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

## TL;DR

This study empirically confirms that most white dwarfs are stable enough in brightness to serve as reliable flux standards in space-based photometry, with some variability linked to specific stellar properties.

## Contribution

The paper provides the first large-scale empirical validation of white dwarfs' stability as flux standards using Kepler data, highlighting key factors affecting their reliability.

## Key findings

- Over 97% of white dwarfs are stable within 1% in Kepler bandpass.
- Binarity, magnetism, and pulsations can cause significant variability.
- White dwarfs hotter than 30,000 K require careful screening.

## 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.