The Visual Orbit of the 1.1-day Spectroscopic Binary \sigma^2 Coronae Borealis from Interferometry at the CHARA Array

TL;DR

This study combines interferometry and spectroscopy to precisely determine the orbit and masses of the close binary  Coronae Borealis, marking the shortest period binary resolved interferometrically, and explores its system context and stellar properties.

Contribution

The paper provides the first resolved visual orbit for  CrB using interferometry, enabling accurate mass measurements of its Sun-like components and insights into its age and system architecture.

Findings

Component masses of 1.137 1.037 M_sun and 1.090 1.036 M_sun.

Resolved the visual orbit of the shortest period binary interferometrically.

Estimated age of 1-3 Gyr based on stellar evolution models.

Abstract

We present an updated spectroscopic orbit and a new visual orbit for the double-lined spectroscopic binary \sigma^2 Coronae Borealis based on radial velocity measurements at the Oak Ridge Observatory in Harvard, Massachusetts and interferometric visibility measurements at the CHARA Array on Mount Wilson. \sigma^2 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 \pm 0.037 M_sun and 1.090 \pm 0.036 M_sun. We have also estimated absolute V-band magnitudes of MV (primary) = 4.35 \pm 0.02 and MV(secondary) = 4.74 \pm 0.02. A comparison with stellar evolution models indicates a relatively young age of 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, \sigma^1 CrB, in a ~ 730-year visual orbit, and a distant M-dwarf binary, \sigma CrB C, at a projected separation of ~ 10 arcmin. 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 \sigma CrB system.