Blackbody temperature of 200+ stellar flares observed with the CoRoT satellite

TL;DR

This study analyzed over 200 stellar flares observed by CoRoT, estimating their blackbody temperatures and energies, revealing lower temperatures than traditionally assumed and providing calibration for Gaia photometry.

Contribution

It significantly increases the number of stellar flare temperature measurements and compares these with solar flare data, offering new insights into flare energetics and temperature distributions.

Findings

Average flare temperature is 6,400 K with a standard deviation of 2,800 K.

Flare energy in the G band ranges from 10^32 to 10^37 erg.

Energy release per area scales with temperature to the power of 2.6.

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 6,400 K with a standard deviation of 2,800 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 9,000 K 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 $10^{32}$ and $10^{37}$ erg and the flare area ranges from 30$\mu$sh to 3 sh (solar hemisphere). The energy release per area in a flare is proportional to $T_{\rm flare}^{2.6}$, at least up to 10,000 K.