title: Galaxy Correlation Statistics of Mock Catalogs for the DEEP2 Survey

abstract:
  The DEEP2 project will obtain redshifts for ~60,000 galaxies between
z~0.7-1.5 in a comoving volume of 7 10^6 Mpc/h^3 for an LCDM universe. The
survey will map four separate 2 by 0.5 degree strips of the sky. To study the
expected clustering, we have constructed mock galaxy catalogs from the GIF
Virgo Consortium simulations. We present two- and three-point correlation
analyses of these mock galaxy catalogs to test how well we will measure these
statistics in the presence of selection biases which will limit the surface
density of galaxies which we can select for spectroscopy. We find that neither
the two-point nor three-point correlation functions are significantly
compromised. We will be able to make simple corrections to account for the
small amount of bias introduced. We quantify the expected redshift distortions
due to random orbital velocities of galaxies within groups and clusters on
small scales of ~1 Mpc/h using the pairwise velocity dispersion sigma_12 and
galaxy-weighted velocity dispersion sigma_1, which we are able to measure
within ~10%. We also estimate the expected large-scale coherent infall of
galaxies due to supercluster formation (``Kaiser effect''). From this measure
we will be able to constrain beta to within ~0.1 at z=1. For the DEEP2 survey
we will combine the correlation statistics with galaxy observables such as
spectral type, morphology, absolute luminosity, and linewidth to measure the
relative biases in different galaxy types. Here we use a counts-in-cells
analysis to measure sigma_8 as a function of redshift and determine the
relative bias between galaxy samples based on absolute luminosity. We expect to
measure sigma_8 to within 10% and detect the evolution of relative bias with
redshift at the 4-5 sigma level.


title: An Overview of the Las Campanas Distant Cluster Survey

abstract:
  We present the Las Campanas Distant Cluster Survey, which has produced over a
thousand galaxy cluster candidates at 0.35 < z < 1.1 (see Gonzalez et al. 2001
for the full catalog). We discuss the technique that enabled us to use short (~
3 min) exposures and a small (1m) telescope to efficiently survey ~ 130 sq.
deg. of sky. Follow-up imaging and spectroscopy using a wide array of
telescopes including the Keck and VLT suggest that the bona-fide cluster
fraction is ~70%. We construct methods to estimate both the redshift and
cluster mass from the survey data themselves and discuss our first result on
large-scale structure, the dependence of the cluster correlation length with
mean cluster separation at z ~ 0.5 (Gonzalez, Zaritsky, & Wechsler 2001).


title:
The Effect of a Binary Source Companion on the Astrometric Microlensing
  Behavior

abstract:
  If gravitational microlensing occurs in a binary-source system, both source
components are magnified, and the resulting light curve deviates from the
standard one of a single source event. However, in most cases only one source
component is highly magnified and the other component (the companion) can be
treated as a simple blending source: blending approximation. In this paper, we
show that, unlike the light curves, the astrometric curves, representing the
trajectories of the source image centroid, of an important fraction of
binary-source events will not be sufficiently well modeled by the blending
effect alone. This is because the centroid shift induced by the source
companion endures to considerable distances from the lens. Therefore, in
determining the lens parameters from astrometric curves to be measured by
future high-precision astrometric instruments, it will be important to take the
full effect of the source companion into consideration.


title: Kinetic Sunyaev-Zel'dovich effect from halo rotation

abstract:
  We discuss the kinetic Sunyaev-Zel'dovich (SZ) contribution to cosmic
microwave background (CMB) temperature fluctuations due to coherent rotational
velocity component of electrons within halos. This effect produces a distinct
dipole-like temperature distribution across the the cluster, and provides a
promising way to measure the angular momentum distribution of gas inside
clusters. Information obtained from such a measurement may provide new insights
to the origin and evolution of angular momentum in hierarchical structure
formation theory. For typical, well relaxed, clusters of mass a few times
10$^{14}$ M$_{\sun}$, the peak fluctuation is of the order a few $\mu$K,
depending on the rotational velocity and the inclination angle of the
rotational axis. For clusters which had underwent a recent merger, the
contribution to temperature fluctuations could be even larger. This dipole
signature is similar to the one produced by lensed CMB towards galaxy clusters,
though the lensing contribution spans a larger angular extent than the one due
to rotational scattering as the former depends on the gradient of the cluster
potential. Since the lensing contribution towards clusters are aligned with the
large scale CMB gradient, when higher resolution observations towards clusters
are combined with a wide field CMB map, these two effects can be separated. An
additional, but less important, source of confusion is the dipolar pattern
produced by the moving-lens effect involving, again, the gradient of the
cluster potential and the transverse velocity. The angular power spectrum of
temperature anisotropies produced by the halo rotation is expected to be
smaller than those due to the thermal SZ and peculiar velocity kinetic SZ
effects.


title:
Turning to the Dark Side: Evidence for Circumburst Extinction of
  Gamma-Ray Bursts with Dark Optical Afterglows

abstract:
  We present evidence that the majority of rapidly-, well-localized gamma-ray
bursts with undetected, or dark, optical afterglows, or `dark bursts' for
short, are most likely the result of extinction by dust in the circumburst
medium. First, we show that the dark bursts cannot be explained by a failure to
image deeply enough quickly enough: We fit a variety of brightness distribution
models to the optical data, and find that approx. 57(+13,-11)% of all bursts,
and approx. 82(+22,-17)% of dark bursts, have afterglows that are fainter than
R = 24 mag 18 hours after the burst. Secondly, we show that dark bursts tend to
be X-ray and radio faint. Thirdly, we show that these correlations, and more
specifically the optical vs. X-ray and optical vs. radio distributions, can be
explained within the framework of the relativistic fireball model if the dark
bursts are extinguished by circumburst dust, and the density of the circumburst
medium spans many orders of magnitude, from densities that are typical of the
Galactic disk to densities that are typical of dense clouds. Finally, we show
that Galactic extinction, host galaxy extinction unrelated to the circumburst
medium, and the following high redshift effects - Lyman limit absorption in the
source frame, absorption by the Ly-alpha forest, absorption by excited
molecular hydrogen in the circumburst medium, and source-frame extinction by
the FUV component of the extinction curve - might contribute to the number of
dark bursts, but only in small numbers.


title:
Dust Sublimation and Fragmentation in the Circumburst Medium: Evidence
  for a Large, Massive Cloud Origin for Gamma-Ray Bursts with Dark Optical
  Afterglows

abstract:
  The distances to which the optical flash destroys dust via sublimation, and
the burst and afterglow change the size distribution of the dust via
fragmentation, are functions of grain size. Furthermore, the sublimation
distance is a decreasing function of grain size, while the fragmentation
distance is a decreasing function of grain size for large grains and an
increasing function of grain size for small grains. We investigate how these
very different, but somewhat complementary, processes change the optical depth
of the circumburst medium. To this end, we adopt a canonical distribution of
graphite and silicate grain sizes, and a simple fragmentation model, and we
compute the post-burst/optical flash/afterglow optical depth of a circumburst
cloud of constant density n and size R as a function of burst and afterglow
isotropic-equivalent X-ray energy E and spectral index alpha, and optical flash
isotropic-equivalent peak luminosity L: This improves upon previous analyses
that consider circumburst dust of a uniform grain size. We find that
circumburst clouds do not significantly extinguish (tau < 0.3) the optical
afterglow if R < 10L_{49}^{1/2} pc, fairly independent of n, E, and alpha, or
if N_H < 5x10^{20} cm^{-2}. On the other hand, we find that circumburst clouds
do significantly extinguish (tau > 3) the optical afterglow if R >
10L_{49}^{1/2} pc and N_H > 5x10^{21} cm^{-2}, creating a so-called `dark
burst'. The majority of bursts are dark, and as circumburst extinction is
probably the primary cause of this, this implies that most dark bursts occur in
clouds of this size and mass M > 3x10^5L_{49} M_{sun}. Clouds of this size and
mass are typical of giant molecular clouds, and are active regions of star
formation.


title:
Evidence for a Molecular Cloud Origin for Gamma-Ray Bursts: Implications
  for the Nature of Star Formation in the Universe

abstract:
  It appears that the majority of rapidly-, well-localized gamma-ray bursts
with undetected, or dark, optical afterglows, or `dark bursts' for short, occur
in clouds of size R > 10L_{49}^{1/2} pc and mass M > 3x10^5L_{49} M_{sun},
where L is the isotropic-equivalent peak luminosity of the optical flash. We
show that clouds of this size and mass cannot be modeled as a gas that is bound
by pressure equilibrium with a warm or hot phase of the interstellar medium
(i.e., a diffuse cloud): Such a cloud would be unstable to gravitational
collapse, resulting in the collapse and fragmentation of the cloud until a
burst of star formation re-establishes pressure equilibrium within the
fragments, and the fragments are bound by self-gravity (i.e., a molecular
cloud). Consequently, dark bursts probably occur in molecular clouds, in which
case dark bursts are probably a byproduct of this burst of star formation if
the molecular cloud formed recently, and/or the result of lingering or latter
generation star formation if the molecular cloud formed some time ago. We then
show that if bursts occur in Galactic-like molecular clouds, the column
densities of which might be universal, the number of dark bursts can be
comparable to the number of bursts with detected optical afterglows: This is
what is observed, which suggests that the bursts with detected optical
afterglows might also occur in molecular clouds. We confirm this by modeling
and constraining the distribution of column densities, measured from absorption
of the X-ray afterglow, of the bursts with detected optical afterglows: We find
that this distribution is consistent with the expectation for bursts that occur
in molecular clouds, and is not consistent with the expectation for bursts that
occur in diffuse clouds. More...


title:
USA Observation of Spectral and Timing Evolution During the 2000
  Outburst of XTE J1550-564

abstract:
  We report on timing and spectral observations of the 2000 outburst of XTE
J1550-564 made by the Unconventional Stellar Aspect (USA) Experiment on board
the Advanced Research and Global Observation Satellite (ARGOS). We observe a
low-frequency quasi-periodic oscillation (LFQPO) with a centroid frequency that
tends to increase with increasing flux and a fractional rms amplitude which is
correlated with the hardness ratio. The evolution of the hardness ratio (4--16
keV/1--4 keV) with time and source flux is examined. The hardness-intensity
diagram (HID) shows a cyclical movement in the clockwise direction and possibly
indicates the presence of two independent accretion flows. We observe a
relationship between the USA 4--16 keV count rate and radio observations and
discuss this in the context of previously observed correlations between X-ray,
radio, optical and IR data. We examine our results in the context of models
invoking two accretion flows: a thin disk and a hot sub-Keplerian flow.


title: Determining the Gamma-Ray Burst Rate as a Function of Redshift

abstract:
  We exploit the 14 gamma-ray bursts (GRBs) with known redshifts z and the 7
GRBs for which there are constraints on z to determine the GRB rate R_{GRB}(z),
using a method based on Bayesian inference. We find that, despite the
qualitative differences between the observed GRB rate and estimates of the SFR
in the universe, current data are consistent with R_{GRB}(z) being proportional
to the SFR.


title: Dark Matter is Baryons

abstract:
  A comet-like, but magnitudes smaller, extremely low albedo interstellar
meteoroid population of fragile aggregates with solar type composition,
measured in space and terrestrially, is most probably the universal dark
matter. Although non-baryonic particles cannot be excluded, only "Big Bang"
cosmology predicts an appreciable fraction of such alternate forms. As more
counter-physics hypotheses are added to fit observation to the expanding
universe assumption, a classical physics alternative proffers dark matter
interactive red shifts normally correlated with distance. The cosmic microwave
background results from size-independent thermal plateau radiation that
emanates from dark matter gravitationally drawn into the Galaxy.


title: The Role of Dust in GRB Afterglows

abstract:
  We show that the clumpy structure of star-forming regions can naturally
explain the fact that 50-70% of GRB afterglows are optical``dark.'' We also
show that dust echos from the GRB and its afterglow, produced by the clumpy
structure of the star-forming region in which the GRB occurs, can lead to
temporal variability and peaks in the NIR, optical, and UV lightcurves of GRB
afterglows.


title: Simulated Radio Images and Light Curves of Young Supernovae

abstract:
  We present calculations of the radio emission from supernovae based on
high-resolution simulations of the hydrodynamics and radiation transfer, using
simple energy density relations which link the properties of the radiating
electrons and the magnetic field to the hydrodynamics. As a specific example we
model the emission from SN1993J, which cannot be adequately fitted with the
often-used analytic mini-shell model, and present a good fit to the radio
evolution at a single frequency. Both free-free absorption and syncrotron self-
absorption are needed to fit the light curve at early times and a circumstellar
density profile of rho~r^-1.7 provides the best fit to the later data. We show
that the interaction of density structures in the ejecta with the reverse
supernova shock may produce features in the radio light curves such as have
been observed. We discuss the use of high-resolution radio images of supernovae
to distinguish between different absorption mechanisms and determine the origin
of specific light curve features. Comparisons of VLBI images of SN1993J with
synthetic model images suggest that internal free-free absorption completely
obscures emission at 8.4 GHz passing through the center of the supernova for
the first few tens of years after explosion. We predict that at 8.4 GHz the
internal free-free absorption is currently declining, and that over the next 40
years the surface brightness of the center of the source should increase
relative to the bright ring of emission seen in VLBI images. Similar absorption
in a nearby supernova would make the detection of a radio pulsar at 1 GHz
impossible for ~150 years after explosion.


title: The nature of the dwarf population in Abell 868

abstract:
  We present the results of a study of the morphology of the dwarf galaxy
population in Abell 868, a rich, intermediate redshift (z=0.154) cluster which
has a galaxy luminosity function with a steep faint-end slope (alpha=-1.26 +/-
0.05). A statistical background subtraction method is employed to study the B-R
colour distribution of the cluster galaxies. This distribution suggests that
the galaxies contributing to the faint-end of the measured cluster LF can be
split into three populations: dIrrs with B-R<1.4; dEs with 1.4<B-R<2.5; and
contaminating background giant ellipticals (gEs) with B-R>2.5. The remvoal of
the contribution of the background gEs from the counts only marginally lessens
the faint-end slope (alpha=-1.22 +/- 0.16). However, the removal of the
contribution of the dIrrs from the counts produces a flat LF (alpha=-0.91 +/-
0.16). The dEs and the dIrrs have similar spatial distributions within the
cluster except that the dIrrs appear to be totally absent within a central
projected radius of about 0.2 Mpc (Ho=75 km/s /Mpc). The number density of both
dEs and dIrrs appear to fall off beyond a projected radius of about 0.35 Mpc.
We suggest that the dE and dIrr populations of A868 have been associated with
the cluster for similar timescales but that evolutionary processes such as
`galaxy harassment' tend to fade the dIrr galaxies while having much less
effect on the dE galaxies. The harassement would be expected to have the
greatest effect on dwarfs residing in the central parts of the cluster.


title: Why Every Bipolar Planetary Nebula is `Unique'

abstract:
  We present the many evolutionary routes that progenitors of bipolar planetary
nebulae (BPNe) can take. Overall, there are about a hundred qualitatively
different evolutionary routes, hence about a hundred qualitatively different
types of BPNe. Within each type there are quantitative differences as well.
Adding the dependence of the appearance on inclination, we find that the number
of different apparent structures of BPN is about equal to, or even larger than
the number of known BPNe and proto-BPNe. Accordingly we argue that every BPN is
a `unique' object in its appearance, but all can be explained within the binary
model paradigm. Therefore, we request a stop to the attaching of adjectives
such as `unique', `peculiar', and `unusual' to BPNe and proto-BPNe, thereby
removing the need to invoke a new model for almost every `unusual' BPN. As a
case study we try to build a binary model for the proto-BPN OH231.8+4.2. In our
preferred model the AGB Mira-type star has a main sequence companion of mass 1
Mo, orbital period of five years, and eccentricity of 0.1.


title:
Cosmological perturbations from multi-field inflation in generalized
  Einstein theories

abstract:
  We study cosmological perturbations generated from quantum fluctuations in
multi-field inflationary scenarios in generalized Einstein theories, taking
both adiabatic and isocurvature modes into account. In the slow-roll
approximation, explicit closed-form long-wave solutions for field and metric
perturbations are obtained by the analysis in the Einstein frame. Since the
evolution of fluctuations depends on specific gravity theories, we make
detailed investigations based on analytic and numerical approaches in four
generalized Einstein theories: the Jordan-Brans-Dicke (JBD) theory, the
Einstein gravity with a non-minimally coupled scalar field, the
higher-dimensional Kaluza-Klein theory, and the $R+R^2$ theory with a
non-minimally coupled scalar field. We find that solutions obtained in the
slow-roll approximation show good agreement with full numerical results except
around the end of inflation. Due to the presence of isocurvature perturbations,
the gravitational potential $\Phi$ and the curvature perturbations ${\cal R}$
and $\zeta$ do not remain constant on super-horizon scales. In particular, we
find that negative non-minimal coupling can lead to strong enhancement of
${\cal R}$ in both the Einstein and higher derivative gravity, in which case it
is difficult to unambiguously decompose scalar perturbations into adiabatic and
isocurvature modes during the whole stage of inflation.


title:
Physical Constraints From Broadband Afterglow Fits:GRB000926 as an
  Example

abstract:
  We develop a model to fit the broadband afterglows of GRBs from the intrinsic
parameters of the fireball's synchrotron emission, and apply it to a few
well-studied events, with the goal of constraining the intrinsic variability of
GRB parameters. We give an example here of fitting to the recent bright event
GRB000926.


title:
Evidence for a heated gas bubble inside the "cooling flow" region of
  MKW3s

abstract:
  We report on the deep Chandra observation of central r=200kpc region of the
cluster of galaxies MKW3s which was previously identified as a moderate cooling
flow cluster. The Chandra image reveals two striking features -- a 100kpc long
and 21kpc wide filament, extending from the center to the south-west and a
nearly circular, 50kpc diameter depression 90 kpc south of the X-ray peak. The
temperature map shows that the filamentary structure is colder while the
surface brightness depression is hotter than the average cluster temperature at
any radius. The hot and the cold regions indicate that both cooling and heating
processes are taking place in the center of MKW3s. We argue that the surface
brightness depression is produced by a heated, low-density gas bubble along the
line of sight. We suggest that the heated bubble is produced by short-lived
nuclear outbursts from the central galaxy.


title: The Centaurus A Northern Middle Lobe as a Buoyant Bubble

abstract:
  We model the northern middle radio lobe of Centaurus A (NGC 5128) as a
buoyant bubble of plasma deposited by an intermittently active jet. The extent
of the rise of the bubble and its morphology imply that the ratio of its
density to that of the surrounding ISM is less than 10^{-2}, consistent with
our knowledge of extragalactic jets and minimal entrainment into the precursor
radio lobe. Using the morphology of the lobe to date the beginning of its rise
through the atmosphere of Centaurus A, we conclude that the bubble has been
rising for approximately 140Myr. This time scale is consistent with that
proposed by Quillen et al. (1993) for the settling of post-merger gas into the
presently observed large scale disk in NGC 5128, suggesting a strong connection
between the delayed re-establishment of radio emission and the merger of NGC
5128 with a small gas-rich galaxy. This suggests a connection, for radio
galaxies in general, between mergers and the delayed onset of radio emission.
In our model, the elongated X-ray emission region discovered by Feigelson et
al. (1981), part of which coincides with the northern middle lobe, is thermal
gas that originates from the ISM below the bubble and that has been uplifted
and compressed. The "large-scale jet" appearing in the radio images of Morganti
et al. (1999) may be the result of the same pressure gradients that cause the
uplift of the thermal gas, acting on much lighter plasma, or may represent a
jet that did not turn off completely when the northern middle lobe started to
buoyantly rise. We propose that the adjacent emission line knots (the "outer
filaments") and star-forming regions result from the disturbance, in particular
the thermal trunk, caused by the bubble moving through the extended atmosphere
of NGC 5128.


title:
Chandra Observations of MRK 273: Unveiling the Central AGN and the
  Extended Hot Gas Halo

abstract:
  We report X-ray observations of the field containing the ultraluminous IRAS
galaxy Mrk~273 Using the ACIS-S3 instrument on board Chandra. The high
resolution X-ray image, for the first time, reveals a compact hard X-ray
nucleus in Mrk~273. Its X-ray energy distribution is well described by a
heavily obscured power-law spectrum plus a narrow $\Feka$ emission line at 6.4
keV. The neutral hydrogen column density is about $4\times10^{23}\cm^{-2}$,
implying an absorption -corrected X-ray luminosity (0.1--10 keV) for the
nucleus of $\Lx\approx 6.5\times 10^{43} \ergs$. There are also bright soft
X-ray clumps and diffuse soft X-ray emissions surrounding the central hard
X-ray nucleus within the $10\arcsec$ of the nuclear region. Its spectrum can be
fitted by a MEKAL thermal model with temperature of about 0.8 keV and high
metallicity ($Z\sim 1.5Z_\odot$) plus emission lines from $\alpha$ elements and
ions. Further outside the central region, the Chandra observations reveal a
very extended hot gas halo with a projected diameter of about $108 \kpc\times
68 \kpc$ and soft X-ray luminosity of $\Lx\approx 1.9\times 10^{41} \ergs$. The
temperature of the hot gas is about 0.62 keV with a low metallicity ($Z \sim
0.1 Z_\odot$). We discuss the nature of the AGN in Mrk~273 and the implications
of our results on the origin of X-ray halos in elliptical galaxies. We also
discuss the properties of Mrk~273x, a background AGN in the Mrk~273 field. The
AGN has an X-ray luminosity of $\Lx \approx 2.43\times 10^{44}\ergs$ in the
0.5-10 keV band. Its X-ray properties resemble those of Seyfert 1 galaxies
while its optical properties are similar to Seyfert 2 galaxies. Such mixed
classifications may be a challenge for the unification scheme of AGNs.


title: Microlensing in M31; Preliminary lightcurves from MEGA

abstract:
  One of the possible astrophysical solutions to the galactic dark matter
problem is the presence of a significant amount of ``dark'' compact objects
(MACHOs) in galactic dark matter halos. MEGA (Microlensing Exploration of the
Galaxy and Andromeda) tries to find proof for or against the presence of
compact objects in the halo of the Andromeda galaxy (M31) by looking for the
microlensing signature that would be induced by these objects. The lightcurves
presented here are preliminary and based on observations of M31 with the Isaac
Newton Telescope (INT) on La Palma during the second half of 1999.


title: Galactic Winds in Starburst Irregular Galaxies

abstract:
  In this paper we present some results of numerical simulations concerning the
development of galactic winds in starburst galaxies. In particular, we focus on
a galaxy similar to IZw18, the most metal-poor galaxy locally known. We compute
the chemio-dynamical evolution of this galaxy, considering the energetic input
and the chemical yields originating from Supernovae (SNe) of Type II and Ia and
from intermediate-mass stars. We consider both single, instantaneous starburst
and two starbursts separated by a quiescent period. In all considered cases a
metal enriched winds develops and in particular the metals produced by Type Ia
SNe are ejected more efficiently than the other metals. We suggest that two
burst of star formation, the first being weaker and the last having an age of
some tenth of Myr, can satisfactorily reproduce the abundances and abundance
ratios found in literature for IZw18


title:
A multi-Lorentzian timing study of the atoll sources 4U 0614+09 and 4U
  1728-34

abstract:
  We present the results of a multi-Lorentzian fit to the power spectra of two
kilohertz QPO sources; 4U 0614+09 and 4U 1728-34. This work was triggered by
recent results of a similar fit to the black-hole candidates (BHCs) GX 339-4
and Cyg X-1 by Nowak in 2000. We find that one to six Lorentzians are needed to
fit the power spectra of our two sources. The use of exactly the same fit
function reveals that the timing behaviour of 4U 0614+09 and 4U 1728-34 is
almost identical at luminosities which are about a factor 5 different. As the
characteristic frequency of the Lorentzians we use the frequency, nu_max, at
which each component contributes most of its variance per log frequency as
proposed by Belloni, Psaltis & van der Klis in 2001. When using nu_max instead
of the centroid frequency of the Lorentzian, the recently discovered hectohertz
Lorentzian is practically constant in frequency. We use our results to test the
suggestions by, respectively, Psaltis Belloni and van der Klis in 1999 and
Nowak in 2000 that the two Lorentzians describing the high-frequency end of the
broad-band noise in BHCs in the low state can be identified with the kilohertz
QPOs in the neutron star low mass X-ray binaries. We find, that when the two
kilohertz QPOs are clearly present, the low-frequency part of the power
spectrum is too complicated to draw immediate conclusions from the nature of
the components detected in any one power spectrum. However, the relations we
observe between the characteristic frequencies of the kilohertz QPOs and the
band-limited noise, when compared to the corresponding relations in BHCs, hint
towards the identification of the second-highest frequency Lorentzian in the
BHCs with the lower kilohertz QPO. They do not confirm the identification of
the highest-frequency Lorentzian with the upper kilohertz QPO.


title:
Coupling emitted light and chemical yields from stars: a basic
  constraint to population synthesis models of galaxies

abstract:
  In this paper we emphasize the close connection between the chemical and
spectrophotometric evolution of stellar systems: Chemical yields from stars
correspond to a precise fraction of their emitted light. We translate this
concept quantitatively. Starting from simple stellar populations, we derive
useful analytical relations to calculate the stellar fuel consumption (emitted
light) as a function of basic quantities predicted by stellar models, i.e. the
mass of the core and the chemical composition of the envelope. The final
formulas explicate the relation between integrated light contribution (total or
limited to particular evolutionary phases), chemical yields and stellar
remnants. We test their accuracy in the case of low- and intermediate-mass
stars, and indicate the way to extend the analysis to massive stars. This
formalism provides an easy tool to check the internal consistency between the
different stellar inputs adopted in galaxy models: The fuel computed by means
of the analytical formulas (corresponding to a given set of chemical yields)
should be compared to the exact values given by the luminosity integration
along the stellar evolutionary tracks or isochrones (corresponding to a given
set of spectrophotometric models). Only if both estimates of the fuel are
similar, the stellar inputs can be considered self-consistent in terms of their
energetics. This sets an important requirement to galaxy models, also in
consideration of the fact that different sources of input stellar data are
frequently used to model their spectro-photometric and chemical evolution.


title: Characteristics Of A Magnetic Buoyancy Driven Solar Dynamo Model

abstract:
  We have developed a hybrid model of the solar dynamo on the lines of the
Babcock-Leighton idea that the poloidal field is generated at the surface of
the Sun from the decay of active regions. In this model magnetic buoyancy is
handled with a realistic recipe - wherein toroidal flux is made to erupt from
the overshoot layer wherever it exceeds a specified critical field ($10^5$ G).
The erupted toroidal field is then acted upon by the alpha effect near the
surface to give rise to the poloidal field. In the first half of this paper we
present a parameter space study of this model, to bring out similarities and
differences between it and other well studied models of the past. In the second
half of this paper we show that the mechanism of buoyant eruptions and the
subsequent depletion of the toroidal field inside the overshoot layer, is
capable of constraining the magnitude of the dynamo generated magnetic field
there, although a global quenching mechanism is still required to ensure that
the magnetic fields do not blow up. We also believe that a critical study of
this mechanism may give us new information regarding the solar interior and end
with an example, where we propose a new method for estimating an upper limit of
the diffusivity within the overshoot layer.


title: High Energy Phenomena in Blazars

abstract:
  Advances in the capabilities of X-ray, gamma-ray and TeV telescopes have
brought new information on the physics of relativistic jets, which are
responsible for the blazar "phenomenon". In particular the broad band
sensitivity of the BeppoSAX satellite, extending up to 100 KeV has allowed
unprecedented studies of their hard X-ray spectra. I summarize here some basic
results and present a unified view of the blazar population, whereby all
sources contain essentially similar jets despite diversities in other
properties, like the presence or absence of emission lines in their optical
spectra. Blazars with emission lines are of particular interest in that it is
possible to estimate both the luminosity of the jet and the luminosity of the
accretion disk. Implications for the origin of the power carried by
relativistic jets, possibly involving rapidly spinning supermassive black holes
are discussed. We suggest that emission line blazars are accreting at near
critical rates, while BL lacs, where emission lines are weak or absent are
highly subcritical.


title: Probing the physics of relativistic jets through X-ray observations

abstract:
  The broad band sensitivity and flexibility of the BeppoSAX satellite have
allowed unprecedented studies of the X-ray emission from blazars. Here we focus
on recent results on the SEDs of a group of blazars with emission lines,
allowing to estimate both the luminosity in the jet and the luminosity of the
accretion disk. Implications for the origin of the power carried by
relativistic jets are considered.


title:
Constraining the Collisional Nature of the Dark Matter Through
  Observations of Gravitational Wakes

abstract:
  We propose to use gravitational wakes as a direct observational probe of the
collisional nature of the dark matter. We calculate analytically the structure
of a wake generated by the motion of a galaxy in the core of an X-ray cluster
for dark matter in the highly-collisional and collisionless limits. We show
that the difference between these limits can be recovered from detailed X-ray
or weak lensing observations. We also discuss the sizes of sub-halos in these
limits. Preliminary X-ray data on the motion of NGC 1404 through the Fornax
group disfavors fluid-like dark matter but does not exclude scenarios in which
the dark matter is weakly collisional.


title: The Long-Term Future of Extragalactic Astronomy

abstract:
  If the current energy density of the universe is indeed dominated by a
cosmological constant, then high-redshift sources will remain visible to us
only until they reach some finite age in their rest-frame. The radiation
emitted beyond that age will never reach us due to the acceleration of the
cosmic expansion rate, and so we will never know what these sources look like
as they become older. As a source image freezes on a particular time frame
along its evolution, its luminosity distance and redshift continue to increase
exponentially with observation time. The higher the current redshift of a
source is, the younger it will appear as it fades out of sight. For the popular
set of cosmological parameters, I show that a source at a redshift z=5-10 will
only be visible up to an age of 4-6 billion years. Arguments relating the
properties of high-redshift sources to present-day counterparts will remain
indirect even if we continue to monitor these sources for an infinite amount of
time. These sources will not be visible to us when they reach the current age
of the universe.


title: Rotational Brownian Motion of a Massive Binary

abstract:
  The orientation of a massive binary undergoes a random walk due to
gravitational encounters with field stars. The rotational diffusion coefficient
for a circular-orbit binary is derived via scattering experiments. The binary
is shown to reorient itself by an angle of order (m/M)^1/2 during the time that
its semi-major axis shrinks appreciably, where M is the binary mass and m the
perturber mass. Implications for the orientations of rotating black holes are
discussed.


title:
Multi-stage Three Dimensional Sweeping and Annealing of Disc Galaxies in
  Clusters

abstract:
  We present new three dimensional, hydrodynamic simulations of the ram
pressure stripping of disc galaxies via interaction with an hot intracluster
medium (ICM). The simulations were carried with the smoothed-particle
hydrodynamics, adaptive mesh 'Hydra' code (SPH-A$P^3$M), with model galaxies
consisting of dark halo, and gas and stellar disc components. The simulations
also include radiative cooling, which is important for keeping the warm,
diffuse gas of moderate density from being unrealistically heated by the ICM.
We examine the role that wind velocity, density and galaxy tilt play in gas
stripping.
  The onset of the ICM wind has a profound effect on the disc gas that is not
immediately stripped. This remnant disc is displaced relative to the halo
center and compressed. This can trigger gravitational instability and the
formation of numerous flocculent spirals. These waves transport angular
momentum outward, resulting in further compression of the inner disc and the
formation of a prominent gas ring. This 'annealing' process makes the inner
disc, which contains much of the total gas mass, resistant to further
stripping, but presumably susceptible to global starbursts.
  When the mass loss and annealing processes go to completion we find that the
total amount of mass lost from a fixed target galaxy is well fit by a simple
power-law function of a dimensionless parameter that combines the ram pressure
and internal properties of the galaxy. (abs. abbreviated)


title: Dark Energy and the Preposterous Universe

abstract:
  A brief review is offered of the theoretical background concerning dark
energy: what is required by observations, what sort of models are being
considered, and how they fit into particle physics and gravitation.
Contribution to the SNAP (SuperNova Acceleration Probe) Yellow Book.


title: Theory and Extragalactic Masers

abstract:
  Theoretical research on extragalactic masers (and hence this review) is
almost entirely directed toward 22 GHz water masers in circumnuclear disks with
the focus being the near ideal masing disk at the nucleus of the galaxy
NGC4258. The discussion here is organized around (1) the excitation and
conditions for the masers, (2) the spatial and spectral appearance of the maser
emission, and (3) the mass accretion rate and structure of the disk. In
addition, a summary is given of the basic physics (spectral linebeadths and
maser polarization) that underlies certain interpretations of these and other
astrophysical masers.


title: Natural Quintessence and Large Extra Dimensions

abstract:
  We examine the late-time (nucleosynthesis and later) cosmological
implications of brane-world scenarios having large (millimeter sized) extra
dimensions. In particular, recent proposals for understanding why the extra
dimensions are so large in these models indicate that moduli like the radion
appear (to four-dimensional observers) to be extremely light, with a mass of
order 10^{-33} eV, allowing them to play the role of the light scalar of
quintessence models. The radion-as-quintessence solves a long-standing problem
since its small mass is technically natural, in that it is stable against
radiative corrections. Its challenges are to explain why such a light particle
has not been seen in precision tests of gravity, and why Newton's constant has
not appreciably evolved since nucleosynthesis. We find the couplings suggested
by stabilization models can provide explanations for both of these questions.
We identify the features which must be required of any earlier epochs of
cosmology in order for these explanations to hold.


title:
Hubble Space Telescope Observations of the CfA Seyfert 2s: Near-infrared
  Surface Photometry and Nuclear Bars

abstract:
  We present near-infrared J and H surface photometry of 24 of the nearby
Seyfert 1.8, 1.9 and 2 galaxies from the CfA Seyfert sample. The excellent
angular resolution of HST probes spatial scales as small as tens of parsecs in
most of these AGN and is sensitive to the presence of nuclear bars and other
potential signatures of the AGN fueling process that channels host galaxy gas
and dust to the nuclear region. We have used elliptical isophote techniques to
search for nuclear bars in all of these galaxies and have employed a
two-dimensional fitting technique to model the nuclear point source and surface
brightness distribution of a bright subsample of these galaxies in an attempt
to alleviate the impact of the nuclear point source on our sensitivity to
nuclear bars. We find stellar nuclear bar candidates in four of these galaxies:
Mrk 471, Mrk 270, Mrk 573, and NGC 5929, nearly 20% of the total sample. The
percentage rises to ~30% when systems with disturbed morphologies or high
inclinations are excluded. The nuclear bars in Mrk 573 and Mrk 270 exhibit some
evidence for dust lanes along their leading edges, analogous to the structures
seen in host galaxy bars, while the dust lanes in Mrk 471 and NGC 5929 exhibit
a more complex morphology. The fact that most of these AGN do not appear to
contain stellar nuclear bars suggests that they are not the fueling mechanism
for most low-luminosity AGN.


title: Growth of supermassive black holes and metallicity in quasars

abstract:
  The strong correlation between the mass of the central supermassive black
hole (SMBH) and the bulge in some galaxies and quasars implies that the
formation of the black hole is somehow linked to the bulge. The measurement of
metallicity by NV/CIV or NV/HeII in quasars allows to discuss a possible way of
formation of the black hole. In this Letter we trace the metallicity along the
possible routes in Rees' diagram in order to test the ways by which SMBHs can
form. We derive a relation between the metallicity and the mass of the SMBH as
$Z\propto M_{BH}$ based on the numerical simulation of the evolution of star
clusters. It is in good agreement with the relation determined by the
metallicity measured by NV/CIV or NV/HeII in Hamann & Ferland's sample. This
lends observational support to the formation of SMBHs via routes R4 or R5,
namely, the evolution of dense star clusters.


title: Seismic study of stellar convective cores

abstract:
  It has been shown that a discontinuity in the derivatives of the sound speed
at the edge of the convective regions inside a star gives rise to a
characteristic oscillatory signal in the frequencies of stellar oscillations.
This oscillatory signal has been suggested as a means to study the base of the
outer convection zone in low mass stars and possibly the outer edge of the
convective core in high mass stars. Using stellar models we show that because
of a phenomenon similar to aliasing in Fourier transform, it may not be
possible to use this signal to detect the convective core. Nevertheless, it may
be possible to determine the size of convective cores using the frequency
separation \nu_{n+1,l}-\nu_{n,l}.


title: The impact of cooling and pre-heating on the Sunyaev-Zel'dovich effect

abstract:
  We use hydrodynamical simulations to assess the impact of radiative cooling
and `pre-heating' on predictions for the Sunyaev--Zel'dovich (SZ) effect.
Cooling significantly reduces both the mean SZ signal and its angular power
spectrum, while pre-heating can give a higher mean distortion while leaving the
angular power spectrum below that found in a simulation without heating or
cooling. We study the relative contribution from high and low density gas, and
find that in the cooling model about 60 per cent of the mean thermal distortion
arises from low overdensity gas. We find that haloes dominate the thermal SZ
power spectrum in all models, while in the cooling simulation the kinetic SZ
power spectrum originates predominantly in lower overdensity gas.


title:
Design Study of CANGAROO-III, Stereoscopic Imaging Atmospheric Cherenkov
  Telescopes for sub-TeV Gamma-ray

abstract:
  CANGAROO-III is an Imaging Atmospheric Cherenkov Telescope (IACT) array of
four 10 m telescopes for very high energy (sub-TeV) gamma-ray astronomy. A
design study of the CANGAROO-III telescope system was carried out using the
Monte Carlo technique in order to optimize the pixel size and the telescope
spacing. Studies were also made of observations at low elevation angles.


title: Wide-Spectrum Slow Magnetoacoustic Waves in Coronal Loops

abstract:
  A model interpreting variations of EUV brightness upward propagating in solar
coronal loops as slow magnetoacoustic waves is developed. A loop is considered
to have a non-zero plane inclination angle and offset of circular loop centre
from the baseline. The model also incorporates effects of dissipation and
gravitational stratification. A linear evolutionary equation is derived and
applied to investigation of slow wave dynamics. Both the non-zero plane
inclination and the offset decrease the growth of the wave amplitude due to
stratification. It is shown that wide spectrum slow magnetoacoustic waves,
consistent with currently available observations in the low frequency part of
the spectrum, can provide the rate of heat deposition sufficient to heat the
loop. In this scenario, the heat would be deposited near the loop footpoints
which agrees with the current observational data.


title: A Weakly Nonlinear Alfvenic Pulse in a Transversely Inhomogeneous Medium

abstract:
  The interaction of a weakly nonlinear Alfv\'enic pulse with an Alfv\'en speed
inhomogeneity in the direction perpendicular to the magnetic field is
investigated. Identically to the phase mixing experienced by a harmonic
Alfv\'en wave, sharp transverse gradients are generated in the pulse by the
inhomogeneity. In the initial stage of the evolution of an initially plane
Alfv\'enic pulse, the transverse gradients efficiently generate transversely
propagating fast magnetoacoustic waves. However, high resolution full MHD
numerical simulations of the developed stage of the pulse evolution show that
the generation saturates due to destructive wave interference. It is shown that
the weakly non-linear description of the generated fast magnetoacoustic wave is
well described by the driven wave equation proposed in Nakariakov, Roberts &
Murawski (1997), and a simple numerical code (2D MacCromack), which solves it
with minimal CPU resources produces identical results to those obtained from
the full MHD code ({\it Lare2d}, Arber et al. 2001). A parametric study of the
phenomenon is undertaken, showing that, contrary to one's expectations, steeper
inhomogenities of the Alfv\'en speed do not produce higher saturation levels of
the fast wave generation. There is a certain optimal gradient of the
inhomogeneity that ensures the maximal efficiency of the fast wave generation.


title:
Integral/IBIS Observations of persistent black hole spectral states
  during the Core Program

abstract:
  The Imager on Board the Integral Satellite (IBIS) is one of the two main
telescopes of Integral, the ESA soft gamma-ray mission to be launched in 2002.
The Integral Core Program will be divided into two main parts, the Galactic
Centre Deep Exposure program and the Galactic Plane Scan for a total amount of
around 6 .6 10^6 seconds each year. In this paper, we will study the visibility
of persist ent galactic black holes as observed by IBIS during these two phases
of the Core Program. We will also present what information may be derived from
the IBIS observations of spectral/temporal properties (variation of the
spectral index, presence/absence of a spectral break, ...) of these binary
systems in different spectral states, in particular in the framework of the
bulk motion Comptonization model.


title:
Exploring the Gamma Ray Horizon with the next generation of Gamma Ray
  Telescopes. Part 1: Theoretical predictions

abstract:
  The physics potential of the next generation of Gamma Ray Telescopes in
exploring the Gamma Ray Horizon is discussed. It is shown that the reduction in
the Gamma Ray detection threshold might open the window to use precise
determinations of the Gamma Ray Horizon as a function of the redshift to either
put strong constraints on the Extragalactic Background Light modeling or to
obtain relevant independent constraints in some fundamental cosmological
parameters.


title: Is the old nova RW UMi (1956) an intermediate polar?

abstract:
  From photometric observations of the old nova RW UMi (1956) we have
discovered the presence of five sub-orbital periodicities. The longest period,
P1 = 54.4 min, always observed, could be the beat period between the orbital
period and the white dwarf (WD) spin period that we assume to be P2 = 33.4 min.
The other suborbital periods could be orbital sidebands with respect to P2
and/or correspond to Keplerian resonance radii. We suggest that in its
post-outburst state, characterized by higher mass transfer rate, RW UMi is an
asynchronous intermediate polar with a truncated accretion disc. If the
magnetic momentum of the WD is $\mu_{34} \sim 0.8$, in its quiescent
pre-outburst state, the nova would appear as a discless, synchronous
intermediate polar.


title: The X-ray view of highly obscured AGN

abstract:
  The properties of Compton-thick AGN are reviewed, with particular emphasis on
BeppoSAX hard X-ray observations. I also discuss evidence for the presence of
Compton-thick, circumnuclear matter in unobscured AGN, and I briefly introduce
the HELLAS2XMM 5-10 keV survey, discussed in more details in other
contributions to this volume.


title:
The SCUBA 8-mJy survey - II: Multiwavelength analysis of bright sub-mm
  sources

abstract:
  We present the results of a multi-wavelength study of the 19 most significant
sub-mm sources detected in the SCUBA 8-mJy survey. As described in Scott et al.
(2001), this survey covers ~260 arcmin^2 using the sub-millimetre camera SCUBA,
to a limiting source detection limit S(850um) ~ 8 mJy. One advantage of this
relatively bright flux-density limit is that accurate astrometric positions are
potentially achievable for every source using existing radio and/or mm-wave
interferometers. However, an associated advantage is that SED-based redshift
constraints should be more powerful than in fainter sub-mm surveys. Here we
therefore exploit the parallel SCUBA 450um data, in combination with existing
radio and ISO data at longer and shorter wavelengths to set constraints on the
redshift of each source. We also analyse new and existing optical and
near-infrared imaging of our SCUBA survey fields to select potential
identifications consistent with these constraints. Our derived SED-based
redshift constraints, and the lack of statistically significant associations
with even moderately bright galaxies allow us to conclude that all 19 sources
lie at z > 1, and at least half of them apparently lie at z > 2.


title: The Fundamental Plane of Spiral Galaxies: Search from Observational Data

abstract:
  The fundamental plane of spiral galaxies was searched from observational
data, which can be approximately represented in observational parameters by $ L
\propto V^2 R $, where $L$, $R$, and $V$ are the luminosity, the linear size of
galactic disk, and the rotation velocity. This plane exists at all optical
bands in our samples of more than 500 spiral galaxies in total. It is more
fundamental than the relationship between any two of the parameters, and can
reduce the residual of the Tully--Fisher $L$--$V$ relations by about 50\%.
Noticed that the power index of $V$ is doubled from that of $R$, which implies
that the total mass and the mass distribution of galaxies plays an important
role in forming the fundamental plane. Involving the third parameter of
galactic size has a strong physical implication on galaxy formation and the
dark--mass distribution.


title: The INTEGRAL/IBIS telescope modelling

abstract:
  The main objective of the IBIS modeling activities is the generation of the
IBIS spectral response matrix. This generation will be done step by step by
firstly constructing "calibrated model" of each IBIS sub-systems. A "calibrated
model" is defined as a GEANT Monte-Carlo model, further checked by intensive
corresponding calibration. These calibrated models will be in a second step
integrated in the whole IBIS Mass Model. This Mass Model will be checked and
refined using the data obtained during the IBIS Telescope calibration, the PLGC
during the ETET period, and the In-flight calibration data acquired during the
whole INTEGRAL mission. The IBIS Mass Model will be used also for computations
of efficiencies and transparencies. Some imaging studies (such as the study of
the diffuse emission) may be also done with the help of the IBIS Mass Model.
The IBIS Mass Model may be used for the simulation of IBIS data in order to
check the different IBIS software.


title:
Estimate of the Cosmological Bispectrum from the MAXIMA-1 Cosmic
  Microwave Background Map

abstract:
  We use the measurement of the cosmic microwave background taken during the
MAXIMA-1 flight to estimate the bispectrum of cosmological perturbations. We
propose an estimator for the bispectrum that is appropriate in the flat sky
approximation, apply it to the MAXIMA-1 data and evaluate errors using
bootstrap methods. We compare the estimated value with what would be expected
if the sky signal were Gaussian and find that it is indeed consistent, with a
$\chi^2$ per degree of freedom of approximately unity. This measurement places
constraints on models of inflation.


title: High-energy neutrino emission from Gamma-Ray Bursts

abstract:
  Gamma-Ray Bursts (GRBs) are expected to efficiently accelerate protons up to
relativistic energies. High-energy photons can originate from decay of neutral
pions produced by the interaction of these protons with the medium surrounding
the source. In the same hadronic chain, high energy neutrinos are expected to
be produced from decay of charged pions, as well as from decay of generated
muons. Neutrinos can travel cosmological distances being much less absorbed
than photons, thus providing a powerful tool for the investigation of cosmic
sources. In the frame of a recently proposed hadronic model for the emission of
high-energy gamma-rays, we estimate the neutrino emission from GRBs and
calculate the neutrino fluxes at Earth as a function of the model parameters.
The detectability of the expected signal by current and future experiments is
also extensively discussed.


title: An Inner Molecular Bar or Disk in NGC 5195

abstract:
  High resolution OVRO CO 1-0 observations of the inner kpc of the
M51-companion NGC 5195 reveal the presence of a kpc-sized bar, or possibly an
inclined disk with a two armed spiral, at the center of the optical bar. The
molecular mass of the feature is 2.7 x 10^8 M_o, half of which is within a
radius of 250 pc. The resulting gas surface density of 10^3 M_o pc^-2 is
typical for starbursts. However, the lack of evidence for current star
formation suggests that either some mechanism is preventing stars from forming,
or the standard CO to H_2 conversion factor substantially overestimates the
available amounts of molecular gas.


title: Formation and Evolution of the Trans-Neptunian Belt and Dust

abstract:
  Trans-Neptunian objects (TNOs) with diameter greater than 100 km currently
moving in not too eccentric orbits could be formed directly by the contraction
of large rarefied condensations. Along with the gravitational influence of
planets, gravitational interactions of TNOs played a certain role in their
orbital evolution as well. More than 20% of Earth-crossing objects could have
come from the trans-Neptunian belt. TNOs and Centaurs (invisible comets mainly
beyond Jupiter) could produce an important contribution to the dust content of
the interplanetary dust cloud.


title:
Characteristics of air showers created by extremely high energy
  gamma-rays

abstract:
  The technique of adjoint cascade equations has been applied to calculate the
properties of extremely high energy gamma-rays in the energy range 10^18--10^22
eV with taking into account the LPM effect and interactions of gamma-rays with
the geomagnetic field. Such characteristics are analysed as the electron and
muon contents at the observation level, the electron cascade curves, the
lateral distribution functions of photoproduced muons.


title:
A Second Intense Burst with Photospheric Radius Expansion from X2127+119
  in M15

abstract:
  In 2000 September we observed a bright X-ray burst from X2127+119 with the
Rossi X-ray Timing Explorer. This burst has a multi-peaked profile, a peak
luminosity of ~6.5x10^{38} erg s^{-1}, a total integrated energy of ~2x10^{40}
ergs, and significant photospheric radius expansion to a maximum extent of
R=118+-5 km. From the luminosity-temperature relation during the expansion
phase we derive estimates for the gravitational redshift at the neutron star
surface, the corrected Eddington luminosity, and the neutron star mass. We
detect no slow (~30s) radial oscillations or fast (100-1200 Hz) coherent
oscillations or QPO during the burst.
  The 2000 September event is only the second burst ever observed from this
globular cluster binary (in M15 = NGC 7078), and it shares many characteristics
with the event detected by Ginga in 1988 October (Dotani et al. 1990; van
Paradijs et al. 1990), the key difference probably being the total amount of
material consumed in the thermonuclear flash.


title:
Parsec-Scale Jet Polarization Properties of a Complete Sample of Active
  Galactic Nuclei at 43 GHz

abstract:
  We present results from the highest resolution polarization imaging survey of
a complete sample of extragalactic radio sources carried out to date. Our
sample consists of a statistically complete flat-spectrum subset of 32 AGNs
from the Pearson-Readhead survey, which has been studied at a variety of
wavelengths and resolutions, including space-VLBI. Our observations were made
with the VLBA at 43 GHz, where the relatively higher resolution and weaker
opacity effects have allowed us to probe magnetic field structures in the jets
of these AGNs much closer to the central engine than in previous studies. At 43
GHz, the bulk of the total intensity and polarized emission in most
flat-spectrum AGNs originates from an unresolved core component located at the
extreme end of a faint jet. The luminosity of the core is positively correlated
with the total source luminosity in soft x-rays, in the optical, and at 5 GHz.
The most strongly polarized cores display electric vectors that are roughly
aligned with the jet axis, which is consistent with a strong transverse shock
that enhances the perpendicular component of the jet magnetic field. Sources
with highly polarized cores also tend to have high optical polarizations and
flatter overall radio spectra. Approximately half of the jets in our sample
display apparently bent morphologies that are suggestive of streaming motions
along a helical path. The straightest jets in the sample tend to display slower
superluminal speeds than those that are significantly bent. We also confirm
that intrinsic differences in the magnetic field properties of BL Lacertae
objects and quasars previously seen on scales of tens of milliarcseconds are
also present in regions much closer to the base of the jet.


title:
On the application of differences in intrinsic fluctuations of Cherenkov
  light images for separation of air showers

abstract:
  The sensitivity of ground-based imaging atmospheric Cherenkov gamma-ray
observatories depends critically on the primary particle identification methods
which are used to retain photon-initiated events and suppress the spurious
background produced by cosmic rays. We suggest a new discrimination technique
which utilizes differences in the fluctuations of the light intensity in the
images of showers initiated by photons and those initiated by protons or
heavier nuclei. The database of simulated events for the proposed VERITAS
observatory has been used to evaluate the efficiency of the new technique.
Analysis has been performed for both a single VERITAS imaging telescope, and a
system of these telescopes. We demonstrate that a discrimination efficiency of
> 1.5 - 2.0 can be achieved in addition to traditional background rejection
methods based on image shape parameters.


title:
H2+ ion in a strong magnetic field: Lowest gerade and ungerade
  electronic states

abstract:
  In the framework of a variational method with a single trial function an
accurate study of the lowest gerade 1g and ungerade 1u electronic states of the
molecular ion $H_2^+$ in a magnetic field is performed. Magnetic field ranges
from 0 to 4.414x10^13 G and orientations of the molecular axis with respect to
the magnetic line 0 \leq theta \leq 90 are considered. A one-parameter gauge
dependent vector potential is used in the Hamiltonian, which is finally
variationally optimized. A well pronounced minimum on the total energy surface
of the (ppe) system in both 1g and 1u states is found for all magnetic fields
and orientations studied. It is shown that for both states the parallel
configuration (theta=0) at equilibrium always corresponds to the minimal total
energy. It is found that for a given theta for both states the magnetic field
growth is always accompanied by an increase in the total and binding energies
as well as a shrinking of the equilibrium distance. We demonstrate that for
B\gtrsim 1.8x10^11 G the molecular ion can dissociate, H2+ -> H + p, over a
certain range of orientations (theta_cr \le theta \le 90), where the minimal
thetaa_cr \simeq 25 occurs for the strongest magnetic field studied,
B=4.414x10^13 G. For B<10^12 G the ion H2+ in 1g, 1u states is the most
compact, being in the perpendicular configuration (theta=90), whereas for
B\gtrsim 10^12 this occurs for an angle < 90. For the 1g state in any
orientation, with the magnetic field growth at B \sim 10^11 G, a two-peak
electronic distribution changes to single-peak one.


title: Clustering of SCUBA galaxies and implications for the Planck mission

abstract:
  The clustering properties of SCUBA-selected galaxies are investigated within
the framework of a unifying scheme relating the formation of QSOs and
spheroids. The theoretical angular correlation function is derived for
different bias functions, corresponding to different values of the ratio
$M_{halo}/M_{sph}$ between the mass of the dark halos hosting such galaxies and
the mass in stars produced at the end of the major star-formation burst. SCUBA
sources are predicted to be strongly clustered, with a clustering strength
increasing with mass. Comparisons with the best available measurements show
better fits for $M_{halo}/M_{sph}\simeq 100$. The model can also account for
the clustering of Lyman-break galaxies, seen as the optical counterpart of low-
to intermediate-mass primeval spheroidal galaxies. Best agreement is once again
obtained for high values of the $M_{halo}/M_{sph}$ ratio. We also discuss
implications for small scale fluctuations observed at different wavelengths by
forthcoming experiments such as the Planck mission aimed at mapping the Cosmic
Microwave Background (CMB).


title: Near Infrared Spectra of Compact Planetary Nebulae

abstract:
  This paper continues our study of the behaviour of near infrared helium
recombination lines in planetary nebula. We find that the 1.7007um 4^3D-3^3P
HeI line is a good measure of the HeI recombination rate, since it varies
smoothly with the effective temperature of the central star. We were unable to
reproduce the observed data using detailed photoionisation models at both low
and high effective temperatures, but plausible explanations for the difference
exist for both. We therefore conclude that this line could be used as an
indicator of the effective temperature in obscured nebula. We also
characterised the nature of the molecular hydrogen emission present in a
smaller subset of our sample. The results are consistent with previous data
indicating that ultraviolet excitation rather than shocks is the main cause of
the molecular hydrogen emission in planetary nebulae.


title:
The Relationship Between the Circular Polarization and the Magnetic
  Field for Astrophysical Masers with Weak Zeeman Splitting

abstract:
  The relationship between the magnetic field and the circular polarization of
astrophysical maser radiation due to the Zeeman effect under idealized
conditions is investigated when the Zeeman splitting is much smaller than the
spectral linebreadth and when radiative saturation is significant. The
description of the circular polarization, as well as inferences about the
magnetic field from the observations, are clearest when the rate for stimulated
emission is much less than the Zeeman splitting. The calculations here are
performed in this regime, which is relevant for some (if not most) observations
of astrophysical masers. We demonstrate that Stokes-$V$ is proportional to the
Zeeman splitting and the fractional linear polarization is independent of the
Zeeman splitting when the ratio of the Zeeman splitting to the spectral line
breadth is small---less than about 0.1. In contrast to its behavior for
ordinary spectral lines, the circular polarization for masers that are at least
partially saturated does not decrease with increasing angle between the
magnetic field and the line-of-sight until they are nearly perpendicular.


title:
Long-duration neutron star X-ray transients in quiescence: the Chandra
  observation of KS 1731-260

abstract:
  I will briefly discuss the implications of the recent quiescent Chandra
observation of the long-duration neutron star transient KS 1731-260 (Wijnands
et al. 2001a) on models for quiescent systems other than the Brown et al.
(1998) cooling neutron star model. However, the Chandra results are not very
constraining; for those models to be consistent with the data, one only has to
assume that the system parameters of KS 1731-260 (e.g., the neutron star spin
rate and magnetic field properties; orbital parameters) are very similar to
those of the other systems. I will also discuss the available quiescent data of
other long-duration neutron star transients in the context of the Brown et al.
(1998) model.


title:
Suppression of Gravitational Structure Formation by Cosmological
  Accretion Heating

abstract:
  As increasingly precise information about the spectrum of the cosmic
microwave background fluctuations is gathered with balloon and satellite
experiments, interest has grown in foreground sources of opacity affecting
these observations. One potentially important source is electron scattering
produced by a post-recombination luminosity source, which would significantly
attenuate the higher harmonics in the spectrum. If such an ionization source
exists, then it would also heat the universe, hence increasing the Jeans mass
and suppressing early gravitational structure formation. Here we consider the
effects of such heating. We concentrate on one type of ionization source:
luminosity generated by accretion onto primordial compact objects. We show that
if such objects generate enough luminosity to affect the CMB power spectrum,
then they would produce enough heat to prevent the formation of 1 sigma
collapsed objects until redshifts of about 5, significantly less than the
redshift at which baryonic collapse could otherwise occur. Such processes would
leave signatures detectable by upcoming instruments such as NGST, SIRTF, and
SWIFT.


title: Spectroscopy with Single Dish Radio Telescopes

abstract:
  This chapter is in three parts. The first presents the fundamental equations
of level populations and radiative transfer which govern spectral line emission
and absorption. Lines in the cm-wave band have similarities which allow us to
simplify the equations. The further simplification of a two level system (a
good approximation for H I gives the familiar formulae for the 21-cm line.
  The second part of the lesson deals with mapping, and the combination of
single dish and interferometer data. We consider the effect of gridding single
dish data using a convolving function. Mapping speeds and techniques are
discussed.
  The third part discusses the spectral line cube and its moments. The use of
the first moments to determine the dynamical structure of a disk is discussed.


title: The Star Formation History of NGC 6822

abstract:
  Images of five fields in the Local Group dwarf irregular galaxy NGC 6822
obtained with the {\it Hubble Space Telescope} in the F555W and F814W filters
are presented. Photometry for the stars in these images was extracted using the
Point-Spread-Function fitting program HSTPHOT/MULTIPHOT. The resulting
color-magnitude diagrams reach down to $V\approx26$, a level well below the red
clump, and were used to solve quantitatively for the star formation history of
NGC 6822. Assuming that stars began forming in this galaxy from low-metallicity
gas and that there is little variation in the metallicity at each age, the
distribution of stars along the red giant branch is best fit with star
formation beginning in NGC 6822 12-15 Gyr ago. The best-fitting star formation
histories for the old and intermediate age stars are similar among the five
fields and show a constant or somewhat increasing star formation rate from 15
Gyr ago to the present except for a possible dip in the star formation rate
from 3 to 5 Gyr ago. The main differences among the five fields are in the
higher overall star formation rate per area in the bar fields as well as in the
ratio of the recent star formation rate to the average past rate. These
variations in the recent star formation rate imply that stars formed within the
past 0.6 Gyr are not spatially very well mixed throughout the galaxy.


title:
Southern Galactic Plane Survey Measurements of the Spatial Power
  Spectrum of Interstellar H I in the Inner Galaxy

abstract:
  Using data from the Southern Galactic Plane Survey we have measured the
spatial power spectrum of the interstellar neutral atomic hydrogen in the
fourth Galactic quadrant. This function shows the same power law behavior that
has been found for H I in the second quadrant of the Milky Way and in the
Magellanic Clouds, with the same slope. When we average over velocity intervals
broader than the typical small-scale velocity dispersion, we find that the
slope steepens, from approx. -3 to -4 for the warm gas, as predicted by
theories of interstellar turbulence if the column density fluctuations are
dominated by variations in the gas density on small spatial scales. The cool
gas shows a different increase of slope, that suggests that it is in the regime
of turbulence dominated by fluctuations in the velocity field. Overall, these
results confirm that the small scale structure and motions in the neutral
atomic medium are well described by a turbulent cascade of kinetic energy.


title:
Measurement of the cosmic microwave background bispectrum on the COBE
  DMR sky maps

abstract:
  We measure the angular bispectrum of the cosmic microwave background (CMB)
radiation anisotropy from the COBE Differential Microwave Radiometer (DMR)
four-year sky maps. The angular bispectrum is the harmonic transform of the
three-point correlation function, analogous to the angular power spectrum, the
harmonic transform of the two-point correlation function. First, we study
statistical properties of the bispectrum and the normalized bispectrum. We find
the latter more useful for statistical analysis; the distribution of the
normalized bispectrum is very much Gaussian, while the bare bispectrum
distribution is highly non-Gaussian. Then, we measure 466 modes of the
normalized bispectrum, all independent combinations of three-point
configurations up to a maximum multipole of 20, the mode corresponding to the
DMR beam size. By measuring 10 times as many modes as the sum of previous work,
we test Gaussianity of the DMR maps. We compare the data with the simulated
Gaussian realizations, finding no significant detection of the normalized
bispectrum on the mode-by-mode basis. We also find that the previously reported
detection of the normalized bispectrum is consistent with a statistical
fluctuation. By fitting a theoretical prediction to the data for the primary
CMB bispectrum, which is motivated by slow-roll inflation, we put a weak
constraint on a parameter characterizing non-linearity in inflation.
Simultaneously fitting the foreground bispectra estimated from interstellar
dust and synchrotron template maps shows that neither dust nor synchrotron
emissions significantly contribute to the bispectrum at high Galactic latitude.
We conclude that the DMR map is consistent with Gaussianity.


title:
Exploratory Chandra Observations of the Highest-Redshift Quasars: X-rays
  from the Dawn of the Modern Universe

abstract:
  We report exploratory Chandra observations of 14 high-redshift (z=4.06-5.27),
optically selected quasars. Ten of these quasars are detected, increasing the
number of z>4 X-ray detected quasars by 71%. Our detections include four of the
five highest-redshift X-ray detected quasars to date, among them SDSSp
J021043.17-001818.4, the highest-redshift (z=4.77) radio-loud quasar detected
in the X-ray band. The four undetected objects are the Broad Absorption Line
quasars SDSSp J112956.10-014212.4 and SDSSp 160501.21-011220.0, the weak
emission-line quasar SDSSp J153259.96-003944.1, and the quasar PSS 1435+3057. A
comparison of the quasars' spectral energy distributions (by means of the
optical-to-X-ray spectral index, alpha_ox) with those of lower-redshift samples
indicates that the Chandra quasars are X-ray fainter by a factor of approx 2.
X-ray faintness could be associated with the presence of large amounts of gas
in the primeval galaxies harboring these high-redshift quasars, as suggested by
recent studies conducted on z>4 quasars in other bands. Using the current
Chandra data, predictions for the next generation of X-ray observatories,
Constellation-X and Xeus, are also provided.


title:
Testing The Friedmann Equation: The Expansion of the Universe During
  Big-Bang Nucleosynthesis

abstract:
  In conventional general relativity, the expansion rate H of a
Robertson-Walker universe is related to the energy density by the Friedmann
equation. Aside from the present day, the only epoch at which we can constrain
the expansion history in a model-independent way is during Big-Bang
Nucleosynthesis (BBN). We consider a simple two-parameter characterization of
the behavior of H during BBN and derive constraints on this parameter space,
finding that the allowed region of parameter space is essentially
one-dimensional. We also study the effects of a large neutrino asymmetry within
this framework. Our results provide a simple way to compare an alternative
cosmology to the observational requirement of matching the primordial
abundances of the light elements.


title: Cosmic-Ray Rejection by Laplacian Edge Detection

abstract:
  Conventional algorithms for rejecting cosmic-rays in single CCD exposures
rely on the contrast between cosmic-rays and their surroundings, and may
produce erroneous results if the Point Spread Function (PSF) is smaller than
the largest cosmic-rays. This paper describes a robust algorithm for cosmic-ray
rejection, based on a variation of Laplacian edge detection. The algorithm
identifies cosmic-rays of arbitrary shapes and sizes by the sharpness of their
edges, and reliably discriminates between poorly sampled point sources and
cosmic-rays. Examples of its performance are given for spectroscopic and
imaging data, including HST WFPC2 images.


title: Observations of Gamma-ray Bursts with the Rossi X-ray Timing Explorer

abstract:
  The role of the Rossi X-ray Timing Explorer (RXTE) in the study of Gamma-ray
Bursts (GRBs) is reviewed. Through April 2001, the All-Sky Monitor (ASM) and
the Proportional Counter Array (PCA) instruments have detected 30 GRBs. In 16
cases, an early celestial position was released to the community, sometimes in
conjunction with IPN results. The subsequent optical and radio searches led to
the detection of 5 x-ray afterglows, to at least 6 optical or radio afterglows,
to 3 of the 17 secure redshifts known at this writing, and to 2 other likely
redshifts. The decay curves of early x-ray afterglows have been measured. The
rapid determination of the location of GRB 970828 and the absence of optical
afterglow at that position gave one of the first indications that GRBs occur in
star-forming regions (Groot et al. 1998, ApJ 493, L27). The location of GRB
000301C led to the determination of a break in the optical decay rate (Rhoads
and Fruchter 2001, ApJ 546, 117) which is evidence for a jet, and to
variability in the optical light curve that could represent gravitational
lensing (Garnavich, Loeb, and Stanek 2000, ApJ 544, L11). X-ray light curves of
GRB from the ASM in conjunction with gamma-ray light curves exhibit striking
differences in different bands and may reveal the commencement of the x-ray
afterglow (Smith et al. 2001, ApJ submitted, astroph 0103357).


title:
Molecular Gas Properties in the Central Kiloparsec of Barred and
  Unbarred Spirals

abstract:
  We study the molecular gas properties in the central kiloparsec of 29 barred
and 15 unbarred spirals from the BIMA Survey of Nearby Galaxies (SONG). We find
that the mean nuclear molecular gas surface density of barred spirals
(<Sigma_{nuc}>=309 +/- 71 Msun pc^{-2}) is three times higher than that of
unbarred spirals (<Sigma_{nuc}>=107 +/- 29 Msun pc^{-2}). Nine out of the
eleven bars with Sigma_{nuc} > 300 Msun pc^{-2} are early types. Comparison
with estimates of the star formation threshold density (Sigma_{crit}) indicates
that enhanced star formation in bars may be due to a larger fraction having
Sigma_{nuc} > typical Sigma_{crit}. We also find that barred spirals are more
centrally concentrated than unbarred spirals. The median value of the
concentration parameter for barred spirals
(f_{con}=Sigma_{nuc}/Sigma_{disk}=27.7) is a factor of four higher than that
for the unbarred spirals (f_{con}=6.2). Finally we investigate the dependence
of the central concentration on bar properties and find it may be weakly
correlated with the bulge size, but is not correlated with the bar length. This
suggests that inner Lindblad resonances, bar ellipticity and circumnuclear star
formation play important roles in determining the gas accretion in the central
kiloparsec.
  See http://www.astro.caltech.edu/~kartik/thesis.html for more detailed
description of these thesis results. This research was made possible with
funding from NSF grants AST-9981308, AST-9981289 and AST-9981546.


title: MAXIMUS: Exploiting the Full Power of OzPoz

abstract:
  We propose a new multi-object spectrograph for the VLT. MAXIMUS (MAXimum
MUltiplex Spectrograph) will fully exploit the multiplexing capabilities of the
OzPoz fibre positioner in order to extend and complement FLAMES and VIMOS in
covering observational parameter space, and to meet the increasing demand for
multi-object spectroscopy by ESO users in the next decade.


title: Populations of Dwarfs in Clusters of Galaxies: Environmental Connections

abstract:
  Despite their apparent fragile appearance, dwarf spheroidals are the most
common galaxy type in clusters. In this paper we consider some of the issues
associated with two major models for the origin of these dwarfs: primeval
galaxies which formed with the cluster and the modification of accreted
systems. We argue that the present observational evidence, derived from the
Virgo and Perseus clusters, points to infall as the origin of many of these
objects.


title:
Clustering Properties of Galaxies at z~4 in the Subaru/XMM Deep Survey
  Field

abstract:
  We study the clustering properties of about 1200 z~4 Lyman Break Galaxy (LBG)
candidates with i'<26 which are selected by color from deep BRi' imaging data
of a 618 arcmin^2 area in the Subaru/XMM-Newton Deep Field taken with Subaru
Prime Focus Camera. The contamination and completeness of our LBG sample are
evaluated, on the basis of the Hubble Deep Field North (HDFN) objects, to be
17% and 45%, respectively. We derive the angular correlation function over
theta = 2''-1000'', and find that it is fitted fairly well by a power law,
omega(theta)=A_omega theta^{-0.8}, with A_omega = 0.71 +/- 0.26. We then
calculate the correlation length r0 (in comoving units) of the two-point
spatial correlation function xi(r) = (r/r0)^{-1.8} from A_omega using the
redshift distribution of LBGs derived from the HDFN, and find r0=2.7
(+0.5/-0.6) h^{-1} Mpc in a Lambda-dominated universe (Omega_m=0.3 and
Omega_Lambda=0.7). This is twice larger than the correlation length of the dark
matter at z~4 predicted from an analytic model by Peacock & Dodds but about
twice smaller than that of bright galaxies predicted by a semi-analytic model
of Baugh et al. We find an excess of omega(theta) on small scales (theta < 5'')
departing from the power law fit over 3 sigma significance levels. Interpreting
this as due to galaxy mergers, we estimate the fraction of galaxies undergoing
mergers in our LBG sample to be 3.0 +/- 0.9%, which is significantly smaller
than those of galaxies at intermediate redshifts.


title: Hydrostatic Expansion and Spin Changes During Type I X-Ray Bursts

abstract:
  We present calculations of the spin-down of a neutron star atmosphere due to
hydrostatic expansion during a Type I X-ray burst. We show that (i) Cumming and
Bildsten overestimated the spin-down of rigidly-rotating atmospheres by a
factor of two, and (ii) general relativity has a small (5-10%) effect on the
angular momentum conservation law. We rescale our results to different neutron
star masses, rotation rates and equations of state, and present some detailed
rotational profiles. Comparing with recent observations of large frequency
shifts in MXB 1658-298 and 4U 1916-053, we find that the spin-down expected if
the atmosphere rotates rigidly is a factor of two to three less than the
observed values. If differential rotation is allowed to persist, we find that
the upper layers of the atmosphere spin down by an amount comparable to the
observed values; however, there is no compelling reason to expect the observed
spin frequency to be that of only the outermost layers. We conclude that
hydrostatic expansion and angular momentum conservation alone cannot account
for the largest frequency shifts observed during Type I bursts.


title: Likelihood Analysis of sub-TeV Gamma-rays from RXJ1713-39

abstract:
  We have detected gamma-rays from RXJ1713$-$39 in the energy range between 400
GeV and 5 TeV using a new kind of analysis: likelihood analysis. The
statistical significance of the measurement is greater than 8 $\sigma$. The
details of this analysis method are presented.


title:
Possibility of Direct Measurement of the Acceleration of the Universe
  Using 0.1 Hz Band Laser Interferometer Gravitational Wave Antenna in Space

abstract:
  It may be possible to construct a laser interferometer gravitational wave
antenna in space with $h_{rms}\sim 10^{-27}$ at $ f\sim 0.1{\rm Hz}$ in this
century. We show possible specification of this antenna which we call DECIGO.
Using this antenna we show that 1) typically $ 10^5$ ($10^4\sim 10^6$) chirp
signals of coalescing binary neutron stars per year may be detected with S/N
$\sim 10^4$. 2) We can directly measure the acceleration of the universe by ten
years observation of binary neutron stars. 3) The stochastic gravitational
waves of $\Omega_{GW}\gsim 10^{-20}$ predicted by the inflation may be detected
by correlation analysis for which effects of the recent cosmic acceleration
would become highly important. Our formula for phase shift due to accelerating
motion might be also applied for binary sources of LISA.


title: The deeply embedded starburst in SBS 0335-052

abstract:
  We present 4-micron ISAAC imaging and spectroscopy of the extremely
metal-poor dwarf galaxy SBS 0335-052, aimed at a better understanding of the
dust in this low-metallicity galaxy. The 4-micron emission turns out to be very
compact, confined to the brightest pair of Super Star Clusters (SSCs). The
Ks-L$^\prime$ color is extremely red, and the $L^\prime$ emission is consistent
with the extrapolation of the ISO mid-infrared spectral energy distribution
(SED). From hydrogen recombination lines and a fit to the near-/mid-infrared
SED, we confirm a visual extinction of >= 15 mag. Our data suggest that the
sites of the optical and infrared emission are distinct: the optical spectral
lines come from an almost dustless region with a high star formation rate and a
few thousand OB stars. This region lies along the line-of-sight to a very dusty
central star cluster in which there are more than three times as many massive
stars, completely hidden in the optical. From the extinction, we derive an
upper limit for the dust mass of 10^5 M$_\odot$ which could be produced by
recent supernovae.


title:
Galaxy Mass and Luminosity Scaling Laws Determined by Weak Gravitational
  Lensing

abstract:
  We present new measurements of scaling laws relating the luminosity of
galaxies to the amplitude and shape of their dark matter halos. Early imaging
and spectroscopic data from the Sloan Digital Sky Survey are used to make weak
lensing measurements of the surface mass density contrast Delta Sigma_+ around
classes of lens objects. This surface mass density contrast as a function of
radius is a measure of the galaxy-mass correlation function (GMCF). Because
spectroscopic redshifts are available for all lens objects, the mass and
distance scales are well constrained. The GMCF measured around ~31,000 lenses
is well fit by a power law of the form
  Delta Sigma_+ = (2.5+0.7-0.6) (R/1 Mpc)^{-0.8+-0.2} h M_sun pc^-2.
  We compare this GMCF to galaxy luminosity, type, and environment, and find
that it varies strongly with all three. We quantify these variations by
comparing the normalization of a fit to the inner 260 h^-1 kpc, M_260, to the
galaxy luminosity. While M_260 is not strongly related to luminosity in bluest
band u', there is a simple, linear relation between M_260 and luminosity in
redder bands (g', r', i', and z'). We test the universality of these
mass-to-light scalings by independently measuring them for spiral and
elliptical galaxies,and for galaxies in a variety of environments. We find
remarkable consistency in these determinations in the red bands, especially i'
and z'. This consistency across a wide range of systems suggests that the
measured scaling represents an excellent cosmic average, and that the
integrated star formation history of galaxies is strongly related to the dark
matter environments in which they form.


title:
Structure of Dark Matter Halos From Hierarchical Clustering: II.
  Universality and Self-Similarity in Cluster-Sized Halos

abstract:
  We investigate the structure of the dark matter halo formed in three
different cold dark matter scenarios. We performed N-body simulations of
formation of 13 cluster-sized halos. In all runs, density cusps proportional to
$r^{-1.5}$ developed at the center. This result was independent of the
cosmological models we simulated. We could not reproduce the cusp shallower
than $r^{-1.5}$, which was obtained in some of previous studies. We also found
that in all runs the density structure evolves in a self-similar way, even in
$\Omega\ne 1$ universes. These results show that the formation of structural
form is a process decoupled from a background cosmology.


title: Diffuse gamma-ray line emission from multiple OB Associations in Cygnus

abstract:
  The COMPTEL observations of the diffuse galactic 1.809 MeV emission
attributed to the radioactive decay of 26Al have confirmed the diffuse nature
of this interstellar emission line. One of the most significant features of the
reconstructed intensity pattern is a flux enhancement in the direction of the
Cygnus region. This region is fairly young and contains a wealth of massive
stars, most of them grouped in the Cygnus OB associations. Multi-frequency
model fitting strongly supports the hypothesis of massive stars and their
descendent supernovae being the dominant sources of interstellar 26Al as
observed by COMPTEL.
  Massive stars and supernovae are known to impart a large amount of kinetic
energy into the surrounding ISM which lead to shockregions and large cavities.
In addition, a large fraction of the electro-magnetic radiation of massive
stars lies in the extreme ultra-violet causing photoionisation of the
surrounding interstellar medium.
  We applied a population synthesis model in combination with an analytic model
of the expansion of superbubbles to the Cygnus OB associations. The model
predicts the expected 1.809 MeV flux and the gamma-ray line intensity due to
interstellar 60Fe. We compute the sizes and expansion parameters of the
expected HI-structures and the free-free emission intensities due to the
photoionizing radiation from massive stars within this region of the sky. We
discuss our present understanding of the Cygnus region with respect to the
massive star census and history. Our model assigns about 70% of the 1.809 MeV
intensity to six known OB associations, about 20% to known isolated sources and
roughly 10% to an unkown diffuse component.


title: Scattered light models of the dust shell around HD 179821

abstract:
  The dust shell around the evolved star HD 179821 has been detected in
scattered light in near-IR imaging polarimetry observations. Here, we subtract
the contribution of the unpolarized stellar light to obtain an intrinsic linear
polarization of between 30 and 40 per cent in the shell which seems to increase
with radial offset from the star. The J and K band data are modelled using a
scattering code to determine the shell parameters and dust properties. We find
that the observations are well described by a spherically symmetric
distribution of dust with an inverse square density law, indicating that when
mass-loss was occurring, the mass-loss rate was constant. The models predict
that the detached nature of a spherically symmetric, optically thin dust shell,
with a distinct inner boundary, will only be apparent in polarized flux. This
is in accordance with the observations of this and other optically thin
circumstellar shells, such as IRAS 17436+5003. By fitting the shell brightness
we derive an optical depth to the star which is consistent with V band
observations and which, assuming a distance of 6 kpc, gives an inner shell
radius of 1.44 X 10^{15} m, a dust number density of 2.70 X 10^{-1} m^{-3}. and
a dust mass of 0.08 Msun. We have explored axisymmetric shell models but
conclude that any deviations from spherical symmetry in the shell must be
slight, with an equator-to-pole density contrast of less than 2:1. We have not
been able to simultaneously fit the high linear polarizations and the small
(E(J-K)=-0.3) colour excess of the shell and we attribute this to the unusual
scattering properties of the dust. We suggest that the dust grains around HD
179821 are either highly elongated or consist of aggregates of smaller
particles.


title:
ASCA X-ray observations of the disk wind in the dwarf nova Z
  Camelopardalis

abstract:
  We present ASCA observations of the dwarf nova Z Camelopardalis during
outburst and during a transition from quiescence to another outburst.
  At the beginning of the transition the X-ray count rate was an order of
magnitude higher and the spectrum much harder than during the outburst. As the
transition progressed, the spectrum remained hard as the X-ray flux decreased
by a factor of 3, with no spectral softening. Spectral modelling reveals an
optically-thin, high-temperature component (kT$\approx$10 keV) which dominates
the transition observation and is also observed during outburst. This is
expected from material accreting onto the white dwarf surface. The outburst
spectra require additional emission at lower temperatures, either through an
additional discrete temperature component, or a combination of a cooling flow
model and an ionised absorber.
  Fits to both observations show large amounts of absorption
($N_H=8-9\times10^{21}$cm$^{-2}$), two orders of magnitude greater than the
measured interstellar value, and consistent with UV measurements of the
outburst. This suggests that a disk wind is present even in the earliest stages
of outburst, possibly before the outburst heating wave has reached the boundary
layer.


title: The Quiescent Spectrum of the AM CVn star CP Eri

abstract:
  We used the 6.5m MMT to obtain a spectrum of the AM CVn star CP Eri in
quiescence. The spectrum is dominated by He I emission lines, which are clearly
double peaked with a peak-to-peak separation of ~1900 km/s. The spectrum is
similar to that of the longer period AM CVn systems GP Com and CE 315, linking
the short and the long period AM CVn systems. In contrast with GP Com and CE
315, the spectrum of CP Eri does not show a central 'spike' in the line
profiles, but it does show lines of SiII in emission. The presence of these
lines indicates that the material being transferred is of higher metallicity
than in GP Com and CE 315, which, combined with the low proper motion of the
system, probably excludes a halo origin of the progenitor of CP Eri. We
constrain the primary mass to M_1>0.27 M_sun and the orbital inclination to 33
degr < i < 80 degr. The presence of the He I lines in emission opens up the
possibility for phase resolved spectroscopic studies which allows a
determination of the system parameters and a detailed study of helium accretion
disks under highly varying circumstances.


title: On the Nature of the NGC 1275 System

abstract:
  Sub-arcsecond images, taken in B, R, and H-Alpha filters, and area
spectroscopy obtained with the WIYN 3.5-m telescope provide the basis for an
investigation of the unusual structures in the stellar body and ionized gas in
and around the Perseus cluster central galaxy, NGC 1275. Our H-Alpha filter is
tuned to gas at the velocity of NGC 1275, revealing complex, probably
unresolved, small-scale features in the extended ionized gas, located up to
50/h kpc from NGC 1275. The mean H-Alpha surface brightness varies little along
the outer filaments; this, together with the complex excitation state
demonstrated by spectra, imply that the filaments are likely to be tubes, or
ribbons, of gas. The morphology, location and inferred physical parameters of
the gas in the filaments are consistent with a model whereby the filaments form
through compression of the intracluster gas by relativistic plasma emitted from
the active nucleus of NGC 1275. Imaging spectroscopy with the Densepak fiber
array on WIYN suggests partial rotational support of the inner component of low
velocity ionized gas. We confirm and extend evidence for features in the
stellar body of NGC 1275, and identify outer stellar regions containing very
blue, probably very young, star clusters. We interpret these as evidence for
recent accretion of a gas-rich system, with subsequent star formation. We
suggest that two main processes, which may be causally connected, are
responsible for the rich phenomenology of the NGC 1275 system -- NGC 1275
experienced a recent merger/interaction with a group of gas-rich galaxies, and
recent outflows from its AGN have compressed the intracluster gas, and perhaps
the gas in the infalling galaxies, to produce a complex web of filaments.
(Abridged)


title:
COSMOSOMAS: A Circular Scanning Instrument to Map the Sky at Centimetric
  Wavelengths

abstract:
  We describe the first instrument of a Cosmic Microwave Background experiment
for mapping cosmological structures on medium angular scales (the COSMOSOMAS
experiment) and diffuse Galactic emission. The instrument is located at Teide
Observatory (Tenerife) and is based on a circular scanning sky strategy. It
consists of a 1 Hz spinning flat mirror directing the sky radiation into a 1.8
m off-axis paraboloidal antenna which focuses it on to a cryogenically cooled
HEMT-based receiver operating in the frequency range 12--18 GHz. The signal is
split by a set of three filters, allowing simultaneous observations at 13, 15
and 17 GHz, each with a 1 GHz bandpass. A 1-5 degree resolution sky map
complete in RA and covering 20 degrees in declination is obtained each day at
these frequencies. The observations presented here correspond to the first
months of operation, which have provided a map of ~9000 square degrees on the
sky centred at DEC = +31 degrees with sensitivities of 140, 150 and 250 microK
per beam area in the channels at 13, 15 and 17 GHz respectively. We discuss the
design and performance of the instrument, the atmospheric effects, the
reliability of the data obtained and prospects of achieving a sensitivity of 30
microK per beam in two years of operation.


title: Cooling Flows of Self-Gravitating, Rotating, Viscous Systems

abstract:
  We obtain self-similar solutions that describe the dynamics of a
self-gravitating, rotating, viscous system. We use simplifying assumptions; but
explicitly include viscosity and the cooling due to the dissipation of energy.
By assuming that the turbulent dissipation of energy is as power law of the
density and the speed v_{rms} and for a power-law dependence of viscosity on
the density, pressure, and rotational velocity, we investigate turbulent
cooling flows. It has been shown that for the cylindrically and the spherically
cooling flows the similarity indices are the same, and they depend only on the
exponents of the dissipation rate and the viscosity model. Depending on the
values of the exponents, which the mechanisms of the dissipation and viscosity
determine them, we may have solutions with different general physical
properties. The conservation of the total mass and the angular momentum of the
system strongly depends on the mechanisms of energy dissipation and the
viscosity model.


title:
Infall, Outflow, Rotation, and Turbulent Motions of Dense Gas within NGC
  1333 IRAS 4

abstract:
  Millimeter wavelength observations are presented of NGC 1333 IRAS 4, a group
of highly-embedded young stellar objects in Perseus, that reveal motions of
infall, outflow, rotation, and turbulence in the dense gas around its two
brightest continuum objects, 4A and 4B. These data have finest angular
resolution of approximately 2" (0.0034 pc) and finest velocity resolution of
0.13 km/s. Infall motions are seen from inverse P-Cygni profiles observed in
H2CO 3_12-2_11 toward both objects, but also in CS 3-2 and N2H+ 1-0 toward 4A,
providing the least ambiguous evidence for such motions toward low-mass
protostellar objects. Outflow motions are probed by bright line wings of H2CO
3_12-2_11 and CS 3-2 observed at positions offset from 4A and 4B, likely
tracing dense cavity walls. Rotational motions of dense gas are traced by a
systematic variation of the N2H+ line velocities, and such variations are found
around 4A but not around 4B. Turbulent motions appear reduced with scale, given
N2H+ line widths around both 4A and 4B that are narrower by factors of 2 or 3
than those seen from single-dish observations. Minimum observed line widths of
approximately 0.2 km/s provide a new low, upper bound to the velocity
dispersion of the parent core to IRAS 4, and demonstrate that turbulence within
regions of clustered star formation can be reduced significantly. A third
continuum object in the region, 4B', shows no detectable line emission in any
of the observed molecular species.