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L'effet de microlentille gravitationnelle dans la recherche de planètes extra-solaires et dans le sondage d'atmosphères d'étoiles géantes du Bulbe

Abstract : A galactic microlensing effect occurs when a luminous object (the source) located in the Bulge of the Milky Way is temporarily magnified by an intervening star (the "microlens'') passing close to its line of sight. This phenomenom is used for searching extra-solar planets and constraining their abundance, as well as probing the atmosphere of Bulge giant stars.

The PLANET collaboration (Probing Lensing Anomalies NETwork) monitors carefully chosen ongoing microlensing events on a round-the-clock basis from observatories in the southern hemisphere. Mathematical and numerical methods are developed to deal with both the highly non-linear equations and the wide parameter space plagued with many local minima.

Microlensing exoplanet detection is possible because planets can induce perturbations to the standard lensing light curves. Its sensitivity can go down to Earth-mass planets, thanks to gravitational caustics that arise from a binary lens. If crossed by the source, additional secondary magnification peaks in the light curve can occur. OGLE 2005-BLG-390Lb is the third extra-solar planet detected by this method so far, and its discovery is reported here. It is the lightest exoplanet to date - about five Earth masses - located at a rather large distance of its star, that is about three astronomical units.

A selection of microlensing events monitored during the 1995-2004 period was used to derive limits on exoplanets abundance around red dwarf stars. The method is described and detection efficiency diagrams are provided as a basis of the statistical analysis.

Last, a differential magnification effect over the disk of the source star is used as a tool to probe Bulge giants stellar atmospheres. Limb-darkening parameters of a set of stars have been measured and compared to atmosphere models. Moreover, a high-resolution spectroscopic monitoring of a Bulge G5III giant at 9 kpc made possible both the measurement of the individual lines equivalent width and the direct detection of its chromosphere.
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https://tel.archives-ouvertes.fr/tel-00012057
Contributor : Arnaud Cassan <>
Submitted on : Sunday, July 9, 2006 - 7:26:42 PM
Last modification on : Wednesday, December 9, 2020 - 3:11:57 PM
Long-term archiving on: : Saturday, April 3, 2010 - 11:03:58 PM

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  • HAL Id : tel-00012057, version 1

Citation

Arnaud Cassan. L'effet de microlentille gravitationnelle dans la recherche de planètes extra-solaires et dans le sondage d'atmosphères d'étoiles géantes du Bulbe. Astrophysique [astro-ph]. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00012057⟩

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