Extremely rare binary stars discovered in Brno

Brno, 26 June 2016

Brno team of astrophysicists has found several candidates for the extremely rare binary stars whose one component is a pulsating variable star RR Lyrae. If the interpretation is correct, team results suggest that the second component of such systems can be red dwarfs, as well as black holes. The work also showed that the orbital period of the binary stars can be much longer than originally anticipated. The study, which significantly expands the list of these rare objects, is a major success.

Team around dr. Jiri Liska, from the Department of Theoretical Physics and Astrophysics at Masaryk University in Brno, and dr. Marek Skarka, MU graduate, currently at the Academy of Sciences in Budapest, managed to identify 11 candidates for extreme rare binaries. These rare star systems contain a pulsating variable RR Lyrae stars, which play a vital role in astrophysics, for example, in determining distances. Their finding the binaries and independent determination of their masses is an important step towards understanding the properties of these stars.

Besides the 20 candidate binaries discovered last year by a team of Chilean astronomers in the Galactic bulge, the publication of the 11 new candidates is the second largest list of its kind. The Brno astrophysicists, however, analyzed the Galactic field stars, which is still rare feat. For the discovery and analysis of potential new binaries authors took advantage of the fact that the orbiting RR Lyrae star around an invisible companion, causes apparently a small cyclic changes in its pulsation period - accelerating or delaying the observed light changes (a phenomenon known as Light-travel time effect). The authors also compiled a database of all known candidates and additionally conducted a detailed analysis of binarity of another currently the most promising candidate object - TU UMa (O-C diagram at right). Their work was therefore divided into two separate studies published in prestigious journals - the British Monthly Notices of the Royal Astronomical Society and European Astronomy & Astrophysics.

Brno research group also showed that binaries with RR Lyrae component can have no orbital period of only several years, as by this time expected, but even a few dozen, in some cases more than a hundred years! The survey weights of unobserved companions also suggests that the second component of binaries could be both red dwarfs (very small, cool stars) and degenerate remnants of stars such as white dwarfs or neutron stars. Perhaps the most interesting candidates are the stars with the designation SS Cet and AT Ser located in Cetus and Serpens. Their weights suggest that their companions are neutron stars or even black holes.

Contact the head of the observation:
dr. Jiří Liška , jiriliska@post.cz
dr. Marek Skarka , marek.skarka@gmail.com

More information in published studies: Cyclic variations in O-C diagrams of field RR Lyrae stars as a result of LiTE a New analysis of the light time effect in TU Ursae Majoris

New on-line databasis of known candidates

Mgr. Lenka Zychová, zychova@physics.muni.cz