EDP Sciences
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Volume 386, Number 1, April IV 2002
Page(s) 244 - 248
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020208

A&A 386, 244-248 (2002)
DOI: 10.1051/0004-6361:20020208

S Orionis: A Mira-type variable with a marked period decrease

P. Merchán Benítez and M. Jurado Vargas

Departamento de Física, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain
    e-mail: pedromer@unex.es

(Received 14 November 2001 / Accepted 30 January 2002)

We studied the pulsational period of the Mira star S Orionis based on visual observations that cover a total of 71 years. We found that the period decreased markedly from around 445 days to 397 days in approximately 16 years, between JD 2438000 and JD 2444000. The rate of this period variation was of the order of 0.007 day/day, too fast for the usual variations observed in most Mira variables. This result is in good agreement with the theoretical models that suggest a helium-shell flash as the cause of these large-period variations. In particular, the variation of the period and luminosity indicates that this Mira star may now be in an immediate post-primary helium-shell flash state.

Key words: stars: AGB and post-AGB -- stars: individual: S Ori -- methods: data analysis

Offprint request: M. Jurado Vargas, mjv@unex.es

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