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Astron. Astrophys. 361, 189-200 (2000)

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Comparative abundance analysis of the hot main sequence stars and their progeny in open cluster M 25

R.E. Luck 1,2, S.M. Andrievsky 3,4, V.V. Kovtyukh 3,4, S.A. Korotin 3,4 and Yu.V. Beletsky 3

1 Department of Astronomy, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7215, USA (luck@fafnir.astr.cwru.edu)
2 Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under contract with the U.S. National Science Foundation
3 Department of Astronomy, Odessa State University, Shevchenko Park, 65014 Odessa, Ukraine
4 Isaac Newton Institute in Chile, Odessa Branch (scan@deneb.odessa.ua; serkor@skyline.od.ua)

Received 23 May 2000 / Accepted 7 July 2000


Remarkable inconsistencies between elemental abundances in the main sequence stars and their progeny F-G supergiants are discussed. Comparative abundance analysis of the hot main sequence stars, the cepheid U Sgr and two cool supergiants belonging to young open cluster M 25 is performed. The detected disaccord in the abundances of carbon, oxygen and other elements between these stars having a common origin but occupying at present different evolutionary stages may be due to the fact that the chemical anomalies observed in B stars are caused by the mechanism of the radiative diffusion in the upper atmosphere layers. The chemical composition of B stars determined spectroscopically may not reflect correctly their true chemical composition, nor the chemical composition of the interstellar medium. On the other hand such abundance anomalies are not expected for F-G supergiants which have suffered the large scale mixing in the red giant phase. The observed abundances for these objects are much more reliable as a reference point in the study of galactic chemical evolution.

Three new Be stars are discovered in M 25. Our study has doubled the number of Be stars known in this cluster.

Key words: stars: abundances – stars: atmospheres – Galaxy: open clusters and associations: general – Galaxy: open clusters and associations: individual: M 25

Send offprint requests to: S.M. Andrievsky

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© European Southern Observatory (ESO) 2000

Online publication: September 5, 2000