title:
Photon Dominated Regions in Low UV Fields: A Study of The Peripheral
  Region of L1204/S140

abstract:
  We have carried out an in-depth study of the peripheral region of the
molecular cloud L1204/S140, where the far ultraviolet radiation and the density
are relatively low. Our observations test theories of photon-dominated regions
(PDRs) in a regime that has been little explored. CII 158 micron and OI 63
micron lines are detected by ISO at all 16 positions along a 1-dimensional cut
in right ascension. Emission from molecular hydrogen rotational transitions, at
28 and 17 micron, was also detected at several positions. The CII, OI, and
molecular hydrogen intensities along the cut show much less spatial variation
than do the rotational lines of CO and other CO isotopes. The average CII and
OI intensities and their ratio are consistent with models of PDRs with low FUV
radiation (Go) and density. The best-fitting model has Go about 15 and density,
n about 1000 per cubic cm. Standard PDR models underpredict the intensity in
the H2 rotational lines by up to an order of magnitude. This problem has also
been seen in bright PDRs and attributed to factors, such as geometry and
gas-grain drift, that should be much less important in the regime studied here.
The fact that we see the same problem in our data suggests that more
fundamental solutions, such as higher H2 formation rates, are needed. Also, in
this regime of low density and small line width, the OI line is sensitive to
the radiative transfer and geometry. Using the ionization structure of the
models, a quantitative analysis of timescales for ambipolar diffusion in the
peripheral regions of the S140 cloud is consistent with a theory of
photoionization-regulated star formation. Observations of CII in other galaxies
differ both from those of high Go PDRs in our galaxy and from the low Go
regions we have studied. ~


title: Hidden star-formation in the cluster of galaxies Abell 1689

abstract:
  At a redshift of 0.18, Abell 1689 is so far the most distant cluster of
galaxies for which substantial mid-infrared (MIR) data have been published. We
present here the follow-up optical photometric and spectroscopic observations
which were used to study the individual properties of the galaxies members of
A1689. Sources with a low [15 micron] / [6.75 micron] flux ratio typically
consist of luminous passive early-type galaxies while those with a high MIR
color index are mainly luminous, blue, emission-line, morphologically disturbed
spirals, i.e. the star-forming galaxies usually associated with the
'Butcher-Oemler' effect. On the other hand, at least 30% of the 15 micron
sources have optical counterparts showing no evidence of current star-formation
activity, while their 15 micron emission is most likely due to obscured star
formation. We argue that the LW3 luminosity measured in the cluster members is
a reliable tracer of the total infrared luminosity, L(IR). We derive from L(IR)
a star-formation rate free of dust extinction, SFR(IR), which we compare with
that determined in the optical from the flux of the [OII] emission line,
SFR(opt). The highest total star formation rates (11 Msun/yr) and dust
extinction are measured in those galaxies exhibiting in their optical spectrum
a signature of a dusty starburst. In contrast, none of the galaxies with
post-starburst optical spectra has been detected by ISOCAM. We find a median
SFR(IR) of the LW3-detected galaxies of 2 Msun/yr, that is ten times higher
than the median SFR(opt) of the [OII] detected galaxies. The ratio
SFR(IR)/SFR(opt) is in fact very high, ranging between 10 and 100 for
LW3-detected galaxies with [OII] emission. We conclude that a major part, at
least 90%, of the star formation activity taking place in Abell 1689 is hidden.


title: Chandra reveals the Dynamic Structure of the Inner Crab Nebula

abstract:
  We present a series of monitoring observations of the Crab Nebula with the
Chandra X-ray Observatory, focusing on the temporal evolution of the structure.
This series of 8 observations, spanning a period of approximately six months,
shows the dynamic nature of the inner X-ray structures. We detected outward
moving ``wisps'' from the recently discovered inner ring seen in optical
observations. We also find that the inner ring itself shows temporal variations
in structure. The torus also appears to be expanding. Such temporal variations
generally match the canonical scenario that an expanding synchrotron nebula
injected from the pulsar is confined by the supernova ejecta.


title:
WIYN Open Cluster Study. X. The K-Band Magnitude of the Red Clump as a
  Distance Indicator

abstract:
  In an effort to improve the utility of the helium burning red clump
luminosity as a distance indicator, we explore the sensitivity of the K-band
red clump absolute magnitude Mk(RC) to metallicity and age. We rely upon JK
photometry for 14 open clusters and two globulars from the 2nd Incremental Data
Release of the 2MASS Point Source Catalog. The distances, metallicities, and
ages of the open clusters are all on an internally consistent system, while the
K(RC) values are measured from the 2MASS data. For clusters younger than ~2
Gyr, Mk(RC) is insensitive to metallicity but shows a dependence on age. In
contrast, for clusters older than ~2 Gyr, Mk(RC) is influenced primarily by the
metallicity of the population and shows little or no dependence on the age.
Theoretical red clump models based on the formalism of Girardi et al. reinforce
this finding. Over comparable metallicity and age ranges, our average Mk(RC)
value is in accord with that based on solar-neighborhood red clump stars with
HIPPARCOS parallaxes. Lastly, we compute the distance to the open cluster NGC
2158 using our red clump calibration. Adopting an age of 1.6 +/- 0.2 Gyr and
[Fe/H] = -0.24 +/- 0.06, our calibration yields a distance of (m-M)v = 14.38
+/- 0.09.


title: The REFLEX Cluster Survey: Probing the Mass Distribution in the Universe

abstract:
  We summarize some of the major results obtained so far from the REFLEX survey
of X-ray clusters of galaxies, concentrating on the latest measurements of the
cluster X-ray luminosity function and two-point correlation function. The
REFLEX luminosity function provides the most homogeneous census of the
distribution function of masses in the local Universe, representing a unique
zero-redshift reference quantity for evolutionary studies. On the other hand,
the observed clustering of REFLEX clusters is very well described both in
amplitude and shape by the correlation function computed for a low-Omega_M CDM
model. The bidimensional correlation map xi(r_p,pi) shows no stretching along
the line of sight, indicating negligible spurious effects in the sample, with
at the same time a clear compression of the contours as expected in the
presence of coherent large-scale motions.


title:
The Energy Spectrum of Cosmic Rays Above $3 \times 10^{17}$ eV as
  measured with the Haverah Park Array

abstract:
  Air showers recorded by the Haverah Park Array during the years 1974 - 1987
have been re-analysed. For the original estimate of the energy spectrum, a
relationship between the ground parameter $\rho$(600) and the primary energy,
as determined by Hillas in the 1970s, was used. Here we describe the energy
spectrum obtained using the QGSJET98 interaction model in the CORSIKA Monte
Carlo code, together with GEANT to simulate the detailed detector response to
ground particles. A new energy spectrum in the range 3 $\times$ 10$^{17}$ eV to
4 $\times$ 10$^{18}$ eV is presented.


title: High-Resolution Spectroscopy of G191-B2B in the Extreme Ultraviolet

abstract:
  We report a high-resolution (R=3000-4000) spectroscopic observation of the DA
white dwarf G191-B2B in the extreme ultraviolet band 220-245 A. A low- density
ionised He component is clearly present along the line-of-sight, which if
completely interstellar implies a He ionisation fraction considerably higher
than is typical of the local interstellar medium. However, some of this
material may be associated with circumstellar gas, which has been detected by
analysis of the C IV absorption line doublet in an HST STIS spectrum. A stellar
atmosphere model assuming a uniform element distribution yields a best fit to
the data which includes a significant abundance of photospheric He. The
99-percent confidence contour for the fit parameters excludes solutions in
which photospheric He is absent, but this result needs to be tested using
models allowing abundance gradients.


title: The Nature of Dark Matter

abstract:
  Cold Dark Matter (CDM) has become the standard modern theory of cosmological
structure formation. Its predictions appear to be in good agreement with data
on large scales, and it naturally accounts for many properties of galaxies. But
despite its many successes, there has been concern about CDM on small scales
because of the possible contradiction between the linearly rising rotation
curves observed in some dark-matter-dominated galaxies vs. the $1/r$ density
cusps at the centers of simulated CDM halos. Other CDM issues on small scales
include the very large number of small satellite halos in simulations, far more
than the number of small galaxies observed locally, and problems concerning the
angular momentum of the baryons in dark matter halos. The latest data and
simulations have lessened, although not entirely resolved, these concerns.
Meanwhile, the main alternatives to CDM that have been considered to solve
these problems, self-interacting dark matter (SIDM) and warm dark matter (WDM),
have been found to have serious drawbacks.


title:
Spatial Resolution of High-Velocity Filaments in the Narrow-Line Region
  of NGC 1068: Associated Absorbers Caught in Emission?

abstract:
  Using the HST STIS spectrograph we have obtained a grid of [O III] and H-beta
emission-line spectra at 0"05x0"19 and 60 km/s (FWHM) resolution that covers
much of the NLR of NGC 1068. We find emitting knots that have blueshifted
radial velocities up to 3200 km/s relative to galaxy systemic, are 70-150 pc NE
of the nucleus and up to 40 pc from the radio jet, emit several percent of the
NLR line flux but no significant continuum, span velocity extents of up to 1250
km/s but a small fraction of the sky seen from the nucleus, coincide with a
region of enhanced IR coronal-line emission, and have ionized masses $\sim$200
Msun/ne4 (ne4=10^4 cm^{-3}). We argue that the blueshifted knots are ablata
from disintegrating molecular clouds that are being photoionized by the AGN,
and are being accelerated readiatively by the AGN or mechanically by the radio
jet. In their kinematic properties, the knots resemble the associated absorbers
seen projected on the UV continua of some AGN. Between 2"5-4"5 from the
nucleus, emission is redshifted relative to systemic, a pattern that we
interpret as gas in the galaxy disk being pushed away from us by the NE radio
lobe.


title:
X-raying the Ultraluminous Infrared Starburst Galaxy and Broad
  Absorption Line QSO, Markarian 231, with Chandra

abstract:
  With 40 ks of Chandra ACIS-S3 exposure, new information on both the starburst
and QSO components of the X-ray emission of Markarian 231, an ultraluminous
infrared galaxy and Broad Absorption Line QSO, has been obtained. The bulk of
the X-ray luminosity is emitted from an unresolved nuclear point source, and
the spectrum is remarkably hard with the majority of the flux emitted above 2
keV. Most notably, significant nuclear variability (a decrease of ~45% in
approximately 6 hours) at energies above 2 keV indicates that Chandra has
probed within light hours of the central black hole. Though we concur with
Maloney & Reynolds that the direct continuum is not observed, this variability
coupled with the 188 eV upper limit on the equivalent width of the FeKalpha
emission line argues against the reflection-dominated model put forth by these
authors based on their ASCA data. Instead, we favor a model in which a small,
Compton-thick absorber blocks the direct X-rays, and only indirect, scattered
X-rays from multiple lines of sight can reach the observer. Extended soft,
thermal emission encompasses the optical extent of the galaxy and exhibits
resolved structure. An off-nuclear X-ray source with a 0.35-8.0 keV luminosity
of L_X=7x10^{39} erg s^{-1}, consistent with the ultraluminous X-ray sources in
other nearby starbursts, is detected. We also present an unpublished FOS
spectrum from the HST archive showing the broad C IV absorption.


title:
Absolute Proper Motions to B~22.5: IV. Faint, Low Velocity White Dwarfs
  and the White Dwarf Population Density Law

abstract:
  The reduced proper motion diagram (RPMD) for a complete sample of faint stars
with high accuracy proper motions in the North Galactic Pole field SA57 is
investigated. Eight stars with very large reduced proper motions are identified
as faint white dwarf candidates. We discriminate these white dwarf candidates
from the several times more numerous QSOs based on proper motion and
variability.
  We discuss the implausibility that these stars could be any kind of survey
contaminant. If {\it bona fide} white dwarfs, the eight candidates found here
represent a portion of the white dwarf population hitherto uninvestigated by
previous surveys by virtue of the faint magnitudes and low proper motions. The
newly discovered stars suggest a disk white dwarf scaleheight larger than the
values of 250-350 pc typically assumed in assessments of the local white dwarf
density. Both a <V/V_{max}> and a more complex maximum likelihood analysis of
the spatial distribution of our likely thin disk white dwarfs yield
scaleheights of 400-600 pc while at the same time give a reasonable match to
the local white dwarf volume density found in other surveys.
  Our results could have interesting implications for white dwarfs as potential
MACHO objects. We can place some direct constraints (albeit weak ones) on the
contribution of halo white dwarfs to the dark matter of the Galaxy. Moreover,
the elevated scale height that we measure for the thin disk could alter the
interpretation of microlensing results to the extent of making white dwarfs
untenable as the dominant MACHO contributor. (Abridged)


title:
Spectroscopic Study of IRAS 19285+0517(PDS 100): A Rapidly Rotating
  Li-Rich K Giant

abstract:
  We report on photometry and high-resolution spectroscopy for IRAS 19285+0517.
The spectral energy distribution based on visible and near-IR photometry and
far-IR fluxes shows that the star is surrounded by dust at a temperature of
$T_{\rm {d}}$ $\sim$ 250 K. Spectral line analysis shows that the star is a K
giant with a projected rotational velocity $v sin i$ = 9 $\pm$ 2 km s$^{-1}$.
We determined the atmospheric parameters: $T_{\rm {eff}}$ = 4500 K, log $g$ =
2.5, $\xi_{t}$ = 1.5 km s$^{-1}$, and [Fe/H] = 0.14 dex. The LTE abundance
analysis shows that the star is Li-rich (log $\epsilon$(Li) = 2.5$\pm$0.15),
but with essentially normal C, N, and O, and metal abundances. Spectral
synthesis of molecular CN lines yields the carbon isotopic ratio
$^{12}$C/$^{13}$C = 9 $\pm$3, a signature of post-main sequence evolution and
dredge-up on the RGB. Analysis of the Li resonance line at 6707 \AA for
different ratios $^{6}$Li/$^{7}$Li shows that the Li profile can be fitted best
with a predicted profile for pure $^{7}$Li. Far-IR excess, large Li abundance,
and rapid rotation suggest that a planet has been swallowed or, perhaps, that
an instability in the RGB outer layers triggered a sudden enrichment of Li and
caused mass-loss.


title: Compact Star Clusters in Nearby Dwarf Irregular Galaxies

abstract:
  Nearby dwarf irregular galaxies were searched for compact star clusters using
data from the HST archives. Three of the galaxies were found to host both
populous clusters (M_V<-9.5 at a fiducial age of 10 Myr) and super-star
clusters (M_V<-10.5 at 10 Myr). Four other dwarf galaxies, two of which contain
populous and super-star clusters, were drawn from the literature. We find upper
limits to integrated galactic M_B and star formation rate for the formation of
these clusters. However, galaxies brighter and more active than these limits
rarely form them. Yet when they do form, the associated star formation activity
is very high, with numerous compact clusters of similar age in the same complex
and often evidence for a galaxy-wide perturbation as the trigger. This tendency
to concentrate star formation in localized regions of high column density is
consistent with previous suggestions that self-gravity must be strong and the
pressure must be high to allow a cool phase of gas to exist in equilibrium.
Statistical considerations emphasize the peculiarity of super-star clusters in
dwarf galaxies, which are too small to sample the cluster mass function to that
extreme. We suggest that triggered large-scale flows and ambient gravitational
instabilities in the absence of shear make the clouds that form super-star
clusters in small galaxies. This is unlike the case in spirals where density
wave flows and scale-free compression from turbulence dominate. Further compar-
isons with spirals give insight into Larsen & Richtler's relation between star
formation rate per unit area and the fraction of young stars in massive dense
clusters. We suggest that this relation is the result of a physical connection
between maximum cluster mass, interstellar pressure, column density, and star
formation rate, combined with a size-of-sample effect.


title: The X-ray Spectrum of Supernova Remnant 1987A

abstract:
  We discuss the X-ray emission observed from Supernova Remnant 1987A with the
Chandra X-ray Observatory. We analyze a high resolution spectrum obtained in
1999 October with the high energy transmission grating (HETG). From this
spectrum we measure the strengths and an average profile of the observed X-ray
lines. We also analyze a high signal-to-noise ratio CCD spectrum obtained in
2000 December. The good statistics (~ 9250 counts) of this spectrum and the
high spatial resolution provided by the telescope allow us to perform
spectroscopic analyses of different regions of the remnant. We discuss the
relevant shock physics that can explain the observed X-ray emission. The X-ray
spectra are well fit by plane parallel shock models with post-shock electron
temperatures of ~ 2.6 keV and ionization ages of ~ 6 x 10^10 cm^3/s. The
combined X-ray line profile has a FWHM of ~ 5000 km/s, indicating a blast wave
speed of ~ 3500 km/s. At this speed, plasma with a mean post-shock temperature
of ~ 17 keV is produced. This is direct evidence for incomplete electron-ion
temperature equilibration behind the shock. Assuming this shock temperature, we
constrain the amount of collisionless electron heating at the shock front at
T_e0 / T_s = 0.11 (+0.02,-0.01). We find that the plasma has low metallicity
(abundances are ~ 0.1 -- 0.4 solar) and is nitrogen enriched (N/O ~ 0.8 by
number), similar to that found for the equatorial ring. Analysis of the spectra
from different regions of the remnant reveals slight differences in the
parameters of the emitting plasma. The plasma is cooler near the optical Spot 1
(at position angle ~ 30 degrees) and in the eastern half of the remnant, where
the bright optical spots are found, than in the western half, consistent with
the presence of slower (~ 500 km/s) shocks entering denser ring material.


title:
Physical Conditions in Lyman Break Galaxies Derived From Rest-Frame UV
  Spectra

abstract:
  We present the results of detailed studies of the astrophysical conditions in
z~3 Lyman Break Galaxies (LBGs), placing particular emphasis on what is learned
from LBG rest frame UV spectra. By drawing from our database of ~1000 spectra,
and constructing higher S/N composite spectra from galaxies grouped according
to properties such as luminosity, extinction, morphology, and environment, we
can show how the rest-frame UV spectroscopic properties systematically depend
on other galaxy properties. Such information is crucial to understanding the
detailed nature of LBGs, and their impact on the surrounding IGM.


title:
Resolved nuclear CO(1-0) emission in APM08279+5255: Gravitational
  lensing by a naked cusp?

abstract:
  The ultraluminous broad absorption line quasar APM08279+5255 is one of the
most luminous systems known. Here, we present an analysis of its nuclear
CO(1-0) emission. Its extended distribution suggests that the gravitational
lens in this system is highly elliptical, probably a highly inclined disk. The
quasar core, however, lies in the vicinity of naked cusp, indicating that
APM08279+5255 is truly the only odd-image gravitational lens. This source is
the second system for which the gravitational lens can be used to study
structure on sub-kpc scales in the molecular gas associated with the AGN host
galaxy. The observations and lens model require CO distributed on a scale of
$\sim 400$ pc. Using this scale, we find that the molecular gas mass makes a
significant, and perhaps dominant, contribution to the total mass within a
couple hundred parsecs of the nucleus of APM08279+5255.


title: A Re-examination of the "Planetary" Lensing Events in M22

abstract:
  We have carried out further analysis of the tentative, short-term
brightenings reported by Sahu et al. (2001), which were suggested to be
possible lensings of Galactic-bulge stars by free-floating planets in the
globular cluster M22. Closer examination shows that--unlikely as it may
seem--small, point-like cosmic rays had hit very close to the same star in both
of a pair of cosmic-ray-split images, which cause the apparent brightenings of
stars at the times and locations reported. We show that the observed number of
double hits is consistent with the frequency of cosmic rays in WFPC2 images,
given the number of stars and epochs observed. Finally, we point to ways in
which cosmic rays can be more directly distinguished.


title: Outburst of Possible Eclipsing Symbiotic Variable AS 289

abstract:
  We discovered major brightenings of the symbiotic variable AS 289 in 1984 and
1995. During the outburst phase in 1996, we detected a temporary drop of the
brightness. We consider that an eclipse is responsible for the fading episode
of AS 289 during outburst, as in FG Ser or V1413 Aql. The profile of light
curve suggests the eclipse may be grazing total, while the brightness at
minimum is considerably brighter than the pre-outburst level, implying that a
certain fraction of the outbursting source remain uneclipsed.


title: Proper initial conditions for long-term integrations of the solar system

abstract:
  An optimization program is used to re-adjust the initial conditions, in order
to reproduce as closely as possible the predictions of a complete ephemeris by
using simplified equations of motion in the numerical integration. The
adjustment of the initial conditions is illustrated in the transition from the
DE406 complete long-range ephemeris to a Newtonian model considering only the
Sun and the four major planets. It is also used to best reproduce this same
DE406 ephemeris, based on post-Newtonian equations for a system of mass points
and including the Moon and asteroids, by using a Newtonian calculation
corrected by the Schwarzschild effects of the Sun and restricted to the ten
major bodies of the solar system.


title: Compressional Heating of Accreting White Dwarfs in CV's

abstract:
  In recent years several Dwarf Novae (DN) systems have been observed in
quiescence, when the accretion rate is low and the WD photosphere can be
directly detected. The WDs are observed to cool after the DN outburst from high
effective temperatures to lower effective temperatures (T_eff) thought to be
indicative of the thermal state of the deep interior of the WD. Sion has argued
that the most likely energy source for this quiescent luminosity is the
gravitational compression of the WD interior, which rejuvenates an otherwise
cold WD into a much hotter state. We are undertaking a theoretical study of the
compressional heating of WD's, extending down to the very low time averaged
accretion rates, <Mdot>~10^{-11}M_sun/yr, applicable to the post-turnaround
CV's (the ``TOADS''). Nuclear burning is unstable at these <Mdot>'s, so we have
incorporated the recurrent heating and cooling of the WD throughout the
classical novae limit cycle. In addition to self-consistently finding the range
of T_eff as a function of <Mdot> during the cycle, we also self-consistently
find the ignition masses. Comparing these theoretical masses to the observed
ejected masses will tell us whether the WD mass in CV's is secularly increasing
or decreasing. We close by comparing our results to the accumulated
observations of quiescent DN and making predictions for the colors of low
<Mdot> CV's in quiescence that are applicable to searches for faint CVs in the
field and galactic globular clusters.


title: Star formation histories of late-type dwarfs outside the Local Group

abstract:
  We describe the star formation histories of three late-type dwarfs located
outside the Local Group: IZw18, NGC1569 and NGC1705. The results are based on
the application of the method of synthetic colour-magnitude diagrams to deep
HST photometric data. All the examined galaxies were already forming stars at
the reached lookback time and show no evidence of long quiescent phases. The
obtained scenarios are quite similar to those derived for other galaxies of
this morphological type, both inside and outside the Local Group.


title: Large Gas Disks in Radiogalaxies

abstract:
  Large-scale (up to 100 kpc) HI structures have been found in three radio
galaxies using the WSRT and the VLA. In one case, the HI has been detected in
emission while in the other two HI absorption is detected against the radio
lobes. In at least two of the three studied radio galaxies the HI appears to be
distributed in a large disk and the large amount of neutral gas detected (>
10^9 M_sun) indicates that it is resulting from mergers of gas-rich galaxies.
The relatively regular structure and kinematics of these disks suggest that the
merger must have happened more than 10^8 yrs ago, therefore supporting the idea
that the radio activity starts late after the merger. In these low redshift
radio galaxies we may witness the processes that are more efficiently and
frequently happening at high-z.


title:
Faint Cataclysmic Variables in Quiescence: Globular Cluster and Field
  Surveys

abstract:
  Current evolutionary models imply that most Cataclysmic Variables (CVs) have
P_orb<2 hours and are Dwarf Nova (DN) systems that are quiescent most of the
time. Observations of nearby quiescent DN find that the UV spectrum is
dominated by the hot white dwarf (WD), indicating that it provides a
significant fraction of the optical light in addition to the quiescent disk and
main sequence companion. Hence, identifying a faint, quiescent CV in either the
field or a globular cluster (GC) from broadband colors depends on our ability
to predict the WD contribution in quiescence. We are undertaking a theoretical
study of the compressional heating of WDs, extending down to very low time
averaged accretion rates, <Mdot>~10^{-11}M_sun/yr, which allows us to
self-consistently find the T_eff} of the WD. We demonstrate here that most of
the compressional heating occurs in the freshly accreted envelope and that the
WD core temperature reaches a fixed value on a timescale less than typical
evolutionary times. Since nuclear burning is unstable at these <Mdot>'s, we
have incorporated the recurrent heating and cooling of the WD core throughout
the classical novae limit cycle in order to find the T_eff-<Mdot> relations.
Comparing to observations of field DN confirms the <Mdot>-P_orb relation of
disrupted magnetic braking. We also predict broad-band colors of a quiescent CV
as a function of <Mdot> and companion mass and show that this leads to the
identification of what may be many CVs in deep HST images of GCs.


title: Reanalysis of Ichinohe's Observations of RU Cam

abstract:
  The W Vir-type variable star, RU Cam, once claimed to have stopped pulsation,
has been known to show irregularly variable amplitude. It has also shown from
the analysis of the VSOLJ archive that visual observers of the VSOLJ have
recorded the cessation of pulsation and its possible resumption, together with
the phase of large-amplitude variation around 1910. We present the result of
reanalysis of Ichinohe's original data until 1911, by using the Hipparcos
V-magnitudes of the comparison stars. The range of light variation was
8.26-9.33, giving an amplitude of 1.07 mag. Our new analysis, however, rather
disproves the existence of the secondary maximum which Ichinohe (1909)
described, giving a more consistent, typical W Vir-type, light curve with those
of other observers at that epoch.


title: The ROSEBUD experiment at Canfranc: 2001 report

abstract:
  The ROSEBUD experiment for Direct Dark Matter detection settled in 1999 in
the Canfranc Underground Laboratory. The first phase of the experiment was
dedicated to the understanding and reduction of the radioactive background
following successive removals of the radioimpure materials. Sapphire (25g, 50g)
and germanium (67g) absorbers were used. Thresholds respectively lower than
1keV and 450 eV were achieved on these detectors. The second phase of the
experiment plans to use scintillating bolometers to discriminate between
recoiling nuclei and electrons. Prototypes using commercial CaWO4 (54g) and BGO
(46g) were designed for this purpose. While internal contamination was found
and identified in both targets, neutron calibrations revealed their high
discrimination power. A 6 keV threshold on the heat channel of the BGO
bolometer points out the interest of such a novel material, for Dark Matter
research on neutralinos having spin-dependent or spin-independent interactions.


title: The phase-diagram of cosmological baryons

abstract:
  We investigate the behaviour of cosmological baryons at low redshifts $z<5$
after reionization through analytic means. In particular, we study the
density-temperature phase-diagram which describes the history of the gas. We
show how the location of the matter in this $(\rho,T)$ diagram expresses the
various constraints implied by usual hierarchical scenarios. This yields robust
model-independent results which agree with numerical simulations. The IGM is
seen to be formed via two phases: a ``cool'' photo-ionized component and a
``warm'' component governed by shock-heating. We also briefly describe how the
remainder of the matter is distributed over galaxies, groups and clusters. We
recover the fraction of matter and the spatial clustering computed by numerical
simulations. We also check that the soft X-ray background due to the ``warm''
IGM component is consistent with observations. We find in the present universe
a baryon fraction of 7% in hot gas, 24% in the warm IGM, 38% in the cool IGM,
9% within star-like objects and, as a still un-observed component, 22% of dark
baryons associated with collapsed structures, with a relative uncertainty no
larger than 30% on these numbers.


title:
Reexamination of the galaxy formation-regulated gas evolution model in
  groups and clusters

abstract:
  As an alternative explanation of the entropy excess and the steepening of the
X-ray luminosity-temperature relation in groups and clusters, the galaxy
formation-regulated gas evolution (GG) model proposed recently by Bryan makes
an attempt to incorporate the formation of galaxies into the evolution of gas
without additional heating by nongravitational processes. This seems to provide
a unified scheme for our understanding of the structures and evolution of both
galaxies and gas in groups and clusters. In this paper, we present an extensive
comparison of the X-ray properties of groups and clusters predicted by the GG
model and those revealed by current X-ray observations, using various large
data sources in the literature and also taking the observational selection
effects into account. These include an independent check of the fundamental
working hypothesis of the GG model, i.e., galaxy formation was less efficient
in rich clusters than in groups, a new test of the radial gas distributions
revealed by both the gas mass fraction and the X-ray surface brightness
profiles, and an reexamination of the X-ray luminosity-temperature and
entropy-temperature relations. In particular, it shows that the overall X-ray
surface brightness profiles predicted by the GG model are very similar in
shape, insensitive to the X-ray temperature, and the shallower X-ray surface
brightness profiles seen at low-temperature systems may arise from the current
observational selection effect. This can be used as the simplest approach to
distinguishing between the GG model and the preheating scenario. The latter
yields an intrinsically shallower gas distribution in groups than in rich
clusters.


title: Molecular gas in late-type galaxies

abstract:
  We present $^{12}$CO(J=1--0) line observations of 22 low-luminosity spiral
galaxies in the Virgo cluster. These data, together with 244 others available
in the literature, allow us to build a large sample that we use to study the
molecular gas properties of galaxies spanning a large range of morphological
types and luminosities and belonging to different environments (clusters -
field). The molecular gas content of the target galaxies is estimated using a
luminosity-dependent X = $N(H_2)/I(CO)$ conversion factor that has been
calibrated on a sample of nearby galaxies. $X$ spans from $\sim$ 10$^{20}$ mol
cm$^{-2}$ (K km s$^{-1})^{-1}$ in giant spirals to $\sim$ 10$^{21}$ mol
cm$^{-2}$ (K km s$^{-1})^{-1}$ in dwarf irregulars. The value of the $X$
conversion factor is found consistent with a value derived independently from
dust masses estimated from FIR fluxes, with a metallicity-dependent dust to gas
ratio. The relationships between X and the UV radiation field (as traced by the
$H\alpha+[NII] E.W.$), the metallicity and the H band luminosity are analysed.
We show that the molecular gas contained in molecular clouds or complexes is of
the order of 15% of the total gas on average whatever the luminosity or the
Hubble type of the galaxies. We discuss the relation between the star formation
rate and the molecular gas content and estimate the average star formation
efficiency of late-type galaxies.


title:
Harmonic analysis of cosmic microwave background data I: ring reductions
  and point-source catalogue

abstract:
  We present a harmonic model for the data analysis of an all-sky cosmic
microwave background survey, such as Planck, where the survey is obtained
through ring-scans of the sky. In this model, resampling and pixelisation of
the data are avoided. The spherical transforms of the sky at each frequency, in
total intensity and polarization, as well as the bright-point-source catalogue,
are derived directly from the data reduced onto the rings. Formal errors and
the most significant correlation coefficients for the spherical transforms of
the frequency maps are preserved. A clean and transparent path from the
original samplings in the time domain to the final scientific products is thus
obtained. The data analysis is largely based on Fourier analysis of rings; the
positional stability of the instrument's spin axis during these scans is a
requirement for the data model and is investigated here for the Planck
satellite. Brighter point sources are recognised and extracted as part of the
ring reductions and, on the basis of accumulated data, used to build a
catalogue. The analysis of the rings is performed iteratively, involving a
range of geometric and detector response calibrations. The reconstructed
spherical transforms of the sky form the input to the subsequent analysis
stages. Although the methods in this paper were developed with the data
processing for Planck in mind, many aspects should have wider application, such
as in the construction of real-space pixelised maps. (Abridged)


title:
Harmonic analysis of cosmic microwave background data II: from ring-sets
  to the sky

abstract:
  Despite the fact that the physics of the cosmic microwave background
anisotropies is most naturally expressed in Fourier space, pixelised maps are
almost always used in the analysis and simulation of microwave data. A
complementary approach is investigated here, in which maps are used only in the
visualisation of the data, and the temperature anisotropies and polarization
are only ever expressed in terms of their spherical multipoles. This approach
has a number of advantages: there is no information loss (assuming a
band-limited observation); deconvolution of asymmetric beam profiles and the
temporal response of the instrument are naturally included; correlated noise
can easily be taken into account, removing the need for additional destriping;
polarization is also analysed in the same framework; and reliable estimates of
the spherical multipoles of the sky and their errors are obtained directly for
subsequent component separation and power spectrum estimation. The formalism
required to analyse experiments which survey the full sky by scanning on
circles is derived here, with particular emphasis on the Planck mission. A
number of analytical results are obtained in the limit of simple scanning
strategies. Although there are non-trivial computational obstacles to be
overcome before the techniques described here can be implemented at high
resolution, if these can be overcome the method should allow for a more robust
return from the next generation of full-sky microwave background experiments.


title:
The 3-point function in the large scale structure: I. The weakly
  non-linear regime in N-body simulations

abstract:
  This paper presents a comparison of the predictions for the 2 and 3-point
correlation functions of density fluctuations, xi_2 and xi_3, in gravitational
perturbation theory (PT) against large Cold Dark Matter (CDM) simulations. This
comparison is made possible for the first time on large weakly non-linear
scales (>10 Mpc/h) thanks to the development of a new algorithm to estimate
correlation functions for millions of points in only a few minutes. Previous
studies in the literature comparing the PT predictions of the 3-point
statistics to simulations have focused mostly on Fourier space, angular space
or smoothed fields. Results in configuration space, such as the ones presented
here, were limited to small scales were leading order PT gives a poor
approximation. Here we also propose and apply a method for separating the first
and subsequent orders contributions to PT by combining different output times
from the evolved simulations. We find that in all cases there is a regime were
simulations do reproduce the leading order (tree-level) predictions of PT for
the reduced 3-point function Q_3 ~ xi_3/ xi_2^2. For steeply decreasing
correlations (such as the standard CDM model) deviations from the tree-level
results are important even at relatively large scales, ~ 20 Mpc/h. On larger
scales xi_2 goes to zero and the results are dominated by sampling errors. In
more realistic models (like the Lambda CDM cosmology) deviations from the
leading order PT become important at smaller scales ~ 10 Mpc/h, although this
depends on the particular 3-point configuration. (abridge)


title: Magnetic fields of isolated neutron stars: evidence for decay

abstract:
  We show, that different types of isolated neutron stars (INSs) show evidence
in favor of magnetic field decay in these objects, and discuss how observations
of INSs can help to constrain models of field decay.


title:
Monitoring RXTE Observations of Markarian 348: the origin of the column
  density variations

abstract:
  We analyze 37 RXTE observations of the type 2 Seyfert galaxy Mrk348 obtained
during a period of 14 months. We confirm the spectral variability previous
reported by Smith et al., in the sense that thecolumn density decreases by a
factor of ~3 as the count rate increases. Column density variations could
possibly originate either due to the random drift of clouds within the
absorption screen, or due to photoionization processes. Our modeling of the
observed variations implies that the first scenario is more likely. These
clouds should lie in a distance of >2 light years from the source, having a
diameter of a few light days and a density of >10^7 cm^(-3), hence probably
residing outside the Broad Line Region.


title:
The size of a quasar's mid-IR emission region inferred from microlensed
  images of Q2237+0305

abstract:
  We use published mid-IR and V-band flux ratios for images A and B of
Q2237+0305 to demonstrate that the size of the mid-IR emission region has a
scale comparable to or larger than the microlens Einstein Radius (ER, ~10^17 cm
for solar mass stars). Q2237+0305 has been monitored extensively in the R and
V-bands for ~15 years. The variability record shows significant microlensing
variability of the optical emission region, and has been used by several
studies to demonstrate that the optical emission region is much smaller than
the ER for solar-mass objects. For the majority of the monitoring history, the
optical flux ratios have differed significantly from those predicted by
macro-models. In contrast, recent observations in mid-IR show flux ratios
similar to those measured in the radio, and to predictions of some lens models,
implying that the mid-IR flux is emitted from a region that is at least 2
orders of magnitude larger than the optical emission region. We have calculated
the likeli-hood of the observed mid-IR flux ratio as a function of mid-IR
source size given the observed V-band flux ratio. The expected flux ratio for a
source having dimensions of ~1 ER is a sensitive function of the macro model
adopted. However we find that the probability of source size given the observed
flux ratios is primarily sensitive to the ratio of the macro-model
magnifications. The majority of published macro models for Q2237+0305 yield a
flux ratio for images B and A of 0.8 - 1.1. By combining probabilities from the
ratios A/B and C/D we infer that the diameter of a circular IR emission region
is >1ER with >95% confidence. For microlensing by low-mass stars, this source
size limit rules out non-thermal processes such as synchrotron as mechanisms
for mid-IR emission.


title: Constraints on the mass-profile of the lens galaxy G2237+0305

abstract:
  Published parametric models of the Einstein Cross gravitational lens
demonstrate that the image geometry can be reproduced by families of models. In
particular, the slope of the mass-profile for the lens galaxy is unconstrained.
However, recent models predict a dependence of image flux ratios on the slope
of the mass profile. We use this dependence to constrain the mass profile by
calculating the likelihood of the slope using published mid-IR flux ratios
(including microlensing variability). We find that the galaxy is likely to be
flatter than isothermal, and therefore that the mass-to-light ratio is
decreasing in the inner kpc.


title: The Coimbra Experiment: Report from Group 12

abstract:
  We describe the approach adopted by our group to derive the star formation
history (SFH) of the chosen LMC field, as part of the experiment to compare the
predictions obtained by different groups with the synthetic Colour-Magnitude
diagram method. We point out what are the evolutionary characteristics of the
observed stellar populations, and present the SFH scenario which appears to
better account for them. We emphasize the importance of adopting a {\it
critical} approach when dealing with this method.


title:
High-resolution simulations of stellar collisions between equal-mass
  main-sequence stars in globular clusters

abstract:
  We performed high-resolution simulations of two stellar collisions relevant
for stars in globular clusters. We considered one head-on collision and one
off-axis collision between two 0.6 M_sun main sequence stars. We show that a
resolution of about 100 000 particles is sufficient for most studies of the
structure and evolution of blue stragglers. We demonstrate conclusively that
collision products between main-sequence stars in globular clusters do not have
surface convection zones larger than 0.004 M_sun after the collision, nor do
they develop convection zones during the `pre-main-sequence' thermal relaxation
phase of their post-collision evolution. Therefore, any mechanism which
requires a surface convection zone (i.e. chemical mixing or angular momentum
loss via a magnetic wind) cannot operate in these stars. We show that no disk
of material surrounding the collision product is produced in off-axis
collisions. The lack of both a convection zone and a disk proves a continuing
problem for the angular momentum evolution of blue stragglers in globular
clusters.


title:
Spectropolarimetric Clues to the Structure and Evolutionary Status of
  MWC 349A

abstract:
  We present visible-wavelength spectropolarimetric measurements of the
emission-line star MWC 349A and its close optical companion MWC 349B, conducted
with the HPOL spectropolarimeter on both the 0.9 m telescope at the University
of Wisconsin's Pine Bluff Observatory and the 3.5 m WIYN telescope on Kitt
Peak. Our measurements allow us to estimate the interstellar polarization
contribution and thus constrain the intrinsic polarization of MWC 349A, which
we find to be consistent in position angle with the dusty disk seen
perpendicular to the bipolar outflow. Our analysis reopens the possibility that
MWC 349A may be part of the Cyg OB2 association, suggests that it is not a
physical companion to MWC 349B, and supports the classification of MWC 349A as
a pre-main sequence B[e] star.


title: Clues on the nature of low-z radio sources from the 2dFGRS

abstract:
  We use redshift determinations and spectral analysis of galaxies in the 2dF
Galaxy Redshift Survey to study the properties of local radio sources with
$S\ge 1$ mJy.


title: Chandra Observations of the Eastern Limb of the Vela Supernova Remnant

abstract:
  We present results from two Chandra/ACIS observations of the so-called Vela
``Bullet D'' region on the eastern limb of the Vela supernova remnant. The
Bullet D region is a bright X-ray feature, identified by Aschenbach et al.
(1995) from the ROSAT All-Sky Survey, which protrudes beyond the blast wave on
the eastern side of the remnant. It has been suggested that this feature is a
fragment of supernova ejecta which is just now pushing beyond the position of
the main blast wave. An alternate explanation is that the feature is a
``break-out'' of the shock in which inhomogeneities in the ambient medium cause
the shock to be non-spherical. The Chandra image shows a fragmented,
filamentary morphology within this region. The Chandra spectra show strong
emission lines of O, Ne, and Mg. Equilibrium ionization models indicate that
the O and Ne abundances are significantly enhanced compared to solar values.
However, non-equilibrium ionization models can fit the data with solar O
abundances and Ne abundances enhanced by only a factor of two. The Chandra data
are more consistent with the shock breakout hypothesis, although they cannot
exclude the fragment of ejecta hypothesis.


title: A Fast Bar in the Post-Interaction Galaxy NGC 1023

abstract:
  We measured the bar pattern speed, $\om$, of the SB0 galaxy NGC 1023 using
the Tremaine-Weinberg (1984) method with stellar-absorption slit spectroscopy.
The morphology and kinematics of the \hi gas outside NGC 1023 suggest it
suffered a tidal interaction, sometime in the past, with one of its dwarf
companions. At present, however, the optical disc is relaxed. If the disc had
been stabilized by a massive dark matter halo and formed its bar in the
interaction, then the bar would have to be slow. We found $\om = 5.0 \pm 1.8$
\kmsa, so that the bar ends near its co-rotation radius. It is therefore
rotating rapidly and must have a maximum disc.


title: The stellar content of the Galaxy: the white dwarf population

abstract:
  On the basis of theoretical evolutionary expectations, we develop a Galactic
model reproducing star counts and synthetic color-magnitude diagrams of field
stars, which include the white dwarf (WD) population. In this way we are able
to evaluate the expected occurrence of WDs in deep observations at the various
photometric bands and Galactic coordinates, discussing the contribution of the
WDs of the various Galactic components. The effects on the theoretical
predictions of different WD evolutionary models, ages, initial mass functions
and relations between progenitor mass and WD mass are discussed.


title: Exploring the intergalactic medium with VLT/UVES

abstract:
  The remarkable efficiency of the UVES spectrograph at the VLT has made it
possible to push high-resolution, high-S/N ground observations of the Ly-a
forest down to z~1.5, gaining new insight into the physical conditions of the
intergalactic medium and its evolution over more than 90% of the cosmic time.
The universal expansion, the UV ionizing background and the gravitational
condensation of structures are the driving factors shaping the number density
and the column density distribution of the absorbers. A (limited) contribution
of UV photons produced by galaxies is found to be important to reproduce the
observed evolutionary pattern at very high and low redshift. The Lyman forest
contains most of the baryons, at least at z>1.5, and acts as a reservoir for
galaxy formation. The typical Doppler parameter at a fixed column density is
measured to slightly increase with decreasing redshift, but the inferred
temperature at the mean density is increasing with redshift. The signatures of
HeII reionization and feedback from the formation of galactic structures have
possibly been detected in the Lyman forest.


title: Search for Molecular Gas in the quasar SDSS 1044-0125 at z=5.73

abstract:
  We report upper limits on CO J=2--1 and CO J=5--4 emission from the quasar
SDSSp J104433.04-012502.2 at z=5.73 from observations made with the
Berkeley-Illinois-Maryland-Association Array. Previously reported limits on CO
J=6--5 emission (Iwata et al. 2001) were obtained at z=5.80, which is now
thought to be off by 1%, and the observations likely missed the relevant
redshifts for molecular gas. The new $3\sigma$ upper limits on the line
luminosities are $L^{'}_{CO}(2-1) < 5.1 \times 10^{10}$ K km s$^{-1}$ pc$^2$
and $L^{'}_{CO}(5-4) < 3.0 \times 10^{10}$ K km s$^{-1}$ pc$^2$, assuming 200
km s$^{-1}$ linewidth. The CO J=5--4 observations place an upper limit on warm,
dense molecular gas mass comparable to amounts derived for some other high
redshift quasar systems from detections of this line. The limit on CO J=2--1
emission suggests that excitation bias does not affect this conclusion. In
addition, no molecular gas rich companion galaxies are found in a $\sim1.4$ Mpc
field surrounding the quasar.


title: Kinematics of Planetary Nebulae in M 51's Tidal Tail

abstract:
  The galaxy pair NGC 5194/95 (M 51) is one of the closest and best known
interacting systems. Despite its notoriety, however, many of its features are
not well studied. Extending westward from NGC 5195 is a low surface brightness
tidal tail, which can only be seen in deep broadband exposures. Our previous [O
III] lambda 5007 planetary nebulae (PN) survey of M 51 recovered this tidal
tail, and presented us with a opportunity to study the kinematics of a galaxy
interaction in progress. We report the results of a spectroscopy survey of the
PN, aimed at determining their kinematic properties. We then use these data to
constrain new self-consistent numerical models of the system.


title: The AGN content of hard X-ray surveys

abstract:
  Multiwavelength observations of the hard X-ray selected sources discovered by
BeppoSAX, Chandra and XMM-Newton surveys have significantly improved our
knowledge of the AGN population. The increasing number of X-ray obscured AGN so
far discovered confirms the prediction of those AGN synthesis models for the
X-ray background based on the Unified scheme. However, follow-up optical
observations of hard X-ray selected sources indicate that their optical
properties are quite varied and the simple relations between optical and X-ray
absorption are by no means without exception. Moreover, there is evidence of a
substantial number of luminous X-ray sources hosted by apparently normal
galaxies. In this paper the results obtained from multiwavelength observations
of hard X-ray selected sources discovered by BeppoSAX and XMM-Newton are
presented and briefly discussed.


title:
Spectroscopic binaries in a sample of ROSAT X-ray sources south of the
  Taurus molecular clouds

abstract:
  We report the results of our radial-velocity monitoring of spectroscopic
binary systems in a sample of X-ray sources from the ROSAT All Sky Survey south
of the Taurus-Auriga star-forming region. The original sample of approximately
120 sources by Neuhaeuser et al. was selected on the basis of their X-ray
properties and the visual magnitude of the nearest optical counterpart, in such
a way as to promote the inclusion of young objects. Roughly 20% of those
sources have previously been confirmed to be very young. We focus here on the
subset of the original sample that shows variable radial velocities (43
objects), a few of which have also been flagged previously as being young. New
spectroscopic orbits are presented for 42 of those systems. Two of the
binaries, RXJ0528.9+1046 and RXJ0529.3+1210, are indeed weak-lined T Tauri
stars likely to be associated with the Lambda Orionis region. Most of the other
binaries are active objects of the RS CVn-type, including several W UMa and
Algol systems. We detect a strong excess of short-period binaries compared to
the field, and an unusually large fraction of double-lined systems, as well as
an overall high frequency of binaries out of the original sample. These results
can be understood as selection effects. A short description of the physical
properties of each binary is provided, and a comparison with evolutionary
tracks is made using the stellar density as a distance-independent measure of
evolution (abridged).


title: Aspects of Galaxy Formation

abstract:
  I describe some of the current challenges in galaxy formation theory with
applications to formation of disks and of spheroids. Forthcoming deep surveys
of galaxies with Keck and VLT will provide high quality spectra of $\sim 10^5$
galaxies that will probe stellar populations and star formation rates at
redshift unity. This will help refine our phenomenological knowledge of galaxy
evolution and enable robust predictions to be developed for future
breakthroughs in understanding galaxy formation at high redshift that are
anticipated with NGST and with the proposed new generation of 30 metre-class
telescopes.


title:
Deuterium Toward WD1634-573: Results from the Far Ultraviolet
  Spectroscopic Explorer (FUSE) Mission

abstract:
  We use Far Ultraviolet Spectrocopic Explorer (FUSE) observations to study
interstellar absorption along the line of sight to the white dwarf WD1634-573
(d=37.1+/-2.6 pc). Combining our measurement of D I with a measurement of H I
from Extreme Ultraviolet Explorer data, we find a D/H ratio toward WD1634-573
of D/H=(1.6+/-0.5)e-5. In contrast, multiplying our measurements of D I/O
I=0.035+/-0.006 and D I/N I=0.27+/-0.05 with published mean Galactic ISM gas
phase O/H and N/H ratios yields D/H(O)=(1.2+/-0.2)e-5 and
D/H(N)=(2.0+/-0.4)e-5, respectively. Note that all uncertainties quoted above
are 2 sigma. The inconsistency between D/H(O) and D/H(N) suggests that either
the O I/H I and/or the N I/H I ratio toward WD1634-573 must be different from
the previously measured average ISM O/H and N/H values. The computation of
D/H(N) from D I/N I is more suspect, since the relative N and H ionization
states could conceivably vary within the LISM, while the O and H ionization
states will be more tightly coupled by charge exchange.


title: The Epoch of Helium Reionization

abstract:
  We study the reionization of Helium II by quasars using a numerical approach
that combines 3D radiative transfer calculations with cosmological
hydrodynamical simulations. Sources producing the ionizing radiation are
selected according to an empirical quasar luminosity function and are assigned
luminosities according to their intrinsic masses. We present models in which
these parameters are varied and examine characteristics of the resultant
reionization process that distinguish the various cases. In addition, we
extract artificial spectra from the simulations and quantify statistical
properties of the spectral features in each model. We find that the most
important factor affecting the evolution of He II reionization is the
cumulative number of ionizing photons that are produced by the sources.
Comparisons between He II opacities measured observationally and those obtained
by our analysis reveal that the available ranges in plausible values for the
parameters provide enough leeway to provide a satisfactory match. However, one
property common to all our calculations is that the epoch of Helium II
reionization must have occurred at a redshift between 3 < z < 4. If so, future
observational programs will be able to directly trace the details of the
ionization history of helium and probe the low density phase of the
intergalactic medium during this phase of the evolution of the Universe.


title:
Discovery of a tight correlation between pulse lag/luminosity and
  jet-break times: a connection between gamma-ray burst and afterglow
  properties

abstract:
  A correlation is presented between the pulse lag and the jet-break time for
seven BATSE gamma-ray bursts with known redshifts. This is, to our best
knowledge, the first known direct tight correlation between a property of the
gamma-ray burst phase (the pulse lag) and the afterglow phase (the jet-break
time). As pulse lag and luminosity have been found to be correlated this also
represents a correlation between peak luminosity and jet-break time. Observed
timescales (variability or spectral lags) as well as peak luminosity naturally
have a strong dependence on the Lorentz factor of the outflow and so we propose
that much of the variety among GRBs has a purely kinematic origin (the speed or
direction of the outflow).
  We explore a model in which the variation among GRBs is due to a variation in
jet-opening angles, and find that the narrowest jets have the fastest outflows.
We also explore models in which the jets have similar morphology and size, and
the variation among bursts is caused by variation in viewing angle and/or due
to a velocity profile. The relations between luminosity, variability, spectral
lag and jet-break time can be qualitatively understood from models in which the
Lorentz factor decreases as a function of angle from the jet axis. One expects
to see high luminosities, short pulse lags and high variability as well as an
early jet-break time for bursts viewed on axis, while higher viewing
inclinations will yield lower luminosities, longer pulse lags, smoother bursts
and later jet-break times.


title:
3--4 $\mu$m Spectroscopy of Seyfert 2 Nuclei to Quantitatively Assess
  the Energetic Importance of Compact Nuclear Starbursts

abstract:
  We report on 3--4 $\mu$m slit spectroscopy of 13 Seyfert 2 nuclei. The 3.3
$\mu$m polycyclic aromatic hydrocarbon (PAH) emission is used to estimate the
magnitudes of compact ($<$ a few 100 pc) nuclear starbursts and to resolve the
controversy over their energetic importance in Seyfert 2 nuclei. For three
selected Seyfert 2 nuclei that have been well studied in the UV, the magnitudes
of the compact nuclear starbursts estimated from the 3.3 $\mu$m PAH emission
(with no extinction correction) are in satisfactory quantitative agreement with
those based on the UV after extinction correction. Based directly on our 3--4
$\mu$m slit spectra, the following two main conclusions are drawn: (1) except
in one case, the observed nuclear 3--4 $\mu$m emission is dominated by AGN and
not by starbursts, and (2) compact nuclear starbursts are detected in 6 out of
13 Seyfert 2 nuclei, but cannot dominate the energetics of the galactic
infrared dust emission in the majority of the observed Seyfert 2 galaxies. For
several sources for which Infrared Space Observatory spectra taken with larger
apertures and/or soft X-ray data are available, these data are combined with
our 3--4 $\mu$m slit spectra, and it is suggested that (3) extended (kpc scale)
star-formation activity is energetically more important than compact nuclear
starbursts, and contributes significantly to the infrared luminosities of
Seyfert 2 galaxies, and (4) the bulk of the energetically significant extended
star-formation activity is of starburst type rather than quiescent normal disk
star-formation; the extended starbursts are responsible for the
superwind-driven soft X-ray emission from Seyfert 2 galaxies. Finally, it is
implied that more powerful AGNs tend to be related to more powerful compact
nuclear starbursts.


title: SETHI@Berkeley- A Piggyback 21-cm Sky Survey at Arecibo

abstract:
  SETI@home observes a 2.5 MHz bandwidth centered on 1420 MHz near the 21-cm
line using a short line feed at Arecibo which provides a 6' beam. This feed
sits on Carriage House 1. During normal astronomical observations with the new
Gregorian dome the feed scans across the sky at twice the sidereal rate. We are
using the SETI@home receiver to obtain about 4.4x10^6 HI spectra per year with
integration time of 5 seconds per spectrum. We have accumulated 2.6 years of
data covering most of the sky observable from Arecibo. This survey has much
better angular resolution than previous single dish surveys and better
sensitivity than existing or planned interferometric surveys.


title:
ECHA J0843.3-7905: Discovery of an 'old' classical T Tauri star in the
  eta Chamaeleontis cluster

abstract:
  A limited-area survey of the eta Chamaeleontis cluster has identified 2 new
late-type members. The more significant of these is ECHA J0843.3-7905 (= IRAS
F08450-7854), a slowly-rotating (P = 12 d) M2 classical T Tauri (CTT) star with
a spectrum dominated by Balmer emission. At a distance of 97 pc and cluster age
of approx 9 Myr, the star is a nearby rare example of an 'old' CTT star and
promises to be a rewarding laboratory for the study of disk structure and
evolution in pre-main sequence (PMS) stars. The other new member is the M4
weak-lined T Tauri (WTT) star ECHA J0841.5-7853, which is the lowest mass (M =
0.2 M_sun) primary known in the cluster.


title:
VLBI Monitoring Observations of Water Masers Around the Semi-Regular
  Variable Star R Crateris

abstract:
  We monitored water-vapor masers around the semi-regular variable star R
Crateris with the Japanese VLBI Network (J-Net) at the 22 GHz band during four
epochs with intervals of one month. The relative proper motions and
Doppler-velocity drifts of twelve maser features were measured. Most of them
existed for longer than 80 days. The 3-D kinematics of the features indicates a
bipolar expanding flow. The major axis of the asymmetric flow was estimated to
be at P.A. = 136 degrees. The existence of a bipolar outflow suggests that a
Mira variable star had already formed a bipolar outflow. The water masers are
in a region of apparent minimum radii of 1.3 x 10^12 m and maximum radii of 2.6
x 10^12 m, between which the expansion velocity ranges from 4.3 to 7.4 km/s.
These values suggest that the water masers are radially accelerated, but still
gravitationally bound, in the water-maser region. The most positive and
negative velocity-drifting features were found relatively close to the systemic
velocity of the star. We found that the blue-shifted features are apparently
accelerated and the red-shifted apparently decelerated. The acceleration of
only the blue-shifted features seems to be consistent with that of the
expanding flow from the star.


title: Detection of an Eclipse during the 1987 Outburst of U Sco

abstract:
  U Sco is a recurrent nova which showed recorded outbursts in 1863, 1906,
1936, 1979, 1987, and most recently in 1999. The eclipsing nature of the object
was discovered after the 1987 outburst. We examined our time-series
photographic observations obtained during on 1987 May 20, which fortuitously
covered the primary minimum (depth 0.8 mag). This postive detection of an
eclipse during the outburst makes the first epoch observation of the U Sco
eclipse during the 1987-1999 outburst interval.


title:
The 1996-1997 Fading of V651 Mon, the Binary Central Star of the
  Planetary Nebula NGC 2346

abstract:
  V651 Mon is the binary central star of the bipolar planetary nebula NGC 2346.
The star showed the second-ever deep fading in 1996-1997, which was presumably
caused by obscuration by a dust cloud in the planetary nebula, as was proposed
to explain the 1981-1985 event. The entire duration of the 1996-1997 event was
\~400 d, remarkably shorter than the 1981-1985 event, suggesting that the
obscuring body was smaller or had a larger tangential velocity. The most
remarkable feature in this event was the presence of a sharply defined
transient clearing (brightening). From the time-scale of the variation, we
propose an upper limit of the projected scale of several times ~10^11 cm of the
structure responsible for the brightening. This observation provides the first
evidence for a sharply defined, small lucent structure within the obscuring
body around the central star of NGC 2346


title: The kinematics of lopsided galaxies

abstract:
  Lopsidedness is a common feature in galaxies, both in the distribution of
light and in the kinematics. We investigate the kinematics of a model for
lopsided galaxies that consists of a disc lying off-centre in a dark halo, and
circling around the halo centre. We search for families of stable, closed,
non-crossing orbits, and assume that gas in our galaxies moves on these orbits.
Several of our models show strong lopsided gas kinematics, especially the ones
in which the disc spins around its axis in a retrograde sense compared to its
motion around the halo centre. We are able to reproduce the HI velocity map of
the kinematically lopsided galaxy NGC 4395.
  The lopsidedness in our models is most pronounced in the models where the
halo provides a relatively large fraction of the total mass at small radii.
This may explain why the gas shows lopsidedness more frequently in late-type
galaxies, which are dominated by dark matter. Surfaces of section show large
regions of irregular orbits in the models where the halo density is low. This
may indicate that these models are unstable.


title: Pulsar Glitch Behaviour and AXPs, SGRs and DTNs

abstract:
  Large pulsar glitches seem to be common to all radio pulsars and to exhibit a
universal behaviour connecting the rate of occurrence, event size and
interglitch relaxation that can be explained if the glitches are due to angular
momentum exchange in the neutron star. This has implications for the energy
dissipation rate. The large timing excursions observed in SGRs are not similar
to the pulsar glitches. The one glitch observed in an AXP is very similar to
pulsar glitches and demonstrates that typical neutron star glitch response
occurs when the external torque is constant for an extended period of time. In
the long run the timing variations of both the AXPs and the SGRs are much
stronger than the timing noise of radio pulsars but comparable with the
behaviour of accreting sources. For the DTNs, the thermal luminosities do not
seem compatible with cooling ages and statistics if these sources are
magnetars. The energy dissipation rates implied by the dynamical behaviour of
glitching pulsars will provide the luminosities of the DTNs under propeller
spindown torques supplied by fossil disks on neutron stars with conventional
10$^{12}$ G dipole magnetic fields.


title: The tricky galactic cluster NGC2420

abstract:
  We discuss the CM diagram of the galactic cluster NGC2420 to the light of
current theoretical predictions. By relying on the most recent updating of the
physical input, one finds too luminous theoretical He burning stars together
with the evidence for a misfitting of the lower portion of the MS. Moreover one
finds two well known overshooting signatures, as given by i) the large
extension of the "hook" preceding the overall contraction gap, and ii) the
scarcity of stars just at the end of the gap. We show that the overluminosity
of He burning stars appears as a constant prediction of models based on updated
physics, whereas alternative assumptions about the Equation of State can
account for the MS fitting. Moreover, due to the scarse statistical
significance of the observational sample, one finds that overshooting
signatures can be present also in canonical (without overshooting) predictions.
We conclude that, unfortunately, NGC2420 does not keep the promise to be of
help in costraining the actual dimensions of convective cores in H burning MS
stars, suggesting in the meantime that using clumping He burning stars as
theoretical standard candle is at least a risky procedure. In this context the
need for firmer constraints about the reddening of galactic clusters is shortly
discussed.


title: Chemodynamical Modelling of Galaxy Formation and Evolution

abstract:
  We present our recently developed 3-dimensional chemodynamical code for
galaxy evolution. This code follows the evolution of different galactic
components like stars, dark matter and different components of the interstellar
medium (ISM), i.e. a diffuse gaseous phase and the molecular clouds. Stars and
dark matter are treated as collisionless N-body systems. The ISM is numerically
described by a smoothed particle hydrodynamics (SPH) approach for the diffuse
gas and a sticky particle scheme for the molecular clouds. Additionally, the
galactic components are coupled by several phase transitions like star
formation, stellar death or condensation and evaporation processes within the
ISM. As an example we show the dynamical and chemical evolution of a star
forming dwarf galaxy with a total baryonic mass of $2 \cdot 10^9 M_\odot$.
After a moderate collapse phase the stars and the molecular clouds follow an
exponential radial distribution, whereas the diffuse gas shows a central
depression as a result of stellar feedback. The metallicities of the galactic
components behave quite differently with respect to their temporal evolution as
well as their radial distribution. Especially, the ISM is at no stage well
mixed.


title: Early humps in WZ Sge stars

abstract:
  Photometric humps in outburst that are locked with the binary orbital period
have been observed exclusively in the early phase of outbursts of WZ Sge stars.
It is suggested that this "early hump" phenomenon is the manifestation of the
tidal 2:1 resonance in accretion disks of binary systems with extremely low
mass ratios. The "early humps" can be understood by the two-armed spiral
pattern of tidal dissipation generated by the 2:1 resonance, first discussed by
Lin & Papaloizou (1979). The tidal removal of angular momentum from the disk
during outbursts of dwarf novae, an important feature, is discussed in the
context of the disk instability model. The ordering of tidal truncation radius,
the 3:1 and 2:1 resonance radius in systems of different mass ratio naturally
leads to a classification of dwarf nova systems in three groups according to
their mass ratio. The WZ Sge stars are those systems which have the lowest mass
ratios and are therefore characterized by "early humps".


title:
The implications for helioseismology of experimental uncertainties in
  Newton's constant

abstract:
  The experimental uncertainties in G between different experiments have
important implications for helioseismology. We show that these uncertainties
for the standard solar model lead to a range in the value of the square of the
sound speed in the nuclear region that is as much as 0.15% higher than the
inverted helioseismic sound speed. While a lower value of G is preferred for
the standard model, any definite prediction is masked by the uncertainties in
the solar models available in the literature. However future refinements of
helioseismology with an accuracy of the order of 1E-3 to 1E-4 in the square of
the sound speed, especially in combination with precision measurements of the
8B solar neutrino flux should be capable of independently testing these
experimental values of G.


title: BeppoSAX Spectral Survey of BL Lacs - new spectra and results

abstract:
  We present BeppoSAX LECS, MECS, and PDS spectra of eleven X-ray selected BL
Lacertae objects. Combining these sources with the ones presented elsewhere we
have a sample of 21 BL Lacs from the Einstein Medium Sensitivity and Einstein
Slew Survey. The sample shows strong correlations of several physical
parameters with the peak frequency of the synchrotron branch of the spectral
energy distribution. In particular the peak frequency is correlated to the
X-ray spectral shape: objects with the peak near to the X-ray band show harder
and straighter X-ray spectra than those of the low energy peaked sources. This
work shows that the recently proposed unification scenario for different types
of blazars can hold also within the class of high frequency peaked BL Lac
objects.


title: Effects of neutrino oscillations on the supernova signal in LVD

abstract:
  We study the impact of neutrino oscillations on the supernova neutrino signal
in the Large Volume Detector (LVD). The number of expected events for a
galactic supernova (D=10 kpc) is calculated, assuming neutrino masses and
mixing that explain solar and atmospheric neutrino results. The possibility to
detect neutrinos in different channels makes LVD sensitive to different
scenarios for neutrino properties, such as normal or inverted neutrino mass
hierarchy, and/or adiabatic or non adiabatic MSW resonances associated to
U(e3). Of particular importance are the charged current reactions on carbon:
oscillations increase by almost one order of magnitude the number of events
expected from this channel.


title: A new 21-cm absorber identified with an $L \sim L^\star$ galaxy

abstract:
  We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted
21-cm absorption from the $z=0.437$ metal line absorption system towards PKS
1243-072. HI absorption is clearly detected; the absorption profile has a
velocity spread of $\sim 20$ km/s. Detection of 21-cm absorption indicates that
the absorber has an HI column density large enough to be classified as a damped
Lyman-$\alpha$ system. Follow up ground based optical imaging and spectroscopy
allow us to identify the absorber with an $L \sim L^\star$ galaxy at an impact
parameter of $\sim 9.8$ kpc from the line of sight to the QSO. The absorbing
galaxy is unusual in that it has bright emission lines. On the basis of the
optical spectrum we are unable to uniquely classify the galaxy since its
emission line ratios lie in the transition region between starburst and Seyfert
II type spectra.


title: TeV Blazars and Cosmic Infrared Background Radiation

abstract:
  The recent developments in studies of TeV radiation from blazars are
highlighted and the implications of these results for derivation of
cosmologically important information about the cosmic infrared background
radiation are discussed.


title:
A New Measurement of the X-ray Temperature Function of Clusters of
  Galaxies

abstract:
  We present a newly measured X-ray temperature function of galaxy clusters
using a complete flux-limited sample of 61 clusters. The sample is constructed
with the total survey area of 8.14 steradians and the flux limit of 1.99e-11
ergs/s/cm^2 in the 0.1-2.4keV band. X-ray temperatures and fluxes of the sample
clusters were accurately measured with ASCA and ROSAT data. The derived
temperature function covers an unprecedentedly wide temperature range of
1.4-11keV. By fitting these data with theoretically predicted temperature
functions given by the Press-Schechter formalism together with a recent
formation approximation and the CDM power spectrum, we obtained tight and
individual constraints on Omega_m,0 and sigma_8. We also employed the
Formation-Epoch model in which the distribution in the formation epoch of
clusters as well as the temperature evolution are taken into account, showing
significantly different results. Systematics caused by the uncertainty in the
mass-temperature relation are studied and found to be as large as the
statistical errors.


title: Comments on the paper astro-ph/0103335 by C Rubano and P Scudellaro

abstract:
  We briefly comment on a paper by Rubano and Scudellaro [astro-ph/0103335]
where they found general exact solutions for two classes of exponential
potentials in a scalar field model for quintessence. In that paper the authors
were led to some interesting conclusions after a proper choice of the
integration constants. By using dimensionless variables we show that the
integration constants can be found explicitly without additional assumptions.
In consequence we revise some results and conclusions in that paper. We also
reproduce observations for Type-1a supernovae with good accuracy.


title:
On formation rate of close binaries consisting of a super-massive black
  hole and a white dwarf

abstract:
  The formation rate of a close binary consisting of a super-massive black hole
and a compact object (presumably a white dwarf) in galactic cusps is calculated
with help of the so-called loss cone approximation. For a power low cusp of
radius $r_{a}$, the black hole mass $M\sim 10^{6}M_{\odot}$, this rate $\dot
N_{wd}\sim 4\cdot 10^{-5}K(p}\sqrt{{GM\over r_{a}^{3}}}\approx 3\cdot
10^{-9}K(p){({M\over 10^{6}M_{\odot}})}^{1/2}{({r_{a}\over
1pc})}^{-3/2}yr^{-1}$. The function $K(p)$ depends on parameter $p$ determining
the cusp profile, and for the standard cusp profiles with $p=1/4$ $K(p)\sim 2$.
We estimate the probability ${\it Pr}$ of finding of a compact object orbiting
around a black hole with period $P$ in one particular galaxy to be ${\it
Pr}\sim 10^{-7}{({P/10^{3}s\over M/10^{6}M_{\odot}})}^{8/3}
{({M/10^{6}M_{\odot}\over r_{a}/ 1pc})}^{3/2}$. The object with the period
$P\sim 10^{3} s$ emits gravitational waves with amplitude sufficient to be
detected by LISA type gravitational wave anatenna from the distance $\sim
10^{3}Mpc$. Based on estimates of masses of super-massive black holes in nearby
galaxies, we speculate that LISA would detect several such events during its
mission.


title:
The Effect of Changes in the ASCA Calibration on the Fe-Kalpha Lines in
  Active Galaxies

abstract:
  The ASCA calibration has evolved considerably since launch and indeed, is
still evolving. There have been concerns in the literature that changes in the
ASCA calibration have resulted in the Fe-Kalpha lines in active galaxies (AGN)
now being systematically narrower than was originally thought. If this were
true, a large body of ASCA results would be impacted. In particular, it has
been claimed that the broad red wing (when present) of the Fe-Kalpha line has
been considerably weakened by changes in the ASCA calibration. We demonstrate
explicitly that changes in the ASCA calibration over a period of about eight
years have a negligible effect on the width, strength, or shape of the
Fe-Kalpha lines. The reduction in both width and equivalent width is only ~8%
or less. We confirm this with simulations and individual sources, as well as
sample average profiles. The average profile for type 1 AGN is still very
broad, with the red wing extending down to ~4 keV. The reason for the claimed,
apparently large, discrepancies is that in some sources the \fekalfa line is
complex, and a single-Gaussian model, being an inadequate description of the
line profile, picks up different portions of the profile with different
calibration. Single-Gaussian fits do not therefore model all of the line
emission in some sources, in which case they do not compare old and current
calibration since the models do not then describe the data.


title:
No disks around low-mass stars and brown dwarfs in the young sigma
  Orionis cluster?

abstract:
  We report on the analysis of 2MASS near-infrared data of a sample of low-mass
stars and brown dwarfs in the sigma Orionis cluster. Youth and cluster
membership have been spectroscopically confirmed using the Li I spectral line.
We find little evidence in the JHKs colour-colour diagram for near-infrared
excess emission for these cluster members. By comparison with model
expectations, at most 2 out of 34 stars show (H-K) colour consistent with a
near-infrared excess. This scarcity of near-infrared signatures of
circumstellar disks in the lower-mass and substellar regimes of this cluster
contrasts with findings in younger clusters, hinting at an age dependence of
the disk frequency. Taking into account the apparent cluster age, our result
supports the idea of a relatively fast (few Myr) disk dissipation and extends
this conclusion to the substellar regime. We also find some evidence that, in
this cluster, the disk frequency as measured by the Ks-band excess may be mass
dependent.


title: Effects on the structure of the universe of an accelerating expansion

abstract:
  Recent experimental results from supernovae Ia observations have been
interpreted to show that the rate of expansion of the universe is increasing.
Other recent experimental results find strong indications that the universe is
``flat.'' In this paper, I investigate some solutions of Einstein's field
equations which go smoothly between Schwarzschild's relativistic gravitational
solution near a mass concentration to the Friedmann-Lemaitre expanding universe
solution. In particular, the static, curved-space extension of the Lemaitre-
Schwarzschild solution in vacuum is given. Uniqueness conditions are discussed.
One of these metrics preserves the ``cosmological equation.'' We find that when
the rate of expansion of the universe is increasing, space is broken up into
domains of attraction. Outside a domain of attraction, the expansion of the
universe is strong enough to accelerate a test particle away from the domain
boundary. I give a domain-size--mass relationship. This relationship may very
well be important to our understanding of the large scale structure of the
universe.


title:
The KPNO International Spectroscopic Survey. III. [O III]-selected
  Survey List

abstract:
  The KPNO International Spectroscopic Survey (KISS) is an objective-prism
survey for extragalactic emission-line objects. It combines many of the
features of previous slitless spectroscopic surveys with the advantages of
modern CCD detectors, and is the first purely digital objective-prism survey
for emission-line galaxies. Here we present the first list of emission-line
galaxy candidates selected from our blue spectral data, which cover the
wavelength range 4800 -- 5500 A. In most cases, the detected emission line is
[O III]5007. The current survey list covers a one-degree-wide strip located at
Dec = 29 deg 30' (B1950.0) and spanning the right ascension range 8h 30m to 17h
0m. An area of 116.6 deg^2 is covered. A total of 223 candidate emission-line
objects have been selected for inclusion in the survey list (1.91 deg^-2). We
tabulate accurate coordinates and photometry for each source, as well as
estimates of the redshift, emission-line flux, and equivalent width based on
measurements of the digital objective-prism spectra. The median apparent
magnitude of the sample is B = 18.2, and galaxies with redshifts approaching z
= 0.1 are detected. The properties of the KISS emission-line galaxies are
examined using the available observational data, and compared to previous
surveys carried out with photographic plates as well as with the
H-alpha-selected portion of KISS.


title: The puzzling compact sources in supernova remnants

abstract:
  X-ray images of some young supernova remnants show bright point sources which
have not been detected in radio, optical and gamma-ray bands. Despite the
similarity of the X-ray spectra of these objects, they show a variety of
temporal properties. Most likely, they are neutron stars whose properties (spin
periods? magnetic fields? environments?) are different from those of radio
and/or gamma-ray pulsars. We present an overview of observational results on
several objects of this class -- the central sources of Cassiopeia A, RX
J0852-4622, RCW 103, Puppis A, and PKS 1209-51/52 -- with emphasis on the
recent Chandra observations.


title:
Do the Fundamental Constants Vary in the Course of the Cosmological
  Evolution?

abstract:
  We estimate the cosmological variation of the proton-to-electron mass ratio
\mu=m_p/m_e by measuring the wavelengths of molecular hydrogen transitions in
the early universe. The analysis is performed using high spectral resolution
observations (FWHM ~ 7 km/s) of two damped Lyman-\alpha systems at
z_{abs}=2.3377 and 3.0249 observed along the lines of sight to the quasars Q
1232+082 and Q 0347-382 respectively. The most conservative result of the
analysis is a possible variation of \mu over the last ~ 10 Gyrs, with an
amplitude \Delta\mu/\mu = (5.7+-3.8)x10^{-5}. The result is significant at the
1.5\sigma level only and should be confirmed by further observations. This is
the most stringent estimate of a possible cosmological variation of \mu
obtained up to now.


title: Cosmological constraints on quintessential halos

abstract:
  A complex scalar field has recently been suggested to bind galaxies and
flatten the rotation curves of spirals. Its cosmological behavior is thoroughly
investigated here. Such a field is shown to be a potential candidate for the
cosmological dark matter that fills up a fraction Omega_cdm = 0.3 of the
Universe. However, problems arise when the limits from galactic dynamics and
some cosmological constraints are taken simultaneously into account. A free
complex field, associated to a very small mass m = 10^{-23} eV, has a correct
cosmological behavior in the early Universe, but behaves today mostly as a real
axion, with a problematic value of its conserved quantum number. On the other
hand, an interacting field with quartic coupling lambda = 0.1 has a more
realistic mass m = 1 eV and carries a quantum number close to the photon number
density. Unlike a free field, it would be spinning today in the complex plane -
like the so-called ``spintessence''. Unfortunately, the cosmological evolution
of such field in the early Universe is hardly compatible with constraints from
nucleosynthesis and structure formation.


title: Environment, Ram Pressure, and Shell Formation in HoII

abstract:
  Neutral hydrogen VLA D-array observations of the dwarf irregular galaxy HoII,
a prototype galaxy for studies of shell formation, are presented. HI is
detected to radii over 16' or 4 R_25, and M_HI=6.44x10^8 M_sun. The total HI
map has a comet-like appearance suggesting that HoII is affected by ram
pressure from an intragroup medium (IGM). A rotation curve corrected for
asymmetric drift was derived and an analysis of the mass distribution yields a
total mass 6.3x10^9 M_sun, of which about 80% is dark. HoII lies northeast of
the M81 group's core, along with Kar52 (M81dwA) and UGC4483. No signs of
interaction are observed and it is argued that HoII is part of the NGC2403
subgroup, infalling towards M81. A case is made for ram pressure stripping and
an IGM in the M81 group. Stripping of the disk outer parts would require an IGM
density n_IGM>=4.0x10^-6 atoms/cm^3 at the location of HoII. This corresponds
to 1% of the virial mass of the group uniformly distributed over a volume just
enclosing HoII and is consistent with the X-ray properties of small groups. It
is argued that existing observations of HoII do not support self-propagating
star formation scenarios, whereby the HI holes and shells are created by
supernova explosions and stellar winds. Many HI holes are located in low
surface density regions of the disk, where no star formation is expected or
observed. Ram pressure has the capacity to enlarge preexisting holes and lower
their creation energies, helping to bridge the gap between the observed star
formation rate and that required to create the holes. (abridged)


title: The Soft Gamma-Ray Spectral Variability of Cygnus X-1

abstract:
  We have used observations of Cygnus X-1 from the Compton Gamma-Ray
Observatory (CGRO) and BeppoSAX to study the variation in the MeV gamma-ray
emission between the hard and soft spectral states, using spectra that cover
the energy range 20 keV up to 10 MeV. These data provide evidence for
significant spectral variability at energies above 1 MeV. In particular,
whereas the hard X-ray flux decreases during the soft state, the flux at
energies above 1 MeV increases, resulting in a significantly harder gamma-ray
spectrum at energies above 1 MeV. This behavior is consistent with the general
picture of galactic black hole candidates having two distinct spectral forms at
soft gamma-ray energies. These data extend this picture, for the first time, to
energies above 1 MeV. We have used two different hybrid thermal/non-thermal
Comptonization models to fit broad band spectral data obtained in both the hard
and soft spectral states. These fits provide a quantitative estimate of the
electron distribution and allow us to probe the physical changes that take
place during transitions between the low and high X-ray states. We find that
there is a significant increase (by a factor of ~4) in the bolometric
luminosity as the source moves from the hard state to the soft state.
Furthermore, the presence of a non-thermal tail in the Comptonizing electron
distribution provides significant constraints on the magnetic field in the
source region.


title: HST Spectroscopy of the Nucleus of M33

abstract:
  We have used Hubble Space Telescope to obtain moderate resolution 1150-5700
Ang. spectroscopy of the nucleus of M33 and a blue star ~1 arcsec NNW of the
nucleus in an attempt to find the optical counterpart of the nuclear X-ray
source and to characterize stellar populations in the nuclear region. The STIS
spectra of the nucleus can be modelled in terms of two starbursts, one with a
mass of about 9000 solar masses at 40 Myrs and the other with a mass of about
76,000 solar masses at 1 Gyrs. The blue star is a late type O giant, with no
obvious spectral anomalies to indicate that it is associated with the luminous
X-ray source. The nuclear region is not heavily reddened; 2200 Ang absorption
features in the spectra of both the nucleus and the star are weak. The data and
the star formation history support the hypothesis that the M33 nuclear source,
the brightest persistent source in the Local group, is an ~10 solar mass black
hole binary.


title: Primordial Black Holes in an Accelerating Universe

abstract:
  General expressions are given for the generation of Primordial Black Holes
(PBH) in a universe with a presently accelerated expansion due to a(n
effective) cosmological constant. We give expressions both for a powerlaw
scalefree primordial spectrum and for spectra which are not of that type.
Specializing to the case of a pure cosmological constant $\Lambda$ and assuming
flatness, we show that a comological constant with $\Omega_{\Lambda,0}=0.7$
will decrease the mass variance at the PBH formation time by about 15% compared
with a critical density universe.


title: Near Infrared Observations of Galactic Black Hole Candidates

abstract:
  We report on several European Southern Observatory (ESO) near-infrared (NIR)
observational campaigns aimed at understanding the nature of galactic black
hole candidates. Our results, including NIR photometry of the sources GRO
J1655-40, GRS 1739-278, GRS 1716-249, GRS 1121-68 and GX 339-4, show that all
the sources but GRO J1655-40 are consistent with low-mass stars as the
companion star of the binary system.
  By locating the counterparts on a colour-magnitude diagram (CMD), we better
constrain the spectral type of the companion star of three of the systems
considered here, and confirm a fourth one. The spectral types are respectively:
M0-5 V for GRS 1716-249, F8-G2 III for GX 339-4 and later than F5 V for GRS
1739-278. We confirm the already known spectral type of the companion in GRS
1121-68 (K0-5 V). The location of GRO J1655-40 on the CMD is consistent with
the sub-giant luminosity class and with this source crossing the Hertzsprung
gap. However, a non-stellar emission seems to contribute to the NIR flux of
this source.


title: LensCLEANing JVAS B0218+357 to determine H0

abstract:
  We use the radio ring in JVAS B0218+357 to constrain the mass models with
LensCLEAN. H0 is determined from the resulting model and the time delay.
B0218+357 is one of the best systems to reduce systematic errors in H0 and may
thus be called a "golden lens".


title:
Numerical Methods of Star Formation History Measurement and Applications
  to Seven Dwarf Spheroidals

abstract:
  A comprehensive study of the measurement of star formation histories from
colour-magnitude diagrams (CMDs) is presented, with an emphasis on a variety of
subtle issues involved in the generation of model CMDs and maximum likelihood
solution. Among these are the need for a complete sampling of the synthetic
CMD, the use of of proper statistics for dealing with Poisson-distributed data
(and a demonstration of why chi-square must not be used), measuring full
uncertainties in all reported parameters, quantifying the goodness-of-fit, and
questions of binning the CMD and incorporating outside information. Several
example star formation history measurements are given. Two examples involve
synthetic data, in which the input and recovered parameters can be compared to
locate possible flaws in the methodology (none were apparent) and measure the
accuracy with which ages, metallicities, and star formation rates can be
recovered. Solutions of the histories of seven Galactic dwarf spheroidal
companions (Carina, Draco, Leo I, Leo II, Sagittarius, Sculptor, and Ursa
Minor) illustrate the ability to measure star formation histories given a
variety conditions -- numbers of stars, complexity of star formation history,
and amount of foreground contamination. Significant measurements of ancient >8
Gyr star formation are made in all seven galaxies. Sculptor, Draco, and Ursa
Minor appear entirely ancient, while the other systems show varying amounts of
younger stars.


title:
The Relationship Between Masers and Massive Star Formation: What Can Be
  Learned from the Infrared?

abstract:
  The infrared represents an alternative wavelength regime in which to study
the environments of maser emission, while at the same time complementing the
information obtained through radio techniques. The near infrared (1-2 microns)
yields information on outflows, shocks, and reflected dust emission, while the
thermal infrared (3-30 microns) yields information on the thermal dust
distribution around stars. Thus, the infrared regime yields important clues in
determining whether masers exist in shocks, outflows, circumstellar accretion
disks, or in the dense medium close to protostars.


title: Modeling Non-Confined Coronal Flares: Dynamics and X-Ray Diagnostics

abstract:
  Long-lasting, intense, stellar X-ray flares may approach conditions of
breaking magnetic confinement and evolving in open space. We explore this
hypothesis with hydrodynamic simulations of flares occurring in a non-confined
corona: model flares are triggered by a transient impulsive heating injected in
a plane-parallel stratified corona. The plasma evolution is described by means
of a numerical 2-D model in cylindrical geometry R,Z. We explore the space of
fundamental parameters. As a reference model, we consider a flare triggered by
a heating pulse that would cause a 20 MK flare if delivered in a 40000 km long
closed loop. The modeled plasma evolution is described. The X-ray emission,
spectra and light curves at the ASCA/SIS focal plan, and in two intense X-ray
lines (Mg XI at 9.169 A and Fe XXI at 128.752 A), have been synthesized from
the models. The results are discussed and compared to features of confined
events, and scaling laws are derived. The light curves invariably show a very
rapid rise, a constant phase as long as the constant heating is on, and then a
very fast decay, on time scales of few seconds, followed by a more gradual one
(few minutes). We show that this evolution of the emission, and especially the
fast decay, together with other potentially observable effects, are intrinsic
to the assumption of non-confinement. Their lack indicates that observed
long-lasting stellar X-ray flares should involve plasma strongly confined by
magnetic fields.


title: The Optical Polarization of Near-Infrared Selected QSOs

abstract:
  Optical broad-band polarimetry is presented for near-infrared color-selected
AGN classified QSOs based on their K-band luminosity. More than 10% of a sample
of 70 QSOs discovered in the Two Micron All Sky Survey (2MASS) with J-K > 2 and
M_K < -23 show high broad-band linear polarization (P > 3%), and values range
to a maximum of P = 11%. High polarization tends to be associated with the most
luminous objects at K, and with QSOs having the highest near-IR-to-optical flux
ratios. The 2MASS QSO sample includes objects possessing a wide range of
optical spectral types. High polarization is seen in two of 22 broad
emission-line (Type 1) objects, but 1/4 of the QSOs of intermediate spectral
type (Type 1.5-1.9) are highly polarized. None of the nine QSOs classified as
Type 2 exhibit P > 3%. It is likely that the unavoidable inclusion of
unpolarized starlight from the host galaxy within the observation aperture
results in reduced polarization for the narrow emission-line objects. The high
polarization of 2MASS-discovered QSOs supports the conclusion inferred from
their near-IR and optical colors, that the nuclei of many of these objects are
obscured to some degree by dust. The 2MASS QSO sample is compared to other,
predominantly radio-quiet, QSOs and is found to be consistent with the idea
that the orientation of AGN to the line of sight plays a major role in
determining their observed properties.