Multiperiodic pulsations in the Be stars NW Serpentis and V1446 Aquilae^*

¹ Observatorio Astronómico. Universidad de Valencia. Edificio Institutos de investigación. Polígono la Coma, 46980 Paterna, Valencia, Spain e-mail: juan.gutierrez-soto@uv.es
² GEPI, UMR 8111 du CNRS, Observatoire de Paris-Meudon, 92195 Meudon, France
³ ICMUV, Edificio Institutos de investigación, Polígono la Coma, 46980 Paterna, Valencia, Spain
⁴ Instituto de Astrofísica de Andalucía (CSIC) Camino Bajo de Huétor, 24, 18008 Granada, Spain
⁵ LESIA, UMR 8109 du CNRS, Observatoire de Paris-Meudon, 92195 Meudon, France
⁶ Royal Observatory of Belgium, 3 avenue Circulaire, 1180 Brussels, Belgium

Received: 5 March 2007
Accepted: 6 June 2007

Abstract

Aims.We present accurate photometric time series of two Be stars: NW Ser and V1446 Aql. Both stars were observed at the Observatorio de Sierra Nevada (Granada) in July 2003 with an automatic four-channel Strömgren photometer. We also present a preliminary theoretical study showing that the periodic variations exhibited by these stars can be due to pulsation.

Methods.An exhaustive Fourier analysis together with a least-square fitting has been carried out on the time series for all four Strömgren bands. Several independent frequencies and non-periodic trends explain most of the variance. A theoretical non-adiabatic code applied to stellar models for these stars shows that g-modes are unstable.

Results.Both stars show rapid variations in amplitude, probably due to a beating phenomenon. Four significant frequencies have been detected for each star. Comparison of the observed amplitude ratios for each pulsational frequency with those calculated from theoretical pulsation codes allows us to estimate the pulsation modes associated with the different detected frequencies. NW Ser seems also to show unstable p-modes and thus could be one of the newly discovered β Cephei and SPB hybrid stars. Further spectroscopic observations are planned to study the stability of the detected frequencies.