EDP Sciences
Free access
Volume 400, Number 2, March III 2003
Page(s) 599 - 612
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030068

A&A 400, 599-612 (2003)
DOI: 10.1051/0004-6361:20030068

NRPs and circumstellar activity in HD 127972

R. S. Levenhagen1, N. V. Leister1, J. Zorec2, E. Janot-Pacheco1, A. M. Hubert3 and M. Floquet3

1  Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo, CUASO 05508-900 São Paulo, Brazil
2  Institut d'Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France
3  Observatoire de Paris-Meudon, GEPI, FRE/2459, 92195 Meudon Cedex, France

(Received 8 July 2002 / Accepted 19 December 2002)

Line profile variations (lpv) in He I, Fe II, Mg II and Si II transitions were detected in the Be star $\eta$ Cen (HD 127972) by means of high resolution and S/N spectroscopic observations obtained in six epochs from May 1996 to April 2001. They were interpreted in terms of nonradial pulsations (NRPs). Time analysis was performed using Cleanest algorithm and showed the following frequencies with high order of significance: 0.61 c/d, 1.48 c/d, 3.81 c/d, 5.31 c/d, 9.24 c/d and 10.35 c/d. From phase variation diagrams we estimated mode degrees $\ell$ in the range 3-8. If the 10.35 c/d frequency is considered the first harmonic of 5.31 c/d, the corresponding azimuthal number of the mode is $\vert m \vert = 4\pm2$. Except for 0.61 c/d, all other frequencies are compatible with NRPs. During the period of progressive activity enhancement in the He I 6678 line, a strengthening of Balmer emission lines was observed. From Mar. 12 to Mar. 23, 2000, we noticed rapid variations of both H $\alpha$ peak separation and V/R ratios. Using a simple model for the H $\alpha$ line emission formation, we outlined an explanation for the season-averaged H $\alpha$ emission variation in terms of changes of the mass density in the circumstellar envelope. The fundamental parameters of $\eta$ Cen were analyzed using several methods. The adopted ones account for the stellar fast rotation, which helped us not only to estimate the stellar rotational frequency, but also to show that the star is in the middle of its main sequence life span.

Key words: stars: emission-line, Be -- stars: oscillations -- stars: individual: $\eta$ Cen -- stars: fundamental parameters -- techniques: spectroscopic -- line: profiles

Offprint request: R. S. Levenhagen, savarino@astro.iag.usp.br

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