Identifying flare locations through exoplanet transit occultations

ABSTRACT Low mass stars known as M dwarfs are the most common stars in the Galaxy, with long lifespans, a high occurrence rate of rocky planets, and close-in habitable zones. However, high stellar activity in the form of frequent flaring and any associated coronal mass ejections may drive atmospheric escape with the bombardment of radiation and high-energy particles, drastically impacting the habitability of these systems. The stellar latitude where flares and coronal mass ejections occur determines the space weather that exoplanets are subject to, with high-energy particle events associated with equatorial flares producing significant atmospheric erosion. However, the flaring latitudes for M dwarfs remain largely unconstrained. To aid in the effort to locate these flaring regions, we explore the applicability of flare occultations using optical photometry to identify the latitudes of flares. As a planet transits in front of an ongoing flare, the timing and geometry of the transit can be used to constrain the latitude and longitude of the flare. We predict the probability of detecting an occultation for known transiting planets and eclipsing binaries. From this, we estimate that 3–22 detectable occultations exist within the Transiting Exoplanet Survey Satellite primary mission photometry, with the majority occurring in eclipsing binary observations. To demonstrate this technique, we analyse a candidate flare occultation event for the eclipsing binary CM Draconis.