MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri

TL;DR

This study used the MOST satellite to observe 66 white light flares on Proxima Centauri over 37.6 days, revealing flare frequencies and energies that impact planetary habitability and transit detection.

Contribution

First extensive monitoring of Proxima Centauri's white light flares with detailed flare frequency and energy distribution analysis.

Findings

Proxima Centauri exhibits a high flare rate despite slow rotation.

Flares with energies of 10^{28} erg occur 63 times daily.

Superflares of 10^{33} erg happen about 8 times annually.

Abstract

We present a study of white light flares from the active M5.5 dwarf Proxima Centauri using the Canadian microsatellite MOST. Using 37.6 days of monitoring data from 2014 and 2015, we have detected 66 individual flare events, the largest number of white light flares observed to date on Proxima Cen. Flare energies in our sample range from $10^{29}$-$10^{31.5}$ erg. The flare rate is lower than that of other classic flare stars of similar spectral type, such as UV Ceti, which may indicate Proxima Cen had a higher flare rate in its youth. Proxima Cen does have an unusually high flare rate given its slow rotation period, however. Extending the observed power-law occurrence distribution down to $10^{28}$ erg, we show that flares with flux amplitudes of 0.5% occur 63 times per day, while superflares with energies of $10^{33}$ erg occur ~8 times per year. Small flares may therefore pose a great difficulty in searches for transits from the recently announced 1.27 M_earth Proxima b, while frequent large flares could have significant impact on the planetary atmosphere.