title:
A Search for Variable Stars and Planetary Occultations in NGC2301 I:
  Techniques

abstract:
  We observed the young open cluster NGC 2301 for 14 nights in Feb. 2004 using
the orthogonal transfer CCD camera (OPTIC). We used PSF shaping techniques
("square stars") during the observations allowing a larger dynamic range (4.5
magnitudes) of high photometric precision results ($\le$2 mmag) to be obtained.
These results are better than similar observing campaigns using standard CCD
imagers. This paper discusses our observational techniques and presents initial
results for the variability statistics found in NGC 2301. Details of the
variability statistics as functions of color, variability type, stellar type,
and cluster location will appear in paper II.


title: The Spitzer Space Telescope First-Look Survey: Neutral Hydrogen Emission

abstract:
  The Spitzer Space Telescope (formerly SIRTF) extragalactic First-Look Survey
covered about 5 square degrees centered on J2000 17:18 +59:30 in order to
characterize the infrared sky with high sensitivity. We used the 100-m Green
Bank Telescope to image the 21cm Galactic HI emission over a 3x3 degree field
covering this position with an effective angular resolution of 9.8 arcmin and a
velocity resolution of 0.62 km/s. In the central square degree of the image the
average column density is N(HI) = 2.5 x 10^{20} cm-2 with an rms fluctuation of
0.3 x 10^{20}. The Galactic HI in this region has a very interesting structure.
There is a high-velocity cloud, several intermediate-velocity clouds (one of
which is probably part of the Draco nebula), and narrow-line low velocity
filaments. The HI emission shows a strong and detailed correlation with dust.
Except for the high-velocity cloud, all features in the HI map have
counterparts in an E(B-V) map derived from infrared data. Relatively high
E(B-V)/N(HI) ratios in some directions suggest the presence of molecular gas.
The best diagnostic of such regions is the peak HI line brightness temperature,
not the total N(HI): directions where Tb > 12 K have E(B-V)/N(HI) significantly
above the average value. The data corrected for stray radiation have been
released via the Web.


title: An OVI Baryon Census of the Low-z Warm-Hot Intergalactic Medium

abstract:
  Intergalactic absorbers along lines of sight to distant quasars are a
powerful diagnostic for the evolution and content of the intergalactic medium
(IGM). In this study, we use the FUSE satellite to search 129 known lya
absorption systems at z<0.15 toward 31 AGN for corresponding absorption from
higher Lyman lines and the important metal ions OVI. We detect OVI in 40
systems over a smaller range of column density than seen in HI. The
co-existence of OVI and HI suggests a multiphase IGM, with warm photoionized
and hot ionized components. With improved OVI detection statistics, we find a
steep distribution in OVI column density, dN(OVI)/dN_OVI N_OVI^(-2.2+-0.1),
suggesting that numerous weak OVI absorbers contain baryonic mass comparable to
the rare strong absorbers. The total cosmological mass fraction in this hot gas
is at least Omega_WHIM=(0.0022+-0.0003. Gas in the WHIM at 10^5-6 K contributes
at least 4.8+-0.9% of the total baryonic mass at z<0.15. We then combine
empirical scaling relations for the observed "multiphase ratio", N_HI/N_OVI
N_HI^(0.9+-0.1), and for hydrogen overdensity in cosmological simulations, N_HI
delta_H^{0.7}, with the HI photoionization correction to derive the mean oxygen
metallicity, Z_O (0.09 Z_sun)(f_OVI/0.2)^(-1) in the low-z multiphase gas.
Given the spread in the empirical relations and in f_OVI, the baryon content in
the OVI WHIM could be as large as 10%. Our survey is based on a large
improvement in the number of OVI absorbers (40 vs. 10) and total redshift
pathlength (dz 2.2 vs. dz 0.5) compared to earlier surveys.


title: Are two kinds of dark matter seen in Galactic gamma rays?

abstract:
  Excesses of Galactic gamma rays in the 1-100 GeV region observed by EGRET and
by WMAP have been interpreted as signals of dark matter (LSP) annihilation. We
argue that the excess of TeV gamma rays from the Galactic center observed by
H.E.S.S. signals a heavier dark matter component with a very small relic
density.


title: Chandra Observations of MBM12 and Models of the Local Bubble

abstract:
  Chandra observations toward the nearby molecular cloud MBM12 show
unexpectedly strong and nearly equal foreground O VIII and O VII emission. As
the observed portion of MBM12 is optically thick at these energies, the
emission lines must be formed nearby, coming either from the Local Bubble (LB)
or charge exchange with ions from the Sun. Equilibrium models for the LB
predict stronger O VII than O VIII, so these results suggest that the LB is far
from equilibrium or a substantial portion of O VIII is from another source,
such as charge exchange within the Solar system. Despite the likely
contamination, we can combine our results with other EUV and X-ray observations
to reject LB models which posit a cool recombining plasma as the source of LB
X-rays.


title: Dealing with Dark Energy

abstract:
  Discoveries in the last few years have revolutionized our knowledge of the
universe and our ideas of its ultimate fate. Measurements of the expansion of
the universe show that it is not slowing down under normal gravity but
accelerating due to an unknown, gravitationally repulsive ``dark energy''. This
may be a clue to new properties of quantum physics or of gravity beyond
Einstein. I present an overview of the puzzles of dark energy and the means for
unraveling them through cosmological probes, on both a generally accessible and
a technical level. I also highlight the strong benefits of meshing supernova
distance and weak lensing methods. Next generation experiments such as the
Supernova/Acceleration Probe (SNAP) satellite would measure the supernova
distance-redshift relation to high accuracy and map the evolution of structure
and dark matter through gravitational lensing. These observations will explore
the frontiers of physics and aim to uncover what makes up the still unknown 95%
of our universe.


title: Deep Extragalactic X-ray Surveys

abstract:
  Deep surveys of the cosmic X-ray background are reviewed in the context of
observational progress enabled by the Chandra X-ray Observatory and the X-ray
Multi-Mirror Mission-Newton. The sources found by deep surveys are described
along with their redshift and luminosity distributions, and the effectiveness
of such surveys at selecting active galactic nuclei (AGN) is assessed. Some key
results from deep surveys are highlighted including (1) measurements of AGN
evolution and the growth of supermassive black holes, (2) constraints on the
demography and physics of high-redshift AGN, (3) the X-ray AGN content of
infrared and submillimeter galaxies, and (4) X-ray emission from distant
starburst and normal galaxies. We also describe some outstanding problems and
future prospects for deep extragalactic X-ray surveys.


title:
Active Galactic Nuclei in the Sloan Digital Sky Survey: I. Sample
  Selection

abstract:
  We have compiled a large sample of low-redshift active galactic nuclei (AGN)
identified via their emission line characteristics from the spectroscopic data
of the Sloan Digital Sky Survey. Since emission lines are often contaminated by
stellar absorption lines, we developed an objective and efficient method of
subtracting the stellar continuum from every galaxy spectrum before making
emission line measurements. The distribution of the measured H$\alpha$ Full
Width at Half Maxima values of emission line galaxies is strongly bimodal, with
two populations separated at about 1,200km s$^{-1}$. This feature provides a
natural separation between narrow-line and broad-line AGN. The narrow-line AGN
are identified using standard emission line ratio diagnostic diagrams. 1,317
broad-line and 3,074 narrow-line AGN are identified from about 100,000 galaxy
spectra selected over 1151 square degrees. This sample is used in a companion
paper to determine the emission-line luminosity function of AGN.


title:
Low-frequency constraints on the spectra of the lobes of the microquasar
  GRS 1758-258

abstract:
  I present low-frequency observations of the lobes of the microquasar GRS
1758-258, which, together with earlier radio observations, provide the best
constraints yet on the lobe spectra, and show that they are consistent with the
electron energy indices expected from standard shock acceleration models. There
is no statistically significant evidence for synchrotron ageing along the
length of the lobes, which is consistent with expectation if the magnetic field
strength is close to the minimum-energy value. If the environment of the lobes
has typical ISM properties, the lobes will dissipate on timescales of thousands
of years or less, long before synchrotron ageing can become significant.


title:
Highly Ionized High-Velocity Clouds: Hot Intergalactic Medium or
  Galactic Halo?

abstract:
  We use spectroscopic data from HST and FUSE to study the wide range of
ionization states of the "highly ionized high-velocity clouds". Studied
extensively in OVI absorption, these clouds are usually assumed to be infalling
gas in the Galactic halo at distances less than 50 kpc. An alternative model
attributes the OVI (and OVII X-ray absorption) to cosmological structures of
low-density, shock-heated intergalactic gas, distributed over 1-3 Mpc
surrounding the Milky Way. The latter interpretation is unlikely, owing to the
enormous required mass of gas (4x10^12 M_solar). Our detection, in 9 of 12
sight lines, of low ionization stages (CII/III/IV; SiII/III/IV) at similar high
velocities as OVI requires gas densities far above that (n_H=5x10^-6 cm^-3)
associated with the warm-hot intergalactic medium (WHIM). These HVCs are
probably cooling, multiphase gas in the Galactic halo, bow-shocks and
interfaces between clouds falling through a hot, rotating gaseous halo. The
velocity segregation of these HVCs in Galactic coordinates is consistent with a
pattern in which infalling clouds reflect the sense of Galactic rotation, with
peculiar velocities superposed.


title: Multi-epoch VLBA observations of T Tauri South

abstract:
  In this Letter, we present a series of seven observations of the compact,
non-thermal radio source associated with T Tauri South made with the Very Long
Baseline Array over the course of one year. The emission is found to be
composed of a compact structure most certainly originating from the
magnetosphere of an underlying pre-main sequence star, and a low-brightness
extension which may result from reconnection flares at the star-disk interface.
The accuracy of the absolute astrometry offered by the VLBA allows very precise
determinations of the trigonometric parallax and proper motion of T Tau South.
The proper motion derived from our VLBA observations agrees with that measured
with the VLA over a similar period to better than 2 mas yr$^{-1}$, and is fully
consistent with the infrared proper motion of T Tau Sb, the pre-main sequence M
star with which the radio source has traditionally been associated. The
parallax, $\pi$ = 7.07 $\pm$ 0.14 mas, corresponds to a distance of
141.5$^{+2.8}_{-2.7}$ pc.


title: The Weak Lensing Bispectrum

abstract:
  Weak gravitational lensing of background galaxies offers an excellent
opportunity to study the intervening distribution of matter. While much
attention to date has focused on the two-point function of the cosmic shear,
the three-point function, the {\it bispectrum}, also contains very useful
cosmological information. Here, we compute three corrections to the bispectrum
which are nominally of the same order as the leading term. We show that the
corrections are small, so they can be ignored when analyzing present surveys.
However, they will eventually have to be included for accurate parameter
estimates from future surveys.


title:
Discovery of the accretion-powered millisecond X-ray pulsar IGR
  J00291+5934

abstract:
  We report on observations of the sixth accretion-powered millisecond pulsar,
IGR J00291+5934, with the Rossi X-Ray Timing Explorer. The source is a faint,
recurrent X-ray transient initially identified by INTEGRAL. The 599 Hz (1.67
ms) pulsation had a fractional rms amplitude of 8% in the 2-20 keV range, and
its shape was approximately sinusoidal. The pulses show an energy-dependent
phase delay, with the 6-9 keV pulses arriving up to 85 us earlier than those at
lower energies. No X-ray bursts, dips, or eclipses were detected. The neutron
star is in a circular 2.46 hr orbit with a very low-mass donor, most likely a
brown dwarf. The binary parameters of the system are similar to those of the
first known accreting millisecond pulsar, SAX J1808.4-3658. Assuming that the
mass transfer is driven by gravitational radiation and that the 2004 outburst
fluence is typical, the 3-yr recurrence time implies a distance of at least 4
kpc.


title: Properties of Type Ia Supernova Host Galaxies

abstract:
  We study the effect of environment on the properties of type Ia supernovae by
analyzing the integrated spectra of 57 host galaxies. Integrated spectra of
galaxies best represent the global properties of the host and can be used to
directly compare with spectra of high-redshift galaxies. From the spectra we
deduce the metallicity, current star-formation rate and star-formation history
of the hosts and compare these to the supernova decline rate which is an
indicator of the luminosity. Our results show no significant correlation
between spiral host galaxy metallicity and SNIa light curve decline rate. The
Hydrogen-alpha equivalent width (EW) of the host galaxy is an indicator the
current star-formation rate compared to average rate in the past. The range of
SNIa luminosities increases with decreasing EW which suggests that the
variation in SNIa {56}Ni production is primarily due to progenitor mass and
population age.


title: The Evolutionary History of the Elliptical Galaxy NGC 1052

abstract:
  We have obtained Keck spectra for 16 globular clusters (GCs) associated with
the merger remnant elliptical NGC 1052, as well as a long-slit spectrum of the
galaxy. We derive ages, metallicities and abundance ratios from simple stellar
population models using the methods of Proctor & Sansom (2002), applied to
extragalactic GCs for the first time. We find all of the GCs to be ~13 Gyr old
according to simple stellar populations, with a large range of metallicities.
  From the galaxy spectrum we find NGC 1052 to have a luminosity-weighted
central age of ~2 Gyr and metallicity of [Fe/H]~+0.6. No strong gradients in
either age or metallicity were found to the maximum radius measured (~1 kpc).
However, we do find a strong radial gradient in alpha-element abundance, which
reaches a very high central value. The young central starburst age is
consistent with the age inferred from the HI tidal tails and infalling gas of
\~1 Gyr. Thus, although NGC 1052 shows substantial evidence for a recent merger
and an associated starburst, it appears that the merger did not induce the
formation of new GCs, perhaps suggesting that little recent star formation
occurred. This interpretation is consistent with ``frosting'' models for
early-type galaxy formation. (Abridged)


title:
Thermal Processing of Silicate Dust in the Solar Nebula: Clues from
  Primitive Chondrite Matrices

abstract:
  The most abundant matrix minerals in chondritic meteorites, hydrated
phyllosilicates and ferrous olivine crystals, formed predominantly in asteroids
during fluid-assisted metamorphism. We infer that they formed from minerals
present in three less altered carbonaceous chondrites that have silicate
matrices composed largely of micrometer- and nanometer-sized grains of
crystalline forsterite, Mg2SiO4, and enstatite MgSiO3, and amorphous,
ferromagnesian silicate. Compositional and structural features of enstatite and
forsterite suggest that they formed as condensates that cooled below 1300 K at
\~1000 K/h. Most amorphous silicates are likely to be solar nebula condensates
also, as matrix, which is approximately solar in composition, is unlikely to be
a mixture of genetically unrelated materials with different compositions. Since
chondrules cooled at 10-1000 K/h, and matrix and chondrules are chemically
complementary, most matrix silicates probably formed close to chondrules in
transient heating events. Shock heating is favored as nebular shocks capable of
melting millimeter-sized aggregates vaporize dust. The crystalline and
amorphous silicates in the primitive chondrite matrices share many
characteristic features with silicates in chondritic interplanetary dust
particles suggesting that most of the crystalline silicates and possibly some
amorphous silicates in the interplanetary dust particles are also nebular
condensates. Except for small amounts of refractory oxides that formed with
Ca-Al-rich inclusions at the inner edge of the disk and presolar dust, most of
the crystalline silicate dust that accreted into chondritic asteroids and
long-period comets appears to have formed from shock heating at ~2-10 AU.
Forsterite crystals around young stars may have a similar origin.


title:
EVN observations of eleven GHz-Peaked-Spectrum radio sources at
  2.3/8.4GHz

abstract:
  We present results of EVN observations of eleven GHz-Peaked-Spectrum (GPS)
radio sources at 2.3/8.4 GHz. These sources are from the classical ''bright''
GPS source samples with peak flux densities $>$ 0.2 Jy and spectral indices
$\alpha < -0.2$ ($S \propto \nu^{-\alpha}$) in the optically thick regime of
their convex spectra. Most of the target sources did not have VLBI images at
the time this project started. The aim of the work is to find Compact Symmetric
Object (CSO) candidates from the ''bright'' GPS samples. These CSOs play a key
role in understanding the very early stage of the evolution of individual radio
galaxies. The reason for investigating GPS source samples is that CSO
candidates are more frequently found among this class of radio sources. In fact
both classes, GPS and CSO, represent a small fraction of the flux limited and
flat-spectrum samples like PR+CJ1 (PR: Pearson-Readhead survey, CJ1: the first
Caltech--Jodrell Bank survey) and CJF (the Caltech--Jodrell Bank flat spectrum
source survey) with a single digit percentage progressively decreasing with
decreasing flux density limit. Our results, with at least 3, but possibly more
CSO sources detected among a sample of 11, underline the effectiveness of our
approach. The three confirmed CSO sources (1133+432, 1824+271, and 2121$-$014)
are characterized by a symmetric pair of resolved components, each with steep
spectral indices. Five further sources (0144+209, 0554$-$026, 0904+039,
0914+114 and 2322$-$040) can be considered likely CSO candidates. The remaining
three sources (0159+839, 0602+780 and 0802+212) are either of core-jet type or
dominated by a single component at both frequencies.


title:
The Impact of Gravitational Redshift on Systemic Water Maser Emission in
  NGC 4258

abstract:
  NGC 4258 is well known for its 22 GHz water maser features that appear to
reside in a thin Keplerian disk orbiting at R_0=0.13 pc. The influence of
gravitational redshift on the level of maser saturation and the line strength
and width of systemic water maser emission is studied. The effective
gravitational velocity shift along the gain path through the disk amounts to
about twice the thermal velocity width of H2O molecules at 500 K for a masing
ring of thickness 0.2R_0. This GR induced frequency shift has a sign opposite
to the shift caused by the projected velocity difference vector of Keplerian
motion on the blue side of the systemic maser emission and has the same sign on
the red systemic side. Consequently, the negative optical depth that a line
photon sees as it traverses the masing disk along a path of minimal Keplerian
velocity gradient is larger on the blue side. Note that one is not concerned
here with an overall shift in the maser spectrum caused by the fact that the
masing ring as a whole is located in the black hole's potential well, i.e., it
is the change in the gravitational potential along the gain path that matters.
It is found, for a Schwarzschild metric, that saturation is enhanced
(suppressed) for systemic blue-shifted (red-shifted) maser features by
gravitational redshift of line photons. Approaching peak flux systemic features
are, on average, brighter, due to saturation, and wider (~2 km/s), due to
rebroadening, than their receding counterparts (~1 km/s). The effects are
consistent with observations that span several years, i.e., over periods longer
than needed for disk material to move through the systemic emission region.
Further confirmation of this effect can follow by combining all available
systemic 22 GHz data over the past two decades (abridged).


title: High Mach-number Bondi--Hoyle--Lyttleton flow around a small accretor

abstract:
  In this paper, we discuss a two-dimensional numerical study of isothermal
high Mach number Bondi--Hoyle--Lyttleton flow around a small accretor. The flow
is found to be unstable at high Mach numbers, with the instability appearing
even for a larger accretor. The instability appears to be the unstable radial
mode of the accretion column predicted by earlier analytic work.


title:
Stabilization of helium shell burning by rotation in accreting white
  dwarfs

abstract:
  The currently favored scenario for the progenitor evolution of Type Ia
supernovae (SNe Ia) presumes that white dwarfs in close binary systems grow to
the Chandrasekhar limit via mass accretion from their non-degenerate
companions. However, the accreted hydrogen and/or helium usually participate
thermally unstable or even violent nuclear reactions in a geometrically
confined region, due to the compactness of the white dwarf. Since shell flashes
induced by the thermal instability might induce significant loss of mass,
efficient mass increase of white dwarfs by hydrogen and/or helium accretion has
been seriously questioned. A good understanding of the stability of
thermonuclear shell sources is therefore crucial in order to investigate the
evolution of accreting white dwarfs as SNe Ia progenitors. Here, we present a
quantitative criterion for the thermal stability of thermonuclear shell
sources, and discuss the effects of rotation on the stability of helium shell
burning in helium accreting CO white dwarfs with Mdot \approx 10^{-7} ...
10^{-6} Msun/yr. In particular, we show that, if the effects of rotation are
properly considered, helium shell sources are significantly stabilized, which
might increase the likelihood for accreting white dwarfs to grow to the
Chandrasekhar limit.


title:
Modeling CHANDRA Low Energy Transmission Grating Spectrometer
  Observations of Classical Novae with PHOENIX

abstract:
  We use the PHOENIX code package to model the X-ray spectrum of Nova V4743
Sagittarii observed with the LETGS onboard the Chandra satellite on 19 March
2003. To analyze nova atmospheres and related systems with an underlying
nuclear burning envelope at X-ray wavelengths, it was necessary to update the
code with new microphysics. We demonstrate that the X-ray emission is dominated
by thermal bremsstrahlung and that the hard X-rays are dominated by Fe and N
absorption. Preliminary models are calculated assuming solar abundances. It is
shown that the models can be used to determine element abundances in the nova
ejecta by increasing the absorption in the shell.


title:
The r-mode instability: Analytical solution with gravitational radiation
  reaction

abstract:
  Analytical r-mode solutions are investigated within the linearized theory in
the case of a slowly rotating, Newtonian, barotropic, non-magnetized,
perfect-fluid star in which the gravitational radiation (GR) reaction force is
present. For the GR reaction term we use the 3.5 post-Newtonian order expansion
of the GR force, in order to include the contribution of the current quadrupole
moment. We find the explicit expression for the r-mode velocity perturbations
and we conclude that they are sinusoidal with the same frequency as the
well-known GR force-free linear r-mode solution, and that the GR force drives
the r-modes unstable with a growth timescale that agrees with the expression
first found by Lindblom, Owen and Morsink. We also show that the amplitude of
these velocity perturbations is corrected, relatively to the GR force-free
case, by a term of order W^6, where W is the angular velocity of the star.


title: The Pierre Auger Observatory -Status and Prospects -

abstract:
  The southern Pierre Auger Observatory is presently under construction in
Malargue, Mendoza, Argentina. It combines two complementary air shower
observation techniques; the detection of particles at ground and the
observation of associated fluorescence light generated in the atmosphere above
the ground. Experimentally, this is being realised by employing an array of
1600 water Cherenkov detectors, distributed over an area of 3000 km^2, and
operating 24 wide-angle Schmidt telescopes, positioned at four sites at the
border of the ground array. The Observatory will reach its full size in 2006.
However, with the 540 tanks and 12 telescopes presently in operation, the
Pierre Auger Observatory has become the largest world-wide cosmic ray
experiment already now. This paper sketches the experimental set-up and
discusses the current status. In parallel to the ongoing completion of the
experiment, a large number of events have been detected with energies above
10^19 eV. The data are used to verify both the performance of the individual
detector components as well as to test the quality of the hybrid event
reconstruction. All results obtained so far are very promising and they
underline the great advantages of the chosen hybrid approach.


title: The Decay of Accreting Triple Systems as Brown Dwarf Formation Scenario

abstract:
  We investigate the dynamical decay of non-hierarchical accreting triple
systems and its implications on the ejection model as Brown Dwarf formation
scenario. A modified chain-regularization scheme is used to integrate the
equations of motion, that also allows for mass changes over time as well as for
momentum transfer from the accreted gas mass onto the bodies. We integrate an
ensemble of triple systems within a certain volume with different accretion
rates, assuming several prescriptions of how momentum is transferred onto the
bodies. We follow their evolution until the systems have decayed. We analyze
the end states and decay times of these systems and determine the fraction of
Brown Dwarfs formed, their escape speeds as well as the semi-major axis
distribution of the formed Brown Dwarf binaries. We find that the formation
probability of Brown Dwarfs depends strongly on the assumed momentum transfer
which is related to the motion of the gas. Due to ongoing accretion and
consequent shrinkage of the systems, the median escape velocity is increased by
a factor of 2 and the binary separations are decreased by a factor of 5
compared with non-accreting systems. Furthermore, the obtained semi-major axis
distribution drops off sharply to either side of the median, which is also
supported by observations. We conclude that accretion and momentum transfer of
accreted gas during the dynamical decay of triple systems is able to produce
the observed distribution of close binary Brown Dwarfs, making the ejection
model a viable option as Brown Dwarf formation scenario.


title: On the nature of EXO 0423.4-0840

abstract:
  We present a Chandra observation of the candidate BL Lac object EXO
0423.4-0840. The X-ray emission from EXO 0423.4-0840 is clearly extended, and
is associated with an optical early-type galaxy, MCG-01-12-005, at the centre
of cluster ClG 0422-09. We do not detect a point source which can be associated
with a BL Lac, but we found a small radio source in the centre of
MCG-01-12-005. The cluster gas temperature mapped by the Chandra observation
drops continuously from 80 kpc towards the centre, and is locally single phase.
We measure a metallicity profile which declines outwards with a value 0.8 Z_sun
in the centre, dropping to 0.35 Z_sun at larger radius, which we interpret as a
superposition of cluster gas and a dense interstellar medium (ISM) in the
central galaxy. Although the temperature profile suggests that conduction is
not efficient, the ISM and intra-cluster medium seem not to have mixed. The
entropy profile declines continuously towards the centre, in agreement with
recent results on groups and clusters. The radio source appears to have had
some effect in terms of gas heating, as seen in the small scale (~10 kpc)
entropy core, and the asymmetric hard emission on the same scale.


title: Modelling Alkali Line Absorption and Molecular Bands in Cool DAZs

abstract:
  Two peculiar stars showing an apparent extremely broadened and strong NaI D
absorption have been discovered in surveys for cool white dwarfs by Oppenheimer
et al. (2001) and Harris et al. (SDSS, 2003). We discuss the nature of these
objects using PHOENIX atmosphere models for metal-poor brown dwarfs/very low
mass stars, and new white dwarf LTE and NLTE models for hydrogen- and
helium-dominated atmospheres with metals. These include complete molecular
formation in chemical equilibrium and a model for the alkali resonance line
broadening based on the damping profiles of Allard et al. (2003), as well as
new molecular line opacities for metal hydrides. First results of our
calculations indicate good agreement with a hydrogen-dominated WD atmosphere
with a Na abundance roughly consistent with a state of high accretion. We
analyse deviations of the abundances of Na, K, Mg and Ca from the cosmic
pattern and comment on implications of these results for standard accretion
scenarios.


title: Evolution of oxygen isotopic composition in the inner solar nebula

abstract:
  Changes in the chemical and isotopic composition of the solar nebula with
time are reflected in the properties of different constituents that are
preserved in chondritic meteorites. CR carbonaceous chondrites are among the
most primitive of all chondrite types and must have preserved solar nebula
records largely unchanged. We have analyzed the oxygen and magnesium isotopes
in a range of the CR constituents of different formation temperatures and ages,
including refractory inclusions and chondrules of various types. The results
provide new constraints on the time variation of the oxygen isotopic
composition of the inner (<5 AU) solar nebula - the region where refractory
inclusions and chondrules most likely formed. A chronology based on the decay
of short-lived 26Al (t1/2 ~ 0.73 Ma) indicates that the inner solar nebula gas
was 16O-rich when refractory inclusions formed, but less than 0.8 Ma later, gas
in the inner solar nebula became 16O-poor and this state persisted at least
until CR chondrules formed ~1-2 Myr later. We suggest that the inner solar
nebula became 16O-poor because meter-size icy bodies, which were enriched in
17,18O due to isotopic self-shielding during the ultraviolet photo dissociation
of CO in the protosolar molecular cloud or protoplanetary disk, agglomerated
outside the snowline, drifted rapidly towards the Sun, and evaporated at the
snowline. This led to significant enrichment in 16O-depleted water, which then
spread through the inner solar system. Astronomical studies of the spatial
and/or temporal variations of water abundance in protoplanetary disks may
clarify these processes.


title: Crown Detectors to Observe Horizontal and Upward Air-Showers

abstract:
  Cerenkov Telescopes and Scintillators set on a Crown-like arrays facing the
Horizons may reveal far Cosmic Rays Showers, nearer Anti-Neutrino-Electron +
Electron --> W- shower in air and upgoing Tau Neutrino + N--> tau + X, -->
Shower, Earth-Skimming tau air-showers. Even UHE SUSY Chi + e--> Selectron-->
Chi + e at tens PeVs-EeV energy may blaze at Horizons, as anti-neutrino
electron at Glashow peak - Burst shower. We show first estimate on down and
up-going Horizontal Showers traces for present and future Magic-like Crown
Arrays and their correlated Scintillator-like twin Crown Arrays. The one mono
or stereo-Magic elements facing the Horizons are already comparable to present
Amanda underground neutrino detector.


title:
Observations of the Transient X-ray Pulsar KS 1947+300 by the INTEGRAL
  and RXTE Observatories

abstract:
  We analyze the observations of the X-ray pulsar KS 1947+300 performed by the
INTEGRAL and RXTE observatories over a wide (3-100 keV) X-ray energy range. The
shape of the pulse profile was found to depend on the luminosity of the source.
Based on the model of a magnetized neutron star, we study the characteristics
of the pulsar using the change in its spin-up rate. We estimated the magnetic
field strength of the pulsar and the distance to the binary.


title: Twenty-one centimeter tomography with foregrounds

abstract:
  Twenty-one centimeter tomography is emerging as a powerful tool to explore
the end of the cosmic dark ages and the reionization epoch, but it will only be
as good as our ability to accurately model and remove astrophysical foreground
contamination. Previous treatments of this problem have focused on the angular
structure of the signal and foregrounds and what can be achieved with limited
spectral resolution (bandwidths in the 1 MHz range). In this paper we introduce
and evaluate a ``blind'' method to extract the multifrequency 21cm signal by
taking advantage of the smooth frequency structure of the Galactic and
extragalactic foregrounds. We find that 21 cm tomography is typically limited
by foregrounds on scales $k\ll 1h/$Mpc and limited by noise on scales $k\gg
1h/$Mpc, provided that the experimental bandwidth can be made substantially
smaller than 0.1 MHz. Our results show that this approach is quite promising
even for scenarios with rather extreme contamination from point sources and
diffuse Galactic emission, which bodes well for upcoming experiments such as
LOFAR, MWA, PAST, and SKA.


title: Preliminary analysis of an extreme helium sdO star: BD+25 4655

abstract:
  Preliminary analysis of CCD spectra obtained by the 6m SAO telescope is
presented. We have used simple H-He NLTE model atmospheres computed by TLUSTY
to derive the basic parameters of the star.


title:
The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda I
  and Andromeda III

abstract:
  (Abridged) We present the results of variable star searches of the M31 dwarf
spheroidal companions Andromeda I and Andromeda III using the Hubble Space
Telescope. A total of 100 variable stars were found in Andromeda I, while 56
were found in Andromeda III. One variable found in Andromeda I and another in
Andromeda III may be Population II Cepheids. In addition to this variable in
Andromeda III, another four variables are anomalous Cepheids. We found 72
fundamental mode RR Lyrae stars and 26 first-overtone mode RR Lyrae stars in
Andromdea I giving mean periods of 0.575 day and 0.388 day, respectively. One
likely RR Lyrae was not classified. For Andromeda III, 39 RR Lyrae stars are
pulsating in the fundamental mode with a mean period of 0.657 day and 12 are in
the first-overtone mode with a mean period of 0.402 day. While Andromeda I has
a mean period that is consistent with its metallicity, the mean period of the
fundamental mode RR Lyrae in Andromeda III is larger than expected. In
Andromeda I, we found two RR Lyrae stars which are noticeably fainter than the
horizontal branch. We discuss the possibility that these stars are associated
with the recently discovered stellar stream in the halo of M31. We find
<V_RR>=25.14+/-0.04 mag for Andromeda I resulting in a distance of 765+/-25
kpc. For Andromeda III, <V_RR>=25.01+/-0.04 mag giving a distance of 740+/-20
kpc. The relation between specific frequency of anomalous Cepheids and mean
metallicity of the galaxy in the M31 dwarf spheroidal galaxies follows the same
relation as the Galactic dwarf spheroidal galaxies.


title: Origins of the 1/4 keV Soft X-Ray Background

abstract:
  Snowden and coworkers have presented a model for the 1/4 keV soft X-ray
diffuse background in which the observed flux is dominated by a ~ 10^6 K
thermal plasma located in a 100-300 pc diameter bubble surrounding the Sun, but
has significant contributions from a very patchy Galactic halo. Halo emission
provides about 11% of the total observed flux and is responsible for half of
the H I anticorrelation. The remainder of the anticorrelation is presumably
produced by displacement of disk H I by the varying extent of the local hot
bubble (LHB). The ROSAT R1 and R2 bands used for this work had the unique
spatial resolution and statistical precision required for separating the halo
and local components, but provide little spectral information. Some consistency
checks had been made with older observations at lower X-ray energies, but we
have made a careful investigation of the extent to which the model is supported
by existing sounding rocket data in the Be (73-111 eV) and B bands (115-188 eV)
where the sensitivities to the model are qualitatively different from the ROSAT
bands. We conclude that the two-component model is well supported by the
low-energy data. We find that these combined observations of the local
component may be consistent with single-temperature thermal emission models in
collisional ionization equilibrium if depleted abundances are assumed. However,
different model implementations give significantly different results, offering
little support for the conclusion that the astrophysical situation is so
simple.


title:
Constraining age and metallicity of bulges embedded in low surface
  brightness galaxies

abstract:
  We present results from deep Magellan and VLT long slit optical spectroscopy
for a sample of 19 face-on low surface brightness galaxies (LSBGs) selected
from the sample of Galaz et al. (2002). In particular, we compute Lick/IDS
indices for the light emitted by the bulges hosted by these galaxies. Similar
procedure is performed for a sample of 14 face-on high surface brightness
sample from the sample of Peletier & Balcells (1996). Results indicate that
bulges of LSBGs are metal poorer, compared to those hosted by HSBGs, supporting
the hypothesis that stellar formation rates have been stable low during the
lifetime of these galaxies. We compare our results with those of Bergmann,
Jorgensen & Hill (2003).


title:
Redshifted 21 cm Emission From the Pre-Reionization Era II. HII Regions
  Around Individual Quasars

abstract:
  We use cosmological simulations of reionization to predict the effect of
large HII regions around individual high-redshift quasars on the possible
signal from the redshifted 21cm line of neutral hydrogen in the
pre-reionization era. We show that these HII regions appear as ``spectral
dips'' in frequency space with equivalent widths in excess of 3 mK MHz or
depths in excess of about 1.5 mK, and that they are by far the most prominent
cosmological signals in the redshifted HI distribution.
  These spectral dips are expected to be present in almost every line of sight.
If the spectral dips of a large enough sample of HII regions are well resolved
in frequency space, the distribution of line depth and equivalent width in
frequency with a known observing beamsize can be used to infer the HII region
size distribution and the mean difference in neutral hydrogen density between
the \HII regions (which may contain self-shielded neutral gas clumps) and the
surrounding medium, providing a powerful test for models of reionization.


title: Simultaneous X-ray and Optical Observations of EX Hydrae

abstract:
  The intermediate polar, EX Hydrae, was the object of a large simultaneous
multiwavelength observational campaign during 2000 May - June. Here we present
the Rossi X-ray Timing Explorer photometry and optical photometry and
spectroscopy from ground-based observatories obtained as part of this campaign.
Balmer line radial velocities and Doppler maps provide evidence for an extended
bulge along the outer edge of the accretion disk and some form of
extended/overflowing material originating from the hot spot. In addition, the
optical binary eclipse possesses an extended egress shoulder, an indication
that an additional source (other than the white dwarf) is coming out of
eclipse. We also compare the X-ray and optical results with the results
obtained from the EUV and UV observations from the multiwavelength data set.


title:
The Assembly of Diversity in the Morphologies and Stellar Populations of
  High-Redshift Galaxies

abstract:
  We have studied the evolution in the morphologies, sizes, stellar-masses,
colors, and internal color dispersion (ICD) of galaxies at z=1 and 2.3, using a
near-IR, flux-limited catalog for the HDF-N. At z=1 most luminous galaxies have
morphologies of early-to-mid Hubble-types, and many show transformations
between their rest-frame UV-optical morphologies. Galaxies at z=2.3 have
compact and irregular morphologies with no clearly evident Hubble-sequence
candidates. The mean galaxy size grows from z=2.3 to 1 by 40%, and the density
of galaxies larger than 3 kpc increases by 7 times. At z=1, the size-luminosity
distribution is broadly consistent with that of local galaxies, with passive
evolution. However, galaxies at z=2.3 are smaller than the large present-day
galaxies, and must continue to grow in size and stellar mass. We have measured
the galaxies' UV-optical ICD, which quantifies differences in morphology and
the relative amount of on-going star-formation. The mean and scatter in
galaxies' total colors and ICD increase from z=2.3 to 1. At z=1 many galaxies
with large ICD are spirals, with a few irregular systems. Few z=2.3 galaxies
have high ICD, and those that do are actively merging. We interpret this as
evidence for the presence of older and more diverse stellar populations at z=1
that are not generally present at z>2. We conclude that the star-formation
histories of galaxies at z>2 are dominated by discrete, recurrent bursts, which
quickly homogenize the galaxies' stellar content, and are possibly associated
with mergers. The increase in the stellar-population diversification by z<1.4
implies that merger-induced starbursts occur less frequently than at higher
redshifts, and more quiescent star-forming modes dominate. This transition
coincides with the emergence of Hubble-sequence galaxies. [Abridged]


title: Can Astronomy Manage Its Data?

abstract:
  Astronomy has a distinguished tradition of using technology to accelerate the
quality and effectiveness of science, and data-intensive initiatives such as
the Virtual Observatory lead the way amongst other fields of science. However,
astronomical data are not uniformly well-managed, and our current freedom to
create open-access databases is threatened by those who would like all data to
be subject to strict Intellectual Property controls. We, like other fields of
science, need to establish and agree on a set of guiding principles for the
management of astronomical data.


title: Periodicities of Quasar Redshifts in Large Area Surveys

abstract:
  We test the periodicity of quasar redshifts in the 2dF and SDSS surveys. In
the overall surveys redshift peaks are already apparent in the brighter
quasars. But by analyzing sample areas in detail it is shown that the redshifts
fit very closely the long standing Karlssson formula and strongly suggest the
existence of preferred values in the distribution of quasar redshifts.
  We introduce a powerful new test for groups of quasars of differing redshifts
which not only demonstrates the periodicity of the redshifts, but also their
physical association with a parent galaxy. Further such analyses of the large
area surveys should produce more information on the properties of the
periodicity.


title: Hypervirial Models of Stellar Systems

abstract:
  A family of cusped potential-density pairs is presented for modelling
galaxies and dark haloes. The density profile is cusped like 1/r^(2-p) at small
radii. The distribution function is simple and takes the form L^(p-2)
E^[(3p+1)/2] where E is the binding energy and L is the angular momentum. The
models all possess the remarkable property that the virial theorem holds
locally, from which they earn their name as the hypervirial family. Famously,
this property was first discovered by Eddington to hold for the Plummer model
in 1916. In fact, the seductive properties of the Plummer model extend to the
whole hypervirial family, including the members possessing the cosmologically
important cusps of 1/r or 1/r^1.5 or 1/r^1.33. The intrinsic and projected
properties of the family of models are discussed in some detail.


title: Galaxy Models with Tangentially Anisotropic Velocity Distributions

abstract:
  This paper provides two families of flexible and simple galaxy models.
Representatives of many of the families possess the important cosmological
cusps, with the density behaving like 1/r or 1/r^1.33 or 1/r^1.5 at small
radii. The density falls off between 1/r^3 and 1/r^5 at large radii. We provide
analytic and anisotropic distribution functions for all the models. Unlike many
existing methods, our algorithm can yield tangentially anisotropic velocity
dispersions in the outer parts, and so is useful for modeling populations of
satellite galaxies and substructure in host galaxy halos. As an application, we
demonstrate the degeneracy between mass and anisotropy for the satellite galaxy
population of the Milky Way. This can introduce a factor of ~3 uncertainty in
the mass of the Milky Way as inferred from the kinematics of the satellite
population.


title:
Observations of Solar Flare Doppler Shift Oscillations with the Bragg
  Crystal Spectrometer on Yohkoh

abstract:
  Oscillations in solar coronal loops appear to be a common phenomenon.
Transverse and longitudinal oscillations have been observed with both the
Transition Region and Coronal Explorer and Extreme Ultraviolet Imaging
Telescope imaging experiments. Damped Doppler shift oscillations have been
observed in emission lines from ions formed at flare temperatures with the
Solar Ultraviolet Measurements of Emitted Radiation Spectrometer. These
observations provide valuable diagnostic information on coronal conditions and
may help refine our understanding of coronal heating mechanisms. I have
initiated a study of the time dependence of Doppler shifts measured during
flares with the Bragg Crystal Spectrometer (BCS) on Yohkoh. This Letter reports
the detection of oscillatory behavior in Doppler shifts measured as a function
of time in the emission lines of S XV and Ca XIX. For some flares, both lines
exhibit damped Doppler shift oscillations with amplitudes of a few km/s and
periods and decay times of a few minutes. The observations appear to be
consistent with transverse oscillations. Because the BCS observed continuously
for almost an entire solar cycle, it provides numerous flare data sets, which
should permit an excellent characterization of the average properties of the
oscillations.


title:
Thermal emission from Isolated Neutron Stars and their surface magnetic
  field: going quadrupolar?

abstract:
  In the last few years considerable observational resources have been devoted
to study the thermal emission from isolated neutron stars. Detailed XMM and
Chandra observations revealed a number of features in the X-ray pulse profile,
like asymmetry, energy dependence, and possible evolution of the pulse profile
over a time scale of months or years. Here we show that these characteristics
may be explained by a patchy surface temperature distribution, which is
expected if the magnetic field has a complex structure in which higher order
multipoles contribute together with the dipole. We reconsider these effects
from a theoretical point of view, and discuss their implications to the
observational properties of thermally emitting neutron stars.


title:
Gravitationally lensed radio emission associated with SMM J16359+6612, a
  multiply imaged submillimeter galaxy behind A2218

abstract:
  We report the detection of discrete, lensed radio emission from the multiply
imaged, z=2.516 submillimetre selected galaxy, SMM J16359+6612. All three
images are detected in deep WSRT 1.4 GHz and VLA 8.2 GHz observations, and the
radio positions are coincident with previous sub-mm SCUBA observations of this
system. This is the widest separation lens system to be detected in the radio
so far, and the first time that multiply imaged lensed radio emission has been
detected from a star forming galaxy -- all previous multiply-lensed radio
systems being associated with radio-loud AGN. Taking into account the total
magnification of ~45, the WSRT 1.4 GHz observations suggest a star formation
rate of 500 Solar mass/yr. The source has a steep radio spectrum (alpha -0.7)
and an intrinsic flux density of just 3 microJy at 8.2 GHz. Three other SCUBA
sources in the field are also detected by the WSRT, including SMMJ16359+66118,
a singly imaged (and magnified) arclet at z=1.034. Higher resolution radio
observations of SMMJ16359+6612 (and other highly magnified star forming
galaxies) provide a unique opportunity to study the general properties and
radio morphology of intrinsically faint, distant and obscured star forming
galaxies. They can also help to constrain the technical specification of next
generation radio telescopes, such as the Square Kilometre Array.


title: Galactic Positrons From Localized Sources

abstract:
  The anomalous bump in the cosmic ray positron to electron ratio at $10 GeV$
can be explained as being a component from a point source that was originally
harder than the primary electron background and degrades due to synchrotron and
inverse Compton losses in the Galaxy while propagating to the Earth's vicinity.
The fit is better than can be obtained with homogeneous injection and is
attributed to a minimum age threshold. Annihilating neutralinos can provide a
fair fit to the data if they have a mass just above 1/2 the mass of the $Z^o$
and if they annihilate primarily in distant density concentrations in the
Galaxy. A possible observational consequence of this scenario would be intense
inverse Comptonization of starlight at the Galactic center, with a sharp energy
cutoff in the emergent photons as a possible signature of the neutralino mass.


title: Rapid variability of the arcsec-scale X-ray jets of SS 433

abstract:
  We present the X-ray images of all the available Chandra observations of the
galactic jet source SS 433. We have studied the morphology of the X-ray images
and inspected the evolution of the arcsec X-ray jets, recently found to be
manifestations of in situ reheating of the relativistic gas downstream in the
jets. The Chandra images reveal that the arcsec X-ray jets are not steady long
term structures; the structure varies, indicating that the reheating processes
have no preference for a particular precession phase or distance from the
binary core. Three observations made within about five days in May 2001, and a
60 ks observation made in July 2003 show that the variability of the jets can
be very rapid, from timescales of days to (possibly) hours. The three May 2001
images show two resolved knots in the east jet getting brighter one after the
other, suggesting that a common phenomenon might be at the origin of the
sequential reheatings of the knots. We discuss possible scenarios and propose a
model to interpret these brightenings in terms of a propagating shock wave,
revealing a second, faster outflow in the jet.


title:
Mass Selection Bias in Galaxy Cluster Peculiar Velocities from the
  Kinetic Sunyaev-Zel'dovich Effect

abstract:
  Upcoming surveys for galaxy clusters using the Sunyaev-Zel'dovich effect are
potentially sensitive enough to create a peculiar velocity catalog. The
statistics of these peculiar velocities are sensitive to cosmological
parameters. We develop a method to explore parameter space using N-body
simulations in order to quantify dark matter halo velocity statistics which
will be useful for cluster peculiar velocity observations. We show that mass
selection bias from a kinetic Sunyaev-Zel'dovich velocity catalog forecasts rms
peculiar velocities with a much more complicated Omega_m dependency than
suggested by linear theory. In addition, we show that both two-point functions
for velocities disagree with linear theory predictions out to separations of
approx. 40 Mpc/h. A pedagogical appendix is included developing linear theory
notation with respect to the two-point peculiar velocity functions.


title: Clusters and groups of galaxies in the 2dF galaxy redshift survey

abstract:
  We create a new catalogue of groups and clusters for the 2dF GRS final
release sample. We show that the variable linking length friends-of-friends
(FoF) algorithms used so far yield groups with sizes that grow systematically
with distance from the observer, but FoF algorithms with a constant linking
length are free from this fault. We apply the FoF algorithm with a constant
linking length for the 2dF GRS, compare for each group its potential and
kinetic energies and remove galaxies with excess random velocities. Our sample
contains 7657 groups in the Northern part, and 10058 groups in the Southern
part of the 2dF survey with membership Ng >= 2. We analyze selection effects of
the catalogue and compare our catalogue of groups with other recently published
catalogues based on the 2dF GRS. We also estimate the total luminosities of our
groups, correcting for group members fainter than the observational limit of
the survey. The cluster catalogues are available at our web-site
(http://www.aai.ee/~maret/2dfgr.html)


title: Constraints on the ionizing flux emitted by T Tauri stars

abstract:
  We present the results of an analysis of ultraviolet observations of T Tauri
Stars (TTS). By analysing emission measures taken from the literature we derive
rates of ionizing photons from the chromospheres of 5 classical TTS in the
range ~10^41-10^44 photons/s, although these values are subject to large
uncertainties. We propose that the HeII/CIV line ratio can be used as a
reddening-independent indicator of the hardness of the ultraviolet spectrum
emitted by TTS. By studying this line ratio in a much larger sample of objects
we find evidence for an ionizing flux which does not decrease, and may even
increase, as TTS evolve. This implies that a significant fraction of the
ionizing flux from TTS is not powered by the accretion of disc material onto
the central object, and we discuss the significance of this result and its
implications for models of disc evolution. The presence of a significant
ionizing flux in the later stages of circumstellar disc evolution provides an
important new constraint on disc photoevaporation models.


title:
Photometric Confirmation of MACHO Large Magellanic Cloud Microlensing
  Events

abstract:
  We present previously unpublished photometry of three Large Magellanic Cloud
(LMC) microlensing events and show that the new photometry confirms the
microlensing interpretation of these events. These events were discovered by
the MACHO Project alert system and were also recovered by the analysis of the
5.7 year MACHO data set. This new photometry provides a substantial increase in
the signal-to-noise ratio over the previously published photometry and in all
three cases, the gravitational microlensing interpretation of these events is
strengthened. The new data consist of MACHO-Global Microlensing Alert Network
(GMAN) follow-up images from the CTIO 0.9 telescope plus difference imaging
photometry of the original MACHO data from the 1.3m "Great Melbourne" telescope
at Mt. Stromlo. We also combine microlensing light curve fitting with
photometry from high resolution HST images of the source stars to provide
further confirmation of these events and to show that the microlensing
interpretation of event MACHO-LMC-23 is questionable. Finally, we compare our
results with the analysis of Belokurov, Evans & Le Du who have attempted to
classify candidate microlensing events with a neural network method, and we
find that their results are contradicted by the new data and more powerful
light curve fitting analysis for each of the four events considered in this
paper. The failure of the Belokurov, Evans & Le Du method is likely to be due
to their use of a set of insensitive statistics to feed their neural networks.


title:
Evolutionary constraints on the masses of the components of HDE
  226868/Cyg X-1 binary system

abstract:
  Calculations carried out to model the evolution of HDE 226868, under
different assumptions about the stellar wind mass loss rate, provide robust
limits on the present mass of the star. It has to be in the range 40 +- 5 solar
masses if the distance to the system is in the range 1.95 to 2.35 kpc and the
effective temperature of HDE 226868 in the range 30000 to 31000 K. Extending
the possible intervals of these parameters to 1.8 to 2.35 kpc and 28000 to
32000 K, one gets for the mass of the star the range 40 +- 10 solar masses.
Including into the analysis observational properties such as the profiles of
the emission lines, rotational broadening of the absorption lines and the
ellipsoidal light variations, one can estimate also the mass of the compact
component. It has to be in the ranges 20 +- 5 solar masses and 13.5 to 29 solar
masses for the cases described above. The same analysis (using the evolutionary
models and the observational properties listed above) yields lower limit to the
distance to the system of about 2.0 kpc, if the effective temperature of HDE
226868 is higher than 30000 K. This limit to the distance does not depend on
any photometric or astrometric considerations.


title: A Spitzer Study of Dusty Disks in the Scorpius-Centaurus OB Association

abstract:
  We have obtained Spitzer Space Telescope MIPS observations of 40 F- and
G-type common proper motion members of the Scorpius-Centaurus OB Association
with ages between 5 and 20 Myr at 24 micron and 70 micron. We report the
detection of fourteen objects which possess 24 micron fluxes >30% larger than
their predicted photospheres, tentatively corresponding to a disk fraction of
>35%, including seven objects which also possess 70 micron excesses >100 times
larger than their predicted photospheres. The 24 micron plus 70 micron excess
sources possess high fractional infrared luminosities, LIR/L* = 7.0e-4 -
3.0e-3; either they possess optically thin, dusty beta Pictoris-like disks or
compact, opaque HD 98800-like disks.


title: Dark-Energy Evolution Across the Cosmological-Constant Boundary

abstract:
  We explore the properties of dark energy models for which the
equation-of-state, w, defined as the ratio of pressure to energy density,
crosses the cosmological-constant boundary w = -1. We adopt an empirical
approach, treating the dark energy as an uncoupled fluid or a generalized
scalar field. We describe the requirements for a viable model, in terms of the
equation-of-state and sound speed. A generalized scalar field cannot safely
traverse w = -1, although a pair of scalars with w > -1 and w < -1 will work. A
fluid description with a well-defined sound speed can also cross the boundary.
Contrary to expectations, such a crossing model does not instantaneously
resemble a cosmological constant at the moment w = -1 since the density and
pressure perturbations do not necessarily vanish. But because a dark energy
with w < -1 dominates only at very late times, and because the dark energy is
not generally prone to gravitational clustering, then crossing the
cosmological-constant boundary leaves no distinct imprint.


title:
X-ray Luminosity and Absorption Column Fluctuations in the H2O Maser
  Galaxy NGC 4258 from Weeks to Years

abstract:
  We report monitoring of the 0.3-10 keV spectrum of NGC4258 with XMM over 1.5
years.We als o report reprocessing of an overlapping series of archival Chandra
observations. By including earlier ASCA and SAX observations, we present a new,
nine-year time series of models fit to the X-ray spectrum of NGC4258. Over the
nine years, the photoelectric absorbing column (~10^23 cm^-2) did not vary
detectably, except for a ~40% drop between two ASCA epochs separated by 3 years
and a ~60% rise between two XMM epochs separated by just 5 months. In contrast,
factor of 2-3 changes are seen in absorbed flux on the timescale of years.
These are uncorrelated with changes in absorbing column and indicative of
central engine variability. The most rapid change in luminosity (5-10 keV) that
we detect is ~30% over 19 days. The warped disk, a known source of H2O maser
emission in NGC4258, is believed to cross the line of sight to the central
engine. We propose that the variations in absorbing column arise from
inhomogeneities sweeping across the line of sight in the rotating disk at the
radius where the disk crosses the line of sight. We estimate that the
inhomogeneities are ~10^15 cm in size at the crossing radius of 0.29 pc,
slightly smaller than the expected scale height of the disk. This result thus
provides strong evidence that the warped accretion disk is the absorber. This
is the first direct confirmation that obscuration in type-2 AGN may, in some
cases, arise in thin, warped accretion disks, rather than in geometrically
thick tori. We do not detect Fe Kalpha line emission in any of our XMM spectra.
We do not observe evidence of absorption lines in the XMM or reprocessed
Chandra data.


title: Emission-line profile modelling of structured T Tauri magnetospheres

abstract:
  We present hydrogen emission line profile models of magnetospheric accretion
onto Classical T Tauri stars. The models are computed under the Sobolev
approximation using the three-dimensional Monte Carlo radiative-transfer code
TORUS. We have calculated four illustrative models in which the accretion flows
are confined to azimuthal curtains - a geometry predicted by
magneto-hydrodynamical simulations. Properties of the line profile variability
of our models are discussed, with reference to dynamic spectra and
cross-correlation images. We find that some gross characteristics of observed
line profile variability are reproduced by our models, although in general the
level of variability predicted is larger than that observed. We conclude that
this excessive variability probably excludes dynamical simulations that predict
accretion flows with low degrees of axisymmetry.


title:
Can We Probe the Atmospheric Composition of an Extrasolar Planet from
  its Reflection Spectrum in a High-Magnification Microlensing Event?

abstract:
  We revisit the possibility of detecting an extrasolar planet around a
background star as it crosses the fold caustic of a foreground binary lens.
During such an event, the planet's flux can be magnified by a factor of ~100 or
more. The detectability of the planet depends strongly on the orientation of
its orbit relative to the caustic. If the source star is inside the
inter-caustic region, detecting the caustic-crossing planet is difficult
against the magnified flux of its parent star. In the more favorable
configuration, when the star is outside the inter-caustic region when the
planet crosses the caustic, a close-in Jupiter-like planet around a Sun-like
star at a distance of 8 kpc is detectable in 8-minute integrations with a 10m
telescope at maximal S/N~15 for phase angle ~10 degrees. In this example, we
find further that the presence of methane, at its measured abundance in
Jupiter, and/or water, sodium and potassium, at the abundances expected in
theoretical atmosphere models of close-in Jupiters, could be inferred from a
non-detection of the planet in strong broad absorption bands at 0.6-1.4 microns
caused by these compounds, accompanied by a S/N~10 detection in adjacent bands.
We conclude that future generations of large telescopes might be able to probe
the composition of the atmospheres of distant extrasolar planets.


title: A Study of Synthetic and Observed H_alpha Spectra of TT Hydrae

abstract:
  The formation and properties of accretion discs and circumstellar material in
Algol-type systems is not very well understood. In order to study the
underlying physics of these structures, we have calculated synthetic Halpha
spectra of TT Hya, which is an Algol-type eclipsing binary with an accretion
disc. Both the primary and secondary stars were considered in the calculations
as well as a disc surrounding the primary. The Roche model for the secondary
star was assumed. The synthetic spectra cover all the phases including primary
eclipse and are compared with the observed spectra. The influence of various
effects and free parameters of the disc on the emerging spectrum was studied.
This enabled us to put some constraints on the geometry, temperature, density
and velocity fields within the disc. Differences found between the observed and
synthetic spectra unravel the existence of a gas stream as well as a hotter
disc-gas interaction region. An additional cooler circumstellar region between
the C1 and C2 Roche surfaces is suggested to account for various observed
effects. A new computer code called {\sc{shellspec}} was created for this
purpose and is briefly described in this work as well. It is designed to solve
simple radiative transfer along the line of sight in 3D moving media. The
scattered light from a central object is taken into account assuming an
optically thin environment. Output intensities are then integrated through the
2D projection surface of a 3D object. The assumptions of the code include LTE
and optional known state quantities and velocity fields in 3D.


title:
Phase Functions and Light Curves of Wide Separation Extrasolar Giant
  Planets

abstract:
  We calculate self-consistent extrasolar giant planet (EGP) phase functions
and light curves for orbital distances ranging from 0.2 AU to 15 AU. We explore
the dependence on wavelength, cloud condensation, and Keplerian orbital
elements. We find that the light curves of EGPs depend strongly on wavelength,
the presence of clouds, and cloud particle sizes. Furthermore, the optical and
infrared colors of most EGPs are phase-dependent, tending to be reddest at
crescent phases in $V-R$ and $R-I$. Assuming circular orbits, we find that at
optical wavelengths most EGPs are 3 to 4 times brighter near full phase than
near greatest elongation for highly-inclined (i.e., close to edge-on) orbits.
Furthermore, we show that the planet/star flux ratios depend strongly on the
Keplerian elements of the orbit, particularly inclination and eccentricity.
Given a sufficiently eccentric orbit, an EGP's atmosphere may make periodic
transitions from cloudy to cloud-free, an effect that may be reflected in the
shape and magnitude of the planet's light curve. Such elliptical orbits also
introduce an offset between the time of the planet's light curve maximum and
the time of full planetary phase, and for some sets of orbital parameters, this
light curve maximum can be a steeply increasing function of eccentricity. We
investigate the detectability of EGPs by proposed space-based direct-imaging
instruments.


title: The SDSS u-band Galaxy Survey: Luminosity functions and evolution

abstract:
  We construct and analyze a u-band selected galaxy sample from the SDSS
Southern Survey, which covers 275 sq. deg. The sample includes 43223 galaxies
with spectroscopic redshifts in the range 0.005<z<0.3 and with 14.5<u<20.5. The
S/N in the u-band Petrosian aperture is improved by coadding multiple epochs of
imaging data and by including sky-subtraction corrections. Luminosity functions
for the near-UV ^{0.1}u band (322+-26 nm) are determined in redshift slices of
width 0.02, which show a highly significant evolution in M^{star} of -0.8+-0.1
mag between z=0 and 0.3; with M^{star} = -18.84+-0.05 (AB mag), log phi^{star}
= -2.06+-0.03 (Mpc^{-3}) and log rho_L = 19.11+-0.02 (W Hz^{-1} Mpc^{-3}) at
z=0.1. The faint-end slope determined for z<0.06 is given by alpha=-1.05+-0.08.
This is in agreement with recent determinations from GALEX at shorter
wavelengths. Comparing our z<0.3 luminosity density measurements with 0.2<z<1.2
from COMBO-17, we find that the 280-nm density evolves as rho_L proportional to
(1+z)^{beta} with beta=2.1+-0.2; and find no evidence for any change in slope
over this redshift range. By comparing with other measurements of cosmic star
formation history, we estimate that the effective dust attenuation at 280 nm
has increased by 0.8+-0.3 mag between z=0 and 1.


title: The EBEX Experiment

abstract:
  EBEX is a balloon-borne polarimeter designed to measure the intensity and
polarization of the cosmic microwave background radiation. The measurements
would probe the inflationary epoch that took place shortly after the big bang
and would significantly improve constraints on the values of several
cosmological parameters. EBEX is unique in its broad frequency coverage and in
its ability to provide critical information about the level of polarized
Galactic foregrounds which will be necessary for all future CMB polarization
experiments. EBEX consists of a 1.5 m Dragone-type telescope that provides a
resolution of less than 8 arcminutes over four focal planes each of 4 degree
diffraction limited field of view at frequencies up to 450 GHz. The experiment
is designed to accommodate 330 transition edge bolometric detectors per focal
plane, for a total of up to 1320 detectors. EBEX will operate with frequency
bands centered at 150, 250, 350, and 450 GHz. Polarimetry is achieved with a
rotating achromatic half-wave plate. EBEX is currently in the design and
construction phase, and first light is scheduled for 2008.


title:
Phase Transition Between superfluid and Normal states of Neutrons in
  Neutron Stars--The Origin of Glitches of Pulsars

abstract:
  Starting from a neutron star heating mechanism by the magnetic dipole
radiation from the 3^P_2 neutron superfluid vortices in neutron stars, we
propose a neutron phase oscillation model which describes the phase transition
between the normal neutron Fermi fluid and the 3^P_2 neutron superfluid
vortices at the transition temperature of T_{trans}=(5-6)\times 10^8 K. With
this model, we can give qualitative explanation to most of the pulsar glitches
observed up to date.


title: An Empirical Calibration of the Completeness of the SDSS Quasar Survey

abstract:
  Spectra of nearly 20000 point-like objects to a Galactic reddening corrected
magnitude of i=19.1 have been obtained to test the completeness of the SDSS
quasar survey. The spatially-unresolved objects were selected from all regions
of color space, sparsely sampled from within a 278 sq. deg. area of sky covered
by this study. Only ten quasars were identified that were not targeted as
candidates by the SDSS quasar survey (including both color and radio source
selection). The inferred density of unresolved quasars on the sky that are
missed by the SDSS algorithm is 0.44 per sq. deg, compared to 8.28 per sq. deg.
for the selected quasar density, giving a completeness of 94.9(+2.6,-3.8) to
the limiting magnitude. Omitting radio selection reduces the color-only
selection completeness by about 1%. Of the ten newly identified quasars, three
have detected broad absorption line systems, six are significantly redder than
other quasars at the same redshift, and four have redshifts between 2.7 and 3.0
(the redshift range where the SDSS colors of quasars intersect the stellar
locus). The fraction of quasars missed due to image defects and blends is
approximately 4%, but this number varies by a few percent with magnitude.
Quasars with extended images comprise about 6% of the SDSS sample, and the
completeness of the selection algorithm for extended quasars is approximately
81%, based on the SDSS galaxy survey. The combined end-to-end completeness for
the SDSS quasar survey is approximately 89%. The total corrected density of
quasars on the sky to i=19.1 is estimated to be 10.2 per sq. deg.


title:
Relativistic Corrections to the Sunyaev-Zeldovich Effect for Clusters of
  Galaxies. V. Effect of the Motion of the Observer

abstract:
  We extend the formalism of the relativistic thermal and kinematical
Sunyaev-Zeldovich effects to the observer's system (the Solar System) moving
with a velocity $\beta_{S}$ with respect to the cosmic microwave background
radiation. We confirm the results recently obtained by Chluba, Huetsi, and
Sunyaev in the lowest order of the observer's velocity $\beta_{S}. We give a
more general analytic expression for the thermal and kinematical
Sunyaev-Zeldovich effects corresponding to the observer's system with the power
series expansion approximation in terms of $\theta_{e}$. It is found that the
effect of the motion of the observer on the Sunyaev-Zeldovich effect will
become important in the future high precision observation projects of the
Sunyaev-Zeldovich effect.


title: CMBR Constraint on a Modified Chaplygin Gas Model

abstract:
  In this paper, a modified Chaplygin gas model of unifying dark energy and
dark matter with exotic equation of state $p=B\rho-\frac{A}{\rho^{\alpha}}$
which can also explain the recent accelerated expansion of the universe is
investigated by the means of constraining the location of the peak of the CMBR
spectrum. We find that the result of CMBR measurements does not exclude the
nonzero value of parameter $B$, but allows it in the range $-0.35\lesssim
B\lesssim0.025$.


title: A comprehensive range of X-ray ionized reflection models

abstract:
  X-ray ionized reflection occurs when a surface is irradiated with X-rays so
intense that its ionization state is determined by the ionization parameter xi
propto F/n, where F is the incident flux and n the gas density. It occurs in
accretion, onto compact objects including black holes in both active galaxies
and stellar-mass binaries, and possibly in gamma-ray bursts. Computation of
model reflection spectra is often time-consuming. Here we present the results
from a comprehensive grid of models computed with our code, which has now been
extended to include what we consider to be all energetically-important
ionization states and transitions. This grid is being made available as an
ionized-reflection model, REFLION, for XSPEC.


title: Emission line galaxies in clusters

abstract:
  At the present epoch, clusters of galaxies are known to be a hostile
environment for emission-line galaxies, which are more commonly found in low
density regions outside of clusters. In contrast, going to higher redshifts the
population of emission-line galaxies in clusters becomes progressively more
conspicuous, and large numbers of star-forming late-type galaxies are observed.
I present an overview of the observational findings and the theoretical
expectations regarding the evolution of emission-line galaxies in dense
environments, discussing the properties of these galaxies and the current
evidence for environmental influences on their evolution.


title: On the composition of ices incorporated in Ceres

abstract:
  We use the clathrate hydrate trapping theory (Lunine & Stevenson 1985) and
the gas drag formalism of Weidenschilling (1977) to calculate the composition
of ices incorporated in the interior of Ceres. In the spirit of the work of Cyr
et al. (1998), and using a time dependent solar nebula model, we show that icy
solids can drift from beyond 5 AU to the present location of the asteroid and
be preserved from vaporization. We argue that volatiles were trapped in the
outer solar nebula under the forms of clathrate hydrates, hydrates and pure
condensates prior to having been incorporated in icy solids and subsequently in
Ceres. Under the assumption that most of volatiles were not vaporized during
the accretion phase and the thermal evolution of Ceres, we determine the per
mass abundances with respect to H2O of CO2, CO, CH4, N2, NH3, Ar, Xe, and Kr in
the interior of the asteroid. The Dawn space mission, scheduled to explore
Ceres in August 2014 (Russel et al. 2004), may have the capacity to test some
predictions. We also show that an in situ measurement of the D/H ratio in H2O
in Ceres could constrain the distance range in the solar nebula where its icy
planetesimals were produced.


title: Expanding advanced civilizations in the universe

abstract:
  The 1950 lunch-table remark by Enrico Fermi `Where is everybody' has started
intensive scientific and philosophical discussions about what we call nowadays
the `Fermi paradox': If there had been ever a single advanced civilization in
the cosmological history of our galaxy, dedicated to expansion, it would have
had plenty of time to colonize the entire galaxy via exponential growth. No
evidence of present or past alien visits to earth are known to us, leading to
the standard conclusion that no advanced expanding civilization has ever
existed in the milky-way \cite{Webb}. This conclusion rest fundamentally on the
ad-hoc assumption, that any alien civilizations dedicated to expansion at one
time would remain dedicated to expansions forever. Considering our limited
knowledge about alien civilizations we need however to relax this basic
assumption. Here we show that a substantial and stable population of expanding
advanced civilization might consequently exist in our galaxy.


title:
Spectroscopy of GRB 021004: a structured jet ploughing through a massive
  stellar wind

abstract:
  We present spectra of the afterglow of GRB 021004 taken with WHT ISIS and VLT
FORS1 at three epochs spanning 0.49--6.62 days after the burst. We observe
strong absorption likely coming from the host galaxy, alongside absorption in
HI, SiIV and CIV with blueshifts of up to 2900 km/s from the explosion centre
which we assume originates close to the progenitor. We find no significant
variability of these spectral features. We investigate the origin of the
outflowing material and evaluate various possible progenitor models. The most
plausible explanation is that these result in the fossil stellar wind of a
highly evolved Wolf-Rayet star. However, ionization from the burst itself
prevents the existence of HI, SiIV and CIV close to the afterglow surface where
the fast stellar wind should dominate, and large amounts of blueshifted
hydrogen are not expected in a Wolf-Rayet star wind. We propose that the
Wolf-Rayet star wind is enriched by a hydrogen-rich companion, and that the GRB
has a structured jet geometry in which the gamma rays emerge in a small opening
angle within the wider opening angle of the cone of the afterglow. This
scenario is able to explain both the spectral line features and the irregular
light curve of this afterglow.


title:
Physical implications of INTEGRAL/SPI gamma-ray line measurements of the
  2003 October 28 solar flare

abstract:
  The very powerful X-class solar flare of 2003 October 28 was detected with
the INTEGRAL spectrometer as an intense gamma-ray flash of about 15 minutes.
Despite the non-standard incidence of the solar gamma-rays, time-resolved
spectra including several nuclear gamma-ray lines were obtained. Such a
measurement with a high-energy-resolution instrument can provide valuable
information of the isotopic abundances of the ambient solar material, as well
as the composition, directionality and energy spectra of the accelerated
nuclei. First results on the measured gamma-ray line ratios and time history of
the neutron-capture line are presented.


title:
Simultaneous X-ray and UV spectroscopy of the Seyfert 1 galaxy NGC
  5548.II. Physical conditions in the X-ray absorber

abstract:
  We present the results from a 500 ks Chandra observation of the Seyfert 1
galaxy NGC 5548. We detect broadened emission lines of O VII and C VI in the
spectra, similar to those observed in the optical and UV bands. The source was
continuously variable, with a 30 % increase in luminosity in the second half of
the observation. No variability in the warm absorber was detected between the
spectra from the first 170 ks and the second part of the observation. The
velocity structure of the X-ray absorber is consistent with the velocity
structure measured simultaneously in the ultraviolet spectra. We find that the
highest velocity outflow component, at -1040 km/s, becomes increasingly
important for higher ionization parameters. This velocity component spans at
least three orders of magnitude in ionization parameter, producing both highly
ionized X-ray absorption lines (Mg XII, Si XIV) as well as UV absorption lines.
A similar conclusion is very probable for the other four velocity components.
Based upon our observations, we argue that the warm absorber probably does not
manifest itself in the form of photoionized clumps in pressure equilibrium with
a surrounding wind. Instead, a model with a continuous distribution of column
density versus ionization parameter gives an excellent fit to our data. From
the shape of this distribution and the assumption that the mass loss through
the wind should be smaller than the accretion rate onto the black hole, we
derive upper limits to the solid angle as small as 10^{-4} sr. From this we
argue that the outflow occurs in density-stratified streamers. The density
stratification across the stream then produces the wide range of ionization
parameter observed in this source. Abridged.


title:
INTEGRAL/IBIS search for e-e+ annihilation radiation from the Galactic
  Center Region

abstract:
  Electron-positron annihilation radiation from the Galactic Center region has
been detected since the seventies, but its astrophysical origin is still a
topic of a scientific debate. We have analyzed data of the gamma-ray imager
IBIS/ISGRI onboard of ESA's INTEGRAL platform in the e$^{-}$e$^{+}$ line.
During the first year of the missions Galactic Center Deep Exposure no evidence
for point sources at 511 keV has been found in the ISGRI data; the $2 \sigma$
upper limit for resolved single point sources is estimated to be $1.6\times
10^{-4} ph cm^{-2} s^{-1}$.


title: Ultra-high energy cosmic ray propagation in the Universe

abstract:
  This paper summarizes recent developments in the study of the propagation of
ultra-high energy cosmic ray protons or nuclei in the Universe, with emphasis
on the consequences of energy losses and on the influence of extra-galactic
magnetic fields.


title:
The s-process weak component: uncertainties due to convective
  overshooting

abstract:
  Using a new s-nucleosynthesis code, coupled with the stellar evolution code
Star2003, we performed simulations to study the impact of the convection
treatment on the s-process during core He-burning of a 25 Msun star (ZAMS mass)
with an initial metallicity of Z=0.02. Particular attention was devoted to the
impact of the extent of overshooting on the s-process efficiency. The results
show enhancements of about a factor 2-3 in s-process efficiency (measured as
the average overproduction factor of the 6 s-only nuclear species with
$60\lesssim A\lesssim 90$) with overshooting parameter values in the range
0.01-0.035, compared to results obtained with the same model but without
overshooting. The impact of these results on the p-process model based on type
II supernovae is discussed.


title:
Measured Cosmological Mass Density in the WHIM: the Solution to the
  'Missing Baryons' Problem

abstract:
  We review the current high-significance X-ray detections of Warm-Hot
Intergalactic Medium (WHIM) filaments at z>0 along the lines of sight to the
two blazars Mrk 421 (z=0.03) and 1ES 1028+511 (z=0.361). For these WHIM
filaments, we derive ionization corrections and, when possible, metallicity
estimates. This allows us to obtain refined estimates of the number density of
O VII WHIM systems down to the O VII column density sensitivity of our
observations, and most importantly, a measurement of the cosmological mass
density Omega_b^{WHIM} in the WHIM, at redshift z<0.361. These estimates agree
well with model predictions and with the total estimated amount of missing
baryons in the local Universe, although errors are large, due to the still
limited number of systems. We conclude discussing future observational
strategies and mission designs for WHIM studies.


title: Centrally Condensed Collapse of Starless Cores

abstract:
  Models of self-gravitating gas in the early stages of pressure-free collapse
are compared for initial states which are equilibrium layers, cylinders, and
Bonnor-Ebert spheres. For each geometrical case the density profile has an
inner region of shallow slope surrounded by an outer region of steep slope, and
the profile shape during early collapse remains similar to the profile shape of
the initial equilibrium. The two-slope density structure divides the spherical
collapse history into a starless infall phase and a protostellar accretion
phase. The similarity of density profiles implies that Bonnor-Ebert fits to
observed column density maps may not distinguish spherical cores from oblate or
prolate cores, and may not distinguish static cores from collapsing cores. The
velocity profiles discriminate better than the density profiles between initial
geometries and between collapse ages. The infall velocity generally has a
subsonic maximum value, which is approximately equal to the initial velocity
dispersion times the ratio of collapse age to central free-fall time.
  Observations of starless core line profiles constrain collapse models.
Collapse from initial states which are strongly condensed and slightly prolate
is consistent with infall asymmetry observed around starless cores, and is more
consistent than collapse from initial states which are weakly condensed, and/or
oblate. Spherical models match observed inward speeds 0.05-0.09 km/s over
0.1-0.2 pc, if the collapse has a typical age 0.3-0.5 free fall times, and if
it began from a centrally condensed state which was not in stable equilibrium.
In a collapsing core, optically thin line profiles should broaden and develop
two-peak structure as seen in L1544.


title:
Chemical Constraints on the Water and Total Oxygen Abundances in the
  Deep Atmosphere of Saturn

abstract:
  Thermochemical equilibrium and kinetic calculations for the trace gases CO,
PH3, and SiH4 give three independent constraints on the water and total oxygen
abundances of Saturn's deep atmosphere. A lower limit to the water abundance of
H2O/H2 > 1.7 x 10^-3 is given by CO chemistry while an upper limit of H2O/H2 <
5.5 x 10^-3 is given by PH3 chemistry. A combination of the CO and PH3
constraints indicates a water enrichment on Saturn of 1.9 to 6.1 times the
solar system abundance (H2O/H2 = 8.96 x 10^-4). The total oxygen abundance must
be at least 1.7 times the solar system abundance (O/H2 = 1.16 x 10^-3) in order
for the SiH4 to remain below a detection limit of SiH4/H2 < 2 x 10^-10. A
combination of the CO, PH3, and SiH4 constraints suggests that the total oxygen
abundance on Saturn is 3.2 to 6.4 times the solar system abundance. Our results
indicate that oxygen on Saturn is less enriched than other heavy elements (such
as C and P) relative to a solar system composition. This work was supported by
NASA NAG5-11958.


title: The discrepancy between solar abundances and helioseismology

abstract:
  There have been recent downward revisions of the solar photospheric
abundances of Oxygen and other heavy elements. These revised abundances along
with OPAL opacities are not consistent with seismic constraints. In this work
we show that the recently released OP opacity tables cannot resolve this
discrepancy either. While the revision in opacities does not seem to resolve
this conflict, an upward revision of Neon abundance in solar photosphere offers
a possible solution to this problem.


title: Inflationary Perturbations and Precision Cosmology

abstract:
  Inflationary cosmology provides a natural mechanism for the generation of
primordial perturbations which seed the formation of observed cosmic structure
and lead to specific signals of anisotropy in the cosmic microwave background
radiation. In order to test the broad inflationary paradigm as well as
particular models against precision observations, it is crucial to be able to
make accurate predictions for the power spectrum of both scalar and tensor
fluctuations. We present detailed calculations of these quantities utilizing
direct numerical approaches as well as error-controlled uniform approximations,
comparing with the (uncontrolled) traditional slow-roll approach. A simple
extension of the leading-order uniform approximation yields results for the
power spectra amplitudes, the spectral indices, and the running of spectral
indices, with accuracy of the order of 0.1% - approximately the same level at
which the transfer functions are known. Several representative examples are
used to demonstrate these results.


title: The Evolution of Binary Fractions in Globular Clusters

abstract:
  We study the evolution of binary stars in globular clusters using a new Monte
Carlo approach combining a population synthesis code (StarTrack), and a simple
treatment of dynamical interactions in the dense cluster core using a new tool
for computing 3-body and 4-body interactions (Fewbody). We find that the
combination of stellar evolution and dynamical interactions (binary-single and
binary-binary) leads to a rapid depletion of the binary population in the
cluster core. The maximum binary fraction today in the core of a typical dense
cluster like 47 Tuc, assuming an initial binary fraction of 100%, is only about
5-10%. We show that this is in good agreement with recent HST observations of
close binaries in the core of 47 Tuc, provided that a realistic distribution of
binary periods is used to interpret the results. Our findings also have
important consequences for the dynamical modeling of globular clusters,
suggesting that ``realistic models'' should incorporate much larger initial
binary fractions than has usually been done in the past.


title: Finding Clusters in SZ Surveys

abstract:
  We use simulated maps to investigate the ability of high resolution, low
noise surveys of the CMB to create catalogues of Clusters of galaxies by
detecting the characteristic signature imprinted by the Sunyaev Zeldovich
effect. We compute the completeness of the catalogues in our simulations for
several survey strategies, and evaluate the relative merit of some Fourier and
wavelet based filtering techniques.


title: Ultrahigh energy cosmic rays from collisional annihilation revisited

abstract:
  We re-examine collisional annihilation of superheavy dark matter particles in
dark matter density spikes in the galactic halo as a possible source of
ultrahigh energy cosmic rays. We estimate the possible flux in a way that does
not depend on detailed assumptions about the density profiles of dark matter
clumps. The result confirms that collisional annihilation is compatible with
annihilation cross sections below the unitarity bounds for superheavy dark
matter if the particles can form dense cores in dark matter substructure, and
it provides estimates for core sizes and densities. The ensuing clumpy source
distribution in the galactic halo will be tested within a few years of
operation of the Pierre Auger observatory.


title: Sensitive VLBI Observations of the z = 4.7 QSO BRI 1202-0725

abstract:
  We present sensitive phase-referenced VLBI results on the radio continuum
emission from the z=4.7 double source BRI 1202-0725. The observations were
carried out at 1425 MHz using the Very Long Baseline Array (VLBA), the phased
Very Large Array (VLA), and the Green Bank Telescope (GBT). Our sensitive VLBI
images of BRI 1202-0725 at 0.25 x 0.14 arcsec resolution show a continuum
structure in each of its two components. Fitting Gaussian models to these
continuum structures yield total flux densities of 315 +/- 38 and 250 +/- 39
microJy, for the northern and the southern components, respectively. The
estimated intrinsic brightness temperatures of these continuum structures are
about 2 x 10^4 K. Neither component is detected at the full VLBI resolution (29
mas x 7 mas), with a 4 sigma point source upper limit of 40 microJy/beam, or an
upper limit to the intrinsic brightness temperature of 6.7 x 10^5 K. The
highest angular resolution with at least a 4sigma detection is about 85 mas. At
this resolution, the images reveal a single continuum feature in the northern
component of BRI 1202-0725, and two continuum features in the southern
component, separated by 320 mas. This is similar to the structures seen in the
high resolution images of the CO emission. The extent of the observed continuum
sources at 1.4 GHz and the derived brightness temperatures are consistent with
nuclear starbursts. Moreover, the absence of any compact high-brightness
temperature source suggests that thereis no radio-loud AGN in BRI 1202-0725.


title: Statistical Confirmation of a Stellar Upper Mass Limit

abstract:
  We derive the expectation value for the maximum stellar mass (m_max) in an
ensemble of N stars, as a function of the IMF upper-mass cutoff (m_up) and N.
We statistically demonstrate that the upper IMF of the local massive star
census observed thus far in the Milky Way and Magellanic Clouds clearly
exhibits a universal upper mass cutoff around 120 - 200 M_sun for a Salpeter
IMF, although the result is more ambiguous for a steeper IMF.


title: Hierarchical Triggering of Star Formation by Superbubbles in W3/W4

abstract:
  It is generally believed that expanding superbubbles and mechanical feedback
from massive stars trigger star formation, because there are numerous examples
of superbubbles showing secondary star formation at their edges. However, while
these systems show an age sequence, they do not provide strong evidence of a
causal relationship. The W3/W4 Galactic star-forming complex suggests a
three-generation hierarchy: the supergiant shell structures correspond to the
oldest generation; these triggered the formation of IC 1795 in W3, the
progenitor of a molecular superbubble; which in turn triggered the current
star-forming episodes in the embedded regions W3-North, W3-Main, and W3-OH. We
present UBV photometry and spectroscopic classifications for IC 1795, which
show an age of 3 - 5 Myr. This age is intermediate between the reported 6 - 20
Myr age of the supergiant shell system, and the extremely young ages (10^4 -
10^5 yr) for the embedded knots of ultracompact HII regions, W3-North, W3-Main,
and W3-OH. Thus, an age sequence is indeed confirmed for the entire W3/W4
hierarchical system. This therefore provides some of the first convincing
evidence that superbubble action and mechanical feedback are indeed a
triggering mechanism for star formation.


title:
The Effects of Radiative Cooling on the Entropy Distribution of
  Intracluster Gas

abstract:
  High resolution X-ray observations indicate that the entropy profiles in the
central regions of some massive cooling flow clusters are well approximated by
powerlaws. McCarthy and coworkers recently accounted for this trend with an
analytic model that includes the detailed effects of radiative cooling.
Interestingly, these authors found that cooling (and subsequent inflow of the
gas) naturally establishes approximate steady-state powerlaw entropy profiles
in the cores of clusters. However, the origin of this behavior and its
dependence on initial conditions have yet to be elucidated. In the present
study, we explain this trend in the context of the self-similar cooling wave
model developed previously by Bertschinger (1989). It is shown that the
logarithmic slope of the entropy profile in the cores of relaxed cooling flow
clusters is given by a simple analytic function that depends only on the
logarithmic slopes of the local gravitational potential and the cooling
function. We discuss a number of potentially interesting uses of the above
result, including: (1) a way of measuring the shapes of gravitational
potentials of cooling flow clusters (which may, for example, be compared with
the results of the standard hydrostatic equilibrium method); (2) a simple
method for constructing realistic analytic cluster models that include the
effects of radiative cooling; and (3) a test of the reliability of cooling
routines implemented in analytic models and hydrodynamic simulations.


title: The IMF Long Ago and Far Away: Faint Stars in the Ursa Minor dSph Galaxy

abstract:
  The dwarf spheroidal galaxy in Ursa Minor is apparently dark-matter
dominated, and is of very low surface brightness, with total luminosity only
equal to that of a globular cluster. Indeed its dominant stellar population is
old and metal-poor, very similar to that of a classical halo globular cluster
in the Milky Way Galaxy. However, the environment in which its stars formed was
clearly different from that in the globular clusters in the Milky Way Galaxy --
what was the stellar IMF in this external galaxy a long time ago? The fossil
record of long-lived, low-mass stars contains the luminosity function,
derivable from simple star counts. This is presented here. The mass function
requires a robust mass-luminosity relation, and we describe the initial results
to determine this, from our survey for eclipsing low-mass binaries in old open
clusters. The massive star IMF at early times is constrained by elemental
abundances in low-mass stars, and we discuss the available data. All data are
consistent with an invariant IMF, most probably of Salpeter slope at the
massive end, with a turnover at lower masses.


title:
Models of Five Absorption Line Systems Along the Line of Sight Toward
  PG0117+213

abstract:
  We present our investigation into the physical conditions of the gas in five
intervening quasar absorption line systems along the line of sight toward the
quasar PG 0117+213, with redshifts of z=0.57, z=0.72, z=1.04, z=1.32 and
z=1.34. Photoionization modeling of HST, Keck I, and Palomar data, using the
code Cloudy, is employed to derive densities and metallicities of the multiple
phases of gas required to fit the absorption profile for each system. We
discuss the implications of these models for galaxy evolution, including the
interpretation of ``CIV deficiency'' and damped Lyman alpha absorbers (DLAs),
and the relationships between galaxy morphology, galaxy luminosity, and
absorption signature.