Low-amplitude variations detected by CoRoT in the B8IIIe star HD 175869

¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, place Jules Janssen, 92195 Meudon Cedex, France e-mail: juan.gutierrez-soto@uv.es
² LESIA, Observatoire de Paris, CNRS, Université Paris Diderot, place Jules Janssen, 92195 Meudon Cedex, France
³ Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080 Granada, Spain
⁴ Observatori Astronòmic de la Universitat de València, Ed. Instituts d'Investigació, Polígon La Coma, 46980 Paterna, València, Spain
⁵ Royal Observatory of Belgium, 3 Avenue Circulaire, 1180 Brussels, Belgium
⁶ Departamento de Geociências, Universidade Estadual de Ponta Grossa, Av. General Carlos Cavalcanti, 4748 Ponta Grossa, 84.030-900, Brazil
⁷ Shelyak Instruments, Les Roussets, 38420 Revel, France
⁸ Universidade de São Paulo, Instituto de Astronomia, Geofísica e Ciências Atmosféricas – IAG, Departamento de Astronomia, Rua do Matão 1226, 05508-900 São Paulo, Brazil

Received: 20 February 2009
Accepted: 13 July 2009

Abstract

Context. The origin of the short-term variability in Be stars remains a matter of controversy. Pulsations and rotational modulation are the components of the favored hypothesis.

Aims. We present our analysis of CoRoT data of the B8IIIe star HD 175869 observed during the first short run in the center direction (SRC1).

Methods. We review both the instrumental effects visible in the CoRoT light curve and the analysis methods used by the CoRoT Be team. We applied these methods to the CoRoT light curve of the star HD 175869. A search for line-profile variations in the spectroscopic data was also performed. We also searched for a magnetic field, by applying the LSD technique to spectropolarimetric data.

Results. The light curve exhibits low-amplitude variations of the order of 300 μmag with a double wave shape. A frequency within the range determined for the rotational frequency and 6 of its harmonics are detected. The main frequency and its first harmonic exhibit amplitude variations of a few days. Other significant frequencies of low-amplitude from 25 to a few μmag are also found. The analysis of line profiles from ground-based spectroscopic data does not detect any variation. In addition, no Zeeman signature was found.

Conclusions. Inhomogeneities caused by stellar activity in or just above the photosphere are proposed to produce the photometric variability detected by CoRoT in the Be star HD 175869. The hypothesis that non-radial pulsations are the origin of these variations cannot be excluded.