title: The Most Luminous Galaxies

abstract:
  Ultraluminous galaxies in the local universe (z$\leq$0.2) emit the bulk of
their energy in the mid and far-infrared. The multiwavelength approach to these
objects has shown that they are advanced mergers of gas-rich spiral galaxies.
Galaxy-galaxy collisions took place on all cosmological time-scales, and nearby
mergers serve as local analogs to gain insight into the physical processes that
lead to the formation and trans-formation of galaxies in the more distant
universe. Here I review multiwavelength observations --with particular emphasis
on recent results obtained with ISO-- of mergers of massive galaxies driving
the formation of: 1) luminous infrared galaxies, 2) elliptical galaxy cores, 3)
luminous dust-enshrouded extranuclear starbursts, 4) symbiotic galaxies that
host AGNs, and 5) tidal dwarf galaxies. The most important implication for
studies on the formation of galaxies at early cosmological timescales is that
the distant analogs to the local ultraluminous infrared galaxies are invisible
in the ultraviolet and optical wavelength rest-frames and should be detected as
sub-millimeter sources with no optical counterparts.


title:
Molecular hydrogen at z=1.973 toward Q0013-004: Dust depletion pattern
  in damped Lyman-alpha systems

abstract:
  We study the dust depletion pattern in eight well separated components of the
z=1.973, logN(HI)=20.83, damped Lyman-alpha system toward Q0013-004, four of
which have detectable H2 absorption. The apparent correlation between the
abundance ratios [Fe/S] and [Si/S] in the components indicates that the
abundance pattern is indeed due to dust-depletion. In particular, we find
evidence for depletion similar to what is observed in cold gas of the Galactic
disk ([Fe/Zn]=-1.59, Fe/S=-1.74, Zn/S=-0.15, [Si/S]=-0.85) in one of the
weakest components in which molecular hydrogen is detected with logN(H2)=16.5.
This is the first time such a large depletion is seen in a DLA system. This
observation supports the possibility that current samples of DLA systems might
be biased against the presence of cold and dusty gas along the line of sight.
The overall metallicities of this peculiar DLA system in which OI and CII are
spread over 1050 km/s are [P/H]=-0.64, [Zn/H]=-0.74 and [S/H]=-0.82 relative to
solar. The sub-DLA system at z=1.96753 has [P/H]>0.06, [Zn/H]>-0.02 and
[S/H]>-0.18. The overall molecular fraction is in the range -2.7<logf<-0.6. CO
is not detected (logN(CO)/N(HI)<-8) and HD could be present at z=1.97380. We
show that the presence of H2 is closely related to the physical conditions of
the gas: high particle density together with low temperature. The observed
excitation of high J H2 levels and the molecular fraction show large variations
from one component to the other suggesting that the UV radiation field is
highly inhomogeneous throughout the system. Gas pressure, estimated from CI
absorptions, is larger than what is observed in the ISM of our Galaxy. All this
is probably a consequence of intense star-formation activity in the vicinity of
the absorbing gas. (Abridged)


title: Radio continuum and CO emission in star-forming galaxies

abstract:
  We combine the radio continuum images from the NRAO VLA Sky Survey with the
CO-line observations from the extragalactic CO survey of the Five College Radio
Astronomy Observatory to study the relationship between molecular gas and the
star formation rate within the disks of 180 spiral galaxies at 45" resolution.
We find a tight correlation between these quantities. On average, the ratio
between the radio continuum and the CO emission is constant, within a factor of
3, both inside the same galaxy and from galaxy to galaxy. The mean star
formation efficiency deduced from the radio continuum corresponds to convert
3.5% of the available molecular gas into stars on a time scale of 10^8 yr and
depends weakly on general galaxy properties, such as Hubble type or nuclear
activity. A comparison is made with another similar analysis performed using
the H_alpha luminosity as star formation indicator. The overall agreement we
find between the two studies reinforces the use of the radio luminosity as star
formation rate indicator not only on global but also on local scales.


title: 3D-MHD simulations of an accretion disk with star-disk boundary layer

abstract:
  We present global 3D MHD simulations of geometrically thin but unstratified
accretion disks in which a near Keplerian disk rotates between two bounding
regions with initial rotation profiles that are stable to the MRI. The inner
region models the boundary layer between the disk and an assumed more slowly
rotating central, non magnetic star. We investigate the dynamical evolution of
this system in response to initial vertical and toroidal fields imposed in a
variety of domains contained within the near Keplerian disk. Cases with both
non zero and zero net magnetic flux are considered and sustained dynamo
activity found in runs for up to fifty orbital periods at the outer boundary of
the near Keplerian disk. Simulations starting from fields with small radial
scale and with zero net flux lead to the lowest levels of turbulence and
smoothest variation of disk mean state variables. For our computational set up,
average values of the Shakura & Sunyaev (1973) $\alpha$ parameter in the
Keplerian disk are typically $0.004\pm 0.002.$ Magnetic field eventually always
diffuses into the boundary layer resulting in the build up of toroidal field
inward angular momentum transport and the accretion of disk material. The mean
radial velocity, while exhibiting large temporal fluctuations is always
subsonic. Simulations starting with net toroidal flux may yield an average
$\alpha \sim 0.04.$ While being characterized by one order of magnitude larger
average $\alpha$, simulations starting from vertical fields with large radial
scale and net flux may lead to the formation of persistent non-homogeneous,
non-axisymmetric magnetically dominated regions of very low density.


title:
Tomographic Separation of Composite Spectra. IX. The Massive Close
  Binary HD 115071

abstract:
  We present the first orbital elements for the massive close binary, HD
115071, a double-lined spectroscopic binary in a circular orbit with a period
of 2.73135 +/- 0.00003 days. The orbital semiamplitudes indicate a mass ratio
of M_2/M_1 = 0.58 +/- 0.02 and yet the stars have similar luminosities. We used
a Doppler tomography algorithm to reconstruct the individual component optical
spectra, and we applied well known criteria to arrive at classifications of
O9.5 V and B0.2 III for the primary and secondary, respectively. We present
models of the Hipparcos light curve of the ellipsoidal variations caused by the
tidal distortion of the secondary, and the best fit model for a Roche-filling
secondary occurs for an inclination of i = 48.7 +/- 2.1 degrees. The resulting
masses are 11.6 +/- 1.1 and 6.7 +/- 0.7 solar masses for the primary and
secondary, respectively, so that both stars are very overluminous for their
mass. The system is one of only a few known semi-detached, Algol-type binaries
that contain O-stars. We suggest that the binary has recently emerged from
extensive mass transfer (possibly through a delayed contact and common envelope
process).


title:
The MACHO Project LMC Variable Star Inventory: XII. Three Cepheid
  Variables in Eclipsing Binaries

abstract:
  We present a method for solving the lightcurve of an eclipsing binary system
which contains a Cepheid variable as one of its components as well as the
solutions for three eclipsing Cepheids in the Large Magellanic Cloud (LMC). A
geometric model is constructed in which the component stars are assumed to be
spherical and on circular orbits. The emergent system flux is computed as a
function of time, with the intrinsic variations in temperature and radius of
the Cepheid treated self-consistently. Fitting the adopted model to photometric
observations, incorporating data from multiple bandpasses, yields a single
parameter set best describing the system. This method is applied to three
eclipsing Cepheid systems from the MACHO Project LMC database: MACHO ID's
6.6454.5, 78.6338.24 and 81.8997.87. A best-fit value is obtained for each
system's orbital period and inclination and for the relative radius, color and
limb-darkening coefficients of each star. Pulsation periods and
parameterizations of the intrinsic color variations of the Cepheids are also
obtained and the amplitude of the radial pulsation of each Cepheid is measured
directly. The system 6.6454.5 is found to contain a 4.97-day Cepheid, which
cannot be definitely classified as Type I or Type II, with an unexpectedly
brighter companion. The system 78.6338.24 consists of a 17.7-day, W Vir Class
Type II Cepheid with a smaller, dimmer companion. The system 81.8997.87
contains an intermediate-mass, 2.03-day overtone Cepheid with a dimmer, red
giant secondary.


title: First optical light from the supernova remnant G 17.4-2.3

abstract:
  Deep optical CCD images of the supernova remnant G 17.4-2.3 were obtained and
faint emission has been discovered. The images, taken in the emission lines of
Halpha+[N II], [S II] and [O III], reveal filamentary structures in the east,
south-east area, while diffuse emission in the south and central regions of the
remnant is also present. The radio emission in the same area is found to be
well correlated with the brightest optical filament. The flux calibrated images
suggest that the optical filamentary emission originates from shock-heated gas
([S II]/Halpha > 0.4), while the diffuse emission seems to originate from an
HII region ([S II]/Halpha < 0.3). Furthermore, deep long-slit spectra were
taken at the bright [O III] filament and clearly show that the emission
originates from shock heated gas. The [O III] flux suggests shock velocities
into the interstellar "clouds" greater than 100 km/s, while the [S II]
6716/6731 ratio indicates electron densities ~240 cm^{-3}. Finally, the Halpha
emission has been measured to be between 7 to 20 x 10^{-17} erg s^{-1} cm^{-2}
arcsec^{-2}.


title: The Type IIn SN 1995G: Interaction with the CSM

abstract:
  We present the photometric and spectroscopic evolution of the type IIn SN
1995G in NGC 1643, on the basis of 4 years of optical and infrared
observations. This supernova shows very flat optical light curves similar to SN
1988Z, with a slow decline rate at all times. The spectra are characterized by
strong Balmer lines with multiple components in emission and with a P-Cygni
absorption component blueshifted by only 700 km/s. This feature indicates the
presence of a slowly expanding shell above the SN ejecta as in the case of SNe
1994aj and 1996L. As in other SNe IIn the slow luminosity decline cannot be
explained only with a radioactive energy input and an additional source of
energy is required, most likely that produced by the interaction between
supernova ejecta and a pre--existent circumstellar medium. It was estimated
that the shell material has a density n(H) >> 10^8 cm^-3, consistent with the
absence of forbidden lines in the spectra. About 2 years after the burst the
low velocity shell is largely overtaken by the SN ejecta and the luminosity
drops at a faster rate.


title: Automating the Synthetic Field Method:Application to Sextans A

abstract:
  We have automated the ``Synthetic Field Method'' developed by Gonzalez et
al.(1998) and used it to measure the opacity of the ISM in the Local Group
dwarf galaxy Sextans A by using the changes in counts of background galaxies
seen through the foreground system. The Sextans A results are consistent with
the observational relation found by Cuillandre et al. (2001) between dust
opacity and HI column density in the outer parts of M31.


title:
Triaxial stellar systems following the r^{1/n} luminosity law: an
  analytical mass-density expression, gravitational torques and the bulge/disc
  interplay

abstract:
  We have investigated the structural and dynamical properties of triaxial
stellar systems whose surface brightness profiles follow the r^{1/n} luminosity
law - extending the analysis of Ciotti (1991) who explored the properties of
spherical r^{1/n} systems. A new `analytical' expression that accurately
reproduces the spatial (i.e. deprojected) luminosity density profiles (error <
0.1%) is presented for detailed modelling of the Sersic family of luminosity
profiles. We evaluate both the symmetric and the non--axisymmetric components
of the gravitational potential and force, and compute the torques as a function
of position. For a given triaxiality, stellar systems with smaller values of n
have a greater non-axisymmetric gravitational field component. We also explore
the strength of the non-axisymmetric forces produced by bulges with differing n
and triaxiality on systems having a range of bulge-to-disc ratios. The
increasing disc-to-bulge ratio with increasing galaxy type (decreasing n) is
found to heavily reduce the amplitude of the non-axisymmetric terms, and
therefore reduce the possibility that triaxial bulges in late-type systems may
be the mechanism or perturbation for nonsymmetric structures in the disc. Using
seeing-convolved r^{1/n}-bulge plus exponential-disc fits to the K-band data
from a sample of 80 nearby disc galaxies, we probe the relations between galaxy
type, Sersic index n and the bulge-to-disc luminosity ratio. These relations
are shown to be primarily a consequence of the relation between n and the total
bulge luminosity. In the K-band, the trend of decreasing bulge-to-disc
luminosity ratio along the spiral Hubble sequence is predominantly, although
not entirely, a consequence of the change in the total bulge luminosity; the
trend between the total disc luminosity and Hubble type is much weaker.


title: On the recent history of star formation in the BCD galaxy VII Zw403

abstract:
  The recent history of star formation in the BCD galaxy VII Zw403, is analysed
with accounts for the dynamics of the remnant generated either by an
instantaneous burst or by a continuous star formation event.
  We have re-observed VII Zw403 with a better sensitivity corresponding to the
threshold H$_{\alpha}$ flux $8.15 \times 10^{-17}$ erg cm$^{-2}$ s$^{-1}$. The
total H$_{\alpha}$ luminosity derived from our data is much larger than
reported before, and presents a variety of ionized filaments and incomplete
shells superimposed on the diffuse H$_{\alpha}$ emission. This result has a
profound impact on the predicted properties of the starburst blown superbubble.
Numerical calculations based on the previous H$_{\alpha}$ data, predict two
different scenarios of star formation able to match simultaneously all observed
parameters. These are an instantaneous burst of star formation with a total
mass of $5 \times 10^5$ M$_{\odot}$ and a star-forming event with a constant
SFR = $4 \times 10^{-3}$ M$_{\odot}$ yr$^{-1}$, which lasts for 35 Myrs. The
numerical calculations based on the energy input rate derived from our
observations predict a short episode of star formation lasting less than 10
Myrs with a total star cluster mass $\sim (1 - 3) \times 10^6$ M$_{\odot}$.


title:
1RXS J232953.9+062814: A Dwarf Nova with a 64-minute Orbital Period and
  a Conspicuous Secondary Star

abstract:
  We present spectroscopy and time-series photometry of the newly discovered
dwarf nova 1RXS J232953.9+062814. Photometry in superoutburst reveals a
superhump with a period of 66.06(6) minutes. The low state spectrum shows
Balmer and HeI emission on a blue continuum, and in addition shows a rich
absorption spectrum of type K4 +- 2. The absorption velocity is modulated
sinusoidally at P_orb = 64.176(5) min, with semi-amplitude K = 348(4) km/s. The
low-state light curve is double-humped at this period, and phased as expected
for ellipsoidal variations. The absorption strength does not vary appreciably
around the orbit. The orbital period is shorter than any other cataclysmic
variable save for a handful of helium-star systems and V485 Centauri (59
minutes). The secondary is much hotter than main sequence stars of similar
mass, but is well-matched by helium-enriched models, indicating that the
secondary evolved from a more massive progenitor. A preliminary calculation in
which a 1.2 solar-mass star begins mass transfer near the end of H burning
matches this system's characteristics remarkably well.


title:
Angular momentum induced phase transition in spherical gravitational
  systems: N-body simulations

abstract:
  The role of thermodynamics in the evolution of systems evolving under purely
gravitational forces is not completely established. Both the infinite range and
singularity in the Newtonian force law preclude the use of standard techniques.
However, astronomical observations of globular clusters suggests that they may
exist in distinct thermodynamic phases. Here, using dynamical simulation, we
investigate a model gravitational system which exhibits a phase transition in
the mean field limit. The system consists of rotating, concentric, mass shells
of fixed angular momentum magnitude and shares identical equilibrium properties
with a three dimensional point mass system satisfying the same condition. The
mean field results show that a global entropy maximum exists for the model, and
a first order phase transition takes place between "quasi-uniform" and
''core-halo'' states, in both the microcanonical and canonical ensembles. Here
we investigate the evolution and, with time averaging, the equilibrium
properties of the isolated system. Simulations were carried out in the
transition region, at the critical point, and in each clearly defined
thermodynamic phase, and striking differences were found in each case. We find
full agreement with mean field theory when finite size scaling is accounted
for. In addition, we find that (1) equilibration obeys power law behavior, (2)
virialization, equilibration, and the decay of correlations in both position
and time, are very slow in the transition region, suggesting the system is also
spending time in the metastable phase, (3) there is strong evidence of
long-lived, collective, oscillations in the supercritical region.


title: A disrupted circumstellar torus inside eta Carinae's Homunculus Nebula

abstract:
  We present thermal infrared images of the bipolar nebula surrounding eta
Carinae at six wavelengths from 4.8 to 24.5 microns. These were obtained with
the MIRAC3 camera system at the Magellan Observatory. Our images reveal new
intricate structure in the bright core of the nebula, allowing us to
re-evaluate interpretations of morphology seen in images with lower resolution.
Complex structures in the core might not arise from a pair of overlapping rings
or a cool (110 K) and very massive dust torus, as has been suggested recently.
Instead, it seems more likely that the arcs and compact knots comprise a warm
(350 K) disrupted torus at the intersection of the larger polar lobes. Some of
the arcs appear to break out of the inner core region, and may be associated
with equatorial features seen in optical images. The torus could have been
disrupted by a post-eruption stellar wind, or by ejecta from the Great Eruption
itself if the torus existed before that event. Kinematic data are required to
rule out either possibility.


title:
On the reliability of initial conditions for dissipationless
  cosmological simulations

abstract:
  We present the study of ten random realizations of a density field
characterized by a cosmological power spectrum P(k) at redshift z=50. The
reliability of such initial conditions for n-body simulations are tested with
respect to their correlation properties. The power spectrum P(k), and the mass
variance sigmaM(r) do not show detectable deviations from the desired behavior
in the intermediate range of scales between the mean interparticle distance and
the simulation volume. The estimator for xi(r) is too noisy to detect any
reliable signal at the initial redshift z=50. The particle distributions are
then evolved forward until z=0. This allows us to explore the cosmic variance
stemming from the random nature of the initial conditions. With cosmic variance
we mean the fact that a simulation represents a single realization of the
stochastic initial conditions whereas the real Universe contains many
realizations of regions of the size of the box; this problem affects most
importantly the scales at about the fundamental mode. We study morphological
descriptors of the matter distribution such as the genus, as well as the
internal properties of the largest object(s) forming in the box. We find that
the scatter is at least comparable to the scatter in the fundamental mode.


title: Fabry-Perot Survey of Emission-Line Galaxies

abstract:
  The recent results from a deep Fabry-Perot survey of nearby active and
star-forming galaxies are presented. Line-emitting material is detected over
two orders of magnitude in galactocentric radius, from the 100-pc scale of the
active or starbursting nucleus out to several 10s of kpc, sometimes well beyond
the optical confines of the host galaxies. The excitation and dynamical
properties of the nuclear gas are studied to constrain the impact of galactic
winds on the host galaxies and their environment. The properties of the warm
ionized material on the outskirts of galaxies provide important clues for
understanding galaxy formation and evolution. A new technique to search for
starburst-driven wind galaxy candidates is discussed. The next generation of
Fabry-Perot instruments on large telescopes promises to improve the sensitivity
of emission-line galaxy surveys at least tenfold.


title:
The Star Formation Rate Intensity Distribution Function -- Comparison of
  Observations with Hierarchical Galaxy Formation

abstract:
  Recently, Lanzetta et al. (2002) have measured the distribution of star
formation rate intensity in galaxies at various redshifts. This data set has a
number of advantages relative to galaxy luminosity functions; the effect of
surface-brightness dimming on the selection function is simpler to understand,
and this data set also probes the size distribution of galactic disks. We
predict this function using semi-analytic models of hierarchical galaxy
formation in a LCDM cosmology. We show that the basic trends found in the data
follow naturally from the redshift evolution of dark matter halos. The data are
consistent with a constant efficiency of turning gas into stars in galaxies,
with a best-fit value of 2%, where dust obscuration is neglected; equivalently,
the data are consistent with a cosmic star formation rate which is constant to
within a factor of two at all redshifts above two. However, the practical
ability to use this kind of distribution to measure the total cosmic star
formation rate is limited by the predicted shape of an approximate power law
with a smoothly varying power, without a sharp break.


title:
Frequently Asked Questions on the Luminosity--Temperature relation in
  Groups and Clusters

abstract:
  Efforts to understand the deviation of the L--T relation from a simple
scaling law valid for clusters and groups have triggered a number of
interesting studies on the subject. Techniques and approaches differ widely but
most works agree on the important role played by gas cooling and heating
sources like AGNs and SNe. Observations set useful constraints on the evolution
of the intracluster medium (ICM): a 100KeV/cm^2 entropy floor in the core of
groups and about 5--15% of baryons being converted into stars. However,
essential details like the nature of the dominant heating mechanism and the
quantitative importance of cooling still need to be addressed. I suggest that a
new generation of high resolution N-body simulations and a quantitative
comparison of results between different approaches is required to improve
results and increase our understanding of the problem.


title:
Echelle spectroscopy of Ca II HK activity in Southern Hemisphere planet
  search targets

abstract:
  We present the results of ultraviolet echelle spectroscopy of a sample of
fifty nine F,G,K and M stars from the Anglo-Australian Planet Search target
list. Ca II activity indices, which are essential in the interpretation of
planet detection claims, have been determined for these stars and placed on the
Mount Wilson Rhk system.


title: AGN Populations from Optical Identification of ASCA Surveys

abstract:
  To understand luminous AGNs in the z<1 universe, the ASCA AGN samples are the
best at present. Combining the identified sample of AGNs from ASCA Large Sky
Survey and Medium Sensitivity Survey, the sample of hard X-ray selected AGNs
have been expanded up to 108 AGNs above the flux limit of 10^{-13} erg s^{-1}
cm^{-2} in the 2-10 keV hard X-ray band. We discuss the fraction of absorbed
AGNs in the hard X-ray selected AGN sample, and nature of absorbed luminous
AGNs.


title: Molecular Hydrogen in the Lagoon: H2 line emission from Messier 8

abstract:
  The 2.12 micron v=1-0 S(1) line of molecular hydrogen has been imaged in the
Hourglass region of M8. The line is emitted from a roughly bipolar region,
centred around the O7 star Herschel 36. The peak H2 1-0 S(1) line intensity is
8.2 x 10E-15 erg s-1 cm-2 arcsec-2. The line centre emission velocity varies
from -25 kms in the SE lobe to +45 kms in the NW lobe. The distribution is
similar to that of the CO J=3-2 line. The H2 line appears to be shock-excited
when a bipolar outflow from Herschel 36 interacts with the ambient molecular
cloud. The total luminosity of all H2 lines is estimated to be ~ 16 Lsun and
the mass of the hot molecular gas ~9 x 10E-4 Msun (without any correction for
extinction).


title: The Stellar Initial Mass Function in Primordial Galaxies

abstract:
  In the context of star formation through fragmentation of an extremely
metal-deficient protogalactic cloud, the gravitational collapse of filamentary
gas clouds is explored with 1D numerical hydrodynamics coupled with
non-equilibrium chemistry of H$_2$ and HD. It is found that the cloud evolution
is governed mainly by the initial central density ($n_{\rm c,0}$) and H$_2$
abundance ($x_{\rm H_2,0}$). In particular, the evolution of low-density
filaments bifurcates at a threshold H$_2$ abundance of $x_{\rm H_2,cr}\simeq 3
\times 10^{-3}$, beyond which HD cooling overwhelms H$_2$ cooling. The
contraction of a low density filament with $x_{\rm H_2, 0}\gtrsim x_{\rm
H_2,cr}$ is strongly decelerated when $n_{\rm c}$ reaches a critical density of
HD, and the filament is expected to fragment at $\sim 10^{7}$ cm$^{-3}$. The
fragment mass is lowered to be $\approx 10M_\odot$. In contrast, the
contraction of a low density filament with $x_{\rm H_2, 0}\lesssim x_{\rm
H_2,cr}$ is regulated by H$_2$ cooling. In this case, the fragment mass is as
high as $\approx 10^2M_\odot$. For a high-density filament, the cloud evolution
is governed by H$_2$ cooling. The fragmentation is not expected to take place
until the cloud becomes opaque in H$_2$ lines at $n_{\rm c,0}\sim 10^{12-13}$
cm$^{-3}$, so that the fragment mass is reduced to 1-2 M$_\odot$. As a result,
the stellar IMF could be bimodal and deficient in sub-solar mass stars, where
the high mass peak is around $10M_\odot$ or $10^2M_\odot$, dependently on
$n_{\rm c,0}$ and $x_{\rm H_2,0}$.


title: Statefinder -- a new geometrical diagnostic of dark energy

abstract:
  We introduce a new cosmological diagnostic pair $\lbrace r,s\rbrace$ called
Statefinder. The Statefinder is dimensionless and, like the Hubble and
deceleration parameters $H(z)$ and $q(z)$, is constructed from the scale factor
of the Universe and its derivatives only. The parameter $r(z)$ forms the next
step in the hierarchy of geometrical cosmological parameters used to study the
Universe after $H$ and $q$, while the parameter $s(z)$ is a linear combination
of $q$ and $r$ chosen in such a way that it does not depend upon the dark
energy density $\Omega_X(z)$. The Statefinder pair $\lbrace r,s\rbrace$ is
algebraically related to the the dark energy pressure-to-energy ratio
$w=p/\epsilon$ and its time derivative, and sheds light on the nature of dark
energy/quintessence. Its properties allow to usefully differentiate between
different forms of dark energy with constant and variable $w$, including a
cosmological constant ($w = -1$). The Statefinder pair can be determined to
very good accuracy from a SNAP type experiment.


title: The Magnetic Field Structure in W51A

abstract:
  We present 850 micron imaging polarimetry of the W51A massive star forming
region performed with SCUBA on the JCMT. From the polarimetry we infer the
column-averaged magnetic field direction, projected onto the plane of the sky.
We find that the magnetic field geometry in the region is complicated. We
compare the field geometry with 6 cm and CS J=7-6 emission and determine that
the magnetic field must be relatively weak and plays a passive role, allowing
itself to be shaped by pressure forces and dynamics in the ionised and neutral
gases. Comparisons are drawn between our data and 1.3 mm BIMA interferometric
polarimetry data, from which we conclude that the magnetic field must increase
in importance as we move to smaller scales and closer to sites of active star
formation.


title: Magnetic Aggregation I: Aggregation Dynamics and Numerical Modelling

abstract:
  Focussing on preplanetary grains growth, we discuss the properties of dust
aggregation driven by magnetic dipole forces. While there is no direct evidence
for the existence of magnetic grains present in the solar nebula, there are
reasons to assume they may have been present. We derive analytical expressions
for the cross-section of two interacting dipoles. The effective cross section
depends upon the strength of the magnetic dipoles and the initial velocities.
For typical conditions the magnetic cross section is between 2 and 3 orders of
magnitude larger than the geometric cross section. We study the growth dynamics
of magnetic grains and find that the mass of the aggregates should increase
with time like t^3.2 whereas Brownian motion growth behaves like t^2. A
numerical tool is introduced which can be used to model dust aggregation in
great detail, including the treatment of contact forces, aggregate
restructuring processes and long-range forces. This tool is used to simulate
collisions between magnetic grains or clusters and to validate the analytical
cross-sections. The numerically derived cross section is in excellent agreement
with the analytical expression. The numerical tool is also used to demonstrate
that structural changes in the aggregates during collisions can be significant.


title:
Cluster cross sections for strong lensing: analytic and numerical lens
  models

abstract:
  The statistics of gravitationally lensed arcs was recognised earlier as a
potentially powerful cosmological probe. However, while fully numerical models
find orders of magnitude difference between the arc probabilities in different
cosmological models, analytic models tend to find markedly different results.
We introduce in this paper an analytic cluster lens model which improves upon
existing analytic models in four ways. (1) We use the more realistic
Navarro-Frenk-White profile instead of singular isothermal spheres, (2) we
include the effect of cosmology on the compactness of the lenses, (3) we use
elliptical instead of axially symmetric lenses, and (4) we take the intrinsic
ellipticity of sources into account. While these improvements to the analytic
model lead to a pronounced increase of the arc probability, comparisons with
numerical models of the same virial mass demonstrate that the analytic models
still fall short by a substantial margin of reproducing the results obtained
with numerical models. Using multipole expansions of cluster mass
distributions, we show that the remaining discrepancy can be attributed to
substructure inside clusters and tidal fields contributed by the cluster
surroundings, effects that cannot reasonably and reliably be mimicked in
analytic models.


title: Sub-millimetre observations of the Hubble Deep Field and Flanking Fields

abstract:
  We present an extended analysis of the SCUBA observations of the Hubble Deep
Field (HDF), expanding the areal coverage of the Hughes et al. 1998 study by a
factor of ~1.8 and containing at least three further sources in addition to the
five in that study. We also announce the public release of the reduced data
products. The map is the deepest ever made in the sub-millimetre, obtained in
excellent conditions (median 850um optical depth of 0.16). Two independent
reductions were made, one with SURF and the other with a wholly algorithmic IDL
analysis which we present in detail here. Of the three new sources, all appear
to be at z>~0.9 and one is provisionally associated with an Extremely Red
Object (I-K>5). There appears to be no significant cross-correlation signal
between the 850um fluctuations and sources detected by ISOCAM, the VLA or
Chandra, nor with Very Red Objects (I-K>4), nor quasars and quasar candidates
in the HDF (notwithstanding a small number of individual weak candidate
detections). This is consistent with interpretations where the 850um-selected
galaxies are at higher redshifts than those currently probed by ISOCAM/VLA, and
predominantly not Compton-thin AGN. There are only one or two compelling cases
for the radio source being the sub-mm source. Nevertheless, most SCUBA-HDF
point sources have a nearby radio source apparently well-separated from the
sub-mm centroid.


title: Implications of Lag-Luminosity Relationship for Unified GRB Paradigms

abstract:
  Spectral lags are deduced for 1437 long GRBs with peak fluxes extending to
near the BATSE trigger threshold. The lags are modeled to approximate the
observed distribution in the peak flux-lag plane, realizing a noise-free
representation. Assuming a two-branch lag-luminosity relationship, the lags are
self- consistently corrected for cosmological effects to yield distributions in
luminosity, distance, and redshift. The results have several consequences for
GRB populations -- including a possible nearby subpopulation of low-luminosity,
long-lag GRBs -- and for unified gamma-ray/afterglow scenarios which would
account for afterglow break times and gamma-ray spectral evolution in terms of
jet opening angle, viewing angle, or a profiled jet with variable Lorentz
factor.


title: Black Holes in Galactic Nuclei: the Promise and the Facts

abstract:
  It has long been suspected that Active Galactic Nuclei are powered by
accretion of matter onto massive black holes and this belief implies their
presence in the nuclei of most nearby galaxies as "relics" of past activity.
Just a few years ago this was considered a paradigm but, recently, new
ground-based and Hubble Space Telescope observations are producing a
breakthrough in our knowledge on massive black holes. I will review the
evidence for the existence of black holes in galactic nuclei and how their
presence is related to host galaxy properties and AGN activity.


title: Light-year Scale Radio Cores in Four LINER Galaxies

abstract:
  The LINER galaxies NGC 2911, NGC 3079, NGC 3998, and NGC 6500 were observed
at 5 GHz with the European VLBI Network at a resolution of 5 milliarcsecond and
found to possess flat-spectrum, variable, high-brightness temperature ($T_{\rm
B} > 10^8$ K) radio cores. These radio characteristics reinforce the view that
these LINERs host central engines associated with active galactic nuclei.


title:
Observations of the Hubble Deep Field South with the Infrared Space
  Observatory - I. Observations, data reduction and mid-infrared source counts

abstract:
  We present results from a deep mid-infrared survey of the Hubble Deep Field
South (HDF-S) region performed at 7 and 15 micron with the CAM instrument on
board the Infrared Space Observatory (ISO). The final map in each band was
constructed by the coaddition of four independent rasters, registered using
bright sources securely detected in all rasters, with the absolute astrometry
being defined by a radio source detected at both 7 and 15 micron. We sought
detections of bright sources in a circular region of radius 2.5 arcmin at the
centre of each map, in a manner that simulations indicated would produce highly
reliable and complete source catalogues using simple selection criteria.
Merging source lists in the two bands yielded a catalogue of 35 distinct
sources, which we calibrated photometrically using photospheric models of
late-type stars detected in our data. We present extragalactic source count
results in both bands, and discuss the constraints they impose on models of
galaxy evolution models, given the volume of space sampled by this galaxy
population.


title:
Classification of 2.4-45.2 Micron Spectra from the ISO Short Wavelength
  Spectrometer

abstract:
  The Infrared Space Observatory observed over 900 objects with the Short
Wavelength Spectrometer in full-grating-scan mode (2.4-45.2 micron). We have
developed a comprehensive system of spectral classification using these data.
Sources are assigned to groups based on the overall shape of the spectral
energy distribution (SED). The groups include naked stars, dusty stars, warm
dust shells, cool dust shells, very red sources, and sources with emission
lines but no detected continuum. These groups are further divided into
subgroups based on spectral features that shape the SED such as silicate or
carbon-rich dust emission, silicate absorption, ice absorption, and
fine-structure or recombination lines. Caveats regarding the data and data
reduction, and biases intrinsic to the database, are discussed. We also examine
how the subgroups relate to the evolution of sources to and from the main
sequence and how this classification scheme relates to previous systems.


title: Unifying MeV-blazars with GeV-blazars

abstract:
  We demonstrate that the spectral differences between Flat Spectrum Radio
Quasars (FSRQ) with steep gamma-ray spectra (MeV-blazars) and FSRQ with flat
gamma-ray spectra (GeV-blazars) can be explained by assuming that in the
MeV-blazars, the production of gamma-rays is dominated by Comptonization of
infrared radiation of hot dust, whereas in the GeV-blazars -- by Comptonization
of broad emission lines. Additional ingredient, required to reach satisfactory
unification, is an assumption that the radiating electrons are accelerated via
a two step process, in the lower energy range -- following instabilities driven
by shock-reflected ions, and in the higher energy range -- via resonant
scatterings off Alfven waves. Our model predicts that on average, the
MeV-blazars should vary on longer time scales than GeV-blazars.


title:
Neutrino Induced Upward Going Muons from a Gamma Ray Burst in a Neutrino
  Telescope of Km^2 Area

abstract:
  The number of neutrino induced upward going muons from a single Gamma Ray
Burst (GRB) expected to be detected by the proposed kilometer scale IceCube
detector at the South Pole location has been calculated. The effects of the
Lorentz factor, total energy of the GRB emitted in neutrinos and its distance
from the observer (red shift) on the number of neutrino events from the GRB
have been examined. The present investigation reveals that there is possibility
of exploring the early Universe with the proposed kilometer scale IceCube
neutrino telescope.


title:
Observations of the Hubble Deep Field South with the Infrared Space
  Observatory - II. Associations and star formation rates

abstract:
  We present results from a deep mid-IR survey of the Hubble Deep Field South
(HDF-S) region performed at 7 and 15um with the CAM instrument on board ISO. We
found reliable optical/near-IR associations for 32 of the 35 sources detected
in this field by Oliver et al. (2002, Paper I): eight of them were identified
as stars, one is definitely an AGN, a second seems likely to be an AGN, too,
while the remaining 22 appear to be normal spiral or starburst galaxies. Using
model spectral energy distributions (SEDs) of similar galaxies, we compare
methods for estimating the star formation rates (SFRs) in these objects,
finding that an estimator based on integrated (3-1000um) IR luminosity
reproduces the model SFRs best. Applying this estimator to model fits to the
SEDs of our 22 spiral and starburst galaxies, we find that they are forming
stars at rates of ~1-100 M_sol/yr, with a median value of ~40M_sol/yr, assuming
an Einstein - de Sitter universe with a Hubble constant of 50 km/s/Mpc, and
star formation taking place according to a Salpeter (1955) IMF across the mass
range 0.1-100M_sol. We split the redshift range 0.0<z<0.6 into two equal-volume
bins to compute raw estimates of the star formation rate density contributed by
these sources, assuming the same cosmology and IMF as above and computing
errors based on estimated uncertainties in the SFRs of individual galaxies. We
compare these results with other estimates of the SFR density made with the
same assumptions, showing them to be consistent with the results of Flores et
al. (1999) from their ISO survey of the CFRS 1415+52 field. However, the
relatively small volume of our survey means that our SFR density estimates
suffer from a large sampling variance, implying that our results, by
themselves, do not place tight constraints on the global mean SFR density.


title: Cosmological consequences of short distance physics

abstract:
  Inflation can act as a space-time microscope for Planck or string scale
effects, leaving potentially observable traces in the primordial perturbation
spectrum. I discuss two frameworks that were used recently to study this
phenomenon: nonlinear dispersion and short distance uncertainty.


title: Electromagnetic Pulse from Final Gravitational Stellar Collapse

abstract:
  We employ an effective gravitational stellar final collapse model which
contains the relevant physics involved in this complex phenomena: spherical
radical infall in the Schwarzschild metric of the homogeneous core of an
advanced star, giant magnetic dipole moment, magnetohydrodynamic material
response and realistic equations of state (EOS). The electromagnetic pulse is
computed both for medium size cores undergoing hydrodynamic bounce and large
size cores undergoing black hole formation. We clearly show that there must
exist two classes of neutron stars, separated by maximum allowable masses:
those that collapsed as solitary stars (dynamical mass limit) and those that
collapsed in binary systems allowing mass accretion (static neutron star mass).
Our results show that the electromagnetic pulse spectrum associated with black
hole formation is a universal signature, independent of the nuclear EOS. Our
results also predict that there must exist black holes whose masses are less
than the static neutron star stability limit.


title: Influence of Resonances on Spectral Formation of X-Ray Lines in Fe XVII

abstract:
  New theoretical results from large-scale relativistic close coupling
calculations reveal the precise effect of resonances in collisional excitation
of x-ray lines of Ne-like Fe XVII. Employing the Breit-Pauli R-matrix method
and a 89-level eigenfunction expansion including up to n = 4 levels shows
significant resonance enhancement of the collision strengths of forbidden and
intercombination transitions. The present results differ from all previous
calculations, heretofore without detailed resonance structures, and should help
resolve longstanding discrepancies. In particular, the present line ratios of
three benchmark diagnostic lines 3C, 3D, and 3E at 15.014, 15.265, and 15.456 A
respectively, are in excellent agreement with two independent measurements on
Electron-Beam-Ion-Traps [Laming et al, Astrophys. J, 545, L161 (2000) and Brown
et al, Astrophys. J, 502, 1015 (1998)]. The strong energy dependence due to
resonances in these and other cross sections is demonstrated for the first
time. It is of general importance and strongly manifests itself in x-ray plasma
diagnostics.


title:
Constraints on reionization from the thermal history of the
  intergalactic medium

abstract:
  The temperature of the diffuse, photo-heated intergalactic medium (IGM)
depends on its reionization history because the thermal time scales are long.
The widths of the hydrogen Lyman-alpha absorption lines seen in the spectra of
distant quasars that arise in the IGM can be used to determine its temperature.
We use a wavelet analysis of the Lyman-alpha forest region of quasar spectra to
demonstrate that there is a relatively sudden increase in the line widths
between redshifts z=3.5 and 3.0, which we associate with entropy injection
resulting from the reionization of HeII. The subsequent fall-off in temperature
after z~3.5, is consistent with a thermal evolution dominated by adiabatic
expansion. If, as expected, the temperature also drops rapidly after hydrogen
reionization, then the high temperatures inferred from the line widths before
HeII reionization imply that hydrogen reionization occurred below redshift z=9.


title:
Observations of the Isotropic Diffuse Gamma-ray Background with the
  EGRET Telescope

abstract:
  An Isotropic Diffuse Gamma-Ray Background (IDGRB) in the spectral range
30-10,000 MeV was first reported in the early 1970's using measurements made by
the SAS-2 instrument. Data recorded by the Energetic Gamma Ray Experiment
Telescope (EGRET) on board the Compton Gamma Ray Observatory (CGRO) over the
last 4 years are analysed in order to extract the best measurement yet made of
the IDGRB. Extensive analysis of the EGRET instrumental background is presented
in order to demonstrate that an uncontaminated data set can be extracted from
the EGRET data. A model of the high latitude galactic diffuse foreground
emission is presented and the existence of an IDGRB is confirmed. Spatial and
spectral analysis of this background is presented. In addition, point source
analysis at high galactic latitudes is performed to reveal the existence of a
population of extragalactic sources. The characteristics of this population are
examined and models of its flux distribution are reported. The question of
whether the IDGRB is composed of unresolved point sources is addressed using
fluctuation analysis. Finally, possible future directions for gamma ray
astronomy are examined through simulations of a future gamma ray telescope: the
Gamma-ray Large Area Space Telescope (GLAST). The GLAST baseline design is
described and its scientific performance is evaluated. The ability of this
telescope to detect 1,000-10,000 new extragalactic sources is demonstrated and
the likely impact on the study of the IDGRB is considered.


title:
Additional TWA Members? : Spectroscopic verification of kinematically
  selected TWA candidates

abstract:
  We present spectroscopic measurements of the 23 new candidate members of the
TW Hydrae Association from Makarov & Fabricius (2000). Based on Halpha and Li
6708 A strengths together with location on a color-magnitude diagram for
Hipparcos TWA candidates, we found only three possible new members (TYC
7760-0835-1, TYC 8238-1462-1, and TYC 8234-2856-1) in addition to the already
known member, TWA 19. This eliminated most of the candidates more distant than
100 pc. Three Tycho stars, almost certainly members of the Lower Centaurus Crux
association, are the most distant members of the TWA. A claim of isotropic
expansion of TWA has to be re-evaluated based on our new results. Generally,
one cannot identify new members of a diffuse nearby stellar group based solely
on kinematic data. To eliminate interlopers with similar kinematics,
spectroscopic verification is essential.


title: Probing the Dark Ages with Metal Absorption Lines

abstract:
  Recent observations of high redshift quasars at z~6 have finally revealed
complete Gunn-Peterson absorption. However, this at best constrains the
volume-weighted and mass-weighted hydrogen neutral fractions to be greater than
10^-3 and 10^-2 respectively; stronger constraints are not possible due to the
high optical depth for hydrogen Lyman transitions. Here I suggest certain metal
lines as tracers of the hydrogen neutral fraction. These lines should cause
unsaturated absorption when the IGM is almost fully neutral, if it is polluted
to metallicities Z ~ 10^-3.5--10^-2.5 Z_solar. Such a minimal level of metal
pollution is inevitable in the middle to late stages of reionization unless
quasars rather than stars are the dominant source of ionizing photons. The OI
line at 1302 Angstroms is particularly promising: the OI and H ionization
potentials are almost identical, and OI should be in very tight charge exchange
equilibrium with H. The SiII 1260 Angstrom transition might also be observable.
At high redshift, overdense regions are the first to be polluted to high
metallicity but the last to remain permanently ionized, due to the short
recombination times. Such regions should produce a fluctuating OI and SiII
forest which, if observed, would indicate large quantities of neutral hydrogen.
The OI forest may already be detectable in the SDSS z=6.28 quasar. If seen in
future high-redshift quasars, the OI and SiII forests will probe the topology
of reionization and metal pollution in the early universe. If in additional the
HI optical depth can be measured from the damping wing of a high-redshift
gamma-ray burst, they will yield a very robust measure of the metallicity of
the high-redshift universe.


title:
Activity in Very Cool Stars: Magnetic Dissipation in late-M and L Dwarf
  Atmospheres

abstract:
  Recent observations show that chromospheric activity in late-M and L dwarfs
is much lower than in the earlier M types, in spite of comparatively rapid
rotation. We investigate the possibility that this drop-off in activity results
from the very high electrical resistivities in the dense, cool and
predominantly neutral atmospheres of late-M and L dwarfs. We calculate magnetic
field diffusivities in the atmospheres of objects with effective temperatures
in the range 3000-1500 (mid-M to L), using the atmospheric structure models of
Allard and Hauschildt. We find that the combination of very low ionization
fraction and high density in these atmospheres results in very large
resistivities due to neutral-charged particle collisions, and efficient field
diffusion. The resistivities are found to increase with both decreasing optical
depth, and decreasing effective temperature. As a result, any existing magnetic
fields are increasingly decoupled from atmospheric motions as one moves from
mid-M to L; we quantify this through a simple Reynolds number calculation.
This, coupled with the difficulty in transporting magnetic stresses through the
highly resistive atmosphere, can account for the observed drop in activity from
mid-M to L, assuming activity in these objects is magnetically driven. We also
examine the issue of acoustic heating, and find that this appears inadequate to
explain the observed H-alpha fluxes in mid-M to L dwarfs. Consequently,
magnetic heating does seem to be the most viable mechanism for generating
activity in these objects. Finally, we speculate on a possible flare mechanism
in these cool dwarfs.


title: Non-Radiative Accretion and Thermodynamics

abstract:
  It has been suggested that the laws of thermodynamics are violated by what we
have called a convection-dominated accretion flow (or a 1/2-law accretion flow)
-- an accretion flow characterized by a constant outflow of energy. We show
that both the 1/2-law flow and the Bondi flow (also known as ADAF, advection
dominated accretion flow) are thermodynamically admissible.


title:
The Angular Momentum Distribution within Halos in Different Dark Matter
  Models

abstract:
  We study the angular momentum profile of dark matter halos for a statistical
sample drawn from a set of high-resolution cosmological simulations of $256^3$
particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and
the halos are selected to have at least $3\times 10^4$ particles in order to
reliably measure the angular momentum profile. In contrast with the recent
claims of Bullock et al., we find that the degree of misalignment of angular
momentum within a halo is very high. About 50 percent of halos have more than
10 percent of halo mass in the mass of negative angular momentum $j$. After the
mass of negative $j$ is excluded, the cumulative mass function $M(<j)$ follows
approximately the universal function proposed by Bullock et al., though we
still find a significant fraction of halos ($\sim 50%$) which exhibit
systematic deviations from the universal function. Our results, however, are
broadly in good agreement with a recent work of van den Bosch et al.. We also
study the angular momentum profile of halos in a Warm Dark Matter (WDM) model
and a Self-Interacting Dark Matter (SIDM) model. We find that the angular
momentum profile of halos in the WDM is statistically indistinguishable from
that in the CDM model, but the angular momentum of halos in the SIDM is reduced
by the self-interaction of dark matter.


title: Thermal Instability and Magnetic Pressure in the Turbulent ISM

abstract:
  We review recent results on the nonlinear development of thermal instability
in the context of the turbulent atomic interstellar medium (ISM). First, we
pre- sent a brief summary of the linear theory, remarking that, in the atomic
ISM, the wave mode is stable at small scales. Next, we revisit the growth of
isolated entropy perturbations in initially unstable gas, as a function of the
ratio $\eta$ of the cooling to the dynamical crossing times. Third, we consider
the evolution of {\it velocity} perturbations. These correspond to the wave
mode, and are stable at moderate amplitudes and small scales, as confirmed
numerically. Fourth, we consider the behavior of magnetic pressure in turbulent
regimes. We propose that recent findings of a poor B-rho correlation at low rho
are due to the different B-rho scalings for the slow and fast modes of non-
linear MHD waves. This implies that, in fully turbulent regimes, the magnetic
field may not be a very efficient source of pressure, and that polytropic de-
scriptions of magnetic pressure are probably not adequate. Finally, we discuss
simulations of the ISM (and resolution issues) concerned with the possibility
of significant amounts of gas being in the ``lukewarm'' temperature range be-
tween the warm and cold stable phases. The mass fraction in this range in-
creases, and the phase segregation decreases, as smaller scales are considered.
We attribute this to the enhanced stability of moderate, adiabatic-like veloc-
ity fluctuations with $\eta \gg 1$, to the recycling of gas from the dense to
the diffuse phase by stellar energy injection, and to the magnetic field not
being strongly turbulent there, possibly providing additional stability. Final-
ly, we suggest that the lukewarm gas can be observationally distinguished
through simultaneous determination of two of its thermodynamic variables.


title:
Partial Field Opening and Current Sheet Formation in the Disk
  Magnetosphere

abstract:
  In this paper I analyze the process of formation of thin current structures
in the magnetosphere of a conducting accretion disk in response to the
field-line twisting brought about by the rotation of the disk relative to the
central star. I consider an axisymmetric force-free magnetically-linked
star--disk configuration and investigate the expansion of the poloidal field
lines and partial field-line opening caused by the differential rotation
between the star and a nonuniformly-rotating disk. I present a simple
analytical model that describes the asymptotic behavior of the field in the
strong-expansion limit. I demonstrate the existence of a finite (of order one
radian) critical twist angle, beyond which the poloidal field starts inflating
very rapidly. If the relative star--disk twist is enhanced locally, in some
finite part of the disk (which may be the case for a Keplerian disk that
extends inward significantly closer to the central star than the corotation
radius), then, as the twist is increased by a finite amount, the field
approaches a partially-open configuration, with some field lines going out to
infinity. Simultaneous with this partial field opening, a very thin, radially
extended current layer forms, thus laying out a way towards reconnection in the
disk magnetosphere. Reconnection, in turn, leads to a very interesting scenario
for a quasi-periodic behavior of magnetically-linked star--disk systems with
successive cycles of field inflation, opening, and reconnection.


title: The jet power extracted from a magnetized accretion disc

abstract:
  We consider the power of a relativistic jet accelerated by the magnetic field
of an accretion disc. It is found that the power extracted from the disc is
mainly determined by the field strength and configuration of the field far from
the disc. Comparing with the power extracted from a rotating black hole, we
find that the jet power extracted from a disc can dominate over that from the
rotating black hole. But in some cases, the jet power extracted from a rapidly
rotating hole can be more important than that from the disc even if the
poloidal field threading the hole is not significantly larger than that
threading the inner edge of the disc. The results imply that the radio-loudness
of quasars may be governed by its accretion rate which might be regulated by
the central black hole mass. It is proposed that the different disc field
generation mechanisms might be tested against observations of radio-loud
quasars if their black hole masses are available.


title: Dark Energy and the quietness of the Local Hubble Flow

abstract:
  The linearity and quietness of the Local ($< 10 Mpc$) Hubble Flow (LHF) in
view of the very clumpy local universe is a long standing puzzle in standard
and in open CDM cosmogony. The question addressed in this paper is whether the
antigravity component of the recently discovered dark energy can cool the
velocity flow enough to provide a solution to this puzzle. We calculate the
growth of matter fluctuations in a flat universe containing a fraction
$\Omega_X(t_0)$ of dark energy obeying the time independent equation of state
$p_X = w \rho_X$. We find that dark energy can indeed cool the LHF. However the
dark energy parameter values required to make the predicted velocity dispersion
consistent with the observed value $v_{rms}\simeq 40km/sec$ have been ruled out
by other observational tests constraining the dark energy parameters $w$ and
$\Omega_X$. Therefore despite the claims of recent qualitative studies dark
energy with time independent equation of state can not by itself explain the
quietness and linearity of the Local Hubble Flow.


title:
The log(N)-log(S) and the Broadband Properties of the Sources in the
  HELLAS2XMM Survey

abstract:
  We present the first results from an XMM-Newton serendipitous medium-deep
survey, which covers nearly three square degrees. We show the log(N)-log(S)
distributions for the 0.5-2, 2-10 and 5-10 keV bands, which are found to be in
good agreement with previous determinations and with the predictions of XRB
models. In the soft band we detect a break at fluxes around 5x10^-15 cgs. In
the harder bands, we fill in the gap at intermediate fluxes between deeper
Chandra and XMM-Newton observations and shallower BeppoSAX and ASCA surveys.
Moreover, we present an analysis of the broad-band properties of the sources.


title: XMM-Newton EPIC observations of Her X-1

abstract:
  We present spin-resolved X-ray data of the neutron star binary Her X-1. We
find evidence that the Iron line at 6.4 keV originates from the same location
as the blackbody X-ray component. The line width and energy varies over both
the spin period and the 35 day precession period. We also find that the
correlation between the soft and hard X-ray light curves varies over the 35 day
period.


title: Probing the dark energy with redshift space quasar clustering distortion

abstract:
  We have run Monte Carlo simulations, for quasar clustering redshift
distortions in the Two-Degree Field QSO Redshift Survey (2QZ), in order to
elicit the power of redshift distortions (geometric Alcock-Paczynski and linear
kinematic) to constrain the cosmological density and equation of state
parameters, Omega_{m0}, Omega_{x0}, w, of a pressureless matter + dark energy
model. It turns out that, for the cosmological constant case (w = -1), the test
is especially sensitive to the difference Delta := Omega_{m0} - Omega_{Lambda
0}, whereas for the spatially flat case (k = 0), it is quite competitive with
SNAP and DEEP, besides being complimentary to them; furthermore, we find that,
whereas not knowing the actual value of the bias does not compromise the
correct recovering of Delta, taking into account the linear velocity effect is
absolutely relevant, all within the 2 sigma confidence level.


title:
Hard Pomeron Enhanced Cascade Production and Flux Shadowing in
  High-Energy Neutrino Astrophysics

abstract:
  Various implications of new, non-perturbative pomeron inspired enhancement of
small-x neutrino-nucleon structure functions for high-energy neutrino
astrophysics are discussed. At x larger than 10^{-5} these functions are given
by perturbative QCD, while at lower x they are determined by a specific
generalization of F_2^{ep}(x,Q^2) description, proposed by A. Donnachie and P.
V. Landshoff (their two-component model comprises hard and soft pomerons), to
neutrino-nucleon scattering case.
  We found that i) such enhancement causes the most rapid growth of
neutrino-nucleon cross-sections at high energies, ii) pomeron effects may be
perceptible in the rates of neutrino induced events in future giant detectors
and iii) the rate of high-energy neutrino flux evolution (due to absorption
(CC+NC) and regeneration (NC)) on its pass through a large column depth of
matter may be subjected to additional influence of hard pomeron. Solving
transport equations for the initially power-law decreasing neutrino spectra, we
have evaluated shadow factors for several column depths and spectrum indices.
The results are compared with analogous calculations, performed within a
trivial small-x extrapolation of structure functions. Hard pomeron enhanced
high-energy shadow factors are found to be many orders of magnitude lower than
those obtained within ordinary perturbative QCD.


title: X-ray Emission from Haloes of Simulated Disc Galaxies

abstract:
  Bolometric and 0.2-2 keV X-ray luminosities of the hot gas haloes of
simulated disc galaxies have been calculated at redshift z=0. The TreeSPH
simulations are fully cosmological and the sample of 44 disc galaxies span a
range in characteristic circular speeds of V_c = 130-325 km/s. The galaxies
have been obtained in simulations with a considerable range of physical
parameters, varying the baryonic fraction, the gas metallicity, the
meta-galactic UV field, the cosmology, the dark matter type, and also the
numerical resolution. The models are found to be in agreement with the (few)
relevant X-ray observations available at present. The amount of hot gas in the
haloes is also consistent with constraints from pulsar dispersion measures in
the Milky Way. Forthcoming XMM and Chandra observations should enable much more
stringent tests and provide constraints on the physical parameters. We find
that simple cooling flow models over-predict X-ray luminosities by up to two
orders of magnitude for high (but still realistic) cooling efficiencies
relative to the models presented here. Our results display a clear trend that
increasing cooling efficiency leads to decreasing X-ray luminosities at z=0.
The reason is found to be that increased cooling efficiency leads to a
decreased fraction of hot gas relative to total baryonic mass inside of the
virial radius at present. At gas metal abundances of a third solar this hot gas
fraction becomes as low as just a few percent. We also find that most of the
X-ray emission comes from the inner parts (inner about 20 kpc) of the hot
galactic haloes. Finally, we find for realistic choices of the physical
parameters that disc galaxy haloes possibly were more than one order of
magnitude brighter in soft X-ray emission at z=1, than at present.


title: Elemental Abundances in Stellar Coronae with XMM-Newton

abstract:
  The XMM-Newton Reflection Grating Spectrometer Team has obtained observations
ofa large number of coronal sources of various activity levels, ages, and
spectraltypes. In particular, X-ray bright RS CVn binary systems display
saturated coronal emission with spectral lines characteristic of hot (10-30 MK)
plasma. Furthermore, we have obtained XMM-Newton data from young solar analogs
both within and outside the X-ray saturation regime. We have simultaneously
analyzed the EPIC MOS and RGS data from these objects and have obtained coronal
abundances of various elements (e.g., C, N, O, Ne, Mg, Si, Fe). We show that
there is evidence for a transition from an Inverse First Ionization Potential
(FIP) effect in most active stars to a ``normal'' solar-like FIP effect in less
active stars. We discuss this result with regard to photospheric abundances.


title: Magnetic flares and outflows from structured accretion disc coronae

abstract:
  We present a model for magnetic structured coronae above accretion discs. On
the shortest timescales, spatially and temporally correlated coronal flares can
explain X-ray temporal and spectral variability observed in Seyfert galaxies.
In particular, power density spectra, flux-spectral index and flux-variance
correlations are naturally accounted for by the model. More dramatic spectral
variations (i.e. state transitions in GBHC) are associated with parameters
varying on longer timescales, such as accretion rate, coronal strength or
geometry of the inner disc. In the framework of the standard Shakura--Sunyaev
accretion disc theory, here we discuss why energetically dominant coronae at
low accretion rates are ideal sites for launching powerful MHD driven outflows.
Then, if the outflow is radiatively inefficient, then so is the source overall,
even without advection being relevant for the dynamics of the accretion flow.
This could be an alternative scenario for LLAGN and GBHC in their low/hard
state, and may have consequences for our understanding of the accretion history
of the universe.


title:
Radio emission from the A3571 cluster complex: the final stage of a
  cluster merger?

abstract:
  In this paper we report and discuss the results of a radio survey in the
A3571 cluster complex, a structure located in the Shapley Concentration core,
and formed by the three clusters A3571, A3572 and A3575. The survey was carried
out simultaneously at 22 cm and 13 cm with the Australia Telescope Compact
Array, and led to the detection of 124 radio sources at 22 cm. The radio source
counts in this region are in agreement with the background counts. Among the 36
radio sources with optical counterpart, six have measured redshift which places
them at the distance of the A3571 cluster complex, and nine radio sources have
optical counterparts most likely members of this cluster complex. All radio
galaxies emit at low power level, i.e. logP$_{22cm}$ (W Hz$^{-1}$) $\le$ 22.6.
A number of them are likely to be starburst galaxies. The radio luminosity
function of early type galaxies is in agreement with that derived by Ledlow &
Owen (1996) if we restrict our analysis to the A3571 cluster. On the basis of
the multiwavelength properties of the A3571 cluster complex, we propose that it
is a very advanced merger, and explain the radio properties derived from our
study in the light of this hypothesis.


title: The Chandra LETG and XMM-Newton Spectra of HR 1099

abstract:
  The X-ray luminous RS CVn binary system HR 1099 has been observed on several
occasions in the early phases of \textit{Chandra} and \textit{XMM-Newton}. A
very hot (up to 40 MK) dominant coronal plasma has been identified from the
high-resolution spectroscopic data; cooler plasma is seen down to about 3 MK.
We recently obtained 100 ksec in \textit{Chandra}'s Guest Observer Program to
study the corona of HR 1099 with the High-Resolution Camera (HRC-S) and the Low
Energy Transmission Grating (LETG) across the complete temperature range above
1 MK. The data provide an unprecedented view of spectral lines and continua at
high resolution between 1 and 175 \AA. We present our investigations on the
Chandra LETGS observation of HR 1099 into the context of the latest results
obtained with XMM-Newton.


title: The Las Campanas Distant Cluster Survey -- The Correlation Function

abstract:
  We present the first non-local (z>0.2) measurement of the cluster-cluster
spatial correlation length, using data from the Las Campanas Distant Cluster
Survey (LCDCS). We measure the angular correlation function for
velocity-dispersion limited subsamples of the catalog at estimated redshifts of
0.35<z_{est}<0.575, and derive spatial correlation lengths for these clusters
via the cosmological Limber equation. The correlation lengths that we measure
for clusters in the LCDCS are consistent both with local results for the APM
cluster catalog and with theoretical expectations based upon the Virgo
Consortium Hubble Volume simulations and the analytic predictions. Despite
samples containing over 100 clusters, our ability to discriminate between
cosmological models is limited because of statistical uncertainty.


title:
Electron impact excitation of helium-like oxygen up to n = 4 levels
  including radiation damping

abstract:
  The primary X-ray diagnostic lines in He-like ions are mainly excited by
electron impact from the ground level to the n = 2 levels, but at high
temperatures n > 2 levels are also excited. In order to describe the atomic
processes more completely collision strengths are computed for OVII including
for the first time all of the following: (i) relativistic fine structure, (ii)
levels up to the n = 4, and (iii) radiation damping of autoionizing resonances.
The calculations are carried out using the Breit-Pauli R-matrix (BPRM) method
with a 31-level eigenfunction expansion. Resonance structures in collision
strengths are delineated in detail up to the n = 4 thresholds. For highly
charged He-like ions radiation damping of autoionizing resonances is known to
be significant. We investigate this effect in detail and find that while
resonances are discernibly damped radiatively as the series limit n --> infty
is approached from below, the overall effect on effective cross sections and
rate coefficients is found to be very small. Collision strengths for the
principal lines important in X-ray plasma diagnostics, w,x,y and z,
corresponding to the 4 transitions to the ground level 1s^2 (^1S_0) <-- 1s2p
(^1P^o_1), 1s2p (^3P^o_2), 1s2p (^3P^o_1), 1s2s (^3S_1), are explicitly shown.
It is found that the effective collision strength of the forbidden z-line is up
to a factor of 4 higher at T < 10^6 K than previous values. This is likely to
be of considerable importance in the diagnostics of photoionized astrophysical
plasmas. Significant differences are also found with previous works for several
other transitions. This work is carried out as part of the Iron Project-RmaX
Network.


title: EVN observations of candidate Compact Symmetric Objects

abstract:
  We present pc-scale images of ten Compact Symmetric Objects (CSO) candidates
observed with the European VLBI network (EVN). Five radio sources have been
observed at 1.6 GHz, and five more at 2.3/8.4 GHz, the latter subsample with
the inclusion in the VLBI array of 3 antennae normally used for geodesy. These
objects were selected from existing samples of GHz Peaked Spectrum (GPS) radio
sources with the purpose to find and/or confirm the CSO classification. These
new VLBI observations allow us to confirm the classification of two CSO
candidates, and to find a few new ones. The association of GPS radio galaxies
with a CSO morphology is strengthened by our findings, and this result suggests
an efficient way to increase the number of known CSOs by means of VLBI
observations of compact radio galaxies showing a convex radio spectrum.


title: Detailed analysis of Balmer lines in cool dwarf stars

abstract:
  An analysis of H alpha and H beta spectra in a sample of 30 cool dwarf and
subgiant stars is presented using MARCS model atmospheres based on the most
recent calculations of the line opacities. A detailed quantitative comparison
of the solar flux spectra with model spectra shows that Balmer line profile
shapes, and therefore the temperature structure in the line formation region,
are best represented under the mixing length theory by any combination of a low
mixing-length parameter alpha and a low convective structure parameter y. A
slightly lower effective temperature is obtained for the sun than the accepted
value, which we attribute to errors in models and line opacities. The programme
stars span temperatures from 4800 to 7100 K and include a small number of
population II stars. Effective temperatures have been derived using a
quantitative fitting method with a detailed error analysis. Our temperatures
find good agreement with those from the Infrared Flux Method (IRFM) near solar
metallicity but show differences at low metallicity where the two available
IRFM determinations themselves are in disagreement. Comparison with recent
temperature determinations using Balmer lines by Fuhrmann (1998, 2000), who
employed a different description of the wing absorption due to self-broadening,
does not show the large differences predicted by Barklem et al. (2000). In
fact, perhaps fortuitously, reasonable agreement is found near solar
metallicity, while we find significantly cooler temperatures for low
metallicity stars of around solar temperature.


title: The systemic velocities of four long-period cataclysmic variable stars

abstract:
  Although a large number of orbital periods of cataclysmic variable stars
(CVs) have been measured, comparison of period and luminosity distributions
with evolutionary theory is affected by strong selection effects. A test has
been discovered which is independent of these selection effects and is based
upon the kinematics of CVs (Kolb & Stehle, 1996). If the standard models of
evolution are correct then long-period (P_orb > 5 hrs) CVs should be typically
less than 1.5 Gyr old, and their line-of-sight velocity dispersion
($\sigma_\gamma$) should be small. We present results from a pilot study which
indicate that this postulate is indeed true. Four long-period dwarf novae (EM
Cyg, V426 Oph, SS Cyg and AH Her) were observed over a complete orbit, in order
that accurate radial velocities be obtained. We find values of -1.7, 5.4, 15.4
and 1.8 km/s with uncertainties of order 3 km/s, referred to the dynamical
Local Standard of Rest (LSR), leading to a dispersion of ~ 8 km/s. Calculation
of a 95 per cent confidence interval gives the result 4 < \sigma_\gamma < 28
km/s compared to a prediction of 15 km/s. We also have an improved
determination of mass donor spectral type, K_2 and q for the four systems.


title: Constraining halo properties from galaxy-galaxy lensing and photo-z

abstract:
  Here we present results from a maximum likelihood analysis of galaxy-galaxy
weak lensing effects as measured in a 12.5' x 12.5' field obtained at the
Nordic Optical Telescope, on La Palma, Spain. The analysis incorporates
photometric redshifts and gives circular velocities consistent with previous
weak lensing work.


title:
The ESO Nearby Abell Cluster Survey. XI. Segregation of cluster galaxies
  and subclustering

abstract:
  We study luminosity and morphology segregation of over 3000 cluster galaxies
in an ensemble cluster of 59 rich, nearby galaxy clusters observed in the ESO
Nearby Cluster Survey (ENACS). Within this sample we identify those galaxies
that are in substructures. We compare the distribution of projected
clustercentric distance, R, and 'normalized' relative line-of-sight velocity,
v, of several subsamples, using the 2D Kolmogorov-Smirnov test. We find
evidence of luminosity segregation only for the ellipticals outside
substructure and brighter than M_R = -22.0 +/- 0.1 (h0=100 km/s/Mpc). We
confirm the well-known segregation of early- and late-type galaxies. The early
and late spirals (Sa--Sb and Sbc--Ir respectively) outside substructure also
appear to have different (R,v)-distributions. In each morphological class, the
galaxies within substructure have different (R,v)-distributions from the
galaxies that are not in substructure. Among the samples of galaxies that are
not in substructure, at least 3 ensembles can and must be distinguished:
[E+S0], S_early, and [S_late+ELG]. The [E+S0] ensemble is most centrally
concentrated and has a fairly low velocity dispersion that hardly varies with
radius. The [S_late+ELG] ensemble is least concentrated and has the highest
velocity dispersion, which increases significantly towards the centre. The
(R,v)-distribution of S_early galaxies is intermediate between those of the two
other ensembles. Among the galaxies within substructure the S0 and [S_late+ELG]
galaxies have different (R,v) distributions. We discuss briefly the
implications of our results for processes of galaxy destruction and
transformation within clusters. [ABRIDGED]


title: Primordial perturbations from inflation

abstract:
  I review the standard analysis of adiabatic scalar and tensor perturbations
produced by slow-roll inflation driven by a single scalar field, before going
on to discuss recent work on the role of non-adiabatic modes during and after
inflation. Isocurvature perturbations correlated with adiabatic modes may be
produced during multi-field inflation and would give valuable information about
the physics of the early universe. A significant contribution from correlated
isocurvature perturbations is not ruled out by present data, but should be
either detected or ruled out by future observations.


title: Lensing results from the Red-sequence Cluster Survey

abstract:
  We present a variety of weak lensing results based on the ongoing analysis of
R_C-band imaging data from the Red-Sequence Cluster Survey (RCS). We briefly
discuss the weak lensing signal induced by intervening large scale structure
(cosmic shear), and study the properties of the dark matter halos surrounding
galaxies with 19.5<R_C<21 (which have a median redshift of z=0.35) using a
parametrized mass model for the galaxy mass distribution. This allows us for
the first time to constrain the extent of the halos. We find a robust upper
limit for the truncation parameter s<470 h^{-1} kpc (99.7% confidence). We also
study the biasing properties of these galaxies as a function of scale. We find
that both the bias parameter b and the galaxy-mass cross-correlation
coefficient r vary with scale (on scales 0.1-6 h^{-1} Mpc). Interestingly, we
find that r=0.57^{+0.08}_{-0.07} on scales ~0.5 h^{-1} Mpc.


title: Powerful obscured AGN in Chandra cluster fields

abstract:
  Models for the origin of the hard X-ray background have suggested that
sources with the most accretion activity lie hidden in highly obscured AGN. We
report on our study of hard, serendipitous sources in the fields of Chandra
clusters with fluxes close to the turn-over in the source-counts. These include
two Type II quasars with measured X-ray luminosities >10^{45} ergs per second
and column-densities >10^{23} cm^{-2}, one possibly being Compton-thick. Both
show indications of redshifted Fe K\alpha line emission. Radiative transfer
modelling of the broad-band spectrum of a highly-magnified source with deep
ISOCAM detections implies the presence of warm-to-hot dust obscuring a quasar
with L_{UV}>10^{45} ergs per second. Multi-wavelength spectroscopic and
photometric follow-up of the optically-faint sources suggests that these
objects are found in the centres of massive evolved galaxies at a range of
redshifts, with red optical / near-infrared colours dominated by the host
galaxy. Detailed source identification is difficult due to the paucity of
strong emission features, especially in the infrared. We present the main
results from a sample of near-infrared spectra of optically-faint sources
obtained with 4 m and 8 m telescopes. Through the study of the harder and
brighter X-ray background source population, we are likely to be viewing the
most intense phase of the growth of supermassive black holes.


title: The Inner Structure of LambdaCDM Halos I: A Numerical Convergence Study

abstract:
  We present a comprehensive set of convergence tests which explore the role of
various numerical parameters on the equilibrium structure of a simulated dark
matter halo. We report results obtained with two independent, state-of-the-art,
multi-stepping, parallel N-body codes: PKDGRAV and GADGET. We find that
convergent mass profiles can be obtained for suitable choices of the
gravitational softening, timestep, force accuracy, initial redshift, and
particle number. For softenings chosen so that particle discreteness effects
are negligible, convergence in the circular velocity is obtained at radii where
the following conditions are satisfied: (i) the timestep is much shorter than
the local orbital timescale; (ii) accelerations do not exceed a characteristic
acceleration imprinted by the gravitational softening; and (iii) enough
particles are enclosed so that the collisional relaxation timescale is longer
than the age of the universe. The most stringent requirement for convergence is
typically that imposed on the particle number by the collisional relaxation
criterion, which implies that in order to estimate accurate circular velocities
at radii where the density contrast may reach $\sim 10^6$, the region must
enclose of order 3000 particles (or more than a few times $10^6$ within the
virial radius). Applying these criteria to a galaxy-sized $\Lambda$CDM halo, we
find that the spherically-averaged density profile becomes progressively
shallower from the virial radius inwards, reaching a logarithmic slope
shallower than -1.2 at the innermost resolved point, $r \sim 0.005 r_{200}$,
with little evidence for convergence to a power-law behaviour in the inner
regions.


title: Multi-wavelength behaviour of IIIZw2

abstract:
  IIIZw2 was observed with XMM-Newton in July 2000. Its X-ray spectrum can be
described by a powerlaw of photon index Gamma = 1.7 with a Gaussian line at 6.7
keV. There is no significant evidence of intrinsic absorption within the source
or of a soft X-ray excess.
  Multi-wavelength light curves over a period of 25 years show related
variations from the radio to the X-rays. We interpret the radio to optical
emission as synchrotron radiation, self-absorbed in the radio/millimeter
region, and the X-rays as mainly due to Compton up-scattering of low-energy
photons by the population of high-energy electrons that give rise to the
synchrotron radiation.


title: Photochemical model of impact-produced lunar atmosphere

abstract:
  The Lunar Prospector mission detected hydrogen-containing compounds in the
lunar polar regions. We have considered the comet hypothesis of the origin of
polar volatiles on the Moon. In the present paper we use our model of a comet
impact with photochemical processes to be included to estimate chemical
composition of volatiles which can be captured by the cold traps.


title:
Statistics: Handle with Care, Detecting Multiple Model Components with
  the Likelihood Ratio Test

abstract:
  The likelihood ratio test (LRT) and the related $F$ test, do not (even
asymptotically) adhere to their nominal $\chi^2$ and $F$ distributions in many
statistical tests common in astrophysics, thereby casting many marginal line or
source detections and non-detections into doubt. Although there are many
legitimate uses of these statistics, in some important cases it can be
impossible to compute the correct false positive rate. For example, it has
become common practice to use the LRT or the $F$ test for detecting a line in a
spectral model or a source above background despite the lack of certain
required regularity conditions. In these and other settings that involve
testing a hypothesis that is on the boundary of the parameter space, {\it
contrary to common practice, the nominal $\chi^2$ distribution for the LRT or
the $F$ distribution for the $F$ test should not be used}. In this paper, we
characterize an important class of problems where the LRT and the $F$ test fail
and illustrate this non-standard behavior. We briefly sketch several possible
acceptable alternatives, focusing on Bayesian posterior predictive
probability-values. We present this method in some detail, as it is a simple,
robust, and intuitive approach. This alternative method is illustrated using
the gamma-ray burst of May 8, 1997 (GRB 970508) to investigate the presence of
an Fe K emission line during the initial phase of the observation.


title:
Light scattering by an elongated particle: spheroid versus infinite
  cylinder

abstract:
  Using the method of separation of variables and a new approach to
calculations of the prolate spheroidal wave functions, we study the optical
properties of very elongated (cigar-like) spheroidal particles. A comparison of
extinction efficiency factors of prolate spheroids and infinitely long circular
cylinders is made. For the normal and oblique incidence of radiation, the
efficiency factors for spheroids converge to some limiting values with an
increasing aspect ratio a/b provided particles of the same thickness are
considered.
  These values are close to, but do not coincide with the factors for infinite
cylinders. The relative difference between factors for infinite cylinders and
elongated spheroids ($a/b \ga 5$) usually does not exceed 20 % if the following
approximate relation between the angle of incidence $\alpha (in degrees)$ and
the particle refractive index m=n+ki takes the place: $\alpha \ga 50 |m-1| + 5$
where $1.2 \la n \la 2.0$ and $k \la 0.1$. We show that the quasistatic
approximation can be well used for very elongated optically soft spheroids of
large sizes.


title:
Multiple scattering of polarized radiation by non-spherical grains:
  first results

abstract:
  We present the first numerical radiative transfer simulation of multiple
light scattering in dust configurations containing aligned non-spherical
(spheroidal) dust grains. Such models are especially important if one wants to
explain the circular polarization of light, observed in a variety of
astronomical objects. The radiative transfer problem is solved on the basis of
the Monte Carlo method. Test simulations, confirming the correct numerical
implementation of the scattering mechanism, are presented. As a first
application, we investigate the linear and circular polarization of light
coming from a spherical circumstellar shell. This shell contains perfectly
aligned prolate or oblate spheroidal grains. The most remarkable features of
the simulated linear polarization maps are so-called polarization null points
where the reversal of polarization occurs. They appear in the case when the
grain alignment axis is perpendicular to the line of sight. The maps of
circular polarization have a sector-like structure with maxima at the ends of
lines inclined to the grain alignment axis by $\pm 45\degr$.


title:
The Optical Identification of the X-ray Burster X1746-370 in the
  Globular Cluster NGC6441

abstract:
  We find convincing observational evidence to confirm the optical
identification of the X-ray burster X1746-370 located in the globular cluster
NGC6441. Chandra/HRC-I imaging yields a much improved X-ray position for the
source, which we show to be fully consistent with our rederived position of a
UV-excess star, U1, in the same astrometric reference frame. In addition, the
smaller Chandra X-ray error circle excludes the only other blue stars
previously identified in the old Einstein circle. We have also obtained Hubble
Space Telescope/STIS time-resolved optical spectra of star U1. Although there
are no strong line features, the flux distribution demonstrates U1 to be
unusually bright in the blue and faint in the red, consistent with earlier
WFPC2 photometry. More notably, the flux level of the continuum is seen to vary
significantly compared to stars of similar brightness. Indeed, the lightcurve
can plausibly be fit by a 5.73 hr period sinusoid, which is the period of the
recurring X-ray dips seen in this source. The presence of modulations in both
wavelengths strengthens the case for an orbital origin, and therefore deepens
the puzzle of the unusual energy independent X-ray dips. Lastly, we note that
X1746-370 remains the longest period confirmed X-ray burster in a globular
cluster, and the only one with a period typical of the galactic population as a
whole.


title: PKS 1830-211: A Face-On Spiral Galaxy Lens

abstract:
  We present new Hubble Space Telescope images of the gravitational lens PKS
1830-211, which allow us to characterize the lens galaxy and update the
determination of the Hubble constant from this system. The I-band image shows
that the lens galaxy is a face-on spiral galaxy with clearly delineated spiral
arms. The southwestern image of the background quasar passes through one of the
spiral arms, explaining the previous detections of large quantities of
molecular gas and dust in front of this image. The lens galaxy photometry is
consistent with the Tully-Fisher relation, suggesting the lens galaxy is a
typical spiral galaxy for its redshift. The lens galaxy position, which was the
main source of uncertainty in previous attempts to determine H_0, is now known
precisely. Given the current time delay measurement and assuming the lens
galaxy has an isothermal mass distribution, we compute H_0 = 44 +/- 9 km/s/Mpc
for an Omega_m = 0.3 flat cosmological model. We describe some possible
systematic errors and how to reduce them. We also discuss the possibility
raised by Courbin et al. (2002), that what we have identified as a single lens
galaxy is actually a foreground star and two separate galaxies.


title: Journey to the edge of time: The GREAT mission

abstract:
  We are surrounded by radiation that originated from the big bang. It has
traveled to us from the farthest reaches of the Universe, carrying with it an
unaltered record of the beginning of time and space. The radiation is in the
form of gravitational waves - propagating ripples in the curvature of
spacetime. We describe a mission to detect these Gravitational Echos Across
Time (GREAT) that would open up a new window on the very early universe. By
studying the gravitational echoes of the big bang we will gain insight into the
fundamental structure of matter, gravity, and how the Universe formed.


title: Smoking Quasars: a New Source for Cosmic Dust

abstract:
  Although dust is widely found in astrophysics, forming dust is surprisingly
difficult. The proper combination of low temperature (<2000 K) and high density
is mainly found in the winds of late-type giant and supergiant stars which, as
a result, are the most efficient sources of dust known. Dust ejected from these
stars into the interstellar medium has multiple important effects, including
obscuring background objects and enhancing star formation.
  We show here that quasars are also naturally copious producers of dust, if
the gas clouds producing their characteristic broad lines are part of an
outflowing wind. This offers an explanation for the strong link between quasars
and dust, for the heavy nuclear obscuration around many quasars and introduces
a new means of forming dust at early cosmological times.


title:
Hubble Space Telescope Expansion Parallaxes of the Planetary Nebulae NGC
  6578, NGC 6884, NGC 6891, and IC 2448

abstract:
  We have combined two epochs of Hubble Space Telescope WFPC2 imaging data with
ground-based expansion velocities to determine distances to three planetary
nebulae (NGC 6578, NGC 6884, and IC 2448). We used two variants of the
expansion parallax technique--a gradient method and a magnification method--to
determine the distances. The results from the two methods agree to within the
errors. A fourth nebula was included in the study (NGC 6891), but the expansion
was too small to determine the distance, and only a lower limit was obtained.
This is the first paper in a series which will examine at least 24 nebulae in
total.


title: Dynamics of the Central kpc in Barred Galaxies: Theory and Modeling

abstract:
  The central kpc of barred galaxies exhibits a wealth of morphological
information on different components with clear dynamical consequences. These
include nuclear rings, spirals, bars, and more. We argue that this morphology
is driven by large-scale stellar bars and analyze its consequences for gas
dynamics and the distribution of star-forming regions. Specifically, we focus
on gas flows in nested bar systems and study their origin, as well as the
gravitational decoupling of gaseous nuclear bars with and without gas
self-gravity. We find that the gas response in nested bars differs profoundly
from that in single bars, and that no offset dust lanes form in the nuclear
bars.


title: A Cosmic Perspective from Lapland in 2001

abstract:
  A convergence of ideas, observations and technology have led to the greatest
period of cosmological discovery yet. Over the past three years we have
determined the basic features of our Universe. We are now challenged to make
sense of what we have found. The outcome of planned experiments and
observations as well as new ideas will be required. If we succeed, ours truly
will be a Golden Age of Cosmology.


title: The Measure of Cosmological Parameters

abstract:
  New, large, ground and space telescopes are contributing to an exciting and
rapid period of growth in observational cosmology. The subject is now far from
its earlier days of being data-starved and unconstrained, and new data are
fueling a healthy interplay between observations and experiment and theory. I
briefly review here the status of measurements of a number of quantities of
interest in cosmology: the Hubble constant, the total mass-energy density, the
matter density, the cosmological constant or dark energy component, and the
total optical background light.


title: The New Cosmology

abstract:
  Over the past three years we have determined the basic features of our
Universe. It is spatially flat; accelerating; comprised of 1/3 a new form of
matter, 2/3 a new form of energy, with some ordinary matter and a dash of
massive neutrinos; and it apparently began from a great burst of expansion
(inflation) during which quantum noise was stretched to astrophysical size
seeding cosmic structure. This ``New Cosmology'' greatly extends the highly
successful hot big-bang model. Now we have to make sense of it. What is the
dark matter particle? What is the nature of the dark energy? Why this mixture?
How did the matter -- antimatter asymmetry arise? What is the underlying cause
of inflation (if it indeed occurred)?


title: Making Sense Of The New Cosmology

abstract:
  Over the past three years we have determined the basic features of the
Universe -- spatially flat; accelerating; comprised of 1/3 a new form of
matter, 2/3 a new form of energy, with some ordinary matter and a dash of
massive neutrinos; and apparently born from a burst of rapid expansion during
which quantum noise was stretched to astrophysical size seeding cosmic
structure. The New Cosmology greatly extends the highly successful hot big-bang
model. Now we have to make sense of all this: What is the dark matter particle?
What is the nature of the dark energy? Why this mixture? How did the matter --
antimatter asymmetry arise? What is the underlying cause of inflation (if it
indeed occurred)?


title:
Chandra Observations of a New Supernova Remnant AX
  J1843.8-0352/G28.6-0.1

abstract:
  AX J1843.8-0352 is a new X-ray SNR identified to the radio complex G28.6-0.1
with the ASCA satellite. Chandra discovered two distinct components from this
SNR: non-thermal and thin thermal X-ray emissions. The non-thermal component is
fitted with a power-law spectrum of photon index 2.0. The morphology is
complicated, but roughly an elliptical shape with a mean diameter of about
7'-10'. The east to south rims of the ellipse are associated with the
non-thermal radio sources C, F and G (Helfand et al. 1989). The power-law slope
of the radio spectrum can be smoothly connected to that of X-rays with a break
at around the optical-IR band, hence would be due to synchrotron X-rays
accelerated probably to > 1 TeV at the shell of the SNR. The thermal component
near the southeast rim is a thin plasma of about 0.8 keV temperature. It has
the appearance of a "Tadpole" figure with a head of 30"x 40"-size and a tail of
30"-long. Although this emission is associated with the west part of the radio
source F, the absorption is about two times larger than that of the non-thermal
X-rays, the bulk of the SNR emission. Therefore, together with the peculiar
morphology, whether the thermal plasma is a part of the SNR or a background
object is unclear.


title:
Diffuse X-rays in the Galactic center region -- The zoo of iron line
  clumps, non-thermal filaments and hot plasmas --

abstract:
  This paper reports the diffuse X-ray features around the Galactic center
observed with Chandra. We confirm the ASCA and Ginga discoveries of the
large-scale thin-thermal plasma with strong lines in the Galactic center
region. In addition, many small clumps of emission lines from neutral (6.4 keV
line) to He-like (6.7 keV line) irons are discovered. The 6.4 keV line clumps
would be reflection nebulae, while those of the 6.7 keV line are likely SNRs.
We also find emission lines of intermediate energy between 6.5-6.7 keV, which
are attributable to young SNRs in non equilibrium ionization. Non-thermal
filaments or belts with X-ray spectra of no emission line are found, suggesting
the Fermi acceleration site in a rapidly expanding shell. All these suggest
that multiple-supernovae or extremely large explosion had occurred around the
Galactic center region in the recent past.


title:
Thermoluminescence of Simulated Interstellar Matter after Gamma-ray
  Irradiation

abstract:
  Interstellar matter is known to be strongly irradiated by radiation and
several types of cosmic ray particles. Simulated interstellar matter, such as
forsterite $\rm Mg_{2}SiO_{4}$, enstatite $\rm MgSiO_{3}$ and magnesite $\rm
MgCO_{3}$ has been irradiated with the $\rm ^{60}Co$ gamma-rays in liquid
nitrogen, and also irradiated with fast neutrons at 10 K and 70 K by making use
of the low-temperature irradiation facility of Kyoto University Reactor
(KUR-LTL. Maximum fast neutron dose is $10^{17}n_f{\rm /cm^{2}}$).
  After irradiation, samples are stored in liquid nitrogen for several months
to allow the decay of induced radioactivity. We measured the luminescence
spectra of the gamma ray irradiated samples during warming to 370K using a
spectrophotometer. For the forsterite and magnesite, the spectra exhibit a
rather intense peak at about 645 -- 655 nm and 660 nm respectively, whereas
luminescence scarcely appeared in olivine sample. The spectra of forsterite is
very similar to the ERE of the Red Rectangle.