Photometric variability of the Be star CoRoT-ID 102761769^⋆

¹ Observatório Astronômico/DEGEO, Universidade Estadual de Ponta Grossa, Av. Carlos Cavalcanti 4748, 84030-900, Ponta Grossa, PR, Brazil
e-mail: memilio@uepg.br
² Universidade de São Paulo/IAG-USP, rua do Matão 1226, 05508-900 Cidade Universitária São Paulo, SP, Brazil
³ Observatoire de Meudon LESIA, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
⁴ Observatori Astronòmic de la Universitat de València, Edifici Instituts d’Investigació, Polígon La Coma, 46980 Paterna, València, Spain
⁵ Instituto de Astrofísica de Andalucía (CSIC), CP 3004, Granada, Spain
⁶ Observatoire de Meudon GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
⁷ Royal Observatory of Belgium, 3 avenue circulaire, 1180 Brussels, Belgium
⁸ European Organization for Astronomical Research in the Southern Hemisphere, Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile

Received: 16 January 2010
Accepted: 13 June 2010

Abstract

Context. Classical Be stars are rapid rotators of spectral type late O to early A and luminosity class V-III, which exhibit Balmer emission lines and often a near infrared excess originating in an equatorially concentrated circumstellar envelope, both produced by sporadic mass ejection episodes. The causes of the abnormal mass loss (the so-called Be phenomenon) are as yet unknown.

Aims. For the first time, we can now study in detail Be stars outside the Earth’s atmosphere with sufficient temporal resolution. We investigate the variability of the Be Star CoRoT-ID 102761769 observed with the CoRoT satellite in the exoplanet field during the initial run.

Methods. One low-resolution spectrum of the star was obtained with the INT telescope at the Observatorio del Roque de los Muchachos. A time series analysis was performed using both cleanest and singular spectrum analysis algorithms to the CoRoT light curve. To identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT-ID 102761769 by varying its main physical parameters inside the uncertainties discussed.

Results. We found two close frequencies related to the star. They are 2.465 cd^-1 (28.5 μHz) and 2.441 cd^-1 (28.2 μHz). The precision to which those frequencies were found is 0.018 cd^-1 (0.2 μHz). The projected stellar rotation was estimated to be 120 kms^-1 from the Fourier transform of spectral lines. If CoRoT-ID 102761769 is a typical Galactic Be star it rotates near the critical velocity. The critical rotation frequency of a typical B5-6 star is about 3.5 cd^-1 (40.5 μHz), which implies that the above frequencies are really caused by stellar pulsations rather than star’s rotation.