title:
Large-Scale Structures behind the Southern Milky Way in the Great
  Attractor Region

abstract:
  A deep optical galaxy search behind the southern Milky Way and a subsequent
redshift survey of the identified obscured galaxies traces clusters and
superclusters into the deepest layers of Galactic foreground extinction (A_B <=
3^m - 5^m). In the Great Attractor region, we have identified a low-mass
cluster (the Centaurus-Crux cluster) at (l, b, v, sigma) = (305.5deg, +5.5deg,
6214 km/s, 472 km/s) and found that ACO 3627 (the Norma cluster) at (l, b, v,
sigma) = (325.3deg, -7.2deg, 4844 km/s, 848 km/s) is the most massive cluster
in the Great Attractor region known to date. It is comparable in virial mass,
richness and size to the well-known but more distant Coma cluster. The Norma
cluster most likely marks the bottom of the potential well of the Great
Attractor. It is located at the intersection of two main large-scale
structures, the Centaurus Wall and the Norma supercluster. The flow field
observed around the Great Attractor probably is caused by the confluence of
these two massive structures.


title: X-Ray Observation of the L1157 Dark Cloud Region with ASCA

abstract:
  ASCA observation of a region containing a Class 0 protostar, IRAS 20386+6751
in the L1157 dark cloud, has been carried out. The protostar was not detected,
and the 95% upper limit to the luminosity depends on assumed Nh : Lx(0.5-10
keV) < 1.1e31 erg/s for Nh = 1e23 cm^-2. A Class I protostar in L1152, IRAS
20353+6742, in the same field was also undetected with the upper limit about
three times as much as the L1157 level. Besides these non detections, nine new
X-ray sources were detected and spectral analysis was performed for 4 sources.
One object (AXJ 2038+6801) shows a hard spectrum with a temperature kT = 8 keV
or a power-law photon index = 2.0 and absorbed with Nh = 2e22 cm^-2. Another
fainter one (AXJ 2036+6800) has a soft spectrum with most of the emission
falling below 2 keV. We examine possible nature of these new X-ray sources
based on their spectral properties.


title:
High-Resolution Spectroscopy from 3050 to 10000 A of the HDF-S QSO
  J2233-606 with UVES at the ESO VLT

abstract:
  We report on high-resolution observations ($\Re \simeq 45000$) of the Hubble
Deep Field South QSO J2233-606 obtained with the VLT UV-Visual Echelle
Spectrograph (UVES). We present spectral data for the wavelength region $3050 <
\lambda < 10000$ \AA. The $S/N$ ratio of the final spectrum is about 50 per
resolution element at 4000 \AA, 90 at 5000 \AA, 80 at 6000 \AA, 40 at 8000 \AA.
Redshifts, column densities and Doppler widths of the absorption features have
been determined with Voigt-profile fitting. A total of 621 lines have been
measured. In particular 270 Ly-alpha lines, 41 Ly-beta and 24 systems
containing metal lines have been identified. Together with other data in the
literature, the present spectrum confirms that the evolution of the number
density of Ly-alpha lines with $\log N($\huno$) > 14$ has an upturn at $z \sim
1.4-1.6$.


title:
VLBA observations of SiO masers: Arguments in favor of radiative pumping
  mechanisms

abstract:
  We have performed VLBA observations of the SiO v=1 and v=2 J=1-0 masers in
two AGB stars, TX Cam and IRC +10011. We confirm the ring-like spatial
distribution, previously found in several AGB objects, as well as the
tangential polarization pattern, already reported for TX Cam. Both properties,
that seem to be systematic in this kind of objects, are characteristic of
radiatively pumped SiO masers. On the contrary, we do not confirm the previous
report on the spatial coincidence between the J=1-0 v=1 and 2 masers, a result
that would have argued in favor of collisional pumping. We find that both lines
sometimes arise from nearby spots, typically separated by 1-2 mas, but are
rarely coincident. The discrepancy with previous results is explained by the
very high spatial resolution of our observations, ~ 0.5 mas, an order of
magnitude better than in the relevant previously published experiment.


title: Detection limits in space-based transit observations

abstract:
  From simulations of transit observations, it is found that the detectability
of extrasolar planets depends only on two parameters: The signal-to-noise ratio
during a transit, and the number of data points observed during transits. All
other physical parameters describing transit configurations (planet and star
size, orbital period, orbital half axis, latitude of the transit across star)
can be reduced to these two parameters. In turn, once the dependency between
transit detectability and these two parameters has been determined, predictions
for an instrument's ability to detect transits by any combination of physical
parameters can be derived with ease. These predictions are applied to the
Eddington proposal of a combined Astroseismology/Transit-detection space
mission currently under study by ESA, which is described briefly.


title: Properties of the double beta model for intracluster gas

abstract:
  We present an extensive study of the double beta model for the X-ray surface
brightness profiles of clusters, and derive analytically the gas density and
total masses of clusters under the hydrostatic equilibrium hypothesis. It is
shown that the employment of the double beta model instead of the conventional
single beta model can significantly improve the goodness of fit to the observed
X-ray surface brightness profiles of clusters, which will in turn lead to a
better determination of the gas and total mass distributions in clusters. In
particular, the observationally fitted beta parameter for the extended
component in a double beta model may become larger. This opens a new
possibility of resolving the long-standing beta discrepancy for clusters. Using
an ensemble of 33 ROSAT PSPC observed clusters drawn from the Mohr, Mathiesen &
Evrard (1999) sample, we find that the asymptotic value of beta_{fit} is
(0.83+-0.33) at large radii, consistent with both the average spectroscopic
parameter beta_{spec}=(0.78+-0.37) and the result given by numerical
simulations.


title:
Linear dynamics of the solar convection zone: excitation of waves in
  unstably stratified shear flows

abstract:
  In this paper we report on the nonresonant conversion of convectively
unstable linear gravity modes into acoustic oscillation modes in shear flows.
The convectively unstable linear gravity modes can excite acoustic modes with
similar wave-numbers. The frequencies of the excited oscillations may be
qualitatively higher than the temporal variation scales of the source flow,
while the frequency spectra of the generated oscillations should be
intrinsically correlated to the velocity field of the source flow. We
anticipate that this nonresonant phenomenon can significantly contribute to the
production of sound waves in the solar convection zone.


title:
Possible Discrimination between Gamma Rays and Hadrons using Cerenkov
  Photon Timing Measurements

abstract:
  Atmospheric \v{C}erenkov Technique is an established methodology to study
$TeV$ energy gamma rays. However the challenging problem has always been the
poor signal to noise ratio due to the presence of abundant cosmic rays. Several
ingenious techniques have been employed to alleviate this problem, most of
which are centred around the \v{C}erenkov image characteristics. However there
are not many techniques available for improving the signal to noise ratio of
the data from wavefront sampling observations. One such possible technique is
to use the \v{C}erenkov photon arrival times and identify the species dependent
characteristics in them. Here we carry out systematic monte carlo simulation
studies of the timing information of \v{C}erenkov photons at the observation
level. We have parameterized the shape of the \v{C}erenkov shower front as well
as the pulse shapes in terms of experimentally measurable quantities. We
demonstrate the sensitivity of the curvature of the shower front, pulse shape
parameters as well as the photon arrival time jitter to primary species and
show their efficiency in improving the signal to noise ratio. The effect of
limiting the \v{C}erenkov telescope opening angle by using a circular focal
point mask, onthe efficacy of the parameters has also been studied for each of
the parameters. Radius of the shower front, pulse decay time and photon arrival
time jitter have been found to be the most promising parameters which could be
used to discriminate $\gamma -$ray events from the background. We also find
that the efficiency of the first two parameters increases with zenith angle and
efficiency of pulse decay time decreases with increasing altitude of
observation.


title: Weakly Self-Interacting Dark Matter and the Structure of Dark Halos

abstract:
  We study the formation of dark halos in a $\Lambda$CDM universe under the
assumption that Cold Dark Matter particles have a finite cross-section for
elastic collisions. We compare evolution when CDM mean free paths are
comparable to halo sizes with the collisionless and fluid limits. We show that
a few collisions per particle per Hubble time at halo centre can substantially
affect the central density profile. Cross-sections an order of magnitude larger
produce sufficient relaxation for rich clusters to develop core radii in the
range 100-200 $h^{-1}$kpc. The structural evolution of halos is a competition
between collisional relaxation caused by individual particle interactions and
violent relaxation resulting from the infall and merging processes by which
clusters grow. Although our simulations concentrate on systems of cluster size,
we can scale our results to address the halo structure expected for dwarf
galaxies. We find that collision cross-sections sufficiently large to
significantly modify the cores of such galaxies produce cluster cores which are
too large and/or too round to be consistent with observation. Thus the simplest
model for self-interacting dark matter is unable to improve fits to published
dwarf galaxy rotation curves without violating other observational constraints.


title:
Inner edge of neutron-star crust with SLy effective nucleon-nucleon
  interactions

abstract:
  The boundary between the solid crust, assumed to be in complete thermodynamic
equilibrium (cold catalyzed matter), and the liquid core of a neutron star is
studied using Skyrme SLy effective N-N interactions. An approximate value of
the density at the inner edge of the crust is obtained from the threshold for
the instability of homogeneous $npe$ matter with respect to small periodic
density perturbations. Calculations of the bottom layer of the crust are
performed within the Compressible Liquid Drop Model. Spherical nuclei are
energetically preferred over exotic ones (cylinders, plates, tubes, bubbles),
down to the inner edge of the crust, found at the density 0.08 fm^{-3}.


title: Reconstructing the ZOA from Galaxy Peculiar Velocities

abstract:
  Galaxy peculiar velocity data provide important dynamical clues to the
structures obscured by the Zone of Avoidance (hereafter, ZOA) with resolution
>~ 500km/s. This indirect probe complements the very challenging approach of
directly mapping of the distribution of galaxies behind the Milky Way. In this
work, the Wiener filter method is applied to reconstruct the 3D density and
velocity distributions of the universe, within ~8000km/s, using SEcat the
largest peculiar velocity catalog yet. This catalog is a combination of the SFI
spiral galaxy peculiar velocity catalog and the newly completed nearby
early-type galaxy peculiar velocity catalog, ENEAR. The recovered density is
smoothed with 900km/s Gaussian. The main reconstructed structures are
consistent with those extracted from the IRAS 1.2-Jy redshift galaxy catalogs.
The revealed structures are identified and their robustness and significance
are discussed.


title: A proper motion study of the globular cluster M10

abstract:
  We present the first proper motion study of M10 (NGC6254). Absolute proper
motions of about 532 stars in the field of the globular cluster M10 were
determined with respect to Hipparcos and ACT reference stars. In addition to
photographic plates of Bonn and Shanghai also wide field CCD observations as
second epoch plates were used. The wide field CCD observations show an accuracy
comparable to that of the photographic plates. A good coincidence of the
solutions based on reference stars from Hipparcos and from ACT was found. Our
final proper motions allow a sufficient separation of cluster and field stars.
Two population II Cepheids were confirmed to be members of M10. The absolute
proper motion of M10 was determined and combined with its distance from the Sun
and its radial velocity. The space motion and metallicity of M10 indicates the
characteristics of a halo object with an orbit reaching to a maximal z-distance
of less than 3kpc.


title:
ISO observations of the Wolf-Rayet galaxy NGC 7714 and its companion
  object NGC 7715

abstract:
  The interacting system Arp 284 consisting of the Wolf-Rayet galaxy NGC 7714
and its irregular companion NGC 7715 was observed using the Infrared Space
Observatory. Deconvolved ISOCAM maps of the galaxies using the 14.3, 7.7 and 15
micron LW3, LW6 and LW9 filters, along with ISOPHOT spectrometry of the nuclear
region of NGC 7714 were obtained and are presented. Strong ISOCAM emission was
detected from the central source in NGC 7714, along with strong PAH features,
the emission line [Ar II], molecular hydrogen at 9.66 microns and a blend of
features including [S IV] at 10.6 microns. IR emission was not detected from
the companion galaxy NGC 7715, the bridge linking the two galaxies or from the
partial stellar ring in NGC 7714 where emission ceases abruptly at the
interface between the disk and the ring.
  The morphology of the system can be well described by an off-centre collision
between the two galaxies. The LW3/LW2, where the LW2 flux was synthesized from
the PHOT-SL spectrum, LW9/LW6 and LW3/LW6 ratios suggest that the central burst
within NGC 7714 is moving towards the post-starburst phase, in agreement with
the age of the burst. Diagnostic tools including the ratio of the integrated
PAH luminosity to the 40 to 120 microns infrared luminosity and the
far-infrared colours reveal that despite the high surface brightness of the
nucleus, the properties of NGC 7714 can be explained in terms of a starburst
and do not require the prescence an AGN.


title:
Magnetic flares and the optical variability of the X-ray transient XTE
  J1118+480

abstract:
  The simultaneous presence of a strong quasi periodic oscillation of period of
about 10 seconds in the optical and X-ray lightcurves of the X-ray transient
XTE J1118+480 suggests that a significant fraction of the optical flux
originates from the inner part of the accretion flow, where most of the X-rays
are produced. We present a model of magnetic flares in an accretion disc corona
where thermal cyclo-synchrotron emission contributes significantly to the
optical emission, while the X-rays are produced by inverse Compton scattering
of the soft photons produced by dissipation in the underlying disc and by the
synchrotron process itself. Given the observational constraints, we estimate
the values for the coronal temperature, optical depth and magnetic field
intensity, as well as the accretion rate for the source. Within our model we
predict a correlation between optical and hard X-ray variability and an
anticorrelation between optical and soft X-rays. We also expect optical
variability on flaring timescales (about tens of milliseconds), with a power
density spectrum similar to the one observed in the X-ray band. Finally we use
both the available optical/EUV/X-ray spectral energy distribution and the low
frequency time variability to discuss limits on the inner radius of the
optically thick disc.


title: Disk-galaxy density distribution from orbital speeds using Newton's law

abstract:
  Given the dimensions (including thickness) of an axisymmetric galaxy,
Newton's law is used in integral form to find the density distributions
required to match a wide range of orbital speed profiles. Newton's law is not
modified and no dark matter halos are required. The speed distributiions can
have extreme shapes if they are reasonably smooth. Several examples are given.


title:
Air shower simulation using {\sc geant4} and commodity parallel
  computing

abstract:
  We present an evaluation of a simulated cosmic ray shower, based on {\sc
geant4} and {\sc top-c}, which tracks all the particles in the shower. {\sc
top-c} (Task Oriented Parallel C) provides a framework for parallel algorithm
development which makes tractable the problem of following each particle. This
method is compared with a simulation program which employs the Hillas thinning
algorithm.


title: Simulation of Water Cerenkov Detectors Using {\sc geant4}

abstract:
  We present a detailed simulation of the performance of water Cerenkov
detectors suitable for use in the Pierre Auger Observatory. Using {\sc geant4},
a flexible object-oriented simulation program, including all known physics
processes, has been developed. The program also allows interactive
visualization, and can easily be modified for any experimental setup.


title:
Precessing jets interacting with interstellar material as the origin for
  the light curves of gamma-ray bursts

abstract:
  We present an internal shock model with external characteristics for
explaining the complicated light curves of gamma-ray bursts. Shocks produce
gamma-rays in the interaction between a precessing beam of relativistic
particles and the interstellar medium. Each time the particle beam passes the
same line of sight with the observer the inter stellar medium is pushed
outward. Subsequent interactions between the medium and the beam are delayed by
the extra distance to be traveled for the particles before the shock can form.
This results in a natural retardation and leads to an intrinsic asymmetry in
the produced light curves for gamma-ray bursts. In addition we account for the
cooling of the electron-proton plasma in the shocked region, which gives rise
to an exponential decay in the gamma-ray flux. The combination of these effects
and the precessing jet of ultra relativistic particles produces light curves
which can be directly compared with observed gamma-ray burst light curves. We
illustrate the model by fitting a number of observed gamma-ray bursts which are
hard to explain with only a precessing jet. With a genetic algorithm we are
able to fit several observed gamma-ray bursts with remarkable accuracy. We find
that for different bursts the observed fluence, assuming isotropic emission,
easily varies over four orders of magnitude from the energy generated
intrinsically.


title:
A Statistical Examination of the Short Term Stability of the Upsilon
  Andromedae System

abstract:
  Because of the high eccentricities (~0.3) of two of the possible planets
about the star Upsilon Andromeda, the stability of the system requires careful
study. We present results of 1000 numerical simulations which explore the
orbital parameter space as constrained by the observations. The orbital
parameters of each planet are chosen from a Gaussian error distribution, and
the resulting configuration is integrated for 1,000,000 years. We find that 84%
of these integrations are stable. Configurations in which the eccentricity of
the third planet is <0.3 are always stable, but when the eccentricity is >0.45
the system is always unstable, typically producing a close encounter between
the second and third planets. A similar exercise with the gas giants in our own
Solar System sampled with the same error distribution was performed.
Approximately 81% of these simulations were stable for 10^6 years.


title: High-Redshift, Radio-Loud Quasars

abstract:
  I discuss two programs to study radio-loud quasars at high (z>4) redshift.
Quasars are the most luminous, non-transient objects known and are observed to
the earliest cosmic epochs. At lower redshifts, radio-loud quasars are
associated with host galaxies having deVaucoleurs profiles. By association,
identifying and studying a sample of high-redshift, radio-loud quasars provides
important clues to the early Universe and potentially probes early-type galaxy
formation. The first aspect of this proceeding discusses an extensive search
for high-redshift, radio-loud quasars culled from matching the FIRST radio
catalog with the 2nd generation Palomar Sky Survey. The second aspect of this
proceeding concerns studying the radio properties of optically-selected z>4
quasars. At the time of this conference, only seven z>4 quasars were in the
literature. The first program discussed herein uncovers three new such sources,
while the second program identifies an additional five. We use the new samples
to study the evolution of the radio-loud fraction, finding no evolution in this
quantity between redshift z>2 and z>4 for -26>M(B)>-28.


title:
The Physical Conditions of the X-ray Emission Line Regions in the
  Circinus Galaxy

abstract:
  We present a detailed X-ray spectral analysis of the Circinus Galaxy using
archival data obtained with the ASCA satellite. The spectrum shows numerous
emission lines in the soft X-ray band from highly ionized ions, as well as
Compton reflection and fluorescent lines from neutral or near-neutral matter.
We analyze the spectrum in the context of a self-consistent recombination
cascade model and find that a nearly flat differential emission measure (DEM)
distribution in ionization parameter fits the data. For a fixed solid angle
distribution of matter surrounding a point source, this corresponds to a run of
electron density of the form, n(r) ~ r^(-3/2), which is suggestive of Bondi
accretion onto a central compact mass. Using this density profile and comparing
the resulting emission spectra with the ASCA data, the size of the X-ray
emission line region is estimated to be < 1 kpc. We also show that the derived
density as a function of radius is compatible with the X-ray recombination line
emission region being the confining medium of the coronal line regions.


title: Hubble Space Telescope Imaging of the Circinus Galaxy

abstract:
  We present an HST imaging study of the nearby (4 Mpc distant) Circinus
galaxy, which contains the nearest type 2 Seyfert nucleus and prominent
circumnuclear star formation. Images have been obtained in the
[OIII]$\lambda$5007, H$\alpha$ and H$_2$ v=1--0 S(1) emission lines, and in the
green (5470 \AA), red (8140 \AA) and near infrared (2.04 and 2.15 $\mu$m)
continua. An image in the [Fe II] $\lambda$1.644 $\mu$m line has been taken
with a ground-based telescope. The [OIII] and H$\alpha$ images reveal the
detailed structure of the complex of streamers and knots of high-excitation
gas, which extends out of the galaxy disk. The morphology some 250 pc from the
nucleus strongly suggests that the high-excitation gas is concentrated on the
surface of a hollow cone with apex close to the nucleus. Such a structure may
result through entrainment of dense gas from a circumnuclear torus in the
galaxy disk by a low density, outflowing wind or jet. Within 40 pc of the
nucleus, the high-excitation gas takes the form of a striking, filled V-shaped
structure extending in the same direction as the larger scale high-excitation
emission. This `V' can be described as an ionization cone, though a
matter-bounded structure is also possible. The implied collimation of the
ionizing photons or gaseous outflow must occur within 2 pc of the apex of the
cone, presumed to be the location of the nucleus. The H$\alpha$ image shows a
complex structure of HII regions, including the well known starburst ring of
radius 150 - 270 pc. In addition, there is a more compact (40 pc radius),
elliptical ring of HII regions around the `ionization cone'. We argue that this
latter ring, which we call the nuclear ring, is intrinsically circular and
located in the plane of the galaxy disk. Abstract truncated.


title:
Evidence of thick obscuring matter revealed in the X-ray spectrum of the
  Z=4.28 quasar RXJ1028.6-0844

abstract:
  We report the discovery of an unambiguous, substantial low-energy cutoff in
the broad band X-ray spectrum of the radio quasar RXJ1028.6-0844 at a redshift
of 4.276 obtained with the ASCA satellite, which we preferably explained as
indication of excess X-ray absorption. The equivalent hydrogen column density
of the absorbing matter, depending on the redshift and metallicity, ranges from
2.5x10**21 cm**(-2) for local absorption up to 2.1x10**23 cm**(-2) (solar
metallicity) or 1.6x10**24 cm**(-2) (10% solar metallicity) for absorption at
the quasar redshift. Such a value is among the largest found for high-redshift
radio quasars. The absorption, if interpreted as being produced close to the
quasar, may indicate the presence of a remarkably large amount of obscuring
matter in the quasar environment in the early universe. Implications of the
result for the possible origins of the absorbing matter are discussed,
concerning especially galactic intervening matter, cool intracluster gas, and
ambient medium around the quasar jet. The quasar itself has an enormous
apparent luminosity of at least about 2.6x10**47 erg/s (H0=50, q0=0.5) and a
power law photon index of 1.67(+0.07,-0.04) in the 2-50keV band in the source
rest frame.


title: Thermal and Nonthermal X-Ray Emission in SNR RCW 86

abstract:
  Supernova remnants may exhibit both thermal and nonthermal X-ray emission.
Such remnants can be distinguished by the weakness of their X-ray lines,
because of the presence of a strong nonthermal X-ray continuum. RCW 86 is a
remnant with weak lines, resulting in low and peculiar abundances when thermal
models alone are used to interpret its X-ray spectrum. This indicates the
presence of a strong nonthermal synchrotron continuum. We analyze ASCA X-ray
spectra of RCW 86 with the help of both nonequilibrium ionization thermal
models and nonthermal synchrotron models. A two-temperature thermal model and a
simple nonthermal model with an exponential cutoff (plus interstellar
absorption) give reasonable results. We obtain blast wave velocity of 800 km/s,
the shock ionization age of 1-3x10^11 s/cm^3, and the break in nonthermal
spectra at 2-4x10^16 Hz. The strength of nonthermal continuum correlates well
with the radio brightness in the bright SW section of the remnant. This is
convincing evidence for X-ray synchrotron emission in RCW 86.


title: M87 at 90cm: A Different Picture

abstract:
  We report new radio imaging of the large scale radio structure of M87 with
the VLA at 90 cm. These new images show the complex structure of the radio
emission more clearly than previous attempts, some of which date back to the
1940's. The images suggest that the outward flow from the M87 nucleus extends
well beyond the 2 kpc jet. Two ``bubbles'' of synchrotron emission appear to be
inflated by this flow. A simple model of the emission, combined with our
knowledge of the inner jet, suggests that the energy input into this region
from the M87 nucleus exceeds the energy being radiated away as X-rays. This
argues that the region within 40 kpc of the center of M87 is currently
dominated by energy input from the M87 nucleus. The gas in the region is
expanding, not flowing inward as is envisioned in the cooling flow model.


title:
Observations of Seyferts by OSSE and parameters of their X-ray/gamma-ray
  sources

abstract:
  We present a summary of spectra of Seyfert galaxies observed by the OSSE
detector aboard Compton Gamma Ray Observatory. We obtain average spectra of
Seyferts of type 1 and 2, and find they are well fitted by thermal
Comptonization. We present detailed parameter ranges for the plasma temperature
and the Compton parameter in the case of spherical and slab geometries. We find
both the average and individual OSSE spectra of Seyfert 2s are significantly
harder than those of Seyfert 1s, which difference can be due to anisotropy of
Compton reflection and/or Thomson-thick absorption.


title: Extended Extragalactic Radio Emission

abstract:
  Extended radio emission and its relation to parent galaxy properties is
briefly reviewed. Our current understanding of the relation between absolute
radio and optical luminosity, radio morphology and linear size is discussed.
The impact of radio jets on dense cluster cores is discussed using M87 as an
example. Finally, the relation of AGN's to star-bursting galaxies at high
redshift is considered.


title: Loose Groups of Galaxies in the Las Campanas Redshift Survey

abstract:
  A ``friends-of-friends'' percolation algorithm has been used to extract a
catalogue of dn/n = 80 density enhancements (groups) from the six slices of the
Las Campanas Redshift Survey (LCRS). The full catalogue contains 1495 groups
and includes 35% of the LCRS galaxy sample. A clean sample of 394 groups has
been derived by culling groups from the full sample which either are too close
to a slice edge, have a crossing time greater than a Hubble time, have a
corrected velocity dispersion of zero, or contain a 55-arcsec ``orphan'' (a
galaxy with a mock redshift which was excluded from the original LCRS redshift
catalogue due to its proximity to another galaxy -- i.e., within 55 arcsec).
Median properties derived from the clean sample include: line-of-sight velocity
dispersion sigma_los = 164km/s, crossing time t_cr = 0.10/H_0, harmonic radius
R_h = 0.58/h Mpc, pairwise separation R_p = 0.64/h Mpc, virial mass M_vir =
(1.90x10^13)/h M_sun, total group R-band luminosity L_tot = (1.30x10^11)/h^2
L_sun, and R-band mass-to-light ratio M/L = 171h M_sun/L_sun; the median number
of observed members in a group is 3.


title:
Using {\sc top-c} for Commodity Parallel Computing in Cosmic Ray Physics
  Simulations

abstract:
  {\sc top-c} (Task Oriented Parallel C) is a freely available package for
parallel computing. It is designed to be easy to learn and to have good
tolerance for the high latencies that are common in commodity networks of
computers. It has been successfully used in a wide range of examples, providing
linear speedup with the number of computers. A brief overview of {\sc top-c} is
provided, along with recent experience with cosmic ray physics simulations.


title: Compact Groups of Galaxies in the Las Campanas Redshift Survey

abstract:
  We have recently extracted a catalog of compact groups of galaxies (CGs) from
the Las Campanas Redshift Survey. This catalog of Las Campanas Compact Groups
(LCCGs) contains 76 CGs with a median redshift of z_med = 0.08. The physical
properties of these CGs are similar to those from the Hickson (1982) and the
Barton et al. (1996) catalogs. Here, we present an atlas of our catalog and
briefly describe its general properties.


title: Interferometric observation of the L483 molecular core

abstract:
  We present the aperture synthesis imaging of C3H2 2_{12}-1_{01} and HCO+ 1-0
lines and of continuum emission at 3.4 mm toward the class 0 young stellar
object, IRAS 18148-0440 in the L483 molecular cloud. The continuum emission is
detected at the IRAS position at a level of 16 mJy, indicating a compact source
with a 0.13 solar mass. The C3H2 delineates an envelope near the IRAS position,
with a size of 3000 AU x 2000 AU in R.A. and Dec. directions, respectively. A
velocity gradient detected only along the axis of outflow can be explained in
terms of free-fall motion of the envelope. The HCO+ line wing extends up to the
velocity of +- 6 km s^{-1} relative to the systemic one, and the high velocity
material shows a symmetric bipolarity and extends over 2' or 0.1 pc along the
east-west direction. It is found that the outflow material is clumpy and the
opening angle is widest for the slowest moving component. The core component of
the HCO+ 1-0 line exhibits an anti-infall asymmetry not only in interferometric
but also in single dish observations. It is attributable to the slow isotropic
outward motion of gas between the flattened envelope and the collimated
outflow.


title: Can we see a rotating gravitational lens?

abstract:
  It is known that the rotation of a gravitational lens affects properties of
images. We consider an inverse problem: If the lens is dark, can we infer its
rotation from the observed images? We find that, up to the first order in the
gravitational constant G, a rotating lens is not distinguishable from a
non-rotating one. The quadrupole contribution to the deflection angle is also
calculated for a general, extended lens object.


title: Survey of rotation curves for northern spiral edge-on galaxies

abstract:
  Rotational curves are measured for almost complete sample of 308 northern
spiral galaxies using the 6-m telescope. For observations we selected edge-on
galaxies from RFGC catalog with apparent axial ratio a/b>8, angular diameter
a<2', and declinations delta>+38deg above the Arecibo belt. About 97% of the
galaxies are detected in the H-alpha line. For them a typical rotation curve
extends till 87% of the standard galaxy radius. The rotation curve amplitude
shows close correlation with a width of the HI line. The median radial velocity
for the galaxies is 7800 km/sec, and the median maximum of the rotation curves
is 137 km/s. These new observational data will be used to study cosmic
streamings of galaxies seen on a scale of 200 Mpc.


title: Simulations of Foreground Effects for CMB Polarization

abstract:
  We use a simple model to investigate the effect of polarized Galactic
foreground emission on the ability of planned CMB missions to detect and model
CMB polarization. Emission from likely polarized sources (synchrotron and
spinning dust) would dominate the polarization of the microwave sky at
frequencies below 90 GHz if known Galactic foregrounds are at least 10%
polarized at high latitude (|b| > 30 deg). Maps of polarization at frequencies
below 90 GHz will likely require correction for foreground emission to enable
statistical analysis of the individual Stokes Q or U components. The
temperature-polarization cross-correlation is less affected by foreground
emission, even if the foreground polarization is highly correlated with the
foreground intensity. Polarized foregrounds, even if uncorrected, do not
dominate the uncertainty in the temperature-polarization cross-correlation for
instrument noise levels typical of the MAP experiment. Methods which remove
galactic signals at the cost of signal to noise ratio should carefully balance
the value of rejecting faint foregrounds with the cost of increased instrument
noise.


title:
Origin of the high energy proton component below the geomagnetic cutoff
  in near earth orbit

abstract:
  The high flux proton component observed by AMS below the geomagnetic cutoff
can be well accounted for by assuming these particles to be secondaries
originating from the interaction of Cosmic Ray protons with the atmosphere.
Simulation results are reported


title: Thermal X-ray composites as an effect of projection

abstract:
  A new possibility to explain the nature of thermal X-ray composites (TXCs),
i.e. a class of supernova remnants (SNRs) with a thermal X-ray centrally-filled
morphology within a radio shell, as a projection effect of the 2- or
3-dimensional shell-like SNR evolved in a nonuniform medium with scale-height
<10 pc is proposed. Both X-ray and radio morphologies, as well as the basic
theoretical features of this kind of SNR and the surrounding medium, are
considered. Theoretical properties of a shell-like SNR evolved at the edge of a
molecular cloud correspond to the observed properties of TXCs if the gradient
of the ambient density does not lie in the projection plane and the magnetic
field is nearly aligned with the line of sight. So, at least a part of objects
from the class may be interpreted within the framework of the considered
effect. The proposed model suggests that SNRs with barrel-like radio and
centrally-brightened thermal X-ray morphologies should exist. The model allows
us to consider TXCs as prospective sources of proton origin gamma-rays.


title: Neutrinos in physics, astrophysics, and cosmology

abstract:
  A brief review of neutrino anomalies in particle physics and of the role
played by neutrinos in cosmology and astrophysics is presented. The main part
of the talk is dedicated to the impact of neutrinos and in particular of
neutrino oscillations on BBN and to a possible spatial variation of primordial
abundances.


title:
5@5 - a 5 GeV energy threshold array of imaging atmospheric Cherenkov
  telescopes at 5 km altitude

abstract:
  We discuss the concept and the performance of a powerful future ground-based
astronomical instrument - a stereoscopic array of several large imaging
atmospheric Cherenkov telescopes installed at a very high mountain elevation of
about 5 km a.s.l. or more - for the study of the gamma-ray sky at energies from
several GeV to 100 GeV.


title:
Analytic Inversion of Emission Lines of Arbitrary Optical Depth for the
  Structure of Supernova Ejecta

abstract:
  We derive a method for inverting emission line profiles formed in supernova
ejecta. The derivation assumes spherical symmetry and homologous expansion
(i.e., $v(r) \propto r$), is analytic, and even takes account of occultation by
a pseudo-photosphere. Previous inversion methods have been developed which are
restricted to optically thin lines, but the particular case of homologous
expansion permits an analytic result for lines of {\it arbitrary} optical
depth. In fact, we show that the quantity that is generically retrieved is the
run of line intensity $I_\lambda$ with radius in the ejecta. This result is
quite general, and so could be applied to resonance lines, recombination lines,
etc. As a specific example, we show how to derive the run of (Sobolev) optical
depth $\tau_\lambda$ with radius in the case of a pure resonance scattering
emission line.


title: Clues to Quasar Broad Line Region Geometry and Kinematics

abstract:
  We present evidence that the high-velocity CIV lambda 1549 emission line gas
of radio-loud quasars may originate in a disk-like configuration, in close
proximity to the accretion disk often assumed to emit the low-ionization lines.
For a sample of 36 radio-loud z~2 quasars we find the 20--30% peak width to
show significant inverse correlations with the fractional radio core-flux
density, R, the radio axis inclination indicator. Highly inclined systems have
broader line wings, consistent with a high-velocity field perpendicular to the
radio axis. By contrast, the narrow line-core shows no such relation with R, so
the lowest velocity CIV-emitting gas has an inclination independent velocity
field. We propose that this low-velocity gas is located at higher
disk-altitudes than the high-velocity gas. A planar origin of the high-velocity
CIV-emission is consistent with the current results and with an accretion
disk-wind emitting the broad lines. A spherical distribution of randomly
orbiting broad-line clouds and a polar high-ionization outflow are ruled out.


title: Quantifying Morphological Evolution from Low to High Redshifts

abstract:
  Establishing the morphological history of ordinary galaxies was one of the
original goals for the Hubble Space Telescope, and remarkable progress toward
achieving this this goal has been made. How much of this progress has been at
the expense of the Hubble sequence? As we probe further out in redshift space,
it seems time to re-examine the underlying significance of Hubble's tuning fork
in light of the the spectacular and often bizarre morphological characteristics
of high redshift galaxies. The aim of this review is to build a morphological
bridge between high-redshift and low-redshift galaxy populations, by using
quantitative morphological measures to determine the maximum redshift for which
the Hubble sequence provides a meaningful description of the galaxy population.
I will outline the various techniques used to quantify high-redshift galaxy
morphology, highlight the aspects of the Hubble sequence being probed by these
techniques, and indicate what is getting left behind. I will argue that at
higher redshifts new techniques (and new ideas) that place less emphasis on
classical morphology and more emphasis on the link between morphology and
resolved stellar populations are needed in order to probe the evolutionary
history of high-redshift galaxies.


title: Some Musings on Globular Cluster Systems

abstract:
  Globular cluster systems exhibit a bewildering variety of characteristics. No
single scenario appears to be able to account for the wide range of specific
globular cluster frequencies that are observed in galaxies of various types.
The fraction of all star formation that produces massive bound clusters differs
from galaxy to galaxy, and (in some cases) appears to vary with time. Presently
available data strongly suggest that the specific cluster forming frequency is
highest during violent bursts of star formation. Globular cluster systems show
a wide variety of color (metallicity) distributions, with many luminous
galaxies having double (or even multiple) metallicity peaks that were probably
produced during distinct episodes of cluster formation. The bulk of the
globulars in the main body of the Galactic halo appear to have formed during a
single short-lived burst that took place ~ 13 Gyr ago. This was followed by a
second, perhaps more extended, burst associated with the formation of the
Galactic bulge. A few metal-rich clusters may also be associated with the
formation of the Galactic Thick Disk. Finally many of the clusters beyond RGc ?
15 kpc might have been formed in dwarf spheroidal galaxies that, after a few
Gyr, were accreted by the main body of the Galactic halo. Some of these outer
clusters are younger, and less luminous, than the majority of globular clusters
formed at smaller Galactocentric distances.


title:
Exploring the gravitationally lensed system HE 1104-1805: Near-IR
  Spectroscopy

abstract:
  (Abridged) A new technique for the spatial deconvolution of spectra is
applied to near-IR (0.95 - 2.50 micron) NTT/SOFI spectra of the lensed,
radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is
revealed between 1.5 and 2.5 micron. It is used in combination with previous
optical and IR photometry to infer a plausible redshift in the range 0.8 < z <
1.2. Modeling of the system shows that the lens is probably composed of the red
galaxy seen between the quasar images and a more extended component associated
with a galaxy cluster with fairly low velocity dispersion (~ 575 km/s). The
spectra of the two lensed images of the source show no trace of reddening at
the redshift of the lens nor at the redshift of the source. Additionally, the
difference between the spectrum of the brightest component a nd that of a
scaled version of the faintest component is a featureless continuum. Broad and
narrow emission lines, including the FeII features, are perfectly subtracted.
The very good quality of our spectrum makes it possible to fit precisely the
optical Fe II feature, taking into account the underlying continuum over a wide
wavelength range. HE 1104-1805 can be classified as a weak Fe II emitter.
Finally, the slope of the continuum in the brightest image is steeper than the
continuum in the faintest image and supports the finding by Wisotzki et al.
(1993) that the brightest image is microlensed. This is particularly
interesting in view of the new source reconstruction methods from
multiwavelength photometric monitoring.


title:
The LBDS Hercules sample of millijansky radio sources at 1.4 GHz: I.
  Multi-colour photometry

abstract:
  The results are presented of an extensive programme of optical and infrared
imaging of radio sources in a complete subsample of the Leiden-Berkeley Deep
Survey. The LBDS Hercules sample consists of 72 sources observed at 1.4 GHz,
with flux densities S(1.4) >= 1.0 mJy, in a 1.2 deg^2 region of Hercules. This
sample is almost completely identified in the g, r, i and K bands, with some
additional data available at J and H. The magnitude distributions peak at r ~=
22 mag, K ~= 16 mag and extend down to r ~= 26 mag, K ~= 21 mag. The K-band
magnitude distributions for the radio galaxies and quasars are compared with
those of other radio surveys. At S(1.4) <~ 1 Jy, the K-band distribution does
not change significantly with radio flux density. The sources span a broad
range of colours, with several being extremely red (r-K >~ 6). Although small,
this is the most optically complete sample of millijansky radio sources
available at 1.4 GHz, and is ideally suited to study the evolution of the radio
luminosity function out to high redshifts.


title: Cosmological Parameters from Velocities, CMB and Supernovae

abstract:
  We compare and combine likelihood functions of the cosmological parameters
Omega_m, h and sigma_8, from peculiar velocities, CMB and type Ia supernovae.
These three data sets directly probe the mass in the Universe, without the need
to relate the galaxy distribution to the underlying mass via a "biasing"
relation. We include the recent results from the CMB experiments BOOMERANG and
MAXIMA-1. Our analysis assumes a flat Lambda CDM cosmology with a
scale-invariant adiabatic initial power spectrum and baryonic fraction as
inferred from big-bang nucleosynthesis. We find that all three data sets agree
well, overlapping significantly at the 2 sigma level. This therefore justifies
a joint analysis, in which we find a joint best fit point and 95 per cent
confidence limits of Omega_m=0.28 (0.17,0.39), h=0.74 (0.64,0.86), and
sigma_8=1.17 (0.98,1.37). In terms of the natural parameter combinations for
these data sigma_8 Omega_m^0.6 = 0.54 (0.40,0.73), Omega_m h = 0.21
(0.16,0.27). Also for the best fit point, Q_rms-ps = 19.7 muK and the age of
the universe is 13.2 Gyr.


title: The Type Ia Supernova Width-Luminosity Relation

abstract:
  Observations of type Ia supernovae at high redshifts have become an important
tool for studying the geometry of the universe. The relation between the
duration of the peak phase of a type Ia supernova's lightcurve and its
luminosity (broader is brighter) forms the cornerstone of this measurement, yet
it is a purely empirical relation. In this paper we show that the relation is a
natural consequence of the radiation transport in type Ia supernovae and
suggest constraints on the nature of the explosions which arise from our
interpretation of the observed relation. The principle parameter underlying the
relation is the mass of radioactive 56Ni produced in the explosion. The
relation is shown to be relatively insensitive to most other parameters in
Chandrasekhar-mass explosions. Cosmological results are thus unlikely to suffer
from systematic effects stemming from evolution in the explosions' progenitors.


title: Lyman alpha Transfer in a thick, dusty, and static medium

abstract:
  We developed a Monte Carlo code that describes the resonant Lyman alpha line
transfer in an optically thick, dusty, and static medium. The code was tested
against the analytic formula derived by Neufeld (1990). We explain the line
transfer mechanism for a wide range of line center optical depths by tracing
histories of photons in the medium. We find that photons escape from the medium
by a series of wing scatterings, during which polarization may develop. We
applied our code to examine the amount of dust extinction around the Lyman
alpha in primeval galaxies. Brief discussions on the astrophysical application
of our work are presented.


title: Gauge choice and geodetic deflection in conformal gravity

abstract:
  Conformal gravity has been proposed as an alternative theory of gravity which
can account for flat galactic rotation curves without recourse to copious
quantities of dark matter. However it was shown that for the usual choice of
the metric, the result is catastrophic for null or highly relativistic
geodesics, the effect is exactly the opposite yielding an effective repulsion
and less deflection in this case. It is the point of this paper, that any
result for massive geodesics depends on the choice of conformal gauge, in
contradistinction to the case of null geodesics. We show how it is possible to
choose the gauge so that the theory is attractive for all geodesics.


title:
CU Comae: a new field double-mode RR Lyrae, the most metal poor
  discovered to date

abstract:
  We report the discovery of a new double-mode RR Lyrae variable (RRd) in the
field of our Galaxy: CU Comae. CU Comae is the sixth such RRd identified to
date and is the most metal-poor RRd ever detected. Based on BVI CCD photometry
spanning eleven years of observations, we find that CU Comae has periods
P0=0.5441641 +/-0.0000049d and P1=0.4057605 +/-0.0000018d. The amplitude of the
primary (first-overtone) period of CU Comae is about twice the amplitude of the
secondary (fundamental) period. The combination of the fundamental period of
pulsation P0 and the period ratio of P1/P0=0.7457 places the variable on the
metal-poor side of the Petersen diagram, in the region occupied by M68 and M15
RRd's. A mass of 0.83 solar masses is estimated for CU Comae using an updated
theoretical calibration of the Petersen diagram. High resolution spectroscopy
(R=30,000) covering the full pulsation cycle of CU Comae was obtained with the
2.7 m telescope of the Mc Donald Observatory, and has been used to build up the
radial velocity curve of the variable. Abundance analysis done on the four
spectra taken near minimum light (phase: 0.54 -- 0.71) confirms the metal poor
nature of CU Comae, for which we derive [Fe/H]=-2.38 +/-0.20. This value places
this new RRd at the extreme metal-poor edge of the metallicity distribution of
the RR Lyrae variables in our Galaxy.


title:
Re-processing the Hipparcos Transit Data and Intermediate Astrometric
  Data of spectroscopic binaries. I. Ba, CH and Tc-poor S stars

abstract:
  The Intermediate Astrometric Data (IAD) and Transit Data (TD) made available
by ESA after the Hipparcos mission make it possible to re-process the
observations of any Hipparcos entry. This paper illustrates how TD and IAD may
be used in conjunction with the orbital parameters of spectroscopic binaries to
improve the astrometric parameters of binaries considered as single stars in
the original reduction process. That approach has been applied to 81 dwarf
barium stars, strong and mild barium stars, CH stars, and Tc-poor S stars for
which spectroscopic orbits became available recently. Among these 81 systems,
23 yield reliable astrometric orbits, thus making it possible to evaluate on
real data the impact of an unrecognized orbital motion on the proper motion
(Wielen, 1997, A&A 325, 367). Comparison of the proper motion from the
Hipparcos catalogue with that re-derived in the present work indicates that the
former are indeed far off the present value for binaries with periods in the
range 3 to about 8 years. Hipparcos parallaxes of unrecognized spectroscopic
binaries turn out to be reliable, except for systems with periods close to 1
year, as expected. Finally, we show that, even when a complete orbital
revolution was observed by Hipparcos, the inclination is unfortunately seldom
precise.


title:
Forming Clusters of Galaxies as the Origin of Unidentified GeV Gamma-Ray
  Sources

abstract:
  Over half of GeV gamma-ray sources observed by the EGRET experiment have not
yet been identified as known astronomical objects. There is an isotropic
component of such unidentified sources, whose number is about 60 in the whole
sky. Here we calculate the expected number of dynamically forming clusters of
galaxies emitting gamma-rays by high energy electrons accelerated in the shock
wave when they form, in the framework of the standard theory of structure
formation. We find that a few tens of such forming clusters should be
detectable by EGRET and hence a considerable fraction of the isotropic
unidentified sources can be accounted for, if about 5% of the shock energy is
going into electron acceleration. We argue that these clusters are very
difficult to detect in x-ray or optical surveys compared with the conventional
clusters, because of their extended angular size of about 1 degree. Hence they
define a new population of ``gamma-ray clusters''. If this hypothesis is true,
the next generation gamma-ray telescopes such as GLAST will detect more than a
few thousands of gamma-ray clusters. It would provide a new tracer of
dynamically evolving structures in the universe, in contrast to the x-ray
clusters as a tracer of hydrodynamically stabilized systems. We also derive the
strength of magnetic field required for the extragalactic gamma-ray background
by structure formation to extend up to 100 GeV as observed, that is about
10^{-5} of the shock-heated baryon energy density.


title: The evolution of type 1 AGN at 15um from the ELAIS

abstract:
  We present the first preliminary estimate of the evolution of type 1 AGNs at
15 um. A new sample of sources selected from the ELAIS-S1 survey has been used
together with the RMS sample. The ELAIS-S1 survey covers an effective area of
2.2 deg^2 (total: 4 deg^2) down to 1.2 mJy at 15 um. Spectroscopic
identifications have been carried out in the range 17.2<R<20.0 at the 3.6m/ESO,
NTT/ESO and 2dF/AAT. The luminosity function is steeper at bright luminosities
in comparison to the previous estimates of Rush, Malkan & Spinoglio (1993). The
evolution is compatible with a Pure Luminosity Evolution model with
L(z)=L(0)(1+z)^3.4.


title:
A Search for Stars of Very Low Metal Abundance. V. Photoelectric UBV
  Photometry of Metal-Weak Candidates from the Northern HK Survey

abstract:
  We report photoelectric UBV data for 268 metal-poor candidates chosen from
the northern HK objective-prism/interference-filter survey of Beers and
colleagues. Over 40 % of the stars have been observed on more than one night,
and most have at least several sets of photometric measurements. Reddening
estimates, preliminary spectroscopic measurements of abundance, and type
classifications are reported.


title: A spectroscopic study of field BHB star candidates

abstract:
  New spectroscopic observations (R=15000 and 40000) are given for 31 nearby (V
< 11) BHB star candidates. IUE low-resolution spectra are available for most of
them. New determinations of temperature, gravity, reddening and abundances were
obtained from these data using models computed by Castelli with an updated
version of the ATLAS9 code. A summary of the visual photometry for these stars
(including new photometry obtained at Kitt Peak) is also given. All 31
candidates are halo stars. We classify 28 as BHB stars because: (1) They lie
close to the ZAHB (in a similar position to globular cluster BHB stars) in the
Teff vs. log g plot. (2) Their distribution of vsini (less than 40 km/s) is
similar to that found for the BHB stars in globular clusters. (3) Their [Fe/H]
lies between -0.99 and -2.95 (mean [Fe/H] -1.67, dispersion 0.42 dex) which is
similar to that found for field halo RR Lyrae and red HB stars but more metal-
poor than for halo globular clusters. Field BHB stars with Teff greater than
8500 K show the He I (4471 A) line corresponding to solar abundance. (4) They
show a similar average enhancement of the alpha-elements ([Mg/Fe] = +0.43 +/-
0.04 and [Ti/Fe] = +0.44 +/- 0.02) to that found for other halo field stars of
similar metallicity. Comments are given on a further 25 stars that have
previously been suggested to be BHB stars; these were not included in our
sample because they did not fulfil one or more of the above criteria.


title:
Toward a Symmetrization of Gravity I. Classical Formulation: Results and
  Predictions; Dark Matter With a Difference

abstract:
  We propose an additional term in the classical gravitational force law, which
is repelling in nature, and which may solve the dark matter problem. As an
inverse cube field interaction, it operates over 4 real spatial dimensions and
its effect on our observable 3-D space may account both for flat rotation
curves and standard Newtonian dynamics at small radial distances. By utilizing
cosmological clustering scales, we can derive the universal interaction
strength, and show that this naturally leads to an altered Planck mass that
becomes the neutron/proton rest mass. Moreover, the correct value for the
electron rest mass can be predicted using only classical electrostatics coupled
with the current theory. On cosmological scales, the interaction easily
accounts for the acceleration of the Hubble flow.


title:
HST-STIS Observations of the Cygnus Loop: Spatial Structure of a
  Non-radiative Shock

abstract:
  We present a spatially-resolved ultraviolet spectrum of a non-radiative shock
front in the Cygnus Loop, obtained with the Space Telescope Imaging
Spectrograph (STIS) on board the Hubble Space Telescope (HST). The spectrum
covers the wavelength range 1118 - 1716 angstroms, with an effective spectral
resolution of ~12 angstroms. The 0.1" spatial resolution of these data provides
a huge improvement over earlier ultraviolet spectra, allowing us to study the
spatial distribution of high ionization line emission directly behind the shock
front. We are able to isolate individual shock features in our spectrum by
comparing the STIS spectrum with a WFPC2 H-alpha image of the region. Isolating
the brightest shock tangency, we identify lines of NV, CIV, HeII, OV, OIV] and
SiIV, and NIV] as well as the hydrogen 2-photon continuum. The NV line peaks
about 0.3" behind the CIV and HeII emission and is spatially broader. Also, the
observed line ratios of CIV and HeII to NV are higher in our bright shock
spectrum than in previous observations of the same filament obtained through
much larger apertures, indicating that there must be a more widely distributed
component of the NV emission. We calculate shock models and show that the
observed separation between the CIV and NV emission zones and observed line
intensities constrain the combinations of shock velocity and pre-shock density
that are allowed.


title:
Hot HB stars in globular clusters - Physical parameters and consequences
  for theory. V. Radiative levitation versus helium mixing

abstract:
  Atmospheric parameters (effective temperature Teff, surface gravity log g),
masses and helium abundances are derived for 42 hot horizontal branch (HB)
stars in the globular cluster NGC 6752. For 19 stars we derive magnesium and
iron abundances as well and find that iron is enriched by a factor of 50 on
average with respect to the cluster abundance whereas the magnesium abundances
are consistent with the cluster abundance. Radiation pressure may levitate
heavy elements like iron to the surface of the star in a diffusive process.
Taking into account the enrichment of heavy elements in our spectroscopic
analyses we find that high iron abundances can explain part, but not all, of
the problem of anomalously low gravities along the blue HB. The blue HB stars
cooler than about 15,100 K and the sdB stars (Teff > 20,000 K) agree well with
canonical theory when analysed with metal-rich ([M/H] = +0.5) model
atmospheres, but the stars in between these two groups remain offset towards
lower gravities and masses. Deep Mixing in the red giant progenitor phase is
discussed as another mechanism that may influence the position of the blue HB
stars in the (Teff, log g)-plane but not their masses.


title:
Tracing the Mass during Low-Mass Star Formation. I. Submillimeter
  Continuum Observations

abstract:
  We have obtained 850 and 450 micron continuum maps of 21 low mass cores with
SED's ranging from pre-protostellar to Class I (18K < Tbol < 370K), using SCUBA
at the JCMT. In this paper we present the maps, radial intensity profiles, and
photometry. Pre-protostellar cores do not have power-law intensity profiles,
whereas the intensity profiles of Class 0 and Class I sources can be fitted
with power laws over a large range of radii. A substantial number of sources
have companion sources within a few arcminutes (2 out of 5 pre-protostellar
cores, 9 out of 16 Class 0/I sources). The mean separation between sources is
10800 AU. The median separation is 18000 AU including sources without
companions as a lower limit. The mean value of the spectral index between 450
and 850 microns is 2.8 +- 0.4, with PPCs having slightly lower spectral indices
(2.5 +- 0.4). The mean mass of the sample, based on the dust emission in a 120
arcsecond aperture, is 1.1 +- 0.9 solar masses. For the sources fitted by
power-law intensity distributions (I_nu(b)/I_nu(0) = (b/b_0) ^ m), the mean
value of m is 1.52 +- 0.45 for Class 0 and I sources at 850 microns and 1.44 +-
0.25 at 450 microns. Based on a simple analysis, assuming the emission is in
the Rayleigh-Jeans limit and that T_d(r) ~ r ^ {-0.4}, these values of m
translate into power-law density distributions (n ~ r ^ {-p}) with p ~ 2.1.
However, we show that this result may be changed by more careful consideration
of effects such as beam size and shape, finite outer radii, more realistic
T_d(r), and failure of the Rayleigh-Jeans approximation.


title:
The Equilibrium Structure of Cosmological Halos: Dwarf Galaxies to X-ray
  Clusters

abstract:
  An analytical model for the postcollapse equilibrium structure of virialized
objects which condense out of the cosmological background universe is described
and compared with observations and simulations of cosmological halos. The model
is based upon the assumption that virialized halos are isothermal, which leads
to a prediction of a unique nonsingular isothermal sphere for the equilibrium
structure, with a core density which is proportional to the mean background
density at the epoch of collapse. These predicted nonsingular isothermal
spheres are in good agreement with observations of the internal structure of
dark-matter-dominated halos from dwarf galaxies to X-ray clusters. Our model
also reproduces many of the average properties of halos in CDM simulations to
good accuracy, suggesting that it is a useful analytical approximation for
halos which form from realistic initial conditions. While CDM N-body
simulations find profiles with a central cusp, our nonsingular model matches
the simulated halos outside the innermost region well. This model may also be
of interest as a description of halos in nonstandard CDM models like
self-interacting dark matter, which have been proposed to eliminate the
discrepancy between the cuspy halos of standard CDM simulations and observed
halos with uniform-density cores.


title:
Mid-infrared imaging and spectrophotometry of N 66 in the SMC with
  ISOCAM

abstract:
  We present observations with the mid-infrared camera ISOCAM on board ISO of
the major star-forming region N66 in the Small Magellanic Cloud and of its
surroundings. These observations were performed with broad filters and the CVF
giving a spectral resolution of about 40. In addition, CO(2-1) data are
presented, allowing us to identify and study how hot dust relates with the
different phases of the Interstellar Medium present in N66. The spectra are
dominated by the strong emission of fine structure line. Monochromatic maps
have been made in the [NeIII] 15.6 microns and [SIV] 10.5 microns line. There
are significant differences between their distributions, due to the effects of
density and of shocks. Aromatic Infrared Bands are seen at various places in
the field but they are generally faint. They exhibit a variety of shapes and
relative intensities, suggesting that a diversity of carbonaceous materials are
present. Silicate emission is also clearly visible in the central condensation
and in a few others and emission from hot small grains longward of 10 microns
is present in the whole region. All these dust components are heated by the
very strong far UV radiation of the many young, massive stars contained in the
region. The interstellar radiation field (ISRF) at 1600 A is >= 10^5 times the
ISRF of the solar neighborhood in the peaks of MIR emission. The relative
contributions of the dust components to the MIR spectra seem to depend on the
intensity and the hardness of the far UV field. In general the 15/6.75 microns
intensity ratio is higher than in relatively quiescent galactic regions but it
is not as high as expected for a linear increase with ISRF. We interpret this
behavior as due to the destruction of both AIBs carriers and VSGs in a very
high ISRF.


title:
The inverse cascade and nonlinear alpha-effect in simulations of
  isotropic helical hydromagnetic turbulence

abstract:
  A numerical model of isotropic homogeneous turbulence with helical forcing is
investigated. The resulting flow, which is essentially the prototype of the
alpha^2 dynamo of mean-field dynamo theory, produces strong dynamo action with
an additional large scale field on the scale of the box (at wavenumber k=1;
forcing is at k=5). This large scale field is nearly force-free and exceeds the
equipartition value. As the magnetic Reynolds number R_m increases, the
saturation field strength and the growth rate of the dynamo increase. However,
the time it takes to built up the large scale field from equipartition to its
final super-equipartition value increases with magnetic Reynolds number. The
large scale field generation can be identified as being due to nonlocal
interactions originating from the forcing scale, which is characteristic of the
alpha-effect. Both alpha and turbulent magnetic diffusivity eta_t are
determined simultaneously using numerical experiments where the mean-field is
modified artificially. Both quantities are quenched in a R_m-dependent fashion.
The evolution of the energy of the mean field matches that predicted by an
alpha^2 dynamo model with similar alpha and eta_t quenchings. For this model an
analytic solution is given which matches the results of the simulations. The
simulations are numerically robust in that the shape of the spectrum at large
scales is unchanged when changing the resolution from 30^3 to 120^3 meshpoints,
or when increasing the magnetic Prandtl number (viscosity/magnetic diffusivity)
from 1 to 100. Increasing the forcing wavenumber to 30 (i.e. increasing the
scale separation) makes the inverse cascade effect more pronounced, although it
remains otherwise qualitatively unchanged.


title:
A cloud model of active galactic nuclei: the iron K-alpha line
  diagnostics

abstract:
  The origin and the profile of the iron K-alpha line from active galactic
nuclei is being studied. The model with a quasi-spherical distribution of
clouds around a compact galactic nucleus is explored in which the intrinsic
spectral feature around 6-7 keV is substantially affected by Comptonization of
primary X-rays. The predicted spectral profiles are influenced mainly by motion
of the clouds in strong gravitational field of the centre, and by orientation
of the source with respect to the observer. The case of the Seyfert galaxy
MCG-6-30-15 is examined in more detail and free parameters of the model are
determined. A robust result is obtained: acceptable fits to the observed
profile correspond to the spherical distribution of the clouds with strong
self-obscuration effects and with rather high value of ionization parameter.
This is a different situation from that considered in the model of a cold
illuminated disc. Nevertheless, geometrically flat (disc-type) configurations
are not rejected.


title: HCN in the inner envelope of {chi} Cygni

abstract:
  We have detected the (0,11c,0)J=3-2 and (0,0,0)J=8-7 transitions of HCN
towards the S star {chi} Cygni. The excitation requirements of these
transitions are too high to be satisfied in the outer envelope of the star, and
the emission must originate within {solar}20 stellar radii, ie. the molecule
must be forming close to the star. This conclusion is supported by a model for
AGB stars in which molecules including HCN form in a shocked wind close to the
stellar surface.


title:
ORFEUS II Echelle spectra: Molecular hydrogen at high velocities toward
  HD 93521

abstract:
  Absorption lines of interstellar molecular hydrogen in the far ultraviolet
(FUV) have been observed in the spectrum of the O9.5 halo star HD 93521,
located some 1500 pc from the Galactic plane. During the second flight of the
ORFEUS-SPAS mission a spectrum with the Echelle spectrometer has been recorded
with a total integration time of 1740 s. The resolution achieved was about
10.000 with a signal-to-noise ratio of up to 25. For the first time two
components of molecular hydrogen have been observed in absorption at velocities
of -12 km/s in the Galactic disk and at -62 km/s located presumably in the
Galactic halo. The column densities derived from a standard curve of growth
analysis were found to be N(H_2) = 10^17.0 cm^-2 for the disk component and
N(H_2) = 10^14.6 cm^-2 respectively for the component located in the Galactic
halo.


title: Self-Regulation of Star Formation in Low Metallicity Clouds

abstract:
  We investigate the process of self-regulated star formation via
photodissociation of hydrogen molecules in low metallicity clouds. We evaluate
the influence region's scale of a massive star in low metallicity gas clouds
whose temperatures are between 100 and 10000 Kelvin. A single O star can
photodissociate hydrogen molecules in the whole of the host cloud. If
metallicity is smaller than about 10^{-2.5} of the solar metallicity, the
depletion of coolant of the the host cloud is very serious so that the cloud
cannot cool in a free-fall time, and subsequent star formation is almost
quenched. On the contrary, if metallicity is larger than about 10^{-1.5} of the
solar metallicity, star formation regulation via photodissociation is not
efficient. The typical metallicity when this transition occurs is about 1/100
of the solar metallicity. This indicates that stars do not form efficiently
before the metallicity becomes larger than about 1/100 of the solar metallicity
and we considered that this value becomes the lower limit of the metallicity of
luminous objects such as galaxies.


title:
Simulations of Observations with the Optical Monitor of the X-Ray
  Multi-Mirror Satellite

abstract:
  This paper addresses the question of the observations to be performed with
the Optical Monitor (OM) of the X-ray Multi-Mirror Satellite (XMM) under
several aspects. First, we discuss XMM-OM's photometric system and its colour
transformations towards the standard UBV system. Second, we establish a set of
procedures to determine the temperature and the amount of interstellar
absorption affecting the observed stars. Last, we address the possibility of
isolating quasars in multidimensional colour diagrams based on the XMM-OM
filter set.


title:
Evolution of the probability distribution function of galaxies in
  redshift-space

abstract:
  We present a new analytic calculation for the redshift-space evolution of the
1-point galaxy Probability Distribution Function (PDF). The nonlinear evolution
of the matter density field is treated by second-order Eulerian perturbation
theory and transformed to the galaxy density field via a second-order local
biasing scheme. We then transform the galaxy density field to redshift space,
again to second order. Our method uses an exact statistical treatment based on
the Chapman-Kolmogorov equation to propagate the probability distribution of
the initial mass field to the final redshifted galaxy density field. We derive
the moment generating function of the PDF and use it to find a new, closed-form
expression for the skewness of the redshifted galaxy distribution. We show that
our formalism is general enough to allow a non-deterministic (or stochastic)
biasing prescription. We demonstrate the dependence of the redshift space PDF
on cosmological and biasing parameters. Our results are compared with existing
models for the PDF in redshift space and with the results of biased N-body
simulations. We find that our PDF accurately models the redshift space
evolution and the nonlinear biasing.


title:
Chemical Abundances and Ionizing Clusters of HII Regions in the LINER
  Galaxy NGC 4258

abstract:
  We present long-slit observations in the optical and near infrared of eight
HII regions in the spiral galaxy NGC 4258. Six of the observed regions are
located in the SE inner spiral arms and the other two are isolated in the
northern outer arms. A detailed analysis of the physical conditions of the gas
has been performed. For two of the regions, an electron temperature has been
derived from the [SIII] 6312 A line. For the rest, an empirical calibration
based on the red and near infrared sulphur lines has been used. The oxygen
abundances derived by both methods are found to be significantly lower (by a
factor of two) than previously derived by using empirical calibrations based on
the optical oxygen lines. In the brightest region, 74C, the observation of a
prominent feature due to Wolf-Rayet stars provides an excellent constraint over
some properties of the ionizing clusters. In the light of the current
evolutionary synthesis models, no consistent solution is found to explain at
the same time both the WR feature characteristics and the emission line
spectrum of this region. In principle, the presence of WR stars could lead to
large temperature fluctuations and also to a hardening of the ionizing
radiation. None of these effects are found in region 74C for which the electron
temperatures found from the [SIII] 6312A and the Paschen discontinuity at 8200A
are equal within the errors and the effective temperature of the ionizing
radiation is estimated at around 35,300K. Both more observations of confirmed
high metallicity regions and a finer metallicity grid for the evolutionary
synthesis models are needed in order to understand the ionizing populations of
HII regions.


title: The Fall of the Quasar Population

abstract:
  We derive quantitative predictions of the optical and X-ray luminosity
functions (LF) for QSs in the redshift range $z<3$. Based on BH paradigm, we
investigate how the accretion is controlled by the surrounding structures, as
these grow hierarchically. We argue that for $z < 3$ efficient black hole
fueling is triggered by the encounters of a gas-rich host with its companions
in a group. The dispersion of the dynamical parameters in the encounters
produces a double power-law LF. Strong luminosity evolution (LE) is produced as
these encounters deplete the gas supply in the host; an additional, milder
density evolution obtains since the interactions become progressively rarer as
the groups grow richer but less dense. From the agreement with the optical and
the X-ray data, we conclude that the evolution of the bright quasars is
articulated in two ways. Earlier than $z~3$ the gas-rich protogalaxies grow by
merging, which also induces parallel growth of central holes accreting at
Eddington rates. In the later era of group assemblage the host encounters with
companions drive onto already existing holes further but meager accretion;
these consume the gas in the hosts, and cause supply-limited emissions which
are intermittent, go progressively sub-Eddington and peter out. Then other
fueling processes come to the foreground; we discuss the faint emissions,
especially noticeable in X-rays, which are expected when hosts in the field
cannibalize satellite galaxies with their meager gas contents.


title: Rapid Synchrotron Flares from BL Lacertae Detected by ASCA and RXTE

abstract:
  We report the variable X-ray emission from BL Lacertae detected in the ASCA
ToO observation conducted during the EGRET and RXTE pointings, coincident with
the 1997 July outburst. The source showed a historically high state of X-ray,
optical, and gamma-ray emission, with its 2-10 keV flux peaking at ~3.3 E-11
erg/cm2/s. This is more than 3 times higher than the value measured by ASCA in
1995. We detected two rapid flares which occured only in the soft X-ray band,
while the hard X-ray flux also increased, but decayed with a much longer time
scale. Together with the requirement of a very steep and varying power law
dominating the soft X-ray band in addition to the hard power law, we suggest
that both the high energy end of the synchrotron spectrum and the hard inverse
Compton spectrum were visible in this source during the outburst. We discuss
the possible origins of the observed variability time scales, and interpret the
short time scales of the soft X-ray variability as reflecting the size of the
emission region.


title: Spatial and Energy Distribution of Muons in Gamma-induced Air Showers

abstract:
  The FLUKA Monte Carlo program is used to calculate the effects of
hadroproduction by primary gamma rays incident upon the earth's atmosphere; for
the results presented in this paper, only primary angles at 0 degrees from
zenith are considered. The FLUKA code is believed to be quite accurate in
reproducing experimental photon hadroproduction data in the 1 GeV to 10 TeV
energy range studied. The charged pions which are so produced can decay to
muons with sufficient energy to reach ground level. The number of these muons
and their radial and energy distribution are studied for incident gamma ray
energies from 1 GeV to 10 TeV. The number of these muons is not negligible;
they can, in certain circumstances, be used to study potential sources of gamma
rays like gamma ray bursts. It is found, for example, that a 10 TeV incident
primary gamma ray produces, on average, 3.4 muons which reach ground level; the
gamma ray energy which produces the maximum number of muons at ground level
depends on the spectral index of the primary gamma spectrum, a constant which
describes how the primary gamma flux rises with decreasing primary energy. An
example: for a differential spectral index of 2.7, there is a broad maximum
number of muons coming from ~ 30 GeV primary gamma ray energy.


title: Study of the depletion effect in the cluster MS1008-1224

abstract:
  We present a detailed study of the depletion effect (the radial manifestation
of the magnification bias) in the cluster MS1008-1224. Following our results
concerning the simulations of depletion curves (see Mayen and Soucail, 2000
(astro-ph/0003332) for a complete description of the code), we propose to
constrain the mass profile of the cluster and the main characteristics of its
potential (orientation and ellipticity). This application is based solely on
deep photometry of the field and does not require the measurement of the shape
parameters of the faint background galaxies.


title: The Stability of Disks in Cusped Potentials

abstract:
  We confirm that a high rate of shear at the center is able to stabilize an
entire stellar disk against bar-forming (m=2) modes, irrespective of the dark
halo density. Our simulations of unstable power-law disks also yield the growth
rate and pattern speed of the dominant lop-sided (m=1) mode in close agreement
with that predicted by linear theory in our cleanest case. The one-armed modes,
which dominate models with extensive disks, can be controlled by tapering the
outer disk. Two-armed instabilities of hard-centered disks are more difficult
to identify because they are easily overwhelmed by particle noise.
Nevertheless, we have detected the predicted m=2 modes in simulations with very
large numbers of particles. Such bisymmetric instabilities in these disks are
provoked only by sharp edges and are therefore easily eliminated.
  We have constructed a cool disk model with an almost flat rotation curve and
a quasi-exponential density profile that is unambiguously stable. The halo in
this stable model has a large core radius, with the disk and bulge providing
almost all the rotational support in the inner parts.


title: Galaxies behind the Milky Way and the Great Attractor

abstract:
  Dust and stars in the plane of the Milky Way create a "Zone of Avoidance" in
the extragalactic sky. Galaxies are distributed in gigantic labyrinth
formations, filaments and great walls with occasional dense clusters. They can
be traced all over the sky, except where the dust within our own galaxy becomes
too thick - leaving about 25% of the extragalactic sky unaccounted for. Our
Galaxy is a natural barrier which constrains the studies of large-scale
structures in the Universe, the peculiar motion of our Local Group of galaxies
and other streaming motions (cosmic flows) which are important for
understanding formation processes in the Early Universe and for cosmological
models. Only in recent years have astronomers developed the techniques to peer
through the disk and uncover the galaxy distribution in the Zone of Avoidance.
I present the various observational multi-wavelength procedures (optical, far
infrared, near infrared, radio and X-ray) that are currently being pursued to
map the galaxy distribution behind our Milky Way. Particular emphasis is given
to discoveries in the Great Attractor region -- a from streaming motions
predicted huge overdensity centered behind the Galactic Plane. The recently
unveiled massive rich cluster A3627 seems to constitute the previously
unidentified core of the Great Attractor.


title:
Radio galaxy selected clusters at high redshift and associated ERO
  overdensities

abstract:
  Galaxy clusters at high redshift present a superb opportunity to study galaxy
evolution, with large galaxy samples at fixed distances. Several lines of
evidence point towards large formation redshifts and passive evolution for
cluster ellipticals. At redshifts larger than z~0.8, this picture rests on data
from only a handful of rich clusters. We have observed four potential clusters
to sample sparser environments in a critical redshift range, 0.8 < z < 1.2. We
compare the photometric evolution and radial density profiles in our clusters
with more massive clusters studied in a similar manner. We also highlight the
overdense ERO (I-K>5) population, significantly redder than the old elliptical
population at the cluster redshift. We discuss the implications of our clusters
at high redshift, and possible differences in environment from richer clusters
at similar redshifts selected through X-ray or optical techniques.


title:
The Bright Gamma-Ray Burst 991208 - Tight Constraints on Afterglow
  Models from Observations of the Early-Time Radio Evolution

abstract:
  The millimeter wavelength emission from GRB 991208 is the second brightest
ever detected, yielding a unique data set. We present here well-sampled spectra
and light curves over more than two decades in frequency for a two-week period.
This data set has allowed us for the first time to trace the evolution of the
characteristic synchrotron self-absorption frequency nu_a and peak frequency
nu_m, and the peak flux density F_m: we obtain nu_a \propto t^{-0.15 +- 0.12},
nu_m \propto t^{-1.7 +- 0.4}, and $_m \propto t^{-0.47 +- 0.11}. From the radio
data we find that models of homogeneous or wind-generated ambient media with a
spherically symmetric outflow can be ruled out. A model in which the
relativistic outflow is collimated (a jet) can account for the observed
evolution of the synchrotron parameters, the rapid decay at optical
wavelengths, and the observed radio to optical spectral flux distributions that
we present here, provided that the jet transition has not been fully completed
in the first two weeks after the event. These observations provide additional
evidence that rapidly decaying optical/X-ray afterglows are due to jets and
that such transitions either develop very slowly or perhaps never reach the
predicted asymptotic decay F(t) \propto t^{-p}.


title:
On the Origin of the Iron K Line in the Spectrum of the Galactic X-ray
  Background

abstract:
  We propose a mechanism for the origin of the Galactic ridge X-ray background
that naturally explains the properties of the Fe K line, specifically the
detection of the centroid line energy below 6.7 keV and the apparent broadness
of the line. Motivated by recent evidence of nonthermal components in the
spectrum of the Galactic X-ray/gamma-ray background, we consider a model that
is a mixture of thermal plasma components of perhaps supernova origin and
nonthermal emission from the interaction of low energy Cosmic ray electrons
(LECRe) with the interstellar medium. The LECRe may be accelerated in supernova
explosions or by ambient interstellar plasma turbulence. Atomic collisions of
fast electrons produce characteristic nonthermal, narrow X-ray emission lines
that can explain the complex Galactic background spectrum. Using the ASCA GIS
archival data from the Scutum arm region, we show that a two-temperature
thermal plasma model with kT~0.6 and ~2.8 keV, plus a LECRe component models
the data satisfactorily. Our analysis rules out a purely nonthermal origin for
the emission. It also rules out a significant contribution from low energy
Cosmic ray ions, because their nonthermal X-ray production would be accompanied
by a nuclear gamma-ray line diffuse emission exceeding the upper limits
obtained using OSSE, as well as by an excessive Galaxy-wide Be production rate.
The proposed model naturally explains the observed complex line features and
removes the difficulties associated with previous interpretations of the data
which evoked a very hot thermal component (kT~7 keV).


title: The Effect of Gasdynamics on the Structure of Dark Matter Halos

abstract:
  Adaptive SPH and N-body simulations were carried out to study the effect of
gasdynamics on the structure of dark matter halos that result from the
gravitational instability and fragmentation of cosmological pancakes. Such
halos resemble those formed in a hierarchically clustering CDM universe and
serve as a test-bed model for studying halo dynamics. With no gas, the density
profile is close to the universal profile identified previously from N-body
simulations of structure formation in CDM. When gas is included, the gas in the
halo is approximately isothermal, and both the dark matter and the gas have
singular central density profiles which are steeper than that of the dark
matter with no gas. This worsens the disagreement between observations of
constant density cores in cosmological halos and the singular ones found in
simulations. We also find that the dark matter velocity distribution is less
isotropic than found by N-body simulations of CDM, because of the strongly
filamentary substructure.


title: Source depth for solar p-modes

abstract:
  Theoretically calculated power spectra are compares with observed solar
p-mode velocity power spectra over a range of mode degree and frequency. The
depth for the sources responsible for exciting p-modes of frequency 2.0 mHz is
determined from the asymmetry of their power spectra and found to be about 800
km below the photosphere for quadrupole sources and 150 km if sources are
dipole. The source depth for high frequency oscillations of frequency greater
than about 6 mHz is 180 (50) km for quadrupole (dipole) sources.


title: Monte Carlo Simulations of Globular Cluster Dynamics

abstract:
  We have developed a new parallel supercomputer code based on Henon's Monte
Carlo method for simulating the dynamical evolution of globular clusters. This
new code allows us to calculate the evolution of a cluster containing a
realistic number of stars (N ~ 10^5 - 10^6) in about a day of computing time.
The discrete, star-by-star representation of the cluster in the simulation
allows us to treat naturally a number of important processes, including single
and binary star evolution, all dynamical interactions of single stars and
primordial binaries, and tidal interactions with the Galaxy.


title:
GRB 991216 Joins the Jet Set: Discovery and Monitoring of its Optical
  Afterglow

abstract:
  The optical light curve of the energetic gamma-ray burst GRB 991216 is
consistent with jet-like behavior in which a power-law decay steepens from
t**(-1.22 +/- 0.04) at early times to t**(-1.53 +/- 0.05) in a gradual
transition at around 2 d. The derivation of the late-time decay slope takes
into account the constant contribution of a host or intervening galaxy which
was measured 110 d after the event at R = 24.56 +/- 0.14, although the light
curve deviates from a single power law whether or not a constant term is
included. The early-time spectral energy distribution of the afterglow can be
described as F_nu ~ nu**(-0.74 +/- 0.05) or flatter between optical and X-ray,
which, together with the slow initial decay, is characteristic of standard
adiabatic evolution in a uniformly dense medium. Assuming that a reported
absorption-line redshift of 1.02 is correct, the apparent isotropic energy of
6.7 x 10**53 erg is reduced by a factor of ~ 200 in the jet model, and the
initial half-opening angle is ~ 6 deg. GRB 991216 is the third good example of
a jet-like afterglow (following GRB 990123 and GRB 990510), supporting a trend
in which the apparently most energetic gamma-ray events have the narrowest
collimation and a uniform ISM environment. This, plus the absence of evidence
for supernovae associated with jet-like afterglows, suggests that these events
may originate from a progenitor in which angular momentum plays an important
role but a massive stellar envelope or wind does not, e.g., the coalescence of
a compact binary.


title: The Multiband Photometry of the GRB Host Galaxies

abstract:
  We present photometric multiband spectral energy distributions for the GRB
host galaxies: GRB 971214, GRB 970508, GRB 980613, GRB 980703 and GRB 990123
obtained with the 6-m telescope of SAO RAS. Using SEDs for the starburst
galaxies, we made estimates of K-correction values and estimated the absolute
magnitudes of the GRB host galaxies within the range of cosmological
parameters. The comparison of the broad band spectra of these galaxies with the
spectra of galaxies of different morphological types (Connolly et al, 1995, AJ,
110, 1071) shows that the GRB host galaxies are best fitted by the spectral
properties of S2-S5 averaged SEDs of starburst galaxies.


title: Signs of the cusps in binary lenses

abstract:
  The cusps of the caustics of any gravitational lens model can be classified
into positive and negative ones. This distinction lies on the parity of the
images involved in the creation/destruction of pairs occurring when a source
crosses a caustic in a cusp. In this paper, we generalize the former definition
of the sign of the cusps. Then we apply it to the binary lens. We demonstrate
that the cusps on the axis joining the two lenses are positive while the others
are negative. To achieve our objective, we combine catastrophe theory, usually
employed in the derivation of the properties of caustics, with perturbative
methods, in order to simplify calculations and get readable results. Extensions
to multiple lenses are also considered.


title:
A Dust Cloud of Ganymede Maintained by Hypervelocity Impacts of
  Interplanetary Micrometeoroids

abstract:
  A dust cloud of Ganymede has been detected by in-situ measurements with the
dust detector onboard the Galileo spacecraft. The dust grains have been sensed
at altitudes below five Ganymede radii (Ganymede radius = $\rm 2,635 km$). Our
analysis identifies the particles in the dust cloud surrounding Ganymede by
their impact direction, impact velocity, and mass distribution and implies that
they have been kicked up by hypervelocity impacts of micrometeoroids onto the
satellite's surface. We calculate the radial density profile of the particles
ejected from the satellite by interplanetary dust grains. We assume the yields,
mass and velocity distributions of the ejecta obtained from laboratory impact
experiments onto icy targets and consider the dynamics of the ejected grains in
ballistic and escaping trajectories near Ganymede. The spatial dust density
profile calculated with interplanetary particles as impactors is consistent
with the profile derived from the Galileo measurements. The contribution of
interstellar grains as projectiles is negligible. Dust measurements in the
vicinities of satellites by spacecraft detectors are suggested as a beneficial
tool to obtain more knowledge about the satellite surfaces, as well as dusty
planetary rings maintained by satellites through the impact ejecta mechanism.


title: The Observation of Lunar Impacts

abstract:
  The intense activity of cratering on the Moon and in the inner regions of the
solar system was accomplished during the first 10^9 years [1]. Occasionally,
some impact events occur even nowadays. In Section 1, we treat, from a
historical point of view, the Earth-based observation of lunar impacts. In
Section 2, we consider the visibility conditions of such events evaluating the
luminosity of the background upon which an impact shines. In Section~3, the
luminosity of an impact is discussed. The occurrence of lunar impact events
outside of meteor shower periods is calculated using the hourly rate of the
sporadic meteors and their population index. The evidence of a larger rate of
impacts of meteoroids in the past under these hypotheses is presentend in the
last section.


title:
Detection of the thermal radio continuum emission from the G9.62+0.19-F
  Hot Core

abstract:
  We present new high resolution and high sensitivity multi-frequency VLA radio
continuum observations of the G9.62+0.19-F hot molecular core. We detect for
the first time faint centimetric radio continuum emission at the position of
the core. The centimetric continuum spectrum of the source is consistent with
thermal emission from ionised gas. This is the first direct evidence that a
newly born massive star is powering the G9.62+0.19-F hot core.


title: Kelvin-Helmholtz instability in three dimensional radiative jets

abstract:
  The analysis of the stability properties of astrophysical jets against
Kelvin-Helmholtz (or shear-layer) instabilities plays a basic role in the
understanding the origin and physical characteristics of these objects.
Numerical simulations by Bodo et al. (1998) have shown that the
three-dimensional non-linear evolution of KH instabilities in supersonic jets
is substantially faster than in the two-dimensional case, leading to a cascade
of modes towards smaller scales and a very effective mixing and momentum
transfer to the ambient medium. On the other hand, Rossi et al. (1997) and
Micono et al. (1998) found, in two dimensions, that radiative losses tend to
reduce and delay mixing effects and momentum transfer to the ambient medium. In
this paper, as a logical next step, we investigate the effects of radiative
losses on the stability of 3D supersonic jets, assuming that the internal jet
density is initially lower, equal and higher than the ambient medium,
respectively. We find that light and equal-density radiative jets evolve in a
qualitatively similar fashion with respect to the corresponding adiabatic ones.
Conversely, we note substantial differences in the evolution of heavy jets:
they remain more collimated and do not spread out, while the momentum gained by
the ambient medium stays within ~ 5 jet radii.


title:
Detection of a spectroscopic transit by the planet orbiting the star
  HD209458

abstract:
  We report the first detection of a planetary transit by spectroscopic
measurements. We have detected the distortion of the stellar line profiles
during a planetary transit. With the ELODIE spectrograph we took a sequence of
high precision radial velocities of the star HD209458 at time of a transit of
its planet. We detected an anomaly in the residuals of the orbit. The shape and
the amplitude of the anomaly are modeled as a change of the mean stellar line
profile resulting from the planet crossing the disk of the rotating star. The
planetary orbit is in the same direction as the stellar rotation. Using the
photometric transit to constrain the timing and the impact parameters of the
transit, we measure an angle alpha=3.9d between the orbital plane and the
apparent equatorial plane as well as a vsini=3.75(+-)1.25 kms-1. With
additional constrains on the inclination of the star and on the statistics of
the line of sight distribution, we can set an upper limit of 30d to the angle
between the orbital plane and the stellar equatorial plane.


title: Temperature and Density Gradients Across the Nucleus of M82

abstract:
  This paper presents 12CO J=3-2, 13CO J=3-2, C18O J=3-2, and 13CO J=2-1
spectra of the irregular starburst galaxy M82 taken with the 15 m James Clerk
Maxwell Telescope. All maps exhibit a double peaked morphology, despite
evidence that the higher J transitions are optically thick. This morphology
suggests that the double peaked structure is not the result of an edge-on torus
of molecular gas as is commonly assumed. We observe line ratio gradients that
can best be explained by a temperature gradient increasing from NE to SW in
conjunction with a density gradient that increases in the opposite sense. These
gradients may have been caused by the interaction with M81, resulting in
increased star formation that both heats and depletes the molecular gas in the
SW lobe of M82.


title: The Properties of the X-Ray-Selected EMSS Sample of BL Lac Objects

abstract:
  We present updated and complete radio, optical and X-ray data for BL Lacs in
the Einstein Medium Sensitivity Survey (EMSS). The complete "M91" sample first
presented in Morris et al. is updated to include 26 BL Lacs in total and we
define a new, virtually complete sample consisting of 41 EMSS BL Lacs (the
"D40" sample). New high signal-to-noise, arcsecond-resolution VLA observations
are also presented for eleven EMSS BL Lacs, completing VLA observations of the
M91 sample. The addition of four new objects, as well as updated X-ray flux and
redshift information, has increased the v/v_max value for the M91 sample to
0.399\pm0.057; and v/v_max = 0.427\pm0.045 for the newly defined D40 sample. In
conjunction with other studies of X-ray-selected BL Lac (XBL) samples, these
results solidify negative evolution for XBLs, especially for more extreme
high-energy-peaked BL Lacs. The observed v/v_max, spectral and radio properties
of XBLs are completely consistent with being the beamed population of
low-luminosity, FR-1 radio galaxies. However, our VLA observations do confirm
that XBLs are too core-dominated to be consistent with a beamed population of
FR-1s seen at intermediate angles, as suggested by the unified model, if XBLs
have moderate outflow velocities (gamma approx 5).


title:
Reconstructing the evolution of double helium white dwarfs: envelope
  loss without spiral-in

abstract:
  The unique core-mass - radius relation for giants with degenerate helium
cores enables us to reconstruct the evolution of three observed double helium
white dwarfs with known masses of both components.
  The last mass transfer phase in their evolution must have been a spiral-in.
In the formalism proposed by Webbink (1984), we can constrain the efficiency of
the deposition of orbital energy into the envelope to be $1 \la \alpha \la 6$,
for an envelope structure parameter $\lambda=0.5$. We find that the two
standard mass transfer types (stable mass transfer and spiral-in) are both
unable to explain the first phase of mass transfer for these three binaries.
  We use a parametric approach to describe mass transfer in low-mass binaries,
where both stars are of comparable mass and find that the orbital
characteristics of the observed double helium white dwarfs can be well
reproduced if the envelope of the primary is lost with ~1.5 times the specific
angular momentum of the initial binary. In this case no substantial spiral-in
occurs.