The mass of the planet-hosting giant star β Geminorum determined from its p-mode oscillation spectrum^⋆,⋆⋆

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg Germany
e-mail: artie@tls-tautenburg.de
² Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
³ Department of Physics, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
⁴ Institut für Astronomie, Universität, Wien Türkenschanzstrasse 17, 1180 Vienna, Austria
⁵ 1234 Hewlett Place, Victoria, BC V8S 4P7, Canada
⁶ Institute for Computational Astrophysics, Department of Astronomy and Physics, Saint Mary’s University, Halifax, NS B3H 3C3, Canada
⁷ Observatoire Astronomque du Mont Mégantic, Départment de Physique, Université de Montréal C.P. 6128, Succursale: Centre-Ville, Montréal, QC H3C 3J7, Canada
⁸ Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada
⁹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 102138, USA

Received: 3 April 2012
Accepted: 21 May 2012

Abstract

Aims. Our aim is to use precise radial velocity measurements and photometric data to derive the frequency spacing of the p-mode oscillation spectrum of the planet-hosting star β Gem. This spacing along with the interferometric radius for this star can then be used to derive an accurate stellar mass.

Methods. We use a long time series of over 60 h of precise stellar radial velocity measurements of β Gem taken with an iodine absorption cell at the echelle spectrograph mounted on the 2 m Alfred Jensch Telescope. We also present complementary photometric data for this star taken with the MOST microsatellite spanning 3.6 d. A Fourier analysis is used to derive the frequencies that are present in each data set.

Results. The Fourier analysis of the radial velocity data reveals the presence of up to 17 significant pulsation modes in the frequency interval 10−250 μHz. Most of these fall on a grid of equally-spaced frequencies having a separation of 7.14 ± 0.12 μHz. An analysis of 3.6 days of high precision photometry taken with the MOST space telescopes shows the presence of up to 16 modes, six of which are consistent with modes found in the spectral (radial velocity) data. This frequency spacing is consistent with high overtone radial pulsations; however, until the pulsation modes are identified we cannot be sure if some of these are nonradial modes or even mixed modes. The radial velocity frequency spacing along with angular diameter measurements of β Gem via interferometry results in a stellar mass of M = 1.91 ± 0.09 M_⊙. This value confirms the intermediate mass of the star determined using stellar evolutionary tracks.

Conclusions.β Gem is confirmed to be an intermediate mass star. Stellar pulsations in giant stars along with interferometric radius measurements can provide accurate determinations of the stellar mass of planet hosting giant stars. These can also be used to calibrate stellar evolutionary tracks.