Abundances, Dust, and Physical Conditions in the LMC ISM

Details Abundances, Dust, and Physical Conditions in the LMC ISM Abundances, Dust, and Physical Conditions in the LMC ISM

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9757w&link_type=abstract

HST Proposal ID #9757

Physics

Hst Proposal Id #9757 Ism And Circumstellar Matter

Scientific paper

STIS echelle spectra of the SMC star Sk 155 have revealed patterns of gas-phase interstellar abundances {and corresponding depletions into dust} that have not been seen in the Galactic ISM. In particular, Mg and Si {generally thought to be major dust constituents} are essentially undepleted in the SMC gas -- even for components with severe depletions of Fe and Ni. We propose to obtain similar spectra of 3 LMC stars -- sampling different regions of the LMC characterized by different UV extinction curves -- first to see whether such "anomalous" abundances might also be present in the LMC {as suggested by some FUSE spectra} and then to explore the relationships between interstellar abundances, depletions, physical conditions, and dust properties in environments characterized by low metallicity and moderately strong radiation fields. These would be the first extensive UV spectra of any LMC targets at resolutions better than 6 km/s. The analysis of these spectra will have significant implications for {1} making models of interstellar dust grains {which currently rely heavily on silicates}; {2} understanding the relationships between depletions, dust, and H_2 {which may be somewhat different in the Milky Way, LMC, and SMC}; {3} understanding the processes affecting the ionization balance in diffuse interstellar clouds {e.g., charge exchange with large molecules, cosmic-ray ionization}; {4} testing theoretical cloud models {which predict higher pressures in such environments}; and {5} interpreting the gas-phase abundances observed for QSO absorption-line systems {which exhibit some similar properties}.

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