title: Cooling Radiation and the Lyman-alpha Luminosity of Forming Galaxies

abstract:
  We examine the cooling radiation from forming galaxies in hydrodynamic
simulations of the LCDM model (cold dark matter with a cosmological constant),
focusing on the Ly-alpha line luminosities of high-redshift systems. Primordial
composition gas condenses within dark matter potential wells, forming objects
with masses and sizes comparable to the luminous regions of observed galaxies.
As expected, the energy radiated in this process is comparable to the
gravitational binding energy of the baryons, and the total cooling luminosity
of the galaxy population peaks at z ~= 2. However, in contrast to the classical
picture of gas cooling from the \sim 10^6 K virial temperature of a typical
dark matter halo, we find that most of the cooling radiation is emitted by gas
with T < 20,000 K. As a consequence, roughly 50% of this cooling radiation
emerges in the Ly-alpha line. While a galaxy's cooling luminosity is usually
smaller than the ionizing continuum luminosity of its young stars, the two are
comparable in the most massive systems, and the cooling radiation is produced
at larger radii, where the Ly-alpha photons are less likely to be extinguished
by dust. We suggest, in particular, that cooling radiation could explain the
two large (\sim 100 kpc), luminous (L_{Ly-alpha} \sim 10^{44} erg s^{-1})
``blobs'' of Ly-alpha emission found in Steidel et al.'s (1999) narrow band
survey of a z = 3 proto-cluster. Our simulations predict objects of the
observed luminosity at about the right space density, and radiative transfer
effects can account for the observed sizes and line widths. We discuss
observable tests of this hypothesis for the nature of the Ly-alpha blobs, and
we present predictions for the contribution of cooling radiation to the
Ly-alpha luminosity function of galaxies as a function of redshift.


title:
Newtonian hydrodynamics of the coalescence of black holes with neutron
  stars III: Irrotational binaries with a stiff equation of state

abstract:
  We present a hydrodynamical study of the final stages of inspiral in a black
hole-neutron star (NS) binary. We use a Newtonian 3D SPH code, and model the NS
with a stiff (index G=3 and G=2.5) polytropic equation of state and the black
hole as a Newtonian point mass. Our initial conditions correspond to
irrotational binaries in equilibrium (approximating the NS as a compressible
ellipsoid), and we have explored configurations with different initial mass
ratios, 0.2< q=M_ns/M_bh<0.5. The dynamical evolution is followed for ~23ms. We
include gravitational radiation losses in the quadrupole approximation for a
point-mass binary. For G=3, after an initial episode of mass transfer, the NS
is not completely disrupted and a remnant core remains in orbit about the black
hole. For G=2.5 the disruption is more complex, with the NS being totally
disrupted during a second periastron passage. The accretion disc formed around
the black hole contains ~0.2 solar masses. A nearly baryon-free axis is always
present in the system, and only modest beaming of a relativistic fireball that
could give rise to a GRB would be sufficient to avoid baryon contamination.
Around 0.01 solar masses may be dynamically ejected from the system, and could
contribute substantially to the amount of observed galactic r-process material.
We calculate the gravitational radiation waveforms in the quadrupole
approximation. We also present the results of simulations that have used
spherical NSs relaxed in isolation as initial conditions, in order to gauge the
effect of using non-equilibrium initial conditions on the coalescence.


title: Testing the AGN models for the X-ray background

abstract:
  We will briefly examine the following three issues related to the AGN
synthesis models for X-ray background: 1) the possibility that absorbed AGNs
evolve faster than unabsorbed ones; 2) the existence of the still debated
population of luminous absorbed AGNs, the so-called QSO2s; 3) the behavior of
the AGN density at a redshift above ~3.


title:
Multiwavelength observations of clusters of galaxies and the role of
  cluster mergers

abstract:
  Some clusters of galaxies have been identified as powerful sources of
non-thermal radiation, from the radio to X-ray wavelengths. The classical
models proposed for the explanation of this radiation usually require large
energy densities in cosmic rays in the intracluster medium and magnetic fields
much lower that those measured using the Faraday rotation. We study here the
role that mergers of clusters of galaxies may play in the generation of the
non-thermal radiation, and we seek for additional observable consequences of
the model. We find that if hard X-rays and radio radiation are respectively
interpreted as inverse Compton scattering (ICS) and synchrotron emission of
relativistic electrons, large gamma ray fluxes are produced, and for the Coma
cluster, where upper limits are available, these limits are exceeded. We also
discuss an alternative and testable model that naturally solves the problems
mentioned above.


title: Opening the ultra high energy cosmic ray window from the top

abstract:
  While several arguments can be proposed against the existence of particles
with energy in excess of $(3-5)\times 10^{19}$ eV in the cosmic ray spectrum,
these particles are actually observed and their origin seeks for an
explanation. After a description of the problems encountered in explaining
these ultra-high energy cosmic rays (UHECRs) in the context of astrophysical
sources, we will review the so-called {\it Top-Down} (TD) Models, in which
UHECRs are the result of the decay of very massive unstable particles, possibly
created in the Early Universe. Particular emphasis will be given to the
signatures of the TD models, likely to be accessible to upcoming experiments
like Auger.


title:
The Shapley Supercluster. II. Spectroscopic observations in a wide area
  and general morphology

abstract:
  We report 2868 new multi-object spectroscopic measurements of galaxy
redshifts in an area roughly 12\deg$\times$ 6\deg (right ascension $\times$
declination) centered on the Shapley Supercluster (SSC). These correspond to
2627 different galaxies. Including other measurements reported in the
literature, the total number of galaxies with measured redshifts in a
19\deg$\times$ 16\deg area centered on the supercluster now reaches 5090. Of
these, 2949 lie in the redshift range 9,000 - 18,000 km s$^{-1}$, which we
tentatively identify with the SSC. This unprecedented sample allows a quite
detailed qualitative morphological study of the SSC. Based on the
three-dimensional distribution of galaxies and clusters of galaxies, we
identify several sub-condensations of the supercluster, as well as walls and
filaments connecting them. We also find another supercluster in the background,
at redshift $\sim$ 23,000 km s$^{-1}$.


title:
The Shapley Supercluster. III. Collapse dynamics and mass of the central
  concentration

abstract:
  We present the first application of a spherical collapse model to a
supercluster of galaxies. Positions and redshifts of $\sim 3000$ galaxies in
the Shapley Supercluster (SSC) are used to define velocity caustics that limit
the gravitationally collapsing structure in its central part. This is found to
extend at least to $8 h^{-1}$ Mpc of the central cluster, A 3558, enclosing 11
ACO clusters. Infall velocities reach $\sim 2000$ km s$^{-1}$. Dynamical models
of the collapsing region are used to estimate its mass profile. An upper bound
on the mass, based on a pure spherical infall model, gives $M(<8 h^{-1}{\rm
Mpc}) ^{<}_{\sim} 1.3\times 10^{16}h^{-1}M_\odot$ for an Einstein-de Sitter
(critical) Universe and $M(<8 h^{-1}{\rm Mpc}) ^{<}_{\sim} 8.5\times
10^{15}h^{-1}M_\odot$ for an empty Universe. The model of Diaferio & Geller
(1997), based on estimating the escape velocity, gives a significantly lower
value, $M(<8 h^{-1}{\rm Mpc})\approx 2.1\times 10^{15}h^{-1}M_\odot$, very
similar to the mass found around the Coma cluster by the same method (Geller et
al. 1999), and comparable to or slightly lower than the dynamical mass in the
virialized regions of clusters enclosed in the same region of the SSC. In both
models, the overdensity in this region is substantial, but far from the value
required to account for the peculiar motion of the Local Group with respect to
the cosmic microwave background.


title: Asymmetric Beams in Cosmic Microwave Background Anisotropy Experiments

abstract:
  We propose a new formalism to handle asymmetric beams in the data analysis of
cosmic microwave background anisotropy experiments. For any beam shape, the
formalism finds the optimal circularly symmetric equivalent and is thus easily
adaptable to existing data analysis methods. We demonstrate certain key points
by using a simulated highly elliptic beam, and the beams and data of the
MAXIMA-1 experiment, where the asymmetry is mild. In particular, we show that
in both cases the formalism does not bias the angular power spectrum estimates.
We analyze the limitations of the formalism and find that it is well suited for
most practical situations.


title: Inter-Scale Correlations as Measures of CMB Gaussianity

abstract:
  A description of CMB temperature fluctuations beyond the power spectrum is
important for verifying models of structure formation, especially in view of
forthcoming high-resolution observations. We argue that higher-order statistics
of inter-scale correlations, because of their low cosmic variance, may be
effective in detecting non-Gaussian features in the CMB. Inter-scale
correlations are generically produced in defect-based models of structure
formation. We analytically study properties of general higher-order cumulants
of Fourier components of homogeneous random fields and design a new set of
statistics suitable for small-scale data analysis. Using simulated non-Gaussian
fields, we investigate the performance of the proposed statistics in presence
of a Gaussian background and pixel noise, using the bispectrum as the
underlying cumulant. Our numerical results suggest that detection of
non-Gaussian features by our method is reliable if the power spectrum of the
non-Gaussian components dominates that of the Gaussian background and noise
within at least a certain range of accessible scales.


title: Primordial Spectrum of Gauge Fields from Inflation

abstract:
  We show that conformal invariance of gauge fields is naturally broken in
inflation, having as a consequence amplification of gauge fields. The resulting
spectrum of the field strength is approximately B_L ~ L^(-1), where L is the
relevant coherence scale. One realisation of our scenario is scalar
electrodynamics with a scalar whose mass is large enough to evade observational
constraints - the obvious candidates being supersymmetric partners of the
standard-model fermions. Our mechanism also leads naturally to amplification of
the standard-model Z-boson field due to its coupling to the electroweak Higgs
field. At preheating, the spectrum of the Z field is transferred to the
hypercharge field, which remains frozen in the plasma and is converted into a
magnetic field at the electroweak phase transition. With a reasonable model of
field evolution one obtains a magnetic field strength of the order of
$10^{-29}$ Gauss on a scale of 100 pc, the size of the largest turbulent eddy
in a virialised galaxy. Resonant amplification in preheating can lead to
primordial fields as large as $10^{-24}$ Gauss, consistent with the seed field
required for the galactic dynamo mechanism.


title:
Effect of the Environment on the Fundamental Plane of Elliptical
  Galaxies

abstract:
  We present an analysis of interacting E/S0 galaxies location on the
Fundamental Plane. Using the NEMO package, we performed N-body simulations of
close encounters and mergers between two spherical galaxies. We followed how
structural and dynamical parameters (central density, half-mass radius and
velocity dispersion)of galaxies are changed during the encounter. We analysed
the dependence of these changes on initial mass concentration and presence of
dark halo. The results of our simulations are used to discuss the Fundamental
Plane for interacting early-type galaxies.


title: A Sensitive Search for Methane in the Infrared Spectrum of Tau Bootis

abstract:
  We have searched for a methane signature in the infrared spectrum of tau
Bootis, produced by the planetary companion. The observations comprise 598
low-noise, high resolution spectra near 3.28 microns, which we analyze by
cross-correlating with a modeled planetary spectrum based on the work of
Burrows and Sharp (1999), and Sudarsky et al. (2000). The 3-sigma random noise
level of our analysis is 0.00006 stellar continuum flux units, and the
confusion noise limit - measuring the resemblence of a cross-correlation
feature to the spectrum of methane - is 0.00025.
  We find a significant cross-correlation amplitude of 0.00033 continuum units
at a velocity near that of the star. This is likely due to methane from a
low-mass companion in a long-period orbit. Fischer, Butler and Marcy (2000)
report a long-term velocity drift indicative of such a companion. But the
system is known to be a visual binary with an eccentric orbit, and is rapidly
approaching periastron. Whether the visual companion can account for our
observations and the Fischer et al. velocity drift depends on knowing the orbit
more precisely. The stability of planetary orbits in this system also depends
crucially on the properties of the binary orbit. A second cross-correlation
feature, weaker and much more diffuse, has intensity amplitude 0.0002 continuum
units and occurs at a velocity amplitude of 71 +/-10 km/sec, in agreement with
the orbit claimed for the planet by Cameron et al. (1999). Like the first
feature, it has passed several tests designed to reject systematic errors. We
discuss the possibility that this second feature is due to the planet.


title: Baryons in the Warm-Hot Intergalactic Medium

abstract:
  Approximately 30-40% of all baryons in the present day universe reside in a
warm-hot intergalactic medium (WHIM), with temperatures between 10^5<T<10^7 K.
This is a generic prediction from six hydrodynamic simulations of currently
favored structure formation models having a wide variety of numerical methods,
input physics, volumes, and spatial resolutions. Most of these warm-hot baryons
reside in diffuse large-scale structures with a median overdensity around
10-30, not in virialized objects such as galaxy groups or galactic halos. The
evolution of the WHIM is primarily driven by shock heating from gravitational
perturbations breaking on mildly nonlinear, non-equilibrium structures such as
filaments. Supernova feedback energy and radiative cooling play lesser roles in
its evolution. WHIM gas is consistent with observations of the 0.25 keV X-ray
background without being significantly heated by non-gravitational processes
because the emitting gas is very diffuse. Our results confirm and extend
previous work by Cen & Ostriker and Dave' et al.


title: The First Acoustics Peak CMBR and Cosmic Total Density

abstract:
  Boomerang measured the first peak in CMBR to be at location of $l_D=196\pm
6$, which excites our strong interesting in it. A widely cited formula is
$l_D\simeq 200\Omega_T^{-0.50}$ to estimate the cosmic total density. Weinberg
shows it is not correct and should be $l_D\propto \Omega_T^{-1.58}$ near the
interest point $(\Omega_m,\Omega_\Lambda)=(0.3,0.7)$. We show further that it
should be $l_D\propto \Omega_T^{-1.43}\Omega_m^{-0.147}$ or
$\Omega_T^{-1.92}\Omega_\Lambda^{0.343}$ near the same point in the more
veracious sense if we consider the effect from the sound horizon. We draw a
contour graph for the peak location, show that the recent data favor to a
closed universe with about $\Omega_T\simeq 1.03$. If we insist on obtaining a
flat universe, a point $(0.36,0.64)$, i.e., more matter and less vacuum energy,
is still possible, which has a more right-side first peak $l_D=208$ in CMBR and
a smaller acceleration parameter $-q_0=0.10$ for the $z=0.4$ redshift SNIa.


title: The cluster environments of powerful radio-loud and radio-quiet AGN

abstract:
  The spatial clustering amplitude (B_{gq}) is determined for a sample of 44
powerful AGN at z~0.2. No significant difference is detected in the richness of
the cluster environments of the radio-loud and radio-quiet sub-samples, both of
which typically inhabit environments as rich as Abell Class ~0. Comparison with
radio luminosity-matched samples from Hill & Lilly (1991) and Wold et al.
(2000a) suggests that there is no epoch-dependent change in environment
richness out to at least z>=0.5 for either radio galaxies or radio quasars.
Comparison with the APM cluster survey shows that, contrary to current
folklore, powerful AGN do not avoid rich clusters, but rather display a spread
in cluster environment which is perfectly consistent with being drawn at random
from the massive elliptical population. Finally, we argue that virtually all
Abell class ~0 clusters contained an active galaxy during the epoch of peak
quasar activity at z~2.5.


title: Deep Optical Imaging of A Compact Group of Galaxies, Seyfert's Sextet

abstract:
  In order to investigate the dynamical status of Seyfert's Sextet (SS), we
have obtained a deep optical ($VR+I$) image of this group. Our image shows that
a faint envelope, down to a surface brightness $\mu_{\rm optical}$(AB) $\simeq
27$ mag arcsec$^{-2}$, surrounds the member galaxies. This envelope is
irregular in shape. It is likely that this shape is attributed either to
recent-past or to on-going galaxy interactions in SS. If the member galaxies
have experienced a number of mutual interactions over a long timescale, the
shape of the envelope should be rounder. Therefore, the irregular-shaped
morphology suggests that SS is in an early phase of dynamical interaction among
the member galaxies. It is interesting to note that the soft X-ray image
obtained with ROSAT (Pildis et al. 1995) is significantly similar in
morphology. We discuss the possible future evolution of SS briefly.


title: On the Origin of the Rotation Curves of Dark-Matter-Dominated Galaxies

abstract:
  Rotation curves of dark-matter-dominated galaxies measure the mass profiles
of galactic halos and thereby test theories of their cosmological origin. While
attention has focused lately on the possible discrepancy at small
galactocentric radii between observed rotation curves and the singular density
profiles predicted by N-body simulations of the Cold Dark Matter (CDM) model,
the observed rotation curves nevertheless contain valuable additional
information with which to test the theory and constrain the fundamental
cosmological parameters, despite this uncertainty at small radii.
  An analytical model we derived elsewhere for the postcollapse equilibrium of
cosmological halos as truncated, nonsingular, isothermal spheres (TIS)
reproduces many of the average properties of halos in CDM simulations to good
accuracy, including the density profiles outside the central region. The
circular velocity profile of this TIS model is, moreover, in excellent
agreement with the observed ones and yields the mass and formation epoch of an
observed halo from the parameters of its rotation curve. This allows us to
predict correlations amongst rotation curve parameters, such as the maximum
velocity and the radius at which it occurs, for different mass halos forming at
different epochs in the CDM model. As an example, we derive the observed
v_max-r_max relation analytically, with preference for the flat Lambda-CDM
model.


title: A Spectroscopic Analysis of the Energetic Type Ic `Hypernova' SN 1997ef

abstract:
  The properties of the bright and energetic Type Ic SN 1997ef are investigated
using a Monte Carlo spectrum synthesis code. Analysis of the earliest spectra
is used to determine the time of outburst. The changing features of the
spectrum and the light curve are used to probe the ejecta and to determine
their composition, verifying the results of explosion calculations. Since
synthetic spectra computed using our best explosion model CO100 are only
moderately good reproductions of the observations, the inverse approach is
adopted, and a density structure is derived by demanding that it gives the best
possible fit to the observed spectrum at every epoch analysed. It is found that
the density structure of model CO100 is adequate at intermediate velocities
(5000--25000 km/s), but that a slower density decline ($\rho \propto r^{-4}$)
is required to obtain the extensive line blending at high velocities
(25000--50000 km/s). The `best fit' density distribution results in somewhat
different parameters for the SN, namely an ejecta mass of 9.6$M_\odot$ and an
explosion kinetic energy of 1.75 x 10^{52} erg. The modified density structure
is used to compute a synthetic light curve, which is found to agree very well
with the observed bolometric light curve around maximum. The amount of
radioactive $^{56}$Ni produced by the SN is confirmed at 0.13$M_\odot$. In the
context of an axisymmetric explosion, a somewhat smaller kinetic energy than
that of SN 1998bw may have resulted from the non alignment of the symmetry axis
of the SN and the line of sight. This might also explain the lack of evidence
for a Gamma Ray Burst correlated with SN 1997ef.


title: Molecular hydrogen emission in Cygnus A

abstract:
  We present J, H and K-band spectroscopy of Cygnus A, spanning 1.0-2.4 micron
in the rest-frame and hence several rovibrational H2, H recombination and
[FeII] emission lines. The lines are spatially extended by up to 6kpc from the
nucleus, but their distinct kinematics indicate that the three groups (H, H2
and [FeII]) are not wholly produced in the same gas. The broadest line,
[FeII]1.644, exhibits a non-gaussian profile with a broad base (FWHM=1040
km/s), perhaps due to interaction with the radio source. Extinctions to the
line-emitting regions substantially exceed earlier measurements based on
optical H recombination lines.
  Hard X-rays from the quasar nucleus are likely to dominate the excitation of
the H2 emission. The results of Maloney, Hollenbach and Tielens (1996) are thus
used to infer the total mass of gas in H2 v=1-0 S(1)-emitting clouds as a
function of radius, for gas densities of 10^3 and 10^5 cm^-3, and stopping
column densities N_H=10^22-10^24 cm^-2. Assuming azimuthal symmetry, at least
2.3E8 Msun of such material is present within 5kpc of the nucleus, if the
line-emitting clouds see an unobscured quasar spectrum. Alternatively, if the
bulk of the X-ray absorption to the nucleus inferred by Ueno et al. (1994)
arises in a circumnuclear torus, the implied gas mass rises to 10^10 Msun. The
latter plausibly accounts for 10^9 yr of mass deposition from the cluster
cooling flow, for which Mdot \simeq 10 Msun/yr within this radius.


title: Galaxy clustering in the Herschel deep field

abstract:
  (abridged) We present a study of the angular correlation function as measured
in the William Herschel Deep Field. This field covers 50 arcmin$^2$ and with it
we are able to investigate the scaling of the angular correlation function to
$B\sim28$, $R, I\sim 26$,$K\sim20$ and $H\sim22.5$. We compare our measurements
to results obtained from the smaller Hubble Deep Field. To interpret our
results, we use a model which correctly predicts colours, number counts and
redshift distributions for the faint galaxy population. We find that at fixed
separation the amplitude of $\omega(\theta)$ measured in $BRI$ bandpasses is
lower than the predictions of a model containing with no luminosity evolution
and stable clustering growth in proper co-ordinates. However, in the
near-infrared bandpasses, our measurements are consistent with the predictions
of an essentially non-evolving $K-$ selected galaxy redshift distribution. In
the range $B\sim27-28$ we find that our correlation amplitudes are independent
of magnitude, which is consistent with the observed flattening of the number
count slope and correspondingly slower increase of the cosmological volume
element expected at these magnitudes. Our measurements in all bandpasses are
consistent with a rapid growth of galaxy clustering ($0 < \epsilon < 2 $ in the
normal parametrisation) on the sub-Mpc scales which our survey probes. We
demonstrate that this rapid growth of clustering is consistent with the
predictions of biased models of galaxy formation, which indicate that a rapid
rate of clustering growth is expected for the intrinsically faint galaxies
which dominate our survey.


title: Binary Globular Clusters

abstract:
  The dynamics of a close binary system of globular clusters is considered. It
is shown that the star transfer process from one of the components to the other
should lead to the decrease of dimension of the first cluster with simultaneous
increase of the dimension of the second cluster. The rates of variations of
clusters' sizes due to the mutual tidal interaction between the components, as
well as of the orbital rotation of the binary system on the evolution of
clusters' sizes, are estimated. The results may be attributed to the double
nuclei observed in certain galaxies.


title: Superbox - An Efficient Code for Collisionless Galactic Dynamics

abstract:
  We present Superbox, a particle-mesh code with high resolution sub-grids and
an NGP (nearest grid point) force-calculation scheme based on the second
derivatives of the potential. Superbox implements a fast low-storage
FFT-algorithm, giving the possibility to work with millions of particles on
desk-top computers. Test calculations show energy and angular momentum
conservation to one part in 10^5 per crossing-time. The effects of grid and
numerical relaxation remain negligible, even when these calculations cover a
Hubble-time of evolution. As the sub-grids follow the trajectories of
individual galaxies, the code allows a highly resolved treatment of
interactions in clusters of galaxies, such as high-velocity encounters between
elliptical galaxies and the tidal disruption of dwarf galaxies. Excellent
agreement is obtained in a comparison with a direct-summation N-body code
running on special-purpose Grape3 hardware. The orbital decay of satellite
galaxies due to dynamical friction obtained with Superbox agrees with
Chandrasekhar's treatment when the Coulomb logarithm is approximately 1.5.


title: From kinematics to dynamics in thin galactic disk

abstract:
  We present a method for recovering the distribution functions of edge-on thin
axisymmetric disks directly from their observable kinematic properties. The
most generally observable properties of such a stellar system are the
line-of-sight velocity distributions of the stars at different projected radii
along the galaxy. If the gravitational potential is known, then the general
two-integral distribution function can be reconstructed using the shapes of the
high-velocity tails of these line-of-sight distributions. If the wrong
gravitational potential is adopted, then a distribution function can still be
constructed using this technique, but the low-velocity parts of the observed
velocity distributions will not be reproduced by the derived dynamical model.
Thus, the gravitational potential is also tightly constrained by the observed
kinematics.


title: A strategy for finding gravitationally-lensed distant supernovae

abstract:
  Distant Type Ia and II supernovae (SNe) can serve as valuable probes of the
history of the cosmic expansion and star formation, and provide important
information on their progenitor models. At present, however, there are few
observational constraints on the abundance of SNe at high redshifts. A major
science driver for the Next Generation Space Telescope (NGST) is the study of
such very distant supernovae. In this paper we discuss strategies for finding
and counting distant SNe by using repeat imaging of super-critical intermediate
redshift clusters whose mass distributions are well-constrained via modelling
of strongly-lensed features. For a variety of different models for the star
formation history and supernova progenitors, we estimate the likelihood of
detecting lensed SNe as a function of their redshift. In the case of a survey
conducted with HST, we predict a high probability of seeing a supernova in a
single return visit with either WFPC-2 or ACS, and a much higher probability of
detecting examples with z>1 in the lensed case. Most events would represent
magnified SNe II at z~1, and a fraction will be more distant examples. We
discuss various ways to classify such events using ground-based infrared
photometry. We demonstrate an application of the method using the HST archival
data and discuss the case of a possible event found in the rich cluster AC 114
(z=0.31).


title:
A Search for the Optical/Infrared Counterpart of the Anomalous X-ray
  Pulsar 1E 1841-045

abstract:
  We have carried out a search for the optical and infrared counterpart of the
Anomalous X-ray Pulsar 1E 1841-045, which is located at the center of the
supernova remnant Kes73. We present the first deep optical and infrared images
of the field of 1E 1841-045, as well as optical spectroscopy results that
exclude the brightest objects in the error circle as possible counterparts. A
few of the more reddened objects in this region can be considered as
particularly interesting candidates, in consideration of the distance and
absorption expected from the association with Kes73. The strong interstellar
absorption in the direction of the source does not allow to completely exclude
the presence of main sequence massive companions.


title:
Radio Emission from the Composite Supernova Remnant G326.3-1.8
  (MSH15-56)

abstract:
  High resolution radio observations of the composite supernova remnant (SNR)
G326.3-1.8 or MSH 15-56 with the Australia Telescope Compact Array show details
of both the shell and the bright plerion which is offset about 1/3 of the
distance from the center of the SNR to the shell. The shell appears to be
composed of thin filaments, typical of older shell SNRs. The central part of
the elongated plerion is composed of a bundle of parallel ridges which bulge
out at the ends and form a distinct ring structure on the northwestern end. The
magnetic field with a strength of order 45 microGauss, is directed along the
axis of the ridges but circles around the northwestern ring. This plerion is
large and bright in the radio but is not detected in x-ray or optical
wavelengths. There is, however, a faint hard x-ray feature closer to the shell
outside the plerion. Perhaps if the supernova explosion left a rapidly moving
magnetar with large energy input but initially rapid decay of both relativistic
particles and magnetic field, the observed differences with wavelength could be
explained.


title:
Interstellar Seeing. I. Superresolution Techniques Using Radio
  Scintillation

abstract:
  Interstellar scintillation can be used to probe transverse sizes of radio
sources on scales inaccessible to the nominal resolution of any terrestrial
telescope, e.g. $\lesssim 10^{-6}$ arc sec. Methodology is presented that
exploits this superresolution phenomenon for both single aperture and
interferometer observations. The treatment applies to the saturated
(strong-scattering) regime and holds for both thin screens and extended media.
A general signal model for radio sources is presented, {\it scintillated
amplitude modulated noise}, which applies to compact, incoherent synchrotron
sources such as AGNs and gamma-ray burst sources and also to known, coherent
sources such as masers and pulsars. The exact probability density function for
measured intensities and interferometric visibilities is obtained by solving a
general Fredholm problem. An approximate density function is also obtained by
using the equivalent number of degrees of freedom in scintillation modulations.
The scintillation modulation variance is presented, which includes the effects
of source structure and time-bandwidth averaging in the signal processing. Two
Bayesian methods are outlined for inferring the sizes of emission regions that
use first order statistics of the intensity and visibility. Intensity
cross-correlation methods for inferring source sizes are also given. Intensity
interferometry in the the radio context is compared to the optical intensity
interferometry of Hanbury-Brown and Twiss.


title: Detection of the old stellar component of the major Galactic bar

abstract:
  We present near-IR colour--magnitude diagrams and star counts for a number of
regions along the Galactic plane. It is shown that along the l=27 b=0 line of
sight there is a feature at 5.7 +-0.7kpc with a density of stars at least a
factor two and probably more than a factor five times that of the disc at the
same position. This feature forms a distinct clump on an H vs. J-H diagram and
is seen at all longitudes from the bulge to about l=28, but at no longitude
greater than this. The distance to the feature at l=20 is about 0.5kpc further
than at l=27 and by l=10 it has merged with, or has become, the bulge. Given
that at l=27 and l=21 there is also a clustering of very young stars, the only
component that can reasonably explain what is seen is a bar with half length of
around 4kpc and a position angle of about 43+-7.


title: Interstellar Seeing. II. The Case of the Vela Pulsar: Source Unresolved

abstract:
  I use a method based on interstellar scintillations for discerning
information about source sizes on scales less than one micro-arc sec. I use a
comprehensive model for a pulsar signal, scintillated amplitude modulated
noise, that includes source fluctuations and noise statistics. The method takes
into account time-frequency averaging in the signal processing as well as
effects due to source structure. The method is applied to interferometric
visibility data on the Vela pulsar which show slightly less scintillation
modulation than expected for a point source in the strong scattering regime.
The decreased scintillation modulation is likely to be due exclusively to
time-frequency averaging rather than from any source size effects. The implied
upper limit on source extent, derived through Bayesian inference, is compared
to predictions that take into account beaming from the relativistic plasma flow
in neutron star magnetospheres. The upper limit for the transverse source size
($\lesssim 400$ km at 95% confidence for a pulsar distance of 0.5 kpc) is
easily consistent with conventional models for radio emission regions in pulsar
magnetospheres that place them well inside the light cylinder at only a few
neutron-star radii from the star's surface.


title: Attenuation of Beaming Oscillations Near Neutron Stars

abstract:
  Observations with RXTE have revealed kilohertz quasi-periodic brightness
oscillations (QPOs) from nearly twenty different neutron-star low-mass X-ray
binaries (LMXBs). These frequencies often appear as a pair of kilohertz QPOs in
a given power density spectrum. In many models the higher-frequency of these
QPOs is a beaming oscillation at the frequency of a nearly circular orbit at
some radius near the neutron star. In such models it is expected that there
will also be beaming oscillations at the stellar spin frequency and at
overtones of the orbital frequency, but no strong QPOs have been detected at
these frequencies. We therefore examine the processes that can attenuate
beaming oscillations near neutron stars, and in doing so extend the work on
this subject that was initiated by the discovery of lower-frequency QPOs from
LMXBs. Among our main results are (1)in a spherical scattering cloud, all
overtones of rotationally modulated beaming oscillations are attenuated
strongly, not just the even harmonics, and (2)it is possible to have a
relatively high-amplitude modulation near the star at, e.g., the stellar spin
frequency, even if no peak at that frequency is detectable in a power density
spectrum taken at infinity. We discuss the application of these results to
modeling of kilohertz QPOs.


title:
Low-mass spectroscopic binaries in the Hyades: a candidate brown dwarf
  companion

abstract:
  We have used the HIRES echelle spectrograph in the Keck I telescope to obtain
high-resolution spectroscopy of 51 late-type M dwarfs in the Hyades cluster.
Cross-correlating the calibrated data against spectra of white dwarfs allows us
to determine heliocentric velocities with an accuracy of +/- 0.3 km/s. Twenty
seven stars were observed at two epochs in 1997; two stars, RHy 42 and RHy 403,
are confirmed spectroscopic binaries. RHY 42 is a double-lined, equal-mass
system; RHy 403 is a single-lined, short-period binary, P ~ 1.275 days. RHy
403A has an absolute magnitude of M_I = 10.85, consistent with a mass of 0.15
M(Sun). The systemic mass function has a value of 0.0085, which, combined with
the non-detection of a secondary peak in the cross-correlation function,
implies 0.095 > M_2 > 0.06 M (Sun), and the strong possibility that the
companion is the first Hyades brown dwarf to be identified. Unfortunately, the
maximum expected angular separation in the system is only 0.25 mas. Five other
low-mass Hyads are identified as possible spectroscopic binaries, based either
on repeat observations or comparison between the observed radial velocity and
the value expected for Hyades cluster members. Combined with HST imaging data,
we infer a binary fraction between 23 and 30 . All of the stars are
chromospherically active. RHy 281 was caught in mid-flare and, based on that
detection, we estimate a flaring frequency of 2.5% for low-mass Hyades stars.
Nine stars have rotational velocities, v sin(i), exceeding 20 km/s and most of
the sample have detectable rotation. We examine the H-alpha emission
characteristics of low-mass cluster members and show that there is no evidence
for a correlation with rotation.


title:
Empirical Verification of the Fe II Oscillator Strengths in the FUSE
  Bandpass

abstract:
  We report empirical determinations of atomic oscillator strengths, or
f-values, for 11 ground-state transitions of Fe II in the wavelength range 1050
to 1150 Ang. We use ultraviolet absorption line observations of interstellar
material towards stars in the Galaxy and the Magellanic Clouds taken with
Copernicus, the Goddard High Resolution Spectrograph on-board the Hubble Space
Telescope, and the Far Ultraviolet Spectroscopic Explorer. We derive absolute
oscillator strengths by a combination of the apparent optical depth, component
fitting, and curve-of-growth fitting techniques. Our derived oscillator
strengths are generally in excellent agreement with recent theoretical
calculations by Raassen & Uylings using the orthogonal operator technique.
However, we identify three of the eleven transitions studied here whose
f-values seem to be incompatible with these calculations, by as much as a
factor of two. We suggest revisions to these f-values based upon our analysis.


title:
Compton-Thick X-ray Absorption in the Seyfert Galaxies Tololo 0109-383
  and ESO 138-G1

abstract:
  We present analyses of the ASCA X-ray spectra of two Seyfert galaxies, Tololo
0109-383 and ESO 138-G1. In both cases, spectral fitting reveals two
statistically acceptable continuum models: Compton reflection and partial
covering. Both spectra have strong iron K-alpha lines, with equivalent widths
greater than 1.5 keV. These large equivalent widths are suggestive of heavier
obscuration than that directly indicated by the partial-covering models
(approximately 2 x 10^23 cm^-2), with the actual column densities being
`Compton-thick' (i.e. N_H > 1.5 x 10^24 cm^-2). We use the hard X-ray/[O III]
flux correlation for Seyferts and data from the literature to provide
additional support for this hypothesis. Since Tololo 0109-383 is known to have
optical type 1 characteristics such as broad Balmer line components and Fe II
emission, this result marks it as a notable object.


title:
Spatial Variability in the Ratio of Interstellar Atomic Deuterium to
  Hydrogen. II. Observations toward Gamma2 Velorum and Zeta Puppis by the
  Interstellar Medium Absorption Profile Spectrograph

abstract:
  To measure interstellar atomic deuterium abundances, we used the Interstellar
Medium Absorption Profile Spectrograph (IMAPS) to obtain spectra of gamma2 Vel
and zeta Pup over the wavelength interval 930-1150 A at a resolving power of
80,000. The interstellar D I features are resolved and cleanly separated from
interstellar H I in the Ly-delta and Ly-epsilon profiles of both sight lines,
and also in the Ly-gamma profile of zeta Pup. The D I profiles were modeled
using a velocity template derived from several N I lines in the IMAPS spectra
recorded at higher S/N. To find the best D I column density, we minimized
chi-squares for model D I profiles that included not only the N(D I) as a free
parameter, but also the effects of several potential sources of systematic
error which could also be varied. For both stars, H I column densities were
measured by analyzing Ly-alpha absorption profiles in a large number of IUE
high dispersion spectra. Ultimately we found that D/H = 2.18(+0.36,-0.31)e-5
for gamma2 Vel and 1.42(+0.25,-0.23)e-5 for zeta Pup, values that contrast
markedly with D/H derived in Paper I for delta Ori (the stated errors are 90%
confidence limits). Evidently, the atomic D/H ratio in the ISM, averaged over
path lengths of 250 to 500 pc, exhibits significant spatial variability.
Furthermore, variations in D/H do not appear to be anticorrelated with N/H.
Within the framework of standard Big Bang Nucleosynthesis, the large value of
D/H found toward gamma2 Vel is equivalent to a cosmic baryon density of Omega_B
h^2 = 0.023 (+-0.002), which we regard as an upper limit since there is no
correction for the destruction of deuterium in stars.


title: The star formation history of resolved galaxies: Composite H-R diagram

abstract:
  I discuss the information provided by color-magnitude diagrams of different
absolute magnitude limits in the study of the star formation histories of
nearby galaxies. I review the recent progress made in the field, with emphasis
on the results for Local Group dwarf galaxies.


title:
First Results from the X-ray and Optical Survey of the Chandra Deep
  Field South

abstract:
  We present our first results from 130 ks of X-ray observations obtained with
the Advanced CCD Imaging Spectrometer on the Chandra X-ray Observatory. We
reach a flux of 2 X 10^(-16) erg s^(-1) cm^(-2) in the 0.5-2 keV soft band and
2 X 10^(-15) erg s^(-1) cm^(-2) in the 2-10 keV hard band. For the optical
identification we carried out a survey in VRI with the FORS-1
imaging-spectrometer on the ANTU telescope (UT-1 at VLT) complete to R <= 26.
This dataset was complemented with data from the ESO Imaging Survey (EIS) in
the UBJK bands and the ESO Wide Field Imager Survey (WFI) in the B band. The
positional accuracy of the X-ray detections is of order of 1'' in the central
6'. Optical identifications are found for ~90% of the sources. We obtain the
cumulative spectra of the faint and bright X-ray sources in the sample. A power
law fit in the range 2-10 keV using the galactic value of N_H ~ 8 x 10^(19)
cm^(-2), yields a photon index of Gamma = 1.70+-0.06 and 1.35+-0.10 for the
bright and faint sample respectively, showing a flattening of the spectrum at
lower fluxes. We discuss the LogN-LogS relationship and the discrete source
contribution to the integrated X-ray sky flux. In the soft band, the sources
now detected at fluxes below 10^(-15) erg s^(-1) cm^(-2) contribute (4.0 +-
0.3) X 10^(-12) erg cm^(-2)s^(-1) deg^(-2) to the total XRB. The flux resolved
in the hard band down to the flux limit of 2 X 10^(-15) erg s^(-1) cm^(-2) now
contributes a total of 1.6 X 10^(-11) erg cm^(-2) s^(-1) deg^(-2) which amounts
to a fraction of 60-80% of the total measured background. This result confirms
that the XRB is due to the integrated contribution of discrete sources, but
shows that there is still a relevant fraction (at least 20%) of the hard XRB to
be resolved at fluxes below 10^(-15) erg s^(-1) cm^(-2). (ABRIDGED)


title: On the Abundance Gradient of the Galactic Disk

abstract:
  Estimates of the gas temperature in planetary nebulae obtained from the [O
III] emission line ratio and from the Balmer discontinuity indicate differences
reaching up to 6000 K (Liu and Danziger 1993). The [O III] temperature is
commonly used to obtain the ionic fractions of highly ionized ions,
particularly the O++ and Ne++ ions when using the empirical method to calculate
the elemental abundances of photoionized gas from the observed emission line
intensities. However, if the gas temperature is overestimated, the elemental
abundances may be underestimated, in particular, it may lead to an uncorrect
elemental abundance gradient of the Galaxy, usually used as a constraint for
the chemical evolution models. Using Monte Carlo simulations, we calculate the
systematic error, introduced in the abundance gradient obtained from planetary
nebulae by an overestimation of the gas temperature. The results indicate that
the abundance gradient in the Galaxy should be steeper than previously assumed.


title: Comparison of photometric parameters of LSB and HSB edge-on galaxies

abstract:
  Photometric parameters of stellar disks and bulges for several edge-on
galaxies from the Catalog of Flat Galaxies (FGC) were determined. We discuss a
difference between photometric parameters of LSB and HSB galaxies from our
sample.
  Also we present results of R CCD photometry of edge-on galaxy RFGC 3647.
Deprojecting this galaxy we show that it has thin LSB disk (central surface
brightness $22^m.2$ in R) and high ratio of radial to vertical scale lengths.
It is shown that initially gaseous disk of the galaxy was unstable and its
velocity dispersion was low. Stellar disk of this LSB galaxy was not heated
significantly since that time.


title:
The luminosity dependence of clustering and higher order correlations in
  the PSCz survey

abstract:
  We investigate the spatial clustering of galaxies in the PSCz galaxy redshift
survey, as revealed by the two-point correlation function, the luminosity mark
correlations, and the moments of counts-in-cells. We construct volume-limited
subsamples at different depths, and search for a luminosity dependence of the
clustering pattern. We find no statistically significant effect in either the
two-point correlation function or the mark correlations and so we take each
subsample (of different characteristic luminosity) as representing the same
statistical process. We then carry out a counts-in-cells analysis of the
volume-limited subsamples, including a rigorous error calculation based on the
recent theory of Szapudi, Colombi and Bernardeau. In this way, we derive the
best estimates to date of the skewness and kurtosis of IRAS galaxies in
redshift space. Our results agree well with previous measurements in both the
parent angular catalogue, and in the derived redshift surveys. This is in
contrast with smaller, optically selected surveys, were there is a discrepancy
between the redshift space and projected measurements. Predictions from cold
dark matter theory, obtained using the recent semi-analytical model of galaxy
formation of Benson {\it et al}, provide an excellent description of our
clustering data.


title: The redshift and the ordinary host galaxy of GRB 970228

abstract:
  The gamma-ray burst of 28 February 1997 (GRB 970228) ushered in the discovery
of the afterglow phenomenon. Despite intense study of the host galaxy, however,
the nature of the host and the distance to the burst eluded the community. Here
we present the measurement of the redshift of GRB 970228, and, based on its
spectroscopic and photometric properties, identify the host as an
underluminous, but otherwise normal galaxy at redshift z=0.695 undergoing a
modest level of star formation. At this redshift, the GRB released an isotropic
equivalent energy of E = (6.8 +/- 0.5) x 10^51 erg [30-2000 keV restframe]. We
find no evidence that the host is much bluer or forming stars more rigorously
than the general field population. In fact, by all accounts in our analysis
(color-magnitude, magnitude-radius, star-formation rate, Balmer-break
amplitude) the host properties appear typical for faint blue field galaxies at
comparable redshifts.


title: Multicolor Observations of a Planetary Transit of HD 209458

abstract:
  We present B, V, R, I and Z-band photometric observations of HD 209458 during
the transit by its planetary companion on UT 1999 November 15 with the
University of Hawaii 0.6m and 2.2m telescopes and the High Altitude Observatory
STARE telescope. The detailed shape of the transit curve is predicted to vary
with color due primarily to the color-dependent limb-darkening of the star, but
potentially due as well to the effect of color-dependent opacity in the
planetary atmosphere. We model the light curves and present refined values for
the transit timing and orbital period, useful for planning future observations
of the planetary transit. We also derive significantly improved measurements of
the planetary radius, R_p = 1.55 +/- 0.10 R_Jup, stellar radius, R_s = 1.27 +/-
0.05 R_Sun, and orbital inclination, i = 85.9 +/- 0.5 deg. The derived
planetary radius favors evolutionary models in which the planet has a low
albedo.


title:
Robustly Unstable Eigenmodes of the Magnetoshearing Instability in
  Accretion Disk

abstract:
  The stability of nonaxisymmetric perturbations in differentially rotating
astrophysical accretion disks is analyzed by fully incorporating the properties
of shear flows. We verify the presence of discrete unstable eigenmodes with
complex and pure imaginary eigenvalues, without any artificial disk edge
boundaries, unlike Ogilvie & Pringle(1996)'s claim. By developing the
mathematical theory of a non-self-adjoint system, we investigate the nonlocal
behavior of eigenmodes in the vicinity of Alfven singularities at
omega_D=omega_A, where omega_D is the Doppler-shifted wave frequency and
omega_A=k_// v_A is the Alfven frequency. The structure of the spectrum of
discrete eigenmodes is discussed and the magnetic field and wavenumber
dependence of the growth rate are obtained. Exponentially growing modes are
present even in a region where the local dispersion relation theory claims to
have stable eigenvalues. The velocity field created by an eigenmode is
obtained, which explains the anomalous angular momentum transport in the
nonlinear stage of this stability.


title: Cosmic Inflation

abstract:
  I review the current status of the theory of Cosmic Inflation. My discussion
covers the motivation and implementation of the idea, as well as an analysis of
recent successes and open questions. There is a special discussion of the
physics of ``cosmic coherence'' in the primordial perturbations. The issue of
coherence is at the heart of much of the success inflation theory has achieved
at the hands of the new microwave background data. While much of this review
should be useful to anyone seeking to update their knowledge of inflation
theory, I have also made a point of including basic material directed at
students just starting research.


title:
Generic Spectrum and Ionization Efficiency of a Heavy Initial Mass
  Function for the First Stars

abstract:
  We calculate the generic spectral signature of an early population of massive
stars at high redshifts. For metal-free stars in the mass range of 100-1000
solar masses, we find that the combined spectral luminosity per unit stellar
mass is almost independent of the mass distribution of these stars. To zeroth
order, the generic spectrum resembles a black-body with an effective
temperature of ~10^5 K, making these stars highly efficient at ionizing
hydrogen and helium. The production rate of ionizing radiation per stellar mass
by stars more massive than 100 solar masses is larger by about an order of
magnitude for hydrogen and He I, and by about two orders of magnitude for He
II, than the emission from a standard initial mass function. This would result
in unusually strong hydrogen and helium recombination lines from the
surrounding interstellar medium. It could also alleviate the current difficulty
of ionizing the intergalactic medium at z>6 with the cosmic star formation rate
inferred at somewhat lower redshifts.


title: Conference Summary: Mapping the Hidden Universe

abstract:
  Two curiously connected topics provided a novel focus for this meeting in
Guanajuato, Mexico, 22--29, February, 2000. Two days were devoted to
discussions of galaxy surveys deep into the Galactic plane and to modeling of
the distribution of matter that makes use of quasi-full-sky coverage. Then the
meeting turned its attention for four further days to a look at the Universe
from surveys based on HI selection. How distorted is the world view of the
optical chauvinist?


title:
Rapid State Transitions in the Galactic Black Hole Candidate Source GRS
  1915+105

abstract:
  We examine the X-ray spectral and temporal behavior of the Galactic black
hole candidate source GRS 1915+105 during its spectral state transition
observed in 1997 March - August. The source was making a slow transition from a
low-hard state to a high-soft state in about three months and during this
transition it was exhibiting a series of fast variations which can be
classified as bursts. During one type of bursts, called the irregular bursts,
it was found that the source makes rapid transitions between two intensity
states. We have analyzed the RXTE PCA data obtained on 1997 June 18 (when the
source was making rapid state transitions) and compared the results with two
sets of data each pertaining to the low hard-state and high-soft states. We
find that the power density spectrum (PDS) during the burst shows remarkable
similarity to that seen during the high-soft state of the source. The PDS
during the quiescence, on the other hand, is quite flat and is very similar to
the PDS commonly seen during the canonical low-hard state of black hole X-ray
binaries. A low frequency QPO at $\sim$3 Hz is observed during the quiescence,
a property seen during the low-hard state of the source. The X-ray spectrum of
the source during quiescence is similar to the spectrum seen during the
low-hard state of the source and the spectra during the burst and high-soft
state are very similar to each other. These observations corroborate the
suggestion made by Yadav et al. (1999) that during the irregular bursts the
source shows spectral state variations at very fast time scales. We explain
such fast state changes using the two component accretion flow model in which
the accretion disk consists of a geometrically thin (and optically thick)
standard disk co-existing with an advection dominated hot thick disk.


title: A Circular Statistical Method for Extracting Rotation Measures

abstract:
  We propose a new method for the extraction of Rotation Measure from spectral
polarization data. The method is based on maximum likelihood analysis and takes
into account the circular nature of the polarization data. The method is
unbiased and statistically more efficient than the standard $\chi^2$ procedure.
We also find that the method is computationally much faster than the standard
$\chi^2$ procedure if the number of data points are very large.


title:
The Fundamental Plane of field early-type galaxies at intermediate
  redshift

abstract:
  We present preliminary results on the evolution of the stellar populations of
field early-type galaxies (E/S0) from z=0.4 to z=0. The diagnostic tool used in
this study is the Fundamental Plane (FP), a tight empirical correlation between
their central velocity dispersion (sigma), effective radius (Re), and effective
surface brightness (SBe), which is observed to hold in the local Universe.
Using HST-WFPC2 archive images and spectra obtained at the ESO-3.6m telescope
we measured the FP parameters for a sample of ~30 field E/S0s at z=0.2-0.4.
Remarkably, field E/S0s at intermediate redshift also define a tight FP, with
scatter unchanged with respect to that of local samples. The intermediate
redshift FP is offset from the local one, in the sense that, for given RE and
sigma, galaxies are brighter at z=0.4 than at z=0. The implication of the
offset of the FP in terms of passive evolution of the stellar population
depends on its star formation history. In a single burst scenario, the stellar
populations of field E/S0s were formed at z=0.8-1.6 (Omega=0.3;
Omega_{Lambda}=0.7; H_0=50 km/s/Mpc). Alternatively, the bulk of stars (90% in
mass) can be formed at high redshift (z~3), and the rest in a secondary burst
occurred more recently (z~0.5-0.8).


title: Dirac equation in Kerr geometry and its solution

abstract:
  Chandrasekhar separated the Dirac equation for spinning and massive particles
in Kerr geometry into radial and angular parts. In the present review, we
present solutions of the complete wave equation and discuss how the Dirac wave
scatters off Kerr black holes. The eigenfunctions, eigenvalues and reflection
and transmission co-efficients are computed for different Kerr parameters. We
compare the solutions with several parameters to show how a spinning black hole
distinguishes mass and energy of incoming waves. Very close to the horizon, the
solutions become independent of the particle parameters indicating an
universality of the behaviour.


title: Advective Accretion Flows: Ten Years Later

abstract:
  Ten years have passed since the global solutions of advective accretion disks
around black holes and neutron stars were first discovered. Since then they are
enjoying support from observers almost on a daily basis, more so in recent days
with the launching of very high resolution satellites. This review presents the
development of the subject of advective accretion in last twenty five years
leading to the global solutions and their applications. It also shows that
apart from the standard Keplerian disk features in most part of the accretion
flow, future models must incorporate the essential features of the advective
disks, such as the advection of energy and entropy by the flow, centrifugal
barrier supported boundary layer of a black hole, steady and non-steady shocks,
the bulk motion Comptonization of matter close to the black hole, outflows from
the centrifugal barrier etc. Since black holes are `black', methods of their
identification must be indirect, and therefore, the solutions must be known
very accurately. On the horizon, matter moves supersonically, but just before
that it is subsonic due to centrifugal pressure dominated boundary layer or
CENBOL where much of the infall energy is released and outflows are generated.
In this review, we show that advective flow models treat accretion and winds
onto black holes and neutron stars in the same footing. Similarly treated are
the steady and time-dependent behaviour of the boundary layers of neutron stars
and the black holes!


title:
Delayed X-Ray Afterglows from Obscured Gamma-Ray Bursts in Star-Forming
  Regions

abstract:
  For Gamma-Ray Bursts occurring in dense star-forming regions, the X-ray
afterglow behavior minutes to days after the trigger may be dominated by the
small-angle scattering of the prompt X-ray emission off dust grains. We give a
simple illustrative model for the X-ray light curves at different X-ray
energies, and discuss possible implications. A bump followed by a steeper decay
in soft X-rays is predicted for bursts which are heavily obscured in the
optical.


title: Imaging Performance of the XMM-Newton X-ray telescopes

abstract:
  The in-orbit imaging performance of the three X-ray telescopes on board of
the X-ray astronomy observatory XMM-Newton is presented and compared with the
performance measured on ground at the MPE PANTER test facility. The comparison
shows an excellent agreement between the on ground and in-orbit performance.


title: KPD1930+2752 - a candidate Type Ia supernova progenitor

abstract:
  We present spectra of the pulsating sdB star KPD1930+2752 which confirm that
this star is a binary. The radial velocities measured from the H-alpha and
HeI6678 spectral lines vary sinusoidally with the same period (2h 17m) as the
ellipsoidal variability seen by Billeres et al. (2000). The amplitude of the
orbital motion (349.3+-2.7 km/s) combined with the canonical mass for sdB stars
(0.5 solar masses) implies a total mass for the binary of 1.47+-0.01 solar
masses The unseen companion star is almost certainly a white dwarf star. The
binary will merge within about 200 million years due to gravitational wave
radiation. The accretion of helium and other elements heavier than hydrogen
onto the white dwarf which then exceeds the Chandrasekhar mass (1.4 solar
masses) is a viable model for the cause of Type Ia supernovae. KPD1930+2752 is
the first star to be discovered which is a good candidate for the progenitor of
a Type Ia supernova of this type which will merge on an astrophysically
interesting timescale.


title: Dynamical masses, time-scales, and evolution of star clusters

abstract:
  This review discusses (i) dynamical methods for determining the masses of
Galactic and extragalactic star clusters, (ii) dynamical processes and their
time-scales for the evolution of clusters, including evaporation, mass
segregation, core collapse, tidal shocks, dynamical friction and merging. These
processes lead to significant evolution of globular cluster systems after their
formation.


title: Satellite observations of thought experiments close to a black hole

abstract:
  Since black holes are `black', methods of their identification must
necessarily be indirect. Due to very special boundary condition on the horizon,
the advective flow behaves in a particular way, which includes formation of
centrifugal pressure dominated boundary layer or CENBOL where much of the
infall energy is released and outflows are generated. The observational aspects
of black holes must depend on the steady and time-dependent properties of this
boundary layer. Several observational results are written down in this review
which seem to support the predictions of thought experiments based on this
advective accretion/outflow model. In future, when gravitational waves are
detected, some other predictions of this model could be tested as well.


title: The environments of FRII radio sources

abstract:
  Using ROSAT observations, we estimate gas pressures in the X-ray-emitting
medium surrounding 63 FRII radio galaxies and quasars. We compare these
pressures with the internal pressures of the radio-emitting plasma estimated by
assuming minimum energy or equipartition. In the majority of cases (including
12/13 sources with modelled, spatially resolved X-ray emission) radio sources
appear to be underpressured with respect to the external medium, suggesting
that simple minimum-energy arguments underestimate the sources' internal energy
density. We discuss possible departures from the minimum energy condition and
the consequences of our result for models of the dynamics of radio galaxies, in
particular self-similar models (Kaiser & Alexander 1997).


title:
The environments and ages of extragalactic radio sources inferred from
  multi-frequency radio maps

abstract:
  A 3-dimensional model of the synchrotron emissivity of the cocoons of
powerful extragalactic radio sources of type FRII is constructed. Bulk backflow
and energy losses of the relativistic electrons, radiative and adiabatic, are
self-consistently taken into account. Thus the model is an extension of
spectral aging methods including the underlying source dynamics into the age
estimates. The discrepancies between spectral ages and dynamical ages arising
from earlier methods are resolved. It is also shown that diffusion of
relativistic particles within the cocoon is unlikely to significantly change
the particle spectrum and thus the emitted radio spectrum. Projection along the
line of sight yields 1 or 2-dimensional surface brightness distributions which
can be compared with observations. From the model parameters constraints on the
source age, the density of the source environment and the angle to the line of
sight can be derived. Application of the method to Cygnus A, 3C 219 and 3C 215
show that the method provides robust estimates for the model parameters for
sources with comparatively regularly shaped radio lobes. The resolution of the
radio maps required is only moderate. Within the large uncertainties for the
orientation angle, the three example sources are found to be consistent with
orientation-based unification schemes of radio-loud AGN. In the case of Cygnus
A the gas density of the environment is found to agree with independent X-ray
measurements. For 3C 219 and 3C 215 the densities derived from the model are
apparently too low. It is suggested that these discrepancies are caused by
overestimates of slope and core radius of $\beta$-models for the gas density
distribution from X-ray observations for clusters hosting powerful radio
sources.


title:
The combination of ground-based astrometric compilation catalogues with
  the HIPPARCOS Catalogue. II. Long-term predictions and short-term predictions

abstract:
  The combination of ground-based astrometric compilation catalogues, such as
the FK5 or the GC, with the results of the ESA Astrometric Satellite HIPPARCOS
produces for many thousands of stars proper motions which are significantly
more accurate than the proper motions derived from the HIPPARCOS observations
alone. In Paper I (Wielen et al. 1999, A&A 347, 1046) we have presented a
method of combination for single stars (SI mode). The present Paper II derives
a combination method which is appropriate for an ensemble of 'apparently
single-stars' which contains undetected astrometric binaries. In this case the
quasi-instantaneously measured HIPPARCOS proper motions and positions are
affected by 'cosmic errors', caused by the orbital motions of the photo-centers
of the undetected binaries with respect to their center-of-mass. In contrast,
the ground-based data are 'mean values' obtained from a long period of
observation. We derive a linear 'long-term prediction' (LTP mode) for epochs
far from the HIPPARCOS epoch T_H ~ 1991.25, and a linear 'short-term
prediction' (STP mode) for epochs close to T_H. The most accurate prediction
for a position at an arbitrary epoch is provided by a smooth, non-linear
transition from the STP solution to the LTP solution. We present an example for
the application of our method, and we discuss the error budget of our method
for the FK6 (a combination of the FK5 with HIPPARCOS) and for the combination
catalog GC+HIP. For the basic fundamental stars, the accuracy of the FK6 proper
motions in the LTP mode is better than that of the HIPPARCOS proper motions
(taking here the cosmic errors into account) by a factor of more than 4.


title:
An optical and X-ray study of the peculiar narrow-line quasar QSO
  0117-2837

abstract:
  We present an optical and X-ray study of the quasar QSO 0117-2837. It
exhibits an interesting combination of optical and X-ray properties: Despite
its extremely steep observed X-ray spectrum (Gamma_x ~ -4 when fit by a simple
powerlaw), its Balmer lines are fairly broad. A two-component Gaussian fit to
H_beta yields FWHM_{Hbeta, broad} ~ 4000 km/s, and places QSO 0117-2837 in the
`zone of avoidance' in the FWHM_{Hbeta}-Gamma_x diagram.
  A time variability analysis shows that QSO 0117-2837 is another case of
Narrow-line Sy1 galaxy (NLSy1 hereafter) which does not show any X-ray
variability during the observation.
  The results are discussed in view of the NLSy1 character of QSO 0117-2837.


title:
The Cosmic Microwave Background for a Nearly Flat Compact Hyperbolic
  Universe

abstract:
  The fluctuations of the cosmic microwave background (CMB) are investigated
for a hyperbolic universe with finite volume. Four-component models with
radiation, matter, vacuum energy, and an extra spatially constant dark energy
X-component are considered. The general solution of the Friedmann equation for
the cosmic scale factor a(eta) is given for the four-component models in terms
of the Weierstrass P-function. The lower part of the angular power spectra C_l
of the CMB anisotropy is computed for nearly flat models with Omega_tot <=
0.95. It is shown that the particular compact fundamental cell, which is
considered in this paper, leads to a suppression in C_l for l<10 and Omega_tot
<= 0.9.


title: Uncertainties on Clusters of Galaxies Distances

abstract:
  We investigate in this paper the error on the cluster redshift estimate as a
function of: (1) the number of galaxy structures along the line of sight; (2)
the morphology of the clusters (regular/substructures); (3) the nature of the
observed galaxies (cD/normal galaxies); (4) the number of observed galaxies;
and (5) the distance of the clusters. We find that if we use cD galaxies we
have errors of less than 2% (at the 1-$\sigma$ level) for the cluster distances
except when the clusters are very complex. In those cases when we use five
redshift measurements along the cluster lines of sight to compute the mean
redshift, the mean redshift estimate error is less than 5% for the clusters
closer than z=0.30. The same error of 5% for clusters in z=[0.30;0.60] requires
about 12 redshifts measurements.


title:
Evolution of globular cluster systems in elliptical galaxies. I.
  Log-normal initial mass function

abstract:
  We study the evolution of globular cluster systems (GCS) in elliptical
galaxies and explore the dependence of their main properties on the mass and
the size of the host galaxy.The dependence of the evolution of the GCS mass
function (GCMF), of the fraction of surviving clusters and of the ratio of the
final to initial mass in clusters on the structure of the host galaxy as well
as their variation with the galactocentric distance inside individual host
galaxies has been thoroughly investigated.After a survey over a large number of
different host galaxies we have restricted our attention to a sample of
galaxies with effective masses and radii equal to those observed for
dwarf,normal and giant ellipticals. We show that, in spite of large differences
in the fraction of surviving clusters, the final mean masses of the GCMF in
massive galaxies are very similar to each other with a small galaxy-to-galaxy
dispersion;low-mass compact galaxies tend to have smaller values of the final
mean mass and a larger galaxy-to-galaxy dispersion. These findings are in
agreement with those of recent observational analyses. The fraction of
surviving clusters increases with the mass of the host galaxy. We show that a
small difference between the initial and the final mean mass and dispersion of
the GCMF and the lack of a significant radial dependence of the mean mass
inside individual galaxies do not necessarily imply that evolutionary processes
have been unimportant in the evolution of the initial population of clusters.
For giant galaxies most disruption occurs within the effective radius while for
low-mass galaxies a significant disruption of clusters takes place also at
larger galactocentric distances. The dependence of the results obtained on the
initial mean mass of the GCMF is investigated. (abridged)


title: Mapping the star formation history of Mrk86: I. Data and models

abstract:
  We have obtained optical (BVR, [OIII]5007 and Halpha), near infrared (JHK)
imaging and long-slit optical spectroscopy for the Blue Compact Dwarf galaxy
Mrk86 (NGC2537). In this paper, the first of two, we present optical-near-
infrared colors and emission-line fluxes for the currently star-forming
regions, intemediate aged starburst and underlying stellar population. We also
describe the evolutionary synthesis models used in Paper II. The R and Halpha
luminosity distributions of the galaxy star-forming regions show maxima at
M_R=-9.5 and L_Halpha=10^37.3 erg s^-1. The underlying stellar population shows
an exponential surface brigthness profile with central value, mu_E,0=21.5 mag
arcsec^-2, and scale, alpha=0.88 kpc, both measured in the R-band image. In the
galaxy outer regions, dominated by this component, no significant color
gradients are observed. Finally, a set of evolutionary synthesis models have
been developed, covering a wide range in metallicity and burst strength.


title: BeppoSAX Observations of Markarian 501 in June 1999

abstract:
  We present the preliminary results of a long BeppoSAX observation of the BL
Lac object Mkn501 carried out in June 1999. The source was fainter than found
during the BeppoSAX pointings of 1997 and 1998, but is still detected with a
good signal-to-noise ratio up to ~40 keV. The X-ray spectrum in the energy
range 0.1-40 keV, produced through synchrotron radiation, is steeper than in
the previous years, it is clearly curved, and peaks (in nu*F_nu) at ~0.5 keV.
This energy is much lower than those at which the synchrotron component was
found to peak in 1997 and 1998. Some intraday variability suggests that
activity of the source on small time scales accompanies the large long time
scale changes of brightness and spectrum.


title: Keck Mid-Infrared Imaging of the QSO 2237+0305

abstract:
  Using the Long Wavelength Spectrometer on Keck I, we have imaged the
gravitationally lensed radio quiet quasi-stellar object (QSO) 2237+0305 at 8.9
and 11.7 microns for the first time. The mid-infrared flux ratios are
inconsistent with the optical flux ratios, but agree with the radio flux ratios
and with some published gravitational lens models. These flux ratios indicate
that the infrared emission is not affected by microlensing, which rules out the
synchrotron emission model. The infrared emission is likely produced by hot
dust extended on a length scale of more than 0.03 parsecs. The spectral energy
distribution further implies a narrow range of dust temperatures, suggesting
that the dust may be located in a shell extending between ~1 to 3 parsecs from
the nucleus, and intercepting about half of the QSO luminosity.


title:
Mapping the star formation history of Mrk86: II. Stellar populations and
  global interpretation

abstract:
  In this paper, continuation of Gil de Paz et al. (Paper I), we derive the
main properties of the stellar populations in the Blue Compact Dwarf galaxy
Mrk86. Ages, stellar masses, metallicites and burst strengths have been
obtained using the combination of Monte Carlo simulations, a maximum likelihood
estimator and Cluster and Principal Component Analysis. The three stellar
populations detected show well defined properties. We have studied the
underlying stellar population, which shows an age between 5-13 Gyr and no
significant color gradients. The intermediate aged (30 Myr old) central
starburst show a very low dust extinction with high burst strength and high
stellar mass content (9 10^6 M_sun). Finally, the properties of 46
low-metallicity star-forming regions were also studied. The properties derived
suggest that the most recent star-forming activity in Mrk86 was triggered by
the evolution of a superbubble originated at the central starburst by the
energy deposition of stellar winds and supernova explosions. Finally, different
mechanisms for the star formation triggering in this massive central starburst
are studied, including the merging with a low mass companion and the
interaction with UGC4278.


title:
The distance modulus of the Small Magellanic Cloud based on double-mode
  Cepheids

abstract:
  We employ the very recent photometric data of the OGLE project together with
stellar atmosphere and linear pulsation models to determine the distance
modulus of the Small Magellanic Cloud from its double-mode Cepheids. Based on
the requirement of obtaining the same distance modulus DM from the two types of
variables (fundamental & first overtone and first & second overtone), we get
DM=19.05 mag, with a very small statistical error (standard deviation) of 0.017
mag. Various systematic and zero point ambiguities (primarily those of the
color - temperature transformation) lead to an error of +/-0.13 mag (estimated
3 sigma deviation). This result is in very good agreement with the distance
modulus of the Large Magellanic Cloud of 18.5 mag, derived earlier from cluster
double-mode RR Lyrae stars.


title: Pulsar Jets: Implications for Neutron Star Kicks and Initial Spins

abstract:
  We study implications for the apparent alignment of the spin axes,
proper-motions, and polarization vectors of the Crab and Vela pulsars. The spin
axes are deduced from recent Chandra X-ray Observatory images that reveal jets
and nebular structure having definite symmetry axes. The alignments indicate
these pulsars were born either in isolation or with negligible velocity
contributions from binary motions. We examine the effects of rotation and the
conditions under which spin-kick alignment is produced for various models of
neutron star kicks. If the kick is generated when the neutron star first forms
by asymmetric mass ejection or/and neutrino emission, then the alignment
requires that the protoneutron star possesses an original spin with period
$P_s$ much less than the kick timescale, thus spin-averaging the kick forces.
The kick timescale ranges from 100 ms to 10 s depending on whether the kick is
hydrodynamically driven or neutrino-magnetic field driven. For hydrodynamical
models, spin-kick alignment further requires the rotation period of an
asymmetry pattern at the radius near shock breakout (>100 km) to be much less
than ~100 ms; this is difficult to satisfy unless rotation plays a dynamically
important role in the core collapse and explosion ($P_s\lo 1$ ms). Aligned kick
and spin vectors are inherent to the slow process of asymmetric electromagnetic
radiation from an off-centered magnetic dipole. We reassess the viability of
this effect, correcting a factor of 4 error in Harrison and Tademaru's
calculation that increases the size of the effect. To produce a kick velocity
of order a few hundred km/s requires that the neutron star be born with an
initial spin close to 1 ms and that spindown due to r-mode driven gravitational
radiation be inefficient compared to standard magnetic braking.


title:
LiBeB, O and Fe Evolution: Refractory Element and Cosmic Ray Transport
  Delays

abstract:
  Employing a Monte-Carlo based evolutionary code, we show that the delay of Fe
deposition relative to O, due to the incorporation of supernova ejecta
refractories in high velocity grains, can account for the rise of [O/Fe] with
decreasing [Fe/H]. The predicted behavior of refractory Mg, Si, Ca and Ti, and
volatile S, namely that the refractories should not show the rise, but that the
behavior of S should be similar to that of O, appears to be confirmed (Takeda
et al. 2000, astro-ph/0007007). The delayed deposition of Be, due to cosmic ray
transport in a relatively low density medium, leads to consistency of primary
Be evolution as a function of both [Fe/H] and [O/H].


title: Comptonization in the accretion column of the X-ray pulsar GX~1+4

abstract:
  X-ray observations of the binary pulsar GX 1+4 made using the Rossi X-ray
Timing Explorer (RXTE) satellite between February 1996 and May 1997 were
analysed to quantify source spectral variation with luminosity.
  Mean Proportional Counter Array (PCA) spectra over the range 2-40 keV are
best fitted with a Comptonization model, with source spectrum temperature T_0
approx 1-1.3 keV, plasma temperature T_e approx 6-10 keV, and optical depth tau
approx 2-6. The range of fitted T_0 was consistent with the source spectrum
originating at the neutron star polar cap, with Compton scattering taking place
primarily in the hot plasma of the accretion column. Both the fitted optical
depth and plasma temperature vary significantly with the source flux. The
variation of the optical depth (and hence the density of the scattering region)
with luminosity strongly suggests increasing cross-sectional area of the
accretion column at higher accretion rate Mdot.
  The wide range of source luminosity spanned by archival observations of GX
1+4 offers evidence for two distinct spectral states above and below L_X approx
2*10^{37} erg/s (2-60 keV, assuming a source distance of 10 kpc). GX 1+4
additionally exhibits dramatic hourly variations in neutral column density n_H
indicative of density variations in the stellar wind from the giant companion.


title: Noise-driven evolution in stellar systems: Theory

abstract:
  We present a theory for describing the evolution of a galaxy caused by
stochastic events such as weak mergers, transient spiral structure, orbiting
blobs, etc. This noise excites large-scale patterns that drives the evolution
of the galactic density profile. In dark-matter haloes, the repeated stochastic
perturbations preferentially ring the lowest-order modes of the halo with only
a very weak dependence on the details of their source. Shaped by these modes,
the profile quickly takes on a nearly self-similar form. We show that this form
has the features of the ``universal profile'' reported by Navarro, Frenk, &
White independent of initial conditions in a companion paper. In this sense,
this noise-driven process is a near-equilibrium form of violent relaxation.


title: Noise-driven evolution in stellar systems: A universal halo profile

abstract:
  Using the theory describing the evolution of a galaxy halo due to stochastic
fluctuations developed in the companion paper, we show that a halo quickly
evolves toward the same self-similar profile, independent of its initial
profile and concentration. The self-similar part of profile takes the form of a
double power law with inner and outer exponents taking the values near -1.5 and
-3 respectively. The precise value of the inner exponent depends on the
magnitude and duration of the noisy epoch and most likely on form of the inner
profile to start. The outer exponent is the result of evolution dominated by
the external l=1 multipole resulting from the inner halo's response to noise.
  Three different noise processes are studied: (1) a bombardment by blobs of
mass small compared to the halo mass (`shrapnel'); (2) orbital evolution of
substructure by dynamical friction (`satellites'); and (3) noise caused by the
orbit of blobs in the halo (`black holes'). The power spectra in the shrapnel
and satellite cases is continuous and results in the double power law form,
independent of initial conditions. The power spectrum for black holes is
discrete and has a different form with a much slower rate of evolution. A
generic prediction of this study is that noise from transient processes will
drive evolution toward the same double power law with only weak constraints on
the noise source and initial conditions.


title: Scattering of Dirac Waves off Kerr Black Holes

abstract:
  Chandrasekhar separated the Dirac equation for spinning and massive particles
in Kerr geometry into radial and angular parts. Here we solve the complete wave
equation and find out how the Dirac wave scatters off Kerr black holes. The
eigenfunctions, eigenvalues and reflection and transmission co-efficients are
computed. We compare the solutions with several parameters to show how a
spinning black hole distinguishes mass and energy of incoming waves. Very close
to the horizon the solutions become independent of the particle parameters
indicating an universality of the behaviour.


title: Dissipative N - body code for galaxy evolution

abstract:
  The evolving galaxy is considered as a system of baryonic fragments embedded
into the static dark nonbaryonic (DH) and baryonic (BH) halo and subjected to
gravitational and viscous interactions. Although the chemical evolution of each
separate fragment is treated in the frame of one -- zone close box model with
instantaneous recycling, its star formation (SF) activity is a function of mean
local gas density and, therefore, is strongly influenced by other interacting
fragments. In spite of its simplicity this model provides a realistic
description of the process of galaxy formation and evolution over the Hubble
timescale.


title:
Modeling the star formation in galaxies using the Chemo - dynamical SPH
  code

abstract:
  A new Chemo - Dynamical Smoothed Particle Hydrodynamic (CD - SPH) code is
presented. The disk galaxy is described as a multi - fragmented gas and star
system, embedded in a cold dark matter halo. The star formation (SF) process,
SNII, SNIa and PN events as well as chemical enrichment of gas have been
considered within the framework of the standard SPH model. Using this model we
describe the dynamical and chemical evolution of triaxial disk - like galaxies.
It is found that such approach provides a realistic description of the process
of formation, chemical and dynamical evolution of disk galaxies over a
cosmological timescale.


title: X-ray afterglow detection of the short gamma-ray burst 991014

abstract:
  GRB 991014 is one of the shortest gamma-ray bursts detected so far with the
Wide Field Cameras aboard BeppoSAX, both in gamma-rays and X-rays. The duration
is 9.6 sec in 2-28 keV and 3.2 sec in 40 to 700 keV (as measured between the
times when 5 and 95% of the burst photons have been accumulated). We refine the
InterPlanetary Network annulus of the burst, present the detection of the X-ray
afterglow of GRB 991014 within this refined annulus, and discuss X-ray and
gamma-ray observations of the prompt and afterglow emission. Except for the
briefness of the prompt event, no other unusual aspects were found in the
prompt and afterglow observations as compared to such measurements in previous
gamma-ray bursts.


title: Hierarchical Galaxy Formation

abstract:
  We describe the GALFORM semi-analytic model for calculating the formation and
evolution of galaxies in hierarchical models. It improves upon, and extends,
the Cole et al 1994 model. The model employs a new Monte-Carlo algorithm to
follow the merging evolution of dark matter halos with arbitrary mass
resolution. It incorporates realistic descriptions of the density profiles of
dark matter halos and their gas content; follows the chemical evolution of gas
and stars, and the associated production of dust; and includes a detailed
calculation of the sizes of disks and spheroids. Wherever possible, our
prescriptions for modelling individual physical processes are based on results
of numerical simulations. We apply our methods to the LCDM cosmology
(Omega_0=0.3, Lambda_0=0.7), and find good agreement with a wide range of
properties of the local galaxy population: the B-band and K-band luminosity
functions, the distribution of colours for the population as a whole, the ratio
of ellipticals to spirals, the distribution of disk sizes, and the current cold
gas content of disks. (Abridged)


title: The First Hours of a Core Collapse Supernova

abstract:
  New two-dimensional, high-resolution calculations of a core collapse
supernova in a 15 Msol blue supergiant are presented, which cover the entire
evolution from shock revival until the first few hours of the explosion.
Explosive nucleosynthesis, its dependence upon convective mixing during the
first second of the evolution and the growth of Rayleigh-Taylor instabilities
at the composition interfaces of the progenitor star are all modeled
consistently and allow for a comparison with observational data. We confirm our
earlier findings, that the perturbations induced by neutrino driven convection
are sufficiently strong to seed large-scale Rayleigh-Taylor mixing and to
destroy the onion-shell structure of the stellar He-core. As in our earlier
calculations, the strong deceleration of the nickel clumps in the layers
adjacent to the He/H interface suggests that the high velocities of iron-group
elements observed in SN 1987A cannot be explained on the basis of currently
favored progenitor models. Possible solutions to this dilemma and the
implications of the mixing for type Ib explosions are briefly discussed.


title:
Interpreting the optical data of the Hubble Deep Field South: colors,
  morphological number counts and photometric redshifts

abstract:
  We present an analysis of the optical data of the Hubble Deep Field South. We
derive F300W(AB), F450W(AB), F606W(AB) and F814W(AB) number counts for galaxies
in all four bands. The slope is steeper at shortest wavelengths: we estimated
gamma(F300W(AB))=0.47, gamma(F450W(AB))=0.35, gamma(F606W(AB))=0.28 and
gamma(F814W(AB))=0.28. Morphological number counts are actually dominated by
late type galaxies, while early type galaxies show a decreasing slope at faint
magnitudes. Combining this information with photometric redshifts, we notice
that galaxies contributing with a steep slope to morphological number counts
(i.e. spiral and irregular galaxies) have z>1, suggesting a moderate merging.
However we emphasize that any cut in apparent magnitude at optical wavelengths
results in samples biased against elliptical galaxies, affecting as a
consequence the redshift distributions and the implications on the evolution of
galaxies along the Hubble sequence.


title: On the abundance of collapsed objects

abstract:
  The redshift dependence of the abundance of collapsed objects places strong
constraints on cosmological models of structure formation. We apply a recently
proposed model describing the anisotropic collapse of inhomogeneous spatial
domains. Compared with the spherical top-hat model, this generic model leads to
significantly more collapsed objects at high redshifts: at redshift one and on
the scale of rich clusters a factor of 65. Furthermore, for a fixed
normalization of the initial fluctuation spectrum (\sigma_8=1), we predict four
times as much presently collapsed objects on the mass-scale of rich clusters
within the standard CDM cosmogony, compared to the spherical collapse.


title: The cluster environments of the z~1 3CR radio galaxies

abstract:
  An analysis of the environments around a sample of 28 3CR radio galaxies with
redshifts 0.6 < z < 1.8 is presented, based primarily upon K--band images down
to K ~ 20 taken using the UK Infrared Telescope (UKIRT). A net overdensity of
K-band galaxies is found in the fields of the radio galaxies, with the mean
excess counts being comparable to that expected for clusters of Abell Class 0
richness. A sharp peak is found in the angular cross-correlation amplitude
centred on the radio galaxies, which, for reasonable assumptions about the
luminosity function of the galaxies, corresponds to a spatial cross-correlation
amplitude between those determined for low redshift Abell Class 0 and Abell
Class 1 clusters.


title: CLASS B0827+525: `Dark lens' or binary radio-loud quasar?

abstract:
  We present radio, optical, near-infrared and spectroscopic observations of
the source B0827+525. We consider this source as the best candidate from the
Cosmic Lens All-Sky Survey (CLASS) for a `dark lens' system or binary
radio-loud quasar. The system consists of two radio components with somewhat
different spectral indices, separated by 2.815 arcsec. VLBA observations show
that each component has substructure on a scale of a few mas. A deep K-band
exposure with the W.M.Keck-II Telescope reveals emission near both radio
components. The K-band emission of the weaker radio component appears extended,
whereas the emission from the brighter radio component is consistent with a
point source. Hubble Space Telescope F160W-band observations with the NICMOS
instrument confirms this. A redshift of 2.064 is found for the brighter
component, using the LRIS instrument on the W.M.Keck-II Telescope. The
probability that B0827+525 consists of two unrelated compact flat-spectrum
radio sources is ~3%, although the presence of similar substructure in both
component might reduce this.
  We discuss two scenarios to explain this system: (i) CLASS B0827+525 is a
`dark lens' system or (ii) B0827+525 is a binary radio-loud quasar. B0827+525
has met all criteria that thus far have in 100% of the cases confirmed a source
as an indisputable gravitational lens system. Despite this, no lens galaxy has
been detected with m_F160W<=23 mag. Hence, we might have found the first binary
radio-loud quasar. At this moment, however, we feel that the `dark lens'
hypothesis cannot yet be fully excluded.


title: Beat-Frequency Models of Kilohertz QPOs

abstract:
  Kilohertz QPO sources are reasonably well-characterized observationally, but
many questions remain about the theoretical framework for these sources and the
consequent implications of the observations for disk physics, strong gravity,
and dense matter. We contrast the predictions and implications of the most
extensively studied class of kilohertz QPO models, the beat-frequency models,
with those of alternative classes of models. We also discuss the expected
impact of new observations of these sources with satellites such as Chandra,
XMM, and Constellation-X.


title: What Fraction of Gravitational Lens Galaxies Lie in Groups?

abstract:
  We predict how the observed variations in galaxy populations with environment
affect the number and properties of gravitational lenses in different
environments. Two trends dominate: lensing strongly favors early-type galaxies,
which tend to lie in dense environments, but dense environments tend to have a
larger ratio of dwarf to giant galaxies than the field. The two effects nearly
cancel, and the distribution of environments for lens and non-lens galaxies are
not substantially different (lens galaxies are slightly less likely than
non-lens galaxies to lie in groups and clusters). We predict that about 20% of
lens galaxies are in bound groups (defined as systems with a line-of-sight
velocity dispersion sigma in the range 200 < sigma < 500 km/s), and another
roughly 3% are in rich clusters (sigma > 500 km/s). Therefore at least roughly
25% of lenses are likely to have environments that significantly perturb the
lensing potential. If such perturbations do not significantly increase the
image separation, we predict that lenses in groups have a mean image separation
that is about 0.2'' smaller than that for lenses in the field and estimate that
20-40 lenses in groups are required to test this prediction with significance.
The tail of the distribution of image separations is already illuminating.
Although lensing by galactic potential wells should rarely produce lenses with
image separations theta >~ 6'', two such lenses are seen among 49 known lenses,
suggesting that environmental perturbations of the lensing potential can be
significant. Further comparison of theory and data will offer a direct probe of
the dark halos of galaxies and groups and reveal the extent to which they
affect lensing estimates of cosmological parameters.


title:
The Bright SHARC Survey: The Selection Function and its Impact on the
  Cluster X-ray Luminosity Function

abstract:
  We present the results of a set of simulations designed to quantify the
selection function of the Bright SHARC survey for distant clusters. The
statistical significance of the simulations relied on the creation of thousands
of artificial clusters with redshifts and luminosities in the range 0.25<z<0.95
and 0.5<L_X<10x10^44 erg/s (0.5-2.0 keV). We created 1 standard and 19 varied
distribution functions, each of which assumed a different set of cluster,
cosmological and operational parameters. The parameters we varied included the
values of Omega_0, Omega_Lambda, Beta, core radius and ellipticity. We also
investigated how non-standard surface brightness profiles; cooling flows; and
the ROSAT pointing target, influence the selection function in the Bright SHARC
survey. For our standard set we adopted the parameters used during the
derivation of the Bright SHARC Cluster X-ray Luminosity Function (CXLF), i.e.
Omega_0=1, Omega_Lambda=0 and an isothermal Beta model with beta=0.67, r_c=250
kpc and e=0.15. We found that certain parameters have a dramatic effect on our
ability to detect clusters, e.g. the presence of a NFW profile or a strong
cooling flow profile, or the value of r_c and beta. Other parameters had very
little effect, e.g. the type of ROSAT target and the cluster ellipticity. We
show also that all the tested parameters have only a small influence on the
computed luminosity of the clusters except the presence of a strong cooling
flow. We conclude that the CXLF presented in Nichol et al. (1999) is robust
(under the assumption of standard parameters), but stress the importance of
cluster follow-up in order to better constrain the morphology of the distant
clusters found in the Bright SHARC and other surveys.


title: Cosmological magnetic fields by parametric resonance?

abstract:
  We investigate the possibility that electromagnetic fluctuations are
amplified in expanding universe by parametric resonance, during the oscillatory
regime of a scalar field to which they are coupled. We consider scalar
electrodynamics and we find that electromagnetic fluctuations undergo
exponential instabilities. This mechanism could have some relevance for the
problem of large scale primordial magnetic fields.


title: Precursors of gamma-ray bursts: a clue to the burster's nature

abstract:
  In relativistic strongly magnetized winds outflowing from the fast-rotating
compact progenitors of gamma-ray bursts (GRBs) there are three regions where
powerful high-frequency emission may be generated: (i) the thermal photosphere,
(ii) the region of the internal wind instability and (iii) the region of the
wind interaction with an ambient gas. This results in a multicomponent
structure of GRBs. The emission from the thermal photosphere may be observed as
a weak precursor to the main burst. The precursor should have a blackbody-like
spectrum with the mean energy of photons of $\sim 1$ MeV, and its intensity
should be tens to hundreds of times smaller than that of the main GRB emission.
Observations of such precursors with future $\gamma$-ray missions like GLAST
can clarify the nature of bursters.


title: On the Relation Between Radio and Non-Radio Elliptical Galaxies

abstract:
  Empirical evidence suggests that elliptical galaxies hosting a radio source
may not be different from normal non-radio ellipticals. To test this
possibility, we use Monte Carlo simulations to reproduce the distribution of
radio galaxies in the radio-optical luminosity plane. The input parameters of
the simulation are the optical luminosity function (LF) of ellipticals and the
radio LF of radio galaxies, linked by a function giving the probability for an
elliptical to be a radio galaxy.
  Simulations reproduce the observations well, supporting unification of radio
and non-radio ellipticals, provided that the probability of an elliptical
hosting a radio source is proportional to the square of its optical luminosity.
  The difference of 0.5 magnitudes in average optical luminosity between FRI
and FRII radio galaxies is also explained in this framework.