Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (δ Orionis A)

Abstract

-2 -We present the first double-lined spectroscopic orbital elements for the central binary in the massive triple, δ Orionis A. The solutions are based on fits of crosscorrelation functions of IUE high dispersion UV spectra and He I λ6678 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 y. 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 ∆m = −2.5 log(F s /F p ) = 2.6 ± 0.2 in the UV and ∆m = 2.5 ± 0.3 at 6678Å. The widths of the UV cross-correlation functions are used to estimate the projected rotational velocities, V sin i = 157 ± 6 km s −1 and 138 ± 16 km s −1 for the primary and secondary, respectively (which implies that the secondary rotates 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 = 67 • − 77 • . The lower limit corresponds to a near Roche-filling configuration that has an absolute magnitude which is consistent with the photometrically determined distance to Ori OB1b, the Orion Belt cluster in which δ Ori resides. The i = 67 • solution results in masses of M p = 11.2 M ⊙ and M s = 5.6 M ⊙ , both of which are substantially below 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, δ 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 λ6678 indicative of an early B-type star. The tertiary may be a rapid rotator (V sin i ≈ 300 km s −1 ) or a spectroscopic binary.

The X-ray spectrum ofδOrionis observed by LETGS aboardChandra

“…These changes are about .12 m for the primary eclipse and .07m for the secondary eclipse (Harvin et al 2002). This corresponds to a decrease of about 11% during the primary eclipse and of about 6% during the secondary eclipse.…”

“…This is a change of about 5%. During the observation the phase of the binary system was 0.83−0.02, derived from Harvin et al (2002), or 0.87-0.07, as derived from Mayer et al (2010). This implies that the secondary is in front of the primary during the observation.…”

“…Different stellar mass values are given in the literature. Harvin et al (2002) give M p = 10.3 M as average with R p = 11 R and for the secondary star M s = 5.2 M and R s = 4 R , while Mayer et al (2010) suggest values of M p = 25 M with R s = 16−17 R . The primary and secondary stars are separated by 33 R , equivalent to 3 R p .…”

“…(a) Van Leeuwen (2007). (b) Miller et al (2002), taken from Harvin et al (2002). (c) Miller et al (2002), taken from Voels et al (1989).…”

Ion contribution to the astrophysical important 388.86, 471.32 and 501.56 nm He I spectral lines broadening

“…Izotov et al (2001) use these lines to derive the 4 He abundance in the Metal-deficient Blue Compact Dwarf Galaxies Tol 1214-277 and Tol 65 1 . In the work by Harvin et al (2002) the 667.82 nm line profile has been used to investigate the physical properties of the Massive Compact Binary in the Triple Star System HD 36486 (δ Orionis A). The 587.56 nm spectral line has been used by Labrosse & Gouttebroze (2001) to estimate the formation of the helium spectrum in solar quiescent prominences and, also, by Muglach & Schmidt (2001) to determine the height and dynamics of the quiet solar chromosphere at the limb.…”