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Session SAIt-PNPS-PNCG-ASGaia

Globular cluster spectroscopy
Piercarlo Bonifacio
(GEPI - Observatoire de Paris - CNRS -Univ. Paris Diderot)
The Globular Clusters are an important component of the Galactic Halo, although in terms of mass they represent less than 1/10 of the mass of the Halo, their integrated luminosity is large and thus allows to trace the Halo at large distances. Their colour-magnitude diagrams are fairly simple, which has, for a long time, led to the notion that Globular Clusters are composed by a coeval single stellar population and ideal test-bench for stellar evolution theories. In the twenty years between roughly 1980 and 2000 great advances were made in the studies of Globular Clusters thanks to the availability of two-dimensional solid state detectors which allowed to build accurate colour-magnitude diagrams with statistically significant numbers of stars. Starting from the end of the 1990's the advent of the 8m class telescopes opened up the possibility of high resolution spectroscopic studies, which, for the nearest clusters, extend down to the Main Sequence. A major step forward with respect to the study of the brightest giants afforded by the 4m telescopes. The surpises then began to come and the detailed chemical abundance patterns which became available, clearly pointed towards a complex chemical evolution and the presence of multiple stellar populations. This was later confirmed by the detection of multiple Main Sequences and Sub Giant branches in some Globular Clusters. Detailed chemical abundances is not the only result coming from high resolution spectra, the availability of radial velocities with accuracy of 1 m/s makes some Globular Clusters and ideal test-bench for alternative theories of gravity, such as MOND. In this review I will give my personal perception of the most exciting advances in the field of Globular Cluster spectroscopy in the last years.



Open Clusters as tracers of the Galactic disk
Angela Bragaglia
(INAF-Osservatorio Astronomico di Bologna)
Open clusters are one of the best tracers of the properties of the thin disk of our Galaxy. I will concentrate on the metallicity distribution defined by open clusters and on its evolution with time, since this offers important information for the models of formation and chemical enrichment of the disk. I will also discuss how results of the Gaia satellite will influence our understanding of the open clusters and the Galactic disk.



Dwarf Galaxies in the Local Group: Cornerstones for Stellar Astrophysics and Cosmology
G. Bono, P.B. Stetson, A.R. Walker, M. Fabrizio, M. Monelli, M. Nonino, plus Carina Collaboration
(Universita' di Roma Tor Vergata)
Dwarf galaxies have been the crossroad of significant theoretical and observational efforts, but we still lack firm constraints corncerning their formation and evolution.They are also fundamental laboratories to investigate the impact of the environment on star formation and on chemical evolution in stellar systems that are 3-4 order of magnitudes smaller than giant galaxies and to constrain the evolutionary properties of metal-poor, intermadiate-mass stars. We present some recent results concerning the dwarf spheroidal Carina and the dwarf irregular IC10. In particular, we focus our attention on the evolutionary properties of their stellar populations using accurate and deep color-magnitude diagrams together with homogeneous sets of isochrones and helium burning evolutonary models. We also briefly discuss the impact that the transition from old, low-mass (horizontal branch) to intermediate-age (red clump) helium burning stars has in constraining the star formation history of complex stellar systems.


Chemical Abundances and the Enrichment History of Local Group Dwarf Galaxies
V. Hill
(Laboratoire Cassiopée, Observatoire de la Côte d'Azur)
At the lower end of galaxy masses, the classical dwarf spheroidal galaxies (dSph) allow to probe chemical enrichement on the smallest scales, and perhaps in its simplest expression. Particularly interesting are the issues concerning the efficency with which metals are retained or lost in these shallow potential wells. Another fundamental issue concerns the earliest epochs of star formation: are first stars formed in similar ways and proportions in all halos ?

In this talk I will review the chemical abundances of individual stars in the nearby classical dwarf spheroidal galaxies that have become available in increasing numbers (sample size and galaxies probed) in the last decade, in particular those obtained with FLAMES on VLT by the DART collaboration, highlighting the power of detailed chemical abundance patterns of large samples of stars to unravel the various evolutionnary paths followed by dSph galaxies. The intrisic evolution of those classical dSph systems will also be compared to ultra-faint dSph. Special emphasis will be given to the oldest and most metal-poor populations in dwarf galaxies, discussing the search for this eluding population, its detection and characterization, and the inferred relation between the Milky-Way halo and the early evolution of dSph galaxies.



Stellar populations in M31
Rodrigo Ibata
(Observatoire de Strasbourg)
In recent years the Andromeda galaxy has become the target of large, campaigns to survey its stellar populations from the centre to the outermost reaches of the halo. This flurry of activity, which has included large imaging programmes with the CFHT and spectroscopic follow-up with Keck will soon be complemented with a high-resolution panoramic survey of the disk with HST. These new photometric and kinematic data are giving us a uniquely detailed view of the structure and dynamics of the closest giant disk galaxy to the Milky Way. We are now able to study the large scale trends of galactic components and detect a plethora of small sub-structures. I will discuss the consequences of these findings for our understanding of galactic formation and the distribution of dark matter.



Spectro-photocentric variability and photometric variability of evolved stars: consequences on Gaia measurements
A. Chiavassa, E. Pasquato, A. Jorissen, S. Sacuto, B. Freytag, H. G. Ludwig, P. Cruzalebes, Y. Rabbia, A. Spang, O. Chesneau, and C. Babusiaux
(Mac Planck for Astrophysics)
Red supergiant stars are characterized by large granules on their surface which cause surface inhomogeneities and shock waves. We explore the impact of the granulation on the photocentric and photometric variability using 3D simulations of convection with CO5BOLD and the post-processing radiative transfer code OPTIM3D to compute intensity maps and spectra in Gaia G band. Finally, we find how many RSGs will have their Gaia astrometry altered by such surface granulation.



Multiple populations in GCs, a theoretical point of view
T. Decressin, H. Baumgardt, P. Kroupa, C. Charbonnel, G. Meynet
(Argelander-Institut für Astronomie)
Globular clusters exhibit peculiar chemical patterns where Fe and heavy elements are constant inside a given cluster while light elements (Li to Al) show strong star-to-star variations. Multiple branches have been discovered in several globular cluster which are related to these abundance variations. This pattern can be explained by self-pollution of the intracluster gas by recycling the wind ejected by first generation stars. I will present the current status of these polluters and some related issues about globular cluster dynamical evolution.


Massive spectroscopic analysis: the stellar population in three CoRoT/Exoplanet fields
Jean-Christophe Gazzano, Magali Deleuil, Patrick De Laverny, Alejandra Recio-Blanco, François Bouchy, Claire Moutou
(Laboratoire d'Astrophysique de Marseille)
Future is bright for massive surveys targeting thousands of stars. Most of these studies however require an accurate determination of stellar parameters such as effective temperature, abundances, or Vsini. This could be achieved only by combining multi-fibre spectroscopic observations with automated analysis software. We carried out a first study that demonstrates the feasibility of such an approach in three CoRoT/Exoplanet fields. We adapted and trained MATISSE, an algorithm initially developed to carry out the spectral analysis of Gaia/RVS spectra, to characterise the stellar population in these CoRoT/Exoplanet fields. This study was performed on the Mg I b spectral range observed with the FLAMES/GIRAFFE multi-fibre instrument at ESO. We measured the radial velocity, an estimate of the projected rotational velocity, the effective temperature, the surface gravity, the overall metallicity and the alpha-enhancement for more than 1 000 stars. Hence, we built the foundations for any study regarding transiting planet detection probabilities or Galactic structures within the CoRoT fields. This survey will be soon completed by new FLAMES observations and could be easily adapted to any other instrument.



Tracing the stellar mass assembly in the COSMOS field
Ilbert, Salvato, Le Floc'h, Aussel, Capak and the COSMOS team
(LAM)
Stellar mass assembly is the result of a complex interplay between numerous physical processes like cold gas accretion, AGN and supernovae feedback, merger. A clear and comprehensive picture describing the physical processes which regulate the stellar mass assembly is still missing in galaxy formation scenario. I will present the stellar mass assembly and star formation history measured in the 2 sq-deg COSMOS field.


A sparse population of very young stars in Cepheus
A. Klutsch, D. Montes, P. Guillout, A. Frasca, F.-X. Pineau, N. Grosso, E. Marilli, J. Lòpez-Santiago
(Universidad Complutense de Madrid)
Once mixed in the ambient galactic plane stellar population, young stars are virtually indiscernible because neither their global photometric properties nor the presence of nearby gas can help to disentangle them from older ones. Nevertheless, in the RasTyc sample, we discovered 4 lithium-rich field stars displaying the same space motion, which are located within a few degrees from each other on the celestial sphere close to Cepheus flare region and at the similar distance of the Sun. Both physical and kinematical indicators show that all stars are very young, with ages in the range 10 - 20 Myr. Using multivariate analysis methods, we selected optical counterparts of XMM/RASS X-ray sources cross-identified with late-type stars, which are located around these 4 young stars. Recent intermediate- and high-resolution spectroscopic observations of this sample allowed us to discover additional lithium-rich sources. Our preliminary results show that some of them share the same space motion as our 4 original stars. They have properties rather similar to the members of the TW Hydrae association, although they are slightly older and located in the northern hemisphere.


Properties of the thick disc far from the Solar neighbourhood
Georges Kordopatis, Patrick de Laverny, Alejandra Recio-Blanco, Albert Bijaoui and Christophe Ordenovic
(Observatoire de la Côte d'Azur)
Vertical gradients in kinematics, metallicities and spatial structure are crucial ingredients of Galaxy formation models. For that purpose,a spectroscopic survey of nearly 700 stars towards l$\sim$270, b$\sim$47 has been made, to detect and characterize possible stellar sub-populations in the Galactic Thick disc. MATISSE algorithm has been used to obtain the atmospherical parameters of the stars (Teff, logg, [M/H]) and Y$^2$ isochrones to get the distances. We present here results obtained, as well as a comparison with Besançon's model of the Milky Way of the metallicities, distances and kinematics obtained for that sample.



Improvement of atomic models for NLTE radiative transfer in late type stars
Thibault Merle, Frédéric Thévenin, Bernard Pichon, Lionel Bigot
(Observatoire de la Côte d'Azur)
We present our first results of improved N-LTE IR line profiles of Ca II and Mg I in good agreement with observations on the Sun. This work prepares us to analyze future RVS data of the Gaia mission. To do this we updated atomic models of magnesium and calcium. This work on NLTE effects will be also applied to correct determination of LTE chemical abundances of late type metal poor stars.



A SINFONI Integral Field Spectroscopy Survey for Damped Lyman-alpha Systems
Peroux, Bouche, Kulkarni, York and Vladilo
(Laboratoire d'Astrophysique de Marseille)
Details of processes through which galaxies convert their gas into stars need to be studied in order to obtain a complete picture of galaxy formation. One way to tackle these phenomena is to relate the HI gas and the stars in galaxies. Integral field spectroscopy provides an efficient way of detecting faint galaxies near bright quasars, further providing immediate redshift confirmation. We report the detection of H-alpha emission from a DLA and a sub-DLA galaxy. We derive SFR=1.8 M_sun/yr at impact parameter b=25 kpc towards quasar Q0302-223 for the DLA at z_abs=1.009 and SFR=2. M_sun/yr at b=39 kpc towards Q1009-0026 for the sub-DLA at z_abs=0.887. We use the NII/H-alpha ratio to derive the HII emission metallicities and compare them with the neutral gas HI absorption metallicities derived from high-resolution spectra. We also study the dynamical properties of these objects. While the DLA towards Q0302-223 is found to be dispersion-dominated, the sub-DLA towards Q1009-0026 shows clear signatures of rotation. We use a proxy to circular velocity to estimate the mass of the halo in which the sub-DLA resides and find $M\_halo=10^{12.6} M\_sun$. We also derive dynamical masses of these objects, and find $M\_dyn=10^{10.3} M\_sun$ and $10^{10.7} M\_sun$. For one of the two systems (towards Q0302-223), we are able to derive a stellar mass of $M\_*=10^{9.5} M\_sun$ from Spectral Energy Distribution fit. Our work illustrates that detailed studies of quasar absorbers can offer entirely new insights into our knowledge of the interaction between stars and the interstellar gas in galaxies.



Impact of stellar rotation on the age determination of five open clusters
SANTORO, Luca ; THEVENIN, Fredéric ; PICHON, Bernard
(CNRS)
In the context of the FLAME (*) working group of the Gaia data processing consortium, we study the effects of rotation on the age determination of open clusters.

On one hand, we present rotational velocity distributions of stars for different open clusters : Pleiades, Alpha Persei, Hyades, Praesepe and Blanco-1 using the statistical inversion of Chandrasekar-Munch.

On the other hand, to validate our work, we compare our results for the Hyades with models (including rotation) obtained with Cesam2k .

(*) : Final Luminosity, Ages and Mass Estimation



Discovery of a stellar stream in the outer Galactic halo
D. Valls-Gabaud, A. Sollima, D. Martinez Delgado
(GEPI - Observatoire de Paris)



Tests of MATISSE on large spectral datasets from the ESO archive
C.C.Worley, P. de Laverny, A. Recio-Blanco, V. Hill and A.Bijaoui, Y. Vernisse
(Observatoire de la Cote d'Azur)
The automated stellar classification algorithm, MATISSE, has been developed at the Observatoire de la Côte d'Azur (OCA) as a means of determining stellar temperatures, gravities and chemical abundances for large samples of stellar spectra. It has been selected by the Gaia DPAC as one of the key programmes to be used in the analysis of the spectra that will be obtained by the Radial Velocity Spectrometer (RVS) on the European Space Agency's (ESA) Gaia satellite. A key stage in the development of MATISSE is to test its performance on large spectral datasets in order to identify and address issues with analyzing real spectra prior to the launch of Gaia in 2012. Under the GSP-Spectroscopy Work Package this testing is being carried out on large datasets of spectra from the ESO archive. Preliminary results regarding the analysis of the archived FEROS spectra will be presented.




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suivant: Poster contributions monter: sf2a_boa précédent: Poster contributions
Samuel Boissier 2010-06-16