title: Galaxy mergers with various mass ratios: properties of remnants

abstract:
  We study galaxy mergers with various mass ratios using N-body simulations,
with an emphasis on the unequal-mass mergers in the relatively unexplored range
of mass-ratios 4:1-10:1. Our recent work (Bournaud et al. 2004) shows that the
above range of mass ratio results in hybrid systems with spiral-like luminosity
profiles but with elliptical-like kinematics, as observed in the data analysis
for a sample of mergers by Jog & Chitre (2002). In this paper, we study the
merger-remnants for mass ratios from 1:1 to 10:1 while systematically covering
the parameter space. We obtain the morphological and kinematical properties of
the remnants, and also discuss the robustness and the visibility of disks in
the merger remnants with a random line-of-sight. We show that the mass ratios
1:1-3:1 give rise to elliptical remnants whereas the mass ratios 4.5:1-10:1
produce the hybrid systems with mixed properties. We find that the transition
between disk-like and elliptical remnants occurs between a narrow mass-range of
4.5:1-3:1. The unequal-mass mergers are more likely to occur than the standard
equal-mass mergers studied in the literature so far, and we discuss their
implications for the evolution of galaxies.


title:
High Mass Star Formation I: The Mass Distribution of Submillimeter
  Clumps in NGC 7538

abstract:
  We present submillimeter continuum maps at 450 and 850 microns of a 12 x 8
arcminute region of the NGC 7538 high-mass star-forming region, made using the
Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell
Telescope. We used an automated clump-finding algorithm to identify 67 clumps
in the 450 micron image and 77 in the 850 micron image. Contrary to previous
studies, we find a positive correlation between high spectral index, alpha, and
high submillimeter flux, with the difference being accounted for by different
treatments of the error beam. We interpret the higher spectral index at
submillimeter peaks as a reflection of elevated dust temperature, particularly
when there is an embedded infrared source, though it may also reflect changing
dust properties. The clump mass-radius relationship is well-fit by a power law
of the form M \propto R^(-x) with x = 1.5-2.1, consistent with theories of
turbulently-supported clumps. According to our most reliable analysis, the
high-mass end (approx. 100-2700 M_sun) of the submillimeter clump mass function
in NGC 7538 follows a Salpeter-like power law with index 2.0 +/- 0.3. This
result agrees well with similar studies of lower-mass regions rho Oph and Orion
B. We interpret the apparent invariance of the shape of the clump mass function
over a broad range of parent cloud masses as evidence for the self-similarity
of the physical processes which determine it. This result is consistent with
models which suggest that turbulent fragmentation, acting at early times, is
sufficient to set the clump mass function.


title: A Search for Unresolved Double Degenerates Using IUE Archives

abstract:
  We present preliminary results of a study aimed at detecting double white
dwarf systems using a method based on a comparison of optical and UV spectra
for 141 DA stars drawn from the IUE archives. In particular, we are looking for
dicrepancies between optical and UV temperatures. Even though known unresolved
degenerate binaries stand out in this comparison, most temperature differences
can probably be attributed to the presence of reddening, or the presence of
heavy elements. We are in the process of securing additional optical
spectroscopic observations to increase the number of stars in our analysis.


title:
Influence of the Coriolis force on the instability of slowly pulsating B
  stars

abstract:
  This paper explores the effect of rotation on the kappa-mechanism instability
of slowly pulsating B stars. A new nonadiabatic code, that adopts the so-called
`traditional approximation' to treat the Coriolis force, is used to investigate
the influence exerted by rotation over the stability of stellar models covering
the mass range 2.5 M_sun <= M_* <= 13.0 M_sun. The principal finding is that,
for all modes considered apart from the prograde sectoral class, rotation
shifts the kappa-mechanism instability toward higher luminosities and effective
temperatures; these shifts are accompanied by broadenings in the extent of
instability strips. Such behaviour is traced to the shortening of mode periods
under the action of the Coriolis force. Instability strips associated with
prograde sectoral modes behave rather differently, being shifted to marginally
lower luminosities and effective temperatures under the influence of rotation.
  The implications of these results are discussed in the context of the
observational scarcity of pulsation in B-type stars having significant
rotation; various scenarios are explored to explain the apparent dichotomy
between theory and observations. Furthermore, the possible significance of the
findings to Be stars is briefly examined.


title: An upper limit to the masses of stars

abstract:
  There is no accepted upper mass limit for stars. Such a basic quantity
escapes both theory, because of incomplete understanding of star formation, and
observation, because of incompleteness in surveying the Galaxy. The Arches
cluster is ideal for such a test, being massive enough to expect stars at least
as massive as 400 solar masses, and young enough for its most massive members
to still be visible. It is old enough to be free of its natal molecular cloud,
and close enough, and at a well-established distance, for us to discern its
individual stars. Here I report an absence of stars with initial masses greater
than 130 M_Sun in the Arches cluster, where the typical mass function predicts
18. I conclude that this indicates a firm limit of 150 M_Sun for stars as the
probability that the observations are consistent with no limit is 10^-8.


title:
The very early optical afterglow of GRBs, revealing the nature of the
  ejecta

abstract:
  We show that if the GRB ejecta itself is magnetized or neutron-rich, the very
early afterglow of GRBs is very different from that powered by a pure ion
fireball. In the Swift era, with the well monitored early afterglow data, we
can potentially diagnose the ejecta composition and reveal the nature of the
central GRB engine.


title:
Luminous X-ray Flares from Low Mass X-ray Binary Candidates in the
  Early-Type Galaxy NGC 4697

abstract:
  We report results of the first search specifically targeting short-timescale
X-ray flares from low-mass X-ray binaries in an early-type galaxy. A new method
for flare detection is presented. In NGC 4697, the nearest, optically luminous,
X-ray faint elliptical galaxy, 3 out of 157 sources are found to display flares
at >99.95% probability, and all show more than one flare. Two sources are
coincident with globular clusters and show flare durations and luminosities
similar to (but larger than) Type-I X-ray superbursts found in Galactic neutron
star (NS) X-ray binaries (XRBs). The third source shows more extreme flares.
Its flare luminosity (~6E39 erg/s) is very super-Eddington for an NS and is
similar to the peak luminosities of the brightest Galactic black hole (BH)
XRBs. However, the flare duration (~70 s) is much shorter than are typically
seen for outbursts reaching those luminosities in Galactic BH sources.
Alternative models for the flares are considered.


title: Growth of Linear Perturbations before the Era of the First Galaxies

abstract:
  We calculate the evolution of linear density and temperature perturbations in
a universe with dark matter, baryons, and radiation, from cosmic recombination
until the epoch of the first galaxies. In addition to gravity, the
perturbations are effected by electron scattering with the radiation, by
radiation pressure, and by gas pressure. We include the effect of spatial
fluctuations in the baryonic sound speed and show that they induce a >10%
change in the baryonic density power spectrum on small scales, and a larger
change on all scales in the power spectrum of gas temperature fluctuations. A
precise calculation of the growth of linear perturbations is essential since
they provide the initial conditions for the formation of galaxies and they can
also be probed directly via cosmological 21cm fluctuations. We also show that
in general the thermal history of the cosmic gas can be measured from 21cm
fluctuations using a small-scale anisotropic cutoff due to the thermal width of
the 21cm line.


title:
Electron-Ion Recombination Rate Coefficients and Photoionization Cross
  Sections for Astrophysically Abundant Elements. IX. Ni XXVI and Ni XXVII for
  UV and X-ray modeling

abstract:
  The inverse processes of photoionization and electron-ion recombination of
(hnu + Ni XXVI --> Ni XXVII + e and (hnu + Ni XXVII --> Ni XXVIII + e) are
studied using the unified method for the total recombination. The method
subsumes both the radiative and di-electronic recombination processes and
enables self-consistent sets of results for photoionization and electron-ion
recombination by using the same wavefunction expansion. Photoionization cross
sections (sigma_PI), recombination cross sections (sigma_{RC}), recombination
collision strengths (Omega_{RC}), and recombination rate coefficients
(alpha_{RC}) are obtained for ionization balance and spectral analysis of UV
and X-ray lines. Level-specific photoionization cross sections and
recombination rates are presented to enable accurate computation of
recombination-cascade matrices for all fine structure levels n(SLJ) up to n <=
10: 98 bound fine structure levels of Ni XXVI with 0 <= l <= 9, 0 <= L <= 11,
1/2 <= J <= 17/2, and 198 levels of Ni XXVII with 0 <= l <= 9, 0 <= L <= 14, 0
<= J <= 10. Total alpha_{RC} for Ni XXVI and Ni XXVII are compared with the
existing values with very good agreement. Total recombination rate coefficients
for the hydrogen-like recombined ion, Ni XXVIII, are also presented. The
calculations are carried out in relativistic Breit-Pauli R-matrix (BPRM)
approximation with inclusion of radiation damping of resonances. With
consideration of all details of the processes, the results, which include the
level specific sigma_{PI} and alpha_{R} calculated for the first time, should
be the most accurate for these ions.


title:
An Extremely Large Excess of 18O in the Hydrogen-Deficient Carbon Star,
  HD 137613

abstract:
  We report the discovery of a uniquely large excess of 18O in the
hydrogen-deficient carbon (HdC) star, HD 137613, based on a spectrum of the
first overtone bands of CO at 2.3-2.4 micron in which three strong absorption
bands of 12C18O are clearly present. Bands of 12C16O also are present but no
bands of 13C16O or 12C17O are seen. We estimate an isotopic ratio 16O/18O ~1.
The Solar value of this ratio is ~500. Neither He-core burning nor He-shell
flash burning can produce the isotopic ratios of oxygen and carbon observed in
HD 137613. However, a remarkable similarity exists between the observed
abundances and those found in the outer layers of the broad He-shell of
early-AGB stars, soon after the end of He-core burning. It is not known how the
outer envelope down to the He-shell could be lost but some mechanism of
enhanced mass loss must be involved. HD 137613 may be a post-early-AGB star
with the outer layers of the former He-burning shell as its photosphere.
  The unusual elemental abundances of the HdC stars resemble those of the R
Coronae Borealis (RCB) stars, but HdC stars do not produce clouds of dust that
produce declines in brightness. None of the other RCB or HdC stars observed
shows significant 18O.


title:
Nonthermal X-radiation of SNR RX J1713.7-3946: The Relations to a Nearby
  Molecular Cloud

abstract:
  The recent X-ray and CO observations of RX J1713.7-3946 show that a
significant fraction of the nonthermal X-ray emission of this unique supernova
remnant associates, in one way or another, with a molecular cloud interacting
with the west part of the shell. This adds a new puzzle in the origin of X-ray
emission which cannot be easily explained within the standard model in
accordance of which X-rays are result of synchrotron radiation of multi-TeV
electrons accelerated by supernova shock waves. We explore an alternative
origin of the X-ray emission assuming that it is produced by secondary
electrons resulting from high energy hadronic interactions in the molecular
gas. Such a scenario could explain in a quite natural way the apparent
correlation between the X-ray and CO morphologies. However, the TeV gamma-ray
emission recently reported by H.E.S.S. significantly constrains the parameter
space of this model. Namely, this mechanism cannot reproduce the bulk of the
observed X-ray flux unless one postulates existence of a PeV cosmic-ray
component penetrating with an unusually hard spectrum into the dense cloud.


title: Dark Energy Stars

abstract:
  Event horizons and closed time-like curves cannot exist in the real world for
the simple reason that they are inconsistent with quantum mechanics. Following
ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago,
and the speaker it is now possible to describe in some detail what happens
physically when one approaches and crosses a region of space-time where
classical general relativity predicts there should be an infinite red shift
surface. This quantum critical physics provides a new perspective on a variety
of enigmatic astrophysical phenomena, including supernovae explosions, gamma
ray bursts, positron emission, and dark matter.


title: Feedback in simulations of disc-galaxy major mergers

abstract:
  Using hydrodynamic simulations of disc-galaxy major mergers, we investigate
the star formation history and remnant properties when various parametrizations
of a simple stellar feedback model are implemented. The simulations include
radiative cooling, a density-dependent star formation recipe and a model for
feedback from massive stars. The feedback model stores supernova feedback
energy within individual gas particles and dissipates this energy on a
time-scale specified by two free parameters; tau_fb, which sets the dissipative
time-scale, and n, which sets the effective equation of state in star-forming
regions. Using a self-consistent disc galaxy, modelled after a local Sbc
spiral, in both isolated and major-merger simulations, we investigate
parametrizations of the feedback model that are selected with respect to the
quiescent disc stability. These models produce a range of star formation
histories that are consistent with the star formation relation found by
Kennicutt. All major mergers produce a population of new stars that is highly
centrally concentrated, demonstrating a distinct break in the r1/4 surface
density profile, consistent with previous findings. The half-mass radius and
one-dimensional velocity dispersion are affected by the feedback model used.
Finally, we compare our results to those of previous simulations of star
formation in disc-galaxy major mergers, addressing the effects of star
formation normalization, the version of smoothed particle hydrodynamics (SPH)
employed and assumptions about the interstellar medium.


title:
Imaging of SDSS z>6 quasar fields: gravitational lensing, companion
  galaxies and the host dark matter halos

abstract:
  We have undertaken deep optical imaging observations of three 6.2<z<6.5
quasar fields in the i' and z' filters. These data are used to search for
foreground galaxies which are gravitationally lensing the quasars and distant
galaxies physically associated with the quasars. Foreground galaxies are found
closer than 5 arcsec from the lines-of-sight of two of the three quasars.
However, the faintness of these galaxies suggests they have fairly low masses
and provide only weak magnifications (mu<1.1). No convincing galaxies
physically associated with the quasars are found and the number of i'-band
dropouts is consistent with that found in random fields. We consider the
expected dark matter halo masses which host these quasars under the assumption
that a correlation between black hole mass and dark matter halo mass exists. We
show that the steepness of the high-mass tail of the halo mass function at this
redshift, combined with realistic amounts of scatter in this correlation, lead
to expected halo masses substantially lower than previously believed. This
analysis can explain the lack of companion galaxies found here and the low
dynamical mass recently published for one of the quasars.


title:
An X-ray study of magnetic field strengths and particle content in FRII
  radio sources

abstract:
  We present a Chandra and XMM-Newton study of X-ray emission from the lobes of
33 classical double radio galaxies and quasars. We report new detections of
lobe-related X-ray emission in 11 sources. Together with previous detections we
find that X-ray emission is detected from at least one radio lobe in ~75
percent of the sample. For all of the lobe detections, we find that the
measured X-ray flux can be attributed to inverse-Compton scattering of the
cosmic microwave background radiation, with magnetic field strengths in the
lobes between (0.3 - 1.3) B_eq, where the value B_eq corresponds to
equipartition between the electrons and magnetic field assuming a filling
factor of unity. There is a strong peak in the magnetic field strength
distribution at B ~ 0.7 B_eq. We find that > 70 percent of the radio lobes are
either at equipartition or electron dominated by a small factor. The
distribution of measured magnetic field strengths differs for narrow-line and
broad-line objects, in the sense that broad-line radio galaxies and quasars
appear to be further from equipartition; however, this is likely to be due to a
combination of projection effects and worse systematic uncertainty in the X-ray
analysis for those objects. Our results suggest that the lobes of classical
double radio sources do not contain an energetically dominant proton
population, because this would require the magnetic field energy density to be
similar to the electron energy density rather than the overall energy density
in relativistic particles.


title:
The Origin of the Spatial Distribution of X-ray luminous AGN in Massive
  Galaxy Clusters

abstract:
  We study the spatial distribution of a 95% complete sample of 508 X-ray point
sources (XPS) detected in the 0.5-2.0 keV band in Chandra ACIS-I observations
of 51 massive galaxy clusters found in the MACS survey. Covering the redshift
range z=0.3-0.7, our cluster sample is statistically complete and comprises all
MACS clusters with X-ray luminosities in excess of 4.5 x 10^44 erg/s (0.1-2.4
keV, h_0=0.7, LCDM). Also studied are 20 control fields that do not contain
clusters. We find the XPS surface density, computed in the cluster restframe,
to exhibit a pronounced excess within 3.5 Mpc of the cluster centers. The
excess, believed to be caused by AGN in the cluster, is significant at the 8.0
sigma confidence level compared to the XPS density observed at the field edges.
No significant central excess is found in the control fields. To investigate
the physical origin of the AGN excess, we study the radial AGN density profile
for a subset of 24 virialized clusters. We find a pronounced central spike
(r<0.5 Mpc), followed by a depletion region at about 1.5 Mpc, and a broad
secondary excess centered at approximately the virial radius of the host
clusters (~2.5 Mpc). We present evidence that the central AGN excess reflects
increased nuclear activity triggered by close encounters between infalling
galaxies and the giant cD-type elliptical occupying the very cluster center. By
contrast, the secondary excess at the cluster-field interface is likely due to
black holes being fueled by galaxy mergers. In-depth spectroscopic and
photometric follow-up observations of the optical counterparts of the XPS in a
subset of our sample are being conducted to confirm this picture.


title:
Multi-wavelength diffraction-limited imaging of the evolved carbon star
  IRC +10216, II

abstract:
  High angular resolution images of IRC +10216 taken at various bandpasses
within the near-infrared h, k & l bands are presented. The maps have the
highest angular resolution yet recovered, and were reconstructed from
interferometric measurements obtained at the Keck 1 telescope in 1997 December
and 1998 April, forming a subset of a 7-epoch monitoring program presented
earlier [paper 1]. Systematic changes with observing wavelength are found and
discussed in context of present geometrical models for the circumstellar
envelope. With these new high-resolution, multi-wavelength data and
contemporaneous photometry, we also re-visit the hypothesis that the bright
compact Core of the nebula (component `A') marks the location of the central
carbon star. We find that directly measured properties of the Core (angular
size, flux density, color temperature) are consistent with a reddened carbon
star photosphere (line-of-sight tau=5.3).


title: The outermost cluster of M31

abstract:
  We report on the identification of a new cluster in the far halo of the M31
galaxy. The cluster, named Bologna 514 (B514) has an integrated magnitude
M_V=-8.5 +- 0.6, and a radial velocity, as estimated from two independent
low-resolution spectra, V_r=-456 +- 23 km/s, which fully confirms its
membership to the M31 system. The observed integrated spectrum is very similar
to those of classical globular clusters. Being located at ~ 4^o (~55 kpc in
projected distance) from the center of the parent galaxy, B514 is by far the
most remote M31 cluster ever discovered. Its projected position, near the
galaxy major axis, and M31-centric velocity, similar to that observed in the
outermost regions of the HI rotation curve, may indicate that it belongs to the
subsystem of M31 clusters that has been recently proposed (Morrison et al.
2004) to be part of the dynamically-cold thin disc of the galaxy.


title: Stream-field interactions in the magnetic accretor AO Piscium

abstract:
  UV spectra of the magnetic accretor AO Psc show absorption features for half
the binary orbit. The absorption is unlike the wind-formed features often seen
in similar stars. Instead, we attribute it to a fraction of the stream that
overflows the impact with the accretion disk. Rapid velocity variations can be
explained by changes in the trajectory of the stream depending on the
orientation of the white-dwarf's magnetic field. Hence we are directly
observing the interaction of an accretion stream with a rotating field. We
compare this behavior to that seen in other intermediate polars and in SW Sex
stars.


title: Theoretical modelling of late-type giant atmospheres: preparing for Gaia

abstract:
  Late type giants (RGB/AGB stars) will be important tracers of the Galactic
morphology and evolution in the framework of Gaia, as they are intrinsically
bright and thus can probe distant stellar populations or those obscured by
interstellar extinction. A realistic representation of their atmospheres and
spectra with stellar atmosphere models is thus of crucial importance, both for
the design and optimization of Gaia instruments, as well as the interpretation
of provided astrophysical data. Our analysis of synthetic photometric colors of
late-type giants based on PHOENIX, MARCS and ATLAS model atmospheres indicates
a general agreement between the current theoretical predictions and
observations in the framework of stationary 1-D model atmospheres. Presently
available models allow temperature determinations of RGB/AGB stars to an
accuracy of ~\pm100 K. In an exploratory study we try to quantify possible
residual systematic effects due to the approximations made in 1-D models using
full 3-D hydrodynamical models. We find that differences in broad-band
photometric colors calculated with 1-D and 3-D models are significant,
translating to the offsets in effective temperature of up to ~70 K. Clearly,
full 3-D hydrodynamical models will help to alleviate such ambiguities in
current theoretical modeling. Additionally, they will allow to study new
phenomena, to open qualitatively new windows for stellar astrophysics in the
Gaia-era.


title:
Beyond the Galaxy with Gaia: evolutionary histories of galaxies in the
  Local Group

abstract:
  Gaia will play an important role in providing information about star
formation histories, merging events, intergalactic streams etc., for nearby
galaxies of the Local Group. One of the most crucial contributions will be
proper motions, especially for stars in the outermost parts of the galaxies,
obtainable for stellar populations to ~150 kpc with RGB stars. Together with
radial velocities for the brightest giants <80 kpc, this will provide
membership information for individual stars and global kinematical picture of
the most nearby galaxies, including the Magellanic Clouds (MCs). Gaia will also
provide photometric metallicities (\sigma([M/H])<0.3) for individual giants
and/or supergiants in dwarf galaxies to ~200 kpc. MSTO ages will be possible
for the youngest stellar populations in the most nearby galaxies (e.g., MCs),
whereas stars on RGB/AGB may provide age estimates for populations to ~150 kpc.
Gaia will allow to study the outermost parts of the galaxies, which (because of
their large spatial extent) are difficult to assess from the ground. Apart from
allowing to clarify the structure and evolution of the dwarf galaxies, this
will also make it possible to investigate galactic tidal debris, thus providing
additional details for the global picture of formation and evolution of the
Milky Way Galaxy.


title:
Realistic Event Rates for Detection of Supermassive Black Hole
  Coalescence by LISA

abstract:
  The gravitational waves generated during supermassive black hole (SMBH)
coalescence are prime candidates for detection by the satellite LISA. We use
the extended Press-Schechter formalism combined with empirically motivated
estimates for the SMBH--dark matter halo mass relation and SMBH occupation
fraction to estimate the maximum coalescence rate for major SMBH mergers.
Assuming efficient binary coalescence, and guided by the lowest nuclear black
hole mass inferred in local galactic bulges and nearby low-luminosity active
galactic nuclei (10^5 Msun) we predict approximately 15 detections per year at
a signal to noise greater than five, in each of the inspiral and ringdown
phases. Rare coalescences between SMBHs having masses in excess of 10^7 Msun
will be more readily detected via gravitational waves from the ringdown phase.


title: Lithium enhancement in X-ray binaries due to stellar rotation

abstract:
  We discuss the high lithium abundances in the secondary stars of X-ray
binaries. We show that no lithium production in these stars is necessary, and
that the abundances can be explained simply due to the tidally locked rotation
of the stars, which lead naturally to slower lithium destruction rates. The
differences in abundances of CVs' secondaries from those of LMXBs had
previously been put forth as evidence that the compact object was related to
the lithium abundance, but this scenario also accounts for the lower lithium
abundances in the secondary stars in cataclysmic variable systems (CVs) than in
low mass X-ray binaries (LMXBs), since these stars have typically lived much
longer before becoming tidally locked short period systems. We point out that
if this scenario is correct, then the globular cluster X-ray binaries' donor
stars should, as a class, show less lithium enhancement relative to other stars
of the same spectral type in the clusters than the field X-ray binaries' donor
stars show.


title:
Three-dimensional Mapping of CDM Substructure at Submillimeter
  Wavelengths

abstract:
  The cold dark matter (CDM) structure formation model predicts that about 5-10
percent of a typical galactic halo of mass $\sim 10^{12} \ms$ is in
substructures with masses $\lesssim 10^8 \ms$. To directly detect such
substructures, we propose to observe dust continuum emission from a strongly
lensed QSO-host galaxy using a large submillimeter interferometer array with a
high angular resolution of $\sim 0.01$arcsec such as the planned Atacama Large
Submillimeter Array (ALMA). To assess their observational feasibility, we
numerically simulate millilensing of an extended circular source by a CDM
substructure modeled as a tidally truncated singular isothermal sphere (SIS)
embedded in a typical QSO-galaxy lens system, B1422+231, modeled as a singular
isothermal ellipsoid (SIE) with an external constant shear and a constant
convergence. Assuming an angular resolution of 0.01arcsec, we find that the
angular positions of $\sim 10^8 \ms$ substructures at several kpc from the
center of the macrolens halo can be directly measured if the size of the dust
continuum emission region and the gradient of the surface brightness at the
position of the perturber are sufficiently large. From the astrometric shift on
a scale of a few times $10~$mas of an image perturbed by a subhalo with respect
to an unperturbed macrolensed image, we can break the degeneracy between
subhalo mass and distance provided that macrolensing parameters are determined
from positions and fluxes of multiple images.


title:
Evidence of vorticity and shear at large angular scales in the WMAP
  data: a violation of cosmological isotropy?

abstract:
  Motivated by the large-scale asymmetry observed in the cosmic microwave
background sky, we consider a specific class of anisotropic cosmological models
-- Bianchi type VII_h -- and compare them to the WMAP first-year data on large
angular scales. Remarkably, we find evidence of a correlation which is ruled
out as a chance alignment at the 3sigma level. The best fit Bianchi model
corresponds to x=0.55, Omega_0=0.5, a rotation axis in the direction
(l,b)=(222degr,-62degr), shear (sigma/H)_0=2.4e-10 and a right--handed
vorticity (omega/H)_0=6.1e-10. Correcting for this component greatly reduces
the significance of the large-scale power asymmetry, resolves several anomalies
detected on large angular scales (ie. the low quadrupole amplitude and
quadrupole/octopole planarity and alignment), and can account for a
non--Gaussian "cold spot" on the sky. Despite the apparent inconsistency with
the best-fit parameters required in inflationary models to account for the
acoustic peaks, we consider the results sufficiently provocative to merit
further consideration.


title: Abundances in Damped Ly-alpha Galaxies

abstract:
  Damped Ly_alpha galaxies provide a sample of young galaxies where chemical
abundances can be derived throughout the whole universe with an accuracy
comparable to that for the local universe. Despite a large spread in redshift,
HI column density and metallicity, DLA galaxies show a remarkable uniformity in
the elemental ratios rather suggestive of similar chemical evolution if not of
an unique population. These galaxies are characterized by a moderate, if any,
enhancement of alpha-elements over Fe-peak elemental abundance with [S/Zn]
about 0 and [O/Zn] about 0.2, rather similarly to the dwarfs galaxies in the
Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution
and possibly two plateaux. In particular, the plateau at low N abundances
([N/H] < -3), is not observed in other atrophysical sites and might be evidence
for primary N production by massive stars.


title: On the proper motion of AXP 1E2259+586

abstract:
  1E2259+586 belongs to the group of anomalous X-ray pulsars (AXP) which are
thought to be magnetars. Accurate measurements of the proper motion for these
interesting objects have not been made. In this work we use the data obtained
by satellites ROSAT, Chandra and XMM-Newton taken in a period of 12 years to
measure the change in position of 1E2259+586 with respect to the three field
sources. Our work yielded an upper limit on the proper motion of ~170 mas/yr
which corresponds to a transverse speed of 2500 km/s, for an assumed distance
of 3 kpc. We also used this upper limit to put a lower limit on the age of the
CTB 109 of ~6 kyr, assuming they are associated. The consistency of right
ascension and declination measurements by different satellites suggest that we
can average these measurements to get the best to date position of 1E2259+586.


title:
Effects of External Tidal Field on the Evolution of Multi-mass Star
  Clusters

abstract:
  We present N-body simulations of realistic globular clusters containing
initial mass function in the galaxy to study effects of tidal field
systematically on the properties of outer parts of globular clusters. Using
NBODY6 which takes into account the two-body relaxation correctly, we
investigate general evolution of globular clusters in galactic tidal field. For
simplicity, we have employed only spherical components (bulge and halo) of the
galaxy. Total number of stars in our simulations was about 20,000. All
simulations were done for several orbital periods in order to understand the
development of the tidal tails. In our scaled down models, the relaxation time
is sufficiently short to show the mass segregation effect, but we did not go
far enough to see the core-collapse, and the fraction of stars lost from the
cluster at the end of simulation is only about 10%. The radial distribution of
extra-tidal stars can be described by a power law with a slope around -3. The
direction of tidal tails are determined by the orbits and locations of the
clusters. We find that the length of tidal tails increases towards the
apogalacticon and decreases towards the perigalacticon. This is an
anti-correlation with the strength of the tidal field, caused by the fact that
the the time-scale for the stars to respond to the potential is similar to the
orbital time-scale of the cluster. When the length of tidal tails decreases
some of the stars in the tidal tails are recaptured by the host cluster. From
the investigation of velocity anisotropy of the model clusters, we find that in
the early stages of globular cluster evolution the clusters have radial
anisotropy in the outermost parts, while clusters are nearly isotropic in the
cental region. The radial anisotropy decreases with time.


title: Radio Emission Associated with the ULX in Holmberg II

abstract:
  We report the detection of radio emission coincident with the ultraluminous
X-ray source (ULX) in Holmberg II. The radio emission is diffuse and resolved,
covering an area ~60 by 40 pc in extent and well-matched to the recently
discovered HeII nebula surrounding the X-ray source. Comparison of the radio
and optical properties of this extended radio emission argue against its
association with either an HII region or supernova remnant. This is additional
evidence that this ULX is not powered by a stellar-mass object whose emission
is relativistically beamed towards the observer, and thus is either a
super-Eddington source or intermediate mass black hole as suggested by optical
observations. Implications of this result to future and existing radio studies
of ULXs are discussed.


title: Evolution of galaxies in clusters

abstract:
  I summarize what is know about the evolution of galaxies in clusters from the
observational point of view presenting results at high (z~1), intermediate
(z~0.5) and low (z~0) redshifts. I comment on the comparison between
observations and predictions of CDM models, highlighting the observational
landmarks more relevant for this comparison, such as the establishment and
evolution of the morphology-density relation, the Butcher-Oemler effect, the
evolution of red galaxies/ellipticals, the star formation histories of galaxies
in clusters, the downsizing effect and the history of mass assembly.


title: Bounds on Expected Black Hole Spins in Inspiraling Binaries

abstract:
  As a first step towards understanding the angular momentum evolution history
of black holes in merging black-hole/neutron-star binaries, we perform
population synthesis calculations to track the distribution of accretion
histories of compact objects in such binaries. We find that there are three
distinct processes which can possibly contribute to the black-hole spin
magnitude: a birth spin for the black hole, imparted at either (i) the collapse
of a massive progenitor star to a black hole or (ii) the accretion-induced
collapse of a neutron star to a black hole; and (iii) an accretion spin-up when
the already formed black hole [via (i) or (ii)] goes through an accretion
episode (through an accretion disk or a common-envelope phase). Our results
show that, with regard to accretion-induced spinup in merging BH-NS binaries
[method (iii) above], only
  {\em accretion episodes associated with common-envelope phases and
hypercritical accretion rates} occur in the formation history of merging black
hole/neutron star binaries. Lacking unambiguous experimental information about
BH birth spins [i.e., regarding the results of processes (i) and (ii)], we
choose two fiducial values for the BH birth angular momentum parameter a=J/M^2,
consistent with observations of (i) NS birth spins (a roughly 0) and (ii) X-ray
binaries (a=0.5). Using these two fiducial values and a conservative upper
bound on the specific angular momentum of accreted matter, we discuss the
expected range of black hole spins in the binaries of interest. We conclude
with comments on the significance of these results for ground-based
gravitational-wave searches of inspiral signals from black hole binaries.


title:
On particle acceleration around shocks II: a fully general method for
  arbitrary shock velocities and scattering media

abstract:
  The probability that a particle, crossing the shock along a given direction,
be reflected backwards along another direction, was shown to be the key element
in determining the spectrum of non--thermal particles accelerated via the Fermi
mechanism around a plane--parallel shock in the test--particle limit. Here an
explicit equation for this probability distribution is given, for both the
upstream and downstream sections. Though analytically intractable, this
equation is solved numerically, allowing the determination of the spectrum in
full generality, without limitation to shock speed or scattering properties. A
number of cases is then computed, making contact with previous numerical work,
in all regimes: Newtonian, trans--relativistic, and fully relativistic.


title:
Experimental N V and Ne VIII low-temperature dielectronic recombination
  rate coefficients

abstract:
  The dielectronic recombination rate coefficients of N V and Ne VIII ions have
been measured at a heavy-ion storage ring. The investigated energy ranges
covered all dielectronic recombination resonances attached to 2s -> 2p (Delta
n=0) core excitations. The rate coefficients in a plasma are derived and
parameterized by using a convenient fit formula. The experimentally derived
rate coefficients are compared with theoretical data by Colgan et al. (2004,
A&A, 417, 1183) and Nahar & Pradhan (1997, ApJ, 111, 339) as well as with the
recommended rate coefficients by Mazzotta et al. (1998, A&A, 133, 403). The
data of Colgan et al. and Nahar & Pradhan reproduce the experiment very well
over the temperature ranges where N V and Ne VIII are expected to exist in
photoionized as well as in collisionally ionized plasmas. In contrast, the
recommendation of Mazzotta et al. agrees with the experimental rate coefficient
only in the temperature range of collisional ionization. At lower temperatures
it deviates from the measured rate coefficient by orders of magnitude. In
addition the influence of external electric fields with field strengths up to
1300 V/cm on the dielectronic recombination rate coefficient has been
investigated.


title: Cosmological Constraints on a Dynamical Electron Mass

abstract:
  Motivated by recent astrophysical observations of quasar absorption systems,
we formulate a simple theory where the electron to proton mass ratio $\mu
=m_{e}/m_{p}$ is allowed to vary in space-time. In such a minimal theory only
the electron mass varies, with $\alpha $ and $m_{p}$ kept constant. We find
that changes in $\mu $ will be driven by the electronic energy density after
the electron mass threshold is crossed. Particle production in this scenario is
negligible. The cosmological constraints imposed by recent astronomical
observations are very weak, due to the low mass density in electrons. Unlike in
similar theories for spacetime variation of the fine structure constant, the
observational constraints on variations in $\mu $ imposed by the weak
equivalence principle are much more stringent constraints than those from
quasar spectra. Any time-variation in the electron-proton mass ratio must be
less than one part in $10^{9}$since redshifts $z\approx 1.$This is more than
one thousand times smaller than current spectroscopic sensitivities can
achieve. Astronomically observable variations in the electron-proton must
therefore arise directly from effects induced by varying fine structure
'constant' or by processes associated with internal proton structure. We also
place a new upper bound of $2\times 10^{-8}$ on any large-scale spatial
variation of $\mu $ that is compatible with the isotropy of the microwave
background radiation.


title: A model for the nonlinear dynamics of turbulent shear flows

abstract:
  We investigate the nonlinear dynamics of turbulent shear flows, with and
without rotation, in the context of a simple but physically motivated closure
of the equation governing the evolution of the Reynolds stress tensor. We show
that the model naturally accounts for some familiar phenomena in parallel shear
flows, such as the subcritical transition to turbulence at a finite Reynolds
number and the occurrence of a universal velocity profile close to a wall at
large Reynolds number. For rotating shear flows we find that, depending on the
Rayleigh discriminant of the system, the model predicts either linear
instability or nonlinear instability or complete stability as the Reynolds
number is increased to large values. We investigate the properties of
Couette-Taylor flows for varying inner and outer cylinder rotation rates and
identify the region of linear instability (similar to Taylor's), as well as
regions of finite-amplitude instability qualitatively compatible with recent
experiments. We also discuss quantitative predictions of the model in
comparison with a range of experimental torque measurements. Finally, we
consider the relevance of this work to the question of the hydrodynamic
stability of astrophysical accretion discs.


title: A broad iron line in the Chandra/HETG spectrum of 4U 1705-44

abstract:
  We present the results of a Chandra 30 ks observation of the low mass X-ray
binary and atoll source 4U 1705-44. Here we concentrate on the study of
discrete features in the energy spectrum at energies below 3 keV, as well as on
the iron Kalpha line, using the HETG spectrometer on board of the Chandra
satellite. Below 3 keV, three narrow emission lines are found at 1.47, 2.0, and
2.6 keV. The 1.47 and 2.6 keV are probably identified with Ly-alpha emission
from Mg XII and S XVI, respectively. The identification of the feature at 2.0
keV is uncertain due to the presence of an instrumental feature at the same
energy. The iron Kalpha line at ~6.5 keV is found to be intrinsically broad
(FWHM ~ 1.2 keV); its width can be explained by reflection from a cold
accretion disk extending down to 15 km from the neutron star center or by
Compton broadening in the external parts of a hot (~2 keV) Comptonizing corona.
We finally report here precise X-ray coordinates of the source.


title: Resolution limits in astronomical images

abstract:
  A method is introduced to derive resolution criteria for various a priori
defined templates of brightness distribution fitted to represent structures and
objects in astronomical images. The method is used for deriving criteria for
the minimum and maximum resolvable sizes of a template. The minimum resolvable
size of a template is determined by the ratio of (SNR-1)/SNR, and the maximum
detectable size is determined by the ratio of 1/SNR. Application of these
criteria is discussed in connection to data from filled-aperture instruments
and interferometers, accounting for different aperture shapes and the effects
of Fourier sampling, tapering, apodization and visibility weighting. Specific
resolution limits are derived for four different templates of brightness
distribution: (1) two-dimensional Gaussian, (2) optically thin spherical shell,
(3) disk of uniform brightness, and (4) ring. The limiting resolution for these
templates changes with SNR similarly to the quantum limit on resolution.
Practical application of the resolution limits is discussed in two examples
dealing with measurements of maximum brightness temperature in compact
relativistic jets and assessments of morphology of young supernova remnants.


title:
The magnetic field of the Large Magellanic Cloud revealed through
  Faraday rotation

abstract:
  We have measured the Faraday rotation toward a large sample of polarized
radio sources behind the Large Magellanic Cloud (LMC), to determine the
structure of this galaxy's magnetic field. The magnetic field of the LMC
consists of a coherent axisymmetric spiral of field strength ~1 microgauss.
Strong fluctuations in the magnetic field are also seen, on small (<0.5
parsecs) and large (~100 parsecs) scales. The significant bursts of recent star
formation and supernova activity in the LMC argue against standard dynamo
theory, adding to the growing evidence for rapid field amplification in
galaxies.


title: X-ray Diagnostics of Broad Absorption Line Quasar Geometry

abstract:
  A new generation of sensitive X-ray measurements are indicating that the
existence of X-ray attenuation column densities,
$N_{H}>10^{24}\mathrm{cm}^{-2}$ is quite common amongst broad absorption line
quasars (BALQSOs). This is significant to the geometry of the broad absorption
line (BAL) outflow. In particular, such an X-ray shield also shields equatorial
accretion disk winds from the UV, thereby preventing high velocity equatorial
outflows from being launched. By contrast, bipolar winds initiated by continuum
radiation pressure from the funnel of a slim accretion disk flare outward (like
a trumpet) and offer vastly different absorbing columns to the X-ray and UV
emission which are emitted from distinct regions of the disk, $\sim 6M$ and
$\sim 10M-40M$, respectively (where $M$ is the radius of the black hole).
Recent numerical work indicates that it is also possible to launch bipolar
outflows from the inner regions of a thin disk. The recent discovery with VLBI
that the Galactic analog of a BALQSO, the X-ray binary Circinus X-1 (with high
velocity P Cygni X-ray absorption lines) is viewed virtually along the radio
jet axis (and therefore along the spin axis of the black hole and the normal to
the accretion disk) has rekindled interest in the bipolar models of BALQSOs. We
explore this possibility by studying the nearest BAL QSO, MRK 231. High
resolution 2-D optical spectroscopy and VLBI mappings of the radio jet axis
indicates that the BAL outflow is parallel to the parsec scale radio jet.


title:
The Millennium Galaxy Catalogue: the space density and surface
  brightness distribution(s) of galaxies

abstract:
  We recover the joint and individual space density and surface brightness
distribution(s) of galaxies from the Millennium Galaxy Catalogue. The MGC is a
local survey spanning 30.9 sq deg and probing approximately one--two mag/sq
arcsec deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS)
or the Sloan Digital Sky Survey (SDSS). The MGC contains 10,095 galaxies to
B_mgc < 20 mag with 96 per cent spectroscopic completeness. We implement a
joint luminosity-surface brightness step-wise maximum likelihood method to
recover the bivariate brightness distribution (BBD) inclusive of most selection
effects. Integrating the BBD over surface brightness we recover the following
Schechter function parameters: phi* = (0.0177 +/- 0.0015) h^3 Mpc^{-3}, M_{B}*
- 5 log h = (-19.60 +/- 0.04) mag and alpha =-1.13 +/- 0.02. Compared to the
2dFGRS (Norberg et al 2002) we find a consistent M* value but a slightly
flatter faint-end slope and a higher normalisation, resulting in a final
luminosity density j_{b_J} = (1.99 +/- 0.17) x 10^8 h L_{odot} Mpc^{-3}. The
MGC surface brightness distribution is a well bounded Gaussian at the M* point
with phi* = (3.5 +/- 0.1) x 10^{-2} h^3 Mpc^{-3}, mu^{e*} = (21.90 +/- 0.01)
mag/sq arcsec and sigma_{ln R_e} = 0.35 +/- 0.01. The characteristic surface
brightness for luminous systems is invariant to M_{B} - 5 log h ~ -19 mag
faintwards of which it moves to lower surface brightness. Higher resolution
(FWHM < 1 arcsec) and deeper (mu_eff > 26 mag/sq arcsec in the B-band)
observations of the local universe are now essential to probe to lower
luminosity and lower surface brightness levels. [abridged]


title:
Neutrinos as a diagnostic of cosmic ray Galactic/extra-galactic
  transition

abstract:
  Motivated by a recent change in viewing the onset of the extra-galactic
component in the cosmic ray spectrum, we have fitted the observed data down to
$10^{8.6}$ GeV and have obtained the corresponding power emissivity. This
transition energy is well below the threshold for resonant $p\gamma$ absorption
on the cosmic microwave background, and thus source evolution is an essential
ingredient in the fitting procedure. Two-parameter fits in the spectral and
redshift evolution indices show that a standard Fermi $E_i^{-2}$ source
spectrum is excluded at larger than 95% confidence level (CL). Armed with the
primordial emissivity, we follow Waxman and Bahcall to derive the associated
neutrino flux on the basis of optically thin sources. For $pp$ interactions as
the generating mechanism, the neutrino flux exceeds the AMANDA-B10 90%CL upper
limits. In the case of $p\gamma$ dominance, the flux is marginally consistent
with AMANDA-B10 data. In the new scenario the source neutrino flux dominates
over the cosmogenic flux at all energies. Thus, should data from AMANDA-II
prove consistent with the model, we show that IceCube can measure the
characteristic power law of the neutrino spectrum, and thus provide a window on
the source dynamics.


title:
Exploring Cosmological Expansion Parametrizations with the Gold SnIa
  Dataset

abstract:
  We use the SnIa Gold dataset to compare LCDM with 10 representative
parametrizations of the recent Hubble expansion history $H(z)$. For the
comparison we use two statistical tests; the usual $\chi_{min}^2$ which is
insensitive to the parametrization number of parameters, and a statistic we
call the p-test which depends on both the value of $\chi_{min}^2$ and the
number $n$ of the parametrization parameters. The p-test measures the
confidence level to which the parameter values corresponding to LCDM are
excluded from the viewpoint of the parametrization tested. For example, for a
linear equation of state parametrization $w(z)=w_0 + w_1 z$ the LCDM parameter
values ($w_0=-1$, $w_1=0$) are excluded at 75% confidence level. We use a flat
prior and $\Omega_{0m}=0.3$. All parametrizations tested are consistent with
the Gold dataset at their best fit. According to both statistical tests, the
worst fits among the 10 parametrizations, correspond to the Chaplygin gas, the
brane world and the Cardassian parametrizations. The best fit is achieved by
oscillating parametrizations which can exclude the parameter values
corresponding to LCDM at 85% confidence level. Even though this level of
significance does not provide a statistically significant exclusion of LCDM (it
is less than $2\sigma$) and does not by itself constitute conclusive evidence
for oscillations in the cosmological expansion, when combined with similar
independent recent evidence for oscillations coming from the CMB and matter
power spectra it becomes an issue worth of further investigation.


title: Pulsar: repeatable Lagrangian singularity

abstract:
  In general, the interior of radially symmetric self-gravitating sphere is
considered in terms of hydrostatic equilibrium (HSE). This approach implies the
possibility of the static being of a body. Such a static state is assumed to be
the result of asymptotic damping of the process of formation. It is shown here
that the damping of this process is impossible: if a sphere vibrates radially,
then compressional wave is singular at the centre; dynamical singularity has no
intermediate stages of the fading; the HSE-state is unachievable.
Self-gravitating sphere perpetually vibrates in essentially singular way, it
contains dynamical central region -- pulsatile Lagrangian cavity. Theoretical
properties of this cavity indicate that this is a pulsar. A pulsar is common
structural feature for every self-gravitating structure.


title: The Prevalence of Cooling Cores in Clusters of Galaxies at z~0.15-0.4

abstract:
  We present a Chandra study of 38 X-ray luminous clusters of galaxies in the
ROSAT Brightest Cluster Sample (BCS) that lie at z~0.15-0.4. We find that the
majority of clusters at moderate redshift generally have smooth, relaxed
morphologies with some evidence for mild substructure perhaps indicative of
recent minor merger activity. Using spatially-resolved spectral analyses, cool
cores appear to still be common at these redshifts. At a radius of 50 kpc, we
find that at least 55 per cent of the clusters in our sample exhibit signs of
mild cooling [t(cool)<10 Gyr], while in the central bin at least 34 per cent
demonstrate signs of strong cooling [t(cool)<2 Gyr]. These percentages are
nearly identical to those found for luminous, low-redshift clusters of
galaxies, suggesting little evolution in cluster cores since z~0.4 and that
heating and cooling mechanisms may already have stabilised by this epoch.
Comparing the central cooling times to central Halpha emission in BCS clusters,
we find a strong correspondence between the detection of Halpha and central
cooling time. (Abridged)


title: Compton scattering in the Klein-Nishina Regime Revisited

abstract:
  In blazars such as 3C 279, GeV gamma-rays are thought to be produced by
inverse Compton scattering of soft photons injected from external sources into
the jet. Because of the large bulk Lorentz factor of the jet, the energy of
soft photons is Doppler shifted in the comoving frame of the jet, and the
scattering is likely to occur in the Klein-Nishina regime. Although the
Klein-Nishina effects are well known, the properties of the electron and
emission spectra have not been studied in detail in the environment of blazars.
We solve the kinetic equation of electrons with the spatial escape term of the
electrons to obtain the electron energy spectrum in the jet and calculated the
observed emission spectrum. In calculations of the Compton losses in the
Klein-Nishina regime, we use the discrete loss formalism to take into account
the significant energy loss in a single scattering. Although the scattering
cross section decreases because of the Klein-Nishina effects, ample gamma rays
are emitted by inverse Compton scattering. When the injection spectrum of
electrons obeys a power law, the electron spectrum does not follow a broken
power law, as a result of the Klein-Nishina effects, and a large number of
high-energy electrons remain in the emitting region.


title:
VLBA Imaging Polarimetry of Active Galactic Nuclei - An Automated
  Approach

abstract:
  We present full polarization Very Long Baseline Array (VLBA) observations at
5 GHz and 15 GHz of 24 compact active galactic nuclei (AGN). These sources were
observed as part of a pilot project to demonstrate the feasibility of
conducting a large VLBI survey to further our understanding of the physical
properties and temporal evolution of AGN jets. The sample is drawn from the
Cosmic Lens All-Sky Survey (CLASS) where it overlaps with the Sloan Digital Sky
Survey at declinations north of 15 degrees. There are 2100 CLASS sources
brighter than 50 mJy at 8.4 GHz, of which we have chosen 24 for this pilot
study. All 24 sources were detected and imaged at 5 GHz with a typical dynamic
range of 500:1, and 21 of 24 sources were detected and imaged at 15 GHz. Linear
polarization was detected in 8 sources at both 5 and 15 GHz, allowing for the
creation of Faraday rotation measure (RM) images. The core RMs for the sample
were found to have an average absolute value of 390 +/- 100 rad/m^2. We also
present the discovery of a new Compact Symmetric Object, J08553+5751. All data
were processed automatically using pipelines created or adapted for the survey.


title:
Stellar disks and halos of the edge-on spiral galaxies: NGC 891, NGC
  4144 and NGC 4244

abstract:
  The results of the stellar photometry of the images ACS/WFC and WFPC2 of the
HST are used to study stellar population and spatial distribution of stars in
three edge-on galaxies: NGC 891, NGC 4144 and NGC 4244. The measuring of the
number density of the old stars revealed two stellar substructures in these
galaxies: thick disk and halo. The borders of these substructures consisting
mainly of red giants, are determined by the change of number density gradient
of the old stars. The revealed halos have flattened shapes and extend up to 25
kpc from the galaxy planes. The obtained results of number density
distributions of different type stars perpendicular to the galaxy planes allow
us to verify our stellar model of spiral galaxies. Using the determination of
the tip of red giant branch (TRGB method) we have derived the following
distances: D = 9.82 Mpc (NGC 891), D = 7.24 Mpc (NGC 4144), D = 4.29 Mpc (NGC
4244).


title: Batch discovery of nine z~1 clusters using x-ray and K or R,z' images

abstract:
  We present results of an initial search for clusters of galaxies at z~1 and
above, using data from 2.9 square degrees of XMM-Newton images. By selecting
weak potentially extended X-ray sources with faint or no identifications in
deep, ground-based optical imaging, we have constructed a starting sample of 19
high redshift cluster candidates. Near-IR and R,z' imaging of these fields
identified nine of them as high redshift systems. Six of these were confirmed
spectroscopically, three at z~1.0 and the other three in 0.8<z<0.92 range. The
remaining three systems have solid photometric evidence to be at z_phot ~ 0.8,
1.0 and 1.3. The present sample significantly increases the number of such
clusters. The measured density of z>~1 clusters, after discarding "low"
redshift systems at z <~ 0.92 is about 1.7 /deg2 (with 68 % confidence interval
equal to [1.0,2.9]) for f_X >~2.5 10^{-15} ergs/cm2/s ([0.5-2] keV) and this is
a lower limit, having screened not all potential z~1 candidate clusters.
Coordinates, x-ray measures and evidence for nine x-ray selected high redshift
clusters is given.


title:
What will anisotropies in the clustering pattern in redshifted 21 cm
  maps tell us?

abstract:
  The clustering pattern in high redshift HI maps is expected to be anisotropic
due to two distinct reasons, the
  Alcock-Paczynski effect and the peculiar velocities, both of which are
sensitive to the cosmological parameters. The signal is also expected to be
sensitive to the details of the HI distribution at the epoch when the radiation
originated. We use simple models for the HI distribution at the epoch of
reionizaation and the post-reionization era to investigate exactly what we hope
to learn from future observations of the anisotropy pattern in HI maps. We find
that such observations will probably tell us more about the HI distribution
than about the background cosmological model. Assuming that reionization can be
described by spherical, ionized bubbles all of the same size with their centers
possibly being biased with respect to the dark matter, we find that the
anisotropy pattern at small angles is expected to have a bump at the
characteristic angular size of the individual bubbles whereas the large scale
anisotropy pattern will reflect the size and the bias of the bubbles. The
anisotropy also depends on the background cosmological parameters, but the
dependence is much weaker. Under the assumption that the HI in the
post-reionization era traces the dark matter with a possible bias, we find that
changing the bias and changing the background cosmology has similar effects on
the anisotropy pattern. Combining observations of the anisotropy with
independent estimates of the bias, possibly from the bi-spectrum, may allow
these observations to constrain cosmological parameters.


title: How does disk gravity really influence type-I migration ?

abstract:
  We report an analytical expression for the locations of Lindblad resonances
induced by a perturbing protoplanet, including the effect of disk gravity.
Inner, outer and differential torques are found to be enhanced compared to
situations where a keplerian velocity field for the dynamics of both the disk
and the planet is assumed. Inward migration is strongly accelerated when the
disk gravity is only accounted for in the planet orbital motion. The addition
of disk self-gravity slows down the planet drift but not enough to stop it.


title:
Detection of pulsations and a spectral feature in the X-ray emission of
  the isolated neutron star 1RXS J214303.7+065419/RBS 1774

abstract:
  We report on the results of a deep XMM-Newton observation of RBS 1774, the
most recent dim isolated neutron star candidate found in the ROSAT archive
data. Spectral and timing analysis of the high-quality PN and MOS data confirm
the association of this source with an isolated neutron star. The spectrum is
thermal and blackbody-like, and there is evidence at a significance level >
4sigma that the source is an X-ray pulsar, with spin period of 9.437 s.
Spectral fitting reveils the presence of an absorption feature at ~0.7 keV, but
at this level data do not have enough resolution to allow us to discriminate
between an absorption line or an edge. We compare the newly measured properties
of RBS 1774 with those of other known dim isolated neutron stars, and discuss
possible interpretations for the absorption feature.


title:
XMM-Newton EPIC and OM Observations of Her X-1 over the 35 d Beat Period
  and an Anomalous Low State

abstract:
  We present the results of a series of XMM-Newton EPIC and OM observations of
Her X-1, spread over a wide range of the 35 d precession period. We confirm
that the spin modulation of the neutron star is weak or absent in the low state
- in marked contrast to the main or short-on states. The strong fluorescence
emission line at ~6.4 keV is detected in all observations (apart from one taken
in the middle of eclipse), with higher line energy, width and normalisation
during the main-on state. In addition, we report the detection of a second line
near 7 keV in 10 of the 15 observations taken during the low-intensity states
of the system. We discuss these observations in the context of previous
observations, investigate the origin of the soft and hard X-rays and consider
the emission site of the 6.4keV and 7keV emission lines.


title:
The extended Lyman-alpha emission surrounding the z=3.04 radio-quiet
  QSO1205-30: Primordial infalling gas illuminated by the quasar?

abstract:
  We present spectroscopic observations obtained with the FORS1 instrument on
the ESO VLT under good seeing conditions of the radio-quiet z_em = 3.04 quasar
Q1205-30 and its associated extended Lyman-alpha emission. The extended
Lyman-alpha emission was originally found in a deep narrow band image targeting
a z_abs = z_em Lyman-limit system in the spectrum of the QSO. Using spectral
point-spread function fitting to subtract the QSO spectrum, we clearly detect
the extended Lyman-alpha emission as well as two foreground galaxies at small
impact parameters (2.12 +- 0.04 and 2.77 +- 0.07 arcsec). The redshifts of the
two foreground galaxies are found to be z = 0.4732 and z = 0.865. We determine
the redshift and velocity profile for the extended Lyman-alpha emission, and
analyzing the velocity offsets between eight QSO emission lines we refine the
quasar redshift determination. We use the new redshifts to infer the geometry
of the complex. We find that the extended Lyman-alpha emission is clearly
associated with the quasar. A Lyman-alpha luminosity of 5.6 x 10^43 erg s^-1
places this extended emission at the high luminosity end of the few previous
detections around radio-quiet quasars. The extended Lyman-alpha emission is
best explained by hydrogen falling into the dark matter halo inhabited by the
quasar.


title: Observational constraints on interacting quintessence models

abstract:
  We determine the range of parameter space of Interacting Quintessence Models
that best fits the recent WMAP measurements of Cosmic Microwave Background
temperature anisotropies. We only consider cosmological models with zero
spatial curvature. We show that if the quintessence scalar field decays into
cold dark matter at a rate that brings the ratio of matter to dark energy
constant at late times,the cosmological parameters required to fit the CMB data
are: \Omega_x = 0.43 \pm 0.12, baryon fraction \Omega_b = 0.08 \pm 0.01, slope
of the matter power spectrum at large scals n_s = 0.98 \pm 0.02 and Hubble
constant H_0 = 56 \pm 4 km/s/Mpc. The data prefers a dark energy component with
a dimensionless decay parameter c^2 =0.005 and non-interacting models are
consistent with the data only at the 99% confidence level. Using the Bayesian
Information Criteria we show that this exra parameter fits the data better than
models with no interaction. The quintessence equation of state parameter is
less constrained; i.e., the data set an upper limit w_x \leq -0.86 at the same
level of significance. When the WMAP anisotropy data are combined with
supernovae data, the density parameter of dark energy increases to \Omega_x
\simeq 0.68 while c^2 augments to 6.3 \times 10^{-3}. Models with quintessence
decaying into dark matter provide a clean explanation for the coincidence
problem and are a viable cosmological model, compatible with observations of
the CMB, with testable predictions. Accurate measurements of baryon fraction
and/or of matter density independent of the CMB data, would support/disprove
these models.


title: Discovery of magnetic fields in hot subdwarfs

abstract:
  We present polarisation measurements of sdB and sdO stars using FORS1 on the
VLT. The observations were made as part of a project to determine whether
magnetic fields in two super-metal-rich stars can explain their extreme
abundance peculiarities. Field strengths of up to ~1.5 kG have been measured at
varying levels of significance in each of our six targets, however no clear
evidence was found between apparently normal subdwarfs and the metal-rich
objects. The origin of the magnetic fields is unknown. We also discuss the
implications of our measurements for magnetic flux conservation in late stages
of stellar evolution.


title: Detection of TeV Gamma-Rays from extended sources with Milagro

abstract:
  The Milagro gamma-ray observatory employs a water Cherenkov detector to
observe extensive air showers produced by high-energy particles impacting in
the Earth's atmosphere. A 4800 m$^{2}$ pond instrumented with 723 8" PMTs
detects Cherenkov light produced by secondary air-shower particles. An array of
175 4000 liter water tanks surrounding the central pond detector was recently
added, extending the physical area of the Milagro observatory to 40,000 m$^{2}$
and substantially increasing the sensitivity of the detector. Because of its
wide field of view and high duty cycle, Milagro is ideal for monitoring the
northern sky almost continuously ($>$90% duty cycle) in the 100 GeV to 100 TeV
energy range. Here we discuss the first detection of TeV gamma-rays from the
inner Galactic plane region. We also report the detection of an extended TeV
source coincident with the EGRET source 3EG J0520+2556, as well as the
observation of extended TeV emission from the Cygnus region of the Galactic
plane.


title:
Properties of detached shells around carbon stars: Evidence of
  interacting winds

abstract:
  The nature of the mechanism responsible for producing the spectacular,
geometrically thin, spherical shells found around some carbon stars has been an
enigma for some time. Based on extensive radiative transfer modelling of both
CO line emission and dust continuum radiation for all objects with known
detached molecular shells, we present compelling evidence that these shells
show clear signs of interaction with a surrounding medium. The derived masses
of the shells increase with radial distance from the central star while their
velocities decrease. A simple model for interacting winds indicate that the
mass-loss rate producing the faster moving wind has to be almost two orders of
magnitudes higher (~10^-5 solar masses per year) than the slower AGB wind (a
few 10^-7 solar masses per year) preceding this violent event. At the same
time, the present-day mass-loss rates are very low indicating that the epoch of
high mass-loss rate was relatively short, on the order of a few hundred years.
This, together with the number of sources exhibiting this phenomenon, suggests
a connection with He-shell flashes (thermal pulses). We report the detection of
a detached molecular shell around the carbon star DR Ser, as revealed from new
single-dish CO (sub-)millimetre line observations. The properties of the shell
are similar to those characterising the young shell around U Cam.


title: Westerbork HI observations of high-velocity clouds near M31 and M33

abstract:
  We have undertaken high-resolution follow-up of a sample of high velocity HI
clouds apparently associated with M31. Our sample was chosen from the
population of high-velocity clouds (HVCs) detected out to 50 kpc projected
radius of the Andromeda Galaxy by Thilker et al. (2004) with the Green Bank
Telescope. Nine pointings were observed with the Westerbork Synthesis Radio
Telescope to determine the physical parameters of these objects and to find
clues to their origin. One additional pointing was directed at a similar object
near M33. At 2' resolution we detect 16 individual HVCs around M31 and 1 HVC
near M33 with typical HI masses of a few times 10^5 solar masses and sizes of
the order of 1 kpc. Estimates of the dynamical and virial masses of some of the
HVCs indicate that they are likely gravitationally dominated by additional mass
components such as dark matter or ionised gas. Twelve of the clouds are
concentrated in an area of only 1 by 1 degree at a projected separation of less
than 15 kpc from the disk of M31. This HVC complex has a rather complicated
morphological and kinematical structure and partly overlaps with the giant
stellar stream of M31, suggesting a tidal origin. Another detected feature is
in close proximity, in both position and velocity, with NGC 205, perhaps also
indicative of tidal processes. Other HVCs in our survey are isolated and might
represent primordial, dark-matter dominated clouds.


title: Chandra Observations of 12 Luminous Red Quasars

abstract:
  We present results of a study of 12 dust-reddened quasars with 0.4 < z < 2.65
and reddenings in the range 0.15 < E(B-V) < 1.7. We obtained ACIS-S X-ray
spectra of these quasars, estimated the column densities towards them, and
hence obtained the gas:dust ratios in the material obscuring the quasar. We
detect all but one of the red quasars in the X-rays. Even though there is no
obvious correlation between the X-ray determined column densities of our
sources and their optical color or reddening, all of the sources show absorbed
X-ray spectra. When we correct the luminosity for absorption, they can be
placed among luminous quasars; therefore our objects belong to the group of
high luminosity analogues of the sources contributing to the X-ray background
seen in deep X-ray observations. Such sources are also found in serendipitous
shallow X-ray surveys. There is a hint that the mean spectral slope of the red
quasar is higher than that of normal, unobscured quasars, which could be an
indication for higher accretion rates and/or an evolutionary effect. We
investigate the number density of these sources compared to type 2 AGN based on
the X-ray background and estimate how many moderate luminosity red quasars may
be found in deep X-ray fields.


title:
Quasar Spectrum Classification with PCA - II: Introduction of Five
  Classes, Artificial Quasar Spectrum, the Mean Flux Correction Factor dF,and
  the Identification of Emission Lines in the Ly alpha Forest

abstract:
  We investigate the variety in quasar UV spectra (1020-1600A) with emphasis on
the weak emission lines in the Ly alpha forest region using principal component
analysis (PCA). This paper is a continuation of Suzuki et al. (2005, Paper I),
but with a different approach. We use 50 smooth continuum fitted quasar spectra
(0.14 < z < 1.04) taken by the Hubble Space Telescope (HST) Faint Object
Spectrograph. Three weak emission lines in the Ly alpha forest are identified
as FeII 1070.95A, FeII+FeIII 1123.17A, and CIII* 1175.88A. Using first two
standardized PCS coefficients, we introduce five classifications: Class Zero
and Class I-IV. These classifications will guide us in finding the continuum
level in the Ly alpha forest, and we discuss the characteristics of each class.
We show weak emission lines in the Ly alpha forest become eminent for Class III
and IV. By actively using PCS, we can generate artificial quasar spectra which
are useful to test the detection of quasars, DLAs, and the continuum
calibration. We provide 10,000 artificially generated spectra. We show that the
power-law extrapolated continuum is inadequate to perform precise measurements
of the mean flux in the Ly alpha forest because of the weak emission lines and
the extended tails of Ly alpha and Ly beta/OVI emission lines. We introduce a
correction factor dF such that the true mean flux <F> can be related to
<F_{Power-Law}> that is measured by using power-law continuum extrapolation:
<F> = <F_{Power-Law}> dF. The correction factor dF ranges from 0.84 to 1.05
with a mean of 0.947 and a standard deviation of 0.031 for our 50 quasars. This
result means that we miss 5.3% of flux on average and we show that there are
cases where we would miss 16% of flux using a power-law extrapolation.


title:
The Bolocam Lockman Hole Millimeter-Wave Galaxy Survey: Galaxy
  Candidates and Number Counts

abstract:
  We present results of a new deep 1.1 mm survey using Bolocam, a
millimeter-wavelength bolometer array camera designed for mapping large fields
at fast scan rates, without chopping. A map, galaxy candidate list, and derived
number counts are presented. This survey encompasses 324 arcmin^2 to an rms
noise level (filtered for point sources) of 1.4 mJy/beam and includes the
entire regions surveyed by the published 8 mJy 850 micron JCMT SCUBA and 1.2 mm
IRAM MAMBO surveys. We reduced the data using a custom software pipeline to
remove correlated sky and instrument noise via a principal component analysis.
Extensive simulations and jackknife tests were performed to confirm the
robustness of our source candidates and estimate the effects of false
detections, bias, and completeness. In total, 17 source candidates were
detected at a significance > 3.0 sigma, with six expected false detections.
Nine candidates are new detections, while eight candidates have coincident
SCUBA 850 micron and/or MAMBO 1.2 mm detections. From our observed number
counts, we estimate the underlying differential number count distribution of
submillimeter galaxies and find it to be in general agreement with previous
surveys. Modeling the spectral energy distributions of these submillimeter
galaxies after observations of dusty nearby galaxies suggests extreme
luminosities of L = 1.0-1.6 x 10^13 L_solar and, if powered by star formation,
star formation rates of 500-800 M_solar/yr.


title:
VLA Polarimetry Observations of PKS 2322-123; Estimating Magnetic Fields
  in the Abell 2597 Cluster

abstract:
  We present 5, 8, and 15 GHz total intensity and polarimetric observations of
the radio source PKS 2322-123 taken with the Very Large Array (VLA). This small
(11 kpc) source is located at the center of the cooling-core cluster Abell
2597. The inner X-ray structure, the radio morphology, and the steep spectral
index (alpha = -1.8) in the lobes, all suggest that the radio emission is
confined by the ambient X-ray gas. We detect a small region of polarized flux
in the southern lobe and are able to calculate a Faraday rotation measure (RM)
of 3620 rad/m/m over this region. Based on these observations and Chandra X-ray
data we suggest that the southern lobe has been deflected from its original
southwestern orientation to the south and into our line-of-sight. Using the
observed RMs and our calculated electron density profiles, and assuming both a
uniform and tangled magnetic field topology, we estimate a lower limit of the
line-of-sight cluster magnetic field, B = 2.1 microgauss.


title:
Diagnosing the outflow from the SGR 1806-20 Giant Flare with Radio
  Observations

abstract:
  On 2004 Dec. 27, the soft gamma repeater (SGR) 1806-20 emitted the brightest
giant flare (GF) ever detected from an SGR, with an (isotropic) energy release
$\sim 100$ times greater than the only two other known SGR GFs. It was followed
by a very bright, fading radio afterglow. Extensive follow-up radio
observations provided a wealth of information with unprecedented astrometric
precision, revealing the temporal evolution of the source size, along with
densely sampled light curves and spectra. Here we expand on our previous work
on this source, by explaining these observations within one self-consistent
dynamical model. In this scenario, the early radio emission is due to the
outflow ejected during the GF energizing a thin shell surrounding a
pre-existing cavity, where the observed steep temporal decay of the radio
emission seen beginning on day 9 is attributed to the adiabatic cooling of the
shocked shell. The shocked ejecta and external shell move outward together,
driving a forward shock into the ambient medium, and are eventually decelerated
by a reverse shock. As we show in Gelfand et al. (2005), the radio emission
from the shocked external medium naturally peaks when significant deceleration
occurs, and then decays relatively slowly. The dynamical modeling of the
collision between the ejecta and the external shell together with the observed
evolution of the source size (which is nicely reproduced in our model) suggest
that most of the energy in the outflow was in mildly relativistic material,
with an initial expansion velocity $v/c \lesssim 0.7d_{15}$, for a distance of
$15d_{15}$ kpc to SGR 1806-20. An initially highly relativistic outflow would
not have produced a long coasting phase at a mildly relativistic expansion
velocity, as was observed.


title:
Self-Similar Evolution of Relativistic Shock Waves Emerging from
  Plane-Parallel Atmospheres

abstract:
  We study the evolution of the ultra-relativistic shock wave in a
plane-parallel atmosphere adjacent to a vacuum and the subsequent breakout
phenomenon. When the density distribution has a power law with the distance
from the surface, there is a self-similar motion of the fluid before and after
the shock emergence. The time evolution of the Lorentz factor of the shock
front is assumed to follow a power law when the time is measured from the
moment at which the shock front reaches the surface. The power index is found
to be determined by the condition for the flow to extend through a critical
point. The energy spectrum of the ejected matter as a result of the shock
breakout is derived and its dependence on the strength of the explosion is also
deduced. The results are compared with the self-similar solution for the same
problem with non-relativistic treatment.


title:
Three Li-rich K giants: IRAS 12327-6523, IRAS 13539-4153, and IRAS
  17596-3952

abstract:
  We report on spectroscopic analyses of three K giants previously suggested to
be Li-rich: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952.
High-resolution optical spectra and the LTE model atmospheres are used to
derive the stellar parameters: ($T_{\rm eff}$, log $g$, [Fe/H]), elemental
abundances, and the isotopic ratio $^{12}$C/$^{13}$C. IRAS 13539-4153 shows an
extremely high Li abundance of $\log\epsilon$(Li) $\approx$ 4.2, a value ten
times more than the present Li abundance in the local interstellar medium. This
is the third highest Li abundance yet reported for a K giant. IRAS 12327-6523
shows a Li abundances of $\log\epsilon$(Li)$\approx$ 1.4. IRAS 17596-3952 is a
rapidly rotating ($V{\sin i}$ $\approx$ 35 km s$^{-1}$) K giant with
$\log\epsilon$(Li) $\approx$ 2.2. Infrared photometry which shows the presence
of an IR excess suggesting mass-loss. A comparison is made between these three
stars and previously recognized Li-rich giants.


title:
A possible observational evidence for $\theta^{-2}$ angular distribution
  of opening half-angle of GRB jets

abstract:
  We propose a method to estimate the pseudo jet opening half-angle of GRBs
using the spectral peak energy ($\Ep$)--peak luminosity relation (so called
Yonetoku relation) as well as the $\Ep$--collimation-corrected $\gamma$-ray
energy relation (so called Ghirlanda relation). For bursts with known jet break
times and redshifts, we compared the pseudo jet opening half-angle with the
standard one and found that the differences are within a factor 2. We apply the
method to 689 long GRBS. We found that the distribution function of the pseudo
jet opening half-angle obeys $f(\theta_j)\propto\theta_j^{-2.2 \pm 0.2}$ with
possible cutoffs for $\theta_j < 0.04$ and $\theta_j > 0.3$ although the
log-normal fit is also possible. $\theta^{-2}$ distribution is compatible with
the structured jet model. From the distribution function we found that the
beaming correction for the rate of GRBs is $\sim 340$, which means $\sim
10^{-5}$ yr$^{-1}$ galaxy$^{-1}$ or only one in $10^2$ type Ib/c supernovae. We
also found the evolution of the distribution function as a function of the
redshift.


title: Unstable Bar and Spiral Modes of Disk Galaxies

abstract:
  We study bisymmetric modes of angular wavenumber 2 for flat stellar disks in
potentials with smooth cores. Stars either all circulate in the same direction
or a small fraction may counter-rotate. The bisymmetric modes are unstable
unless there is a sufficiently large external halo or bulge. We find two modes
for each disk: a more central fundamental mode and a more extensive and more
spiral (trailing) secondary mode. The fundamental mode is particularly
sensitive to the orbital population in the central part of the disk. Depending
on that population, it varies from a small compact bar to a trailing spiral
that is almost as wound as the secondary mode. All modes rotate too rapidly for
there to be an inner Lindblad resonance. They transfer angular momentum from
the central to the outer regions of the disk. Most of them release
gravitational energy and convert it to kinetic energy, which also flows
outwards through the disk.


title:
Probing the Spatial Distribution of the Interstellar Dust Medium by High
  Angular Resolution X-ray Halos of Point Sources

abstract:
  We studied the X-ray dust scattering halos around 17 bright X-ray point
sources using {\it Chandra} data. We use an iterative method to resolve the
halos at small scattering angles from the zeroth order data in CC-mode or the
first order data in TE-mode which is not or less piled-up. Using the halo
models of Weingartner $&$ Draine (2001, WD01) and Mathis, Rumpl $&$ Nordsieck
(1977, MRN) to fit the halo profiles, we get the hydrogen column densities and
the spatial distributions of the scattering dust grains along the line of
sights (LOS) to these sources. We find that the scattering dust density very
close to these sources is much higher than the normal interstellar medium. For
X-ray pulsars GX 301-2 and Vela X-1 with companions of strong stellar winds,
the X-ray absorption column densities are much higher than the derived
scattering column densities, because of the dense media around the X-ray
sources produce extremely small angle scatterings which are indistinguishable
from the point sources even with \textit{Chandra}'s angular resolution. For LMC
X-1, most of the scattering and absorption occur in Large Magellanic Cloud,
rather than in the Milky Way. From the obtained X-rays spectra, the cold gas
absorption and thus the quivalent hydrogen column is determined. We have
obtained the linear correlation between $N_{H}$ derived from spectral fits and
the one derived from the halo model WD01 and MRN (except for GX 301-2 and Vela
X-1): $N_{H,WD01} = (0.720\pm0.009) \times N_{H,abs} + (0.051\pm0.013)$ and
$N_{N, MRN} = (1.156\pm0.016) \times N_{H,abs} + (0.062\pm0.024)$ in the units
$10^{22}$ cm$^{-2}$. High angular resolution X-ray dust scattering halos offer
an excellent potential for probing the spatial distributions of interstellar
dust medium.


title: Discovery of Solar Rieger Periodicities in Another Star

abstract:
  The Rieger periods are solar cycles with a time scale of months, which are
present in both flaring activity and sunspot occurrence. These short-term
periodicities, tentatively explained by equatorially trapped Rossby-type waves
modulating the emergence of magnetic flux at the surface, are considered a
peculiar and not yet fully understood solar phenomenon. We chose a stellar
system with solar characteristics, UX Arietis, and performed a timing analysis
of two 9-year datasets of radio and optical observations. The analysis reveals
a 294-day cycle. When the two 9-year datasets are folded with this period, a
synchronization of the peak of the optical light curve (i.e., the minimum spot
coverage) with the minimum radio flaring activity is observed. This close
relationship between two completly independent curves makes it very likely that
the 294-day cycle is real. We conclude that the process invoked for the Sun of
a periodical emergence of magnetic flux may also be applied to UX Arietis and
can explain the cyclic flaring activity triggered by interactions between
successive cyclic emergences of magnetic flux.


title: The Redshift-Space Two Point Correlation Function of ELAIS-S1 Galaxies

abstract:
  We investigate the clustering properties of galaxies in the recently
completed ELAIS-S1 redshift survey through their spatial two point
autocorrelation function. We used a sub-sample of the ELAIS-S1 catalog covering
approximately 4 deg^2 and consisting of 148 objects selected at 15 micron with
a flux >0.5 mJy and redshift z<0.5. We detected a positive signal in the
correlation function that, in the range of separations 1-10 h mpc is well
approximated by a power law with a slope gamma = 1.4 and a correlation length s
=5.4 h mpc. This result is in good agreement with the redshift-space
correlation function measured in more local samples of mid infrared selected
galaxies like the IRAS PSC$z$ redshift survey. This suggests a lack of
significant clustering evolution of infrared selected objects out to $z=0.5$
that is further confirmed by the consistency found between the correlation
functions measured in a local (z<0.2) and a distant (0.2<z<0.5) subsample of
ELAIS-S1 galaxies. We also confirm that optically selected galaxies in the
local redshift surveys, especially those of the SDSS sample, are significantly
more clustered than infrared objects.


title: Discovery of disc precession in the M31 dipping X-ray binary Bo 158

abstract:
  We present results from three XMM-Newton observations of the M31 low mass
X-ray binary XMMU J004314.4+410726.3 (Bo 158), spaced over 3 days in 2004,
July. Bo 158 was the first dipping LMXB to be discovered in M31. Periodic
intensity dips were previously seen to occur on a 2.78-hr period, due to
absorption in material that is raised out of the plane of the accretion disc.
The report of these observations stated that the dip depth was anti-correlated
with source intensity. However, our new observations do not favour a strict
intensity dependance, but rather suggest that the dip variation is due to
precession of the accretion disc. This is to be expected in LMXBs with a mass
ratio <~ 0.3 (period <~ 4 hr), as the disc reaches the 3:1 resonance with the
binary companion, causing elongation and precession of the disc. A smoothed
particle hydrodynamics simulation of the disc in this system shows retrograde
rotation of a disc warp on a period of ~11 P_orb, and prograde disc precession
on a period of ~29 P_orb. This is consistent with the observed variation in the
depth of the dips. We find that the dipping behaviour is most likely to be
modified by the disc precession, hence we predict that the dipping behaviour
repeats on a 81+/-3 hr cycle.


title:
Metallicity of M dwarfs I. A photometric calibration and impact on the
  mass-luminosity relation at the bottom of the main sequence

abstract:
  We obtained high resolution ELODIE and CORALIE spectra for both components of
20 wide visual binaries composed of an F-, G- or K-dwarf primary and an M-dwarf
secondary. We analyse the well understood spectra of the primaries to determine
metallicities ([Fe/H]) for these 20 systems, and hence for their M dwarf
components. We pool these metallicities with determinations from the literature
to obtain a precise (+- 0.2 dex) photometric calibration of M dwarf
metallicities. This calibration represents a breakthrough in a field where
discussions have had to remain largely qualitative, and it helps us demonstrate
that metallicity explains most of the large dispersion in the empirical V-band
mass-luminosity relation. We examine the metallicity of the two known M-dwarf
planet-host stars, Gl 876 (+0.02 dex) and Gl 436 (-0.03 dex), in the context of
preferential planet formation around metal-rich stars. We finally determine the
metallicity of the 47 brightest single M dwarfs in a volume limited sample, and
compare the metallicity distributions of solar-type and M-dwarf stars in the
solar neighbourhood.


title: The extended hard X-ray emission from the Vela Plerion

abstract:
  We present the results of a broad band (3-200 keV) spectral analysis of
BeppoSAX and XMM-Newton observations of the Vela plerion. The hard X-ray (> 15
keV) emission is found to be extended over a region of 12'-15' radius,
corresponding to a size of about 1.0--1.3 pc for a source distance of 290 pc. A
single power law does not give an acceptable fit while a broken power law or a
log-parabolic law nicely fit the data. The former spectral model has the photon
index Gamma_1 = 1.66 +/- 0.01 for energies lower than the break value equal to
12.5 keV and the index Gamma_2 = 2.01 +/- 0.05 up to about 200 keV. The total
X-ray luminosity of the Vela plerionis L_X=5.5E+33 erg/s, which implies a
conversion factor of the spin--down power of about 1.E-03.


title:
Cooling of Accelerated Nucleons and Neutrino Emission in Gamma-Ray
  Bursts

abstract:
  Using Monte Carlo simulations, we demonstrate photopion production from
Fermi-accelerated protons and the resulting neutrino production in gamma-ray
bursts. Unless internal shocks occur at quite large distance from the center,
ultra high-energy protons are depleted by photopion production and synchrotron
radiation. Internal shocks at fiducial distance cause neutrino bursts, which
accompany gamma-ray bursts originating from electromagnetic cascades.


title:
Discovery of > 200 RR Lyrae Variables in M62: An Oosterhoff I Globular
  Cluster with a Predominantly Blue HB

abstract:
  We report on the discovery of a large number of RR Lyrae variable stars in
the moderately metal-rich Galactic globular cluster M62 (NGC 6266), which
places it among the top three most RR Lyrae-rich globular clusters known.
Likely members of the cluster in our studied field, from our preliminary number
counts, include about 130 fundamental-mode (RRab) pulsators, with <P(ab)> =
0.548 d, and about 75 first-overtone (RRc) pulsators, with <P(c)> = 0.300 d.
The average periods and the position of the RRab variables with well-defined
light curves in the Bailey diagram both suggest that the cluster is of
Oosterhoff type I. However, the morphology of the cluster's horizontal branch
(HB) is strikingly similar to that of the Oosterhoff type II globular cluster
M15 (NGC 7078), with a dominant blue HB component and a very extended blue
tail. Since M15 and M62 differ in metallicity by about one dex, we conclude
that metallicity, at a fixed HB type, is a key parameter determining the
Oosterhoff status of a globular cluster and the position of its variables in
the Bailey diagram.


title: The E_{peak}^{rest} -E_{rad} correlation in GRBs in the BATSE catalog

abstract:
  The energy emission involved in a Gamma-Ray Burst evidently can be estimated
only provided that we know the distance to the source. The same is true for the
peak energy of the event in the source rest frame. Redshifts have been actually
measured only for about 40 events. In order to check if it is possible to
extend the $E_{peak}^{rest}$ - $E_{rad}$ relation originally found by
\citet{Am02} to a larger number of events, we make use of the pseudo-redshift
estimate proposed by \citet{Att03} and of the spectra published by
\citet{Band93}. We thus obtain a completely independent set of events which
indeed follows the same $E_{peak}^{rest}$ - $E_{rad}$ relation and confirms it.


title:
Final results of the EDELWEISS-I dark matter search with cryogenic
  heat-and-ionization Ge detectors

abstract:
  The final results of the EDELWEISS-I dark matter search using cryogenic
heat-and-ionization Ge detectors are presented. The final data sample
corresponds to an increase by a factor five in exposure relative to the
previously published results. A recoil energy threshold of 13 keV or better was
achieved with three 320g detectors working simultaneously over four months of
stable operation. Limits on the spin-independent cross-section for the
scattering of a WIMP on a nucleon are derived from an accumulated fiducial
exposure of 62 kg.d.


title: Sources of oscillation frequency increase with rising solar activity

abstract:
  We analyze and interpret SOHO/MDI data on oscillation frequency changes
between 1996 and 2004 focusing on differences between activity minimum and
maximum of solar cycle 23. We study only the behavior of the centroid
frequencies, which reflect changes averaged over spherical surfaces. Both the
f-mode and p-mode frequencies are correlated with general measures of the sun's
magnetic activity. However, the physics behind each of the two correlations is
quite different. We show that for the f-modes the dominant cause of the
frequency increase is the dynamical effect of the rising magnetic field. The
relevant rise must occur in subphotospheric layers reaching to some 0.5 - 0.7
kG at a depth of about 5 Mm. However, the implied constraints also require the
field change in the atmosphere to be so small that it has only a tiny dynamical
effect on p-mode frequencies. For p-modes, the most plausible explanation of
the frequency increase is a less than 2 percent decrease in the radial
component of the turbulent velocity in the outer layers. Lower velocity implies
a lower efficiency of the convective transport, hence lower temperature, which
also contributes to the p-mode frequency increase.


title: An Independent Derivation of the Oxford Jet Kinetic Luminosity Formula

abstract:
  This letter presents a theoretical derivation of an estimate for a radio
source jet kinetic luminosity. The expression yields jet powers that are
quantitatively similar to a more sophisticated empirical relation published by
the Willott, Blundell and Rawlings at Oxford. The formula allows one to
estimate the jet kinetic luminosity from the measurement of the optically thin
radio lobe emission in quasars and radio galaxies. Motivated by recent X-ray
observation, the derivation assumes that most of the energy in the lobes is in
plasma thermal energy with a negligible contribution from magnetic energy (not
equipartition). The close agreement of the two independent expressions makes
the veracity of these estimates seem very plausible.


title: Evidence for isotropic emission in GRB991216

abstract:
  The issue of the possible presence or absence of jets in GRBs is here
re-examined for GRB991216. We compare and contrast our theoretically predicted
afterglow luminosity in the 2-10 keV band for spherically symmetric versus
jetted emission. At these wavelenghts the jetted emission can be excluded and
data analysis confirms spherical symmetry. These theoretical fits are expected
to be improved by the forthcoming data of the Swift mission.


title:
A Re-brightening of the Radio Nebula associated with the 2004 December
  27 giant flare from SGR 1806--20

abstract:
  The 2004 Dec. 27 giant Gamma-ray flare detected from the magnetar SGR 1806-20
created an expanding radio nebula which we have monitored with the Australia
Telescope Compact Array and the Very Large Array. These data indicate that
there was an increase in the observed flux ~25 days after the initial flare
that lasted for ~8 days, which we believe is the result of ambient material
swept-up and shocked by this radio nebula. For a distance to SGR 1806-20 of 15
kpc, using the properties of this rebrightening we infer that the initial blast
wave was dominated by baryonic material of mass M>10^{24.5} g. For an initial
expansion velocity v~0.7c (as derived in an accompanying paper), we infer this
material had an initial kinetic energy E>10^{44.5} ergs. If this material
originated from the magnetar itself, it may have emitted a burst of ultra-high
energy (E > 1 TeV) neutrinos far brighter than that expected from other
astrophysical sources.


title: Constraints on Very High Energy gamma-ray emission from Gamma-Ray Bursts

abstract:
  The Milagro gamma-ray observatory employs a water Cherenkov detector to
observe extensive air showers produced by high energy particles interacting in
the Earth's atmosphere. Milagro has a wide field of view and high duty cycle,
monitoring the northern sky almost continuously in the 100 GeV to 100 TeV
energy range. Milagro is, thus, uniquely capable of searching for very
high-energy emission from gamma-ray bursts (GRBs) during the prompt emission
phase. Detection of >100 GeV counterparts would place powerful constraints on
GRB mechanisms. Twenty-five satellite-triggered GRBs occurred within the field
of view of Milagro between January 2000 and December 2001. We have searched for
counterparts to these GRBs and found no significant emission from any of the
burst positions. Due to the absorption of high-energy gamma rays by the
extragalactic background light, detections are only expected to be possible for
redshifts less than ~0.5. Three of the GRBs studied have measured redshifts.
GRB 010921 has a redshift low enough (0.45) to allow an upper limit on the
fluence to place an observational constraint on potential GRB models.