EDP Sciences
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Volume 457, Number 1, October I 2006
Page(s) 335 - 341
Section Planets and planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20065445

A&A 457, 335-341 (2006)
DOI: 10.1051/0004-6361:20065445

Confirmation of the planet hypothesis for the long-period radial velocity variations of $\beta$ Geminorum

A. P. Hatzes1, W. D. Cochran2, M. Endl2, E. W. Guenther1, S. H. Saar3, G. A. H. Walker4, S. Yang5, M. Hartmann1, M. Esposito1, D. B. Paulson6 and M. P. Döllinger7

1  Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
    e-mail: artie@tls-tautenburg.de
2  McDonald Observatory, The University of Texas at Austin, Austin, TX 78712, USA
3  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138
4  1234 Hewlett Place, Victoria, BC, V8S 4P7, Canada
5  Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6, Canada
6  Planetary Systems Branch, Code 693, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
7  European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany

(Received 18 April 2006 / Accepted 16 June 2006)

Aims.Our aim is to confirm the nature of the long period radial velocity measurements for $\beta$ Gem first found by Hatzes & Cochran (1993).
Methods.We present precise stellar radial velocity measurements for the K giant star $\beta$ Gem spanning over 25 years. An examination of the Ca II K emission, spectral line shapes from high resolution data ( $R = 210\,000$), and Hipparcos photometry was also made to discern the true nature of the long period radial velocity variations.
Results. The radial velocity data show that the long period, low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. Furthermore, the Ca II K emission, spectral line bisectors, and Hipparcos photometry show no significant variations of these quantities with the radial velocity period. An orbital solution assuming a stellar mass of 1.7 $M_\odot$ yields a period, P = 589.6 days, a minimum mass of 2.3 $M_{\rm Jupiter}$, and a semi-major axis, a = 1.6 AU. The orbit is nearly circular (e = 0.02).
Conclusions.The data presented here confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). $\beta$ Gem is one of six intermediate mass stars known to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common.

Key words: star: individual: $\beta$ Gem -- techniques: radial velocities -- planetary systems

© ESO 2006