title:
Formation of cuspy density profiles - a generic feature of collisionless
  gravitational collapse

abstract:
  Using the formalism of the spherical infall model the structure of collapsed
and virialized dark halos is calculated for a variety of scale-free initial
conditions. In spite of the scale-free cosmological nature of the problem, the
collapse of individual objects is not self-similar. Unlike most of previous
calculations the dynamics used here relies only on adiabatic invariants and not
on self-similarity. The paper focuses on the structure of the innermost part of
the collapsed halos and addresses the problem of central density cusps. The
slopes of density profiles at 1% of virial radius are calculated for a variety
of cosmological models and are found to vary with the mass of the halos and
power spectrum of the initial conditions. The inner slopes range between r^-2.3
and r^-2 with the limiting case of r^-2 reached for the largest masses. The
steep cusps found here correspond to the limiting case where all particles move
on radial orbits. The introduction of angular momentum will make the density
profile shallower. We expect this to resolve the discrepancy found between the
calculated profiles and the ones found in high resolution N-body simulations,
where the exponent ranges from -0.5 to -1.5. The robust prediction here is that
collisionless gravitational collapse in an expanding universe is expected to
form density cups and not halos with a core structure.


title:
BeppoSAX broad-band observations of low-redshift quasars: Spectral
  curvature and iron K_alpha lines

abstract:
  We present results from BeppoSAX observations of 10 low redshift quasars. The
quasars are part of the Laor et al. (1997) sample of 23 optically selected PG
quasars with redshift <0.4 and low Galactic absorption along the line of sight.
Significant spectral curvature is detected for the 6 quasars with the highest
signal to noise ratio in their low energy spectra. The average curvature can be
parameterized as a flattening of the underlying power law by Delta_alpha ~ 0.5
above ~1 keV. We find that quasars with a steeper soft X-ray (0.1-2 keV)
spectrum tend to be steeper also at higher (2-10 keV) energies. The
distribution of the best fit 2-10 keV slopes is similar to that found for other
radio-quiet AGN and characterized by a large dispersion around the mean:
alpha_E ~ 1.0+/-0.3. Iron K_alpha lines are detected in 4 quasars. In the
narrow-line quasar PG 1115+407, the rest frame line energy (6.69+/-0.11 keV)
and equivalent width (580+/-280 eV) are consistent with those found in a few
low redshift narrow-line Seyfert 1 galaxies (NLSy1). This, together with the
similarity of the 0.1-10 keV X-ray continuum, suggests that this quasar is the
higher redshift and luminosity analog of a NLSy1. In the broad line quasar PG
0947+396, the rest-frame line energy suggests fluorescence from cold iron. The
line equivalent width (> 400 eV) is however about 2-3 times higher than that
usually found in Seyfert 1 galaxies. The high energy power-law slopes and the
iron line emission properties seem to be unrelated to the X-ray luminosity.


title: Hot and Cold Dark Matter Search with GENIUS

abstract:
  GENIUS is a proposal for a large volume detector to search for rare events.
An array of 40-400 'naked' HPGe detectors will be operated in a tank filled
with ultra-pure liquid nitrogen. After a description of performed technical
studies of detector operation in liquid nitrogen and of Monte Carlo simulations
of expected background components, the potential of GENIUS for detecting WIMP
dark matter, the neutrinoless double beta decay in 76-Ge and low-energy solar
neutrinos is discussed.


title: Electron-positron outflow from black holes and the formation of winds

abstract:
  The collapse of young massive stars or the coalescence of a black
hole-neutron star binary is expected to give rise to a black hole-torus system.
When the torus is strongly magnetized, the black hole produces
electron-positron outflow along open magnetic field-lines. Through curvature
radiation in gaps, this outflow rapidly develops into a $e^\pm\gamma$-wind,
which is ultra-relativistic and of low comoving density, proposed here as a
possible input to GRB fireball models.


title: Infrared photometry of z~1 3C quasars

abstract:
  We present JHKL' photometry of a complete sample of steep-spectrum radio-loud
quasars from the revised 3CR catalogue in the redshift range 0.65 < z < 1.20.
After correcting for contributions from emission lines and the host galaxies,
we investigate their spectral energy distributions (SEDs) around 1 micron.
About 75% of the quasars are tightly grouped in the plane of optical spectral
index, alpha_lo, versus near-infrared spectral index, alpha_hi, with the median
value of alpha_lo close to the canonical value, and the median alpha_hi
slightly flatter. We conclude that the fraction of moderately-obscured, red
quasars decreases with increasing radio power, in accordance with the `receding
torus' model which can also explain the relatively flat median near-infrared
spectra of the 3CR quasars. Two of the red quasars have inverted infrared
spectral indices, and we suggest that their unusual SEDs might result from a
combination of dust-scattered and transmitted quasar light.


title:
The standard and degenerate primordial nucleosynthesis versus recent
  experimental data

abstract:
  We report the results on Big Bang Nucleosynthesis (BBN) based on an updated
code, with accuracy of the order of 0.1% on He4 abundance, compared with the
predictions of other recent similar analysis. We discuss the compatibility of
the theoretical results, for vanishing neutrino chemical potentials, with the
observational data. Bounds on the number of relativistic neutrinos and baryon
abundance are obtained by a likelihood analysis. We also analyze the effect of
large neutrino chemical potentials on primordial nucleosynthesis, motivated by
the recent results on the Cosmic Microwave Background Radiation spectrum. The
BBN exclusion plots for electron neutrino chemical potential and the effective
number of relativistic neutrinos are reported. We find that the standard BBN
seems to be only marginally in agreement with the recent BOOMERANG and MAXIMA-1
results, while the agreement is much better for degenerate BBN scenarios for
large effective number of neutrinos, N_\nu \sim 10.


title: On neutron star/supernova remnant associations

abstract:
  It is pointed out that a cavity supernova (SN) explosion of a moving massive
star could result in a significant offset of the neutron star (NS) birth-place
from the geometrical centre of the supernova remnant (SNR). Therefore: a) the
high implied transverse velocities of a number of NSs (e.g. PSR B1610-50, PSR
B1757-24, SGR0525-66) could be reduced; b) the proper motion vector of a NS
should not necessarily point away from the geometrical centre of the associated
SNR; c) the circle of possible NS/SNR associations could be enlarged. An
observational test is discussed, which could allow to find the true
birth-places of NSs associated with middle-aged SNRs, and thereby to get more
reliable estimates of their transverse velocities.


title: Non equilibrium spectra of degenerate relic neutrinos

abstract:
  We calculate the exact kinetic evolution of cosmic neutrinos until complete
decoupling, in the case when a large neutrino asymmetry exists. While not
excluded by present observations, this large asymmetry can have relevant
cosmological consequences and in particular may be helpful in reconciling
Primordial Nucleosynthesis with a high baryon density as suggested by the most
recent observations of the Cosmic Microwave Background Radiation. By solving
numerically the Boltzmann kinetic equations for the neutrino distribution
functions, we find the momentum-dependent corrections to the equilibrium
spectra and briefly discuss their phenomenological implications.


title:
Distinguishing RBL-like objects and XBL-like objects with the peak
  emission frequency of the overall energy spectrum

abstract:
  We investigate quantitatively how the peak emission frequency of the overall
energy spectrum is at work in distinguishing RBL-like and XBL-like objects. We
employ the sample of Giommi et al. (1995) to study the distribution of BL
Lacertae objects with various locations of the cutoff of the overall energy
spectrum. We find that the sources with the cutoff located at lower frequency
are indeed sited in the RBL region of the $\alpha_{ro}-\alpha_{ox}$ plane,
while those with the cutoff located at higher frequency are distributed in the
XBL region. For a more quantitative study, we employ the BL Lacertae samples
presented by Sambruna et al. (1996), where, the peak emission frequency, $\nu
_p$, of each source is estimated by fitting the data with a parabolic function.
In the plot of $\alpha_{rx}-\log \nu_p$ we find that, in the four different
regions divided by the $\alpha_{rx}=0.75$ line and the $\log \nu_p=14.7$ line,
all the RBL-like objects are inside the upper left region, while most XBL-like
objects are within the lower right region. A few sources are located in the
lower left region. No sources are in the upper right region. This result is
rather quantitative. It provides an evidence supporting what Giommi et al.
(1995) suggested: RBL-like and XBL-like objects can be distinguished by the
difference of the peak emission frequency of the overall energy spectrum.


title:
Present limits to cosmic bubbles from the COBE-DMR three point
  correlation function

abstract:
  The existence of large scale voids in several galaxy surveys suggests the
occurence of an inflationary first order phase transition. This process
generates primordial bubbles that, before evolving into the present voids,
leave at decoupling a non-Gaussian imprint on the CMB. I this paper we evaluate
an analytical expression of the collapsed three point correlation function from
the bubble temperature fluctuations. Comparing the results with COBE-DMR
measures, we obtain upper limits on the allowed non-Gaussianity and hence on
the bubble parameters.


title: On the photodissociation of H2 by the first stars

abstract:
  The first star formation in the universe is expected to take place within
small protogalaxies, in which the gas is cooled by molecular hydrogen. However,
if massive stars form within these protogalaxies, they may suppress further
star formation by photodissociating the H2. We examine the importance of this
effect by estimating the timescale on which significant H2 is destroyed. We
show that photodissociation is significant in the least massive protogalaxies,
but becomes less so as the protogalactic mass increases. We also examine the
effects of photodissociation on dense clumps of gas within the protogalaxy. We
find that while collapse will be inhibited in low density clumps, denser ones
may survive to form stars.


title: BeppoSAX Observations of Bright Radio Galaxies

abstract:
  BeppoSAX observations of Broad Line Radio Galaxies (BLRGs) have shown that
they have a considerable variety of spectral properties and important
differences with respect to their radio-quiet counter-part Seyfert 1s. In radio
galaxies the soft photons are often absorbed by cold material. In contrast, in
Seyfert 1s the soft photons are generally absorbed by warm gas. The iron lines,
always detected in Seyfert 1s, are not always present in BLRGs and generally
are weak. In addition, small iron line equivalent widths seem to correspond to
weak reflection components in radio galaxies.
  The emerging picture of BLRGs is complex. Probably several X-ray components,
jet, accretion flow and molecular torus, mixed in different way in different
objects, contribute to the production of their X-ray spectrum and determine the
observed variety. The weakness of the reprocessed features can be explained
either by a dilution of the Seyfert-like continuum from non-thermal (jet)
radiation or by an accretion gas that is hot and geometrically thick close to
the black hole and cold geometrically thin (i.e. able to reprocess the primary
X-ray radiation) at larger radii.


title: A simple method of determining the Hubble constant

abstract:
  Bidirectional relativistic proper motions of radio components of nearby
extragalactic sources give a strong constraint on the determination of the
Hubble constant $H_0$. Under the assumption that the real velocity of radio
components of extragalactic sources is not less than that of Galactic sources,
the value of $H_0$ can be estimated at a high level of accuracy. The assumption
is reasonable due to the general belief that the activity in the core of
galaxies must be more powerful than that of stars. This method is simple and
with only one uncertainty --- the real velocity of components. This uncertainty
is related to the value of the real velocity of componenets of Galactic sources
and the latter is always well-determined (note that the determination is
independent of $H_0$ and the distance of Galactic sources can be directly
measured at a rather high level of accuracy). Hopefully the method will play an
important role in future research to fix the value of $H_0$. With the data of
the three sources available so far and the assumption that the real velocity of
componenets of at least one of the sources is not less than a known velocity of
componenets of a Galactic source, the constant is estimated to be within
$27.08kms^{-1}Mpc^{-1} < H_0 \leq 53.15kms^{-1}Mpc^{-1}$ with this method.


title: A New Association of Post-T Tauri Stars Near The Sun

abstract:
  Observing ROSAT sources in 20 x 25 deg centered at the high latitude active
star ER Eri, we found evidences for a new young nearby association (~30Myr
at~60pc), the Horologium Association (HorA), formed by at least 10 probable and
6 possible members, some being Post-T Tauri stars. We examine several
requirements that characterize a young association and they, together, create a
strong evidence for the reality of the HorA. In fact, the Li line intensities
are between those of the oldest classical T Tauri stars and the ones of the
Local Association stars. The space velocities of the HorA relative to the Sun,
U= -9.5+/-1.0, V = -20.9 +/- 1.1, W = -2.1 +/- 1.9, are not far from those of
the Local Association. We suggest that some hotter and non-X-ray active stars,
with similar space velocities, could be massive members of the HorA, among
them, the nearby Be star Achernar. The maximum of the mass distribution
function of the HorA is around 0.8 solar masses. At its distance, the projected
size of the HorA, ~50 pc, would be larger than our surveyed area and many other
members could have been missed. We also observed 3 control regions, two at
northern and southern galactic latitudes and a third one in the known TW Hya
Association (TWA), and the properties and distribution of their young stars
strengthen the reality of the HorA. Contrary to the TWA, the only known
binaries in the HorA are 2 very wide systems. The HorA is much more isolated
from clouds and older than the TWA and could give some clues about the lifetime
of the disks around T Tauri stars. Actually, none of the proposed members is an
IRAS source indicating an advanced stage of the evolution of their accreting
disks. ER Eri itself was found to be a RS CVn-like system.


title: On the velocity of the Vela pulsar

abstract:
  It is shown that if the shell of the Vela supernova remnant is responsible
for nearly all the scattering of the Vela pulsar, then the scintillation and
proper motion velocities of the pulsar can only be reconciled with each other
in the case of nonzero transverse velocity of the scattering material. A
possible origin of large-scale transverse motions in the shell of the Vela
supernova remnant is discussed.


title:
Detection of Strong Clustering of Extremely Red Objects: Implications
  for the Density of z > 1 Ellipticals

abstract:
  We present the results of a wide-field survey for extremely red objects (EROs
hereafter), the widest so far, based on Ks and R band imaging. The survey
covers 701 arcmin^2 and it is 85% complete to Ks\leq18.8 over the whole area
and to Ks\leq19.2 over 447.5 arcmin^2. Thanks to the wide field covered, a
complete sample of about 400 EROs with R-Ks\geq5 was selected. The distribution
of the EROs on the sky is strongly inhomogeneous, being characterized by
overdensities and large voids. We detect at the 8 sigma level a strong
clustering signal of the EROs which is about an order of magnitude larger than
the clustering of K-selected field galaxies in the same magnitude range. A
smooth trend of increasing clustering amplitude with the R-Ks color is
observed. These results are strong evidence that the largest fraction of EROs
is composed of high-z ellipticals, of which we detect for the first time the
z\simgt1 large scale structure clustering signal. We show how the surface
density variations of the ERO population found in our survey can explain the
highly discrepant results obtained so far on the density of z > 1 ellipticals,
and we briefly discuss the main implications of our results for the evolution
of elliptical galaxies. The number counts and the colors of the K-selected
field galaxies are also presented and briefly discussed.


title: A disk-wind model with correct crossing of all MHD critical surfaces

abstract:
  The classical Blandford & Payne (1982) model for the magnetocentrifugal
acceleration and collimation of a disk-wind is revisited and refined. In the
original model, the gas is cold and the solution is everywhere subfast
magnetosonic. In the present model the plasma has a finite temperature and the
self-consistent solution of the MHD equations starts with a subslow
magnetosonic speed which subsequently crosses all critical points, at the slow
magnetosonic, Alfven and fast magnetosonic separatrix surfaces. The superfast
magnetosonic solution thus satisfies MHD causality. Downstream of the fast
magnetosonic critical point the poloidal streamlines overfocus towards the axis
and the solution is terminated. The validity of the model to disk winds
associated with young stellar objects is briefly discussed. ~


title: The Eta Chamaeleontis Cluster: Origin in the Sco-Cen OB Association

abstract:
  A young, nearby compact aggregate of X-ray emitting pre-main sequence stars
was recently discovered in the vicinity of eta Cha (B8V). In this paper, we
further investigate this cluster: its membership, its environs and origins.
ROSAT HRI X-ray data for the cluster's T Tauri stars show high levels of
magnetic activity and variability. The cluster has an anomalous X-ray
luminosity function compared to other young clusters, deficient in stars with
low, but detectable X-ray luminosities. This suggests that many low-mass
members have escaped the surveyed core region. Photographic photometry from the
USNO-A2.0 catalog indicates that additional, X-ray-quiet members exist in the
cluster core region. The components of the eclipsing binary RS Cha, previously
modeled in the literature as post-MS with discordant ages, are shown to be
consistent with being coeval pre-MS stars. We compute the Galactic motion of
the cluster from Hipparcos data, and compare it to other young stars and
associations in the fourth Galactic quadrant. The kinematic study shows that
the eta Cha cluster, the TW Hya association, and a new group near epsilon Cha,
probably originated near the giant molecular cloud complex that formed the two
oldest subgroups of the Sco-Cen OB association roughly 10-15 Myr ago. Their
dispersal is consistent with the velocity dispersions seen in giant molecular
clouds. A large H I filament and dust lane located near eta Cha has been
identified as part of a superbubble formed by Sco-Cen OB winds and supernova
remnants. The passage of the superbubble may have terminated star-formation in
the eta Cha cluster and dispersed its natal molecular gas.


title: Type Ia Supernova Explosion Models: Homogeneity versus Diversity

abstract:
  Type Ia supernovae (SN Ia) are generally believed to be the result of the
thermonuclear disruption of Chandrasekhar-mass carbon-oxygen white dwarfs,
mainly because such thermonuclear explosions can account for the right amount
of Ni-56, which is needed to explain the light curves and the late-time
spectra, and the abundances of intermediate-mass nuclei which dominate the
spectra near maximum light. Because of their enormous brightness and apparent
homogeneity SN Ia have become an important tool to measure cosmological
parameters. In this article the present understanding of the physics of
thermonuclear explosions is reviewed. In particular, we focus our attention on
subsonic (``deflagration'') fronts, i.e. we investigate fronts propagating by
heat diffusion and convection rather than by compression. Models based upon
this mode of nuclear burning have been applied very successfully to the SN Ia
problem, and are able to reproduce many of their observed features remarkably
well. However, the models also indicate that SN Ia may differ considerably from
each other, which is of importance if they are to be used as standard candles.


title:
Low and High Ionization Absorption Properties of Mg II
  Absorption-Selected Galaxies at Intermediate Redshifts. I. General Properties

abstract:
  We present extensive metal-line absorption properties for 45 absorption
systems that were selected by their Mg II absorption at redshifts between 0.4
and 1.4. For each system the properties of several chemical species are
determined, including a wide range of ionization conditions. In the optical,
the absorption systems have been observed at ~6 km/s resolution with
HIRES/Keck, which covered Mg II, several Fe II transitions, Mg I, and in some
cases (depending upon redshift), Ca II, Ti II, Mn II, and Al III. Ultraviolet,
lower resolution (~230 km/s) Faint Object Spectrograph data (1600 - 3275 Ang)
were obtained from the Hubble Space Telescope archive. These spectra covered Al
II, Al III, Si II, Si III, Si IV, C II, C III, C IV, N V, O VI, and several
Lyman series transitions, with coverage dependent upon the absorption system
redshift. From these data, we infer that Mg II absorbing galaxies at
intermediate redshifts have multiphase gaseous structures.


title:
Low and High Ionization Absorption Properties of Mg II
  Absorption-Selected Galaxies at Intermediate Redshifts. II. Taxonomy,
  Kinematics, and Galaxies

abstract:
  [Abridged] We examine a sample of 45 Mg II absorption-selected systems over
the redshift range 0.4 to 1.4. Mg II and Fe II absorption profiles were
observed at a resolution of ~6 km/s with HIRES/Keck. Lyman-alpha and C IV data
were measured in archival FOS/HST spectra (~230 km/s). We perform a
multivariate analysis of W(MgII), W(FeII), W(CIV) and W(Lya) (rest-frame)
equivalent widths and the Mg II kinematic spread. We find five categories of Mg
II absorbers: "Classic", "C IV-deficient", "Single/Weak", "Double", and
"DLA/HI-Rich". There is a strong connection between low-ionization kinematics
and the location of an absorber on the W(CIV)-W(MgII) plane. In most absorbers
a significant fraction of the C IV arises in a phase separate from Mg II. Many
of the C IV profiles are resolved in the FOS spectra due to velocity
structure.. For 16 galaxies, we compare the available absorption-line
properties (taken from Churchill et al. 2000, Paper I) to the galaxy properties
but find no significant (greater than 3-sigma) correlations, although several
suggestive trends are apparent. We compare the locations of our intermediate
redshift absorbers on the W(CIV)-W(MgII) plane with those of lower and higher
redshift data taken from the literature and find evidence for evolution that is
connected with the Mg II kinematics. We discuss the potential of using the
above categorizations of absorbers to understand the evolution in the
underlying physical processes giving rise to the gas and governing its
ionization phases and kinematics.


title:
The Sun's acoustic asphericity and magnetic fields in the solar
  convection zone

abstract:
  The observed splittings of solar oscillation frequencies can be employed to
separate the effects of internal solar rotation and to estimate the
contribution from a large-scale magnetic field or any latitude-dependent
thermal perturbation inside the Sun. The surface distortion estimated from the
rotation rate in the solar interior is found to be in good agreement with the
observed oblateness at solar surface. After subtracting out the estimated
contribution from rotation, there is some residual signal in the even splitting
coefficients, which may be explained by a magnetic field of approximately 20 kG
strength located at a depth of 30000 km below the surface or an equivalent
aspherical thermal perturbation. An upper limit of 300 kG is derived for a
toroidal field near the base of the convection zone.


title:
Consequences of parton's saturation and string's percolation on the
  developments of cosmic ray showers

abstract:
  At high gluon or string densities, gluons' saturation or the strong
interaction among strings, either forming colour ropes or giving rise to
string's percolation, induces a strong suppression in the particle
multiplicities produced at high energy. This suppression implies important
modifications on cosmic ray shower development. In particular, it is shown that
it affects the depth of maximum, the elongation rate, and the behaviour of the
number of muons at energies around 10^{17}-10^{18} eV. The existing cosmic ray
data point out in the same direction.


title:
Clusters AgeS Experiment. RR Lyr Variables in the Globular Cluster NGC
  6362

abstract:
  We present V and B-band CCD photometry of 35 RR Lyr stars in the southern
hemisphere globular cluster NGC 6362. Fourier decomposition of the light curves
was used to estimate the basic properties of these variables. From the analysis
of the RRc stars we obtain a mean mass of M=0.531+/-0.014 $M_\odot$, luminosity
log L=1.656+/-0.006, effective temperature Teff=7429+/-20, and helium abundance
Y=0.292+/-0.002. The mean values of the absolute magnitude, metallicity (on
Jurcsik's scale) and effective temperature for 14 RRab stars with "regular"
light curves are: M_V=0.86+/-0.01, [Fe/H]=-0.93+/-0.04 and Teff=6555+/-25,
respectively. From the B-V colors, periods and metallicities of the RRab stars
we estimate the color excess for NGC 6362 to be equal to E(B-V)=0.08+/-0.01.
Using this value we derive the colors of the blue and red edges of the
instability strip in NGC 6362 to be $(B-V)^{BE}_0=0.17$ and
$(B-V)^{RE}_0=0.43$. From the relations between the Fourier coefficients of
RRab and RRc stars and their absolute magnitudes we estimate the apparent
distance modulus to NGC 6362 to be (m-M)_V=14.46+/-0.10. From the mean value of
log L of the RRc stars we obtain 14.59+/-0.03. The V-band light curves of three
of the RRc stars exhibit changes in amplitude of over 0.1 mag on the time scale
of around one week. Near the radial 1st overtone frequency we find one or two
peaks, which strongly suggests that these variables belong to the newly
identified group of non-radial pulsating RR Lyr stars.


title:
Cosmological Evolution Models for QSO/AGN Luminosity Functions: Effects
  of Spectrum-Luminosity Correlation and Massive Black Hole Remnants

abstract:
  We investigate a large number of cosmological evolution models for QSOs and
Active Galactic Nuclei (AGN). We introduce a spectrum-luminosity correlation as
a new input parameter and adopt the estimated mass function (MF) of massive
black holes in centers of nearby galactic nuclei as a constraint to distinguish
among different QSO/AGN models. We explore three basic types of
phenomenological scenarios; (i) Models with multiple short-lived ($\sim$ a few
$10^{6-8}$ yrs) populations, (ii) Models with a single long-lived ($\sim 10^9$
yr) QSO population, and (iii) Models with recurrent QSO/AGN activities which
are driven by long-term variabilities of the disk instability type. In each
model, we derive the expected theoretical luminosity function (LF) and the MF
of black holes which grow through mass accretion. We assess the plausibility of
each model based on whether each model's LF and MF are compatible with the
observed data. We find that the best fits to the observed LFs are obtained in
the model with multiple short-lived populations and without any significant
spectral evolution. This finding suggests that the QSO populations may be
composed of many short-lived generations ($\sim$ a few 10$^8$ yrs) and that
there is no significant spectral evolution within each generation. On the other
hand, we also show that there is no satisfactory model which can simultaneously
account for the observed LF and the estimated MF. We speculate that some of the
present-day black holes (BHs) found in galactic nuclei may have formed without
undergoing the QSO/AGN phase.


title: Jets in quasars, microquasars and gamma-ray bursts

abstract:
  Relativistic outflows are common in accreting and forming black holes.
Despite the enormous differences in scale, stellar-mass black holes in X-ray
binaries and supermassive black holes in Galactic Nuclei produce jets with
analogous properties. In both are observed two types of relativistic outflows:
1) quasi-steady compact jets with flat-spectrum, and 2) episodic large-scale
ejections with steep-spectrum and apparent superluminal motions. Because of the
short time scale of the phenomena in black hole binaries, the formation of
synchrotron jets is associated to changes in the X-ray thermal emission from
the accretion disk. Besides, the most common class of gamma-ray bursts can be
conceived as extreme microquasars, since they are afterglows from
ultra-relativistic jets associated to the formation of black holes at
cosmological distances.


title: The jet of 3C 273 observed with ROSAT HRI

abstract:
  ROSAT HRI observations of 3C 273 reveal X-ray emission all along the
optically visible jet with the peak of emission at the inner end. Whereas the
X-ray emission from the innermost knot A is consistent with a continuation of
the radio-to-optical synchrotron continuum, a second population of particles
with higher maximum energy has to be invoked to explain the X-ray emission from
knots B, C and D in terms of synchrotron radiation. Inverse Compton emission
could account for the X-ray flux from the hot spot. We detect a faint X-ray
halo with a characteristic scale of 29 kpc and particle density on the order of
6 x 10^4 m^-3, higher than previously thought.


title: Hard component of ultra-high energy cosmic rays and vortons

abstract:
  Observed events of ultra-high energy cosmic rays may indicate a hard
component for the energy spectrum of their flux, which might have origin in the
decay of long-lived vortons presumably condensed in the galactic halo. To be
consistent with the needed present density, vortons may have been formed during
the breaking of an abelian symmetry contained in a large GUT group like E6 and
a part of them could have survived the destabilization caused by the
electroweak transition.


title:
Supernovae data: Cosmological Constant or ruling out the Cosmological
  Principle ?

abstract:
  Analysed in the framework of homogeneous FLRW models, the magnitude-redshift
data from high redshift supernovae yield, as a primary result, a strictly
positive cosmological constant. Another reading of the currently published
measurements does not exclude a possible ruling out of the Cosmological
Principle and, thus, also, of the cosmological constant hypothesis. It is shown
how shortly coming data can be used to settle this fondamental issue,
pertaining to both cosmology and particle physics.


title:
Getting the Red Out: A Stellar Approach to Determining Spatial
  Variations of Interstellar Dust

abstract:
  By employing two different spectroscopic techniques we have mapped out the
variable ISM dust extinction endemic to globular cluster M4. We derive an
average E(B-V) reddening of 0.33 +/- 0.01 and R = 3.4 +/- 0.4, both in good
agreement with previous studies of M4. For individual stars in the most heavily
reddened regions of M4, we find E(B-V) values significantly higher than those
inferred by studies of interstellar gas; for heavily reddened regions, the gas
measured in column density measurements may not completely trace the dust.


title: On the intensity of the cosmic X-ray background

abstract:
  Measurements of the intensity of the cosmic X-ray background (XRB) carried
out over small solid angles are subject to spatial variations due to the
discrete nature of the XRB. This cosmic variance can account for the dispersion
of XRB intensity values found within the ASCA, BeppoSAX and ROSAT missions
separately. However there are differences among the values obtained in the
different missions which are not due to spatial fluctuations but, more likely,
to systematic cross-calibration errors. Prompted by recent work which shows
that ROSAT PSPC has calibration differences with all the other missions, we
compute a bayesian estimate for the XRB intensity at 1 keV of
10.0^{+0.6}_{-0.9} keV/cm2/s/keV/sr (90 per cent confidence errors) using the
ASCA and BeppoSAX data points. However, this value is still significantly
larger than the HEAO-1 intensity measured over many thousands of square degrees
(8 keV/cm2/s/keV/sr).


title:
Accretion disk models and their X-ray reflection signatures. I. Local
  spectra

abstract:
  X-ray illumination of accretion disks is an invaluable diagnostic of the
structure of these disks because of the associated iron K$\alpha$ emission.
Here we point out that the resulting reflected spectra depend very sensitively
on the geometry of the X-ray source, and that this fact can be efficiently used
to test these models observationally. In particular, we discuss three different
accretion disk geometries: the ``lamppost model'', accretion disks with
magnetic flares, and the model with a full corona overlying a cold thin disk.
We show that in the case of the lamppost model, unless the X-ray luminosity of
the central source is larger than that of the cold disk by a factor of 10 or
more, a significant fraction of iron in the ionized skin of the disk is in the
hydrogen and helium-like ions. Because these ions have large fluorescence
yields, the resulting reflected spectra look strongly ionized, with Equivalent
Width (EW) of the line {\em increasing} with X-ray luminosity $L_x$ up to the
maximum of $\sim 500$ eV. This situation contrasts to the magnetic flare model,
where the large X-ray flux near flares completely ionizes the skin of the disk
and thus the resulting spectra appear to be that from a neutral material. The
line EW in this model {\em anti-correlates} with X-ray luminosity, and becomes
arbitrarily small when $L_x$ is a good fraction of the Eddington luminosity.
Finally, in the full corona case, due to the additional pressure and weight of
the corona, the gas pressure (and its density) below the corona is always large
enough to make the gas very cool and effectively neutral. No highly ionized
skin forms in such a model. If the corona is Thomson thin, then EW of the line
does not depend on the accretion disk or corona luminosities for the full
corona model.


title:
The INT Search for Metal-Poor Stars. Spectroscopic Observations and
  Classification via Artificial Neural Networks

abstract:
  With the dual aims of enlarging the list of extremely metal-poor stars
identified in the Galaxy, and boosting the numbers of moderately
metal-deficient stars in directions that sample the rotational properties of
the thick disk, we have used the 2.5m Isaac Newton Telescope and the
Intermediate Dispersion Spectrograph to carry out a survey of brighter
(primarily northern hemisphere) metal-poor candidates selected from the HK
objective-prism/interference-filter survey of Beers and collaborators. Over the
course of only three observing runs (15 nights) we have obtained
medium-resolution (resolving power ~ 2000) spectra for 1203 objects (V ~
11-15). Spectral absorption-line indices and radial velocities have been
measured for all of the candidates. Metallicities, quantified by [Fe/H], and
intrinsic (B-V)o colors have been estimated for 731 stars with effective
temperatures cooler than roughly 6500 K, making use of artificial neural
networks (ANNs), trained with spectral indices. We show that this method
performs as well as a previously explored Ca II K calibration technique, yet it
presents some practical advantages. Among the candidates in our sample, we
identify 195 stars with [Fe/H] <= -1.0, 67 stars with [Fe/H] <= -2.0, and 12
new stars with [Fe/H] <= -3.0. Although the EFECTIVE YIELD of metal-poor stars
in our sample is not as large as previous HK survey follow-up programs, the
rate of discovery per unit of telescope time is quite high.


title:
Complete RXTE Spectral Observations of the Black Hole X-ray Nova XTE
  J1550-564

abstract:
  We report on the X-ray spectral behavior of the exceptionally bright X-ray
nova XTE J1550-564 during its 1998-99 outburst. Our study is based on 209
pointed observations using the PCA and HEXTE instruments onboard the Rossi
X-ray Timing Explorer spanning 250 days and covering the entire double-peaked
eruption that occurred from 1998 September until 1999 May. The spectra are fit
to a model including multicolor blackbody disk and power-law components. The
source is observed in the very high and high/soft outburst states of black hole
X-ray novae. During the very high state, when the power-law component dominated
the spectrum, the inner disk radius is observed to vary by more than an order
of magnitude; the radius decreased by a factor of 16 in one day during a 6.8
Crab flare. If the larger of these observed radii is taken to be the last
stable orbit, then the smaller observed radius would imply that the inner edge
of the disk is inside the event horizon! However, we conclude that the apparent
variations of the inner disk radius observed during periods of increased
power-law emission are probably caused by the failure of the multicolor
disk/power-law model; the actual physical radius of the inner disk may remain
fairly constant. This interpretation is supported by the fact that the observed
inner disk radius remains approximately constant over 120 days in the high
state, when the power-law component is weak, even though the disk flux and
total flux vary by an order of magnitude. The mass of the black hole inferred
by equating the approximately constant inner disk radius observed in the
high/soft state with the last stable orbit for a Schwarzschild black hole is
M_BH = 7.4 M_sun (D/6 kpc) (cos i)^{-1/2}.


title: Hipparcos, IUE, and the Stellar Content of the Solar Neighbourhood

abstract:
  The spectroscopic parallaxes in the Hipparcos catalogue can be used to
translate absolute stellar fluxes observed at Earth to the fluxes emerging at
the stellar surface for nearby stars. The comparison of these fluxes with the
predictions of theoretical model atmospheres allows us to determine the
effective temperature and the metallicity of the stars. It is suggested that is
possible to study the stellar content of the solar neighbourhood making use of
the large number of ultraviolet spectra in the archive of the IUE satellite.


title:
Proton and Electron Acceleration through Magnetic Turbulence in
  Relativistic Outflows

abstract:
  Low frequency electromagnetic turbulence is generated in relativistically
outflowing plasma that sweeps up particles from the surrounding environment.
Electrons are energized by stochastic gyroresonant acceleration with the
turbulence produced by the isotropization of captured protons and charged dust.
Protons are accelerated stochastically by the dust-induced turbulence.
Analytical solutions for the proton and electron energy distributions are
obtained and used to calculate broadband synchrotron emission. The solutions
are compared with generic spectral behavior of blazars and gamma-ray bursts.
Dust captured by a blast wave can generate turbulence that could accelerate
protons to very high energies.


title: Extra-Solar Planets

abstract:
  The discovery of the first extra-solar planet surrounding a main-sequence
star was announced in 1995, based on very precise radial velocity (Doppler)
measurements. A total of 34 such planets were known by the end of March 2000,
and their numbers are growing steadily. The newly-discovered systems confirm
some of the features predicted by standard theories of star and planet
formation, but systems with massive planets having very small orbital radii and
large eccentricities are common and were generally unexpected. Other techniques
being used to search for planetary signatures include accurate measurement of
positional (astrometric) displacements, gravitational microlensing, and pulsar
timing, the latter resulting in the detection of the first planetary mass
bodies beyond our Solar System in 1992. The transit of a planet across the face
of the host star provides significant physical diagnostics, and the first such
detection was announced in 1999. Protoplanetary disks, which represent an
important evolutionary stage for understanding planet formation, are being
imaged from space. In contrast, direct imaging of extra-solar planets
represents an enormous challenge. Long-term efforts are directed towards
infrared space interferometry, the detection of Earth-mass planets, and
measurement of their spectral characteristics. Theoretical atmospheric models
provide predictions of planetary temperatures, radii, albedos, chemical
condensates, and spectral features as a function of mass, composition and
distance from the host star. Efforts to characterise planets occupying the
`habitable zone', in which liquid water may be present, and indicators of the
presence of life, are advancing quantitatively.


title: Ionization physics evidence for magnetic flare origin of X-rays in AGN

abstract:
  We present full disk X-ray reflection spectra for two currently popular
accretion flow geometries for AGN -- the lamppost model frequently used to
discuss the iron line reverberation in AGN, and the model where the X-rays are
produced in magnetic flares above a cold accretion disk (AD). The lamppost
spectra contain several spectroscopic features characteristic of highly ionized
material that are not seen in the X-ray spectra of most AGN. The magnetic flare
model, on the other hand, produces reflected spectra that are roughly a
super-position of a power-law and a {\em neutral-like} reflection and iron
K$\alpha$ line, and are thus more in line with typical AGN X-ray spectra.
Furthermore, because of the difference in the ionization structure of the
illuminated material in the two models, the line equivalent width increases
with the X-ray luminosity, $L_x$, for the lamppost, and decreases with $L_x$
for the flare model. In light of these theoretical insights, recent iron line
reverberation studies of AGN, the X-ray Baldwin effect, and the general lack of
X-ray reflection features in distant quasars all suggest that, for high
accretion rates, the cold accretion disk is covered by a Thomson thick,
completely ionized skin. Because the latter is only possible when the X-rays
are concentrated to small emitting regions, we believe that this presents a
strong evidence for the magnetic flare origin of X-rays in AGN.


title:
The Behind The Plane Survey - source selection, identifications and
  completeness

abstract:
  We present details of the Behind The Plane survey of IRAS galaxies, which
extends the PSCz survey to cover the 93% of the sky with complete and reliable
IRAS data from the Point Source Catalog. At low latitudes, our catalogue is not
complete to 0.6Jy, but the incompleteness is physically understood and can be
corrected for. IRAS galaxies at low latitudes are heavily or completely
obscured optically, and are heavily outnumbered by Galactic sources with
similar IRAS properties. We have used radio, optical, mm, near and far-infrared
data to identify the galaxies, and the 2D catalogue is now complete. We have
used optical and HI spectroscopy to obtain redshifts for the galaxies; the
southern spectroscopy is completed and the north nearly so.


title: A New Narrow-Line Seyfert 1 galaxy : RXJ1236.9+2656

abstract:
  We report identification of a narrow-line Seyfert 1 galaxy RXJ1236.9+2656.
X-ray emission from the NLS1 galaxy undergoes long-term variability with
0.1--2.0 keV flux changing by a factor of 2 within about 3 yr. The ROSAT PSPC
spectrum of RXJ1236.9+2656 is well represented by a power-law of Gamma = 3.7
absorbed by matter in our own Galaxy (N_H = 1.33X10^20 cm**-2). Intrinsic soft
X-ray luminosity of the NLS1 galaxy is estimated to be 1.5X10^43 erg/s in the
energy band of 0.1-2.0 keV. The optical spectrum of RXJ1236.9+2656 is typical
of NLS1 galaxies and shows narrow Balmer emission lines (1100 km/s < FWHM <
1700 km/s) of Hbeta, Halpha, and forbidden lines of [O III] and [N II]. Fe II
multiplets, usually present in optical spectra of NLS1 galaxies, are also
detected in RXJ1236.9+2656.


title: Interpolation of Discretely-Sampled Density Fields

abstract:
  We present a new technique for the interpolation of discretely-sampled
non-negat ive scalar fields across regions of missing data. Any set of basis
functions can be used, though the method is fastest when they are close to
orthogonal. We sho w how the technique may be efficiently applied when the
discrete sampling rate v aries across the field. Regularisation is desirable to
avoid over-fitting noisy data, and is necessary when the regions of missing
data are larger than the requ ired resolution. We present and investigate
methods for such regularisation.


title: Active Nucleus in a Poststarburst Galaxy : KUG 1259+280

abstract:
  We report the discovery of an active nucleus in a poststarburst galaxy,
KUG1259+280. High resolution X-ray imaging observations with ROSAT HRI show
that X-ray emission from KUG1259+280 is unresolved. X-ray emission from
KUG1259+280 is highly variable, an episode in which X-ray intensity changed by
a factor 2.5 within about 1300s has been detected. ROSAT PSPC spectra of this
galaxy is found to be well represented by a steep power law of photon index
4.25, and a change in the absorbing column within about a day is indicated. The
rest frame intrinsic X-ray luminosity of KUG1259+280 is found to be
3.6-4.7X10^42 erg/s similar to that of low luminosity Seyfert galaxies. Mass of
the central massive object within KUG1259+280 is estimated to be in the range
of 10^5-10^7 M_sun. Optical spectrum of the nuclear region of the galaxy is
complex and shows Balmer absorption and collisionally excited lines of [OIII],
and [NII]. The presence of forbidden emission lines and the absence of Balmer
emission lines in spectrum of KUG1259+280 could be due to photoionization by a
diluted power-law continuum modified by enhanced stellar absorption due to a
poststarburst event. Estimated Balmer line strengths free of stellar
absorptions and forbidden line strengths indicate the nucleus of KUG1259+280 to
be LINER-like in nature. However, the low-ionization forbidden line [OI]6300
usually present in LINER spectra, is not detected in the spectrum of
KUG1259+280. X-ray characteristics -- variability, point-like appearance,
luminosity and steepness of spectrum indicate that nucleus in KUG1259+280 is
active and perhaps like that of narrow-line Seyfert type 1 galaxies.


title: The Genesis of Cosmological Tracker Fields

abstract:
  The role of the quintessence field as a probable candidate for the repulsive
dark energy, the conditions for tracking and the requisites for tracker fields
are examined. The concept of `integrated tracking' is introduced and a new
criterion for the existence of tracker potentials is derived assuming monotonic
increase in the scalar energy density parameter \Omega_\phi with the evolution
of the universe as suggested by the astrophysical constraints. It provides a
technique to investigate generic potentials of the tracker fields. The general
properties of the tracker fields are discussed and their behaviour with respect
to tracking parameter \epsilon is analyzed. It is shown that the tracker fields
around the limiting value \epsilon \simeq \frac 23 give the best fit with the
observational constraints.


title:
The afterglow of the short/intermediate-duration gamma-ray burst GRB
  000301C: A jet at z=2.04

abstract:
  We present Ulysses and NEAR data from the detection of the short or
intermediate duration (2 s) gamma-ray burst GRB000301C (2000 March 1.41 UT).
The gamma-ray burst (GRB) was localised by the Inter Planetary Network (IPN)
and RXTE to an area of 50 arcmin^2. A fading optical counterpart was
subsequently discovered with the Nordic Optical Telescope (NOT) about 42h after
the burst. The GRB lies at the border between the long-soft and the short-hard
classes of GRBs. If GRB000301C belongs to the latter class, this would be the
first detection of an afterglow to a short-hard burst. We present UBRI and JHK
photometry from the time of the discovery until 11 days after the burst.
Finally, we present spectroscopic observations of the optical afterglow
obtained with the ESO VLT Antu telescope 4 and 5 days after the burst. The
optical light curve is consistent with being achromatic from 2 to 11 days after
the burst and exhibits a break. A broken power-law fit yields a shallow
pre-break decay power-law slope of a_1=-0.72+-0.06, a break time of
t_b=4.39+-0.26 days after the burst, and a post-break slope of a_2=-2.29+-0.17,
which is best explained by a sideways expanding jet in an ambient medium of
constant mean density. In the optical spectrum we find absorption features that
are consistent with FeII, CIV, CII, SiII and Ly-a at a redshift of
2.0404+-0.0008. We find evidence for a curved shape of the spectral energy
distribution of the observed afterglow. It is best fitted with a power-law
spectral distribution with index b ~ -0.7 reddened by an SMC-like extinction
law with A_V~0.1 mag. Based on the Ly-a absorption line we estimate the HI
column density to be log(N(HI))=21.2+-0.5. This is the first direct indication
of a connection between GRB host galaxies and Damped Ly-a Absorbers.


title: Chemical composition of evolved stars in the open cluster M 67

abstract:
  High-resolution spectra of six core helium-burning `clump' stars and three
giants in the open cluster M 67 have been obtained with the SOFIN spectrograph
on the Nordic Optical Telescope to investigate abundances of up to 25 chemical
elements. Abundances of carbon were studied using the C2 Swan (0,1) band head
at 5635.5 A. The wavelength interval 7980-8130 A with strong CN features was
analysed in order to determine nitrogen abundances and 12C/13C isotope ratios.
The oxygen abundances were determined from the [O I] line at 6300 A.
  The overall metallicity of the cluster stars was found to be close to solar
([Fe/H]=-0.03+-0.03). Compared with the Sun and other dwarf stars of the
Galactic disk, as well as with dwarf stars of M 67 itself, abundances in the
investigated stars suggest that carbon is depleted by about 0.2 dex, nitrogen
is enhanced by about 0.2 dex and oxygen is unaltered. Among other mixing-
sensitive chemical elements an overabundance of sodium may be suspected. The
mean C/N and 12C/13C ratios are lowered to the values of 1.7+-0.2 and 24+-4 in
the giants and to the values of 1.4+-0.2 and 16+-4 in the clump stars. These
results suggest that extra mixing of CN-cycled material to the stellar surface
takes place after the He-core flash. Abundances of heavy chemical elements in
all nine stars were found to be almost identical and close to solar.


title: Quasistellar Objects: Intervening Absorption Lines

abstract:
  We briefly review, at a level appropriate for graduate students and
non-specialists, the field of quasar absorption lines (QALs). Emphasis is on
the intervening absorbers. We present the anatomy of a quasar spectrum due to
various classes of intervening absorption systems, and a brief historical
review of each absorber class (Lyman-alpha forest and Lyman limit systems, and
metal-line and damped Lyman-alpha absorbers). We also provide several heuristic
examples on how the physical properties of both the intergalactic medium and
the gaseous environments associated with earlier epoch galaxies can be inferred
from QALs. The evolution of these environments from z=4 are discussed.


title:
The FIRST Sample of Ultraluminous Infrared Galaxies at High Redshift I.
  Sample and Near-IR Morphologies

abstract:
  We present a new sample of distant ultraluminous infrared galaxies. The
sample was selected from a positional cross--correlation of the IRAS Faint
Source Catalog with the FIRST database. Objects from this set were selected for
spectroscopy by virtue of following the well-known star-forming galaxy
correlation between 1.4 GHz and 60 micron flux, and by being optically faint on
the POSS. Optical identification and spectroscopy were obtained for 108 targets
at the Lick Observatory 3m telescope. Most objects show spectra typical of
starburst galaxies, and do not show the high ionization lines of active
galactic nuclei. The redshift distribution covers 0.1 < z < 0.9, with 13
objects at z > 0.5 and an average redshift of 0.31. K-band images were obtained
at the IRTF, Lick, and Keck observatories in sub-arcsec seeing of all optically
identified targets. About 2/3 of the objects appear to be interacting galaxies,
while the other 1/3 appear to be normal. Nearly all the identified objects have
far-IR luminosities greater than 10^11 L_sun, and ~25% have L_FIR > 10^12
L_sun.


title: Possible Evidence for a Truncated Thin Disk in Seyfert 1 Galaxy NGC4593

abstract:
  We compile the multi-band spectral energy distribution (SED) of Seyfert 1
galaxy NGC4593, and investigate its optical-to-ultraviolet (OUV) continuum and
iron K\alpha line profile. No strong ``big blue bump'' is found in OUV band.
The iron K\alpha line profile is not as broad as expected from a disk which
extends down to the last stable orbit. Both of them can be modeled by a
truncated thin disk, and support the existence of a truncated thin disk in the
system. It is of much interest that NGC4593 may be a typical object with an
accretion rate \dot{m}=\dot{M}/M_{Edd} \sim 0.01-0.1 and harbors a two
component accretion flow: an outer thin disk and an inner hot flow--possibly
ADAF, analogous to the low and intermediate state of low mass X-ray binaries
(LMXB).


title: The IRAS view of the Local Universe

abstract:
  We summarise results for the predicted density and peculiar velocity fields
from the PSCz survey. We have used a generalisation of the Path Interchange
Zeldovich Approximation to determine the velocity field; the most remarkable
feature being a coherent large-scale flow along the baseline connecting the
Local Supercluster, Centaurus and the Shapley Concentration. Comparison of the
predicted and observed bulk flows gives a value of beta = 0.50+-0.1.
  We re-examine the PSCz dipole, with improved redshift completeness at
low-latitudes and using PIZA to estimate real-space distances. We find the
dipole to be stable between 80 and 180 hMpc, although there appears to be a
significant contribution to the dipole around 200 hMpc. The overall
misalignment with the CMB dipole remains at 20degrees. The implied value of
beta is in the range 0.40-0.55 with statistical error +-0.1. We also present
the density field and a preliminary dipole analysis from the almost completed
Behind The Plane survey, which extends the PSCz to cover 93% of the sky
including the proposed core of the Great Attractor. We find a density peak at
(325,-5,3500km/s), about half as massive as Centaurus or Pavo-Indus, and
forming part of a continuous filament linking them across the Plane. We also
find evidence for a much larger `Greater Attractor' directly behind the GA, at
a distance of 125 hMpc, and more massive than the Shapley concentration.
  At large distances the dipole direction is in much improved agreement with
the CMB: at 250-300hMpc, the misalignment is only 5-10 degrees, though this
depends on the incompleteness corrections made. The dipole amplitude implies a
value for the parameter beta of 0.44+-0.1.


title: Dwarf galaxy formation induced by galaxy interactions

abstract:
  Growing evidence has been accumulated for that some gas-rich dwarf galaxies
are formed from material liberated by galaxy collisions and/or mergers. Also,
gas-poor dwarf elliptical galaxies are often found in the central regions of
clusters of galaxies. These observations suggest strongly that the formation of
most dwarf galaxies is linked to galaxy interactions. Therefore, now seems like
the right time to investigate the formation efficiency of such tidal dwarf
galaxies. Adopting the galaxy interaction scenario proposed by Silk & Norman,
we find that if only a few dwarf galaxies are formed in each galaxy collision,
we are able to explain the observed morphology-density relations for both dwarf
and giant galaxies in the field, groups of galaxies, and clusters of galaxies.
It seems worthwhile noting that the tidal dwarf formation may be coupled with
the transformation from gas-rich disk galaxies to early-type galaxies such as
S0 and elliptical galaxies.


title: UV Background-Induced Bifurcation of the Galactic Morphology

abstract:
  Based upon a novel paradigm of the galaxy formation under UV background, the
evolutionary bifurcation of pregalactic clouds is confronted with observations
on elliptical and spiral galaxies. The theory predicts that the dichotomy
between the dissipational and dissipationless galaxy formation stems from the
degree of self-shielding from the UV background radiation. This is demonstrated
on a bifurcation diagram of collapse epochs versus masses of pregalactic
clouds. Using the observed properties, the collapse epochs are assessed for
each type of galaxies with attentive mass estimation. By the direct comparison
of the theory with the observations, it turns out that the theoretical
bifurcation branch successfully discriminates between elliptical and spiral
galaxies. This suggests that the UV background radiation could play a profound
role for the differentiation of the galactic morphology into the Hubble
sequence.


title:
A Survey for Faint Stars of Large Proper Motion Using Extra Poss II
  Plates

abstract:
  We have conducted a search for new stars of high proper motion ($\geq$0.4
arcsec yr$^{-1}$) using POSS II fields for which an extra IIIaF (red) plate of
good quality exists, along with useable IIIaJ (blue) and IV-N (infrared) plates
taken at epochs differing by a minimum of 1.5 years. Thirty-five fields at
Galactic latitudes $|b| \geq$ 20$^o$ were measured, covering some 1378 deg$^2$,
or 3.3% of the sky. Searches with three plate combinations as well as all four
plates were also made. Seven new stars were found with $\mu \geq$0.5 arcsec
yr$^{-1}$, which were therefore missed in the Luyten Half Second (LHS) Catalog.
One of these is a common proper motion binary consisting of two subdwarf M
stars; another is a cool white dwarf with probable halo kinematics. As a test
of our completeness -- and of our ability to test that of Luyten -- 216 of 230
catalogued high proper motion stars were recovered by the software, or 94%.
Reasons for incompleteness of the LHS are discussed, such as the simple fact
that POSS II plates have deeper limiting magnitudes and greater overlap than
did POSS I. Nonetheless, our results suggest that the LHS is closer to 90%
complete than recent estimates in the literature (e.g 60%), and we propose a
reason to account for one such lower estimate. The conclusion that the LHS
Catalog is more complete has implications for the nature of the halo dark
matter. In particular it strengthens the constraint on the local density of
halo stars, especially white dwarfs at M$_V\sim$17-18.


title: Infrared Properties of SiO Maser Sources in Late-Type Stars

abstract:
  Results of an SiO maser survey for the late-type stars selected by the IRTS
(Infrared Telescope in Space) are presented. We have detected SiO J=1-0, v=1
and/or v=2 lines in 27 stars out of 59 stars. The maser intensity increases
with the depth of the H2O absorption in the infrared spectra and redness of the
2.2 and 12 micron color. The column densities of the water vapor in the target
stars are estimated from the depth of the water absorption in the IRTS spectra.
We found that the SiO maser was detected mostly in the stars with the column
density of water vapor higher than 3x10^19-3x10^20 cm^-2. We further estimate
the density of hydrogen molecules in the outer atmosphere corresponding to
these column densities, obtaining 10^9 - 10^10 cm^-3 as a lower limit. These
values are roughly in agreement with the critical hydrogen density predicted by
models for the excitation of the SiO masers. It is possible that the SiO masers
are excited in clumps with even higher than this density. The present results
provide useful information on the understanding of the physical conditions of
the outer atmospheres in late-type stars.


title: Turbulent Molecular Cloud Cores: Rotational Properties

abstract:
  The rotational properties of centrally condensed, turbulent molecular cloud
cores with velocity fields that are characterized by Gaussian random fields are
investigated. It is shown that the observed line width-size relationship can be
reproduced if the velocity power spectrum is a power-law with P(k)=k**n and
n=-3 to -4. The line-of-sight velocity maps of these cores show velocity
gradients that can be interpreted as rotation. For n=-4, both, the deduced
values of the angular velocity Omega=1.6 km/s/pc * (R/0.1 pc)**0.5 and the
scaling relations between Omega and the core radius R are in very good
agreement with the observations. As a result of the dominance of long
wavelength modes, the cores also have a net specific angular momentum with an
average value of j=7*(10**20)*(R/0.1 pc)**(1.5) cm**2/s with a large spread.
Their internal dimensionless rotational parameter is beta=0.03, independent of
the scale radius R. In general, the line-of-sight velocity gradient of an
individual turbulent core does not provide a good estimate of its internal
specific angular momentum. We find however that the distribution of the
specific angular momenta of a large sample of cores which are described by the
same power spectrum can be determined very accurately from the distribution of
their line-of-sight velocity gradients Omega using the simple formula
j=p*Omega*R*R where p depends on the density distribution of the core and has
to be determined from a Monte-Carlo study. Our results show that for centrally
condensed cores the intrinsic angular momentum is overestimated by a factor of
2-3 if p=0.4 is used.


title: Magnetic collimation of the solar and stellar winds

abstract:
  We resolve the paradox that although magnetic collimation of an isotropic
solar wind results in an enhancement of its proton flux along the polar
directions, several observations indicate a wind proton flux peaked at the
equator. To that goal, we solve the full set of the time-dependent MHD
equations describing the axisymmetric outflow of plasma from the magnetized and
rotating Sun, either in its present form of the solar wind, or, in its earlier
form of a protosolar wind. Special attention is directed towards the
collimation properties of the solar outflow at large heliocentric distances.
For the present day solar wind it is found that the poloidal streamlines and
fieldlines are only slightly focused toward the solar poles. However, even such
a modest compression of the flow by the azimuthal magnetic field would lead to
an increase of the mass flux at the polar axis by about 20% at 1 AU, relatively
to its value at the equator, for an initially isotropic at the base wind,
contrary to older and recent (Prognoz, Ulysses, SOHO) observations. For the
anisotropic in heliolatitude wind with parameters at the base inferred from in
situ observations by ULYSSES/SWOOPS and SOHO/CDS the effect of collimation is
almost totally compensated by the initial velocity and density anisotropy of
the wind. This effect should be taken into account in the interpretation of the
recent SOHO observations by the SWAN instrument. Similar simulations have been
performed for a five- and ten-fold increase of the solar angular velocity
corresponding presumably to the wind of an earlier phase of our Sun. For such
conditions it is found that for initially radial streamlines, the azimuthal
magnetic field created by the fast rotation focus them toward the rotation axis
and forms a tightly collimated jet.


title:
The Dark and Luminous Matter coupling in the formation of spheroids: a
  SPH investigation

abstract:
  Using N-body/hydrodynamical simulations which include prescriptions for Star
Formation, Feed-Back and Chemical Evolution, we explore the interaction between
baryons and Dark Matter at galactic scale. The N-body simulations are performed
using a Tree-SPH code that follows the evolution of individual DM halos inside
which stars form from cooling gas, and evolve delivering in the interstellar
medium mass, metals, and energy. We examine the formation and evolution of a
giant and a dwarf elliptical galaxy of total mass 10^12 and 10^9 solar masses,
respectively. Starting from an initial density profile like the universal
Navarro profile in the inner region, baryons sink towards the center due to
cooling energy losses. At the end of the collapse, the innermost part (1/20 of
the halo size) of the galaxy is baryon-dominated, whereas the outer regions are
DM dominated. The Star Formation proceeds at much faster speed in the giant
galaxy where a spheroid of 8 \times 10^10 solar masses is formed in 2 Gyr, with
respect to the dwarf galaxy where the spheroid of 2 \times 10^7 solar masses is
formed in 4 Gyr. For the two objects the final distribution of stars is well
fitted by a Hernquist profile with effective radii of r_e = 30 kpc, and 2.8
kpc, respectively. The dark-to-luminous tarnsition radius r_IBD occurs roughly
at 1 r_e, as in real ellipticals. The DM halo density evolution is
non-adiabatic and does not lead to a core radius.


title:
Comment on ``Violation of the Greisen-Zatsepin-Kuzmin Cutoff: A Tempest
  in a (Magnetic) Teapot? Why Cosmic Ray Energies above $10^{20}$ eV May Not
  Require New Physics''

abstract:
  In a recent letter [1] with the same title, Farrar and Piran offered an
explanation for the near isotropy of the arrival directions [2] of ultrahigh
energy cosmic rays (UHECRs) and the apparent absence [3] of the so called `GZK
cutoff' in their spectrum around $10^{20}$ eV due to pion photoproduction on
the cosmic background radiation (CMB) that was predicted independently by
Greisen [4] and by Zatsepin and Kuz'min [5]. They suggested that the
extragalactic magnetic fields near the Milky Way are strong enough to deflect
and isotropise the arrival directions of the UHECRs from a few nearby sources
for which their travel time to Earth is shorter than their attenuation time by
pion photoproduction on the CMB. They also estimated that this allows active
galactic nuclei (AGNs) or gamma ray bursts (GRBs) to be the source of the
UHECRs. However, these suggestions are inconsistent with various observations


title: BeppoSAX - ROSAT PSPC observations of the Shapley Supercluster: A3562

abstract:
  We present a combined analysis of the BeppoSAX and ROSAT PSPC observation of
the cluster of galaxies A3562, a massive member of the core of the Shapley
Supercluster. With a complex and interacting structure composed from two groups
of galaxies and A3558 to the West, the surface brightness of A3562 shows excess
in the sectors to East and South when compared with an azimuthally averaged
model of the emission. The emission tends to be flatter, and the distribution
of the gas broader, along the merging axis and in opposition to the two groups.
We present the first determination of the gradients of the gas temperature and
metallicity for a cluster in the Shapley region at large distance from cluster
center. From an analysis of the BeppoSAX data in annuli and sectors, we observe
both the profiles to be flat within 8 arcmin (0.62 Mpc), with an
emission-weighted values of kT = 5.1+-0.2 keV and Z = 0.39+-0.05 Zsolar. The
value of the temperature is consistent with recent ASCA measurements and is
significantly higher than previous estimates obtained from ROSAT and EXOSAT. We
discuss the possible reasons of this disagreement. Between 8 and 20 arcmin, the
plasma temperature declines to about 3.2 keV. When a polytropic profile is used
to represent the gas temperature profile, the best fit polytropic index is
1.16+-0.03. These results imply a total mass within the virial radius of 3.9
(+-0.4) 10^14 h_50^-1 Msolar, between 40 and 80 per cent lower than the optical
estimate, and a gas mass fraction of about 30 per cent.


title: Solar cycle induced variations in GONG p-mode frequencies and splittings

abstract:
  We have analysed the recently available GONG p-mode frequencies and splitting
coefficients for a period of three and half years, including the rapidly rising
phase of solar cycle 23. The analysis of mean frequency shift with different
activity indices shows that the shift is equally correlated with both magnetic
and radiative indices. During the onset of the new cycle 23, we notice that the
change in $b_4$ splitting coefficient is more prominent than the change in
$b_2$. We have estimated the solar rotation rate with varying depth and
latitude. In the equatorial region, the rotation first increases with depth and
then decreases, while an opposite behaviour is seen in the polar region. We
also find a small but significant temporal variation in the rotation rate at
high latitudes.


title: The Formation of Stellar Clusters: Gaussian Initial Conditions II

abstract:
  Using hydrodynamic simulations we investigate the time evolution and
fragmentation of regions within molecular clouds which have lost their
turbulent support leading to gravitational contraction. The initial density
distributions are described by random Gaussian fluctuations with varying slopes
x of the power spectrum P(k) ~ k^-x, covering the range from flat (x=0) to very
steep spectra (x=3). We consider molecular cloud volumes containing different
masses relative to the average Jeans mass M_J, from 1 M_J to 222 M_J. This
parameter study extends the detailed analysis of systems with initially P(k) ~
k^-2 and mass 222 M_J presented by Klessen & Burkert (2000). The dynamical
evolution of the simulated molecular cloud regions is insensitive to the slope
of the initial density fluctuation spectrum. The system evolves into a
complicated network of intersecting filaments and collapsing clumps leading to
the formation of a compact cluster of accreting and interacting embedded
protostellar cores. The cluster builds up as bound entity, but dissolves later
due to collisional effects. In all simulations, the mass spectrum of collapsed
cores is very broad, has approximately log-normal shape and peaks roughly at
the average Jeans mass. This supports the hypothesis that the average Jeans
mass is the main parameter determining the peak in the stellar spectrum, and
suggests that the interplay between self-gravity on the one side and thermal
and turbulent pressure on the other side is the dominant process that regulates
the formation of stellar clusters.


title:
Characterizing the non-linear growth of large-scale structure in the
  Universe

abstract:
  The local Universe displays a rich hierarchical pattern of galaxy clusters
and superclusters. The early Universe, however, was almost smooth, with only
slight 'ripples' seen in the cosmic microwave background radiation. Models of
the evolution of structure link these observations through the effect of
gravity, because the small initially overdense fluctuations attract additional
mass as the Universe expands. During the early stages, the ripples evolve
independently, like linear waves on the surface of deep water. As the
structures grow in mass, they interact with other in non-linear ways, more like
waves breaking in shallow water. We have recently shown how cosmic structure
can be characterized by phase correlations associated with these non-linear
interactions, but hitherto there was no way to use that information to reach
quantitative insights into the growth of structures. Here we report a method of
revealing phase information, and quantify how this relates to the formation of
a filaments, sheets and clusters of galaxies by non-linear collapse. We use a
new statistic based on information entropy to separate linear from non-linear
effects and thereby are able to disentangle those aspects of galaxy clustering
that arise from initial conditions (the ripples) from the subsequent dynamical
evolution.


title:
The Rotation Curve of the Large Magellanic Cloud and the Implications
  for Microlensing

abstract:
  The rotation of the disk of the Large Magellanic Cloud (LMC) is derived from
the radial velocities of 422 carbon stars. New aspects of this analysis include
the propagation of uncertainties in the LMC proper motion with a Monte Carlo,
and a self-consistent modeling of the rotation curve and disk kinematics. The
rotation curve is well fit by a truncated, finite-thickness exponential disk
model with no dark halo. The velocity dispersion in radial bins decreases from
22 to 15 km/s, then increases to 20 km/s at larger radii. Constant-thickness
models in virial equilibrium cannot be reconciled with the data even if the
effects of LMC or Galactic dark halos are included. If the disk is virialized,
the LMC disk is flared. We model the velocity dispersion at large radii (R > 6
kpc) as a maximal flared disk under the influence of the Galactic dark halo,
which favors a mean density for the latter of 0.00025 M_sol/pc^3 at the LMC
distance. LMC stellar kinematics play an important role in elucidating the
nature of MACHOs, a dark population inferred from LMC microlensing. We have
constructed a truncated and flared maximal disk model for the LMC which is
kinematically based. Our model does not include a nonvirialized component such
as tidal debris. Our upper limit on the self-lensing optical depth is in good
agreement with that obtained from less sophisticated models, and is an order of
magnitude too small to account for the MACHO microlensing signal [Abridged].


title: The density of extremely red objects around high-z radio-loud AGN

abstract:
  We present the results of a K-band imaging survey of 40 arcmin^{2} in fields
around 14 radio-loud AGN (6 radio galaxies and 8 quasars) with z>1.5. The
survey, 80% complete to K<19.2 and complemented by R-band imaging, aimed at
investigating whether extremely red objects (EROs) are present in excess around
high-z AGN, and to study the environment of z>1.5 radio galaxies and radio-loud
quasars. At $18<K<19$ the differential galaxy counts in our fields suggest a
systematic excess over the general field counts. At K<19.2, we find an excess
of galaxies with R-K>6 compared to the general field. Consistently, we also
find that the R-K colour distribution of all the galaxies in the AGN fields are
significantly redder than the colour distribution of the field galaxies. On the
other hand, the distribution of the R-K colours is undistinguishable from that
of galaxies taken from literature fields around radio-loud quasars at 1<z<2. We
discuss the main implications of our findings and we compare the possible
scenarios which could explain our results.


title: Initial conditions for hybrid inflation

abstract:
  In hybrid inflation models, typically only a tiny fraction of possible
initial conditions give rise to successful inflation, even if one assumes
spatial homogeneity. We analyze some possible solutions to this initial
conditions problem, namely assisted hybrid inflation and hybrid inflation on
the brane. While the former is successful in achieving the onset of inflation
for a wide range of initial conditions, it lacks sound physical motivation at
present. On the other hand, in the context of the presently much discussed
brane cosmology, extra friction terms appear in the Friedmann equation which
solve this initial conditions problem in a natural way.


title: What if pulsars are born as strange stars?

abstract:
  The possibility and the implications of the idea, that pulsars are born as
strange stars, are explored. Strange stars are very likely to have atmospheres
with typical mass of $\sim 5\times 10^{-15}M_\odot$ but bare polar caps almost
throughout their lifetimes, if they are produced during supernova explosions. A
direct consequence of the bare polar cap is that the binding energies of both
positively and negatively charged particles at the bare quark surface are
nearly infinity, so that the vacuum polar gap sparking scenario as proposed by
Ruderman & Sutherland should operate above the cap, regardless of the sense of
the magnetic pole with respect to the rotational pole. Heat can not accumulate
on the polar cap region due to the large thermal conductivity on the bare quark
surface. We test this ``bare polar cap strange star'' (BPCSS) idea with the
present broad band emission data of pulsars, and propose several possible
criteria to distinguish BPCSSs from neutron stars.


title: The Space Density of low redshift AGN

abstract:
  We present a new determination of the optical luminosity function (OLF) of
active galactic nuclei (AGN) at low redshifts (z<0.15) based on Hubble Space
Telescope (HST) observations of X-ray-selected AGN. The HST observations have
allowed us to derive a true nuclear luminosity function for these AGN. The
resulting OLF illustrates a two-power-law form similar to that derived for QSOs
at higher redshifts. At bright magnitudes, M_B<-20, the OLF derived here
exhibits good agreement with that derived from the Hamburg/ESO QSO survey.
However, the single power law form for the OLF derived from the Hamburg/ESO
survey is strongly ruled out by our data at M_B>-20. Although the estimate of
the OLF is best-fit by a power law slope at M_B<-20.5 that is flatter than the
slope of the OLF derived at z>0.35, the binned estimate of the low redshift OLF
is still consistent with an extrapolation of the $z>0.35$ OLF based on pure
luminosity evolution.


title:
Ionization, Kinematics, and Extent of the Diffuse Ionized Gas Halo of
  NGC 5775

abstract:
  We present key results from deep spectra of the Diffuse Ionized Gas (DIG)
halo of the edge-on galaxy NGC 5775. [NII]6583 has been detected up to about
z=13 kpc above the plane in one of two vertically oriented long slits -- making
this the spiral galaxy with the greatest spectroscopically detected halo extent
in emission. Key diagnostic line ratios have been measured up to about z=8 kpc,
allowing the source of ionization and physical state to be probed. Ionization
by a dilute radiation field from massive stars in the disk can explain some of
the line ratio behavior, but departures from this picture are clearly
indicated, most strongly by the rise of [OIII]/Halpha with z. Velocities of the
gas in both slits approach the systemic velocity of the galaxy at several kpc
above the plane. We interpret this trend as a decrease in rotation velocity
with z, with essentially no rotation at heights of several kpc. Such a trend
was observed in the edge-on galaxy NGC 891, but here much more dramatically.
This falloff is presumably due to the gravitational potential changing with z,
but will also depend on the hydrodynamic nature of the disk-halo cycling of gas
and projection effects. More detailed modeling of the ionization and kinematics
of this and other edge-ons will be presented in future papers.


title:
A Further Analysis of a Cosmological Model of Quintessence and Scalar
  Dark Matter

abstract:
  We present the complete solution to a 95% scalar field cosmological model in
which the dark matter is modeled by a scalar field $\Phi$ with the scalar
potential $V(\Phi)=V_{o}[ \cosh {(\lambda \sqrt{\kappa_{o}}\Phi)}-1]$ and the
dark energy is modeled by a scalar field $\Psi$, endowed with the scalar
potential $\tilde{V}(\Psi)=\tilde{V_{o}}[ \sinh {(\alpha
\sqrt{\kappa_{o}}\Psi)}] ^{\beta}$. This model has only two free parameters,
$\lambda$ and the equation of state $\omega_{\Psi}$. With these potentials, the
fine tuning and the cosmic coincidence problems are ameliorated for both dark
matter and dark energy and the models agrees with astronomical observations.
For the scalar dark matter, we clarify the meaning of a scalar Jeans lenght and
then the model predicts a suppression of the Mass Power Spectrum for small
scales having a wave number $k > k_{min,\Phi}$, where $k_{min,\Phi} \simeq 4.5
h {\rm Mpc}^{-1}$ for $\lambda \simeq 20.28$. This last fact could help to
explain the dearth of dwarf galaxies and the smoothness of galaxy core halos.
  From this, all parameters of the scalar dark matter potential are completely
determined. The dark matter consists of an ultra-light particle, whose mass is
$m_{\Phi} \simeq 1.1\times 10^{-23} {\rm eV}$ and all the success of the
standard cold dark matter model is recovered. This implies that a scalar field
could also be a good candidate as the dark matter of the Universe.


title: Infrared interferometric observations of young stellar objects

abstract:
  We present infrared observations of four young stellar objects using the
Palomar Testbed Interferometer (PTI). For three of the sources, T Tau, MWC 147
and SU Aur, the 2.2 micron emission is resolved at PTI's nominal fringe spacing
of 4 milliarcsec (mas), while the emission region of AB Aur is over-resolved on
this scale. We fit the observations with simple circumstellar material
distributions and compare our data to the predictions of accretion disk models
inferred from spectral energy distributions. We find that the infrared emission
region is tenths of AU in size for T Tau and SU Aur and ~1 AU for MWC 147.


title: HIIphot: Automated Photometry of HII Regions Applied to M51

abstract:
  We have developed a robust, automated method, hereafter designated HIIphot,
which enables accurate photometric characterization of HII regions while
permitting genuine adaptivity to irregular source morphology. HIIphot utilizes
object-recognition techniques to make a first guess at the shapes of all
sources then allows for departure from such idealized ``seeds'' through an
iterative growing procedure. Photometric corrections for spatially coincident
diffuse emission are derived from a low-order surface fit to the background
after exclusion of all detected sources. We present results for the
well-studied, nearby spiral M51 in which 1229 HII regions are detected above
the 5-sigma level. A simple, weighted power-law fit to the measured H-alpha
luminosity function (HII LF) above log L_H-alpha = 37.6 gives alpha =
-1.75+/-0.06, despite a conspicuous break in the HII LF observed near L_H-alpha
= 10^38.9. Our best- fit slope is marginally steeper than measured by Rand
(1992), perhaps reflecting our increased sensitivity at low luminosities and to
notably diffuse objects. HII regions located in interarm gaps are
preferentially less luminous than counterparts which constitute M51's
grand-design spiral arms and are best fit with a power-law slope of alpha =
-1.96+/-0.15. We assign arm/interarm status for HII regions based upon the
varying surface brightness of diffuse emission as a function of position
throughout the image. Using our measurement of the integrated flux contributed
by resolved HII regions in M51, we estimate the diffuse fraction to be
approximately 0.45 -- in agreement with the determination of Greenawalt et al.
(1998). Automated processing of degraded datasets is undertaken to gauge
systematic effects associated with limiting spatial resolution and sensitivity.


title:
High Energy Neutrinos from Gamma Ray Bursts: Event Rates in Neutrino
  Telescopes

abstract:
  Following Waxman and Bahcall we calculate the event rate, energy and zenith
angle dependence of neutrinos produced in the fireball model of gamma ray
bursts (GRB). We emphasize the primary importance of i) burst-to-burst
fluctuations and ii) absorption of the neutrinos in the Earth. From the
astronomical point of view, we draw attention to the sensitivity of neutrino
measurements to the boost Lorentz factor of the fireball $\Gamma$, which is
central to the fireball model, and only indirectly determined by follow-up
observations. Fluctuations result in single bursts emitting multiple neutrinos,
making it possible to determine the flavor composition of a beam observed after
a baseline of thousands of Megaparsecs.


title: Crust-core coupling and r-mode damping in neutron stars: a toy model

abstract:
  R-modes in neutron stars with crusts are damped by viscous friction at the
crust-core boundary. The magnitude of this damping, evaluated by Bildsten and
Ushomirsky (BU) under the assumption of a perfectly rigid crust, sets the
maximum spin frequency for a neutron star spun up by accretion in a Low-Mass
X-ray binary (LMXB). In this paper we explore the mechanical coupling between
the core r-modes and the elastic crust, using a toy model of a constant density
neutron star with a constant shear modulus crust. We find that, at spin
frequencies in excess of ~50 Hz, the r-modes strongly penetrate the crust. This
reduces the relative motion (slippage) between the crust and the core compared
to the rigid crust limit. We therefore revise down, by as much as a factor of
10^2-10^3, the damping rate computed by BU, significantly reducing the maximal
possible spin frequency of neutron star with a solid crust. The dependence of
the crust-core slippage on the spin frequency is complicated, and is very
sensitive to the physical thickness of the crust. If the crust is sufficiently
thick, the curve of the critical spin frequency for the onset of the r-mode
instability becomes multi-valued for some temperatures; this is related to the
avoided crossings between the r-mode and the higher-order torsional modes in
the crust. The critical frequencies are comparable to the observed spins of
neutron stars in LMXBs and millisecond pulsars.


title: Young Circumstellar Disks Near Evolved Massive Stars and Supernovae

abstract:
  There is increasing evidence that low mass stars with circumstellar disks can
be born close to massive stars, in some cases within tenths of a pc. If the
disks have lifetimes greater than those of the more massive stars, they are
exposed to the radiation fields and gas flows from the late evolutionary phases
and supernovae of the massive stars. The fast flows from supernovae are likely
to give some stripping of mass from the disks, but do not typically lead to
complete disruption of the disks. In the slow wind from a red supergiant star,
there is the possibility of gravitational accretion of wind matter onto the
circumstellar disk. In the supernova explosion of a red supergiant, the
radiative flux at the time of shock breakout can heat and ionize a nearby disk,
leading to transient, narrow line emission. There are consequences for the
solar nebula if it was born ~0.2 pc from a massive star that became a red
supergiant. Accretion from the wind could supply a substantial amount of 26Al
to the disk. The high radiative luminosity of the eventual supernova could lead
to the melting of dust grains and the formation of chondrules. The passage of
the supernova ejecta could drive a shock wave in the disk, heating it.


title: Implications of the X-Ray Properties of Pulsar Nebulae

abstract:
  A plausible model for the Crab Nebula is one in which a particle dominated,
highly relativistic wind from the pulsar passes through a shock front in which
the particles attain a power law energy distribution. The electrons and
positrons lose energy radiating synchrotron emission. Here, a one zone version
of the model is developed and applied to observations of X-ray pulsar nebulae.
Efficient conversion of pulsar spin-down power to X-ray luminosity is expected
if the observed electrons are in the synchrotron cooling regime and their
energy spectrum is similar to that in the Crab Nebula. In this case, the
relation between X-ray luminosity and pulsar spin-down power depends only
weakly on the model parameters. The dependence is stronger for a steeper
particle spectrum, as appears to be present in N157B, and the efficiency of
X-ray production can be lower. If the electrons are not in the cooling regime,
the X-ray luminosity can be low, as appears to be the case for the compact
nebula around the Vela pulsar. Slow cooling is likely to be caused by a
sub-equipartition magnetic field in the radiating region. Observations can
place constraints on the uncertain physics of relativistic MHD shocks. The
model is related to those developed for gamma-ray burst afterglows.


title: Gone with the wind: the origin of S0 galaxies in clusters

abstract:
  We present the first 3-dimensional high resolution hydro-dynamical
simulations of the interaction between the hot ionised intra-cluster medium and
the cold interstellar medium of spiral galaxies. Ram pressure and
turbulent/viscous stripping removes 100% of the atomic hydrogen content of
luminous galaxies like the Milky Way within 100 million years. These mechanisms
naturally account for the morphology of S0 galaxies, the rapid truncation of
star formation implied by spectroscopic observations, as well as a host of
observational data on the HI morphology of galaxies in clusters.


title: Galactosynthesis: Halo Histories, Star Formation, and Disks

abstract:
  We investigate the effects of a variety of ingredients that must enter into a
realistic model for disk-galaxy formation, focusing primarily on the
Tully-Fisher (TF) relation and its scatter in several wavebands. Our main
findings are: (a) the slope, normalization, and scatter of the TF relation
across various wavebands is determined {\em both} by halo properties and star
formation in the disk; (b) TF scatter owes primarily to the spread in formation
redshifts. The scatter can be measurably reduced by chemical evolution, and
also in some cases by the weak anti-correlation between peak height and spin;
(c) multi-wavelength constraints can be important in distinguishing between
models which appear to fit the TF relation in I or K; (d) successful models
seem to require that the bulk of disk formation cannot occur too early (z>2) or
too late (z<0.5), and are inconsistent with high values of $\Omega_0$; (e) a
realistic model with the above ingredients can reasonably reproduce the
observed z=0 TF relation in {\em all} bands (B, R, I, and K). It can also
account for the z=1 B-band TF relation and yield rough agreement with the local
B and K luminosity functions and B-band surface-brightness--magnitude relation.
The remarkable agreement with observations suggests that the amount of gas that
is expelled or poured into a disk galaxy must be small, and that the specific
angular momentum of the baryons must roughly equal that of the halo; there is
little room for angular momentum transfer. In an appendix we present analytic
fits to stellar-population synthesis models.


title: The White Dwarf Cooling Age of the Open Cluster NGC 2420

abstract:
  We have used deep HST WFPC2 observations of two fields in NGC 2420 to produce
a cluster CMD down to V = 27. After imposing morphological selection criteria
we find eight candidate white dwarfs in NGC 2420. Our completeness estimates
indicate that we have found the terminus of the WD cooling sequence. We argue
that the cluster distance modulus is likely to be close to 12.10 with E(B-V) =
0.04. With these parameters we find a white dwarf cooling age for NGC 2420 of
2.0 +- 0.20 (1 sigma) Gyrs. The 0.20 Gyr uncertainty includes errors in the
photometry, sequence fitting, precursor time scales, and theoretical white
dwarf cooling time scales. Comparing the cluster white dwarf cooling age to
ages derived from stellar isochrone fitting we find a preference for ages
derived from models incorporating convective overshoot.


title: ASCA Observation of the Crab-Like Supernova Remnant 3C58

abstract:
  We present here the X-ray observation of a Crab-like supernova remnant (SNR)
3C58 with ASCA. We find that the integrated energy spectrum over the nebula is
consistent with previous results, showing a power-law spectrum with the photon
index $\gamma = 2.2-2.4$ modified by interstellar absorption of about
$(3-4)\times 10^{21}{\rm cm^{-2}}$. Inclusion of a blackbody component which is
attributable to the central compact source significantly improves the spectral
fit. Stringent upper limits for any line emitting thin hot plasma are
established. We find for the first time that the nebular spectrum is harder in
the central part of the SNR, becoming softer toward the periphery, while the
absorption column is uniform across the nebula. Correspondingly, the nebular
size decreases with increasing photon energy which is a steeper function of
radius than that of the Crab nebula. The results are compared with synchrotron
energy loss models and the nature of the putative pulsar is discussed. Timing
analysis was performed to search for pulsed X-ray emission from the central
compact source. No significant pulsations are observed, and we present the
upper limit for the pulsed fraction.


title:
Magnetic Field Evolution of Accreting Neutron Stars IV - Effect of the
  Curvature of Space-Time

abstract:
  The evolution of the magnetic field in an accreting neutron star is
investigated using a fully general relativistic treatment and assuming that
initially the currents supporting the field are completely confined to the
crust. We find that the field decay slows down due to the inclusion of the
curvature of space-time but the final results do not differ significantly from
those obtained assuming a flat space-time. We also find that such modifications
are small compared to the uncertainties introduced by a lack of precise
knowledge of the neutron star micro-physics.


title: Equilibrium configurations of relativistic White Dwarfs

abstract:
  The Feynman-Metropolis-Teller treatment for compressed atoms is here
reconsidered in the framework of the relativistic generalised Fermi-Thomas
model, obtained by Ruffini et al. Physical properties of a zero temperature
plasma is thus investigated and the resulting equation of state, which keeps
into account quantum, relativistic and electromagnetic effects, is applied to
the study of equilibrium configurations of relativistic White Dwarfs.
  It is shown that numerical evaluation of such configuration leads, for the
same central density $\rho_c$, to smaller values of radius R and of mass M than
in the classical works of Chandrasekhar and Salpeter, the deviations being most
marked at the lowest densities (up to 30% from the
  Chandrasekhar model and 10% from the Salpeter one for $\rho_c \sim
10^6g/cm^3$, corresponding to $M \sim 0.2 M_{\odot}$).
  At high densities we considered the occurrence of inverse beta decays, whose
effect is to introduce gravitational instability of the configurations. We
consequently find the maximum mass of White Dwarfs, which, for an Oxygen and an
Iron WD, is respectively $1.365 M_{\odot}$ and $1.063 M_{\odot}$.


title: On the Critical Mass: the case of white dwarfs

abstract:
  We recall the generalization of the Feynman-Metropolis-Teller approximation
for a compressed atom using a relativistic Fermi-Thomas model. These results
within a Wigner-Seitz approximation lead to a new equation of state for white
dwarfs and to a new value of their critical mass, smaller than the one obtained
by Chandrasekhar. The possible observations of these effects in binary neutron
stars are outlined.


title:
Formation of a tidal dwarf galaxy in the interacting system Arp 245 (NGC
  2992/93)

abstract:
  Among the various phenomena observed in interacting galaxies is the ejection
due to tidal forces of material into the intergalactic medium and its
subsequent rearranging which can lead to the formation of self-gravitating
tidal dwarf galaxies
  (TDGs). We investigate this process with a detailed multiwavelength study of
the interacting system Arp 245 (NGC 2992/3) and a numerical model of the
collision.
  The system is observed at an early stage of the interaction, about 100 Myr
after perigalacticon, though at a time when tidal tails have already developed.
  Our HI map shows prominent counterparts to the optical tails. Whereas the
stellar and gaseous components of the plume that originates from NGC 2992
match, the stellar and HI tails emanating from NGC 2993 have a different
morphology. In particular, the HI forms a ring, a feature that has been
successfully reproduced by our numerical simulations. The HI emission in the
system as a whole peaks at the tip of the NGC 2992 tail where a gas reservoir
of about
  10^9 Msun, about 60% of the HI towards NGC 2992, coincides with a
star-forming optical condensation,
  A245N. The latter tidal object exhibits properties ranging between those of
dwarf irregular galaxies (structural parameters, gas content, star formation
rate) and those of spiral disks
  (metallicity, star formation efficiency, stellar population). Prompted by the
questions raised for this particular object, we discuss some issues related to
the definition and identification of TDGs (abridged)


title: FUSE Observations of the HD Molecule toward HD 73882

abstract:
  The Lyman and Werner band systems of deuterated molecular hydrogen (HD) occur
in the far UV range below 1200 A. The high sensitivity of the FUSE mission can
give access, at moderate resolution, to hot stars shining through translucent
clouds, in the hope of observing molecular cores in which deuterium is
essentially in the form of HD. Thus, the measurement of the HD/H2 ratio may
become a new powerful tool to evaluate the deuterium abundance, D/H, in the
interstellar medium. We report here on the detection of HD toward the high
extinction star HD 73882 [E(B-V)=0.72]. A preliminary analysis is presented.


title: Reconstructing PSCz with a Generalised PIZA

abstract:
  We present a generalized version of the Path Interchange Zel'dovich
Approximation (PIZA), for use with realistic galaxy redshift surveys. PIZA is a
linear particle-based Lagrangian method which uses the present day positions of
galaxies to reconstruct both the initial density field and the present day
peculiar velocity field. We generalize the method by mapping galaxy positions
from redshift-space to real-space in the Local Group frame, and take the
selection function into account by minimizing the mass weighted action. We have
applied our new method to mock galaxy catalogues, and find it offers an
improvement in the accuracy of reconstructions over linear theory. We have
applied our method to the all-sky IRAS Point Source Catalogue Redshift Survey.
Applying PIZA to PSCz, we are able to obtain the peculiar velocity field, the
dipole, bulk velocities, and the distortion parameter. From the dipole, we find
that beta=0.51+/-0.14. We compare the PSCz bulk velocity with that of Mk III
and conclude that beta=0.5+/-0.15. We compare the PSCz dipole with that of SFI
and find that beta=0.5+/-0.1.