High Contrast Imaging with Gaussian Aperture Pupil Masks (GAPMs)

Abstract

Gaussian aperture pupil masks (GAPMs) can in theory achieve the contrast requisite for directly imaging an extrasolar planet around a nearby solar type star. We outline the process of designing, fabricating, and testing a GAPM for use on current telescopes and specifically the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. We find that the initial prototype observations are quite successful, achieving a contrast similar to a traditional Lyot coronagraph without blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab we can reproduce the expected PSF reasonably well and with a single aperture design which achieves $\sim4 \times 10^{-5}$ contrast at 10$\lambda/D$. We find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast at these levels.