title: Planetary transits and stellar variability

abstract:
  This thesis focuses on the detection of extrasolar planets via the transit
method, and more specifically addresses issues relevant to the preparation of
upcoming space missions such as CoRoT, Kepler, Eddington, aiming to detect
terrestrial planets. The automated detection of transits in tens of thousands
of noisy light curves is a challenging task because of the brief, shallow and
rare nature of the sought-after signal. I developed a Bayesian transit
detection algorithm and tested it through Monte Carlo simulations. This led to
a number of improvements to the algorithm, resulting in a maximum likelihood
box-fitting approach that is simpler and, for detection purposes, more
effective. I also developed an empirical model of the intrinsic
micro-variability of the parent stars, which constitutes one of the main
performance limitations for space-based transit searches, and used this model
to optimise variability filters. These tools were used to identify optimal
regions of the stellar parameter space to be targeted by missions such as CoRoT
and Eddington, through Monte Carlo simulations and participation in the first
CoRoT blind transit detection exercise. Recently, the same tools have been used
to analyse ground-based data from the University of New South Wales planet
search project, leading to the identification of several potential transiting
planet candidates.


title: Testing the Gamma-Ray Burst Energy Relationships

abstract:
  Building on Nakar & Piran's analysis of the Amati relation relating gamma-ray
burst peak energies E_p and isotropic energies E_iso, we test the consistency
of a large sample of BATSE bursts with the Amati and Ghirlanda (which relates
peak energies and actual gamma-ray energies E_gamma) relations. Each of these
relations can be expressed as a ratio of the different energies that is a
function of redshift (for both the Amati and Ghirlanda relations) and beaming
fraction f_B (for the Ghirlanda relation). The most rigorous test, which allows
bursts to be at any redshift, corroborates Nakar & Piran's result--88% of the
BATSE bursts are inconsistent with the Amati relation--while only 1.6% of the
bursts are inconsistent with the Ghirlanda relation if f_B=1. Even when we
allow for a real dispersion in the Amati relation we find an inconsistency.
Modelling the redshift distribution results in an energy ratio distribution for
the Amati relation that is shifted by an order of magnitude relative to the
observed distribution; any sub-population satisfying the Amati relation can
comprise at most ~18% of our burst sample. A similar analysis of the Ghirlanda
relation depends sensitively on the beaming fraction distribution for small
values of f_B; for reasonable estimates of this distribution about a third of
the burst sample is inconsistent with the Ghirlanda relation. Our results
indicate that these relations are an artifact of the selection effects of the
burst sample in which they were found; these selection effects may favor
sub-populations for which these relations are valid.


title: Massive Stars in the SGR 1806-20 Cluster

abstract:
  We report the discovery of additional hot and massive stars in the cluster
surrounding the soft gamma repeater SGR 1806-20, based upon UKIRT and Keck
near-infrared spectroscopy. Of the newly identified stars, three are Wolf-Rayet
stars of types WC8, WN6, and WN7, and a fourth star is an OB supergiant. These
three stars, along with four previously discovered, imply a cluster age of
\~3.0-4.5 Myr, based on the presence of WC stars and the absence of red
supergiants. Assuming coevality, this age suggests that the progenitor of SGR
1806-20 had an initial mass greater than ~50 Msun. This is consistent with the
suggestion that SGRs are post-supernovae end states of massive progenitors, and
may suggest that only massive stars evolve into magnetars that produce SGRs. It
also suggests that very massive stars can evolve into neutron stars, not just
black holes, as recently predicted by theory. The cluster age also provides
constraints on the very high mass object, LBV 1806-20.


title:
Supernova Remnant 1987A: The Latest Report from the Chandra X-Ray
  Observatory

abstract:
  We continue monitoring supernova remnant (SNR) 1987A with the {\it Chandra
X-ray Observatory}. As of 2004 January, bright X-ray spots in the northwest and
the southwest are now evident in addition to the bright eastern ring. The
overall X-ray spectrum, Since 2002 December, can be described by a planar shock
with an electron temperature of $\sim$2.1 keV. The soft X-ray flux is now 8
$\times$ 10$^{-13}$ ergs cm$^{-2}$ s$^{-1}$, which is about five times higher
than four years ago. This flux increase rate is consistent with our prediction
based on an exponential density distribution along the radius of the SNR
between the H{\small II} region and the inner ring. We still have no direct
evidence of a central point source, and place an upper limit of $L_X$ = 1.3
$\times$ 10$^{34}$ ergs s$^{-1}$ on the 3$-$10 keV band X-ray luminosity.


title:
Constraining Warm Dark Matter candidates including sterile neutrinos and
  light gravitinos with WMAP and the Lyman-alpha forest

abstract:
  The matter power spectrum at comoving scales of (1-40) h^{-1} Mpc is very
sensitive to the presence of Warm Dark Matter (WDM) particles with large free
streaming lengths. We present constraints on the mass of WDM particles from a
combined analysis of the matter power spectrum inferred from the large samples
of high resolution high signal-to-noise Lyman-alpha forest data of Kim et al.
(2004) and Croft et al. (2002) and the cosmic microwave background data of
WMAP. We obtain a lower limit of m_wdm > 550 eV (2 sigma for early decoupled
thermal relics and m_wdm > 2.0 keV (2 sigma) for sterile neutrinos. We also
investigate the case where in addition to cold dark matter a light thermal
gravitino with fixed effective temperature contributes significantly to the
matter density. In that case the gravitino density is proportional to its mass,
and we find an upper limit m_{3/2} < 16 eV (2 sigma). This translates into a
bound on the scale of supersymmetry breaking, Lambda_{susy} < 260 TeV, for
models of supersymmetric gauge mediation in which the gravitino is the lightest
supersymmetric particle.


title:
A Stellar Wind Bubble Coincident with the Anomalous X-ray Pulsar 1E
  1048.1-5937: Are Magnetars Formed From Massive Progenitors?

abstract:
  We present 21-cm HI observations from the Southern Galactic Plane Survey of
the field around the anomalous X-ray pulsar 1E 1048.1-5937, a source whose
X-ray properties imply that it is a highly magnetized neutron star (a
"magnetar"). These data reveal an expanding hydrogen shell, GSH 288.3-0.5-28,
centered on 1E 1048.1-5937, with a diameter of 35x23 pc (for a distance of 2.7
kpc) and an expansion velocity of approx 7.5 km/s. We interpret GSH
288.3-0.5-28 as a wind bubble blown by a 30-40 M_sun star, but no such central
star can be readily identified. We suggest that GSH 288.3-0.5-28 is the wind
bubble blown by the massive progenitor of 1E 1048.1-5937, and consequently
propose that magnetars originate from more massive progenitors than do radio
pulsars. This may be evidence that the initial spin period of a neutron star is
correlated with the mass of its progenitor, and implies that the magnetar birth
rate is only a small fraction of that for radio pulsars.


title:
Resolving the Steep Spectrum Emission in the Central Radio Source in
  ZwCl 0735.7+7421

abstract:
  It has long been know that an extremely steep spectrum radio source lies at
the center of ZwCl 0735.7+7421, a galaxy cluster with high X-ray luminosity and
a cooling core. In this Letter, we present VLA observations of this radio
source at both 1425 and 325 MHz. With a resolution below 21'' (75 kpc) for both
1425 and 325 MHz, we show the morphology of the central source, and find that
it is most likely a large (400 kpc) radio galaxy rather than diffuse cluster
emission. We estimate a steep spectral index of $\alpha_{325}^{1400} = -1.54$
for the core (although it may be contaminated by lobe emission), while the
outer lobes are extremely steep objects, both with $\alpha_{325}^{1400} <
-3.1$. We also find evidence for restarted core activity in the form of a set
of inner lobes oriented at a somewhat different angle from the outer lobes. A
spectral analysis extending the frequency range down to 74 MHz appears to show
a turnover at very low frequencies. Comparison of the minimum energy radio
pressures with the average thermal pressure surrounding the radio cavities from
McNamara et al.(2005) shows that the radio lobes appear to be roughly in
pressure balance with the thermal gas.


title:
A Novel Color Parameter As A Luminosity Calibrator for Type Ia
  Supernovae

abstract:
  Type Ia supernovae (SNe Ia) provide us with a unique tool for measuring
extragalactic distances and determining cosmological parameters. As a result,
the precise and effective calibration for peak luminosities of SNe Ia becomes
extremely crucial and thus is critically scrutinized for cosmological
explorations. In this Letter, we reveal clear evidence for a tight linear
correlation between peak luminosities of SNe Ia and their $B-V$ colors $\sim
12$ days after the $B$ maximum denoted by $\Delta C_{12}$. By introducing such
a novel color parameter, $\Delta C_{12}$, this empirical correlation allows us
to uniformly standardize SNe Ia with decline rates $\Delta m_{15}$ in the range
of $0.8<\Delta m_{15}<2.0$ and to reduce scatters in estimating their peak
luminosities from $\sim 0.5$ mag to the levels of 0.18 and 0.12 mag in the $V$
and $I$ bands, respectively. For a sample of SNe Ia with insignificant
reddenings of host galaxies [e.g., E$(B-V)_{host}\lsim 0.06$ mag], the scatter
drops further to only 0.07 mag (or 3-4% in distance), which is comparable to
observational accuracies and is better than other calibrations for SNe Ia. This
would impact observational and theoretical studies of SNe Ia and cosmological
scales and parameters.


title: Are jets in symbiotic stars driven by magnetic fields?

abstract:
  We compare two scenarios to launch jets -- formation by MHD processes or
formation by thermal pressure in the boundary layer (BL) -- with respect to
their compatibility with observational data of jets in symbiotic stars,
especially in the well studied jet source MWC 560. Finally, we discuss points
of further research to be done.


title:
Modelling the Milky Way through adiabatic compression of cold dark
  matter halo

abstract:
  We use the adiabatic compression theory to build a physically well -
motivated Milky Way mass model in agreement with the observational data. The
visible mass of the Galaxy is distributed in a spheroidal bulge and a multi -
components disc parametrized by three galactic parameters, the Sun distance to
the galactic centre, R_0, the total bulge mass, M_{bulge}, and the local disc
surface density, \Sigma_{\odot}. To model the dark matter component, we
adiabatically compress a Navarro, Frenk and White (NFW) halo (with
concentration $c$ and total mass M_{vir}) for fixed values of the spin
parameter, \lambda, the fraction of the mass in baryons, $m_b$, and the thin
disc contribution to total angular momentum, j_d. An iterative selection
procedure is used to explore in very detail the wide space of parameters only
selecting those combinations of {R_0, M_{bulge}, \Sigma_{\odot}, \lambda, m_b,
j_b, c, M_{vir}} that give rise to a Milky Way model in agreement with the
observational constraints. This analysis leads us to conclude that only models
with R_0 = 8.5 kpc, $0.8 x 10^{10} M_{\odot} < M_{bulge} < 1.6 x 10^{10}
M_{\odot}$ and $49 M_{\odot} pc^{-2} \le \Sigma_{\odot} \le 56 M_{\odot}
pc^{-2}$ can be reconciled with the set of observational constraints. As regard
the parameters entering the adiabatic compression, we find $0.03 \le \lambda
\le 0.10$ and $0.04 \le m_b \le 0.10$, while the final estimates of the
parameters describing the initial halo profile turn out to be $5
\stackrel{<}{\sim} c \stackrel{<}{\sim} 12$ and $7 x 10^{11} M_{\odot}
\stackrel{<}{\sim} M_\mathrm{vir} \stackrel{<}{\sim} 17 x 10^{11} M_{\odot}$
(all at 95.7% CL).


title: On the Origin of the most massive stars around R136

abstract:
  We discuss the signature of a peculiar constellation of very massive stars at
a projected distance of 2-3 pc around R136a. We discuss various scenarios for
its possible origin, such as independent clusters, triggered star formation,
supernovae, and ejections via dynamical interactions. If the latter scenario
were the correct one this would have significant implications on the way to
probe the conditions in dense stellar cores, and on the evolution of massive
clusters in general.


title:
The global kinematics of the Dumbbell planetary nebula (NGC 6853, M27,
  PN G060.8-03.6)

abstract:
  Spatially resolved profiles of the HeII 6560 A, Halpha and [N II] 6548 & 6584
A nebular emission lines have been obtained in two orthogonal long cuts over
the Dumbbell planetary nebula. The central HeII 6560 A emitting volume of the
bright dumbbell structure is shown to be particularly inert with an expansion
velocity of <= 7 km/s. This is enveloped by an inner [O III] 5007 A emitting
shell expanding at 13 km/s, an outer [O III] 5007 A shell expanding at 31 km/s
which is on the inside of the outer [N II] 6584 A emitting shell expanding at
35 km/s. A new Halpha + [N II] 6548 & 6584 A continuum-subtracted image of the
15' diameter halo has also been compared with recent proper motion measurements
of the central star and the present line profiles from the halo's inner edge.
Interaction with the ambient interstellar medium is suggested. The bright [N
II] 6584 A emitting shell must be running into this relatively inert halo with
a differential velocity of >= 25 km/s. The present results are compared with
currents models for the creation of planetary nebulae.


title: Clumpy tori around active galactic nuclei

abstract:
  We discuss the question whether the matter in dusty tori around active
galactic nuclei has a smooth or a clumpy structure. Nenkova, Ivezic & Elitzur
(2002) have argued that the lack of emission feature in the SEDs of type 1 AGN
galaxies combined with a clear absorption feature in type 2 AGN can be
explained if the circumnuclear dust is distributed in discrete clumps. Our aim
is to verify this. We use multi-dimensional radiative transfer models of smooth
and clumpy tori, and compare the SEDs of equivalent smooth and clumpy models.
We find that the 10 micron emission feature of the clumpy models, when seen
almost face-on, is not appreciably reduced compared to the equivalent smooth
models. Some of the clumpy models have a weak or even absent 10 micron feature,
but so do some of the smooth models. On the whole the SEDs of clumpy and smooth
tori are similar, but some details are different. The absorption feature seen
at edge-on inclinations appears to be less deep in the clumpy models than in
the smooth models, and the average flux in the near-infrared regime is stronger
in the clumpy models. Moreover, at these inclinations the clumpy models have a
slightly wider SED. Whether these differences are unique enough to be used as a
diagnostic for clumpiness of AGN tori is not yet clear.


title: Possible influence of Dark Energy on the Dark Matter Relic Abundance

abstract:
  Although a direct interaction between WIMP CDM candidates and scalar
Quintessence fields (sources of Dark Energy) poses severe phenomenological
threats, yet it is possible that the presence of Quintessence produces profound
deviations in the expansion rate of the early Universe at the moment of WIMP
decoupling, hence causing significant enhancements of the relic DM abundance.
We consider the occurrence of such a phenomenon in a couple of physically
interesting situations, kination and scalar-tensor theories of gravity where
the scalar component plays the role of Quintessence. The consequences for
supersymmetric DM candidates are briefly discussed.


title: 30 Doradus - a Template for "Real Starbursts"?

abstract:
  30 Doradus is the closest massive star forming region and the best studied
template of a starburst. In this conference paper we first summarize the
properties of 30 Doradus and its stellar core, R136. We discuss the effects of
insufficient spatial resolution and cluster density profiles on dynamical mass
estimates of super star clusters, and show that their masses can be easily
overestimated by a factor of ten or more. From a very simple model, with
R136-like clusters as representative building blocks, we estimate typical
luminosities of the order 10^11 L_o for starburst galaxies.


title: The Fractal Dimension of Projected Clouds

abstract:
  The interstellar medium seems to have an underlying fractal structure which
can be characterized through its fractal dimension. However, interstellar
clouds are observed as projected two-dimensional images, and the projection of
a tri-dimensional fractal distorts its measured properties. Here we use
simulated fractal clouds to study the relationship between the tri-dimensional
fractal dimension (D_f) of modeled clouds and the dimension resulting from
their projected images. We analyze different fractal dimension estimators: the
correlation and mass dimensions of the clouds, and the perimeter-based
dimension of their boundaries (D_per). We find the functional forms relating
D_f with the projected fractal dimensions, as well as the dependence on the
image resolution, which allow to estimatethe "real" D_f value of a cloud from
its projection. The application of these results to Orion A indicates in a
self-consistent way that 2.5 < D_f < 2.7 for this molecular cloud, a value
higher than the result D_per+1 = 2.3 some times assumed in literature for
interstellar clouds.


title: Biases in abundance derivations for metal-rich nebulae

abstract:
  Using ab-initio photoionization models of giant HII regions, we test methods
for abundance determinations based on a direct measurement of the electron
temperature, now possible even for moderate to high-metallicity objects. We
find that, for metallicities larger than solar, the computed abundances deviate
systematically from the real ones, generally by larger amounts for more
metal-rich HII regions. We discuss the reasons for this, and present diagrams
allowing the reader to better understand the various factors coming into play.
We briefly discuss less classical methods to derive abundances in metal-rich
HII regions. In particular, we comment on the interest of the oxygen and carbon
recombination lines. We also show that, contrary to the case of giant HII
regions, the physical conditions in bright extragalactic planetary nebulae are
such that their chemical composition can be accurately derived even at high
metallicities. Thus, extragalactic planetary nebulae are promising potential
probes of the metallicity of the interstellar medium in the internal parts of
spiral galaxies as well as in metal-rich elliptical galaxies.


title:
Multi-fluid shocks in clusters of galaxies: entropy, sigma_ v-T, M-T and
  L_x-T scalings

abstract:
  The nonthermal phenomena in clusters of galaxies are considered in the
context of the hierarchical model of cosmic structure formation by accretion
and merging of the dark matter (DM) substructures.Accretion and merging
processes produce large-scale gas shocks. The plasma shocks are expected to be
collisionless. In the course of cluster's aggregation, the shocks, being the
main gas-heating agent, generate turbulent magnetic fields and accelerate
energetic particles via collisionless multi-fluid plasma relaxation processes.
The intracluster gas heating and entropy production rate by a collisionless
shock may differ significantly from that in a single-fluid collisional shock.
Simple scaling relations for postshock ion temperature and entropy as functions
of shock velocity in strong collisionless multi-fluid shocks are presented. We
show that the multi-fluid nature of the collisionless shocks results in high
gas compression, reduced entropy production and modified sigma_v-T, M-T and
L_x-T scalings. The scaling indexes estimated for a simple model of a strong
accretion multi-fluid shock are generally consistent with observations. Soft
X-ray and extreme ultraviolet photons dominate the emission of strong accretion
shock precursors that appear as large-scale filaments. Magnetic fields,
turbulence and energetic particles constitute the nonthermal components
contributing into the pressure balance, energy transport and emission of
clusters. Nonthermal emission of energetic particles could be a test to
constrain the cluster properties.


title: High energy processes in microquasars

abstract:
  Microquasars are X-ray binary stars with the capability to generate
relativisticjets. It is expected that microquasars are gamma-ray sources,
because of the analogy with quasars and because the theoretical models predict
emission at such energy range. In addition, from observational arguments, there
are two microquasars that appear as the possible counterparts for two
unidentified high-energy gamma-ray sources.


title: Arbitrarily Degenerate Helium White Dwarfs as Donors in AM CVn Binaries

abstract:
  We apply the Deloye & Bildsten (2003) isentropic models for donors in
ultracompact low-mass X-ray binaries to the AM CVn population of ultracompact,
interacting binaries. The mass-radius relations of these systems' donors in the
mass range of interest ($M_2<0.1 \msun$) are not single-valued, but
parameterized by the donor's specific entropy. This produces a range in the
relationships between system observables, such as orbital period, $\Porb$, and
mass transfer rate, $\Mdot$. For a reasonable range in donor specific entropy,
$\Mdot$ can range over several orders of magnitude at fixed $\Porb$. We
determine the unique relation between $\Mdot$ and $M_2$ in the AM CVn systems
with known donor to accretor mass ratios, $q=M_2/M_1$. We use structural
arguments, as well as each system's photometric behavior, to place limits on
$\Mdot$ and $M_2$ in each. Most systems allow a factor of about 3 variation in
$\Mdot$, although V803 Cen, if the current estimates of its $q$ are accurate,
is an exception and must have $M_2 \approx 0.02 \msun$ and $\Mdot \approx
10^{-10} \msun$ yr$^{-1}$. Our donor models also constrain each donor's core
temperature, $T_c$, range and correlate $T_c$ with $M_2$. We examine how
variations in donor specific entropy across the white dwarf family
\citep{nele01a} of AM CVn systems affects this population's current galactic
distribution. Allowing for donors that are not fully degenerate produces a
shift in systems towards longer $\Porb$ and higher $\Mdot$ increasing the
parameter space in which these systems can be found. This shift increases the
fraction of systems whose $\Porb$ is long enough that their gravity wave (GW)
signal is obscured by the background of detached double white dwarf binaries
that dominate the GW spectrum below a frequency $\approx 2$ mHz.


title:
Interaction between stars and an inactive accretion disc in a galactic
  core

abstract:
  We discuss the structure of a central stellar cluster whose dynamics is
influenced by gravitation of a supermassive black hole and by the dissipative
interaction of orbiting stars with an accretion disc. We also take the effect
of disc self-gravity into account. We show that the cluster properties are
determined predominantly by the radial profile of the disc surface density. To
this aim we develop a simple steady-state model of the central cluster and we
estimate the rate at which stars migrate to the centre.
  This model is relevant for central regions of an active galactic nucleus
(AGN) containing a rather dense accretion medium. In passing we also briefly
mention a possibility that a fossil (inactive) disc could exist in the centre
of our own Galaxy. Such a hypothetical disc could perturb the motion of stars
and set them on highly elliptic trajectories with small pericentre distances.
The required mass of the disc is less than one percent of the central black
hole mass, i.e. below the upper limit permitted by present accuracy of the
orbital parameters of S-stars in the Galactic Centre.


title: Polarization signatures of strong gravity in black-hole accretion discs

abstract:
  We discuss the effects of strong gravity on the polarization properties of a
black hole accretion disc. The intrinsic polarization is computed taking into
account light scattered on the disc surface and using different approximations.
The gravitational field of a black hole influences the Stokes parameters of
reflected radiation propagating to a distant observer. The lamp-post model is
explored as an example of a specific geometrical arrangement relevant for AGNs.
The degree and the angle of polarization are computed as functions of the
observer inclination angle, of the inner radius of the disc emitting region,
and of other parameters of the model. The expected polarization should be
detectable by new generation polarimeters. This contribution extends results
reported in our recent paper (MNRAS 355, 1005; 2004).


title:
Radio emission from cosmic ray air showers: simulation results and
  parametrization

abstract:
  We have developed a sophisticated model of the radio emission from extensive
air showers in the scheme of coherent geosynchrotron radiation, providing a
theoretical foundation for the interpretation of experimental data from current
and future experiments. Having verified the model through comparison of
analytic calculations, Monte Carlo simulations and historical experimental
data, we now present the results of extensive simulations performed with our
Monte Carlo code. Important results are the absence of significant asymmetries
in the total field strength emission pattern, the spectral dependence of the
radiation, the polarization characteristics of the emission (allowing an
unambiguous test of the geomagnetic emission mechanism), and the dependence of
the radio emission on important air shower and observer parameters such as the
shower zenith angle, the primary particle energy, the depth of the shower
maximum and the observer position. An analytic parametrization incorporating
the aforementioned dependences summarizes our results in a particularly useful
way.


title: Phenomenological Quantum Gravity: the birth of a new frontier?

abstract:
  In the last years a general consensus has emerged that, contrary to
intuition, quantum-gravity effects may have relevant consequences for the
propagation and interaction of high energy particles. This has given birth to
the field of ``Phenomenological Quantum Gravity'' We review some of the aspects
of this new, very exciting frontier of Physics.


title: Edge-on T Tauri stars

abstract:
  Using the UVES echelle spectrograph at the ESO VLT we obtained
two-dimensional high-resolution (R = 50 000) spectra of the edge-on disk
objects HH30*, HK Tau B, and HV Tau C. For comparison purposes we also observed
with the same equipment both the classical T Tauri star HL Tau and the active
late-type star LDN 1551-9. The spectra of all three observed edge-on disks
consist of a T Tauri emission and absorption line spectrum with superimposed
jet emission lines. Analysis of the spectra confirmed that the disks are
completely opaque at visible wavelengths and that light from the central
objects reaches us only via scattering layers above and below the disk planes.
The central objects of our targets were found to be normal T Tauri stars
showing moderate but different amounts of veiling of their photospheric
spectra, indicating different accretion rates or evolutionary stages. We
suggest that all classical T Tauri stars (CTTSs) show this observed morphology
when viewed edge-on. Part of the jet emission from edge-on systems is directly
visible to us in the forbidden lines as well as in Halpha and He I, a finding
which contradicts the present paradigm of a pure magnetospheric accretion
origin for the formation of hydrogen and helium emission lines in moderately
active CTTSs. From a comparison with those Taurus-Auriga CTTSs for which the
inclination is reliably known, we conclude that the view angle of CTTS systems
is one of the key parameters governing apparent Halpha emission strength in the
T Tauri class. We discuss the various possible formation regions for the Na I D
lines and show that profiles similar to observed ones can be formed at the base
of the disk wind.


title:
Basic properties of galaxy clustering in the light of recent results
  from the Sloan Digital Sky Survey

abstract:
  We discuss some of the basic implications of recent results on galaxy
correlations published by the SDSS collaboration. In particular we focus on the
evidence which has been recently presented for the scale and nature of the
transition to homogeneity in the galaxy distribution, and results which
describe the dependence of clustering on luminosity. The two questions are in
fact strictly entangled, as the stability of the measure of the amplitude of
the correlation function depends on the scale at which the mean density becomes
well defined. We note that the recent results which indicate the convergence to
well defined homogeneity in a volume equivalent to that of a sphere of radius
70 Mpc/h, place in doubt previous detections of ``luminosity bias'' from
measures of the amplitude of the correlation function. We emphasize that the
way to resolve these issues is to first use, in volume limited samples
corresponding to different ranges of luminosity, the unnormalized two point
statistics to establish the scale (and value) at which the mean density becomes
well defined. We note also that the recent SDSS results for these statistics
are in good agreement with those obtained by us through analyses of many
previous samples, confirming in particular that the galaxy distribution is well
described by a fractal dimension D ~ 2 up to a scale of at least 20 Mpc/h. We
discuss critically the agreement of this new data with current theoretical
models.


title:
Preliminary results on galactic dark matter from the complete EROS2
  microlensing survey

abstract:
  The EROS-2 collaboration has conducted a survey of the Magellanic Clouds
between July 1996 and February 2003 (6.7 years), in order to search for
microlensing phenomena due to putative machos (massive astronomical compact
halo objects). About 55 million stars were monitored over 100 deg^2, typically
with 400 to 500 measurements per star, simultaneously in two wide passbands.
The full EROS-2 Magellanic Cloud data set was processed using the same program
chain, and a photometric database was constructed. The lightcurves of the
brightest 33 million stars were then searched for the characteristic signature
of microlensing phenomena, in the wide timescale range of 1 to 1000 days
(corresponding to macho masses ranging from about 0.01 solar mass to a few
hundred solar masses). The sensitivity of this new analysis is better by a
factor 4. The new EROS-2 microlensing candidates towards the LMC and the
corresponding (preliminary) final limits from EROS-2 on the macho content of
the halo are presented; they are by far not numerous enough to account for the
galactic dark matter. We have also followed, whenever possible, the
microlensing candidates that were previously published by the EROS and MACHO
collaborations. 1 MACHO and 2 EROS LMC candidates have shown subsequent
variability and cannot be considered to be serious candidates.


title: The calcium isotopic anomaly in magnetic CP stars

abstract:
  Chemically peculiar stars in the magnetic sequence can show the same isotopic
anomaly in calcium previously discovered for mercury-manganese stars in the
non-magnetic sequence. In extreme cases, the dominant isotope is the exotic
48^Ca. Measurements of Ca II lines arising from 3d-4p transitions reveal the
anomaly by showing shifts up to 0.2 AA for the extreme cases - too large to be
measurement errors. We report measurements of miscellaneous objects, including
two metal-poor stars, two apparently normal F-stars, an Am-star, and the N-star
U Ant. Demonstrable anomalies are apparent only for the Ap stars. The largest
shifts are found in rapidly oscillating Ap stars and in one weakly magnetic Ap
star, HD 133792. We note the possible relevance of these shifts for the GAIA
mission.


title: Keynote Lecture: Galactic and Extragalactic Bubbles

abstract:
  The observational and theoretical state of Galactic and extragalactic bubbles
are reviewed. Observations of superbubbles are discussed, with some emphasis on
nearby bubbles such as the Local Bubble (LB) and the Loop I superbubble (LI).
Analytical bubble theory is revisited, and similarity solutions, including the
time-dependent energy input by supernova explosions according to a Galactic
initial mass function (IMF), are studied. Since the agreement with observations
is not convincing in case of the LB, we present high resolution 3D AMR
simulations of the LB and LI in an inhomogeneous background medium. It is
demonstrated that both the morphology and recently published FUSE data on OVI
absorption line column densities can be well understood, if the LB is the
result of about 20 supernova explosions from a moving group, and the LB age is
about 14.7 Myrs.


title: The XMM-Newton view of PG quasars: II. Properties of the Fe K-alpha line

abstract:
  The properties of the fluorescence Fe K-alpha emission lines of a sample of
38 quasars (QSOs) observed with XMM-Newton are studied. These objects are
included in the optically selected sample from the Palomar-Green (PG) Bright
Quasar Survey with an X-ray luminosity 1.3E43<L(2-10 keV)<5.1E45 ergs/s and
z<1.72. For each object in the sample, we investigated the presence of both
narrow and broad iron lines in detail. A total of 20 out of the 38 QSOs show
evidence of an Fe K-alpha emission line with a narrow profile. The majority of
the lines are consistent with an origin in low ionization material, which is
likely to be located in the outer parts of the accretion disk, the molecular
torus, and/or the Broad Line Region. The average properties of the narrow Fe
K-alpha emission line observed in the sample are similar to those of Seyfert
type galaxies as inferred from recent XMM-Newton and Chandra studies. A broad
line has been significantly detected in only three objects. Furthermore, we
studied the relationship between the equivalent width (EW) of the iron line and
the hard band X-ray luminosity for radio quiet quasars. The analysis indicates
that no clear correlation between the strength of the line and the hard X-ray
luminosity is present, and our results do not show compelling evidence for an
anticorrelation between these two quantities, i.e. the so-called X-ray Baldwin
effect.


title: Atomic and Molecular Gas in Colliding Galaxy Systems: I. The Data

abstract:
  We present HI and CO(1-0) interferometric observations of 10 comparable-mass
interacting systems obtained at the Very Large Array (VLA) and the Owens Valley
Radio Observatory (OVRO) millimeter array. The primary intent of this study is
to investigate the response of cold gas during the early stages of collision of
massive disk galaxies. The sample sources are selected based on their
luminosity (M_B < -19), projected separation (5-40 kpc), and single dish
CO(1-0) content (S_{CO} > 20 Jy km/s). These selection criteria result in a
sample that primarily consists of systems in the early stages of an interaction
or a merger. Despite this sample selection, 50% of the systems show long HI
tidal tails indicative of a tidal disruption in a prograde orbit. In addition,
all (4/4) of the infrared luminous pairs (LIRGs) in the sample show long HI
tails, suggesting that the presence of a long HI tail can be a possible
signature of enhanced star formation activity in a collision of gas-rich
galaxies. More than half of the groups show a displacement of HI peaks from the
stellar disks. The CO(1-0) distribution is generally clumpy and widely
distributed, unlike in most IR-selected late stage mergers -- in fact, CO peaks
are displaced from the stellar nucleus in 20% (4/18) of the galaxies with
robust CO detection. HI and CO(1-0) Position Velocity Diagrams (PVDs) and
rotation curves are also presented, and their comparison with the numerical
simulation analyzed in Paper I show evidence for radial inflow and wide
occurrences of nuclear molecular rings. These results are further quantified by
examining physical and structural parameters derived in comparison with
isolated systems in the BIMA SONG sample in our forthcoming paper.


title:
Earth-mass dark-matter haloes as the first structures in the early
  Universe

abstract:
  The Universe was nearly smooth and homogeneous before a redshift of z = 100,
about 20 million years after the Big Bang. After this epoch, the tiny
fluctuations imprinted upon the matter distribution during the initial
expansion began to collapse because of gravity. The properties of these
fluctuations depend on the unknown nature of dark matter, the determination of
which is one of the biggest challenges in present-day science. Here we report
supercomputer simulations of the concordance cosmological model, which assumes
neutralino dark matter (at present the preferred candidate), and find that the
first objects to form are numerous Earth-mass dark-matter haloes about as large
as the Solar System. They are stable against gravitational disruption, even
within the central regions of the Milky Way. We expect over 10^15 to survive
within the Galactic halo, with one passing through the Solar System every few
thousand years. The nearest structures should be among the brightest sources of
gamma-rays (from particle-particle annihilation).


title:
The Rise and Fall of the Cosmic String Theory for Cosmological
  Perturbations

abstract:
  The cosmic string theory for cosmological fluctuations is a good example of
healthy scientific progress in cosmology. It is a well defined physically
motivated model that has been tested by cosmological observations and has been
ruled out as a primary source of primordial fluctuations. Until about fifteen
years ago, the cosmic string theory of cosmological perturbations provided one
of the two physically motivated candidate theories for the generation of
primordial perturbations. The cosmological data that appeared during the last
decade have been compared with the well defined predictions of the theory and
have ruled out cosmic strings as a primary source of primordial cosmological
perturbations. Since cosmic strings are predicted to form after inflation in a
wide range of microphysical theories including (supersymmetric and fundamental
string theories) their observational bounds may serve a source of serious
constraints for these theories. This is a pedagogical review of the historical
development, the main predictions of the cosmic string theory and the
constraints that have been imposed on it by cosmological observations. Recent
lensing events that could be attributed to lighter cosmic strings are also
discussed.


title: BBN and the Primordial Abundances

abstract:
  The relic abundances of the light elements synthesized during the first few
minutes of the evolution of the Universe provide unique probes of cosmology and
the building blocks for stellar and galactic chemical evolution, while also
enabling constraints on the baryon (nucleon) density and on models of particle
physics beyond the standard model. Recent WMAP analyses of the CBR temperature
fluctuation spectrum, combined with other, relevant, observational data, has
yielded very tight constraints on the baryon density, permitting a detailed,
quantitative confrontation of the predictions of Big Bang Nucleosynthesis with
the post-BBN abundances inferred from observational data. The current status of
this comparison is presented, with an emphasis on the challenges to astronomy,
astrophysics, particle physics, and cosmology it identifies.


title:
Chondrule-Forming Shock Fronts in the Solar Nebula: A Possible Unified
  Scenario for Planet and Chondrite Formation

abstract:
  Chondrules are mm-sized spherules found throughout primitive, chondritic
meteorites. Flash heating by a shock front is the leading explanation of their
formation. However, identifying a mechanism for creating shock fronts inside
the solar nebula has been difficult. In a gaseous disk capable of forming
Jupiter, the disk must have been marginally gravitationally unstable at and
beyond Jupiter's orbit. We show that this instability can drive inward spiral
shock fronts with shock speeds of up to about 10 km/s at asteroidal orbits,
sufficient to account for chondrule formation. Mixing and transport of solids
in such a disk, combined with the planet-forming tendencies of gravitational
instabilities, results in a unified scenario linking chondrite production with
gas giant planet formation.


title: High-Energy Neutrino Astronomy

abstract:
  Kilometer-scale neutrino detectors such as IceCube are discovery instruments
covering nuclear and particle physics, cosmology and astronomy. Examples of
their multidisciplinary missions include the search for the particle nature of
dark matter and for additional small dimensions of space. In the end, their
conceptual design is very much anchored to the observational fact that Nature
accelerates protons and photons to energies in excess of 10^{20} and 10^{13}
eV, respectively. The cosmic ray connection sets the scale of cosmic neutrino
fluxes. In this context, we discuss the first results of the completed AMANDA
detector and the reach of its extension, IceCube. Similar experiments are under
construction in the Mediterranean. Neutrino astronomy is also expanding in new
directions with efforts to detect air showers, acoustic and radio signals
initiated by neutrinos with energies similar to those of the highest energy
cosmic rays.


title:
Probing decisive answers to dark energy questions from cosmic
  complementarity and lensing tomography

abstract:
  We study future constraints on dark energy parameters determined from several
combinations of CMB experiments, supernova data, and weak lensing surveys with
and without tomography. In this analysis, we look in particular for
combinations that will bring the uncertainties to a level of precision tight
enough (a few percent) to answer decisively some of the dark energy questions.
We probe the dark energy using two variants of its equation of state, and its
energy density.We consider a set of 13 cosmological and systematic parameters,
and assume reasonable priors on the lensing and supernova systematics. We
consider various lensing surveys: a wide survey with f_{sky}=0.7, and with 2
(WLT2) and 5 (WLT5) tomographic bins; a deep survey with 10 bins (WLT10). The
constraints found from Planck, 2000 supernovae with z_max=0.8, and WLT2 are:
{sigma(w_0)=0.086, sigma(w_1)=0.069}, {sigma(w_0)=0.088, sigma(w_a)=0.11}, and
{sigma(E_1)=0.029, sigma(E_2)=0.065}. With 5 bins, we find {sigma(w_0)=0.04,
sigma(w_1)=0.034}, {sigma(w_0)=0.041, sigma(w_a)=0.056}, and {sigma(E_1)=0.012,
sigma(E_2)=0.049}. Finally, we find from Planck, 2000 supernovae with
z_max=1.5, and WLT10 with f_{sky}=0.1: {sigma(w_0)=0.032, sigma(w_1)=0.027},
{sigma(w_0)=0.033, sigma(w_a)=0.040}, and {sigma(E_1)=0.01, sigma(E_2)=0.04}.
Although some worries remain about other systematics, our study shows that
after the combination of the 3 probes, lensing tomography with many redshift
bins and large coverages of the sky has the potential to add key improvements
to the dark energy parameter constraints. However, the requirement for very
ambitious and sophisticated surveys in order to achieve some of the constraints
or to improve them suggests the need for new tests to probe the nature of dark
energy in addition to constraining its equation of state. (Abriged)


title: A Gemini Observation of the Anomalous X-ray Pulsar 1RXS J170849-400910

abstract:
  The anomalous X-ray pulsars (AXPs) represent a growing class of neutron stars
discovered at X-ray energies. While the nature of their multi-wavelength
emission mechanism is still under debate, evidence has been recently
accumulating in favor of their magnetar nature. Their study in the optical and
infrared (IR) wavelengths has recently opened a new window to constrain the
proposed models. We here present a brief overview of AXPs and our Gemini-South
observation of 1RXS J170849-400910, which is a relatively bright AXP discovered
with ROSAT and later found to be an 11 s X-ray pulsar by ASCA. The observation
was taken with the near-IR imager Flamingos in J (1.25 um), H (1.65 um), and Ks
(2.15 um). We confirm the recent detection by Israel et al. (2003) of a source
coincident with the Chandra source (candidate `A'). Our derived magnitudes of J
= 20.6 (0.2), H = 18.6 (0.2), and Ks = 17.1 (0.2) are consistent with those
derived by Israel et al. (2003), and indicate that if this source is indeed the
IR counterpart to 1RXS J170849-400910, then there is no evidence of variability
from this AXP. However, given the lack of IR variability and the relatively
high IR to X-ray flux of this source when compared to the other AXPs, we
conclude that this source is unlikely the counterpart of the AXP, and that the
other source (candidate `B') within the Chandra error circle should not be
ruled out as the counterpart. Further monitoring of these sources and a deep
observation of this complex field are needed to confirm the nature of these
sources and their association with the AXP.


title: Dynamics of Quintessence with Thermal Interactions

abstract:
  The cosmological dynamics of minimally coupled scalar field that couple to
the background matter with thermal interactions is investigated in exponential
potential. The conditions for the existence and stability of various critical
points as well as their cosmological implications are obtained. Although we
show that the effects of thermal interaction such as depressing the
equation-of-state parameter of quintessence, is only important at the early
time, the evolution of equation-of-state parameter of quintessence is
manifested. The upper bound is required on the coupling between quintessence
and relativistic relic particles such as photons and neutrinos.


title: On the Magnetic Field in the Kiloparsec-Scale Jet of Radio Galaxy M 87

abstract:
  Several low-power kiloparsec-scale jets in nearby radio galaxies are known
for their synchrotron radiation extending up to optical and X-ray photon
energies. Here we comment on high-energy gamma-ray emission of one particular
object of this kind, i.e. the kiloparsec-scale jet of M 87 radio galaxy,
resulting from comptonization of the starlight photon field of the host galaxy
by the synchrotron-emitting jet electrons. In the analysis, we include
relativistic bulk velocity of the jet, as well as the Klein-Nishina effects. We
show, that upper limits to the kiloparsec-scale jet inverse-Compton radiation
imposed by HESS and HEGRA Cherenkov Telescopes - which detected a variable
source of VHE gamma-ray emission within 0.1 deg (~30 kpc) of the M 87 central
region - give us an important constraint on the magnetic field strength in this
object, namely that the magnetic field cannot be smaller than the equipartition
value (referring solely to the radiating electrons) in the brightest knot of
the jet, and most likely, is even stronger. In this context, we point out a
need for the amplification of the magnetic energy flux along the M 87 jet from
the sub-parsec to kiloparsec scales, suggesting the turbulent dynamo as a
plausible process responsible for the aforementioned amplification.


title: VST - VLT Survey Telescope Integration Status

abstract:
  The VLT Survey Telescope (VST) is a 2.6m aperture, wide field, UV to I
facility, to be installed at the European Southern Observatory (ESO) on the
Cerro Paranal Chile. VST was primarily intended to complement the observing
capabilities of VLT with wide-angle imaging for detecting and
pre-characterising sources for further observations with the VLT.


title:
Observations of the Blandford-Znajek and the MHD Penrose processes in
  computer simulations of black hole magnetospheres

abstract:
  In this paper we report the results of axisymmetric relativistic MHD
simulations for the problem of Kerr black hole immersed into a rarefied plasma
with ''uniform'' magnetic field. The long term solution shows properties which
are significantly different from those of the initial transient phase studied
recently by Koide(2003). The topology of magnetic field lines within the
ergosphere is similar to that of the split-monopole model with a strong current
sheet in the equatorial plane. Closer inspection reveals a system of isolated
magnetic islands inside the sheet and ongoing magnetic reconnection. No regions
of negative hydrodynamic ''energy at infinity'' are seen inside the ergosphere
and the so-called MHD Penrose process does not operate. Yet, the rotational
energy of the black hole continues to be extracted via purely electromagnetic
mechanism of Blandford and Znajek(1977). However, this is not followed by
development of strong relativistic outflows from the black hole. Combined with
results of other recent simulations this signals a potential problem for the
standard MHD model of relativistic astrophysical jets should they still be
observed at distances as small as few tens of gravitational radii from the
central black hole.


title:
Adiabatic And Entropy Perturations In Inflationary Models Based On
  Non-linear Sigma Model

abstract:
  The scalar perturbations in inflationary models, based on a two-component
diagonal non-linear sigma model, are considered. For inhomogeneities generated
at an inflationary stage, the law of motion of the comoving curvature ${\cal
R}$ is obtained (without using the slow roll approximations). A formal
expressions for the power spectrum and its spectral index are obtained, which
are valid and after the slow-roll stage. As an example, an inflationary model
with a massive scalar field and quadratic curvature corrections is studied
numerically.


title: Long-slit and Fabry-Perot spectroscopy of collisional ring galaxy Arp 10

abstract:
  We present results of Fabry-Perot and long-slit spectroscopy of the peculiar
galaxy Arp 10. The ionized gas velocity field shows evidence for significant
radial motions in both outer and inner galactic rings. Long-slit spectroscopy
reveals gradients of age and metallicity of stellar population in agreement
with the propagating nature of star formation in the galaxy. We present strong
evidence that a small ``knot'' at 5 arcsec from the center of Arp 10 is its
dwarf elliptic satellite, the most probable ``intruder'' responsible for
triggering the expanding rings in Arp 10.


title:
Elementary Heating Events - Magnetic Interactions Between Two Flux
  Sources. III Energy Considerations

abstract:
  The magnetic field plays a crucial role in heating the solar corona, but the
exact energy release mechanism(s) is(are) still unknown. Here, we investigate
in detail, the process of magnetic energy release in a situation where two
initially independent flux systems are forced into each other. Work done by the
foot point motions goes in to building a current sheet in which magnetic
reconnection takes place. The scaling relations of the energy input and output
are determined as functions of the driving velocity and the strength of fluxes
in the independent flux systems. In particular, it is found that the energy
injected into the system is proportional to the distance travelled not the rate
of travel. Similarly, the rate of Joule dissipation is related to the distance
travelled. Hence, rapidly driven foot points lead to bright, intense, but
short-lived events, whilst slowly driven foot points produce weaker, but
longer-lived brightenings. Integrated over the lifetime of the events both
would produce the same heating if all other factors were the same. A strong
overlying field has the affect of creating compact flux lobes from the sources.
These appear to lead to a more rapid injection of energy, as well as a more
rapid release of energy. Thus, the stronger the overlying field the more
compact and more intense the heating. This means observers must know the rate
of movement of the magnetic fragments involved in an events, as well as
determine the strength and orientation of the surrounding field to be able to
predict anything about the energy dissipated.


title:
Metallicity and HI Column Density Properties of Damped Lyman-$\alpha$
  Systems

abstract:
  Based on the disk galaxy formation theory within the framework of standard
LCDM hierarchical picture, we selected modelled DLAs, according to their
observational criterion, by Monte Carlo simulation with the random inclinations
being considered, to examine their observed properties. By best-fitting the
predicted metallicity distribution to the observed ones, we get the effective
yield for DLAs about 0.25Z_sun, which is comparable to those for SMC and LMC.
And the predicted distribution is the same as that of observation at the
significant level higher than 60%. The predicted column density distribution of
modelled DLAs is compared with the observed ones with the corresponding number
density, gas content being discussed. We found that the predicted number
density n(z) at redshift 3 agree well with the observed value, but the gas
content \Omega_DLA is about 3 times larger than observed since our model
predicts more DLA systems with higher column density. It should be noted that
the predicted star formation rate density contributed by DLAs is consistent
with the most recent observations if the star formation timescale in DLAs is
assumed to be 1 to 3 Gyr. Meanwhile, the connection between DLAs and LBGs is
discussed by comparing their UV luminosity functions which shows that the DLAs
host galaxies are much fainter than LBGs. We also predict that only few percent
of DLAs can host LBGs which is also consistent with current observations.
However, there is a discrepancy between model prediction and observation in the
correlation between metallicity and HI column density for DLAs. We suggest that
this could result from either the inadequacy of Schmidt-type star formation law
at high redshift, the diversities of DLA populations, or the model limitations.


title: On the distance, reddening and progenitor of V838 Mon

abstract:
  Extensive optical and infrared photometry as well as low and high resolution
spectroscopy are used as inputs in deriving robust estimates of the reddening,
distance and nature of the progenitor of V838 Mon. The reddening is found to
obey the R_V=3.1 law and amounts to (i) E(B-V)=0.86 from the interstellar NaI
and KI lines, (ii) E(B-V)=0.88 from the energy distribution of the B3V
component and (iii) E(B-V)=0.87 from the progression of extinction along the
line of sight. The adopted E(B-V)=0.87(+/-0.01) is also the amount required by
fitting the progenitor with theoretical isochrones of appropriate metallicity.
The distance is estimated from (a) the galactic kinematics of the three
components of the interstellar lines, (b) the amount of extinction vs the HI
column density and vs the dust emission through the whole Galaxy in that
direction, from (c) spectrophotometric parallax to the B3V companion, from (d)
comparison of the observed color-magnitude diagram of field stars with 3D
stellar population models of the Galaxy, from (e) comparison of theoretical
isochrones with the components of the binary system in quiescence and found to
be around 10 kpc. Pre-outburst optical and IR energy distributions show that
the component erupting in 2002 was brighter and hotter than the B3V companion.
The best fit is obtained for a 50,000 K source, 0.5 mag brighter than the B3V
companion. Comparison with theoretical isochrones suggests an age of 4 million
year for the system and a mass around 65 M(sun) for the progenitor of the
outbursting component, which at the time of the outburst was approaching the
Carbon ignition stage in its core. The 2002 event is probably just a shell
thermonuclear event in the outer envelope of the star.


title: On gravitational lensing by deflectors in motion

abstract:
  Gravitational lensing by a spinning deflector in translational motion
relative to the observer is discussed in the weak field, slow motion
approximation. The effect of rotation, which generates an intrinsic
gravito-magnetic field, separates from that due to radial motion. Corrections
to the lens equation, deflection angle and time delay are derived.


title:
Quantitative H and K band spectroscopy of Galactic OB-stars at medium
  resolution

abstract:
  In this paper we have analyzed 25 Galactic O and early B-stars by means of H
and K band spectroscopy, with the primary goal to investigate to what extent a
lone near-IR spectroscopy is able to recover stellar and wind parameters
derived in the optical. Most of the spectra have been taken with SUBARU IRCS,
at a resolution of 12,000, and with a very high S/N (200 or better). In order
to synthesize the strategic H/He lines, we have used our recent, line-blanketed
version of FASTWIND. First we investigated the predicted behaviour of the
strategic lines. In contradiction to what one expects from the optical in the
O-star regime, almost all photospheric H/HeI/HeII H/K band lines become
stronger if the gravity decreases. Concerning H and HeII, this finding is
related to the behaviour of Stark broadening as a function of electron density,
which in the line cores is different for members of lower (optical) and higher
(IR) series. Regarding HeI, the predicted behaviour is due to some subtle NLTE
effects resulting in a stronger overpopulation of the lower level when the
gravity decreases. For most of our objects, we obtained good fits, except for
the line cores of Br_gamma in early O-stars with significant mass-loss, where
this discrepancy might be an indirect effect of clumping. After having derived
the stellar and wind parameters from the IR, we have compared them to results
from previous optical analyses. Overall, the IR results coincide in most cases
with the optical ones within the typical errors usually quoted for the
corresponding parameters, i.e, an uncertainty in Teff of 5%, in log g of 0.1
dex and in Mdot of 0.2 dex, with lower errors at higher wind densities.
Outliers above the 1-sigma level where found in four cases with respect to log
g and in two cases for Mdot.


title: New Catalogs of Compact Radio Sources in the Galactic Plane

abstract:
  Archival data have been combined with recent observations of the Galactic
plane using the Very Large Array to create new catalogs of compact centimetric
radio sources. The 20 cm source catalog covers a longitude range of -20 deg < l
< 120 deg; the latitude coverage varies from +- 0.8 deg to +- 2.7 deg. The
total survey area is ~331 sq deg; coverage is 90% complete at a flux density
threshold of ~14 mJy, and over 5000 sources are recorded. The 6 cm catalog
covers 43 sq deg in the region -10 deg < l < 42 deg, |b| < 0.4 deg to a 90%
completeness threshold of 2.9 mJy; over 2700 sources are found. Both surveys
have an angular resolution of ~6 arcsec. These catalogs provide a 30% (at 20
cm) to 50% (at 6 cm) increase in the number of high-reliability compact sources
in the Galactic plane, as well as providing greatly improved astrometry,
uniformity, and reliability; they should prove useful for comparison with new
mid- and far-infrared surveys of the Milky Way.


title: The young, active binary star EK Draconis

abstract:
  EK Dra (HD 129333) is a young, active, nearby star that is orbited by a low
mass companion. By combining new speckle observations with old and new radial
velocity measurements we find that the orbit is highly eccentric with
e=0.82\pm0.03, and we derive the true masses of both components. The masses are
$0.9\pm0.1 {\rm M}_\odot$ and $0.5\pm0.1 {\rm M}_\odot$, for the primary and
secondary, respectively. From high resolution spectra we derive a new $T_{\rm
eff}$ of $5700\pm70$ K, and a $\log g$ of $4.37\pm0.10$, which is different to
previous estimates. However, the new spectroscopic distance differs by only
5.8% to the distance derived by parallax measurement of the Hipparcos satellite
and thus the stellar parameters are presumably more realistic than older
determinations. We derive a somewhat higher value for the metallicity of
$[Fe/H]=-0.16\pm0.07$. EK Dra turns out to be one of the few nearby young stars
which will evolve similar to the sun. The precise radial velocity measurements
taken in the course of this program also allows us to shed more light on to the
activity of this star. In 2001 and 2002 we find a periodic signal of the radial
velocity variations with a period of $2.767\pm0.005$ days which we interpret as
the rotation period. This signal vanishes in 2003. However the signal can be
recovered if only the spectra in which the photospheric lines are asymmetric
are used. On the other hand, we do not find a close correlation between the
asymmetry of photospheric lines and the radial velocity.


title: On Multiwavelength Emission and Morphology of Large-Scale Quasar Jets

abstract:
  We propose that the knots of the large-scale jets in powerful radio sources
represent moving and separate portions of the jet matter, with the excess
kinetic power. This can explain many morphological properties of quasar jets -
like high knot-to-interknot brightness contrasts, frequency-independent knot
profiles and almost universal extents of the knot regions - independently of
the exact emission mechanisms responsible for producing broad-band jet
emission. We briefly discuss a possible connection between this scenario and
the idea of highly modulated/intermittent activity of the jet engine.


title: On the Magnetic Field in Quasar and FR II Large-Scale Jets

abstract:
  Here we report systematic comparison of the spectral properties of
large-scale jets, hotspots and extended lobes in quasars and FR II radio
galaxies recently observed with Chandra and ASCA. We argue that if the strong
X-ray emission of the jet knots in these objects results from comptonisation of
the CMB photons, as usually considered, the powerful large-scale jets are most
likely far from the minimum-power condition in the sense that the magnetic
field thereby is below equipartition. We also show that the X-ray emission of
the hot-spots and lobes in the compiled dataset agrees with the minimum-power
condition. In this context, we point out the need for substantial amplification
of the magnetic field within the terminal shocks of powerful large-scale jets
of quasars and FR II sources.


title:
A planet-sized transiting star around OGLE-TR-122 - Accurate mass and
  radius near the Hydrogen-burning limit

abstract:
  We report the discovery and characterisation of OGLE-TR-122b, the smallest
main-sequence star to date with a direct radius determination. OGLE-TR-122b
transits around its solar-type primary every 7.3-days. With M=0.092+-0.009 Mo
and R=0.120 +0.024-0.013 Ro, it is by far the smallest known eclipsing M-dwarf.
The derived mass and radius for OGLE-TR-122b are in agreement with the
theoretical expectations. OGLE-TR-122b is the first observational evidence that
stars can indeed have radii comparable or even smaller than giant planets. In
such cases, the photometric signal is exactly that of a transiting planet and
the true nature of the companion can only be determined with high-resolution
spectroscopy.


title: On the Magnetic Field in Kpc-Scale Jets of FR I Radio Galaxies

abstract:
  The energy content of large-scale jets in FR I radio galaxies is still an
open issue. Here we show that upper limits on the high-energy and very
high-energy gamma-ray emission of the kpc-scale jet in M 87 radio galaxy
imposed by EGRET, Whipple, and - most importantly - HEGRA and HESS
observations, provide important constraints on the magnetic field strength in
this object. In particular, a non-detection of gamma-ray radiation from the
brightest part of this jet (knot A), expected from the inverse-Compton
scattering of the starlight photons by the synchrotron-emitting jet electrons,
implies that the magnetic field cannot be smaller than the equipartition value
(referring solely to the radiating ultrarelativistic electrons), and most
likely, is even stronger. In this context, we point out several consequences of
the obtained result for the large-scale jet structures in FR I radio galaxies
and the M 87 jet in particular. For example, we discuss a potential need for
amplification of the magnetic field energy flux along these jets (from sub-pc
to kpc scales), suggesting a turbulent dynamo as a plausible process
responsible for the aforementioned amplification.


title: Matter Power Spectrum for Convex Quartessence

abstract:
  The possibility of unifying dark-matter and dark-energy has recently
attracted considerable interest. In this so called quartessence scenario, a
single component is responsible for both the clustering of matter and the
accelerated expansion of the universe. A model archetype for such scenario is
provided by the Chaplygin gas. Although this model is in agreement with the
data on the expansion history, problems arise in the power spectrum of density
fluctuations for adiabatic perturbations. In this contribution we consider
other quartessence models and confirm that instabilities and oscillations in
the matter power spectrum are a characteristic of more generic quartessence
models, namely those with a convex equation of state. We show that, as in the
Chaplygin case, this kind of problem can be solved by considering intrinsic
non-adiabatic perturbations such that, as an initial condition, the perturbed
fluid is gradient pressure free. We also discuss how the problems of adiabatic
quartessence can be circumvented by other types of equations of state.


title:
Signatures of Primordial Non-Gaussianity in the Large-Scale Structure of
  the Universe

abstract:
  We discuss how primordial (e.g. inflationary) non-Gaussianity in the
cosmological perturbations is left imprinted in the Large-Scale Structure of
the universe. Our findings show that the information on the primordial
non-Gaussianity set on super-Hubble scales flows into Post-Newtonian terms,
leaving an observable imprint in the Large-Scale Structure. Future
high-precision measurements of the statistics of the dark matter density and
peculiar velocity fields will allow to pin down the primordial non-Gaussianity,
thus representing a tool complementary to studies of the Cosmic Microwave
Background anisotropies.


title: Doppler follow-up of OGLE planetary transit candidates in Carina

abstract:
  We present the results of our high-resolution spectroscopic follow-up of 42
planetary transit candidates in Carina from the OGLE survey. This follow-up has
already allowed the discovery of three new transiting exoplanets, OGLE-TR-111,
113 and 132, presented in earlier Letters (Bouchy et al. 2004, Pont et al.
2004). Here we analyse the data for the remaining 39 candidates. The radial
velocity data show that most of them are eclipsing binaries, in very varied
configurations. Precise radial velocity orbits were derived for 15 binaries,
revealing 9 transits of small stars (generally M-dwarfs) in front of F-G
dwarfs, 1 grazing equal-mass eclipsing binary, 4 triple and 1 quadruple
systems. A remaining 14 systems appear binary, but the exact orbit is uncertain
or was not determined. 2 objects do not show any radial velocity variations in
phase with the transit signal, and 6 do not possess spectral lines strong
enough for a reliable cross-correlation function to be measured. Among these
last two categories, up to 6 objects are suspected false positives of the
photometric transit detection. Finally 2 objects are unsolved cases that
deserve further observations. Our study illustrates the wide variety of cases
that can mimic photometric planetary transits, and the importance of
spectroscopic follow-up. Multi-fiber capacities and an optimized follow-up
strategy, which we present here, can help deal with the high number of
candidates that are likely to turn up in the near future. (abridged)


title:
The extreme flare in III Zw 2: Evolution of a radio jet in a Seyfert
  galaxy

abstract:
  A very detailed monitoring of a radio flare in the Seyfert I galaxy III Zw 2
with the VLA and the VLBA is presented. The relative astrometry in the VLBA
observations was precise on a level of a few microarcseconds. Spectral and
spatial evolution of the source are closely linked and these observations
allowed us to study in great detail a textbook example of a synchrotron
self-absorbed jet. We observe a phase where the jet gets frustrated, without
expansion and no spectral evolution. Then the jet breaks free and starts to
expand with apparent superluminal motion. This expansion is accompanied by a
strong spectral evolution. The results are a good confirmation of synchrotron
theory and equipartition for jets.


title: Formation of Ultracompact X-ray Binaries in Dense Star Clusters

abstract:
  Bright, ultracompact X-ray binaries observed in dense star clusters, such as
Galactic globular clusters, must have formed relatively recently, since their
lifetimes as persistent bright sources are short (e.g., ~10^8 yr above 10^36
erg/s for a 1.4 Msun neutron star accreting from a degenerate helium companion
with an initial mass of ~0.2 Msun). Therefore, we can use the present
conditions in a cluster core to study possible dynamical formation processes
for these sources. Here we show that direct physical collisions between neutron
stars and red giants can provide a sufficient formation rate to explain the
observed numbers of bright sources. These collisions produce tight, eccentric
neutron star -- white dwarf binaries that decay to contact by gravitational
radiation on timescales ~10^6-10^10 yr, usually shorter and often much shorter
than the cluster age.


title:
Merging of globular clusters within inner galactic regions. I. Do they
  survive the tidal interaction?

abstract:
  The main topic of this paper is the investigation of the modes of interaction
of globular clusters (GCs) moving in the inner part of a galaxy. This is
tackled by means of high-resolution N-body simulations, whose first results are
presented in this article. Our simulations dealt with primordial very massive
(order of 10^7 solar masses) GCs that were able to decay, because of dynamical
friction, into the inner regions of triaxial galaxies on a time much shorter
than their internal relaxation time. To check the disruptive role of both tidal
forces and GC-GC collisions, we maximised the tidal interaction considering GCs
on quasi-radial orbits.
  The available CPU resources allowed us to follow 8 oscillations of the GCs
along their orbits and the main findings are: i) clusters with an initial high
enough King concentration parameter (c>=1.2), preserve up to 50% of their
initial mass; ii) the inner density distribution of the survived clusters keep
a King model profile; iii) GC-GC collisions have a negligible effect with
respect to that caused by the passage through the galactic center; iv) the
orbital energy dissipation due to the tidal interaction is of the same order of
that caused by dynamical friction; v) complex sub-structures like "ripples" and
"clumps" formed, as observed around real clusters.
  These findings support the validity of the hypothesis of merging of GCs in
the galactic central region, with modes that deserve further careful
investigations.


title: A numerical comparison of theories of violent relaxation

abstract:
  Using N-body simulations with a large set of massless test particles we
compare the predictions of two theories of violent relaxation, the well known
Lynden-Bell theory and the more recent theory by Nakamura. We derive ``weaken''
versions of both theories in which we use the whole equilibrium coarse-grained
distribution function as a constraint instead of the total energy constraint.
We use these weaken theories to construct expressions for the conditional
probability $K_i(\tau)$ that a test particle initially at the phase-space
coordinate $\tau$ would end-up in the $i$'th macro-cell at equilibrium. We show
that the logarithm of the ratio $R_{ij}(\tau) \equiv K_i(\tau)/K_j(\tau)$ is
directly proportional to the initial phase-space density $f_0(\tau)$ for the
Lynden-Bell theory and inversely proportional to $f_0(\tau)$ for the Nakamura
theory. We then measure $R_{ij}(\tau)$ using a set of N-body simulations of a
system undergoing a gravitational collapse to check the validity of the two
theories of violent relaxation. We find that both theories are at odds with the
numerical results, qualitatively and quantitatively.


title: Discovery of Spectroscopic Variations in the DAB White Dwarf GD 323

abstract:
  We report the discovery of spectroscopic variations in GD 323, the
prototypical DAB white dwarf. Simultaneous optical spectroscopic observations
over five consecutive nights of GD 323 and of PG 1234+482, a non-variable
comparison DA white dwarf of similar brightness, are used to reveal
quasi-periodic variations in both the hydrogen and helium absorption lines over
a timescale of hours. The amplitude of the variation of the equivalent width of
Hbeta is ~30 %. Moreover, the strength of the hydrogen lines is shown to vary
in opposite phase from that of He I 4471. These results suggest that the model
currently thought to be the most viable to account for the simultaneous
presence of hydrogen and helium lines in GD 323, namely a static stratified
atmosphere, may need to be reexamined. Instead, a model with an inhomogeneous
surface composition, resulting perhaps from the dilution of a thin hydrogen
atmosphere with the underlying helium convection zone, may be a better
representation of GD 323. The observed variation timescale of ~3.5 hours is
consistent with the slow rotation rate of white dwarf stars.


title:
IRAS 16293-2442B: A Compact, Possibly Isolated Protoplanetary Disk in a
  Class 0 Object

abstract:
  Theoretical arguments suggest that protoplanetary disks around young stars
should start small and grow with the addition of high angular momentum material
to reach the radii of several hundred AUs that characterize the disks around
optically visible T Tauri stars. Examples of much more compact disks, with
radii much less than 100 AU, have been found around some very young stars, but
in all cases tidal truncation from a near binary companion provides a ready
explanation for the small disk size. We report here an example of a compact,
possibly isolated disk around the class 0 object IRAS16293-2422B, which is
thought to be among the youngest protostars known. This disk has a Gaussian
half power radius of only $\sim$8 AU, and a detailed, self-consistent,
accretion disk model indicates an outer radius of only 26 AU. This discovery
supports the notion that protoplanetary disks start small and grow with time,
although other explanations for the compact size cannot be ruled out, including
gravitational instability in its outer parts and tidal truncation from the
close approach of a now distant stellar companion.


title: Lost & Found Dark Matter in Elliptical Galaxies

abstract:
  There is strong evidence that the mass in the Universe is dominated by dark
matter, which exerts gravitational attraction but whose exact nature is
unknown. In particular, all galaxies are believed to be embedded in massive
haloes of dark matter. This view has recently been challenged by surprisingly
low random stellar velocities in the outskirts of ordinary elliptical galaxies,
which were interpreted as indicating a lack of dark matter (Mendez et al. 2001;
Romanowsky et al. 2003). Here we show that the low velocities are in fact
compatible with galaxy formation in dark-matter haloes. Using numerical
simulations of disc-galaxy mergers, we find that the stellar orbits in the
outer regions of the resulting ellipticals are very elongated. These stars were
torn by tidal forces from their original galaxies during the first close
passage and put on outgoing trajectories. The elongated orbits, combined with
the steeply falling density profile of the observed tracers, explain the
observed low velocities even in the presence of large amounts of dark matter.
Projection effects when viewing a triaxial elliptical can lead to even lower
observed velocities along certain lines of sight.


title:
Molecular freeze-out as a tracer of the thermal and dynamical evolution
  of pre- and protostellar cores

abstract:
  Radiative transfer models of multi-transition observations are used to
determine molecular abundances as functions of position in pre- and
protostellar cores. The data require a "drop" abundance profile with radius,
with high abundances in the outermost regions probed by low excitation 3 mm
lines, and much lower abundances at intermediate zones probed by higher
frequency lines. The results are illustrated by detailed analysis of CO and
HCO+ lines for a subset of objects. We propose a scenario in which the
molecules are frozen out in a region of the envelope where the temperature is
low enough (<= 40 K) to prevent immediate desorption, but where the density is
high enough (> 10^4-10^5 cm^{-3}) that the freeze-out timescales are shorter
than the lifetime of the core. The size of the freeze-out zone is thereby a
record of the thermal and dynamical evolution of the cores. Fits to CO data for
a sample of 16 objects indicate that the size of the freeze-out zone decreases
significantly between Class 0 and I objects, explaining the variations in, for
example, CO abundances with envelope masses. However, the corresponding
timescales are 10^{5+/-0.5} years, with no significant difference between Class
0 and I objects. These timescales suggest that the dense pre-stellar phase with
heavy depletions lasts only a short time, of order 10^5 yr, in agreement with
recent chemical-dynamical models.


title:
Observations of Rapid Disk-Jet Interaction in the Microquasar GRS
  1915+105

abstract:
  We present evidence that ~ 30 minute episodes of jet formation in the
Galactic microquasar GRS 1915+105 may sometimes entirely be a superposition of
smaller, faster phenomena. We base this conclusion on simultaneous X-ray and
infrared observations in July 2002, using the Rossi X-ray Timing Explorer and
the Palomar 5 meter telescope. On two nights, we observed quasi-periodic
infrared flares from GRS 1915+105, each accompanied by a set of fast
oscillations in the X-ray light curve (indicating an interaction between the
jet and accretion disk). In contrast to similar observations in 1997, we find
that the duration of each X-ray cycle matches the duration of its accompanying
infrared flare, and we observed one instance in which an isolated X-ray
oscillation occurred at the same time as a faint infrared "subflare" (of
duration ~ 150 seconds) superimposed on one of the main flares. From these
data, we are able to conclude that each X-ray oscillation had an associated
faint infrared flare and that these flares blend together to form, and entirely
comprise, the ~ 30 minute events we observed. Part of the infrared emission in
1997 also appears to be due to superimposed small flares, but it was
overshadowed by infrared-bright ejections associated with the appearance of a
sharp "trigger" spike in each X-ray cycle that were not present in 2002. We
also study the evolution of the X-ray spectrum and find significant differences
in the high energy power law component, which was strongly variable in 1997 but
not in 2002. Taken together, these observations reveal the diversity of ways in
which the accretion disk and jet in black hole systems are capable of
interacting and solidify the importance of the trigger spike for large
ejections to occur on ~ 30 minute timescales in GRS 1915+105.


title: Mini-dark halos with intermediate mass black holes

abstract:
  We argue that the Milky Way (MW) contains thousands intermediate mass black
holes (IMBHs) and minihalos with a fraction of IMBHs still being enshrouded in
extremely dense mini-spikes of dark matter (DM) particles. Each containing
$10^6\msun$ of dark particles and no baryons in a sphere of 50 pc radius, the
minihalos are dense enough to survive the Milky Way tide with the nearest
minihalo within 2 kpc from the Sun. The IMBH is formed off-centre in a minihalo
by gas accretion, and its growth adiabatically compresses a finite density of
surrounding dark matter into a $r^{-1.5}$ mini-spike. Some IMBHs recentre on
their minihalos after dynamical friction, and some IMBHs are ejected by birth
kicks. Detectable by GLAST, the mini-spikes and minihalos should stand out the
background and dominate the neutralino annihilation in the smooth MW and
satellite galaxies. If they are the unidentified EGRET sources, upper limits
can be set on the branching ratio of neutralino annihilation. The supermassive
BH of the MW, if orginates from an IMBH, is also likely enshrouded with a
mini-spike.


title:
Directly Measured Limit on the Interplanetary Matter Density from
  Pioneer 10 and 11

abstract:
  The Pioneer 10 and 11 spacecraft had exceptional deep-space navigational
capabilities. The accuracies of their orbit reconstruction were limited,
however, by a small, anomalous, Doppler frequency drift that can be interpreted
as an acceleration of (8.74 +/- 1.33) x 10^{-8} cm/s^2 directed toward the Sun.
We investigate the possibility that this anomaly could be due to a drag on the
spacecraft from their passing through the interplanetary medium. Although this
mechanism is an appealing one, the existing Pioneer radiometric data would
require an unexpectedly high mass density of interplanetary dust for this
mechanism to work. Further, the magnitude of the density would have to be
nearly constant at distances ~ 20-70 AU. Therefore, it appears that such an
explanation is very unlikely, if not ruled out. Despite this, the measured
frequency drift by itself places a directly-measured, model-independent limit
of \lessim 3 x 10^{-19} g/cm^3 on the mass density of interplanetary dust in
the outer(~20-70 AU) solar system. Lower experimental limits can be placed if
one presumes a model that varies with distance. An example is the limit \lessim
6 x 10^{-20} g/cm^3 obtained for the model with an axially-symmetric density
distribution that falls off as the inverse of the distance. We emphasize that
the limits obtained are experimentally-measured, in situ limits. A mission to
investigate the anomaly would be able to place a better limit on the density,
or perhaps even to measure it.


title: Astrophysical water masers: Line profiles analysis

abstract:
  The changes in the spectral line profile of the 22GHz H2O maser are
calculated as a function of emerging maser flux. We address not only the
narrowing and re-broadening of the maser lines, but also the deviations of
Gaussian symmetry as a result of the various hyperfine components of the 22 GHz
maser line. Non-LTE models of the H2O maser transition, including hyperfine
structure and cross-relaxation, are compared with high spectral resolution Very
Long Baseline Interferometry (VLBI) observations of the H2O masers in the
circumstellar envelopes (CSEs) of a sample of late-type stars. This yields
estimates on the thermal width in the maser region as well as the emerging
maser flux and thus the level of saturation. We also discuss the effect of a
velocity gradient along the maser path on the line widths and shapes of the
line profile and the effect of the geometry of the maser region. We find that
the typical velocity shift along the maser path is of the order of 1.0 km/s.
The effect of this shift on the shape of the maser spectrum is difficult to
distinguish from the effect of the hyperfine components.


title:
The magnetic field around late-type stars revealed by the circumstellar
  H2O masers

abstract:
  Through polarization observations, circumstellar masers are excellent probes
of the magnetic field in the envelopes of late-type stars. Whereas observations
of the polarization of the SiO masers close to the star and on the OH masers
much further out were fairly commonplace, observations of the magnetic field
strength in the intermediate density and temperature region where the 22 GHz
water masers occur have only recently become possible. Here we present the
analysis of the circular polarization, due to Zeeman splitting, of the water
masers around the Mira variable stars U Her and U Ori and the supergiant VX
Sgr. We present an upper limit of the field around U Her that is lower but
consistent with previous measurements, reflecting possible changes in the
circumstellar envelope. The field strengths around U Ori and VX Sgr are shown
to be of the order of several Gauss. Moreover, we show for the first time that
large scale magnetic fields permeate the circumstellar envelopes of an evolved
star; the polarization of the water masers around VX Sgr reveals a dipole field
structure. We discuss the coupling of the magnetic field with the stellar
outflow, as such fields could possibly be the cause of distinctly aspherical
mass-loss.


title:
HE 0141-3932: a bright QSO with an unusual emission line spectrum and
  associated absorption

abstract:
  HE 0141-3932 (zem = 1.80) is a bright blue radio-quite quasar with an
unusually weak Ly-alpha emission line. Large redshift differences (Delta z =
0.05) are observed between high ionization and low ionization emission lines.
Absorption systems identified at zabs = 1.78, 1.71, and 1.68 show mild
oversolar metallicities (Z ~= 1-2Zsolar) and can be attributed to the
associated gas clouds ejected from the circumnuclear region. The joint analysis
of the emission and absorption lines leads to the conclusion that this quasar
is seen almost pole-on. Its apparent luminosity may be Doppler boosted by ~10
times. The absorbing gas shows a high abundance of Fe, Mg and Al ([Fe, Mg,
Al/C] ~= 0.15 +/- 0.10) along with underabundance of N ([N/C] <= -0.5). This
abundance pattern is at variance with current chemical evolution models of QSOs
predicting [N/C] >= 0$ and [Fe/C] < 0 at Z ~ Zsolar.


title: Detection of Intracluster Planetary Nebulae in the Coma Cluster

abstract:
  [OIII] lambda 5007AA emission lines of 16 intracluster planetary nebulae
candidates in the Coma cluster were detected with a Multi-Slit Imaging
Spectroscopy (MSIS) technique using FOCAS on the Subaru telescope. The
identification of these faint emission sources as PNe is supported by (i) their
point-like flux distribution in both space and wavelength, with tight limits on
the continuum flux; (ii) the identification of the second [OIII] lambda 4959
line in the only object at high enough velocity that this line too falls into
the filter bandpass; (iii) emission line fluxes consistent with PNe at 100 Mpc
distance, in the range 2.8 x 10^{-19} - 1.7 x 10^{-18} erg/s/cm^2; and (iv) a
narrow velocity distribution approximately centered on the systemic velocity of
the Coma cluster. Comparing with the velocities of galaxies in our field, we
conclude that the great majority of these candidates would be intracluster PNe,
free floating in the Coma cluster core. Their velocity dispersion is ~760 km/s,
and their mean velocity is lower than that of the galaxies. The velocity
distribution suggests that the intracluster stellar population has different
dynamics from the galaxies in the Coma cluster core.


title: Coronal properties of G-type stars in different evolutionary phases

abstract:
  We report on the analysis of XMM-Newton observations of three G-type stars in
very different evolutionary phases: the weak-lined T Tauri star HD 283572, the
Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Com.
They all have high X-ray luminosity (10^31 erg/s for HD 283572 and 31 Com and
10^30 erg/s for EK Dra). We compare the Emission Measure Distributions (EMDs)
of these active coronal sources, derived from high-resolution XMM-Newton
grating spectra, as well as the pattern of elemental abundances vs. First
Ionization Potential (FIP). We also perform time-resolved spectroscopy of a
flare detected by XMM from EK Dra. We interpret the observed $EMD$s as the
result of the emission of ensembles of magnetically confined loop-like
structures with different apex temperatures. Our analysis indicates that the
coronae of HD 283572 and 31 Com are very similar in terms of dominant coronal
magnetic structures, in spite of differences in the evolutionary phase, surface
gravity and metallicity. In the case of EK Dra the distribution appears to be
slightly flatter than in the previous two cases, although the peak temperature
is similar.


title:
ISM Properties in Low-Metallicity Environments III. The Dust Spectral
  Energy Distributions of II Zw 40, He 2-10 and NGC 1140

abstract:
  We present new 450 and 850 micron SCUBA data and 1.3 mm MAMBO data of the
dwarf galaxies II Zw 40, He 2-10 and NGC 1140. Additional ISOCAM, IRAS as well
as ground based data are used to construct the observed mid-infrared to
millimeter spectral energy distribution of these galaxies. These spectral
energy distributions are modeled in a self-consistent way, as was achieved with
NGC 1569 (Galliano et al., 2003), synthesizing both the global stellar
radiation field and the dust emission, with further constraints provided by the
photoionisation of the gas. Our study shows that low-metallicity galaxies have
very different dust properties compared to the Galaxy.
  Our main results are: (i) a paucity of PAHs which are likely destroyed by the
hard penetrating radiation field, (ii) a very small (3-4 nm) average size of
grains, consistent with the fragmentation and erosion of dust particles by the
numerous shocks, (iii) a significant millimetre excess in the dust spectral
energy distribution which can be explained by the presence of ubiquitous very
cold dust (T=5-9 K) accounting for 40 to 80 % of the total dust mass, probably
distributed in small clumps. We derive a range of gas-to-dust mass ratios
between 300 and 2000, larger than the Galactic values and dust-to-metals ratios
of 1/30 to 1/2. The modeled dust size distributions are used to synthesize an
extinction curve for each galaxy. The UV slopes of the extinction curves
resemble that observed in some regions in the Large Magellanic Cloud. The 2175
angstrom bumps of the modeled extinction curves are weaker than that of the
Galaxy, except in the case of II Zw 40, where we are unable to accurately
constrain the 2175 angstrom bump carrier.


title:
Discovery of more than two thousand white dwarfs in the globular cluster
  Omega Centauri

abstract:
  We present deep multiband (F435W, F625W, and F658N) photometric data of the
Globular Cluster Omega Cen collected with the Advanced Camera for Surveys on
board of the Hubble Space Telescope. We identified in the (F435W-F625W, F435W)
plane more than two thousand White Dwarf (WD) candidates using three out of
nine available pointings. Such a large sample appears in agreement with
predictions based on the ratio between WD and Horizontal Branch (HB)
evolutionary lifetimes. We also detected ~ 1600 WDs in the (F658N-F625W, F625W)
plane, supporting the evidence that a large fraction of current cluster WDs are
$H_\alpha$ bright.


title:
A spectroscopic event of eta Car viewed from different directions: The
  data and first results

abstract:
  We present spectroscopic observations with high spectral resolution of eta
Car as seen by the SE lobe of the Homunculus nebula over the 2003.5
"spectroscopic event". The observed spectra represent the stellar spectrum
emitted near the pole of the star and are much less contaminated with nebular
emission lines than direct observations of the central object. The "event" is
qualitatively similar near the pole to what is observed in direct spectra of
the star (more equator-on at 45 degree), but shows interesting differences. The
observations show that the equivalent width changes of H alpha emission and
other lines are less pronounced at the pole than in the line of sight. Also the
absorption components appear less variable. A pronounced high-velocity
absorption is present near the event in the He I lines indicating a
mass-ejection event. This feature is also seen, but less pronounced, in the
hydrogen lines. HeII4686 emission is observed for a brief period of time near
the event and appears, if corrected for light travel time, to precede similar
emission in the direct view. Our observations indicate that the event is
probably not only a change in ionization and excitation structure or a simple
eclipse-like event.


title:
The structural and scaling properties of nearby galaxy clusters: I - The
  universal mass profile

abstract:
  We present the integrated mass profiles for a sample of ten nearby (z<=0.15),
relaxed galaxy clusters, covering a temperature range of [2-9]keV, observed
with XMM-Newton. The mass profiles were derived from the observed gas density
and temperature profiles under the hypothesis of spherical symmetry and
hydrostatic equilibrium. All ten mass profiles are well described by an
NFW-type profile over the radial range from 0.01 to 0.5 R_200, where R_200 is
the radius corresponding to a density contrast of 200 with respect to the
critical density at the cluster redshift. A King model is inconsistent with
these data. The derived concentration parameters and total masses are in the
range c_200=4-6 and M_200=1.2 10^14-1.2 10^15 Msol, respectively. Our
qualitative and quantitative study of the mass profile shape shows, for the
first time, direct and clear observational evidence for the universality of the
total mass distribution in clusters. The mass profiles scaled in units of R_200
and M_200 nearly coincide, with a dispersion of less than 15% at 0.1 R_200. The
c_200--M_200 relation is consistent with the predictions of numerical
simulations for a LCDM cosmology, taking into account the measurement errors
and expected intrinsic scatter. Our results provide further strong evidence in
favour of the Cold Dark Matter cosmological scenario and show that the dark
matter collapse is well understood at least down to the cluster scale.


title: A deep, wide-field search for substellar members in NGC 2264

abstract:
  We report the first results of our ongoing campaign to discover the first
brown dwarfs (BD) in NGC 2264, a young (3 Myr), populous star forming region
for which our optical studies have revealed a very high density of potential
candidates - 236 in $<$ 1 deg$^2$ - from the substellar limit down to at least
$\sim$ 20 M$_{\rm Jup}$ for zero reddening. Candidate BD were first selected
using wide field ($I,z$) band imaging with CFH12K, by reference to current
theoretical isochrones. Subsequently, 79 (33%) of the $I,z$ sample were found
to have near-infrared 2MASS photometry ($JHK_s$ $\pm$ 0.3 mag. or better),
yielding dereddened magnitudes and allowing further investigation by comparison
with the location of NextGen and DUSTY isochrones in colour-colour and
colour-magnitude diagrams involving various combinations of $I$,$J$,$H$ and
$K_s$. We discuss the status and potential substellarity of a number of
relatively unreddened (A$_{\rm v}$ $<$ 5) likely low-mass members in our
sample, but in spite of the depth of our observations in $I,z$, we are as yet
unable to unambiguously identify substellar candidates using only 2MASS data.
Nevertheless, there are excellent arguments for considering two faint (observed
$I$ $\sim$ 18.4 and 21.2) objects as cluster candidates with masses
respectively at or rather below the hydrogen burning limit. More current
candidates could be proven to be cluster members with masses around 0.1
M$_{\odot}$ {\it via} gravity-sensitive spectroscopy, and deeper near-infrared
imaging will surely reveal a hitherto unknown population of young brown dwarfs
in this region, accessible to the next generation of deep near-infrared
surveys.


title:
The 3-point function in large scale structure: redshift distortions and
  galaxy bias

abstract:
  We study the behavior of the three-point correlation function xi_3 of dark
matter and mock galaxies, concentrating on the effects of redshift-space
distortions and the determination of galaxy bias parameters in current redshift
galaxy surveys. On large scales, redshift space distortions tend to wash out
slightly the configuration dependence of the reduced 3-point function Q3 ~
xi_3/xi_2^2. On smaller scales (< 10 Mpc/h), Q3 develops a characteristic
U-shape anisotropy between elongated and open triangles due to the effects of
velocity dispersion. We show that this shape is quite universal, very weakly
dependent on scale, initial spectral index or cosmological parameters and
should be detectable in current galaxy surveys even if affected by shot-noise
or galaxy bias. We present a detailed method for obtaining constraints on
galaxy bias parameters from measurements of Q3 in current galaxy redshift
surveys, based on the eigenmode analysis similar to the one developed for the
bispectrum. We show that our method recovers the bias parameters introduced
into mock galaxies by a HOD prescription and is also able to handle potential
systematics in the case when a smaller number than ideal of mock catalogs is
used to estimate the covariance matrix. We find that current redshift surveys
(e.g. SDSS or 2dFGRS) are just about large enough to get interesting new
constraints on bias.


title:
Testing the locality of transport in self-gravitating accretion discs -
  II. The massive disc case

abstract:
  In this paper, we extend our previous analysis (Lodato & Rice 2004) of the
transport properties induced by gravitational instabilities in cooling, gaseous
accretion discs to the case where the disc mass is comparable to the central
object. In order to do so, we have performed global, three-dimensional smoothed
particle hydrodynamics simulations of massive discs. These new simulations show
a much more complex temporal evolution with respect to the less massive case.
Whereas in the low disc mass case a self-regulated, marginally stable state
(characterized by an approximately constant radial profile of the stability
parameter $Q$) is easily established, in the high disc mass case we observe the
development of an initial transient and subsequent settling down in a
self-regulated state in some simulations, or a series or recurrent spiral
episodes, with low azimuthal wave number $m$, in others. Accretion in this last
case can therefore be a highly variable process. On the other hand, we find
that the secular evolution of the disc is relatively slow. In fact, the
time-average of the stress induced by self-gravity results in accretion
time-scales much longer than the dynamical timescale, in contrast with previous
isothermal simulations of massive accretion discs. We have also compared the
resulting stress tensor with the expectations based on a local theory of
transport, finding no significant evidence for global wave energy transport.