Period spacings in red giants II. Automated measurement

TL;DR

This paper presents an automated method to measure gravity period spacings in red giants using Kepler data, enabling large-scale analysis of stellar interiors and evolution with high precision.

Contribution

The authors developed a simple, efficient automated technique for measuring mixed-mode period spacings in red giants, extending previous semi-automated approaches and enabling analysis of over 6,100 stars.

Findings

Confirmed the regularity of gravity-mode patterns in red giants.

Revealed the dependence of period spacings on stellar mass and metallicity.

Automated measurement of period spacings for thousands of stars.

Abstract

The space missions CoRoT and Kepler have provided photometric data of unprecedented quality for asteroseismology. A very rich oscillation pattern has been discovered for red giants, including mixed modes that are used to decipher the red giants interiors. They carry information on the radiative core of red giant stars and bring strong constraints on stellar evolution. Since more than 15,000 red giant light curves have been observed by Kepler, we have developed a simple and efficient method for automatically characterizing the mixed-mode pattern and measuring the asymptotic period spacing. With the asymptotic expansion of the mixed modes, we have revealed the regularity of the gravity-mode pattern. The stretched periods were used to study the evenly space periods with a Fourier analysis and to measure the gravity period spacing, even when rotation severely complicates the oscillation spectra. We automatically measured gravity period spacing for more than 6,100 Kepler red giants. The results confirm and extend previous measurements made by semi-automated methods. We also unveil the mass and metallicity dependence of the relation between the frequency spacings and the period spacings for stars on the red giant branch. The delivery of thousands of period spacings combined with all other seismic and non-seismic information provides a new basis for detailed ensemble asteroseismology.