When flux standards go wild: white dwarfs in the age of Kepler

Abstract

White dwarf stars have been used as flux standards for decades, thanks to their staid simplicity. We have empirically tested their photometric stability by analyzing the light curves of 398 high-probability candidates and spectroscopically confirmed white dwarfs observed during the original Kepler mission and later with K2 Campaigns 0−8. We find that the vast majority (>97 per cent) of non-pulsating and apparently isolated white dwarfs are stable to better than 1 per cent in the Kepler bandpass on 1-hr to 10-d timescales, confirming that these stellar remnants are useful flux standards. From the cases that do exhibit significant variability, we caution that binarity, magnetism, and pulsations are three important attributes to rule out when establishing white dwarfs as flux standards, especially those hotter than 30 000 K.

White Dwarf Rotation as a Function of Mass and a Dichotomy of Mode Line Widths: Kepler Observations of 27 Pulsating DA White Dwarfs through K2 Campaign 8

“…used for our extractions in Table 2, along with the CCD channel from which the observations were read out. Channel 48 and especially Channel 58 are susceptible to rolling band pattern noise, which can lead to long-term systematics in the light curve (see Section 3 of Hermes et al 2017a and references therein).…”

The occurrence of planets and other substellar bodies around white dwarfs using K2

“…Secondly, some targets have a main-sequence (MS) companion that contributes a significant fraction of the observed flux. Therefore, the total sample has been cross-correlated with a list of high-probability and confirmed white dwarfs (Hermes et al 2017) 1 . Lastly, there are a dozen duplicate objects within the sample.…”

An Isolated White Dwarf with 317 s Rotation and Magnetic Emission

“…These data are a unique resource for exploring white dwarf variability; the quality and quantity of observations taken are unparalleled. There are a variety of isolated white dwarf variable types represented within the Kepler sample: Vanderburg et al (2015) discovered transiting exoplanetary debris, Hermes et al (2017b) investigate pulsators, Hallakoun et al (2018) explore possible debris accretion, and Maoz et al (2015) and Hermes et al (2017a) discuss objects that present variation likely due to surface spots.…”