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suivant: Session SF2A monter: Session SAIt-PNPS-PNCG-ASGaia précédent: Session SAIt-PNPS-PNCG-ASGaia

Poster contributions

The VIMOS VLT Deep Survey: the group catalogue
Cucciati, O.; Marinoni, C.; Iovino, A.; Bardelli, S.; Adami, C.; Mazure, A. and VVDS collaboration
(Laboratoire d'Astrophysique de Marseille)
We present a homogeneous and complete catalogue of optical galaxy groups identified in the VIMOS-VLT Deep Survey (VVDS). We use mock catalogues extracted from the Millennium simulation to study the potential systematics that might affect the overall distribution of the identified systems, and also to asses how well galaxy redshifts trace the line-of-sight velocity dispersion of the underlying mass overdensity. We train on these mock catalogues the adopted group-finding technique (the Voronoi-Delaunay Method, VDM), to recover in a robust and unbiased way the redshift and velocity dispersion distributions of groups and maximize the level of completeness (C) and purity (P) of the group catalogue. We identify 318(/144) VVDS groups with at least 2(/3) members within 0.2<=z<=1.0, globally with C=60% and P=50%. We use the group sample to study the redshift evolution of the fraction f_b of blue galaxies (U-B<=1) within 0.2<=z<=1 in both groups and in the whole ensemble of galaxies irrespectively of their environment.

Chemical heterogeneity of A stars in open clusters and Gaia
M. Gebran & R. Monier
(Université de Barcelone (DAM))
Abundance anomalies have been determined at the surface of many field and open cluster A and F dwarfs. These abundance anomalies are most likely caused by microscopic diffusion at work within the stable envelopes of A stars. However diffusion can be countercted by several other mixing processes such as convection, rotational mixing and mass loss. The typical patterns encountered are underabundances of Ca and/or Sc as well as overabundances of iron peak elements and rare earths. Non magnetic A/F stars with such patterns are classified as Am/Fm. We present a short review the surface abundances patterns of A/F stars in the Pleiades (100 Myr), Coma Berenices (450 Myr) and Hyades (650 Myr) open clusters. Real star-to-star variations of the abundances for several chemical elements in the A dwarfs in these clusters. The derived abundances are then compared to evolutionary models from the Montreal group. The results show that there are hydrodynamical processes acting within the radiative zone of these stars and hindering the effects of microscopic diffusion (mixing processes/mass loss).

In the context of the Gaia mission, we did some simulation in order to predict the number of A stars that Gaia will observe and their respective photometric/spectroscopic attainable accuracies.

Gaia RVS spectra will observe the CaII triplet and therefore yield valuable information concerning the statistics of Am/Fm stars in our Galaxy. Using Gaia astrometry data, more accurate ages (particularly for clusters) will be determined which will allow us, by comparing the predictions of the models and the observed abundance pattern, to constrain the physics and the transport processes included in the evolutionary models. An importing issue of this analysis will be the determination of the rotational velocities of the sample of A stars (up to V12-13 mag). This will yield valuable information about the formation and the evolution of these stars. Slowly rotating early A-type stars could originate from phenomena of angular momentum loss and redistribution undergone during pre-main-sequence phases.

EROS-2 Archive : Implementation and Applications
Jean-Baptiste Marquette, Eric Lesquoy
(Institut d'Astrophysique de Paris)
The EROS-2 experiment (Expérience de Recherche d'Objets Sombres) conducted between July 1996 and March 2003 a large-scale photometric survey towards the Magellanic Clouds and the Galactic center, in order to probe the eventual presence of compact objects (the so-called MACHOs) in the galactic Halo. This survey produced a unique and extremely large set of photometric light curves for more than 87 millions of stellar objects over more than 200 square degrees in two large non-standard passbands. We plan to make these data publicly available in 3 stages : (i) publication of the light curves through the database of the Time Series Center (Harvard University, PI: Pavlos Protopapas); (ii) publication of the catalogs through the CDS (Strasbourg); (iii) publication of the images through a VO architecture to be defined. The systematic astrometric calibration of these images is currently under process. Various projects are already using this EROS-2 database, other projects are encouraged to apply.

Spectral Analysis of the Stars Members of the Open Cluster M6: Preliminary Results
T. Kilicoglu, R. Monier, and L. Fossati
(Ankara University)
Open clusters are important laboratories for stellar astrophysics. One generally assumes that stars members of an open cluster have same initial chemical composition, same age, and same distance. Thus, the differences in abundance among the stars in a cluster usually reflect the competition between radiative diffusion and hydrodynamical process (mixing by rotation). The spectral analyses of open clusters allow us to perform detailed abundance analysis for most A and F member stars. The derived abundance patterns can than be compared to the prediction of self-consistent evolutionary processes including transport processes. We have used the Giraffe spectrograph, attached to 8 meter class VLT telescope (Chile), to derive elemental abundance of the open cluster M6 (age of $\sim$100 million years). We present preliminary results: determination of effective temperatures and surface gravities of 62 stars in M6 using the available Geneva 7 color photometric observations. Preliminary abundance determination from one low resolution and two high resolution regions including 4500 - 5100 A, 5140-5350 A, and 5590-5835 A, respectively, are presented for the star CD-32 13109.

GALEX NUV Lyman Break Galaxies
G. Williger, L. Haberzettl, M. Lehnert, N. Nesvadba, D. Valls-Gabaud
(Univ. de Nice)
We present results of a search for Lyman break galaxies at 1.5<2.5 in the GOODS-S using a NUV-dropout technique in combination with color-selection criteria. We were able to select a sample of 201 LBG-candidates. We compare our selection efficiencies to BM/BX- and BzK-selection methods, techniques solely based on ground-based data-sets, we see a higher success rate in detecting star forming galaxies in the purely studied redshift interval. For our LBG-candidate sample we estimate ages, masses, star formation rates, and extinction from SED models. We find about 15% of our LBG-candidates are comparable to infrared luminous LBGs or sub-millimeter galaxies.

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suivant: Session SF2A monter: Session SAIt-PNPS-PNCG-ASGaia précédent: Session SAIt-PNPS-PNCG-ASGaia
Samuel Boissier 2010-06-16