title: Magnetic lensing of extremely high energy cosmic rays in a galactic wind

abstract:
  We show that in the model of Galactic magnetic wind recently proposed to
explain the extremely high energy (EHE) cosmic rays so far observed as
originating from a single source (M87 in the Virgo cluster), the magnetic field
strongly magnifies the fluxes and produces multiple images of the source. The
apparent position on Earth of the principal image moves, for decreasing
energies, towards the galactic south. It is typically amplified by an order of
magnitude at $E/Z\sim 2\times 10^{20}$ eV, but becomes strongly demagnified
below $10^{20}$ eV. At energies below $E/Z\sim 1.3\times 10^{20}$ eV, all
events in the northern galactic hemisphere are due to secondary images, which
have huge amplifications ($>10^2$). This model would imply strong asymmetries
between the north and south galactic hemispheres, such as a (latitude
dependent) upper cut-off value below $2\times 10^{20}$ eV for CR protons
arriving to the south and lower fluxes in the south than in the north above
$10^{20}$ eV. The large resulting magnifications reduce the power requirements
on the source, but the model needs a significant tunning between the direction
to the source and the symmetry axis of the wind. If more modest magnetic field
strengths were assumed, a scenario in which the observed EHE events are heavier
nuclei whose flux is strongly lensed becomes also plausible and would predict
that a transition from a light composition to a heavier one could take place at
the highest energies.


title: Galaxy Distances via Rotational Parallaxes

abstract:
  Accurate distances to stars and galaxies allow for significant tests of
stellar evolution, galaxy formation and evolution and cosmology. NASA's Space
Interferometry Mission (SIM) will obtain precision [1-30 microarcsec]
astrometry for 10-20k objects brighter than V=20 mag.
  In this paper we discuss a method to determine the distance of nearby spiral
galaxies using the technique of rotational parallaxes, and show that it is
possible to achieve distance errors of only a few percent. With such distances
at hand, it becomes possible to determine an accurate zero-point for the
Tully-Fisher relation, one of the tools to measure distances throughout the
universe.
  The rotational parallax method employs the common orbital motions of a of
stars within a galaxy to determine their distance. For stars on circular
orbits, the two proper motions and the radial velocity suffice to determine the
inclination of the orbit, the rotational velocity and the distance. Several
factors complicate the application of this simple technique to real galaxies:
1) the target galaxy may have substantial space-motion, 2) stars in real
galaxies are not on circular orbits (e.g. due to spiral-arm streaming motions
or induced by random motions), 3) stars in the galaxy are at significantly
different distances from the Sun (the near side of M 31 is ~5% closer than the
far side).
  Notwithstanding these complication, distances can be determined to within
several percent for the nearest spirals. (abridged)


title:
The Spatial and Kinematic Distributions of Cluster Galaxies in a LCDM
  Universe -- Comparison with Observations

abstract:
  We combine dissipationless N-body simulations and semi-analytic models of
galaxy formation to study the spatial and kinematic distributions of cluster
galaxies in a LCDM cosmology. We investigate how the star formation rates,
colours and morphologies of galaxies vary as a function of distance from the
cluster centre and compare our results with the CNOC1 survey of galaxies from
15 X-ray luminous clusters in the redshift range 0.18 to 0.55. In our model,
gas no longer cools onto galaxies after they fall into the cluster and their
star formation rates decline on timescales of 1-2 Gyr. Galaxies in cluster
cores have lower star formation rates and redder colours than galaxies in the
outer regions because they were accreted earlier. Our colour and star formation
gradients agree with those those derived from the data. The difference in
velocity dispersions between red and blue galaxies observed in the CNOC1
clusters is also well reproduced by the model. We assume that the morphologies
of cluster galaxies are determined solely by their merging histories.
Morphology gradients in clusters arise naturally, with the fraction of bulge-
dominated galaxies highest in cluster cores. We compare these gradients with
the CNOC1 data and find excellent agreement for bulge-dominated galaxies. The
simulated clusters contain too few galaxies of intermediate bulge-to-disk
ratio, suggesting that additional processes may influence the morphological
evolution of disk-dominated galaxies in clusters. Although the properties of
the cluster galaxies in our model agree extremely well with the data, the same
is not true of field galaxies. Both the star formation rates and the colours of
bright field galaxies appear to evolve much more strongly from redshift 0.2 to
0.4 in the CNOC1 field sample than in our simulations.


title: Cosmic Ray Rejection and Readout Efficiency for Large-Area Arrays

abstract:
  We present an algorithm to optimally process uniformly sampled array image
data obtained with a nondestructive readout. The algorithm discards full wells,
removes cosmic ray (particle) hits and other glitches, and makes a nearly
optimum estimate of the signal on each pixel. The algorithm also compresses the
data. The computer requirements are modest, and the results are robust. The
results are shown and compared to results of Fowler sampled and processed data.
Non-ideal detector performance may require some additional code, but this is
not expected to cost much processing time. Known types of detector faults are
addressed.


title: A Good Long Look at the Black Hole Candidates LMC X-1 and LMC X-3

abstract:
  We present results from 170ksec long RXTE observations of LMC X-1 and LMC
X-3, taken in 1996 December, where their spectra can be described by a disc
black body plus an additional soft (Gamma~2.8) high-energy power-law (detected
up to 50keV in LMC X-3). These observations, as well as archival ASCA
observations, constrain any narrow Fe line present in the spectra to have an
equivalent width <90eV, broad lines (~150eV EW, \sigma ~ 1keV) are permitted.
We also study the variability of LMC X-1. Its X-ray power spectral density
(PSD) is approximately f^{-1} between 10^{-3} and 0.3Hz with a rms variability
of ~7%. Above 5keV the PSD shows evidence of a break at f > 0.2Hz, possibly
indicating an outer disc radius of ~1000GM/c^2 in this likely wind-fed system.
Furthermore, the coherence function between variability in the > 5keV band and
variablity in the lower energy bands is extremely low. We discuss the
implications of these observations for the mechanisms.


title: Lopsidedness in dwarf irregular galaxies

abstract:
  We quantify the amplitude of the lopsidedness, the azimuthal angular
asymmetry index, and the concentration of star forming regions, as represented
by the distribution of the H$\alpha$ emission, in a sample of 78 late-type
irregular galaxies. We bin the observed galaxies in two groups representing
blue compact galaxies (BCDs) and low surface brightness dwarf galaxies (LSBs).
The light distribution is analysed with a novel algorithm, which allows
detection of details in the light distribution pattern.
  We find that while the asymmetry of the underlying continuum light,
representing the older stellar generations, is relatively small, the H$\alpha$
emission is very asymmetric and is correlated in position angle with the
continuum light.
  We test a model of random star formation over the extent of a galaxy by
simulating HII regions in artificial dwarf galaxies. The implication is that
random star formation over the full extent of a galaxy may be generated in LSB
dwarf-irregular galaxies but not in BCD galaxies.


title: Discovery of Recurring Soft to Hard State Transitions in LMC X-3

abstract:
  We present the analysis of an RXTE monitoring campaign of the canonical soft
state black hole candidates LMC X-1 and LMC X-3. In contrast to LMC X-1, which
does not exhibit any periodic spectral changes, we find that LMC X-3 exhibits
stron spectral variability on time scales of days to weeks. For typical RXTE
ASM count rates, the luminosity variations of LMC X-3 are due to changes of the
phenomenological disk blackbody temperature. During episodes of especially low
luminosity (ASM count rates < 0.6 counts/sec), kT strongly decreases and the
power law significantly hardens to a photon index of ~1.8. These changes are
consistent with state changes of LMC X-3 from the soft state to the canonical
hard state of galactic black hole candidates. We argue that the long term
variability of LMC X-3 might be due to a wind-driven limit cycle such as
discussed by Shields et al. (1986)


title: Phase Transition to Hyperon Matter in Neutron Stars

abstract:
  Recent progress in the understanding of the high density phase of neutron
stars advances the view that a substantial fraction of the matter consists of
hyperons. The possible impacts of a highly attractive interaction between
hyperons on the properties of compact stars are investigated. We find that a
hadronic equation of state with hyperons allows for a first order phase
transition to hyperonic matter. The corresponding hyperon stars can have rather
small radii of R=8 km.


title:
Multiwavelength Examination of the COS-B Field 2CG 075+00 Yields a
  Blazar Identification for 3EG J2016+3657

abstract:
  We present a high-energy study of the intriguing COS-B gamma-ray field, 2CG
075+00, in order to search for possible counterparts. New EGRET data show that
the COS-B emission probably corresponds to two localized gamma-ray sources, 3EG
J2016+3657 and 3EG J2021+3716. Spectral fits to these EGRET sources, assuming a
power-law model, yield photon indices of ~ 2 for each object. We examine
archival ROSAT and ASCA X-ray data which overlap both EGRET error boxes, and
find several point sources in the region to a flux limit of approximately 6.5 x
10^{-13} erg cm^{-2} s^{-1}. We conclude that the most probable candidate for
3EG J2016+3657 is the compact, variable, flat-spectrum radio and millimeter
source B2013+370 (G74.87+1.22) which has blazar-like properties. The other
source, 3EG J2021+3716, remains unidentified.


title:
The Spin Period, Luminosity and Age Distributions of Anomalous X-Ray
  Pulsars

abstract:
  We consider the accretion model for anomalous X-ray pulsars proposed recently
by Chatterjee, Hernquist and Narayan, in which the emission is powered by
accretion from a fossil disk formed by the fallback of material from a
supernova explosion. We demonstrate that this model is able to account for the
spin period, luminosity and age distributions of the observed population of
AXPs for reasonable and broad distributions of the free parameters of the
model, namely, the surface magnetic field of the neutron star, the mass of its
accretion disk and its initial spin period. In particular, this model is able
statistically to account for the puzzlingly narrow observed spin distribution
of the AXPs. We show also that if the establishment of fallback accretion disks
around isolated neutron stars is a universal phenomenon, then a fairly large
minority ($\sim 20%$) of these objects become X-ray bright AXPs or X-ray faint
systems spinning down by propeller action, while the rest become radio pulsars.


title: Anomalous Radio-Wave Scattering from Interstellar Plasma Structures

abstract:
  This paper considers scattering screens that have arbitrary spatial
variations of scattering strength transverse to the line of sight, including
screens that are spatially well confined, such as disks and filaments. We
calculate the scattered image of a point source and the observed pulse shape of
a scattered impulse. The consequences of screen confinement include: (1) Source
image shapes that are determined by the physical extent of the screen rather
than by the shapes of much-smaller diffracting microirregularities. These
include image elongations and orientations that are frequency dependent. (2)
Variation with frequency of angular broadening that is much weaker than the
trademark \nu^{-2} scaling law (for a cold, unmagnetized plasma), including
frequency-independent cases; and (3) Similar departure of the pulse broadening
time from the usually expected \nu^{-4} scaling law. We briefly discuss
applications that include scattering of pulses from the Crab pulsar by
filaments in the Crab Nebula; image asymmetries from Galactic scattering of the
sources Cyg X-3, Sgr A*, and NGC 6334B; and scattering of background active
galactic nuclei by intervening galaxies. We also address the consequences for
inferences about the shape of the wavenumber spectrum of electron density
irregularities, which depend on scaling laws for the image size and the pulse
broadening. Future low-frequency (< 100 MHz) array observations will also be
strongly affected by the Galactic structure of scattering material. Our
formalism is derived in the context of radio scattering by plasma density
fluctuations. It is also applicable to optical, UV and X-ray scattering by
grains in the interstellar medium.


title:
Making Clean Energy with a Kerr Black Hole: a Tokamak Model for
  Gamma-Ray Bursts

abstract:
  In this paper we present a model for making clean energy with a Kerr black
hole. Consider a Kerr black hole with a dense plasma torus spinning around it.
A toroidal electric current flows on the surface of the torus, which generates
a poloidal magnetic field outside the torus. On the surface of the tours the
magnetic field is parallel to the surface. The closed magnetic field lines
winding around the torus compress and confine the plasma in the torus, as in
the case of tokamaks. Though it is unclear if such a model is stable, we look
into the consequences if the model is stable. If the magnetic field is strong
enough, the baryonic contamination from the plasma in the torus is greatly
suppressed by the magnetic confinement and a clean magnetosphere of
electron-positron pairs is built up around the black hole. Since there are no
open magnetic field lines threading the torus and no accretion, the power of
the torus is zero. If some magnetic field lines threading the black hole are
open and connect with loads, clean energy can be extracted from the Kerr black
hole by the Blandford-Znajek mechanism.
  The model may be relevant to gamma-ray bursts. The energy in the Poynting
flux produced by the Blandford-Znajek mechanism is converted into the kinetic
energy of the electron-positron pairs in the magnetosphere around the black
hole, which generates two oppositely directed jets of electron-positron pairs
with super-high bulk Lorentz factors. The jets collide and interact with the
interstellar medium, which may produce gamma-ray bursts and the afterglows.


title: A Color Analysis of the NICMOS Parallel Image Archive

abstract:
  We present a photometric analysis of all high Galactic lattitude (|b| > 20d)
broad-band parallel images taken by the Near Infrared Camera and Multi-Object
Spectrometer (NICMOS) instrument during its initial lifetime in HST Cycle 7.
These images, taken through the F110W and F160W filters, reach a mean 3-sigma
limiting magnitude of approximately 22 in both bands, and cover a total area of
approximately 92 square arcminutes. The reddest of the 358 galaxies detected
have F110W-F160W colors and F160W magnitudes consistent with being a
combination of both dusty star-forming and evolved early-type galaxies at 1 < z
< 2. The surface density of these galaxies is comparable to that of the
population of Extremely Red Objects (EROs) discovered in ground-based surveys
(~ 100 deg-2), suggesting that EROs also represent a combination of both galaxy
types in this redshift range. Roughly 10% of the detected galaxies appear to be
blue compact dwarf galaxies at z < 1, a result consistent with studies of the
HST Medium Deep Survey Fields. The surface density of these objects down to
magnitude of 22 in F160W is ~ 300 deg-2. None of the 681 point sources detected
have F110W-F160W colors matching those expected for QSOs whose continua have
been significantly reddened by internal dust. Our data limit the surface
density of such QSOs to be < 50 deg-2 down the mean limiting magnitudes of the
sample images. Since the surface density of QSOs detected on the basis of
ultraviolet excess in optical surveys to comparable depth is ~ 100 deg-2, this
argues against the suggestion that dust-reddened QSOs comprise the undetected
majority of the QSO population. The F110W-F160W color can also be used to
identify unreddened QSOs at z > 8, but we find no such candidates. This is
consistent with the evidence that QSO space density declines sharply at z > 5.


title: RXTE Studies of Long-Term X-ray Spectral Variations in 4U 1820-30

abstract:
  We present the results of detailed spectral studies of the ultra-compact low
mass X-ray binary (LMXB) 4U 1820-30 carried out with the Rossi X-ray Timing
Explorer (RXTE) during 1996-7. 4U 1820-30 is an ``atoll'' source X-ray burster
(XRB) located in the globular cluster NGC 6624. It is known to have an 11
minute binary period and a ~176 day modulation in its 2--12 keV flux.
Observations were made with the PCA and HEXTE instruments on RXTE at roughly
one-month intervals to sample this long-term period and study flux-related
spectral changes. There are clear correlations between our fitted spectral
parameters and both the broad-band (2--50 keV) flux and the position in the
color-color diagram, as described by the parameter S_a introduced by Mendez et
al. (1999). In addition, we find a strong correlation between the position in
the color-color diagram and the frequencies of the kilohertz quasi-periodic
oscillations (kHz QPOs) reported by Zhang et al. (1998). This lends further
support to the notion that evidence for the last stable orbit in the accretion
disk of 4U 1820-30 has been observed. For a model consisting of Comptonization
of cool photons by hot electrons plus an additional blackbody component, we
report an abrupt change in the spectral parameters at the same accretion rate
at which the kHz QPOs disappear. For a model consisting of a multicolor disk
blackbody plus a cut-off power law, we find that the inner disk radius reaches
a minimum at the same accretion rate at which the kHz QPO frequency saturates,
as expected if the disk reaches the last stable orbit. Both models face
theoretical and observational problems when interpreted physically for this
system.


title:
RXTE Studies of X-ray Spectral Variations with Accretion Rate in 4U
  1915-05

abstract:
  We present the results of detailed spectral studies of the ultra-compact low
mass X-ray binary (LMXB) 4U 1915-05 carried out with the Rossi X-ray Timing
Explorer (RXTE) during 1996. 4U 1915-05 is an X-ray burster (XRB) known to
exhibit a ~199-day modulation in its 2--12 keV flux. Observations were
performed with the PCA and HEXTE instruments on RXTE at roughly one-month
intervals to sample this long-term period and study accretion rate-related
spectral changes. We obtain good fits with a model consisting of a blackbody
and an exponentially cut-off power law. The spectral parameters are strongly
correlated with both the broad-band (2--50 keV) luminosity and the position in
the color-color diagram, with the source moving from a low hard state to a high
soft state as the accretion rate increases. The blackbody component appears to
drive the spectral evolution. Our results are consistent with a geometry in
which the soft component arises from an optically thick boundary layer and the
hard component from an extended Comptonizing corona. Comparing our results with
those of a similar study of the brighter source 4U 1820-30 (Bloser et al.
2000), we find that the two ultra-compact LMXBs occupy similar spectral states
even though the transitions occur at very different total luminosities.


title: Observations of Type I Bursts from Neutron Stars

abstract:
  Observations of Type I X-ray bursts have long been taken as evidence that the
sources are neutron stars. Black body models approximate the spectral data and
imply a suddenly heated neutron star cooling over characteristic times of
seconds to minutes. The phenomena are convincingly explained in terms of
nuclear burning of accreted gas on neutron stars with low mass companion stars.
Prospects are promising that detailed theory and data from RXTE and future
missions will lead to better determinations of important physical parameters
(neutron star mass and radius, composition of the accreting gas, distance of
the source). Among the variety of bursts observed, there are probably
representatives of different kinds of explosive burning. RXTE's discovery of a
2.5 ms persistent coherent period from one Type I burster has now linked
bursters indisputably to the epitome of a neutron star, a fast spinning
magnetic compact object. Oscillations in some bursts had already been thought
to arise from the neutron stars' rotations. Detailed observations of these
oscillations are touchstones of how the explosive bursts originate and
progress, as well as independent measures of the neutron star parameters.


title:
Dense gas in nearby galaxies XIII. CO submillimeter line emission from
  the starburst galaxy M82

abstract:
  12CO 1-0,2-1,4-3,7-6, and 13CO 1-0, 2-1, and 3-2 line was mapped with angular
resolutions of 13" - 22" toward the nuclear region of starburst galaxy M82. The
difference of lobe spacings in submillimeter (~15") and millimeter (~26") lines
indicates the presence of a `low' and a `high' CO excitation component. An LVG
excitation analysis of the submillimeter lines leads to inconsistencies, since
area and volume filling factors are almost the same, resulting in cloud sizes
along the lines-of-sight that match the entire size of the M82 starburst
region. Nevertheless, LVG column densities agree with estimates derived from
the dust emission in the far infrared and at submillimeter wavelengths.
Accounting for high UV fluxes and variations in kinetic temperature and
assuming that the observed emission arises from photon dominated regions (PDRs)
resolves the problems related to an LVG treatment of the radiative transfer.
12CO/13CO line intensity ratios > 10 indicate that the bulk of the CO emission
arises in UV-illuminated diffuse cloud fragments of small column density and
sub-parsec cloud sizes with area filling factors >> 1. Thus CO arises from
quite a different gas component than the classical high density tracers. The
dominance of such a diffuse molecular interclump medium also explains observed
high [CI}/CO line intensity ratios. PDR models do not allow a determination of
the relative abundances of 12CO to 13CO. Ignoring magnetic fields, the CO gas
appears to be close to the density limit for tidal disruption. A warm diffuse
ISM not only dominates the CO emission in the starburst region of M82 but is
also ubiquitous in the central region of our Galaxy, where tidal stress,
cloud-cloud collisions, shocks, high gas pressure, and high stellar densities
may all contribute to the formation of a highly fragmented molecular debris.


title: Photometric study of fields of nearby pulsars with the 6m telescope

abstract:
  Fields of Geminga, PSR B0950+08, PSR J1908+0734 and PSR J0108-1431 have been
observed within the program of optical investigation of nearby neutron stars
carried out with the 6m telescope. Our multicolour BVR_cI_c photometry has
yielded the following magnitudes of Geminga: V=25.3+/-0.4; R_c=25.4+/-0.3. The
estimates of the 3\sigma upper limits in the B and I_c bands are 25.4 and 24.9,
respectively. This is in agreement with previous observations of Geminga. We
have suggested candidate for optical counterpart of PSR B0950+08, with
R_c=25.4+/-0.3. When compared to the HST data obtained in UV its flux shows
that this old pulsar can be brighter in near-IR than in near-UV. We have
obtained for the first time images of the fields of PSR J1908+0734 and PSR
J0108-1431. Although no optical counterparts have been detected, the magnutude
upper limits obtained suggest further observations of these pulsars.


title: The Universe behind the Milky Way

abstract:
  Due to the foreground extinction of the Milky Way, galaxies appear
increasingly fainter the closer they lie to the Galactic Equator, creating a
"zone of avoidance" of about 25% in the distribution of optically visible
galaxies. A "whole-sky" map of galaxies is essential, however, for
understanding the dynamics in our local Universe, in particular the peculiar
velocity of the Local Group with respect to the Cosmic Microwave Background and
velocity flow fields such as in the Great Attractor region. Various dynamically
important structures behind the Milky Way have only recently been made
``visible'' through dedicated deep surveys at various wavelengths. The wide
range of observational searches (optical, near infrared, far infrared, radio
and X-ray) for galaxies in the Zone of Avoidance are reviewed, including a
discussion on the limitations and selection effects of these partly
complementary approaches. The uncovered and suspected large-scale structures
are summarized. Reconstruction methods of the density field in the Zone of
Avoidance are described and the resulting predictions compared with
observational evidence. The comparison between reconstructed density fields and
the observed galaxy distribution allow derivations of the density and biasing
parameters Omega_0 and b.


title: Numerical Simulations in Cosmology I: Methods

abstract:
  This lecture gives a short introduction to different methods used in
cosmology. The focus is on major features of N-body simulations: equations,
main numerical techniques, effects of resolution, and methods of halo
identification.


title: Numerical Simulations in Cosmology II: Spatial and Velocity Biases

abstract:
  We give a summary of recent results on spatial and velocity biases in
cosmological models. Progress in numerical techniques made it possible to
simulate halos in large volumes with a such accuracy that halos survive in
dense environments of groups and clusters of galaxies. Halos in simulations
look like real galaxies, and, thus, can be used to study the biases --
differences between galaxies and the dark matter. The biases depend on scale,
redshift, and circular velocities of selected halos. Two processes seem to
define the evolution of the spatial bias: (1) statistical bias and (2) merger
bias (merging of galaxies, which happens preferentially in groups, reduces the
number of galaxies, but does not affect the clustering of the dark matter).
There are two kinds of velocity bias. The pair-wise velocity bias is
b_12=0.6-0.8 at r< 5Mpc/h, z=0. This bias mostly reflects the spatial bias and
provides almost no information on the relative velocities of the galaxies and
the dark matter. One-point velocity bias is a better measure of the velocities.
Inside clusters the galaxies should move slightly faster (b_v =1.1-1.3) than
the dark matter. Qualitatively this result can be understood using the Jeans
equations of the stellar dynamics. For the standard LCDM model we find that the
correlation function and the power spectrum of galaxy-size halos at z=0 are
antibiased on scales r<5Mpc/h and k=(0.15-30)h/Mpc.


title: Numerical Simulations in Cosmology III: Dark Matter Halos

abstract:
  Properties of dark matter halos are reviewed. Taken from different
publications, we present results on (1) the mass and velocity functions, (2)
density and velocity profiles, and (3) concentration of halos. In the range of
radii r=(0.005-1)rvir the density profile for a quiet isolated halo is very
accurately approximated by a fit suggested by Moore etal (1997):
rho=1/x^1.5(1+x^1.5), where x=r/rs and rs is a characteristic radius. The fit
suggested by Navarro et al (1995) rho= 1/x(1+x)^2, also gives a very
satisfactory approximation with relative errors of about 10% for radii not
smaller than 1% of the virial radius. The mass function of z=0 halos with mass
below 10^{13}Msun/h is approximated by a power law with slope alpha =-1.85. The
slope increases with the redshift. The velocity function of halos with Vmax<
500km/s is also a power law with the slope beta= -3.8-4. The power-law extends
to halos at least down to 10km/s. It is also valid for halos inside larger
virialized halos. The concentration of halos depends on mass (more massive
halos are less concentrated) and environment, with isolated halos being less
concentrated than halos of the same mass inside clusters. Halos have intrinsic
scatter of concentration: at 1sigma level halos with the same mass have
Delta(log{c_vir})=0.18 or, equivalently, DeltaVmax/Vmax =0.12. Velocity
anisotropy for both subhalos and the dark matter is approximated by beta(r)
=0.15+2x/[x^2+4], where x is radius in units of the virial radius.


title: Recent Observations of X-Ray Emission from Galactic Binary Neutron Stars

abstract:
  Recent measurements of young accreting binary neutron stars are determining
more precise magnetic field and accretion parameters. A low magnetic field
accreting, millisecond pulsar has finally been found in a binary burster. At
least 20 low-mass binaries have exhibited high frequency oscillations,
300--1200 Hertz. The majority have, for some range of luminosity, the pair of
quasiperiodic oscillations that have never been seen in a black hole candidate.
Recent evidence from burst oscillations strengthens the case that the
difference frequency of this pair is close to the spin frequency of the neutron
star. These oscillations are correlated with the spectra, luminosity, and low
frequency oscillations. Quasiperiodic oscillations are also seen sometimes in
strong magnetic field pulsars, where their origin can be closely examined.


title: Time-series Spectroscopy of Pulsating sdB Stars: PG1605+072

abstract:
  We report the detection of velocity variations in the pulsating sdB star, PG
1605+072. Oscillations are detected at the same frequencies found from
photometry and have amplitudes of up to 14 km/s for H$\beta$. The strongest
oscillation found in previous photometric observations is not evident in our
spectroscopy or photometry, and may be absent due to beating of closely spaced
modes. Phase differences between spectroscopy and B magnitude photometry imply
that maximum brightness occurs not long after maximum radius. We have also
found evidence of variation in the observed amplitudes of five Balmer lines,
with a decrease in amplitude of the strongest mode blueward from H$\beta$. This
effect is not expected and a longer time-series will be needed to clarify it.


title:
Epochs of Maximum Light and Bolometric Light Curves of Type Ia
  Supernovae

abstract:
  We present empirical fits to the UBVRI light curves of type Ia supernovae.
These fits are used to objectively evaluate light curve parameters. We find
that the relative times of maximum light in the filter passbands are very
similar for most objects. Surprisingly the maximum at longer wavelengths is
reached earlier than in the B and V light curves. This clearly demonstrates the
complicated nature of the supernova emission. Bolometric light curves for a
small sample of well-observed SNe Ia are constructed by integration over the
optical filters. In most objects a plateau or inflection is observed in the
light curve about 20-40 days after bolometric maximum. The strength of this
plateau varies considerably among the individual objects in the sample.
Furthermore the rise times show a range of several days for the few objects
which have observations early enough for such an analysis. On the other hand,
the decline rate between 50 and 80 days past maximum is remarkably similar for
all objects, with the notable exception of SN 1991bg. The similar late decline
rates for the supernovae indicate that the energy release at late times is very
uniform; the differences at early times is likely due to the radiation
diffusing out of the ejecta. With the exception of SN 1991bg, the range of
absolute bolometric luminosities of SNe Ia is found to be at least a factor of
2.5. The nickel masses derived from this estimate range from 0.4 to 1.1 Msun.
It seems impossible to explain such a mass range by a single explosion
mechanism, especially since the rate of gamma-ray escape at late phases seems
to be very uniform.


title:
Ultra-strong Elelctric Fields and Vacuum Breakdown: Search for an
  Astrophysical Scenario

abstract:
  In some models of $\gamma$-ray bursts super-strong electric fields ($E\sim
10^{14} {\rm statvolt cm}^{-1}$) have been surmized. Such large fields may
provide copious pair production through vacuum polarization. Here we examine
various astrophysical scenarios where huge electric field can be present. It is
shown that when the conditions for quantistic vacuum breakdown are met, pair
creation through conventional processes is likely to be always more important.
Although of great physical interest, quantum pair production seems therefore of
little astrophysical relevance.


title: Meteor Stream Membership Criteria

abstract:
  Criteria for the membership of individual meteors in meteor streams are
discussed from the point of view of their mathematical and also physical
properties. Discussion is also devoted to the motivation. It is shown that
standardly used criteria (mainly D-criterion of Southworth and Hawkins, 1963)
have unusual mathematical properties in the sense of a term ``distance'',
between points in a phase space, and, physical motivation and realization for
the purpose of obtaining their final form is not natural and correct, and,
moreover, they lead also to at least surprising astrophysical results. General
properties of possible criteria are discussed. A new criterion for the
membership in meteor streams is suggested. It is based on probability theory.
Finally, a problem of meteor orbit determination for known parent body is
discussed.


title:
Far infrared extragalactic background radiation: I. Source counts with
  ISOPHOT

abstract:
  As a part of the ISOPHOT CIRB (Cosmic Infrared Background Radiation) project
we have searched for point-like sources in eight fields mapped at two or three
wavelengths between 90 and 180um. Most sources are previously unknown and based
on the far-infrared (FIR) spectral energy distributions dust-enshrouded,
distant galaxies form a significant fraction of the sources. We present a list
of the new extragalactic FIR-sources and discuss the uncertainties of the
source detection from the ISOPHOT maps. We estimate the source number densities
at 90, 150 and 180um and at flux density levels down to 100mJy to be 10^5, 2
10^5, and 3 10^5 1/sr, respectively. Strong galaxy evolution models are in best
agreement with our results, although the number of detections exceeds most
model predictions. No-evolution models can be rejected at a high confidence
level. Comparison with COBE results indicates that at 90um the detected sources
correspond to some 20% of the extragalactic background light. At longer
wavelengths the corresponding fraction is closer to 10%.


title:
The Observed Mass Profiles of Dark Halos and The Formation Epochs of
  Galaxies

abstract:
  We have determined the mass profiles of dark halos in 83 objects observed by
ASCA. The point spread function of X-ray telescope was deconvoled by the
Richardson-Lucy algorithm and the temperature profiles were calculated to
obtain the mass profiles. The derived mass profiles are consistent with the NFW
model in 0.01-1.0 r_virial. We found a good correlation between the scale
radius r_s and the characteristic mass density \delta_c, which indicates the
self-similarity of dark halos. The spectrum index of primordial density
fluctuation, P(k) \propto k^n, was determined from the slope of r_s - delta_c
relation. For M_200=10^12-10^15 M_solar, our analysis gives n=-1.2 +/- 0.3 with
a confidence level of 90%. The mass density of dark halos is a good indicator
of the mean mass density of the universe at the time when the halos were
assembled, z=z_f. Assuming delta_c \propto (1+z_f)^3, we have determined the
epoch when each dark halo was assembled. Our analysis indicates that the field
elliptical galaxies and groups of galaxies formed approximately at 1+z_f ~ 15
and at 1+z_f ~ 7-10 respectively.


title: Dynamic Work Distribution for PM Algorithm

abstract:
  Although poor for small dynamic scales, the Particle-Mesh (PM) model allows
in astrophysics good insight for large dynamic scales at low computational
cost. Furthermore, it is possible to employ a very high number of particles to
get high mass resolution. These properties could be exploited by suitable
parallelization of the algorithm. In PM there are two types of data: the
particle data, i.e. position and velocity, which are stored in one-dimensional
arrays of N elements, and the grid data, i.e. density and force, which are
stored in three-dimensional arrays $M\times M\times M$ in size. Since
individual particles can change cell under the action of gravitational force,
parallelization is a real challenge on parallel machine and must account for
the machine architecture. We have implemented a dynamic work distribution
through agenda parallelism. By subdividing the work in small tasks, the
implementation is well balanced, scalable and efficient also for clustered
particle distributions. In this contribution we describe this efficient, load
balanced, parallel implementation of PM algorithm on Cray T3E at CINECA and
show its performances on cosmological simulation results.


title:
The synthesis of the light Mo and Ru isotopes: how now, no need for an
  exotic solution ?

abstract:
  The most detailed calculations of the p-process call for its development in
the O/Ne layers of Type II supernovae. In spite of their overall success in
reproducing the solar system content of p-nuclides, they suggest a significant
underproduction of the light Mo and Ru isotopes. On grounds of a model for the
explosion of a 25 solar mass star with solar metallicity, we demonstrate that
this failure might just be related to the uncertainties left in the rate of the
22Ne(alpha,n)25Mg neutron producing reaction. The latter indeed have a direct
impact on the distribution of the s-process seeds for the p-process.


title: Dynamics and properties of chiral cosmic strings in Minkowski space

abstract:
  Chiral cosmic strings are produced naturally at the end of inflation in
supersymmetric models where the symmetry is broken via a D-term. Consequently
in such theories, where both inflation and cosmic strings contribute to the
density and CMBR (microwave background) perturbations, it is necessary to
understand the evolution of chiral cosmic string networks. We study the
dynamics of chiral cosmic strings in Minkowski space and comment on a number of
differences with those of Nambu-Goto strings. To do this we follow the work of
Carter and Peter who showed that the equations of motion for chiral cosmic
strings reduce to a wave equation and two constraints, only one of which is
different from the familiar Nambu-Goto constraints. We study chiral string loop
solutions consisting of many harmonics and determine their self-intersection
probabilities, and comment on the possible cosmological significance of these
results.


title: Limits of crystallographic methods for detecting space topology

abstract:
  We investigate to what extent the cosmic crystallographic methods aimed to
detect the topology of the universe using catalogues of cosmic objects would be
damaged by various observational uncertainties. We find that the topological
signature is robust in the case of Euclidean spaces, but is very fragile in the
case of compact hyperbolic spaces. Comparing our results to the presently
accepted range of values for the curvature parameters, the best hopes for
detecting space topology rest on elliptical space models.


title:
Limits on the accretion rates onto massive black holes in nearby
  galaxies

abstract:
  The radio emission from supermassive black holes in nearby early-type
galaxies can be used to test possible explanations for their low luminosities.
We calculate the expected contribution from thermal synchrotron emission from
hot accretion flows to the high radio frequency observations of NGC 2300, NGC
1399, NGC 4278 and NGC 4594. We find that, in all cases, and in accordance with
our previous findings, hot flows accreting close to their Bondi rates
overestimate significantly the observed fluxes. This implies that simply
assuming a low radiative efficiency for the accreting gas is not enough to
explain their low luminosities. Smaller central densities and accretion rates,
as expected in the presence of strong mass loss or convection in the flows, can
help reconcile the models with observations. We also show that a significant
contribution to the high-frequency radio spectra can be due to non-thermal
synchrotron emission from the small scale radio jets observed in these systems,
allowing for even lower accretion rates in the inflows. We suggest that these
outflows or jets may dump significant energy into the surronding medium close
to the accretion radius and so reduce the accretion rates onto these systems.
We discuss the relationship between the radio flux and black hole mass for the
observed sample and its potential importance for probing accretion models.


title: Exploring the high frequency emission of radio loud X-ray binaries

abstract:
  We report millimetre-wave continuum observations of the X-ray binaries Cygnus
X-3, SS 433, LSI+61 303, Cygnus X-1 and GRS 1915+105. The observations were
carried out with the IRAM 30 m-antenna at 250 GHz (1.25 mm) from 1998 March 14
to March 20. These millimetre measurements are complemented with centimetre
observations from the Ryle Telescope, at 15 GHz (2.0 cm) and from the Green
Bank Interferometer at 2.25 and 8.3 GHz (13 and 3.6 cm). Both Cygnus X-3 and SS
433 underwent moderate flaring events during our observations, whose main
spectral evolution properties are described and interpreted. A significant
spectral steepening was observed in both sources during the flare decay, that
is likely to be caused by adiabatic expansion, inverse Compton and synchrotron
losses. Finally, we also report 250 GHz upper limits for three additional
undetected X-ray binary stars: LSI+65 010, LSI+61 235 and X Per.


title:
Spectroscopy and Component Masses of the Eclipsing Dwarf Nova
  HS0907+1902

abstract:
  HS0907+1902 was recently discovered to be one of a handful of deeply
eclipsing dwarf novae with periods longward of the 2 -- 3 hr `gap'. This paper
presents orbit-resolved spectra and time series photometry of an eclipse. The
apparent velocity amplitude of the M-dwarf secondary is K_2 = 297 +- 15 km/s.
The phase of the radial velocities of the H-alpha emission line wings agrees
accurately (for once) with the phase of the white-dwarf motion deduced from the
eclipse, and an estimate of the emission-line velocity amplitude yields K1 =
115 +- 7 km/s. The eclipse width is delta-phi = 0.060 +- 0.005. At face value,
these measurements yield mass estimates of M1 = 0.99 +- 0.12 solar masses for
the white dwarf and M2 = 0.38 +- 0.06 solar masses for the secondary. The
eclipse width and nominal mass ratio constrain the binary inclination to be
77.3 +- 0.9 degree. The influence of systematic uncertainties on these values
is discussed; the conclusion that the white dwarf is somewhat more massive than
typical field white dwarfs appears to be robust.
  The H-alpha emission line profile out of eclipse is only slightly
double-peaked, but the line shows a strong rotational disturbance in eclipse.
Models of the line profile through eclipse using a flat, Keplerian disk do not
give a good quantitative match to the observations.


title:
The evolution Equation of Cosmological density perturbation in
  Einstein-Cartan gravity

abstract:
  The evolution equation of linear cosmic density perturbations in the realm of
Einstein-Cartan theory of gravity is obtained.The de Sitter metric fluctuation
is computed in terms of the spin-torsion background density.


title: The Abundance of Interstellar Boron

abstract:
  We use new Space Telescope Imaging Spectrograph (STIS) and archival Goddard
High Resolution Spectrograph (GHRS) observations to study interstellar B II
1362 and O I 1355 absorption along seven sightlines. Our new column density
measurements, combined with measurements of four sightlines from the
literature, allow us to study the relative B/O abundances over a wide range of
interstellar environments. We measure sightline-integrated relative gas-phase
abundances in the range [B/O] = -1.00 to -0.17, and our data show the B/O
abundances are anticorrelated with average sightline densities over the range
log <n_H> ~ -1.3 to +0.7. Detailed comparisons of the B II and O I line shapes
show that the B/O ratio is significantly higher in warm interstellar clouds
than in cool clouds. These results are consistent with the incorporation of
boron into dust grains in the diffuse ISM. Since boron is likely incorporated
into grains, we derive a lower limit to the present-day total (gas+dust)
interstellar boron abundance of B/H > (2.5+/-0.9)x10^-10. The effects of dust
depletion and ionization differences from element to element will make it very
difficult to reliably determine 11B/10B along most interstellar sightlines.


title: What are MACHOs? Interpreting LMC microlensing

abstract:
  I discuss two hypotheses that might explain LMC microlensing: the Halo
stellar remnant lensing hypothesis and the unvirialized LMC lensing hypothesis.
I show that white dwarfs cannot contribute substantially to the cosmic baryon
budget; they are strongly constrained by chemical evolution and background
light measurements. Although there have been some claims of direct optical
detections of white dwarfs in the Halo, I show how the full sample of direct
optical searches for halo lenses do not support the Halo lens hypothesis.
  N-body simulations suggest that the LMC may be naturally excited out of
virial equilibrium by tidal forcing from the Milky Way. New measurements of LMC
kinematics not only do not rule out the unvirialized LMC lensing hypothesis,
but even moderately favor it (at 95% confidence).


title: Star formation in clusters: early sub-clustering in the Serpens core

abstract:
  We present high resolution interferometric and single dish observations of
molecular gas in the Serpens cluster-forming core. Star formation does not
appear to be homogeneous throughout the core, but is localised in spatially-
and kinematically-separated sub-clusters. The stellar (or proto-stellar)
density in each of the sub-clusters is much higher than the mean for the entire
Serpens cluster. This is the first observational evidence for the hierarchical
fragmentation of proto-cluster cores suggested by cluster formation models.


title: Temporal properties of flares in accretion disk coronae

abstract:
  Using a non-linear Monte-Carlo code we investigate the radiative response of
an accretion disk corona system to static homogeneous flares. We model a flare
by a rapid (comparable to the light crossing time) energy dissipation in the
corona or the disk.
  If the flares originate from the disk, the coronal response to the soft
photon shots produces a strongly non-linear Comptonised radiation output, with
complex correlation/anti-correlations between energy bands. This behavior
strongly differs from those found with usual linear calculations.
  Thus any model for the rapid aperiodic variability of X-ray binaries invoking
a varying soft photon input as a source for the hard X-ray variability has to
take into account the coronal temperature response.
  On the other hand, if the flare is due to a violent heating of the corona,
when the perturbation time scale is of the order of a few corona light crossing
times, the shot spectrum evolves from hard to soft.
  This general trend is independent of the shot profile and geometry.
  We show that for short dissipation time, the time averaged spectra are
generally harder than in steady state situation. In addition, annihilation line
and high energy tails can be produced without need for non-thermal processes.


title:
VLA radio continuum observations of a new sample of high redshift radio
  galaxies

abstract:
  We present new deep multi-frequency radio-polarimetric images of a sample of
high redshift radio galaxies (HzRGs), having redshift between 1.7 and 4.1. The
radio data at 4.7 and 8.2 GHz were taken with the Very Large Array in the A
configuration and provide a highest angular resolution of 0.2''. Maps of total
intensity, radio spectral index, radio polarization and internal magnetic field
are presented for each source. The morphology of most objects is that of
standard FRII double radio sources, but several contain multiple hot-spots in
one or both lobes. Compared to similar samples of HzRGs previously imaged,
there is a higher fraction (29%) of compact steep spectrum sources (i.e.
sources with a projected linear size less than 20 kpc). Radio cores are
identified in about half of the sample and tend to have relatively steep
spectra (alpha < -1). Polarization is detected in all but 4 sources, with
typical polarization at 8.2 GHz of around 10-20%. The Faraday rotation can be
measured in most of the radio galaxies: the observed rotation measure (RM) of 8
radio sources exceeds 100 rad m^{-2} in at least one of the lobes, with large
gradients between the two lobes. We find no dependence of Faraday rotation with
other properties of the radio sources. If the origin of the Faraday rotation is
local to the sources, as we believe, then the intrinsic RM is more than a 1000
rad m^{-2}. Because low redshift radio galaxies residing at the center of
clusters usually show extreme RMs, we suggest that the high-z large RM sources
also lie in very dense environments. Finally, we find that the fraction of
powerful radio galaxies with extreme Faraday rotation increases with redshift,
as would be expected if their average environment tends to become denser with
decreasing cosmic epoch.


title: L483: A Protostar In Transition From Class 0 to Class I

abstract:
  We present molecular-line observations toward the dense core in L483 and its
bipolar outflow powered by the Class 0 object IRAS 18148-0440. CO (carbon
monoxide) maps show that the outflow is well collimated and asymmetric, and
that its gas is warmer than the surrounding cloud by at least a factor of 2.
H2CO (formaldehyde) lines toward the outflow show prominent high-velocity wings
and evidence for an H2CO abundance enhancement of a factor of 20. At ambient
velocities, these lines show strong self-absorption and a brighter blue peak, a
characteristic signature of inward motions. Finally, and in contrast with the
outflows from other Class 0 objects, the CH3OH (methanol) lines in L483 do not
show high velocity wings, and no evidence for abundance enhancement is found in
this molecule or in SiO (silicon monoxide). Comparing the physical and chemical
properties of the outflow in L483 with those of other outflows from Class 0 and
Class I sources, we find that the L483 outflow is somewhat intermediate between
these types. This suggests that the L483 central source has already started its
transition between Class 0 and Class I, and that its mixed properties
illustrate how this transition occurs.


title:
A large age for the pulsar B1757-24 from an upper limit on its proper
  motion

abstract:
  The "characteristic age" of a pulsar usually is considered to approximate its
true age, but this assumption has led to some puzzling results, including the
fact that many pulsars with small characteristic ages have no associated
supernova remnants. The pulsar B1757-24 is located just beyond the edge of a
supernova remnant; the properties of the system indicate that the pulsar was
born at the centre of the remnant, but that it has subsequently overtaken the
expanding blast-wave. With a characteristic age of 16,000 yr, this implies an
expected proper motion by the pulsar of 63-80 milliarcsec per year. Here we
report observations of the nebula surrounding the pulsar which limit its proper
motion to less than 25 mas/yr, implying a minimum age of 39,000 yr. A more
detailed analysis argues for a true age as great as 170,000 yr, significantly
larger than the characteristic age. From this result and other discrepancies
associated with pulsars, we conclude that characteristic ages seriously
underestimate the true ages of pulsars.


title:
Synthetic post-Asymptotic Giant Branch evolution: basic models and
  applications to disk populations

abstract:
  We explore the realm of post-Asymptotic Giant Branch (post-AGB) stars from a
theoretical viewpoint, by constructing synthetic population of transition
objects, proto-Planetary Nebulae, Planetary Nebulae Nuclei, and post-Planetary
Nebulae objects. We use the Montecarlo procedure to filter out the populations
accordingly to a given set of assumptions. We explore the parameter space by
studying the effects of the Initial Mass Function (IMF), the Initial Mass-Final
Mass Relation (IMFMR), the transition time (t_tr), the envelope mass at the end
of the envelope ejection (Me_r), the planetary nebula lifetime t_PN, the
hydrogen- and helium-burning phases of the central stars. The results are
discussed on the basis of the HR diagram distributions, on the Mv-t plane, and
with mass histograms. We found that: (1) the dependence of the synthetic
populations on the assumed IMF and IMFMR is generally mild; (2) the Me_r
indetermination produces very high indeterminations on the t_tr and thus on the
resulting post-AGB populations; (3) the synthetic models give a test check for
the ratio of He- to H-burning PNNi. In this paper, disk post-AGB populations
are considered. Future applications will include Magellanic Clouds PNe, and
populations of bulges and elliptical galaxies.


title:
Geometric Conditions on the Type of Matter Determining the Flat Behavior
  of the Rotational Curves in Galaxies

abstract:
  In an arbitrary axisymmetric stationary spacetime, we determine the
expression for the tangential velocity of test objects following a circular
stable geodesic motion in the equatorial plane, as function of the metric
coefficients. Next, we impose the condition, observed in large samples of disks
galaxies, that the magnitude of such tangential velocity be radii independent,
obtaining a constraint equation among the metric coefficients, and thus
arriving to an iff condition: The tangential velocity of test particles is
radii independent iff the metric coefficients satisfied the mentioned
constraint equation. Furthermore, for the static case, the constraint equation
can be easily integrated, leaving the spacetime at the equatorial plane
essentially with only one independent metric coefficient. With the geometry
thus fixed, we compute the Einstein tensor and equate it to and arbitrary
stress energy tensor, in order to determined the type of energy-matter which
could produce such a geometry. Within an approximation, we deduce a constraint
equation among the components of the stress energy tensor. We test in that
constraint equation several well known types of matter, which have been
proposed as dark matter candidates and are able to point for possible right
ones. Finally, we also present the spherically symmetric static case and apply
the mentioned procedure to perfect fluid stress energy tensor, recovering the
Newtonian result as well as the one obtained in the axisymmetric case. We also
present arguments on the need to use GR to study non dust types of matter.


title: Overview of the Far Ultraviolet Spectroscopic Explorer Mission

abstract:
  The Far Ultraviolet Spectroscopic Explorer satellite observes light in the
far-ultraviolet spectral region, 905 - 1187 A with high spectral resolution.
The instrument consists of four coaligned prime-focus telescopes and Rowland
spectrographs with microchannel plate detectors. Two of the telescope channels
use Al:LiF coatings for optimum reflectivity from approximately 1000 to 1187 A
and the other two use SiC coatings for optimized throughput between 905 and
1105 A. The gratings are holographically ruled to largely correct for
astigmatism and to minimize scattered light. The microchannel plate detectors
have KBr photocathodes and use photon counting to achieve good quantum
efficiency with low background signal. The sensitivity is sufficient to examine
reddened lines of sight within the Milky Way as well as active galactic nuclei
and QSOs for absorption line studies of both Milky Way and extra-galactic gas
clouds. This spectral region contains a number of key scientific diagnostics,
including O VI, H I, D I and the strong electronic transitions of H2 and HD.


title: The Nuclear Dynamics of M32. I. Data and Stellar Kinematics

abstract:
  We have obtained optical long-slit spectroscopy of the nucleus of M32 using
the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. The
stellar rotation velocity and velocity dispersion, as well as the full
line-of-sight velocity distribution (LOSVD), were determined as a function of
position along the slit using two independent spectral deconvolution
algorithms. We see three clear kinematical signatures of the nuclear black
hole: a sudden upturn, at ~0.3 arc seconds from the center, in the stellar
velocity dispersions; a flat or rising rotation curve into the center; and
strong, non-Gaussian wings on the central LOSVD. The central velocity
dispersion is ~130 km/s (Gaussian fit) or ~175 km/s (corrected for the wings).
Both the velocity dispersion spike and the shape of the central LOSVD are
consistent with the presence of a supermassive compact object in M32 with a
mass in the range 2-5 x 10^6 solar masses. These data are a significant
improvement on previous stellar kinematical data, making M32 the first galaxy
for which the imprint of the black hole's gravitation on the stellar velocities
has been observed with a resolution comparable to that of gas-dynamical
studies.


title:
On-Orbit Performance of the Far Ultraviolet Spectroscopic Explorer
  (FUSE) Satellite

abstract:
  Launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed
by an extensive period of calibration and characterization as part of the
preparation for normal satellite operations. Major tasks carried out during
this period include initial coalignment, focusing and characterization of the
four instrument channels, and a preliminary measurement of the resolution and
throughput performance of the instrument. We describe the results from this
test program, and present preliminary estimates of the on-orbit performance of
the FUSE satellite based on a combination of this data and prelaunch laboratory
measurements.


title: EUVE Observations of Hercules X-1 During a Short High State Turn-On

abstract:
  Observations of Hercules X-1 by the Extreme Ultraviolet Explorer (EUVE)
covering low state and the early part of the Short High state are reported
here. This is the first EUV observation of this part of the 35-day cycle of Her
X-1. The low state portion of the EUV light curve (prior to the start of the
Short High state) has similar properties as that following the end of the Short
High state (Leahy and Marshall, 1999). This is evidence that the low state EUV
emission is primarily due to EUV reflection from the companion star HZ Her. The
EUV lightcurve during the Short High state is pulsed and closely resembles the
average 2-12 keV X-ray Short High state lightcurve indicating that the EUV
emission, like the X-ray emission, originates near the neutron star. The Short
High state EUV spectrum is consistent with a blackbody of temperature 0.13 keV
and radius 230 km. The Short High state EUV spectrum and pulse shape are
similar to that in the soft X-rays (0.1 - 1 keV). The most likely origin of the
EUV emission is reprocessed X-rays from the inner edge of the accretion disk,
and the radius of the inner edge of the accretion disk is likely to be small,
consistent with that determined from analysis of the X-ray pulse shape
evolution (Scott, Leahy and Wilson, 2000).


title: Inflation with a Planck-scale frequency cutoff

abstract:
  The implementation of a Planck-scale high frequency and short wavelength
cutoff in quantum theories on expanding backgrounds may have potentially
nontrivial implications, such as the breaking of local Lorentz invariance and
the existence of a yet unknown mechanism for the creation of vacuum modes. In
scenarios where inflation begins close to the cutoff scale, these effects could
have observable consequences as trans-Planckian modes are redshifted to
cosmological scales. In close analogy with similar studies of Hawking
radiation, a simple theory of a minimally coupled scalar field in de Sitter
space is studied, with a high frequency cutoff imposed by a nonlinear
dispersion relation. Under certain conditions the model predicts deviations
from the standard inflationary scenario. We also comment on the difficulties in
generalizing fluid models of Hawking radiation to cosmological space-times.


title: An Emission-Line Search for Star-Forming Dwarf Galaxies Toward Abell 851

abstract:
  (Abridged) We present deep, narrow-band images of the redshift 0.41 galaxy
cluster Abell 851 (Cl 0939+4713) which isolate [OII] 3726,29 line emission. The
[OII]-selected galaxies lie within a projected clustercentric distance of 2
Mpc. The sample is complete to magnitude m_{5129}(AB) = 24.0$ for galaxies with
emission-line equivalent widths greater than about 11\angs in the observed
frame. Color, brightness, and equivalent-width criteria are used to identify
foreground interlopers (steep 4000 A break across the filters) and candidates
for Ly-alpha emission at z=3.31. The number density of star-forming galaxies
toward Cl~0939+4713 is three to four times higher than that of a similar column
through the field at z=0.4. Galaxies in the cluster sample have lower [OII]
equivalent widths than similarly selected field galaxies at $z \sim 0.4$
however, and we suggest that while the density of galaxies is higher in the
cluster the star-formation activity in individual galaxies is supressed
relative to their counterparts in the field. The relatively small enhancement
in the surface density of the [OII]-selected population toward the cluster core
leads us to believe the [OII]-selected galaxies reside in the outer regions of
the cluster. We identify a population of starburst galaxies among the
[OII]-emitters based on their blue g-i color. The majority of the
[OII]-selected galaxies appear to be related to the normal spiral galaxy
population, but the bursting population is dominated by intrinsically faint
galaxies of below average size. We suggest that this population is composed
primarily of dwarf galaxies and discuss their relation to the dwarf galaxies in
present day clusters.


title: On the Formation of Massive Stars by Accretion

abstract:
  (Abriged) At present, there are two scenarios for the formation of massive
stars: 1) The accretion scenario and 2) The coalescence scenario, which implies
the merging of intermediate mass stars. We examine here some properties of the
first one. We calculate three different sets of birthlines, i.e. tracks
followed by a continuously accreting star. First, three models with a constant
accretion rate ($\dot{M}_{\rm{accr}}$ = $10^{-6}$, $10^{-5}$, $10^{-4}$
M$_{\odot}$ yr$^{-1}$). Then several birthlines following the accretion models
of Bernasconi and Maeder (\cite{BM96}), which have $\dot{M}_{\rm{accr}}$
increasing only slightly with mass. Finally we calculate several birthlines for
which $\dot{M}_{accr} = \dot{M}_{\mathrm{ref}} ({\frac{M}{M_{\odot}}})
^{\phi}$, with values of $\phi$ equal to 0.5, 1.0 and 1.5 and also for
different values of $\dot{M}_{\mathrm{ref}}$. The best fit to the observations
of PMS stars in the HR diagram is achieved for $\phi$ between 1.0 or 1.5 and
for $\dot{M}_{\mathrm{ref}} \simeq 10^{-5}$ M$_{\odot}$ yr$^{-1}$.
Considerations on the lifetimes favour values of $\phi$ equal to 1.5. These
accretion rates do well correspond to those derived from radio and IR
observations of mass outflows. We emphasize the importance of the accretion
scenario for shaping the IMF, and in particular for determining the upper mass
limit of stars. In the accretion scenario, this upper mass limit will be given
by the mass for which the accretion rate is such that the accretion induced
shock luminosity is of the order of the Eddington luminosity.


title: Spectroscopic confirmation of clusters from the ESO imaging survey

abstract:
  We measure redshifts for 67 galaxies in the field of six cluster candidates
from the ESO Imaging Survey (EIS). The cluster candidates are selected in the
EIS patches C and D among those with estimated mean redshifts between 0.5 and
0.7. The observations were made with EFOSC2 at the 3.6m ESO telescope.
  In the six candidate cluster fields, we identify 19 possible sets of 2 to 7
galaxies in redshift space. In order to establish which of the 19 sets are
likely to correspond to real dense systems we compare our counts with those
expected from a uniform distribution of galaxies with given luminosity
function. In order to take into account the effect of the Large Scale
Structure, we modulate the probability computed from the luminosity function
with random samplings of the Canada-France Redshift Survey.
  We find that four out of six candidate EIS clusters are likely to correspond
to real systems in redshift space (> 95 % confidence level). Two of these
systems have mean redshift in agreement with the redshift estimate given by the
matched filter algorithm. The other two systems have significantly lower
redshifts.
  We discuss the implications of our results in the context of our ongoing
research projects aimed at defining high-redshift optically-selected cluster
samples.


title:
Constraints on Particle Acceleration from the Diffuse Isotropic
  Gamma-Ray Background

abstract:
  Gamma rays trace accelerated particles, and the observed flux of
extragalactic gamma rays therefore constrains the global efficiency for
particle acceleration. Extragalactic jets in active galactic nuclei can account
for the gamma ray background if their particle acceleration efficiency
considerably exceeds ~ 18 per cent which would imply that particle acceleration
is an essential part of the thermodynamics in these sources.


title: Helioseismic determination of Beryllium neutrinos produced in the Sun

abstract:
  We provide a determination of the Beryllium neutrino luminosity directly by
means of helioseismology, without using additional assumptions. We have
constructed solar models where Beryllium neutrino, ($\nu_{Be}$) production is
artificially changed by varying in an arbitrary way the zero energy
astrophysical S-factor $S_{34}$ for the reaction $^3{\rm He}+^4{\rm He}\to
^7{\rm Be}+ \gamma$.
  Next we have compared the properties of such models with helioseismic
determinations of photospheric helium abundance, depth of the convective zone
and sound speed profile. We find that helioseismology directly confirms the
production rate of $\nu_{Be}$ as predicted by SSMs to within $\pm 25%$
($1\sigma$ error). This constraint is somehow weaker than that estimated from
uncertainties of the SSM ($\pm 10%$), however it relies on direct observational
data.


title: Pulsars in the Westerbork Northern Sky Survey

abstract:
  I have searched the Westerbork Northern Sky Survey (WENSS) source list for
detections of known radio pulsars. A source with a flux density greater than
five times the local noise level is found near the positions of 25 pulsars. The
probability that one out of these 25 sources is a chance coincidence is about
10%. I have looked at the WENSS maps of the non-detected pulsars. A flux
density between three and five times the local noise level is found near the
positions of 14 of these non-detected pulsars. There is a 50 percent
probability that (at least) one of these marginal detections is just a noise
fluctuation. Fourteen radio pulsars, which according to earlier flux
measurements have flux densities above three times the WENSS noise level, are
not detected. Of the 39 pulsars detected in the WENSS 19 are also detected in
the NRAO VLA Sky Survey (NVSS). By combining the WENSS and NVSS flux densities
for these 19 pulsars spectral indices are obtained that differ by up to 50%
from the long term averaged values reported in the literature. This affects the
reliability of pulsar candidates that are selected on the basis of their
WENSS-NVSS spectral index.


title: Searches for Quasars at z > 5

abstract:
  Quasars continue to be the most luminous objects known in the universe but
are now rivaled by galaxies for having the largest redshifts. I review current
techniques for finding quasars at z > 5 and the status of current optical
surveys. I compare the spectra of known quasars with z \approx 5 with the
spectra of some recently discovered galaxies with z > 5 to see what we may
expect in the future from surveys for high redshift quasars and galaxies. The
prominent emission lines of quasars should make them easier to detect and
confirm spectroscopically than the z > 5 galaxies discovered so far. An update
section to May, 2000 discusses new discoveries made after the meeting.


title: The flatness of the Universe is robust

abstract:
  We combine the two balloon experiments BOOMERANG and MAXIMA-1 with our
previous fit which used 9 constraints and concluded that the Universe is flat.
The result is that the flatness is robust, $\Omega_0 = 0.97 \pm 0.05$.


title: New exact solutions for inflationary cosmological perturbations

abstract:
  From a general ansatz for the effective potential of cosmological
perturbations we find new, exact solutions in single-scalar-field inflation: a
three parameter family of exact inflationary solutions that encompasses all
exact solutions that have been known previously (power-law inflation, Easther's
model, and a generalised version of Starobinsky's solution). The main feature
of this new family is that the spectral indices are scale dependent.


title: Tracking Extended Quintessence

abstract:
  We study the cosmological role of a Tracking Field $\phi$ in Extended
Quintessence scenarios (TEQ), where the dynamical vacuum energy driving the
acceleration of the universe today is coupled with the Ricci scalar, $R$, with
a term of the form $F(\phi)R/2$, where $F(\phi) = 1/8\pi
G+\xi(\phi^{2}-\phi_{0}^{2})$. Tracker solutions for these NMC models, with
inverse power-law potentials, possess an initial enhancement of the scalar
field dynamics, named $R$-boost, caused by the Ricci scalar in the Klein-Gordon
equation. During this phase the field performs a "gravitational" slow rolling
which we model analytically, with energy density scaling as $(1+z)^{2}$. We
evolve linear perturbations in TEQ models assuming Gaussian scale-invariant
initial spectrum. We obtain significant changes in the Integrated Sachs Wolfe
effect and in the acoustic peaks locations on the Cosmic Microwave Background,
as well as in the turnover on the matter power spectrum. All these corrections
may assume positive as well as negative values, depending on the sign of the
NMC parameter $\xi$. We give analytical formulas describing all these effects.
We show that they can be as large as $10 - 30%$ with respect to equivalent
cosmological constant and ordinary tracking Quintessence models, respecting all
the existing experimental constraints on scalar-tensor theories of gravity.
These results demonstrate that the next decade data will provide deep
constraints on the nature of the dark energy in the Universe, as well as the
structure of the theory of gravity.


title: Two Ways of Biasing Galaxy Formation

abstract:
  We calculate the galaxy bispectrum in both real and redshift space adopting
the most common prescriptions for local Eulerian biasing and Lagrangian
evolving-bias model. We show that the two biasing schemes make measurably
different predictions for these clustering statistics. The Eulerian
prescription implies that the galaxy distribution depends only on the
present-day local mass distribution, while its Lagrangian counterpart relates
the current galaxy distribution to the mass distribution at an earlier epoch
when galaxies first formed. Detailed measurement of the galaxy bispectrum (of
its reduced amplitude) can help establish whether galaxy positions are
determined by the current mass distribution or an earlier mass distribution.


title: UV excess galaxies: Wolf-Rayet galaxies

abstract:
  We discuss V and R band photometry for 67% of the Sullivan et al. 2000 SA57
ultraviolet-selected galaxy sample. In a sample of 176 UV-selected galaxies,
Sullivan et al. 2000 find that 24% have (UV-B) colors too blue for consistency
with starburst spectral synthesis models. We propose that these extreme blue,
UV excess galaxies are Wolf-Rayet (WR) galaxies, starburst galaxies with strong
UV emission from WR stars. We measure a median (V-R)=0.38+-0.06 for the
UV-selected sample, bluer than a sample optically selected at R but consistent
with starburst and WR galaxy colors. We demonstrate that redshifted WR emission
lines can double or triple the flux through the UV bandpass at high redshifts.
Thus the (UV-B) color of a WR galaxy can be up to 1.3 mag bluer at high
redshift, and the expected selection function is skewed to larger redshifts.
The redshift distribution of the extreme blue, UV excess galaxies matches the
selection function we predict from the properties of WR galaxies.


title: Cosmic Intelligence and Black Holes

abstract:
  The paper is devoted to a new direction in SETI. After a general discussion
of the field, the authors put forth the hypothesis that the black holes may
serve as a physical substratum for intelligent beings. This hypothesis is based
on four parallels between the brain-psyche system, on the one hand, and black
holes, on the other. (1) The descriptions of brain and psyche, in the system
brain-psyche, are complementary to each other, as descriptions by internal and
external observers of a black hole in Susskind-t'Hooft's schema. (2) There is
an aspect of the inner structure of a black hole in Kerr's model of the
rotating black hole that is isomorphic to the structure of the human subjective
domain in the psychological model of reflexion. (3) Both black holes and the
brain-psyche system have a facet which can be represented using thermodynamic
concepts. (4) The brain lends itself to a holographic description; as has been
recently demonstrated by Susskind, black holes can also be described
holographically. The authors speculate that the intelligent black holes can
generate other black holes by triggering creation of massive stars from which
new black holes arise after the stars' collapse. In addition, the authors
analyze certain strange phenomena related to the birth of young massive stars
which may or may not be connected with such a triggering.


title: A catalogue of symbiotic stars

abstract:
  We present a new catalogue of symbiotic stars. In our list we include 188
symbiotic stars as well as 28 objects suspected of being symbiotic. For each
star, we present basic observational material: coordinates, V and K magnitudes,
ultraviolet (UV), infrared (IR), X-ray and radio observations. We also list the
spectral type of the cool component, the maximum ionization potential observed,
references to finding charts, spectra, classifications and recent papers
discussing the physical parameters and nature of each object. Moreover, we
present the orbital photometric ephemerides and orbital elements of known
symbiotic binaries, pulsational periods for symbiotic Miras, Hipparcos
parallaxes and information about outbursts and flickering.


title:
Discovery of 424 ms pulsations from the radio-quiet neutron star in the
  PKS 1209-52 supernova remnant

abstract:
  The central source of the supernova remnant PKS 1209-52 was observed with the
Advanced CCD Imaging Spectrometer aboard Chandra X-ray observatory on 2000
January 6-7. The use of the Continuos Clocking mode allowed us to perform the
timing analysis of the data with time resolution of 2.85 ms and to find a
period P=0.42412927+/-2.3e-7 s. The detection of this short period proves that
the source is a neutron star. It may be either an active pulsar with
unfavorably directed radio beam or a truly radio-silent neutron star whose
X-ray pulsations are caused by a nonuniform distribution of surface
temperature. To infer the actual properties of this neutron star, the period
derivative should be measured.


title:
On the Optical Light Curves of Afterglows from Jetted Gamma-ray Burst
  Ejecta: Effects of Parameters

abstract:
  Due to some refinements in the dynamics, we can follow the overall evolution
of a realistic jet numerically till its bulk velocity being as small as $\beta
c \sim 10^{-3} c$. We find no obvious break in the optical light curve during
the relativistic phase itself. However, an obvious break does exist at the
transition from the relativistic phase to the non-relativistic phase, which
typically occurs at time $t \sim 10^6$ --- $10^{6.5}$ s (i.e., 10 --- 30 d).
The break is affected by many parameters, such as the electron energy fraction
$\xi_{\rm e}$, the magnetic energy fraction $\xi_{\rm B}^2$, the initial half
opening angle $\theta_0$, and the medium number density $n$. Increase of any of
them to a large enough value will make the break disappear. Although the break
itself is parameter-dependent, afterglows from jetted GRB remnants are
uniformly characterized by a quick decay during the non-relativistic phase,
with power law timing index $\alpha \geq 2.1$. This is quite different from
that of isotropic fireballs, and may be of fundamental importance for
determining the degree of beaming in $\gamma$-ray bursts observationally.


title: Merging neutron stars: asymmetric systems

abstract:
  Results of 3D, Newtonian hydrodynamic calculations of the last stages of the
inspiral and the final coalescence of neutron star binary systems are
described. The focus is on sligthly asymmetric systems with the asymmetry
stemming either from different spins or different masses of the binary
components. Implications for nucleosynthesis and gamma ray bursts are
discussed. Test calculations for the used viscosity scheme are provided in the
appendix.


title:
Towards global-phase-delay VLBI astrometry: observations of QSO 1150+812
  and BL 1803+784

abstract:
  On 18 November 1993, we observed the QSO 1150+812 and the BL Lac object
1803+784, nearly 15\deg apart on the sky, with a VLBI array, simultaneously
recording at 8.4 and 2.3 GHz. Using difference astrometry techniques, we
determined the coordinates of 1803+784 relative to those of 1150+812 to be
\Delta\alpha = 6h 7m 33.18469 arcsec +- 0.00020 arcsec \Delta\delta = -2deg 30'
25''.13557 +- 0''.00075 These standard errors contain estimated contributions
from the propagation medium, the effects of source opacity, and the possible
misidentification of the reference point in some of the maps. We obtained
comparably accurate and consistent relative positions of the radio sources with
GPS-based ionosphere corrections, thus demonstrating that dual-frequency
observations are not required for state-of-the-art accuracy in VLBI astrometry.
These results also demonstrate the feasibility of using single-frequency
measurements for sources separated by 15$^\circ$ on the sky, and open the
avenue for the application of this technique on a full-sky scale.


title: ISO detection of a 60micron source near GRB970508

abstract:
  The Infrared Space Observatory observed the field of the $\gamma$--ray burst
GRB 970508 with the CAM and PHT instruments on May 21 and 24, 1997 and with PHT
in three filters in November 1997. A source at 60 $\mu$m (flux in May of $66\pm
10$ mJy) was detected near the position of the host galaxy of this
$\gamma$--ray burst. The source was detected again in November 1997, at a
marginally lower flux ($43\pm 13$ mJy). A Galactic cirrus origin and a stellar
origin for the emission can be ruled out on the basis of the infrared colours.
The marginal evidence for variability in the 60 $\mu$m flux between May and
November is not sufficient to warrant interpretation of the source as transient
fireball emission. However, the infrared colours are physically reasonable if
attributed to conventional dust emission from a single blackbody source. The
probability of detecting a 60 $\mu$m by chance in a PHT beam down to a
detection limit of 50 mJy is $\sim 5\times 10^{-3}$. If the source is at the
redshift of the host galaxy of the $\gamma$--ray burst the fluxes and upper
limits at wavelengths from 12 $\mu$m to 170 $\mu$m indicate it is an
ultraluminous infrared galaxy (L$_{\rm ir} \sim 2\times 10^{12}$ L$_{\sun}$).
The star formation rate is estimated to be several hundred solar masses per
year, depending significantly on model-dependent parameters. If this source is
associated with the host galaxy of GRB 970508, progenitor models which
associate GRBs with star-forming regions are favoured.


title:
A Measurement of the Temperature-Density Relation in the Intergalactic
  Medium Using a New Lyman-alpha Absorption Line Fitting Method

abstract:
  The evolution of the temperature in the intergalactic medium is related to
the reionization of hydrogen and helium, and has important consequences for our
understanding of the Lya forest and of galaxy formation in gravitational models
of large-scale structure. We measure the temperature-density relation of
intergalactic gas from Lya forest observations of eight quasar spectra with
high resolution and signal-to-noise ratio, using a new line fitting technique
to obtain a lower cutoff of the distribution of line widths from which the
temperature is derived. We carefully test the accuracy of this technique to
recover the gas temperature with a hydrodynamic simulation. The temperature at
redshift z=(3.9, 3.0, 2.4) is best determined at densities slightly above the
mean: T_star=(20200\pm2700, 20200\pm1300, 22600\pm1900)K (statistical error
bars) for gas density (in units of the mean density) Delta_star=(1.42\pm0.08,
1.37\pm0.11, 1.66\pm0.11). The power-law index of the temperature-density
relation, defined by T=T_star(Delta/Delta_star)^{gamma-1}, is gamma-1=
(0.43\pm0.45, 0.29\pm0.30, 0.52\pm0.14) for the same three redshifts. The
temperature at the fixed over-density Delta=1.4 is T_1.4=(20100\pm2800,
20300\pm1400, 20700\pm1900)K. These temperatures are higher than expected for
photoionized gas in ionization equilibrium with a cosmic background, and can be
explained by a gradual additional heating due to on-going HeII reionization.
The measurement of the temperature reduces one source of uncertainty in the
lower limit to the baryon density implied by the observed mean flux decrement.
We find that the temperature cannot be reliably measured for under-dense gas,
because the velocities due to expansion always dominate the widths of the
corresponding weak lines.


title:
Implications of the cosmic infrared background for light production and
  the star formation history in the Universe

abstract:
  The Cosmic Background due to the integrated radiation from galaxies over the
whole life of the Universe is reviewed. We find that this background is well
constrained by measurements. The total power in the background is in the range
60-93 nW/m2/sr. The data show the existence of a minimum separating the direct
stellar radiation from the infrared part due to radiation reemitted by dust.
This reemitted dust radiation is about 1-2.6 time the background power in the
optical/near-IR thus much larger than the same ratio measured locally (30%).
The far-infrared and submillimeter background is likely to be dominated by
redshifted infrared galaxies. The long wavelength spectrum of the background
being significantly flatter than the spectrum of these galaxies it strongly
constrains the far-infrared radiation production rate history which must
increase by a factor larger than 10 between the present time and a redshift 1
and then stays rather constant at higher redshift, contrary to the ultraviolet
radiation production rate which decreases rapidly.
  Several models of galaxy evolution have been proposed to explain the
submillimeter background. In this paper we do not propose a new model; we
systematically explore the allowed range of evolution histories allowed by the
data. If infrared galaxies are mostly powered by starbursts as indicated by
recent observations, this infrared production history reflects the history of
starbursts in the Universe.


title: Zinc as a tracer of metallicity evolution of Damped Lyman alpha systems

abstract:
  Zinc is a good indicator of metallicity in Damped Lyman alpha (DLA) systems
because it is almost unaffected by dust depletion. However, the use of zinc as
a tracer of metallicity evolution has been hampered by the difficulty of
detecting the Zn II resonance lines at high redshift. The measurement of zinc
abundance in a DLA system at z_abs > 3 obtained by means of the UVES
spectrograph at the VLT prompted us to re-analyse the full sample of zinc
abundances present in the literature to search for a metallicity-redshift
relation in DLA systems. The study of the metallicities of individual systems
shows evidence for an anti-correlation between [Zn/H] and redshift supported by
different types of statistical tools. The zinc metallicity decreases by -0.3
+/- 0.1 dex per unit redshift interval in the range 0.5 <~ z_abs <~ 3.5. This
rate is in good agreement with that found by Savaglio, Panagia & Stiavelli
(2000) in their recent study of DLA abundances corrected for dust depletion.
The present result does not require a knowledge of the dust depletion
pattern(s) in DLA systems. On the other hand, the analysis of the
column-density weighted metallicity of the sample, <Z>, does not show a clear
evidence for redshift evolution, consistent with previous studies of zinc
abundances. We propose that the apparent lack of evolution of <Z> is due to the
combination of selection bias effects together with the extreme sensitivity of
<Z> to low-number statistics.


title:
Effects of Luminosity Functions Induced by Relativistic Beaming on
  Statistics of Cosmological Gamma-Ray Bursts

abstract:
  We study the effects of the beaming-induced luminosity function on statistics
of observed GRBs, assuming the cosmological scenario. We select and divide the
BATSE 4B data into 588 long bursts (T$_{90}>2.5$ sec) and 149 short bursts
(T$_{90}<2.5$ sec), and compare the statistics calculated in each subgroup. The
$<V/V_{\rm max}>$ of the long bursts is $ 0.2901\pm 0.0113$, and that of the
short bursts is $0.4178\pm 0.0239$, which is a Euclidean value. For luminosity
function models, we consider a cylindrical-beam and a conic-beam. We take into
account the spatial distribution of GRB sources as well. A broad luminosity
function is naturally produced when one introduces beaming of GRBs. We
calculate the maximum detectable redshift of GRBs, $z_{\rm max}$. The estimated
$z_{\rm max}$ for the cylindrical-beam case is as high as $\sim 14$ for the
long bursts and $\sim 3$ for the short bursts. The large $z_{\rm max}$ value
for the short bursts is rather surprising in that the $<V/V_{\rm max}>$ for
this subgroup is close to the so-called Euclidean value, 0.5. We calculate the
fraction of bursts whose redshifts are larger than a certain redshift $z'$,
i.e. $f_{\rm > z'}$. When we take $z'=3.42$ and apply the luminosity function
derived for the cylindrical-beam, the expected $f_{\rm > z'}$ is $\sim 75 %$
for long bursts. When we increase the opening angle of the conic beam to
$\Delta \theta =3^\circ.0$, $f_{\rm > z'}$ decreases to $\sim 20 %$ at $ {\rm
z'=3.42}$. We conclude that the beaming-induced luminosity functions are
compatible with the redshift distribution of observed GRBs and that the
apparent Euclidean value of $<V/V_{\rm max}>$ may not be due to the Euclidean
space distribution but to the luminosity distribution.


title:
Evolutionary models for very-low-mass stars and brown dwarfs with dusty
  atmospheres

abstract:
  We present evolutionary calculations for very-low-mass stars and brown dwarfs
based on synthetic spectra and non-grey atmosphere models which include dust
formation and opacity, i.e. objects with $\te\simle 2800$ K. The interior of
the most massive brown dwarfs is shown to develop a conductive core after $\sim
2$ Gyr which slows down their cooling. Comparison is made in optical and
infrared color-magnitude diagrams with recent late-M and L-dwarf observations.
The saturation in optical colors and the very red near-infrared colors of these
objects are well explained by the onset of dust formation in the atmosphere.
Comparison of the faintest presently observed L-dwarfs with these dusty
evolutionary models suggests that dynamical processes such as turbulent
diffusion and gravitational settling are taking place near the photosphere. As
the effective temperature decreases below $\te\approx 1300-1400$ K, the colors
of these objects move to very blue near-infrared colors, a consequence of the
ongoing methane absorption in the infrared. We suggest the possibility ofa
brown dwarf dearth in $J,H,K$ color-magnitude diagrams around this temperature.


title:
Large-Scale Power Spectrum and Structures From the ENEAR galaxy Peculiar
  Velocity Catalog

abstract:
  We estimate the mass density fluctuations power spectrum (PS) on large scales
by applying a maximum likelihood technique to the peculiarvelocity data of the
recently completed redshift-distance survey of early-type galaxies (ENEAR). The
general results are in agreement with the high amplitude power spectra found
from similar analysis of other independent all-sky catalogs of peculiar
velocity data such as MARK III and SFI. For Lambda & Open CDM COBE normalized
PS models, the best-fit parameters are confined by a contour approximately
defined by Omega h^{1.3}=0.377+-0.08 and Omega h^{0.88}=0.517+-0.083,
respectively. Gamma-shape models, free of COBE normalization, resultsin the
weak constraint of $\Gamma \geq 0.17$ and in the rather stringent constraint of
sigma_8 Omega^{0.6}=1.0+-0.25. All quoted uncertainties refer to 3-sigma
confidence-level. The calculated PS is used as a prior for Wiener
reconstruction of the density field at different resolutions and the
three-dimensional velocity field within a volume of radius ~80 Mpc/h. All major
structures in the nearby universe are recovered and are well matched to those
predicted from all-sky redshift surveys.


title: Chandra Detection of an X-ray Flare from the Brown Dwarf LP 944-20

abstract:
  We have detected a bright X-ray flare from the nearby brown dwarf LP 944-20
with the Chandra/ACIS-S. This is an old (500 Myr), rapidly rotating,
lithium-bearing M9 object, with a bolometric luminosity of 6e29 ergs cm-2 s-1.
It was only detected by Chandra during an X-ray flare of duration 1-2 hours
near the end of a 12.1 hour observation. The peak X-ray luminosity was
1.2(+0.5/-0.3)e26 ergs cm-2 s-1 in the brightest ~550 seconds, corresponding to
Lx/Lbol ~ 2e-4. A total of 2e29 ergs was released during the 43,773 sec
observation, giving a time-averaged Lx/Lbol ~ 7e-6. LP 944-20 was not detected
before the flare, with a 3 sigma upper limit on the emission at Lx/Lbol < 2e-6
(Lx<1e24 ergs cm-2 s-1). This is faint for a rapidly rotating late-type star,
and establishes a record lower limit to the quiescent flux about an order of
magnitude below the flux limit (and a factor of 5 below the Lx/Lbol limit)
placed on quiescent X-ray emission from the M8 dwarf VB 10. The inferred
flaring duty cycle is comparable to that measured via variable H-alpha emission
for other late M-type, fully convective stars.


title: Mapping the X-ray Emitting Ejecta in Cassiopeia A with Chandra

abstract:
  We present X-ray emission line equivalent width images of the bright Galactic
supernova remnant Cassiopeia A for the elements Si, S, Ar, Ca, and Fe using a
50,000 s observation with the Advanced CCD Imaging Spectrometer on the Chandra
X-ray Observatory. The images essentially identify the bulk of detectable
ejecta of these elements over a wide range of surface brightness, and show
morphologies distinctly different from that of the broadband X-ray emission and
of the 4-6 keV continuum emission. The Si, S, Ar, and Ca maps, while different
in turn from those of Fe, show that these X-ray emitting ejecta are distributed
similarly to the fast optical ejecta knots, and clearly delineate the X-ray
counterpart of the northeast optical jet. Low surface brightness regions just
outside the bright shell in the north and west are also shown to have strong
line emission. The strong Fe emission is exterior to that of other elements in
the east, as previously noted, but is generally coincident elsewhere. The
projected interior has relatively little emission traced by high line
equivalent widths.


title: Glitches in Southern Pulsars

abstract:
  Timing observations of 40 mostly young pulsars using the ATNF Parkes radio
telescope between 1990 January and 1998 December are reported. In total, 20
previously unreported glitches and ten other glitches were detected in 11
pulsars. These included 12 glitches in PSR J1341$- $6220, corresponding to a
glitch rate of 1.5 glitches per year. We also detected the largest known
glitch, in PSR J1614$-$5047, with $\Delta\nu_g/\nu \approx 6.5 \times 10^{-6}$
where $\nu = 1/P$ is the pulse frequency. Glitch parameters were determined
both by extrapolating timing solutions to inter-glitch intervals and by
phase-coherent timing fits across the glitch(es). Analysis of glitch
parameters, both from this work and from previously published results, shows
that most glitches have a fractional amplitude $\Delta\nu_g/\nu$ of between
$10^{-8}$ and $10^{-6}$. There is no consistent relationship between glitch
amplitude and the time since the previous glitch or the time to the following
glitch, either for the ensemble or for individual pulsars. As previously
recognised, the largest glitch activity is seen in pulsars with ages of order
10$^4$ years, but for about 30 per cent of such pulsars, no glitches were
detected in the 8-year data span. There is some evidence for a new type of
timing irregularity in which there is a significant increase in pulse frequency
over a few days, accompanied by a decrease in the magnitude of the slowdown
rate. Fits of an exponential recovery to post-glitch data show that for most
older pulsars, only a small fraction of the glitch decays. In some younger
pulsars, a large fraction of the glitch decays, but in others, there is very
little decay.


title: How Galaxies Disguise Their Ages

abstract:
  We calculate the contribution to Balmer line indices from far ultraviolet
component sources. We find that this is significant, and may lead to
identification of spurious age differences of the order of a total span of
$\sim 6$ Gyrs or $\sim 15%$ size bursts observed a few Gyrs after star
formation stops. We suggest that claims for intermediate age populations in
early-type galaxies may need to be reconsidered in the light of this new
evidence.


title: Cirrus spectra of low surface brightness regions

abstract:
  We have studied the galactic cirrus in low surface brightness regions using
ISOPHOT raster maps at 90, 150 and 180um. Observations are used to determine
dust emission spectra and dust temperatures. The data extend to longer
wavelengths than IRAS observation. Compared with DIRBE data the resolution and
the sensitivity are better and this makes it possible to study faint cirrus
emission in individual fields.
  We will discuss the calibration of the observations and present results of a
comparison between ISOPHOT and DIRBE surface brightness values. The
correspondence was found to be better than 30%. At 90um the ISOPHOT surface
brightnesses tend to be slightly higher than the DIRBE values while at longer
wavelength the situation is reversed.
  Surface brightness variations caused by cirrus fluctuations make it possible
to determine the spectrum of the dust emission. Cirrus spectra were obtained
for six fields with surface brightnesses in the range 1-2 MJy/sr after the
Zodiacal light and the contribution of extragalactic sources have been
subtracted. Assuming f^2 emissivity law the dust temperatures are in the range
18-20 K. Temperature variations can be seen even within individual fields.
These values are higher than values from DIRBE but this can be explained by
differences in the calibration.


title: ISOPHOT CIRB project: FIR source counts at 90, 150 and 180 um

abstract:
  Far-infrared maps obtained with ISOPHOT have been searched for point-like
sources. The majority of the 55 sources is believed to be extragalactic and in
most cases no previously known sources can be associated with them. Based on
the far-infrared spectral energy distributions it is likely that
dust-enshrouded, distant galaxies form a significant fraction of the sources.
  We estimate the number densities of extragalactic sources at 90, 150 and 180
um wavelengths and at flux density levels down to 100 mJy. The counts are
compared with models of galaxy evolution. The counts exceed the predictions of
current models, even those with strong evolution, and no-evolution models are
rejected at a high confidence level.
  Comparison with recent results from COBE mission indicates that at 90 um the
detected sources correspond to over 20% of the extragalactic background light.
At longer wavelengths the corresponding fraction is 10%.


title: Unusual quiescent X-ray activity from XTE J0421+560 (CI Cam)

abstract:
  We report on BeppoSAX observations of the X-ray transient XTE J0421+560 in
quiescence 156, 541, and ~690 days after the maximum of the 1998 April
outburst. In the first observation the source was soft with a power-law photon
index of 4.0 (+1.9 -0.9) and absorption, NH, of (1.1 +4.9 -1.1) X 10^21
atom/cm2. In the second observation, the source brightened by a factor ~15 in
the 1-10 keV energy range, became significantly harder with a photon index of
1.86 (+0.27 -0.32) and was strongly absorbed with NH = (4.0 +/- 0.8) X 10^23
atom/cm2. There is evidence for a narrow emission line in both spectra at \~7
keV. In the third observation, the source had faded by a factor ~$8 from the
previous observation to below the BeppoSAX detection level. It is possible that
these variations result from orbital motion of a compact object around the B[e]
star companion with the intense, absorbed, spectrum arising during passage
through dense circumstellar material. If this is the case, the system may be
continuing to exhibit periodic activity.