Spectroscopic observations of delta orionis

Abstract

The H α 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 Å mm–1 reciprocal dispersion and resolution 0.3 Å at λ6562.817 Å. 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 1.3×10–7 M Θ per year. An analysis has been carried on the radial velocity data of earlier observers and the present radial velocity data. It is found that the orbital elements change. The presence of apsidal motion is confirmed by the increasing value of ω. The radial velocity of the centre of mass, γ, shows periodic variation. These observations confirm the presence of a third body. The values of K (mean amplitude), P(period),a sini, and mass function f(m), indicate a regular decrease, thereby confirming the mass transfer/mass loss from the system.