title: Problems for MOND in Clusters and the Ly-alpha Forest

abstract:
  The observed dynamics of gas and stars on galactic and larger scales cannot
be accounted for by self-gravity, indicating that there are large quantities of
unseen matter, or that gravity is non-Newtonian in these regimes. Milgrom's
MOdified Newtonian Dynamics (MOND) postulates that Newton's laws are modified
at very low acceleration, and can account for the rotation curves of galaxies
and some other astrophysical observations, without dark matter. Here we apply
MOND to two independent physical systems: Ly-alpha absorbers and galaxy
clusters. While physically distinct, both are simple hydrodynamical systems
with characteristic accelerations in the MOND regime. We find that Ly-alpha
absorbers are somewhat smaller than in Newtonian gravity with dark matter, but
the result depends crucially on the (unknown) background acceleration field in
which they are embedded. In clusters MOND appears to explain the observed
(baryonic) mass-temperature relation. However, given observed gas density and
enclosed mass profiles and the assumption of hydrostatic equilibrium, MOND
predicts radial temperature profiles which disagree badly with observations. We
show this explicitly for the Virgo, Abell 2199 and Coma clusters, but the
results are general, and seem very difficult to avoid. If this discrepancy is
to be resolved by positing additional (presumably baryonic) dark matter, then
this dark matter must have ~1-3 times the cluster gas mass within 1 Mpc. This
result strongly disfavors MOND as an alternative to dark matter (Abridged).


title:
Self-Similar Hot Accretion Flow onto a Rotating Neutron Star: Structure
  and Stability

abstract:
  We present analytical and numerical solutions which describe a hot, viscous,
two-temperature accretion flow onto a rotating neutron star or any other
rotating compact star with a surface. We assume Coulomb coupling between the
protons and electrons, and free-free cooling from the electrons. Outside a thin
boundary layer, where the accretion flow meets the star, we show that there is
an extended settling region which is well-described by two self-similar
solutions: (i) a two-temperature solution which is valid in an inner zone
$r\le10^{2.5}$ ($r$ is in Schwarzchild units), and (ii) a one-temperature
solution at larger radii. In both zones, $\rho\propto r^{-2}, \Omega\propto
r^{-3/2}, v\propto r^0, T_p\propto r^{-1}$; in the two-temperature zone,
$T_e\propto r^{-1/2}$. The luminosity of the settling zone arises from the
rotational energy of the star as the star is braked by viscosity. Hence the
luminosity and the flow parameters (density, temperature, angular velocity) are
independent of $\dot M$. The settling solution described here is not
advection-dominated, and is thus different from the self-similar ADAF found
around black holes. When the spin of the star is small enough, however, the
present solution transforms smoothly to a (settling) ADAF.
  We carried out a stability analysis of the settling flow. The flow is
convectively and viscously stable and is unlikely to have strong winds or
outflows. Unlike another cooling-dominated system --- the SLE disk, --- the
settling flow is thermally stable provided that thermal conduction is taken
into account. This strong saturated-like thermoconduction does not change the
structure of the flow.


title:
V and R-band Galaxy Luminosity Functions and Low Surface Brightness
  Galaxies in the Century Survey

abstract:
  We use 64 square degrees of deep V and R CCD images to measure the local V
and R band luminosity function of galaxies. The V_0<16.7 and R_0<16.2 redshift
samples contain 1250 galaxies and are 98% complete. We apply k-corrections
before the magnitude selection so that the completeness is to the same depth
for all spectral types. The V and R faint end slopes are surprisingly
identical: alpha = -1.07+-0.09. Representative Schechter function parameters
for H_0=100 are: M^*_R = -20.88+-0.09, phi^*_R = 0.016+-0.003 Mpc^-3 and M^*_V
= -20.23+-0.09, phi^*_V = 0.020+-0.003 Mpc^-3. The V and R local luminosity
densities, j_R = (1.9+-0.6)x10^8 and j_V = (2.2+-0.7)x10^8 L_sun, are in
essential agreement with the recent 2dF and SDSS determinations.
  All low surface brightness (LSB) galaxies fall in the large scale structure
delineated by high surface brightness galaxies. The properties and surface
number density of our LSB galaxies are consistent with the LSB galaxy catalog
of O'Neil, Bothun & Cornell, suggesting that our samples are complete for LSB
galaxies to the magnitude limits. We measure colors, surface brightnesses, and
luminosities for our samples, and find strong correlations among these galaxy
properties.


title:
Another Channel to detect Close-in Binary Companions via Gravitational
  Microlensing

abstract:
  Gaudi & Gould (1997) showed that close companions of remote binary systems
can be efficiently detected by using gravitational microlensing via the
deviations in the lensing light curves induced by the existence of the lens
companions. In this paper, we introduce another channel to detect faint
close-in binary companions by using microlensing. This method utilizes a
caustic-crossing binary lens event with a source also composed of binary stars,
where the companion is a faint star. Detection of the companion is possible
because the flux of the companion can be highly amplified when it crosses the
lens caustic. The detection is facilitated since the companion is more
amplified than the primary because it, in general, has a smaller size than the
primary, and thus experiences less finite source effect. The method is
extension of the previous one suggested to detect close-in giant planets by
Graff & Gaudi (2000) and Lewis & Ibata (2000) and further developed by Ashton &
Lewis (2001). From the simulations of realistic Galactic bulge events, we find
that companions of K-type main sequence or brighter can be efficiently detected
from the current type microlensing followup observations by using the proposed
method. We also find that compared to the method of detecting lens companions
for which the efficiency drops significantly for binaries with separations
$\lesssim 0.2$ of the angular Einstein ring radius, the proposed method has an
important advantage of being able to detect companions with substantially
smaller separations down to order of 0.01 \theta_E.


title: Measuring the Black Hole Spin in Sgr A*

abstract:
  The polarized mm/sub-mm radiation from Sgr A* is apparently produced by a
Keplerian structure whose peak emission occurs within several Schwarzschild
radii (r_S=2GM/c^2) of the black hole. The Chandra X-ray counterpart, if
confirmed, is presumably the self-Comptonized component from this region. In
this paper, we suggest that sub-mm timing observations could yield a signal
corresponding to the period P_0 of the marginally stable orbit, and therefore
point directly to the black hole's spin a. Sgr A*'s mass is now known to be
(2.6\pm 0.2)\times 10^6 M_\odot (an unusually accurate value for supermassive
black hole candidates), for which 2.7 min<P_0<36 min, depending on the value of
a and whether the Keplerian flow is prograde or retrograde. A Schwarzschild
black hole (a=0) should have P_0 ~ 20 min. The identification of the orbital
frequency with the innermost stable circular orbit is made feasible by the
transition from optically thick to thin emission at sub-mm wavelengths. With
stratification in the emitter, the peak of the sub-mm bump in Sgr A*'s spectrum
is thus produced at the smallest radius. We caution, however, that theoretical
uncertainties in the structure of the emission region may still produce some
ambiguity in the timing signal. Given that Sgr A*'s flux at $\nu\sim 1$ mm is
several Jy, these periods should lie within the temporal-resolving capability
of sub-mm telescopes using bolometric detectors. A determination of P_0 should
provide not only a value of a, but it should also define the angular momentum
vector of the orbiting gas in relation to the black hole's spin axis. In
addition, since the X-ray flux detected by Chandra appears to be the
self-Comptonized mm to sub-mm component, these temporal fluctuations may also
be evident in the X-ray signal.


title: Numerical Analyses of Weakly Nonlinear Velocity-Density Coupling

abstract:
  We study evolution of various statistical quantities of smoothed cosmic
density and velocity fields using N-body simulations. The parameter
  $C\equiv <V^2\delta>/(<V^2> <\delta^2>)$ characterizes nonlinear coupling of
these two fields and determines behavior of bulk velocity dispersion as a
function of local density contrast.
  It is found that this parameter depends strongly on the smoothing scale even
in quasi-linear regimes where the skewness parameter
  $S_3$ is nearly constant and close to the predicted value by the second-order
perturbation theory. We also analyze weakly nonlinear effects caused by an
adaptive smoothing known as the gather approach.


title:
Accretion physics of AM Herculis binaries, I. Results from
  one-dimensional stationary radiation hydrodynamics

abstract:
  We have solved the one-dimensional stationary two-fluid hydrodynamic
equations for post-shock flows on accreting magnetic white dwarfs simultaneous
with the fully frequency and angle-dependent radiative transfer for cyclotron
radiation and bremsstrahlung. Magnetic field strengths B = 10 to 100 MG are
considered. At given B, this theory relates the properties of the emission
region to a single physical parameter, the mass flow density (or accretion rate
per unit area). We present the normalized temperature profiles and fit formulae
for the peak electron temperature, the geometrical shock height, and the column
density of the post-shock flow. The results apply to pillbox-shaped emission
regions. With a first-order temperature correction they can also be used for
narrower columns provided they are not too tall.


title:
COMPTEL Observations of the Blazar PKS 1622-297 during a Gamma-Ray High
  State in 1995

abstract:
  PKS 1622-297 was detected as a source of gamma-rays by the EGRET experiment
at energies above 100 MeV during a gamma-ray outburst June and July 1995. We
analyzed the COMPTEL data (0.75 - 30 MeV) of this time period to investigate
the behaviour of PKS 1622-297 at lower gamma-ray energies. The blazar is
significantly (5.7 sigma) detected by COMPTEL at energies above 10 MeV. Below
10 MeV the source is only marginally (3-10 MeV band) or not (below 3 MeV)
detected. The summed MeV spectrum shows a 'hard' (alpha < 2, ~ E^(-alpha))
shape and, if combined with the simultaneous EGRET spectrum, a spectral break
at MeV energies is indicated. We present the COMPTEL results (light curves,
spectra) and compare them to results derived in neighbouring energy bands, in
particular to the EGRET one.


title: The Sunyaev-Zeldovich Effect: Current Status and Future Prospects

abstract:
  The detailed spectral and spatial characteristics of the signature imprinted
on the cosmic microwave background (CMB) radiation by Compton scattering of the
radiation by electrons in the hot gas in clusters of galaxies - the
Sunyaev-Zeldovich (S-Z) effect - are of great astrophysical and cosmological
significance. In recent years observations of the effect have improved
tremendously; high signal-to-noise images of the effect (at low microwave
frequencies) can now be obtained by interferometric arrays. In the near future,
high frequency measurements of the effect will be made with ground based and
balloon-borne telescopes equipped with bolometeric arrays. Towards the end of
the decade the PLANCK satellite will carry out an extensive S-Z survey over a
wide frequency range. Along with the improved observational capabilities, the
theoretical description of the effect, and its use as a precise cosmological
probe, have been considerably advanced. In this review, I briefly discuss the
nature and significance of the effect, its exact theoretical description, the
current observational status, and prospects for the near future.


title: AGN: The High-Energy Status before INTEGRAL

abstract:
  Much progress in the knowledge of the high-energy emission (>50 keV) from
Active Galactic Nuclei has been made during the last decade, predominately by
the experiments aboard the Compton Gamma-Ray Observatory. After the end of the
CGRO mission and prior to the upcoming INTEGRAL mission the current status of
high-energy emission properties and scenarios is summarized for different AGN
classes. In addition, prospects for INTEGRAL observations of AGN are given.


title: Chandra measurements of 3C 220.1's X-ray core and cluster

abstract:
  We report results of an 18 ks exposure with the ACIS instrument on Chandra of
the powerful z = 0.62 radio galaxy 3C 220.1. The X-ray emission separates into
cluster gas of emission-weighted kT ~ 5 keV and 0.7-12 keV luminosity (to a
radius of 45 arcsec) 5.6 x 10^44 ergs s^-1, and unresolved emission (coincident
with the radio core). While the extended X-ray emission is clearly thermal in
nature, a straightforward cooling-flow model, even in conjunction with a
point-source component, is a poor fit to the radial profile of the X-ray
emission. This is despite the fact that the measured properties of the gas
suggest a massive cooling flow of ~ 130 M_\odot yr^-1, and the data show weak
evidence for a temperature gradient. The central unresolved X-ray emission has
a power-law spectral energy index \alpha ~ 0.7 and 0.7-12 keV luminosity 10^45
ergs s^-1, and any intrinsic absorption is relatively small. The two-point
spectrum of the core emission between radio and X-ray energies has \alpha_rx =
0.75. Since this is a flatter spectrum than seen in other sources where the
X-ray emission is presumed to be radio-related, regions close to the AGN in
this source may dominate the central X-ray output, as is believed to be the
case for lobe-dominated quasars. Simple unification models would be challenged
if this were found to be the case for a large fraction of high-power radio
galaxies.


title: The stellar content of the super star clusters in NGC 1569

abstract:
  We discuss HST FOS ultraviolet spectroscopy and NICMOS near-infrared
photometry of four young super star clusters in the central region of the
irregular starburst galaxy NGC 1569. The new observations coupled with previous
HST WFPC2 photometry and ground-based optical spectroscopy allow us to isolate
and age-date the hot and cool stellar components of these massive clusters. We
analyze the two components A1 and A2 of the brightest super star cluster NGC
1569-A. This cluster received previous attention due to the simultaneous
presence of Wolf-Rayet stars and red supergiants. The FOS spectra provide the
first evidence for O-stars in NGC 1569-A, indicating a young (5 Myr) stellar
component in A1 and/or A2. Comparison with other high-mass star-forming regions
suggests that the O- and Wolf-Rayet stars are spatially coincident. If so,
cluster A2 could be the host of the very young O- and Wolf-Rayet population,
and the somewhat older red supergiants could be predominantly located in A1.
The mass-to-light ratio of NGC 1569-A1 is analyzed in five optical and infrared
photometric bands and compared to evolutionary synthesis models. No indications
for an anomalous initial mass function are found, consistent with a scenario
where this cluster is the progenitor of present-day globular clusters. The
clusters A1 and A2 are compared to clusters B and #30. The latter two clusters
are older and fully dominated by red supergiants. All four super star clusters
provide a significant fraction (20 - 25%) of the total optical and
near-infrared light in the central region of the galaxy. The photometric
properties of the super star cluster population in NGC 1569 resemble those of
the populous clusters in the Magellanic Clouds.


title:
Inversion of the Lyman-$\alpha$ forest: 3D investigation of the
  intergalactic medium

abstract:
  We discuss the implementation of Bayesian inversion methods in order to
recover the properties of the intergalactic medium from observations of the
neutral hydrogen Lyman-$\alpha$ absorptions observed in the spectra of high
redshift quasars (the so-called Lyman-$\alpha$ forest). We use two
complementary schemes (i) a constrained Gaussian random field linear approach
and (ii) a more general non-linear explicit Bayesian deconvolution method which
offers in particular the possibility to constrain the parameters of the
equation of state for the gas. While relying on prior assumption for the
two-point correlation functions, we show how to recover, at least
qualitatively, the 3D topology of the large scale structures in redshift space
by inverting a suitable network of adjacent, low resolution lines of sight. We
also discuss the inversion of single lines of sight observed at high spectral
resolution. Our preliminary investigations suggest that the explicit Bayesian
method can be used to derive quantitative information on the physical state of
the gas. Redshift distortion is considered by simultaneous constrained
reconstruction of the velocity and the density field in real space while
assuming statistical correlation between the two fields. The method seems to
work well in the strong prior regime where peculiar velocities are assumed to
be the most likely realization in the density field. Finally, we investigate
the effect of line of sight separation and number of lines of sight. Our
analyses suggest that multiple low resolution lines of sight could be used to
improve most likely velocity reconstruction on a high resolution line of sight.


title: Panel Discussion on Observing Simulations and Simulating Observations

abstract:
  N-body simulations of star cluster evolution have reached a high degree of
realism, by incorporating more and more elements of stellar dynamics, stellar
evolution, and hydrodynamics. At the end of this conference, six participants
discussed how to present the increasingly realistic data from star cluster
simulations in a way that is most useful for a direct comparison with
observations.


title:
New Insights from HST Studies of Globular Cluster Systems II: Analysis
  of 29 S0 Systems

abstract:
  We examine the globular cluster systems (GCS) of a sample of 34 S0 galaxies
from a WFPC2 snapshot survey in the V and I-bands. Of these 34 galaxies, 29
have measurable globular cluster systems. The mean color of the GCSs of
individual galaxies vary from V-I=0.85 mag to V-I=1.17 mag. The average color
of GCSs in all 29 S0 galaxies, V-I=1.00 +/- 0.07 mag, is similar to the value
of V-I=1.04 +/- 0.04 derived for ellipticals in a companion paper. The mean
metallicity of a cluster system is correlated to the luminosity (or mass) of
the host galaxy, but is not dependent on the Hubble type. Our measurements of
the local specific frequency, on the other hand, confirm that the cluster
formation efficiency is a function of Hubble type. The mean local specific
frequency of our sample within the WFPC2 field-of-view is 1.0 +/- 0.6, lower
than S_(N Local)=2.4 +/- 1.8 derived for ellipticals in a similar analysis.
Although we are able to confirm a bimodal color distribution in only one galaxy
from the shallow 'snapshot' images analyzed in this paper statistical tests
suggest that 10-20% of S0s are bimodal it at the present level of photometric
accuracy. There are no significant trends in GCS properties with membership or
location of the S0 host in a galaxy cluster. We have measured the turnover
luminosity of the globular cluster luminosity function (GCLF) for the richest
few GCSs and find the GCLF distances to be in agreement with other estimates.
The globular clusters in S0 galaxies have average half-light radii of ~2.6 pc
which is similar to that of other galaxies, including our own.


title:
Early galaxy evolution from deep wide field star counts. II. First
  estimate of the thick disc mass function

abstract:
  Star counts at high and intermediate galactic latitudes, in the visible and
the near infrared, are used to determine the density law and the initial mass
function of the thick disc population. The combination of shallow fields
dominated by stars at the turnoff with deep fields allows the determination of
the thick disc mass function in the mass range 0.2-0.8 Msun. Star counts are
compared with simulations of a synthesis population model. The fit is based on
a maximum likelihood criterion. The best fit model gives a scale height of 800
pc, a scale length of 2500 pc and a local density of 10e-3 stars/pc3 or 7.1e-4
Msun/pc3 for Mv<8. The IMF is found to follow a power law with a slope
alpha=-0.5. This is the first determination of the thick disc mass function.


title: CDM and Strong Lensing: Concord or Conflict?

abstract:
  (Abridged) Using the number and sizes of observed gravitational lenses, I
derive upper limits on the dark matter content of elliptical galaxies. Galaxies
built from Cold Dark Matter (CDM) mass distributions are too concentrated to
comfortably satisfy these limits; SCDM is ruled out, and LCDM is only
marginally consistent with the data. Thus, lensing adds to the evidence that
CDM mass distributions are too concentrated on kiloparsec scales to agree with
real galaxies, and extends the argument to elliptical galaxies. By contrast,
the lack of central images in radio lenses implies that the central densities
of CDM galaxies are too low on ~10 parsec scales, even if supermassive black
holes are included. Self-interacting dark matter, or any other modification to
regular cold dark matter, must simultaneously reduce the densities on
kiloparsec scales and increase the densities on parsec scales in order to
satisfy the unique constraints from lensing.


title: Studies of Hard X-ray Tails in Z sources with RXTE/HEXTE

abstract:
  We report RXTE results of spectral analyses of three (Sco X-1, GX 349+2, and
Cyg X-2) out of the 6 known Z sources, with emphasis in the hard X-ray
emission. No hard X-ray tails were found for Cyg X-2 (< 8.4E-5 photons cm**-2
s**-1, 50-100 keV, 3 sigma) and for GX 349+2 (< 7.9E-5 photons cm**-2 s**-1,
50-100 keV, 3 sigma). For Sco X-1 a variable hard X-ray tail (with an average
flux of 2.0E-3 photons cm**-2 s**-1, 50-100 keV) has already been reported. We
compare our results to reported detections of a hard component in the spectrum
of Cyg X-2 and GX 349+2. We argue that, taking into account all the results on
detections of hard X-ray tails in Sco X-1 and GX 349+2, the appearance of such
a component is correlated with the brightness of the thermal component.


title:
Relativistic Effects on X-ray Emissions from Accretion Disks around
  Black Holes

abstract:
  Special and general relativistic effects on the X-ray emissions, especially
the continuum spectra, from the accretion disks around black holes are
investigated using the ray-tracing method. Because both the special and general
relativistic effects are more important at distances closer to the black hole,
the relativistic modifications to the emitted X-ray spectra are more
significant at higher energies. In a simple accretion disk precession model,
the relativistic effects can account for the energy dependence of the QPO
amplitude and phase-lags observed in several black hole binaries. The dramatic
QPO phase-lag transitions only show up when the central black hole is spinning
rapidly. The narrow distribution of the observed system inclination angles of
black hole binaries may be due to the selection effect caused by the
relativistic effects around black holes.


title: Hard X-ray properties of blazars

abstract:
  We have considered all blazars observed in the X-ray band and for which the
slope of the X-ray spectrum is available. We have collected 421 spectra of 268
blazars, including 12 archival unpublished ASCA spectra of 7 blazars whose
analysisis presented here. The X-ray spectra of blazars show trends as a
function of their power, confirming that the blazar overall energy distribution
can be parameterized on the basis of one parameter only, i.e. the bolometric
luminosity. This is confirmed by the relatively new hard (2-10 keV) X-ray data.
Our results confirm the idea that in low power objects the X-ray emission
mechanism is the synchrotron process, dominating both the soft and the hard
X-ray emissions. Low energy peaked BL Lac objects are intermediate, often
showing harder spectra in the hard X-ray band, suggesting that the synchrotron
process dominates in the soft band, with the inverse Compton process dominating
at high energies. The most powerful objects have X-ray spectra that are flat
both in the soft and in the hard band, consistent with a dominating inverse
Compton component.


title: IRAS 11590-6452 in BHR 71 - a binary protostellar system?

abstract:
  New AAT near-infrared and SEST 12CO J=2-1 observations are combined with
existing ISO mid-infrared and ATCA cm radio continuum observations to examine
the protostellar content of the Bok globule BHR 71. Together with observations
of Herbig-Haro objects, these data show: (1) Two protostellar sources, IRS1 and
IRS2, with a separation of ~17 arcsec (3400 AU) are located within BHR 71. (2)
Each protostar is driving its own molecular outflow. The outflow from IRS1 is
much larger in extent, is more massive, and dominates the CO emission. (3) Both
protostars are associated with Herbig-Haro objects and shock excited 2.122
micron H2 v=1-0S(1) emission, which coincide spatially with their CO outflows.
(4) IRS1 is associated with cm continuum emission, with a flat or rising
spectrum which is consistent with free-free emission, a signpost of
protostellar origin.


title: Topics in Basic Maser Theory

abstract:
  This review covers some of the developments in basic theory of astronomical
masers over the past ten years. Topics included are the effects of three
dimensional geometry and polarization, with special emphasis on the differences
between maser and non-maser radiation.


title:
Spatially-Resolved O II Recombination Line Observations of the Ring
  Nebula, NGC 6720

abstract:
  We present spatially-resolved spectral of O II permitted lines and [O III]
forbidden lines in the Ring Nebula NGC 6720. We find significant differences in
the spatial distribution of the O II and [O III] lines. The [O III] emission
follows the H-beta emission measure; however, the O II emission peaks closer to
the central star. This suggests that radiative recombination may not be the
primary mechanism for producing the O II lines. O+2 abundances derived from O
II lines are 5-10 times larger than those derived from [O III] in the region
within 20" of the central star, but agree to within 0.2-0.3 dex outside this
region. The [O III] electron temperature rises smoothly from about 10,000 K in
the outer shell to about 12,000 K in the center; we see no evidence for a
temperature jump that would be associated with a shock. If temperature
fluctuations are responsible for the discrepancy in O+2 abundances, the average
temperature would have to be approximately 6,500 K in the He$^{+2}$ zone and
about 9,000 K in the outer shell in order to force the [O III]-derived
abundance to equal that derived from O II. We therefore argue that temperature
fluctuations can not explain the abundance discrepancy. The O II emission does
not peak at the locations of dusty knots, creating difficulties for models
which explain the O II - [O III] discrepancy by density fluctuations. We
examine the possibility high-temperature dielectronic recombination in a
central hot bubble enhances the O II line strengths in the central nebula.
However, comparison of recombination rates with collisional excitation rates
shows that the increase in recombination emission due to dielectronic
recombination at T ~ 10^5 K is not sufficient to overcome the increase in [O
III] emission. (Abridged)


title: Diffuse Gamma-Rays from Local Group Galaxies

abstract:
  Diffuse gamma-ray radiation in galaxies is produced by cosmic ray
interactions with the interstellar medium. With the completion of EGRET
observations, the only extragalactic object from which there has been a
positive detection of diffuse gamma-ray emission is the Large Magellanic Cloud.
We systematically estimate the expected diffuse gamma-ray flux from Local Group
galaxies, and determine their detectability by new generation gamma-ray
observatories such as GLAST. For each galaxy, the expected gamma-ray flux
depends only on its total gas content and its cosmic ray flux. We present a
method for calculating cosmic ray flux in these galaxies in terms of the
observed rate of supernova explosions, where cosmic ray acceleration is
believed to take place. The difficulty in deriving accurate supernova rates
from observational data is a dominant uncertainty in our calculations. We
estimate the gamma-ray flux for Local Group galaxies and find that our
predictions are consistent with the observations for the LMC and with the
observational upper limits for the Small Magellanic Cloud and M31. Both the
Andromeda galaxy, with a flux of $\sim 1.0 \times 10^{-8}$ photons sec$^{-1}$
cm$^{-2}$ above 100 MeV, and the SMC, with a flux of $\sim 1.7 \times 10^{-8}$
photons sec$^{-1}$ cm$^{-2}$ above 100 MeV, are expected to be observable by
GLAST. M33 is at the limit of detectability with a flux of $\sim 0.11 \times
10^{-8}$ sec$^{-1}$ cm$^{-2}$. Other Local Group galaxies are at least two
orders of magnitude below GLAST sensitivity.


title: Physics of Collisionless GRB Shocks and Their Radiation Properties

abstract:
  We present a theory of ultrarelativistic collisionless shocks based on the
relativistic kinetic two-stream instability. We demonstrate that the shock
front is unstable to the generation of small-scale, randomly tangled magnetic
fields. These fields are strong enough to scatter the energetic incoming (in
the shock frame) protons and electrons over pitch angle and, therefore, to
convert their kinetic energy of bulk motion into heat with very high
efficiency. This validates the use of MHD approximation and the shock jump
conditions in particular. The effective collisions are also necessary for the
diffusive Fermi acceleration of electrons to operate and produce an observed
power-law. Finally, these strong (sub-equipartition) magnetic fields are also
required for the efficient synchrotron-type radiation emission from the shocks.
  The predicted magnetic fields have an impact on polarization properties of
the observed radiation (e.g., a linear polarization from a jet-like ejecta and
polarization scintillations in radio for a spherical one) and on its spectrum.
We present an analytical theory of jitter radiation, which is emitted when the
magnetic field is correlated on scales smaller then the gyration (Larmor)
radius of the accelerated electrons. A composite jitter+synchrotron model of
GRB $\gamma$-ray emission from internal shocks is capable of resolving many
puzzles of GRB spectra, such as the violation of the ``line of death'', sharp
spectral breaks, and multiple spectral components seen in some bursts (good
examples are GRB910503, GRB910402, etc.). We stress that simultaneous detection
of both spectral components opens a way to a precise diagnostics of the
conditions in GRB shocks. We also discuss the relation of our results to other
systems, such as internal shocks in blazars, radio lobes, and supernova shocks.


title: Aspects of the dynamics underlying solar and stellar dynamo models

abstract:
  Observations of the Sun and solar-type stars continue to reveal phenomena
whose understanding is very likely to require a nonlinear framework. Here we
shall concentrate on two such phenomena, namely the grand minima type behaviour
observed in the Sun and solar-type stars and the recent dynamical variations of
the differential rotation in the solar convection zone, deduced from the
helioseismic observations, and discuss how their explanations have recently
motivated the development/employment of novel ideas from nonlinear dynamics.


title:
ADONIS observations of X-ray emitting late B-type stars in Lindroos
  systems

abstract:
  We present adaptive optics JHKs imaging observations of three main-sequence
late B-type stars listed in the Lindroos Catalogue: HD123445, HD127971 and
HD129791. Given their spectral types, these stars should not be X-ray emitters.
However, they have been detected by ROSAT and their X-ray emission has been
attributed to possible unresolved late-type companions. We have carried out
near-IR observations with ADONIS at the ESO 3.6m but have not detected any
late-type companions close to HD127971 and HD129791. This result leads us to
conclude that either (i) they are spectroscopic binaries with unresolved
low-mass companions, or (ii) they are intrinsic X-ray emitters. While the
former case would be consistent with the reported high multiplicity of
early-type (A and B) stars, the latter would yield a revision of stellar
activity theories which do not predict X-ray emission from these stars. On the
other hand, HD123445 does indeed show visual companions, namely an apparent
subarcsecond faint (Ks=10mag) binary system at a projected separation of 5"
from the late-B type star. The JHKs magnitudes and colors of the components are
consistent with a pair of Pre Main Sequence (PMS) K-type stars at 140 pc, i.e.
possible members of the Upper Centaurus Lupus association. In this case the
reported X-ray emission can be ascribed to the new binary system. Nevertheless,
spectroscopy is required to confirm the possible PMS nature of the pair.


title:
Spatiotemporal fragmentation and the uncertainties in the solar rotation
  law

abstract:
  Analyses of recent helioseismic data indicate that the dynamical regimes at
the base of the convection zone can be different from those observed at the
top, having either significantly shorter periods or non--periodic behaviour.
  Recently spatiotemporal fragmentation/bifurcation has been proposed as a
dynamical mechanism to account for the multi-mode behaviour that is possibly
observed in the solar convection zone, without requiring separate physical
mechanisms with different time scales at different depths.
  Here we study the robustness of this mechanism with respect to changes to the
zero order rotation profile, motivated by the uncertainties of and differences
between the various reductions of the helioseimic data. We find that
spatiotemporal fragmentation is a common feature of the reductions investigated


title:
Gravitational Equilibrium in the Presence of a Positive Cosmological
  Constant

abstract:
  We reconsider the virial theorem in the presence of a positive cosmological
constant Lambda. Assuming steady state, we derive an inequality of the form rho
>= A (Lambda / 4 pi GN) for the mean density rho of the astrophysical object.
With a minimum at Asphere = 2, its value can increase by several orders of
magnitude as the shape of the object deviates from a spherically symmetric one.
This, among others, indicates that flattened matter distributions like e.g.
clusters or superclusters, with low density, cannot be in gravitational
equilibrium.


title: A Very Radio-Loud Narrow-Line Seyfert 1: PKS 2004-447

abstract:
  We have discovered a very radio-loud Narrow-Line Seyfert 1 candidate: PKS
2004-447. This Seyfert is consistent with the formal definition for NLS1s,
although it does not have quite the same spectral features as some typical
members of this subclass. Only ROSAT survey data is available at X-ray
wavelengths, so it has not been possible to compare this source with other
NLS1s at these wavelengths. A full comparison of this source with other members
of the subclass will improve our physical understanding of NLS1s. In addition,
using standard calculations, we estimate the central black hole to have a mass
of $\sim 5 \times 10^6 M_{\odot}$. This does not agree with predictions in the
literature, that radio-loud AGN host very massive black holes.


title: Upper limits on O VI Emission From Voyager

abstract:
  We have examined 426 {\it Voyager} fields distributed across the sky for
\ion{O}{6} ($\lambda \lambda$ 1032/1038 \AA) emission from the Galactic diffuse
interstellar medium. No such emission was detected in any of our observed
fields. Our most constraining limit was a 90% confidence upper limit of 2600
\phunit on the doublet emission in the direction (l, b) = (117\fdegree3,
50\fdegree6). Combining this with an absorption line measurement in nearly the
same direction allows us to place an upper limit of 0.01 cm$^{-3}$ on the
electron density of the hot gas in this direction. We have placed 90%
confidence upper limits of less than or equal to 10,000 \phunit on the
\ion{O}{6} emission in 16 of our 426 observations.


title:
Oxygen Line Formation in Late-F through Early-K Disk/Halo Stars:
  Infrared O I Triplet and [O I] Lines

abstract:
  In order to investigate the formation of O {\sc i} 7771--5 and [O {\sc i}]
6300/6363 lines, extensive non-LTE calculations for neutral atomic oxygen were
carried out for wide ranges of model atmosphere parameters, which are
applicable to early-K through late-F halo/disk stars of various evolutionary
stages. The formation of the triplet O {\sc i} lines was found to be well
described by the classical two-level-atom scattering model, and the non-LTE
correction is practically determined by the parameters of the line-transition
itself without any significant relevance to the details of the oxygen atomic
model. This simplifies the problem in the sense that the non-LTE abundance
correction is essentially determined only by the line-strength ($W_{\lambda}$),
if the atmospheric parameters of $T_{\rm eff}$, $\log g$, and $\xi$ are given,
without any explicit dependence of the metallicity; thus allowing a useful
analytical formula with tabulated numerical coefficients. On the other hand,
our calculations lead to the robust conclusion that LTE is totally valid for
the forbidden [O {\sc i}] lines. An extensive reanalysis of published
equivalent-width data of O {\sc i} 7771--5 and [O {\sc i}] 6300/6363 taken from
various literature resulted in the conclusion that, while a reasonable
consistency of O {\sc i} and [O {\sc i}] abundances was observed for disk stars
($-1 \la [{\rm Fe}/{\rm H}] \la 0$), the existence of a systematic abundance
discrepancy was confirmed between O {\sc i} and [O {\sc i}] lines in
conspicuously metal-poor halo stars ($-3 \la [{\rm Fe}/{\rm H}] \la -1$)
without being removed by our non-LTE corrections, i.e., the former being larger
by $\sim 0.3$ dex at $-3 \la [{\rm Fe}/{\rm H}] \la -2$.


title: The metal-rich nature of stars with planets

abstract:
  With the goal of confirming the metallicity "excess" present in stars with
planetary-mass companions, we present in this paper a high-precision
spectroscopic study of a sample of dwarfs included in the CORALIE extrasolar
planet survey. The targets were chosen according to the basic criteria that 1)
they formed part of a limited volume and 2) they did not present the signature
of a planetary host companion. A few stars with planets were also observed and
analysed; namely, HD 6434, HD 13445, HD 16141, HD 17051, HD 19994, HD 22049, HD
28185, HD 38529, HD 52265, HD 190228, HD 210277 and HD 217107. For some of
these objects there had been no previous spectroscopic studies. The
spectroscopic analysis was done using the same technique as in previous work on
the metallicity of stars with planets, thereby permitting a direct comparison
of the results. The work described in this paper thus represents the first
uniform and unbiased comparison between stars with and without planetary-mass
companions in a volume-limited sample. The results show that 1) stars with
planets are significantly metal-rich, and 2) that the source of the metallicity
is most probably "primordial". The results presented here may impose serious
constraints on planetary system formation and evolution models.


title:
A numerical solution of the inverse problem in classical celestial
  mechanics, with application to Mercury's motion

abstract:
  It is attempted to obtain the masses of the celestial bodies, the initial
conditions of their motion, and the constant of gravitation, by a global
parameter optimization. First, a numerical solution of the N-bodies problem for
mass points is described and its high accuracy is verified. The osculating
elements are also accurately computed. This solution is implemented in the
Gauss iterative algorithm for solving nonlinear least-squares problems. This
algorithm is summarized and its efficiency for the inverse problem in celestial
mechanics is checked on a 3-bodies problem. Then it is used to assess the
accuracy to which a Newtonian calculation may reproduce the DE403 ephemeris,
that involves general-relativistic corrections. The parameter optimization
allows to reduce the norm and angular differences between the Newtonian
calculation and DE403 by a factor 10 (Mercury, Pluto) to 100 (Venus). The
maximum angular difference on the heliocentric positions of Mercury is ca. 220"
per century before the optimization, and ca. 20" after it. The latter is still
far above the observational accuracy. On the other hand, Mercury's longitude of
the perihelion is not affected by the optimization: it keeps the linear advance
of 43" per century.
  Key words: Mercury's perihelion. Parameter optimization. Mechanics of point
masses.


title:
Probability Distribution Function of Cosmological Density Fluctuations
  from Gaussian Initial Condition: Comparison of One- and Two-point Log-normal
  Model Predictions with N-body Simulations

abstract:
  We quantitatively study the probability distribution function (PDF) of
cosmological nonlinear density fluctuations from N-body simulations with
Gaussian initial condition. In particular, we examine the validity and
limitations of one-point and two-point log-normal PDF models against those
directly estimated from the simulations. We find that the one-point log-normal
PDF describes very accurately the cosmological density distribution even in the
nonlinear regime (the rms variance \sigma_{nl} \simlt 4 and the over-density
\delta \simlt 100). Furthermore the two-point log-normal PDFs are also in good
agreement with the simulation data from linear to fairly nonlinear regime,
while slightly deviate from them for \delta \simlt -0.5. Thus the log-normal
PDF can be used as a useful empirical model for the cosmological density
fluctuations. While this conclusion is fairly insensitive to the shape of the
underlying power spectrum of density fluctuations P(k), models with substantial
power on large scales, i.e., n\equiv d\ln P(k)/d \ln k \simlt -1, are better
described by the log-normal PDF. On the other hand, we note that the one-to-one
mapping of the initial and the evolved density fields consistent with the
log-normal model does not approximate the broad distribution of their mutual
correlation even on average. Thus the origin of the phenomenological log-normal
PDF approximation still remains to be understood.


title:
Highly abundant HCN in the inner hot envelope of GL 2591: probing the
  birth of a hot core?

abstract:
  We present observations of the v2=0 and vibrationally excited v2=1 J=9-8
rotational lines of HCN at 797 GHz toward the deeply embedded massive young
stellar object GL 2591, which provide the missing link between the extended
envelope traced by lower-J line emission and the small region of hot (T_ex >=
300 K), abundant HCN seen in 14 micron absorption with the Infrared Space
Observatory (ISO). The line ratio yields T_ex=720^+135_-100 K and the line
profiles reveal that the hot gas seen with ISO is at the velocity of the
protostar, arguing against a location in the outflow or in shocks. Radiative
transfer calculations using a depth-dependent density and temperature structure
show that the data rule out a constant abundance throughout the envelope, but
that a model with a jump of the abundance in the inner part by two orders of
magnitude matches the observations. Such a jump is consistent with the sharp
increase in HCN abundance at temperatures >~230 K predicted by recent chemical
models in which atomic oxygen is driven into water at these temperatures.
Together with the evidence for ice evaporation in this source, this result
suggests that we may be witnessing the birth of a hot core. Thus, GL 2591 may
represent a rare class of objects at an evolutionary stage just preceding the
`hot core' stage of massive star formation.


title: New CMBR data and the cosmic neutrino background

abstract:
  New precision Cosmic Microwave Background Radiation (CMBR) anisotropy data
are beginning to constrain physics beyond the standard model, for example in
the form of additional light particle species. These constraints are
complementary to what can be obtained from big bang nucleosynthesis (BBN)
considerations because they apply to much later times. We derive a constraint
on the equivalent number of neutrino species, N_\nu, from the presently
available data. Specifically we analyse two different CMBR data sets to test
the robustness of our results. Analyzing only CMBR data yields an upper bound
of N_\nu < 17 (95% confidence). Adding large scale structure (LSS) data from
the PSC-z survey tightens the upper bound slightly. However, the addition of
LSS data gives a non-trivial {\it lower} bound of N_\nu > 1.5/2.5 (95%
confidence) for the two data sets. This is the first independent indication of
the presence of the cosmological neutrino background which is predicted by the
standard model, and seen in big bang nucleosynthesis. The value $N_\nu = 0$ is
disfavoured at 3\sigma and 4\sigma for the two data sets respectively.


title:
The gravitational wave signal from the Galactic disk population of
  binaries containing two compact objects

abstract:
  We review the properties of Galactic binaries containing two compact objects,
as derived by means of population synthesis. Using this information we
calculate the gravitational wave signal of these binaries. At frequencies below
f ~< 2 mHz the double white dwarf population forms an unresolved background for
the low-frequency gravitational wave detector LISA. Above this limit some few
thousand double white dwarfs and few tens of binaries containing neutron stars
will be resolved. Of the resolved double white dwarfs ~500 have a total mass
above the Chandrasekhar limit. About ~95 of these have a measurable frequency
change allowing a determination of their chirp mass. We discuss the properties
of the resolved systems.


title:
The problem of the Pleiades distance. Constraints from Stromgren
  photometry of nearby field stars

abstract:
  The discrepancy between the Pleiades cluster distance based on Hipparcos
parallaxes and main sequence fitting is investigated on the basis of Stromgren
photometry of F-type stars. Field stars with the same metallicity as the
Pleiades have been selected from the m1 index and a technique has been
developed to locate the ZAMS of these field stars in color-magnitude diagrams
based on the color/temperature indices b-y, v-y, and beta. Fitting the Pleiades
to these ZAMS relations results in a distance modulus of 5.61+/-0.03 mag in
contrast to the Hipparcos modulus of 5.36+/-0.06 mag. Hence, we cannot confirm
the recent claim by Grenon (1999) that the distance problem is solved by
adopting a low metallicity of the Pleiades ([Fe/H]=-0.11) as determined from
Geneva photometry. The metallicity sensitivity of the ZAMS determined by the
field stars is investigated, and by combining this sensitivity in all three
color/temperature indices b-y, v-y, and beta we get a independent test of the
Pleiades distance modulus which support our value of 5.61 mag. Furthermore, the
field star sample used for the comparison is tested against theoretical
isochrones of different ages to show that evolutionary effects in the field
star sample are not biasing our distance modulus estimate significantly.
Possible explanations of the Pleiades distance problem are discussed and it is
suggested that the discrepancy in the derived moduli may be linked to a
non-spherical shape of the cluster.


title:
Limits to the Mass and the Radius of the Compact Star in SAX
  J1808.4--3658 and Their Implications

abstract:
  We show that a survey of equations of state and observations of X-ray
pulsations from SAX J1808.4-3658 give 2.27 solar mass as the upper limit of the
compact star mass. The corresponding upper limit of the radius comes out to be
9.73 km. We also do a probabilistic study to estimate the lower limit of the
mass of the compact star. Such a limit puts useful constraints on equations of
state. We also discuss the implications of the upper mass limit for the the
evolutionary history of the source, as well as the detection of it in radio
frequencies. We envisage that the possible observation of radio-eclipse may be
able to rule out several soft equation of state models, by setting a moderately
high value for the lower limit of inclination angle.


title:
A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree
  Survey

abstract:
  We have measured the surface density of galaxies toward 14 X-ray-selected
cluster candidates at redshifts greater than z=0.46, and we show that they are
associated with rich galaxy concentrations. We find that the clusters range
between Abell richness classes 0-2, and have a most probable richness class of
one. We compare the richness distribution of our distant clusters to those for
three samples of nearby clusters with similar X-ray luminosities. We find that
the nearby and distant samples have similar richness distributions, which shows
that clusters have apparently not evolved substantially in richness since
redshift z =0.5. We compare the distribution of distant X-ray clusters in the
L_x--richness plane to the distribution of optically-selected clusters from the
Palomar Distant Cluster Survey. The optically-selected clusters appear overly
rich for their X-ray luminosities when compared to X-ray-selected clusters.
Apparently, X-ray and optical surveys do not necessarily sample identical mass
concentrations at large redshifts. This may indicate the existence of a
population of optically rich clusters with anomalously low X-ray emission. More
likely, however, it reflects the tendency for optical surveys to select
unvirialized mass concentrations, as might be expected when peering along
large-scale filaments.


title:
Neutrino Pair Emission from Cooper Pair Breaking and Recombination in
  Superfluid Quark Matter

abstract:
  For the low energy Standard Model neutrino-matter interactions, we calculate
neutrino pair ($\nu\bar\nu$) emissivites in superfluid quark matter. Just below
the critical temperature, Cooper pairs continuously break and recombine,
resulting in the emission of $\nu\bar \nu$ pairs with a rate that greatly
exceeds the standard quark modified Urca and bremsstrahlung rates. At the same
baryon density in baryonic and quark matter, the ratio of baryon to quark
$\nu\bar\nu$ emissivites lies in the range 2-5 for the densities of interest in
the long-term cooling of solar mass compact stars. We also find that in matter
containing hyperons, $\nu\bar\nu$ emission can occur with hyperons of all
species.


title: The Observation of Lunar Impacts. Part II

abstract:
  The frequency and the characteristics of lunar impacting meteorites are
reconsidered under the general assumption of belonging to the sporadic
meteoroids. We develop the model for evaluating the luminous energy detected in
the visual band during the impact. The values obtained are consistent with the
luminosity of an Earth's meteor as seen at the Moon's distance, although we
recover significantly smaller magnitudes for the lunar impacts with respect to
other authors.


title:
Constraints on the long-range properties of gravity from weak
  gravitational lensing

abstract:
  Weak gravitational lensing provides a means of testing the long-range
properties of gravity. Current measurements are consistent with standard
Newtonian gravity and inconsistent with substantial modifications on Mpc
scales. The data allows long range gravity to deviate from a 1/r potential only
on scales where standard cosmology would use normal gravity but be dominated by
dark matter. Thus, abnormal gravity theories must introduce two fine-tuning
scales -- an inner scale to explain flat rotation curves and an outer scale to
force a return to Newtonian gravity on large scales -- and these scales must
coincidently match the scales produced by the dark matter theory after evolving
the universe for 10 billion years starting from initial conditions which are
exquisitely determined from the cosmic microwave background.


title: An optical inverse-Compton hotspot in 3C196?

abstract:
  Several hotspots of FRII radio sources have previously been detected in the
X-ray at a flux level consistent with the X-rays being due to inverse-Compton
scattering of radio synchrotron photons (`synchrotron self-Compton'), if the
magnetic fields in the hotspots are close to their equipartition values.
However, the number of hotspots compact and bright enough to exhibit detectable
X-ray emission is small, so it is worth searching for synchrotron self-Compton
emission in the optical, in spite of the obvious observational difficulties of
such an approach. In this note I report on a possible detection of an optical
inverse-Compton hotspot in a deep Hubble Space Telescope observation of the
distant quasar 3C196, at a level which implies a hotspot magnetic field
strength close to equipartition if the electrons have a low-energy cutoff
around gamma ~ 500.


title:
Understanding Cluster Gas Evolution and Fine-Scale CMB Anisotropy with
  Deep Sunyaev-Zel'dovich Effect Surveys

abstract:
  We investigate the impact of gas evolution on the expected yields from deep
Sunyaev-Zel'dovich (SZ) effect surveys as well as on the expected SZ effect
contribution to fine scale anisotropy in the Cosmic Microwave Background. The
approximate yields from SZ effect surveys are remarkably insensitive to gas
evolution, even though the observable properties of the resulting clusters can
be markedly different. The CMB angular power spectrum at high multipoles due to
the SZ effect from clusters is quite sensitive to gas evolution. We show that
moderate resolution SZ effect imaging of clusters found in deep SZ effect
surveys should allow a good understanding of gas evolution in galaxy clusters,
independent of the details of the nature of the gas evolution. Such an
understanding will be necessary before precise cosmological constraints can be
set from yields of large cluster surveys.


title: Supermassive Black Holes in Nuclei of Galaxies

abstract:
  We review the motivation and search for supermassive black holes (BHs) in
galaxies. Energetic nuclear activity provides indirect but compelling evidence
for BH engines. Ground-based dynamical searches for central dark objects are
reviewed in Kormendy & Richstone (1995, ARA&A, 33, 581). Here we provide an
update of results from the HST. As of 2001 March, dynamical BH detections are
available for at least 37 galaxies. The demographics of these objects lead to
the following conclusions: (1) BH mass correlates with the luminosity of the
bulge component of the host galaxy. The median BH mass fraction is 0.13% of the
mass of the bulge. (2) BH mass correlates with the mean velocity dispersion of
the bulge inside its effective radius. For the best mass determinations, the
scatter is consistent with the measurement errors. (3) BH mass correlates with
the luminosity of the high-density central component in disk galaxies
independent of whether this is a real bulge (a mini-elliptical, believed to
form via a merger-induced dissipative collapse and starburst) or a
``pseudobulge'' (believed to form by inward transport of disk material). (4) BH
mass does not correlate with the luminosity of galaxy disks. If pure disks
contain BHs, then their masses are much smaller than 0.13% of the mass of the
disk. We conclude that present observations show no dependence of BH mass on
the details of whether BH feeding happens rapidly during a collapse or slowly
via secular evolution of the disk. The above results increasingly support the
hypothesis that the major events that form a bulge or elliptical galaxy and the
main growth phases of its BH -- when it shone like a quasar -- were the same
events.


title: Composite Quasar Spectra From the Sloan Digital Sky Survey

abstract:
  We have created a variety of composite quasar spectra using a homogeneous
data set of over 2200 spectra from the Sloan Digital Sky Survey (SDSS). The
quasar sample spans a redshift range of 0.044 <= z <= 4.789, and an absolute r'
magnitude range of -18.0 to -26.5. The median composite covers a rest
wavelength range from 800 - 8555A, and reaches a peak signal-to-noise ratio of
over 300 per 1A resolution element in the rest frame. We have identified over
80 emission line features in the spectrum. Emission line peak velocity shifts
of the broad permitted and semi-forbidden lines are strongly correlated with
ionization energy, as previously suggested, but we find that the narrow
forbidden lines are also shifted by amounts which are strongly correlated with
ionization energy. The magnitude of the forbidden line shifts is < 100 km/s,
compared to shifts of up to 550 km/s for some of the permitted and
semi-forbidden lines. At wavelengths longer than the Ly-a emission, the
continuum of the geometric mean composite is well-fit by two power-laws, with a
break at approximately 5000A. The frequency power law index, alpha_nu, is -0.44
from 1300 - 5000A, and -2.45 redward of about 5000A. The abrupt change in slope
can be accounted for partly by host galaxy contamination at low redshift.
Stellar absorption lines, including higher-order Balmer lines, seen in the
composites suggest that young or intermediate age stars make a significant
contribution to the light of the host galaxies. An electronic table of the
median quasar template is available.


title:
Ultra-high energy cosmic rays from annihilation of superheavy dark
  matter

abstract:
  We consider the possibility that ultra-high energy cosmic rays originate from
the annihilation of relic superheavy dark-matter particles. We find that a
cross section of <sigma_A v> ~ 10^{-26}cm^2 (M_X/10^{12}GeV)^{3/2} is required
to account for the observed rate of super-GZK events if the superheavy dark
matter follows a Navarro-Frenk-White density profile. This would require
extremely large-l contributions to the annihilation cross section. We also
calculate the possible signature from annihilation in sub-galactic clumps of
dark matter and find that the signal from sub-clumps dominates and may explain
the observed flux with a much smaller cross section than if the superheavy dark
matter is smoothly distributed. Finally, we discuss the expected anisotropy in
the arrival directions of the cosmic rays, which is a characteristic signature
of this scenario.


title:
Probing the Intergalactic Medium with the Lyman alpha forest along
  multiple lines of sight to distant QSOs

abstract:
  (abridged) We present an effective implementation of analytical calculations
of the Lyalpha opacity distribution of the Intergalactic Medium (IGM) along
multiple lines of sight (LOS) to distant quasars in a cosmological setting.
This method fully accounts for the expected correlations between LOS and the
cosmic variance in the large-scale modes of the dark matter distribution.
Strong correlations extending up to ~300 kpc (proper) and more are found at
redshift z~2->3, in agreement with observations. These correlations are
investigated using the cross-correlation coefficient and the cross-power
spectrum of the flux distribution along different LOS and by identifying
coincident absorption features as fitted with a Voigt profile fitting routine.
The cross-correlation coefficient between the LOS can be used to constrain the
shape-parameter Gamma of the power spectrum if the temperature and the
temperature density relation of the IGM can be determined indepedently. We also
propose a new technique to recover the 3D linear dark matter power spectrum by
integrating over 1D flux cross-spectra which is complementary to the usual
`differentiation' of 1D auto-spectra. The cross-power spectrum suffers much
less from errors uncorrelated in different LOS, like those introduced by
continuum fitting. Investigations of the flux correlations in adjacent LOS
should thus allow to extend studies of the dark matter power spectrum with the
Lyalpha forest to significantly larger scales than is possible with flux
auto-power spectra. 30 pairs with separation of 1-2 arcmin should be sufficient
to determine the 1D cross-spectrum at scales of 60 Mpc/h with an accuracy of
about 30% if the error is dominated by cosmic variance.


title: Kinematic properties of gas and stars in 20 disc galaxies

abstract:
  Ionized gas and stellar kinematical parameters have been measured along the
major axis of 20 nearby disc galaxies. We discuss the properties of each sample
galaxy distinguishing between those characterized by regular or peculiar
kinematics. In early-type disc galaxies ionized gas tends to rotate faster than
stars and to have a lower velocity dispersion, whereas in late-type spirals gas
and stars show almost the same rotation velocities and velocity dispersions.
Incorporating the early-type disc galaxies studied by Bertola et al. (1995),
Fisher (1997) and Corsini et al. (1999), we have compiled a sample of some 40
galaxies for which the major-axis radial profiles of both the stellar and
gaseous components have been measured. The value of the stellar velocity
dispersion measured at Re/4 turns out to be strongly correlated with the galaxy
morphological type, while the gaseous velocity dispersion is not and sometimes
takes values above the range expected from thermal motions or small-scale
turbulence.


title: Simulations of MHD Turbulence in a Strongly Magnetized Medium

abstract:
  We analyze 3D numerical simulations of driven incompressible
magnetohydrodynamic (MHD) turbulence in a periodic box threaded by a moderately
strong external magnetic field. We sum over nonlinear interactions within
Fourier wavebands and find that the time scale for the energy cascade is
consistent with the Goldreich-Sridhar model of strong MHD turbulence. Using
higher order longitudinal structure functions we show that the turbulent
motions in the plane perpendicular to the local mean magnetic field are similar
to ordinary hydrodynamic turbulence while motions parallel to the field are
consistent with a scaling correction which arises from the eddy anisotropy. We
present the structure tensor describing velocity statistics of Alfvenic and
pseudo-Alfvenic turbulence. Finally, we confirm that an imbalance of energy
moving up and down magnetic field lines leads to a slow decay of turbulent
motions and speculate that this imbalance is common in the interstellar medium
where injection of energy is intermittent both in time and space.


title:
The V-EUV Delay for Dwarf Nova Outbursts: A Case Study for VW Hydri, U
  Geminorum, and SS Cygni

abstract:
  We present a parameter study using time dependent calculations of the thermal
limit cycle model for dwarf nova outbursts.
  Our goal is to delineate the dependence of the delay between the initial
rapid rise of the visual and EUV fluxes during the start of an outburst on
model parameters, concentrating on three bright, nearby systems for which
complete optical and EUV observations exist - VW Hyi, U Gem, and SS Cyg. For
these systems we infer that the outburst must be triggered at ~0.7-0.8 of the
outer disk radius to produce delays which are in accord with observations. We
also see a stagnation or period of slow warming (first noted by Mineshige)
during the early stages of thermal instability, but find it does not influence
the V-EUV delay since it precedes the rapid rise in V at the start of the
outburst. We find that if one decreases the surface density in the inner disk,
interior to the instigation radius, the V-EUV delay can be lengthened by as
much as a factor of two. In addition, we find there to be a weak relation
between the V-EUV delay and the value of the alpha viscosity parameter in
quiescence.


title:
Electron-Ion Recombination on Grains and Polycyclic Aromatic
  Hydrocarbons

abstract:
  With the high-resolution spectroscopy now available in the optical and
satellite UV, it is possible to determine the neutral/ionized column density
ratios for several different elements in a single cloud. Assuming ionization
equilibrium for each element, one can make several independent determinations
of the electron density. For the clouds for which such an analysis has been
carried out, these different estimates disagree by large factors, suggesting
that some process (or processes) besides photoionization and radiative
recombination might play an important role in the ionization balance. One
candidate process is collisions of ions with dust grains.
  Making use of recent work quantifying the abundances of polycyclic aromatic
hydrocarbon molecules and other grains in the interstellar medium, as well as
recent models for grain charging, we estimate the grain-assisted ion
recombination rates for several astrophysically important elements. We find
that these rates are comparable to the rates for radiative recombination for
conditions typical of the cold neutral medium. Including grain-assisted ion
recombination in the ionization equilibrium analysis leads to increased
consistency in the various electron density estimates for the gas along the
line of sight to 23 Orionis. However, not all of the discrepancies can be
eliminated in this way; we speculate on some other processes that might play a
role. We also note that grain-assisted recombination of H+ and He+ leads to
significantly lower electron fractions than usually assumed for the cold
neutral medium.


title: Temporal characteristics of the X-ray emission of NGC 7469

abstract:
  We present a study of the time variability of NGC 7469, based on a ~30 d
RXTE/PCA observation. Variability is seen across the X-ray band, and spectral
changes are observed. The softness ratio is correlated with the ultraviolet
flux, but appears to show more rapid variability. The RMS variability parameter
calculated on ~1d time scales is significantly variable, and sharp increases
are seen close to the periods where the spectrum is hardest. Cross correlation
of 2-4 keV, 4-10 keV and 10-15 keV light curves show a peak at zero delay, but
the CCFs are skewed towards positive lags (i.e. the soft leading the hard) with
an apparent time lag of about 0.5d. The power spectral density (PSD) function
in the 2-10 keV band shows no clear features - for example periodicities or
breaks - but a power law is a rather poor fit, particularly to the high
frequency spectrum. The normalized PSD in the soft X-ray band shows a larger
amplitude of variability on long time scales but the hard X-ray PSD is flatter,
and shows more power on time scales less than about 1d. Our data broadly
support the idea that the X-rays are produced by Compton upscattering of
lower-energy seed photons, as had been previously concluded. They are difficult
to reconcile with models in which the sole source of variability is the seed
photons, and more likely suggest a variability process intrinsic to the X-ray
corona. Our interpretation for these results is that the low-frequency
variability in NGC 7469 does arise via variations in the Compton seed photons,
but that the high frequency variability arises from the coronal heating
mechanism (truncated)


title: Imaging Polarimetric Observations of a New Circumstellar Disk System

abstract:
  Few circumstellar disks have been directly observed. Here we use sensitive
differential polarimetric techniques to overcome atmospheric speckle noise in
order to image the circumstellar material around HD 169142. The detected
envelope or disk is considerably smaller than expectations based on the
measured strength of the far-IR excess from this system.


title:
Microlensing and the Surface Brightness Profile of the Afterglow Image
  of GRB 000301C

abstract:
  The optical afterglow of Gamma-Ray Burst (GRB) 000301C exhibited a
significant, short-timescale deviation from the power-law flux decline expected
in the standard synchrotron shock model. Garnavich, Loeb & Stanek found that
this deviation was well-fit by an ad hoc model in which a thin ring of emission
is microlensed by an intervening star. We revisit the microlensing
interpretation of this variability, first by testing whether microlensing of
afterglow images with realistic surface brightness profiles (SBPs) can fit the
data, and second by directly inverting the observed light curve to obtain a
non-parametric measurement of the SBP. We find that microlensing of realistic
SBPs can reproduce the observed deviation, provided that the optical emission
arises from frequencies above the cooling break. Conversely, if the variability
is indeed caused by microlensing, the SBP must be significantly
limb-brightened. Specifically, greater than 60% of the flux must originate from
the outer 25% of the area of the afterglow image. The latter requirement is
satisfied by the best fit theoretical SBP. The underlying optical/infrared
afterglow lightcurve is consistent with a model in which a jet is propagating
into a uniform medium with the cooling break frequency below the optical band.


title:
ASCA Observations of Temperature Structure and Metal Distribution in the
  Perseus Cluster of Galaxies

abstract:
  Large-scale distributions of hot-gas temperature and Fe abundance in the
Perseus cluster have been studied with multi-pointing observations by the GIS
instrument on ASCA. Within a radius of 20' from the cluster center, the energy
spectra requires two temperature components, in which the cool component
indicates kT ~ 2 keV and the hot-component temperature shows a significant
decline from about 8 keV to 6 keV toward the center. In the outer region of the
cluster, the temperature shows a fluctuation with an amplitude of about 2 keV
and suggest that a western region at ~16' from the cluster center is relatively
hotter. As for the Fe abundance, a significant decline with radius is detected
from 0.44 solar at the center to ~0.1 solar at a 50' offset region. If observed
Fe-K line intensity within 4' from the center is suppressed by a factor of 2
due to the resonance scattering effect, the corrected Fe mass density follows
the galaxy distribution. Finally, our results do not support the large-scale
velocity gradients previously reported from the same GIS data.


title:
Warm gas in central regions of nearby galaxies. Extended mapping of
  CO(3-2) emission

abstract:
  We have mapped the CO(3-2) line emission from several nearby galaxies, using
the Heinrich-Hertz-Telescope. Our investigation includes twelve galaxies of
various types and in different stages of star forming activity.
  The main results of this CO(3-2) survey are: 1. In none of the observed
objects the emission is confined to the nucleus, as claimed in some earlier
publications. CO(3-2) emission can be detected for some objects to the same
extent as the CO(2-1) and the CO(1-0) lines. 2. The emission is more
concentrated to the vicinity of star forming structures than the lower CO
transitions. This is shown by decreasing line ratios from the very centres
towards larger radii. 3. The CO(3-2) luminosity is stronger in objects that
contain a nuclear starburst or morphological peculiarities. 4. The line ratios
seem to be independent of Hubble type, color or luminosity. Most galaxies with
enhanced central star formation show line ratios of ~1.3 in the very centre and
\~1.0 at a radius of about 1kpc. Objects with a ring-like molecular gas
distribution or normal galaxies show lower ratios. 5. Starburst galaxies show
CO(3-2) emission also in their disks. The line intensities there are higher
than that of normal galaxies.


title:
New rest wavelength determinations for 7 mid-infrared fine structure
  lines by ISO-SWS

abstract:
  Observations of the planetary nebulae NGC6302, NGC6543 and NGC7027 by the
Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory
(ISO) have been used to determine rest wavelengths of spectral lines. We report
on improved accuracies for wavelengths of 7 mid-infrared ionic fine structure
lines.


title: A catalogue of IJK photometry of Planetary Nebulae with DENIS

abstract:
  Near-infrared photometry of planetary nebulae (PNe) allows the classification
of those objects. We present the largest homogeneous sample so far, obtained
with the Deep Near Infrared Southern Sky Survey (DENIS).


title: On the estimation of the current value of the cosmological constant

abstract:
  We advance the viewpoint that only relevant modes of the vacuum fluctuations,
namely, with wavelengths conditioned by the size, homogeneity, geometry and
topology of the Universe, do contribute into the cosmological constant. A
formula is derived which relates the cosmological constant with the size of the
Universe and the three fundamental constants: the velocity of light, Planck and
Newton gravitational constants. Then the current value of the cosmological
constant remarkably agrees with the value indicated by distant supernovae
observations, i.e. is of the order of the critical density. Thus the
cosmological constant had to be smaller than the matter density in the past and
will be bigger in the future.


title: The Progenitors of Subluminous Type Ia Supernovae

abstract:
  We find that spectroscopically peculiar subluminous SNe Ia come from an old
population. Of the sixteen subluminous SNe Ia known, ten are found in E/S0
galaxies, and the remainder are found in early-type spirals. The probability
that this is a chance occurrence is only 0.2%. The finding that subluminous SNe
Ia are associated with an older stellar population indicates that for a
sufficiently large lookback time (already accessible in current high redshift
searches) they will not be found. Due to a scarcity in old populations,
hydrogen and helium main sequence stars and He red giant stars that undergo
Roche lobe overflow are unlikely to be the progenitors of subluminous SNe Ia.
Earlier findings that overluminous SNe Ia (dM15(B) < 0.95) come from a young
progenitor population are confirmed. The fact that subluminous SNe Ia and
overluminous SNe Ia come from different progenitor populations and also have
different properties is a prediction of the CO white dwarf merger progenitor
scenario.


title:
Day-Scale Variability of 3C 279 and Searches for Correlations in
  Gamma-Ray, X-Ray, and Optical Bands

abstract:
  Light curves of 3C 279 are presented in optical (R-band), X-rays (RXTE/PCA),
and gamma rays (CGRO/EGRET) for 1999 Jan-Feb and 2000 Jan-Mar. During both of
those epochs the gamma-ray levels were high, and all three observed bands
demonstrated substantial variation, on time scales as short as one day.
Correlation analyses provided no consistent pattern, although a rather
significant optical/gamma-ray correlation was seen in 1999, with a gamma-ray
lag of ~2.5 days, and there are other suggestions of correlations in the light
curves. For comparison, correlation analysis is also presented for the
gamma-ray and X-ray light curves during the large gamma ray flare in 1996 Feb
and the two gamma-bright weeks leading up to it; the correlation at that time
was strong, with a gamma-ray/X-ray offset of no more than 1 day.


title:
Probing the Core Structure of Dark Halos with Tangential and Radial Arc
  Statistics

abstract:
  We study the arc statistics of gravitational lensing generated by dark matter
halos in order to probe their density profile. We characterize the halo profile
by two parameters, the inner slope of the central cusp $\alpha$, and the median
amplitude of the concentration parameter, $c_{\rm norm}$, for a halo of mass
$10^{14}h^{-1}M_\odot$ at $z=0$, and compute the numbers of tangential and
radial arcs produced by gravitational lensing of galaxy clusters. We find that
the number of arcs divided by the number of halos is a good statistic which is
sensitive to both $c_{\rm norm}$ and $\alpha$ with very weak dependence on the
cosmological parameters. If the arc samples with well-defined selection
criteria for the clusters become available, one can strongly constrain both
$c_{\rm norm}$ and $\alpha$. While our tentative comparison with the existing
observational data indicates that the inner density profile of dark halos is
indeed as steep as predicted by recent simulations ($\alpha \sim 1.5$), the
homogeneous samples of tangential and radial arcs are required for more
quantitative discussions.


title: Gas-phase H2O and CO2 toward massive protostars

abstract:
  We present a study of gas-phase H2O and CO2 toward a sample of 14 massive
protostars with the Short Wavelength Spectrometer (SWS) on board the Infrared
Space Observatory (ISO). Modeling of the H2O spectra using a homogeneous model
with a constant excitation temperature T_ex shows that the H2O abundances
increase with temperature, up to a few times 10^-5 with respect to H2 for the
hottest sources (T_ex ~500 K). This is still a factor of 10 lower than the H2O
ice abundances observed toward cold sources in which evaporation is not
significant (Keane et al. 2001). Gas-phase CO2 is not abundant in our sources.
The abundances are nearly constant for T_ex>~100 K at a value of a few times
10^-7, much lower than the solid-state abundances of ~1--3 times 10^-6
(Gerakines et al. 1999). For both H2O and CO2 the gas/solid ratio increases
with temperature, but the increase is much stronger for H2O than for CO2,
suggesting a different type of chemistry. In addition to the homogeneous
models, a power law model has been developed for one of our sources, based on
the physical structure of this region as determined from submillimeter data by
van der Tak et al. (1999). The resulting H2O model spectrum gives a good fit to
the data.


title: Mu- and Tau-Neutrino Spectra Formation in Supernovae

abstract:
  The mu- and tau-neutrinos emitted from a proto-neutron star are produced by
nucleonic bremsstrahlung N + N -> N + N + nu + nu-bar and pair annihilation e^+
+ e^- -> nu + nu-bar, reactions which freeze out at the "energy sphere." Before
escaping from there to infinity the neutrinos diffuse through the "scattering
atmosphere," a layer where their main interaction is elastic scattering on
nucleons nu + N -> N + nu. If these collisions are taken to be iso-energetic as
in all numerical supernova simulations, the neutrino flux spectrum escaping to
infinity depends only on the medium temperature T_ES and the thermally averaged
optical depth tau_ES at the energy sphere. For tau_ES = 10-50 one finds for the
spectral flux temperature of the escaping neutrinos T_flux = 0.5-0.6 T_ES.
Including energy exchange (nucleon recoil) in nu + N -> N + nu can shift T_flux
both up or down. Delta T_flux depends on tau_ES, on the scattering atmosphere's
temperature profile, and on T_ES. Based on a numerical study we find that for
typical conditions Delta T_flux/T_flux is between -10% and -20%, and even for
extreme parameter choices does not exceed -30%. The exact value of Delta
T_flux/T_flux is surprisingly insensitive to the assumed value of the nucleon
mass, i.e. the exact efficiency of energy transfer between neutrinos and
nucleons is not important as long as it can occur at all. Therefore,
calculating the nu_mu and nu_tau spectra does not seem to require a precise
knowledge of the nuclear medium's dynamical structure functions.


title: The loss-cone problem in dense nuclei

abstract:
  We address the classical problem of star accretion onto a supermassive
central gaseous object in a galactic nucleus. The resulting supermassive
central gas-star object is assumed to be located at the centre of a dense
stellar system for which we use a simplified model consisting of a Plummer
model with an embedded density cusp using stellar point masses. From the number
of stars belonging to the loss-cone, which plunge onto the central object on
elongated orbits from outside, we estimate the accretion rate taking into
account a possible anisotropy of the surrounding stellar distribution. The
total heating rate in the supermassive star due to the loss-cone stars plunging
onto it is estimated. This semi-analytical study, revisiting and expanding
classical paper's work, is a starting point of future work on a more detailed
study of early evolutionary phases of galactic nuclei.
  It merits closer examination, because it is one of the key features for the
link between cosmology and galaxy formation.


title:
The 2dF Galaxy Redshift Survey: The power spectrum and the matter
  content of the universe

abstract:
  The 2dF Galaxy Redshift Survey has now measured in excess of 160000 galaxy
redshifts. This paper presents the power spectrum of the galaxy distribution,
calculated using a direct FFT-based technique. We argue that, within the
k-space region 0.02<k<0.15 h Mpc^-1, the shape of this spectrum should be close
to that of the linear density perturbations convolved with the window function
of the survey. This window function and its convolving effect on the power
spectrum estimate are analyzed in detail. By convolving model spectra, we are
able to fit the power-spectrum data and provide a measure of the matter content
of the universe. Our results show that models containing baryon oscillations
are mildly preferred over featureless power spectra. Analysis of the data
yields 68% confidence limits on the total matter density times the Hubble
parameter \Omega_m h = 0.20 +/- 0.03, and the baryon fraction \Omega_b/\Omega_m
= 0.15 +/- 0.07, assuming scale-invariant primordial fluctuations.


title: Viability of primordial black holes as short period gamma-ray bursts

abstract:
  It has been proposed that the short period gamma-ray bursts, which occur at a
rate of $\sim 10 {\rm yr^{-1}}$, may be evaporating primordial black holes
(PBHs). Calculations of the present PBH evaporation rate have traditionally
assumed that the PBH mass function varies as $M_{{\rm BH}}^{-5/2}$. This mass
function only arises if the density perturbations from which the PBHs form have
a scale invariant power spectrum. It is now known that for a scale invariant
power spectrum, normalised to COBE on large scales, the PBH density is
completely negligible, so that this mass function is cosmologically irrelevant.
For non-scale-invariant power spectra, if all PBHs which form at given epoch
have a fixed mass then the PBH mass function is sharply peaked around that
mass, whilst if the PBH mass depends on the size of the density perturbation
from which it forms, as is expected when critical phenomena are taken into
account, then the PBH mass function will be far broader than $ M_{{\rm
BH}}^{-5/2}$. In this paper we calculate the present day PBH evaporation rate,
using constraints from the diffuse gamma-ray background, for both of these mass
functions. If the PBH mass function has significant finite width, as recent
numerical simulations suggest, then it is not possible to produce a present day
PBH evaporation rate comparable with the observed short period gamma-ray burst
rate. This could also have implications for other attempts to detect
evaporating PBHs.


title: Population Synthesis of Pulsars: Magnetic Field Effects

abstract:
  New results based on methods of population synthesis, concerning magnetic
field effects on the evolution of pulsars are reported. The present study
confirms that models with timescales for the magnetic field decay longer than
the pulsar lifetime are in better agreement with data. These new simulations
indicate that the diagram log($P\dot P$) - log($t_s$) alone cannot be used to
test field decay models. The dispersion of the values of the initial period and
magnetic field can explain the observed behaviour of the data points in such a
diagram. The simulations also indicate that the statistical properties of
anomalous X-ray pulsars and soft-gamma repeaters (magnetar candidates) are
compatible with those derived for objects born in the high side tail of the
magnetic field distribution. The predicted birth rate of neutron stars having
field strengths in excess of 10$^{14}$ G is one object born each 750 yr.


title:
A search for signatures of quasar evolution: Comparison of the shapes of
  the rest-frame optical/UV continua of quasars at z>3 and z~0.1

abstract:
  For 15 bright (V<17.5), high redshift (z>3) quasars, we have obtained IR
spectra and photometry, and optical spectrophotometry and photometry, which we
use to construct their rest-frame 1285-5100 AA spectral energy distributions
(SEDs). High resolution spectroscopy for 7 and L' detections of 4 extend their
SEDs shortwards of Ly_alpha or redwards of 7500 AA. The average luminosities
within a set of narrow, line-free, windows are computed. Power law fits to
those from 1285 to 5100 AA, but excluding the 2000-4000 AA region of the
FeII+BaC `small bump', adequately characterize the continuum shapes of most of
the objects and yield optical/UV spectral indices (aouv: fnu ~ nu^{aouv}).
  To look for signs of evolution, we compare the distribution of the aouv for
the z>3 quasars with that for a set of 27 z~0.1 quasars which are matched to
the high redshift(z) ones in evolved luminosity. The mean (median) aouv for the
high and low z samples are -0.32(-0.29) and -0.38(-0.40), respectively. Neither
the distributions nor means differ significantly. The distributions of aouv for
both samples span a wide range however, with Delta~1, which could be understood
as the result of both a diversity in the emitted continua themselves and in the
amounts of intrinsic extinction undergone.
  A clear difference between the high and low z samples occurs in the region of
`small bump'. The power law fit residuals for the low z sample show a
systematic excess from 2200-3000 AA ; this feature is weak or absent in the
high z sample. Further study is needed, but the `small bump' evolution could
reflect differences in iron abundance or FeII energy source, or alternatively,
an intrinsic turnover in the continuum itself which is present at low but not
at high z. (Abridged)


title:
Fe K_alpha line: A tool to probe massive binary black holes in Active
  Galactic Nuclei?

abstract:
  Hierarchical mergers of galaxies can form binary black holes (BBHs) since
many or most galaxies have central massive black holes (BHs). It is possible
that some BBHs exist in active galactic nuclei (AGNs). We argue that each BH
may be surrounded by an accretion disc with a different inclination angle to
the line of sight (due to different BH spin directions and the
Bardeen-Petterson effect). The observed Fe K_alpha line profile from a BBH
system is a combination of the lines from the inner regions of the two discs,
which is significantly affected by the inclination angles of the two discs. The
Fe K_alpha line profile associated with BBHs may have an unusual shape with
double or more peaks as well as short-term variability, which can be
distinguished from the Fe K_alpha line properties of some other possible
models. We suggest that with the improvement of resolution in X-ray astronomy,
Fe K_alpha line profiles be a potential tool to probe the existence of massive
BBHs in AGNs. The Fe K_alpha line profile associated with BBHs may also provide
a tool to investigate the dynamics in strong gravitation field (e.g. providing
evidence of the Bardeen-Petterson effect).


title:
The Mass of the Convective Zone in FGK Main Sequence Stars and the
  Effect of Accreted Planetary Material on Apparent Metallicity Determinations

abstract:
  The mass of the outer convective zone in FGK main sequence stars decreases
dramatically with stellar mass. Therefore, any contamination of a star's
atmosphere by accreted planetary material should affect hotter stars much more
than cool stars. If recent suggestions that high metal abundances in stars with
planets are caused by planetesimal accretion are correct, then metallicity
enhancements in earlier-type stars with planets should be very pronounced. No
such trend is seen, however.


title: A Chandra Survey of Broad Absorption Line Quasars

abstract:
  We have carried out a survey with the Chandra X-ray Observatory of a sample
of 10 optically bright broad absorption line (BAL) QSOs. Eight out of ten
sources are detected. The 6 brightest X-ray sources have only high ionization
BALs (hiBALs), while the 4 faintest all show low ionization BALs (loBALs). We
perform a combined spectral fit for hiBAL QSOs to determine the mean spectral
parameters of this sample. We derive an underlying best-fit power-law slope
Gamma=1.8+/-0.35, consistent with the mean slope for radio-quiet quasars from
ASCA, but BALQSOs require a (restframe) absorbing column of 6.5e22, with a
partial covering fraction of 80%. Removing the absorption component from our
best-fit spectral model yields a range of alphaOX from 1.55 to 2.28. All 6
hiBAL QSOs have de-absorbed X-ray emission consistent with non-BAL QSOs of
similar luminosity. The spectral energy distributions of the hiBAL QSOs - both
the underlying power-law slope and alphaOX provide the first conclusive
evidence that BALQSOs have appeared to be X-ray weak because of intrinsic
absorption, and that their underlying emission is consistent with non-BAL QSOs.
By contrast, removal of the best-fit absorption column detected in the hiBAL
QSOs still leaves the 4 loBAL QSOs as unusually X-ray faint for their optical
luminosities.


title: The Energy Distribution of Gamma-Ray Bursts

abstract:
  The distribution of the apparent total energy emitted by a gamma-ray burst
reflects not only the distribution of the energy actually released by the burst
engine, but also the distribution of beaming angles. Using the observed energy
fluences, the detection thresholds and burst redshifts for three burst samples,
I calculate the best-fit parameters for lognormal and power-law distributions
of the apparent total energy. Two of the samples include a small number of
bursts with spectroscopic redshifts, while the third sample has 220 bursts with
redshifts determined by the proposed variability-luminosity correlation. I find
different sets of parameter values for the three burst samples. The Bayesian
odds ratio cannot distinguish between the two model distribution functions for
the two smaller burst samples with spectroscopic redshifts, but does favor the
lognormal distribution for the larger sample with variability-derived
redshifts. The data do not rule out a distribution with a low energy tail which
is currently unobservable. I find that neglecting the burst detection threshold
biases the fitted distribution to be narrower with a higher average value than
the true distribution; this demonstrates the importance of determining and
reporting the effective detection threshold for bursts in a sample.


title: Cosmic Background of Gravitational Waves from Rotating Neutron Stars

abstract:
  The extragalactic background of gravitational waves produced by tri-axial
rotating neutron stars was calculated, under the assumption that the properties
of the underlying pulsar population are the same of those of the galactic
population, recently derived by Regimbau & de Freitas Pacheco (2000). For an
equatorial ellipticity of $\epsilon$ = 10$^{-6}$, the equivalent density
parameter due to gravitational waves has a maximum amplitude in the range
2$\times10^{-11}-3\times10^{-9}$, around 0.9-1.5 kHz. The main reasons
affecting the theoretical predictions are discussed. This background is
comparable to that produced by the ''ring-down'' emission from distorted black
holes. The detection possibility of this background by a future generation of
gravitational antennas is also examined.


title: Thermal structure and cooling of neutron stars with magnetized envelopes

abstract:
  The thermal structure of neutron stars with magnetized envelopes is studied
using modern physics input. The relation between the internal (T_i) and local
surface temperatures is calculated and fitted by analytic expressions for
magnetic field strengths B from 0 to 10^{16} G and arbitrary inclination of the
field lines to the surface. The luminosity of a neutron star with dipole
magnetic field is calculated and fitted as a function of B, T_i, stellar mass
and radius. In addition, we simulate cooling of neutron stars with magnetized
envelopes. In particular, we analyse ultramagnetized envelopes of magnetars and
also the effects of the magnetic field of the Vela pulsar on the determination
of critical temperatures of neutron and proton superfluids in its core.


title:
Chemical Abundances from Inversions of Stellar Spectra: Analysis of
  Solar-Type Stars with Homogeneous and Static Model Atmospheres

abstract:
  Spectra of late-type stars are usually analyzed with static model atmospheres
in local thermodynamic equilibrium (LTE) and a homogeneous plane-parallel or
spherically symmetric geometry. The energy balance requires particular
attention, as two elements which are particularly difficult to model play an
important role: line blanketing and convection. Inversion techniques are able
to bypass the difficulties of a detailed description of the energy balance.
Assuming that the atmosphere is in hydrostatic equilibrium and LTE, it is
possible to constrain its structure from spectroscopic observations. Among the
most serious approximations still implicit in the method is a static and
homogeneous geometry. In this paper, we take advantage of a realistic
three-dimensional radiative hydrodynamical simulation of the solar surface to
check the systematic errors incurred by an inversion assuming a plane-parallel
horizontally-homogeneous atmosphere. The thermal structure recovered resembles
the spatial and time average of the three-dimensional atmosphere. Furthermore,
the abundances retrieved are typically within 10% (0.04 dex) of the abundances
used to construct the simulation. The application to a fairly complete dataset
from the solar spectrum provides further confidence in previous analyses of the
solar composition. There is only a narrow range of one-dimensional thermal
structures able to fit the absorption lines in the spectrum of the Sun. With
our carefully selected dataset, random errors are about a factor of two smaller
than systematic errors. A small number of strong metal lines can provide very
reliable results. We foresee no major difficulty in applying the technique to
other similar stars, and obtaining similar accuracies, using spectra with a
resolving power about 50,000 and a signal-to-noise ratio as low as 30.


title:
Circumnuclear obscuration of the Circinus galaxy by a
  starburst-radiation supported wall

abstract:
  We consider the radiation-hydrodynamical formation of a dusty wall in the
circumnuclear regions of the Circinus Seyfert 2 galaxy. We focus on the
radiative flux force due to the circumnuclear starburst, the nuclear starburst
and the active galactic nucleus (AGN), and analyze the equilibrium
configuration and stability of the dusty gas in the circumnuclear regions. The
mass distributions used to model the gravitational fields are determined by the
observed rotation velocities of the stars and of the gas. Moreover, by using
the simple stellar evolution in the circumnuclear starburst, the bolometric
luminosity of the starburst is estimated as a function of time. As a result, it
is shown that the radiation force by the circumnuclear starburst does play an
important role to build up a radiatively-supported dusty wall of $\la$ 100 pc,
which obscures the circumnuclear regions with $A_V$ of a few magnitudes. It is
also found that the age of a circumnuclear starburst when the circumnuclear
regions are enshrouded by the dusty wall is constrained to be $\la 10^8$ yr,
which is consistent with the age observationally inferred for the starburst, $4
10^7$ yr $-1.5 10^8$ yr.


title: Detection of new sources of 4765-MHz OH masing

abstract:
  We have used the Australia Telescope Compact Array (ATCA) to make a sensitive
search for maser emission from the 4765-MHz transition of OH towards a sample
of 55 star formation regions. Maser emission with peak flux densities in excess
of 100 mJy were detected in 14 sites, with 10 of these being new discoveries.
Unlike the ground-state OH transitions the 4765-MHz transition is not predicted
to be circularly polarised and none of the masers observed have detectable
levels of linear, or circular polarisation. Combining our results with those of
previous high resolution observations of other OH transitions we are able to
investigate various theoretical models for the pumping of OH masers.


title: Nonthermal Phenomena in Clusters of Galaxies

abstract:
  Recent observations of high energy (> 20 keV) X-ray emission in a few
clusters extend and broaden our knowledge of physical phenomena in the
intracluster space. This emission is likely to be nonthermal, probably
resulting from Compton scattering of relativistic electrons by the cosmic
microwave background radiation. Direct evidence for the presence of
relativistic electrons in some 30 clusters comes from measurements of extended
radio emission in their central regions. I first review the results from RXTE
and BeppoSAX measurements of a small sample of clusters, and then discuss their
implications on the mean values of intracluster magnetic fields and
relativistic electron energy densities. Implications on the origin of the
fields and electrons are briefly considered.


title: The visible environment of galaxies with counterrotation

abstract:
  In this paper we present a statistical study of the environments of 49
galaxies in which there is gas- or stellar- counterrotation. The number of
possible companions in the field (to apparent magnitude 22), their size and
concentration were considered. All the statistical parameters were analysed by
means of Kolgomorov-Smirnov tests, using a control sample of 43 galaxies
without counterrotation. From our data, no significant differences between the
counter-rotating and control samples appear. This is different to Seyfert or
radio-loud galaxies which lie in environments with a higher density of
companions. On the contrary, if a weak tendency exists, for galaxies with gas
counterrotation only, it is discovered in regions of space where the large
scale density of galaxies is smaller. Our results tend to disprove the
hypothesis that counterrotation and polar rings derive from a recent
interaction with a small satellite or a galaxy of similar size. To a first
approximation, they seem to follow the idea that all galaxies are born through
a merger process of smaller objects occurring very early in their life, or that
they derive from a continuous, non-traumatic infall of gas that formed stars
later. Whatever the special machinery is which produces counterrotation or
polar rings instead of a co-planar, co-rotating distribution of gas and stars,
it seems not to be connected to the present galaxy density of their
environments.