title: Radio Properties of Infrared Selected Galaxies in the IRAS 2 Jy Sample

abstract:
  The radio counterparts to the IRAS Redshift Survey galaxies are identified in
the NRAO VLA Sky Survey (NVSS) catalog. Our new catalog of the infrared
flux-limited (S60 >= 2 Jy) complete sample of 1809 galaxies lists accurate
radio positions, redshifts, and 1.4 GHz radio and IRAS fluxes. This sample is
six times larger in size and five times deeper in redshift coverage (to z ~
0.15) compared with those used in earlier studies of the radio and far-infrared
(FIR) properties of galaxies in the local volume. The well known radio-FIR
correlation is obeyed by the overwhelming majority (>98%) of the
infrared-selected galaxies, and the radio AGNs identified by their excess radio
emission constitute only about 1% of the sample, independent of the IR
luminosity. These FIR-selected galaxies can account for the entire population
of late-type field galaxies in the local volume, and their radio continuum may
be used directly to infer the extinction-free star formation rate in most
cases. Both the 1.4 GHz radio and 60 micron infrared luminosity functions are
reasonably well described by linear sums of two Schechter functions, one
representing normal, late-type field galaxies and the second representing
starbursts and other luminous infrared galaxies. The integrated FIR luminosity
density for the local volume is 4.8+/-0.5 x 10^7 L(sun) per Mpc^3, less than
10% of which is contributed by the luminous infrared galaxies with L(FIR) >
10^{11} L(sun) . The inferred extinction-free star formation density for the
local volume is 0.015 +/- 0.005 solar mass per year per Mpc^3.


title: The Initial Mass Function and its Variation

abstract:
  The observed distribution of IMF shapes can be understood as statistical
sampling from a universal IMF and variations that result from stellar-dynamical
processes. However, young star clusters appear to have an IMF biased towards
low-mass stars when compared to the Galactic disk IMF, which comprises an
average populated by star-formation episodes occurring Gyrs ago. In addition to
this tentative but exciting deduction, this text outlines some of the stumbling
blocks hindering the production of rigorous IMF determinations, and discusses
the most robust evidence for structure in it. Also, it is stressed that an
invariant IMF should not be expected.


title: On the X-ray fast-time variability of Sco X-2 (GX 349+2)

abstract:
  We have analysed archived Ginga data on the Z source Sco X-2 (GX349+2). We
present the first detailed investigation of its X-ray fast-time variability, as
a function of position in the Z track. During the two-day observation over the
period 5-7 March 1989, the source was in the so-called flaring branch, and the
lower part of the so-called normal branch. We found broad peaked noise with a
centroid frequency and width of ~4-7 Hz and ~6-12 Hz respectively. The peaked
noise was strongest in the lower flaring branch, with a maximum fractional rms
amplitude of ~3 %. We conclude that it is not a manifestation of atoll source
high frequency noise, as had been suggested, and compare it with the power
spectral features seen in other Z sources. We find that the peaked noise is
markedly different to the quasi-periodic oscillations found in the normal and
flaring branches of Sco X-1; however it bears some resemblance to that seen in
the flaring branch of Cyg X-2 at low overall intensities.


title:
Pulsar motions from neutrino oscillations induced by a violation of the
  equivalence principle

abstract:
  We analize a possible explanation of the pulsar motions in terms of resonant
neutrino transitions induced by a violation of the equivalence principle (VEP).
Our approach, based on a parametrized post-Newtonian (PPN) expansion, shows
that VEP effects give rise to highly directional contributions to the neutrino
oscillation length. These terms induce anisotropies in the linear and angular
momentum of the emitted neutrinos, which can account for both the observed
translational and rotational pulsar motions. The violation needed to produce
the actual motions is completely compatible with the existing bounds.


title: The optical afterglow and host galaxy of GRB000926

abstract:
  We present the discovery of the Optical Transient (OT) of the long-duration
gamma-ray burst GRB000926. The optical transient was detected independently
with the Nordic Optical Telescope and at Calar Alto 22.2 hours after the burst.
At this time the magnitude of the transient was R = 19.36. The transient faded
with a decay slope of about 1.7 during the first two days after which the slope
increased abruptly (within a few hours) to about 2.4. The light-curve started
to flatten off after about a week indicating the presence of an underlying
extended object. This object was detected in a deep image obtained one month
after the GRB at R=23.87+-0.15 and consists of several compact knots within
about 5 arcsec. One of the knots is spatially coincident with the position of
the OT and hence most likely belongs to the host galaxy. Higher resolution
imaging is needed to resolve whether all the compact knots belong to the host
galaxy or to several independent objects. In a separate paper we present a
discussion of the optical spectrum of the OT, and its inferred redshift (Moller
et al. in prep.).


title:
NICS-TNG infrared spectroscopy of NGC1068: the first extragalactic
  measurement of [PII] and a new tool to constrain the origin of [FeII] line
  emission in galaxies

abstract:
  We report 0.9-1.4 micron spectroscopic observations of NGC1068 collected
during the commissioning phase of the near infrared camera spectrometer (NICS)
of the Telescopio Nazionale Galileo (TNG). These yielded the first
extragalactic measurement of [PII] (1.188 micron) line emission. In the central
0.75"x2" the [FeII]/[PII] line-intensity ratio is close to unity, similar to
that measured in the Orion bar and a factor of about 20 smaller than in
supernova remnants. This indicates that most of iron is locked into grains and,
therefore, argues against shock excitation being the primary origin of [FeII]
line emission in the central regions of NGC1068.
  We propose the [FeII]/[PII] ratio as a simple and effective tool to study and
perhaps resolve the long debated questions related to the origin of [FeII] line
emission and, more generally, to constrain the role of shock excitation in
active galaxies.


title:
Measuring the galaxy power spectrum with multiresolution decomposition
  -- II. diagonal and off-diagonal power spectra of the LCRS galaxies

abstract:
  The power spectrum estimator based on the discrete wavelet transform (DWT)
for 3-dimensional samples has been studied. The DWT estimator for
multi-dimensional samples provides two types of spectra with respect to
diagonal and off-diagonal modes, which are very flexible to deal with
configuration-related problems in the power spectrum detection. With simulation
samples and mock catalogues of the Las Campanas redshift survey (LCRS), we show
(1) the slice-like geometry of the LCRS doesn't affect the off-diagonal power
spectrum with ``slice-like'' mode; (2) the Poisson sampling with the LCRS
selection function doesn't cause more than 1-$\sigma$ error in the DWT power
spectrum; and (3) the powers of peculiar velocity fluctuations, which cause the
redshift distortion, are approximately scale-independent. These results insure
that the uncertainties of the power spectrum measurement are under control. The
scatter of the DWT power spectra of the six strips of the LCRS survey is found
to be rather small. It is less than 1-$\sigma$ of the cosmic variance of mock
samples in the wavenumber range $0.1 < k < 2$ h Mpc$^{-1}$. To fit the detected
LCRS diagonal DWT power spectrum with CDM models, we find that the best-fitting
redshift distortion parameter $\beta$ is about the same as that obtained from
the Fourier power spectrum. The velocity dispersions $\sigma_v$ for SCDM and
$\Lambda$CDM models are also consistent with other $\sigma_v$ detections with
the LCRS. A systematic difference between the best-fitting parameters of
diagonal and off-diagonal power spectra has been significantly measured. This
indicates that the off-diagonal power spectra are capable of providing
information about the power spectrum of galaxy velocity field.


title: Progenitors of GRB originated in the dense star cluster

abstract:
  The evidences are given for the origin of the GRB progenitors from the ready
stellar remnants in result of the dynamical interaction in the dense star
clusters. In this way the close binaries of compact objects may form and then
merge, often after ejecting from the parent cluster. The GRB may trigger star
formation in the gaseous partiall sphere and occurence of the GRB afterglows
near the star formation regions may be connected with the successive GRB
origins in the same parent cluster. The observed distributions of GRB
afterglows in Z and in distance to the galactic centers are compatible with the
origin of many GRBs in the (present day classical) globular clusters, which
were younger than 2 Gyr at the time of many GRBs events.


title:
A new deuterium abundance measurement from a damped Ly-alpha system at
  z_abs = 3.025

abstract:
  We present the first D/H measurement in a damped Ly-alpha system at z_abs =
3.025 towards QSO 0347-3819 obtained from the UVES-VLT spectra. The DLA
absorber has a metallicity of [Zn/H] = -1.25 and a relatively simple velocity
structure, with two dominating components detected in several metal lines. The
hydrogen Lyman series can be followed down to Ly12 thanks to the high UV-Blue
efficiency of UVES. The best fit of the Lyman series lines, and in particular
of Ly5, Ly8, Ly10 and Ly12, relatively free of local contamination, is obtained
when the DI absorption is included in the two main components. The measured
deuterium column density yields D/H = (2.24+/-0.67) 10^{-5} close to other low
D/H values from Lyman limit systems. The corresponding values for the baryon to
photon ratio and the baryon density derived from D/H are eta = 6 10^{-10} and
Omega_b h^2 = 0.023 respectively.


title:
The 2dF QSO Redshift Survey - IV. The QSO Power Spectrum from the 10k
  Catalogue

abstract:
  (ABRIDGED) We present a power spectrum analysis of the 10K catalogue from the
2dF QSO Redshift Survey. We compare the redshift-space power spectra of QSOs to
those measured for galaxies and Abell clusters at low redshift and find that
they show similar shapes in their overlap range, 50-150h^{-1}Mpc, with
P_QSO(k)\propto k^{-1.4}. The amplitude of the QSO power spectrum at z~1.4 is
almost comparable to that of galaxies at the present day if Omega_m=0.3 and
Omega_Lambda=0.7 (the Lambda cosmology), and a factor of ~3 lower if Omega_m=1
(the EdS cosmology) is assumed. The amplitude of the QSO power spectrum is a
factor of ~10 lower than that measured for Abell clusters at the present day.
At larger scales, the QSO power spectra continue to rise robustly to ~400
h^{-1}Mpc, implying more power at large scales than in the APM galaxy power
spectrum measured by Baugh & Efstathiou.
  We split the QSO sample into two redshift bins and find little evolution in
the amplitude of the power spectrum. The QSO power spectrum may show a spike
feature at ~90h^{-1}Mpc assuming the Lambda cosmology or ~65 h^{-1}Mpc assuming
an EdS cosmology. Although the spike appears to reproduce in both the North and
South strips and in two independent redshift ranges, its statistical
significance is still marginal and more data is needed to test further its
reality.
  We compare the QSO power spectra to CDM models to obtain a constraint on the
shape parameter, Gamma. For two choices of cosmology (Omega_m=1, Omega_Lambda=0
and Omega_m=0.3, Omega_Lambda=0.7), we find the best fit model has Gamma~0.1
+-0.1.


title: Bubbles in galactic haloes

abstract:
  We briefly discuss a possible interconnection of vertical HI structures
observed in the Milky Way Galaxy with large scale blow-outs caused by the
explosions of multiple clustered SNe. We argue that the observed OB
associations can produce only about 60 such events, or approximately one
chimney per 3 kpc$^2$ within the solar circle. We also discuss the overall
properties of HI shells in nearby face-on galaxies and the distribution of
H$\alpha$ and dust in edge-on galaxies. We argue that the presence of dust in
galactic haloes may indicate that radiation pressure is the most probable
mechanism capable of transporting dust to large heights above the galactic
plane. In order to make this possible, the galactic magnetic field must have a
strong vertical component. We mention that SNe explosions can initiate the
Parker instability which in turn creates large scale magnetic loops with a
strong vertical component. Recent observations of nearby edge-on galaxies
favour this suggestion.


title:
Cluster physics from joint weak gravitational lensing and
  Sunyaev-Zel'dovich data

abstract:
  We present a self consistent method to perfom a joint analysis of
Sunyaev-Zel'dovich and weak gravitational lensing observation of galaxy
clusters. The spatial distribution of the cluster main constituents is
described by a perturbative approach. Assuming the hydrostatic equilibrium and
the equation of state, we are able to deduce, from observations, maps of
projected gas density and gas temperature. The method then naturally entails a
X-ray emissivity prediction which can be compared to observed X-ray emissivity
maps. When tested on simulated clusters (noise free), this prediction turns out
to be in very good agreement with the simulated surface brightness. The
simulated and predicted surface brightness images have a correlation
coefficient higher than 0.9 and the total flux differ by 0.9 % or 9 % in the
two simulated clusters we studied. The method should be easily used on real
data in order to provide a physical description of the cluster physics and of
its constituents. The tests performed show that we can recover the amount and
the spatial distributions of both the baryonic and non-baryonic material with
an accuracy better than 10 %. So, in principle, in it might indeed help to
alleviate some well known bias affecting, eg baryon fraction measurements.


title: The radio-loudness dichotomy: environment or black-hole mass?

abstract:
  The results of a comprehensive study of the cluster environments and
black-hole masses of an optically matched sample of radio-loud and radio-quiet
quasars are presented. No evidence is found for a difference in large-scale
environments, with both quasar classes found to be located in clusters of Abell
class $\sim0$ . Conversely, virial black-hole mass estimates based on
H$_{\beta}$ line-widths show a clear difference in the quasar black-hole mass
distributions. Our results suggest that a black-hole mass of
$\sim10^{9}\Msolar$ is required to produce a powerful radio-loud quasar, and
that it is black-hole mass and accretion rate which hold the key to the
radio-loudness dichotomy.


title:
Mapping the inner accretion disk of the galactic black hole J1550-564
  through its rise to outburst

abstract:
  We study the spectral properties of the first 14 observations of the rise to
outburst phase of the X-ray transient J1550-564. Using the PCA and HEXTE
instruments, we find that the 3-200 keV spectra smoothly pass from a standard
low/hard state to a very high state. The classic high state is never
encountered possibly indicating that it is not a phenomenon of the rise phase.
We find that the individual PCA spectra can be fitted adequately by a disk
black body and a thermal Comptonization model which includes reflection. Once
the very high state is reached there is clear spectral curvature of the
continuum which possibly indicates the presence of a composite
thermal/non-thermal plasma. Detailed modelling of the reflection parameters
shows a sharp increase in mean ionization at the onset of the transition
between the low state and very high state. There is a related variability in
the reflected fraction but its exact value depends on the continuum model used.
We can constrain the inner radius using relativistic smearing and while there
are large uncertainties, the data are incompatible with a disk extending to the
last stable orbit in either state. Since the system is on the rise to outburst,
the disk instability models strongly imply that there is no standard inner disk
at the time the low state spectrum is observed. This is compatible with a
truncated disk, filled by an X-ray hot, advection dominated accretion flow.
However, magnetic flares above the outbursting disk can also match the observed
spectra once the effects of either outflow and/or strong photoionization of the
surface of the disk are included.


title: General Properties of Recurrent Bursts from SGRs

abstract:
  General properties of SGR bursts are considered using observational data
collected in the Konus catalog of SGR activity.


title: Stochastic Gravitational Radiation from Phase Transitions

abstract:
  A stochastic background of gravitational radiation from cosmological
processes in the very early Universe is potentially detectable. We review the
gravitational radiation which may arise from cosmological phase transitions,
covering both bubble collisions and turbulence as sources. Prospects for
detecting a direct signal from the electroweak phase transition or other
cosmological sources with a space-based laser interferometer are discussed.


title: On the Fast Spectral Variability of GRBs

abstract:
  Fast spectral variability of gamma-ray burst emission is considered for a
number of events seen by the Konus-Wind experiment. The variability manifests
itself as a strong correlation between instantaneous energy flux $F$ and peak
energy $E_p$. In the ($F,E_p$) plane, the correlation produces distinct tracks
in the form of branches and loops representing the different parts of a burst
time history. Despite the variety of features seen in different events, the
main characteristics of the spectral evolution produce a quite consistent
pattern.


title: Thermal stability of self-gravitating, optically thin accretion disks

abstract:
  In the dynamics of accretion disks, the presence of collective effects
associated with the self-gravity of the disk is expected to affect not only the
momentum transport, but also the relevant energy balance equations, which could
differ substantially from the non-self-gravitating case. Here we follow the
picture that, when the disk is sufficiently cold, the stirring due to
Jeans-related instabilities acts as a source of effective heating. The
corresponding reformulation of the energy equations allows us to: ({\it i})
demonstrate how self-regulation can be established, so that the stability
parameter $Q$ is maintained close to a threshold value, with weak dependence on
radius; ({\it ii}) rediscuss the opacity properties in the self-gravitating
regime. In particular, we show that, if cooling is dominated by {\it
bremsstrahlung}, an optically thin stationary accretion solution is thermally
stable, even in the non-advective case, provided the disk is self-gravitating.
The details of the cooling function have little effect on the structure of such
accretion disk, which is in any case brought by self-gravity to self-regulate.
This condition of self-gravitating accretion is expected to be appropriate for
the outer regions of many disks of astrophysical interest. With the
reformulation of the energy equations described in this paper we have also
secured: ({\it iii}) a starting point for the study of the emission properties
of self-gravitating accretion disks; ({\it iv}) a tool to analyze the structure
of the transition region, where the disk becomes self-gravitating.


title: Magnetic Fields and the Cosmic Microwave Background

abstract:
  Observations of the high degree of isotropy of the cosmic microwave
background are commonly believed to indicate that the Universe is `almost'
Friedmann-Lemaitre-Robertson-Walker (at least since the time of last
scattering). Theoretical support for this belief comes from the so-called
Ehlers-Geren-Sachs Theorem. We show that a generalization of this theorem rules
out any strong magnetic fields in the Universe. Our theoretical result is
model-independent and includes the case of inhomogeneous magnetic fields,
complementing previous results. We thus prove that cosmic microwave background
observations severely constrain all types of primordial and protogalactic
magnetic fields in the universe.


title:
Prospects for radio detection of extremely high energy cosmic rays and
  neutrinos in the Moon

abstract:
  We explore the feasibility of using the Moon as a detector of extremely high
energy (>10^19 eV) cosmic rays and neutrinos. The idea is to use the existing
radiotelescopes on Earth to look for short pulses of Cherenkov radiation in the
GHz range emitted by showers induced just below the surface of the Moon when
cosmic rays or neutrinos strike it. We estimate the energy threshold of the
technique and the effective aperture and volume of the Moon for this detection.
We apply our calculation to obtain the expected event rates from the observed
cosmic ray flux and several representative theoretical neutrino fluxes.


title: Revisiting the calculations of inflationary perturbations

abstract:
  We present a new approximation scheme that allows us to increase the accuracy
of analytical predictions of the power spectra of inflationary perturbations
for two specific classes of inflationary models. Among these models are chaotic
inflation with a monomial potential, power-law inflation and natural inflation
(inflation at a maximum). After reviewing the established first order results
we calculate the amplitudes and spectral indices for these classes of models at
higher orders in the slow-roll parameters for scalar and tensorial
perturbations.


title: Pair Multiplicities and Pulsar Death

abstract:
  Through a simple model of particle acceleration and pair creation above the
polar caps of rotation-powered pulsars, we calculate the height of the
pair-formation front (PFF) and the dominant photon emission mechanism for the
pulsars in the Princeton catalog. We find that for most low- and moderate-field
pulsars, the height of the pair formation front and the final Lorentz factor of
the primary beam is set by nonresonant inverse Compton scattering (NRICS), in
the Klein-Nishina limit. NRICS is capable of creating pairs over a wide range
of pulsar parameters without invoking a magnetic field more complicated than a
centered dipole, although we still require a reduced radius of curvature for
most millisecond pulsars. For short-period pulsars, the dominant process is
curvature radiation, while for extremely high-field pulsars, it is resonant
inverse Compton scattering (RICS). The dividing point between NRICS dominance
and curvature dominance is very temperature-dependent; large numbers of pulsars
dominated by NRICS at a stellar temperature of $10^6$ K are dominated by
curvature at $10^5$ K. We apply these results to pulsar death-line calculations
and to the issue of particle injection into the Crab Nebula.


title: The Evolution of Radio Galaxies at Intermediate Redshift

abstract:
  We describe a new estimate of the radio galaxy 1.4 GHz luminosity function
and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and
color selection have been used to select Bj<23.5 early-type galaxies from the
Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields.
Approximately 230 radio galaxies have then been selected by matching early-type
galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz
luminosity function of radio galaxies measure significant evolution over the
observed redshift range. For an Omega_M=1 cosmology the evolution of the radio
power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and
3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray
selected AGN and is consistent with the same physical process being responsible
for the optical and radio luminosity evolution of AGN.


title:
The extraordinarily bright optical afterglow of GRB 991208 and its host
  galaxy

abstract:
  Observations of the extraordinarily bright optical afterglow (OA) of GRB
991208 started 2.1 d after the event. The flux decay constant of the OA in the
R-band is -2.30 +/- 0.07 up to 5 d, which is very likely due to the jet effect,
and after that it is followed by a much steeper decay with constant -3.2 +/-
0.2, the fastest one ever seen in a GRB OA. A negative detection in several
all-sky films taken simultaneously to the event implies either a previous
additional break prior to 2 d after the occurrence of the GRB (as expected from
the jet effect). The existence of a second break might indicate a steepening in
the electron spectrum or the superposition of two events. Once the afterglow
emission vanished, contribution of a bright underlying SN is found, but the
light curve is not sufficiently well sampled to rule out a dust echo
explanation. Our determination of z = 0.706 indicates that GRB 991208 is at 3.7
Gpc, implying an isotropic energy release of 1.15 x 10E53 erg which may be
relaxed by beaming by a factor > 100. Precise astrometry indicates that the GRB
coincides within 0.2" with the host galaxy, thus given support to a massive
star origin. The absolute magnitude is M_B = -18.2, well below the knee of the
galaxy luminosity function and we derive a star-forming rate of 11.5 +/- 7.1
Mo/yr. The quasi-simultaneous broad-band photometric spectral energy
distribution of the afterglow is determined 3.5 day after the burst (Dec 12.0)
implying a cooling frequency below the optical band, i.e. supporting a jet
model with p = -2.30 as the index of the power-law electron distribution.


title: Magnetic Screening in Accreting Neutron Stars

abstract:
  We investigate whether the magnetic field of an accreting neutron star may be
diamagnetically screened by the accreted matter. We assume the freshly
accumulated material is unmagnetized, and calculate the rate at which the
intrinsic stellar magnetic flux is transported into it by Ohmic diffusion. We
calculate the one-dimensional steady-state magnetic field profiles, and show
that the magnetic field strength decreases as one moves up through the outer
crust and ocean by roughly (Mdot/0.02 Mdot_Edd) orders of magnitude, where Mdot
is the accretion rate and Mdot_Edd the Eddington accretion rate. We show that
buoyancy instabilities set a limit to the strength of any buried field of
roughly 10^10-10^11 G.
  Our results show that magnetic screening is ineffective for Mdot<0.01
Mdot_Edd, so that, no matter how the accreted material joins onto the star, the
underlying stellar field should always be evident. In this respect, we point
out the only known persistently-pulsing accreting X-ray millisecond pulsar, SAX
J1808.4-3658, has an accretion rate of 10^-3 Mdot_Edd, far below the regime
where magnetic screening can play a role.
  Most steadily accreting neutron stars in low-mass X-ray binaries in our
Galaxy accrete at rates where screening would be effective if the simplified
magnetic and accretion geometry we adopt were correct. If screened, then the
underlying field will emerge after accretion halts, on a timescale of only
100--1000 years, set by the Ohmic diffusion time across the outer crust. It
thus seems unlikely that screening alone can explain the low magnetic fields of
the millisecond radio pulsars.


title:
The NACRE Thermonuclear Reaction Compilation and Big Bang
  Nucleosynthesis

abstract:
  The theoretical predictions of big bang nucleosynthesis (BBN) are dominated
by uncertainties in the input nuclear reaction cross sections. In this paper,
we examine the impact on BBN of the recent compilation of nuclear data and
thermonuclear reactions rates by the NACRE collaboration. We confirm that the
adopted rates do not make large overall changes in central values of
predictions, but do affect the magnitude of the uncertainties in these
predictions. Therefore, we then examine in detail the uncertainties in the
individual reaction rates considered by NACRE. When the error estimates by
NACRE are treated as 1\sigma limits, the resulting BBN error budget is similar
to those of previous tabulations. We propose two new procedures for deriving
reaction rate uncertainties from the nuclear data: one which sets lower limits
to the error, and one which we believe is a reasonable description of the
present error budget. We propagate these uncertainty estimates through the BBN
code, and find that when the nuclear data errors are described most accurately,
the resulting light element uncertainties are notably smaller than in some
previous tabulations, but larger than others. Using these results, we derive
limits on the cosmic baryon-to-photon ratio $\eta$, and compare this to
independent limits on $\eta$ from recent balloon-borne measurements of the
cosmic microwave background radiation (CMB). We discuss means to improve the
BBN results via key nuclear reaction measurements and light element
observations.


title:
Evolution of the Luminosity Function and Colors of Galaxies in a
  Lambda-CDM Universe

abstract:
  The luminosity function of galaxies is derived from a cosmological
hydrodynamic simulation of a Lambda cold dark matter (CDM) universe with the
aid of a stellar population synthesis model. At z=0, the resulting B band
luminosity function has a flat faint end slope of \alpha \approx -1.15 with the
characteristic luminosity and the normalization in a fair agreement with
observations, while the dark matter halo mass function is steep with a slope of
\alpha \approx -2. The colour distribution of galaxies also agrees well with
local observations. We also discuss the evolution of the luminosity function,
and the colour distribution of galaxies from z=0 to 5. A large evolution of the
characteristic mass in the stellar mass function due to number evolution is
compensated by luminosity evolution; the characteristic luminosity increases
only by 0.8 mag from z=0 to 2, and then declines towards higher redshift, while
the B band luminosity density continues to increase from z=0 to 5 (but only
slowly at z>3).


title:
Real-Time Difference Imaging Analysis of MOA Galactic Bulge Observations
  During 2000

abstract:
  We describe observations carried out by the MOA group of the Galactic Bulge
during 2000 that were designed to detect efficiently gravitational microlensing
of faint stars in which the magnification is high and/or of short duration.
These events are particularly useful for studies of extra-solar planets and
faint stars. Approximately 17 degrees square were monitored at a sampling rate
of up to 6 times per night. The images were analysed in real-time using a
difference imaging technique. Twenty microlensing candidates were detected, of
which 8 were alerted to the microlensing community whilst in progress.
Approximately half of the candidates had high magnifications (>~10), at least
one had very high magnification (>~50), and one exhibited a clear parallax
effect. The details of these events are reported here, together with details of
the on-line difference imaging technique. Some nova-like events were also
observed and these are described, together with one asteroid.


title: Hydrogen model atmospheres for white dwarf stars

abstract:
  We present a detailed calculation of model atmospheres for DA white dwarfs.
Our atmosphere code solves the atmosphere structure in local thermodynamic
equilibrium with a standard partial linearization technique, which takes into
account the energy transfer by radiation and convection. This code incorporates
recent improved and extended data base of collision induced absorption by
molecular hydrogen. We analyse the thermodynamic structure and emergent flux of
atmospheres in a range 2500 < Teff < 60000$ K and 6.5 < log g < 9.0. Bolometric
correction and colour indices are provided for a subsample of the model grid.
Comparison of the colours is made with published observational material and
results of other recent model calculations. Motivated by the increasing
interest on helium core white dwarfs, we analyse the photometric
characteristics of these stars during their cooling, using evolutionary models
recently available. Effective temperatures, surface gravities, masses and ages
have been determined for some helium core white dwarf candidates, and their
possible binary nature is briefly discussed.


title:
A Chandra Study of Sgr A East: A Supernova Remnant Regulating The
  Activity Of Our Galactic Center?

abstract:
  We report on the X-ray emission from the shell-like, non-thermal radio source
Sgr A East located in the inner few parsecs of the Galaxy based on observations
made with the ACIS detector on board Chandra. This is the first time Sgr A East
has been clearly resolved from other complex structures in the region. The
X-ray emitting region is concentrated within the central $\simeq 2$ pc of the
larger radio shell. The spectrum shows strong K$\alpha$ lines from highly
ionized ions of S, Ar, Ca, and Fe. A simple isothermal plasma model gives
electron temperature $\sim 2$ keV, absorption column $\sim 1 \times 10^{23}$
H/cm^2, luminosity $\sim 8 \times 10^{34}$ ergs/s in the 2--10 keV band, and
gas mass $\sim 2\eta^{1/2}$ M$_{\odot}$ with a filling factor $\eta$. The
plasma appears to be rich in heavy elements, over-abundant by roughly a factor
of four with respect to solar abundances, and shows a spatial gradient of
elemental abundance: the spatial distribution of iron is more compact than that
of the lighter elements. The gas mass and elemental abundance of the X-ray
emission support the long-standing hypothesis that Sgr A East is a supernova
remnant (SNR), maybe produced by the Type II supernova explosion of a massive
star with a main-sequence mass of 13--20 M$_\odot$. The combination of the
radio and X-ray morphologies classifies Sgr A East as a new metal-rich ``mixed
morphology'' (MM) SNR. The size of the Sgr A East radio shell is the smallest
of the known MM SNRs, which strongly suggests that the ejecta have expanded
into a very dense interstellar medium. The ejecta-dominated chemical
compositions of the plasma indicate that the ambient materials should be highly
homogeneous. The relation between Sgr A East and the massive blackhole Sgr A*
is discussed.


title:
Study by MOA of extra-solar planets in gravitational microlensing events
  of high magnification

abstract:
  A search for extra-solar planets was carried out in three gravitational
microlensing events of high magnification, MACHO 98-BLG-35, MACHO 99-LMC-2, and
OGLE 00-BUL-12. Photometry was derived from observational images by the MOA and
OGLE groups using an image subtraction technique. For MACHO 98-BLG-35,
additional photometry derived from the MPS and PLANET groups was included.
Planetary modeling of the three events was carried out in a super-cluster
computing environment. The estimated probability for explaining the data on
MACHO 98-BLG-35 without a planet is <1%. The best planetary model has a planet
of mass ~(0.4-1.5) X 10^-5 M_Earth at a projected radius of either ~1.5 or ~2.3
AU. We show how multi-planet models can be applied to the data. We calculated
exclusion regions for the three events and found that Jupiter-mass planets can
be excluded with projected radii from as wide as about 30 AU to as close as
around 0.5 AU for MACHO 98-BLG-35 and OGLE 00-BUL-12. For MACHO 99-LMC-2, the
exclusion region extends out to around 10 AU and constitutes the first limit
placed on a planetary companion to an extragalactic star. We derive a
particularly high peak magnification of ~160 for OGLE 00-BUL-12. We discuss the
detectability of planets with masses as low as Mercury in this and similar
events.


title: Relativistic velocity singularities

abstract:
  Relativistic and non-relativistic fluid equations can exhibit finite time
singular solutions including density singularities appearing in collapse or
compression systems and gradient singularities in shock waves. However, only
the non-relativistic fluid equations have been shown to exhibit finite-time
velocity singularities, v tending to infinity in this regime. As this limit
violates the cosmic speed limit v<c, where c is the speed of light, it is
unclear how velocity singularity source terms in the non-relativistic equations
are modified in the relativistic equations. This paper uses a driven system to
demonstrate that singular points within the relativistic fluid equations can
generate finite time relativistic velocity singularities v tending to c.


title: The jet model for Sgr A*: radio and X-ray spectrum

abstract:
  The preliminary detection of the Galactic Center black hole Sgr A* in X-rays
by the Chandra mission, as well as recent mm-VLBI measurements, impose strict
constraints on this source. Using a relativistic jet model for Sgr A*, we
calculate the synchrotron and synchrotron self-Compton emission. The predicted
spectrum provides an excellent fit to the radio spectrum and the the X-ray
observations. Limits on the infrared flux and the low X-ray flux require a
high-energy cut-off in the electron spectrum at gamma_e ~< 100. The implied
lack of a significant power-law tail of high-energy electrons also suppresses
the appearance of the extended, optically thin radio emission usually seen in
astrophysical jets. The jet therefore appears rather compact and naturally
satisfies current VLBI limits. The initial parameters of the model are tightly
constrained by the radio spectrum and the "submm-bump" in particular. While the
jet most likely is coupled to some kind of accretion flow, we suggest that the
most visible signatures can be produced by this outflow. If SSC emission from
the jet contributes to the Sgr A* spectrum, significant variability in X-rays
would be expected. The model could be generic for other low-luminosity AGN or
even X-ray binaries.


title: Perturbed Friedmann cosmologies filled with dust and radiation

abstract:
  An infinite number of perturbed k=0 Friedmann cosmologies filled with dust
and radiation is found. As we go up the sequence, the solutions contain an
increasing number of integration functions. With the coordinate gauge adopted
to co-move with the perturbed matter, the solution of a pair of coupled
equations for the trace h of the metric perturbations and for the radiation
density perturbations \delta\rho_r is the key to the problem. An estimate is
given of the temperature variation of the cosmic microwave background radiation
due to the Sachs-Wolfe effect. It is found that the temperature fluctuations
can grow faster than in the absence of radiation.


title:
Chemical evolution and depletion pattern in Damped Lyman-alpha (DLA)
  systems

abstract:
  In this paper we point out a previously unnoticed anticorrelation between the
observed abundance ratio [X/Zn] (where Zn is assumed to be undepleted and X
stands for the refractories Fe, Cr and Ni) and metal column density
([Zn/H]+log(N{HI})) in DLAs. We suggest that this trend is an unambiguous sign
of dust depletion, since metal column density is a measure of the amount of
dust along the line of sight. Assuming that DLAs are (proto-)galactic disks and
using detailed chemical evolution models with metallicity dependent yields we
study chemical evolution and dust depletion patterns for alpha and iron-peak
elements in DLAs. When observational constraints on the metal column density of
DLAs are taken into account (as suggested in Boisse et al. 1998) we find that
our models reproduce fairly well the observed mild redshift evolution of the
abundances of 8 elements (Al, Si, S, Cr, Mn, Fe, Zn and Ni) as well as the
observed scatter at a given redshift. By considering the aforementioned
dependence of abundance ratios on metal column density, we further explore the
general dust depletion pattern in DLAs, comparing to our model results and to a
solar reference pattern. We suggest that further measurements of the key
elements, i.e. Zn, S and Mn, will help to gain more insight into the nature of
DLAs. In any case, the presently uncertain nucleosynthesis of Zn in massive
stars (on which a large part of these conclusions is based) should be carefully
scrutinised.


title: Evidence Supporting the Universality of the IMF

abstract:
  The stellar initial mass function (IMF) is an underlying distribution
function which determines many important observables, from the number of
ionizing photons in a population of some age and metallicity, through the
creation rate of various chemical elements, to the mass to light ratio of a
system. This significance, together with the empirical difficulty to determine
the IMF robustly, and the near complete lack of any robust theoretical
predictor, has allowed investigators freedom to treat the IMF as a continuously
variable parameterisation of astrophysicists' ignorance of complexity. An
ability to vary a parameter in a model is not the same as a true variation in a
physical system. A more instructive approach is to use available data to
constrain possible variations, and thereby to allow identification of those
other aspects of an observed system whose understanding can be improved.
Ideally, the most sensitive physical variable, or its parameterisation, should
be the best constrained. A fundamental null hypothesis, which we defend here,
is that the IMF is a universal invariant function, so that all apparent
variations may be ascribed to other variables, and to irreducible statistical
sampling fluctuations.


title: The Large-Scale Tidal Velocity Field

abstract:
  We present a method for decomposing the cosmological velocity field in a
given volume into its divergent component due to the density fluctuations
inside the volume, and its tidal component due to the matter distribution
outside the volume. The input consists of the density and velocity fields that
are reconstructed either by POTENT or by Wiener Filter from a survey of
peculiar velocities. The tidal field is further decomposed into a bulk velocity
and a shear field. The method is applied here to the Mark III data within a
sphere of radius 60 Mpc/h about the Local Group, and to the SFI data for
comparison. We find that the tidal field contributes about half of the
Local-Group velocity with respect to the CMB, with the tidal bulk velocity
pointing to within ~ 30 degrees of the CMB dipole. The eigenvector with the
largest eigenvalue of the shear tensor is aligned with the tidal bulk velocity
to within ~ 40 degrees. The tidal field thus indicates the important dynamical
role of a super attractor of mass (2-5) x 10^17 M_sun/h Omega^0.4 at ~ 150
Mpc/h, coinciding with the Shapley Concentration. There is also a hint for the
dynamical role of two big voids in the Supergalactic Plane. The results are
consistent for the two data sets and the two methods of reconstruction.


title: Velocity and density spectra of the Small Magellanic Cloud

abstract:
  This paper reports results on the statistical analysis of HI turbulence in
the Small Magellanic Cloud (SMC). We use 21 cm channel maps, obtained with the
Australia Telescope Compact Array and the Parkes telescope, and analyze the
spectrum of observed intensity fluctuations as a function of the velocity slice
thickness. We confirm predictions by Lazarian & Pogosyan (2000) on the change
of the power law index and establish the spectra of 3-D density and velocity.
The obtained spectral indices, -3.3 and -3.4, are slightly more shallow than
the predictions for the Kolmogorov spectrum. This contrasts to the predictions
for the shock-type spectra that are steeper than the Kolmogorov one. The nature
of the energy injection in the SMC is unclear as no distinct energy injection
scales are observed up to the entire scale of the SMC.


title:
Discovery of a bipolar and highly variable mass outflow from the
  symbiotic binary StHa 190

abstract:
  A highly and rapidly variable bipolar mass outflow from StHa 190 has been
discovered, the first time in a yellow symbiotic star. Permitted emission lines
are flanked by symmetrical jet features and multi-component P-Cyg profiles,
with velocities up to 300 km/sec. Given the high orbital inclination of the
binary, if the jets leave the system nearly perpendicular to the orbital plane,
the de-projected velocity equals or exceeds the escape velocity (1000 km/sec).
StHa190 looks quite peculiar in many other respects: the hot component is an
O-type sub-dwarf without an accretion disk or a veiling nebular continuum and
the cool component is a G7 III star rotating at a spectacular 105 km/sec unseen
by a large margin in field G giants.


title: The Variability of R,N,C Stars from HIPPARCOS and AAVSO Data

abstract:
  Accurate photometry was obtained for all programme stars during the 3.3-year
HIPPARCOS mission. The final observing programme included several hundred Mirae
(M), semiregular (SR) long-period and irregular (L) variables. A detailed
calibration of the aging of the optics allowed the evaluation of very precise
magnitudes over the whole range of star colours.
  Since the time coverage of the satellite observations was not sufficient to
describe the behaviour of M, SR, or L type variables, smooth curves were fitted
statistically to the dense AAVSO observations. These curves were then
transformed to the HIPPARCOS system in order to complement the HIPPARCOS
photometry and thus produce precise light curves with fuller time coverage, for
a set of several hundred late-type variables, including most Carbon stars
brighter than V = 12.4 at minimum luminosity.
  A preliminary discussion of the behaviour of C stars, as observed from the
space in the broad Hp band, is given.


title: Intra-Day Variability and the Interstellar Medium Towards 0917+624

abstract:
  The intra-day variable source 0917+624 displays annual changes in its
timescale of variability. This is explained in terms of a scintillation model
in which changes in the variability timescale are due to changes in the
relative velocity of the scintillation pattern as the Earth orbits the sun.
(see also astro-ph/0102050)


title: Evolution of Power Spectrum in Non-Gaussian Models

abstract:
  Evolution of power spectrum is studied for non-Gaussian models of structure
formation. We generalize the dark-matter-approach to these models and find that
the evolved spectrum at weakly nonlinear regime is mainly determined by a
simple integral of the dark-matter-halo mass function in this approach.
  We also study the change of the nonlinear spectrum within the current
observational constraint of the primordial non-Gaussianity.


title:
Evolution of photoionization and star formation in starbursts and HII
  galaxies

abstract:
  We analyze the stellar and nebular energy distributions of starbursts using
our evolutionary synthesis model PEGASE coupled to the photoionization code
CLOUDY. The originality of this study is to relate the evolution and the
metallicity of the starburst to the past star formation history of the host
galaxy.We compare our model predictions to an observed sample of ~750
starbursts. the most striking feature from line ratio fitting is the decreasing
spread in ionization parameter U at high metallicity Z. The best fits of
emission line ratios are obtained with a combination of a high- and a
low-ionization components. No additional source of ionizing photons --shocks or
hidden AGN -- is needed. Colors and equivalent widths are fitted in coherency
with emission line ratios. An underlying population is needed, even for
small-aperture observations. This evolved population not only reddens the
continuum and dilutes the equivalent width of the emission lines, but also
participates in the ionization process. Its main effect on line ratios is to
maintain a high level of excitation when the burst stops. Models combining
underlying populations typical of Hubble sequence galaxies and instantaneous
starbursts with ages between 0 and 8 Myr agree satisfactorily with all the
data.


title: Morphology of the large-scale structure

abstract:
  The Minkowski functionals are a mathematical tool to quantify morphological
features of patterns. Some applications to the matter distribution in galaxy
catalogues and N-body simulations are reviewed, with an emphasis on the effects
of cosmic variance. The conclusions are that (i) the observed large-scale
morphology is sensitive to cosmic variance on scales much larger than the
nonlinear length (approx. 8 Mpc/h), and (ii) the large-scale morphology
predicted by simulations is thus affected by finite-size effects, but
nonetheless a Lambda-CDM model is favored.


title:
Mm/submm observations of symbiotic binary stars: implications for the
  mass loss and mass exchange

abstract:
  We discuss mm/submm spectra of a sample of symbiotic binary systems, and
compare them with popular models proposed to account for their radio emission.
We find that radio emission from quiescent S-type systems originates from a
conical region of the red giant wind ionized by the hot companion (the STB
model), whereas more complicated models involving winds from both components
and their interaction are required to account for radio emission of active
systems. We also find that the giant mass-loss rates derived from our
observations are systematically higher than those for single cool giants. This
result is in agreement with conclusions derived from IRAS observations and with
requirements of models for the hot component.


title: A Rapid X-ray Flare in the Radio-loud Narrow Line Quasar PKS 0558-504

abstract:
  We report the detection of a very short time scale flare in the radio-loud
narrow line quasars PKS 0558-504 by using ASCA. The X-ray count rates increased
and decreased by a factor of two in 33 minutes, and possibly by 40% in as short
as two minutes during this flare, confirming that such flare event does occur
in this object with imaging detectors. The implied largest rate of change in
luminosity in 0.8-10 keV alone, dL/dt=(1.8+/-0.4) 10^{42} ergs s^-2, is several
times higher than the limit sets for the isotropic emitting plasma around a
Kerr black hole. Either emission from a relativistic boosting jet or a magnetic
heated corona may explain such high radiative efficiency. Magnetic field with a
strength of at least a few 10^4 Gauss is required in the latter case. The
spectrum during this flare is significant harder than the average one. Three
radio loud narrow line active galactic nuclei (AGN) possess considerably
smaller black holes than in radio loud AGN in bright quasar survey, indicating
they are still in a phase of the rapid growth of the black hole by accretion.


title:
HI deficiency in the galaxy cluster ACO 3627. ATCA observations in the
  Great Attractor region

abstract:
  ATCA 21 cm HI observations of the rich galaxy cluster ACO 3627 in the Great
Attractor region are presented. Three fields of 30' diameter located within one
Abell radius of ACO 3627 were observed with a resolution of 15'' and an rms
noise of \sim 1 mJy/beam. Only two galaxies were detected in these fields. We
compare their HI distribution to new optical R-band images and discuss their
velocity fields. The first galaxy is a gas-rich unperturbed spiral whereas the
second shows a peculiar HI distribution. The estimated 3-sigma HI mass limit of
our observations is \sim 7 x 10^8 M_{\odot} for a line width of 150 km s^{-1}.
The non-detection of a considerable number of luminous spiral galaxies
indicates that the spiral galaxies are HI deficient. The low detection rate is
comparable to the HI deficient Coma cluster (Bravo-Alfaro et al. 2000). ACO
3627 is a bright X-ray cluster. We therefore suspect that ram pressure
stripping is responsible for the HI deficiency of the bright cluster spirals.


title:
Evolution of isolated neutron stars in globular clusters: number of
  Accretors

abstract:
  With a simple model from the point of view of population synthesis we try to
verify an interesting suggestion made by Pfahl & Rappaport (2001) that dim
sources in globular clusters (GCs) can be isolated accreting neutron stars
(NSs). Simple estimates show, that we can expect about 0.5-1 accreting isolated
NS per typical GC with $M=10^5 M_{\odot}$ in correspondence with observations.
Properties of old accreting isolated NSs in GCs are briefly discussed. We
suggest that accreting NSs in GCs experienced significant magnetic field decay.


title: Departure from Axisymmetry in Planetary Nebulae

abstract:
  Many planetary nebulae (PNe) exhibit distinctly non-axisymmetric structure in
either (i) the shape of the nebula, or (ii) in the off-centered position of the
illuminating star. By examining a large number of well resolved images of PNe
we estimate that about 30-50 percents of all PNe exhibit distinctly
non-axisymmetric structure. In this paper, we discuss how such departures from
axisymmetry can arise from the binary nature of the progenitors of the PNe. The
scenarios include (a) relatively close binaries with eccentric orbits, and (b)
longer orbital period systems with either circular or eccentric orbits. In
order to assess the fraction of PNe whose non-axisymmetric morphologies are
expected to arise in binary systems, we have carried out a detailed population
synthesis study. The expected deviations from axisymmetry are classified for
each binary and the results tabulated. We find that about 25 percents of
elliptical and 30-50 percents of bipolar PNe are expected to acquire
non-axisymmetric structure from binary interactions.


title:
Electron-Ion Recombination Rate Coefficients and Photoionization Cross
  Sections for Astrophysically Abundant Elements VI. Ni II

abstract:
  We present the first detailed ab initio quantum mechanical calculations for
total and state-specific recombination rate coefficients for e + Ni III --> Ni
II. These rates are obtained using a unified treatment for total electron-ion
recombination that treats the nonresonant radiative recombination and the
resonant dielectronic recombination in a self-consistent unified manner in the
close coupling approximation. Large-scale calculations are carried out using a
49-state wavefunction expansion from core configurations 3d^8, 3d^74s, and
3d^64p that permits the inclusion of prominent dipole allowed core transitions.
These extensive calculations for the recombination rates of Ni II required
hundreds of CPU hours on the Cray T90. The total recombination rate
coefficients are provided for a wide range of temperature. The state-specific
recombination rates for 532 bound states of doublet and quartet symmetries, and
the corresponding photoionization cross sections for leaving the core in the
ground state, are presented. Present total recombination rate coefficients
differ considerably from the currently used data in astrophysical models.


title: Gas Dynamic Stripping and X-Ray Emission of Cluster Elliptical Galaxies

abstract:
  Detailed 3-D numerical simulations of an elliptical galaxy orbiting in a
gas-rich cluster of galaxies indicate that gas dynamic stripping is less
efficient than the results from previous, simpler calculations (Takeda et al.
1984; Gaetz et al. 1987) implied. This result is consistent with X-ray data for
cluster elliptical galaxies. Hydrodynamic torques and direct accretion of
orbital angular momentum can result in the formation of a cold gaseous disk,
even in a non-rotating galaxy. The gas lost by cluster galaxies via the process
of gas dynamic stripping tends to produce a colder, chemically enriched cluster
gas core. A comparison of the models with the available X-ray data of cluster
galaxies shows that the X-ray luminosity distribution of cluster galaxies may
reflect hydrodynamic stripping, but also that a purely hydrodynamic treatment
is inadequate for the cooler interstellar medium near the centre of the galaxy.


title:
Searching for fluctuations in the IGM temperature using the Lyman alpha
  forest

abstract:
  We propose a statistical method to search for fluctuations in the temperature
of the intergalactic medium (IGM) using the Lyman $\alpha$ forest. The power on
small scales ($\sim 25 \km/\s$) is used as a thermometer and fluctuations of
this power are constrained. The method is illustrated using Q1422+231. We see
no evidence of temperature fluctuations. We show that in a model with two
temperatures that occupy comparable fractions of the spectra, the ratio of
small scale powers is constrained to be smaller than 3.5 (corresponding to a
factor of 2.5 in temperature). We show that approximately ten quasars are
needed constrain factors of two fluctuations in small scale power power.


title:
On the Contribution of Unresolved Galactic Stars to the Diffuse Soft
  X-ray Background

abstract:
  Using stellar luminosity functions derived from ROSAT data, the contributions
of Galactic stars to the diffuse X-ray background are calculated for ROSAT PSPC
energy bands. The model follows that of Guillout et al. (1996), but uses ROSAT
rather than {\it Einstein} data to determine the intrinsic luminosity
distributions. The model adequately predicts the numbers of stellar sources
observed in deep ROSAT surveys. The contribution of unresolved stellar sources
to the ROSAT All-Sky Survey at the Galactic poles is 6.85, 4.76, and 4.91
$\times$ counts s$^{-1}$ arcmin$^{-2}$ in bands R12 (1/4 keV), R45(3/4 keV),
and R67(1.5 keV), respectively, which is equivalent to 4.66, 31.3 and 26.9
$\times10^{-14}$ ergs cm$^{-2}$ s$^{-1}$ deg$^{-2}$.


title:
Antiprotons below 200 MeV in the interstellar medium: perspectives for
  observing exotic matter signatures

abstract:
  Most cosmic ray antiprotons observed near the Earth are secondaries produced
in collisions of energetic cosmic ray (CR) particles with interstellar gas. The
spectrum of secondary antiprotons is expected to peak at ~2 GeV and decrease
sharply at lower energies. This leaves a low energy window in which to look for
signatures of exotic processes such as evaporation of primordial black holes or
dark matter annihilation. In the inner heliosphere, however, modulation of CRs
by the solar wind makes analysis difficult. Detecting these antiprotons outside
the heliosphere on an interstellar probe removes most of the complications of
modulation. We present a new calculation of the expected secondary antiproton
flux (the background) as well as a preliminary design of a light-weight,
low-power instrument for the interstellar probe to make such measurements.


title:
The Ultraviolet-Far Infrared Energy Budget of the Gravitationally Lensed
  Lyman Break Galaxy MS1512-cB58

abstract:
  A 2-hour service-mode SCUBA observation of the gravitationally-lensed Lyman
break galaxy MS1512-cB58 resulted in a 3 sigma upper limit of 3.9 mJy at 850um.
A comparison of this upper limit with values expected from rest-UV/optical
measurements of extiction suggests that dust temperature (T_d) and/or
emissivity index (beta) in cB58 may be substantially higher than is seen in
local galaxies, or that the attenuation curve in cB58 may be even gentler than
the already quite mild SMC dust law. If dust temperature T_d and emissivity
index beta in cB58 are similar to those seen in local IRAS-seleceted galaxies,
then cB58's dust mass is M_d <~ 10^7.7 Msun and its star formation rate is SFR
<~ 10 Msun/yr (for q_0=0.1, H_0=75 km/s/Mpc). This SFR upper limit is lower
than the star formation rate measured from Halpha, thus giving further support
to the notion that (T_d, beta) values in cB58 are higher than those seen in
local galaxies. It thus appears that our understanding of dust in this
extensively studied Lyman break galaxy is poor, and observations at other
wavelentghs are needed to better understand dust at high redshift. Such
observations can be provided by the upcoming SIRTF mission for which cB58's
expected flux densities are calculated.


title:
A Compton Up-scattering Model for Soft Lags in the Lower Kilohertz QPO
  in 4U1608-52

abstract:
  An empirical Compton up-scattering model is described which reproduces both
the fractional amplitude (RMS) vs. energy and the soft time lags in the 830 Hz
QPO observed in 4U1608-52 on Mar. 3, 1996. A combination of two coherent
variations in the coronal and soft photon temperatures (with their relative
contributions determined by enforcing energy conservation) gives rise to the
QPO's energy dependent characteristics. All input parameters to the model, save
a characteristic plasma size and the fraction of Comptonized photons impinging
on the soft photon source, are derived from the time-averaged photon energy
spectrum of the same observation. Fits to the fractional RMS and phase lag data
for this kilohertz QPO imply that the spatial extent of the plasma is in the
range from 4 to 15 km.


title: The IMF of open star clusters with Tycho-2

abstract:
  We studied the fields of nine nearby open star clusters based on the Tycho-2
catalogue. The clusters are: Blanco 1, Stock 2, the alpha Per cluster, the
Pleiades, NGC 2451, IC 2391, Praesepe, IC 2602, and NGC 7092. We determined
membership probabilities for the stars in the cluster fields from the stellar
proper motions and used the Tycho-2 photometry to compute the initial mass
function (IMF) of the clusters from the main sequence turn-off point down to
approx. 1 M_sun. We found IMF slopes ranging from Gamma=-0.69 down to
Gamma=-2.27 (when the Salpeter (1955) value would be Gamma=-1.35). We also
studied the membership of individual stars of special astrophysical interest.
In some cases previous results had to be revised. As a by-product, we
investigated some general properties of the Tycho-2 catalogue; we confirmed
that the Tycho-2 proper motions show only marginal deviations from the
Hipparcos catalogue. On the other hand, in some regions the completeness of the
catalogue seems to decrease at magnitudes brighter than claimed by Hog et al.
(2000).


title: Supernovae in Molecular Clouds

abstract:
  Supernovae are expected to occur near the molecular material in which the
massive progenitor star was born, except in cases where the photoionizing
radiation and winds from the progenitor star and its neighbors have cleared out
a region. The clumpy structure in molecular clouds is crucial for the remnant
evolution; the supernova shock front can become radiative in the interclump
medium and the radiative shell then collides with molecular clumps. The
interaction is relevant to a number of phenomena: the hydrodynamics of a
magnetically supported dense shell interacting with molecular clumps; the
molecular emission from shock waves, including the production of the OH 1720
MHz maser line; the relativistic particle emission, including radio synchrotron
and gamma-ray emission, from the dense radiative shell; and the possible
gravitational instability of a compressed clump.


title: Theoretical Implications of the Gamma-Ray Burst - Supernova Connection

abstract:
  Although observations of circumstellar shock interactions around supernovae
are generally consistent with a 1/r**2 density profile wind surrounding the
progenitor star, this is not true for GRB (gamma-ray burst) afterglows.
However, GRB 991208 and GRB 000301C may be consistent with wind interaction if
the injection particle spectrum is a broken power law. Circumstellar dust echos
can place constraints on supernova and GRB progenitors, but have been clearly
observed only around SN 1987A. Excess emission observed in two GRB afterglows
is more likely to have a supernova origin. An interstellar dust echo, causing
the light curve to flatten out, is a possibility for GRB afterglows, but is not
likely to be observable.


title:
The Tolman Surface Brightness Test for the Reality of the Expansion. I.
  Calibration of the Necessary Local Parameters

abstract:
  The extensive CCD photometry by Postman & Lauer (1995, ApJ, 440, 28) in the
Cape/Cousins R photometric band for first ranked cluster elliptical and S0
galaxies in 118 low redshift clusters is analyzed for the correlations between
average surface brightness, linear radius, and absolute magnitude. The purpose
is to calibrate the correlations between these three parameters in the limit of
zero redshift. These local correlations provide the comparisons to be made in
Paper IV with the sample of early-type galaxies at high redshift in search of
the Tolman surface brightness signal of (1 + z)^4 if the expansion is real.
Surface brightness averages are calculated at various metric radii in each
galaxy in the sample. The definition of such radii by Petrosian (1976, ApJ,
209, L1) uses ratios of observed surface photometric data. The observed surface
brightnesses are listed for 118 first ranked cluster galaxies at Petrosian eta
radii of 1.0, 1.3, 1.5, 1.7, 2.0, and 2.5 mag. The three local diagnostic
correlation diagrams are defined and discussed. We review the Tolman test and
show that, although recipes from the standard cosmological model that already
have the Tolman signal incorporated are required to calculate linear radii and
absolute magnitudes from the observed data, the test is nevertheless free from
the hermeneutical circularity dilemma occasionally claimed in the literature.
The reasons are the observed mean surface brightness (1) is independent of any
assumptions of cosmological model, (2) does not depend on the existence of a
Tolman signal because it is calculated directly from the data using only
angular radii and apparent magnitudes, and (3) can be used to search for the
Tolman signal because it carries the bulk of that signal.


title:
The Tolman Surface Brightness Test for the Reality of the Expansion. II.
  The Effect of the Point-Spread Function and Galaxy Ellipticity on the Derived
  Photometric Parameters

abstract:
  To complete the Tolman surface brightness test on the reality of the
expansion of the Universe, we need to measure accurately the surface brightness
profiles of the high-redshift galaxy sample. We, therefore, investigate the
effects of various sizes of point-spread-functions composed of telescope
diffraction, CCD pixel resolutions, and ground-based seeing on the measurements
of mean surface brightness. We have done the calculations using two synthetic
galaxies of effective radii of 0.70" and 0.25" with point-spread functions of
0.1, 0.3, and 0.9 arcseconds. We have also compared actual observations of
three high-redshift galaxies in the cluster Cl 1324 + 3011 (z = 0.76) made both
with the Keck telescopes in seeing of about 0.9" and with HST which has a PSF
that is approximately ten times smaller. The conclusion is that HST data can be
used as far into the galaxy image as a Petrosian metric radius of eta = 1.3
magnitudes, whereas the ground-based data will have systematic errors of up to
2.9 magnitudes in the mean surface brightness at eta values of less than 2.2
magnitudes. In the final section, we compare the differences in derived average
surface brightness for nearly circular galaxy images compared with highly
flattened images. The comparison is made by using the two reduction procedures
of (1) integrating the profile curves using circular apertures, and (2)
approximating an ``equivalent circular'' galaxy that is highly elongated by
using an ``effective'' radius of sqrt{ab}, where a and b are the semi-major and
semi-minor axis, respectively, of the best-fitting ellipse. The conclusion is
that the two methods of reduction give nearly identical results and that either
method can be used to analyze the low and high-redshift galaxy samples used in
the Tolman test.


title:
Possible Local Spiral Counterparts to Compact Blue Galaxies at
  Intermediate Redshift

abstract:
  We identify nearby disk galaxies with optical structural parameters similar
to those of intermediate-redshift compact blue galaxies. By comparing HI and
optical emission-line widths, we show that the optical widths substantially
underestimate the true kinematic widths of the local galaxies. By analogy,
optical emission-line widths may underrepresent the masses of intermediate-z
compact objects. For the nearby galaxies, the compact blue morphology is the
result of tidally-triggered central star formation: we argue that interactions
and minor mergers may cause apparently compact morphology at higher redshift.


title: Analysis of Stars Common to the IRAS and HIPPARCOS Surveys

abstract:
  For about 11,000 stars observed in the HIPPARCOS Survey and detected by IRAS
we calculate bolometric luminosities by integrating their spectral energy
distributions from the B band to far-IR wavelengths. We present an analysis of
the dependence of dust emission on spectral type and correlations between the
luminosity and dust emission for about 1000 sources with the best data
(parallax error less than 30%, error in luminosity of about 50% or better).
This subsample includes stars of all spectral types and is dominated by K and M
giants.
  We use the IRAS [25]-[12] color to select stars with emission from
circumstellar dust and show that they are found throughout the
Hertzsprung-Russell diagram, including on the main sequence. Clear evidence is
found that M giants with dust emission have luminosities about 3 times larger
(about 3000 Lsun) than their counterparts without dust, and that mass loss on
the asymptotic giant branch for both M and C stars requires a minimum
luminosity of order 2000 Lsun. Above this threshold the mass-loss rate seems to
be independent of, or only weakly dependent on, luminosity. We also show that
the mass-loss rate for these stars is larger than the core mass growth rate,
indicating that their evolution is dominated by mass loss.


title: 100-year Mass Loss Modulations on the Asymptotic Giant Branch

abstract:
  We analyze the differences in infrared circumstellar dust emission between
oxygen rich Mira and non-Mira stars, and find that they are statistically
significant. In particular, we find that these stars segregate in the K-[12]
vs. [12]-[25] color-color diagram, and have distinct properties of the IRAS LRS
spectra, including the peak position of the silicate emission feature. We show
that the infrared emission from the majority of non-Mira stars cannot be
explained within the context of standard steady-state outflow models. The
models can be altered to fit the data for non-Mira stars by postulating
non-standard optical properties for silicate grains, or by assuming that the
dust temperature at the inner envelope radius is significantly lower (300-400
K) than typical silicate grain condensation temperatures (800-1000 K). We argue
that the latter is more probable and provide detailed model fits to the IRAS
LRS spectra for 342 stars. These fits imply that 2/3 of non-Mira stars and 1/3
of Mira stars do not have hot dust ($>$ 500 K) in their envelopes. The absence
of hot dust can be interpreted as a recent (order of 100 yr) decrease in the
mass-loss rate. The distribution of best-fit model parameters agrees with this
interpretation and strongly suggests that the mass loss resumes on similar time
scales. Such a possibility appears to be supported by a number of spatially
resolved observations (e.g. recent HST images of the multiple shells in the Egg
Nebula) and is consistent with new dynamical models for mass loss on the
Asymptotic Giant Branch.


title: The Nearest Neighbor Alignment of Cluster X-ray Isophotes

abstract:
  We examine the orientations of rich galaxy cluster X-ray isophotes with
respect to their rich nearest neighbors using existing samples of Abell cluster
position angles measured from {\it Einstein} and {\it ROSAT} observations. We
study a merged subset of these samples using updated and improved positions and
redshifts for Abell/ACO clusters. We find high confidence for alignment, which
increases as nearest neighbor distance is restricted. We conclude that there is
a strong alignment signal in all this data, consistent with gravitational
instability acting on Gaussian perturbations.


title:
An Infrared Camera for Leuschner Observatory and the Berkeley
  Undergraduate Astronomy Lab

abstract:
  We describe the design, fabrication, and operation of an infrared camera
which is in use at the 30-inch telescope of the Leuschner Observatory. The
camera is based on a Rockwell PICNIC 256 x 256 pixel HgCdTe array, which is
sensitive from 0.9-2.5 micron. The primary purpose of this telescope is for
undergraduate instruction. The cost of the camera has been minimized by using
commercial parts whereever practical. The camera optics are based on a modified
Offner relay which forms a cold pupil where stray thermal radiation from the
telescope is baffled. A cold, six-position filter wheel is driven by a
cryogenic stepper motor, thus avoiding any mechanical feed throughs. The array
control and readout electronics are based on standard PC cards; the only custom
component is a simple interface card which buffers the clocks and amplifies the
analog signals from the array.


title: The growth of structure in the intergalactic medium

abstract:
  A {\it stochastic adhesion} model is introduced, with the purpose of
describing the formation and evolution of mildly nonlinear structures, such as
sheets and filaments, in the intergalactic medium (IGM), after hydrogen
reionization. The model is based on replacing the overall force acting on the
baryon fluid -- as it results from the composition of local gravity, pressure
gradients and Hubble drag -- by a mock external force, self-consistently
calculated from first-order perturbation theory. A small kinematic viscosity
term prevents shell-crossing on small scales (which arises because of the
approximate treatment of pressure gradients). The emerging scheme is an
extension of the well-known adhesion approximation for the dark matter
dynamics, from which it only differs by the presence of a small-scale `random'
force, characterizing the IGM. Our algorithm is the ideal tool to obtain the
skeleton of the IGM distribution, which is responsible for the structure
observed in the low-column density Ly$\alpha$ forest in the absorption spectra
of distant quasars.


title: Heating of X-Ray Hot Gas in Groups by Blast Waves

abstract:
  In order to find the conditions which determine whether X-Ray hot gas in
galaxy groups (intragroup gas; IGG) is heated externally or internally, we
investigate the evolution of blast waves in galaxy groups growing on a
hierarchical clustering scenario. We find that the blast waves driven by
quasars are confined in groups and heat the IGG internally at z<~ 1. However,
at z>~ 1, they expel the IGG from groups; the expelled gas may fall back into
the groups later as externally heated gas. Moreover, this may explain the
observed low metal abundance of IGG. For blast waves driven by strong
starbursts, the shift of the fate of blast waves occurs at z~ 3. On the other
hand, although blast waves driven by weak starbursts do not expel IGG from
groups, the heating efficiency decreases at z>~ 3 because of radiative cooling.
It will be useful to compare these results with XMM-Newton observations.


title: Are Compact Hyperbolic Models Observationally Ruled Out?

abstract:
  We revisit the observational constraints on compact(closed) hyperbolic(CH)
models from cosmic microwave background(CMB). We carry out Bayesian analyses
for CH models with volume comparable to the cube of the present curvature
radius using the COBE-DMR data and show that a slight suppression in the
large-angle temperature correlations owing to the non-trivial topology explains
rather naturally the observed anomalously low quadrupole which is incompatible
with the prediction of the standard infinite Friedmann-Robertson-Walker models.
While most of positions and orientations are ruled out, the likelihoods of CH
models are found to be much better than those of infinite counterparts for some
specific positions and orientations of the observer, leading to less stringent
constraints on the volume of the manifolds. Even if the spatial geometry is
nearly flat as $\Omega_{tot}=0.9-0.95$, suppression of the angular power on
large angular scales is still prominent for CH models with volume much less
than the cube of the present curvature radius if the cosmological constant is
dominant at present.


title:
Automated stellar classification for large surveys: a review of methods
  and results

abstract:
  Current and future large astronomical surveys will yield multiparameter
databases on millions or even billions of objects. The scientific exploitation
of these will require powerful, robust, and automated classification tools
tailored to the specific survey. Partly motivated by this, the past five to ten
years has seen a significant increase in the amount of work focused on
automated classification and its application to astronomical data. In this
article, I review this work and assess the current status of automated stellar
classification, with particular regard to its potential application to large
astronomical surveys. I examine both the strengths and weaknesses of the
various techniques and how they have been applied to different classification
and parametrization problems. I finish with a brief look at the developments
still required in order to apply a stellar classifier to a large survey.


title: An introduction to artificial neural networks

abstract:
  Artificial neural networks are algorithms which have been developed to tackle
a range of computational problems. These range from modelling brain function to
making predictions of time-dependent phenomena to solving hard (NP-complete)
problems. In this introduction we describe a single, yet very important, type
of network known as a feedforward network. This network is a mathematical model
which can be trained to learn an arbitrarily complex relationship between a
data and a parameter domain, so can be used to solve interpolation and
classification problems. We discuss the structure, training and interpretation
of these networks, and their implementation, taking the classification of
stellar spectra as an example.


title: Polarization tensors in a strong magnetic field

abstract:
  The vacuum polarization tensor in strong external magnetic fields has been
evaluated numerically for various strengths of magnetic fields and momenta of
photons under the threshold of the $e^{\pm}$ pair creation. The fitting formula
has been obtained which reproduces the calculated results within 10 % of error.
The proper time method is employed further to obtain the retarded polarization
tensor for finite temperature plasmas.


title:
New Tests of Lorentz Invariance Following from Observations of the
  Highest Energy Cosmic Gamma Rays

abstract:
  We use the recent reanalysis of multi-TeV gamma-ray observations of Mrk 501
to constrain the Lorentz invariance breaking parameter involving the maximum
electron velocity. Our limit is two orders of magnitude better than that
obtained from the maximum observed cosmic-ray electron energy.


title:
Testing a model of variability of X-ray reprocessing features in Active
  Galactic Nuclei

abstract:
  A number of recent results from X-ray observations of Active Galactic Nuclei
involving the Fe K alpha line (reduction of line variability compared to the
X-ray continuum variability, the X-ray ``Baldwin effect'') were attributed to a
presence of a hot, ionized skin of an accretion disc, suppressing emission of
the line. The ionized skin appears as a result of the thermal instability of
X-ray irradiated plasma. We test this hypothesis by computing the Thomson
thickness of the hot skin on top of the 'alpha P_tot' Shakura-Sunyaev disc, by
simultaneously solving the vertical structure of both the hot skin and the
disc. We then compute a number of relations between observable quantities, e.g.
the hard X-ray flux, amplitude of the observed reprocessed component,
relativistic smearing of the K alpha line, the r.m.s. variability of the hard
X-rays. These relations can be compared to present and future observations. We
point out that this mechanism is unlikely to explain the behaviour of the X-ray
source in MCG-6-30-15, where there is a number of arguments against the
existence of a thick hot skin, but it can work for some other Seyfert 1
galaxies.


title: The evolution of emission lines in HII galaxies

abstract:
  We constructed diagnostic diagrams using emission line ratios and equivalent
widths observed in several samples of HII galaxies. The diagrams are compared
to predictions from new photoionization models for evolving starbursts. We find
that HII galaxies from objective-prism surveys are not reproduced by models of
instantaneous starbursts surrounded by constant density, ionization bounded HII
regions. The observed relations between emission line ratios and Hb equivalent
width (W(Hb)) can be understood if older stellar populations are not negligible
in HII galaxies. Also, different dust obscuration for stars and gas and leakage
of Lyman continuum photons from the observed HII regions can be important. As a
result, HII galaxies selected from objective-prism surveys are unlikely to
contain many objects in which the most recent starburst is older than about
5~Myr. The observed increase of [OI]/Hb with decreasing W(Hb) can result from
the dynamical effects of winds and supernovae. This interpretation provides
also a natural explanation of the small range of ionization parameters in giant
HII regions. The [OIII]/Hb vs [OII]/Hb diagnostic diagram cannot be fully
understood in terms of pure photoionization models and indicate the need for
additional heating sources. The [NII]/[OII] ratio is shown to increase as W(Hb)
decreases. A possible explanation is an N/O increase due to gradual enrichment
by winds from Wolf-Rayet stars on a time scale of 5 Myr. (abridged abstract)


title: Binary Population Synthesis: Methods, Normalization, and Surprises

abstract:
  In this paper we present a brief overview of population synthesis methods
with a discussion of their main advantages and disadvantages. In the second
part, we present some recent results from synthesis models of close binary
compact objects with emphasis on the predicted rates, their uncertainties, and
the model input parameters the rates are most sensitive to. We also report on a
new evolutionary path leading to the formation of close double neutron stars
(NS), with the unique characteristic that none of the two NS ever had the
chance to be recycled by accretion. Their formation rates turn out to be
comparable to or maybe even higher than those of recycled NS-NS binaries (like
the ones observed), but their detection probability as binary pulsars is much
smaller because of their short lifetimes. We discuss the implications of such a
population for gravitational-wave detection of NS-NS inspiral events, and
possibly for gamma-ray bursts and their host galaxies.


title:
UVES observations of a damped Ly-alpha system at z_abs = 4.466 towards
  the quasar APM BR J0307-4945

abstract:
  We present the first high-resolution (6.2 to 7.7 km/s FWHM) spectra of the
APM BR J0307-4945 quasar at z_em = 4.73 obtained with UVES on the 8.2m VLT
Kueyen telescope. We focus our analysis on a damped Ly-alpha (DLA) system at
z_abs = 4.466 with a neutral hydrogen column density N(HI) = (4.68 +/- 0.97)
10^{20} cm^{-2}. It is the most distant DLA system known to the present date,
observed when the age of the universe was only 1.3 Gyr. It shows complex low-
and high-ionization line profiles spanning ~240 and 300 km/s in velocity space
respectively. We derive accurate abundances for N, O, Al, Si and Fe, and place
a lower limit on C and an upper limit on Ni: [N/H] = -3.07 +/- 0.15, [O/H] =
-1.63 +/- 0.19, [Al/H] = -1.79 +/- 0.11, [Si/H] = -1.54 +/- 0.11, [Fe/H] =
-1.97 +/- 0.19, [C/H] > -1.63 and [Ni/H] < -2.35. The derived high metallicity,
1/90 solar, shows that this very young absorber (< 1.3 Gyr) has already
experienced a significant metal enrichment. The [O/Si] ratio is nearly solar
suggesting a limited amount of dust, the relative [Si,O/Fe] abundance ratios
show a similar enhancement as observed in the Milky Way stars with comparable
metallicities, and the [N/O] ratio is very low. All these results point to an
enrichment pattern dominated by Type II supernovae which suggests a Milky Way
type evolutionary model.


title: The radial pulsation of AI Aurigae

abstract:
  We present an analysis of eleven years of Stromgren by photometry of the red
semiregular variable star AI Aurigae. An early period determination of 63.9
days is confirmed by the long-term light curve behaviour. The light curve shows
semi-regular changes with a mean period of 65 days reaching an amplitude of 0.6
mag in some cycles. The b-y colour changes perfectly parallel the V light
curve, suggesting radial oscillation to be the main reason for the observed
variations. We estimate the main characteristics of the star (mass, radius,
effective temperature) that suggest radial pulsation in fundamental or first
overtone mode.


title: Structure of Sagittarius A* at 86 GHz using VLBI Closure Quantities

abstract:
  At radio wavelengths, images of the compact radio source Sagittarius A* (Sgr
A*) in the Galactic Center are scatter broadened with a lambda^2 dependence due
to an intervening ionized medium. We present VLBI observations of Sgr A* at 86
GHz using a six station array including the VLBA antennas at Pie Town, Fort
Davis and Los Alamos, the 12m antenna at Kitt Peak and the millimeter arrays at
Hat Creek and Owens Valley. To avoid systematic errors due to imperfect antenna
calibration, the data were modeled using interferometric closure information.
The data are best modeled by a circular Gaussian brightness distribution of
FWHM 0.18 +- 0.02 mas. The data are also shown to be consistent with an
elliptical model corresponding to the scattering of a point source. The source
structure in the N-S direction, which is less well determined than in the E-W
direction due to the limited N-S (u,v) coverage of the array, is constrained to
be less than 0.27 mas by these measurements. These results are consistent with
extrapolations of intrinsic structure estimates obtained with VLBI at 7mm
wavelength assuming the intrinsic size of Sgr A* has a greater dependence than
lambda^0.9 with wavelength.


title:
Discovery of Coupling between Periodic and Aperiodic Variability and
  X-ray Quasi-periodic Oscillations from Her X-1

abstract:
  We report the discovery of coupling between periodic and aperiodic
variability and ~12-mHz X-ray quasi-periodic oscillations (QPOs) from the X-ray
binary pulsar Her X-1 using data from the Rossi X-Ray Timing Explorer. We found
two different couplings, one during the pre-eclipse dips and the other during
the normal state of the source, using a method which directly compares the
low-frequency power-density spectra (PDS) with those of the sidebands around
the coherent pulse frequency. The pre-eclipse dip lightcurves show significant
time variation of photon counts, and this variation appears in the PDS as both
strong mHz powers and well-developed sidebands around the coherent pulse
frequency. The linear correlation coefficients between the mHz PDS and the
sideband PDS obtained from two pre-eclipse dip data segments are 0.880 +- 0.003
and 0.982 +- 0.001, respectively. This very strong coupling demonstrates that
the amplitudes of the coherent pulsations are almost exactly modulated by the
aperiodic variabilities, suggesting that both the periodic and aperiodic
variabilities are related to time variation of obscuration of X-rays from the
central pulsar by an accretion disk during pre-eclipse dips. We also found weak
coupling during the normal state of the source, together with ~12-mHz QPOs. The
normal state coupling seems to reconcile with the prediction that the aperiodic
variabilities from X-ray binary pulsars are due to time-varying accretion flows
onto the pulsar's magnetic poles. If the ~12-mHz QPOs are due to global-normal
disk oscillations caused by the gravitational interactions between the central
pulsar and the accretion disk, the inferred inner-disk radius is roughly
comparable to the magnetospheric radius, ~1 10^8 cm.


title:
The prompt emission of GRB990712 with BeppoSAX: evidence of a transient
  X-ray emission feature

abstract:
  We report on the prompt X- and gamma-ray observations of GRB990712 with the
BeppoSAX Gamma-Ray Burst Monitor and Wide Field Camera No. 2. Due to Sun
constraints, we could not perform a follow-up observation with the BeppoSAX
Narrow Field Instruments. The light curve of the prompt emission shows two
pulses and a total duration of about 40s in X-rays. In gamma-rays the event is
even shorter. The 2-700 keV spectral emission with time shows a discontinuity
in the peak energy Ep of the E F(E) spectrum: Ep is above our energy passband
during the first pulse and goes down to ~10 keV during the second pulse.
Another peculiarity is noted in this event for the first time: the possible
evidence of a 2s duration emission feature during the tail of the first pulse.
The feature is consistent with either a Gaussian profile with centroid energy
of 4.5 keV or a blackbody spectrum with kTbb ~1.3 keV. We discuss the possible
origin of the feature. The most attractive possibility is that we are observing
the thermal emission of a baryon-loaded expanding fireball, when it becomes
optically thin.


title: Discovery of a High-Energy Gamma-Ray-Emitting Persistent Microquasar

abstract:
  Microquasars are stellar x-ray binaries that behave as a scaled down version
of extragalactic quasars. The star LS 5039 is a new microquasar system with
apparent persistent ejection of relativistic plasma at a 3 kiloparsec distance
from the sun. It may also be associated with a gamma-ray source discovered by
the Energetic Gamma Ray Experiment Telescope (EGRET) on board the COMPTON-Gamma
Ray Observatory satellite. Before the discovery of LS 5039, merely a handful of
microquasars had been identified in the Galaxy, and none of them was detected
in high-energy gamma-rays.


title: Inflationary perturbations from a potential with a step

abstract:
  We use a numerical code to compute the density perturbations generated during
an inflationary epoch which includes a spontaneous symmetry breaking phase
transition. A sharp step in the inflaton potential generates $k$ dependent
oscillations in the spectrum of primordial density perturbations. The amplitude
and extent in wavenumber of these oscillations depends on both the magnitude
and gradient of the step in the inflaton potential. We show that observations
of the cosmic microwave background anisotropy place strong constraints on the
step parameters.


title:
The disc instability model for X-ray transients: evidence for truncation
  and irradiation

abstract:
  We study the prospect of explaining the outbursts of Soft X-ray Transients
(SXTs) by the thermal-viscous instability in a thin disc. This instability is
linked to hydrogen ionization and is significantly changed when irradiation of
the disc by X-rays from the inner regions is included. We present the first
numerically reliable, physically consistent calculations of the outburst cycles
which include the effects of accretion disc irradiation. The decay from
outburst is governed by irradiation, as pointed out by King & Ritter (1998),
leading to slow exponential decays. At the end of the outburst, the disc is
severely depleted, which lengthens the time needed to rebuild mass to the
critical density for an outburst. Despite this, the long recurrence times and
quiescent X-ray luminosities of SXTs still require the inner disc to be
replaced by another type of flow in quiescence, presumably a hot advection
dominated accretion flow (ADAF). We include the effects of such truncation and
show that the resulting lightcurves are conclusively similar to those of SXTs
like A0620-00. We conclude that the two-alpha disc instability model provides
an adequate description of the outbursts of SXTs when both truncation and
irradiation are included. The values for the viscosities in outburst and in
quiescence are comparable to those used in CVs. We discuss the model in the
context of present observations.


title: Spatial Diffusion of Stars in the Inner Galactic Bulge

abstract:
  Star formation in the inner few hundred pc of the Galactic bulge occurs in a
flattened molecular layer called the central molecular zone (CMZ). Serabyn &
Morris (1996) suggest that the star formation in the CMZ has been sustained for
the lifetime of the Galaxy, and that the resulting agglomeration of stars
formed in the CMZ has resulted in the prominent r^-2 stellar density cusp at
the Galactic center having about the same physical extent as the CMZ. This
"central cusp" is somewhat less flat than the CMZ; thus the population of stars
formed in the CMZ appears to have diffused out to larger latitudes. We
hypothesize that such vertical diffusion is driven by the scattering of stars
off the giant molecular clouds (GMC) in the CMZ, and perform numerical
simulations of the scattering between stars and GMCs in the presence of the
non-axisymmetric background potential. The simulation results show that the
time scale for an initially flattened stellar population to achieve an aspect
ratio of the observed OH/IR stars in the inner bulge, 1 to 2 Gyr, agrees well
with the estimated age of those OH/IR stars.


title: Simulations of Astrophysical Fluid Instabilities

abstract:
  We present direct numerical simulations of mixing at Rayleigh-Taylor unstable
interfaces performed with the FLASH code, developed at the ASCI/Alliances
Center for Astrophysical Thermonuclear Flashes at the University of Chicago. We
present initial results of single-mode studies in two and three dimensions. Our
results indicate that three-dimensional instabilities grow significantly faster
than two-dimensional instabilities and that grid resolution can have a
significant effect on instability growth rates. We also find that unphysical
diffusive mixing occurs at the fluid interface, particularly in poorly resolved
simulations.


title: A dusty torus around the luminous young star LkHa 101

abstract:
  A star forms when a cloud of dust and gas collapses. It is generally believed
that this collapse first produces a flattened rotating disk, through which
matter is fed onto the embryonic star at the center of the disk. When the
temperature and density at the center of the star pass a critical threshold,
thermonuclear fusion begins. The remaining disk, which can still contain up to
0.3 times the mass of the star, is then sculpted and eventually dissipated by
the radiation and wind from the newborn star. Unfortunately this picture of the
structure and evolution of the disk remains speculative because of the lack of
morphological data of sufficient resolution and uncertainties regarding the
underlying physical processes. Here we present resolved images of a young star,
LkHa 101 in which the structure of the inner accretion disk is resolved. We
find that the disk is almost face-on, with a central gap (or cavity) and a hot
inner edge. The cavity is bigger than previous theoretical predictions, and we
infer that the position of the inner edge is probably determined by sublimation
of dust grains by direct stellar radiation, rather than by disk reprocessing or
the viscous heating processes as usually assumed.


title:
Structure of gaseous flows in semidetached binaries after mass transfer
  termination

abstract:
  The results of three-dimensional numerical simulations of mass transfer in
semidetached binaries after mass transfer termination is presented and the
structure of residual accretion disk was investigated. It was shown that after
the mass transfer termination the quasi-elliptic accretion disk becomes
circular. It was also shown that the cessation of mass transfer results in
changing of the structure of the accretion disk: the second arm of spiral shock
is appeared as well as a new dense formation (blob), the latter moving through
the disk with variable velocity. The blob doesn't smear out under the action of
dissipation but is sustained by interaction with arms of spiral shock for
practically all the lifetime of the disk.
  We also analyze the dependence of disk's lifetime on the value of viscosity.
For the value of parameter $\alpha$ that is typical for observing accretion
disk ($\alpha\sim0.01$) the lifetime of residual disk is found to be equal to
50 orbital periods.


title:
Detecting Galactic MACHOs with VERA through Astrometric Microlensing of
  Distant Radio Sources

abstract:
  In this paper we investigate the properties of astrometric microlensing of
distant radio sources (QSOs and radio galaxies) due to MACHOs, and discuss
their implications for VERA (VLBI Exploration of Radio Astrometry). First we
show that in case of astrometric microlensing of distant sources, the event
duration is only a function of the lens mass and tangential velocity, but
independent of the lens distance, in contrast to the well-known three-fold
degeneracy for photometric microlensing. Moreover, the lens mass $M$ is scaled
by the tangential velocity $v_\perp$ as $M\propto v_\perp$, rather than
$M\propto v_\perp^2$ which is the case for photometric microlensing. Thus, in
astrometric microlensing the dependence of the lens mass on the unknown
parameter $v_\perp$ is weaker, indicating that the duration of astrometric
microlensing event is a better quantity to study the mass of lensing objects
than that of photometric microlensing. We also calculate the optical depth and
event rate, and show that within 20$^\circ$ of the galactic center a typical
event rate for 10 $\mu$as-level shift is larger than $2.5 \times 10^{-4}$ event
per year, assuming that a quarter of the halo is made up with MACHOs. This
indicates that if one monitors a few hundred sources for $\sim$20 years, such
an astrometric microlensing event is detectable. Since a typical event duration
is found to be fairly long (5 to 15 years), the frequency of the monitoring
observation can be relatively low, i.e., once per six months, which is rather
reasonable for practical observations. We discuss practical strategy for
observing astrometric microlensing with VERA, and argue that an astrometric
microlensing event due to MACHOs can be detected by VERA within a few decades.