Reding, Joshua S.Hermes, J.J.Vanderbosch, Z.Dennihy, ErikKaiser, B.C.Mace, C.B.Dunlap, B.H.Clemens, J.C.2021-03-122021-03-12Joshua S Reding, J.J. Hermes, Z. Vanderbosch, E. Dennihy, B.C. Kaiser, C.B. Mace, B.H. Dunlap, J.C. Clemens. "An Isolated White Dwarf with 317 s Rotation and Magnetic Emission." The Astrophysical Journal, Volume 894, Issue 1, pp. 19 - 19. https://doi.org/10.3847/1538-4357/ab82391538-4357https://hdl.handle.net/2144/42251We 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 K2 Campaign 10. The behavior is associated with a magnetic (B = 5.0 MG) spot on the stellar surface, making the 317.278 s 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.p. 19en-US© 2020. The American Astronomical Society. All rights reserved.White dwarf starsMagnetic variable starsExtrasolar rocky planetsStellar mergersStellar rotationAstronomical and space sciencesAtomic, molecular, nuclear, particle and plasma physicsPhysical chemistry (incl. structural)Astronomy & astrophysicsArticle10.3847/1538-4357/ab8239562236