Instability strip

RV Tauri variables are also often considered to lie on the instability strip, occupying the area to the right of the brighter Cepheids (at lower temperatures), since their stellar pulsations are attributed to the same mechanism.

When the sufficient energy has been radiated away, overlying the stellar material once again causes the He II layer to contract, and the cycle starts from the beginning.

For most Cepheids, this creates a distinctly asymmetrical observed light curve, increasing rapidly to maximum and slowly decreasing back down to minimum.

In the specific region of more luminous stars above the instability strip are found the yellow hypergiants which have irregular pulsations and eruptions.

The hotter luminous blue variables may be related and show similar short- and long-term spectral and brightness variations with irregular eruptions.