PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2020
- DOI:
- 10.1093/mnras/staa3123
- arXiv:
- arXiv:2010.02978
- Bibcode:
- 2020MNRAS.499.3738O
- Keywords:
-
- stars: abundances;
- stars: chemically peculiar;
- stars: fundamental parameters;
- stars: individual: PHL 417;
- stars: oscillations;
- subdwarfs;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- MNRAS Accepted 5 October 2020, 12 pages, 9 figures