Five-minute P Modes Detected in Doppler Shift Measurement on Alpha Centauri

A spectrophotometer using the principle of optical resonance spectroscopy, designed for the goal of identifying radial and weakly non radial eigenmodes in the five minute range in the case of stars, is discussed. The conclusion of the first test of this new instrument was that if the observation can be photon noise limited (i.e., in total absence of any instrumental source of noise), the five-minute solar oscillation could still be detected by removing the Sun far enough for its magnitude to become zero or one. Such a situation is very closely represented by the observation of Alpha Centauri A, because it is a G2 V star, very similar to the Sun, with a mass of 1.1 in solar unit. Six nights were granted to this program on a 3.6m telescope, from 22 to 28 May 1983. Two and half nights provided over 20 hours of data of photometric quality good enough for analysis.