A&A 454, 943-949 (2006)
DOI: 10.1051/0004-6361:20064946

Precise radial velocities of giant stars

I. Stable stars

S. Hekker¹, S. Reffert¹, A. Quirrenbach¹, D. S. Mitchell², D. A. Fischer³, G. W. Marcy⁴ and R. P. Butler<sup>5

1</sup>  Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
    e-mail: saskia@strw.leidenuniv.nl
²  California Polytechnic State University, San Luis Obispo, CA 93407, USA
³  Department of Physics and Astronomy, San Francisco State University, 1600 Holloway, San Francisco, CA 94132, USA
⁴  Department of Astronomy, University of California at Berkeley, 601 Campbell Hall, Berkeley, CA 94720, USA
⁵  Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305, USA

(Received 1 February 2006 / Accepted 18 April 2006 )

Abstract
Context.Future astrometric missions such as SIM PlanetQuest need very stable reference stars. K giants have large luminosities, which place them at large distances and thus the jitter of their photocenters by companions is relatively small. Therefore K giants would be best suited as references. To confirm this observationally a radial velocity survey is performed to quantify the level of intrinsic variability in K giants.
Aims.From this radial velocity survey we present 34 K giants with an observed standard deviation of the radial velocity of less than 20 m/s. These stars are considered "stable" and can be used as radial velocity standards.
Methods.The radial velocity survey contains 179 K giants. All K giants have a declination between and and visual magnitude of 3-6 mag. The Coudé Auxiliary Telescope (CAT) at UCO/Lick Observatory is used to obtain radial velocities with an accuracy of 5-8 m/s. The number of epochs for the 34 stable stars ranges from 11 to 28 with a total timespan of the observations between 1800 and a little over 2200 days.
Results.The observational results of the 34 "stable" stars are shown together with a discussion about their position in the M_V vs. B-V diagram and some conclusions concerning the radial velocity variability of K giants. These results are in agreement with the theoretical predictions. K giants in a certain range of the M_V vs. B-V diagram are suitable reference stars.

Key words: techniques: radial velocity observations -- stars: late-type

© ESO 2006

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