title:
Sub-Milliarcsecond Imaging of Quasars and Active Galactic Nuclei. II.
  Additional Sources

abstract:
  We report further results from our imaging survey at 15GHz (lambda=2 cm) with
the Very Long Baseline Array. This paper presents single epoch images for 39
sources, bringing the total number of objects in the sample to 171. Our sample
is representative of a complete unbiased sample and it will be used for
statistical analysis of source properties. We compare the observed brightness
temperatures derived from our VLBA observations to those derived from total
intensity variations at 22 and 37 GHz. These are consistent with intrinsic
brightness temperatures in the range 10^10 to 10^12 K. We also present three
new spectroscopic redshift values: z=0.517+/-0.001 for 0026+346,
z=1.591+/-0.003 for 0727-115, and z=0.2016+/-0.0004 for 1155+251.
  Images from this VLBA 2 cm survey are available on the Internet under
http://www.cv.nrao.edu/2cmsurvey.


title: Regimes of Pulsar Pair Formation and Particle Energetics

abstract:
  We investigate the conditions required for the production of
electron-positron pairs above a pulsar polar cap (PC) and the influence of pair
production on the energetics of the primary particle acceleration. Assuming
space-charge limited flow acceleration including the inertial frame-dragging
effect, we allow both one-photon and two-photon pair production by either
curvature radiation (CR) photons or photons resulting from inverse-Compton
scattering of thermal photons from the PC by primary electrons. We find that,
while only the younger pulsars can produce pairs through CR, nearly all known
radio pulsars are capable of producing pairs through non-resonant
inverse-Compton scatterings. The effect of the neutron star equations of state
on the pair death lines is explored. We show that pair production is
facilitated in more compact stars and more massive stars. Therefore accretion
of mass by pulsars in binary systems may allow pair production in most of the
millisecond pulsar population. We also find that two-photon pair production may
be important in millisecond pulsars if their surface temperatures are above
about three million degrees K. Pulsars that produce pairs through CR will have
their primary acceleration limited by the effect of screening of the electric
field. In this regime, the high-energy luminosity should follow a $L_{HE}
\propto \dot E_{rot}^{1/2}$ dependence. The acceleration voltage drop in
pulsars that produce pairs only through inverse-Compton emission will not be
limited by electric field screening. In this regime, the high-energy luminosity
should follow a $L_{HE} \propto \dot E_{rot}$ dependence. Thus, older pulsars
will have significantly lower gamma-ray luminosity.


title: Positioning errors and efficiency in fiber spectrographs

abstract:
  The use of wide-field multi-object fiber-input spectrographs for large
redshift surveys introduces the possibility of variations in the observed
signal-to-noise ratio across the survey area due to errors in positioning the
fibers with respect to the target image positions, leading to
position-dependent errors in the survey catalog. This paper brings together a
comprehensive description of the sources of fiber-to-image position errors in
different instrument designs, and quantifies their effects on the efficiency
with which signal is recorded. For point sources, a function relating a
fractional efficiency and an equivalent aperture correction to the
fiber-to-image position error, the fiber diameter and the image size is plotted
for typical values of fiber and image sizes found in current instruments. The
tools required by observers to maximize the efficiency of fiber-spectrographic
surveys are discussed.


title: Varying $\alpha$ in the early universe: CMB, LSS and FMA

abstract:
  I review recent constraints on and claimed detections of a time-varying
fine-structure constant $\alpha$, and discuss our own work, particularly on the
effects of $\alpha$ in the cosmic microwave background and large-scale
structure. Our results are consistent with no variation in $\alpha$ from the
epoch of recombination to the present day, and restrict any such variation to
be less than about 4%. The forthcoming MAP and Planck experiments will be able
to break most of the currently existing degeneracies between $\alpha$ and other
parameters, and measure $\alpha$ to better than percent accuracy.


title:
Theoretical isochrones in several photometric systems I.
  Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging
  Survey filter sets

abstract:
  We provide tables of theoretical isochrones in several photometric systems.
To this aim, the following steps are followed: (1) First, we re-write the
formalism for converting synthetic stellar spectra into tables of bolometric
corrections. The resulting formulas can be applied to any photometric system,
provided that the zero-points are specified by means of either ABmag, STmag,
VEGAmag, or a standard star system that includes well-known spectrophotometric
standards. Interstellar absorption can be considered in a self-consistent way.
(2) We assemble an extended and updated library of stellar intrinsic spectra.
It is mostly based on non-overshooting ATLAS9 models, suitably extended to both
low and high effective temperatures. This offers an excellent coverage of the
parameter space of Teff, logg, and [M/H]. We briefly discuss the main
uncertainties and points still deserving more improvement. (3) From the
spectral library, we derive tables of bolometric corrections for
Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging
Survey systems (this latter consisting on the WFI, EMMI, and SOFI filter sets).
(4) These tables are used to convert several sets of Padova isochrones into the
corresponding absolute magnitudes and colours, thus providing a useful database
for several astrophysical applications. All data files are made available in
electronic form.


title: The Infrared Counterpart of the X-ray Burster KS 1731--260

abstract:
  We present JK' infrared images of the X-ray transient KS 1731--260, obtained
in 1997 and in 1998 with IRAC2b at the ESO/MPI 2.2-m telescope at La Silla.
Using as a reference the recent Chandra position, we confirm the identification
of the X-ray source with the previously proposed counterpart (Wijnands et al.
2001b), for which we measure J=17.32 +/- 0.2 and K' = 16.36 +/- 0.18. The
source was entering a low X-ray state at the epoch of our observations, and the
accretion disk was still dominating the infrared flux. Indeed, when compared
with the only published magnitudes in the J-band (Orosz et al. 2001), obtained
with the source in quiescence, our photometry confirms the fading of the
counterpart during the decay of the RXTE/ASM lightcurve.


title:
High-Resolution Measurements of Intersystem Bands of Carbon Monoxide
  toward X Persei

abstract:
  In an echelle spectrum of X Per acquired with the Space Telescope Imaging
Spectrograph we have identified individual rotational lines of 11
triplet-singlet (intersystem) absorption bands of ^12CO. Four bands provide
first detections for interstellar clouds. From a comparison with the zeta Oph
sight line we find that X Per is obscured by a higher 12CO column density of
1.4 x 10^16 cm-2. Together with the high spectral resolution of 1.3 km s-1,
this allows (i) an improved measurement of previously published f-values for
seven bands, and (ii) an extraction of the first astrophysical oscillator
strengths for d-X (8-0), (9-0), and (10-0), as well as for e-X (12-0). The
^13CO d-X (12-0) band, previously suspected to exist toward zeta Oph, is now
readily resolved and modeled. Our derived intersystem f-values for ^12CO
include a few mild (leq 34%) disagreements with recent predictions from a
perturbation analysis calculated for the interstellar excitation temperature.
Overall, the comparison confirms the superiority of employing multiple singlet
levels in the calculations of mixing coefficients over previous single-level
predictions.


title: The curvature condition for self-consistent scale-free galaxies

abstract:
  We modify the curvature condition for the existence of self-consistent
scale-free discs, introduced by Zhao, Carollo & de Zeeuw. We survey the
parameter space of the power-law discs, and show that the modified curvature
condition is in harmony with the results of Schwarzschild's numerical orbit
superposition method. We study the orbital structure of the power-law discs,
and find a correlation between the population of centrophobic banana orbits and
the non-self-consistency index. We apply the curvature condition to other
families of scale-free elongated discs and find that it rules out a large range
of power-law slopes and axis ratios. We generalize the condition, and apply it,
to three-dimensional scale-free axisymmetric galaxy models.


title: Improved synthetic spectra of helium-core white dwarf stars

abstract:
  We examine the emergent fluxes from helium-core white dwarfs following their
evolution from the end of pre-white dwarf stages down to advanced cooling
stages. For this purpose, we include a detailed treatment of the physics of the
atmosphere, particularly an improved representation of the state of the gas by
taking into account non-ideal effects according to the so-called occupation
probability formalism. The present calculations also incorporate hydrogen line
opacity from Lyman, Balmer and Paschen series, pseudo-continuum absorptions and
new updated induced-dipole absorption from H$_2$-H$_2$, H$_2$-He and H-He
pairs. We find that the non-ideal effects and line absorption alter the
appearance of the stellar spectrum and have a significant influence upon the
photometric colours in the UBVRI-JHKL system. This occurs specially for hot
models $T_{\rm eff}\ga 8000$ due to line and pseudo-continuum opacities, and
for cool models $T_{\rm eff}\la 4000$ where the perturbation of atoms and
molecules by neighbour particles affects the chemical equilibrium of the gas.
In the present study, we also include new cooling sequences for helium-core
white dwarfs of very low mass (0.160 and 0.148 M$_\odot$) with metallicity
$Z=0.02$. These computations provide theoretical support to search for and
identify white dwarfs of very low mass, specially useful for recent and future
observational studies of globular cluster, where these objects have began to be
detected.


title:
The Infrared Spectral Energy Distribution of Normal Star-Forming
  Galaxies: Calibration at Far-Infrared and Submillimeter Wavelengths

abstract:
  New far-infrared and submillimeter data are used to solidify and to extend to
long wavelengths the empirical calibration of the infrared spectral energy
distribution (SED) of normal star-forming galaxies. As was found by Dale et al.
(2001), a single parameter family, characterized by f_nu(60 microns)/f_nu(100
microns), is adequate to describe the range of normal galaxy spectral energy
distributions observed by IRAS and ISO from 3 to 100 microns. However,
predictions based on the first generation models at longer wavelengths (122 to
850 microns) are increasingly overluminous compared to the data for smaller
f_nu(60 microns)/f_nu(100 microns), or alternatively, for weaker global
interstellar radiation fields. After slightly modifying the
far-infrared/submillimeter dust emissivity in those models as a function of the
radiation field intensity to better match the long wavelength data, a suite of
SEDs from 3 microns to 20 cm in wavelength is presented. Results from relevant
applications are also discussed, including submillimeter-based photometric
redshift indicators, the infrared energy budget and simple formulae for
recovering the bolometric infrared luminosity, and dust mass estimates in
galaxies. Regarding the latter, since galaxy infrared SEDs are not
well-described by single blackbody curves, the usual methods of estimating dust
masses can be grossly inadequate. The improved model presented herein is used
to provide a more accurate relation between infrared luminosity and dust mass.


title:
The Lower Main Sequence and Mass Function of the Globular Cluster
  Messier 4

abstract:
  The deepest optical image ever in a globular star cluster, a Hubble Space
Telescope (HST) 123 orbit exposure in a single field of Messier 4, was obtained
in 2 filters (F606W, F814W) over a 10 week period in early 2001. A somewhat
shallower image obtained in 1995 allowed us to select out cluster and field
objects via their proper motion displacement resulting in remarkably clean
color-magnitude diagrams that reach to V = 30, I = 28. The cluster main
sequence luminosity function contains very few stars fainter than MV = 15.0, MI
= 11.8 which, in both filters, is more than 2 magnitudes brighter than our
limit. This is about the faintest luminosity seen among field Population II
subdwarfs of the same metallicity. However, there remains a sprinkling of
potential cluster stars to lower luminosity all the way down to our limiting
magnitudes. These latter objects are significantly redder than any known
metal-poor field subdwarf. Comparison with the current generation of
theoretical stellar models implies that the masses of the lowest luminosity
cluster stars observed are near 0.09 Msun. We derive the mass function of the
cluster in our field and find that it is very slowly rising towards the lowest
masses with no convincing evidence of a turnover even below 0.1 Msun. The
formal slope between 0.65 and 0.09 Msun is alpha = 0.75 (Salpeter of 2.35) with
a 99% confidence interval 0.55 - 1.05. A consistency check between these slopes
and the number of observed cluster white dwarfs yields a range of possible
conclusions, one of which is that we have indeed seen the termination of the
white dwarf cooling sequence in M4.


title: The White Dwarf Cooling Sequence of the Globular Cluster Messier 4

abstract:
  We present the white dwarf sequence of the globular cluster M4, based on a
123 orbit Hubble Space Telescope exposure, with limiting magnitude V = 30, I =
28. The white dwarf luminosity function rises sharply for I >25.5, consistent
with the behaviour expected for a burst population. The white dwarfs of M4
extend to approximately 2.5 magnitudes fainter than the peak of the local
Galactic disk white dwarf luminosity function. This demonstrates a clear and
significant age difference between the Galactic disk and the halo globular
cluster M4. Using the same standard white dwarf models (Hansen 1999) to fit
each luminosity function yields ages of 7.3 +/- 1.5 Gyr for the disk and 12.7
+/- 0.7 Gyr for M4 (2-sigma statistical errors).


title:
Star formation in the warped outer pseudoring of the spiral galaxy NGC
  3642

abstract:
  NGC 3642 was classified as a spiral galaxy with three rings and no bar. We
have performed an HI and optical study of this nearly face-on galaxy. We find
that the nuclear ring might in fact be part of an inner one-armed spiral, that
could be driving nuclear accretion and feeding the central activity in the
inner kpc. The inner ring is faint, and the outer ring is a rather ill-defined
pseudoring. Furthermore, the size ratio of the rings is such that they cannot
be due to a single pattern speed linking them together.
  The outer pseudoring is peculiar, since it lies in the faint outer parts of
the disk, where star formation is still going on at 1.4 times the optical
radius. Higher HI column densities are associated with these regions and the
atomic gas layer is warped. These perturbations affect only the outer disk,
since the kinematics within the main body conforms well to an ordinary
differentially rotating disk.
  We propose here that both nuclear activity and star formation in the warped
outer parts might be linked to the fact that NGC 3642 is located in a rich
environment, where its close neighbors show clear signs of merging. Our
suggestion is that NGC 3642 has captured recently a low-mass, gas-rich dwarf,
and star formation was triggered in this infalling external gas that produced
also a pronounced warp in the gaseous disk.


title:
Unexplained Sets of Seismographic Station Reports and A Set Consistent
  with a Quark Nugget Passage

abstract:
  In 1984 Edward Witten proposed that an extremely dense form of matter
composed of up, down, and strange quarks may be stable at zero pressure
(Witten, 1984). Massive nuggets of such dense matter, if they exist, may pass
through the Earth and be detectable by the seismic signals they generate (de
Rujula and Glashow, 1984). With this motivation we investigated over 1 million
seismic data reports to the U.S. Geological Survey for the years 1990-1993 not
associated with epicentral sources. We report two results: (1) with an average
of about 0.16 unassociated reports per minute after data cuts, we found a
significant excess over statistical expectation for sets with ten or more
reports in ten minutes; and (2) in spite of a very small a priori probability
from random reports, we found one set of reports with arrival times and other
features appropriate to signals from an epilinear source. This event has the
properties predicted for the passage of a nugget of strange quark matter (SQM)
through the earth, although there is no direct confirmation from other
phenomenologies.


title: Structure of the Universe: An Approach Based on Gravitational Energy

abstract:
  An approach to modelling the universe based on the requisites of
gravitational energy. This model is explained as it relates to the stages of
the universal life cycle and the continued existence of the universe as it is
known today. The article attempts to reconcile the most common problems with
physical models of the universe and overcome doubt as to its validity through
the most common questions.


title:
Collapse of a Rotating Supermassive Star to a Supermassive Black Hole:
  Fully Relativistic Simulations

abstract:
  We follow the collapse in axisymmetry of a uniformly rotating, supermassive
star (SMS) to a supermassive black hole (SMBH) in full general relativity. The
initial SMS of arbitrary mass $M$ is marginally unstable to radial collapse and
rotates at the mass-shedding limit. The collapse proceeds homologously early on
and results in the appearance of an apparent horizon at the center. Although
our integration terminates before final equilibrium is achieved, we determine
that the final black hole will contain about 90% of the total mass of the
system and have a spin parameter $J/M^2 \sim 0.75$. The remaining gas forms a
rotating disk about the nascent hole.


title: Astrophysical implications of binary black holes in BL Lacertae objects

abstract:
  Some BL Lacertae objects show a periodic behaviour in their light curves that
is often attributed to the orbital motion of a central binary black hole
system. On this basis, and assuming a circular orbit, Rieger and Mannheim have
recently proposed a method to determine the orbital parameters of the binary
system from the observed quantities, {\it i.e.} the signal periodicity, the
flux ratio between maximum and minimum signal and the power law spectral index
of the photon flux. However, since these binary black holes are expected to
originate from galactic mergers, they could well be on eccentric orbits, which
might not circularize for a substantial time. We therefore generalize the
treatment proposed by Rieger and Mannheim by taking into account the effect of
the orbital eccentricity of the binary system. We apply the model to three
well-observed Markarian objects: MKN 501, MKN 421 and MKN 766 that most likely
host a binary system in their centers. Some astrophysical implications of this
model are also investigated with particular emphasis to the gravitational
radiation emission from the binary black holes. Under particular conditions
(e.g. for some values of the orbital separation, eccentricity and Lorentz
factor) one can obtain signals above the sensitivity threshold of the LISA
detector.


title: Nucleosynthesis in gamma-ray bursts outflows

abstract:
  It is shown that fusion of neutrons and protons to He-4 nuclei occurs in
gamma-ray burst outflows in a process similar to big-bang nucleosynthesis in
the early Universe. Only the surviving free neutrons can then decouple
kinematically from the charged fluid so that the multi-GeV neutrino signal
predicted from inelastic nuclear n-p collisions is significantly reduced. It is
also argued that a sizeable fraction of ultra-high energy cosmic rays
accelerated in gamma-ray bursts should be He-4 nuclei.


title: Spectrophotometry of massive star forming regions with GTC

abstract:
  In these latest years, the detection of Wolf-Rayet (WR) stars in Giant HII
Regions (GHRs) has yielded several questions about our current understanding of
massive stars evolution and hot expanding atmospheres, the age of the ionizing
populations and their impact onto the physical properties of GHRs. Here, we
present spectrophotometric observations of 4 extragalactic GHRs which show WR
features in their spectra. Our goal is to reproduce simultaneously the observed
WR properties and the emission line spectra with the help of current
evolutionary synthesis models. Finally, we address the main advantages that GTC
will provide to our better understanding of massive star forming regions.


title: Stellar Populations in Circumnuclear Star Forming Regions

abstract:
  We present a study of the stellar populations and gas physical conditions in
Circumnuclear Star Forming Regions (CNSFR) based on broad and narrow band
photometry and spectrophotometric data, which have been analyzed with the use
of evolutionary population synthesis and photoionization models. It is found
that most CNSFR show composite stellar populations of slightly different ages.
They seem to have the highest abundances in HII region-like objects, showing
also N/O overabundances and S/O underabundances by a factor of about three.
Also, CNSFR as a class, segregate from the disk HII region family, clustering
around smaller $\eta$' values, and thereforefore higher ionizing temperatures.


title:
Probing the dark side: Constraints on the dark energy equation of state
  from CMB, large scale structure and Type Ia supernovae

abstract:
  We have reanalysed constraints on the equation of state parameter, w_Q =
P/rho, of the dark energy, using several cosmological data sets and relaxing
the usual constraint w_Q > -1. We find that combining Cosmic Microwave
Background, large scale structure and Type Ia supernova data yields a
non-trivial lower bound on w_Q. At 95.4% confidence we find, assuming a flat
geometry of the universe, a bound of -2.68 < w_Q < -0.78 if w_Q is taken to be
a completely free parameter. Reassuringly we also find that the constraint w_Q
> -1 does not significantly bias the overall allowed region for w_Q. When this
constraint is imposed the 95.4% confidence bound is -1 < w_Q < -0.71. Also, a
pure cosmological constant (w = -1) is an excellent fit to all available data.
Based on simulations of future data from the Planck CMB experiment and the SNAP
and SNfactory supernova experiments we estimate that it will be possible to
constrain w_Q at the 5% level in the future.


title:
Constraints on the interaction and self-interaction of dark energy from
  cosmic microwave background

abstract:
  It is well-known that even high quality cosmic microwave background (CMB)
observations are not sufficient on their own to determine the equation of state
of the dark energy, due to the effect of the so-called geometric degeneracy at
large multipoles and the cosmic variance at small ones. In contrast, we find
that CMB data can put tight constraints on another fundamental property of the
dark energy, namely its coupling to dark matter. We compare the current
high-resolution CMB data to models of dark energy characterized by an inverse
power law or exponential potential and by the coupling to dark matter. We
determine the curve of degeneracy between the dark energy equation of state and
the dimensionless Hubble parameter h and show that even an independent perfect
determination of h may be insufficient to distinguish dark energy from a pure
cosmological constant with the current dataset. On the other hand, we find that
the interaction with dark matter is firmly bounded, regardless of the
potential. In terms of the dimensionless ratio \beta of the dark energy
interaction to gravity, we find \beta <0.16 (95% c.l.). This implies that the
effective equation of state between equivalence and tracking has been close to
the pure matter equation of state within 1% and that scalar gravity is at least
40 times weaker than tensor gravity. Further, we show that an experiment
limited by cosmic variance only, like the Planck mission, can put an upper
bound \beta < 0.05 (95% c.l.). This shows that CMB observations have a strong
potentiality not only as a test of cosmic kinematics but also as a
gravitational probe.


title: Discovery of three nearby L dwarfs in the Southern Sky

abstract:
  We report the discovery of three L dwarfs in the solar vicinity within 30
parsecs. These objects were originally found as proper motion objects from a
combination of R and I photographic plates measured as part of the SuperCOSMOS
Sky Surveys. We subsequently identified these objects as bona fide brown dwarf
candidates on the basis of their R-I colour, as first criterion, and
subsequently their J-K colours when the infrared data were available from the
2MASS database. Spectroscopic observations in the optical with the ESO
3.6m/EFOSC2 and in the near-infrared with the NTT/SOFI led to the
classification of their spectral types as early L dwarfs.


title: Comments on the Final Orbital Separation in Common Envelope Evolution

abstract:
  I study some aspects of common envelope evolution, where a compact star
enters the envelope of a giant star. I show that in some binary systems under a
narrow range of parameters, a substantial fraction of the giant stellar
envelope is lost before the onset of the common envelope. The reduced envelope
mass at the onset of the common envelope implies that the binary system emerges
from the common envelope with a relatively large orbital separation. I
therefore caution against a simple treatment, which omits this process, in the
study of systems that evolved through a common envelope phase and ended with a
relatively large orbital separation, e.g., PG1115+166. A fraction of the
envelope that is lost while the companion is still outside the giant stellar
envelope is accreted by the companion. The companion may form an accretion disk
and blow two jets. I propose this scenario for the formation of the bipolar
planetary nebula NGC 2346, which has a binary nucleus with an orbital period
longer than that of any other known binary system in planetary nebulae. Because
this scenario, of a late common envelope phase, occurs for a narrow range of
parameters, I expect it to be applicable to a small, but non-negligible, number
of systems.


title: NGC 1912 and NGC 1907: a close encounter between open clusters ?

abstract:
  The possible physical relation between the closely projected open clusters
NGC 1912 (M 38) and NGC 1907 is investigated. Previous studies suggested a
physical pair based on similar distances, and the present study explores in
more detail the possible interaction. Spatial velocities are derived from
available radial velocities and proper motions, and the past orbital motions of
the clusters are retrieved in a Galactic potential model. Detailed N-body
simulations of their approach suggest that the clusters were born in different
regions of the Galaxy and presently experience a fly-by.


title: Frontiers of the Universe: What do we know, what do we understand?

abstract:
  In this talk I summarize the topics addressed during the conference. We have
discussed the most relevant cosmological observations of the last say 10 years
and their implications for our understanding of the Universe. My finding
throughout this meeting has been that it is amazing how our knowledge of
cosmological parameters has improved during the last years. It comes as a
surprise to many, that the simplest inflationary model of adiabatic
perturbations agrees well with present data. But it is frustrating that we have
not made any progress in identifying the dark matter, in contrary, we have
supplemented it by what we call the 'dark energy', a gravitationally and
esthetically repulsive component which is even more mysterious than the dark
matter. We have no understanding about the origin of these two most abundant
energy components of the present Universe.


title: First X-ray observations of the polar CE Gru

abstract:
  We report the detection of the polar CE Gru in X-rays for the first time. We
find evidence for a dip seen in the hard X-ray light curve which we attribute
to the accretion stream obscuring the accretion region in the lower hemisphere
of the white dwarf. The X-ray spectrum can be fitted using only a shock model:
there is no distinct soft X-ray component. We suggest that this is because the
reprocessed component is cool enough so that it is shifted into the UV. We
determine a mass for the white dwarf of ~1.0Msun.


title: Fast Reconnection in a Two-Stage Process

abstract:
  Magnetic reconnection plays an essential role in the generation and evolution
of astrophysical magnetic fields. The best tested and most robust reconnection
theory is that of Parker and Sweet. According to this theory, the reconnection
rate scales with magnetic diffusivity lambda as lambda^0.5. In the interstellar
medium, the Parker-Sweet reconnection rate is far too slow to be of interest.
Thus, a mechanism for fast reconnection seems to be required. We have studied
the magnetic merging of two oppositely directed flux systems in weakly ionized,
but highly conducting, compressible gas. In such systems, ambipolar diffusion
steepens the magnetic profile, leading to a thin current sheet. If the ion
pressure is small enough, and the recombination of ions is fast enough, the
resulting rate of magnetic merging is fast, and independent of lambda. Slow
recombination or sufficiently large ion pressure leads to slower merging which
scales with lambda as lambda^0.5. We derive a criterion for distinguishing
these two regimes, and discuss applications to the weakly ionized ISM and to
protoplanetary accretion disks.


title:
Eccentricity Evolution of Extrasolar Multiple Planetary Systems due to
  the Depletion of Nascent Protostellar Disks

abstract:
  Most extrasolar planets are observed to have eccentricities much larger than
those in the solar system. Some of these planets have sibling planets, with
comparable masses, orbiting around the same host stars. In these multiple
planetary systems, eccentricity is modulated by the planets' mutual secular
interaction as a consequence of angular momentum exchange between them. For
mature planets, the eigenfrequencies of this modulation are determined by their
mass and semi-major axis ratios. But, prior to the disk depletion, self gravity
of the planets' nascent disks dominates the precession eigenfrequencies. We
examine here the initial evolution of young planets' eccentricity due to the
apsidal libration or circulation induced by both the secular interaction
between them and the self gravity of their nascent disks. We show that as the
latter effect declines adiabatically with disk depletion, the modulation
amplitude of the planets' relative phase of periapse is approximately invariant
despite the time-asymmetrical exchange of angular momentum between planets.
However, as the young planets' orbits pass through a state of secular
resonance, their mean eccentricities undergo systematic quantitative changes.
For applications, we analyze the eccentricity evolution of planets around
Upsilon Andromedae and HD168443 during the epoch of protostellar disk
depletion. We find that the disk depletion can change the planets' eccentricity
ratio. However, the relatively large amplitude of the planets' eccentricity
cannot be excited if all the planets had small initial eccentricities.


title: Arm Structure in Anemic Spiral Galaxies

abstract:
  Anemic galaxies have less prominent star formation than normal galaxies of
the same Hubble type. Previous studies showed they are deficient in total
atomic hydrogen but not in molecular hydrogen. Here we compare the combined
surface densities of HI and H2 at mid-disk radii with the Kennicutt threshold
for star formation. The anemic galaxies are below threshold, which explains
their lack of prominent star formation, but they are not much different than
other early type galaxies, which also tend to be below threshold. The spiral
wave amplitudes of anemic and normal galaxies were also compared, using images
in B and J passbands from the OSU Bright Spiral Galaxy Survey. Anemic galaxies
have normal spiral wave properties too, with the same amplitudes and radial
dependencies as other galaxies of the same arm class. Because of the lack of
gas, spiral waves in early type galaxies and anemics do not have a continuous
supply of stars with low velocity dispersions to maintain a marginally stable
disk. As a result, they are either short-lived, evolving toward lenticulars and
S0 types in only a few rotations at mid-disk, or they are driven by the
asymmetries associated with gas removal in the cluster environment.


title: The massive double-lined O-type binary HD 165052

abstract:
  We present a new optical spectroscopic study of the O-type binary HD 165052
based on high- and intermediate-resolution CCD observations. We re-investigated
the spectral classification of the binary components, obtaining spectral types
of O6.5 V and O7.5 V for the primary and secondary, respectively, finding that
both stars display weak C {\sc iii} $\lambda5696$ emission in their spectra. We
also determined a radial-velocity orbit for HD 165052 with a period of 2.95510
$\pm$ 0.00001 d, and semiamplitudes of 94.8 and 104.7 $\pm$ 0.5 km s$^{-1}$,
resulting in a mass ratio $Q = 0.9$. From a comparison with previous
radial-velocity determinations, we found evidence of apsidal motion in the
system. Several signatures of wind-wind collision, such as phase-locked
variability of the X-ray flux and the Struve-Sahade effect, are also
considered. It was also found that the reddening in the region should be
normal, in contrast with previous determinations.


title: Power-law Tails from Dynamical Comptonization in Converging Flows

abstract:
  The effects of bulk motion comptonization on the spectral formation in a
converging flow onto a black hole are investigated. The problem is tackled by
means of both a fully relativistic, angle-dependent transfer code and a
semi-analytical, diffusion-approximation method. We find that a power-law
high-energy tail is a ubiquitous feature in converging flows and that the two
approaches produce consistent results at large enough accretion rates, when
photon diffusion holds. Our semi-analytical approach is based on an expansion
in eigenfunctions of the diffusion equation. Contrary to previous
investigations based on the same method we find that, although the power-law
tail at really large energies is always dominated by the flatter spectral mode,
the slope of the hard X-ray portion of the spectrum is dictated by the second
mode and it approaches Gamma=3 at large accretion rate, irrespective of the
model parameters. The photon index in the tail is found to be largely
independent on the spatial distribution of soft seed photons when the accretion
rate is either quite low (< 5 in Eddington units) or sufficiently high (> 10).
On the other hand, the spatial distribution of source photons controls the
photon index at intermediate accretion rates, when Gamma switches from the
first to the second mode. Our analysis confirms that a hard tail with photon
index Gamma <3 is produced by the up-scattering of primary photons onto
infalling electrons if the central object is a black hole.


title: Events in the life of a cocoon surrounding a light, collapsar jet

abstract:
  According to the collapsar model, gamma-ray bursts are thought to be produced
in shocks that occur after the relativistic jet has broken free from the
stellar envelope. If the mass density of the collimated outflow is less than
that of the stellar envelope, the jet will then be surrounded by a cocoon of
relativistic plasma. This material would itself be able to escape along the
direction of least resistance, which is likely to be the rotation axis of the
stellar progenitor, and accelerate in approximately the same way as an
impulsive fireball. We discuss how the properties of the stellar envelope have
a decisive effect on the appearance of a cocoon propagating through it. The
relativistic material that accumulated in the cocoon would have enough kinetic
energy to substantially alter the structure of the relativistic outflow, if not
in fact provide much of the observed explosive power. Shock waves within this
plasma can produce gamma-ray and X-ray transients, in addition to the standard
afterglow emission that would arise from the deceleration shock of the cocoon
fireball.


title:
Observation of High Energy Atmospheric Neutrinos with the Antarctic Muon
  and Neutrino Detector Array

abstract:
  The Antarctic Muon and Neutrino Detector Array (AMANDA) began collecting data
with ten strings in 1997. Results from the first year of operation are
presented. Neutrinos coming through the Earth from the Northern Hemisphere are
identified by secondary muons moving upward through the array. Cosmic rays in
the atmosphere generate a background of downward moving muons, which are about
10^6 times more abundant than the upward moving muons. Over 130 days of
exposure, we observed a total of about 300 neutrino events. In the same period,
a background of 1.05*10^9 cosmic ray muon events was recorded. The observed
neutrino flux is consistent with atmospheric neutrino predictions. Monte Carlo
simulations indicate that 90% of these events lie in the energy range 66 GeV to
3.4 TeV. The observation of atmospheric neutrinos consistent with expectations
establishes AMANDA-B10 as a working neutrino telescope.


title: Disturbance Ecology from nearby Supernovae

abstract:
  Monte Carlo simulations of Galactic Supernovae are carried out to study the
rate of nearby events, which may have a direct effect on Earth's ecology though
ionizing radiation and cosmic ray bombardment. A nearby supernova may have left
a radioactive imprint (60Fe) in recent galactic history.


title: B1524-136: A CSS quasar with two-sided radio jets

abstract:
  We present MERLIN, global VLBI and VLBA observations of the high-luminosity,
compact steep-spectrum quasar B1524$-$136 at cm wavelengths. These observations
reveal well-defined radio jets on both sides of the active nucleus, a situation
which is almost unique amongst high-luminosity radio quasars. However, the
radio jets on opposite sides are very dissimilar, and the overall radio
structure appears highly distorted. We discuss possible implications of these
observations.


title: Maximum entropy method for reconstruction of the CMB images

abstract:
  We propose a new approach for the accurate reconstruction of cosmic microwave
background distributions from observations containing in addition to the
primary fluctuations the radiation from unresolved extragalactic point sources
and pixel noise. The approach uses some effective realizations of the
well-known maximum entropy method and principally takes into account {\it a
priori} information about finiteness and spherical symmetry of the power
spectrum of the CMB satisfying the Gaussian statistics.


title: Five-Dimrnsional Cosmological Theory of Unified Space, Time and Velocity

abstract:
  A five-dimensional cosmological theory of gravitation that unifies space,
time and velocity is presented


title:
A 10-day ASCA Observation of the Narrow-line Seyfert~1 galaxy IRAS
  13224-3809

abstract:
  (Abridged) We present an analysis of a 10-day continuous ASCA observation of
the narrow-line Seyfert 1 galaxy IRAS 13224-3809. The soft (0.7-1.3 keV) and
hard (1.3-10 keV) X-ray band light curves binned to 5000s reveal trough-to-peak
variations by a factor >25 and 20, respectively. The light curves in the soft
and hard bands are strongly correlated without any significant delay. However,
this correlation is not entirely due to changes in the power-law flux alone but
also due to changes in the soft X-ray hump emission above the power law. The
presence of a soft X-ray hump below 2 keV, previously detected in ROSAT and
ASCA data, is confirmed. Time resolved spectroscopy using daily sampling
reveals changes in the power-law slope, with Gamma in the range 1.74-2.47,
however, day-to-day variations in Gamma are not significant. The Soft hump
emission is found to dominate the observed variability on a timescale of a
week, but on shorter timescales (20000s) the power-law component appears to
dominate the observed variability. Flux resolved spectroscopy reveals that at
high flux levels the power law becomes steeper and the soft hump more
pronounced. The steepening of the photon index with the fluxes in the soft and
hard bands can be understood in the framework of disk/corona models in which
accretion disk is heated by viscous dissipation as well as by reprocessing of
hard X-rays following an X-ray flare resulting from coronal dissipation through
magnetic reconnection events.


title: Blunting the Spike: the CV Minimum Period

abstract:
  The standard picture of CV secular evolution predicts a spike in the CV
distribution near the observed short-period cutoff P_0 ~ 78 min, which is not
observed. We show that an intrinsic spread in minimum (`bounce') periods P_b
resulting from a genuine difference in some parameter controlling the evolution
can remove the spike without smearing the sharpness of the cutoff. The most
probable second parameter is different admixtures of magnetic stellar wind
braking (at up to 5 times the GR rate) in a small tail of systems, perhaps
implying that the donor magnetic field strength at formation is a second
parameter specifying CV evolution. We suggest that magnetic braking resumes
below the gap with a wide range, being well below the GR rate in most CVs, but
significantly above it in a small tail.


title: Measuring the baryon content of the universe: BBN vs CMB

abstract:
  The relic abundance of baryons - the only form of stable matter whose
existence we are certain of - is a crucial parameter for many cosmological
processes, as well as material evidence that there is new physics beyond the
Standard Model. We discuss recent determinations of the cosmological baryon
density from analysis of the abundances of light elements synthesised at the
end of ``the first three minutes'', and from the observed temperature
anisotropies imprinted on small angular-scales in the cosmic microwave
background when the universe was about 100,000 yr old.


title:
Spectral & Photometric Evolution of Simple Stellar Populations at
  Various Metallicities

abstract:
  A new set of evolutionary synthesis spectra are presented for {\bf S}imple
{\bf S}tellar {\bf P}opulations ({\bf SSP}s) covering ranges in metallicity
from $ 0.02 \leq Z/Z_{\odot} \leq 2.5$ and ages from $4\cdot 10^6$ yr $\leq t
\leq 16$ Gyr. They are based on the most recent isochrones from the Padova
group that extend earlier models by the inclusion of the thermal pulsing AGB
phase for stars in the mass range $2 M_{\odot} \leq m \leq 7 M_{\odot}$ in
accordance with the fuel consumption theorem. We show that with respect to
earlier models, inclusion of the TP-AGB phase leads to significant changes in
the $(V-I)$ and $(V-K)$ colors of SSPs. Using model atmosphere spectra from
Lejeune et al, we calculate the spectral evolution of single burst populations
of various metallicities. Isochrone spectra are convolved with filter response
functions to describe the time evolution of luminosities and colors in various
filter systems. The models and their results are not only intended for use in
the interpretation of star clusters but also for combination with any kind of
dynamical galaxy formation and/or evolution model that contains a star
formation criterion. We also present the time evolution of ejection rates for
gas and metals for two different {\bf I}nitial {\bf M}ass {\bf F}unctions ({\bf
IMF}s) as well as cosmological and evolutionary corrections for all the filters
as a function of redshift and two different cosmologies. Extensive data files
are provided in the electronic version, at CDS, and at our above www-address.


title: Pipeline Processing of VLBI Data

abstract:
  As part of an on-going effort to simplify the data analysis path for VLBI
experiments, a pipeline procedure has been developed at JIVE to carry out much
of the data reduction required for EVN experiments in an automated fashion.
This pipeline procedure runs entirely within AIPS, the standard data reduction
package used in astronomical VLBI, and is used to provide preliminary
calibration of EVN experiments correlated at the EVN MkIV data processor. As
well as simplifying the analysis for EVN users, the pipeline reduces the delay
in providing information on the data quality to participating telescopes, hence
improving the overall performance of the array. A description of this pipeline
is presented here.


title: The Intergalactic Medium and the Energy Distribution of Quasars

abstract:
  The ionizing spectral energy distribution of quasars is known to exhibit a
steepening of the distribution short-ward of 1050\AA. It has been assumed that
this change of power-law index from -1 to -2 is intrinsic to the quasars. We
study an alternative interpretation, in which a tenuous absorption screen is
responsible for the change of index. A successful spectral fit is obtained
using a total hydrogen density distribution decreasing with redshift as $\sim
(1+z)^{\xi}$ with $\xi$ of the order -3.5 if we suppose that the ionization
state of the intervening gas is controlled by the line-of-sight quasar. This
interpretation is not compatible, however, with the relative weakness of the
observed quasar intensities with respect to that of the local background
metagalactic radiation. Therefore, our interpretation in its present form
cannot be sustained.


title: First optical identification of a suprsoft X-ray source in M31

abstract:
  We propose the first association of an optical counterpart with a luminous
supersoft X-ray source in M31, RX J0044.0+4118, observed with ROSAT in July
1991. The PSPC position is at 1.6" angular distance from a candidate nova in
outburst in September of 1990. This is interesting because the incidence of
classical novae among supersoft X-ray sources is an open question. The proposed
optical counterpart was measured at R~17.7 in September of 1990, and it had
faded to R>19.2 when it was observed again after 70 days.
  The light curve was too sparsely monitored for definite conclusions on the
speed class of the nova. No other variable objects with V<23.5 were found in
the ROSAT spatial error box. We evaluate that the probability that a classical
or recurrent nova was in outburst in the ROSAT error box in the few years
preceding the observation is very small, so the proposed identification is
meaningful. We also show evidence that the associated supersoft X-ray source
turned off in the third year after the outburst.


title:
The X-ray emission from Nova V382 Velorum: II. The super-soft component
  observed with BeppoSAX

abstract:
  Nova Velorum 1999 (V382 Vel) was observed by BeppoSAX 6 months after optical
maximum and was detected as a bright X-ray supersoft source, with a count rate
3.454+-0.002 cts/s in the LECS. It was the softest and most luminous supersoft
source observed with this instrument. The flux in the 0.1-0.7 keV range was not
constant during the observation. It dropped by a factor of 2 in less than 1.5
hour and then was faint for at least 15 minutes, without significant spectral
changes.
  The observed spectrum is not well fit with atmospheric models of a hot,
hydrogen burning white dwarf. This is due mainly to a supersoft excess in the
range 0.1-0.2 keV, but the fit can be significantly improved at higher energy
if at least one emission feature is superimposed. We suggest that a
``pseudocontinuum'' was detected, consisting of emission lines in the supersoft
X-ray range superimposed on the thermal continuum of a white dwarf atmosphere.
As a result, an accurate determination of the effective temperature and gravity
of the white dwarf at this post-outburst stage is not possible.


title: The Anomalous X-ray Pulsars

abstract:
  The Anomalous X-ray Pulsars (AXPs) are a small class of pulsars with spin
periods in the 6-12 s range, very soft X-ray spectra, secular spin down on time
scales of ~10^3-10^5 years, and lack of bright optical counterparts. Two,
possibly three, of them are close to the centre of shell-like supernova
remnants. AXPs are one of the most enigmatic classes of galactic high-energy
sources. Isolated neutron stars powered by the loss of rotational energy can be
excluded on energetic grounds. The models based on neutron stars involve either
accretion (perhaps from a fossil disk around an isolated neutron star) or the
decay of a very strong magnetic field (10^14-10^15 G). We review the models and
the observational properties of AXPs, including recent XMM-Newton and Chandra
observations. We also present some unpublished ASCA data.


title: First High Contrast Imaging Using a Gaussian Aperture Pupil Mask

abstract:
  Placing a pupil mask with a gaussian aperture into the optical train of
current telescopes represents a way to attain high contrast imaging that
potentially improves contrast by orders of magnitude compared to current
techniques. We present here the first observations ever using a gaussian
aperture pupil mask (GAPM) on the Penn State near-IR Imager and Spectrograph
(PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. Two nearby stars were
observed, $\epsilon$ Eridani and $\mu$ Her A. A faint companion was detected
around $\mu$ Her A, confirming it as a proper motion companion. Furthermore,
the observed H and K magnitudes of the companion were used to constrain its
nature. No companions or faint structure were observed for $\epsilon$ Eridani.
We found that our observations with the GAPM achieved contrast levels similar
to our coronographic images, without blocking light from the central star. The
mask's performance also nearly reached sensitivities reported for other ground
based adaptive optics coronographs and deep HST images, but did not reach
theoretically predicted contrast levels. We outline ways that could improve the
performance of the GAPM by an order of magnitude or more.


title: The time delay of the quadruple quasar RX J0911.4+0551

abstract:
  We present optical lightcurves of the gravitationally lensed components A
(=A1+A2+A3) and B of the quadruple quasar RX J0911.4+0551 (z = 2.80). The
observations were primarily obtained at the Nordic Optical Telescope between
1997 March and 2001 April and consist of 74 I-band data points for each
component. The data allow the measurement of a time delay of 146 +- 8 days (2
sigma) between A and B, with B as the leading component. This value is
significantly shorter than that predicted from simple models and indicates a
very large external shear. Mass models including the main lens galaxy and the
surrounding massive cluster of galaxies at z = 0.77, responsible for the
external shear, yield H_0 = 71 +- 4 (random, 2 sigma) +- 8 (systematic)
km/s/Mpc. The systematic model uncertainty is governed by the surface-mass
density (convergence) at the location of the multiple images.


title: Star formation thresholds and galaxy edges: why and where

abstract:
  We study global star formation thresholds in the outer parts of galaxies by
investigating the stability of disk galaxies embedded in dark halos. The disks
are self-gravitating, contain metals and dust, and are exposed to UV radiation.
We find that the critical surface density for the existence of a cold
interstellar phase depends only weakly on the parameters of the model and
coincides with the empirically derived surface density threshold for star
formation. Furthermore, it is shown that the drop in the thermal velocity
dispersion associated with the transition from the warm to the cold gas phase
triggers gravitational instability on a wide range of scales. The presence of
strong turbulence does not undermine this conclusion if the disk is
self-gravitating. Models based on the hypothesis that the onset of thermal
instability determines the star formation threshold in the outer parts of
galaxies can reproduce many observations, including the threshold radii, column
densities, and the sizes of stellar disks as a function of disk scale length
and mass. Finally, prescriptions are given for implementing star formation
thresholds in (semi-)analytic models and three-dimensional hydrodynamical
simulations of galaxy formation.


title:
The afterglow and complex environment of the optically dim burst GRB
  980613

abstract:
  We report the identification of the optical afterglow of GRB 980613 in R- and
I-band images obtained between 16 and 48 hours after the gamma-ray burst. Early
near-infrared (NIR) H and K' observations are also reported. The afterglow was
optically faint (R ~ 23) at discovery but did not exhibit an unusually rapid
decay (power-law decay slope alpha < 1.8 at 2 sigma). The optical/NIR spectral
index (beta_RH < 1.1) was consistent with the optical-to-X-ray spectral index
(beta_RX ~ 0.6), indicating a maximal reddening of the afterglow of ~0.45 mag
in R. Hence the dimness of the optical afterglow was mainly due to the fairly
flat spectral shape rather than internal reddening in the host galaxy. We also
present late-time HST/STIS images of the field in which GRB 980613 occurred,
obtained 799 days after the burst. These images show that GRB 980613 was
located close to a very compact, blue V = 26.1 object inside a complex region
consisting of star-forming knots and/or interacting galaxy fragments.
Therefore, GRB 980613 constitutes a strong case for the association of
cosmological gamma-ray bursts with star-forming regions.


title: On The Spectral Energy Dependence of Gamma-Ray Burst Variability

abstract:
  The variable activity of a gamma-ray burst (GRB) source is thought to be
correlated with its absolute peak luminosity - a relation that, if confirmed,
can be used to derive an independent estimate of the redshift of a GRB. We find
that bursts with highly variable light curves have greater nu-F_nu spectral
peak energies, when we transform these energies to the cosmological rest frame
using the redshift estimates derived either from optical spectral features or
from the luminosity-variability distance indicator itself. This positive
correlation between peak energy and variability spans ~ 2 orders of magnitude
and appears to accommodate GRB 980425, lending credibility to the association
of this burst with SN 1998bw. The existence of such a correlation not only
provides an interesting clue to the nature of this luminosity indicator but
potentially reinforces the validity of the redshift estimates derived from this
method. It also implies that the rest frame GRB peak energy is correlated with
the intrinsic luminosity of the burst, as has been suggested in the past as an
explanation of the observed hardness-intensity correlation in GRBs.


title:
The origin of the young stellar population in the solar neighborhood - a
  link to the formation of the Local Bubble?

abstract:
  We have analyzed the trajectories of moving stellar groups in the solar
neighborhood in an attempt to estimate the number of supernova explosions in
our local environment during the past 20 million years. Using Hipparcos stellar
distances and the results of kinematical analyses by Asiain et al. (1999a) on
the Pleiades moving groups, we are able to show that subgroup B1, consisting of
early type B stars up to 10 Msun, but lacking more massive objects, has passed
through the local interstellar medium within less than 100 pc. Comparing the
stellar content of B1 with the initial mass function derived from the analysis
of galactic OB associations, we estimate the number of supernova explosions and
find that about 20 supernovae must have occurred during the past ~ 10 - 20
million years, which is suggested to be the age of the Local Bubble; the age of
the star cluster is about ~ 20 - 30 million years. For the first time, this
provides strong evidence that the Local Bubble must have been created and
shaped by multi-supernova explosions and presumably been reheated more than 1
million years ago, consistent with recent findings of an excess of 60Fe in a
deep ocean ferromanganese crust. Calculating similarity solutions of an
expanding superbubble for time-dependent energy input, we show that the number
of explosions is sufficient to explain the size of the Local Bubble. The
present energy input rate is about $\dot E_{SN}$ ~ 5 x 10^36 erg/s, in good
agreement with the estimated local soft X-ray photon output rate. It seems
plausible that the origin of the Local Bubble is also linked to the formation
of the Gould Belt, which originated about 30-60 Myrs ago.


title:
Classifying Luyten Stars Using An Optical-Infrared Reduced Proper Motion
  Diagram

abstract:
  We present a V-J reduced proper motion (RPM) diagram for stars in the New
Luyten Two-Tenths (NLTT) catalog. In sharp contrast to the RPM diagram based on
the original NLTT data, this optical-infrared RPM diagram shows distinct tracks
for white dwarfs, subdwarfs, and main-sequence stars. It thereby permits the
identification of white-dwarf and subdwarf candidates that have a high
probability of being genuine.


title:
The Star Formation History and Mass Function of the Double Cluster h and
  Chi Persei

abstract:
  The h and Chi Per "double cluster" is examined using wide-field (0.98 deg x
0.98 deg) CCD UBV imaging supplemented by optical spectra of several hundred of
the brightest stars. Restricting our analysis to near the cluster nuclei, we
find identical reddenings (E(B-V)=0.56+/-0.01), distance moduli (11.85+/-0.05),
and ages (12.8+/-1.0 Myr) for the two clusters. In addition, we find an IMF
slope for each of the cluster nuclei that is quite normal for high-mass stars,
Gamma=-1.3+/-0.2, indistinguishable from a Salpeter value. We derive masses of
3700 M_Sun (h) and 2800 M_Sun (Chi) integrating the PDMF from 1 to 120 M_Sun.
There is evidence of mild mass segregation within the cluster cores. Our data
are consistent with the stars having formed at a single epoch; claims to the
contrary are very likely due to the inclusion of the substantial population of
early-type stars located at similar distances in the Perseus spiral arm, in
addition to contamination by G and K giants at various distances. We discuss
the uniqueness of the double cluster, citing other examples of such structures
in the literature, but concluding that the nearly identical nature of the two
cluster cores is unusual. We fail to settle the long-standing controversy
regarding whether or not the double cluster is the core of the Per OB1
association, and argue that this may be unanswerable with current techniques.
We also emphasize the need for further work on the pre-main sequence population
of this nearby and highly interesting region.


title:
Imaging the Circumstellar Environments of Young Binaries in Southern
  Star-Forming Regions

abstract:
  A sample of 14 pre-main sequence visual binary systems in southern
star-forming regions were imaged at 2 um with the Keck I telescope to search
for tertiary companions, scattered-light disks, and compact nebulae at linear
scales of 5-100 AU. Speckle holography was used to produce images with
diffraction-limited resolution and high dynamic range, and photometry in four
filters between J (1.25 um) and L' (3.8 um) was used to provide a diagnostic of
the infrared excess. Of the 14 visual binary systems studied, 9 contain
components which show evidence for resolved structure. Two of them (WSB 18 and
B59-1) have well-resolved tertiary companions separated from the primary stars
by ~100 mas. The remainder are only marginally resolved at the diffraction
limit of the telescope. Sz 116, AS 205, Elias 2-22, ESO H alpha 282, and B59-2
each have one component which is marginally-resolved along one axis and
unresolved on the perpendicular axis, consistent with tertiaries at separations
between ~6 and 40 mas. If all of these systems are hierarchical triples, then
fully half of the nominal binaries in the sample are triple. The primaries in
Elias 2-49 and WSB 71 are marginally resolved along all position angles,
suggesting the presence of dust halos. No disks were unambiguously detected in
the sample.


title: The global magnetic topology of AB Doradus

abstract:
  We have used Zeeman-Doppler maps of the surface field of the young, rapid
rotator AB Dor (P = 0.514 days) to extrapolate the coronal field, assuming it
to be potential. We find that the topology of the large-scale field is very
similar in all three years for which we have images. The corona divides cleanly
into regions of open and closed field. The open field originates in two
mid-latitude regions of opposite polarity separated by about 180 degrees of
longitude. The closed field region forms a torus extending almost over each
pole, with an axis that runs through these two longitudes. We have investigated
the effect on the global topology of different forms of flux in the
unobservable hemisphere and in the dark polar spot where the Zeeman signal is
suppressed. The flux distribution in the unobservable hemisphere affects only
the low latitude topology, whereas the imposition of a unidirectional polar
field forces the polar cap to be open. This contradicts observations that
suggest that the closed field corona extends to high latitudes and leads us to
propose that the polar cap may be composed of multipolar regions.


title:
Temperature Profiles and Spectra of Accretion Disks around Rapidly
  Rotating Neutron Stars

abstract:
  We calculate temperature profiles and X-ray spectra of accretion disks around
rapidly rotating neutron stars considering the full effect of general
relativity. Computed disk temperatures and luminosities are compared with the
EXOSAT data to constrain the properties of five low-mass-X-ray-binary sources.
We fit our model-spectra with an analytical function, which can in turn be used
for routine spectral fitting work. Our equation-of-state dependent spectral
model may be useful to constrain the equation-of-state models of neutron stars.
We also compare the properties of a rotating neutron star with those of a
rotating strange star with the hope of giving a possible way to identify a
strange star, which will be important for the verification of
strange-quark-matter hypothesis.


title:
Les incompatibilites entre la theorie standard de l'extinction
  interstellaire et l'observation

abstract:
  The standard interpretation of the extinction curve does not agree with some
observations. The light we receive from a reddened star must be contaminated by
starlight scattered at very small angular distances from the star. The true
extinction curve is a straight line from the near infrared to the far-UV. If
so, all interstellar dust models must be questionned. A second conclusion is
that the average properties of interstellar grains may be much more uniform
than previously thought.
  --
  L'interpretation standard de la courbe d'extinction de la lumiere par la
matiere interstellaire n'est pas en accord avec certaines observations. Cela
s'explique seulement si la lumiere des etoiles rougies est contaminee par de la
lumiere diffusee a tres faible angle de diffusion. La courbe d'extinction
exacte est alors une ligne droite du proche infrarouge jusqu'a l'UV lointain.
Cela remet en question tous les modeles de poussiere utilises a l'heure
actuelle. Il n'y a egalement pas lieu de supposer de variation des proprietes
moyennes des grains d'une region de l'espace a l'autre.


title: The Evolution of Nova V382 Vel 1999

abstract:
  We report results of spectroscopic observations of V382 Vel (Nova Vel 1999)
carried out at La Silla between 5 and 498 days after maximum light (23 May
1999, V(max) $\sim 2.3\pm 0.1$). The analysis of the photometric and
spectroscopic evolution shows this object to be a {\sl fast nova} belonging to
the Fe II {\sl broad} spectroscopic class. A distance of 1.7 kpc ($\pm 20%$) is
derived from the maximum magnitude vs. rate of decline relationship after
correcting for the small reddening toward the nova, E(B--V)$\lsim 0.10$. From
the measured H$\alpha$ flux and the associated rate of expansion we derive an
approximate mass for the ejected shell, M$_{env}\lsim 10^{-5}$ M$_\odot$. We
have also observed during the early decline a broad, short-lived ($\lsim$ 10
days) feature at 6705-6715 \AA for which several identifications are possible,
one of which is the lithium doublet at 6708 \AA and which could place an
empirical limit on the lithium production that might occur during the outburst
of a {\sl fast nova}. The high luminosity at maximum, M$_v=-8.9$, and the
relatively small height above the galactic plane ($z\lsim 160$pc) suggest that
V382 Vel originated from a massive white dwarf, likely in the mass range
1.1--1.2 M$_\odot$.


title:
Sur la contamination de la lumiere des etoiles par de la lumiere
  diffusee a tres faible angle

abstract:
  The scattered starlight which contaminates the spectrum of a reddened star
depends on l as 1/lambda^n (n*4), and must be attributed to small particles.
Surprisingly these particules, which have a quasi-isotropic phase function, do
not participate to the brightness of the nebulae. The importance of the
intensity of the scattered light present in the spectrum of reddened stars can
be explained only if the scattering is coherent. The intensity of the scattered
light is then proportional to the square of the number of particles, and is
concentrated within an angle of 10^{-8}" from the star. The scatterers can be
small grains, or, atoms or molecules from the gas. Hydrogen satisfies the
conditions imposed to the scatterers.
  --
  La lumiere diffusee qui contamine le spectre des etoiles rougies a une
dependance en 1/lambda^n (n>=4), caracteristique de particules petites devant
la longueur d'onde. Il est surprenant que ces particules, qui doivent diffuser
de facon quasi-isotrope, ne contribuent pas a la brillance des nebuleuses.
L'importance de la lumiere diffusee par ces petites particules dans le spectre
d'une etoile rougie s'explique seulement si la diffusion est coherente.
L'intensite diffusee est alors proportionnelle au carre du nombre de
diffuseurs. Vue par l'observateur, elle est concentree dans un angle inferieur
a 10{-8}'' de l'etoile. Les diffuseurs peuvent etre des petits grains, ou, des
atomes ou molecules du gaz. L'hydrogene satisfait remarquablement aux
conditions que les observations imposent aux diffuseurs.


title:
The Effect of Cooling and Preheating on the X-ray Properties of Clusters
  of Galaxies

abstract:
  We calculate X-ray properties of present-day galaxy clusters from
hydrodynamical cosmological simulations of the LCDM cosmology and compare these
with recent X-ray observations. Results from three simulations are presented,
each of which uses the same initial conditions: a standard adiabatic,
Non-radiative model, a Radiative model that includes radiative cooling of the
gas, and a Preheating model that also includes cooling but in addition
impulsively heats the gas prior to cluster formation. At the end of the
simulations, the global cooled baryon fractions in the latter two runs are 15
per cent and 0.4 per cent respectively which bracket the recent result from the
K-band luminosity function. We construct cluster catalogues which consist of
over 500 clusters and are complete in mass down to 1.18*10^{13} Msun/h. While
clusters in the Non-radiative model behave in accord with the self-similar
picture, those of the other two models reproduce key aspects of the observed
X-ray properties: the core entropy, temperature-mass and luminosity-temperature
relations are all in good agreement with recent observations. This agreement
stems primarily from an increase in entropy with respect to the Non-radiative
clusters. Although the physics affecting the intra-cluster medium is very
different in the two models, the resulting cluster entropy profiles are very
similar.


title: Stellar-Mass Black Holes in the Solar Neighborhood

abstract:
  We search for nearby, isolated, accreting, ``stellar-mass'' (3 to
$100M_\odot$) black holes. Models suggest a synchrotron spectrum in visible
wavelengths and some emission in X-ray wavelengths. Of 3.7 million objects in
the Sloan Digital Sky Survey Early Data Release, about 150,000 objects have
colors and properties consistent with such a spectrum, and 87 of these objects
are X-ray sources from the ROSAT All Sky Survey. Thirty-two of these have been
confirmed not to be black-holes using optical spectra. We give the positions
and colors of these 55 black-hole candidates, and quantitatively rank them on
their likelihood to be black holes. We discuss uncertainties the expected
number of sources, and the contribution of blackholes to local dark matter.


title: The spectral index of the ionizing continuum of quasars

abstract:
  The ionizing spectral energy distribution of quasars exhibits a steepening of
the distribution short-ward of 1200 A. The change of the power-law index from
approximately -1 to -2 so far has been interpreted as being intrinsic to
quasars. We study an alternative interpretation, in which a tenuous absorption
screen is responsible for the change of index. We find that the most successful
function of HI with z requires that the ionization fraction be independent of
the metagalactic background radiation, that is frozen in. This implies that the
putative component should be of sufficiently low density that it could not
recombine (while the background is subsiding) and/or cool from a high
temperature state.


title: Dynamics of Dark Matter Cusps

abstract:
  Formation and disruption of dark-matter cusps are reviewed. Accumulation of
baryons at the center of a halo can displace the dark matter, converting
singular density cusps into low-density cores. The displaced mass can be of
order 10 M_b with M_b the mass of the infalling population. If M_b is
identified with the masses of the black holes currently observed at the centers
of bright galaxies, predicted core radii are ~a few hundred pc. Other
mechanisms, such as early mass outflow, may explain the large dark-matter cores
in dwarf and low-surface-brightness galaxies. Predictions of dark matter
annihilation radiation from the center of the Milky Way galaxy are shown to be
strongly dependent on the galaxy's merger history.


title: What Causes P-mode Asymmetry Reversal?

abstract:
  The solar acoustic p-mode line profiles are asymmetric. Velocity spectra have
more power on the low-frequency sides, whereas intensity profiles show the
opposite sense of asymmetry. Numerical simulations of the upper convection zone
have resonant p-modes with the same asymmetries and asymmetry reversal as the
observed modes. The temperature and velocity power spectra at optical depth
$\tau_{\rm cont} = 1$ have the opposite asymmetry as is observed for the
intensity and velocity spectra. At a fixed geometrical depth, corresponding to
$<\tau_{\rm cont}>=1$, however, the temperature and velocity spectra have the
same asymmetry. This indicates that the asymmetry reversal is produced by
radiative transfer effects and not by correlated noise.


title: The Population of Faint Optically-Selected AGN at z~3

abstract:
  We discuss a sample of 29 AGN (16 narrow-lined and 13 broad-lined) discovered
in a spectroscopic survey of ~1000 star-forming Lyman-break galaxies (LBGs) at
z~3. Reaching apparent magnitudes of R_{AB}=25.5, the sample includes
broad-lined AGN approximately 100 times less UV-luminous than most surveys to
date covering similar redshifts, and the first statistical sample of
UV/optically-selected narrow-lined AGN at high redshift. The fraction of
objects in our survey with clear evidence for AGN activity is ~3%. A
substantial fraction, perhaps even most, of these objects would not have been
detected in even the deepest existing X-ray surveys. We argue that these AGN
are plausibly hosted by the equivalent of LBGs. The UV luminosities of the
broad-lined AGN in the sample are compatible with Eddington-limited accretion
onto black holes that satisfy the locally determined M_{BH} versus M_{bulge}
relation given estimates of the stellar masses of LBGs. The clustering
properties of the AGN are compatible with their being hosted by objects similar
to LBGs. The implied lifetime of the active AGN phase in LBGs, if it occurs
some time during the active star-formation phase, is ~10^7 years.


title:
A Constraint on the Gravitational Lensing Magnification and Age of the
  Redshift z=6.28 Quasar SDSS 1030+0524

abstract:
  The recent discovery of bright quasars around redshift z=6 suggests that
black holes (BHs) with masses in excess of 10^9 Msun have already assembled at
a very early stage in the evolution of the universe. An alternative
interpretation is that these quasars are powered by less massive BHs, but their
fluxes are strongly magnified through gravitational lensing by intervening
galaxies. Here we analyze the flux distribution of the Ly alpha emission of the
quasar with the highest known redshift, SDSS 1030+0524, at z=6.28. We show that
this object could not have been magnified by lensing by more than a factor of
five. The constraint arises from the large observed size, 30 (comoving) Mpc, of
the ionized region around this quasar, and relies crucially only on the
assumption that the quasar is embedded in a largely neutral IGM. Based on the
line/continuum ratio of SDSS 1030+0524, we argue further that this quasar also
cannot be beamed by a significant factor. We conclude that the minimum mass for
its resident BH is 4 x 10^8 Msun (for magnification by a factor of five); if
the mass is this low, then the quasars had to switch on prior to redshift z=9.
  From the size of the ionized region, we are also able to place an absolute
lower bound on the age of this quasar at t > 2 x 10^7 years.


title: X-ray Rich GRB, Photospheres and Variability

abstract:
  We investigate the relationship between the quasi-thermal baryon-related
photosphere in relativistic outflows, and the internal shocks arising outside
them, which out to a limiting radius may be able to create enough pairs to
extend the optically thick region. Variable gamma-ray light curves are likely
to arise outside this limiting pair-forming shock radius, while X-ray excess
bursts may arise from shocks occurring below it; a possible relation to X-ray
flashes is discussed. This model leads to a simple physical interpretation of
the observational gamma-ray variability-luminosity relation.


title:
The Link Between Rotation Curve Type and Spiral Arm Structure in Disk
  Galaxies

abstract:
  Over the last decade it has become clear that there is a decoupling between
the old stellar disk and young stellar disk in spiral galaxies. This has led to
a scheme for classifying galaxies on the basis of their near-infrared
morphology. The near-infrared provides a more physical framework for
classifying galaxies as it is both relatively free from extinction and it
traces the old stellar population, i.e. the dominant stellar mass distribution.
The `dust penetrated class' is dependent upon the spiral pitch angle of arms.
We have observed 8 galaxies with UFTI on UKIRT in the K-band in order to
investigate the theoretical link between disk dynamics and arm morphology,
which is suggested both from numerical models and the dust penetrated class. We
find that the pitch angle of spiral arms, i, correlates well with the shear
rate of rotation curves, $A/\omega$ (where A is the first Oort constant and
$\omega$ is the rotational velocity), over the same radial range.


title: Axino as Cold Dark Matter Candidate

abstract:
  The possibility of the CDM axino is presented. From the early days of
supersymmetry, axino has been considered as hot dark matter and warm dark
matter. But the CDM axino has been considered quite recently. It is because the
low reheating temperature of the universe is gaining momentum recently from
various considerations in particle cosmology. I present a general introduction
on the CDM's, in particular the axino, the calculation on the axino density in
the universe, and the constraints imposed on the axino parameters.


title:
Theoretical models for classical Cepheids. VIII. Effects of helium and
  heavy elements abundance on the Cepheid distance scale

abstract:
  Previous nonlinear fundamental pulsation models for classical Cepheids with
metal content Z <= 0.02 are implemented with new computations at super-solar
metallicity (Z=0.03, 0.04) and selected choices of the helium-to-metal
enrichment ratio DeltaY/Delta Z. On this basis, we show that the location into
the HR diagram of the Cepheid instability strip is dependent on both metal and
helium abundance, moving towards higher effective temperatures with decreasing
the metal content (at fixed Y) or with increasing the helium content (at fixed
Z). The contributions of helium and metals to the predicted Period-Luminosity
and Period-Luminosity-Color relations are discussed, as well as the
implications on the Cepheid distance scale. Based on these new results, we
finally show that the empirical metallicity correction suggested by Cepheid
observations in two fields of the galaxy M101 may be accounted for, provided
that the adopted helium-to-metal enrichment ratio is reasonably high (Delta
Y/Delta Z ~ 3.5).


title:
The stellar population of NGC5634. A globular cluster in the Sagittarius
  dSph Stream?

abstract:
  We present the first (V,V-I) Color -- Magnitude Diagram (CMD) for the poorly
studied globular cluster NGC 5634. The CMD shows a steep Red Giant Branch (RGB)
and a predominantly blue Horizontal Branch (HB): both these characteristics
suggest a low metal content for this cluster. From the position of the RGB in
the CMD we estimate [Fe/H] = -1.94 +/- 0.10 and E(B-V)=0.06 +/- 0.01. The CMD
presented here reaches V\simeq 23, allowing us to obtain the first measure of
the Main Sequence Turn-Off (TO) V_{TO}= 21.22 +/- 0.15 for this cluster. By
combining this figure with the apparent luminosity of the Zero Age HB (ZAHB),
V_{ZAHB}=17.90 +/- 0.10 we obtain Delta V^{HB}_{TO}=3.32 +/- 0.16, a value
which is fully compatible with that derived for the bulk of Galactic globulars.
We also derive a true distance modulus of (m-M)_0 = 17.17 +/- 0.12
corresponding to a distance of ~ 27.2 kpc. Most interestingly, the cluster is
shown to have position and radial velocity fully compatible with the orbit of
the Sgr dwarf spheroidal (dSph) galaxy. The similarity between the stellar
populations of the cluster and the Sgr globular Ter 8 and the metal poor
population of the Sgr dSph, also suggest that NGC 5634 was a former member of
this disrupting galaxy, torn off by the Galactic tidal field and now lost in
the Sgr Stream.


title:
Primordial black holes in braneworld cosmologies: Formation,
  cosmological evolution and evaporation

abstract:
  We consider the population evolution and evaporation of primordial black
holes in the simplest braneworld cosmology, Randall-Sundrum type II. We
demonstrate that black holes forming during the high-energy phase of this
theory (where the expansion rate is proportional to the density) have a
modified evaporation law, resulting in a longer lifetime and lower temperature
at evaporation, while those forming in the standard regime behave essentially
as in the standard cosmology. For sufficiently large values of the AdS radius,
the high-energy regime can be the one relevant for primordial black holes
evaporating at key epochs such as nucleosynthesis and the present. We examine
the formation epochs of such black holes, and delimit the parameter regimes
where the standard scenario is significantly modified.


title: Biases in Cometary Catalogues and Planet X

abstract:
  Two sets of investigators -- Murray (1999) and Matese, Whitman & Whitmire
(1999) -- have recently claimed evidence for an undiscovered Solar System
planet from possible great circle alignments in the aphelia directions of the
long period comets. However, comet discoveries are bedevilled by selection
effects. These include anomalies caused by the excess of observers in the
northern as against the southern hemisphere, seasonal and diurnal biases,
directional effects which make it harder to discover comets in certain regions
of the sky, as well as sociological biases. The stream proposed by Murray is
shown on an equal area Hammer-Aitoff projection. The addition of newer data
weakens the case for the alignment. There is also evidence that the subsample
in the stream is affected by seasonal and north-south biases. The stream
proposed by Matese et al. is most obvious in the sample of dynamically new
comets, and especially in those whose orbits are best known. The most recent
data continues to maintain the overpopulation in this great circle. This
pattern in the data occurs about once in a thousand times by chance. Numerical
integrations are used to demonstrate that a planet by itself can reduce the
perihelia of comets in its orbital plane to sufficiently small values so that
they could be discovered from the Earth. There is a need for a sample of long
period comets that is free from unknown or hard-to-model selection effects.
Such will be provided by the European Space Agency satellite GAIA.


title: HI in elliptical galaxies

abstract:
  Neutral hydrogen is an important component of the interstellar medium in
elliptical galaxies as well as a potentially valuable mass tracer. Until
recently, HI surveys of early-type galaxies have been sparse and inhomogeneous
but this has changed with the advent of the HI Parkes All-Sky Survey (HIPASS;
Barnes et al. 2001). We discuss HIPASS observations of a sample of ~2500 nearby
E/S0 galaxies, as well as detailed HI imaging of a range of individual objects.


title:
Non-Gaussian Signatures in the Cosmic Background Radiation from Warm
  Inflation

abstract:
  We calculate the bispectrum of the gravitational field fluctuations generated
during warm inflation, where dissipation of the vacuum potential during
inflation is the mechanism for structure formation. The bispectrum is non--zero
because of the self--interaction of the scalar field. We compare the
predictions with those of standard, or `supercooled', inflationary models, and
consider the detectability of these levels of non--Gaussianity in the
bispectrum of the cosmic microwave background. We find that the levels of
non--Gaussianity for warm and supercooled inflation are comparable, and
over--ridden by the contribution to the bispectrum due to other physical
effects. We also conclude that the resulting bispectrum values will be
undetectable in the cosmic microwave background for both the MAP and Planck
Surveyor satellites.


title:
Effects of a burst of formation of first-generation stars on the
  evolution of galaxies

abstract:
  First-generation (Population III) stars in the universe play an important
role inearly enrichment of heavy elements in galaxies and intergalactic medium
and thus affect the history of galaxies. The physical and chemical properties
of primordial gas clouds are significantly different from those of present-day
gas clouds observed in the nearby universe because the primordial gas clouds do
not contain any heavy elements which are important coolants in the gas.
Previous theoretical considerations have suggested that typical masses of the
first-generation stars are between several $M_\odot$ and $\approx 10 M_\odot$
although it has been argued that the formation of very massive stars (e.g., $>
100 M_\odot$) is also likely. If stars with several $M_\odot$ are most popular
ones at the epoch of galaxy formation, most stars will evolve to hot (e.g.,
$\gtrsim 10^5$ K), luminous ($\sim 10^4 L_\odot$) stars with gaseous and dusty
envelope prior to going to die as white dwarf stars. Although the duration of
this phase is short (e.g., $\sim 10^5$ yr), such evolved stars could contribute
both to the ionization of gas in galaxies and to the production of a lot of
dust grains if the formation of intermediate-mass stars is highly enhanced. We
compare gaseous emission-line properties of such nebulae with some interesting
high-redshift galaxies such asIRAS F10214+4724 and powerful radio galaxies.


title: The Degree of CO Depletion in Pre-stellar Cores

abstract:
  We present new results on CO depletion in a sample of nearby pre-stellar
cores, based on observations of the millimeter C17O and C18O lines and the 1.3
mm dust emission with the IRAM 30m telescope. In most cases, the distribution
of CO is much flatter than that of the dust, whereas other tracers, like N2H+,
still probe the latter. In the centre of these objects, we estimate CO to be
underabundant by a factor 4-15 depending on the cores. The CO underabundance is
more pronounced in the central regions and appears to decrease with increasing
distance from the core centre. This underabundance is most likely due to the
freezing out of CO onto the dust grains in the cold, dense parts of the cores.
We find evidence for an increase of the CO depletion degree with the core
density.


title: Topology of the universe from COBE-DMR; a wavelet approach

abstract:
  In this paper we pursue a new technique to search for evidence of a finite
Universe, making use of a spherical mexican-hat wavelet decomposition of the
microwave background fluctuations. Using the information provided by the
wavelet coefficients at several scales we test whether compact orientable flat
topologies are consistent with the COBE-DMR data. We consider topological sizes
ranging from half to twice the horizon size. A scale-scale correlation test
indicates that non-trivial topologies with appropriate topological sizes are as
consistent with the COBE-DMR data as an infinite universe. Among the finite
models the data seems to prefer a Universe which is about the size of the
horizon for all but the hypertorus and the triple-twist torus. For the latter
the wavelet technique does not seem a good discriminator of scales for the
range of topological sizes considered here, while a hypertorus has a preferred
size which is 80% of the horizon. This analysis allows us to find a best fit
topological size for each model, although cosmic variance might limit our
ability to distinguish some of the topologies.


title:
What do HST and Chandra tell us about the jet and the nuclear region of
  the radio galaxy 3C270?

abstract:
  The HST/STIS ultraviolet image of the FR I radio galaxy 3C270 shows the
presence of a jet-like structure emerging from the position of the nucleus.
This feature, which represents the first jet-like component ever detected in
the UV in a radio galaxy with jets lying almost on the plane of the sky, has
the same position angle as the jet in the radio and X-ray images. We propose
two different scenarios for the origin of the emission: i) non-thermal
synchrotron from a mildly relativistic component of the jet; ii) scattered
light from the nucleus, where a BL Lac source may be hosted. Either of these
pictures would have important consequences for the AGN unification schemes and
for our knowledge of the jet structure. In the Chandra image a faint
counter-jet is also present. From a comparative analysis of the HST images and
Chandra X-ray spectrum, we find that the nucleus is only moderately obscured.
The obscuring structure might well reside in the geometrically thin dark disk
observed on large scales. This fits the scenario in which a standard
geometrically and optically thick torus is not present in FR I radio galaxies.


title:
The Eclipsing Binary BG Geminorum: Improved Constraints on the Orbit and
  the Structure of the Accretion Disk

abstract:
  We describe new optical photometric and spectroscopic observations of the
semi-detached eclipsing binary BG Geminorum. A large change in the amount of Mg
I absorption at secondary maximum indicates the presence of cool material in
the outer edge of the disk surrounding the unseen primary star. Detection of
weak He I emission implies a hot radiation source at the inner edge of the
disk. If the velocity variations in the Hbeta emission line track the orbital
motion of the primary star, the primary star has an orbital semiamplitude of K1
= K(Hbeta) = 16.0 +- 4.6 km/sec. This result yields a mass ratio, q = 0.22 +-
0.07, consistent with the q = 0.1 derived from the large ellipsoidal variation.
Despite this progress, the nature of the primary star - B-type star or black
hole - remains uncertain.


title: Ultrahigh energy cosmic rays from dark matter annihilation

abstract:
  Annihilation of clumped superheavy dark matter provides an interesting
explanation for the origin of ultrahigh energy cosmic rays.
  The predicted anisotropy signal provides a unique signature for this
scenario.


title:
SPIFI: a direct-detection imaging spectrometer for submillimeter
  wavelengths

abstract:
  The South Pole Imaging Fabry-Perot Interferometer (SPIFI) is the first
instrument of its kind -- a direct-detection imaging spectrometer for astronomy
in the submillimeter band. SPIFI's focal plane is a square array of 25 silicon
bolometers cooled to 60 mK; the spectrometer consists of two cryogenic,
scanning Fabry-Perot interferometers in series with a 60 mK bandpass filter.
The instrument operates in the short submillimeter windows (350 microns, 450
microns) available from the ground, with spectral resolving power selectable
between 500 and 10000. At present, SPIFI's sensitivity is within a factor 1.5-3
of the photon background limit, comparable to the best heterodyne
spectrometers. The instrument's large bandwidth and mapping capability provide
substantial advantages for specific astrophysical projects, including deep
extragalactic observations. In this article we present the motivation for and
design of SPIFI and its operational characteristics on the telescope.


title: Multicolor flickering studies of X1822-371

abstract:
  We report on the analysis of high-speed multicolor photometry of the
eclipsing X-ray binary X1822-371. We used new eclipse timings to derive a
revised optical ephemeris. A quadratic fit to the eclipse timings is not
statistically significant but suggests that the orbital period is increasing on
a timescale of P/|Pdot|= (4.2 +/- 1.4) 10^6 yr. We find no systematic delay or
advance of the optical timings with respect to the X-ray timings. Average UBVRI
light curves show the deep eclipse of the disc by the secondary star
superimposed on the broader and shallower occultation of the inner disc regions
by the outer disc (dip), and an orbital hump centred at phase +0.25 which is
mostly seen in the U and B bands. The starting phase of the dip occurs earlier
for shorter wavelengths, while the egress occurs at the same phase in all
bands. This suggests that the thickening of the outer, occulting disc rim is
gradual with azimuth at ingress but decreases sharply at egress. We fit
synthetic photometry to the extracted colors of the inner and outer disc
regions to estimate their effective temperatures. We find Teff= (9+/-5) 10^7 K
and Teff= (6+/-2) 10^4 K, respectively, for the inner and outer disc regions.
The orbital dependency of the flickering activity is derived from the mean
scatter of the individual light curves with respect to the average UBVRI light
curves. The flickering curves show a broad eclipse at the dipping phases, the
depth of which decreases with increasing wavelength. The blue, eclipsed
flickering component is associated with the inner disc regions and can be
fitted by a blackbody spectrum of Teff= (2.1+/-0.8) 10^8 K, whereas the
uneclipsed flickering component probably arises from the outermost disc regions
and is well described by a blackbody of Teff= (9.6+/-0.7) 10^3 K.


title:
New Understanding of Large Magellanic Cloud Structure, Dynamics and
  Orbit from Carbon Star Kinematics

abstract:
  We derive general expressions for the LMC velocity field which we fit to
kinematical data for 1041 carbon stars. We demonstrate that all previous
studies of LMC kinematics have made unnecessary over-simplifications that have
led to incorrect estimates of important structural parameters. We compile and
improve LMC proper motion estimates to support our analysis. We find that the
kinematically determined position angle of the line of nodes is 129.9 +/- 6.0
deg. The LMC inclination changes at a rate di/dt = -103 +/- 61 deg/Gyr, a
result of precession and nutation induced by Milky Way tidal torques. The LMC
rotation curve V(R) has amplitude 49.8 +/- 15.9 km/s, 40% lower than what has
previously (and incorrectly) been inferred from e.g. HI. The dynamical center
of the carbon stars is consistent with the center of the bar and the center of
the outer isophotes, but not with the HI kinematical center. The enclosed mass
inside 8.9 kpc is (8.7 +/- 4.3) x 10^9 M_sun, more than half of which is due to
a dark halo. The LMC has a larger vertical thickness than has traditionally
been believed. Its V/sigma is less than the value for the Milky Way thick disk.
We discuss the implications for the LMC self-lensing optical depth. We
determine the LMC velocity and orbit in the Galactocentric rest frame and find
it to be consistent with the range of velocities that has been predicted by
models for the Magellanic Stream. The Milky Way dark halo must have mass >4.3 x
10^{11} M_sun and extent >39 kpc for the LMC to be bound. We predict the LMC
proper motion velocity field, and discuss techniques for kinematical distance
estimation. [ABRIDGED]


title: Molecular Gas in Elliptical Galaxies: Distribution and Kinematics

abstract:
  I present interferometric images (approx. 7" resolution) of CO emission in
five elliptical galaxies and nondetections in two others. These data double the
number of elliptical galaxies whose CO emission has been fully mapped. The
sample galaxies have 10^8 to 5x10^9 solar masses of molecular gas distributed
in mostly symmetric rotating disks with diameters of 2 to 12 kpc. Four out of
the five molecular disks show remarkable alignment with the optical major axes
of their host galaxies. The molecular masses are a few percent of the total
dynamical masses which are implied if the gas is on circular orbits. If the
molecular gas forms stars, it will make rotationally supported stellar disks
which will be very similar in character to the stellar disks now known to be
present in many ellipticals. Comparison of stellar kinematics to gas kinematics
in NGC 4476 implies that the molecular gas did not come from internal stellar
mass loss because the specific angular momentum of the gas is about three times
larger than that of the stars.


title:
Multipole (E1, M1, E2, M2) transition wavelengths and rates between
  states with n<= 6 in heliumlike carbon, nitrogen, oxygen, neon, silicon, and
  argon

abstract:
  Transition wavelengths and rates are given for E1, E2, M1, and M2 transitions
between singlet and triplet S, P, D, and F states in heliumlike ions of
astrophysical interest: carbon, nitrogen, oxygen, neon, silicon, and argon. All
possible transitions between states with n <= 6 are considered. Wave functions
and energies are calculated using the relativistic configuration-interaction
(CI) method including both Coulomb and Breit interactions. For transitions to
the ground state, the present theoretical wavelengths agree to five digits with
precise measurements.


title: Obscured AGN: the hidden side of the X-ray Universe

abstract:
  Most Active Galactic Nuclei (AGN) are `obscured', i.e. the nucleus is hiding
behind a screen of absorbing material. The advantage of having the nucleus
obscured is to make easier the observations of those emission components which
originate in circumnuclear matter outside the absorbing regions, because in
this case they are not outshined by the nuclear emission. This is particularly
important in X-rays, where spatial resolution is (with the notable exception of
Chandra) poorer than in the optical, and the study of circumnuclear regions is
often based on spectral analysis only.
  The properties of circumnuclear matter, in the light of recent high spectral
and/or angular resolution $Chandra$ and XMM--Newton observations, will be
reviewed in Sec.2. In Sec.3 we will discuss obscured AGN in the framework of
the Unification Model. Recent discoveries of X-ray obscured Seyfert 1, and of
X-ray loud but optically normal galaxies, are calling for a revision of the
Unification Model.
  Obscured AGN have also a cosmological relevance. Not only are they a
fundamental ingredient of synthesis models of the Cosmic X-ray Background
(XRB), but provide a link between the XRB and the Cosmic Infrared Background,
as briefly discussed in Sec.4.


title: The Role of Magnetic Helicity Transport in Nonlinear Galactic Dynamos

abstract:
  We consider the magnetic helicity balance for the galactic dynamo in the
framework of the local dynamo problem, as well as in the no-z model (which
includes explicitly the radial distribution of the magnetic fields). When
calculating the magnetic helicity balance we take into account the
redistribution of the small-scale and large-scale magnetic fields between the
magnetic helicities, as well as magnetic helicity transport and diffusion due
to small-scale turbulence. We demonstrate that the magnetic helicity flux
through the galactic disc boundaries leads to a steady-state magnetic field
with magnetic energy comparable to the equipartition energy of the turbulent
motions of the interstellar medium. If such flux is ignored, the steady-state
magnetic field is found to be much smaller than the equipartition field. The
total magnetic helicity flux through the boundaries consists of both an
advective flux and a diffusive flux. The exact ratio of these contributions
seems not to be crucial for determining the strength of the steady-state
magnetic field and its structure. However at least some diffusive contribution
is needed to smooth the magnetic helicity profile near to the disc boundaries.
The roles of various transport coefficients for magnetic helicity are
investigated, and the values which lead to magnetic field configurations
comparable with those observed are determined.


title: The Quest for the Cosmological Parameters

abstract:
  The following review presents an attempt to discuss various issues of current
interest in Observational Cosmology, the selection of which as well as the
emphasis given, reflects my own preference and biases. After presenting some
Cosmological basics, for which I was aided by excellent text-books, I emphasize
on attempts to determine some of the important cosmological parameters; the
Hubble constant, the curvature and total mass content of the Universe. The
outcome of these very recent studies is that the "concordance" model, that fits
the majority of observations, is that with Omega_m+ Omega_Lambda=1,
Omega_Lambda ~ 0.7, Ho ~ 70 km/sec Mpc, Omega_B ~ 0.04 and spectral index of
primordial fluctuation spectrum, the inflationary value n ~ 1. I apologise
before hand for the many important works that I may have omitted.