Optical Emission from Stellar Flares

Abstract

Optical observations of stellar flares on late-type stars are common, particularly in the U and B bands of the Johnson system. The reason for this preference is the large proportionate increase in the flux in the ultraviolet during flares on late-type stars, as compared to the quiescent stellar continuum which peaks in the near infra-red. Thus the contrast with the photosphere of the quiet star makes detection of flares much easier in the near ultraviolet than at longer wavelengths. Whilst single band, U or B, observations have provided very useful information on the statistics of flares, they are inadequate in their lack of spectral information. Only from spectral information can we hope to gain insight into the processes that give rise to the optical emission and thereby ultimately, to realistic flare models.