Letter to the Editor
The environment of the fast rotating star Achernar
High-resolution thermal infrared imaging with VISIR in BURST mode
LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon Cedex, France e-mail: Pierre.Kervella@obspm.fr
2 Lab. Univ. d'Astrophysique de Nice (LUAN), CNRS UMR 6525, UNSA, Parc Valrose, 06108 Nice, France
3 Observatoire de la Côte d'Azur, CNRS UMR 6203, Département GEMINI, BP 4229, 06304 Nice Cedex 4, France
Accepted: 19 September 2007
Context.It is expected that Be stars are surrounded by circumstellar envelopes, and that a significant fraction have companions. Achernar (α Eri) is the nearest Be star, and is thus a favourable target to search for their signatures using high resolution imaging.
Aims.We aim at detecting circumstellar material or companions around Achernar at distances of a few tens of AU.
Methods.We obtained diffraction-limited thermal IR images of Achernar using the BURST mode of the VLT/VISIR instrument.
Results.The images obtained in the PAH1 band show a point-like secondary source located 0.280″ north-west of Achernar. Its emission is 1.8% of the flux of Achernar in this band, but is not detected in the PAH2, SiC and NeII bands.
Conclusions.The flux from the detected secondary source is compatible with a late A spectral type main sequence companion to Achernar. The position angle of this source (almost aligned with the equatorial plane of Achernar) and its projected linear separation (12.3 AU at the distance of Achernar) favor this interpretation.
Key words: stars: individual: Achernar / methods: observational / techniques: high angular resolution / stars: emission-line, Be
© ESO, 2007