EDP Sciences
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Volume 383, Number 3, March I 2002
Page(s) 905 - 915
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011809

A&A 383, 905-915 (2002)
DOI: 10.1051/0004-6361:20011809

Variability of the H $\alpha$ spectral line in the interacting binary AX Monocerotis

A. Puss1, 2 and L. Leedjärv1

1  Tartu Observatory, EE 61602 Tõravere, Estonia
2  Tartu University, Department of Physics, EE 50090, 4 Tähe Street, Tartu, Estonia

(Received 5 October 2001 / Accepted 17 December 2001)

The interacting binary system AX Mon (K-giant + B(e) star) has been observed at the Tartu Observatory, Estonia, from 1985 to 2000. In the present paper, mostly the behaviour of the hydrogen H $\alpha$ line from 1996 to 2000 is investigated. We have found that the H $\alpha$ profiles are variable on time scales from hours to years, with main features appearing around the conjunctions of the stars (K-star in front). Those features include weakening of the main absorption component of the P Cygni like profile and appearance of additional absorption and/or emission components. Occasionally, the H $\alpha$ line as a whole shifts on the wavelength scale. All those effects seem to occur much stronger at every second conjunction, which we propose to call "strong" conjunctions. We propose that this variability is due to a gas cloud close to the Be star. This cloud is a region, where a stream of matter from the K-giant collides with the circumstellar gas from the Be-star. The mass transfer process seems to have become more unstable than in 1960s. It is possible that a cyclic behaviour of the H $\alpha$ line with a periodicity of about two orbital periods is present.

Key words: stars: binaries: spectroscopic - stars: emission-line, Be - stars: individual: AX Mon

Offprint request: A. Puss, alar@aai.ee

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