Characterization of the power excess of solar-like oscillations in red giants with Kepler

TL;DR

This study characterizes the oscillation power excess in Kepler red giants, derives new scaling relations for asteroseismic parameters, and investigates the influence of stellar properties and evolutionary stages on oscillation features.

Contribution

It introduces a new method for deriving oscillation amplitudes and provides comprehensive scaling relations, enhancing understanding of red giant oscillations and their dependence on stellar parameters.

Findings

Derived new scaling relations for oscillation parameters.

Confirmed the impact of helium burning on mass-radius relations.

Identified a subset of red giants with weak dipole modes.

Abstract

We aim to describe the oscillation power excess observed in Kepler red giants, and to investigate empirical scaling relations governing these parameters. From these scalings relations, we derive new physical properties of red giant oscillations. Various different methods were compared in order to validate the processes and to derive reliable output values. For consistency, a single method was then used to determine scaling relations for the relevant global asteroseismic parameters: mean mode height, mean height of the background signal superimposed on the oscillation power excess, width of the power excess, bolometric amplitude of the radial modes and visibility of non-radial modes. A method for deriving oscillation amplitudes is proposed, which relies on the complete identification of the red giant oscillation spectrum. The comparison of the different methods has shown the important role of the way the background is modelled. The convergence reached by the collaborative work enables us to derive significant results concerning the oscillation power excess. We obtain several scaling relations, and identify the influence of the stellar mass and the evolutionary status. The effect of helium burning on the red giant interior structure is confirmed: it yields a strong mass-radius relation for clump stars. We find that none of the amplitude scaling relations motivated by physical considerations predict the observed mode amplitudes of red giant stars. In parallel, the degree-dependent mode visibility exhibits important variations. Both effects seem related to the significant influence of the high mode mass of non-radial mixed modes. A family of red giants with very weak dipole modes is identified, and its properties are analyzed.