title: K 4-47: a planetary nebula excited by photons and shocks

abstract:
  K 4-47 is an unusual planetary nebula composed of a compact high-ionization
core and a pair of low-ionization knots. Long-slit medium-resolution spectra of
the knots and core are analyzed in this paper. Assuming photoionization from
the central star, we have derived physical parameters for all the nebular
components, and the (icf) chemical abundances of the core, which appear similar
to Type-I PNe for He and N/O but significantly deficient in oxygen. The nebula
has been further modelled using both photoionization (CLOUDY) and shock
(MAPPINGS) codes. From the photoionization modelling of the core, we find that
both the strong auroral [O III] 4363A and [N II] 5755A emission lines observed
and the optical size of the core cannot be accounted for if a homogeneus
density is adopted. We suggest that a strong density stratification, matching
the high-density core detected at radio wavelengths and the much lower density
of the optical core, might solve the problem. From the bow-shock modelling of
the knots, on the other hand, we find that knots' chemistry is also represented
by Type-I PN abundances, and that they would move with velocities of 250 - 300
km/s.


title: HI Distribution and Kinematics of UGCA 86

abstract:
  We present 21-cm HI line and 408 MHz and 1.4 GHz continuum observations of
the dwarf galaxy UGCA 86 with the DRAO synthesis telescope. UGCA 86 is detected
in the continuum at 408 MHz (S_{408} = 120 +/- 30 mJy) and 1.4 GHz (S_{1400} =
79 +/- 3 mJy). The HI structure of UGCA 86 is complex, with two separate
components: a rotating disk and a highly elongated spur that is kinematically
disjunct from the disk. The HI disk is centered on the optical galaxy with
similar axial ratio and orientation of the major axis. An area of the disk with
a peculiar velocity of 25 km/s relative to the regular rotation of the disk is
found on the southern side, where most of the star formation is concentrated.
The spur is seen along the minor axis of UGCA 86 and overlaps in part with the
disk. Towards the optical center of UGCA 86, the velocity difference between
the spur and the disk is 40 km/s, about one third of the rotation velocity of
the HI disk at 6 kpc from the center. This implies a large radial component of
the orbital velocity of the spur, and therefore a significantly non-circular
orbit. The velocity dispersion of the disk is 8.8 km/s, whereas the velocity
dispersion of the spur varies from 10 km/s to 30 km/s. A possible tidal origin
of the spur is considered in view of the proximity of the large Scd galaxy IC
342. However, evidence that the spur is located far outside the plane of the HI
disk, and the absence of evidence for a warp in the outer HI disk, poses a
problem for the interpretation of the spur as a tidal tail induced by IC 342.
Detailed modelling of the IC 342/UGCA 86 system will be required before a tidal
origin of the spur can be dismissed conclusively. The possibility that the spur
is part of the nascent cloud of UGCA 86 or the remains of a small dwarf galaxy
is presented as an alternative interpretation.


title:
A Determination of the Chemical Composition of Alpha Centauri A from
  Strong Lines

abstract:
  Using the theory of collisional line broadening developed by Anstee and
O'Mara (1991, 1995) and the spectrum synthesis software developed by John Ross,
the abundances of Fe, Mg, Ca and Na in Alpha Centauri A are determined from
strong lines. The abundances are approximately 0.2 dex higher than in the Sun.
The derived abundances are independent of non-thermal motions in the atmosphere
of Alpha Centauri A.
  The microturbulence obtained from medium-strong lines using the abundances
obtained from the strong lines is 1.34 +/- 0.12 km/s, i.e., 0.20 km/s larger
than in the Sun, which is fully consistent with the lower surface gravity of
Alpha Centauri A. This microturbulence can then be used in determination of the
abundance of other elements for which there are no strong lines in the
spectrum.
  This thesis is the first application of this theory to determine abundances
and the microturbulence of Alpha Centauri A. Recent results are published by
Doyle et al.(astro-ph/0407468)


title: Dense Ionized and Neutral Gas Surrounding Sgr A*

abstract:
  We present high resolution H41a hydrogen recombination line observations of
the 1.2' (3 pc) region surrounding Sgr A* at 92 GHz using the OVRO Millimeter
Array with an angular resolution of 7" x 3" and velocity resolution of 13 km/s.
New observations of H31a, H35a, H41a, and H44a lines were obtained using the
NRAO 12-m telescope, and their relative line strengths are interpreted in terms
of various emission mechanisms. These are the most extensive and most sensitive
observations of recombination line to date. Observations of HCO+ (1 - 0)
transition at 89 GHz are also obtained simultaneously with a 40% improved
angular resolution and 4-15 times improved sensitivity over previous
observations, and the distribution and kinematics of the dense molecular gas in
the circumnuclear disk (CND) are mapped and compared with those of the ionized
gas. The line brightness ratios of the hydrogen recombination lines are
consistent with purely spontaneous emission from 7000 K gas with n_e = 20,000
cm$^{-3}$ near LTE condition. A virial analysis suggests that the most
prominent molecular gas clumps in the CND have mean densities of 10^7 cm^{-3},
sufficient to withstand the tidal shear in the Galactic Center region.
Therefore, these clumps may survive over several dynamical times, and the CND
may be a dynamically stable structure. We estimate a total gas mass of 3 x 10^5
solar mass for the CND. \


title: Planetary Nebulae Kinematics in M31

abstract:
  We present kinematics of 135 planetary nebulae in M31 from a survey covering
3.9 square degrees and extending out to 15 kpc from the southwest major axis
and more than 20 kpc along the minor axis. The majority of our sample, even
well outside the disk, shows significant rotational support (mean line-of-sight
velocity 116 km/s). We argue that these PN belong to the outer part of M31's
large de Vaucouleurs bulge. Only five PN have velocities clearly inconsistent
with this fast rotating bulge. All five may belong to tidal streams in M31's
outer halo. One is projected on the Northern Spur, and is counter-rotating with
respect to the disk there. Two are projected along the major axis at X=-10 kpc
and have M32-like velocities; they could be debris from that galaxy. The
remaining two halo PN are located near the center of the galaxy and their
velocities follow the gradient found by Ibata et al. (2004), implying that
these PN could belong to the Southern Stream. If M31 has a non-rotating,
pressure-supported halo, we have yet to find it, and it must be a very minor
component of the galaxy.


title: Multiple inflation and the WMAP 'glitches'

abstract:
  Observations of anisotropies in the cosmic microwave background by the
Wilkinson Microwave Anisotropy Probe suggest the possibility of oscillations in
the primordial density perturbation. Such deviations from the usually assumed
scale-free spectrum were predicted in the multiple inflation model wherein
`flat direction' fields undergo rapid phase transitions due to the breaking of
supersymmetry by the large vacuum energy driving inflation. This causes sudden
changes in the mass of the (gravitationally coupled) inflaton and interrupts
its slow roll. We calculate analytically the resulting modifications to the
density perturbation and demonstrate how the oscillations arise.


title: Metals and Dust in Intermediate-redshift Damped Ly-alpha Galaxies

abstract:
  We report spectroscopic observations with the Multiple Mirror Telescope for
11 damped Lyman-alpha absorbers (DLAs) or strong DLA candidates at 0.1 < z <
1.5, including several absorbers discovered in the Sloan Digital Sky Survey. In
particular, we have measured absorption lines of Zn II, Cr II, Ni II, Fe II, Mn
II, Ti II, Ca II, and Si II. These measurements have doubled the sample of Zn
and Cr measurements at z < 1. The average relative abundance patterns in these
objects are very similar to those found for high-redshift DLAs reported in the
literature. Our observations suggest that the dust content, as determined by
[Cr/Zn], does not show much change with redshift. We also examine the sample
for correlation of [Cr/Zn] with estimates of the quasar reddening. Our data
suggest that the global mean metallicity of DLAs, as measured by the gas phase
abundance of Zn, at best shows a weak evolution with redshift over the range
0.4 < z <3.9.


title:
Locating the Warm-Hot Intergalactic Medium in the Simulated Local
  Universe

abstract:
  We present an analysis of mock spectral observation of warm-hot intergalactic
medium (WHIM) using a constrained simulation of the local universe. The
simulated map of oxygen emission lines from local WHIM reproduces well the
observed structures traced by galaxies in the real local universe. We further
attempt to perform mock observations of outer parts of simulated Coma cluster
and A3627 adopting the expected performance of DIOS (Diffuse Intergalactic
Oxygen Surveyor), which is proposed as a dedicated soft X-ray mission to search
for cosmic missing baryons. We find that WHIMs surrounding nearby clusters are
detectable with a typical exposure time of a day, and thus constitute realistic
and promising targets for DIOS. We also find that an X-ray emitting clump in
front of Coma cluster, recently reported in the XMM-Newton observation, has a
counterpart in the simulated local universe, and its observed spectrum can be
well reproduced in the simulated local universe if the gas temperature is set
to the observationally estimated value.


title: Weak Lensing and Supernovae: Complementary Probes of Dark Energy

abstract:
  Weak lensing observations and supernova observations, combined with CMB
observations, can both provide powerful constraints on dark energy properties.
Considering statistical errors only, we find luminosity distances inferred from
2000 supernovae and large-scale (l < 1000) angular power spectra inferred from
redshift-binned cosmic shear maps place complementary constraints on w_0 and
w_a where w(z) = w_0 + w_a(a-1). Further, each set of observations can
constrain higher-dimensional parameterizations of w(z); we consider eigenmodes
of the w(z) error covariance matrix and find such datasets can each constrain
the amplitude of about 5 w(z) eigenmodes. We also consider another
parameterization of the dark energy.


title:
A New Method for Studying the Topology of the Universe from the Cosmic
  Microwave Background

abstract:
  The standard method for observationally confirming the existence of a
predicted finite topology of the universe involves searching for the repetition
of the same finite or extended source in different directions. However, serious
problems are encountered when studying both types of sources, finite and
extended. In studying a finite source, such as a star, galaxy, or quasar, the
problem of its evolution must be dealt with. The same source seen in different
directions is observed at different distances (i.e., ages), making its
identification extremely difficult. Studying extended sources, such as
circles-in-the-sky (CIS) within the cosmic microwave background (CMB), is also
problematic since it requires an unrealistic zero width last scattering surface
(LSS) to produce the predicted identical temperatures on the circles. It is
shown here that these temperatures are no longer identical when a realistic
finite width LSS is taken into account. A new method for studying the topology
of the universe which avoids the above mentioned problems in studying both
finite and extended sources is suggested here. It consists of searching for
increased temperature fluctuations in the regions of the intersections of the
LSS with the faces of the fundamental polyhedron of the finite topology.
Appreciably greater fluctuations are predicted in these regions. A worked-out
example is given.


title:
Maser mechanism of optical pulsations from anomalous X-ray pulsar
  4U0142+61

abstract:
  A maser curvature emission mechanism in the presence of curvature drift is
used to explain the optical pulsations from anomalous X-ray pulsars. For the
source of AXP0142+61,the optical pulsation occurs at the radial distance
$R(\nu_M)\sim 4.75\times 10^9$ cm to the neutron star. The corresponding
curvature maser frequency is about $\nu_M\approx1.39\times 10^{14}$ Hz. The
result is consistent with the observation of the optical pulsations from the
anomalous X-ray pulsar 4U0142+61.


title:
Absence of Dwarf Galaxies at High Redshifts: Evidence from a Galaxy
  Group

abstract:
  The galaxy group NGC 5044 consists of a luminous giant elliptical galaxy
surrounded by a cluster of approximately 160 low luminosity and dwarf galaxies,
mostly of early type. The cumulative projected radial distribution of dwarf
galaxies in the NGC 5044 group, unlike distributions of more luminous galaxies
in rich clusters, does not follow a projected dark matter (NFW) profile.
Instead, a deficiency or absence of low luminosity galaxies is apparent in NGC
5044 within about 350 kpc, about one third of the current group virial radius.
Most of the dwarf galaxies identified in NGC 5044 entered the virial radius at
redshifts less than about 2 or 3, and very few entered at higher redshifts. The
peculiar, non-NFW shape of the projected cumulative dwarf galaxy distribution
in NGC 5044 within 350 kpc resembles the characteristic shallow cumulative
distribution of dark subhalos that are also known to be relatively young.
Dynamical friction is unlikely to explain the apparent lack of group member
galaxies at small radii in NGC 5044.


title: Very high energy gamma rays from the direction of Sagittarius A*

abstract:
  We report the detection of a point-like source of very high energy (VHE)
gamma-rays coincident within 1' of Sgr A*, obtained with the H.E.S.S. array of
Cherenkov telescopes. The gamma-rays exhibit a power-law energy spectrum with a
spectral index of -2.2 +/- 0.09 +/- 0.15 and a flux above the 165 GeV threshold
of (1.82 +/- 0.22) * 10^-7 m^-2 s^-1. The measured flux and spectrum differ
substantially from recent results reported in particular by the CANGAROO
collaboration.


title:
Some astrophysical implications of dark matter and gas profiles in a new
  galaxy clusters model

abstract:
  The structure of the dark matter and the thermodynamical status of the hot
gas in galaxy clusters is an interesting and widely discussed topic in modern
astrophysics. Recently, Rasia et al. (2004) have proposed a new dynamical model
for the mass density profile of clusters of galaxies as a result of a set of
high resolution hydrodynamical simulations of structure formation. We
investigate the lensing properties of this model evaluating the deflection
angle, the lensing potential and the amplification of the images. We reserve
particular attention to the structure and position of the critical curves in
order to see whether this model is able to produce radial and tangential arcs.
To this aim, we also investigate the effect of taking into account the
brightest cluster galaxy in the lensing potential and the deviations from
spherical symmetry mimicked by an external shear. We also analyze the
implication of the gas density and temperature profiles of the Rasia et
al.(2004) model on the properties of the X - ray emission and the
comptonization parameter that determines the CMBR temperature decrement due to
the Sunyaev - Zel'dovich effect.


title: Beaming effects in GRBs and orphan afterglows

abstract:
  The overall dynamical evolution and radiation mechanism of $\gamma$-ray burst
jets are briefly introduced. Various interesting topics concerning beaming in
$\gamma$-ray bursts are discussed, including jet structures, orphan afterglows
and cylindrical jets. The possible connection between $\gamma$-ray bursts and
neutron star kicks is also addressed.


title: Radiating Collapse with Vanishing Weyl stresses

abstract:
  In a recent approach in modelling a radiating relativistic star undergoing
gravitational collapse the role of the Weyl stresses was emphasised. It is
possible to generate a model which is physically reasonable by approximately
solving the junction conditions at the boundary of the star. In this paper we
demonstrate that it is possible to solve the Einstein field equations and the
junction conditions exactly. This exact solution contains the Friedmann dust
solution as a limiting case. We briefly consider the radiative transfer within
the framework of extended irreversible thermodynamics and show that
relaxational effects significantly alter the temperature profiles.


title: The VLA-COSMOS Survey: I. Radio Identifications from the Pilot Project

abstract:
  We present a catalog of 246 radio sources found in the central 1 degree of
the COSMOS field at 1.4GHz. The VLA pilot project data have a resolution of
1.9"x1.6" and an rms noise limit of ~25-100uJy/beam covering 0.837 sqrdeg.
About 20 radio sources are clearly extended and most of them appear to be
double-lobed radio galaxies. We find evidence for a cluster of 7 radio sources
with an extent of ~10' southeast of the COSMOS field center. This VLA pilot
project was undertaken to demonstrate the feasibility of wide-field mosaicking
at 2'' resolution at 1.4GHz using the VLA in its A array configuration. The
7-point mosaic data was used to develop the techniques necessary for reduction
and analysis. These data will provide the initial astrometric frame for the
optical (ground- and space-based) data of the COSMOS 2 sqrdeg survey. In
addition, it demonstrates the feasibility of obtaining deep (rms ~ few uJy)
radio imaging of this field at 1.4GHz, since the brightest radio emission peak
detected within the area covered has a flux density of 13mJy/beam and no strong
side-lobes from sources surrounding the COSMOS field were detected. Comparison
of the number counts to other deep radio surveys shows that the COSMOS field is
a representative deep field in the radio domain.


title:
Group analysis of structure equations for stars in radiative and
  convective equilibrium

abstract:
  It is proposed to use the Lie group theory of symmetries of differential
equations to investigate the system of equations describing a static star in a
radiative and convective equilibrium. It is shown that the action of an
admissible group induces a certain algebraic structure in the set of all
solutions, which can be used to find a family of new solutions. We have
demonstrated that, in the most general case, the equations admit an infinite
parameter group of quasi-homologous transformations. We have found invariants
of the symmetries group which correspond to the fundamental relations
describing a physical characteristic of the stars such as the
Hertzsprung-Russell diagram or the mass-luminosity relation. In this way we can
suggest that group invariants have not only purely mathematical sense, but
their forms are closely associated with the basic empirical relations.


title: Solar System Formation Deduced from Observations of Matter

abstract:
  Aspects of our Solar System's formation are deduced from observations of the
chemical nature of matter. Massive cores are indicative of
terrestrial-planet-composition-similarity to enstatite chondrite meteorites,
whose highly-reduced state of oxidation may be thermodynamically stable in
solar matter only at elevated temperatures and pressures. Consistent with the
formation of Earth as envisioned by Arnold Eucken, thermodynamic considerations
lead to the deduction that the terrestrial planets formed by
liquid-condensation, raining out from the central regions of hot, gaseous
protoplanets. The mass of protoplanetary-Earth, estimated to be 275-305mE, is
similar to the mass of Jupiter, 318mE. Solar primordial gases and volatile
elements were separated from the terrestrial planets early after planet
formation, presumably during some super-luminous solar event, perhaps even
before Mercury had completely formed. The
pre-super-luminosity-terrestrial-planet mass distribution appears to be more
consistent with observations of the close-in gas-giants of other planetary
systems than the present-day-terrestrial-planet mass distribution. Although
primarily formed by raining out from the centers of hot, gaseous protoplanets,
evidence for the Earth and, by inference for the other terrestrial planets,
suggests some outer, minor, secondary accretion of oxidized matter in the
grain-growth accumulation way envisioned by George W. Wetherill. By contrast,
the so-called "standard model" for our Solar System's formation has flawed
conceptual underpinnings and would lead to the contradiction of terrestrial
planets having insufficiently massive cores.


title: Einstein's gravitational lensing and nonlinear electrodynamics

abstract:
  In 1936 Einstein predicted the phenomenon presently known as gravitational
lensing (GL). A prime feature of GL is the magnification, because of the
gravitational field, of the star visible surface as seen from a distant
observer. We show here that nonlinear electrodynamics (NLED) modifies in a
fundamental basis Einstein's general relativistic (GR) original derivation. The
effect becomes apparent by studying the light propagation from a strongly
magnetic ($B$) pulsar (SMP). Unlike its GR counterpart, the photon dynamics in
NLED leads to a new effective GL, which depends also on the $B$-field
permeating the pulsar. The apparent radius of a SMP appears then unexpectedly
diminished, by a large factor, as compared to the classical Einstein's
prediction. This may prove very crucial in determining physical properties of
high $B$-field stars from their X-ray emission.


title: Planetary formation in the Gamma-Cephei system

abstract:
  We numerically investigate under which conditions the planet detected at 2.1
AU of Gamma-Cephei could form through the core-accretion scenario despite the
perturbing presence of the highly eccentric companion star. We first show that
the initial stage of runaway accretion of kilometer-sized planetesimals is
possible within 2.5 AU from the central star only if large amounts of gas are
present. In this case, gaseous friction induces periastron alignment of the
orbits which reduces the otherwise high mutual impact velocities due to the
companion's secular perturbations. The following stage of mutual accretion of
large embryos is also modeled. According to our simulations, the giant impacts
among the embryos always lead to a core of 10 Mearth within 10 Myr, the average
lifetime of gaseous discs. However, the core always ends up within 1.5 AU from
the central star. Either the core grows more quickly in the inner region of the
disc, or it migrates inside by scattering the residual embryos


title: Brans-Dicke Scalar Field as a Unique k-essence

abstract:
  In the present work, the Brans-Dicke theory of gravity is taken as a possible
theory of k-essence coupled to gravity and then the role played by the
Brans-Dicke scalar field in relation to the unified model for dark matter and
dark energy is explored. It has been realized that the BD scalar field does
indeed play a role of a k-essence, but in a very unique way which distinguishes
it from other k-essence fields studied in the literature such as the
(generalized) Chaplygin gas or the purely kinetic k-essence studied recently by
Scherrer. That is, instead of providing an interpolation between the dark
matter-like evolution and the dark energy-like evolution, the BD theory
predicts the emergence of a yet-unknown {\it zero acceleration} epoch which is
an intermediate stage acting as a ``crossing bridge'' between the decelerating
matter-dominated era and the accelerating phase.


title: An Overview of The VERITAS Prototype Telescope And Camera

abstract:
  VERITAS (the Very Energetic Radiation Imaging Telescope Array System) is the
next generation ground-based gamma-ray observatory that is being built in
southern Arizona by a collaboration of ten institutions in Canada, Ireland, the
U.K. and the U.S.A. VERITAS is designed to operate in the range from 50 GeV to
50 TeV with optimal sensitivity near 200 GeV; it will effectively overlap with
the next generation of space-based gamma-ray telescopes. The first phase of
VERITAS, consisting of four telescopes of 12 m aperture, will be operational by
the time of the GLAST launch in 2007. Eventually the array will be expanded to
include the full array of seven telescopes on a filled hexagonal grid of side
80 m. A prototype VERITAS telescope with a reduced number of mirrors and signal
channels has been built. Its design and performance is described here. The
prototype is scheduled to be upgraded to a full 499 pixel camera with 350
mirrors during the autumn of 2004.


title:
The 2002 Outburst of the Black-Hole X-ray Binary 4U 1543-47: Optical and
  Infrared Light Curves

abstract:
  We have obtained simultaneous optical and near infrared observations of 4U
1543-47 during its 2002 outburst. The most striking feature of the outburst
light curve is the secondary maximum which appears after the object transitions
into the low-hard state. This secondary maximum is much stronger in the
infrared bands than optical. We suggest that the origin of the secondary
maximum flux may be synchrotron radiation associated with a jet. Close infrared
monitoring may lead to reliable triggers for simultaneous multiwavelength
campaigns to study jet formation processes.


abstract:
  We report on a 50 ksec XMM-Newton observation of the double pulsar system
J0737-3039 performed on April 2004. We present results of the spectral analysis
of these data combined with the much shorter Chandra pointing performed on
January 2004. Black body emission with effective temperature of
0.20^{+0.02}_{-0.02} keV (90% confidence level) and emission radius
75^{+30}_{-9} m for a distance of 0.5 kpc (implying a 0.5-10 keV luminosity
\~6x10^{29} erg/s) is a viable interpretation, calling for a stream of
particles accelerated in the magnetosphere of PSR J0737-3039A and depositing
their kinetic energy in the magnetic polar cap of PSR J0737-3039A or of the
companion PSR J0737-3039B. A single power-law emission model implies a very
steep photon index Gamma=4.2^{+2.1}_{-1.2} and a suspiciously high hydrogen
column density, whereas a photon index Gamma=2 does not provide an adequate
description of the XMM-Newton and Chandra data. A two component model (a black
body plus a power-law with Gamma=2) is statistically acceptable, but the
additional power-law component is not required by the data.


title:
Finding Extrasolar Planets in the Stellar Graveyard with the Hubble
  Space Telescope

abstract:
  In order to directly image an extrasolar planet, the large contrast between a
star and a companion planet must be overcome. White Dwarfs (WDs) are the
remnants of stars > 1 M_sun and are orders of magnitude dimmer, making searches
for planets and brown dwarfs (BDs) possible. We present the preliminary results
of a survey of 7 hydrogen white dwarfs with photospheric metal lines (DAZs) for
substellar and planetary objects, using NICMOS on the Hubble Space Telescope
(HST). The extremely high contrast available with the NICMOS coronagraph allows
7-12 M_Jup planets to be detected to within 10-30 AU of the primary WD. This
represents the first concerted search for planetary objects around stars that
were more massive than the sun. Our results show that there are candidates
around three of the seven stars, which are awaiting confirmation through common
proper motion studies, some of which can only be confirmed through another
observation with HST. Continuing studies of WDs will constrain planet formation
scenarios for more massive stars and provide a sample of planets to study with
future space missions such as JWST and SIM.


title: Infall of the Elliptical Galaxy NGC 1404 into the Fornax Cluster

abstract:
  We use three Chandra observations, totalling 134.3 ks, to constrain the
dynamical motion of NGC1404 falling towards the dominant elliptical NGC1399
through the Fornax ICM. NGC1404's surface brightness profile shows a sharp edge
\~8 kpc from its center in the direction of NGC 1399, characteristic of
jump-like temperature and density discontinuities from ram-pressure stripping
of the galaxy gas. We find the temperature of the galaxy gas inside the edge is
\~2.8 times cooler (kT=0.55^{+0.01}_{-0.02} keV; abundance A =
0.73^{+0.65}_{-0.16} solar) than the cluster gas (kT,A = 1.53^{+0.10}_{-0.13}
keV, 0.42^{+0.2}_{-0.13} solar). We use the shape of the surface brightness
profile to fit the edge position, power law index of the density distribution
inside the edge, and density discontinuity at the edge. The electron density
inside the edge (3.9-4.3 x 10^{-3} cm^{-3}) depends strongly on the gas
abundance; while the density of the ICM (7-8 x10^{-4} cm^{-3}) depends strongly
on the assumed relative distance between NGC1404 and NGC1399. The pressure jump
(1.7-2.1) across the edge and the cluster free-stream region implies a Mach
number 0.83-1.03 and velocity 531-657 km/s for NGC1404 relative to the ICM. The
inclination angle of the motion inferred using the relative radial velocity
between NGC1404 and NGC1399 as representative of that between NGC1404 and the
ICM, is uncomfortably large (>40 deg.) given the sharpness of the edge,
suggesting either a non-zero impact parameter between the galaxies, or that
NGC1399 is moving radially with respect to the cluster ICM.


title: XMM-Newton observations of warm absorbers in PG quasars

abstract:
  We present XMM-Newton EPIC observations of warm absorbers in the quasars PG
1114+445 and PG 1309+355, both of which exhibit evidence for absorption by warm
material in the line-of-sight. We find the absorption in PG 1114+445 to be in
two phases, a `hot' phase with a log ionisation parameter xi of 2.57, and a
`cooler' phase with log xi of 0.83; an unresolved transition array (UTA) of
M-shell iron is observed in the cooler phase. The absorption in this quasar is
similar to that observed in the Seyfert 1 NGC 3783. The absorption in PG
1309+355 consists of a single phase, with log xi of 1.87. The absorbing gas
lies at distances of 10^{18} - 10^{22} cm from the continuum radiation sources
in these AGN, which suggests that it could originate in a wind emanating from a
molecular torus. We derive distances assuming that these X-ray warm absorbers
have the same velocity as the UV warm absorbers observed in these quasars. The
distances to the warm absorbers from the central continuum source scale
approximately with the square root of the AGN ionising luminosity, a result
consistent with the warm absorber originating as a torus wind. The kinetic
luminosities of these outflowing absorbers represent insignificant fractions (<
10^{-3}) of the energy budgets of the AGN.


title: Approaching the dynamics of hot nucleons in supernovae

abstract:
  All recent numerical simulations agree that stars in the main sequence mass
range of 9-40 solar masses do not produce a prompt hydrodynamic ejection of the
outer layers after core collapse and bounce. Rather they suggest that stellar
core collapse and supernova explosion are dynamically distinct astrophysical
events, separated by an unspectacular accretion phase of at least ~40 ms
duration. As long as the neutrinospheres remain convectively stable, the
explosion dynamics is determined by the neutrons, protons, electrons and
neutrinos in the layer of impact-heated matter piling up on the protoneutron
star. The crucial role of neutrino transport in this regime has been emphasized
in many previous investigations. Here, we search for efficient means to address
the role of magnetic fields and fluid instabilities in stellar core collapse
and the postbounce phase.


title: Observing the Ultrahigh Energy Universe with OWL Eyes

abstract:
  The goal of the Orbiting Wide-field Light-collectors (OWL) mission is to
study the origin and physics of the highest energy particles known in nature,
the ultrahigh energy cosmic rays (UHECRs). The OWL mission consists of
telescopes with UV sensitive cameras on two satellites operating in tandem to
view in stereo the development of the giant particle showers induced in the
Earth's atmosphere by UHECRs. This paper discusses the characteristics of the
OWL mission.


title:
Internal and External Alignment of the Shapes and Angular Momenta of
  LCDM Halos

abstract:
  (Abridged) We investigate how the shapes and angular momenta of galaxy and
group mass dark matter halos in a LCDM N-body simulation are correlated
internally, and how they are aligned with respect to the location and
properties of surrounding halos. We explore these relationships down to halos
of much lower mass (10^11/h Msun) than previous studies. The halos are
triaxial, with c/a ratios of 0.6+-0.1. More massive halos are more flattened.
The principal axes are very well aligned within 0.6 r_vir. The angular momentum
vectors are also reasonably well aligned except between the very outermost and
very innermost regions of the halo. The angular momentum vectors tend to align
with the minor axes, with a mean misalignment of ~25 degrees, and lie
perpendicular to the major and intermediate axes. The properties of a halo at
0.4 r_vir are quite characteristic of the properties at most other radii within
the halo. There is a very strong tendency for the minor axes of halos to lie
perpendicular to large scale filaments. This alignment extends to much larger
separations for group and cluster mass halos than for galaxy mass halos. As a
consequence, the intrinsic alignments of galaxies are likely weaker than
previous predictions, which were based on the shapes of cluster mass halos. The
angular momenta of the highest concentration halos tend to point toward other
halos. The angular momenta of galaxy mass halos point parallel to filaments,
while those of group and cluster mass halos show a very strong tendency to
point perpendicular to the filaments. This suggests that group and cluster mass
halos acquire most of their angular momentum from major mergers along
filaments, while the accretion history of mass and angular momentum onto galaxy
mass halos has been smoother.


title:
Substructure in the Circumstellar Disk around the Young Star AU Mic (GJ
  803)

abstract:
  Keck adaptive optics imaging with a physical resolution of 0.4 AU resolves
the inner (15-80 AU) disk of AU Mic (GJ 803), the nearest known scattered light
disk to Earth. The inner disk is asymmetric and possesses a sharp change in
structure at 35 AU. The disk also shows spatially localized enhancements and
deficits at 25-40 AU separations. The overall morphology points to the
influence of unseen larger bodies and resembles structures expected from recent
planet formation. AU Mic is coeval with the archetypical debris disk system
beta Pic, and the similarities between their two disks point to synchronous
disk evolution. Multiple indications of substructure appear to be common in
circumstellar disks at an age of ~12 Myr.


title: The Evolutionary Status of Clusters of Galaxies at z ~ 1

abstract:
  Combined HST, X-ray, and ground-based optical studies show that clusters of
galaxies are largely "in place" by $z \sim 1$, an epoch when the Universe was
less than half its present age. High resolution images show that elliptical,
S0, and spiral galaxies are present in clusters at redshifts up to $z \sim
1.3$. Analysis of the CMDs suggest that the cluster ellipticals formed their
stars several Gyr earlier, near redshift 3. The morphology--density relation is
well established at $z\sim1$, with star-forming spirals and irregulars residing
mostly in the outer parts of the clusters and E/S0s concentrated in dense
clumps. The intracluster medium has already reached the metallicity of
present-day clusters. The distributions of the hot gas and early-type galaxies
are similar in $z\sim1$ clusters, indicating both have largely virialized in
the deepest potentials wells. In spite of the many similarities between
$z\sim1$ and present-day clusters, there are significant differences. The
morphologies revealed by the hot gas, and particularly the early-type galaxies,
are elongated rather than spherical. We appear to be observing the clusters at
an epoch when the sub-clusters and groups are still assembling into a single
regular cluster. Support for this picture comes from CL0152 where the gas
appears to be lagging behind the luminous and dark mass in two merging
sub-components. Moreover, the luminosity difference between the first and
second brightest cluster galaxies at $z\sim1$ is smaller than in 93% of
present-day Abell clusters, which suggests that considerable luminosity
evolution through merging has occurred since that epoch. Evolution is also seen
in the bolometric X-ray luminosity function.


title: The Environmental Impact of Supermassive Black Holes

abstract:
  The supermassive black holes observed at the centers of almost all
present-day galaxies, had a profound impact on their environment. I highlight
the principle of self-regulation, by which supermassive black holes grow until
they release sufficient energy to unbind the gas that feeds them from their
host galaxy. This principle explains several observed facts, including the
correlation between the mass of a central black hole and the depth of the
gravitational potential well of its host galaxy, and the abundance and
clustering properties of bright quasars in the redshift interval of z~2-6. At
lower redshifts, quasars might have limited the maximum mass of galaxies
through the suppression of cooling flows in X-ray clusters. The seeds of
supermassive black holes were likely planted in dwarf galaxies at redshifts
z>10, through the collapse of massive or supermassive stars. The minimum seed
mass can be identified observationally through the detection of gravitational
waves from black hole binaries by Advanced LIGO or LISA. Aside from shaping
their host galaxies, quasar outflows filled the intergalactic medium with
magnetic fields and heavy elements. Beyond the reach of these outflows, the
brightest quasars at z>6 have ionized exceedingly large volumes of gas (tens of
comoving Mpc) prior to global reionization, and must have suppressed the faint
end of the galaxy luminosity function in these volumes before the same occurred
through the rest of the universe.


title: Mass-producing spectra: The SDSS spectrographic system

abstract:
  The Sloan Digital Sky Survey is the largest redshift survey conducted to
date, and the principal survey observations have all been conducted on the
dedicated SDSS 2.5m and 0.5m telescopes at Apache Point Observatory. While the
whole survey has many unique features, this article concentrates on a
description of the systems surrounding the dual fibre-input spectrographs that
obtain all the survey spectra and that are capable of recording 5,760
individual spectra per night on an industrial, consistent, mass-production
basis. It is hoped that the successes and lessons learned will prove
instructive for future large spectrographic surveys.


title:
Long-term evolution of orbits about a precessing oblate planet: 1. The
  case of uniform precession

abstract:
  It was believed until very recently that a near-equatorial satellite would
always keep up with the planet's equator (with oscillations in inclination, but
without a secular drift). As explained in Efroimsky and Goldreich (2004), this
opinion originated from a wrong interpretation of a (mathematically correct)
result obtained in terms of non-osculating orbital elements. A similar analysis
carried out in the language of osculating elements will endow the planetary
equations with some extra terms caused by the planet's obliquity change. Some
of these terms will be nontrivial, in that they will not be amendments to the
disturbing function. Due to the extra terms, the variations of a planet's
obliquity may cause a secular drift of its satellite orbit inclination. In this
article we set out the analytical formalism for our study of this drift. We
demonstrate that, in the case of uniform precession, the drift will be
extremely slow, because the first-order terms responsible for the drift will be
short-period and, thus, will have vanishing orbital averages (as anticipated 40
years ago by Peter Goldreich), while the secular terms will be of the second
order only. However, it turns out that variations of the planetary precession
make the first-order terms secular. For example, the planetary nutations will
resonate with the satellite's orbital frequency and, thereby, may instigate a
secular drift. A detailed study of this process will be offered in the
subsequent publication, while here we work out the required mathematical
formalism and point out the key aspects of the dynamics.

categories: astro-ph math.DS nlin.SI physics.class-ph


title: Substructure in Dwarf Galaxies

abstract:
  Recent years have seen a series of large-scale photometric surveys with the
aim of detecting substructure in nearby dwarf galaxies. Some of these objects
display a varying distribution of each stellar population, reflecting their
star formation histories. Also, dwarf galaxies are dominated by dark matter,
therefore luminous substructure may represent a perturbation in the underlying
dark material. Substructure can also be the effect of tidal interaction, such
as the disruption of the Sagittarius dSph by the Milky Way. Therefore,
substructure in dwarf galaxies manifests the stellar, structural and kinematic
evolution of these objects.


title: Dependence of General Relativistic Accretion on Black Hole Spin

abstract:
  We propose a novel approach to the investigation of how black hole spin
influences the behavior of astrophysical accretion. We examine the terminal
behavior of general relativistic, multi-transonic, hydrodynamic advective
accretion in the Kerr metric, by analyzing various dynamical as well as
thermodynamic properties of accreting matter extremely close to the event
horizon, as a function of Kerr parameter $a$. The examination of the transonic
properties of such flows can be useful in self-consistently discriminating
between prograde and retrograde relativistic accretion, and in studying the
spectral signatures of black hole rotation.


title: Radio and X-ray Observations of PSR B0540-69

abstract:
  PSR B0540-69 is one of a small handful of pulsars known to emit giant pulses
and the only extra-galactic pulsar known to do so. We observed the pulsar for a
total of 72 hr over a 6 month interval and detected 141 giant pulses. We have
obtained correct phasing between the radio arrival times of the giant pulses
and the X-ray pulse profile. The giant pulses occur in two phase windows,
located 6.7 ms before and 5.0 ms after the midpoint of the X-ray profile. We
have detected the integrated profile of the pulsar at 1.4 GHz with a flux
density of only 24 micro-Jy. The statistics of the giant pulses are clearly
power-law and it is likely that the giant pulses contribute only a few per cent
to the integrated pulse flux density, similar to other pulsars with giant pulse
emission. Simultaneous X-ray and radio observations show no significant
increase in the X-ray flux at the time of the radio giants. The relative
enhancements in the X-ray emission must be at least 5.5 times smaller than in
the radio.


title:
Cosmic Ray Scattering and Streaming in Compressible Magnetohydrodynamic
  Turbulence

abstract:
  Recent advances in understanding of magnetohydrodynamic (MHD) turbulence call
for revisions in the picture of cosmic ray transport. In this paper we use
recently obtained scaling laws for MHD modes to obtain the scattering frequency
for cosmic rays. Using quasilinear theory we calculate gyroresonance with MHD
modes (Alfv\'{e}nic, slow and fast) and transit-time damping (TTD) by fast
modes. We provide calculations of cosmic ray scattering for various phases of
interstellar medium with realistic interstellar turbulence driving that is
consistent with the velocity dispersions observed in diffuse gas. We account
for the turbulence cutoff arising from both collisional and collisionless
damping. We obtain analytical expressions for diffusion coefficients that enter
Fokker-Planck equation describing cosmic ray evolution. We obtain the
scattering rate and show that fast modes provide the dominant contribution to
cosmic ray scattering for the typical interstellar conditions in spite of the
fact that fast modes are subjected to damping. We determine how the efficiency
of the scattering depends on the characteristics of ionized media, e.g. plasma
$\beta$. We calculate the range of energies for which the streaming instability
is suppressed by the ambient MHD turbulence.


title: Dust Dynamics in Compressible MHD Turbulence

abstract:
  We calculate the relative grain-grain motions arising from interstellar
magnetohydrodynamic (MHD) turbulence. The MHD turbulence includes both fluid
motions and magnetic fluctuations. While the fluid motions accelerate grains
through hydro-drag, the electromagnetic fluctuations accelerate grains through
resonant interactions. We consider both incompressive (Alfv\'{e}n) and
compressive (fast and slow) MHD modes and use descriptions of MHD turbulence
obtained in Cho & Lazarian (2002). Calculations of grain relative motion are
made for realistic grain charging and interstellar turbulence that is
consistent with the velocity dispersions observed in diffuse gas, including
cutoff of the turbulence from various damping processes. We show that fast
modes dominate grain acceleration, and can drive grains to supersonic
velocities. Grains are also scattered by gyroresonance interactions, but the
scattering is less important than acceleration for grains moving with
sub-Alfv\'{e}nic velocities. Since the grains are preferentially accelerated
with large pitch angles, the supersonic grains will be aligned with long axes
perpendicular to the magnetic field. We compare grain velocities arising from
MHD turbulence with those arising from photoelectric emission, radiation
pressure and H$_{2}$ thrust. We show that for typical interstellar conditions
turbulence should prevent these mechanisms from segregating small and large
grains. Finally, gyroresonant acceleration is bound to preaccelerate grains
that are further accelerated in shocks. Grain-grain collisions in the shock may
then contribute to the overabundance of refractory elements in the composition
of galactic cosmic rays.


title: Alignment of Dust in Molecular Clouds

abstract:
  Polarimetry is one of the most informative techniques of studying magnetic
fields in molecular clouds. How reliable the interpretation of the polarization
maps in terms of magnetic fields is the issue that the grain alignment theory
addresses.
  We show that grain alignment involves several processes acting
simultaneously, but on different time-scales. We explain that rotating dust
grains get substantial magnetic moment that allows them precess fast about
magnetic field lines. As the result, grains preserve their orientation to
magnetic field when the magnetic field direction fluctuates. We point out to
the importance of internal alignment, i.e. the process forces grain axes to be
aligned in respect to the grain angular momentum. We show that subtle quantum
effects, in particular relaxation related to nuclear magnetic moments of atoms
composing the grain, brings to live complex grain motions, e.g. flips. These
flips substantially alter the dynamics of grain and limit the applicability of
earlier theories that did not account for them. We also briefly review basic
physical processes involved in the alignment of grain angular momentum in
respect to interstellar magnetic field. We claim that the bulk of existing
observational data is consistent with the radiative torque alignment mechanism.
In particular, we show that large grains that are known to exist in the cores
of molecular clouds may be aligned by the attenuated external interstellar
radiation field.


title: Scaling, Intermittency and Decay of MHD Turbulence

abstract:
  We discuss a few recent developments that are important for understanding of
MHD turbulence.
  First, MHD turbulence is not so messy as it is usually believed. In fact, the
notion of strong non-linear coupling of compressible and incompressible motions
along MHD cascade is not tenable. Alfven, slow and fast modes of MHD turbulence
follow their own cascades and exhibit degrees of anisotropy consistent with
theoretical expectations. Second, the fast decay of turbulence is not related
to the compressibility of fluid. Rates of decay of compressible and
incompressible motions are very similar. Third, viscosity by neutrals does not
suppress MHD turbulence in a partially ionized gas. Instead, MHD turbulence
develops magnetic cascade at scales below the scale at which neutrals damp
ordinary hydrodynamic motions. Forth, density statistics does not exhibit the
universality that the velocity and magnetic field do. For instance, at small
Mach numbers the density is anisotropic, but it gets isotropic at high Mach
numbers. Fifth, the intermittency of magnetic field and velocity are different.
Both depend on whether the measurements are done in local system of reference
oriented along the local magnetic field or in the global system of reference
related to the mean magnetic field.


title:
Obtaining Statistics of Turbulent Velocity from Astrophysical Spectral
  Line Data

abstract:
  Turbulence is a crucial component of dynamics of astrophysical fluids
dynamics, including those of ISM, clusters of galaxies and circumstellar
regions. Doppler shifted spectral lines provide a unique source of information
on turbulent velocities. We discuss Velocity-Channel Analysis (VCA) and its
offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical
description of the spectral line statistics. Those techniques are well suited
for studies of supersonic turbulence. We stress that a great advantage of VCS
is that it does not necessary require good spatial resolution. Addressing the
studies of mildly supersonic and subsonic turbulence we discuss the criterion
that allows to determine whether a traditional tool for such a research,
namely, Velocity Centroids are dominated by density or velocity. We briefly
discuss the use of higher order correlations as the means to study
intermittency of turbulence. We discuss observational data available and
prospects of the field.


title: BVR photometry of a newly identified RS CVn binary star HD 61396

abstract:
  BVR photometry of a recently identified RS CVn binary star HD61396, carried
out during 2001, is presented. The new photometry reveal significant evolution
in the shape and amplitude of light curve when compared with those reported
earlier by Padmakar etal (2000). The traditional two-starspot model has been
used to obtain the spot parameters from the observed light curve. Changes in
the spot area and their location on the stellar surface are discernible from
the extracted parameters from the new photometry.


title:
Optical data of meteoritic nano-diamonds from far-ultraviolet to
  far-infrared wavelengths

abstract:
  We have used different spectroscopic techniques to obtain a consistent
quantitative absorption spectrum of a sample of meteoritic nano-diamonds in the
wavelength range from the vacuum ultraviolet (0.12 $\mu$m) to the far infrared
(100 $\mu$m). The nano-diamonds have been isolated by a chemical treatment from
the Allende meteorite (Braatz et al.2000). Electron energy loss spectroscopy
(EELS) extends the optical measurements to higher energies and allows the
derivation of the optical constants (n & k) by Kramers-Kronig analysis. The
results can be used to restrain observations and to improve current models of
the environment where the nano-diamonds are expected to have formed. We also
show that the amount of nano-diamond which can be present in space is higher
than previously estimated by Lewis et al. (1989).


title:
Delays in dwarf novae: VW Hyi, the tidal instability and enhanced mass
  transfer models

abstract:
  We discuss the multi-wavelength predictions of the two models proposed for SU
UMa stars, i.e the enhanced mass transfer (EMT) and the tidal thermal
instability (TTI) models. We focus on the systematic differences of the
suggested scenarios before discussing the model predictions together with the
observations of the best-studied SU UMa system, VW Hyi. We find that assuming
the standard form of the viscosity parameter alpha, both models predict only
outbursts being triggered at the inner edge of the accretion disc. In the TTI
model the superoutbursts are triggered when the outer radius of the disc
reaches a certain value, i.e. the 3:1 resonance radius. In contrast, the EMT
scenario predicts superoutbursts when the disc mass exceeds a critical value.
This causes the EMT model to be much more sensitive to mass transfer variations
than the TTI model. In both models we find the predicted UV and EUV delays in
agreement with the observations of VW Hyi for alpha_hot/alpha_cold<=4. In
addition both models can generate precursor outbursts which are more pronounced
at short wavelengths, in agreement with observations. Variations found in the
observed light curve of single systems (e.g. VW Hyi) as well as the difference
between ordinary SU UMa stars and ER UMa systems are a natural outcome of the
EMT model while the TTI model fails to explain them.


title:
Study of cosmogenic radiocarbon concentration variations in the Earth's
  atmosphere during solar activity of Mounder minimum (1645-1715)

abstract:
  Variations of radiocarbon concentration have been studied in annual rings for
the last 350 years (1600-1950)on the basis of our experimental research using
methods of spectral analysis. From this interval of time special attention is
paid to the so-called period of the Maunder minimum (1645-1715) of solar
activity. In the experimental series of corresponding period two types of
periodicity are revealed: 20 year and 8 year.


title:
A wavelet add-on code for new-generation N-body simulations and data
  de-noising (JOFILUREN)

abstract:
  Wavelets are a new and powerful mathematical tool, whose most celebrated
applications are data compression and de-noising. In Paper I (Romeo, Horellou &
Bergh 2003, astro-ph/0302343), we have shown that wavelets can be used for
removing noise efficiently from cosmological, galaxy and plasma N-body
simulations. The expected two-orders-of-magnitude higher performance means, in
terms of the well-known Moore's law, an advance of more than one decade in the
future. In this paper, we describe a wavelet add-on code designed for such an
application. Our code can be included in common grid-based N-body codes, is
written in Fortran, is portable and available on request from the first author.
The code can also be applied for removing noise from standard data, such as
signals and images.


title:
Detailed theoretical models for extra-solar planet-host stars: The "red
  stragglers" HD37124 and HD46375

abstract:
  In this paper we analyse and discuss the HR Diagram position of two
extra-solar planet-host stars - HD37124 and HD46375 - by means of theoretical
stellar evolution models. This work was triggered by the results obtained by
Laws et al. (2003) who found that these stars were in contradiction to the
expectation based on their high metallicity. Fixing the age of both stars with
the value based on their chromospheric activity levels and computing our own
evolutionary models using the CESAM code, we are able to reproduce the observed
luminosity, effective temperature and metallicity of both stars for a set of
stellar parameters that are astrophysically reliable even if it is non-trivial
to interpret the absolute values for these parameters. Our results are
discussed in the context of the stellar properties of low mass stars.


title:
The AGASA/SUGAR Anisotropies and TeV Gamma Rays from the Galactic
  Center: A Possible Signature of Extremely High-energy Neutrons

abstract:
  Recent analysis of data sets from two extensive air shower cosmic ray
detectors shows tantalizing evidence of an anisotropic overabundance of cosmic
rays towards the Galactic Center (GC) that ``turns on'' around $10^{18}$ eV. We
demonstrate that the anisotropy could be due to neutrons created at the
Galactic Center through charge-exchange in proton-proton collisions, where the
incident, high energy protons obey an $\sim E^{-2}$ power law associated with
acceleration at a strong shock. We show that the normalization supplied by the
gamma-ray signal from EGRET GC source 3EG J1746-2851 -- ascribed to pp induced
neutral pion decay at GeV energies -- together with a very reasonable spectral
index of 2.2, predicts a neutron flux at $\sim 10^{18}$ eV fully consistent
with the extremely high energy cosmic ray data. Likewise, the normalization
supplied by the very recent GC data from the HESS air-Cerenkov telescope at
\~TeV energies is almost equally-well compatible with the $\sim 10^{18}$ eV
cosmic ray data. Interestingly, however, the EGRET and HESS data appear to be
themselves incompatible. We consider the implications of this discrepancy. We
discuss why the Galactic Center environment can allow diffusive shock
acceleration at strong shocks up to energies approaching the ankle in the
cosmic ray spectrum. Finally, we argue that the shock acceleration may be
occuring in the shell of Sagittarius A East, an unusual supernova remnant
located very close to the Galactic Center. If this connection between the
anisotropy and Sagittarius A East could be firmly established it would be the
first direct evidence for a particular Galactic source of cosmic rays up to
energies near the ankle.


title:
Consequences of short range interactions between dark matter and protons
  in galaxy clusters

abstract:
  Protons gain energy in short range collisions with heavier dark matter
particles (DMPs) of comparable velocity dispersion. We examine the conditions
under which the heating of baryons by scattering off DMPs can offset radiative
cooling in the cores of galaxy clusters. Collisions with a constant cross
section independent of the relative velocity of the colliding particles, cannot
produce stable thermal balance. In this case, avoiding an unrealistic increase
of the central temperatures yields the upper bound on the cross-section,
\sigma_xp<10^-25 cm^2 (m_x/m_p), where m_x and m_p are the DMP and proton mass,
respectively. A stable balance, however, can be achieved for a power law
dependence on the relative velocity, V, of the form \sigma_xp \propto V^a with
a<-3. An advantage of this heating mechanism is that it preserves the metal
gradients observed in clusters.


title: Generalized Chaplygin Gas in a modified gravity approach

abstract:
  We study the generalized Chaplygin gas (GCG) scenario in a modified gravity
approach. That is, we impose that our universe has a pure dust configuration,
and allow for a modification of gravity that yields a GCG specific scale factor
evolution. Moreover, assuming that this new hypothetical gravity theory obeys a
generalization of Birkhoff's law, we determine the Schwarzschild-like metric in
this new modified gravity. We also study the large scale structure formation in
this model. Both the linear and non-linear growth are studied together with the
growth of the velocity fluctuation in the linear perturbation theory. We
compare our results with those corresponding to the $\Lambda$CDM model and
discuss possible distinguishable features.


title: The Star Clusters of the Small Magellanic Cloud: Age Distribution

abstract:
  We present age measurements for 195 star clusters in the Small Magellanic
Cloud based on comparison of integrated colors measured from the Magellanic
Clouds Photometric Survey with models of simple stellar populations. We find
that the modeled nonuniform changes of cluster colors with age can lead to
spurious age peaks in the cluster age distribution, that the observed numbers
of clusters with age, t, declines smoothly as t^{-2.1}, that for an assumed
initial cluster mass function scaling as M^{-2} the dependence of the cluster
disruption time on mass is proportional to M^{0.48}, that despite the apparent
abundance of young clusters the dominant epoch of cluster formation was the
initial one, and that there are significant differences in the spatial
distribution of clusters of different ages. Because of limited precision in our
age measurements, we cannot address the question of detailed correspondence
between the cluster age function and the field star formation history. However,
this sample provides an initial guide for which clusters to target in more
detailed studies of specific age intervals.


title:
Observation by an Air-Shower Array in Tibet of the Multi-TeV Cosmic-Ray
  Anisotropy due to Terrestrial Orbital Motion Around the Sun

abstract:
  We report on the solar diurnal variation of the galactic cosmic-ray intensity
observed by the Tibet III air shower array during the period from 1999 to 2003.
In the higher-energy event samples (12 TeV and 6.2 TeV), the variations are
fairly consistent with the Compton-Getting anisotropy due to the terrestrial
orbital motion around the sun, while the variation in the lower-energy event
sample (4.0 TeV) is inconsistent with this anisotropy. This suggests an
additional anisotropy superposed at the multi-TeV energies, e.g. the solar
modulation effect. This is the highest-precision measurement of the
Compton-Getting anisotropy ever made.


title:
VLT/UVES constraints on the cosmological variability of the
  fine-structure constant

abstract:
  We propose a new methodology for probing the cosmological variability of
alpha from pairs of FeII lines (SIDAM, single ion differential alpha
measurement) observed in individual exposures from a high resolution
spectrograph. By this we avoid the influence of the spectral shifts due to (i)
ionization inhomogeneities in the absorbers and (ii) non-zero offsets between
different exposures. Applied to the FeII lines of the metal absorption line
system at zabs = 1.839 in the spectrum of Q1101-264 obtained by means of the
UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT),
SIDAM provides da/a = (2.4+/-3.8) 10^{-6}. The zabs = 1.15 FeII system toward
HE0515-4414 has been re-analyzed by this method thus obtaining for the combined
sample da/a = (0.4+/-1.5) 10^{-6}. These values are shifted with respect to the
Keck/HIRES mean da/a = (-5.7+/-1.1) 10^{-6} (Murphy et al. 2004) at very high
confidence level (95%). The fundamental photon noise limitation in the da/a
measurement with the VLT/UVES is discussed to figure the prospects for future
observations. It is suggested that with a spectrograph of 10 times the UVES
dispersion coupled to a 100m class telescope the present Oklo level (da/a >=
4.5 10^{-8}) can be achieved along cosmological distances with differential
measurements of da/a.


title: CIRPASS: description, performance and astronomical results

abstract:
  The Cambridge Infra-red Panoramic Survey Spectrograph (CIRPASS) is described.
This near-infrared (NIR) spectrograph has been used on the 8m Gemini-South
Telescope, the 3.9m Anglo-Australian Telescope (AAT) and the 4.2m William
Herschel Telescope (WHT). Its performance in both integral field mode and
multi-object mode is discussed and some scientific highlights are presented. A
multi-IFU system, which is currently under construction, is also described.


title:
Hard X-ray view of the past activity of Sgr A* in a natural Compton
  mirror

abstract:
  We report the association of the recently discovered hard X-ray source IGR
J17475-2822 with the giant molecular cloud Sgr B2 in the Galactic Center
region. The broad band (3-200 keV) spectrum of the source constructed from data
of different observatories strongly supports the idea that the X-ray emission
of Sgr B2 is Compton scattered and reprocessed radiation emitted in the past by
the Sgr A* source. We conclude that 300-400 years ago Sgr A* was a low
luminosity (L ~ 1.5e39 erg/s at 2-200 keV) AGN with a characteristic hard X-ray
spectrum (photon index Gamma ~ 1.8). We estimate the mass and iron abundance of
the Sgr B2 scattering gas at 2e6 Msun (r/10pc)^2 and 1.9 solar, respectively
(where r is the radius of the cloud).


title: Spin-Orbit Evolution Of Short-Period Planets

abstract:
  The negligible eccentricity of all extra solar planets with periods less than
six days can be accounted for by dissipation of tidal disturbances within their
envelopes which are induced by their host stars. In the period range of 7-21
days, planets with circular orbits coexist with planets with eccentric orbits.
These will be referred to as the borderline planets. We propose that this
discrepancy can be attributed to the variation in spin-down rates of young
stars. In particular, prior to spin-down, dissipation of a planet's tidal
disturbance within the envelope of a sufficiently rapidly spinning star can
excite eccentricity growth, and for a more slowly spinning star, at least
reduce the eccentricity damping rate. In contrast, tidal dissipation within the
envelope of a slowly spinning low-mass mature star can enhance the eccentricity
damping process. Based on these results, we suggest that short-period planets
around relatively young stars may have a much larger dispersion in eccentricity
than those around mature stars. We also suggest that because the rate of
angular momentum loss from G and K dwarfs via stellar winds is much faster than
the tidal transfer of angular momentum between themselves and their very-short
(3-4 days) period planets, they cannot establish a dynamical configuration in
which the stellar and planetary spins are approximately parallel and
synchronous with the orbital frequency. In principle, however, such
configurations may be established for planets (around G and K dwarfs) with
orbital periods of up to several weeks. In contrast to G and K dwarfs, the
angular momentum loss due to stellar winds is much weaker in F dwarfs. It is
therefore possible for synchronized short-period planets to exist around such
stars. The planet around Tau Boo is one such example.


title:
TeV $\gamma$-radiation from Dark Matter annihilation in the Galactic
  center

abstract:
  Recent observations of the Galactic center with ground based gamma-ray
instruments have revealed a TeV (10$^{12}$ eV) gamma-ray signal consistent with
the position of Sgr A*. The derived luminosity of the signal above 1 TeV is a
few $10^{34} \mathrm{erg} \mathrm{s}^{-1}$ which is slightly more than e.g. the
gamma-ray luminosity of the Crab nebula and a plausible identification could be
a conventional albeit strong gamma-ray source. The observations with the
H.E.S.S. system of Cherenkov telescopes have decreased the solid angle
subtended by the error box by more than a factor of hundred with respect to the
previous observations of the VERITAS and CANGAROO groups. After studying the
observed energy spectrum and angular distribution of the excess as seen by the
H.E.S.S. experiment, a massive Dark Matter candidate with a minimum mass of 12
TeV (90 % c.l.) and an upper limit on the WIMP density for $r<10$ pc of $1261
M_\odot \mathrm{pc}^{-3} \times (< \sigma v>/3\cdot10^{-26}
\mathrm{cm}^3\mathrm{s}^{-1})^{-1/2}$ is required to explain the observed flux
by an annihilation signal. The angular distribution of the excess events is
consistent with a cuspy profile with $\rho(r)\propto r^{-\alpha}$ with
$\alpha>1.0$ at a confidence level of 90 %. Even though the mass and the cross
section of the Dark Matter constituents are unexpectedly high in the framework
of most models of nonbaryonic Dark Matter, it can not be ruled out.


title:
Cyclic Period Changes in Close Binaries: A Light Travel Time Effect or a
  Symptom of Magnetic Activity?

abstract:
  Years to decade-long cyclic period changes have been observed in many classes
of close binaries. A common explanation invoked for these cyclic period changes
is the gravitational influence of an unseen third body upon the close binary
pair. The effects of an unseen third body must be strictly periodic, and not
all of these observed period variations match this prediction. Douglas Hall
noted almost 20 years ago that Algol binaries with cyclic period changes always
had a convective, rapidly rotating secondary star. This secondary star has the
seeds for a powerful magnetic dynamo, and the suggestion was made that magnetic
activity was the cause of the observed cyclic period changes.
  In this paper I will review the observational evidence for a magnetic cycle
driving the observed cyclic period changes. I will also discuss the theoretical
framework which now exists to explain how the magnetic cycle can alter the
orbital period of a close binary. I will close by discussing an ongoing
observational effort to test the predictions of the magnetic activity-cyclic
period change connection.


title: Altair's inclination from line profile analysis

abstract:
  We present a detailed spectroscopic study of line broadening in the A7IV-V
star Altair. In a wavelength region covering 690AA we reconstruct the overall
broadening profile taking into account more than 650 spectral lines. From the
broadening profile we determine the projected rotational velocity vsini, derive
an upper limit for the equatorial velocity v from the shape of the profile and
search for signatures of differential rotation. Our redetermined value of vsini
is (227 +-11)km/s. Measuring the first two zeros of the Fourier transformed
broadening profile yield no signatures of differential rotation. We derive that
Altair is seen under an inclination angle higher than i=68deg and it rotates at
v<245km/s or slower than 53% of breakup velocity on a 1sigma level.


title:
Size is Everything: Universal Features of Quasar Microlensing with
  Extended Sources

abstract:
  We examine the effect that the shape of the source brightness profile has on
the magnitude fluctuations of images in quasar lens systems due to
microlensing. We do this by convolving a variety of accretion disk models
(including Gaussian disks, uniform disks, "cones," and a Shakura-Sunyaev
thermal model) with two magnification maps in the source plane, one with
convergence kappa = 0.4 and shear gamma = 0.4 (positive parity), and the other
with kappa = gamma = 0.6 (negative parity). By looking at magnification
histograms of the convolutions and using chi-squared tests to determine the
number of observations that would be necessary to distinguish histograms
associated with different disk models, we find that, for circular disk models,
the microlensing fluctuations are relatively insensitive to all properties of
the models except the half-light radius of the disk. Shakura-Sunyaev models are
sufficiently well constrained by observed quasar properties that we can
estimate the half-light radius at optical wavelengths for a typical quasar. If
Shakura-Sunyaev models are appropriate, the half-light radii are very much
smaller than the Einstein rings of intervening stars and the quasar can be
reasonably taken to be a point source except in the immediate vicinity of
caustic crossing events.


title: Gravitational Microlensing of Fractal Sources

abstract:
  Gravitational microlensing has proven to be a powerful tool in the study of
quasars, providing some of the strongest limits on the scales of structure in
the central engine. Typically sources are considered to be smoothly varying on
some particular scale; such simple sources result in recognisable time scales
in microlensing light curves from which the size of the source can be
determined. Various emission processes, however, result in sources with a
fractal appearance, possessing structure on a range of scales. Here, the
gravitational microlensing of such fractal sources at the heart of quasars is
considered. It is shown that the resulting light curves reflect the fractal
nature of the sources, possessing pronounced structure at various scales,
markedly different to the case with the random distribution of emission clouds
that are typically considered. Hence, the determination of a characteristic
scale of variability in a microlensing light curve may not necessarily reveal
the size of the individual emission clouds, the key value that is required to
determine the physical state of the emission region, rather it may correspond
to a particular hierarchy in a fractal structure. Current X-ray satellites can
detect such fractal structure via the monitoring of gravitationally lensed
quasars during a microlensing event, providing a test of high energy emission
processes in quasars.


title: The Canis Major Dwarf Galaxy

abstract:
  Recent observational evidence suggests that the Sagittarius dwarf galaxy
represents the only major ongoing accretion event in the Galactic halo,
accounting for the majority of stellar debris identified there. This paper
summarizes the recent discovery of another potential Milky Way accretion event,
the Canis Major dwarf galaxy. This dwarf satellite galaxy is found to lie just
below the Galactic plane and appears to be on an equatorial orbit. Unlike
Sagittarius, which is contributing to the Galactic halo, the location and
eventual demise of Canis Major suggests that it represents a building block of
the thick disk.


title: On Bars, Bulges and Fuelling of Active Galactic Nuclei

abstract:
  Both fuelling of a central black hole and the build-up of bulges are -- at
least theoretically -- facilitated by non-axisymmetric potentials. It is argued
here that the recently established surface brightness division between
bulge-dominated galaxies that dominate the local type 2 AGN luminosity
function, and disk-dominated galaxies that host (at best) weak AGN can be
understood in terms of a simple bar-instability criterion.


title: [O I] 6300 A Emission from Disks Around Herbig Ae/Be Stars

abstract:
  We present high spectral-resolution optical spectra of 49 Herbig Ae/Be stars
in a search for the [O I] 6300.2 A line. The vast majority of the stars in our
sample show narrow (FWHM < 100 km/s) emission lines, centered on the stellar
radial velocity. Some stars in our sample show double-peaked lines profiles,
with peak-to-peak separations of about 10 km/s. The presence and strength of
the [O I] line emission appears to be well correlated with the far-infrared
energy distribution of each source: stars with a strong excess at 60 micron
have in general stronger [O I] emission than stars with weaker 60 micron
excesses. We interpret the observed [O I] 6300.2 A line profiles as arising in
the surface layers of the protoplanetary disks surrounding Herbig Ae/Be stars.


title:
Probing the time-variation of the fine-structure constant: Results based
  on Si IV doublets from a UVES sample

abstract:
  We report a new constraint on the variation of the fine-structure constant
based on the analysis of 15 Si IV doublets selected from a ESO-UVES sample. We
find \Delta\alpha/\alpha = (+0.15+/-0.43) x 10^-5 over a redshift range of
1.59< z < 2.92 which is consistent with no variation in \alpha. This result
represents a factor of three improvement on the constraint on
\Delta\alpha/\alpha based on Si IV doublets compared to the published results
in the literature. The alkali doublet method used here avoids the implicit
assumptions used in the many-multiplet method that chemical and ionization
inhomogeneities are negligible and isotopic abundances are close to the
terrestrial value.


title: Star Formation in Clusters

abstract:
  HST is very well tailored for observations of extragalactic star clusters.
One obvious reason is HST's high spatial resolution, but equally important is
the wavelength range offered by the instruments on board HST, in particular the
blue and near-UV coverage which is essential for age-dating young clusters. HST
observations have helped establish the ubiquity of young massive clusters
(YMCs) in a wide variety of star-forming environments, from dwarf galaxies and
spiral disks to nuclear starbursts and mergers. These YMCs have masses and
sizes similar to those of old globular clusters (GCs), and the two may be
closely related. A large fraction of all stars seem to be born in clusters, but
most clusters disrupt rapidly and the stars disperse to become part of the
field population. In most cases studied to date the luminosity functions of
young cluster systems are well fit by power-laws dN(L)/dL ~ L^-2, and the
luminosity of the brightest cluster can (with few exceptions) be predicted from
simple sampling statistics. Mass functions have only been constrained in a few
cases, but appear to be well approximated by similar power-laws. The absence of
any characteristic mass scale for cluster formation suggests that star clusters
of all masses form by the same basic process, without any need to invoke
special mechanisms for the formation of YMCs. It is possible, however, that
special conditions can lead to the formation of a few YMCs in some dwarfs where
the mass function is discontinuous. Further studies of mass functions for star
clusters of different ages may help test the theoretical prediction that the
power-law mass distribution observed in young cluster systems can evolve
towards the approximately log-normal distribution seen in old GC systems.


title: Planets opening dust gaps in gas disks

abstract:
  We investigate the interaction of gas and dust in a protoplanetary disk in
the presence of a massive planet using a new two-fluid hydrodynamics code. In
view of future observations of planet-forming disks we focus on the condition
for gap formation in the dust fluid. While only planets more massive than 1
Jupiter mass (MJ) open up a gap in the gas disk, we find that a planet of 0.1
MJ already creates a gap in the dust disk. This makes it easier to find
lower-mass planets orbiting in their protoplanetary disk if there is a
significant population of mm-sized particles.


title:
The relationship between radio luminosity and black-hole mass in
  optically-selected quasars

abstract:
  Using a sample of more than 6000 quasars from the Sloan digital sky survey
(SDSS) we compare the black-hole mass distributions of radio-loud and
radio-quiet quasars. Based on the virial black-hole mass estimator the
radio-loud quasars (RLQs) are found to harbour systematically more massive
black holes than radio-quiet quasars (RQQs) with very high significance
(>>99.99%), with mean black-hole masses of <\log(M_{bh}/\Msun)>=8.89\pm0.02 and
<\log(M_{bh}/\Msun)>=8.69\pm0.01 for the RLQs and RQQs respectively. Crucially,
the new RLQ and RQQ samples have indistinguishable distributions on the
redshift-optical luminosity plane, excluding the possibility that either
parameter is responsible for the observed black-hole mass difference. Moreover,
this black-hole mass difference is shown to be in good agreement with the
optical luminosity difference observed between RLQ and RQQ host galaxies at low
redshift (i.e. \Delta M_{host}=0.4-0.5 magnitudes). Within the SDSS samples,
black-hole mass is strongly correlated with both radio luminosity and the
radio-loudness $\mathcal{R}$ parameter (>7 sigma significance), although the
range in radio luminosity at a given black-hole mass is several orders of
magnitude. It is therefore clear that the influence of additional physical
parameters or evolution must also be invoked to explain the quasar
radio-loudness dichotomy.


title:
The POINT-AGAPE Microlensing Survey: First Constraint on MACHOs towards
  M31

abstract:
  To reveal the galactic dark matter in the form of MACHOs ("Massive
Astrophysical Compact Halo Objects"), the POINT-AGAPE collaboration is carrying
out a search for gravitational microlensing towards M31. A clear microlensing
signal is detected. The high-threshold analysis of 3-year data leads to 7
bright and short microlensing candidates. The preliminary estimation of the
detection efficiency implies that less than 25% (60%) of standard halos can be
composed of objects with masses between 10^{-4} and 10^{-1} (10^{-1} and 1)
solar mass at the 95% C.L. This result is compatible with previous microlensing
results towards the Magellanic Clouds and gives the first constraints on MACHOs
for a distant spiral galaxy.


title: High-mass star formation within the bright-rimmed cloud SFO 79

abstract:
  We report Radio Recombination Line (RRL) and continuum observations toward
the IRAS point source 16362--4845, embedded within the Bright-Rimmed Cloud
(BRC) SFO 79, a small molecular cloud lying at the edge of the HII region RCW
108. High resolution observations of the H92alpha hydrogen recombination line
and of the continuum emission (3.6 and 6 cm) confirm the presence of a resolved
Ultra Compact (UC) HII region embedded within the molecular cloud. The
integrated radio fluxes suggest the source of the ionisation to be an O9 Zero
Age Main Sequence (ZAMS) star. Millimetre observations of 12CO, 13CO and C18O
(J=1--0) molecular lines reveal the presence of a molecular condensation offset
\~30 arcsec to the north of the IRAS position on the boundary of the UC HII
region. Analysis of 2MASS data has led to the identification of a small IR
cluster of Young Stellar Objects (YSOs) that are positionally coincident with
the UC HII region, lying to the south east of the peak of the radio emission.
Moreover, the UC HII region appears to be extended in the direction of the IR
cluster, which suggests that the radio emission and the IR cluster are in some
way related to each other. MSX 8.3 micron and 21.3 micron images have been used
to trace the large scale structure of the BRC, revealing the presence of a
Photo Dominated Region (PDR) and three embedded thermal sources within the
molecular cloud. The alignment of the three thermal sources along a line
parallel to the bright rim suggests that they could have been triggered by the
propagation of a plane parallel shock through the cloud.


title: The unusual morphology of the intragroup medium in NGC 5171

abstract:
  We present the results of a 24 ks XMM-Newton observation of the NGC 5171
group of galaxies. NGC 5171 is unusual in that it is an X-ray bright group (L >
10^42 erg/s), with irregular contours which are not centred on a bright galaxy.
The global spectrum is adequately described by a single temperature APEC model
with T = 0.96 +/- 0.04 keV, and Z = 0.13 +/- 0.02 Zsol, in good agreement with
previous ROSAT data. We find the X-ray contours are centred on a bright ridge
of emission stretching from the BGG to a nearby galaxy. Spectral mapping
reveals this ridge to be both cool (T ~ 1.1 keV) and metallic (Z ~ 0.4 Zsol) in
comparison to its surrounding, suggesting it is the result of a tidal
interaction between the two galaxies. Optical data reveals the member galaxies
to have a high velocity dispersion (sigma = 494 +/- 99 km/s), and a
significantly non-Gaussian velocity distribution, suggesting the group is in
the process of merging. A region of hot gas with T = 1.58 +/- 0.36 keV is found
to the West of the bright central ridge, and we interpret this as shock-heating
resulting from the merging. A further region of emission to the South-East of
the bright central ridge, with T = 1.14 +/- 0.13 keV, is probably associated
with a background group, four times more distant.


title:
The Origins and Evolutionary Status of B Stars Found Far From the
  Galactic Plane I: Composition and Spectral Features

abstract:
  The existence of faint blue stars far above the galactic plane, which have
spectra that are similar to nearby Population I B stars, present several
interesting questions. Among them are: Can a Population I B star travel from
the disk to a position many kiloparsecs above the plane in a relatively short
main sequence lifetime? Is it possible that single massive star formation is
occurring far from the galactic plane? Are these objects something else
masquerading as main sequence B stars? This paper (the first of two) analyzes
the abundances of a sample of these stars and reveals several which are
chemically similar to nearby Population I B stars while others clearly have
abundance patterns more like those expected in BHB or PAGB stars. Several of
those with old evolved star abundances also have interesting features of note
in their spectra. We also consider why this sample does not have any classical
Be stars and identify at least two nearby solar metallicity BHB stars.


title: Mass Segregation in the Globular Cluster Palomar 5 and its Tidal Tails

abstract:
  We present the stellar main sequence luminosity function (LF) of the
disrupted, low-mass, low-concentration globular cluster Palomar 5 and its
well-defined tidal tails, which emanate from the cluster as a result of its
tidal interaction with the Milky Way. The results of our deep (B ~ 24.5)
wide-field photometry unequivocally indicate that preferentially fainter stars
were removed from the cluster so that the LF of the cluster's main body
exhibits a significant degree of flattening compared to other globular
clusters. There is clear evidence of mass segregation, which is reflected in a
radial variation of the LFs. The LF of the tidal tails is distinctly enhanced
with faint, low-mass stars. Pal 5 exhibits a binary main sequence, and we
estimate a photometric binary frequency of roughly 10%. Also the binaries show
evidence of mass segregation with more massive binary systems being more
strongly concentrated toward the cluster center.


title:
Multi-Temperature Blackbody Spectra of Thin Accretion Disks With and
  Without a Zero-Torque Inner Boundary Condition

abstract:
  The standard spectral model for analyzing the soft component of thermal
emission from a thin accretion disk around a black hole is the
multi-temperature blackbody (MTB) model. The widely used implementation of this
model, which is known as ``diskbb,'' assumes nonzero torque at the inner edge
of the accretion disk. This assumption is contrary to the classic and current
literature on thin-disk accretion, which advocates the use of a zero-torque
boundary condition. Consequently, we have written code for a zero-torque model,
``ezdiskbb,'' which we compare to the nonzero-torque model diskbb by fitting
RXTE spectra of three well-known black hole binaries: 4U 1543-47, XTE
J1550-564, and GRO J1655-40. The chief difference we find is that the
zero-torque model gives a value for the inner disk radius that is about 2.2
times smaller than the value given by diskbb. This result has important
implications, especially for the determination of black-hole angular momentum
and mass accretion rate.


title: Discovery of the Near-IR Afterglow and of the Host of GRB 030528

abstract:
  The rapid dissemination of an arcmin-sized HETE-2 localization of the
long-duration X-ray flash GRB 030528 led to a ground-based multi-observatory
follow-up campaign. We report the discovery of the near-IR afterglow, and also
describe the detection of the underlying host galaxy in the optical and near-IR
bands. The afterglow is classified as "optically dark" as it was not detected
in the optical band. The K-band photometry presented here suggests that the
lack of optical detection was simply the result of observational limitations
(lack of rapid and deep observations plus high foreground extinction). Simple
power law fits to the afterglow in the K-band suggest a typically decay with a
slope of alpha=1.2. The properties of the host are consistent with the idea
that GRB hosts are star forming blue galaxies. The redshift of GRB 030528 can
not be determined accurately, but the data favour redshifts less than unity. In
addition, we present an optical and near-IR analysis of the X-ray source CXOU
J170354.0--223654 from the vicinity of GRB 030528.


title: Optical polarimetric observations of the microquasar LS 5039

abstract:
  We present the first optical polarimetric observations of the runaway
microquasar LS 5039. Our results reveal the presence of a large amount (~5%) of
polarized emission towards this binary system. By combining polarimetric and
spectroscopic observations of some stars in the field together with available
statistical information on the galactic interstellar polarization of the
region, we have estimated and subtracted the contribution of the interstellar
polarization in this direction. As a result, we obtain an intrinsic
polarization of ~3% for the object, much higher than what would be expected
from jet emission in the optical domain. We suggest that the polarized light
originates by electron Thomson scattering in the stellar envelope of the
companion star. This allows us to constrain the size of the region where the
polarized emission originates, as well as estimating the scattering electronic
density and the wind velocity at such distance.


title:
Co-moving frame radiative transfer in spherical media with arbitrary
  velocity fields

abstract:
  Recently, with the advances in computational speed and availability there has
been a growth in the number and resolution of fully 3-D hydrodynamical
simulations. However, all of these simulations are purely hydrodynamical and
there has been little attempt to include the effects of radiative transfer
except in a purely phenomenological manner because the computational cost is
too large even for modern supercomputers. While there has been an effort to
develop 3-D Monte Carlo radiative transfer codes, most of these have been for
static atmospheres or have employed the Sobolev approximation, which limits
their applicability to studying purely geometric effects such as macroscopic
mixing. Also the computational requirements of Monte Carlo methods are such
that it is difficult to couple with 3-D hydrodynamics. Here, we present an
algorithm for calculating 1-D spherical radiative transfer in the presence of
non-monotonic velocity fields in the co-moving frame. Non-monotonic velocity
flows will occur in convective, and Raleigh--Taylor unstable flows, in flows
with multiple shocks, and in pulsationally unstable stars such as Mira and
Cepheids. This is a first step to developing fully 3-D radiative transfer than
can be coupled with hydrodynamics. We present the computational method and the
results of some test calculations.


title: Parsec scale properties of nearby BL Lacs

abstract:
  We present new radio data completing the imaging for a sample of 30 nearby (z
< 0.2) BL Lac objects on parsec and kiloparsec scale. The sample is composed of
both high and low luminosity sources and it is therefore an ideal test bed for
unified schemes in the low power regime. VLBI and VLA data are used, thus
providing information on both extended and inner, beamed components. We find
morphologies and jet parameters consistent with a parent population composed of
FR I radio galaxies, i.e. in agreement with the unified scheme. We also present
a comparison to high quality HST data; we find a correlation between the radio
and optical core luminosities, and speculate about the accretion rates for the
central black holes.


title: Abundances of Extremely Metal-Poor Star Candidates

abstract:
  We present chemical abundances for 110 stars identified in objective-prism
surveys as candidates to be very metal-poor. The abundances are derived from
high S/N, intermediate-resolution spectra obtained with the Keck Observatory
Echelle Spectrometer and Imager. An additional 25 stars with well-determined
abundances ranging from [Fe/H]$=-1.5$ and -3.2 were observed and the results
used to help calibrate our analysis and determine the accuracy of our abundance
determinations. Abundances for the program stars were measured for Fe, Mg, Ca,
Ti, Cr and Ba with an accuracy of approximately 0.3 dex. 53 of the stars in our
sample have [Fe/H]<= -2, 22 have [Fe/H]<= -2.5 and 13 stars have [Fe/H]<= -2.9.
Surprisingly, approximately one third of the sample is relatively metal rich
with [Fe/H]>-1.5. In addition to identifying a number of extremely metal-poor
stars, this study also shows that moderate-resolution spectra obtained with the
Keck Echelle Spectrometer and Imager yield relatively accurate abundances for
stars as faint as V=14 in modest exposure time (~20 minutes). This capability
will prove useful if the so-far elusive stars at [Fe/H]<-4 turn out to be
mostly fainter than V=15.


title:
Unidentified gamma-ray sources off the Galactic plane as low-mass
  microquasars?

abstract:
  A subset of the unidentified EGRET gamma-ray sources with no active galactic
nucleus or other conspicuous counterpart appears to be concentrated at medium
latitudes. Their long-term variability and their spatial distribution indicate
that they are distinct from the more persistent sources associated with the
nearby Gould Belt. They exhibit a large scale height of 1.3 +/- 0.6 kpc above
the Galactic plane. Potential counterparts for these sources include
microquasars accreting from a low-mass star and spewing a continuous jet.
Detailed calculations have been performed of the jet inverse Compton emission
in the radiation fields from the star, the accretion disc, and a hot corona.
Different jet Lorentz factors, powers, and aspect angles have been explored.
The up-scattered emission from the corona predominates below 100 MeV whereas
the disc and stellar contributions are preponderant at higher energies for
moderate (~15 deg) and small (~1 deg) aspect angles, respectively. Yet, unlike
in the high-mass, brighter versions of these systems, the external Compton
emission largely fails to produce the luminosities required for 5 to 10 kpc
distant EGRET sources. Synchrotron-self-Compton emission appears as a promising
alternative.


title: Astrophysical Constraints on Scalar Field Models

abstract:
  We use stellar structure dynamics arguments to extract bounds on the relevant
parameters of scalar field models: the putative scalar field mediator of a
fifth force with a Yukawa potential, the new variable mass particle (VAMP)
models, and a phenomenologically viable model to explain the Pioneer anomaly.
We consider the polytropic gas model to estimate the effect of these models on
the hydrostatic equilibrium equation and fundamental quantities such as the
central temperature. The current bound on the solar luminosity is used to
constrain the relevant parameters of each model.


title:
Electric fields at the quark surface of strange stars in the
  color-flavor locked phase

abstract:
  It is shown that extremely strong electric fields may be generated at the
surface of strange quark matter in the color-flavor locked phase because of the
surface effects. Some properties of strange stars made of this matter are
briefly discussed.


title:
TeV blazar gamma-ray emission produced by a cooling pile-up particle
  energy distribution function

abstract:
  We propose a time-dependent one-zone model based on a quasi-Maxwellian
`pile-up' distribution in order to explain the time-averaged high energy
emission of TeV blazars. The instantaneous spectra are the result of the
synchrotron and synchrotron self-Compton emission (SSC) of ultra-relativistic
leptons. The particle energy distribution function (EDF) is computed in a
self-consistent way, taking into account an injection term of fresh particles,
a possible pair creation term, and the particles radiative cooling. The source
term is not a usual power-law but rather a `pile-up' distribution, which can
result from the combination of a stochastic heating via second order Fermi
process and radiative cooling. To validate this approach, we have performed
time-averaged fits of the well-known TeV emitter Mrk 501 during the 1997
flaring activity period taking into account the attenuation of the high energy
component by cosmic diffuse infrared background (DIrB) and intrinsic absorption
via the pair creation process. The model can reproduce very satisfactorily the
observed spectral energy distribution (SED). A high Lorentz factor is required
to avoid strong pair production; in the case of smaller Lorentz factor, an
intense flare in the GeV range is predicted due to the sudden increase of soft
photons density below the Klein-Nishina threshold. The possible relevance of
such a scenario is discussed.


title: A near-infrared study of the NGC 7538 star forming region

abstract:
  We present sub-arcsecond (FWHM ~ 0".7), NIR JHKs-band images and a high
sensitivity radio continuum image at 1280 MHz, using SIRIUS on UH 88-inch
telescope and GMRT. The NIR survey covers an area of ~ 24 arcmin^2 with
10-sigma limiting mags of ~ 19.5, 18.4, and 17.3 in J, H, and Ks-band,
respectively. Our NIR images are deeper than any JHK surveys to date for the
larger area of NGC 7538 star forming region. We construct JHK CC and J-H/J and
H-K/K CM diagrams to identify YSOs and to estimate their masses. Based on these
CC and CM diagrams, we identified a rich population of YSOs (Class I and Class
II), associated with the NGC 7538 region. A large number of red sources (H-K >
2) have also been detected around NGC 7538. We argue that these red stars are
most probably PMS stars with intrinsic color excesses. Most of YSOs in NGC 7538
are arranged from the N-W toward S-E regions, forming a sequence in age: the
diffuse H II region (N-W, oldest: where most of the Class II and Class I
sources are detected); the compact IR core (center); and the regions with the
extensive IR reflection nebula and a cluster of red young stars (S-E and S). We
find that the slope of the KLF of NGC 7538 is lower than the typical values
reported for the young embedded clusters, although equally low values have also
been reported in the W3 Main star forming region. From the slope of the KLF and
the analysis by Megeath et al. (1996), we infer that the embedded stellar
population is comprised of YSOs with an age of ~ 1 Myr. Based on the comparison
between models of PMS stars with the observed CM diagram we find that the
stellar population in NGC 7538 is primarily composed of low mass PMS stars
similar to those observed in the W3 Main star forming region.


title:
The Capodimonte Deep Field I - Presentation of the survey and first
  follow-up studies

abstract:
  We present the Capodimonte Deep Field (OACDF), a deep field covering an area
of 0.5 square degrees in the B, V, R optical bands plus six medium-band filters
in the wavelength range 773--913 nm. The field reaches the following limiting
AB magnitudes: B~25.3, V~24.8 and R~25.1 and contains about 50000 extended
sources in the AB magnitude range 18 < R < 25 . Hence, it is intermediate
between deep pencil beam surveys and very wide but shallow surveys. The main
scientific goal of the OACDF is the identification and characterization of
early-type field galaxies at different look-back times in order to study
different scenarios of galaxy formation. Parallel goals include the search for
groups and clusters of galaxies and the search for rare and peculiar objects
(gravitational lenses, QSOs, halo White Dwarfs). In this paper we describe the
OACDF data reduction, the methods adopted for the extraction of the photometric
catalogs, the photometric calibration and the quality assessment of the
catalogs by means of galaxy number counts, spectroscopic and photometric
redshifts and star colors. We also present the first results of the search for
galaxy overdensities. The depth of the OACDF and its relatively large spatial
coverage with respect to pencil beam surveys make it a good tool for further
studies of galaxy formation and evolution in the redshift range 0--1, as well
as for stellar studies.