[Previous] | [Session 60] | [Next]
P. Mudumba, T. Sivarani (Indian Institute of Astrophysics), P. Garcia-Lario (ISO Data Centre, Madrid, Spain), A. Manchado (IAC, Tenerife, Spain)
We have carried out an analysis of the high resolution optical spectra of post-AGB candidates SAO 85766 (IRAS 18062+2410), SAO 34504 (IRAS 22272+5435), HD 187885 (IRAS 19500-1709), HD 331319 (IRAS 19475+3119), HD 168625 (IRAS 18184-1623) and IRAS 10215-5916. All these objects have far-infrared colors similar to planetary nebulae and proto- planetary nebulae. Some of these are high galactic latitude stars.
The spectrum of SAO 85766 shows several permitted and forbidden emission lines and low excitation nebular emission lines. We find the chemical composition of SAO 85766 to be similar to that of high galatcic latitude hot post-AGB stars with under abundance of carbon. The variations observed in the spectrum of SAO 85766 indicates that it is rapidly evolving into a planetary nebula ( similar to that SAO 244567 (Hen 1357)).
SAO 34504 and HD 187885 are post-AGB stars with 21 micron emission feature. We have determined the atmospheric parameters and chemical composition of these stars and confirm the over abundance of carbon and s-process elements. These two stars appear to have evovled from the carbon star phase on the AGB and are now carbon-rich post-AGB stars.
The evolutionary status of HD 331319, HD 168625 and IRAS 10215-5916 is not clear. They may be low mass stars in post-AGB phase of evolution, or, they may be massive popI supergiants. The chemical composition analysis of all the above mentioned stars is presented.