Zeta^2 Coronae Borealis, a Spectroscopic Triple System Including an Asynchronous Close Binary

Abstract

Using the 1-m telescope at Ritter Observatory, we took 36 observations of zeta^2 Coronae Borealis with a fiber-fed echelle spectrograph. From these observations, zeta^2 CrB was found to be a triple system and a new spectroscopic orbit was calculated. This orbit has two periods, a 1.72357 day period for the inner binary composed of zeta^2 CrB A & B and a 251 day period for the outer binary composed of zeta^2 CrB AB & C. The inner binary is a double-lined spectroscopic binary composed of two B7 V stars. The inner binary's center of mass (zeta^2 CrB AB) describes a long-period single-lined variation identified with the outer binary. The inner binary period is significantly shorter than the 12.5842 day period previously calculated by Abhyankar & Sarma (1966). The inner binary possesses an essentially circular orbit (e = 0.01) while the outer binary has an eccentric orbit (e = 0.48). From the widths of their Si II 6371 A lines, the vsini's were calculated to be 46 +/- 7 km s^-1 for zeta^2 CrB A and 7.5 +/- 2 km s^-1 for zeta^2 CrB B. As zeta^2 CrB A & B have similar masses, their different rotational velocities make this system a sensitive test of synchronization theories.