title:
A Robust Measure of Tidal Circularization in Coeval Binary Populations:
  The solar-type spectroscopic Binary Population in The Open Cluster M35

abstract:
  We present a new homogeneous sample of 32 spectroscopic binary orbits in the
young (~ 150 Myr) main-sequence open cluster M35. The distribution of orbital
eccentricity vs. orbital period (e-log(P)) displays a distinct transition from
eccentric to circular orbits at an orbital period of ~ 10 days. The transition
is due to tidal circularization of the closest binaries. The population of
binary orbits in M35 provide a significantly improved constraint on the rate of
tidal circularization at an age of 150 Myr. We propose a new and more robust
diagnostic of the degree of tidal circularization in a binary population based
on a functional fit to the e-log(P) distribution. We call this new measure the
tidal circularization period. The tidal circularization period of a binary
population represents the orbital period at which a binary orbit with the most
frequent initial orbital eccentricity circularizes (defined as e = 0.01) at the
age of the population. We determine the tidal circularizationperiod for M35 as
well as for 7 additional binary populations spanning ages from the pre
main-sequence (~ 3 Myr) to late main-sequence (~ 10 Gyr), and use Monte Carlo
error analysis to determine the uncertainties on the derived circularization
periods. We conclude that current theories of tidal circularization cannot
account for the distribution of tidal circularization periods with population
age.


title: 350 micron Galactic Center Dust Observations with SHARC II

abstract:
  We present first and preliminary submillimeter continuum images of the
Galactic Center region obtained with the new Caltech Submillimeter Observatory
facility camera SHARC II. The instrument allows 350 micron observations with
unprecedented sensitivity and instantaneous spatial coverage. The stability of
the SHARC II detectors combined with the large number of available pixels
allows a non-differential scanning mode that does not require the observation
of a reference off-source position. Here we present large-scale 350 micron dust
continuum images from the Sgr A and Sgr C regions, as well as the detection of
sub-mm dust continuum emission from the IRAS 25 micron source AFGL5376. This
source is produced in a large-scale shock that extends well above the Galactic
plane.


title: Short-term optical variability of high-redshift QSO's

abstract:
  This paper presents results of a search for short-term variability in the
optical band of selected high-luminosity, high-redshift radio-quiet quasars.
Each quasar has been monitored typically for 2 - 4 hours with a time resolution
of 2 - 5 minutes and a photometric accuracy of about 0.01 - 0.02 mag. Due to
the significant redshift (z>2), the covered wavelength range falls into the UV
region (typically 1500 - 2500A). We found no statistical evidence for any
continuum variations larger than 0.01 - 0.02 for any of the monitored objects.
Our results suggest that the presence of a short-term variability in
radio-quiet quasars is unlikely even in the UV region, contrary to reports by
other authors. This conclusion holds true at least for high-luminosity (large
black hole mass and accretion rate?) objects. The results are consistent with
the idea that significant short-term (less than 1 hour) variations in AGN,
where observed, should be attributed primarily to processes in a relativistic
jet.


title: A Revised Geometry for the Magnetic Wind of theta^1 Orionis C

abstract:
  Theta^1 Ori is thought to be a hot analog of Bp variables because its optical
and UV line and X-ray continuum fluxes modulate regularly over the
magnetic/rotational period. A flattened magnetosphere surrounding co-rotates
with these stars, producing a periodic modulation of emission and absorption
components of the UV resonance lines, as well as of optical H and He lines. In
this paper we examine these modulations in detail and point out that the
far-blue and near-red wings of C IV and N V resonance lines exhibit
anticorrelated modulations, causing mild flux elevations at moderate redshifts
at edge-on phase (phi=0.5). However, the lines do not exhibit rest-frame
absorption features, the usual signatures of cool static disks surrounding Bp
stars. We suggest that this behavior can be explained by the existence of two
geometrically distinct wind regions separated by the local magnetic Alfven
radius. Wind streams emerging outside this point are forced outward by
radiative forces and eventually expand outward radially to infinity - this
matter produces the far-blue wing absorptions at phi=0.5. Interior streams
follow closed loops and collide at the magnetic equator with counterstreams.
There they coalesce and fall back to the star along their original field lines
- these are responsible for mild emissions at this same phase. The rapid
circulation of the interior wind component back to the star is responsible for
the absence of static disk features.


title: PSR J1022+1001: Profile Stability & Precision Timing

abstract:
  We present an investigation of the morphology and arrival times of integrated
radio pulses from the binary millisecond pulsar PSR J1022+1001. This pulsar is
renowned for its poor timing properties, which have been postulated to
originate from variability in its average pulse profile. Although a sub-class
of long-period pulsars are known to exhibit mode changes that give rise to very
large deviations in their integrated profiles, this was the first millisecond
pulsar thought to have an unstable mean profile. As part of a precision timing
program at the Parkes radio telescope we observed this pulsar between January
2003 and March 2004 using a coherent de-dispersion system (CPSR2). A study of
morphological variability during our brightest observations suggests that the
pulse profile varies by at most a few percent, similar to the uncertainty in
our calibration. Unlike previous authors, we find that this pulsar times
extremely well. In five minute integrations of 64 MHz bands we obtain a
weighted RMS residual of just 2.27 microseconds. The reduced chi-squared of our
best fit is 1.43, which suggests that this pulsar can be timed to high accuracy
with standard cross-correlation techniques. Combining relativistic constraints
with the pulsar mass function and consideration of the Chandrasekhar mass limit
on the white dwarf companion, we can constrain the inclination angle of the
system to lie within the range 37 < i < 56 degrees. For reasonable pulsar
masses, this suggests that the white dwarf is at least 0.9 solar masses. We
also find evidence for secular evolution of the projected semi-major axis.


title: Geodetic Precession in PSR J1141-6545

abstract:
  We present observations that show dramatic evolution of the mean pulse
profile of the relativistic binary pulsar J1141--6545 over a period of five
years. This is consistent with precession of the pulsar spin axis due to
relativistic spin-orbit coupling. Observations made between 1999 and 2004 with
a number of instruments at the Parkes radio telescope demonstrate a steady,
secular evolution of the mean total intensity profile, which increases in width
by more than 50 percent during the five year period. Analysis of the changing
position angle of the linearly polarised component of the mean profile suggests
that our line of sight is shifting closer to the core of the emission cone. We
find that the slope of the position angle swing across the centre of the pulse
steepens with time and use a simplified version of the rotating vector model to
constrain the magnitude and direction of the change in our line of sight angle
relative to the pulsar magnetic axis. The fact that we appear to be moving
deeper into the emission cone is consistent with the non-detection of this
pulsar in previous surveys.


title: Pulsars and Gravitational Wave Detection

abstract:
  The number of known millisecond pulsars has dramatically increased in the
last few years. Regular observations of these pulsars may allow gravitational
waves with frequencies ~10^-9 Hz to be detected. A ``pulsar timing array'' is
therefore complimentary to other searches for gravitational waves using
ground-based or space-based interferometers that are sensitive to much higher
frequencies. In this review we describe 1) the basic methods for using an array
of pulsars as a gravitational wave detector, 2) the sources of the potentially
detectable waves, 3) current limits on individual sources and a stochastic
background and 4) the new project recently started using the Parkes radio
telescope.


title:
Torque bistability in the interaction between a neutron star
  magnetosphere and a thin accretion disc

abstract:
  We present a time-dependent model of the interaction between a neutron star
magnetosphere and a thin (Shakura-Sunyaev) accretion disc, where the extent of
the magnetosphere is determined by balancing outward diffusion and inward
advection of the stellar magnetic field at the inner edge of the disc. The
nature of the equilibria available to the system is governed by the magnetic
Prandtl number Pm and the ratio \xi of the corotation radius to the Alfven
radius. For \xi > Pm^0.3, the system can occupy one of two stable states, where
the torques are of opposite signs. If the star is spinning up initially, in the
absence of extraneous perturbations, \xi decreases until the spin-up
equilibrium vanishes, the star subsequently spins down, and the torque
asymptotes to zero. Vortex-in-cell simulations of the Kelvin-Helmholtz
instability suggest that the transport speed across the mixing layer between
the disc and magnetosphere is less than the shear speed when the layer is thin,
unlike in previous models.


title: Thermonuclear supernova models, and observations of Type Ia supernovae

abstract:
  In this paper, we review the present state of theoretical models of
thermonuclear supernovae, and compare their predicitions with the constraints
derived from observations of Type Ia supernovae. The diversity of explosion
mechanisms usually found in one-dimensional simulations is a direct consequence
of the impossibility to resolve the flame structure under the assumption of
spherical symmetry. Spherically symmetric models have been successful in
explaining many of the observational features of Type Ia supernovae, but they
rely on two kinds of empirical models: one that describes the behaviour of the
flame on the scales unresolved by the code, and another that takes account of
the evolution of the flame shape. In contrast, three-dimensional simulations
are able to compute the flame shape in a self-consistent way, but they still
need a model for the propagation of the flame in the scales unresolved by the
code. Furthermore, in three dimensions the number of degrees of freedom of the
initial configuration of the white dwarf at runaway is much larger than in one
dimension. Recent simulations have shown that the sensitivity of the explosion
output to the initial conditions can be extremely large. New paradigms of
thermonuclear supernovae have emerged from this situation, as the Pulsating
Reverse Detonation. The resolution of all these issues must rely on the
predictions of observational properties of the models, and their comparison
with current Type Ia supernova data, including X-ray spectra of Type Ia
supernova remnants.


title:
Tip of the Red Giant Branch distances to galaxies with composite stellar
  populations

abstract:
  (Abridged) We have investigated the reliability of the widely used I-band Tip
of the RGB relative distances for a sample of Local Group galaxies with complex
Star Formation Histories (SFR) and Age Metallicity Relationships (AMR) namely
the LMC, SMC and LGS3. The use of the K-band is also discussed. By employing
theoretical stellar population synthesis techniques, we find that using actual
determinations of SFR and AMR of the LMC and SMC, their RGB is populated by
stars much younger (by 9 Gyr) than the Galactic globular cluster counterparts,
on which the I-band (and K-band) TRGB absolute magnitude is calibrated. This
age difference induces a bias in both the photometric metallicity estimates
based on the comparison of RGB colours with globular cluster ones, and the TRGB
distances. The extent of the distance bias is strongly dependent on the
specific TRGB technique applied, and on the assumed I-band BC scale adopted;
the correction to apply to the SMC-LMC distance modulus ranges from 0 up to
+0.10 mag. LGS3 is an example of galaxy populated mainly by old stars, so that
photometric metallicity and distance estimates using globular cluster
calibrations are reliable. However, the relative distance moduli between
Magellanic Clouds and LGS3 are affected by the population effects discussed for
the LMC and SMC. The corrections to apply to the K-band TRGB distances are
larger than the I-band case. Our results clearly show that the presence of a
well developed RGB in the CMD of a stellar system with a complex SFR does not
guarantee that it is populated by globular cluster-like red giants, and
therefore the TRGB method for distance determination has to be applied with
caution.


title: Fe VII lines in the spectrum of RR Telescopii

abstract:
  Thirteen transitions within the ground 3d^2 configuration of Fe VII are
identified in ultraviolet and optical spectra of the symbiotic star RR
Telescopii obtained with the STIS instrument of the Hubble Space Telescope. The
line fluxes are compared with theoretical data computed with the recent atomic
data of K.A. Berrington et al., and high resolution optical spectra from
VLT/UVES are used to identify blends. Seven branching ratios are measured, with
three in good agreement with theory and one affected by blending. The
lambda5277/lambda4943 branching ratio is discrepant by > 3 sigma, indicating
errors in the atomic data for the lambda5277 line. A least-squares minimization
scheme is used to simultaneously derive the temperature, T, and density, N_e,
of the RR Tel nebula, and the interstellar extinction, E(B-V), towards RR Tel
from the complete set of emission lines. The derived values are: log T/K = 4.50
+/- 0.23, log N_e/cm^-3=7.25 +/- 0.05, and E(B-V)<0.27. The extinction is not
well-constrained by the Fe VII lines, but is consistent with the more accurate
value E(B-V)=0.109^{+0.052}_{-0.059} derived here from the Ne V
lambda2974/lambda1574 ratio in the STIS spectrum. Large differences between the
K.A. Berrington et al. electron excitation data and the earlier F.P. Keenan &
P.H. Norrington data-set are demonstrated, and the latter is shown to give
worse agreement with observations.


title:
Search for massive protostellar candidates in the southern hemisphere:
  I. Association with dense gas

abstract:
  (Abridged) We have observed CS and C17O lines, and 1.2 mm cont. emission
towards a sample of 130 high-mass protostellar candidates with DEC<-30 deg.
This is the first step of the southern extension of a project started more than
a decade ago aimed at the identification of massive protostellar candidates. We
selected from the IRAS PSC 429 sources which potentially are compact molecular
clouds. The sample is divided into two groups: the 298 sources with
[25-12]>0.57 and [60-12]>1.30 we call 'High' sources, the remaining 131 we call
'Low' sources. In this paper, we check the association with dense gas and dust
in 130 'Low' sources. We find a detection rate of ca. 85% in CS, demonstrating
a tight association with dense molecular clumps. Among the sources detected in
CS, ca. 76% have also been detected in C17O and ca. 93% in the 1.2 mm cont.
Mm-cont. maps show the presence of clumps with diameters 0.2-2 pc and masses
from a few Msun to 10^5 Msun; H2 volume densities lie between ca. 10^{4.5} and
10^{5.5} cm^{-3}. The L(bol) are 10^3-10^6 Lsun, consistent with embedded
high-mass objects. Based on our results and those found in the literature for
other samples, we conclude that our sources are massive objects probably in a
stage prior to the formation of an HII region. We propose a scenario in which
'High' and 'Low' sources are both made of a massive clump hosting a high-mass
protostellar candidate and a nearby stellar cluster. The difference might be
due to the fact that the IRAS 12mu flux, the best discriminant between the two
groups, is dominated by the emission from the cluster in 'Lows' and from the
massive protostellar object in 'Highs'.


title: On the pulse-width statistics in radio pulsars

abstract:
  The Monte Carlo simulations of pulsar periods, pulse-widths and magnetic
inclination angles are performed. Using the available observational data sets
we study a possible trial parent distribution functions by means of the
Kolmogorov-Smirnov significance tests. We also use an additional condition that
the numbers of generated interpulses, whether from both magnetic poles or from
single pole, are at the observed levels. We conclude that the parent
distribution function of magnetic inclination angles is neither flat nor cosine
but it is a more complicated function with a local maximum near alpha=25deg and
another weaker one near alpha=90deg. The plausible distribution function of
pulsar periods is represented by the gamma function. The beaming fraction
describing the fraction of observable radio pulsars is about 0.12.


title: On the Binarity of Carbon-Enhanced, Metal-Poor Stars

abstract:
  We report on a programme to monitor the radial velocities of a sample of
candidate and confirmed carbon-enhanced, metal-poor (CEMP) stars. We observed
45 targets using the Echelle Spectrographs of three 4m class telescopes. Radial
velocities for these objects were calculated by cross-correlation of their
spectra with the spectrum of HD 140283, and have errors < 1 km/s. Sixteen of
our programme's targets have reported carbon excess, and nine of these objects
also exhibit s-process enhancements (CEMP-s). We combine these stars' radial
velocities with other literature studies in search of binarity. The search
reveals that four of our CEMP-s stars (44%) are in binary systems. Using the
analysis of Lucatello et al. (2004), we find that all the CEMP-s stars in our
sample are binaries. This conclusion implies that CEMP-s stars may be the very
metal-poor relatives of CH and Ba II stars, which are believed to have acquired
their peculiar abundance patterns by mass transfer from a thermally-pulsing AGB
companion.


title: The Ultimate Halo Mass in a LCDM Universe

abstract:
  In the far future of an accelerating LCDM cosmology, the cosmic web of
large-scale structure consists of a set of increasingly isolated halos in
dynamical equilibrium. We examine the approach of collisionless dark matter to
hydrostatic equilibrium using a large N-body simulation evolved to scale factor
a = 100, well beyond the vacuum--matter equality epoch, a_eq ~ 0.75, and 53/h
Gyr into the future for a concordance model universe (Omega_m ~ 0.3,
Omega_Lambda ~ 0.7). The radial phase-space structure of halos -- characterized
at a < a_eq by a pair of zero-velocity surfaces that bracket a dynamically
active accretion region -- simplifies at a > 10 a_eq when these surfaces merge
to create a single zero-velocity surface, clearly defining the halo outer
boundary, rhalo, and its enclosed mass, mhalo. This boundary approaches a fixed
physical size encompassing a mean interior density ~ 5 times the critical
density, similar to the turnaround value in a classical Einstein-deSitter
model. We relate mhalo to other scales currently used to define halo mass
(m200, mvir, m180b) and find that m200 is approximately half of the total
asymptotic cluster mass, while m180b follows the evolution of the inner zero
velocity surface for a < 2 but becomes much larger than the total bound mass
for a > 3. The radial density profile of all bound halo material is well fit by
a truncated Hernquist profile. An NFW profile provides a somewhat better fit
interior to r200 but is much too shallow in the range r200 < r < rhalo.


title: Fueling and morphology of central starbursts

abstract:
  Of the mechanisms proposed to bring gaseous fuel into the central starburst
regions of a galaxy, non-axisymmetries in the gravitational potential set up by
interactions or by bars are among the most promising. Nevertheless, direct
observational evidence for a connection between interactions and bars on the
one hand, and starburst (as well as AGN) activity on the other, remains patchy.
These general issues are reviewed before proceeding to discuss, within this
context, massive star formation in the circumnuclear regions of spiral
galaxies, in particular star-forming nuclear rings and pseudo-rings. Such rings
are common, and are closely linked to the dynamics of their host galaxy, which
in almost all cases is barred. The possible existence of a population of
nuclear rings on scales which are too small for detection with standard ground-
or even space-based techniques will be discussed.


title: Modeling Dynamics in the Central Regions of Disk Galaxies

abstract:
  The central regions of disk galaxies are hosts to supermassive black holes
whose masses show a tight correlation with the properties of surrounding
stellar bulges. While the exact origin of this dependency is not clear, it can
be related to the very basic properties of dark matter halos and the associated
gas and stellar dynamics in the central kpc of host galaxies. In this review we
discuss some of the recent developments in modeling the wide spectrum of
dynamical processes which can be affiliated with the above phenomena, such as
the structure of molecular tori in AGN, structure formation in triaxial halos,
and dissipative and non-dissipative dynamics in nested bar systems, with a
particular emphasis on decoupling of gaseous nuclear bars. We also briefly
touch on the subject of fueling the nuclear starbursts and AGN.


title: Time Domain Explorations With Digital Sky Surveys

abstract:
  One of the new frontiers of astronomical research is the exploration of time
variability on the sky at different wavelengths and flux levels. We have
carried out a pilot project using DPOSS data to study strong variables and
transients, and are now extending it to the new Palomar-QUEST synoptic sky
survey. We report on our early findings and outline the methodology to be
implemented in preparation for a real-time transient detection pipeline. In
addition to large numbers of known types of highly variable sources (e.g., SNe,
CVs, OVV QSOs, etc.), we expect to find numerous transients whose nature may be
established by a rapid follow-up. Whereas we will make all detected variables
publicly available through the web, we anticipate that email alerts would be
issued in the real time for a subset of events deemed to be the most
interesting. This real-time process entails many challenges, in an effort to
maintain a high completeness while keeping the contamination low. We will
utilize distributed Grid services developed by the GRIST project, and implement
a variety of advanced statistical and machine learning techniques.


title:
The prospects for finding brown dwarfs in eclipsing binary systems and
  measuring brown dwarf properties

abstract:
  We present the results of a simulation to investigate the prospects of
measuring mass, age, radius, metallicity and luminosity data for brown dwarfs
in fully eclipsing binary systems around late K and early M dwarfs identified
by ultra-wide-field transit surveys. These surveys will monitor approximately a
million K and M dwarfs at a level sufficient to detect transits of low
luminosity companions. We look at the current observational evidence for such
systems, and suggest that about 1% of late K and early-mid M dwarfs could have
a very close BD companion. With this assumption, and using the SuperWASP
transit survey as an example, our simulation predicts that 400 brown dwarfs in
fully eclipsing binary systems could be discovered. All of these eclipsing
binaries could yield accurate brown dwarf mass and radius measurements. By
inferring the brown dwarf effective temperature distribution, assuming a
uniform age spread and an alpha=0.5 companion brown dwarf mass function, the
simulation estimates that brown dwarf brightness could also be measurable (at
the 10% level) for about 60 of these binary systems from the secondary eclipse.
Irradiation of the brown dwarfs will be below the 10% level for about 70% of
these systems, meaning that the measured brown dwarf brightnesses should
generally be the same as those of free-floating counterparts. The predicted age
distribution of the primaries is dominated by young systems, and about 20
binaries could be younger than 1Gyr. We suggest that many of these young binary
systems will be members of ``kinematic moving groups'', allowing their ages to
be accurately constrained.


title: Chandra Observations of WZ Sge in Superoutburst

abstract:
  We present seven separate Chandra observations of the 2001 superoutburst of
WZ Sge. The high-energy outburst was dominated by intense EUV emission lines,
which we interpret as boundary layer emission scattered into our line of sight
in an accretion disc wind. The direct boundary layer emission was hidden from
view, presumably by the accretion disc. The outburst orbital hump (OOH) was
detected in the EUV, but the common superhump was not, indicating a geometric
mechanism in the former and a dissipative mechanism in the latter. X-rays
detected during outburst were not consistent with boundary layer emission and
we argue that there must be a second source of X-rays in dwarf novae in
outburst.


title:
The stellar mass function of galaxies to z ~ 5 in the Fors Deep and
  GOODS-S fields

abstract:
  We present a measurement of the evolution of the stellar mass function (MF)
of galaxies and the evolution of the total stellar mass density at 0<z<5. We
use deep multicolor data in the Fors Deep Field (FDF; I-selected reaching
I_AB=26.8) and the GOODS-S/CDFS region (K-selected reaching K_AB=25.4) to
estimate stellar masses based on fits to composite stellar population models
for 5557 and 3367 sources, respectively. The MF of objects from the GOODS-S
sample is very similar to that of the FDF. Near-IR selected surveys hence
detect the more massive objects of the same principal population as do
I-selected surveys. We find that the most massive galaxies harbor the oldest
stellar populations at all redshifts. At low z, our MF follows the local MF
very well, extending the local MF down to 10^8 Msun. The faint end slope is
consistent with the local value of alpha~1.1 at least up to z~1.5. Our MF also
agrees very well with the MUNICS and K20 results at z<2. The MF seems to evolve
in a regular way at least up to z~2 with the normalization decreasing by 50% to
z=1 and by 70% to z=2. Objects having M>10^10 Msun which are the likely
progenitors of todays L* galaxies are found in much smaller numbers above z=2.
However, we note that massive galaxies with M>10^11 Msun are present even to
the largest redshift we probe. Beyond z=2 the evolution of the mass function
becomes more rapid. We find that the total stellar mass density at z=1 is 50%
of the local value. At z=2, 25% of the local mass density is assembled, and at
z=3 and z=5 we find that at least 15% and 5% of the mass in stars is in place,
respectively. The number density of galaxies with M>10^11 Msun evolves very
similarly to the evolution at lower masses. It decreases by 0.4 dex to z=1, by
0.6 dex to z=2, and by 1 dex to z=4.


title:
STIS ultraviolet/optical spectroscopy of `warm' ultraluminous infrared
  galaxies

abstract:
  (Abridged) We present high spatial resolution ultraviolet and optical
spectroscopy, obtained using the Space Telescope Imaging Spectrograph on board
the Hubble Space Telescope, of nuclear structures within four `warm'
Ultraluminous Infrared Galaxies (ULIRGs). We find an AGN in at least three, and
probably all four of our sample, hosted in a compact, optically luminous
`knot'. In three cases these knots were previously identified as a putative AGN
nucleus from multiband optical imaging. Three of the sample also harbor a
starburst in one or more knots, suggesting that the optically luminous knots
seen in local ULIRGs are the most likely sites of the dust-shrouded starburst
and AGN activity that power the infrared emission. The four AGN have a diverse
range of properties; two are classical narrow line AGN, one shows both broad
and narrow lines and evidence for lines of sight from the narrow through to the
broad line regions, and one is plausibly a FeLoBAL AGN. The probable presence
in one object of an FeLoBAL AGN, which are extremely rare in the QSO
population, supports the idea that LoBAL AGN may be youthful systems shrouded
in gas and dust rather than AGN viewed along a certain line of sight. The three
starbursts for which detailed constraints are possible show a smaller range in
properties; all three bursts are young with two having ages of ~4Myr and the
third having an age of 20Myr, suggesting that ULIRGs undergo several bursts of
star formation during their lifetimes. None of the starbursts show evidence for
Initial Mass Function slopes steeper than about 3.3. The metallicities of the
knots for which metallicities can be derived are all at least 1.5 times the
Solar value. The properties of one further starburst knot are consistent with
it being the forming core of an elliptical galaxy.


title: Formation and Evolution of the Self-Interacting Dark Matter Halos

abstract:
  We have derived the first, fully-cosmological, similarity solutions for CDM
halo formation in the presence of nongravitational collisionality, which
provides an analytical theory of the effect of the self-interacting dark matter
(SIDM) hypothesis on halo density profiles. Collisions transport heat inward,
which produces a constant-density core, while continuous infall pumps energy
into the halo to stabilize the core against gravothermal catastrophe. These
solutions improve upon earlier attempts to model the formation and evolution of
SIDM halos, offer deeper insight than existing N-body experiments, and yield a
more precise determination of the dependence of halo density profile on the
value of the CDM self-interaction cross section. Different solutions arise for
different values of the dimensionless collisionality parameter Q = s rho_b r_v
\~ r_v/l_mfp, where s is the scattering cross section per unit mass, rho_b is
the cosmic mean matter density, r_v is halo virial radius and l_mfp is the
collision mean free path. The maximum flattening of central density occurs for
an intermediate value of Q, Q_th, at which the halo is maximally relaxed to
isothermality. The density profiles with constant-density cores preferred by
dwarf and LSB rotation curves are best fit by the maximally-flattened (Q=Q_th)
solution. If we assume that dwarfs and LSB galaxies formed at their typical
collapse epoch in LCDM, then the value of s which makes Q=Q_th is s ~ 200
cm^{2}/g, much higher than previous estimates, s ~ 0.5-5 cm^{2}/g, based on
N-body experiments. If s is independent of collision velocity, then the same
value s ~ 200 cm^{2}/g would make Q>Q_th for clusters, which typically formed
only recently, resulting in relatively less flattening of their central density
profile and a smaller core.


title: Dark Matter Candidates

abstract:
  It is now widely accepted that most of mass--energy in the universe is
unobserved except by its gravitational effects. Baryons make only about 4% of
the total, with "dark matter" making up about 23% and the "dark energy"
responsible for the accelerated expansion of the universe making up the
remainder. We focus on the dark matter, which is the primary constituent of
galaxies. We outline the observed properties of this material, enumerating some
candidates covering 90 orders of magnitude in mass. Finally, we argue that the
weak scale (100 GeV) is relevant to new physics, including the dark matter
problem.


title:
On the Relationship between the Continuum Enhancement and Hard X-ray
  Emission in a White-Light Flare

abstract:
  We investigate the relationship between the continuum enhancement and the
hard X-ray (HXR) emission of a white-light flare on 2002 September 29. By
reconstructing the RHESSI HXR images in the impulsive phase, we find two bright
conjugate footpoints (FPs) on the two sides of the magnetic neutral line. Using
the thick-target model and assuming a low-energy cutoff of 20 keV, the energy
fluxes of non-thermal electron beams bombarding FPs A and B are estimated to be
1.0 10^10 and 0.8 10^10 ergs/cm^2/s, respectively. However, the continuum
enhancement at the two FPs is not simply proportional to the electron beam
flux. The continuum emission at FP B is relatively strong with a maximum
enhancement of about 8% and correlates temporally well with the HXR profile;
however, that at FP A is less significant with an enhancement of only about
4-5%, regardless of the relatively strong beam flux. By carefully inspecting
the Halpha line profiles, we ascribe such a contrast to different atmospheric
conditions at the two FPs. The Halpha line profile at FP B exhibits a
relatively weak amplitude with a pronounced central reversal, while the profile
at FP A is fairly strong without a visible central reversal. This indicates
that in the early impulsive phase of the flare, the local atmosphere at FP A
has been appreciably heated and the coronal pressure is high enough to prevent
most high-energy electrons from penetrating into the deeper atmosphere; while
at FP B, the atmosphere has not been fully heated, the electron beam can
effectively heat the chromosphere and produce the observed continuum
enhancement via the radiative backwarming effect.


title:
Correlations among Multi-Wavelength Luminosities of Star-Forming
  Galaxies

abstract:
  It has been known for two decades that a tight correlation exists between
far-infrared (FIR) and radio (1.4 and 4.8 GHz) global fluxes/luminosities from
galaxies, which may be explained in terms of massive star formation activities
in these galaxies. For this very reason, a correlation might also exist between
X-ray and FIR/radio global luminosities of galaxies. We analyze data from {\it
ROSAT} All-Sky Survey and {\it IRAS} to show that such correlation does indeed
exist between FIR (42.5$-122.5\mu$m) and soft X-ray (0.1$-$2.4keV) luminosities
in active star-forming galaxies (ASFGs).In order to establish a physical
connection between the $L_{\rmX}-L_{\rm FIR}$ correlation and global star
formation rate (SFR) in galaxies, we empirically derive both $L_{\rm X}-L_{\rm
B}$ and $L_{\rm FIR}-L_{\rm B}$ relations. Futhermore, we propose a relation
between soft X-ray luminosity and SFR in star-forming galaxies. To further
understand the $L_{\rm X}-L_{\rm FIR}$ relation, we construct an empirical
model in which both FIR and X-ray emissions consist of two components with one
being closely associated with star formation and the other not.


title:
Safety in numbers: Gravitational Lensing Degradation of the Luminosity
  Distance-Redshift Relation

abstract:
  Observation of the expansion history of the Universe allows exploration of
the physical properties and energy density of the Universe's various
constituents. Standardizable candles such as Type Ia supernovae remain one of
the most promising and robust tools in this endeavor, by allowing for a direct
measure of the luminosity distance-redshift curve, and thereby producing
detailed studies of the dark energy responsible for the Universe's currently
accelerating expansion. As such observations are pushed to higher redshifts,
the observed flux is increasingly affected by gravitational lensing
magnification due to intervening structure along the line-of-sight. We simulate
and analyze the non-Gaussian probability distribution function of
de/amplification due to lensing of standard candles, quantify the effect of a
convolution over many independent sources (which acts to restore the intrinsic
average (unlensed) luminosity due to flux conservation), and compute the
additional uncertainty due to lensing on derived cosmological parameters. For
example, the ``degradation factor'' due to lensing is a factor of three
reduction in the effective number of usable supernovae at z=1.5 (for sources
with intrinsic flux dispersion of 10%). We also derive a useful expression for
the effective increased dispersion in standard candles due to lensing, as a
function of redshift.


title:
Optical polarization from aligned atoms as a new diagnostic of
  Astrophysical magnetic fields

abstract:
  Population of levels of the hyperfine and fine split ground state of an atom
is affected by radiative transitions induced by anisotropic radiation flux.
Such aligned atoms precess in the external magnetic field and this affects
properties of polarized radiation arising from both scattering and absorption
by atoms. As the result the degree of light polarization depends on the
direction of the magnetic field. This provides a perspective tool for studies
of astrophysical magnetic fields using optical and UV polarimetry. We provide
calculations for several atoms and ions that can be used to study magnetic
fields in interplanetary medium, interstellar medium, circumstellar regions and
quasars.


title:
A Circular Planetary Nebula around the OH/IR Star OH 354.88-0.54 (V1018
  Sco)

abstract:
  New deep, high-resolution H-alpha imagery from the UK Schmidt Telescope
(UKST) Unit's H-alpha survey of the Southern Galactic Plane reveals the
presence of a faint, highly circular, planetary nebula surrounding a very long
period variable star (now known as V1018 Sco), first discovered as a 1612-MHz
OH maser, OH 354.88-0.54. The nebular phase-lag distance, diameter, and radial
velocity are 3.2kpc, 0.3pc, and 13km/s, respectively. Combining the maser
attributes with near-, mid-, and far-infrared data and with our optical
spectrum of the ring we conclude that the object was an intermediate mass AGB
star (initial stellar mass >4Msun in which the fast wind has recently turned
on, ionizing previously shed circumstellar material. Hence, we speculate that
we may be witnessing a hitherto unobserved phase of PN evolution, in which a PN
has only recently started to form around a star that is unequivocally still in
its AGB


title:
Extragalactic Planetary Nebulae: Observational Challenges & Future
  Prospects

abstract:
  The study of extragalactic planetary nebulae (EPN) is a rapidly expanding
field. The advent of powerful new instrumentation such as the PN spectrograph
has led to an avalanche of new EPN discoveries both within and between
galaxies. We now have thousands of EPN detections in a heterogeneous selection
of nearby galaxies and their local environments, dwarfing the combined galactic
detection efforts of the last century. Key scientific motivations driving this
rapid growth in EPN research and discovery have been the use of the PNLF as a
standard candle, as dynamical tracers of their host galaxies and dark matter
and as probes of Galactic evolution. This is coupled with the basic utility of
PN as laboratories of nebula physics and the consequent comparison with theory
where population differences, abundance variations and star formation history
within and between stellar systems informs both stellar and galactic evolution.
Here we pose some of the burning questions, discuss some of the observational
challenges and outline some of the future prospects of this exciting,
relatively new, research area as we strive to go fainter, image finer, see
further and survey faster than ever before and over a wider wavelength regime


title: Proposed nomenclature for Extragalactic Planetary Nebulae

abstract:
  The ability to identify and distinguish between the wide variety of celestial
objects benefits from application of a systematic and logical nomenclature.
This often includes value-added information within the naming convention which
can aid in placing the object positionally either via an RA/DEC or l,b
concatenation. All new nomenclatures should be created following IAU
guidelines. However as the number density of specific object types on the sky
increases, as in the case of PN in external galaxies, a useful positional
identifier becomes problematic. This brief but timely paper attempts to
progress the debate on this vexing issue for the case of extragalactic
planetary nebulae (EPN). There is a clear need to rationalise the current
ad-hoc system now that many thousands of Extragalactic PN are being discovered.


title:
Age and Metallicity Estimation of Globular Clusters from Stromgren
  Photometry

abstract:
  We present a new technique for the determination of age and metallicity in
composite stellar populations using Stromgren filters. Using principal
component (PC) analysis on multi-color models, we isolate the range of values
necessary to uniquely determine age and metallicity effects. The technique
presented herein can only be applied to old (tau > 3 Gyrs) stellar systems
composed of simple stellar populations, such as globular clusters and
elliptical galaxies. Calibration using new photometry of 40 globular clusters
with spectroscopic [Fe/H] values and main sequence fitted ages links the PC
values to the Str\"omgren colors for an accuracy of 0.2 dex in metallicity and
0.5 Gyrs in age.


title:
Exoplanets imaging with a Phase-Induced Amplitude Apodization
  Coronagraph - I. Principle

abstract:
  Using 2 aspheric mirrors, it is possible to apodize a telescope beam without
losing light or angular resolution: the output beam is produced by
``remapping'' the entrance beam to produce the desired light intensity
distribution in a new pupil. We present the Phase-Induced Amplitude Apodization
Coronagraph (PIAAC) concept, which uses this technique, and we show that it
allows efficient direct imaging of extrasolar terrestrial planets with a
small-size telescope in space. The suitability of the PIAAC for exoplanet
imaging is due to a unique combination of achromaticity, small inner working
angle (about 1.5 $\lambda/d$), high throughput, high angular resolution and
large field of view. 3D geometrical raytracing is used to investigate the
off-axis aberrations of PIAAC configurations, and show that a field of view of
more than 100 $\lambda/d$ in radius is available thanks to the correcting
optics of the PIAAC. Angular diameter of the star and tip-tilt errors can be
compensated for by slightly increasing the size of the occulting mask in the
focal plane, with minimal impact on the system performance. Earth-size planets
at 10 pc can be detected in less than 30s with a 4m telescope. Wavefront
quality requirements are similar to classical techniques.


title: Far-ultraviolet Spectroscopy of Magnetic Cataclysmic Variables

abstract:
  We have obtained HST/STIS data for a total of eleven polars as part of a
program aimed to compile a homogeneous database of high-quality far-ultraviolet
(FUV) spectra for a large number of cataclysmic variables (CVs). Of the eleven
polars, eight were found in a state of low accretion activity (V347Pav, VVPup,
V834Cen, BLHyi, MRSer, STLMi, RXJ1554.2+2721 and V895Cen) and three in a state
of high activity (CDInd, ANUMa and UWPic). The STIS spectra of the low-state
polars unambiguously reveal the photospheric emission of their white dwarf (WD)
primaries. We have used pure hydrogen WD models to fit the FUV spectra of the
low-state systems (except RX J1554.2+2721, which is a high-field polar) in
order to measure the WD effective temperatures. In all cases, the fits could be
improved by adding a second component, which is presumably due to residual
accretion onto the magnetic pole of the WD. The WD temperatures obtained range
from 10800K to 14200K for log g = 8.0. Comparing the WD temperatures of polars
to those of non-magnetic CVs, we find that at any given orbital period the WDs
in polars are colder than those in non-magnetic CVs. The temperatures of polars
below the period gap are consistent with gravitational radiation as the only
active angular momentum loss mechanism. The differences in WD effective
temperatures between polars and non-magnetic CVs are significantly larger above
the period gap, suggesting that magnetic braking in polars might be reduced by
the strong field of the primary.


title:
Cosmic crystallography using short-lived objects - active galactic
  nuclei

abstract:
  Cosmic crystallography is based on the principle that peaks in the pair
separation histogram (PSH) of objects in a catalogue should be induced by the
high number of topologically lensed pairs that are separated by Clifford
translations, in excess to ``random'' pairs of objects. Here we present
modifications of this method that successively improve the signal-to-noise
ratio by removing a large part of the noise and then false signals induced by
selection effects. Given the transient nature of the most readily available
tracer objects, active galactic nuclei (AGNs), the former is possible because a
natural filter for removing many of the noise pairs is available: when counting
pairs of objects in order to create PSHs, only those with nearly identical
redshifts need to be counted. This redshift filter (a maximum value of $\Delta
z/z = 0.005$) was applied to a compilation of AGN catalogues. Further noise was
removed by applying a second filter, a maximum angle $\Delta \theta =0.075$
rad, and a minimum number of pairs $\protect\npairs=3$ to find each ``bunch of
pairs'' (BoP) where the {\em vectors} (in Euclidean comoving space) defined by
pairs are required to be nearly equal, whereas in the PSH only the {\em
lengths} must be nearly equal. These filters reveal significant signals, which,
however, are due to selection effects. A third filter, a minimum length
$\Lselec=150$ {\hMpc} between the (parallel) vectors in a BoP, is found to
effectively remove these selection effect pairs. After application of these
successive filters, no significant topological signal was found.


title: Spin Correlation in Binary Systems

abstract:
  We examine the correlation of projected rotational velocities in binary
systems. It is an extension of previous work (Steinitz and Pyper, 1970; Levato,
1974). An enlarged data basis and new tests enable us to conclude that there is
indeed correlation between the projected rotational velocities of components of
binaries. In fact we suggest that spins are already correlated.


title: On the progenitor of V838 Monocerotis

abstract:
  We summarize and analyze the available observational data on the progenitor
and the enviroment of V838 Mon. From the available photometric data for the
progenitor of V838 Mon we exclude the possibility that the object before
eruption was an evolved red giant star (AGB or RGB star). We find that most
likely it was a main sequence or pre-main sequence star of ~ 5-10 M_sun. From
the light echo structure and evolution we conclude that the reflecting dust is
of interstellar nature rather than blown by V838 Mon in the past. We discuss
the IRAS and CO data for interstellar medium observed near the position of V838
Mon. Several interstellar molecular regions have radial velocities similar to
that of V838 Mon, so dust seen in the light echo might be related to one of
them.


title:
Spectral energy distributions and luminosities of galaxies and AGN in
  the SPITZER SWIRE Legacy Survey

abstract:
  We discuss optical associations, spectral energy distributions and
photometric redshifts for SWIRE sources in the ELAIS-N1 area and the Lockman
Validation Field. The band-merged IRAC (3.6, 4.5, 5.8 and 8.0 mu) and MIPS (24,
70, 160 mu) data have been associated with optical UgriZ data from the INT Wide
Field Survey in ELAIS-N1, and with our own optical Ugri data in Lockman-VF. The
spectral energy distributions of selected ELAIS sources in N1 detected by
SWIRE, most with spectroscopic redshifts, are modelled in terms of a simple set
of galaxy and quasar templates in the optical and near infrared, and with a set
of dust emission templates (cirrus, M82 starburst, Arp 220 starburst, and AGN
dust torus) in the mid infrared. The optical data, together with the IRAC 3.6
and 4.5 mu data, have been used to determine photometric redshifts. For
galaxies with known spectroscopic redshifts there is a notable improvement in
the photometric redshift when the IRAC data are used, with a reduction in the
rms scatter from 10% in (1+z) to 7%. The photometric redshifts are used to
derive the 3.6 and 24 mu redshift distribution and to compare this with the
predictions of models. For those sources with a clear mid infrared excess,
relative to the galaxy starlight model used for the optical and near infrared,
the mid and far infrared data are modelled in terms of the same dust emission
templates. The proportions found of each template type are: cirrus 31%, M82
29%, Arp 220 10%, AGN dust tori 29%. The distribution of the different infrared
sed types in the L_{ir}/L_{opt} versus L_{ir} plane, where L_{ir} and L_{opt}
are the infrared and optical bolometric luminosities, is discussed.


title: Evolutionary Memory in Binary Systems?

abstract:
  Correlation between the spins (rotational velocities) in binaries has
previously been established. We now continue and show that the degree of spin
correlation is independent of the components' separation. Such a result might
be related for example to Zhang's non-linear model for the formation of binary
stars from a nebula.


title:
Dynamical modelling of stars and gas in NGC2974: determination of
  mass-to-light ratio, inclination and orbital structure by Schwarzschild's
  method

abstract:
  We study the large-scale stellar and gaseous kinematics of the E4 galaxy
NGC2974, based on panoramic integral-field data obtained with SAURON. We
quantify the velocity fields with Fourier methods (kinemetry), and show that
the large-scale kinematics is largely consistent with axisymmetry. We construct
general axisymmetric dynamical models for the stellar motions using
Schwarzschild's orbit-superposition method, and compare the inferred
inclination and mass-to-light ratio with the values obtained by modelling the
gas kinematics. Both approaches give consistent results. However we find that
the stellar models provide fairly weak constraints on the inclination. The
intrinsic orbital distribution of NGC2974, which we infer from our model, is
characterised by a large-scale stellar component of high angular momentum. We
create semi-analytic test models, resembling NGC2974, to study the ability of
Schwarzschild's modelling technique to recover the given input parameters
(mass-to-light ratio and inclination) and the distribution function. We also
test the influence of a limited spatial coverage on the recovery of the
distribution function (i.e. the orbital structure). We find that the models can
accurately recover the input mass-to-light ratio, but we confirm that even with
perfect input kinematics the inclination is only marginally constrained. This
suggests a possible degeneracy in the determination of the inclination, but
further investigations are needed to clarify this issue. For a given potential,
we find that the analytic distribution function of our test model is well
recovered by the three-integral model within the spatial region constrained by
integral-field kinematics.


title:
Anisotropies in the Neutrino Fluxes and Heating Profiles in
  Two-dimensional, Time-dependent, Multi-group Radiation Hydrodynamics
  Simulations of Rotating Core-Collapse Supernovae

abstract:
  Using the 2D multi-group, flux-limited diffusion version of the code
VULCAN/2D, that also incorporates rotation, we have calculated the collapse,
bounce, shock formation, and early post-bounce evolutionary phases of a
core-collapse supernova for a variety of initial rotation rates. This is the
first series of such multi-group calculations undertaken in supernova theory
with fully multi-D tools. We find that though rotation generates
pole-to-equator angular anisotropies in the neutrino radiation fields, the
magnitude of the asymmetries is not as large as previously estimated. Moreover,
we find that the radiation field is always more spherically symmetric than the
matter distribution, with its plumes and convective eddies. We present the
dependence of the angular anisotropy of the neutrino fields on neutrino
species, neutrino energy, and initial rotation rate. Only for our most rapidly
rotating model do we start to see qualitatively different hydrodynamics, but
for the lower rates consistent with the pre-collapse rotational profiles
derived in the literature the anisotropies, though interesting, are modest.
This does not mean that rotation does not play a key role in supernova
dynamics. The decrease in the effective gravity due to the centripetal effect
can be quite important. Rather, it means that when a realistic mapping between
initial and final rotational profiles and 2D multi-group
radiation-hydrodynamics are incorporated into collapse simulations the
anisotropy of the radiation fields may be only a secondary, not a pivotal
factor, in the supernova mechanism.


title:
Identification of a complete sample of northern ROSAT All-Sky Survey
  X-ray sources. VIII. The late-type stellar component

abstract:
  We present results of an investigation of the X-ray properties, age
distribution, and kinematical characteristics of a high-galactic latitude
sample of late-type field stars selected from the ROSAT All-Sky Survey (RASS).
The sample comprises 254 RASS sources with optical counterparts of spectral
types F to M distributed over six study areas located at |b| >= 20 degr, and
DEC >= -9 degr. A detailed study was carried out for the subsample of ~200 G,
K, and M stars. Lithium abundances were determined for 179 G-M stars. Radial
velocities were measured for most of the 141 G and K type stars of the sample.
Combined with proper motions these data were used to study the age distribution
and the kinematical properties of the sample. Based on the lithium abundances
half of the G-K stars were found to be younger than the Hyades (660 Myr). About
25% are comparable in age to the Pleiades (100 Myr). A small subsample of 10
stars is younger than the Pleiades. They are therefore most likely pre-main
sequence stars. Kinematically the PMS and Pleiades-type stars appear to form a
group with space velocities close to the Castor moving group but clearly
distinct from the Local Association.


title: CCD uvby-beta photometry of the young open cluster NGC 663

abstract:
  NGC 663 is a young, moderately rich open cluster, known to contain one of the
largest fractions of Be stars among all galactic clusters. In this work we
present CCD uvby-beta photometry for stars in its central area. We have used
these data to obtain the main cluster physical parameters. We find that the
reddening is highly variable, with values ranging from E(b-y)=0.639+/-0.032 in
the central part to E(b-y)=0.555+/-0.038 in the south-east. The distance
modulus is found to be 11.6+/-0.1 mag.(2.1 Kpc), and the age log t=7.4+/-0.1
years (25+7/-5 Myr). The age obtained is consistent with the interpretation of
the Be phenomenon as an evolutionary effect.


title: The Disk Atmospheres of Three Herbig Ae/Be Stars

abstract:
  We present infrared (IR) spectrophotometry ($R \simeq 180$) of three Herbig
Ae/Be stars surrounded by possible protoplanetary disks: HD 150193, HD100546
and HD 179218. We construct a mid-IR spectral energy distributions (SED) for
each object by using $7.6 - 13.2$ \micron HIFOGS spectra, 2.4 -- 45 \micron\
spectrophotometry from the {\it ISO} SWS, the 12, 25, 60, and 100 \micron\
photometric points from IRAS, and for HD 179218, photometric bolometric data
points from the Mt. Lemmon Observing Facility. The SEDs are modeled by using an
expanded version of the \citet{chigol97} two-layer, radiative and hydrostatic
equilibrium, passive disk. This expanded version includes the emission from
Mg-pure crystalline olivine (forsterite) grains in the disk surface layer. HD
150193 contains no crystals while HD 100546 and HD 179218 respectively show
evidence of having crystalline silicates in the surface layers of their disks.
We find that the inner region of HD100546 has a 37% higher
crystalline-to-amorphous silicate ratio in its inner disk region ($\leq 5$ AU)
compared to the outer disk region, while the inner disk region of HD 179218 has
a 84% higher crystalline-to-amorphous silicate ratio in its inner disk region
($\leq 5$ AU) compared to the outer region. HD 150193 is best-fit by a small
disk ($\sim 5$ AU in radius) while HD 100546 and HD 179218 are best fit by
larger disks ($\sim 150$ AU in radius).


title:
Non-parametric mass reconstruction of A1689 from strong lensing data
  with SLAP

abstract:
  We present the mass distribution in the central area of the cluster A1689 by
fitting over 100 multiply lensed images with the non-parametric Strong Lensing
Analysis Package (SLAP, Diego et al. 2004). The surface mass distribution is
obtained in a robust way finding a total mass of 0.25E15 M_sun/h within a 70''
circle radius from the central peak. Our reconstructed density profile fits
well an NFW profile with small perturbations due to substructure and is
compatible with the more model dependent analysis of Broadhurst et al. (2004a)
based on the same data. Our estimated mass does not rely on any prior
information about the distribution of dark matter in the cluster. The peak of
the mass distribution falls very close to the central cD and there is
substructure near the center suggesting that the cluster is not fully relaxed.
We also examine the effect on the recovered mass when we include the
uncertainties in the redshift of the sources and in the original shape of the
sources. Using simulations designed to mimic the data, we identify some biases
in our reconstructed mass distribution. We find that the recovered mass is
biased toward lower masses beyond 1 arcmin (150 kpc) from the central cD and
that in the very center we may be affected by degeneracy problems. On the other
hand, we confirm that the reconstructed mass between 25'' and 70'' is a robust,
unbiased estimate of the true mass distribution and is compatible with an NFW
profile.


title:
The Surprisingly Steep Mass Profile of Abell 1689, from a Lensing
  Analysis of Subaru Images

abstract:
  Subaru observations of A1689 (z=0.183) are used to derive an accurate,
model-independent mass profile for the entire cluster, r<2 Mpc/h, by combining
magnification bias and distortion measurements. The projected mass profile
steepens quickly with increasing radius, falling away to zero at r~1.0 Mpc/h,
well short of the anticipated virial radius. Our profile accurately matches
onto the inner profile, r<200 kpc/h, derived from deep HST/ACS images. The
combined ACS and Subaru information is well fitted by an NFW profile with
virial mass, (1.93 \pm 0.20)10^15 M_sun, and surprisingly high concentration,
c_vir=13.7^{+1.4}_{-1.1}, significantly larger than theoretically expected
(c_vir~4), corresponding to a relatively steep overall profile. A slightly
better fit is achieved with a steep power-law model that has its 2D logarithmic
slope -3 and core radius theta_c~1.7' (r_c~210 kpc/h), whereas an isothermal
profile is strongly rejected. These results are based on a reliable sample of
background galaxies selected to be redder than the cluster E/S0 sequence. By
including the faint blue galaxy population a much smaller distortion signal is
found, demonstrating that blue cluster members significantly dilute the true
signal for r~400 kpc/h. This contamination is likely to affect most weak
lensing results to date.


title:
Bypass to Turbulence in Hydrodynamic Accretion Disks: An Eigenvalue
  Approach

abstract:
  Cold accretion disks such as those in star-forming systems, quiescent
cataclysmic variables, and some active galactic nuclei, are expected to have
neutral gas which does not couple well to magnetic fields. The turbulent
viscosity in such disks must be hydrodynamic in origin, not
magnetohydrodynamic. We investigate the growth of hydrodynamic perturbations in
a linear shear flow sandwiched between two parallel walls. The unperturbed flow
is similar to plane Couette flow but with a Coriolis force included. Although
there are no exponentially growing eigenmodes in this system, nevertheless,
because of the non-normal nature of the eigenmodes, it is possible to have a
large transient growth in the energy of perturbations. For a constant angular
momentum disk, we find that the perturbation with maximum growth has a
wave-vector in the vertical direction. The energy grows by more than a factor
of 100 for a Reynolds number R=300 and more than a factor of 1000 for R=1000.
Turbulence can be easily excited in such a disk, as found in previous numerical
simulations. For a Keplerian disk, on the other hand, similar vertical
perturbations grow by no more than a factor of 4, explaining why the same
simulations did not find turbulence in this system. However, certain other
two-dimensional perturbations with no vertical structure do exhibit modest
growth. For the optimum two-dimensional perturbation, the energy grows by a
factor of ~100 for R~10^4.5 and by a factor of 1000 for R~10^6. It is
conceivable that these two-dimensional disturbances might lead to
self-sustained turbulence. The Reynolds numbers of cold astrophysical disks are
much larger even than 10^6, therefore, hydrodynamic turbulence may be possible
in disks.

categories: astro-ph cond-mat.soft cond-mat.stat-mech physics.flu-dyn


title:
Bypass to Turbulence in Hydrodynamic Accretion: Lagrangian Analysis of
  Energy Growth

abstract:
  Despite observational evidence for cold neutral astrophysical accretion
disks, the viscous process which may drive the accretion in such systems is not
yet understood. While molecular viscosity is too small to explain the observed
accretion efficiencies by more than ten orders of magnitude, the absence of any
linear instability in Keplerian accretion flows is often used to rule out the
possibility of turbulent viscosity. Recently, the fact that some fine tuned
disturbances of any inviscid shear flow can reach arbitrarily large transient
growth has been proposed as an alternative route to turbulence in these
systems. We present an analytic study of this process for 3D plane wave
disturbances of a general rotating shear flow in Lagrangian coordinates, and
demonstrate that large transient growth is the generic feature of
non-axisymmetric disturbances with near radial leading wave vectors. The
maximum energy growth is slower than quadratic, but faster than linear in time.
The fastest growth occurs for two dimensional perturbations, and is only
limited by viscosity, and ultimately by the disk vertical thickness.
  After including viscosity and vertical structure, we find that, as a function
of the Reynolds number, R, the maximum energy growth is approximately 0.4
(R/log R)^{2/3}, and put forth a heuristic argument for why R > 10^4 is
required to sustain turbulence in Keplerian disks. Therefore, assuming that
there exists a non-linear feedback process to replenish the seeds for transient
growth, astrophysical accretion disks must be well within the turbulent regime.
However, large 3D numerical simulations running for many orbital times, and/or
with fine tuned initial conditions, are required to confirm Keplerian
hydrodynamic turbulence on the computer.


title:
Gravitational Theory, Galaxy Rotation Curves and Cosmology without Dark
  Matter

abstract:
  Einstein gravity coupled to a massive skew symmetric field F_{\mu\nu\lambda}
leads to an acceleration law that modifies the Newtonian law of attraction
between particles. We use a framework of non-perturbative renormalization group
equations as well as observational input to characterize special
renormalization group trajectories to allow for the running of the effective
gravitational coupling G and the coupling of the skew field to matter. The
latter lead to an increase of Newton's constant at large galactic and
cosmological distances. For weak fields a fit to the flat rotation curves of
galaxies is obtained in terms of the mass (mass-to-light ratio M/L) of
galaxies. The fits assume that the galaxies are not dominated by exotic dark
matter and that the effective gravitational constant G runs with distance
scale. The equations of motion for test particles yield predictions for the
solar system and the binary pulsar PSR 1913+16 that agree with the
observations. The gravitational lensing of clusters of galaxies can be
explained without exotic dark matter. An FLRW cosmological model with an
effective G=G(t) running with time can lead to consistent fits to cosmological
data without assuming the existence of exotic cold dark matter.


title: A Wide-Field Survey of the Fornax Dwarf Spheroidal Galaxy

abstract:
  The results of a photometric survey of the Fornax dwarf spheroidal galaxy are
presented herein. Accurate photometry in two colours (V and I) was collected
over a 10 square degree area centred on the Fornax system with the aim of
searching for extra-tidal structure. The data were complete to a magnitude of
V=20, or approximately one magnitude brighter than the Fornax red clump stars.
Stars were selected with a colour and magnitude lying near the Fornax red giant
branch, thereby reducing contamination from the field star population. We were
thus able to probe the outer structure of this dwarf galaxy. Immediately
visible was a shell-like structure located 1.3 degrees NW from the centre of
Fornax, approximately 30 arcmin beyond the nominal tidal radius at this
position angle. We have measured the absolute visual magnitude of this feature
to be M_V ~ -7. The feature is aligned with a previously reported shell (age
approximately 2 Gyr) located near the core radius of Fornax. A statistical
analysis of the extra-tidal stellar distribution further revealed two lobes
situated on the Fornax minor axis which are aligned with the two shell-like
features. The two-lobed structure combined with the two shells provide strong
evidence that Fornax has experienced a merger event in the relatively recent
past.


title: Reconstructing Sunyaev-Zeldovich clusters in future CMB experiments

abstract:
  We present a new method for component separation aimed to extract
Sunyaev-Zeldovich (SZ) galaxy clusters from multifrequency maps of Cosmic
Microwave Background (CMB) experiments. This method is designed to recover
non-Gaussian, spatially localized and sparse signals. We first characterize the
cluster non-Gaussianity by studying it on simulated SZ maps. We the apply our
estimator on simulated observations of the Planck and Atacama Cosmology
Telescope (ACT) experiments. The method presented here outperforms
multi-frequency Wiener filtering both in the reconstructed average intensity
for given input and in the associated error. In the absence of point source
contamination, this technique reconstructs the ACT (Planck) bright (big)
clusters central y parameter with an intensity which is about 84 (43) per cent
of the original input value. The associated error in the reconstruction is
about 12 and 27 per cent for the 50 (12) ACT (Planck) clusters considered. For
ACT, the error is dominated by beam smearing. In the Planck case the error in
the reconstruction is largely determined by the noise level: a noise reduction
by a factor 7 would imply almost perfect reconstruction and 10 per cent error
for a large sample of clusters. We conclude that the selection function of
Planck clusters will strongly depend on the noise properties in different sky
regions, as well as from the specific cluster extraction method assumed.


title: Light Elements in Main Sequence Stars: Li, Be, B, C, O

abstract:
  The abundances of the {\it rare} light elements, Li, Be, and B, provide clues
about stellar structure and evolution, about Galactic evolution and about their
nucleosynthesis, including production during the Big Bang. The abundances of
the {\it abundant} light elements, C and O, reveal information about the
chemical history of the Galaxy and the mass spectrum of early generations of
stars.


title: Dating COINS: Kinematic Ages for Compact Symmetric Objects

abstract:
  We present multi-epoch VLBA observations of Compact Symmetric Objects (CSOs)
from the COINS sample (CSOs Observed In the Northern Sky). These observations
allow us to make estimates of, or place limits on, the kinematic ages for those
sources with well-identified hot spots. This study significantly increases the
number of CSOs with well-determined ages or limits. The age distribution is
found to be sharply peaked under 500 years, suggesting that many CSOs die
young, or are episodic in nature, and very few survive to evolve into FR II
sources like Cygnus A. Jet components are found to have higher velocities than
hot spots which is consistent with their movement down cleared channels. We
also report on the first detections of significant polarization in two CSOs,
J0000+4054 (2.1%) and J1826+1831 (8.8%). In both cases the polarized emission
is found in jet components on the stronger side of the center of activity.


title: Star Formation Efficiencies and Star Cluster Formation

abstract:
  Starbursts produce large numbers of Young Star Clusters (YSCs). Multi-color
photometry in combination with a dedicated SED analysis tool allows to derive
ages, metallicities, ${\rm E_{B-V}}$, and masses including $1 \sigma$
uncertainties for individual clusters and, hence, mass functions for YSC
systems. The mass function, known to be Gaussian for old Globular Cluster (GC)
systems, is still controversial for YSC systems. GC formation is expected in
massive gas-rich spiral -- spiral mergers because of their high global star
formation efficiencies and observed in $\geq 1$ Gyr old merger remnants. Yet it
has not been possible to identify young GCs among YSC populations. We suggest a
compactness parameters involving masses and half-light radii of YSCs to
investigate if young GCs are formed in starbursts and if the ratio of young GCs
to more loosely bound star clusters depends on galaxy type, mass, burst
strength, etc.


title:
Close-coupling calculations of low-energy inelastic and elastic
  processes in $^4$He collisions with H$_2$: A comparative study of two
  potential energy surfaces

abstract:
  The two most recently published potential energy surfaces (PESs) for the
HeH$_2$ complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd,
Martin, and Peterson) surfaces, are quantitatively evaluated and compared
through the investigation of atom-diatom collision processes. The BMP surface
is expected to be an improvement, approaching chemical accuracy, over all
conformations of the PES compared to that of the MR surface. We found
significant differences in inelastic rovibrational cross sections computed on
the two surfaces for processes dominated by large changes in target rotational
angular momentum. In particular, the H$_2$($\nu=1, j=0$) total quenching cross
section computed using the BMP potential was found to be a factor of $~$1000
larger than that obtained with the MR surface.


title: Molecular Hydrogen Formation on Ice Under Interstellar Conditions

abstract:
  The results of experiments on the formation of molecular hydrogen on low
density and high density amorphous ice surfaces are analyzed using a rate
equation model. The activation energy barriers for the relevant diffusion and
desorption processes are obtained. The more porous morphology of the low
density ice gives rise to a broader spectrum of energy barriers compared to the
high density ice. Inserting these parameters into the rate equation model under
steady state conditions we evaluate the production rate of molecular hydrogen
on ice-coated interstellar dust grains.


title: Non-axisymmetric Structure of Accretion Disks in Be/X-ray Binaries

abstract:
  The non-axisymmetric structure of accretion disks around the neutron star in
Be/X-ray binaries is studied by analyzing the results from three dimensional
(3D) Smoothed Particle Hydrodynamics (SPH) simulations. It is found that ram
pressure due to the phase-dependent mass transfer from the Be-star disk excites
a one-armed, trailing spiral structure in the accretion disk around the neutron
star. The spiral wave has a transient nature; it is excited around the
periastron, when the material is transferred from the Be disk, and is gradually
damped afterwards. It is also found that the orbital phase-dependence of the
mass-accretion rate is mainly caused by the inward propagation of the spiral
wave excited in the accretion disk.


title:
The two sided parsec scale structure of the Low Luminosity Active
  Galactic Nucleus in NGC 4278

abstract:
  We present new Very Long Baseline Interferometry observations of the LINER
galaxy NGC 4278. The observations were taken with the Very Long Baseline Array
(VLBA) and a single antenna of the Very Large Array (VLA) at 5 GHz and 8.4 GHz
and have a linear resolution of <0.1 pc. Our radio data reveal a two sided
structure, with symmetric S-shaped jets emerging from a flat spectrum core. We
fit the jet brightness with gaussian components, which we identify from a
previous observation taken five years before. By comparing the positions of the
components in the two epochs, we measure motions between 0.45 +/- 0.14 and 3.76
+/- 0.65 mas, corresponding to apparent velocities < 0.2c, and to ages in the
range 8.3 - 65.8 years. Assuming that the radio morphology is intrinsically
symmetric and its appearance is governed by Doppler beaming effects, we find
that NGC4278 has mildly relativistic jets (beta ~ 0.75), closely aligned to the
line-of-sight (2 degrees < theta < 4 degrees). Alternatively, the source could
be oriented at a larger angle and asymmetries could be related to the jet
interaction with the surrounding medium. We also present new simultaneous VLA
observations between 1.4 and 43 GHz, and a 5 GHz light curve between 1972 and
2003. The radio spectrum can be fit by a relatively steep power-law (alpha =
0.54). We find significant variability at 5 GHz. All these arguments indicate
that the radiation from NGC 4278 is emitted via the synchrotron process by
relativistic particles accelerated by a supermassive black hole. Despite a much
lower power, this is the same process that takes place in ordinary radio loud
AGNs.


title: V4332 Sagittarii revisited

abstract:
  The eruption of V4332 Sgr discovered in February 1994 shows striking
similarities to that of V838 Mon started in January 2002. The nature of these
eruptions is, however, enigmatic and unclear. We present new photometric and
spectroscopic data on V4332 Sgr obtained in April-May 2003 at the SAAO. The
obtained spectrum shows an unusual emission-line component superimposed on an
early M-type stellar spectrum. The emission-line spectrum is of very low
excitation and is dominated by lines from neutral elemets (NaI, FeI, CaI) and
molecular bands (TiO, ScO, AlO). We also analyse all the observational data,
mainly photometric measurements, available for V4332 Sgr. This allows us to
follow the evolution of the effective temperature, radius and luminosity of the
object since February 1994 till 2003. We show that the observed decline of
V4332 Sgr can be accounted for by a gravitational contraction of an inflated
stellar envelope. The combined optical and infrared photometry in 2003 shows
that apart from the M-type stellar component there is a strong infrared excess
in the KLM bands. This excess was absent in the 2MASS measurements done in 1998
but was probably starting to appear in K in 1999 when the object was observed
in the DENIS survey. We interpret the results in terms of a stellar merger
scenario proposed by Soker & Tylenda. The infrared excess is likely to be due
to a disc-like structure which is either of protostellar nature or has been
produced during the 1994 eruption and stores angular momentum from the merger
event.


title:
Performance analysis of direct N-body algorithms for astrophysical
  simulations on distributed systems

abstract:
  We discuss the performance of direct summation codes used in the simulation
of astrophysical stellar systems on highly distributed architectures. These
codes compute the gravitational interaction among stars in an exact way and
have an O(N^2) scaling with the number of particles. They can be applied to a
variety of astrophysical problems, like the evolution of star clusters, the
dynamics of black holes, the formation of planetary systems, and cosmological
simulations. The simulation of realistic star clusters with sufficiently high
accuracy cannot be performed on a single workstation but may be possible on
parallel computers or grids. We have implemented two parallel schemes for a
direct N-body code and we study their performance on general purpose parallel
computers and large computational grids. We present the results of timing
analyzes conducted on the different architectures and compare them with the
predictions from theoretical models. We conclude that the simulation of star
clusters with up to a million particles will be possible on large distributed
computers in the next decade. Simulating entire galaxies however will in
addition require new hybrid methods to speedup the calculation.


title:
A first XMM-Newton look at the most X-ray-luminous galaxy cluster RX
  J1347.5-1145

abstract:
  We present the first results from an XMM-Newton observation of RX
J1347.5-1145 (z=0.451), the most luminous X-ray cluster of galaxies currently
known, with a luminosity L_X = 6.0 \pm 0.1 \times 10^{45} erg/s in the [2-10]
keV energy band. The cluster has an overall temperature of kT=10.0 \pm 0.3 keV
and is not isothermal: the temperature profile shows a decline in the outer
regions and a drop in the centre, indicating the presence of a cooling core.
The spectral analysis identifies a hot region at radii 50-200 kpc to south-east
of the main X-ray peak, at a position consistent with the subclump seen in the
X-ray image. Excluding the data of the south-east quadrant, the cluster appears
relatively relaxed and we estimate a total mass within 1 Mpc of 1.0 \pm 0.2
\times 10^{15} M_sun.


title:
Structure of visible and dark matter components in spiral galaxies at
  redshifts z = 0.5-0.9

abstract:
  We have constructed self-consistent light and mass distribution models for
four disk galaxies at redshifts z = 0.48, 0.58, 0.81 and 0.88, using the HST
archive WFPC2 observations and rotation curves measured by Vogt et al. (1996)
and Rigopoulou et al. (2002). The models consist of three components: a bulge,
a disk and a dark matter halo. Similarly to the sample studied in Paper I (Tamm
& Tenjes, 2003), light distribution of the galaxies in the outer parts is
clearly steeper than a simple exponential disk. After applying k-corrections,
calculated mass-to-light ratios for galactic disks within the maximum disk
assumption are M/L_B = 0.9, 7.4, 4.3 and 1.4, respectively. Together with the
galaxies from Paper I, the mean <M/L_B> = 2.5 at <z> ~0.9, indicating no
significant evolution of M/L_B with redshift. Central densities of dark matter
halos for an isothermal model are 0.008, 0.035, 0.013, and 0.022 in units
M_sun/pc^3, respectively. Together with the galaxies from Paper I, the DM
central density of the four galaxies at mean readshift <z> ~0.9 is rho(0) =
(0.012-0.028) M_sun/pc^3, also showing no significant evolution with redshift.


title:
XMM-Newton observation of 4U 1543-475: the X-ray spectrum of a
  stellar-mass black-hole at low luminosity

abstract:
  We report the results of an observation of the galactic black-hole binary 4U
1543-475 performed by XMM-Newton on 2002 August 18, about two months after the
start of an outburst detected by Rossi-XTE. Despite the relatively low flux of
the source, corresponding to a luminosity Lx ~ 4x10^34 erg/s (i.e. about
10^(-5) times the Eddington luminosity), we could obtain a good quality
spectrum thanks to the high throughput of the XMM-Newton EPIC instrument. The
spectrum is well fit by a power law with photon index 1.9-2 without any
evidence for iron emission lines or for thermal emission from an accretion
disk. We could estimate an upper-limit on the disk bolometric luminosity as a
function of the colour temperature: it is always lower than ~10^33 erg/s, i.e.
less than 10 % of the source total luminosity. Finally, we evaluated that the
disk colour temperature must satisy the condition kTcol<0.25 keV in order to
obtain an acceptable value for the disk inner radius.


title: Generation of Gravitational Radiation in Dusty Plasmas and Supernovae

abstract:
  We present a novel nonlinear mechanism for exciting a gravitational radiation
pulse (or a gravitational wave) by dust magnetohydrodynamic (DMHD) waves in
dusty astrophysical plasmas. We derive the relevant equations governing the
dynamics of nonlinearly coupled DMHD waves and a gravitational wave (GW). The
system of equations is used to investigate the generation of a GW by
compressional Alfv\'{e}n waves in a type II supernova. The growth rate of our
nonlinear process is estimated, and the results are discussed in the context of
the gravitational radiation accompanying supernova explosions.


title: Radiodetection of Cosmic Ray Extensive Air Showers

abstract:
  We present the characteristics and performance of a demonstration experiment
devoted to the observation of ultra high- energy cosmic ray extensive air
showers using a radiodetection technique. In a first step, one antenna narrowed
band filtered acting as trigger, with a 4 $\sigma$ threshold above sky
background-level, was used to tag any radio transient in coincidence on the
antenna array. Recently, the addition of 4 particle detectors has allowed us to
observe cosmic ray events in coincidence with antennas.


title: Current views on low-mass star formation

abstract:
  The process that leads to the formation and early evolution of low-mass stars
is in a broad sense well understood theoretically and carefully traced
observationally. The largest uncertainties in this framework reside in the
poorly known initial conditions for the origin and gravitational collapse of
dense cores within molecular clouds. In this review, we will discuss the
evidence for an accelerated pattern of star formation in clusters and
associations, the physical origin of this phenomenon, and the age spread in
low-mass star forming regions. On the latter issue, we will show how the
observation of lithium depletion in young clusters, such as the Orion Nebula
Cluster and the Upper Scorpius association, can provide an independent estimate
of their ages and age spreads with important implications on the understanding
of the initial conditions and history of star formation.


title: Age spreads in clusters and associations: the lithium test

abstract:
  We report the evidence that several low-mass stars (<~0.4 Msun) of the Orion
and Upper Scorpius clusters have lithium abundances well below the interstellar
value. Due to time-dependent depletion, our result implies stellar ages greater
than ~5 Myr, suggesting that star formation has been proceeding for a long time
in these systems.


title: Quiet time particle acceleration in interplanetary space

abstract:
  We propose a model for the acceleration of charged particles in
interplanetary space that appear during quiet time periods, that is, not
associated with solar activity events like intense flares or coronal mass
ejections. The interaction of charged particles with modeled turbulent
electromagnetic fields, which mimic the fields observed in the interplanetary
medium, is studied. The turbulence is modeled by means of a dynamical
system,the Gledzer-Ohkitani-Yamada (GOY) shell model, which describes the gross
features of the Navier-Stokes equations. The GOY model is used to build a 3-D
velocity field, which in turn is used to numerically solve the ideal
magneto-hydrodynamic (MHD) induction equation, while the electric field is
calculated from the ideal Ohm's law. Particle acceleration in such an
environment is investigated by test particle simulations, and the resulting
energy distributions are discussed and compared to observations of suprathermal
electrons and ions during quiet periods in interplanetary space.


title: Strange Quark Matter in Stars: A General Overview

abstract:
  The physics of strange quark matter in the core of compact stars and recent
compact star data is reviewed. Emphasis is put on the possible existence of a
third family of strange quark stars.


title: IRIS: A new generation of IRAS maps

abstract:
  The Infrared Astronomical Satellite (IRAS) had a tremendous impact on many
areas of modern astrophysics. In particular it revealed the ubiquity of
infrared cirrus that are a spectacular manifestation of the interstellar medium
complexity but also an important foreground for observational cosmology. With
the forthcoming Planck satellite there is a need for all-sky complementary data
sets with arcminute resolution that can bring informations on specific
foreground emissions that contaminate the Cosmic Microwave Background
radiation. With its 4 arcmin resolution matching perfectly the high-frequency
bands of Planck, IRAS is a natural data set to study the variations of dust
properties at all scales. But the latest version of the images delivered by the
IRAS team (the ISSA plates) suffer from calibration, zero level and striping
problems that can preclude its use, especially at 12 and 25 micron. In this
paper we present how we proceeded to solve each of these problems and enhance
significantly the general quality of the ISSA plates in the four bands (12, 25,
60 and 100 micron). This new generation of IRAS images, called IRIS, benefits
from a better zodiacal light subtraction, from a calibration and zero level
compatible with DIRBE, and from a better destriping. At 100 micron the IRIS
product is also a significant improvement from the Schlegel et al. (1998) maps.
IRIS keeps the full ISSA resolution, it includes well calibrated point sources
and the diffuse emission calibration at scales smaller than 1 degree was
corrected for the variation of the IRAS detector responsivity with scale and
brightness. The uncertainty on the IRIS calibration and zero level are
dominated by the uncertainty on the DIRBE calibration and on the accuracy of
the zodiacal light model.


title:
Physical properties of the solar magnetic photosphere under the MISMA
  hypothesis III: sunspot at disk center

abstract:
  Small-scale fluctuations of magnetic field and velocity may be responsible
for the Stokes asymmetries observed in all photospheric magnetic structures
(the MISMA hypothesis). We support the hypothesis showing that atmospheres with
optically-thin micro-structure reproduce the polarization of FeI 6301 A and FeI
6302 A observed in a sunspot. Ten thousand spectra were fitted by model MISMAs
with two magnetic components interleaved along the line-of-sight. Combining all
the fits, we set up a semi-empirical model sunspot characterized by two
components with very different magnetic field inclination. The major component,
which contains most of the mass, is more vertical than the minor component. The
field lines of the minor component are inclined below the horizontal plane
throughout the penumbra. Magnetic field lines and mass flows are parallel,
consequently, both upflows and downflows are present everywhere on the
penumbra. Major and minor components have very different velocities (several
hundred m/s for the major component versus 10 km/s for the minor component),
but the mass transported per unit time is similar. The similarity between the
vertical mass flow and the magnetic flux of the two components suggests that
field lines emerging as major component may return to the photosphere as minor
component. If so, the observed magnetic field strength difference between
components leads to a siphon flow whose magnitude and direction agree with the
inferred Evershed flow. Several tests support the internal consistency of the
retrieved model sunspot. The magnetic field vector {B} does not violate the
{nabla {B}=0} condition. The model sunspot reproduces the net circular
polarization of the observed lines, plus the abnormal behavior of FeI 15648 A.


title: On "Pulsar dynamics: magnetic dipole model revisited"

abstract: Comments on the article "Pulsar dynamics: magnetic dipole model revisited".


title: Turbulence in Class 0 and Class I protostellar envelopes

abstract:
  We estimate the levels of turbulence in the envelopes of Class 0 and I
protostars using a model based on measurements of the peak separation of
double-peaked asymmetric line profiles. We use observations of 20 protostars of
both Class 0 and I taken in the HCO+ (J=3-2) line that show the classic
double-peaked profile. We find that some Class 0 sources show high levels of
turbulence whilst others demonstrate much lower levels. In Class I protostars
we find predominantly low levels of turbulence. The observations are consistent
with a scenario in which Class 0 protostars form in a variety of environments
and subsequently evolve into Class I protostars. The data do not appear to be
consistent with a recently proposed scenario in which Class 0 protostars can
only form in extreme environments.


title: The prestellar and protostellar population of R Coronae Australis

abstract:
  We present 450 and 850 um maps of R Coronae Australis. We compare the maps to
previous surveys of the region, and shed new light on the previously unknown
nature of the protostellar sources at the centre of the cloud. We clarify the
nature of two millimetre sources previously discovered in lower resolution
data. We identify one new Class 0 protostar that we label SMM 1B, and we
measure the envelope masses of a number of more evolved protostars. We identify
two new prestellar cores that we call SMM 1A and SMM 6.


title: Apodized Pupil Lyot Coronagraphs for Arbitrary Telescope Apertures

abstract:
  In the context of high dynamic range imaging, this study presents a
breakthrough for the understanding of Apodized Pupil Lyot Coronagraphs, making
them available for arbitrary aperture shapes. These new solutions find
immediate application in current, ground-based coronagraphic studies (Gemini,
VLT) and in existing instruments (AEOS Lyot Project). They also offer the
possiblity of a search for an on-axis design for TPF. The unobstructed aperture
case has already been solved by Aime et al. (2002) and Soummer et al. (2003).
Analytical solutions with identical properties exist in the general case and,
in particular, for centrally obscured apertures. Chromatic effects can be
mitigated with a numerical optimization. The combination of analytical and
numerical solutions enables the study of the complete parameter space (central
obstruction, apodization throughput, mask size, bandwidth, and Lyot stop size).


title:
A near-IR spectroscopic search for very-low-mass cool companions to
  notable DA white dwarfs

abstract:
  We have undertaken a detailed near-IR spectroscopic analysis of eight notable
white dwarfs, predominantly of southern declination. In each case the spectrum
failed to reveal compelling evidence for the presence of a spatially
unresolved, cool, late-type companion. Therefore, we have placed an approximate
limit on the spectral-type of a putative companion to each degenerate. From
these limits we conclude that if GD659, GD50, GD71 or WD2359-434 possesses an
unresolved companion then most probably it is substellar in nature
(M<0.072Msun). Furthermore, any spatially unresolved late-type companion to RE
J0457-280, RE J0623-374, RE J0723-274 or RE J2214-491 most likely has
M<0.082Msun. These results imply that if weak accretion from a nearby late-type
companion is the cause of the unusual photospheric composition observed in a
number of these degenerates then the companions are of very low mass, beyond
the detection thresholds of this study. Furthermore, these results do not
contradict a previously noted deficit of very-low-mass stellar and brown dwarf
companions to main sequence F,G,K and early-M type primaries (a<1000AU).


title: A new population of extended, luminous star clusters in the halo of M31

abstract:
  We present three new clusters discovered in the halo of M31 which, although
having globular-like colours and luminosities,have an unusually large
half-light radii, ~30 pc. They lie at projected galactocentric distances of
approx. 15 to 35 kpc. These objects begin to fill the gap in parameter space
between globular clusters and dwarf spheroidals, and are unlike any clusters
found in the Milky Way, or elsewhere to date. Basic photometric and derived
King profile fit parameters are given, and we discuss possible origins and
their relationships to other populations.


title: Broad Iron Lines in AGN and X-ray Binaries

abstract:
  Several AGN and black hole X-ray binaries show a clear very broad iron line
which is strong evidence that the black holes are rapidly spinning. Detailed
analysis of these objects shows that the emission line is not significantly
affected by absorption and that the source variability is principally due to
variation in amplitude of a power-law. Underlying this is a much less variable,
relativistically-smeared, reflection-dominated, component which carries the
imprint of strong gravity at a few gravitational radii. The strong
gravitational light bending in these regions then explains the power-law
variability as due to changes in height of the primary X-ray source above the
disc. The reflection component, in particular its variability and the profile
of the iron line, enables us to study the innermost regions around an
accreting, spinning, black hole.


title:
Strong latitudinal shear in the shallow convection zone of a rapidly
  rotating A-star

abstract:
  We have derived the mean broadening profile of the star V102 in the region of
the open cluster IC4665 from high resolution spectroscopy. At a projected
equatorial rotation velocity of vsini = (105 +- 12)km/s we find strong
deviation from classical rotation. We discuss several scenarios, the most
plausible being strong differential rotation in latitudinal direction. For this
scenario we find a difference in angular velocity of DeltaOmega = 3.6 +- 0.8
rad/d (DeltaOmega/Omega = 0.42 +- 0.09). From the Halpha line we derive a
spectral type of A9 and support photometric measurements classifying IC4665
V102 as a non-member of IC4665. At such early spectral type this is the
strongest case of differential rotation observed so far. Together with three
similar stars, IC4665 V102 seems to form a new class of objects that exhibit
extreme latitudinal shear in a very shallow convective envelope.


title: X-ray Flares from Markarian 501

abstract:
  Motivated by the recent finding of hierarchical X-ray flaring phenomenon in
Mrk 421, we conducted a systematic search for X-ray flares from Mrk 501,
another well-known TeV blazar, by making use of the rich {\em RXTE} archival
database. We detected flares over a wide range of timescales, from months down
to minutes, as in the case of Mrk 421. However, the flares do not seem to occur
nearly as frequently in Mrk 501 as in Mrk 421 on any of the timescales. The
flaring hierarchy also seems apparent in Mrk 501, suggesting that it might be
common among TeV blazars. The results seem to imply a scale-invariant physical
origin of the flares (large or small). The X-ray spectrum of the source shows a
general trend of hardening toward the peak of long-duration flares, with
indication of spectral hysteresis, which is often seen in TeV blazars. However,
the data are not of sufficient quality to allow us to draw definitive
conclusions about spectral variability associated with more rapid but weaker
flares. We critically examine a reported sub-hour X-ray flare from Mrk 501, in
light of intense background flaring activity at the time of the observation,
and concluded that the flare is likely an artifact. On the other hand, we did
identify a rapid X-ray flare that appears to be real. It lasted only for about
15 minutes, during which the flux of the source varied by about 30%.
Sub-structures are apparent in its profile, implying variabilities on even
shorter timescales. Such rapid variabilities of Mrk 501 place severe
constraints on the physical properties of the flaring region in the jet, which
have serious implications on the emission models proposed for TeV blazars.


title:
Short time-scale optical variability of the dwarf Seyfert nucleus in NGC
  4395

abstract:
  We present optical spectroscopic observations of the least-luminous known
Seyfert 1 galaxy, NGC 4395, which was monitored every half-hour over the course
of 3 nights. The continuum emission varied by ~35 per cent over the course of 3
nights, and we find marginal evidence for greater variability in the blue
continuum than the red. A number of diagnostic checks were performed on the
data in order to constrain any systematic or aperture effects. No correlations
were found that adequately explained the observed variability, hence we
conclude that we have observed real intrinsic variability of the nuclear
source. No simultaneous variability was measured in the broad H-beta line,
although given the difficulty in deblending the broad and narrow components it
is difficult to comment on the significance of this result. The observed short
time-scale continuum variability is consistent with NGC 4395 having an
intermediate-mass (~10^5 solar masses) central supermassive black hole, rather
than a very low accretion rate. Comparison with the Seyfert 1 galaxy NGC 5548
shows that the observed variability seems to scale with black hole mass in
roughly the manner expected in accretion models. However the absolute
time-scale of variability differs by several orders of magnitude from that
expected in simple accretion disc models in both cases.