LONG-PERIOD RADIAL-VELOCITY VARIATIONS OF ARCTURUS

High-precision radial velocities of Arcturus measured on 43 occasions from 1981 through 1985 show a 500 m s⁻¹ range. This range is much larger than the external errors of our observations (typically 13 m s⁻¹) confirming the radial-velocity variability of Arcturus that has been previously reported by our group and others based on shorter observational time spans. Using a nonlinear least-squares technique, we have determined a number of multiperiodic models which give a good representation of our velocities simultaneously with those of Smith, McMillan, and Merline (1987).The small-amplitude short-period components of these models could represent the Arcturus analog of the solar five-minute oscillations. Confirmation of this interpretation will require additional observations to help sort out the aliasing problems for these components. Regardless of which aliases are chosen to represent the short-period oscillations, our best-fitting models require the period of the largest-amplitude component to be 640 days or longer. A long-period component could be caused by some surface effect such as convective motions or modulation of the radial velocity by rotation. Alternatively, a long-period component could be caused by motion of Arcturus as it orbits with a low-mass companion around their common center of mass.