title:
Mu and Tau Neutrino Thermalization and Production in Supernovae:
  Processes and Timescales

abstract:
  We investigate the rates of production and thermalization of $\nu_\mu$ and
$\nu_\tau$ neutrinos at temperatures and densities relevant to core-collapse
supernovae and protoneutron stars. Included are contributions from electron
scattering, electron-positron annihilation, nucleon-nucleon bremsstrahlung, and
nucleon scattering. For the scattering processes, in order to incorporate the
full scattering kinematics at arbitrary degeneracy, the structure function
formalism developed by Reddy et al. (1998) and Burrows and Sawyer (1998) is
employed. Furthermore, we derive formulae for the total and differential rates
of nucleon-nucleon bremsstrahlung for arbitrary nucleon degeneracy in
asymmetric matter. We find that electron scattering dominates nucleon
scattering as a thermalization process at low neutrino energies
($\epsilon_\nu\lesssim 10$ MeV), but that nucleon scattering is always faster
than or comparable to electron scattering above $\epsilon_\nu\simeq10$ MeV. In
addition, for $\rho\gtrsim 10^{13}$ g cm$^{-3}$, $T\lesssim14$ MeV, and
neutrino energies $\lesssim60$ MeV, nucleon-nucleon bremsstrahlung always
dominates electron-positron annihilation as a production mechanism for
$\nu_\mu$ and $\nu_\tau$ neutrinos.


title: The High-Ionization Nuclear Emission-Line Region of Seyfert Galaxies

abstract:
  Recently Murayama & Taniguchi proposed that a significant part of the
high-ionization nuclear emission-line region (HINER) in Seyfert nuclei arises
from the inner wall of dusty tori because type 1 Seyfert nuclei (S1s) show the
excess HINER emission with respect to type 2 Seyfert ones (S2s). This means
that the radiation from the HINER has the anisotropic property and thus
statistical properties of the HINER emission can be used to investigate the
viewing angle toward dusty tori for various types of Seyfert nuclei. In order
to investigate viewing angles toward various types of Seyferys, we apply this
HINER test to them.
  Our main results are as follows. (1) The NLS1s are viewed from a more face-on
view toward dusty tori than the S2s. However, the HINER properties of the NLS1s
are indistinguishable from those of the S1s. (2) The type 1.5 Seyferts appear
to comprise heterogeneous populations. (3) The type 1.8 and 1.9 Seyferts and
the objects showing either a broad Pa_beta line or polarized broad Balmer lines
are seen from a large inclination angle and the emission from the BLRs of such
objects reaches us through optically-thin parts of dusty tori. These three
results support strongly the current unified model of Seyfert nuclei. And, (4)
the line ratios of [Fe X]6374 to the low-ionization emission-lines have rather
isotropic property than those of [Fe VII]6087. Therefore it is suggested that
the [Fe X] emission is not useful investigating the viewing angle toward the
dusty torus in Seyfert nuclei. The most plausible reason seems that the [Fe X]
emission is spatially extended and thus its strength tends to show less viewing
angle dependence.


title: The Nuclear Activity of the Galaxies in the Hickson Compact Groups

abstract:
  In order to investigate the nuclear activity of galaxies residing in compact
groups of galaxies, we present results of our optical spectroscopic program
made at Okayama Astrophysical Observatory. We have performed optical
spectroscopy of 69 galaxies which belong to 31 Hickson Compact Groups (HCGs) of
Galaxies. Among them, three galaxies have discordant redshifts. Further,
spectral quality is too poor to classify other three galaxies. Therefore, we
describe our results for the remaining 63 galaxies.
  Our main results are summarized below. (1) We have found in our sample; 28
AGN, 16 HII nuclei, and 19 normal galaxies which show no emission line. We used
this HCG sample for statistical analyses. (2) Comparing the frequency
distributions of activity types between the HCGs and the field galaxies whose
data are taken from Ho, Filippenko, & Sargent (382 field galaxies), we find
that the frequency of HII nuclei in the HCGs is significantly less than that in
the field. However, this difference may be due to selection bias that our HCG
sample contains more early-type galaxies than the field, because it is known
that HII nuclei are rarer in early-type galaxies than in later ones. (3)
Applying correction this morphological bias to the HCG sample, we find that
there is no statistically significant difference in the frequency of occurrence
of emission-line galaxies between the HCGs and the field. This implies that the
dense galaxy environment in the HCGs does not affect triggering both the AGN
activity and the nuclear starburst. We discuss some implications on the nuclear
activity in the HCG galaxies.


title:
Deep X-Ray Observations of Supernova Remnants G359.1-0.5 and G359.0-0.9
  with ASCA

abstract:
  We present the results of deep ASCA observations of two shell-like radio
supernova remnants (SNRs) located in the direction to the Galactic center (GC)
region. Unlike the radio morphology, G359.1-0.5 shows center-filled X-rays with
prominent K-alpha lines of He-like silicon and H-like sulfur. The plasma
requires at least two temperature components: a silicon-dominated cool plasma
of 0.6keV temperature and a sulfur-dominated higher temperature plasma of
4.4keV. Because the absorption column is ~ 6x10^22 H cm^-2, this SNR would be
near to the GC. The spherical plasma is attributable to supernova ejecta with
the total mass of Si and S being about 0.1 solar mass and 0.3 solar mass,
respectively. X-rays from G359.0-0.9 trace the partial shell structure of the
radio emission. The spectrum is well fitted to a single-temperature plasma of
0.4keV with a non-solar abundance of magnesium or iron. Because the absorption
column is not very large, ~ 1.8x10^22 H cm^-2, G359.0-0.9 would be in front of
the GC region. The total supernova energy, interstellar density near to the
X-ray emitting shell and age of the SNR are estimated to be 1.2x10^51erg,
0.5cm^-3, and 1.8x10^4yr, respectively. We also discuss possible implications
on the origin of the large-scale hot plasma surrounding the GC.


title: On the Structure of Advective Accretion Disks At High Luminosity

abstract:
  Global solutions of optically thick advective accretion disks around black
holes are constructed. The solutions are obtained by solving numerically a set
of ordinary differential equations corresponding to a steady axisymmetric
geometrically thin disk. We pay special attention to consistently satisfy the
regularity conditions at singular points of the equations. For this reason we
analytically expand a solution at the singular point, and use coefficients of
the expansion in our iterative numerical procedure. We obtain consistent
transonic solutions in a wide range of values of the viscosity parameter alpha
and mass acretion rate. We compare two different form of viscosity: one takes
the shear stress to be proportional to the pressure, while the other uses the
angular velocity gradient-dependent stress.
  We find that there are two singular points in solutions corresponding to the
pressure-proportional shear stress. The inner singular point locates close to
the last stable orbit around black hole. This point changes its type from a
saddle to node depending on values of alpha and accretion rate. The outer
singular point locates at larger radius and is always of a saddle-type. We
argue that, contrary to the previous investigations, a nodal-type inner
singular point does not introduce multiple solutions. Only one integral curve,
which corresponds to the unique global solution, passes simultaneously the
inner and outer singular points independently of the type of inner singular
point. Solutions with the angular velocity gradient-dependent shear stress have
one singular point which is always of a saddle-type and corresponds to the
unique global solution. The structure of accretion disks corresponding to both
viscosities are similar.


title: Model of peak separation in the gamma lightcurve of the Vela pulsar

abstract:
  The separation $\del$ between two peaks in the gamma-ray pulse profile is
calculated as a function of energy for several polar cap models with
curvature-radiation-induced cascades. The Monte Carlo results are interpreted
with the help of analytical approximations and discussed in view of the recent
data analysis for the Vela pulsar (Kanbach 1999). We find that the behaviour of
$\del$ as a function of photon energy $\epsilon$ depends primarily on local
values of the magnetic field, $B_{\rm local}$, in the region where
electromagnetic cascades develop. For low values of $B_{\rm local}$ ($<
10^{12}$ G), $\del(\epsilon)$ is kept constant. However, for stronger magnetic
fields ($\ga 10^{12}$ G) in the hollow-column model $\del$ decreases with
increasing photon energy at a rate dependent on maximum energy of beam
particles as well as on viewing geometry. There exists a critical photon energy
$\et$ above which the relation $\del(\epsilon)$ changes drastically: for
$\epsilon > \et$, in hollow-column models the separation $\del$ increases
(whereas in filled-column model it decreases) rapidly with increasing
$\epsilon$, at a rate of $\sim 0.28$ of the total phase per decade of photon
energy. The existence of critical energy $\et$ is a direct consequence of
one-photon magnetic absorption effects. In general, $\et$ is located close to
the high-energy cutoff of the spectrum, thus photon statistics at $\et$ should
be very low. That will make difficult to verify the existence of $\et$ in real
gamma-ray pulsars. Spectral properties of the Vela pulsar would favour those
models which use low values of magnetic field in the emission region ($B_{\rm
local} \simless 10^{11}$ G) which in turn implies a constant value of the
predicted $\del$ within EGRET range.


title: Interaction in Abell 2256: the BeppoSAX view

abstract:
  We present results from a spatially resolved spectral analysis of the merging
cluster Abell 2256. The long integration time (135 ks) and the good spatial
resolution of the MECS onboard BeppoSAX allow us to derive a new and
substantially improved measurement of the temperature structure. We find that,
within a central region of the cluster, where the effects of the merger are
visible in the ROSAT surface brightness image, the azimuthally averaged
projected temperature is remarkably flat; outside this region the projected
temperature rapidly declines. The BeppoSAX data also shows clear evidence of an
azimuthal temperature gradient in the 4'-8' (0.4-0.8 Mpc) radial bin, oriented
in the same direction as the merger itself. Our metal abundance profile shows,
for the first time, firm evidence of an abundance gradient in a rich merging
cluster. Intriguingly the abundance map shows, in the SE sector, i.e. the one
furthest away from the merger, a sharp factor of two drop in abundance at a
radius comparable to the core radius of the cluster. A possible interpretation
is that, prior to the merger event, a cooling flow had already developed in the
core of the infalling subgroup, as suggested by Fabian and Daines (1991). The
interaction between the substructures would have disrupted the cooling flow
thereby re-heating and re-mixing the gas. As the merger in A2256 is still in a
relatively early stage, the gas located on the side opposite to the merger
event would still retain the low abundances associated with the intra-cluster
medium (ICM) prior to the cooling flow disruption.


title:
A Population of very young Brown Dwarfs and free-floating Planets in
  Orion

abstract:
  We describe the results of a very deep imaging survey of the Trapezium
Cluster in the IJH bands, using the UKIRT high resolution camera UFTI.
Approximately 32% of the 515 point sources detected are brown dwarf candidates,
including several free floating objects with masses below the Deuterium burning
(planetary) threshold at 0.013 solar masses, which are detectable because of
their extreme youth. We have confidence that almost all the sources detected
are cluster members, since foreground contamination is minimal in the 33
arcmin^2 area surveyed and the dense backdrop of OMC-1 obscures all background
stars at these wavelengths. Extinction is calculated from the (J-H)colours,
permitting accurate luminosity estimates and temperatures are derived from the
dereddened (I-J) colours. There is some evidence for a cut-off in the
luminosity function below the level corresponding to several Jupiter masses,
which may represent the bottom end of the IMF. Since star formation is complete
in the Trapezium this limit could have wide significance, if confirmed.
However, it could well be an effect of the dispersal of the molecular cloud by
the central O-type stars, a process whose timescale will vary between star
formation regions.


title: Primordial black holes, phase transitions, and the fate of the universe

abstract:
  Phase transitions in the early universe are prime settings for the production
of primordial black holes, since they can break the relatively quiescent
homogeneity and isotropy of Friedmann-Robertson-Walker (FRW) cosmologies. These
epochs of "symmetry breaking," moreover, can affect the subsequent development
of spacetime by changing the evolution of some FRW parameters, including the
present age and density of the universe. We discuss the relative importance of
such effects on constraining mechanisms of black hole formation.


title:
A correlation between the SiO and the Fe 6.4 keV line emission from the
  Galactic center

abstract:
  In this letter we present a map of the GC in the 1-0 line of SiO covering the
same region than the ASCA observations of the Fe 6.4 keV line. The SiO emission
is restricted to molecular clouds with radial velocity between 10 and 60 km/s
in the Sgr A and Sgr B complexes. We find a correlation between the SiO
morphology and the spatial distribution of the Fe 6.4 keV line, on the large
scale and also within Sgr A and Sgr B. The SiO abundance increases by a factor
of 20 in the regions with strong Fe 6.4 keV line. This indicates that the Fe
6.4 keV line mainly arises from molecular clouds with large gas phase abundance
of refractory elements. We discuss the implications of the correlation on the
origin of the hard X-rays, and the heating and the chemistry of the molecular
clouds in the GC


title: One relation for self-gravitating bodies

abstract:
  The relation between the gravitational potential energy, W, the central
potential, U, and the mass, M: W/U/M is considered for various homogeneous and
inhomogeneous self-gravitating bodies.


title: On the origin of the universe

abstract:
  It has been proven recently that the Standard Model of particle physics has
electric charge quantization built into it. It has also been shown by the
author that there was no electric charge in the early universe. Further it is
shown here that the restoration of the full Standard Model symmetry (as in the
Early Universe) leads to the result that `time', `light', along with it's
velocity c and the theory of relativity, all lose any physical meaning. The
physical Universe as we know it, with its space-time structure, disappears in
this phase transition. Hence it is hypothesized here that the Universe came
into existence when the Standard Model symmetry $SU(3)_C \otimes SU(2)_L
\otimes U(1)_Y$ was spontaneously broken to $SU(3)_C \otimes U(1)_{em}$. This
does not require any spurious extensions of the Standard Model and in a simple
and consistent manner explains the origin of the Universe within the framework
of the Standard Model itself.


title: Features of Nucleosynthesis and Neutrino Emission from Collapsars

abstract:
  In this study we present two indicators that will reflect the difference
between collapsars and normal collapse-driven supernovae. They are products of
explosive nucleosynthesis and neutrino emission. In the collapsar model, it is
natural to consider that the product of explosive nucleosynthesis depends on
the zenith angle because the system becomes highly asymmetric in order to
generate a fire ball. We also consider the detectability of the HNRs which is
located nearby our Galaxy. As a result, the number of the HNRs is estimated to
be 5 $\times$ ($10^2$ -- $10^{-3}$), whose chemical composition can be
spatially resolved. Using the optimistic estimate, more HNRs will be found and
it will be possible to discuss on the chemical composition statistically. As
for the energy spectrums of neutrinos, they are not thermalized in a collapsar
because the density of the accretion disk is much lower than that of a neutron
star. The energy spectrums of (anti-)electron neutrinos from hypernovae will be
mainly determined by the process of electron (positron) capture on free proton
(neutron). It is also noted that high energy tail is not dumped in the case of
hypernovae because the density of emitting region is low. Total energy of
neutrino from hypernovae will depend on a lot of physical parameters such as
total accreting mass and mass accretion rate, which are quite contrary to the
situation of the normal collapse-driven supernovae. Therefore there will be a
large variety of total neutrino's energies among collapsars. In the case of SN
1998bw, we think that the matter around the equatorial plane might be ejected
from the system, which resulted in the formation of relatively weak jets and
faint GRB 980425.


title: The massive stellar content in NGC604 and its evolutionary state

abstract:
  The ultraviolet resonance wind stellar lines, the nebular optical emission
lines and the higher order terms of the Balmer series and HeI absorption lines
detected in the spectra of NGC 604 are interpreted using evolutionary models
optimized for young star forming regions. The evolutionary state and the
massive stellar content of the region is derived in a self-consistent way.
  The three techniques applied suggest that the central ionizing cluster in NGC
604 is very young, 3 Myr old, and that the stars in the cluster were formed in
an instantaneous burst following a Salpeter or flatter IMF, having stars more
massive that 80 Msol. The stellar cluster is able to provide most of the
ionizing photons needed to photoionize the whole nebula, and the wind power to
form the central shell structure where the cluster core is located. The stellar
cluster is affected by an extinction similar to the average extinction that
affects the ionized gas. The estimated number of massive stars in the cluster
is also in agreement with that derived from previous studies based on the
detection of individual stars. The results that we present here support the use
of these techniques for the interpretation of the integrated light of more
distant star forming regions


title:
An Improved Red Spectrum of the Methane or T-dwarf SDSS 1624+0029: Role
  of the Alkali Metals

abstract:
  A Keck~II low resolution spectrum shortward of ome-micron is presented for
SDSS 1624+0029, the first field methane or T dwarf discovered in the Sloan
Digital Sky Survey. Significant flux is detected down to the spectrum's short
wavelength limit of 6200\AA. The spectrum exhibits a broad absorption feature
centered at 7700\AA, which we interpret as the K~I 7665/7699 resonance doublet.
The observed flux declines shortward of 7000\AA, due most likely to the red
wing of the Na~I doublet. Both Cs~I doublet lines are detected more strongly
than in an earlier red spectrum. Neither Li~I absorption nor H$\alpha$ emission
are detected. An exploratory model fit to the spectrum suggests that the shape
of the red spectrum can be primarily accounted for by the broad wings of the
K~I and Na~I doublets. This behavior is consistent with the argument proffered
by Burrows, Marley and Sharp that strong alkali absorption is principally
responsible for depressing T dwarf spectra shortward of 1$\mu$m. In particular,
there seems no compelling reason at this time to introduce dust or an
additional opacity source in the atmosphere of the SDSS object. The width of
the K~I and strengths of the Cs~I lines also indicate that the Sloan object is
warmer than Gl~229B.


title: A few things we do not know about the sun and F stars and G stars

abstract:
  WE do not know how to make realistic model atmospheres; understand
convection; consider the variation in microturbulent velocity; understand
spectroscopy; have good spectra of the sun or any other star; have energy
distributions for the sun or any other star; know how to determine abundances;
know the abundances of the sun or any other star; have good atomic and
molecular data; One half the lines in the solar spectrum are not identified. We
should get our own house in order before worrying about the neighbors.


title: Radio Pulsars in Terzan 5

abstract:
  We report on searches of the globular cluster Terzan 5 for low luminosity and
accelerated radio pulsars using the 64-m Parkes radio telescope. One new
millisecond pulsar, designated PSR J1748-2446C, was discovered, having a period
of 8.44ms. Timing measurements using the 76-m Lovell radio telescope at Jodrell
Bank show that it is a solitary pulsar and lies close to the core of the
cluster. We also present the results of timing measurements which show that the
longer-period pulsar PSR J1748-2444 (formerly known as PSR B1744-24B) lies 10
arcmin from the core of the cluster and is unlikely to be associated with the
cluster. We conclude that there are further pulsars to be detected in the
cluster.


title:
Stellar parameters from very low resolution spectra and medium band
  filters: Teff, logg and [M/H] using neural networks

abstract:
  Large scale, deep survey missions such as GAIA will collect enormous amounts
of data on a significant fraction of the stellar content of our Galaxy. These
missions will require a careful optimisation of their observational systems in
order to maximise their scientific return, and will require reliable and
automated techniques for parametrizing the very large number of stars detected.
To address these two problems, I investigate the precision to which the three
principal stellar parameters (Teff, logg, [M/H]) can be determined as a
function of spectral resolution and signal-to-noise (SNR) ratio, using a large
grid of synthetic spectra. The parametrization technique is a neural network,
which is shown to provide an accurate three-dimensional physical
parametrization of stellar spectra across a wide range of parameters. It is
found that even at low resolution (50-100 AA FWHM) and SNR (5-10 per resolution
element), Teff and \met can be determined to 1% and 0.2 dex respectively across
a large range of temperatures (4000-30000 K) and metallicities (-3.0 to +1.0
dex), and that logg is measurable to +/- 0.2 dex for stars earlier than solar.
The accuracy of the results is probably limited by the finite parameter
sampling of the data grid. The ability of medium band filter systems (with
10-15 filters) for determining stellar parameters is also investigated.
Although easier to implement in a unpointed survey, it is found that they are
only competitive at higher SNRs (> 50).


title:
Achieving a wide field near infrared camera for the Calar Alto 3.5m
  telescope

abstract:
  The ongoing development of large infrared array detectors has enabled wide
field, deep surveys to be undertaken. There are, however, a number of
challenges in building an infrared instrument which has both excellent optical
quality and high sensitivity over a wide field. We discuss these problems in
the context of building a wide field imaging camera for the 3.5m telescope at
Calar Alto with the new 2K*2K HgCdTe HAWAII-2 focal plane array. Our final
design is a prime focus camera with a 15' field-of-view, called Omega 2000. To
achieve excellent optical quality over the whole field, we have had to dispense
with the reimaging optics and cold Lyot stop. We show that creative baffling
schemes, including the use of undersized baffles, can compensate for the lost K
band sensitivity. A moving baffle will be employed in Omega 2000 to allow full
transmission in the non-thermal J and H bands.


title:
A New Strategy for the Routine Detection & Imaging of Faint Radio
  Sources with VLBI

abstract:
  In this paper I outline a new strategy for the routine detection and imaging
of faint (sub-mJy and microJy) radio sources with VLBI and SVLBI. The strategy
relies on a combination of in-beam phase-referencing, wide-field VLBI imaging
and simultaneous correlation of multiple field centres. A combination of these
techniques, together with the steeply rising radio source counts observed at cm
wavelengths, permit routine high resolution observations of radio sources
previously considered too faint for conventional VLBI.


title: 2D Numerical Simulation of Stellar Convection

abstract:
  The dynamics and thermal structure of the surface layers of stars with outer
convection zones can be studied in some detail by means of numerical
simulations of time-dependent compressible convection. In an effort to
investigate the properties of ``stellar granulation'' as a function of spectral
type, we have carried out elaborate 2-dimensional radiation hydrodynamics
calculations of surface convection for a variety of stellar parameters. The
main features of these simulations are reviewed, with particular reference to
standard mixing length models.


title:
Effects of Photospheric Temperature Inhomogeneities on Lithium Abundance
  Determinations (2D)

abstract:
  Based on detailed 2D radiation hydrodynamics (RHD) simulations, we have
investigated the effects of photospheric temperature inhomogeneities induced by
convection on spectroscopic determinations of the lithium abundance.
Computations have been performed both for the solar case and for a metal-poor
dwarf. NLTE effects are taken into account, using a five-level atomic model for
LiI. Comparisons are presented with traditional 1D models having the same
effective temperature and gravity. The net result is that, while LTE results
differ dramatically between 1D and 2D models, especially in the metal-poor
case, this does not remain true when NLTE effects are included: 1D/2D
differences in the inferred NLTE Li abundance are always well below 0.1 dex.
The present computations still assume LTE in the continuum. New computations
removing this assumption are planned for the near future.


title: VLA Polarimetry of Two Extended Radio Galaxies

abstract:
  Multi-wavelength VLA observations of two extended radio galaxies, 0235-197
and 1203+043 are presented. There is some evidence from earlier studies that
these two sources exhibit low frequency (<1 GHz) variability. This work shows
that both sources have linear polarizations, if any, below the detection limits
at 320 MHz, so we cannot explain the variability as being due to instrumental
polarization effects as has been suggested for 3C159. Refractive scintillation
may be the cause of the variability in 0235-197. This would require the
existence of a bright, compact component in one of the hot spots seen in these
observations. This is not implausible but the resolution of this observational
program is insufficent to address that question. The radio source 1203+043
lacks any bright compact component thereby ruling out a refractive
scintillation mechanism for its variability. Consequently, it is possible that
claims of variability in this source are spurious. However, the 320 MHz VLA
observations show that 1203+043 has an `X'-shaped radio structure. This is a
rare morphology for the brightness distribution of a radio galaxy; the
implications of this are examined.


title: The Properties of Hypernovae: SNe Ic 1998bw, 1997ef, and SN IIn 1997cy

abstract:
  We discuss the properties of the hyper-energetic Type Ic supernovae (SNe Ic)
1998bw and 1997ef and Type IIn supernova (SN IIn) 1997cy. SNe Ic 1998bw and
1997ef are characterized by their large luminosity and the very broad spectral
features. Their observed properties can be explained if they are very energetic
SN explosions with the kinetic energy of $E_{\rm K} \gsim 1\times10^{52}$ erg,
originating probably from the core collapse of the bare C+O cores of massive
stars ($\sim 30-40$M$_\odot$). At late times, both the light curves and the
spectra suggest that the explosions may have been asymmetric; this may help us
understand the claimed connection with GRB's. The Type IIn SN 1997cy is even
more luminous than SN 1998bw and the light curve declines more slowly than
$^{56}$Co decay. We model such a light curve with circumstellar interaction,
which requires the explosion energy of $\sim 5 \times 10^{52}$ erg. Because
these kinetic energies of explosion are much larger than in normal
core-collapse SNe, we call objects like these SNe "hypernovae". The mass of
$^{56}$Ni in SN 1998bw is estimated to be as large as 0.5 - 0.7 $M_\odot$ from
both the maximum brightness and late time emission spectra, which suggests that
the asymmetry may not be extreme.


title:
Monte Carlo inversion of hydrogen and metal lines from QSO absorption
  spectra

abstract:
  A new method, based on the simulated annealing algorithm and aimed at the
inverse problem in the analysis of intergalactic (interstellar) complex spectra
of hydrogen and metal lines, is presented. We consider the process of line
formation in clumpy stochastic media accounting for fluctuating velocity and
density fields (mesoturbulence). This approach generalizes our previous Reverse
Monte Carlo and Entropy-Regularized Minimization methods which were applied to
velocity fluctuations only. The method allows one to estimate, from an observed
system of spectral lines, both the physical parameters of the absorbing gas and
appropriate structures of the velocity and density distributions along the line
of sight. The validity of the computational procedure is demonstrated using a
series of synthetic spectra that emulate the up-to-date best quality data. HI,
CII, SiII, CIV, SiIV, and OVI lines, exhibiting complex profiles, were fitted
simultaneously. The adopted physical parameters have been recovered with a
sufficiently high accuracy. The results obtained encourage the application of
the proposed procedure to the analysis of real observational data.


title: Simulation of primordial object formation

abstract:
  We have included the chemical rate network responsible for the formation of
molecular Hydrogen in the N-body hydrodynamic code, Hydra, in order to study
the formation of the first cosmological at redshifts between 10 and 50. We have
tested our implementation of the chemical and cooling processes by comparing
N-body top hat simulations with theoretical predictions from a semi-analytic
model and found them to be in good agreement. We find that post-virialization
properties are insensitive to the initial abundance of molecular hydrogen. Our
main objective was to determine the minimum mass ($M_{SG}(z)$) of perturbations
that could become self gravitating (a prerequisite for star formation), and the
redshift at which this occurred. We have developed a robust indicator for
detecting the presence of a self-gravitating cloud in our simulations and find
that we can do so with a baryonic particle mass-resolution of 40 solar masses.
We have performed cosmological simulations of primordial objects and find that
the object's mass and redshift at which they become self gravitating agree well
with the $M_{SG}(z)$ results from the top hat simulations. Once a critical
molecular hydrogen fractional abundance of about 0.0005 has formed in an
object, the cooling time drops below the dynamical time at the centre of the
cloud and the gas free falls in the dark matter potential wells, becoming self
gravitating a dynamical time later.


title: X-ray Spectra of a large sample of Quasars with ASCA

abstract:
  The results from an X-ray spectral analysis of a large sample of quasars,
observed with ASCA, are presented. Data reduction leaves 62 quasars, 35
radio-loud and 27 radio-quiet, suitable for spectral analysis. Differences are
found between the radio-quiet quasars (RQQs) and the radio-loud quasars (RLQs),
in agreement with previous studies. A correlation between Gamma and optical
H-beta was also found for the radio-quiet quasars in this sample, whereby the
steepest X-ray spectra tend to be found in those objects with narrow H-beta
widths. The correlation is significant at >99% confidence, confirming the
well-known trend between Gamma and H-beta FWHM in Seyfert 1s (Brandt et al.
1997), but at higher luminosities. Other spectral complexities are observed
from this sample. A soft X-ray excess, with blackbody temperatures in the range
100 - 300 eV, is seen in many low z radio-quiet quasars. In most cases the
temperatures are probably too hot to originate directly from the disk. Iron K
line emission features are also found in the RQQs; but often from partially
ionised material. Indeed in the highest luminosity RQQs there is neither
evidence for iron line emission nor the reflection component expected from disk
models. These observations can be explained by an increase in the quasar
accretion rate with luminosity, leading to an increase in the ionisation state
of the surface layers of the disk. The occurrence of ionised or `warm'
absorbers is rare in this sample, with only 5 detections. However excess
neutral X-ray absorption is found towards several of the high z, predominantly
radio-loud, quasars. Although found to increase with quasar redshift, this
`intrinsic' absorption may be associated with radio-loud AGN.


title: Galactic Worm 123.4-1.5: A Mushroom-shaped HI Cloud

abstract:
  The Dominion Radio Astrophysical Observatory's Synthesis Telescope provides
the highest resolution data (1 arcmin and 0.82 km/s) to date of an HI worm
candidate. Observed as part of the Canadian Galactic Plane Survey,
mushroom-shaped GW 123.4-1.5 extends only a few hundred parsecs, contains ~10^5
solar masses of neutral hydrogen, and appears unrelated to a conventional shell
or chimney structure. Our preliminary Zeus-2d models use a single off-plane
explosion with a modest (~10^{51} ergs) energy input. These generic simulations
generate, interior to an expanding outer blast wave, a buoyant cloud whose
structure resembles the morphology of the observed feature. Unlike typical
model superbubbles, the stem can be narrow because its width is not governed by
the pressure behind the blast wave nor the disk scale height. Using this type
of approach it should be possible to more accurately model the thin stem and
other details of GW 123.4-1.5 in the future.


title: First order Fermi acceleration at multiple oblique shocks

abstract:
  Numerical results for particle acceleration at multiple oblique shocks are
presented. We calculate the steady state spectral slope of test particles
accelerated by the first order Fermi process. The results are compared to
analytical treatments, for parameters, where the diffusion approximation does
apply. Effects of injection and finite shock extend are included
phenomenologically. We find the spectrum of accelerated particles to harden
substantially at multiple oblique shocks and discuss the influence of the
number of shocks compared to the obliquity itself.


title: Supernovae

abstract:
  The properties of supernovae (SNe) are reviewed. It is shown that the
observed characteristics of the morphological classes of SNe (types Ia, Ib/c,
II) can be explained in terms of two basic explosion mechanisms, i.e. core
collapse of massive stars and thermonuclear explosion of low/moderate mass
stars.
  The study of SNe can provide valuable insight in the late phases of the
evolution of their progenitors and, therefore, can constrain the theory of
stellar evolution quite tightly.
  Also, bright SNe of type Ia can be used to probe the Universe up to high
redshifts, allowing us to measure cosmological constants and to gain valuable
information on the formation and evolution of galaxies.
  The case of SN 1987A is discussed in some detail: it appears that in this
event a number of predictions were astonishingly well verified but still many
aspects were completely at variance with "common wisdom" expectations,
indicating that the SN phenomenon is still not fully understood.


title: Models for the Magnitude-Distribution of Brightest Cluster Galaxies

abstract:
  The brightest, or first-ranked, galaxies (BCGs) in rich clusters show a very
small dispersion in luminosity, making them excellent standard candles. This
small dispersion has raised questions about the nature of BCGs. Are they simply
the extremes of normal galaxies formed via a stochastic process, or do they
belong to a special class of atypical objects? Arguments have been proposed on
both sides of the debate. Bhavsar (1989) suggested that the distribution in
magnitudes can only be explained by a two-population model. Thus, a new
controversy has arisen. Do first-ranked galaxies consist of one or two
populations of objects? We examine an older and newer data set and present our
results. Two-population models do better than do one-population models. A
simple model where a random boost in the magnitude of a fraction of bright
normal galaxies forms a class of atypical galaxies best describes the observed
distribution of BCG magnitudes. Moreover, the parameters that describe the
model and the parameters of the boost have a strong physical basis.


title: The Sunyaev-Zel'dovich Effect in Abell 370

abstract:
  We present interferometric measurements of the Sunyaev-Zel'dovich (SZ) effect
towards the galaxy cluster Abell 370. These measurements, which directly probe
the pressure of the cluster's gas, show the gas distribution to be strongly
aspherical, as do the x-ray and gravitational lensing observations. We
calculate the cluster's gas mass fraction in two ways. We first compare the gas
mass derived from the SZ measurements to the lensing-derived gravitational mass
near the critical lensing radius. We also calculate the gas mass fraction from
the SZ data by deprojecting the three-dimensional gas density distribution and
deriving the total mass under the assumption that the gas is in hydrostatic
equilibrium (HSE). We test the assumptions in the HSE method by comparing the
total cluster mass implied by the two methods and find that they agree within
the errors of the measurement. We discuss the possible systematic errors in the
gas mass fraction measurement and the constraints it places on the matter
density parameter, OmegaM.


title:
Evidence of Multiple r-Process Sites in the Early Galaxy: New
  Observations of CS 22892-052

abstract:
  First results are reported of a new abundance study of neutron-capture
elements in the ultra-metal-poor (UMP; [Fe/H] = -3.1) halo field giant star CS
22892-052. Using new high resolution, high signal-to-noise spectra, abundances
of more than 30 neutron-capture elements (Z>30) have been determined. Six
elements in the 40<Z<56 domain (Nb, Ru, Rh, Pd, Ag and Cd) have been detected
for the first time in a UMP star. Abundances are also derived for three of the
heaviest stable elements (Os, Ir, and Pb). A second transition of thorium,
Th{4086}, confirms the abundance deduced from the standard Th{4019} line, and
an upper limit to the abundance of uranium is established from the absence of
the U{3859} line. As found in previous studies, the abundances of the heavier
(Z>=56) stable neutron-capture elements in CS 22892-052 match well the scaled
solar system r-process abundance distribution. From the observed Th abundance,
an average age of ~= 16 +/- 4 Gyr is derived for cs22892-052, consistent with
the lower age limit of ~= 11 Gyr derived from the upper limit on the U
abundance. The concordance of scaled solar r-process and CS 22892-052
abundances breaks down for the lighter neutron-capture elements, supporting
previous suggestions that different r-process production sites are responsible
for lighter and heavier neutron-capture elements.


title:
Kinematics of Metal-Poor Stars in the Galaxy. III. Formation of the
  Stellar Halo and Thick Disk as Revealed from a Large Sample of
  Non-Kinematically Selected Stars

abstract:
  (Abbreviated) We present a detailed analysis of the space motions of 1203
solar-neighborhood stars with metal abundances [Fe/H] <= -0.6, on the basis of
a recently revised and supplemented catalog of metal-poor stars selected
without kinematic bias (Beers et al. 2000). This sample, having available
proper motions, radial velocities, and distance estimates for stars with a wide
range of metal abundances, is by far the largest such catalog to be assembled
to date. Unlike essentially all previous kinematically selected catalogs, the
metal-poor stars in our sample exhibit a diverse distribution of orbital
eccentricities, e, with no apparent correlation between [Fe/H] and e. This
demonstrates, clearly and convincingly, that the evidence offered by Eggen,
Lynden-Bell, and Sandage (1962) for a rapid collapse of the Galaxy, an apparent
correlation between the orbital eccentricity of halo stars with metallicity, is
basically the result of their proper-motion selection bias. However, even in
our non-kinematically selected sample, we have identified a small concentration
of high-e stars at [Fe/H] = -1.7, which may originate, in part, from infalling
gas during the early formation of the Galaxy. The implications of our results
for the formation of the Galaxy are also discussed, in particular in the
context of the currently favored CDM theory of hierarchical galaxy formation.


title: L1551NE - Discovery of a Binary Companion

abstract:
  L1551NE is a very young (class 0 or I) low-mass protostar located close to
the well-studied L1551 IRS5. We present here evidence, from 1.3mm continuum
interferometric observations at ~1'' resolution, for a binary companion to
L1551NE. The companion, whose 1.3mm flux density is ~1/3 that of the primary
component, is located 1.43'' (~230 A.U. at 160pc) to the southeast. The
millimeterwave emission from the primary component may have been just barely
resolved, with deconvolved size ~0.82"x0.70" (~131x112 A.U.). The companion
emission was unresolved (<100 A.U.). The pair is embedded within a flattened
circum-binary envelope of size ~5.4'' x 2.3'' (~860 x 370 A.U.). The masses of
the three components (i.e. from the cicumstellar material of the primary star
and its companion, and the envelope) are approximately 0.044, 0.014 and 0.023
Mo respectively.


title: Redshifts of CLASS Radio Sources

abstract:
  Spectroscopic observations of a sample of 42 flat-spectrum radio sources from
the Cosmic Lens All-Sky Survey (CLASS) have yielded a mean redshift of $<z> =
1.27$ with an RMS spread of 0.95, at a completeness level of 64%. The sample
consists of sources with a 5-GHz flux density of 25-50 mJy, making it the
faintest flat-spectrum radio sample for which the redshift distribution has
been studied. The spectra, obtained with the Willam Herschel Telescope (WHT),
consist mainly of broad-line quasars at $z>1$ and narrow-line galaxies at
$z<0.5$. Though the mean redshift of flat-spectrum radio sources exhibits
little variation over more than two orders of magnitude in radio flux density,
there is evidence for a decreasing fraction of quasars at weaker flux levels.
In this paper we present the results of our spectroscopic observations, and
discuss the implications for constraining cosmological parameters with
statistical analyses of the CLASS survey.


title: Galactic contamination in the QMAP experiment

abstract:
  We quantify the level of foreground contamination in the QMAP Cosmic
Microwave Background (CMB) data with two objectives: (a) measuring the level to
which the QMAP power spectrum measurements need to be corrected for foregrounds
and (b) using this data set to further refine current foreground models. We
cross-correlate the QMAP data with a variety of foreground templates. The 30
GHz Ka-band data is found to be significantly correlated with the Haslam 408
MHz and Reich and Reich 1420 MHz synchrotron maps, but not with the Diffuse
Infrared Background Experiment (DIRBE) 240, 140 and 100 micron maps or the
Wisconsin H-Alpha Mapper (WHAM) survey. The 40 GHz Q-band has no significant
template correlations. We discuss the constraints that this places on
synchrotron, free-free and dust emission. We also reanalyze the
foreground-cleaned Ka-band data and find that the two band power measurements
are lowered by 2.3% and 1.3%, respectively.


title: A ROSAT HRI study of the open cluster NGC 3532

abstract:
  NGC 3532 is a very rich southern open cluster of age ~200-350 Myr; it is
therefore a good candidate to investigate the X-ray activity-age-rotation
relationship at ages intermediate between the Pleiades and the Hyades, where,
to our knowledge, X-rays studies exist for only one cluster (NGC 6475). We have
performed an X-ray study of NGC 3532 using HRI observations retrieved from the
ROSAT archive. The observations have a limiting sensitivity $L_{\mathrm x} \sim
4 \times 10^{28}$ erg sec$^{-1}$ in the center of the field. We detected ~50
X-ray sources above a $4 \sigma$ threshold, half of which have a known optical
counterpart within 10 arcsec; 15 of the X-ray sources have at least one cluster
member as optical counterpart.
  A comparison of NGC 3532 with the nearly coeval cluster NGC 6475 indicates
that the former cluster is considerably X-ray underluminous with respect to NGC
6475. However, because of the existence of possible selection effects,
additional X-ray and optical observations are needed before definitively
concluding that the X-ray properties of NGC 3532 and NGC 6475 are significantly
different.


title: Optical studies of the X-ray transient XTE J2123-058 -I. Photometry

abstract:
  We present optical photometry of the X-ray transient XTE J2123-058, obtained
in July-October 1998. The light curves are strongly modulated on the 5.95hrs
orbital period, and exhibit dramatic changes in amplitude and form during the
decline. We used synthetic models which include the effect of partial eclipses
and X-ray heating effects, to estimate the system parameters, and we constrain
the binary inclination to be i=73+-4 degrees. The model is successful in
reproducing the light curves at different stages of the decay by requiring the
accretion disc to become smaller and thinner by 30% as the system fades by 1.7
mags in the optical. From Aug 26 the system reaches quiescence with a mean
magnitude of R=21.7+-0.1 and our data are consistent with the optical
variability being dominated by the companion's ellipsoidal modulation.


title: Electron energy losses near pulsar polar caps: a Monte Carlo approach

abstract:
  We use Monte Carlo approach to study the energetics of electrons accelerated
in a pulsar polar gap. As energy-loss mechanisms we consider magnetic Compton
scattering of thermal X-ray photons and curvature radiation. The results are
compared with previous calculations which assumed that changes of electron
energy occurred smoothly according to approximations for the average energy
loss rate due to the Compton scattering. We confirm a general dependence of
efficiency of electron energy losses due to inverse Compton mechanism on the
temperature and size of a thermal polar cap and on the pulsar magnetic field.
However, we show that trajectories of electrons in energy-altitude space as
calculated in the smooth way do not always coincide with averaged Monte Carlo
behaviour. In particular, for pulsars with high magnetic field strength
($B_{pc} > 3\times 10^{12}$ G) and low thermal polar cap temperatures ($T <
5\times 10^6$ K) final electron Lorentz factors computed with the two methods
may differ by a few orders of magnitude. We discuss consequences for particular
objects with identified thermal X-ray spectral components like Geminga, Vela,
and PSR B1055-52.


title: On mesogranulation, network formation and supergranulation

abstract:
  We present arguments which show that in all likelihood mesogranulation is not
a true scale of solar convection but the combination of the effects of both
highly energetic granules, which give birth to strong positive divergences
(SPDs) among which we find exploders, and averaging effects of data processing.
The important role played by SPDs in horizontal velocity fields appears in the
spectra of these fields where the scale $\sim$4 Mm is most energetic; we
illustrate the effect of averaging with a one-dimensional toy model which shows
how two independent non-moving (but evolving) structures can be transformed
into a single moving structure when time and space resolution are degraded.
  The role of SPDs in the formation of the photospheric network is shown by
computing the advection of floating corks by the granular flow. The coincidence
of the network bright points distribution and that of the corks is remarkable.
We conclude with the possibility that supergranulation is not a proper scale of
convection but the result of a large-scale instability of the granular flow,
which manifests itself through a correlation of the flows generated by SPDs.


title:
Simultaneous optical polarimetry and X-ray data of the near synchronous
  polar RX J2115-5840

abstract:
  We present simultaneous optical polarimetry and X-ray data of the near
synchronous polar RX J2115-5840. We model the polarisation data using the
Stokes imaging technique of Potter et al. We find that the data are best
modelled using a relatively high binary inclination and a small angle between
the magnetic and spin axes. We find that for all spin-orbit beat phases, a
significant proportion of the accretion flow is directed onto the lower
hemisphere of the white dwarf, producing negative circular polarisation. Only
for a small fraction of the beat cycle is a proportion of the flow directed
onto the upper hemisphere. However, the accretion flow never occurs near the
upper magnetic pole, whatever the orientation of the magnetic poles. This
indicates the presence of a non-dipole field with the field strength at the
upper pole significantly higher. We find that the brightest parts of the hard
X-ray emitting region and the cyclotron region are closely coincident.


title: Cosmological Reionization

abstract:
  In popular cosmological scenarios, some time beyond a redshift of 10, stars
within protogalaxies created the first heavy elements; these systems, together
perhaps with an early population of quasars, generated the ultraviolet
radiation and mechanical energy that reheated and reionized the cosmos. The
history of the Universe during and soon after these crucial formative stages is
recorded in the all-pervading intergalactic medium (IGM), which contains most
of the ordinary baryonic material left over from the big bang. Throughout the
epoch of structure formation, the IGM becomes clumpy and acquires peculiar
motions under the influence of gravity, and acts as a source for the gas that
gets accreted, cools, and forms stars within galaxies, and as a sink for the
metal enriched material, energy, and radiation which they eject.


title: Giant Cyclones in Gaseous Discs of Spiral Galaxies

abstract:
  We report detection of giant cyclonic vortices in the gaseous disc of the
spiral galaxy NGC 3631 in the reference frame rotating with the spiral pattern.
A presence of such structures was predicted by the authors for galaxies, where
the radial gradient of the perturbed velocity exceeds that of the rotational
velocity. This situation really takes place in NGC 3631.


title: The extinction curve of the lensing galaxy of B1152+199 at z=0.44

abstract:
  We present UBVRIz' photometry of the gravitational lens candidate CLASS
B1152+119 obtained with the Nordic Optical Telescope. The two QSO components
are resolved in the B, V, R, I and z' bands confirming the lensing nature of
the system. The z=0.44 lens galaxy is clearly detected in B, R, I and z' and
its position is found to be almost coincident with the faint QSO image which is
heavily extincted (relative to the brighter QSO image) by dust in the lens
galaxy. The extinction curve of the lens galaxy derived from the relative
photometry is well fitted by a Galactic extinction law with 1.3 < R_V < 2.0 and
E(B-V) ~ 1. From a simple model of the system we predict a time delay of ~ 60
days.


title: The Chandra Iron-L X-Ray Line Spectrum of Capella

abstract:
  An analysis of the iron L-shell emission in the publicly available spectrum
of the Capella binary system, as obtained by the High Energy Transmission
Grating Spectrometer on board the Chandra X-ray Observatory, is presented. The
atomic-state model, based on the HULLAC code, is shown to be especially
adequate for analyzing high-resolution x-ray spectra of this sort. Almost all
of the spectral lines in the 10 - 18 Angstrom wavelength range are identified.
It is shown that, for the most part, these lines can be attributed to emission
from L-shell iron ions in the Capella coronae. Possibilities for electron
temperature diagnostics using line ratios of Fe16+ are demonstrated. It is
shown that the observed iron-L spectrum can be reproduced almost entirely by
assuming a single electron temperature of kTe= 600 eV. This temperature is
consistent with both the measured fractional ion abundances of iron and with
the temperature derived from ratios of Fe16+ lines. A volume emission measure
of 1053 cm-3 is calculated for the iron L-shell emitting regions of the Capella
coronae indicating a rather small volume of 1029 cm3 for the emitting plasma if
an electron density of 1012 cm-3 is assumed.


title:
Iterative Maps with Hierarchical Clustering for the Observed Scales of
  Astrophysical and Cosmological Structures

abstract:
  We derive, in order of magnitude, the observed astrophysical and cosmological
scales in the Universe, from neutron stars to superclusters of galaxies, up to,
asymptotically, the observed radius of the Universe. This result is obtained by
introducing a recursive scheme of alternating hierachical mechanisms of
three-dimensional and two-dimensional close packings of gravitationally
interacting objects. The iterative scheme yields a rapidly converging geometric
sequence, which can be described as a hierarchical clustering of aggregates,
having the observed radius of the Universe as its fixed point.


title: Combination Frequencies in the Fourier Spectra of White Dwarfs

abstract:
  Combination frequencies are observed in the Fourier spectra of pulsating DA
and DB white dwarfs. They appear at sums and differences of frequencies
associated with the stellar gravity-modes. Brickhill (1992) proposed that the
combination frequencies result from mixing of the eigenmode signals as the
surface convection zone varying in depth when undergoing pulsation. This depth
changes cause time-dependent thermal impedance, which mix different harmonic
frequencies in the light curve.
  Following Brickhill's proposal, we developed analytical expressions to
describe the amplitudes and phases of these combination frequencies. The
parameters that appear in these expressions are: the depth of the stellar
convection zone when at rest, the sensitivity of this depth towards changes in
stellar effective temperature, the inclination angle of the stellar pulsation
axis with respect to the line of sight, and lastly, the spherical degrees of
the eigenmodes involved in the mixing. Adopting reasonable values for these
parameters, we apply our expressions to a DA and a DB variable white dwarf. We
find reasonable agreement between theory and observation, though some
discrepancies remain unexplained. We show that it is possible to identify the
spherical degrees of the pulsation modes using the combination frequencies.


title:
The Galactic Exoplanet Survey Telescope: A Proposed Space-Based
  Microlensing Survey for Terrestrial Extra-Solar Planets

abstract:
  We present a conceptual design for a space based Galactic Exoplanet Survey
Telescope (GEST) which will use the gravitational microlensing technique to
detect extra solar planets with masses as low as that of Mars at all
separations >~ 1 AU. The microlensing data would be collected by a diffraction
limited, wide field imaging telescope of ~ 1.5m aperture equipped with a large
array of red-optimized CCD detectors. Such a system would be able to monitor
$\sim 2\times 10^8$ stars in $\sim 6$ square degrees of the Galactic bulge at
intervals of 20-30 minutes, and it would observe $\sim 12000$ microlensing
events in three bulge seasons. If planetary systems like our own are common,
GEST should be able to detect $\sim 5000$ planets over a 2.5 year lifetime. If
gas giants like Jupiter and Saturn are rare, then GEST would detect $\sim 1300$
planets in a 2.5 year mission if we assume that most planetary systems are
dominated by planets of about Neptune's' mass. Such a mission would also
discover $\sim 100$ planets of an Earth mass or smaller if such planets are
common. This is a factor of $\sim 50$ better than the most ambitious ground
based programs that have been proposed. GEST will also be sensitive to planets
which have been separated from their parent stars.


title:
Kinematics of Metal-Poor Stars in the Galaxy. II. Proper Motions for a
  Large Non-Kinematically Selected Sample

abstract:
  We present a revised catalog of 2106 Galactic stars, selected without
kinematic bias, and with available radial velocities, distance estimates, and
metal abundances in the range 0.0 <= [Fe/H] <= -4.0. This update of the Beers
and Sommer-Larsen (1995) catalog includes newly-derived homogeneous photometric
distance estimates, revised radial velocities for a number of stars with
recently obtained high-resolution spectra, and refined metallicities for stars
originally identified in the HK objective-prism survey (which account for
nearly half of the catalog) based on a recent re-calibration. A subset of 1258
stars in this catalog have available proper motions, based on measurements
obtained with the Hipparcos astrometry satellite, or taken from the updated
Astrographic Catalogue (AC 2000; second epoch positions from either the Hubble
Space Telescope Guide Star Catalog or the Tycho Catalogue), the Yale/San Juan
Southern Proper Motion (SPM) Catalog 2.0, and the Lick Northern Proper Motion
(NPM1) Catalog. Our present catalog includes 388 RR Lyrae variables (182 of
which are newly added), 38 variables of other types, and 1680 non-variables,
with distances in the range 0.1 to 40 kpc.


title: The Role of Heating and Enrichment in Galaxy Formation

abstract:
  We show that the winds identified with high-redshift low-mass galaxies may
strongly affect the formation of stars in more massive galaxies that form
later. With 3D realizations of a simple linear growth model we track gas
shocking, metal enrichment, and cooling, together with dark halo formation. We
show that outflows typically strip baryonic material out of collapsing
intermediate mass halos, suppressing star formation. More massive halos can
trap the heated gas but collapse late, leading to a broad bimodal redshift
distribution, with a larger characteristic mass associated with the lower
redshift peak. This scenario accounts for the observed bell-shaped luminosity
function of early type galaxies, explains the small number of Milky Way
satellite galaxies relative to Cold Dark Matter models predictions, and
provides a possible explanation for the lack of metal poor G-dwarfs in the
solar neighborhood and the more general lack of low-metallicity stars in
massive galaxies relative to ``closed-box'' models of chemical enrichment.
Intergalactic medium heating from outflows should produce spectral distortions
in the cosmic microwave background that will be measurable with the next
generation of experiments.


title: Quintessence-like Dark Matter in Spiral Galaxies

abstract:
  Through the geodesic analysis of a static and axially symmetric space time,
we present conditions on the state equation of an isotropic perfect fluid
$p=\omega d$, when it is considered as dark matter in spiral galaxies. The main
conclusion is that it can be an exotic fluid ($-1<\omega <-1/3$) as it is found
for Quintessence at cosmological scale.


title: Initial operation of the International Gravitational Event Collaboration

abstract:
  The International Gravitational Event Collaboration, IGEC, is a coordinated
effort by research groups operating gravitational wave detectors working
towards the detection of millisecond bursts of gravitational waves. Here we
report on the current IGEC resonant bar observatory, its data analysis
procedures, the main properties of the first exchanged data set. Even though
the available data set is not complete, in the years 1997 and 1998 up to four
detectors were operating simultaneously. Preliminary results are mentioned.


title:
[OII]3727 Emission from the Companion to the Quasar BR 1202-0725 at
  z=4.7

abstract:
  Results of a narrow-band imaging for the redshifted [OII]3727 emission around
a quasar at z=4.7 obtained with the Subaru telescope and CISCO (a Cassegrain
near infrared camera) are presented. A significant emission line is detected in
the narrow-band H_2 (v=1-0 S(1)) filter at a location 2.4" northwest from the
quasar, where the presence of a companion has been reported in Lyman alpha
emission and the rest-frame UV continuum. We identify this line as [OII]3727
emission and confirm that the source really is a companion at z=4.7. The
[OII]3727 flux from the companion is estimated to be 2.5 x 10^{-17} erg s^{-1}
cm^{-2}. If the companion is a star forming object, the inferred star formation
rate is as high as 45-230 M_{solar} yr^{-1} even without assuming the
extinction correction. This value is higher than those derived from the Lyman
alpha emission or from the UV continuum. Thus, provided that the difference is
caused by dust extinction, the extinction corrected star formation rate is
calculated to be 45 to 2300 M_{solar} yr^{-1} depending on the assuming
extinction curves.


title: Accretion and Emission Processes in AGN: the UV-X Connection

abstract:
  The main characteristics of the average spectrum of radio quiet AGN in the UV
and X-ray range are reviewed, and the emission mechanisms are discussed in the
framework of accretion disk models, in particular the ``irradiated cold
relativistic disk". It is shown that some problems arise in confronting the
predictions of the model to the observations. We propose an alternative model
in terms of a hot disk surrounded by a cold Compton thick medium. Finally we
mention problems with remote regions of the accretion disk.


title:
Lopsided Galaxies, Weak Interactions and Boosting the Star Formation
  Rate

abstract:
  To investigate the link between weak tidal interactions in disk galaxies and
the boosting of their recent star formation, we obtain images and spatially
integrated spectra (3615A < lambda < 5315A) for 40 late-type spiral galaxies
(Sab-Sbc) with varying degrees of lopsidedness (a dynamical indicator of weak
interactions). We quantify lopsidedness as the amplitude <A_1> of the m=1
Fourier component of the azimuthal surface brightness distribution, averaged
over a range of radii. We compare the young stellar content, quantified by
EW(H\delta_abs) and the strength of the 4000 Angstrom break (D_4000), with
lopsidedness and find a 3-4 sigma correlation between the two. We also find a
3.2 sigma correlation between EW(H\beta_emission) and lopsidedness. Using the
evolutionary population synthesis code of Bruzual & Charlot we model the
spectra as an ``underlying population'' and a superimposed ``boost population''
with the aim of constraining the fractional boost in the SFR averaged over the
past 0.5 Gyr (the characteristic lifetime of lopsidedness). From the difference
in both EW(H\delta_abs) and D_4000 between the most and least symmetric thirds
of our sample, we infer that ~ 1x10^9 M_solar of stars are formed over the
duration of a lopsided event in addition to the ``underlying'' SFH (assuming a
final galactic stellar mass of 10^10 M_solar). This corresponds to a factor of
8 increase in the SFR over the past 5x10^8 years. For the nuclear spectra, all
of the above correlations except D_4000 vs. <A_1> are weaker than for the disk,
indicating that in lopsided galaxies, the SF boost is not dominated by the
nucleus.


title:
The head-tail structure of high-velocity clouds - A survey of the
  northern sky

abstract:
  We present new observational results on high-velocity clouds (HVCs) based on
an analysis of the Leiden/Dwingeloo HI survey. We cataloged all HVCs with NHI >
1 10^19 cm^-2 and found 252 clouds that form a representative flux limited
sample. The detailed analysis of each individual HVC in this sample revealed a
significant number of HVCs (nearly 20%) having simultaneously a velocity and a
column density gradient. These HVCs have a cometary appearance in the
position-velocity representation and are called henceforward head-tail HVCs (HT
HVCs). The head is the region with the highest column density of the HVC, while
the column density of the tail is in general much lower (by a factor of 2 - 4).
The absolute majority of the cataloged HVCs belongs to the well known HVC
complexes. With exception of the very faint HVC complex L, all HVC complexes
contain HT HVCs. The HT HVCs were analyzed statistically with respect to their
physical parameters like position, velocity (v_LSR,v_GSR), and column density.
We found a linear correlation between the fraction of HVCs having a head-tail
structure and the peak column density of the HVCs. While there is no
correlation between the fraction of HT HVCs and v_LSR, we found a dependence of
the fraction of HT HVCs and v_GSR. There is no significant correlation between
the fraction of HT HVCs and the parameters galactic longitude and latitude. The
HT HVCs may be interpreted as HVCs that are currently interacting with their
ambient medium. In the context of this model the tails represent material that
is stripped off from the HVC core. We discuss the implications of this model
for galactic and extragalactic HVCs.


title:
Narrow Line Seyfert 1 Galaxies and the Evolution of Galaxies & Active
  Galaxies

abstract:
  Narrow Line Seyfert 1 galaxies (NLS1s) are intriguing due to their continuum
as well as emission line properties. The observed peculiar properties of the
NLS1s are believed to be due to accretion rate close to Eddington limit. As a
consequence, for a given luminosity,
  NLS1s have smaller black hole (BH) masses compared to normal Seyfert
galaxies. Here we argue that NLS1s might be Seyfert galaxies in their early
stage of evolution and as such may be low redshift, low luminosity analogues of
high redshift quasars. We propose that NLS1s may reside in rejuvenated, gas
rich galaxies. We also argue in favor of collisional ionization for production
of FeII in active galactic nuclei (AGN).


title: Eigenvector Sky Subtraction

abstract:
  We develop a new method for estimating and removing the spectrum of the sky
from deep spectroscopic observations; our method does not rely on simultaneous
measurement of the sky spectrum with the object spectrum. The technique is
based on the iterative subtraction of continuum estimates and Eigenvector sky
models derived from Singular Value Decompositions (SVD) of sky spectra, and sky
spectra residuals. Using simulated data derived from small telescope
observations we demonstrate that the method is effective for faint objects on
large telescopes. We discuss simple methods to combine our new technique with
the simultaneous measurement of sky to obtain sky subtraction very near the
Poisson limit.


title: The recent star formation history of the Hipparcos solar neighbourhood

abstract:
  We use data from the Hipparcos catalogue to construct colour-magnitude
diagrams for the solar neighbourhood, which are then treated using advanced
Bayesian analysis techniques to derive the star formation history, $SFR(t)$, of
this region over the last 3 Gyr. The method we use allows the recovery of the
underlying $SFR(t)$ without the need of assuming any {\it a priori} structure
or condition on $SFR(t)$, and hence yields a highly objective result. The
remarkable accuracy of the data permits the reconstruction of the local
$SFR(t)$ with an unprecedented time resolution of $\approx 50 $ Myr. A $SFR(t)$
having an oscillatory component of period $\approx 0.5$ Gyr is found,
superimposed on a small level of constant star formation activity. Problems
arising from the non-uniform selection function of the Hipparcos satellite are
discussed and treated. Detailed statistical tests are then performed on the
results, which confirm the inferred $SFR(t)$ to be compatible with the observed
distribution of stars.


title:
Power law burst and inter-burst interval distributions in the solar
  wind: turbulence or dissipative SOC ?

abstract:
  We calculate for the first time the probability density functions (PDFs) P of
burst energy e, duration T and inter-burst interval tau for a known turbulent
system in nature. Bursts in the earth-sun component of the Poynting flux at 1
AU in the solar wind were measured using the MFI and SWE experiments on the
NASA WIND spacecraft. We find P(e) and P(T) to be power laws, consistent with
self-organised criticality (SOC). We find also a power law form for P(tau) that
distinguishes this turbulent cascade from the exponential P(tau) of ideal SOC,
but not from some other SOC-like sandpile models. We discuss the implications
for the relation between SOC and turbulence.


title:
A Search for Stars of Very Low Metal Abundance. IV. uvbyCa Observations
  of Metal-Weak Candidates from the Northern HK Survey

abstract:
  CCD photometry on the uvbyCa system has been obtained for 521 candidate
metal-poor stars from the northern hemisphere HK survey of Beers and
colleagues. Reddening corrections, classifications of stars by luminosity
class, and the derivation of metal abundances based on Stromgren indices m1 and
hk are described and presented, along with preliminary spectroscopic estimates
of abundance. A number of extremely metal-poor stars with [Fe/H] less than or
equal to -2.50 are identified.


title:
Metallicity of Red Giants in the Galactic Bulge from Near-Infrared
  Spectroscopy

abstract:
  We present K-band spectra of more than 110 M giants in Galactic bulge fields
interior to -4 degrees and as close as 0.2 degrees of the Galactic Center. From
the equivalent widths of three features in these spectra, EW(Na),EW(Ca), and
EW(CO) we calculate [Fe/H] for the stars with a calibration derived from
globular clusters Stephens et al (2000). The mean [Fe/H] for each field is in
good agreement with the results from Frogel et al. (1999) based on the slope of
the giant branch method. We find no evidence for a metallicity gradient along
the minor or major axes of the inner bulge (R < 0.6 kpc). A metallicity
gradient along the minor axis, found earlier, arises when fields located at
larger galactic radius are included. However, these more distant fields are
located outside of the infrared bulge defined by the COBE/DIRBE observations.
We compute the [Fe/H] distribution for the inner bulge and find a mean value of
-0.21 dex with a full width dispersion of 0.30 dex, close to the values found
for Baade's Window (BW) by Sadler et al. (1996) and to a theoretical prediction
for a bulge formed by dissipative collapse Molla et al (2000).


title: MHD Models of Axisymmetric Protostellar Jets

abstract:
  We present the results of a series of axisymmetric time-dependent
magnetohydrodynamic (MHD) simulations of the propagation of cooling, overdense
jets, motivated by the properties of outflows associated with young stellar
objects. A variety of initial field strengths and configurations are explored
for both steady and time-variable (pulsed) jets. Even apparently weak magnetic
fields with strengths B < 60 micro-G in the pre-shocked jet beam can have a
significant effect on the dynamics, for example by altering the density, width,
and fragmentation of thin shells formed by cooling gas. A linear analysis
predicts that axisymmetric pinch modes of the MHD Kelvin-Helmholtz instability
should grow only slowly for the highly supermagnetosonic jets studied here; we
find no evidence for them in our simulations. Some of our models appear
unstable to current-driven pinch modes, however the resulting pressure and
density variations induced in the jet beam are not large, making this mechanism
an unlikely source of emission knots in the jet beam. In the case of pulsed
jets, radial hoop stresses confine shocked jet material in the pulses to the
axis, resulting in a higher density in the pulses in comparison to purely
hydrodynamic models.


title:
Determination of Masses and Radii of the Massive Eclipsing Binary System
  HV 2543 in the Large Magellanic Cloud

abstract:
  We present a V light curve of the eclipsing binary system HV 2543 (Sk-67 117)
in the Large Magellanic Cloud based on CCD images acquired between the years
1995 and 1998. We have analysed this light curve and published radial velocity
data, finding that this system is semidetached, with the secondary (less
massive and less luminous component) filling its Roche lobe. From our analysis
with the Wilson-Devinney code, we estimated the following masses and radii for
the components of HV 2543: M1=25.63 +- 0.7, R1=15.54 +- 0.4, M2=15.63 +- 1.0
and R2=13.99 +- 0.4, in solar units. On the basis of B and V photometry of the
field stars, we found that HV 2543 is member of an OB association, perhaps
related to which the massive binary system Sk-67 105 belongs.


title: VSOP Observations of a Sub-Parsec Accretion Disk

abstract:
  The physical conditions in the inner parsec of accretion disks believed to
orbit the central black holes in active galactic nuclei can be probed by
imaging the absorption of background radio emission by ionized gas in the disk.
We report high angular resolution observations of the nearby galaxy NGC 4261
which show evidence for free-free absorption by a thin, nearly edge-on disk at
several frequencies. The angular width, and probably the depth, of the
absorption appears to increase with decreasing frequency, as expected. Because
free-free absorption is much larger at lower frequencies, the longest possible
baselines are needed to provide adequate angular resolution; observing at
higher frequencies to improve resolution will not help.


title: Space VLBI at Low Frequencies

abstract:
  At sufficiently low frequencies, no ground-based radio array will be able to
produce high resolution images while looking through the ionosphere. A
space-based array will be needed to explore the objects and processes which
dominate the sky at the lowest radio frequencies. An imaging radio
interferometer based on a large number of small, inexpensive satellites would
be able to track solar radio bursts associated with coronal mass ejections out
to the distance of Earth, determine the frequency and duration of early epochs
of nonthermal activity in galaxies, and provide unique information about the
interstellar medium. This would be a "space-space" VLBI mission, as only
baselines between satellites would be used. Angular resolution would be limited
only by interstellar and interplanetary scattering.


title: Deeply penetrating banded zonal flows in the solar convection zone

abstract:
  Helioseismic observations have detected small temporal variations of the
rotation rate below the solar surface corresponding to the so-called `torsional
oscillations' known from Doppler measurements of the surface. These appear as
bands of slower and faster than average rotation moving equatorward. Here we
establish, using complementary helioseismic observations over four years from
the GONG network and from the MDI instrument on board SOHO, that the banded
flows are not merely a near-surface phenomenon: rather they extend downward at
least 60 Mm (some 8% of the total solar radius) and thus are evident over a
significant fraction of the nearly 200 Mm depth of the solar convection zone.


title:
N$_2^+$ and CO$^+$ in Comets 122P/1995 S1 (deVico) and C/1995 O1
  (Hale-Bopp)

abstract:
  We observed comets 122P/1995\,S1 (deVico) and C/1995\,O1 (Hale-Bopp) with
high spectral resolving power in order to determine the ratio of N$_2^+$/CO$^+$
in their comae. While we clearly detected the CO$^+$ in both of these comets,
no N$_2^+$ was detected in either comet. From these spectra, we derive
sensitive upper limits for N$_2^+$/CO$^+$. These upper limits are substantially
below other reported detections of N$_2^+$/CO$^+$ in other comets. We discuss
the prior N$_2^+$ detections and compare them with our observations. The
abundance of N$_2$ in comets is important to our understanding of the
condensation of ices in the solar nebula. In addition, N$_2$ is a tracer of Ar
so study of N$_2$ allows an understanding of the role of comets for delivering
volatiles to the terrestrial planets. It appears that many, if not most, comets
are depleted in N$_2$ and it will be necessary to search for a mechanism for
depleting this molecule in order to be consistent with current models of the
solar nebula.


title:
Radial Temperature Profiles of 11 Clusters of Galaxies Observed With
  BeppoSAX

abstract:
  We have derived azimuthally-averaged radial temperature profiles of the X-ray
gas contained within 11 clusters of galaxies with redshift z=0.03-0.2 with
BeppoSAX. Each of the 11 clusters have had their radial temperature profiles
previously determined with ASCA. We find that the temperature profiles of these
clusters are generally flat or increase slightly out to ~30% of the virial
radius, and that a decline in temperature of 14% out to 30% of the virial
radius is ruled out at the 99% confidence level. This is in accordance with a
previous ROSAT PSPC study and an ASCA study by White (1999), but in
disagreement with an ASCA study by Markevitch et al. (1998) that found on
average that cluster temperature profiles decreased significantly with radius.


title:
Primordial fractal density perturbations and structure formation in the
  Universe: 1-Dimensional collisionless sheet model

abstract:
  Two-point correlation function of galaxy distribution shows that the
structure in the present Universe is scale-free up to a certain scale (at least
several tens Mpc), which suggests that a fractal structure may exist. If small
primordial density fluctuations have a fractal structure, the present
fractal-like nonlinear structure below the horizon scale could be naturally
explained. We analyze the time evolution of fractal density perturbations in
Einstein-de Sitter universe, and study how the perturbation evolves and what
kind of nonlinear structure will come out. We assume a one-dimensional
collisionless sheet model with initial Cantor-type fractal perturbations. The
nonlinear structure seems to approach some attractor with a unique fractal
dimension, which is independent of the fractal dimensions of initial
perturbations. A discrete self-similarity in the phase space is also found when
the universal nonlinear fractal structure is reached.


title: Speckle Imaging: a boon for astronomical observations

abstract:
  The speckle imaging is a photographic technique that resolves objects viewed
through severely distorted media. The results are insensitive to the errors
caused by apparent size of the isoplanatic patch and the telescope aberrations.
In this article, a short descriptions of the atmospheric turbulence and its
effect on the flat wavefront from a stellar source is presented; the
shortcomings of the conventional long-exposure images in the presence of
Earth's atmosphere are discussed. The advantages of the speckle interferometric
technique over conventional imaging are enumerated. The technical details of
the method, basic Fourier optics, data analysis procedures are also described.


title: Broad-Band X-Ray Study of a Transient Pulsar RX J0059.2-7138

abstract:
  We report on the results of the ASCA and ROSAT observations on RX
J0059.2-7138, a transient X-ray pulsar in the Small Magellanic Cloud. The
barycentric pulse period has been precisely determined to be 2.763221 +-
0.000004 s. The pulse shape is almost identical in all of the energy bands. The
pulse fraction increases with the photon energy below ~2 keV, while it is
nearly constant at ~37% above ~2 keV. The X-ray spectrum has been found to
consist of two components. One is dominant above 2 keV, and exhibits sinusoidal
pulsations. This component is well described by a typical model found in many
X-ray binary pulsars, a power-law of photon index 0.4 with an exponential
cut-off at 6.5 keV. The other is dominant below 1 keV and shows no significant
pulsation. This component is represented by either a broken power-law with
photon indices of 2.6 and 5.1 below and above a break energy of 0.9 keV, or a
metal-poor thin-thermal plasma with a temperature of 0.37 keV. The
phase-averaged luminosity is ~1E38 erg s^-1 (0.1-10.0 keV) for both components.
A hint of oxygen over-abundance is found in the absorbing column, possibly due
to circumstellar gas ejected from an evolved companion.


title:
Tests of Statistical Methods for Estimating Galaxy Luminosity Function
  and Applications to the Hubble Deep Field

abstract:
  We studied the statistical methods for the estimation of the luminosity
function (LF) of galaxies. We focused on four nonparametric estimators:
$1/V_{\rm max}$ estimator, maximum-likelihood estimator of Efstathiou et al.
(1988), Cho{\l}oniewski's estimator, and improved Lynden-Bell's estimator. The
performance of the $1/V_{\rm max}$ estimator has been recently questioned,
especially for the faint-end estimation of the LF. We improved these estimators
for the studies of the distant Universe, and examined their performances for
various classes of functional forms by Monte Carlo simulations. We also applied
these estimation methods to the mock 2dF redshift survey catalog prepared by
Cole et al. (1998). We found that $1/V_{\rm max}$ estimator yields a completely
unbiased result if there is no inhomogeneity, but is not robust against
clusters or voids. This is consistent with the well-known results, and we did
not confirm the bias trend of $1/V_{\rm max}$ estimator claimed by Willmer
(1997) in the case of homogeneous sample. We also found that the other three
maximum-likelihood type estimators are quite robust and give consistent results
with each other. In practice we recommend Cho{\l}oniewski's estimator for two
reasons: 1. it simultaneously provides the shape and normalization of the LF;
2. it is the fastest among these four estimators, because of the algorithmic
simplicity. Then, we analyzed the photometric redshift data of the Hubble Deep
Field prepared by Fern\'{a}ndez-Soto et al. (1999) using the above four
methods. We also derived luminosity density $\rho_{\rm L}$ at $B$- and
$I$-band. Our $B$-band estimation is roughly consistent with that of Sawicki,
Lin, & Yee (1997), but a few times lower at $2.0 < z < 3.0$. The evolution of
$\rho_{\rm L}(I)$ is found to be less prominent.


title: A Simple Model for the Absorption of Starlight by Dust in Galaxies

abstract:
  We present a new model to compute the effects of dust on the integrated
spectral properties of galaxies, based on an idealized prescription of the main
features of the interstellar medium (ISM). The model includes the ionization of
HII regions in the interiors of the dense clouds in which stars form and the
influence of the finite lifetime of these clouds on the absorption of
radiation. We compute the production of emission lines and the absorption of
continuum radiation in the HII regions and the subsequent transfer of line and
continuum radiation in the surrounding HI regions and the ambient ISM. This
enables us to interpret simultaneously all the observations of a homogeneous
sample of nearby UV-selected starburst galaxies, including the ratio of far-IR
to UV luminosities, the ratio of Halpha to Hbeta luminosities, the Halpha
equivalent width, and the UV spectral slope. We show that the finite lifetime
of stellar birth clouds is a key ingredient to resolve an apparent discrepancy
between the attenuation of line and continuum photons in starburst galaxies. In
addition, we find that an effective absorption curve proportional to
lambda^-0.7 reproduces the observed relation between the ratio of far-IR to UV
luminosities and the UV spectral slope. We interpret this relation most simply
as a sequence in the overall dust content of the galaxies. The shallow
wavelength dependence of the effective absorption curve is compatible with the
steepness of known extinction curves if the dust has a patchy distribution. In
particular, we find that a random distribution of discrete clouds with optical
depths similar to those in the Milky Way provides a consistent interpretation
of all the observations. Our model for absorption can be incorporated easily
into any population synthesis model. (abridged)


title:
Non-Linear gravitational growth of large scale structures inside and
  outside standard Cosmology

abstract:
  We reconsider the problem of gravitational structure formation inside and
outside General Relativity (GR), both in the weakly and strongly non-linear
regime. We show how these regimes can be explored observationally through
clustering of high order cumulants and through the epoch of formation,
abundance and clustering of collapse structures, using Press-Schechter
formalism and its extensions. We address the question of how different are
these predictions when using a non-standard theory of Gravity. We study
examples of cosmologies that do not necessarily obey Einstein's field
equations: scalar-tensor theories (STT), such as Brans-Dicke (BD), parametrized
with $\omega$, a non-standard parametrisation of the Hubble law, $H^2=
a^{-3(1+\epsilon)}$, or a non-standard cosmic equation of state $p=\gamma\rho$,
where $\gamma$ can be chosen irrespective of the cosmological parameters
($\Omega_M$ and $\Omega_\Lambda$). We present some preliminary bounds on
$\gamma$, $\omega$ and $\epsilon$ from observations of the skewness and
kurtosis in the APM Galaxy Survey. This test is independent of the overall
normalization of rms fluctuations. We also show how abundances and formation
times change under these assumptions. Upcoming data on non-linear growth will
place strong constraints on such variations from the standard paradigm.


title:
The mass surface density in the local disk and the chemical evolution of
  the Galaxy

abstract:
  We have studied the effect of adopting different values of the total baryonic
mass surface density in the local disk at the present time in a model for the
chemical evolution of the Galaxy. We have compared our model results with the
G-dwarf metallicity distribution, the amounts of gas, stars, stellar remnants,
infall rate and SN rate in the solar vicinity, and with the radial abundance
gradients and gas distribution in the disk. This comparison strongly suggests
that the value of the total baryonic mass surface density in the local disk
which best fits the observational properties should lie in the range 50-75 Msun
pc-2, and that values outside this range should be ruled out.


title: Is the [CO] index an age indicator for star forming galaxies?

abstract:
  The classical [CO] index, i.e. the strength of the CO first overtone
absorption bands starting at 2.29 micron, is sometimes used to constrain the
maximum age of star formation events in galaxies. In this paper we critically
analyze
  - theoretical models which could predict either a factor of >2 drop or a
pronounced increase of [CO] at ages older than 100 Myr, depending on the
evolutionary tracks one adopts
  - observational data for young clusters in the LMC which do not show any
strong relationship between the CO index and cluster age.
  The above scenario indicates that the value of [CO] does not provide a
reliable tool for estimating the age of stellar populations older than about 10
Myr, i.e. after the first red supergiants have been formed.
  The contradictory results of theoretical models reflect problems in treating
the evolution along the Asymptotic Giant Branch (AGB). In particular, those
evolutionary synthesis models using stellar tracks which do not include the
thermal pulsing AGB phase produce too weak CO features at 100-1000 Myr, i.e. in
the range of ages when the near infrared emission is dominated by thermal
pulsing AGB stars.


title:
The Properties of Molecular Hydrogen toward the Orion Belt Stars from
  Observations by the Interstellar Medium Absorption Profile Spectrograph

abstract:
  Absorption features from the Lyman and Werner bands of interstellar molecular
hydrogen were recorded by the Interstellar Medium Absorption Profile
Spectrograph (IMAPS) at a wavelength resolving power R=80,000 in the spectra of
delta Ori and epsilon Ori. The objective was to find and study more examples of
an unusual phenomenon found for one of the velocity components of H2 in the
spectrum of zeta Ori by Jenkins & Peimbert (1997). Specifically, they detected
a gradual shift in velocity and broadening for features arising from
progressively higher rotational excitations J. This effect appears to be absent
in the spectra of both delta and epsilon Ori, which are only a few degrees away
in the sky from zeta Ori. The absence of atomic material at a large negative
velocity in the spectra of delta and epsilon Ori (and its presence in zeta Ori)
supports a proposal by Jenkins & Peimbert that the line of sight to zeta
intercepts a bow shock facing away from us, perhaps created by the collision of
wind-like material with some foreground obstruction. For both stars, the H2
absorption features are separated into two velocity components. Total H2 column
densities toward delta and epsilon Ori are 5.5e14 and 1.9e16 cm^-2,
respectively. The rotation temperatures of the molecules with J > 2 toward
epsilon Ori indicate that the gas is in the general vicinity of the stars that
emit UV fluxes capable of rotationally pumping the molecules. For the strongest
component of H2 toward delta Ori, the pumping rate is lower and consistent with
a general UV flux level in the plane of the Galaxy.


title:
Counts and Sizes of Galaxies in the Hubble Deep Field - South:
  Implications for the Next Generation Space Telescope

abstract:
  Science objectives for the Next Generation Space Telescope (NGST) include a
large component of galaxy surveys, both imaging and spectroscopy. The Hubble
Deep Field datasets include the deepest observations ever made in the
ultraviolet, optical and near infrared, reaching depths comparable to that
expected for NGST spectroscopy. We present the source counts, galaxy sizes and
isophotal filling factors of the HDF-South images. The observed integrated
galaxy counts reach >500 galaxies per square arcminute at AB<30. We extend
these counts to faint levels in the infrared using models. The trend previously
seen that fainter galaxies are smaller, continues to AB=29 in the high
resolution HDF-S STIS image, where galaxies have a typical half-light radius of
0.1 arcseconds. Extensive Monte Carlo simulations show that the small measured
sizes are not due to selection effects until >29mag. Using the HDF-S NICMOS
image, we show that galaxies are smaller in the near infrared than they are in
the optical. We analyze the isophotal filling factor of the HDF-S STIS image,
and show that this image is mostly empty sky even at the limits of galaxy
detection, a conclusion we expect to hold true for NGST spectroscopy. At the
surface brightness limits expected for NGST imaging, however, about a quarter
of the sky is occupied by the outer isophotes of AB<30 galaxies. We discuss the
implications of these data on several design concepts of the NGST near-infrared
spectrograph. We compare the effects of resolution and the confusion limit of
various designs, as well as the multiplexing advantages of either multi-object
or full-field spectroscopy. We argue that the optimal choice for NGST
spectroscopy of high redshift galaxies is a multi-object spectrograph (MOS)
with target selection by a micro electro mechanical system (MEMS) device.


title: Type Ia Supernovae: Progenitors and Evolution with Redshift

abstract:
  Relatively uniform light curves and spectral evolution of Type Ia supernovae
(SNe Ia) have led to the use of SNe Ia as a ``standard candle'' to determine
cosmological parameters. Whether a statistically significant value of the
cosmological constant can be obtained depends on whether the peak luminosities
of SNe Ia are sufficiently free from the effects of cosmic and galactic
evolutions.
  Here we first review the single degenerate scenario for the Chandrasekhar
mass white dwarf (WD) models of SNe Ia. We identify the progenitor's evolution
and population with two channels: (1) the WD+RG (red-giant) and (2) the WD+MS
(near main-sequence He-rich star) channels. In these channels, the strong wind
from accreting WDs plays a key role, which yields important age and metallicity
effects on the evolution.
  We then address the questions whether the nature of SNe Ia depends
systematically on environmental properties such as metallicity and age of the
progenitor system and whether significant evolutionary effects exist. We
suggest that the variation of the carbon mass fraction $X$(C) in the C+O WD (or
the variation of the initial WD mass) causes the diversity of the brightness of
SNe Ia. This model can explain the observed dependences of SNe Ia brightness on
the galaxy types and the distance from the galactic center.
  Finally, applying the metallicity effect on the evolution of SN Ia
progenitors, we make a prediction of the cosmic supernova rate history as a
composite of the supernova rates in different types of galaxies.


title: Extended X-ray emission in the radio loud galaxy 3C 382

abstract:
  ROSAT/HRI observations of the powerful radio-loud galaxy 3C382 reveal
extended X-ray emission associated with the source. On the basis of this new
spatial component, a previous ROSAT/PSPC spectral analysis of the source is
revised. Allowing for the presence of an additional thermal component in the
PSPC spectrum, the non-thermal component is found to be compatible with the
extrapolation of the well defined 3C382 - 2-10 keV - power-law spectrum into
the soft X-rays. The thermal -extended- component would then account for the
soft excess emission previously reported for this source. The origin of this
thermal component is not clear. Its luminosity compares with that of rich Abell
clusters; yet, the galaxy environment in 3C382 appears of moderate optical
richness. An alternative is that it is due to a massive extended gaseous
atmosphere sustained by the deep gravitational potential well of 3C382.


title:
Homogeneity of Stellar Populations in Early-Type Galaxies with Different
  X-ray Properties

abstract:
  We have found the stellar populations of early-type galaxies are homogeneous
with no significant difference in color or Mg2 index, despite the dichotomy
between X-ray extended early-type galaxies and X-ray compact ones. Since the
X-ray properties reflect the potential gravitational structure and hence the
process of galaxy formation, the homogeneity of the stellar populations implies
that the formation of stars in early-type galaxies predat es the epoch when the
dichotomy of the potential structure was established.


title: The CFH Optical PDCS survey (COP) I: The Data

abstract:
  This paper presents and gives the COP (COP: CFHT Optical PDCS; CFHT:
Canada-France-Hawaii Telescope; PDCS: Palomar Distant Cluster Survey) survey
data. We describe our photometric and spectroscopic observations with the MOS
multi-slit spectrograph at the CFH telescope. A comparison of the photometry
from the PDCS (Postman et al. 1996) catalogs and from the new images we have
obtained at the CFH telescope shows that the different magnitude systems can be
cross-calibrated. After identification between the PDCS catalogues and our new
images, we built catalogues with redshift, coordinates and V, I and
Rmagnitudes. We have classified the galaxies along the lines of sight into
field and structure galaxies using a gap technique (Katgert et al. 1996). In
total we have observed 18 significant structures along the 10 lines of sight.


title: The Enigmatic Radio Afterglow of GRB 991216

abstract:
  We present wide-band radio observations spanning from 1.4 GHz to 350 GHz of
the afterglow of GRB 991216, taken from 1 to 80 days after the burst. The
optical and X-ray afterglow of this burst were fairly typical and are explained
by a jet fireball. In contrast, the radio light curve is unusual in two
respects: (a) the radio light curve does not show the usual rise to maximum
flux on timescales of weeks and instead appears to be declining already on day
1 and (b) the power law indices show significant steepening from the radio
through the X-ray bands. We show that the standard fireball model, in which the
afterglow is from a forward shock, is unable to account for (b) and we conclude
that the bulk of the radio emission must arise from a different source. We
consider two models, neither of which can be ruled out with the existing data.
In the first (conventional) model, the early radio emission is attributed to
emission from the reverse shock as in the case of GRB 990123. We predict that
the prompt optical emission would have been as bright (or brighter) than 8th
magnitude. In the second (exotic) model, the radio emission originates from the
forward shock of an isotropically energetic fireball (10^54 erg) expanding into
a tenuous medium (10^-4 cm^-3). The resulting fireball would remain
relativistic for months and is potentially resolvable with VLBI techniques.
Finally, we note that the near-IR bump of the afterglow is similar to that seen
in GRB 971214 and no fireball model can explain this bump.


title:
A model for the alternating phase lags associated with QPOs in X-ray
  binaries

abstract:
  We present a theoretical model for the alternating phase lags associated with
QPO fundamental and harmonic frequencies observed in some Galactic black-hole
candidates. We assume that the accretion flow exhibits a transition from an
outer cool, optically thick accretion disk to a hot, inner advection-dominated
accretion flow (ADAF), and that the QPOs are related to small-scale
oscillations of the accretion rate and the transition radius. We present an
analytical estimate of the expected phase lags at the fundamental and first
harmonic frequencies of the QPOs and perform detailed time-dependent
Monte-Carlo simualtions of the radiation transport in the oscillating ADAF /
cool disk system. We find that this model is well suited to reproduce
alternating phase lags between the fundamental and the first harmonic. It also
naturally explains the trend observed in GRS 1915+105 that, as the soft X-ray
luminosity increases, the QPO frequency increases and the phase lag associated
with the QPO fundamental frequency changes sign from positive to negative. The
relation between the disk temperature and the QPO frequency observed in GRS
1915+105 is consistent with a secular instability modulating the disk
evaporation at the transition radius.