Volume 377, Number 1, October I 2001
|Page(s)||156 - 160|
|Section||Interstellar and circumstellar matter|
|Published online||15 October 2001|
FN Aquilae -an unusual Cepheid with anomalous CNO abundances*
Astronomical Observatory of Odessa State University, Odessa 65014, Ukraine e-mail: firstname.lastname@example.org
2 Isaac Newton Institute of Chile, Odessa Branch, Ukraine
3 Special Astrophysical Observatory, Russian Academy of Sciences, Nizhny Arkhyz, Stavropol Territory 369167, Russia e-mail: email@example.com
4 Isaac Newton Institute of Chile, SAO RAS Branch, Russia
Corresponding author: I. A. Usenko, firstname.lastname@example.org
Accepted: 23 July 2001
Spectroscopic analysis of the classical Cepheid FN Aql from three high-resolution CCD spectra near minimum and maximum light gives the following results: 1) Mean K; log and km s-1; 2) Metallicities derived for each phase are consistent with each other and close to the solar value; 3) The Cepheid is crossing the instability strip for at least the third time. 4) It has anomalously low carbon ( dex) and nitrogen ( dex) abundances, which is unusual for a Cepheid not crossing the instability strip for the first time. Since FN Aql is an IRAS object and candidate protoplanetary nebulae according to Volk & Kwok ([CITE]), we assume that the star's peculiarities are caused either by envelope loss after the second dredge-up or that it is an unusual Cepheid for which existing nucleosynthesis and mixing models are unable to reproduce the CNO abundance pattern.
Key words: stars: abundances / stars: variables: Cepheids
© ESO, 2001
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