High-order adaptive optics requirements for direct detection of extrasolar planets: Application to the SPHERE instrument

TLDR

Detecting extrasolar planets demands extremely high‑contrast, long‑exposure imaging at near‑infrared and visible wavelengths, and the level of adaptive‑optics correction directly determines exposure time while calibration of static instrument defects limits detectivity. The paper proposes a feasibility study of an extreme adaptive‑optics subsystem for the SPHERE planet‑finder instrument. The extreme AO system must correct atmospheric turbulence and internal instrument aberrations to achieve the required high‑contrast imaging.

Abstract

The detection of extrasolar planets implies an extremely high-contrast, long-exposure imaging capability at near infrared and probably visible wavelengths. We present here the core of any Planet Finder instrument, that is, the extreme adaptive optics (XAO) subsystem. The level of AO correction directly impacts the exposure time required for planet detection. In addition, the capacity of the AO system to calibrate all the instrument static defects ultimately limits detectivity. Hence, the extreme AO system has to adjust for the perturbations induced by the atmospheric turbulence, as well as for the internal aberrations of the instrument itself. We propose a feasibility study for an extreme AO system in the frame of the SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument, which is currently under design and should equip one of the four VLT 8-m telescopes in 2010.