Elemental Abundance Analysis of Three Post-AGB Candidates

Details Elemental Abundance Analysis of Three Post-AGB Candidates Elemental Abundance Analysis of Three Post-AGB Candidates

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...193.4508r&link_type=abstract

American Astronomical Society, 193rd AAS Meeting, #45.08; Bulletin of the American Astronomical Society, Vol. 30, p.1318

Astronomy and Astrophysics

Astronomy

Scientific paper

We present an LTE abundance analysis of three post-AGB candidates: IRAS Z02229+6208, IRAS 07430+1115, and IRAS 19114+0002, based on high-resolution spectra (lambda /Delta lambda ~ 50,000). Abundance results show that IRAS Z022229 and IRAS 07430 are slightly metal-deficient ([Fe/H]=-0.5) and overabundant in C, N, and s-process elements. This is in general agreement with the expected nucleosynthesis and deep convective mixing during the preceding AGB phase. Most importantly, both the stars are found to have a high abundance of Li. Thus our results suggest that these two stars may be successors of the small group of carbon-rich and Li-rich AGB stars. We also present an analysis of the circumstellar molecular absorption spectra (C2 & CN) of both stars. The derived expansion velocities, Vexp = -11.3 km s(-1) and -10.7 km s(-1) for IRAS Z02229 and IRAS 07430, respectively, are typical of values found for post-AGB stars. This brings to eight the number of post-AGB stars for which clear C,N, and s-process elemental over abundances are found. The elemental abundance results of IRAS 19114 are found to be [Fe/H]=-0.1, [C/Fe]=+0.2, [N/Fe]=+1.1, [alpha -process/Fe]=+0.5, and s-process elements [Y+Zr+La+Ce+Nd/Fe]=+0.4. The values of total CNO elements ([C+N+O/Fe]=+0.5), s-process elements, and the ratio O/C=2.6 suggest that the photosphere of IRAS 19114 is contaminated with both the H- and He-burning products and HD 179821 may be an intermediate-mass post-AGB star. However, the strength of the O I triplet lines at 7774 Angstroms and the interstellar Na I D1 & D2 components indicate that the star is a more luminous object (Mbol ~ - 8.9+/- 1), and therefore a massive supergiant. Thus, while this study of IRAS 19114 contributes important new observational data, an unambiguous determination of its evolutionary status has yet to be determined. This research was supported by grants to B.J.H from NASA (NAG5-1223) and the NSF (AST-9315107)

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