KIC 7582608: a new Kepler roAp star with frequency variability

D. L. Holdsworth, B. Smalley, D. W. Kurtz, J. Southworth, M. S. Cunha, K. I. Clubb

Abstract
We analyse the fifth rapidly oscillating Ap (roAp) star reported in the Kepler field, KIC 7582608, discovered with the SuperWASP (Wide Angle Search for Planets) project. The object shows a high-frequency pulsation at 181.7324 d⁻¹ (P = 7.9 min) with an amplitude of 1.45 mmag, and low-frequency rotational modulation corresponding to a period of 20.4339 d with an amplitude of 7.64 mmag. Spectral analysis confirms the Ap nature of the target, with characteristic lines of Eu ii, Nd iii and Pr iii present. The spectra are not greatly affected by broadening, which is consistent with the long rotational period found from photometry. From our spectral observations we derive a lower limit on the mean magnetic field modulus of 〈B〉 = 3.05 ± 0.23 kG. Long cadence Kepler observations show a frequency quintuplet split by the rotational period of the star, typical for an oblique pulsator. We suggest the star is a quadrupole pulsator with a geometry such that i ∼ 66° and β ∼ 33°. We detect frequency variations of the pulsation in both the WASP and Kepler data sets on many time-scales. Linear, non-adiabatic stability modelling allows us to constrain a region on the Hertzsprung–Russell diagram where the pulsations are unstable, an area consistent with observations.

Keywords
asteroseismology - techniques: photometric - stars: chemically peculiar - stars: individual: KIC 7582608 - stars: oscillations

Monthly Notices of the Royal Astronomical Society
Volume 443, Page 2049
September 2014

DOI: 10.1093/mnras/stu1303
ADS Bibliographic code: 2014MNRAS.443.2049H