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D.S. Mitchell, S. Frink, A. Quirrenbach (UC San Diego), D.A. Fischer (UC Berkeley)
We have observed a sample of 182 K giants at Lick Observatory over the past 2.5 years, using the Hamilton Spectrograph in conjunction with the Iodine Cell. This yields radial velocities with precisions of about 5-7 m/s. The stars in our sample have been selected from the Hipparcos Catalogue and are believed to be bona-fide single stars. Two thirds of the stars show radial velocity dispersions of less than about 50 m/s, with a peak at about 20 m/s.
Some stars show short-term variations on the order of days that seem to be rather random, whereas other stars show long-term trends of the order of years. The radial velocity curves of some of the stars suggest periodic variations with periods of the order of 1-2 years, which could be due either to non-radial pulsations or the rotational modulation of surface features. We find that redder K giants in general show larger radial velocity variations, whereas we do not find a clear correlation between radial velocity variations and photometric variability.
The author(s) of this abstract have provided an email address for comments about the abstract: dsm@physics.ucsd.edu