EDP Sciences
Free access
Volume 472, Number 2, September III 2007
Page(s) 649 - 652
Section Planets and planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20066987

A&A 472, 649-652 (2007)
DOI: 10.1051/0004-6361:20066987

Discovery of a planet around the K giant star 4 Ursae Majoris

M. P. Döllinger1, 2, A. P. Hatzes3, L. Pasquini1, E. W. Guenther3, M. Hartmann3, L. Girardi4, and M. Esposito3, 5

1  European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
    e-mail: mdoellin@eso.org.de
2  Max-Planck-Institut für Astrophysik, Garching bei München, Germany
3  Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
4  INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
5  Dipartimento di Fisica "E.R. Caianiello", Universita di Salerno, via S. Allende, 84081 Baronissi (Salerno), Italy

(Received 20 December 2006 / Accepted 2 March 2007)

For the past 3 years we have been monitoring a sample of 62 K giant stars using precise stellar radial velocity measurements with high accuracy taken at the Thüringer Landessternwarte Tautenburg. We search for sub-stellar companions to giant stars and try to understand the nature of the diverse radial velocity variations exhibited by K giant stars. We present precise stellar radial velocity measurements of the K1III giant star 4 UMa (HD 73108). These were obtained using the coudé echelle spectrograph of 2-m Alfred Jensch Telescope. The wavelength reference for the radial velocity measurements was provided by an iodine absorption cell. Our measurements reveal that the radial velocity of 4 UMa exhibits a periodic variation of 269.3 days with a semiamplitude K = 216.8 m s-1. A Keplerian orbit with an eccentricity, e = 0.43 $\pm$ 0.02 is the most reasonable explanation for the radial velocity variations. The orbit yields a mass function, $f(m) = (2.05 \pm 0.24) \times 10^{- 7}~M_{\odot}$. From our high resolution spectra we calculate a metallicity of -0.25 $\pm$ 0.05 and derive a stellar mass of 1.23  $M_{\odot} \pm 0.15$ for the host star. The K giant star 4 UMa hosts a substellar companion with minimum mass $M\sin i = 7.1 \pm 1.6 ~M_{\rm Jupiter}$.

Key words: star: general -- stars: variables -- stars: individual: 4 UMa -- techniques: radial velocities -- stars: late-type -- stars: planetary systems

© ESO 2007