title:
Binary black holes and tori in AGN II. Can stellar winds constitute a
  dusty torus?

abstract:
  We determine the properties of the stellar torus that we showed in a previous
paper to result as a product of two merging black holes. If the surrounding
stellar cluster is as massive as the binary black hole, the torque acting on
the stars ejects a fraction which extracts all the binary's angular momentum on
scales of ~10^7 yr, and a geometrically thick torus remains. In the present
article we show that a certain fraction of the stars has winds, shaped into
elongated tails by the central radiation pressure, which are optically thick
for line of sights aligned with them. These stars are sufficiently numerous to
achieve a covering factor of 1, so that the complete torus is optically thick.
We find the parameters of such a patchy torus to be in the right range to
explain the observed large column densities in AGN and their temporal
variations on time scales of about a decade. Within this model the BAL quasars
can be interpreted as quasars seen at intermediate inclination angles, with the
line of sight grazing the edge of the torus. The opening angle of the torus is
wider for major mergers and thus correlates with the central luminosity. In
this picture the spin of the merged black hole is possibly dominated by the
orbital angular momentum of the binary. Thus the spin of the merged black hole
points into a new direction, and consequently the jet experiences a spin-flip
according to the spin-paradigm. This re-orientation could be an explanation for
the X-shaped radio galaxies, and the advancing of a new jet through the ambient
medium for Compact Symmetric Objects.


title:
Are the Narrow Line Regions in Active Galaxies Dusty and Radiation
  Pressure Dominated?

abstract:
  The remarkable similarity between emission spectra of narrow line regions
(NLR) in Seyfert Galaxies has long presented a mystery. In photoionization
models, this similarity implies that the ionization parameter is nearly always
the same, about U ~ 0.01. Here we present dusty, radiation-pressure dominated
photoionization models that can provide natural physical insight into this
problem. In these models, dust and the radiation pressure acting on it provide
the controlling factor in moderating the density, excitation and surface
brightness of photoionized NLR structures. Additionally, photoelectric heating
by the dust is important in determining the temperature structure of the
models. These models can also explain the coexistence of the low-,
intermediate- and coronal ionization zones within a single self-consistent
physical structure. The radiation pressure acting on dust may also be capable
of driving the fast (~3000 km/s) outflows such as are seen in the HST
observations of NGC 1068.


title: Are high-redshift DLA galxies Lyman-break galaxies?

abstract:
  We use deep HST STIS and NICMOS images of three spectroscopically confirmed
galaxy counterparts of high-redshift damped Ly-alpha (DLA) absorbers (one of
which is a new discovery) to test the hypothesis that high-redshift DLA
galaxies are Lyman-break galaxies. If this hypothesis is correct the emission
properties of DLA galaxies must lie within the range of emission properties
measured for Lyman-break galaxies of similar absolute magnitude. This will be
true regardless of selection biases in the sample of detected DLA galaxies. We
test this prediction using several emission properties: half-light radius,
radial profile (Sersic n parameter), optical-to-near-infrared colour,
morphology, Ly alpha emission equivalent width, and Ly alpha emission velocity
structure. In all cases the measured values for the DLA galaxies lie within the
range measured for the population of Lyman-break galaxies. None of the
measurements is in conflict with the prediction. We conclude that the measured
emission properties of the three DLA galaxies studied here are consistent with
the conjecture that high-redshift DLA galaxies are Lyman-break galaxies. We
show that this result does not conflict with the observation that the few
high-redshift DLA galaxies discovered are mostly fainter than spectroscopically
confirmed L* Lyman-break galaxies.


title: Adaptive Optics imaging of Quasar Hosts

abstract:
  We present the results of adaptive-optics imaging of 12 (z < 0.6) quasars in
the H and K bands using the PUEO system mounted on the Canada-France-Hawaii
telescope. The QSOs (m_V > 15.0) themselves are used as reference for the
correction. The images, obtained under poor seeing conditions, have typical
spatial resolution of FWHM ~ 0.3arcsec before deconvolution. The deconvolved
H-band image of PG 1700+514 has a spatial resolution of 0.16arcsec and reveals
a wealth of details on the companion and the host-galaxy. The comparison
between the HST and CFHT images of PG 1700+514 shows how powerful and
competitive ground-based AO can be. Close companions and obvious signs of
interactions are found in 4 out of the 12 objects. The 2D images of 3 of the
host-galaxies unambiguously reveal bars and spiral arms. The morphology of the
other host-galaxies are difficult to determine from 1D surface brightness
profiles and deeper images are needed that could be obtained with AO systems on
10m class telescopes. Analysis of mocked data shows that elliptical galaxies
are always recognized as such, whereas disk hosts can be missed for small disk
scale lengths and large QSO contributions.


title: Enhancement of alpha-Elements in Dynamical Models of Elliptical Galaxies

abstract:
  In this paper we present a quantitative analysis of the chemical abundances
in "monolithic" N-body-Tree-SPH models of elliptical galaxies to determine
whether the ratio [alpha/Fe] increases with the galaxy mass as suggested by
observational data.


title: The Rees-Sciama effect and the primordial nucleosynthesis

abstract:
  It is known that, theoretically, the Rees-Sciama effect may cause arbitrarily
large additional redshifts in the cosmic microwave background radiation due to
transparent expanding voids having sizes comparable with the size of horizon.
Therefore, again theoretically, eventual huge voids existing immediately after
the recombination may essentially change the predictions of the theory of big
bang nucleosynthesis. If this eventuality holds, then the dark matter can be
dominantly baryonic and, simultaneously, one can be in accordance with the
predictions of primordial nucleosynthesis theory. Studying this eventuality one
arrives at the result that the observed extreme isotropy of the cosmic
microwave background radiation rejects the existence of any such huge voids,
and hence this eventuality does not hold.


title: Spatial features of non-thermal SZ effect in galaxy clusters

abstract:
  We investigate the spatial behaviour of the total comptonization parameter
$y_{tot}$ evaluated for a galaxy cluster containing two population of
electrons: the thermal population, with energy around some KeV and whose trace
is evident in the X-ray emission of the ICM (Intra-Cluster Medium), and the
relativistic population, which give rise to the radio halo emission found in
several clusters of galaxies. We present the first results obtained from our
analysis showing that there are remarkable features in such spatial trend,
which might throw a new light in understanding the cluster internal processes.


title:
V2540 Oph (Nova Oph 2002): Large-Amplitude Slow Nova with Strong
  Post-Outburst Oscillations

abstract:
  V2540 Oph (Nova Oph 2002) is a classical nova discovered by Katsumi Haseda
and Yuji Nakamura on 2002 January 24. The light curve of this nova shows strong
post-outburst oscillations as were observed in V1178 Sco and V4361 Sgr.
Accurate astrometry of the nova yeilded an upper limit of 21 mag for the nova
precursor. In combination with the observed decline rate, We propose that the
nova should have either a short orbital period or a high inclination. We
suggest that V2540 Oph may be analogous to V2214 Oph, a presumed magnetic nova
inside the period gap.


title: Near-IR spectroscopy of planetary nebulae precursors

abstract:
  We present near-IR spectroscopy of a sample of 30 IRAS sources recently
identified as late AGB stars, post-AGB stars or early
  PNe. The spectra obtained are centered at various wavelengths covering the
molecular hydrogen v=1-0 S(1) and v=2-1 S(1) emission lines, the recombination
lines of hydrogen Br-gamma, Pf-gamma and Br-alpha, and the CO[v=2-0] first
overtone bandhead at 2.294 microns. As a result of these observations we have
increased from 4 to 13 the total number of proto-PNe detected in molecular
hydrogen. When the molecular hydrogen is fluorescence-excited the detection
rate is found to be directly correlated with the evolutionary stage of the
central star, rather than with the nebular morphology. In contrast,
shocked-excited molecular hydrogen is detected only in strongly bipolar
proto-PNe, sometimes even at an early stage in the post-AGB phase. The strong
correlation of shocked-excited molecular hydrogen emission with bipolarity
found confirms the result previously reported by Kastner et al. (1996) in
evolved PNe. However, our results show that this correlation does not exist in
the case of fluorescence-excited molecular hydrogen.


title: Bar-Halo Interaction and Bar Growth

abstract:
  I show that strong bars can grow in galactic discs, even when the latter are
immersed in haloes whose mass within the disc radius is comparable to, or
larger than, the mass of the disc. I argue that this is due to the response of
the halo and in particular to the destabilising influence of the halo resonant
stars. Via this instability mechanism the halo can stimulate, rather than
restrain, the growth of the bar.


title: Models of Type Ia Supernova Explosions

abstract:
  Type Ia supernovae have become an indispensable tool for studying the
expansion history of the universe, yet our understanding of the explosion
mechanism is still incomplete. We describe the variety of discussed scenarios,
sketch the most relevant physics, and report recent advances in
multidimensional simulations of Chandrasekhar mass white dwarf explosions.


title: The Kozai Mechanism and the Evolution of Binary Supermassive Black Holes

abstract:
  We consider the dynamical evolution of bound, hierarchical triples of
supermassive black holes that might be formed in the nuclei of galaxies
undergoing sequential mergers. The tidal force of the outer black hole on the
inner binary produces eccentricity oscillations through the Kozai mechanism,
and this can substantially reduce the gravitational wave merger time of the
inner binary. We numerically calculate the merger time for a wide range of
initial conditions and black hole mass ratios, including the effects of
octupole interactions in the triple as well as general relativistic periastron
precession in the inner binary. The semimajor axes and the mutual inclination
of the inner and outer binaries are the most important factors affecting the
merger time. We find that for a random distribution of inclination angles and
approximately equal mass black holes, it is possible to reduce the merger time
of a near circular inner binary by more than a factor of ten in over fifty
percent of all cases. We estimate that a typical exterior quadrupole moment
from surrounding matter in the galaxy may also be sufficient to excite
eccentricity oscillations in supermassive black hole binaries, and also
accelerate black hole mergers.


title: Multifractal fits to the observed main belt asteroid distribution

abstract:
  Dohnanyi's (1969) theory predicts that a collisional system such as the
asteroidal population of the main belt should rapidly relax to a power-law
stationary size distribution of the kind $N(m)\propto m^{-\alpha}$, with
$\alpha$ very close to 11/6, provided all the collisional response parameters
are independent on size. The actual asteroid belt distribution at observable
sizes, instead, does not exhibit such a simple fractal size distribution.
  We investigate in this work the possibility that the corresponding cumulative
distribution may be instead fairly fitted by multifractal distributions. This
multifractal behavior, in contrast with the Dohnany fractal distribution, is
related to the release of his hypothesis of self-similarity.


title:
Absorbers and Globular Cluster Formation in Powerful High Redshift Radio
  Galaxies

abstract:
  A radiative hydrodynamic simulation for a typical, powerful high redshift
radio galaxy is presented. The jet is injected at one third the speed of light
into a 10000 times denser, homogeneous medium. In the beginning of the
simulation, the bow shock consists of a spherical shell that is similar to a
spherical blast wave. This shell cools radiatively down to approximately 10,000
K, providing after 6 Mio yrs a neutral column of 3.8 x 10^21 cm^-2 around the
whole system. The shell starts to fragment and forms condensations. This
absorbing screen will cover a smaller and smaller fraction of the radio source,
and therefore the emission line region, and eventually form stars in typically
10,000 globular clusters of one million solar masses. Approximately 10^9 solar
masses are entrained into the radio cocoon. This gas, cooling and illuminated
from the radio source, could be the emission line gas observed in high
redshifted radio galaxies and radio loud quasars. The neutral column behind the
bow shock can account for the absorption found in almost all of the small
sources. The globular cluster excess of approximately 10^4 systems found in
present day brightest cluster galaxies (BCGs), which are believed to be the
vestiges of these objects, is consistent with the presented scenario.


title: Correlations at large scale

abstract:
  We show point processes generated in different ways and having different
structure, presenting very similar power-law two--point correlation functions
at small scales and quite different shapes at large scales.


title: A Chandra observation of the X-ray environment and jet of 3C31

abstract:
  We have used a deep Chandra observation of the central regions of the
twin-jet FRI radio galaxy 3C31 to resolve the thermal X-ray emission in the
central few kiloparsecs of the host galaxy, NGC 383, where the jets are thought
to be decelerating rapidly. This allows us to make high-precision measurements
of the density, temperature and pressure distributions in this region, and to
show that the X-ray emitting gas in the centre of the galaxy has a cooling time
of only 5 times 10^7 years. In a companion paper these measurements are used to
place constraints on models of the jet dynamics.
  A previously unknown one-sided X-ray jet in 3C31, extending up to 8 arcsec
from the nucleus, is detected and resolved. Its structure and steep X-ray
spectrum are similar to those of X-ray jets known in other FRI sources, and we
attribute the radiation to synchrotron emission from a high-energy population
of electrons. In situ particle acceleration is required in the region of the
jet where bulk deceleration is taking place.
  We also present X-ray spectra and luminosities of the galaxies in the Arp 331
chain of which NGC 383 is a member. The spectrum and spatial properties of the
nearby bright X-ray source 1E 0104+3153 are used to argue that the soft X-ray
emission is mostly due to a foreground group of galaxies rather than to the
background broad absorption-line quasar.


title: The Pattern Speed of the OH/IR Stars in the Milky Way

abstract:
  We show how the continuity equation can be used to determine pattern speeds
in the Milky Way Galaxy (MWG). This method, first discussed by Tremaine &
Weinberg in the context of external galaxies, requires projected positions,
$(l,b)$, and line-of-sight velocities for a spatially complete sample of
relaxed tracers. If the local standard of rest (LSR) has a zero velocity in the
radial direction ($u_{\rm LSR}$), then the quantity that is measured is $\Delta
V \equiv \Omega_p R_0 - V_{\rm LSR}$, where $\Omega_p$ is the pattern speed of
the non-axisymmetric feature, $R_0$ is the distance of the Sun from the
Galactic centre and $V_{\rm LSR}$ is the tangential motion of the LSR,
including the circular velocity. We use simple models to assess the reliability
of the method for measuring a single, constant pattern speed of either a bar or
spiral in the inner MWG. We then apply the method to the OH/IR stars in the
ATCA/VLA OH 1612 MHz survey of Sevenster et al, finding $\Delta V = 252 \pm 41$
km/s, if $u_{\rm LSR} = 0$. Assuming further that $R_0 = 8$ kpc and $V_{\rm
LSR} = 220$ \kms, this gives $\Omega_p = 59\pm 5$ km/s/kpc with a possible
systematic error of perhaps 10 km/s/kpc. The non-axisymmetric feature for which
we measure this pattern speed must be in the disc of the MWG.


title:
A morphological comparison between the central region in AGN and normal
  galaxies using HST data

abstract:
  We study the morphology of the central region of a sample of Active Galactic
Nuclei (AGN) and a ``control'' sample of normal galaxies using archival
observations of the WFPC2 instrument onboard the Hubble Space Telescope (HST).
We use the ellipse fitting technique in order to get a good description of the
inner ``smooth'' light distribution of the galaxy. We then divide the observed
galaxy image by the artificial image from the fitted ellipses in order to
detect morphological signatures in the central region around the nucleus of the
galaxy. We perform quantitative comparisons of different subgroups of our
sample of galaxies (according to the Hubble type and the nuclear activity of
the galaxies) by calculating the average amplitude of the structures that are
revealed with the ellipse fitting technique. Our main conclusions are as
follows: 1) All AGNs show significant structure in their inner 100 pc and 1 kpc
regions whose amplitude is similar in all of them, independent of the Hubble
type of the host galaxy. 2) When considering early-type galaxies, non-AGN
galaxies show no structure at all, contrary to what we find for AGN. 3) When
considering late-type galaxies, both AGN and non-AGN galaxies show significant
structure in their central region. Our results are consistent with the
hypothesis that all early-type galaxies host a supermassive black hole, but
only those that have enough material in the central regions to fuel it show an
active nucleus. The situation is more complicated in late-type galaxies. Either
not all of them host a central black hole, or, in some of them, the material
inside the innermost 100 pc region is not transported to the scales of the
central engine for some reason, or the large amount of gas and dust hides the
active nucleus from our sight.


title: Introductory review to the historical development of modern cosmology

abstract:
  This talk introduces the contributions of the lecturers to the international
summer school ``Historical Development of Modern Cosmology'' held at the
Universidad Internacional Men\'endez Pelayo, Valencia, Spain, during September
18-22 2000.


title: Four New Delta Scuti Pulsators from a Variability Survey of 131 Stars

abstract:
  In a photometric variability survey of 131 stars with B < 14 mag, we have
found four new Delta Scuti stars. We were sensitive to oscillation amplitudes
as low as a few mmag. The detection rate of short-period (P < 0.1 d) pulsating
variable stars, which may be relevant for planned large variability surveys
such as GAIA, POI, and even the LSST, was therefore 3%. All four new variable
stars have low pulsation amplitude (tens of mmag), and one has a very short
period (0.0198 d). This star is one of the fastest known Delta Scuti pulsators.
The short period of this variable star makes it observationally tractable, and
it may therefore be a particularly good candidate for asteroseismological
studies. All four new variable stars will add to the cadre of low-amplitude and
relatively short-period Delta Scuti stars that are potentially useful for
learning about the structure of stars on or near the main sequence, slightly
more massive than the Sun.


title: Broadband Spectra and Variability of BL Lacertae in 2000

abstract:
  We have organized an extensive multiwavelength campaign on BL Lacertae in the
second half of 2000. Simultaneous or quasi-simultaneous observations were taken
at radio frequencies, in the optical - carried out by the WEBT collaboration -,
in X-rays - using BeppoSAX and RXTE -, and at VHE gamma-rays with the CAT and
HEGRA Cherenkov telescope facilities. In this paper, we are presenting first
results from this campaign. The WEBT optical campaign achieved an unprecedented
time coverage, virtually continuous over several 10 - 20 hour segments, and
revealed intraday variability on time scales of ~ 1.5 hours. The X-ray
observations of Nov. 1 - 2, 2000, revealed significant variability on similar
time scales, and provided evidence for the synchrotron spectrum extending out
to ~ 10 keV during that time. At higher energies, the onset of the hard
power-law commonly observed in radio-loud quasars and radio-selected BL Lac
objects is seen. From the energy-resolved X-ray variability patterns, we find
evidence that electron cooling might not be dominated by one single radiation
mechanism; rather, a combination of synchrotron and Compton cooling seems to be
required.


title: A Pattern Speed in the Galaxy's OH/IR Stars

abstract:
  We use the Tremaine-Weinberg method, adapted to the Milky Way, to measure a
pattern speed in OH/IR stars located in the inner MW.


title: Bar Dynamical Friction and Disk Galaxy Dark Matter Content

abstract:
  I present some new results, from simulations and observations, of the
constraints bar pattern speeds place on the dark matter content of disk
galaxies.


title: On rotationally driven meridional flows in stars

abstract:
  A quasi-steady state model of the consequences of rotation on the
hydrodynamical structure of a stellar radiative zone is derived, by studying in
particular the role of centrifugal and baroclinic driving of meridional motions
in angular-momentum transport. This nonlinear problem is solved numerically
assuming axisymmetry of the system, and within some limits, it is shown that
there exist simple analytical solutions. The limit of slow rotation recovers
  Eddington-Sweet theory, whereas it is shown that in the limit of rapid
rotation, the system settles into a geostrophic equilibrium. The behaviour of
the system is found to be controlled by one parameter only, linked to the
Prantl number, the stratification and the rotation rate of the star.


title: A late-time transition in the cosmic dark energy?

abstract:
  We study constraints from the latest CMB, large scale structure (2dF,
Abell/ACO, PSCz) and SN1a data on dark energy models with a sharp transition in
their equation of state, w(z). Such a transition is motivated by models like
vacuum metamorphosis where non-perturbative quantum effects are important at
late times. We allow the transition to occur at a specific redshift, z_t, to a
final negative pressure -1 < w_f < -1/3. We find that the CMB and supernovae
data, in particular, prefer a late-time transition due to the associated delay
in cosmic acceleration. The best fits (with 1 sigma errors) to all the data are
z_t = 2.0^{+2.2}_{-0.76}, \Omega_Q = 0.73^{+0.02}_{-0.04} and w_f = -1^{+0.2}.


title:
The Early Angular Momentum History of Low Mass Stars: Evidence for a
  Regulation Mechanism

abstract:
  We examine the early angular momentum history of stars in young clusters via
197 photometric periods in fields flanking the Orion Nebula Cluster (ONC), 81
photometric periods in NGC 2264, and 202 measurements of v sin i in the ONC
itself. We show that PMS stars spanning an age range from 0.1 to 3 Myr do not
appear to conserve stellar angular momentum as they evolve down their
convective tracks, but instead preserve the same range of periods even though
they have contracted by about a factor of three. This result seems to require a
mechanism that regulates the angular velocities of young stars. We discuss
several candidate mechanisms. The most plausible appears to be disk-locking,
though most of our stars do not have (I-K) excesses suggestive of disks.
However, a decisive test of this hypothesis requires a more sensitive
diagnostic than the (I-K) excesses used here.


title:
Detection of the velocity dipole in the radio galaxies of the NRAO VLA
  Sky Survey

abstract:
  We are in motion against the cosmic backdrop. This motion is evidenced by the
systematic temperature shift - or dipole anisotropy - observed in the Cosmic
Microwave Background radiation (CMB). Because of the Doppler effect, the
temperature of the CMB is 0.1 per cent higher in our direction of motion
through the Universe. If our standard cosmological understanding is correct,
this dipole should also be present as an enhancement in the surface density of
distant galaxies. The main obstacle in finding this signal is the very uneven
distribution of nearby galaxies in the Local Supercluster, which drowns out the
small cosmological imprint. Here we report the first detection of the expected
dipole anisotropy in the galaxy distribution, in a survey of galaxies detected
in radio waves. Radio galaxies are mostly located at cosmological distances, so
the contamination from nearby clusters should be small. With local radio
sources removed, we find a dipole anisotropy in the radio galaxy distribution
in the same direction as the CMB, close to the expected amplitude. This result
is confirmation of the standard cosmological interpretation of the CMB.


title:
Multicomponent radiatively driven stellar winds III. Radiative-acoustic
  waves in a two-component wind

abstract:
  We study stability of isothermal two-component radiatively driven stellar
winds against one-dimensional perturbations larger than the Sobolev length, and
radiative-acoustic waves in such stellar winds. We perform linear perturbation
analysis in comoving fluid-frames of individual components and obtain
dispersion relation in the common fluid-frame. For high density winds the
velocity difference between velocities of both components is relatively small
and the wind is stable for radiative-acoustic waves discovered originally by
Abbott, in accordance with the previous studies of the one-component wind.
However, for such high density winds we found new types of waves including a
special case of "frozen-in" wavy patterns. On the other hand, if the velocity
difference between wind components is sufficiently large (for low density
winds) then the multicomponent stellar wind is unstable even for large scale
perturbations and ion runaway occurs. Thus, isothermal two-component stationary
solutions of the radiatively line driven stellar wind with an abrupt lowering
of the velocity gradient are unstable.


title:
PSR J1740-5340: accretion inhibited by radio-ejection in a binary
  millisecond pulsar in the Globular Cluster NGC 6397

abstract:
  We present an evolutionary scenario for the spin-up and evolution of binary
millisecond pulsars, according to which the companion of the pulsar PSR J
1740-5340, recently discovered as a binary with orbital period of 32.5 hr in
the Globular Cluster NGC 6397, is presently in a phase of ``radio-ejection''
mass loss from the system. At present, Roche lobe overflow due to the nuclear
evolution of the pulsar companion and to systemic angular momentum losses by
magnetic braking is still going on, but accretion is inhibited by the momentum
exerted by the radiation of the pulsar on the matter at the inner Lagrangian
point. The presence of this matter around the system is consistent with the
long lasting irregular radio eclipses seen in the system. Roche lobe
deformation of the mass losing component is also necessary to be compatible
with the optical light curve. The "radio-ejection" phase had been recently
postulated by us to deal with the problem of the lack of submillisecond pulsars
(Burderi et al. 2001, ApJ, 560, L71).


title:
Spectral mapping of the spiral structures in IP Pegasi on the decline
  from an outburst

abstract:
  (abridged) We report eclipse mapping of time resolved spectroscopy of the
dwarf nova IP Pegasi on the late decline from the May 1993 outburst. The spiral
arms are still visible some 8 days after the onset of the outburst. Their
fractional contribution to the continuum emission is similar to that measured
close to outburst maximum, whereas their orientation is rotated by 58 degrees
with respect to the spirals seen in the eclipse map at outburst maximum.
Velocity-resolved light curves across the Halpha and the HeI lines show the
classical rotational disturbance, with the blue side of the line being eclipsed
earlier than the red side. The differences between the Halpha and the HeI maps
are significant. The spiral arms are clearly seen in the HeI maps, with the
receding arm being stronger in the red side while the approaching arm is
stronger in the blue side of the line. The analysis of the Halpha maps suggests
that this emission arises mainly from a large and vertically-extended region
which we interpret as an outflowing (and spiraling) disc wind. The spectrum of
the uneclipsed light is dominated by a strong, blueshifted and narrow Halpha
emission line superimposed on a red continuum and can be understood as a
combination of emission from an M5V secondary star plus optically thin emission
from the outer parts of the vertically-extended disc wind. The inner disc
regions show an emission line spectrum with a strong and broad Halpha component
superimposed on a flat continuum. This is in marked contrast with the results
from the spectral mapping of nova-like variables of comparable inclination and
mass ratio and suggests that intrinsically different physical conditions hold
in the inner disc regions of outbursting dwarf novae and nova-like systems.


title:
Metallicity and Kinematics of M31's Outer Stellar Halo from a Keck
  Spectrocscopic Survey

abstract:
  We present multislit CaII near-infrared triplet spectroscopy with the Keck
10-m telescope/LRIS of 99 M31 halo red giant candidates in the apparent mag
range 20<I<22 in a SE minor axis field at R=19kpc. The spectra are used to
isolate M31 halo red giants from foreground Milky Way dwarf stars, background
compact field galaxies and M31 disk giants. The observed radial velocity
distribution shows an equal mix of M31 halo giants, fit by a Gaussian of width
150km/s centered on -300km/s (M31 systemic velocity), and foreground Galactic
dwarfs with v<~0km/s. A secure sample of 29 M31 red giant stars is identified
on the basis of radial velocity (and, in 4 cases, B-I color). For this sample,
there is rough agreement between photometric and spectroscopic [Fe/H]
estimates. The [Fe/H] distribution of M31 halo giants has an rms >0.6 dex,
spans the full 2dex range over which [Fe/H] measurement methods are calibrated,
and has a mean/median value around <[Fe/H]>=-1.9 to -1.1dex and possibly higher
since the high-[Fe/H] end of the distribution is not well constrained by our
sample. Our data on M31 field halo giants suggest that they are more metal-rich
than their Milky Way counterparts, similar to M31 and Milky Way globular
clusters, consistent with a scenario in which the halo is built from accretion
of small stellar subsystems. There are 4 stars in the secure M31 sample with
unusually strong Ca lines (>~solar [Fe/H]) at a common velocity of -340km/s
close to M31's systemic velocity, similar to what might be expected for M31
disk giants on the minor axis. The M31 disk would have to be large and/or
warped to account for these stars. More likely, these stars are metal-rich
debris from a past accretion event in M31's halo.


title: Dark Halo Shapes and the Fate of Stellar Bars

abstract:
  We investigate the stability of trajectories in barred galaxies with mildly
triaxial halos by means of Liapunov exponents. This method is perfectly
suitable for time-dependent 3D potentials where surfaces of sections and other
simple diagnostics are not applicable. We find that when halos are
centrally-concentrated most trajectories starting near the plane containing the
bar become chaotic. Moreover, the shape of many of the remaining regular
trajectories do not match the bar density distribution, being too round.
Therefore, time-independent self-consistent solutions are highly unlikely to be
found. When the non-rotating non-axisymmetric perturbation in the potential
reaches 10%, almost all trajectories integrated are chaotic and have large
Liapunov exponents. No regular trajectories aligned with the bar have been
found. Hence, if the evolution of the density figure is directly related to the
characteristic timescale of orbital instability, bar dissolution would take
place on a timescale of few dynamical times. The slowly rotating
non-axisymmetric contribution to the potential required for the onset of
widespread chaotic behavior is remarkably small. Systems consisting of
centrally-concentrated axisymmetric halos and stellar bars thus appear to be
structurally unstable, and small (1%) deviations from perfect axisymmetry
should result in a bar dissolution on a timescale significantly smaller than
the Hubble time. Since halos found in CDM simulations of large scale structure
are both centrally-concentrated and triaxial it is unlikely that stellar bars
embedded in such halos would form and survive unless the halos are modified
during the formation of the baryonic component.


title: Detection of a supernova signature associated with GRB 011121

abstract:
  Using observations from an extensive monitoring campaign with the Hubble
Space Telescope we present the detection of an intermediate-time flux excess
which is redder in color relative to the afterglow of GRB 011121, currently
distinguished as the gamma-ray burst with the lowest known redshift. The red
``bump,'' which exhibits a spectral roll-over at ~7200 Angstrom, is well
described by a redshifted Type Ic supernova that occurred approximately at the
same time as the gamma-ray burst event. The inferred luminosity is about half
that of the bright supernova 1998bw. These results serve as compelling evidence
for a massive star origin of long-duration gamma-ray bursts. Models that posit
a supernova explosion weeks to months preceding the gamma-ray burst event are
excluded by these observations. Finally, we discuss the relationship between
spherical core-collapse supernovae and gamma-ray bursts.


title:
SPICES II. Optical and Near-Infrared Identifications of Faint X-Ray
  Sources from Deep Chandra Observations of Lynx

abstract:
  We present our first results on field X-ray sources detected in a deep, 184.7
ks observation with the ACIS-I camera on Chandra. The observations target the
Lynx field of SPICES, and contains three known X-ray-emitting clusters out to
z=1.27. Not including the known clusters, in the 17'x17' ACIS-I field we detect
132 sources in the 0.5-2 keV (soft) X-ray band down to a limiting flux of
\~1.7e-16 erg/cm2/s and 111 sources in the 2-10 keV (hard) X-ray band down to a
limiting flux of ~1.3e-15 erg/cm2/s. The combined catalog contains a total of
153 sources, of which 42 are detected only in the soft band and 21 are detected
only in the hard band. Confirming previous Chandra results, we find that the
fainter sources have harder X-ray spectra, providing a consistent solution to
the long-standing `spectral paradox'. From deep optical and near-infrared
follow-up data, 77% of the X-ray sources have optical counterparts to I=24 and
71% of the X-ray sources have near-infrared counterparts to K=20. Four of the
24 sources in the near-IR field are associated with extremely red objects
(EROs; I-K>4). We have obtained spectroscopic redshifts with the Keck
telescopes of 18 of the Lynx Chandra sources. These sources comprise a mix of
broad-lined active galaxies, apparently normal galaxies, and two late-type
Galactic dwarfs. Intriguingly, one Galactic source is identified with an M7
dwarf exhibiting non-transient, hard X-ray emission. We review non-AGN
mechanisms to produce X-ray emission and discuss properties of the Lynx Chandra
sample in relation to other samples of X-ray and non-X-ray sources.


title:
M75, a Globular Cluster with a Trimodal Horizontal Branch. I.
  Color-Magnitude Diagram

abstract:
  Deep UBVI photometry for a large field covering the distant globular cluster
M75 (NGC 6864) is presented. We confirm a previous suggestion (Catelan et al.
1998a) that M75 possesses a bimodal horizontal branch (HB) bearing striking
resemblance to the well-known case of NGC 1851. In addition, we detect a third,
smaller grouping of stars on the M75 blue tail, separated from the bulk of the
blue HB stars by a gap spanning about 0.5 mag in V. Such a group of stars may
correspond to the upper part of a very extended, though thinly populated, blue
tail. Thus M75 appears to have a trimodal HB. The presence of the "Grundahl
jump" is verified using the broadband U filter. We explore the color-magnitude
diagram of M75 with the purpose of deriving the cluster's fundamental
parameters, and find a metallicity of [Fe/H] = -1.03 +/- 0.17 dex and -1.24 +/-
0.21 dex in the Carretta & Gratton (1997) and Zinn & West (1984) scales,
respectively. We discuss earlier suggestions that the cluster has an
anomalously low ratio of bright red giants to HB stars. A differential age
analysis with respect to NGC 1851 suggests that the two clusters are
essentially coeval.


title: Iron abundance in HII regions

abstract:
  Optical CCD spectra are used to determine the Fe abundances at several
positions inside seven bright Galactic HII regions. The observed [FeIII] line
ratios are compared with the predictions of different sets of collision
strengths and transition probabilities for this ion to select the atomic data
providing the best fit to the observations. The values found for the Fe++ and
Fe+ abundances, along with ionization correction factors for the contribution
of Fe3+, obtained from available grids of photoionized models, imply that the
Fe/O ratio in the ionized gas is between 2% and 30% of solar. The Fe abundances
derived for each area are correlated both with the degree of ionization and the
colour excess. A possible explanation is suggested, namely the presence of a
population of small grains, probably originating from the fragmentation of
larger grains. These small grains would release Fe atoms into the gas after the
absorption of energetic photons; the small grains surviving this destruction
process would be swept out of the ionized region by the action of radiation
pressure or stellar winds. An indication of a further and more efficient
destruction agent is given by the high Fe abundance derived for a position
sampling the optical jet H399 in M20, where dust destruction due to shock waves
has presumably taken place.


title:
Physical Parameter Eclipse Mapping of the quiescent disc in V2051
  Ophiuchi

abstract:
  We analyse simultaneous UBVR quiescent light curves of the cataclysmic
variable V2051 Oph using the Physical Parameter Eclipse Mapping method in order
to map the gas temperature and surface density of the disc for the first time.
The disc appears optically thick in the central regions and gradually becomes
optically thin towards the disc edge or shows a more and more dominating
temperature inversion in the disc chromosphere. The gas temperatures in the
disc range from about 13500 K near the white dwarf to about 6000 K at the disc
edge. The intermediate part of the disc has temperatures of 9000 K to 6500 K.
  The quiescent disc (chromosphere) shows a prominent bright region with
temperatures of 10500 K around the impact region of the stream from the
secondary with an extension towards smaller azimuths. The disc has a size of
0.53 +- 0.03 R_L1 and a mass accretion rate of between dM/dt = 10^15 g/s to
10^17g/s. The light curves must include an uneclipsed component, a hot
chromosphere and/or a disc wind.
  The PPEM method allows us to determine a new distance of 146+-20pc,
compatible with previous rough estimates. For the white dwarf we then
reconstruct a temperature of 19600 K, if the lower hemisphere of the white
dwarf is occulted by the disc.
  We find that although V2051 Oph is very similar to the SU UMa type dwarf
novae HT Cas, OY Car and Z Cha, there must be a substantial difference in order
to explain its unique light curve. For further details and results see paper.


title: A High Resolution X-ray spectrum of the LINER Galaxy M81

abstract:
  We present the soft X-ray spectrum of the LINER galaxy M81 from a long
observation with the XMM-Newton RGS. As well as continuum emission from the
active nucleus, the spectrum shows emission lines from multi temperature
collisionally ionized gas. The emission lines are significantly broader than
the RGS point-source spectral resolution, and in the cross dispersion direction
the emission lines are detected adjacent to, as well as coincident with, the
active nucleus. This implies that they originate in a region of more than an
arcminute (~ 1 kpc) spatial extent. A good fit to the whole RGS spectrum can be
found using a model consisting of an absorbed power law from the active nucleus
and a 3 temperature thermal plasma. Two of the thermal plasma components have
temperatures of 0.18+-0.04 keV and 0.64+-0.04 keV, characteristic of the hot
interstellar medium produced by supernovae; the combined luminosity of these
two plasma components accounts for all the unresolved bulge X-ray emission seen
in the Chandra observation by Tennant et al (2001). The third component has a
higher temperature (~1.7 keV) and we propose X-ray binaries in the bulge of M81
as the most likely source of this emission.


title: Sources Variability With Planck LFI

abstract:
  Planck LFI (Low Frequency Instrument) will produce a complete survey of the
sky at millimeter wavelengths. Data stream analysis will provide the
possibility to reveal unexpected millimeter sources and to study their flux
evolution in time at different frequencies. We describe here the main
implications and discuss data analysis methods. Planck sensitivities typical
for this kind of detection are taken into account. We present also preliminary
results of our simulation activity.


title: ULIRGs: Origin and Evolution

abstract:
  We present our preliminary results on the study of the high luminosity ULIRGs
(log(LFIR) > 12.3) in the 1Jy sample. Deep, high resolution optical R images
with 7 arcmin x 7 arcmin field of view for 2/3 of the whole sample, show that
they are generally found in very rich environments, they seem to be late stage
merger products (long tidal tails are found in only 3 systems) and all of them
show multiple nuclei (double nuclei in 11: 2HII, 4 LINERs, 4 Sy2 and 1 Sy1).
GTC first light instruments are very well suited for addressing the question of
the energy source of ULIRGs, together with a more refined view of the proposed
evolutionary sequence.


title:
The Stellar Populations in spiral disks.III. Constraining their
  evolutionary histories

abstract:
  We study the old problem of the uniqueness of chemical evolution models by
analyzing a set of multiphase models for the galaxy NGC 4303 computed for a
variety of plausible physical input parameters.
  Our aim is to determine if the input parameters may be strongly constrained
when nebular abundances and stellar spectral indices radial distributions are
used. We run a large number of models (500) for NGC 4303 varying the input
parameters. Less than 4% of the models (19) fit the present day observational
data within a region of 95% probability. The number of models reduces to ~1%
(6) when we also ask them to reproduce the time-averaged abundances represented
by the spectral indices. Thus, by proving that only a small fraction of models
are favored in reproducing the present day radial abundance distributions and
the spectral indices data simultaneously, we show that these spectral indices
provide strong time-dependent additional constraints to the possible star
formation and chemical histories of spiral disks.


title: Constraining the evolutionary histories of spiral disks

abstract:
  We study the old problem of the uniqueness of chemical evolution models. We
showed in Molla et al. (1999) that multiphase models for three Virgo cluster
galaxies were able to reproduce the observed radial distributions of spectral
indices Mg2 and Fe52. But those models may fit the present-epoch radial
distributions with different star formation histories. The two spectral indices
are in turn affected by the well known age-metallicity degeneracy which
prevents the disentagling of age and metallicity for single stellar
populations. In this work we face both issues by analyzing a set of multiphase
models for the Virgo galaxy NGC 4303


title: Radial Gradients of abundances

abstract:
  We have computed a set of multiphase chemical evolution models in which the
radial mass distribution of each theoretical galaxy is calculated using the
Universal Rotation Curve from Persic, Salucci & Steel (1996). We obtain the
chemical evolution for galaxies of different masses and morphological types by
changing the efficiencies to form molecular clouds and stars according these
types.
  We obtain the radial distribution of diffuse and molecular gas, the star
formation rate, and abundances for 15 elements for each galaxy.


title:
A Hubble Space Telescope Lensing Survey of X-ray Luminous Galaxy
  Clusters: III. A Multiply-imaged Extremely Red Galaxy at z=1.6

abstract:
  We present near-infrared spectroscopy and Hubble Space Telescope (HST)
imaging of EROJ003707+0909.5, the brightest of three gravitationally-lensed
images of an Extremely Red Object (ERO) at z=1.6, in the field of the massive
cluster A68 (z=0.255). We exploit the superlative resolution of our HST data
and the enhanced spatial resolution and sensitivity afforded by the lens
amplification to reconstruct the source-plane properties of this ERO. Our
morphological and photometric analysis reveals that EROJ003707 is an L*
early-type disk-galaxy and we estimate that ~10 per cent of EROs with
(R-K)>=5.3 and K<=21 may have similar properties. The unique association of
passive EROs with elliptical galaxies therefore appears to be too simplistic.
We speculate on the evolution of EROJ003707: if gas continues to cool onto this
galaxy in the manner predicted by hierarchical galaxy formation models, then by
the present day, EROJ003707 could evolve into a very luminous spiral galaxy.


title:
The runaway instability of thick discs around black holes. I. The
  constant angular momentum case

abstract:
  We present results from a numerical study of the runaway instability of thick
discs around black holes. This instability is an important issue for most
models of cosmic gamma-ray bursts, where the central engine responsible for the
initial energy release is such a system consisting of a thick disc surrounding
a black hole. We have carried out a comprehensive number of time-dependent
simulations aimed at exploring the appearance of the instability. Our study has
been performed using a fully relativistic hydrodynamics code. The general
relativistic hydrodynamic equations are formulated as a hyperbolic
flux-conservative system and solved using a suitable Godunov-type scheme. We
build a series of constant angular momentum discs around a Schwarzschild black
hole. Furthermore, the self-gravity of the disc is neglected and the evolution
of the central black hole is assumed to be that of a sequence of exact
Schwarzschild black holes of varying mass. The black hole mass increase is thus
determined by the mass accretion rate across the event horizon. In agreement
with previous studies based on stationary models, we find that by allowing the
mass of the black hole to grow the disc becomes unstable. Our hydrodynamical
simulations show that for all disc-to-hole mass ratios considered (between 1
and 0.05), the runaway instability appears very fast on a dynamical timescale
of a few orbital periods, typically a few 10 ms and never exceeding 1 s for our
particular choice of the mass of the black hole ($2.5 \mathrm{M_\odot}$) and a
large range of mass fluxes ($\dot{m} \ga 10^{-3} \mathrm{M_{\odot}/s}$). The
implications of our results in the context of gamma-ray bursts are briefly
discussed.


title: Local characteristic algorithms for relativistic hydrodynamics

abstract:
  Numerical schemes for the general relativistic hydrodynamic equations are
discussed. The use of conservative algorithms based upon the characteristic
structure of those equations, developed during the last decade building on
ideas first applied in Newtonian hydrodynamics, provides a robust methodology
to obtain stable and accurate solutions even in the presence of
discontinuities. The knowledge of the wave structure of the above system is
essential in the construction of the so-called linearized Riemann solvers, a
class of numerical schemes specifically designed to solve nonlinear hyperbolic
systems of conservation laws. In the last part of the review some astrophysical
applications of such schemes, using the coupled system of the
  (characteristic) Einstein and hydrodynamic equations, are also briefly
presented.


title: Deep H I Survey of the Spiral Galaxy NGC 2403

abstract:
  High sensitivity H I observations of the nearby spiral galaxy NGC 2403
obtained with the VLA are presented and discussed. The properties of the
extended, differentially rotating H I layer with its H I holes, spiral
structure and outer warp are described. In addition, these new data reveal the
presence of a faint, extended and kinematically anomalous component. This shows
up in the H I line profiles as extended wings of emission towards the systemic
velocity. In the central regions these wings are very broad (up to 150 km/s)
and indicate large deviations from circular motion. We have separated the
anomalous gas component from the cold disk and have obtained for it a separate
velocity field and a separate rotation curve. The mass of the anomalous
component is 1/10 of the total H I mass. The rotation velocity of the anomalous
gas is 25-50 km/s lower than that of the disk. Its velocity field has
non-orthogonal major and minor axes that we interpret as due to an overall
inflow motion of 10-20 km/s towards the centre of the galaxy. The picture
emerging from these observations is that of a cold H I disk surrounded by a
thick and clumpy H I layer characterized by slower rotation and inflow motion
towards the center. The origin of this anomalous gas layer is unclear. It is
likely, however, that it is related to the high rate of star formation in the
disk of NGC 2403 and that its kinematics is the result of a galactic fountain
type of mechanism. We suggest that these anomalous H I complexes may be
analogous to a part of the High Velocity Clouds of our Galaxy.


title:
Rotational Broadening and Doppler Tomography of the Quiescent X-Ray Nova
  Centaurus X-4

abstract:
  We present high and intermediate resolution spectroscopy of the X-ray nova
Centaurus X-4 during its quiescent phase. Our analysis of the absorption
features supports a K3-K5V spectral classification for the companion star,
which contributes approximately 75 % of the total flux at Halpha. Using the
high resolution spectra we have measured the secondary star's rotational
broadening to be V_rot*sin(i) = 43 +/- 6 km/s and determined a binary mass
ratio of q=0.17 +/- 0.06. Combining our results for K_2 and q with the
published limits for the binary inclination, we constrain the mass of the
compact object and the secondary star to the ranges 0.49 < M_1 < 2.49 Msun and
0.04 < M_2 < 0.58 Msun. A Doppler image of the Halpha line shows emission
coming from the secondary star, but no hotspot is present. We discuss the
possible origins of this emission.


title: The detection and X-ray evolution of galaxy groups at high redshift

abstract:
  We describe some of the first X-ray detections of groups of galaxies at high
redshifts (z~0.4), based on the UK deep X-ray survey of McHardy et al (1998).
Combined with other deep ROSAT X-ray surveys with nearly complete optical
identifications, we investigate the X-ray evolution of these systems. We find
no evidence for evolution of the X-ray luminosity function up to z=0.5 at the
low luminosities of groups of galaxies and poor clusters (Lx>3e42 erg/s),
although the small sample size precludes very accurate measurements. This
result confirms and extends to lower luminosities current results based on
surveys at brighter X-ray fluxes. The evolution of the X-ray luminosity
function of these low luminosity systems is more sensitive to the thermal
history of the intra-group medium (IGM) than to cosmological parameters. Energy
injection into the IGM (from for example supernovae or AGN winds) is required
to explain the X-ray properties of nearby groups. The observed lack of
evolution suggests that the energy injection occured at redshifts z>0.5.


title: The Evolution of Copper in the Globular Cluster Omega Centauri

abstract:
  Copper abundances are presented for 40 red-giant stars in Omega Cen as well
as 15 red-giant members of the globular clusters NGC288, NGC362, NGC3201,
NGC6752, and M4. A comparison with the halo field star pattern indicates that,
unlike the field stars, Omega Cen displays a constant ratio of [Cu/Fe] -0.5 all
the way from [Fe/H]=-2.0 to -0.8. At the metallicity of [Fe/H]= -0.8, the
values of [Cu/Fe] in Omega Cen fall below the corresponding mean ratio in the
field stars by roughly 0.5 dex. If copper is produced primarily in type Ia
supernovae (SN Ia), the lack of an increase in [Cu/Fe] in Omega Cen would
suggest very little contribution from SN Ia to its chemical evolution within
the metallicity range from [Fe/H] of -2.0 up to -0.8.


title: Heated Cooling Flows

abstract:
  In conventional models of galactic and cluster cooling flows widespread
cooling (mass dropout) is assumed to avoid accumulation of unacceptably large
central masses. However, recent XMM observations have failed to find spectral
evidence for locally cooling gas. This has revived the notion that cooling
flows are heated by some process such as an intermittent, low-level AGN
involving supermassive black holes in the central galaxy. To explore this
hypothesis, we consider the gasdynamical consequences of galactic cooling flows
heated by many different scenarios without specifying the detailed physics of
the heating process. We are unable to find a single acceptable heated flow in
reasonable agreement with well observed hot gas temperature and density
profiles, even using finely tuned parameters. Idealized flows in which
radiative cooling is perfectly balanced by global heating are grossly
incompatible with observations. Flows heated by episodic central feedback
generate quasi-cyclic changes in the hot gas density profile which are not
supported by current observations. Paradoxically, centrally heated (or
pressurized) cooling flows experience spontaneous non-linear compressions that
result in spatially widespread cooling instabilities. Therefore, spectral
evidence for cooling gas is difficult to avoid by central heating.


title: Palomar 13: An Unusual Stellar System in the Galactic Halo

abstract:
  We have measured Keck/HIRES radial velocities for 30 candidate red giants in
the direction of Palomar 13: an object traditionally cataloged as a compact,
low-luminosity globular cluster. From a sample of 21 confirmed members, we find
a systemic velocity of 24.1 km/s and a projected, intrinsic velocity dispersion
of 2.2 km/s. Although small, this dispersion is several times larger than that
expected for a globular cluster of this luminosity and central concentration.
Taken at face value, this dispersion implies a mass-to-light ratio of ~ 40 (in
solar units) based on the best-fit King-Michie model. The surface density
profile of Palomar 13 also appears to be anomalous among Galactic globular
clusters -- depending upon the details of background subtraction and
model-fitting, Palomar 13 either contains a substantial population of
"extra-tidal" stars, or it is far more spatially extended than previously
suspected. The full surface density profile is equally well-fit by a
King-Michie model having a high concentration and large tidal radius, or by a
NFW model. We examine -- and tentatively reject -- a number of possible
explanations for the observed characteristics of Palomar 13 (e.g., velocity
"jitter" among the red giants, spectroscopic binary stars, non-standard mass
functions, modified Newtonian dynamics), and conclude that the two most
plausible scenarios are either catastrophic heating during a recent
perigalacticon passage, or the presence of a massive dark halo. Thus, the
available evidence suggests that Palomar 13 is either a globular cluster which
is now in the process of dissolving into the Galactic halo, or a faint,
dark-matter-dominated stellar system (ABRIDGED).


title: High-resolution spectroscopy of QY Sge -- An obscured RV Tauri variable?

abstract:
  The first high-resolution optical spectra of QY Sge are presented and
discussed. Menzies & Whitelock (1988) on the basis of photometry and
low-resolution spectra suggested that this G0I supergiant was obscured by dust
and seen only by scattered light from a circumstellar reflection nebula. The
new spectra confirm and extend this picture. Photospheric lines are unusually
broad indicating scattering of photons from dust in the stellar wind. Presence
of very broad Na D emission lines is confirmed. Sharp emission lines from low
levels of abundant neutral metal atoms are reported for the first time. An
abundance analysis of photospheric lines shows that the stellar atmosphere is
of approximately solar composition but with highly condensible (e.g., Sc and
Ti) elements depleted by factors of 5 to 10.


title:
Effects of lower boundary conditions on the stability of radiative
  shocks

abstract:
  Thermal instabilities can cause a radiative shock to oscillate, thereby
modulating the emission from the post-shock region. The mode frequencies are
approximately quantised in analogy to those of a vibrating pipe. The stability
properties depend on the cooling processes, the electron-ion energy exchange
and the boundary conditions. This paper considers the effects of the lower
boundary condition on the post-shock flow, both ideally and for some specific
physical models. Specific cases include constant perturbed velocity, pressure,
density, flow rate, or temperature at the lower boundary, and the situation
with nonzero stationary flow velocity at the lower boundary. It is found that
for cases with zero terminal stationary velocity, the stability properties are
insensitive to the perturbed hydrodynamic variables at the lower boundary. The
luminosity responses are generally dependent on the lower boundary condition.


title: Rapid Calculation of Theoretical CMB Angular Power Spectra

abstract:
  We have developed a fast method for predicting the angular power spectrum,
C_l, of the cosmic microwave background given cosmological parameters and a
primordial power spectrum of perturbations. After pre--computing the radiation
temperature and gravitational potential transfer functions over a small
sub--space of the total model parameter space, the rest of the model space (six
or more cosmological parameters and arbitrarily many primordial power spectrum
parameters) is reached via rapid analytic and semi--analytic approximations
which are highly accurate on all angular scales for which linear perturbation
theory applies. A single power spectrum can be calculated in ~ 1 second on a
desktop computer. We discuss applications to cosmological parameter estimation.


title: Complex shock structure in the western hot-spot of Pictor A

abstract:
  We have carried out simulations of supersonic light jets in order to model
the features observed in optical and radio images of the western hot-spot in
the radio galaxy Pictor A. We have considered jets with density ratios eta=1e-2
- 1e-4, and Mach numbers ranging between 5 and 50. From each simulation, we
have generated ray-traced maps of radio surface brightness at a variety of jet
inclinations, in order to study the appearance of time-dependent luminous
structures in the vicinity of the western hot-spot. We compare these rendered
images with observed features of Pictor A. A remarkable feature of Pictor A
observations is a bar-shaped "filament" inclined almost at right angles to the
inferred jet direction and extending 24" (10.8 /h kpc) along its longest axis.
The constraints of reproducing the appearance of this structure in simulations
indicate that the jet of Pictor A lies nearly in the plane of the sky. The
results of the simulation are also consistent with other features found in the
radio image of Pictor A. This filament arises from the surging behaviour of the
jet near the hot-spot; the surging is provoked by alternate compression and
decompression of the jet by the turbulent backflow in the cocoon. We also
examine the arguments for the jet in Pictor A being at a more acute angle to
the line of sight and find that our preferred orientation is just consistent
with the limits on the brightness ratio of the X-ray jet and counter-jet. We
determine from our simulations, the structure function of hot-spot brightness
and also the cumulative distribution of the ratio of intrinsic hot-spot
brightnesses. The latter may be used to quantify the use of hot-spot ratios for
the estimation of relativistic effects.


title:
HI Absorption in the Gigamaser Galaxy TXS 2226-184 and the Relation
  between HI Absorption and Water Emission

abstract:
  We report on the discovery of HI in absorption toward the gigamaser galaxy
TXS2226-184 using the VLA. The absorption appears to consist of two components
-- one with a width of 125 km/s, and one broader (420 km/s), both toward the
compact radio source in the nucleus of the galaxy. Based on these large
velocity widths we suggest that the HI absorption is produced in the central
parsecs of the galaxy, on a similar scale to that which gives rise to the water
maser emission. This brings to eight the number of galaxies known to exhibit
both water masers and HI absorption. We explore the relationship between these
two phenomena, and present a physically motivated (but unfruitful) search for
water maser emission in five radio galaxies known to exhibit strong HI
absorption.


title:
Photon vs Energy Magnitude Systems and the Measurement of the
  Cosmological Parameters

abstract:
  The relative brightnesses of standard candles have long been known to be
potentially powerful probes of distance. The distance modulus, the difference
between observed and absolute magnitudes, has been associated with the values
of the cosmological parameters: Hubble's constant H_0, the mass density Omega_M
and the cosmological constant Omega_Lambda. In the literature the relationship
between these parameters and the distance modulus is calculated for an energy
magnitude system; the Johnson-Cousins magnitude system used in observations is
in fact a photon-counting system. In this paper, we present the relation
between observed and absolute photon magnitudes in terms of the familiar energy
distance modulus and derive the correct form of the K-correction. The
differences between energy and photon systems are small relative to the
measurement errors of contemporary high-redshift supernova searches. The
distinction must be made, however, for precision cosmological measurements such
as those planned for Type Ia supernovae.


title: Clustering at high redshift

abstract:
  The addition of deep near infrared images to the database provided by the
HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline
and address a number of key issues including the total stellar content of
baryonic mass, the effects of dust extinction, the dependence of morphology on
the rest frame wavelength, the photometric redshifts, the detection and nature
of extremely red objects (EROs). For these reasons deep near infrared images
were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks
bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A
multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the
HDF-S has been produced. Photometric redshifts have been generated both fitting
templates to the observed SEDs and with neural network techniques.
Spectroscopic observations of the 9 candidates with I_AB <24.25 have confirmed
all of them to be galaxies with 2<z<3.5. The photometric redshifts for all the
galaxies brighter than I_AB< 27.5 have been used to study the evolution of
galaxy clustering in the interval 0<z<4.5.


title:
Modelling the IGM and the Lyalpha forest at high redshift from the dark
  matter distribution

abstract:
  A variety of approximate schemes for modelling the low-density Intergalactic
Medium (IGM) in the high-redshift Universe is compared to the results of a
large high-resolution hydro-dynamical simulation. These schemes use either an
analytical description of the dark matter distribution and the IGM or numerical
simulations of the DM distributions combined with different approximate
relations between dark matter field and the gas distribution. Schemes based on
a filtering of the dark matter distribution with a global Jeans scale result in
a rather poor description of the gas distribution. An adaptive filtering which
takes into account the density/temperature dependence of the Jeans scale is
required. A reasonable description of the gas distribution can be achieved
using a fit of the mean relation between the dark matter and gas densities in
the hydro-dynamical simulation to relate dark matter and gas distribution. In
the hydro-dynamical simulations deviations from this mean relation are
correlated with gradients in the dark matter peculiar velocity field indicative
of shocks in the gas component. A scheme which takes into account this
correlation results in a further improved gas distribution. Such adaptive
filtering schemes applied to dark matter simulations will be very well suited
for studies of statistical properties of the Lyalpha forest which investigate
the IGM and the underlying dark matter distribution and require a large dynamic
range and/or an extensive parameter study.


title:
Homoclinic crossing in open systems: Chaos in periodically perturbed
  monopole plus quadrupolelike potentials

abstract:
  The Melnikov method is applied to periodically perturbed open systems modeled
by an inverse--square--law attraction center plus a quadrupolelike term. A
compactification approach that regularizes periodic orbits at infinity is
introduced. The (modified) Smale-Birkhoff homoclinic theorem is used to study
transversal homoclinic intersections. A larger class of open systems with
degenerated (nonhyperbolic) unstable periodic orbits after regularization is
also briefly considered.


title:
Simulation-Based Investigation of a Model for the Interaction Between
  Stellar Magnetospheres and Circumstellar Accretion Disks

abstract:
  We examine, parametrically, the interaction between the magnetosphere of a
rotating, young stellar object (YSO) and a circumstellar accretion disk using
2.5-D (cylindrically symmetric) numerical magnetoydrodynamic simulations. The
interaction drives a collimated outflow, and we find that the jet formation
mechanism is robust. For variations in initial disk density of a factor of 16,
variations of stellar dipole strength of a factor of 4, and for various initial
conditions with respect to the disk truncation radius and the existence of a
disk field, outflows with similar morphologies were consistently produced.
Secondly, the system is self-regulating, where the outflow properties depend
relatively weakly on the parameters above. The large scale magnetic field
structure rapidly evolves to a configuration that removes angular momentum from
the disk at a rate that depends most strongly on the field and weakly on the
rotation rate of the foot-points of the field in the disk and the mass outflow
rate. Third, the simulated jets are episodic, with the timescale of jet
outbursts identical to the timescale of magnetically induced oscillations of
the inner edge of the disk. To better understand the physics controlling these
disk oscillations, we present a semi-analytical model and confirm that the
oscillation period is set by the spin down rate of the disk inner edge.
Finally, our simulations offer strong evidence that it is indeed the
interaction of the stellar magnetosphere with the disk, rather than some
primordial field in the disk itself, that is responsible for the formation of
jets from these systems.


title: The Gravitomagnetic Field and Penrose Processes

abstract:
  Results from general relativistic theoretical Monte Carlo computer
simulations of Compton scattering and e-e+ pair production processes in the
ergosphere of a supermassive (10^8 solar mass) rotating black hole are
presented. Particles from an accretion disk fall into the ergosphere and
scatter off particles that are in bound equatorially and nonequatorially
confined orbits. The Penrose mechanism, in general, allows rotational energy of
a Kerr black hole to be extracted by scattered particles escaping from the
ergosphere to infinity (i.e., large distances from the black hole). The results
of these model calculations show that a form of the Penrose mechanism is
capable of producing the observed high energy particles (up to of order GeV)
emitted by quasars and other active galactic nuclei (AGNs), without the
necessity of the external electromagnetic field of the accretion disk.
Importantly, these model calculations show that the Lense-Thirring effect,
i.e., the dragging of inertial frames into rotation, caused by the angular
momentum of the rotating black hole, results in a gravitomagnetic (GM) force
being exerted on the scattered escaping particles. Inside the ergosphere, where
this dragging is severe, in appears that the GM vector field lines are frame
dragged into the positive azimuthal direction, i.e., the direction of rotation
of the black hole. The resulting GM force acting on the Penrose scattered
particles produces symmetrical and asymmetrical (or one-sided) particle
emissions in the polar direction, consistent with the astrophysical jets
observed in radio strong AGNs. Note, these Penrose processes can apply to any
size rotating black hole.


title:
Possible evidence for the pulsed X-ray emission from outer gap in PSR
  B1937+21?

abstract:
  The fastest millisecond pulsar PSR B1937+21 presents an interpulse separated
from the main pulse by nealy 180^o at radio frequencies. Recently, the ASCA
observations (Takahashi et al. 2001) detected pulsed X-ray emission from this
pulsar. Only a single narrow X-ray pulse is observed, which is coincident with
the radio interpulse in phase. We investigate the possible origin of the pulsed
X-rays from the polar cap (PC) accelerators or the outer gap (OG) accelerators
in the frame of PC model and OG model, respectively, by assuming a dipolar
magnetic field structure and the same radio emission pattern from its poles for
the pulsar. The OG model can naturally explain the main observational facts.
For the PC model, the coincidence between the X-ray pulse and the radio
interpulse can not be reproduced in the assumed case. However when considering
possible deviation from our assumption, PC model may still be valid for this
pulsar in some cases.


title: X-ray Variability of Blazars

abstract:
  Critical progress in our understanding of high energy emission from AGN has
been determined in the last 10 years by X-ray monitoring campaigns with many
space missions, notably ROSAT, ASCA, RXTE, BeppoSAX, and XMM, often in
conjunction with observations at other frequencies. The emphasis of the present
review is on recent findings about X-ray variability of blazars. Among AGN,
these exhibit the largest amplitude variations of the X-ray emission, often
well correlated with variations at higher energies (GeV and TeV radiation). The
accurate sampling of the X-ray spectra over more than three decades in energy,
made possible by the wide energy range of BeppoSAX, has also shown strong
spectral variability in blazar active states, suggesting extreme electron
energies and leading to the identification of a class of `extreme synchrotron'
sources.


title:
Perturbative approach to the astrometric microlensing due to an
  extrasolar planet

abstract:
  We have developed a perturbative approach to microlensing due to an
extrasolar planetary lens. In particular, we have found analytic formulae for
triple images. We have used the formulae to investigate the astrometric
microlensing due to the extrasolar planetary lens, in expectation of dramatic
improvements in the precision of the future astrometric measurements. For a
weak lensing case, we have shown how the maximum angular size and the typical
time scale of the anomalous shift of the lightcentroid are dependent on the
mass ratio and angular separation between the star and the planet.


title: Does the Slim-Disk Model Correctly Consider Photon-Trapping Effects?

abstract:
  We investigate the photon-trapping effects in the super-critical black hole
accretion flows by solving radiation transfer as well as the energy equations
of radiation and gas. It is found that the slim-disk model generally
overestimates the luminosity of the disk at around the Eddington luminosity
(L_E) and is not accurate in describing the effective temperature profile,
since it neglects time delay between energy generation at deeper inside the
disk and energy release at the surface. Especially, the photon-trapping effects
are appreciable even below L ~ L_E, while they appear above ~ 3L_E according to
the slim disk. Through the photon-trapping effects, the luminosity is reduced
and the effective temperature profile becomes flatter than r^{-3/4} as in the
standard disk. In the case that the viscous heating is effective only around
the equatorial plane, the luminosity is kept around the Eddington luminosity
even at very large mass accretion rate, Mdot>>L_E/c^2. The effective
temperature profile is almost flat, and the maximum temperature decreases in
accordance with rise in the mass accretion rate. Thus, the most luminous radius
shifts to the outer region when Mdot/(L_E/c^2) >> 10^2. In the case that the
energy is dissipated equally at any heights, the resultant luminosity is
somewhat larger than in the former case, but the energy-conversion efficiency
still decreases with increase of the mass accretion rate, as well. The most
luminous radius stays around the inner edge of the disk in the latter case.
Hence, the effective temperature profile is sensitive to the vertical
distribution of energy production rates, so is the spectral shape. Future
observations of high L/L_E objects will be able to test our model.


title: Neutron stars properties viewed by the ENU model

abstract:
  Up-to-now known characteristics of radio pulsars, such as mass limits,
magnetic field intensity, rotational period, and maximum radiation are mainly
of empirical nature. Applying the Expansive Nondecelerative Universe model
(ENU) into the issue allows to offer a deeper theoretical explanation of the
known parameters and to estimate their limits. Using the ENU approach the
following values related to synchrotron radiation emitting radio pulsars were
estimated: the lower and upper limits of magnetic field intensity are B(min) =
8.6 x 10^6 T, and B(max) = 9.4 x 10^8 T, respectively, the maximum rotation
period reaches 3.9 s, the maximum radiation output of a pulsar is P(max) = 5.6
x 10^29 W (all the values relate to radio pulsars with 1.4 solar masses and
radius 1.0 x 10^4 m and are mass and radius dependent). These values are in
accordance with the experimental observations.


title:
MAD-4-MITO, a Multi Array of Detectors for ground-based mm/submm SZ
  observations

abstract:
  The last few years have seen a large development of mm technology and
ultra-sensitive detectors devoted to microwave astronomy and astrophysics. The
possibility to deal with large numbers of these detectors assembled into
multi--pixel imaging systems has greatly improved the performance of microwave
observations, even from ground--based stations, especially combining the power
of multi--band detectors with their new imaging capabilities. Hereafter, we
will present the development of a multi--pixel solution devoted to
Sunyaev--Zel'dovich observations from ground--based telescopes, that is going
to be operated from the Millimetre and Infrared Testagrigia Observatory.


title:
The dynamics of the Circumnuclear Disk and its environment in the
  Galactic centre

abstract:
  We address the question of the dynamics in the inner 50 pc of the Galactic
Centre. In a first step we investigate the cloud-cloud collision rate in the
Circumnuclear Disk (CND) with the help of a three dimensional N-body code using
gas particles that can have inelastic collisions. The CND might be a longer
lived structure than previously assumed. The whole disk-like structure of the
CND can thus survive for several million years. A realistic simulation of the
CND shows the observed disk height structure. In a second step the environment
of the CND is taken into account. Retrograde and prograde encounters of a cloud
of several 10^4 M_solar falling onto an already existing nuclear disk using
different energy loss rates per collision are simulated. The influence of the
energy loss rate per collision on the evolution of the mass accretion and cloud
collision rates is strongest for a prograde encounter. A composite data cube of
two different snapshots of a prograde encounter together with the CND shows
striking similarity with the observed Sgr A cloud complex. The current
appearance of the Galactic Centre environment can thus be explained by at least
two dynamically distinct features together with the CND. The current mass
accretion rate within the CND ranges between 10^-3 and 10^-4 M_solar yr^-1. It
can rise up to several 10^-2 M_solar yr^-1 during massive accretion events.


title: MOND mass-to-light ratios for galaxy groups

abstract:
  I estimate MOND M/L values for nine galaxy groups that were recently studied
by Tully et al.. Instead of the large M/L values that they find with Newtonian
dynamics (up to 1200 solar units) the MOND estimates cluster around 1 solar
unit. Tully et al. find a systematic and significant difference between the M/L
values of groups that do not contain luminous galaxies and those that do:
Dwarfs-only groups have larger M/L values (by a factor of about 5). The MOND
M/L values do not show this trend; the Newtonian disparity is traced back to
the dwarfs-only groups having systematically smaller intrinsic accelerations
(similar sizes, but rather smaller velocity dispersions).


title:
Big Bang nucleosynthesis, matter-antimatter regions, extra relativistic
  species, and relic gravitational waves

abstract:
  Provided that matter-antimatter domains are present at the onset of big bang
nucleosynthesis (BBN), the number of allowed additional relativistic species
increases, compared to the standard scenario when matter-antimatter domains are
absent. The extra relativistic species may take the form of massless fermions
or even massless bosons, like relic gravitons. The number of additional degrees
of freedom compatible with BBN depends, in this framework, upon the typical
scale of the domains and the antimatter fraction. Since the presence of
matter-antimatter domains allows a reduction of the neutron to proton ratio
prior to the formation of 4He, large amounts of radiation-like energy density
are allowed. Our results are compared with other constraints on the number of
supplementary relativistic degrees of freedom and with different nonstandard
BBN scenarios where the reduction of the neutron to proton ratio occurs via a
different physical mechanism. The implications of our considerations for the
upper limits on stochastic gravitational waves backgrounds of cosmological
origin are outlined.


title: Chandra LETGS Observation of the Active Binary Algol

abstract:
  A high-resolution spectrum obtained with the low-energy transmission grating
onboard the Chandra observatory is presented and analyzed. Our analysis
indicates very hot plasma with temperatures up to T=15-20MK from the continuum
and from ratios of hydrogen-like and helium-like ions of Si, Mg, and Ne. In
addition lower temperature material is present since OVII and NVI are detected.
Two methods for density diagnostics are applied. The He-like triplets from NVII
to SiXIII are used and densities around 10^11 cm^-3 are found for the low
temperature ions. Taking the UV radiation field from the B star companion into
account, we find that the low-Z ions can be affected by the radiation field
quite strongly, such that densities of 3 10^10 cm^-3 are also possible, but
only assuming that the emitting plasma is immersed in the radiation field. For
the high temperature He-like ions only low density limits are found. Using
ratios of FeXXI lines produced at similar temperatures are sensitive to lower
densities but again yield only low density limits. We thus conclude that the
hot plasma has densities below 10^12 cm^-3. Assuming a constant pressure corona
we show that the characteristic loop sizes must be small compared to the
stellar radius and that filling factors below 0.1 are unlikely.


title:
Three Type I X-ray bursts from Cyg X-2: Application of Analytical Models
  for Neutron Star Mass and Radius Determination

abstract:
  We study the spectral and temporal properties of three Type I X-ray bursts
observed from Cyg X-2 with the Rossi X-ray Timing Explorer. Despite the short
time durations (~ 5 sec) these bursts show radial expansion of order of several
neutron star (NS) radii. We apply the analytical models of spectral formation
during the expansion and contraction stages to derive physical conditions for
the matter in the burning zone close to the surface of the NS as well as the NS
mass-radius relation. Our results, combined with statistical errors, show that
the central object is a compact star with mass ~1.4 solar masses and radius ~9
km. Our results favor the softer equation of state for neutron star matter.


title:
Eclipsing binary millisecond pulsar PSR J1740-5340 -- evolutionary
  considerations and observational test

abstract:
  We perform evolutionary calculations for a binary system with initial
parameters: $M_{sg,i}$= 1$M\odot$ and $M_{ns,i}$= 1.4 $M\odot$ and
$P_{orb,i}(RLOF)$= 1.27 d to produce observed binary parameters for the PSR
J1740--5340. Our calculations support model proposed by D'Amico et al. (2001)
in which this binary may be progenitor of a millisecond pulsar + helium white
dwarf system. We propose observational test to verify this hypothesis. If the
optical companion lack of carbon lines in its spectrum shows but the oxygen and
nitrogen lines are present then our model correctly describes the evolutionary
stage of PSR J1740--5340.


title: ROSAT X-ray observations of the dwarf galaxy Holmberg II

abstract:
  We present a study of the irregular dwarf galaxy Holmberg II based on ROSAT
PSPC observations (total exposure time: 22 ksec). Holmberg II is a nearby (3.2
Mpc), well-studied dwarf irregular galaxy. It is famous for its interstellar
medium which is dominated by expanding structures such as HI holes and shells.
We search for X-ray emission from point sources as well as for diffuse
emission, down to the detection limit of the ROSAT data. Using X-ray hardness
ratio diagrams we differentiate between thermal plasma and power-law X-ray
spectra which helps to determine the nature of the individual sources.
Correlating the X-ray data with complementary observations ranging from the
far-ultraviolet to the radio regime we increase the probability of correctly
identifying sources belonging to Holmberg II. We did not detect soft X-ray
emission originating from hot gas within supergiant HI shells above our
luminosity sensitivity limit of (L_limit(0.1 - 2.1 keV) ~ 10^{37}erg/s). This
finding can probably be attributed to blow-out in the case of the largest holes
and insufficient sensitivity (due to strong photoelectric absorption) in case
of the smaller HI holes. However we find faint X-ray sources well beyond the
stellar body but within the HI distribution of Holmberg II, which suggests the
presence of X-ray binaries. This indicates that star formation has taken place
across the entire gaseous disk of Holmberg II in the past, some of which may
have created the structures seen in the ISM at large galactocentric radii.


title:
Asymptotic behavior of a stratified perturbation in a three dimensional
  expanding Universe

abstract:
  The non-linear evolution of a stratified perturbation in a three dimensional
expanding Universe is considered. A general Lagrangian scheme (Q model) is
introduced and numerical investigations are performed. The asymptotic
contraction of the core of the agglomeration is studied. A power-law scaling is
detected and an heuristic interpretation of the numerical findings is provided.
An asymptotic equation for the multi-stream velocity flow is derived and it is
shown to agree quantitatively with the dynamics of the Q model. The relation to
the adhesion model is discussed.


title: The triggered star formation in rotating disks

abstract:
  The gravitational instability of expanding shells triggering the formation of
clouds and stars is analyzed. Disks with different scale-heights, ambient and
shell velocity dispersions, mid-plane densities, rotation rates and shear rates
are explored with three dimensional numerical simulations in the thin shell
approximation. Three conditions for the shell collapse are specified: the first
is that it happens before a significant blow-out, the second requires that the
shell collapses before it is distorted by Coriolis forces and shear, and the
third requires that the internal pressure in the accumulated gas is small and
the fragmentation is achieved within the expansion time. The gas-rich and
slowly rotating galaxies are the best sites of the triggered star formation,
concluding that its importance has been much larger at the times of galaxy
formation compared to the present epoch.


title:
Measured Mass Loss Rates of Solar-like Stars as a Function of Age and
  Activity

abstract:
  Collisions between the winds of solar-like stars and the local ISM result in
a population of hot hydrogen gas surrounding these stars. Absorption from this
hot H I can be detected in high resolution Lyman-alpha spectra of these stars
from the Hubble Space Telescope. The amount of absorption can be used as a
diagnostic for the stellar mass loss rate. We present new mass loss rate
measurements derived in this fashion for four stars (Epsilon Eri, 61 Cyg A, 36
Oph AB, and 40 Eri A). Combining these measurements with others, we study how
mass loss varies with stellar activity. We find that for the solar-like GK
dwarfs, the mass loss per unit surface area is correlated with X-ray surface
flux. Fitting a power law to this relation yields Mdot ~ Fx^(1.15+/-0.20). The
active M dwarf Proxima Cen and the very active RS CVn system Lambda And appear
to be inconsistent with this relation. Since activity is known to decrease with
age, the above power law relation for solar-like stars suggests that mass loss
decreases with time. We infer a power law relation of Mdot ~ t^(-2.00+/-0.52).
This suggests that the solar wind may have been as much as 1000 times more
massive in the distant past, which may have had important ramifications for the
history of planetary atmospheres in our solar system, that of Mars in
particular.


title: Hydrodynamical Study of Advective Accretion flow around Neutron Stars

abstract:
  Here we study the accretion process around a neutron star, especially for the
cases where shock does form in the accretion disk. In case of accretion flows
around a black hole, close to the horizon matter is supersonic. On the other
hand for the case of neutron stars and white dwarfs, matter must be subsonic
close to the inner boundary. So the nature of the inflowing matter around
neutron stars and white dwarfs are strictly different from that around black
holes in the inner region of the disk. Here we discuss a few phenomena and the
corresponding solutions of hydrodynamic equations of matter in an accretion
disk around a slowly rotating neutron star without magnetic field.


title: Are quasars accreting at super-Eddington rates?

abstract:
  In a previous paper, Collin & Hur\'e (2001), using a sample of Active
Galactic Nuclei (AGN) where the mass has been determined by reverberation
studies (Kaspi et al. 2000), have shown that if the optical luminosity is
emitted by a steady accretion disc, about half of the objects are accreting
close to or higher than the Eddington rate. We conclude here that this result
is unavoidable, unless the masses are strongly underestimated by reverberation
studies, which does not seem to be the case. There are three issues to the
problem: 1. Accretion proceeds at Eddington or super-Eddington rates through
thick discs. Several consequences follow: an anti-correlation between the line
widths of the lines and the Eddington ratios, and a decrease of the Eddington
ratio with an increasing black hole mass. Extrapolated to all quasars, these
results imply that the amount of mass locked in massive black holes should be
larger than presently thought. 2. The optical luminosity is not produced
directly by the gravitational release of energy, and super-Eddington rates are
not required. The optical luminosity has to be emitted by a dense and thick
medium located at large distances from the center (10$^3$ to $10^4$
gravitational radii). It can be due to reprocessing of the X-ray photons from
the central source in a geometrically thin warped disc, or in dense "blobs"
forming a geometrically thick system, which can be a part of the accretion flow
or the basis of an outflow. 3. Accretion discs are completely "non standard".
Presently neither the predictions of models nor the observed spectral
distributions are sufficient to help choosing between these solutions.


title:
Is there a 1998bw-like supernova in the afterglow of gamma ray burst
  011121?

abstract:
  We use the very simple and successful Cannonball Model (CB) of gamma ray
bursts (GRBs) and their afterglows (AGs) to analyze the observations of the
strongly extinct optical AG of the relatively nearby GRB 011121, which were
made with ground-based telescopes at early times, and with the HST at later
time. We show that GRB 011121 was indeed associated with a 1998bw-like
supernova at the GRB's redshift, as we had specifically predicted for this GRB
before the supernova could be observed.


title: Mass Power Spectrum in a Universe Dominated by the Chaplygin Gas

abstract:
  The mass power spectrum for a Universe dominated by the Chaplygin gas is
evaluated numerically from scales of the order of the Hubble horizon to 100
Mpc. The results are compared with a pure baryonic Universe and a cosmological
constant model. In all three cases, the spectrum increases with k, the
wavenumber of the perturbations. The slope of the spectrum is higher for the
baryonic model and smaller for the cosmological constant model, the Chaplygin
gas interpolating these two models. The results are analyzed in terms of the
sound velocity of the Chaplygin gas and the moment the Universe begins to
accelerate.


title:
Stringent Constraints on Cosmological Neutrino-Antineutrino Asymmetries
  from Synchronized Flavor Transformation

abstract:
  We assess a mechanism which can transform neutrino-antineutrino asymmetries
between flavors in the early universe, and confirm that such transformation is
unavoidable in the near bi-maximal framework emerging for the neutrino mixing
matrix. We show that the process is a standard Mikheyev-Smirnov-Wolfenstein
flavor transformation dictated by a synchronization of momentum states. We also
show that flavor ``equilibration'' is a special feature of maximal mixing, and
carefully examine new constraints placed on neutrino asymmetries. In
particular, the big bang nucleosynthesis limit on electron neutrino degeneracy
xi_e < 0.04 does not apply directly to all flavors, yet confirmation of the
large-mixing-angle solution to the solar neutrino problem will eliminate the
possibility of degenerate big bang nucleosynthesis.


title:
First gamma-rays from galaxy clusters. Preliminary evidence of the
  association of galaxy clusters with EGRET unidentified gamma-ray sources

abstract:
  The vast majority of the celestial gamma-ray sources detected so far have not
yet been identified with secure counterparts at other wavelenghts. Here we
report the preliminary evidence of a probable association between galaxy
clusters and unidentified gamma-ray sources of high galactic latitude (|b|>20
deg) in the Third EGRET catalog. All of the clusters which are most probably
associated with EGRET sources show evidence of strong radio emission either
because they host radio galaxies/sources in their environments or because they
have a radio halo or relic inhabiting their intracluster medium. The cluster
radio emission suggests that the relativistic particles (electrons, protons),
which are diffusing in the intracluster medium, might be also responsible for
their gamma-ray emission. Beyond the spatial associations of clusters with
unidentified EGRET sources, we found a correlation between the radio flux at
1.4 GHz of the cluster's brightest source and the gamma-ray flux, F(>100 MeV),
of the associated EGRET source. For the most probable EGRET-cluster
associations we also found a further correlation between the X-ray luminosity
of galaxy clusters and the gamma-ray luminosity of the associated gamma-ray
source under the hypothesis that the EGRET sources have the same cluster
redshifts. Such correlations are consistent with the theoretical expectations
and strengthen the probability of a true, physical association between galaxy
clusters and gamma-ray sources.


title: XMM-Newton observations of the asynchronous polar BY Cam

abstract:
  We report observations of the asynchronous polar BY Cam made using
XMM-Newton. We find evidence for two accretion regions which have significantly
different spectra. In both regions we find evidence for hard X-ray emission
from the post-shock flow while we observe a distinct soft X-ray blackbody
component in only one. We detect two emission lines in the RGS detectors which
we attribute to Nitrogen NVI and NVII: the first time that Nitrogen lines have
been detected in an X-ray spectrum of a cataclysmic variable. In the time
interval where we observe short timescale variability we find the hard X-ray
light curve is correlated with the softest energies in the sense that the hard
X-rays trail the soft X-rays and are anti-correlated. We suggest that there are
a small number of dense blobs of material which impact the white dwarf without
forming a shock and release an amount of optically thick material which
obscures hard X-rays for a short duration.


title: Neural Networks and Photometric Redshifts

abstract:
  We present a neural network based approach to the determination of
photometric redshift. The method was tested on the Sloan Digital Sky Survey
Early Data Release (SDSS-EDR) reaching an accuracy comparable and, in some
cases, better than SED template fitting techniques. Different neural networks
architecture have been tested and the combination of a Multi Layer Perceptron
with 1 hidden layer (22 neurons) operated in a Bayesian framework, with a Self
Organizing Map used to estimate the accuracy of the results, turned out to be
the most effective. In the best experiment, the implemented network reached an
accuracy of 0.020 (interquartile error) in the range 0<zphot<0.3, and of 0.022
in the range 0<zphot<0.5.


title:
The radio galaxy 3C 356 and clues to the trigger mechanisms for powerful
  radio sources

abstract:
  We present deep near-infrared images, taken with Subaru Telescope, of the
region around the z=1.08 radio source 3C 356 which show it to be associated
with a poor cluster of galaxies. We discuss evidence that this cluster
comprises two subclusters traced by the two galaxies previously proposed as
identifications for 3C 356, which both seem to harbour AGN, and which have the
disturbed morphologies expected if they underwent an interpenetrating collision
at the time the radio jets were triggered. We explain the high luminosity and
temperature of the diffuse X-ray emission from this system as the result of
shock-heating of intracluster gas by the merger of two galaxy groups. Taken
together with the results on other well-studied powerful radio sources, we
suggest that the key ingredient for triggering a powerful radio source, at
least at epochs corresponding to z~1, is a galaxy--galaxy interaction which can
be orchestrated by the merger of their parent subclusters. This provides an
explanation for the rapid decline in the number density of powerful radio
sources since z~1. We argue that attempts to use distant radio-selected
clusters to trace the formation and evolution of the general cluster population
must address ways in which X-ray properties can be influenced by the radio
source, both directly, by mechanisms such as inverse-Compton scattering, and
indirectly, by the fact that the radio source may be preferentially triggered
at a specific time during the formation of the cluster.


title:
Beam Models for Gamma-Ray Bursts Sources: Outflow Structure, Kinematics
  and Emission Mechanisms

abstract:
  The variety of gamma-ray burst phenomenology could be largely attributable to
differences in the opening angle of an isotropic outflow or to a standard type
of event viewed from different orientations. Motivated by this currently
popular idea, we study the effects of varying the energy per unit solid angle
in the unsteady expelled outflow by an increase either in the bulk Lorentz
factor or in the baryon loading. We apply these models to interpret the
observed correlations between variability, luminosity and spectral peak energy
and find that while the latter scenario fails to provide a good description,
bursts produced by collisions between similar mass shells but with increasingly
large Lorentz factors are both more variable and have larger peak spectral
energies. We present detailed internal shock calculations confirming this
interpretation and discuss the roles various timescales, radii and the optical
thickness of the wind play in determining this wide range of behaviors.
Finally, we discuss the variety of scenarios in which large variations of the
source expansion velocity are naturally expected.