An unusually large gaseous transit in a debris disc

Abstract

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 on to 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.