Ultraviolet spectra of planetary nebulae. VII. The abundance of carbon in the very low excitation nebula HE 2-131.

Abstract

Features observed in infrared spectra suggest that certain very low excitation (VLE) nebulae have low C/O abundance ratios (Cohen & Barlow 1980; Aitken & Roche 1982). Fluxes in the multiplets [O II] _sun2470 and [O II] λ2326 have been measured for the VLE nebula He 2-131 = HD 138403 using lUE high-dispersion spectra. An analysis similar to that of Harrington et al. (1980) for IC 418 gives C/O = 0.3 for He 2-131, compared with C/O = 1.3 for IC 418 and 0.6 for the Sun.