The environment of the fast rotating star Achernar high-resolution thermal infrared imaging with VISIR in BURST mode

Context. It is expected that Be stars are surrounded by circumstellar envelopes, and that a significant fraction have companions. Achernar (alpha 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.