as tr o - ph / 9 41 10 16 3 N ov 9 4 Solar - like oscillations in

We have observed evidence for p-mode oscillations in the G0 IV star Boo (V = 2:68). This represents the rst clear evidence of solar-like oscillations in a star other than the Sun. We used a new technique which measures uctuations in the temperature of the star via their eeect 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 12684 low-dispersion spectra. In the power spectrum of the equivalent-width measurements, we nd an excess of power at frequencies around 850 Hz (period 20 minutes) which consists of a regular series of peaks with a spacing of = 40:3 Hz. We identify thirteen oscillation modes, with frequency separations in agreement with theoretical expectations. Similar observations of the daytime sky show the ve-minute solar oscillations at the expected frequencies. 1 1. INTRODUCTION The remarkable success of helioseismology in probing the interior of the Sun has motivated many attempts to detect analogues of the solar ve-minute oscillations in other stars. The measurement of oscillation frequencies would place important constraints on stellar model parameters and provide a strong test of evolutionary theory. However, despite several claims in the literature, it is fair to say that there has been no unambiguous detection of solar-like oscillations in any star except the Sun. The diiculty with observing stellar oscillations lies in their very small amplitudes. Most previous attempts have used high-resolution spectroscopy to look for periodic Doppler shifts in spectral features (Gelly A second method is diierential CCD photom-etry, which measures uctuations in the integrated stellar luminosity (Gilliland et al. 1993). The observations reported here use a new technique which, like diierential CCD photometry, exploits the fact that stellar oscillations are acoustic waves and hence aaect the temperature of the star. We measure these temperature uctuations, not via changes in the stellar luminosity, but rather through their eeect on the equivalent widths of the Balmer lines. The equivalent-width method is complementary to diierential photometry, since the latter is applied to stellar clusters while the new method is used to observe isolated bright stars. However, unlike photome-try, the measurement of equivalent widths is insensitive to atmospheric scintillation, because one is measuring the strength of a line relative to that of the continuum. Indeed, from several hours of test observations of Cen taken with the ESO New Technology Telescope in July …