Østensen, R.H.Jeffery, C.S.Saio, H.Hermes, J.J.Telting, J.H.Vučković, M.Vos, J.Baran, Andrzej S.Reed, M.D.2021-03-152021-03-152020-10-29R.H. Østensen, C.S. Jeffery, H. Saio, J.J. Hermes, J.H. Telting, M. Vučković, J. Vos, A.S. Baran, M.D. Reed. 2020. "PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data." Monthly Notices of the Royal Astronomical Society, Volume 499, Issue 3, pp. 3738 - 3748. https://doi.org/10.1093/mnras/staa31230035-87111365-2966https://hdl.handle.net/2144/42261The Kepler spacecraft observed the hot subdwarf star PHL 417 during its extended K2 mission, and the high-precision photometric light curve reveals the presence of 17 pulsation modes with periods between 38 and 105 min. From follow-up ground-based spectroscopy, we find that the object has a relatively high temperature of 35 600 K, a surface gravity of log g / cm s^-2 = 5.75 and a supersolar helium abundance. Remarkably, it also shows strong zirconium lines corresponding to an apparent +3.9 dex overabundance compared with the Sun. These properties clearly identify this object as the third member of the rare group of pulsating heavy-metal stars, the V366-Aquarii pulsators. These stars are intriguing in that the pulsations are inconsistent with the standard models for pulsations in hot subdwarfs, which predicts that they should display short-period pulsations rather than the observed longer periods. We perform a stability analysis of the pulsation modes based on data from two campaigns with K2. The highest amplitude mode is found to be stable with a period drift, P, of less than 1.1 × 10^−9 s s^−1. This result rules out pulsations driven during the rapid stages of helium flash ignition.p. 3738 - 3748en-USThis article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 499, Issue 3, pp. 3738–3748. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Stars: abundancesStars: chemically peculiarStars: fundamental parametersStars: individual: PHL 417Stars: oscillationsSubdwarfsAstronomical and space sciencesAstronomy & astrophysicsArticle10.1093/mnras/staa3123582946