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

¹ The Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland
² Laboratory for Astronomy and Solar Physics, Code 681, Goddard Space Flight Centre, Greenbelt, MD 20771, USA
³ National Optical Astronomy Observatories, Tucson, AZ 85726, USA
⁴ Department of Astronomy, University of Maryland, College Park, MD 20742, USA

Corresponding author: R. Ryans, R.Ryans@qub.ac.uk

Received: 23 August 2002
Accepted: 4 February 2003

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 differ from previous estimates based on LTE model atmospheres, probably due to non-LTE effects. 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.