title:
A Near-Solar Metallicity, Nitrogen-Deficient Lyman Limit Absorber
  Associated with two S0 Galaxies

abstract:
  From UV spectra of the bright quasar PHL 1811 recorded by FUSE and the E140M
configuration on STIS, we have determined the abundances of various atomic
species in a Lyman limit system at z = 0.0809 with log N(H I) = 17.98.
Considerably more hydrogen may be in ionized form, since the abundances of C
II, Si II, S II and Fe II are very large compared to that of O I, when compared
to their respective solar abundance ratios. Our determination [O/H] = -0.19 in
the H I-bearing gas indicates that the chemical enrichment of the gas is
unusually high for an extragalactic QSO absorption system. However, this same
material has an unusually low abundance of nitrogen, [N/O] < -0.59, indicating
that there may not have been enough time during this enrichment for secondary
nitrogen to arise from low and intermediate mass stars. In an earlier
investigation we found two galaxies at nearly the same redshift as this
absorption system and displaced by 34 and 87 kpc from the line of sight. An
r-band image recorded by the ACS on HST indicates these are S0 galaxies. One or
both of these galaxies may be the source of the gas, which might have been
expelled in a fast wind, by tidal stripping, or by ram-pressure stripping.
Subtraction of the ACS point-spread function from the image of the QSO reveals
the presence of a face-on spiral galaxy under the glare of the quasar; although
it is possible that this galaxy may be responsible for the Lyman limit
absorption, the exact alignment of the QSO with the center of the galaxy
suggests that the spiral is the quasar host.


title: On the Nature of X-ray Sources in Early-Type Galaxies

abstract:
  We show that the observed relationship between the fraction of low-mass X-ray
binaries (LMXBs) found in globular clusters (GCs) and the GC-specific frequency
for early-type galaxies is consistent with an LMXB formation model in which the
field population of LMXBs is formed in situ via primordial binary formation.
The suggestion that a significant fraction of the field LMXB population in
early-type galaxies was formed in GCs is not required by the data. Finally, we
discuss observational studies that will test this model more thoroughly.


title: Bayesian model selection and isocurvature perturbations

abstract:
  Present cosmological data are well explained assuming purely adiabatic
perturbations, but an admixture of isocurvature perturbations is also
permitted. We use a Bayesian framework to compare the performance of
cosmological models including isocurvature modes with the purely adiabatic
case; this framework automatically and consistently penalizes models which use
more parameters to fit the data. We compute the Bayesian evidence for fits to a
dataset comprised of WMAP and other microwave anisotropy data, the galaxy power
spectrum from 2dFGRS and SDSS, and Type Ia supernovae luminosity distances. We
find that Bayesian model selection favours the purely adiabatic models, but so
far only at low significance.


title:
An overdensity of galaxies at z=5.9 +/-0.2 in the Ultra Deep Field
  confirmed using the ACS grism

abstract:
  We present grism spectra taken with the Advanced Camera for Surveys to
identify 29 red sources with (i'-z') > 0.9 in the Hubble Ultra Deep Field
(HUDF). Of these 23 are found to be galaxies at redshifts between z=5.4 and
6.7, identified by the break at 1216 angstrom due to IGM absorption; two are
late type dwarf stars with red colors; and four are galaxies with colors and
spectral shape similar to dust reddened or old galaxies at redshifts z~1-2.
This constitutes the largest uniform, flux-limited sample of spectroscopically
confirmed galaxies at such faint fluxes z'<27.5.
  Many are also among the most distant spectroscopically confirmed galaxies (at
redshifts up to z=6.7).
  We find a significant overdensity of galaxies at redshifts z=5.9 +/- 0.2.
Nearly two thirds of the galaxies in our sample (15/23) belong to this peak.
Taking into account the selection function and the redshift sensitivity of the
survey, we get a conservative overdensity of at least a factor of two along the
line-of-sight. The galaxies found in this redshift peak are also localized in
the plane of the sky in a non-random manner, occupying about half of the ACS
chip. Thus the volume overdensity is a factor of four. The star-formation rate
derived from detected sources in this overdense region is sufficient to
reionize the local IGM.


title:
An Overdensity of Lyman-alpha Emitters at Redshift z=5.7 near the Hubble
  Ultra Deep Field

abstract:
  We have identified an obvious and strong large scale structure at redshift
z=5.75 in a wide (31 by 33 arcminute) field, narrowband survey of the Chandra
Deep Field South region. This structure is traced by 17 candidate Lyman alpha
emitters, among which 12 are found in an 823nm filter (corresponding to Lyman
alpha at z=5.77 +- 0.03) and 5 in an 815nm image (z=5.70 +- 0.03). The Lyman
alpha emitters in both redshift bins are concentrated in one quadrant of the
field. The Hubble Ultra Deep Field, Chandra Deep Field South, and GOODS-South
fields all lie near the edge of this overdense region. Our results are
consistent with reports of an overdensity in the UDF region at z=5.9. This
structure is the highest redshift overdensity found so far.


title: Megaton Water Cerenkov Detectors and Astrophysical Neutrinos

abstract:
  Although formal proposals have not yet been made, the UNO and
Hyper-Kamiokande projects are being developed to follow-up the tremendously
successful program at Super-Kamiokande using a detector that is 20-50 times
larger. The potential of such a detector to continue the study of astrophysical
neutrinos is considered and contrasted with the program for cubic kilometer
neutrino observatories.


title:
Far-Ultraviolet Observations of the Globular Cluster NGC 2808 Revisited:
  Blue Stragglers, White Dwarfs and Cataclysmic Variables

abstract:
  We present a reanalysis of far-ultraviolet (FUV) observations of the globular
cluster NGC 2808 obtained with the Hubble Space Telescope. These data were
first analyzed by Brown and coworkers, with an emphasis on the bright, blue
horizontal branch (HB) stars in this cluster. Here, our focus is on the
population of fainter FUV sources, which include white dwarfs (WDs), blue
stragglers (BSs) and cataclysmic variables (CVs). We have therefore constructed
the deepest FUV-NUV colour-magnitude diagram of NGC 2808 and also searched for
variability among our FUV sources. Overall, we have found approx. 40 WD,
approx. 60 BS and approx. 60 CV candidates; three of the BSs and two of the CV
candidates are variable. We have also recovered a known RR Lyrae star in the
core of NGC 2808, which exhibits massive (approx. 4 mag) FUV variability. We
have investigated the radial distribution and found that our CV and BS
candidates are more centrally concentrated than the HBs and WD candidates. This
might be an effect of mass segregation, but could as well be due to the
preferential formation of such dynamically-formed objects in the dense cluster
core. For one of our CV candidates we found a counterpart in WFPC2 optical data
published by Piotto and coworkers.


title:
The Millennium Arecibo 21-cm Absorption Line Survey. IV. Statistics of
  Magnetic Field, Column Density, and Turbulence

abstract:
  We discuss observations of the magnetic field, column density, and turbulence
in the Cold Neutral Medium (CNM). The observed quantities are only indirectly
related to the intrinsic astronomical ones. We relate the observed and
intrinsic quantities by relating their univariate and bivariate probability
distribution functions (pdfs). We find that observations of the line-of-sight
component of magnetic field do not constrain the pdf of the total field very
well, but do constrain the median value of the total field.
  In the CNM, we find a well-defined median magnetic field 6.0 +/-1.8
microGauss. The CNM magnetic field dominates thermal motions. Turbulence and
magnetism are in approximate equipartition. We find the probability
distribution of HI column density Nperp in the sheets closely follows Nperp^-1
over a range of two orders of magnitude, 0.026 < Nperp < 2.6 (times 10^20
cm^-2). The bivariate distributions are not well enough determined to constrain
structural models of CNM sheets.


title:
Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies.
  I.Observational Results

abstract:
  We present optical spectra and emission-line ratios of 12 Narrow-Line Seyfert
1 (NLS1) galaxies that we observed to study the ionizing EUV continuum. A
common feature in the EUV continuum of active galactic nuclei is the big blue
bump (BBB), generally associated with thermal accretion disk emission. While
Galactic absorption prevents direct access to the EUV range, it can be mapped
by measuring the strength of a variety of forbidden optical emission lines that
respond to different EUV continuum regions. We find that narrow emission-line
ratios involving [OII]3727, Hbeta, [OIII]5007, [OI]6300, Halpha,[NII]6583, and
[SII]6716,6731 indicate no significant difference between NLS1s and Broad-Line
Seyfert 1 (BLS1) galaxies, which suggests that the spectral energy
distributions of their ionizing EUV - soft X-ray continua are similar. The
relative strength of important forbidden high ionization lines like [NeV]3426
compared to HeII4686 and the relative strength of [FeX]6374 appear to show the
same range as in BLS1 galaxies. However, a trend of weaker
F([OI]6300)/F(Halpha) emission-line ratios is indicated for NLS1s compared to
BLS1s. To recover the broad emission-line profiles we used Gaussian components.
This approach indicates that the broad Hbeta profile can be well described with
a broad component (FWHM = 3275 +- 800 km/s) and an intermediate broad component
(FWHM = 1200 +- 300 km/s). The width of the broad component is in the typical
range of normal BLS1s. The emission-line flux that is associated with the broad
component in these NLS1s amounts to at least 60% of the total flux. Thus it
dominates the total line flux, similar to BLS1 galaxies.


title:
A theoretical look at the direct detection of giant planets outside the
  Solar System

abstract:
  Astronomy is at times a science of unexpected discovery. When it is, and if
we are lucky, new intellectual territories emerge to challenge our views of the
cosmos. The recent indirect detections using high-precision Doppler
spectroscopy of now more than one hundred giant planets orbiting more than one
hundred nearby stars is an example of such rare serendipity. What has been
learned has shaken our preconceptions, for none of the planetary systems
discovered to date is like our own. However, the key to unlocking a planet's
chemical, structural, and evolutionary secrets is the direct detection of the
planet's light. I review the embryonic theory of the spectra, atmospheres, and
light curves of irradiated giant planets and put this theory into the context
of the many proposed astronomical campaigns to image them.


title:
Molecular Hydrogen in Star-forming regions: implementation of its
  micro-physics in Cloudy

abstract:
  Much of the baryonic matter in the Universe is in the form of H2 which
includes most of the gas in galactic and extragalactic interstellar clouds.
Molecular hydrogen plays a significant role in establishing the thermal balance
in many astrophysical environments and can be important as a spectral
diagnostic of the gas. Modeling and interpretation of observations of such
environments requires a quantitatively complete and accurate treatment of H2.
Using this micro-physical model of H2, illustrative calculations of
prototypical astrophysical environments are presented. This work forms the
foundation for future investigations of these and other environments where H2
is an important constituent.


title: Cl 1205+44, a fossil group at z = 0.59

abstract:
  This is a report of Chandra, XMM-Newton, HST and ARC observations of an
extended X-ray source at z = 0.59. The apparent member galaxies range from
spiral to elliptical and are all relatively red (i'-Ks about 3). We interpret
this object to be a fossil group based on the difference between the brightness
of the first and second brightest cluster members in the i'-band, and because
the rest-frame bolometric X-ray luminosity is about 9.2x10^43 h70^-2 erg s^-1.
This makes Cl 1205+44 the highest redshift fossil group yet reported. The
system also contains a central double-lobed radio galaxy which appears to be
growing via the accretion of smaller galaxies. We discuss the formation and
evolution of fossil groups in light of the high redshift of Cl 1205+44.


title: CMB Constraints on the Holographic Dark Energy Model

abstract:
  We calculate the angular scale of the acoustic oscillation from the BOOMERANG
and WMAP data on the cosmic microwave background (CMB) to constrain the
holographic dark energy model recently proposed by Li. We find that only the
phantom-like holographic dark energy survives the cosmological tests. This is,
however, inconsistent with the positive energy condition implicitly assumed in
constructing Li's model. Therefore the model is marginally ruled out by the
present CMB data. As a supplementary check, we also calculate the suppression
of the matter density fluctuation due to the late time integrated Sach-Wolfe
effect by the holographic dark energy, the result is within the tolerance of
the cosmic variance. Some aspect about the saturation of the cosmic holographic
bound is also discussed.


title:
Two alternative approaches to a stellar interior theory. Which of them
  is correct?

abstract:
  All fundamental physical principles are confirmed by numerous experiments and
practical certainty and have unambiguous interpretation. But physics of stars
is based on few measured effects only. It gives some freedom for figments of
the imagination. The goal of this paper is to compare two alternative
astrophysical models with measurement data.


title: Measuring Extinction Curves of Lensing Galaxies

abstract:
  We critique the method of constructing extinction curves of lensing galaxies
using multiply imaged QSOs. If one of the two QSO images is lightly reddened or
if the dust along both sightlines has the same properties then the method works
well and produces an extinction curve for the lensing galaxy. These cases are
likely rare and hard to confirm. However, if the dust along each sightline has
different properties then the resulting curve is no longer a measurement of
extinction. Instead, it is a measurement of the difference between two
extinction curves. This "lens difference curve'' does contain information about
the dust properties, but extracting a meaningful extinction curve is not
possible without additional, currently unknown information. As a quantitative
example, we show that the combination of two Cardelli, Clayton, & Mathis (CCM)
type extinction curves having different values of R(V) will produce a CCM
extinction curve with a value of R(V) which is dependent on the individual R(V)
values and the ratio of V band extinctions. The resulting lens difference curve
is not an average of the dust along the two sightlines. We find that lens
difference curves with any value of R(V), even negative values, can be produced
by a combination of two reddened sightlines with different CCM extinction
curves with R(V) values consistent with Milky Way dust (2.1 < R(V) < 5.6). This
may explain extreme values of R(V) inferred by this method in previous studies.
But lens difference curves with more normal values of R(V) are just as likely
to be composed of two dust extinction curves with R(V) values different than
that of the lens difference curve. While it is not possible to determine the
individual extinction curves making up a lens difference curve, there is
information about a galaxy's dust contained in the lens difference curves.


title: V838 Mon: light echo evolution and distance estimate

abstract:
  Following its 2002 February eruption, V838 Mon developed a light echo that
continues to expand and evolve as light from the outburst scatters off
progressively more distant circumstellar and/or interstellar material.
Multi-filter images of the light echo, obtained with the South African
Astronomical Observatory (SAAO) 1.0-m telescope between 2002 May and 2004
December, are analysed and made available electronically. The expansion of the
light echo is measured from the images and the data compared with models for
scattering by a thin sheet and a thin shell of dust. From these model results
we infer that the dust is likely in the form of a thin sheet distant from the
star, suggesting that the material is of interstellar origin, rather than being
from earlier stages in the star's evolution. Although the fit is uncertain, we
derive a stellar distance of ~ 9 kpc and a star-dust distance of ~ 5 pc, in
good agreement with recent results reported from other methods. We also present
JHKL and Cousins UBVRI photometry obtained at the SAAO during the star's
second, third and fourth observing seasons post-outburst. These data show
complex infrared colour behaviour while V838 Mon is slowly brightening in the
optical.


title: Quasar Lensing Statistics and Omega_Lambda: What Went Wrong?

abstract:
  In the pre-WMAP, pre-Supernova-Ia-Hubble-diagram era, quasar lensing
statistics stubbornly indicated low values of Omega_Lambda. In contrast, a
number of recent lensing statistics studies either find the data support the
standard Lambda-CDM picture, or simply take the standard cosmological
parameters as a given. Have the data or the analyses changed or improved, and
how? I review several of the ``historical'' and the more recent studies, and
show that there is no particular measurement, assumption, or model parameter in
the old studies that was grossly wrong. Instead, at least several effects,
operating together, are likely required in order to achieve agreement between
the observations and the currently standard cosmology. Most likely among these
effects are: a somewhat lower lensing cross section for elliptical galaxies
than assumed in the past; some loss of lensed quasars in optical samples due to
extinction by the lenses; and a somewhat lower-than-standard value of
Omega_Lambda ~ 0.6. The agreement between recent model calculations and the
results of radio lens surveys may be fortuitous, and due to a cancellation
between the errors in the input parameters for the lens population and the
cosmology, on the one hand, and for the source population, on the other hand.


title: Supernova Rates in Galaxy Clusters

abstract:
  Measurements of SN rates in different environments and redshifts can shed
light on the nature of SN-Ia progenitors, star formation history, and chemical
enrichment history. I summarize some recent work by our group in this area, and
discuss the implications. The current evidence favors production of most of the
iron in the ICM (and perhaps everywhere) by core-collapse SNe, rather than
SNe-Ia. These SNe may have been produced by the first, top-heavy-IMF,
generation of stars that reionized the Universe. Improved rate measurements can
sharpen the picture, and I describe our recent efforts in this direction.


title: Optical follow-up of BL Lac candidates in the 2BL sample

abstract:
  We investigate the nature of the BL Lac candidates in the northern part of
the 2BL sample (\cite{Londish02}) searching for optical variability by means of
$R_C$ band photometry with the Asiago 1.8 and Loiano 1.5 meter telescopes
during years 2002, 2003 and 2004. We also made aperture photometry of the
candidates on the plates available on the web from the Palomar and UK Schmidt
telescopes. No significant variability was detected for the majority of the
objects without detected radio and/or X-ray emissions, while clear variability
was found for the few sources of the sample with strong radio and/or X-ray
emission, which is a constant feature of the "classical" BL Lacs. Some
considerations on the nature of the 2BL sources are made, taking into account
their most recent data available in proper motions catalogues (SuperCOSMOS,
USNO-B1) and in the Sloan Digital Sky Survey.


title:
First Release of Gauss-Legendre Sky Pixelization (GLESP) software
  package for CMB analysis

abstract:
  We report the release of the Gauss--Legendre Sky Pixelization (GLESP)
software package version 1.0. In this report we present the main features and
functions for processing and manipulation of sky signals. Features for CMB
polarization is underway and to be incorporated in a future release. Interested
readers can visit http://www.glesp.nbi.dk (www.glesp.nbi.dk) and register for
receiving the package.


title: Magnetic fields of B and Herbig Ae stars measured with FORS1 at the VLT

abstract:
  We present the results of a magnetic survey with FORS1 in polarimetric mode
of a sample of B and Herbig Ae stars with previously undetected magnetic
fields. For the first time a mean longitudinal magnetic field at a level higher
than 3 sigma has been detected in one normal B star, two HgMn stars, one PGa
star and four SPB stars. The observations of the three Herbig Ae stars (also
known as Vega-like stars) reveal a definite longitudinal magnetic field in the
star HD139614 at 4.8 sigma level: <B_z>=-450+-93 G. This is the largest
magnetic field ever diagnosed for a Herbig Ae star. A hint of a magnetic field
is found in the other two stars, HD144432 and HD144668, for which magnetic
fields are measured at the ~1.6 sigma and ~2.5 sigma level respectively.


title:
Evolution of Magnetic Fields in Stars Across the Upper Main Sequence:
  Results from Recent Measurements with FORS 1 at the VLT

abstract:
  We rediscuss the evolutionary state of upper main sequence magnetic stars
using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and
definitely determined longitudinal magnetic fields. FORS1 at the VLT in
spectropolarimetric mode has been used to carry out a systematic search for
magnetic fields in chemically peculiar stars whose magnetic field has never
been studied before. We confirm our previous results obtained from the study of
Ap and Bp stars with accurate measurements of the mean magnetic field modulus
and mean quadratic magnetic fields that the distribution of the magnetic stars
of mass below 3 M_o differs significantly from that of normal stars in the same
temperature range. Normal A stars occupy the whole width of the main sequence,
without a gap, whereas magnetic stars are concentrated towards the centre of
the main-sequence band. We show that, in contrast, higher mass magnetic Bp
stars may well occupy the whole main-sequence width.


title: Rotation periods for stars of the TW Hydrae association

abstract:
  We have conducted a photometric study of late-type members of the TW Hydrae
association (TWA) and measured the rotation periods for 16 stars in 12 systems.
For TWA stars listed by Webb et al. and Sterzik et al. (TWA 1-13; led by TW Hya
= TWA 1) we find a median period of 4.7 d. However, for stars that we measured
in the TWA 14-19 group identified by Zuckerman et al., we find a median period
of only 0.7 d. The period distributions of the two groups cannot be reconciled
at the 3-sigma significance level. Using photometric arguments supported by the
Hipparcos distance to HD 102458 (= TWA 19A), we find that TWA 14-19 reside at
an average distance of d \approx 90 pc, spatially at the near boundary of the
Lower Centaurus-Crux (LCC) subgroup of the Ophiuchus-Scorpius-Centaurus OB-star
association (OSCA). Proper motions for HD 102458, TWA 14, 18 and 19B link these
stars to the LCC subgroup. From Hertzsprung-Russell (H-R) diagram placement, we
derive an age of \approx 17 Myr for the HD 102458 system that may be the
representative age for the TWA 14-19 group. Merging various lines of evidence,
we conclude that these stars form a spatially- and rotationally-distinct
population of older pre-main sequence (PMS) stars, rather than being an
extension of the TWA beyond those stars associated with TW Hya that have an age
of \sim 10 Myr and reside at d \approx 55 pc. Instead, TWA 14-19 likely
represent the population of low-mass stars still physically associated with the
LCC subgroup.


title:
Photometric biases due to stellar blending: implications for measuring
  distances, constraining binarity and detecting exoplanetary transits

abstract:
  We investigate blending, binarity and photometric biases in crowded-field CCD
imaging. For this, we consider random blend losses, which correspond to the
total number of stars left undetected in unresolved blends. We present a simple
formula to estimate blend losses, which can be converted to apparent magnitude
biases using the luminosity function of the analyzed sample. Because of the
used assumptions, our results give lower limits of the total bias and we show
that in some cases even these limits point toward significant limitations in
measuring apparent brightnesses of ``standard candle'' stars, thus distances to
nearby galaxies. A special application is presented for the OGLE-II BVI maps of
the Large Magellanic Cloud. We find a previously neglected systematic bias up
to 0.2-0.3 mag for faint stars (V~18.0-19.0) in the OGLE-II sample, which
affects LMC distance measurements using RR Lyrae and red clump stars. We also
consider the effects of intrinsic stellar correlations, i.e. binarity, via
calculating two-point correlation functions for stellar fields around seven
recently exploded classical novae. In two cases, for V1494 Aql and V705 Cas,
the reported close optical companions seem to be physically correlated with the
cataclysmic systems. Finally, we find significant blend frequencies up to
50-60% in the samples of wide-field exoplanetary surveys, which suggests that
blending calculations are highly advisable to be included into the regular
reduction procedure.


title:
A Statistical Study of Gamma-Ray Emitting Solar Flares Observed with
  Yohkoh

abstract:
  Gamma-ray emitting solar flares observed with Yohkoh were analyzed from a
statistical viewpoint. The four-band hard X-ray (15--95 keV) photometric data,
taken with the Hard X-ray Telescope onboard Yohkoh, were utilized in
combination with the spectro-photometric gamma-ray (0.2--30 MeV) data obtained
with the Gamma-Ray Spectrometer. The GOES class was also incorporated. Out of
2788 X-ray flares observed from 1991 October to 2001 December, 178 events with
strong hard X-ray emission were selected. Among them, 40 flares were further
found to show significant gamma-ray emission. A fractal dimension analysis and
multi-band color--color plots of the 40 flares suggest that their soft X-ray to
MeV gamma-ray spectral energy distributions involve at least four independent
parameters. These are: (1) the overall flare size; (2) the relative intensities
of the thermal vs. non-thermal signals; (3) the gamma-ray to hard X-ray
intensity ratio; and (4) the hard X-ray spectral slope. These results are
examined for possible selection effects. Also, the meanings of the third
parameter are briefly considered.


title:
Super Helium-Rich Population and the Origin of Extreme Horizontal-Branch
  Stars in Globular Clusters

abstract:
  Recent observations for the color-magnitude diagrams (CMDs) of the massive
globular cluster Omega Centauri have shown that it has a striking double main
sequence (MS), with a minority population of bluer and fainter MS well
separated from a majority population of MS stars. Here we confirm, with the
most up-to-date Y2 isochrones, that this special feature can only be reproduced
by assuming a large variation (Delta Y = 0.15) of primordial helium abundance
among several distinct populations in this cluster. We further show that the
same helium enhancement required for this special feature on the MS can by
itself reproduce the extreme horizontal-branch (HB) stars observed in Omega
Cen, which are hotter than normal HB stars. Similarly, the complex features on
the HBs of other globular clusters, such as NGC 2808, are explained by large
internal variations of helium abundance. Supporting evidence for the
helium-rich population is also provided by the far-UV (FUV) observations of
extreme HB stars in these clusters, where the enhancement of helium can
naturally explain the observed fainter FUV luminosity for these stars. The
presence of super helium-rich populations in some globular clusters suggests
that the third parameter, other than metallicity and age, also influences CMD
morphology of these clusters.


title:
A small X-ray corona of the narrow-angle tail radio galaxy NGC 1265
  soaring through the Perseus cluster

abstract:
  A deep Chandra observation of NGC 1265 (3C 83.1B), the prototype for the
narrow-angled-tailed (NAT) radio galaxy, reveals a small cool X-ray thermal
corona (~ 0.6 keV) embedded in the hot ICM of the Perseus cluster (~ 6.7 keV).
The corona is asymmetric with a sharp edge (~ 2.2'', or 0.8 kpc from the
nucleus) to the south and an extension to the north (at least ~ 8'' from the
nucleus), which is interpreted as the action of ram pressure while solely the
static ICM confinement is unable to explain. We estimate that the corona is
moving with a velocity of ~ 2.4 - 4.2 times the local sound speed to the south.
The presence of the sharp edge for this small corona indicates that the
transport processes are largely suppressed by the magnetic field there. The
magnetic field around the corona also suppresses heat conduction by at least a
factor of ~ 60 across the corona boundary. We conclude that it is unrealistic
to study the interaction of the small X-ray coronae with the hot ICM without
the consideration of the roles that magnetic field plays, a factor not included
in current simulations. An absorbed (N_H=1.5-3x10^22 cm^-2) nucleus is also
detected, which is not usual for FR I radio galaxies. Weak X-ray emission from
three inner radio knots in the jets is also detected. Indentations at the east
and west of the corona indicate interaction between the jets and the X-ray
corona. Narrow jets carry great amounts of energy out of the central AGN and
release the energy outside the corona, preserving the tiny and vulnerable
corona. This case reveals that the inner kpc core of the corona of massive
galaxies can survive both high-speed stripping and powerful AGN feedback. Thus,
the cooling of the X-ray coronae potentially provides fuel to the central SMBH
in rich environments where the amount of the galactic cold gas is at a minimum.


title: Turbulence Generation by Substructure Motion in Clusters of Galaxies

abstract:
  Clusters of galaxies form through major merger and/or absorption of smaller
groups. In fact, some characteristic structures such as cold fronts, which are
likely relevant to moving substructures, are found by {\it Chandra}. It is
expected that moving substructures generate turbulence in the intracluster
medium (ICM). Such turbulence probably plays a crucial role in mixture and
transport of gas energy and heavy elements, and particle acceleration. The {\it
Astro-E2} satellite, which is planned to be launched in 2005, will detect
broadened lines due to turbulent motion. In order to explore the
above-mentioned issues, it is important to investigate the generation processes
and structure of ICM turbulence. We investigate the ICM dynamical evolution in
and around a moving substructure with three-dimensional hydrodynamical
simulations. Eddy-like structures develop near the boundary between the
substructure and the ambient ICM through Kelvin-Helmholtz instabilities.
Because of these structures, characteristic patterns appear in the
line-of-sight velocity distribution of the ICM.


title:
Structure and kinematics of edge-on galaxy discs -- V. The dynamics of
  the stellar discs

abstract:
  In earlier papers in this series we determined the intrinsic stellar disc
kinematics of fifteen intermediate to late type edge-on spiral galaxies using a
dynamical modeling technique. From the photometry we find that intrinsically
more flattened discs tend to have a lower face-on central surface brightness
and a larger dynamica mass-to-light ratio. This observation suggests that at a
constant maximum rotational velocity lower surface brightness discs have
smaller vertical stellar velocity dispersions.Although the individual
uncertainties are large, we find from the dynamical modeling that at least
twelve discs are submaximal. The average disc contributes 53$\pm$4 percent to
the observed rotation at 2.2 disc scalelengths, with a 1$\sigma$ scatter of 15
percent. This percentage becomes somewhat lower when effects of finite disc
flattening and gravity by the dark halo and the gas are taken into account.
Since boxy and peanut-shaped bulges are probably associated with bars, the
result suggests that at 2.2$h_{\rm R}$ the submaximal nature of discs is
independent of barredness. The possibility remains that very high surface
brightness discs are maximal.We confirm that the radial stellar disc velocity
dispersion is related to the galaxy maximum rotational velocity. The scatter in
this $\sigma-v_{\rm max}$ relation appears to correlate with the disc
flattening, face-on central surface brightness and dynamical mass-to-light
ratio. Low surface brightness discs tend to be more flattened and have smaller
stellar velocity dispersions. The findings are consistent with the observed
correlation between disc flattening and dynamical mass-to-light ratio.


title: Comparison of map-making algorithms for CMB experiments

abstract:
  We have compared the cosmic microwave background (CMB) temperature anisotropy
maps made from one-year time ordered data (TOD) streams that simulated
observations of the originally planned 100 GHz Planck Low Frequency Instrument
(LFI). The maps were made with three different codes. Two of these, ROMA and
MapCUMBA, were implementations of maximum-likelihood (ML) map-making, whereas
the third was an implementation of the destriping algorithm. The purpose of
this paper is to compare these two methods, ML and destriping, in terms of the
maps they produce and the angular power spectrum estimates derived from these
maps. The difference in the maps produced by the two ML codes was found to be
negligible. As expected, ML was found to produce maps with lower residual noise
than destriping. In addition to residual noise, the maps also contain an error
which is due to the effect of subpixel structure in the signal on the
map-making method. This error is larger for ML than for destriping. If this
error is not corrected a bias will be introduced in the power spectrum
estimates. This study is related to Planck activities.


title:
An estimate of the SN kick velocities for High Mass X-ray Binaries in
  the SMC

abstract:
  This work investigates the possible supernova kick velocities imposed on HMXB
systems in the Small Magellanic Cloud. Comparisons are made between the
location of such systems and the locations of young, stellar clusters on the
premise that these may represent the birthplace of many of these systems.
Measurements of the separation of clusters and HMXBs,and an estimate of the
typical lifetimes of these systems, leads to a minimum average space velocity
30 km/s. This value is compared to theoretical estimates.


title: Modeling the Photopolarimetric Variability of AA Tau

abstract:
  We present Monte Carlo scattered light models of a warped disk that reproduce
the observed photopolarimetric variability of the classical T Tauri star AA
Tau. For a system inclination of 75 deg and using an analytic description for a
warped inner disk, we find that the shape and amplitude of the
photopolarimetric variability are reproduced with a warp which occults the
star, located at 0.07 au, amplitude 0.016 au, extending over radial and
azimuthal ranges 0.0084 au and 145 deg. We also show a time sequence of high
spatial resolution scattered light images, showing a dark shadow cast by the
warp sweeping round the disk. Using a modified smooth particle hydrodynamics
code, we find that a stellar dipole magnetic field of strength 5.2 kG, inclined
at 30 deg to the stellar rotation axis can reproduce the required disk warping
to explain AA Tau's photopolarimetric variability.


title:
Discovery of the INTEGRAL X/Gamma-ray transient IGR J00291+5934: a
  Comptonised accreting ms pulsar ?

abstract:
  We report the discovery of a high-energy transient with the IBIS/ISGRI
detector on board the INTEGRAL observatory. The source, namely IGR J00291+5934,
was first detected on 2nd December 2004 in the routine monitoring of the
IBIS/ISGRI 20--60 keV images. The observations were conducted during Galactic
Plane Scans, which are a key part of the INTEGRAL Core Programme observations.
After verifying the basic source behaviour, the discovery was announced on 3rd
December. The transient shows a hard Comptonised spectrum, with peak energy
release at about 20 keV and a total luminosity of ~ 0.9E36 erg/s in the 5--100
keV range, assuming a distance of 3 kpc. Following the INTEGRAL announcement of
the discovery of IGR J00291+5934, a number of observations were made by other
instruments. We summarise the results of those observations and, together with
the INTEGRAL data, identifiy IGR J00291+5934 as the 6th member of a class of
accreting X-ray millisecond pulsars.


title:
New insights into the structure of early-type galaxies: the Photometric
  Plane at z~0.3

abstract:
  We study the Photometric Plane (PHP), namely the relation between the
effective radius re, the mean surface brightness within that radius <mi>e, and
the Sersic index n, in optical (R and I) and near-infrared (K) bands for a
large sample of early-type galaxies (ETGs) in the rich cluster MS1008-1224 at
z=0.306. The PHP relation has an intrinsic dispersion of ~32% in re, and turns
out to be independent of waveband. This result is consistent with the fact that
internal colour gradients of ETGs can have only a mild dependence on galaxy
luminosity (mass). There is no evidence for a significant curvature in the PHP.
We show that this can be explained if this relation origins from a systematic
variation of the specific entropy of ETGs along the galaxy sequence, as was
suggested from previous works. The intrinsic scatter of the PHP is
significantly smaller than for other purely photometric relations, such as the
Kormendy relation and the photometric Fundamental Plane, which is constructed
by using colours in place of velocity dispersions. The scatter does not depend
on the waveband and the residuals about the plane do not correlate with
residuals of the colour-magnitude relation. Finally, we compare the
coefficients of the PHP at z~0.3 with those of ETGs at z~0, showing that the
PHP is a valuable tool to constrain the luminosity evolution of ETGs with
redshift. The slopes of the PHP do not change significantly with redshift,
while the zero-point is consistent with cosmological dimming of the surface
brightness in an expanding universe plus the passive fading of galaxy stellar
populations with a high formation redshift (z_f >1-2).


title: Statistics of gravitational lenses in the clumpy Universe

abstract:
  We evaluate the effect of small scale inhomogeneities on large scale
observations within the statistics of gravitationally lensed quasars. At this
aim, we consider a cosmological model whose large scale properties (dynamics,
matter distribution) are the same as in Friedmann-Lemaitre models, but whose
matter distribution is locally inhomogeneous. We use the well known Dyer-Roder
distances to allow a simple analytical expression of the optical depth, and pay
particular attention on the different role played by the different notions of
distances (filled beam angular diameter distance and Dyer-Roder distances) when
calculating this quantity, following the prescription from Ehlers & Schneider
for a coherent formalism. We find that the expected number of gravitationally
lensed quasars is a decreasing function of the clumpiness parameter.


title: Multimode Resonant Coupling in Pulsating Stars

abstract:
  We consider evolution of an unstable acoustic mode interacting with an
ensemble of stable g-modes. We show that the static multimode solution does not
exist. We then find the condition for the stability of the statistical
equilibrium.
  Performing numerical integration of amplitude equations for a simplified
system we find that the acoustic mode amplitude exhibits a large irregular
variability on the timescale given by the inverse of the growth rate.
  The g-mode pairs are excited in significantly wider range of detuning
parameters than it is implied by the parametric instability criterion applied
to the average amplitude. However, the number of interacting g-mode pairs is
reduced because the pairs differing in the detuning parameter by less than
their damping rates are synchronized and effectively act as a single pair.
  We apply the multimode resonant coupling theory to a realistic stellar model.
We choose a seismic model of the Delta Scuti star XX Pyxidis. Although for some
l=2 modes we find amplitudes of the order of a few milimagnitudes, the typical
amplitudes of low-degree modes are much higher. Taking into account the
rotational splitting results in decrease of amplitudes by a factor of few which
is not enough to obtain consistency with observations. We conclude that in this
star and likely in all evolved Delta Scuti stars, the resonant mode coupling
cannot be the dominant amplitude limiting effect. The nonresonant saturation of
the driving effect must play the role.


title: The Stellar Populations of M31 Halo Substructure

abstract:
  We present the first results from our survey of stellar substructure in the
outskirts of M31 using the Advanced Camera for Surveys (ACS) on board the
Hubble Space Telescope. We discuss the stellar populations associated with five
prominent stellar overdensities discovered during the course of our panoramic
ground-based imaging survey with the Isaac Newton Telescope Wide-Field Camera
(INT WFC); a sixth pointing targets a region of `clean' halo. The
colour-magnitude diagrams (CMDs), which contain between ~10,000--90,000 stars
and reach four magnitudes below the horizontal branch, reveal clear variations
in morphology between most fields, indicating that the age and/or metallicity
mix of stars is not constant at large radius. This directly confirms the
existence of large-scale population inhomogeneities within the halo of M31 and
lends further support to the notion that M31 has formed, at least in part,
through satellite accretions. We find a striking similarity between the
populations of the giant stellar stream and those of another overdensity, the
NE shelf, which lies north-east of the galaxy center. If these overdensities
are associated with the same population, then the difference in their red clump
magnitudes implies the NE shelf lies in front of the stream by several tens of
kpc, in good agreement with recent orbit calculations for the stream
progenitor.


title:
Search for TeV emission from the region around PSR B1706-44 with the
  H.E.S.S. experiment

abstract:
  The region around PSR B1706-44 has been observed with the H.E.S.S. imaging
atmospheric Cherenkov telescopes in 2003. No evidence for gamma-ray emission in
the TeV range was found at the pulsar position or at the radio arc which
corresponds to the supernova remnant G 343.1-2.3. The 99% confidence level flux
upper limit at the pulsar position is Ful(E > 350GeV) = 1.4e-12 /cm^2/s
assuming a power law with photon index of 2.5 and Ful(E > 500GeV) = 1.3e-12
/cm^2/s without an assumption on the spectral shape. The reported upper limits
correspond to 8% of the flux from an earlier detection by the CANGAROO
experiment.


title: Spitzer and ISO Galaxy Counts in the Mid-Infrared

abstract:
  Galaxy source counts that simultaneously fit the deep mid-infrared surveys at
24 microns and 15 microns made by the Spitzer Space Telescope and the Infrared
Space Observatory (ISO) respectively are presented for two phenomenological
models. The models are based on starburst and luminous infrared galaxy
dominated populations. Both models produce excellent fits to the counts in both
wavebands and provide an explanation for the high redshift population seen in
the longer Spitzer 24 micron band supporting the hypothesis that they are
luminous-ultraluminous infrared galaxies at z=2-3, being the mid-infrared
counterparts to the sub-mm galaxy population. The source counts are
characterized by strong evolution to redshift unity, followed by less drastic
evolution to higher redshift. The number-redshift distributions in both
wavebands are well explained by the effect of the many mid-infrared features
passing through the observation windows. The sharp upturn at around a
milliJansky in the 15 micron counts in particular depends critically on the
distribution of mid-infrared features around 12 microns, in the assumed
spectral energy distribution.


title: On Star Formation and the Non-Existence of Dark Galaxies

abstract:
  We investigate whether a baryonic dark galaxy or `galaxy without stars' could
persist indefinitely in the local universe, while remaining stable against star
formation. To this end, a simple model has been constructed to determine the
equilibrium distribution and composition of a gaseous protogalactic disk.
Specifically, we determine the amount of gas that will transit to a Toomre
unstable cold phase via the H2 cooling channel in the presence of a UV--X-ray
cosmic background radiation field.
  All but one of the models are predicted to become unstable to star formation.
Moreover, we find that all our model objects would be detectable via HI line
emission, even in the case that star formation is potentially avoided. These
results are consistent with the non-detection of isolated extragalactic HI
clouds with no optical counterpart (galaxies without stars) by HIPASS.
  Additionally, where star formation is predicted to occur, we determine the
minimum interstellar radiation field required to restore gravothermal
stability, which we then relate to a minimum global star formation rate. This
leads to the prediction of a previously undocumented relation between HI mass
and star formation rate that is observed for a wide variety of dwarf galaxies
in the HI mass range 10^8--10^10 M_sun. The existence of such a relation
strongly supports the notion that the well observed population of dwarf
galaxies represent the minimum rates of self-regulating star formation in the
universe. (Barely abridged)


title:
Cosmological evolution of Alpha driven by a general coupling with
  Quintessence

abstract:
  A general model for the cosmological evolution of the fine structure constant
\alpha driven by a typical Quintessence scenario is presented. We consider a
coupling between the Quintessence scalar \phi and the electromagnetic kinetic
term F^2, given by a general function B_F(\phi). We study the dependence of the
cosmological \Delta\alpha(t) upon the functional form of B_F and discuss the
constraints imposed by the data. We find that different cosmological histories
for \Delta\alpha(t) are possible within the avaliable constraints. We also find
that Quasar absorption spectra evidence for a time variation of alpha, if
confirmed, is not incompatible with Oklo and meteorites limits.


title: Broad band variability of SS433: Accretion disk at work?

abstract:
  We present broad band power spectra of variations of SS433 in radio, optical
and X-ray spectral bands. We show that at frequencies lower than 1e-5 Hz the
source demonstrates the same variability pattern in all these bands. The broad
band power spectrum can be fitted by one power law down to frequencies ~1e-7 Hz
with flattening afterwards. Such a flattening means that on time scales longer
than ~1e7 sec the source variability becomes uncorrelated. This naturally leads
to the appearance of quasi-poissonian flares in the source light curve, which
have been regularly observed in radio and optical spectral bands. The radio
flux power spectrum appears to have a second break at Fourier frequencies ~1e-5
Hz which can be caused by the smearing of the intrinsic radio variability on
timescale of the light-crossing time of the radio emitting region. We find a
correlation of the radio and optical fluxes of SS433 and the radio flux is
delayed by about ~2 days with respect to the optical one. Power spectra of
optical and X-ray variabilities continue with the same power law from 1e-7 Hz
up to ~0.01-0.05 Hz. The broad band power spectrum of SS433 can be interpreted
in terms of self-similar accretion rate modulations in the accretion disk
proposed by Lyubarskii (1997) and elaborated by Churazov et al. (2001). We
discuss a viscous time-scale in the accretion disk of SS433 in implication to
the observed broad band power spectrum.


title:
Detection of thermal X-ray emission in the halo of the plerionic
  supernova remnant G21.5-0.9

abstract:
  The detection of a soft thermal X-ray component in the spectrum of a bright
knot in the halo of the plerion G21.5-0.9 is reported. Using a collisional
ionization equilibrium model for an hot optically thin plasma, a temperature
$kT=0.12-0.24$ kev, a mass of 0.3--1.0 M$_\odot$ and a density of 1.6-6
cm$^{-3}$ is derived. The spectral analysis suggests a possible overabundance
of Silicon with respect to the solar value in the knot; if this will be
confirmed this object may be a clump of shocked ejecta.


title:
Discovering Gravitational Lenses Through Measurements Of Their Time
  Delays

abstract:
  We consider the possibility that future wide-field time-domain optical
imaging surveys may be able to discover gravitationally lensed quasar pairs
through serendipitous measurements of their time delays. We discuss the merits
such a discovery technique would have relative to conventional lens searches.
Using simulated quasar lightcurves, we demonstrate that in a survey which
observes objects several times each lunar cycle over the course of five years,
it is possible to improve the efficiency of a gravitational lens search by 2-3
orders of magnitude through the use of time delay selection. In the most
advantageous scenario considered, we are able to improve efficiency by a factor
of 1000 with no loss of completeness. In the least advantageous scenario, we
are able to improve efficiency by a factor of 110 while reducing completeness
by a factor of 9. We show that window function effects associated with the
length of the observing season are more important than the total number of
datapoints in determining the effectiveness of this method. We also
qualitatively discuss several complications which might be relevant to a real
time delay search.


title:
Bayesian Analysis of the (Generalized) Chaplygin Gas and Cosmological
  Constant Models using the 157 gold SNe Ia Data

abstract:
  The generalized Chaplygin gas model (GCGM) contains 5 free parameters, here,
they are constrained through the type Ia supernovae data, i.e., the ``gold
sample'' of 157 supernovae data. Negative and large positive values for
$\alpha$ are taken into account. The analysis is made by employing the Bayesian
statistics and the prediction for each parameter is obtained by marginalizing
on the remained ones. This procedure leads to the following predictions:
$\alpha = - 0.75^{+4.04}_{-0.24}$, $H_0=65.00^{+1.77}_{-1.75}$, $\Omega_{k0} =
- 0.77^{+1.14}_{-5.94}$, $\Omega_{m0} = 0.00^{+1.95}_{-0.00}$, $\Omega_{c0} =
1.36^{+5.36}_{-0.85}$, $\bar A = 1.000^{+0.000}_{-0.534}$. Through the same
analysis the specific case of the ordinary Chaplygin gas model (CGM), for which
$\alpha = 1$, is studied. In this case, there are now four free parameters and
the predictions for them are: $H_0 = 65.01^{+1.81}_{-1.71}$, $\Omega_{k0} = -
2.73^{+1.53}_{-0.97}$, $\Omega_{m0} = 0.00^{+1.22}_{-0.00}$, $\Omega_{c0} =
1.34^{+0.94}_{-0.70}$, $\bar A = 1.000^{+0.000}_{-0.270}$. To complete the
analysis the $\Lambda$CDM, with its three free parameters, is considered. For
all these models, particular cases are considered where one or two parameters
are fixed. The age of the Universe, the deceleration parameter and the moment
the Universe begins to accelerate are also evaluated. The quartessence
scenario, is favoured. A closed (and in some cases a flat) and accelerating
Universe is also preferred. The CGM case $\alpha = 1$ is far from been ruled
out, and it is even preferred in some particular cases. In most of the cases
the $\Lambda$CDM is disfavoured with respect to GCGM and CGM.


title:
A Discovery of Rapid Optical Flares from Low-Luminosity Active Nuclei in
  Massive Galaxies

abstract:
  We report a serendipitous discovery of six very low-luminosity active
galactic nuclei (AGNs) only by optical variability in one-month baseline. The
detected flux variability is ~ 1-5% of the total luminosity of host galaxies.
Careful subtraction of host galaxy components in nuclear regions indicates that
the fractional variability (Delta F / F) of the nuclei is of order unity. At
least one of them is showing a compelling flaring activity within just a few
days, which appears to be quite different from previously known AGN
variability. We obtained spectroscopic data for the one showing the largest
flare and confirmed that it is in fact an AGN at z = 0.33 with an estimated
black hole mass of ~10^8 M_sun. As a possible interpretation, we suggest that
these activities are coming from the region around the black hole event
horizon, which is physically similar to the recently discovered near-infrared
flares of our Galactic nucleus. It is indicated that our Galaxy is not special,
and that surprisingly rapid flaring activity in optical/near-infrared bands may
be commonly hidden in nuclei of apparently normal galaxies with low Eddington
ratios, in contrast to the variability of well-studied luminous AGNs or
quasars.


title: XMM-Newton Observations of High Redshift Quasars

abstract:
  We report on our XMM observations of the high redshift quasars BR 2237--0607
(z=4.558) and BR 0351--1034 (z=4.351), together with 14 other z>4 objects found
in the XMM public archive. Contrary to former reports, we do not find high
redshift radio-loud quasars to be more absorbed than their radio-quiet
counterparts. We find that the optical to X-ray spectral index alpha-ox is
correlated with the luminosity density at 2500 A, but does not show a
correlation with redshift. The mean 2-10 keV power-law slope of the 9 high
redshift radio-quiet quasars in our sample for which a spectral analysis can be
performed is alpha-x1.23+-0.48, similar to alpha-x=1.19 found from the ASCA
observations of low redshift Narrow-Line Seyfert 1 galaxies (NLS1s), and
significantly different from alpha-x=0.78 found for low redshift Broad-Line
Seyfert galaxies. While the optical/UV spectra of low to high redshift quasars
look remarkably similar, we find a first indication of a difference in their
X-ray spectrum. The steep X-ray spectral index suggests high Eddington ratios
L/L_Edd. These observations give credence to the hypothesis of Mathur (2000)
that NLS1s are low luminosity cousins of high redshift quasars, both likely to
be in their early evolutionary stage.


title:
Mapping of electromagnetic negative-phase-velocity propagation in the
  ergosphere of a rotating black hole

abstract:
  We report on the occurrence of negative-phase-velocity (NPV) planewave
propagation in the ergosphere of a rotating black hole. By implementing the
Kerr metric, it is demonstrated that regions of NPV propagation are
concentrated at the equator of the ergosphere, while NPV propagation is less
common towards the polar regions. Increasing the angular velocity of the black
hole exaggerates the NPV concentration at the equator. NPV propagation is not
observed outside the stationary limit surface.


title:
Optical observations of the young supernova remnant SNR 0540-69.3 and
  its pulsar

abstract:
  We have used the ESO NTT/EMMI and VLT/FORS1 instruments to examine the LMC
supernova remnant 0540-69.3 as well as its pulsar (PSR B0540-69) and
pulsar-powered nebula in the optical range.Spectroscopic observations of the
remnant covering the range of 3600-7350 A centered on the pulsar produced
results consistent with those of Kirshner et al. (1989), but also revealed many
new emission lines. The most important are [Ne III] 3869, 3967 and Balmer lines
of hydrogen. In both the central part of the remnant, as well as in nearby H II
regions, the [O III] temperature is higher than about 20 000 K, but lower than
previously estimated. For PSR B0540-69, previous optical data are mutually
inconsistent: HST/FOS spectra indicate a significantly higher absolute flux and
steeper spectral index than suggested by early time-resolved groundbased UBVRI
photometry. We show that the HST and VLT spectroscopic data for the pulsar have
more then about 50% nebular contamination, and that this is the reason for the
previous difference. Using HST/WFPC2 archival images obtained in various bands
from the red part of the optical to the NUV range we have performed an accurate
photometric study of the pulsar, and find that the spectral energy distribution
of the pulsar emission has a negative slope with 1.07 +/- 0.2. This is steeper
than derived from previous UBVRI photometry, and also different from the almost
flat spectrum of the Crab pulsar. We also estimate that the proper motion of
the pulsar is 4.9 +/- 2.3 mas/yr, corresponding to a transverse velocity of
1190 +/- 560 km/s, projected along the southern jet of the pulsar nebula.


title:
X-ray/UV Observing Campaign on the Mrk 279 AGN Outflow: A Global Fitting
  Analysis of the UV Absorption

abstract:
  We present an analysis of the intrinsic UV absorption in the Seyfert 1 galaxy
Mrk 279 based on simultaneous long observations with the Hubble Space Telescope
(41 ks) and the Far Ultraviolet Spectroscopic Explorer (91 ks). To extract the
line-of-sight covering factors and ionic column densities, we separately fit
two groups of absorption lines: the Lyman series and the CNO lithium-like
doublets. For the CNO doublets we assume that all three ions share the same
covering factors. The fitting method applied here overcomes some limitations of
the traditional method using individual doublet pairs; it allows for the
treatment of more complex, physically realistic scenarios for the
absorption-emission geometry and eliminates systematic errors that we show are
introduced by spectral noise. We derive velocity-dependent solutions based on
two models of geometrical covering -- a single covering factor for all
background emission sources, and separate covering factors for the continuum
and emission lines. Although both models give good statistical fits to the
observed absorption, we favor the model with two covering factors because: (a)
the best-fit covering factors for both emission sources are similar for the
independent Lyman series and CNO doublet fits; (b) the fits are consistent with
full coverage of the continuum source and partial coverage of the emission
lines by the absorbers, as expected from the relative sizes of the nuclear
emission components; and (c) it provides a natural explanation for variability
in the Ly$\alpha$ absorption detected in an earlier epoch. We also explore
physical and geometrical constraints on the outflow from these results.


title:
A Chandra X-ray survey of nearby dwarf starburst galaxies: I. Data
  reduction and results

abstract:
  (abridged) We present an analysis of Chandra X-ray observations of a sample
of eight dwarf starburst galaxies (I Zw 18, VII Zw 403, NGC 1569, NGC 3077, NGC
4214, NGC 4449, NGC 5253, and He 2-10). Extended, diffuse X-ray emission is
detected in all but two of the objects. Unresolved sources were found within
all dwarf galaxies (total: 55 sources). These point sources are well fit by
power law, thermal plasma, or black body models. Ten of the point sources
exceed an X-ray luminosity of 10^39 erg s^-1 (ultraluminous X-ray sources). In
those galaxies where diffuse X-ray emission is detected, this emission (with
X-ray luminosities ranging from 4x10^38 erg s^-1 to 2x10^40 erg s^-1) contains
most (60-80 per cent) of the X-ray photons. This diffuse emission can be well
fit by MeKaL one-temperature thermal plasma models once the contribution from
the unresolved point sources is subtracted properly. The diffuse X-ray
component is significantly extended, reaching as far as 0.5-5 kpc into the
outskirts of their hosts. Temperatures of various regions within the galaxies
range from 1.6-7.6x10^6 K. With few exceptions, temperatures of the hot gas are
remarkably uniform, hovering around 2-3x10^6 K. Temperatures of the coronal gas
in the outer regions are in general ~2-3 times lower than those found in the
central regions. Fits to the diffuse emission do not allow strong constraints
to be put on the metallicities of the emitting plasmas. However, the derived
metallicities are compatible with those determined from their HII regions. An
alpha/Fe ratio of ~2 is indicated for the hot gas within at least three objects
(NGC 1569, NGC 4449, and He 2-10).


title:
The distance modulus determined from Carmeli's cosmology fits the
  accelerating universe data of the high-redshift type Ia supernovae without
  dark matter

abstract:
  The velocity of the Hubble expansion has been added to General Relativity by
Moshe Carmeli and this resulted in new equations of motion for the expanding
universe. For the first time the observational magnitude-redshift data derived
from the high-$z$ supernova teams has been analysed in the framework of the
Carmeli theory and the fit to that theory is achieved without the inclusion of
any dark matter. Best fits to the data yield an averaged matter density for the
universe at the present epoch $\Omega_{m} \approx 0.021$, which falls well
within the measured values of the baryonic matter density. And the best
estimate of $\Omega_{\Lambda} + \Omega_{m} \approx 1.021$ at the present epoch.
The analysis also clearly distinguishes that the Hubble expansion of the
universe is speed-limited.


title: Non-Gaussian Radio-Wave Scattering in the Interstellar Medium

abstract:
  It was recently suggested by Boldyrev & Gwinn that the characteristics of
radio scintillations from distant pulsars are best understood if the
interstellar electron-density fluctuations that cause the time broadening of
the radio pulses obey non-Gaussian statistics. In this picture the density
fluctuations are inferred to be strong on very small scales ($\sim 10^8-10^{10}
{cm}$). We argue that such density structures could correspond to the ionized
boundaries of molecular regions (clouds) and demonstrate that the power-law
distribution of scattering angles that is required to match the observations
arises naturally from the expected intersections of our line of sight with
randomly distributed, thin, approximately spherical ionized shells of this
type. We show that the observed change in the time-broadening behavior for
pulsar dispersion measures $\lesssim 30 {\rm pc} {\rm cm}^{-3}$ is consistent
with the expected effect of the general ISM turbulence, which should dominate
the scattering for nearby pulsars. We also point out that if the clouds are
ionized by nearby stars, then their boundaries may become turbulent on account
of an ionization front instability. This turbulence could be an alternative
cause of the inferred density structures. An additional effect that might
contribute to the strength of the small-scale fluctuations in this case is the
expected flattening of the turbulent density spectrum when the eddy sizes
approach the proton gyroscale.

categories: astro-ph nlin.CD physics.flu-dyn physics.plasm-ph


title:
A Chandra X-ray survey of nearby dwarf starburst galaxies: II. Starburst
  properties and outflows

abstract:
  (abridged) We present a comprehensive comparison of the X-ray properties of a
sample of eight dwarf starburst galaxies observed with Chandra (I Zw 18, VII Zw
403, NGC 1569, NGC 3077, NGC 4214, NGC 4449, NGC 5253, He 2-10). In Paper I we
presented in detail the data reduction and analysis of the individual galaxies.
For the unresolved X-ray sources we find the following: point sources are in
general located close to bright HII regions, rims of superbubbles, or young
stellar clusters. The number of X-ray point sources appears to be a function of
the current star formation rate and the blue luminosity of the hosts.
Ultraluminous X-ray sources are only found in those dwarf galaxies which are
currently interacting. The power law index of the combined cumulative X-ray
point source luminosity function is alpha=0.24+/-0.06, shallower than that of
more massive starburst galaxies (alpha=0.4-0.8) and of non-starburst galaxies
(alpha~1.2). For those galaxies showing extended X-ray emission (6 out of the 8
galaxies), we derive the following: Superwinds develop along the steepest
gradient of the HI distribution with volume densities of 0.02-0.06 cm^-3,
pressures of 1-3x10^5 K cm^-3, thermal energies of 2-30x10^54 erg, and hot gas
masses of 2-20x10^6 Mo (~1 per cent of the HI masses). The mechanical
luminosities of the developing superwinds are energetic enough to overcome the
gravitational potentials of their host galaxies. This scenario is supported by
the overpressures of the hot gas compared to the ambient ISM. Extended HI
envelopes such as tidal tails, however, may delay outflows on timescales
exceeding those of the cooling time of the hot gas.


title:
The Luminosity and Metallicity Relation of distant luminous infrared
  galaxies

abstract:
  Oxygen abundances [12+log(O/H)] in the interstellar medium of a large sample
of distant (z>0.4) luminous infrared galaxies (LIRGs) were estimated from their
extinction corrected emission-line ratios, on the basis of the VLT/FORS2
spectra with good S/N and moderate resolution. These LIRGs were selected from
ISOCAM deep survey fields (CFRS, UDSR, UDSF). They show oxygen abundances
ranging from 8.36 to 8.93, with a median value of 8.67, which is 0.5 lower than
that of the local bright disks (i.e., L*) at the given magnitude. A significant
fraction of distant large disks are indeed LIRGs. Such massive disks could have
formed ~50% of their metals and stellar masses since z~1.


title:
Can Recently Derived Solar Photospheric Abundances Be Consistent with
  Helioseismology?

abstract:
  Recent solar abundance analyses (Asplund et al. 2004; Lodders 2003) revise
downward the abundances of C, N, O, Ne, and Ar, which reduces the solar
photospheric Z/X to 0.017, and Z to ~0.013. Solar models evolved with standard
opacities and diffusion treatment using these new abundances give poor
agreement with helioseismic inferences for sound speed profile, convection zone
helium abundance, and convection zone depth. Here we present helioseismic
results for evolved solar models with these reduced photospheric abundances,
trying varying diffusion treatments. We compare results for models with no
diffusion, enhanced thermal diffusion, and enhanced diffusion of C, N, O, Ne,
and Mg only. We find that while each of these models provides some improvements
compared to a solar model evolved with the new abundances and standard physics,
none restores the good agreement with helioseismology attained using the
earlier abundances of, e.g., Grevesse & Sauval (1998). We suggest that opacity
increases of about 20% for conditions below the convection zone, or the
possibility of accretion of lower-Z material at the surface as the sun arrived
at the main sequence, should be investigated to restore agreement. In addition,
the new abundance determinations should be re-considered, as, if they are
correct, it will be difficult to reconcile solar models with helioseismic
results.


title:
Constraints on the Sum of Neutrino Masses from Cosmology and their
  impact on world neutrino data

abstract:
  We derive upper limits on the sum of neutrino masses from an updated
combination of data from Cosmic Microwave Background experiments and Galaxy
Redshifts Surveys. The results are discussed in the context of three-flavor
neutrino mixing and compared with neutrino oscillation data, with upper limits
on the effective neutrino mass in Tritium beta decay from the Mainz and Troitsk
experiments and with the claimed lower bound on the effective Majorana neutrino
mass in neutrinoless double beta decay from the Heidelberg-Moscow experiment.


title: First results from the ESO VLTI Calibrators Program

abstract:
  The ESO Very Large Telescope Interferometer (VLTI) is one of the leading
interferometric facilities. It is equipped with several 8.2 and 1.8m
telescopes, a large number of baselines up to 200m, and with several subsystems
designed to enable high quality measurements and to improve significantly the
limits of sensitivities currently available to long-baseline interferometry.
The full scientific potential of the VLTI can be exploited only if a consistent
set of good quality calibrators is available. For this, a large number of
observations of potential calibrators have been obtained during the
commissioning phase of the VLTI. These data are publicly available. We briefly
describe the interferometer, the VINCI instrument used for the observations,
the data flow from acquisition to processed results, and we present and comment
on the volume of observations gathered and scrutinized. The result is a list of
191 calibrator candidates, for which a total of 12066 observations can be
deemed of satisfactory quality. We present a general statistical analysis of
this sample, using as a starting point the angular diameters previously
available in the literature.We derive the general characteristics of the VLTI
transfer function, and its trend with time in the period 2001 through mid-2004.
A second paper will be devoted to a detailed investigation of a selected
sample, aimed at establishing a VLTI-based homogeneous system of calibrators.


title:
The Hanle and Zeeman Effects in Solar Spicules: A Novel Diagnostic
  Window on Chromospheric Magnetism

abstract:
  An attractive diagnostic tool for investigating the magnetism of the solar
chromosphere is the observation and theoretical modeling of the Hanle and
Zeeman effects in spicules, as shown in this letter for the first time. Here we
report on spectropolarimetric observations of solar chromospheric spicules in
the He I 10830 \AA multiplet and on their theoretical modeling accounting for
radiative transfer effects. We find that the magnetic field in the observed
(quiet Sun) spicular material at a height of about 2000 km above the visible
solar surface has a strength of the order of 10 G and is inclined by
approximately $35^{\circ}$ with respect to the local vertical direction. Our
empirical finding based on full Stokes-vector spectropolarimetry should be
taken into account in future magnetohydrodynamical simulations of spicules.


title: Do accretion discs regulate the rotation of young stars?

abstract:
  We present a photometric study of I-band variability in the young cluster IC
348. The main purpose of the study was to identify periodic stars. In all we
find 50 periodic stars, of which 32 were previously unknown. For the first time
in IC 348, we discover periods in significant numbers of lower-mass stars (M <
0.25 Msun) and classical T-Tauri stars. This increased sensitivity to
periodicities is due to the enhanced depth and temporal density of our
observations, compared with previous studies. The period distribution is at
first glance similar to that seen in the Orion Nebula Cluster, with the
higher-mass stars (M > 0.25 Msun) showing a bi-modal period distribution
concentrated around periods of 2 and 8 days, and the lower-mass stars showing a
uni-modal distribution, heavily biassed towards fast rotators. Closer
inspection of the period distribution shows that the higher mass stars show a
significant dearth of fast rotators, compared to the Orion Nebula Cluster,
whilst the low mass stars are rotating significantly faster than those in
Orion. We find no correlation between rotation period and K-L colour or H-alpha
equivalent width.
  We also present a discussion of our own IC 348 data in the context of
previously published period distributions for the Orion Nebula Cluster, the
Orion Flanking Fields and NGC 2264. We find that the previously claimed
correlation between infrared excess and rotation period in the ONC might in
fact result from a correlation between infrared excess and mass. We also find a
marked difference in period distributions between NGC 2264 and IC 348, which
presents a serious challenge to the disc locking paradigm, given the similarity
in ages and disc fractions between the two clusters.


title: Analysis of the carbon-rich very metal-poor dwarf G77-61

abstract:
  We present an analysis of the carbon dwarf G77-61, a known binary, based on
high resolution Keck spectra. G77-61 has a very-low metallicity, although not
as extreme as what was previously conjectured. This star is very
carbon-enhanced, the spectra showing very strong CH, CN, and C$_2$ bands of
both $^{13}$C and $^{12}$C isotopes. Atomic lines are sparse, and often
blended, but we were able to derive abundances for Na, Mg, Ca, Cr, Mn, and Fe.
Its [Fe/H] of -4.03$\pm$0.1 places it among the lowest metallicity stars known,
and its very high [C/Fe]=+2.6, and [N/Fe]=+2.6 among the most C and N-rich
metal-poor stars. The carbon isotopic ratio is $^{12}$C/$^{13}C=5\pm$1. No
overabundance of s- or r-process elements is detectable, but the upper limits
that can be set on these overabundances are not very constraining.


title: Density structure of the Horsehead nebula photo-dissociation region

abstract:
  We present high angular resolution images of the H$_2$ 1-0 S(1) line emission
obtained with the Son of ISAAC (SOFI) at the New Technology Telescope (NTT) of
the Horsehead nebula. These observations are analysed in combination with
H$\alpha$ line emission, aromatic dust, CO and dust continuum emissions. The
Horsehead nebula illuminated by the O9.5V star $\sigma$ Ori ($\chi \sim$ 60)
presents a typical photodissociation region (PDR) viewed nearly edge-on and
offers an ideal opportunity to study the gas density structure of a PDR. The
H$_2$ fluorescent emission observations reveal extremely sharp and bright
filaments associated with the illuminated edge of the nebula which spatially
coincides with the aromatic dust emission. Analysis of the H$_2$ fluorescent
emission, sensitive to both the far-UV radiation field and the gas density, in
conjunction with the aromatic dust and H$\alpha$ line emission, brings new
constraints on the illumination conditions and the gas density in the outer PDR
region. Furthermore, combination of this data with millimeter observations of
CO and dust continuum emission allows us to trace the penetration of the far-UV
radiation field into the cloud and probe the gas density structure throughout
the PDR. From comparison with PDR model calculations, we find that i) the gas
density follows a steep gradient at the cloud edge, with a scale length of 0.02
pc (or 10'') and $n_H\sim 10^4$ and $10^5$ cm$^{-3}$ in the H$_2$ emitting and
inner cold molecular layers respectively, and ii) this density gradient model
is essentially a constant pressure model, with $P\sim$4 $10^6$ K cm$^{-3}$. The
constraints derived here on the gas density profile are important for the study
of physical and chemical processes in PDRs and provide new insight into the
evolution of interstellar clouds.


title: An HST Search for Substellar Companions in the Young Cluster IC 348

abstract:
  We present the results of a HST WFPC2 search for substellar companions to
members of the star-forming cluster IC 348. The detection limits for companions
to low-mass stars and brown dwarfs in the PC images are dm_791=0, 2.5, and 5.5
at separations of 0.05", 0.1", and 0.3", respectively, which correspond to
M_2/M_1=1, 0.3, and 0.1 at 15, 30, and 90 AU. Meanwhile, for heavily saturated
solar-mass primaries in the WFC images, the limits are dm_791=0 and 6
(M_2/M_1=1 and 0.04) at 0.2" and 0.4". The sky limiting magnitude of m_791~26
at large separations from a primary corresponds to a mass of ~0.006 M_sun. For
the two faintest candidate companions appearing in these data, we have obtained
0.8-2.5 um spectra with SpeX at the IRTF, which we classify as cluster members
with spectral types near M6, corresponding to masses of ~0.1 M_sun. Thus, no
probable substellar companions are detected in this survey. The frequencies of
stellar and substellar companions within 0.4-5" (120-1600 AU) from low-mass
stars in IC 348 agree with measurements in the field. The factor of ~3-10
deficiency in brown dwarfs relative to stars among companions at wide
separations in IC 348 and across the much larger range of separations probed
for field stars is equal within the uncertainties to the deficiency in brown
dwarfs in measurements of mass functions of isolated objects. In other words,
when defined relative to stars, the brown dwarf "desert" among companions is
also present among isolated objects, which is expected if stellar and
substellar companions form in the same manner as their free-floating
counterparts. Meanwhile, among the 14 substellar primaries in our survey of IC
348, no companions are detected. This absence of wide binary brown dwarfs is
statistically consistent with the frequency of wide binary stars in IC 348.


title:
Biermann Mechanism in Primordial Supernova Remnant and Seed Magnetic
  Fields

abstract:
  We study generation of magnetic fields by the Biermann mechanism in the
pair-instability supernovae explosions of first stars. The Biermann mechanism
produces magnetic fields in the shocked region between the bubble and
interstellar medium (ISM), even if magnetic fields are absent initially. We
perform a series of two-dimensional magnetohydrodynamic simulations with the
Biermann term and estimate the amplitude and total energy of the produced
magnetic fields. We find that magnetic fields with amplitude
$10^{-14}-10^{-17}$ G are generated inside the bubble, though the amount of
magnetic fields generated depend on specific values of initial conditions. This
corresponds to magnetic fields of $10^{28}-10^{31}$ erg per each supernova
remnant, which is strong enough to be the seed magnetic field for galactic
and/or interstellar dynamo.


title: The brightest OH maser in the sky: a flare of emission in W75 N

abstract:
  A flare of maser radio emission in the OH-line 1665 MHz has been discovered
in the star forming region W75 N in 2003, with the flux density of about 1000
Jy. At the time it was the strongest OH maser detected during the whole history
of observations since the discovery of cosmic masers in 1965. The flare
emission is linearly polarized with a degree of polarization near 100%. A
weaker flare with a flux of 145 Jy was observed in this source in 2000 - 2001,
which was probably a precursor of the powerful flare. Intensity of two other
spectral features has decreased after beginning of the flare. Such variation of
the intensity of maser condensation emission (increasing of one and decreasing
of the other) can be explained by passing of the magneto hydrodynamic shock
across regions of enhanced gas concentration.


title:
Neutral hydrogen absorption at milliarcsecond resolutions: The radio
  galaxy 3C293

abstract:
  We present new milliarcsecond resolution observations of the H1 absorption
against the kiloparsec scale inner jet of the radio galaxy 3C293. Using a
combination of observations obtained with global VLBI, MERLIN and the VLA we
have imaged the strong and extensive neutral hydrogen absorption against the
radio core and jet of this source across a wide range of angular scales.
  In this proceedings we will present these new combined milliarcsecond scale
VLBI results alongside our previous lower resolution MERLIN studies of the H1
absorption in this source. This study will allow us to investigate the
distribution and dynamics of the H1 absorption in the centre of this source
from scales of arcseconds to a few milliarcsecond.


title:
Nonlinear Stability of Newtonian Galaxies and Stars from a Mathematical
  Perspective

abstract:
  The stability of equilibrium configurations of galaxies or stars are time
honored problems in astrophysics. We present mathematical results on these
problems which have in recent years been obtained by Yan Guo and the author in
the context of the Vlasov-Poisson and the Euler-Poisson model. Based on a
careful analysis of the minimization properties of conserved quantities--the
total energy and so-called Casimir functionals--non-linear stability results
are obtained for a wide class of equilibria.


title: The Iron Line Background

abstract:
  We investigate the presence of iron line emission among faint X-ray sources
identified in the 1Ms Chandra Deep Field South and in the 2Ms Chandra Deep
Field North. Individual source spectra are stacked in seven redshift bins over
the range z=0.5-4. We find that iron line emission is an ubiquitous property of
X-ray sources up to z~3. The measured line strengths are in good agreement with
those expected by simple pre-Chandra estimates based on X-ray background
synthesis models. The average rest frame equivalent width of the iron line does
not show significant changes with redshift.


title: Hot Baryons and the Distribution of Metals in the Intergalactic Medium

abstract:
  We use the observed number and column-density distributions of intergalactic
O VI absorbers to constrain the distribution of metals in the low-redshift
intergalactic medium (IGM). In this simple model the metals in the O VI
absorbers are assumed to be produced in and propagated from low-redshift
galaxies drawn from a real sample, in this case the Sloan Digital Sky Survey
(SDSS). This model can explain the observed dN/dz of metals seen in O VI
absorbers if these metals are dispersed out to ~ 200 kpc by galaxies down to L
\~ 0.01 - 0.1 L_r^*. Massive galaxies (L ~ L_r^*) by themselves cannot provide
the necessary enrichment unless they can enrich volumes out to $\gtrsim 0.5 - 1
Mpc. Alternatively, our model allows an estimate of the fraction of O VI
absorbers directly caused by galaxies rather than hot IGM. With this assumption
we explore the possible connections between the intergalactic O VI absorbers
and the known populations of highly-ionized high-velocity clouds (HVCs)
surrounding the Milky Way. Our model predicts that more sensitive, complete
surveys optimized to uncover weaker O VI absorbers will find the tentative
turnover below log N(O VI) ~ 13.5 to be a real effect resulting from the
apparently limited volumes over which galaxies can enrich the IGM. If so, it
would indicate that metals are not as widespread throughout the low-density IGM
as they are assumed to be in cosmological simulations of the WHIM.


title:
Probing the nature of the ISM in Active Galactic Nuclei through HI
  absorption

abstract:
  The physical and kinematical conditions of the gas surrounding an active
galactic nucleus (AGN) offer key diagnostics for understanding the processes
occurring in the inner few kpc around the nucleus. Neutral hydrogen can give
important insights on these regions. Apart from probing the presence of gas in
relatively settled conditions (i.e. circumnuclear disks/tori) it can also trace
the presence of extreme outflows. Some examples of these phenomena are briefly
presented. For the study of the neutral hydrogen around AGN the high resolution
offered by the VLBI is crucial in order to locate the regions where the
absorption occurs and to study in detail the kinematics of the gas. Recent VLBI
results are discussed here.


title:
The Distance and Metallicity of the Newly Discovered, Nearby Irregular
  Galaxy HIZSS3

abstract:
  HIZSS3 is an H I source in the Zone of Avoidance. Its radio characteristics
are consistent with it being nearby (~ 1.8 Mpc) low-mass dwarf irregular (dIm)
galaxy. It contains a modest H II region, but its stellar population has not
been resolved by optical observations. MMT spectra of the H II region are used
to derive the line-of-sight extinction (E(B-V) = 1.41 +/- 0.04) and gas
metallicity (log O/H + 12 ~ 7.8). ESO VLT near-IR images clearly reveal a
resolved stellar population. Narrow-band Pbeta images of the H II region are
used in combination with previously published Halpha data to obtain an
independent line-of-sight extinction estimate: E(B-V) = 1.32 +/- 0.04. The
adopted foreground extinction is E(B-V) = 1.36 +/- 0.06. Based on the K-band
luminosity function and K,J-K color-magnitude diagram, the apparent magnitude
and color of the tip of the red-giant branch (TRGB) are derived. In turn, these
parameters are combined with the adopted foreground extinction to estimate the
distance (1.69 +/- 0.07 Mpc) and mean red giant branch metallicity ([Fe/H] =
-0.5 +/- 0.1). As an ensemble, these new observations significantly strengthen
the conclusion that HIZSS3 is a newly discovered low-mass dIm lurking behind
the Milky Way in the outskirts of the Local Group.


title:
The first three years of the outburst and light-echo evolution of V838
  Mon and the nature of its progenitor

abstract:
  V838 Mon has undergone one of the most mysterious stellar outbursts on
record, with (a) a large amplitude (Delta B ~ 10 mag) and multi-maxima
photometric pattern, (b) a cool spectral type at maximum becoming cooler and
cooler with time during the descent, until it reached the never-seen-before
realm of L-type supergiants, never passing through optically thin or nebular
stages, (c) the development of a spectacular, monotonically expanding
light-echo in the circumstellar material, and (d) the identification of a
massive and young B3V companion, unaffected by the outburst. In this talk we
review the photometric and spectroscopic evolution during the first three full
years of outburst, the light-echo development and infer the nature of the
progenitor, which was brighter and hotter in quiescence than the B3V companion
and with an inferred ZAMS mass of about 65 Msun.


title: A New Godunov Scheme for MHD, with Application to the MRI in disks

abstract:
  We describe a new numerical scheme for MHD which combines a higher order
Godunov method (PPM) with Constrained Transport. The results from a selection
of multidimensional test problems are presented. The complete test suite used
to validate the method, as well as implementations of the algorithm in both F90
and C, are available from the web. A fully three-dimensional version of the
algorithm has been developed, and is being applied to a variety of
astrophysical problems including the decay of supersonic MHD turbulence, the
nonlinear evolution of the MHD Rayleigh-Taylor instability, and the saturation
of the magnetorotational instability in the shearing box. Our new simulations
of the MRI represent the first time that a higher-order Godunov scheme has been
applied to this problem, providing a quantitative check on the accuracy of
previous results computed with ZEUS; the latter are found to be reliable.


title: A Dynamical Method for Measuring Masses of Stars with Transiting Planets

abstract:
  As a planet transits the face of a star, it accelerates along the
line-of-sight. The changing delay in the propagation of photons produces an
apparent deceleration of the planet across the sky throughout the transit. This
persistent transverse deceleration breaks the time-reversal symmetry in the
transit lightcurve of a spherical planet in a circular orbit around a perfectly
symmetric star. For `hot Jupiter' systems, ingress advances at a higher rate
than egress by a fraction of 10^{-4}-10^{-3}. Forthcoming space telescopes such
as Kepler or COROT will reach the sensitivity required to detect this
asymmetry. The scaling of the fractional asymmetry with stellar mass M and
planetary orbital radius R as M/R^2 is different from the scaling of the
orbital period as (M/R^3)^{-1/2}. Therefore, this effect constitutes a new
method for a purely dynamical determination of the mass of the star, which is
currently inferred indirectly with theoretical uncertainties based on spectral
modeling. Radial velocity data for the reflex motion of the star can then be
used to determine the planet's mass. Although orbital eccentricity could
introduce a larger asymmetry than the light propagation delay, the eccentricity
is expected to decay by tidal dissipation to negligible values for a close-in
planet with no perturbing third body. Future detection of the eclipse of a
planet's emission by its star could be used to measure the light propagation
delay across the orbital diameter, 46.7(R/7x10^{11}cm) seconds, and also
determine the stellar mass from the orbital period.


title: 3D SPH Simulations of Shocks in Accretion Flows around black holes

abstract:
  We present the simulation of 3D time dependent flow of rotating ideal gas
falling into a Schwarzschild black hole. It is shown that also in the 3D case
steady shocks are formed in a wide range of parameters (initial angular
momentum and thermal energy). We therefore highlight the stability of the
phenomenon of shock formation in sub keplerian flows onto black holes, and
reenforce the role of the shocks in the high luminosity emission from black
hole candidates. The simulations have been performed using a parallelized code
based on the Smoothed Particles Hydrodynamics method (SPH). We also discuss
some properties of the shock problem that allow its use as a quantitative test
of the accuracy of the used numerical method. This shows that the accuracy of
SPH is acceptable although not excellent.


title: Magnetic Fields in Diffuse H I and Molecular Clouds

abstract:
  This book chapter reviews the current state of observations of magnetic
fields in diffuse H I and in dense molecular clouds. It covers techniques for
measuring magnetic fields, the analysis of the observations, and the role of
magnetic fields in the physics of interstellar clouds and in the star formation
process.


title: Where Are All The Fallback Disks? Constraints on Propeller Systems

abstract:
  Fallback disks are expected to form around new-born neutron stars following a
supernova explosion. In almost all cases, the disk will pass through a
propeller stage. If the neutron star is spinning rapidly (initial period $\sim
10$ ms) and has an ordinary magnetic moment ($\sim 10^{30}$ G cm$^3$), the
rotational power transferred to the disk by the magnetic field of the neutron
star will exceed the Eddington limit by many orders of magnitude, and the disk
will be rapidly disrupted. Fallback disks can thus survive only around
slow-born neutron stars and around black holes, assuming the latter do not
torque their surrounding disks as strongly as do neutron stars. This might
explain the apparent rarity of fallback disks around young compact objects.


title: Properties of the H-alpha-emitting Circumstellar Regions of Be Stars

abstract:
  Long-baseline interferometric observations obtained with the Navy Prototype
Optical Interferometer of the H-alpha-emitting envelopes of the Be stars eta
Tauri and beta Canis Minoris are presented. For compatibility with the
previously published interferometric results in the literature of other Be
stars, circularly symmetric and elliptical Gaussian models were fitted to the
calibrated H-alpha observations. The models are sufficient in characterizing
the angular distribution of the H-alpha-emitting circumstellar material
associated with these Be stars. To study the correlations between the various
model parameters and the stellar properties, the model parameters for eta Tau
and beta CMi were combined with data for other Be stars from the literature.
After accounting for the different distances to the sources and stellar
continuum flux levels, it was possible to study the relationship between the
net H-alpha emission and the physical extent of the H-alpha-emitting
circumstellar region. A clear dependence of the net H-alpha emission on the
linear size of the emitting region is demonstrated and these results are
consistent with an optically thick line emission that is directly proportional
to the effective area of the emitting disk. Within the small sample of stars
considered in this analysis, no clear dependence on the spectral type or
stellar rotation is found, although the results do suggest that hotter stars
might have more extended H-alpha-emitting regions.


title: Isotopic abundance of nitrogen and carbon in distant comets

abstract:
  The 12C14N/12C15N and 12C14N/13C14N isotopic ratios have been determined in
comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT) and C/2003 K4 (LINEAR) at
heliocentric distances of, respectively, 2.7, 3.7 and 2.6 AU. These ratios have
also been measured at r ~ 1 AU. No significant differences were found between
all determinations, nor with the value obtained for other comets. If confirmed,
the discrepancy between the nitrogen isotopic ratios from optical and
millimeter measurements on CN and HCN would rule out HCN as a major parent of
the cometary CN radicals.


title: The Challenge of Wide-Field Transit Surveys: The Case of GSC 01944-02289

abstract:
  Wide-field searches for transiting extra-solar giant planets face the
difficult challenge of separating true transit events from the numerous false
positives caused by isolated or blended eclipsing binary systems. We describe
here the investigation of GSC 01944-02289, a very promising candidate for a
transiting brown dwarf detected by the Transatlantic Exoplanet Survey (TrES)
network. The photometry and radial velocity observations suggested that the
candidate was an object of substellar mass in orbit around an F star. However,
careful analysis of the spectral line shapes revealed a pattern of variations
consistent with the presence of another star whose motion produced the
asymmetries observed in the spectral lines of the brightest star. Detailed
simulations of blend models composed of an eclipsing binary plus a third star
diluting the eclipses were compared with the observed light curve and used to
derive the properties of the three components. Our photometric and
spectroscopic observations are fully consistent with a blend model of a
hierarchical triple system composed of an eclipsing binary with G0V and M3V
components in orbit around a slightly evolved F5 dwarf. We believe that this
investigation will be helpful to other groups pursuing wide-field transit
searches as this type of false detection could be more common than true
transiting planets, and difficult to identify.


title: Time-Dependent Models for Dark Matter at the Galactic Center

abstract:
  The prospects of indirect detection of dark matter at the galactic center
depend sensitively on the mass profile within the inner parsec. We calculate
the distribution of dark matter on sub-parsec scales by integrating the
time-dependent Fokker-Planck equation, including the effects of
self-annihilations, scattering of dark matter particles by stars, and capture
in the supermassive black hole. We consider a variety of initial dark matter
distributions, including models with very high densities ("spikes") near the
black hole, and models with "adiabatic compression" of the baryons. The
annihilation signal after 10 Gyr is found to be substantially reduced from its
initial value, but in dark matter models with an initial spike,
order-of-magnitude enhancements can persist compared with the rate in
spike-free models, with important implications for indirect dark matter
searches with GLAST and Air Cherenkov Telescopes like HESS and CANGAROO.


title:
New Light on the Formation and Evolution of M31 and its Globular Cluster
  System

abstract:
  We present spectroscopic ages, metallicities, and [alpha/Fe] ratios for 70
globular clusters in M31 that were derived from Lick line-index measurements.
In addition to a population of old (>10 Gyr) globular clusters with a wide
range of metallicities, from about -2.0 dex to solar values, we find evidence
for a population of intermediate-age globular clusters with ages between ~5 and
8 Gyr and a mean metallicity around [Z/H]=-0.6. We also confirm the presence of
young M31 globular clusters that were recently identified by Beasley et al.
(2004), which have ages <1 Gyr and relatively high metallicities around -0.4
dex. The M31 globular cluster system has a clearly super-solar mean
[alpha/Fe]=0.14\pm0.04 dex. Intermediate-age and young objects show roughly
solar abundance ratios. We find evidence for an age-[alpha/Fe] relation in the
sense that younger clusters have smaller mean [alpha/Fe] ratios. From a
comparison of indices, mostly sensitive to carbon and/or nitrogen abundance,
with SSP model predictions for nitrogen-enhanced stellar populations, we find a
dichotomy in nitrogen enhancement between young and old M31 globular clusters.
The indices of objects older than 5 Gyr are consistent with a factor of three
or higher in nitrogen enhancement compared to their younger counterparts. Using
kinematical data from Morrison et al. (2004) we find that the globular cluster
sub-population with halo kinematics is old (>9 Gyr), has a bimodal metallicity
distribution, and super-solar [alpha/Fe]. Disk globular clusters have a wider
range of ages, are on average more metal-rich, and have a slightly smaller mean
[alpha/Fe] ratio. (abridged)


title: An Unsplit Godunov Method for Ideal MHD via Constrained Transport

abstract:
  We describe a single step, second-order accurate Godunov scheme for ideal MHD
based on combining the piecewise parabolic method (PPM) for performing spatial
reconstruction, the corner transport upwind (CTU) method of Colella for
multidimensional integration, and the constrained transport (CT) algorithm for
preserving the divergence-free constraint on the magnetic field. We adopt the
most compact form of CT, which requires the field be represented by
area-averages at cell faces. We demonstrate that the fluxes of the
area-averaged field used by CT can be made consistent with the fluxes of the
volume-averaged field returned by a Riemann solver if they obey certain simple
relationships. We use these relationships to derive new algorithms for
constructing the CT fluxes at grid cell corners which reduce exactly to the
equivalent one-dimensional solver for plane-parallel, grid-aligned flow. We
show that the PPM reconstruction algorithm must include multidimensional terms
for MHD, and we describe a number of important extensions that must be made to
CTU in order for it to be used for MHD with CT. We present the results of a
variety of test problems to demonstrate the method is accurate and robust.