Solar-like oscillations in red giants observed with Kepler: comparison of global oscillation parameters from different methods

TL;DR

This study compares global oscillation parameters of red giants derived from Kepler data using various methods, finding consistent results within a few percent but highlighting the importance of accounting for stochastic uncertainties in stellar modeling.

Contribution

It systematically evaluates differences in oscillation parameters obtained by multiple methods and quantifies uncertainties due to stochastic oscillation realizations in red giants.

Findings

Results for nu_max and <delta nu> agree within a few percent across methods.

Uncertainties from stochastic realizations are significant and should be considered.

Parameters are robust to analysis method variations.

Abstract

The large number of stars for which uninterrupted high-precision photometric timeseries data are being collected with \textit{Kepler} and CoRoT initiated the development of automated methods to analyse the stochastically excited oscillations in main-sequence, subgiant and red-giant stars. Aims: We investigate the differences in results for global oscillation parameters of G and K red-giant stars due to different methods and definitions. We also investigate uncertainties originating from the stochastic nature of the oscillations. Methods: For this investigation we use Kepler data obtained during the first four months of operation. These data have been analysed by different groups using already published methods and the results are compared. We also performed simulations to investigate the uncertainty on the resulting parameters due to different realizations of the stochastic signal. Results: We obtain results for the frequency of maximum oscillation power (nu_max) and the mean large separation (<delta nu>) from different methods for over one thousand red-giant stars. The results for these parameters agree within a few percent and seem therefore robust to the different analysis methods and definitions used here. The uncertainties for nu_max and <delta nu> due to differences in realization noise are not negligible and should be taken into account when using these results for stellar modelling.