Primary variability period versus absolute W_J, Ks for OGLE-III SRVs in the LMC (crosses) and SMC (circles), with tones of blue and red indicating O- and C-rich sources, respectively. Black lines are best fits to the PL sequences of LPVs in the LMC (from Soszyński et al. 2007, adjusted for a distance modulus μ = 18.49). More precisely, the best fits to sequences C′, C, and D are shown as solid or dashed lines depending on whether they were obtained on the sample of O- or C-rich stars. The dotted lines correspond to sequences A and B, which are referred to as a₃ and a₂ by Soszyński et al. (2007). Thick grey lines are used to exclude periods from the sample (see text and Table 1).