Utrecht Echelle spectroscopy of a flare in VB 8

Very high-resolution (R similar to 110 000) spectroscopic observations of t he very low-mass star VB 8, obtained with the Utrecht Echelle spectrograph (UES), are presented. A flare occurred during the third of a series of four consecutive spectra. This event produced significant enhancement in the st rength of the emission Lines of He I D-3 and H alpha in VB 8, as well as a filling up of some but not all atomic absorption lines, and a weakening of the gamma TiO bandheads at 705.4 and 712.5 nm. Core emission in the Na I D- 1, D-2 and KI 769.9-nm resonance lines also became stronger during the flar e. Other very low-mass stars observed with the same instrumental configurat ion include GJ 406 and VB 10. The UES spectrum of VB 8 is compared with the se. In particular, VB 10 appears to have a lower gravity than VB 8, indicat ing a lower age and a smaller mass which could be very close to the substel lar mass limit for solar metallicity.