Dr. LIAO Wenping and her colleagues from Yunnan Observatories of the Chinese Academy of Sciences have found a special quintuple stellar system composed of an active and deep contact binary, single-lined spectroscopic binary and a visual companion. The finding reveals that companion stars play a very important role in the formation and evolution of close binaries.

The results were published in The Astrophysical Journal on March 15.

The researchers used 1-m, 60-cm and 70-cm telescopes at Yunnan Observatories to carry out a long-term multicolor photometric observation, and the 2.16-m telescope in Xinglong station for a spectra observation. Additionally, they collected data and information from worldwide photometric surveys. Based on all the available data, they analyzed and studied the contact binary V410 Aur in detail for the first time.

Although the tertiary component around V410 Aur has been detected in the spectroscopic observations and photometric solutions, it is not clearly seen in the light travel time effect (LTTE).

In order to study the physical and orbital characteristics of the tertiary companion, they analyzed the orbital period changes for the system based on 117 new eclipse times and those collected from the literature. They found a cyclical variation and analyzed it for the LTTE caused by the tertiary companion. Then, they calculated the minimum mass of the third body, which was much larger than the inferred value of spectroscopic investigation.

The results indicated that the spectroscopic tertiary component was a single-lined spectroscopic binary with an unseen component. "We find that V410 Aur is an active and deep contact binary with a relatively large additional light contribution," said Dr. LIAO.

Finally, they calculated the distance parameter of the system by considering Gaia astrometry parameters. They found that the contact binary, single-lined spectroscopic binary and the visual companion detected by Gaia are at practically the same distance from the Sun, which confirmed the physical bond between them. Thus, V410 Aur contains a single-lined spectroscopic binary with a visual companion in a quintuple stellar system.

Their results indicate that the interaction between components in multiple star system can drive not only the formation of close binaries but also the formation of low mass ratio and deep overcontact binaries (such as V410 Aur), which may merger into a rapidly rotating single star and result in bright red nova explosions.