Infrared Spectroscopic Studies of Gases in the Circumstellar Environments of Young Stellar Objects

The building blocks of planets in planet-forming ("protoplanetary") disks are assembled early in the lifetime of a young star. The gas disks are relatively short-lived, with a half-life of about 3 million years, as chemical reactions modify the reservoir of material from the natal molecular cloud. Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of protoplanetary disks around T Tauri stars show emission from H₂O and absorption from other gases, sometimes consistent with formaldehyde, H₂CO , and other times consistent with formic acid, HCOOH, in the 5-7.5 μm region. SOFIA-EXES spectra of YSOs that follow up on these Spitzer-IRS studies are presented. How the gaseous features observed between 5-7.5 μm relate to those at other wavelengths is discussed. This work suggests that water and organic molecules, which are crucial for life as we know it, are present in the habitable zones of stars at a very early age [of 1-3 million years].