A study of the massive O-type binary IOTA Orionis.

Abstract

Iota Orionis is an O9 III+B1 III binary with a highly eccentric orbit. Using coudé spectra the authors have updated its ephemeris and established a value for the apsidal motion. Combining the orbital elements, the astrophysical data (the primary is an O9 III standard star in the Orion Association), and photometry through a grazing eclipse, they have determined the dimensions of the system with, they believe, some precision. This shows that at periastron, the centres of the stars are separated only by about 1.5 times the sum of the radii, which suggests that strong tidal forces will be generated and enhanced mass loss may be expected. The authors have searched for evidence of this in a sequence of high resolution IUE spectra taken through periastron passage; some perturbations of the wind lines of C IV, N V and Si IV are seen but it is not clear that they are phase-related. Sharp components of the wind lines appear to have decoupled from the orbital motion.