Hitting a New Low: The Unique 28 h Cessation of Accretion in the TESS Light Curve of YY Dra (DO Dra)

Abstract

We present the Transiting Exoplanet Surveying Satellite (TESS ) light curve of the intermediate polar YY Draconis (YY Dra, also known as DO Dra). The power spectrum indicates that while there is stream-fed accretion for most of the observational period, there is a day-long, flat-bottomed low state at the beginning of 2020 during which the only periodic signal is ellipsoidal variation and there is no appreciable flickering. We interpret this low state to be a complete cessation of accretion, a phenomenon that has been observed only once before in an intermediate polar. Simultaneous groundbased observations of this faint state establish that when accretion is negligible, YY Dra fades to g = 17.37 ± 0.12, which we infer to be the magnitude of the combined photospheric contributions of the white dwarf and its red dwarf companion. Using survey photometry, we identify additional low states in 2018-2019 during which YY Dra repeatedly fades to-but never below-this threshold. This implies relatively frequent cessations in accretion. Spectroscopic observations during future episodes of negligible accretion can be used to directly measure the field strength of the white dwarf by Zeeman splitting. Separately, we search newly available catalogs of variable stars in an attempt to resolve the long-standing dispute over the proper identifier of this system.

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

“…The SAP light curve of Paloma shows a gentle parabolic curvature, while the PDCSAP light curve lacks any overall trend. To determine which light curve to use, we follow the general approach of Hill et al (2022) and compare both the SAP and PDCSAP light curves against simultaneous r-band photometry from the Zwicky Transient Facility (ZTF; Bellm et al 2019). We used linear regressions to compare the flux of the seven available ZTF observations with the simultaneous TESS observations and found that the PDCSAP light curve agreed well with the ZTF data, with a coefficient of determination of r 2 P DCSAP = 0.54.…”