The Properties of V1016 Orionis, the Eclipsing Binary in the Trapezium System θ ¹ Orionis A

We have obtained high-dispersion spectroscopy, Strömgren y photometry, and Bessel BV measurements of the eclipsing binary V1016 Ori, which is part of the triple system θ 1 Ori A that is one of the four bright Trapezium stars. The analysis of this system has been difficult because of the nebulosity, its 65.433 day orbital period, and its ∼20 hr long primary eclipse. With an eccentricity of 0.644, the orbit’s orientation causes the secondary eclipse to occur at phase 0.121. For our analysis using the Wilson–Devinney program, 17 sets of UBVR primary eclipse photometry from the literature were also incorporated. The zero-age main-sequence B0.5 V primary has a mass of 15.01 ± 0.32 M ⊙ and a radius of 4.20 ± 0.05 R ⊙ . The mass of the G pre-main-sequence secondary is 2.83 ± 0.14 M ⊙ , and its radius is 6.42 ± 0.07 R ⊙ . The primary’s temperature was fixed at 30,500 K, and the secondary’s was determined to be 5552 ± 500 K. Our new ephemeris includes a changing period. The Rossiter–McLaughlin effect, seen in the radial velocities of the primary, is very asymmetric, indicating a very large obliquity angle. Comparison with evolutionary models from the Isochrones and Stellar Tracks series, which is based on the models of the Modules and Experiments in Stellar Astrophysics, indicates an age of about 0.7 Myr.