The far-ultraviolet flux from Lambda Orionis A

Abstract

Digicon observations of emission-line intensities in the H II region around Lambda Ori are used to determine the effective UV ionizing flux from Lambda Ori A. It appears that the flux shortward of 353 A (and perhaps shortward of 504 A) is significantly less than predicted from calculations of static stellar atmospheres. The discrepancy between theory and observation may be a consequence of the existence of an extended atmosphere due to radiation-pressure-driven mass loss. The results are consistent with those obtained from UV absorption-line studies made with the Copernicus satellite and with radio recombination-line data for compact H II regions.