Probing Red Giant Interiors with G-Dominated Mixed Modes I: The Cases of KIC 9145955, KIC 9970396, KIC 9882316 and KIC 11968334

TL;DR

This study uses g-dominated mixed modes in Kepler red giants to probe their core structures, revealing a possible correlation between convective overshooting and stellar mass, and precisely measuring core rotation rates.

Contribution

It introduces a mode-identification technique for distinguishing p- and g-dominated modes, improving asteroseismic modeling of red giant interiors.

Findings

Convective overshooting parameter increases with stellar mass.

Stars over 1.4 solar masses require higher overshooting parameter.

Core rotation rate of KIC 11968334 is precisely measured.

Abstract

We perform a detailed asteroseismic analysis of four red giants observed by Kepler: KIC 9145955, KIC 9970396, KIC 9882316, and KIC 11968334. Our study is based on individual oscillation frequencies, with particular emphasis on gravity-dominated (g-dominated) mixed modes. These modes are highly sensitive to the deep stellar interior and serve as powerful diagnostics of core structure, convective overshooting, and internal rotation. Moreover, surface effects have minimal impact on g-dominated mixed modes. To ensure accurate frequency matching between observations and theoretical models, we apply a mode-identification technique that effectively distinguishes p-dominated from g-dominated modes. Although a definitive confirmation of this trend requires a substantially larger asteroseismic sample, our best-fitting models suggest that the derived convective overshooting parameter ($f_{ov}$) increases with stellar mass. In particular, within our sample the star with a mass exceeding $1.4M_{\odot}$ requires $f_{ov} > 0.01$, whereas lower-mass red giants tend to have $f_{ov}$ <0.01. In addition, the average core rotation rate of KIC 11968334 is precisely determined to be $0.7409\pm0.0113 \mu$Hz from the asteroseismic model.