The Keplerspacecraft observed the hot subdwarf star PHL 417 during its extended K2mission, 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, P̊, of less than 1.1 × 10−9 s s−1. This result rules out pulsations driven during the rapid stages of helium flash ignition.
Physics, Astronomy, and Materials Science
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2020 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Stars: abundances, Stars: chemically peculiar, Stars: fundamental parameters, Stars: individual: PHL 417, Stars: oscillations, Subdwarfs
Østensen, R. H., C. Simon Jeffery, Hideyuki Saio, J. J. Hermes, J. H. Telting, Maja Vučković, Joris Vos, A. S. Baran, and M. D. Reed. "PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data." Monthly Notices of the Royal Astronomical Society 499, no. 3 (2020): 3738-3748.
Monthly Notices of the Royal Astronomical Society