A more complex vibration in pulsating stars than the fundamental mode. For example, in the first overtone mode of radial pulsation, a shell of material within the star periodically swells and contracts. The second overtone arises when two concentric shells are expanding and contracting. Most Cepheid variables pulsate in the fundamental mode but some also pulsate in the first overtone as well; these are termed beat Cepheids. Some rare cases, such as Polaris, pulsate only in the first overtone. Cepheids which are thought to pulsate only in the second overtone have been found in the Small Magellanic Cloud. See also Pulsation Mode.
Subjects: Astronomy and Astrophysics.