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

TL;DR

This study uses high-resolution thermal infrared imaging to investigate the circumstellar environment of Achernar, revealing a potential stellar companion aligned with the star's equatorial plane, contributing to understanding Be star envelopes.

Contribution

First thermal IR imaging with VISIR in BURST mode to detect a potential companion near Achernar, providing new insights into its circumstellar environment.

Findings

Detected a point-like source 0.280" from Achernar in PAH1 band

Source may be a main sequence companion of spectral type A7V

No detection of the source in other IR bands

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.