An X-ray flare observed from van Biesbroeck 8.
Tagliaferri, G.; Doyle, J. G.; Giommi, P.
Netherlands, United Kingdom
Abstract
An X-ray flare was detected on the previously unknown flare-star van Biesbroeck 8 ( = Gl 644 C). The total energy of the event in the 0.05-2 keV energy range was 8 x 10 to the 31st erg/s with a mean luminosity of 1.8 x 10 to 28th erg/s. This implies an emission measure of about 6 x 10 to the 50th/cu cm, and adopting a simple loop model an electron density of 10 to the 11th/cu cm or greater. It is estimated that the flare covered 1-4 percent of the stellar surface. Quiescent X-ray emission from VB 8 was detected during an Einstein-HRI observation. These properties of VB 8 suggest that stars later than M 5 can be very active X-ray emitters.