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

On the nature of cosmological time

Time is a parameter playing a central role in our most fundamental modeling of natural laws. Relativity theory shows that the comparison of times measured by different clocks depends on their relative motions and on the strength of the gravitational field in which they are embedded. In standard cosmology, the time parameter is the one measured by fundamental clocks, i.e. clocks at rest with respect to the expanding space. This proper time is assumed to flow at a constant rate throughout the whole history of the Universe. We make the alternative hypothesis that the rate at which cosmological time flows depends on the dynamical state of the Universe. In thermodynamics, the arrow of time is strongly related to the second law, which states that the entropy of an isolated system will always increase with time or, at best, stay constant. Hence, we assume that time measured by fundamental clocks is proportional to the entropy of the region of the Universe that is causally connected to them. Under that simple assumption, we build a cosmological model that explains the Type Ia Supernovae data (the best cosmological standard candles) without the need for exotic dark matter nor dark energy.Comment: 5 pages, 4 figures, submitted to MNRA

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

Analysis of luminosity distributions of strong lensing galaxies: subtraction of diffuse lensed signal

Strong gravitational lensing gives access to the total mass distribution of galaxies. It can unveil a great deal of information about the lenses dark matter content when combined with the study of the lenses light profile. However, gravitational lensing galaxies, by definition, appear surrounded by point-like and diffuse lensed signal that is irrelevant to the lens flux. Therefore, the observer is most often restricted to studying the innermost portions of the galaxy, where classical fitting methods show some instabilities. We aim at subtracting that lensed signal and at characterising some lenses light profile by computing their shape parameters. Our objective is to evaluate the total integrated flux in an aperture the size of the Einstein ring in order to obtain a robust estimate of the quantity of ordinary matter in each system. We are expanding the work we started in a previous paper that consisted in subtracting point-like lensed images and in independently measuring each shape parameter. We improve it by designing a subtraction of the diffuse lensed signal, based only on one simple hypothesis of symmetry. This extra step improves our study of the shape parameters and we refine it even more by upgrading our half-light radius measurement. We also calculate the impact of our specific image processing on the error bars. The diffuse lensed signal subtraction makes it possible to study a larger portion of relevant galactic flux, as the radius of the fitting region increases by on average 17\%. We retrieve new half-light radii values that are on average 11\% smaller than in our previous work, although the uncertainties overlap in most cases. This shows that not taking the diffuse lensed signal into account may lead to a significant overestimate of the half-light radius. We are also able to measure the flux within the Einstein radius and to compute secure error bars to all of our results

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&

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&

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

Deep near-infrared imaging of the HE0450-2958 system

The QSO HE0450-2958 and the companion galaxy with which it is interacting, both ultra luminous in the infrared, have been the subject of much attention in recent years, as the quasar host galaxy remained undetected. This led to various interpretations on QSO and galaxy formation and co-evolution, such as black hole ejection, jet induced star formation, dust obscured galaxy, or normal host below the detection limit. We carried out deep observations in the near-IR in order to solve the puzzle concerning the existence of any host. The object was observed with the ESO VLT and HAWK-I in the near-IR J-band for 8 hours. The images have been processed with the MCS deconvolution method (Magain, Courbin & Sohy, 1998), permitting accurate subtraction of the QSO light from the observations. The compact emission region situated close to the QSO, called the blob, which previously showed only gas emission lines in the optical spectra, is now detected in our near-IR images. Its high brightness implies that stars likely contribute to the near-IR emission. The blob might thus be interpreted as an off-centre, bright and very compact host galaxy, involved in a violent collision with its companion.Comment: 4 pages, 3 figures, accepted for publication in A&

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