Non-thermal phenomena in the atmosphere of hot subdwarfs : X-ray upper limit for BD -3 2179.

Abstract

The investigation of the nonthermal phenomena in the atmosphere of hot sublimunous stars (sdO) provides information for the study of the subatmospheric structure in evolved stars. It is noted that large mass outflows have been measured from extensive ultraviolet (IUE) observations in a number of sdO stars, which also seem to exhibit a large microturbulent activity. An upper limit of about 10 to the 31st erg/sec is found for the X-ray luminosity of the mass losing sdO star BD3deg2179 observed with the Einstein satellite. These results are compared with the X-ray fluxes of early type stars and of other subluminous stars. It is determined that the observed upper limit for the X-ray luminosity of this star is in agreement with the f(x)/f(bol) flux ratio of the O stars.