title: Discovery of a large dust disk around the nearby star AU Microscopium

abstract:
  We present the discovery of a circumstellar dust disk surrounding AU
Microscopium (AU Mic, GJ 803, HD 197481). This young M star at 10 parsec has
the same age and origin as beta Pictoris, another nearby star surrounded by a
dust disk. The AU Mic disk is detected between 50 AU and 210 AU radius, a
region where dust lifetimes exceed the present stellar age. Thus, AU Mic is the
nearest star where we directly observe the solid material required for planet
formation. Since 85% of stars are M-type, the AU Mic disk provides new clues on
how the majority of planetary systems might form and evolve.


title:
Nuclear Stellar Populations in the Infrared Space Observatory Atlas of
  Bright Spiral Galaxies

abstract:
  To understand the nuclear stellar populations and star formation histories of
the nuclei of spiral galaxies, we have obtained K-band nuclear spectra for 41
galaxies and H-band spectra for 20 galaxies in the ISO Atlas of Bright Spiral
Galaxies. In the vast majority of the subsample (80%), the near-infrared
spectra suggest that evolved red stars completely dominate the nuclear stellar
populations and that hot young stars are virtually non-existent. The signatures
of recent star formation activity are only found in 20% of the subsample, even
though older red stars still dominate the stellar populations in these
galaxies. Given the dominance of evolved stars in most galaxy nuclei and the
nature of the emission lines in the galaxies where they were detected, we
suggest that nuclear star formation proceeds in the form of instantaneous
bursts. The stars produced by these bursts comprise only ~2% of the total
nuclear stellar mass in these galaxies, but we demonstrate how the nuclear
stellar populations of normal spiral galaxies can be built up through a series
of these bursts. The bursts were detected only in Sbc galaxies and later, and
both bars and interactions appeared to be sufficient but not necessary triggers
for the nuclear star formation activity. The vast majority of galaxies with
nuclear star formation were classified as HII galaxies. With one exception,
LINERs and transition objects were dominated by older red stars, which
suggested that star formation was not responsible for generating these
galaxies' optical line emission.


title:
The Lifetimes of Molecular Cloud Cores: What is the Role of the Magnetic
  Field?

abstract:
  We discuss the lifetimes and evolution of dense cores formed as turbulent
density fluctuations in magnetized, isothermal molecular clouds. We consider
numerical simulations in which we measure the cores' magnetic criticality and
Jeans stability in relation to the magnetic criticality of their ``parent
clouds'' (the numerical boxes). In subcritical boxes, dense cores do not form,
and collapse does not occur. In supercritical boxes, some cores collapse, being
part of larger clumps that are supercritical from the start, and whose central,
densest regions (the cores) are initially subcritical, but rapidly become
supercritical, presumably by accretion along field lines. Numerical artifacts
are ruled out. The time scales for cores to go from subcritical to
supercritical and then collapse are a few times the core free-fall time,
$\tfc$. Our results suggest that cores are out-of-equilibrium, transient
structures, rather than quasi-magnetostatic configurations.


title:
Phase-Space Structure of Dark-Matter Haloes: Scale-Invariant PDF Driven
  by Substructure

abstract:
  We present a method for computing the 6-dimensional coarse-grained
phase-space density $f(x,v)$ in an N-body system, and derive its distribution
function $v(f)$. The method is based on Delaunay tessellation, where $v(f)$ is
obtained with an effective fixed smoothing window over a wide $f$ range. The
errors are estimated, and $v(f)$ is found to be insensitive to the sampling
resolution or the simulation technique. We find that in gravitationally relaxed
haloes built by hierarchical clustering, $v(f)$ is well approximated by a
robust power law, $v(f) \propto f^{-2.5 \pm 0.05}$, over more than 4 decades in
$f$, from its virial level to the numerical resolution limit. This is tested to
be valid in the $\Lambda$CDM cosmology for haloes with masses
$10^9-10^{15}\msun$, indicating insensitivity to the slope of the initial
fluctuation power spectrum. By mapping the phase-space density in position
space, we find that the high-$f$ end of $v(f)$ is dominated by the ``cold''
subhaloes rather than the parent-halo central region and its global spherical
profile. The value of $f$ in subhaloes near the virial radius is typically
$>100$ times higher than its value at the halo centre, and it decreases
gradually from outside in toward its value at the halo centre. This seems to
reflect phase mixing due to mergers and tidal effects involving puffing up and
heating. The phase-space density can thus provide a sensitive tool for studying
the evolution of subhaloes during the hierarchical buildup of haloes. It
remains to be understood why the evolved substructure adds up to the actual
universal power law of $v(f) \propto f^{-2.5}$. It seems that this behaviour
results from the hierarchical clustering process and is not a general result of
violent relaxation.


title: The Globular Cluster System of the Canis Major Dwarf Galaxy

abstract:
  Prompted by the discovery of the accreted Canis Major dwarf galaxy and its
associated globular cluster (GC) system (Martin etal.), we investigate the
contribution of accreted GCs to the Galactic system. The Canis Major GCs, and
those associated with the Sagittarius dwarf galaxy, exhibit a range of
galactocentric radii, prograde and retrograde motions, and horizontal branch
morphologies, indicating that such properties are of limited use in identifying
accreted GCs. By contrast, we find that the age-metallicity relation (AMR) of
these dwarf galaxies is distinct from that of the main Galactic GC distribution
at intermediate-to-high metallicities ([Fe/H] > -1.3). The accretion of GCs
with a distinct AMR would explain much of the apparent age spread in the
Galactic GC system. The Canis Major and Sagittarius AMRs are similar to those
of other Local Group dwarf galaxies and are consistent with a simple closed-box
chemical enrichment model -- a further indication that these GCs formed outside
of the Milky Way. The Canis Major GCs all have smaller-than-average sizes for
their galactocentric distances, lending further support to their origin outside
of the Milky Way. Our findings suggest that accretion of similar mass dwarfs
does not appear to have played a major role in building the stellar mass of the
thick disk or bulge of the Milky Way.


title:
CMB Observations with a Compact Heterogeneous 150 GHz Interferometer in
  Chile

abstract:
  We report on the design, first observing season, and analysis of data from a
new prototype millimeter-wave interferometer, MINT. MINT consists of four 145
GHz SIS mixers operating in double-sideband mode in a compact heterogeneous
configuration. The signal band is subdivided by a monolithic channelizer, after
which the correlations between antennas are performed digitally. The typical
receiver sensitivity in a 2 GHz band is 1.4 mK sqrt(s). MINT observed the
cosmic microwave background (CMB) from the Chilean Altiplano. The site has a
median nighttime atmospheric temperature of 9 K at zenith (exclusive of the
CMB). Observations of Mars, Jupiter, and a telescope-mounted calibration source
establish the system's phase and magnitude stability. MINT is the first
CMB-dedicated interferometer to operate above 50 GHz. The same type of system
can be used to probe the Sunyaev-Zel'dovich effect in galaxy clusters near the
SZ null at 217 GHz. We present an analysis of sideband-separated, digitally
sampled data recorded by the array. Based on 215 hours of data taken in late
2001, we set an upper limit on the CMB anisotropy in a band of width Delta
ell=700 around ell=1540 of delta T < 105 microK (95% conf). Increased
sensitivity can be achieved with more integration time, greater bandwidth, and
more elements.


title: Gamma-ray Spectra due to Cosmic-ray Interactions with Dense Gas Clouds

abstract:
  Gamma-ray spectra from cosmic-ray proton and electron interactions with dense
gas clouds have been calculated using a Monte Carlo event simulation code,
GEANT4. Such clouds are postulated as a possible form of baryonic dark matter
in the Universe. The simulation fully tracks the cascade and transport
processes that are important in a dense medium, and the resulting gamma-ray
spectra are computed as a function of cloud column-density. These calculations
are used for predicting the Galactic diffuse gamma-ray spectrum that may be
contributed by baryonic dark matter; the results are compared with data from
the EGRET instrument, and used to constrain the fraction of Galactic dark
matter that may be in the form of dense gas clouds. In agreement with previous
authors, we find useful constraints on the fraction of Galactic dark matter
that may be in the form of low column-density clouds ($\Sigma \la 10 g
cm^{-2}$). However, this fraction rises steeply in the region $\Sigma \sim 10^2
g cm^{-2}$, and for $\Sigma \ga 200 g cm^{-2}$ we find that baryonic dark
matter models are virtually unconstrained by the existing gamma-ray data.


title: Deep near-infrared observations of W3 Main star forming region

abstract:
  We present a deep JHKs-band imaging survey of the W3 Main star forming
region, using the near-infrared camera, SIRIUS, mounted on the University of
Hawaii 2.2m telescope. The near-infrared survey covers an area of ~ 24 sq.
arcmin with 10 sigma limiting magnitudes of ~ 19.0, 18.1, and 17.3 in J, H, and
Ks-band, respectively. We construct JHK color-color and J/J-H and K/H-K
color-magnitude diagrams to identify young stellar objects and estimate their
masses. Based on these color-color and color-magnitude diagrams, a rich
population of YSOs is identified which is associated with the W3 Main region. A
large number of previously unreported red sources (H-K > 2) have also been
detected around W3 Main. We argue that these red stars are most probably
pre-main sequence stars with intrinsic color excesses. We find that the slope
of the Ks-band luminosity function of W3 Main is lower than the typical values
reported for the young embedded clusters. The derived slope of the KLF is the
same as that found by Megeath et al. (1996), from which analysis by Megeath et
al. indicates that the W3 Main region has an age in the range of 0.3--1 Myr.
Based on the comparison between models of pre-main sequence stars with the
observed color-magnitude diagram we find that the stellar population in W3 Main
is primarily composed of low mass pre-main sequence stars. We also report the
detection of isolated young stars with large infrared excesses which are most
probably in their earliest evolutionary phases.


title: Dynamics of Intermediate Mass Black Holes in Star Clusters

abstract:
  We have followed the evolution of multi-mass star clusters containing massive
central black holes by N-body simulations on the GRAPE6 computers of Tokyo
University. We find a strong cluster expansion and significant structural
changes of the clusters. Star clusters with IMBHs have power-law density
profiles $rho ~ r^{-alpha}$ with slopes $alpha=1.55$ inside the influence
sphere of the central black hole. This leads to a constant density profile of
bright stars in projection, which rules out the presence of intermediate mass
black holes in core collapse clusters. If the star clusters are surrounded by a
tidal field, a central IMBH speeds up the destruction of the cluster until a
remnant of a few hundred stars remains, which stays bound to the IMBH for a
long time. We also discuss the efficiency of different detection mechanisms for
finding IMBHs in star clusters.


title:
Relativistic Version of Landau Theory of Fermi Liquid in Presence of
  Strong Quantizing Magnetic Field- An Exact Formalism

abstract:
  An exact formalism for the relativistic version of Landau theory of Fermi
liquid in presence of strong quantizing magnetic field is developed. Both
direct and exchange type interactions with scalar and vector coupling cases are
considered.


title:
High-amplitude, long-term X-ray variability in the solar-type star HD
  81809: the beginning of an X-ray activity cycle?

abstract:
  We present the initial results from our XMM program aimed at searching for
X-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhat
more evolved than the Sun, and with a less massive companion) with a pronounced
8.2 yr chromospheric cycle, as evident from from the Mt. Wilson program data.
We present here the results from the initial 2.5 years of XMM observations,
showing that large amplitude (a factor of approx. 10) modulation is present in
the X-ray luminosity, with a clearly defined maximum in mid 2002 and a steady
decrease since then. The maximum of the chromospheric cycle took place in 2001;
if the observed X-ray variability is the initial part of an X-ray cycle, this
could imply a phase shift between chromospheric and coronal activity, although
the current descent into chromospheric cycle minimum is well reflected into the
star's X-ray luminosity. The observations presented here provide clear evidence
for the presence of large amplitude X-ray variability coherent with the
activity cycle in the chromosphere in a star other than the Sun.


title:
The magnetic field along the jets of NGC 4258 as deduced from high
  frequency radio observations

abstract:
  We present 2.4" resolution, high sensitivity radio continuum observations of
the nearby spiral galaxy NGC 4258 in total intensity and linear polarization
obtained with the Very Large Array at 3.6 cm (8.44 GHz). The radio emission
along the northern jet and the center of the galaxy is polarized and allows
investigation of the magnetic field. Assuming energy-equipartition between the
magnetic field and the relativistic particles and distinguishing between (1) a
relativistic electron-proton jet and (2) a relativistic electron-positron jet,
we obtain average magnetic field strengths of about (1) 310\muG and (2) 90\muG.
The rotation measure is determined to range from -400 to -800 rad/m^2 in the
northern jet. Correcting the observed E-vectors of polarized intensity for
Faraday rotation, the magnetic field along the jet turns out to be orientated
mainly along the jet axis. An observed tilt with respect to the jet axis may
indicate also a toroidal magnetic field component or a slightly helical
magnetic field around the northern jet.


title: The chaotic behavior of the black hole system GRS 1915+105

abstract:
  A modified non-linear time series analysis technique, which computes the
correlation dimension $D_2$, is used to analyze the X-ray light curves of the
black hole system GRS 1915+105 in all twelve temporal classes. For four of
these temporal classes $D_2 $ saturates to $\approx 4-5$ which indicates that
the underlying dynamical mechanism is a low dimensional chaotic system. Of the
other eight classes, three show stochastic behavior while five show deviation
from randomness. The light curves for four classes which depict chaotic
behavior have the smallest ratio of the expected Poisson noise to the
variability ($ < 0.05$) while those for the three classes which depict
stochastic behavior is the highest ($ > 0.2$). This suggests that the temporal
behavior of the black hole system is governed by a low dimensional chaotic
system, whose nature is detectable only when the Poisson fluctuations are much
smaller than the variability.


title: Molecular Gas around the Double Nucleus in M83

abstract:
  The center of M83, a barred starburst galaxy with a double nucleus, has been
observed in the CO(J=2-1) and CO(J=3-2) lines with the Submillimeter Array. The
molecular gas shows a distribution and kinematics typical for barred galaxies
at kpc radii, but reveals unusual kinematics around the double nucleus in the
central 300 pc. Our CO velocity data show that the visible nucleus in M83 is at
least 3" (65 pc) away from the galaxy's dynamical center, which most likely
coincides with the center of symmetry previously determined in K band and is
suggested to host another nucleus. We discovered high-velocity molecular gas
associated with the visible off-center nucleus, and also found a steep velocity
gradient across it. We attribute these features to a gas disk rotating around
the off-center nucleus, which may be the remnant of a small galaxy accreted by
M83. The dynamical mass of this component is estimated to be 3x10^8 Msun within
a radius of 40 pc. The dynamical perturbation from the off-center nucleus may
have played a key role in shaping the lopsided starburst.


title: Properties of Isolated Disk Galaxies

abstract:
  A sample of isolated galaxies (IsG), selected by the ratio, $f$, between
inner and tidal forces acting upon a galaxy, is presented. The analysis of the
Coma cluster lead us to adopt the criterion $f\leq -4.5$ for IsG. The
candidates are from the CfA catalog with cz $\leq$5000 km/s, |b|> 40\deg, DEC
$\ge -$2.5\deg. The sample contains 203 objects from the initial 1706. We also
selected a sample (N=130) of perturbed galaxies, i.e., with companions (with
known z, $\Delta(cz)\le 500$ km/s), $f\geq-$2. The comparison of both samples
shows significant differences in morphology, size, mass, luminosity and colors.
Sc spirals are more frequent among IsG, and S0s among perturbed galaxies. IsG
appear to be smaller, less luminous and bluer than interacting objects. We also
found that bars are twice as frequent among perturbed galaxies in particular
for early S and S0. The perturbed galaxies have higher L$_{FIR}$/L$_B$ and
M$_{mol}$/L$_B$ ratios, but the atomic gas content is similar for the two
samples. The L-size and M-L relations shows similar trends, the main difference
being the almost total absence of big, bright and massive galaxies among the
IsG, and the almost total absence of small, faint and low mass galaxies among
the perturbed systems. The evolution induced by interactions, would therefore
proceed from late, small, faint and low mass S to earlier, bigger, more
luminous and more massive S and S0 galaxies, producing at the same time a
larger fraction of barred galaxies, but preserving the same relations between
global parameters. The properties of local IsG are similar to those of high
redshift galaxies, suggesting that the present day isolated galaxies could be
quietly evolved, unused {\sl building blocks} surviving in low density
environments.


title: Life and Death of Young Dense Star Clusters near the Galactic Center

abstract:
  We discuss the structural change and degree of mass segregation of young
dense star clusters within about 100pc of the Galactic center. In our
calculations, which are performed with GRAPE-6, the equations of motion of all
stars and binaries are calculated accurately but the external potential of the
Galaxy is solved (semi)analytically. The simulations are preformed to model the
Arches star cluster. We find that star clusters with are less strongly
perturbed by the tidal field and dynamical friction are much stronger affected
by mass segregation; resulting in a significant pile-up of massive stars in the
cluster center. At an age of about 3.5Myr more than 90 per cent of the stars
more massive than ~10Msun are concentrated within the half-mass radius of the
surviving cluster. Star clusters which are strongly perturbed by the tidal
field of the parent Galaxy are much less affected by mass segregation.


title: Stars of extragalactic origin in the solar neighborhood

abstract:
  We computed the spatial velocities and the galactic orbital elements using
Hipparcos data for 77 nearest main-sequence F-G-stars with published the iron,
magnesium, and europium abundances determined from high dispersion spectra and
with the ages estimated from theoretical isochrones. A comparison with the
orbital elements of the globular clusters that are known was accreted by our
Galaxy in the past reveals stars of extragalactic origin. We show that the
relative elemental abundance ratios of r- and \alpha- elements in all the
accreted stars differ sharply from those in the stars that are genetically
associated with the Galaxy. According to current theoretical models, europium
is produced mainly in low mass Type II supernovae (SNe II), while magnesium is
synthesized in larger amounts in high mass SN II progenitors. Since all the old
accreted stars of our sample exhibit a significant Eu overabundance relative to
Mg, we conclude that the maximum masses of the SNII progenitors outside the
Galaxy were much lower than those inside it are. On the other hand, only a
small number of young accreted stars exhibit low negative ratios $[Eu/Mg] < 0$.
The delay of primordial star formation burst and the explosions of high mass
SNe II in a relatively small part of extragalactic space can explain this
situation. We provide evidence that the interstellar medium was weakly mixed at
the early evolutionary stages of the Galaxy formed from a single proto-galactic
cloud and that the maximum mass of the SN II progenitors increased in it with
time simultaneously with the increase in mean metallicity.


title: Absorption in Gamma Ray Burst afterglows

abstract:
  We studied the X-ray and optical absorption properties of 13 Gamma Ray Burst
(GRB) afterglows observed by BeppoSAX. We found that X-ray absorption in
addition to the Galactic one along the line of sight is highly statistically
significant in the two cases with the best statistics (probability >99.9%). In
three other cases the presence of X-ray absorption is marginally significant
(probability 97%). Measured rest frame equivalent hydrogen column densities NH
range from 0.1 to 10.0 x 10^22 cm-2 (at 90% confidence level) assuming a solar
metal abundance. X-ray absorption may be common, although the quality of
present data does not allow us to reach a firm conclusion. The rest frame NH
derived from XMM and Chandra data as quoted in the literature are in good
agreement with the BeppoSAX estimates. For the same GRB afterglow sample we
evaluated the rest frame visual extinction AVr. We fitted the optical-NIR
afterglow photometry with a power law model corrected by four different
extinction curves. By comparing X-ray absorptions and optical extinction, we
found that if a Galactic-like dust grain size distribution is assumed, a dust
to gas ratio lower than the one observed in the Galaxy is required by the data.
A dust to gas ratio 1/10 than the Galactic one, has been tested using the Small
Magellanic Cloud extinction curve, which produces inconsistent results.
Alternative scenarios to explain simultaneously the optical and X-ray data
involve dust with grain size distributions biased toward large grains. Possible
mechanisms that can bring to such a grain size distribution are discussed.


title: Modelling Faraday Screens in the Interstellar Medium

abstract:
  Maps of Galactic polarized continuum emission at 1408, 1660, and 1713 MHz
towards the local Taurus molecular cloud complex were made with the Effelsberg
100-m telescope. Minima in the polarized emission which are located at the
boundary of a molecular cloud were detected. Beside high rotation measures and
unusual spectral indices of the polarized intensity, these features are
associated with the molecular gas. At the higher frequencies the minima get
less distinct. We have modelled the multi-frequency observations by placing
magneto-ionic Faraday screens at the distance of the molecular cloud. In this
model Faraday rotated background emission adds to foreground emission towards
these screens. The systematic variation of the observed properties is the
result of different line-of-sight lengths through the screen assuming spherical
symmetry. For a distance of 140 pc to the Taurus clouds the physical sizes of
the Faraday screens are of the order of 2 pc. In this paper we describe the
data calibration and modelling process for one such object. We find an
intrinsic rotation measure of about -29 rad/m^{2} to model the observations. It
is pointed out that the observed rotation measure differs from the physical.
Further observational constraints from H-alpha observations limit the thermal
electron density to less than 0.8 cm^{-3}, and we conclude that the regular
magnetic field strength parallel to the line-of-sight exceeds 20 micro Gauss to
account for the intrinsic rotation measure.


title: A Single Circumstellar Disk in the SVS 13 Close Binary System

abstract:
  We present Very Large Array observations at 7 mm of the sources IRAS 2A, IRAS
2B, MMS2, MMS3 and SVS 13, in the NGC1333 region. SVS 13 is a young close
binary system whose components are separated by 65 AU in projection. Our high
angular resolution observations reveal that only one of the components of the
SVS 13 system (VLA 4B) is associated with detectable circumstellar dust
emission. This result is in contrast with the well known case of L1551 IRS5, a
binary system of two protostars separated by 45 AU, where each component is
associated with a disk of dust. Both in SVS 13 and in L1551 IRS5 the emission
apparently arises from compact accretion disks, smaller than those observed
around single stars, but still massive enough to form planetary systems like
the solar one. These observational results confirm that the formation of
planets can occur in close binary systems, either in one or in both components
of the system, depending on the specific angular momentum of the infalling
material.


title:
Stability of Terrestrial Planets in the Habitable Zone of Gl 777 A, HD
  72659, Gl 614, 47 Uma and HD 4208

abstract:
  We have undertaken a thorough dynamical investigation of five extrasolar
planetary systems using extensive numerical experiments. The systems Gl 777 A,
HD 72659, Gl 614, 47 Uma and HD 4208 were examined concerning the question of
whether they could host terrestrial like planets in their habitable zones
(=HZ). First we investigated the mean motion resonances between fictitious
terrestrial planets and the existing gas giants in these five extrasolar
systems. Then a fine grid of initial conditions for a potential terrestrial
planet within the HZ was chosen for each system, from which the stability of
orbits was then assessed by direct integrations over a time interval of 1
million years. The computations were carried out using a Lie-series integration
method with an adaptive step size control. This integration method achieves
machine precision accuracy in a highly efficient and robust way, requiring no
special adjustments when the orbits have large eccentricities. The stability of
orbits was examined with a determination of the Renyi entropy, estimated from
recurrence plots, and with a more straight forward method based on the maximum
eccentricity achieved by the planet over the 1 million year integration.
Additionally, the eccentricity is an indication of the habitability of a
terrestrial planet in the HZ; any value of e>0.2 produces a significant
temperature difference on a planet's surface between apoapse and periapse. The
results for possible stable orbits for terrestrial planets in habitable zones
for the five systems are summarized as follows: for Gl 777 A nearly the entire
HZ is stable, for 47 Uma, HD 72659 and HD 4208 terrestrial planets can survive
for a sufficiently long time, while for Gl 614 our results exclude terrestrial
planets moving in stable orbits within the HZ.


title: Spectroscopy and 3D imaging of the Crab nebula

abstract:
  Spectroscopy of the Crab nebula along different slit directions reveals the 3
dimensional structure of the optical nebula. On the basis of the linear radial
expansion result first discovered by Trimble (1968), we make a 3D model of the
optical emission. Results from a limited number of slit directions suggest that
optical lines originate from a complicated array of wisps that are located in a
rather thin shell, pierced by a jet. The jet is certainly not prominent in
optical emission lines, but the direction of the piercing is consistent with
the direction of the X-ray and radio jet. The shell's effective radius is ~ 79
seconds of arc, its thickness about a third of the radius and it is moving out
with an average velocity 1160 km/s.


title: The cored distribution of dark matter in spiral galaxies

abstract:
  We present the HI data for 5 spiral galaxies that, along with their Halpha
rotation curves, are used to derive the distribution of dark matter within
these objects. A new method for extracting rotation curves from HI data cubes
is presented; this takes into account the existence of a warp and minimises
projection effects. The rotation curves obtained are tested by taking them as
input to construct model data cubes that are compared to the observed ones: the
agreement is excellent. On the contrary, the model data cubes built using
rotation curves obtained with standard methods, such as the first-moment
analysis, fail the test. The HI rotation curves agree well with the Halpha
data, where they coexist. Moreover, the combined Halpha + HI rotation curves
are smooth, symmetric and extended to large radii.
  The rotation curves are decomposed into stellar, gaseous and dark matter
contributions and the inferred density distribution is compared to various mass
distributions: dark haloes with a central density core, $\Lambda$ Cold Dark
Matter ($\Lambda$CDM) haloes (NFW, Moore profiles), HI scaling and MOND. The
observations point to haloes with constant density cores of size $r_{core} \sim
r_{opt}$ and central densities scaling approximately as $\rho_0 \propto
r_{core}^{-2/3}$. $\Lambda$CDM models (which predict a central cusp in the
density profile) are in clear conflict with the data. HI scaling and MOND
cannot account for the observed kinematics: we find some counter-examples.


title:
Large-scale wind structures in OB supergiants: a search for rotationally
  modulated H\alpha variability

abstract:
  We present the results of a long-term monitoring campaign of the H\alpha line
in a sample of bright OB-supergiants (O7.5-B9) that aims at detecting
rotationally modulated changes potentially related to the existence of
large-scale wind structures. A total of 22 objects were monitor ed during 36
nights spread over 6 months in 2001-2002. Coordinated broad-band photometric
observations were also obtained for some targets. Conspicuous evidence for
variability in H\alpha is found for the stars displaying a feature contaminated
by wind emission. Most changes take place on a daily time-scale, although
hourly variations are also occasionally detected. Convincing evidence for a
cyclical pattern of variability in H\alpha has been found in 2 stars: HD 14134
and HD 42087 (periodic signals are also detected in other stars, but
independent confirmation is required). Rotational modulation is suggested from
the similarity between the observed recurrence time-scales (in the range 13-25
days) and estimated periods of stellar rotation. We call attention to the
atypical case of HD 14134 which exhibits a clear 12.8-d periodicity both in the
photometric and in the spectroscopic data sets. This places this object among a
handful of early-type stars where one may observe a clear link between extended
wind structures and photospheric disturbances. Further modelling may test the
hypothesis that azimuthally-extended wind streams are responsible for the
patterns of spectral variability in our target stars.


title:
Infrared spectroscopy of a brown dwarf companion candidate near the
  young star GSC 08047-00232 in Horologium

abstract:
  We present infrared H- and K-band spectra of a companion candidate 3" north
of the young star GSC 08047-00232, a probable member of the nearby young
Horologium association. From previously obtained JHK-band colors and the
magnitude difference between primary and companion candidate, the latter could
well be substellar (Neuh"auser et al. 2003) with the spectral type being
roughly M7-L9 from the JHK colors (Chauvin et al. 2003). With the H- and K-band
spectra now obtained with ISAAC at the VLT, the spectral type of the companion
candidate is found to be M6-9.5. Assuming the same age and distance as for the
primary star (~35 Myrs, 50 to 85 pc), this yields a mass of ~25 Jupiter masses
for the companion, hence indeed substellar. After TWA-5 B and HR 7329 B, this
is the third brown dwarf companion around a nearby (up to 100 pc) young (up to
100 Myrs) star. A total of three confirmed brown dwarf companions (any mass,
separation above 50 AU) around 79 stars surveyed in three young nearby
associations corresponds to a frequency of 6 \pm 4 % (with a correction for
missing companions which are almost on the same line-of-sight as the primary
star instead of being separated well), consistent with the expectation, if
binaries have the same mass function as field stars. Hence, it seems that there
is no brown dwarf desert at wide separations.


title: Phantom k-essence cosmologies

abstract:
  We devise a method to obtain a phantom version of FRW k-essence cosmologies
with homogeneous k-fields by applying form-invariance transformations. It can
be seen that the transformation performs the maps $H\toH$ and
$\rho+p\to-(\rho+p)$, which in turn give $\gamma\to\gamma$ and $a\to a^{-1}$.
The discussion is presented in a general setup, valid for FRW k-essence
cosmologies, and then we discuss power-law solutions for illustration purposes.
First, we deal with models such that the gradient of the k-field is not
constant, which include standard and generalized tachyon cosmologies. We
concentrate on the usual tachyon and show the phantom symmetry involves a
change in the potential and that it generates an extended super-accelerated
tachyon field. Then, we turn our attention to models for which the time
derivative of the k-field is not constant, and we show the transformation can
be implemented without changing the potential at all.


title: Close stars and accretion in Low Luminosity Active Galactic Nuclei

abstract:
  Quasar accretion disks are believed to form stars by self-gravity. Low
Luminosity Active Galactic Nuclei (LLAGN) are much dimmer galactic centers, and
are often believed to be quasars that ran out of gaseous fuel. LLAGN accretion
disks should thus co-exist with thousands to millions of stars or proto-stars
left from the previous stronger accretion activity. In principle, these stars
may produce several important effects: (i) contribute to the optical/UV spectra
of some LLAGN; (ii) reprocessing of the stellar radiation in the dusty disks
could dominate the LLAGN infra-red spectra; (iii) deplete the (accretion) gas
disk much faster than it can accrete onto the supper-massive black hole (SMBH);
(iv) stars, individually or in groups, may slow down and modulate the accretion
flow significantly due to their inertia. In this way they may produce the LLAGN
cut-off disks; (v) alternatively, frequent enough stellar collisions and
resulting stellar disruptions could keep the inner disk empty. Here we explore
these ideas. We find that, despite ``low'' luminosities of LLAGN,
unrealistically high stellar densities are required to make a sizable radiative
contribution to the (HST) optical/UV spectra of these galactic nuclei. Stellar
contribution to the infrared spectrum is more likely. Further, if LLAGN are in
a quasi steady-state for as long as 10^7 years or more, too high stellar
densities would again be required to significantly affect the dynamics of
accretion flow. However, if LLAGN are ``short''-lived phenomena, e.g. t < 10^5
years, quiescent states of quiescence-outburst cycles, then embedded stars may
be much more important through the mass effects (iii) -- (v). With observations
of LLAGN becoming progressively better, it will be more and more difficult to
neglect the presence of close stars in and around nuclear accretion disks.


title:
X-ray Properties of Pre--Main-Sequence Stars in the Orion Nebula Cluster
  with Known Rotation Periods

abstract:
  We re-analyze all archival Chandra/ACIS observations of the Orion Nebula
Cluster (ONC) to study the X-ray properties of a large sample of
pre--main-sequence (PMS) stars with optically determined rotation periods. Our
goal is to elucidate the origins of X-rays in PMS stars by seeking out
connections between the X-rays and the mechanisms most likely driving their
production--rotation and accretion. In our sample X-ray luminosity is
significantly correlated with stellar rotation, in the sense of decreasing
Lx/Lbol with more rapid rotation, suggesting that these stars are in the
"super-saturated" regime of the rotation-activity relationship. However, we
also find that stars with optical rotation periods are significantly biased to
high Lx. This is not the result of magnitude bias in the optical
rotation-period sample but rather to the diminishingly small amplitude of
optical variations in stars with low Lx. Evidently, there exists in the ONC a
population of stars whose rotation periods are unknown and that possess lower
average X-ray luminosities than those of stars with known rotation periods.
These stars may sample the linear regime of the rotation-activity relationship.
Accretion also manifests itself in X-rays, though in a somewhat
counterintuitive fashion: While stars with spectroscopic signatures of
accretion show harder X-ray spectra than non-accretors, they show lower X-ray
luminosities and no enhancement of X-ray variability. We interpret these
findings in terms of a common origin for the X-ray emission observed from both
accreting and non-accreting stars, with the X-rays from accreting stars simply
being attenuated by magnetospheric accretion columns. This suggests that X-rays
from PMS stars have their origins primarily in chromospheres, not accretion.


title: Metal-Poor Globular Clusters and Galaxy Formation

abstract:
  We demonstrate a significant (> 5-sigma) correlation between the mean color
of metal-poor globular cluster (GC) systems and parent galaxy luminosity. A
Bayesian Markov Chain Monte Carlo method is introduced to find the mean color,
and is easily generalizable to quantify multimodality in other astronomical
datasets. We derive a GC color--galaxy luminosity relation of the form Z ~ L^
(0.15 +/- 0.03). When combined with evidence against a single primordial GC
metallicity--galaxy luminosity relation for protogalactic fragments, the
existence of such a correlation is evidence against both accretion and major
merger scenarios as an explanation of the entire metal-poor GC systems of
luminous galaxies. However, our relation arises naturally in an in situ picture
of GC formation, and is consistent with the truncation of metal-poor GC
formation by reionization. A further implication is that the ages of metal-poor
GCs in dwarf galaxies constrain the main epoch of galaxy formation in
hierarchical models. If the ages of old metal-poor GCs in Local Group dwarfs (>
11 Gyr) are typical of those in dwarfs elsewhere, then the bulk of galaxy
assembly (at least in clusters and groups) must have occurred at z > 2.5,
contrary to the predictions of some structure formation models.


title:
A Luminous Lyman-alpha Emitting Galaxy at Redshift z=6.535: Discovery
  and Spectroscopic Confirmation

abstract:
  We present a redshift z=6.535 galaxy discovered by its Lyman alpha emission
in a 9180A narrowband image from the Large Area Lyman Alpha (LALA) survey. The
Ly-a line luminosity (1.1e43 erg/s) is among the largest known for star forming
galaxies at z=6.5. The line shows the distinct asymmetry that is characteristic
of high-redshift Ly-a. The 2 sigma lower bound on the observer-frame equivalent
width is > 530A. This is hard to reconcile with a neutral intergalactic medium
unless the Ly-a line is intrinsically strong and is emitted from its host
galaxy with an intrinsic Doppler shift of several hundred km/s. If the IGM is
ionized, it corresponds to a rest frame equivalent width > 40A after correcting
for Ly-a forest absorption.
  We also present complete spectroscopic followup of the remaining candidates
with line flux > 2e-17 erg/cm2/s in our 1200 square arcminute narrowband image.
These include another galaxy with a strong emission line at 9136A and no
detected continuum flux, which however is most likely an [OIII] source at
z=0.824 based on a weak detection of the [OIII] 4959A line.


title:
Time-resolved X-ray spectral modeling of an intermediate burst from
  SGR1900+14 observed by HETE-2/FREGATE and WXM

abstract:
  We present a detailed analysis of a 3.5 s long burst from SGR1900+14 which
occurred on 2001 July 2. The 2-150 keV time-integrated energy spectrum is well
described by the sum of two blackbodies whose temperatures are approximately
4.3 and 9.8 keV. The time-resolved energy spectra are similarly well fit by the
sum of two blackbodies. The higher temperature blackbody evolves with time in a
manner consistent with a shrinking emitting surface. The interpretation of
these results in the context of the magnetar model suggests that the two
blackbody fit is an approximation of an absorbed, multi-temperature spectrum
expected on theoretical grounds rather than a physical description of the
emission. If this is indeed the case, our data provide further evidence for a
strong magnetic field, and indicate that the entire neutron was radiating
during most of the burst duration.


title: UV/Optical Emission Accompanying Gamma-ray Burst

abstract:
  We discuss the possible simultaneously UV/optical emission accompanying
Gamma-ray bursts (GRBs). We show that as long as the intrinsic spectrum of GRB
can extend to $\sim$10 GeV or higher, there is a large amount of relativistic
$e^\pm$ pairs generated due to the annihilation of the soft $\gamma-$rays with
the very energetic photons, which dominates over the electrons/positrons
associated with the fireball, no matter the fireball is highly magnetized or
not (For the highly magnetized fireball, the magnetic field is ordered, the
high linear polarization of the multi-wavelength emission is expected). We find
that these $e^\pm$ pairs can power an UV flash with $m\simeq 12-13{\rm th}$
magnitude, and the corresponding optical emission can be up to $m_{\rm
R}\simeq15-16{\rm th}$ magnitude. Such bright UV emission can be detected by
the upcoming satellite Swift, planned for launch in early 2004. The behavior of
the optical-UV spectrum ($F_{\nu}\propto \nu^{5/2}$) differs significantly from
that of the reverse shock emission ($F_{\nu}\propto \nu^{-\beta/2}$, $\beta
\simeq 2.2$), which is a signature of the emission accompanying with GRB. The
mild optical emission can be detected with the ROTSE-IIIa telescope system, if
the response to the GRB alert is fast enough.


title: WMAP Constraints on Decaying Cold Dark Matter

abstract:
  We re-formulate cosmological perturbations in the decaying cold dark matter
model, and calculate cosmological microwave background (CMB) anisotropies. By
comparing our theoretical predictions with recent observational data from the
Wilkinson Microwave Anisotropy Probe(WMAP), we derive a new bound on the
abundance and lifetime of decaying dark matter particles. We show that the data
of WMAP alone do not prefer the decaying cold dark matter model: the lifetime
is constrained to \Gamma^{-1}> 123 Gyr at 68% C.L. (52 Gyr at 95.4% C.L.) when
cold dark matter consists only of such decaying particles. We also consider a
more general case in which cold dark matter consists of both stable and
decaying particles, and show that the constraint generalizes down to
\Omega_{DDM}h^2 < -0.5 (Gamma^{-1}/1 Gyr)^{-1}+0.12 for \Gamma^{-1} > 5 Gyr at
95.4% C.L.. These bounds are robust and widely applicable, because they are
derived only from gravitational effects and therefore do not rely on the
details of decay channels or decay products.


title: Jet emission in NGC1052 at radio, optical, and X-ray frequencies

abstract:
  We present a combined radio, optical, and X-ray study of the nearby LINER
galaxy NGC 1052. Data from a short (2.3 ksec) {\it CHANDRA} observation of NGC
1052 reveal the presence of various jet-related X-ray emitting regions, a
bright compact core and unresolved knots in the jet structure as well as an
extended emitting region inside the galaxy well aligned with the radio
synchrotron jet-emission. The spectrum of the extended X-ray emission can best
be fitted with a thermal model with $kT = (0.4-0.5)$ keV, while the compact
core exhibits a very flat spectrum, best approximated by an absorbed power-law
with $N_{\rm H} = (0.6-0.8) \times 10^{22} {\rm cm^{-2}}$. We compare the radio
structure to an optical ``structure map'' from a {\it Hubble Space Telescope}
({\it HST}) observation and find a good positional correlation between the
radio jet and the optical emission cone. Bright, compact knots in the jet
structure are visible in all three frequency bands whose spectrum is
inconsistent with synchrotron emission.


title:
Observational tests of the evolution of spheroidal galaxies and
  predictions for SIRTF/Spitzer cosmological surveys

abstract:
  Granato et al(2004) have elaborated a physically grounded model exploiting
the mutual feedback between star-forming spheroidal galaxies and the active
nuclei growing in their cores to overcome, within the hierarchical clustering
scenario for galaxy formation, one of the main challenges facing such scenario,
the fact that massive spheroidal galaxies appear to have formed earlier and
faster than predicted by previous models. Adopting the choice by Granato et al
for the parameters governing the history of the SF,of chemical abundances and
of the gas and dust content of galaxies, we are left with only two parameters
affecting the time and mass dependent SED of spheroidal galaxies. After
complementing the model with a simple description of evolutionary properties of
starburst, normal late-type galaxies and AGNs we have successfully compared the
model with a broad variety of observational data, deep K-band, ISO, IRAS,
SCUBA, radio counts, the corresponding redshift distributions, the IR
background spectrum, and also with data for EROs. We also present detailed
predictions for the GOODS and SWIRE surveys with the Spitzer Space Telescope.
We find that the GOODS deep survey at 24$\mu$m and the SWIRE surveys at 70 and
160$\mu$m are likely to be severely confusion limited. The GOODS surveys in the
IRAC channels are expected to resolve most of the background, to explore the
full passive evolution phase of spheroidal galaxies and most of their active
star-forming phase, detecting galaxies up to z\simeq 4. A substantial number of
high z star-forming spheroidal galaxies should also be detected by the 24\mum
SWIRE and GOODS surveys, while the 70 and 160\mum will be particularly useful
to study the evolution of such galaxies in the range 1 \lsim z \lsim
2.[abridged]


title: Star Formation at z~6: The UDF-Parallel ACS Fields

abstract:
  We report on the i-dropouts detected in two exceptionally deep ACS fields
(B_{435}, V_{606}, i_{775}, and z_{850} with 10 sigma limits of 28.8, 29.0,
28.5, and 27.8, respectively) taken in parallel with the UDF NICMOS
observations. Using an i-z>1.4 cut, we find 30 i-dropouts over 21 arcmin^2 down
to z_AB=28.1, or 1.4 i-dropouts arcmin^{-2}, with significant field-to-field
variation (as expected from cosmic variance). This extends i-dropout searches
some ~0.9^m further down the luminosity function than was possible in the GOODS
field, netting a ~7x increase in surface density. An estimate of the size
evolution for UV bright objects is obtained by comparing the composite radial
flux profile of the bright i-dropouts (z<27.2) with scaled versions of the
HDF-N + HDF-S U-dropouts. The best-fit is found with a (1+z)^{-1.57_{-0.53}
^{+0.50}} scaling in size (for fixed luminosity), extending lower redshift
(1<z<5) trends to z~6. Adopting this scaling and the brighter i-dropouts from
both GOODS fields, we make incompleteness estimates and construct a z~6 LF in
the rest-frame continuum UV (~1350 A) over a 3.5 magnitude baseline, finding a
shape consistent with that found at lower redshift. To evaluate the evolution
in the LF from z~3.8, we make comparisons against different scalings of a lower
redshift B-dropout sample. Though a strong degeneracy is found between
luminosity and density evolution, our best-fit model scales as (1+z)^{-2.8} in
number and (1+z)^0.1 in luminosity, suggesting a rest-frame continuum UV
luminosity density at z~6 which is just 0.38_{-0.07} ^{+0.09}x that at z~3.8.
Our inclusion of size evolution makes the present estimate lower than previous
z~6 estimates.


title:
Prompt Ultraviolet-to-Soft-X-Ray Emission of Gamma-Ray Bursts:
  Application to GRB 031203?

abstract:
  We discuss the prompt emission of GRBs, allowing for $\gamma\gamma$ pair
production and synchrotron self-absorption. The observed hard spectra suggest
heavy pair-loading in GRBs. The re-emission of the generated pairs results in
the energy transmission from high-energy gamma-rays to long-wavelength
radiation. Due to strong self-absorption, the synchrotron radiation by pairs is
in optically thick regime, showing a thermal-like spectral bump in the
extreme-ultraviolet/soft X-ray band, other than the peak from the main burst.
Recently, the prompt soft X-ray emission of GRB 031203 was detected thanks to
the discovery of a delayed dust echo, and it seems to be consistent with the
model prediction of a double-peak structure. The confirmation of the
thermal-like feature and the double-peak structure by observation would
indicate that the dominant radiation mechanism in GRBs is synchrotron rather
than inverse-Compton radiation.


title: Phase-Space Structure & Substructure of Dark Halos

abstract:
  A method is presented for computing the 6-D phase-space density f(x,v) and
its PDF v(f) in an N-body system. It is based on Delaunay tessellation,
yielding v(f) with a fixed smoothing window over a wide f range, independent of
the sampling resolution. It is found that in a gravitationally relaxed halo
built by hierarchical clustering, v(f) is a robust power law, v(f) f^{-2.5 \pm
0.05}, over more than 4 decades in f, from its virial level to the current
resolution limit. This is valid for halos of different sizes in the LCDM
cosmology, indicating insensitivity to the initial-fluctuation power spectrum
as long as the small-scale fluctuations were not completely suppressed. By
mapping f in position space, we find that the high-f contributions to v(f) come
from the "cold" subhalos within the parent halo rather than the halo central
region and its global spherical profile. The f in subhalos near the halo virial
radius is more than 100 times higher than at the halo center, and it decreases
gradually with decreasing radius. This indicates phase mixing due to mergers
and tidal effects involving puffing up and heating. The phase-space structure
provides a sensitive tool for studying the evolution of subhalos during the
buildup of halos. One wishes to understand why the substructure adds up to the
universal power law in v(f). It seems that the f^{-2.5} behavior is related to
the hierarchical clustering process and is not a general result of violent
relaxation.


title: Cooling of Neutron Stars. Hadronic Model

abstract:
  We study the cooling of isolated neutron stars. The main cooling regulators
are introduced: EoS, thermal transport, heat capacity, neutrino and photon
emissivity, superfluid nucleon gaps. Neutrino emissivity includes main
processes. A strong impact of medium effects on the cooling rates is
demonstrated. With taking into account of medium effects in reaction rates and
in nucleon superfluid gaps modern experimental data can be well explained.


title: Cooling of neutron stars with color superconducting quark cores

abstract:
  We show that within a recently developed nonlocal, chiral quark model the
critical densities for a phase transition to color superconducting quark matter
under neutron star conditions can be low enough that these phases occur in
compact star configurations with masses below 1.4 M_sun. We study the cooling
of these objects in isolation for different values of the gravitational mass
and thus different composition and structure of the interior. Our equation of
state allows for a 2SC phase with a large quark gap Delta ~ 100 MeV for u and d
quarks of two colors, a normal quark matter phase and their coexistence in a
mixed phase within the hybrid star interior. We argue that, if the phases with
unpaired quarks were allowed, the corresponding hybrid stars would cool too
fast to describe the neutron star cooling data existing by today. We
incorporate other attractive channels permitting a weak pairing of the residual
quarks which remained unpaired in the 2SC phase and demonstrate that the model
does not contradict the cooling data if the weak pairing gaps are of the order
of 0.1 MeV.


title:
Stability of rigidly rotating relativistic stars with soft equations of
  state against gravitational collapse

abstract:
  We study secular stability against a quasi-radial oscillation for rigidly
rotating stars with soft equations of state in general relativity. The
polytropic equations of state with polytropic index $n$ between 3 and 3.05 are
adopted for modeling the rotating stars. The stability is determined in terms
of the turning-point method. It is found that (i) for $n \agt 3.04$, all the
rigidly rotating stars are unstable against the quasi-radial oscillation and
(ii) for $n \agt 3.01$, the nondimensional angular momentum parameter $q \equiv
cJ/GM^2$ (where $J$, $M$, $G$, and $c$ denote the angular momentum, the
gravitational mass, the gravitational constant, and the speed of light,
respectively) for all marginally stable rotating stars is larger than unity. A
semi-analytic calculation is also performed, and good agreement with the
numerical results is confirmed. The final outcome after axisymmetric
gravitational collapse of rigidly rotating and marginally stable massive stars
with $q > 1$ is predicted, assuming that the rest-mass distribution as a
function of the specific angular momentum is preserved and that the pressure
never halt the collapse. It is found that even for $1 < q \alt 2.5$, a black
hole may be formed as a result of the collapse, but for $q \agt 2.5$, the
significant angular momentum will prevent the direct formation of a black hole.


title:
Burial of the polar magnetic field of an accreting neutron star. I.
  Self-consistent analytic and numerical equilibria

abstract:
  The hydromagnetic structure of a neutron star accreting symmetrically at both
magnetic poles is calculated as a function of accreted mass, M_a, and polar cap
radius,starting from a centered magnetic dipole and evolving through a
quasistatic sequence of two-dimensional, Grad-Shafranov equilibria. The
calculation is the first to track fully the growth of high-order magnetic
multipoles, due to equatorward hydromagnetic spreading, while simultaneously
preserving flux freezing and a self-consistent mass-flux distribution.
Equilibria are constructed numerically by an iterative scheme and analytically
by Green functions. Two key results are obtained, with implications for
recycled pulsars. (i) The mass required to significantly reduce the magnetic
dipole moment, 10^{-5} Msun, greatly exceeds previous estimates (~ 10^{-10}
Msun), which ignored the confining stress exerted by the compressed equatorial
magnetic field. (ii) Magnetic bubbles, disconnected from the stellar surface,
form in the later stages of accretion (M_a > 10^{-4} Msun).


title:
Different Velocity Dependences of Physical Conditions of High- and
  Low-Ionization Lines in Broad-Line Regions

abstract:
  We present results from a study of high- and low-ionization emission line
ratios as a function of projected velocity for a sample of eight active
galactic nuclei (AGNs). Our results are based on analysis of high
signal-to-noise optical and Hubble Space Telescope (HST) UV spectra. Comparing
the emission line ratios to those predicted by photoionization models indicates
that the physical conditions responsible for the high-ionization emission lines
are consistent with a wind, whereas those of the low-ionization lines are
consistent with a virialized disk.


title: Polarization experiments

abstract:
  Possible instrumental set--ups for the measurement of CMB polarization are
reviewed in this article. We discuss existing and planned instruments, putting
special emphasis on observational, instrumental, and data processing issues for
the detection of very low polarization signals of prime cosmological interest.
A short prospective summary is included.


title: Quiet Sun X-rays as Signature for New Particles

abstract:
  We have studied published data from the Yohkoh solar X-ray mission, with the
purpose of searching for signals from radiative decays of new, as yet
undiscovered massive neutral particles. This search is based on the prediction
that solar axions of the Kaluza-Klein type should result in the emission of
X-rays from the Sun direction beyond the limb with a characteristic radial
distribution. These X-rays should be observed more easily during periods of
quiet Sun. An additional signature is the observed emission of hard X-rays by
SMM, NEAR and RHESSI. The recent observation made by RHESSI of a continuous
emission from the non-flaring Sun of X-rays in the 3 to ~15 keV range fits the
generic axion scenario. This work also suggests new analyses of existing data,
in order to exclude instrumental effects; it provides the rationale for
targeted observations with present and upcoming (solar) X-ray telescopes, which
can provide the final answer on the nature of the signals considered here. Such
measurements become more promising during the forthcoming solar cycle minimum
with an increased number of quiet Sun periods.


title: The metallicity dependence of the Cepheid PL-relation

abstract:
  A sample of 37 Galactic, 10 LMC and 6 SMC cepheids is compiled for which
individual metallicity estimates exist and BVIK photometry in almost all cases.
The Galactic cepheids all have an individual distance estimate available. For
the MC objects different sources of photometry are combined to obtain improved
periods and mean magnitudes. A multi-parameter Period-Luminosity relation is
fitted to the data which also solves for the distance to the LMC and SMC. When
all three galaxies are considered, without metallicity effect, a significant
quadratic term in log P is found, as previously observed and also predicted in
some theoretical calculations. For the present sample it is empirically
determined that for log P < 1.65 linear PL-relations may be adopted, but this
restricts the sample to only 4 LMC and 1 SMC cepheid. Considering the Galactic
sample a metallicity effect is found in the zero point in the VIWK PL-relation
(-0.6 \pm 0.4 or -0.8 \pm 0.3 mag/dex depending on the in- or exclusion of one
object), in the sense that metal-rich cepheids are brighter. The small
significance is mostly due to the fact that the Galactic sample spans a narrow
metallicity range. The error is to a significant part due to the error in the
metallicity determinations and not to the error in the fit. Including the 5 MC
cepheids broadens the observed metallicity range and a metallity effect of
about -0.27 \pm 0.08 mag/dex in the zero point is found in VIWK, in agreement
with some previous empirical estimates, but now derived using direct
metallicity determinations for the cepheids themselves.


title: XMM-Newton observations of the dwarf nova YZ Cnc in quiescence

abstract:
  We present results from the XMM observations of the dwarf nova YZ Cnc in a
quiescent state. We have performed a detailed time series analysis of the
resulting light curves. Unusually, we do not detect any orbital modulation in
the UV, with only marginal evidence for X-ray modulation on this period.
Although there are peaks in the X-ray periodograms at periods less than 5000 s,
we attribute them to red noise effects and assign significance to them using a
novel approach. The variability in the UV and optical bands can also be
modelled as a result of aperiodic variability (red noise) in the system. There
is evidence that the UV and X-ray fluxes are anti-correlated with a time delay
of about 100 s, with the UV lagging behind the X-ray emission. This
anti-correlation is intriguing, but is only present on two occasions lasting
several 1000 s each. The X-ray spectrum shows similar emission features to
other dwarf novae and is well fitted using a multi-temperature emission model.
We measure a relatively high X-ray luminosity of ~1.4x10^{32} ergs/s, although
this is consistent with a low binary inclination. Finally, we find evidence for
a possible -1200km/s blue shift in the fitted Fe K line energies, possibly
indicating the presence of an outflow in this low inclination system.


title: On the Jet Activity in 3C 273

abstract:
  In this paper we comment on the possibility for intermittent jet activity in
quasar 3C 273 on different time-scales. We propose, that striking morphology of
the large-scale radio jet in this source, as well as the apparent lack of its
counterpart on the opposite side of the active center, may be explained in a
framework of a restarting jet model. In particular, we propose that 3C 273
radio source is intrinsically two-sided, and represents an analogue of
double-double radio galaxies, but only inclined at a small angle to the line of
sight. In this case, the apparent one-sideness of the kiloparsec-scale radio
structure may be due to combined Doppler and time-travel effects alone, if the
3C 273 large-scale jet itself is relativistic and matter-dominated. We also
propose, that knotty morphology of the discussed jet, which is observed now
additionally at optical and X-ray frequencies, indicates modulation in the jet
kinetic power. This, together with the variability of the jet at small (parsec)
scales, indicates that the jet activity in 3C 273, and possibly in other
similar sources, is variable/modulated/intermittent over many different
time-scales.


title: Design studies for a European Gamma-ray Observatory

abstract:
  We discuss preliminary studies concerning a large-diameter gamma-ray
telescope, to be part of an array of telescopes installed at the existing
observation site on the Canary island of La Palma. One of the telescopes in the
array will be MAGIC, presently the largest existing gamma ray telescope and the
most performant world wide at low energy. A second telescope of the same class
is under construction. Eventually, we will want to install one or more devices
giving access to even lower gamma-ray energy; they will be larger than MAGIC by
roughly a linear factor two, and are code-named ECO-1000 (for a mirror surface
of 1000 sq.m.).
  We discuss the technologies needed to reach the physical low-energy limit.
They exist at the component level, but have to be field-tested; we propose to
implement and integrate the most critical components in a MAGIC-class
telescope, such that the eventual extrapolation to a larger device becomes a
fully predictable step. If financing can be found, such tests can be completed
on a timescale such that a proposal for the first true low-theshold (< 8 GeV)
telescope can be made in 2007, and its construction completed in 2009/2010.


title: A new calculation of the mass fraction of primordial black holes

abstract:
  We revisit the calculation of the abundance of primordial black holes (PBHs)
formed from primordial density perturbations, using a formation criterion
derived by Shibata and Sasaki which refers to a metric perturbation variable
rather than the usual density contrast. We implement a derivation of the PBH
abundance which uses peaks theory, and compare it to the standard calculation
based on a Press--Schechter-like approach. We find that the two are in
reasonable agreement if the Press--Schechter threshold is in the range
$\Delta_{{\rm th}} \simeq 0.3$ to 0.5, but advocate use of the peaks theory
expression which is based on a sounder theoretical footing.


title: Massive star formation and tidal structures in HCG 31

abstract:
  We present new broad-band optical and near-infrared CCD imaging together with
deep optical intermediate-resolution spectroscopy of the Hickson Compact Group
31. We analyze the morphology and colors of the stellar populations of the
galaxies, as well as the kinematics, physical conditions and chemical
composition of the ionized gas in order to get a more complete view on the
origin and evolution of the system. We estimate the ages of the most recent
star formation bursts of the system, finding an excellent consistency among the
values obtained with different indicators and starburst models. We find that
member F hosts the youngest starburst of the group, showing a substantial
population of Wolf-Rayet stars. The chemical abundances are fairly similar in
all the members of the group despite their very different absolute magnitudes.
We argue that the use of traditional metallicity-luminosity relations based on
the absolute $B$-magnitude is not appropriate for dwarf starburst galaxies,
because their luminosity is dominated by the transient contribution of the
starburst to the blue luminosity. We think that members E and F of the group
are candidate tidal dwarf galaxies because of their high metallicity, their
kinematics, and the absence of underlying old stellar populations. Finally, we
propose that HCG~31 is suffering several almost simultaneous interaction
processes. The most relevant of these processes are: (a) the merging of members
A and C, that would have produced two optical tidal tails; and (b) a fly-by
encounter between G and the A+C complex, that would have produced an \ion{H}{1}
tidal tail from the stripping of the external gas of A+C, from which members F
and E have originated.


title: Submillimeter Galaxies as Tracers of Mass Assembly at Large M

abstract:
  Luminous submillimeter galaxies (SMGs) have been known for some time to
produce a substantial fraction of the far-IR/submillimeter background. New
observations show that these systems are not only very luminous, but also very
massive. Here we present results from (a) a survey of SMGs' molecular line
emission, which has confirmed Keck optical redshifts and revealed their high
gas and dynamical masses; and (b) a detailed case study of the rest-frame
optical emission from one SMG, which has revealed its high metallicity and old
stellar population. We infer a high z~2.7 comoving number density of galaxies
with baryonic masses greater than 10^11 solar masses; this is not accounted for
in current semi-analytic models of galaxy evolution.


title: The A&A Experience With Impact Factors

abstract:
  There is a widespread impression that the scientific journal "Astronomy &
Astrophysics" (A&A) has a smaller impact, as measured by citations to articles,
than some of the other major astronomy journals. This impression was apparently
supported - and probably created - by the Journal Citation Report (JCR), which
is prepared annually by the Institute of Scientific Information (ISI) Web of
Knowledge. The published poor impact factor of A&A was in fact wrong and was
due to a serious flaw in the method used by ISI Web of Knowledge to determine
it. The resulting damage inflicted upon A&A by the JCR is incalculable.


title: The locality of transport in self-gravitating accretion discs

abstract:
  In this paper we examine the issue of characterising the transport associated
with gravitational instabilities in relatively cold discs, discussing in
particular the conditions under which it can be described within a local,
viscous framework. We present the results of global, three-dimensional, SPH
simulations of self-gravitating accretion discs, in which the disc is cooled
using a simple parametrisation for the cooling function. Our simulations show
that the disc settles in a ``self-regulated'' state, where the axisymmetric
stability parameter $Q\approx 1$ and where transport and energy dissipation are
dominated by self-gravity. We have computed the gravitational stress tensor and
compared our results with expectations based on a local theory of transport. We
find that, as long as the disc mass is smaller than $0.25M_{\star}$ and the
aspect ratio $H/R\lesssim 0.1$, transport is determined locally, thus allowing
for a viscous treatment of the disc evolution.


title:
Searching for periods in X-ray observations using Kuiper's test.
  Application to the ROSAT PSPC archive

abstract:
  We use Kuiper's test to detect periodicities in X-ray and gamma-ray
observations. Like Rayleigh's test, it uses the individual photon arrival
times, and is therefore well suited to the analysis of faint sources. Our
method makes it possible to take into account the discontinuities in the
observation, and to completely get rid of the contamination that results from
them. This makes it particularly adapted to the search of periods long compared
to the total observation duration. We propose a semi-analytical approach to
determine the effective number of trial frequencies when searching for unknown
periods over a frequency range. This approach can be easily adapted to other
tests. We show that, using Kuiper's test, we can recover periods in frequency
domains where other tests are completely confused by contamination. We finally
search the entire ROSAT Position-Sensitive Proportional Counter (PSPC) archive
for long periods, and find 28 new periodic-source candidates.


title: Absolute Timing of the Crab Pulsar with RXTE

abstract:
  We have monitored the phase of the main X-ray pulse of the Crab pulsar with
the Rossi X-ray Timing Explorer (RXTE) for almost eight years, since the start
of the mission in January 1996. The absolute time of RXTE's clock is
sufficiently accurate to allow this phase to be compared directly with the
radio profile. Our monitoring observations of the pulsar took place bi-weekly
(during the periods when it was at least 30 degrees from the Sun) and we
correlated the data with radio timing ephemerides derived from observations
made at Jodrell Bank. We have determined the phase of the X-ray main pulse for
each observation with a typical error in the individual data points of 50 us.
The total ensemble is consistent with a phase that is constant over the
monitoring period, with the X-ray pulse leading the radio pulse by
0.0102+/-0.0012 period in phase, or 344+/-40 us in time. The error estimate is
dominated by a systematic error of 40 us in the radio data, arising from
uncertainties in the variable amount of pulse delay due to interstellar
scattering and instrumental calibration. The statistical error is 0.00015
period, or 5 us. The separation of the main pulse and interpulse appears to be
unchanging at time scales of a year or less, with an average value of
0.4001+/-0.0002 period. There is no apparent variation in these values with
energy over the 2-30 keV range. The lag between the radio and X-ray pulses may
be constant in phase (rotational) or constant in time (linear pathlength). We
are not (yet) able to distinguish between these two interpretations.


title:
Gravitational Waves from Stellar Collapse: Correlations to Explosion
  Asymmetries

abstract:
  The collapse of massive stars not only produces observable outbursts across
the entire electromagnetic spectrum but, for Galactic (or near-Galactic)
supernovae, detectable signals for ground-based neutrino and gravitational wave
detectors. Gravitational waves and neutrinos provide the only means to study
the actual engine behind the optical outbursts: the collapsed stellar core.
While the neutrinos are most sensitive to details of the equation of state,
gravitational waves provide a means to study the mass asymmetries in this
central core. We present gravitational wave signals from a series of
3-dimensional core-collapse simulations with asymmetries derived from initial
perturbations caused by pre-collapse convection, core rotation, and low-mode
convection in the explosion engine itself. A Galactic supernovae will allow us
to differentiate these different sources of asymmetry. Combining this signal
with other observations of the supernova, from neutrinos to gamma-rays to the
compact remnant, dramatically increases the predictive power of the
gravitational wave signal. We conclude with a discussion of the gravitational
wave signal arising from collapsars, the leading engine for long-duration
gamma-ray bursts.


title: Molecular Hydrogen in the Ionized Region of Planetary Nebulae

abstract:
  This paper presents an analysis of the concentration of the hydrogen molecule
inside the ionized region of planetary nebulae. The equations corresponding to
the ionization and chemical equilibria of H, H+, H-, H2, H2+, and H3+ are
coupled with the equations of ionization and thermal balance for a photoionized
atomic gas. Forty different reactions related to the formation or the
destruction of these species are included. The presence of dust is taken into
account, since grains act as catalysts for the production of H2, as well as
shield the molecules against the stellar ionizing radiation. We analyze the
effect of the stellar ionizing continuum, as well as of the gas and grain
properties on the calculated H2 mass. It is shown that a significant
concentration of H2 can survive inside the ionized region of planetary nebulae,
mostly in the inner region of the recombination zone. The total H2 to total
hydrogen mass ratio inside the ionized region increases with the central star
temperature, and, depending on the PN physical conditions, it can be of the
order of 10^-6 or even higher. The increase of the recombination zone with the
stellar temperature can account for such correlation. This can explain why the
H2 emission is more frequently observed in bipolar planetary nebulae (Gatley's
rule), since this kind of object has typically hotter stars. Applying our
results for the planetary nebula NGC 6720, we obtain an H2 to hydrogen mass
ratio similar to the value obtained from the observed H2 line emission.


title: The Complex Neutral Gas Dynamics Of The Dwarf Starburst Galaxy NGC 625

abstract:
  We present new multi-configuration HI aperture synthesis imaging of the
nearby dwarf starburst galaxy NGC 625 obtained with the Australia Telescope
Compact Array. Total HI column density images show gas well-aligned with the
optical major axis, and low-column density HI extending to > 6 optical scale
lengths. The HI velocity field, on the other hand, is highly disturbed, with
neutral gas at nearly all detected velocities within the central region. After
considering various interpretations, we find that a blowout scenario most
accurately describes the data. Since at our resolution we do not detect any
large evacuated holes in the HI disk, we interpret this blowout to be the
result of the extended (both spatially and temporally) star formation event
which NGC 625 has undergone in the last 100 Myr. This is one of the clearest
examples of HI outflow detected in a dwarf galaxy. We find no obvious external
trigger for this extended star formation event. We detect strong radio
continuum emission from the largest HII regions; comparing to our HST and
ground-based H Alpha fluxes suggests either appreciable amounts of extinction
toward the star formation regions, or the contribution of non-thermal sources
to the radio continuum luminosity.


title: Extended Tidal Structure In Two Lyman Alpha-Emitting Starburst Galaxies

abstract:
  We present new VLA C-configuration HI imaging of the Lyman Alpha-emitting
starburst galaxies Tol 1924-416 and IRAS 08339+6517. The effective resolution
probes neutral gas structures larger than 4.7 kpc in Tol 1924-416, and larger
than 8.1 kpc in IRAS 08339+6517. Both systems are revealed to be tidally
interacting: Tol 1924-416 with ESO 338-IG04B (6.6 arcminutes = 72 kpc minimum
separation), and IRAS 08339+6517 with 2MASX J08380769+6508579 (2.4 arcminutes =
56 kpc minimum separation). The HI emission is extended in these systems, with
tidal tails and debris between the target galaxies and their companions. Since
Lyman Alpha emission has been detected from both of these primary systems,
these observations suggest that the geometry of the ISM is one of the factors
affecting the escape fraction of Lyman Alpha emission from starburst
environments. Furthermore, these observations argue for the importance of
interactions in triggering massive star formation events.


title: Multiply-imaged submm galaxy in a z~2.5 group

abstract:
  We present observations of a remarkable submillimetre-selected galaxy,
SMMJ16359+6612. This distant galaxy lies behind the core of a massive cluster
of galaxies, A2218, and is gravitationally lensed by the foreground cluster
into three discrete images which were identified in deep submillimetre maps of
the cluster core at both 450 and 850micron. Subsequent follow-up using deep
optical and NIR images identify a faint counterpart to each of the 3 images,
with similar red optical--NIR colours and HST morphologies. By exploiting a
detailed mass model for the cluster lens we estimate that the combined images
of this galaxy are magnified by a factor of ~45, implying that this galaxy
would have un-lensed magnitudes K_s=22.9 and I=26.1, and an un-lensed 850micron
flux density of only 0.8mJy. Moreover, the highly constrained lens model
predicted the redshift of SMMJ16359+6612 to be z=2.6+/-0.4. We confirm this
estimate using deep optical and NIR Keck spectroscopy, measuring a redshift of
z=2.516. SMMJ16359+6612 is the faintest submm-selected galaxy so far identified
with a precise redshift. Thanks to the large gravitational magnification of
this source, we identify 3 sub-components in this submm galaxy, which are also
seen in the NIRSPEC data, arguing for either a strong dust (lane) absorption or
a merger. Interestingly, there are 2 other highly-amplified galaxies at almost
identical redshifts in this field (although neither is a strong submm emitter).
The 3 galaxies lie within a ~100kpc region on the background sky, suggesting
this submm galaxy is located in a dense high-redshift group.


title: Was the Universe Reionized at Redshift 10?

abstract:
  Recently, Pello et al. (2004) claimed to have discovered a galaxy at a
redshift z=10, and identified a feature in its spectrum with a hydrogen
Lyman-alpha emission line. If this identification is correct, we show that the
intergalactic medium (IGM) around the galaxy must be significantly ionized;
otherwise, the damping wing of Lyman-alpha absorption by the neutral IGM would
have greatly suppressed the emission line. We find either that the large-scale
region surrounding this galaxy must have been largely reionized by z=10 (with a
neutral fraction <0.4) or that the stars within the galaxy must be massive
(>100 solar masses), and hence capable of producing a sufficiently large HII
region around it. We generalize these conclusions and derive the maximum
Lyman-alpha line flux for a given UV continuum flux of galaxies prior to the
epoch of reionization.


title:
A Study of CO Emission in High Redshift QSOs Using the Owens Valley
  Millimeter Array

abstract:
  Searches for CO emission in high-redshift objects have traditionally suffered
from the accuracy of optically-derived redshifts due to lack of bandwidth in
correlators at radio observatories. This problem has motivated the creation of
the new COBRA continuum correlator, with 4 GHz available bandwidth, at the
Owens Valley Radio Observatory Millimeter Array. Presented here are the first
scientific results from COBRA. We report detections of redshifted CO(J=3-2)
emission in the QSOs SMM J04135+10277 and VCV J140955.5+562827, as well as a
probable detection in RX J0911.4+0551. At redshifts of z=2.846, z=2.585, and
z=2.796, we find integrated CO flux densities of 5.4 Jy km/s, 2.4 Jy km/s, and
2.9 Jy km/s for SMM J04135+10277, VCV J140955.5+562827, and RX J0911.4+0551,
respectively, over linewidths of Delta(V_{FWHM}) ~ 350 km/s. These
measurements, when corrected for gravitational lensing, correspond to molecular
gas masses of order M(H_2) ~ 10^{9.6-11.1} solar masses, and are consistent
with previous CO observations of high-redshift QSOs. We also report 3-sigma
upper limits on CO(3-2) emission in the QSO LBQS 0018-0220 of 1.3 Jy km/s. We
do not detect significant 3mm continuum emission from any of the QSOs, with the
exception of a tentative (3-sigma) detection in RX J0911.4+0551 of S_{3mm}=0.92
mJy/beam.


title: The Evolution of Supernovae in the Winds of Massive Stars

abstract:
  We study the evolution of supernova remnants in the circumstellar medium
formed by mass loss from the progenitor star. The properties of this
interaction are investigated, and the specific case of a 35 $\msun$ star is
studied in detail. The evolution of the SN shock wave in this case may have a
bearing on other SNRs evolving in wind-blown bubbles, especially SN 1987A.


title: Age of the Universe in the Cardassian Model

abstract:
  The age of the universe is obtained in a subset of Cardassian models by using
WMAP data. Cardassian expansion is a modification to the Friedmann equation
that allows the universe to be flat, matter dominated, and accelerating,
without a vacuum component. Since this model changes the evolution of the
universe, we should not a priori expect the Cardassian age to be the same as
the WMAP Friedmann derived result of 13.7 +/- 0.2 Gyrs. However, in the subset
of Cardassian models we consider, we discover that the age of the universe
varies from 13.4 - 13.8 Gyr over the range of parameter space we explore, a
result close to that of the standard Lambda Cold Dark Matter model. The Hubble
constant h, which may also vary in these models, likewise varies little from
the Friedmann result.


title:
Timing and Spectroscopy of Accreting X-ray Pulsars: the State of
  Cyclotron Line Studies

abstract:
  A great deal of emphasis on timing in the RXTE era has been on pushing toward
higher and higher frequency phenomena, particularly kHz QPOs. However, the
large areas of the RXTE pointed instruments provide another capability which is
key for the understanding of accreting X-ray pulsars -- the ability to
accumulate high quality spectra in a limited observing time. For the accreting
X-ray pulsars, with their relatively modest spin frequencies, this translates
into an ability to study broad band spectra as a function of pulse phase. This
is a critical tool, as pulsar spectra are strong functions of the geometry of
the "accretion mound" and the observers' viewing angle to the ~10^12 G magnetic
field. In particular, the appearance of "cyclotron lines" is sensitively
dependent on the viewing geometry, which must change with the rotation of the
star. These spectral features, seen in only a handful of objects, are quite
important, as they give us our only direct measure of neutron star magnetic
fields. Furthermore, they carry a great deal of information as to the geometry
and physical conditions in the accretion mound. In this paper, we review the
status of cyclotron line studies with the RXTE. We present an overview of
phase-averaged results and give examples of observations which illustrate the
power of phase-resolved spectroscopy.


title:
Correlations of Power-law Spectral and QPO Features In Black Hole
  Candidate Sources

abstract:
  Recent studies have shown that strong correlations are observed between low
frequency QPO`s and the spectral power law index for a number of black hole
candidate sources (BHC's), when these sources exhibit quasi-steady hard x-ray
emission states. The dominant long standing interpretation of QPO's is that
they are produced in and are the signature of the thermal accretion disk.
Paradoxically, strong QPO`s are present even in the cases where the thermal
component is negligible. We present a model which identifies the origin of the
QPO's and relates them directly to the properties of a compact coronal region
which is bounded by the adjustment from Keplerian to sub-Keplerian inflow into
the BH and which is primarily responsible for the observed power law spectrum.
The model also predicts the relationship between high and low frequency QPO's
and shows how BH's can be unique identified from observations of the soft
states of NS's and BHC's.


title: Polarization observations of nine southern millisecond pulsars

abstract:
  Mean pulse profiles and polarization properties are presented for nine
southern pulsars. The observations were made using the Parkes radio telescope
at frequencies near 1330 MHz; three of the nine pulsars were also observed at
660 MHz. A very high degree of circular polarization was observed in PSR
J1603-7202. Complex position angle variations which are not well described by
the rotating-vector model were observed in PSRs J2124-3358 and J2145-0750, both
of which have very wide profiles. Rotation measures were obtained for all nine
pulsars, with two implying relatively strong interstellar magnetic fields.


title: Nucleation of quark matter in neutron stars cores

abstract:
  We consider the general conditions of quark droplets formation in high
density neutron matter. The growth of the quark bubble (assumed to contain a
sufficiently large number of particles) can be described by means of a
Fokker-Planck equation. The dynamics of the nucleation essentially depends on
the physical properties of the medium it takes place. The conditions for quark
bubble formation are analyzed within the frameworks of both dissipative and
non-dissipative (with zero bulk and shear viscosity coefficients) approaches.
The conversion time of the neutron star to a quark star is obtained as a
function of the equation of state of the neutron matter and of the microscopic
parameters of the quark nuclei. As an application of the obtained formalism we
analyze the first order phase transition from neutron matter to quark matter in
rapidly rotating neutron stars cores, triggered by the gravitational energy
released during the spinning down of the neutron star. The endothermic
conversion process, via gravitational energy absorption, could take place, in a
very short time interval, of the order of few tens seconds, in a class of dense
compact objects, with very high magnetic fields, called magnetars.


title: A Jet Model of the Galactic Center Nonthermal Radio Filaments

abstract:
  Protostellar sources in star forming regions are responsible for driving jets
with flow velocities ranging between 300 and 400 km s$^{-1}$. This class of
jets consists of highly collimated outflows which include thermal knots with
number densities estimated to be greater than that of their ambient medium. On
the other hand, extragalactic FR I jets consist of light fluid with low Mach
number burrowing through a denser medium as the magnetized jets radiate
nonthermal emission. Both protostellar and extragalactic jets are believed to
be launched by accretion disks. Here we consider a jet model in which the
characteristics common to both protostellar and extragalactic jets are used to
explain the origin of nonthermal filaments in the Galactic center region. We
argue that these filaments are analogous to FR I extragalactic sources but are
launched by embedded young stars or clusters of stars in star-forming regions.


title:
On the time variation of c, G, and h and the dynamics of the cosmic
  expansion

abstract:
  Several authors have recently explored the idea that physical constants such
as c and G might vary over time and have formulated theories describing this
variation that can address a range of cosmological problems. Such work
typically invokes a generic parameterization which assumes a power-law
variation with the expansion scale factor, R. This work offers alternative,
physically motivated definitions for the parameters c, G, and h based on the
Machian premise that these dimensional quantities reflect global dynamics of
the expansion geometry. Together with a postulated conservation law and
equations of motion, the implications of this theory for Friedmann models are
examined, and found to yield several interesting conclusions including: (1)
natural solutions to the horizon, flatness, and lambda problems, (2) the
prediction of a flat, Omega_0 = 1 universe, (3) different forms for some
cosmological scaling laws, (4) an apparent fit to observations of Type Ia
supernovae without invoking a cosmological constant, (5) equivalence between
our Universe and a black hole and apparent consistency of the model with the
Holographic Principle, and (6) potentially testable predictions for the time
variation of physical parameters, including values for c_dot and h_dot that are
small but non-zero today and a value for G_dot that was negative and nonzero
during radiation domination and decayed to effectively zero upon the epoch of
matter domination. While this work does not attempt to provide the complete
theoretical foundation that must ultimately underlie any theory that could
naturally marry traditional physics with the notion of time-varying physical
parameters, it is written in the hope that it might stimulate further progress
towards this end.


title:
Gamma-ray Emission Properties from Mature Pulsars in the Galaxy and in
  the Gould Belt

abstract:
  We study the $\gamma$-ray emission properties of pulsars by using a new
self-consistent outer gap model. The outer gap can exist in pulsars with age
over million years old if the effect of magnetic inclination angle as well as
the average properties of the outer gap are considered. The mature $\gamma$-ray
pulsars, whose ages are between 0.3 to 3 million years old, are able to move up
to high galactic latitude. Moreover, their $\gamma$-ray luminosity are weaker
and their spectra are softer than those of younger $\gamma$-ray pulsars in the
galactic plane significantly. We use a Monte Carlo method to simulate the
statistical properties of $\gamma$-ray pulsars in the Galaxy as well as in the
Gould Belt. We find that $\gamma$-ray pulsars located at $\mid b \mid <
5^{\circ}$ and located at $\mid b \mid > 5^{\circ}$ have very different
properties. High galactic latitude $\gamma$-ray pulsars are dominated by mature
pulsars with longer periods, weaker fluxes and softer spectra. If the pulsar
birth rate in the Galaxy and the Gould Belt are $\sim 10^{-2}yr^{-1}$ and $\sim
2\times 10^{-5}yr^{-1}$ respectively, there are 42 and 35 radio-quiet
$\gamma$-ray pulsars for $\mid b \mid < 5^{\circ}$ and $\mid b \mid >
5^{\circ}$ respectively. Radio-quiet $\gamma$-ray pulsars from the Gould Belt
are 2 and 13 for $\mid b \mid < 5^{\circ}$ and $\mid b \mid > 5^{\circ}$
respectively. We suggest that a good fraction of unidentified EGRET
$\gamma$-ray sources may be these radio-quiet $\gamma$-ray pulsars. Furthermore
$\gamma$-ray pulsars located at $\mid b \mid > 5^{\circ}$ satisfies $L_{\gamma}
\propto L^{\beta}_{sd}$ whereas $L_{\gamma} \propto L^{\delta}_{sd}$ for
$\gamma$-ray pulsars in the galactic plane, where $\beta \sim 0.6$ and $\delta
\sim 0.3$ respectively.


title:
On the Stability of a Planetary System Embedded in the Beta Pictoris
  Debris Disk

abstract:
  It has recently been stated that the warp structure observed around the star
Beta Pictoris may be due to four planets embedded in its debris disk (Wahhaj et
al., 2003). It, therefore, becomes important to investigate for what range of
parameters, and for how long such a multibody system will be dynamically
stable. We present the results of the numerical integration of the suggested
planetary system for different values of the mass and radii of the planets, and
their relative positions and velocities. We also present a statistical analysis
of the results in an effort to understand the relation between the different
regions of the parameter-space of the system and the duration of the orbital
stability of the embedded planets.


title: A comprehensive CCD photometric study of the open cluster NGC 2421

abstract:
  We present the $UBVRI$ CCD photometry in the region of the open cluster NGC
2421. Radius of the cluster is determined as $\sim$ 3$^\prime$.0 using stellar
density profile. Our Study indicates that metallicity of the cluster is $Z
\sim$ 0.004. The reddening $E(B-V) = 0.42\pm$0.05 mag is determined using two
colour $(U-B)$ versus $(B-V)$ diagram. By combining the 2MASS $JHK$ data with
the optical data we determined $E(J-K) = 0.20\pm$0.20 mag and $E(V-K) =
1.15\pm$0.20 mag for this cluster. Colour-excess diagrams show normal
interstellar extinction law in the direction of the cluster. We determined the
distance of the cluster as 2.2$\pm$0.2 Kpc by comparing the ZAMS with the
intrinsic CM diagram of the cluster. The age of the cluster has been estimated
as 80$\pm$20 Myr using the stellar isochrones of metallicity $Z = 0.004$. The
mass function slope $x = 1.2\pm0.3$ has been derived by applying the
corrections of field stars contamination and data incompleteness. Our analysis
indicate that the cluster NGC 2421 is dynamically relaxed.


title: Cores of Dark Matter Halos Correlate with Disk Scale Lengths

abstract:
  We investigate in detail the mass distribution obtained by means of high
resolution rotation curves of 25 galaxies of different morphological types. The
dark matter contribution to the circular rotation velocity is well-described by
resorting to a dark component whose density shows an inner core, i.e. a central
constant density region. We find a very strong correlation between the core
radius size $R_C$ and the stellar exponential scale length $R_D$: $R_C \simeq
13 (\frac {R_D} {5 {\rm kpc}})^{1.05} {\rm kpc} $, and between $R_C$ and the
galaxy dynamical mass at this distance, $M_{dyn}(R_C)$. These relationships
would not be expected if the core radii were the product of an incorrect
decomposition procedure, or the biased result of wrong or misunderstood
observational data. The very strong correlation between the dark and luminous
scale lengths found here seems to hold also for different Hubble types and
opens new scenarios for the nature of the dark matter in galaxies.


title:
Search for low energy neutrinos in correlation with the 8 events
  observed by the EXPLORER and NAUTILUS detectors in 2001

abstract:
  We report on a search for low-energy neutrino (antineutrino) bursts in
correlation with the 8 time coincident events observed by the gravitational
waves detectors EXPLORER and NAUTILUS (GWD) during the year 2001. The search,
conducted with the LVD detector (INFN Gran Sasso National Laboratory, Italy),
has considered several neutrino reactions, corresponding to different neutrino
species, and a wide range of time intervals around the (GWD) observed events.
No evidence for statistically significant correlated signals in LVD has been
found. Assuming two different origins for neutrino emission, the cooling of a
neutron star from a core-collapse supernova or from coalescing neutron stars
and the accretion of shocked matter, and taking into account neutrino
oscillations, we derive limits to the total energy emitted in neutrinos and to
the amount of accreting mass, respectively.


title:
Curious Variables Experiment (CURVE). IX Draconis - a Clue for
  Understanding Evolution of Cataclysmic Variable Stars

abstract:
  We report extensive photometry of frequently outbursting dwarf nova IX
Draconis. During five months of observations the star went into three
superoutbursts and seven ordinary outbursts. This allowed us to determine its
supercycle and cycle lengths as equal to 54 +/- 1 and 3.1 +/- 0.1 days,
respectively. During the Sep 2003 superoutburst, which had the best
observational coverage, IX Dra displayed clear superhumps with a period of
Psh=0.066968(17) days. This period was constant during the whole superoutburst.
Another period, which was clearly present in the light curve of IX Dra in
superoutburst, had a value of 0.06646(6) days and we interpret it as the
orbital period of the binary. Thus IX Dra is the first SU UMa star showing
orbital modulation during the entire superoutburst. The beat between these two
periods is the main cause of an unusual phase reversal of superhumps - a
phenomenon which was previously observed in ER UMa. If our interpretation of
the second periodicity is correct, IX Dra has an extremely low period excess
$\epsilon$ equal to only 0.76% +/- 0.03%. This implies very low mass ratio
q=0.035 +/- 0.003, which strongly suggests that the system contains a brown
dwarf-like degenerate secondary of mass ~0.03 Mo and that IX Dra is the most
evolved dwarf nova known. Such a very low mass ratio results in the outer edge
of the accretion disk reaching 80% of the distance between the components of
the system. In turn, this allows the disk particles to enter a 2:1 resonance
and leads to the appearance of the orbital period in the light curve of the
entire superoutburst.The high level of activity and brightness of IX Dra
indicate that very old cataclysmic variables go through episodes of increased
activity leading to loss of angular momentum through mass loss from the system.


title:
The cosmic infrared background (CIRB) and the role of the "local
  environment of galaxies" in the origin of present-day stars

abstract:
  A combination of evidence is presented suggesting that the majority of the
stars in today's galaxies were born during a luminous infrared phase (LIRP)
triggered by the local environment of galaxies. The CIRB is a fossil record of
these LIRPs and therefore reflects the influence of triggered star formation
through galaxy-galaxy interactions, including non merging tidal encounters.
This scenario, in which galaxies experienced several LIRPs in their history, is
consistent with the measured redshift evolution of the cosmic density of star
formation rates and of stellar masses of galaxies.


title: The Universality of Initial Conditions for Globular Cluster Formation

abstract:
  We investigate a simple model for globular cluster (GC) formation. We
simulate the violent relaxation of initially homogeneous isothermal stellar
spheres and show that it leads to the formation of clusters with radial density
profiles that match the observed profiles of GCs. The best match is achieved
for dynamically unevolved clusters. In this model, all the observed
correlations between global GC parameters are accurately reproduced if one
assumes that all the clusters initially had the same value of the stellar
density and the velocity dispersion. This suggests that the gas which formed
GCs had the same values of density and temperature throughout the universe.