Flares, Rotation, and Planets of the AU Mic System from TESS Observations

TL;DR

This paper analyzes TESS observations of the young star AU Mic, studying stellar activity, flare behavior, and transiting planets, including new detections and refined planetary parameters with observed transit timing variations.

Contribution

It provides a combined analysis of TESS data including 20-second cadence observations, detecting more flares, refining planetary parameters, and identifying transit timing variations.

Findings

Increased flare detection with 20-second data

Refined parameters for AU Mic b with transit timing variations

Detection of a new planet, AU Mic c, with 18.86-day period

Abstract

AU Mic is a young ($\sim$24 Myr), pre-Main Sequence M~dwarf star that was observed in the first month of science observations of the Transiting Exoplanet Survey Satellite (TESS) and re-observed two years later. This target has photometric variability from a variety of sources that is readily apparent in the TESS light curves; spots induce modulation in the light curve, flares are present throughout (manifesting as sharp rises with slow exponential decay phases), and transits of AU Mic b may be seen by eye as dips in the light curve. We present a combined analysis of both TESS Sector 1 and Sector 27 AU Mic light curves including the new 20-second cadence data from TESS Year 3. We compare flare rates between both observations and analyze the spot evolution, showing that the activity levels increase slightly from Sector 1 to Sector 27. Furthermore, the 20-second data collection allows us to detect more flares, smaller flares, and better resolve flare morphology in white light as compared to the 2-minute data collection mode. We also refine the parameters for AU Mic b by fitting three additional transits of AU Mic b from Sector 27 using a model that includes stellar activity. We show that the transits exhibit clear transit timing variations (TTVs) with an amplitude of $\sim$80 seconds. We also detect three transits of a 2.8 $R_\oplus$ planet, AU Mic c, which has a period of 18.86 days.