Détection de naines brunes et planètes géantes gazeuses à grande séparationutilisant des images d’archive
Decades of astronomical data collection provided by dedicated instruments have led to a large amount of images taken at different wavelengths, resolutions and depths of field that remain, for the most part, unexploited (eg 2MASS , WISE, SPITZER, SDSS). Developments of new data processing algorithms gives a new value to these images taken years earlier. This project aims at discovering new low-mass companions with large separations around young low-mass stars (M-type) using archive images. 2MASS J, H and Ks band images were used to identify the candidates. Seven candidates were identified using a combination of two algorithms that were applied on a judicious selection of 2 812 stars. The method combined a point spread function substraction algorithm based on a linear combination of reference stars and an algorithm inspired by differential imaging. Five of them had already been identified by other teams. One was probably an M9 star from the field and the other an L3—, potentially a member of the young association AB Doradus. This research confirms, like others before, the low occurence rate of planetary mass and brown dwarf companions at large separations (Á 100 AU) around young low mass stars. This conclusion led us to develop of an alternative detection method sensitive to companions on short orbits (< 40 AU). This second project, partially completed, aims to demonstrate that it is possible to detect objects with planetary masses orbiting young sun-like stars (G–F–A) regardless of their separation. This is possible thanks to the new generation of high dispersion infrared spectrographs. Spectral processing applied on synthetic observations has confirmed that one can detect objects with an object/star brightness ratio down to 10´5. Only 1h exposure time with an instrument like SPIROU is enough to detect companions with an atmosphere mainly composed of molecules. The spectral processing consists of cross-correlation and spectral subtraction algorithms inspired by methods used in differential imaging.
Brown dwarfs Exoplanets Young stars Archive images Image processing High-resolution IR spectroscopy