Properties of Sun-like stars with planets: rho(1) Cancri, tau Bootis, and nu Andromedae

Planets have been reported orbiting the Sun-like stars rho(1) Cnc, tau Boo, and upsilon And based on low-amplitude radial velocity variations. We have derived information on the first two stars from analysis of spectra, as well as parallel records of high-precision Stromgren b and y photometry and Ca II H + K fluxes. In the case of rho(1) Cnc, the upper limit (peak to peak) of nondetection of photometric variability at the orbital period is Delta y similar to 0.0004 mag. The possibility of a planetary transit cannot be ruled out completely from the photometric data. Variations of the Ca II fluxes suggest a rotational period of similar to 42 days, in agreement with the inferred upsilon sin i similar to 2 km s(-1). The age of rho(1) Cnc is similar to 5 Gyr, based on its average Ca II flux and a relation between Ca II flux and age. The star tau Boo, unlike the other reported solar-type stars with planets, is relatively young (similar to 2 Gyr) Despite its young age, it is photometrically nonvariable at the orbital period with an amplitude of Delta(b + y)/2 similar to 0.0004 mag (peak to peak); however, small-amplitude interseasonal variability is seen. No planetary transits were found in the photometry, which limits the inclination of the planet's orbital plane to Earth's Line of sight to less than 83 degrees (where 90 degrees is coplanar). The Ca II record shows a weakly significant rotational period near 3.3 days, coincident with the orbital period of the companion. The Ca II record also shows a period of 116 days that has persisted for 30 years and is not seen in the photometric record. The persistence and timescale of this Ca II variation mean that it has no counterpart in Sun-like magnetic activity. The amplitude of the reflex velocity of the parent star (similar to 450 m s(-1)) is much larger than the radial velocity perturbations expected from the presence of either surface inhomogeneities or line-bisector variations. Thus the anticipated perturbations from those stellar effects do not refute the inference of reflex velocities. We have few Ca II flux measurements for upsilon And. Its age and rotational period are estimated to be similar to 5 Gyr and 12 days, respectively. Our results for rho(1) Cnc and tau Boo are consistent with the explanation of planets as the cause of the velocity variations.