Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 475, Issue 1, Pages 981-998Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stx3079
Keywords
stars: evolution; stars: oscillations
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Funding
- NASA's Science Mission Directorate
- Australian Research Council DP [DP150104667]
- Danish National Research Foundation [DNRF106]
- National Natural Science Foundation of China [11503039, 11427901, 11273007, 10933002]
- Deutscher Akademischer Austauschdienst (DAAD) through the Go8 Australia-Germany Joint Research Co-operation Scheme
- UK Science and Technology Facilities Council (STFC)
- Science and Technology Facilities Council [ST/M00077X/1] Funding Source: researchfish
- STFC [ST/M00077X/1] Funding Source: UKRI
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Stellar models rely on a number of free parameters. High-quality observations of eclipsing binary stars observed by Kepler offer a great opportunity to calibrate model parameters for evolved stars. Our study focuses on six Kepler red giants with the goal of calibrating the mixing-length parameter of convection as well as the asteroseismic surface term in models. We introduce a new method to improve the identification of oscillation modes that exploits theoretical frequencies to guide the mode identification ('peak-bagging') stage of the data analysis. Our results indicate that the convective mixing-length parameter (alpha) is approximate to 14 per cent larger for red giants than for the Sun, in agreement with recent results from modelling the APOGEE stars. We found that the asteroseismic surface term (i.e. the frequency offset between the observed and predicted modes) correlates with stellar parameters (T-eff, log g) and the mixing-length parameter. This frequency offset generally decreases as giants evolve. The two coefficients a(-1) and a(3) for the inverse and cubic terms that have been used to describe the surface term correction are found to correlate linearly. The effect of the surface term is also seen in the p-g mixed modes; however, established methods for correcting the effect are not able to properly correct the g-dominated modes in late evolved stars.
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