The pulsations of the B5IVe star HD 181231 observed with CoRoT and ground-based spectroscopy ^*,**

¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France e-mail: coralie.neiner@obspm.fr
² Institut d'Astrophysique Spatiale (IAS), bâtiment 121, 91405 Orsay Cedex, France
³ Royal Observatory of Belgium, 3 avenue circulaire, 1180 Brussel, Belgium
⁴ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
⁵ Observatori Astronòmic de la Universitat de València, ED. Instituts d'Investigatió, Poligon La Coma, 46980 Paterna, València, Spain
⁶ INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁷ Institute of Astronomy, University of Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
⁸ Shelyak Instruments, Les Roussets, 38420 Revel, France
⁹ Castanet Tolosan Observatory, 6 place Clemence Isaure, 31320 Castanet Tolosan, France
¹⁰ R. Venezuela 29, 3 Esq., 1500-618 Lisboa, Portugal
¹¹ University of Sao Paulo, Brazil
¹² Observatório Astronômico/DEGEO, Universidade Estadual de Ponta Grossa, Av. Carlos Cavalcanti, 4748 Ponta Grossa, Paraná, Brazil

Received: 28 February 2009
Accepted: 16 July 2009

Abstract

Context. HD 181231 is a B5IVe star, which has been observed with the CoRoT satellite during ~5 consecutive months and simultaneously from the ground in spectroscopy and spectropolarimetry.

Aims. By analysing these data, we aim to detect and characterize as many pulsation frequencies as possible, to search for the presence of beating effects possibly at the origin of the Be phenomenon. Our results will also provide a basis for seismic modelling.

Methods. The fundamental parameters of the star are determined from spectral fitting and from the study of the circumstellar emission. The CoRoT photometric data and ground-based spectroscopy are analysed using several Fourier techniques: Clean-ng, Pasper, and Tisaft, as well as a time-frequency technique. A search for a magnetic field is performed by applying the LSD technique to the spectropolarimetric data.

Results. We find that HD 181231 is a B5IVe star seen with an inclination of ~45 degrees. No magnetic field is detected in its photosphere. We detect at least 10 independent significant frequencies of variations among the 54 detected frequencies, interpreted in terms of non-radial pulsation modes and rotation. Two longer-term variations are also detected: one at ~14 days resulting from a beating effect between the two main frequencies of short-term variations, the other at ~116 days due either to a beating of frequencies or to a zonal pulsation mode.

Conclusions. Our analysis of the CoRoT light curve and ground-based spectroscopic data of HD 181231 has led to the determination of the fundamental and pulsational parameters of the star, including beating effects. This will allow a precise seismic modelling of this star.