Stellar 5 min Oscillations

Abstract

Abstract.Estimates are given for the amplitudes of stochastically excited oscillations in Main Sequence stars and cool giants; these were obtained using the equipartition between convective and pulsational energy which was originally proposed by Goldreich and Keeley. The amplitudes of both velocity and luminosity perturbation generally increase with increasing mass along the Main Sequence as long as convection transports a major fraction of the total flux, and the amplitudes also increase with the age of the model. The 1.5 M 0 ZAMS model, of spectral type FO, has velocity amplitudes ten times larger than those found in the Sun. For very luminous red supergiants luminosity amplitudes of up to about OTl are predicted, in rough agreement with observations presented by Maeder.

Giant star seismology

“…Stochastically excited mode amplitudes were first estimated by Goldreich and Keeley (1977). Their results were used by Christensen-Dalsgaard and Frandsen (1983b) in a first estimate of the expected mode amplitudes of stochastically excited oscillations across the HR diagram. This was later summarized by in a widely used relation according to which the mode amplitudes roughly scale as L/M.…”

Sounding stellar interiors

“…In cooler stars we expect excitation of solar-like oscillations. Christensen-Dalsgaard and Frandsen (1983) provided a crude prediction of the amplitudes and period ranges. Unfortunately, none of the announced detections has been confirmed by independent teams of observers.…”

Inverse Problems in Asteroseismology

“…As our Sun is not thought of as being particularly exceptional, it was obviously expected that other stars similar to the Sun should also exhibit solar-like oscillations (e.g., Christensen-Dalsgaard 1984). In addition to oscillations in solar-like stars, Christensen-Dalsgaard and Frandsen (1983) further predicted that lowmass giant stars should harbor these kinds of oscillations as well, as these stars also have convective envelopes. Moreover, these stars harbor mixed modes: modes that behave like acoustic oscillations in the envelope and gravity mode oscillations in the core (e.g., Dziembowski et al 2001).…”