SOLARLIKE OSCILLATIONS IN ETA-BOO

We have observed evidence for p-mode oscillations in the GO IV star η BOO (V=2.68). This represents the first clear evidence of solarlike oscillations in a star other than the Sun. We used a new technique which measures fluctuations in the temperature of the star via their effect on the equivalent widths of the Balmer lines. The observations were obtained over six nights with the 2.5 m Nordic Optical Telescope on La Palma and consist of 12 684 low-dispersion spectra. In the power spectrum of the equivalent-width measurements, we find an excess of power at frequencies around 850 μHz (period 20 min) which consists of a regular series of peaks with a spacing of Δv=40.3 μHz. We identify 13 oscillation modes, with frequency separations in agreement with theoretical expectations. Similar observations of the daytime sky show the 5 min solar oscillations at the expected frequencies.