UU Herculis star

A UU Herculis star is a semiregular variable, somewhat Cepheid-like in its behavior, but that pulsates with two different periods (see double-mode variable) and has occasional standstills. One theory suggests that UU Herculis stars are relatively low-mass post-asymptotic giant branch stars in a stage of evolution in which their spectra mimic those of more massive supergiants.