title: Using Balmer line profiles to investigate convection in A and F stars

abstract:
  Balmer lines are an important diagnostic of stellar atmospheric structure,
since they are formed at a wide range of depths within the atmosphere. The
different Balmer lines are formed at slightly different depths making them
useful atmospheric diagnostics. The low sensitivity to surface gravity for
stars cooler than ~8000 K makes them excellent diagnostics in the treatment of
atmospheric convection. For hotter stars Balmer profiles are sensitive to both
effective temperature and surface gravity. Provided we know the surface gravity
of these stars from some other method (e.g. from eclipsing binary systems), we
can use them to determine effective temperature.
  In previous work, we have found no significant systematic problems with using
uvby photometry to determine atmospheric parameters of fundamental (and
standard) stars. In fact, uvby was found to be very good for obtaining both
Teff and log g. Using Halpha and Hbeta profiles, we have found that both the
Canuto & Mazzitteli and standard Kurucz mixing-length theory without
approximate overshooting are both in agreement to within the uncertainties of
the fundamental stars. Overshooting models were always clearly discrepant. Some
evidence was found for significant disagreement between all treatments of
convection and fundamental values around 8000~9000K, but these results were for
fundamental stars without fundamental surface gravities. We have used stars
with fundamental values of both Teff and log g to explore this region in more
detail.


title: 300x Faster Matlab using MatlabMPI

abstract:
  The true costs of high performance computing are currently dominated by
software. Addressing these costs requires shifting to high productivity
languages such as Matlab. MatlabMPI is a Matlab implementation of the Message
Passing Interface (MPI) standard and allows any Matlab program to exploit
multiple processors. MatlabMPI currently implements the basic six functions
that are the core of the MPI point-to-point communications standard. The key
technical innovation of MatlabMPI is that it implements the widely used MPI
``look and feel'' on top of standard Matlab file I/O, resulting in an extremely
compact (~250 lines of code) and ``pure'' implementation which runs anywhere
Matlab runs, and on any heterogeneous combination of computers. The performance
has been tested on both shared and distributed memory parallel computers (e.g.
Sun, SGI, HP, IBM and Linux). MatlabMPI can match the bandwidth of C based MPI
at large message sizes. A test image filtering application using MatlabMPI
achieved a speedup of ~300 using 304 CPUs and ~15% of the theoretical peak (450
Gigaflops) on an IBM SP2 at the Maui High Performance Computing Center. In
addition, this entire parallel benchmark application was implemented in 70
software-lines-of-code (SLOC) yielding 0.85 Gigaflop/SLOC or 4.4 CPUs/SLOC,
which are the highest values of these software price performance metrics ever
achieved for any application. The MatlabMPI software will be available for
download.


title: alpha :a constant that is not a constant?

abstract:
  We review the observational information on the constancy of the fine
structure constant alpha. We find that small improvements on the measurement of
^{187}Re lifetime can provide significant progress in exploring the range of
variability suggested by QSO data. We also discuss the effects of a time
varying alpha on stellar structure and evolution. We find that radioactive
dating of ancient stars can offer a new observational window.


title:
Bright CO ro-vibrational emission lines in the class I source GSS 30
  IRS1: Probing the inner disk of a young embedded star

abstract:
  We present a 4.5-4.85 micron R=5000 spectrum of the low mass class I young
stellar object GSS 30 IRS1 (L=25L_sun) in the rho Ophiuchus core, observed with
the infrared spectrometer (ISAAC) on the Very Large Telescope (VLT-UT1). Strong
line emission from the ro-vibrational transitions of 12CO and 13CO is detected.
In total more than 40 distinct lines are seen in the covered region. The line
emission is spatially extended and detected up to 2" = 320 AU from the central
source but is spectrally unresolved (Delta v < 30 km/s). This is the first time
strong emission in the fundamental ro-vibrational band from CO has been
observed from an embedded young stellar object. The line fluxes were modeled
using a 1-dimensional full radiative transfer code, which shows that the
emission is fully consistent with a gas in LTE at a single well constrained
temperature (T=515+/-5 K). Furthermore, the ratios between lines from the two
detected isotopic species of CO show that the 12CO lines must be optically
thick. However, this is inconsistent with the observed spatial extent of the
emission, since this implies such low CO column densities that the lines are
optically thin. A likely solution to the discrepancy is that the lines are
emitted by a smaller more dense region and then scattered in the bipolar cavity
present around the central star. This gives a rough estimate of the total
molecular gas mass of 1-100 M_earth and a physical extent of ~20-100 AU. We
propose that the most likely origin of the line emission is post-shocked gas in
a dense dissociative accretion shock from the inner 10-50 AU of a circumstellar
disk. The presence of a shock capable of dissociating molecules in the disk
will have implications for the chemical evolution of disks around young low
mass stars.


title: A new look at dynamo cycle amplitudes

abstract:
  We explore the dependence of the amplitude of stellar dynamo cycle
variability (as seen in the Mount Wilson Ca II HK timeseries data) on other
stellar parameters. We find that the fractional cycle amplitude A_cyc (i.e. the
ratio of the peak-to-peak variation to the average) decreases somewhat with
mean activity, increases with decreasing effective temperature, but is not
correlated with inverse Rossby number Ro^{-1}. We find that A_cyc increases
with the ratio of cycle and rotational frequencies omega_cyc/Omega along two,
nearly parallel branches.


title: Solar and stellar dynamos -- latest developments

abstract:
  Recent progress in the theory of solar and stellar dynamos is reviewed.
Particular emphasis is placed on the mean-field theory which tries to describe
the collective behavior of the magnetic field. In order to understand solar and
stellar activity, a quantitatively reliable theory is necessary. Much of the
new developments center around magnetic helicity conservation which is seen to
be important in numerical simulations. Only a dynamical, explicitly time
dependent theory of alpha-quenching is able to describe this behavior
correctly.


title: The helicity issue in large scale dynamos

abstract:
  The connection between helically isotropic MHD turbulence and mean-field
dynamo theory is reviewed. The nonlinearity in the mean-field theory is not yet
well established, but detailed comparison with simulations begin to help select
viable forms of the nonlinearity. The crucial discriminant is the magnetic
helicity, which is known to evolve only on a slow resistive time scale in the
limit of large magnetic Reynolds number. Particular emphasis is put on the
possibility of memory effects, which means that an additional explicitly
time-dependent equation for the nonlinearity is solved simultaneously with the
mean-field equations. This approach leads to better agreement with the
simulations, while it would also produce more favorable agreement between
models and stellar dynamos.


title: Antideuterons as a probe of primordial black holes

abstract:
  In most cosmological models, primordial black holes (PBHs) should have formed
in the early Universe. Their Hawking evaporation into particles could
eventually lead to the formation of antideuterium nuclei. This paper is devoted
to a first computation of this antideuteron flux. The production of these
antinuclei is studied with a simple coalescence scheme, and their propagation
in the Galaxy is treated with a well-constrained diffusion model. We compare
the resulting primary flux to the secondary background, due to the spallation
of protons on the interstellar matter. Antideuterons are shown to be a very
sensitive probe for primordial black holes in our Galaxy. The next generation
of experiments should allow investigators to significantly improve the current
upper limit, nor even provide the first evidence of the existence of
evaporating black holes.


title: Quintessence and the Relic Density of Neutralinos

abstract:
  The archetypal model for the recently discovered dark energy component of the
universe is based on the existence of a scalar field whose dynamical evolution
comes down today to a non-vanishing cosmological constant. In the past - before
big-bang nucleosynthesis for that matter - that scalar field could have gone
through a period of kination during which the universe has expanded at a much
higher pace than what is currently postulated in the standard radiation
dominated cosmology. I examine here the consequences of such a period of
kination on the relic abundance of neutralinos and find that the latter could
be much higher - by three orders of magnitude - than what is estimated in the
canonical derivation. I shortly discuss the implications of this scenario for
the dark matter candidates and their astrophysical signatures.
  This new version contains a discussion - see section 2 - of the overshooting
problem and offers perspectives to reconcile an initial period of violent
kination with the existence of a cosmological constant today.


title: Dust-Induced Systematic Errors in UV-Derived Star Formation Rates

abstract:
  Rest-frame far-ultraviolet (FUV) luminosities form the `backbone' of our
understanding of star formation at all cosmic epochs. FUV luminosities are
typically corrected for dust by assuming that extinction indicators which have
been calibrated for local starbursting galaxies apply to all star-forming
galaxies. I present evidence that `normal' star-forming galaxies have
systematically redder UV/optical colors than starbursting galaxies at a given
FUV extinction. This is attributed to differences in star/dust geometry,
coupled with a small contribution from older stellar populations. Folding in
data for starbursts and ultra-luminous infrared galaxies, I conclude that SF
rates from rest-frame UV and optical data alone are subject to large (factors
of at least a few) systematic uncertainties because of dust, which cannot be
reliably corrected for using only UV/optical diagnostics.


title:
The Twice-Overlooked, Second FR II Broad Absorption Line Quasar LBQS
  1138-0126

abstract:
  We report the correct classification of an overlooked Fanaroff-Riley class II
radio-loud quasar with broad absorption lines, only the second such object so
identified. The rare properties of this quasar, LBQS 1138-0126, are twice
overlooked. First LBQS 1138-0126 was found in the Large Bright Quasar Survey
but only noted as a possible broad absorption line quasar without additional
follow-up. Later LBQS 1138-0126 was rediscovered and classified as a radio-loud
broad absorption line quasar but not recognized as an FR II radio source. We
describe the radio, absorption line, and optical polarization properties of
LBQS 1138-0126 and place it in context with respect to related quasars. In
particular, spectropolarimetry shows that LBQS 1138-0126 has high continuum
polarization increasing from 3% in the red (rest-frame 2400 Angstroms) to over
4% in the blue (rest-frame 1650 Ansgtroms), essentially confirming the
intrinsic nature of the absorption. The polarization position angle rotates
from about -30 degrees in the red to about 0 degrees in the blue; the radio
lobe position angle is 52 degrees for comparison. LBQS 1138-0126 is
additionally notable for being one of the most radio-loud broad absorption line
quasars, and for having low-ionization broad absorption lines as well.


title: Modeling Brown Dwarfs, L Dwarfs, and T Dwarfs

abstract:
  In this brief contribution, I touch on a subset of recent efforts in spectral
and opacity modeling aimed at improving our understanding of brown dwarfs, L
dwarfs, and T dwarfs. I discuss theoretical calculations of the alkali line
profiles, newly generated CrH opacities, new evidence for refractory rainout in
T dwarfs from optical spectral measurements, and the distinction between brown
dwarfs and planets.


title: On-Axis Orphan Afterglows

abstract:
  In many GRB inner engine models the highly relativistic GRB jets are engulfed
by slower moving matter. This could result in different beaming for the prompt
$\gamma$-ray emission and for the lower energy afterglow. In this case we
should expect that some observer will see {\it on-axis orphan afterglows}:
X-ray, optical and radio afterglows within the initial relativistic ejecta with
no preceding GRB; The prompt $\gamma$-ray emission is pointing elsewhere. We
show that the observations of the WFC on BeppoSAX constrain with high certainty
the prompt X-ray beaming factor to be less than twice the prompt $\gamma$-ray
beaming. The results of Ariel 5 are consistent with this interpretation. The
RASS from ROTSE and HEAO-1 constrain the X-ray beaming factor at 400 and 20
minutes after the burst respectively to be comparable and certainly not much
larger than the $\gamma$-ray beaming factor. There is no direct limit on the
optical beaming. However, we show that observations of several months with
existing hardware could result in a useful limit on the optical beaming factor
of GRB afterglows.


title:
Optical and Near-Infrared Imaging of the IRAS 1-Jy Sample of
  Ultraluminous Infrared Galaxies: II. The Analysis

abstract:
  The present paper discusses the results from an analysis of the images
presented in Paper I (astro-ph/0207373) supplemented with new spectroscopic
data obtained at Keck. All but one object in the 1-Jy sample show signs of a
strong tidal interaction/merger. Multiple mergers involving more than two
galaxies are seen in no more than 5 of the 118 (< 5%) systems. None of the 1-Jy
sources is in the first-approach stage of the interaction, and most (56%) of
them harbor a single disturbed nucleus and are therefore in the later stages of
a merger. Seyfert galaxies (especially those of type 1), warm ULIGs
(f_{25}/f_{60} > 0.2) and the more luminous systems (> 10^{12.5} L_sun) all
show a strong tendency to be advanced mergers with a single nucleus. An
analysis of the surface brightness profiles of the host galaxies in
single-nucleus sources reveals that about 73% of the R and K' surface
brightness profiles are fit adequately by an elliptical-like R^{1/4}-law. These
elliptical-like 1-Jy systems have luminosities, half-light radii, and R-band
axial ratio distribution that are similar to those of normal (inactive)
intermediate-luminosity ellipticals and follow with some scatter the same mu_e
- r_e relation. These elliptical-like hosts are most common among merger
remnants with Seyfert 1 nuclei (83%), Seyfert 2 optical characteristics (69%)
or mid-infrared (ISO) AGN signatures (80%). In general, the results from the
present study are consistent with the merger-driven evolutionary sequence
``cool ULIGs --> warm ULIGs --> quasars,'' although there are many exceptions.
(abridged)


title:
An Upper Limit on the Temporal Variations of the Solar Interior
  Stratification

abstract:
  We have analyzed changes in the acoustic oscillation eigenfrequencies
measured over the past 7 years by the GONG, MDI and LOWL instruments. The
observations span the period from 1994 to 2001 that corresponds to half a solar
cycle, from minimum to maximum solar activity.
  These data were inverted to look for a signature of the activity cycle on the
solar stratification. A one-dimensional structure inversion was carried out to
map the temporal variation of the radial distribution of the sound speed at the
boundary between the radiative and convective zones. Such variation could
indicate the presence of a toroidal magnetic field anchored in this region.
  We found no systematic variation with time of the stratification at the base
of the convection zone. However we can set an upper limit to any fractional
change of the sound speed at the level of $3 \times 10^{-5}$.


title: Helioseismology

abstract:
  Oscillations detected on the solar surface provide a unique possibility for
investigations of the interior properties of a star. Through major
observational efforts, including extensive observations from space, as well as
development of sophisticated tools for the analysis and interpretation of the
data, we have been able to infer the large-scale structure and rotation of the
solar interior with substantial accuracy, and we are beginning to get
information about the complex subsurface structure and dynamics of sunspot
regions, which dominate the magnetic activity in the solar atmosphere and
beyond. The results provide a detailed test of the modeling of stellar
structure and evolution, and hence of the physical properties of matter assumed
in the models. In this way the basis for using stellar modeling in other
branches of science is very substantially strengthened; an important example is
the use of observations of solar neutrinos to constrain the properties of the
neutrino.


title: Soft X-ray Spectra of Seyfert 2 Galaxies

abstract:
  High resolution spectroscopic observations of Seyfert galaxies with Chandra
and XMM-Newton allows us to study the detailed ionization and thermal
structures of the X-ray absorbing/emitting material in the circumnuclear
environment. The vast improvement in the spectral resolving power by more than
an order of magnitude enables us, for the first time, to unambiguously
distinguish the dominant line emission mechanisms and to measure its dynamical
properties as well. The X-ray band harbors spectral transitions from a wide
range of ionization states, including valence-shell transitions in K-shell and
L-shell ions from most cosmically abundant elements, as well as inner-shell
transitions of iron and other mid-Z elements, which can be probed through
absorption measurements. The X-ray spectrum, therefore, provides simultaneous
velocity and column density constraints of highly ionized to only slightly
ionized gas harbored in many of these systems. We summarize recent results that
have emerged from observations of Seyfert 2 galaxies with the grating
spectrometers onboard Chandra and XMM-Newton. We give particular emphasis to an
empirical physical model that we have developed based on the observed spectra,
and how it can be used for comparative studies with Seyfert 1 galaxies to test
the AGN unification scenarios.


title: Ultr-Luminous Infrared Galaxies: QSOs in Formation?

abstract:
  We present new near-infrared Keck and VLT spectroscopic data on the stellar
dynamics in late stage, ultra-luminous infrared galaxy (ULIRG) mergers . We now
have information on the structural and kinematic properties of 18 ULIRGs, 8 of
which contain QSO-like active galactic nuclei. The host properties (velocity
dispersion, effective radius, effective surface brightness, M_K) of
AGN-dominated and star formation dominated ULIRGs are similar. ULIRGs fall
remarkably close to the fundamental plane of early type galaxies. They populate
a wide range of the plane, are on average similar to L*-rotating ellipticals,
but are well offset from giant ellipticals and optically/UV bright, low-z
QSOs/radio galaxies. ULIRGs and local QSOs/radio galaxies are very similar in
their distributions of bolometric and extinction corrected near-IR
luminosities, but ULIRGs have smaller effective radii and velocity dispersions
than the local QSO/radio galaxy population. Hence, their host masses and
inferred black hole masses are correspondingly smaller. The latter are more
akin to those of local Seyfert galaxies. ULIRGs thus resemble local QSOs in
their near-IR and bolometric luminosities because they are (much more)
efficiently forming stars and/or feeding their black holes, and not because
they have QSO-like, very massive black holes. We conclude that ULIRGs as a
class cannot evolve into optically bright QSOs. They will more likely become
quiescent, moderate mass field ellipticals or, when active, might resemble the
X-ray bright, early type galaxies that have recently been found by the Chandra
Observatory.


title: Molecular Diagnostics of Supernova Remnant Shocks

abstract:
  We have undertaken a study of radio and infrared molecular-line emission
towards several SNRs in order to investigate molecular signatures of SNR
shocks, and to test models for OH maser production in SNRs. Here we present
results on G349.7+0.2.


title: Representations of world coordinates in FITS

abstract:
  The initial descriptions of the FITS format provided a simplified method for
describing the physical coordinate values of the image pixels, but deliberately
did not specify any of the detailed conventions required to convey the
complexities of actual image coordinates. Building on conventions in wide use
within astronomy, this paper proposes general extensions to the original
methods for describing the world coordinates of FITS data. In subsequent
papers, we apply these general conventions to the methods by which spherical
coordinates may be projected onto a two-dimensional plane and to
frequency/wavelength/velocity coordinates.


title:
The Probability Distribution of Binary Pulsar Coalescence Rates. I.
  Double Neutron Star Systems in the Galactic Field

abstract:
  Estimates of the Galactic coalescence rate (R) of close binaries with two
neutron stars (NS-NS) are known to be uncertain by large factors (about two
orders of magnitude) mainly due to the small number of systems detected as
binary radio pulsars. We present an analysis method that allows us to estimate
the Galactic NS-NS coalescence rate using the current observed sample and,
importantly, to assign a statistical significance to these estimates and to
calculate the allowed ranges of values at various confidence levels. The method
involves the simulation of selection effects inherent in all relevant radio
pulsar surveys and a Bayesian statistical analysis for the probability
distribution of the rate. The most likely values for the total Galactic
coalescence rate (R_peak) lie in the range 2-60 per Myr depending on different
pulsar population models. For our reference model 1, where the most likely
estimates of pulsar population properties are adopted, we obtain R_tot =
8_{-5}^{+9} per Myr at a 68% statistical confidence level. The corresponding
range of expected detection rates of NS-NS inspiral are 3_{-2}^{+4}x10^{-3} per
yr for the initial LIGO and 18_{-11}^{+21} per yr for the advanced LIGO.


title:
The Type Ia Supernova 1999aw: a Probable 1999aa-like Event In a
  Low-Luminosity Host Galaxy

abstract:
  SN 1999aw was discovered during the first campaign of the Nearby Galaxies
Supernova Search (NGSS) project. This luminous, slow-declining (Delta m_{15}
(B) = 0.81 \pm 0.03) Type Ia supernova was noteworthy in at least two respects.
First, it occurred in an extremely low luminosity host galaxy that was not
visible in the template images, nor in initial subsequent deep imaging.
Secondly, the photometric and spectral properties of this supernova indicate
that it very likely was similar to the subclass of Type Ia supernovae whose
prototype is SN 1999aa. This paper presents the BVRI and J_{s} HK_{s}
lightcurves of SN 1999aw (through 100 days past maximum light), as well as
several epochs of optical spectra. From these data we calculate the bolometric
light curve, and give estimates of the luminosity at maximum light and the
initial ^{56}Ni mass. In addition, we present deep BVI images obtained recently
with the Baade 6.5-meter telescope at Las Campanas Observatory which reveal the
remarkably low-luminosity host galaxy.


title: Numerical Studies of Cosmic Ray Injection and Acceleration

abstract:
  A numerical scheme that incorporates a thermal leakage injection model into a
combined gas dynamics and cosmic ray (CR, hereafter) diffusion-convection code
has been developed. The particle injection is followed numerically by filtering
the diffusive flux of suprathermal particles across the shock to the upstream
region according to a velocity-dependent transparency function that controls
the fraction of leaking particles. We have studied CR injection and
acceleration efficiencies during the evolution of CR modified planar shocks for
a wide range of initial shock Mach numbers, $M_0$, assuming a Bohm-like
diffusion coefficient. The injection process is very efficient when the
subshock is strong, leading to fast and significant modification of the shock
structure. As the CR pressure increases, the subshock weakens and the injection
rate decreases accordingly, so that the subshock does not disappear. Although
some fraction of the particles injected early in the evolution continue to be
accelerated to ever higher energies, the postshock CR pressure reaches an
approximate time-asymptotic value due to a balance between fresh
injection/acceleration and advection/diffusion of the CR particles away from
the shock. We conclude that the injection rates in strong parallel shocks are
sufficient to lead to rapid nonlinear modifications to the shock structures and
that self-consistent injection and time-dependent simulations are crucial to
understanding the non-linear evolution of CR modified shocks.


title:
A statistical detection of gamma-ray emission from galaxy clusters:
  implications for the gamma-ray background and structure formation

abstract:
  The origin of the diffuse extragalactic, high-energy gamma-ray background
(EGRB) filling the Universe remains unknown. The spectrum of this extragalactic
radiation, as measured by the EGRET on-board CGRO, is well-fit by a power law
across nearly four decades in energy, from 30 MeV to 100 GeV. It has been
estimated that not more than a quarter of the diffuse gamma-ray background
could be due to unresolved point sources. Recent studies have suggested that
much of the diffuse background could originate from the up-scatter of CMB
photons by relativistic electrons produced by shock waves in the IGM during
large-scale structure formation. In this work we search for evidence of
gamma-ray emission associated with galaxy clusters by cross-correlating high
Galactic latitude EGRET data with Abell clusters. Our results indicate a
possible association of emission with clusters at a >3-sigma level. For a
subset of the 447 richest (R>=2) clusters the mean surface brightness excess is
1.2x10^-6 ph cm^-2 s^-1 sr^-1 (>100MeV), corresponding to a typical non-thermal
bolometric luminosity of L_{gamma} ~ 1x10^44 erg s^-1. Extrapolating this
measurement and assuming no evolution we conservatively estimate that ~ 1-10 of
the EGRB could originate from clusters with z<1. For this cluster population
the predicted non-thermal luminosity is in excellent agreement with our
measurement, suggesting that the clusters have experienced mass accretion
within the last 10^9 yrs. If correct, then future gamma-ray missions, such as
GLAST should be able to directly detect nearby galaxy clusters.


title: A Spectroscopic Survey of a Sample of Active M Dwarfs

abstract:
  A moderate resolution spectroscopic survey of Fleming's sample of 54 X-ray
selected M dwarfs with photometric distances less than 25 pc is presented.
Radial and rotation velocities have been measured by fits to the H-alpha
profiles. Radial velocities have been measured by cross correlation. Artificial
broadening of an observed spectrum has produced a relationship between H-alpha
FWHM and rotation speed, which we use to infer rotation speeds for the entire
sample by measurement of the H-alpha emission line. We find 3 ultra-fast
rotators (UFRs, vsini > 100km/s), and 8 stars with 30 < vsini < 100 km/s. The
UFRs have variable emission. Cross-correlation velocities measured for
ultra-fast rotators (UFRs) are shown to depend on rotation speed and the
filtering used. The radial velocity dispersion of the sample is 17 km/s. A new
double emission line spectroscopic binary with a period of 3.55 days has been
discovered, and another known one is in the sample. Three other objects are
suspected spectroscopic binaries, and at least six are visual doubles. The only
star in the sample observed to have significant lithium is a known TW Hya
Association member, TWA 8A. These results show that there are a number of young
(< 10^8 yr) and very young (< 10^7 yr) low mass stars in the immediate solar
neighbourhood. The H-alpha activity strength does not depend on rotation speed.
Our fast rotators are less luminous than similarly fast rotators in the
Pleiades. They are either younger than the Pleiades, or gained angular momentum
in a different way.


title: Representations of celestial coordinates in FITS

abstract:
  In Paper I, Greisen & Calabretta (2002) describe a generalized method for
assigning physical coordinates to FITS image pixels. This paper implements this
method for all spherical map projections likely to be of interest in astronomy.
The new methods encompass existing informal FITS spherical coordinate
conventions and translations from them are described. Detailed examples of
header interpretation and construction are given.


title:
On the Electric Field Screening by Electron-Positron Pairs in the Pulsar
  Magnetosphere II

abstract:
  We study on the self-consistency of the pulsar polar cap model, i.e., the
problem of whether the field-aligned electric field is screened by
electron-positron pairs that are injected beyond the pair production front. We
solve the one-dimensional Poisson equation along a magnetic field line, both
analytically and numerically, for a given current density incorporating effects
of returning positrons, and we obtain the conditions for the electric-field
screening. The formula which we obtained gives the screening distance and the
return flux for given primary current density, field geometry and pair creation
rate at the pair production front.
  If the geometrical screening is not possible, for instance, on field lines
with a super-Goldreich-Julian current, then the electric field at the pair
production front is constrained to be fairly small in comparison with values
expected typically by the conventional polar cap models. This is because (1)
positive space charge by pair polarization is limited to a small value, and (2)
returning of positrons leave pair electrons behind. A previous belief that pair
creation with a pair density higher than the Goldreich-Julian density
immediately screens out the electric field is unjustified at least for for a
super Goldreich-Julian current density. We suggest some possibilities to
resolve this difficulty.


title: The r-mode instability of neutron stars with the superfluid core

abstract:
  This paper has been withdrawn by the authors, due to inappropriate
discussions in Discussions.


title: A Near-Infrared Survey for Galactic Wolf-Rayet Stars

abstract:
  Most of the Milky Way's evolved massive stellar population is hidden from
view. We can attempt to remedy this situation with near-infrared observations,
and in this paper we present our method for detecting Wolf-Rayet stars in
highly extincted regions and apply it to the inner Galaxy. Using narrow band
filters at K-band wavelengths, we demonstrate how WR stars can be detected in
regions where they are optically obscured. Candidates are selected for
spectroscopic follow-up from our relative line and continuum photometry. The
final results of applying this method with a NIR survey in the Galactic plane
will provide a more complete knowledge of the structure of the galactic disk,
the role of metallicity in massive stellar evolution, and environments of
massive star formation. In this paper we briefly describe the survey set-up and
report on recent progress. We have discovered four emission-line objects in the
inner Galaxy: two with nebular emission lines, and two new WR stars, both of
late WC subtype.


title: First Light SOFIA Instruments

abstract:
  The Stratospheric Observatory For Infrared Astronomy SOFIA will become
operational with the next two years. It will be the biggest astronomical
airborne observatory ever build, comprising a 3m-class telescope onboard a
Boeing 747SP. A suite of first-light instruments is under development striving
for cutting edge technology to make SOFIA a milestone in infrared astronomy.
Here we present an overview over the instrumentation and an update on the
current status.


title:
IP Pegasi: Investigation of the accretion disk structure. Searching
  evidences for spiral shocks in the quiescent accretion disk

abstract:
  We present the results of spectral investigations of the cataclysmic variable
IP Peg in quiescence. Optical spectra obtained on the 6-m telescope at the
Special Astrophysical Observatory (Russia), and on the 3.5-m telescope at the
German-Spanish Astronomical Center (Calar Alto, Spain), have been analysed by
means of Doppler tomography and Phase Modelling Technique. From this analysis
we conclude that the quiescent accretion disk of IP Peg has a complex
structure. There are also explicit indications of spiral shocks. The Doppler
maps and the variations of the peak separation of the emission lines confirm
this interpretation. We have detected that all the emission lines show a rather
considerable asymmetry of their wings varying with time. The wing asymmetry
shows quasi-periodic modulations with a period much shorter than the orbital
one. This indicates the presence of an emission source in the binary rotating
asynchronously with the binary system. We also have found that the brightness
of the bright spot changes considerably during one orbital period. The spot
becomes brightest at an inferior conjunction, whereas it is almost invisible
when it is located on the distant half of the accretion disk. Probably, this
phenomenon is due to an anisotropic radiation of the bright spot and an eclipse
of the bright spot by the outer edge of the accretion disk.


title: Rarefaction Shocks, Shock Errors and Low Order of Accuracy in ZEUS

abstract:
  We show that there are simple one dimensional problems for which the MHD
code, ZEUS, generates significant errors, whereas upwind conservative schemes
perform very well on these problems.


title: Superclusters with thermal SZ effect surveys

abstract:
  We use a simple analytic model to compute the angular correlation function of
clusters identified in upcoming thermal SZ effect surveys. We then compute the
expected fraction of close pairs of clusters on the sky that are also close
along the line of sight. We show how the expected number of cluster pairs as a
function of redshift is sensitive to the assumed biasing relation between the
cluster and the mass distribution. We find that, in a LambdaCDM model, the
fraction of physically associated pairs is 70% for angular separations smaller
than 20 arcmin and clusters with specific flux difference larger than 200 mJy
at 143 GHz. The agreement of our analytic results with the Hubble volume N-body
simulations is satisfactory. These results quantify the feasibility of using SZ
surveys to compile catalogues of superclusters at any redshifts.


title: Disk-Halo Model for Flat-Spectrum T Tauri Stars

abstract:
  We explore the origin of the flat spectrum seen in some T Tauri stars by
considering a three-component structure: a central star, a circumstellar disk,
and a dusty halo. The radiative energy transport is faithfully treated by
solving the angle- and frequency-dependent radiative transfer equation in two
space dimensions assuming axisymmetry, and hence the radiative equilibrium
temperature in the disk and halo is determined simultaneously. The disk is
effectively heated by the scattering and reprocessing of stellar radiation
through the halo. The large mid- to far-infrared excess originates from the
photosphere of the warmed disk, resulting in a flat spectrum, as observed. The
halo which we consider is observed as a compact reflection nebula, and is
discriminated from extended, disk-like envelopes around flat-spectrum T Tauri
stars. We show that the overall spectral shape of flat-spectrum T Tauri stars
can be reproduced by the present disk-halo model.


title: The quiescent X-ray emission of three transient X-ray pulsars

abstract:
  We report on BeppoSAX and Chandra observations of three Hard X-Ray Transients
in quiescence containing fast spinning (P<5 s) neutron stars: A 0538-66, 4U
0115+63 and V 0332+53. These observations allowed us to study these transients
at the faintest flux levels thus far. Spectra are remarkably different from the
ones obtained at luminosities a factor >10 higher, testifying that the
quiescent emission mechanism is different. Pulsations were not detected in any
of the sources, indicating that accretion of matter down to the neutron star
surface has ceased. We conclude that the quiescent emission of the three X-ray
transients likely originates from accretion onto the magnetospheric boundary in
the propeller regime and/or from deep crustal heating resulting from
pycnonuclear reactions during the outbursts.


title: Dark Matter, Dark Energy and the Chaplygin Gas

abstract:
  We formulate a Zel'dovich-like approximation for the Chaplygin gas equation
of state P = -A/rho, and sketch how this model unifies dark matter with dark
energy in a geometric setting reminiscent of M-theory.


title:
Comparison of the Black Hole and Fermion Ball Scenarios of the Galactic
  Center

abstract:
  After discussion of the properties of degenerate fermion balls, we analyze
the orbit of the star S0-1, which has a projected distance of ~5 light-days to
Sgr A*, in the supermassive black hole as well as in the fermion ball scenarios
of the Galactic center. It is shown that both scenarios are consistent with the
data, as measured during the last 6 years by Genzel and coworkers and by Ghez
and coworkers. We show that the z-v_z phase space, which fits the data, is much
larger for the fermion ball than for the black hole scenario. Future
measurements of the positions or radial velocities of S0-1 and S0-2, which
could be orbiting within such a fermion ball, may reduce this allowed phase
space and eventually rule out one of the currently acceptable scenarios.


title: Dynamical evolution of high velocity clouds in the intergalactic medium

abstract:
  HI observations of high-velocity clouds (HVCs) indicate, that they are
interacting with their ambient medium. Even clouds located in the very outer
  Galactic halo or the intergalactic space seem to interact with their ambient
medium. In this paper, we investigate the dynamical evolution of high velocity
neutral gas clouds moving through a hot magnetized ambient plasma by means of
two-dimensional magnetohydrodynamic plasma-neutral gas simulations.
  This situation is representative for the fast moving dense neutral gas
cloudlets in the Magellanic Stream as well as for high velocity clouds in
general. The question on the dynamical and thermal stabilization of a cold
dense neutral cloud in a hot thin ambient halo plasma is numerically
investigated. The simulations show the formation of a comet-like head-tail
structure combined with a magnetic barrier of increased field strength which
exerts a stabilizing pressure on the cloud and hinders hot plasma from
diffusing into the cloud.
  The simulations can explain both the survival times in the intergalactic
medium and the existence of head-tail high velocity clouds.


title:
A Millisecond Pulsar Optical Counterpart with Large-Amplitude
  Variability in the Globular Cluster 47 Tucanae

abstract:
  Using extensive HST imaging, combined with Chandra X-ray and Parkes radio
data, we have detected the optical binary companion to a second millisecond
pulsar (MSP) in the globular cluster 47 Tucanae. This faint (V=22.3) blue
(V-I=0.7) star shows a large amplitude (60-70%) sinusoidal variation in both V
and I. The period (3.19066 hr) and phase of the variation match those of the
MSP 47 Tuc W (which does not have an accurate radio timing position) to within
0.5 seconds and 1.2 minutes respectively, well within the ~1sigma errors. The
phase dependence of the intensity and color implies that heating of a tidally
locked companion causes the observed variations. The eclipsing nature of this
MSP in the radio, combined with the relatively large companion mass (> 0.13
solar masses) and the companion's position in the color-magnitude diagram,
suggest that the companion is a main sequence star, a rare circumstance for an
MSP companion. This system is likely to have had a complex evolution and
represents an interesting case study in MSP irradiation of a close companion.
We present evidence for another optical variable with similar properties to the
companion of 47 Tuc W. This variable may also be an MSP companion, although no
radio counterpart has yet been detected.


title: Dynamical models for jet deceleration in the radio galaxy 3C 31

abstract:
  We present a dynamical analysis of the flow in the jets of the low-luminosity
radio galaxy 3C 31 based on our earlier geometrical and kinematic model and on
estimates of the external pressure and density distributions from Chandra
observations. We apply conservation of particles, energy and momentum to derive
the variations of pressure and density along the jets and show that there are
self-consistent solutions for deceleration by injection of thermal matter. We
initially take the jets to be in pressure equilibrium with the external medium
at large distances from the nucleus and the momentum flux to be energy flux/c;
we then progressively relax these constraints. We infer that the jets are
over-pressured compared with the external medium where they start to expand
rapidly. Local minima in the density and pressure and maxima in the mass
injection rate and Mach number occur at approximately 3 kpc. Further out, the
jets decelerate smoothly with a Mach number close to 1. The mass injection rate
we infer is comparable with that expected from stellar mass loss at 1 - 2 kpc,
but significantly exceeds it at large distances. We conclude that entrainment
from the galactic atmosphere is the dominant mass input process far from the
nucleus, but that stellar mass loss may also contribute closer in. The
occurrence of a significant over-pressure where expansion begins leads us to
suggest that there is a stationary shock system, perhaps caused by
reconfinement of an initially free jet. Our results are compatible with a jet
consisting of electron-positron plasma on parsec scales which picks up thermal
matter from stellar mass loss to reach the inferred density and mass flux at 1
kpc, but we cannot rule out an electron-proton composition with a low-energy
cut-off. [Abridged]


title: The optical counterpart of the ultra-luminous x-ray source NGC 5204 X-1

abstract:
  We use archival HST/WFPC2 V and I band images to show that the optical
counterpart to the ultra-luminous x-ray source NGC 5204 X-1, reported by
Roberts et al., is composed of two sources separated by 0.5''. We have also
identified a third source as a possible counterpart, which lies 0.8'' from the
nominal x-ray position. PSF fitting photometry yields V-band magnitudes of
20.3, 22.0 and 22.4 for the three sources. The V-I band colours are 0.6, 0.1,
and -0.2, respectively (i.e. the fainter sources are bluer). We find that all
V-I colours and luminosities are consistent with those expected for young
stellar clusters (age <10 Myr).


title:
Multiwavelength Observation of SS433 Jet Interaction with the
  Interstellar Medium

abstract:
  SS433 is an X-ray binary emitting persistent relativistic double sided jets
that expand into the surrounding W50 radio nebula. The SS433/W50 system is then
an excellent laboratory for studying relativistic jet interaction with the
surrounding interstellar medium. In this context, part of W50 nebula has been
mapped with ISOCAM at 15 micron, where the large scale X-ray jets are observed.
I will show the results, particularly on the W50 western lobe, on two emitting
regions detected in IR with IRAS, and observed in millimeter wavelength
(CO(1-0) transition). It is uncertain whether these regions are due to heated
dust by either young stars or the relativistic jet, or to synchrotron emission
from shock re-acceleration regions as in some extragalactic jets from AGN. In
this latter case, INTEGRAL might detect soft gamma-ray emission.


title: Fitting the Supernova Type Ia Data with the Chaplygin Gas

abstract:
  The supernova type Ia observational data are fitted using a model with cold
dark matter and the Chaplygin gas. The Chaplygin gas, which is characterized by
a negative pressure varying with the inverse of density, represents in this
model the dark energy responsible for the accelaration of the universe. The
fitting depends essentially on four parameters: the Hubble constant, the
velocity of sound of the Chaplygin gas and the fraction density of the
Chaplygin gas and the cold dark matter. The best fitting model is obtained with
H_0 = 65 km/Mpc.s, $c_s^2 \sim 0.92c$ and Omega_{c0} = 1, Omega_{m0} = 0, that
is, a universe completely dominated by the Chaplygin gas. This reinforces the
possibility that the Chaplygin gas may unify dark matter and dark energy, as it
has already been claimed in the literature.


title:
Chandra Observations of the Evolving Core of the Starburst Galaxy NGC
  253

abstract:
  Chandra observations of the core of the nearby starburst galaxy NGC 253
reveal a heavily absorbed source of hard X-rays embedded within the nuclear
starburst region. The source has an unabsorbed, 2 to 10 keV luminosity of
>=10^39 erg/s and photoionizes the surrounding gas. We observe this source
through a dusty torus with a neutral absorbing column density of NH ~ 2x10^23
cm^-2. The torus is hundreds of pc across and collimates the starburst-driven
nuclear outflow. We suggest that the ionizing source is an intermediate-mass
black hole or a weakly accreting supermassive black hole, which may signal the
beginnings or endings of AGN activity.


title:
NGC 5506 Unmasked as a Narrow Line Seyfert 1: A Direct View of the Broad
  Line Region using Near-IR Spectroscopy

abstract:
  This letter presents incontrovertible evidence that NGC5506 is a Narrow Line
Seyfert 1 (NLSy1). Our new 0.9-1.4 micron spectrum of its nucleus clearly shows
the permitted OI 1.1287 micron line (with full width at half maximum <2000
km/s) and the `1 micron FeII lines'. These lines can only originate in the
optically-thick broad line region (BLR) and, among Seyfert nuclei the latter
series of lines are seen only in NLSy1s. The obscuration to the BLR, derived
from a rough estimate of the OI 1.1287 micron / OI 8446 Angstrom ratio and from
the reddening of the near-IR Paschen lines, is A_v > 5. Together, these results
make NGC5506 the first identified case of an optically-obscured NLSy1. This new
classification helps explain its radio to X-ray properties, which until now
were considered highly anomalous. However, interesting new concerns are raised:
e.g., NGC5506 is unusual in hosting both a `type 1' AGN and a nuclear water
vapor megamaser. As the brightest known NLSy1, NGC5506 is highly suitable for
study at wavebands less affected by obscuration.


title:
The Chandra Deep Field North Survey. XII. The Link Between Faint X-ray
  and Radio Source Populations

abstract:
  We investigate the relationship between faint X-ray and 1.4 GHz radio source
populations detected within 3' of the Hubble Deep Field North using the 1 Ms
Chandra and 40 uJy VLA surveys. Within this region, we find that ~42% of the 62
X-ray sources have radio counterparts and ~71% of the 28 radio sources have
X-ray counterparts; thus a 40 uJy VLA survey at 1.4 GHz appears to be
well-matched to a 1 Ms Chandra observation. Among the different source
populations sampled, we find that the majority of the 18 X-ray detected
emission-line galaxies (ELGs) have radio and mid-infrared ISOCAM counterparts
and appear to be luminous star-forming galaxies at z=0.3-1.3. Importantly, the
radio-detected ELGs make up ~35% of the X-ray source population at 0.5-8.0 keV
X-ray fluxes between ~(1-5)x10e-16 erg/cm2/s and signal the emergence of the
luminous, high-z starburst galaxy population in the X-ray band. We find that
the locally-determined correlation between X-ray luminosities and 1.4 GHz radio
luminosity densities of the late-type galaxies can easily be extended to
include the luminous intermediate-redshift ELGs, suggesting that the X-ray and
radio emission processes are generally associated in star-forming galaxies.
This result implies that the X-ray emission can be used as an indicator of star
formation rate for star-forming galaxies. Finally, we show that there appear to
be two statistically distinct types of ISOCAM-detected star-forming galaxies:
those with detectable radio and X-ray emission and those without. The latter
type may have stronger mid-infrared emission-line features that increase their
detectability at mid-infrared wavelengths.


title: Carbon Isotopic Abundances in the Red Giants of Omega Centauri (NGC5139)

abstract:
  Carbon-12 and carbon-13 abundances are measured in eleven red-giant members
of the globular cluster Omega Centauri via observations of first-overtone CO
bands near 2.3 microns. The mean value for the entire sample is <12C/13C>= 4.3
+/-0.4, with nine giants equal, within the errors, to the equilibrium ration of
12C/13C= 3.5. No correlation is found within Omega Cen between 12C/13C and the
abundance of iron. The relation between 12C/13C and other abundance ratios,
such as [O/Fe], {Na/Fe], or [Al/Fe] are also discussed.


title: A New Dynamical Mean-Field Dynamo Theory and Closure Approach

abstract:
  We develop a new nonlinear mean field dynamo theory that couples field growth
to the time evolution of the magnetic helicity and the turbulent electromotive
force, $\emfb$. We show that the difference between kinetic and current
helicities emerges naturally as the growth driver when the time derivative of
$\emfb$ is coupled into the theory. The solutions predict significant field
growth in a kinematic phase and a saturation rate/strength that is magnetic
Reynolds number dependent/independent in agreement with numerical simulations.
The amplitude of early time oscillations provides a diagnostic for the closure.


title: Relativistic Jets in Collapsars

abstract:
  We examine the propagation of 2-dimensional relativistic jets through the
stellar progenitor in the collapsar model for gamma-ray bursts. In agreement
with previous studies, we find that relativistic jets are collimated by their
passage through the stellar mantle. Interaction of these jets with the star and
their own cocoons also causes mixing that sporadically decelerates the flow. We
speculate that this mixing instability is chiefly responsible for the variable
Lorentz factor needed in the internal shock model and for the complex light
curves seen in many GRBs. In all cases studied, the jet is shocked deep inside
the star following a brief period of adiabatic expansion. The jet that finally
emerges from the star thus has a moderate Lorentz factor, modulated by mixing,
and a very large internal energy. In a second series of calculations, we follow
the escape of that sort of jet. Because of the large ratio of internal to
kinetic energy in both the jet and its cocoon, the opening angle of the final
jet is significantly greater than at breakout. A small amount of material
emerges at large angles, but with a Lorentz factor still sufficiently large to
make a weak GRB. This leads us to propose a "unified model" in which a variety
of high energy transients, ranging from x-ray flashes to "classic" GRBs, may be
seen depending upon the angle at which a standard collapsar is observed. We
also speculate that the breakout of a relativistic jet and its collision with
the stellar wind will produce a brief transient with properties similar to the
class of "short-hard" GRBs. Implications of our calculations for GRB light
curves, the luminosity-variability relation, and the GRB-supernova association
are also discussed. (Abridged)


title:
Pulsar Wind Nebulae and Particle Acceleration in the Pulsar
  Magnetosphere

abstract:
  This paper deals with the Crab Nebula problem to suggest that particle
acceleration takes place not only at the inner shock but also over a larger
region in the nebula with disordered magnetic field.
  Kennel and Cornoniti (1984) constructed a spherically symmetric model of the
Crab Nebula and concluded that the pulsar wind which excites the nebular is
kinetic-energy dominant (KED) because the nebula flow induced by KED wind is
favorable to explain the nebula spectrum and expansion speed. This is true even
with new Chandra observation, which provides newly the spatially resolved
spectra. We have shown below with 3D modelling and the Chandra image that pure
toroidal magnetic field and KED wind are incompatible with the Chandra
observation.


title: Cyclical period changes in Z Chamaeleontis

abstract:
  We report the identification of cyclical changes in the orbital period of the
eclipsing dwarf nova Z Cha. We used times of mid-eclipse collected from the
literature and our new eclipse timings to construct an
observed-minus-calculated diagram covering 30 years of observations
(1972-2002). The data present cyclical variations that can be fitted by a
linear plus sinusoidal function with period 28+/-2 yr and amplitude 1.0+/-0.2
minute. The statistical significance of this period by an F-test is larger than
99.9%. The derived fractional period change, Delta P/P= 4.4 x 10^{-7}, is
comparable to that of other short-period cataclysmic variables (CVs), but is
one order of magnitude smaller than those of the long-period CVs. Separate fits
to the first and second half of the data lead to ephemerides with quite
different cycle periods and amplitudes, indicating that the variation is not
sinusoidal or, most probably, is not strictly periodic. The observed cyclical
period change is possibly caused by a solar-type magnetic activity cycle in the
secondary star. An incremental variation in the Roche lobe of the secondary
star of Delta R_{L2}/R_{L2} = 1.7 x 10^{-4} is required in order to explain
both the observed period change and the modulation of the quiescent brightness
previously reported by Ak, Ozkan & Mattei.


title:
Possible geometries of afterglow generation in the gamma-ray burst
  GRB990705

abstract:
  The absorption feature detected in the prompt X-ray emission of GRB990705 has
important consequences for its circum-burst environment and therefore on its
afterglows. Here we investigate whether the circum-burst environment
constrained by the absorption feature could be consistent with the observed
H-band afterglow, which exhibits an earlier power law decay but a much faster
decay about one day after the burst. Two possible geometries of the
afterglow-emitting regions are suggested: 1) afterglow emission produced by the
impact of the fireball on the surrounding torus, which serves as the absorbing
material of the X-ray feature, as would be expected in the models involving
that a supernova explosion precedes the gamma-ray burst by some time;
2)afterglow emission produced in the dense circum-burst medium inside the
torus. In case 1), the faster decay at the later time is attributed to the
disappearance of the shock due to the counter-pressure in the hot torus
illuminated by the burst and afterglow photons. For case 2), the circum-burst
medium density is found to be very high ($n\ga 10^4-10^5 {\rm cm^{-3}}$) if the
emitting plasma is a jet or even higher if it is spherical. Future better
observations of afterglows of GRBs that have absorption features might make it
possible to make a more definite choice between these two scenarios.


title: X-ray Astronomical Polarimetry in the XEUS Era

abstract:
  X-ray Polarimetry is almost as old as X-ray Astronomy. Since the first
discovery of X-ray sources theoretical analysis suggested that a high degree of
linear polarization could be expected due either to the, extremely non thermal,
emission mechanism or to the transfer of radiation in highly asymmetric
systems. The actual implementation of this subtopic was, conversely, relatively
deceiving. This is mainly due to the limitation of the conventional techniques
based on the Bragg diffraction at 45deg, or on Thomson scattering around 90deg.
Acually no X-ray Polarimeter has been launched since 25 years. Nevertheless the
expectations from such measurement on several astrophysical targets including
High and Low Mass X-Ray Binaries, isolated neutron Stars, Galactic and
Extragalactic Black Holes is extremely attractive. We developed a new technique
to measure the linear polarization of X-ray sources. It is based on the
visualization of photoelectron tracks in a, finely subdivided, gas filled
detector (micropattern). The initial direction of the photoelectron is derived
and from the angular distribution of the tracks the amount and angle of
polarization is computed. This technique can find an optimal exploitation in
the focus of XEUS-1. Even in a very conservative configuration (basically the
already existing prototype) the photoelectric polarimeter could perform
polarimetry at % level on many AGNs. Further significant improvements can be
expected from a technological development on the detector and with the use of
XEUS-2 telescope.


title: Antimatter in the Universe

abstract:
  Different scenarios of baryogenesis are briefly reviewed from the point of
view of possibility of generation of cosmologically interesting amount of
antimatter. It is argued that creation of antimatter is possible and natural in
many models. In some models not only anti-helium may be produced but also a
heavier anti-elements and future observations of the latter would be critical
for discovery or establishing stronger upper limits on existence of antimatter.
Incidentally a recent observation of iron-rich quasar may present a support to
one special model of antimatter creation.


title: The multimode pulsation of the delta Scuti star V784 Cassiopeae

abstract:
  We present an analysis of new Johnson and Stromgren photometric and
medium-resolution spectroscopic observations of the delta Scuti type variable
star V784 Cassiopeae. The data were obtained in three consecutive years between
1999 and 2001. The period analysis of the light curve resulted in the detection
of four frequencies ranging from 9.15 c/d to 15.90 c/d, while there is a
suggestion for more, unresolved frequency components, too. The mean Stromgren
indices and Hipparcos parallax were combined to calculate the following
physical parameters: <T_eff>=7100+-100 K, log g=3.8+-0.1, M_bol=1.50+-0.15 mag.
The position of the star in the HR diagram was used to derive evolutionary mass
and age yielding to a consistent picture of an evolved delta Scuti star with a
mixture of radial plus non-radial modes.


title: Results from a Second RXTE Observation of the Coma Cluster

abstract:
  The RXTE satellite observed the Coma cluster for 177 ksec during November and
December 2000, a second observation motivated by the intriguing results from
the first 87 ksec observation in 1996. Analysis of the new dataset confirms
that thermal emission from isothermal gas does not provide a good fit to the
spectral distribution of the emission from the inner 1 degree radial region.
While the observed spectrum may be fit by emission from gas with a substantial
temperature gradient, it is more likely that the emission includes also a
secondary non-thermal component. If so, non-thermal emission comprises ~8% of
the total 4--20 keV flux. Interpreting this emission as due to Compton
scattering of relativistic electrons (which produce the known extended radio
emission) by the cosmic microwave background radiation, we determine that the
mean, volume-averaged magnetic field in the central region of Coma is B =
0.1-0.3 microgauss.


title:
Mid-Infrared Spectroscopy of Infrared Luminous Galaxies with
  Sub-Arcsecond Resolution

abstract:
  Low spectral resolution (delta lambda/lambda ~ 50) mid-infrared observations
with high angular resolution (0.3--0.5'') using the Long Wavelength
Spectrometer on the Keck I Telescope are reported of the nuclei of five highly
luminous infrared bright galaxies. Spectra of eight distinct nuclei, ranging in
luminosity from 10^11 L_sun to >10^12 L_sun have been obtained. Four of the
nuclei show the characteristic PAH emission features, i.e. 11.3 micron emission
as well as the 8.6 micron shoulder of the 7.7 micron band. The other nuclei
show either weak PAH emission bands or no evidence for these bands. The high
spatial resolution of the observations reveals extended emission in the 11.3
micron PAH band associated with several of the compact nuclear sources. When
proper account is taken of the diffuse PAH emission, most of the compact
sources show little or no directly associated PAH emission. The diffuse PAH
emission is extended over spatial scales of 100--500 pc; its presence shows
that there is significant circumnuclear UV/optical emission exciting the
aromatic bands, most likely associated with circumnuclear starbursts. After the
spectra of the nuclear sources are corrected for the spectrum of the diffuse
PAH emission, the peak apparent silicate optical depth at 9.7 microns can be as
great as 15, corresponding to > 150 magnitudes of visible light extinction.
Because of the large silicate optical depths, mid-infrared spectra are not
probing the nature of the true nuclei in the most opaque compact sources.


title: Evolution of the cluster X-ray scaling relations since z>0.4

abstract:
  We derive correlations between X-ray temperature, luminosity, and gas mass
for a sample of 22 distant, z>0.4, galaxy clusters observed with Chandra. We
detect evolution in all three correlations between z>0.4 and the present epoch.
In particular, in the Omega=0.3, Lambda=0.7 cosmology, the luminosity
corresponding to a fixed temperature scales approximately as (1+z)**(1.5+-0.3);
the gas mass for a fixed luminosity scales as (1+z)**(-1.8+-0.4); and the gas
mass for a fixed temperature scales as (1+z)**(-0.5+-0.4) (all uncertainties
are 90% confidence). We briefly discuss the implication of these results for
cluster evolution models.


title:
X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A
  Puzzling Disconnectedness

abstract:
  We present optical broadband (B and R) observations of the Seyfert 1 nucleus
NGC 3516, obtained at Wise Observatory from March 1997 to March 2002,
contemporaneously with X-ray 2-10 keV measurements with RXTE. With these data
we increase the temporal baseline of this dataset to 5 years, more than triple
to the coverage we have previously presented for this object. Analysis of the
new data does not confirm the 100-day lag of X-ray behind optical variations,
tentatively reported in our previous work. Indeed, excluding the first year's
data, which drive the previous result, there is no significant correlation at
any lag between the X-ray and optical bands. We also find no correlation at any
lag between optical flux and various X-ray hardness ratios. We conclude that
the close relation observed between the bands during the first year of our
program was either a fluke, or perhaps the result of the exceptionally bright
state of NGC 3516 in 1997, to which it has yet to return. Reviewing the results
of published joint X-ray and UV/optical Seyfert monitoring programs, we
speculate that there are at least two components or mechanisms contributing to
the X-ray continuum emission up to 10 keV: a soft component that is correlated
with UV/optical variations on timescales >1 day, and whose presence can be
detected when the source is observed at low enough energies (about 1 keV), is
unabsorbed, or is in a sufficiently bright phase; and a hard component whose
variations are uncorrelated with the UV/optical.


title:
Application of MHD Disk Wind Solutions to Planetary/Protoplanetary
  Nebulae

abstract:
  Winds from accretion disks have been proposed as the driving source for
precessing jets and extreme bipolar morphologies in Planetary Nebulae (PNe) and
proto-PNe (pPNe). In this paper we address the applicability MHD disk wind
models to PNe and pPNe. We first review Pelletier & Pudritz's (1992) non
self-similar approach to magneto-centrifugal disk winds. We then discuss
conditions which may occur in PNe and pPNe accretion disks that form via binary
interactions. Finally, examining conditions on dimensionless parameters needed
for the magneto-centrifugal disk wind model, we show that such winds can
recover the observed momentum and energy input rates for PNe and pPNe. High
accretion rates ($M_a \approx 10^{-4}$ \mdot) may be required in the latter
case. We find that the observed {\it total} energy and momentum in pPNe can be
recovered with disk wind models using existing disk formation scenarios. When
combined with existing scenarios for accretion disk formation from disrupted
stellar companions, our models may provide an explanation for the existence of
high speed polar knots (FLIERS) observed in some PNe.


title:
Smoothed particle hydrodynamics for galaxy formation simulations:
  improved treatments of multiphase gas, of star formation and of supernovae
  feedback

abstract:
  We investigate a new implementation of the Smoothed Particle Hydrodynamics
technique (SPH) designed to improve the realism with which galaxy formation can
be simulated. In situations where cooling leads to the coexistence of phases of
very different density and temperature, our method substantially reduces
artificial overcooling near phase boundaries, prevents the exclusion of hot gas
from the vicinity of cold ``clouds'', and allows relative motion of the two
phases at each point. We demonstrate the numerical stability of our scheme in
the presence of extremely steep density and temperature gradients, as well as
in strong accretion shocks and cooling flows. In addition, we present new
implementations of star formation and feedback which simulate the effect of
energy injection into multiphase gas more successfully than previous schemes.
Our feedback recipes deposit thermal energy separately in cold dense gas and
hot diffuse gas, and can explicitly reinject cold gas into the hot phase. They
make it possible to damp star formation effectively, to reheat cold gas, and to
drive outflows into the galaxy halo and beyond. We show feedback effects to be
strongest in small mass objects where much of the gas can be expelled. After
idealised tests, we carry out a first low resolution study of galaxy formation
in a $\Lambda$CDM universe. Feedback results in substantial and mass-dependent
reductions in the total baryonic mass gathered onto the final object as well as
in significant modulation of the star formation history.


title:
Mechanical Alignment of Suprathermal Paramagnetic Cosmic-Dust Granules:
  the Cross-Section Mechanism

abstract:
  We develop a comprehensive quantitative description of the cross-section
mechanism discovered several years ago by Lazarian. This is one of the
processes that determine grain orientation in clouds of suprathermal cosmic
dust. The cross-section mechanism manifests itself when an ensemble of
suprathermal paramagnetic granules is placed in a magnetic field and is subject
to ultrasonic gas bombardment. The mechanism yields dust alignment whose
efficiency depends upon two factors: the geometric shape of the granules, and
the angle Phi between the magnetic line and the gas flow. We calculate the
quantitative measure of this alignment, and study its dependence upon the said
factors. It turns out that, irrelevant of the grain shape, the action of a flux
does not lead to alignment if Phi = arccos(1/sqrt{3}).


title: On the Mass of M31

abstract:
  Recent work by several groups has established the properties of the dwarf
satellites to M31. We reexamine the reported kinematics of this group employing
a fresh technique we have developed previously. By calculating the distribution
of a chi statistic (which we define in the paper) for the M31 system, we
conclude that the total mass (disk plus halo) of the primary is unlikely to be
as great as that of our own Milky Way. In fact the chi distribution for M31
indicates that, like NGC 3992, it does not have a massive halo. In contrast,
the analysis of the satellites of NGC 1961 and NGC 5084 provides strong
evidence for massive halos surrounding both spiral galaxies.


title:
A CLEAN-based Method for Deconvolving Interstellar Pulse Broadening from
  Radio Pulses

abstract:
  Multipath propagation in the interstellar medium distorts radio pulses, an
effect predominant for distant pulsars observed at low frequencies. Typically,
broadened pulses are analyzed to determine the amount of propagation-induced
pulse broadening, but with little interest in determining the undistorted pulse
shapes. In this paper we develop and apply a method that recovers both the
intrinsic pulse shape and the pulse broadening function that describes the
scattering of an impulse. The method resembles the CLEAN algorithm used in
synthesis imaging applications, although we search for the best pulse
broadening function, and perform a true deconvolution to recover intrinsic
pulse structre. As figures of merit to optimize the deconvolution, we use the
positivity and symmetry of the deconvolved result along with the mean square
residual and the number of points below a given threshold. Our method makes no
prior assumptions about the intrinsic pulse shape and can be used for a range
of scattering functions for the interstellar medium. It can therefore be
applied to a wider variety of measured pulse shapes and degrees of scattering
than the previous approaches. We apply the technique to both simulated data and
data from Arecibo observations.


title:
The coronal topology of the rapidly rotating K0 dwarf, AB Doradus I.
  Using surface magnetic field maps to model the structure of the stellar
  corona

abstract:
  We re-analyse spectropolarimetric data of AB Dor taken in 1996 December using
a surface imaging code that can model the magnetic field of the star as a
non-potential current-carrying magnetic field. We find that a non-potential
field needs to be introduced in order to fit the dataset at this epoch. This
non-potential component takes the form of a strong unidirectional azimuthal
field of a similar strength to the radial field. This azimuthal field is
concentrated around the boundary of the dark polar spot recovered at the
surface of the star using Doppler imaging. As polarization signatures from the
center of starspots are suppressed, it is unclear whether or not this
non-potential component genuinely represents electric current at the unspotted
surface or whether it results from the preferred detection of horizontal field
in starspot penumbrae. This model contains 20% more energy than the
corresponding potential field model at the surface. This amount of free energy
drops to under 1% about 1R* above the photosphere.
  We use these surface maps to model the coronal structure of the star. The
mixed radial polarities at the pole in the surface maps support closed coronal
loops in the high latitude regions, indicating that a component of the X-ray
emission may originate in this area. Assuming that the field remains closed out
to 5R*, we find stable surfaces where prominences may form out to the observed
distances using this coronal model.


title: Origin of Radially Increasing Stellar Scaleheight in a Galactic Disk

abstract:
  For the past twenty years, it has been accepted that the vertical scaleheight
of the stellar disk in spiral galaxies is constant with radius. However, there
is no clear physical explanation for this in the literature. Here we calculate
the vertical stellar scaleheight for a self-gravitating stellar disk including
the additional gravitational force of the HI and H_2 gas and the dark matter
halo. We apply our model to two edge-on galaxies, NGC 891 and NGC 4565, and
find that the resulting scaleheight shows a linear increase of nearly a factor
of two within the optical disk for both these galaxies. Interestingly, we show
that the observed data when looked at closely, do not imply a constant
scaleheight but actually support this moderate flaring in scaleheight.


title:
The three-point correlation function of cosmic shear: I. The natural
  components

abstract:
  Previous work on three-point statistics of cosmic shear has mainly
concentrated on the convergence, or on aperture measures of the shear. However,
as has become clear recently for the two-point statistics of cosmic shear, the
basic quantity that should be used is the correlation function: first, it is
much easier to measure from observational data, since it is immune against
complicated geometries of data fields; second, all other (linear) 2-pt
statistics can be expressed as integrals over the correlation function. The
situation is the same for the 3-pt statistics. However, in contrast to the 2-pt
correlation function, the invariants of the shear 3-pt correlation function
have not been employed yet. Here we consider the transformation properties of
the shear 3-pt correlation function under rotations. We show that there are
four complex linear combinations of components of the 3-pt correlation
function, which we shall call `natural components', since they are multiplied
just by a phase factor for arbitrary rotations, but do not mix. In particular,
their moduli are invariant under rotations and thus (non-linear) invariants of
the 3-pt correlation function. In terms of these natural components, the
invariance of the statistical properties of the shear field under parity
transformations are easily obtained. Our results do not apply only to cosmic
shear, but also to other quantities with the same mathematical properties --
that of a polar. For example, practically every relation derived here applies
also to the polarization of the cosmic microwave background radiation.


title:
The Munich Near-Infrared Cluster Survey -- IV. Biases in the
  Completeness of Near-Infrared Imaging Data

abstract:
  We present the results of completeness simulations for the detection of point
sources as well as redshifted elliptical and spiral galaxies in the K'-band
images of the Munich Near-Infrared Cluster Survey (MUNICS). The main focus of
this work is to quantify the selection effects introduced by threshold-based
object detection algorithms used in deep imaging surveys. Therefore, we
simulate objects obeying the well-known scaling relations between effective
radius and central surface brightness, both for de Vaucouleurs and exponential
profiles. The results of these simulations, while presented for the MUNICS
project, are applicable in a much wider context to deep optical and
near-infrared selected samples. We investigate the detection probability as
well as the reliability for recovering the true total magnitude with Kron-like
(adaptive) aperture photometry. The results are compared to the predictions of
the visibility theory of Disney and Phillipps in terms of the detection rate
and the lost-light fraction. Additionally, the effects attributable to seeing
are explored. The results show a bias against detecting high-redshifted massive
elliptical galaxies in comparison to disk galaxies with exponential profiles,
and that the measurements of the total magnitudes for intrinsically bright
elliptical galaxies are systematically too faint. Disk galaxies, in contrast,
show no significant offset in the magnitude measurement of luminous objects.
Finally we present an analytic formula to predict the completeness of
point-sources using only basic image parameters.


title:
The expected thermal precursors of gamma-ray bursts in the internal
  shock model

abstract:
  The prompt emission of gamma-ray bursts probably comes from a highly
relativistic wind which converts part of its kinetic energy into radiation via
the formation of shocks within the wind itself. Such "internal shocks" can
occur if the wind is generated with a highly non uniform distribution of the
Lorentz factor. We estimate the expected photospheric emission of such a wind
when it becomes transparent. We compare this thermal emission (temporal profile
+ spectrum) to the non-thermal emission produced by the internal shocks. In
most cases, we predict a rather bright thermal emission that should already
have been detected. This favors acceleration mechanisms for the wind where the
initial energy input is under magnetic rather than thermal form. Such scenarios
can produce thermal X-ray precursors comparable to those observed by GINGA and
WATCH/GRANAT.


title:
Kinematics of Galaxies in the Hubble Deep Field South: Discovery of a
  Very Massive Spiral at z=0.6

abstract:
  We report the first results from a study of the internal kinematics, based on
spatially resolved H_alpha velocity profiles, of three galaxies at redshift
z~0.6 and one at redshift z~0.8, detected by ISOCAM in the Hubble Deep Field
South. The kinematics are derived from high resolution near-infrared VLT
spectroscopy. One of the galaxies is a massive spiral which possesses a very
large rotational velocity of 460 km/s and contains a mass of 10^12 M_solar
(within 20 kpc), significantly higher than the dynamical masses measured in
most other local and high redshift spirals. Two of the galaxies comprise a
counter-rotating interacting system, while the fourth is also a large spiral.
The observed galaxies are representative examples of the morphologies
encountered among ISOCAM galaxies. The mass-to-light (M /L_bol) ratios of
ISOCAM galaxies lie between those of local luminous IR galaxies and massive
spirals. We measure an offset of 1.6+/-0.3 mag in the rest frame B-band and of
0.7+/-0.3 mag in the rest frame I-band when we compare the four ISOCAM galaxies
to the local Tully-Fisher B and I-band relations. We conclude that the large IR
luminosity of the ISOCAM population results from a combination of large mass
and efficient triggering of star formation. Since ISOCAM galaxies contribute
significantly to the Cosmic Infrared Background our results imply that a
relatively small number of very massive and IR luminous objects contribute
significantly to the IR background and star formation activity near z~0.7.


title:
Gravitational wave detection using electromagnetic modes in a resonance
  cavity

abstract:
  We present a proposal for a gravitational wave detector, based on the
excitation of an electromagnetic mode in a resonance cavity. The mode is
excited due to the interaction between a large amplitude electromagnetic mode
and a quasi-monochromatic gravitational wave. The minimum metric perturbation
needed for detection is estimated to the order 7.10^(-23) using current data on
superconducting niobium cavities. Using this value together with different
standard models predicting the occurrence of merging neutron star or black hole
binaries, the corresponding detection rate is estimated to 1-20 events per
year, with a `table top' cavity of a few meters length.


title: The ISO Galactic Metallicity Gradient Revisited

abstract:
  Two independent groups (Giveon et al. 2002; Martin-Hernandez et al. 2002)
have recently investigated the Galactic metallicity gradient as probed by ISO
observations of mid-infrared emission lines from HII regions. We show that the
different gradients inferred by the two groups are due to differing source
selection and differing extinction corrections. We show that both data sets in
fact provide consistent results if identical assumptions are made in the
analysis. We present a consistent set of gradients in which we account for
extinction and variation in electron temperature across the disk.


title: Compact Intraday Variable Radio Cores: New Observational Approaches

abstract:
  The evidence for refractive interstellar scintillation (RISS) being the main
cause for rapid intraday variations (Intraday Variability, IDV) in Quasars and
BL Lacs has recently become stronger. If IDV is still a complex composition of
extrinsic and source intrinsic effects, the intrinsic part of the IDV pattern
should show up in the millimeter and sub-millimeter regime due to the frequency
dependence of RISS. Hence, observations at higher frequencies are essential in
order to exclude RISS as the sole cause of IDV. Here we report on our new
attempt to search for rapid variations at much higher frequencies. In addition,
the possibility of a direct detection of the postulated scattering screen in
front of IDV sources will be discussed. Our recent line observations towards a
few IDV sources lead to the first detection of a high latitude molecular cloud
in front of an intraday variable radio core.


title: Morphological Classification of the OSU Bright Spiral Galaxy Survey

abstract:
  To quantify the distribution of bar shapes in spiral galaxies, we have
analysed 113 H-band and 89 B-band galaxy images from the Ohio State University
Bright Spiral Galaxy Survey. Parameters measuring bar shape and position along
the Hubble sequence were obtained in each waveband. Evidence was found for a
bimodality in the distribution of bar shape, implying that barred and unbarred
galaxies are not just the extrema of a single distribution, and that any
evolution between these two states must occur on a rapid timescale. Objective
bar shapes measured in the H-band were found to be more closely related to
visual classifications than B-band bar strengths, as the B-band images are
somewhat compromised by localised star formation, especially in later-type
systems. Galaxies were found to be more centrally concentrated in the infrared.
Later type galaxies showed greater asymmetry in the optical than the infrared,
presumably again due to localised star formation, but on average the bar
strengths in the two bands were found to be the same.


title:
The lambda Bootis phenomenon: interaction between a star and a diffuse
  interstellar cloud

abstract:
  The lambda Bootis stars, a group of late B to early F-type population I
stars, have surface abundances that resemble the general metal depletion
pattern found in the interstellar medium. Inspired by the recent result that
the fundamental parameters of these peculiar stars differ in no respect from a
comparison sample of normal stars, the hypothesis of an interaction between a
star and a diffuse interstellar cloud is considered as a possible explanation
of the peculiar abundance pattern. It is found that such a scenario is able to
explain the selective accretion of interstellar gas depleted in condensable
elements as well as the spectral range of the lambda Bootis phenomenon.


title: Exploring Brown Dwarf Disks in rho Oph

abstract:
  This paper discusses evidence for and properties of disks associated to brown
dwarfs in the star-forming region rho-Oph. We selected nine objects fr om the
ISOCAM survey of Bontemps et al. (2001) that have detections in the two
mid-infrared bands (6.7 and 14.3 um), relatively low extinction and low
luminosity. We present low-resolution near-infrared spectra in the J, H and K
bands, and determine for each source spectral type, extinction, effective
temperature a nd luminosity by comparing the spectra to those of field dwarfs
and to the most recent model stellar atmospheres. The results indicate that
eight objects have spectral types M6-M7.5, effective temperature of 2600-2700
K, one has a later spectral type (M8.5) and lower temperature (about 2400 K).
The derived extinctions range between Av~2 and 8 mag. The location of the
objects on the HR diagram, in spite of the uncertainties of the evolutionary
tracks for young objects of substellar mass, indicates that all the objects are
very young and have masses below about 0.08 Msun. The coolest object in our
sample has mass in the range 8-12 Mjup (0.008-0.012 Msun). In all cases, the
mid-infrared excess is consistent with the predictions of mode ls of disks
irradiated by the central object, showing that circumstellar disks are commonly
associated to young brown dwarfs and plan etary-mass objects. Finally, we
discuss possible variations of the disk geometry among different objects, as
well as the possibility of using these data to discriminate between various f
ormation scenarios.


title:
Gabor Transforms on the Sphere with Applications to CMB Power Spectrum
  Estimation

abstract:
  The Fourier transform of a dataset apodised with a window function is known
as the Gabor transform. In this paper we extend the Gabor transform formalism
to the sphere with the intention of applying it to CMB data analysis. The Gabor
coefficients on the sphere known as the pseudo power spectrum is studied for
windows of different size. By assuming that the pseudo power spectrum
coefficients are Gaussian distributed, we formulate a likelihood ansatz using
these as input parameters to estimate the full sky power spectrum from a patch
on the sky. Since this likelihood can be calculated quickly without having to
invert huge matrices, this allows for fast power spectrum estimation. By using
the pseudo power spectrum from several patches on the sky together, the full
sky power spectrum can be estimated from full-sky or nearly full-sky
observations.


title: The missing M dwarfs

abstract:
  We present evidence which indicates the luminosity functions of star forming
regions, open star clusters and the field dips between spectral types M7-M8. We
attribute this to a sharp local drop in the luminosity-mass relation and
speculate that this is caused by the beginning of dust formation in the
atmospheres of objects in this effective temperature regime. This effect is not
predicted by the current generation of low mass stellar/substellar evolutionary
models. If our interpretation is correct then this result has important
implications for investigations concerned with the mass functions of star
forming regions and young open star clusters. For example, it suggests that
some brown dwarfs have higher masses than previously thought.


title:
A 2.4 - 12 microns spectrophotometric study with ISO of Cygnus X-3 in
  quiescence

abstract:
  We present mid-infrared spectrophotometric results obtained with the ISO on
the peculiar X-ray binary Cygnus X-3 in quiescence, at orbital phases 0.83 to
1.04. The 2.4-12 microns continuum radiation observed with ISOPHOT-S can be
explained by thermal free-free emission in an expanding wind with, above 6.5
microns, a possible additional black-body component with temperature T ~ 250 K
and radius R ~ 5000 solar radii at 10 kpc, likely due to thermal emission by
circumstellar dust. The observed brightness and continuum spectrum closely
match that of the Wolf-Rayet star WR 147, a WN8+B0.5 binary system, when
rescaled at the same 10 kpc distance as Cygnus X-3. A rough mass loss estimate
assuming a WN wind gives ~ 1.2 10^{-4} M(sun)/yr. A line at ~ 4.3 microns with
a more than 4.3 sigma detection level, and with a dereddened flux of 126 mJy,
is interpreted as the expected He I 3p-3s line at 4.295 microns, a prominent
line in the WR 147 spectrum. These results are consistent with a
Wolf-Rayet-like companion to the compact object in Cygnus X-3 of WN8 type, a
later type than suggested by earlier works.


title:
About the morphology of dwarf spheroidal galaxies and their dark matter
  content

abstract:
  The morphological properties of the Carina, Sculptor and Fornax dwarfs are
investigated using new wide field data with a total area of 29 square degrees.
The stellar density maps are derived, hinting that Sculptor possesses tidal
tails indicating interaction with the Milky Way. Contrary to previous studies
we cannot find any sign of breaks in the density profiles for the Carina and
Fornax dwarfs. The possible existence of tidal tails in Sculptor and of King
limiting radii in Fornax and Carina are used to derive global M/L ratios,
without using kinematic data. By matching those M/L ratios to kinematically
derived values we are able to constrain the orbital parameters of the three
dwarfs. Fornax cannot have M/L smaller than 3 and must be close to its
perigalacticon now. The other extreme is Sculptor that needs to be on an orbit
with an eccentricity bigger than 0.5 to be able to form tidal tails despite its
kinematic M/L.


title:
Velocity dispersions and cluster properties in the SARS (Southern Abell
  Redshift Survey) clusters. Paper II

abstract:
  We report an analysis of the dynamical structure of clusters of galaxies from
a survey of photometric and spectroscopic observations in the fields of
southern Abell Clusters. We analyze the galaxy velocity field in extended
regions up to 7 h^-1 Mpc from cluster centers and we estimate mean velocity
dispersions and their radial dependence. Only one from a total number of 41
Abell clusters does not correspond to a dynamically bound system. However, four
of these bound objects are double clusters. We estimate that 20 % (7 clusters)
of the 35 remaining are subject to serious projection effects. Normalizing the
clustercentric distances by means of the overdensity radius r_200, and the
velocity dispersion profiles (VDPs) by the corresponding mean cluster velocity
dispersion, we computed the average VDP. Our results indicate a flat behavior
of the mean VDP at large distances from the cluster center. Nevertheless, we
found that for the inner part of the clusters (r/r_200 leq 1) the VDP is up to
a 10% smaller than at larger radii.


title: MOND rotation curves for spiral galaxies with Cepheid-based distances

abstract:
  Rotation curves for four spiral galaxies with recently determined
Cepheid-based distances are reconsidered in terms of modified Newtonian
dynamics (MOND). For two of the objects, NGC 2403 and NGC 7331, the rotation
curves predicted by MOND are compatible with the observed curves when these
galaxies are taken to be at the Cepheid distance. For NGC 3198, the largest
distance for which reasonable agreement is obtained is 10% smaller than the
Cepheid-based distance; i.e., MOND clearly prefers a smaller distance. This
conclusion is unaltered when new near-infrared photometry of NGC 3198 is taken
as the tracer of the stellar mass distribution. For the large Sc spiral, NGC
2841, MOND requires a distance which is at least 20% larger than the
Cepheid-based distance. However, the discrepancy of the Tully-Fisher and SNIa
distances with the Cepheid determination casts some doubt upon the Cepheid
method in this case.


title:
Detectibility of Hydrogen Mixing in Type Ia Supernova pre-Maximum
  Spectra

abstract:
  The presence of a small amount of hydrogen is expected in most single
degenerate scenarios for producing a Type Ia supernova (SN Ia). While hydrogen
may be detected in very early high resolution optical spectra, in early radio
spectra, and in X-ray spectra, here we examine the possibility of detecting
hydrogen in early low resolution spectra such as those that will be obtained by
proposed large scale searches for nearby SNe Ia. We find that definitive
detections will require both very early spectra (less than 5 days after
explosion) and perhaps slightly higher amounts of hydrogen than are currently
predicted to be mixed into the outer layers of SNe Ia. Thus, the non-detection
of hydrogen so far does not in and of itself rule out any current progenitor
models. Nevertheless, very early spectra of SNe Ia will provide significant
clues to the amount of hydrogen present and hence to the nature of the SN Ia
progenitor system. Spectral coverage in both the optical and IR will be
required to definitively identify hydrogen in low resolution spectra.


title: Heating, conduction and minimum temperatures in cooling flows

abstract:
  There is mounting observational evidence from Chandra for strong interaction
between keV gas and AGN in cooling flows. It is now widely accepted that the
temperatures of cluster cores are maintained at a level of 1 keV and that the
mass deposition rates are lower than earlier ROSAT/Einstein values. Recent
theoretical results suggest that thermal conduction can be very efficient even
in magnetized plasmas. Motivated by these discoveries, we consider a ``double
heating model'' which incorporates the effects of simultaneous heating by both
the central AGN and thermal conduction from the hot outer layers of clusters.
Using hydrodynamical simulations, we demonstrate that there exists a family of
solutions that does not suffer from the cooling catastrophe. In these cases,
clusters relax to a stable final state, which is characterized by minimum
temperatures of order 1 keV and density and temperature profiles consistent
with observations. Moreover, the accretion rates are much reduced, thereby
reducing the need for excessive mass deposition rates required by the standard
cooling flow models.


title: Drifting Sub-Pulse Analysis Using the Two-Dimensional Fourier Transform

abstract:
  The basic form of drifting sub-pulses is that of a periodicity whose phase
depends (approximately linearly) on both pulse longitude and pulse number. As
such, we argue that the two-dimensional Fourier transform of the longitude-time
data (called the Two-Dimensional Fluctuation Spectrum; 2DFS) presents an ideal
basis for studies of this phenomenon. We examine the 2DFS of a pulsar signal
synthesized using the parameters of an empirical model for sub-pulse behaviour.
We show that the transform concentrates the modulation power to a relatively
small area of phase space in the region corresponding to the characteristic
frequency of sub-pulses in longitude and pulse number. This property enables
the detection of the presence and parameters of drifting sub-pulses with great
sensitivity even in data where the noise level far exceeds the instantaneous
flux density of individual pulses. The amplitude of drifting sub-pulses is
modulated in time by scintillation and pulse nulling and in longitude by the
rotating viewing geometry (with an envelope similar to that of the mean pulse
profile). In addition, sub-pulse phase as a function of longitude and pulse
number can differ from that of a sinusoid due to variations in the drift rate
(often associated with nulling) and through the varying rate of traverse of
magnetic azimuth afforded by the sight line. These deviations from uniform
sub-pulse drift manifest in the 2DFS as broadening of the otherwise
delta-function response of a uniform sinusoid. We show how these phase and
amplitude variations can be extracted from the complex spectrum.


title: The Massive Wolf-Rayet Binary HDE318016 (=WR 98)

abstract:
  We present the discovery of OB type absorption lines superimposed to the
emission line spectrum, and the first double-lined orbital elements for the
massive Wolf-Rayet binary HDE 318016 (=WR 98), a spectroscopic binary in a
circular orbit with a period of 47.825 days. The semiamplitudes of the orbital
motion of the emission lines differ from line to line, indicating mass ratios
between 1 and 1.7 for MWR/MOB.


title:
Comptonization and reflection of X-ray radiation and the X-ray-radio
  correlation in the chi-states of GRS 1915+105

abstract:
  We present a comprehensive X-ray study of four years of pointed RXTE
observations of GRS 1915+105 in the chi-state. We interpret the behavior of the
hard power law tail spectrum as coming from inverse Compton scattering of soft
disk photons on a thermally dominated hybrid corona above the accretion disk.
GRS 1915+105 shows a strong, variable reflection amplitude. As in other BHC and
in Seyfert galaxies, a correlation between the power law slope and the
reflection was found. Also, the radio fluxes at 2.25 GHz and 15 GHz correlate
with the power law slope, thus revealing a connection between the outflowing
matter and the comptonizing region in the chi-states.


title: SPI science prospects

abstract:
  With the launch of ESA's INTEGRAL satellite in october 2002, a gamma-ray
observatory will become available to the scientific community that combines
imaging and spectroscopic capacities in the 20 keV to 10 MeV energy range. In
this paper, we summarise the science prospects of the SPI spectrometer aboard
INTEGRAL which provides unprecedented spectral resolution with good imaging
capabilities and high sensitivity. Emphasise will be given to the key
objectives of SPI which are the determination of the galactic positron origin,
the study of galactic star formation and nucleosynthesis activity via the
radioactive trace isotopes 26Al and 60Fe, and the study of nucleosynthesis in
supernova explosions and the gamma-ray line emission from their remnants.


title: A Cosmic Battery Reconsidered

abstract:
  We revisit the problem of magnetic field generation in accretion flows onto
black holes owing to the excess radiation force on electrons. This excess force
may arise from the Poynting-Robertson effect.
  Instead of a recent claim of the generation of dynamically important magnetic
fields, we establish the validity of earlier results from 1977 which show only
small magnetic fields are generated.
  The radiative force causes the magnetic field to initially grow linearly with
time. However, this linear growth holds for only a {\it restricted} time
interval which is of the order of the accretion time of the matter.
  The large magnetic fields recently found result from the fact that the linear
growth is unrestricted.
  A model of the Poynting-Robertson magnetic field generation close to the
horizon of a Schwarzschild black hole is solved exactly using General
Relativity, and the field is also found to be dynamically insignificant.
  These weak magnetic fields may however be important as seed fields for
dynamos.


title: Disks around Young Brown Dwarfs

abstract:
  We present some results from a systematic survey for disks around
spectroscopically identified young brown dwarfs and very low mass stars. We
find that ~75% of our sample show intrinsic IR excesses, indicative of
circum(sub)stellar disks. The observed excesses are correlated with Halpha
emission, consistent with a common disk accretion origin. Because the excesses
are modest, conventional analyses using only IR colors would have missed most
of the sources with disks. In the same star-forming regions, we find that disks
around brown dwarfs and T Tauri stars are contemporaneous; assuming coevality,
this demonstrates that substellar disks are at least as long-lived as stellar
disks. Altogether, the frequency and properties of circumstellar disks are
similar from the stellar regime down to the substellar and planetary-mass
regime. This offers compelling evidence of a common origin for most stars and
brown dwarfs.


title: Is Messier 74 a barred spiral galaxy?

abstract:
  We have obtained ground-based I, J and K band images of the spiral galaxy,
Messier 74 (NGC 628). This galaxy has been shown to possess a circumnuclear
ring of star formation from both near-infrared spectroscopy of CO absorption
and sub-millimetre imaging of CO emission. Circumnuclear rings of star
formation are believed to exist only as a result of a bar potential. In this
paper we show evidence for a weak oval distortion in the centre of M74. We use
the results of Combes & Gerin (1985) to suggest that this weak oval potential
is responsible for the circumnuclear ring of star formation observed in M74.