High Resolution IR Spectroscopic Surveys for Protoplanetary Systems with Silicon Immersion Gratings

摘要

The breakthrough of silicon immersion grating technology at Penn State has the ability to revolutionize high-resolution infrared spectroscopy at large ground-based telescopes. Fabrication of high quality silicon grisms and immersion gratings up to 2 inches in dimension has become a routine process thanks to newly developed techniques. Silicon immersion gratings with etched dimensions of ～ 4 inches are being developed at Penn State. This immersion grating will be able to provide diffraction-limited spectral resolution of R = 300,000 at 2.2 micron, or 130,000 at 4.6 micron. To take full advantage of this high dispersing device for high resolution IR spectroscopy at high efficiency, high order adaptive optics is required to fully correct wavefronts distorted by atmospheric turbulence, to reach Strehl ratio of at least ～50%. IR spectroscopy with R > 100,000 opens up new possibilities in investigating the total mass and location of protoplanets through observing absorption lines from the CO fundamental bands at 4.6 microns and other molecular bands formed in the dynamic gaps created by protoplanets. It can also be used to study the density, temperature and composition of the environment where planets form. Large aperture telescopes with low thermal background are essential for ground-based observations to have enough sensitivity for observing thousands of nearby T Tauri stars to study planet formation. The results of protoplanet mass and location distribution will be compared to those of planets obtained from Doppler radial velocity surveys to investigate whether orbital migration and dynamical scattering play a significant role in planet formation and evolution. Future perspectives for developing silicon immersion gratings with sizes larger than 4 inches will also be discussed.