NRPs and circumstellar activity in HD 127972^*

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

Corresponding author: R. S. Levenhagen, savarino@astro.iag.usp.br

Received: 8 July 2002
Accepted: 19 December 2002

Abstract

Line profile variations (lpv) in He i, Fe ii, Mg ii and Si ii transitions were detected in the Be star η Cen (HD 127972) by means of high resolution and 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 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 . 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 Hα peak separation and ratios. Using a simple model for the Hα line emission formation, we outlined an explanation for the season-averaged Hα emission variation in terms of changes of the mass density in the circumstellar envelope. The fundamental parameters of η 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.