2006A&A...454..943H

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. From this radial velocity survey we present 34 K giants with an observed standard deviation of the radial velocity of less than 20m/s. These stars are considered ``stable'' and can be used as radial velocity standards. The radial velocity survey contains 179 K giants. All K giants have a declination between -30° and +65° and visual magnitude of 3-6mag. The Coude Auxiliary Telescope (CAT) at UCO/Lick Observatory is used to obtain radial velocities with an accuracy of 5-8m/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. 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.