title: Cosmological Magnetic Fields and CMBR Polarization

abstract:
  A simple introduction to physics of CMBR polarization and the Faraday
rotation of the latter in cosmic magnetic field is presented. The content of
the lecture is the following: 1. Description of polarization of photons. 2.
Polarization field of CMBR. 3. Faraday effect. 4. Cosmic magnetic fields. 5.
Faraday rotation of CMBR polarization.


title: A Detailed Spectroscopic and Photometric Analysis of DQ White Dwarfs

abstract:
  We present an analysis of spectroscopic and photometric observations of cool
DQ white dwarfs based on improved model atmosphere calculations. In particular,
we revise the atmospheric parameters of the trigonometric parallax sample of
Bergeron, Leggett, & Ruiz, and discuss the astrophysical implications on the
temperature scale and mean mass, as well as the chemical evolution of these
stars. We also analyze 40 new DQ stars discovered in the first data release of
the Sloan Digital Sky Survey. Our analysis confirms that effective temperatures
derived from model atmospheres including carbon are significantly lower than
the temperatures obtained from pure helium models. Similarly the mean mass of
the trigonometric parallax sample, <M> = 0.62 Mo, is significantly lower than
that obtained from pure helium models, <M> = 0.73 Mo, and more consistent with
the spectroscopic mean mass of DB stars, <M> = 0.59 Mo, the most likely
progenitors of DQ white dwarfs. We find that DQ stars form a remarkably well
defined sequence in a carbon abundance versus effective temperature diagram;
below Teff~10,000 K, carbon pollution decreases monotonically with decreasing
effective temperature. Improved evolutionary models including diffusion and
connecting to the PG 1159 phase are used to infer a typical value for the
thickness of the helium layer M_He/M_* between 10^{-3} and 10^{-2}, compatible
with the predictions of post-AGB models.


title: Simulations of Stellar Collisions Involving Pre-Main Sequence Stars

abstract:
  In this paper, we present the results of smoothed particle hydrodynamic (SPH)
simulations of collisions between pre-main sequence stars and a variety of
other kinds of stars. Simulations over a range of impact parameters and
velocities were performed. We find that pre-main sequence stars tend to ``wrap
themselves'' around their impactor. We discuss the probable evolutionary state
of products of collisions between pre-main sequence stars and pre-main
sequence, main sequence, giant branch, and compact stars. The nature of the
collision product does not depend strongly on the impact parameter or the
velocity of the collision.


title: Radiation transport in diffractive media

abstract:
  We consider radiation transport theory applied to non-dispersive but
refractive media. This setting is used to discuss Minkowski's and Abraham's
electromagnetic momentum, and to derive conservation equations independent of
the choice of momentum definition. Using general relativistic kinetic theory,
we derive and discuss a radiation gas energy-momentum conservation equation
valid in arbitrary curved spacetime with diffractive media.


title: Galaxy Cluster Assembly at z=0.37

abstract:
  We present X-ray and spectroscopic confirmation of a cluster assembling from
multiple, distinct galaxy groups at z=0.371. Initially detected in the Las
Campanas Distant Cluster Survey, the structure contains at least four X-ray
detected groups that lie within a maximum projected separation of 4 Mpc and
within dv=550 km/s of one another. Using Chandra imaging and wide-field optical
spectroscopy, we show that the individual groups lie on the local sigma-T
relation, and derive a total mass of M>=5e14 solar masses for the entire
structure. We demonstrate that the groups are gravitationally bound to one
another and will merge into a single cluster with >=1/3 the mass of Coma. We
also find that although the cluster is in the process of forming, the
individual groups already have a higher fraction of passive members than the
field. This result indicates that galaxy evolution on group scales is key to
developing the early-type galaxies that dominate the cluster population by z~0.


title: Identifying Lenses with Small-Scale Structure. II. Fold Lenses

abstract:
  When the source in a 4-image gravitational lens lies close to a "fold"
caustic, two of the lensed images lie close together. If the lens potential is
smooth on the scale of the separation between the two close images, then the
difference between their fluxes should approximately vanish, Rfold =
(F1-F2)/(F1+F2) \approx 0. Violations of this "fold relation" in observed
lenses are thought to indicate the presence of structure on scales smaller than
the separation between the close images. We study the fold relation and find it
to be more subtle and rich than was previously realized. The degree to which
Rfold can differ from zero for realistic smooth lenses depends not only on the
distance of the source from the caustic, but also on its location along the
caustic, and on the angular structure of the lens potential. Thus, it is
impossible to say from Rfold alone whether observed flux ratios are anomalous
or not. Instead, we must consider the full distribution of Rfold values that
can be obtained from smooth potentials that reproduce the separation between
the two close images and the distance to the next nearest image. We analyze the
generic and specific features of this distribution, and then show that 5 of the
12 known lenses with fold configurations have flux ratio anomalies: B0712+472,
SDSS 0924+0219, PG 1115+080, B1555+375, and B1933+503. Combining this with our
previous analysis revealing anomalies in 3 of the 4 known lenses with cusp
configurations, we conclude that at least half (8/16) of all 4-image lenses
that admit generic, local analyses exhibit flux ratio anomalies indicative of
small-scale structure. The fold and cusp relations do not reveal the nature of
the implied small-scale structure, but do provide the formal foundation for
substructure studies. [Abridged]


title: Rapid Growth of Black Holes in Massive Star-Forming Galaxies

abstract:
  The tight relationship between the masses of black holes and galaxy spheroids
in nearby galaxies implies a causal connection between the growth of these two
components. Optically luminous quasars host the most prodigious accreting black
holes in the Universe and can account for >30% of the total cosmological
black-hole growth. As typical quasars are not, however, undergoing intense star
formation and already host massive black holes [>10^(8) M(Sun)], there must
have been an earlier pre-quasar phase when these black holes grew [mass range
  ~10^(6)-10^(8) M(Sun)]. The likely signature of this earlier stage is
simultaneous black-hole growth and star formation in distant (i.e., z>1; >8
billion light years away) luminous galaxies. Here we report ultra-deep X-ray
observations of distant star-forming galaxies that are bright at submillimetre
wavelengths. We find that the black holes in these galaxies are growing almost
continuously throughout periods of intense star formation. This activity
appears to be more tightly associated with these galaxies than any other coeval
galaxy populations. We show that the black-hole growth from these galaxies is
consistent with that expected for the pre-quasar phase.


title: Distant red galaxies in the Hubble Ultra Deep Field

abstract:
  We take advantage of the Hubble Ultra Deep Field (UDF) data to study the
restframe optical and ultra violet (UV) morphologies of the novel population of
Distant Red Galaxies (DRGs). Six galaxies with J-Ks > 2.3 are found to Ks=21.5,
five of which have photometric redshifts z_phot > 2, corresponding to a surface
density of 0.9/arcmin^2. The surface brightness distributions of the z_phot > 2
galaxies are better represented by exponential disks than R^{1/4}-laws. Two of
the z_phot > 2 galaxies are extended, while three have compact morphologies.
The restframe optical morphology of the z_phot > 2 galaxies is quite different
from the restframe UV morphology: all the galaxies have red central components
which dominate in the NICMOS H_{160}-band images, and distinct off-center blue
features which show up in (and often dominate) the ACS images. The mean
measured effective radius of the z_phot > 2 galaxies is <r_e> =1.9+/-1.4 kpc,
similar (within the errors) to the mean size of LBGs at similar redshifts. All
the DRGs are resolved in the ACS images, while four are resolved in the NICMOS
images. Two of the z_phot > 2 galaxies are bright X-ray sources and hence host
AGN. The diverse restframe optical and UV morphological properties of DRGs
derived here suggest that they have complex stellar populations, consisting of
both evolved populations that dominate the mass and the restframe optical
light, and younger populations, which show up as patches of star formation in
the restframe UV light; in many ways resembling the properties of normal local
galaxies. This interpretation is supported by fits to the broadband SEDs, which
for all five z_phot > 2 are best represented by models with extended star
formation histories and substantial amounts of dust.


title:
The evolution of the cluster X-ray scaling relations in the WARPS sample
  at 0.6<z<1.0

abstract:
  The X-ray properties of a sample of 11 high-redshift (0.6<z<1.0) clusters
observed with Chandra and/or XMM are used to investigate the evolution of the
cluster scaling relations. The observed evolution of the L-T and M-L relations
is consistent with simple self-similar predictions, in which the properties of
clusters reflect the properties of the universe at their redshift of
observation. When the systematic effect of assuming isothermality on the
derived masses of the high-redshift clusters is taken into account, the
high-redshift M-T and Mgas-T relations are also consistent with self-similar
evolution. Under the assumption that the model of self-similar evolution is
correct and that the local systems formed via a single spherical collapse, the
high-redshift L-T relation is consistent with the high-z clusters having formed
at a significantly higher redshift than the local systems. The data are also
consistent with the more realistic scenario of clusters forming via the
continuous accretion of material. The slope of the L-T relation at
high-redshift (B=3.29+/-0.38) is consistent with the local relation, and
significantly steeper then the self-similar prediction of B=2. This suggests
that the non-gravitational processes causing the steepening occurred at z>1 or
in the early stages of the clusters' formation, prior to their observation. The
properties of the intra-cluster medium at high-redshift are found to be similar
to those in the local universe. The mean surface-brightness profile slope for
the sample is 0.66+/-0.05, the mean gas mass fractions within R2500 and R200
are 0.073+/-0.010 and 0.12+/-0.02 respectively, and the mean metallicity of the
sample is 0.28+/-0.16 solar.


title: Evolutionary Signatures in the Formation of Low-Mass Protostars

abstract:
  We present an evolutionary picture of a forming star. We assume a singular,
isothermal sphere as the initial state of the core that undergoes collapse as
described by \citet{shu77}. We include the evolution of a first hydrostatic
core at early times and allow a disk to grow as predicted by \citet{adams86}.
We use a 1-dimensional radiative transfer code to calculate the spectral energy
distribution for the evolving protostar from the beginning of collapse to the
point when all envelope material has accreted onto the star+disk system. Then,
we calculate various observational signatures ($T_{bol}$, $L_{bol}/L_{smm}$,
and infrared colors) as a function of time.
  As defined by the bolometric temperature criterion, the Class 0 stage should
be very short, while the Class I stage persists for much of the protostar's
early life. We present physical distinctions among the classes of forming stars
and calculate the observational signatures for these classes. Finally, we
present models of infrared color-magnitude diagrams, as observed by the Spitzer
Space Telescope, that should be strong discriminators in determining the stage
of evolution for a protostar.


title: Detection of Thermal Emission from an Extrasolar Planet

abstract:
  We present Spitzer Space Telescope infrared photometric time series of the
transiting extrasolar planet system TrES-1. The data span a predicted time of
secondary eclipse, corresponding to the passage of the planet behind the star.
In both bands of our observations, we detect a flux decrement with a timing,
amplitude, and duration as predicted by published parameters of the system.
This signal represents the first direct detection of (i.e. the observation of
photons emitted by) a planet orbiting another star. The observed eclipse depths
(in units of relative flux) are 0.00066 +/- 0.00013 at 4.5um and 0.00225 +/-
0.00036 at 8.0um. These estimates provide the first observational constraints
on models of the thermal emission of hot Jupiters. Assuming that the planet
emits as a blackbody, we estimate an effective temperature of T_p=1060 +/- 50
K. Under the additional assumptions that the planet is in thermal equilibrium
with the radiation from the star and emits isotropically, we find a Bond albedo
of A = 0.31 +/- 0.14. This would imply that the planet absorbs the majority of
stellar radiation incident upon it, a conclusion of significant impact to
atmospheric models of these objects. We compare our data to a
previously-published model of the planetary thermal emission, which predicts
prominent spectral features in our observational bands due to water and carbon
monoxide. Based on the time of secondary eclipse, we present an upper limit on
the orbital eccentricity that is sufficiently small that we conclude that tidal
dissipation is unlikely to provide a significant source of energy interior to
the planet.(abridged)


title: Extracting New Physics from the CMB

abstract:
  We review how initial state effects generically yield an oscillatory
component in the primordial power spectrum of inflationary density
perturbations. These oscillatory corrections parametrize unknown new physics at
a scale $M$ and are potentially observable if the ratio $H_{infl}/M$ is
sufficiently large. We clarify to what extent present and future CMB data
analysis can distinguish between the different proposals for initial state
corrections.


title: B335: A Laboratory for Astrochemistry in a Collapsing Cloud

abstract:
  We present observations of 25 transitions of 17 isotopologues of 9 molecules
toward B335. With a goal of constraining chemical models of collapsing clouds,
we compare our observations, along with data from the literature, to models of
chemical abundances. The observed lines are simulated with a Monte Carlo code,
which uses various physical models of density and velocity as a function of
radius. The dust temperature as a function of radius is calculated
self-consistently by a radiative transfer code. The gas temperature is then
calculated at each radius, including gas-dust collisions, cosmic rays,
photoelectric heating, and molecular cooling. The results provide the input to
the Monte Carlo code. We consider both {\it ad hoc} step function models for
chemical abundances and abundances taken from a self-consistent modeling of the
evolution of a star-forming core. The step function models can match the
observed lines reasonably well, but they require very unlikely combinations of
radial variations in chemical abundances. Among the self-consistent chemical
models, the observed lines are matched best by models with somewhat enhanced
cosmic-ray ionization rates and sulfur abundances. We discuss briefly the steps
needed to close the loop on the modeling of dust and gas, including off-center
spectra of molecular lines.


title:
Effects of Gravitational Microlensing on P-Cygni Profiles of Type Ia
  Supernovae

abstract:
  A brief description of the deformed spectra of microlensed SNe Ia is
presented. We show that microlensing amplification can have significant effects
on line profiles. The resonance-scattering code SYNOW is used to compute the
intensity profile in the rest frame of the supernova. The observed
(microlensed) spectral lines are predicted assuming a simple stellar-size
deflector, and are compared to unlensed cases to show the effects microlensing
by solar-size deflectors can have on spectral lines. We limit our work to
spherically symmetric deflectors.


title:
Effects of Pulsar Rotation on Timing Measurements of the Double Pulsar
  System J0737-3039

abstract:
  We study the effect of pulsar rotation on timing of binary pulsars, with
particular emphasis on the double pulsar system J0737-3039. Special
relativistic aberration due to the orbital motion of pulsar changes both the
longitude and colatitude of the emission direction with respect to the pulsar
spin axis. The former gives rise to a shift of the arrival time of the pulse
centroid (this is the conventional ``longitudinal'' aberration delay), the
latter results in a distortion (contraction or dilation) of the pulse profile
on the orbital timescale. The amplitude of pulse distortion depends inversely
on the variation of polarization position angle across the pulse. For small
angle between the pulsar magnetic and spin axes, as inferred for PSR
J0737-3039A from polarimetric observations, the pulse distortion is significant
(\sim 1%) and the associated ``latitudinal'' aberration delay is much larger
than the longitudinal one. By monitoring the arrival time of separate pulse
components as a function of pulsar orbital phase, the latitudinal aberration
delay may be easily measured with the current timing precision, thus
constraining the spin geometry of the system. The latitudinal delay can also be
detected by monitoring system's orbital parameters on the geodetic precession
timescale. Because of the near edge-on orbital orientation of the PSR
J0737-3039 system, general relativistic bending of pulsar A's radio beam near
its superior conjunction also introduces spin-dependent time delays of similar
order of magnitude as the aberration delays. In addition, light bending splits
the pulse profile into two variable components, corresponding to two
gravitationally lensed images of the source. Detection of lensing effects is
challenging, but may be possible with existing technology.


title: Sulphur chemistry and molecular shocks: the case of NGC1333-IRAS2

abstract:
  We present SO and SO2 observations in the region of the low mass protostar
IRAS2/NGC1333. The East-West outflow originating from this source has been
mapped in four transitions of both SO and SO2. In addition, CS observations
published in the literature have been used. We compute the SO, SO2 and CS
column densities and the physical conditions at several positions of the
outflow using LTE and a non-LTE LVG approximations. The SO2/SO and CS/SO
abundance ratios are compared with the theoretical predictions of a chemical
model adapted to the physical conditions in the IRAS2 outflow. The SO2/SO
abundance ratios are constant in the two lobes of the outflow whereas CS/SO is
up to 6 times lower in the shocked gas of the East lobe than in the West one.
The comparison with the chemical model allows us to constrain the age of the
outflow produced by IRAS2 to >5e3yr. We find low densities and temperatures for
the outflow of IRAS2 (< 1e6 cm-3 and >70 K) from SO and SO2 emission probably
because the two molecules trace the cooled entrained material. The East lobe of
the outflow shows denser gas compared to the West lobe. We also discuss some
constraints on the depleted form of sulphur.


title:
Comment on the paper "Diffusive Synchrotron Radiation from Relativistic
  Shocks of Gamma-Ray Burst Sources" by G. D. Fleishman

abstract:
  We strongly disagree with the criticism by G. Fleishman, which has been
published on the astro-ph arXiv (astro-ph/0502245), of our paper on jitter
radiation from GRB shocks (Medvedev 2000, ApJ, 540, 704). In this note, we
present the rebuttal of all critical points raised, demonstrating that our
original paper (i) contains no errors, and (ii) correctly describes prompt GRB
emission spectra.


title:
The Physical Properties and Effective Temperature Scale of O-type Stars
  as a Function of Metallicity. II. Analysis of 20 More Magellanic Cloud Stars,
  and Results from the Complete Sample

abstract:
  We analyze the optical and UV spectra of an additional sample of 20
Magellanic Cloud O stars, and draw conclusions from the complete sample of 40
stars. We find (1) The SMC O3-7 dwarfs are about 4000 K cooler than their
Galactic counterparts; this is in the sense expected from the decreased
signficiance of line-blanketing and wind-blanketing at lower metallicities. The
difference decreases with later types, becoming negligible by B0 V. A similar
difference is found for the supergiants. (2) The wind momentum of these stars
scales with luminosity and metallicty in the ways predicted by
radiatively-driven wind theory. (3) A comparison of the masses derived from
spectroscopy with those derived from stellar evolutionary theory shows a
significant discrepancy for stars hotter than 45000, although good agreement is
found for cooler stars. (4) For the hottest O stars (O2-3.5) neither the
NIII/NIV ratio, nor even the HeI/HeII ratio, does a good job of predicting the
effective temperature by itself. Instead, a full analysis is needed to derive
physical parameters. Thus there are O3.5V stars which are as hot or hotter than
stars classified as O2V. (5) The two stars with the most discordant radial
velocities in our sample happen to be O3 "field stars". This provides the first
compelling observational evidence that the "field" O stars in the Magellanic
Clouds may be runaway OB stars, ejected from their birth place.


title:
Multiwavelength Observations and State Transitions of an Ultra-luminous
  Supersoft X-ray Source: Evidence for an Intermediate-Mass Black Hole

abstract:
  We report the results of Chandra and XMM-Newton observations of an
ultra-luminous supersoft X-ray source in M101. M101 ULX-1 underwent 2 outbursts
in 2004 during which the peak bolometric luminosities reached 1e41 erg/s. The
outburst spectra were very soft and can generally be fitted with a blackbody
model with temperatures of 50-160 eV. In two of the observations, absorption
edges at 0.33 keV, 0.56 keV, 0.66 keV, and 0.88 keV were found. A cool
accretion disk was also found in the 2004 December outburst. During the low
luminosity state, a power-law tail was seen up to 7 keV. It is clear the source
changed from a low/hard state to a high/soft state. In addition, it showed at
least 5 outbursts between 1996 and 2004. This is the first ultra-luminous X-ray
source for which recurrent outbursts with state transitions similar to Galactic
X-ray binaries have been observed. From the Hubble Space Telescope data, we
found an optical counterpart to the source. During the 2004 outbursts, we also
performed radio and ground-based optical observations. All the results strongly
suggest that the accreting object is a > 2800 solar mass black hole.


title: The Differential Lifetimes of Protostellar Gas and Dust Disks

abstract:
  We construct a protostellar disk model that takes into account the combined
effect of viscous evolution, photoevaporation and the differential radial
motion of dust grains and gas. For T Tauri disks, the lifetimes of dust disks
that are mainly composed of millimeter sized grains are always shorter than the
gas disks' lifetimes, and become similar only when the grains are fluffy
(density < 0.1 g cm^{-3}). If grain growth during the classical T Tauri phase
produces plenty of millimeter sized grains, such grains completely accrete onto
the star in 10^7 yr, before photoevaporation begins to drain the inner gas disk
and the star evolves to the weak line T Tauri phase. In the weak line phase,
only dust-poor gas disks remain at large radii (> 10 AU), without strong signs
of gas accretion nor of millimeter thermal emission from the dust. For Herbig
AeBe stars, the strong photoevaporation clears the inner disks in 10^6 yr,
before the dust grains in the outer disk migrate to the inner region. In this
case, the grains left behind in the outer gas disk accumulate at the disk inner
edge (at 10-100 AU from the star). The dust grains remain there even after the
entire gas disk has been photoevaporated, and form a gas-poor dust ring similar
to that observed around HR 4796A. Hence, depending on the strength of the
stellar ionizing flux, our model predicts opposite types of products around
young stars. For low mass stars with a low photoevaporation rate, dust-poor gas
disks with an inner hole would form, whereas for high mass stars with a high
photoevaporation rate, gas-poor dust rings would form. This prediction should
be examined by observations of gas and dust around weak line T Tauri stars and
evolved Herbig AeBe stars.


title: Brane World Cosmology, the CMB and the Radion

abstract:
  Recent developments in the theory of extra dimensions have opened up avenues
to confront such theories with cosmological tests. We discuss a brane-world
model with a bulk scalar field, motivated by supergravity. The low-energy
effective action is derived and physical constraints on the parameters of the
model discussed. The cosmological evolution of the brane-world moduli is
investigated and it is shown that one of the moduli is a quintessence field.
The CMB predictions are computed. Finally, the possibility that the radion
field in brane-worlds could be a chameleon field is investigated.


title:
New photometric and spectroscopic observations of the Seyfert galaxy Mrk
  315

abstract:
  We present new important results about the intermediate-type Seyfert galaxy
Mrk 315, recently observed through optical imaging and integral-field
spectroscopy. Broad-band images were used to study the morphology of the host
galaxy, narrow-band H-alpha images to trace the star forming regions, and
middle-band [O III] images to evidence the distribution of the highly ionised
gas. Some extended emission regions were isolated and their physical properties
studied by means of flux calibrated spectra. High resolution spectroscopy was
used to separate different kinematic components in the velocity fields of gas
and stars. Some peculiar features characterise this apparently undisturbed and
moderately isolated active galaxy. Such features, already investigated by other
authors, are re-analysed and discussed in the light of these new observations.
The most relevant results we obtained are: the multi-tiers structure of the
disc; the presence of a quasi-ring of regions with star formation much higher
than previous claims; a secondary nucleus confirmed by a stellar component
kinematically decoupled by the main galaxy; a new hypothesis about the
controversial nature of the long filament, initially described as hook-shaped,
and more likely made of two independent filaments caused by interaction events
between the main galaxy and two dwarf companions.


title: HST and spectroscopic observations of the L1551 IRS5 jets (HH154)

abstract:
  We have carried out a thorough optical study of the closest star formation
jet. The inner arcminute surrounding the class 0/I binary protostar L1551 IRS5
and its associated jet (HH154) have been observed using the Hubble Space
Telescope with the WFPC2 camera, the ESO New Technology Telescope with the EMMI
spectrograph and the Nordic Optical Telescope with the ALFOSC spectrograph.
This data set is compared to earlier ground based imaging with the aim to study
the evolution of this particular jet, and its possible interaction with the
molecular material in the bipolar molecular outflow associated with this
source. The velocity field of the jet is mapped out. The highest velocities are
found in the vicinity of the recently discovered X-ray source emanating from a
shock in this jet. The energy radiated by the X-ray source is compatible with
these velocities. The \halpha and \hbeta emission from the jet is used to
determine the extinction, which is found to increase inwards in the jet towards
the protostar. The extinction towards the X-ray source is consistent with the
one determined from the X-ray spectrum.


title: X-ray Confirmation of the Intermediate Polar HT Cam

abstract:
  We report on the first pointed X-ray observations with XMM-Newton and RXTE
satellites of the X-ray source RXJ0757.0+6306=HT Cam. We detect a strong 515s
X-ray modulation confirming the optical photometric period found in 1998, which
definitively assigns this source to the intermediate polar class of magnetic
cataclysmic variables. The lack of orbital sidebands in the X-rays indicates
that the X-ray period is the spin period of the accreting white dwarf.
Simultaneous ultraviolet and optical B-band photometry acquired with the
XMM-Newton Optical Monitor and coordinated optical UBVRI photometric data
acquired at the Nordic Optical Telescope (La Palma) show that the optical pulse
is in phase with the X-rays and hence originates in the magnetically confined
accretion flow. The lack of ultraviolet spin modulation suggests that
accretion-induced heating on the white dwarf surface is not important in this
source. Spectral analyses of XMM-Newton EPIC and RGS spectra show that HT Cam
has a multi-temperature spectrum and, contrary to most intermediate polars, it
does not suffer from strong absorption. With its 86min orbital period, HT Cam
is then the third confirmed system of this class below the 2-3hr period gap
accreting at a low rate.


title:
An XMM-Newton observation of the multiple system HD167971 (O5-8V + O5-8V
  + (O8I)) and the young open cluster NGC6604

abstract:
  We discuss the results of two XMM-Newton observations of the open cluster
NGC6604 obtained in April and September 2002. We concentrate mainly on the
multiple system HD167971 (O5-8V + O5-8V + (O8I)). The soft part of the EPIC
spectrum of this system is thermal with typical temperatures of about 2 10^6 to
9 10^6 K. The nature (thermal vs non-thermal) of the hard part of the spectrum
is not unambiguously revealed by our data. If the emission is thermal, the high
temperature of the plasma (~ 2.3 10^7 to 4.6 10^7 K) would be typical of what
should be expected from a wind-wind interaction zone within a long period
binary system. This emission could arise from an interaction between the
combined winds of the O5-8V + O5-8V close binary system and that of the more
distant O8I companion. Assuming instead that the hard part of the spectrum is
non-thermal, the photon index would be rather steep (~3). Moreover, a marginal
variability between our two XMM-Newton pointings could be attributed to an
eclipse of the O5-8V + O5-8V system. The overall X-ray luminosity points to a
significant X-ray luminosity excess of about a factor 4 possibly due to
colliding winds. Considering HD167971 along with several recent X-ray and radio
observations, we propose that the simultaneous observation of non-thermal
radiation in the X-ray (below 10.0 keV) and radio domains appears rather
unlikely. Our investigation of our XMM-Newton data of NGC6604 reveals a rather
sparse distribution of X-ray emitters. Including the two bright non-thermal
radio emitters HD168112 and HD167971, we present a list of 31 X-ray sources...
(see paper for full abstract)


title:
Measurement of the Shadowing of High-Energy Cosmic Rays by the Moon: A
  Search for TeV-Energy Antiprotons

abstract:
  The shadowing of high-energy cosmic rays by the Moon has been observed with a
significance of 9.4 standard deviations with the L3+C muon spectrometer at
CERN. A significant effect of the Earth magnetic field is observed. Since no
event deficit on the east side of the Moon has been observed, an upper limit at
90% confidence level on the antiproton to proton ratio of 0.11 is obtained for
primary energies around 1 TeV.


title: Braneworld black holes in cosmology and astrophysics

abstract:
  The braneworld description of our universe entails a large extra dimension
and a fundamental scale of gravity that might be lower by several orders of
magnitude compared to the Planck scale. An interesting consequence of the
braneworld scenario is in the nature of spherically symmetric vacuum solutions
to the brane gravitational field equations which could represent black holes
with properties quite distinct compared to ordinary black holes in
4-dimensions. We discuss certain key features of some braneworld black hole
geometries. Such black holes are likely to have diverse cosmological and
astrophysical ramifications. The cosmological evolution of primordial
braneworld black holes is described highlighting their longevity due to
modified evaporation and effective accretion of radiation during the early
braneworld high energy era. Observational abundance of various evaporation
products of the black holes at different eras impose constraints on their
initial mass fraction. Surviving primordial black holes could be candidates of
dark matter present in galactic haloes. We discuss gravitational lensing by
braneworld black holes. Observables related to the relativistic images of
strong field gravitational lensing could in principle be used to distinguish
between different braneworld black hole metrics in future observations.


title: Spiral density wave generation by vortices in Keplerian flows

abstract:
  We perform a detailed analytical and numerical study of the dynamics of
perturbations (vortex/aperiodic mode, Rossby and spiral-density waves) in 2D
compressible disks with a Keplerian law of rotation. We draw attention to the
process of spiral-density wave generation from vortices, discussing, in
particular, the initial, most peculiar stages of wave emission. We show that
the linear phenomenon of wave generation by vortices in smooth (without
inflection points) shear flows found by using the so-called non-modal approach,
is directly applicable to the present case. After an analytical non-modal
description of the physics and characteristics of the spiral-density wave
generation/propagation in the local shearing-sheet model, we follow the process
of wave generation by small amplitude coherent circular vortex structures, by
direct global numerical simulation, describing the main features of the
generated waves.


title:
Black hole physics and astrophysics: The GRB-Supernova connection and
  URCA-1 - URCA-2

abstract:
  We outline the confluence of three novel theoretical fields in our modeling
of Gamma-Ray Bursts (GRBs): 1) the ultrarelativistic regime of a shock front
expanding with a Lorentz gamma factor $\sim 300$; 2) the quantum vacuum
polarization process leading to an electron-positron plasma originating the
shock front; and 3) the general relativistic process of energy extraction from
a black hole originating the vacuum polarization process. There are two
different classes of GRBs: the long GRBs and the short GRBs. We here address
the issue of the long GRBs. [...] We are specially interested, in this report,
to a subclass of long GRBs which appear to be accompanied by a supernova
explosion. We are considering two specific examples: GRB980425/SN1998bw and
GRB030329/SN2003dh [...].


title:
The Blackholic energy: long and short Gamma-Ray Bursts (New perspectives
  in physics and astrophysics from the theoretical understanding of Gamma-Ray
  Bursts, II)

abstract:
  [...] We turn then to the theoretical developments in the short GRBs: we
first report some progress in the understanding the dynamical phase of
collapse, the mass-energy formula and the extraction of blackholic energy which
have been motivated by the analysis of the short GRBs. In this context progress
has also been accomplished on establishing an absolute lower limit to the
irreducible mass of the black hole as well as on some critical considerations
about the relations of general relativity and the second law of thermodynamics.
We recall how this last issue has been one of the most debated in theoretical
physics in the past thirty years due to the work of Bekenstein and Hawking.
Following these conceptual progresses we analyze the vacuum polarization
process around an overcritical collapsing shell. We evidence the existence of a
separatrix and a dyadosphere trapping surface in the dynamics of the
electron-positron plasma generated during the process of gravitational
collapse. We then analyze, using recent progress in the solution of the
Vlasov-Boltzmann-Maxwell system, the oscillation regime in the created
electron-positron plasma and their rapid convergence to a thermalized spectrum.
We conclude by making precise predictions for the spectra, the energy fluxes
and characteristic time-scales of the radiation for short-bursts. If the
precise luminosity variation and spectral hardening of the radiation we have
predicted will be confirmed by observations of short-bursts, these systems will
play a major role as standard candles in cosmology. These considerations will
also be relevant for the analysis of the long-bursts when the baryonic matter
contribution will be taken into account.


title: High mass X-ray binaries in the SMC: the luminosity function

abstract:
  We study population of compact X-ray sources in the Small Magellanic Cloud
using the archival data of XMM-Newton observatory. The total area of the survey
is ~1.5 square degrees with the limiting sensitivity of ~10^{-14} erg/s/cm^2,
corresponding to the luminosity of ~4.3\cdot 10^{33} erg/s at the SMC distance.
Out of ~150 point sources detected in the 2--8 keV energy band, ~3/4 are
background CXB sources, observed through the SMC. Based on the properties of
the optical and near-infrared counterparts of the detected sources we
identified likely HMXB candidates, and sources, whose nature is uncertain,
thus, providing a lower and upper limits on the luminosity distribution of
HMXBs in the observed part of the SMC.
  The observed number of HMXBs is consistent with the prediction based on SFR
estimates derived from the supernovae frequency and analysis of color-magnitude
diagrams of the stellar population. If, on the contrary, the true value of the
SFR is better represented by FIR, H_alpha and UV based estimators, then the
abundance of HMXBs in the SMC may significantly (by a factor of as much as ~10)
exceed the value derived for the Milky Way and other nearby galaxies.
  The shape of the observed distribution at the bright end is consistent with
the universal HMXB XLF. At the faint end, L_X>2* 10^{34} erg/sec, the upper
limit on the luminosity function is consistent with while the lower limit is
significantly flatter than the L^{-0.6} power law.


title:
Asymptotic behavior of Cardassian cosmologies with exponential
  potentials

abstract:
  In this paper we analyze the asymptotic behavior of Cardassian cosmological
models filled with a perfect fluid and a scalar field with an exponential
potential. Cardassian cosmologies arise from modifications of the Friedmann
equation, and among the different proposals within that framework we will
choose those of the form $3H^2-\rho\propto \rho^n$ with $n<1$. We construct two
three dimensional dynamical systems arising from the evolution equations,
respectively adapted for studying the high and low energy limits. Using
standard dynamical systems techniques we find the fixed points and characterize
the solutions they represent. We pay especial attention to the properties
inherent to the modifications and compare with the (standard) unmodified
scenario. Among other interesting results, we find there are no late-time
tracking attractors.


title: Weak lensing analysis in three dimensions

abstract:
  We present a comprehensive full-sky 3-dimensional analysis of the
weak-lensing fields and their corresponding power spectra. Using the formalism
of spin-weight spherical harmonics and spherical Bessel functions, we relate
the two-point statistics of the harmonic expansion coefficients of the weak
lensing shear and convergence to the power spectrum of the matter density
perturbations, and derive small-angle limits. Such a study is relevant in view
of the next generation of large-scale weak lensing surveys which will provide
distance information about the sources through photometric redshifts. This
opens up the possibility of accurate cosmological parameter estimation via weak
lensing, with an emphasis on the equation of state of dark energy.


title:
The environmental dependence of galaxy colors in intermediate redshift
  X-ray-selected clusters

abstract:
  We present a wide-field imaging study of the colors of bright galaxies in 12
X-ray selected clusters and groups of galaxies at z ~ 0.3. The systems cover
one of the largest ranges in X-ray luminosity (Lx ~ 10^43 - 10^45 erg/s), and
hence mass, of any sample studied at this redshift. We find that the `red'
galaxies form a tight color-magnitude relation (CMR) and that neither the slope
nor zero-point of this relation changes significantly over the factor of 100 in
X-ray luminosity of our sample. Using stellar population synthesis models we
find our data allow a maximum possible change of 2 Gyrs in the typical age of
the galaxies on the CMR over the range of Lx of our sample. We also measure the
fraction of blue galaxies (fb) relative to the CMR in our clusters and find a
low value of fb ~ 0.1 and find that there is no correlation between fb and Lx
over our large Lx range. However, both the CMR and fb do depend on cluster
radius, with the zero-point of the CMR shifting blueward in B-R by 0.10 +/-
0.036 magnitudes out to 0.75 times the virial radius, equivalent to a
luminosity weighted age gradient of ~ 2.5 Gyrs per log(radius). It thus appears
that the global cluster environment, in the form of cluster mass (Lx), has
little influence on the properties of bright cluster galaxies, whereas the
local environment, in the form of galaxy density (radius), has a strong effect.
The range of ~ 100 in Lx corresponds to a factor of ~ 40 in ram-pressure
efficiency, suggesting that ram-pressure stripping, or other mechanisms that
depend on cluster mass like tidal stripping or harassment, are unlikely to be
solely responsible for changing the galaxy population from the `blue' star
forming galaxies, that dominate low density environments, to the `red' passive
galaxies that dominate cluster cores.(abridged)


title:
The OH (1720 MHz) Supernova Remnant Masers in W44: MERLIN and VLBA
  Polarization Observations

abstract:
  Full-polarization MERLIN and VLBA observations of the 1720-MHz maser emission
from the OH molecule in the supernova remnant W44 are presented. Zeeman
splitting has been directly resolved between right- and left-circularly
polarized spectra indicating magnetic field strengths of B~0.50 mG. The
position angle of the linear polarization is in good agreement with the
orientation of the shocked gas at the supernova remnant/molecular cloud
interface. Based on MERLIN data having a resolution of 200 milliarcseconds
(mas) and VLBA data with a resolution of 15 mas, the masers are measured to
have deconvolved angular sizes of 50 to 350 mas (150 to 1000 AU) with compact
cores 20 mas (60 AU) in size, consistent with theoretical expectation and
previous observations.


title: V4140 Sgr: a short period dwarf nova with a peculiar behavior

abstract:
  We report on time series of CCD photometry of V4140 Sgr between 1991 and
2001. The analysis reveals that the object was in the decline from an outburst
in 1992 and again in outburst in 2001. The historical light curve collected by
amateur astronomers shows low amplitude (1-2 mag) outbursts 5-10 days long,
recurrent every 80-90 days, confirming its dwarf nova nature. We derive an
outburst decline time scale of 1.2 days mag$^{-1}$. Eclipse mapping techniques
were applied to data both in quiescence and in outburst to derive accretion
disc surface brightness maps. A distance of $d = 170 \pm 30$ pc is obtained
from a method similar to that used to constrain the distance to open clusters.
  From this distance, disc radial brightness temperature distributions are
determined. The temperatures in the quiescent disc vary from $6 000$ K in the
inner regions to $3 000$ K near the outer disc and are flatter than the $T
\propto r^{-{3/4}}$ law for optically thick steady-state disc. The outburst
occurs mainly with a significant increase in brightness of the intermediate and
outer disc regions. The disc temperatures remain below the critical effective
temperature $T_{\rm crit}$ at all disc radii during outburst. The radial
temperature distributions in quiescence and in outburst are significantly
different from those of other dwarf novae of similar orbital period. These
results cannot be explained within the framework of the disc instability model.
We suggest that the small amplitude outbursts of V4140 Sgr are caused by bursts
of enhanced mass transfer rate from the secondary star.


title: Efficient radiative transfer modelling with SKIRT

abstract:
  We present SKIRT, a three-dimensional Monte Carlo radiative transfer code
developed to study dusty galaxies. We discuss SKIRT's most important
characteristics and present a number of applications. In particular, we focus
on the kinematical aspect of SKIRT. We demonstrate that dust attenuation mimics
the presence of dark matter around elliptical galaxies and that it severely
affects the rotation curves of edge-on galaxies.


title: Pulsars and Their Nebulae as EGRET Sources

abstract:
  At the end of the EGRET mission, only 6-8 Galactic sources had been
identified as young pulsars. Since then, several energetic pulsars have been
discovered in EGRET error boxes along the Galactic plane, as well as several
pulsar wind nebulae from which pulsations have not yet been discovered. Some of
these nebulae are associated with moderately variable EGRET sources, suggesting
that the gamma-ray emission might be coming from the nebula rather than from
the pulsar magnetosphere. There is also a population of unidentified EGRET
sources at mid-Galactic latitudes which have been proposed to be either nearby
middle-aged pulsars or millisecond pulsars. I review the current status of
observational studies of pulsars associated with EGRET sources and what they
suggest the upcoming AGILE and GLAST gamma-ray missions might observe.


title:
UV to Mid-IR Observations of Star-forming Galaxies at z~2: Stellar
  Masses and Stellar Populations

abstract:
  We present the broad-band UV through mid-infrared spectral energy
distributions (SEDs) of a sample of 72 spectroscopically-confirmed star-forming
galaxies at z=2.30+/-0.3. Located in a 72 arcmin-squared field centered on the
bright background QSO, HS1700+643, these galaxies were pre-selected to lie at
z~2 based solely on their rest-frame UV colors and luminosities, and should be
representative of UV-selected samples at high redshift. In addition to deep
ground-based photometry spanning from 0.35-2.15 microns, we make use of
Spitzer/IRAC data, which probes the rest-frame near-IR at z~2. The range of
stellar populations present in the sample is investigated with simple,
single-component stellar population synthesis models. Emphasizing stellar mass
estimates, which are less subject to systematic uncertainties than other
parameters, we find <log(M*/Msun)>=10.32+/-0.51 for the sample. Allowing for
the possibility of episodic star formation, we find that typical galaxies in
our sample could contain up to three times more stellar mass in an old
underlying burst than what was inferred from single-component modeling. In
contrast, mass estimates for the most massive galaxies in the sample (M*>10^11
Msun) are fairly insensitive to the method used to model the stellar
population. Galaxies in this massive tail, which are also the oldest objects in
the sample, could plausibly evolve into the passive galaxies discovered at
z~1.7 with near-IR selection techniques. In the general framework of
hierarchical galaxy formation and mergers, which implies episodic
star-formation histories, galaxies at high redshift may pass in and out of
UV-selected and near-IR color-selected samples as they evolve from phases of
active star formation to quiescence and back again (Abridged).


title:
Detecting Dark Matter Annihilation with CMB Polarization : Signatures
  and Experimental Prospects

abstract:
  Dark matter (DM) annihilation during hydrogen recombination (z ~ 1000) will
alter the recombination history of the Universe, and affect the observed CMB
temperature and polarization fluctuations. Unlike other astrophysical probes of
DM, this is free of the significant uncertainties in modelling galactic
physics, and provides a method to detect and constrain the cosmological
abundances of these particles. We parametrize the effect of DM annihilation as
an injection of ionizing energy at a rate e_{dm}, and argue that this simple
"on the spot'' modification is a good approximation to the complicated
interaction of the annihilation products with the photon-electron plasma.
Generic models of DM do not change the redshift of recombination, but change
the residual ionization after recombination. This broadens the surface of last
scattering, suppressing the temperature fluctuations and enhancing the
polarization fluctuations. We use the temperature and polarization angular
power spectra to measure these deviations from the standard recombination
history, and therefore, indirectly probe DM annihilation. (abridged)


title:
Subaru Mid-infrared Imaging of the Quadruple Lenses PG1115+080 and
  B1422+231: Limits on Substructure Lensing

abstract:
  We present mid-infrared imaging at 11.7 mu m for the quadruple lens systems,
PG1115+080 and B1422+231, using the cooled mid-infrared camera and spectrometer
(COMICS) attached on the Subaru telescope. These lensed QSOs are characterized
by their anomalous optical and radio flux ratios as obtained for (A1, A2)
images of PG1115+080 and (A, B, C) images of B1422+231, respectively, i.e.,
such flux ratios are hardly reproduced by lens models with smooth mass
distribution. Our mid-infrared observations for these images have revealed that
the mid-infrared flux ratio A2/A1 of PG1115+080 is virtually consistent with
smooth lens models (but inconsistent with the optical flux ratio), whereas for
B1422+231, the mid-infrared flux ratios among (A, B, C) are in good agreement
with the radio flux ratios. We also identify a clear infrared bump in the
spectral energy distributions of these QSOs, thereby indicating that the
observed mid-infrared fluxes originate from a hot dust torus around a QSO
nucleus. Based on the size estimate of the dust torus, we place limits on the
mass of a substructure in these lens systems, causing the anomalous optical or
radio flux ratios. For PG1115+080, the mass of a substructure inside an
Einstein radius, M_E, is < 16 Msun, corresponding to either a star or a
low-mass CDM subhalo having the mass of M_{100}^{SIS} < 2.2 * 10^4 Msun inside
radius of 100 pc if modeled as a singular isothermal sphere (SIS). For
B1422+231, we obtain M_E > 209 Msun, indicating that a CDM subhalo is more
likely, having the mass of M_{100}^{SIS} > 7.4 * 10^4 Msun


title:
NGC 300: an extremely faint, outer stellar disk observed to 10 scale
  lengths

abstract:
  We have used the Gemini Multi-object Spectrograph (GMOS) on the Gemini South
8m telescope in exceptional conditions (0.6" FWHM seeing) to observe the outer
stellar disk of the Sculptor group galaxy NGC 300 at two locations. At our
point source detection threshold of r' = 27.0 (3-sigma) mag, we trace the
stellar disk out to a radius of 24', or 2.2 R_25 where R_25 is the 25
mag/arcsec**2 isophotal radius. This corresponds to about 10 scale lengths in
this low-luminosity spiral (M_B = -18.6), or about 14.4 kpc at a cepheid
distance of 2.0 +/- 0.07 Mpc. The background galaxy counts are derived in the
outermost field, and these are within 10% of the mean survey counts from both
Hubble Deep Fields. The luminosity profile is well described by a nucleus plus
a simple exponential profile out to 10 optical scale lengths. We reach an
effective surface brightness of 30.5 mag/arcsec**2 (2-sigma) at 55%
completeness which doubles the known radial extent of the optical disk. These
levels are exceedingly faint in the sense that the equivalent surface
brightness in B or V is about 32 mag/arcsec**2. We find no evidence for
truncation of the stellar disk. Only star counts can be used to reliably trace
the disk to such faint levels, since surface photometry is ultimately limited
by nonstellar sources of radiation. In the Appendix, we derive the expected
surface brightness of one such source: dust scattering of starlight in the
outer disk.


title: HT Camelopardalis: The simplest intermediate polar spin pulse

abstract:
  The intermediate polar HT Cam is unusual in that it shows no evidence for
dense absorption in its spectrum. We analyse an XMM-Newton observation of this
star, which confirms the absence of absorption and shows that the X-ray
spin-pulse is energy independent. The modulation arises solely from occultation
effects and can be reproduced by a simple geometrical model in which the lower
accretion footprint is fainter than the upper one.
  We suggest that the lack of opacity in the accretion columns of HT Cam, and
also of EX Hya and V1025 Cen, results from a low accretion rate owing to their
being below the cataclysmic variable period gap.


title: The Space Density of Moderate Luminosity Active Galaxies at z=3

abstract:
  We present an estimate of the space density of Active Galactic Nuclei (AGN)
at z=3. Combining deep X-ray data with Lyman Break Galaxy (LBG)
colour-selection in the rest-frame UV makes for highly efficient identification
of AGN in a narrow redshift range (z~2.5-3.5). Using Chandra data from the
Groth-Westphal Strip and the Hubble Deep Field North, we find a total of 15
X-ray detected LBGs at z~3, the majority of which are unlikely to have been
identified in blanket followup surveys of X-ray detected objects. We find the
comoving space density of moderate luminosity AGN at z=3 to be a factor ~10
higher than the most powerful objects. The available data are consistent with a
roughly constant space density of MLAGN from z=0.5-3, and they are also
consistent with a mild decline in the space density above z=1 as predicted by
the luminosity-dependent density evolution models of Ueda et al. (2003). This
strong AGN activity at z=3 argues against previous suggestions that the
majority of black hole accretion occurs at low redshift. A further implication
of our investigation is that, as far as can be determined from current data,
the majority of the AGN population at z~3 are selected by the LBG dropout
technique. Although this is sensitive to AGN with a UV-excess due to an
accretion disk, it predominantly identifies star-forming galaxies. A
significant fraction of X-ray sources seem likely to be hosted by these more
typical LBGs, further strengthening the starburst-AGN connection at high
redshift.


title:
Identification of 13 DB + dM and 2 DC + dM binaries from the Sloan
  Digital Sky Survey

abstract:
  We present the identification of 13 DB + dM binaries and 2 DC + dM binaries
from the Sloan Digital Sky Survey (SDSS). Before the SDSS only 2 DB + dM
binaries and 1 DC + dM binary were known. At least three, possibly 8, of the
new DB + dM binaries seem to have white dwarf temperatures well above 30000 K
which would place them in the so called DB-gap. Finding these DB white dwarfs
in binaries may suggest that they have formed through a different evolutionary
channel than the ones in which DA white dwarfs transform into DB white dwarfs
due to convection in the upper layers.


title:
The origin of nitrogen: Implications of recent measurements of N/O in
  Galactic metal-poor stars

abstract:
  Recent new high-precision abundance data for Galactic halo stars suggest
important primary nitrogen production in very metal-poor massive stars. Here,
we compute a new model for the chemical evolution of the Milky Way aimed at
explaining these new abundance data. The new data can be explained by adopting:
a) the stellar yields obtained from stellar models that take into account
rotation and b) an extra production of nitrogen in the very metal-poor massive
stars. In particular, we suggest an increase of nearly a factor of 200 in 14N
for a star of 60 Msun and 40 for a star of 9Msun, for metallicities below
Z=10$^{-5}$, with respect to the yields given in the literature for Z=10$^{-5}$
and rotational velocity of 300 km/s. We show that once we adopt the above
prescriptions, our model is able to predict high N/O abundance ratios at low
metallicities and still explains the nitrogen abundances observed in thin disk
stars in the solar vicinity. The physical motivation for a larger nitrogen
production in massive stars in very metal-poor environments could be the fact
that some stellar models as well as observational data suggest that at low
metallicities stars rotate faster. If this is the case, such large nitrogen
production seen in the pristine phases of the halo formation would not
necessarily happen in Damped Lyman-alpha systems which have metallicities
always above [Fe/H]$\simeq -$2.5, and could have been pre-enriched. We also
compute the abundance gradient of N/O along the Galactic disk and show that a
negative gradient is predicted once we adopt stellar yields where rotation is
taken into account. The latter result implies that intermediate mass stars
contribute less to the primary nitrogen than previously thought.


title:
On Mechanics and Thermodynamics of a stellar galaxy in a two-component
  virial system and the Fundamental Plane

abstract:
  The paper confirms the existence of a special configuration (among the
infinite number of virial states) which a B stellar(Baryonic) component may
assume inside a given D dark halo potential well.This satisfies the d'Alembert
Principle of virtual works and its typical dimension works as a scale length
(tidal radius)induced on the gravitational field of the bright component by the
dark one.Its dynamic and thermodynamic properties are here analyzed in
connection with the physical reason for the existence of the Fundamental Plane
(FP) for ellipticals.The analysis is performed by using 2-component models with
two power-law density profiles and two homogeneous cores and compared with some
observable scaling relations for pressure supported ellipticals.The virial
equilibrium stages of the 2-component system have to occur after a previous
violent relaxation phase. If the stellar B component is allowed to cool slowly
its virial evolution consists of a sequence of contractions with enough time to
rearrange the virial equilibrium after any step. The thermodynamic process
during the dynamical evolution is so divided into a sequence of transformations
which are irreversible but occur between two quasi-equilibrium stages.The
analysis allows the conclusion that the induced scale length is a real
confinement for the stellar system. The presence of this specific border on the
space of the baryonic luminous component has to be regarded as the physical
reason why a stellar galaxy belongs to the FP and why astrophysical objects,
with a completely different history and formation, but characterized by a tidal
radius (as the globular clusters are) lie on the same FP. An other problem
addressed is how this special configuration may be reached and why an
elliptical is not completely relaxed in respect to its dark halo.


title:
The XMM-Newton Needles in the Haystack Survey: the local X-ray
  luminosity function of 'normal' galaxies

abstract:
  In this paper we estimate the local (z<0.22) X-ray luminosity function of
`normal' galaxies derived from the XMM-Newton Needles in the Haystack Survey.
This is an on-going project that aims to identify X-ray selected `normal'
galaxies (i.e. non-AGN dominated) in the local Universe. We are using a total
of 70 XMM-Newton fields covering an area of 11 sq. degrees which overlap with
the Sloan Digital Sky Survey Data Release-2. `Normal' galaxies are selected on
the basis of their resolved optical light profile, their low X-ray--to--optical
flux ratio (log(f_x/f_o)<-2) and soft X-ray colours. We find a total of 28
candidate `normal' galaxies to the 0.5-8 keV band flux limit of ~2x10^{-15}
cgs. Optical spectra are available for most sources in our sample (82 per
cent). These provide additional evidence that our sources are bona-fide
'normal' galaxies with X-ray emission coming from diffuse hot gas emission
and/or X-ray binaries rather than a supermassive black hole. Sixteen of our
galaxies have narrow emission lines or a late-type Spectral Energy Distribution
(SED) while the remaining 12 present only absorption lines or an early-type
SED. Combining our XMM-Newton sample with 18 local (z<0.22) galaxies from the
Chandra Deep Field North and South surveys, we construct the local X-ray
luminosity function of `normal' galaxies. This can be represented with a
Schechter form with a break at L* ~ 3x10^{41} cgs and a slope of ~1.78+/-0.12.
Using this luminosity function and assuming pure luminosity evolution of the
form
  (1+z)^{3.3} we estimate a contribution to the X-ray background from `normal'
galaxies of 10-20 per cent (0.5-8 keV). Finally, we derive, for the first time,
the luminosity functions for early and late type systems separately.


title: Hint for Quintessence-like Scalars from Holographic Dark Energy

abstract:
  We use the generalized holographic dark energy model, in which both the
cosmological constant (CC) and Newton's constant G_N are scale-dependent, to
set constraints on the renormalization-group (RG) evolution of both quantities
phrased within quantum field theory (QFT) in a curved background. Considering
the case in which the energy-momentum tensor of ordinary matter stays
individually conserved, we show from the holographic dark energy requirement
that the RG laws for the CC and G_N are completely determined in terms of the
lowest part of the particle spectrum of an underlying QFT. From simple
arguments one can then infer that the lowest-mass fields should have a Compton
wavelength comparable with the size of the current Hubble horizon. Hence,
although the models with the variable CC (or with both the CC and the G_N
varying) are known tolead to successful cosmologies without introducing a new
light degree of freedom, we nonetheless find that holography actually brings us
back to the quintessence proposal. An advantage of having two different
components of the vacuum energy in the cosmological setting is also briefly
mentioned.


title:
Carbon monoxide in the solar atmosphere I. Numerical method and
  two-dimensional models

abstract:
  The radiation hydrodynamic code CO5BOLD has been supplemented with the
time-dependent treatment of chemical reaction networks. Advection of particle
densities due to the hydrodynamic flow field is also included. The radiative
transfer is treated frequency-independently, i.e. grey, so far. The upgraded
code has been applied to two-dimensional simulations of carbon monoxide (CO) in
the non-magnetic solar photosphere and low chromosphere. For this purpose a
reaction network has been constructed, taking into account the reactions which
are most important for the formation and dissociation of CO under the physical
conditions of the solar atmosphere. The network has been strongly reduced to 27
reactions, involving the chemical species H, H2, C, O, CO, CH, OH, and a
representative metal. The resulting CO number density is highest in the cool
regions of the reversed granulation pattern at mid-photospheric heights and
decreases strongly above. There, the CO abundance stays close to a value of 8.3
on the usual logarithmic abundance scale with [H]=12 but is reduced in hot
shock waves which are a ubiquitous phenomenon of the model atmosphere. For
comparison, the corresponding equilibrium densities have been calculated, based
on the reaction network but also under assumption of instantaneous chemical
equilibrium by applying the Rybicki & Hummer (RH) code by Uitenbroek (2001).
Owing to the short chemical timescales, the assumption holds for a large
fraction of the atmosphere, in particular the photosphere. In contrast, the CO
number density deviates strongly from the corresponding equilibrium value in
the vicinity of chromospheric shock waves. Simulations with altered reaction
network clearly show that the formation channel via hydroxide (OH) is the most
important one under the conditions of the solar atmosphere.


title: Detection of Near-IR CO Absorption Bands in R Coronae Borealis Stars

abstract:
  R Coronae Borealis (RCB) stars are hydrogen-deficient, carbon-rich pulsating
post-AGB stars that experience massive irregular declines in brightness caused
by circumstellar dust formation. The mechanism of dust formation around RCB
stars is not well understood. It has been proposed that CO molecules play an
important role in cooling the circumstellar gas so that dust may form. We
report on a survey for CO in a sample of RCB stars. We obtained H- and K-band
spectra including the first and second overtone CO bands for eight RCB stars,
the RCB-like star, DY Per and the final-helium-flash star, FG Sge. The first
and second overtone CO bands were detected in the cooler (T(eff)<6000 K) RCB
stars, Z Umi, ES Aql, SV Sge and DY Per. The bands are not present in the
warmer (T(eff)>6000 K) RCB stars, R CrB, RY Sgr, SU Tau, XX Cam. In addition,
first overtone bands are seen in FG Sge, a final-helium-flash star that is in
an RCB-like phase at present. Effective temperatures of the eight RCB stars
range from 4000 to 7250 K. The observed photospheric CO absorption bands were
compared to line-blanketed model spectra of RCB stars. As predicted by the
models, the CO bands are strongest in the coolest RCB stars and not present in
the warmest. No correlation was found between the presence or strength of the
CO bands and dust formation activity in the stars.


title: Abundance trends in kinematical groups of the Milky Way's disk

abstract:
  We have compiled a large catalogue of metallicities and abundance ratios from
the literature in order to investigate abundance trends of several alpha and
iron peak elements in the thin disk and the thick disk of the Galaxy. The
catalogue includes 743 stars with abundances of Fe, O, Mg, Ca, Ti, Si, Na, Ni
and Al in the metallicity range -1.30 < [Fe/H] < +0.50. We have checked that
systematic differences between abundances measured in the different studies
were lower than random errors before combining them. Accurate distances and
proper motions from Hipparcos, and radial velocities from several sources have
been retreived for 639 stars and their velocities (U,V,W) and galactic orbits
have been computed. Ages of 322 stars have been estimated with the Bayesian
method of isochrone fitting developped by Pont & Eyer (2004). Two samples
kinematically representative of the thin and thick disks have been selected,
taking into account the Hercules stream which is intermediate in kinematics,
but with a probable dynamical origin. [Abridged...]


title:
On the formation of energy spectra of synchrotron X-rays and inverse
  Compton gamma-rays in binary systems with luminous optical stars

abstract:
  In this paper we study formation broad band energy spectra of electrons due
to synchrotron radiation and inverse Compton (IC) scattering. The effect of
transition of IC cooling from the Thomson regime to the Klein-Nishina regime
can be very significant in the environments where radiation density dominates
over the magnetic field density. We discuss impact of this effect on the
formation of synchrotron and IC radiation components of TeV electrons in binary
systems with very luminous optical stars. Such a scenario can be realized, for
example, at the wind termination shock of the pulsar in PSR B1259-63/SS2883 or
in the jets of microquasars. The calculations are based on the solution of
Boltzmann equation using precise differential Compton cross-section.


title: The luminosity dependence of the Type 1 AGN fraction

abstract:
  Using a complete, magnitude-limited sample of active galaxies from the Sloan
Digital Sky Survey (SDSS) we show that the fraction of broad-line (Type 1)
active galactic nuclei increases with luminosity of the isotropically-emitted
[O III] narrow emission line. Our results are quantitatively in agreement with,
and far less uncertain than, similar trends found from studies of X-ray and
radio-selected active galaxies. While the correlation between broad-line
fraction and luminosity is qualitatively consistent with the receding torus
model, its slope is shallower and we therefore propose a modification to this
model where the height of the torus increases slowly with AGN luminosity. We
demonstrate that the faint-end slope of the AGN luminosity function steepens
significantly when a correction for `missing' Type 2 objects is made and that
this can substantially affect the overall AGN luminosity density extrapolated
from samples of more luminous objects.


title: Freeze-out and coagulation in pre-protostellar collapse

abstract:
  We study the changes in physical and chemical conditions during the collapse
of a pre--protostellar core, starting from initial conditions appropriate to a
dense molecular cloud and proceeding to the ``completely depleted'' limit. We
follow the evolution of the ionization degree and the ionic composition as
functions of time and density. The processes of freeze--out on to the dust
grains and coagulation of the grains were treated simultaneously with the
chemical evolution of the medium.When proceeding at close to its maximum rate,
coagulation has important consequences for the degree of ionization and the
ionic composition of the medium, but its effect on the freeze--out of the
neutral species is modest.An innovation of our study is to calculate the grain
charge distribution which is significant because H+ ions recombine on the
surfaces of negatively charged grains. We also consider the observational
result that N-containing species, such as NH3 and N2H+,remain in the gas phase
at densities for which CO and other C--containing molecules appear to have
frozen on to grain surfaces. We conclude that recent measurements of the
adsorption energies of N2 and CO invalidate the interpretation of these
observations in terms of the relative volatilities of N2 and CO. We consider an
alternative explanation,in terms of low sticking coefficients for either
molecular or atomic N. We find that, irrespective of the nitrogen chemistry,the
main gas phase ion is either H+ or H3+ (and its deuterated isotopes) at
densities above 10^5; whether H+ or H3+ predominates depends sensitively on the
rate of increase in grain size (decrease in grain surface area per unit volume
of gas) during core contraction.Our calculations show that H+ will predominate
if grain coagulation proceeds at close to its maximum rate, and H3+ otherwise.


title:
The response of primordial abundances to a general modification of
  $G_{\rm N}$ and/or of the early universe expansion rate

abstract:
  We discuss the effects of a possible time variation of the Newton constant
$G_{\rm N}$ on light elements production in Big Bang Nucleosyntesis (BBN). We
provide analytical estimates for the dependence of primordial abundances on the
value of the Newton constant during BBN. The accuracy of these estimates is
then tested by numerical methods. % Moreover, we determine numerically the
response of each element to an arbitrary time-dependent modification of the
early universe expansion rate. Finally, we determine the bounds on possible
variations of $G_{\rm N}$ which can be obtained from the comparison of
theoretical predictions and observational data.


title: The X-ray luminosity function and number counts of spiral galaxies

abstract:
  (abridged) A detailed comparison is performed of the LFs compiled at
infrared, radio and optical wavelengths and converted into XLFs using available
relations with the XLF directly estimated in the 0.5--2 keV energy band from
X-ray surveys (Norman et al). We find that the XLF from the local sample of
IRAS galaxies (Takeuchi et al) provides a good representation of all available
data samples; pure luminosity evolution of the form (1+z)^\eta, with \eta< ~3,
is favoured over pure density. The local X-ray luminosity density is also well
defined. We discuss different estimates of the galaxies LogN-LogS, selected
from the Chandra Deep Fields with different selection criteria: these have
similar slopes, but normalisations scattered within a factor ~2, of the same
order of the Poissonian error on the counts. We compare the observed LogN-LogS
with the counts predicted by integrating our reference z=0 XLF. By using number
counts alone, it is not possible to discriminate between density and luminosity
evolution; however, the evolution of galaxies must be stopped in both cases at
z~1-2. The contribution of galaxies to the X-ray background is found to be in
the range 6%--12%. Making use of cosmic star formation models, we find that the
X-ray LogN-LogS might be not compatible with very large star formation rates at
z ~ 3 as suggested by sub-mm observations in Blain et al. 1999. As to the
content of current and, possibly, future X-ray surveys, we determine the
fraction of galaxies around the current flux limit: (30+-12 %). At fainter
fluxes the fraction of galaxies will probably rise, and overcome the counts
from AGN at fluxes < ~10^{-17} erg/s/cm^2.


title:
The NICMOS Ultra Deep Field: Observations, Data Reduction, and Galaxy
  Photometry

abstract:
  This paper describes the observations and data reduction techniques for the
version 2.0 images and catalog of the NICMOS Ultra Deep Field Treasury program.
All sources discussed in this paper are based on detections in the combined
NICMOS F110W and F160W bands only. The NICMOS images are drizzled to 0.09 arc
second pixels and aligned to the ACS UDF F850LP image which was rebinned to the
same pixel scale. These form the NICMOS version 2.0 UDF images. The catalog
sources are chosen with a conservative detection limit to avoid the inclusion
of numerous spurious sources. The catalog contains 1293 objects in the 144 x
144 arc sececonds NICMOS subfield of the UDF. The 5 sigma signal to noise level
is an average 0.6 arc second diameter aperture AB magnitude of ~27.7 at 1.1 and
1.6 microns. The catalog sources, listed in order of right ascension, satisfy a
minimum signal to noise criterion of 1.4 sigma in at least 7 contiguous pixels
of the combined F110W and F160W image


title:
Comment on "Gamma-ray burst early afterglows: reverse shock emission
  from an arbitrarily magnetized ejecta" by Zhang and Kobayashi (2004)

abstract:
  Zhang and Kobayashi (2004) attempted to calculate early afterglow emission
from a system of forward and reverse shocks in GRB outflows for the case of
magnetized ejecta. We point out a fundamental error in the underlying dynamical
model. According to the authors, energy and momentum carried by the magnetic
field of the ejecta are not transfered to the forward shock. This is an
incorrect assumption that invalidates the results.


title: Scaling of Multi-Tension Cosmic Superstring Networks

abstract:
  Brane inflation in superstring theory ends when branes collide, initiating
the hot big bang. Cosmic superstrings are produced during the brane collision.
The cosmic superstrings produced in a D3-brane-antibrane inflationary scenario
have a spectrum: $(p,q)$ bound states of $p$ fundamental (F) strings and $q$
D-strings, where $p$ and $q$ are coprime. By extending the velocity-dependent
one-scale network evolution equations for abelian Higgs cosmic strings to allow
a spectrum of string tensions, we construct a coupled (infinite) set of
equations for strings that interact through binding and self-interactions. We
apply this model to a network of $(p,q)$ superstrings. Our numerical solutions
show that $(p,q)$ networks rapidly approach a stable scaling solution. We also
extract the relative densities of each string type from our solutions.
Typically, only a small number of the lowest tension states are populated
substantially once scaling is reached. The model we study also has an
interesting new feature: the energy released in $(p,q)$ string binding is by
itself adequate to allow the network to reach scaling. This result suggests
that the scaling solution is robust. To demonstrate that this result is not
trivial, we show that choosing a different form for string interactions can
lead to network frustration.


title:
A 10 micron spectroscopic survey of Herbig Ae star disks: grain growth
  and crystallization

abstract:
  We present spectroscopic observations of a large sample of Herbig Ae stars in
the 10 micrometer spectral region. We perform compositional fits of the spectra
based on properties of homogeneous as well as inhomogeneous spherical
particles, and derive the mineralogy and typical grain sizes of the dust
responsible for the 10 $\mu$m emission. Several trends are reported that can
constrain theoretical models of dust processing in these systems: i) none of
the sources consists of fully pristine dust comparable to that found in the
interstellar medium, ii) all sources with a high fraction of crystalline
silicates are dominated by large grains, iii) the disks around more massive
stars (M >~ 2.5 M_sun, L >~ 60 L_sun) have a higher fraction of crystalline
silicates than those around lower mass stars, iv) in the subset of lower mass
stars (M <~ 2.5 M_sun) there is no correlation between stellar parameters and
the derived crystallinity of the dust. The correlation between the shape and
strength of the 10 micron silicate feature reported by van Boekel et al. (2003)
is reconfirmed with this larger sample. The evidence presented in this paper is
combined with that of other studies to present a likely scenario of dust
processing in Herbig Ae systems. We conclude that the present data favour a
scenario in which the crystalline silicates are produced in the innermost
regions of the disk, close to the star, and transported outward to the regions
where they can be detected by means of 10 micron spectroscopy. Additionally, we
conclude that the final crystallinity of these disks is reached very soon after
active accretion has stopped.


title:
A contemporaneous infrared flash from a long gamma-ray burst: an echo
  from the central engine

abstract:
  The explosion that results in a cosmic gamma-ray burst (GRB) is thought to
produce emission from two physical processes -- the activity of the central
engine gives rise to the high-energy emission of the burst through internal
shocking and the subsequent interaction of the flow with the external
environment produces long-wavelength afterglow. While afterglow observations
continue to refine our understanding of GRB progenitors and relativistic
shocks, gamma-ray observations alone have not yielded a clear picture of the
origin of the prompt emission nor details of the central engine. Only one
concurrent visible-light transient has been found and was associated with
emission from an external shock. Here we report the discovery of infrared (IR)
emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of
GRB 041219a. Our robotic telescope acquired 21 images during the active phase
of the burst, yielding the earliest multi-colour observations of any
long-wavelength emission associated with a GRB. Analysis of an initial IR pulse
suggests an origin consistent with internal shocks. This opens a new
possibility to study the central engine of GRBs with ground-based observations
at long wavelengths.


title: The Galaxy Distribution Function from the 2MASS Survey

abstract:
  We determine the spatial distribution function of galaxies from a wide range
of samples in the 2MASS survey. The results agree very well with the form of
the distribution predicted by the theory of cosmological gravitational
many-body galaxy clustering. On large scales we find a value of the clustering
parameter b = 0.867 +/- 0.026, in agreement with b = 0.83 +/- 0.05 found
previously for the Pisces-Perseus supercluster. We measure b(theta) as a
function of scale, since this is a powerful test of the applicability of
computer simulations. The results suggest that when galaxies clustered they
were usually surrounded by individual, rather than by communal haloes.


title: Radiative transfer in decomposed domains

abstract:
  An efficient algorithm for calculating radiative transfer on massively
parallel computers using domain decomposition is presented. The integral
formulation of the transfer equation is used to divide the problem into a local
but compute-intensive part for calculating the intensity and optical depth
integrals, and a nonlocal part for communicating the intensity between adjacent
processors. The waiting time of idle processors during the nonlocal
communication part does not have a severe impact on the scaling. The wall clock
time thus scales nearly linearly with the inverse number of processors.


title:
Testing models of supermassive black hole seed formation through gravity
  waves

abstract:
  We study the gravitational wave background produced from the formation and
assembly of supermassive black holes within the cosmological paradigm of
hierarchical structure formation. In particular, we focus on a supermassive
black hole formation scenario in which the present-day population of
supermassive black holes is built from high-mass seed black holes and we
compute the concomitant spectrum of gravitational radiation produced by mergers
of the seed black holes. We find that this scenario predicts a large,
gravitational wave background that should be resolved into individual sources
with space interferometers such as the proposed Laser Interferometric Space
Antenna (LISA). The number of inspiral, merger and ringdown events above a
signal to noise ratio of 5 that result from massive black hole seeds is of
order 10^3. This prediction is robust and insensitive to several of the details
of the model. We conclude that an interferometer such as LISA will be able to
effectively rule out or confirm a class of models where supermassive black
holes grow from high-mass seed black holes and may be able to place strong
limits on the role of mergers as a channel for supermassive black hole growth.
Supermassive black hole seeds likely form in the earliest proto-galactic
structures at high redshift and the masses of supermassive black holes are
known to be strongly correlated with the potentials of the spheroids in which
they reside, therefore these results imply that space interferometers can be
used as a powerful probe of the physics of galaxy formation and proto-galaxy
formation at very high redshift.


title:
Stars in the USNO-B1 Catalog with Proper Motions Between 1.0 and 5.0
  arcseconds per year

abstract:
  This paper examines a subset of objects from the USNO-B1 catalogue with
listed proper motions between 1.0 and 5.0 arcseconds per year. We look at the
degree of contamination within this range of proper motions, and point out the
major sources of spurious high proper motion objects. Roughly 0.1% of the
objects in the USNO-B1 catalogue with listed motions between 1.0 and 5.0
arcseconds per year are real. Comparison with the revised version of Luyten's
Half Second catalogue indicates that USNO-B1 is only about 47% complete for
stars in this range. Preliminary studies indicate that there may be a dip in
completeness in USNO-B1 for objects with motions near 0.1 arcseconds per year.
We also present two new stars with motions between 1.0 and 5.0 arcseconds per
year, 36 new stars with confirmed motions between 0.1 and 1.0 arcseconds per
year, several new common proper motion pairs, and the recovery of LHS237a
(VBs3).


title: On the dynamics of the satellite galaxies in NGC 5044

abstract:
  The NGC 5044 galaxy group is dominated by a luminous elliptical galaxy which
is surrounded by ~160 dwarf satellites. The projected number density profile of
this dwarf population deviates within ~1/3 of the virial radius from a
projected NFW-profile, which is assumed to approximate the underlying total
matter distribution. By means of a semi-analytic model we demonstrate that the
interplay between gravitation, dynamical friction and tidal mass loss and
destruction can explain the observed number density profile. We use only two
parameters in our models: the total to stellar mass fraction of the satellite
halos and the disruption efficiency. The disruption efficiency is expressed by
a minimum radius. If the tidal radius of the galaxy (halo) falls below this
radius the galaxies is assumed to become unobservable. The preferred parameters
are an initial total to stellar mass fraction of ~20 and a disruption radius of
4 kpc. In that model about 20% of all the satellites are totally disrupted on
their orbits within the group environment. Dynamical friction is less important
in shaping the inner slope of the number density profile since the reduction in
mass by tidal forces lowers the impact of the friction term. The main
destruction mechanism is tide. In the preferred model the total B-band
luminosity of all the disrupted galaxies is about twice the observed luminosity
of the central elliptical galaxy, indicating that a significant fraction of
stars are scattered into the intragroup medium.(Abridged)


title:
2D Simulations of the Line-Driven Instability in Hot-Star Winds: II.
  Approximations for the 2D Radiation Force

abstract:
  We present initial attempts to include the multi-dimensional nature of
radiation transport in hydrodynamical simulations of the small-scale structure
that arises from the line-driven instability in hot-star winds. Compared to
previous 1D or 2D models that assume a purely radial radiation force, we seek
additionally to treat the lateral momentum and transport of diffuse
line-radiation, initially here within a 2D context. A key incentive is to study
the damping effect of the associated diffuse line-drag on the dynamical
properties of the flow, focusing particularly on whether this might prevent
lateral break-up of shell structures at scales near the lateral Sobolev angle
of ca. $1^{\rm o}$. We first explore nonlinear simulations that cast the
lateral diffuse force in the simple, local form of a parallel viscosity.
Second, to account for the lateral mixing of radiation associated with the
radial driving, we next explore models in which the radial force is azimuthally
smoothed over a chosen scale. Third, to account for both the lateral line-drag
and the lateral mixing in a more self-consistent way, we explore further a
method first proposed by Owocki (1999), which uses a restricted 3-ray approach
that combines a radial ray with two oblique rays set to have an impact
parameter $p < R_{\ast}$ within the stellar core. From numerical simulations,
we find that, compared to equivalent 1-ray simulations, the high-resolution
3-ray models show systematically a much higher lateral coherence.... (Full
abstract in paper)


title:
Weibel Instability Driven by Relativistic Pair Jets: Particle
  Acceleration, Magnetic Field Generation, and Emission

abstract:
  Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., Buneman, Weibel and
other two-stream instabilities) created in collisionless shocks are responsible
for particle (electron, positron, and ion) acceleration. Using a 3-D
relativistic electromagnetic particle (REMP) code, we have investigated
particle acceleration associated with a relativistic jet front propagating into
an ambient plasma. We find that the growth times of the Weibel instability in
electron-positron jets are not affected by the (electron-positron or
electron-ion) ambient plasmas. However, the amplitudes of generated local
magnetic fields in the electron-ion ambient plasma are significantly larger
than those in the electron-positron ambient plasma.


title:
A Search for Radio Emission from the Young 16-ms X-ray Pulsar PSR
  J0537-6910

abstract:
  PSR J0537-6910 is a young, energetic, rotation-powered X-ray pulsar with a
spin period of 16 ms located in the Large Magellanic Cloud. We have searched
for previously undetected radio pulsations (both giant and standard) from this
pulsar in a 12-hour observation taken at 1400 MHz with the Parkes 64-m radio
telescope. The very large value of the magnetic field at the light cylinder
radius suggests that this pulsar might be emitting giant radio pulses like
those seen in other pulsars with similar field strengths. No radio emission of
either kind was detected from the pulsar, and we have established an upper
limit of ~ 25 mJy kpc^2 for the average 1400-MHz radio luminosity of PSR
J0537-6910. The 5-sigma single-pulse detection threshold was ~ 750 mJy for a
single 80-us sample. These limits are likely to be the best obtainable until
searches with greatly improved sensitivity can be made with next-generation
radio instruments.


title:
A Note on "Probing the existence of the $E_{peak}$-$E_{iso}$ correlation
  in long Gamma Ray Bursts" by Ghirlanda et al. - astro-ph/0502186

abstract:
  In Nakar & Piran (2004) we have shown that a large fraction of BATSE bursts
cannot satisfy the Amati relation between the isotropic energy - peak energy of
GRBs. Our results have been corroborated by a further analysis carried out by
Band and Preece (2005). Recently Ghirlanda et al. (2005) claimed that when the
exact distribution of the scatter around the Amati relation is taken into
account, the BATSE sample is consistent with the Amati relation. We show that
the probability that the BATSE sample is consistent with the Amati relation
(including the scattering), as found by Ghirlanda et al. (2005) for a sample of
23 bursts with known redshift, is vanishingly small.


title: Force-Free Magnetosphere of an Accreting Kerr Black Hole

abstract:
  I consider a stationary axisymmetric force-free degenerate magnetosphere of a
rotating Kerr black hole surrounded by a thin Keplerian infinitely-conducting
accretion disk. I focus on the closed-field geometry with a direct magnetic
coupling between the disk and the event horizon. I first present a simple
physical argument that shows how the black hole's rotation limits the radial
extent of the force-free link. I then confirm this result by solving
numerically the general-relativistic force-free Grad--Shafranov equation in the
magnetosphere, using the regularity condition at the inner light cylinder to
determine the poloidal current. I indeed find that force-free solutions exist
only when the magnetic link between the hole and the disk has a limited extent
on the disk surface. I chart out the maximum allowable size of this
magnetically-connected part of the disk as a function of the black hole spin. I
also compute the angular momentum and energy transfer between the hole and the
disk that takes place via the direct magnetic link. I find that both of these
quantities grow rapidly and that their deposition becomes highly concentrated
near the inner edge of the disk as the black hole spin is increased.


title: The Rise and Citation Impact of astro-ph in Major Journals

abstract:
  The rise in the use of the arXiv preprint server (astro-ph) over the past
decade has led to a major shift in the way astronomical research is
disseminated. Schwarz & Kennicutt (2004) recently found that Astrophysical
Journal papers posted to astro-ph are cited roughly twice as often as papers
that are not posted, suggesting that the preprint server has become the primary
resource for many astronomers to keep up with the literature. I describe a
simple method to determine the adoption rate and citation impact of astro-ph
over time for any journal using NASA's Astrophysics Data System (ADS). I use
the ADS to document the rise in the adoption of astro-ph for three major
astronomy journals, and to conduct a broad survey of the citation impact of
astro-ph in 13 different journals. I find that the factor of two boost in
citations for astro-ph papers is a common feature across most of the major
astronomy journals.


title: Can Life develop in the expanded habitable zones around Red Giant Stars?

abstract:
  We present some new ideas about the possibility of life developing around
sub-giant and red giant stars. Our study concerns the temporal evolution of the
habitable zone. The distance between the star and the habitable zone, as well
as its width, increases with time as a consequence of stellar evolution. The
habitable zone moves outward after the star leaves the main sequence, sweeping
a wider range of distances from the star until the star reaches the tip of the
asymptotic giant branch. If life could form and evolve over time intervals from
$5 \times 10^8$ to $10^9$ years, then there could be habitable planets with
life around red giant stars. For a 1 M$_{\odot}$ star at the first stages of
its post main-sequence evolution, the temporal transit of the habitable zone is
estimated to be of several 10$^9$ years at 2 AU and around 10$^8$ years at 9
AU. Under these circumstances life could develop at distances in the range 2-9
AU in the environment of sub-giant or giant stars and in the far distant future
in the environment of our own Solar System. After a star completes its first
ascent along the Red Giant Branch and the He flash takes place, there is an
additional stable period of quiescent He core burning during which there is
another opportunity for life to develop. For a 1 M$_{\odot}$ star there is an
additional $10^9$ years with a stable habitable zone in the region from 7 to 22
AU. Space astronomy missions, such as proposed for the Terrestrial Planet
Finder (TPF) and Darwin should also consider the environments of sub-giants and
red giant stars as potentially interesting sites for understanding the
development of life.


title:
A Link between Prompt Optical and Prompt Gamma-Ray Emission in Gamma-Ray
  Bursts

abstract:
  The prompt optical emission that arrives with gamma-rays from a cosmic
gamma-ray burst (GRB) is a signature of the engine powering the burst, the
properties of the ultra-relativistic ejecta of the explosion, and the ejecta's
interactions with the surroundings. Until now, only GRB 990123 had been
detected at optical wavelengths during the burst phase. Its prompt optical
emission was variable and uncorrelated with the prompt gamma-ray emission,
suggesting that the optical emission was generated by a reverse shock arising
from the ejecta's collision with the surrounding material. Here we report
prompt optical emission from GRB 041219a. It is variable and correlated with
the prompt gamma-rays, indicating a common origin for the optical light and the
gamma-rays. Within the context of the standard fireball model of GRBs, we
attribute this new optical component to internal shocks driven into the burst
ejecta by variations of the inner engine. The correlated optical emission is a
direct probe of the jet isolated from the medium. The timing of the
uncorrelated optical emission is strongly dependent on the nature of the
medium.


title:
Theoretical Interpretation of the Measurements of the Secondary Eclipses
  of TrES-1 and HD209458b

abstract:
  We calculate the planet-star flux-density ratios as a function of wavelength
from 0.5 microns to 25 microns for the transiting extrasolar giant planets
TrES-1 and HD209458b and compare them with the recent Spitzer/IRAC-MIPS
secondary eclipse data in the 4.5, 8.0, and 24 micron bands. With only three
data points and generic calibration issues, detailed conclusions are difficult,
but inferences regarding atmospheric composition, temperature, and global
circulation can be made. Our models reproduce the observations reasonably well,
but not perfectly, and we speculate on the theoretical consequences of
variations around our baseline models. One preliminary conclusion is that we
may be seeing in the data indications that the day side of a close-in
extrasolar giant planet is brighter in the mid-infrared than its night side,
unlike Jupiter and Saturn. This correspondence will be further tested when the
data anticipated in other Spitzer bands are acquired, and we make predictions
for what those data may show.


title: Properties of Extremely Red Objects in an Overdense Region

abstract:
  We use a serendipitously discovered overdensity of extremely red objects
(EROs) to study the morphologies and cumulative surface number density of EROs
in a dense environment. Our extremely deep imaging allows us to select very
faint EROs, reaching Ks=21, or ~2 magnitudes fainter than the L* of passively
evolving ellipticals at z=1.5. We find that the shape of the ERO cumulative
surface number density in our overdense field mimics that of the field ERO
population over all magnitudes down to Ks=21 but with a factor of 3-4 higher
normalization. The excellent seeing in our images (0.4" in Ks and 0.6" in R)
allows for morphological classification of the brighter (Ks<19) EROs and we
find a mix of morphologies including interacting systems and disks; the
fraction of pure bulges (at most 38%), galaxies with disks (at least 46%), and
interacting systems (at least 21%) is consistent with morphological fractions
in field ERO studies. The similarity in the shape of the cumulative surface
density and morphological mix between our overdense field and the field ERO
population suggests that ERO galaxies in overdense regions at z~1-2 may not
have had an appreciably different history than those in the field.


title: Why Optically--Faint AGN Are Faint: The Spitzer Perspective

abstract:
  Optically--faint X-ray sources (those with f_X/f_R > 10) constitute about 20%
of X-ray sources in deep surveys, and are potentially highly obscured and/or at
high redshift. Their faint optical fluxes are generally beyond the reach of
spectroscopy. For a sample of 20 optically--faint sources in CDFS, we compile
0.4--24 um photometry, relying heavily on Spitzer. We estimate photometric
redshifts for 17 of these 20 sources. We find that these AGN are
optically--faint both because they lie at significantly higher redshifts
(median z ~ 1.6) than most X-ray--selected AGN, and because their spectra are
much redder than standard AGN. They have 2--8 keV X-ray luminosities in the
Seyfert range, unlike the QSO--luminosities of optically--faint AGN found in
shallow, wide--field surveys. Their contribution to the X-ray Seyfert
luminosity function is comparable to that of z>1 optically--bright AGN.