title: The radial extinction profiles of late-type galaxies

abstract:
  We have used UV (FOCA) and FIR (IRAS) images of six nearby late type galaxies
to study the radial variation of the UV extinction (deduced from the FIR/UV
ratio). We compare the UV extinction gradient with other extinction indicators
(Balmer decrement) and search for a relation between the extinction, the
metallicity and the gas surface density among our galaxies. We detect in our
small sample a clear relation between extinction and metallicity. These
observed relations are used to calibrate an empirical recipe useful for
extinction correction in the UV, visible and near-infrared images of late type
galaxies.


title: The Impact of Heavy Nuclei on the Cosmogenic Neutrino Flux

abstract:
  As ultra-high energy cosmic ray protons propagate through the universe, they
undergo photo-meson interactions with the cosmic microwave background,
generating the `cosmogenic' neutrino flux. If a substantial fraction of the
cosmic ray primaries are heavy nuclei rather than protons, however, they would
preferentially lose energy through photo-disintegration, so the corresponding
neutrino flux may be substantially depleted. We investigate this issue using a
Monte Carlo simulation of cosmic ray propagation through interagalactic
radiation fields and assess the impact of the altered neutrino fluxes on next
generation neutrino telescopes.


title: The Location of the Core in M81

abstract:
  We report on VLBI observations of M81*, the northwest-southeast oriented
nuclear core-jet source of the spiral galaxy M81, at five different frequencies
between 1.7 and 14.8 GHz. By phase referencing to supernova 1993J we can
accurately locate the emission region of M81* in the galaxy's reference frame.
Although the emission region's size decreases with increasing frequency while
the brightness peak moves to the southwest, the emission region seems sharply
bounded to the southwest at all frequencies. We argue that the core must be
located between the brightness peak at our highest frequency (14.8 GHz) and the
sharp bound to the southwest. This narrowly constrains the location of the
core, or the purported black hole in the center of the galaxy, to be within a
region of +/-0.2 mas or +/-800 AU (at a distance of ~4 Mpc). This range
includes the core position that we determined earlier by finding the most
stationary point in the brightness distribution of M81* at only a single
frequency. This independent constraint therefore strongly confirms our earlier
core position. Our observations also confirm that M81* is a core-jet source,
with a one-sided jet that extends to the northeast from the core, on average
curved somewhat to the east, with a radio spectrum that is flat or inverted
near the core and steep at the distant end. The brightness peak is
unambiguously identified with the variable jet rather than the core, which
indicates limitations in determining the proper motion of nearby galaxies and
in refining the extragalactic reference frame.


title:
The formation and habitability of terrestrial planets in the presence of
  hot jupiters

abstract:
  `Hot jupiters,' giant planets with orbits very close to their parent stars,
are thought to form farther away and migrate inward via interactions with a
massive gas disk. If a giant planet forms and migrates quickly, the
planetesimal population has time to re-generate in the lifetime of the disk and
terrestrial planets may form (Armitage 2003). We present results of simulations
of terrestrial planet formation in the presence of hot jupiters, broadly
defined as having orbital radii <= 0.5 AU. We show that terrestrial planets
similar to those in the Solar System can form around stars with hot jupiters,
and can have water contents equal to or higher than the Earth's. For small
orbital radii of hot jupiters (e.g. 0.15, 0.25 AU) potentially habitable
planets can form, but for semi-major axes of 0.5 AU or greater their formation
is suppressed. We show that the presence of an outer giant planet such as
Jupiter does not enhance the water content of the terrestrial planets, but
rather decreases their formation and water delivery timescales. We speculate
that asteroid belts may exist interior to the terrestrial planets in systems
with hot jupiters.


title:
The Collapse of Differentially Rotating Supermassive Stars: Conformally
  Flat Simulations

abstract:
  We investigate the gravitational collapse of rapidly rotating relativistic
supermassive stars by means of a 3+1 hydrodynamical simulations in conformally
flat spacetime of general relativity. We study the evolution of differentially
rotating supermassive stars of $q \equiv J/M^{2} \sim 1$ ($J$ is the angular
momentum and $M$ is the gravitational mass of the star) from the onset of
radial instability at $R/M \sim 65$ ($R$ is the circumferential radius of the
star) to the point where the conformally flat approximation breaks down. We
find that the collapse of the star of $q \gtrsim 1$, a radially unstable
differentially rotating star form a black hole of $q \lesssim 1$. The main
reason to prevent formation of a black hole of $q \gtrsim 1$ is that quite a
large amount of angular momentum stays at the surface. We also find that most
of the mass density collapses coherently to form a supermassive black hole with
no appreciable disk nor bar. In the absence of nonaxisymmetric deformation, the
collapse of differentially rotating supermassive stars from the onset of radial
instability are the promising sources of burst and quasinormal ringing waves in
the Laser Interferometer Space Antenna.


title:
A Study of the Composition of Ultra High Energy Cosmic Rays Using the
  High Resolution Fly's Eye

abstract:
  The composition of Ultra High Energy Cosmic Rays (UHECR) is measured with the
High Resolution Fly's Eye cosmic ray observatory (HiRes) data using the Xmax
technique. Data were collected in stereo between 1999 November and 2001
September. The data are reconstructed with well-determined geometry.
Measurements of the atmospheric transmission are incorporated in the
reconstruction. The detector resolution is found to be 30 g cm^-2 in Xmax and
13% in Energy. The Xmax elongation rate between 10^18.0 eV and 10^19.4 eV is
measured to be 54.5 +/- 6.5 (stat) +/- 4.5 (sys) g cm^-2 per decade. This is
compared to predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction
models for both protons and iron nuclei. CORSIKA-generated Extensive Air
Showers (EAS) are incorporated directly into a detailed detector Monte Carlo
program. The elongation rate and the Xmax distribution widths are consistent
with a constant or slowly changing and predominantly light composition. A
simple model containing only protons and iron nuclei is compared to QGSJet and
SIBYLL. The best agreement between the model and the data is at 80% protons for
QGSJet and 60% protons for SIBYLL.


title: Mirror matter-type dark matter

abstract:
  There are six main things which any non-baryonic dark matter theory should
endeavour to explain: (1) The basic dark matter particle properties [mass,
stability, darkness]; (2) The similarity in cosmic abundance between ordinary
and non-baryonic dark matter, $\Omega_B \sim \Omega_{dark}$; (3) Large scale
structure formation; (4) Microlensing (MACHO) events; (5) Asymptotically flat
rotation curves in spiral galaxies; (6) The impressive DAMA/NaI annual
modulation signal. Only mirror matter-type dark matter is capable of explaining
all six of these desirable features. The purpose of this article is to provide
an up-to-date and pedagogical review of this dark matter candidate.


title: T Dwarfs and the Substellar Mass Function. I. Monte Carlo Simulations

abstract:
  Monte Carlo simulations of the field substellar mass function (MF) are
presented. Starting from various representations of the MF below 0.1 M$_{\sun}$
and the stellar birth rate, luminosity functions (LFs) and T$_{eff}$
distributions are produced for comparison with observed samples. These
distributions exhibit distinct minima in the mid-type L dwarf regime followed
by a rise in number density for fainter/cooler brown dwarfs, predicting many
more T-type and cooler brown dwarfs in the field even for relatively shallow
mass functions. Deuterium-burning brown dwarfs dominate field objects with 400
$\leq$ T$_{eff}$ $\leq$ 2000 K, while non-fusing brown dwarfs make up a
substantial proportion of field dwarfs with T$_{eff}$ $\leq$ 500 K. The shape
of the substellar LF is fairly consistent for various assumptions of the
Galactic birth rate, choice of evolutionary model, and adopted age and mass
ranges, particularly for field T dwarfs, which as a population provide the best
constraints for the field substellar MF. Exceptions include a depletion of
objects with 1200 $\leq$ T$_{eff}$ $\leq$ 2000 K in ``halo'' systems.
Unresolved multiple systems tend to enhance features in the observed LF and may
contribute significantly to the space density of very cool brown dwarfs.
However, these effects are small ($<$ 10% for T$_{eff} \lesssim 300$ K) for
binary fractions typical for brown dwarf systems (10--20%). An analytic
approximation to correct the observed space density for unresolved multiple
systems in a magnitude-limited survey is derived. [ABRIDGED]


title: Intracluster Planetary Nebulae as Probes of Intracluster Starlight

abstract:
  I review the progress in research on Intracluster Planetary Nebulae (IPN).
Hundreds of IPN candidates have now been found in the Virgo and Fornax galaxy
clusters, and searches of two nearby galaxy groups have made. From the results
thus far, approximately 10 - 20% of all stars in Virgo and Fornax are in an
intracluster component, but there are few such stars in galaxy groups. From the
spatial distribution of IPN, it appears that the intracluster stars are
clustered, in agreement with tidal-stripping scenarios. In Virgo, the IPN have
a large line-of-sight depth, which implies that the bulk of intracluster stars
in this cluster derive from late-type galaxies and dwarfs. I also discuss other
important developments in IPN research such as the detection of intracluster H
II regions, a possible detection of IPN in the Coma Cluster, and future
observational and theoretical developments.


title: X-ray Lines in Gamma-ray Bursts and Cerenkov Line Mechanism

abstract:
  X-ray emission and absorption features are of great importance in our
understanding the nature and environment of gamma-ray bursts (GRBs). So far,
iron emission lines have been detected in at least four GRB afterglows. In this
paper, the observational properties and physical constraints on materials
surrounding GRB sources are reviewed, and several classes of theoretical models
are also discussed. We will specially concentrate on the Cerenkov line
mechanism, in which the broad iron lines are expected, and a small mass of Fe
is required to produce the large line luminosity. In addition, our
interpretation can favor the recent jet unified model for different classes of
gamma-ray bursts with a standard energy reservoir.


title: Origin of Tidal Dissipation in Jupiter: I. Properties of Inertial-Mode

abstract:
  We study global inertial-modes with the purpose of unraveling the role they
play in the tidal dissipation process of Jupiter. For spheres of uniformly
rotating, neutrally buoyant fluid, we show that the partial differential
equation governing inertial-modes can be separated into two ordinary
differential equations when the density is constant, or when the density has a
power-law dependence on radius. For more general density dependencies, we show
that one can obtain an approximate solution to the inertial-modes that is
accurate to the second order in wave-vector. Frequencies of inertial-modes are
limited to $\omega < 2 \Omega$ ($\Omega$ is the rotation rate), with modes
propagating closer to the rotation axis having higher frequencies. An
inertial-mode propagates throughout much of the sphere with a relatively
constant wavelength, and a wave amplitude that scales with density as
$1/\sqrt{\rho}$. It is reflected near the surface at a depth that depends on
latitude, with the depth being much shallower near the special latitudes
$\theta = \cos^{-1} \pm \omega/2\Omega$. Around this region, this mode has the
highest wave amplitude as well as the sharpest spatial gradient (the
``singularity belt''), thereby incurring the strongest turbulent dissipation.
Inertial-modes naturally cause small Eulerian density perturbations, so they
are only weakly coupled to the tidal potential. In a companion paper, we
attempt to apply these results to the problem of tidal dissipation in Jupiter.


title: Origin of Tidal Dissipation in Jupiter: II. the Value of Q

abstract:
  The process of tidal dissipation inside Jupiter is not yet understood. Its
tidal quality factor ($Q$) is inferred to lie between $10^5$ and $10^6$. We
examine effects of inertial-modes on tidal dissipation in a neutrally bouyant,
core-less, uniformly rotating planet. The rate of dissipation caused by
resonantly excited inertial-modes depends on the following three parameters:
how well they are coupled to the tidal potential, how strongly they are
dissipated (by the turbulent viscosity), and how densely distributed they are
in frequency. We find that as a function of tidal frequency, the $Q$ value
exhibits large fluctuations, with its maximum value set by the group of
inertial-modes that have a typical offset from an exact resonance of order
their turbulent damping rates. In our model, inertial-modes shed their tidally
acquired energy very close to the surface within a narrow latitudinal zone (the
'singularity belt'), and the tidal luminosity escapes freely out of the planet.
Strength of coupling between the tidal potential and inertial-modes is
sensitive to the presence of density discontinuities inside Jupiter. In the
case of a discreet density jump (as may be caused by the transition between
metallic and molecular hydrogen), we find a time-averaged $Q \sim 10^7$. Even
though it remains unclear whether tidal dissipation due to resonant
inertial-modes is the correct answer to the problem, it is impressive that our
simple treatment here already leads to three to five orders of magnitude
stronger damping than that from the equilibrium tide. Moreover, our conclusions
are not affected by the presence of a small solid core, a different
prescription for the turbulent viscosity, or nonlinear mode coupling, but they
depend critically on the static stability in the upper atmosphere of Jupiter.


title: An XTE Archival Search for Coherent X-ray Pulsations in LMXB 4U 1820-30

abstract:
  As part of a large-scale search for coherent pulsations from LMXBs in the
RXTE archive, we have completed a detailed series of searches for coherent
pulsations of 4U 1820-30 -- an ultracompact LMXB with a binary period of 11.4
min, located in the globular cluster NGC6624. The short binary period implies
any coherent signal would be highly accelerated, so we used phase modulation
searches, orbital-parameter-fitting coherent searches, and standard
acceleration searches to give significant sensitivity to millisecond
pulsations. We searched, in four energy bands and at a range of luminosities, a
total of 34 archival RXTE observations, 32 of which had on-source integration
times longer than 10 ks, and some of which were made consecutively which
allowed us to combine them. We found no pulsations. Using our phase modulation
search technique, which we ran on all 34 observations, we have been able to
place the first stringent (95% confidence) pulsed fraction limits of <~0.8% for
all realistic spin frequencies (i.e. <~2kHz) and likely companion masses
(0.02Msun <= M_c <= 0.3Msun). Using our orbital-parameter-fitting coherent
search, which we ran on only 11 selected observations, we have placed a pulsed
fraction limit of <~0.3% for spin frequencies <~1.25kHz and companion masses M_
<= 0.106Msun. By contrast, all five LMXBs known to emit coherent pulsations
have intrinsic pulsed fractions in the range 3% to 7% when pulsations are
observed. Hence, our searches rule out pulsations with significantly lower
pulsed fractions than those already observed.


title: The Color-Magnitude Effect in Early-Type Cluster Galaxies

abstract:
  We present the analysis of the color-magnitude relation (CMR) for a sample of
57 X-ray detected Abell clusters within the redshift interval 0.02 <= z <=
0.18. We use the B-R vs R color-magnitude plane to establish that the CMR is
present in all our low-redshift clusters and can be parameterized by a single
straight line.We find that the CMRs for this large cluster sample of different
richness and cluster types are consistent with having universal properties. The
k-corrected color of the individual CMRs in the sample at a fixed absolute
magnitude have a small intrinsic dispersion of ~0.05 mag. The slope of the CMR
is consistent with being the same for all clusters, with the variations
entirely accountable by filter band shifting effects. We determine the mean of
the dispersion of the 57 CMRs to be 0.074 mag, with a small rms scatter of
0.026 mag. However, a modest amount of the dispersion arises from photometric
measurement errors and possible background cluster superpositions; and the
derived mean dispersion is an upper limit. Models which explain the CMR in
terms of metallicity and passive evolution can naturally reproduce the observed
behavior of the CMR in this paper. The observed properties of the CMR are
consistent with models in which the last episode of significant star formation
in cluster early-type galaxies occurred significantly more than ~3 Gyr ago, and
that the core set of early-type galaxies in clusters were formed more than 7
Gyr ago. (abridged)


title: Making waves on CMB power spectrum and inflaton dynamics

abstract:
  We discuss cosmic microwave background anisotropies in models with an
unconventional primordial power spectrum. In particular, we consider an initial
power spectrum with some ``spiky'' corrections. Interestingly, such a
primordial power spectrum generates ``wavy'' structure in the CMB angular power
spectrum.


title:
Mass accumulation efficiency in helium shell flashes for various white
  dwarf masses

abstract:
  We have calculated the mass accumulation efficiency during helium shell
flashes on white dwarfs (WDs) of mass 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, and
$1.35 M_{\odot}$ for the helium accretion rates $\log\dot M_{\rm He} \
(M_{\odot}$ yr$^{-1}) = -7.4$ to -5.8. This efficiency is a crucial factor for
binary evolutions of Type Ia supernovae. For less massive WDs ($< 0.8 \
M_{\odot}$) no wind mass loss occurs and all the accreted mass accumulates on
the WD if the Roche lobe size is large enough. The efficiency takes the minimum
values in between 1.1 and 1.2 $M_{\odot}$ WD for a given mass accretion rate
and increases in both less and more massive WDs. The mass accumulation
efficiency is larger than 0.5 for $\log\dot M_{\rm He} \geq -6.72$ in all the
WD masses.


title: Six Years of Gamma Ray Burst Observations with BeppoSAX

abstract:
  I give a summary of the prompt X-/gamma-ray detections of Gamma Ray Bursts
(GRBs) with the BeppoSAX satellite and discuss some significant results
obtained from the study of the prompt emission of these GRBs obtained with the
BeppoSAX Gamma Ray Burst Monitor and Wide Field Cameras.


title: Disorder resistivity of solid neutron-star matter

abstract:
  Lower limits are found for the disorder resistivity of solid neutron-star
matter in the neutron-drip region which is amorphous and heterogeneous in
nuclear charge. This temperature-independent resistivity, large compared with
that produced by phonon scattering, has direct consequences for theories of
neutron-star magnetic field generation and evolution.


title: Accurate radius and mass of the transiting exoplanet OGLE-TR-132b

abstract:
  The exoplanet OGLE-TR-132b belongs to the new class of very hot giant
planets, together with OGLE-TR-56b and OGLE-TR-113b, detected by their
transits. Recently, radial velocity measurements provided a planetary mass
estimate for OGLE-TR-132b. The planet parameters, however, were poorly cons
trained, because of the very shallow transit in the OGLE light curve. In this
letter, based on new VLT/FORS2 photometric follow-up of OGLE-TR-132 of
unprecedented quality (1.2 millimagnitude relative photometry), we confirm the
planetary nature of the orbiting object, and we derive an accurate measurement
of its radius and mass: 1.13 +- 0.08 R_J and 1.19 +- 0.13 M_J. The refined
ephemeris of OGLE-TR-132 transits is T_0 = 2453142.5888 and P = 1.689857 days.


title: Red giant stars in NGC 5128

abstract:
  I present a selection of results obtained from VLT FORS1 and ISAAC
photometric monitoring of late-type giants in NGC 5128 (=Centaurus A). The
combination of optical and near-IR photometry allows to probe the full
metallicity range of the stars on the upper red giant branch, thanks to
combined low-metallicity sensitivity of the optical and high-metallicity
sensitivity of the near-IR bands. The metallicity distribution covers a wide
range with the mean value around [M/H] ~ -0.45 dex. The near-IR monitoring of
the variable AGB stars allows to gain insights into the age distribution. The
period distribution of these long period variables indicates only about 10%
contribution of the intermediate-age component (age < 5 Gyr) to the
predominantly old stellar halo. Among the brightest, large amplitude and long
period variables only very few have near-IR and optical colors consistent with
carbon-rich giants.


title:
Improving XMM-Newton EPIC pn data at low energies: method and
  application to the Vela SNR

abstract:
  High quantum efficiency over a broad spectral range is one of the main
properties of the EPIC pn camera on-board XMM-Newton. The quantum efficiency
rises from ~75% at 0.2 keV to ~100% at 1 keV, stays close to 100% until 8 keV,
and is still ~90% at 10 keV. The EPIC pn camera is attached to an X-ray
telescope which has the highest collecting area currently available, in
particular at low energies (more than 1400 cm2 between 0.1 and 2.0 keV). Thus,
this instrument is very sensitive to the low-energy X-ray emission. However,
X-ray data at energies below ~0.2 keV are considerably affected by detector
effects, which become more and more important towards the lowest transmitted
energies. In addition to that, pixels which have received incorrect offsets
during the calculation of the offset map at the beginning of each observation,
show up as bright patches in low-energy images. Here we describe a method which
is not only capable of suppressing the contaminations found at low energies,
but which also improves the data quality throughout the whole EPIC pn spectral
range. This method is then applied to data from the Vela supernova remnant.


title:
Earth-skimming UHE Tau Neutrinos at the Fluorescence Detector of Pierre
  Auger Observatory

abstract:
  Ultra high energy neutrinos are produced by the interaction of hadronic
cosmic rays with the cosmic radiation background. More exotic scenarios like
topological defects or new hadrons predict even larger fluxes. In particular,
Earth-skimming tau neutrinos could be detected by the Fluorescence Detector
(FD) of Pierre Auger Observatory. A detailed evaluation of the expected number
of events has been performed for a wide class of neutrino flux models. An
updated computation of the neutrino-nucleon cross section and of the tau energy
losses has been carried out. For the most optimistic theoretical models, about
one Earth-skimming neutrino event is expected in several years at FD.


title:
ISOCAM observations in the Lockman Hole - II The 14.3 micron deep
  survey: data reduction, catalogue and source counts

abstract:
  We present a new analysis of the ISOCAM 14.3 micron deep survey in a 20x20
square arcmins area in the Lockman Hole. This survey is intermediate between
the ultra-deep surveys and the shallow surveys in the ELAIS fields. The data
have been analyzed with the method presented by Lari et al. (2001). We have
produced a catalogue of 283 sources detected above the 5-sigma threshold, with
fluxes in the interval 0.1-8 mJy. The catalogue is 90% complete at 1 mJy. The
positional accuracy, estimated from the cross-correlation of infrared and
optical sources, is around 1.5 arcsec. The search for the optical counterparts
of the sources in the survey is performed on a medium-deep r' band optical
image (5-sigma depth of r'=25), making use of the radio detections when
available. The photometry has been checked through simulations and by comparing
the data with those presented in a shallower and more extended ISOCAM survey in
the Lockman Hole, that we have presented in a companion paper. Only 15% of the
14.3 micron sources do not have an optical counterpart down to r'=25 mag. We
use the 6.7/14.3 micron colour as a star/galaxy separator, together with a
visual inspection of the optical image and an analysis of the observed Spectral
Energy Distribution of the ISOCAM sources. The stars in the sample turn out to
be only 6% of the sample. We discuss the 14.3 micron counts of extragalactic
sources, combining our catalogue with that obtained from the shallower ISOCAM
survey. The data in the two surveys are consistent, and our results fully
support the claims in previous works for the existence of an evolving
population of infrared galaxies, confirming the evident departure from
non-evolutionary model predictions.


title: K-band Properties of Well-Sampled Groups of Galaxies

abstract:
  We use a sample of 55 groups and 6 clusters of galaxies ranging in mass from
7 x 10^11 Msun to 1.5 x 10^15 Msun to examine the correlation of the Ks-band
luminosity with mass discovered by Lin et al. (2003). We use the 2MASS catalog
and published redshifts to construct complete magnitude limited redshift
surveys of the groups. From these surveys we explore the IR photometric
properties of groups members including their IR color distribution and
luminosity function. Although we find no significant difference between the
group Ks luminosity function and the general field, there is a difference
between the color distribution of luminous group members and their counterparts
(generally background) in the field. There is a significant population of
luminous galaxies with H-Ks > 0.35 which are rarely, if ever, members of the
groups in our sample. The most luminous galaxies which populate the groups have
a very narrow range of IR color. Over the entire mass range covered by our
sample, the Ks luminosity increases with mass as L ~ M^(0.64 +/- 0.06) implying
that the mass-to-light ratio in the Ks-band increases with mass. The agreement
between this result and earlier investigations of essentially non-overlapping
sets of systems shows that this window in galaxy formation and evolution is
insensitive to the selection of the systems and to the details of the mass and
luminosity computations.


title:
On the multiplicity of the O-star Cyg OB2 #8A and its contribution to
  the gamma-ray source 3EG J2033+4118

abstract:
  We present the results of an intensive spectroscopic campaign in the optical
waveband revealing that Cyg OB2 #8A is an O6 + O5.5 binary system with a period
of about 21.9 d. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal
radio emitter. We discuss the binarity of this star in the framework of a
campaign devoted to the study of non-thermal emitters, from the radio waveband
to gamma-rays. In this context, we attribute the non-thermal radio emission
from this star to a population of relativistic electrons, accelerated by the
shock of the wind-wind collision. These relativistic electrons could also be
responsible for a putative gamma-ray emission through inverse Compton
scattering of photospheric UV photons, thus contributing to the yet
unidentified EGRET source 3EG J2033+4118.


title:
Oscillations of vertically integrated relativistic tori -II.
  Axisymmetric modes in a Kerr spacetime

abstract:
  This is the second of a series of papers investigating the oscillation
properties of relativistic, non-selfgravitating tori orbiting around black
holes. Extending the work done in a Schwarzschild background, we here consider
the axisymmetric oscillations of vertically integrated tori in a Kerr
spacetime. The tori are modeled with a number of different non-Keplerian
distributions of specific angular momentum and we discuss how the oscillation
properties depend on these and on the rotation of the central black hole. We
first consider a local analysis to highlight the relations between acoustic and
epicyclic oscillations in a Kerr spacetime and subsequently perform a global
eigenmode analysis to compute the axisymmetric p modes. In analogy with what
found in a Schwarzschild background, these modes behave as sound waves that are
modified by rotation and are globally trapped in the torus. For constant
distributions of specific angular momentum, the eigenfrequencies appear in a
sequence 2:3:4:... which is essentially independent of the size of the disc and
of the black hole rotation. For non-constant distributions of angular momentum,
on the other hand, the sequence depends on the properties of the disc and on
the spin of the black hole, becoming harmonic for sufficiently large tori. We
also comment on how p modes could explain the high frequency quasi-periodic
oscillations observed in low-mass X-ray binaries with a black hole candidate
and the properties of an equivalent model in Newtonian physics.


title: SMA CO(J=3-2) interferometric observations of the central region of M51

abstract:
  We present the first interferometric CO(J=3-2) observations (beam size of
3.9"x1.6" or 160pc x 65pc) with the Submillimeter Array (SMA) toward the center
of the Seyfert 2 galaxy M51. The image shows a strong concentration at the
nucleus and weak emission from the spiral arm to the northwest. The integrated
intensity of the central component in CO(J=3-2) is almost twice as high as that
in CO(J=1-0), indicating that the molecular gas within an ~80 pc radius of the
nucleus is warm (>~100 K) and dense (~10^4 cm^-3). Similar intensity ratios are
seen in shocked regions in our Galaxy, suggesting that these gas properties may
be related to AGN or starburst activity. The central component shows a linear
velocity gradient (~1.4 km/s/pc) perpendicular to the radio continuum jet,
similar to that seen in previous observations and interpreted as a
circumnuclear molecular disk/torus around the Seyfert 2 nucleus. In addition,
we identify a linear velocity gradient (~0.7 km/s/pc) along the jet. Judging
from the energetics, the velocity gradient can be explained by supernova
explosions or energy and momentum transfer from the jet to the molecular gas
via interaction, which is consistent with the high intensity ratio.


title: The Luminosity Function of Early-Type Galaxies at z~0.75

abstract:
  We measure the luminosity function of morphologically selected E/S0 galaxies
from $z=0.5$ to $z=1.0$ using deep high resolution Advanced Camera for Surveys
imaging data. Our analysis covers an area of $48\Box\arcmin$ (8$\times$ the
area of the HDF-N) and extends 2 magnitudes deeper ($I\sim24$ mag) than was
possible in the Deep Groth Strip Survey (DGSS). At $0.5<z<0.75$, we find
$M_B^*-5\log h_{0.7}=-21.1\pm0.3$ and $\alpha=-0.53\pm0.2$, and at
$0.75<z<1.0$, we find $M_B^*-5\log h_{0.7}=-21.4\pm0.2$. These luminosity
functions are similar in both shape and number density to the luminosity
function using morphological selection (e.g., DGSS), but are much steeper than
the luminosity functions of samples selected using morphological proxies like
the color or spectral energy distribution (e.g., CFRS, CADIS, or COMBO-17). The
difference is due to the `blue', $(U-V)_0<1.7$, E/S0 galaxies, which make up to
$\sim30%$ of the sample at all magnitudes and an increasing proportion of faint
galaxies. We thereby demonstrate the need for {\it both morphological and
structural information} to constrain the evolution of galaxies.
  We find that the `blue' E/S0 galaxies have the same average sizes and Sersic
parameters as the `red', $(U-V)_0>1.7$, E/S0 galaxies at brighter luminosities
($M_B<-20.1$), but are increasingly different at fainter magnitudes where
`blue' galaxies are both smaller and have lower Sersic parameters. Fits of the
colors to stellar population models suggest that most E/S0 galaxies have short
star-formation time scales ($\tau<1$ Gyr), and that galaxies have formed at an
increasing rate from $z\sim8$ until $z\sim2$ after which there has been a
gradual decline.


title: Stochastic relativistic shock-surfing acceleration

abstract:
  We study relativistic particles undergoing surfing acceleration at
perpendicular shocks. We assume that particles undergo diffusion in the
component of momentum perpendicular to the shock plane due to moderate
fluctuations in the shock electric and magnetic fields. We show that dN/dE, the
number of surfing-accelerated particles per unit energy, attains a power-law
form, dN/dE \propto E^{-b}. We calculate b analytically in the limit of weak
momentum diffusion, and use Monte Carlo test-particle calculations to evaluate
b in the weak, moderate, and strong momentum-diffusion limits.


title: Dynamical Relaxation of the Dark Matter to Baryon Ratio

abstract:
  A scalar field interacting differently with dark matter and baryons may
explain why their ratio is of order unity today. We provide three working
examples, checking them against the observations of CMB, Large Scale Structure,
supernovae Ia, and post-newtonian tests of gravity. Such a scenario could make
life much easier for supersymmetric dark matter candidates.


title:
HEXIT-SAT: a mission concept for X-ray grazing incidence telescopes from
  0.5 to 70 keV

abstract:
  While the energy density of the Cosmic X-ray Background (CXB) provides a
statistical estimate of the super massive black hole (SMBH) growth and mass
density in the Universe, the lack, so far, of focusing instrument in the 20-60
keV (where the CXB energy density peaks), frustrates our effort to obtain a
comprehensive picture of the SMBH evolutionary properties. HEXIT-SAT (High
Energy X-ray Imaging Telescope SATellite) is a mission concept capable of
exploring the hard X-ray sky with focusing/imaging instrumentation, to obtain
an unbiased census of accreting SMBH up to the redshifts where galaxy formation
peaks, and on extremely wide luminosity ranges. This will represent a leap
forward comparable to that achieved in the soft X-rays by the Einstein
Observatory in the late 70'. In addition to accreting SMBH, and very much like
the Einstein Observatory, this mission would also have the capabilities of
investigating almost any type of the celestial X-ray sources. HEXIT-SAT is
based on high throughput (>400 cm2 @ 30 keV; >1200 cm2 @ 1 keV), high quality
(15 arcsec Half Power Diameter) multi-layer optics, coupled with focal plane
detectors with high efficiency in the full 0.5-70keV range. Building on the
BeppoSAX experience, a low-Earth, equatorial orbit, will assure a low and
stable particle background, and thus an extremely good sensitivity for faint
hard X-ray sources. At the flux limits of 1/10 microCrab (10-30 keV) and 1/3
microCrab (20-40 keV) (reachable in one Msec observation) we should detect ~100
and ~40 sources in the 15 arcmin FWHM Field of View respectively, thus
resolving >80% and ~65% of the CXB where its energy density peaks.


title: A VLT/FORS2 Multi-Slit Search for Lyman-alpha Emitting Galaxies at z~6.5

abstract:
  We present results from a deep spectroscopic search in the 9150A atmospheric
window for z~6.5 Lyman-alpha emitting galaxies using the VLT/FORS2. Our
multi-slit+narrow-band filter survey covers a total spatial area of 17.6 sq.
arcmin in four different fields and reaches fluxes down to 5x10^(-18)
erg/s/cm^2 (7 sigma detection). Our detection limit is significantly fainter
than narrow-band searches at this redshift and fainter also than the unlensed
brightness of Hu et al.'s HCM6A at z=6.56, and thus provides better overlap
with surveys at much lower redshifts. Eighty secure emission line galaxies are
detected. However, based on their clear continuum emission shortward of the
line or the presence of multiple lines, none of these can be Ly-alpha emission
at z~6.5. Our null result of finding no z~6.5 Ly-alpha emitters suggests that
the number density of Ly-alpha emitters with L>2x10^(42) erg/s declines by ~2
between z~3 and z~6.5.


title:
ISOCAM observations in the Lockman Hole - I The 14.3 micron shallow
  survey: data reduction, catalogue, and optical identifications

abstract:
  We present the image and catalogue of the 14.3 micron shallow survey of 0.55
square degrees in the region of the Lockman Hole (10h52m03s +57d21m46s, J2000)
with the Infrared Space Observatory (ISO). The data have been analyzed with the
recent algorithm by Lari et al. (2001) conceived to exploit ISO data in an
optimal way, especially in the case of shallow surveys with low redundancy.
Photometry has been accurately evaluated through extensive simulations and also
the absolute calibration has been checked using a set of 21 stars detected at
14.3 micron, optical, and near-IR bands. On the basis of simulations, we
evaluate that the survey is 80%, 50%, and 20% complete at 0.8, 0.6, and 0.45
mJy, respectively. Below the 20% completeness limit, fluxes are generally
overestimated since the sources are preferentially detected if their positions
correspond to positive oscillations of the noise. Moreover, from a comparison
with the deep survey, we estimate that only sources brighter than 0.45 mJy are
highly reliable. Only 5% of these sources do not have optical counterparts down
to r'=25. Since none of the Spitzer imaging bands cover the 14.3 micron
wavelength range, this data set will remain unique until the advent of the
James Webb Space Telescope.


title:
The Fall of AGN and the Rise of Star-Forming Galaxies: A Close Look at
  the Chandra Deep Field X-ray Number Counts

abstract:
  We investigate the X-ray number counts in the 1-2 Ms Chandra Deep Fields
(CDFs) to determine the contributions of faint X-ray source populations to the
extragalactic X-ray background (XRB). X-ray sources were separated into Active
Galactic Nuclei (AGN), star-forming galaxies, and Galactic stars based on
several criteria. We find that AGN continue to dominate the number counts in
the 0.5-2.0 keV and 2-8 keV bands. At flux limits of ~2.5e-17 erg cm-2 s-1
(0.5-2.0 keV) and ~1.4e-16 erg cm-2 s-1 (2-8 keV), the overall AGN source
densities are 7166 (+304/-292) and 4558 (+216/-207) sources deg-2,
respectively; these are factors of ~10-20 higher than found in the deepest
optical spectroscopic surveys. While still a minority, the number counts of
star-forming galaxies climb steeply such that they eventually achieve source
densities of 1727 (+187/-169) and 711 (+270/-202) sources deg-2 at the CDF
0.5-2.0 keV and 2-8 keV flux limits, respectively. Adopting recent XRB flux
densities measurements, the CDFs resolve a total of 89.5% (+5.9%/-5.7%) and
86.9% (+6.6%/-6.3%) of the extragalactic 0.5-2.0 keV and 2-8 keV XRBs,
respectively. Extrapolation of the number-count slopes can easily account for
the entire 0.5-2.0 keV and 2-8 keV XRBs to within statistical errors. We also
revisit the reported differences between the CDF-North and CDF-South number
counts, finding that the two fields are consistent except for sources in the
2-8 keV band below F(2-8 keV)~1e-15 erg cm-2 s-1, where deviations gradually
increase to ~3.9 sigma.


title: Accurate Calorimetry of GRB 030329

abstract:
  We report late-time observations of the radio afterglow of GRB 030329. The
light curves show a clear achromatic flattening at 50 days after the explosion.
We interpret this flattening as resulting from the blast wave becoming
trans-relativistic. Modeling of this transition enables us to make estimates of
the energy content of the burst, regardless of the initial jet structure or the
distribution of initial Lorentz factors of the ejecta. We find, in accordance
with other events, that GRB 030329 is well-described by an explosion with total
energy of a few times 10^51 erg expanding into a circumburst medium with a
density of order unity.


title:
Cosmology and the Halo Occupation Distribution from Small-Scale Galaxy
  Clustering in the Sloan Digital Sky Survey

abstract:
  We use the projected correlation function w_p(r_p) of a volume-limited
subsample of the Sloan Digital Sky Survey (SDSS) main galaxy redshift catalogue
to measure the halo occupation distribution (HOD) of the galaxies of the
sample. Simultaneously, we allow the cosmology to vary within cosmological
constraints imposed by cosmic microwave background experiments in a Lambda-CDM
model. We find that combining w_p(r_p) for this sample alone with the
observations by WMAP, ACBAR, CBI and VSA can provide one of the most precise
techniques available to measure cosmological parameters. For a minimal flat
six-parameter Lambda-CDM model with an HOD with three free parameters, we find
Omega_m=0.278^{+0.027}_{-0.027}, sigma_8=0.812^{+0.028}_{-0.027}, and
H_0=69.8^{+2.6}_{-2.6}km s^{-1} Mpc^{-1}; these errors are significantly
smaller than from CMB alone and similar to those obtained by combining CMB with
the large-scale galaxy power spectrum assuming scale-independent bias. The
corresponding HOD parameters describing the minimum halo mass and the
normalization and cut-off of the satellite mean occupation are
M_min=(3.03^{+0.36}_{-0.36})x 10^{12} h^{-1} M_sun, M_1 =
(4.58^{+0.60}_{-0.60})x 10^{13} h^{-1} M_sun, and kappa=4.44^{+0.51}_{-0.69}.
When more parameters are added to the HOD model, the error bars on the HOD
parameters increase because of degeneracies, but the error bars on the
cosmological parameters do not increase greatly. Similar modeling for other
galaxy samples could reduce the statistical errors on these results, while more
thorough investigations of the cosmology dependence of nonlinear halo bias and
halo mass functions are needed to eliminate remaining systematic uncertainties,
which may be comparable to statistical uncertainties.


title: Millisecond Pulsars in X-Ray Binaries

abstract:
  Despite considerable evidence verifying that millisecond pulsars are spun up
through sustained accretion in low-mass X-ray binaries (LMXBs), it has proven
surprisingly difficult to actually detect millisecond X-ray pulsars in LMXBs.
There are only 5 accretion-powered millisecond X-ray pulsars known among more
than 80 LMXBs containing neutron stars, but there are another 11 "nuclear
powered" millisecond pulsars which reveal their spin only during brief,
thermonuclear X-ray bursts. In addition, 2 of the accretion-powered pulsars
also exhibit X-ray burst oscillations, and their unusual properties, along with
the absence of persistent pulsations in most LMXBs, suggest that the magnetic
fields in many LMXBs may be hidden by accreted material. Interestingly, the
nuclear-powered pulsars offer a statistically unbiased probe of the spin
distribution of recycled pulsars and show that this distribution cuts off
sharply above 730 Hz, well below the breakup spin rate for most neutron star
equations of state. This indicates that some mechanism acts to halt or balance
spin-up due to accretion and that submillisecond pulsars must be very rare (and
are possibly nonexistent). It is unclear what provides the necessary angular
momentum sink, although gravitational radiation is an attractive possibility.


title:
An Unbiased Measurement of Ho through Cosmic Background Imager
  Observations of the Sunyaev-Zel'dovich Effect in Nearby Galaxy Clusters

abstract:
  We present Ho results from Cosmic Background Imager (CBI) observations of the
Sunyaev-Zel'dovich Effect (SZE) in 7 galaxy clusters, A85, A399, A401, A478,
A754, A1651, and A2597. These observations are part of a program to study a
complete, volume-limited sample of low-redshift (z<0.1), X-ray selected
clusters. Our focus on nearby objects allows us to study a well-defined,
orientation unbiased sample, minimizing systematic errors due to cluster
asphericity. We use density models derived from ROSAT imaging data and
temperature measurements from ASCA and BeppoSAX spectral observations. We
quantify in detail sources of error in our derivation of Ho, including
calibration of the CBI data, density and temperature models from the X-ray
data, Cosmic Microwave Background (CMB) primary anisotropy fluctuations, and
residuals from radio point source subtraction. From these 7 clusters we obtain
a result of Ho = 67^{+30}_{-18}, ^{+15}_{-6} km/s/Mpc for an unweighted sample
average. The respective quoted errors are random and systematic uncertainties
at 68% confidence. The dominant source of error is confusion from intrinsic
anisotropy fluctuations.


title:
Limits on WIMP dark matter using scintillating CaWO4 cryogenic detectors
  with active background suppression

abstract:
  We present first significant limits on WIMP dark matter by the phonon-light
technique, where combined phonon and light signals from a scintillating
cryogenic detector are used. Data from early 2004 with two 300 g CRESST-II
prototype detector modules are presented, with a net exposure of 20.5 kg days.
The modules consist of a CaWO4 scintillating ``target'' crystal and a smaller
cryogenic light detector. The combination of phonon and light signals leads to
a strong suppression of non-nuclear recoil backgrounds. Using this information
to define an acceptance region for nuclear recoils we have 16 events from the
two modules, corresponding to a rate for nuclear recoils between 12 and 40 keV
of (0.87 +- 0.22) events/(kg day). This is compatible with the rate expected
from neutron background, and most of these events lie in the region of the
phonon-light plane anticipated for neutron-induced recoils. A particularly
strong limit for WIMPs with coherent scattering results from selecting a region
of the phonon-light plane corresponding to tungsten recoils, where the best
module shows zero events.


title: Mutiwavelength Observations of Radio Galaxy 3C 120 with XMM-Newton

abstract:
  We present XMM-Newton observations of the radio galaxy 3C 120. The hard X-ray
spectrum contains a marginally resolved Fe I K-alpha emission line with
FWHM=9,000 km/s and an equivalent width of 57 eV. The line arises via
fluorescence in a broad-line region with covering fraction of 0.4. There is no
evidence of relativistically broad Fe K-alpha, contrary to some previous
reports. The normal equivalent widths of the X-ray and optical emission lines
exclude a strongly beamed synchrotron component to the hard X-ray and optical
continua. There is an excess of 0.3-2 keV soft X-ray continuum over an
extrapolation of the hard X-ray power-law, which may arise in a disk corona.
Analysis of an archival Chandra image shows that extended emission from the jet
and other sources contributes <3% of the total X-ray flux. A break in the X-ray
spectrum below 0.6 keV indicates an excess neutral hydrogen column density of
N_H=1.57 * 10^21 cm^{-2}. However, the neutral absorber must have an oxygen
abundance of <1/50 of the solar value to explain the absence of an intrinsic or
intervening O I edge. There is no ionized absorption in the soft X-ray
spectrum, but there is a weak, narrow O VIII Ly-alpha emission line. We do not
detect previously claimed O VIII absorption from the intervening intergalactic
medium. Radio observations at 37 GHz show a fast, high frequency flare starting
8 days after the XMM-Newton observation. However, this has no obvious effect on
the X-ray spectrum. The X-ray spectrum, including the soft excess, became
harder as the X-ray flux decreased, with an estimated pivot energy of 40 keV.
The UV and soft X-ray fluxes are strongly correlated over the 120 ks duration
of the XMM-Newton observation. This is qualitatively consistent with
Comptonization of UV photons by a hot corona. (Abridged)


title: Giant pulses in Pulsar PSR B0031-07

abstract:
  We report on observations of the recently detected (Kuzmin et al. 2004) giant
pulses (GPs) from the pulsar PSR B0031-07 at 40 and 111 MHz. At 40 MHz the peak
flux density of the strongest pulse is 1100 Jy, which is 400 times as high as
the peak flux density of the average pulse (AP). Peak flux density of the GPs
compared to the AP peak flux density has roughly a power-law distribution with
a slope of -4.5. GPs at 40 MHz are essentially stronger than those ones at 111
MHz. This excess is approximately in inverse proportion to the frequency ratio.
The giant pulses are much narrower than the AP, and cluster in two narrow
regions of the AP near the peaks of the two components of the AP. Some of the
GPs emit at both phases and are double. The separation of the double GP
emission regions depends on frequency. Similarly to the frequency dependence of
the width of the AP, it is less at 111 MHz than at 40 MHz. This suggests that
GPs are emitted from the same region of the magnetosphere as the AP, that is in
a hollow cone over the polar cap instead of the light cylinder region. PSR
B0031-07 as well as the previously detected PSR B1112+50 are the first pulsars
with GPs that do not have a high magnetic field at the light cylinder. One may
suggest that there are two classes of GPs, one associated with high-energy
emission from outer gaps, the other associated with polar radio emission. The
GPs of PSR B0031-07 and PSR B1112+50 are of the second class. The dispersion
measure DM is found to be 10.900 +/- 0.003 pc/cm^{3}.


title:
Late-Time Radio Re-Brightening of Gamma-Ray Burst Afterglows: Evidence
  for Double-Sided Jets

abstract:
  The central engine of gamma-ray bursts (GRBs) is believed to eject
double-sided ultra-relativistic jets. For an observed GRB, one of the twin jets
should point toward us, and is responsible for the prompt gamma-ray and
subsequent afterglow emission. We consider in this Letter the other receding
jet, which will give rise to late-time radio re-brightening (RRB) when it
becomes non-relativistic (NR) and radiative isotropic. The RRB peaks at a time
$5t_{NR}=2(E_{j,51}/n)^{1/3}$ yr after the GRB, where $t_{NR}$ is the observed
NR timescale for the preceding jet, $E_j$ is the jet energy and $n$ is the
ambient medium density. The peak flux is comparable to the preceding-jet
emission at $t_{NR}$. We expect the RRB of GRB 030329 1.7 yr after the burst
with a flux $\sim0.6$ mJy at 15 GHz. The cases of GRBs 970508 and 980703 have
also been discussed. The detection of RRB, which needs dense monitoring
campaign even a few years after a GRB, will be the direct evidence for the
existence of double-sided jets in GRBs, and prove the black hole-disk system
formation in the cores of progenitors.


title:
On the nature of the unidentified X-ray/gamma-ray sources IGR
  J18027-1455 and IGR J21247+5058

abstract:
  We present a multiwavelength study of the environment of the unidentified
X-ray/gamma-ray sources IGR J18027-1455 and IGR J21247+5058, recently
discovered by the IBIS/ISGRI instrument, onboard the INTEGRAL satellite. The
main properties of the sources found inside their position error circles, give
us clues about the nature of these high-energy sources.


title:
The Large Local Hole in the Galaxy Distribution: The 2MASS Galaxy
  Angular Power Spectrum

abstract:
  We present new evidence for a large deficiency in the local galaxy
distribution situated in the 4000 sq.deg. APM survey area. We use models guided
by the 2dF Galaxy Redshift Survey (2dFGRS) n(z) as a probe of the underlying
LSS. We first check the usefulness of this technique by comparing the 2dFGRS
n(z) model prediction with the K-band and B-band number counts extracted from
the 2MASS and 2dFGRS parent catalogues over the 2dFGRS Northern and Southern
declination strips, before turning to a comparison with the APM counts. We find
that the APM counts in both the B and K-bands indicate a deficiency in the
local galaxy distribution of approx. 30% to z=0.1 over the entire APM survey
area. We examine the implied significance of such a large local hole,
considering several possible forms for the real-space correlation function. We
find that such a deficiency in the APM survey area indicates an excess of power
at large scales over what is expected from the correlation function observed in
the 2dFGRS correlation function or predicted from $\Lambda$CDM Hubble Volume
mock catalogues. In order to check further the clustering at large scales in
the 2MASS data, we have calculated the angular power spectrum for 2MASS
galaxies. Although in the linear regime (l<30), LCDM models can give a good fit
to the 2MASS angular power spectrum, over a wider range (l<100) the power
spectrum from Hubble Volume mock catalogues suggests that scale-dependent bias
may be needed for LCDM to fit. However, the modest increase in large-scale
power observed in the 2MASS angular power spectrum is still not enough to
explain the local hole.


title:
Generalized Collapse Solutions with Nonzero Initial Velocities for Star
  Formation in Molecular Cloud Cores

abstract:
  Motivated by recent observations that show starless molecular cloud cores
exhibit subsonic inward velocities, we revisit the collapse problem for
polytropic gaseous spheres. In particular, we provide a generalized treatment
of protostellar collapse in the spherical limit and find semi-analytic
(self-similar) solutions, corresponding numerical solutions, and purely
analytic calculations of the mass infall rates (the three approaches are in
good agreement). This study focuses on collapse solutions that exhibit nonzero
inward velocities at large radii, as observed in molecular cloud cores, and
extends previous work in four ways: (1) The initial conditions allow nonzero
initial inward velocity. (2) The starting states can exceed the density of
hydrostatic equilibrium so that the collapse itself can provide the observed
inward motions. (3) We consider different equations of state, especially those
that are softer than isothermal. (4) We consider dynamic equations of state
that are different from the effective equation of state that produces the
initial density distribution. This work determines the infall rates over a wide
range of parameter space, as characterized by four variables: the initial
inward velocity $\vin$, the overdensity $\overdense$ of the initial state, the
index $\Gamma$ of the static equation of state, and the index $\gamma$ of the
dynamic equation of state. For the range of parameter space applicable to
observed cores, the resulting infall rate is about a factor of two larger than
found in previous theoretical studies (those with hydrostatic initial
conditions and $\vin = 0$).


title:
Non-minimal coupling, exponential potentials and the $w<-1$ regime of
  dark energy

abstract:
  Recent observations and theoretical considerations have motivated the study
of models for dark energy with equation of state characterized by a parameter
$w=p/\rho<-1$. Such models, however, are usually believed to be inviable due to
their instabilities against classical perturbations or potentially catastrophic
vacuum decays. In this paper, we show that a simple quintessential model with
potential $V(\phi)=Ae^{-\sigma\phi}$ and a gravitational coupling of the form
$(1+|\xi|\phi^2)R$ can exhibit, for large sets of initial conditions,
asymptotic de Sitter behavior with $w<-1$ regimes. Nevertheless, the model is
indeed stable at classical and quantum level.


title:
Emergent biological principles and the computational properties of the
  universe

abstract:
  The claim that life is an emergent phenomenon exhibiting novel properties and
principles is often criticized for being in conflict with causal closure at the
microscopic level. I argue that advances in cosmological theory suggesting an
upper bound on the information processing capacity of the universe may resolve
this conflict for systems exceeding a certain threshold of complexity. A
numerical estimate of the threshold places it at the level of a small protein.
The calculation supports the contention that life is an emergent phenomenon.


title: Molecular gas at high redshift: jet-induced star formation?

abstract:
  We present an alternative interpretation of the observations of BR1202-0725
at z=4.695 and show that its properties are consistent with a relativistic jet,
issuing from the quasar core, propagating into the inter-galactic medium and
triggering star formation along its path. Prompted by this finding, we reviewed
all the z>3 objects detected in molecular line emission and found that the
distribution of gas and dust in these sources is often spatially or
kinematically offset from the host galaxy, and preferentially aligned along the
radio axis. These observations suggest to us a scenario in which CO emission
observed in high redshift galaxies is located where it forms: along the sites
of star formation triggered initially by relativistic jets.


title:
Numerical evolution of secular bar-mode instability induced by the
  gravitational radiation reaction in rapidly rotating neutron stars

abstract:
  The evolution of a nonaxisymmetric bar-mode perturbation of rapidly rotating
stars due to a secular instability induced by gravitational wave emission is
studied in post-Newtonian simulations taking into account gravitational
radiation reaction. A polytropic equation of state with the polytropic index
$n=1$ is adopted. The ratio of the rotational kinetic energy to the
gravitational potential energy $T/|W|$ is chosen in the range between 0.2 and
0.26. Numerical simulations were performed until the perturbation grows to the
nonlinear regime, and illustrate that the outcome after the secular instability
sets in is an ellipsoidal star of a moderately large ellipticity $\agt 0.7$. A
rapidly rotating protoneutron star may form such an ellipsoid, which is a
candidate for strong emitter of gravitational waves for ground-based laser
interferometric detectors. A possibility that effects of magnetic fields
neglected in this work may modify the growth of the secular instability is also
mentioned.


title: Cosmological dynamics of scalar fields with O(N) symmetry

abstract:
  In this paper, we study the cosmological dynamics of scalar fields with O(N)
symmetry in general potentials. We compare the phase space of the dynamical
systems of the quintessence and phantom and give the conditions for the
existence of various attractors as well as their cosmological implications. We
also show that the existence of tracking attractor in O(N) phantom models
require the potential with $\Gamma<1/2$, which makes the models with
exponential potential possess no tracking attractor.


title:
2:3 Twin Quasi-Periodic Oscillations in Magnetohydrodynamic Accretion
  Flows

abstract:
  We study the radial and vertical oscillations in the three-dimensional
magnetohydrodynamic (MHD) accretion flows around black holes. General
relativistic effects are taken into account by using pseudo-Newtonian
potential. We find that the structure of MHD flows is changed at $3.8 r_{\rm
s}\leq r\leq 6.3 r_{\rm s}$ and the two pairs of quasi-periodic oscillations
(twin QPOs) are excited in that region. The time evolution of the power
spectrum density (PSD) indicates that these twin QPOs are most likely to be
produced by the resonance between the Keplerian frequency $\nu_{\rm K}$ and the
epicyclic frequency $\nu_{\kappa}$. The PSD shows that the lower peak frequency
$\nu_{\rm l}$ corresponds to $\nu_{\rm K}$, while the upper peak frequency
$\nu_{\rm u}$ corresponds to $\nu_{\rm K} + \nu_{\kappa}$. The ratio of two
peak frequencies is close to 2:3. The results provide the first direct evidence
for the excitation of the resonant disk oscillation in the MHD accretion flows.


title:
The formation and retention of gas giant planets around stars with a
  range of metallicities

abstract:
  The apparent dependence of detection frequency of extrasolar planets on the
metallicity of their host stars is investigated with Monte Carlo simulations
using a deterministic core-accretion planet formation model. According to this
model, gas giants formed and acquired their mass $M_{\rm p}$ through
planetesimal coagulation followed by the emergence of cores onto which gas is
accreted. These protoplanets migrate and attain their asymptotic semi-major
axis $a$ through their tidal interaction with their nascent disk. Based on the
observed properties of protostellar disks, we generate $M_{\rm p}$-$a$
distribution. Our results reproduce the observed lack of planets with
intermediate mass $M_{\rm p} = 10$--100$M_{\oplus}$ and $a \la 3$AU and with
large mass $M_{\rm p} \ga 10^3 M_{\oplus}$ and $a \la 0.2$AU. Based on the
simulated $M_{\rm p}$-$a$ distributions, we also evaluate the metallicity
dependence of fraction of stars harboring planets that are detectable with
current radial velocity survey. If protostellar disks attain the same fraction
of heavy elements which are contained in their host stars, the detection
probability around metal-rich stars would be greatly enhanced because
protoplanetary cores formed in them can grow to several Earth masses prior to
their depletion. These large masses are required for the cores to initiate
rapid gas accretion and to transform into giant planets. The theoretically
extrapolated metallicity dependence is consistent with the observation. This
correlation does not arise naturally in the gravitational-instability scenario.
We also suggest other metallicity dependence of the planet distributions that
can be tested by on-going observations.


title:
Nonlinear current helicity fluxes in turbulent dynamos and alpha
  quenching

abstract:
  Large scale dynamos produce small scale current helicity as a waste product
that quenches the large scale dynamo process (alpha effect). This quenching can
be catastrophic (i.e.intensify with magnetic Reynolds number) unless one has
fluxes of small scale magnetic (or current) helicity out of the system. We
derive the form of helicity fluxes in turbulent dynamos, taking also into
account the nonlinear effects of Lorentz forces due to fluctuating fields. We
confirm the form of an earlier derived magnetic helicity flux term, and also
show that it is not renormalized by the small scale magnetic field, just like
turbulent diffusion. Additional nonlinear fluxes are identified, which are
driven by the anisotropic and antisymmetric parts of the magnetic correlations.
These could provide further ways for turbulent dynamos to transport out small
scale magnetic helicity, so as to avoid catastrophic quenching.


title: Morphology of Galactic Open Clusters

abstract:
  We analyzed the shapes of Galactic open clusters by the star counting
technique with the 2MASS star catalog database. Morphological parameters such
as the ellipticity and size have been derived via stellar density distribution,
weighed by clustering probability. We find that most star clusters are
elongated, even for the youngest star clusters of a few million years old,
which are located near to the Galactic disk. The shapes of young star clusters
must reflect the conditions in the parental molecular clouds and during the
cluster formation process. As an open cluster ages, stellar dynamics cause the
inner part of the cluster to circularize, but the overall radius gets larger
and the stellar density becomes sparser. We discuss how internal relaxation
process competes with Galactic external perturbation during cluster evolution.


title:
Cosmic Microwave Background Polarization and reionization: constraining
  models with a double reionization

abstract:
  Neutral hydrogen around high-z QSO and an optical depth tau ~ 0.17 can be
reconciled if reionization is more complex than a single transition at z ~ 6-8.
Tracing its details could shed a new light on the first sources of radiation.
Here we discuss how far such details can be inspected through planned
experiments on CMB large-scale anisotropy and polarization, by simulating an
actual data analysis. By considering a set of double reionization histories of
Cen (2003) type, a relevant class of models not yet considered by previous
works, we confirm that large angle experiments rival high resolution ones in
reconstructing the reionization history. We also confirm that reionization
histories, studied with the prior of a single and sharp reionization, yield a
biased tau, showing that this bias is generic. We further find a monotonic
trend in the bias for the models that we consider, and propose an explanation
of the trend, as well as the overall bias. We also show that in long-lived
experiments such a trend can be used to discriminate between single and double
reionization patterns.


title: Galaxy Assembly

abstract:
  In a Lambda CDM Universe, galaxies grow in mass both through star formation
and through addition of already-formed stars in galaxy mergers. Because of this
partial decoupling of these two modes of galaxy growth, I discuss each
separately in this biased and incomplete review of galaxy assembly; first
giving an overview of the cosmic-averaged star formation history, and then
moving on to discuss the importance of major mergers in shaping the properties
of present-day massive galaxies. The cosmic-averaged star formation rate, when
integrated, is in reasonable agreement with the build-up of stellar mass
density. Roughly 2/3 of all stellar mass is formed during an epoch of rapid
star formation prior to z=1, with the remaining 1/3 formed in the subsequent 9
Gyr during a period of rapidly-declining star formation rate. The epoch of
important star formation in massive galaxies is essentially over. In contrast,
a significant fraction of massive galaxies undergo a major merger at z<1, as
evidenced by close pair statistics, morphologically-disturbed galaxy counts,
and the build-up of stellar mass in morphologically early-type galaxies. Each
of these methods is highly uncertain; yet, taken together, it is not
implausible that the massive galaxy population is strongly affected by late
galaxy mergers, in excellent qualitative agreement with our understanding of
galaxy evolution in a Lambda CDM Universe.


title:
Nuclear spirals: gas in asymmetric galactic potential with a massive
  black hole

abstract:
  Nuclear spirals can provide a wealth of information about the nuclear
potential in disc galaxies. They form naturally as a gas response to
non-axisymmetry in the gravitational potential, even if the degree of this
asymmetry is very small. Linear wave theory well describes weak nuclear
spirals, but stronger asymmetries in the potential induce waves beyond the
linear regime, which appear as spiral shocks. If a central massive black hole
(MBH) is present, spiral shocks can extend all the way to its immediate
vicinity, and generate gas inflow up to 0.03 Msun/yr. This coincides with the
accretion rates needed to power local Active Galactic Nuclei.


title:
On the spectrum of high-energy cosmic rays produced by supernova
  remnants in the presence of strong cosmic-ray streaming instability and wave
  dissipation

abstract:
  The cosmic-ray streaming instability creates strong magnetohydrodynamic
turbulence in the precursor of a SN shock. The level of turbulence determines
the maximum energy of cosmic-ray particles accelerated by the diffusive shock
acceleration mechanism. The present consideration continues our work Ptuskin &
Zirakashvili (2003). It is assumed that the Kolmogorov type nonlinear wave
interactions together with the ion-neutral collisions restrict the amplitude of
random magnetic field. As a result, the maximum energy of accelerated particles
strongly depends on the age of a SNR. The average spectrum of cosmic rays
injected in the interstellar medium over the course of adiabatic SNR evolution
(the Sedov stage) is approximately $Q(p)p^{2}\propto p^{-2}$ at energies larger
than 10-30 Gev/nucleon and with the maximum particle energy that is close to
the knee position in cosmic ray spectrum observed at $\sim4\times10^{15}$ eV.
At earlier stage of SNR evolution - the ejecta dominated stage described by the
Chevalier-Nadyozhin solution, the particles are accelerated to higher energies
and have rather steep power-law distribution on momentum. These results suggest
that the knee may mark the transition from the ejecta-dominated to the
adiabatic evolution of SNR shocks which accelerate cosmic rays.


title: Neutrino self-polarization effect in matter

abstract:
  The quasi-classical theory of the spin light of neutrino ($SL\nu$) in
background matter, accounting for the neutrino polarization, is developed. The
neutrino transitions $\nu_{L}\to \nu_{R}$ and $\nu_{R}\to \nu_{L}$ rates in
matter are calculated. It is shown that the $SL\nu$ in matter leads to the
neutrino conversion from active $\nu_{L}$ to sterile $\nu_{R}$ states (neutrino
self-polarization effect in matter).


title:
A Spectroscopic study of the non-thermal radio emitter Cyg OB2 #8A:
  Discovery of a new binary system

abstract:
  We present the results of a spectroscopic campaign revealing that the
non-thermal radio emitter Cyg OB2 #8A is an O6 + O5.5 binary system. We propose
the very first orbital solution indicating a period of about 21.9 days. The
system appears to be eccentric (0.24 +/- 0.04) and is likely seen under a
rather low inclination angle. The mass ratio of the components is close to
unity. The impact of the binarity of this star in the framework of our
understanding of non-thermal radio emission from early-type stars is briefly
discussed.


title: RXJ 1821.6+6827: a Cool Cluster at z=0.81 from the ROSAT NEP Survey

abstract:
  We present an analysis of the properties of the cluster of galaxies RXJ
1821.6+6827, or NEP 5281, at a redshift z=0.816+/-0.001. RXJ 1821.6+6827 was
discovered during the optical identification of the X-ray sources in the North
Ecliptic Pole (NEP) region of the ROSAT All-Sky Survey and it is the highest
redshift cluster of galaxies of the NEP survey. We have measured spectroscopic
redshifts for twenty cluster galaxies using the Keck-I and the
Canada-France-Hawai'i (CFH) telescopes. The value for the cluster velocity
dispersion is sigma_V=775(+182,-113) km s-1. The cluster was also observed by
XMM-Newton. Both the optical and X-ray data are presented in this paper. The
cluster has an unabsorbed X-ray flux in the 2-10 keV energy band of F(2-10
keV)=1.24(+0.16,-0.23) x 10-13 erg cm2 s-1 and a K-corrected luminosity in the
same band of L(2-10 keV)=6.32(+76,-0.73)x10^44 h_50^-2 erg s-1 (90% confidence
level). The cluster X-ray bolometric luminosity is
L(BOL,X)=1.35(+0.08,-0.21)x10^45 h_50^-2 erg s-1. The data do not allow fitting
both metal abundance and temperature at the same time. The abundance is
unconstrained and can vary in the range 0.28-1.42 Z_sun while the best fit
X-ray temperature is T=4.7(+1.2,-0.7) keV. This emission weighted X-ray
temperature is a little lower, barely within the uncertainties, than the
predicted temperature, T=6.34(+0.13,-0.35) keV, from the L_X-T_X relation of
local clusters published in the literature. The optically measured
velocitydispersion is consistent with the velocity dispersion expected from the
sigma_V-T_X relationship. We also examine the point X-ray source
RXJ1821.9+6818, or NEP 5330, located to the south east of the cluster which was
identified as a QSO at z=1.692+/-0.008 in the ROSAT NEP survey.


title: Brownian Motion of Black Holes in Dense Nuclei

abstract:
  We evaluate the Brownian motion of a massive particle ("black hole") at the
center of a galaxy using N-body simulations. Our galaxy models have power-law
central density cusps like those observed at the centers of elliptical
galaxies. The simulations show that the black hole achieves a steady-state
kinetic energy that is substantially different than would be predicted based on
the properties of the galaxy model in the absence of the black hole. The reason
appears to be that the black hole responds to stars whose velocities have
themselves been raised by the presence of the black hole. Over a wide range of
density slopes and black hole masses, the black hole's mean kinetic energy is
equal to what would be predicted under the assumption that it is in energy
equipartition with stars lying within a distance ~r_h/2 from it, where r_h is
the black hole's influence radius. The dependence of the Brownian velocity on
black hole mass is approximately <V^2>~ 1/M^{1/(3-gamma)} with gamma the
power-law index of the stellar density profile, rho~1/r^gamma. This is less
steep than the 1/M dependence predicted in a model where the effect of the
black hole on the stellar velocities is ignored. The influence of a stellar
mass spectrum on the black hole's Brownian motion is also evaluated and found
to be consistent with predictions from Chandrasekhar's theory. We use these
results to derive a probability function for the mass of the Milky Way black
hole based on a measurement of its proper motion velocity. Interesting
constraints on M will require a velocity resolution exceeding 0.5 km/s.


title:
Towards a population of HMXB/NS microquasars as counterparts of
  low-latitude unidentified EGRET sources

abstract:
  The discovery of the microquasar LS 5039 well within the 95% conficence
contour of the Unidentified EGRET Source (UES) 3EG J1824-1514 was a major step
towards the possible association between microquasars (MQs) and UESs. The
recent discovery of precessing relativistic radio jets in LS I +61 303, a
source associated for long time with 2CG 135+01 and with the UES 3EG
J0241+6103, has given further support to this idea. Finally, the very recently
proposed association between the microquasar candidate AX J1639.0-4642 and the
UES 3EG J1639-4702 points towards a population of High Mass X-ray Binary
(HMXB)/Neutron Star (NS) microquasars as counterparts of low-latitude
unidentified EGRET sources.


title:
A Redshift z=5.4 Lyman alpha Emitting Galaxy with Linear Morphology in
  the GRAPES/UDF Field

abstract:
  We have discovered an extended Lyman alpha plume associated with a compact
source at redshift 5.4 in slitless spectroscopic data from the Grism ACS
Program for Extragalactic Science (GRAPES) project. The spatial extent of the
emission is about 6 x 1.5 kpc (1 x 0.25 arcsec). Combining our grism data and
the broadband images from the Hubble UltraDeep Field (UDF) images, we find a
Lyman alpha line flux of 2e-17 erg/cm2/s and surface brightness 7e-17
erg/cm2/s/arcsec2. The UDF images show diffuse continuum emission associated
with the Lyman alpha plume (hereafter UDF 5225), with three embedded knots. The
morphology of UDF 5225 is highly suggestive of a galaxy in assembly. It is
moreover possible that the prominent Lyman alpha emission from this object is
due to an active nucleus, and that we are seeing the simultaneous growth
through accretion of a galaxy and its central black hole. Followup observations
at higher spectral resolution could test this hypothesis.


title: Stellar Mass Black Hole Binaries as ULXs

abstract:
  Ultraluminous X-ray sources (ULXs) with Lx > 10^{39} ergs/s have been
discovered in great numbers in external galaxies with ROSAT, Chandra, and XMM.
The central question regarding this important class of sources is whether they
represent an extension in the luminosity function of binary X-ray sources
containing neutron stars and stellar-mass black holes (BHs), or a new class of
objects, e.g., systems containing intermediate-mass black holes (100-1000
Msun). We have carried out a theoretical study to test whether a large fraction
of the ULXs, especially those in galaxies with recent star formation activity,
can be explained with binary systems containing stellar-mass black holes. To
this end, we have applied a unique set of binary evolution models for
black-hole X-ray binaries, coupled to a binary population synthesis code, to
model the ULXs observed in external galaxies. We find that for donor stars with
initial masses >10 Msun the mass transfer driven by the normal nuclear
evolution of the donor star is sufficient to potentially power most ULXs. This
is the case during core hydrogen burning and, to an even more pronounced
degree, while the donor star ascends the giant branch, though the latter phases
lasts only ~5% of the main sequence phase. We show that with only a modest
violation of the Eddington limit, e.g., a factor of ~10, both the numbers and
properties of the majority of the ULXs can be reproduced. One of our
conclusions is that if stellar-mass black-hole binaries account for a
significant fraction of ULXs in star-forming galaxies, then the rate of
formation of such systems is ~3 x 10^{-7} per year normalized to a
core-collapse supernova rate of 0.01 per year.


title: New BBN limits on Physics Beyond the Standard Model from He4

abstract:
  A recent analysis of the He4 abundance determined from observations of
extragalactic HII regions indicates a significantly greater uncertainty for the
He4 mass fraction. The derived value is now in line with predictions from big
bang nucleosynthesis when the baryon density determined by WMAP is assumed.
Based on this new analysis of He4, we derive constraints on a host of particle
properties which include: limits on the number of relativistic species at the
time of BBN (commonly taken to be the limit on neutrino flavors), limits on the
variations of fundamental couplings such as alpha_{em} and G_N, and limits on
decaying particles.


title:
Simultaneous Production of Disk and Lobes: A Single-Wind MHD Model for
  the Eta Carinae Nebula

abstract:
  The luminous blue variable Eta Carinae is surrounded by a complex and highly
structured nebula of ejected material. The best-studied and axisymmetric
components of this outflow consist of bipolar lobes (the ``homunculus'') and an
equatorial ``skirt.'' Recent proper motion measurements suggest that the skirt
was ejected at the same time as the lobes, contrary to the assumptions of all
current theoretical models for the formation of the nebula (which use the skirt
to collimate stellar winds into lobes). We present a magnetohydrodynamic (MHD)
stellar wind model that produces an outflowing disk and bipolar lobes in a
single, steady-state wind. The basic model consists of a wind from a rotating
star with a rotation-axis-aligned dipole magnetic field. The azimuthal
component of the magnetic field, generated by stellar rotation, compresses the
wind toward the equator and also toward the rotation axis, simultaneously
producing an outflowing disk and jet. We use numerical MHD simulations to study
the wind for various amounts of stellar rotation and to show a range of wind
morphologies. In order to produce wide angle lobes similar to the homunculus
(which have roughly a 30 degree opening angle), a high-speed polar wind (with
enhanced energy density) from the star is also required. In that case, the
structure of the wind bears a remarkable resemblance to the skirt plus
homunculus morphology of the Eta Car nebulae, and a significant fraction of the
stellar angular momentum is carried away by the wind. Although the model
assumes a steady-state wind (rather than an eruption) and thermal wind driving
(rather than radiation pressure), the structure of the wind is encouraging.


title: Exploring the Time Domain with the Palomar-QUEST Sky Survey

abstract:
  Exploration of the time variability on the sky over a broad range of flux
levels and wavelengths is rapidly becoming a new frontier of astronomical
research. We describe here briefly the Palomar-QUEST survey being carried out
from the Samuel Oschin 48-inch Schmidt telescope at Palomar. The following
features make the survey an attractive candidate for studying time variability:
anticipated survey area of 12,000 - 15,000 sq. degrees in the drift scan mode,
point source depth of 21st mag. in I under good conditions, near simultaneous
observations in four filters, and at least four passes per year at each
location covered. The survey will yield a large number of transients and highly
variable sources in the near future and in that sense is a prototype of LSST
and Pan-STARRS. We briefly outline our strategy for searching such objects and
the proposed pipeline for detecting transients in real-time.


title: Can Early Type Galaxies Evolve from Fading the Disks of Late Types?

abstract:
  We examine whether early-type galaxies in clusters may have evolved from
later types by the fading of their disks (e.g., as a result of ram-pressure
stripping or strangulation) or by enhancement of the bulge luminosity (e.g.,
due to tidal interactions and mergers). For this purpose, we compare the bulge
and disk luminosities of early- and late-type galaxies and of galaxies at
different radial distances from the cluster center. We find that, in order for
early-type galaxies, including S0s, to have evolved from late-type galaxies,
their bulge luminosities must have been physically enhanced. Disk fading models
cannot explain the differences observed. We then show that galaxy bulges are
systematically brighter at small projected distances from the cluster center,
while disk luminosities are uncorrelated with cluster-centric distance. Our
results suggest that bulge enhancement, not disk fading, distinguishes early
from late types and is thus at least partially responsible for the
morphology-environment relation of bright cluster galaxies.


title:
A Panoramic Halpha Imaging Survey of the z=0.4 cluster Cl0024.0+1652
  with Subaru

abstract:
  We employ panoramic, multicolour (BRz') and narrow-band Halpha imaging of the
cluster Cl0024.0+1652 (z=0.39) from Subaru covering a ~30 arcmin field, to
determine cluster membership and star formation rates for a large sample of
galaxies across a wide field in the cluster, ~10 Mpc. We detect over 500
galaxies in narrow-band emission, with broad-band colours consistent with them
lying at z~0.39. Using this sample we determine the Halpha luminosity function
within the cluster and find that its form is approximately independent of local
density, and is consistent with that seen in the intermediate redshift field
population. This suggests that any density-dependent physical mechanisms which
alter the star formation rate must leave the Halpha luminosity function
unchanged; this is possible if the time-scale for star formation to cease
completely is short compared with a Hubble time. Such short time-scale
transformations are also supported by the presence of a population with
late-type morphologies but no detectable Halpha emission. The fraction of blue
galaxies, and the fraction of galaxies detected in Halpha, decreases strongly
with increasing galaxy density in a manner which is qualitatively similar to
that seen at lower redshifts. This trend is significantly steeper than the
trend with galaxy morphology observed from a panoramic Hubble Space Telescope
image of this cluster; this suggests that the physical mechanisms responsible
for transformations in morphology and star formation rates may be partially
independent. Finally, we compare our data with similar data on clusters
spanning a range of redshifts from 0.2<~z<~0.8 and find little evidence for a
trend in the total amount of star formation in clusters with redshift.


title: LLiST - a new star tracker camera for tip-tilt correction at IOTA

abstract:
  The tip-tilt correction system at the Infrared Optical Telescope Array (IOTA)
has been upgraded with a new star tracker camera. The camera features a
backside-illuminated CCD chip offering doubled overall quantum efficiency and a
four times higher system gain compared to the previous system. Tests carried
out to characterize the new system showed a higher system gain with a lower
read-out noise electron level. Shorter read-out cycle times now allow to
compensate tip-tilt fluctuations so that their error imposed on visibility
measurements becomes comparable to, and even smaller than, that of higher-order
aberrations.


title: H-alpha Stacked Images Reveal Large Numbers of PNe in the LMC

abstract:
  Our new, deep, high resolution H-alpha and matching R-band UKST
multi-exposure stack of the central 25 sq. degrees of the LMC promises to
provide an unprecedented homogeneous sample of >1,000 new PNe. Our preliminary
2dF spectroscopy on the AAT has vindicated our selection process and confirmed
136 new PNe and 57 emission-line stars out of a sample of 263 candidate sources
within an initial 2.5 sq. deg. area. To date approximately one third of the
entire LMC has been scanned for candidates (~7.5 sq.deg.). More than 750 new
emission sources have been catalogued so far along with independent
re-identification of all known and possible PNe found from other surveys. Once
our image analysis is complete, we plan comprehensive spectroscopic follow-up
of the whole sample, not only to confirm our PN candidates but also to derive
nebula temperatures and densities which, with the aid of photoionization
modeling, will yield stellar parameters which are vital for constructing H-R
diagrams for these objects. A prime objective of the survey is to produce a
Luminosity Function which will be the most accurate and comprehensive ever
derived in terms of numbers, magnitude range and evolutionary state; offering
significant new insights into the LMC's evolutionary history. The observation
and measurement of our newly discovered AGB halos around 60% of these PN will
also assist in determining the initial- to final-mass ratios for this phase of
stellar evolution.


title:
A Reexamination of Electron Density Diagnostics for Ionized Gaseous
  Nebulae

abstract:
  We present a comparison of electron densities derived from optical forbidden
line diagnostic ratios for a sample of over a hundred nebulae. We consider four
density indicators, the [O II] $\lambda3729/\lambda3726$, [S II]
$\lambda6716/\lambda6731$, [Cl III] $\lambda5517/\lambda5537$ and [Ar IV]
$\lambda4711/\lambda4740$ doublet ratios. Except for a few H II regions for
which data from the literature were used, diagnostic line ratios were derived
from our own high quality spectra. For the [O II] doublet ratio, we find that
our default atomic data set, consisting of transition probabilities (Aij) from
Zeippen (1982} and collision strengths from Pradhan (1976), fit the
observations well, although at high electron densities, the [O II]doublet ratio
yields densities systematically lower than those given by the [S II] doublet
ratio, suggesting that the ratio of Aij of the [O II]
doublet,$A(\lambda3729)/A(\lambda3726)$, given by Zeippen (1982) may need to be
revised upwards by ~6%. Our analysis also shows that the more recent
calculations of [O II] A value by Zeippen (1987a) and collision strengths by
McLaughlin & Bell (1998) are inconsistent with the observations at the high and
low density limits, respectively, and can therefore be ruled out. We confirm
the earlier result of Copetti & Writzl (2002) that the [O II] A values
calculated by Wiese et al. (1996) yield electron densities systematically lower
than those deduced from the [S II] doublet ratio and that the discrepancy is
most likely caused by errors in the A values calculated by Wiese et al. Using
our default atomic data set for [\ion{O}{ii}], we find that $N_{\rm
e}([\ion{O}{ii}]) \la N_{\rm e}([\ion{S}{ii}]) \approx N_{\rm
e}([\ion{Cl}{iii}])< N_{\rm e}([\ion{Ar} {iv}])$.


title:
Probing a GRB progenitor at a redshift of z=2: a comprehensive observing
  campaign of the afterglow of GRB 030226

abstract:
  We report results from a comprehensive follow-up observing campaign of the
afterglow of GRB 030226, including VLT spectroscopy, VLT polarimetry, and
Chandra X-ray observations. In addition, we present BOOTES-1 wide-field
observations at the time of the occurrence of the burst. First observations at
ESO started 0.2 days after the event when the GRB afterglow was at a magnitude
of R~19 and continued until the afterglow had faded below the detection
threshold (R>26). No underlying host galaxy was found. The optical light curve
shows a break around 0.8 days after the burst, which is achromatic within the
observational errors, supporting the view that it was due to a jetted
explosion. Close to the break time the degree of linear polarization of the
afterglow light was less than 1.1%, which favors a uniform jet model rather
than a structured one. VLT spectra show two absorption line systems at
redshifts z=1.962+/-0.001 and at z=1.986+/-0.001, placing the lower limit for
the redshift of the GRB close to 2. We emphasize that the kinematics and the
composition of the absorbing clouds responsible for these line systems is very
similar to those observed in the afterglow of GRB 021004. This corroborates the
picture in which at least some GRBs are physically related to the explosion of
a Wolf-Rayet star.


title:
A far UV study of interstellar gas towards HD34078: high excitation H2
  and small scale structure - Based on observations performed by the FUSE
  mission and at the CFHT telescope

abstract:
  To investigate the presence of small scale structure in the spatial
distribution of H2 molecules we have undertaken repeated FUSE UV observations
of the runaway O9.5V star, HD34078. In this paper we present five spectra
obtained between January 2000 and October 2002. These observations reveal an
unexpectedly large amount of highly excited H2. Column densities for H2 levels
from (v = 0, J = 0) up to (v = 0, J = 11) and for several v = 1 and v = 2
levels are determined. These results are interpreted in the frame of a model
involving essentially two components: i) a foreground cloud (unaffected by
HD34078) responsible for the H2 (J = 0, 1), CI, CH, CH+ and CO absorptions; ii)
a dense layer of gas (n = 10E4 cm-3) close to the O star and strongly
illuminated by its UV flux which accounts for the presence of highly excited
H2. Our model successfully reproduces the H2 excitation, the CI fine-structure
level populations as well as the CH, CH+ and CO column densities. We also
examine the time variability of H2 absorption lines tracing each of these two
components. From the stability of the J = 0, 1 and 2 damped H2 profiles we
infer a 3 sigma upper limit on column density variations Delta(N(H2))/N(H2) of
5% over scales ranging from 5 to 50 AU. This result clearly rules out any
pronounced ubiquitous small scale "density" structure of the kind apparently
seen in HI. The lines from highly excited gas are also quite stable (equivalent
to Delta(N)/N <= 30%) indicating i) that the ambient gas through which HD34078
is moving is relatively uniform and ii) that the gas flow along the shocked
layer is not subject to marked instabilities


title:
The Star Cluster Population of M51: II. Age distribution and relations
  among the derived parameters

abstract:
  We use archival {\it Hubble Space Telescope} observations of broad-band
images from the ultraviolet (F255W-filter) through the near infrared (NICMOS
F160W-filter) to study the star cluster population of the interacting spiral
galaxy M51. We obtain age, mass, extinction, and effective radius estimates for
1152 star clusters in a region of $\sim 7.3 \times 8.1$ kpc centered on the
nucleus and extending into the outer spiral arms. In this paper we present the
data set and exploit it to determine the age distribution and relationships
among the fundamental parameters (i.e. age, mass, effective radius). Using this
dataset we find: {\it i}) that the cluster formation rate seems to have had a
large increase $\sim$ 50-70 Myr ago, which is coincident with the suggested
{\it second passage} of its companion, NGC 5195, {\it ii}) a large number of
extremely young ($<$ 10 Myr) star clusters, which we interpret as a population
of unbound clusters of which a large majority will disrupt within the next
$\sim$10 Myr, and {\it iii)} that the distribution of cluster sizescan be well
approximated by a power-law with exponent, $ -\eta = -2.2 \pm 0.2$, which is
very similar to that of Galactic globular clusters, indicating that cluster
disruption is largely independent of cluster radius. In addition, we have used
this dataset to search for correlations among the derived parameters. In
particular, we do not find any strong trends between the age and mass, mass and
effective radius, nor between the galactocentric distance and effective radius.
There is, however, a strong correlation between the age of a cluster and its
extinction, with younger clusters being more heavily reddened than older
clusters.


title: A pulsar outer gap model with trans-field structure

abstract:
  We investigate the electrodynamics of an outer gap in the meridional plane of
the aligned-rotator. The charge depletion from the Goldreich-Julian charge
density causes a large electric field along the magnetic field line. The
electrons or the positrons are accelerated by the field-aligned electric field
and radiate the $\gamma$-rays tangentially to the local magnetic field line.
Some of such $\gamma$-rays collide with $X$-rays to materialize as the
electron-positron pairs on different field lines from the field line on which
they were emitted. As a result, the electric field structure is expected to
change across the field lines. Including these trans-field effects, we solve
the formation of the electric field self-consistently with the curvature
radiation and the pair creation processes. The $\gamma$-ray emission and the
pair creation are treated by use of Monte Carlo technique. We demonstrate that
the distribution of the electric field along the field lines is affected by
both the gap geometry and the external currents coming into the gap through the
boundaries. In the electrodynamical model, it has been known that the solution
disappears if the current density carried by the electron-positron pairs
produced in the gap exceeds a critical value. We show that the critical current
density is significantly increased when the trans-field structure is taken into
account. We also find that the location of the inner boundary of the gap shifts
toward the stellar surface from the conventional null surface as the current
density increases. The reason for the shift is derived from the stability
condition of the inner boundary. We also argue that the ideal-MHD condition
holds outside of the gap only when the low energy particles coexist with the
high energy particles migrating from the gap.


title: A study of the 15 micron quasars in the ELAIS N1 and N2 fields

abstract:
  This paper discusses properties of the European Large Area ISO Survey 15
micron quasars and tries to establish a robust method of quasar selection for
future use within the Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE)
framework. The importance of good quality ground-based optical data is
stressed, both for the candidates selection and for the photometric redshifts
estimates. Colour-colour plots and template fitting are used for these
purposes. The properties of the 15 micron quasars sample are studied, including
variability and black hole masses and compared to the properties of other
quasars that lie within the same fields but have no mid-infrared counterparts.
The two subsamples do not present substantial differences and are believed to
come from the same parent population.


title:
Spectral states and transient behaviour of a sample of X-ray bursters
  observed by BeppoSax

abstract:
  During observation campaigns of the Galactic Bulge region, BeppoSAX detected
a total of 21 new X-ray bursters in about 6 years of operation. These sources
are mostly transient and often feature a hard X-ray spectrum, extending up to ~
200 keV. A hard spectrum is generally found in weak, relatively short
outbursts. On the other hand two sources, SAX J1747.0-2853 and SAX
J1750.8-2900, have been seen with soft X-ray transient behaviour. In both
low/hard and high/soft state, a thermal component is observed at energies below
\~10 keV and the spectra are compatible with the same model consisting of a
blackbody or disk blackbody plus a hard or Comptonized component. Light curves
are characterized by either weak, short flares or longer, high luminosity
eruptions with exponential decay.


title: Directional statistics for WIMP direct detection

abstract:
  The direction dependence of the event rate in WIMP direct detection
experiments provides a powerful tool for distinguishing WIMP events from
potential backgrounds. We use a variety of (non-parametric) statistical tests
to examine the number of events required to distinguish a WIMP signal from an
isotropic background when the uncertainty in the reconstruction of the nuclear
recoil direction is included in the calculation of the expected signal. We
consider a range of models for the Milky Way halo, and also study rotational
symmetry tests aimed at detecting non-sphericity/isotropy of the Milky Way
halo. Finally we examine ways of detecting tidal streams of WIMPs. We find that
if the senses of the recoils are known then of order ten events will be
sufficient to distinguish a WIMP signal from an isotropic background for all of
the halo models considered, with the uncertainties in reconstructing the recoil
direction only mildly increasing the required number of events. If the senses
of the recoils are not known the number of events required is an order of
magnitude larger, with a large variation between halo models, and the recoil
resolution is now an important factor. The rotational symmetry tests require of
order a thousand events to distinguish between spherical and significantly
triaxial halos, however a deviation of the peak recoil direction from the
direction of the solar motion due to a tidal stream could be detected with of
order a hundred events, regardless of whether the sense of the recoils is
known.


title: Long-term evolution of FU Orionis objects at infrared wavelengths

abstract:
  We investigate the brightness evolution of 7 FU Orionis systems in the 1-100
micrometer wavelength range using data from the Infrared Space Observatory
(ISO). The ISO measurements were supplemented with 2MASS and MSX observations
performed in the same years as the ISO mission (1995-98). The spectral energy
distributions (SEDs) based on these data points were compared with earlier ones
derived from the IRAS photometry as well as from ground-based observations
carried out around the epoch 1983. In 3 cases (Z CMa, Parsamian 21, V1331 Cyg)
no difference between the two epochs was seen within the measurement
uncertainties. V1057 Cyg, V1515 Cyg and V1735 Cyg have become fainter at
near-infrared wavelengths while V346 Nor has become slightly brighter. V1057
Cyg exhibits a similar flux change also in the mid-infrared. At lambda >= 60
micrometer most of the sources remained constant; only V346 Nor seems to fade.
Our data on the long-term evolution of V1057 Cyg agree with the model
predictions of Kenyon & Hartmann (1991) and Turner et al. (1997) at near- and
mid-infrared wavelengths, but disagree at lambda > 25 micrometer. We discuss if
this observational result at far-infrared wavelengths could be understood in
the framework of the existing models.