KIC 7582608: A new Kepler roAp star with frequency variability

TL;DR

This paper reports the discovery and analysis of KIC 7582608, a new roAp star observed by Kepler, exhibiting high-frequency pulsations, rotational modulation, and frequency variability, with detailed spectral and magnetic field characterization.

Contribution

It presents the first detailed analysis of KIC 7582608, including its pulsation modes, magnetic field, and variability, expanding the understanding of roAp star properties and behaviors.

Findings

High-frequency pulsation at 181.7324 d$^{-1}$ with 1.45 mmag amplitude

Rotational period of 20.4339 days with 7.64 mmag amplitude

Frequency variability observed in pulsations

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 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$\pm$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 $i\sim66^\circ$ and $\beta\sim33^\circ$. 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.