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Ensemble Asteroseimology as a Tool for Stellar Population Inference.
Caitlin Jones (University of Birmingham), William J. Chaplin (University of Birmingham), Yvonne P. Elsworth (University of Birmingham), Andrea Miglio (University of Birmingham)
Using a simple metric we have defined based on a band-pass-filtered estimate of the variance of Kepler light curves for red giant stars, I present the results of work designed to determine the fraction of stars which reside in binary systems in a given population. Simulated power spectra have been created for synthetic Kepler fields, with populations of stars across a range of binary fractions generated by the TRILEGAL code. Using fundamental stellar parameters output by this code, I construct power spectra using existing relations for oscillation amplitudes, frequencies, granulation background and shot noise, and also consider the contribution of mixed modes and l = 1 suppression. I will discuss the decisions we have made with regards to the complexity of the simulated power spectra, and the considerations we have had to make in implementing a more realistic model. Analyses of the artificial data are being used to guide my interpretation of the real data, and, although subject to the limitations of our simulations and our understanding of the some properties of the real population, I will present the results of using this ensemble approach to infer the proportion of the real Kepler red giant branch stars which exist in binary systems. While asteroseismology is already used in detecting individual binary systems, this ensemble approach may provide a useful tool for the study of stellar populations as a whole. We also find that our variance metric discriminates between the red giant branch and red clump stars in the real population, implying that the different physics of stars in these two evolutionary states impacts on the observed oscillation power in a way which is detectable even using this simple metric. I will discuss the success of simulating these two evolutionary states, and our plans for future analysis of this phenomenon.