title:
BeppoSAX spectroscopy of the NGC7078 (M15) globular cluster X-ray source
  X2127+119

abstract:
  Results of a 1999 November 16--17 BeppoSAX observation of the low-mass X-ray
binary X2127+119 located in the globular cluster NGC7078 are presented. The
system is believed to be one where the central neutron star is normally
obscured by the accretion disk, and only X-rays scattered into our line of
sight by an extended accretion disk corona (ADC) are observed. The 0.1--10 keV
lightcurve is energy dependent and shows two partial eclipses separated by the
17.1 hr orbital period. The 0.1--100 keV spectrum is unusually complex, but can
be successfully modeled using a partially covered power-law and disk-blackbody
model. Together with a column consistent with the interstellar value to
NGC7078, about 60% of the source is covered by an additional column of 1E22
atom/cm2. The absorbed component may be X-rays that pass through the outer
layers of the accretion disk. The energy dependent intensity variations by a
factor of ~2 may be modeled as due to a changing normalization of the
disk-blackbody. None of the other spectral parameters appear to clearly depend
on luminosity. The same spectral model is also able to fit an archival ASCA
spectrum.


title:
Constraints on the physical properties of the damped Ly-alpha system of
  Q0000-2619 at z = 3.054

abstract:
  We present the detection of CII and CII* absorption in the z = 3.0543 damped
Ly-alpha system toward Q0000-2619. The derived population ratio implies a fine
structure excitation temperature between 19.6 and 21.6 K. The upper value sets
a strict upper limit on the CMB temperature at this redshift, which is
consistent with the predicted value of 11.05 K from standard cosmology. Under
the assumptions of an ionization degree ranging from 0 to 10%, a gas kinetic
temperature between 100 and 10000 K and a UV field with a Milky Way spectrum,
the density of the absorber is constrained to be between 0.7 and 40 cm^-3 and
the H-ionizing flux between 1 and 80 times the intensity of the Galactic UV
field. If the damped Ly-alpha system is assumed to be homogeneous, the
implication is that its size in the direction of the line of sight must be
between 1 and 100 pc.


title: Explosions During Galaxy Formation

abstract:
  As an idealized model of the effects of energy release by supernovae during
galaxy formation, we consider an explosion at the center of a halo which forms
at the intersection of filaments in the plane of a cosmological pancake by
gravitational instability during pancake collapse. Such halos resemble the
virialized objects found in N-body simulations in a CDM universe and,
therefore, serve as a convenient, scale-free test-bed model for galaxy
formation. ASPH/P3M simulations reveal that such explosions are anisotropic.
The energy and metals are channeled into the low density regions, away from the
pancake plane. The pancake remains essentially undisturbed, even if the
explosion is strong enough to blow away all the gas located inside the halo at
the onset of the explosion and reheat the IGM surrounding the pancake. Infall
quickly replenishes this ejected gas and gradually restores the gas fraction as
the halo mass continues to grow. Estimates of the collapse epoch and SN
energy-release for galaxies of different mass in the CDM model can relate these
results to scale-dependent questions of blow-out and blow-away and their
implication for early IGM heating and metal enrichment and the creation of
dark-matter-dominated dwarf galaxies.


title: A Radio Telescope Search for Axions

abstract:
  The axion is a hypothetical elementary particle and a cold dark matter
candidate. It could dominate potential wells of most astrophysical objects.
Axions spontaneously decay into nearly monochromatic microwave photons. We
present results from a radio telescope search for these axion decay photons of
mass between 298 and 363 micro-eV in Local Group dwarf galaxies. We report a
limit on the axion-to-two-photon coupling constant g > 1.0 x 10^(-9) GeV^(-1).


title: Properties of observed Ly-$\alpha$ forest

abstract:
  The main observed properties of Ly-$\alpha$ absorbers are investigated on the
basis of theoretical model of formation and evolution of DM structure elements.
This model is generally consistent with simulations of absorbers formation and
with statistical description of structure evolution based on the Zel'dovich
theory. The analysis of redshift variations of comoving linear number density
of absorbers was performed in our previous paper.
  We show that the observed characteristics of Doppler parameter can be related
to the size of DM structure elements what allows us to explain the observed
distribution of Doppler parameter. This distribution is found to be consistent
with the Gaussian initial perturbations. The observed characteristics of
entropy and column density, $N_{HI}$, confirm that merging of pancakes is the
main evolutionary process at redshifts $z\geq 2$. The observed sample of
absorbers characterizes mainly the matter distribution within large low density
regions and therefore it is difficult to reconstruct the density field from the
distribution of absorbers.


title: Redshift distribution of {\bf Ly-$\alpha$} lines and metal systems

abstract:
  The observed redshift distribution of Ly-$\alpha$ lines and metal systems is
examined in order to discriminate and to trace the evolution of structure
elements observed in the galaxy distribution, at small redshifts, and to test
the theoretical description of structure evolution. We show that the expected
evolution of filamentary component of structure describes quite well the
redshift distribution of metal systems and stronger Ly-$\alpha$ lines with
$\log(N_{HI})\geq$14, at $z\leq$ 3. The redshift distribution of weaker
Ly-$\alpha$ lines can be attributed to the population of poorer structure
elements (Zel'dovich pancakes), which were formed at high redshifts from the
invisible DM and non luminous baryonic matter, and at lower redshifts they
mainly merged and dispersed.


title: Pre-main sequence binaries with aligned disks ?

abstract:
  We present the results of a study performed with the goal to investigate
whether low-mass pre-main sequence binary stars are formed by multiple
fragmentation or via stellar capture. If binaries form preferentially by
fragmentation, we expect their disks to be co-planar. On the other hand, the
capture scenario will lead to a random distribution of disk orientations. We
performed near-infrared polarization measurements of 49 young close binary
stars in the K band with SOFI at the NTT. The near-infrared excess radiation of
the targets mostly point to the presence of disks. For a major fraction of the
sample, evidence for disks is also obvious from other features (outflows, jets,
Herbig-Haro objects). We derived the disk orientation from the orientation of
the polarization vector of both components of each binary. This statistical
study allows to test which hypothesis (co-planarity, random orientation) is
consistent with the observed distribution of polarimetric


title:
The Absolute Proper Motion of Palomar 12: A Case for Tidal Capture from
  the Sagittarius Dwarf Spheroidal Galaxy

abstract:
  We have measured the absolute proper motion of the young globular cluster Pal
12 with respect to background galaxies, using plate material spanning a 40-year
time baseline, and measuring stars down to a magnitude V~22. The measured
absolute proper motion has an uncertainty of 0.3 mas/yr in each coordinate.
  Pal 12's young age for a globular cluster led to the hypothesis that the
cluster originated in the Large Magellanic Cloud (LMC) and was later captured
by the Milky Way (Lin and Richer 1992). Here we investigate this hypothesis
using the complete kinematical data. We present the orbital characteristics of
Pal 12 and compare them with those of the LMC and Sagittarius dwarf galaxy
(Sgr). The present kinematical data suggest that, from the two parent
candidates for Pal 12, Sgr presents a more plausible case for the host galaxy
than the LMC.
  We explore this scenario in the context of the uncertainties in the orbits
and using two different analyses: the direct comparison of the orbits of Pal 12
and Sgr as a function of time, and the analytical model of Sgr's tidal
disruption developed by Johnson (1998). We find that, within the present
uncertainties of the observables, this scenario is viable in both methods.
Moreover, both methods place this event at the same point in time. Our best
estimate of the time of Pal 12's tidal capture from Sgr is ~ 1.7 Gyr ago.


title: The Far-Infrared emission of Radio Loud and Radio Quiet Quasars

abstract:
  Continuum observations at radio, millimetre, infrared and soft X-ray energies
are presented for a sample of 22 quasars, consisting of flat and steep spectrum
radio loud, radio intermediate and radio quiet objects. The primary
observational distinctions, among the different kinds of quasars in the radio
and IR energy domains are studied using large observational datasets provided
by ISOPHOT on board the Infrared Space Observatory, by the IRAM interferometer,
by the sub-millimetre array SCUBA on JCMT, and by the European Southern
Observatory (ESO) facilities IRAC1 on the 2.2 m telescope and SEST.
  The spectral energy distributions of all quasars from radio to IR energies
are analyzed and modeled with non-thermal and thermal spectral components.
  The dominant mechanism emitting in the far/mid-IR is thermal dust emission in
all quasars, with the exception of flat spectrum radio loud quasars for which
the presence of thermal IR emission remains rather uncertain, since it is
difficult to separate it from the bright non-thermal component. The dust is
predominantly heated by the optical/ultraviolet radiation emitted from the
external components of the AGN. A starburst contributes to the IR emission at
different levels, but always less than the AGN (< 27%). The distribution of
temperatures, sizes, masses, and luminosities of the emitting dust are
independent of the quasar type.


title: Halo Dark Matter and Ultra-High Energy Cosmic Rays

abstract:
  The decay of very heavy metastable relics of the Early Universe can produce
ultra-high energy cosmic rays (UHECRs) in the halo of our own Galaxy. On
distance scales of the order of the halo size, energy losses are
negligible---no Greisen-Zatsepin-Kuzmin cutoff is expected. In this letter we
show that, as a consequence of the hierarchical build up of the halo, this
scenario predicts the existence of small scale anisotropies in the arrival
directions of UHECRs. We also suggest some consequences of this scenario which
will be testable with upcoming experiments, as Auger.


title: Afterglow Emission from Naked Gamma-Ray Bursts

abstract:
  We calculate the {\it afterglow} emission for Gamma-Ray Bursts (GRBs) going
off in an extremely low density medium, referred to as {\it naked bursts}. Our
results also apply to the case where the external medium density falls off
sharply at some distance from the burst. The observed afterglow flux in this
case originates at high latitudes, i.e. where the angle between the fluid
velocity and the observer line of sight is greater than $\Gamma^{-1}$. The
observed peak frequency of the spectrum for naked bursts decreases with
observer time as $t^{-1}$, and the flux at the peak of the spectrum falls off
as $t^{-2}$. The 2--10 keV $X$-ray flux from a naked burst of average fluence
should be observable by the SWIFT satellite for time duration of about $10^3$
longer than the burst variability timescale. The high latitude emission
contributes to the early $X$-ray afterglow flux for any GRB, not just naked
bursts, and can be separated from the shocked inter-stellar medium (ISM)
emission by their different spectral and temporal properties. Measurements of
the high latitude emission could be used to map the angular structure of GRB
producing shells.


title: The Active Nucleus in the Ultraluminous Infrared Galaxy IRAS 08311-2459

abstract:
  Near-infrared spectroscopy using the new Palomar Integral Field Spectrograph
indicates the presence of an AGN (active galactic nucleus) in the ultraluminous
infrared galaxy IRAS 08311-2459. The high-velocity wings of the Paschen-alpha
hydrogen recombination line are seen to be spatially unresolved, and with no
positional offset between red and blue high velocity emission. The [Si VI]
coronal line, with a 167 eV excitation potential, is also spatially unresolved
with a velocity width comparable to that of the broad component of the Pa-alpha
emission. The low velocity component of the Pa-alpha emission is seen to be
rotating, and is extended over about 2 kpc. Molecular hydrogen is also
extended, and elongated along the maximum velocity gradient, sharing the same
rotation profile as the narrow Pa-alpha emission. The simple picture in
agreement with the observations is that of an AGN surrounded by a rotating disk
of star formation. These observations lend strength to the usage of [Si VI] as
a diagnostic of AGN activity in ultraluminous infrared galaxies, and also
highlight the utility of integral field spectroscopy in elucidating subtle
morphological differences in line emitting regions.


title:
How Many Galaxies Fit in a Halo? Constraints on Galaxy Formation
  Efficiency from Spatial Clustering

abstract:
  We study galaxy clustering using halo models, where gravitational clustering
is described in terms of dark matter halos. At small scales, clustering
statistics are dominated by halo density profiles, whereas at large scales,
correlations are the result of combining non-linear perturbation theory with
halo biasing. Galaxies are assumed to follow the dark matter profiles, and
galaxy formation efficiency is given by the number of galaxies as a function of
halo mass. This approach leads to generic predictions: the galaxy power
spectrum shows a power-law behavior even though the dark matter does not, and
the galaxy higher-order correlations show smaller amplitudes at small scales
than their dark matter counterparts, as observed in galaxy catalogs. We find
that requiring to fit both the second and third order moments of the APM
galaxies provides a strong constraint on galaxy formation models. The data at
large scales require that galaxy formation be relatively efficient at small
masses, m =10^10 Msun/h, whereas data at smaller scales require that the number
of galaxies in a halo scale as the mass to the 0.8th power in the high-mass
limit. These constraints are independent of those derived from the luminosity
function or Tully-Fisher relation. We also predict the power spectrum,
bispectrum, and higher-order moments of the mass density field. Although halo
models agree well with measurements of the mass power spectrum and the higher
order Sp parameters in N-body simulations, the model assumption that halos are
spherical leads to disagreement in the configuration dependence of the
bispectrum at small scales. We stress the importance of finite volume effects
in higher-order statistics and show how they can be estimated in this approach.


title: Constraints on Cold H_2 Clouds from Gravitational Microlensing Searches

abstract:
  It has been proposed that the Galaxy might contain a population of cold
clouds in numbers sufficient to account for a substantial fraction of the total
mass of the Galaxy. These clouds would have masses of the order of 10^{-3}
Solar mass and sizes of the order of 10 AU. We consider here the lensing
effects of such clouds on the light from background stars. A semianalytical
formalism for calculation of the magnification event rate produced by such
gaseous lensing is developed, taking into account the spatial distribution of
the dark matter in the Galaxy, the velocity distribution of the lensing clouds
and source stars, and motion of the observer. Event rates are calculated for
the case of gaseous lensing of stars in the Large Magellanic Cloud and results
are directly compared with the results of the search for gravitational
microlensing events undertaken by the MACHO collaboration. The MACHO experiment
strongly constrains the properties of the proposed molecular clouds, but does
not completely rule them out. Future monitoring programs will either detect or
more strongly constrain this proposed population.


title: Kinematic Constraints to the Key Inflationary Observables

abstract:
  The observables $T/S$ and $n-1$ are key to testing and understanding
inflation. ($T$, $S$, and $n-1$ respectively quantify the gravity-wave and
density-perturbation contributions to CMB anisotropy and the deviation of the
density perturbations from the scale-invariant form.) Absent a standard model,
there is no definite prediction for, or relation between, $T/S$ and $n-1$. By
reformulating the equations governing inflation we show that models generally
predict $T/S \approx -5(n-1)$ or 0, and in particular, if $n>0.85$, $T/S$ is
expected to be $>10^{-3}$.


title: The Dynamical Interstellar Medium: Insights from Numerical Models

abstract:
  Numerical models of the dynamical interstellar medium show that interactions
between structures such as supernova remnants and superbubbles are more
important than the structures themselves in determining the behavior of the
ISM. I review the techniques and conclusions of recent global models, focussing
on what they tell us about the formation of star-forming giant molecular
clouds.


title: The structure and kinematics of AGN with ionization cones

abstract:
  Results of 2D spectral observations for 4 Sy galaxies with ionization cones
are presented. Images in the [OIII] line, velocity fields of the ionized gas,
stellar velocity and velocity dispersion fields were obtained at the SAO RAS 6m
telescope. Non-circular gas motions and Z-shaped emission filaments could be
explained as helical waves located in the ionization cone. This waves are
generated by the hydrodynamical instability due to the velocity break between
galactic ISM and outflowing matter from the AGN engine. The axis of cone lies
close to the direction of a nuclear mini bar.


title:
Solar flare radio pulsations as a signature of dynamic magnetic
  reconnection

abstract:
  Decimetric radio observations of the impulsive solar flare on October 5,
1992, 09:25 UT show a long series of quasi-periodic pulsations deeply
modulating a continuum in the 0.6-2 GHz range that is slowly drifting toward
lower frequencies. We propose a model in which the pulsations of the radio flux
are caused by quasi-periodic particle acceleration episodes that result from a
dynamic phase of magnetic reconnection in a large-scale current sheet. The
reconnection is dominated by repeated formation and subsequent coalescence of
magnetic islands (known as ``secondary tearing'' or ``impulsive bursty'' regime
of reconnection), while a continuously growing plasmoid is fed by newly
coalescing islands. Such a model, involving a current sheet and a growing
plasmoid, is consistent with the Yohkoh observations of the same flare (Ohyama
& Shibata 1998). We present two-dimensional MHD simulations of dynamic magnetic
reconnection that support the model. Within the framework of the proposed
interpretation, the radio observations reveal details of plasmoid formation in
flares.


title: Toward High-Precision Astrometry with WFPC2. I. Deriving an Accurate PSF

abstract:
  The first step toward doing high-precision astrometry is the measurement of
individual stars in individual images, a step that is fraught with dangers when
the images are undersampled. The key to avoiding systematic positional error in
undersampled images is to determine an extremely accurate point-spread function
(PSF). We apply the concept of the {\it effective} PSF, and show that in images
that consist of pixels it is the ePSF, rather than the often-used instrumental
PSF, that embodies the information from which accurate star positions and
magnitudes can be derived. We show how, in a rich star field, one can use the
information from dithered exposures to derive an extremely accurate effective
PSF by iterating between the PSF itself and the star positions that we measure
with it. We also give a simple but effective procedure for representing spatial
variations of the HST PSF. With such attention to the PSF, we find that we are
able to measure the position of a single reasonably bright star in a single
image with a precision of 0.02 pixel (2 mas in WF frames, 1 mas in PC), but
with a systematic accuracy better than 0.002 pixel (0.2 mas in WF, 0.1 mas in
PC), so that multiple observations can reliably be combined to improve the
accuracy by $\surd N$.


title: Nuclear Reaction Rates in a Plasma: The Effect of Highly Damped Modes

abstract:
  The fluctuation-dissipation theorem is used to evaluate the screening factor
of nuclear reactions due to the electromagnetic fluctuations in a plasma. We
show that the commonly used Saltpeter factor is obtained if only fluctuations
near the plasma eigenfrequency are assumed to be important (\omega \sim
\omega_{pe}\ll T (\hbar=k_{B}=1)). By taking into account all the fluctuations,
the highly damped ones, with \omega >\omega_{pe}, as well as those with
\omega\leq\omega_{pe}, we find that nuclear reaction rates are higher than
those obtained using the Saltpeter factor, for many interesting plasmas.


title: The Metallicity Distribution Function of Red Giants in the LMC

abstract:
  We report new metallicity determinations for 39 red giants in a 220 square
arcminute region, 1.8 degrees southwest of the bar of the Large Magellanic
Cloud. These abundance measurements are based on spectroscopy of the Ca II
infrared triplet. The metallicity distribution function (MDF) shows a strong
peak at [Fe/H] = -0.57 +/- 0.04. Half the red giants in our field fall within
the range -0.83 < [Fe/H] < -0.41. We find a striking contrast in the shape of
the MDF below [Fe/H] < -1 between our inner disk field and the distant outer
field studied by Olszewski (1993). Our field-star MDF seems similar to that of
the intermediate-age (1-3 Gyr) star clusters. We have also obtained abundance
estimates using Stromgren photometry for ~1000 red giants in the same field.
The Stromgren measurements, which are sensitive to a combination of cyanogen
and iron lines, correlate well with the Ca II measurements, but a
metallicity-dependent offset is found (abridged).


title:
Probing the Interstellar Medium in Early type galaxies with ISO
  observations

abstract:
  Four IRAS-detected early type galaxies were observed with ISO. With the
exception of the 15 micron image of NGC1052, the mid-IR emission from NGC1052,
NGC1155, NGC5866 and NGC6958 at 4.5, 7 and 15 microns show extended emission.
Mid-IR emission from NGC1052, NGC1155, and NGC6958 follows a de Vaucouleurs
profile. The ratio of 15/7 micron flux decreases with radius in these galaxies,
approaching the values empirically observed for purely stellar systems. In
NGC5866, the 7 and 15 micron emission is concentrated in the edge-on dust lane.
All the galaxies are detected in the [CII] line, and the S0s NGC1155 and
NGC5866 are detected in the [OI] line as well. The ISO-LWS observations of the
[CII] line are more sensitive measures of cool, neutral ISM than HI and CO by
about a factor of 10-100. Three of four early type galaxies, namely NGC1052,
NGC6958 and NGC5866, have low ratio FIR/Blue and show a lower [CII]/FIR, which
is due to a softer radiation field from old stellar populations. The low
[CII]/CO ratio in NGC5866 ([CII]/CO(1-0) < 570) confirms this scenario. We
estimate the UV radiation expected from the old stellar populations in these
galaxies and compare it to that needed to heat the gas to account for the
cooling observed [CII] and [OI] lines. In three out of four galaxies, NGC1052,
NGC5866 and NGC6958, the predicted UV radiation falls short by a factor of 2-3.
In view of the observed intrinsic scatter in the "UV-upturn" in elliptical
galaxies and its great sensitivity to age and metallicity effects, this is not
significant. However, the much larger difference (about a factor of 20) between
the UV radiation from old stars and that needed to produce the FIR lines for
NGC 1155 is strong evidence for the presence of young stars, in NGC1155.


title: Outflow from YSO and Angular Momentum Transfer

abstract:
  Dynamical contraction of a slowly-rotating magnetized cloud is studied using
the magnetohydrodynamical (MHD) simulations. In the isothermal stage ($n \la
n_{\rm A} \sim 10^{10}{\rm cm}^{-3}$), the cloud evolves similarly to that
expected from Larson-Penston self-similar solution and experiences the run-away
collapse. However, after the central density exceeds $\sim n_{\rm A}$, an
accretion disk is formed around the adiabatic core. Just outside the core,
outflow is ejected by the effect of magnetic torque (magnetocentrifugal wind).
Since $\sim$ 10% of the mass is ejected with almost all the angular momentum,
the specific angular momentum of the protostellar core reduces to that observed
in main-sequence stars.


title:
Disk-galaxy density distribution from orbital speeds using Newton's law,
  version 1.1

abstract:
  Given the dimensions(including thickness) of an axisymmetric galaxy, Newton's
law is used in integral form to find the density distributions required to
match a wide range of orbital speed profiles. Newton's law is not modified and
no dark-matter halos are required. The speed distributions can have extreme
shapes if they are reasonably smooth. Several examples are given.


title:
On the nature of the FBS blue stellar objects and the completeness of
  the Bright Quasar Survey. II

abstract:
  In Paper I (Mickaelian et al. 1999), we compared the surface density of QSOs
in the Bright Quasar Survey (BQS) and in the First Byurakan Survey (FBS) and
concluded that the completeness of the BQS is of the order of 70% rather than
30-50% as suggested by several authors. A number of new observations recently
became available, allowing a re-evaluation of this completeness. We now obtain
a surface density of QSOs brighter than B = 16.16 in a subarea of the FBS
covering ~2250 deg^2, equal to 0.012 deg^-2 (26 QSOs), implying a completeness
of 53+/-10%.


title: Joule Heating in Neutron Stars under Strong Gravitation

abstract:
  Considering Joule heating caused by the dissipation of the magnetic field in
the neutron star crust to be an efficient mechanism in maintaining a relatively
high surface temperature in very old neutron stars, the role of general
relativity is investigated. It is found that, although the effect of space-time
curvature produced by the intense gravitational field of the star slows down
the decay rate of the magnetic field, modification of the initial magnetic
field configuration and the initial field strength by the space-time curvature
results in increasing the rate of Joule heating. Hence the space-time curvature
supports Joule heating in maintaining a relatively high surface temperature
which is consistent with the bservational detection.


title: The BeppoSAX 2-10 keV Survey

abstract:
  We present the results of a 2-10 keV BeppoSAX survey based on 140 high
galactic latitude MECS fields, 12 of which are deep exposures of ``blank''
parts of the sky. The limiting sensitivity is 5 10^-14 erg cm^-2 s^-1 where
about 25% of the Cosmic X-ray Background (CXB) is resolved into discrete
sources. The logN-logS function, built with a statistically complete sample of
177 sources, is steep and in good agreement with the counts derived from ASCA
surveys. A CXB fluctuation analysis allowed us to probe the logN-logS down to
about 1.5 10^-14 erg cm^-2 s^-1 where the contribution of discrete sources to
the CXB grows to 40-50%. A hardness ratio analysis reveals the presence of a
wide range of spectral shapes and that a fairly large fraction of sources
appear to be heavily absorbed, some of which showing soft components. A
comparison of the flux distribution of different subsamples confirms the
existence of a spectral hardening with decreasing flux. This effect is probably
due to an increasing percentage of absorbed sources at faint fluxes, rather
than to a gradual flattening of the spectral slope. Nearly all the sources for
which adequate ROSAT exposures exist, have been detected in the soft X-rays.
This confirms that soft spectral components are present even in strongly
absorbed objects, and that a large population of sources undetectable below a
few keV does not exist. A Ve/Va test provides evidence for the presence of
cosmological evolution of a magnitude similar to that found in soft X-ray
extragalactic sources. Evolution is present both in normal and absorbed
sources, with the latter population possibly evolving faster,although this
effect could also be the result of complex selection effects.


title: Sloshing in High Speed Galaxy Interactions

abstract:
  Observations of lopsided spiral galaxies motivated us to explore whether the
rapid passage of a companion galaxy could cause them. We examine whether the
center of mass of the visible matter becomes displaced from the center of mass
of the dark halo during the intruder's passage, thereby causing an asymmetric
response and asymmetric structure. Two dimensional $N$-body simulations
indicate that this can happen.
  We also explore some consequences of this offset. These include the center of
mass of the visible disk following a decaying orbit around the halo center of
mass and the development of transient one-armed spirals that persist for up to
six rotation periods.
  We then study the results of a variety of initial conditions based on such
offsets. We report on the results of several runs in which we initially offset
a disk from its halo's center of mass by an amount typical of the above
interaction. In some runs the halo is free to move, while in others it is held
fixed. We used three different mass distributions for the halo in these runs.
We find that the disk's center of mass spiraled inward creating a variety of
observed or observable phenomena including one-armed spirals, massive clumps of
particles, and counter-rotating waves. The systems settle into relatively
axisymmetric configurations. Whether or not the end states included a bar
depended on a variety of initial conditions.


title: The transient X-ray source SAX J2239.3+6116 and its optical counterpart

abstract:
  We have discovered with the Wide Field Cameras on board BeppoSAX the weak
transient X-ray source SAXJ2239.3+6116 whose position coincides with that of
4U2238+60/3A2237+608 and is close to that of the fast transient AT2238+60 and
the unidentified EGRET source 3EG2227+6122. The data suggest that the source
exhibits outbursts that last for a few weeks and peak to a flux of 4E-10
erg/s/cm2 (2-10 keV) at maximum. During the peak the X-ray spectrum is hard
with a photon index of -1.1+/-0.1. Follow-up observations with the Narrow-Field
Instruments on the same platform revealed a quiescent emission level that is
1E+3 times less. Searches through the data archive of the All-Sky Monitor on
RXTE result in the recognition of five outbursts in total from this source
during 1996-1999, with a regular interval time of 262 days. Optical
observations with the KPNO 2.1 m telescope provide a likely optical
counterpart. It is a B0 V to B2 III star with broadened emission lines at an
approximate distance of 4.4 kpc. The distance implies a 2-10 keV luminosity in
the range from 1E+33 to 1E+36 erg/s. The evidence suggests that SAXJ2239.3+6116
is a Be X-ray binary with an orbital period of 262 days.


title: Solar Oscillations and Convection: I. Formalism for Radial Oscillations

abstract:
  We present a formalism for investigating the interaction between pmode
oscillations and convection by analyzing realistic, three-dimensional
simulations of the near-surface layers of the solar convection zone. By
choosing suitable definitions for fluctuations and averages, we obtain a
separation that retains exact equations. The equations for the horizontal
averages contain one part that corresponds directly to the wave equations for a
1-D medium, plus additional terms that arise from the averaging and correspond
to the turbulent pressure gradient in the momentum equation and the divergence
of the convective and kinetic energy fluxes in the internal energy equation.
These terms cannot be evaluated in closed form, but they may be measured in
numerical simulations. The additional terms may cause the mode frequencies to
shift, relative to what would be obtained if only the terms corresponding to a
1-D medium were retained---most straightforwardly by changing the mean
stratification, and more subtly by changing the effective compressibility of
the medium. In the presence of time dependent convection, the additional terms
also have a stochastic time dependence, that acts as a source of random
excitation of the coherent modes. In the present paper, we derive an expression
for the excitation power and test it by applying it to a numerical experiment
of sufficient duration for the excited modes to be spectrally resolved.


title: Cosmic Dust in the 21st Century

abstract:
  The past century of interstellar dust has brought us from first ignoring it
to finding that it plays an important role in the evolution of galaxies.
Current observational results in our galaxy provide a complex physical and
chemical evolutionary picture of interstellar dust starting with the formation
of small refractory particles in stellar atmospheres to their modification in
diffuse and molecular clouds and ultimately to their contribution to star
forming regions. Observations of the properties of dust in very young galaxies
will be an important probe of the rates of star formation in terms of the
production and destruction of dust grains. Future observations of dust at high
spectral and spatial resolution will provide detailed information on processes
in collapsing clouds up to star formation. Space missions to comets in the next
century will first study them in situ but ultimately will bring back pristine
nucleus material which will contain the end product of the collapsing
protosolar molecular cloud at the time of planet formation. If one of the
current theories of the origin of life from comets is correct, laboratory
studies of comet dust grains immersed in water may give direct indications of
prebiotic chemical evolution.


title:
The iron abundance in hot central stars of planetary nebulae derived
  from IUE spectra

abstract:
  We present the first attempt to determine the iron abundance in hot central
stars of planetary nebulae. We perform an analysis with fully metal-line
blanketed NLTE model atmospheres for a sample of ten stars (T_eff >= 70.000 K)
for which high-resolution UV spectra are available from the IUE archive. In all
cases lines of Fe VI or Fe VII can be identified. As a general trend, the iron
abundance appears to be subsolar by 0.5-1 dex, however, the S/N of the IUE
spectra is not sufficient to exclude a solar abundance in any specific case.
Improved spectroscopy by either FUSE or HST is necessary to verify the
possibility of a general iron deficiency in central stars. The suspected
deficiency may be the result of gravitational settling in the case of three
high-gravity objects. For the other stars with low gravity and high luminosity
dust fractionation during the previous AGB phase is a conceivable origin.


title: The Origin of the X-ray and Ultraviolet Emission in NGC 7469

abstract:
  We present a spectral analysis of a 30d, near-continuous observation of the
Seyfert 1 galaxy NGC 7469 with RXTE. Daily integrations show strong spectral
changes during the observation. Ourmain result is that we find the X-ray
spectral index to be correlated with the UV flux. Furthermore, the broad-band
X-ray photon flux is also correlated with the UV continuum. These correlations
point towards a model in which the X-rays originate via thermal Comptonization
of UV seed photons. Furthermore, the UV is also correlated with the
extrapolation of the X-ray power law into the soft X-ray/EUV region. Our data
analysis therefore re-opens the possibility the the UV photons and their
variability arise from reprocessing, as long as the primary source of heating
is photo-electric absorption in the reprocessor, rather than Compton
downscattering, A coherent picture of the X-ray/UV variability can therefore be
constructed whereby absorption and reprocessing of EUV/soft X-rays in a
standard accretion disk produce a variable seed photon distribution which are
in turn up-scattered into the X-ray band. We also find a significant
correlation between the 2-10 keV flux and the 6.4 keV iron K-line suggesting
that at least some portion of the line originates within ~1 lt day of the X-ray
continuum source. Neither the power law photon index nor the Compton reflection
component are correlated with the 2-10 keV flux. The latter is not correlated
with the iron K line flux either. We do find an apparent correlation between
the X-ray spectral index and the strength of the Compton reflection component.
In an Appendix we show, however, that this can be produced by a combination of
statistical and systematic errors. We conclude the apparent variations in the
Compton reflection component may be an artifact of these effects.


title:
What do the UV Spectra of Narrow-line Seyfert 1 Galaxies tell us about
  their BLR?

abstract:
  We study the UV spectra of narrow-line Seyfert~1 (NLSy1) galaxies and compare
them with ``normal'' AGN. Similar to their optical lines, the NLSy1s show
narrower UV lines. They are also characterized by weaker CIV 1549, CIII] 1909,
and stronger AlIII 1857 emission. These UV line properties add to the optical
and X-ray properties known to be part of the Boroson and Green eigenvector 1.
We show that the steep soft-X-rays, which characterize the NLSy1s SEDs, change
the equilibrium of the two phase cloud-intercloud medium resulting in somewhat
higher BLR cloud densities, lower ionization parameter and larger BLR radii.
These modified conditions can explain the unusual emission line properties we
find in NLSy1.
  Using a specific model of an accretion disk with corona presented by Witt,
Czerny and Zycki (1997), we also show that the steep soft and hard-X-ray
continua can be explained if the $L/L_{Edd}$ ratios are larger than in
``normal'' Seyfert1/QSO strengthening earlier suggestions that the $L/L_{Edd}$
is the physical parameter driving this eigenvector.


title:
ORFEUS II echelle spectra: On the influence of iron-group line
  blanketing in the Far-UV spectral range of hot subdwarfs

abstract:
  We present an analysis of the subdwarf O star Feige 67 with a fully
metal-line blanketed NLTE model atmosphere based on high-resolution Far-UV
(912-2000 A) and Near-UV (2000-3400 A) spectra from new ORFEUS II echelle
observations and the IUE final archive. The Far-UV spectra are heavily
blanketed by iron and nickel lines, preventing the detection of the stellar
continuum and complicating the abundance analysis.
  Important points concerning the account for blanketing by millions of
iron-group lines and for an accurate determination of iron and nickel
abundances are discussed: The usage of all theoretically and experimentally
known line opacities of the iron-group elements, the consideration of a broad
wavelength range for a reliable determination of the stellar continuum flux,
and the role of interstellar reddening. This paper outlines a basic approach
for spectral analysis of future high-resolution Far-UV spectra of hot compact
stars. During this study we re-analyzed the iron and nickel abundance of our
exemplary object Feige 67 and confirm their extraordinarily amount.


title:
Dependence of Halo Properties on Interaction History, Environment and
  Cosmology

abstract:
  I present results from numerical N-body simulations regarding the effect of
merging events on the angular momentum distribution of galactic halos as well
as a comparison of halo growth in Press-Schechter vs. N-body methods. A total
of six simulations are used spanning 3 cosmologies: a standard flat Omega_0=1
model, an open Omega_0=0.3 model and a "tilted" flat Omega_0=1 model with
spectral index n=0.8. In each model, one run was conducted using a spatially
uniform grid of particles and one using a refined grid in a large void. In all
three models and all environments tested, the mean angular momentum of merger
remnants (halo interaction products with mass ratios 3:1 or less) is greater
than non-merger remnants. Furthermore, the dispersion in the merger-remnant
angular momentum distribution is smaller than the dispersion of the non-merger
distribution. The interpretation most consistent with the data is that the
orbital angular momentum of the interactors is important in establishing the
final angular momentum of the merger product. I give the angular momentum
distribution which describes the merger remnant population.
  I trace the most massive progenitor of L_* galactic-mass halos (uniform grid)
and 10^{11} solar mass halos (refined void) from redshift z=0 back to z=5.
Monte-Carlo mass histories match simulations reasonably well for the latter
sample. I find that for halos of mass 10^{12} to 10^{14} solar masses, this
method can underestimate the mass of progenitors by 20%, hence yielding
improper formation redshifts of halos. With this caveat, however, the general
shapes of halo mass histories and formation-time distributions are preserved.


title: Resolving the Structure of Cold Dark Matter Halos II

abstract:
  We study the effects of mass and force resolution on the density profiles of
galaxy-size Cold Dark Matter (CDM) halos in a flat, low-density cosmological
model with vacuum energy. We show thatalthough increasing the mass and force
resolution allows us to probe deeper into the inner halo regions, it does not
lead to steeper inner density profiles. Instead, the halo profiles converge at
scales larger than four times the formal resolution or the radius containing
more than 200 particles, whichever is larger. In the simulations presented in
this paper, we are able to probe density profile of a relaxed isolated
galaxy-size halo at scales r=(0.005-1)r_vir. We find that the density
distribution can be well approximated by the profile suggested by Moore etal
(1998): rho= x^{-1.5}(1+x^{1.5})^-1, where x=r/r_s and r_s is the
characteristic radius. The analytical profile proposed by Navarro et al. (1996)
rho= x^{-1}(1+x)^-2, also provides a good fit, with the same relative errors of
about 10% for radii larger than 1% of the virial radius. Both analytical
profiles fit equally well because for high-concentration galaxy-size halos the
differences between these profiles become significant only at scales well below
0.01r_vir. We also find that halos of similar mass may have somewhat different
parameters (characteristic radius, maximum rotation velocity, etc.) and shapes
of their density profiles. We associate this scatter in properties with
differences in halo merger histories and the amount of substructure present in
the analyzed halos.


title: Self-Interacting Dark Matter

abstract:
  Spergel and Steinhardt have recently proposed the concept of dark matter with
strong self-interactions as a means to address numerous discrepancies between
observations of dark matter halos on subgalactic scales and the predictions of
the standard collisionless dark matter picture. We review the motivations for
this scenario and discuss some recent, successful numerical tests. We also
discuss the possibility that the dark matter interacts strongly with ordinary
baryonic matter, as well as with itself. We present a new analysis of the
experimental constraints and re-evaluate the allowed range of cross-section and
mass.


title: Metal Enrichment of the Intergalactic Medium at z=3 by Galactic Winds

abstract:
  Studies of quasar absorption lines reveal that the low density intergalactic
medium at z ~ 3 is enriched to 0.001-0.01 solar metallicity. This enrichment
may have occurred in an early generation of Population III stars at redshift z
>~ 10, by protogalaxies at 6 <~ z <~ 10, or by larger galaxies at 3 <~ z <~ 6.
This paper addresses the third possibility by calculating the enrichment of the
IGM at z >~ 3 by galaxies of baryonic mass >~ 10^8.5 solar masses. We use
already completed cosmological simulations to which we add a prescription for
chemical evolution and metal ejection by winds, assuming that the winds have
properties similar to those observed in local starbursts and Lyman-break
galaxies. Results are given for a number of representative models, and we also
examine the properties of the galaxies responsible for the enrichment as well
as the physical effects responsible for wind escape and propagation. We find
that winds of velocity >~ 200-300 km/s are capable of enriching the IGM to the
mean level observed, though many low-density regions would remain metal free.
Calibrated by observations of Lyman-break galaxies, our calculations suggest
that most galaxies at z >~ 3 should drive winds that can escape and propagate
to large radii. The primary effect limiting the enrichment of low-density IG
gas in our scenario is then the travel time from high- to low-density regions,
implying that the metallicity of low-density gas is a strong function of
redshift.


title:
Enrichment of the Intergalactic Medium by Radiation Pressure Driven Dust
  Efflux

abstract:
  The presence of metals in hot cluster gas and in Ly-alpha absorbers, as well
as the mass-metallicity relation of observed galaxies, suggest that galaxies
lose a significant fraction of their metals to the intergalactic medium (IGM).
Theoretical studies of this process have concentrated on metal removal by
dynamical processes or supernova-driven winds. Here, we investigate the
enrichment of the IGM by the expulsion of dust grains from galaxies by
radiation pressure. We use already completed cosmological simulations, to which
we add dust assuming that most dust can reach the equilibrium point between
radiation pressure and gravitational forces. We find that the expulsion of dust
and its subsequent (partial) destruction in the IGM can plausibly account for
the observed level of C and Si enrichment of the z=3 IGM. At low-z, dust
ejection and destruction could explain a substantial fraction of the metals in
clusters, but it cannot account for all of the chemical species observed. Dust
expelled by radiation pressure could give clusters a visual opacity of up to
0.2-0.5 mag in their central regions even after destruction by the hot
intracluster medium; this value is interestingly close to limits and claimed
observations of cluster extinction. We also comment on the implications of our
results for the opacity of the general IGM. Finally, we suggest a possible
`hybrid' scenario in which winds expel gas and dust into galaxy halos but
radiation pressure distributes the dust uniformly through the IGM.


title: A survey of hard spectrum ROSAT sources 1: X-ray source catalogue

abstract:
  We present a catalogue of 147 serendipitous X-ray sources selected to have
hard spectra (alpha < 0.5) from a survey of 188 ROSAT fields. Such sources must
be the dominant contributors to the X-ray background at faint fluxes. We have
used Monte Carlo simulations to verify that our technique is very efficient at
selecting hard sources: the survey has > 10 times as much effective area to
hard sources as it has to soft sources above a 0.5 - 2 keV flux level of 10^-14
erg/cm^2/s. The distribution of best fit spectral slopes of the hard sources
suggests that a typical ROSAT hard source in our survey has a spectral slope
alpha ~0. The hard sources have a steep number flux relation (dN/dS propto
S^-gamma with a best fit value of gamma = 2.72 +- 0.12) and make up about 15%
of all 0.5 - 2 keV sources with S > 10^-14 erg/cm^2/s. If their N(S) continues
to fainter fluxes, the hard sources will comprise ~ 40% of sources with 5
10^-15 < S < 10^-14. The population of hard sources can therefore account for
the harder average spectra of ROSAT sources with S < 10^-14. They probably make
a strong contribution to the X-ray background at faint fluxes and could be the
solution to the X-ray background spectral paradox.


title:
Eigenvalues of the Stewart-Lyth equation for inflation with a blue
  spectrum

abstract:
  By using the rather stringent nonlinear second order slow-roll approximation,
we reconsider the nonlinear second order Abel equation of Stewart and Lyth. We
determine a new blue eigenvalue spectrum. Some of the discrete values of the
spectral index $n_s$ have consistent fits to the cumulative COBE data as well
as to recent ground-base CMB experiments.


title: Ultra High Energy Cosmic Rays: propagation in the Galaxy and anisotropy

abstract:
  We considered propagation of Ultra High Energy Cosmic Rays (UHECR) through
the galaxy. We investigated models with sources of UHECR distributed in the
same way as Cold Dark Matter (CDM) in a self-consistent way, taking into
account both extra-galactic and Galactic contributions. Using a very simple toy
model of galactic magnetic field we showed that in the case of galactic origin
of UHECRs the anisotropy can reach considerable values. In the case of
extragalactic UHECRs origin the anisotropy appears to be non-vanishing only for
electron and photon components due to synchrotron losses, but it hardly can be
reassured. The reason is an extremely low flux of UHE electrons and a too low
level of gamma-ray anisotropy.


title: Nucleosynthesis in Massive Stars - Including All Stable Isotopes

abstract:
  We present the first calculations to follow the evolution of all stable
isotopes (and their abundant radioactive progenitors) in a finely zoned stellar
model computed from the onset of central hydrogen burning through explosion as
a Type II supernova. The calculations were performed for a 15 solar mass Pop I
star using the most recently available set of experimental and theoretical
nuclear data, revised opacity tables, and taking into account mass loss due to
stellar winds. We find the approximately solar production of proton-rich
isotopes above a mass number of A=120 due to the gamma-process. We also find a
weak s-process, which along with the gamma-process and explosive helium and
carbon burning, produces nearly solar abundances of almost all nuclei from A=60
to 85. A few modifications of the abundances of heavy nuclei above mass 90 by
the s-process are also noted and discussed. New weak rates lead to significant
alteration of the properties of the presupernova core.


title: Small-scale inviscid accretion discs around black holes

abstract:
  Gas falling quasi-spherically onto a black hole forms an inner accretion disc
if its specific angular momentum $l$ exceeds $\lmin\sim r_gc$ where $r_g$ is
the Schwarzschild radius. The standard disc model assumes $l\gg\lmin$. We argue
that, in many black-hole sources, accretion flows have angular momenta just
above the threshold for disc formation, $l\simgt\lmin$, and assess the
accretion mechanism in this regime. In a range $\lmin<l<\lcr$, a small-scale
disc forms in which gas spirals fast into the black hole without any help of
horizontal viscous stresses. Such an `inviscid' disc, however, interacts
inelastically with the feeding infall. The disc-infall interaction determines
the dynamics and luminosity of the accretion flow. The inviscid disc radius can
be as large as $14 r_g$, and the energy release peaks at $2r_g$. The disc emits
a Comptonized X-ray spectrum with a break at $\sim 100$ keV. This accretion
regime is likely to take place in wind-fed X-ray binaries and is also possible
in active galactic nuclei.


title: Free-fall accretion and emitting caustics in wind-fed X-ray sources

abstract:
  In wind-fed X-ray binaries the accreting matter is Compton cooled and falls
freely onto the compact object. The matter has a modest angular momentum $l$
and accretion is quasi-spherical at large distances from the compact object.
Initially small non-radial velocities grow in the converging supersonic flow
and become substantial in the vicinity of the accretor. The streamlines with
$l>(GMR_*)^{1/2}$ (where $M$ and $R_*$ are the mass and radius of the compact
object) intersect outside $R_*$ and form a two-dimensional caustic which emits
X-rays. The streamlines with low angular momentum, $l<(GMR_*)^{1/2}$, run into
the accretor. If the accretor is a neutron star, a large X-ray luminosity
results. We show that the distribution of accretion rate/luminosity over the
star surface is sensitive to the angular momentum distribution of the accreting
matter. The apparent luminosity depends on the side from which the star is
observed and can change periodically with the orbital phase of the binary. The
accretor then appears as a `Moon-like' X-ray source.


title:
On the Mass Profile of Galaxy Cluster CL 0024+1654 Inferred from Strong
  Lensing

abstract:
  Observations of a flat density profile in the cores of dark-matter-dominated
halos on the two extremes of mass for virialized objects in the universe, dwarf
galaxies and galaxy clusters, present a serious challenge to the current
standard theory of structure formation involving Cold Dark Matter (CDM). By
contrast, N-body simulations of halo formation in the latter indicate density
profiles which are singular and steeply rising towards the center. A
flat-density core on the cluster scale is indicated by gravitational lensing
observations, most significantly by the strong-lensing measurements of CL
0024+1654 by the Hubble Space Telescope. A recent re-analysis of this cluster
has suggested that a uniform-density core is not demanded by the data, thereby
eliminating a significant piece of the conflict between the observations and
the CDM theoretical predictions. We show here, however, that the singular mass
profile which that analysis reports as consistent with the lensing measurements
of CL 0024+1654 implies a velocity dispersion which is much higher than the
measured value for this cluster.


title: Strange quark matter in cosmic ray flux and exotic events

abstract:
  There have been several reports of exotic nuclear fragments, with highly
unusual charge to mass ratio, in cosmic ray experiments. Although there exist
experimental uncertainties which make them, at best, only candidate "exotic"
events, it is important to understand what they could be, if they are
eventually confirmed. Among other possible explanations, some authors have
interpreted them to be lumps of strange quark matter (strangelets). A major
problem with such an interpretation is that to reach the earth's surface, they
must possess an unusually high penetrability through the terrestrial
atmosphere. We show that a recently proposed mechanism for the propagation of
strangelets through the earth's atmosphere, together with a proper account of
charge capture and ionisation loss, would solve this problem. We also argue
that this could lead to viable strategies for definitive detection of strange
quark matter in cosmic ray flux using a ground based large area array of
passive detectors.


title:
The morphology of the emission line region of Compact Steep Spectrum
  radio sources

abstract:
  We present the results of HST narrow band imaging of eleven Compact Steep
Spectrum (CSS) radio sources. Five of them (3C 48, 3C 147, 3C303.1, 3C 277.1
and 4C 12.50) were part of a dedicated ``pointed'' program of deep line imaging
([OIII]). For six additional sources (3C 49, 3C 93.1, 3C 138, 3C 268.3, 3C305.1
and 3C343.1) ``snapshot'' images ([OIII] or [OII]) were taken from the HST
archive. In all but one of the targets (3C 49) line emission has been detected
and only in one case (3C 138) is unresolved. In four out five of the sources
with deep observations, the line emission extends well beyond the size of the
radio source but along the radio axis. Structures of similar surface brightness
would have not been seen in the snapshot images. These emission line structures
extend to scales of 10 to 30 kpc and cover a projected angle, when seen from
the nucleus, of 30 to 110 degrees, indicating that the nuclear illumination is
anisotropic. Photon counting arguments also support this interpretation. In six
objects the radio emission extends over more than 1 arcsec. In these cases the
line emission has an elongated structure, linking the nucleus to the
radio-lobes, possibly tracing the path of the invisible radio jets.
Nevertheless the emission line morphologies do not show the bow shocks at the
extremities of the radio lobes expected if they are sources whose expansion is
frustrated by a dense external medium. Our data favour the alternative model in
which CSSs are the young phase of the large size radio sources. When
``pointed'' pure continuum images are available, there appears to be no
alignment between radio and continuum emission which contradicts previous
suggestions based on broad-band HST imaging.


title: HI absorption in radio galaxies

abstract:
  Twenty-two powerful radio galaxies have been searched for HI absorption. We
find the highest probability of detecting HI in absorption among narrow-line
compact (or small) galaxies or galaxies with indication of richer interstellar
medium (i.e. with ongoing or recent star-formation). We discuss the difficulty
in the interpretation of the origin of the HI absorption due to the uncertainty
in the systemic velocity of the galaxies.


title:
Cosmic Microwave Background Radiation anisotropy with primordial
  magnetic fields

abstract:
  Galactic magnetic fields are observed of order $\sim 10^{-6}G$, but their
origin is not definitely known yet. In this paper we consider the primordial
magnetic fields generated in the early universe and analyse their effects on
the density perturbations and the CMBR anisotropy. We assume that the random
magnetic fields have the power law spectrum and satisfy the force-free field
condition.
  The peak heights of the CMBR anisotropy are shown to be shifted upward
depending on the magnetic field strengths relative to the no-magnetic field
case.


title: On the transport of magnetic fields by solar-like stratified convection

abstract:
  The interaction of magnetic fields and stratified convection was studied in
the context of the solar and late type stellar dynamos by using numerical 3D
MHD simulations. The topology of stratified asymmetric and over-turning
convection enables a pumping mechanism that may render the magnetic flux
storage problem obsolete. The inclusion of open boundary conditions leads to a
considerable flux loss unless the open boundary is placed close to the physical
boundary. Simulations including solar-like latitudinal shear indicates that a
toroidal field of several tens of kilo-Gauss may be held down by the pumping
mechanism.


title: Box- and peanut-shaped bulges: I. Statistics

abstract:
  We present a classification for bulges of a complete sample of ~1350 edge-on
disk galaxies derived from the RC3 (Third Reference Catalogue of Bright
Galaxies, de Vaucouleurs et al. 1991). A visual classification of the bulges
using the Digitized Sky Survey (DSS) in three types of b/p bulges or as an
elliptical type is presented and supported by CCD images. NIR observations
reveal that dust extinction does almost not influence the shape of bulges.
There is no substantial difference between the shape of bulges in the optical
and in the NIR. Our analysis reveals that 45% of all bulges are box- and
peanut-shaped (b/p). The frequency of b/p bulges for all morphological types
from S0 to Sd is > 40%. In particular, this is for the first time that such a
large frequency of b/p bulges is reported for galaxies as late as Sd. The
fraction of the observed b/p bulges is large enough to explain the b/p bulges
by bars.


title: Sunyaev-Zel'dovich Effect Review

abstract:
  I review the present observational status of the SZ effect due to the Compton
scattering of the 3K background on the hot electrons of clusters of galaxies. I
raise the relevant issues from theoretical and X-ray aspects of the question
that challenge the present experiments. Future instruments like powerful radio
interferometers and bolometric cameras should give us access to the statistics
of clusters as well as their internal morphology within the next ten years.
They will provide an approach complementary to space experiments (XMM, Chandra,
Planck) for some fundamental cosmological and large scale structure issues.


title: X-rays from the barred galaxy NGC 4303

abstract:
  The late-type galaxy NGC 4303 (M61) is one of the most intensively studied
barred galaxies in the Virgo Cluster. Its prominent enhanced star formation
throughout large areas of the disk can be nicely studied due to its low
inclination of about 27 \degr.
  We present observations of NGC 4303 with the ROSAT PSPC and HRI in the soft
X-ray (0.1-2.4 keV). The bulk of the X-ray emission is located at the nuclear
region. It contributes more than 80% to the total observed soft X-ray flux. The
extension of the central X-ray source and the L_X/L_Halpha ratio point to a low
luminous AGN (LINER) with a circumnuclear star-forming region. Several separate
disk sources can be distinguished with the HRI, coinciding spatially with some
of the most luminous HII regions outside the nucleus of NGC 4303. The total
star formation rate amounts to 1-2 Msun/yr. The X-ray structure follows the
distribution of star formation with enhancement at the bar-typical patterns.
  The best spectral fit consists of a power-law component (AGN and HMXBs) and a
thermal plasma component of hot gas from supernova remnants and superbubbles.
The total 0.1-2.4 keV luminosity of NGC 4303 amounts to 5x10^40 erg/s,
consistent with comparable galaxies, like e.g. NGC 4569.


title:
Extrasolar Planets and the Rotation and Axisymmetrical mass loss of
  evolved stars

abstract:
  I examine the implications of the recently found extrasolar planets on the
planet-induced axisymmetrical mass loss model for the formation of elliptical
planetary nebulae (PNs). This model, which was developed in several earlier
papers by the author and a few collaborators, attributes low departure from
spherical mass loss of upper asymptotic giant branch (AGB) stars to envelope
rotation which results from deposition of planet's orbital angular momentum. It
was predicted that about 50 percent of all sun-like stars have Jupiter-like
planets around them. In light of the new finding that only 5 percent of
sun-like stars do have such planets I revise this prediction. I now predict
that indeed about 50 percent of PNs progenitors do have close planets around
them, but the planets can have much lower masses, as low as 0.01 times
Jupiter's mass. To support this claim I follow the angular momentum evolution
of single stars as they evolve to the post-AGB phase. The prediction that on
average several such planets orbit each star, as in the solar system, still
holds.


title:
Cooling sequences and color-magnitude diagrams for cool white dwarfs
  with hydrogen-atmospheres

abstract:
  We present new cooling sequences, color-magnitude diagrams, and color-color
diagrams for cool white dwarfs with pure hydrogen atmospheres down to an
effective temperature $\te=1500$ K. We include a more detailed treatment of the
physics of the fully-ionized interior, particularly an improved discussion of
the thermodynamics of the temperature-dependent ion-ion and ion-electron
contributions of the quantum, relativistic electron-ion plasma. The present
calculations also incorporate accurate boundary conditions between the
degenerate core and the outermost layers as well as updated atmosphere models
including the H$_2$-H$_2$ induced-dipole absorption. We examine the differences
on the cooling time of the star arising from uncertainties in the initial
carbon-oxygen profile and the core-envelope $L$-$T_c$ relation. The maximum
time delay due to crystallization-induced chemical fractionation remains
substantial, from $\sim 1.0$ Gyr for 0.5 and 1.2 $\msol$ white dwarfs to $\sim
1.5$ Gyr for 0.6 to 0.8 $\msol$ white dwarfs, even with initial stratified
composition profiles, and cannot be ignored in detailed white dwarf cooling
calculations. These cooling sequences provide theoretical support to search for
or identify old disk or halo hydrogen-rich white dwarfs by characterizing their
mass and age from their observational signatures.


title: The Nature of High-Redshift Galaxies

abstract:
  Using semi-analytic models of galaxy formation set within the Cold Dark
Matter (CDM) merging hierarchy, we investigate several scenarios for the nature
of the high-redshift ($z \ga 2$) Lyman-break galaxies (LBGs). We consider a
``collisional starburst'' model in which bursts of star formation are triggered
by galaxy-galaxy mergers, and find that a significant fraction of LBGs are
predicted to be starbursts. This model reproduces the observed comoving number
density of bright LBGs as a function of redshift and the observed luminosity
function at $z\sim 3$ and $z\sim 4$, with a reasonable amount of dust
extinction. Model galaxies at $z \sim 3$ have star formation rates, half-light
radii, I-K colours, and internal velocity dispersions that are in good
agreement with the data. Global quantities such as the star formation rate
density and cold gas and metal content of the Universe as a function of
redshift also agree well. Two ``quiescent'' models without starbursts are also
investigated. In one, the star formation efficiency in galaxies remains
constant with redshift, while in the other, it scales inversely with disc
dynamical time, and thus increases rapidly with redshift. The first quiescent
model is strongly ruled out as it does not produce enough high redshift
galaxies once realistic dust extinction is accounted for. The second quiescent
model fits marginally, but underproduces cold gas and very bright galaxies at
high redshift. A general conclusion is that star formation at high redshift
must be more efficient than locally. The collisional starburst model appears to
accomplish this naturally without violating other observational constraints.


title: Mid infrared emission of nearby Herbig Ae/Be stars

abstract:
  We present mid IR spectro-photometric imaging of a sample of eight nearby ($D
\leq 240$pc) Herbig Ae/Be stars. The spectra are dominated by photospheric
emission (HR6000), featureless infrared excess emission (T~Cha), broad silicate
emission feature (HR5999) and the infrared emission bands (HD 97048, HD 97300,
TY~CrA, HD 176386). The spectrum of HD179218 shows both silicate emission and
infrared emission bands (IEB). All stars of our sample where the spectrum is
entirely dominated by IEB have an extended emission on scales of a few thousand
AU ($\sim 10''$). We verify the derived source extension found with ISOCAM by
multi--aperture photometry with ISOPHT and compare our ISOCAM spectral
photometry with ISOSWS spectra.


title: Cluster Tempreature Evolution: The Mass-Temperature Relation

abstract:
  Evolution of the cluster temperature function is extremely sensitive to the
mean matter density of the universe. Current measurements based on cluster
temperature surveys indicate that Omega_M ~ 0.3 with a 1-sigma statistical
error ~0.1, but the systematic errors in this method are of comparable size.
Many more high-z cluster temperatures will be arriving from Chandra and XMM in
the near future. In preparation for future cluster temperature surveys, this
paper analyses the cluster mass-temperature relation, with the intention of
identifying and reducing the systematic errors it introduces into measurements
of cosmological parameters. We show that the usual derivation of this relation
from spherical top-hat collapse is physically inconsistent and propose a more
realistic derivation based on a hierarchical merging model that more faithfully
reflects the gradual ceasing of cluster evolution in a low-Omega_M universe. We
also analyze the effects of current systematic uncertainties in the M-T
relation and show that they introduce a systematic uncertainty of ~0.1 in the
best-fitting Omega_M. Future improvements in the accuracy of the M-T relation
will most likely come from comparisons of predicted cluster temperature
functions with temperature functions derived directly from large-scale
structure simulations.


title:
The Reionization of the Universe and the Photoevaporation of
  Cosmological Minihalos

abstract:
  The first sources of ionizing radiation to condense out of the dark and
neutral IGM sent ionization fronts sweeping outward through their surroundings,
overtaking other condensed objects and photoevaporating them. This feedback of
universal reionization on cosmic structure formation is demonstrated here by
gas dynamical simulations, including radiative transfer, for a cosmological
minihalo of dark matter and baryons exposed to an external source of ionizing
radiation, either starlight or quasar light, just after the passage of the
global ionization front created by the source.


title:
Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST
  Survey

abstract:
  We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical
spectrum shows unambiguous broad absorption features while its double-lobed
radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type
II radio source. Its radio luminosity places it at the extreme of the recently
established class of radio-loud broad absorption line quasars (Becker et al.
1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate
that FIRST J101614.3+520916 is a typical FR-II quasar which has been
rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep
Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be
estimated from its radio structure and optical brightness, indicating that we
are viewing the system at a viewing angle of > 40 degrees. The position angles
of the radio jet and optical polarization are not well-aligned, differing by 20
to 30 degrees. When combined with the evidence presented by Becker et al.
(2000) for a sample of 29 BAL quasars showing that at least some BAL quasars
are viewed along the jet axis, the implication is that no preferred viewing
orientation is necessary to observe BAL systems in a quasar's spectrum. This,
and the probable young nature of compact steep spectrum sources, leads
naturally to the alternate hypothesis that BALs are an early stage in the lives
of quasars.


title:
Morphologies and ages of star cluster pairs and multiplets in the Small
  Magellanic Cloud

abstract:
  An isophotal atlas of 75 star cluster pairs and multiplets in the Small
Magellanic Cloud is presented, comprising 176 objects. They are concentrated in
the SMC main body. The isophotal contours were made from Digitized Sky Survey
images and showed relevant structural features possibly related to interactions
in about 25% of the sample. Previous N-body simulations indicate that such
shapes could be due to tidal tails, bridges or common envelopes. The diameter
ratio between the members of a pair is preferentially in the range 1 - 2, with
a peak at 1. The projected separation is in the range ~ 3 - 22 pc with a
pronounced peak at ~ 13 pc. For 91 objects it was possible to derive ages from
Colour-Magnitude Diagrams using the OGLE-II photometric survey. The cluster
multiplets in general occur in OB stellar associations and/or HII region
complexes. This indicates a common origin and suggests that multiplets coalesce
into pairs or single clusters in a short time scale. Pairs in the SMC appear to
be mostly coeval and consequently captures are a rare phenomenon. We find
evidence that star cluster pairs and multiplets may have had an important role
in the dynamical history of clusters presently seen as large single objects.


title: Finite temperature corrections to weak rates prior to nucleosynthesis

abstract:
  We have reexamined the electromagnetic corrections to the weak interaction
rates for the transformation of neutrons to protons, and protons to neutrons,
in the early universe, before freeze-out. We derive compact expressions for
these rates in terms of thermal expectation values of products of fields, and
we give explicit constructions of the terms to order e^2. We disagree in
several respects with results in the literature.


title: Recombination spectra of Helium-Like Ions

abstract:
  We calculate the recombination spectra of the He-like ions He~I, C~V, N~VI,
O~VII, Ne~IX, Mg~XI, Si~XIII, S~XV, Ar~XVII, Ca~XIX, and Fe~XXV. We include the
following physical processes: radiative recombination, dielectronic
recombination, three-body recombination, electron impact ionization, and
collisional excitation by electrons, protons, and $\alpha$-particles. The
calculations account for the effects of lowering of the continuum at high
densities and high density corrections to dielectronic recombination.
  Then we construct models for He-like ions for fast computation of their
spectra. Every model includes 29 bound levels up to n=5 and 6 doubly excited
levels that account for the most important satellite lines. The models are
constructed in a way that allows for proper approach to LTE under appropriate
conditions. These models can simultaneously solve for the H/He-like ionization
balance in photoionized or collisionally ionized plasmas and compute emission
spectra including the combined effects of radiative and dielectronic
recombination, collisional excitation, photoionization from excited levels,
fluorescence, and line trapping. The models can be used for any temperature
between 100 and $10^9$K and electron densities of up to $10^{18}$ \cm3. The
models can be easily used within spectral modeling codes or as stand-alone
tools for spectral analysis.
  We present comparisons between the results of the present models and previous
work. Significant differences are found between the present effective
recombination rate coefficients to the $n=2$ and those of previous estimates.
Later, we study various emission line ratio diagnostics under collisional
ionization and photoionized conditions.


title: Internal shocks in the jets of blazars

abstract:
  The development of instabilities leading to the formation of internal shocks
is expected in the relativistic outflows of both gamma-ray bursts and blazars.
The shocks heat the expanding ejecta, generate a tangled magnetic field and
accelerate leptons to relativistic energies. While this scenario has been
largely considered for the origin of the spectrum and the fast variability in
gamma-ray bursts, here we consider it in the contest of relativistic jets of
blazars. We calculate the expected spectra, light curves and time correlations
between emission at different wavelengths. The dynamical evolution of the wind
explains the minimum distance for dissipation (~10^{17} cm) to avoid
$\gamma$--$\gamma$ collisions and the low radiative efficiency required to
transport most of the kinetic energy to the extended radio structures. The
internal shock model allows to follow the evolution of changes, both dynamical
and radiative, along the entire jet, from the inner part, where the jet becomes
radiative and emits at high energies ($\gamma$-jet), to the parsec scale, where
the emission is mostly in the radio band (radio-jet). We have produced some
animations that can be found at http://www.merate.mi.astro.it/~lazzati/3C279/,
in which the temporal and spectral informations are shown together.


title: Essentials of k-essence

abstract:
  We recently introduced the concept of "k-essence" as a dynamical solution for
explaining naturally why the universe has entered an epoch of accelerated
expansion at a late stage of its evolution. The solution avoids fine-tuning of
parameters and anthropic arguments. Instead, k-essence is based on the idea of
a dynamical attractor solution which causes it to act as a cosmological
constant only at the onset of matter-domination. Consequently, k-essence
overtakes the matter density and induces cosmic acceleration at about the
present epoch. In this paper, we present the basic theory of k-essence and
dynamical attractors based on evolving scalar fields with non-linear kinetic
energy terms in the action. We present guidelines for constructing concrete
examples and show that there are two classes of solutions, one in which cosmic
acceleration continues forever and one in which the acceleration has finite
duration.


title:
Extensive molecular gas in the tidal arms near NGC3077 - Birth of a
  dwarf galaxy?

abstract:
  Using the IRAM 30m radio telescope we have mapped the tidal arm feature
south-east of NGC3077 where we recently detected molecular gas in the CO
(J=1-0) and (2-1) transitions. We find that the molecular gas is much more
extended than previously thought (several kpc). The CO emission can be
separated into at least 3 distinct complexes with equivalent radii between
250pc and 700pc and all well confined over a narrow range in velocity. For one
complex we have also obtained a CO (3-2) spectrum using the KOSMA 3m radio
telescope; utilizing an LVG model we find that the kinetic temperature for this
complex must be about 10K, and the H2 volume density between 600 and
10000cm^-3. Mass estimates based on virialization yield a total mass for the
complexes of order 2-4 10^7 M_sun, i.e. more than the estimated molecular mass
within NGC3077 itself. This implies that interactions between galaxies can
efficiently remove heavy elements and molecules from a galaxy and enrich the
intergalactic medium. A comparison of the distribution of HI and CO shows no
clear correlation. However, CO is only found in regions where the HI column
density exceeds 1.1 10^21 cm^-2. HI masses for the molecular complexes mapped
are of the same order as the corresponding molecular masses. Since the tidal
arm with its molecular complexes has all the ingredients to form stars in the
future, we are thus presumably witnessing the birth of a dwarf galaxy. This
process could be important for the formation of dwarf galaxies especially at
larger look-back times in the universe where galaxy interactions may have been
more frequent.


title: ASCA Observations of the Jet Source XTE J1748-288

abstract:
  XTE J1748-288 is a new X-ray transient with a one-sided radio jet. It was
observed with ASCA on 1998/09/06 and 1998/09/26, 100 days after the onset of
the radio-X-ray outburst. The spectra were fitted with an attenuated power-law
model, and the 2-6-keV flux was 4.6 * 10^{-11} erg s^{-1} cm^{-2} and 2.2 *
10^{-12} on 09/06 and 09/26, respectively. The light curve showed that the
steady exponential decay with an e-folding time of 14 days lasted over 100 days
and 4 orders of magnitude from the peak of the outburst. The celestial region
including the source had been observed with ASCA on 1993/10/01 and 1994/09/22,
years before the discovery. In those period, the flux was < 10^{-13} erg s^{-1}
cm^{-2}, below ASCA's detection limit. The jet blob colliding to the
environmental matter was supposedly not the X-ray source, although the emission
mechanism has not been determined. A possible detection of a K line from highly
ionized iron is discussed.


title: Quasar Str\"omgren Spheres Before Cosmological Reionization

abstract:
  Ionizing sources embedded in the neutral intergalactic medium (IGM) before
cosmological reionization generate discrete HII regions. We show that a
sufficiently bright quasar (for example, one tenth as luminous as that recently
discovered by Fan et al.) can ionize a large volume, allowing the transmission
of a substantial fraction of the flux of its intrinsic Lyman alpha emission
line on both sides of the Lyman alpha wavelength. The observed line profile is
richly informative. We show that a sufficiently accurate, high spectral
resolution ($R\approx 10^4$) measurement of the line profile of a bright quasar
is feasible using the Next Generation Space Telescope (NGST) as well as large
ground-based telescopes. Such a measurement has two potentially important
applications. First, the red side of the Lyman alpha emission line provides a
way to measure the quasar lifetime. Second, the blue side provides a direct
measure of the density fluctuations of the intergalactic medium at the quasar
redshift. The estimate of the absorption of the red side is limited by the
accuracy to which the intrinsic profile of the Lyman alpha emission line is
known. The blue side, however, does not sensitively depend on the intrinsic
profile, because the former is much narrower than the latter.


title: The Nature of Solar Polar Rays

abstract:
  We use time series observations from the SOHO and Yohkoh spacecraft to study
solar polar rays. Contrary to our expectations, we find that the rays are
associated with active regions on the sun and are not features of the polar
coronal holes. They are extended, hot plasma structures formed in the active
regions and projected onto the plane of the sky above the polar coronal holes.
We present new observations and simple projection models that match long-lived
polar ray structures seen in limb synoptic maps. Individual projection patterns
last for at least 5 solar rotations.


title:
ATLAS: a Cassegrain spectrograph based on volume phase holographic
  gratings

abstract:
  We are proposing a new spectrograph (ATLAS) which would revolutionise
intermediate-dispersion observations at the AAT. Based on the new technology of
Volume Phase Holographic gratings, and using transmission optics, ATLAS offers
high throughput and a wide field (24'). It will be ideally suited to extensive
surveys of faint objects. It has been designed with a collimated beam diameter
of 150 mm, giving resolution lambda/delta lambda up to nearly 10,000 with a 1.5
arcsecond slit and good efficiency. It will be a dual-beam instrument, to
maximise observing speed and allow optimised optical coatings to be used. The
project is working towards its Concept Design Review which will occur during
2000.


title: Observational Properties of Diffuse Halos in Clusters

abstract:
  The number of known diffuse radio sources in clusters of galaxies has grown
in recent years, making it possible to derive statistical properties of these
sources and of the hosting clusters. We show that diffuse sources are
associated with X-ray luminous clusters which have undergone recent merger
processes. The radio and X-ray structures are often similar, and correlations
are found between radio and X-ray parameters. This is indication of a link
between the diffuse relativistic and thermal plasma in clusters of galaxies.


title: Radio Halos and Relics in Clusters of Galaxies and Detection Statistics

abstract:
  New sensitive VLA observations confirm the existence of halo and relic
sources in 6 Abell clusters where a diffuse emission was found in the NVSS. We
find evidence that the frequency of clusters with halos and relics is larger in
clusters with high X-ray luminosity. The evidence that the occurrence of a halo
source is larger at high redshifts is marginal.


title:
Limits on Cosmic Matter--Antimatter Domains from Big Bang
  Nucleosynthesis

abstract:
  We present detailed numerical calculations of the light element abundances
synthesized in a Universe consisting of matter- and antimatter- domains, as
predicted to arise in some electroweak baryogenesis scenarios. In our
simulations all relevant physical effects, such as baryon-antibaryon
annihilations, production of secondary particles during annihilations, baryon
diffusion, and hydrodynamic processes are coupled to the nuclear reaction
network. We identify two dominant effects, according to the typical spatial
dimensions of the domains. Small antimatter domains are dissipated via neutron
diffusion prior to He4 synthesis at T_He4 \approx 80 keV, leading to a
suppression of the primordial He4 mass fraction. Larger domains are dissipated
below T_He4 via a combination of proton diffusion and hydrodynamic expansion.
In this case the strongest effects on the elemental abundances are due to
anti-p He4 annihilations, leading to an overproduction of He3 relative to H2
and to overproduction of Li6 via non-thermal nuclear reactions. Both effects
may result in light element abundances deviating substantially from the
standard Big Bang Nucleosynthesis yields and from the observationally inferred
values. This allows us to derive stringent constraints on the antimatter
parameters. For some combinations of the parameters, one may obtain both, low
H2 and low He4, at a common value of the cosmic baryon density, a result
seemingly favored by current observational data.


title:
Spectroscopic confirmation of a cluster of galaxies at z=1 in the field
  of the gravitational lens MG2016+112

abstract:
  We present new optical data on the cluster AX J2019+1127 identified by the
X-ray satellite ASCA at z\sim 1 (Hattori et al. 1997). The data suggest the
presence of a high-redshift cluster of galaxies responsible for the large
separation triple quasar MG2016+112. Our deep photometry reveals an excess of
z\sim 1 galaxy candidates, as already suspected by Benitez et al. (1999). Our
spectroscopic survey of 44 objects in the field shows an excess of 6 red
galaxies securely identified at z \sim 1, with a mean redshift of z =1.005 +/-
0.002. We estimate a velocity dispersion of \sigma = 771 (+430/-160) km s(-1)
based on these 6 galaxies and a V-band mass-to-light ratio of 215 (+308/-77)
h_50 M/L_sol. Our observations thus confirm the existence of a massive
structure acting as the lens, which explains the unusual configuration of the
triple quasar. Hence, there is no more need to invoke the existence of a ``dark
cluster'' to understand this lens system.


title: Theory of Low-Mass Stars and Substellar Objects

abstract:
  Since the discovery of the first bona-fide brown dwarfs and extra-solar
planets in 1995, the field of low mass stars and substellar objects has
considerably progressed, both from theoretical and observational
viewpoints.Recent developments in the physics entering the modeling of these
objects have led to significant improvements in the theory and to a better
understanding of their mechanical and thermal properties. This theory can now
be confronted with observations directly in various observational diagrams
(color-color, color-magnitude, mass-magnitude, mass-spectral type), a stringent
and unavoidable constraint which became possible only recently, with the
generation of synthetic spectra. In this paper, we present the current
state-of-the-art general theory of low-mass stars and sub-stellar objects, from
one solar mass to one Jupiter mass, regarding primarily their interior
structure and evolution. This review is a natural complement to the previous
review on the atmosphere of low-mass stars and brown dwarfs (Allard et al
1997). Special attention is devoted to the comparison of the theory with
various available observations. The contribution of low-mass stellar and
sub-stellar objects to the Galactic mass budget is also analysed.


title: Looking Back with Neutrinos

abstract:
  We briefly discuss the history of suggestions for time- of-flight effects due
to non-zero neutrino mass and a recent proposal that such effects can be used
to determine the parameters of cosmology. With neutrinos there is potentially a
much deeper ``look back time'' than with photons. We note a new point, that if
future large scale neutrino detection arrays see long-time secular variations
in counting rate, this could be due to highly redshifted bursts originating in
the early universe.


title: An ISOCAM Absorption Survey of the Structure of Pre-stellar Cloud Cores

abstract:
  We present the results of a mid-infrared (7 micron) imaging survey of a
sample of 24 starless dense cores carried out at an angular resolution of 6
arcsec with the ISOCAM camera aboard the Infrared Space Observatory (ISO). The
targeted cores are believed to be pre-stellar in nature and to represent the
initial conditions of low-mass, isolated star formation. In previous
submillimeter dust continuum studies of such pre-stellar cores, it was found
that the derived column density profiles did not follow a single power-law such
as N[H2] \propto r^(-1) throughout their full extent but flattened out near
their center. These submillimeter observations however could not constrain the
density profiles at radii greater than ~ 10000 AU. The present absorption study
uses ISOCAM's sensitivity to map these pre-stellar cores in absorption against
the diffuse mid-infrared background. The goal was to determine their structure
at radii that extend beyond the limits of sensitivity of the submillimeter
continuum maps and at twiceas good an angular resolution. Among the 24 cores
observed in our survey, a majority of them show deep absorption features. The
starless cores studied here all show a column density profile that flattens in
the center, which confirms the submillimeter emission results. Moreover, beyond
a radius of ~ 5000-10000 AU, the typical column density profile steepens with
distance from core center and gets steeper than N[H2] \propto r^(-1), until it
eventually merges with the low-density ambient molecular cloud. At least three
of the cores present sharp edges at R ~ 15000-30000 AU and appear to be
decoupled from their parent clouds, providing finite reservoirs of mass for
subsequent star formation.


title:
A unified formalism for the core mass-luminosity relations of
  shell-burning stars

abstract:
  The luminosity evolution of stars with highly condensed cores surrounded by
nuclear-burning shell(s) is analytically investigated with the aid of homology
relations. With respect to earlier works using a similar approach (e.g. Refsdal
& Weigert 1970; Kippenhahn 1981), the major improvement is that we derive all
the basic dependences (i.e. on core mass, core radius, and chemical
composition) in a completely generalised fashion, then accounting for a large
range of possible physical properties characterising the burning shell(s).
Parameterised formulas for the luminosity are given as a function of the (i)
relative contribution of the gas to the total pressure (gas plus radiation),
(ii) opacity source, and (iii) dominant nuclear reaction rates. In this way,
the same formalism can be applied to shell-burning stars of various
metallicities and in different evolutionary phases. In particular, we present
some applications concerning the luminosity evolution of RGB and AGB stars with
different chemical compositions, including the case of initial zero
metallicity. It turns out that homology predictions provide a good
approximation to the results of stellar model calculations. Therefore, the
proposed formalism is useful to understand the possible differences in the
luminosity evolution of shell-burning stars within a unified interpretative
framework, and can be as well adopted to improve the analytical description of
stellar properties in synthetic models.


title: The angular power spectra of polarized Galactic synchrotron

abstract:
  We derive the angular power spectra of intensity and polarization of Galactic
synchrotron emission in the range 36 < l < 10^3 from the Parkes survey mapping
the southern Galactic plane at 2.4 GHz. The polarization spectra of both
electric and magnetic parity up to l \simeq 10^3 are approximated very well by
power laws with slope coefficients \simeq 1.4, quite different from the CMB
spectra. We show that no problem should arise from Galactic synchrotron for
measurements of CMB polarization in the cosmological window.


title:
The HST Survey of BL Lacertae Objects: Morphological Properties of Low
  redshift Host Galaxies

abstract:
  We report on the optical properties of a sample of 30 BL Lac host galaxies in
the redshift range $0.03<z<0.2$, as derived from HST observations. All galaxies
are fully resolved in the WFPC2 (F702W filter) images, allowing a quantitative
analysis in two dimensions. Most and possibly all these galaxies have
characteristics very similar to those of ``normal'' giant ellipticals. The
luminosity, ellipticity, isophote twisting and amount of disky or boxy
isophotes are consistent with those found in non-active ellipticals and in
radio galaxies. In all cases the BL Lac nucleus is well centered in the main
body of its host galaxy, a result that argues strongly against the microlensing
hypothesis for any significant fraction of the population. A search for faint
sub-structures in the host galaxies has not revealed notable signatures of
tidal distortions or sub-components (faint disks, bars, X features, etc.), and
with only one exception, there are no prominent dusty features in the central
regions. Instead, the BL Lac host galaxies are smooth and unperturbed,
suggesting that strong external gravitational interactions are not important to
ongoing activity. A careful examination of the environment around the nucleus,
however, shows a high incidence of close companion objects, whose nature
remains unclear pending spectroscopic observations.


title:
Low Redshift QSO Lyman alpha Absorption Line Systems Associated with
  Galaxies

abstract:
  In this paper we present Monte-Carlo simulations of Lyman alpha absorption
systems which originate in galactic haloes, galaxy discs and dark matter (DM)
satellites around big central haloes. It is found that for strong Lyman alpha
absorption lines galactic haloes and satellites can explain ~20% and 40% of the
line number density of QSO absorption line key project respectively. If big
galaxies indeed possess such large numbers of DM satellites and they possess
gas, these satellites may play an important role for strong Lyman alpha lines.
However the predicted number density of Lyman-limit systems by satellites is
\~0.1 (per unit redshift), which is four times smaller than that by halo
clouds. Including galactic haloes, satellites and HI discs of spirals, the
predicted number density of strong lines can be as much as 60% of the HST
result. The models can also predict all of the observed Lyman-limit systems.
The average covering factor within 250 kpc/h is estimated to be ~0.36. And the
effective absorption radius of a galaxy is estimated to be ~150 kpc/h. The
models predict W_r propto rho^{-0.5} L_B^{0.15} (1+z)^{-0.5}. We study the
selection effects of selection criteria similar to the imaging and
spectroscopic surveys. We simulate mock observations through known QSO
lines-of-sight and find that selection effects can statistically tighten the
dependence of line width on projected distance. (abridged)


title:
A Self-Consistent Test of Comptonisation Models Using Bepposax
  Observations of Seyfert Galaxies

abstract:
  We test accurate models of Comptonisation spectra over BeppoSAX observations
of Seyfert galaxies focusing on the long look at NGC 5548. The hot plasma
temperature derived with these models is significantly higher than that
obtained fitting the same data with a power law plus high energy cut off model
for the continuum. This is due to the fact that in anisotropic geometries
Comptonisation spectra show "intrinsic" curvature which moves the fitted high
energy cut-off to higher energies. We also show preliminary results of our
analysis of a sample of 5 other Seyfert galaxies.


title: Pair Creation at Shocks: Application to Agns

abstract:
  We investigate the effect of pair creation on a shock structure. Actually,
particles accelerated by a shock can be sufficiently energetic to boost, via
Inverse Compton process for example, surrounding soft photons above the rest
mass electron energy and thus to trigger the pair creation process. The
increase of the associated pair pressure is thus able to disrupt the plasma
flow and possibly, for too high pressure, to smooth it completely. Reversely,
significant changes of the flow velocity profile may modify the distribution
function of the accelerated particles in such a way that the number of
particles enable to trigger the pair creation process may change, modifying
consequently the pair creation rate. We propose here, using simplifying
assumptions, to study the global behavior of a shock structure in an
environment dominated by pairs.


title: Slow-roll inflation and CMB anisotropy data

abstract:
  We emphasize that the estimation of cosmological parameters from cosmic
microwave background (CMB) anisotropy data, such as the recent high resolution
maps from BOOMERanG and MAXIMA-1, requires assumptions about the primordial
spectra. The latter are predicted from inflation. The physically best-motivated
scenario is that of slow-roll inflation. However, very often, the unphysical
power-law inflation scenario is (implicitly) assumed in the CMB data analysis.
We show that the predicted multipole moments differ significantly in both
cases. We identify several misconceptions present in the literature (and in the
way inflationary relations are often combined in popular numerical codes). For
example, we do not believe that, generically, inflation predicts the relation
n_S - 1 = n_T for the spectral indices of scalar and tensor perturbations or
that gravitational waves are negligible. We calculate the CMB multipole moments
for various values of the slow-roll parameters and demonstrate that an
important part of the space of parameters (n_S, n_T) has been overlooked in the
CMB data analysis so far.


title: Dark Matter and Cold Fractal Clouds

abstract:
  There is strong evidence for a large fraction of dark matter in the Universe.
Some of the evidence and candidates for dark matter are reviewed. Dark matter
in spiral galaxies may be in the form of cold dense clouds of molecular
hydrogen. This model is presented in more detail and perspectives for detecting
the cold H_2 are discussed.


title: X-ray colour maps of the cores of galaxy clusters

abstract:
  We present an analysis of X-ray colour maps of the cores of clusters of
galaxies, formed from the ratios of counts in different X-ray bands. Our
technique groups pixels lying between contours in an adaptively-smoothed image
of a cluster. We select the contour levels to minimize the uncertainties in the
colour ratios, whilst preserving the structure of the object. We investigate
the spatial distributions of cooling gas and absorbing material for a sample of
33 X-ray bright clusters, many containing strong cooling flows, in archival
ROSAT PSPC data. We present colour maps of a sample of the clusters, in
addition to adaptively-smoothed images in different bands. Most of the cooling
flow clusters display little substructure, unlike several of the
non-cooling-flow clusters.
  We fitted an isothermal plasma model with galactic absorption and constant
metallicity to the mid-over-high energy colours in our clusters. Those clusters
with known strong cooling flows have inner contours which fit a significantly
lower temperature than the outer contours. Clusters in the sample without
strong cooling flows show no significant temperature variation. We also had to
increase the levels of absorbing material to fit the low-over-high colours at
the cluster centres. Our results provide more evidence that cooling flows
accumulate absorbing material. No evidence for increased absorption was found
for the non-cooling-flow clusters. [abridged]