title: External Compton Radiation from Rapid Nonthermal Flares in Blazars

abstract:
  In this paper we extend our approach to modeling multifrequency emission
variability from blazars to include external-radiation Compton (ERC) emission
and electron energy losses from inverse Compton scattering of seed photons
originating outside the jet. We consider seed-photon emission from a dusty
molecular torus and the broad line region (BLR) surrounding the central engine.
We establish constraints on the properties of the molecular torus and BLR under
which synchrotron self-Compton (SSC) emission dominates such that the results
obtained in our previous paper are applicable. The focus of this study is on
relative time delays between the light curves observed at different
frequencies. For definiteness, we consider emission resulting from a collision
between relativistic shocks, but the results apply more generally to conditions
involving acceleration of relativistic electrons and/or magnetic field
amplification at any type of front. Unlike SSC emission, ERC flares involving a
constant field of seed photons are not delayed by light travel time of the seed
photons. The main cause of delays is from radiative energy losses, which result
in frequency stratification behind the front and quench the flare first at the
highest frequencies, progressing to lower frequencies as time advances.
However, if the spectrum of electrons injected at the shock front is
characterized by a relatively high value of the minimum energy (a Lorentz
factor $\gamma_{min}\sim100$ is sufficient), the ERC flare in the X-ray band
can be delayed and may even peak after the injection has ceased. This effect is
strongly frequency dependent, with a longer lag at lower frequencies and an
X-ray spectral index that changes rapidly from positive (inverted spectrum) to
steep values.


title:
The Shocking Properties of Supersonic Flows: Dependence of the Thermal
  Overstability on M, alpha, and T_c/T_0

abstract:
  We investigate the Mach number dependence of the radiative overstability of
shocks. We find that the stability of radiative shocks increases with
decreasing Mach number, with the result that M=2 shocks require cooling
exponents < -1.2 to be overstable. The frequency of oscillation of the
fundamental mode has a strong Mach number dependence. We find that feedback
between the cooling region and the cold dense layer (CDL) further downstream is
a function of Mach number, with stronger feedback and oscillation of the
boundary between the CDL and the cooling region occuring at lower Mach numbers.
This feedback can be quantified in terms of the reflection coefficient of sound
waves. An interesting finding is that the stability properties of low Mach
number shocks can be dramatically altered if the shocked gas is able to cool to
temperatures less than the pre-shock value, and it is probable that low Mach
number astrophysical shocks will be overstable in a variety of situations. The
results of this work are relevant to astrophysical shocks with low Mach
numbers, such as supernova remnants (SNRs) immersed in a hot interstellar
medium (e.g., within a starburst region), and shocks in molecular clouds, where
time-dependent chemistry can lead to overstability. (Abridged)


title:
Testing the accuracy of the Hydro-PM approximation in numerical
  simulations of the Lyman-alpha forest

abstract:
  We implement the hydro-PM (HPM) technique (Gnedin & Hui 1998) in the
hydrodynamical simulation code GADGET-II and quantify the differences between
this approximate method and full hydrodynamical simulations of the Lyman-alpha
forest in a concordance LCDM model. At redshifts z=3 and z=4, the differences
between the gas and dark matter (DM) distributions, as measured by the
one-point distribution of density fluctuations, the density power spectrum and
the flux power spectrum, systematically decrease with increasing resolution of
the HPM simulqation. However, reducing these differences to less than a few
percent requires a significantly larger number of grid-cells than particles,
with a correspondingly larger demand for memory. Significant differences in the
flux decrement distribution remain even for very high resolution hydro-PM
simulations, particularly at low redshift. At z=2, the differences between the
flux power spectra obtained from HPM simulations and full hydrodynamical
simulations are generally large and of the order of 20-30 %, and do not
decrease with increasing resolution of the HPM simulation. This is due to the
presence of large amounts of shock-heated gas, a situation which is not
adequately modelled by the HPM approximation. We confirm the results of Gnedin
& Hui (1998) that the statistical properties of the flux distribution are
discrepant by > 5-20 % when compared to full hydrodynamical simulations. The
discrepancies in the flux power spectrum are strongly scale- and
redshift-dependent and extend to large scales. Considerable caution is needed
in attempts to use calibrated HPM simulations for quantitative predictions of
the flux power spectrum and other statistical properties of the Lyman-alpha
forest.


title:
[O II] Emission in Quasar Host Galaxies: Evidence for a Suppressed Star
  Formation Efficiency

abstract:
  The [O II] 3727 line, a commonly used estimator of star formation rate in
extragalactic surveys, should be an equally effective tracer of star formation
in the host galaxies of quasars, whose narrow-line regions are expected to
produce weak low-ionization emission. Quasar spectra generally show little or
no [O II] emission beyond that expected from the active nucleus itself. The
inferred star formation rates in optically selected quasars are typically below
a few solar masses per yr, and some significantly less. Quasars do not appear
to occur coevally with starbursts. Recent observations, on the other hand,
reveal abundant molecular gas in low-redshift quasars. These two results
suggest that the star formation efficiency in quasar host galaxies is somehow
suppressed during the active phase of the nucleus. The low star formation rates
also imply that the nonstellar nucleus powers the bulk of the thermal infrared
emission in radio-quiet quasars.


title: "Low-state" Black Hole Accretion in Nearby Galaxies

abstract:
  I summarize the main observational properties of low-luminosity AGNs in
nearby galaxies to argue that they are the high-mass analogs of black hole
X-ray binaries in the "low/hard" state. The principal characteristics of
low-state AGNs can be accommodated with a scenario in which the central engine
is comprised of three components: an optically thick, geometrically accretion
disk with a truncated inner radius, a radiatively inefficient flow, and a
compact jet.


title: Search for muon enhancement at sea level from transient solar activity

abstract:
  This paper presents first results of an ongoing study of a possible
association between muon enhancements at ground observed by the TUPI telescope
and transient events such as the Sun's X-ray activity. The analysis of the
observed phenomenon by using the GOES satellite archive data seems to indicate
that on most cases the Ground Level Enhancements (GLEs) could potentially be
associated with solar flares. We show that small scale solar flares, those with
prompt X-ray emission classified as C class (power above $10^{-6}Watts m^{-2}$
at 1 AU) may give rise to GLEs, probably associated with solar protons and ions
arriving to the Earth as a coherent particle pulse. The TUPI telescope's high
performance with these energetic solar particles arises mainly from: (1) its
high counting rate (up to $\sim 100$ KHz). This value in most cases is around
100 times higher than other detectors at ground and (2) due to its tracking
system. The telescope is always looking near the direction of the IMF lines.
The GLE's delay in relation of the X-ray prompt emission suggest that shock
driven by corona mass ejection (CME) is an essential requirement for the
particle acceleration efficiency.


title: The Lyman-alpha forest as a probe of fundamental physics

abstract:
  We use LUQAS, a sample of 27 high resolution high signal-to-noise UVES quasar
(QSO) spectra (Kim et al. 2004), and the Croft et al. (2002) sample together
with a set of high resolution large box size hydro-dynamical simulations run
with the code GADGET-II to recover the linear dark matter power spectrum at z>2
and at scales of 1-40 Mpc/h. These scales cannot be probed by any other
observable. We address some of the uncertainties in the theoretical modelling
of the Lyman-alpha forest structures such as the difference between full
hydro-dynamical simulations and a more simplified scheme based on the HPM
(Hydro-Particle-Mesh) technique. We combine these data sets with the Cosmic
Microwave Background (CMB) data of WMAP in order to get tighter constraints on
cosmological parameters. We focus on the recovered values of the power spectrum
amplitude, the primordial spectral index and the running of the primordial
spectral index. By considering models of slow-roll inflation we give
constraints on inflationary parameters. We explore implications for the mass of
a warm dark matter particle, including light gravitinos and sterile neutrinos,
and the perspectives of constraining the neutrino mass.


title:
The Vertical Stellar Kinematics in Face-On Barred Galaxies: Estimating
  the Ages of Bars

abstract:
  In order to perform a detailed study of the stellar kinematics in the
vertical axis of bars, we obtained high signal-to-noise spectra along the major
and minor axes of the bars in a sample of 14 face-on galaxies, and used them to
determine the line of sight stellar velocity distribution, parameterized as
Gauss-Hermite series. With these data, we developed a diagnostic tool that
allows one to distinguish between recently formed and evolved bars, as well as
estimate their ages, assuming that bars form in vertically thin disks,
recognizable by low values for the vertical velocity dispersion sigma_z.
Through N-body realizations of bar unstable disk galaxies we could also check
the time scales involved in the processes which give bars an important vertical
structure. We show that sigma_z in evolved bars is roughly around 100 Km/s,
which translates to a height scale of about 1.4 Kpc, giving support to
scenarios in which bulges form through disk material. Furthermore, the bars in
our numerical simulations have values for sigma_z generally smaller than 50
Km/s even after evolving for 2 Gyr, suggesting that a slow process is
responsible for making bars as vertically thick as we observe. We verify
theoretically that the Spitzer-Schwarzschild mechanism is quantitatively able
to explain these observations if we assume that giant molecular clouds are
twice as much concentrated along the bar as in the remaining of the disk.


title: High-resolution observations of SN 2001gd in NGC 5033

abstract:
  We report on 8.4 GHz VLBI observations of SN2001gd in the spiral galaxy
NGC5033 made on 26 June 2002 and 8 April 2003. Our data nominally suggests a
relatively strong deceleration for the expansion of SN2001gd, but we cannot
dismiss the possibility of a free supernova expansion. From our VLBI
observations on 8 April 2003, we inferred a minimum total energy in
relativistic particles and magnetic fields in the supernova shell of E_min
=(0.3-14) 10^{47} ergs, and a corresponding equipartition average magnetic
field of B_min = (50--350) mG. We also present multiwavelength VLA measurements
of SN2001gd, which are well fit by an optically thin, synchrotron spectrum,
partially absorbed by thermal plasma. We obtain a supernova flux density of
(1.02 +/- 0.05) mJy at the observing frequency of 8.4 GHz for the second epoch,
which results in an isotropic radio luminosity of (6.0 +/- 0.3) * 10^{36} ergs
between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we
report on an XMM-Newton X-ray detection of SN2001gd on 18 December 2002. The
supernova X-ray spectrum is consistent with optically thin emission from a soft
component (associated with emission from the reverse shock) at a temperature
around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of
L_X = 1.4 +/- 0.4 * 10^{39} ergs/s in the (0.3-5) keV band. We suggest that
both radio and X-ray observations of SN2001gd indicate that a circumstellar
interaction similar to that displayed by SN1993J in M81 is taking place.


title: Lithopanspermia in Star Forming Clusters

abstract:
  This paper considers the lithopanspermia hypothesis in star forming groups
and clusters, where the chances of biological material spreading from one solar
system to another is greatly enhanced (relative to the field) due to the close
proximity of the systems and lower relative velocities. These effects more than
compensate for the reduced time spent in such crowded environments. This paper
uses 300,000 Monte Carlo scattering calculations to determine the cross
sections for rocks to be captured by binaries and provides fitting formulae for
other applications. We assess the odds of transfer as a function of the
ejection speed and number of members in the birth aggregate. The odds of any
given ejected meteroid being recaptured by another solar system are relatively
low. Because the number of ejected rocks per system can be large, virtually all
solar systems are likely to share rocky ejecta with all of the other solar
systems in their birth cluster. The number of ejected rocks that carry living
microorganisms is much smaller and less certain, but we estimate that several
million rocks can be ejected from a biologically active solar system. For
typical birth environments, the capture of life bearing rocks is expected to
occur 10 -- 16,000 times per cluster (under favorable conditions), depending on
the ejection speeds. Only a small fraction of the captured rocks impact the
surfaces of terrestrial planets, so that only a few lithopanspermia events are
expected (per cluster).


title:
A Gas-poor Planetesimal Capture Model for the Formation of Giant Planet
  Satellite Systems

abstract:
  Assuming that an unknown mechanism (e.g., gas turbulence) removes most of the
subnebula gas disk in a timescale shorter than that for satellite formation, we
develop a model for the formation of regular (and possibly at least some of the
irregular) satellites around giant planets in a gas-poor environment. In this
model, which follows along the lines of the work of Safronov et al. (1986),
heliocentric planetesimals collide within the planet's Hill sphere and generate
a circumplanetary disk of prograde and retrograde satellitesimals extending as
far out as $\sim R_H/2$. At first, the net angular momentum of this
proto-satellite swarm is small, and collisions among satellitesimals leads to
loss of mass from the outer disk, and delivers mass to the inner disk (where
regular satellites form) in a timescale $\lesssim 10^5$ years. This mass loss
may be offset by continued collisional capture of sufficiently small $< 1$ km
interlopers resulting from the disruption of planetesimals in the feeding zone
of the giant planet. As the planet's feeding zone is cleared in a timescale
$\lesssim 10^5$ years, enough angular momentum may be delivered to the
proto-satellite swarm to account for the angular momentum of the regular
satellites of Jupiter and Saturn.(abridged)


title:
Constraints on the dark energy equation of state from the separation of
  CMB peaks and the evolution of alpha

abstract:
  We introduce a simple parametrization of the dark energy equation of state,
\omega, which is motivated from theory and recent experimental data. The theory
is related to the tracker solution to alleviate the fine tuning problem. Recent
experimental data indicates that the present value of \omega is close to -1. We
analyze the evolution of \omega from the separation of CMB peaks and the time
variation of the fine structure constant, \alpha. We find that -1.00 \leq
\omega^{(0)} \leq -0.971_{-0.027}^{+0.017} and 1.76_{-0.42}^{+0.29} \times
10^{-4} \leq (d \omega / dz)_{z=0} \leq 0.041_{-0.037}^{+0.016} at 95%
confidence level (CL).


title:
Virtual Astronomy, Information Technology, and the New Scientific
  Methodology

abstract:
  All sciences, including astronomy, are now entering the era of information
abundance. The exponentially increasing volume and complexity of modern data
sets promises to transform the scientific practice, but also poses a number of
common technological challenges. The Virtual Observatory concept is the
astronomical community's response to these challenges: it aims to harness the
progress in information technology in the service of astronomy, and at the same
time provide a valuable testbed for information technology and applied computer
science. Challenges broadly fall into two categories: data handling (or "data
farming"), including issues such as archives, intelligent storage, databases,
interoperability, fast networks, etc., and data mining, data understanding, and
knowledge discovery, which include issues such as automated clustering and
classification, multivariate correlation searches, pattern recognition,
visualization in highly hyperdimensional parameter spaces, etc., as well as
various applications of machine learning in these contexts. Such techniques are
forming a methodological foundation for science with massive and complex data
sets in general, and are likely to have a much broather impact on the modern
society, commerce, information economy, security, etc. There is a powerful
emerging synergy between the computationally enabled science and the
science-driven computing, which will drive the progress in science,
scholarship, and many other venues in the 21st century.


title:
TRIDENT: an Infrared Differential Imaging Camera Optimized for the
  Detection of Methanated Substellar Companions

abstract:
  A near-infrared camera in use at the Canada-France-Hawaii Telescope (CFHT)
and at the 1.6-m telescope of the Observatoire du Mont-Megantic is described.
The camera is based on a Hawaii-1 1024x1024 HgCdTe array detector. Its main
feature is to acquire three simultaneous images at three wavelengths across the
methane absorption bandhead at 1.6 microns, enabling, in theory, an accurate
subtraction of the stellar point spread function (PSF) and the detection of
faint close methanated companions. The instrument has no coronagraph and
features fast data acquisition, yielding high observing efficiency on bright
stars. The performance of the instrument is described, and it is illustrated by
laboratory tests and CFHT observations of the nearby stars GL526, Ups And and
Chi And. TRIDENT can detect (6 sigma) a methanated companion with delta H = 9.5
at 0.5" separation from the star in one hour of observing time. Non-common path
aberrations and amplitude modulation differences between the three optical
paths are likely to be the limiting factors preventing further PSF attenuation.
Instrument rotation and reference star subtraction improve the detection limit
by a factor of 2 and 4 respectively. A PSF noise attenuation model is presented
to estimate the non-common path wavefront difference effect on PSF subtraction
performance.


title: Solving the mystery of Iapetus

abstract:
  For a much better-founded theory, check Wing Ip, GEOPHYSICAL RESEARCH
LETTERS, VOL. 33, L16203, doi:10.1029/2005GL025386, 2006 (see also
http://www.agu.org/journals/gl/gl0616/2005GL025386/)


title:
The loopy UV line profiles of RU Lupi: accretion, outflows, and
  fluorescence

abstract:
  We present far-ultraviolet spectra of the classical T Tauri star RU Lupi
covering the 912-1710 A spectral range, as observed by the HST/STIS and FUSE
satellites. We use these spectra, which are rich in emission and absorption
lines, to probe both the accreting and outflowing gas. Absorption in the
Ly-alpha profile constrains the extinction to A_V=0.07 mag, which we confirm
with other diagnostics. We estimate a mass accretion rate of
(5\pm2)\times10^{-8}$ M_\odot/yr using the optical-NUV accretion continuum. The
accreting gas is also detected in bright, broad lines of C IV, Si IV, and N V,
which all show complex structures across the line profile. Many other emission
lines, including those of H_2 and Fe II, are pumped by Ly-alpha. RU Lupi's
spectrum varies significantly in the FUV; our STIS observations occurred when
RU Lupi was brighter than several other observations in the FUV, possibly due
to a high mass accretion rate.


title: Cosmological perturbations for imperfect fluids

abstract:
  Interacting fluids, endowed with bulk viscous stresses, are discussed in a
unified perspective with the aim of generalizing the treatment of cosmological
perturbation theory to the case where both fluctuating decay rates and
fluctuating bulk viscosity coefficients are simultaneously present in the
relativistic plasma. A gauge-invariant treatment of the qualitatively new
phenomena arising in this context is provided. In a complementary approach,
faithful gauge-fixed descriptions of the gravitational and hydrodynamical
fluctuations are developed and exploited. To deepen the interplay between bulk
viscous stresses and fluctuating decay rates, illustrative examples are
proposed and discussed both analytically and numerically. Particular attention
is paid to the coupled evolution of curvature and entropy fluctuations when, in
the relativistic plasma, at least one of the interacting fluids possesses a
fluctuating bulk viscosity coefficient. It is argued that this class of models
may be usefully employed as an effective description of the decay of the
inflaton as well as of other phenomena involving imperfect relativistic fluids.


title: CMB Anisotropy of Spherical Spaces

abstract:
  The first-year WMAP data taken at their face value hint that the Universe
might be slightly positively curved and therefore necessarily finite, since all
spherical (Clifford-Klein) space forms M^3 = S^3/Gamma, given by the quotient
of S^3 by a group Gamma of covering transformations, possess this property. We
examine the anisotropy of the cosmic microwave background (CMB) for all typical
groups Gamma corresponding to homogeneous universes. The CMB angular power
spectrum and the temperature correlation function are computed for the
homogeneous spaces as a function of the total energy density parameter
Omega_tot in the large range [1.01, 1.20] and are compared with the WMAP data.
We find that out of the infinitely many homogeneous spaces only the three
corresponding to the binary dihedral group T*, the binary octahedral group O*,
and the binary icosahedral group I* are in agreement with the WMAP
observations. Furthermore, if Omega_tot is restricted to the interval [1.00,
1.04], the space described by T* is excluded since it requires a value of
Omega_tot which is probably too large being in the range [1.06, 1.07]. We thus
conclude that there remain only the two homogeneous spherical spaces S^3/O* and
S^3/I* with Omega_tot of about 1.038 and 1.018, respectively, as possible
topologies for our Universe.


title:
Evidence for a magnitude-dependent bias in the Hamburg/ESO Survey for
  Damped Lyman-alpha Systems

abstract:
  We present preliminary results from the Hamburg/ESO survey for Damped
Ly-alpha (hereafter, DLA) Systems. This survey is characterized by (i) the good
knowledge of the biases affecting the parent QSO survey, (ii) the brightness
and (iii) the relatively wide magnitude distribution of the background QSOs.
Therefore, it is well-suited to study possible magnitude-dependent biases in
DLA surveys, such as the one expected from dust obscuration. We have
systematically searched for damped Lyman-alpha line candidates in 5 A
resolution spectra of the 188 QSOs that constitute our statistical sample.
These candidates have later been reobserved with UVES at the ESO--Very Large
Telescope (VLT) for confirmation and accurate N(HI) measurements. In the
redshift range covered by the survey, 19 DLA systems have been discovered. Over
the whole survey, we find that the number density, n(z), and cosmological
density of gas, Omega_gas, have comparable values to the ones obtained by
CORALS (Ellison et al. 2001). However, the number densities of DLA systems n(z)
in two sub-samples of equal absorption distance path defined by the magnitude
of the background QSOs differ by a factor of about 5. We estimate that the
probability that n(z) is equal in the two sub-samples is < 0.003. A similar,
only slightly less significant difference is found for Omega_gas.


title: A companion to AB Pic at the planet/brown dwarf boundary

abstract:
  We report deep imaging observations of the young, nearby star AB Pic, a
member of the large Tucana-Horologium as sociation. We have detected a faint,
red source 5.5" South of the star with JHK colors compatible with that of a
young substellar L dwarf. Follow-up observations at two additional epochs
confirm, with a confidence level of 4.7sigma, that the faint red object is a
companion to AB Pic rather than it being a stationary background object. A low
resolution K-band spectrum indicates an early-L spectral type for the
companion. Finally, evolutionary model predictions based on the JHK photometry
of AB Pic b indicate a mass of 13 to 14 MJup if its age is ~30Myr. Is AB Pic b
a massive planet or a minimum mass brown dwarf?


title: Giant Planet Companion to 2MASSW J1207334-393254

abstract:
  We report new VLT/NACO imaging observations of the young, nearby brown dwarf
2MASSW J1207334-393254 and its suggested planetary mass companion (2M1207 b).
Three epochs of VLT/NACO measurements obtained over nearly one year show that
the planetary mass companion candidate shares the same proper motion and, with
a high confidence level, is not a stationary background object. This result
confirms the status of 2M1207 b as of planetary mass (5 times the mass of
Jupiter) and the first image of a planetary mass companion in a different
system than our own. This discovery offers new perspectives for our
understanding of chemical and physical properties of planetary mass objects as
well as their mechanisms of formation.


title: Integral Field Spectroscopy of 23 Spiral Bulges

abstract:
  We have obtained Integral Field Spectroscopy for 23 spiral bulges using
INTEGRAL on the William Herschel Telescope and SPIRAL on the Anglo-Australian
Telescope. This is the first 2D survey directed solely at the bulges of spiral
galaxies. Eleven galaxies of the sample do not have previous measurements of
the stellar velocity dispersion (sigma*). These data are designed to complement
our Space Telescope Imaging Spectrograph program for estimating black hole
masses in the range 10^6-10^8M_sun using gas kinematics from nucleated disks.
These observations will serve to derive the stellar dynamical bulge properties
using the traditional Mgb and CaII triplets. We use both Cross Correlation and
Maximum Penalized Likelihood to determine projected sigma* in these systems and
present radial velocity fields, major axis rotation curves, curves of growth
and sigma* fields. Using the Cross Correlation to extract the low order 2D
stellar dynamics we generally see coherent radial rotation and irregular
velocity dispersion fields suggesting that sigma* is a non-trivial parameter to
estimate.


title:
Orbits in Extended Mass Distributions: General Results and the
  Spirographic Approximation

abstract:
  This paper explores orbits in extended mass distributions and develops an
analytic approximation scheme based on epicycloids (spirograph patterns). We
focus on the Hernquist potential which provides a good model for many
astrophysical systems, including elliptical galaxies, dark matter halos, and
young embedded star clusters. For a given potential, one can readily calculate
orbital solutions as a function of energy and angular momentum using numerical
methods. In contrast, this paper presents a number of analytic results for the
Hernquist potential and proves a series of general constraints showing that
orbits have similar properties for any extended mass distribution (including,
e.g., the NFW profile). We discuss circular orbits, radial orbits, zero energy
orbits, different definitions of eccentricity, analogs of Kepler's law, the
definition of orbital elements, and the relation of these orbits to spirograph
patterns (epicycloids). Over much of parameter space the orbits can be
adequately described (with accuracy better than 10%) using the parametric
equations of epicycloids, thereby providing an analytic description of the
orbits. As an application of this formal development, we find a solution for
the orbit of the Large Magellanic Cloud in the potential of our Galaxy.


title:
Constraints on radiatively inefficient accretion history from Eddington
  ratio distribution of active galactic nuclei

abstract:
  The transition of a standard thin disk to a radiatively inefficient accretion
flow (RIAF) is expected to occur, when the accretion rate is close to the
critical rate. The radiative efficiencies of accretion flows accreting at rates
lower than the critical accretion rate become significantly lower than that of
standard thin disks. It is believed that the initial transition radius is small
just after the accretion mode transition, and then the transition radius
increases with decreasing accretion rate, as suggested by some theoretical
models and observations. Based on such variable transition radius models, we
derive how the dimensionless accretion rate evolves with time from the observed
Eddington ratio distribution for a sample of low-luminosity active galactic
nuclei in the local universe. The derived time-dependent accretion rates show a
rapid decrease after the transition of the standard thin accretion disk to a
RIAF, which is consistent with that derived from the hard X-ray background.


title: Time-Variable Complex Metal Absorption Lines in the Quasar HS1603+3820

abstract:
  We present a new spectrum of the quasar HS1603+3820 taken 1.28 years (0.36
years in the quasar rest frame) after a previous observation with Subaru+HDS.
The new spectrum enables us to search for time variability as an identifier of
intrinsic narrow absorption lines (NALs). This quasar shows a rich complex of C
IV NALs within 60,000 km/s of the emission redshift. Based on covering factor
analysis, Misawa et al. found that the C IV NAL system at z_abs= 2.42--2.45
(System A, at a shift velocity of v_sh = 8,300--10,600 km/s relative to the
quasar) was intrinsic to the quasar. With our new spectrum, we perform time
variability analysis as well as covering factor analysis to separate intrinsic
NALs from intervening NALs for 8 C IV systems. Only System A, which was
identified as an intrinsic system in the earlier paper by Misawa et al., shows
a strong variation in line strength (W_obs ~ 10.4A -> 19.1A). We speculate that
a broad absorption line (BAL) could be forming in this quasar. We illustrate
the plausibility of this suggestion with the help of a simulation. Under the
assumption that a change of ionization state causes the variability, a lower
limit can be placed on the electron density (n_e > 3x10^4 cm^-3) and an upper
limit on the distance from the continuum source (r < 6 kpc). On the other hand,
if the motion of clumpy gas causes the variability (a more likely scenario),
the crossing velocity and the distance from the continuum source are estimated
to be v_cross > 8,000 km/s and r < 3 pc. In this case, the absorber does not
intercept any flux from the broad emission line region, but only flux from the
UV continuum source. If we adopt the dynamical model of Murray et al., we can
obtain a much more strict constraint on the distance of the gas parcel from the
continuum source, r < 0.2 pc.


title: On Bars, Haloes, their Interaction and their Orbital Structure

abstract:
  A live halo plays an active role in the formation and evolution of bars by
participating in the angular momentum redistribution which drives the dynamical
evolution. Angular momentum is emitted mainly by near-resonant material in the
bar region and is absorbed mainly by near-resonant material in the halo and in
the outer disc. This exchange determines the strength of the bar, the decrease
of its pattern speed, as well as its morphology. Thus, contrary to previous
beliefs, a halo can help the bar grow, so that bars growing in galaxies with
responsive massive haloes can become stronger than bars growing in disc
dominated galaxies. During the evolution the halo does not stay axisymmetric.
It forms a bar which is shorter and fatter than the disc bar and stays so all
through the simulation, although its length grows considerably with time. I
discuss the orbital structure in the disc and the halo and compare it with
periodic orbits in analytical barred galaxy potentials. A central mass
concentration (e.g. a central black hole, or a central disc) weakens a bar and
increases its pattern speed. The effect of the central mass concentration
depends strongly on the model, being less strong in models with a massive
concentrated halo and a strong bar.


title: Crystalline Silicate Emission in the Protostellar Binary Serpens--SVS20

abstract:
  We present spatially resolved mid-infrared spectroscopy of the class
I/flat-spectrum protostellar binary system SVS20 in the Serpens cloud core. The
spectra were obtained with the mid-infrared instrument T-ReCS on Gemini-South.
SVS20-South, the more luminous of the two sources, exhibits a mid-infrared
emission spectrum peaking near 11.3 \micron, while SVS20-North exhibits a
shallow amorphous silicate absorption spectrum with a peak optical depth of
$\tau \sim 0.3$. After removal of the the line-of-sight extinction by the
molecular common envelope, the ``protostar-only'' spectra are found to be
dominated by strong amorphous olivine emission peaking near 10 \micron. We also
find evidence for emission from crystalline forsterite and enstatite associated
with both SVS20-S and SVS20-N. The presence of crystalline silicate in such a
young binary system indicates that the grain processing found in more evolved
HAeBe and T Tauri pre-main sequence stars likely begins at a relatively young
evolutionary stage, while mass accretion is still ongoing.


title: The Dynamics of the Magnetoviscous Instability

abstract:
  In dilute astrophysical plasmas, the collisional mean free path of a particle
can exceed its Larmor radius. Under these conditions, the thermal conductivity
and viscosity of the plasma can be dramatically altered. This alteration allows
outwardly decreasing angular velocity or temperature gradients to become
strongly destabilizing. This paper generalizes an earlier, simple analysis of
the viscosity instability, by including the dynamical effects of magnetic field
line tension. Such effects lower the growth rates found in the absence of such
tension, but still allow growth rates in excess of the maximum of the standard
magnetorotational instability. We find very good quantitative agreement with
more complex kinetic treatments of the same process. The combination of large
growth rates and large magnetic Prandtl number suggest that protogalactic disks
are powerful dynamos.


title:
Radial Distribution of Production Rates, Loss Rates and Densities
  Corresponding to Ion Masses <=40 amu in the Inner Coma of Comet Halley:
  Composition and Chemistry

abstract:
  In this paper we have studied the chemistry of C, H, N, O, and S compounds
corresponding to ions of masses <=40 amu in the inner coma of the comet
1P/Halley. The production rates, loss rates, and ion mass densities are
calculated using the Analytical Yield Spectrum approach and solving coupled
continuity equation controlled by the steady state photochemical equilibrium
condition. The primary ionization sources in the model are solar EUV photons,
photoelectrons, and auroral electrons of the solar wind origin. The chemical
model couples ion-neutral, electron-neutral, photon-neutral and electron-ion
reactions among ions, neutrals, electrons, and photons through over 600
chemical reactions. Of the 46 ions considered in the model the chemistry of 24
important ions are discussed in this paper. The calculated ion mass densities
are compared with the Giotto Ion Mass Spectrometer (IMS) and Neutral Mass
Spectrometer (NMS) data at radial distances 1500, 3500, and 6000 km.


title: Classifications of the Host Galaxies of Supernovae, Set III

abstract:
  A homogeneous sample comprising host galaxies of 604 recent supernovae,
including 212 objects discovered primarily in 2003 and 2004, has been
classified on the David Dunlap Observatory system. Most SN 1991bg-like SNe Ia
occur in E and E/Sa galaxies, whereas the majority of SN 1991T-like SNe Ia
occur in intermediate-type galaxies. This difference is significant at the
99.9% level. As expected, all types of SNe II are rare in early-type galaxies,
whereas normal SNe Ia occur in all Hubble types. This difference is significant
at the 99.99% level. A small number of SNe II in E galaxies might be due to
galaxy classification errors, or to a small young-population component in these
mainly old objects. No significant difference is found between the
distributions over Hubble type of SNe Ibc and SNe II. This confirms that both
of these types of objects have similar (massive) progenitors. The present data
show that, in order to understand the dependence of supernova type on
host-galaxy population, it is more important to obtain accurate morphological
classifications than it is to increase the size of the data sample.


title:
Saturated-State Turbulence and Structure from Thermal and
  Magnetorotational Instability in the ISM: Three-Dimensional Numerical
  Simulations

abstract:
  This paper reports on 3D numerical simulations of dynamics and thermodynamics
in the diffuse ISM. Our models are local, account for sheared galactic
rotation, magnetic fields, and realistic cooling, and resolve scales ~1-200 pc.
This combination permits the study of quasi-steady turbulence in a cloudy
medium representing the warm/cold atomic ISM. Turbulence is driven by the
magnetorotational instability (MRI); our models are the first to study the
saturated state of MRI under strongly inhomogeneous conditions, with
cloud/intercloud contrasts of about 100. For volume-averaged densities n=0.25 -
4 cm^3, the saturated-state velocity dispersion ranges from 8-1 km/s, scaling
as n^-0.77. The MRI is therefore likely quite important in driving turbulence
in low-density ISM regions, both at high latitudes in the inner Galaxy,and
throughout the far outer Galaxy. The MRI may be key to suppressing star
formation at large radii in spiral galaxies, where without MRI-driven
turbulence, a thin, cold layer could form and become gravitationally instable.
Our presentation also includes analysis of thermal structure (temperature and
density PDFs are broadened and include extreme departures from equilibrium, but
retain the classical two-phase bimodal character); results on the distribution
of clump masses (the mass spectrum peaks at about 100 solar masses);
comparisons of saturated-state MRI scalings with single-phase simulation
results (we find B^2 is independent of n); and examples of synthetic HI line
profile maps (showing that physical clumps are not easily distinguished in
velocity components, and vice versa).


title:
Solar Control on Jupiter's Equatorial X-ray Emissions: 26-29 November
  2003 XMM-Newton Observation

abstract:
  During November 26-29, 2003 XMM-Newton observed soft (0.2-2 keV) X-ray
emission from Jupiter for 69 hours. The low-latitude X-ray disk emission of
Jupiter is observed to be almost uniform in intensity with brightness that is
consistent with a solar-photon driven process. The simultaneous lightcurves of
Jovian equatorial X-rays and solar X-rays (measured by the TIMED/SEE and GOES
satellites) show similar day-to-day variability. A large solar X-ray flare
occurring on the Jupiter-facing side of the Sun is found to have a
corresponding feature in the Jovian X-rays. These results support the
hypothesis that X-ray emission from Jovian low-latitudes are solar X-rays
scattered from the planet's upper atmosphere, and suggest that the Sun directly
controls the non-auroral X-rays from Jupiter's disk. Our study also suggests
that Jovian equatorial X-rays can be used to monitor the solar X-ray flare
activity on the hemisphere of the Sun that is invisible to space weather
satellites.


title: An Upper Limit on the Expansion Velocity of GRB Candidate SN 2001em

abstract:
  We report on VLBI observations of the Type I b/c supernova 2001em, three
years after the explosion. It had been suggested that SN 2001em might be a
jet-driven gamma ray burst (GRB), with the jet oriented far from the line of
sight so that the GRB would not be visible from earth. To test this conjecture,
we determined the size of SN 2001em. It is only marginally resolved at our
resolution of ~0.9 mas. The 3-sigma upper limit on the major axis angular size
of the radio source was 0.59 mas (FWHM of an elliptical Gaussian),
corresponding to a one-sided apparent expansion velocity of 70,000 km/s for a
distance of 80 Mpc. No low-brightness jet was seen in our image to a level of
4% of the peak brightness. If we assume instead a spherical shell geometry
typical of a supernova, we find the angular radius of SN 2001em was 0.17
(-0.10,+0.06) mas, implying an isotropic expansion velocity of 20,000 (-12,000,
+7,000) km/s, which is comparable to the expansion velocities of supernova
shells. Our observations, therefore, are not consistent with a relativistically
expanding radio source in SN 2001em, but are instead consistent with a
supernova shell origin of SN 2001's radio emission.


title:
Age and Metallicity Estimations in Old Stellar Populations from
  Stromgren Photometry

abstract:
  We present a new technique to determine age and metallicity of old stellar
populations (globular clusters and elliptical galaxies) using an iterative
principal component analysis on narrow band (Str\"omgren) colors. Our technique
is capable of reproducing globular cluster [Fe/H] values to 0.02 dex and CMD
ages to 1.0 Gyrs. We also present preliminary results on the application of our
technique to a sample of high mass, field ellipticals and low mass, cluster
dwarf ellipticals. We confirm the results of earlier studies which find that
globular clusters increase in metallicity with age and that age and metallicity
increase with galaxy mass. However, we find that dwarf ellipticals deviate from
the elliptical sequence by having little to no correlation between age and
metallicity.


title: Updated Colors for Cool Stars in the SDSS

abstract:
  We present updated colors for M and L dwarfs based on photometry from the
third data release of the Sloan Digital Sky Survey (SDSS). These data are
improved in quality and number from earlier results. We also provide updated
equations for determining photometric parallaxes from SDSS colors of late-type
stars. Walkowicz, Hawley & West (2004) have recently presented new techniques
for studying the magnetic activity of low-mass stars and their method relies on
an accurate determination of SDSS color. We derive new relationships between
SDSS colors and other common passbands and present updated formulas from
Walkowicz et al. (2004) for determining the level of magnetic activity in M and
L dwarfs.


title: GU Boo: A New 0.6 Msun Detached Eclipsing Binary

abstract:
  We have found a new low-mass, double-lined, detached eclipsing binary, GU
Boo, among a sample of new variables from the ROTSE-I database. The binary has
an orbital period of 0.488728 +/- 0.000002 days, and estimated apparent
magnitudes Vrotse = 13.7 and I = 11.8. Our analysis of the light and radial
velocity curves of the system yields individual masses and radii of M1= 0.610
+/- 0.007 Msun, M2 = 0.599 +/- 0.006 Msun, R1= 0.623 +/- 0.016 Rsun, R2= 0.620
+/- 0.020 Rsun. The stars in GU Boo are therefore very similar to the
components of the eclipsing binary YY Gem. For this study we have adopted a
mean effective temperature for the binary of Teff = 3870 +/- 130 K. Based on
its space velocities we suggest that GU Boo is a main sequence binary, possibly
with an age of several Gyr. The metallicity of the binary is not well
constrained at this point but we speculate that it should not be very different
from solar. We have compared the physical parameters of GU Boo with current
low-mass stellar models, where we accounted for uncertainties in age and
metallicity by considering a wide range of values for those parameters. Our
comparisons reveal that all the models underestimate the radii of the
components of GU Boo by at least 10-15%. This result is in agreement with the
recent studies of YY Gem and CU Cnc.


title:
Near-UV Observations of CS29497-030: New Constraints on Neutron-Capture
  Nucleosynthesis Processes

abstract:
  Employing spectra obtained with the new Keck I HIRES near-UV sensitive
detector, we have performed a comprehensive chemical composition analysis of
the binary blue metal-poor star CS29497-030. Abundances for 29 elements and
upper limits for an additional seven have been derived, concentrating on
elements largely produced via neutron-capture nucleosynthesis. Included in our
analysis are the two elements that define the termination point of the slow
neutron-capture process, lead and bismuth. We determine an extremely high value
of [Pb/Fe] = +3.65 +/- 0.07 (sigma = 0.13) from three features, supporting the
single-feature result obtained in previous studies. We also detect Bi for the
first time in a metal-poor star. Our derived Bi/Pb ratio is in accord with
those predicted from the most recent FRANEC calculations of the slow
neutron-capture process in low-mass AGB stars. We find that the neutron-capture
elemental abundances of CS29497-030 are best explained by an AGB model that
also includes very significant amounts of pre-enrichment of rapid
neutron-capture process material in the protostellar cloud out of which the
CS29497-030 binary system formed. Thus, CS29497-030 is both an ``r+s'' and
``extrinsic AGB'' star. Furthermore, we find that the mass of the AGB model can
be further constrained by the abundance of the light odd-element [Na/Fe] which
is sensitive to the neutron excess.


title: Observed Properties of Exoplanets: Masses, Orbits, and Metallicities

abstract:
  We review the observed properties of exoplanets found by the Doppler
technique which has revealed 152 exoplanets to date. We focus on our ongoing
18-year survey of 1330 FGKM type stars at Lick, Keck, and the Anglo-Australian
Telescopes carried out with a uniform Doppler precision of 3 m/s. The 104
planets detected in our survey have masses as low as 15 M_Earth orbiting
between 0.03 and 5.5 AU. The mass distribution rises toward the lowest
detectable masses as dN/dM is proportional to M^-1.1. Nearly all giant planets
orbiting within 2 AU of all FGK stars within 30 pc have now been discovered.
The distribution of semi-major axes rises from 0.3 -- 3.0 AU (in bins of Delta
log a), but remains unknown for larger orbits. Extrapolation suggests that 12%
of the FGK stars harbor exoplanets within 20 AU. The median orbital
eccentricity is <e>=0.25 (excluding those tidally circularized), lower than
previously measured . Planets orbiting beyond 3 AU continue to exhibit non-zero
eccentricity, suggesting that the circular orbits of giant planets in our Solar
System are unusual. The occurrence rate of ``hot Jupiters'' within 0.1 AU is
1.2$\pm$0.3 %. The probability of occurrence of planets varies as the square of
the stellar metal abundance, $P \propto N^2_Fe, ranging from $<$3% for stars of
subsolar metallicity to 25% for stars with [Fe/H] > +0.3. Nearly 14% of
planet-bearing stars harbor multiple-planet systems, occasionally locked in
resonances. Kepler and Corot should measure the occurrence of earth-sized
planets. The Space Interferometry Mission (SIM) will detect planets with masses
as low as 3 M_ Earth orbiting within 2 AU of nearby stars and will measure
masses, orbits and multiplicity. These candidate rocky planets will motivate
spectroscopic follow-up by the ``Terrestrial Planet Finder'' and Darwin.}


title: Cosmic Mimicry: Is LCDM a Braneworld in Disguise ?

abstract:
  For a broad range of parameter values, braneworld models display a remarkable
property which we call cosmic mimicry. Cosmic mimicry is characterized by the
fact that, at low redshifts, the Hubble parameter in the braneworld model is
virtually indistinguishable from that in the LCDM cosmology. An important point
to note is that the \Omega_m parameters in the braneworld model and in the LCDM
cosmology can nevertheless be quite different. Thus, at high redshifts (early
times), the braneworld asymptotically expands like a matter-dominated universe
with the value of \Omega_m inferred from the observations of the local matter
density. At low redshifts (late times), the braneworld model behaves almost
exactly like the LCDM model but with a renormalized value of the cosmological
density parameter \Omega_m^{LCDM}. The redshift which characterizes cosmic
mimicry is related to the parameters in the higher-dimensional braneworld
Lagrangian. Cosmic mimicry is a natural consequence of the scale-dependence of
gravity in braneworld models. The change in the value of the cosmological
density parameter is shown to be related to the spatial dependence of the
effective gravitational constant in braneworld theory. A subclass of mimicry
models lead to an older age of the universe and also predict a redshift of
reionization which is lower than z_{reion} \simeq 17 in the LCDM cosmology.
These models might therefore provide a background cosmology which is in better
agreement both with the observed quasar abundance at z \gsim 4 and with the
large optical depth to reionization measured by the Wilkinson Microwave
Anisotropy Probe.


title: The Anthropic Principle and the Duration of the Cosmological Past

abstract:
  The place of an anthropic argument in the discrimination between various
cosmological models is to be reconsidered following the classic criticisms of
Paul C. W. Davies and Frank J. Tipler. Different versions of the anthropic
argument against cosmologies involving an infinite series of past events are
analyzed and applied to several instructive instances. This is not only of
historical significance but presents an important topic for the future of
cosmological research if some of the contemporary inflationary models,
particularly Linde's chaotic inflation, turn out to be correct. Cognitive
importance of the anthropic principle(s) to the issue of extraterrestrial
intelligent observers is reconsidered in this light and several related
problems facing cosmologies with past temporal infinities are also clearly
defined. This issue is not only a clear example of the epistemological
significance of the anthropic principle, but also has consequences for such
diverse topics as SETI studies, epistemological status of cosmological
concepts, theory of observation selection effects, and history of astronomy.


title: Too Early? On the Apparent Conflict of Astrobiology and Cosmology

abstract:
  An interesting consequence of the modern cosmological paradigm is the spatial
infinity of the universe. When coupled with naturalistic understanding of the
origin of life and intelligence, which follows the basic tenets of
astrobiology, and with some fairly incontroversial assumptions in the theory of
observation selection effects, this infinity leads, as Ken Olum has recently
shown, to a paradoxical conclusion. Olum's paradox is related, to the famous
Fermi's paradox in astrobiology and SETI studies. We, hereby, present an
evolutionary argument countering the apparent inconsistency, and show how, in
the framework of a simplified model, deeper picture of the coupling between
histories of intelligent/technological civilizations and astrophysical
evolution of the Galaxy, can be achieved. This strategy has consequences of
importance for both astrobiological studies and philosophy.


title:
On the viability of neutron star black hole binaries as central engines
  of gamma-ray bursts

abstract:
  I discuss three-dimensional SPH simulations of neutron star black hole
encounters. The calculations are performed using a nuclear equation of state
and a multi-flavor neutrino treatment, general relativistic effects are
mimicked using the Paczynski-Wiita pseudo-potential and gravitational radiation
reaction forces. Most of the explored mass range (14 to 20 \msun) has not been
considered before in numerical simulations. The neutron star is always
disrupted during the first approach after most of its mass has been transferred
directly into the hole. In none of the analyzed cases episodic mass transfer is
found. If an accretion disk forms at all, it is relatively cold ($T < 2.5$
MeV), of only moderate density ($\rho \sim 10^{10}$ g/ccm) and substantially
consumed by the hole on the simulation time scale of a few milliseconds. None
of the investigated systems of this study yields conditions that are promising
to launch a GRB. While we cannot completely exclude that a subset of neutron
star black hole binaries, maybe black holes with low masses and very large
initial spins, can produce a GRB, this seems to happen -if at all- only in a
restricted region of the available parameter space. I argue that the difficulty
to form promising disks together with the absence of any observed neutron star
black hole binary may mean that they are insignificant as central engines of
the observed, short-hard GRBs and that the vast majority of the latter ones is
caused by double neutron star coalescences.


title:
Fragmentation and Evolution of Molecular Clouds. I: Algorithm and First
  Results

abstract:
  We present a series of simulations of the fragmentation of a molecular cloud,
leading to the formation of a cluster of protostellar cores. The purpose of
these simulations is to address a specific numerical problem called artificial
fragmentation, that plagues SPH simulations of cloud fragmentation. We argue
that this is a serious problem that needs to be addressed, and that the only
reasonable and practical way to address it is to use a relatively new technique
called particle splitting. Our largest simulation has an effective resolution
of 256^3 particles (much higher than most previous SPH simulations of cloud
fragmentation) and results in the formation of a dense cluster containing ~3000
protostellar cores. It is the first simulation of this kind to properly resolve
the Jeans mass throughout the entire system, at all times, thus preventing
artificial fragmentation.


title: Core Overshoot: An Improved Treatment and Constraints from Seismic Data

abstract:
  We present a comprehensive set of stellar evolution models for Procyon A in
an effort to guide future measurements of both traditional stellar parameters
and seismic frequencies towards constraining the amount of core overshoot in
Procyon A and possibly other stars. Current observational measurements of
Procyon A when combined with traditional stellar modeling only place a large
upper limit on overshoot of alphaOV < 1.1. By carrying out a detailed pulsation
analysis, we further demonstrate, how p- and g-mode averaged spacings can be
used to gain better estimates of the core size. For both p- and g-modes, the
frequency spacings for models without overshoot are clearly separated from the
models with overshoot. In addition, measurements of the l=0 averaged small
p-mode spacings could be used to establish Procyon A's evolutionary stage. For
a fixed implementation of overshoot and under favorable circumstances, the
g-mode spacings can be used to determine the overshoot extent to an accuracy of
+-0.05 Hp. However, we stress that considerable confusion is added due to the
unknown treatment of the overshoot region. This ambiguity might be removed by
analyzing many different stars. A simple non-local convection theory developed
by Kuhfuss is implemented in our stellar evolution code and contrasted with the
traditional approaches. We show that this theory supports a moderate increase
of the amount of convective overshoot with stellar mass of Delta(alphaOV) =
+0.10 between 1.5 Msun and 15 Msun. This theory places an upper limit on
Procyon A's core overshoot extent of ~0.4 Hp which matches the limit imposed by
Roxburgh's integral criterion.


title: The cosmological simulation code GADGET-2

abstract:
  We discuss the cosmological simulation code GADGET-2, a new massively
parallel TreeSPH code, capable of following a collisionless fluid with the
N-body method, and an ideal gas by means of smoothed particle hydrodynamics
(SPH). Our implementation of SPH manifestly conserves energy and entropy in
regions free of dissipation, while allowing for fully adaptive smoothing
lengths. Gravitational forces are computed with a hierarchical multipole
expansion, which can optionally be applied in the form of a TreePM algorithm,
where only short-range forces are computed with the `tree'-method while
long-range forces are determined with Fourier techniques. Time integration is
based on a quasi-symplectic scheme where long-range and short-range forces can
be integrated with different timesteps. Individual and adaptive short-range
timesteps may also be employed. The domain decomposition used in the
parallelisation algorithm is based on a space-filling curve, resulting in high
flexibility and tree force errors that do not depend on the way the domains are
cut. The code is efficient in terms of memory consumption and required
communication bandwidth. It has been used to compute the first cosmological
N-body simulation with more than 10^10 dark matter particles, reaching a
homogeneous spatial dynamic range of 10^5 per dimension in a 3D box. It has
also been used to carry out very large cosmological SPH simulations that
account for radiative cooling and star formation, reaching total particle
numbers of more than 250 million. We present the algorithms used by the code
and discuss their accuracy and performance using a number of test problems.
GADGET-2 is publicly released to the research community.


title:
Statistics of phase correlations as a test for non-Gaussianity of the
  CMB maps

abstract:
  Gaussianity is the very base for derivation of the cosmological parameters
from the CMB angular power spectrum. Non-Gaussian signal, whether originated
from experimental error or primordial source, could mimic extra power in the
power spectrum, thereby leading to a wrong set of parameters. In this paper we
present a new Gaussianity analysis of the derived CMB singals. It is based on
the trigonometric moments of phases, which can be concluded with a ``mean
angle'', allowing us to see the global trend of non-Gaussianity of the signals.
These moments are also closely related to the Pearson's random walks. We apply
these analyses on the derived CMB maps and their different morphologies
manifest themselves through these functions. We also comment on rotational
invariance of the trigonometric moments of phases as a non-Gaussianity test.


title: Numerical biases on IMF determinations created by binning

abstract:
  We detect and quantify significant numerical biases in the determination of
the slope of power laws with Salpeter (or similar) indices from
uniformly-binned data using chi-square minimization. The biases are caused by
the correlation between the number of stars per bin and the assigned weights
and are especially important when the number of stars per bin is small. This
result implies the existence of systematic errors in the values of IMFs
calculated in this way. We propose as an alternative using variable-size bins
and dividing the stars evenly among them. Such variable-size bins yield very
small biases that are only weakly dependent on the number of stars per bin.
Furthermore, we show that they allow for the calculation of reliable IMFs with
only a small total number of stars. Therefore, they are a preferred alternative
to the standard uniform-size binning.


title: Collisionless Damping of Fast MHD Waves in Magneto-rotational Winds

abstract:
  We propose collisionless damping of fast MHD waves as an important mechanism
for the heating and acceleration of winds from rotating stars. Stellar rotation
causes magnetic field lines anchored at the surface to form a spiral pattern
and magneto-rotational winds can be driven. If the structure is a magnetically
dominated, fast MHD waves generated at the surface can propagate almost
radially outward and cross the field lines. The propagating waves undergo
collisionless damping owing to interactions with particles surfing on magnetic
mirrors that are formed by the waves themselves. The damping is especially
effective where the angle between the wave propagation and the field lines
becomes moderately large ($\sim 20$ to $80^{\circ}$). The angle tends naturally
to increase into this range because the field in magneto-rotational winds
develops an increasingly large azimuthal component. The dissipation of the wave
energy produces heating and acceleration of the outflow. We show using
specified wind structures that this damping process can be important in both
solar-type stars and massive stars that have moderately large rotation rates.
This mechanism can play a role in coronae of young solar-type stars which are
rapidly rotating and show X-ray luminosities much larger than the sun. The
mechanism could also be important for producing the extended X-ray emitting
regions inferred to exist in massive stars of spectral type middle B and later.


title:
3D Simulations of the ISM pollution by SNII and SNI in dwarf spheroidal
  galaxies

abstract:
  We present preliminary results of 3-D hydro simulations of the interstellar
medium evolution in dwarf spheroidal galaxies undergoing star formation for the
first time. The star formation is assumed to occur in a sequence of
instantaneus bursts separated by quiescent periods. Different models are made
changing the number and the intensity of the bursts in such a way that the
final mass of the formed stars remains the same. We followed the enrichment of
the ISM taking into account the contribution of both type Ia and II supernovae.
The aim of our models is to find a star formation history compatible with the
observed spread of stellar age and metallicity in such galaxies and to
reproduce the observed mass-metallicity relation.


title:
The Oxford-Dartmouth Thirty Degree Survey II: Clustering of Bright Lyman
  Break Galaxies - Strong Luminosity Dependent Bias at z=4

abstract:
  We present measurements of the clustering properties of bright ($L>L_{*}$)
z$\sim$4 Lyman Break Galaxies (LBGs) selected from the Oxford-Dartmouth Thirty
Degree Survey (ODT). We describe techniques used to select and evaluate our
candidates and calculate the angular correlation function which we find best
fitted by a power law, $\omega(\theta)=A_{w}\theta^{-\beta}$ with $A_{w}=15.4$
(with $\theta$ in arcseconds), using a constrained slope of $\beta=0.8$. Using
a redshift distribution consistent with photometric models, we deproject this
correlation function and find a comoving $r_{0}=11.4_{-1.9}^{+1.7}$
h$_{100}^{-1}$ Mpc in a $\Omega_m=0.3$ flat $\Lambda$ cosmology for
$i_{AB}\leq24.5$. This corresponds to a linear bias value of
$b=8.1_{-2.6}^{+2.0}$ (assuming $\sigma_{8}=0.9$). These data show a
significantly larger $r_{0}$ and $b$ than previous studies at $z\sim4$. We
interpret this as evidence that the brightest LBGs have a larger bias than
fainter ones, indicating a strong luminosity dependence for the measured bias
of an LBG sample. Comparing this against recent results in the literature at
fainter (sub-$L_{*}$) limiting magnitudes, and with simple models describing
the relationship between LBGs and dark matter haloes, we discuss the
implications on the implied environments and nature of LBGs. It seems that the
brightest LBGs (in contrast with the majority sub-$L_{*}$ population), have
clustering properties, and host dark matter halo masses, that are consistent
with them being progenitors of the most massive galaxies today.


title:
XMM-Newton Spectroscopy of the Starburst Dominated Ultra Luminous
  Infrared Galaxy NGC 6240

abstract:
  We present new XMM-Newton observation of the Ultra Luminous Infrared Galaxy
(ULIRG) NGC 6240. We analyze the reflecting grating spectrometer (RGS) data,
and data from the other instruments, and find a starburst dominated 0.5-3 keV
spectrum with global properties resembling those observed in M82 but with a
much higher luminosity. We show that the starburst region can be divided into
an outer zone, beyond a radius of about 2.1 kpc, with a gas temperature of
about 10^7 K and a central region with temperatures in the range (2-6) x 10^7
K. The gas in the outer region emits most of the observed Oviii Lyman-alpha
line and the gas in the inner region the emission lines of higher ionization
ions, including a strong Fexxv line. We also identify a small inner part, very
close to the active nuclei, with typical Seyfert 2 properties including a large
amount of photoionized gas producing a strong Fe K-alpha 6.4 keV line. The
combined abundance, temperature and emission measure analysis indicates super
solar Ne/O, Mg/O, Si/O, S/O and possibly also Fe/O. The analysis suggests
densities in the range of (0.07-0.28) x epsilon^(-1/2) cm^(-3) and a total
thermal gas mass of about 4 x 10^8 x epsilon^(1/2) solar masses, where epsilon
is the volume filling factor. We used a simple model to argue that a massive
starburst with an age of about 2 x 10^7 years can explain most of the observed
properties of the source. NGC 6240 is perhaps the clearest case of an X-ray
bright luminous AGN, in a merger, whose soft X-ray spectrum is dominated by a
powerful starburst.


title: New constraints on MOND from galaxy clusters

abstract:
  We revisit the application of Modified Newtonian Dynamics (MOND) to galaxy
clusters. We confront the high quality X-ray data for eight clusters of
galaxies observed by the \xmm satellite with the predictions of MOND. We obtain
a ratio of the MOND dynamical mass to the baryonic mass of $M_m/M_b=4.94\pm
0.50$ in the outer parts (i.e $r\sim 0.5$ ~ R$_{vir}$), in the concordance
cosmological model where the predicted asymptotic ratio, if any baryons are
present, is $7.7^{+1.4}_{-1.1}$ (at $r\geq 0.3$ ~ R$_{vir}$). We confirm that
the MOND paradigm lowers the discrepancy between the binding mass and the
baryonic mass in clusters by a factor of $\sim 1.6$ at about half the virial
radius. However, at this radius about 80% of the mass is still missing, and as
pointed out by \citet{sanders03}, this necessitates a component of dark baryons
or neutrinos in the cluster core. Concerning the neutrino hypothesis,
application of the new data requires a minimum neutrino mass of $m_\nu>1.74\pm
0.34$ eV to fill this gap. The corresponding 2$\sigma$ lower limit of
$m_\nu>1.06$ eV is marginally inconsistent with the current constraints from
the cluster number counts, and from the CMB and large scale structure data.
MOND must invoke neutrinos to represent the main component that account for the
missing mass problem in clusters.


title: Rigidly Rotating Strange Quark Star

abstract:
  This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0404032 and others.


title: 109 new Galactic open clusters

abstract:
  We present a list of 130 Galactic Open Clusters, found in the All-Sky
Compiled Catalogue of 2.5 Million Stars (ASCC-2.5). For these clusters we
determined and publish a homogeneous set of astrophysical parameters such as
size, membership, motion, distance and age. In a previous work 520 already
known open clusters out of the sample of 1700 clusters from the literature were
confirmed in the ASCC-2.5 using independent, objective methods. Using these
methods the whole sky was systematically screened for the search of new
clusters. The newly detected clusters show the same distribution over the sky
as the known ones. It is found, that without the {\em a-priori} knowledge about
existing clusters our search lead to clusters which are, {\em on average},
brighter, have more members and cover larger angular radii than the 520
previously known ones.


title:
The GRB of 1999 January 23: prompt emission and broad-band afterglow
  modeling

abstract:
  We report on BeppoSAX simultaneous X- and gamma-ray observations of the
bright gamma-ray burst (GRB) 990123. We present the broad-band spectrum of the
prompt emission, including optical, X- and gamma-rays, confirming the
suggestion that the emission mechanisms at low and high frequencies must have
different physical origins. We discuss the X-ray afterglow observed by the
Narrow Field Instruments (NFIs) on board BeppoSAX and its hard X-ray emission
up to 60 keV several hours after the burst, in the framework of the standard
fireball model. The effects of including an important contribution of Inverse
Compton scattering or modifying the hydrodynamics are studied.


title: NGC 4254: a spiral galaxy entering the Virgo cluster

abstract:
  Deep Effelsberg HI spectra of the one-armed, bright Virgo cluster spiral
galaxy NGC 4254 are presented.Five different positions were observed in the 21
cm HI line with the Effelsberg 100-m telescope: one in the center and 4 located
one HPBW to the NE, NW, SW, and SE, respectively, from the galaxy center. The
spectra are compared to existing deep VLA observations, and the single dish and
interferometric HI data are used to constrain a dynamical model which includes
the effects of ram pressure. The peculiar, one-armed spiral pattern of NGC 4254
and its distorted and kinematically perturbed atomic gas distribution can be
explained by a close and rapid encounter ~280 Myr ago with another massive
Virgo galaxy, followed by ram pressure stripping that is still ongoing. The
stripping occurs almost face-on, since the angle between the disk and the
orbital plane is 70 degrees. The galaxy with which NGC 4254 had its encounter
is tentatively identified as the lenticular NGC 4262.


title:
A Photometric Study of the Light Variations of the Triple System DG
  Leonis

abstract:
  Multi-site and multi-year differential photometry of the triple star DG Leo
reveals a complex frequency spectrum that can be modelled as the combination of
at least three Delta Scuti type frequencies in the range 11.5-13 c/d (with
semi-amplitudes of 2-7 mmag) and a superimposed slow variability of larger
amplitude. The period of the slow variation fits very well with half the
orbital period of the inner spectroscopic binary indicating the presence of
ellipsoidal variations caused by the tidally deformed components in a close
configuration. These findings, together with the results of a recent
spectroscopic analysis (showing that the system consists of a pair of mild Am
stars and one A-type component of normal solar composition), infer that DG Leo
is an extremely interesting asteroseismic target. Identification of which
component(s) of this multiple system is (or are) pulsating and determination of
the excited pulsation modes will both contribute to a much better understanding
of the non-trivial link between multiplicity, chemical composition, rotation,
and pulsation in the lower part of the classical Cepheid instability strip.


title:
Wave propagation in a weak gravitational field and the validity of the
  thin lens approximation

abstract:
  Wave effects can be important for the gravitational lensing of gravitational
waves. In such a case, wave optics must be used in stead of geometric optics.
We consider a plane wave entering a lens object and solve numerically the wave
equation for three lens models: the uniform density sphere, the singular
isothermal sphere, and the Hernquist model. By comparing our numerical
solutions with the analytical solutions under the thin lens approximation, we
evaluate the error of this approximation. The results show that the relative
error of the thin lens approximation is small if the geometrical thickness of
the lens is much smaller than the distance between the lens and the observer.


title:
The Stellar Content of Nearby Star-Forming Galaxies. III. Unravelling
  the Nature of the Diffuse Ultraviolet Light

abstract:
  We investigate the nature of the diffuse intra-cluster ultraviolet light seen
in twelve local starburst galaxies, using long-slit ultraviolet spectroscopy
obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble
Space Telescope (HST). We take this faint intra-cluster light to be the field
in each galaxy, and compare its spectroscopic signature with STARBURST99
evolutionary synthesis models and with neighboring star clusters. Our main
result is that the diffuse ultraviolet light in eleven of the twelve starbursts
lacks the strong O-star wind features that are clearly visible in spectra of
luminous clusters in the same galaxies. The difference in stellar features
dominating cluster and field spectra indicate that the field light originates
primarily from a different stellar population, and not from scattering of UV
photons leaking out of the massive clusters. We consider several scenarios to
understand the lack of observed O stars in the field, and their implications
for the origin of the field stellar population. If the field stellar
populations formed in situ, the field must either have an IMF which is steeper
than Salpeter (3.0-3.5) or a Salpeter slope with an upper mass cutoff of 30-50
solar masses. If star formation occurs primarily in star clusters, the field
could be composed of older, faded clusters, and/or a population which is coeval
with the luminous clusters but lower in mass. If the field is composed of
older, dissolving clusters, we estimate that star clusters (regardless of mass)
need to dissolve on timescales 7-10 Myr to create the field (abridged).


title:
A Digital Archive of HI 21 cm Line Spectra of Optically-targeted
  Galaxies

abstract:
  We present a homogeneous compilation of HI spectral parameters extracted from
global 21 cm line spectra for some 9000 galaxies in the local universe
(heliocentric velocity -200 < V_Sun < 28,000 km/s) obtained with a variety of
large single dish radio telescopes but reanalyzed using a single set of
parameter extraction algorithms. Corrections to the observed HI line flux for
source extent and pointing offsets and to the HI line widths for instrumental
broadening and smoothing are applied according to model estimates to produce a
homogenous catalog of derived properties with quantitative error estimates.
Where the redshift is available from optical studies, we also provide flux
measurements for an additional 156 galaxies classified as marginal HI
detections and rms noise limits for 494 galaxies classified as nondetections.
Given the diverse nature of the observing programs contributing to it, the
characteristics of the combined dataset are heterogeneous, and as such, the
compilation is neither integrated HI line flux nor peak flux limited. However,
because of the large statistical base and homogenous reprocessing, the spectra
and spectral parameters of galaxies in this optically targeted sample can be
used to complement data obtained at other wavelengths to characterize the
properties of galaxies in the local universe and to explore the large scale
structures in which they reside.


title: GRB990123: multiwavelength afterglow study

abstract:
  We report on the BeppoSAX and multiwavelength data analysis of the afterglow
of Gamma-Ray Burst (GRB) 990123. Mainly due to its exceptional brightness, this
is the only source for which the Wide Field Cameras have allowed an early
detection of the X-ray afterglow between about 20 and 60 min after the GRB
trigger. Besides, again for the first time, high-energy emission from the
afterglow was detected up to 60 keV. The backwards extrapolation of the
afterglow decay smoothly reconnects with the late GRB emission, thus indicating
that both are consistent with being produced by the same phenomenon. For the
X-ray afterglow we found a power-law decay with index alpha_X = 1.46 +/- 0.04;
the spectrum has a power-law shape with photon index Gamma about 2. An
extensive set of multiwavelength observations on the afterglow, collected from
the literature and made during the BeppoSAX pointing, allowed constructing a
Spectral Flux Distribution. We performed an analysis of the GRB afterglow
emission in the context of the "fireball" model.


title: Magnetic Tower Outflows from a Radial Wire Array Z-pinch

abstract:
  We present the first results of high energy density laboratory astrophysics
experiments which explore the evolution of collimated outflows and jets driven
by a toroidal magnetic field. The experiments are scalable to astrophysical
flows in that critical dimensionless numbers such as the Mach number, the
plasma beta and the magnetic Reynolds number are all in the astrophysically
appropriate ranges. Our experiments use the MAGPIE pulsed power machine and
allow us to explore the role of magnetic pressure in creating and collimating
the outflow as well as showing the creation of a central jet within the broader
outflow cavity. We show that currents flow along this jet and we observe its
collimation to be enhanced by the additional hoop stresses associated with the
generated toroidal field. Although at later times the jet column is observed to
go unstable, the jet retains its collimation. We also present simulations of
the magnetic jet evolution using our two-dimensional resistive
magneto-hydrodynamic (MHD) laboratory code. We conclude with a discussion of
the astrophysical relevance of the experiments and of the stability properties
of the jet.


title: The Dynamics of Radiative Shock Waves: Linear and Nonlinear Evolution

abstract:
  The stability properties of one-dimensional radiative shocks with a power-law
cooling function of the form $\Lambda \propto \rho^2T^\alpha$ are the main
subject of this work. The linear analysis originally presented by Chevalier &
Imamura, is thoroughfully reviewed for several values of the cooling index
$\alpha$ and higher overtone modes. Consistently with previous results, it is
shown that the spectrum of the linear operator consists in a series of modes
with increasing oscillation frequency. For each mode a critical value of the
cooling index, $\alpha_\textrm{c}$, can be defined so that modes with $\alpha <
\alpha_\textrm{c}$ are unstable, while modes with $\alpha > \alpha_\textrm{c}$
are stable. The perturbative analysis is complemented by several numerical
simulations to follow the time-dependent evolution of the system for different
values of $\alpha$. Particular attention is given to the comparison between
numerical and analytical results (during the early phases of the evolution) and
to the role played by different boundary conditions. It is shown that an
appropriate treatment of the lower boundary yields results that closely follow
the predicted linear behavior. During the nonlinear regime, the shock
oscillations saturate at a finite amplitude and tend to a quasi-periodic cycle.
The modes of oscillations during this phase do not necessarily coincide with
those predicted by linear theory, but may be accounted for by mode-mode
coupling.


title:
Highly Clumpy Structure of the Thermal Composite Supernova Remnant 3C391
  Unveiled by Chandra

abstract:
  The nature of the internal thermal X-ray emission seen in ``thermal
composite" supernova remnants is still uncertain. Chandra observation of the
3C391 shows a southeast-northwest elongated morphology and unveils a highly
clumpy structure of the remnant. Detailed spatially resolved spectral analysis
for the small-scale features reveals normal metal abundance and uniform
temperature for the interior gas. The properties of the hot gas comparatively
favor the cloudlet evaporation model as a main mechanism for the ``thermal
composite" X-ray appearance, though radiative rim and thermal conduction may
also be effective. A faint protrusion is found in Si and S lines out of the
southwest radio border.


title: Narrow Band Chandra X-ray Analysis of Supernova Remnant 3C391

abstract:
  We present the narrow-band and the equivalent width (EW) images of the
thermal composite supernova remnant (SNR) 3C391 for the X-ray emission lines of
elements Mg, Si, & S using the Chandra ACIS Observational data. These EW images
reveal the spatial distribution of the emission of the metal species Mg, Si, &
S in the remnant. They have clumpy structure similar to that seen from the
broadband diffuse emission, suggesting that they are largely of interstellar
origin. We find an interesting finger-like feature protruding outside the
southwestern radio border of the remnant, which is somewhat similar to the
jet-like Si structure found in the famous SNR Cas A. This feature may possibly
be the debris of the jet of ejecta which implies an asymmetrical supernova
explosion of a massive progenitor star.


title: Optical Sources Near the Bright X-Ray Source in NGC 1073

abstract:
  New HST observations show that the bright X-ray source in the face-on spiral
galaxy NGC 1073 is located near a ring of recent star formation with an age of
8-16 Myr. This strengthens the association of X-ray sources in spiral galaxies
emitting near or above the Eddington limit for a 20 solar mass black hole with
recent star formation events. Two candidate optical counterparts of the X-ray
source are found. The X-ray to optical flux ratios of both are consistent with
those of low-mass X-ray binaries and higher than most high-mass X-ray binaries,
suggesting that reprocessing of X-rays contributes to the optical light. The
optical magnitude and color of one candidate is consistent with that predicted
for an X-ray binary with an initial donor mass of 6-8 solar masses. However,
the same X-ray binary evolution model underestimates the X-ray luminosity. An
X-ray source list for the field is presented which includes detections of the
nucleus of NGC 1073, three quasars, and an M3e brown dwarf star with high
proper motion.


title:
The Evolutionary Status of Be Stars: Results from a Photometric Study of
  Southern Open Clusters

abstract:
  Be stars are a class of rapidly rotating B stars with circumstellar disks
that cause Balmer and other line emission. There are three possible reasons for
the rapid rotation of Be stars: they may have been born as rapid rotators, spun
up by binary mass transfer, or spun up during the main-sequence (MS) evolution
of B stars. To test the various formation scenarios, we have conducted a
photometric survey of 55 open clusters in the southern sky. Of these, five
clusters are probably not physically associated groups and our results for two
other clusters are not reliable, but we identify 52 definite Be stars and an
additional 129 Be candidates in the remaining clusters. We use our results to
examine the age and evolutionary dependence of the Be phenomenon. We find an
overall increase in the fraction of Be stars with age until 100 Myr, and Be
stars are most common among the brightest, most massive B-type stars above the
zero-age MS (ZAMS). We show that a spin-up phase at the terminal-age MS (TAMS)
cannot produce the observed distribution of Be stars, but up to 73% of the Be
stars detected may have been spun-up by binary mass transfer. Most of the
remaining Be stars were likely rapid rotators at birth.
  Previous studies have suggested that low metallicity and high cluster density
may also favor Be star formation. Our results indicate a possible increase in
the fraction of Be stars with increasing cluster distance from the Galactic
center (in environments of decreasing metallicity). However, the trend is not
significant and could be ruled out due to the intrinsic scatter in our data. We
also find no relationship between the fraction of Be stars and cluster density.


title: The Hubble Slow Roll Expansion for Multi Field Inflation

abstract:
  We examine the dynamics of inflation driven by multiple, interacting scalar
fields and derive a multi field version of the Hubble slow roll expansion. We
show that the properties of this expansion naturally generalize those of the
single field case. We present an analogous hierarchy of slow roll parameters,
and derive the system of ``flow'' equations that describes their evolution, and
show that when this system is truncated at finite order, it can always be
solved exactly. Lastly, we express the scalar and tensor perturbation spectra
in terms of the slow roll parameters.


title: The infrared-dominated jet of 3C401

abstract:
  We present a Hubble Space Telescope image of the FRII radio galaxy 3C 401,
obtained at 1.6 microns with the NICMOS camera in which we identify the
infrared counterpart of the brightest region of the radio jet. The jet has a
complex radio structure and brightens where bending occurs, most likely as a
result of relativistic beaming. We analyze archival data in the radio, optical
and X-ray bands and we derive its spectral energy distribution. Differently
from all of the previously known optical extragalactic jets, the jet in 3C401
is not detected in the X-rays even in a long 48ksec X-ray Chandra exposure and
the infrared emission dominates the overall SED. We propose that the dominant
radiation mechanism of this jet is synchrotron. The low X-ray emission is then
caused by two different effects: i) the lack of any strong external photon
field and ii) the shape of the electron distribution. This affects the location
of the synchrotron peak in the SED, resulting in a sharp cut-off at energies
lower than the X-rays. Thus 3C401 shows a new type of jet which has
intermediate spectral properties between those of FRI, which are dominated by
synchrotron emission up to X-ray energies, and FRII/QSO, which show a strong
high-energy emission due to inverse-Compton scattering of external photons.
This might be a clue for the presence of a continuous ``sequence'' in the
properties of large scale jets, in analogy with the ``blazar sequence'' already
proposed for sub-pc scale jets.


title: The Radio Afterglow and Host Galaxy of the Dark GRB 020819

abstract:
  Of the fourteen gamma-ray bursts (GRBs) localized to better than 2' radius
with the SXC on HETE-2, only two lack optical afterglow detections, and the
high recovery rate among this sample has been used to argue that the fraction
of truly dark bursts is ~10%. While a large fraction of earlier dark bursts can
be explained by the failure of ground-based searches to reach appropriate
limiting magnitudes, suppression of the optical light of these SXC dark bursts
seems likely. Here we report the discovery and observation of the radio
afterglow of GRB 020819, an SXC dark burst, which enables us to identify the
likely host galaxy (probability of 99.2%) and hence the redshift (z=0.41) of
the GRB. The radio light curve is qualitatively similar to that of several
other radio afterglows, and may include an early-time contribution from the
emission of the reverse shock. The proposed host is a bright R = 19.5 mag
barred spiral galaxy, with a faint R ~ 24.0 mag "blob'' of emission, 3" from
the galaxy core (16 kpc in projection), that is coincident with the radio
afterglow. Optical photometry of the galaxy and blob, beginning 3 hours after
the burst and extending over more than 100 days, establishes strong upper
limits to the optical brightness of any afterglow or associated supernova.
Combining the afterglow radio fluxes and our earliest R-band limit, we find
that the most likely afterglow model invokes a spherical expansion into a
constant-density (rather than stellar wind-like) external environment; within
the context of this model, a modest local extinction of A_V ~ 1 mag is
sufficient to suppress the optical flux below our limits.


title: A Puzzling Merger in A3266: the Hydrodynamic Picture from XMM-Newton

abstract:
  Using the mosaic of nine XMM-Newton observations, we study the hydrodynamic
state of the merging cluster of galaxies Abell 3266. The high quality of the
spectroscopic data and large field of view of XMM-Netwon allow us to determine
the thermodynamic conditions of the intracluster medium on scales of order of
50 kpc. A high quality entropy map reveals the presence of an extended region
of low entropy gas, running from the primary cluster core toward the northeast
along the nominal merger axis. The mass of the low entropy gas amounts to
approximately 2e13 solar masses, which is comparable to the baryonic mass of
the core of a rich cluster. We test the possibility that the origin of the
observed low entropy gas is either related to the disruption a preexisting
cooling core in Abell 3266 or to the stripping of gas from an infalling
subcluster companion. We find that both the radial pressure and entropy
profiles as well as the iron abundance of Abell 3266 do not resemble those in
other known cooling core clusters (Abell 478). Thus we conclude that the low
entropy region is subcluster gas in the process of being stripped off from its
dark matter halo. In this scenario the subcluster would be falling onto the
core of A3266 from the foreground. This would also help interpret the observed
high velocity dispersion of the galaxies in the cluster center, provided that
the mass of the subcluster is at most a tenth of the mass of the main cluster.


title: A Hot Wind from the Classical T Tauri Stars: TW Hydrae and T Tauri

abstract:
  Spectroscopy of the infrared He I (10830A) line with KECK/NIRSPEC and
IRTF/CSHELL, and of the ultraviolet C III (977A) and O VI (1032A) emission with
FUSE reveals that the classical T Tauri star TW Hydrae exhibits P Cygni
profiles, line asymmetries, and absorption indicative of a continuous, fast
(~400 km/s), hot (~300,000 K) accelerating outflow with a mass loss rate
\~10^-11 - 10^-12 solar masses per year, or larger. Spectra of T Tauri N appear
consistent with such a wind. The source of the emission and outflow seems
restricted to the stars themselves. Although the mass accretion rate is an
order of magnitude less for TW Hya than for T Tau, the outflow reaches higher
velocities at chromospheric temperatures in TW Hya. Winds from young stellar
objects may be substantially hotter and faster than previously thought.


title:
Evidence for dust reddening in DLAs identified through CaII H&K
  absorption

abstract:
  We present a new sample of 31 CaII(H&K) 3935,3970 absorption line systems
with 0.84<z_abs<1.3 discovered in the spectra of Sloan Digital Sky Survey
(SDSS) Data Release 3 quasars, together with an analysis of their dust content.
The presence of Calcium absorption together with measurements of the MgII 2796,
FeII 2600 and MgI 2853 lines lead to the conclusion that the majority of our
systems are Damped Ly-alpha (DLA) absorbers. The composite spectrum in the rest
frame of the absorber shows clear evidence for reddening. Large and Small
Magellanic Cloud extinction curves provide satisfactory fits, with a best-fit
E(B-V) of 0.06, while the Galactic dust extinction curve provides a poor fit
due to the lack of a strong 2175A feature. A trend of increasing dust content
with equivalent width of CaII is present. Monte Carlo techniques demonstrate
that the detection of reddening is significant at >99.99% confidence. The
discovery of significant amounts of dust in a subsample of DLAs has direct
implications for studies of the metallicity evolution of the universe and the
nature of DLAs in relation to high redshift galaxies. The gas:dust ratio is
discussed. Our results suggest that at least ~40% of the CaII absorption
systems are excluded from the magnitude-limited SDSS quasar sample as a result
of the associated extinction, a fraction similar to the upper limit deduced at
higher redshifts from radio-selected surveys.


title: X-ray Bursts from the Transient Magnetar Candidate XTE J1810-197

abstract:
  We have discovered four X-ray bursts, recorded with the Rossi X-ray Timing
Explorer Proportional Counter Array between 2003 September and 2004 April, that
we show to originate from the transient magnetar candidate XTE J1810-197. The
burst morphologies consist of a short spike or multiple spikes lasting ~1 s
each followed by extended tails of emission where the pulsed flux from XTE
J1810-197 is significantly higher. The burst spikes are likely correlated with
the pulse maxima, having a chance probability of a random phase distribution of
0.4%. The burst spectra are best fit to a blackbody with temperatures 4-8 keV,
considerably harder than the persistent X-ray emission. During the X-ray tails
following these bursts, the temperature rapidly cools as the flux declines,
maintaining a constant emitting radius after the initial burst peak. During the
brightest X-ray tail, we detect a narrow emission line at 12.6 keV with an
equivalent width of 1.4 keV and a probability of chance occurrence less than 4
x 10^-6. The temporal and spectral characteristics of these bursts closely
resemble the bursts seen from 1E 1048.1-5937 and a subset of the bursts
detected from 1E 2259+586, thus establishing XTE J1810-197 as a magnetar
candidate. The bursts detected from these three objects are sufficiently
similar to one another, yet significantly different from those seen from soft
gamma repeaters, that they likely represent a new class of bursts from magnetar
candidates exclusive (thus far) to the anomalous X-ray pulsar-like sources.


title: Lyot Coronagraphy on Giant Segmented-Mirror Telescopes

abstract:
  We present a study of Lyot style (i.e., classical, band-limited, and Gaussian
occulter) coronagraphy on extremely large, highly-segmented telescopes. We show
that while increased telescope diameter is always an advantage for high dynamic
range science (assuming wavefront errors have been corrected sufficiently
well), segmentation itself sets a limit on the performance of Lyot
coronagraphs. Diffraction from inter-segment gaps sets a floor to the
achievable extinction of on-axis starlight with Lyot coronagraphy. We derive an
analytical expression for the manner in which coronagraphic suppression of an
on-axis source decreases with increasing gap size when the segments are placed
in a spatially periodic array over the telescope aperture, regardless of the
details of the arrangement. A simple Lyot stop masking out pupil edges produces
good extinction of the central peak in the point-spread function (PSF), but
leaves satellite images caused by inter-segment gaps essentially unaffected.
Masking out the bright segment gaps in the Lyot plane with a reticulated mask
reduces the satellite images'intensity to a contrast of 5x10^{-9} on a 30 m
telescope with 10 mm gaps, at the expense of an increase in the brightness of
the central peak. The morphology of interesting targets will dictate which Lyot
stop geometry is preferable: the reticulated Lyot stop produces a conveniently
uni-modal PSF, whereas a simple Lyot stop produces an extended array of
satellite spots. A cryogenic reticulate Lyot stop will also benefit both direct
and coronagraphic mid-IR imaging.


title: Covariant Kinetic Theory with an Application to the Coma Cluster

abstract:
  In this paper, we introduce a novel solution to the covariant Landau equation
for a pure electron plasma. The method conserves energy and particle number,
and reduces smoothly to the Rosenbluth potentials of non-relativistic theory.
In addition, we find that a fully relativistic plasma equilibrates in only
1/100th of a Spitzer time--much faster than in the non-relativistic limit--a
factor of significant import to situations in which distortions to a Maxwellian
distribution are produced by anomalous methods of acceleration. To demonstrate
the power of our solution in dealing with hot, astrophysical plasmas, we use
this technique to show that one of the currently considered models--continuous
stochastic acceleration--for the hard X-ray emission in the Coma cluster
actually cannot work because the energy gained by the particles is distributed
to the {\it whole} plasma on a time scale much shorter than that of the
acceleration process itself.


title:
The SAURON project - IV. The mass-to-light ratio, the virial mass
  estimator and the fundamental plane of elliptical and lenticular galaxies

abstract:
  We investigate with unprecedented accuracy the correlations between the
dynamical mass-to-light ratio M/L and other global observables of E and S0
galaxies. We construct two-integral Jeans and three-integral Schwarzschild
dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field
stellar kinematics. We find a tight correlation of the form
(M/L)=(3.80+/-0.14)*(sigma/200 km/s)^(0.84+/-0.07) between the dynamical M/L
(in the I-band) and the luminosity-weighted second moment (sigma) of the
line-of-sight velocity-distribution within Re. The observed rms scatter in M/L
for our sample is 18%, while the inferred intrinsic scatter is ~13%. The
(M/L)-sigma relation can be included in the remarkable series of tight
correlations between sigma and other galaxy global observables. The comparison
of the observed correlations with the predictions of the Fundamental Plane
(FP), and with simple virial estimates, shows that the `tilt' of the FP of
early-type galaxies, is due to a real M/L variation, while structural and
orbital non-homology have a negligible effect. The virial mass is a reliable
estimator of the mass in the central regions of galaxies. The best-fitting
virial relation has the form (M/L)_vir=(5.0+/-0.1)*Re*sigma^2/(L*G). The
comparison of the dynamical M/L with the (M/L)_pop inferred from the analysis
of the stellar population, indicates a median dark matter fraction in
early-type galaxies of ~30% of the total mass inside one Re. (Abridged)


title:
Constraining the Spectrum of Supernova Neutrinos from
  Neutrino-Process-Induced Light-Element Synthesis

abstract:
  We constrain energy spectra of supernova neutrinos through the avoidance of
an overproduction of the 11B abundance during Galactic chemical evolution. In
supernova nucleosynthesis calculations with a parametrized neutrino spectrum as
a function of temperature of mu- and tau-neutrinos and their antiparticles and
total neutrino energy, we find a strong neutrino temperature dependence of 11B
yield. When the yield is combined with observed abundances, the acceptable
range of the temperature of mu- and tau-neutrinos and their antiparticles is
found to be 4.8 and 6.6 MeV. Non-zero chemical potentials would reduce this
temperature range by about 10% for a degeneracy parameter smaller than 3.


title: GRB Progenitors and Environment

abstract:
  The study and knowledge of the environment of Gamma-Ray Bursts is of great
interest from many points of view. For high redshift (z>0.5) events, the
structure of the ambient medium is one of the best indicators of the nature and
properties of the progenitor. It also tells us about the last stages of the
pre-explosion evolution of the progenitor. In addition, it is interesting in
its own as a sample of the interstellar medium in a high redshift galaxy.
Measures of the density and structure of the GRB environment are however
sparse, and different methods yield different, often incompatible, results. I
will review the methods and results with particular emphasis on the case of GRB
021004, a puzzling but highly informative event. I will finally underline the
advancements that will be possible in the Swift era.