1 Introduction

Doppler studies with high-precision instruments and reduction algorithms have been refined dramatically, mainly in the framework of the search for exoplanets. These refinements have led to a breakthrough in the observations of solar-type oscillations, which have now been found repeatedly (Procyon, Martic et al. 1999; $\beta$ Hyi, Bedding et al. 2001; $\alpha$ Cen A, Bouchy & Carrier 2001; $\delta$ Eri, Carrier et al. 2002). The signal-to-noise ratio (S/N) in the oscillation frequency spectra is, for each of these cases, so good that the resemblance with the solar oscillation spectrum is obvious.

Observations of solar-like oscillations in the giant star $\alpha~$UMa have been claimed by Buzasi et al. (2000), based upon space photometry gathered with the star tracker of the WIRE satellite. However, the interpretation of these reported oscillations frequencies is not straightforward. Guenther et al. (2000) find a possible solution in terms of a sequence of radial modes with a few missing orders for a star of 4.0-4.5 $M_{\odot}$. The interpretation is not supported by theoretical calculations by Dziembowski et al. (2001). Velocity observations of Arcturus provide evidence for solar-type oscillations with periods from 1.7 to 8.3 days and a frequency separation of evenly spaced modes of $\Delta \nu \sim 1.2\ \mu$Hz (Merline 1999). WIRE data (Retter et al. 2002), however, points to an excess power at 4.1 $\mu$Hz and a frequency spacing of $\Delta \nu = 0.8~\mu$Hz.

In this Letter, we provide clear evidence for the presence of solar-type oscillations in the giant star $\xi$ Hya (m_V=3.54). This star has a mass close to $M = 3.0~\hbox{$M_{\odot}$ }$, and is thus considerably heavier than the Sun. Moreover, its luminosity amounts to $L \sim 61~\hbox{$L_{\odot}$ }$ and its effective temperature $\ensuremath{T_{\rm eff}} = 5000$ K, which places the star among the giants. In the current Letter we present the first results of our study. Detailed modelling will be presented, when completed, in a subsequent paper.