Program: GS-2021A-FT-213

CO and dust are commonly used as tracers of H2, which must dominate the masses of molecular clouds but is difficult to observe. In this project we are observing stars lying behind molecular clouds to measure the absorption by H2, CO, and dust along multiple lines of sight to determine their relative abundances and their abundance variations within and among clouds. In this proposal we request time to observe one high extinction star in Ophiuchus to complete the project.