HB morphology in each cluster. The Fornax clusters closely
resemble the ``young'' Galactic halo population defined by Zinn. The existence
of the second parameter effect among the Fornax clusters is also confirmed.
Finally, we determine foreground reddening and distance estimates for each
cluster. We find a mean distance modulus to Fornax of (m-M)_0 = 20.66 +/- 0.03
(random) +/- 0.15 (systematic). Our measurements are consistent with a line of
sight depth of 8-10 kpc for this galaxy, matching its projected dimensions, and
incompatible with tidal model explanations for the observed high velocity
dispersions in many dSph galaxies. Dark matter dominance is suggested.


title:
On the Importance of Searching for Oscillations of the Jovian Inner
  Radiation Belt with a Quasi-Period of 40 Minutes

abstract:
  Experiments aboard the Ulysses spacecraft discovered quasi-periodic bursts of
relativistic electrons and of radio emissions with ~40-minute period(QP-40)
from the south pole of Jupiter in February 1992. Such polar QP-40 burst
activities were found to correlate well with arrivals of high-speed solar winds
at Jupiter. We advance the physical scenario that the inner radiation belt(IRB)
within ~2-3 Jupiter's radius, where ralativistic electrons are known to be
trapped via synchrotron emissions, can execute global QP-40 magnetoinertial
oscillations excited by arrivals of high-speed solar winds. Modulated by such
QP-40 IRB oscillations, relativistic electrons trapped in the IRB may escape
from the magnetic circumpolar regions during a certain phase of each 40-min
period to form circumpolar QP-40 electron bursts. Highly beamed synchrotron
emissions from such QP-40 burst electrons with small pitch angles relative to
Jovian magnetic field at ~30-40 Jupiter radius give rise to QP-40 radio bursts
with typical frequencies <0.2MHz. We predict that the synchrotron brightness of
the IRB should vary on QP-40 timescales upon arrivals of high-speed solar winds
with estimated magnitudes larger than 0.1Jy, detectable by ground-based radio
telescopes. Using the real-time solar wind data from the spacecraft ACE, we
show here that shch QP-40 pulsations of Jupiter's polar X-ray hot spot did in
fact coincide with the arrival of high-speed solar wind at Jupiter.


title: Periodicities in Solar Coronal Mass Ejections

abstract:
  Mid-term quasi-periodicities in solar coronal mass ejections (CMEs) during
the most recent solar maximum cycle 23 are reported here for the first time
using the four-year data (February 5, 1999 to February 10, 2003) of the Large
Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric
Observatory (SOHO). In parallel, mid-term quasi-periodicities in solar X-ray
flares (class >M5.0) from the Geosynchronous Operational Environment Satellites
(GOES) and in daily averages of Ap index for geomagnetic disturbances from the
World Data Center (WDC) at the International Association for Geomagnetism and
Aeronomy (IAGA) are also examined for the same four-year time span. Several
conceptual aspects of possible equatorially trapped Rossby-type waves at and
beneath the solar photosphere are discussed.


title: On the Structure of the Free Surface of Self-Binding Quark Matter

abstract:
  The distribution of electrons and of electrical at the free surface if
strange quark matter are determined within the framework of the MIT bag model.
It is shown that, with the allowance for the betta-decay of quarks near the
surface due to the outward escape of electrons, the electric charge density of
quarks at the surface increases by a factor of 17-25, the thickness of the
transitional layer decreases from 230 Fm to 15 Fm, and the field strength
increases by a factor of 1.7. The difference between the chemical potentials of
electrons at the surface and deep layers decreases from 7 MeV to 0.8 MeV, which
increases the limiting possible density of ordinary matter above a strange
quark star.


title: Possible Class of Nearby Gamma-Ray Burst / Gravitational Wave Sources

abstract:
  A possible subclass of gamma-ray bursts -- those with few, wide pulses,
spectral lags of order one to several seconds, and soft spectra -- has been
identified. Their Log[N]-Log[Fp] distribution approximates a -3/2 power-law,
suggesting homogeneity and relatively nearby sources. These mostly dim bursts
account for ~ 50% of the BATSE sample of long bursts near that instrument's
trigger threshold, suggesting that this subluminous class constitutes a more
common variety than the more familiar burst sources which lie at truly
cosmological distances. Theoretical scenarios predicted such a class, motivated
by their exemplar GRB 980425 (SN 1998bw) lying at a distance of ~ 38 Mpc. The
observations are explained by invoking off-axis viewing of the GRB jet and/or
bulk Lorentz factors of order a few. Long-lag bursts show a tendency to
concentrate near the Supergalactic Plane with a quadrupole moment of
-0.10+/-0.04, similar to that for SNe type Ib/c within the same volume. The
rate of the observed subluminous bursts is of order 1/4 that of SNe Ib/c.
Evidence for a sequential relationship between SNe Ib/c and GRBs is critiqued
for two cases, as simultaneity of the SN and GRB events may be important for
detection of the expected gravitational wave signal; at most, SN to GRB delays
appear to be a few days. SN asymmetries and ultrarelativistic GRB jets suggest
the possibility of rapid rotation in the pre-collapse objects, a primary
condition required for highly non-axisymmetric SN collapse to produce strong
gravitational waves.


title: Extremely Close-In Giant Planets from Tidal Capture

abstract:
  Planets that form around stars born in dense stellar environments are subject
to dynamical perturbations from other stars in the system. These perturbations
will strip outer planets, forming a population of free-floating planets, some
of which will be tidally captured before they evaporate from the system. For
systems with velocity dispersion of 1 km/s, Jupiter-mass planets can be
captured into orbits with periods of 0.1-0.4 days, which are generally stable
over a Gyr, assuming quadratic suppression of eddy viscosity in the convective
zones of the host stars. Under this assumption, and that most stars form
several massive planets at separations 5-50 AU, about 0.03% of stars in rich,
mature open clusters should have extremely close-in tidally captured planets.
Approximately 0.005% of field stars should also have such planets, which may be
found in field searches for transiting planets. Detection of a population of
tidally-captured planets would indicate that most stars formed in stellar
clusters. In globular clusters, the fraction of stars with tidally-captured
planets rises to 0.1% -- in conflict with the null result of the transit search
in 47 Tuc. This implies that, if the quadratic prescription for viscosity
suppression is correct, planetary formation was inhibited in 47 Tuc: less than
one planet of Jupiter-mass or greater (bound or free-floating) formed per
cluster star. Less than half of the stars formed solar-system analogs. Brown
dwarfs can also be captured in tight orbits; the lack of such companions in 47
Tuc in turn implies an upper limit on the initial frequency of brown dwarfs in
this cluster. However, this upper limit is extremely sensitive to the highly
uncertain timescale for orbital decay, and thus it is difficult to draw robust
conclusions about the low-mass end of the mass function in 47 Tuc.


title: The Formation of Early-Type Galaxies: Observations to z=1

abstract:
  How does the number density of early-type galaxies (E+S0) evolve with
redshift? What are their star formation histories? Do their mass density
profile and other structural properties evolve with redshift? Answering these
questions is key to understanding how E+S0s form and evolve. I review the
observational evidence on these issues, focusing on the redshift range z=0.1-1,
and compare it to the predictions of current models of galaxy formation.


title: The significance of the largest scale CMB fluctuations in WMAP

abstract:
  We investigate anomalies reported in the Cosmic Microwave Background maps
from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite on very large
angular scales and discuss possible interpretations. Three independent
anomalies involve the quadrupole and octopole:
  1. The cosmic quadrupole on its own is anomalous at the 1-in-20 level by
being low (the cut-sky quadrupole measured by the WMAP team is more strikingly
low, apparently due to a coincidence in the orientation of our Galaxy of no
cosmological significance);
  2. The cosmic octopole on its own is anomalous at the 1-in-20 level by being
very planar;
  3. The alignment between the quadrupole and octopole is anomalous at the
1-in-60 level.
  Although the a priori chance of all three occurring is 1 in 24000, the
multitude of alternative anomalies one could have looked for dilutes the
significance of such a posteriori statistics. The simplest small universe model
where the universe has toroidal topology with one small dimension of order half
the horizon scale, in the direction towards Virgo, could explain the three
items above. However, we rule this model out using two topological tests: the
S-statistic and the matched circle test.


title: Proto-clusters and the clustering of distant galaxies and radio sources

abstract:
  The clustering properties of objects in 3 different radio surveys (NVSS,
FIRST and BOOTES-WSRT) and 2 near-infrared surveys (the ``Daddi field'' and the
FIRES survey) are investigated and compared with studies of various samples of
galaxies, AGN and clusters. At z ~ 1, it seems that the 2dF optical quasars
have a correlation length a factor of about 2 less than powerful radio galaxies
at similar redshifts. This indicates that these two classes of object can not
be ``unified'' by postulating that their main difference is due to their
evolution being at a different stage. It seems much more likely that these QSOs
are predominantly located in field galaxies, while the powerful radio sources
are located preferentially in early types. Furthermore, it appears that both
the extremely red objects (EROs) from the IR surveys and the more luminous
radio sources are similarly clustered and as such are the most clustered
objects known in the z>1 Universe. Even at z ~3 the red J-K galaxies from the
FIRES survey are similarly strongly clustered, at a level of about 3 times
higher than Lyman break galaxies. These clustering properties are consistent
with EROs and radio galaxies being similar objects at different stages of their
evolution. Locally, the most clustered population of objects are clusters of
galaxies. Since the progenitors of these objects -- proto-clusters -- will
therefore also be highly clustered, a good way to locate proto-clusters is to
target fields with very powerful and potentially highly clustered distant z>2
radio sources. The techniques that are currently being used for locating and
studying these proto-clusters are briefly discussed.


title:
Theory of pixel lensing towards M31 -- II. The velocity anisotropy and
  flattening of the MACHO distribution

abstract:
  The POINT-AGAPE collaboration is currently searching for massive compact halo
objects (MACHOs) towards the Andromeda galaxy (M31). The survey aims to exploit
the high inclination of the M31 disk, which causes an asymmetry in the spatial
distribution of M31 MACHOs. Here, we investigate the effects of halo velocity
anisotropy and flattening on the asymmetry signal using simple halo models. For
a spherically symmetric and isotropic halo, we find that the underlying
pixel-lensing rate in far-disk M31 MACHOs is more than 5 times the rate of
near-disk events. We find that the asymmetry is increased further by about 30%
if the MACHOs occupy radial orbits rather than tangential orbits, but is
substantially reduced if the MACHOs lie in a flattened halo. However, even for
haloes with a minor-to-major axis ratio q = 0.3, the numbers of M31 MACHOs in
the far-side outnumber those in the near-side by a factor of ~2. We show that,
if positional information is exploited in addition to number counts, then the
number of candidate events required to confirm asymmetry for a range of
flattened and anisotropic halo models is achievable, even with significant
contamination by variable stars and foreground microlensing events. For
pixel-lensing surveys which probe a representative portion of the M31 disk, a
sample of around 50 candidates is likely to be sufficient to detect asymmetry
within spherical haloes, even if half the sample is contaminated, or to detect
asymmetry in haloes as flat as q = 0.3 provided less than a third of the sample
comprises contaminants. We also argue that, provided its mass-to-light ratio is
less than 100, the recently observed stellar stream around M31 is not
problematic for the detection of asymmetry. (Abstract slightly abridged.)


title: Can modified gravity explain accelerated cosmic expansion?

abstract:
  We show that the recently suggested explanations of cosmic acceleration by
the modification of gravity at small curvature suffer violent instabilities and
strongly disagree with the known properties of gravitational interactions.


title: On the inflationary flow equations

abstract:
  I explore properties of the inflationary flow equations. I show that the flow
equations do not correspond directly to inflationary dynamics. Nevertheless,
they can be used as a rather complicated algorithm for generating inflationary
models. I demonstrate that the flow equations can be solved analytically and
give a closed form solution for the potentials to which flow equation solutions
correspond. I end by considering some simpler algorithms for generating
stochastic sets of slow-roll inflationary models for confrontation with
observational data.


title: Status of the H.E.S.S. Experiment

abstract:
  The H.E.S.S. experiment (High Energy Stereoscopic System) is a new generation
atmospheric Cherenkov detector measuring high-energy (>100 GeV) gamma radiation
from the Universe. This paper briefly explains the imaging Cherenkov technique
and describes the H.E.S.S. project and its current status.


title: An accretion disk and radio spectra of pulsars

abstract:
  On the basis of the unified model of compact radio sources, the dependence of
a turnover frequency in the smoothed radio spectrum of a pulsar upon the ratio
of the dispersion measure to the period of a pulsar is obtained. This relation
is produced by the radial density wave in the accretion disk surrounding a
pulsar. The unified model of compact radio sources gives also the smoothed
spectral indices of radio emission from pulsars as $\alpha=2$ for the gaseous
disk with the temperature profile T=const and $\alpha=3$ for the gaseous disk
with the pressure profile P=const ($F_{\nu} \propto \nu ^{- \alpha} $).


title: The effects of UV background correlations on LyA forest flux statistics

abstract:
  We examine the possible effects of UV background fluctuations on the pixel
flux power spectrum and auto-correlation function of the LyA forest due to a
finite number of sources in an attenuating medium. We consider scenarios in
which QSO sources dominate the contribution to the UV background. To estimate
their contribution, we use the QSO luminosity functions from the 2dF and Sloan
QSO surveys. We estimate self-consistent values for the attenuation length at
the Lyman edge through the Intergalactic Medium using Particle Mesh simulations
of the LyA forest, normalised by the measured mean LyA flux. We examine the
convergence properties of the flux power spectrum and auto-correlation function
under differing assumptions regarding pressure-smoothing. Convergence to better
than 10% in the flux power spectrum at proper wavenumbers k < 0.015s/km
requires a comoving resolution of 30-60kpc/h in a comoving box of size 25Mpc/h
at z = 5, with the requirements becoming more severe at lower redshifts. We
find much better covergence properties for the relative effects of the UV
background fluctuations on the flux power spectrum. The background fluctuations
increase the large-scale power and suppress the power at intermediate scales.
At z < 4, the effect is only at the few percent level. By z > 5, however, the
large-scale power is boosted by more than 50%, suggesting the flux power
spectrum may serve as a useful tool for distinguishing QSO-dominated UV
background scenarios from those dominated by galaxies.


title: Implications of the $\gamma$-ray Polarization of GRB 021206

abstract:
  We compare two possible scenarios for the producing of high level of
polarization within the prompt emission of a GRB: synchrotron emission from a
relativistic jet with a uniform (in space and time) magnetic field and
synchrotron emission from a jet with a random magnetic field in the plane of
the shock. Somewhat surprisingly we find that both scenarios can produce a
comparable level of polarization ($\sim 45-50$% for the uniform field and $\sim
30-35$% for a random field). Uniform time independent field most naturally
arises by expansion of the field from the compact object. It requires a
$10^{12}$G field at the source and a transport of the field as $\propto
R^{-1}$. It {\it does not} imply Poynting flux domination of the energy of the
wind. There is a serious difficulty however, within this scenario, accounting
for particle acceleration (which requires random magnetic fields) both for
Poynting flux and non-Poynting flux domination. Significant polarization can
also arise from a random field provided that the observer is located within
$1/\Gamma$ orientation from a narrow ($\theta_j \sim 1/\Gamma$) jet. While most
jets are wider, the jet of GRB 021206 from which strong polarization was
recently observed, was most likely very narrow. GRB 021206 is among the
strongest bursts ever. Adopting the energy-angle relation we find an estimated
angle of $<1/40$rad or even smaller. Thus, for this particular burst the
required geometry is not unusual. We conclude that the RHESSI observations
suggest that the prompt emission results from synchrotron radiation. However,
in view of the comparable levels of polarizations predicted by both the random
field and the homogeneous field scenarios these observations are insufficient
to rule out or confirm either one.


title: Really Cool Stars and the Star Formation History at the Galactic Center

abstract:
  We present R=550 to 1200 near infrared H and K spectra for a magnitude
limited sample of 79 asymptotic giant branch and cool supergiant stars in the
central ~ 5 pc (diameter) of the Galaxy. We use a set of similar spectra
obtained for solar neighborhood stars with known Teff and Mbol that is in the
same range as the Galactic center (GC) sample to derive Teff and Mbol for the
GC sample. We then construct the Hertzsprung--Russell (HRD) diagram for the GC
sample. Using an automated maximum likelihood routine, we derive a coarse star
formation history of the GC. We find (1) roughly 75% of the stars formed in the
central few pc are older than 5 Gyr; (2) the star formation rate (SFR) is
variable over time, with a roughly 4 times higher star formation rate in the
last 100 Myr compared to the average SFR; (3) our model can only match
dynamical limits on the total mass of stars formed by limiting the IMF to
masses above 0.7 M$_\odot$. This could be a signature of mass segregation or of
the bias toward massive star formation from the unique star formation
conditions in the GC; (4) blue supergiants account for 12 % of the total sample
observed, and the ratio of red to blue supergiants is roughly 1.5; (5) models
with isochrones with [Fe/H] = 0.0 over all ages fit the stars in our HRD better
than models with lower [Fe/H] in the oldest age bins, consistent with the
finding of Ramirez et al. (2000) that stars with ages between 10 Myr and 1 Gyr
have solar [Fe/H].


title: WMAP Bounds on Braneworld Tachyonic Inflation

abstract:
  We analyse the implications of the Wilkinson Microwave Anisotropy Probe
(WMAP) results for a braneworld tachyonic model of inflation. We find that WMAP
bounds on $n_s$ allow us to constrain significantly the parameter space of the
model; in particular, extremely weak string coupling is required, $g_s \sim
10^{-15}$. Moreover, our analysis shows that the running of the scalar spectral
index is within the bounds determined by WMAP for the allowed range of model
parameters; however, it is not possible to obtain $n_s>1$ on large scales and
$n_s<1$ on small scales.


title: SZ polarisation as a probe of the intracluster medium

abstract:
  We present high-resolution hydrodynamical simulations of the degree and
direction of polarisation imprinted on the CMB by the Sunyaev-Zel'dovich effect
in the the line of sight to massive galaxy clusters. We focus on two
contributions which contribute most of the induced CMB polarisation in addition
to the intrinsic CMB quadrupole: the radiation quadrupole seen by electrons due
to their own velocity in the plane normal to the line of sight, and the
radiation quadrupole due to the thermal Sunyaev-Zel'dovich effect, which is
generated by a previous scattering elsewhere in the cores of the local and
nearby clusters. We show that inside the virial radius of a massive cluster,
this latter effect, although being second order in the optical depth, can reach
the level of the former effect. These two effects can, respectively, constrain
the projected tangential velocity and inner density profile of the gas, if they
can be separated with multi-frequency observations. As the information on the
tangential velocity of the ICM gas is combined with the kinetic
Sunyaev-Zel'dovich temperature effect probing the projected radial velocity it
will be possible to constrain the dynamics of the ICM. In particular, future
polarisation observations may be able to trace out the filamentary structure of
the cooler and less dense ionized gas that has not yet been incorporated into
massive clusters. We also discuss how the collapse of a cluster should produce
a peculiar ring-like polarisation pattern which would open a new window to
detect proto-clusters at high redshift.


title: X-ray emission properties of galaxies in Abell 3128

abstract:
  We use archival Chandra X-ray Observatory data to investigate X-ray emission
from early-type galaxies in the rich z=0.06 cluster Abell 3128. By combining
the X-ray count-rates from an input list of optically-selected galaxies, we
obtain a statistical detection of X-ray flux, unbiased by X-ray selection
limits. Using 87 galaxies with reliable Chandra data, X-ray emission is
detected for galaxies down to M_B ~ -19.0, with only an upper limit determined
for galaxies at M_B ~ -18.3. The ratio of X-ray to optical luminosities is
consistent with recent determinations of the low-mass X-ray binary content of
nearby elliptical galaxies. Taken individually, in contrast, we detect
significant (3sigma) flux for only six galaxies. Of these, one is a foreground
galaxy, while two are optically-faint galaxies with X-ray hardness ratios
characteristic of active galactic nuclei. The remaining three detected galaxies
are amongst the optically-brightest cluster members, and have softer X-ray
spectra. Their X-ray flux is higher than that expected from X-ray binaries, by
a factor 2-10; the excess suggests these galaxies have retained their hot
gaseous haloes. The source with the highest L_X / L_B ratio is of unusual
optical morphology with prominent sharp-edged shells. Notwithstanding these few
exceptions, the cluster population overall exhibits X-ray properties consistent
with their emission being dominated by X-ray binaries. We conclude that in rich
cluster environments, interaction with the ambient intra-cluster medium acts to
strip most galaxies of their hot halo gas.


title: Serendipitous Discovery and Parallax of a Nearby L Dwarf

abstract:
  A field star serendipitously observed in a parallax program proved to have a
proper motion of 562 mas/yr and a parallax of 82 +- 2 mas. The star is
identified with 2MASS J07003664+3157266. A Keck LRIS spectrum shows its
spectral type to be L3.5, as expected from its infrared and optical colors and
absolute magnitude. This object had not been previously recognized as an L
dwarf, perhaps because of crowding at its relatively low Galactic latitude (b =
+15.8 degrees).


title:
A study of the Mg II 2796.34 A emission line in late--type normal, and
  RS CVn stars

abstract:
  We carry out an analysis of the Mg II 2796.34 A emission line in RS CVn stars
and make a comparison with the normal stars studied in a previous paper (Paper
I). The sample of RS CVn stars consists of 34 objects with known HIPPARCOS
parallaxes and observed at high resolution with IUE. We confirm that RS CVn
stars tend to possess wider Mg II lines than normal stars having the same
absolute visual magnitude. However, we could not find any correlation between
the logarithmic line width log Wo and the absolute visual magnitude Mv (the
Wilson--Bappu relationship) for these active stars, contrary to the case of
normal stars addressed in Paper I. On the contrary, we find that a strong
correlation exists in the (Mv, log L) plane (L is the absolute flux in the
line). In this plane, normal and RS CVn stars are distributed along two nearly
parallel straight lines with RS CVn stars being systematically brighter by
about 1 dex. Such a diagram provides an interesting tool to discriminate active
from normal stars. We finally analyse the distribution of RS CVn and of normal
stars in the (log L, log Wo) plane, and find a strong linear correlation for
normal stars, which can be used for distance determinations.


title:
Infrared Observations During the Secondary Eclipse of HD 209458 b II.
  Strong Limits on the Infrared Spectrum Near 2.2 Microns

abstract:
  We report observations of the transiting extrasolar planet, HD 209458 b,
designed to detect the secondary eclipse. We employ the method of `occultation
spectroscopy', which searches in combined light (star and planet) for the
disappearance and reappearance of weak infrared spectral features due to the
planet as it passes behind the star and reappears. Our observations cover two
predicted secondary eclipse events, and we obtained 1036 individual spectra of
the HD 209458 system using the SpeX instrument at the NASA IRTF in September
2001. Our spectra extend from 1.9 to 4.2 microns with a spectral resolution of
1500. We have searched for a continuum peak near 2.2 microns (caused by CO and
water absorption bands), as predicted by some models of the planetary
atmosphere to be approximately 6E-4 of the stellar flux, but no such peak is
detected at a level of about 3E-4 of the stellar flux. Our results represent
the strongest limits on the infrared spectrum of the planet to date and carry
significant implications for understanding the planetary atmosphere. In
particular, some models that assume the stellar irradiation is re-radiated
entirely on the sub-stellar hemisphere predict a flux peak inconsistent with
our observations. Several physical mechanisms can improve agreement with our
observations, including the re-distribution of heat by global circulation, a
nearly isothermal atmosphere, and/or the presence of a high cloud.


title: Heating of Galactic Disks by Infalling Satellites

abstract:
  We develop an analytic model to calculate the rate at which galaxy disks are
heated by dark matter substructures orbiting in their halos. The model takes
into account the internal structure, mass function and accretion rate of
satellites expected in the LambdaCDM cosmology, as well as the growth of the
disk by accretion and mergers, but it ignores resonant heating of the disk and
the dynamical effects of spiral arms and bars. We calibrate this model against
N-body simulations and demonstrate that it is able to reproduce the N-body
heating rates to within a factor of 3 in the majority of cases. Our model gives
the distribution of disk scale-heights for galaxies of different luminosities.
For L* spiral galaxies, it predicts a median disk thickness of only 5% of the
radial scale-length if substructure is the only source of heating. The median
disk thickness increases to nearly 20% of the radial scale-length when heating
due to gravitational scattering of stars by molecular clouds is also included.
The latter value is close to the thickness estimated observationally for the
disk of the Milky Way galaxy. The distribution of disk thickness predicted by
the model is also consistent with a recent observational determination for
sub-L* galaxies by Bizyaev & Mitronova. Thus, the observed thickness of the
stellar disks of spiral galaxies seems to be entirely compatible with the
abundance of substructure in dark matter halos predicted by the standard
Lambda-dominated cold dark matter model of structure formation. In an Omega_0=1
universe, our best model of galaxy formation produces similar scale-heights, a
consequence of the fact that similar amounts of substructure are accreted by
halos during the lifetime of the disk in Omega_0=1 and Omega_0=0.3,
Lambda_0=0.7 cold dark matter cosmologies.


title:
A Wide Field Hubble Space Telescope Study of the Cluster Cl0024+1654 at
  z=0.4 II: The Cluster Mass Distribution

abstract:
  (abridged) We present a comprehensive lensing analysis of the rich cluster
Cl0024+1654 based on panoramic sparse-sampled imaging conducted with HST. We
demonstrate an ability to detect reliably weak lensing signals to a cluster
radius of ~5 Mpc where the mean shear is around 1%. The projected mass
distribution reveals a secondary concentration representing 30% of the overall
cluster mass, which is also visible in the distribution of cluster member
galaxies. We normalize the mass profile determined from the shear by assuming
that background galaxies selected with I=23-26 have a redshift distribution
statistically similar to that in the HDFs. Combining strong and weak
constraints, we are able to probe the mass profile of the cluster on scales of
0.1 to 5 Mpc thus providing a valuable test of the universal form proposed by
NFW on large scales. A generalized power law fit indicates a asymptotic density
distribution with 3D slope larger than 2.4. An isothermal mass profile is
therefore strongly rejected, whereas a NFW profile with M_200= 6.1+/-1 10^14
M_sun provides a good fit to the lensing data. We isolate cluster members
according to their optical-near infrared colors; the red cluster light closely
traces the dark matter with a mean mass-to-light ratio of M/L_K~ 40 M/L_sun.
Similar profiles for mass and light on 1-5 Mpc scales are expected if cluster
assembly is largely governed by infalling groups.


title:
The matallicities of star-forming galaxies at intermediate redshifts
  0.47 < z < 0.92

abstract:
  Estimates of the [O/H] metallicity of the star-forming gas in a sample of 66
CFRS galaxies between 0.47 < z < 0.92 have been made based on the flux ratios
of bright emission lines. Most galaxies (> 75%) have the [O/H] ~ 8.9
metallicities that are seen locally in galaxies of similar luminosities.
However, a minority (< 25%) appear to have significantly lower metallicities
[O/H] < 8.6 as indicated by high values of the Pagel R23 parameter. The high
metallicities of the majority of the galaxies suggest that they do not fade to
be low metallicity dwarf galaxies today. Only one of the 66 galaxies has an
optical emission line spectrum similar to the few Lyman break galaxies recently
observed at z ~ 3, emphasizing the differences with that population. The
inferred emission line gas [O/H] metallicity broadly correlates with luminosity
in both the rest B- and J-bands but with considerable scatter introduced. The
metallicity does not appear to correlate well with galaxy size, H-beta strength
or, with the very limited data available, the kinematics. The metallicity does
correlate well with the continuum optical-infrared colors in a way that could
be explained as a combination of effects, none of which should produce large
variations in the M/L ratio. These results support a "down-sizing" picture of
galaxy evolution rather than a "fading dwarf" picture in which the luminous
active galaxies at high redshift are highly brightened dwarf galaxies. The
overall change in metallicity of star-forming galaxies over the last half of
the age of the Universe appears to have been modest, Delta[O/H] = 0.08 +/-
0.06. This is consistent with the age-metallicity relation in the Galactic disk
and is broadly consistent with models for the chemical evolution of the
Universe, especially those that consider different environments.


title:
Constraints on the Inner Cluster Mass Profile and the Power Spectrum
  Normalization from Strong Lensing Statistics

abstract:
  Strong gravitational lensing is a useful probe of both the intrinsic
properties of the lenses and the cosmological parameters of the universe. The
large number of model parameters and small sample of observed lens systems,
however, have made it difficult to obtain useful constraints on more than a few
parameters from lensing statistics. Here we examine how the recent WMAP
measurements help improve the constraining power of statistics from the radio
lensing survey JVAS/CLASS. We find that the absence of theta>3'' lenses in
CLASS places an upper bound of beta<1.25 (1.60) at 68% (95%) CL on the inner
density profile, rho \propto r^{-beta}, of cluster-sized halos. Furthermore,
the favored power spectrum normalization is sigma_8 >= 0.7 (95% CL). We discuss
two possibilities for stronger future constraints: a positive detection of at
least one large-separation system, and next-generation radio surveys such as
LOFAR.


title: M31's Undisturbed Thin Disk of Globular Clusters

abstract:
  We show that there is a subsystem of the M31 globular clusters with THIN DISK
kinematics. These clusters span the entire metallicity range of the M31
globular cluster system, in contrast to the (thick) disk globulars in the Milky
Way which are predominantly metal-rich. Disk globular clusters are found across
the entire disk of M31 and form around 40% of the clusters projected on its
disk. The existence of such a disk system suggests that there was a relatively
large thin disk in place very early in M31's history. Accurate measures of the
ages of these clusters will constrain the epoch of disk formation in M31. There
is currently no strong evidence for differences in age between Milky Way and
M31 globulars. While age differences are subtle for old populations, it is
unlikely that disk clusters with [Fe/H] around -2.0 were formed after
significant star formation began in the galaxy, as the proto-cluster gas would
be enriched by supernova ejecta. Thus it is likely that M31 had a rather large
disk in place at early epochs.
  The very existence of such a cold disk means that M31 has suffered no mergers
with an object of 10% or more of the disk mass since the clusters were formed.
This makes Brown et al (2003)'s suggestion that M31 could have suffered an
equal-mass merger 6-8 Gyr ago less viable.


title: HI Fluctuations at Large Redshifts: II - the Signal Expected for GMRT

abstract:
  For the GMRT, we calculate the expected signal from redshifted HI emission at
two frequency bands centered at 610 and 325 MHz. The study focuses on the
visibility-visibility cross-correlations, proposed earlier as the optimal
statistical estimator for detecting and analyzing this signal. These
correlations directly probe the power spectrum of density fluctuations at the
redshift where the radiation originated, and thereby provide a method for
studying the large scale structures at large redshifts. We present detailed
estimates of the correlations expected between the visibilities measured at
different baselines and frequencies. Analytic fitting formulas representing the
salient features of the expected signal are also provided. These will be useful
in planning observations and deciding an optimal strategy for detecting this
signal.


title: The enigmatic outburst of V445 Puppis - a possible Helium nova?

abstract:
  JHK spectroscopic and photometric observations are reported for the
enigmatic, nova-like, variable V445 Puppis which erupted at the end of 2000.
The near-IR spectra are hydrogen-deficient and unusually rich in CI lines. The
important CI lines are found to be positioned at 1.133, 1.166, 1.175, 1.189,
1.26 and 1.689 microns. Model calculations for the CI lines are done to make
the identification of the lines secure. Photometric data, taken on January 2.90
UT, 2001 shortly after the outburst, show the formation of an optically thin
dust shell around V445 Puppis. The temperature and upper limit for the mass of
the dust shell are estimated to be 1800K and M(dust) ~ 1oe-9 M(sun)
respectively . A subsequent episode of massive dust formation - indicated by
the observed, deep visual dimming - is also seen in JHK images of early
November 2001. V445 Puppis has shown two unusual properties for a nova i) the
hydrogen-deficiency and He/C enrichment of the object as seen from optical and
IR data and ii) synchrotron radio emission which was detected nearly a year
after it's outburst by other workers. The strange nature of the object is
discussed and it is shown that it is difficult to place it in the known
categories of eruptive variables viz. novae (classical, recurrent or
symbiotic); born-again AGB stars; the new class of eruptive variables like V838
Mon; and RCB/HdC stars. Tentative evidence for an accretion disk and binarity
of the V445 Puppis system is presented. It is debated whether V445 Puppis is a
rare Helium nova or an unique object.


title: Photon counting strategies with low light level CCDs

abstract:
  Low light level charge coupled devices (L3CCDs) have recently been developed,
incorporating on-chip gain. They may be operated to give an effective readout
noise much less than one electron by implementing an on-chip gain process
allowing the detection of individual photons. However, the gain mechanism is
stochastic and so introduces significant extra noise into the system. In this
paper we examine how best to process the output signal from an L3CCD so as to
minimize the contribution of stochastic noise, while still maintaining
photometric accuracy.
  We achieve this by optimising a transfer function which translates the
digitised output signal levels from the L3CCD into a value approximating the
photon input as closely as possible by applying thresholding techniques. We
identify several thresholding strategies and quantify their impact on photon
counting accuracy and effective signal-to-noise.
  We find that it is possible to eliminate the noise introduced by the gain
process at the lowest light levels. Reduced improvements are achieved as the
light level increases up to about twenty photons per pixel and above this there
is negligible improvement. Operating L3CCDs at very high speeds will keep the
photon flux low, giving the best improvements in signal-to-noise ratio.


title:
Magnetohydrodynamical Accretion Flows: Formation of Magnetic Tower Jet
  and Subsequent Quasi-Steady State

abstract:
  We present three-dimensional (3-D) magnetohydrodynamical (MHD) simulations of
radiatively inefficient accretion flow around black holes. General relativistic
effects are simulated by using the pseudo-Newtonian potential. We start
calculations with a rotating torus threaded by localized poloidal magnetic
fields with plasma beta, a ratio of the gas pressure to the magnetic pressure,
$\beta =10$ and 100. When the bulk of torus material reaches the innermost
region close to a central black hole, a magnetically driven jet emerges. This
magnetic jet is derived by vertically inflating toroidal fields (`magnetic
tower') and has a two-component structure: low-$\beta$ ($\lsim 1$) plasmas
threaded with poloidal (vertical) fields are surrounded by that with toroidal
fields. The collimation width of the jet depends on external pressure, pressure
of ambient medium; the weaker the external pressure is, the wider and the
longer-lasting becomes the jet. Unless the external pressure is negligible, the
bipolar jet phase ceases after several dynamical timescales at the original
torus position and a subsequent quasi-steady state starts. The black hole is
surrounded by quasi-spherical zone with highly inhomogeneous structure in which
toroidal fields are dominant except near the rotation axis. Mass accretion
takes place mainly along the equatorial plane. Comparisons with other MHD
simulation results and observational implications are discussed.


title: Black Hole Candidates

abstract:
  The state of the searches for isolated black holes, non-accreting black holes
in binary systems and, finally, the accreting black holes in the X-ray binaries
is presented. The third category is, by far, the most important source of
information about the Galactic black holes and it is the main topic of this
review. Different proposed signatures of an accreting black hole are reviewed
(including the growing evidence for the presence of the event horizon in some
systems). The list of 51 black hole candidates compiled with the help of these
signatures is presented. To obtain a conclusive evidence that the candidate is
really a black hole, one needs a dynamical mass estimate indicating that the
mass of the compact object is greater than about 3 solar masses. The
observational methods of obtaining such estimates are briefly discussed. The
application of these methods leads to the list of 18 objects that could be
considered confirmed black holes. Their estimated masses are found to fall in
the range 3.5 to 16 solar masses. Finally, some general remarks concerning
relation of black hole candidates to different classes of X-ray binaries such
as X-ray Novae, microquasars and high/low mass X-ray binaries are presented.
The implications of the properties of black hole binaries for the theory of
stellar evolution are also discussed.


title: V803 Centauri: Helium Dwarf Nova Mimicking a WZ Sge-Type Superoutburst

abstract:
  We observed long-term behavior of the helium dwarf nova V803 Cen, and
clarified the existence of at least two distinct states (state with 77-d
supercycles and standstill-like state) which interchangeably appeared with a
time-scale of 1--2 yr. We also conducted a time-resolved CCD photometry
campaign during the bright outburst in 2003 June. The overall appearance of the
outburst closely resemble that of the late stage of the 2001 outburst of WZ
Sge, consisting of the initial peak stage (superoutburst plateau), the dip, and
the oscillating (rebrightening) states. During the initial peak stage, we
detected large-amplitude superhump-type variation with a period of 0.018686(4)
d = 1614.5(4) s, and during the oscillation stage, we detected variations with
a period of 0.018728(2) d = 1618.1(2) s. We consider that the former period
better represents the superhump period of this system, and the latter
periodicity may be better interpreted as arising from late superhumps. The
overall picture of the V803 Cen outburst resembles that of a WZ Sge-type
outburst, but apparently with a higher mass-transfer rate than in hydrogen-rich
WZ Sge-type stars. We suggest that this behavior may be either the result of
difficulty in maintaining the hot state in a helium disk, or the effect of an
extremely low tidal torque resulting from the extreme mass ratio.


title:
High Performances Corrugated Feed Horns for Space Applications at
  Millimetre Wavelengths

abstract:
  We report on the design, fabrication and testing of a set of high performance
corrugated feed horns at 30 GHz, 70 GHz and 100 GHz, built as advanced
prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission.
The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70
GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz, and
by electro-formation at higher frequencies. The measured performances on side
lobes and return loss meet the stringent Planck requirements over the large
(20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape
and side lobes levels of the dual profiled designs has been demonstrated.


title:
Interferometric Observations of Powerful CO Emission from the three
  Submillimeter Galaxies at z=2.30, 2.51 and 3.35

abstract:
  We report IRAM Plateau de Bure, millimeter interferometry of three z=~2.4 to
3.4, SCUBA deep field galaxies. Our CO line observations confirm the rest-frame
UV/optical redshifts, thus more than doubling the number of confirmed,
published redshifts of the faint submillimeter population and proving their
high-z nature. In all three sources our measurements of the intrinsic gas and
dynamical mass are large (1e10 to 1e11 Msun). In at least two cases the data
show that the submillimeter sources are part of an interacting system. Together
with recent information gathered in the X-ray, optical and radio bands our
observations support the interpretation that the submm-population consists of
gas rich (gas to dynamical mass ratio ~0.5) and massive, composite
starburst/AGN systems, which are undergoing a major burst of star formation and
are evolving into m*-galaxies.


title: Closed Universes, de Sitter Space and Inflation

abstract:
  We present a new approach to constructing inflationary models in closed
universes. Conformal embedding of closed-universe models in a de Sitter
background suggests a quantisation condition on the available conformal time.
This condition implies that the universe is closed at no greater than the 10%
level. When a massive scalar field is introduced to drive an inflationary phase
this figure is reduced to closure at nearer the 1% level. In order to enforce
the constraint on the available conformal time we need to consider conditions
in the universe before the onset of inflation. A formal series around the
initial singularity is constructed, which rests on a pair of dimensionless,
scale-invariant parameters. For physically-acceptable models we find that both
parameters are of order unity, so no fine tuning is required, except in the
mass of the scalar field. For typical values of the input parameters we predict
the observed values of the cosmological parameters, including the magnitude of
the cosmological constant. The model produces a very good fit to the most
recent CMBR data. The primordial curvature spectrum predicts the low-l fall-off
in the CMB power spectrum observed by WMAP. The spectrum also predicts a
fall-off in the matter spectrum at high k, relative to a power law. A further
prediction of our model is a large tensor mode component, with r~0.2.


title: Conservation Laws in Smooth Particle Hydrodynamics: the DEVA Code

abstract:
  We describe DEVA, a multistep AP3M-like-SPH code particularly designed to
study galaxy formation and evolution in connection with the global cosmological
model. This code uses a formulation of SPH equations which ensures both energy
and entropy conservation by including the so-called $\bn h$ terms. Particular
attention has also been paid to angular momentum conservation and to the
accuracy of our code. We find that, in order to avoid unphysical solutions, our
code requires that cooling processes must be implemented in a non-multistep
way.
  We detail various cosmological simulations which have been performed to test
our code and also to study the influence of the $\bn h$ terms. Our results
indicate that such correction terms have a non-negligible effect on some
cosmological simulations, especially on high density regions associated either
to shock fronts or central cores of collapsed objects. Moreover, they suggest
that codes paying a particular attention to the implementation of conservation
laws of physics at the scales of interest, can attain good accuracy levels in
conservation laws with limited computational resources.


title:
Super computers in astrophysics and High Performance simulations of
  self-gravitating systems

abstract:
  The modern study of the dynamics of stellar systems requires the use of
high-performance computers. Indeed, an accurate modelization of the structure
and evolution of self-gravitating systems like planetary systems, open
clusters, globular clusters and galaxies imply the evaluation of body-body
interaction over the whole size of the structure, a task that is
computationally very expensive, in particular when it is performed over long
intervals of time. In this report we give a concise overview of the main
problems of stellar systems simulations and present some exciting results we
obtained about the interaction of globular clusters with the parent galaxy.


title:
Puzzling afterglow's oscillations in GRBs and SGRs: tails of precessing
  Jets

abstract:
  Damped oscillating afterglows in GRB 030329 and in SGR 1900+14 find a natural
explanation in precessing gamma Jet model for both GRBs and SGRs. The very thin
Jet cone (solid angle ratio Delta Omega/Omega less or near 10^{-8}) combines at
once the Supernova power and the apparent huge GRBs output: {dE/dt}_{GRBs}
comparable to {dE/dt}_{SN}* Omega/(Delta Omega), leading to a better
understanding of their remarkable GRB-Super Nova connection shown in early
GRB980425/SN1998bw event and in most recent GRB030329/SN2003dh one. The same
thin beaming offer a understanding of the apparent SGR-X-Pulsar power
connection: {dE/dt}_{SGRs} comparable to {dE/dt}_{Xpuls}*Omega/(Delta Omega).
The precessing Jet model for both GRBs and SGRs, at their different
luminosity,explains the existence of a few identical energy spectra and time
evolution of these two sources leading to their unified understanding. The
spinning-precessing Jet explains the rare mysterious X-Ray precursors in GRBs
and SGRs. The Multi-precessing Jet at peak activity in all band may explain the
puzzling X or optical re-brightening bumps found in last GRB030329 and earliest
SGR 1900+ 14 on 27 August 1998 and on 18 April 2001, as well as the multi-bump
radio light-curve observed in GRB980425 and GRB030329. Rarest micro-quasars in
our galaxy as SS433, and Herbig Haro objects describe these thin precessing Jet
imprint in their 3D relic nebulae shapes.


title: Evidence for a Large Stellar Bar in the LSB Galaxy UGC 7321

abstract:
  Late-type spiral galaxies are thought to be the dynamically simplest type of
disk galaxies and our understanding of their properties plays a key role in the
galaxy formation and evolution scenarios. The low surface brightness (LSB)
galaxy UGC 7321, a nearby, isolated, ``superthin'' edge-on galaxy, is an ideal
object to study those purely disk dominated bulge-less galaxies. Although late
type spirals are believed to exhibit the simplest possible structure, even
prior observations showed deviations from a pure single component exponential
disk in the case of UGC 7321. We present for the first time photometric
evidence for peanut-shaped outer isophotes from a deep optical (R-band) image
of UGC 7321. Observations and dynamical modeling suggest that
boxy/peanut-shaped (b/p) bulges in general form through the buckling
instability in bars of the parent galaxy disks. Together with recent HI
observations supporting the presence of a stellar bar in UGC 7321 this could be
the earliest known case of the buckling process during the evolutionary life of
a LSB galaxy, whereby material in the disk-bar has started to be pumped up
above the disk, but a genuine bulge has not yet formed.


title: Interacting Dark Matter and Dark Energy

abstract:
  We discuss models for the cosmological dark sector in which the energy
density of a scalar field approximates Einstein's cosmological constant and the
scalar field value determines the dark matter particle mass by a Yukawa
coupling. A model with one dark matter family can be adjusted so the
observational constraints on the cosmological parameters are close to but
different from what is predicted by the Lambda CDM model. This may be a useful
aid to judging how tightly the cosmological parameters are constrained by the
new generation of cosmological tests that depend on the theory of structure
formation. In a model with two families of dark matter particles the scalar
field may be locked to near zero mass for one family. This can suppress the
long-range scalar force in the dark sector and eliminate evolution of the
effective cosmological constant and the mass of the nonrelativistic dark matter
particles, making the model close to Lambda CDM, until the particle number
density becomes low enough to allow the scalar field to evolve. This is a
useful example of the possibility for complexity in the dark sector.


title:
A model for electromagnetic extraction of rotational energy and
  formation of accretion-powered jets in radio galaxies

abstract:
  A self-similar solution for the 3D axi-symmetric radiative MHD equations,
which revisits the formation and acceleration of accretion-powered jets in AGNs
and microquasars, is presented. The model relies primarily on electromagnetic
extraction of rotational energy from the disk plasma and forming a
geometrically thin super-Keplerian layer between the disk and the overlying
corona. The outflowing plasma in this layer is dissipative, two-temperature,
virial-hot, advective and electron-proton dominated. The innermost part of the
disk in this model is turbulent-free, sub-Keplerian rotating and
advective-dominated. This part ceases to radiate as a standard disk, and most
of the accretion energy is converted into magnetic and kinetic energies that go
into powering the jet. The corresponding luminosities of these
turbulent-truncated disks are discussed.


title:
The Cluster Expansion for the Self-Gravitating gas and the Thermodynamic
  Limit

abstract:
  We develop the cluster expansion and the Mayer expansion for the
self-gravitating thermal gas and prove the existence and stability of the
thermodynamic limit N, V to infty with N/V^{1/3} fixed. The essential
(dimensionless) variable is here eta = [G m^2 N]/[V^{1/3} T] (which is kept
fixed in the thermodynamic limit). We succeed in this way to obtain the
expansion of the grand canonical partition function in powers of the fugacity.
The corresponding cluster coefficients behave in the thermodynamic limit as
[eta/N]^{j-1} c_j where c_j are pure numbers. They are expressed as integrals
associated to tree cluster diagrams. A bilinear recurrence relation for the
coefficients c_j is obtained from the mean field equations in the Abel form. In
this way the large j behaviour of the c_j is calculated. This large j behaviour
provides the position of the nearest singularity which corresponds to the
critical point (collapse) of the self-gravitating gas in the grand canonical
ensemble. Finally, we discuss why other attempts to define a thermodynamic
limit for the self-gravitating gas fail.


title: A WN4 companion to BD +62 2296 in Cas OB5

abstract:
  I report observations of the triple system BD +62 2296 showing that all its
components are early-type stars, most likely physically related. The faintest
component BD +62 2296B is a hitherto uncatalogued Wolf-Rayet star. The
brightest component, star A, is shown to be a seemingly normal B2.5Ia
supergiant. Long-slit spectroscopy of BD +62 2296B shows it to be a
narrow-lined WN4 star. Given the spatial separation, the two objects are
unlikely to form a physical binary. Spectra of the third visual component, BD
+62 2296C, allow its classification as a B0III star. Such concentration of
massive stars strongly suggests that BD +62 2296 is in reality a very compact
young open cluster in the area of the OB association Cas OB5.


title: The Origin of Cosmic Dust

abstract:
  Large amounts of dust have recently been discovered in high-z galaxies and
QSOs. The stellar winds produced by AGB stars are thought to be the main source
of dust in galaxies, but they cannot produce that dust on a short enough
timescale (<1 Gyr) to explain the results in the high-z galaxies. Supernova
explosions of massive stars (TypeII) are also a potential source, with models
predicting 0.2-4 Msun of dust from each. As massive stars evolve rapidly, on
timescales of a few Myr, these supernovae could be responsible for the high-z
dust. Observations of supernova remnants in the Milky Way have previously only
revealed 10^-7 - 10^-3 Msun of dust each, which is insufficient to explain the
high-z data. Here we report the detection of ~2-4 Msun of cold dust in Cas A.
This implies that supernovae are at least as important as stellar winds in
producing dust in our Galaxy and would have been the dominant source of dust at
high-z.


title:
Abundance Analysis of Planetary Host Stars I. Differential Iron
  Abundances

abstract:
  We present atmospheric parameters and iron abundances derived from
high-resolution spectra for three samples of dwarf stars: stars which are known
to host close-in giant planets (CGP), stars for which radial velocity data
exclude the presence of a close-in giant planetary companion (no-CGP), as well
as a random sample of dwarfs with a spectral type and magnitude distribution
similar to that of the planetary host stars (control). All stars have been
observed with the same instrument and have been analyzed using the same model
atmospheres, atomic data and equivalent width modeling program. Abundances have
been derived differentially to the Sun, using a solar spectrum obtained with
Callisto as the reflector with the same instrumentation. We find that the iron
abundances of CGP dwarfs are on average by 0.22 dex greater than that of no-CGP
dwarfs. The iron abundance distributions of both the CGP and no-CGP dwarfs are
different than that of the control dwarfs, while the combined iron abundances
have a distribution which is very similar to that of the control dwarfs. All
four samples (CGP, no-CGP, combined, control) have different effective
temperature distributions. We show that metal enrichment occurs only for CGP
dwarfs with temperatures just below solar and approximately 300 K higher than
solar, whereas the abundance difference is insignificant at Teff around 6000 K.


title: Giant Molecular Clouds in M33 -- II. High Resolution Observations

abstract:
  We present 12CO(1->0) observations of 45 giant molecular clouds in M33 made
with the BIMA array. The observations have a linear resolution of 20 pc,
sufficient to measure the sizes of most GMCs in the sample. We place upper
limits on the specific angular momentum of the GMCs and find the observed
values to be nearly an order of magnitude below the values predicted from
simple formation mechanisms. The velocity gradients across neighboring,
high-mass GMCs appear preferentially aligned on scales less than 500 pc. If the
clouds are rotating, 40% are counter-rotating with respect to the galaxy. GMCs
require a braking mechanism if they form from the large scale radial
accumulation of gas. These observations suggest that molecular clouds form
locally out of atomic gas with significant braking by magnetic fields to
dissipate the angular momentum imparted by galactic shear. The observed GMCs
share basic properties with those found in the Galaxy such as similar masses,
sizes, and linewidths as well as a constant surface density of 120 M_sun
pc^{-2}. The size-linewidth relationship follows Delta V ~ r^{0.45\pm 0.02},
consistent with that found in the Galaxy. The cloud virial masses imply that
the CO-to-H_2 conversion factor has a value of 2 X 10^20 H2 cm^-2/(K km/s) and
does not change significantly over the disk of M33 despite a change of 0.8 dex
in the metallicity.


title: Calculating Gravitational Wave Signatures from Binary Black Hole Mergers

abstract:
  Calculations of the final merger stage of binary black hole evolution can
only be carried out using full scale numerical relativity simulations. This
article provides a general overview of these calculations, highlighting recent
progress and current challenges.


title:
Warping and Precession of Accretion Disks Around Magnetic Stars:
  Nonlinear Evolution

abstract:
  The inner region of the accretion disk around a magnetized star (T Tauri
star, white dwarf or neutron star) is subjected to magnetic torques that induce
warping and precession of the disk. These torques arise from the interaction
between the stellar field and the induced electric currents in the disk. We
carry out numerical simulations of the nonlinear evolution of warped, viscous
accretion disks driven by the magnetic torques. We show that the disk can
develop into a highly warped steady state in which the disk attains a fixed
(warped) shape and precesses rigidly. The warp is most pronounced at the disk
inner radius (near the magnetosphere boundary). As the system parameters (such
as accretion rate) change, the disk can switch between a completely flat state
(warping stable) and a highly warped state. The precession of warped disks may
be responsible for a variety of quasi-periodic oscillations or radiation flux
variabilities observed in many different systems, including young stellar
objects and X-ray binaries.


title: A Subaru Search for Lyman$\alpha$ Emitters at Redshift 5.7

abstract:
  We present the results of a survey for Ly$\alpha$ emitters at $z\approx 5.7$
based on optical narrow-band ($\lambda_{\rm c} = 8150$ \AA ~ and $\Delta\lambda
= 120$ \AA), and broad-band ($B$, $R_{\rm C}$, $I_{\rm C}$, and $z^\prime$)
observations of the field surrounding the high redshift quasar, SDSSp
J104433.04$-$012522.2, on the 8.2 m Subaru Telescope with the Subaru Prime
Focus Camera, Suprime-Cam. This survey covers a sky area of $\approx 720$
arcmin$^2$ and a co-moving volume of $\simeq 2 \times 10^5 ~ h_{0.7}^{-3}$
Mpc$^3$. We have found 20 candidates of Ly$\alpha$ emitters at $z \approx$ 5.7
with $\Delta z \approx 0.1$. Two of them have been confirmed star-forming
galaxies at $z=5.655$ and $z=5.687$ from our follow-up optical spectroscopy. We
discuss star-formation properties of the 20 objects from a statistical point of
view. Our survey leads to a new estimate of the star formation rate density at
$z \approx 5.7$, $\sim 1.2 \times 10^{-3} h_{0.7} M_\odot$ yr$^{-1}$
Mpc$^{-3}$.


title:
XMM-Newton observation of the ULIRG NGC 6240: The physical nature of the
  complex Fe K line emission

abstract:
  We report on an XMM-Newton observation of the ultraluminous infrared galaxy
NGC 6240. The 0.3-10 keV spectrum can be successfully modelled with: (i) three
collisionally ionized plasma components with temperatures of about 0.7, 1.4,
and 5.5 keV; (ii) a highly absorbed direct power-law component; and (iii) a
neutral Fe K_alpha and K_beta line. We detect a significant neutral column
density gradient which is correlated with the temperature of the three plasma
components. Combining the XMM-Newton spectral model with the high spatial
resolution Chandra image we find that the temperatures and the column densities
increase towards the center.
  With high significance, the Fe K line complex is resolved into three distinct
narrow lines: (i) the neutral Fe K_alpha line at 6.4 keV; (ii) an ionized line
at about 6.7 keV; and (iii) a higher ionized line at 7.0 keV (a blend of the Fe
XXVI and the Fe K_beta line). While the neutral Fe K line is most probably due
to reflection from optically thick material, the Fe XXV and Fe XXVI emission
arises from the highest temperature ionized plasma component.
  We have compared the plasma parameters of the ultraluminous infrared galaxy
NGC 6240 with those found in the local starburst galaxy NGC 253. We find a
striking similarity in the plasma temperatures and column density gradients,
suggesting a similar underlying physical process at work in both galaxies.


title: Evolution of Massive Black Hole Binaries

abstract:
  We present the result of large-scale N-body simulations of the
stellar-dynamical evolution of a massive black-hole binary at the center of a
spherical galaxy. We focus on the dependence of the hardening rate on the
relaxation timescale of the parent galaxy. A simple theoretical argument
predicts that a binary black hole creates the ``loss cone'' around it. Once the
loss cone is formed, the hardening rate is determined by the rate at which
field stars diffuse into the loss cone. Therefore the hardening timescale
becomes proportional to the relaxation timescale. Recent N-body simulations,
however, have failed to confirm this theory and various explanations have been
proposed. By performing simulations with sufficiently large N (up to $10^6$)
for sufficiently long time, we found that the hardening rate does depend on N.
Our result is consistent with the simple theoretical prediction that the
hardening timescale is proportional to the relaxation timescale. This
dependence implies that most massive black hole binaries are unlikely to merge
within the Hubble time through interaction with field stars and gravitational
wave radiation alone.


title: Mercury's spin-orbit model and signature of its dynamical parameters

abstract:
  The 3:2 spin-orbit resonance between the rotational and orbital motions of
Mercury results from a functional dependance on a tidal friction adding to a
non-zero eccentricity with a permanent asymmetry in the equatorial plane of the
planet. The upcoming space missions, MESSENGER and BepiColombo with onboard
instrumentation capable of measuring the Mercury's rotational parameters,
stimulate the objective to attempt to an accurate theory of the planet's
rotation. We have used our BJV relativistic model of solar system integration
including the spin-orbit motion of the Moon. This model had been previously
built in accordance with the requirements of the Lunar Laser Ranging
observational accuracy. We extended this model to the spin-orbit couplings of
the terrestrial planets including Mercury; the updated model is called SONYR
(acronym of Spin-Orbit N-BodY Relativistic model). An accurate rotation of
Mercury has been then obtained. Moreover, the conception of the SONYR model is
suitable for analyzing the different families of hermean rotational librations.
We accurately identify the non-linear relations between the rotation of Mercury
and its dynamical figure (\cmr2, $C_{20}$, and $C_{22}$). Notably, for a
variation of 1% on the \cmr2 value, signatures in the $\phi$ hermean libration
in longitude as well as in the $\eta$ obliquity of the planet are respectively
0.45 arcseconds (as) and 2.4 milliarcseconds (mas). These determinations
provide new constraints on the internal structure of Mercury to be discussed
with the expected accuracy forecasted in the BepiColombo mission (respectively
3.2 and 3.7 as according to Milani et al 2001).


title:
A theoretical analysis of the systematic errors in the Red Clump
  distance to the LMC

abstract:
  We present a detailed analysis of the uncertainty on the theoretical
population corrections to the LMC Red Clump (RC) absolute magnitude, by
employing a population synthesis algorithm to simulate theoretically the
photometric and spectroscopic properties of RC stars, under various assumptions
about the LMC Star Formation Rate (SFR) and Age Metallicity Relationship (AMR).
A comparison of the outcome of our simulations with observations of evolved
low-intermediate mass stars in the LMC allows one to select the combinations of
SFR and AMR that bracket the real LMC star formation history, and to estimate
the systematic error on the associated RC population corrections.
  The most accurate estimate of the LMC distance modulus from the RC method
(adopting the OGLE-II reddening maps for the LMC) is obtained from the K-band
magnitude, and provides (m-M)_{0, LMC}=18.47 +/-0.01(random)
+0.05/-0.06(systematic). Distances obtained from the I-band, or from the
multicolour RC technique which determines at the same time reddening and
distance, both agree (albeit with a slightly larger error bar) with this value.


title: Systematic bias in interstellar magnetic field estimates

abstract:
  Faraday rotation of the polarization plane in magnetized thermal plasma
provides one of the most efficient methods to deduce regular magnetic fields
from radio astronomical observations. Since the Faraday rotation measure RM is
proportional to an integral, along the line of sight, of magnetic field
weighted with thermal electron density, RM is believed to yield the regular
magnetic field averaged over large volume. Here we show that this is not the
case in a turbulent medium where fluctuations in magnetic field and electron
density are not statistically independent, and so contribute to RM. For
example, in the case of pressure equilibrium, magnetic field can be
anticorrelated with plasma density to produce a negative contribution. As a
result, the strength of the regular magnetic field obtained from RM can be
underestimated if the fluctuations in electron density and magnetic field are
neglected. The anticorrelation also reduces the standard deviation of RM. We
further discuss the effect of the positive correlations where the standard
treatment of RM leads to an overestimated magnetic field. Because of the
anisotropy of the turbulent magnetic field, the regular magnetic fields
strength, obtained from synchrotron emission using standard formulae, can be
overestimated. A positive correlation between cosmic-ray number density and
magnetic field leads to an overestimate of the strengths of the regular and
total fields. These effects can explain the difference between the strengths of
the regular Galactic magnetic field as indicated by RM and synchrotron
emissivity data and reconcile the magnetic field strength in the Solar vicinity
with typical strength of regular magnetic fields in external galaxies.


title:
Very high column density and small reddening towards GRB 020124 at z =
  3.20

abstract:
  We present optical and near-infrared observations of the dim afterglow of GRB
020124, obtained between 2 and 68 hours after the gamma-ray burst. The burst
occurred in a very faint (R > 29.5) Damped Ly-alpha Absorber (DLA) at a
redshift of z = 3.198 +- 0.004. The derived column density of neutral hydrogen
is log(N_H) = 21.7 +- 0.2 and the rest-frame reddening is constrained to be
E(B-V) < 0.065, i.e., A_V < 0.20 for standard extinction laws with R_V ~ 3. The
resulting dust-to-gas ratio is less than 11 % of that found in the Milky Way,
but consistent with the SMC and high-redshift QSO DLAs, indicating a low
metallicity and/or a low dust-to-metals ratio in the burst environment. A grey
extinction law (large R_V), produced through preferential destruction of small
dust grains by the GRB, could increase the derived A_V and dust-to-gas ratio.
The dimness of the afterglow is however fully accounted for by the high
redshift: If GRB 020124 had been at z = 1 it would have been approximately 1.8
mag brighter--in the range of typical bright afterglows.


title:
The assembly of massive galaxies from NIR observations of the Hubble
  Deep Field South

abstract:
  We use a deep K(AB)<25 galaxy sample in the Hubble Deep Field South to trace
the evolution of the cosmological stellar mass density from z~ 0.5 to z~3. We
find clear evidence for a decrease of the average stellar mass density at high
redshift, 2<z<3.2, that is 15^{+25}_{-5}% of the local value, two times higher
than what observed in the Hubble Deep Field North. To take into account for the
selection effects, we define a homogeneous subsample of galaxies with
10^{10}M_\odot \leq M_* \leq 10^{11}M_\odot: in this sample, the mass density
at z>2 is 20^{+20}_{-5} % of the local value. In the mass--limited subsample at
z>2, the fraction of passively fading galaxies is at most 25%, although they
can contribute up to about 40% of the stellar mass density. On the other hand,
star--forming galaxies at z>2 form stars with an average specific rate at least
<\dot M/M_*> ~4 x10^{-10} yr$^{-1}$, 3 times higher than the z<~1 value. This
implies that UV bright star--forming galaxies are substancial contributors to
the rise of the stellar mass density with cosmic time. Although these results
are globally consistent with $\Lambda$--CDM scenarios, the present rendition of
semi analytic models fails to match the stellar mass density produced by more
massive galaxies present at z>2.


title: Black hole accretion discs: reality confronts theory

abstract:
  Disc spectra from highly luminous black hole binaries are observed to be
rather simple, despite theoretical predictions to the contrary. We collate the
disc-dominated spectra from multiple observations of 10 separate sources, and
show that these overwhelmingly follow a multi-temperature disc blackbody
spectrum with luminosity proportional to T^4, and that such discs are stable.
These results are in conflict with standard Shakura-Sunyaev alpha-discs
predictions, including proposed modifications such as additional energy loss in
a jet, wind or corona. Accretion disc spectra can be useful, reliable guides to
the disc structure, and should be used to test the next generation of accretion
disc models, in which the disc viscosity is calculated self-consistently from
the magnetically generated turbulent dynamo.


title: HEGRA Contributions to the 28th International Cosmic Ray Conference

abstract:
  This preprint encompasses thirteen individual contributions of the HEGRA
collaboration to the 28th International Cosmic Ray conference in Tsukuba,
Japan. The papers report on results on M87, M31, H1426+428, Mkn421,
1ES1959+650, Scan of the TeV sky, Performance of the system, GeV sources, 54
AGN, and SN1006


title: Physical Evidence for Dark Energy

abstract:
  We present measurements of the angular cross-correlation between luminous red
galaxies from the Sloan Digital Sky Survey and the cosmic microwave background
temperature maps from the Wilkinson Microwave Anisotropy Probe. We find a
statistically significant achromatic positive correlation between these two
data sets, which is consistent with the expected signal from the late
Integrated Sachs-Wolfe (ISW) effect. We do not detect any anti-correlation on
small angular scales as would be produced from a large Sunyaev-Zel'dovich (SZ)
effect, although we do see evidence for some SZ effect for our highest redshift
samples. Assuming a flat universe, our preliminary detection of the ISW effect
provides independent physical evidence for the existence of dark energy.