0 Assigned ID: 614 ----- Attempting Submission 1 (Fri Apr 05 18:33:32 GMT 2019) ----- Numerous theoretical efforts and significant observational constraints indicate that dust formation in the outer atmospheres of evolved stars and in the cooling ejecta of supernovae is insufficient to fully account for dust production in the Milky Way. Additional grain growth in the cold interstellar medium is required. Direct constraints on the growth of dust grains in interstellar clouds comes from detailed knowledge of the depletions of different elements from the gas-phase. However, the observed depletions of phosphorus and chlorine have challenged a straightforward interpretation of the depletion data. One puzzling aspect is that the gas-phase abundances of P and Cl appear to be supersolar in low depletion sight lines. We propose a comprehensive survey of P II and Cl I absorption lines from STIS E140H and E140M spectra along over 80 sight lines probing diverse physical conditions in the local Galactic ISM. FUSE data will be examined to determine the amount of Cl II present. Our focus will be on weak, unsaturated absorption features and our use of recently-updated oscillator strengths will yield the most precise P and Cl abundances derived to date. The improved constraints on the depletion behaviors of P and Cl should offer clarity to the interpretation of gas-phase element depletions. Furthermore, our analysis of neutral chlorine fractions will allow us to disentangle the complex multi-phase gas along each line of sight and may reveal an improved correlation between Cl depletions and the molecular hydrogen fractions associated with the cold dense phase. Dr. Adam Ritchey has expertise in the reduction and analysis of HST/STIS spectra and has been the lead author on several publications focused on interstellar abundances and gas-phase element depletions. He is also the PI of two recent HST programs, which utilized HST/STIS spectra to examine the abundances and physical conditions in various interstellar environments. Dr. Steven Federman is an expert in diffuse atomic and molecular gas and has been involved in previous efforts to examine chlorine and fluorine abundances in diffuse clouds through the analysis of Copernicus, FUSE, and HST spectra. He is also involved with a laboratory astrophysics group at the University of Toledo, which seeks to measure oscillator strengths for astrophysically important atomic transitions. His group is largely responsible for the precise Cl I, Cl II, and P II oscillator strengths that we will adopt in our survey. Dr. Paule Sonnentrucker is an expert in the chemistry of diffuse, dense, and star-forming clouds. She has been involved in numerous surveys of atomic and molecular abundances in the interstellar medium, using FUSE, HST, and Herschel data, and has published empirical oscillator strengths for neutral chlorine lines from FUSE spectra. Galaxies and the IGM 0 Regular false false true false false SUPPORTED