title:
Optical (VRI) Photometry in the Field of the Galaxy Cluster AC 118 at
  z=0.31

abstract:
  We present new photometric V-, R- and I-band data for the rich galaxy cluster
AC 118 at z=0.31. The new photometry covers an area of 8.6x8.6 arcmin$^2$,
corresponding to 2.9$\times$2.9 Mpc$^2$ (H$_0=50$ km s$^{-1}$ Mpc$^{-1}$,
q$_0=0.5$ and $\Lambda = 0$). The data have been collected for a project aimed
at studying galaxy evolution through the color-magnitude relation and the
fundamental plane. We provide a catalogue including all the sources (N = 1206)
detected in the cluster field. The galaxy sample is complete to V=22.8 mag
(N_gal=574), R=22.3 mag (N_gal=649) and I=20.8 mag (N_gal=419). We give
aperture magnitudes within a fixed aperture of 4.4 arcsec and Kron magnitudes.
We also give photometric redshifts for 459 sources for which additional U- and
K-band photometry is available. We derive and discuss the V- and R-band
luminosity functions. The catalogue, which is distributed in electronic form,
is intended as a tool for studies in galaxy evolution.


title:
Modeling the interaction between ICM and relativistic plasma in cooling
  flows: the case of the Perseus Cluster

abstract:
  We argue that the presence of diffuse synchrotron emission forming the
so-called radio mini-halos in some cooling flow clusters can be explained by
reacceleration of relativistic electrons, the necessary energetics being
supplied by the cooling flows themselves. In particular, the reacceleration due
to MHD turbulence has the correct radial dependence on the parameters to
naturally balance the radiative losses. As an application we show that the main
properties of the radio mini-halo in the Perseus cluster (brightness profile,
total radio spectrum and radial spectral steepening) can be accounted for by
the synchrotron radiation from relic relativistic electrons in the cluster,
which are efficiently reaccelerated by MHD turbulence via Fermi-like processes
due to the compression of the cluster magnetic field in the cooling flow
region. Since the presence of an observable radio mini-halo in a cooling flow
region critically depends on the combination of several physical parameters, we
suggest that the rarity of radio mini-halos found in cooling flow clusters is
due to the fact that the physical conditions of the ICM are intermediate
between those which lead to the formation of extended radio halos and those
holding in cooling flows without radio halos. The basic results of our model
remain unchanged even if the cooling flow is stopped somewhere in the innermost
region of the cluster.


title:
Transformation Properties of External Radiation Fields, Energy-Loss
  Rates and Scattered Spectra, and a Model for Blazar Variability

abstract:
  We treat transformation properties of external radiation fields in the proper
frame of a plasma moving with constant speed. The specific spectral energy
densities of external isotropic and accretion-disk radiation fields are derived
in the comoving frame of relativistic outflows, such as those thought to be
found near black-hole jet and gamma-ray burst sources. Nonthermal electrons and
positrons Compton-scatter this radiation field, and high-energy protons and
ions interact with this field through photomeson and photopair production. We
revisit the problem of the Compton-scattered spectrum associated with an
external accretion-disk radiation field, and clarify a past treatment by the
authors. Simple expressions for energy-loss rates and Thomson-scattered spectra
are given for ambient soft photon fields consisting either of a surrounding
external isotropic monochromatic radiation field, or of an azimuthally
symmetric, geometrically thin accretion-disk radiation field. A model for
blazar emission is presented that displays a characteristic spectral and
variability behavior due to the presence of a direct accretion-disk component.
The disk component and distinct flaring behavior can be bright enough to be
detected from flat spectrum radio quasars with {\it GLAST}. Spectral states of
blazars are characterized by the relative importance of the accretion-disk and
scattered radiation fields and, in the extended jet, by the accretion disk,
inner jet, and cosmic microwave background radiation fields.


title:
Optical/Infrared spectroscopy and photometry of the short period binary
  RX J1914+24

abstract:
  We present observations of the proposed double degenerate polar RX J1914+24.
Our optical and infrared spectra show no emission lines. This, coupled with the
lack of significant levels of polarisation provide difficulties for a double
degenerate polar interpretation. Although we still regard the double degenerate
polar model as feasible, we have explored alternative scenarios for
RX~J1914+24. These include a double degenerate algol system, a neutron
star-white dwarf pair and an electrically powered system. The latter model is
particularly attractive since it naturally accounts for the lack of both
emission lines and detectable polarisation in RX J1914+24. The observed X-ray
luminosity is consistent with the predicted power output. If true, then RX
J1914+24 would be the first known stellar binary system radiating largely by
electrical energy.


title: Time-resolved flickering mapping of V2051 Ophiuchi

abstract:
  Although flickering is one of the fundamental signatures of accretion, it is
also the most poorly understood aspect of the accretion processes. A promising
step towards a better undestanding of flickering consists in using the eclipse
mapping method to probe the surface distribution of the flickering sources. We
report on the analysis of light curves of the dwarf nova and strong flicker
V2051 Ophiuchi with eclipse mapping techniques to produce the first maps of the
flickering brightness distribution in an accretion disc.


title: The abundance of dark galaxies

abstract:
  We show that gas in a large fraction of low mass dark matter halos may form
Toomre stable disks, if angular momentum is conserved when the gas contracts.
Such halos would be stable to star formation and therefore remain dark. This
may potentially explain the discrepancy between the predicted and observed
number of dwarf satellites in the Local Group, as well as the deviation between
the predicted and the observed faint end slope of the luminosity function. The
above mechanism does not require a strong variation of the baryon fraction with
the virial mass of the dark halo. We show that model fits to rotation curves
are also consistent with this hypothesis: none of the observed galaxies lie in
the region of parameter space forbidden by the Toomre stability criterion.


title: Magnetized Turbulent Dynamo in Protogalaxies

abstract:
  The prevailing theory for the origin of cosmic magnetic fields is that they
have been amplified to their present values by the turbulent dynamo inductive
action in the protogalactic and galactic medium. Up to now, in calculation of
the turbulent dynamo, it has been customary to assume that there is no back
reaction of the magnetic field on the turbulence, as long as the magnetic
energy is less than the turbulent kinetic energy. This assumption leads to the
kinematic dynamo theory. However, the applicability of this theory to
protogalaxies is rather limited. The reason is that in protogalaxies the
temperature is very high, and the viscosity is dominated by magnetized ions. As
the magnetic field strength grows in time, the ion cyclotron time becomes
shorter than the ion collision time, and the plasma becomes strongly
magnetized. As a result, the ion viscosity becomes the Braginskii viscosity.
Thus, in protogalaxies the back reaction sets in much earlier, at field
strengths much lower than those which correspond to field-turbulence energy
equipartition, and the turbulent dynamo becomes what we call the magnetized
turbulent dynamo. In this paper we lay the theoretical groundwork for the
magnetized turbulent dynamo. In particular, we predict that the magnetic energy
growth rate in the magnetized dynamo theory is up to ten time larger than that
in the kinematic dynamo theory. We also briefly discuss how the Braginskii
viscosity can aid the development of the inverse cascade of magnetic energy
after the energy equipartition is reached.


title: A measurement of weak lensing by large scale structure in RCS fields

abstract:
  We have analysed ~24 square degrees of R_C-band imaging data from the
Red-Sequence Cluster Survey (RCS), and measured the excess correlations between
galaxy ellipticities on scales ranging from 1 to 30 arcminutes. We have used
data from two different telescopes: ~16.4 square degrees of CFHT data and ~7.6
square degrees of CTIO 4-meter data, distributed over 13 widely separated
patches. For the first time, a direct comparison can be made of the lensing
signal measured using different instruments, which provides an important test
of the weak lensing analysis itself. The measurements obtained from the two
telescopes agree well. For the lensing analysis we use galaxies down to a
limiting magnitude of R_C=24, for which the redshift distribution is known
relatively well. This allows us to constrain some cosmological parameters. For
the currently favored $\Lambda$CDM model $(\Omega_m=0.3, \Omega_\Lambda=0.7,
\Gamma=0.21)$ we obtain $\sigma_8=0.81^{+0.14}_{-0.19}$ (95% confidence), in
agreement with the results from Van Waerbeke et al. (2001) which used fainter
galaxies (and consequently higher redshift galaxies). The good agreement
between these two very different weak lensing studies demonstrates that weak
lensing is a useful tool in observational cosmology.


title: A limit on the detectability of the energy scale of inflation

abstract:
  We show that the polarization of the cosmic microwave background can be used
to detect gravity waves from inflation if the energy scale of inflation is
above 3.2 times 10^15 GeV. These gravity waves generate polarization patterns
with a curl, whereas (to first order in perturbation theory) density
perturbations do not. The limiting ``noise'' arises from the second--order
generation of curl from density perturbations, or rather residuals from its
subtraction. We calculate optimal sky coverage and detectability limits as a
function of detector sensitivity and observing time.


title:
Chandra and ASCA Observations of the X-ray-brightest T-Tauri Stars in
  the Rho Ophiuchi Cloud

abstract:
  We present the Chandra ACIS and ASCA GIS results for a series of four
long-term observations on DoAr 21, ROXs 21 and ROXs 31; the X-ray brightest
T-Tauri stars (TTSs) in the Rho Ophiuchi cloud. In the four observations with a
net exposure of ~600 ksec, we found six, three and two flares from DoAr 21,
ROXs 21 and ROXs 31, respectively; hence the flare rate is fairly high. The
spectra of DoAr 21 are well fitted with a single-temperature plasma model,
while those of ROXs 21 and ROXs 31 need an additional soft plasma component.
Since DoAr 21 is younger (~10^5 yr) than ROXs 21 and ROXs 31 (~10^6 yr), these
results may indicate that the soft component gradually increases as T-Tauri
stars age. The abundances are generally sub-solar and vary from element to
element. Both high-FIP (first ionization potential) and low-FIP elements show
enhancement over the mean abundances. An unusual giant flare is detected from
ROXs 31. The peak luminosity and temperature are ~10^33 ergs s^-1 and ~10 keV,
respectively. The temperature reaches its peak value before the flux maximum,
and is nearly constant (4--5 keV) during the decay phase, indicating successive
energy release during the flare. The abundances and absorption show dramatic
variability from the quiescent to flare phase.


title: Cosmoparticle physics - the Challenge to the Millenium

abstract:
  Cosmoparticle physics offers the exciting challenge for the new Millenium to
come to the true knowledge on the basic natural laws and on the way, they
govern the creation and evolution of the Universe with all the forms of its
present energy content. The theory of everything, the true history of the
Universe, based on it, the new sources of energy release and the new means of
energy transfer should come from the prospects of cosmoparticle physics. We may
be near the first positive results in this direction. The methods of
cosmoparticle physics are briefly reviewed.


title: Evolution and Geometry of Hot Spots in Supernova Remnant 1987A

abstract:
  We present ground-based near-infrared imaging and {\em HST} optical imaging
and spectroscopy of the interaction between the ejecta of SN 1987A and its
equatorial circumstellar ring. This interaction has made a transition, from
emission originating in just a few ``hot spots'' at restricted locations in
position angle around the ring, to a collision producing optical emission over
a nearly continuous distribution, with few breaks larger than 45 degrees. The
centroids of the first three spots are measured to move at 2000-3000 km/s,
which we interpret as a lower limit of the velocity of the forward blast front.
Multi-wavelength light curves of the spots show that they do not evolve
uniformly, and change significantly on timescales as short as one month; in
particular the first spot shows a significant break in its lightcurve.
Implications of observed delays between spots appearances are discussed, which
leads to a generalized model of hot spot evolution, and suggests that the early
appearance of the first hot spot is explained by its inward radial position and
a fairly uniform forward blast wave, rather than extraordinary physical
circumstances. Data further suggest that the forward blast is reaching the bulk
of the inner ring material to the east, the density of which appears higher
than elsewhere in the ring. We study the ring geometry, finding evidence
suggestive of an intrinsic ellipticity of 0.95, and find lower and upper
distance limits of 47.9 +/- 0.92 kpc and 54.4 +/- 2.1 kpc, respectively.


title: Strong Lensing Constraints on Small-Scale Linear Power

abstract:
  We place limits on the linear power spectrum on small scales (k > 50 h/Mpc)
using measurements of substructure in gravitational lens galaxies. We find
excellent agreement with the simplest LambdaCDM models, and in conjunction with
other cosmological probes, place constraints on the neutrino mass m_nu, tilt of
the primordial power spectrum n, and mass of the dark matter particle m. We
find n>0.94, and for a Harrison-Zeldovich spectrum, find m_nu<0.74 eV and m>5.2
keV, at 95% confidence.


title:
Spectrophotometric evolution of spiral galaxies with truncated star
  formation: An evolutionary link between spirals and S0s in distant clusters

abstract:
  A one-zone chemo-spectro-photometric model is used to investigate the time
evolution of disk galaxies whose star formation is truncated, and to determine
the dependence of this evolution on the previous star formation history and the
truncation epoch. Truncated spirals show red colors $\sim 1$ Gyr after
truncation, and evolve spectrally from an e(b) type, down through the e(a),
a+k, and k+a classes, to finally become a k type. The exact behavior in this
phase depends on the truncation epoch and the star formation history prior to
truncation. For example, earlier type disks show redder colors and do not show
a+k-type spectra after truncation of star formation. We also discuss a possible
evolutionary link between the k-type galaxies with spiral morphology found in
distant clusters, and present-day S0s, by investigating whether truncated
spirals reproduce the infrared color-magnitude relation of Coma galaxies. We
suggest that only less luminous, later-type disk galaxies whose star formation
is truncated at intermediate and high redshifts can reproduce the red $I-K$
colors observed for S0s in the Coma cluster.


title:
CMB Observations: improvements of the performance of correlation
  radiometers by signal modulation and synchronous detection

abstract:
  Observation of the fine structures (anisotropies, polarization, spectral
distortions) of the Cosmic Microwave Background (CMB) is hampered by
instabilities, 1/f noise and asymmetries of the radiometers used to carry on
the measurements. Addition of modulation and synchronous detection allows to
increase the overall stability and the noise rejection of the radiometers used
for CMB studies. In this paper we discuss the advantages this technique has
when we try to detect CMB polarization. The behaviour of a two channel
correlation receiver to which phase modulation and synchronous detection have
been added is examined. Practical formulae for evaluating the improvements are
presented.


title: A Low Upper Limit to the Lyman Continuum Emission of two galaxies at z 3

abstract:
  Long exposure, long-slit spectra have been obtained in the UV/optical bands
for two galaxies at z=2.96 and z=3.32 to investigate the fraction of ionizing
UV photons escaping from high redshifts galaxies. The two targets are among the
brightest galaxies discovered by Steidel and collaborators and they have
different properties in terms of Lyman-alpha emission and dust reddening. No
significant Lyman continuum emission has been detected. The noise level in the
spectra implies an upper limit of f_{rel,esc}\equiv 3 f(900)/f(1500)< 16% for
the relative escape fraction of ionizing photons, after correction for
absorption by the intervening intergalactic medium. This upper limit is 4 times
lower than the previous detection derived from a composite spectrum of 29 Lyman
break galaxies at z 3.4. If this value is typical of the escape fraction of the
z 3 galaxies, and is added to the expected contribution of the QSO population,
the derived UV background is in good agreement with the one derived by the
proximity effect.


title:
How Cumbersome is a Tenth Order Polynomial?: The Case of Gravitational
  Triple Lens Equation

abstract:
  Three point mass gravitational lens equation is a two-dimensional vector
equation that can be embedded in a tenth order analytic polynomial equation of
one complex variable, and we can solve the one variable equation on the source
trajectories using recipies for Fortran or $C$ (portable for $C$++ or $C_{jj}$)
in Numerical Recipes, or using packages such as Mathemetica, Matlab, etc. This
ready solvability renders fitting microlensing light curves including triple
lenses a normal process, and such was done in a circumbinary planet fit for
MACHO-97-BLG-41. Subsequently, there was a claim that converting the triple
lens equation into the analytic equation was rather cumbersome, and the
impressionable judgement has caused an effect of mysterious impedance around
the perfectly tractable lens equation. There are judgements. Then, there is
nature. We looked up for one of the quantities of highest precision
measurements: electron $g$-factor correction $a_e \equiv g/2-1$. The current
best experimental values of $a_e$ agree to eight significant digits with the
theoretical value, and the theoretical calculation involves more than one
thousand Feynman diagrams -- many orders of magnitude messier than the triple
lens equation coefficients. We seem to have only choice to be compliant to
nature and its appetite for elegant mess and precision numerics. In fact, the
triple lens equation coefficients take up less than a page to write out and are
presented here for users' convenience.


title: On the Spectral Evolution of Cygnus X-2 along its Color-Color Diagram

abstract:
  We report on the results of a broad band (0.1-200 keV) spectral study of Cyg
X-2 using two BeppoSAX observations taken in 1996 and 1997, respectively, for a
total effective on-source time of ~100 ks. The color-color (CD) and
hardness-intensity (HID) diagrams show that the source was in the horizontal
branch (HB) and normal branch (NB) during the 1996 and 1997 observation,
respectively. Five spectra were selected around different positions of the
source in the CD/HID, two in the HB and three in the NB. These spectra are fit
to a model consisting of a disk blackbody, a Comptonization component, and two
Gaussian emission lines at ~1 keV and ~6.6 keV, respectively. The addition of a
hard power-law tail with photon index ~2, contributing ~1.5% of the source
luminosity, improves the fit of the spectra in the HB. We interpret the soft
component as the emission from the inner accretion disk, with inner
temperature, k T_in, varying between 0.8 and 1.7 keV and inner radius, R_in,
varying between 26 and 11 km (assuming an inclination angle of the system of 60
degrees). The Comptonization component is probably emitted by hot plasma
(electron temperature k T_e varying between 3 and ~20 keV, optical depth \tau ~
11-0.4, seed-photon temperature k T_W ~ 1-2.4 keV) surrounding the NS. The
changes in the parameters of the blackbody component indicate that the inner
rim of the disk approaches the NS surface when the source moves from the HB to
the NB, i.e. as the (inferred) mass accretion rate increases. The parameters of
the Comptonized component also change significantly when the source moves from
the HB to the NB. We discuss possible scenarios which can explain these
changes.


title: New era in likelihood analyses of the Local Group acceleration

abstract:
  In maximum-likelihood analyses of the Local Group (LG) acceleration, the
object describing nonlinear effects is the coherence function (CF), i.e. the
cross-correlation coefficient of the Fourier modes of the velocity and gravity
fields. We study the CF both analytically, using perturbation theory, and
numerically, using a hydrodynamic code. The dependence of the function on
Omega_m and the shape of the power spectrum is very weak. The only cosmological
parameter that the CF is strongly sensitive to is the normalization sigma_8 of
the underlying density field. Perturbative approximation for the function turns
out to be accurate as long as sigma_8 is smaller than about 0.3. For higher
normalizations we provide an analytical fit for the CF as a function of sigma_8
and the wavevector. The characteristic decoherence scale which our formula
predicts is an order of magnitude smaller than that determined by Strauss et
al. This implies that present likelihood constraints on cosmological parameters
from analyses of the LG acceleration are significantly tighter than hitherto
reported.


title:
How the X-ray spectrum of a Narrow-Line Seyfert 1 galaxy may be
  reflection dominated

abstract:
  A model for the inner regions of accretion flows is presented where, due to
disc instabilities, cold and dense material is clumped into deep sheets or
rings. Surrounding these density enhancements is hot, tenuous gas where coronal
dissipation processes occur. We expect this situation to be most relevant when
the accretion rate is close to Eddington and the disc is radiation-pressure
dominated, and so may apply to Narrow-Line Seyfert~1 (NLS1) galaxies. In this
scenario, the hard X-ray source is obscured for most observers, and so the
detected X-ray emission would be dominated by reflection off the walls of the
sheets. A simple Comptonization calculation shows that the large photon-indices
characteristic of NLS1s would be a natural outcome of two reprocessors closely
surrounding the hard X-ray source. We test this model by fitting the XMM-Newton
spectrum of the NLS1 1H 0707-495 between 0.5 and 11 keV with reflection
dominated ionized disc models. A very good fit is found with three different
reflectors each subject to the same \Gamma=2.35 power-law. An iron
overabundance is still required to fit the sharp drop in the spectrum at around
7 keV. We note that even a small corrugation of the accretion disc may result
in \Gamma > 2 and a strong reflection component in the observed spectrum.
Therefore, this model may also explain the strength and the variability
characteristics of the MCG-6-30-15 Fe K line. The idea needs to be tested with
further broadband XMM-Newton observations of NLS1s.


title: Four-Body Effects in Globular Cluster Black Hole Coalescence

abstract:
  In the high density cores of globular clusters, multibody interactions are
expected to be common, with the result that black holes in binaries are
hardened by interactions. It was shown by Sigurdsson & Hernquist (1993) and
others that 10 solar mass black holes interacting exclusively by three-body
encounters do not merge in the clusters themselves, because recoil kicks the
binaries out of the clusters before the binaries are tight enough to merge.
Here we consider a new mechanism, involving four-body encounters. Numerical
simulations by a number of authors suggest that roughly 20-50% of binary-binary
encounters will eject one star but leave behind a stable hierarchical triple.
If the orbital plane of the inner binary is strongly tilted with respect to the
orbital plane of the outer object, a secular Kozai resonance, first
investigated in the context of asteroids in the Solar System, can increase the
eccentricity of the inner body significantly. We show that in a substantial
fraction of cases the eccentricity is driven to a high enough value that the
inner binary will merge by gravitational radiation, without a strong
accompanying kick. Thus the merged object remains in the cluster; depending on
the binary fraction of black holes and the inclination distribution of
newly-formed hierarchical triples, this mechanism may allow massive black holes
to accumulate through successive mergers in the cores of globular clusters. It
may also increase the likelihood that stellar-mass black holes in globular
clusters will be detectable by their gravitational radiation.


title:
Magnetoconvection and dynamo coefficients: II. Field-direction dependent
  pumping of magnetic field

abstract:
  We study the pumping of magnetic flux in three-dimensional compressible
magnetoconvection in the context of stellar dynamos. The simulation domain
represents a rectangular section from the lower part of a stellar convection
zone plus the underlying stably stratified layer, with a total depth of up to
five pressure scale heights. Once convection has attained a statistically
stationary state, a magnetic field is introduced. The magnetic field is
subsequently modified by the convective motions, and the resulting pumping
effects are isolated by calculating various coefficients of the expansion of
the electromotive force, uxb, in terms of components of the mean magnetic
field. The dependence of the pumping effects on rotation, latitude and other
parameters is studied. First numerical evidence is found for the existence of
pumping effects in the horizontal directions, unless the rotation axis
coincides with the vertical axis, as is the case on the poles. Evidence is
found that the pumping effects act differently on different components of the
mean magnetic field. Latitudinal pumping is mainly equatorward for toroidal
field, and can be poleward for poloidal field. Longitudinal pumping is mainly
retrograde for the radial field but prograde for the latitudinal field. The
pumping effect in the vertical direction is found to be dominated by the
diamagnetic effect, equivalent to a predominating downward advection with a
maximum speed in the turbulent case of about 10 percent of the rms convective
velocity. Where possible, an attempt is made to identify the physical origin of
the effect. Finally, some consequences of the results for stellar dynamos are
discussed.


title: Spectroscopic Evidence for Starspots on the Secondary Star of SS Cygni

abstract:
  Cataclysmic variables (CVs) are interacting binary systems where a cool,
rapidly rotating secondary star passes material to a white dwarf. If this mass
loss is to continue then there must be continuous angular momentum loss from
the system. By analogy with the Sun and other cool stars, it has been assumed
that magnetic braking is responsible, angular momentum being carried away by an
ionised wind from the secondary star, threading a dynamo-generated magnetic
field. We have discovered TiO absorption in the spectrum of SS Cyg, whose
secondary star should be too hot to show such features. The most likely
explanation of its presence is cool star spots caused by the strong (0.1T)
fields required by the magnetic braking theories.


title:
Metal Abundances of KISS Galaxies. I. Coarse Metal Abundances and the
  Metallicity-Luminosity Relation

abstract:
  We derive metal abundance estimates for a large sample of starbursting
emission-line galaxies (ELGs). Our sample is drawn from the KPNO International
Spectroscopic Survey (KISS) which has discovered over 2000 ELG candidates to
date. Follow-up optical spectra have been obtained for ~900 of these objects. A
three step process is used to obtain metal abundances for these galaxies. We
first calculate accurate nebular abundances for 12 galaxies whose spectra cover
the full optical region from [OII]3726,29 to beyond [SII]6717,31 and include
detection of [OIII]4363. Using secondary metallicity indicators R_23 and p_3,
we calculate metallicities for an additional 59 galaxies with spectra that
cover a similar wavelength range but lack [OIII]4363. The results are used to
calibrate relations between metallicity and two readily observed emission-line
ratios, which allow us to estimate coarse metallicities for 519 galaxies in
total. The uncertainty in these latter abundance estimates is 0.16 dex. From
the large, homogeneously observed sample of star-forming galaxies we identify
low metallicity candidates for future study and investigate the
metallicity-luminosity relation. We find a linear metallicity-luminosity
relation of the following form: 12 + log(O/H) = 4.059 - 0.240 M_B, with an RMS
scatter of 0.252. This result implies that the slope of the metallicity-
luminosity relation is steeper than when dwarf galaxies are considered alone,
and may be evidence that the relationship is not linear over the full
luminosity range of the sample.


title: On modification of the Newton's law of gravity at very large distances

abstract:
  We discuss a Modified Field Theory (MOFT) in which the number of fields can
vary. It is shown that when the number of fields is conserved MOFT reduces to
the standard field theory but interaction constants undergo an additional
renormalization and acquire a dependence on spatial scales. In particular, the
renormalization of the gravitational constant leads to the deviation of the law
of gravity from the Newton's law in some range of scales $r_{\min}<r<r_{\max
}$, in which the gravitational potential shows essentially logarithmic $\sim
\ln r$ (instead of $1/r$) behavior. In this range, the renormalized value of
the gravitational constant $G$ increases and at scales $r > r_{\max}$ acquires
a new constant value $G^{\prime}\sim Gr_{\max}/r_{\min}$. From the dynamical
standpoint this looks as if every point source is surrounded with a halo of
dark matter. It is also shown that if the maximal scale $r_{\max}$ is absent,
the homogeneity of the dark matter in the Universe is consistent with a fractal
distribution of baryons in space, in which the luminous matter is located on
thin two-dimensional surfaces separated by empty regions of ever growing size.


title: Effects of the magnetic fields on the protoneutron star structure

abstract:
  The equation of state of a protoneutron star matter including the effects of
magnetic field, temperature, nuclear asymmetry and trapped neutrinos are
studied. Using the Oppenheimer-Volkoff-Tolman equation global parameters of the
protoneutron star are obtained. Presence of the nuclear asymmetry and magnetic
field make the protoneutron star more compact.


title:
Chandra High-Resolution Spectrum of the Anomalous X-ray Pulsar 4U
  0142+61

abstract:
  We report on a 25 ks observation of the 8.7 s anomalous X-ray pulsar
4U~0142+61 with the High Energy Transmission Grating Spectrometer (HETGS) on
the Chandra X-ray Observatory. The continuum spectrum is consistent with
previous measurements and is well fit by an absorbed power-law + blackbody with
photon index Gamma=3.3+/-0.4 and kT=0.418+/-0.013 keV. No evidence was found
for emission or absorption lines, with an upper limit of ~50 eV on the
equivalent width of broad features in the 2.5-13 A (0.95-5.0 keV) range and an
upper limit of ~10 eV on the equivalent width of narrow features in the
4.1-17.7 A (0.7-3.0 keV) range. If the source is a magnetar, then the absence
of a proton cyclotron line strongly constrains magnetar atmosphere models and
hence the magnetic field strength of the neutron star. We find no strong
features that are indicative of cyclotron absorption for magnetic field
strengths of (1.9-9.8)x10^{14} G. This is still consistent with the dipole
field strength of B=1.3x10^{14} G (at the polar cap) estimated from the
pulsar's spindown.


title:
Evidence for Harmonic Relationships in the High Frequency QPOs of XTE
  J1550-564 and GRO J1655-40

abstract:
  We continue to investigate the X-ray timing and spectral properties of the
black hole binary, XTE J1550-564. For three different groups of observations,
we show evidence that two high-frequency QPOs (HFQPOs) occur simultaneously
near 184 and 276 Hz. In one group, there is also evidence of a broad feature at
92 Hz. In each case, we can model the QPO profiles while assuming that the
central frequencies are related as integral harmonics of a single frequency. We
next investigate the X-ray energy spectra, and we find a systematic increase in
the strength of the power-law component as the stronger of the two HFQPOs
shifts from 276 to 184 Hz. A strikingly similar result is seen for GRO J1655-40
when the stronger HFQPO shifts from 450 to 300 Hz. The fundamental HFQPO
frequencies for the two X-ray sources scale inversely with black hole mass,
which is consistent with the hypotheses that these HFQPOs represent some
oscillation rooted in general relativity (GR) and that the two black holes have
similar values of the dimensionless spin parameter. We discuss physical
mechanisms that may explain these HFQPOs. In particular, a resonance between
the orbital and radial coordinate frequencies in the innner accretion disk, as
proposed by Abramowicz & Kluzniak, would imply moderate values for the
dimensionless spin parameter (0.1 < a < 0.6) for both black holes.


title: Multiple Integral Field Spectroscopy

abstract:
  Integral-field spectroscopy is the most effective method of exploiting the
superb image quality of the ESO-VLT, allowing complex astrophysical processes
to be probed on the angular scales currently accessible only for imaging data,
but with the addition of information in the spectral dimension. We discuss
science drivers and requirements for multiple deployable integral fields for
spectroscopy in the near-infrared. We then describe a fully modular instrument
concept which can achieve such a capability over a 5-10' field with up to 32
deployable integral fields, each fully cryogenic with 1-2.5 micron coverage at
a spectral resolution of ~3000, each with a 4" x 4" field of view sampled at
0.2"/pixel to take advantage of the best K-band seeing.


title:
Evidence for an outer disk in the Prototype `Compact Elliptical' Galaxy
  M32

abstract:
  M32 is the prototype for the relatively rare class of galaxies referred to as
`compact ellipticals'. It has been suggested that M32 may be a tidally
disturbed r^(1/4) elliptical galaxy, or the remnant bulge of a disk-stripped
early-type spiral galaxy. This paper reveals that the surface brightness
profile, the velocity dispersion measurements, and the estimated supermassive
black hole mass in M32 are inconsistent with the galaxy having, and probably
ever having had, an r^(1/4) light profile. Instead, the radial surface
brightness distribution of M32 resembles an almost perfect (bulge + exponential
disk) profile, which is accompanied by a marked increase in the ellipticity
profile and an associated change in the position angle profile where the `disk'
starts to dominate. Compelling evidence that this bulge/disk interpretation is
accurate comes from the best-fitting r^(1/n) bulge model which has a Sersic
index n=1.5, in agreement with the recently discovered relation between a
bulge's Sersic index and the mass of its supermassive black hole. An index n>4
would also be inconsistent with the stellar velocity dispersion of M32. The
bulge-to-disk size ratio r_e /h equals 0.20, and the logarithm of the
bulge-to-disk luminosity ratio log(B/D) equals 0.22, typical of lenticular
galaxies. The effective radius of the bulge is 27" (~100 pc), while the
scale-length of the disk is less well determined: due to possible tidal-
stripping of the outer profile beyond 220-250", the scale-length may be as
large as 1.3 kpc. M32 is a relatively face-on, nucleated, dwarf galaxy with a
low surface brightness disk and a high surface brightness bulge. This finding
brings into question the existence of the compact elliptical class of galaxies.


title:
Chandra HRC and HST observations of NGC6240: resolving the AGN and
  Starburst

abstract:
  We present high spatial resolution X-ray Chandra HRC and HST WFPC2 Halpha
observations of the prototypical infrared luminous galaxy NGC6240. The central
region of this system shows a remarkably complex morphology, with filaments and
loops observed in the optical and X-rays. The total X-ray luminosity is
dominated by the extended emission. Both nuclei are clearly detected in the HRC
image and both appear to be extended. The energetics of the nuclei imply that
the southern nucleus is the more plausible counterpart to the obscured AGN. The
overall SED of the galaxy is in good agreement with a blend of starburst and
AGN components which have similar bolometric luminosities, L_bol ~ 5e45 ergs/s,
with the starburst dominating the observed continuum in the near-IR (K-band),
optical and soft X-ray bands.


title: The Optical Afterglow of GRB 011211

abstract:
  We present early-time optical photometry and spectroscopy of the optical
afterglow of the gamma-ray burst GRB 011211. The spectrum of the optical
afterglow contains several narrow metal lines which are consistent with the
burst occurring at a redshift of 2.140 +/- 0.001. The optical afterglow decays
as a power law with a slope of alpha = 0.83 +/- 0.04 for the first
approximately two days after the burst at which time there is evidence for a
break. The slope after the break is at least 1.4. There is evidence for rapid
variations in the R-band light approximately 0.5 days after the burst. These
variations suggest that there are density fluctuations near the gamma-ray burst
on spatial scales of approximately 40--125 AU. The magnitude of the break in
the light curve, the spectral slope, and the rate of decay in the optical,
suggest that the burst expanded into an ambient medium that is homogeneous on
large scales. We estimate that the local particle density is between
approximately 0.1 and 10 cm^{-3} and that the total gamma-ray energy in the
burst was 1.2--1.9 x 10^{50} erg. This energy is smaller than, but consistent
with, the ``standard'' value of (5 +/- 2) x 10^{50} erg. Comparing the observed
color of the optical afterglow with predictions of the standard beaming model
suggests that the rest-frame V-band extinction in the host galaxy is less than
approximately 0.03 mag.


title: Meausurement of Sky Suface Brightness Fluctuations at lambda = 4 micron

abstract:
  We present a Monte-Carlo technique to probe the cosmic Infrared background
radiation (CIB) with faint source confusion in deep, wide-field 4 micron
images. We report a detection of surface brightness fluctuations using an
ensemble of 5000 pixels. The brightness fluctuations do not show correlated
structure and appear to be dominated by galaxies. We estimate a lower limit
(95% C.L.) on CIB by modeling the number-count behavior of contributing sources
to the detected fluctuations.


title: The Chandra Deep Field-North Survey and the Cosmic X-ray Background

abstract:
  Chandra has performed a 1.4 Ms survey centred on the Hubble Deep Field-North
(HDF-N), probing the X-ray Universe 55-550 times deeper than was possible with
pre-Chandra missions. We describe the detected point and extended X-ray sources
and discuss their overall multiwavelength (optical, infrared, submillimeter,
and radio) properties. Special attention is paid to the HDF-N X-ray sources,
luminous infrared starburst galaxies, optically faint X-ray sources, and
high-to-extreme redshift AGN. We also describe how stacking analyses have been
used to probe the average X-ray emission properties of normal and starburst
galaxies at cosmologically interesting distances. Finally, we discuss plans to
extend the survey and argue that a 5-10 Ms Chandra survey would lay key
groundwork for future missions such as XEUS and Generation-X.


title:
GAIA accuracy on radial velocities assessed from a synthetic spectra
  database

abstract:
  Spectrograph aboard the GAIA satellite operates in the near-IR, in the 8490--
8740 \AA window accessible also from the ground. The most important parameter
yet to be determined is the spectral resolution. Realistic estimates of the
zodiacal light background are obtained and a total of $2\times 10^5$
correlation runs are used to study the accuracy of radial velocity measured by
the spectrograph as a function of resolution, magnitude of the target, its
spectral type and luminosity class. Accuracy better than 2 km/s is achievable
for bright stars if a high enough dispersion is chosen. Radial velocity error
of 5 km/s is at $V=17.5$ for Cepheids and at 17.7 for horizontal branch stars.
Even for very faint objects, with spectra dominated by background and readout
noise, the optimal dispersion is still in the 0.25 / 0.75 \AA/pix range. This
is also true for complicated cases such as spectroscopic binaries or if
information other than radial velocity, i.e. abundances of individual elements
or stellar rotation velocity, is sought after. The results can be scaled to
assess performance of future ground based instruments.


title: Dynamic Hydrogen Ionization

abstract:
  We investigate the ionization of hydrogen in a dynamic Solar atmosphere. We
show that the time scale for ionization/recombination can be estimated from the
eigenvalues of a modified rate matrix where the optically thick Lyman
transitions that are in detailed balance have been excluded. We find that the
time scale for ionization/recombination is dominated by the slow collisional
leakage from the ground state to the first excited state. Throughout the
chromosphere the time scale is long ($10^3$-$10^5$ s), except in shocks where
the increased temperature and density shorten the time scale for
ionization/recombination, especially in the upper chromosphere. Because the
relaxation time scale is much longer than dynamic time scales, hydrogen
ionization does not have time to reach its equilibrium value and its
fluctuations are much smaller than the variation of its statistical equilibrium
value appropriate for the instantaneous conditions. The ionization state tends
to represent the higher temperature of the shocks, and the mean electron
density is up to a factor of six higher than the electron density calculated in
statistical equilibrium from the mean atmosphere. The simulations show that a
static picture and a dynamic picture of the chromosphere are fundamentally
different and that time variations are crucial for our understanding of the
chromosphere itself and the spectral features formed there.


title: Some Properties of the Random Universe

abstract:
  What is the role of the constants of nature in physical theory? I hypothesize
that the observable universe, u0, constitutes a Universal Turing Machine (UTM)
constrained by algorithmically random logical tape parameters defining its
material properties (a physical UTM). The finite non-zero empirical values of
Planck's constant, h, and other constants of nature exemplify those logical
parameters. Their algorithmic randomness is necessary and sufficient for the
consistent operation of a physical UTM. At any given time, ti, these constants
correspond to the first n random halt digits, Omega-n, of Chaitin's Halting
Probability, Omega. Planck's equation E=hv and Boltzmann's relation S=kLogW are
shown to apply to the operation of a physical UTM. The genomic evolution of u0
in constants of nature space (CON space) from an undecidable state in u0's
Planck era to its current ordered condition occurs through the algorithmically
random, symmetry-breaking addition of new constants to the laws by which u0
operates -- a process called logical tunneling. The temperature of u0 for t<=tp
is shown to be T=0K. The energy dissipated when a physical UTM clears its
memory after each computation is proposed as a candidate for cold dark matter
(CDM) and is calculated to comprise 87.5% of the cosmological matter content,
Omega-M, of u0. This result concurs with current astronomical estimates that
87.1% of the matter content of u0 consists of CDM. The energy incorporated in
u0 through the process of logical tunneling from undecidable states of the
complete Universe, E, to decidable states of u0 is suggested as a candidate for
the unexplained "dark energy", Omega-X, hypothesized to drive the accelerating
cosmological expansion of space and believed to constitute 66% of the critical
mass, Omega-0, of the observable universe.


title: Proper motions of new dust in the colliding-wind binary WR 140

abstract:
  The eccentric WR+O binary system WR 140 produces dust for a few months at
intervals of 7.94 yrs coincident with periastron passage. We present the first
resolved images of this dust shell, at binary phases ~0.039 and ~0.055, using
aperture masking techniques on the Keck-I telescope to achieve
diffraction-limited resolution. Proper motions of approximately 1.1
milliarcsecond per day were detected, implying a distance ~1.5 kpc from the
known wind speed. The dust plume observed is not as simple as the ``pinwheel''
nebulae seen around other WR colliding wind binaries, indicating the orbital
plane is highly inclined to our line-of-sight and/or the dust formation is very
clumpy. Follow-up imaging in the mid-infrared and with adaptive optics is
urgently required to track the dust motion further, necessary for unambiguously
determining the orbital geometry which we only partially constrain here. With
full knowledge of the orbital elements, these infrared images can be used to
reconstruct the dust distribution along the colliding wind interface, providing
a unique tool for probing the post-shock physical conditions of violent
astrophysical flows.


title: Precessing microblazars and unidentified gamma-ray sources

abstract:
  The recent discovery by Paredes et al. (2000) of a persistent microquasar
that is positionally coincident with an unidentified gamma-ray source has open
the possibility that other sources in the Third EGRET Catalog could be
interpreted as microquasars as well. In this letter we show that some variable
unidentified EGRET sources in the galactic plane could be produced by faint,
otherwise undetected microquasars with precessing jets. When the jet points
towards the observer, gamma-ray emission resulting from upscattered stellar
photons could be detectable yielding a variable source with weak or
undetectable counterpart at longer wavelengths. Strategies for detecting
these``microblazars'' with forthcoming satellites are briefly discussed.


title: Chandra Observations of the Galactic Center and Nearby Edge-on Galaxies

abstract:
  I review our recent Chandra surveys of the center region of the Milky Way and
other nearby edge-on galaxies. Our Galactic center survey provides an
unprecedented high-resolution, broad-band X-ray panorama of a 0.8x2 square
degree swath along the Galactic plane. Our preliminary analysis has led a
detection of about 1000 discrete sources. We find that the diffuse X-ray
emission dominates over the contribution from faint discrete sources and is
globally associated with distinct interstellar structures observed at radio and
mid-infrared wavelengths. We study how high-energy activities in the center
region affect the immediate vicinity and may influence other aspects of the
Galaxy. We have further observed nearby edge-on late-type disk galaxies in
fields of low foreground Galactic extinction to gain external perspectives of
the global disk/halo interaction. We have detected a giant diffuse
X-ray-emitting corona around the galactic disk of NGC 4631. Extraplanar diffuse
X-ray emission is also detected around NGC 3556. These X-ray-emitting coronae
morphologically resemble the radio halos of these galaxies, indicating a close
connection between outflows of hot gas, cosmic rays, and magnetic field from
the galactic disks. There is only marginal evidence for extraplanar diffuse
X-ray emission in NGC 4244 -- a galaxy with an extremely low star formation
rate. In general, the extraplanar diffuse X-ray emission is evidently related
to recent massive star forming activities in the galactic disks, especially in
their central regions.


title: Gamma-Rays from Intergalactic Shocks

abstract:
  Structure formation in the intergalactic medium (IGM) produces large-scale,
collisionless shock waves, where electrons can accelerate to highly
relativistic energies. Such electrons can Compton scatter cosmic microwave
background photons up to gamma-ray energies. We study the radiation emitted in
this process using a hydrodynamic cosmological simulation of a LCDM universe.
This radiation, extending beyond TeV energies, has roughly constant energy flux
per decade in photon energy, in agreement with the predictions of Loeb & Waxman
(2000). Assuming that a fraction xi_e=0.05 of the shock thermal energy is
transferred to relativistic electrons, as inferred from collisionless
non-relativistic shocks in the interstellar medium, we find that the radiation
energy flux, e^2(dJ/de)~ 50-160 eV cm^-2 s^-1 sr^-1, constitutes ~10% of the
extragalactic gamma-ray background. The associated point-sources are too faint
to account for the ~60 unidentified EGRET gamma-ray sources, but GLAST should
resolve several sources associated with large-scale IGM structures for
xi_e~0.03, and many more sources for larger xi_e. The intergalactic origin of
the radiation can be verified through a cross-correlation with, e.g., the
galaxy distribution that traces the same structure. Its shock-origin may be
tested by a cross-correlation with radio synchrotron radiation, emitted as the
same electrons gyrate in post-shock magnetic fields. We predict that GLAST and
Cherenkov telescopes such as MAGIC, VERITAS and HESS should resolve gamma-rays
from nearby (redshifts z < 0.01) rich galaxy clusters, perhaps in the form of a
\~5-10 Mpc diameter ring-like emission tracing the cluster accretion shock,
with luminous peaks at its intersections with galaxy filaments detectable even
at z~0.025.


title: Cygnus A

abstract:
  We report Chandra imaging-spectroscopy and RXTE spectroscopy of the nearby,
powerful radio galaxy Cygnus A. Various aspects of the results are discussed,
including the X-ray properties of the nucleus, the radio hot spots, the cluster
of galaxies, the prolate cavity in the ICM inflated by the radio jets and
``bands'' of thermal gas which encircle the cavity in its equatorial plane. The
hard X-ray emission of the nucleus extends to 100 keV and originates from an
unresolved source absorbed by a large column density (N$_{\rm H}$ $\simeq$ 2
$\times$ 10$^{23}$ cm$^{-2}$) of gas. The soft ($<$ 2 keV) nuclear emission
exhibits a bi-polar structure which extends $\simeq$ 2 kpc from the nucleus and
is strongly correlated with both optical continuum and emission-line
morphologies. It is suggested that this nebulosity is photoionized by the
nucleus and that the extended X-rays are electron-scattered nuclear radiation.
All four radio hot spots are detected in X-rays, with the emission resulting
from synchrotron self-Compton radiation in an approximately equipartition
field. The temperature of the X-ray emitting intracluster gas drops from
$\simeq 8$ keV more than 100 kpc from the center to $\simeq 5$ keV some 80 kpc
from the center, with the coolest gas immediately adjacent to the radio galaxy.
There is a metallicity gradient in the X-ray emitting gas, with the highest
metallicities ($\sim$ solar) found close to the center, decreasing to $\sim
0.3$ solar in the outer parts. (Abstract truncated).


title:
The Optical Gravitational Lensing Experiment. Search for Planetary and
  Low-Luminosity Object Transits in the Galactic Disk. Results of 2001 Campaign

abstract:
  We present results of an extensive photometric search for planetary and
low-luminosity object transits in the Galactic disk stars commencing the third
phase of the Optical Gravitational Lensing Experiment -- OGLE-III. Photometric
observations of three fields in the direction of the Galactic center (800
epochs per field) were collected on 32 nights during time interval of 45 days.
Out of the total of 5 million stars monitored, about 52~000 Galactic disk stars
with photometry better than 1.5% were analyzed for flat-bottomed eclipses with
the depth smaller than 0.08 mag.
  Altogether 46 stars with transiting low-luminosity objects were detected. For
42 of them multiple transits were observed, a total of 185, allowing orbital
period determination. Transits in two objects: OGLE-TR-40 and OGLE-TR-10, with
the radii ratio of about 0.14 and estimate of the radius of the companion
1.0-1.5R_Jup, resemble the well known planetary transit in HD 209458. The
sample was selected by the presence of apparent transits only, with no
knowledge on any other properties. Hence, it is very well suited for general
study of low-luminosity objects. The transiting objects may be Jupiters, brown
dwarfs, or M dwarfs. Future determination of the amplitude of radial velocity
changes will establish their masses, and will confirm or refute the reality of
the so called ``brown dwarf desert''. The low-mass stellar companions will
provide new data needed for the poorly known mass-radius relation for the lower
main sequence. All photometric data are available to the astronomical community
from the OGLE Internet archive.


title:
The interpretation of the emission spectra of the Seyfert 2 galaxy NGC
  7130. Determination of the AGN and starburst contributions

abstract:
  Detailed modeling of the different regions of NGC 7130 is presented,
accounting for its composite nature of AGN and starburst galaxy. Shock waves,
created by stellar winds from hot massive stars and by supernova ejecta, are
evident in the continuum and line spectra emitted from the clouds. The AGN
starburst connection is discussed on the basis of model results, considering in
particular the distribution of densities and velocities throughout the galaxy.


title:
The 12C/13C ratio in the Planetary Nebula NGC3242 from Hubble Space
  Telescope STIS observations

abstract:
  We present high resolution HST ultraviolet spectroscopy of NGC3242, the only
planetary nebula with a measured abundance of 3He. The Space Telescope Imaging
Spectrograph (STIS) has been used to observe the CIII multiplet near 1908 A.
The presence of 12C and 13C lines at these wavelengths allows a direct estimate
of the carbon isotopic ratio in the ionized gas of the nebula. We have detected
the 12C doublet and obtained an upper limit on the 13C 1909.6 A line, resulting
in a carbon isotopic ratio 12C/13C > 38, in agreement with standard stellar
models. The lack of the 13C line and the presence of the 3He line in the
spectrum indicate that the progenitor star did not undergo a phase of deep
mixing during the last stages of its evolution. The significance of this result
for studies of stellar nucleosynthesis and Galactic chemical evolution is
discussed.


title: The Dynamical Status of the Cluster of Galaxies 1E0657-56

abstract:
  We present the results of a new spectroscopic and photometric survey of the
hot X-ray cluster 1E0657-56, at z=0.296. We determine the presence of a low
velocity dispersion subcluster, which is offset from the main cluster position
by 0.7 Mpc and about 600 km/s. We determine the virial masses and total
luminosities of the cluster and its subcluster, and solve for the two-body
dynamical model. With additional constraints from the results of the analysis
of the cluster X-ray emission by Markevitch et al. (2001), we find that the
subcluster passed through the cluster centre about 0.15 Gyr ago. Taken at face
value the mass of the subcluster is typical of a loose group. It is however
difficult to establish the pre-merger mass of the colliding system. We provide
tentative evidence that the subcluster is in fact the remnant core of a
moderately massive cluster, stripped by the collision with 1E0657-56. The main
cluster dynamics does not seem to have suffered from this collision. On the
contrary, the cluster X-ray properties seem to have been significantly
affected. We also discuss the effect of the subcluster collision in relation to
starburst events and the cluster radio halo.


title:
Development of Hydrodynamic Instability in the Intergalactic Medium of
  the Merging Cluster of Galaxies A3667

abstract:
  A3667, a spectacular merger cluster, was observed by Chandra twice. In this
paper we review the main results of the analysis of these observations. In
particular we show evidence for the presence in the cluster of a 300 kpc
Kelvin-Helmholtz hydrodynamic instability. We discuss the development of such
instability and the structure of the intracluster magnetic filed in light of a
self-consistent cluster dynamical model.


title: The mass function of the Las Campanas loose groups of galaxies

abstract:
  We have determined the mass function of loose groups of galaxies in the Las
Campanas Redshift Survey. Loose groups of galaxies in the LCRS range in mass
from $M \sim 10^{12} {\rm M}_{\sun}$ to $10^{15} {\rm M}_{\sun}$. We find that
the sample is almost complete for masses in the interval $5\cdot 10^{13}-8\cdot
10^{14} {\rm M}_{\sun}$. Comparison of the observed mass function with
theoretical mass functions obtained from N-body simulations shows good
agreement with a CDM model with the parameters $\Omega_m = 0.3$,
$\Omega_{\Lambda} = 0.7$ and the amplitude of perturbations about
$\sigma_8=0.78-0.87$. For smaller masses the mass function of LCRS loose groups
flattens out, differing considerably from the group mass function found by
Girardi and Giuricin (2000) and from mass functions obtained by numerical
simulations.


title: The UZC-SSRS2 Group Catalog

abstract:
  We apply a friends-of-friends algorithm to the combined UZC and SSRS2
redshift surveys to construct a catalog of 1168 groups of galaxies; 411 of
these groups have 5 or more members within the redshift survey. The group
catalog covers 4.69 steradians and all groups exceed a number density contrast
threshold of 80. We demonstrate that the groups catalog is homogeneous across
the two underlying redshift surveys; the catalog of groups and their members
thus provides a basis for other statistical studies of the large-scale
distribution of groups and their physical properties. The median physical
properties of the groups are similar to those for groups derived from
independent surveys including the ESO Key Programme and the Las Campanas
Redshift Survey. We include tables of groups and their members.


title:
HeI 1.083 micron emission and absorption in DG Tau: line excitation in
  jet, hot wind, and accretion flow

abstract:
  We present long-slit spectroscopy and spectro-astrometry of HeI 1.083 micron
emission in the T Tauri star, DG Tau. We identify three components in the HeI
feature: (1) a blueshifted emission component atv -200 km s^-1, (2) a bright
emission component at zero-velocity with a FWZI of ~500 km s^-1, and (3) a
blueshifted absorption feature at velocities between -250 and -500 km s^-1. The
position and velocity of the blueshifted HeI emission coincide with a
high-velocity component (HVC) of the [FeII] 1.257 micron emission, which arises
from a jet within an arcsecond of the star. The presence of such a high
excitation line (excitation energy ~ 20 eV) within the jet supports the
scenario of shock heating. The bright HeI component does not show any spatial
extension, and it is likely to arise from magnetospheric accretion columns.
  The blueshifted absorption shows greater velocities than that in H-alpha,
suggesting that these absorption features arise from the accelerating wind
close to the star.


title: Atomic Polarization and the Hanle Effect

abstract:
  This article presents an introduction to optical pumping, atomic polarization
and the Hanle effect in weakly magnetized stellar atmospheres. Although the
physical processes and the theoretical framework described here are of interest
for applications in a variety of astrophysical contexts (e.g. scattering
polarization in circumstellar envelopes and polarization in astronomical
masers), the article focuses mainly on the quest for understanding the physical
origin of the linearly polarized solar limb spectrum. It considers also the
development of the Hanle effect as a reliable diagnostic tool for making
feasible new advances in solar photospheric and chromospheric magnetism.
Particular emphasis is given to a rigorous modeling of polarization phenomena
as the essential link between theory and observations. Some of the most recent
advances in this field are presented after carefully explaining how the various
radiation pumping mechanisms lead to atomic polarization in the absence and in
the presence of weak magnetic fields.


title: Deuterium chemistry in the primordial gas

abstract:
  We review and update some aspects of deuterium chemistry in the
post-recombination Universe with particular emphasis on the formation and
destruction of HD. We examine in detail the available theoretical and
experimental data for the leading reactions of deuterium chemistry and we
highlight the areas where improvements in the determination of rate
coefficients are necessary to reduce the remaining uncertainties. We discuss
the cooling properties of HD and the modifications to the standard cooling
function introduced by the presence of the cosmological radiation field.
Finally, we consider the effects of deuterium chemistry on the dynamical
collapse of primordial clouds in a simple ``top-hat'' scenario, and we
speculate on the minimum mass a cloud must have in order to be able to cool in
a Hubble time.


title:
The GMOS integral field unit: first integral field spectroscopy with an
  8m telescope

abstract:
  The Gemini Multiobject Spectrograph (GMOS) installed on the Gemini-North
telescope has a facility for integral field spectroscopy over the wavelength
range 0.4-1.0um. GMOS is converted to this mode by the remote insertion of an
integral field unit (IFU) into the beam in place of the masks used for
multiobject spectroscopy. With the IFU deployed, integral field spectroscopy is
available over a fully-filled contiguous field of 5 x 7 arcsec with a sampling
of 0.2 arcsec. A separate field of half the area, but otherwise identical, is
also provided to aid background subtraction. The IFU contains 1500
lenslet-coupled fibres and is the largest-format fibre-based IFU yet tested on
the sky and the first facility of any type for integral field spectroscopy
employed on an 8/10m telescope. We describe the IFU and present results from
commissioning.


title:
The far-infrared energy distributions of Seyfert and starburst galaxies
  in the Local Universe: ISO photometry of the 12 micron active galaxy sample

abstract:
  New far-infrared photometry with ISOPHOT, onboard the Infrared Space
Observatory, is presented for 58 galaxies with homogeneous published data for
another 32 galaxies all belonging to the 12 micron galaxy sample. In total 29
Seyfert 1's, 35 Seyfert 2's and 12 starburst galaxies, about half of the 12
micron active galaxy sample, plus 14 normal galaxies for comparison. The ISO
and the IRAS data are used to define color-color diagrams and spectral energy
distributions (SED). Thermal dust emission at two temperatures (one cold at
15-30K and one warm at 50-70K) can fit the 60-200 micron SED, with a dust
emissivity law proportional to the inverse square of the wavelength. Seyfert
1's and Seyfert 2's are indistinguishable longward of 100 micron, while, as
already seen by IRAS, the former have flatter SEDs shortward of 60 micron. A
mild anti-correlation is found between the [200 - 100] color and the "60 micron
excess". We infer that this is due to the fact that galaxies with a strong
starburst component, and thus a strong 60 micron flux, have a steeper
far-infrared turnover. In non-Seyfert galaxies, increasing the luminosity
corresponds to increasing the star formation rate, that enhances the 25 and 60
micron emission. This shifts the peak emission from around 150 micron in the
most quiescent spirals to shorter than 60 micron in the strongest starburst
galaxies.


title: MERLIN observations of Stephan's Quintet

abstract:
  We present MERLIN L-band images of the compact galaxy group, Stephan's
Quintet. The Seyfert 2 galaxy, NGC 7319, the brightest member of the compact
group, is seen to have a triple radio structure typical of many extra-galactic
radio sources which have a flat spectrum core and two steep spectrum lobes with
hot spots. The two lobes are asymmetrically distributed on opposite sides of
the core along the minor axis of the galaxy. Ultraviolet emission revealed in a
high resolution HRC/ACS HST image is strongly aligned with the radio plasma and
we interpret the intense star formation in the core and north lobe as an event
induced by the collision of the north radio jet with over-dense ambient
material. In addition, a re-mapping of archive VLA L-band observations reveals
more extended emission along the major axis of the galaxy which is aligned with
the optical axis. Images formed from the combined MERLIN and archive VLA data
reveal more detailed structure of the two lobes and hot spots.


title: The complex X-ray spectrum of the supersoft source MR Vel

abstract:
  We present the X-ray spectrum of MR Vel/RXJ0925.7-4758 obtained with the
Medium Energy Grating spectrometer of the Chandra X-ray Telescope. The simplest
models used by earlier authors, stellar atmospheres in combination with a
thermal plasma in collisional ionization equilibrium, cannot explain the
spectrum. Neither does a photo-ionized plasma. We identify P Cygni profiles of
Fe XVII and O VIII, from which we conclude that these lines arise in a wind. We
conclude that major uncertainty exists about the bolometric luminosity of MR
Vel, and perhaps of supersoft sources in general, so that the theoretical
prediction that this luminosity derives from steady nuclear burning cannot be
verified.


title:
Heavy Nuclei Enrichment of the Galactic Cosmic Rays at High Energy:
  Astrophysical Interpretation

abstract:
  A substantial increase of the mean logarithmic mass $<\ln A>$ of galactic
cosmic rays {\em vs} energy has been observed . We study three effects that
could explain this trend i) different source spectra for protons and heavy
nuclei ii) a selective nuclear destruction in flight of heavies iii) a gradient
of the source number and chemical composition in the galactic disk.
  We take advantage of the diffusive cosmic ray propagation model developed at
LAPTH to study specifically the geometrical aspects of the propagation and
extend it to high energy. Using a simple modeling of the spectral knee around
$10^{15}$ eV, a bump in $<\ln A>$ appears. This feature is smoother when the
spectral index of protons is steeper than Fe's.
  We analyze the effects of the rigidity dependence of the diffusion
coefficient and the scale height of the confinement halo and we show that $<\ln
A>$ is most sensitive to the first parameter. Pure geometrical effects are less
determining than the diffusion coefficient spectral index. Subsequently, we
conclude that the physics of cosmic ray confinement is the essential cause of
the heavy nuclei enrichment until $\sim 10^{15}$ eV.


title: Warm Absorbers in Active Galactic Nuclei

abstract:
  Observations of warm absorbers provided new ways to study the nuclear
environments of AGNs. I discuss basic properties of warm absorbers and early
developments with ROSAT, ASCA and HST observations. I briefly touch upon recent
advances made with Chandra and FUSE.


title: Cosmological Deuterium Production in Non-Standard Scenarios

abstract:
  It is widely believed that the cosmic baryon density may be obtained by
inferring deuterium abundances in low-metallicity quasar absorption line
systems. The implicit assumptions which enter this argument are critically
assessed. In particular, the production of deuterium in non-standard Big Bang
nucleosynthesis scenarios, the putative production of deuterium in
astrophysical environments, and the possible destruction of deuterium via
non-standard chemical evolution are discussed.


title:
Collective processes in relativistic plasma and their implications for
  gamma-ray burst afterglows

abstract:
  We consider the effects of collective plasma processes on synchrotron
emission from highly relativistic electrons. We find, in agreement with Sazonov
(1970), that strong effects are possible also in the absence of a
non-relativistic plasma component, due to the relativistic electrons (and
protons) themselves. In contrast with Sazonov, who infers strong effects only
in cases where the ratio of plasma frequency to cyclotron frequency is much
larger than the square of the characteristic electron Lorentz factor, nu_p/nu_B
>> gamma^2, we find strong effects also for 1 << nu_p/nu_B << gamma^2. The
modification of the spectrum is prominent at frequencies nu < nu_{R*} = nu_p
min[gamma, (nu_p/nu_B)^(1/2)], where nu_{R*} generalizes the Razin-Tsytovich
frequency, nu_R = gamma nu_p, to the regime nu_p/nu_B << gamma^2. Applying our
results to gamma-ray burst (GRB) plasmas, we predict a strong modification of
the radio spectrum on minute time scale following the GRB, at the onset of
fireball interaction with its surrounding medium, in cases where the ratio of
the energy carried by the relativistic electrons to the energy carried by the
magnetic field exceeds ~ 10^5. Plausible electron distribution functions may
lead to negative synchrotron reabsorption, i.e to coherent radio emission,
which is characterized by a low degree of circular polarization. Detection of
these effects would constrain the fraction of energy in the magnetic field,
which is currently poorly determined by observations, and, moreover, would
provide a novel handle on the properties of the environment into which the
fireball expands.


title:
Chandra Observations and the Mass Distribution of EMSS1358+6245: Toward
  Constraints on Properties of Dark Matter

abstract:
  Chandra observations of lensing galaxy clusters have now provided accurate
dark matter profiles for several objects in which the intracluster medium is
likely to be in hydrostatic equilibrium. We discuss Chandra observations of the
mass profile of one such cluster, EMSS1358+6245. We find no evidence for
flattening of the mass density profile at radii greater than 50/h_50 kpc . This
result, and similar findings from Chandra observations of other clusters,
appear to rule out models in of dark matter self-interaction proposed to
explain the flat cores of low-surface brightness galaxies.


title:
Implications of the Narrow Period Distribution of Anomalous X-ray
  Pulsars and Soft Gamma-Ray Repeaters

abstract:
  The spin periods of the ten observed Anomalous X-ray Pulsars and Soft
Gamma-ray Repeaters lie in the very narrow range 6-12 s. We use a point
likelihood technique to assess the constraints this clustering imposes on the
birth period and on the final period of such systems. We consider a general law
for their spin evolution described by a constant braking index. We find that,
for positive values of the braking index, the observed clustering requires an
upper cut-off period that is very close to the maximum observed period of about
12 s. We also show that the constraint on the birth period depends very
strongly on the assumed value of the braking index n, ranging from a few
milliseconds for n>2 to a few seconds for n<2. We discuss the possible ways of
tightening these constraints based on similarities with the population of radio
pulsars and with future observations of such sources with current X-ray
observatories.


title: Gamma ray astroparticle physics with GLAST

abstract:
  The energy domain between 10 MeV and hundreds of GeV is an essential one for
the multifrequency study of extreme astrophysical sources. The understanding of
spectra of detected gamma rays is necessary for developing models for
acceleration, emission, absorption and propagation of very high energy
particles at their sources and in space. After the end of EGRET on board the
Compton Gamma Ray Observatory this energy region is not covered by any other
experiment, at least up to 50 GeV where ground Cerenkov telescopes are
beginning to take data. Here we will review the status of the space experiment
GLAST that will fill this energy region from March 2006 with particular
emphasis at the connection with all the other ground and space planned
experiments and at the contribution of GLAST to particle physics.


title: Gas cooling in simulations of the formation of the galaxy population

abstract:
  We compare two techniques for following the cooling of gas and its
condensation into galaxies within high resolution simulations of cosmologically
representative regions. Both techniques treat the dark matter using N-body
methods. One follows the gas using smoothed particle hydrodynamics (SPH) while
the other uses simplified recipes from semi-analytic (SA) models. We compare
the masses and locations predicted for dense knots of cold gas (the `galaxies')
when the two techniques are applied to evolution from the same initial
conditions and when the additional complications of star formation and feedback
are ignored. We find that above the effective resolution limit of the two
techniques, they give very similar results both for global quantities such as
the total amount of cooled gas and for the properties of individual `galaxies'.
The SA technique has systematic uncertainties arising from the simplified
cooling model adopted, while details of the SPH implementation can produce
substantial systematic variations in the galaxy masses it predicts.
Nevertheless, for the best current SPH methods and the standard assumptions of
the SA model, systematic differences between the two techniques are remarkably
small. The SA technique gives adequate predictions for the condensation of gas
into `galaxies' at less than one percent of the computational cost of obtaining
similar results at comparable resolution using SPH.


title:
The internal structure and formation of early-type galaxies: the
  gravitational--lens system MG2016+112 at z=1.004

abstract:
  [Abridged] We combine our measurements of the velocity dispersion and the
surface brightness profile of the lens galaxy D in the system MG2016+112
(z=1.004) with constraints from gravitational lensing to study its internal
mass distribution. We find that: (i) dark matter accounts for >50% of the total
mass within the Einstein radius (99% CL), excluding at the 8-sigma level that
mass follows light inside the Einstein radius with a constant mass-to-light
ratio (M/L). (ii) the total mass distribution inside the Einstein radius is
well-described by a density profile ~r^-gamma' with an effective slope
gamma'=2.0+-0.1+-0.1, including random and systematic uncertainties. (iii) The
offset of galaxy D from the local Fundamental Plane independently constrains
the stellar M/L, and matches the range derived from our models, leading to a
more stringent lower limit of >60% on the fraction of dark matter within the
Einstein radius (99%CL).
  Under the assumption of adiabatic contraction, the inner slope of the dark
matter halo before the baryons collapsed is gamma_i<1.4 (68 CL), marginally
consistent with the highest-resolution cold dark matter simulations that
indicate gamma_i~1.5. This might indicate that either adiabatic contraction is
a poor description of E/S0 formation or that additional processes play a role
as well. Indeed, the apparently isothermal density distribution inside the
Einstein radius, is not a natural outcome of adiabatic contraction models,
where it appears to be a mere coincidence. By contrast, we argue that
isothermality might be the result of a stronger coupling between luminous and
dark-matter, possibly the result of (incomplete) violent relaxation processes.
Hence, we conclude that galaxy D appears already relaxed 8 Gyr ago.


title: Atomic Processes in Planetary Nebulae

abstract:
  A hot central star illuminating the surrounding ionized H II region usually
produces very rich atomic spectra resulting from basic atomic processes:
photoionization, electron-ion recombination, bound-bound radiative transitions,
and collisional excitation of ions. Precise diagnostics of nebular spectra
depend on accurate atomic parameters for these processes. Latest developments
in theoretical computations are described, especially under two international
collaborations known as the Opacity Project (OP) and the Iron Project (IP),
that have yielded accurate and large-scale data for photoionization cross
sections, transition probabilities, and collision strengths for electron impact
excitation of most astrophysically abundant ions. As an extension of the two
projects, a self-consistent and unified theoretical treatment of
photoionization and electron-ion recombination has been developed where both
the radiative and the dielectronic recombination processes are considered in an
unified manner. Results from the Ohio State atomic-astrophysics group, and from
the OP and IP collaborations, are presented. A description of the electronic
web-interactive database, TIPTOPBASE, with the OP and the IP data, and a
compilation of recommended data for effective collision strengths, is given.


title: Mass loading of pulsar winds

abstract:
  The dynamics of relativistic magnetized mass loaded outflows carrying
toroidal magnetic field is analyzed in the context of Pulsar Wind Nebulae
(PWNs). Mass loading is very efficient in slowing down super-relativistic
magnetized flows and weakening of relativistic shocks. We suggest that
weakening of relativistic reverse shocks by mass loading in PWNs is responsible
for the low radiative efficiencies of the majority of the PWNs. Mass loading
may also result in a shock transition near the fast magnetosonic point; this is
unlikely to happen in majority of PWNs. The evolution of magnetized mass loaded
flows beyond the reverse shock is complicated: after initial deceleration to
the minimal velocity required to transport the magnetic flux, the mass loaded
flows have to {\it accelerate}. In order to be able to expand to infinity,
magnetized flows should either become time dependent or destroy the toroidal
magnetic flux by developing internal instabilities. Destruction of the magnetic
flux initiated by mass loading may allow for the flow to slow down to
sub-relativistic velocities and resolve the $\sigma$ paradox of the pulsar wind
nebula.


title: Saturation of the R-mode Instability

abstract:
  Rossby waves (r-modes) in rapidly rotating neutron stars are unstable because
of the emission of gravitational radiation. We study saturation of this
instability by nonlinear transfer of energy to stellar "inertial" oscillation
modes. We present detailed calculations of stellar inertial modes in the WKB
limit, their linear damping by bulk and shear viscosity, and the nonlinear
coupling forces among these modes. The saturation amplitude is derived in the
extreme limits of strong or weak driving by radiation reaction, as compared to
the damping rate of low order inertial modes. We find the saturation energy is
{\it extremely small}, at least four orders of magnitude smaller than that
found by previous investigators. We discuss the consequences of this result for
spin evolution of young neutron stars, and neutron stars being spun up by
accretion in Low Mass X-ray Binaries.We also discuss the detection of these
gravitational waves by LIGO.


title: Braneworld models of dark energy

abstract:
  We explore a new class of braneworld models in which the scalar curvature of
the (induced) brane metric contributes to the brane action. The scalar
curvature term arises generically on account of one-loop effects induced by
matter fields residing on the brane. Spatially flat braneworld models can enter
into a regime of accelerated expansion at late times. This is true even if the
brane tension and the bulk cosmological constant are tuned to satisfy the
Randall--Sundrum constraint on the brane. Braneworld models admit a wider range
of possibilities for dark energy than standard LCDM. In these models the
luminosity distance can be both smaller and larger than the luminosity distance
in LCDM. Whereas models with $d_L \leq d_L(\rm LCDM)$ imply $w = p/\rho \geq
-1$ and have frequently been discussed in the literature, models with $d_L >
d_L(\rm LCDM)$ have traditionally been ignored, perhaps because within the
general-relativistic framework, the luminosity distance has this property {\em
only if} the equation of state of matter is strongly negative ($w < -1$).
Matter with $w < -1$ is beset with a host of undesirable properties, which
makes this model of dark energy unattractive within the conventional framework.
Braneworld models, on the other hand, have the capacity to endow dark energy
with exciting new possibilities without suffering from the problems faced by
models with $w < -1$. For a subclass of parameter values, braneworld dark
energy and the acceleration of the universe are {\em transient} phenomena. In
these models, the universe, after the current period of acceleration, re-enters
the matter dominated regime so that the deceleration parameter $q(t) \to 0.5$
when $t \gg t_0$, where $t_0$ is the present epoch. Such models could help
reconcile an accelerating universe with the requirements of string/M-theory.


title:
XMM-Newton observation of Abell 1835 : temperature, mass and gas mass
  fraction profiles

abstract:
  We present a study of the medium distant cluster of galaxies Abell 1835 based
on XMM-Newton data. The high quality of XMM-Newton data enable us to perform
spectro-imaging of the cluster up to large radii. We determine the gas and
total mass profiles based on the hydrostatic approach using the beta-model and
the temperature profile. For the determination of the temperature profile of
the ICM, which is needed for the mass determination, we apply a double
background subtraction, which accounts for the various kinds of background
present (particle and astrophysical background). We find a basically flat
temperature profile up to 0.75 r_200 with a temperature decrease towards the
center linked to the cooling flow. We obtain a gas mass fraction of (20.7 +/-
3.7)%, which is a lower limit on the baryon fraction in this cluster. Using
this value as baryon fraction for the entire universe, we obtain by combining
our results with results based on primordial nucleosynthesis, an upper limit
for Omega_m < 0.5h_{50}^{-1/2}, which is in good agreement with other recent
studies.


title: A neutral hydrogen survey of polar ring galaxies IV. Parkes observations

abstract:
  A total of 33 polar ring galaxies and polar ring galaxy candidates were
observed in the 21-cm HI line with the 64-m Parkes radio telescope. The
objects, selected by their optical morphology, are all south of declination -39
degrees and in only 5 of them HI had been reported previously. HI line emission
was detected towards 18 objects, though in 3 cases the detection may be
confused by another galaxy in the telescope beam, and one is a marginal
detection. Eight objects were detected for the first time in HI, of which 5 did
not have previously known redshifts.


title:
The UV line spectrum of the soft X-ray transient XTE J1118+480: a CNO
  processed core exposed

abstract:
  We compare UV spectra of the recent soft X-ray transients XTE J1118+480 and
XTE J1859+226. The emission line strengths in XTE J1118+480 strongly suggest
that the accreting material has been CNO processed. We show that this system
must have come into contact with a secondary star of about 1.5 solar masses,
and an orbital period ~15hr, very close to the bifurcation value at which
nuclear and angular momentum loss timescales are similar. Subsequent evolution
to the current period of 4.1 hr was driven by angular momentum loss. In passing
through a period of 7.75 hr the secondary star would have shown essentially
normal surface abundances. XTE J1118+480 could thus represent a slightly later
evolutionary stage of A0620-00. We briefly discuss the broad Ly alpha
absorption wings in XTE J1118+480.


title: The low-mass young stellar population in Orion OB1

abstract:
  We present recent results from our ongoing large scale variability survey of
the Orion OB1 Association. In an area of ~ 25 square degrees we have unveiled
new populations of low-mass young stars over a range of environments, and ages
from 1-2 Myr in Ori OB 1b to roughly 10 Myr in Ori OB 1a. There is a lack of
strong Ha emission and near-IR excesses in the young stars of Ori OB 1a,
suggesting that accretion stops and disks dissipate for most solar type stars
in a few Myr, probably caused by of the onset of planet formation. The absence
of dust and gas in Ori OB 1a is consistent with the picture of star formation
as a rapid process, in which molecular clouds dissipate in just a few Myr after
the first stars are born.


title: Radiatively Driven Plasma Jets around Compact Objects

abstract:
  Matter accreting onto black holes may develop shocks due to the centrifugal
barrier. A part of inflowing matter in the post-shock flow is deflected along
the axis in the form of jets. Post-shock flow which behaves like a Compton
cloud has `hot' electrons emiting high energy photons. We study the effect of
these `hot' photons on the outflowing matter. Radiation from this region could
accelerate the outflowing matter but radiation pressure should also slow it
down. We show that the radiation drag restricts the flow from attaining a very
high velocity. We introduce the concept of an `equilibrium velocity' ($v_{eq}
\sim 0.5c$) which sets the upper limit of the terminal velocity achieved by a
cold plasma due to radiation deposition force in the absence of gravity. If the
injection energy is $E_{in}$, then we find that the terminal velocity
$v_\infty$ satisfies a relation $v_\infty^2 \lsim v_{eq}^2 + 2 E_{in}$.


title: An XMM-Newton Survey of Ultra-Luminous Infrared Galaxies

abstract:
  We present preliminary results of XMM-Newton observations of 5 Ultra-luminous
Infrared Galaxies (ULIRGs), part of a mini-survey program dedicated to 10
ULIRGs selected from the bright IRAS sample. For 3 of them (IRAS 20551-4250,
IRAS 19254-7245 and Mkn 231) we find strong evidence for the presence of a
hidden AGN, while for two others (IRAS 20110-4156 IRAS 22491-1808) the S/N
ratio of the data does not allow us to be conclusive. In particular, we have
detected a strong Fe-K line in the X-ray spectra of IRAS19254-7245, with an
equivalent width (~2 keV) suggestive that most of the energy source in this
object is due to a deeply buried AGN.


title:
Optimal Chandra/XMM-Newton Band-Passes for Detecting Low Temperature
  Groups and Clusters of Galaxies

abstract:
  In this short paper I present the results of a calculation which seeks the
maximum, or optimal, signal-to-noise energy band for galaxy group or cluster
X-ray emission detected by the Chandra and XMM-Newton observatories. Using a
background spectrum derived from observations and a grid of models I show that
the "classical" 0.5-2 keV band is indeed close to optimal for clusters with gas
temperatures >2 keV, and redshifts z<1. For cooler systems however, this band
is generally far from optimal. Sub-keV plasmas can suffer 20-60%
signal-to-noise loss compared to an optimal band, and worse for z>0. The
implication is that current and forthcoming surveys should be carefully
constructed in order to minimize bias against the low mass, low temperature end
of the cluster/group population.


title:
SDSS J124602.54+011318.8: A Highly Variable AGN, Not an Orphan GRB
  Afterglow

abstract:
  The optically variable source SDSS J124602.54+011318.8 first appears in Sloan
Digital Sky Survey (SDSS) data as a bright point source with nonstellar colors.
Subsequent SDSS imaging and spectroscopy showed that the point source declined
or disappeared, revealing an underlying host galaxy at redshift 0.385. Based on
these properties, the source was suggested to be a candidate ``orphan
afterglow'': a moderately beamed optical transient, associated with a gamma-ray
burst (GRB) whose highly beamed radiation cone does not include our line of
sight. We present new imaging and spectroscopic observations of this source.
When combined with a careful re-analysis of archival optical and radio data,
the observations prove that SDSS J124602.54+011318.8 is in fact an unusual
radio-loud AGN, probably in the BL Lac class. The object displays strong
photometric variability on time scales of weeks to years, including several
bright flares, similar to the one initially reported. The SDSS observations are
therefore almost certainly not related to a GRB. The optical spectrum of this
object dramatically changes in correlation with its optical brightness. At the
bright phase, weak, narrow oxygen emission lines and probably a broader
H$\alpha$ line are superposed on a blue continuum. As the flux decreases, the
spectrum becomes dominated by the host galaxy light, with emerging stellar
absorption lines, while both the narrow and broad emission lines have larger
equivalent widths. We briefly discuss the implications of this discovery on the
study of AGNs and other optically variable or transient phenomena.


title: Brown dwarf populations in open clusters

abstract:
  We present the results of multiple simulations of open clusters, modelling
the dynamics of a population of brown dwarf members. We consider the effects of
a large range of primordial binary populations, including the possibilities of
having brown dwarf members contained within a binary system. We also examine
the effects of various cluster diameters and masses. Our examination of a
population of wide binary systems containing brown dwarfs, reveals evidence for
exchange reactions whereby the brown dwarf is ejected from the system and
replaced by a heavier main-sequence star. We find that there exists the
possibility of hiding a large fraction of the brown dwarfs contained within the
primordial binary population. We conclude that it is probable that the majority
of brown dwarfs are contained within primordial binary systems which then hides
a large proportion of them from detection.


title: NASA's Future Missions in X-ray Astronomy

abstract:
  The NASA program in X-ray astronomy has two long term goals: 1) to achieve
sufficient angular resolution to image the event horizon of a black hole (0.1
micro arc sec) and 2) to achieve sufficient collecting area (50-150 sq m) and
angular resolution (0.1-1.0 arc sec) to observe in detail the first black holes
and galaxies at high redshift. These ambitous goals can be used to map out a
series of missions and a technology program. The next major mission will be
Constellation-X which will be dedicated to high resolution X-ray spectroscopy
for launch in ~2010. This mission is a critical step in the roadmap to achieve
these goals. Following Constellation-X NASA is considering two very ambitious
vision missions: MAXIM and Generation-X that will achieve the ultimate
capabilities. The modest missions Astro-E2 and Swift address more focussed
science goals on a rapid development cycle and provide important pathfinders to
the larger missions.


title:
`Hyper Parameters' Approach to Joint Estimation: Applications to
  Cepheid-Calibrated Distances and X-Ray Clusters

abstract:
  We use a generalised procedure for the combined likelihood analysis of
different cosmological probes, the `Hyper-Parameters' method, that allows
freedom in the relative weights of the raw measurements. We perform a joint
analysis of the cepheid-calibrated data from the Hubble Space Telescope Key
Project and the baryon mass fraction in clusters to constrain the total matter
density of the universe, Omega_m, and the Hubble parameter, h. We compare the
results obtained using Hyper-Parameters method with the estimates from standard
chi^2 analysis. We assume that the universe is spatially flat, with a
cosmological constant. We adopt the Big-Bang nucleosynthesis constraint for the
baryon density, assuming the uncertainty is Gaussian distributed. Using this
and the cluster baryon fraction data, we find that the matter density and the
Hubble constant are correlated, Omega_m h^0.5~0.25, with preference for a very
high h. To break the degeneracy, we add in the cepheid-calibrated data and find
the best fit values (Omega_m, h) = (0.26 (+0.06,-0.06),0.72 (+0.04,-0.02)) (68
per cent confindence limits) using the Hyper-Parameters approach. We use the
derived Hyper-Parameters to `grade' the 6 different data sets we analyse.
Although our analysis is free of assumptions about the power spectrum of
fluctuations, our results are in agreement with the Lambda-Cold Dark Matter
`concordance' parameters derived from the Cosmic Microwave Background
anisotropies combined with Supernovae Ia, redshift surveys and other probes.


title: Do Distinct Cosmological Models Predict Degenerate Halo Populations?

abstract:
  Using cosmological N-body simulations, we investigate the influence of the
matter density parameter Omega_m and the linear theory power spectrum P(k) on
statistical properties of the dark matter halo population -- the mass function
n(M), the halo correlation function, and halo pairwise velocity statistics. For
fixed P(k), the effect of changing Omega_m is simple: the halo mass scale M_*
shifts in proportion to Omega_m, pairwise velocities (at fixed M/M_*) are
proportional to Omega_m^{0.6}, and halo clustering at fixed M/M_* is unchanged.
If one simultaneously changes the P(k) amplitude sigma_8 to maintain a "cluster
normalization" condition sigma_8 x Omega_m^{0.5} = const, then n(M) stays
approximately constant near M ~ 5e14 Msun, and halo clustering and pairwise
velocities are similar at fixed M. However, the shape of n(M) changes, with a
decrease of Omega_m from 0.3 to 0.2 producing a ~30% drop in the number of low
mass halos. One can preserve the shape of n(M) over a large dynamic range by
changing the shape of P(k), but the required changes are substantial, and they
significantly alter the halo clustering and halo velocities. The sensitivity of
the dark halo population to cosmological model parameters has encouraging
implications for efforts to constrain cosmology and galaxy bias with observed
galaxy clustering, since the predicted changes in the halo population cannot
easily be masked by altering the way that galaxies occupy halos. A shift in
Omega_m alone would be detected by any dynamically sensitive clustering
statistic; a cluster normalized change to sigma_8 and Omega_m would require a
change in galaxy occupation as a function of M/M_*, which would alter galaxy
clustering; and a simultaneous change to P(k) that preserves the halo mass
function would change the clustering of the halos themselves.


title:
Photometric redshifts from evolutionary synthesis with PEGASE: the code
  ZPEG and the z=0 age constraint

abstract:
  Photometric redshifts are estimated on the basis of template scenarios with
the help of the code ZPEG, an extension of the galaxy evolution model PEGASE.2
and available on the PEGASE web site. The spectral energy distribution (SED)
templates are computed for nine spectral types including starburst, irregular,
spiral and elliptical. Dust, extinction and metal effects are coherently taken
into account, depending on evolution scenarios. The sensitivity of results to
adding near-infrared colors and IGM absorption is analyzed. A comparison with
results of other models without evolution measures the evolution factor which
systematically increases the estimated photometric redshift values by $\Delta
z$ > 0.2 for z > 1.5. Moreover we systematically check that the evolution
scenarios match observational standard templates of nearby galaxies, implying
an age constraint of the stellar population at z=0 for each type. The respect
of this constraint makes it possible to significantly improve the accuracy of
photometric redshifts by decreasing the well-known degeneracy problem. The
method is applied to the HDF-N sample. From fits on SED templates by a
$\chi^2$-minimization procedure, not only is the photometric redshift derived
but also the corresponding spectral type and the formation redshift $z_for$
when stars first formed. Early epochs of galaxy formation z > 5 are found from
this new method and results are compared to faint galaxy count interpretations.
The new tool is available at: http://www.iap.fr/pegase


title: The Expected Properties of Dark Lenses

abstract:
  We investigate the properties of multiple-image gravitational lens systems
formed by dark matter halos. Both the Navarro-Frenk-White (NFW) and Moore et
al. mass profiles are considered, and the effects of quadrupole perturbations
to the lensing potential are taken into account. The systems produced by dark
halos exhibit two generic properties that serve as powerful benchmarks for
scrutinizing individual lens candidates: small flux ratios between the two
brightest images in triples, and detectable odd images. In contrast, most
currently ambiguous quasar pairs consist of two components with flux ratios >
3:1. Such systems are statistical outliers in the expected distribution of dark
lenses, and are therefore likely to be binary quasars.


title: A Toy Model for the Magnetic Connection between a Black Hole and a Disk

abstract:
  A magnetic field connecting a Kerr black hole to a disk rotating around it
can extract energy and angular momentum from the black hole and transfer them
to the disk if the black hole rotates faster than the disk. The energy can be
dissipated and radiated away by the disk, which makes the disk shine without
the need of accretion. In this paper we present a toy model for the magnetic
connection: a single electric current flowing around a Kerr black hole in the
equatorial plane generates a poloidal magnetic field which connects the black
hole to the disk. The rotation of the black hole relative to the disk generates
an electromotive force which in turn generates a poloidal electric current
flowing through the black hole and the disk and produces a power on the disk.
We will consider two cases: (1) The toroidal current flows on the inner
boundary of the disk, which generates a poloidal magnetic field connecting the
horizon of the black hole to a region of the disk {\it beyond} the inner
boundary; (2) The toroidal current flows on a circle inside the inner boundary
of the disk but outside the horizon of the black hole, which generates a
poloidal magnetic field connecting a portion of the horizon of the black hole
to the {\it whole} disk. We will calculate the power produced by the magnetic
connection and the resulting radiation flux of the disk in the absence of
accretion, and compare them with that produced by accretion.