Imaging Exoplanets

Abstract

The principal difficulties in directly imaging extremely faint objects in orbit about nearby stars stem not from the sensitivity or collecting area of telescopes, but rather from the fact that the central star's light drowns out the signal of the faint companion. We have conducted extensive simulations of very high-order adaptive optics (AO) systems with coronagraphic imagers on relatively small telescopes. High-order AO and optimized coronagraphs enable small (< 4m) telescopes to play a critical role in the burgeoning effort to image exoplanets. The key to understanding the benefits of outfitting a 2 to 4-m telescope with extremely high-order AO systems lies in the nature of the AO correction. N act system with Nael actuators projected across the linear diameter, D, of the telescope's pupil can correct the point spread function (PSF) of a star on the optical axis within the angle (θAO = N act.λ/2D. For a system with N act = 10, the AO system corrects the PSF within 5').JD, or five times the diffraction limit. As Nael is increased, successively improved suppression of the seeing halo results, opening a large, as yet unexplored, part of the mass-separation parameter space relevant to faint companion science. For example, an optimized coronagraph behind a 941 element (N act = 34) AO system on a 3.6-m telescope is capable of detecting objects > 14 magnitudes fainter than the central star at separations between 0.2 and 1.5 arcsec in the H-band. Such a system will also solve or quantify many of the problems that exoplanet imaging projects must face in the near future.Key wordsextrasolar planetsadaptive opticscoronagraphybrown dwarfpoint spread functions