Short term variability of DS Tuc A observed with TESS

Abstract

Context. 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.Aims. 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. Methods. 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. 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 ≈ 2 events per day with energy greater than 2 × 10 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.

X-ray flares of the young planet host Ds Tucanae A

“…By using the relationship between flare energy released in the optical band and in X-rays inferred by Flaccomio et al (2018) from the flares observed in the NGC 2264 young star forming region, this limit corresponds to X-ray energies of order of 10 31 erg. The flares we detected in the present XMM-Newton observation seem very rare events that likely released energies in the optical band in excess of 5 × 10 35 erg which are on the very high energy tail of the flare energies observed with TESS by Colombo et al (2022). Furthermore, in the optical band there is a significant fraction of pairs of flares separated by a few ks, similar to the separation of the two flares we observed in X-rays.…”

“…The energy released during the first and second flare are about 8 × 10 34 erg and 5 × 10 34 erg. Colombo et al (2022) used TESS light curves of DS Tuc to study the rate of flares of DS Tuc in the optical band with an analysis of all available sectors through an iterative method based on Gaussian processes. They found that the frequency of flares with energy (in optical band) larger than 2 × 10 32 erg amounts to about 2 per day.…”

“…In the optical band, TESS observed DS Tuc A in six sectors, allowing Colombo et al (2022) to perform a reconstruction of the distribution of the optical flares and their main properties (see also Howard 2022). They also inferred the energies of the X-ray counterparts of TESS flares through the scaling laws of Flaccomio et al (2018) before X-rays observations were available.…”

Searching for flaring star-planet interactions in AU Mic TESS observations

“…Kavanagh et al (2021) found that, based on reconstructions of AU Mic's magnetic field and mass loss rate, AU Mic b could reside in the sub-Alfvénic regime. If this is true, flaring SPI is also possible (Lanza 2018); a recent study even claimed to have visually identified hints of such an interaction in TESS data (Colombo et al 2022). In fact, AU Mic is the most actively flaring star among all currently known exoplanet hosts (Ilin et al in prep.…”

The Flaring TESS Objects of Interest: Flare Rates for all Two Minute Cadence TESS Planet Candidates

“…As a result, ∼15 TOI host stars have measured flare rates (e.g. Günther et al 2020;Pope et al 2021;Gilbert et al 2021;Bogner et al 2021;Colombo et al 2022). Most notably, Medina et al (2020) performed a flare search on all single low mass stars in the southern sky within 15 pc.…”