2009ApJ...707L..73M

Analytical relations are derived for the amplitude of astrometric, photometric, and radial velocity (RV) perturbations caused by a single rotating spot. The relative power of the starspot jitter is estimated and compared with the available data for κ¹ Ceti and HD 166435, as well as with numerical simulations for κ¹ Ceti and the Sun. A Sun-like star inclined at i = 90° at 10 pc is predicted to have an rms jitter of 0.087 µas in its astrometric position along the equator, and 0.38 m/s in radial velocities. If the presence of spots due to stellar activity is the ultimate limiting factor for planet detection, the sensitivity of SIM Lite to Earth-like planets in habitable zones is about an order of magnitude higher than the sensitivity of prospective ultra-precise RV observations of nearby stars.