title:
Multicolour photometry of Balloon 090100001: linking the two classes of
  pulsating hot subdwarfs

abstract:
  We present results of the multicolour UBVR photometry of the high-amplitude
EC14026-type star, Balloon 090100001. The data span over a month and consist of
more than a hundred hours of observations. Fourier analysis of these data led
us to the detection of at least 30 modes of pulsation of which 22 are
independent. The frequencies of 13 detected modes group in three narrow ranges,
around 2.8, 3.8 and 4.7 mHz, where the radial fundamental mode, the first and
second overtones are likely to occur. Surprisingly, we also detect 9
independent modes in the low-frequency domain, between 0.15 and 0.4 mHz. These
modes are typical for pulsations found in PG1716+426-type stars, discovered
recently among cool B-type subdwarfs. The modes found in these stars are
attributed to the high-order g modes. As both kinds of pulsations are observed
in Balloon 090100001, it represents a link between the two classes of pulsating
hot subdwarfs. At present, it is probably the most suitable target for testing
evolutionary scenarios and internal constitution models of these stars by means
of asteroseismology.
  Three of the modes we discovered form an equidistant frequency triplet which
can be explained by invoking rotational splitting of an $\ell$ = 1 mode. The
splitting amounts to about 1.58 $\mu$Hz, leading to a rotation period of 7.1
$\pm$ 0.1 days.


title:
Kinematics of the Galactic Halo from Horizontal Branch stars in the
  Hamburg/ESO Survey

abstract:
  Large samples of Field Horizontal Branch (FHB) stars make excellent tracers
of the Galactic halo; by studying their kinematics, one can infer important
physical properties of our Galaxy. Here we present the results of a
medium-resolution spectroscopic survey of 530 FHB stars selected from the
Hamburg/ESO survey. The stars have a mean distance of ~7 kpc and thus probe the
inner parts of the Milky Way halo. We measure radial velocities from the
spectra in order to test the model of Sommer-Larsen et al., who suggested that
the velocity ellipsoid of the halo changes from radially-dominated orbits to
tangentially-dominated orbits as one proceeds from the inner to the outer halo.
We find that the present data are unable to discriminate between this model and
a more simple isothermal ellipsoid; we suggest that additional observations
towards the Galactic centre might help to differentiate them.


title: The GRB 030328 host: another case of a blue starburst galaxy

abstract:
  We present for the first time the detection of the GRB 030328 host galaxy in
four optical bands equivalent to UBRI. The host galaxy spectral energy
distribution is consistent with a low extinction (E(B-V) < 0.21) starburst
galaxy. The restframe B-band magnitude of the host is M_B ~ -20.4


title:
Formation of Kuiper-belt binaries through multiple chaotic scattering
  encounters with low-mass intruders

abstract:
  The discovery that many trans-neptunian objects exist in pairs, or binaries,
is proving invaluable for shedding light on the formation, evolution and
structure of the outer Solar system. Based on recent systematic searches it has
been estimated that up to 10% of Kuiper-belt objects might be binaries.
However, all examples discovered to-date are unusual, as compared to near-Earth
and main-belt asteroid binaries, for their mass ratios of order unity and their
large, eccentric orbits. In this article we propose a common dynamical origin
for these compositional and orbital properties based on four-body simulations
in the Hill approximation. Our calculations suggest that binaries are produced
through the following chain of events: initially, long-lived quasi-bound
binaries form by two bodies getting entangled in thin layers of dynamical chaos
produced by solar tides within the Hill sphere. Next, energy transfer through
gravitational scattering with a low-mass intruder nudges the binary into a
nearby non-chaotic, stable zone of phase space. Finally, the binary hardens
(loses energy) through a series of relatively gentle gravitational scattering
encounters with further intruders. This produces binary orbits that are well
fitted by Kepler ellipses. Dynamically, the overall process is strongly favored
if the original quasi-bound binary contains comparable masses. We propose a
simplified model of chaotic scattering to explain these results. Our findings
suggest that the observed preference for roughly equal mass ratio binaries is
probably a real effect; that is, it is not primarily due to an observational
bias for widely separated, comparably bright objects. Nevertheless, we predict
that a sizeable population of very unequal mass Kuiper-belt binaries is likely
awaiting discovery.


title:
Accretion in dipole magnetic fields: flow structure and X-ray emission
  of accreting white dwarfs

abstract:
  Field-channelled accretion flows occur in a variety of astrophysical objects,
including T Tauri stars,magnetic cataclysmic variables and X-ray pulsars. We
consider a curvilinear coordinate system and derive a general hydrodynamic
formulation for accretion onto stellar objects confined by a stellar dipole
magnetic field. The hydrodynamic equations are solved to determine the
velocity, density and temperature profiles of the flow. We use accreting
magnetic white-dwarf stars as an illustrative example of astrophysical
applications. Our calculations show that the compressional heating due to the
field geometry is as important as radiative cooling and gravity in determining
the structure of the post-shock flow in accreting white-dwarf stars. The
generalisation of the formulation to accretion flows channelled by higher-order
fields and the applications to other astrophysical systems are discussed.


title:
Relativistic r-modes and Shear viscosity: regularizing the continuous
  spectrum

abstract:
  Within a fully relativistic framework, we derive and solve numerically the
perturbation equations of relativistic stars, including the stresses produced
by a non-vanishing shear viscosity in the stress-energy tensor. With this
approach, the real and imaginary parts of the frequency of the modes are
consistently obtained. We find that, approaching the inviscid limit from the
finite viscosity case, the continuous spectrum is regularized and we can
calculate the quasi-normal modes for stellar models that do not admit solutions
at first order in perturbation theory when the coupling between the polar and
axial perturbations is neglected. The viscous damping time is found to agree
within factor 2 with the usual estimate obtained by using the eigenfunctions of
the inviscid limit and some approximation for the energy dissipation integrals.
We find that the frequencies and viscous damping times for relativistic
$r-$modes lie between the Newtonian and Cowling results. We compare the results
obtained with homogeneous, polytropic and realistic equations of state and find
that the frequencies depend only on the rotation rate and on the compactness
parameter (M/R), being almost independent of the equation of state. Our
numerical results for realistic neutron stars give viscous damping times with
the same dependence on mass and radius as previously estimated, but
systematically larger of about 60%.


title:
A simple method to construct exact density-potential pairs from a
  homeoidal expansion

abstract:
  We start from a study of the density-potential relation for classical
homeoids in terms of an asymptotic expansion for small deviations from
spherical symmetry. We then show that such expansion is a useful device that
allows us to construct a variety of exact density-potential pairs with
spheroidal, toroidal, or triaxial shapes for which the deviation from spherical
symmetry is finite. As concrete analytical applications, we describe: (1) The
construction of a family of toroidal axisymmetric density-potential pairs one
of which is associated with a perfectly flat rotation curve (for a member of
this family, the supporting two-integral phase-space distribution function is
obtained in closed form); (2) The determination of the aperture velocity
dispersion in a wide class of two-integral axisymmetric models not stratified
on homeoids with central black hole, which may be useful for the discussion of
the dynamical contributions to the characteristics of the Fundamental Plane of
early-type galaxies; and (3) For such class of models, the construction of the
v/sigma-ellipticity relation, often considered to assess the role of rotation
in the structure of elliptical galaxies.


title: Faint Fuzzies and the Formation of Lenticular Galaxies

abstract:
  We investigate the dynamical state of a new class of extended star clusters,
known as "Faint Fuzzies", that were discovered in two nearby S0 galaxies, NGC
1023 and NGC 3384. It is shown that the Faint Fuzzies of NGC 1023 lie in a fast
rotating ring-like structure within the galactic disk with mean radius of 5
kpc, rotational velocity of 200 km/s and velocity dispersion of 115 km/s. We
propose a scenario for the origin of Faint Fuzzies that is connected to the
origin of S0 galaxies as a result of galaxy-galaxy interactions in dense
environments. As is apparent in the Cartwheel galaxy, and is confirmed by
numerical simulations, the passage of a small galaxy through, or close to, the
center of a disk galaxy can form a ring of clumpy star formation with a radius
comparable to the Faint Fuzzy ring radius in NGC 1023. In this case, the Faint
Fuzzies are signposts for the transformation of spiral galaxies into
lenticulars via such interactions.


title:
Amplification of Interstellar Magnetic Fields and Turbulent Mixing by
  Supernova-Driven Turbulence Part II - The Role of Dynamical Chaos

abstract:
  In this paper we further advance the study of magnetic field amplification in
the interstellar medium that was started in Balsara et al (2004, Paper I). We
show that the flux growth rate is comparable to the rate of magnetic energy
growth found in Paper I. We also demonstrate the role of intermittency in field
amplification. The density shows a double-peaked PDF, consistent with the
cooling curve that was used. The PDF of the magnetic field shows a high-end
tail, providing a tell-tale signature of the operation of the small scale
dynamo. The magnetic field strength correlates positively with the density. As
a result, the field amplification takes place more vigorously in the lower
temperature, denser gas. The Lagrangian chaos in the simulated turbulent flows
is studied in substantial detail. It is shown that the stretching rate of
material lines as well as the Lyapunov exponents can be used to gain important
insights into the growth of magnetic field. The cancellation exponent for the
small scale supernova-driven dynamo is derived and it is shown that
constructive folding of field lines in the dynamo is very inefficient. We also
show that our Lagrangian approach can yield actual measures of the turbulent
diffusivity in the simulated ISM. The turbulent diffusivity provides insights
into the mixing of elements from supernova ejecta on macroscopic scales. The
high rates of line stretching in interstellar turbulence suggests that the
eventual diffusion of elements at the molecular level is very efficient. Many
of the diagnostics of turbulence that are presented here can be used to make
direct connections between simulations and observations.


title:
The Size of the Radio-Emitting Region in Low-luminosity Active Galactic
  Nuclei

abstract:
  We have used the VLA to study radio variability among a sample of 18 low
luminosity active galactic nuclei (LLAGNs), on time scales of a few hours to 10
days. The goal was to measure or limit the sizes of the LLAGN radio-emitting
regions, in order to use the size measurements as input to models of the radio
emission mechanisms in LLAGNs. We detect variability on typical time scales of
a few days, at a confidence level of 99%, in half of the target galaxies.
Either variability that is intrinsic to the radio emitting regions, or that is
caused by scintillation in the Galactic interstellar medium, is consistent with
the data. For either interpretation, the brightness temperature of the emission
is below the inverse-Compton limit for all of our LLAGNs, and has a mean value
of about 1E10 K. The variability measurements plus VLBI upper limits imply that
the typical angular size of the LLAGN radio cores at 8.5 GHz is 0.2
milliarcseconds, plus or minus a factor of two. The ~ 1E10 K brightness
temperature strongly suggests that a population of high-energy nonthermal
electrons must be present, in addition to a hypothesized thermal population in
an accretion flow, in order to produce the observed radio emission.


title:
Absorption and scattering properties of arbitrarily shaped particles in
  the Rayleigh domain: A rapid computational method and a theoretical
  foundation for the statistical approach

abstract:
  We provide a theoretical foundation for the statistical approach for
computing the absorption properties of particles in the Rayleigh domain. We
present a general method based on the Discrete Dipole Approximation (DDA) to
compute the absorption and scattering properties of particles in the Rayleigh
domain. The method allows to separate the geometrical aspects of a particle
from its material properties. Doing the computation of the optical properties
of a particle once, provides them for any set of refractive indices,
wavelengths and orientations. This allows for fast computations of e.g.
absorption spectra of arbitrarily shaped particles. Other practical
applications of the method are in the interpretation of atmospheric and radar
measurements as well as computations of the scattering matrix of small
particles as a function of the scattering angle. In the statistical approach,
the optical properties of irregularly shaped particles are represented by the
average properties of an ensemble of particles with simple shapes. We show that
the absorption cross section of an ensemble of arbitrarily shaped particles
with arbitrary orientations can always be uniquely represented by the average
absorption cross section of an ensemble of spheroidal particles with the same
composition and fixed orientation. This proves for the first time that the
statistical approach is generally viable in the Rayleigh domain.


title: Metal Enrichment Processes in the Intra-Cluster Medium

abstract:
  We present numerical simulations of galaxy clusters which include interaction
processes between the galaxies and the intra-cluster gas. The considered
interaction processes are galactic winds and ram-pressure stripping, which both
transfer metal-enriched interstellar medium into the intra-cluster gas and
hence increase its metallicity. We investigate the efficiency and time
evolution of the interaction processes by simulated metallicity maps, which are
directly comparable to those obtained from X-ray observations. We find that
ram-pressure stripping is more efficient than quiet (i.e. non-starburst driven)
galactic winds in the redshift interval between 1 and 0. The expelled metals
are not mixed immediately with the intra-cluster gas, but inhomogeneities are
visible in the metallicity maps. Even stripes of higher metallicity that a
single galaxy has left behind can be seen. The spatial distribution of the
metals transported by ram-pressure stripping and by galactic winds are very
different for massive clusters: the former process yields a centrally
concentrated metal distribution while the latter results in an extended metal
distribution.


title:
RXJ0142.0+2131: I. The galaxy content of an X-ray-luminous galaxy
  cluster at z=0.28

abstract:
  We present a photometric and spectroscopic study of stellar populations in
the X-ray-luminous cluster of galaxies RXJ0142.0+2131 at z=0.280. This paper
analyses the results of high signal-to-noise spectroscopy, as well as g'-, r'-,
and i'-band imaging, using the Gemini Multi-Object Spectrograph on Gemini
North. Of 43 spectroscopic targets, we find 30 cluster members over a range in
color. Central velocity dispersions and absorption-line strengths for lines in
the range 3700A < lambda_rest < 5800A are derived for cluster members, and are
compared with a low-redshift sample of cluster galaxies, and single stellar
population (SSP) models. We use a combination of these indicators to estimate
luminosity-weighted mean ages, metallicities ([M/H]), and alpha-element
abundance ratios ([alpha/Fe]).
  RXJ0142.0+2131 is a relatively poor cluster and lacks galaxies with high
central velocity dispersions. Although the red sequence and the Faber-Jackson
relation are consistent with pure passive evolution of the early-type
population with a formation redshift of z_form = 2, the strengths of the 4000A
break and scaling relations between metal line indices and velocity dispersion
reject this model with high significance. By inverting SSP models for the
Hbeta_G, Mgb, and <Fe> line indices, we calculate that, at a given velocity
dispersion and metallicity, galaxies in RXJ0142.0+2131 have luminosity-weighted
mean ages 0.14 +- 0.07 dex older than the low-redshift sample. We also find
that [alpha/Fe] in stellar populations in RXJ0142.0+2131 is 0.14 +- 0.03
greater than at low redshift. All scaling relations are consistent with these
estimated offsets. (abridged)


title:
Parameters of the prompt gamma-ray burst emission estimated with the
  opening angle of jets

abstract:
  We present in this paper an approach to estimate the initial Lorentz factor
of gamma-ray bursts (GRBs) without referring to the delayed emission of the
early afterglow. Under the assumption that the afterglow of the bursts
concerned occurs well before the prompt emission dies away, the Lorentz factor
measured at the time when the duration of the prompt emission is ended could be
estimated by applying the well-known relations of GRB jets. With the concept of
the efficiency for converting the explosion energy to radiation, this Lorentz
factor can be related to the initial Lorentz factor of the source. The
corresponding rest frame peak energy can accordingly be calculated. Applying
this method, we estimate the initial Lorentz factor of the bulk motion and the
corresponding rest frame spectral peak energy of GRBs for a new sample where
the redshift and the break time in the afterglow are known. Our analysis shows
that, in the circumstances, the initial Lorentz factor of the sample would peak
at 200 and would be distributed mainly within $(100,400)$, and the peak of the
distribution of the corresponding rest frame peak energy would be $0.8keV$ and
its main region would be $(0.3keV,3keV)$.


title:
On the Comment by Palle (astro-ph/0503562) on the vorticity and shear of
  the Universe

abstract:
  We show that a recent comment where Palle criticises works regarding CMBR
fluctuations for a particular type of Bianchi models, is incorrect. In
particular, in contrast to the claims of Palle, we point out that Bianchi
models do allow for vorticity.


title:
A simple parameterization of the consequences of deleptonization for
  simulations of stellar core collapse

abstract:
  A simple and computationally efficient parameterization of the
deleptonization, the entropy changes, and the neutrino stress is presented for
numerical simulations of stellar core collapse. The parameterization of the
neutrino physics is based on a bounce profile of the electron fraction as it
results from state-of-the-art collapse simulations with multi-group Boltzmann
neutrino transport in spherical symmetry. Two additional parameters include an
average neutrino escape energy and a neutrino trapping density. The
parameterized simulations reproduce the consequences of the delicate neutrino
thermalization/diffusion process during the collapse phase and provide a by far
more realistic alternative to the adiabatic approximation, which has often been
used in the investigation of the emission of gravitational waves, of
multi-dimensional general relativistic effects, of the evolution of magnetic
fields, or even of the nucleosynthesis in simulations of core collapse and
bounce. For supernova codes that are specifically designed for the postbounce
phase, the parameterization builds a convenient bridge between the point where
the applicability of a stellar evolution code ends and the point where the
postbounce evolution begins.


title: A Parameter-free Statistical Measurement of Halos with Power Spectra

abstract:
  We show that, in the halo model of large-scale structure formation, the
difference between the Fourier and the DWT (discrete wavelet transform) power
spectra provides a statistical measurement of the halos. This statistical
quantity is free from parameters related to the shape of the mass profile and
the identification scheme of halos. That is, the statistical measurement is
invariant in the sense that models with reasonably defined and selected
parameters of the halo models should yield the same difference of the Fourier
and DWT spectra. This feature is useful to extract ensemble averaged properties
of halos, which cannot be obtained with the identification of individual halo.
To demonstrate this point, we show with WIGEON hydrodynamical simulation
samples that the spectrum difference provides a quantitative measurement of the
discrepancy of the distribution of baryonic gas from that of the underlying
dark matter field within halos. We also show that the mass density profile of
halos in physical space can be reconstructed with this statistical measurement.
This profile essentially is the average over an ensemble of halos, including
well virialized halos as well as halos with significant internal substructures.
Moreover, this reconstruction is sensitive to the tail of the mass density
profile. We showed that the profile with $1/r^3$ tail gives very different
result from that of $1/r^2$. Other possible applications of this method are
discussed as well.


title:
High-spatial-resolution observations of NH3 and CH3OH towards the
  massive twin cores NGC6334 I & I(N)

abstract:
  Molecular line observations of NH3 (J,K)=(1,1), (2,2) and CH3OH at 24.93GHz
taken with the Australian Telescope Compact Array (ATCA) toward the massive
twin cores NGC6334 I & I(N) reveal significant variations in the line emission
between the two massive cores. The UCHII region/hot core NGC6334 I exhibits
strong thermal NH3 and CH3OH emission adjacent to the UCHII region and
coincident with two mm continuum peaks observed by Hunter et al. (in prep.). In
contrast, we find neither compact NH3 nor thermal CH3OH line emission toward
NGC6334 I(N). There, the NH3 emission is distributed over a broad region (>1')
without a clear peak, and we find Class I CH3OH maser emission with peak
brightness temperatures up to 7000K. The maser emission peaks appear to be
spatially associated with the interfaces between the molecular outflows and the
ambient dense gas. Peak NH3(1,1) line brightness temperatures >= 70K in both
regions indicate gas temperatures of the same order. NH3 emission is also
detected toward the outflow in NGC6334 I resulting in an estimated rotational
temperature of Trot~19K. Furthermore, we observe CH3OH and NH3 absorption
toward the UCHII region, the velocity structure is consistent with expanding
molecular gas around the UCHII region. Thermal and kinematic effects possibly
imposed from the UCHII region on the molecular core are also discussed.


title: Skyrmion Stars: Astrophysical motivations and implications

abstract:
  We study mass-radius relations for compact stars employing an equation of
state (EOS) of dense matter based on a Skyrme fluid. The zero-temperature
mean-field model is based on mesonic excitations, incorporates the scale
breaking of QCD, and accommodates baryons (nucleons) which arise as a solitonic
configuration of mesonic fields. Stable configurations are obtained for central
densities $\rho_c/\rho_n\leq 5.0$ where $\rho_n=2.575\times 10^{14}$ g/cc is
the nuclear saturation density. These {\it Skyrmion Stars} are mostly fluid,
with a crust which we describe by the EOS of Baym, Pethick and Sutherland.
Their masses and radii are in the range $0.4 \le M/M_{\odot} \le 3.6$ and $13
{\rm km} \le R \le 23 {\rm km}$, respectively. The minimum spin period is
computed to be between $0.7 {\rm ms}\le P \le 2.1 {\rm ms}$. They appear to
have a mass-radius curve quite different from either neutron or quark stars,
and provide a suitable description of the heavier mass neutron stars discovered
recently due to the inherently stiff EOS. Within the same model, we compute the
dominant neutrino emissivity in neutron-rich $\beta$-equilibrated matter, and
determine the cooling behaviour of Skyrmion stars.


title:
Variability of Broad and Blueshifted Component of [OIII]$\lambda$5007 in
  IZWI

abstract:
  Although the existence of asymmetrical profile of [OIII]$\lambda$5007 has
been discovered for ages, its filiation and physics are poorly understood. Two
new spectra of I ZWI taken on Nov 16, 2001 and on Dec 3, 2002 were compared
with the spectra taken by BG92. Following results are obtained. 1)The certain
variations of broad [OIII] during about 10 years separating the observations
are identified. The inferred length scale of broad [OIII] emitting region
ranges from 0.3pc to 3pc. By assuming a Keplerian motion in emitting region,
the material emitting broad [OIII] is likely to be located at transient
emission line region, between BLR and NLR. 2)We find a positive relation
between the FeII emission and flux of H$\beta$(or continuum). On the other
hand, the parameter RFe decreases with ionizing continuum marginally. 3)We
detect a low ionized NLR in I ZWI, because of the low flux ratios
$\rm{[OIII]_{n}/H\beta_{n}}$($\sim1.7$).


title: Magnetars

abstract:
  Ultramagnetized neutron stars or magnetars are magnetically powered neutron
stars. Their strong magnetic fields dominate the physical processes in their
crusts and their surroundings. The past few years have seen several advances in
our theoretical and observational understanding of these objects. In spite of a
surfeit of observations, their spectra are still poorly understood. I will
discuss the emission from strongly magnetized condensed matter surfaces of
neutron stars, recent advances in our expectations of the surface composition
of magnetars and a model for the non-thermal emission from these objects.


title:
Exploring a deep meridional flow hypothesis for a circulation dominated
  solar dynamo model

abstract:
  Circulation-dominated solar dynamo models, which employ a helioseismic
rotation profile and a fixed meridional flow, give a good approximation to the
large scale solar magnetic phenomena, such as the 11-year cycle or the so
called Hale's law of polarities. Nevertheless, the larger amplitude of the
radial shear at the high latitudes makes the dynamo to produce a strong
toroidal magnetic field at high latitudes, in contradiction with the
observations of the sunspots (Sporer`s Law). A possible solution was proposed
by Nandy and Choudhur (2002) in which a deep meridional flow can conduct the
magnetic field inside of a stable layer (the radiative core) and then allow
that it erupts just at lower latitudes. We have recently explored this
hypothesis in a different approximation, using the magnetic buoyancy mechanism
proposed by Dikpaty and Charbonneau (1999) and found that a deep meridional
flow pushes the maximum of the toroidal magnetic field towards the solar
equator, but, in contrast to Nandy and Choudhuri (2002), a second zone of
maximum fields remains at the poles (Guerrero and Munoz (2004)). We here review
these results and also discuss a new possible scenario where the tachocline has
an ellipsoidal shape, following early helioseismologic observations Charbonneau
et. al., (1999), and find that the modification of the geometry of the
tachocline can lead to results which are in good agreement with observations
and opens the possibility to explore in more detail, through the dynamo model,
the place where the magnetic field could be really stored.


title: On the nature of the S stars in the Galactic Center

abstract:
  Davies and King have suggested that the bright stars observed on short-period
orbits about Sgr A* (``S stars'') are old, low-mass stripped AGB stars rather
than young, high-mass main-sequence stars. If the observationally inferred
effective temperatures and luminosities of these stars are correct, however,
then DK have grossly overestimated the post-AGB lifetimes and hence
underestimated the production rate in steady state. In fact, the total mass in
stars stripped over the age of the Galaxy would exceed that of the stellar cusp
bound to Sgr A*. We take issue also with Davies & King's estimates of the
energetics involved in capturing the stars onto their present orbits.


title: Optical Properties of 4248 IRAS Galaxies

abstract:
  We have investigated optical properties of 4248 infrared galaxies (IRGs) by
positionally matching data from the IRAS and the SDSS DR3. Our sample includes
3 hyper luminous infrared galaxies (L >10^13Lsun) and 178 ultra luminous
infrared galaxies (10^12Lsun < L < 10^13Lsun). Our findings are as follows: (i)
more IR luminous galaxies tend to have smaller local galaxy density, being
consistent with the picture where luminous IRGs are created by the
merger-interaction of galaxies that happens more often in lower density
regions; (ii) the fractions of AGNs increase as a function of Lir; (iii) there
is a good correlation between Lir and L[OIII] for AGNs, suggesting both of the
parameters can be a good estimator of the total power of AGNs; (iv) a good
correlation is found between Lir and optically estimated star formation rate
(SFR) for star-forming galaxies, suggesting Lir is a good indicator of galaxy
SFR. However, caution is needed when SFR is estimated using Lir, i.e., high SFR
galaxies selected by Lir is frequently merger/interaction, whereas high SFR
galaxies selected by optical emission is often normal spiral or
Magellanic-cloud like irregular galaxies. (v) more IR luminous galaxies have
slightly larger Halpha/Hbeta ratio; (vi) more IR luminous galaxies have more
centrally-concentrated morphology, being consistent with the morphological
appearance of galaxy-galaxy merger remnants. Optical image of ultra/very
luminous infrared galaxies also show frequent signs of merger/interaction.
(vii) comparison with the SED synthesis models indicate that majority of
luminous infrared galaxies (L > 10^11Lsun) may be in a post-starburst phase,
sharing a similar (but not the same) merger/interaction origin with E+A
galaxies. (abridged)


title:
What Can the Distribution of Intergalactic Metals Tell us About the
  History of Cosmological Enrichment?

abstract:
  I study the relationship between the spatial distribution of intergalactic
metals and the masses and ejection energies of the sources that produced them.
Over a wide range of models, metal enrichment is dominated by the smallest
efficient sources, as the enriched volume scales roughly as E^{3/5} ~ M^{3/5}
while the number density of sources goes as 1/M. In all cases, the earliest
sources have the biggest impact, because fixed comoving distances correspond to
smaller physical distances at higher redshifts. This means that most of the
enriched volume is found around rare peaks, and intergalactic metals are
naturally highly clustered. Furthermore, this clustering is so strong as to
lead to a large overlap between individual bubbles. Thus the typical radius of
enriched z ~ 3 regions should be interpreted as a constraint on groupings of
sources rather than the ejection radius of a typical source. Similarly, the
clustering of enriched regions should be taken as a measurement of source bias
rather than mass.


title: First Results from the CHARA Array. II. A Description of the Instrument

abstract:
  The CHARA Array is a six 1-m telescope optical/IR interferometric array
located on Mount Wilson California, designed and built by the Center for High
Angular Resolution Astronomy of Georgia State University. In this paper we
describe the main elements of the Array hardware and software control systems
as well as the data reduction methods currently being used. Our plans for
upgrades in the near future are also described.


title: J-resolved He I emission predictions in the low-density limit

abstract:
  Determinations of the primordial helium abundance are used in precision
cosmological tests. These require highly accurate He I recombination rate
coefficients. Here we reconsider the formation of He I recombination lines in
the low-density limit. This is the simplest case and it forms the basis for the
more complex situation where collisions are important. The formation of a
recombination line is a two-step process, beginning with the capture of a
continuum electron into a bound state and followed by radiative cascade to
ground. The rate coefficient for capture from the continuum is obtained from
photoionization cross sections and detailed balancing, while radiative
transition probabilities determine the cascades. We have made every effort to
use today's best atomic data. Radiative decay rates are from Drake's
variational calculations, which include QED, fine structure, and
singlet-triplet mixing. Certain high-$L$ fine-structure levels do not have a
singlet-triplet distinction and the singlets and triplets are free to mix in
dipole-allowed radiative decays. We use quantum defect or hydrogenic
approximations to include levels higher than those treated in the variational
calculations. [Abstract clipped]


title:
XBootes: An X-Ray Survey of the NDWFS Bootes Field - Paper I Overview
  and Initial Results

abstract:
  We obtained a 5 ksec deep Chandra X-ray Observatory ACIS-I map of the 9.3
square degree Bootes field of the NOAO Deep Wide-Field Survey. Here we describe
the data acquisition and analysis strategies leading to a catalog of 4642
(3293) point sources with 2 or more (4 or more) counts, corresponding to a
limiting flux of roughly 4(8)x10^{-15} erg cm^{-2}s^{-1} in the 0.5-7 keV band.
These Chandra XBootes data are unique in that they consitute the widest
contiguous X-ray field yet observed to such a faint flux limit. Because of the
extraordinarily low background of the ACIS, we expect only 14% (0.7%) of the
sources to be spurious. We also detected 43 extended sources in this survey.
The distribution of the point sources among the 126 pointings (ACIS-I has a 16
x 16 arcminute field of view) is consistent with Poisson fluctuations about the
mean of 36.8 sources per pointing. While a smoothed image of the point source
distribution is clumpy, there is no statistically significant evidence of large
scale filamentary structure. We do find however, that for theta>1 arcminute,
the angular correlation function of these sources is consistent with previous
measurements, following a power law in angle with slope -0.7. In a 1.4 deg^{2}
sample of the survey, approximately 87% of the sources with 4 or more counts
have an optical counterpart to R ~26 mag. As part of a larger program of
optical spectroscopy of the NDWFS Bootes area, spectra have been obtained for
\~900 of the X-ray sources, most of which are QSOs or AGN.


title: A cross-calibration between Tycho-2 photometry and HST spectrophotometry

abstract:
  I show that Tycho-2 photometry and HST spectrophotometry are accurate and
stable enough to obtain a precise cross-calibration by analyzing a
well-calibrated sample of 256 stars observed with both Hipparcos and HST. Based
on this analysis, I obtain the following photometric zero points in the Vega
magnitude system for Tycho-2: 0.020+-0.001 (B_T-V_T), 0.078+-0.009 (B_T), and
0.058+-0.009 (V_T).


title: The Vega Debris Disk -- A Surprise from Spitzer

abstract:
  We present high spatial resolution mid- and far-infrared images of the Vega
debris disk obtained with the Multiband Imaging Photometer for Spitzer (MIPS).
The disk is well resolved and its angular size is much larger than found
previously. The radius of the disk is at least 43" (330 AU), 70"(543 AU), and
105" (815 AU) in extent at 24, 70 and 160 um, respectively. The disk images are
circular, smooth and without clumpiness at all three wavelengths. The radial
surface brightness profiles imply an inner boundary at a radius of 11"+/-2" (86
AU). Assuming an amalgam of amorphous silicate and carbonaceous grains, the
disk can be modeled as an axially symmetric and geometrically thin disk, viewed
face-on, with the surface particle number density following an r^-1 power law.
The disk radiometric properties are consistent with a range of models using
grains of sizes ~1 to ~50 um. We find that a ring, containing grains larger
than 180 um and at radii of 86-200 AU from the star, can reproduce the observed
850 um flux, while its emission does not violate the observed MIPS profiles.
This ring could be associated with a population of larger asteroidal bodies
analogous to our own Kuiper Belt. Cascades of collisions starting with
encounters amongthese large bodies in the ring produce the small debris that is
blown outward by radiation pressure to much larger distances where we detect
its thermal emission. The dust production rate is >~10^15 g/s based on the MIPS
results. This rate would require a very massive asteroidal reservoir for the
dust to be produced in a steady state throughout Vega's life. Instead, we
suggest that the disk we imaged is ephemeral and that we are witnessing the
aftermath of a large and relatively recent collisional event, and subsequent
collisional cascade.


title: Why Are Radio-Galaxies Prolific Producers of Type Ia Supernovae?

abstract:
  An analysis of SNIa events in early type galaxies from the Cappellaro et al
(1999) database provides conclusive evidence that the rate of type Ia
Supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate
measured in radio-quiet galaxies, i.e. SNIa-rate$(radio-loud galaxies) =
0.43^{+0.19}_{-0.14}h^2_{75}$ SNu as compared to SNIa-rate$(radio-quiet
galaxies) = 0.11^{+0.06}_{-0.03}h^2_{75}$ SNu. The actual value of the
enhancement is likely to be in the range $\sim 2-7$ (P$\sim 10^{-4}$). This
finding puts on robust empirical grounds the results obtained by Della Valle &
Panagia (2003) on the basis of a smaller sample of SNe. We analyse the possible
causes of this result and conclude that the enhancement of SNIa explosion rate
in radio-loud galaxies has the same origin as their being strong radio sources,
but there is no causality link between the two phenomena. We argue that
repeated episodes of interaction and/or mergers of early type galaxies with
dwarf companions, on times-scale of about 1 Gyr, are responsible for inducing
both strong radio activity observed in $\sim$14% of early type galaxies and to
supply an adequate number of SNIa progenitors to the stellar population of
ellipticals.


title: GZK cutoff distortion due to the energy error distribution shape

abstract:
  The observed energy spectrum of ultra high energy cosmic rays (UHECR) is
distorted by errors in the energy reconstruction. Here we show that if the
shape of the error distribution is lognormal, the high end of the cosmic ray
spectrum will be distorted. This is distinct and potentially more significant
than the effect of the magnitude of the error in the energy. We estimate the
UHECR spectrum at the Earth assuming it is originated from a cosmological flux.
We then convolute this flux assuming a lognormal error in the energy. We show
that if the standard deviation of the lognormal error distribution is equal or
larger than 0.25, both the shape and the normalization of the measured energy
spectra will be modified significantly. As a consequence the GZK cutoff might
be sufficiently smeared and as not to be seen. This result is independent of
the power law of the cosmological flux. As a conclusion we show that in order
to establish the presence or not of the GZK feature, not only more data is
needed but also that the shape of the energy error distribution has to be known
well.


title: Superadiabatic-type magnetic amplification in conventional cosmology

abstract:
  We consider the evolution of cosmological magnetic fields in FRW models and
outline a geometrical mechanism for their superadiabatic amplification on large
scales. The mechanism operates within standard electromagnetic theory and
applies to FRW universes with open spatial sections. We discuss the general
relativistic nature of the effect and show how it modifies the adiabatic
magnetic evolution. Assuming a universe that is only marginally open today, we
estimate the main features of the superadiabatically amplified residual field.


title: Slinky Inflation

abstract:
  We present a new approach to quintessential inflation, in which both dark
energy and inflation are explained by the evolution of a single scalar field.
We start from a simple scalar potential with both oscillatory and exponential
behavior. We employ the conventional reheating mechanism of new inflation, in
which the scalar decays to light fermions with a decay width that is
proportional to the scalar mass. Because our scalar mass is proportional to the
Hubble rate, this gives adequate reheating at early times while shutting off at
late times to preserve quintessence and satisfy nucleosynthesis constraints.
  We discuss a simple model which solves the horizon, flatness, and "why now"
problems. Without any additional tuning of parameters, this model satisfies all
constraints from CMB, large scale structure, and nucleosynthesis. The
predictions for the inflationary spectral indices are n_S = n_T = 1. In this
model we are currently beginning the third cosmic epoch of accelerated
expansion.


title:
10^{-7} contrast ratio at 4.5Lambda/D: New results obtained in
  laboratory experiments using nano-fabricated coronagraph and multi-Gaussian
  shaped pupil masks

abstract:
  We present here new experimental results on high contrast imaging of 10^{-7}
at 4.5Lambda/D (Lambda = 0.820 microns) by combining a circular focal plane
mask (coronagraph) of 2.5Lambda/D diameter and a multi-Gaussian pupil plane
mask. Both the masks were fabricated on very high surface quality (Lambda/30)
BK7 optical substrates using nano-fabrication techniques of photolithography
and metal lift-off. This process ensured that the shaped masks have a useable
edge roughness better than Lambda/4 (rms error better than 0.2 microns), a
specification that is necessary to realize the predicted theoretical limits of
any mask design. Though a theoretical model predicts a contrast level of
10^{-12}, the background noise of the observed images was speckle dominated
which reduced the contrast level to 4x10^{-7} at 4.5Lambda/D. The optical setup
was built on the University of Illinois Seeing Improvement System (UnISIS)
optics table which is at the Coude focus of the 2.5-m telescope of the Mt.
Wilson Observatory. We used a 0.820 micron laser source coupled with a 5 micron
single-mode fiber to simulate an artificial star on the optical test bench of
UnISIS.


title:
Thermal and non-thermal nature of the soft excess emission from Sersic
  159-03 observed with XMM-Newton

abstract:
  Several nearby clusters exhibit an excess of soft X-ray radiation which
cannot be attributed to the hot virialized intra-cluster medium. There is no
consensus to date on the origin of the excess emission: it could be either of
thermal origin, or due to an inverse Compton scattering of the cosmic microwave
background. Using high resolution XMM-Newton data of Sersic 159-03 we first
show that strong soft excess emission is detected out to a radial distance of
0.9 Mpc. The data are interpreted using the two viable models available, i.e.,
by invoking a warm reservoir of thermal gas, or relativistic electrons which
are part of a cosmic ray population. The thermal interpretation of the excess
emission, slightly favored by the goodness-of-fit analysis, indicates that the
warm gas responsible for the emission is high in mass and low in metallicity.


title: Long-term Periodicities in the Flux from Low Mass X-ray Binaries

abstract:
  Using data from the All Sky Monitor (ASM) on the Rossi X-ray Timing Explorer
(RXTE) we have searched for long term periodicities in the X-ray flux of GX
1+4, Sco X-2 (GX 349+2), and GX 339-4. For GX 1+4 we also used data from BATSE
and Galactic Centre scans performed by RXTE. We find no evidence for X-ray
modulations at the suggested ~304 d orbital period of GX 1+4. However, we find
tentative evidence for a periodicity at 420 d to 460 d. An upper limit of 15%
peak-to-peak is set on any sinusoidal modulation in the 1.5 - 3.0 keV flux of
Sco X-2 for periods in the 30 to 100 d range. For GX 339-4 we confirm the Low
State modulation and report the detection of significant low-frequency
modulations in both the High State and Very High State. We fail to detect this
modulation in the Off State. We show that if the reported orbital period of GX
339-4 lies in the range 0.5 - 1.7 d, then it is not present in the RXTE ASM
light curve.


title: The Unified Equation of State for Dark Matter and Dark Energy

abstract:
  We assume that dark matter and dark energy satisfy the unified equation of
state: $p=B(z)\rho$, with $p=p_{dE}$, $\rho=\rho_{dm}+\rho_{dE}$, where the
pressure of dark matter $p_{dm}=0$ has been taken into account. A special
function $B=-\frac{A}{(1+z)^{\alpha}}$ is presented, which can well describe
the evolution of the universe. In this model, the universe will end up with a
Big Rip. By further simple analysis, we know other choices of the function $B$
can also describe the universe but lead to a different doomsday.


title:
PPPM and TreePM Methods on GRAPE Systems for Cosmological N-body
  Simulations

abstract:
  We present Particle-Particle-Particle-Mesh (PPPM) and Tree Particle-Mesh
(TreePM) implementations on GRAPE-5 and GRAPE-6A systems, special-purpose
hardware accelerators for gravitational many-body simulations. In our PPPM and
TreePM implementations on GRAPE, the computational time is significantly
reduced compared with the conventional implementations without GRAPE,
especially under the strong particle clustering, and almost constant
irrespective of the degree of particle clustering. We carry out the survey of
two simulation parameters, the PM grid spacing and the opening parameter for
the most optimal combination of force accuracy and computational speed. We also
describe the parallelization of these implementations on a PC-GRAPE cluster, in
which each node has one GRAPE board, and present the optimal configuration of
simulation parameters for good parallel scalability.


title:
Gamma-Ray Background from Neutralino Annihilation in the First
  Cosmological Objects

abstract:
  The paradigm of the neutralino dark matter predicts that the first
gravitationally bound objects are earth-mass sized microhaloes, which would
emit annihilation gamma-rays. Here we show that, though the flux from
individual nearest microhaloes is extremely difficult to detect, meaningful
constraints on their survival probability and internal density profile can be
set by requiring that the galactic and extragalactic gamma-ray background flux
from the microhaloes does not exceed the existing EGRET background data.
Possible disruption of microhaloes by stellar encounters does not significantly
reduce the background flux. If the probability for microhaloes to survive the
hierarchical clustering process of dark matter is as large as indicated by a
recent simulation, they could be a significant component of the observed
background flux in some photon energy range, even with the standard
annihilation cross section and conservative internal density profile of
microhaloes. The integrated gamma-ray flux from microhaloes in the halo of the
Andromeda galaxy may also be detectable by observations in the near future.


title:
Simulating the joint evolution of quasars, galaxies and their
  large-scale distribution

abstract:
  The cold dark matter model has become the leading theoretical paradigm for
the formation of structure in the Universe. Together with the theory of cosmic
inflation, this model makes a clear prediction for the initial conditions for
structure formation and predicts that structures grow hierarchically through
gravitational instability. Testing this model requires that the precise
measurements delivered by galaxy surveys can be compared to robust and equally
precise theoretical calculations. Here we present a novel framework for the
quantitative physical interpretation of such surveys. This combines the largest
simulation of the growth of dark matter structure ever carried out with new
techniques for following the formation and evolution of the visible components.
We show that baryon-induced features in the initial conditions of the Universe
are reflected in distorted form in the low-redshift galaxy distribution, an
effect that can be used to constrain the nature of dark energy with next
generation surveys.


title:
Predicting Single-Temperature Fit to Multi-Component Thermal Plasma
  Spectra

abstract:
  Observed X-ray spectra of hot gas in clusters, groups, and individual
galaxies are commonly fit with a single-temperature thermal plasma model even
though the beam may contain emission from components with different
temperatures. Recently, Mazzotta et al. pointed out that thus derived T_spec
can be significantly different from commonly used definitions of average
temperature, such as emission- or emission measure-weighted T, and found an
analytic expression for predicting T_spec for a mixture of plasma spectra with
relatively hot temperatures (T>3 keV). In this Paper, we propose an algorithm
which can accurately predict T_spec in a much wider range of temperatures
(T>0.5 keV), and for essentially arbitrary abundance of heavy elements. This
algorithm can be applied in the deprojection analysis of objects with the
temperature and metallicity gradients, for correction of the PSF effects, for
consistent comparison of numerical simulations of galaxy clusters and groups
with the X-ray observations, and for estimating how emission from undetected
components can bias the global X-ray spectral analysis.


title: Core Structure of Intracluster Gas: Isothermal Hydrostatic Equilibrium

abstract:
  We investigate core structures of X-ray emitting intracluster gas based on
the so-called beta-model, which is an isothermal hydrostatic model often used
in observational studies. We reconsider the beta-model and find that the virial
temperature T_vir of a cluster may be represented better by beta T_X than T_X,
where beta is the parameter obtained from the X-ray surface brightness and T_X
is the emission-weighted mean temperature of the gas. We investigate 121
clusters observed by ROSAT and ASCA and find that the luminosity-temperature
relation L_X - beta T_X is less steep than L_X - T_X. We classify the clusters
into two core-size groups in order to investigate their properties in detail.
While in the larger core group the core radius is marginally proportional to
the virial radius, no significant relation is found for the smaller core group.
This may suggest that the smaller cores reflect the presence of cD galaxies,
effect of radiative cooling or asymmetry in the surface brightness. We examine
such possibilities, and find that the clusters of smaller cores have shorter
cooling time than the Hubble time, while no significant correlation is found
with cD or asymmetry. We carry out hydrodynamical calculations to simulate the
beta-model, intending to see the behavior of the isothermal gas under the
gravitational potential including the dark matter and galaxies with or without
a central cD galaxy. Calculations show r_c \propto r_vir and T_vir \simeq beta
T consistently with our consideration to the beta-model. Also is found from
calculations that the presence of a large cD galaxy may form a gas core \sim 40
kpc, which seems too small to account for the range of the core sizes, 40--80
kpc, of the smaller core group.


title:
R-Process Nucleosynthesis in MHD Jet Explosions of Core-Collapse
  Supernovae

abstract:
  We investigate $r$-process nucleosynthesis during the magnetohydrodynamical
(MHD) explosion of supernova in a massive star of 13 $M_{\odot}$. Contrary to
the case of the spherical explosion, jet-like explosion due to the combined
effects of the rotation and magnetic field lowers the electron fraction
significantly inside the layers above the iron core. We find that the ejected
material of low electron fraction responsible for the $r$-process comes out
from the silicon rich layer of the presupernova model. This leads to the
production up to the third peak in the solar $r$-process elements. We examine
whether the fission affects the $r$-process paths by using the full nuclear
reaction network with both the spontaneous and $\beta$-delayed fission
included. Moreover, we pay particular attention how the mass formula affects
the $r$-process peaks with use of two mass formulae. It is found that both
formulae can reproduce the global abundance pattern up to the third peak though
detailed distributions are rather different. We point out that there are
variations in the $r$-process nucleosynthesis if the MHD effects play an
important role in the supernova explosion.


title:
X-Ray Spectra of the Narrow-Line Seyfert 1 Galaxy Ton S180 in Comparison
  with Galactic Black Holes

abstract:
  An analysis was made of 0.3-15 keV X-ray spectra of a Narrow-Line Seyfert 1
Galaxy, Ton S180, using archival data from ASCA, RXTE, and XMM-Newton. At
energies above 2.5 keV, a power-law with a photon index of ~ 2.3 successfully
and consistently reproduced the spectra from all of these observatories.
Assuming this power-law component to extend toward lower energies, a soft
excess, which is one of the most remarkable features of Narrow-Line Seyfert 1
Galaxies, is explained by another power-law multiplied by a thermal cutoff at ~
0.4 keV. Some similarities have been observed between this object and Galactic
black hole binaries in very high state, the latter being realized under high
accretion rates. Attempts have been made to interpret the soft excess in terms
of Comptonization of the disk photons by an electron cloud surrounding the
accretion disk, like BHBs in a very high state.


title: C,N,O in lambda Boo stars and in composite spectra

abstract:
  The selective abundance of C, N, O (almost solar) with respect to that of
other elements (underabundant) in lambda Boo stars has been interpreted as a
characteristic peculiarity of these objects, when considered as single stars.
We show here that a similar selective abundance is predicted from the composite
spectra resulting from two unresolved stars in the same temperature range as
the lambda Boo stars.


title: ELT Observations of Supernovae at the Edge of the Universe

abstract:
  We discuss the possibility of using Supernovae as tracers of the star
formation history of the Universe for the range of stellar masses $\sim 3-30$
M$_\odot$ and possibly beyond. We simulate the observations of 350 SNe, up to
$z\sim 15$, made with OWL (100m) telescope.


title:
Doppler imaging of Speedy Mic using the VLT, Fast spot evolution on a
  young K-dwarf star

abstract:
  We study the short-term evolution of starspots on the ultrafast-rotating star
HD197890 ("Speedy Mic" = BO Mic, K 0-2V, P_rot = 0.380 d) based on two Doppler
images taken about 13 stellar rotations apart. Each image is based on spectra
densely sampling a single stellar rotation. The images were reconstructed by
our Doppler imaging code CLDI (Clean-like Doppler imaging) from line profiles
extracted by spectrum deconvolution. Our Doppler images constructed from two
independent wavelength ranges agree well on scales down to 10 degrees on the
stellar surface. In conjunction with nearly parallel V-band photometry our
observations reveal a significant evolution of the spot pattern during as
little as two stellar rotations. We suggest that such a fast spot evolution
demands care when constructing Doppler images of highly active stars based on
spectral time series extending over several stellar rotations. The fast
intrinsic spot evolution on BO Mic impedes the determination of a surface
differential rotation; in agreement with earlier results by other authors we
determine an upper limit of |alpha| < 0.004 +- 0.002.


title:
Towards a physical model of dust tori in Active Galactic Nuclei -
  Radiative transfer calculations for a hydrostatic torus model

abstract:
  We explore physically self-consistent models of dusty molecular tori in
Active Galactic Nuclei (AGN) with the goal of interpreting VLTI observations
and fitting high resolution mid-IR spectral energy distributions (SEDs). The
input dust distribution is analytically calculated by assuming hydrostatic
equilibrium between pressure forces - due to the turbulent motion of the gas
clouds - and gravitational and centrifugal forces as a result of the
contribution of the nuclear stellar distribution and the central black hole.
For a fully three-dimensional treatment of the radiative transfer problem
through the tori we employ the Monte Carlo code MC3D. We find that in
homogeneous dust distributions the observed mid-infrared emission is dominated
by the inner funnel of the torus, even when observing along the equatorial
plane. Therefore, the stratification of the distribution of dust grains - both
in terms of size and composition - cannot be neglected. In the current study we
only include the effect of different sublimation radii which significantly
alters the SED in comparison to models that assume an average dust grain
property with a common sublimation radius, and suppresses the silicate emission
feature at 9.7 micron. In this way we are able to fit the mean SED of both type
I and type II AGN very well. Our fit of special objects for which high angular
resolution observations (less than 0.3 arcseconds) are available indicates that
the hottest dust in NGC 1068 reaches the sublimation temperature while the
maximum dust temperature in the low-luminosity AGN Circinus falls short of 1000
K.


title:
Fe XI emission lines in a high resolution extreme ultraviolet spectrum
  obtained by SERTS

abstract:
  New calculations of radiative rates and electron impact excitation cross
sections for Fe XI are used to derive emission line intensity ratios involving
3s^23p^4 - 3s^23p^33d transitions in the 180-223 A wavelength range. These
ratios are subsequently compared with observations of a solar active region,
obtained during the 1995 flight Solar EUV Research Telescope and Spectrograph
(SERTS). The version of SERTS flown in 1995 incorporated a multilayer grating
that enhanced the instrumental sensitivity for features in the 170 - 225 A
wavelength range, observed in second-order between 340 and 450 A. This
enhancement led to the detection of many emission lines not seen on previous
SERTS flights, which were measured with the highest spectral resolution (0.03
A) ever achieved for spatially resolved active region spectra in this
wavelength range. However, even at this high spectral resolution, several of
the Fe XI lines are found to be blended, although the sources of the blends are
identified in the majority of cases. The most useful Fe XI electron density
diagnostic line intensity ratio is I(184.80 A)/I(188.21 A). This ratio involves
lines close in wavelength and free from blends, and which varies by a factor of
11.7 between N_e = 10^9 and 10^11 cm^-3, yet shows little temperature
sensitivity. An unknown line in the SERTS spectrum at 189.00 A is found to be
due to Fe XI, the first time (to our knowledge) this feature has been
identified in the solar spectrum. Similarly, there are new identifications of
the Fe XI 192.88, 198.56 and 202.42 A features, although the latter two are
blended with S VIII/Fe XII and Fe XIII, respectively.


title:
Localizing Plages on BO Mic, First steps towards chromospheric Doppler
  imaging

abstract:
  We have obtained a densely sampled time series of CaII H&K line profiles of
the ultrafast rotating K-dwarf star BO Mic. Taken at high resolution, the
spectra reveal pronounced variations of the emission core profiles. We
interpret these variations as signs of concentrated chromospherically active
regions, in analogy to solar plages. We further interpret the variations as
partly due to the rapid growth and decay of plages, while other variations
appear to be caused by plages moved over the visible stellar disk by rotation.
The equivalent width of the Ca K core emission changes approximately in
anti-phase to the photospheric brightness, suggesting an association of the
chromospheric plage regions with pronounced dark photospheric spots. We believe
that further analysis of the presented spectral time series will lead to a
chromospheric Doppler image of BO mic.


title: The Devil is in the Details: Compact Structures in Pulsar Wind Nebulae

abstract:
  The large-scale structure of pulsar wind nebulae (PWNe) tells us a
considerable amount about their average magnetic fields, the total particle
input from the pulsar winds, and the confining pressure at their outer
boundaries. However, the details of the pulsar outflow, the sites of shocks and
particle acceleration, the effects of instabilities in the magnetic field, and
the interaction between the relativistic wind and the surrounding ejecta are
contained in small-scale structures, where we observe jets and toroidal
structures, time-varying emission from compact clumps, and filaments in both
the inner and outer regions of the nebulae. Here I review recent observational
studies of compact structures in PWNe and present current scenarios (and
questions) regarding their origin.


title: Structure in the motions of the fastest halo stars

abstract:
  We have analyzed the catalog of 2106 non-kinematically selected metal poor
stars in the solar neighborhood published by Beers et al. (2000), with the goal
of quantifying the amount of substructure in the motions of the fastest halo
stars. We have computed the two-point velocity correlation function for a
subsample of halo stars within 1-2 kpc of the Sun, and found statistical
evidence of substructure, with a similar amplitude to that predicted by high
resolution CDM simulations. The signal is due to a small kinematic group whose
dynamical properties are compared to the stellar "stream", previously
discovered by Helmi et al. (1999). If real, this high velocity moving group
would provide further support to the idea that substructures remain as fossils
from the formation of the Galaxy as expected in the CDM scenario.


title:
Chandra Observation of an X-ray Flare at Saturn: Evidence for Direct
  Solar Control on Saturn's Disk X-ray Emissions

abstract:
  Saturn was observed by Chandra ACIS-S on 20 and 26-27 January 2004 for one
full Saturn rotation (10.7 hr) at each epoch. We report here the first
observation of an X-ray flare from Saturn's non-auroral (low-latitude) disk,
which is seen in direct response to an M6-class flare emanating from a sunspot
that was clearly visible from both Saturn and Earth. Saturn's disk X-ray
emissions are found to be variable on time scales of hours to weeks to months,
and correlated with solar F10.7 cm flux. Unlike Jupiter, X-rays from Saturn's
polar (auroral) region have characteristics similar to those from its disk.
This report, combined with earlier studies, establishes that disk X-ray
emissions of the giant planets Saturn and Jupiter are directly regulated by
processes happening on the Sun. We suggest that these emissions could be
monitored to study X-ray flaring from solar active regions when they are on the
far side and not visible to Near-Earth space weather satellites.


title:
Enhanced X-ray variability from V1647 Ori, the young star in outburst
  illuminating McNeil's Nebula

abstract:
  We report a ~38 ks X-ray observation of McNeil's Nebula obtained with XMM on
2004 April 4. V1647 Ori, the young star in outburst illuminating McNeil's
Nebula, is detected with XMM and appears variable in X-rays. We investigate the
hardness ratio variability and time variations of the event energy distribution
with quantile analysis, and show that the large increase of the count rate from
V1647 Ori observed during the second half of the observation is not associated
with any large plasma temperature variations as for typical X-ray flares from
young low-mass stars. X-ray spectral fitting shows that the bulk (~75%) of the
intrinsic X-ray emission in the 0.5-8 keV energy band comes from a soft plasma
component (0.9 keV) reminiscent of the X-ray spectrum of the classical T Tauri
star TW Hya, for which X-ray emission is believed to be generated by an
accretion shock onto the photosphere of a low-mass star. The hard plasma
component (4.2 keV) contributes ~25% of the total X-ray emission, and can be
understood only in the framework of plasma heating sustained by magnetic
reconnection events. We find a hydrogen column density of NH=4.1E22 cm-2, which
points out a significant excess of hydrogen column density compared to the
value derived from optical/IR observations, consistent with the picture of the
rise of a wind/jet unveiled from ground optical spectroscopy. The X-ray flux
observed with XMM ranges from roughly the flux observed by Chandra on 2004
March 22 (~10 times greater than the pre-outburst X-ray flux) to a value two
times greater than that caught by Chandra on 2004 March 7 (~200 times greater
than the pre-outburst X-ray flux). We have investigated the possibility that
V1647 Ori displays a periodic variation in X-ray brightness as suggested by the
combined Chandra+XMM data set (abridged).


title: The Small-Scale Power Spectrum of Cold Dark Matter

abstract:
  One of the best motivated hypotheses in cosmology states that most of the
matter in the universe is in the form of weakly-interacting massive particles
that decoupled early in the history of the universe and cooled adiabatically to
an extremely low temperature. Nevertheless, the finite temperature and horizon
scales at which these particles decoupled imprint generic signatures on their
small scales density fluctuations. We show that the previously recognized
cut-off in the fluctuation power-spectrum due to free-streaming of particles at
the thermal speed of decoupling, is supplemented by acoustic oscillations owing
to the initial coupling between the cold dark matter (CDM) and the radiation
field. The power-spectrum oscillations appear on the scale of the horizon at
thermal decoupling which corresponds to a mass scale of
\~10^{-4}*(T_d/10MeV)^{-3} solar masses for a CDM decoupling temperature T_d.
The suppression of the power-spectrum on smaller scales by the acoustic
oscillations is physically independent from the free-streaming effect, although
the two cut-off scales are coincidentally comparable for T_d~10MeV and a
particle mass of M~100GeV. The initial conditions for recent numerical
simulations of the earliest and smallest objects to have formed in the
universe, need to be modified accordingly. The smallest dark matter clumps may
be detectable through gamma-ray production from particle annihilation, through
fluctuations in the event rate of direct detection experiments, or through
their tidal gravitational effect on wide orbits of objects near the outer edge
of the solar system.


title:
Comment on Hervik's comment (astro-ph/0504071) on evidence of vorticity
  and shear of the Universe (astro-ph/0503213)

abstract:
  Hervik's comments on my criticism of the paper of Jaffe et al are irrelevant
or wrong.


title: SN 1998A: Explosion of a Blue Supergiant

abstract:
  We present spectroscopic and photometric observations of the peculiar Type II
supernova (SN) 1998A. The light curves and spectra closely resemble those of SN
1987A, suggesting that the SN 1998A progenitor exploded when it was a compact
blue supergiant. However, the comparison with SN 1987A also highlights some
important differences: SN 1998A is more luminous and the spectra show bluer
continua and larger expansion velocities at all epochs. These observational
properties indicate that the explosion of SN 1998A is more energetic than SN
1987A and more typical of SNe II. Comparing the observational data to
simulations, we deduce that the progenitor of SN 1998A was a massive star (~ 25
Mo) with a small pre-supernova radius (< 6 x 10^{12} cm). The Ba II lines,
unusually strong in SN 1987A and some faint II--P events, are almost normal in
the case of SN 1998A, indicating that the temperature plays a key role in
determining their strength.


title:
Constraining dark energy with cross-correlated CMB and Large Scale
  Structure data

abstract:
  We investigate the possibility of constraining dark energy with the
Integrated Sachs Wolfe effect recently detected by cross-correlating the WMAP
maps with several Large Scale Structure surveys. In agreement with previous
works, we found that, under the assumption of a flat universe, the ISW signal
is a promising tool for constraining dark energy. Current available data put
weak limits on a constant dark energy equation of state w. We also find no
constraints on the dark energy sound speed c_e^2. For quintessence-like dark
energy (c_e^2=1) we find w<-0.53, while tighter bounds are possible only if the
dark energy is ``clustered'' (c_e^2=0), in such a case -1.94<w<-0.63 at
2-sigma. Better measurements of the CMB-LSS correlation will be possible with
the next generation of deep redshift surveys. This will provide independent
constraints on the dark energy which are alternative to those usually inferred
from CMB and SN-Ia data.


title: Spectroscopic and Photometric Observations of SN IIn 1995N

abstract:
  We present the results of a long-term program of monitoring of the famous SN
1995N, observed both in photometry (UBVRIJHK bands) and optical spectroscopy.
The observations span a period of about 9 years. These new data, together with
others available in literature, extend from the X-ray wavelengths to the radio,
and allow to estimate the total energy radiated by the supernova over a decade
after its explosion.


title: VLA observations of broad 6-cm excited state OH lines in W49A

abstract:
  Using the Very Large Array (VLA), we observed all three of the 6-cm lines of
the doublet Pi 1/2, J=1/2 state of OH with sub-arcsecond resolution (about 0.4
arcsec) in W49A. While the spatial distribution and the range in velocities of
the 6-cm lines are similar to those of the ground state (18-cm) OH lines, a
large fraction of the total emission in all three 6-cm lines has large
linewidths (about 5 -- 10 km/s) and is spatially-extended, very unlike typical
ground state OH masers which typically are point-like at VLA resolutions and
have linewidths less than 1 km/s. We find brightness temperatures of 5900 K,
4700 K, and greater than 730 K for the 4660-MHz, 4750-MHz, and 4765-MHz lines,
respectively. We conclude that these are indeed maser lines. However, the gains
are about 0.3, again very unlike the 18-cm lines which have gains greater than
10000. We compare the excited state OH emission with that from other molecules
observed with comparable angular resolution to estimate physical conditions in
the regions emitting the peculiar, low-gain maser lines. We also comment on the
relationship with the 18-cm masers


title:
Mid-Infrared Imaging of Active Galaxies: Active Nuclei and Embedded Star
  Clusters

abstract:
  High resolution, mid-infrared (MIR) images of a set of nine nearby active
galaxies are presented. The data were obtained with the TIMMI2 instrument
mounted at the ESO 3.6m telescope using a set of N-band narrow filters. The
resulting images have an angular resolution of 0.6"-1". The MIR emission has
been resolved in four galaxies: NGC253, NGC1365, NGC1808 and NGC7469. The
images unveil a circumnuclear population of unknown MIR sources in NGC1365 and
NGC1808, coincident with radio sources. These MIR/radio sources are interpreted
in terms of embedded young star clusters. A high-resolution MIR map of NGC253
is also presented, and enables the identification of a previously unknown MIR
counterpart to the radio nucleus. Extended MIR emission is detected in NGC7469,
and concurs with previous observations in the NIR and radio. For this source,
an interesting morphological difference between the 10.4mic and the 11.9mic
emission is observed, suggesting the presence of a dust-rich micro-bar. Our MIR
images of Circinus do not show resolved emission from the nucleus down to an
angular scale of 0.5". In the case of NGC2992, an upper limit to the extended
MIR emission can be set. Finally, we provide new MIR flux measurements for the
unresolved AGN in NGC5995, IZw1 and IIZw136.


title:
Variability of Optical \ion{Fe}{ii} Complex in Narrow-Line Seyfert 1
  Galaxy NGC 4051

abstract:
  The variability of optical FeII blends in NGC 4051 is examined from spectra
extracted from the AGN Watch program.In our analysis, the FeII complex are
subtracted and measured with the following results. Firstly, the FeII
variations were detected in NGC 4051 during a 3-year period. The identified
FeII variations followed the variations in continuum closely. Secondly, the EW
of FeII is reported to increase with the rising continuum flux, which is
consistent with previous claims that there is no convincing Baldwin Effect in
optical FeII. Thirdly, by comparing the variations of H$\beta$ and FeII, we
find that RFe scales with continuum flux as $\rm{R_{Fe}\propto (5.0\pm0.8)
\log(L/M)}$, which is significantly different from the theoretical
expectations. Finally, in six selected Seyferts, four out of five Narrow-Line
Seyfert 1 galaxies present positive correlation between RFe and the continuum
flux. The negative correlations are identified in the remaindng two objects
that have relatively broad profiles of H$\beta$ ($\rm{FWHM>1500 km\
s^{-1}}$).We argue that the difference of electron density of broad line clouds
and/or variability behavior of incident high-energy radiation can explain the
dichotomy in variability behavior of RFe.


title:
Discovery of extended VHE gamma-ray emission from the asymmetric pulsar
  wind nebula in MSH 15-52 with H.E.S.S

abstract:
  The Supernova Remnant MSH 15-52 has been observed in very high energy (VHE)
gamma-rays using the H.E.S.S. 4-telescope array located in Namibia. A gamma-ray
signal is detected at the 25 sigma level during an exposure of 22.1 hours live
time. The image reveals an elliptically shaped emission region around the
pulsar PSR B1509-58, with semi-major axis 6' in the NW-SE direction and
semi-minor axis 2' approximately. This morphology coincides with the diffuse
pulsar wind nebula as observed at X-ray energies by ROSAT. The overall energy
spectrum from 280 GeV up to 40 TeV can be fitted by a power law with photon
index Gamma = 2.27 +/- 0.03(stat.) +/- 0.20(syst.). The detected emission can
be plausibly explained by inverse Compton scattering of accelerated
relativistic electrons with soft photons.


title: Relic abundance of mass-varying cold dark matter particles

abstract:
  In models of coupled dark energy and dark matter the mass of the dark matter
particle depends on the cosmological evolution of the dark energy field. In
this note we exemplify in a simple model the effects of this mass variation on
the relic abundance of cold dark matter.


title:
The Dog on the Ship: The "Canis Major Dwarf Galaxy" as an Outlying Part
  of the Argo Star System

abstract:
  Overdensities in the distribution of low latitude, 2MASS giant stars are
revealed by systematically peeling away from sky maps the bulk of the giant
stars conforming to ``isotropic'' density laws generally accounting for known
Milky Way components. This procedure, combined with a higher resolution
treatment of the sky density of both giants and dust allows us to probe to
lower Galactic latitudes than previous 2MASS giant star studies. While the
results show the swath of excess giants previously associated with the
Monoceros ring system in the second and third Galactic quadrants at distances
of 6-20 kpc, we also find a several times larger overdensity of giants in the
same distance range concentrated in the direction of the ancient constellation
Argo. Isodensity contours of the large structure suggest that it is highly
elongated and inclined by about 3 deg to the disk, although details of the
structure -- including the actual location of highest density, overall extent,
true shape -- and its origin, remain unknown because only a fraction of it lies
outside highly dust-obscured, low latitude regions. Nevertheless, our results
suggest that the 2MASS M giant overdensity previously claimed to represent the
core of a dwarf galaxy in Canis Major (l ~ 240 deg) is an artifact of a dust
extinction window opening to the overall density rise to the more significant
Argo structure centered at larger longitude (l ~ 290 +- 10 deg, b ~ -4 +- 2
deg).


title: On the Size Distribution of Close-In Extrasolar Giant Planets

abstract:
  The precisions of extrasolar planet radius measurements are reaching the
point at which meaningful and discriminatory comparisons with theoretical
predictions are can be made. However, care must be taken to account for
selection effects in the transit surveys that detect the transiting planets for
which radius measurements are possible. Here I identify one such selection
effect, such that the number of planets with radius R_p detected in a
signal-to-noise ratio limited transit survey is proportional to R_p^alpha, with
alpha~4-6. In the presence of a dispersion sigma in the intrinsic distribution
of planet radii, this selection effect translates to bias b in the radii of
observed planets. Detected planets are, on average, larger by a fractional
amount b ~ alpha (sigma/<R_p>)^2 relative to the mean radius <R_p> of the
underlying distribution. I argue that the intrinsic dispersion in planetary
radii is likely to be in the range sigma = (0.05-0.13)R_J, where the lower
bound is that expected theoretically solely from the variance in stellar
insolation, and the upper bound is the 95% c.l. upper limit from the scatter in
observed radii. Assuming an arbitrary but plausible value of sigma/<R_p>~10%,
and thus b~6%, I infer a mean intrinsic radius of close-in massive extrasolar
planets of <R_p>=(1.03+/-0.01)R_J. This value reinforces the case for HD209458b
having an anomalously large radius, and may be inconsistent with coreless
models of irradiated giant planets.


title: Tracing the Nature of Dark Energy with Galaxy Distribution

abstract:
  Dynamical Dark Energy (DE) is a viable alternative to the cosmological
constant. Yet, constructing tests to discriminate between Lambda and dynamical
DE models is difficult because the differences are not large. In this paper we
explore tests based on the galaxy mass function, the void probability function
(VPF), and the number of galaxy clusters. At high z the number density of
clusters shows large differences between DE models, but geometrical factors
reduce the differences substantially. We find that detecting a model dependence
in the cluster redshift distribution is a hard challenge. We show that the
galaxy redshift distribution is potentially a more sensitive characteristics.
We do so by populating dark matter halos in Nbody simulations with galaxies
using well-tested Halo Occupation Distribution (HOD). We also estimate the Void
Probability Function and find that, in samples with the same angular surface
density of galaxies in different models, the VPF is almost model independent
and cannot be used as a test for DE. Once again, geometry and cosmic evolution
compensate each other. By comparing VPF's for samples with fixed galaxy mass
limits, we find measurable differences.


title: The Difference Between the Amati and Ghirlanda Relations

abstract:
  It is pointed out that the beaming correction commonly inferred from the
achromatic breaks in the afterglow light curve is biased in situations where
the isotropic equivalent energy is affected by factors other than the spread in
opening angles. In particular, it underestimates the beaming factor of sources
observed off-axis. Here we show that both the slopes and scatters in the Amati
and Ghirlanda relations, and the difference between them, are quantitatively
consistent with a model proposed recently, in which the $E_{iso}-\nu_{peak}$
relation, as originally derived by Amati et al., is due to viewing angle
effects. The quantitative difference between them confirms the relations
between opening angle and break time suggested by Frail et al.


title: X-ray States of Black Hole Binaries in Outburst

abstract:
  A brief review is given for X-ray properties of black hole binary systems.
Topics include the effort to re-define the three states of active accretion,
potential applications for general relativity in the regime of strong gravity,
and the properties of high-frequency QPOs in 7 systems.


title: Evolution of field early-type galaxies: The view from GOODS/CDFS

abstract:
  (Abridged) We explore the evolution of field early-type galaxies on a sample
extracted from GOODS/CDFS. The galaxies are selected by means of a
non-parametric analysis followed by visual inspection. We exclude those
galaxies which are not consistent with an evolution into the Kormendy relation.
The final set comprises 249 galaxies with a median redshift z=0.7. The
distribution of number counts versus apparent magnitude suggests a substantial
decrease of the comoving number density with redshift. The majority of the
galaxies feature passively evolving old stellar populations. One third of those
in the upper half of the redshift distribution have blue colors, in contrast to
only 10% in the lower redshift subsample. An adaptive binning of the color maps
is performed to explore the internal color distribution. We find that most blue
galaxies in our sample feature blue cores whereas most of the red early-types
are passively evolving stellar populations with red cores. The color gradients
and scatter do not evolve with redshift and are compatible with the
observations at z=0 assuming a radial dependence of the metallicity within each
galaxy. This work emphasizes the need for a careful sample selection, as we
found that most of those galaxies which were visually classified as early types
-- but then rejected based on the Kormendy relation -- feature blue colors
characteristic of recent star formation.


title:
Robust determination of optical path difference: fringe tracking at the
  IOTA interferometer

abstract:
  We describe the fringe packet tracking system used to equalise the optical
path lengths at the Infrared Optical Telescope Array (IOTA) interferometer. The
measurement of closure phases requires obtaining fringes on three baselines
simultaneously. This is accomplished using an algorithm based on double Fourier
interferometry for obtaining the wavelength-dependent phase of the fringes and
a group delay tracking algorithm for determining the position of the fringe
packet. The comparison between data acquired with and without the fringe packet
tracker shows about a factor 3 reduction of the error on the closure-phase
measurement. The fringe packet tracker has been able so far to track fringes of
signal-to-noise as low as 1.8 for stars as faint as mH=7.0.


title:
X-ray States of Black-Hole Binaries and Implications for the Mechanism
  of Steady Jets

abstract:
  The three X-ray states of active accretion in black-hole binaries have been
re-defined to focus attention on different physical elements that may
contribute radiation: the accretion disk, a jet, and a compact and radio-quiet
corona. Examples of state evolution are displayed on a time line, and on a
hardness-intensity diagram. The latter format allows a synthesis of these
states with the ``unified model for black hole binary jets'' by Fender,
Belloni, & Gallo (2004). As suggested by Corbel (2004), the ``jet line''
appears to coincide with the hard limit of the SPL state. In GX339-4, the broad
power peaks in the PDS are confined to intermediate and hard states, where a
jet is present. This suggests that these Fourier components are temporal
signatures of non-thermal processes related to the jet mechanism, rather than
properties inherent to a standard accretion disk.


title:
A Possible Late Time $\Lambda$CDM-like Background Cosmology in
  Relativistic MOND Theory

abstract:
  In the framework of Relativistic MOND theory (TeVeS), we show that a late
time background $\Lambda$CDM cosmology can be attained by choosing a specific
$F(\mu)$ that also meets the requirement for the existence of Newtonian and
MOND limits. We investigate the dynamics of the scalar field $\phi$ under our
chosen $F(\mu)$ and show that the "slow roll" regime of $\phi$ corresponds to a
dynamical attractor, where the whole system reduces to $\Lambda$CDM cosmology.


title: The [Fe IV] Discrepancy: Constraining the Iron Abundances in Nebulae

abstract:
  We study the current discrepancy between the model-predicted and measured
concentrations of Fe++ and Fe3+ in ionized nebulae. We calculate a set of
photoionization models, updated with the atomic data relevant to the problem,
and compare their results with those derived for the available nebulae where
both [Fe III] and [Fe IV] lines have been measured. Our new model results are
closer to the measured values than the results of previous calculations, but a
discrepancy remains. This discrepancy translates into an uncertainty in the
derived Fe abundances of a factor up to ~4. We explore the possible causes of
this discrepancy and find that errors in the Fe atomic data may be the most
likely explanation. The discrepancy can be fully accounted for by any of the
following changes: (1) an increase by a factor of ~10 in the recombination rate
(radiative plus dielectronic, or charge transfer) for Fe3+, (2) an increase by
a factor of 2-3 in the effective collision strengths for Fe++, or (3) a
decrease by a factor of 2-3 in the effective collision strengths for Fe3+. We
derive the Fe abundances implied by these three explanations and use the
results to constrain the degree of depletion of Fe in our sample nebulae. The
Galactic H II regions and planetary nebulae are found to have high depletion
factors, with less than 5% of their Fe atoms in the gas phase. The
extragalactic H II regions (LMC 30 Doradus, SMC N88A, and SBS 0335-052) have
somewhat lower depletions. The metal-deficient blue compact galaxy SBS 0335-052
could have from 13% to 40% of Fe in the gas phase. The depletions derived for
the different objects define a trend of increasing depletion at higher
metallicities.


title: The Amplitude of Dark Energy Perturbations

abstract:
  We propose a model which produces dark energy perturbations large enough to
explain the lack of power seen at the quadrupole scale in the cosmic microwave
background. If the dark energy is frozen from horizon exit during inflation
until dark energy domination, then it is not possible to have perturbations in
the dark energy which are large enough. We propose using a tachyonic
amplification mechanism to overcome this. The dark energy is taken to be a
complex scalar field, where the radial field has a Mexican hat potential.
During inflation, the radial component is trapped near the maximum of its
potential. At the end of inflation, it rolls down to the minimum. The dark
energy today is taken to be a pseudo-Nambu-Goldstone boson. The perturbations
generated during inflation are amplified by the rolling of the radial field. We
also examine the use of the variable decay mechanism in order to generate an
anti-correlation between the dark energy perturbations and the curvature
perturbation. We show that using this mechanism then constrains the properties
of the dark energy and its evolution from redshift one until today.


title:
On the nature of Lithium-rich giant stars: constraints from Beryllium
  abundances

abstract:
  We have derived beryllium abundances for 7 Li-rich giant (A(Li) > 1.5) stars
and 10 other Li-normal giants, with the aim of investigating the origin of the
Lithium in the Li-rich giants. In particular, we test the predictions of the
engulfment scenario proposed by Siess & Livio (1999), where the engulfment of a
brown dwarf or one or more giant planets would lead to a simultaneous
enrichment of 7Li and 9Be. We show that regardless their nature, none of the
stars studied in this paper were found to have detectable beryllium. Using
simple dilution arguments we show that the engulfment of an external object as
the sole source of Li enrichment is ruled out by the Li and Be abundance data.
The present results favor the idea that Li has been produced in the interior of
the stars by a Cameron-Fowler process and brought up to the surface by an extra
mixing mechanism.


title:
Proper Motions of the BN Object and the I Radio Source in Orion: Where
  and When Did BN Become a Runaway Star?

abstract:
  We present absolute astrometry of the core of the Orion molecular cloud, made
with Very Large Array archive data taken over the last two decades. Our
analysis reveals that both the BN object and the radio source I have proper
motions: the BN object has a proper motion of $12.6 \pm 0.6$ mas yr$^{-1}$
(corresponding to a velocity of $27 \pm 1$ km s$^{-1}$ at an adopted distance
of 450 pc) to the northwest, while the radio source I has a proper motion of
$5.6 \pm 0.7$ mas yr$^{-1}$ (corresponding to a velocity of $12 \pm 2$ km
s$^{-1}$) to the southeast. The motion of the two sources is nearly
antiparallel, diverging from a point in between them, where they were located
about 500 years ago. These results suggest that the BN object and the radio
source I were part of a multiple young stellar system that disintegrated in the
recent past.


title:
Consequences of Disk Scale Height on LISA Confusion Noise from Close
  White Dwarf Binaries

abstract:
  Gravitational radiation from the Galactic population of close white dwarf
binaries (CWDBs) is expected to produce a confusion-limited signal at the lower
end of the sensitivity band of the Laser Interferometer Space Antenna (LISA).
The canonical scale height of the disk population has been taken to be 90 pc
for most studies of the nature of this confusion-limited signal. This estimate
is probably too low, and the consequences of a more realistic scale height are
investigated with a model of the LISA signal due to populations of close white
dwarf binaries with different scale heights. If the local space density of
CWDBs is held constant, increasing the scale height results in both an increase
in the overall strength of the confusion-limited signal as well as in increase
in the frequency at which the signals become individually resolvable. If the
total number of binaries is held constant, increasing the scale height results
in a reduction of the number of expected bright signals above the
confusion-limited signal at low frequencies. We introduce an estimator for
comparing this transition frequency that takes into account the signal
spreading at higher frequencies.


title:
A high sensitivity HI survey of the sky at delta < -25 deg Final data
  release

abstract:
  We present the final data release of the high sensitivity lambda 21-cm
neutral hydrogen survey of the sky south of delta < -25 degr. A total of 50980
positions lying on a galactic coordinate grid with points spaced by (Delta l,
Delta b) = ((0.5 deg)/cos b, 0.5 deg) were observed with the 30-m dish of the
Instituto Argentino de Radioastronomia (IAR). The angular resolution of the
survey is HPBW = 0.5 deg and the velocity coverage spans the interval -450 km/s
to +400 km/s (LSR). The velocity resolution is 1.27 km/s and the final rms
noise of the entire database is 0.07 K. The data are corrected for stray
radiation and converted to brightness temperatures.


title:
The broad-band X-ray spectrum of the blazar PKS B1830-211 by Chandra and
  INTEGRAL

abstract:
  In this paper we present a broad-band study of the X-ray emission of the
blazar PKS1830-211 based on Chandra and Integral observations. Notwithstanding
the high redshift (z=2.507), it is a bright X-ray source (F(2-10 keV)~10^{-11}
erg cm^{-2} s^{-1}), due to gravitational lensing by an intervening galaxy at
z=0.89. Previous X-ray observations attribute the observed absorption at E<2
keV to the lensing galaxy. Our analysis, although not in contrast with this
hypothesis, suggests also the possibility of an intrinsic (ionized) absorption,
taking place at the front side of the jet. This scenario is also supported by
some evidence, in the same data, of a feature observed at 2.15 keV which can be
interpreted as a blueshifted iron line (v/c ~ 0.18). The SED of PKS1830-211 can
be well modelled by combining a Synchrotron Self-Compton component and an
external source of photons to be scattered up to \gamma-ray energies by
relativistic electrons moving outward in the jet. The main source of low energy
photons is a dust torus at the temperature of 10^3 K as expected in MeV
blazars.


title:
X-ray synchrotron emission from the oblique shock in the jet of the
  powerful radio galaxy 3C 346

abstract:
  We report the first detection, with Chandra, of X-ray emission from the jet
of the powerful narrow-line radio galaxy 3C 346. X-rays are detected from the
bright radio and optical knot at which the jet apparently bends by about 70
degrees. The Chandra observation also reveals a bright galaxy-scale atmosphere
within the previously-known cluster, and provides a good X-ray spectrum for the
bright core of 3C 346. The X-ray emission from the knot is synchrotron
radiation, as seen in lower-power sources. In common with these sources, there
is evidence of morphological differences between the radio/optical and X-ray
structures, and the spectrum is inconsistent with a one-component
continuous-injection model. We suggest that the X-ray-bright knot is associated
with a strong oblique shock in a moderately relativistic, light jet, at about
20 degrees to the line of sight, and that this shock is caused by the jet
interacting with the wake in the cluster medium behind 3C 346's companion
galaxy. The general jet curvature can result from pressure gradients in the
cluster atmosphere.


title:
Restframe I-band Hubble diagram for type Ia supernovae up to redshift z
  ~0.5

abstract:
  We present a novel technique for fitting restframe I-band light curves on a
data set of 42 Type Ia supernovae (SNe Ia). Using the result of the fit, we
construct a Hubble diagram with 26 SNe from the subset at 0.01< z<0.1. Adding
two SNe at z~0.5 yields results consistent with a flat
Lambda-dominated``concordance universe''
($\Omega_M,\Omega_\Lambda$)=(0.25,0.75). For one of these, SN 2000fr, new near
infrared data are presented. The high redshift supernova NIR data are also used
to test for systematic effects in the use of SNe Ia as distance estimators. A
flat, Lambda=0, universe where the faintness of supernovae at z~0.5 is due to
grey dust homogeneously distributed in the intergalactic medium is disfavoured
based on the high-z Hubble diagram using this small data-set. However, the
uncertainties are large and no firm conclusion may be drawn. We explore the
possibility of setting limits on intergalactic dust based on B-I and B-V colour
measurements, and conclude that about 20 well measured SNe are needed to give
statistically significant results. We also show that the high redshift
restframe I-band data points are better fit by light curve templates that show
a prominent second peak, suggesting that they are not intrinsically
underluminous.


title:
The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data
  release of the combined LDS and IAR surveys with improved stray-radiation
  corrections

abstract:
  We present the final data release of observations of lambda 21-cm emission
from Galactic neutral hydrogen over the entire sky, merging the
Leiden/Dwingeloo Survey (LDS: Hartmann & Burton, 1997) of the sky north of
delta = -30 deg with the Instituto Argentino de Radioastronomia Survey (IAR:
Arnal et al., 2000, and Bajaja et al., 2005) of the sky south of delta = -25
deg. The angular resolution of the combined material is HPBW ~ 0.6 deg. The LSR
velocity coverage spans the interval -450 km/s to +400 km/s, at a resolution of
1.3 km/s. The data were corrected for stray radiation at the Institute for
Radioastronomy of the University of Bonn, refining the original correction
applied to the LDS. The rms brightness-temperature noise of the merged database
is 0.07 - 0.09 K. Residual errors in the profile wings due to defects in the
correction for stray radiation are for most of the data below a level of 20 -
40 mK. It would be necessary to construct a telescope with a main beam
efficiency of eta_{MB} > 99% to achieve the same accuracy. The merged and
refined material entering the LAB Survey of Galactic HI is intended to be a
general resource useful to a wide range of studies of the physical and
structural characteristices of the Galactic interstellar environment. The LAB
Survey is the most sensitive Milky Way HI survey to date, with the most
extensive coverage both spatially and kinematically.


title: Efficient Monte Carlo methods for continuum radiative transfer

abstract:
  We discuss the efficiency of Monte Carlo methods in solving continuum
radiative transfer problems. The sampling of the radiation field and
convergence of dust temperature calculations in the case of optically thick
clouds are both studied. For spherically symmetric clouds we find that the
computational cost of Monte Carlo simulations can be reduced, in some cases by
orders of magnitude, with simple importance weighting schemes. This is
particularly true for models consisting of cells of different sizes for which
the run times would otherwise be determined by the size of the smallest cell.
We present a new idea of extending importance weighting to scattered photons.
This is found to be useful in calculations of scattered flux and could be
important for three-dimensional models when observed intensity is needed only
for one general direction of observations. Convergence of dust temperature
calculations is studied for models with optical depths 10-10000. We examine
acceleration methods where radiative interactions inside a cell or between
neighbouring cells are treated explicitly. In optically thick clouds with
strong self-coupling between dust temperatures the run times can be reduced by
more than one order of magnitude. The use of a reference field was also
examined. This eliminates the need for repeating simulation of constant sources
(e.g., background radiation) after the first iteration and significantly
reduces sampling errors. The applicability of the methods for three-dimensional
models is discussed.