Adaptive Optics High Resolution IR Spectroscopy with Silicon Grisms and Immersion Gratings 1 Jian Ge, Dan McDavitt, Abhijit Chakraborty, John Bernecker & Shane Miller 525 Davey Lab, Department of Astronomy & Astrophysics, Penn State University, University Park, PA 16802 Abstract The breakthrough of silicon immersion grating technology at Penn State has the ability to revolutionize high-resolution infrared spectroscopy when it is coupled with adaptive optics at large ground-based telescopes. Fabrication of high quality silicon grism and immersion gratings up to 2 inches in dimension, less than 1% integrated scattered light, and diffraction-limited performance becomes a routine process thanks to newly developed techniques. Silicon immersion gratings with etched dimensions of ~ 4 inches are being developed at Penn State. These immersion gratings will be able to provide a diffraction-limited spectral resolution of R = 300,000 at 2.2 micron, or 130,000 at 4.6 micron. Prototype silicon grisms have been successfully used in initial scientific observations at the Lick 3m telescope with adaptive optics. Complete K band spectra of a total of 6 T Tauri and Ae/Be stars and their close companions at a spectral resolution of R ~ 3000 were obtained. This resolving power was achieved by using a silicon echelle grism with a 5 mm pupil diameter in an IR camera. These results represent the first scientific observations conducted by the high-resolution silicon grisms, and demonstrate the extremely high dispersing power of silicon-based gratings. New discoveries from this high spatial and spectral resolution IR spectroscopy will be reported. The future of silicon-based grating applications in ground-based AO IR instruments is promising. Silicon immersion gratings will make very high-resolution spectroscopy (R > 100,000) feasible with compact instruments for implementation on large telescopes. Silicon grisms will offer an efficient way to implement low-cost medium to high resolution IR spectroscopy (R ~ 1000-50000) through the conversion of existing cameras into spectrometers by locating a grism in the instrument's pupil location. Key Words: Silicon grism, Silicon immersion grating, Infrared, Spectroscopy, adaptive optics 1. Introduction High-resolution infrared spectroscopy is one of the most exciting new fields to be explored in astronomy. Its major applications include the first time study of the structure, physics and chemistry of proto- planetary and planet forming circumstellar disks and search for newly formed extra-solar planets. It also offers unprecedented sensitivity for study of stellar magnetic fields, interstellar medium, stellar abundance and isotopic abundance. High resolution IR spectroscopy is essential for the study of planet formation environments because it can probe the gaseous component of disks around young stars at planet formation distances. At the warm temperatures (100-2000K) and high densities characteristic of disks within a few AU, ro-vibrational and rotational transitions from molecules such as CO and H 2 O dominate the whole IR wavelength region. Thus, high resolution infrared molecular spectroscopy is ideally suited to the study. In order to resolve the 1 Send correspondence to Jian Ge, email: jian@astro.psu.edu , Tel: 814-863-9553, Fax: 814-863-3399