Tomographic separation of composite spectra.: VIII.: The physical properties of the massive compact binary in the triple star system HD 36486 (δ orionis A)

We present the first double-lined spectroscopic orbital elements for the central binary in the massive triple delta Orionis A. The solutions are based on fits of cross-correlation functions of IUE high-dispersion UV spectra and He I lambda6678 profiles. The orbital elements for the primary agree well with previous results, and in particular, we confirm the apsidal advance with a period of 224.5 +/- 4.5 yr. We also present tomographic reconstructions of the primary and secondary stars' spectra that confirm the O9.5 II classification of the primary and indicate a B0.5 III type for the secondary. The relative line strengths between the reconstructed spectra suggest magnitude differences of Deltam = -2.5 log (F-s/F-p) = 2.6 +/- 0.2 in the UV and Deltam = 2.5 +/- 0.3 at 6678 Angstrom. The widths of the UV cross-correlation functions are used to estimate the projected rotational velocities, V sin i = 157 +/- 6 and 138 +/- 16 km s(-1) for the primary and secondary, respectively (which implies that both the primary and the secondary rotate faster than the orbital motion). We used the spectroscopic results to make a constrained fit of the Hipparcos light curve of this eclipsing binary, and the model fits limit the inclination to the range i = 67degrees-77degrees. The lower limit corresponds to a near Roche-filling configuration that has an absolute magnitude that is consistent with the photometrically determined distance to Ori OB1b, the Orion Belt cluster in which delta Ori resides. The i = 67degrees solution results in masses of and both of which are substantially below M-p = 11.2 M-s = 5.6 M., the expected masses for stars of their luminosity. The binary may have experienced a mass ratio reversal caused by case A Roche lobe overflow or the system may have suffered extensive mass loss through a binary interaction (perhaps during a common envelope phase) in which most of the primary's mass was lost from the system rather than transferred to the secondary. We also made three-component reconstructions to search for the presumed stationary spectrum of the close visual companion delta Ori Ab (Hei 42 Ab). There is no indication of the spectral lines of this tertiary in the UV spectrum, but a broad and shallow feature is apparent in the reconstruction of He I lambda6678 indicative of an early B-type star. The tertiary may be a rapid rotator (V sin i approximate to 300 km s(-1)) or a spectroscopic binary.