THE VISUAL ORBIT OF THE 1.1 DAY SPECTROSCOPIC BINARY σ2CORONAE BOREALIS FROM INTERFEROMETRY AT THE CHARA ARRAY

Abstract

We present an updated spectroscopic orbit and a new visual orbit for the double-lined spectroscopic binary σ2 Coronae Borealis (CrB) based on radial velocity measurements at the Oak Ridge Observatory in Harvard, MA and interferometric visibility measurements at the Center for High Angular Resolution Astronomy (CHARA) Array on Mount Wilson in California. σ2 CrB is composed of two Sun-like stars of roughly equal mass in a circularized orbit with a period of 1.14 days. The long baselines of the CHARA Array have allowed us to resolve the visual orbit for this pair, the shortest-period binary yet resolved interferometrically, enabling us to determine component masses of 1.137 ± 0.037 M☉ and 1.090 ± 0.036 M☉. We have also estimated absolute V-band magnitudes of MV(primary) = 4.35 ± 0.02 and MV(secondary) = 4.74 ± 0.02. A comparison with stellar evolution models indicates a relatively young age of 0.1–3 Gyr, consistent with the high-Li abundance measured previously. This pair is the central component of a quintuple system, along with another similar-mass star, σ1 CrB, in a ∼730-year visual orbit, and a distant M-dwarf binary, σ CrB C, at a projected separation of ∼10'. We also present differential proper motion evidence to show that components C & D (ADS 9979C & D) listed for this system in the Washington Double Star Catalog are optical alignments that are not gravitationally bound to the σ CrB system.