Blackbody Temperature of 200+ Stellar Flares Observed with the CoRoT Satellite

Abstract

We estimated blackbody temperature for 209 flares observed at 69 F–K stars, significantly increasing the number of flare temperature determinations. We used the Blue and Red channels obtained by the 27 cm telescope of the CoRoT satellite at high cadence and long duration. The wavelength limits of the channels were estimated using spectra from the Pickles library for the spectral type and luminosity class of each star, provided by the Exodat Database. The temperatures were obtained from the flare energy Blue-to-Red ratio, using the flare equivalent duration and stellar flux in both channels. The expected value of the analyzed flares is equal to 6400 K with a standard deviation of 2800 K, where the mean stellar spectral type, weighted by the number of flares in each spectral subclass, is equal to G6. Contrary to our results, a stellar white-light flare is often assumed to emit as a blackbody with a temperature of 9000 or 10,000 K. Our estimates agree, however, with values obtained for solar flares. The GAIA G-band transmissivity is comparable to that of the CoRoT White channel, which allows us to calibrate the flares to the Gaia photometric system. The energy in the G band of the analyzed flares varies between 1032 and 1037 erg, and the flare area ranges from 30 μsh to 3 sh (solar hemisphere). The energy release per area in a flare is proportional to , at least up to 10,000 K.