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

Abstract

Context: The geometry of the circumstellar envelopes (CSE) surrounding Be stars is still uncertain, although it is often assumed that they are formed by a disk around the stellar equator and a hot polar wind. Achernar (Alpha Eri) is the nearest Be star, and we recently detected a CSE using near-IR interferometry. Aims: Our initial goal was to constrain the geometry and flux contribution of the CSE of Achernar at distances of a few tens of AU from the star, in the thermal IR domain to complement our near-IR interferometric observations. Methods: We obtained diffraction-limited images of Achernar in the thermal infrared using VISIR at the VLT. In order to freeze the turbulence, we used the BURST mode of this instrument. Results: The images obtained in the PAH1 band show a point-like source located 0.280" north-west of Achernar (projected linear separation of 12.3 AU). Its emission is 1.8 % of the flux of Achernar in this band, but is not detected in the PAH2, SiC and NeII bands. We also provide new thermal IR photometry of Achernar in four bands. Conclusions: Being aligned with the expected azimuth of the equatorial plane of Achernar, the detected source could be a main sequence stellar companion. In this case, it apparent brightness would correspond to an A7V spectral type.

arXiv comment4 pages, 4 figures

References in corpus (6)

• The spinning-top Be star Achernar from VLTI-VINCI
• First direct detection of a Keplerian rotating disk around the Be star $\alpha$ Arae using the VLTI/AMBER instrument
• VLTI/VINCI diameter constraints on the evolutionary status of delta Eri, xi Hya, eta Boo
• First VLTI/MIDI observations of a Be star: Alpha Ara
• Testing turbulence model at metric scales with mid-infrared VISIR images at the VLT
• An original interferometric study of NGC 1068 with VISIR BURST mode images

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