Red dwarf-red giant binary pair of stars found

The discovery, which is due to be published in the Monthly Notices of the Royal Astronomical Society later this month reports that the researchers have identified an ultra-cool companion to the bright red giant star Eta Cancri, using the UK Infrared Telescope in Hawaii and the Sloan Digital Sky Survey in New Mexico.

Ultra-cool dwarfs are star-like objects, but with surface temperatures much cooler than normal stars -- less than 2000 degrees (compare this to the Sun's temperature of about 6000 degrees). Exotic dusty clouds condense out at such ultra-cool temperatures, leading to objects that are hybrid in nature -- with characteristics of both stars and giant planets like Jupiter.

Red giant stars are much bigger and more massive, and are evolving towards the end of their life (our Sun will become a red giant in about 5 billion years). But as they evolve towards their demise they can reveal information about their age and chemical composition.

Against the backdrop of unknown ultra-cool cloudy physics, the new binary is providing a beacon to test our understanding. Both members will have a shared history and origin, and the team's detailed studies of the giant star have been able to reveal the age and chemical composition of the ultra-cool companion Eta Cancri B.

The discovery was made by ZengHua Zhang, a researcher previously at the Yunnan Observatory of The Chinese Academy of Sciences and now studying for his PhD with Dr David Pinfield at the University of Hertfordshire Centre for Astrophysics Research.

"China sees it as crucial to pursue excellence in cutting edge astrophysics as part of its fast growing research enterprise" said ZengHua Zhang. "Collaboration with overseas experts is very important to us, and that is why I have come to do my PhD in the University of Hertfordshire."

In the infrared, the "UKIRT Infrared Deep Sky Survey" on the UK Infrared Telescope in Hawaii detected the warm glow of Eta Cancri B. And in the optical (where the human eye is sensitive) the "Sloan Digital Sky Survey" measured its characteristic red colour.

"The power of these large scale sky surveys is yielding many fascinating low temperature discoveries, previously beyond our reach," said Dr. Pinfield. "You have to search for needles in a haystack, but rare finds like Eta Cancri B provide a guiding light for our understanding of the complex atmospheres that enrobe the Sun's coolest neighbours as well as warm giant planets."

The team is making further studies of this crucial binary pair using some of the world's largest telescopes, to fully explore it's qualities as a defining benchmark system.