2023RNAAS...7..180W

Zubenelgenubi = α² Librae is a nearby double-lined spectroscopic binary that forms a quadruple system with α¹ Librae. The radial velocity amplitude for the rapidly rotating primary is subject to a systematic uncertainty and as a result only a lower limit q = 0.81 to the mass ratio has been previously reported. Here we present a VLTI/GRAVITY interferometric observation of Zubenelgenubi in which we measured a K band flux ratio of 74.7%, resulting in isochrone masses M_Aa = 1.95 M_⊙ and M_Ab = 1.79 M_⊙ (q = 0.92). The fact that the projected rotational velocities differ by a factor of three despite the similar masses suggests that the stellar spin axes are significantly misaligned in spite of the small semimajor axis a = 0.52 au or alternatively that the primary is a merger product.