Physics – Optics
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21722602m&link_type=abstract
American Astronomical Society, AAS Meeting #217, #226.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Physics
Optics
Scientific paper
The Hyades is an intermediate-age open cluster with hundreds of main-sequence stars and is thus well-suited to stellar formation and evolution studies. Being nearby with high proper motion, it is a choice cluster for direct-imaging surveys. We conduct a high-contrast adaptive optics (AO) search for late-type companions as faint as MH 15 (late-L/early-T) within 5-230 AU around 88 FGK main-sequence Hyades dwarfs. Departures from the ideal point-spread function (PSF) in the image plane are caused by phase and amplitude errors that redistribute stellar light and limit the achievable contrast. An AO system on a ground-based telescope mitigates the phase errors in the pupil, but constructive interference of spatially coherent light causes amplitude spikes in the PSF called speckles. The locally-optimized combination of images (LOCI) algorithm is used to identify and subtract the quasistatic speckles and static PSF structure, allowing imaging of faint point-source companions. We use LOCI on deep near-infrared AO Hyad imaging at Keck and Lick Observatories. Background objects are subsequently ruled out by comparing relative astrometry in two epochs separated by five years. We present our confirmed Hyades companions. Furthermore, we look ahead to AO for exoplanet-imaging wherein a ''dark hole'' in the PSF facilitates high-contrast imaging. The size of the dark hole is set by the highest spatial frequency controllable by the deformable mirror (DM). Decreasing rejection at increasing spatial frequencies reduces the correction efficiency within the high-contrast region, owing to the nature of the MEMS (micro-electro-mechanical systems) DM transfer function. This effect can be mitigated by a dual-DM ''woofer/tweeter'' AO system whereby each DM controls a different spatial frequency regime. We present empirical results on selecting a woofer DM in order to maintain the dark hole for the upcoming Gemini Planet Imager. (Supported by NASA Michelson Fellowship, NSF Center for Adaptive Optics, Moore Foundation, IGPP, LLNL/DoE.)
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