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1999AJ....117.1834R - Astron. J., 117, 1834-1844 (1999/April-0)
Spectroscopic study of HD 179821 (IRAS 19114+0002): proto-planetary nebula or supergiant?
REDDY B.E. and HRIVNAK B.J.
Abstract (from CDS):
The elemental abundance results of HD 179821 are found to be [Fe/H]=-0.1, [C/Fe]=+0.2, [N/Fe]=+1.3, [O/Fe]=+0.2, [α-process/Fe]=+0.5, and [s-process/Fe]=+0.4. These values clearly differ from the elemental abundances of Population I F supergiants. The C, N, and O abundances and the total CNO abundance value relative to Fe, [C+N+O/Fe]=+0.5, indicate that the photosphere of HD 179821 is contaminated with both the H- and He-burning products of the AGB phase. The evidence for He burning through the 3α process and deep AGB mixing also comes from the observed overabundances of s-process elements. Remarkably, the abundance of the α-process element Na is found to be very large, [Na/Fe]=+0.9.
The ratio O/C=2.6 indicates that the atmosphere is oxygen rich. The results of this abundance study support the argument that HD 179821 is a proto-planetary nebula, probably with an intermediate-mass progenitor. However, the strength of the O I triplet lines at 7774 Å and the distance derived from the interstellar Na I D1 and D2 components imply that the star is a luminous object (Mbol~-8.9±1) and thus a massive supergiant. Thus, while this study contributes important new observational results for this star, an unambiguous determination of its evolutionary status has yet to be achieved.
Abstract Copyright: ∼
Journal keyword(s): Stars: Abundances - Stars: Evolution - Stars: Individual: Alphanumeric: IRAS 19114+0002 (read: IRAS 19114-0002) - Stars: Individual: Henry Draper Number: HD 179821 - Stars: Supergiants
Errata: Erratum vol. 118, p. 1900 (1999)
Simbad objects: 6
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