Short term variability of DS Tuc A observed with TESS

TL;DR

This study develops a new method to identify and analyze impulsive short-term stellar activity in TESS light curves, focusing on the system DS Tuc, to understand energetic events and their potential effects on planetary atmospheres.

Contribution

A novel procedure using Gaussian processes to detect impulsive stellar events in TESS data, validated on AU Mic, and applied to DS Tuc to characterize event frequency and energy distribution.

Findings

Approximately 2 energetic events per day with >2x10^32 erg for DS Tuc.

Evidence of phase-related short-term activity in AU Mic.

Impulsive events tend to be grouped rather than evenly spaced.

Abstract

Impulsive short term variations occur in all kinds of solar-type stars. They are the results of complex phenomena such as the 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 understand their role in modifying the chemical composition or, in some extreme cases, to the disruption of the planetary atmospheres. Here, we present a new procedure developed to identify the impulsive events in TESS light curves. Our goal is to have a simple and effective tool to study the short-term activity of a star using only its light curve, in order to derive its distribution and energetic. As our first case, we studied the system DS Tuc. Our technique consists of fitting the TESS light curves using iteratively Gaussian processes in order to remove all the long-term stellar activity contributions. Then, we identify the impulsive events and, derive amplitudes, time scales and the amount of energy emitted. 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 approx 2 events per day with energy greater than 2x10^32 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 events 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.