Mid-Infrared interferometry of dust around massive evolved stars

We report long-baseline interferometric measurements of circumstellar dust around massive evolved stars with the MIDI instrument on the Very Large Telescope Interferometer and provide spectrally dispersed visibilities in the 8-13 micron wavelength band. We also present diffraction-limited observations at 10.7 micron on the Keck Telescope with baselines up to 8.7 m which explore larger scale structure. We have resolved the dust shells around the late type WC stars WR 106 and WR 95, and the enigmatic NaSt1 (formerly WR 122), suspected to have recently evolved from a Luminous Blue Variable (LBV) stage. For AG Car, the protoypical LBV in our sample, we marginally resolve structure close to the star, distinct from the well-studied detached nebula. The dust shells around the two WC stars show fairly constant size in the 8-13 micron MIDI band, with gaussian half-widths of ~ 25 to 40 mas. The compact dust we detect around NaSt1 and AG Car favors recent or ongoing dust formation. Using the measured visibilities, we build spherically symmetric radiative transfer models of the WC dust shells which enable detailed comparison with existing SED-based models. Our results indicate that the inner radii of the shells are within a few tens of AU from the stars. In addition, our models favor grain size distributions with large (~ 1 micron) dust grains. This proximity of the inner dust to the hot central star emphasizes the difficulty faced by current theories in forming dust in the hostile environment around WR stars. Although we detect no direct evidence for binarity for these objects, dust production in a colliding-wind interface in a binary system is a feasible mechanism in WR systems under these conditions.Comment: 21 pages, 4 tables, 13 figures. Accepted for publication in the Astrophysical Journa

Le portail européen de données Epos-GNSS

National audienceLe système de distribution Epos-GNSS est une e-infrastructure conçue pour diffuser des données et produits GNSS. Le portail de données Epos-GNSS est le point d'accès central du système à ces données

Le portail européen de données Epos-GNSS

National audienceLe système de distribution Epos-GNSS est une e-infrastructure conçue pour diffuser des données et produits GNSS. Le portail de données Epos-GNSS est le point d'accès central du système à ces données

La haute résolution angulaire appliquée à l'étude des enveloppes de poussière circumstellaire d'étoiles évoluées

La technique de Haute Résolution Angulaire par interférométrie longue base dans les longueurs d onde optiques est un thème de recherche en astronomie. Elle permet d atteindre des résolutions spatiales donnant accès à une compréhension plus précise des objets stellaires. Notamment en ce qui concerne les processus d évolution et de formation des enveloppes de poussières circumstellaires d étoiles évoluées auxquelles je me suis intéressé. A l aide de données récentes et de codes numériques de modélisation, nous avons étudié les enveloppes de 5 sources astrophysiques : T Sgr, IRC+10216, HR4049, WR 95 et WR 10,6 pour lesquelles nous avons eu des résultats immédiats et mis en évidence les avancées permises par la HRA. Ces techniques d interférométrie optiques sont encore jeunes et en constant développement. Dans cette perspective, nous avons participé à l étude d APreS-MIDI, un module optique pour l interféromètre MIDI, devenu ensuite l instrument VLTI de deuxième génération MATISSE. Dans ce cadre, nous avons développé une maquette d interféromètre ainsi que mis en place les bases d une nouvelle approche de reconstructions d image appelée FrImage.The technic of High Angular Resolution by long baseline interferometry in optical wavelengths is a field of research in astronomy. It allows to reach the spatial resolution needed to have access to a more precise understanding of stellar sources. This is of relevance in particular for the study of the formation and evolutionary process of the dust environment of evolved stars, topic which catches my attention. With recent data and numerical modeling codes, we studied the envelopes of 5 astropysical targets : T Sgr, IRC+10216, HR4049, WR 95 et WR 106 for which, we obtained immediate results and we could show the progress allowed by the future instruments. These optical interferometry techniques are still young and in perpetual evolution. In this perspective, we partipated to the study of APreS-MIDI, an optical module for the MIDI interferometer, which since became the second generation VLTI instrument MATISSE. In this context, we also developed an interferometer mock-up as well as the bases for a new approach in image reconstruction from interferometry data called FrImage.NICE-BU Sciences (060882101) / SudocSudocFranceF

The EPOS GNSS Data Gateway: concept and access to EPOS GNSS data and metadata

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PlantML: un langage pour une gestion répartie des bioprocédés de dépollution

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XAFS investigations of Y-Ti-enriched nanometric oxides in ODS ferritic steels after neutron irradiation in Experimental Reactors

International audienceThe speciation and structural evolution of yttrium-titanium-enriched nanometric oxides in Oxide Dispersion Strengthened (ODS) ferritic steels have been investigated by X-Ray Absorption Fine Structure (XAFS) spectroscopy and X-Ray Diffraction (XRD) after neutron irradiation up to about 80 dpa in different experimental reactors). The local order and structure evolutions during neutron irradiation are crucial to understand the phase stability of the nanometric precipitates (size of the smallest < 3 nm) homogeneously dispersed in ODS materials, responsible of their excellent creep properties.Here we focus on the results obtained by XAFS at the MARS beamline, located at the Synchrotron SOLEIL facility, which is dedicated to the analysis of radioactive materials. The local structure and speciation of Y-Ti enriched oxides have been characterized by Y K- and Ti K-edges XAFS analysis (including X-ray Absorption Near Edge Spectroscopy (XANES) and Extended X-ray Absorption Fine Structure (EXAFS)) in fluorescence mode for neutron irradiated samples for i) DY, a Fe-12,9Cr-1,46Mo-0,08Mn-0,03Si-2,03Ti-0,45Y (chemical composition in weight percent (Wt%)), irradiated as fuel pin cladding tubes in PHeNIX (France); ii) MA957, a commercial Fe-13,9Cr-0,98Ti-0,26Y (Wt%), irradiated as tensile specimen in SUPERPHeNIX (France), BOR 60 (Russia) and OSIRIS (France).XAFS spectroscopy provides a practical and simple way to study elements of dilutes species over the whole sample volume. However, the interpretation of XAFS data for industrial material where the absorbing atom studied is located in various secondary phases, even in the matrix, is more challenging than for a quite homogeneous and pure material. For this reason, other techniques, such as TEM and XRD have been used, providing complementary information useful to analyze the XAFS data.This presentation will also concern the results obtained by XAFS as a function of the position of the samples during irradiation leading to variations of the neutron flux and temperatures