Optical Interferometric Observations of θ1 Orionis C from NPOI and Implications for the System Orbit

With the Navy Prototype Optical Interferometer (NPOI), the binary system θ1 Orionis C, the most massive member of the Trapezium, was spatially resolved over a time period extending from 2006 February to 2007 March. The data show significant orbital motion over the 14 months, and after combining the NPOI data with previous measurements of the system from the literature, the observations span 10 yr of the orbit. Our results indicate that the secondary did not experience an unusually close periastron passage this year, in contradiction to the prediction of a recently published, highly eccentric ~11 yr orbit. Future observations of this source will be required to improve the orbital solution. Possible implications of the results in terms of system distance are discussed, although a main conclusion of this work is that a definitive orbit solution will require more time to obtain sufficient phase coverage and that the interaction effects expected at periastron did not occur in 2007.