Gas absorption towards the η Tel debris disc: winds or clouds?

Abstract

η Telescopii is a ∼23 Myr old A-type star surrounded by an edge-on debris disc hypothesised to harbour gas. Recent analysis of far- and near-ultraviolet spectroscopic observations of η Tel found absorption features at ∼-23 km s−1 and ∼-18 km s−1 in several atomic lines, attributed to circumstellar and interstellar gas, respectively. In this work, we put the circumstellar origin of the gas to a test by analysing high resolution optical spectroscopy of η Tel and of three other stars with a similar line of sight as η Tel: HD 181327, HD 180575, and ρ Tel. We found absorption features at ∼-23 km s−1 and ∼-18 km s−1 in the Ca ii H&K lines, and at ∼-23 km s−1 in the Na i D1&D2 doublet in η Tel, in agreement with previous findings in the ultraviolet. However, we also found absorption features at ∼-23 km s−1 km s−1 in the Ca ii K lines of the three other stars analysed. This strongly implies that the absorption lines previously attributed to circumstellar gas are more likely due to an interstellar cloud traversing the line of sight of η Tel instead.