Over the recent years, the Petersen diagram for classical pulsators, Cepheids
and RR Lyr stars, populated with a few hundreds of new multiperiodic variables.
We review our analyses of the OGLE data, which resulted in the significant
extension of the known, and in the discovery of a few new and distinct forms of
multiperiodic pulsation. The showcase includes not only radial mode pulsators,
but also radial-non-radial pulsators and stars with significant modulation
observed on top of the beat pulsation. First theoretical models explaining the
new forms of stellar variability are briefly discussed.Comment: 5 pages; to be published in the proceedings of the 22nd Los Alamos
Stellar Pulsation Conference "Wide-field variability surveys: a 21st-century
perspective", San Pedro de Atacama, Chile, Nov. 28 - Dec. 2, 201
