  We used HARPS to measure oscillations in the low-mass star tau Cet. Although
the data were compromised by instrumental noise, we have been able to extract
the main features of the oscillations. We found tau Cet to oscillate with an
amplitude that is about half that of the Sun, and with a mode lifetime that is
slightly shorter than solar. The large frequency separation is 169 muHz, and we
have identified modes with degrees 0, 1, 2, and 3. We used the frequencies to
estimate the mean density of the star to an accuracy of 0.45% which, combined
with the interferometric radius, gives a mass of 0.783 +/- 0.012 M_sun (1.6%).
