1998AJ....115.2571H

We present our data set of same-hemisphere, or fixed-phase, observations of five RS Canum Venaticorum and BY Draconis binaries made with the Solar-Stellar Spectrograph at Lowell Observatory. The purpose of this study is to evaluate the level of intrinsic variability in the components of these systems, and to compare it with variability arising from rotational modulation and from long-term, activity cycle-related variability. We obtain fixed-phase observations by observing tidally locked binaries with near-integral-day periods. The fixed-phase observations reveal that the intrinsic variability of the stellar hemispheres is significantly less than the variability induced by rotational modulation or by long-term, activity-cyclic evolution, but only when several spectral features are considered in tandem. Fixed-phase ``flickering'' of the stellar hemispheres is often apparent at a higher level than the rotational or long-term modulation in individual activity indicators. Interpretation of rotational or long-term modulation in active, late-type stars using data that do not allow quantification of the fixed-phase variability of the stars (i.e., data that do not span several rotational periods) is extremely risky.