10280( 1) - 04/02/04 10:41 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 10280 Version: 1 Check-in Date: 02-Apr-2004 10:40:53 1.Proposal Title: Fundamental Properties of Gas in the Distant Galactic Halo and Leading Arm of the Magellanic Stream ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle 4. Parallel Pointing Tolerance AR 13 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Todd Tripp University of Massachusetts CoI: Dr. Edward B. Jenkins Princeton University N CoI: Dr. Kenneth Sembach Space Telescope Science Institute N CoI: Dr. David V. Bowen Princeton University N ------------------------------------------------------------------------------------ 6. Abstract We propose to use high-resolution archival STIS echelle spectra of a cloud that is located in the Magellanic Stream, and therefore at a distance of ~50 kpc, to obtain detailed observational constraints on the density, pressure, temperature, and ionization structure of gas in the leading arm of the Magellanic Stream. Since this cloud is known to be pressure-confined by the surrounding halo gas, the results will have implications for the physical conditions of the Galactic halo as well. We will apply the following diagnostics to the absorption lines in archival STIS spectra: (1) thermal pressure from C I fine-structure excitation, (2) density constraints from C II*, (3) electron density and temperature from ionization balance, and (4) ionization structure and density constraints from photoionization models. With these physical conditions measurements, we will learn about the nature of O VII and high- velocity O VI absorbers, the evolution of satellite galaxies that pass close to the Milky Way, and whether theoretical work on the ISM in the Milky Way halo agrees with observations. We will also learn about production/destruction of molecular hydrogen in conditions similar to the high-z conditions in which early stars formed. ------------------------------------------------------------------------------------ 10280( 1) - 04/02/04 10:41 - [ 2] Summary Form for Proposal 10280 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category AR ------------------------------------------------------------------------------------------------------------------------------------