We report the first results of a Cycle 12 Hubble Space Telescope SNAP program imaging the C III] 1909A lines in planetary nebulae (PNe) and extragalactic H II regions using WFPC2 with the F185W with the F185W filter. To date(2004 April), four PNe (NGC 6210, NGC 6720, NGC 6826 & NGC 7662) and four H II regions (LMC N160A, SMC N81, NGC 2363 & I Zwicky 18) have been observed.
Using continuum imagery of the nebulae made with HST WFPC2 and the knowledge of the UV spectra of regions in the nebulae from archival HST FOS/STIS or IUE data, the UV continuum contribution to the F185W images is estimated and subtracted out to give images of the nebulae in C III] 1909A. The objectives of the program include: (a) studying the effects that spatial variations in Te, Ne, and dust have on the observed F(1909A)/F(5007A) line ratio across the nebulae, (b) studying the co-spatiality of the C+2 and O+2 ionization structure, and (c) evaluation of the accuracy of using observations of the integrated F(1909A)/F(5007A) line ratio in nebulae for determining the C+2/O+2 ratio and the total C/O abundance ratio in PNe and H II regions.

This research is supported in part by AURA/STScI grants HST-GO-09740 to Rice U., U. Oklahoma, and Williams Col.