Oscillations in red giants

PhD introductory 3-month project

Observations using the Kepler planet-hunting satellite show that low-luminosity red giants undergo oscillations that resemble those excited by convective turbulence in the sun. Analyses of the frequencies of these oscillations reveal that they include a complex combination of pulsation modes, and can provide startling detail about the structures of these stars.

Our work suggests that the complex modes seen in evolved giants (that have reached the top of the red giant or asymptotic giant branches of their evolutionary tracks) are not caused by closely-spaced low-order modes of oscillation, as has been suggested by some researchers.  We observe that the oscillations in luminous red giants change frequency apparently randomly, probably due to the number of convection cells in the envelope changing with time (Wood et al. 2004, Fig. 10). 

This short project will using existing data for a sample of red giant stars from the OGLE II and III, and MACHO surveys. By studying the light curves of these stars, the student will investigate whether we can distinguish between (a) true excitation of discrete modes as in the solar-like oscillations or (b) an oscillator whose frequency varies at random times to a random value within a small range.

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