FAR-ULTRAVIOLET PHOTOMETRY OF ORION STARS

Far-ultraviolet photometric data for early type stars in Orion, in the 1050-1180 and 1230-1350 Å wavelength ranges, were obtained in an Aerobee rocket flight on 30 January 1969. The results corrected for interstellar extinction, appear in good agreement with model atmospheres in the case of main-sequence stars. Bright giant and supergiant stars, however, appear to be up to one magnitude fainter than main-sequence stars of similar spectral class in the 1050-1180 Å range. The present results indicate that the detectors used in a previous flight were lower in sensitivity than was thought, so the results from that flight have been corrected using the present data for stars in common with the previous flight. The far-ultraviolet extinction law for θ Orionis is shown to be abnormal, with the observed extinction far less than predicted on the basis of ultraviolet extinction measurements of other stars, and the observed E(B-V). © 1969 D. Reidel Publishing Company.