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suivant: Poster contributions monter: sf2a_boa précédent: Session ASA

Session ASGaia-PNCG

The chemical enrichment in the halo from first galactic stars
Piercarlo Bonifacio
(GEPI - Observatoire de Paris - CNRS -Univ. Paris Diderot)
The cosmic microwave background and the cosmic expansion can be interpreted as evidence of the fact that the Universe was extremely hot and dense about 14 Gyr ago. Under these physical conditions nuclear reactions could take place and form deuterium, the two stable isotopes of He and traces of 7Li. Formation of heavier nuclei was prevented by the absence of any stable nucleus with A=5 and by the rapid expansion and cooling of the Universe. In the subsequent evolution of the Universe the small density fluctuations lead to the gravitational collapse of the material and at some stage this must have lead to the formation of stars. These stars contributed to the reionisation of the Universe which was over 50% reionised at redshift z=10. Current observations do not allow to study galaxies at these high redshifts, however local stars with ages above 13 Gyr were formed at redshift 10, or larger. Such stars offer us the unique opportunity of having a snapshot of the chemical composition of the ISM at these early epochs. The old, extremely metal-poor (EMP) stars, whose atmospheres provide this crucial information, are very rare and their discovery requires dedicated surveys. I will review the recent advances in this field.


Dynamical modelling of the Galaxy and stellar migration in the disc
Famaey, B. & Minchev, I.
(Observatoire Astronomique de Strasbourg)
We show the effects on the non-axisymmetry of the Galactic potential. In particular, we report that spiral structure interacting with a central bar is an effective mechanism for radial mixing in the disc. This mechanism could account for both the observed age-velocity relation and the absence of age-metallicity relation in the solar neighborhood. We show that observable signatures of this mechanism could be found by GAIA, combined with chemical tagging conducted with a high-resolution ground-based spectrograph.


The dynamical and chemical evolution of dwarf spheroidal galaxies
P. Jablonka
(Observatoire de Paris - EPFL)
Stellar chemical abundances can now be derived in Local Group dwarf galaxies with the same precision as in our Galaxy. These new datasets, combined with chemo-dynamical numerical simulations, dramatically improve our understanding of stellar nucleosynthesis as well as of the formation and evolution of galaxies. I will present some of the latest results, suggest some developments to be undertaken and discuss the benefit of GAIA in this domain.


The Besançon Galaxy model: comparisons to photometric surveys and modelling of the Galactic bulge and discs
Céline Reylé, Annie Robin, Mathias Schultheis, Doug Marshall
(Observatoire de Besançon, Institut UTINAM)
Exploring the in-plane region of our Galaxy is an interesting but challenging quest, because of the complex structure and the highly variable extinction. We here analyse photometric near-infrared data using the Besançon Galaxy Model in order to investigate the shape of the disc and bulge. We present new constraints on the stellar disc, which is shown to be asymetric, and on the bulge, which is found to contain two populations.


Galaxies near and far, one year after the Herschel Launch
Marc Sauvage
(UMR AIM Paris-Saclay)
On may 14th 2009, the Herschel Space Observatory was launched from the Kourou space port. After a few month of calibration and setup (including the full recovery of the HIFI instrument), Herschel has moved into the routine execution of its Key Projects. This review will attempt at covering some of the most exciting results that Herschel is bringing to the field of extragalactic astronomy.


Bayesian model comparison in cosmology with Population Monte Carlo
Kilbinger, M.
(Excellence Cluster Universe + Observatory Munich)
I present a new adaptive importance sampling technique and show applications for cosmological parameter estimation and model selection. Compared to Markov Chain Monte Carlo, Population Monte Carlo (PMC) provides a lower variance and has a simple in-built diagnostics to assess its performance. Since it is completely parallellisable, results can be achieved with significantly reduced wall-clock time. Further, PMC allows the calculation of the Bayesian evidence at no additional computational cost.

I will show results for model selection using CMB, SNIa and BAO data for dark energy and curvature scenarios, and for primordial perturbation models.



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.



3D tomography of local interstellar gas and dust
Séverine Raimond, Rosine Lallement and Jean-Luc Vergely
(LATMOS)
Interstellar absorption data and Strömgren photometric data for target stars possessing a Hipparcos parallax have been combined to build a 3D tomography of local gas and dust. We show the latest inverted 3D distributions within 250 pc, compare gas and dust maps and discuss the present limitations and improvements in progress. Gaia extinction data and follow-up ground-based stellar spectra (e.g. with GYES at the CFHT) will provide a far larger database that should allow a 3D tomography of much higher quality and extended to much larger distances.


Our Galaxy from the synthetic galaxy library for Gaia
Brigitte Rocca-volmerange
(CNRS/Institut d'Astrophysique de Paris et Université Paris sud)
The synthetic galaxy library, templates of the Hubble sequence, is computed for Gaia simulations (Tsalmantza et al, 2009) with the help of the code Pégase(www.iap.fr/pegase). For all types, more precisely Sc spiral, scenarios of galaxy evolution predict detailed stellar populations from which integrated properties (density numbers of stars, stellar, metal/dust gas masses) are deduced.The case of our Galaxy will be analyzed. We complete predictions in the infrared with the code Pégase.3.



Galactic Plane image sharpness as a check on cosmic microwave background mapmaking
Boudewijn F. Roukema
(Torun Centre for Astronomy, Nicolaus Copernicus University)
The largest uncollapsed inhomogeneity in the observable Universe is statistically represented in the quadrupole signal of the cosmic microwave background sky maps as observed by the Wilkinson Microwave Anisotropy Probe (WMAP). The time-ordered-data (TOD) of the WMAP observations define a constant temporal offset of 25.6 ms between the spacecraft positions and the observations. This is not documented in the WMAP Explanatory Supplement. It has recently been suggested that this offset constitutes an error that was ignored in compiling the TOD into all-sky maps, and that this implies that most of the previously estimated quadrupole is artificial. Here, the two possibilities that the timing offset caused an error in (i) calibration of the uncalibrated TOD, or (ii) compilation of the calibrated TOD into sky maps, are investigated. The optimal focussing of bright objects in the Galactic Plane plays a key role in part (ii).



The interplay between gas, dust, and star formation in the M33 galaxy
S. Verley
(Universidad de Granada - LERMA ObsPM)
The spiral galaxy M33 belongs to the local group and allows us to study star formation processes with great accuracy. The Spitzer telescope reaches spatial resolutions of the order of some parsecs and reveals the interactions between young stars and the interstellar medium. We estimated the star formation rate in M33, using Halpha, UV and IR tracers. We tested the radial and local Kennicutt-Schmidt laws in M33 reaching an unprecedented resolution of 180 pc. The Herschel view of the most compact emission in M33 is also presented.





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