Astronomers detect new polar cataclysmic variable

Using the ROentgen SATellite (ROSAT), astronomers have discovered a new cataclysmic variable system of the polar subtype. The new polar, which received the designation ZTF J0112+5827, has an orbital period of approximately 81 minutes. The finding is detailed in a research paper published on the arXiv preprint server.

Cataclysmic variables (CVs) are binary star systems composed of a white dwarf and a normal star companion. They irregularly increase in brightness by a large factor, then drop back down to a quiescent state. Polars are a subclass of cataclysmic variables distinguished from other CVs by the presence of a very strong magnetic field in their white dwarfs.

Now, a team of astronomers led by Jiamao Lin of the Sun Yat-sen University in Zhuhai, China, reports the discovery of a new CV of the polar subclass. By examining the X-ray and cyclotron radiation characteristics of a CV candidate ZTF J0112+5827, they confirmed its polar nature.

"In this article, we present an extensive, in-depth investigation of ZTF J0112+5827. We explored its potential X-ray emission and conducted time-domain spectroscopic observations of this target. We report that ZTF J0112+5827 is a newly identified polar," the researchers wrote.

By analyzing the light curve of ZTF J0112+5827, Lin's team identified peculiar double spikes and found that the system has an orbital period of 80.9 minutes. The spikes in the light curve can be explained by the cyclotron radiation emitted by charged particles on the surface of a white dwarf in ZTF J0112+5827.

The astronomers found that the surface magnetic-field strength of the white dwarf in ZTF J0112+5827 is approximately 38.7 MG, which indicates the system's polar nature. It turned out that there is no accretion disk in ZTF J0112+5827, and therefore the main emissions come from the accretion stream and the magnetic-field lines near the surface of the white dwarf. This further supports the polar classification of ZTF J0112+5827.

Based on the collected data, the authors of the paper estimate that the white dwarf in ZTF J0112+5827 has a mass at a level of 0.8 solar masses, while the mass of the donor star is about 0.07 solar masses. The distance to the system was estimated to be some 1,186 light years.

The astronomers added that ZTF J0112+5827 may become a source of gravitational waves (GWs) in the future, detectable by the Laser Interferometer Space Antenna (LISA) mission planned to be launched into space in 2035.

"Future determinations of the component masses of ZTF J0112+5827 would significantly aid in examining its potential to be detected by LISA for GW signals," the scientists concluded.

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