Bayesian peak bagging analysis of 19 low-mass low-luminosity red giants observed with Kepler

TL;DR

This study performs the first detailed peak bagging analysis on 19 Kepler-observed low-mass, low-luminosity red giants, providing extensive asteroseismic data to test stellar models and refine scaling relations.

Contribution

It introduces a novel application of Bayesian peak bagging to a large sample of red giants, yielding the largest set of mode measurements and revealing new seismic phenomena.

Findings

Identified a change in linewidth-temperature relation at the bottom of the RGB.

Detected a linewidth depression around ν_max in all stars.

Confirmed consistency of maximum mode amplitudes with previous analyses.

Abstract

The currently available Kepler light curves contain an outstanding amount of information but a detailed analysis of the individual oscillation modes in the observed power spectra, also known as peak bagging, is computationally demanding and challenging to perform on a large number of targets. Our intent is to perform for the first time a peak bagging analysis on a sample of 19 low-mass low-luminosity red giants observed by Kepler for more than four years. This allows us to provide high-quality asteroseismic measurements that can be exploited for an intensive testing of the physics used in stellar structure models, stellar evolution and pulsation codes, as well as for refining existing asteroseismic scaling relations in the red giant branch regime. For this purpose, powerful and sophisticated analysis tools are needed. We exploit the Bayesian code Diamonds, using an efficient nested sampling Monte Carlo algorithm, to perform both a fast fitting of the individual oscillation modes and a peak detection test based on the Bayesian evidence. We find good agreement for the parameters estimated in the background fitting phase with those given in the literature. We extract and characterize a total of 1618 oscillation modes, providing the largest set of detailed asteroseismic mode measurements ever published. We report on the evidence of a change in regime observed in the relation between linewidths and effective temperatures of the stars occurring at the bottom of the RGB. We show the presence of a linewidth depression or plateau around $\nu_\mathrm{max}$ for all the red giants of the sample. Lastly, we show a good agreement between our measurements of maximum mode amplitudes and existing maximum amplitudes from global analyses provided in the literature, useful as empirical tools to improve and simplify the future peak bagging analysis on a larger sample of evolved stars.