Photometric and Ca II H and K spectroscopic variations in nearby sun-like stars with planets. III.

We present the results of an analysis of time-series photometry, Ca II H an d K spectrophotometry, and high-dispersion visible spectra of nine nearby S un-like stars recently identified as having planets. For the six stars whos e presumed planets have orbital periods of less than 4 months (tau Boo, 51 Peg, nu And, rho(1) Cnc, rho CrB, and 70 Vir), sine-curve fits to the photo metric data show no variations with semiamplitude greater than 1 or 2 parts in 10(4). Photometric variations in 47 UMa are similarly small, although o ur photometric data of this star are slightly affected by variability of th e comparison star. Nonvariability at this level of precision is sufficient to rule out surface magnetic activity as the cause of the observed radial-v elocity variations in these seven stars and makes nonradial pulsations unli kely as well. Thus, our photometry provides indirect but strong support for true reflex motions-planets-in these seven stars, but cannot yet so suppor t the planetary hypothesis for the two additional stars, 16 Cyg B and Gl 41 1. Continued photometric monitoring of the short-period systems may soon re sult in the direct detection of these planets in reflected light. We have u sed our photometric fluxes to search for possible transits of the extrasola r planets. Transits definitely do not occur in tau Boo, 51 Peg, nu And, and rho(1) Cnc, and probably do not occur in rho CrB and 70 Vir. Our transit-s earch results are inconclusive for 47 UMa, and we cannot address the issue for 16 Cyg B and Gl 411. The precision of our photometry is sufficient to d etect transits of planets even if they are not gas giants, as currently ass umed, but much smaller objects with rocky compositions. The chance of findi ng at least one transit in the six stars is similar to 40%. We find signifi cant year-to-year photometric variability only in tau Boo, which is not onl y the youngest star in the sample but also the star with the shallowest con vective zone. The interseasonal range in its yearly mean photometric flux i s similar to 0.002 mag, roughly twice the 0.0008 mag decadal variation in t he Sun's total irradiance. Monitoring of the relative Ca II H and K fluxes began between 1966 and 1968 for 51 Peg, tau Boo, rho CrB, and Gl 411, betwe en 1990 and 1993 for 47 UMa, 70 Vir, 16 Cyg B, and rho(1) Cnc, and in 1996 for nu And. The data have been newly recalibrated for improved long-term in strumental stability, resulting in better precision of the Ca n records. Fi ve of the nine stars in this study have little or no detectable year-to-yea r variation in Ca II flux. The remaining four show moderate or pronounced v ariability: tau Boo, whose radial-velocity and photometric variations have comparatively high amplitudes; Gl 411, whose planetary companion was inferr ed astrometrically, not spectroscopically; rho(1) Cnc, which may undergo de cadal cyclic activity; and nu And, which shows moderate year-to-year variab ility. Except for 47 UMa, intraseasonal variability consistent with rotatio n was detected in the Ca n records of all stars. However, the rotation peri ods determined for nu And, 70 Vir, and 16 Cyg B are of low confidence. An e xamination of the recalibrated Ca n records for 51 Peg finds a rotation per iod of 22 days, in contrast to our previous result of 37 days. Ages have be en estimated from the mean Ca n flux and, where possible, the rotation peri od. We find general consistency with the ages determined by others comparin g properties determined from high-resolution spectroscopy to evolutionary m odels, although the uncertainties are, in general, large.