KIC 7582608: a newKeplerroAp star with frequency variability

Abstract

We analyse the fifth roAp star reported in the Kepler field, KIC 7582608, discovered with the SuperWASP 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. Spectral analysis confirms the Ap nature of the target, with characteristic lines of rare earth elements present. 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 HR diagram where the pulsations are unstable, an area consistent with observations.