Short-term variability of DS Tucanae A observed with TESS

Abstract

Context. Impulsive short-term variations occur in all kinds of solar-type stars and are the result of complex phenomena such as stellar magnetic field reconnection, low-level variability, or in some cases even star-planet interactions. The radiation arising from these events is often highly energetic and, in stars hosting planets, may interact with the planetary atmospheres. Studying the rate of these energetic phenomena is fundamental to understanding their role in modifying the chemical composition or, in some extreme cases, the disruption of the planetary atmospheres. Aims. Here, we present a new procedure developed to identify the impulsive events in Transit Exoplanet Survey Satellite (TESS) light curves. Our goal is to produce a simple and effective tool with which to study the short-term activity of a star using only its light curve in order to derive the distribution and energy of short-term variations. As our first case, we studied the system DS Tuc. Methods. Our technique consists of fitting the TESS light curves using iteratively Gaussian processes in order to remove all the longterm stellar activity contributions. We then identify the impulsive events and derive amplitudes, timescales, and the amount of energy emitted. Results. We validate our procedure using the AU Mic TESS light curves, obtaining results consistent with those presented in the literature. We estimate the frequency distribution of energetic events for DS Tuc. In particular, we find that there are approximately two events per day with energy greater than 2 × 1032 erg. We find evidence for a favoured stellar phase for short-term activity on AU Mic, and also indications of short-term activity in phase with the planetary orbit. For DS Tuc, we find that the event distribution is not equally spaced in time but often grouped. The resulting distribution may be used to estimate the impact of short-term variability on planetary atmosphere chemical compositions.