Abstract
The Kepler spacecraft provides new opportinuties to observe long term frequency and amplitude modulations of oscillation modes in pulsating stars. We analyzed more than three years of uninterrupted data obtained with this instrument on the hot B subdwarf (sdB) star KIC 10139564 and found clear signatures of nonlinear resonant mode coupling affecting several multiplets. The observed periodic frequency and amplitude modulations may allow for new asteroseismic diagnostics, providing in particular ways to measure linear growth rates of pulsation modes in hot subdwarf stars for the first time.
Highlights
The Kepler spacecraft is a magnificent instrument to observe long term frequency and amplitude modulations of oscillation modes in pulsating stars
We present the analysis of KIC 10139564 showing that some multiplets clearly have amplitudes and frequencies varying with time in a manner that can be related to nonlinear resonant mode coupling
The frequencies in the two lower-left panels show clear signatures of periodic modulations. These modulations can be related to nonlinear resonant mode coupling mechanisms in pulsating stars. This triplet at 5760 μHz at least qualitatively behaves like if it is in the intermediate regime of the resonance, in which the oscillation modes undergo periodic amplitude and frequency modulations with a time scale of roughly a few times the inverse of the growth rate of the pulsating mode [3]
Summary
The Kepler spacecraft is a magnificent instrument to observe long term frequency and amplitude modulations of oscillation modes in pulsating stars. Among the 18 oscillating sdB stars monitored in the Kepler field, KIC 10139564 is the unique p-mode dominated (V361 Hya type) pulsator with low amplitude g-mode oscillations. Its rotation period is ∼ 26 days according to several multiplets with common frequency spacings found in both the g- and p-mode regions.
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