Tatarstan Academy of Sciences

An international team of researchers, which included scientists from the Department of Astronomy and Space Geodesy of the Institute of Physics of Kazan Federal University, discovered a rare cataclysmic variable type AM Hound Dogs (AM CVn), located at a distance of 780 light years from Earth.

The double star system, designated SRGeJ045359.9+622444 (SRGeJ0453 for short), was discovered as part of an international program to search for cataclysmic variables, according to data from the eROSITA X-ray telescope of the Spektr-RG space observatory and the ground-based optical system Zwicky Transient Facility (ZTF). The system consists of a white dwarf with a mass of 0.85 solar masses and a helium star – a donor of matter, its mass is 0.044 solar masses.

“AM Hound Dog stars are a rare type of cataclysmic variables. In these ultracompact double systems, the orbits of the stars are very close. The white dwarf accretes matter from a helium-rich companion star. AM Hound Dog star systems are a kind of natural laboratories for studying accretion processes under extreme conditions. It is believed that such systems are formed as a result of the evolution of cataclysmic variables, where there were processes of mass transfer and formation of a common shell. SRGeJ0453 is the first Hound Dog AM-type source discovered by the eROSITE telescope,” explains Head of Laboratory of Space Sources of X-Ray Radiation.

“The unique data obtained by the eROSITA telescope allowed us to detect SRGeJ0453 among a huge number of X-ray sources, while the ZTF optical system helped to identify the first signs of periodicity characteristic of cataclysmic variables. Such synergy between X-ray and optical surveys of the whole sky demonstrates a huge potential and perspective in the study of astrophysical systems,” says Marat Gilfanov, Chief Research Associate at the Institute of Space Research of the Russian Academy of Sciences, who is the head of the scientific working groups of the Russian eROSITA telescope consortium for building maps of the sky, for cataloging X-ray sources, for galaxies, quasars, and tidal disruption events.

To confirm the data obtained by the observatory Spektr-RG and the ground-based space system ZTF, the largest optical telescopes of the world were involved, one of which, having a mirror diameter of 10 meters, is located in the W. M. Keck Observatory, another – in the Palomar Observatory – is 5 meters wide. Thanks to observations on large telescopes it was possible to obtain high-precision optical spectra and confirm the nature of SRGeJ0453 as a cataclysmic variable type AM Hound Dogs.

The Russian-Turkish KFU telescope RTT-150 played a significant role in investigating the nature of the source.

“Thanks to high-precision photometric observations on the RTT-150 telescope, we have confirmed the variability of the luminosity and determined for the first time the orbital period of the SRGeJ0453 system, which is one of the fundamental parameters of cataclysmic variables. It was found that the bodies rotate around each other with a period of 55 minutes,” adds Senior Research Associate of KFU’s Laboratory of Astrophotometry and Stellar Atmospheres Irek Khamitov.

The scientific results obtained by a group of astronomers have been accepted for publication in The Astrophysical Journal. Now the scientific article can be found on the arXiv preprint server.