Daniel Egret

Multi-wavelength analysis of the dust emission in the Small Magellanic Cloud

We present an analysis of dust grain emission in the diffuse interstellar medium of the Small Magellanic Cloud (SMC). This study is motivated by the availability of 170� m ISOPHOT data covering a large part of the SMC, with a resolution enabling to disentangle the diffuse medium from the star forming regions. After data reduction and subtraction of Galactic foreground emission, we used the ISOPHOT data together with HiRes IRAS data and ATCA/Parkes combined Hi column density maps to determine dust properties for the diffuse medium. We found a far infrared emissivity per hydrogen atom 30 times lower than the Solar Neighborhood value. The modeling of the spectral energy distribution of the dust, taking into account the enhanced interstellar radiation field, gives a similar c onclusion for the smallest grains (PAHs and very small grains) emitting at shorter wavelength. Assuming Galactic dust composition in the SMC, this result implies a difference in the gas-to-dust ratio (GDR) 3 times larger than the difference in metallicity. This low depletion of heavy elements in dust could be specific of the diffuse ISM and not apply for the whole SMC dust if it results from effi cient destruction of dust by supernovae explosions.

The Aladin Interactive Sky Atlas

The subject of this symposium, Multi-Wavelength Sky Surveys naturally invokes a discussion of methods of astronomical object identification and classification: Given a set of objects detected at a certain waveband, how does one integrate the new sources with previous data? The ALADIN system (Paillou et al. 1994) of the CDS is a software package designed to tackle this problem: It provides simultaneous access to digitized sky photographs, catalogs and databases to facilitate direct, visual comparison of user data with previously classified data, as well as automatic source extraction and calibration tools.

An inverse method to interpret colour-magnitude diagrams

An inverse method is developed to determine the star formation history, the age-metallicity relation, and the IMF slope from a colour-magnitude diagram. The method is applied to the Hipparcos HR diagram. We found that the thin disk of our Galaxy shows a peak of stellar formation 1.6 Gyr ago. The stars close to the Sun have a solar metallicity and a mean IMF index equal to 3.2. However, the model and the evolutionary tracks do not correctly reproduce the horizontal giant branch.

The Master Catalogue of stars towards the Magellanic Clouds - I. Multispectral surveys of the Large Magellanic Cloud

The Master Catalogue of stars towards the Magellanic Clouds (MC2) �� is a multi-wavelength reference catalogue. The current paper presents the first results of the MC2 project. We started with a massive cross-identification of the two recently released near-infrared surveys: the DENIS Catalogue towards the Magellanic Clouds (DCMC) with more than 1.3 million sources identified in at least two of the three DENIS filters ( IJK s) and the 2nd Incremental Release of the 2MASS point source catalogue ( JHK s) covering the same region of the sky. Both point source catalogues provide an unprecedented wealth of data on the stellar populations of the Magellanic Clouds (MCs). The cross-matching procedure has been extended to optical wavelength ranges, including the UCAC1 (USNO) and GSC2.2 catalogues. New cross-matching procedures for very large catalogues have been developed and important results on the astrometric and photometric accuracy of the cross-identified catalogues were derived. The cross-matching of large surveys is an essential tool to improve our understanding of their specific contents. This study has been partly supported by the  ��� project that aims at improving access to astronomical

Integrating astronomical data and information services at the CDS

Abstract The CDS is providing several unique services to the world-wide astronomical community: the catalogue service, the SIMBAD database, the ALADIN project, bibliography and literature search, yellow pages, etc. We describe how the CDS works at providing a global perspective on astronomical data and information, with the help of recent technological developments.

Cross-matching DENIS and 2MASS point sources toward the Magellanic Clouds

The recent publications of the DENIS Catalogue towards the Magellanic Clouds (MCs) with more than 1.3 million sources identified in at least two of the three DENIS filters (I J Ks) and of the incremental releases of the 2MASS point source catalogues (J H Ks) covering the same region of the sky, provide an unprecedented wealth of data related to stellar populations in the Mcs. In order to build a reference catalogue of stars towards the Magellanic Clouds, we have performed a cross--identification of these two catalogues. This implied developing new tools for cross--identification and data mining. This study is partly supported by the Astrovirtel program that aims at improving access to astronomical archives as virtual telescopes. The main goal of the present study is to validate new cross--matching procedures for very large catalogues, and to derive results concerning the astrometric and photometric accuracy of these catalogues. The cross--matching of large surveys is an essential tool to improve our understanding of their specific contents. This approach can be considered as a new step towards a Virtual Observatory.

Interoperability tools for the Virtual Observatory

Interoperability is one of the important issues in the current efforts to build the Virtual Observatory. We present here some of the tools which already contribute to the efficient exchange of information between archives and databases.

The VizieR system, a unified interface to astronomical catalogs

We present in this paper some aspects of the VizieR service, as an example of a database connecting to the largest set of astronomical catalogs. We especially emphasize here role of the metadata: how these are acquired from the catalog descriptions, and how they are stored in the system. The specification of relations or links between data are an important part of the metadata, and we use GLU (Generateur de Liens Uniformes=uniform link generator) expressions to describe the links to external databases or services. The basic principles of the GLU system initiated at CDS, as well as some tools based on the GLU protocol, are briefly described. Finally, the on-going developments, especially related to data mining purposes, are presented.

DIVISION XII / COMMISSION 5 / WORKING GROUP VIRTUAL OBSERVATORIES, DATA CENTERS & NETWORKS

The Working Group Virtual Observatories, Data Centers, and Networks was established under Commission 5 at the Prague General Assembly in 2006. The purpose of the WG is to provide IAU oversight of the activities of the International Virtual Observatory Alliance (IVOA, www.ivoa.net/ >), to encourage data centers and other data providers to archive and publish data according to IVOA standards, and to help assure that astronomical research facilities are electronically linked with current network technologies. The WG coordinates activities closely with the WG- FITS , as the IVOA uses FITS as its primary format for binary data exchange, and the WG on Astronomical Data .

Cross Wavelength Comparison of Images and Catalogs

We would like to start this discussion by attempting to make a useful, working distinction between catalogs and databases of astronomical objects. It seems to us that such a distinction could be made based upon the mode of access to the information: A catalog may be considered as a list of objects, almost invariably ordered by coordinates; a database, on the other hand, may be distinguished by its ability to extract a set of objects based on user-given criteria, such as all objects within a certain sky region with magnitudes brighter than m in the blue. Catalogs form the basis of the database, which adds the means of multi-criteria access to the information. In concrete terms, one usually thinks of SIMBAD, NED and LEDA as databases, while an ftp site containing electronic lists of objects may be thought of as a catalog storage warehouse.