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

TL;DR

This study investigates the origin of gas absorption features towards eta Tel, concluding they are likely caused by interstellar clouds rather than circumstellar material, based on high-resolution spectroscopy of eta Tel and similar stars.

Contribution

The paper provides evidence that gas absorption features towards eta Tel are interstellar, challenging previous assumptions of a circumstellar origin, through comparative high-resolution spectroscopic analysis.

Findings

Absorption features at ~-23 km/s are present in eta Tel and other stars.

Features previously attributed to circumstellar gas are also found in other stars.

The absorption lines are more consistent with interstellar clouds than circumstellar gas.

Abstract

eta 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 eta Tel found absorption features at ~-23 km/s and ~-18 km/s 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 eta Tel and of three other stars with a similar line of sight as eta Tel: HD 181327, HD 180575, and rho Tel. We found absorption features at ~-23 km/s and ~-18 km/s in the Ca ii H&K lines, and at ~-23 km/s in the Na i D1&D2 doublet in eta Tel, in agreement with previous findings in the ultraviolet. However, we also found absorption features at ~-23 km/s 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 eta Tel instead.