438 research outputs found
On the influence of blends on the potential of ground-based transit surveys
Transit surveys have to observe many stars all at once in order to compensate
for the rarity of the searched events. Such surveys, especially the ones
observing a deep field of view and/or broadening their stellar images, have to
deal with a relatively high level of crowding. This crowding could lead to a
reduction of the number of detectable transits, and the estimation of the
potential of such surveys without taking into account the influence of blends
could give overoptimistic results. We have developed a code which allows to
estimate the extent by which such a survey is affected by the crowding of the
field of view. Our results show that the influence of blends is important only
for severe levels of crowding and is in general much less crucial than the
influence of red noise.Comment: 6 pages, 4 figures; to be published in Transiting Extrasolar Planets
Workshop, Eds: Cristina Afonso, David Weldrake & Thomas Hennin
Neutrino-Induced Fission and r-Process Nucleosynthesis
An r-process scenario with fission but no fission cycling is considered to
account for the observed abundance patterns of neutron-capture elements in
ultra-metal-poor stars. It is proposed that neutrino reactions play a crucial
role in inducing the fission of the progenitor nuclei after the r-process
freezes out in Type II Supernovae. To facilitate neutrino-induced fission, the
proposed r-process scenario is restricted to occur in a low-density environment
such as the neutrino-driven wind from the neutron star. Further studies to
develop this scenario are emphasized.Comment: 11 pages, 2 figures, to appear in ApJ
A deconvolution-based algorithm for crowded field photometry with unknown Point Spread Function
A new method is presented for determining the Point Spread Function (PSF) of
images that lack bright and isolated stars. It is based on the same principles
as the MCS (Magain, Courbin, Sohy, 1998) image deconvolution algorithm. It uses
the information contained in all stellar images to achieve the double task of
reconstructing the PSFs for single or multiple exposures of the same field and
to extract the photometry of all point sources in the field of view. The use of
the full information available allows to construct an accurate PSF. The
possibility to simultaneously consider several exposures makes it very well
suited to the measurement of the light curves of blended point sources from
data that would be very difficult or even impossible to analyse with
traditional PSF fitting techniques. The potential of the method for the
analysis of ground-based and space-based data is tested on artificial images
and illustrated by several examples, including HST/NICMOS images of a lensed
quasar and VLT/ISAAC images of a faint blended Mira star in the halo of the
giant elliptical galaxy NGC5128 (Cen A).Comment: Institutes: (1) Institut d'Astrophysique et de Geophysique,
Universite de Liege, allee du 6 Aout 17, B-4000 Liege, Belgium; (2) Ecole
Polytechnique Federale de Lausanne (EPFL), Laboratoire d'Astrophysique,
Observatoire, CH-1290 Sauverny, Switzerland; (3) Observatoire de Geneve, 51
Chemin des Maillettes, CH-1290 Sauverny, Switzerland. 8 pages, 8 figures.
Accepted for publication in A&
POX 186: the ultracompact Blue Compact Dwarf Galaxy reveals its nature
High resolution, ground based R and I band observations of the ultra compact
dwarf galaxy POX 186 are presented. The data, obtained with the ESO New
Technology Telescope (NTT), are analyzed using a new deconvolution algorithm
which allows one to resolve the innermost regions of this stellar-like object
into three Super-Star Clusters (SSC). Upper limits to both masses (M\sim 10^5
M_{\odot}) and the physical sizes (\le 60pc) of the SSCs are set. In addition,
and maybe most importantly, extended light emission underlying the compact
star-forming region is clearly detected in both bands. The R-I color rules out
nebular H\alpha contamination and is consistent with an old stellar population.
This casts doubt on the hypothesis that Blue Compact Dwarf Galaxies (BCDG) are
young galaxies.Comment: 4 figures postscript, 2 tables, to appear in A&A main journa
Slit and integral-field optical spectroscopy of the enigmatic quasar HE0450-2958
Interest in the quasar HE0450-2958 arose following the publication of the
non-detection of its expected massive host, leading to various interpretations.
This article investigates the gaseous and stellar contents of the system
through additional VLT/FORS slit spectra and integral field spectroscopy from
VLT/VIMOS. We apply our MCS deconvolution algorithm on slit spectra for the
separation of the QSO and diffuse components, and develop a new method to
remove the point sources in Integral Field Spectra, allowing extraction of
velocity maps, narrow-line images, spatially resolved spectra or ionization
diagrams of the surroundings of HE0450-2958. The whole system is embedded in
gas, mostly ionized by the QSO radiation field and shocks associated with radio
jets. The observed gas and star dynamics are unrelated, revealing a strongly
perturbed system. Despite longer spectroscopic observations, the host galaxy
remains undetected.Comment: 9 pages, 13 figures, in press in A&
Exploring the gravitationally lensed system HE 1104-1805: Near-IR Spectroscopy
(Abridged) A new technique for the spatial deconvolution of spectra is
applied to near-IR (0.95 - 2.50 micron) NTT/SOFI spectra of the lensed,
radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is
revealed between 1.5 and 2.5 micron. It is used in combination with previous
optical and IR photometry to infer a plausible redshift in the range 0.8 < z <
1.2. Modeling of the system shows that the lens is probably composed of the red
galaxy seen between the quasar images and a more extended component associated
with a galaxy cluster with fairly low velocity dispersion (~ 575 km/s). The
spectra of the two lensed images of the source show no trace of reddening at
the redshift of the lens nor at the redshift of the source. Additionally, the
difference between the spectrum of the brightest component a nd that of a
scaled version of the faintest component is a featureless continuum. Broad and
narrow emission lines, including the FeII features, are perfectly subtracted.
The very good quality of our spectrum makes it possible to fit precisely the
optical Fe II feature, taking into account the underlying continuum over a wide
wavelength range. HE 1104-1805 can be classified as a weak Fe II emitter.
Finally, the slope of the continuum in the brightest image is steeper than the
continuum in the faintest image and supports the finding by Wisotzki et al.
(1993) that the brightest image is microlensed. This is particularly
interesting in view of the new source reconstruction methods from
multiwavelength photometric monitoring.Comment: to be published in A&A, 8 pages, 9 postscript figure
The Old Halo metallicity gradient: the trace of a self-enrichment process
Based on a model of globular cluster self-enrichment published in a previous
paper, we present an explanation for the metallicity gradient observed
throughout the galactic Old Halo. Our self-enrichment model is based on the
ability of globular cluster progenitor clouds to retain the ejecta of a first
generation of Type II Supernovae. The key point is that this ability depends on
the pressure exerted on the progenitor cloud by the surrounding protogalactic
medium and therefore on the location of the cloud in the protoGalaxy. Since
there is no significant (if any) metallicity gradient in the whole halo, we
also present a review in favour of a galactic halo partly build via accretions
and mergers of satellite systems. Some of them bear their own globular clusters
and therefore ``contaminate'' the system of globular clusters formed ``in
situ'', namely within the original potential well of the Galaxy. Therefore, the
comparison between our self-enrichment model and the observational data should
be limited to the genuine galactic globular clusters, the so-called Old Halo
group.Comment: 11 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Quasar Host Orientation and Polarization: Insights into the Type 1/Type 2 Dichotomy
We investigate correlations between the optical linear polarization position
angle and the orientation of the host galaxy/extended emission of Type 1 and
Type 2 Radio-Loud (RL) and Radio-Quiet (RQ) quasars. We have used high
resolution Hubble Space Telescope (HST) data and deconvolution process to
obtain a good determination of the host galaxy orientation. With these new
measurements and a compilation of data from the literature, we find a
significant correlation between the polarization position angle and the
position angle of the major axis of the host galaxy/extended emission. The
correlation appears different for Type 1 and Type 2 objects and depends on the
redshift of the source. Interpretations in the framework of the unification
model are discussed.Comment: 3 pages, 1 figure, to appear in "The Nuclear Region, Host Galaxy and
Environment of Active Galaxies", eds. E. Benitez, I. Cruz-Gonzalez and Y.
Krongold, RevMexAA (Serie de Conferencias
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses X. Modeling based on high-precision astrometry of a sample of 25 lensed quasars: consequences for ellipticity, shear, and astrometric anomalies
(abridged) Gravitationally lensed quasars can be used as powerful
cosmological and astrophysical probes. We can (i) infer the Hubble constant
based on the time-delay technique, (ii) unveil substructures along the l.o.s.
toward distant galaxies, and (iii) compare the shape and the slope of baryons
and dark matter distributions in galaxies. To reach these goals, we need
high-accuracy astrometry and morphology measurements of the lens. In this work,
we first present new astrometry for 11 lenses with measured time delays. Using
MCS deconvolution on NIC2 HST images, we reached an astrometric accuracy of
about 1-2.5 mas and an accurate shape measurement of the lens galaxy. Second,
we combined these measurements with those of 14 other systems to present new
mass models of these lenses. This led to the following results: 1) In 4
double-image quasars, we show that the influence of the lens environment on the
time delay can easily be quantified and modeled, hence putting these lenses
with high priority for time-delay determination. 2) For quadruple-image
quasars, the difficulty often encountered in reproducing the image positions to
milli-arcsec accuracy (astrometric anomaly) is overcome by explicitly including
the nearest visible galaxy in the model. However, one anomalous system
(J1131-1231) does not show any luminous perturber in its vicinity, and three
others (WFI2026-4536, WFI2033-4723, and B2045+265) have problematic modeling.
These 4 systems are the best candidates for a pertubation by a dark matter
substructure. 3) We find a significant correlation between the PA of the light
and of the mass distributions in lensing galaxies. In contrast with other
studies, we find that the ellipticity of the light and of the mass also
correlate well, suggesting that the overall spatial distribution of matter is
not very different from the baryon distribution in the inner \sim 5 kpc of
lensing galaxies.Comment: Accepted for publication in Astronomy and Astrophysics abridged
abstrac
Understanding the relations between QSOs and their host galaxies from combined HST imaging and VLT spectroscopy
The host galaxies of six nearby QSOs are studied on the basis of high
resolution HST optical images and spatially resolved VLT slit spectra. The gas
ionization and velocity are mapped as a function of the distance to the central
QSO. In the majority of the cases, the QSO significantly contributes to the gas
ionization in its whole host galaxy, and sometimes even outside.
Reflection or scattering of the QSO \ha line from remote regions of the
galaxy is detected in several instances. The line shifts show that, in all
cases, the matter responsible for the light reflection moves away from the QSO,
likely accelerated by its radiation pressure.
The two faintest QSOs reside in spirals, with some signs of a past
gravitational perturbation. One of the intermediate luminosity QSOs resides in
a massive elliptical containing gas ionized (and probably pushed away) by the
QSO radiation. The other medium-power object is found in a spiral galaxy
displaying complex velocity structure, with the central QSO moving with respect
to the bulge, probably as a result of a galactic collision. The two most
powerful objects are involved in violent gravitational interactions and one of
them has no detected host.
These results suggest that (1) large-scale phenomena, such as galactic
collisions, are closely related to the triggering and the feeding of the QSO
and (2) once ignited, the QSO has significant influence on its large-scale
neighborhood (often the whole host and sometimes further away).Comment: Accepted for publication in ApJ. 31 pages, 17 figures, 3 table
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