Asteroseismology of red giants: photometric observations of Arcturus by SMEI

TL;DR

This study analyzes 2.5 years of photometric data from SMEI to identify stellar oscillations, damping times, and granulation properties of the red giant Arcturus, revealing strong oscillation modes and potential overtones.

Contribution

It provides the first detailed characterization of Arcturus's oscillation modes, damping times, and granulation properties using long-term space-based photometry.

Findings

Detected a strong oscillation mode at 3.51 micro-Hertz

Estimated damping time of 24 days for the mode

Measured granulation timescale of 0.50 days

Abstract

We present new results on oscillations of the K1.5 III giant Arcturus (alpha Boo), from analysis of just over 2.5 yr of precise photometric observations made by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. A strong mode of oscillation is uncovered by the analysis, having frequency 3.51+/-0.03 micro-Hertz. By fitting its mode peak, we are able offer a highly constrained direct estimate of the damping time (tau = 24+/-1 days). The data also hint at the possible presence of several radial-mode overtones, and maybe some non-radial modes. We are also able to measure the properties of the granulation on the star, with the characteristic timescale for the granulation estimated to be 0.50+/-0.05 days.