An unusually large gaseous transit in a debris disc

TL;DR

This paper reports the detection of an unusually large and long-lasting transient gas absorption event in the debris disc star HD 37306, likely caused by an exocometary break-up releasing a substantial amount of gas.

Contribution

It presents the first observation of a large, prolonged gaseous transit in a debris disc, expanding understanding of gas dynamics in such systems.

Findings

Detected a broad, long-lasting gas absorption event in HD 37306.

The event is consistent with an exocometary break-up releasing gas.

The gas likely formed a ring or torus structure around the star.

Abstract

We present the detection of an unusually large transient gas absorption in several ionized species in the debris disc star HD 37306 using high-resolution optical spectra. We have been analysing a large sample of debris discs searching for circumstellar gas absorptions aiming to determine the frequency of gas in debris discs. HD 37306 stood out showing remarkably broad absorptions superimposed onto several photospheric Ca ii, Fe ii and Ti ii lines. The observed absorptions, unlike typical exocometary transits, lasted for at least eight days. Here we analyse simultaneous spectroscopic and photometric data of the event and evaluate different scenarios that might explain the observed features. We conclude that the most likely scenario might be an exocometary break-up releasing a significant amount of gas close to the star, producing an occulting "ring"/"torus" shape.