title:
Feeding the black hole with condensing accretion flows: radiatively
  efficient and radiatively inefficient cases

abstract:
  We study the accretion flow of a hot gas captured by the black hole gravity
in the presence of a thin cold accretion disk. Such geometrical arrangement is
expected in Active Galactic Nuclei (AGN) and in galactic X-ray binary systems
because both hot and cold gases are present in the black hole vicinity.
Previous astrophysical literature concentrated on the evaporation of the cold
disk in the classical heat conduction limit. Here we consider the inverse
process, i.e. condensation of the hot gas onto the cold disk. We find two
distinct condensation regimes. (i) In the classical thermal conduction limit,
the radiative cooling in the hot gas itself force condensation above a certain
critical accretion rate. Most of the flow energy in this case is re-emitted as
X-ray radiation. (ii) Below a certain minimum accretion rate, the hot electrons
are collisionless and the classical heat flux description becomes invalid. We
use the ``non-local'' heat flux approach borrowed from the terrestrial laser
heated plasma experiments. Due to their very large mean free path, the hot
particles penetrate deep into the cold disk where the radiative losses are
significant enough to enable condensation. In this case the hot flow energy is
inconspicuously re-radiated by the transition layer in many UV and especially
optical recombination lines (e.g., Ly$\alpha$, $H\alpha$, H$\beta$) as well as
via the optically thick disk emission. We derive an approximate analytical
solution for the dynamics of the hot condensing flow. If the cold disk is
inactive, i.e. accumulating mass for a future accretion outburst, then the
two-phase flows appear radiatively inefficient. These condensing solutions may
be relevant to \sgra, low luminosity AGN, and transient binary accreting
systems in quiescence.


title:
The Detection of 13CO and Other Apparent Abundance Anomalies in the
  Secondary Stars of Long-Period Cataclysmic Variables

abstract:
  We present moderate resolution (R > 1,800) infrared K-band spectra of twelve
long-period (Porb > 6 hr) cataclysmic variables. We detect absorption lines
from the photospheres of the secondary stars in every system, even though two
of the m were undergoing outubrsts. We have attempted to assign spectral types
to each of the secondary stars, and these classifications are generally
consistent with previous determinations/estimates. We find evidence for
abundance anomalies that include enhancements and/or deficits for all of the
species commonly found in the K-band spectra of G- and K-type dwarfs. There is,
however, only one common abundance anomaly: extremely weak CO features. Only
two of the twelve objects appeared to have normal levels of CO absorption. We
interpret this as evidence for low carbon abundances. In addition, we detect
13CO absorption in four of the twelve objects. Depleted levels of 12C and
enhanced levels of 13C indicate that material that has been processed in the
CNO cycle is finding its way into the photospheres of CV secondary stars. In
systems with luminous accretion disks, we find that the spectrum of the
secondary star is contaminated by a source that flattens (reddens) the
continuum. While free-free or classical accretion disk spectra are flatter than
the blackbody-like spectra of G and K dwarfs, removal of such contamination
from the K-band data results in spectra in which the absorption features become
too strong to be consistent with those of G and K dwarfs.


title: Active Galactic Nuclei Emission-Line Properties Versus Eddington Ratio

abstract:
  We analyze UV spectra for a large sample of 578 Type 1 AGNs and derive
Eddington ratios, L/Ledd, from the bolometric luminosities and emission line
widths for each object in the sample. The sample spans 5 orders of magnitude in
supermassive black hole (SMBH) mass, 7 orders of magnitude in luminosity, and a
redshift range from 0 <= z <= 5. We include a sample of 26 low-redshift
Narrow-Line Seyfert 1s (NLS1s) for comparative analysis. The NLS1s have
slightly larger than average L/Ledd ratios (and smaller SMBH masses) for their
luminosities, but those L/Ledd values are still substantially below the average
for luminous quasars. A large fraction (27%) of the objects overall have L/Ledd
> 1, which might be explained by non-spherically symmetric accretion. We find
no trend between L/Ledd and either redshift or SMBH mass. Composite spectra
sorted by L/Ledd show an unusual emission-line behavior: nearly constant peak
heights and decreasing FWHMs with increasing L/Ledd. This is in marked contrast
to the emission-line behaviors with luminosity, SMBH mass, and FWHM(C IV),
which clearly show trends analogous to the Baldwin Effect: decreasing line
peaks and equivalent widths with increasing luminosity, SMBH mass, and FWHM.
The origins of the unusual behavior with L/Ledd are not understood, but one
implication is that metallicity estimates based on emission line ratios
involving nitrogen show no trend with L/Ledd in the composite spectra created
from different ranges in L/Ledd. The NLS1 composite, however, shows a slightly
high metallicity for its SMBH mass and luminosity. Our earlier work suggests
that host galaxy mass, correlated with SMBH mass and AGN luminosity, is the
fundamental parameter affecting BLR metallicities. Some secondary effect, not
related to L/Ledd, must be enhancing the metallicities in NLS1s.


title: The Formation of Dust Lanes: Implications for Galaxy Evolution

abstract:
  We find that disk galaxies show a sharp, mass-dependent transition in the
structure of their dusty ISM. Dust lanes are a generic feature of massive disks
with V_rot>120km/s, but are completely absent in galaxies with V_rot<120km/s.
The transition reflects an increase in the scale height of the cold ISM in low
mass galaxies, driven by larger turbulent velocities supporting the gas layer,
rather than sharp drops in the gas surface density. We identify the
V_rot=120km/s transition with the onset of gravitational instabilities in high
mass galaxies. The instabilities lead to fragmentation and gravitational
collapse along spiral arms, smaller gas scale heights, lower turbulent
velocities, and thus to narrow dust lanes. The drop in velocity dispersion may
be due either to a switch in the driving mechanism for turbulence or to a
change in the response of the ISM to supernovae after the ISM has collapsed to
a dense layer. The resulting smaller gas scale height can lead to significant
increases in the star formation rate when disk instabilities are present, and
may explain the Kennicutt surface density threshold for star formation. Our
data suggest that star formation will be systematically less efficient in low
mass disks with V_c<120km/s, leading to star formation timescales longer than
the gas accretion timescale. This effect can suppress the metallicity and
nucleosynthetic yields of low mass disks, and thus explain the disk
mass-metallicity relationship without invoking galactic SN-driven outflows. The
transitions in disk stability, dust structure, and/or star formation efficiency
may also be responsible for observed changes in the slope of the Tully-Fisher
relation, in the sharp increase in the thickness of dwarf galaxy disks, and in
the onset of bulges in galaxies with V_rot>120km/s. (Abridged)


title: The Nature of SN 1961V

abstract:
  The nature of SN 1961V has been uncertain. Its peculiar optical light curve
and slow expansion velocity are similar to those of super-outbursts of luminous
blue variables (LBVs), but its nonthermal radio spectral index and declining
radio luminosity are consistent with decades-old supernovae (SNe). We have
obtained Hubble Space Telescope STIS images and spectra of the stars in the
vicinity of SN 1961V, and find Object 7 identified by Filippenko et al. to be
the closest to the optical and radio positions of SN 1961V. Object 7 is the
only point source detected in our STIS spectra and only its H-alpha emission is
detected; it cannot be the SN or its remnant because of the absence of
forbidden lines. While the H-alpha line profile of Object 7 is remarkably
similar to that of eta Car, the blue color (similar to an A2Ib supergiant) and
lack of appreciable variability are unlike known post-outburst LBVs. We have
also obtained Very Long Baseline Array (VLBA) observations of SN 1961V at 18
cm. The non-detection of SN 1961V places a lower limit on the size of the
radio-emitting region, 7.6 mas or 0.34 pc, which implies an average expansion
velocity in excess of 4,400 km/s, much higher than the optical expansion
velocity measured in 1961. We conclude the following: (1) A SN occurred in the
vicinity of SN 1961V a few decades ago. (2) If the SN 1961V light maximum
originates from a giant eruption of a massive star, Object 7 is the most
probable candidate for the survivor, but its blue color and lack of significant
variability are different from a post-outburst eta Car. (3) The radio SN and
Object 7 could be physically associated with each other through a binary
system. (4) Object 7 needs to be monitored to determine its nature and
relationship to SN 1961V.


title:
A new method for measuring the CMB temperature quadrupole with an
  accuracy better than cosmic variance

abstract:
  We present a new method for measuring the CMB temperature quadrupole, using
large scale CMB polarization. The method exploits the fact that CMB
polarization is partially sourced by the local temperature quadrupole. We link
the temperature with the polarization spectrum directly by relating the local
quadrupole at the onset of reionization to both of them. The dominant
contribution is at l<30 and since we use many l values, we can reduce the error
significantly below cosmic variance. In particular, for our fiducial model, the
error on the temperature quadrupole is reduced to 24%. This has the potential
of reducing the probability of a low quadrupole by two orders of magnitude.


title: L' and M' Photometry of Ultracool Dwarfs

abstract:
  We have compiled L' and M' photometry of 63 single and binary M, L,and T
dwarfs obtained at UKIRT using the MKO filter set. This compilation includes
new L' data for 8 L dwarfs and 13 T dwarfs and new M' data for 7 L dwarfs, 5 T
dwarfs, and Gl 229A. We compute L_bol, BC_K, and T_eff for 42 dwarfs whose
flux-calibrated JHK spectra, L' photometry, and trigonometric parallaxes are
available, and we estimate these quantities for 9 other dwarfs whose parallaxes
and flux-calibrated spectra have been obtained. BC_K is a well-behaved function
of near-IR spectral type with a dispersion of ~0.1 mag for types M6-T5; it is
significantly more scattered for types T5-T9. T_eff declines steeply and
monotonically for types M6-L7 and T4-T9, but is nearly constant at ~1450 K for
types L7-T4 with assumed ages of ~3 Gyr. This constant T_eff is evidenced by
nearly unchanging values of L'-M' between types L6 and T3. We compare the
observed K, L', and M' luminosities of L and T dwarfs in our sample with those
predicted by model atmospheres with varying surface gravities and sedimentation
efficiencies. The models indicate that the L3-T4.5 dwarfs generally have higher
gravities (log g = 5.0-5.5) than the T6-T9 dwarfs (log g = 4.5-5.0). The
predicted M' luminosities of T dwarfs are 1.5-2.5 times larger than those
derived empirically for the T dwarfs in our sample. This discrepancy is
attributed to absorption at 4.5-4.9 um by CO, which is not expected under the
condition of chemical equilibrium assumed in the models. We determine that the
L3 dwarf Kelu-1 and the T0 dwarf SDSS J0423-0414 are probable binary systems.
We compute log(L_bol/L_sun) = -5.73 +/- 0.05 and T_eff = 600-750 K for the T9
dwarf 2MASS J0415-0935, which supplants Gl 570D as the least luminous and
coolest brown dwarf presently known.


title:
Nitrogen and Oxygen Abundance Variations in the Outer Ejecta of Eta
  Carinae: Evidence for Recent Chemical Enrichment

abstract:
  We present optical spectra of the ionized `Outer Ejecta' of Eta Carinae that
reveal differences in chemical composition at various positions. In particular,
young condensations just outside the dusty Homunculus Nebula show strong
nitrogen lines and little or no oxygen -- but farther away, nitrogen lines
weaken and oxygen lines become stronger. The observed variations in the
apparent N/O ratio may signify either that the various blobs were ejected with
different abundances, or more likely, that the more distant condensations are
interacting with normal-composition material. The second hypothesis is
supported by various other clues involving kinematics and X-ray emission, and
would suggest that Eta Car is enveloped in a ``cocoon'' deposited by previous
stellar-wind mass loss. In particular, all emission features where we detect
strong oxygen lines are coincident with or outside the soft X-ray shell. In
either case, the observed abundance variations suggest that Eta Car's ejection
of nitrogen-rich material is a recent phenomenon -- taking place in just the
last few thousand years. Thus, Eta Carinae may be at a critical stage of
evolution when ashes of the CNO cycle have just appeared at its surface.
Finally, these spectra reveal some extremely fast nitrogen-rich material, with
Doppler velocities up to 3200 km/s, and actual space velocities that may be
much higher. This is the fastest material yet seen in Eta Car's nebula, but
with unknown projection angles its age is uncertain.


title:
Discovery of Face-On Counterparts of Chain Galaxies in the Tadpole ACS
  Field

abstract:
  The background field of the Tadpole galaxy image taken with the Hubble Space
Telescope ACS contains 87 clump-clusters that are probably low-inclination
versions of the 69 chain galaxies we found in a previous paper. This conclusion
follows from the similarity in colors and apparent magnitudes of the brightest
clumps in the clump-clusters and chain galaxies, and from the similarity
between the distribution of axial ratios for the combined sample and the
distribution for normal disk galaxies. These distributions are consistent with
chains and clump-clusters being disks viewed at random angles with intrinsic
axial ratios of 0.1-0.2 or less. The disks appear to be gas-rich galaxies at
z=1 to 2 that are forming an early generation of stars in a small number of
very large star complexes.


title:
Dynamical Evolution of Rotating Stellar Systems: III. The Effect of Mass
  Spectrum

abstract:
  We have studied the dynamical evolution of rotating star clusters with mass
spectrum using a Fokker-Planck code. As a simplest multi-mass model, we first
investigated the two-component clusters. Rotation is found to accelerate the
dynamical evolution through the transfer of angular momentum outward, as well
as from the high masses to the low masses. However, the degree of acceleration
depends sensitively on the assumed initial mass function since dynamical
friction, which generates mass segregation, also tends to accelerate the
evolution, and the combined effect of both is not linear or multiplicative. As
long as dynamical friction dominates in the competition with angular momentum
exchange the heavy masses lose random energy and angular momentum, sink towards
the centre, but their remaining angular momentum is sufficient to speed them up
rotationally. This is gravo-gyro instability. As a consequence, we find that
the high mass stars in the central parts rotate faster than low mass stars.
This leads to the suppression of mass segregation compared to the non-rotating
clusters. From the study of multi-component models, we observe similar trends
to the two-component models in almost all aspects. The mass function changes
less drastically for clusters with rotation. Unlike non-rotating clusters, the
mass function depends on $R$ and $z$. Our models are the only ones that can
predict mass function and other quantities to be compared with new
observations.


title: Non-Markov Excursion Set Model of Dark Matter Halo Abundances

abstract:
  The excursion set model provides a convenient theoretical framework to derive
dark matter halo abundances. This paper generalizes the model by introducing a
more realistic merging and collapse process. A new parameter regulates the
influence of the environment and thus the coherence (non-Markovianity) of the
merging and the collapse of individual mass shells. The model mass function
also includes the effects of an ellipsoidal collapse. Analytic approximations
of the halo mass function are derived for scale-invariant power spectra with
the slopes $n=0,-1,-2$. The $n=-2$ mass function can be compared with the
results obtained from the `Hubble volume' simulations. A significant detection
of non-Markovian effects is found for an assumed accuracy of the simulated mass
function of 10%.


title: HD108: the mystery deepens with XMM-Newton observations

abstract:
  In 2001, using a large spectroscopic dataset from an extensive monitoring
campaign, we discovered that the peculiar Of star HD108 displayed spectacular
line variations. This strange behaviour could be attributed to a variety of
models, and an investigation of the high energy properties of HD108 was
crucially needed to test the predictions from these models. Our dedicated
XMM-Newton observation of HD108 shows that its spectrum is well represented by
a two temperature thermal plasma model with kT_1\sim0.2 keV and kT_2sim1.4 keV.
In addition, we find that the star does not display any significant short-term
changes during the XMM-Newton exposure. Compared to previous Einstein and ROSAT
detections, it also appears that HD108 does not present long-term flux
variations either. While the dramatic line variations continue to modify
HD108's spectrum in the optical domain, the X-ray emission of the star appears
thus surprisingly stable: no simple model is for the moment able to explain
such an unexpected behaviour.
  Thanks to its high sensitivity, the XMM-Newton observatory has also enabled
the serendipitous discovery of 57 new X-ray sources in the field of HD108.
Their properties are also discussed in this paper.


title:
Non-stationary hyperaccretion of stellar-mass black holes in three
  dimensions: Torus evolution and neutrino emission

abstract:
  We present three-dimensional hydrodynamic simulations of the evolution of
selfgravitating, thick accretion discs around hyperaccreting stellar-mass black
holes. The black hole-torus systems are considered to be remnants of compact
object mergers, in which case the disc is not fed by an external mass reservoir
and the accretion is non-stationary. Our models take into account viscous
dissipation, described by an alpha-law, a detailed equation of state for the
disc gas, and an approximate treatment of general relativistic effects on the
disc structure by using a pseudo-Newtonian potential for the black hole
including its possible rotation and spin-up during accretion. Magnetic fields
are ignored. The neutrino emission of the hot disc is treated by a
neutrino-trapping scheme, and the neutrino-antineutrino annihilation near the
disc is evaluated in a post-processing step. Our simulations show that the
neutrino emission and energy deposition by neutrino-antineutrino annihilation
increase sensitively with the disc mass, with the black hole spin in case of a
disc in corotation, and in particular with the alpha-viscosity. We find that
for sufficiently large alpha-viscosity neutrino-antineutrino annihilation can
be a viable energy source for gamma-ray bursts.


title:
The cosomological evolution of the environments of powerful radio
  galaxies

abstract:
  We present the results from the analysis of 26 extragalactic radio sources of
type FRII which were observed with the VLA at 5 GHz and around the 1.4 GHz
band. The sources were selected to have redshifts in the range $ 0.3<z<1.3$,
radio powers between $6.9 \times 10^{26} {\rm WHz^{-1}}<P_{151 {\rm MHz}}<1.3
\times 10^{28} {\rm WHz^{-1}}$ and angular size $\theta \ge 10''$. We found
that the depolarisation and the rms variations in the rotation measure
increased with redshift. The flux values obtained from the observations were
used to derive by means of analytical modelling the jet--power, density of the
central environment, age of the source and its lobe pressure and the results
were then compared with the observations. We find no significant correlations
with the density parameter suggesting that the depolarisation and the rms
variations in the rotation measure are indicative of the environment becoming
more disordered rather than denser. The age and size of a source are correlated
and both were found to be independent of redshift and radio--power. Jet--power
strongly correlated with the radio--power. The lobe pressure was found to be
anti--correlated with size which could explain why there are no sources beyond
a few Mpc in size. We found no significant correlation between size and density
which demonstrates that the sample is a fair representation of the population.


title: An uncatalogued optical HII region at the outskirts of the Galaxy

abstract:
  We present NOT optical observations of a clump (l = 127.9435 deg, b = +1.8298
deg), embedded in an extended, irregularly shaped, diffuse optical nebula. This
condensation shows an emission-line spectrum typical of classic HII regions.
Although its location on the sky coincides with a nearby extended photoionized
region recently identified by Cichowolski et al. (2003) in radio data from the
Canadian Galactic Plane Survey (CGPS), the systemic velocity of this ~ 1
arcmin-sized HII region, V_LSR = -71$\pm$12 km/s, poses it far out in the
Galaxy, beyond the Perseus arm. The location of this region in the Galaxy is
supported by HI structures visible at comparable radial velocity on CGPS data.
We argue that this HII region might belong to an outer Galactic arm. The
emission line ratios of the surrounding extended nebula, whose radial velocity
is consistent with that of the small HII region, are typical of photoionized
gas in the low density limit. Smaller clumps of comparable surface brightness
are visible within the optical boundaries of the extended, faint nebula. After
comparison of the optical data with far infrared and radio observations, we
conclude that this nebula is an HII region, ~ 70 pc in size, probably
photoionized by an association of OB stars and surrounded by a ring of neutral
hydrogen.


title: Bulges or Bars from Secular Evolution?

abstract:
  We use high resolution collisionless $N$-body simulations to study the
secular evolution of disk galaxies and in particular the final properties of
disks that suffer a bar and perhaps a bar-buckling instability. Although we
find that bars are not destroyed by the buckling instability, when we decompose
the radial density profiles of the secularly-evolved disks into inner S\'ersic
and outer exponential components, for favorable viewing angles, the resulting
structural parameters, scaling relations and global kinematics of the bar
components are in good agreement with those obtained for bulges of late-type
galaxies. Round bulges may require a different formation channel or
dissipational processes.


title: Brane-world cosmological perturbations

abstract:
  Brane-world models provide a phenomenology that allows us to explore the
cosmological consequences of some M theory ideas, and at the same time to use
precision cosmology as a test of these ideas. In order to achieve this, we need
to understand how brane-world gravity affects cosmological dynamics and
perturbations. This introductory review describes the key features of
cosmological perturbations in a brane-world universe.


title:
The role of the Initial Mass Function in modelling the Intra-Cluster
  Medium

abstract:
  The expected metal enrichment of the intra-cluster medium (ICM) and the
partition of metals between cluster galaxies and the hot ICM depends on the
stellar Initial Mass Function (IMF). The choice of the IMF in simulations of
clusters has also important consequences on the "cold fraction", which is a
fundamental constraint on cluster physics.
  We discuss the chemical enrichment and the cold fraction in clusters as
predicted with different IMFs, by means of a straightforward approach that is
largely independent of the details of chemical evolution models or simulations.
We suggest this simple approach as a guideline to select the input parameters
and interpret the results of more complex models and hydrodynamical
simulations.


title: The highest-energy cosmic rays

abstract:
  This paper begins with a pedagogical discussion of the propagation of cosmic
rays and the showers produced when a cosmic ray primary hits the upper
atmosphere. The paper focusses cosmic rays, with energy > 10^19 eV. Emphasis is
placed on the shower properties that are relevant to the detection of cosmic
rays by surface arrays and fluorescence telescopes. The two major experiments,
AGASA and HiRes are described in some detail. Then the experimental results are
reviewed. It is no surprise that more data will be needed. But it is also true
that improved analysis and further data from HiRes can make significant
improvements in the experimental situation.


title: Vlavov and Poisson equations in the context of self-gravitating systems

abstract:
  We present Vlasov's equation and its association with Poisson's equation in
the context of modelling self-gravitating systems such as Globular Clusters or
Galaxies. We first review the classical hypotheses of the model. We continue
with a presentation of the Hamilton-Morrison structure of Vlasov's equation to
study the equilibrium and the stability of self-gravitating systems. Finally,
we present some preliminary results concerning some properties of the time
dependent solutions of the Vlasov-Poisson system.


title:
Identification of Emission Lines in the Low-Ionization Strontium
  Filament Near Eta Carinae

abstract:
  We have obtained deep spectra from 1640 to 10100A with the Space Telescope
Imaging Spectrograph (STIS) of the Strontium Filament, a largely neutral
emission nebulosity lying close to the very luminous star Eta Carinae and
showing an uncommon spectrum. Over 600 emission lines, both permitted and
forbidden, have been identified. The majority originates from neutral or
singly-ionized iron group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Sr is the
only neutron capture element detected. The presence of Sr II, numerous strong
Ti II and V II lines and the dominance of Fe I over Fe II are notable
discoveries. While emission lines of hydrogen, helium, and nitrogen are
associable with other spatial structures at other velocities within the
Homunculus, no emission lines from these elements correspond to the spatial
structure or velocity of the Sr Filament. Moreover, no identified Sr Filament
emission line requires an ionization or excitation energy above approximately 8
eV. Ionized gas extends spatially along the aperture, oriented along the polar
axis of the Homunculus, and in velocity around the Strontium Filament. We
suggest that the Strontium Filament is shielded from ultraviolet radiation at
energies above 8 eV, but is intensely irradiated by the central star at
wavelengths longward of 1500A.


title: Hadronic Decay of Late-Decaying Particles and Big-Bang Nucleosynthesis

abstract:
  We study the big-bang nucleosynthesis (BBN) scenario with late-decaying
exotic particles with lifetime longer than $\sim 1$ sec. With a late-decaying
particle in the early universe, predictions of the standard BBN scenario can be
significantly altered. Therefore, we derive constraints on its primordial
abundance. We pay particular attention to hadronic decay modes of such
particles. We see that the non-thermal production process of D, ${\rm ^{3}He}$
and ${\rm ^6Li}$ provides a stringent upper bound on the primordial abundance
oflate-decaying particles with hadronic branching ratio.


title: Magnetized cosmic walls

abstract:
  Nonlinear growth of one-dimensional density structures with a frozen-in
magnetic field is investigated in Newtonian cosmology. A mechanism of magnetic
field amplification is discussed. We discuss the relation between the initial
conditions for the velocity field and the basic time-scales determining the
growth of the magnetized structure.


title: Magnetic amplification in cylindrical cosmological structure

abstract:
  We derive the amplification of the cosmological magnetic field associated
with forming gravitational structure. The self-similar solutions of
magnetohydrodynamic equations are computed both in linear and nonlinear
regimes. We find that the relatively fast magnetic field enhancement becomes
substantial in the nonlinear phase.


title: Complete Depletion in prestellar cores

abstract:
  We have carried out calculations of ionization equilibrium and deuterium
fractionation for conditions appropriate to a completely depleted, low mass
pre--protostellar core, where heavy elements such as C, N, and O have vanished
from the gas phase and are incorporated in ice mantles frozen on dust grain
surfaces. We put particular emphasis on the interpretation of recent
observations of H2D+ towards the centre of the prestellar core L1544 (Caselli
et al. 2003) and also compute the ambipolar diffusion timescale. We consider
explicitly the ortho and para forms of H2,H3+, and H2D+. Our results show that
the ionization degree under such conditions depends sensitively on the grain
size distribution or, more precisely, on the mean grain surface area per
hydrogen nucleus. Depending upon this parameter and upon density, the major ion
may be H+, H3+, or D3+. We show that the abundance of ortho-H2D+ observed
towards L1544 can be explained satisfactorily in terms of a complete depletion
model and that this species is, as a consequence, an important tracer of the
kinematics of prestellar cores.


title: A Physical Classification Scheme for Blazars

abstract:
  Blazars are currently separated into BL Lacertae objects (BL Lacs) and flat
spectrum radio quasars (FSRQ) based on the strength of their emission lines.
This is done rather arbitrarily by defining a diagonal line in the Ca H&K break
value -- equivalent width plane, following Marcha et al. We readdress this
problem and put the classification scheme for blazars on firm physical grounds.
We study ~100 blazars and radio galaxies from the Deep X-ray Radio Blazar
Survey (DXRBS) and 2 Jy radio survey and find a significant bimodality for the
narrow emission line [OIII] 5007. This suggests the presence of two physically
distinct classes of radio-loud AGN. We show that all radio-loud AGN, blazars
and radio galaxies, can be effectively separated into weak- and strong-lined
sources using the [OIII] 5007 -- [OII] 3727 equivalent width plane. This plane
allows one to disentangle orientation effects from intrinsic variations in
radio-loud AGN. Based on DXRBS, the strongly beamed sources of the new class of
weak-lined radio-loud AGN are made up of BL Lacs at the ~75 per cent level,
whereas those of the strong-lined radio-loud AGN include mostly (~97 per cent)
quasars.


title: The anti-hierarchical growth of supermassive black holes

abstract:
  I present a new method to unveil the history of cosmic accretion and the
build-up of SMBH in the nuclei of galaxies, based on observations of the
evolving radio and (hard) X-ray luminosity functions of AGN. The fundamental
plane of black hole activity discovered by Merloni, Heinz & Di Matteo (2003) is
used as a mass and accretion rate estimator. I adopt the local BH mass function
as a boundary condition to integrate backwards in time the continuity equation
for the SMBH evolution, neglecting the role of mergers. Under the most general
assumption that accretion proceeds in a radiatively efficient way above a
certain rate, and in a radiatively inefficient way below, the redshift
evolution of the mass and accretion rate functions are calculated
self-consistently. The only tunable parameters are the accretion efficiency and
the critical ratio of the X-ray to Eddington luminosity at which the transition
between accretion modes takes place. For fiducial values of these parameters, I
found that half (85%) of the local BH mass density was accumulated at redshift
z<1 (z<3), mostly in radiatively efficient episodes of accretion. The evolution
of the BH mass function between z=0 and z~3 shows clear signs of an
anti-hierarchical behaviour: while the majority of the most massive objects (M
> 10^9) were already in place at z~3, lower mass ones mainly grew at
progressively lower redshift. Also, the average accretion rate decreases with
time. Consequently, sources in the radiatively inefficient regime of accretion
only begin to dominate the comoving accretion energy density in the universe at
z<1. I discuss the implications of these results for the efficiency of
accretion onto SMBH, the quasars lifetimes and duty cycles and the history of
AGN feedback in the form of mechanical energy output (abriged).


title:
Metallicity and the spectral energy distribution and spectral types of
  dwarf O-stars

abstract:
  We present a systematic study of the effect of metallicity on the stellar
spectral energy distribution (SED) of O main sequence (dwarf) stars, focussing
on the hydrogen and helium ionizing continua, and on the optical and near-IR
lines used for spectral classification. The spectra are based on non-LTE line
blanketed atmosphere models with stellar winds calculated using the CMFGEN code
of Hillier & Miller (1998). We draw the following conclusions. First, we find
that the total number of Lyman photons emitted is almost independent of line
blanketing effects and metallicity for a given effective temperature. This is
because the flux that is blocked by the forest of metal lines at wavelengths
shorter than 600 Angstrom is redistributed mainly within the Lyman continuum.
Second, the spectral type, as defined by the ratio of the equivalent widths of
HeI 4471 Angstrom and HeII 4542 Angstrom, is shown to depend noticeably on the
microturbulent velocity in the atmosphere, on metallicity and, within the
luminosity class of dwarfs, on gravity. Third, we confirm the decrease in the
effective temperature for a given spectral type due to the inclusion of line
blanketing recently found by e.g. Martins et al. (2002). Finally, we find that
the SED below ~450 Angstrom is highly dependent on metallicity. This is
reflected in the behaviour of nebular fine-structure line ratios such as
[NeIII]/[NeII] 15.5/12.8 and [ArIII]/[ArII] 9.0/7.0 micron. This dependence
complicates the use of these nebular ratios as diagnostic tools for the
effective temperature determination of the ionizing stars in HII regions and
for age dating of starburst regions in galaxies.


title:
Follow-Up Chandra Observations of Three Candidate Tidal Disruption
  Events

abstract:
  Large-amplitude, high-luminosity soft X-ray flares were detected by the ROSAT
All-Sky Survey in several galaxies with no evidence of Seyfert activity in
their ground-based optical spectra. These flares had the properties predicted
for a tidal disruption of a star by a central supermassive black hole. We
report Chandra observations of three of these galaxies taken a decade after
their flares that reveal weak nuclear X-ray sources that are from 240 to 6000
times fainter than their luminosities at peak, supporting the theory that these
were special events and not ongoing active galactic nucleus (AGN) variability.
The decline of RX J1624.9+7554 by a factor of 6000 is consistent with the
(t-t_D)^(-5/3) decay predicted for the fall-back phase of a tidal disruption
event, but only if ROSAT was lucky enough to catch the event exactly at its
peak in 1990 October. RX J1242.6-1119A has declined by a factor of 240, also
consistent with (t-t_D)^(-5/3). In the H II galaxy NGC 5905 we find only
resolved, soft X-ray emission that is undoubtedly associated with starburst
activity. When accounting for the starburst component, the ROSAT observations
of NGC 5905, as well as the Chandra upper limit on its nuclear flux, are
consistent with a (t-t_D)^(-5/3) decay by at least a factor of 1000. Although
we found weak Seyfert~2 emission lines in Hubble Space Telescope spectra of NGC
5905, indicating that a low-luminosity AGN was present prior to the X-ray
flare, we favor a tidal disruption explanation for the flare itself.


title:
High sensitivity measurements of the CMB power spectrum with the
  extended Very Small Array

abstract:
  We present deep Ka-band ($\nu \approx 33$ GHz) observations of the CMB made
with the extended Very Small Array (VSA). This configuration produces a
naturally weighted synthesized FWHM beamwidth of $\sim 11$ arcmin which covers
an $\ell$-range of 300 to 1500. On these scales, foreground extragalactic
sources can be a major source of contamination to the CMB anisotropy. This
problem has been alleviated by identifying sources at 15 GHz with the Ryle
Telescope and then monitoring these sources at 33 GHz using a single baseline
interferometer co-located with the VSA. Sources with flux densities $\gtsim 20$
mJy at 33 GHz are subtracted from the data. In addition, we calculate a
statistical correction for the small residual contribution from weaker sources
that are below the detection limit of the survey.
  The CMB power spectrum corrected for Galactic foregrounds and extragalactic
point sources is presented. A total $\ell$-range of 150-1500 is achieved by
combining the complete extended array data with earlier VSA data in a compact
configuration. Our resolution of $\Delta \ell \approx 60$ allows the first 3
acoustic peaks to be clearly delineated. The is achieved by using mosaiced
observations in 7 regions covering a total area of 82 sq. degrees. There is
good agreement with WMAP data up to $\ell=700$ where WMAP data run out of
resolution. For higher $\ell$-values out to $\ell = 1500$, the agreement in
power spectrum amplitudes with other experiments is also very good despite
differences in frequency and observing technique.


title: The Effect of Metallicity on Cepheid-Based Distances

abstract:
  We have used the Wide Field and Planetary Camera 2 on board the Hubble Space
Telescope to obtain V and I images of seven nearby galaxies. For each, we have
measured a distance using the tip of the red giant branch (TRGB) method. By
comparing the TRGB distances to published Cepheid distances, we investigate the
metallicity dependence of the Cepheid period-luminosity relation. Our sample is
supplemented by 10 additional galaxies for which both TRGB and Cepheid
distances are available in the literature, thus providing a uniform coverage in
Cepheid abundances between 1/20 and 2 (O/H)solar. We find that the difference
between Cepheid and TRGB distances decreases monotonically with increasing
Cepheid abundance, consistent with a mean metallicity dependence of the Cepheid
distance moduli of (delta(m-M))/(delta[O/H]) = -0.24 +- 0.05 mag/dex.


title: Linking halo mass to galaxy luminosity

abstract:
  In this paper we present a new, essentially empirical, model for the relation
between the mass of a dark matter halo/subhalo and the luminosity of a galaxy
hosted in it. To estimate this, we replace the assumption of linearity between
light and mass fluctuations with the assumption of monotonicity between galaxy
light and halo or subhalo mass. We are enabled to proceed with this less
restrictive ansatz by the availability of new, very high resolution dark matter
simulations and more detailed and comprehensive global galactic luminosity
functions.
  We find that the relation between halo/subhalo mass and hosted galaxy
luminosity is fairly well fit by a double power law, while that between halo
mass and group luminosity is fairly well fit by a two branch function, with
both branches double power laws. Both relations asymptote to $L\propto M^4$ at
low $M$, while at high mass the former follows $L\propto M^{0.28}$ and the
latter $L\propto M^{0.9}$.
  We also derive results for the occupation number, luminosity function of
cluster galaxies, group luminosity function and multiplicity function. Then,
using some additional assumptions, we further derive results for biasing
between mass and light and mass and galaxy number, light distribution function
and the void probability distribution. Our results for the most part seem to
match well with observations and previous expectations. We feel this is a
potentially powerful way of modelling this relation, since the main inputs are
readily testable against dark matter simulation results and galaxy surveys.
(abridged)


title: Fragmentation in Massive Star Formation

abstract:
  Studies of evolved massive stars indicate that they form in a clustered mode.
During the earliest evolutionary stages, these regions are embedded within
their natal cores. Here, we show high-spatial-resolution interferometric dust
continuum observations disentangling the cluster-like structure of a young
massive star-forming region. The derived protocluster mass distribution is
consistent with the stellar initial mass function. Thus, fragmentation of the
initial massive cores may determine the initial mass function and the masses of
the final stars. This implies that stars of all masses can form via accretion
processes, and coalescence of intermediate-mass protostars appears not to be
necessary.


title:
General relativistic hydrodynamics with viscosity: contraction,
  catastrophic collapse, and disk formation in hypermassive neutron stars

abstract:
  Viscosity and magnetic fields drive differentially rotating stars toward
uniform rotation, which has important consequences in many astrophysical
contexts. For example, merging binary neutron stars can form a "hypermassive"
remnant, i.e. a differentially rotating star with a mass greater than the
maximum allowed by uniform rotation. The removal of the centrifugal support
provided by differential rotation can lead to delayed collapse of the remnant
to a black hole, accompanied by a burst of gravitational radiation. Both
magnetic fields and viscosity alter the structure of differentially rotating
stars on secular timescales, making numerical tracking of the evolution
difficult. Here, we present the first simulations of rapidly rotating stars
with shear viscosity in full general relativity. We self-consistently include
viscosity in our relativistic hydrodynamic code to solve the relativistic
Navier-Stokes equations both in axisymmetry and in full 3+1 dimensions. In
axisymmetry, we follow secular evolution with high resolution over dozens of
rotation periods (thousands of M). We find that viscosity operating in a
hypermassive star generically leads to the formation of a compact, uniformly
rotating core surrounded by a low-density disk. These uniformly rotating cores
are often, but not always, unstable to gravitational collapse. In the unstable
cases, we follow the collapse and determine the mass and the spin of the final
black hole and ambient disk. In all cases studied, the rest mass of the
resulting disk is found to be 10-20% of the original star, whether surrounding
a uniformly rotating core or a rotating black hole. This study foreshadows more
detailed, future simulations of secular processes, including magnetic effects,
in relativistic stars.


title: Probing Gravitation, Dark Energy, and Acceleration

abstract:
  The acceleration of the expansion of the universe arises from unknown
physical processes involving either new fields in high energy physics or
modifications of gravitation theory. It is crucial for our understanding to
characterize the properties of the dark energy or gravity through cosmological
observations and compare and distinguish between them. In fact, close
consistencies exist between a dark energy equation of state function w(z) and
changes to the framework of the Friedmann cosmological equations as well as
direct spacetime geometry quantities involving the acceleration, such as
``geometric dark energy'' from the Ricci scalar. We investigate these
interrelationships, including for the case of superacceleration or phantom
energy where the fate of the universe may be more gentle than the Big Rip.


title: Bulgeless Galaxies and their Angular Momentum Problem

abstract:
  The specific angular momentum of Cold Dark Matter (CDM) halos in a
$\Lambda$CDM universe is investigated. Their dimensionless specific angular
momentum $\lambda'=\frac{j}{\sqrt{2}V_{vir} R{vir}}$ with $V_{vir}$ and
$R_{vir}$ the virial velocity and virial radius, respectively depends strongly
on their merging histories. We investigate a set of $\Lambda$CDM simulations
and explore the specific angular momentum content of halos formed through
various merging histories. Halos with a quiet merging history, dominated by
minor mergers and accretion until the present epoch, acquire by tidal torques
on average only 2% to 3% of the angular momentum required for their rotational
support ($\lambda'=0.02$). This is in conflict with observational data for a
sample of late-type bulgeless galaxies which indicates that those galaxies
reside in dark halos with exceptionally high values of $\lambda' \approx
0.06-0.07$. Minor mergers and accretion preserve or slowly increase the
specific angular momentum of dark halos with time. This mechanism is however
not efficient enough in order to explain the observed spin values for late-type
dwarf galaxies. Energetic feedback processes have been invoked to solve the
problem that gas loses a large fraction of its specific angular momentum during
infall. Under the assumption that dark halos hosting bulgeless galaxies acquire
their mass via quiescent accretion, our results indicate yet another serious
problem: the specific angular momentum gained during the formation of these
objects is not large enough to explain their observed rotational
properties,even if no angular momentum would be lost during gas infall.


title:
SMA outflow/disk studies in the massive star-forming region
  IRAS18089-1732

abstract:
  SMA observations of the massive star-forming region IRAS 18089-1732 in the
1mm and 850mu band reveal outflow and disk signatures in different molecular
lines. The SiO(5--4) data show a collimated outflow in the northern direction.
In contrast, the HCOOCH3(20--19) line, which traces high-density gas, is
confined to the very center of the region and shows a velocity gradient across
the core. The HCOOCH3 velocity gradient is not exactly perpendicular to the
outflow axis but between an assumed disk plane and the outflow axis. We
interpret these HCOOCH3 features as originating from a rotating disk that is
influenced by the outflow and infall. Based on the (sub-)mm continuum emission,
the mass of the central core is estimated to be around 38M_sun. The dynamical
mass derived from the HCOOCH3 data is 22Msun, of about the same order as the
core mass. Thus, the mass of the protostar/disk/envelope system is dominated by
its disk and envelope. The two frequency continuum data of the core indicate a
low dust opacity index beta ~ 1.2 in the outer part, decreasing to beta ~ 0.5
on shorter spatial scales.


title:
What the Optical Recombination Lines Can Tell Us About the Broad Line
  Regions of Active Galactic Nuclei

abstract:
  We investigate the effect of a global change in the ionizing continuum level
on the behavior of the strong optical broad emission-lines seen in spectra of
the nuclear emission-line regions of active galactic nuclei (AGN), including
the Balmer lines, HeI 5876, and HeII 4686. Unlike most of the prominent heavy
element lines found in the UV, the optical hydrogen and helium recombination
lines' emissivities are strongly dependent upon the incident continuum flux,
since these lines arise out of excited states whose optical depths depend upon
the incident flux of photons. Using photoionization calculations we determine
the luminosity-dependent responsivities of these lines for a general model of
the broad emission line region (BLR), with the purpose of establishing them as
important probes of the physical conditions within the BLR of AGNs. The
dependence of these lines' emissivities on the incident photon flux invokes a
dependence in their responsivities on distance from the central continuum
source. In particular, the responsivities of these lines are generally
anti-correlated with the incident photon flux. Thus, their responsivities vary
with distance within the BLR for a fixed continuum luminosity and change with
time as the continuum source varies. Consequently, after correcting for light
travel time effects the response of the Balmer and optical helium lines should
generally be strongest during low continuum luminosity states. Responsivity
that depends upon photon flux and continuum state may explain a number of
outstanding problems currently under investigation in broad line variability
studies of these and other emission lines. [Abridged]


title:
Rotational sweepback of magnetic field lines in geometrical models of
  pulsar radio emission

abstract:
  We study the rotational distortions of the vacuum dipole magnetic field in
the context of geometrical models of the radio emission from pulsars. We find
that at low altitudes the rotation deflects the local direction of the magnetic
field by at most an angle of the order of r_n^2, where r_n = r/Rlc, r is the
radial distance of the radio emission and Rlc is the light cylinder radius. To
the second order in r_n, this distortion is symmetrical with respect to the
plane containing the dipole axis and the rotation axis (Omega-mu plane). The
lowest order distortion which is asymmetrical with respect to the Omega-mu
plane is third order in r_n. We show, however, that the influence of the
sweepback on the outer boundary of the open field line region (open volume) is
a much larger effect, of the order of r_n^1/2. The open volume is shifted
backwards with respect to the rotation direction by an angle delta_ov ~ 0.2
sin(alpha) r_n^1/2 where alpha is the dipole inclination with respect to the
rotation axis. The associated phase shift of the pulse profile Delta_phi_ov ~
0.2 r_n^1/2 can easily exceed the shift due to combined effects of aberration
and propagation time delays (=~ 2r_n). This strongly affects the misalignment
of the center of the PA curve and the center of the pulse profile, thereby
modifying the delay-radius relation. Contrary to intuition, the effect of
sweepback dominates over other effects when emission occurs at low altitudes.
For r_n <~ 0.003 the shift becomes negative, ie. the center of the position
angle curve precedes the profile center. With the sweepback effect included,
the modified delay-radius relation predicts larger emission radii and is in
much better agreement with the other methods of determining r_n.


title:
The Case for Optically-Thick High Velocity Broad Line Region Gas in
  Active Galactic Nuclei

abstract:
  A combined analysis of the profiles of the main broad quasar emission lines
in both Hubble Space Telescope and optical spectra shows that while the
profiles of the strong UV lines are quite similar, there is frequently a strong
increase in the Ly-alpha/H-alpha ratio in the high-velocity gas. We show that
the suggestion that the high velocity gas is optically-thin presents many
problems. We show that the relative strengths of the high velocity wings arise
naturally in an optically-thick BLR component. An optically-thick model
successfully explains the equivalent widths of the lines, the Ly-alpha/H-alpha
ratios and flatter Balmer decrements in the line wings, the strengths of CIII]
and the lambda 1400 blend, and the strong variability of high-velocity,
high-ionization lines (especially HeII and HeI).


title: A Census of the Chamaeleon I Star-Forming Region

abstract:
  Optical spectroscopy has been obtained for 179 objects that have been
previously identified as possible members of the cluster, that lack either
accurate spectral types or clear evidence of membership, and that are optically
visible (I<18). I have used these spectroscopic data and all other available
constraints to evaluate the spectral classifications and membership status of a
total sample of 288 candidate members of Chamaeleon I that have appeared in
published studies of the cluster. The latest census of Chamaeleon I now
contains 158 members, 8 of which are later than M6 and thus are likely to be
brown dwarfs. I find that many of the objects identified as members of
Chamaeleon I in recent surveys are actually field stars. Meanwhile, 7 of 9
candidates discovered by Carpenter and coworkers are confirmed as members, one
of which is the coolest known member of Chamaeleon I at a spectral type of M8
(~0.03 M_sun). I have estimated extinctions, luminosities, and effective
temperatures for the members and used these data to construct an H-R diagram
for the cluster. Chamaeleon I has a median age of ~2 Myr according to
evolutionary models, and hence is similar in age to IC 348 and is slightly
older than Taurus (~1 Myr). The measurement of an IMF for Chamaeleon I from
this census is not possible because of the disparate methods with which the
known members were originally selected, and must await an unbiased,
magnitude-limited survey of the cluster.


title: Modified Friedmann Cosmologies - theory & observations

abstract:
  We investigate a class of Cardassian scenarios of the universe evolution in
notions of the qualitative theory of dynamical systems. This theory allows us
to analyze all solutions for all possible initial conditions on the phase
plane. In the Cardassian models we find that big-rip singularities are present
as a typical behavior in the future if $n<0$. Some exact solutions for the flat
Cardassian models as well as a duality relation were found. In turn from the
statistical analysis of Knop's SNIa data, without any priors on matter content
in the model, we obtain that at the 99% confidence level this big-rip scenario
will reach. The potential function for the Hamiltonian description of dynamics
is reconstructed from the SNIa data (inverse dynamical problem). We also
pointed out the statistical analysis results depend oversensitively on the
choice of the model parameter $\mathcal{M}$.


title:
Quasi-Periodic Oscillations from Low-Mass X-Ray Binaries with Neutron
  Stars

abstract:
  Before the launch of the Rossi X-ray Timing Explorer (RXTE) it was recognized
that neutron star accretion disks could extend inward to very near the neutron
star surface, and thus be governed by millisecond timescales. Previous missions
lacked the sensitivity to detect them. The kilohertz quasi-periodic
oscillations (QPO) that RXTE discovered are often, but not always, evident in
the X-ray flux. In 8 years RXTE has found kilohertz signals in about a fourth
of 100 low-mass X-ray binaries (LMXB) containing neutron stars. The observed
power spectra have simple dominant features, the two kilohertz oscillations, a
low frequency oscillation, and band-limited white noise. They vary
systematically with changes in other source properties and offer the
possibility of comparison with model predictions. New information from the
millisecond pulsars resolves some questions about the relations of the QPO and
the spin. Coherence, energy spectrum and time lag measurements have indicated
systematic behaviors, which should constrain mechanisms.


title:
Type Ia Supernova Discoveries at z>1 From the Hubble Space Telescope:
  Evidence for Past Deceleration and Constraints on Dark Energy Evolution

abstract:
  We have discovered 16 Type Ia supernovae (SNe Ia) with the Hubble Space
Telescope (HST) and have used them to provide the first conclusive evidence for
cosmic deceleration that preceded the current epoch of cosmic acceleration.
These objects, discovered during the course of the GOODS ACS Treasury program,
include 6 of the 7 highest-redshift SNe Ia known, all at z>1.25, and populate
the Hubble diagram in unexplored territory. The luminosity distances to these
and 170 previous SNe Ia are provided. A purely kinematic interpretation of the
SN Ia sample provides evidence at the > 99% confidence level for a transition
from deceleration to acceleration or similarly, strong evidence for a cosmic
jerk. Using a simple model of the expansion history, the transition between the
two epochs is constrained to be at z=0.46 +/- 0.13. The data are consistent
with the cosmic concordance model of Omega_M ~ 0.3, Omega_Lambda~0.7
(chi^2_dof=1.06), and are inconsistent with a simple model of evolution or dust
as an alternative to dark energy. For a flat Universe with a cosmological
constant. When combined with external flat-Universe constraints we find w=-1.02
+ 0.13 - 0.19 (and $<-0.76 at the 95% confidence level) for an assumed static
equation of state of dark energy, P = w\rho c^2. Joint constraints on both the
recent equation of state of dark energy, $w_0$, and its time evolution, dw/dz,
are a factor of ~8 more precise than its first estimate and twice as precise as
those without the SNe Ia discovered with HST. Our constraints are consistent
with the static nature of and value of w expected for a cosmological constant
(i.e., w_0 = -1.0, dw/dz = 0), and are inconsistent with very rapid evolution
of dark energy. We address consequences of evolving dark energy for the fate of
the Universe.


title:
The contribution of primordial binaries to the blue straggler population
  in 47 Tucanae

abstract:
  The recent observation (Ferraro et al. 2003b) of the blue straggler
population in 47 Tucanae gives the first detailed characterization of their
spatial distribution in the cluster over its entire volume. Relative to the
light distribution, blue stragglers appear to be overabundant in the core and
at large radii. The observed surface density profile shows a central peak, a
zone of avoidance and a rise beyond twenty core radii. In light of these
findings we explored the evolution of blue stragglers mimicking their dynamics
in a multi-mass King model for 47 Tucanae. We find that the observed spatial
distribution can not be explained within a purely collisional scenario in which
blue stragglers are generated exclusively in the core through direct mergers.
An excellent fit is obtained if we require that a sizable fraction of blue
stragglers is generated in the peripheral regions of the cluster inside
primordial binaries that evolve in isolation experiencing mass-transfer.


title: Phase Transitions in Nucleonic Matter and Neutron-Star Cooling

abstract:
  A new scenario for neutron-star cooling is proposed, based on the
correspondence between pion condensation, occurring in neutron matter due to
critical spin-isospin fluctuations, and the metal-insulator phase transition in
a two-dimensional electron gas. Beyond the threshold density for pion
condensation, where neutron-star matter loses its spatial homogeneity, the
neutron single-particle spectrum acquires an insulating gap that quenches
neutron contributions to neutrino-production reactions and to the star's
specific heat. In the liquid phase at densities below the transition point,
spin-isospin fluctuations are found to play dual roles. On the one hand, they
lead to a multi-sheeted neutron Fermi surface that extends to low momenta,
thereby activating the normally forbidden direct-Urca cooling mechanism; on the
other, they amplify the nodeless $P$-wave neutron superfluid gap while
suppressing $S$-wave pairing. In this picture, lighter stars without a
pion-condensed core experience slow cooling, while enhanced cooling occurs in
heavier stars through direct-Urca emission from a narrow shell of the interior.


title: Extended complex scalar field as quintessence

abstract:
  In this paper, we show the possibility that an extended complex scalar field
can be considered as an extended complex quintessence. For this model, we
derive the basic equations with a parameter $\eta $ which govern the evolution
of the Universe. Our model may contain a complex quintessence model for $\eta
=-1$ and a real quitessence model for $\eta =0$.


title: Light on Dark Matter

abstract:
  Galaxies are lighthouses that sit atop peaks in the density field. There is
good observational evidence that these lighthouses do not provide a uniform
description of the distribution of dark matter.


title:
Constraining the solutions of an inverse method of stellar population
  synthesis

abstract:
  In three previous papers (Pelat 1997, 1998 and Moultaka & Pelat 2000), we set
out an inverse stellar population synthesis method which uses a database of
stellar spectra. Unlike other methods, this one provides a full knowledge of
all possible solutions as well as a good estimation of their stability;
moreover, it provides the unique approximate solution, when the problem is
overdetermined, using a rigorous minimization procedure. In Boisson et al.
(2000), this method has been applied to 10 active and 2 normal galaxies. In
this paper we analyse the results of the method after constraining the
solutions. Adding {\it a priori} physical conditions on the solutions
constitutes a good way to regularize the synthesis problem. As an illustration
we introduce physical constraints on the relative number of stars taking into
account our present knowledge of the initial mass function in galaxies. In
order to avoid biases on the solutions due to such constraints, we use
constraints involving only inequalities between the number of stars, after
dividing the H-R diagram into various groups of stellar masses. We discuss the
results for a well-known globular cluster of the galaxy M31 and discuss some of
the galaxies studied in Boisson et al. (2000). We find that, given the spectral
resolution and the spectral domain, the method is very stable according to such
constraints (i.e. the constrained solutions are almost the same as the
unconstrained one). However, an additional information can be derived about the
evolutionary stage of the last burst of star formation, but the precise age of
this particular burst seems to be questionable.


title: X-Ray Emission from the Double Pulsar System J0737-3039

abstract:
  We report on a 10 ksec observation of the double pulsar system J0737-3039
obtained with the Chandra X-ray Observatory's Advanced CCD Imaging
Spectrometer. We detect the system as a point source with coordinates (J2000)
RA = 07:37:51.23, Decl. = -30:39:40.9, making this the first double neutron
star system to be detected at X-ray energies. Only 77 source counts are
detected. The data are represented satisfactorily by a power-law spectrum with
photon index = 2.9 +/- 0.4. The inferred 0.2-10 keV luminosity is approximately
2e30 erg/s for a distance of 0.5 kpc. We do not detect any significant
variability with orbital phase in these data, which span one full orbit. These
results are consistent with the X-ray emission originating solely from the
magnetosphere of the energetic A pulsar, with an efficiency for conversion of
rotational energy to X-rays in this band of roughly 0.04%, although we cannot
exclude other possibilities.


title: The Counter Arc to MS1512-cB58 and a Companion Galaxy

abstract:
  We present near-infrared spectra of ``A2'', the primary counter arc to the
gravitationally lensed galaxy MS1512-cB58. The spectra showredshifted H-alpha,
[NII], [OIII], and H-beta at z=2.728 +/- 0.001. We observe the same
H-alpha/[OIII] ratio as cB58, which together with the redshift confirms that A2
is indeed another image of a single background galaxy. Published lensing
reconstruction reports that A2 is a magnification of the entire source, while
cB58 is an image of only a part. At marginal significance, A2 shows higher line
to continuum ratios than cB58 (by a factor of about 2), suggesting a
non-uniform ratio of young to old stars across the galaxy. We observe a second
emission line source in the slit. This object, ``W5'', is predicted to be a
lensed image of another galaxy at a redshift similar to cB58. W5 is blueshifted
from cB58 by about 400 km/s and has a significantly lower H-alpha/[OIII] ratio,
confirming that it is an image of a different background galaxy in a group with
cB58. The H-alpha emission line in W5 implies a star formation rate of 6
Msun/yr (H_0 = 70 km/s/Mpc, Omega_M=0.3, Omega_L=0.7), after correcting for
lensing magnification.


title: Near-Infrared Colors of Hard X-ray Selected Active Galactic Nuclei

abstract:
  We present results of near-infrared photometry (J, H, K_S) for a sample of
active galactic nuclei (AGNs) obtained from hard X-ray surveys with ASCA. The
sample covers the AGNs at z=0.1-1 with L(2-10keV)=10^42-10^46 erg/s with very
high completeness. The fraction of red (J-K_S>2 mag) AGNs in our sample is
2(+-1)%, which is comparable to that for optically- or UV-selected
quasi-stellar objects (QSOs, i.e. luminous AGNs). The number of red AGNs found
in our sample is also consistent with that expected from the surface density of
red AGNs found in 2MASS by Cutri et al. (2001). We find that the
anomalously-small dust-to-gas ratios in circumnuclear gas, which is seen in
some AGNs with Seyfert-class luminosity, also occur in the QSOs (AGNs with
luminosity of L(2-10keV) > 10^44.5 erg/s). For all the QSOs with an X-ray
absorption of N_H > 10^22 /cm2 in our sample, the values of A_V/N_H are smaller
than the Galactic value by a factor of 5 to 100. Since a fraction of this
population among the QSOs in our sample is about 30%, such fraction of
optical/UV-selected type 1 QSOs known to date may show type 2 nature in X-ray.


title: Comprehensive analysis of RGU photometry in the direction to M5

abstract:
  The RGU-photographic investigation of an intermediate latitude field in the
direction to the Galactic center is presented. 164 extra-galactic objects,
identified by comparison of Minnesota and Basel charts, are excluded from the
program. Also, a region with size 0.104 square-degrees, contaminated by cluster
(M5) stars and affected by background light of the bright star HD 136202 is
omitted. Contrary to previous investigations, a reddening of $E(B-V)=0.046$,
corresponding to E(G-R)=0.07 mag is adopted. The separation of dwarfs and
evolved stars is carried out by an empirical method, already applied in some of
our works. A new calibration for the metallicity determination is used for
dwarfs, while the absolute magnitude determination for stars of all categories
is performed using the procedures given in the literature. There is good
agreement between the observed logarithmic space density histograms and the
galactic model gradients. Also, the local luminosity function agrees with
Gliese's (1969) and Hipparcos' (Jahreiss & Wielen 1997) luminosity functions,
for stars with $2<M(G)\leq8$ mag. For giants, we obtained two different local
space densities from comparison with two Galactic models, i.e. $D^{*}(0)=6.63$,
close to that of Gliese (1969), and $D^{*}(0)=6.79$. A metallicity gradient,
$d[Fe/H]/dz= -0.20$ dex/kpc, is detected for dwarfs (only) with absolute
magnitudes $4<M(G)\leq6$, corresponding to a spectral type interval F5-K0.


title: Solving the discrepancy among the light elements abundances and WMAP

abstract:
  Within the standard big bang nucleosynthesis (BBN) and cosmic microwave
background (CMB) framework, the baryon density measured by the Wilkinson
Microwave Anisotropy Probe (WMAP) or the primordial D abundance is much higher
than the one measured by the $^4$He or $^7$Li abundances. To solve the
discrepancy, we propose a scenario in which additional baryons appear after
BBN. We show that simply adding the baryons can not be a solution but the
existence of a large lepton asymmetry before BBN makes the scenario successful.
These extra baryons and leptons, in addition to the initial baryons which exist
before the BBN, can be all produced from $Q$-balls.


title:
The environmental dependence of radio-loud AGN activity and star
  formation in the 2dFGRS

abstract:
  By combining the 2-degree Field Galaxy Redshift Survey with the NRAO VLA Sky
Survey at 1.4 GHz, the environments of radio loud AGN in the nearby Universe
are investigated using both local projected galaxy densities and a
friends-of-friends group finding algorithm. Radio-loud AGN are preferentially
located in galaxy groups and poor-to-moderate richness galaxy clusters. The AGN
fraction appears to depend more strongly on the large-scale environment (group,
cluster, etc) in which a galaxy is located than on its more local environment,
except at the lowest galaxy surface densities where practically no radio-loud
AGN are found. The ratio of absorption-line to emission-line AGN changes
dramatically with environment, with essentially all radio-loud AGN in rich
environments showing no emission lines. This result could be connected with the
lack of cool gas in cluster galaxies, and may have important consequences for
analyses of optically-selected AGN, which are invariably selected on emission
line properties. The local galaxy surface density of the absorption-line AGN is
strongly correlated with radio luminosity, implying that the radio luminosities
may be significantly boosted in dense environments due to confinement by the
hot intracluster gas.
  The environments of a radio-selected sample of star forming galaxies are also
investigated to provide an independent test of optical studies. In line with
those studies, the fraction of star forming galaxies is found to decrease
strongly with increasing local galaxy surface density; this correlation extends
across the whole range of galaxy surface densities, with no evidence for the
density threshold found in some optical studies.


title:
The origin and structure of clumps along molecular outflows: the test
  case of CB3

abstract:
  We investigate the origin of the small, chemically rich molecular clumps
observed along the main axis of chemically rich outflows such as CB3 and L1157.
We develop a chemical model where we explore the chemical evolution of these
clumps, assuming they are partially pre-existing to the outflow, or
alternatively newly formed by the impact of the outflow on the surrounding
medium. The effects of the impact of the outflow are reproduced by density and
temperature changes in the clump. We find that the observed abundances of
CH3OH, SO and SO2 are best reproduced by assuming a scenario where the dense
molecular gas observed is probably pre-existing in the interstellar medium
before the formation of their exciting (proto)stars and that the clumpiness and
the rich chemistry of the clumps are a consequence of a pre-existing density
enhancement and of its interaction with the outflow.


title: Measuring Dark Matter Flows in Merging Clusters of Galaxies

abstract:
  The Rees-Sciama effect produced in mergers of galaxy clusters is discussed,
and an analytical approximation to compute this effect from numerical
simulations is given. Using this approximation and a novel toy model describing
the physics of the merger, we characterize the spatial properties and
symmetries of the Rees-Sciama signal. Based on these properties, we propose a
method to extract the physical parameters of the merger, which relies on the
computation of the quadrupole moment of the observed brightness distribution on
the sky. The relationships between the quadrupole coefficients and the physical
parameters of the merger (physical separation, projection angle on the sky and
angular momentum) are discussed. Finally, we propose a method to co-add
coherently the RS signals from a sample of cluster mergers, in order to achieve
an statistical detection of the effect for those cases where individual signals
are masked by the kinetic SZ effect, the primordial CMB components, and by
observational noise.


title: XMM-Newton observations of polars in low accretion states

abstract:
  We have made a series of snap-shot observations of 37 polars using
XMM-Newton. We found that 16 of these systems were in a low, or much reduced,
accretion state. Of those, 6 were not detected in X-rays. This suggests that in
any survey of polars, around half will be in a low accretion state. We tested
if there was a bias towards certain orbital periods: this is not the case. Of
the 10 systems which were detected at low, but significant rates in X-rays, 8
showed significant variability in their X-ray light curves. This implies that
non-uniform accretion still takes place during low accretion epochs. The
bolometric luminosity of these systems is ~10^30 ergs s, two orders of
magnitude less than for systems in a high accretion state. The X-ray spectra
show no evidence of a distinct soft X-ray component. However, the X-ray and UV
data imply that such a low temperature component exists: its temperature is low
enough for its flux distribution to move outside the bandpass of the X-ray
instruments.


title:
A completely analytical family of dynamical models for spherical
  galaxies and bulges with a central black hole

abstract:
  We present a family of spherical models for elliptical galaxies and bulges
consisting of a stellar component and a central black hole. All models in this
family share the same stellar density profile, which has a steep central cusp.
The gravitational potential of each models is a linear combination of the
potential generated selfconsistently by the stars and the potential of a
central black hole. The relative importance of these two contributions is a
free parameter in the models. Assuming an isotropic dynamical structure, almost
all kinematical properties of these models can be calculated analytically. In
particular, they form the first simple dynamical models for galaxies with a
central black hole where the distribution function and differential energy
distribution can be written completely in terms of elementary functions only.
We also present various extensions of this family to models with anisotropic
orbital structures. Also for these dynamical models, the distribution function
and its moments can be expressed completely in terms of elementary functions.
  This family is useful for a large range of applications, in particular to
generate initial conditions for N-body and hydrodynamical simulations to model
galactic nuclei with a central black hole.


title:
Imaging the first light: experimental challenges and future perspectives
  in the observation of the Cosmic Microwave Background Anisotropy

abstract:
  Measurements of the cosmic microwave background (CMB) allow high precision
observation of the Last Scattering Surface at redshift $z\sim$1100. After the
success of the NASA satellite COBE, that in 1992 provided the first detection
of the CMB anisotropy, results from many ground-based and balloon-borne
experiments have showed a remarkable consistency between different results and
provided quantitative estimates of fundamental cosmological properties. During
2003 the team of the NASA WMAP satellite has released the first improved
full-sky maps of the CMB since COBE, leading to a deeper insight into the
origin and evolution of the Universe. The ESA satellite Planck, scheduled for
launch in 2007, is designed to provide the ultimate measurement of the CMB
temperature anisotropy over the full sky, with an accuracy that will be limited
only by astrophysical foregrounds, and robust detection of polarisation
anisotropy. In this paper we review the experimental challenges in high
precision CMB experiments and discuss the future perspectives opened by second
and third generation space missions like WMAP and Planck.


title: Are Domain Walls ruled out ?

abstract:
  Recent analysis of the combined data of cosmic microwave background, galaxy
clustering and supernovae type Ia observations have set strong constraints on
the equation of state parameter $w_X$. The upper bound $w_X < -0.82$ at 95%
c.l. rules out an important class of models, the domain walls ($-2/3 < w_X <
-1/3$). Here we revisit the issue of domain walls as a possible alternative to
the standard $\Lambda$-CDM model by questioning the assumptions made in the
choice of priors of the data analysis. The results of our investigation show
that domain walls can provide a good fit to the WMAP data for a different
choice of priors with ``lower'' values of the Hubble parameter ($h<0.65$), (as
indicated by Sunyaev-Zeldovich and time delays for gravitational lensing
observations), and ``higher'' values of the matter density ($\Omega_m > 0.35$),
(in agreement with recent measurements of the temperature-luminosity relation
of distant clusters observed with the XMM-Newton satellite). In this new
perspective, their existence would lead to important implications for the CMB
constraints on cosmological and inflationary parameters.


title:
1WGA J2223.7-0206: a Narrow-Line Quasi-Stellar Object in the XMM-Newton
  field of view of 3C445

abstract:
  We report the discovery of a Narrow Line QSO located at about 1.3' from the
Broad Line Radio Galaxy 3C445. The source,1WGA J2223.7-0206, although already
revealed by ROSAT has never been optically identified previously. An XMM-Newton
observation of 3C445 has allowed, for the first time, an accurate X-ray
spectral study of 1WGA J2223.7-0206, revealing an ultra-soft spectrum and fast
flux variations typical of Narrow Line AGN. The 0.2-10 keV spectrum is well
represented by a power law (Gamma=2.5) plus a black body component (kT = 117
eV) absorbed by Galactic NH. About 80% of the X-ray flux is emitted below 2
keV. The 0.2-2 keV flux is observed to decrease by about a factor 1.6 in about
5000 s. The optical observations, triggered by the X-ray study, confirm the
Narrow Line AGN nature of this source. The continuum is blue with typical AGN
emission lines, pointing to a redshift z=0.46. The full width half maximum of
H_beta is 2000 km/secand the flux rat io [OIII}]/H_beta=0.21. The optical
luminosity (M_R=-23.2) and the point-like appearance in the optical images
identify 1WGA J2223.7-0206 as a Narrow Line QSO. From the optical-UV-X-ray
Spectral Energy Distribution we obtain a lower limit of the bolometric
luminosity of 1WGA J2223.7-0206 (L_bol > 3 10^{45} erg/sec) implying, for
accretion rates close to the Eddington limit, a black hole mass M_BH > 2.4 x
10^{7} M_{\odot}


title:
An IRAS High Resolution Image Restoration (HIRES) Atlas of All
  Interacting Galaxies in the IRAS Revised Bright Galaxy Sample

abstract:
  We present high-resolution (30"-1') 12, 25, 60, and 100 micron images of 106
interacting galaxy systems contained in the IRAS Revised Bright Galaxy Sample
(RBGS, Sanders et al. 2003), a complete sample of all galaxies having a 60
micron flux density greater than 5.24 Jy. These systems were selected to have
at least two distinguishable galaxies separated by less than three average
galactic diameters, and thus we have excluded very widely separated systems and
very advanced mergers. The new complete survey has the same properties as the
prototype survey of Surace et al. 1993. We find no increased tendency for
infrared-bright galaxies to be associated with other infrared bright galaxies
among the widely separated pairs studied here. We find small enhancements in
far-infrared activity in multiple galaxy systems relative to RBGS
non-interacting galaxies with the same blue luminosity distribution. We also
find no differences in infrared activity (as measured by infrared color and
luminosity) between late and early-type spiral galaxies.


title: Growth of Intermediate-Mass Black Holes in Globular Clusters

abstract:
  We present results of numerical simulations of sequences of binary-single
scattering events of black holes in dense stellar environments. The simulations
cover a wide range of mass ratios from equal mass objects to 1000:10:10 solar
masses and compare purely Newtonian simulations to simulations in which
Newtonian encounters are interspersed with gravitational wave emission from the
binary. In both cases, the sequence is terminated when the binary's merger time
due to gravitational radiation is less than the arrival time of the next
interloper. We find that black hole binaries typically merge with a very high
eccentricity (0.93 < e < 0.95 pure Newtonian; 0.85 < e < 0.90 with
gravitational wave emission) and that adding gravitational wave emission
decreases the time to harden a binary until merger by ~ 30% to 40%. We discuss
the implications of this work for the formation of intermediate-mass black
holes and gravitational wave detection.


title:
Spatial distributions of the REFLEX-DXL galaxy clusters at z~0.3
  observed by XMM-Newton

abstract:
  We present XMM-Newton results on the spatially resolved temperature profiles
of eight massive galaxy clusters of a volume-limited sample at redshifts
$z\sim0.3$ (REFLEX-DXL sample) and an additional luminous cluster at
$z=0.2578$, selected from the REFLEX survey. Useful temperature measurements
could be performed out to radii with overdensity 500 ($r_{500}$). The scaled
temperature distributions show good similarities. We discovered diversities in
the temperature gradients at the outer cluster radii with examples of both flat
and strongly decreasing profiles which call for different physical
interpretations. We found an indication of the 'warm-hot' gas existing in or
around the hot clusters. Using RXCJ0307.0-2840 we demonstrate that the errors
on the mass estimates are within 25% up to r_{500}.


title:
Constraints on Neutron Star Parameters from Burst Oscillation Light
  Curves of the Accreting Millisecond Pulsar XTE J1814-338

abstract:
  Detailed modeling of the millisecond brightness oscillations during
thermonuclear bursts from low mass X-ray binaries can provide important
information about neutron star structure. Until now the implementation of this
idea has not been entirely successful, largely because of the negligible
harmonic content in burst oscillation lightcurves. However, the recent
discovery of non-sinusoidal burst oscillation lightcurves from the accreting
millisecond pulsar XTE J1814-338 has changed this situation. We, therefore, for
the first time, make use of this opportunity to constrain neutron star
parameters. In our detailed study of the lightcurves of 22 bursts, we fit the
burst oscillation lightcurves with fully general relativistic models that
include light-bending and frame-dragging for lightcurve calculation, and
compute numerically the structure of neutron stars using realistic equations of
state. We find that for our model and parameter grid values, at the 90%
confidence level, Rc^2/GM > 4.2 for the neutron star in XTE J1814-338. We also
find that the photons from the thermonuclear flash come out through the layers
of accreted matter under conditions consistent with Thomson scattering, and
show that the secondary companion is a hydrogen burning main sequence star,
with possible bloating (probably due to X-ray heating).


title: PHL 1811: The Local Prototype of the Lineless High-z SDSS QSOs

abstract:
  Abridged) In the SDSS, several unusual QSOs have been discovered that have
very blue rest-frame UV spectra but no discernible emission lines. Their UV
spectra strongly resemble that of the newly discovered quasar PHL 1811
($z=0.192$; $\rm M_{V}=-25.9$). With magnitudes of $B = 14.4$ and $R = 14.1$,
PHL 1811 is the second brightest quasar known with $z>0.1$ after 3C 273.
Optically it is classified as a Narrow-line Seyfert 1 galaxy (NLS1). Objects of
this class are generally strong soft X-ray emitters, but a BeppoSAX observation
of PHL 1811 showed that it is anomalously X-ray weak. The inferred
$\alpha_{ox}$ was 1.9--2.1, much steeper than the nominal value of 1.6 for
quasars of this optical luminosity, and comparable to the X-ray weakest
quasars. Follow-up {\it Chandra} observations reveal a variable, unabsorbed
X-ray spectrum and confirm that it is intrinsically X-ray weak.


title: Stellar models of evolved secondaries in CVs

abstract:
  In this paper we study the impact of chemically evolved secondaries on CV
evolution. We find that when evolved secondaries are included a spread in the
secondary mass-orbital period plane comparable to that seen in the data is
produced for either the saturated prescription for magnetic braking or the
unsaturated model commonly used for CVs. We argue that in order to explain this
spread a considerable fraction of all CVs should have evolved stars as the
secondaries. The evolved stars become fully convective at lower orbital
periods. Therefore, even if there was an abrupt decrease in magnetic braking
for fully convective stars (contrary to open cluster data) it would not be
expected to produce a sharp break in the period distribution for CVs. We also
explore recent proposed revisions to the angular momentum loss rate for single
stars, and find that only modest increases over the saturated prescription are
consistent with the overall observed spindown pattern. We compare predictions
of our models with diagnostics of the mass accretion rate in WDs and find
results intermediate between the saturated and the older braking prescription.
Taken together these suggest that the angular momentum loss rate may be higher
in CV secondaries than in single stars of the same rotation period, but is
still significantly lower than in the traditional model. Alternative
explanations for the CV period gap are discussed.


title: Compact binaries in globular clusters

abstract:
  In dense stellar systems the frequent dynamical interactions between stars
play a crucial role in the formation and evolution of compact binaries. We
study these processes using a novel approach combining a state-of-the-art
binary population synthesis code with a simple treatment of dynamical
interactions in dense star cluster cores. Here we focus on the dynamical and
evolutionary processes leading to the formation of compact binaries containing
white dwarfs in dense globular clusters. We demonstrate that dynamics can
increase by factors ~ 2 - 100 the production rates of interesting binaries such
as cataclysmic variables, ``nonflickerers'' (He white dwarfs with a heavier
dark companion), merging white dwarf binaries with total masses above the
Chandrasekhar limit, and white dwarf binaries emitting gravitational waves in
the LISA band.


title: Modelling Galaxies with a Multi-Phase ISM in 3d

abstract:
  We present a modified TREESPH code to model galaxies in 3d. The model
includes a multi-phase description of the interstellar medium which combines
two numerical techniques. A diffuse warm/hot gas phase is modelled by SPH while
a sticky particle scheme is used to represent a cloudy medium. Interaction
processes, such as star formation and feedback, cooling and mixing by
condensation and evaporation, are taken into account. Here we apply our model
to the evolution of a Milky Way type galaxy. After an initial stage, a
quasi-equilibrium state is reached. It is characterised by a star formation
rate of ~1 M_sun/year. Condensation and evaporation rates are in balance at
0.1-1 M_sun/year.


title: On the Vertical Structure of Radiation-Dominated Accretion Disks

abstract:
  The vertical structure of black hole accretion disks in which radiation
dominates the total pressure is investigated using a three-dimensional
radiation-MHD calculation. The domain is a small patch of disk centered 100
Schwarzschild radii from a black hole of 10^8 Solar masses, and the stratified
shearing-box approximation is used. Magneto-rotational instability converts
gravitational energy to turbulent magnetic and kinetic energy. The gas is
heated by magnetic dissipation and by radiation damping of the turbulence, and
cooled by diffusion and advection of radiation through the vertical boundaries.
The resulting structure differs in several fundamental ways from the standard
Shakura-Sunyaev picture. The disk consists of three layers. At the midplane,
the density is large, and the magnetic pressure and total accretion stress are
less than the gas pressure. In lower-density surface layers that are optically
thick, the magnetic pressure and stress are greater than the gas pressure but
less than the radiation pressure. Horizontal density variations in the surface
layers exceed an order of magnitude. Magnetic fields in the regions of greatest
stress are buoyant, and dissipate as they rise, so the heating rate declines
more slowly with height than the stress. Much of the dissipation occurs at low
column depth, and the interior is cooler and less radiation-dominated than in
the Shakura-Sunyaev model with the same surface mass density and flux. The mean
structure is convectively stable.


title: Differential Rotation in Weakly-Magnetized Neutron Star Atmospheres

abstract:
  The atmospheres of weakly-magnetized neutron stars expand hydrostatically and
rotate differentially during thermonuclear X-ray bursts. Differential rotation
is probably related to the frequency drifts of millisecond burst oscillations
exhibited by about a dozen nuclear-powered X-ray pulsars. Here, we analyze the
linear stability of this differential rotation with respect to local,
axisymmetric, multi-diffusive MHD perturbations, at various heights in the
neutron star atmosphere. Unstable magneto-rotational modes are identified from
within to well above the burning layers. Properties of the fastest growing
modes depend sensitively on the local magnetic field geometry. Linear estimates
suggest that momentum transport due to magneto-rotational instabilities can
affect atmospheric rotation profiles on time-scales relevant to burst
oscillations. This transport would likely strengthen the coherence of burst
oscillations and contribute to their drifts.


title: Quintessence and Thermal Matter

abstract:
  We investigate the effects of thermal interactions on tracking models of
quintessence. We show that even Planck-suppressed interactions between matter
and the quintessence field can alter its evolution. The dark energy equation of
state is in many cases strongly affected by matter couplings. We obtain a bound
on the coupling between quintessence and relativistic relic particles such as
the photon or neutrino.


title:
Predicting Planets in Known Extra-Solar Planetary Systems I: Test
  Particle Simulations

abstract:
  Recent work has suggested that many planetary systems lie near instability.
If all systems are near instability, an additional planet must exist in stable
regions of well-separated extra-solar planetary systems to push these systems
to the edge of stability. We examine the known systems by placing massless test
particles in between the planets and integrating for 1-10 million years. We
find that some systems, HD168443 and HD74156, eject nearly all test particles
within 2 million years. However we find that HD37124, HD38529, and 55Cnc have
large contiguous regions in which particles survive for 10 million years. These
three systems, therefore, seem the most likely candidates for additional
companions. Furthermore HD74156 and HD168443 must be complete and therefore
radial velocity surveys should only focus on detecting more distant companions.
We also find that several systems show stable regions that only exist at
nonzero eccentricities.


title: The Variability of Sagittarius A* at Centimeter Wavelengths

abstract:
  We present the results of a 3.3-year project to monitor the flux density of
Sagittarius A* at 2.0, 1.3, and 0.7 cm with the VLA. The fully calibrated light
curves for Sgr A* at all three wavelengths are presented. Typical errors in the
flux density are 6.1%, 6.2%, and 9.2% at 2.0, 1.3, and 0.7 cm, respectively.
There is preliminary evidence for a bimodal distribution of flux densities,
which may indicate the existence of two distinct states of accretion onto the
supermassive black hole. At 1.3 and 0.7 cm, there is a tail in the distribution
towards high flux densities. Significant variability is detected at all three
wavelengths, with the largest amplitude variations occurring at 0.7 cm. The rms
deviation of the flux density of Sgr A* is 0.13, 0.16, and 0.21 Jy at 2.0, 1.3,
and 0.7 cm, respectively. During much of this monitoring campaign, Sgr A*
appeared to be relatively quiescent compared to results from previous
campaigns. At no point during the monitoring campaign did the flux density of
Sgr A* more than double its mean value. The mean spectral index of Sgr A* is
alpha=0.20+/-0.01, with a standard deviation of 0.14. The spectral index
appears to depend linearly on the observed flux density at 0.7 cm with a
steeper index observed during outbursts. This correlation is consistent with
the expectation for outbursts that are self-absorbed at wavelengths of 0.7 cm
or longer and inconsistent with the effects of simple models for interstellar
scintillation. Much of the variability of Sgr A*, including possible time lags
between flux density changes at the different wavelengths, appears to occur on
time scales less than the time resolution of our observations (8 days). Future
observations should focus on the evolution of the flux density on these time
scales.


title:
Models for Solar Abundance Stars with Gravitational Settling and
  Radiative Accelerations: Application to M67 and NGC188

abstract:
  Evolutionary models taking into account radiative accelerations, thermal
diffusion, and gravitational settling for 28 elements, including all those
contributing to OPAL stellar opacities, have been calculated for solar
metallicity stars of 0.5 to 1.4 solar masses. The Sun has been used to
calibrate the models. Isochrones are fitted to the observed color-magnitude
diagrams (CMDs) of M67 and NGC188, and ages of 3.7 and 6.4 Gyr are respectively
determined. Convective core overshooting is not required to match the turnoff
morphology of either cluster, including the luminosity of the gap in M67,
because central convective cores are larger when diffusive processes are
treated. This is due mainly to the enhanced helium and metal abundances in the
central regions of such models. The observation of solar metallicity open
clusters with ages in the range 4.8--5.7Gyr would further test the calculations
of atomic diffusion in central stellar regions: according to non-diffusive
isochrones, clusters should not have gaps near their main-sequence turnoffs if
they are older than ~4.8Gyr, whereas diffusive isochrones predict that gaps
should persist up to ages of ~5.7Gyr. Surface abundance isochrones are also
calculated. In the case of M67 and NGC188, surface abundance variations are
expected to be small. Abundance differences between stars of very similar Teff
are expected close to the turnoff, especially for elements between P and Ca.
Moreover, in comparison with the results obtained for giants, small generalized
underabundances are expected in main-sequence stars. The lithium to beryllium
ratio is discussed briefly and compared to observations.


title:
Distribution of Faraday Rotation Measure in Jets from Active Galactic
  Nuclei II. Prediction from our Sweeping Magnetic Twist Model for the Wiggled
  Parts of AGN Jets and Tails

abstract:
  Distributions of Faraday rotation measure (FRM) and the projected magnetic
field derived by a 3-dimensional simulation of MHD jets are investigated based
on our "sweeping magnetic twist model". FRM and Stokes parameters were
calculated to be compared with radio observations of large scale wiggled AGN
jets on kpc scales. We propose that the FRM distribution can be used to discuss
the 3-dimensional structure of magnetic field around jets and the validity of
existing theoretical models, together with the projected magnetic field derived
from Stokes parameters. In the previous paper, we investigated the basic
straight part of AGN jets by using the result of a 2-dimensional axisymmetric
simulation. The derived FRM distribution has a general tendency to have a
gradient across the jet axis, which is due to the toroidal component of the
magnetic field generated by the rotation of the accretion disk. In this paper,
we consider the wiggled structure of the AGN jets by using the result of a
3-dimensional simulation. Our numerical results show that the distributions of
FRM and the projected magnetic field have a clear correlation with the large
scale structure of the jet itself, namely, 3-dimensional helix. Distributions,
seeing the jet from a certain direction, show a good matching with those in a
part of 3C449 jet. This suggests that the jet has a helical structure and that
the magnetic field (especially the toroidal component) plays an important role
in the dynamics of the wiggle formation because it is due to a current-driven
helical kink instability in our model.


title: Future Japanese missions for the study of warm-hot intergalactic medium

abstract:
  We present our proposal for a small X-ray mission DIOS (Diffuse Intergalactic
Oxygen Surveyor) to perform survey observations of warm-hot intergalactic
medium using OVII and OVIII emission lines. This will be proposed to a small
satellite program planned by ISAS/JAXA in Japan for a launch in 2008. The
instrument consists of an array of TES microcalorimeters with an energy
resolution 2 eV, cooled by mechanical coolers. The X-ray telescope will employ
4-stage reflection mirrors with a focal length as short as 70 cm and an angular
resolution 2'. In addition to DIOS, we briefly describe the NeXT (New X-ray
Telescope) mission, which is a larger Japanese X-ray observatory to be launched
in 2010 and plans to explore non-thermal processes in the universe.


title: Maps of the Cosmos: The Cosmic Microwave Background

abstract:
  Since the IAU XXIV meeting in 2000, the CMB anisotropy has matured from being
one of a number of cosmological probes to forming the bedrock foundation for
what is now the standard model of cosmology. The large advances over the past
three years have come from making better and better maps of the cosmos. We
review the state of measurements of the anisotropy and outline some of what we
have learned since 2000. The recent advancements may be placed roughly into
three categories: 1) What we learn from the CMB with minimal input from other
cosmic measurements such as the Hubble constant; 2) What we learn from the CMB
in combination with other probes of large scale structure; and 3) What we learn
by using the CMB as a back light. Future directions are also discussed. It is
clear: we have much more to learn from the CMB anisotropy.


title:
An HST parallax of the distant cataclysmic variable V1223 Sgr, its
  system parameters, and accretion rate

abstract:
  Using the Hubble space Telescope Fine Guidance Sensor, we have measured the
trigonometric parallax of the bright cataclysmic variable 1223 Sgr. The
absolute parallax is pi(abs)= 1.96+-0.18mas, making V1223 Sgr the most distant
CV with a well-determined trigonometric parallax. This distance, a Lutz-Kelker
correction, and the previously measured extinction yield an absolute visual
high-state magnitude Mv=4.0+-0.2. We outline a model, which is consistent with
the observed spin-down of the white dwarf and provides for much of the
UV/optical emission by reverberation of X-rays. From previous X-ray and
UV/optical data, we derive an accretion luminosity Lacc=(2.6+-0.8)e34 erg/s, a
white dwarf mass M_1=0.93+-0.12Msun, and an accretion rate dot M=(1.4+-0.3)e17
g/s.