Asteroseismology revealing trapped modes in KIC 10553698A

• Published in: Astronomy and astrophysics (Berlin) 2014-09, Vol.569, p.1-14
• Main Authors: Østensen, R. H., Telting, J. H., Reed, M. D., Baran, A. S., Nemeth, P., Kiaeerad, F.
• Format: Article
• Language: English
• Subjects: Amplitudes; Asymptotic properties; binaries: close; Indication; Photometry; Pulsation; Sampling; stars: individual: KIC 10553698; stars: oscillations; subdwarfs; Trapping; White dwarf stars
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/201423611

The subdwarf-B pulsator, KIC 10553698A, is one of 16 such objects observed with a one-minute sampling rate 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-1. 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⊙.