Astronomers at the California Institute of Technology (Caltech) and other institutions identified two new polars by examining data from the Spektr-RG (SRG) space observatory and the Zwicky Transient Facility (ZTF). The discovery is detailed in an article published on the arXiv pre-print site on June 9.
CVs are binary star systems that consist of a white dwarf and a normal star partner. They fluctuate in brightness by a huge factor, then return to a quiescent condition. Polars are a kind of cataclysmic variable distinguishable from others by the existence of a strong magnetic field in their white dwarfs.
A team of astronomers led by Caltech's Antonio C. Rodriguez has discovered two new polars, designated ZTFJ0850+0443 and ZTFJ0926+0105. The finding was made by crossmatching the eROSITA Final Equatorial Depth Survey (eFEDS) database with ZTF Data Release 5 forced photometry (DR5).
"Through a crossmatch of the eFEDS dataset with ZTF historical photometry, we uncovered two polars: ZTFJ0850+0443 and ZTFJ0926+0105," the researchers said in their report.
According to the research, ZTFJ0850+0443 is an eclipsing polar with an orbital period of 1.72 hours located 3,260 light years from Earth. Its white dwarf has a mass of around 0.81 solar masses, while the companion star has a mass of about 0.12 solar masses. The data indicate that ZTFJ0850+0443 is most likely a low-field polar with a magnetic field strength of less than 10 MG.
ZTFJ0926+0105 is a non-eclipsing polar with an orbital period of around 1.48 hours at a distance of roughly 1,200 light years. It has a more normal polar magnetic field strength—at least 26 MG. The team was unable to determine the mass of ZTFJ0926+0105 since it is not eclipsed.
The astronomers concluded that their discovery demonstrates the value of the eFEDS survey in augmenting ZTF for detecting new catastrophic variables. Furthermore, they stated that using the ESA's Gaia satellite, they would be able to acquire accurate luminosities of the newly discovered polars. The recently released Gaia Data Release 3 (DR3), which was released on June 13, may be very beneficial in this situation.
"Schwope et al. (2021) found an eclipsing polar using an eROSITA/SRG crossmatch with Gaia utilising a private eRASS dataset," the researchers said.
Rodriguez's team's research is part of a bigger follow-up investigation of the eFEDS/ZTF footprint.Such investigations should help overcome observational biases in prior optical-only searches for catastrophic variables, leading straight to accurate volume-limited CV studies.
Written by:
HASHIR BIN SHAHID
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