Oscillation mode lifetimes of red giants observed during the initial and first anticentre long run of CoRoT

TL;DR

This study measures the lifetimes of oscillation modes in red giants using long-term CoRoT data, demonstrating the effects of data length and noise, and confirming theoretical predictions about mode lifetime dependencies.

Contribution

It introduces a method to correct mode lifetime measurements for observational biases and provides empirical validation of theoretical models for red giant oscillations.

Findings

Mode lifetimes depend on frequency and mode degree.

Data length, gaps, and noise significantly affect lifetime measurements.

Corrected measurements align with theoretical predictions.

Abstract

Long timeseries of data increase the frequency resolution in the power spectrum. This allows for resolving stochastically excited modes with long mode lifetimes, as well as features that are close together in frequency. The CoRoT fields observed during the initial run and second long run partly overlap, and stars in this overlapping field observed in both runs are used to create timeseries with a longer timespan than available from the individual runs. We aim to measure the mode lifetimes of red giants and compare them with theoretical predictions. We also investigate the dependence of the mode lifetimes on frequency and the degree of the oscillation modes. We perform simulations to investigate the influence of the gap in the data between the initial and second long run, the total length of the run and the signal-to-noise ratio on the measured mode lifetime. This provides us with a correction factor to apply to the mode lifetimes measured from a maximum likelihood fit to the oscillation frequencies. We find that the length of the timeseries, the signal-to-noise ratio and possible gaps do have a non-negligible effect on the measurements of the mode lifetime of stochastically excited oscillation modes, but that we can correct for it. For the four stars for which we can perform a fit of the oscillation frequencies, we find that the mode lifetimes depend on frequency and on degree of the mode, which is in quantitative agreement with theoretical predictions.