An analysis of the optical spectra of the post-asymptotic giant branch stars LSIV -12 111 and HD 341617

Abstract

High spectral resolution and signal-to-noise observations of the absorption and emission line spectra in two post- asymptotic-giant-branch (PAGB) stellar candidates, LSIV 12 111 and HD 314617 are discussed. The absorption line spectra have been analysed using non-LTE model atmosphere techniques to determine stellar atmospheric parameters and chemical compositions, both in absolute terms and relative to a standard star, HD 13841. The atmospheric parameters dier from previous estimates based on LTE model atmospheres, probably due to non-LTE eects. In turn these imply stellar masses that are generally larger than have been previously estimated. Both PAGB candidates have relative uniform underabundances of metals with mean values of 0.35 dex for LSIV 12 111 and 0.50 dex for HD 314617. Furthermore, their abundance patterns are remarkably similar to that observed for optically bright, F-type PAGBs. From the emission spectra, the plasma parameters and angular size of the circumstellar material are constrained, and these are consistent with previous estimates and with a PAGB evolutionary stage.