second submission -2007122312 Assigned ID: 272 ----- Attempting Submission 1 (Thu Mar 05 18:33:06 GMT 2020) ----- HST Phase I Proposal 272 successfully submitted. Receipt: # 272-1 ----- Attempting Submission 2 (Fri Mar 06 23:02:23 GMT 2020) ----- We propose to use HST-COS spectra to conduct a comprehensive survey of the metallicities of high- and intermediate-velocity clouds (HVCs/IVCs). These objects serve as test particles for modeling Galactic phenomena, such as the Galactic Fountain, tidal streams and accreting low-metallicity gas. The properties of the latter type also appear similar those of intergalactic gas clouds seen in QSO absorption lines, and thus may hold clues to understanding the IGM. HVC and IVC metallicities have been measured in ~25 sightlines for ~5 complexes and a few smaller clouds. The HST archive contains many unanalyzed spectra serependitiously intersecting many other HVCs and IVCs. As the oxygen/hydrogen and sulphur/hydrogen ratios are only weakly affected by dust and ionization effects, we will use the OI-1302 and SII-1250/1253/1259 lines in 200 spectra to measure the metallicity in 11 different cloud complexes (pierced by 5-50 sightlines) and about 50 individual smaller clouds. The resulting metallicities will allow us to identify the origin of each cloud and even study metallicity variations across some large clouds. Combined with the HVC/IVC distances and an understanding of their motions, we can then determine flow rates for the Fountain and for infall, as well as determine the extent of the Leading Arm of the Magellanic Stream, which will constrain recent improvements in modeling. The PI Dr Bart Wakker has an extensive background in studies of the interstellar and intergalactic medium, having published over 100 papers on these subjects, using data from ground-based radio and optical telescopes, as well as many of the UV space instruments (IUE, FUSE, FOS, GHRS, STIS, COS), being PI on 11 HST observing and 4 HST archival projects, as well as Co-PI or Admin-PI on 7 others. Dr Andrew Fox is an expert in the reduction, analysis, and interpretation of HST/COS spectra of diffuse gas in the Universe. He has led five HST GO proposals in closely related science areas (Milky Way CGM), all of which have led to refereed publications and NASA press releases, and has first-authored 11 ApJ papers using UV spectroscopy. Dr Taesun Kim has long experience with analyzing spectra of background QSOs, especially in terms of deriving good line parameters by means of line fitting. She has led three HST GO/AR proposals and was Co PI on five additional ones. She has authored 10 and co-authored about 30 papers on physical conditions in IGM systems and statistics of IGM absorption lines. Dr. Nicolas Lehner is an expert in the reduction, analysis, and interpretation of HST/COS spectra of interstellar, intergalactic, and circumgalactic gas in the Universe at all redshifts. He is the PI of several HST GO and AR programs, including one Large and two Legacy programs that all led to numerous refereed publications and several NASA press releases. Dr. Philipp Richter is highly experienced UV spectroscopists with decades of experience in the study of interstellar and intergalactic media and their influence on galaxy evolution. He has led HST/COS proposals and/or first author papers in this subject, including some of the first papers with measurements of HVC metallicities. He will offer advice, expertise, and judgement on the interpretation and modeling of the results. Dr. Joel Bregman has spent most of his career in the area of the gaseous medium of galaxies, clusters, and the IGM, and was responsible for making the connection between high-velocity clouds and the Galactic Fountain. He has published a number of papers in the areas of cooling flows and feedback both in X-ray, UV astronomy, and theory. He has worked with and published both HST imaging data and spectral data. Dr David French recenrly finished a PhD thesis based on data from HST COS and STIS, studying the Lyman alpha absorption lines associated with nearby galaxies. He is an expert in UV data fitting, analysis, and interpretation and is doing the HI Lyman series analysis of FUSE spectra. Dr Elena D'Onghia is an expert in numerical simulations of the Magellanic Stream and will coordinate the modeling of the Leading Arm. Mr Scott Lucchini is a graduate student working with D'Onghia on the modeling of the Stream and has implemented new additions to the simulation. Dr Blair Savage has specialized in ultraviolet spectroscopic studies of the physical state of the ISM and IGM from the very beginning of ultraviolet space astronomy. His ultraviolet observational studies have utilized the OAO-2, the Copernicus satellite, IUE, GHRS, FOS, STIS, COS and FUSE. He has been involved in 260 refereed publications describing ISM and IGM results. Stellar Populations and the Interstellar Medium 0 Regular false false true false false SUPPORTED