Asteroseismology revealing trapped modes in KIC 10553698A

Østensen, R. H. and Telting, J. H. and Reed, M. D. and Baran, A. S. and Németh, Péter and Kiaeerad, F. (2014) Asteroseismology revealing trapped modes in KIC 10553698A. ASTRONOMY & ASTROPHYSICS, 569. ISSN 0004-6361

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Abstract

The subdwarf-B pulsator, KIC 10553698A, is one of 16 such objects observed with one-minute sampling for most of the duration of the Kepler Mission. Like most of these stars, it displays a rich g-mode pulsation spectrum with several clear multiplets that maintain regular frequency splitting. We identify these pulsation modes as components of rotationally split multiplets in a star rotating with a period of ∼41 d. From 162 clearly significant periodicities, we are able to identify 156 as likely components of ℓ = 1 or ℓ = 2 multiplets. For the first time we are able to detect ℓ = 1 modes that interpose in the asymptotic period sequences and that provide a clear indication of mode trapping in a stratified envelope, as predicted by theoretical models. A clear signal is also present in the Kepler photometry at 3.387 d. Spectroscopic observations reveal a radial-velocity amplitude of 64.8 km/s. We find that the radial-velocity variations and the photometric signal have phase and amplitude that are perfectly consistent with a Doppler-beaming effect and conclude that the unseen companion, KIC 10553698B, must be a white dwarf most likely with a mass close to 0.6 M⊙

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