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Astron. Astrophys. 323, 789-796 (1997)

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Is UU Herculis a post-AGB star?

V.G. Klochkova , V.E. Panchuk and E.L. Chentsov

Special Astrophysical Observatory, N.Arkhyz, 357147 Russia

Received 9 January 1996 / Accepted 23 July 1996

Abstract

In order to understand the evolutionary status of the anomalous supergiant UU Her, the prototype of the class of variable supergiants located at high galactic latitudes, we obtained several high-resolution spectra of this star, with the 6m telescope, over 5 years. This material was used for a search of possible temporal variations of the radial velocity at different depths in the photosphere and for studying the chemical composition. The average radial velocity [FORMULA] suggests that UU Her belongs to the old population of the Galaxy. No systematic dependence of the velocity on depth of the line formation layer or on ionization and excitation potential is observed. The radial velocity of the [FORMULA] absorption differs strongly from the average photospheric velocity.

The iron abundance in the photosphere of UU Her is significantly lower than that of the Sun: [FORMULA]. The enhancement of nitrogen relatively to iron content [FORMULA] in combination with the carbon underabundance [FORMULA] suggests that only a first dredge-up episode occurred. The Na content is normal relatively to iron, therefore there is no evidence for dredging-up of Ne-Na cycle products. The heavy s-process metals Y, Ba are depleted relative to H and Fe, which again implies that the third dredge-up did not occur.

From the high luminosity ([FORMULA]), the large radial velocity and the chemical abundance pattern, we conclude that UU Her is a low-mass halo star, but not a post-AGB star.

Key words: stars: abundances – stars: AGB and post-AGB – stars: individual: UU Her

Send offprint requests to: V.G. Klochkova

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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