Astronomers discover two new polars

(ORDO NEWS) — Analyzing data from the Spectrum-RG Space Observatory (SRG) and the Zwicky Center for Transients (ZTF), astronomers from the California Institute of Technology (Caltech) and other institutions have discovered two new polars. The discovery is reported in an article published June 9 in the arXiv preprint repository.

Cataclysmic variables (CVs) are binary star systems consisting of a white dwarf and a normal companion star. They irregularly increase brightness to a large extent and then return to a dormant state. Polaris are a subclass of cataclysmic variables, distinguished from other CVs by the presence of a very strong magnetic field in their white dwarfs.

A team of astronomers led by Antonio C. Rodriguez at Caltech has discovered two new pole stars, designated ZTFJ0850+0443 and ZTFJ0926+0105. The discovery was the result of matching the eROSITA Final Equatorial Depth Survey (eFEDS) catalog with ZTF Data Release 5 (DR5) forced photometry.

“We discovered two polars, ZTFJ0850+0443 and ZTFJ0926+0105, by crossing the eFEDS dataset and ZTF archival photometry,” the researchers wrote in their paper.

According to the study, ZTFJ0850+0443 is an eclipsing polar with an orbital period of 1.72 hours, located at a distance of about 3,260 light-years from Earth.

Its white dwarf has a mass of about 0.81 solar masses, and the mass of the companion star is estimated at about 0.12 solar masses. The results obtained suggest that ZTFJ0850+0443 is most likely a low-polarity one with a magnetic field strength of less than 10 MG.

At a distance of about 1,200 light-years is ZTFJ0926+0105, a non-exlibrating polar star with an orbital period of about 1.48 hours. It has a more typical magnetic field strength for polar stars – at least 26 MG. Given that ZTFJ0926+0105 is not eclipsing, the team was unable to measure the mass of its white dwarf.

The astronomers concluded that their discovery shows how important the eFEDS tool, in addition to ZTF, is in discovering new cataclysmic variables.

In addition, they added that ESA’s Gaia satellite would provide accurate data on the luminosity of the newly discovered polar stars. In this context, the recent Gaia Data Release 3 (DR3), published on June 13, can be very helpful.

“Schwope and others have identified an eclipsing pole star by sharing eROSITA/SRG with Gaia using their own eRASS dataset,” the scientists noted.

The study by Rodriguez’s team is part of a larger eFEDS/ZTF follow-up analysis. Such investigations may be useful in overcoming observational errors in previous searches for cataclysmic variables with optics alone and will lead directly to accurate investigations.

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