Instabilities in the excitation of non-radial pulsation modes in the δ Scuti star BV Circini^*

INAF - Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy

Corresponding author: luciano@merate.mi.astro.it

Received: 28 July 2003
Accepted: 21 October 2003

Abstract

High resolution spectroscopic observations obtained in 1995 of the δ Scuti star BV Circini are analyzed and the results compared with those obtained by Mantegazza et al. ([CITE]) from spectroscopic observations in 1996 and 1998. Non-radial pulsation modes both of low and high degree have been observed. Most of them are the same detected in the other two campaigns, however the strongest high–degree one (14.62 cd^-1) is different from that observed in 1996 (13.85 cd^-1), which in turn is different from that observed in 1998 (17.28 cd^-1). The 13.85 cd^-1 mode is the only one of these independently detected in the three seasons, in which it kept about the same amplitude. One high-degree retrograde mode at 1.48 cd^-1 has been independently detected in the three campaigns. The mode amplitude variations are discussed and it is shown that large variations can occur from one year to the next. The mode identifications performed on the three datasets by means of the fit of line profile variations supply results in good agreement among themselves. The high degree prograde modes have azimuthal orders between 12 and 14, while the retrograde one is about 7. Finally the stellar pulsation spectrum as derived from all the available spectroscopic and photometric data, and which consists of about 20 terms, is discussed.