2004JAVSO..32....9P

RV Tauri (RVT) variables are old, low-mass, yellow supergiant pulsating variable stars whose light curves show alternating deep and shallow minima. They are related to Population II Cepheid (CW) variables and to yellow semiregular (SRD) variables. We describe the results of self-correlation analysis of a large body of visual photometry of 9 bright RVT and SRd variables, namely AG Aur, AV Cyg, SU Gem, AC Her, SX Her, TT Oph, UZ Oph, TX Per, and V Vul. Self-correlation analysis, which probes the cycle-to-cycle behavior of a variable, averaged over a dataset, has proven to be a useful tool for investigating these stars, because their classification is actually based on their cycle-to-cycle behavior. Our results are consistent with those of our analysis of RVT and CW variables in the Large Magellanic Cloud (Percy, Hosic, and Leigh 2003), and support the view that the RV Tauri phenomenon has two dimensions: (i) the relative depths of the primary and secondary minima, and (ii) the number of cycles over which the alternating minima correlate. If the RVT phenomenon is due to the presence of two pulsation modes, then these dimensions are equivalent to: (i) the relative amplitudes of the two modes, and (ii) the closeness of the ratio of the pulsation periods to 2:1. There is therefore a "spectrum" of behavior from CW to RVT to SRd, depending on the values of these two parameters.