The following document lists the file abstract/DGARNETT_HII_SPEC.abs
from catalogue VI/111.
A plain copy of the file
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===================================================================== ==> In this proposal, more time is being requested for DGARNETT.SWS_NES ===================================================================== This is a joint proposal for programs DGARNETT.SWS_NES and MEDMUNDS.PROPISO. We request supplemental ISO observing time to recover science lost because of the reduced sensitivity of the SWS. We will make deep full grating scans with SWS and LWS of one very metal-rich H II region in the spiral galaxy M51 (twice solar Z) and the very metal-poor H II galaxy SBS 0335-052 (2% solar Z). The data will be used to measure a variety of nebular IR emission lines which are important coolants and abundance diagnostics in the ionized gas. Because of their weak sensitivity to electron temperature, the IR fine-structure lines can be used to measure heavy element abundances with greater reliability than high-excitation optical forbidden lines, especially in metal-rich nebulae where electron temperature measurements are not available. We will confront two very pressing problems of H II region physics: (1) the relation between optical emission line strengths and abundances for low-excitation H II regions in the inner parts of spiral galaxies; this is poorly known because electron temperatures can not be measured in such objects, and unique photoionization models for such nebulae are sensitive to competing influences of dust, density and abundance variations; and (2) are there large systematic uncertainties in the abundance scale due to electron temperature fluctuations within ionized nebulae. Measurement of the IR emission lines in these nebulae will allow us to (i) determine, for the first time, accurate chemical abundances in the gas at metallicities above solar; (ii) greatly improve the calibration of strong- line abundance indicators for giant H II regions at high metallicities, with considerable benefit to the field of chemical evolution of galaxies; and (iii) test the importance of temperature fluctuations by comparing abundances from optical and IR forbidden lines. Deep spectra may reveal the presence of organic molecular features and rotational lines of H2, whose presence in very metal poor dwarf galaxies is completely uncertain.