GLOBAL ACOUSTIC-OSCILLATIONS ON ALPHA-BOOTIS

Precise radial velocity measurements of the K2 III star α Boo (Arcturus) using a magnetooptical filier (MOF) have been performed. Results of a 2 week observing run using the GHRIL facility at the Nasmith focus of the 4.2 m William Herschel Telescope of the Observatorio del Roque de los Muchachos in 1988 April-May are presented. The noise level obtained for the power spectra of the individual nightly observations is of the order of 1 ms-1. The radial barycentric velocity of Arcturus turns out to be -5021 ± 5 ms-1. When data from the whole run are jointly analyzed, several equispaced peaks in frequency appear in the range of a few μHz, the highest amplitude being some 60 ms-1 at 4.3 μHz (2.7 days). The most probable frequency spacing seems to be 5.0 μHz, while the frequency cutoff is around 80 μHz.