Slowly-Pulsating B-type (SPB) stars

The slowly-pulsating B-type (SPB) stars (occasionally 53 Per variables) are mid-B-type dwarfs and subgiants that, like the β Cephei variables, are unstable to pulsation because of an opacity bump caused by iron-group elements. Unlike the β Cephei variables, the pulsations are high-order gravity modes, like the γ Doradus variables but with a different driving mechanism.

The SPBs usually pulsate with multiple periods longer than about 1 day.

• 53 Persei