Recently, Prof. MENG Xiangcun and Dr. LI Jiao from Yunnan Observatories of Chinese Academy of Sciences found that sdB star may be the surviving companion in some supernova remnants (SNRs), which provides a new clue for searching the surviving companion in some SNRs. The study was published in Monthly Notices of the Royal Astronomical Society.

It has been found that the expansion of our universe is accelerating. Type Ia supernova (SNe Ia) is the best distance indicator, but the progenitor of SNe Ia is still unknown.

Generally, the progenitor model of SNe Ia involves the accretion of a carbon oxygen white dwarf (COWD) from the normal star (single degenerate model, SD) or the merger of two CO WDs (double degenerate model, DD). Searching the surviving companion star in a supernova remnant (SNR) is a powerful way to distinguish the different models, since the SD model predicts that the companion is left in the SNR, but is not for the DD model.

In this study, researchers discovered that at the moment of supernova explosion, the companion may be a mian-sequence (MS), red-giant (RG) or sdB star, even if the progenitor system is a WD + MS one. Such a result may naturally explain many observational results.

For example, the result may explain why the environment around the famous SN 2011fe and 2014J are so clear, and the UV excess from the collision between supernova ejecta and the RG companion.

In addition, their result predicted that the candidate in supernova remnant N103B would be helium-rich if the candidate is the surviving companion. Especially, researchers suggested that the surviving companion in Kepler’s supernova remnant could be an sdB star, which mainly emits at ultraviolet band, e.g. U or B band.

"If future observation can verify the sdB star as the companion nature of Kepler’s supernova, all the properties of the Kepler’s supernova remnant may be well explained, and the argument between the SD and the DD model would come to an end, which would be a great improvement on the SN Ia science.” said Prof. MENG.

This work was supported by the National Natural Science Foundation of China.