Recently, Dr. LIAO Wenping, Prof. QIAN Shengbang and Dr. LI Linjia from Yunnan Observatories of the Chinese Academy of Sciences obtained new results in the field of close binaries in multiple star systems. They find a special "triplet" system in non-coplanar orbit panel.The results of this study were online published in Monthly Notices of the Royal Astronomical Society.

The eclipsing binary CN Lyn is a very intriguing and rare triplet system in which three components have equal masses. However, it is still unclear whether there is a physical connection between the tertiary and the central eclipsing binary. Researchers want to know what are their physical and orbital characteristics.

In order to study their orbital characteristics and explore the formation and evolution of close binary stars, researchers have continuously monitored the object with 1-m and 60-cm telescopes at Yunnan Observatories in recent five years. They obtained a series of new eclipse times of CN Lyn. Additionally, they collected the light curve data from worldwide photometric surveys, such as SWASP (SuperWide Angle Search for Planets) and KWS (Kamogata/Kiso/Kyoto Wide-field Survey), obtained more eclipse times. Based on all available data, they gave a detailed analysis of the orbital period changes for the system.

Through the analysis of the Observed minus Calculated (O-C) diagram (“O” refers to the observed times of the eclipse egress, while “C” refers to those computed with a linear ephemeris), they detected that the arrival times of the eclipse photos change cyclically when the binary is periodically close to or far away from the Sun, i.e. the light travel time effect, which reveals that it is a physically related "triplet" system, and the third body is orbiting the central eclipsing binary in an eccentric orbit.

Combining the analysis of spectroscopic, photometric and the light travel time effect, researchers find that the third body is non-coplanar to the orbit of the central eclipsing binary. The inclination between the orbital plane of the third body and that of the central eclipsing binary is as high as sixty-five degrees. These results show that the third body drives the formation of the central eclipsing binary by removing angular momentum from it.

Their analysis results of low dispersion spectrum observed with the 2.16-m telescope in Xinglong station show that the metallicity of the system is only about one fifth of the solar metallicity, indicating that it is an old system.

The characteristics of rare composition, non-coplanar orbit, eccentric orbit and low metallicity of the triplets all indicate that the CN Lyn system can provide valuable information on the formation and evolution of binary and multiple star systems, a problem of active research and debate.

Contact:

LIAO, Wenping, Yunnan Observatories, CAS

liaowp@ynao.ac.cn