title:
Variable stars in the globular cluster NGC 3201. I. Multimode SX
  Phe-type variables

abstract:
  We report on the discovery of eleven multimode SX Phoenicis--type blue
stragglers in the field of the southern globular cluster NGC 3201. In these
variables both radial and non-radial modes are excited. For three variables the
derived period ratio is close to that observed in SX Phoenicis itself,
suggesting that these stars are pulsating in the fundamental and the
first-overtone radial modes. Using the McNamara (1997) period-luminosity
relation we have estimated the apparent distance modulus to NGC 3201 to be
14.08$\pm0.06\pm0.1$mag.


title:
Chemical abundances of planet-host stars: Results for alpha and Fe-group
  elements

abstract:
  In this paper, we present a study of the abundances of Si, Ca, Sc, Ti, V, Cr,
Mn, Co, and Ni in a large set of stars known to harbor giant planets, as well
as in a comparison sample of stars not known to have any planet ary-mass
companions. We have checked for possible chemical differences between planet
hosts and field stars without known planets. Our results show that overall, and
for a given value of [Fe/H], the abundance trends for the planet hosts are
nearly indistinguishable from those of the field stars. In general, the trends
show no discontinuities,and the abundance distributions of stars with giant
planets are high [Fe/H] extensions to the curves traced by the field dwarfs
without planets. The only elements that might present slight differences
between the two groups of stars are V, Mn, and to a lesser extent Ti and Co. We
also use the available data to describe galactic chemical evolution trends for
the elements studied. When comparing the results with former studies, a few
differences emerge for the high [Fe/H] tail of the distribution, a region that
is sampled with unprecedented detail in our analysis.


title: Kinematics of Tidal Debris from Omega Centauri's Progenitor Galaxy

abstract:
  We present the kinematic properties of a tidally disrupted dwarf galaxy in
the Milky Way, based on the hypothesis that its central part once contained the
most massive Galactic globular cluster, omega Cen. Dynamical evolution of a
self-gravitating progenitor galaxy that follows the present-day and likely past
orbits of omega Cen is calculated numerically and the kinematic nature of their
tidal debris is analyzed, combined with randomly generated stars comprising
spheroidal halo and flat disk components. We show that the retrograde rotation
of the debris stars at $\sim -100$ km/s accords with a recently discovered,
large radial velocity stream at $\sim 300$ km/s towards the Galactic longitude
of $\sim 270^\circ$. These stars also contribute, only in part, to a reported
retrograde motion of the outer halo at the North Galactic Pole. The prospects
for future debris searches and the implications for the early evolution of the
Galaxy are briefly presented.


title:
An Unusual Discontinuity in the X-ray Surface Brightness Profile of NGC
  507: Evidence of an Abundance Gradient?

abstract:
  We present results from a 45 ks Chandra/ACIS-I observation of the nearby
($z=0.01646$) NGC 507 group. The X-ray surface brightness profile of the outer
region of the group is well described by an isothermal $\beta$-profile
consistent with earlier ROSAT observations. We find a sharp edge or
discontinuity in the radial surface brightness profile 55 kpc E and SE of NGC
507 covering a $\sim125^\circ$ arc. At the sharpest part of the discontinuity,
the surface brightness declines by a factor of $\sim$2 over a distance of 6.9
kpc ($\sim 15''$). The inner and outer gas temperatures across the
discontinuity differ by only about 0.2 keV (interior and exterior gas
temperatures are 1.2 and 1.3 keV, respectively). Spectral analysis indicates
that there is a large gradient in the elemental abundance across the
discontinuity, and comparison with the low resolution NVSS radio maps suggests
that the discontinuity is aligned with a low surface brightness radio lobe. We
conclude that the appearance of this discontinuity is the result of the
transport of high abundance material from the center of the galaxy by the
expanding radio lobe, similar to structures seen in {\em Chandra} observations
of Perseus A and Hydra A.


title:
X-ray Emission from the Hot ISM and SW Radio Lobe of the Nearby Radio
  Galaxy Centaurus A

abstract:
  We present results from two {\em Chandra}/ACIS-I observations and one {\em
XMM-Newton} observation of X-ray emission from the ISM and the inner radio
lobes of the nearby radio galaxy Centaurus A. The ISM has an average radial
surface brightness profile that is well described by a $\beta$-model profile
with index $\beta$=0.40$\pm$0.04 and a temperature of $k_BT_{ISM}\sim$0.29 keV
beyond 2 kpc from the nucleus. We find that diffuse X-ray emission is
coincident with the outer half of the southwest radio lobe, and a bright X-ray
enhancement is detected along the edge of the lobe. On the basis of energetic
and lifetime arguments, we reject a nonthermal explanation for this emission.
We model this emission as a thin, hot shell or cap of X-ray emitting plasma
surrounding the radio lobe that was created by the supersonic inflation of the
lobe. This plasma shell is both hotter than ($k_BT_{SH}\sim$2.9 keV) and
greatly overpressurized relative to the ambient ISM indicating supersonic
expansion. We estimate that the lobe is expanding into the ISM at approximately
Mach 8.5 or 2400 km s$^{-1}$. We are not directly observing the bow shock, but
rather the cooler, denser material that is accumulating ahead of the contact
discontinuity. The thermal energy in the shell is a significant fraction of the
thermal energy of the hot ISM, demonstrating the possibility that the hot ISM
of early galaxies can be re-energized by outflows from nuclear activity.
Interestingly, no similarly bright X-ray emission is detected in or along the
edge of the NE lobe, implying that there are differences in the dynamics and
evolution of the kpc-scale radio components.


title: Searches for Fast Radio Transients

abstract:
  We discuss optimal detection of fast radio transients from astrophysical
objects while taking into account the effects of propagation through
intervening ionized media, including dispersion, scattering and
scintillation.Our analysis applies to the giant-pulse phenomenon exhibited by
some pulsars, for which we show examples, and to radio pulses from other
astrophysical sources, such as prompt radio emission from gamma-ray burst
sources and modulated signals from extra-terrestrial civilizations.


title: Searches for Giant Pulses from Extragalactic Pulsars

abstract:
  We discuss the giant-pulse phenomenon exhibited by pulsars and the distances
to which giant pulses might be detected from extragalactic pulsars. We describe
the conditions under which a single-pulse search is more sensitive than a
standard periodicity search. We find that, for certain pulse-amplitude
distribution power laws and time series lengths, single-pulse searches can be
superior. We present the results of searches toward several extragalactic
targets, including M33, the LMC (PSR B0540-69) and several other galaxies.
While we have not conclusively detected giant pulses from any of these targets,
these searches illustrate the methodology of, issues related to and
difficulties in these types of searches.


title:
SOHO CTOF Observations of Interstellar He+ Pickup Ion Enhancements in
  Solar Wind Compression Regions

abstract:
  We present a recent analysis with 1996 SOHO CELIAS CTOF data, which reveals
correlations of He+ pickup ion fluxes and spectra with the magnetic field
strength and solar wind density. The motivation is to better understand the
ubiquitous large variations in both pickup ion fluxes and their velocity
distributions found in interstellar pickup ion datasets. We concentrate on time
periods of that can be associated with compression regions in the solar wind.
Along with enhancements of the overall pickup ion fluxes, adiabatic heating and
acceleration of the pickup ions are also observed in these regions. Transport
processes that lead to the observed compressions and related heating or
acceleration are discussed. A shift in velocity space associated with traveling
interplanetary compression regions is observed, and a simple model presented to
explain this phenomenon based on the conserved magnetic adiabatic moment.


title: The Disk-Jet Connection in Microquasars and AGN

abstract:
  We propose a new model for the disk-jet connection in black hole x-ray
transients and active galactic nuclei. In our model, the inner part of the
accretion disk around the central black hole switches between two states. In
one state, the accretion energy is dissipated locally (some within the disk,
some within a corona) to produce the observed disk luminosity. In the second
state, the accretion energy is deposited into the bulk flow of a relativistic
jet. We associate the transition between the two states with the generation of
a global, poloidal magnetic field. We show that this model can explain the
observed behavior of black hole accretors.


title:
An Unexplained 10 Degree - 40 Degree Shift in the Location of Some
  Diverse Neutral Atom Data at 1 AU

abstract:
  Four different data sets pertaining to the neutral atom environment at 1 AU
are presented and discussed. These data sets include neutral solar wind and
interstellar neutral atom data from IMAGE/LENA, energetic hydrogen atom data
from SOHO/HSTOF and plasma wave data from the magnetometer on ISEE-3.
Surprisingly, these data sets are centered between 262 degrees and 292 degrees
ecliptic longitude, about 10 degrees - 40 degrees from the upstream
interstellar neutral flow direction at 254 degrees resulting from the motion of
the Sun relative to the local interstellar cloud. Some possible explanations
for this offset, none of which is completely satisfactory, are discussed.


title: Ten Major Challenges in Cosmology

abstract:
  What are the important unanswered questions in cosmology? The choice as to
which are the most important is somewhat personal. In the view of the author,
the ten topics chosen here for discussion must be included among the most
fundamental. Present cosmological theory is unable to fully describe the
evolution of the universe from the time of the Big Bang and a lack of
observations makes it difficult to verify theoretical predictions. The
questions posed here will only be answered when we have both better theory and
more observations.


title:
Future Probes of the Primordial Scalar and Tensor Perturbation Spectra:
  Prospects from the CMB, Cosmic Shear and High-Volume Redshift Surveys

abstract:
  Detailed study of the scalar and tensor perturbation spectra can provide much
information about the primordial fluctuation-generator, be it inflation or
something else. The tensor perturbation spectrum may be observable through its
influence on CMB polarization, but only if the tensor-to-scalar ratio, r = T/S,
is greater than about 10^{-5}. The tensor tilt can be measured with an error of
sigma(n_T) that decreases with r from 0.1 at r=0.001 to 0.02 at r = 0.1.
Current CMB constraints on the scalar perturbation spectrum can be improved by
higher--resolution CMB observations and/or by tomographic cosmic shear
observations. These can both shrink errors on the tilt (n_S) and running (n_S'=
dn_S/d\ln k) to the 10^{-3} level. Stunning as these results would be, it may
become very desirable to improve upon them an order of magnitude further in
order to study the expected departures from n_S' = 0. Such improvements are
likely to require observation of three--dimensional clustering over very large
volumes. Unfortunately, to get down to the 10^{-4} level will require a sparse
spectroscopic redshift survey with about 10^9 galaxies spread over a volume
less than but comparable to that of the observable Universe.


title:
Signatures of Galaxy-Cluster Interactions: Tully-Fisher Observations at
  z~0.1

abstract:
  We have obtained new optical imaging and spectroscopic observations of 78
galaxies in the fields of the rich clusters Abell 1413 (z = 0.14), Abell 2218
(z = 0.18) and Abell 2670 (z = 0.08). We have detected line emission from 25
cluster galaxies plus an additional six galaxies in the foreground and
background, a much lower success rate than what was found (65%) for a sample of
52 lower-richness Abell clusters in the range 0.02 < z < 0.08. We have combined
these data with our previous observations of Abell 2029 and Abell 2295 (both at
z = 0.08), which yields a sample of 156 galaxies. We evaluate several
parameters as a function of cluster environment: Tully-Fisher residuals,
H-alpha equivalent width, and rotation curve asymmetry, shape and extent.
Although H-alpha is more easily detectable in galaxies that are located further
from the cluster cores, we fail to detect a correlation between H-alpha extent
and galaxy location in those where it is detected, again in contrast with what
is found in the clusters of lesser richness. We fail to detect any
statistically significant trends for the other parameters in this study. The
zero-point in the z~0.1 Tully-Fisher relation is marginally fainter (by 1.5
sigma) than that found in nearby clusters, but the scatter is essentially
unchanged.


title: The Dynamic Behavior of Soft Gamma Repeaters

abstract:
  Soft Gamma Repeaters (SGRs) undergo changes in their pulse properties and
persistent emission during episodes of intense burst activity. Both SGR 1900+14
and SGR 1806-20 have shown significant changes in their spin-down rates during
the last several years, yet the bulk of this variability is not correlated with
burst activity. SGR 1900+14 has undergone large changes in flux and a dramatic
pulse profile change following burst activity in 1998. The flux level of SGR
1627$-$41 has been decreasing since its only recorded burst activity. Here, we
review the global properties of SGRs as well as the observed dynamics of the
pulsed and persistent emission properties of SGR 1900+14, SGR 1806-20 and SGR
1627-41 during and following burst active episodes and discuss what
implications these results have for the burst emission mechanism, the magnetic
field dynamics of magnetars, the nature of the torque variability, and SGRs in
general.


title:
Comptonization in Super-Eddington Accretion Flow and Growth Timescale of
  Supermassive Black Holes

abstract:
  Super-Eddington accretion onto black holes (BHs) may occur at ultraluminous
compact X-ray sources in nearby galaxies, Galactic microquasars and narrow-line
Seyfert 1 galaxies (NLS1s). Effects of electron scattering (opacity and
Comptonization) and the relativistic correction (gravitational redshift and
transverse Doppler effect) on the emergent spectra from super-Eddington
accretion flows onto non-rotating BHs are examined for 10^{1.5} and 10^{6.5}
M_sun BH masses (M_BH). With mdot [= Mdot / (L_Edd / c^2), where Mdot is the
accretion rate] > 100, the spectral hardening factor via electron scattering is
\lesssim 2.3 - 6.5. Due to the mdot-sensitive hardening factor, the color
temperature of the innermost radiation is not proportional to L^{0.25},
differing from the simplest standard accretion disk. The model is applied to
optical--soft X-ray emission from NLS1s. We pick up one NLS1, namely PG
1448+273 with an inferred M_BH of 10^{6.4} M_sun, among the highest mdot
candidates. The broadband spectral distribution is successfully reproduced by
the model with an extremely high mdot (= 1000) and the viscosity parameter
alpha of 0.01. This implies that this object, as well as some other highest
mdot systems, is really young: the inferred age, M_BH / Mdot, is about 10^6
years. We also briefly discuss the distribution of mdot for transient and
highly variable NLS1s, finding that those are located at 3 \lesssim mdot
\lesssim 300. Such a moderately high accretion rate is indicative of thermal
instability. Furthermore, mdot for a possible type-2 counterpart of NLS1s, NGC
1068, is found to be similar to mdot for NLS1s.


title:
Theoretical Considerations on the Properties of Accreting Millisecond
  Pulsars

abstract:
  We examine a number of evolutionary scenarios for the recently discovered
class of accretion-powered millisecond X-ray pulsars in ultracompact binaries,
including XTE J0929-314 and XTE J1751-305, with orbital periods of 43.6 and
42.4 minutes, respectively. We focus on a particular scenario that can
naturally explain the present-day properties of these systems. This model
invokes a donor star that was either very close to the TAMS (i.e.,
main-sequence turnoff) at the onset of mass transfer or had sufficient time to
evolve during the mass-transfer phase. We have run a systematic set of detailed
binary evolution calculations with a wide range of initial donor masses and
degrees of (nuclear) evolution at the onset of mass transfer. In general, the
models whose evolutionary tracks result in the best fits to these ultracompact
binaries start mass transfer with orbital periods of ~15 hr, then decrease to a
minimum orbital period of less than or about 40 minutes, and finally evolve
back up to about 43 minutes. We also carry out a probability analysis based on
the measured mass functions of XTE J0929-314 and XTE J1751-305, and combine
this with the results of our binary evolution models and find that the donor
stars currently have masses in the range of about 0.012 - 0.025 solar masses,
and radii of about 0.042 - 0.055 solar radii, and that these radii are likely
to be factors of about 1.1 - 1.3 times larger than the corresponding
zero-temperature ones. We also find that the interiors of the donors are
largely composed of helium and that the surface hydrogen abundances are almost
certainly less than 10% (by mass).


title: Properties of cluster satellites in hydrodynamical simulations

abstract:
  We analyze the dynamical and thermal evolution of dark matter and ICM in
hydrodynamical Tree-SPH simulations of galaxy clusters. Starting from a sample
of 17 high-resolution objects, with virial mass ranging from 3 10^{14} to 1.7
10^{15} M_sun, we follow the build-up of the systems in dark matter and hot gas
through the repeated merging of satellites along their merging history trees.
We measure the self-bound mass fraction of subhaloes as a function of time
after the merging, estimate the satellite mean orbital properties as a function
of the mass ratio with the main cluster at merging time, and study the
evolution of their internal velocity dispersion, gas temperature and entropy as
the substructure is disrupted by various dynamical processes, reaching
eventually thermo-dynamic equilibrium in the gravitational potential of the
main cluster. We model some relevant properties of subhalo orbits, as the time
of the first pericentric and apocentric passages, and the typical distances and
velocities at the corresponding times. This survival study can be used to
interpret the dynamics of observed merging clusters; as an example we apply our
results to the system 1E0657-56. We show that, in the light of our results, the
most likely interpretation of the data for this cluster points to the merger of
a small group with mass M\approx 1 10^{13} M_sun with a massive cluster with
M\approx 1.3 10^{15} M_sun.


title:
Emission line galaxies at 9200 A, including a multi-component galaxy
  system at z =6.43

abstract:
  This paper has been temporarily withdrawn by the authors.
  Subsequent observations with the VLT have shown that the high equivalent
width line emission from the candidate z=6.4 galaxy most likely is associated
with an unusually strong lined low redshift galaxy to the north west. The paper
will be revised accordingly and resubmitted.


title:
SDSS J092455.87+021924.9: an Interesting Gravitationally Lensed Quasar
  from the Sloan Digital Sky Survey

abstract:
  We report the discovery of a new gravitationally lensed quasar from the Sloan
Digital Sky Survey, SDSS J092455.87+021924.9 (SDSS J0924+0219). This object was
selected from among known SDSS quasars by an algorithm that was designed to
select another known SDSS lensed quasar (SDSS 1226-0006A,B). Five separate
components, three of which are unresolved, are identified in photometric
follow-up observations obtained with the Magellan Consortium's 6.5m Walter
Baade telescope at Las Campanas Observatory. Two of the unresolved components
(designated A and B) are confirmed to be quasars with z=1.524; the velocity
difference is less than 100 km sec^{-1} according to spectra taken with the W.
M. Keck Observatory's Keck II telescope on Mauna Kea. A third stellar
component, designated C, has the colors of a quasar with redshift similar to
components A and B. The maximum separation of the point sources is 1.78". The
other two sources, designated G and D, are resolved. Component G appears to be
the best candidate for the lensing galaxy. Although component D is near the
expected position of the fourth lensed component in a four image lens system,
its properties are not consistent with being the image of a quasar at z~1.5.
Nevertheless, the identical redshifts of components A and B and the presence of
component C strongly suggest that this object is a gravitational lens. Our
observations support the idea that a foreground object reddens the fourth
lensed component and that another unmodeled effect (such as micro- or
milli-lensing) demagnificates it, but we cannot rule out the possibility that
SDSS0924+0219 is an example of the relatively rare class of ``three component''
lens systems.


title: On the Origin of the Inner Structure of Halos

abstract:
  We calculate by means of the Press-Schechter formalism the density profile
developed by dark-matter halos during accretion, i.e., the continuous
aggregation of small clumps. We find that the shape of the predicted profile is
similar to that shown by halos in high-resolution cosmological simulations.
Furthermore, the mass-concentration relation is correctly reproduced at any
redshift in all the hierarchical cosmologies analyzed, except for very large
halo masses. The role of major mergers, which can cause the rearrangement of
the halo structure through violent relaxation, is also investigated. We show
that, as a result of the boundary conditions imposed by the matter continuously
infalling into the halo during the violent relaxation process, the shape of the
density profile emerging from major mergers is essentially identical to the
shape the halo would have developed through pure accretion. This result
explains why, according to high-resolution cosmological simulations, relaxed
halos of a given mass have the same density profile regardless of whether they
have had a recent merger or not, and why both spherical infall and hierarchical
assembly lead to very similar density profiles. Finally, we demonstrate that
the density profile of relaxed halos is not affected either by the capture of
clumps of intermediate mass.


title:
New infrared star clusters in the Northern and Equatorial Milky Way with
  2MASS

abstract:
  We carried out a survey of infrared star clusters and stellar groups on the
2MASS J, H and K_s all-sky release Atlas in the Northern and Equatorial Milky
Way (350 < l < 360, 0 < l < 230). The search in this zone complements that in
the Southern Milky Way (Dutra et al. 2003a). The method concentrates efforts on
the directions of known optical and radio nebulae. The present study provides
167 new infrared clusters, stellar groups and candidates. Combining the two
studies for the whole Milky Way, 346 infrared clusters, stellar groups and
candidates were discovered, whereas 315 objects were previously known. They
constitute an important new sample for future detailed studies.


title:
A search for Low Surface Brightness galaxies in the near-infrared I.
  Selection of the sample

abstract:
  A sample of about 3,800 Low Surface Brightness (LSB) galaxies was selected
using the all-sky near-infrared (J, H and K_s-band) 2MASS survey. The selected
objects have a mean central surface brightness within a 5 arcsec radius around
their centre fainter than 18 mag/sq.arcsec in the K_s band, making them the
lowest surface brightness galaxies detected by 2MASS. A description is given of
the relevant properties of the 2MASS survey and the LSB galaxy selection
procedure, as well as of basic photometric properties of the selected objects.
The latter properties are compared to those of other samples of galaxies, of
both LSBs and `classical' high surface brightness (HSB) objects, which were
selected in the optical. The 2MASS LSBs have a (B_T_c)-(K_T) colour which is on
average 0.9 mag bluer than that of HSBs from the NGC. The 2MASS sample does not
appear to contain a significant population of red objects.


title: Impact-Generated Dust Clouds Surrounding the Galilean Moons

abstract:
  Tenuous dust clouds of Jupiter's Galilean moons Io, Europa, Ganymede and
Callisto have been detected with the in-situ dust detector on board the Galileo
spacecraft. The majority of the dust particles have been sensed at altitudes
below five radii of these lunar-sized satellites. We identify the particles in
the dust clouds surrounding the moons by their impact direction, impact
velocity, and mass distribution. Average particle sizes are 0.5 to $\rm 1 \mu
m$, just above the detector threshold, indicating a size distribution with
decreasing numbers towards bigger particles. Our results imply that the
particles have been kicked up by hypervelocity impacts of micrometeoroids onto
the satellites' surfaces. The measured radial dust density profiles are
consistent with predictions by dynamical modeling for satellite ejecta produced
by interplanetary impactors (Krivov et al., PSS, 2003, 51, 251--269), assuming
yield, mass and velocity distributions of the ejecta from laboratory
measurements. The dust clouds of the three outer Galilean moons have very
similar properties and are in good agreement with the model predictions for
solid ice-silicate surfaces. The dust density in the vicinity of Io, however,
is more than an order of magnitude lower than expected from theory. This may be
due to a softer, fluffier surface of Io (volcanic deposits) as compared to the
other moons. The log-log slope of the dust number density in the clouds vs.
distance from the satellite center ranges between --1.6 and --2.8. Appreciable
variations of number densities obtained from individual flybys with varying
geometry, especially at Callisto, might be indicative of leading-trailing
asymmetries of the clouds due to the motion of the moons with respect to the
field of impactors.


title: Galactic Stellar and Substellar Initial Mass Function

abstract:
  We review recent determinations of the present day and initial mass functions
in various components of the Galaxy, disk, spheroid, young and globular
clusters. As a general feature, the IMF is well described by a power-law form
for $m\ga 1 \msol$ and a lognormal form below. The extension of the disk IMF
into the brown dwarf (BD) regime is in good agreement with observations and
yields a disk BD number-density comparable to the stellar one $\sim 0.1 \pc3$.
The IMF of young clusters is found to be consistent with the disk field IMF,
providing the same correction for unresolved binaries. The spheroid IMF relies
on much less robust grounds. Within all the uncertainties, it is found to be
similar to the one derived for globular clusters, and is well represented also
by a lognormal form with a characteristic mass slightly larger than for the
disk. The IMF characteristic of early star formation remains undetermined, but
different observational constraints suggest that it does not extend below $\sim
1 \msol$. These IMFs allow a reasonably robust determination of the Galactic
present-day and initial stellar and brown dwarf contents. They also have
important galactic implications in yielding more accurate mass-to-light ratio
determinations. The M/L ratios obtained with the disk and the spheroid IMF
yield values 1.8 and 1.4 smaller than a Salpeter IMF, respectively. This
general IMF determination is examined in the context of star formation theory.
(shortened)


title:
ISOGAL: A deep survey of the obscured inner Milky Way with ISO at 7 and
  15 micron and with DENIS in the near-infrared

abstract:
  The ISOGAL project is an infrared survey of specific regions sampling the
Galactic Plane selected to provide information on Galactic structure,stellar
populations,stellar mass-loss and the recent star formation history of the
inner disk and Bulge of the Galaxy. ISOGAL combines 7 and 15 micron ISOCAM
observations - with a resolution of 6'' at worst - with DENIS IJKs data to
determine the nature of the sources and theinterstellar extinction. We have
observed about 16 square degrees with a sensitivity approaching 10-20mJy,
detecting ~10^5 sources,mostly AGB stars,red giants and young stars. The main
features of the ISOGAL survey and the observations are summarized in this
paper,together with a brief discussion of data processing and quality. The
primary ISOGAL products are described briefly (a full description is given in
Schuller et al. 2003, astro-ph/0304309): viz. the images and theISOGAL-DENIS
five-wavelength point source catalogue. The main scientific results already
derived or in progress are summarized. These include astrometrically calibrated
7 and 15um images,determining structures of resolved sources; identification
and properties of interstellar dark clouds; quantification of the infrared
extinction law and source dereddening; analysis of red giant and (especially)
AGB stellar populations in the central Bulge,determining luminosity,presence of
circumstellar dust and mass--loss rate,and source classification,supplemented
in some cases by ISO/CVF spectroscopy; detection of young stellar objects of
diverse types,especially in the inner Bulge with information about the present
and recent star formation rate; identification of foreground sources with
mid-IR excess. These results are the subject of about 25 refereed papers
published or in preparation.


title: Galaxy interactions - poor starburst triggers

abstract:
  We report on a study of tidally triggered star formation in galaxies, based
on spectroscopic/photometric observations in the optical/near-IR of a magnitude
limited sample of 59 systems of interacting and merging galaxies and a
comparison sample of 38 normal isolated galaxies. In contrast to results from
previous investigations, our global UBV colours do not support a significant
enhancement of starforming activity in the interacting/merging galaxies. We
claim that this is true also for Arp galaxies. A moderate increase in star
formation is found in the very centres of the interacting galaxies contributing
marginally to the total luminosity. The interacting and in particular the
merging galaxies are characterized by increased far infrared (hereafter FIR)
luminosities and temperatures that weakly correlate with the central activity.
The L(FIR)/L(B) ratio however, is remarkably similar in the two samples,
indicating that true starbursts normally are not hiding in the central regions
of the FIR luminous cases. The gas mass-to-luminosity ratio in optical-IR is
practically independent of luminosity, lending further support to the paucity
of true massive starburst galaxies triggered by interactions/mergers. Our
conclusion is that interacting and merging galaxies, from the global star
formation aspect, generally do not differ dramatically from scaled up versions
of normal, isolated galaxies. No drastic change with redshift is expected.


title:
On the newtonian limit and cut--off scales of isothermal dark matter
  halos with cosmological constant

abstract:
  We examine isothermal dark matter halos in hydrostatic equilibrium with a
cosmological constant Lambda =Omega_\Lambda rho_{crit}c^2, where
Omega_\Lambda=0.7, and rho_{crit} is the present value of the critical density
with h=0.65. The Newtonian limit of General Relativity yields equilibrium
equations that are different from those arising by merely coupling an
``isothermal sphere'' to the Lambda-field within a Newtonian framework. The
conditions for the existence and stability of circular geodesic orbits show the
existence of (I) an ``isothermal region'' (0<r<r_2), circular orbits are stable
and all variables behave almost identically to those of an isothermal sphere;
(II) an ``asymptotic region'' (r>r_1) dominated by the Lambda-field, where the
Newtonian potential oscillates and circular orbits exist in disconnected
patches of the domain of r; (III) a ``transition region'' (r_2<r<r_1), circular
orbits exist but are unstable. We also find that no stable configuration exists
with central density, rho_c, smaller than 2 Lambda, hence any galactic haloes
which virialized at $z< 30$ in must have rho_c >0.008 M_\odot {pc}^3, in
agreement with rotation curve studies of dwarf galaxies. Since r_2 marks the
largest radius of a stable circular orbit, it provides a ``cut off'' radius.
For current estimates of rho_c and velocity dispersion of galactic structures,
this is around five times larger than the virialization radius. The effects of
the Lambda$--field can hence be ignored in structure formation models, but
could be significant in the dynamics of superclusters in the linear regime or
of gravitational clustering at large scales.


title:
A Magnetic Bomb Scenario for Relativistic Jet Events in the Microquasar
  GRS 1915+105

abstract:
  We present a magnetic bomb scenario for the multiwavelength behavior during
"Type B" relativistic jet events in the microquasar GRS 1915+105. These events
are characterized by a hard X-ray dip which terminates in a soft X-ray spike.
The scenario, based on the suspended accretion model for long gamma-ray bursts,
posits a magnetic dynamo around an accreting Kerr black hole which reaches the
Van Putten-Levinson critical value of poloidal magnetic field energy-to-kinetic
energy (E_B/E_k ~= 1/15) in the inner accretion disk. The toroidal inner
accretion disk subsequently becomes unstable, and the poloidal magnetic field
energy in the inner torus magnetosphere is promptly released as it disconnects
from the black hole -- the magnetic bomb (``B-bomb'') explosion. This scenario
matches the long-duration time-scale and spectral evolution of the hard X-ray
dip, and the short-duration time-scale and energetics of the soft X-ray spike
of type B events, as well as correlated features in the infrared and radio
wavebands. We discuss some implications of these results for understanding the
formation of relativistic jets in black hole systems.


title:
Correlated radio:X-ray emission in the hard states of Galactic
  microquasars

abstract:
  We present results of our study of correlated radio and X-ray emission in two
black hole candidates and Galactic microquasars GRS 1915+105 and Cygnus X-1 in
their steady long term hard states, along with Cygnus X-3 (using data obtained
from RXTE-ASM, CGRO-BATSE and GBI). We detect a pivotal behavior in the X-ray
spectrum of GRS 1915+105, correlated to the radio emission. Similar to the
results obtained for Cygnus X-3, the flux of X-rays softer than the pivoting
point correlates with the radio emission, while the corresponding harder X-ray
flux anti-correlates with both the radio and the softer X-ray emission, in this
state. We examine all the previously reported correlations of X-ray properties
with the radio emission in Galactic microquasars and argue that these are
consistent with a general picture where a spectral pivoting is a common feature
in these sources with the shape of the spectrum determining the flux of radio
emission, during the hard states. We also detect a general monotonic increase
in the radio emission of these sources with the soft X-ray emission spanning
about 5 orders of magnitude. We qualitatively explain these findings with a Two
Component Advective Flow model where the location of a boundary layer between
the thin disk and the Comptonizing region determines the spectral shape and
also the amount of outflow.


title: The Ionizing Efficiency of the First Stars

abstract:
  We investigate whether a single population of first stars could have
influenced both the metal enrichment and reionization of the high-redshift
intergalactic medium (IGM), by calculating the generated ionizing radiation per
unit metal yield as a function of the metallicity of stellar populations. We
examine the relation between the ionizing radiation and carbon created by the
first stars, since the evidence for the widespread enrichment of the IGM at
redshifts $z$ about 3-4 comes from the detection of C IV absorption. We find
that the number of ionizing photons per baryon generated in association with
the detected IGM metallicity may well exceed that required for a late hydrogen
reionization at $z$ of about 6, by up to a factor of 10-20 for metal-free stars
in a present-day initial mass function (IMF). This would be in agreement with
similar indications from recent observations of the microwave background and
the high-$z$ IGM. In addition, the contribution from intermediate-mass stars to
the total metal yield, neglected in past works, substantially impacts such
calculations. Lastly, a top-heavy IMF is not necessarily preferred as a more
efficient high-$z$ source of ionizing radiation, based on nucleosynthetic
arguments in association with a given level of IGM enrichment.


title:
The formation of galaxy stellar cores by the hierarchical merging of
  supermassive black holes

abstract:
  We investigate a hierarchical structure formation scenario in which galaxy
stellar cores are created from the binding energy liberated by shrinking
supermassive black hole (SMBH) binaries. The binary orbital decay heats the
surrounding stars, eroding a preexisting 1/r^2 stellar cusp. We follow the
merger history of dark matter halos and associated SMBHs via cosmological Monte
Carlo realizations of the merger hierarchy from early times to the present in a
LCDM cosmology. Massive black holes get incorporated through a series of
mergers into larger and larger halos, sink to the center owing to dynamical
friction, accrete a fraction of the gas in the merger remnant to become
supermassive, and form a binary system. Stellar dynamical processes drive the
binary to harden and eventually coalesce. A simple scheme is applied in which
the loss cone is constantly refilled and a constant density core forms due to
the ejection of stellar mass. We find that a model in which the effect of the
hierarchy of SMBH interactions is cumulative and cores are preserved during
galaxy mergers produces at the present epoch a correlation between the `mass
deficit' (the mass needed to bring a flat inner density profile to a 1/r^2
cusp) and the mass of the nuclear SMBH, with a normalization and slope
comparable to the observed relation. Models in which the mass displaced by the
SMBH binary is replenished after every major galaxy merger appear instead to
underestimate the mass deficit observed in `core' galaxies.


title:
Balmer Lines as Diagnostics of Physical Conditions in AGN Broad Emission
  Line Regions

abstract:
  Using a well known method for laboratory plasma diagnostic, the
Boltzmann-plot, we discuss the physical properties in Broad Line Region (BLR)
of Active Galactic Nuclei (AGN). We apply the Boltzmann-plot method to Balmer
lines on a sample of 14 AGN, finding that it may indicate the existence of
"Case B" recombination or Partial Local Thermodynamical Equilibrium (PLTE). For
BLR of AGN, where PLTE exists, we estimated the electron temperature and
density of BLR. The estimated electron temperature ($T\sim 13000 - 37000$ K)
are in good agreement with previous estimates. The estimated electron densities
depend on opacity of the emitting plasma in BLR. They are from $N_e\sim 10^9\rm
cm^{-3}$ for optically thick to $N_e\sim 10^{14}\rm cm^{-3}$ for optically thin
emission plasma in BLR. The estimated electron temperature has been shown to be
velocity dependent, and it decreases for higher velocities. Although the
alternative explanation than PLTE indicated by Boltzmann-plot may be considered
(e.g. high intrinsic reddening), the method may give the quick estimate of
physical conditions in BLR before to apply the sophisticated methods.


title:
On the influence of Stark broadening on Si I lines in stellar
  atmospheres

abstract:
  We study the influence of Stark broadening and stratification effects on Si\i
lines in the rapidly oscillating (roAp) star 10 Aql, where the Si\i 6142.48 \AA
and 6155.13 \AA lines are asymmetrical and shifted. First we have calculated
Stark broadening parameters using the semiclassical perturbation method for
three Si\i lines: 5950.2 \AA, 6142.48 \AA and 6155.13 \AA. We revised the
synthetic sp$ calculation code taking into account both Stark width and shift
for these lines. From the comparison of our calculations with the observations
we found that Stark broadening + the stratification effect can explain
asymmetry of the Si\i 6142.48 \AA and 6155.13 \AA lines in the atmospere of
roAp star 10 Aql.


title: The Chandra Deep Field-North Survey. XIII. 2 Ms Point-Source Catalogs

abstract:
  We present catalogs for the ~2 Ms Chandra Deep Field-North, currently the
deepest X-ray observation of the Universe in the 0.5-8.0 keV band. Five hundred
and three (503) X-ray sources are detected over an ~448 sq.arcmin area in up to
seven bands; 20 of these X-ray sources lie in the Hubble Deep Field-North.
Source positions are determined using matched-filter and centroiding
techniques; the median positional uncertainty is ~0.3 arcsecs. The X-ray colors
of the detected sources indicate a broad variety of source types, although
absorbed AGNs (including some possible Compton-thick sources) are clearly the
dominant type. We also match lower significance X-ray sources to optical
counterparts and provide a list of 79 optically bright R<~23) lower
significance Chandra sources. The majority of these sources appear to be
starburst and normal galaxies. We investigate the source-free background,
determine the maximum photon-limited exposures, and investigate source
confusion. These analyses directly show that Chandra can achieve significantly
higher sensitivities in an efficient nearly photon-limited manner and be
largely free of source confusion. To allow consistent comparisons, we have also
produced point-source catalogs for the ~1 Ms Chandra Deep Field-South (CDF-S).
Three hundred and twenty-six (326) X-ray sources are included in the main
Chandra catalog, and an additional 42 optically bright X-ray sources are
included in a lower significance Chandra catalog. We find good agreement with
the photometry of the previously published CDF-S catalogs; however, we provide
significantly improved positional accuracy (ABRIDGED).


title: The Gravitational Wave Background from Cosmological Compact Binaries

abstract:
  We use a population synthesis approach to characterise, as a function of
cosmic time, the extragalactic close binary population descended from stars of
low to intermediate initial mass. The unresolved gravitational wave (GW)
background due to these systems is calculated for the 0.1-10 mHz frequency band
of the planned Laser Interferometer Space Antenna (LISA). This background is
found to be dominated by emission from close white dwarf-white dwarf pairs. The
spectral shape can be understood in terms of some simple analytic arguments. To
quantify the astrophysical uncertainties, we construct a range of evolutionary
models which produce populations consistent with Galactic observations of close
WD-WD binaries. The models differ in binary evolution prescriptions as well as
initial parameter distributions and cosmic star formation histories. We compare
the resulting background spectra, whose shapes are found to be insensitive to
the model chosen, and different to those found recently by Schneider et al.
(2001). From this set of models, we constrain the amplitude of the
extragalactic background to be 1E-12 < Omega(1 mHz) < 6E-12, in terms of
Omega(f), the fraction of closure density received in gravitational waves in
the logarithmic frequency interval around f.


title:
Topological properties of the Cosmic Microwave Background polarization
  map

abstract:
  Rapid progress has been made in observations of the temperature anisotropies
of the Cosmic Microwave Background (CMB). These observations have enabled
cosmologists to characterize the state of the universe at recombination, and
observational efforts are now being directed towards obtaining the polarization
map of the CMB. Here we draw an analogy between the CMB polarization map and
nematic liquid crystals, pointing out that the two have similar defects. Making
use of known results in the theory of defect formation we predict the
statistical distribution of defects in the CMB polarization map and provide a
novel tool for probing the CMB at large angular scales.


title:
Numerical Simulations of Astrophysical Jets from Keplerian Disks with
  Periodic Ejection

abstract:
  We present 2.5-dimensional time-dependent simulations of nonrelativistic and
nonradiative outflows from sinusoidally perturbed Keplerian accretion disks. A
sinusoidal perturbation is introduced in the velocity of the gas ejected from
the surface of the disk into a cold corona. In the simulations, the disk is a
fixed boundary from which the gas is ejected with a pulsed velocity. The
maximum value of this velocity is taken to be a thousandth of the local
Keplerian disk velocity. It was found that for large periods, the structures in
the jet tend to fragment into smaller substructures. For small values of the
period, the structures tend to dissipate, while for medium values of the
period, they tend to persist.


title: Kuiper Belt Object Sizes and Distances from Occultation Observations

abstract:
  There are several observational campaigns under way to detect kilometer size
foreground Kuiper Belt Objects (KBOs) through their occultation of background
stars. The interpretation of an occultation light curve, unfortunately, is
affected by a geometric degeneracy such that one is unable to determine the KBO
size independent of its distance. This degeneracy can be broken through a
precise measurement of the relative velocity obtained from simultaneous
observations of individual events. While an array of telescopes spread over an
area of few square kilometers can be employed, it is unlikely that the relative
velocity can be measured to the required accuracy to help break this geometric
degeneracy. The presence of diffraction fringes in KBO occultation light
curves, when projected sizes of occulted stars are smaller than the Fresnel
scale, improves determination of size and distance significantly. In this
regard, we discuss the potential role of a dedicated satellite mission for KBO
occultation observations. If dwarf stars at the V-band magnitudes of 14th and
fainter can be monitored at time intervals of 0.1 seconds with normalized flux
errors at the level of 1%, the occultation observations will allow individual
KBO sizes and distances to be determined at the level of a few percent or
better.


title: A Microcalorimeter and Bolometer Model

abstract:
  The standard non-equilibrium theory of noise in ideal bolometers and
microcalorimeters fails to predict the performance of real devices due to
additional effects that become important at low temperature. In this paper we
extend the theory to include the most important of these effects, and find that
the performance of microcalorimeters operating at 60 mK can be quantitatively
predicted. We give a simple method for doing the necessary calculations,
borrowing the block diagram formalism from electronic control theory.


title: Internal Extinction in Spiral Galaxies in the Near Infrared

abstract:
  In order to study the effects of internal extinction in spiral galaxies we
search for correlations of near infrared (NIR) photometric parameters with
inclination. We use data from the 2 Micron All-Sky Survey (2MASS) Extended
Source Catalog (XSC) on 15,224 spiral galaxies for which we also have
redshifts. For 3035 of the galaxies, I-band photometry is available which is
included in the analysis. From the simple dependence of reddening on
inclination we derive a lower limit to the difference in magnitude between the
face-on and edge-on aspect of 0.9, 0.3 and 0.1 magnitudes in I (0.81 um), J
(1.25 um) and H (1.65 um) bands. We find that the faintest isophotal radius
reported in the XSC (at the 21st mag/arc sq level) is closer to the centers of
the galaxies than other common isophotal measures (e.g. the 23.5 mag/arc sq
radius in I-band), and argue that it should not be assumed to represent an
outer isophote at which galaxies are transparent at all viewing angles. A
simple linear extinction law (i.e. Delta M = gamma log(a/b)) is not adequate
for the full range of disk inclinations and we adopt both a bi-linear and a
quadratic law. A simple photometric model is used to explain the observed
behavior. Internal extinction depends on galaxy luminosity. We show that for
galaxies with a K total magnitude dimmer than -20, -20.7 and -20.9 the data
indicates zero extinction in J, H and K respectively, while disk opacity
increases monotonically with increasing disk luminosity.


title:
Emission-Line Diagnostics of the Central Engines of Weak-Line Radio
  Galaxies

abstract:
  A handful of well-studied Weak-Line Radio Galaxies (WLRGs) have been
traditionally classified as Low Ionization Nuclear Emission-line Regions
(LINERs), suggesting that these two groups of AGNs might be related. In this
paper, we present new optical emission-line measurements for twenty Weak-Line
Radio Galaxies which we supplement with measurements for an additional four
from the literature. Classifying these objects by their emission-line ratios,
we find that 50% of the objects are robustly classified as LINERs while an
additional 25% are likely to be LINERs. Photoionization calculations show that
the Spectral Energy Distribution of the well-studied WLRG 3C 270 (NGC 4261) is
able to produce the observed emission-line ratios, but only if the UV emission
seen by the narrow emission-line gas is significantly higher than that
observed, implying A_V = 2.5-4.2 magnitudes along our line of sight to the
nucleus. From the photoionization calculations, we find that the emission-line
gas must have an ionization parameter between 10^-3.5 and 10^-4.0 and a wide
range in hydrogen density (10^2-10^6 cm^-3) to reproduce the measured
emission-line ratios, similar to the properties inferred for the emission-line
gas in LINERs. Thus, we find that properties of the emission-line gas as well
as the underlying excitation mechanism are indeed similar in LINERs and WLRGs.
By extension, the central engines of accretion-powered LINERs and WLRGs, which
do host an accreting black hole, may be qualitatively similar.


title:
High-Resolution Near-Infrared Imaging and Polarimetry of Four
  Proto-Planetary Nebulae

abstract:
  High-resolution near-infrared HST NICMOS (F160W, F222M) images and
polarization (2 um) observations were made of four bipolar proto-planetary
nebulae (PPNs): IRAS 17150-3224, IRAS 17441-2411, IRAS 17245-3951, and IRAS
16594-4656. The first three of these are viewed nearly edge-on, and for the
first time the central stars in them are seen. Color maps reveal a reddened
torus between the bipolar lobes in the edge-on cases, with bluer lobes. The
polarization values are high, with maximum values ranging from 40 to 80%. The
polarization patterns are basically centrosymmetric, with some deviations in
the low polarization equatorial regions. For IRAS 17150-3224, circumstellar
arcs are seen at 1.6 um, along with a newly-discovered loop in the equatorial
region. Bright caps are seen at the end of the lobes, indicating that they are
not open-ended. A distinct point-symmetric pattern is seen in the strengths of
the polarization vectors, especially in IRAS 17150-3224. HST NICMOS
observations provide a valuable complement to the WFPC2 visible images in
deriving the basic structure of bipolar PPNs.


title:
Lens or Binary? Chandra Observations of the Wide Separation Broad
  Absorption Line Quasar Pair UM425

abstract:
  We have obtained a 110 ksec Chandra ACIS-S exposure of UM425, a pair of QSOs
at z=1.47 separated by 6.5 arcsec, which show remarkably similar emission and
broad absorption line (BAL) profiles in the optical/UV. Our 5000 count X-ray
spectrum of UM425A (the brighter component) is well-fit with a power law
(photon spectral index Gamma=2.0) partially covered by a hydrogen column of
3.8x10^22 cm^-2. The underlying power-law slope for this object and for other
recent samples of BALQSOs is typical of radio-quiet quasars, lending credence
to the hypothesis that BALs exist in every quasar. Assuming the same Gamma for
the much fainter image of UM425B, we detect an obscuring column 5 times larger.
We search for evidence of an appropriately large lensing mass in our Chandra
image and find weak diffuse emission near the quasar pair, with an X-ray flux
typical of a group of galaxies at redshift z ~ 0.6. From our analysis of
archival HST WFPC2 and NICMOS images, we find no evidence for a luminous
lensing galaxy, but note a 3-sigma excess of galaxies in the UM425 field with
plausible magnitudes for a z=0.6 galaxy group. However, the associated X-ray
emission does not imply sufficient mass to produce the observed image
splitting. The lens scenario thus requires a dark (high M/L ratio) lens, or a
fortuitous configuration of masses along the line of sight. UM425 may instead
be a close binary pair of BALQSOs, which would boost arguments that
interactions and mergers increase nuclear activity and outflows.


title: Two new bright Ae stars

abstract:
  Two newly identified Ae stars, nu Cyg and kappa UMa, were discovered in the
course of the Magnetic Survey of Bright MS stars (Monin et al. 2002). We pre
sent their Halpha profiles along with measurements of their equivalent width
and parameters of emission features. Emission in the Halpha line of nu Cyg is
variable on a time scale of 3 years. kappa UMa exhibits weak emission which is
rather stable. The emission is thought to arise from a circumstellar disk, and
we have estimated the size of that disk.Both new emission stars are IRAS
sources. Their IR color excesses are consistent with those of classical Ae
stars. Thus, nu Cyg and kappa UMa appear not to belong to the class of Herbig
Ae/Be stars. We argue that the frequency of Ae stars may be underestimated due
to the difficulty of detection of weak emission in some A stars.


title:
The Kinematics and Physical Conditions of the Ionized Gas in NGC 4593
  from Chandra High-Energy Grating Spectroscopy

abstract:
  We observed the Seyfert 1 galaxy NGC 4593 with the Chandra high energy
transmission gratings and present a detailed analysis of the soft X-ray
spectrum. We measure strong absorption lines from He-like O, Ne, Mg, Si, H-like
N, O, Ne, Mg, Si and highly ionized Fe XIX-XXV. Only the NLya, OLya and MgLya
lines appear to be marginally resolved. We identify a spectral feature at $\sim
0.707$ keV with a neutral Fe L edge, which might suggest that there is dust
along the line-of-sight to \ngc. Neutral Si absorption, which might also be
expected from absorption due to dust is present (though not significantly) in
the form of a weak neutral Si edge. We also detect, at marginal signficance,
NLya and O VII (r) 1s-2p ($\lambda 21.602 $) absorption at $z \sim 0$, due to a
hot medium in our Local Group. The soft X-ray spectrum of NGC 4593 is
adequately described by a simple, single-zone photoionized absorber with an
equivalent Hydrogen column density of $5.37^{+1.45}_{-0.79} \times 10^{21} \
\rm{cm}^{-2}$ and an ionization parameter of $\log \xi= 2.52^{+0.06}_{-0.04}$
ergs cm $\rm{s}^{-1}$ although there remain some features which are not
identified. Although the photoionized gas almost certainly is comprised of
matter in more than one ionization state and may consist of several kinematic
components, data with better signal-to-noise ratio and better spectral
resolution are required to justify a more complex model.


title: Color Gradients in Early-Type Galaxies in ABELL 2199

abstract:
  We performed B and R band surface photometry for E/S0 galaxies in a nearby
rich cluster ABELL 2199 to investigate their B-R color gradients
(d(B-R)/dlogr). Our aims are to study statistical properties of the color
gradients and, by comparing them with those in less dense environments, to
examine environmental dependence of color gradients in elliptical galaxies. We
studied the distribution of the B-R color gradients in the cluster ellipticals
and found that the mean value of the color gradients is -0.09 +- 0.04 mag/dex,
which can be converted to a metallicity gradient (dlogZ/dlogr) of ~ -0.3 +- 0.1
assuming an old stellar population. We further studied the relations between
the B-R color gradients and global properties of the galaxies. Our data suggest
that for the galaxies brighter than L*, more luminous and larger galaxies tend
to have steeper color gradients. The typical value of the color gradients seems
to be consistent with a recent monolithic collapse model and the correlation
could also appear if elliptical galaxies formed through the monolithic
collapse. On the contrary, it is found based on data from the literature that
any such trend is clearly weaker for ellipticals in less dense environments,
while the distribution of the color gradients is quite similar to that found in
the rich cluster. Based on the results from our data and the published data, we
discuss formation process of elliptical galaxy and its environmental
dependence.


title: The Optical Emission from Gamma-ray Quasars

abstract:
  We present photometric observations of six radio-loud quasars that were
detected by the COMPTEL gamma-ray telescope. The data encompasses seven
wavebands in the optical and near-infrared. After correction for Galactic
extinction, we find a wide range in optical slopes. Two sources are as blue as
optically-selected quasars, and are likely to be dominated by the accretion
disc emission, while three others show colours consistent with a red
synchrotron component. We discuss the properties of the COMPTEL sample of
quasars, as well as the implications our observations have for multi-wavelength
modelling of gamma-ray quasars.


title: Widespread acetaldehyde near the Galactic Centre

abstract:
  We present Giant Meterwave Radio Telescope images of the 1065 MHz emission
from the 1_11 -> 1_10 rotational transition of acetaldehyde (CH3CHO) in the
molecular cloud complex Sgr B2. Our observations are unique in that they have a
high spatial resolution (~4"), while still being sensitive to large-scale
emission. Most complex organic molecules in this cloud (e.g. acetone, methyl
formate, acetic acid) are concentrated in a very small core, ~0.1pc across. In
contrast, acetaldehyde is found to be spread over a region at least 100 times
larger in extent. The line emission is confined to regions with radio continuum
emission and correlates well (in both position and velocity) with formaldehyde
absorption towards this continuum; this is consistent with earlier single dish
results suggesting that it is likely to be weakly mased. Our observations also
suggest that grain mantle destruction by shocks plays an important role in the
observed gas phase abundance of CH3CHO in Sgr B2.


title:
The origin of X-ray emission of two distant (z>1) cluster candidate with
  XMM-Newton

abstract:
  We present here a study of XMM-Newton data of two distant galaxy cluster
candidates. One of these was discovered serendipitously in near infrared data,
CL J0533-2411, the other one corresponds to the cluster EIS J0533-2412 part of
the EIS cluster survey. The estimated redshift of CL J0533-2411 is z=1.2-1.7.
EIS J0533-2412 is a rich system (Lambda_cl=299), with a spectroscopically
confirmed redshift of z=1.3. Both galaxy concentrations show firm X-ray
detections, located within 30" of their optical center. However, we cannot
resolve the sources with XMM-Newton. If the X-ray emission originates from the
X-ray emitting intra-cluster medium (ICM) it would be extremely concentrated
which is rather unlikely (core radii below 14 h_{65}^{-1}kpc and 40
h_{65}^{-1}kpc, respectively). We argue that the X-ray sources are more likely
AGN members of the galaxy concentrations. We set an upper limit for the
bolometric luminosity of a hot ICM in the range ~0.7-2.1 10^{44}
h_{65}^{-2}erg/s for CL J0533-2411, depending on the exact redshift. For EIS
J0533-2412 the limit is L_bol=(6.2+/-1.4) 10^{43} h_{65}^{-2}erg/s. We
interpret our result in the following way: EIS J0533-2412 (and possibly CL
J0533-2411) are proto-clusters and show matter overdensities before collapse,
which explains the low significance of extended X-ray emission.


title:
Clues on the evolution of the Carina dwarf spheroidal galaxy from the
  color distribution of its red giant stars

abstract:
  The thin red giant branch (RGB) of the Carina dwarf spheroidal galaxy appears
at first sight quite puzzling and seemingly in contrast with the presence of
several distinct bursts of star formation. In this Letter, we provide a
measurement of the color spread of red giant stars in Carina based on new BVI
wide-field observations, and model the width of the RGB by means of synthetic
color-magnitude diagrams. The measured color spread, Sigma{V-I}=0.021 +/-
0.005, is quite naturally accounted for by the star-formation history of the
galaxy. The thin RGB appears to be essentially related to the limited age range
of its dominant stellar populations, with no need for a metallicity dispersion
at a given age. This result is relatively robust with respect to changes in the
assumed age-metallicity relation, as long as the mean metallicity over the
galaxy lifetime matches the observed value ([Fe/H] = -1.91 +/- 0.12 after
correction for the age effects). This analysis of photometric data also sets
some constraints on the chemical evolution of Carina by indicating that the
chemical abundance of the interstellar medium in Carina remained low throughout
each episode of star formation even though these episodes occurred over many
Gyr.


title: A Census of the Young Cluster IC 348

abstract:
  We present a new census of the stellar and substellar members of the young
cluster IC 348. We have obtained images at I and Z for a 42'x28' field
encompassing the cluster and have combined these measurements with previous
optical and near-infrared photometry. From spectroscopy of candidate cluster
members appearing in these data, we have identified 122 new members, 15 of
which have spectral types of M6.5-M9, corresponding to masses of 0.08-0.015
M_sun by recent evolutionary models. The latest census for IC 348 now contains
a total of 288 members, 23 of which are later than M6 and thus are likely to be
brown dwarfs. From an extinction-limited sample of members (A_V<=4) for a
16'x14' field centered on the cluster, we construct an IMF that is unbiased in
mass and nearly complete for M/M_sun>=0.03 (<=M8). In logarithmic units where
the Salpeter slope is 1.35, the mass function for IC 348 rises from high masses
down to a solar mass, rises more slowly down to a maximum at 0.1-0.2 M_sun, and
then declines into the substellar regime. In comparison, the similarly-derived
IMF for Taurus from Briceno et al. and Luhman et al. rises quickly to a peak
near 0.8 M_sun and steadily declines to lower masses. The distinctive shapes of
the IMFs in IC 348 and Taurus are reflected in the distributions of spectral
types, which peak at M5 and K7, respectively. These data provide compelling,
model-independent evidence for a significant variation of the IMF with
star-forming conditions.


title:
A Code for Stellar Binary Evolution and its Application to the Formation
  of Helium White Dwarfs

abstract:
  We present a numerical code intended for calculating stellar evolution in
close binary systems. In doing so, we consider that mass transfer episodes
occur when the stellar size overflows the corresponding Roche lobe. In such
situation we equate the radius of the star with the equivalent radius of the
Roche lobe. This equation is handled implicitly together with those
corresponding to the whole structure of the star. We describe in detail the
necessary modifications to the standard Henyey technique for treating the mass
loss rate implicitly together with thin outer layers integrations.
  We have applied this code to the calculation of the formation of low mass,
helium white dwarfs in low mass close binary systems. We found that the global
numerical convergence properties are fairly good. In particular, the onset and
end of mass transfer episodes is computed automatically.


title: A maximum likelihood approach to the destriping technique

abstract:
  The destriping technique is a viable tool for removing different kinds of
systematic effects in CMB related experiments. It has already been proven to
work for gain instabilities that produce the so-called 1/f noise and periodic
fluctuations due to e.g. thermal instability. Both effects when coupled with
the observing strategy result in stripes on the observed sky region. Here we
present a maximum-likelihood approach to this type of technique and provide
also a useful generalization. As a working case we consider a data set similar
to what the Planck satellite will produce in its Low Frequency Instrument
(LFI). We compare our method to those presented in the literature and find some
improvement in performance. Our approach is also more general and allows for
different base functions to be used when fitting the systematic effect under
consideration. We study the effect of increasing the number of these base
functions on the quality of signal cleaning and reconstruction. This study is
related to Planck LFI activities.


title: Swift Pointing and Gravitational-Wave Bursts from Gamma-Ray Burst Events

abstract:
  The currently accepted model for gamma-ray burst phenomena involves the
violent formation of a rapidly rotating solar-mass black hole. Gravitational
waves should be associated with the black-hole formation, and their detection
would permit this model to be tested. Even upper limits on the
gravitational-wave strength associated with gamma-ray bursts could constrain
the gamma-ray burst model. This requires joint observations of gamma-ray burst
events with gravitational and gamma-ray detectors. Here we examine how the
quality of an upper limit on the gravitational-wave strength associated with
gamma-ray bursts depends on the relative orientation of the gamma-ray-burst and
gravitational-wave detectors, and apply our results to the particular case of
the Swift Burst-Alert Telescope (BAT) and the LIGO gravitational-wave
detectors. A result of this investigation is a science-based ``figure of
merit'' that can be used, together with other mission constraints, to optimize
the pointing of the Swift telescope for the detection of gravitational waves
associated with gamma-ray bursts.


title:
On particle acceleration around shocks. II: on the diffuse scattering by
  moving media

abstract:
  The probability that a particle, crossing the shock along a given direction,
be reflected backwards along another direction, was shown to be the key element
in determining the spectrum of non--thermal particles accelerated via Fermi
mechanism around a shock. Here an explicit equation for this probability
distribution is given, for both the upstream and downstream sections. Though
analytically intractable, this equation can be easily solved numerically.


title: New Low-Mass Members of the Taurus Star-Forming Region

abstract:
  Briceno et al. recently used optical imaging, data from the Two-Micron
All-Sky Survey (2MASS), and follow-up spectroscopy to search for young low-mass
stars and brown dwarfs in 8 square degrees of the Taurus star-forming region.
By the end of that study, there remained candidate members of Taurus that
lacked the spectroscopic observations needed to measure spectral types and
determine membership. In this work, we have obtained spectroscopy of the 22
candidates that have A_V<=8, from which we find six new Taurus members with
spectral types of M2.75 through M9. The new M9 source has the second latest
spectral type of the known members of Taurus (~0.02 M_sun). Its spectrum
contains extremely strong emission in H_alpha (W~950 A) as well as emission in
He I 6678 A and the Ca II IR triplet. This is the least massive object known to
exhibit emission in He I and Ca II, which together with the strong H_alpha are
suggestive of intense accretion.


title: How did the metals in a giant star originate?

abstract:
  The chemical composition of stars with extremely low metal contents (taking
``metals'' to mean all elements other than hydrogen and helium) provides us
with information on the masses of the stars that produced the first metals.
Such a direct connection is not possible, however, if the surface of the star
has been polluted by enriched material, either dredged from the star's interior
or transferred from a companion star. Here we argue that, in the case of
HE0107-5240 (ref. 1), the most iron poor star known, the oxygen abundance could
be a discriminant: a ratio of [O/Fe] exceeding +3.5 would favour a pristine
origin of metals, whereas an [O/Fe] ratio of less than +3 would favour the
pollution hypothesis. Using this criterion, we suggest how the required
information on oxygen abundance might be obtained.


title: CMB-induced Cluster Polarization as a Cosmological Probe

abstract:
  Scattering of the temperature anisotropy quadrupole by free electrons in
galaxy clusters leads to a secondary polarization signal in the cosmic
microwave background (CMB) fluctuations. At low redshifts, the temperature
quadrupole contains a significant contribution from the integrated Sachs-Wolfe
(ISW) effect associated with the growth of density fluctuations. Using
polarization data from a sample of clusters over a wide range in redshift, one
can statistically establish the presence of the ISW effect and determine its
redshift evolution. Given the strong dependence of the ISW effect on the
background cosmology, cluster polarization can eventually be used as a powerful
probe of dark energy. As a further application, we also discuss how it might be
used to understand the potential lack of power on large scales.


title: Weak Lensing from Space I: Instrumentation and Survey Strategy

abstract:
  A wide field space-based imaging telescope is necessary to fully exploit the
technique of observing dark matter via weak gravitational lensing. This first
paper in a three part series outlines the survey strategies and relevant
instrumental parameters for such a mission. As a concrete example of hardware
design, we consider the proposed Supernova/Acceleration Probe (SNAP). Using
SNAP engineering models, we quantify the major contributions to this
telescope's Point Spread Function (PSF). These PSF contributions are relevant
to any similar wide field space telescope. We further show that the PSF of SNAP
or a similar telescope will be smaller than current ground-based PSFs, and more
isotropic and stable over time than the PSF of the Hubble Space Telescope. We
outline survey strategies for two different regimes - a ``wide'' 300 square
degree survey and a ``deep'' 15 square degree survey that will accomplish
various weak lensing goals including statistical studies and dark matter
mapping.


title: Weak Lensing from Space II: Dark Matter Mapping

abstract:
  We study the accuracy with which weak lensing measurements could be made from
a future space-based survey, predicting the subsequent precisions of
3-dimensional dark matter maps, projected 2-dimensional dark matter maps, and
mass-selected cluster catalogues. As a baseline, we use the instrumental
specifications of the Supernova/Acceleration Probe (SNAP) satellite. We first
compute its sensitivity to weak lensing shear as a function of survey depth.
Our predictions are based on detailed image simulations created using
`shapelets', a complete and orthogonal parameterization of galaxy morphologies.
We incorporate a realistic redshift distribution of source galaxies, and
calculate the average precision of photometric redshift recovery using the SNAP
filter set to be Delta z=0.034. The high density of background galaxies
resolved in a wide space-based survey allows projected dark matter maps with a
rms sensitivity of 3% shear in 1 square arcminute cells. This will be further
improved using a proposed deep space-based survey, which will be able to detect
isolated clusters using a 3D lensing inversion techniques with a 1 sigma mass
sensitivity of approximately 10^13 solar masses at z~0.25. Weak lensing
measurements from space will thus be able to capture non-Gaussian features
arising from gravitational instability and map out dark matter in the universe
with unprecedented resolution.


title: Weak Lensing from Space III: Cosmological Parameters

abstract:
  Weak gravitational lensing provides a unique method to directly map the dark
matter in the universe and measure cosmological parameters. Current weak
lensing surveys are limited by the atmospheric seeing from the ground and by
the small field of view of existing space telescopes. We study how a future
wide-field space telescope can measure the lensing power spectrum and skewness,
and set constraints on cosmological parameters. The lensing sensitivity was
calculated using detailed image simulations and instrumental specifications
studied in earlier papers in this series. For instance, the planned
SuperNova/Acceleration Probe (SNAP) mission will be able to measure the matter
density parameter Omega_m and the dark energy equation of state parameter w
with precisions comparable and nearly orthogonal to those derived with SNAP
from supernovae. The constraints degrade by a factor of about 2 if redshift
tomography is not used, but are little affected if the skewness only is
dropped. We also study how the constraints on these parameters depend upon the
survey geometry and define an optimal observing strategy.


title: Contact Binaries

abstract:
  Despite being the most abundant (by space density) of interacting binary
stars, W Ursae Majoris (W UMa) stars are not understood structurally. Their
stellar components are in physical contact, and share a common convective
envelope. Observations demand large-scale energy exchange between components,
as do considerations of hydrostatic and thermal equilibrium. Yet solutions in
complete equilibrium can account for only a few of the bluest W UMa binaries.
Models which permit departures from thermal equilibrium can reproduce the
observable properties of later-type W UMa binaries, but they develop relaxation
oscillations, during a substantial portion of which the binary components break
thermal contact and develop very different effective temperatures, contrary to
observational statistics. Massive, early-type contact binaries are also known
to exist, but the nature of energy and mass exchange in common radiative
envelopes remains virtually unexplored.


title: Black Hole Accretion Disks On The Edge

abstract:
  The local axisymmetric stability of hydrodynamical and magnetized,
nearly-Keplerian gaseous accretion disks around non-rotating black holes is
examined in the vicinity of the classical marginally-stable orbit (at radii ~
R_ms). An approximate Paczynski-Wiita pseudo-Newtonian potential is used.
Hydrodynamical disks are linearly unstable inside a radius which differs
slightly from the classical R_ms value because of finite pressure and radial
stratification effects. Linear stresses associated with unstable hydrodynamical
modes vanish exactly at the radius of marginal stability and are generally
positive inside of that radius. When a magnetic field is introduced, however,
the concept of radius of marginal stability becomes largely irrelevant because
there are linearly unstable magneto-rotational modes everywhere. Associated
linear stresses are positive and continuous across the region of hydrodynamical
marginal stability, even for large-scale "hydro-like" modes subject only to
weak magnetic tension. This conclusion is valid for arbitrarily thin disks (in
ideal MHD) and it does not require a large-scale "radially-connecting" magnetic
field. Results on hydrodynamical diskoseismic modes trapped in deep
relativistic potential wells should be revised to account for the
short-wavelength Alfven-like behavior of inertio-gravity waves in magnetized
disks.


title:
Preparing the COROT space mission: incidence and characterisation of
  pulsation in the Lower Instability Strip

abstract:
  By pursuing the goal to find new variables in the COROT field-of-view we
characterised a sample of stars located in the lower part of the instability
strip. Our sample is composed of stars belonging to the disk population in the
solar neighbourhood. We found that 23% of the stars display multiperiodic light
variability up to few mmag of amplitude. uvbyBeta photometry fixed most of the
variables in the middle of the instability strip and high-resolution
spectroscopy established that they have vsin i>100 km/s. The comparison with
delta Sct stars in the whole Galaxy shows slightly different features, i.e.,
most delta Sct stars have a 0.05-mag redder (b-y)_0 index and lower vsin i
values. Additional investigation in the open cluster NGC 6633 confirms the same
incidence of variability, i.e., around 20%. The wide variety of pulsational
behaviours of delta Sct stars (including unusual objects such as a variable
beyond the blue edge or a rapidly rotating high-amplitude pulsator) makes them
very powerful asteroseismic tools to be used by COROT. Being quite common among
bright stars, delta Sct stars are suitable targets for optical observations
from space.


title:
Constraints on a Universal IMF from UV to Near-IR Galaxy Luminosity
  Densities

abstract:
  We obtain constraints on the slope of a universal stellar initial mass
function (IMF) over a range of cosmic star-formation histories (SFH) using
z=0.1 luminosity densities in the range from 0.2 to 2.2 microns. The age-IMF
degeneracy of integrated spectra of stellar populations can be broken for the
Universe as a whole by using direct measurements of (relative) cosmic SFH from
high-redshift observations. These have only marginal dependence on
uncertainties in the IMF, whereas, fitting to local luminosity densities
depends strongly on both cosmic SFH and the IMF. We fit to these measurements
using population synthesis and find the best-fit IMF power-law slope to be
Gamma=1.15+-0.2 (0.5 < M/M_solar < 120). This slope is in good agreement with
the Salpeter IMF slope (Gamma=1.35). A strong upper limit of Gamma<1.7 is
obtained which effectively rules out the Scalo IMF due to its too low fraction
of high-mass stars. This upper limit is at the 99.7% confidence level if we
assume a closed-box chemical evolution scenario and 95% if we assume constant
solar metallicity. Fitting to the H-alpha line luminosity density, we obtain a
best-fit IMF slope in good agreement with that derived from broadband
measurements. Marginalizing over cosmic SFH and IMF slope, we obtain (95% conf.
ranges, h=1): omega_stars = 1.1-2.0 E-3 for the stellar mass density; rho_sfr =
0.7-4.1 E-2 M_solar/yr/Mpc^3 for the star-formation rate density, and; rho_L =
1.2-1.7 E+35 W/Mpc^3 for the bolometric, attenuated, stellar, luminosity
density (0.09-5 microns). Comparing this total stellar emission with an
estimate of the total dust emission implies a relatively modest average
attenuation in the UV (<=1 magnitude at 0.2 microns).


title: Diffusion and Settling in Ap/Bp Stars

abstract:
  Ap/Bp stars are magnetic chemically peculiar early A and late B type stars of
the main sequence. They exhibit peculiar surface abundance anomalies that are
thought to be the result of gravitational settling and radiative levitation.
The physics of diffusion in these stars are reviewed briefly and some model
predictions are discussed. While models reproduce some observations reasonably
well, more work is needed before the behavior of diffusing elements in a
complex magnetic field is fully understood.


title: Roche Lobe Overflow from Dwarf Stellar Systems

abstract:
  We use both analytical analyses and numerical simulations to examine the
evolution of residual gas within tidally-limited dwarf galaxies and globular
clusters. If the gas sound speed exceeds about 10% of the central velocity
dispersion, as is the case for ionized gas within small stellar systems, the
gas shall have significant density at the tidal radius, and the gas may be lost
on timescales as short as a few times the sound crossing time of the system. In
colder systems, the density at the tidal radius is much lower, greatly reducing
the mass loss rate, and the system may retain its gas for a Hubble time. The
tidally removed gas shall follow an orbit close to that of the original host
system, forming an extended stream of ionized, gaseous debris. Tidal mass loss
severely limits the ability of dwarf systems to continuously form stars. The
ordinary gas content in many dwarf galaxies is fully ionized during high
red-shift epochs, possibly preventing star formation in some systems, leading
to the formation of starless, dark-matter concentrations. In either the field
or in the center of galaxy clusters, ionized gas may be retained by dwarf
galaxies, even though its sound speed may be comparable to or even exceed the
velocity dispersion. These processes may help to explain some observed
differences among dwarf galaxy types, as well as observations of the haloes of
massive galaxies.


title:
Formation scenarios for the young stellar associations between galactic
  longitudes l = 280-360 deg

abstract:
  We investigate the spatial distribution, the space velocities and age
distribution of the pre-main sequence (PMS) stars belonging to Ophiuchus, Lupus
and Chamaeleon star-forming regions (SFRs), and of the young early-type star
members of the Scorpius-Centaurus OB association. These young stellar
associations extend over the galactic longitude range from 280 deg. to 360
deg., and are at a distance interval of around 100 and 200 pc. This study is
based on a compilation of distances, proper motions and radial velocities from
the literature for the kinematic properties, and of basic stellar data for the
construction of Hertzsprung-Russel diagrams. Although there was no well-known
OB association in Chamaeleon, the distances and the proper motions of a group
of 21 B- and A-type stars, taken from the Hipparcos Catalogue, lead us to
propose that they form a young association. We show that the young early-type
stars of the OB associations and the PMS stars of the SFRs follow a similar
spatial distribution, i.e., there is no separation between the low and the
high-mass young stars. We find no difference in the kinematics nor in the ages
of these two populations studied. We analyze the different scenarios for the
triggering of large-scale star-formation that have been proposed up to now, and
argue that most probably we are observing a spiral arm that passes close to the
Sun. The alignment of young stars and molecular clouds and the average velocity
of the stars in the opposite direction to the Galactic rotation agree with the
expected behavior of star formation in nearby spiral arms.


title: The Extragalactic Distance Scale

abstract:
  Significant progress has been made during the last 10 years toward resolving
the debate over the expansion rate of the Universe. The current value of the
Hubble parameter, Ho, is now arguably known with an accuracy of 10%, largely
due to the tremendous increase in the number of galaxies in which Cepheid
variable stars have been discovered. Increasingly accurate secondary distance
indicators, many calibrated using Cepheids, now provide largely concordant
measurements of Ho well out into the Hubble flow, and deviations from the
smooth Hubble flow allow us to better measure the dynamical structure of the
local Universe. The change in the Hubble parameter with redshift provided the
first direct evidence for acceleration and "dark energy" in the Universe.
Extragalactic distance measurements are central to determining the size, age,
composition, and fate of the Universe. We discuss remaining systematic
uncertainties, particularly related to the Cepheid calibration, and identify
where improvements are likely to be made in the next few years.


title:
On Exact Polytropic Equilibria of Self-Gravitating Gaseous and Radiative
  Systems: Their Application to Molecular Cloud Condensation

abstract:
  We propose a novel mathematical method to construct an exact polytropic
sphere in self-gravitating hydrostatic equilibrium, improving the non-linear
Poisson equation. The central boundary condition for the present equation
requires a ratio of gas pressure to total one at the centre, which is uniquely
identified by the whole mass and molecular weight of the system. The special
solution derived from the Lane-Emden equation can be reproduced. This scheme is
now available for modelling the molecular cloud cores in interstellar media.
The mass-radius relation of the first core is found to be consistent with the
recent results of radiation hydrodynamic simulations.


title:
Intrinsic Variability and Field Statistics for the Vela Pulsar: 2.
  Systematics and Single-Component Fits

abstract:
  Individual pulses from pulsars have intensity-phase profiles that differ
widely from pulse to pulse, from the average profile, and from phase to phase
within a pulse. Widely accepted explanations do not exist for this variability
or for the mechanism producing the radiation. The variability corresponds to
the field statistics, particularly the distribution of wave field amplitudes,
which are predicted by theories for wave growth in inhomogeneous media. This
paper shows that the field statistics of the Vela pulsar (PSR B0833-45) are
well-defined and vary as a function of pulse phase, evolving from Gaussian
intensity statistics off-pulse to approximately power-law and then lognormal
distributions near the pulse peak to approximately power-law and eventually
Gaussian statistics off-pulse again. Detailed single-component fits confirm
that the variability corresponds to lognormal statistics near the peak of the
pulse profile and Gaussian intensity statistics off-pulse. The lognormal field
statistics observed are consistent with the prediction of stochastic growth
theory (SGT) for a purely linear system close to marginal stability. The
simplest interpretations are that the pulsar's variability is a direct
manifestation of an SGT state and the emission mechanism is linear (either
direct or indirect), with no evidence for nonlinear mechanisms like
modulational instability and wave collapse which produce power-law field
statistics. Stringent constraints are placed on nonlinear mechanisms: they must
produce lognormal statistics when suitably ensemble-averaged. Field statistics
are thus a powerful, potentially widely applicable tool for understanding
variability and constraining mechanisms and source characteristics of coherent
astrophysical and space emissions.


title:
Intrinsic Variability and Field Statistics for the Vela Pulsar: 3.
  Two-Component Fits and Detailed Assessment of Stochastic Growth Theory

abstract:
  The variability of the Vela pulsar (PSR B0833-45) corresponds to well-defined
field statistics that vary with pulsar phase, ranging from Gaussian intensity
statistics off-pulse to approximately power-law statistics in a transition
region and then lognormal statistics on-pulse, excluding giant micropulses.
These data are analyzed here in terms of two superposed wave populations, using
a new calculation for the amplitude statistics of two vectorially-combined
transverse fields. Detailed analyses show that the approximately power-law and
lognormal distributions observed are fitted well at essentially all on-pulse
phases by Gaussian-lognormal and double-lognormal combinations, respectively.
These good fits, plus the smooth but significant variations in fit parameters
across the source, provide strong evidence that the approximately power-law
statistics observed in the transition region are not intrinsic. Instead, the
data are consistent with normal pulsar emission having lognormal statistics at
all phases. This is consistent with generation in an inhomogeneous source
obeying stochastic growth theory (SGT) and with the emission mechanism being
purely linear (either direct or indirect). A nonlinear mechanism is viable only
if it produces lognormal statistics when suitably ensemble-averaged. Variations
in the SGT fit parameters with phase imply that the radiation is relatively
more variable near the pulse edges than near the center, as found in earlier
work. In contrast, Vela's giant micropulses come from a very restricted phase
range and have power-law statistics with indices ($6.7 \pm 0.6$) not
inconsistent with nonlinear wave collapse. These results imply that normal
pulses have a different source and generation mechanism than giant micropulses,
as suggested previously on other grounds.


title: Galactic structure studies with BATC star counts

abstract:
  We report the first results of star counts carried out with the National
Astronomical Observatories (NAOC) 60/90 cm Schmidt Telescope in 15
intermediate-band filters from 3000 to 10000 {\AA} in the BATC survey. We
analyze a sample of over 1400 main sequence stars ($14\le$V$\le21$), which lie
in the field with central coordinates R.A.=$09^h53^m13^s.30$ and
DEC=47$^\circ49^{\prime}00^{\prime\prime}.0$ (J2000). The field of view is 0.95
deg$^{2}$, and the spatial scale was $1\arcsec.67$. In our model, the
distribution of stars perpendicular to the plane of the Galaxy is given by two
exponential disks (thin disk plus thick disk) and a de Vaucouleurs halo. Based
on star counts, we derive the scale heights of the thin disk to be
$320^{+14}_{-15}$ pc and of the thick disk to be $640^{+30}_{-32}$ pc,
respectively, with a local density of $7.0\pm1%$ of the thin disk. We find that
the observed counts support an axial ratio of $c/a\le0.6$ for a de Vaucouleurs
$r^{1/4}$ law, implying a more flattened halo.
  We also derive the stellar luminosity function (SLF) for the thin disk, and
it partly agrees with the Hipparcos luminosity function.


title: Chaos or Order in Double Barred Galaxies?

abstract:
  Bars in galaxies are mainly supported by particles trapped around closed
periodic orbits. These orbits respond to the bar's forcing frequency only and
lack free oscillations. We show that a similar situation takes place in double
bars: particles get trapped around orbits which only respond to the forcing
from the two bars and lack free oscillations. We find that writing the
successive positions of a particle on such an orbit every time the bars align
generates a closed curve, which we call a loop. Loops allow us to verify
consistency of the potential. As maps of doubly periodic orbits, loops can be
used to search the phase-space in double bars in order to determine the
fraction occupied by ordered motions.


title: Angular dimensions of planetary nebulae

abstract:
  We have measured angular dimensions of 312 planetary nebulae from their
images obtained in Halpha (or Halpha + [NII]). We have applied three methods of
measurements: direct measurements at the 10% level of the peak surface
brightness, Gaussian deconvolution and second-moment deconvolution. The results
from the three methods are compared and analysed. We propose a simple
deconvolution of the 10% level measurements which significantly improves the
reliability of these measurements for compact and partially resolved nebulae.
Gaussian deconvolution gives consistent but somewhat underestimated diameters
compared to the 10% measurements. Second-moment deconvolution gives results in
poor agreement with those from the other two methods, especially for poorly
resolved nebulae. From the results of measurements and using the conclusions of
our analysis we derive the final nebular diameters which should be free from
systematic differences between small (partially resolved) and extended (well
resolved) objects in our sample.


title: On the Size Difference between Red and Blue Globular Clusters

abstract:
  Several recent studies have reported a mean size difference of about 20%
between the metal-rich and metal-poor subpopulations of globular clusters (GCs)
in a variety of galaxies. In this paper we investigate the possibility that the
size difference might be a projection effect, resulting from a correlation
between cluster size and galactocentric distance, combined with different
radial distributions of the GC subpopulations. We find that projection effects
may indeed account for a size difference similar to the observed one, provided
that there is a steep relation between GC size and galactocentric distance in
the central parts of the GC system and that the density of GCs flattens off
near the center in a manner similar to a King profile. For more centrally
peaked distributions, such as a de Vaucouleurs law, or for shallower
size-radius relations, projection effects are unable to produce the observed
differences in the size distributions.


title:
Disentangling microlensing and differential extinction in the double QSO
  HE0512-3329

abstract:
  We present the first separate spectra of both components of the
small-separation double QSO HE0512-3329 obtained with HST/STIS in the optical
and near UV. The similarities especially of the emission line profiles and
redshifts strongly suggest that this system really consists of two lensed
images of one and the same source.
  The emission line flux ratios are assumed to be unaffected by microlensing
and are used to study the differential extinction effects caused by the lensing
galaxy. Fits of empirical laws show that the extinction properties seem to be
different on both lines of sight. With our new results, HE0512-3329 becomes one
of the few extragalactic systems which show the 2175 AA absorption feature,
although the detection is only marginal.
  We then correct the continuum flux ratio for extinction to obtain the
differential microlensing signal. Since this may still be significantly
affected by variability and time-delay effects, no detailled analysis of the
microlensing is possible at the moment.
  This is the first time that differential extinction and microlensing could be
separated unambiguously. We show that, at least in HE0512-3329, both effects
contribute significantly to the spectral differences and one cannot be analysed
without taking into account the other. For lens modelling purposes, the flux
ratios can only be used after correcting for both effects.


title:
Mergers between elliptical galaxies and the thickening of the
  fundamental plane

abstract:
  We have carried out computer simulations to study the effect of merging on
the fundamental plane (FP) relation. Initially, systems are spherical Jaffe
models following a simple scaling relation (M/R_e^2 = constant). They have been
put on the FP by imposing different M/L values. Various orbital characteristics
have been considered. Our results show that the merger remnants lie very close
to the FP of the progenitors. Although non-homology is introduced by the
merging process, mergers among homologous galaxies leave a pre-existing
FP-relation intact. As a side result we find that variations in the point of
view lead to non-negligible scatter about the FP.


title: An analysis of two-layer models for circumstellar disks

abstract:
  The two-layer disk models of Chiang & Goldreich (1997, henceforth CG) and its
derivatives are popular among astronomers because of their simplicity and the
clear predictions they make for the SEDs of T Tauri stars and Herbig Ae/Be
stars. Moreover, they can be computed quickly, which is a great advantage when
fitting observations using automated procedures. In this paper we wish to
assess the accuracy and reliability of 2-layer models, by comparing them to
detailed vertical structure models with accurate 1+1D radiative transfer. We
focus on the shape of the SED, and the predicted height and "flaring index" of
the disk. We first consider models where scattering is set to zero. We find
that 2-layer models overestimate significantly the near-infrared flux, and we
suggest a simple way of correcting this effect, at least in part. At longer
wavelengths, the SED of two-layer models often show a two-bump structure, which
is absent in 1+1D models. Nevertheless, overall agreement is reasonably good,
and the differences are in most cases within 30%. At (sub)-mm wavelengths the
differences may even be less. The shape of the disk, as measured by its
pressure and surface scale height and by the flaring angle are also well
reproduced by two-layer models. When scattering is included in the 1+1D models,
the differences become larger, especially in the near-infrared. We suggest
simple ways to include scattering in two-layer models and discuss their
reliability. We do not compare the two-layer models to full 2-D/3-D models, so
the conclusions remain valid only within the annulus-by-annulus approximation.


title: The Basics of Lensing

abstract:
  The basic equations and geometry of gravitational lensing are described, as
well as the most important contexts in which it is observed in astronomy:
strong lensing, weak lensing and microlensing.


title: Spectropolarimetry of the borderline Seyfert 1 galaxy ESO 323-G077

abstract:
  We report the detection of high linear polarization in the bright Seyfert 1
galaxy ESO 323-G077. Based on optical spectropolarimetry with FORS1 at the VLT
we find a continuum polarization which ranges from 2.2 % at 8300A to 7.5 % at
3600A. Similar amounts of linear polarization are found for the broad emission
lines, while the narrow lines are not polarized. The position angle of the
polarization is independent of the wavelength and found to be perpendicular to
the orientation of the extended [OIII] emission cone of this galaxy. Within the
standard model of Seyfert nuclei the observations can be well understood
assuming that this AGN is observed at an inclination angle where the nucleus is
partially obscured and seen mainly indirectly in the light scattered by dust
clouds within or above the torus and the illuminated inner edge of the dust
torus itself. Hence we conclude that ESO 323-G077 is a borderline Seyfert 1
galaxy which can provide important information on the geometric properties of
active nuclei.