Spectroscopic observations of delta orionis

Abstract

The Hα profile in the spectrum of δ Orionis shows phase-dependent changes, with a period of variation equal to the orbital period fo the binary system. The profile shape changes from a normal absorption profile at zero phase to a P Cygni-type at a later phase, to an absorption profile having emission at the centre of the profile, to a normal absorption profile at the end of the period. The spectra have been obtained at the Cassegrain focus of Kavalur Observatory telescopes (50 and 100 cm) at 17.2 A mm−1 reciprocal dispersion and resolution 0.3 A at λ 6562.817 A. Assuming that the P Cygni profile is formed by a spherically-symmetrical region, the analysis gives a shell radius of 2.18 stellar radius and an electron density in the shell equal to 6.54×10−9 cm−3, with the observed expansion velocity of 50 km/s−1, a mass loss of 1.3×10−7M⊙ per year.