title:
The RR Lyrae Star Period - K-band Luminosity Relation of the Globular
  Cluster M3

abstract:
  That the RR Lyrae star period -- K-band luminosity relation is a promising
tool as a distance indicator in the Milky Way and Local Group of Galaxies is
apparent on observational and theoretical grounds in the literature. Less clear
is the sensitivity of the relation, and consequently the physics of horizontal
branch stars, to differences in stellar environment. In this paper, the first
measurement of the (fundamental) period -- K-band luminosity relation for the
central region of a globular cluster is presented. It is based on a sample of
seven RR Lyrae stars imaged with adaptive optics. In addition, the relation for
the outer region has been reanalyzed, and is found to be in good agreement with
both the previous estimate by Longmore et al. (1990), and with the inner region
relation, especially when irregular and double-mode RR Lyrae stars are
excluded. Importantly, there is no difference between the slope of the inner
and outer region relation within measurement uncertainties, suggesting no
difference in evolutionary state (luminosity). Taking the M3 distance modulus
as 15.0 +/- 0.07mag, the period -- absolute K-band magnitude relation derived
by linear least squares fitting is: M_K = -0.96 (+/- 0.10) - 2.42 (+/- 0.16)Log
Po for the inner region. Excluding irregular variable stars, the outer region
relation is: M_K = -1.07 (+/- 0.10) - 2.38 (+/- 0.15)Log Po. This good
agreement provides further strong support for the near-IR period-luminosity
relation as a distance indicator.


title: Circularly Symmetric Apodization via Starshaped Masks

abstract:
  Recently, we introduced a class of shaped pupil masks, called spiderweb
masks, that produce point spread functions having annular dark zones. With such
masks, a single image can be used to probe a star for extrasolar planets. In
this paper, we introduce a new class of shaped pupil masks that also provide
annular dark zones. We call these masks starshaped masks. Given any circularly
symmetric apodization function, we show how to construct a corresponding
starshaped mask that has the same point-spread function (out to any given outer
working distance) as obtained by the apodization.


title: Nascent starbursts in synchrotron-deficient galaxies with hot dust

abstract:
  Three nearby galaxies which have abnormally high infrared to radio continuum
ratios, NGC 1377, IC 1953 and NGC 4491, are investigated with a view to
understanding the physical origin of their peculiarity. We review the existing
data and present new radio continuum measurements along with near-infrared
integral-field spectroscopy and molecular gas observations. The three galaxies
have low luminosities but starburst-like infrared colors; in NGC 1377, no
synchrotron emission is detected at any wavelength; in IC 1953, the observed
synchrotron component is attributable to the spiral disk alone, and is lacking
in the central regions; the radio spectrum of NGC 4491 is unusually flat. We
also compare and contrast them with NGC 4418, a heavily extinguished galaxy
which shares some attributes with them. After examining various scenarios, we
conclude that these galaxies are most likely observed within a few Myr of the
onset of an intense star formation episode after being quiescent for at least ~
100 Myr. This starburst, while heating the dust, has not produced optical
signatures nor a normal amount of cosmic rays yet. We briefly discuss the
statistics of such galaxies and what they imply for star formation surveys.


title: Arc statistics with realistic cluster models

abstract:
  Arc statistics is known to be a powerful cosmological tool. Numerical lensing
simulations show that orders of magnitude differences in the number of {\em
giant} arcs on the whole sky are expected in different cosmological models. In
this paper, we discuss the analytic and numerical methods in arc statistics and
show that analytic models fail to reproduce the efficiency for strong lensing
of more realistic numerical cluster models. Then, we discuss two recent
extensions of the lensing simulations, i.e. the effects of cD galaxies in the
lensing clusters and the impact of cluster mergers on arc statistics. We show
that cD galaxies can increase the lensing cross sections for long and thin arcs
by perhaps up to $\sim50%$, while major mergers can change the cluster
efficiency for producing such arcs by up to one order of magnitude.


title: Photometric Variability at the L/T Dwarf Boundary

abstract:
  We have monitored the photometric variability of nine field L and T brown
dwarfs for 10 nights during the course of one month with the Palomar 60 inch
Telescope Near-Infrared Camera. Results of statistical analyses indicate that
at least three of the nine targets show significant evidence for variability,
and three more are possibly variable. Fractional deviations from the median
flux vary from 5% to 25%. Two of the variable targets, 2MASS 0030-14 (L7) and
SDSS 0151+12 (T1), have marginally significant peaks in their periodograms. The
phased light curves show evidence for periodic behavior on timescales of 1.5
hours and 3.0 hours respectively. No significant correlations between
variability amplitude and spectral type or (J-K_s) color are found. While it is
clear that variability exists in objects near the L/T dwarf boundary, we find
no evidence that variability near the L/T boundary is more likely than it is
for early L dwarfs.


title: A Turbulent Origin for Flocculent Spiral Structure in Galaxies

abstract:
  The flocculent structure of star formation in 7 galaxies has a Fourier
transform power spectrum for azimuthal intensity scans with a power law slope
that increases systematically from -1 at large scales to -1.7 at small scales.
This is the same pattern as in the power spectra for azimuthal scans of HI
emission in the Large Magellanic Clouds and for flocculent dust clouds in
galactic nuclei. The steep part also corresponds to the slope of -3 for
two-dimensional power spectra that have been observed in atomic and molecular
gas surveys of the Milky Way and the Large and Small Magellanic Clouds. The
same power law structure for star formation arises in both flocculent and grand
design galaxies, which implies that the star formation process is the same in
each. Fractal Brownian motion models that include discrete stars and an
underlying continuum of starlight match the observations if all of the emission
is organized into a global fractal pattern with an intrinsic 1D power spectrum
having a slope between 1.3 and 1.8. We suggest that the power spectrum of
optical light in galaxies is the result of turbulence, and that large-scale
turbulent motions are generated by sheared gravitational instabilities which
make flocculent spiral arms first and then cascade to form clouds and clusters
on smaller scales.


title:
A Turbulent Origin for Flocculent Spiral Structure in Galaxies: II.
  Observations and Models of M33

abstract:
  Fourier transform power spectra of azimuthal scans of the optical structure
of M33 are evaluated for B, V, and R passbands and fit to fractal models of
continuum emission with superposed star formation. Power spectra are also
determined for Halpha. The best models have intrinsic power spectra with 1D
slopes of around -0.7pm0.7, significantly shallower than the Kolmogorov
spectrum (slope =-1.7) but steeper than pure noise (slope=0). A fit to the
power spectrum of the flocculent galaxy NGC 5055 gives a steeper slope of
around -1.5pm0.2, which could be from turbulence. Both cases model the optical
light as a superposition of continuous and point-like stellar sources that
follow an underlying fractal pattern. Foreground bright stars are clipped in
the images, but they are so prominent in M33 that even their residual affects
the power spectrum, making it shallower than what is intrinsic to the galaxy. A
model consisting of random foreground stars added to the best model of NGC 5055
fits the observed power spectrum of M33 as well as the shallower intrinsic
power spectrum that was made without foreground stars. Thus the optical
structure in M33 could result from turbulence too.


title: Cosmological results from the 2dF Galaxy Redshift Survey

abstract:
  The 2dF Galaxy Redshift Survey (2dFGRS) has produced a three-dimensional map
of the distribution of 221,000 galaxies covering 5% of the sky and reaching out
to a redshift z=0.3. This is first map of the large-scale structure in the
local Universe to probe a statistically representative volume, and provides
direct evidence that the large-scale structure of the Universe grew through
gravitational instability. Measurements of the correlation function and power
spectrum of the galaxy distribution have provided precise measurements of the
mean mass density of the Universe and the relative contributions of cold dark
matter, baryons, and neutrinos. The survey has produced the first measurements
of the galaxy bias parameter and its variation with galaxy luminosity and type.
Joint analysis of the 2dFGRS and cosmic microwave background power spectra
gives independent new estimates for the Hubble constant and the vacuum energy
density, and constrains the equation of state of the vacuum.


title:
Numerical tests of dynamical friction in gravitational inhomogeneous
  systems

abstract:
  In this paper, I test by numerical simulations the results of Del Popolo &
Gambera (1998),dealing with the extension of Chandrasekhar and von Neumann's
analysis of the statistics of the gravitational field to systems in which
particles (e.g., stars, galaxies) are inhomogeneously distributed. The paper is
an extension of that of Ahmad & Cohen (1974), in which the authors tested some
results of the stochastic theory of dynamical friction developed by
Chandrasekhar & von Neumann (1943) in the case of homogeneous gravitational
systems. It is also a continuation of the work developed in Del Popolo
(1996a,b), which extended the results of Ahmad & Cohen (1973), (dealing with
the study of the probability distribution of the stochastic force in
homogeneous gravitational systems) to inhomogeneous gravitational systems.
Similarly to what was done by Ahmad & Cohen (1974) in the case of homogeneous
systems, I test, by means of the evolution of an inhomogeneous system of
particles, that the theoretical rate of force fluctuation d F/dt describes
correctly the experimental one, I find that the stochastic force distribution
obtained for the evolved system is in good agreement with the Del Popolo &
Gambera (1998) theory. Moreover, in an inhomogeneous background the friction
force is actually enhanced relative to the homogeneous case.


title:
The energy spectrum of cosmic rays above 10^15 eV as derived from air
  Cherenkov light measurements in Yakutsk

abstract:
  The Yakutsk array observes the Cherenkov light emitted by UHECR in
atmosphere. Recently, an autonomous subarray is added consisting of
photomultipliers to measure the showers in the knee region. Our aim is to
analyze the combined data set in order to derive the cosmic ray spectrum in the
energy range as wide as possible using the same technique.
  The advantage of the air Cherenkov light measurement is the model independent
estimation of the EAS primary energy using the total light flux emitted in the
atmosphere. A set of the light lateral distributions observed in the extended
energy range is presented also.


title:
Molecular Evolution in Collapsing Prestellar Cores II: The Effect of
  Grain-surface Reactions

abstract:
  The molecular evolution that occurs in collapsing prestellar cores is
investigated. To model the dynamics, we adopt the Larson-Penston (L-P) solution
and analogues with slower rates of collapse. For the chemistry, we utilize the
new standard model (NSM) with the addition of deuterium fractionation and
grain-surface reactions treated via the modified rate approach. The use of
surface reactions distinguishes the present work from our previous model. We
find that these reactions efficiently produce H2O, H2CO, CH3OH, N2, and NH3
ices. In addition, the surface chemistry influences the gas-phase abundances in
a variety of ways. The current reaction network along with the L-P solution
allows us to reproduce satisfactorily most of the molecular column densities
and their radial distributions observed in L1544. The agreement tends to worsen
with models that include strongly delayed collapse rates. Inferred radial
distributions in terms of fractional abundances are somewhat harder to
reproduce. In addition to our standard chemical model, we have also run a model
with the UMIST gas-phase chemical network. The abundances of gas-phase
S-bearing molecules such as CS and CCS are significantly affected by
uncertainties in the gas-phase chemical network. In all of our models, the
column density of N2H+ monotonically increases as the central density of the
core increases during collapse from 3 10^4 cm-3 to 3 10^7 cm-3. Thus, the
abundance of this ion can be a probe of evolutionary stage. Molecular D/H
ratios in assorted cores are best reproduced in the L-P picture with the
conventional rate coefficients for fractionation reactions. If we adopt the
newly measured and calculated rate coefficients, the D/H ratios, especially
N2D+/N2H+, become significantly lower than the observed values.


title:
Wave Effects in Gravitational Lensing of Gravitational Waves from
  Chirping Binaries

abstract:
  In the gravitational lensing of gravitational waves, the wave optics should
be used instead of the geometrical optics when the wavelength $\lambda$ of the
gravitational waves is longer than the Schwarzschild radius of the lens mass
$M_L$. For the gravitational lensing of the chirp signals from the coalescence
of the super massive black holes at the redshift $z_S\sim 1$ relevant to LISA,
the wave effects become important for the lens mass smaller than $\sim 10^8
M_{\odot}$. For such cases, we compute how accurately we can extract the mass
of the lens and the source position from the lensed signal. We consider two
simple lens models: the point mass lens and the SIS (Singular Isothermal
Sphere). We find that the lens mass and the source position can be determined
within $\sim 0.1% [(S/N)/10^3]^{-1}$ for the lens mass larger than $10^8
M_{\odot}$ and $\gsim 10% [(S/N)/10^3]^{-1}$ for the lens mass smaller than
$10^7 M_{\odot}$ due to the diffraction effect, where $(S/N)$ is the signal to
noise ratio of the unlensed chirp signals. For the SIS model, if the source
position is outside the Einstein radius, only a single image exists in the
geometrical optics approximation so that the lens parameters can not be
determined. While in the wave optics cases we find that the lens mass can be
determined even for $M_L < 10^8 M_{\odot}$. For the point mass lens, one can
extract the lens parameters even if the source position is far outside the
Einstein radius. As a result, the lensing cross section is an order of
magnitude larger than that for the usual strong lensing of light.


title: Search for relic neutralinos with Milagro

abstract:
  The neutralino, the lightest stable supersymmetric particle, is a strong
theoretical candidate for the missing astronomical "dark matter". Depending on
their annihilation cross section, relic neutralinos from early formation of the
Universe trapped in orbits around massive objects may currently be annihilating
at measurable rates. The Minimal Supersymmetric extension of the Standard Model
predicts that the gamma rays emerging from one of the annihilation modes will
give a distinct monochromatic signal with energy between 100GeV and 10TeV,
depending on the neutralino mass. An additional "continuum" spectrum signal of
photons will be produced by the decay of secondaries produced in the
non-photonic annihilation modes.
  Milagro is an air shower array which uses the water Cherenkov technique and
is capable of detecting TeV gamma rays from the direction of the Sun with an
angular resolution of less than a degree. It is the first instrument capable of
establishing a limit on the gamma-ray flux from neutralino annihilations near
the Sun.
  In this report results of a search for neutralino to photon annihilation with
the Milagro gamma-ray observatory are presented.


title: A Concept for an STJ-based Spectrograph

abstract:
  We describe a multi-order spectrograph concept suitable for 8m-class
telescopes, using the intrinsic spectral resolution of Superconducting
Tunneling Junction detectors to sort the spectral orders. The spectrograph
works at low orders, 1-5 or 1-6, and provides spectral coverage with a
resolving power of R~8000 from the atmospheric cutoff at 320 nm to the long
wavelength end of the infrared H or K band at 1800 nm or 2400 nm. We calculate
that the spectrograph would provide substantial throughput and wavelength
coverage, together with high time resolution and sufficient dynamic range. The
concept uses currently available technology, or technologies with short
development horizons, restricting the spatial sampling to two linear arrays;
however an upgrade path to provide more spatial sampling is identified. All of
the other challenging aspects of the concept - the cryogenics, thermal baffling
and magnetic field biasing - are identified as being feasible.


title: Cool stars in NGC 2547 and pre main sequence lithium depletion

abstract:
  We present the results of a spectroscopic survey of X-ray selected, low-mass
candidate members of the young open cluster NGC 2547. Using a combination of
photometry, spectroscopic indices and radial velocities we refine our candidate
list and then use our spectroscopy to study the progression of lithium
depletion in low-mass pre main sequence stars. We derive lithium abundances or
upper limits for all our candidate members, which have effective temperatures
in the range 5000>Teff>3200K, and compare these with predictions for lithium
burning and depletion provided by a number of models and also with the lithium
depletion seen in younger and older stars. We find that some models can
reproduce the lithium abundance pattern of NGC 2547 if the cluster has an age
of ~20-35Myr, which is also indicated by fits to low-mass isochrones in the
Hertzsprung-Russell diagram. But the lack of significant further lithium
depletion between NGC 2547 and older clusters argues for an age of at least
50Myr, more in keeping with the lack of lithium observed in even fainter NGC
2547 candidates. We show that reconciliation of these age estimates may require
additions to the physics incorporated in current generations of pre main
sequence models.


title: Primordial Magnetic Fields and Causality

abstract:
  We discuss the implications of causality on a primordial magnetic field. We
show that the residual field on large scales is much more suppressed than
usually assumed and that a helical component is even more reduced. Due to this
strong suppression, even maximal primordial fields generated at the electroweak
phase transition can just marginally seed the fields in clusters, but they
cannot leave any detectable imprint on the cosmic microwave background.


title: Intrinsic Redshifts and the Hubble Constant

abstract:
  We show that the V_CMB velocities of the Fundamental Plane (FP) clusters
studied in the Hubble Key Project appear to contain the same discrete
"velocities" found previously by us and by Tifft to be present in normal
galaxies. Although there is a particular Hubble constant associated with our
findings we make no claim that its accuracy is better than that found by the
Hubble Key Project. We do conclude, however, that if intrinsic redshifts are
present and are not taken into account, the Hubble constant obtained will be
too high.


title: Squeezars: Tidally powered stars orbiting a massive black hole

abstract:
  We propose that there exists a class of transient sources, "squeezars", which
are stars caught in highly eccentric orbits around a massive (m<10^8 Mo) black
hole (MBH), whose atypically high luminosity (up to a significant fraction of
their Eddington luminosity) is powered by tidal interactions with the MBH.
Their existence follows from the presence of a mass sink, the MBH, in the
galactic center, which drives a flow of stars into nearly radial orbits to
replace those it has destroyed. We consider two limits for the stellar response
to tidal heating: surface heating with radiative cooling ("hot squeezars") and
bulk heating with adiabatic expansion ("cold squeezars"), and calculate the
evolution of the squeezar orbit, size, luminosity and effective temperature.
The squeezar formation rate is only ~0.05 that of tidal disruption flares, but
squeezar lifetimes are many orders of magnitude longer, and so future
observations of squeezars in nearby galaxies can probe the tidal process that
feeds MBHs and the effects of extreme tides on stars. The mean number of
squeezars orbiting the Galactic MBH is estimated at 0.1-1.


title: Orbital inspiral into a massive black hole in a galactic center

abstract:
  A massive black hole (MBH) in a galactic center drives a flow of stars into
nearly radial orbits to replace those it destroyed. Stars whose orbits cross
the event horizon r_s or the tidal disruption radius r_t are promptly destroyed
in an orbital period P. Stars with orbital periapse r_p slightly larger than
the sink radius q=max(r_s,r_t) may slowly spiral in due to dissipative
interactions with the MBH, e.g. gravitational wave emission, tidal heating or
accretion disk drag, with observable consequences and implications for the MBH
growth rate. Unlike prompt destruction, the inspiral time is typically >>P.
This time is limited by the same scattering process that initially deflected
the star into its eccentric orbit, since it can deflect it again to a wider
orbit where dissipation is inefficient. The ratio between slow and prompt event
rates is therefore much smaller than that implied by the ratio of
cross-sections, ~r_p/q, and so only prompt disruption contributes significantly
to the mass of the MBH. Conversely, most stars that scatter off the MBH survive
the extreme tidal interaction ("tidal scattering"). We derive general
expressions for the inspiral event rate and the mean number of inspiraling
stars, and show that the survival probability of tidally scattered stars is ~1,
and that the number of tidally heated stars ("squeezars") and gravity wave
emitting stars in the Galactic Center is ~0.1-1.


title: Introductory Overview of Modern Cosmology

abstract:
  A basic modern picture of the universe is given here. The lectures start from
the historical ideas of a static universe. Then I move on to Newtonian
cosmology and derive the main cosmological equations in the framework of
Newtonian mechanics for the sake of simplicity. With a qualitative description
of general relativity, the expansion of the universe and elementary idea of the
hot Big Bang models are introduced. The problems of the hot Big Bang, inflation
and structure formation are explained here in simple language.


title: Modeling the dynamical evolution of the M87 globular cluster system

abstract:
  We study the dynamical evolution of the M87 globular cluster system (GCS)
with a number of numerical simulations. We explore a range of different initial
conditions for the GCS mass function (GCMF), for the GCS spatial distribution
and for the GCS velocity distribution. We confirm that an initial power-law
GCMF like that observed in young cluster systems can be readily transformed
through dynamical processes into a bell-shaped GCMF. However,only models with
initial velocity distributions characterized by a strong radial anisotropy
increasing with the galactocentric distance are able to reproduce the observed
constancy of the GCMF at all radii.We show that such strongly radial orbital
distributions are inconsistent with the observed kinematics of the M87 GCS. The
evolution of models with a bell-shaped GCMF with a turnover similar to that
currently observed in old GCS is also investigated. We show that models with
this initial GCMF can satisfy all the observational constraints currently
available on the GCS spatial distribution,the GCS velocity distribution and on
the GCMF properties.In particular these models successfully reproduce both the
lack of a radial gradient of the GCS mean mass recently found in an analysis of
HST images of M87 at multiple locations, and the observed kinematics of the M87
GCS.Our simulations also show that evolutionary processes significantly affect
the initial GCS properties by leading to the disruption of many clusters and
changing the masses of those which survive.The preferential disruption of inner
clusters flattens the initial GCS number density profile and it can explain the
rising specific frequency with radius; we show that the inner flattening
observed in the M87 GCS spatial distribution can be the result of the effects
of dynamical evolution on an initially steep density profile. (abridged)


title: Observing the Reionization Epoch Through 21 Centimeter Radiation

abstract:
  We study the observability of the reionization epoch through the 21 cm
hyperfine transition of neutral hydrogen. We use a high-resolution cosmological
simulation (including hydrodynamics) together with a fast radiative transfer
algorithm to compute the evolution of 21 cm emission from the intergalactic
medium (IGM) in several different models of reionization. We show that the mean
brightness temperature of the IGM drops from dT_b~25 mK to dT_b~0.01 mK during
overlap (over a frequency interval of ~25 MHz), while the root mean square
brightness temperature fluctuations on small scales drop abruptly from ~10 mK
before overlap to ~0.1 mK at the end of overlap. We show that 21 cm
observations can efficiently discriminate models with a single early
reionization epoch from models with two distinct reionization episodes.


title:
High Energy Photons, Neutrinos and Gravitational Waves from Gamma-Ray
  Bursts

abstract:
  Most of the current knowldege about GRB is based on electromagnetic
observations at MeV and lower energies. Here we focus on some recent
theoretical work on GRB, in particular the higher energy (GeV-TeV) photon
emission, and two potentially important non-electromagnetic channels, the TeV
and higher energy neutrino signals, and the gravitational wave signals expected
from GRB.


title: Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data

abstract:
  For a complete 12 micron flux-limited sample of 207 IRAS sources, we have
extracted light curves in seven infrared bands between 1.25 - 60 microns using
the database of the DIRBE instrument on the COBE satellite. Using previous
infrared surveys, we filtered these light curves to remove datapoints affected
by nearby companions. In the time-averaged DIRBE color-color plots, we find
clear segregation of semi-regulars, Mira variables, carbon stars, OH/IR stars,
and red giants without circumstellar dust and with little or no visual
variation. The DIRBE 1.25 - 25 micron colors become progressively redder and
the variability in the DIRBE database increases along the oxygen-rich sequence
non-dusty slightly varying red giants -> SRb/Lb -> SRa -> Mira -> OH/IR and the
carbon-rich SRb/Lb -> Mira sequence. This supports previous assertions that
these are evolutionary sequences involving the continued production and
ejection of dust. Carbon stars are redder than oxygen-rich stars for the same
variability type, except in the F(12)/F(25) ratio. Of the 28 sources in the
sample not previous noted to be variable, 18 are clearly variable in the DIRBE
data, with amplitudes of variation of ~0.9 magnitudes at 4.9 microns and ~0.6
magnitudes at 12 microns, consistent with them being very dusty Mira-like
variables. The light curves of the semi-regular variable L2 Pup are
particularly remarkable. The maxima at 1.25, 2.2, and 3.5 microns occur 10 - 20
days before those at 4.9 and 12 microns, and, at 4.9 and 12 microns, another
maximum is seen between the two near-infrared maxima.


title:
Gravitational lensing constraints on dark energy from modified Friedmann
  equations

abstract:
  The existence of a dark energy component has usually been invoked as the most
plausible way to explain the recent observational results. However, it is also
well known that effects arising from new physics (e.g., extra dimensions) can
mimic the gravitational effects of a dark energy through a modification of the
Friedmann equation. In this paper we investigate some observational
consequences of a flat, matter dominated and accelerating/decelerating scenario
in which this modification is given by $H^{2} = g(\rho_m, n, q)$ where
$g(\rho_m, n, q)$ is a new function of the energy density $\rho_m$, the
so-called generalized Cardassian models. We mainly focus our attention on the
constraints from statistical properties of gravitationally lensed quasars on
the parameters $n$ and $q$ that fully characterize the models. We show that
these models are in agreement with the current gravitationally lensed quasar
data for a large interval of the $q - n$ parametric space. The dependence of
the acceleration redshift (the redshift at which the universe begins to
accelerate) on these parameters is also briefly discussed.


title:
How Spectral Shapes of Magnetic Energy and Magnetic Helicity Influence
  their Respective Decay Time Scales

abstract:
  It is shown that in magnetohydrodynamics, the shapes of the magnetic energy
and magnetic helicity spectra can influence whether the magnetic helicity
resistive dissipation time scale is longer, equal to, or shorter than that of
magnetic energy. The calculations highlight that magnetic helicity need not
always dissipate significantly more slowly than magnetic energy. While this may
be implicitly understood in detailed studies of magnetic helicity in plasma
devices, it is not sufficiently emphasized in elementary discussions comparing
magnetic helicity vs. magnetic energy evolution. Measuring magnetic energy and
helicity decay times may provide a posteriori insight into the initial spectra.


title: The Radio-FIR correlation: Is MHD Turbulence the Cause?

abstract:
  The radio - far infrared correlation is one of the tightest correlations
found in astronomy. Many of the models explaining this correlation rely on the
association of of global magnetic field strength with gas density. In this
letter we put forward that the physical reason for this association lies within
the processes of magnetohydrodynamic turbulence.


title: Determining the shape of the Universe using discrete sources

abstract:
  Suppose we have identified three clusters of galaxies as being topological
copies of the same object. How does this information constrain the possible
models for the shape of our Universe? It is shown here that, if the Universe
has flat spatial sections, these multiple images can be accommodated within any
of the six classes of compact orientable 3-dimensional flat space forms.
Moreover, the discovery of two more triples of multiple images in the
neighbourhood of the first one, would allow the determination of the topology
of the Universe, and in most cases the determination of its size.


title:
The Faint Cepheids of the Small Magellanic Cloud: an evolutionary
  selection effect?

abstract:
  Two problems about the faintest Small Magellanic Cloud (SMC) Cepheids are
addressed. On one hand evolutionary tracks fail to cross the Cepheid
Instability Strip for the highest magnitudes (i.e. I-mag~17) where Cepheids are
observed; Mass-Luminosity relations (ML) obtained from evolutionary tracks
disagree with Mass-Luminosity relations derived from observations. We find that
the above failures concern models built with standard input physics as well as
with non-standard ones. The present work suggests that towards highest
magnitudes, Cepheids stars undergo a selection effect caused by evolution: only
the most metal poor stars cross the Instability Strip during the ``blue loop''
phase and are therefore the only ones which can be observed at low luminosity.
This solution enables us to reproduce the shape of the lower part of the
Instability Strip and improves the agreement between observed and theoretical
ML-relations. Some issues are discussed, among them Beat Cepheids results argue
strongly in favor of our hypothesis.


title: Symmetry Parameters of CSS Sources: Evidence of Fuelling?

abstract:
  The compact steep spectrum (CSS) and gigahertz peaked spectrum (GPS) sources
are widely believed to be young radiosources, with ages <10^6 yr. If the
activity in the nucleus is fuelled by the supply of gas, one might find
evidence of this gas by studying the structural and polarisation
characteristics of CSS sources and their evolution through this gas. In this
paper we discuss some of the possible `smoking-gun' evidence of this gas which
may have triggered and fuelled the radio source.


title: The Discovery of Sgr A*

abstract:
  The compact radio source Sgr A* is associated with a 3.6 million black hole
at the center of the Milky Way. The radio source was discovered in February
1974 by Bruce Balick and Robert L.Brown. The National Radio Astronomy
Observatory's Green Bank 35 km radio link interferometer was used. We discuss
other observations in the years 1965-1985 as well as early VLBI observations.
The name Sgr A* was used for the first time in 1982 by Robert L.Brown and has
become the accepted name in the intervening years.


title: The Galactic Center as a Dark Matter Gamma-Ray Source

abstract:
  The EGRET telescope has identified a gamma-ray source at the Galactic center.
We point out here that the spectral features of this source are compatible with
the gamma-ray flux induced by pair annihilations of dark matter weakly
interacting massive particles (WIMPs). We show that the discrimination between
this interpretation and other viable explanations will be possible with GLAST,
the next major gamma-ray telescope in space, on the basis of both the spectral
and the angular signature of the WIMP-induced component. If, on the other hand,
the data will point to an alternative explanation, we prove that there will
still be the possibility for GLAST to single out a weaker dark matter source at
the Galactic center. The potential of GLAST has been explored both in the
context of a generic simplified toy-model for WIMP dark matter, and in a more
specific setup, the case of dark matter neutralinos in the minimal supergravity
framework. In the latter, we find that even in the case of moderate dark matter
densities in the Galactic center region, there are portions of the parameter
space which will be probed by GLAST.


title: The Formation of Spheroidal Stellar Systems

abstract:
  We summarize current models of the formation of spheroidal stellar systems.
Whereas globular clusters form in an efficient mode of star formation inside
turbulent molecular clouds, the origin of galactic spheroids, that is bulges,
dwarf ellipticals, and giant ellipticals, is directly coupled with structure
formation and merging of structures in the Universe. Disks are the fundamental
building blocks of galaxies and the progenitors of galactic spheroids. The
origin of the various types of spheroids and their global properties can be
understood as a result of disk heating by external perturbations, internal disk
instabilities, or minor and major mergers.


title:
Two 100 Mpc-scale structures in the 3-D distribution of radio galaxies
  and their implications

abstract:
  We present unequivocal evidence for a huge (~80 x 100 x 100 Mpc^3)
super-structure at redshift z=0.27 in the 3-D distribution of radio galaxies
from the TONS08 sample, confirming tentative evidence for such a structure from
the 7C redshift survey (7CRS). A second, newly discovered super-structure is
also less securely found at redshift 0.35 (of dimensions ~100 x 100 x 100
Mpc^3). We present full observational details on the TONS08 sample which was
constructed to probe structures in the redshift range 0 < z < 0.5 by matching
NVSS sources with objects in APM catalogues to obtain a sample of optically
bright (E ~ R < 19.83), radio faint (1.4-GHz flux density S_1.4 > 3 mJy) radio
galaxies in the same 25 deg^2 area as part-II of the 7CRS. Out of the total
sample size of 84 radio galaxies, at least 25 are associated with the two ~100
Mpc-scale super-structures. We use quasi-linear structure formation theory to
estimate the number of such structures expected in the TONS08 volume if the
canonical value for radio galaxy bias is assumed. Under this assumption, the
structures represent ~ 4-5 sigma peaks in the primordial density field and
their expected number is low (~10^-2 - 10^-4). Fortunately, there are several
plausible explanations (many of which are testable) for these low probabilities
in the form of potential mechanisms for boosting the bias on large scales.
These include: the association of radio galaxies with highly biased rich
clusters in super-structures, enhanced triggering by group/group mergers, and
enhanced triggering and/or redshift space distortion in collapsing systems as
the growth of super-structures moves into the non-linear regime (abridged).


title: An estimate of \Omega_m without priors

abstract:
  Using mean relative peculiar velocity measurements for pairs of galaxies, we
estimate the cosmological density parameter $\Omega_m$ and the amplitude of
density fluctuations $\sigma_8$. Our results suggest that our statistic is a
robust and reproducible measure of the mean pairwise velocity and thereby the
$\Omega_m$ parameter. We get $\Omega_m = 0.30^{+0.17}_{-0.07}$ and $\sigma_8 =
1.13^{+0.22}_{-0.23}$. These estimates do not depend on prior assumptions on
the adiabaticity of the initial density fluctuations, the ionization history,
or the values of other cosmological parameters.


title: Active galactic nuclei and the minor merger hypothesis

abstract:
  We have investigated the dynamics of the merging process in the minor merger
hypothesis for active galactic nuclei. We find that for a satellite galaxy to
be able to merge directly with the nucleus of the host galaxy (for example, to
give rise to the compact dust discs which are seen in early type active
galaxies) requires the initial orbit of the satellite to be well aimed. For the
case of the host galaxy being a disc galaxy, if the initial orbits of the
satellites are randomly oriented with respect to the host galaxy, then the
orbits of those which reach the host nuclear regions in a reasonable time, are
also fairly randomly oriented once they reach the nucleus. We note that this
result might be able to provide an explanation of why the jet directions in the
nuclei of Seyfert galaxies are apparently unrelated to the plane of the galaxy
discs.


title:
Cosmological Variation of the Fine Structure Constant from an
  Ultra-Light Scalar Field: The Effects of Mass

abstract:
  Cosmological variation of the fine structure constant $\alpha$ due to the
evolution of a spatially homogeneous ultra-light scalar field ($m \sim H_0$)
during the matter and $\Lambda$ dominated eras is analyzed. Agreement of
$\Delta \alpha/\alpha$ with the value suggested by recent observations of
quasar absorption lines is obtained by adjusting a single parameter, the
coupling of the scalar field to matter.
  Asymptotically $\alpha(t)$ in this model goes to a constant value
$\bar{\alpha} \approx \alpha_0$ in the early radiation and the late $\Lambda$
dominated eras. The coupling of the scalar field to (nonrelativistic) matter
drives $\alpha$ slightly away from $\bar{\alpha}$ in the epochs when the
density of matter is important.
  Simultaneous agreement with the more restrictive bounds on the variation
$|\Delta \alpha/\alpha|$ from the Oklo natural fission reactor and from
meteorite samples can be achieved if the mass of the scalar field is on the
order of 0.5--0.6 $H_\Lambda$, where $H_\Lambda = \Omega_\Lambda^{1/2} H_0$.
  Depending on the scalar field mass, $\alpha$ may be slightly smaller or
larger than $\alpha_0$ at the times of big bang nucleosynthesis, the emission
of the cosmic microwave background, the formation of early solar system
meteorites, and the Oklo reactor. The effects on the evolution of $\alpha$ due
to nonzero mass for the scalar field are emphasized.
  An order of magnitude improvement in the laboratory technique could lead to a
detection of $(\dot{\alpha}/\alpha)_0$.


title: Electron acceleration and heating in collisionless magnetic reconnection

abstract:
  We discuss electron acceleration and heating during collisionless magnetic
reconnection by using the results of implicit kinetic simulations of Harris
current sheets. We consider and compare electron dynamics in plasmas with
different \beta values and perform simulations up to the physical mass ratio.
We analyze the typical trajectory of electrons passing through the reconnection
region, we study the electron velocity, focusing on the out-of-plane velocity,
and we discuss the electron heating along the in-plane and out-of-plane
directions.


title: The hierarchical formation of a stellar cluster

abstract:
  Recent surveys of star forming regions have shown that most stars, and
probably all massive stars, are born in dense stellar clusters. The mechanism
by which a molecular cloud fragments to form several hundred to thousands of
individual stars has remained elusive. Here, we use a numerical simulation to
follow the fragmentation of a turbulent molecular cloud and the subsequent
formation and early evolution of a stellar cluster containing more than 400
stars. We show that the stellar cluster forms through the hierarchical
fragmentation of a turbulent molecular cloud. This leads to the formation of
many small subclusters which interact and merge to form the final stellar
cluster. The hierarchical nature of the cluster formation has serious
implications in terms of the properties of the new-born stars. The higher
number-density of stars in subclusters, compared to a more uniform distribution
arising from a monolithic formation, results in closer and more frequent
dynamical interactions. Such close interactions can truncate circumstellar
discs, harden existing binaries, and potentially liberate a population of
planets. We estimate that at least one-third of all stars, and most massive
stars, suffer such disruptive interactions.


title: Rotational Evolution of Protoneutron Stars

abstract:
  We study the rotational evolution of a protoneutron star with hyperons and
nucleons or solely nucleons in its core due to the escape of the trapped
neutrinos. It is found that at the early stage of its evolution, the stellar
crust contracts significantly, consequently the star spins up. At the late
stage, a the protoneutron star with hyperons, it keeps shrinking and spinning
up till all the trapped neutrinos escape. Consequently, the distribution of the
stellar initial spin periods is skewed toward shorter periods. For a
protoneutron star with only nucleons, the expansion of its core dominates, and
the stellar rotation slows down. After the neutrinos escape, the range of the
spin periods is narrower than the initial one, but the distribution is still
nearly uniform. If the hyperonic star is metastable, its rotational frequency
accelerates distinguishedly before it collapses to a black hole.


title: Depletion of small dust grains in the early stages of molecule formation

abstract:
  ISOCAM allowed the observation of diffuse interstellar regions where the
transition from atomic to molecular gas takes place. In this contribution we
report on spectacular variations of small dust grains abundance in such regions
observed with ISOCAM. In the four cirrus-like clouds observed, we note a
systematic disappearance of small dust grains in regions where CO emission
starts to appear. We suggest that the variations of the small dust grain
abundance observed here are related to the damping of the gas turbulent motions
that favors the coagulation of dust through grain-grain collisions.


title: X-ray Dip Monitoring of XB 1916-053

abstract:
  We report on the long term monitoring of X-ray dips from the ultracompact
low-mass X-ray binary (LMXB) XB 1916-053. Roughly one-month interval
observations were carried out with the Rossi X-ray Timing Explorer (RXTE)
during 1996, during which the source varied between dim, hard states and more
luminous, soft states. The dip spectra and dip lightcurves were compared
against both the broadband luminosity and the derived mass accretion rate Mdot.
The dips spectra could be fitted by an absorbed blackbody plus cut-off power
law non-dip spectral model, with additional absorption ranging from 0 to >100 x
10^22 cm^-2. The amount of additional blackbody absorption was found to vary
with the source luminosity. Our results are consistent with an obscuration of
the inner disk region by a partially ionized outer disk. The size of the
corona, derived from the dip ingress times, was found to be ~10^9 cm. The
corona size did not correlate with the coronal temperature, but seemed to
increase when \Mdot also increased. We discuss our findings in the context of
an evaporated accretion disk corona model and an ADAF-type model.


title:
The Chandra Deep Field-North Survey. XV. Optically Bright, X-ray Faint
  Sources

abstract:
  We have analyzed optically bright, X-ray faint [OBXF; i.e., log(fX/fR) < -2]
sources identified in an 178.9 square arcminute area within the Chandra Deep
Field-North (CDF-N) 2 Ms survey. We find 43 OBXF sources in this area,
comprising ~15% of the X-ray sources above a 0.5--2 keV flux of 2.3e-17 erg
cm^-2 s^-1. We present spectroscopic identifications for 42 of the OBXF sources
and optical spectra for 25, including 5 previously unpublished redshifts. Deep
optical imaging data (either HST or ground-based) are presented for all the
OBXF sources. The OBXF population consists mainly of normal and starburst
galaxies detected out to cosmologically significant distances (i.e., to a
median redshift of z=0.297 and a full redshift range z=0.06-0.845). This is
notable since these distances equate to look-back times of up to ~8 Gyr; we are
thus provided with a window on the X-ray emission from galaxies at redshifts
much closer to the cosmic star formation peak than was possible prior to
Chandra.
  The X-ray luminosity distribution of OBXF sources extends to higher
luminosity than does that of "normal" galaxies indicating that a significant
fraction are likely dominated by low-luminosity AGN (LLAGN) or vigorous star
formation. By combining the detected X-ray counts, we find the average OBXF
X-ray spectrum to be consistent with a Gamma=2.0 power law. The 0.5--2 keV log
N-log S for the OBXF galaxies is much steeper (alpha=-1.7) than for the general
X-ray source population. Indeed, the number of OBXF sources has doubled between
the 1~Ms and 2~Ms survey, rising sharply in numbers at faint fluxes. The
extragalactic OBXF sources are found to contribute ~1-2% of the soft
extragalactic X-ray background.


title:
Discovery of Radio/X-ray/Optical Resolved Supernova Remnants in the
  Center of the Andromeda Galaxy

abstract:
  We have detected a spatially resolved supernova remnant (SNR) in the center
of the Andromeda Galaxy, in radio, X-ray, and optical wavelengths. These
observations provide the highest spatial resolution imaging of a
radio/X-ray/optical SNR in that galaxy to date. The multi-wavelength
morphology, radio spectral index, X-ray colors, and narrow-band optical imaging
are consistent with a shell-type SNR. A second SNR is also seen resolved in
both radio and X-ray. By comparing the morphological sturcture of the SNRs in
different wavelengths and with that in our own Galaxy, we can study the shock
morphologies of SNRs in the Andromeda Galaxy. The proximity of the SNRs to the
core suggests high interstellar medium density in the vicinity of the SNRs in
the center of the Andromeda Galaxy.


title: A Free, Fast, Simple and Efficient TVD MHD Code

abstract:
  We describe a numerical method to solve the magnetohydrodynamic (MHD)
equations. The fluid variables are updated along each direction using the flux
conservative, 2nd order, total variation diminishing (TVD), upwind scheme of
Jin and Xin. The magnetic field is updated separately in two-dimensional
advection-constraint steps. The electromotive force (EMF) is computed in the
advection step using the TVD scheme, and this same EMF is used immediately in
the constraint step in order to preserve \grad.B=0 without the need to store
intermediate fluxes. Operator splitting is used to extend the code to three
dimensions, and Runge-Kutta is used to get second order accuracy in time. The
advantages of this code are high resolution per grid cell, second order
accuracy in space and time, enforcement of the \grad.B=0 constraint to machine
precision, no memory overhead, speed, and simplicity. A 3-D Fortran
implementation less than 400 lines long is made freely available. We also
implemented a fully scalable message-passing parallel MPI version. We present
tests of the code on MHD waves and shocks.


title: Gravitational Lensing by Large Scale Structures: A Review

abstract:
  We review all the cosmic shear results obtained so far, with a critical
discussion of the present strengths and weaknesses. We discuss the future
prospects and the role cosmic shear could play in a precision cosmology era.


title: MatlabMPI

abstract:
  The true costs of high performance computing are currently dominated by
software. Addressing these costs requires shifting to high productivity
languages such as Matlab. MatlabMPI is a Matlab implementation of the Message
Passing Interface (MPI) standard and allows any Matlab program to exploit
multiple processors. MatlabMPI currently implements the basic six functions
that are the core of the MPI point-to-point communications standard. The key
technical innovation of MatlabMPI is that it implements the widely used MPI
``look and feel'' on top of standard Matlab file I/O, resulting in an extremely
compact (~250 lines of code) and ``pure'' implementation which runs anywhere
Matlab runs, and on any heterogeneous combination of computers. The performance
has been tested on both shared and distributed memory parallel computers (e.g.
Sun, SGI, HP, IBM, Linux and MacOSX). MatlabMPI can match the bandwidth of C
based MPI at large message sizes. A test image filtering application using
MatlabMPI achieved a speedup of ~300 using 304 CPUs and ~15% of the theoretical
peak (450 Gigaflops) on an IBM SP2 at the Maui High Performance Computing
Center. In addition, this entire parallel benchmark application was implemented
in 70 software-lines-of-code, illustrating the high productivity of this
approach. MatlabMPI is available for download on the web
(www.ll.mit.edu/MatlabMPI).


title: Particle Acceleration in Relativistic Jets due to Weibel Instability

abstract:
  Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas.
Plasma waves and their associated instabilities (e.g., the Buneman instability,
two-streaming instability, and the Weibel instability) created in the shocks
are responsible for particle (electron, positron, and ion) acceleration. Using
a 3-D relativistic electromagnetic particle (REMP) code, we have investigated
particle acceleration associated with a relativistic jet front propagating
through an ambient plasma with and without initial magnetic fields. We find
only small differences in the results between no ambient and weak ambient
magnetic fields. Simulations show that the Weibel instability created in the
collisionless shock front accelerates particles perpendicular and parallel to
the jet propagation direction. While some Fermi acceleration may occur at the
jet front, the majority of electron acceleration takes place behind the jet
front and cannot be characterized as Fermi acceleration. The simulation results
show that this instability is responsible for generating and amplifying highly
nonuniform, small-scale magnetic fields, which contribute to the electron's
transverse deflection behind the jet head. The ``jitter'' radiation (Medvedev
2000) from deflected electrons has different properties than synchrotron
radiation which is calculated in a uniform magnetic field. This jitter
radiation may be important to understanding the complex time evolution and/or
spectral structure in gamma-ray bursts, relativistic jets, and supernova
remnants.


title: A Search for O VI in the Winds of B-Type Stars

abstract:
  We have conducted a survey of FUSE spectra of 235 Galactic B-type stars in
order to determine the boundaries in the H-R diagram for the production of the
superion O VI in their winds. By comparing the locations and morphology of
otherwise unidentified absorption features in the vicinity of the O VI
resonance doublet with the bona fide wind profiles seen in archival IUE spectra
of the resonance lines of N V, Si IV and C IV, we were able to detect
blueshifted O VI lines in the spectra of giant and supergiant stars with
temperature classes as late as B1. No features attributable to O VI were
detected in dwarfs later than B0, or in stars of any luminosity class later
than B1, although our ability to recognize weak absorption features in these
stars is severely restricted by blending with photospheric and interstellar
features. We discuss evidence that the ratio of the ion fractions of O VI and N
V is substantially different in the winds of early B-type stars than O-type
stars.


title:
A Large, Uniform Sample of X-ray Emitting AGN: Selection Approach and an
  Initial Catalog from the ROSAT All-Sky and Sloan Digital Sky Surveys

abstract:
  Many open questions in X-ray astronomy are limited by the relatively small
number of objects in uniform optically-identified samples, especially when rare
subclasses are considered, or subsets isolated to search for evolution or
correlations between wavebands. We describe initial results of a program aimed
to ultimately yield 10^4 X-ray source identifications--a sample about an order
of magnitude larger than earlier efforts. The technique employs X-ray data from
the ROSAT All-Sky Survey (RASS), and optical imaging and spectroscopic followup
from the Sloan Digital Sky Survey (SDSS). Optical objects in the SDSS catalogs
are automatically cross-correlated with RASS X-ray source positions; then
priorities for follow-on SDSS optical spectra of candidate counterparts are
automatically assigned using an algorithm based on the known fx/fopt ratios for
various classes of X-ray emitters. SDSS parameters for optical morphology,
magnitude, colors, plus FIRST radio data, serve as proxies for object class.
  Initial application of this approach to 1400 deg^2 of sky provides a catalog
of 1200 spectroscopically confirmed quasars/AGN that are probable RASS
identifications. Most of the IDs are new, and only a few percent of the AGN are
likely to be random superpositions. The magnitude and redshift ranges of the
counterparts extend over 15<m<21 and 0.03<z<3.6. Although most IDs are quasars
and Sy 1s, a variety of other AGN subclasses are also sampled. Substantial
numbers of rare AGN are found, including more than 130 narrow-line Seyfert 1s
and 45 BL Lac candidates. These results already provide a sizeable set of new
IDs, show utility of the sample in multi-waveband studies, and demonstrate the
capability of the RASS/SDSS approach to efficiently proceed towards the largest
homogeneously selected/observed sample of X-ray emitting AGN. Abridged Abstract


title: Black Hole -- Bulge Relation for Narrow-Line Objects

abstract:
  It has been thought that narrow-line Seyfert 1 galaxies are likely to be in
the early stages of the evolution of active galaxies. To test this suggestion,
the ratios of the central massive black hole (MBH) mass to the bulge mass
($M_{\rm bh}/M_{\rm bulge}$) were estimated for 22 Narrow Line AGNs (NL AGNs).
It is found that NL AGNs appear to have genuinely lower MBH/Bulge mass ratio
($M_{\rm bh}/M_{\rm bulge}$). The mean $ log(M_{\rm bh}/M_{\rm bulge})$ for 22
NL AGNs is $-3.9\pm 0.07$, which is an order of magnitude lower than that for
Broad Line AGNs and quiescent galaxies. We suggest a nonlinear MBH/Bulge
relation and find there exists a relation between the $M_{\rm bh}/M_{\rm
bulge}$ and the velocity dispersion, $\sigma$, derived from the [O ${\rm \small
III}$] width. A scenario of MBH growth for NL AGNs is one of our
interpretations of the nonlinear MBH/Bulge relation. The MBH growth timescales
for 22 NL AGNs were calculated, with a mean value $(1.29\pm0.24)\times 10^{8}$
yr. Another plausible interpretation is also possible: that NL AGNs occur in
low-$M_{\rm bulge}$ galaxies and that in such galaxies $M_{\rm bh}/M_{\rm
bulge}$ is lower than that in galaxies with a higher $M_{\rm bulge}$, if we
consider that NL AGNs already have their ``final'' $M_{\rm bh}/M_{\rm bulge}$.
More information of the bulge in NL AGNs is needed to clarify the black hole --
bulge relation.


title: Accretion rates and accretion efficiency in AGNs

abstract:
  We used the standard geometrical thin accretion theory to obtain the
accretion rates in Seyfert 1 galaxies and quasars. Combining accretion rates
with the bolometric luminosity, we obtained the accretion efficiency. We found
most of Seyfert 1 galaxies and radio quiet quasars have lower accretion
efficiencies while most of the radio loud quasars possess higher accretion
efficiencies. This finding further implies most of radio loud quasars possess
Kerr black holes while Seyfert 1 galaxies and radio quiet quasars may not
possess Kerr black holes. Considering the difference of the accretion
efficiency we found there is a strong correlation between the accretion rate in
units of the Eddington accretion rate and the width of the H$\beta$ emission
line and most of AGNs are not accreting at Super-Eddington rates.


title: Cosmology of Nonlinear Oscillations

abstract:
  The nonlinear oscillations of a scalar field are shown to have cosmological
equations of state with $w = p / \rho$ ranging from $-1 < w < 1$. We
investigate the possibility that the dark energy is due to such oscillations.


title:
First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations:
  Dark Energy Induced Correlation with Radio Sources

abstract:
  The first-year WMAP data, in combination with any one of a number of other
cosmic probes, show that we live in a flat \Lambda-dominated CDM universe with
\Omega_m ~ 0.27 and \Omega_\Lambda ~ 0.73. In this model the late-time action
of the dark energy, through the integrated Sachs-Wolfe effect, should produce
CMB anisotropies correlated with matter density fluctuations at z<2 (Crittenden
& Turok 1996). The measurement of such a signal is an important independent
check of the model. We cross-correlate the NRAO VLA Sky Survey radio source
catalog (Condon et al. 1998) with the WMAP data in search of this signal, and
see indications of the expected correlation. Assuming a flat \Lambda-CDM
cosmology, we find \Omega_\Lambda>0 (95% CL, statistical errors only) with the
peak of the likelihood at \Omega_\Lambda=0.68, consistent with the preferred
WMAP value. A closed model with \Omega_m=1.28, h=0.33, and no dark energy
component (\Omega_\Lambda=0), marginally consistent with the WMAP CMB TT
angular power spectrum, would produce an anti-correlation between the matter
distribution and the CMB. Our analysis of the cross-correlation of the WMAP
data with the NVSS catalog rejects this cosmology at the 3\sigma level.


title:
Optical Spectropolarimetry of Quasi-Stellar Objects Discovered by the
  Two-Micron All Sky Survey

abstract:
  Highly polarized QSOs discovered in the Two-Micron All Sky Survey (2MASS)
have been observed to determine the source(s) of optical polarization in this
near-infrared color-selected sample. Broad emission lines are observed in the
polarized flux spectra of most objects, and the polarization of the lines is at
about the same level and position angle as the continuum. Generally, the
continuum is bluer and the broad-line Balmer decrement is smaller in polarized
light than for the spectrum of total flux. Narrow emission lines are much less
polarized than the broad lines and continuum for all polarized objects. These
properties favor scattering by material close to a partially obscured and
reddened active nucleus, but exterior to the regions producing the broad-line
emission, as the source of polarized flux in 2MASS QSOs. The largely
unpolarized narrow-line features require that the electrons or dust polarizing
the light be located at distances from the nucleus not much greater than the
extent of the narrow emission-line region. In addition to known
high-polarization objects, four 2MASS QSOs with AGN spectral types of 1.9 and 2
were observed to search for hidden broad emission-line regions. Broad lines
were detected in polarized light for two of these objects, and the polarizing
mechanism appears to be the same for these objects as for the highly polarized
QSOs in the sample that readily show broad emission lines in their spectra. The
observations also show that starlight from the host galaxy contributes a
significant amount of optical flux, especially for the narrow-line objects, and
support the suggestion that many 2MASS QSOs are measured to have low
polarization simply because of dilution of the polarized AGN light by the host
galaxy.


title:
GENIE observations of small scale astrophysical processes in star
  forming regions and quasars

abstract:
  The VLTI/GENIE configuration will operate using at least 4 of the VLTI
telescopes (and possibly with one or more of the AT telescopes in the future if
adaptive optics become available on them). GENIE effectively can be thought of
as a 'smart' coronagraph, enabling high dynamic range imaging to be achieved at
moderate spatial resolution, with high rejection of the emission of a central
bright point source. However, but this bright source rejection may only provide
a rather moderate image quality (due to the few baselines and transfer function
on the sky). Operated in this way, only limited image reconstruction is
possible since classical radio and millimeter wavelength interferometry
techniques are not directly applicable to the outputs of optical
interferometers because the absolute phases are generally not measured.
However, measurements of visibility and closure phase could lead to situations
where image reconstruction becomes possible. This paper addresses the issue of
whether there are areas outside of the exoplanet search where it might be able
to make a useful impact on astronomy.


title:
Near-infrared spectroscopy of nearby Seyfert galaxies - II. Molecular
  content and coronal emission

abstract:
  We present sub-arcsec near-infrared 1.5 - 2.5 micron moderate resolution
long-slit spectra of eight nearby Seyfert galaxies (z<0.01), both parallel to
the ionization cone and perpendicular to it. These spectra complement similar
data on six Seyferts, presented in Reunanen, Kotilainen & Prieto (2002). Large
concentrations of molecular gas (H2) are present in the nucleus regardless of
the Seyfert type. The spatial extent of the H2 emission is larger perpendicular
to the cone than parallel to it in 6/8 (75 %) galaxies, in agreement with the
unified models of Active Galactic Nuclei. Broad BrGamma was detected in nearly
half of the optically classified Seyfert 2 galaxies, including two objects with
no evidence for hidden polarized Broad Line Region. Nuclear [FeII] emission is
generally blueshifted which together with high BrGamma/[FeII] ratios suggests
shocks as the dominant excitation mechanism in Seyfert galaxies. Bright coronal
emission lines [SiVI] and [SiVII] are common in Seyferts, as they are detected
in ~60 % of the galaxies. In three galaxies the coronal lines are extended only
in the direction parallel to the cone. This could be explained by shock
excitation due to the jet or superwind interacting with the interstellar
medium.


title: Constraining the curvaton scenario

abstract:
  We analyse the curvaton scenario in the context of supersymmetry.
Supersymmetric theories contain many scalars, and therefore many curvaton
candidates. To obtain a scale invariant perturbation spectrum, the curvaton
mass should be small during inflation $m \ll H$. This can be achieved by
invoking symmetries, which suppress the soft masses and non-renormalizable
terms in the potential. Other model-independent constraints on the curvaton
model come from nucleosynthesis, gravitino overproduction, and thermal damping.
The curvaton can work for masses $m \gtrsim 10^4 \GeV$, and very small
couplings (e.g. $h \lesssim 10^{-6}$ for $m \lesssim 10^8 \GeV$).


title: RR Lyrae Distance Scale: Theory and Observations

abstract:
  The RR Lyrae distance scale is reviewed. In particular, we discuss
theoretical and empirical methods currently adopted in the literature.
Moreover, we also outline pros and cons of optical and near-infrared mean
magnitudes to overcome some of the problems currently affecting RR Lyrae
distances. The importance of the K-band Period-Luminosity-Metallicity (PLZ_K)
relation for RR Lyrae is also discussed, together with the absolute calibration
of the zero-point. We also mention some preliminary results based on NIR (J,K)
time series data of the LMC cluster Reticulum. This cluster hosts a sizable
sample of RR Lyrae and its distance is found to be 18.45 +/- 0.04 mag using the
predicted PLZ_K relation and 18.51 +/- 0.06 using the PLZ_J relation. We
briefly discuss the evolutionary status of Anomalous Cepheids and their
possible use as distance indicators. Finally, we point out some possible
improvements to improve the intrinsic accuracy of theory and observations.


title:
High resolution spectroscopy and emission line imaging of DEM L 71 with
  XMM-Newton

abstract:
  The X-ray emission from the supernova remnant DEM L 71 is measured and
analysed using the high-resolution cameras and spectrometers on board
XMM-Newton. The spectrum from the outer shell is reproduced very well by two
plasma components of kT = 0.3 and 0.8 keV. The abundance value from this shell
is consistent with the average LMC values. More extreme temperature variations
are possibly indicated by spatial variations in the O VII forbidden/resonance
line ratio, which could imply that in some regions the plasma is cooling
dramatically and recombining. However, an alternative and equally interesting
possibility is that the variation in forbidden/resonance ratios is due to
resonant scattering, which would reduce resonance line emission along lines of
sight with a high O VII column density. The inner region is hotter (kT = 1.1
keV) and shows enhanced Fe and Si abundances. We estimate the Fe and Si ejecta
mass to be 0.7-1.1 M_sun and 0.1--0.15 M_sun, respectively. The morphology,
mass estimates and abundances strongly suggest that DEM L 71 is the result of a
type Ia explosion, as indicated by previous measurements.


title: Hot and cold bubbles in M87

abstract:
  The X-ray data obtained with XMM-Newton is used to investigate the complex
structure of the gas in the atmosphere of the Virgo cluster around M87. We
construct a simple model for the temperature and density distribution. This
model implies that the cumulative mass of the cluster gas is a power-law of its
entropy index, $kT n^{-2/3}$, similar to the Hydra cluster. This supports the
idea that such power-laws are a direct consequence of gas cooling in a
gravitational potential. In the cluster atmosphere hot bubbles of gas injected
by the AGN are rising buoyantly. We estimate the age of these structures from
the synchrotron radio data and find that this `radiative age' is consistent
with the estimated dynamical timescale. However, this requires a spatial
separation of the relativistic particles from the magnetic field. The age
estimates suggest an activity cycle of the AGN in M87 of roughly $10^8$ years.
We show that the largest radio structures are consistent with being the
remnants of buoyant bubbles injected by the AGN during an even earlier activity
cycle. The wakes behind the currently rising hot bubbles uplift cold gas from
the cluster centre. Using a simple model for the trajectory of the cold gas, we
demonstrate that the observations by XMM-Newton of a mix of hot and cold gas in
the cluster atmosphere in the vicinity of the radio structure can be explained
in this scenario. This may also explain the ridges of enhanced X-ray emission
from cold gas observed with CHANDRA.


title: The Local Group Census: planetary nebulae in IC 10, Leo A and Sextans A

abstract:
  In the framework of our narrow-band survey of the Local Group galaxies, we
present the results of the search for planetary nebulae (PNe) in the dwarf
irregular galaxies IC10, LeoA and SextansA. Using the standard on-band/off-band
technique, sixteen new candidate PNe have been discovered in the closest
starburst galaxy, IC10. The optical size of this galaxy is estimated to be much
larger than previously thought, considering the location of the new PNe in an
area of 3.6 kpc X 2.7 kpc. We also confirm the results of previous studies for
the other two dwarf irregular galaxies, with the detection of one candidate PN
in LeoA and another one in SextansA. We review the number of planetary nebulae
discovered in the Local Group to date and their behaviour with metallicity. We
suggest a possible fall in the observed number of PNe when [Fe/H]$<<$-1.0,
which might indicate that below this point the formation rate of PNe is much
lower than for stellar populations of near Solar abundances. We also find
non-negligible metallicity effects on the [OIII] luminosity of the brightest PN
of a galaxy.


title: The 590 days long term periodicity of the microquasar GRS 1915+105

abstract:
  We report on the discovery of a 590 days long term periodicity in the hard
X-ray component of the microquasar \grs found from a comprehensive study of
more than four years of {\it RXTE} observations. The periodicity is also
observed in the hard X-ray flux observed by BATSE, and in the radio flux as
seen with the {\it Green Bank Interferometer} and the {\it Ryle Telescope}. We
discuss various possible explanations, including the precession of a radiation
induced warped accretion disk.


title:
Building up the Galactic Halo: The Sagittarius dSph and the globular
  cluster M22

abstract:
  The Sagittarius dwarf spheroidal (Sgr) and a few paculiar Galactic Globular
Clusters (GGC) can be considered as building blocks of theGalactic Halo. We
present a series of results based on a wide field photometry of the Sgr system
and the GGC M22. In particular for Sgr we present: (1) the detection of the
RGB-bump, a feature that together with the shape of the RGB can be used to
constrain the allowed range of age and metallicity and (2) the detection of a
clear blue horizontal branch which probes the existance of a metal poor
population. In the case of M22 we present clear evidence that differential
reddening is the primary cause for the observed spread of the evolutionary
sequences.


title: Warm Molecular Hydrogen and Ionized Neon in the HH2 Outflow

abstract:
  We report on spectro-imaging observations of the Herbig-Haro 2 outflow with
the ISOCAM camera onboard the Infrared Space Observatory (ISO). The [Ne II}]
12.81 microns and [Ne III]15.55 microns lines are detected only towards the jet
working surface (HH 2H), consistent with the high excitation of this knot in
the optical range, while H2 pure rotational emission is found all over the
shocked region HH 2. The low energy transition S(2) traces warm gas (T approx.
400K) peaked towards knots E-F and extended ejecta (T approx. 250-380) with
masses of a few 0.001 solar mass in the high-velocity CO outflow extending
between the powering source and HH 2. Such emission could arise from
low-velocity C-type shocks (v= 10-15 km/s). The higher transitions S(3)-S(7)
trace the emission of hot shocked gas (T= 1000-1400K) from individual optical
knots in the HH 2 region. The ortho to para (OTP) ratio exhibits large spatial
variations between 1.2 (E) and 2.5 (H), well below its value at LTE. The
emission of the S(3)-S(7) lines is well accounted for by planar C-shock models
with a typical velocity V= 20-30 km/s propagating into a medium of density
10^4-10^5 cm-3 with an initial OTP ratio close to 1 in the pre-shock gas. In
the leading edge of the jet, where the geometry of the emission allows a simple
modelling, a good agreement is found with velocities derived from the optical
proper motions measured in the ionized gas.


title:
High Performance Commodity Networking in a 512-CPU Teraflop Beowulf
  Cluster for Computational Astrophysics

abstract:
  We describe a new 512-CPU Beowulf cluster with Teraflop performance dedicated
to problems in computational astrophysics. The cluster incorporates a cubic
network topology based on inexpensive commodity 24-port gigabit switches and
point to point connections through the second gigabit port on each Linux
server. This configuration has network performance competitive with more
expensive cluster configurations and is scaleable to much larger systems using
other network topologies. Networking represents only about 9% of our total
system cost of USD$561K. The standard Top 500 HPL Linpack benchmark rating is
1.202 Teraflops on 512 CPUs so computing costs by this measure are
$0.47/Megaflop. We also describe 4 different astrophysical applications using
complex parallel algorithms for studying large-scale structure formation,
galaxy dynamics, magnetohydrodynamic flows onto blackholes and planet formation
currently running on the cluster and achieving high parallel performance. The
MHD code achieved a sustained speed of 2.2 teraflops in single precision or 44%
of the theoretical peak.


title: A Planetary Companion to gamma Cephei A

abstract:
  We report on the detection of a planetary companion in orbit around the
primary star of the binary system $\gamma$ Cephei. High precision radial
velocity measurements using 4 independent data sets spanning the time interval
1981--2002 reveal long-lived residual radial velocity variations superimposed
on the binary orbit that are coherent in phase and amplitude with a period or
2.48 years (906 days) and a semi-amplitude of 27.5 m s$^{-1}$. We performed a
careful analysis of our Ca II H & K S-index measurements, spectral line
bisectors, and {\it Hipparcos} photometry. We found no significant variations
in these quantities with the 906-d period. We also re-analyzed the Ca II
$\lambda$8662 {\AA} measurements of Walker et al. (1992) which showed possible
periodic variations with the ``planet'' period when first published. This
analysis shows that periodic Ca II equivalent width variations were only
present during 1986.5 -- 1992 and absent during 1981--1986.5. Furthermore, a
refined period for the Ca II $\lambda$8662 {\AA} variations is 2.14 yrs,
significantly less than residual radial velocity period. The most likely
explanation of the residual radial velocity variations is a planetary mass
companion with $M$ sin $i$ = 1.7 $M_{Jupiter}$ and an orbital semi-major axis
of $a_2$ $=$ 2.13 AU. This supports the planet hypothesis for the residual
radial velocity variations for $\gamma$ Cep first suggested by Walker et al.
(1992). With an estimated binary orbital period of 57 years $\gamma$ Cep is the
shortest period binary system in which an extrasolar planet has been found.
This system may provide insights into the relationship between planetary and
binary star formation.


title:
The GAIA Astrometric Survey of the Solar Neighborhood and its
  Contribution to the Target Database for DARWIN/TPF

abstract:
  We evaluate the potential of the ESA Cornerstone Mission GAIA in helping
populate the database of nearby stars ($d < 25$ pc) for subsequent target
selection for DARWIN/TPF. The GAIA high-precision astrometric measurements will
make it an ideal tool for a complete screening of the expected several
thousands stars within 25 pc in order to identify and characterize (or rule out
the presence of) Jupiter signposts. GAIA astrometry will be instrumental in
complementing radial velocity surveys of F-G-K stars, and will more effectively
search for massive planets the large database of nearby M dwarfs, which are
less easily accessible with precision spectroscopy. The ability to determine
the actual planet masses and inclination angles for detected systems,
especially those with low-mass primaries (M $< 0.6$ M$_\odot$), stems as a
fundamental contribution GAIA will make toward the final target selection for
DARWIN/TPF, thus complementing exo-zodiacal dust emission observations from
ground-based observatories such as Keck, LBTI, and VLTI.


title:
Further Evidence for Quantized Intrinsic Redshifts in Galaxies: Is the
  Great Attractor a Myth?

abstract:
  Evidence was presented recently suggesting that the Fundamental Plane (FP)
clusters studied in the Hubble Key Project may contain quantized intrinsic
redshift components that are related to those reported by Tifft. Here we report
the results of a similar analysis using 55 spiral (Sc and Sb) galaxies, and 36
Type Ia supernovae (SnIa) galaxies. We find that even when many more objects
are included in the sample there is still clear evidence that the same
quantized intrinsic redshifts are present and superimposed on the Hubble flow.
We find Hubble constants of Ho = 60.0 and 57.5 km s^(-1) Mpc^(-1) for the Sc
and Sb galaxies respectively. For the SnIa galaxies we find Ho = 58. These
values are considerably lower than the value of Ho = 72 reported by the Hubble
Key Project, but are good in agreement with the value Ho = 60 found for
intermediate redshifts using the Sunyaev-Zel'dovich (SZ) effect. Evidence is
also presented that suggests that the presence of unaccounted for intrinsic
redshifts may have led us incorrectly to the conclusion that a "great
attractor" is needed to explain the velocity data. The 91 galaxies examined
here also offer new, independent confirmations of the importance of the
redshift increment zf = 0.62.


title: A Horizon Ratio Bound for Inflationary Fluctuations

abstract:
  We demonstrate that the gravity wave background amplitude implies a robust
upper bound on the ratio: \lambda / H^{-1} < e^60, where \lambda is the proper
wavelength of fluctuations of interest and H^{-1} is the horizon at the end of
inflation. The bound holds as long as the energy density of the universe does
not drop faster than radiation subsequent to inflation. This limit implies that
the amount of expansion between the time the scales of interest leave the
horizon and the end of inflation, denoted by e^N, is also bounded from above,
by about e^60 times a factor that involves an integral over the first slow-roll
parameter. In other words, the bound on N is model dependent -- we show that
for vast classes of slow-roll models, N < 67. The quantities, \lambda / H^{-1}
or N, play an important role in determining the nature of inflationary scalar
and tensor fluctuations. We suggest ways to incorporate the above bounds when
confronting inflation models with observations. As an example, this bound
solidifies the tension between observations of cosmic microwave background
(CMB) anisotropies and chaotic inflation with a \phi^4 potential by closing the
escape hatch of large N (< 62).


title: On Variations in the Peak Luminosity of Type Ia Supernovae

abstract:
  We explore the idea that the observed variations in the peak luminosities of
Type Ia supernovae originate in part from a scatter in metallicity of the
main-sequence stars that become white dwarfs. Previous, numerical, studies have
not self-consistently explored metallicities greater than solar.
One-dimensional Chandrasekhar mass models of SNe Ia produce most of their 56Ni
in a burn to nuclear statistical equilibrium between the mass shells 0.2 and
0.8 solar masses, for which the electron to nucleon ratio is constant during
the burn. We show analytically that, under these conditions, charge and mass
conservation constrain the mass of 56Ni produced to depend linearly on the
original metallicity of the white dwarf progenitor. Detailed post-processing of
W7-like models confirms this linear dependence. The effect that we identify is
most evident at metallicities larger than solar, and is in agreement with
previous self-consistent calculations over the metallicity range common to both
calculations. The observed scatter in the metallicity (1/3--3 times solar) of
the solar neighborhood is enough to induce a 25% variation in the mass of 56Ni
ejected by Type Ia supernovae. This is sufficient to vary the peak V-band
brightness by approximately 0.2. This scatter in metallicity is present out to
the limiting redshifts of current observations (z < 1). Sedimentation of 22Ne
can possibly amplify the variation in 56Ni mass up to 50%. Further numerical
studies can determine if other metallicity-induced effects, such as a change in
the mass of the 56Ni-producing region, offset or enhance this variation.


title: Gamma-ray bursts as X-ray depth-gauges of the Universe

abstract:
  We discuss the X-ray flux of gamma-ray burst afterglows at redshifts in the
range 3-30, including the effects of the intergalactic He II absorption. We
point out that strong X-ray lines may form locally in burst afterglows starting
minutes after the trigger. This can provide distinctive X-ray distance
indicators out to the redshifts where the first generation of massive stars
form.


title: Dust emission from the most distant quasars

abstract:
  We report observations of three SDSS z>6 QSOs at 250 GHz (1.2mm) using the
117-channel Max-Planck Millimeter Bolometer (MAMBO-2) array at the IRAM
30-meter telescope. J1148+5251 (z=6.41) and J1048+4637 (z=6.23) were detected
with 250 GHz flux densities of 5.0 +- 0.6 mJy and 3.0 +- 0.4 mJy, respectively.
J1630+4012 (z=6.05) was not detected with a 3 sigma upper limit of 1.8 mJy.
Upper flux density limits from VLA observations at 43 GHz for J1148+5251 and
J1048+4637 imply steeply rising spectra, indicative of thermal infrared
emission from warm dust. The far-infrared luminosities are estimated to be
\~10^13 L_sun, and the dust masses ~10^8 M_sun, assuming Galactic dust
properties. The presence of large amounts of dust in the highest redshift QSOs
indicates that dust formation must be rapid during the early evolution of QSO
host galaxies. Dust absorption may hinder the escape of ionizing photons which
reionize the intergalactic medium at this early epoch.


title: Variation of Physical constants, Redshift and the Arrow of time

abstract:
  Theories of fundamental physics as well as cosmology must ultimately not only
account for the structure and evolution of the universe and the physics of
fundamental interactions, but also lead to an understanding of why this
particular universe follows the physics that it does. Such theories must
ultimately lead to an understanding of the values of the fundamental constants
themselves. However, all such efforts have failed, leaving fundamental
constants outside of any physical theories. In this paper we take a different
approach than the usual evolutionary picture where the physics itself is
assumed invariant. We study numerical relations among fundamental constants
starting from relationships first proposed by Weinberg (1972). We have shown
(Kafatos et al.2000) that they turn out to be equivalent to the relations found
by Dirac (1937). Then a new scaling hypothesis relating the speed of light $c$
and the scale of the universe $R$ is explored.


title: Interaction of GRB Fireballs with Ambient Medium

abstract:
  The customary picture of the fireball deceleration by an external medium
neglects two physical agents in the problem that are important at radii
R<10^{17} cm: a radiative precursor (the prompt GRB) and a relativistic front
of free neutrons. The radiative precursor preaccelerates the medium and loads
it with e+- pairs. This provides a new explanation for the early optical
flashes in GRBs. The front of free neutrons must form in a standard baryonic
fireball and change the mechanism of the fireball deceleration. The neutron
effect, however, disappears if the fireball is strongly dominated by the
Poynting flux. The neutrons thus provide a unique link between the progenitor
physics and the observed external blast wave. The explosion mechanism at
R<10^{17} cm is testable with upcoming observations of early afterglows.


title:
Constraints on pulsar magnetospheric and wind parameters for the compact
  nebulae of Vela and PSR B1706-44

abstract:
  We present a new model for the synchrotron compact nebular emissions for Vela
and PSR B1706-44, and derive fundamental pulsar/plerion parameters such as the
pair production multiplicity, M, and wind magnetization parameter, sigma. The
pair cascade above the pulsar polar cap, combined with the energy from the
pulsar wind, injects a pair plasma into the surrounding environment. This wind,
consisting of particles and fields, is shocked by the environment, resulting in
synchrotron emission from "thermalized" pairs in a compact nebula. The broad
band nebular spectrum depends crucially on the spindown power, distance, pair
multiplicity, pulsar wind shock radius and sigma at this shock. We construct
such a model for the particle spectra in the compact X-ray nebula of Vela and
PSR B1706-44. Fits to the multiwavelength spectra of these sources indicate
that 300<M<1000, whereas 0.05<sigma<0.5 for Vela. The same sigma interval (as
for Vela) was independently derived from the radial gradients of the X-ray
compact nebular emission from both Vela and PSR B1706-44, giving us confidence
in our results. The M we derive for Vela is too small to be explained by
curvature losses in the open magnetoshere of Vela, but the presence of optical
pulsed photons could modify the predicted multiplicity.


title: A deep 6.7um survey in the SSA13 field with ISO

abstract:
  We present results of a deep mid-infrared survey in the SSA13 field with the
Infrared Space Observatory (ISO). In order to probe the near-infrared light at
high redshifts, we surveyed the field with the broad band LW2 (5-8.5um) filter
of the mid-infrared camera ISOCAM. Adopting a highly redundant imaging strategy
for the 23 hour observation and carefully treating gradual changes in the
detector responsivity caused by a very high rate of cosmic ray impacts, we
succeeded in reaching an 80% completeness limit of 16uJy in the central 7
arcmin2 region. Utilizing the signal-to-noise ratio map, we detected 65 sources
down to 6uJy in the 16 arcmin2 field. Integral galaxy number counts at 6.7um
are then derived, reaching 1.3e4/deg2 at the faint limit with a slope of -1.6
between 13uJy and 130uJy. Integrating individual sources in this flux range,
the resolved fraction of the extragalactic background light at 6.7um is
estimated to be 0.56nW/m2/sr. These results, which reach a flux limit three
times fainter than those in the Hubble Deep Fields, are in fairly good
agreement with a model prediction by Franceschini et al. (1997). Finally, we
discuss the relation of distant massive E/S0 galaxies to the faint 6.7um galaxy
population.


title: Black hole versus cosmological horizon entropy

abstract:
  The generalized second law of thermodynamics states that entropy always
increases when all event horizons are attributed with an entropy proportional
to their area. We test the generalized second law by investigating the change
in entropy when dust, radiation and black holes cross a cosmological event
horizon. We generalize for flat, open and closed Friedmann-Robertson-Walker
universes by using numerical calculations to determine the cosmological horizon
evolution. In most cases the loss of entropy from within the cosmological
horizon is more than balanced by an increase in cosmological event horizon
entropy, maintaining the validity of the generalized second law of
thermodynamics. However, an intriguing set of open universe models show an
apparent entropy decrease when black holes disappear over the cosmological
event horizon. We anticipate that this apparent violation of the generalized
second law will disappear when solutions are available for black holes embedded
in arbitrary backgrounds.


title: On the Non-observability of Recent Biogenesis

abstract:
  In a previous paper we addressed the question "Does the Rapid Appearance of
Life on Earth Suggest that Life is Common in the Universe?" The
non-observability of recent biogenesis is a self-selection effect that needs to
be considered if inferences are to be drawn from the rapidity of terrestrial
biogenesis. We discuss several approaches that have been proposed to take this
effect into account.


title: Second-order Perturbations of the Friedmann World Model

abstract:
  We consider instability of the Friedmann world model to the second-order in
perturbations. We present the perturbed set of equations up to the second-order
in the Friedmann background world model with general spatial curvature and the
cosmological constant. We consider systems with the completely general
imperfect fluids, the minimally coupled scalar fields, the electro-magnetic
field, and the generalized gravity theories. We also present the case of null
geodesic equations, and the one based on the relativistic Boltzmann equation.
In due stage a decomposition is made for the scalar-, vector- and tensor-type
perturbations which couple each other to the second-order. Gauge issue is
resolved to each order. The basic equations are presented without imposing any
gauge condition, thus in a gauge-ready form so that we can use the full
advantage of having the gauge freedom in analysing the problems. As an
application we show that to the second-order in perturbation the relativistic
pressureless ideal fluid of the scalar-type reproduces exactly the known
Newtonian result. As another application we rederive the large-scale conserved
quantities (of the pure scalar- and tensor-perturbations) to the second order,
first shown by Salopek and Bond, now from the exact equations. Several other
applications are made as well.


title: Outflowing material in the zem = 4.92 BAL QSO SDSS~J160501.21-011220.0

abstract:
  We present the analysis of two BALs seen in the spectrum of the QSO SDSS
J160501.21-011220.0. Our UVES spectrum shows two well detached BALs at z(abs)=
4.685 and 4.855. The system at z(abs)= 4.855 covers the background source
completely suggesting that the gas is located outside the BLR. On the contrary
the system at z(abs)= 4.685 has a covering factor of ~0.9. The observed H I
absorption line together with the limits on C II and Si II absorptions suggest
that 16<log N(H I) (cm^{-2})<~17 in z(abs) = 4.855 absorption system.
Comparison with models show that the observed column densities of N V, Si IV
and C IV in this system require that N is underabundant by more than a factor 3
compared to Si if the ionizing radiation is similar to a typical QSO spectrum.
This is contrary to what is usually derived for the emission line gas in QSOs.
We show that the relative suppression in the N V column density can be
explained for Solar abundance ratios or abundance ratios typical of Starburst
abundances if an ionizing spectrum devoid of X-rays is used instead. Thus, if
the composition of BAL is like that of BLR then it is most likely that the
cloud sees a spectrum devoid of X-rays similar to what we observe from this
QSO. This is consistent with the fact that none of our models have high Compton
optical depth to remove X-rays from the QSO. Similar arguments lead to the
conclusion that the system at z(abs)= 4.685 as well is not Compton thick. The
estimated black hole mass is 8 10^8 solar mass suggesting the accretion onto
the seed black hole must have started as early as z = 11.


title:
Graviton Mass, Quintessence and Oscillatory Character of the Universe
  Evolution

abstract:
  It is shown that using the relativistic field theory of gravity (RTG) and
measured value of $\Omega_{tot}$ one can obtain the upper limit on the graviton
mass with 95%C.L.: $m\leq 1.6\cdot 10^{-66}$ [g]; within the $(1\sigma)$ range
its probable value is $m_{g}= 1.3\cdot 10^{-66}$ [g]. It is pointed out that
according to RTG the presence of the quintessence is necessary to explain the
Universe accelerated expansion. Experimental data on the Universe age and dark
matter density allow one to determine the range of possible values of the $\nu$
parameter in the equation of quintessence state and indicate characteristic
time, which corresponds to the beginning and cessation of the accelerated
expansion epoch, as well as the time period of the maximal expansion, which
corresponds to the half-period of the oscillatory evolution of the Universe.


title:
Do We Need Stars to Reionize the Universe at High Redshifts? Early
  Reionization by Decaying Heavy Sterile Neutrinos

abstract:
  A remarkable result of the Wilkinson Microwave Anisotropy Probe (WMAP)
observations is that the universe was significantly reionized at large
redshifts. The standard explanation is that massive stars formed early and
reionized the universe around redshift z=17. Here we explore an alternative
possibility, in which the universe was reionized in two steps. An early boost
of reionization is provided by a decaying sterile neutrino, whose decay
products, relativistic electrons, result in partial ionization of the smooth
gas. We demonstrate that a neutrino with a mass of m_nu ~ 200 MeV and a decay
time of t ~ 4 * 10^{15} s can account for the electron scattering optical depth
tau=0.16 measured by WMAP without violating existing astrophysical limits on
the cosmic microwave and gamma ray backgrounds. Reionization is then completed
by subsequent star formation at lower redshifts. This scenario alleviates
constraints on structure formation models with reduced small-scale power, such
as those with a running or tilted scalar index, or warm dark matter models.


title: From Molecular Cores to Planet-forming Disks: A SIRTF Legacy Program

abstract:
  Crucial steps in the formation of stars and planets can be studied only at
mid-infrared to far-infrared wavelengths, where SIRTF provides an unprecedented
improvement in sensitivity. We will use all three SIRTF instruments (IRAC,
MIPS, and IRS) to observe sources that span the evolutionary sequence from
molecular cores to protoplanetary disks, encompassing a wide range of cloud
masses, stellar masses, and star-forming environments. In addition to targeting
about 150 known compact cores, we will survey with IRAC and MIPS (3.6 to 70
micron) the entire areas of five of the nearest large molecular clouds for new
candidate protostars and substellar objects as faint as 0.001 solar
luminosities. We will also observe with IRAC and MIPS about 190 systems likely
to be in the early stages of planetary system formation(ages up to about 10
Myr), probing the evolution of the circumstellar dust, the raw material for
planetary cores. Candidate planet-forming disks as small as 0.1 lunar masses
will be detectable. Spectroscopy with IRS of new objects found in the surveys
and of a select group of known objects will add vital information on the
changing chemical and physical conditions in the disks and envelopes. The
resulting data products will include catalogs of thousands of previously
unknown sources, multiwavelength maps of about 20 square degrees of molecular
clouds, photometry of about 190 known young stars, spectra of at least 170
sources, ancillary data from ground-based telescopes, and new tools for
analysis and modeling. These products will constitute the foundations for many
follow-up studies with ground-based telescopes, as well as with SIRTF itself
and other space missions such as SIM, JWST, Herschel, and TPF.


title: Nebular vs. Stellar Wind Abundances in NGC 6543

abstract:
  An early analysis of Chandra observations of the planetary nebula NGC 6543
suggested that the location and the derived temperature for the X-ray emitting
region is inconsistent with the abundances measured for this object (Chu et al.
2001). We revisit observations of this source (following significant updates to
both the reprocessing and extraction software) in order to propose a resolution
to this apparent anomaly. Our re-analysis using abundances found from
observations in the infrared, optical, and ultraviolet suggests that the
location and temperature of the X-ray emission from NGC 6543 is consistent with
nebular abundances expected for the source.


title:
Complex Optical-X-ray Correlations in the Narrow-Line Seyfert 1 Galaxy
  NGC 4051

abstract:
  This paper presents the results of a dense and intensive X-ray and optical
monitoring of the narrow-line Seyfert 1 galaxy NGC 4051 carried out in 2000.
Results of the optical analysis are consistent with previous measurements. The
amplitude of optical emission line variability is a factor of two larger than
that of the underlying optical continuum, but part or all of the difference can
be due to host-galaxy starlight contamination or due to the lines being driven
by the unseen UV continuum, which is more variable than the optical continuum.
We measured the lag between optical lines and continuum and found a lower, more
accurate broad line region size of 3.0+-1.5 light days in this object. The
implied black hole mass is M_BH=5(+6,-3)x10^5 M_sun; this is the lowest mass
found, so far, for an active nucleus. We find significant evidence for an
X-ray-optical (XO) correlation with a peak lag of about <1 day, although the
centroid of the asymmetric correlation function reveals that part of the
optical flux varies in advance of the X-ray flux by 2.4+-1.0 days. This complex
XO correlation is explained as a possible combination of X-ray reprocessing and
perturbations propagating from the outer (optically emitting) parts of the
accretion disc into its inner (X-ray emitting) region.


title: An absorption event in the X-ray lightcurve of NGC 3227

abstract:
  We have monitored the Seyfert galaxy NGC 3227 with the Rossi X-ray Timing
Explorer (RXTE) since January 1999. During late 2000 and early 2001 we observed
an unusual hardening of the 2-10 keV X-ray spectrum which lasted several
months. The spectral hardening was not accompanied by any correlated variation
in flux above 8 keV. We therefore interpret the spectral change as transient
absorption by a gas cloud of column density 2.6 10^23 cm^-2 crossing the line
of sight to the X-ray source. A spectrum obtained by XMM-Newton during an early
phase of the hard-spectrum event confirms the obscuration model and shows that
the absorbing cloud is only weakly ionised. The XMM-Newton spectrum also shows
that ~10% of the X-ray flux is not obscured, but this unabsorbed component is
not significantly variable and may be scattered radiation from a large-scale
scattering medium. Applying the spectral constraints on cloud ionisation
parameter and assuming that the cloud follows a Keplerian orbit, we constrain
the location of the cloud to be R~10-100 light-days from the central X-ray
source, and its density to be n_H~10^8cm^-3, implying that we have witnessed
the eclipse of the X-ray source by a broad line region cloud.