Asteroseismology based on high time-resolution and high dispersion spectroscopy

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The vertical wavelengths of the oscillations found in roAp stars are so short that the amplitude and phase of the variation of each spectroscopic line are highly dependent on the level of the line profile. We carried out a numerical simulation of line-profile variation by taking account of the finite thickness of the line-forming layer. We demonstrated how effective this treatment is.Barycentric corrections made to the timing of Kepler observations break the regular time-sampling of the data. A consequence is that Nyquist aliases are split into multiplets that can be identified by their shape. We provided an analytical derivation of the phenomenon, alongside demonstrations with simulated and real Kepler data.Observations indicate that a circumstellar disk is formed around a Be star while the stellar rotation is below the break-up velocity. I proposed a working hypothesis to explain this mystery by taking account of the effect of leaky waves upon angular momentum transfer.