PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data. Issue 3 (10th October 2020)

• Record Type: Journal Article
• Authors: Østensen, R H; Jeffery, C S; Saio, H; Hermes, J J; Telting, J H; Vučković, M; Vos, J; Baran, A S; Reed, M D
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 499:Issue 3(2020)
• Page Start: 3738
• Page End: 3748
• Publication Date: 2020-10-10
• Subjects: stars: abundances -- stars: chemically peculiar -- stars: fundamental parameters -- stars: individual: PHL 417 -- stars: oscillations -- subdwarfs; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3123
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The 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 $\log g / {\rm cm\, s^{-2}}\, =\, 5.75$ 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, $\dot{P}$, of less than 1.1 × 10 −9 s s −1 . This result rules out pulsations driven during the rapid stages of helium flash ignition.