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Session 20 - Molecular Clouds, Dense Cores, and Protostars.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[20.09] Abundances and Depletions Towards the Orion Nebula

R. Y. Shuping, T. P. Snow (CASA, U. Colorado, Boulder)

This paper presents an absorption line study for \th, based on IUE archival data. The line of sight as determined by O'Dell et al. 1993 is assumed to consist of two major cloud complexes: the ``neutral lid'' and some thin foreground material. A key problem is improving the S/N for IUE spectra and this is discussed in some detail. Column densities are derived from fitting equivalent widths of the interstellar lines to a semi-empirical curve ofgrowth (COG). These COGs are derived from high resolution data which resolve the cloud component structure on the line of sight (LOS), and it is assumed that the atomic species follow this structure. Abundances and depletions are calculated for the clouds and compared to emission line studies of the Orion nebula itself. Also, the depletions are compared to other sightlines with different far ultraviolet extinction behavior in hopes of shedding some light on dust models. The \lym line yields a column density for hydrogen of \log N(H I) = 21.60 \pm 0.1\ (cm^-2). Ionization balance gives an electron density of n_e = 2 - 4 \times 10^-3\ cm^-3 in the ``neutral lid'', which in turn yields a lower limit for the hydrogen density of n_H \sim 4 - 8\ cm^-3. An interesting and anomalous result is that Zn is found to be depleted from solar by \sim -1\ dex, and its role as an undepleted abundance standard (and possible errors) is discussed.

Program listing for Monday