Zuckerman 9417158 This research involves observational study and theoretical analysis of the gas that might accompany circumstellar disks of dust. Sensitive studies of gas orbiting young stars of known age could provide important constraints for theories of solar system formation, in particular time scales involved for the building of Jupiter-like planets from residual interplanetary gas. Jupiter and Saturn likely formed from such gas durine the time that it was retained in the solar nebula, typically up to about 10 million years. The primary objective of the study is to use the largest and most sensitive millimeter wavelength radio telescopes to measure the mass of gaseous material that orbits stars with ages between one and ten million years, when giant planet formation is predicted. Very recently, identification of a sample of stars with likely ages in the critical time interval have been identified and the IRAM 30-m radio telescope has detected molecular gas orbiting many of these stars. In this regard millimeter wavelength molecular spectroscopy is an especially valuable tool since, in addition to a measure of gas mass, it provides a diagnostic of disk kinematics and chemistry. The age of a young target star may be estimated in a variety of ways including, for example, its location in the sky relative to dusty molecular clouds, its luminosity relative to main sequence stars of the same temperature, and the strength of certain key lines in its optical spectrum. Concerning the latter, the proposed research includes measurements of optical lines of lithium, calcium, and hydrogen atoms using high resolution eschelle spectrographs. ***
