Discovery, observations, and modelling of a new eclipsing polar: MASTER OT J061451.70–272535.5

Abstract

We report the discovery of a new eclipsing polar, MASTER OT J061451.70-272535.5, detected as an optical transient by MASTER auto-detection software at the recently commissioned MASTER-SAAO telescope. Time resolved (10-20 s) photometry with the SAAO 1.9-m, and 1.0-m telescopes, utilizing the SHOC EM-CCD cameras, revealed that the source eclipses, with a period of 2.08 hours (7482.9±3.5 s). The eclipse light curve has a peculiar morphology, comprising an initial dip, where the source brightness drops to ∼50% of the pre-eclipse level before gradually increasing again in brightness. A second rapid ingress follows, where the brightness drops by ∼60-80%, followed by a more gradual decrease to zero flux. We interpret the eclipse profile as the result of an initial obscuration of the accretion hot-spot on the magnetic white dwarf by the accretion stream, followed by an eclipse of both the hot-spot and the partially illuminated stream by the red dwarf donor star. This is similar to what has been observed in other eclipsing polars such as HU Aqr, but here the stream absorption is more pronounced. The object was subsequently observed with South African Large Telescope (SALT) using the Robert Stobie Spectrograph (RSS). This revealed a spectrum with all of the Balmer lines in emission, a strong He ii 4686Å line with a peak flux greater than that of Hβ, as well as weaker He i lines. The spectral features, along with the structure of the light curve, suggest MASTER OT J061451.70-272535.5 is a new magnetic cataclysmic variable, most likely of the synchronised Polar subclass.

Discovery of Two Polars from a Crossmatch of ZTF and the SRG/eFEDS X-Ray Catalog

“…The u-band flux is larger during posteclipse due to the absence of pre-eclipse self-absorption by the accretion curtain. Previous observations and numerical simulations have been able to reproduce remarkably similar lightcurves (Breytenbach et al 2019;Zhilkin et al 2019).…”