Orbital parameters of the hierarchical triplet system CN Lyn

Abstract

ABSTRACT CN Lyn is an intriguing triplet system that contains three equal-mass components. However, the orbital parameters of this rare triple system are still unknown. By monitoring the system since 2016 October 19, 13 eclipse times have been obtained. We discover that the observed minus calculated (O − C) diagram of CN Lyn shows a cyclical variation with a period of 15.80 (± 0.40) years and a projected semi-major axis of 0.0074 (± 0.0008) days. The orbital properties of the third body are investigated by analysing the light travel time effect. It is found that the third body is orbiting the central binary in an eccentric orbit (e3 ∼ 0.38 (± 0.18)). The orbital inclination is determined to be i3 = 25°, which reveals that the third body is non-coplanar to the orbit of the central eclipsing binary. This is the reason why investigators did not detect a clear periodicity in the radial velocities of the third body. By analysing one low-dispersion spectrum obtained with the 2.16-m telescope in Xinglong station, stellar atmospheric parameters of CN Lyn were derived. It is shown that the system has a low metallicity that is only about 21.5 per cent of the solar metallicity. The rare composition, eccentric orbit, low metallicity, and low orbital inclination of the triplets all indicate that the CN Lyn system can provide valuable information on the formation of multiple star systems, a matter of active research and debate.