Improving Earth-like planets' detection with an ELT: the differential radial velocity experiment

Abstract

Context. Direct detection of Earth-like planets around a nearby star is extremely difficult for ground-based telescopes equipped with the eXtreme Adaptative Optics system. Aims. We propose to combine high-precision radial velocity with an ELT to detect extrasolar planets with a feasible coronagraph. Methods. In this context, we investigated the detectability of Earth-like extrasolar planets with an ELT of 42 m equipped with the spectro-coronagraphic instrument in an eXtrem Adaptive Optics system. Those stellar residuals left uncorrected by the XAO wavefront correction (Strehl ratio >85%) system need to be calibrated. We propose calibrating them by the radial velocity measurement of the planet in a multiple spectrum correlation process. Results. This method allows detection of Terrestrial planets with an ELT but requires a long exposure time (≈200 h) Conclusions. The technique overcomes the main coronagraphic limitation due to the pinned and the low variable speckles and opens a way to detect directly exoplanets with large ground-based telescopes equipped with an efficient XAO system.