Detection and high-resolution spectroscopy of a huge flare on the old M 9 dwarf DENIS 104814.7-395606.1

Abstract

We report a flare on the M 9 dwarf DENIS 104814.7-395606.1, whose mass places it directly at the hydrogen burning limit. The event was observed in a spectral sequence during 1.3 h. Line shifts to bluer wavelengths were detected in Hα, Hβ, and in the Na I D lines, indicating mass motions. In addition we detect a flux enhancement on the blue side of the two Balmer lines in the last spectrum of our series. We interpret this as rising gas cloud with a projected velocity of about 100 km s-1 which may lead to mass ejection. The higher Balmer lines Hγ to H 8 are not seen due to our instrumental setup, but in the last spectrum there is strong evidence for H9 being in emission.