Innovative technologies for and observational studies of star and planet formation
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I summarize the optical design, fabrication, and performance of silicon diffractive optics for astronomical spectrographs. The first set of optical devices includes diffraction-limited, high-throughput silicon grisms for JWST-NIRCam. These grisms served as pathfinders to Silicon immersion gratings, which offer size and cost savings for high-resolution near-infrared spectrographs. I demonstrate the production and optical evaluation of the immersion grating that enabled IGRINS at the McDonald Observatory. This grating provides spectral resolution R=40,000 over the H and K near-infrared band atmospheric windows 1.5-2.5 micron. Electron-beam lithography offers much higher precision over contact mask photolithography for the production of Si immersion gratings. Electron-beam patterned prototypes are stepping-stones to monolithic Si gratings for iSHELL and GMTNIRS. The monolithic design of Si immersion gratings presents a limitation for scaling up the grating size, since existing fabrication equipment cannot handle monolithic silicon pucks. The size limitation can be overcome by direct-bonding Si substrates to optical prisms. I demonstrate a technique to measure interfacial gaps as small as 14 nm between the bonding interfaces, which produce 0.2% transmission loss. These technologies will enable the direct measurement of the atmospheric properties of extrasolar planets in the next decade. IGRINS is now measuring fundamental properties of young solar-mass stars; low luminosity young brown dwarfs are below the sensitivity limit of existing high spectral resolution near-IR spectrographs. My approach to the discovery and characterization of young brown dwarfs therefore employs low-resolution R~2000 near-IR spectroscopy. I confirm and characterize 17 candidate young stars and brown dwarfs reported by Allers and collaborators. All 17 sources have circumstellar disks. Using deep optical, near-infrared, and mid-infrared photometry, I search an off-core region towards the nearby ~1 Myr Ophiuchus star forming cluster for candidate young stars and brown dwarfs. Multi-object I-band spectroscopy of 419 candidates reveals 12 new members. Ten of these have no evidence for mid-IR excess emission from 3.6 to 8.0 micron. The disk fraction for spectral types M4 and later towards this region of Ophiuchus is 5/15. Two of the disk sources have edge-on disks, pointing to a high edge-on disk fraction. I discuss possible sources of contamination in the survey.