EDP Sciences
Free access
Volume 484, Number 1, June II 2008
Page(s) L13 - L16
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200809765
Published online 22 April 2008

A&A 484, L13-L16 (2008)
DOI: 10.1051/0004-6361:200809765


The close-in companion of the fast rotating Be star Achernar

P. Kervella1, A. Domiciano de Souza2, and Ph. Bendjoya2

1  LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
    e-mail: Pierre.Kervella@obspm.fr
2  Lab. H. Fizeau, CNRS UMR 6525, Univ. de Nice-Sophia Antipolis, Observatoire de la Côte d'Azur, 06108 Nice Cedex 2, France

Received 11 March 2008 / Accepted 16 April 2008

Context. The Be stars are massive dwarf or subgiant stars that present temporary emission lines in their spectrum, and particularly in the H${\alpha}$ line. The mechanism triggering these Be episodes is currently unknown, but binarity could play an important role.
Aims. Previous observations with the VLT/VISIR instrument (Kervella & Domiciano de Souza 2007, A&A, 474, L49) revealed a faint companion to Achernar, the brightest Be star in the sky. The present observations are intended to characterize the physical nature of this object.
Methods. We obtained near-IR images and an H-band spectrum of Achernar B using the VLT/NACO adaptive optics systems.
Results. Our images clearly show the displacement of Achernar B over a portion of its orbit around Achernar A. Although there are not enough data to derive the orbital parameters, they indicate a period of about 15 yr. The projected angular separation of the two objects in December 2007 was less than 0.15$\arcsec$, or 6.7 AU at the distance of Achernar.
Conclusions. From its flux distribution in the near- and thermal-infared, Achernar B is most likely an A1V-A3V star. Its orbital period appears similar to the observed pseudo-periodicity of the Be phenomenon of Achernar. This indicates that an interaction between A and B at periastron could be the trigger of the Be episodes.

Key words: stars: individual: Achernar -- techniques: high angular resolution -- stars: emission-line, Be -- stars: binaries: close

© ESO 2008