SIMBAD references

We have used self-correlation–a simple form of variogram analysis–to study 33 RV Tauri and related stars in the LMC, using MACHO data. We confirm the periods and classifications of Alcock et al. and discuss a few stars of special interest. We find that self-correlation is a useful adjunct to Fourier analysis, especially for stars whose classification is based on their cycle-to-cycle behavior. In particular, it can identify stars whose behavior is more complicated than the standard ``alternating deep and shallow minima'' and begin to investigate the question of whether the Population II Cepheids, the RV Tauri variables, and the SRd variables form a continuous sequence from periodicity to irregularity. Our results also emphasize that the RV Tauri phenomenon has two dimensions: the relative depths of adjacent minima and the number of cycles over which the alternating minima persist.