title:
Magnetic Field Decay in Neutron Stars. Analysis of General Relativistic
  Effects

abstract:
  An analysis of the role of general relativistic effects on the decay of
neutron star's magnetic field is presented. At first, a generalized induction
equation on an arbitrary static background geometry has been derived and,
secondly, by a combination of analytical and numerical techniques, a comparison
of the time scales for the decay of an initial dipole magnetic field in flat
and curved spacetime is discussed. For the case of very simple neutron star
models, rotation not accounted for and in the absence of cooling effects, we
find that the inclusion of general relativistic effects result, on the average,
in an enlargement of the decay time of the field in comparison to the flat
spacetime case. Via numerical techniques we show that, the enlargement factor
depends upon the dimensionless compactness ratio ${\epsilon}={2GM \over
c^{2}R}$, and for ${\epsilon}$ in the range $(0.3~,~0.5)$, corresponding to
compactness ratio of realistic neutron star models, this factor is between 1.2
to 1.3. The present analysis shows that general relativistic effects on the
magnetic field decay ought to be examined more carefully than hitherto. A brief
discussion of our findings on the impact of neutron stars physics is also
presented.


title: A Short History of the Missing Mass and Dark Energy Paradigms

abstract:
  In 1900 it was believed that almost 100% of the mass of the Universe resided
in stars. Now, in the year 2000, such stars (and cold gas) are known to account
for only ~1% its mass. The remaining mass of the Universe is thought to reside
in hot baryons (~3%), cold dark matter (~30%) and dark energy (~66%). The
present paper traces the evolution of our thinking about the density of the
Universe during the Twentieth Century, with special emphasis on the of the
discovery of cold dark matter.


title: Dynamics of line-driven disk winds in Active Galactic Nuclei

abstract:
  We present the results of time-dependent hydrodynamic calculations of line-
driven winds from accretion disks in AGN. To calculate the radiation force, we
take into account radiation from the disk and the central engine. The gas
temperature and ionization state in the wind are calculated self-consistently.
We find that a disk accreting onto a 10^8 MSUN black hole at the rate of 1.8
MSUN/YR can launch a wind at about 10^16 cm from the central engine. The X-rays
from the central object are attenuated by the disk atmosphere so they cannot
prevent the local disk radiation from pushing matter away from the disk. For a
reasonable X-ray opacity, the disk wind can be accelerated by the central UV
radiation to velocities of up to 15000 km/s at a distance of about 10^17 cm
from the central engine. The covering factor of the disk wind is $\sim 0.2$.
The wind is unsteady and consists of an opaque, slow vertical flow near the
disk that is bounded on the polar side by a high-velocity stream. A typical
column density through the fast stream is a few 10^23 cm^-2. The fast stream
contributes nearly 100% to the total wind mass loss rate of 0.5 MSUN/YR.


title: Testing theories that predict time variation of fundamental constants

abstract:
  We consider astronomical and local bounds on time variation of fundamental
constants to test some generic Kaluza-Klein-like models and some particular
cases of Beckenstein theory. Bounds on the free parameters of the different
theories are obtained. Furthermore, we find that none of the proposed models,
is able to explain recent results [Webb99,Webb00] claiming an observed
variation of the fine structure constant from quasar absorption systems at
redshifts $0.5<z<3$.


title: Giant Molecular Outflows Powered by Protostars in L1448

abstract:
  We present sensitive, large-scale maps of the CO J=1-0 emission of the L1448
dark cloud. These maps were acquired using the On-The-Fly capability of the
NRAO 12-meter telescope. CO outflow activity is seen in L1448 on parsec-scales
for the first time. Careful comparison of the spatial and velocity distribution
of our high-velocity CO maps with previously published optical and
near-infrared images and spectra has led to the identification of six distinct
CO outflows. We show the direct link between the heretofore unknown, giant,
highly-collimated, protostellar molecular outflows and their previously
discovered, distant optical manifestations. The outflows traced by our CO
mapping generally reach the projected cloud boundaries. Integrated intensity
maps over narrow velocity intervals indicate there is significant overlap of
blue- and red-shifted gas, suggesting the outflows are highly inclined with
respect to the line-of-sight, although the individual outflow position angles
are significantly different. The velocity channel maps also show that the
outflows dominate the CO line cores as well as the high-velocity wings. The
magnitude of the combined flow momenta, as well as the combined kinetic energy
of the flows, are sufficient to disperse the 50 solar mass NH3 cores in which
the protostars are currently forming, although some question remains as to the
exact processes involved in redirecting the directionality of the outflow
momenta to effect the complete dispersal of the parent cloud.


title:
The descendents of Lyman Break Galaxies in galaxy clusters: spatial
  distribution and orbital properties

abstract:
  We combine semi-analytical methods with a ultra-high resolution simulation of
a galaxy cluster (of mass 2.3 10^14h-1Msolar, and 4 10^6 particles within its
virial radius) formed in a standard CDM universe to study the spatial
distribution and orbital properties of the present-day descendents of Lyman
Break Galaxies (LBGs). At the present time only five (out of 12) of halos
containing LBGs survive as separate entities inside the cluster virial radius.
Their circular velocities are in the range 200 - 550 km/sec. Seven halos merged
together to form the central object at the very center of the cluster. Using
semi-analytical modeling of galaxy evolution we show that descendents of halos
containing LBGs now host giant elliptical galaxies. Galaxy orbits are radial,
with a pericenter to apocenter ratio of about 1:5. The orbital eccentricities
of LBGs descendents are statistically indistinguishable from those of the
average galaxy population inside the cluster, suggesting that the orbits of
these galaxies are not significantly affected by dynamical friction decay after
the formation of the cluster's main body. In this cluster, possibly due to its
early formation time, the descendents of LBGs are contained within the central
60% of the cluster virial radius and have an orbital velocity dispersion lower
than the global galaxy population, originating a mild luminosity segregation
for the brightest cluster members. Mass estimates based only on LBGs
descendents (especially including the central cD) reflect this bias in space
and velocity and underestimate the total mass of this well virialized cluster
by up to a factor of two compared to estimates using at least 20 cluster
members.


title:
The effects of numerical resolution on hydrodynamical surface convection
  simulations and spectral line formation

abstract:
  The computationally demanding nature of radiative-hydrodynamical simulations
of stellar surface convection warrants an investigation of the sensitivity of
the convective structure and spectral synthesis to the numerical resolution and
dimension of the simulations, which is presented here. With too coarse a
resolution the predicted spectral lines tend to be too narrow, reflecting
insufficient Doppler broadening from the convective motions, while at the
currently highest affordable resolution the line shapes have converged
essentially perfectly to the observed profiles. Similar conclusions are drawn
from the line asymmetries and shifts. In terms of abundances, weak FeI and FeII
lines show a very small dependence (~0.02 dex) while for intermediate strong
lines with significant non-thermal broadening the sensitivity increases (~0.10
dex). Problems arise when using 2D convection simulations to describe an
inherent 3D phenomenon, which translates to inaccurate atmospheric velocity
fields and temperature and pressure structures. In 2D the theoretical line
profiles tend to be too shallow and broad compared with the 3D calculations and
observations, in particular for intermediate strong lines. In terms of
abundances, the 2D results are systematically about 0.1 dex lower than for the
3D case for FeI lines. Furthermore, the predicted line asymmetries and shifts
are much inferior in 2D. Given these shortcomings and computing time
considerations it is better to use 3D simulations of even modest resolution
than high-resolution 2D simulations.


title:
Line formation in solar granulation: I. Fe line shapes, shifts and
  asymmetries

abstract:
  Realistic ab-initio 3D, radiative-hydrodynamical convection simulations of
the solar granulation have been applied to FeI and FeII line formation. In
contrast to classical analyses based on hydrostatic 1D model atmospheres the
procedure contains no adjustable free parameters but the treatment of the
numerical viscosity in the construction of the 3D, time-dependent,
inhomogeneous model atmosphere and the elemental abundance in the 3D spectral
synthesis. However, the numerical viscosity is introduced purely for numerical
stability purposes and is determined from standard hydrodynamical test cases
with no adjustments allowed to improve the agreement with the observational
constraints from the solar granulation. The non-thermal line broadening is
mainly provided by the Doppler shifts arising from the convective flows in the
solar photosphere and the solar oscillations. The almost perfect agreement
between the predicted temporally and spatially averaged line profiles for weak
Fe lines with the observed profiles and the absence of trends in derived
abundances with line strengths, seem to imply that the micro- and
macroturbulence concepts are obsolete in these 3D analyses. Furthermore, the
theoretical line asymmetries and shifts show a very satisfactory agreement with
observations with an accuracy of typically 50-100 m/s on an absolute velocity
scale. The remaining minor discrepancies point to how the convection
simulations can be refined further.


title: Line formation in solar granulation: II. The photospheric Fe abundance

abstract:
  The solar photospheric Fe abundance has been determined using realistic ab
initio 3D, time-dependent, hydrodynamical model atmospheres. The study is based
on the excellent agreement between the predicted and observed line profiles
directly rather than equivalent width, since the intrinsic Doppler broadening
from the convective motions and oscillations provide the necessary non-thermal
broadening. Thus, three of the four hotly debated parameters (equivalent
widths, microturbulence and damping enhancement factors) in the center of the
recent solar Fe abundance dispute regarding FeI lines no longer enter the
analysis, leaving the transition probabilities as the main uncertainty. Both
FeI (using the samples of lines of both the Oxford and Kiel studies) and FeII
lines have been investigated, which give consistent results: log FeI = 7.44 +-
0.05 and log FeII = 7.45 +- 0.10. Also the wings of strong FeI lines return
consistent abundances, log FeII = 7.42 +- 0.03, but due to the uncertainties
inherent in analyses of strong lines we give this determination lower weight
than the results from weak and intermediate strong lines. In view of the recent
slight downward revision of the meteoritic Fe abundance log Fe = 7.46 +- 0.01,
the agreement between the meteoritic and photospheric values is very good, thus
appearingly settling the debate over the photospheric Fe abundance from FeI
lines.


title:
Line formation in solar granulation: III. The photospheric Si and
  meteoritic Fe abundances

abstract:
  Using realistic hydrodynamical simulations of the solar surface convection as
3D, time-dependent, inhomogeneous model atmospheres, the solar photospheric Si
abundance has been determined to be log Si = 7.51 +- 0.04. This constitutes a
difference of 0.04 dex compared with previous estimates based on the 1D
Holweger-M\"uller (1974) model, of which half is attributable to the adopted
model atmosphere and the remaining part to the improved quantum mechanical
broadening treatment. As a consequence, all meteoritic abundances should be
adjusted downwards by the same amount. In particular the meteoritic Fe
abundance will be log Fe = 7.46 +- 0.01, in good agreement with the recently
determined photospheric Fe abundance (Asplund et al. 2000b). The existing
uncertainties unfortunately prevent an observational confirmation of the
postulated effects of elemental migration of metals in the Sun.


title:
Velocity and Mass Functions of Galactic Halos: Evolution and
  Environmental Dependence

abstract:
  We study the distribution functions of mass and circular velocity for dark
matter halos in N-body simulations of the $\Lambda$CDM cosmology, addressing
redshift and environmental dependence. The dynamical range enables us to
resolve subhalos and distinguish them from "distinct" halos. The mass function
is compared to analytic models, and is used to derive the more observationally
relevant circular velocity function. The distribution functions in the velocity
range 100--500 km/s are well fit by a power-law with two parameters, slope and
amplitude. We present the parameter dependence on redshift and provide useful
fitting formulae. The amplitudes of the mass functions decrease with z, but,
contrary to naive expectation, the comoving density of halos of a fixed
velocity ~200 km/s actually increases out to z=5. This is because high-z halos
are denser, so a fixed velocity corresponds to a smaller mass. The slope of the
velocity function at z=0 is as steep as ~ -4, and the mass and velocity
functions of distinct halos steepen with increasing z, while the functions of
subhalos do not steepen with $z$, and become even flatter at z>2. A simple
observable prediction is that the slope of the velocity function of isolated
galaxies is steeper than that of galaxies in groups by as much as unity,
reflecting the density biasing of high-velocity halos. We confirm that the
Press-Schechter approximation typically overestimates the halo mass function by
a factor of ~2, while modified approximations provide improved predictions.


title: Measurement of the Parallax of PSR B0950+08 Using the VLBA

abstract:
  A new technique has been developed to remove the ionosphere's distorting
effects from low frequency VLBI data. By fitting dispersive and non-dispersive
components to the phases of multi-frequency data, the ionosphere can be
effectively removed from the data without the use of {\em a priori} calibration
information. This technique, along with the new gating capability of the VLBA
correlator, was used to perform accurate astrometry on pulsar B0950+08,
resulting in a much improved measurement of this pulsar's proper motion
($\mu_{\alpha} = -1.6 \pm 0.4$ mas/yr, $\mu_{\delta} = 29.5 \pm 0.5$ mas/yr)
and parallax ($\pi = 3.6 \pm 0.3$ mas). This puts the pulsar at a distance of
$280 \pm 25$ parsecs, about twice as far as previous estimates, but in good
agreement with models of the electron density in the local bubble.


title: Strong Evolution in the Luminosity-Velocity Relation at z>1?

abstract:
  We present a method for constraining the evolution of the galaxy
luminosity-velocity (LV) relation in hierarchical scenarios of structure
formation. The comoving number density of dark-matter halos with circular
velocity of 200 km/s is predicted in favored CDM cosmologies to be nearly
constant over the redshift range 0<z<5. Any observed evolution in the density
of bright galaxies implies in turn a corresponding evolution in the LV
relation. We consider several possible forms of evolution for the zero-point of
the LV relation and predict the corresponding evolution in galaxy number
density. The Hubble Deep Field suggests a large deficit of bright (M_V < -19)
galaxies at 1.4 < z < 2. If taken at face value, this implies a dimming of the
LV zero-point by roughly 2 magnitudes. Deep, wide-field, near-IR selected
surveys will provide more secure measurements to compare with our predictions.


title: A Glitch in an Anomalous X-ray Pulsar

abstract:
  We report the detection of a sudden spin-up of the 11 s anomalous X-ray
pulsar 1RXS J170849.0-4000910 in regular timing observations made with the
Rossi X-ray Timing Explorer. The event, which occurred between MJD 51446 (1999
September 25) and 51472 (1999 October 21), is well characterized by an increase
in the rotational frequency of magnitude (Delta nu / nu) = (6.2 +/- 0.3) x
10^-7 and an increase in the rate of spin down (Delta \dot\nu / \dot\nu) =
(1.38 +/- 0.25) x 10^-2. These values are very similar to those of glitches
observed in the Vela radio pulsar and other young radio pulsars. The event
therefore suggests that the internal structure of this anomalous X-ray pulsar
is similar to those of the radio pulsars. In particular, it implies that the
fractional moment of inertia in neutron superfluid that is not corotating with
the crust is >= 1 %. The detection of a glitch in this anomalous X-ray pulsar
constrains models for the origin of glitches in neutron stars. Most notably, it
challenges models that preclude glitches in long-period pulsars, and, under the
magnetar hypothesis, suggests that large glitches can occur in hot neutron
stars. The glitch is consistent with the predictions of the magnetar model for
anomalous X-ray pulsars, but accretion-powered scenarios cannot be excluded
using our observations alone.


title:
A Structural and Dynamical Study of Late-Type, Edge-On Galaxies: I.
  Sample Selection and Imaging Data

abstract:
  We present optical (B & R) and infrared (K_s) images and photometry for a
sample of 49 extremely late-type, edge-on disk galaxies selected from the Flat
Galaxy Catalog of Karenchentsev et al. (1993). Our sample was selected to
include galaxies with particularly large axial ratios, increading the
likelihood that the galaxies in the sample are truly edge-on. We have also
concentrated the sample on galaxies with low apparent surface brightness, in
order to increase the representation of intrinisically low surface brightness
galaxies. Finally, the sample was chosen to have no apprarent bulges or optical
warps so that the galaxies represent undisturbed, ``pure disk'' systems. The
resulting sample forms the basis for a much larger spectroscopic study designed
to place constraints on the physical quantities and processes which shape disk
galaxies. The imaging data presented in this paper has been painstakingly
reduced and calibrated to allow accurate surface photometry of features as
faint as 30 mag/sqr-arcsec in B and 29 mag/sqr-arcsec in R on scales larger
than 10 arcsec. Due to limitations in sky subtraction and flat fielding, the
infrared data can reach only to 22.5 mag/sqr-arcsec in K_s on comparable
scales. As part of this work, we have developed a new method for quantifying
the reliability of surface photometry, which provides useful diagnostics for
the presence of scattered light, optical emission from infrared cirrus, and
other sources of non-uniform sky backgrounds.


title:
The influence of inverse Compton scattering on GRB afterglows: one
  possible way to flatten and steepen the light curves

abstract:
  The fireball model of gamma-ray bursts predicted that when the energetic
blast wave encountered the surrounding medium, there will be afterglow
emission, and the subsequent afterglow observations appeared to confirm this
prediction. In this simplest fireball model, the electrons have been
accelerated to a power law energy distribution in a relativistic blast wave,
then they give afterglow emission through synchrotron radiation. Up to now
synchrotron radiation is believed to be the main mechanism of GRB emission,
however, here we will show that under some circumstances, the inverse Compton
scattering (ICS) may play an important role, and can change the light curves of
GRB afterglows. Here we investigate the effects of ICS in the relativistic case
(the surrounding medium density $\rho \propto r^{-2}$) and in the
non-relativistic case (for both $\rho =constant$ and $\rho \propto r^{-2}$), we
find that in the relativistic case the effect of ICS is usually important,
while in the non-relativistic case, this effect is usually unimportant, unless
the surrounding medium density is very high. We show that if ICS is important,
then it can flatten and steepen the light curves of GRB afterglows, and this
may provide the explanation for some afterglow observations.


title: The Clustering of Colour Selected Galaxies

abstract:
  We present measurements of the angular correlation function of galaxies
selected from a B_J=23.5 multicolour survey of two 5 degree by 5 degree fields
located at high galactic latitudes. The galaxy catalogue of approximately
400,000 galaxies is comparable in size to catalogues used to determine the
galaxy correlation function at low-redshift. Measurements of the z=0.4
correlation function at large angular scales show no evidence for a break from
a power law though our results are not inconsistent with a break at >15 Mpc.
Despite the large fields-of-view, there are large discrepancies between the
measurements of the correlation function in each field, possibly due to dwarf
galaxies within z=0.11 clusters near the South Galactic Pole.
  Colour selection is used to study the clustering of galaxies z=0 to z=0.4.
The galaxy correlation function is found to strongly depend on colour with red
galaxies more strongly clustered than blue galaxies by a factor of 5 at small
scales. The slope of the correlation function is also found to vary with colour
with gamma=1.8 for red galaxies while gamma=1.5 for blue galaxies. The
clustering of red galaxies is consistently strong over the entire magnitude
range studied though there are large variations between the two fields. The
clustering of blue galaxies is extremely weak over the observed magnitude range
with clustering consistent with r_0=2 Mpc. This is weaker than the clustering
of late-type galaxies in the local Universe and suggests galaxy clustering is
more strongly correlated with colour than morphology. This may also be the
first detection of a substantial low redshift galaxy population with clustering
properties similar to faint blue galaxies.


title:
Formation of Cavities, Filaments, and Clumps by the Non-linear
  Development of Thermal and Gravitational Instabilities in the Interstellar
  Medium under Stellar Feedback

abstract:
  Based on our high resolution, two-dimensional hydrodynamical simulations, we
propose that large cavities may be formed by the nonlinear development of the
combined thermal and gravitational instabilities, without need for stellar
energy injection in a galaxy modeling the Large Magellanic Clouds (LMC). Our
numerical model of the star formation allows us to follow the evolution of the
blastwaves due to supernovae in the inhomogeous, multi-phase, and
turbulent-like media self-consistently. Formation of kpc-scale inhomogeneity,
such as cavities, observed HI map of the LMC, is suppressed by frequent
supernovae (average supernova rate for the whole disk is ~0.001/yr). However
the supernova explosions are necessary for the hot component (T_g > 10^{6-7}
K). Position-velocity maps show that kpc-scale shells/arcs formed through the
nonlinear evolution in a model without stellar energy feedback has similar
kinematics to explosional phenomena, such as supernovae. We also find that
dense clumps and filamentary structure are formed due to a natural consequence
of the non-linear evolution of the multi-phage ISM. Although the ISM in a small
scale looks turbulent-like and transient, the global structure of the ISM is
quasi-stable. We compare the observations of HI and molecular gas of the LMC
with the numerically obtained HI and CO map. The morphology and statistical
properties of the numerical HI and CO maps are discussed.


title: Self-similar collapse of collisional gas in an expanding Universe

abstract:
  Similarity solutions are found for the adiabatic collapse of density
perturbations $\delta M/M \propto r^{-s}$ $(s>0)$ in a flat universe containing
collisional gas only. The solutions are obtained for planar, cylindrical, and
spherical perturbations with zero initial pressure. For adiabatic index
$\gamma\ge 4/3$, a shock develops at a fixed fraction of the current turnaround
distance. Near the center of a spherical perturbations with $\gamma>4/3$ and
$s>1/2$, the gas is in quasi-hydrostatic equilibrium (pressure supported) and
has an asymptotic power law density profile, $\rho\sim r^{-3s/(s+1)}$,
independent of $\gamma$. For $s\le 1/2$, the profile depends on $\gamma$, the
pressure is finite, the temperature decreases inward, and gravity dominates
pressure causing a continuous inward flow. Although for $1/2<s<2$ the
temperature decreases at the center, the gas is pressure supported. The
pressure is finite in cylindrical perturbations for $s\le
2(\gamma-1)/(3\gamma-4)$, and in planar perturbations for any $s>0$. We also
derive the asymptotic behaviour of the gas variables near the center in a
universe dominated by collisionless matter. In such a universe, the gas in a
spherical perturbation with $s<2$ cannot be pressure supported and the
temperature approaches a constant near the center. The solutions and the
asymptotic behaviour are relevant for modelling the gas distribution in galaxy
clusters and pancake-like superclusters, and determining the structure of
haloes of self-interacting dark matter with large interaction cross section.


title: A project of a new detector for direct Dark Matter search: MACHe3

abstract:
  MACHe3 (MAtrix of Cells of superfluid He3) is a project of a new detector for
direct Dark Matter (DM) search. A cell of superfluid He3 has been developed and
the idea of using a large number of such cells in a high granularity detector
is proposed.This contribution presents, after a brief description of the
superfluid He3 cell, the simulation of the response of different matrix
configurations allowing to define an optimum design as a function of the number
of cells and the volume of each cell. The exclusion plot and the predicted
interaction cross-section for the neutralino as a photino are presented.


title: Observational Implications of Precessing Protostellar Discs and Jets

abstract:
  We consider the dynamics of a protostellar disc in a binary system where the
disc is misaligned with the orbital plane of the binary, with the aim of
determining the observational consequences for such systems. The disc wobbles
with a period approximately equal to half the binary's orbital period and
precesses on a longer timescale. We determine the characteristic timescale for
realignment of the disc with the orbital plane due to dissipation. If the
dissipation is determined by a simple isotropic viscosity then we find, in line
with previous studies, that the alignment timescale is of order the viscous
evolution timescale. However, for typical protostellar disc parameters, if the
disc tilt exceeds the opening angle of the disc, then tidally induced shearing
within the disc is transonic. In general, hydrodynamic instabilities associated
with the internally driven shear result in extra dissipation which is expected
to drastically reduce the alignment timescale. For large disc tilts the
alignment timescale is then comparable to the precession timescale, while for
smaller tilt angles $\delta$, the alignment timescale varies as $(\sin
\delta)^{-1}$. We discuss the consequences of the wobbling, precession and
rapid realignment for observations of protostellar jets and the implications
for binary star formation mechanisms.


title: Wavelet entropy as a measure of solar cycle complexity

abstract:
  Using wavelet analysis approach, we can derive a measure of the disorder
content of solar activity, following the temporal evolution of the so-called
wavelet entropy. The interesting feature of this parameter is its ability to
extract a dynamical complexity information, in terms of frequency distribution
of the energy content, avoiding restrictions, common in the nonlinear dynamics
theory, such as stationarity. The analysis is performed on the monthly time
series of sunspot numbers. From the time behaviour of the wavelet entropy we
found a clear increase in the disorder content of solar activity for the
current 23th solar cycle. This result suggests general low accuracies for
current solar cycleprediction methods. Moreover, we pointed out a possible
connection between wavelet entropy behaviour and solar excursion phases of
solar dipole.


title:
X-ray observations of the starburst galaxy NGC 253:II. Extended emission
  from hot gas in the nuclear area, disk, and halo

abstract:
  Spatial and spectral analysis of deep ROSAT HRI and PSPC observations of the
near edge-on starburst galaxy NGC 253 reveal diffuse soft X-ray emission, which
contributes 80% to its total X-ray luminosity (L$_{\rm X} = 5 10^{39}$ \ergsec,
corrected for foreground absorption). The nuclear area, disk, and halo
contribution to the luminosity is about equal. The starburst nucleus itself is
highly absorbed and not visible in the ROSAT band.
  We describe in detail spectra and morphology of the emission from the nuclear
area, disk and halo and compare our results to observations at other
wavelengths and from other galaxies. (abridged)


title: The Small-scale Structure in Interstellar HI: A Resolvable Puzzle

abstract:
  During the past decade or so, measurements of Galactic HI absorption using
VLBI against extra-galactic sources, as well as multi-epoch observatios in
pulsar directions, have detected small-scale transverse variations
corresponding to tens of AU at the distance of the absorbing matter. Hitherto
these measurements have been interpreted as small-scale structure in the HI
distribution with densities n_{HI} ~ 10^4-10^5 per cc, orders of magnitude
greater than those of the parsec-scale structure. Naturally it is difficult to
imagine how such structures could exist in equilibrium with other components of
the ISM.
  In this paper we show that structure on all scales contributes to the
differences on neighbouring lines of sight, and that the observed differences
can be accounted for by a natural extension of the distribution of
irregularities in the distribution of HI opacities at larger scales, using a
single power law. This, in our opinion, should put an end to the decades long
puzzle of the so-called small-scale structure in HI and other species in the
Galaxy.


title:
X-ray and optical follow-up observations of the August 1998 X-ray
  transient in NGC6440

abstract:
  The BeppoSAX Wide Field Cameras detected a transient in NGC6440 on 1998 Aug
22. ROSAT did not detect this source on 1998 Sep 8, indicating that the X-ray
flux had decreased by a factor 400 at least, and/or that the X-ray spectrum had
become appreciably softer. Analysis of archival ROSAT HRI data reveals two
sources associated with NGC6440; one of these may be the transient in
quiescence. We have also obtained B and R images of NGC6440 on 1998 Aug 26 and
again on 1999 July 15, when the transient had returned to quiescence.
Subtraction of these images reveals one object in the core which was brighter
in B, but not in R, during the X-ray outburst. We estimate B=22.7 and (B-R)o<0
on 1998 Aug 26, which makes it a viable candidate counterpart.


title:
The likely detection of pulsed high-energy gamma-ray emission from
  millisecond pulsar PSR J0218+4232

abstract:
  We report circumstantial evidence for the first detection of pulsed
high-energy gamma-ray emission from a millisecond pulsar, PSR J0218+4232, using
data collected with the Energetic Gamma Ray Experiment (EGRET) on board the
Compton Gamma Ray Observatory (CGRO). The EGRET source 3EG J0222+4253 is shown
to be spatially consistent with PSR J0218+4232 for the energy range 100 - 300
MeV. Above 1 GeV the nearby BL Lac 3C 66A is the evident counterpart, and
between 300 MeV and 1 GeV both sources contribute to the gamma-ray excess.
Folding the 100-1000 MeV photons with an accurate radio ephemeris of PSR
J0218+4232 yields a double peaked pulse profile with a ~3.5 sigma modulation
significance and with a peak separation of ~0.45 similar to the 0.1-10 keV
pulse profile.


title: Regimes Of Helium Burning

abstract:
  The burning regimes encountered by laminar deflagrations and ZND detonations
propagating through helium-rich compositions in the presence of buoyancy-driven
turbulence are analyzed. Particular attention is given to models of X-ray
bursts which start with a thermonuclear runaway on the surface of a neutron
star, and the thin shell helium instability of intermediate-mass stars. In the
X-ray burst case, turbulent deflagrations propagating in the lateral or radial
directions encounter a transition from the distributed regime to the flamlet
regime at a density of 10^8 g cm^{-3}. In the radial direction, the purely
laminar deflagration width is larger than the pressure scale height for
densities smaller than 10^6 g cm^{-3}. Self-sustained laminar deflagrations
travelling in the radial direction cannot exist below this density. Similarily,
the planar ZND detonation width becomes larger than the pressure scale height
at 10^7 g cm^{-3}, suggesting that a steady-state, self-sustained detonations
cannot come into existance in the radial direction. In the thin helium shell
case, turbulent deflagrations travelling in the lateral or radial directions
encounter the distributed regime at densities below 10^7 g cm^{-3}, and the
flamelet regime at larger densities. In the radial direction, the purely
laminar deflagration width is larger than the pressure scale height for
densities smaller than 10^4 g cm^{-3}, indicating that steady-state laminar
deflagrations cannot form below this density. The planar ZND detonation width
becomes larger than the pressure scale height at 5 10^4 g cm^{-3}, suggesting
that steady-state, self-sustained detonations cannot come into existance in the
radial direction.


title: High-Redshift Galaxies in Cold Dark Matter Models

abstract:
  We use hydrodynamic cosmological simulations to predict the star formation
properties of high-redshift galaxies (z=2-6) in five variants of the
inflationary cold dark matter scenario, paying particular attention to z=3, the
redshift of the largest "Lyman-break galaxy" (LBG) samples. Because we link the
star formation timescale to the local gas density, the rate at which a galaxy
forms stars is governed mainly by the rate at which it accretes cooled gas from
the surrounding medium. At z=3, star formation in most of the simulated
galaxies is steady on 200 Myr timescales, and the instantaneous star formation
rate (SFR) is correlated with total stellar mass. However, there is enough
scatter in this correlation that a sample selected above a given SFR threshold
may contain galaxies with a fairly wide range of masses. The redshift history
and global density of star formation in the simulations depend mainly on the
amplitude of mass fluctuations in the underlying cosmological model. The three
models whose mass fluctuation amplitudes agree with recent analyses of the
Lyman-alpha forest also reproduce the observed luminosity function of LBGs
reasonably well, though the dynamic range of the comparison is small and the
theoretical and observational uncertainties are large. The models with higher
and lower amplitudes appear to predict too much and too little star formation,
respectively, though they are not clearly ruled out. The intermediate amplitude
models predict SFR ~ 30-40 Msun/yr for galaxies with a surface density 1 per
arcmin^2 per unit redshift at z=3. They predict much higher surface densities
at lower SFR, and significant numbers of galaxies with SFR > 10 Msun/yr at z >=
5.


title: Thermonuclear Explosions of Chandrasekhar-Mass White Dwarfs

abstract:
  We present a new way of modeling turbulent thermonuclear deflagration fronts
in Chandrasekhar-mass white dwarfs, consisting of carbon and oxygen, undergoing
a type Ia supernova explosion. Our approach is a front capturing/tracking
hybrid scheme, based on a level set method, which treats the front as a
mathematical discontinuity and allows for full coupling between the front
geometry and the flow field. First results of the method applied to the problem
of type Ia supernovae are discussed. It will be shown that even in 2-D and even
with a physically motivated sub-grid model numerically ``converged'' results
are difficult to obtain.


title: The velocity field of young stars in the solar neighbourhood

abstract:
  A sample of O- and B-type stars with Hipparcos astrometric data, ages
computed from Str\"omgren photometry and radial velocities, has been used to
characterize the structure, age and kinematics of the Gould Belt system. The
local spiral structure of our galaxy is determined from this sample, and also
from a sample of Hipparcos Cepheid stars.
  The Gould Belt, with an orientation with respect to the galactic plane of
$i_{\mathrm{G}} = 16$-$22^\circ$ and $\Omega_{\mathrm{G}} = 275$-$295^\circ$,
extends up to a distance of 600 pc from the Sun. Roughly the 60-65% of the O
and B stars younger than 60 Myr in the solar neighbourhood belong to this
structure. Our results indicate that the kinematical behaviour of this system
is complex, with an expansion motion in the solar neighbourhood ($R <$ 300 pc).
  In the frame of the Lin's theory, and analysing the O and B stars further
than 600 pc and the Cepheids, we found a galactic spiral structure
characterized by a 4-arm spiral pattern with the Sun located at $\psi_\odot =
350$-$355 \pm 30^\circ$ -- near the Sagittarius-Carina arm -- and outside the
corotation circle. The angular rotation speed of the spiral pattern was found
to be $\Omega_{\mathrm{p}} = 31$-$32 \pm 4$ km s$^{-1}$ kpc$^{-1}$.


title:
FUSE Observations of the Galactic and Intergalactic Medium Towards
  H1821+643

abstract:
  We have obtained moderate resolution spectra of the bright QSO H1821+643
(z=0.297) in the wavelength interval 990-1185A with FUSE. Strong, complex OVI
1032 and FeII 1145 absorption arising in gas above several spiral arms and the
outer warp of our Galaxy is detected. We have identified absorption by a high
negative-velocity (-215 km/s) component of OVI, which corresponds to the
limiting velocity of v_LSR = 190+/-20 km/s for Milky Way gas along this line of
sight, assuming corotation of disk and halo gas and a flat rotation curve for
the outer galaxy. We report the detection of four absorbers in the
intergalactic medium, through detections of Lyman beta at z=0.2454 and
z=0.1213, Lyman delta, epsilon, zeta in a system at z=0.2249, CIII 977 at
z=0.1705, and OVI 1032 at z=0.12137. The FUSE data show that the Lyman
absorbers at z=0.225 are composed of 2 components separated by 70 km/s.
Finally, we have observed associated absorption from OIII 832, OIV 787, and
possibly SV 786 at the redshift of the QSO (z= 0.297). NeVIII 770,780 is not
detected in this associated system. When combined with the previous detection
of associated OVI 1032 (Savage et al, 1998), we conclude that this system is a
multiphase absorber, and we discuss the origin of the absorption in this
context.


title: Type Ia Supernovae and their implications for cosmology

abstract:
  Models for Type Ia Supernovae (SNe Ia) are reviewed. It is shown that there
are strong reasons to believe that most SNe Ia represent thermonuclear
disruptions of C-O white dwarfs, when these white dwarfs reach the
Chandrasekhar limit and ignite carbon at their centers.
  Different progenitor scenarios are reviewed critically and the strengths and
weaknesses of each scenario are presented in detail. It is argued that
theoretical considerations currently favor single-degenerate models, in which
the white dwarf accretes from a subgiant or giant companion. However, it is
still possible that more than one progenitor class contributes to the observed
sample. The relation of the different models to the use of SNe Ia for the
determination of cosmological parameters is discussed. It is shown that while
the observed diversity of SNe Ia may argue for the existence of different
progenitor classes, this does not affect the interpretation of an accelerating
expansion of the universe.


title:
The detection of spiral arm modulation in the stellar disk of an
  optically flocculent and an optically grand design galaxy

abstract:
  Two dimensional Fourier spectra of near-infrared images of galaxies provide a
powerful diagnostic tool for the detection of spiral arm modulation in stellar
disks. Spiral arm modulation may be understood in terms of interference
patterns of outgoing and incoming density wave packets or modes. The brightness
along a spiral arm will be increased where two wave crests meet and
constructively interfere, but will be decreased where a wave crest and a wave
trough destructively interfere. Spiral arm modulation has hitherto only been
detected in grand design spirals (such as Messier 81). Spiral arm amplitude
variations have the potential to become a powerful constraint for the study of
galactic dynamics. We illustrate our method in two galaxies: NGC 4062 and NGC
5248. In both cases, we have detected trailing and leading m=2 waves with
similar pitch angles. This suggests that the amplification mechanism is the
WASER type II. In this mechanism, the bulge region reflects (rather than
refracts) incoming waves with no change of pitch angle, but only a change of
their sense of winding. The ratio between the amplitudes of the leading and the
trailing waves is about 0.5 in both cases, wherein the higher amplitude is
consistently assigned to the trailing (as opposed to leading) mode. The results
are particularly significant because NGC 5248 is an optically grand design
galaxy, whereas NGC 4062 is optically flocculent. NGC 4062 represents the very
first detection of spiral arm modulation in the stellar disk of an optically
flocculent galaxy.


title: Poststarburst Models of LINERs

abstract:
  Since the discovery of low-ionization nuclear emission-line regions in many
galaxies (LINERs), it has been recognized that they constitute a class of
active galactic nuclei (AGNs) which are thought to be powered by gas accretion
onto a central, supermassive black hole. LINERs are observed in approximately
one third of galaxies in the local universe and it has been often thought that
they harbor an AGN-like central engine with moderate activity. However, some
LINERs show no direct evidence for AGNs such as broad emission lines, radio
jets, hard X-ray emission, spectral energy distributions which are inconsistent
with starlight, and so on. For such LINERs (a subset of type 2 LINERs), we
present new poststarburst models which explain some of their most important
optical narrow emission-line ratios. In these models, the ionization sources
are planetary nebula nuclei (PNNs) with temperature of ~ 10^5 K which appear in
the late-phase evolution of intermediate-mass stars with mass between ~ 3
M_solar and ~ 6 M_solar. Such PNNs left in a typical starburst nucleus can
produce an Halpha luminosity of L(Halpha) ~ 10^38 ergs s^-1 for typical
poststarburst LINERs and ~ 10^39 ergs s^-1 only in exceptionally bright cases.
The PNN phase lasts until the death of the lowest-mass stars formed in the
starburst, which is ~ 5 x 10^8 yr for an assumed lower limit of the initial
mass function of 3 M_solar. This long duration appears consistent with the
observed higher frequency of occurrence of LINERs if every galaxy could
experience the starburst activity several times in its life. We therefore
propose that some LINERs which show no direct evidence for AGNs may be
poststarburst nuclei powered by a cluster of PNNs.


title:
Orbital Motion of Resonant Clumps in Dusty Circumstellar Disks as a
  Signature of an Embedded Planet

abstract:
  We have applied a powerful numerical approach to compute, with a high
resolution, the structure of dusty circumstellar disks with embedded planets.
We emphasize some testable implications of our simulations which would verify
the presence of a planet via thermal emission of one or more dusty clumps which
are in mean motion resonances with the planet. In particular, our simulations
indicate that Vega may have a massive planet of m~2 m_J (m_J being Jupiter's
mass) at a distance of 50-60 AU, and Epsilon Eri may have a less massive planet
of m~0.2 m_J at a similar distance of 55-65 AU. This conclusion is testable:
Each resonant feature is stationary in the reference frame co-rotating with the
planet, but it is not so for the observer at Earth. Therefore, if our
interpretation of asymmetric clumps in circumstellar disks as dynamical
resonant structures is correct, the above pattern revolves around the star with
an angular velocity of (1.2-1.6) deg/yr (Vega) and (0.6-0.8) deg/yr (Epsilon
Eri) -- a prediction that can be tested on a timescale of several years.


title: X-ray emission from Lindroos binary systems

abstract:
  We present a study of the X-ray emission from binary systems extracted from
the Lindroos catalogue (Lindroos 1986) based on the ROSAT All-Sky survey as
well as ROSAT PSPC and HRI pointings. The studied sample consists of visual
binary systems comprised of early-type primaries and late-type secondaries. The
ages of the systems were determined by Lindroos (1985) from uvbybeta photometry
of the primaries. These ages range between 33 and 135 Myr, so if the late-type
secondaries are physically bound to the early-type primaries, they could be
Post-T Tauri stars (PTTS). We have found strong X-ray emission from several
secondaries. This fact together with their optical and IR data, make them bona
fide PTTS candidates. We have also detected X-ray emission from several
early-type primaries and, in particular, from most of the late-B type stars.
Because their HRI hardness ratios are similar to those from resolved late-type
stars, the presence of an unresolved late-type companion seems to be the cause
of this emission.


title: An infrared background--TeV gamma-ray crisis?

abstract:
  We consider the implications of the recent determination of the universal
infrared background for the propagation of photons up to 20 TeV from the active
galaxy Markarian 501 as observed by HEGRA. At 20 TeV the mean free path for
photon-photon collisions on the infrared background would be much shorter than
the distance to Markarian 501, implying absorption factors of the order of
exp(-10), or greater, and consequently an excessive power output for this
active galaxy. Possible solutions of this problem are discussed.


title:
Is MS1054-03 an exceptional cluster? A new investigation of ROSAT/HRI
  X-ray data

abstract:
  We reanalyzed the ROSAT/HRI observation of MS1054-03, optimizing the channel
HRI selection and including a new exposure of 68 ksec. From a wavelet analysis
of the HRI image we identify the main cluster component and find evidence for
substructure in the west, which might either be a group of galaxies falling
onto the cluster or a foreground source. Our 1-D and 2-D analysis of the data
show that the cluster can be fitted well by a classical betamodel centered only
20arcsec away from the central cD galaxy. The core radius and beta values
derived from the spherical model(beta = 0.96_-0.22^+0.48) and the elliptical
model (beta = 0.73+/-0.18) are consistent. We derived the gas mass and total
mass of the cluster from the betamodel fit and the previously published ASCA
temperature (12.3^{+3.1}_{-2.2} keV). The gas mass fraction at the virial
radius is fgas = (14[-3,+2.5]+/-3)% for Omega_0=1, where the errors in brackets
come from the uncertainty on the temperature and the remaining errors from the
HRI imaging data. The gas mass fraction computed for the best fit ASCA
temperature is significantly lower than found for nearby hot clusters,
fgas=20.1pm 1.6%. This local value can be matched if the actual virial
temperature of MS1054-032 were close to the lower ASCA limit (~10keV) with an
even lower value of 8 keV giving the best agreement. Such a bias between the
virial and measured temperature could be due to the presence of shock waves in
the intracluster medium stemming from recent mergers. Another possibility, that
reconciles a high temperature with the local gas mass fraction, is the
existence of a non zero cosmological constant.


title:
Detection of Lead in the Carbon-Rich, Very Metal-Poor Star LP625-44: A
  Strong Constraint on s-Process Nucleosynthesis at Low Metallicity

abstract:
  We report the detection of the Pb I 4057.8A line in the very metal-poor
([Fe/H]=-2.7), carbon-rich star, LP625-44. We determine the abundance of Pb
([Pb/Fe] = 2.65) and 15 other neutron-capture elements. The abundance pattern
between Ba and Pb agrees well with a scaled solar system s-process component,
while the lighter elements (Sr-Zr) are less abundant than Ba. The enhancement
of s-process elements is interpreted as a result of mass transfer in a binary
system from a previous AGB companion, an interpretation strongly supported by
radial velocity variations of this system.
  The detection of Pb makes it possible, for the first time, to compare model
predictions of s-process nucleosynthesis in AGB stars with observations of
elements between Sr and Pb. The Pb abundance is significantly lower than the
prediction of recent models (e.g., Gallino et al. 1998), which succeeded in
explaining the metallicity dependence of the abundance ratios of light
s-elements (Sr-Zr) to heavy ones (Ba-Dy) found in previously observed
s-process-enhanced stars. This suggests that one should either (a) reconsider
the underlying assumptions concerning the 13C-rich s-processing site
(13C-pocket) in the present models, or (b) investigate alternative sites of
s-process nucleosynthesis in very metal-poor AGB stars.


title: Cosmological two-fluid thermodynamics

abstract:
  We reveal unifying thermodynamic aspects of so different phenomena as the
cosmological electron-positron annihilation, the evaporation of primordial
black holes with a narrow mass range, and the ``deflationary'' transition from
an initial de Sitter phase to a subsequent standard
Friedmann-Lema\^{\i}tre-Robertson-Walker begin (FLRW) behavior.


title:
Models for the interpretation of CaT and the blue Spectral Indices in
  Elliptical Nuclei

abstract:
  We present a grid of theoretical models where the calculation of absorption
line spectral indices in both the blue and red wavelength ranges is done with
the same evolutionary synthesis code. We have computed some of these indices:
CaT, NaI, MgI in the near infrared and Mgb, Mg2, Fe52, Fe53, NaD and Hbeta, in
the blue-visible range, for Single Stellar Population (SSP) of 6 different
metallicities, (Z=0.0004,0.001, 0.004, 0.008, 0.02 and 0.05), and ages from 4
Myr to 20 Gyr.
  From the comparison of these evolutionary synthesis models with a compilation
of elliptical galaxy data from the literature, we find that the observed CaT
index follows the blue <Fe> index rather than Mg2 as the models predict. If
this implies an over-abundance [Mg/Ca] and we take into account the masses of
stars which produce Mg and Ca, these stars could form in a time scale shorter
than 5 Myr from the beginning of the star formation process. Alternatively, an
IMF biased towards very massive stars (M > 40 Msun) at the early epoch of star
formation in elliptical nuclei has to be assumed. We also suggest to revise the
calculation of the nucleosynthesis yield of Magnesium.
  By using the diagnostic diagram CaT-Hbeta to disentangle age and metallicity
in such populations, we obtain around solar abundances and a sequence of ages
between 4 and 16 Gyr for the galaxy sample.


title:
Deep far infrared ISOPHOT survey in "Selected Area 57", I. Observations
  and source counts

abstract:
  We present here the results of a deep survey in a 0.4 sq.deg. blank field in
Selected Area 57 conducted with the ISOPHOT instrument aboard ESAs Infrared
Space Observatory (ISO) at both 60 um and 90 um. The resulting sky maps have a
spatial resolution of 15 x 23 sq.arcsec. per pixel which is much higher than
the 90 x 90 sq.arcsec. pixels of the IRAS All Sky Survey. We describe the main
instrumental effects encountered in our data, outline our data reduction and
analysis scheme and present astrometry and photometry of the detected point
sources. With a formal signal to noise ratio of 6.75 we have source detection
limits of 90 mJy at 60 um and 50 mJy at 90 um. To these limits we find
cumulated number densities of 5+-3.5 per sq.deg. at 60 um and 14.8+-5.0 per
sq.deg.at 90 um. These number densities of sources are found to be lower than
previously reported results from ISO but the data do not allow us to
discriminate between no-evolution scenarios and various evolutionary models.


title: Potential equations for plasmas round a rotating black hole

abstract:
  The generalized Helmholtz equations of relativistic multifluid plasmas can be
integrated for axisymmetric equilibria in close analogy to the magnetic flux
conservation law in ideal magnetohydrodynamics (J. D. Bekenstein and E. Oron,
Phys. Rev. D 18, 1809 (1978)). The results are, for each fluid component, two
flux functions and a potential equation for the poloidal stream function.
Ampere's equation for the four-potential A_\nu is reduced to two coupled
equations for the time-like and the toroidal component. So we have altogether
four potential equations for a two-component plasma; they can be derived from a
variational principle.


title: Episodic lithium production by extra-mixing in red giants

abstract:
  The recent discovery of low-mass red giants with enhanced atmospherical Li
abundance in galactic low-metallicity stellar clusters adds to the mysterious
phenomenon of the Li-rich giants. We propose a combined scenario for the
Li-enrichment: engulfing a giant planet (or brown dwarf) by a red giant
(external source) activates inside the giant the "7Be-mechanism" producing Li
internally. This episodical Li-production can happen at any time on the red
giant branch and is naturally followed by Li-depletion as is observed.
Limitations of our scenario are discussed as well.


title: Multiphase Smoothed-Particle Hydrodynamics

abstract:
  We adapt the Smoothed-Particle Hydrodynamics technique to allow a multiphase
fluid in which SPH particles of widely differing density may be freely
intermixed. Applications include modelling of galaxy formation and cooling
flows.


title: Cluster Correlation in Mixed Models

abstract:
  We evaluate the dependence of the cluster correlation length r_c on the mean
intercluster separation D_c, for three models with critical matter density,
vanishing vacuum energy (Lambda = 0) and COBE normalized: a tilted CDM (tCDM)
model (n=0.8) and two blue mixed models with two light massive neutrinos
yielding Omega_h = 0.26 and 0.14 (MDM1 and MDM2, respectively). All models
approach the observational value of sigma_8 (and, henceforth, the observed
cluster abundance) and are consistent with the observed abundance of Damped
Lyman_alpha systems. Mixed models have a motivation in recent results of
neutrino physics; they also agree with the observed value of the ratio
sigma_8/sigma_25, yielding the spectral slope parameter Gamma, and nicely fit
LCRS reconstructed spectra. We use parallel AP3M simulations, performed in a
wide box (side 360/h Mpc) and with high mass and distance resolution, enabling
us to build artificial samples of clusters, whose total number and mass range
allow to cover the same D_c interval inspected through APM and Abell cluster
clustering data. We find that the tCDM model performs substantially better than
n=1 critical density CDM models. Our main finding, however, is that mixed
models provide a surprisingly good fit of cluster clustering data.


title: Multichannel interference mitigation methods in radio astronomy

abstract:
  Radio-astronomical observations are increasingly corrupted by RF
interference, and online detection and filtering algorithms are becoming
essential. To facilitate the introduction of such techniques into radio
astronomy, we formulate the astronomical problem in an array signal processing
language, and give an introduction to some elementary algorithms from that
field. We consider two topics in detail: interference detection by rank
estimation of short-term covariance matrices, and spatial filtering by subspace
estimation and projection. We discuss experimental data collected at the
Westerbork radio telescope, and illustrate the effectiveness of the space-time
detection and blanking process on the recovery of a 3C48 absorption line in the
presence of GSM mobile telephony interference.


title: The 12C/13C-ratio in cool carbon stars

abstract:
  We present observations of circumstellar millimetre-wave 13CO line emission
towards a sample of 20 cool carbon stars. Using a detailed radiative transfer
model we estimate the circumstellar 12CO/13CO-ratios, which we believe
accurately measure the important stellar 12C/13C-ratios. For those optically
bright carbon stars where it is possible, our derived 12C/13C-ratios are
compared with the photospheric results, obtained with different methods. Our
estimates agree well with those of Lambert et al. (1986).
  It is shown that a straightforward determination of the 12CO/13CO-ratio from
observed line intensity ratios is often hampered by optical depth effects, and
that a detailed radiative transfer analysis is needed in order to determine
reliable isotope ratios.


title:
The MACHO Project LMC Variable Star Inventory. IX. Frequency Analysis of
  the First Overtone RR Lyrae Stars and the Indication for Nonradial Pulsations

abstract:
  More than 1300 variables classified provisionally as first overtone RR Lyrae
pulsators in the MACHO variable star database of the Large Magellanic Cloud
(LMC) have been subjected to standard frequency analysis. Based on the remnant
power in the prewhitened spectra, we found 70% of the total population to be
monoperiodic. The remaining 30% (411 stars) are classified as one of 9 types
according to their frequency spectra. Several types of RR Lyrae pulsational
behavior are clearly identified here for the first time. Together with the
earlier discovered double-mode (fundamental & first overtone) variables this
study increased the number of the known double-mode stars in the LMC to 181.
During the total 6.5yr time span of the data, 10% of the stars show strong
period changes. We also discovered two additional types of multifrequency
pulsators with low occurrence rates of 2% for each. In the first type there
remains one closely spaced component after prewhitening by the main pulsation
frequency. In the second type the number of remnant components is two, they are
also closely spaced, and, in addition, they are symmetric in their frequency
spacing relative to the central component. This latter type of variables is
associated with their relatives among the fundamental pulsators, known as
Blazhko variables. Their high frequency (~20%) among the fundamental mode
variables versus the low occurrence rate of their first overtone counterparts
makes it more difficult to explain Blazhko phenomenon by any theory depending
mainly on the role of aspect angle or magnetic field. Current theoretical
models invoke nonradial pulsation components in these stars.


title:
On the Thermal Instability in a Contracting Gas Cloud and Formation of a
  Bound Cluster

abstract:
  We perform linear analysis of thermal instability in a contracting large
cloud filled with warm HI gas and investigate the effect of metallicity and
radiation flux. When the cloud reaches critical density n_f, the cloud
fragments into cool, dense condensations because of thermal instability. For a
lower metallicity gas cloud, the value of n_f is high. Collision between
condensations will produce self-gravitating clumps and stars thereafter. From
the result of calculation, we suggest that high star formation efficiency and
bound cluster formation are realized in low-metallicity and/or strong-radiation
environments.


title: Polarized Sub-Millimetre Emission from Filamentary Molecular Clouds

abstract:
  We model the sub-millimetre polarization patterns that are expected for
filamentary clouds that are threaded by helical magnetic fields. We previously
developed a three parameter model of such clouds (Fiege & Pudritz 2000a), which
are described by a concentration parameter $C$, and two flux to mass ratios
$\Gz$ and $\Gphi$ to specify the mass loading of the poloidal and toroidal
field lines respectively. Our models provide a simple and purely geometric
explanation for the well-known ``polarization hole'' effect, in which the
sub-millimetre polarization percentage decreases toward the regions of peak
intensity. This occurs because of a cancellation between contributions to the
polarization from the ``backbone'' of poloidal flux along the filament's axis
and its surrounding envelope, which is dominated by the toroidal field
component. A systematic exploration of our parameter space allows us to
classify the polarization patterns due to filaments aligned approximately
perpendicular to the plane of the sky into three basic types. The polarization
vectors are parallel to filaments when $\ratio\appleq 0.1$, where $\Bzs$ and
$\Bphis$ are respectively the poloidal and toroidal magnetic field components
at the outer surface of the filament. The polarization vectors are
perpendicular to filaments when $\ratio\appgeq 0.33$. Intermediate cases result
in polarization patterns that contain $90^\circ$ flips in the orientation of
the polarization vectors. The flips are symmetric about the central axis for
filaments oriented parallel to the plane of the sky, but more complicated
asymmetric patters result from filaments that are inclined at some angle.


title: Transient Low-Mass X-Ray Binaries in Quiescence

abstract:
  We summarize the quiescent X-ray observations of transient low-mass X-ray
binaries. These observations show that, in quiescence, binaries containing
black holes are fainter than those containing neutron stars. This has triggered
a number of theoretical ideas about what causes the quiescent X-ray emission.
For black hole binaries, the options are accretion onto the black hole or
coronal emission from the rapidly rotating stellar companion. There are more
possibilities for the neutron stars: accretion, thermal emission from the
surface or non-thermal emission from a ``turned-on'' radio pulsar. We review
recent theoretical work on these mechanisms and note where current observations
can distinguish between them. We highlight the re-analysis of the quiescent
neutron star emission by Rutledge and collaborators that showed thermal
emission to be a predominant contributor in many of these systems. Our
knowledge of these binaries is bound to dramatically improve now that the
Chandra and XMM satellites are operating successfully,


title:
Big Bang Leftovers in the Microwave: Cosmology with the Cosmic Microwave
  Background Radiation

abstract:
  We combine detections of anisotropy in the Cosmic Microwave Background
radiation with observations of inhomogeneity in the large-scale distribution of
galaxies to test the predictions of models of cosmological structure formation.
This combination probes spatial scales varying by three orders of magnitude,
including a significant region where the two types of data overlap. We examine
Cold Dark Matter models with adiabatic density perturbations, isocurvature
models, and a topological defects model. We set upper limits on the neutrino
mass and find the primordial power spectrum needed to reconcile an apparent
disagreement between structure formation observations and direct observations
of cosmological parameters.
  Present and future observations of Cosmic Microwave Background anisotropy
suffer from foreground contamination. We develop detailed predictions for
microwave emission from radio and infrared-bright galaxies and the
Sunyaev-Zeldovich effect from clusters. We present realistic simulations of the
microwave sky, produced as part of the `WOMBAT Challenge' exercise, and
introduce a pixel-space method for subtracting foreground contamination which
can be tested on these simulations.


title:
Simulation of the Spherically Symmetric Stellar Core Collapse, Bounce,
  and Postbounce Evolution of a 13 Solar Mass Star with Boltzmann Neutrino
  Transport, and Its Implications for the Supernova Mechanism

abstract:
  With exact three-flavor Boltzmann neutrino transport, we simulate the stellar
core collapse, bounce, and postbounce evolution of a 13 solar mass star in
spherical symmetry, the Newtonian limit, without invoking convection. In the
absence of convection, prior spherically symmetric models, which implemented
approximations to Boltzmann transport, failed to produce explosions. We are
motivated to consider exact transport to determine if these failures were due
to the transport approximations made and to answer remaining fundamental
questions in supernova theory. The model presented here is the first in a
sequence of models beginning with different progenitors. In this model, a
supernova explosion is not obtained. We discuss the ramifications of our
results for the supernova mechanism.


title: Chromospheric Activity in Metal-Poor Dwarfs

abstract:
  We have obtained echelle spectra with the Hubble Space Telescope (HST) of the
MgII 2800A region of ten stars whose metallicities range from 1/300 to 1/3 that
of the Sun, and whose space velocities suggest a halo or old thick-disk origin.
Spectra of all ten show double-peaked emission in the MgII core, very much like
the quiet Sun. A half-dozen non-rotating stars were observed more than once,
and show at most a low level of variability in the emission flux, comparable to
that of quiet stars of solar metallicity. For four stars, we have obtained
Lyman-alpha spectra at 0.2A resolution; all four show emission. The data thus
strongly suggest that chromospheric activity at a minimum level is present in
all stars of near-solar temperature, regardless of age or metallicity. While
this points to non-magnetic sources such as acoustic waves, a contribution from
globally-organized magnetic fields is possible at a low level. We plan a longer
series of MgII and Lyman alpha observations to constrain this.


title: The 2dF QSO Redshift Survey - I. The Optical QSO Luminosity Function

abstract:
  We present a determination of the optical QSO luminosity function and its
cosmological evolution with redshift for a sample of over 6000 QSOs identified
primarily from the first observations of the 2dF QSO Redshift Survey (2QZ). For
QSOs with -26 < M_B < -23 and 0.35 < z < 2.3, we find that pure luminosity
evolution (PLE) models provide an acceptable fit to the observed redshift
dependence of the luminosity function. The luminosity function is best fit by a
two-power-law function of the form. Exponential luminosity evolution models,
both as a function of look-back time, and as a general second-order polynomial
with redshift, were found to provide acceptable fits to the dataset comprising
the 2QZ and the Large Bright Quasar Survey. Exponential evolution with
look-back time is prefered for q_0=0.05, while the polynomial evolution model
is prefered for q_0=0.5. The shape and evolution of the LF at low redshifts
(z<0.5) and/or high luminosities, not currently well sampled by the 2dF QSO
survey, may show departures from pure luminosity evolution, but the results
presented here show that over a significant range of redshift, PLE is a good
description of QSO evolution.


title: A BeppoSAX and ROSAT view of the RCW86 supernova remnant

abstract:
  We present a spectral analysis of the Northern and Southwestern rim of the
RCW86 X-ray shell, pointing out the remarkable differences between these two
parts of the same object. In the North, a single temperature Non Equilibrium of
Ionization emission model describes the data well, and the derived abundances
of O, Ne, Mg, Si, S, Ar and Fe are in agreement with expected metal depletion
behind a fast shock moving in the interstellar medium. If the initial explosion
energy was $\sim 10^{51}$ erg, the derived distance and age are
$1.18^{+0.17}_{-0.16}$ kpc and $1630^{+440}_{-360}$ yr, fully consistent with
the association to the historical supernova SN185. The X-ray emission from the
SW is described by a two-temperature emission model with kT$_{\rm h}=5.7$ keV
and kT$_{\rm l}=1.0$ keV. There is evidence of overabundant metals in the
high-temperature component, thus indicating the presence of ejecta. In this
case, a Type Ia SN is to be preferred over a more energetic Type II event,
which would imply a more distant and older remnant fully in its Sedov phase.


title: HI Observations of the starburst galaxy NGC 2146

abstract:
  NGC 2146 is a peculiar spiral galaxy which is currently undergoing a major
burst of star formation and is immersed in a extended HI structure that has
morphological and kinematical resemblence to a strong tidal interaction. This
paper reports aperture synthesis observations carried out in the 21cm line with
the Very Large Array (VLA - The National Radio Astronomy Observatory (NRAO) is
operated by Associated Universities, Inc. under cooperative agreement with the
National Science Foundation.) of two fields positioned to optimally cover the
HI streams to the north and south of the galaxy, along with a 300 ft total
power spectral mapping program to recover the low surface brightness extended
emission. The observations reveal elongated streams of neutral hydrogen towards
both the north and the south of the optical galaxy extending out up to 6
Holmberg radii. The streams are not in the principle plane of rotation of the
galaxy, but instead are suggestive of a tidal interaction between NGC 2146 and
a LSB companion that was destroyed by the encounter and remains undetected at
optical wavelengths. Part of the southern stream is turning back to fall into
the main galaxy, where it will create a long-lived warp in the HI disk of NGC
2146. Analysis of the trajectory of the outlying gas suggests that the closest
encounter took place about 0.8 billion years ago and that infall of debris will
continue for a similar time span.


title:
Constraints on source and lens parameters from microlensing variability
  in QSO 0957+561 A,B

abstract:
  From regular monitoring of the Double Quasar QSO 0957+561 A,B there is now
general agreement on a time delay of about 416 days. This has made it possible
to determine the microlensing residual in the light-curve, see Pelt et al.
(1998). We have used two significant microlensing features: 1) A ``quiet''
period with a variability less than 0.05 mag lasting about 8 years, and 2) A
change in the residual of 0.25 mag during a time interval of about 5 years. The
first feature gives a lower limit for the lens mass, 'M', for a given
normalized source radius, 'r', whereas the second feature gives an upper limit.
We have considered the amount of mass in a continuum to be a free parameter
with possible values between 0% (all mass in lenses) and 90%. At a significance
level of 1% the mass can only be constrained within a rather wide range (1e-06
M_solar to 5 M_solar). For the radius 'R' of the source an upper limit of 1e16
cm is found, whereas the normalized source radius 'r' is restricted to be
smaller than 30. At a level of 10%, however, the range of possible masses is
much narrower (2e-03 M_solar to 0.5 M_solar), and the upper limit of R is about
6e15 cm, whereas the value of 'r' is restricted to be less than 2. We have used
an effective transverse velocity 'V' equal to 600 km/s.


title: Modelling Radioactivities and other Observables from OB Associations

abstract:
  Recent observations of the diffuse Galactic gamma-ray glow at 1.809 MeV,
attributed to the radioactive decay of 26Al, point towards a massive star
origin of this radioactive isotope. Wolf Rayet stars and core-collapse
supernovae appear to dominate the production of this isotope. Massive stars are
commonly located in clusters and OB associations, regions of recent star
formation. We thus discuss the temporal evolution of 26Al, and 60Fe within
evolving OB associations. The goal of this study is to utilize the associated
gamma-ray lines as a diagnostic tool for the study of correlated star
formation, and also to provide more detailed models for the interpretation of
data obtained with COMPTEL on the Compton Observatory. We investigate the
effects of possible aluminum yield enhancements, predicted for some massive
close binary systems. In addition to the ejection of chemically processed
matter, massive stars also drive strong stellar winds and emit large fluxes of
ionizing radiation. This energy and radiation input into the interstellar
medium (ISM) is crucial for the dynamical evolution of the gas and subsequent
star forming activity in the galactic disk. We discuss population synthesis
models for a variety of star formation histories, and compare the predicted
gamma-ray line lightcurves to COMPTEL measurements in the Cygnus region.
Radioactive tracers such as 26Al and 60Fe provide a unique gamma-ray tracer of
Galactic star formation activity, complementary to other methods using spectral
information in the radio, IR or optical bands.


title:
Structure of the MgII and damped Lyman-alpha systems along the line of
  sight to APM 08279+5255

abstract:
  A study of the absorption systems toward the gravitationally lensed quasar
APM 08279+5255 is presented. Most of the MgII systems in the redshift range
1.2-2.07, although saturated, show large residuals at the bottom of the lines.
The most likely interpretation is that individual clouds within MgII halos do
cover only one of the two brightest QSO images. This reveals that MgII halos
are made of a collection of clouds of radius smaller than about 1 kpc. Two
strong MgII absorbers at z = 1.062 and 1.181 are studied in detail. This is the
first time that the NaI3303 doublet is detected in such high redshift systems.
Together with the detection of the MgI2852 transition, this strongly constrains
the physical characteristics of the gas. The N(NaI)/N(MgI) ratio is found to be
larger than unity, implying that the gas is cool and neutral. The column
densities of NaI, CaII, MgI, TiII, MnII and FeII observed at z = 1.1801 are
very close to that observed along the line of sight towards 23 Ori in our
Galaxy. The shape of the QSO continuum and the relative depletion of Fe, Ti, Mn
and Ca are consistent with the presence of dust at z = 1 (AV = 0.5 mag).
Altogether it is found that the HI column density at z = 1 is of the order of 1
to 5 10**21 cm-2, the corresponding metallicity is in the range 1--0.3 Zsol.
The objects associated with these two systems could both contribute to the lens
together with another possible strong system at z = 1.1727 and the strong
Lyman-alpha system at z = 2.974. The probable damped Ly-alpha system at z =
2.974 has 19.8 < log N(HI) < 20.3. The transverse dimension of the absorber is
larger than 200 pc. Abundances relative to solar are -2.31, -2.26, -2.10, -2.35
and -2.37 for, respectively, Fe, Al, Si, C and O (for log N(HI) = 20.3).
(Abridged)


title:
Ambipolar Filamentation of Turbulent Magnetic Fields : A numerical
  simulation

abstract:
  We present the results of a 2-D, two fluid (ions and neutrals) simulation of
the ambipolar filamentation process, in which a magnetized, weakly ionized
plasma is stirred by turbulence in the ambipolar frequency range. The higher
turbulent velocity of the neutrals in the most ionized regions gives rise to a
non-linear force driving them out of these regions, so that the initial
ionization inhomogeneities are strongly amplified. This effect, the ambipolar
filamentation, causes the ions and the magnetic flux to condense and separate
from the neutrals, resulting in a filamentary structure.


title:
delta-invariant for Quasi-periodic Oscillations and Physical Parameters
  of 4U 0614+09 binary

abstract:
  The recently formulated Two Oscillator (TO) model interprets the lowest of
the kilohertz frequencies of the twin peak quasi-periodic oscillations in X
-ray binaries as the Keplerian frequency nu_K. The high twin frequency nu_h in
this model holds the upper hybrid frequency relation to the rotational
frequency of the neutron star's magnetosphere Omega: nu_h^2=nu_K^2+
4(Omega/2pi)^2. The vector Omega is assumed to have an angle delta with the
normal to the disk. The first oscillator in the TO model allows one to
interpret the horizontal branch observed below 100 Hz as the lower mode of the
Keplerian oscillator under the influence of the Coriolis force, with frequency
nu_L being dependent on nu_h, nu_K and delta. For some stars such as 4U
0614+09, Sco X-1 and 4U 1702-42, nu_h, nu_K and nu_L have been observed
simultaneously providing the opportunity to check the central prediction of the
TO model: the constancy of delta for a particular source. Given the
considerable variation of each of these three frequencies, the existence of an
observational invariant with a clear physical interpretation as a global
parameter of the neutron star magnetosphere is an important test of the TO
model. Using the results of recent observations of 4U 0614+09 we verify the
existence of this invariant and determine the angle delta=15^o.6+/- 0.^o5 for
this star. The second oscillator in the model deals with a radial (presumably
sound) oscillation and diffuse process in the viscous layer surrounding the
neutron star. Our analysis of the viscous oscillation frequency nu_V and the
break frequency nu_b of the diffusion shows that the spin value of the inner
boundary of the transition layer for 4U 0614+09 is at least two times more than
values for 4U 1728-34 and Sco X-1.


title: Mid-infrared diagnostics to distinguish AGNs from starbursts

abstract:
  We present new mid-infrared (MIR) diagnostics to distinguish emission of
active galactic nuclei (AGN) from that originating in starburst regions. Our
method uses empirical spectroscopic criteria based on the fact that MIR
emission from star forming or active galaxies arises mostly from HII regions,
photo-dissociation regions (PDRs) and AGNs. The analysis of the strength of the
6.2micron Unidentified Infrared Band (UIB) and the MIR continuum shows that
UIBs are very faint or absent in regions harboring the intense and hard
radiation fields of AGNs and pure HII regions, where the UIB carriers could be
destroyed. The MIR signature of AGNs is the presence of an important continuum
in the 3-10micron band which originates from very hot dust heated by the
intense AGN radiation field. Using these two distinct spectral properties found
in our MIR templates, we build diagnostic diagrams which provide quantitative
estimates of the AGN, PDR and HII region contribution in a given MIR spectrum.
This new MIR classification can be used to reveal the presence of AGNs highly
obscured by large columns of dust.


title: Spatial resolution bias in the mid-infrared Starburst/AGN classification

abstract:
  We present the effects of limited spatial resolution to the observed
mid-infrared (MIR) spectrum of an active galactic nucleus (AGN) surrounded by a
disk with massive star forming regions. Using MIR observations of the face-on
nearby Seyfert 1 galaxy NGC 6814, we vary the observing aperture and examine
the evolution of the observed AGN/starburst fraction with our MIR diagnostic.
We show that the spatial resolution of ISOCAM is sufficient to disentangle AGN
from starburst features in nuclear regions of nearby galaxies (D<50Mpc).
However, with the exception of a few ultra-luminous galaxies, dilution effects
hide completely the AGN contribution in more distant galaxies.


title:
The bar-mode instability in differentially rotating neutron stars:
  Simulations in full general relativity

abstract:
  We study the dynamical stability against bar-mode deformation of rapidly
spinning neutron stars with differential rotation. We perform fully
relativistic 3D simulations of compact stars with $M/R \geq 0.1$, where $M$ is
the total gravitational mass and $R$ the equatorial circumferential radius. We
adopt an adiabatic equation of state with adiabatic index $\Gamma=2$. As in
Newtonian theory, we find that stars above a critical value of $\beta \equiv
T/W$ (where $T$ is the rotational kinetic energy and $W$ the gravitational
binding energy) are dynamically unstable to bar formation. For our adopted
choices of stellar compaction and rotation profile, the critical value of
$\beta = \beta_{dGR}$ is $\sim 0.24-0.25$, only slightly smaller than the
well-known Newtonian value $\sim 0.27$ for incompressible Maclaurin spheroids.
The critical value depends only very weakly on the degree of differential
rotation for the moderate range we surveyed. All unstable stars form bars on a
dynamical timescale. Models with sufficiently large $\beta$ subsequently form
spiral arms and eject mass, driving the remnant to a dynamically stable state.
Models with moderately large $\beta \gtrsim \beta_{dGR}$ do not develop spiral
arms or eject mass but adjust to form dynamically stable ellipsoidal-like
configurations. If the bar-mode instability is triggered in supernovae collapse
or binary neutron star mergers, it could be a strong and observable source of
gravitational waves. We determine characteristic wave amplitudes and
frequencies.


title: The Rapidly Fading Afterglow from the Gamma-Ray Burst of 1999 May 6

abstract:
  We report on the discovery of the radio afterglow from the gamma-ray burst
(GRB) of 1999 May 6 (GRB 990506) using the Very Large Array (VLA). The radio
afterglow was detected at early times (1.5 days), but began to fade rapidly
sometime between 1 and 5 days after the burst. If we attribute the radio
emission to the forward shock from an expanding fireball, then this rapid onset
of the decay in the radio predicts that the corresponding optical transient
began to decay between 1 and 5 minutes after the burst. This could explain why
no optical transient for GRB 990506 was detected in spite of numerous searches.
The cause of the unusually rapid onset of the decay for the afterglow is
probably the result of an isotropically energetic fireball expanding into a low
density circumburst environment. At the location of the radio afterglow we find
a faint (R ~ 24 mag) host galaxy with a double morphology.


title: Generation of Cosmic Magnetic Fields at Recombination

abstract:
  It is shown that the standard cosmological model predicts {\it ab initio}
generation of large-scale but very small-amplitude cosmic magnetic fields at
the epoch of recombination of the primeval plasma. Matter velocities dominated
by coherent flows on a scale $L\approx 50h^{-1}(1+z)^{-1}$ Mpc lead to a dipole
of radiation flux in the frame of the moving matter. Thomson scattering of the
radiation differentially accelerates the electrons and ions, creating
large-scale coherent electric currents and magnetic fields. This process is
analyzed using magnetohydrodynamic equations which include a modification of
Ohm's law describing the effect of Thomson drag on the electrons. The field
strength is estimated to be $B\simeq 10^{-20}$G.


title: The Dark Matter Telescope

abstract:
  Weak gravitational lensing enables direct reconstruction of dark matter maps
over cosmologically significant volumes. This research is currently
telescope-limited. The Dark Matter Telescope (DMT) is a proposed 8.4 m
telescope with a 3 degree field of view, with an etendue of 260 $(m.
degree)^2$, ten times greater than any other current or planned telescope. With
its large etendue and dedicated observational mode, the DMT fills a nearly
unexplored region of parameter space and enables projects that would take
decades on current facilities. The DMT will be able to reach 10-sigma limiting
magnitudes of 27-28 magnitude in the wavelength range .3 - 1 um over a 7 square
degree field in 3 nights of dark time. Here we review its unique weak lensing
cosmology capabilities and the design that enables those capabilities.


title:
Radio Sources in Low-Luminosity Active Galactic Nuclei. I. VLA
  Detections of Compact, Flat-Spectrum Cores

abstract:
  We report a 0.2" resolution, 15 GHz survey of a sample of 48 low-luminosity
active galactic nuclei with the Very Large Array. Compact radio emission has
been detected in 57% (17 of 30) of LINERs and low-luminosity Seyferts, at least
15 of which have a flat to inverted radio spectrum (alpha > -0.3). The compact
radio cores are found in both type 1 (i.e. with broad Halpha) and type 2
(without broad Halpha) nuclei. The 2 cm radio power is significantly correlated
with the emission-line ([OI] lambda6300) luminosity. While the present
observations are consistent with the radio emission originating in star-forming
regions, higher resolution radio observations of 10 of the detected sources,
reported in a companion paper (Falcke et al. 2000), show that the cores are
very compact (< pc), of high brightness temperature (T(b) >= 10^8K) and
probably synchrotron self-absorbed, ruling out a starburst origin. Thus, our
results suggest that at least 50% of low-luminosity Seyferts and LINERs in the
sample are accretion powered, with the radio emission presumably coming from
jets or advection-dominated accretion flows. We have detected only 1 of 18
`transition' (i.e. LINER + HII) nuclei observed, indicating their radio cores
are significantly weaker than those of `pure' LINERs.


title:
Radio Sources in Low-Luminosity Active Galactic Nuclei. II. VLBI
  Detections of Compact Radio Cores and Jets in a Sample of LINERs

abstract:
  We have used the VLBA at 5 GHz to observe all galaxies with nuclear radio
flux densities above 3.5 mJy found in a VLA survey at 15 GHz of a sample of
nearby LINER galaxies. All galaxies were detected revealing high brightness
temperature ($T_{b} \ga 10^8$ K) radio sources. Free-free emission is unlikely
since it greatly overpredicts the soft X-ray luminosities. We infer the
presence of AGN-like, non-thermal radio emission most likely powered by
under-fed black holes. Together with our VLA sample we estimate from our
observations that at least half of LINER galaxies host genuine AGN. We find no
evidence for highly inverted radio cores as predicted in the ADAF model: the
(non-simultaneous) spectral indices are on average around $\alpha=0.0$. In the
two brightest sources we detect some extended emission, which appears to
originate in jets in at least one of these galaxies. Together with the spectral
indices this suggests that the nuclear emission at centimeter radio waves is
largely dominated by emission from radio jets, very similar to the situation in
more luminous AGN. The energy released in these jets could be a significant
fraction of the energy budget in the accretion flow.


title:
Weak lensing surveys and the intrinsic correlation of galaxy
  ellipticities

abstract:
  We explore the possibility that an intrinsic correlation between galaxy
ellipticities arising during the galaxy formation process may account for part
of the shear signal recently reported by several groups engaged in weak lensing
surveys. Using high resolution N-body simulations we measure the projected
ellipticities of dark matter halos and their correlations as a function of pair
separation. With this simplifying, but not necessarily realistic assumption
(halo shapes as a proxy for galaxy shapes), we find a positive detection of
correlations up to scales of at least 20 h^-1mpc (limited by the box size). The
signal is not strongly affected by variations in the halo finding technique, or
by the resolution of the simulations. We translate our 3d results into angular
measurements of ellipticity correlation functions and shear variance which can
be directly compared to observations. We also measure similar results from
simulated angular surveys made by projecting our simulation boxes onto the
plane of the sky and applying a radial selection function. Interestingly, the
shear variance we measure is a small, but not entirely negligible fraction
(from ~10-20 %) of that seen by the observational groups, and the ellipticity
correlation functions approximately mimic the functional form expected to be
caused by weak lensing. The amplitude depends on the width in redshift of the
galaxy distribution. If photometric redshifts are used to pick out a screen of
background galaxies with a small width, then the intrinsic correlation may
become comparable to the weak lensing signal. Although we are dealing with
simulated dark matter halos, whether there is a signal from real galaxies could
be checked with a nearby sample with known redshifts.


title: [OII] Emission, Eigenvector 1 and Orientation in Radio-quiet Quasars

abstract:
  We present supportive evidence that the Boroson and Green eigenvector 1 is
not driven by source orientation. Until recently it was generally accepted that
eigenvector 1 does not depend on orientation as it strongly correlates with
[OIII]5007 emission, thought to be an isotropic property. However, recent
studies of radio-loud AGN have questioned the isotropy of [OIII] emission and
concluded that [OII]3727 emission is isotropic. In this paper we investigate
the relation between eigenvector 1 and [OII] emission in radio-quiet BQS
(Bright Quasar Survey) quasars, and readdress the issue of orientation as the
driver of eigenvector 1. We find significant correlations between eigenvector 1
and orientation independent [OII] emission, which implies that orientation does
not drive eigenvector 1. The luminosities and equivalent widths of [OIII] and
[OII] correlate with one another, and the range in luminosities and equivalent
widths is similar. This suggests that the radio-quiet BQS quasars are largely
free of orientation dependent dust effects and ionization dependent effects in
the narrow-line region. We also conclude that neither the [OIII] emission nor
the [OII]/[OIII] ratio are dependent on orientation in our radio-quiet BQS
quasar sample, contrary to recent results found for radio-loud quasars.


title: Einstein Cluster Alignments Revisited

abstract:
  We have examined whether the major axes of rich galaxy clusters tend to point
toward their nearest neighboring cluster. We have used the data of Ulmer,
McMillan, and Kowalski, who used position angles based on X-ray morphology. We
also studied a subset of this sample with updated positions and distances from
the MX Northern Abell Cluster Survey (for rich clusters ($R \geq 1$) with well
known redshifts). A Kolmogorov-Smirnov (KS) test showed no significant signal
for nonrandom angles on any scale $\leq 100h^{-1}$Mpc. However, refining the
null hypothesis with the Wilcoxon rank-sum test, we found a high confidence
signal for alignment. Confidence levels increase to a high of 99.997% as only
near neighbors which are very close are considered. We conclude there is a
strong alignment signal in the data, consistent with gravitational instability
acting on Gaussian perturbations.


title: X-ray Line Diagnostics of Hot Accretion Flows around Black Holes

abstract:
  We compute X-ray emission lines from thermal plasma in hot accretion flows.
We show that line profiles are strong probes of the gas dynamics, and we
present line-ratio diagnostics which are sensitive to the distribution of mass
with temperature in the flow. We show how these can be used to constrain the
run of density with radius, and the size of the hot region. We also present
diagnostics which are primarily sensitive to the importance of recombination
versus collisional ionization, and which could help discriminate ADAFs from
photoionization-dominated accretion disk coronae. We apply our results to the
Galactic center source Sagittarius A* and to the nucleus of M87. We find that
the brightest predicted lines are within the detection capability of current
$X$-ray instruments.


title:
The role of nonthermal electrons in the optical continuum of stellar
  flares

abstract:
  We explore the possibility that the continuum emission in stellar flares is
powered by nonthermal electrons accelerated during the flares. We compute the
continuum spectra from an atmospheric model for a dMe star, AD Leo, at its
quiescent state, when considering the nonthermal excitation and ionisation
effects by precipitating electron beams. The results show that if the electron
beam has an energy flux large enough, the U band brightening and, in
particular, the U-B colour are roughly comparable with observed values for a
typical large flare. Moreover, for electron beams with a moderate energy flux,
a decrease of the emission at the Paschen continuum appears. This can explain
at least partly the continuum dimming observed in some stellar flares. Adopting
an atmospheric model for the flaring state can further raise the continuum flux
but it yields a spectral colour incomparable with observations. This implies
that the nonthermal effects may play the chief role in powering the continuum
emission in some stellar flares.


title: PSR J1907+0918 - a young radio pulsar near SGR 1900+14 and G42.8+0.6

abstract:
  We have extensively searched for periodic signals from the soft-gamma
repeater SGR 1900+14, at 430 and 1410 MHz with the Arecibo telescope. Our
observations did not reveal the 5.16-s periodicity discovered at X-ray
wavelengths by Hurley et al. (1998). We place pulsed flux-density upper limits
of 150 and 30 uJy at 430 and 1410 MHz respectively. In the course of the 1410
MHz search we discovered a 226-ms radio pulsar, PSR J1907+0918. Its period
derivative implies that the age of J1907+0918 is only 38 kyr, making it one of
the youngest members of the known pulsar population. Independent lines of
evidence in support of this apparent youth are the unusually high degree of
circular polarization and a relatively flat radio spectrum. The close proximity
of this young radio pulsar to the supernova remnant G42.8+0.6 poses a problem
for the proposed association between the G42.8+0.6 and SGR 1900+14.


title:
Relativistic Corrections to the Sunyaev-Zel'dovich Effect for Clusters
  of Galaxies. V. Multiple Scattering

abstract:
  We extend the formalism for the calculation of the relativistic corrections
to the Sunyaev-Zel'dovich effect for clusters of galaxies and include the
multiple scattering effects. We present a systematic method for the inclusion
of the multiple scattering effects. The multiple scattering contribution is
found to be very small compared with the single scattering contribution. For
high-temperature galaxy clusters of k_{B}T_{e} = 15keV, the ratio of the both
contributions is -0.3% in the Wien region. In the Rayleigh--Jeans region the
ratio is -0.03%. Therefore the multiple scattering contribution is safely
neglected for the observed galaxy clusters.


title:
X-rays and regions of star formation: a combined ROSAT-HRI/near-to-mid
  IR study of the rho Oph dark cloud

abstract:
  We have obtained two deep exposures of the rho Oph cloud core region with the
ROSAT HRI. The improved position accuracy (1"-6") with respect to previous
recent X-ray observations (ROSAT PSPC, and ASCA) allows us to remove positional
ambiguities for the detected sources. We also cross-correlate the X-ray
positions with IR sources found in the ISO-ISOCAM survey of the same region at
6.7 and 14.3 \mum, in addition to sources known from ground-based observations,
which are young stars. We find that there is no statistically significant
difference between the X-ray luminosity functions of HRI-detected Class II and
Class III sources, i.e., T Tauri stars with and without disks, confirming that
the contribution of these disks to X-ray emission or absorption, must be small.
Most of the sources are variable, and their variability is consistent with a
solar-like (hence magnetic) flare origin. We use the information given both by
the ISOCAM survey and by our HRI deep exposure to study the T Tauri star
population of the rho Oph dense cores. We confirm that essentially all Class II
and Class III sources are X-ray emitters, and that a strong correlation exists
between their X-ray luminosity, L_X, and their stellar luminosity, L_*, with
L_X/L_* ~ 1E-4. Most of the new ISOCAM Class II sources are not detected,
however, which we explain by the fact that their X-ray luminosities
``predicted'' on the basis of this correlation are too faint to be detected by
the HRI. We predict that ~40 unknown faint or embedded Class III sources remain
to be discovered in X-rays in the HRI/ISOCAM overlapping area, down to a limit
of L_X ~ 3 \times 1E28 erg/s. We show that the bulk of these unknown Class III
sources should be made of low- to very low-mass stars. Prospects for future
detections with XMM-Newton and Chandra are discussed.


title:
Relativistic beaming effects in the spectra of cores and hotspots in
  radio galaxies and quasars

abstract:
  We present the results of multi-wavelength observations of cores and hotspots
at L, C, X and U bands with the Very Large Array, of a matched sample of radio
galaxies and quasars selected from the Molonglo Reference Catalogue. We use
these observations to determine the spectra of cores and hotspots, and test the
unified scheme for radio galaxies and quasars. Radio cores have been detected
at all wavelengths in all the quasars in our sample, while only $\sim$ 50% of
the galaxies have detected cores in at least one wavelength. The degree of core
prominence in this sample is consistent with the unified scheme for radio
galaxies and quasars. A comparison of the distributions of the two-point
spectral index of the cores in our sample of lobe-dominated quasars (LDQs) with
a matched sample of core-dominated quasars (CDQs) shows that the distributions
for these two classes are significantly different, consistent with the
expectations of the unified scheme. The difference in the spectral indices of
the two hotspots on opposite sides are also significantly larger for quasars
than radio galaxies, as expected in the unified scheme. We also investigate the
relationship between the spectral index of the hotspots and redshift or
luminosity for our sample of sources.


title: Dust versus Supernova Cosmology

abstract:
  Here we present some critical discussions about the systematic uncertainty by
dust extinction in the recent cosmological results of high-redshift Type Ia
supernovae. First we argue that the currently available data do not robustly
exclude the cosmologically significant extinction either by the reddening check
or the dispersion argument because of the observational uncertainties, even in
the case of ordinary dust that reddens. Then we discuss two theoretical
possibilities that high-z supernovae have larger extinction and hence they are
fainter than local supernovae: the intergalactic dust and host galaxy
evolution. Optical and near-infrared observations for a large number of
supernovae with improved photometric accuracy are required to reject these
possibilities and derive a compelling cosmological result.