# Convective-core overshoot and suppression of oscillations: Constraints from red giants in NGC6811

## TL;DR

This study uses Kepler data to analyze oscillations in red giants of NGC6811, revealing insights into their core processes, including convective overshoot, and challenging recent theories on mode suppression.

## Contribution

It provides new observational constraints on convective-core overshoot and mode suppression in red giants, based on detailed asteroseismic analysis of cluster stars.

## Key findings

- Stars are helium-core-burning red giants.
- Two groups with different oscillation spectra identified.
- Constraints on convective-core overshoot derived.

## Abstract

Using data from the NASA spacecraft Kepler, we study solar-like oscillations in red-giant stars in the open cluster NGC6811. We determine oscillation frequencies, frequency separations, period spacings of mixed modes and mode visibilities for eight cluster giants. The oscillation parameters show that these stars are helium-core-burning red giants. The eight stars form two groups with very different oscillation power spectra; the four stars with lowest Delta_nu-values display rich sets of mixed l=1 modes, while this is not the case for the four stars with higher Delta_nu. For the four stars with lowest Delta_nu, we determine the asymptotic period spacing of the mixed modes, DeltaP, which together with the masses we derive for all eight stars suggest that they belong to the so-called secondary clump. Based on the global oscillation parameters, we present initial theoretical stellar modeling which indicate that we can constrain convective-core overshoot on the main sequence and in the helium-burning phase for these ~2M_sun stars. Finally, our results indicate less mode suppression than predicted by recent theories for magnetic suppression of certain oscillation modes in red giants.