title:
A new approach to gravitational clustering: a path-integral formalism
  and large-N expansions

abstract:
  We show that the formation of large-scale structures through gravitational
instability in the expanding universe can be fully described through a
path-integral formalism. We derive the action S[f] which gives the statistical
weight associated with any phase-space distribution function f(x,p,t). This
action S describes both the average over the Gaussian initial conditions and
the Vlasov-Poisson dynamics. Next, applying a standard method borrowed from
field theory we generalize our problem to an N-field system and we look for an
expansion over powers of 1/N. We describe three such methods and we derive the
corresponding equations of motion at the lowest non-trivial order for the case
of gravitational clustering. This yields a set of non-linear equations for the
mean $\fb$ and the two-point correlation G of the phase-space distribution f,
as well as for the response function R. These systematic schemes match the
usual perturbative expansion on quasi-linear scales but should also be able to
handle the non-linear regime. Our approach can also be extended to non-Gaussian
initial conditions and may serve as a basis for other tools borrowed from field
theory.


title:
A study of the stability regions in the planetary system HD 74156 - Can
  it host earthlike planets in habitable zones?

abstract:
  Using numerical methods we thoroughly investigate the dynamical stability in
the region between the two planets found in HD 74156. The two planets with
minimum masses 1.56 M_JUP (HD 74156b) and 7.5 M_JUP (HD 74156c), semimajor axes
0.276 AU and 3.47 AU move on quite eccentric orbits (e=0.649 and 0.395). There
is a region between 0.7 and 1.4 AU which may host additional planets which we
checked via numerical integrations using different dynamical models. Besides
the orbital evolution of several thousands of massless regarded planets in a
three-dimensional restricted 4-body problem (host star, two planets + massless
bodies) we also have undertaken test computation for the orbital evolution for
fictive planets with masses of 0.1, 0.3 and 1 M_JUP in the region between
HD74156b and HD74156c. For direct numerical integrations up to 10^7 years we
used the Lie-integrator, a method with adaptive stepsize; additionally we used
the Fast Lyapunov Indicators as tool for detecting chaotic motion in this
region. We emphasize the important role of the inner resonances (with the outer
planet) and the outer resonances (with the inner planet) with test bodies
located inside the resonances. In these two "resonance" regions almost no
orbits survive. The region between the 1:5 outer resonance (0.8 AU) and the 5:1
inner resonance (1.3 AU), just in the right position for habitability, is also
very unstable probably due to three-body-resonances acting there. Our results
do not strictly "forbid" planets to move there, but the existence of a planet
on a stable orbit between 0.8 and 1.3 AU is unlikely.


title: A Modified chi^2-Test for CMB Analyses

abstract:
  We present a new general procedure for determining a given set of quantities.
To this end, we define certain statistic, that we call 'modified $\chi^2$'
($\chi^2_M$), because of its similarity with the standard $\chi^2$. The terms
of this $\chi^2_M$ are made up of the fluctuations of an unbiased estimator of
some statistical quantities, and certain weights. Only the diagonal terms of
the covariance matrix explicitly appear in our statistic, while the full
covariance matrix (and not its inverse) is implicitly included in the
calculation of the weights. Choosing these weights we may obtain, through
minimising the $\chi^2_M$, the estimator that provides the minimum RMS, either
for those quantities or for the parameters on which these quantities depend. In
this paper, we describe our method in the context of Cosmic Microwave
Background experiments, in order to obtain either the statistical properties of
the maps, or the cosmological parameters. The test here is constructed out of
some estimator of the two-point correlation function at different angles. For
the problem of one parameter estimation, we show that our method has the same
power as the maximum likelihood method. We have also applied this method to
Monte Carlo simulations of the COBE-DMR data, as well as to the actual 4-year
data, obtaining consistent results with previous analyses. We also provide a
very good analytical approximation to the distribution function of our
statistic, which could also be useful in other contexts.


title: Can Planck-scale physics be seen in the cosmic microwave background ?

abstract:
  We investigate the potential of observations of anisotropies in the cosmic
microwave background (CMB) and large-scale structure in the Universe to detect
possible modifications of standard inflationary models by physics beyond the
Planck scale. A generic model of primordial density fluctuations is
investigated, and we derive constraints on its parameters from current data. We
conclude that the currently available data do not put very stringent
constraints on this model. Furthermore, we use simulated power spectra from the
Sloan Digital Sky Survey (SDSS) and the Planck satellite to show that it is
unlikely that a trans-Planckian signature of this type can be detected in CMB
and large-scale structure data.


title: Microwave Emission from Aligned Dust

abstract:
  Polarized microwave emission from dust is an important foreground that may
contaminate polarized CMB studies unless carefully accounted for. We discuss
potential difficulties associated with this foreground, namely, the existence
of different grain populations with very different emission/polarization
properties and variations of the polarization yield with grain temperature. In
particular, we discuss observational evidence in favor of rotational emission
from tiny PAH particles with dipole moments, i.e. ``spinning dust'', and also
consider magneto-dipole emission from strongly magnetized grains. We argue that
in terms of polarization, the magneto-dipole emission may dominate even if its
contribution to total emissivity is subdominant. Addressing polarized emission
at frequencies larger than approsimately 100 GHz, we discuss the complications
arising from the existence of dust components with different temperatures and
possibly different alignment properties.


title: Self-regulating supernova heating in interstellar medium simulations

abstract:
  Numerical simulations of the multi-phase interstellar medium have been
carried out, using a 3D, nonlinear, magnetohydrodynamic, shearing-box model,
with random motions driven by supernova explosions. These calculations
incorporate the effects of magnetic fields and rotation in 3D; these play
important dynamical roles in the galaxy, but are neglected in many other
simulations. The supernovae driving the motions are not arbitrarily imposed,
but occur where gas accumulates into cold, dense clouds; their implementation
uses a physically motivated model for the evolution of such clouds. The process
is self-regulating, and produces mean supernova rates as part of the solution.
Simulations with differing mean density show a power law relation between the
supernova rate and density, with exponent 1.7; this value is within the range
suggested from observations (taking star formation rate as a proxy for
supernova rate). The global structure of the supernova driven medium is
strongly affected by the presence of magnetic fields; e.g. for one solution the
filling factor of hot gas is found to vary from 0.19 (with no field) to 0.12
(with initial mid-plane field B_0=6 muG).


title: The cosmic evolution of the galaxy luminosity density

abstract:
  We reconstruct the history of the cosmic star formation in the universe by
means of detailed chemical evolution models for galaxies of different
morphological types. We consider a picture of coeval, non-interacting evolving
galaxies where ellipticals experience intense and rapid starbursts within the
first Gyr after their formation, and spirals and irregulars continue to form
stars at lower rates up to the present time. Such models allow one to follow in
detail the evolution of the metallicity of the gas out of which the stars are
formed. We normalize the galaxy population to the B band luminosity function
observed in the local Universe and study the redshift evolution of the
luminosity densities in the B, U, I and K bands calculating galaxy colors and
evolutionary corrections by means of a detailed synthetic stellar population
model. Our predictions indicate that the decline of the galaxy luminosity
density between redshift 1 and 0 observed in the U, B and I bands is caused
mainly by star-forming spiral galaxies which slowly exhaust their gas
reservoirs. Elliptical galaxies have dominated the total luminosity density in
all optical bands at early epochs, when all their stars formed by means of
rapid and very intense star-bursts. Irregular galaxies bring a negligible
contribution to the total luminosity density in any band at any time.
(abridged)


title: The Luminosity-Size and Mass-Size Relations of Galaxies out to z~3

abstract:
  The luminosity-size and stellar mass-size distributions of galaxies out to
z~3 is presented. We use very deep near-infrared images of the Hubble Deep
Field South in the J_s, H, and K_s bands, taken as part FIRES at the VLT, to
follow the evolution of the optical rest-frame sizes of galaxies. For a total
of 168 galaxies with K_{s,AB}<23.5, we find that the rest-frame V-band sizes
r_{e,V} of luminous galaxies (<L_V>~2x10^{10}h^{-2}L_sun) at 2<z<3 are 3 times
smaller than for equally luminous galaxies today. In contrast, the mass-size
relation has evolved relatively little: the size at mass
<M_*>~2x10^{10}h^{-2}M_sun, has changed by 20(+-20)% since z~2.5. Both results
can be reconciled by the fact that the stellar M/L ratio is lower in the
luminous high z galaxies than in nearby ones because they have young stellar
populations. The lower incidence of large galaxies at z~3 seems to reflect the
rarity of galaxies with high stellar mass.


title: Distances and ages of NGC 6397, NGC 6752 and 47 Tuc

abstract:
  Distances and absolute ages for the globular clusters NGC6397, NGC6752, and
47 Tuc are obtained using Main Sequence Fitting. Accurate reddenings and metal
abundances (errors of 0.005 mag and 0.04 dex) are obtained by comparing B-V,
b-y colours and UVES spectra for clusters TO-stars and subgiants with similar
data for Hipparcos subdwarfs, using a reddening free temperature indicator
(Halpha). Errors in distances and ages are 0.07 mag and 1 Gyr. NGC6397 and
NGC6752 have ages of 13.5\pm 1.1 and 13.4\pm 1.1 Gyr, while 47 Tuc is probably
about 2.6 Gyr younger, in agreement with results obtained by techniques
sensitive to relative ages. Considering possible systematic errors, the age of
the oldest globular clusters is 13.4\pm 0.8\pm 0.6 Gyr (random and systematic
errors). This age is fully compatible with WMAP results, and indicates that the
oldest Galactic globular clusters formed within the first 1.7 Gyr after the Big
Bang, corresponding to a redshift of z\geq 2.5, in a standard LambdaCDM model.
The epoch of formation of the (inner halo) globular clusters lasted about 2.6
Gyr, ending at a time corresponding to a redshift of z\geq 1.3. Once combined
with values of Ho given by WMAP and by the HST Key Project, our age estimate
provides a robust upper limit at 95% level of confidence of Omega_M<0.57,
indicating the need for a vacuum energy independent of results from type Ia SNe
and clusters of galaxies. Using cluster distances, we derive a value of
M_V(HB)=(0.22\pm 0.05)([Fe/H]+1.5)+(0.56\pm 0.07) for the zero point of the
relation between the horizontal branch absolute magnitude and metallicity. When
combined with the apparent average luminosity of the RR Lyrae stars in the LMC
by Clementini et al. (2003), this zero point provides a new estimate of the
distance modulus to the LMC: (m-M)o=18.50\pm 0.09.


title: Observational constraints on braneworld chaotic inflation

abstract:
  We examine observational constraints on chaotic inflation models in the
Randall-Sundrum Type II braneworld. If inflation takes place in the high-energy
regime, the perturbations produced by the quadratic potential are further from
scale-invariance than in the standard cosmology, in the quartic case more or
less unchanged, while for potentials of greater exponent the trend is reversed.
We test these predictions against a data compilation including the WMAP
measurements of microwave anisotropies and the 2dF galaxy power spectrum. While
in the standard cosmology the quartic potential is at the border of what the
data allow and all higher powers excluded, we find that in the high-energy
regime of braneworld inflation even the quadratic case is under strong
observational pressure. We also investigate the intermediate regime where the
brane tension is comparable to the inflationary energy scale, where the
deviations from scale-invariance prove to be greater.


title: Curvature quintessence matched with observational data

abstract:
  Quintessence issues can be achieved by taking into account higher order
curvature invariants into the effective action of gravitational field. Such an
approach is naturally related to fundamental theories of quantum gravity which
predict higher order terms in loop expansion of quantum fields in curved
space-times. In this framework, we obtain a class of cosmological solutions
which are fitted against cosmological data. We reproduce encouraging results
able to fit high redshift supernovae and WMAP observations. The age of the
universe and other cosmological parameters are discussed in this context.


title: Radial velocities of "slow movers" - call for observations

abstract:
  This paper presents a list of suggested stars for radial velocity
measurements. We explain here in brief the research project for which the
radial velocity of the "slow movers" i.e. small proper motion stars are
necessary. Basing on this study we prepared a list of 1100 stellar targets with
very accurate positions, proper motions and trigonometric parallaxes but
without radial velocity measurements. Distributions of stellar brightnesses and
spectral types among these stars are presented as well as its "most wanted"
subset. We announce the begin of the radial velocity measurements to be
conducted with our new echelle spectrograph just put into operation and offer
some coordination for observations of targets that cannot be reached from our
location.


title: Dynamical Masses of Young Stars in Multiple Systems

abstract:
  We present recent measurements of the orbital motion in the young binaries DF
Tau and ZZ Tau, and the hierarchical triple Elias 12, that were obtained with
the Fine Guidance Sensors on the HST and at the Keck Observatory using adaptive
optics. Combining these observations with previous measurements from the
literature, we compute preliminary orbital parameters for DF Tau and ZZ Tau. We
find that the orbital elements cannot yet be determined precisely because the
orbital coverage spans only about 90 degr in position angle. Nonetheless, the
range of possible values for the period and semi-major axis already defines a
useful estimate for the total mass in DF Tau and ZZ Tau, with values of
0.90{+0.85}{-0.35} M_sun and 0.81{+0.44}{-0.25} M_sun, respectively, at a
fiducial distance of 140 pc.


title: BeppoSAX and multiwavelength observations of BL Lacertae in 2000

abstract:
  We present two BeppoSAX observations of BL Lac (2200+420) as part of a
multiwavelength campaign performed in 2000. The source was in different states
of activity: in June, the X-ray spectrum was faint and hard (alpha sim 0.8),
with positive residuals towards low energies. In October we detected the
highest [2-10] keV flux ever measured for the source. During this observation,
the spectrum was soft (alpha sim 1.56) up to 10 keV, while above this energy a
hard component was dominating. The BeppoSAX data are confirmed by simultaneous
RXTE short observations. During the first observation the soft X-ray flux was
variable on timescales of a few hours, while the hard X-ray flux was almost
constant. During the second observation, instead, the soft spectrum displayed
an erratic behaviour with large variations (up to factors 3-4) on timescales
smaller than 2 hrs. The analysis of the multiwavelength SED of October
evidenced an intriguing feature: the optical and X-ray sections of the SED are
misaligned, while in the prevailing standard picture, they are both thought to
be produced via synchrotron emission. We suggested four scenarios to account
for this discrepancy: a higher than galactic dust-to-gas ratio towards the
source, the first detection of bulk Compton emission in the X-ray band, the
presence of two synchrotron emitting regions located at different distances
from the nucleus, the detection of a Klein-Nishina effect on the synchrotron
spectrum. We evidenced the favorable and critical points of each scenario, but,
at present, we cannot discriminate between them.


title: Coordinated Multiwavelength Observations of BL Lacertae in 2000

abstract:
  BL Lacertae was the target of an extensive multiwavelength monitoring
campaign in the second half of 2000. Simultaneous or quasi-simultaneous
observations were taken at radio (UMRAO and Metsaehovi) and optical(WEBT
collaboration) frequencies, in X-rays (BeppoSAX and RXTE), and at VHE
gamma-rays (HEGRA). The WEBT optical campaign achieved an unprecedented time
coverage, virtually continuous over several 10 - 20 hour segments. It revealed
intraday variability on time scales of ~ 1.5 hours and evidence for spectral
hardening associated with increasing optical flux. During the campaign, BL
Lacertae underwent a major transition from a rather quiescent state prior to
September 2000, to a flaring state for the rest of the year. This was also
evident in the X-ray activity of the source. BeppoSAX observations on July
26/27 revealed a rather low X-ray flux and a hard spectrum, while a BeppoSAX
pointing on Oct. 31 - Nov. 2, 2000, indicated significant variability on time
scales of < a few hours, and provided evidence for the synchrotron spectrum
extending out to ~ 10 keV during that time. During the July 26/27 observation,
there is a tantalizing, though not statistically significant, indication of a
time delay of ~ 4 - 5 hr between the BeppoSAX and the R-band light curve. Also,
a low-significance detection of a time delay of 15 d between the 14.5 GHz and
the 22 GHz radio light curves is reported. Several independent methods to
estimate the co-moving magnetic field in the source are presented, suggesting a
value of ~ 2 e_B^{2/7} G, where e_B is the magnetic-field equipartition factor
w.r.t. the electron energy density in the jet.


title: Black Widow Pulsars: the Price of Promiscuity

abstract:
  The incidence of evaporating 'black widow' pulsars (BWPs) among all
millisecond pulsars (MSPs) is far higher in globular clusters than in the
field. This implies a special formation mechanism for them in clusters. Cluster
MSPs in wide binaries with WD companions exchange them for turnoff-mass stars.
These new companions eventually overflow their Roche lobes because of
encounters and tides. The millisecond pulsars eject the overflowing gas from
the binary, giving mass loss on the binary evolution timescale. The systems are
only observable as BWPs at epochs where this evolution is slow, making the mass
loss transparent and the lifetime long. This explains why observed BWPs have
low-mass companions. We suggest that at least some field BWPs were ejected from
globular clusters or entered the field population when the cluster itself was
disrupted.


title: Local u'g'r'i'z' Standard Stars in the Chandra Deep Field-South

abstract:
  Because several observing programs are underway in various spectral regimes
to explore the Chandra Deep Field South (CDF-S), the value of local photometric
standards is obvious. As part of an NOAO Surveys Program to establish
u'g'r'i'z' standard stars in the southern hemisphere, we have observed the
central region of the CDF-S to create local standards for use by other
investigators using these filters. As a courtesy, we present the CDF-S
standards to the public now, although the main program will not finish until
mid-2005.


title:
Massive star clusters in ongoing galaxy interactions -- clues to cluster
  formation

abstract:
  We present HST WFPC2 observations, supplemented by ground-based H-alpha data,
of the star-cluster populations in two pairs of interacting galaxies, selected
for being in very different kinds of encounters seen at different stages.
Dynamical information and n-body simulations provide the details of encounter
geometry, mass ratio, and timing. In NGC 5752/4, we see a weak encounter well
past closest approach, after about 2.5x10^8 years. The large spiral NGC 5754
has a normal population of disk clusters, while the companion NGC 5752 exhibits
a rich population of luminous clusters with a flatter luminosity function. The
strong, ongoing encounter in NGC 6621/2, seen about 10^8 years past closest
approach between roughly equal-mass galaxies, has produced a rich population of
luminous clusters, particularly young and bright in a small region between the
nuclei. This region is dynamically interesting, so strongly perturbed that the
rotation curve reverses sign. Cluster formation requires a threshold level of
perturbation, with stage of the interaction less important. The location of the
most active star formation in NGC 6621/2 draws attention to a possible role for
the Toomre stability threshold in shaping star formation in interacting
galaxies. The rich cluster populations in NGC 5752 and 6621 show that direct
contact between gas-rich galaxy disks is not a requirement to form luminous
clusters, and that they can be triggered by processes happening within a single
galaxy disk (albeit triggered by external perturbations). (Abridged)


title: Dark matter annihilation in the halo of the Milky Way

abstract:
  If the dark matter in the Universe is made of weakly self-interacting
particles, they may self-annihilate and emit gamma-rays. We use high resolution
numerical simulations to estimate directly the annihilation flux from the
central regions of the Milky Way and from dark matter substructures in its
halo. Although such estimates remain uncertain because of their strong
dependence on the structure of the densest regions, our numerical experiments
suggest that less direct calculations have overestimated the emission both from
the centre and from halo substructure. We estimate a maximal enhancement of at
most a factor of a few with respect to a smooth spherical halo of standard
Navarro-Frenk-White (NFW) structure. We discuss detection strategies for the
next generation of gamma-ray detectors and find that the annihilation flux may
be detectable, regardless of uncertainties about the densest regions, for the
annihilation cross-sections predicted by currently popular elementary particle
models for the dark matter.


title:
Locations of Auroral Kilometric Radiation Bursts Inferred From
  Multi-Spacecraft Wideband Cluster VLBI Observations i: Description of
  Technique and Initial Results

abstract:
  The Cluster Wideband Data instrument has been used to determine the locations
of auroral kilometric radiation (AKR) using very long baseline interferometry.
The technique involves cross-correlating individual AKR bursts from all six
Cluster baselines using time and frequency filtered waveforms. We report the
locations of over 1,700 individual AKR bursts during six observing epochs
between 10 July 2002 and 22 January 2003 when the Cluster constellation was
high above the southern or northern hemisphere. In general we find that the AKR
burst locations lie along magnetic field lines which map onto the nighttime
auroral zone as expected from previous AKR studies. The distribution of AKR
auroral footprint locations at each epoch had a overall spatial scale between
1000 - 2000 km, much larger than the positional uncertainty of an individual
AKR burst location magnetic footprint, but a small fraction of the auroral
oval. For two of the six epochs, there was a significant drift in the mean
location of AKR activity over a period of 1-2 hours. The drift was
predominantly in latitude at one epoch and in longitude at the other, with
average drift speed V ~ 80-90 m s-1 at the AKR emission location.


title:
Generalized Chaplygin gas with $\alpha = 0$ and the $\Lambda CDM$
  cosmological model

abstract:
  The generalized Chaplygin gas model is characterized by the equation of state
$p = - \frac{A}{\rho^\alpha}$. It is generally stated that the case $\alpha =
0$ is equivalent to a model with cosmological constant and dust ($\Lambda
CDM$). In this work we show that, if this is true for the background equations,
this is not true for the perturbation equations. Hence, the mass spectrum
predicted for both models may differ.


title:
Nuclear-Powered Millisecond Pulsars and the Maximum Spin Frequency of
  Neutron Stars

abstract:
  Millisecond pulsars are neutron stars (NSs) that are thought to have been
spun-up by mass accretion from a stellar companion. It is unknown whether there
is a natural brake for this process, or if it continues until the centrifugal
breakup limit is reached at submillisecond periods. Many NSs that are accreting
from a companion exhibit thermonuclear X-ray bursts that last tens of seconds,
caused by unstable nuclear burning on their surfaces. Millisecond brightness
oscillations during bursts from ten NSs (as distinct from other rapid X-ray
variability that is also observed) are thought to measure the stellar spin, but
direct proof of a rotational origin has been lacking. Here, we report the
detection of burst oscillations at the known spin frequency of an accreting
millisecond pulsar, and we show that these oscillations always have the same
rotational phase. This firmly establishes burst oscillations as nuclear-powered
pulsations tracing the spin of accreting NSs, corroborating earlier evidence.
The distribution of spin frequencies of the 11 nuclear-powered pulsars cuts off
well below the breakup frequency for most NS models, supporting theoretical
predictions that gravitational radiation losses can limit accretion torques in
spinning up millisecond pulsars.


title: Interpreting the Observed Clustering of Red Galaxies at z~3

abstract:
  Daddi et al. have recently reported strong clustering of a population of red
galaxies at z~3 in the Hubble Deep Field-South. Fitting the observed angular
clustering with a power law of index -0.8, they infer a comoving correlation
length r_0~8 Mpc/h; for a standard cosmology, this r_0 would imply that the red
galaxies reside in rare, M>10^{13} Msun/h halos, with each halo hosting ~100
galaxies to match the number density of the population. Using the framework of
the halo occupation distribution (HOD) in a $\Lambda$CDM universe, we show that
the Daddi et al. data can be adequately reproduced by less surprising models,
e.g., models with galaxies residing in halos of mass M>M_min=6.3x10^{11} Msun/h
and a mean occupation Navg(M)=1.4(M/M_min)^{0.45} above this cutoff. The
resultant correlation functions do not follow a strict power law, showing
instead a clear transition from the 1-halo dominated regime, where the two
galaxies of each pair reside in the same dark matter halo, to the 2-halo
dominated regime, where the two galaxies of each pair are from different halos.
The observed high-amplitude data points lie in the one-halo-dominated regime,
so these HOD models are able to explain the observations despite having smaller
correlation lengths, r_0~5 Mpc/h. HOD parameters are only loosely constrained
by the current data because of large sample variance and the lack of clustering
information on scales that probe the 2-halo regime. If our explanation of the
data is correct, then future observations covering a larger area should show
that the large scale correlations lie below a \theta^{-1.8} extrapolation of
the small scale points. Our models of the current data suggest that the red
galaxies are somewhat more strongly clustered than UV-selected Lyman-break
galaxies and have a greater tendency to reside in small groups.


title: The X-ray jet and central structure of the active galaxy NGC 315

abstract:
  We report the Chandra detection of resolved X-ray emission of luminosity 3.5
\times 10^{40} ergs s^{-1} (0.4--4.5 keV) and power-law energy spectral index
alpha = 1.5 \pm 0.7 from a roughly 10 arcsec length of the north-west radio jet
in NGC 315. The X-ray emission is brightest at the base of the radio-bright
region about 3 arcsec from the nucleus, and is consistent with a synchrotron
origin. At a projected distance of 10 arcsec from the core, the jet is in
approximate pressure balance with an external medium which is also detected
through its X-ray emission and which has kT \approx 0.6 \pm 0.1 keV, consistent
with earlier ROSAT results. The high spatial resolution and sensitivity of
Chandra separates nuclear unresolved emission from the extended thermal
emission of the galaxy atmosphere with higher precision than possible with
previous telescopes. We measure an X-ray luminosity of 5.3 \times 10^{41} ergs
s^{-1} (0.4--4.5 keV) and a power-law energy index of alpha = 0.4 \pm 0.4 for
the nuclear component.


title:
L' and M' Standard Stars for the Mauna Kea Observatories Near-Infrared
  System

abstract:
  We present L'and M' photometry, obtained at UKIRT using the Mauna Kea
Observatories Near-IR filter set, for 46 and 31 standard stars, respectively.
The L' standards include 25 from the UKIRT in-house "Bright Standards" with
magnitudes deriving from Elias et al. (1982) and observations at the IRTF in
the early 1980s, and 21 fainter stars. The M' magnitudes derive from the
results of Sinton & Tittemore (1984). We estimate the average external error to
be 0.015 mag for the bright L' standards and 0.025 mag for the fainter L'
standards, and 0.026 mag for the M' standards. The new results provide a
network of homogeneously observed standards, and establish reference stars for
the MKO system, in these bands. They also extend the available standards to
magnitudes which should be faint enough to be accessible for observations with
modern detectors on large and very large telescopes.


title:
Clustering of galaxies at z=3 around the probable Damped Ly-alpha
  absorber towards QSO APM 08279+5255

abstract:
  [Abridged] We present results on the clustering og Lyman break galaxies
(LBGs) around a probable damped Ly-alpha absorption (DLA) line cloud at
z_DLA=2.974 from deep UBVI images of the field containing the quasar APM
08279+5255 (z=3.91). The large area covered by our images, 0.31 deg^2 or 40x40
Mpc co-moving at z=3, and their depth (27.6 mag arcsec^{-2}), allow us to
identify 450 LBG candidates brighter than I(AB)=24.80 at 2.75<z<3.25. LBG
candidates were selected using photometric redshift techniques that include
priors within a redshift slice of width Wz=0.15 centered at z_DLA.
  Within that redshift slice, we find an enhancement of galaxies near the DLA
using both the surface density and an estimator of the 3-D spatial
over-density. The surface overdensity (3\times) is significant at the >95%
significance level on scales 2.5<r<5 Mpc co-moving and imply that some DLA
could reside in high density regions.


title: Differentiating between Modified Gravity and Dark Energy

abstract:
  The nature of the fuel that drives today's cosmic acceleration is an open and
tantalizing mystery. We entertain the suggestion that the acceleration is not
the manifestation of yet another new ingredient in the cosmic gas tank, but
rather a signal of our first real lack of understanding of gravitational
physics. By requiring that the underlying gravity theory respects Birkhoff's
law, we derive the modified gravitational force-law necessary to generate any
given cosmology, without reference to the fundamental theory, revealing
modifications of gravity at scales typically much smaller than today's horizon.
We discuss how through these modifications, the growth of density
perturbations, the late-time integrated Sachs--Wolfe effect, and even
solar-system measurements may be sensitive to whether today's cosmic
acceleration is generated by dark energy or modified gravitational dynamics,
and are subject to imminent observational discrimination. We argue how these
conclusions can be more generic, and probably not dependent on the validity of
Birkhoff's law.


title:
Comment on "Detection of small comets with a ground-based telescope" by
  Frank and Sigwarth

abstract:
  Frank and Sigwarth (2001,JGRSP,106,A3,3665; FS) report on an optical search
for small comets in which they report detection of nine faint trails. FS claim
that these trails are produced by low-mass, low-albedo ob-jects whose inferred
number density is consistent with that predicted by the small comet hypothesis.
The images used for the search were the same as those obtained in a previous
unsuccessful optical search for small comets reported by Mutel and Fix (2000,
JGRSP,105,24907; MF). The results of these two independent analyses of the same
image dataset are not formally in disagreement, since all detections reported
by FS are fainter than the minimum detectable magnitude limit (16.5) determined
by MF. However, since the conclusions are quite different, we have
independently re-analyzed the original search images for evidence of the faint
detections reported by FS. In particular, we have carefully examined whether
the three putative trails whose positions are available satisfy several
necessary criteria for a candidate grouping of excess-count pixels to be caused
by a celestial object. While we have not evaluated the formal statistical
significance of faint detections, all three claimed detections fail one or more
independent criteria required for a valid detection. In addition, both the
level and shape of the claimed integral detection rate versus magnitude are in
strong disagreement with the inte-gral number density of the small comets
hypothesis. We conclude that unless the remaining claimed detections can prove
otherwise, the lack of detections after "careful examination" of the 1,500
search images described in FS provides the most compelling evidence yet
published against the small comet hypothesis.


title: Optical Interferometry in Astronomy

abstract:
  Here I review the current state of the field of optical stellar
interferometry, concentrating on ground-based work although a brief report of
space interferometry missions is included. We pause both to reflect on decades
of immense progress in the field as well as to prepare for a new generation of
large interferometers just now being commissioned (most notably, the CHARA,
Keck and VLT Interferometers). First, this review summarizes the basic
principles behind stellar interferometry needed by the lay-physicist and
general astronomer to understand the scientific potential as well as technical
challenges of interferometry. Next, the basic design principles of practical
interferometers are discussed, using the experience of past and existing
facilities to illustrate important points. Here there is significant discussion
of current trends in the field, including the new facilities under construction
and advanced technologies being debuted. This decade has seen the influence of
stellar interferometry extend beyond classical regimes of stellar diameters and
binary orbits to new areas such as mapping the accretion disks around young
stars, novel calibration of the Cepheid Period-Luminosity relation, and imaging
of stellar surfaces. The third section is devoted to the major scientific
results from interferometry, grouped into natural categories reflecting these
current developments. Lastly, I consider the future of interferometry,
highlighting the kinds of new science promised by the interferometers coming
on-line in the next few years. I also discuss the longer-term future of optical
interferometry, including the prospects for space interferometry and the
possibilities of large-scale ground-based projects. Critical technological
developments are still needed to make these projects attractive and affordable.


title: Source of Atomic Hydrogen in the Atmosphere of HD 209458b

abstract:
  Atomic hydrogen loss at the top of HD 209458b's atmosphere has been recently
detected Vidal-Madjar et al. 2003. We have developed a 1-dimensional model to
study the chemistry in the upper atmosphere of this extrasolar "hot jupiter".
The 3 most abundant elements (other than He), as well as 4 parent molecules are
included in this model, viz., H, C, O, H2, CO, H2O, and CH4. The higher
temperatures (~ 1000 K) and higher stellar irradiance (~6x10^5 W m^{-2})
strongly enhance and modify the chemical reaction rates in this atmosphere. Our
two main results are that (a) the production of atomic hydrogen in the
atmosphere is mainly driven by H2O photolysis and reaction of OH with H2, and
is not sensitive to the exact abundances of CO, H2O, and CH4, and (b) H2O and
CH4 can be produced via the photolysis of CO followed by the reactions with H2.


title:
A New Method for Calculating Arrival Distribution of Ultra-High Energy
  Cosmic Rays above 10^19 eV with Modifications by the Galactic Magnetic Field

abstract:
  We present a new method for calculating arrival distribution of UHECRs
including modifications by the galactic magnetic field. We perform numerical
simulations of UHE anti-protons, which are injected isotropically at the earth,
in the Galaxy and record the directions of velocities at the earth and outside
the Galaxy for all of the trajectories. We then select some of them so that the
resultant mapping of the velocity directions outside the Galaxy of the selected
trajectories corresponds to a given source location scenario, applying
Liouville's theorem. We also consider energy loss processes of UHE protons in
the intergalactic space. Applying this method to our source location scenario
which is adopted in our recent study and can explain the AGASA observation
above 4 \times 10^{19} eV, we calculate the arrival distribution of UHECRs
including lower energy (E>10^19 eV) ones. We find that our source model can
reproduce the large-scale isotropy and the small-scale anisotropy on UHECR
arrival distribution above 10^19 eV observed by the AGASA. We also demonstrate
the UHECR arrival distribution above 10^19 eV with the event number expected by
future experiments in the next few years. The interesting feature of the
resultant arrival distribution is the arrangement of the clustered events in
the order of their energies, reflecting the directions of the galactic magnetic
field. This is also pointed out by Alvarez-Muniz et al.(2002). This feature
will allow us to obtain some kind of information about the composition of
UHECRs and the magnetic field with increasing amount of data.


title:
The equilibrium of the dense electron-nuclear plasma in the
  gravitational field. The magnetic fields and masses of stars

abstract:
  The equilibrium of a hot dense plasma in a gravitational field is considered.
  From the standard equilibrium equations, the energy minimum at density about
$10^{25}$ particles per $cm^3$ and temperature about $10^7 K$ was found. This
effect plays an important role for astrophysics. It enables to explain the
mechanism of the star magnetic field generation and to make a prediction for
the spectrum of a star mass with a wholly satisfactory agreement for the
observation data.


title:
Radiation-driven winds of hot luminous stars. XV. Constraints on the
  mass-luminosity relation of central stars of planetary nebulae

abstract:
  We present a new model atmosphere analysis of nine central stars of planetary
nebulae. This study is based on a new generation of realistic stellar model
atmospheres for hot stars; state-of-the-art, hydrodynamically consistent,
spherically symmetric model atmospheres that have been shown to correctly
reproduce the observed UV spectra of massive Population I O-type stars. The
information provided by the wind features (terminal velocity, mass loss rate)
permits to derive the physical size of each central star, from which we can
derive the stellar luminosity, mass and distance, without having to assume a
relation between stellar mass and luminosity taken from the theory of stellar
structure and AGB and post-AGB evolution. The results of our analysis are quite
surprising: we find severe departures from the generally accepted relation
between post-AGB central star mass and luminosity.


title: The atoll source states of 4U 1608-52

abstract:
  We have studied the atoll source 4U 1608-52 using a large data set obtained
with the Rossi X-ray Timing Explorer. We find that the timing properties of 4U
1608-52 are almost exactly identical to those of the atoll sources 4U 0614+09
and 4U 1728-34 despite the fact that contrary to these sources 4U 1608-52 is a
transient covering two orders of magnitude in luminosity. The frequencies of
the variability components of these three sources follow a universal scheme
when plotted versus the frequency of the upper kilohertz QPO, suggesting a very
similar accretion flow configuration. If we plot the Z sources on this scheme
only the lower kilohertz QPO and HBO follow identical relations. Using the
mutual relations between the frequencies of the variability components we
tested several models; the transition layer model, the sonic point beat
frequency model, and the relativistic precession model. None of these models
described the data satisfactory. Recently, it has been suggested that the atoll
sources (among them 4U 1608-52) trace out similar three-branch patterns as the
Z sources in the color-color diagram. We have studied the relation between the
power spectral properties and the position of 4U 1608-52 in the color-color
diagram and conclude that the timing behavior is not consistent with the idea
that 4U 1608-52 traces out a three-branched Z shape in the color-color diagram
along which the timing properties vary gradually, as Z sources do.


title:
On the detectability of gamma-rays from Dark Matter annihilation in the
  Local Group with ground-based experiments

abstract:
  Recent studies have suggested the possibility that the lightest
supersymmetric particle is a suitable dark matter candidate. In this
theoretical framework, annihilations in high density environments like the
center of dark matter haloes may produce an intense flux of gamma-rays. In this
paper we discuss the possibility of detecting the signatures of neutralino
annihilation in nearby galaxies with next generation ground-based detectors.


title: Host Galaxies of low z Radio-loud Quasars: A search of HST archives

abstract:
  We searched the HST archives for unpublished WFPC2 images of low redshift
(z<0.5) radio loud quasars (RLQ). This led to the identification of 11 objects.
We present here the results of the analysis of these images from which we
derive the properties of their host galaxies. All objects are clearly resolved
and their surrounding nebulosity is consistent with an elliptical galaxy model.
These new data, together with previous published HST observations, form a
sample of 34 sources which significantly expands all previous studies of low
redshift RLQ based on HST data. For this full sample we derive the average
absolute magnitude of the host galaxies <M_R>=-24.01+/-0.48, and the effective
radius <R_e>=10.5+/-3.7kpc. No significant correlation is found between the
nucleus and the host galaxy luminosity. Using the relationship between black
hole mass (M_BH) and bulge luminosity we investigate the relation between M_BH
and total radio power for RLQ and compare with other classes of radio sources.
The overall distribution of AGN in the plane M_BH-P(radio) exhibits a trend for
increasing M_BH with increasing P(radio) but with a substantial spread. RLQ
occupy the region of most powerful sources and most massive BH. The quasars
appear to emit over a wide range of power with respect to their Eddington
luminosity as deduced by the estimated M_BH.


title: A peculiar type-I X-ray burst from GRS 1747-312

abstract:
  We report the serendipitous detection with the Rossi X-ray Timing Explorer of
a long and peculiar X-ray burst whose localization is consistent with one known
X-ray burster (GRS 1747-312) and which occurred when that source was otherwise
quiescent. The peculiar feature concerns a strong radius expansion of the
neutron star photosphere, which occurred not within a few seconds from the
start of the burst, as is standard in radius-expansion bursts, but 20 s later.
This suggests that two different layers of the neutron star may have undergone
thermonuclear runaways: a hydrogen-rich and a hydrogen-poor layer. The reason
for the delay may be related to the source being otherwise quiescent.


title: Chandra Observations of the Faintest Low-Mass X-ray Binaries

abstract:
  There exists a group of persistently faint galactic X-ray sources that, based
on their location in the galaxy, high L_x/L_opt, association with X-ray bursts,
and absence of low frequency X-ray pulsations, are thought to be low-mass X-ray
binaries (LMXBs). We present results from Chandra observations for eight of
these systems: 4U 1708-408, 2S 1711-339, KS 1739-304, SLX 1735-269, GRS
1736-297, SLX 1746-331, 1E 1746.7-3224, and 4U 1812-12. Locations for all
sources, excluding GRS 1736-297, SLX 1746-331, and KS 1739-304 (which were not
detected) were improved to 0.6" error circles (90% confidence). Our
observations support earlier findings of transient behavior of GRS 1736-297, KS
1739-304, SLX 1746-331, and 2S 1711-339 (which we detect in one of two
observations). Energy spectra for 4U 1708-408, 2S 1711-339, SLX 1735-269, 1E
1746.7-3224, and 4U 1812-12 are hard, with power law indices typically 1.4-2.1,
which are consistent with typical faint LMXB spectra.


title: Non-radial motion and the NFW profile

abstract:
  The self-similar infall model (SSIM) is normally discussed in the context of
radial orbits in spherical symmetry. However it is possible to retain the
spherical symmetry while permitting the particles to move in Keplerian
ellipses, each having the squared angular momentum peculiar to their 'shell'.
The spherical 'shell', defined for example by the particles turning at a given
radius, then moves according to the radial equation of motion of a 'shell'
particle. The 'shell' itself has no physical existence except as an ensemble of
particles, but it is convenient to sometimes refer to the shells since it is
they that are followed by a shell code. In this note we find the distribution
of squared angular momentum as a function of radius that yields the NFW density
profile for the final dark matter halo. It transpires that this distribution is
amply motivated dimensionally. An effective 'lambda' spin parameter is roughly
constant over the shells. We also study the effects of angular momentum on the
relaxation of a dark matter system using a three dimensional representation of
the relaxed phase space.


title:
Non-axisymmetric instabilities in shocked accretion flows with
  differential rotation

abstract:
  The linear stability of a shocked isothermal accretion flow onto a black hole
is investigated in the inviscid limit. The outer shock solution, which was
previously found to be stable with respect to axisymmetric perturbations, is,
however, generally unstable to non-axisymmetric ones. Eigenmodes and growth
rates are obtained by numerical integration of the linearized equations. The
mechanism of this instability is based on the cycle of acoustic waves between
their corotation radius and the shock. It is a form of the Papaloizou-Pringle
instability, modified by advection and the presence of the shock. As such it
can be generalized to non isothermal shocked accretion flows. Blobs and
vortices are generated by the shock as a by-product of the instability.


title: Multiple-field inflation and the CMB

abstract:
  In this paper, we investigate some consequences of multiple-field inflation
for the cosmic microwave background radiation (CMB). We derive expressions for
the amplitudes, the spectral indices and the derivatives of the indices of the
CMB power spectrum in the context of a very general multiple-field theory of
slow-roll inflation, where the field metric can be non-trivial. Both scalar
(adiabatic, isocurvature and mixing) and tensor perturbations are treated and
the differences with single-field inflation are discussed. From these
expressions, several relations are derived that can be used to determine the
importance of multiple-field effects observationally from the CMB. We also
study the evolution of the total entropy perturbation during radiation and
matter domination and the influence of this on the isocurvature spectral
quantities.


title:
A Homogeneous Sample of Sub-DLAs I: Construction of the Sample and
  Chemical Abundance Measurements

abstract:
  In this first paper of a series, we report on the use of quasar spectra
obtained with the UVES high resolution spectrograph and available through the
ESO VLT archive to build the first sample of sub-DLA systems, absorbers with HI
column densities > 10^{19} cm^{-2} but lower than the classical definition of
damped Ly-alpha systems (DLAs) 2x10^{20} cm^{-2}. A systematic investigation of
the properties of these systems and a comparison with those of the DLAs (Paper
II of this series; Peroux et al. 2003b) is expected to provide new clues on the
association of high column density absorbers with galaxies and on the overall
evolution of the neutral hydrogen gas mass and metal content in the Universe.
In the spectra of 22 quasars which were found suitable for a sub-DLA search, we
identified 12 sub-DLAs and 1 borderline case between the DLA and sub-DLA
systems in the redshift interval z = 1.8-4.3. We measured the column densities
of HI and up to 16 ions of low-, intermediate- and high-ionization. We further
investigated the significance of the ionization corrections in the
determination of the chemical abundances from the low-ionization ions in the
sub-DLA HI column density range. Using the predictions of different ion ratios
as a function of the ionization parameter computed with the CLOUDY software
package, we have estimated that with the exception of one case, the ionization
corrections to the abundances of 9 systems for which we were able to constrain
the ionization parameter, are lower than 0.2 dex for all of the elements except
AlII and ZnII down to HI column densities of log N(HI) = 19.3 cm^{-2}. We
finally present the first sub-DLA chemical abundance database which contains
the abundance measurements of 11 different elements (O, C, Si, N, S, Mg, Al,
Fe, Ni, Zn, and Cr).


title:
A Homogeneous Sample of Sub-DLAs II: Statistical, Kinematic and Chemical
  Properties

abstract:
  Damped Ly-alpha Systems (DLAs), with N(HI)>2*10^20 cm^{-2}, observed in
quasars have allowed us to quantify the chemical content of the Universe over
cosmological scales. Such studies can be extended to lower N(HI), in the
sub-DLA range (10^19<N(HI)<2*10^20 cm^{-2}), which are systems believed to
contain a large fraction of the neutral hydrogen at z>3.5. In this paper, we
use a homogeneous sample of sub-DLAs from the ESO UVES archives presented in
Paper I (Dessauges-Zavadsky et al. 2003), to observationally determine for the
first time the column density distribution, f(N), down to N(HI)=10^19 cm^{-2}.
The results are in good agreement with the predictions from Peroux et al.
(2003). We present the kinematic and clustering properties of this survey. We
compare low- and high-ionization transition widths and find that the sub-DLAs
properties roughly span the parameter space of DLAs. We analyse the chemical
content of this sample in conjunction with abundances from 72 DLAs taken from
the literature. We compute the HI column density-weighted mean abundance which
is believed to be an indicator of the Universe's metallicity. Although the
number statistics is limited, the results suggest a slightly stronger evolution
in the sub-DLA range. The evolution we probe is not due to their lower dust
content. Therefore these systems might be associated with a different class of
objects which better trace the overall chemical evolution of the Universe.
Finally, we present abundance ratios of [Si/Fe], [O/Fe], [C/Fe] and [Al/Fe],
but it is difficult to decipher whether the observed values are the effect of
nucleosynthesis or are due to differential dust depletion. The metallicities
are compared with two different sets of models of galaxy evolution in order to
provide constraints on the morphology of the absorbers [abridged].


title: Observations of DG Tauri with the Keck Interferometer

abstract:
  We present the first science results from the Keck Interferometer, a
direct-detection infrared interferometer utilizing the two 10-meter Keck
telescopes. The instrument and system components are briefly described. We then
present observations of the T Tauri object DG Tau, which is resolved by the
interferometer. The resolved component has a radius of 0.12 to 0.24 AU,
depending on the assumed stellar and extended component fluxes and the model
geometry used. Possible origins and implications of the resolved emission are
discussed.


title:
Polarization of the Atmosphere as a Foreground for Cosmic Microwave
  Background Polarization Experiments

abstract:
  We quantify the level of polarization of the atmosphere due to Zeeman
splitting of oxygen in the Earth's magnetic field and compare it to the level
of polarization expected from the polarization of the cosmic microwave
background radiation. The analysis focuses on the effect at mid-latitudes and
at large angular scales. We find that from stratospheric balloon borne
platforms and for observations near 100 GHz the atmospheric linear and circular
polarized intensities is about 10^{-12} and 100 x 10^{-9} K, respectively,
making the atmosphere a negligible source of foreground. From the ground the
linear and circular polarized intensities are about 10^{-9} and 100 x 10^{-6}
K, making the atmosphere a potential source of foreground for the CMB E (B)
mode signal if there is even a 1% (0.01%) conversion of circular to linear
polarization in the instrument.


title: Introducing EMILI: Computer Aided Emission Line Identification

abstract:
  The identification of spectral lines can be a tedious process requiring the
interrogation of large spectroscopic databases, but it does lend itself to
software algorithms that can determine the characteristics of candidate line
identifications. We present here criteria used for the identification of lines
and a logic developed for a line identification software package called EMILI,
which uses the v2.04 Atomic Line List as the basic line database. EMILI
considers all possible database transitions within the wavelength uncertainties
for observed optical emission lines and computes an approximate intensity for
each candidate line. It searches for other multiplet members that are expected
to be seen with each candidate line, and rank orders all of the tentative line
identifications for each observed line based on a set of criteria. When applied
to the spectra of the Orion Nebula and the planetary nebula IC 418, EMILI's
recommended line ID's agree well with those of previous traditional manual line
assignments. The existence of a semi-automated procedure should give impetus to
the study of very high signal-to-noise spectra, enabling the identification of
previously unidentified spectral lines to be handled with ease and consistency.


title:
The role of Violent Magnetic Reconnection on the Production of the Large
  Scale Superluminal Ejections of the Microquasar GRS 1915+105

abstract:
  We here propose that the large scale superluminal ejections observed in the
galactic microquasar GRS 1915+105 during radio flare events are produced by
violent magnetic reconnection episodes in the corona just above the inner edge
of the magnetized accretion disk that surrounds the central $\sim 10 M_{\odot}$
black hole. The process occurs when a large scale magnetic field is established
by turbulent dynamo in the inner disk region with a ratio between the
gas$+$radiation and the magnetic pressures $\beta \simeq 1$, implying a
magnetic field intensity of $\sim 7 \times 10^8$ G. During this process,
substantial angular momentum is removed from the disk by the wind generated by
the vertical magnetic flux therefore increasing the disk mass accretion to a
value near (but below) the critical one ($\dot M \sim 10^{19} $ g s$^{-1}$).
Part of the magnetic energy released by reconnection heats the coronal gas
($T_c \lesssim 5 \times 10^8 $ K) that produces a steep, soft X-ray spectrum
with luminosity $L_X \simeq 10^{39} $ erg s$^{- 1}$, in consistency with
observations. The remaining magnetic energy released goes to accelerate the
particles to relativistic velocities ($v \sim v_A \sim c$, where $v_A$ is the
Alfv\'en speed) in the reconnection site through first-order Fermi processes.
In this context, two possible mechanisms have been examined which produce
power-law electron distributions $N(E) \propto E^{-\alpha_E}$, with $\alpha_E =
5/2, 2$, and corresponding synchrotron radio power-law spectra with spectral
indices which are compatible with that observed during the flares ($ S_{\nu}
\propto \nu^{-0.75, - 0.5}$).


title: Evolution of second-order cosmological perturbations

abstract:
  We present a method for constructing gauge-invariant cosmological
perturbations which are gauge-invariant up to second order. As an example we
give the gauge-invariant definition of the second-order curvature perturbation
on uniform density hypersurfaces. Using only the energy conservation equation
we show that this curvature perturbation is conserved at second order on large
scales for adiabatic perturbations.


title:
A Study of the Afterglows of Four GRBs: Constraining the Explosion and
  Fireball Model

abstract:
  We employ a fireball model of the GRB explosion to constrain intrinsic and
environmental parameters of four events with good broadband afterglow data;
GRB970508, GRB980329, GRB980703, and GRB000926. Using standard assumptions of
constant circumburst density and no evolution of the fraction of the explosion
energy in the post-shock magnetic field, we investigate the uniformity of the
derived explosion and shock physics parameters among the events. We find
densities that range from those of the ISM to diffuse clouds, energies
comparable to the total GRB gamma-ray energy, collimations from near-isotropy
to 0.04 rad, substantial electron energy fractions of 10-30% with energy
distribution indices of 2.1-2.9 and magnetic energy fractions from 0.2-25%. We
also investigate the level to which the data constrain standard model
assumptions, such as the magnetic field evolution, and the allowed density
profiles of the medium. Fits generally improve slightly with an increasing
magnetic energy fraction epB. Good fits can be produced with epB accumulating
or decaying with the shock strength over the afterglow as epB~gamma^x;
-2<=x<=+1. The data are not very sensitive to increasing density profiles,
allowing good fits even with density ~r^10. Some parameter values change by up
to an order of magnitude under altered assumptions; parameters of even good
fits cannot be taken at face value. The data are sensitive to decreasing
densities; r^-2 profiles may produce reasonable fits; steeper profiles, even
r^-2.5, will not fit the data.


title: Formation of the Galactic Halo

abstract:
  Recent observational and theoretical work suggests that the formation of the
Galactic stellar halo involved both dissipative processes and the accretion of
subfragments. With present data, the fraction of the halo for which an
accretion origin can be substantiated is small, of order 10 percent. The
kinematics of the best halo field star samples show evidence for both
dissipative and dissipationless formation processes. Models of star-forming
dissipative collapse, in a cosmological context and including feedback from
star formation, do not confirm the simple relations between metallicity,
rotation velocity, and orbital eccentricity for halo stars as originally
predicted. The new model predictions are much closer to the observed
distributions, which have generally been interpreted as evidence for an
accretion origin. These results are broadly consistent with a hierarchical
galaxy formation model, but the details remain to be worked out.


title:
Observational evidence for a correlation between peak-luminosities and
  beaming in GRBs

abstract:
  We calculate the unseen-but-true GRB-event rate from a current flux-limited
sample of 33 GRBs with individually measured redshifts. We consider a GRB-event
rate which is proportional to the star-formation rate, in view of the GRB-SNe
association in SN1998bw and GRB030329. By fitting a log-normal distribution of
GRB peak-luminosities, we find a ratio of about 450 for the true-to-observed
GRB-event rates. This provides an independent derivation of the GRB-beaming
factor of about 500 obtained by Frail et al. (2001) from sources with standard
GRB-energies. We discuss applications to GRB980425.


title: Simulations of nonhelical hydromagnetic turbulence

abstract:
  Nonhelical hydromagnetic forced turbulence is investigated using large scale
simulations on up to 256 processors and $1024^3$ meshpoints. The magnetic
Prandtl number is varied between 1/8 and 30, although in most cases it is
unity. When the magnetic Reynolds number is based on the inverse forcing
wavenumber, the critical value for dynamo action is shown to be around 35 for
magnetic Prandtl number of unity. For small magnetic Prandtl numbers we find
the critical magnetic Reynolds number to increase with decreasing magnetic
Prandtl number. The Kazantsev $k^{3/2}$ spectrum for magnetic energy is
confirmed for the kinematic regime, i.e. when nonlinear effects are still
unimportant and when the magnetic Prandtl number is unity. In the nonlinear
regime, the energy budget converges for large Reynolds numbers (around 1000)
such that for our parameters about 70% is in kinetic energy and about 30% is in
magnetic energy. The energy dissipation rates are converged to 30% viscous
dissipation and 70% resistive dissipation. Second order structure functions of
the Elsasser variables give evidence for a $k^{-5/3}$ spectrum. Nevertheless,
the three-dimensional spectrum is close to $k^{-3/2}$, but we argue that this
is due to the bottleneck effect. The bottleneck effect is shown to be equally
strong both for magnetic and nonmagnetic turbulence, but it is far weaker in
one-dimensional spectra that are normally studied in laboratory turbulence.
Structure function exponents for other orders are well described by the
She-Leveque formula, but the velocity field is significantly less intermittent
and the magnetic field is more intermittent than the Elsasser variables.


title:
Magnetic Field Morphology of Orion-IRc2 from 86 GHz SiO Maser
  Polarization Images

abstract:
  In an attempt to probe the magnetic field morphology near the massive young
star Orion-IRc2, we mapped the linear polarization of its J=2-1 SiO masers, in
both the v=0 and v=1 vibrational levels, with 0.5 arcsec resolution. The
intense v=1 masers are confined to a narrow zone 40 AU from the star. Their
polarization position angles vary significantly on time scales of years. For
the v=1 masers the stimulated emission rate R is likely to exceed the Zeeman
splitting g\Omega due to any plausible magnetic field; in this case the maser
polarization need not correlate with the field direction. The much weaker v=0
masers in the ground vibrational level lie 100-700 AU from IRc2, in what
appears to be a flared disk. Their fractional polarizations are as high as 50%.
The polarization position angles vary little across the line profile or the
emission region, and appear to be stable in time. The position angle, P.A. = 80
degrees, we measure for the J=2-1 masers differs by 70 degrees from that
measured for the J=1-0 SiO transition, possibly because of Faraday rotation in
the foreground, Orion A, HII region. A rotation measure RM = 3.3 \times 10^4
rad m$^{-2}$ is required to bring the J=2-1 and J=1-0 position angles into
concordance. The intrinsic polarization position angle for both transitions is
then 57 degrees, parallel to the plane of the putative disk. Probably the
magnetic field threads the disk poloidally. There is little evidence for a
pinched or twisted field near the star.


title: Modelling Collision Products of Triple-Star Mergers

abstract:
  In dense stellar clusters, binary-single and binary-binary encounters can
ultimately lead to collisions involving two or more stars. A comprehensive
survey of multi-star collisions would need to explore an enormous amount of
parameter space, but here we focus on a number of representative cases
involving low-mass main-sequence stars. Using both Smoothed Particle
Hydrodynamics (SPH) calculations and a much faster fluid sorting software
package (MMAS), we study scenarios in which a newly formed product from an
initial collision collides with a third parent star. By varying the order in
which the parent stars collide, as well as the orbital parameters of the
collision trajectories, we investigate how factors such as shock heating affect
the chemical composition and structure profiles of the collision product. Our
simulations and models indicate that the distribution of most chemical elements
within the final product is not significantly affected by the order in which
the stars collide, the direction of approach of the third parent star, or the
periastron separations of the collisions. We find that the sizes of the
products, and hence their collisional cross sections for subsequent encounters,
are sensitive to the order and geometry of the collisions. For the cases that
we consider, the radius of the product formed in the first (single-single star)
collision ranges anywhere from roughly 2 to 30 times the sum of the radii of
its parent stars. The final product formed in our triple-star collisions can
easily be as large or larger than a typical red giant. We therefore expect the
collisional cross section of a newly formed product to be greatly enhanced over
that of a thermally relaxed star of the same mass.


title: Super Star Clusters in the Blue Dwarf Galaxy UM 462

abstract:
  I present optical observations of the Blue Compact Dwarf Galaxy UM 462. The
images of this galaxy show several bright compact sources. A careful study of
these sources has revealed their nature of young Super Star Clusters. The ages
determined from the analysis of the stellar continuum and $H\alpha$ are between
few and few tens Myr. The total star formation taking place into the clusters
is about 0.05 $\mathrm{M_{\odot}/yr}$. The clusters seem to be located at the
edges of two large round-like structures, possibly shells originated in a
previous episode of star formation. The sizes of the shells compare well with
the ages of the clusters. Evidence for the presence of an evolved underlying
stellar population is found.


title: Oxygen Abundances in Metal-Poor Stars

abstract:
  We present oxygen abundances derived from both the permitted and forbidden
oxygen lines for 55 subgiants and giants with [Fe/H] values between -2.7 and
solar with the goal of understanding the discrepancy in the derived abundances.
A first attempt, using \teff{} values from photometric calibrations and surface
gravities from luminosities, obtained agreement between the indicators for
turn-off stars, but the disagreement was large for evolved stars. We find that
the difference in the oxygen abundances derived from the permitted and
forbidden lines is most strongly affected by \teff{}, and we derive a new
\teff{} scale based on forcing the two sets of lines to give the same oxygen
abundances. These new parameters, however, do not agree with other observables,
such as theoretical isochrones or Balmer-line profile based \teff{}
determinations. Our analysis finds that one-dimensional, LTE analyses (with
published NLTE corrections for the permitted lines) cannot fully resolve the
disagreement in the two indicators without adopting a temperature scale
incompatible with other temperature indicators. We also find no evidence of
circumstellar emission in the forbidden lines, removing such emission as a
possible cause for the discrepancy.


title: Superhumps in the Rarely Outbursting SU UMa-Type Dwarf Nova, HO Delphini

abstract:
  We observed the 1994, 1996 and 2001 outbursts of HO Del. From the detection
of secure superhumps, HO Del is confirmed to be an SU UMa-type dwarf nova with
a superhump period of 0.06453(6) d. Based on the recent observations and the
past records, the outbursts of HO Del are found to be relatively rare, with the
shortest intervals of superoutbursts being ~740 d. Among SU UMa-type dwarf
novae with similar outburst intervals, the outburst amplitude (~5.0 mag) is
unusually small. HO Del showed a rather rapid decay of the superhump
amplitudes, and no regrowth of the amplitudes during the later stage, in
contrast to the commonly observed behavior in SU UMa-type dwarf novae with long
outburst intervals. We positively identified HO Del with a ROSAT X-ray source,
and obtained a relatively large X-ray luminosity of 10^(31.1+/-0.2) erg/s. We
also performed a literature survey of SU UMa-type dwarf novae, and presented a
new set of basic statistics. The SU UMa-type dwarf novae with a brightening
trend or with a regrowth of superhumps near the termination of a superoutburst
are found to be rather tightly confined in a small region on the (superhump
period-supercycle length) plane. These features may provide a better
observational distinction for the previously claimed subgroup of dwarf novae
(Tremendous Outburst Amplitude Dwarf Novae).


title:
Observations of the neutral hydrogen surrounding the radio quiet neutron
  star RX J0822-4300 in Puppis A

abstract:
  We have observed the HI distribution in an area 40' x 40' around the neutron
star candidate RX J0822-4300, which is located in the supernova remnant Puppis
A. The observations of the 21 cm line were obtained with the Australia
Telescope Compact Array (ATCA) and were combined with single dish data from the
Southern Galactic Plane Survey. The spatial resolution is 90", and the velocity
resolution, 1 km/s . A sensitivity of ~ 0.7 K was achieved. The results
revealed a double lobed feature of reduced emission at +16 km/s, centered on
the central compact object (CCO), and aligned with an HI hole blueshifted by 13
km/s. The HI depressions have probably been created by the sweeping up of ~ 2
solar masses. The alignement between the lobes and the optical expansion centre
of Puppis A suggests that the CCO could be ejecting two opposite jets. The
velocity at which the two lobes are best defined allowed us to confirm that the
distance to Puppis A is 2.2 kpc, based on a systemic velocity of +16 km/s. The
hydrogen column density computed using this systemic velocity is consistent
with estimates from models for X-ray spectra, thus reinforcing our conclusion
that the kinematic distance is 2.2 k pc.


title: A Planet in a Circular Orbit with a 6 Year Period

abstract:
  Precision Doppler velocity measurements from the 3.9--m Anglo-Australian
Telescope reveal a planet with a 6 year period orbiting the G5 dwarf HD 70642.
The a = 3.3 AU orbit has a low eccentricity (e = 0.1), and the minimum (\msini)
mass of the planet is 2.0 \mjup. The host star is metal rich relative to the
Sun, similar to most stars with known planets. The distant and approximately
circular orbit of this planet makes it a member of a rare group to emerge from
precision Doppler surveys.


title:
The Small Scale Anisotropies, the Spectrum and the Sources of Ultra High
  Energy Cosmic Rays

abstract:
  We calculate the number density and luminosity of the sources of ultra high
energy cosmic rays (UHECRs), using the information about the small scale
anisotropies and the observed spectra. We find that the number of doublets and
triplets observed by AGASA can be best reproduced for a source density of $\sim
10^{-5} Mpc^{-3}$, with large uncertainties. The spectrum of UHECRs implies an
energy input of $\sim 6\times 10^{44} erg yr^{-1} Mpc^{-3}$ above $10^{19}$ eV
and an injection spectrum $\propto E^{-2.6}$. A flatter injection spectrum,
$E^{-2.4}$, can be adopted if the sources have luminosity evolution $\propto
(1+z)^4$. The combination of these two pieces of information suggests that the
single sources should on average have a cosmic ray luminosity above $10^{19}$
eV of $L_{source}\approx 2\times 10^{42} erg s^{-1}$, weakly dependent upon the
injection spectrum. Unfortunately, with the limited statistics of events
available at present, there are approximately one-two orders of magnitude
uncertainty in the source density provided above. We make predictions on the
expected performances of the Auger and EUSO experiments, with particular
attention for the expected improvements in our understanding of the nature of
the sources of UHECRs. We find that a critical experimental exposure $\Sigma_c$
exists, such that experiments with exposure larger than $\Sigma_c$ can detect
at least one event from each source at energies above $10^{20}$ eV. This
represents a unique opportunity to directly count and identify the sources of
UHECRs.


title: Discovery of a luminous water megamaser in the FRII radiogalaxy 3C403

abstract:
  We report the first detection of a water megamaser in a radio-loud galaxy,
3C403. This object has been observed as part of a small sample of FRIIs with
evidence of nuclear obscuration. The isotropic luminosity of the maser is ~1200
L(sun). With a recessional velocity of cz ~ 17680 km/s it is the most distant
water maser so far reported. The line arises from the densest interstellar gas
component ever observed in a radio-loud galaxy. Two spectral features are
observed, likely bracketing the systemic velocity of the galaxy. These may
either arise from the tangentially seen parts of a nuclear accretion disk or
from dense warm gas interacting with the radio jets.


title: Abundances from the Integrated Light of Globular Clusters and Galaxies

abstract:
  It is currently impossible to determine the abundances and ages of the
stellar populations of distant, dense stellar systems star by star. Therefore,
methods to analyze the composite light of stellar systems are required. I
review the modelling and analysis of integrated spectra of the stellar
populations of individual globular clusters, globular cluster systems,
early-type galaxies, and the bulges of spiral galaxies, with a focus on their
abundances and abundance ratios. I conclude with a list of continuing
difficulties in the modelling that complicate the interpretation of integrated
spectra as well as a look ahead to new methods and new observations.


title: Time resolved spectroscopy of GRB030501 using INTEGRAL

abstract:
  The Gamma-ray instruments on-board INTEGRAL offer an unique opportunity to
perform time resolved analysis on GRBs. The imager IBIS allows accurate
positiioning of GRBs and broad band spectral analysis, while SPI provides high
resolution spectroscopy. GRB 030501 was discovered by the INTEGRAL Burst Alert
System in the ISGRI field of view. Although the burst was fairly weak (fluence
F = 3.5 * 10^-6 erg cm^-2 in the 20-200 keV energy band) it was possible to
perform time resolved spectroscopy with a resolution of a few seconds. The GRB
shows a spectrum in the 20 - 400 keV range which is consistent with a spectral
photon index of -1.7. No emission line or spectral break was detectable in the
spectrum. Although the flux seems to be correlated with the hardness of the GRB
spectrum, there is no clear soft to hard evolution seen over the duration of
the burst. The INTEGRAL data have been compared with results from the Ulysses
and RHESSI experiments.


title: Dark Energy Present and Future

abstract:
  By studying the present cosmological data, particularly on CMB, SNeIA and
LSS, we find that the future fate of the universe, for simple linear models of
the dark energy equation-of-state, can vary between the extremes of (I) a
divergence of the scale factor in as little as 7 Gyr; (II) an infinite lifetime
of the universe with dark energy dominant for all future time; (III) a
disappearing dark energy where the universe asymptotes as $t \to \infty$ to
$a(t) \sim t^{2/3}$ {\it i.e.} matter domination. Precision cosmological data
hint that a dark energy with equation of state $w = P/\rho < -1$ and hence
dubious stability is viable. Here we discuss for any $w$ nucleation from
$\Lambda > 0$ to $\Lambda = 0$ in a first-order phase transition. The critical
radius is argued to be at least of galactic size and the corresponding
nucleation rate glacial, thus underwriting the dark energy's stability and
rendering remote any microscopic effect.


title: First Microlensing Events From The MEGA Survey Of M31

abstract:
  We present the first M31 candidate microlensing events from the Microlensing
Exploration of the Galaxy and Andromeda (MEGA) survey. MEGA uses several
telescopes to detect microlensing towards the nearby Andromeda galaxy, M31, in
order to establish whether massive compact objects are a significant
contribution to the mass budget of the dark halo of M31. The results presented
here are based on observations with the Isaac Newton Telescope on La Palma,
during the 1999/00 and 2000/01 observing seasons. In this data set, 14 variable
sources consistent with microlensing have been detected, 12 of which are new
and 2 have been reported previously by the POINT-AGAPE group. A preliminary
analysis of the spatial and timescale distributions of the candidate events
support their microlensing nature. We compare the spatial distributions of the
candidate events and of long-period variable stars, assuming the chances of
finding a long-period variable and a microlensing event are comparable. The
spatial distribution of our candidate microlensing events is more far/near side
asymmetric than expected from the detected long-period variable distribution.
The current analysis is preliminary and the asymmetry not highly significant,
but the spatial distribution of candidate microlenses is suggestive of the
presence of a microlensing halo.


title:
Predictions on high frequency polarization properties of extragalactic
  radio sources and implications for CMB polarization measurements

abstract:
  We present a method to simulate the polarization properties of extragalactic
radio sources at microwave frequencies. Polarization measurements of nearly
2x10^6 sources at 1.4 GHz are provided by the NVSS survey. Using this catalogue
and the GB6 survey, we study the distribution of the polarization degree of
both steep- and flat-spectrum sources. We find that the polarization degree is
anti-correlated with the flux density for the former population, while no
correlation is detected for the latter. The available high-frequency data are
exploited to determine the frequency dependence of the distribution of
polarization degrees. Using such information and the evolutionary model by
Toffolatti et al. (1998), we estimate the polarization power spectrum of
extragalactic radio sources at \geq 30 GHz and their contamination of CMB
polarization maps. Two distinct methods to compute point-source polarization
spectra are presented, extending and improving the one generally used in
previous analyses. While extragalactic radio sources can significantly
contaminate the CMB E-mode power spectrum only at low frequencies (<30 GHz),
they can severely constrain the detectability of the CMB B-mode up to ~100 GHz.


title: Selection and photometric properties of K+A galaxies

abstract:
  Two different simple measurements of galaxy star formation rate with
different timescales are compared empirically on $156,395$ fiber spectra of
galaxies with $r<17.77$ mag taken from the Sloan Digital Sky Survey in the
redshift range $0.05<z<0.20$: a ratio $\Aamp / \Kamp$ found by fitting a linear
sum of an average old stellar poplulation spectrum (\Kamp) and average A-star
spectrum (\Aamp) to the galaxy spectrum, and the equivalent width (EW) of the
$\Halpha$ emission line. The two measures are strongly correlated, but there is
a small clearly separated population of outliers from the median correlation
that display excess $\Aamp /\Kamp$ relative to \Halpha EW. These ``K+A'' (or
``E+A'') galaxies must have dramatically decreased their star-formation rates
over the last $\sim 1$ Gyr. The K+A luminosity distribution is very similar to
that of the total galaxy population. The K+A population appears to be
bulge-dominated, but bluer and higher surface-brightness than normal
bulge-dominated galaxies; it appears that K+A galaxies will fade with time into
normal bulge-dominated galaxies. The inferred rate density for K+A galaxy
formation is $\sim 10^{-4} h^3 Mpc^{-3} Gyr^{-1}$ at redshift $z\sim 0.1$.
These events are taking place in the field; K+A galaxies don't primarily lie in
the high-density environments or clusters typical of bulge-dominated
populations.


title:
Capturing a star formation burst in galaxies infalling onto the cluster
  Abell 1367

abstract:
  The discovery of a striking astrophysical laboratory in the cluster of
galaxies Abell 1367 (Sakai et al. 2002) is confirmed with independent imaging
and spectroscopic observations and further investigated in the present
analysis. Two giant and ten dwarf/HII galaxies, members to a group, are
simultaneously undergoing a burst of star formation. Redshift measurements
suggest that the group galaxies are in the process of falling into the cluster
at very high speed. We explore two possible mechanisms that could have
triggered the short-lived stellar burst we are witnessing: the first, internal
to the group itself, via tidal interactions among its members, the hypothesis
favoured by Sakai et al. (2002); the second associated with the high velocity
infall of the group galaxies into the cluster intergalactic medium. We present
evidences in favour and against the two hypotheses.


title: First Detection of Millimeter Dust Emission from Brown Dwarf Disks

abstract:
  We report results from the first deep millimeter continuum survey targeting
Brown Dwarfs (BDs). The survey led to the first detection of cold dust in the
disks around two young BDs (CFHT-BD-Tau 4 and IC348 613), with deep JCMT and
IRAM observations reaching flux levels of a few mJy. The dust masses are
estimated to be a few Earth masses assuming the same dust opacities as usually
applied to TTauri stars.


title: Compact Stellar X-ray Sources in Normal Galaxies

abstract:
  This paper reviews recent results on populations of compact X-ray sources in
galaxies, mostly based on Chandra and Newton-XMM work.


title: Synchrotron Polarization at High Galactic Latitude

abstract:
  We present preliminary results from mapping the high-latitude Galactic
polarization with the Effelsberg Telescope at $\lambda$21 cm. Structures on the
resulting maps are mostly on the scale of several degrees. The results show
detection of polarization over most of the field, at the level of tens of
percent of the synchrotron emission. The evidence of more structure in Stokes Q
and U rather than in $\sqrt{Q^2+U^2}$ suggests the existence of Faraday
rotation.


title:
On the cross correlation between the arrival direction of ultra-high
  energy cosmic rays, BL Lacertae, and EGRET detections: A new way to identify
  EGRET sources?

abstract:
  With the aim of testing recent claims for a particularly strong correlation
between ultra-high energy cosmic rays (UHECRs), observed with the AGASA and the
Yakutsk experiments, and a sample of BL Lacertae (BL Lacs), we here conduct a
blind statistical assessment. We search for associations between the same set
of BL Lac objects and the arrival directions of 33 relevant UHECRs observed
with the Haverah Park and the Volcano Ranch experiments. Within the accuracy of
angle determination, there are no positional coincidences. The probability that
this null result arises as a statistical fluctuation from the strongly
correlated case is less than 5%. This implies that the possible correlation
between the arrival directions of UHECRs and BL Lacs is not statistically
sustained. We discuss the impact of our findings on the propose additional
connection among UHECRs, BL Lacs, and EGRET gamma-ray blazars. Recently, such
an association was used as classification technique for EGRET sources. Here we
show that its main underlying hypothesis, i.e., the EGRET angular uncertainty
is twice that quoted in the Third EGRET Catalog, underestimates the goodness of
existing gamma-ray data.


title: Precision Primordial $^4$He Measurement with CMB Experiments

abstract:
  Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are
two major pillars of cosmology. Standard BBN accurately predicts the primordial
light element abundances ($^4$He, D, $^3$He and $^7$Li), depending on one
parameter, the baryon density. Light element observations are used as a
baryometers. The CMB anisotropies also contain information about the content of
the universe which allows an important consistency check on the Big Bang model.
In addition CMB observations now have sufficient accuracy to not only determine
the total baryon density, but also resolve its principal constituents, H and
$^4$He. We present a global analysis of all recent CMB data, with special
emphasis on the concordance with BBN theory and light element observations. We
find $\Omega_{B}h^{2}=0.025+0.0019-0.0026$ and $Y_{p}=0.250+0.010-0.014$
(fraction of baryon mass as $^4$He) using CMB data alone, in agreement with
$^4$He abundance observations. With this concordance established we show that
the inclusion of BBN theory priors significantly reduces the volume of
parameter space. In this case, we find $\Omega_{B}h^2=0.0244+0.00137-0.00284$
and $Y_p = 0.2493+0.0006-0.001$. We also find that the inclusion of deuterium
abundance observations reduces the $Y_p$ and $\Omega_{B}h^2$ ranges by a factor
of $\sim $2. Further light element observations and CMB anisotropy experiments
will refine this concordance and sharpen BBN and the CMB as tools for precision
cosmology.


title:
Critical analysis of the luminosity functions per galaxy type measured
  from redshift surveys

abstract:
  [ABRIDGED] I perform a detailed comparison of the shape of the optical
luminosity functions as a function of galaxy class and filter, which have been
obtained from redshift surveys with an effective depth ranging from z~0.01 to
z~0.6. This analysis is based on the M* and alpha Schechter parameters. I
provide complete tables of all the existing measurements, converted into the
UBVRcIc Johnson-Cousins system wherever necessary. By using as reference the
intrinsic luminosity functions per morphological type measured from local
galaxy concentrations (Jerjen et al 1997), I establish that the variations in
the luminosity functions from survey to survey and among the galaxy classes are
related to the criteria for galaxy classification used in the surveys, as these
determine the amount of mixing of the morphological types within a given class.
When using a spectral classification with inaccurate spectrophotometric
calibrations, the luminosity functions are biased by type contamination with a
smooth variation from type to type poorly related to the intrinsic luminosity
functions per morphological type. In the case of multi-fiber spectroscopy,
galaxy classification based on rest-frame colors might then provide better
estimates of the intrinsic luminosity functions. All the existing surveys fail
to measure the Gaussian luminosity functions for Spiral galaxies. Most surveys
based on visual morphological classification also have their E/S0 luminosity
functions contaminated at the faint end, except for analyses based on either
multi-slit spectroscopy or medium-filter spectrophotometry combined with CCD
photometry. These contamination effects are presumably due to dwarf galaxies.
Measuring reliable intrinsic luminosity functions will thus require a more
coherent approach in separating the giant and dwarf galaxy types.


title:
Stellar and Dynamical Masses of Ellipticals in the Sloan Digital Sky
  Survey

abstract:
  We study the variation of the dark matter mass fraction of elliptical
galaxies as a function of their luminosity, stellar mass, and size using a
sample of 29,469 elliptical galaxies culled from the Sloan Digital Sky Survey.
We model ellipticals as a stellar Hernquist profile embedded in an
adiabatically compressed dark matter halo. This model allows us to estimate a
dynamical mass ($M_{dynm}$) at the half-light radius from the velocity
dispersion of the spectra, and to compare these to the stellar mass estimates
($M_{*}$) from Kauffmann et al (2003). We find that $M_{*}/L$ is independent of
luminosity, while $M_{dynm}/L$ increases with luminosity, implying that the
dark matter fraction increases with luminosity. We also observe that at a fixed
luminosity or stellar mass, the dark matter fraction increases with increasing
galaxy size or, equivalently, increases with decreasing surface brightness:
high surface brightness galaxies show almost no evidence for dark matter, while
in low surface brightness galaxies, the dark matter exceeds the stellar mass at
the half light radius. We relate this to the fundamental plane of elliptical
galaxies, suggesting that the tilt of this plane from simple virial predictions
is due to the dark matter in galaxies. We find that a simple model where
galaxies are embedded in dark matter halos and have a star formation efficiency
independent of their surface brightness explains these trends. We estimate the
virial mass of ellipticals as being approximately 7-30 times their stellar
mass, with the lower limit suggesting almost all of the gas within the virial
radius is converted into stars.


title:
The N Enrichment and Supernova Ejection of the Runaway Microquasar LS
  5039

abstract:
  We present an investigation of new optical and ultraviolet spectra of the
mass donor star in the massive X-ray binary LS 5039. The optical band spectral
line strengths indicate that the atmosphere is N-rich and C-poor, and we
classify the stellar spectrum as type ON6.5 V((f)). The N-strong and C-weak
pattern is also found in the stellar wind P Cygni lines of N V 1240 and C IV
1550. We suggest that the N-enrichment may result from internal mixing if the
O-star was born as a rapid rotator, or the O-star may have accreted N-rich gas
prior to a common-envelope interaction with the progenitor of the supernova. We
re-evaluated the orbital elements to find an orbital period of P=4.4267 +/-
0.0010 d. We compared the spectral line profiles with new non-LTE,
line-blanketed model spectra, from which we derive an effective temperature
T_eff = 37.5 +/- 1.7 kK, gravity log g = 4.0 +/- 0.1, and projected rotational
velocity V sin i = 140 +/- 8 km/s. We fit the UV, optical, and IR flux
distribution using a model spectrum and extinction law with parameters E(B-V)=
1.28 +/- 0.02 and R= 3.18 +/- 0.07. We confirm the co-variability of the
observed X-ray flux and stellar wind mass loss rate derived from the H-alpha
profile, which supports the wind accretion scenario for the X-ray production in
LS 5039. Wind accretion models indicate that the compact companion has a mass
M_X/M_sun = 1.4 +/- 0.4, consistent with its identification as a neutron star.
The observed eccentricity and runaway velocity of the binary can only be
reconciled if the neutron star received a modest kick velocity due to a slight
asymmetry in the supernova explosion (during which >5 solar masses was
ejected).


title:
Formation of massive stars and black holes in self-gravitating AGN
  discs, and gravitational waves in LISA band

abstract:
  We propose a scenario in which massive stars form at the outer edges of an
AGN accretion disc. We analyze the dynamics of a disc forming around a
supermassive black hole, in which the angular momentum is transported by
turbulence induced by the disc's self-gravity. We find that once the surface
density of the disc exceeds a critical value, the disc fragments into dense
clumps. The biggest clumps collapse and form massive stars, which produce
few-tens-solar-mass black holes at the end of their evolution. The embedded
black holes will interact gravitationally with the massive accretion disc and
be dragged towards the central black hole. Merger of a disc-born black hole
with the central black hole will produce a burst of gravitational waves. If the
central black hole is accreting at a rate comparable to the Eddington limit,
the gas drag from the accretion disc will not alter significantly the dynamics
of the final year of merger, and the gravitational waves should be observable
by LISA. We argue that for a reasonable range of parameters such mergers will
be detected monthly, and that the gravitational-wave signal from these mergers
is distinct from that of other merger scenarios. Also, for some plausible black
hole masses and accretion rates, the burst of gravitational waves should be
accompanied by a detectable change in the optical luminosity of the central
engine.


title:
The radio afterglow from the giant flare of SGR 1900+14: the same
  mechanism as afterglows from classic gamma-ray bursts?

abstract:
  A radio afterglow was detected following the 1998 August 27 giant flare from
the soft gamma repeater (SGR) 1900+14. Its short-lived behavior is quite
different from the radio nebula of SGR 1806-20, but very similar to radio
afterglows from classic gamma-ray bursts (GRBs). Motivated by this, we attempt
to explain it with the external shock model as invoked in the standard theory
of GRB afterglows. We find that the light curve of this radio afterglow is not
consistent with the forward shock emission of an ultra-relativistic outflow,
which is suggested to be responsible for the initial hard spike of the giant
flare. Nevertheless, shock emission from a mildly or sub-relativistic outflow
expanding into the interstellar medium could fit the observations. The possible
origin for this kind of outflow is discussed, based on the magnetar model for
SGRs. Furthermore, we suggest that the presence of an ultra-relativistic
fireball from SGR giant flares could be tested by rapid radio to optical
follow-up observations in the future.


title: Star Formation and the Hall Effect

abstract:
  The breakdown of flux-freezing in molecular clouds and protostellar discs is
usually approximated by ambipolar diffusion at low densities or by resistive
diffusion at high densities. Here I discuss an intermediate regime in which the
Hall term in the conductivity tensor is significant, and the vector evolution
of the magnetic field -- and therefore the evolution of the system under
consideration -- is dramatically altered. Calculations of charged particle
abundances in dense gas in molecular clouds and protostellar discs demonstrate
that Hall diffusion is important over a surprisingly broad range of conditions.


title: Dust Formation in Very Massive Primordial Supernovae

abstract:
  At redshift z>5 Type II supernovae (SNII) are the only known dust sources
with evolutionary timescales shorter than the Hubble time. We extend the model
of dust formation in the ejecta of SNII by Todini & Ferrara (2001) to
investigate the same process in pair-instability supernovae (PISN), which are
though to arise from the explosion of the first, metal free, very massive
(140-260 Msun) cosmic stars. We find that 15%-30% of the PISN progenitor mass
is converted into dust, a value >10 times higher than for SNII; PISN dust
depletion factors (fraction of produced metals locked into dust grains) range
between 0.3 and 0.7. These conclusions depend very weakly on the mass of the
PISN stellar progenitor, which instead affects considerably the composition and
size distribution. For the assumed temperature evolution, grain condensation
starts 150-200 days after the explosion; the dominant compounds for all
progenitor masses are SiO2 and Mg2SiO4 while the contribution of amorphous
carbon and magnetite grains grows with progenitor mass; typical grain sizes
range between 0.001 and a few 0.1 micron and are always smaller than 1 micron.
We give a brief discussion of the implications of dust formation for the IMF
evolution of the first stars, cosmic reionization and the intergalactic medium.


title:
Three years in the coronal life of AB Dor. I. Plasma emission measure
  distributions and abundances at different activity levels

abstract:
  The young active star AB Dor (K1 IV-V) has been observed 16 times in the last
three years with the XMM-Newton and Chandra observatories, totalling 650 ks of
high-resolution X-ray spectra. The XMM/RGS observations with the highest and
lowest average emission levels have been selected to study the coronal
properties of AB Dor in two different activity levels. We compare the results
based on the XMM data with those obtained from a higher resolution Chandra/HETG
spectrum, using the same line-based analysis technique. We have reconstructed
the plasma Emission Measure Distribution vs. temperature (EMD) in the range log
T(K) ~ 6.1-7.6, and we have determined the coronal abundances of AB Dor,
obtaining consistent results between the two instruments.The overall shape of
the EMD is also consistent with the one previously inferred from EUVE data. The
EMD shows a steep increase up to the peak at log T (K) ~ 6.9 and a substantial
amount of plasma in the range log T (K) ~ 6.9-7.3. The coronal abundances show
a clear trend of increasing depletion with respect to solar photospheric
values, for elements with increasing First Ionization Potential (FIP), down to
the Fe value ([Fe/H]=-0.57), followed by a more gradual recovery of the
photospheric values for elements with higher FIP. He-like triplets and Fe XXI
and Fe XXII lines ratios indicate electron densities log ne~10.8 cm^-3 at log
T(K) ~ 6.3 and log ne ~ 12.5 at log T(K) ~ 7, implying plasma pressures steeply
increasing with temperature. These results are interpreted in the framework of
a corona composed of different families of magnetic loop structures, shorter
than the stellar radius and in isobaric conditions, having pressures increasing
with the maximum plasma temperature, and which occupy a small fraction (f ~
10^-4 - 10^-6) of the stellar surface.


title: Gravitational Wave detection through microlensing?

abstract:
  It is shown that accurate photometric observations of a relatively
high--magnification microlensing event ($A\gg 1$), occurring close to the line
of sight of a gravitational wave (GW) source, represented by a binary star, can
allow the detection of subtle gravitational effects. After reviewing the
physical nature of such effects, it is discussed to what extent these phenomena
can actually be due to GWs. Expressions for the amplitude of the phenomena and
the detection probability are supplied.