Extraction of extrasolar planet spectra from realistically-simulated, wavefront-corrected, coronagraph fields

摘要

The observation of an extrasolar planet in reflected light using a coronagraphic telescope requires a several-orders-of-magnitude reduction of scattered light around a star by controlling instrumental wavefront errors with deformable mirrors (DMs). This creates a "dark hole" in the background in which diminished speckles of scattered light are at a level similar to or less than that of a planet. There are a number of methods for detecting the planet in this dark field, including image subtraction from another telescope orientation. However, extracting the spectrum of the planet from such a field may be more difficult because the chromatic variation of the speckles can hide spectral features, and the need to disperse the light on a detector increases noise. To investigate the conditions in which spectral extractions are feasible, a physical optics propagation simulation was created of a band-limited Lyot coronagraphic telescope with realistic phase and amplitude errors on each optic and dual sequential DMs to correct the resulting wavefront errors. The Electric Field Conjugation method was used to set the DMs to create a broadband (25%) dark hole from λ = 625-878 nm. Simulated planet spectra were then extracted from within this hole using a variety of methods including roll subtraction and spectral filtering. The results of these experiments are presented.