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

B. Smalley, E. Niemczura, S. J. Murphy, H. Lehmann, D. W. Kurtz, D. L. Holdsworth, M. S. Cunha, L. Balona, M. Briquet, H. Bruntt, P. De Cat, P. Lampens, A. O. Thygesen, K. Uytterhoeven

Abstract
We report the identification of 61.45 d−1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, 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 Teff = 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−1. 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 antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teff 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.

Keywords
Asteroseismology, techniques: photometric, stars: abundances, stars: chemically peculiar, stars: individual: KIC 4768731, stars: oscillations

Monthly Notices of the Royal Astronomical Society
Volume 452, Issue 4, Page 3334
2015 October

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia
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