Solar-like oscillations in the G8 V star τ Ceti^*

¹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal e-mail: [mcunha;Mario.Monteiro]@astro.up.pt
² Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark e-mail: [tct;hans;jcd;srf;karoff;fpp]@phys.au.dk
³ Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney 2006, Australia e-mail: bedding@Physics.usyd.edu.au
⁴ Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, BP 8, 13376 Marseille Cedex 12, France e-mail: bouchy@iap.fr
⁵ Gemini Observatory, 670 N. A'ohoku Pl., Hilo, HI 96720, USA e-mail: tdall@eso.org
⁶ Departamento de Matematica Aplicada da Faculdade de Ciencias da Universidade do Porto, Portugal
⁷ Blackett Laboratory, Imperial College London, South Kensington, London SW7 2BW, UK

Received: 5 August 2008
Accepted: 18 November 2008

Abstract

We used HARPS to measure oscillations in the low-mass star τ Cet. Although the data were compromised by instrumental noise, we have been able to extract the main features of the oscillations. We found τ 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 μHz, 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 (1.6%).