The 1st measurement of the Lyman continuum emission from normal stars

Abstract

We report the first measurements of Lyman continuum emission from non-degenerate stars. The Wide Field Camera on-board ROSAT detected strong emission from Beta CMa (B1 II-III) and Epsilon CMa (B2 II). Both Kurucz LTE line-blanketed and Mihalas NLTE unblanketed model atmospheres can match the observed count rate for Beta CMa within the known constraints on T(eff) and N(H). For Epsilon CMa, we find that the interstellar column must be at most 9 x 10 exp 17/sq cm, and probably much lower still, to explain the very strong EUV flux. We also find marginal evidence for regular variability in the Lyman continuum emission for Beta CMa, but not at the dominant period of the known optical pulsations.