We report the discovery of short-period photometric variability and modulated Zeeman-split hydrogen emission in SDSSJ125230.93-023417.72 (EPIC 228939929), a variable white dwarf star observed at long cadence in \textit{K2} Campaign 10. The behavior is associated with a magnetic (B=5.0 MG) spot on the stellar surface, making the 317.278-second period a direct measurement of the stellar rotation rate. This object is therefore the fastest-rotating apparently isolated (without a stellar companion) white dwarf yet discovered, and the second found to exhibit chromospheric Balmer emission after GD 356, in which the emission has been attributed to a unipolar inductor mechanism driven by a possible rocky planet. We explore the properties and behavior of this object, and consider whether its evolution may hold implications for white dwarf mergers and their remnants.
@article{arxiv.2003.10450,
title = {An Isolated White Dwarf with 317-Second Rotation and Magnetic Emission},
author = {Joshua S. Reding and J. J. Hermes and Z. Vanderbosch and E. Dennihy and B. C. Kaiser and C. B. Mace and B. H. Dunlap and J. C. Clemens},
journal= {arXiv preprint arXiv:2003.10450},
year = {2020}
}
Comments
11 pages, 6 figures, 3 tables. Accepted for publication in ApJ