Oscillations in Arcturus from WIRE photometry

Observations of the red giant Arcturus (Alpha Boo) obtained with the star tracker on the Wide Field Infrared Explorer (WIRE) satellite during a baseline of 19 successive days in 2000 July-August are analysed. The amplitude spectrum has a significant excess of power at low-frequencies. The highest peak is at about 4.1 micro-Hz (2.8 d), which is in agreement with previous ground-based radial velocity studies. The variability of Arcturus can be explained by sound waves, but it is not clear whether these are coherent p-mode oscillations or a single mode with a short life-time.