Modelling Kepler Red Giants in Eclipsing Binaries:Calibrating the Mixing Length Parameter with Asteroseismology

Abstract

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 which 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 about 14% 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 (Teff, 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.

References in corpus (9)

• Modules for Experiments in Stellar Astrophysics (MESA)
• ADIPLS -- the Aarhus adiabatic oscillation package
• Correcting stellar oscillation frequencies for near-surface effects
• A new correction of stellar oscillation frequencies for near-surface effects
• Mixed modes in red giants: a window on stellar evolution
• Testing the asteroseismic scaling relations for Red Giants with Eclipsing Binaries Observed by Kepler
• Improvements to stellar structure models, based on a grid of 3D convection simulations. II. Calibrating the mixing-length formulation
• The Stagger-grid: A grid of 3D stellar atmosphere models - III. The relation to mixing-length convection theory
• The asteroseismic surface effect from a grid of 3D convection simulations. I. Frequency shifts from convective expansion of stellar atmospheres

Cited by in corpus (3)

• Damping rates and frequency corrections of Kepler LEGACY stars
• Carbon Isotope Ratios in M10 Giants
• Mixing-length estimates from binary systems. A theoretical investigation on the estimation errors