2001/10/31 by James A. Harvin, J. A. Harvin, Douglas R. Gies +5 · 48 citations
Physics and Astronomy · #Angular momentum #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Binary number #Binary star #Light curve #Orbital elements #Orbital motion #Physics #Primary (astronomy) #Spectral line #Stars #Stellar classification #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/324705
published in The Astrophysical Journal 565(2), 1216-1230 (IOP Publishing) · 27 pages, 15 figures in press, the Astrophysical Journal, February 1, 2002
arxiv created 2001/10/31 · openalex publication_date 2002/02/01 · arxiv updated 2012/08/27 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 cross-correlation 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 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 Δ m = -2.5 log( F s / F p ) = 2.6 ± 0.2 in the UV and Δ m = 2.5 ± 0.3 at 6678 Å. 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 = 67°-77°. 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 δ Ori resides. The i = 67° solution results in masses of M p = 11.2 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.