KIC 4768731: a bright long-period roAp star in the Kepler Field

TL;DR

This paper reports the discovery and detailed analysis of a bright, long-period rapidly oscillating Ap star in the Kepler field, revealing stable pulsation amplitudes, variable frequencies, and specific elemental abundance patterns.

Contribution

It provides the first detailed characterization of KIC 4768731 as a long-period roAp star with stable pulsation amplitudes and insights into its spectral line variations and elemental abundances.

Findings

Detected 61.45 d^-1 oscillations with stable amplitudes over 4 years.

Identified elemental abundance variations correlated with brightness phases.

Found no significant radial velocity change over 4 years.

Abstract

We report the identification of 61.45 d^-1 (711.2 mu Hz) oscillations, with amplitudes of 62.6-mu mag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V=9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of T_eff = 8100 +/- 200 K, log g = 4.0 +/- 0.2, [Fe/H] = +0.31 +/- 0.24 and v sin i = 14.8 +/- 1.6 km/s. Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in anti-phase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar T_eff and log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr.