Kepler K2 and TESS observations of two magnetic cataclysmic variables: The new asynchronous polar SDSS J084617.11+245344.1 and Paloma

TL;DR

This study presents Kepler K2 and TESS observations of two magnetic cataclysmic variables, identifying a new asynchronous polar with an unusually long orbital period and clarifying the spin period of Paloma, revealing complex accretion behaviors.

Contribution

First detailed long-duration light curves of two asynchronous polars, including a newly identified system with the longest known orbital period among such stars, and refined spin period measurements.

Findings

SDSS J084617.11+245344.1 is a new asynchronous polar with a 4.64 h orbital period.

Paloma's spin period is confirmed as 2.27 h, resolving previous ambiguities.

The systems exhibit complex beat phenomena affecting accretion geometry and light curve morphology.

Abstract

There have been relatively few published long-duration, uninterrupted light curves of magnetic cataclysmic variable stars in which the accreting white dwarf's rotational frequency is slightly desynchronized from the binary orbital frequency (asynchronous polars). We report Kepler K2 and TESS observations of two such systems. The first, SDSS J084617.11+245344.1, was observed by the Kepler spacecraft for 80 days during Campaign 16 of the K2 mission, and we identify it as a new asynchronous polar with a likely 4.64 h orbital period. This is significantly longer than any other asynchronous polar, as well as all but several synchronous polars. Its spin and orbital periods beat against each other to produce a conspicuous 6.77 d beat period, across which the system's accretion geometry gradually changes. The second system in this study, Paloma, was observed by TESS for one sector and was already known to be asynchronous. Until now, there had been an ambiguity in its spin period, but the TESS power spectrum pinpoints a spin period of 2.27 h. During the resulting 0.7 d spin-orbit beat period, the light curve phased on the spin modulation alternates between being single- and double-humped. We explore two possible explanations for this behavior: the accretion flow being diverted from one of the poles for part of the beat cycle, or an eclipse of the emitting region responsible for the second hump.