The Quadruple System HIP 45734

HIP 45734 is a quadruple system of 2 + 2 architecture located at 68 pc from the Sun. The outer 9″ system A,B has a period of ∼10⁴ yr. The subsystem Aa,Ab is a visual binary with a period of 20.1 yr and an eccentricity of 0.78. Its periastron in 2019.1 was observed spectroscopically, yielding masses (1.10 ± 0.04 and 0.98 ± 0.03 ${{ \mathcal M }}_{\odot }$ ) and orbital parallax, 14.90 ± 0.37 mas. The masses, luminosities, and colors approximately agree with evolutionary models of main-sequence stars. Component Aa has a detectable lithium line, whereas in Ab it is absent. The pair Ba,Bb is a single-lined spectroscopic binary with a period of 0.55552 day and an orbital inclination of ∼45° derived by modeling the rotationally broadened line profile with flat bottom. The mass of Bb is ∼0.4 ${{ \mathcal M }}_{\odot }$ . Star B is chromospherically active (an X-ray source); its flux is modulated with the orbital period by starspots, in addition to occasional flares. The system is probably older than ∼600 Myr; it does not belong to any known moving group.