Slowly Pulsating B star (SPB)
setâre-ye âhesté tapande-ye gune-ye B
Fr.: étoile B pulsante à longue période
A member of a class of → B stars that are situated along the → main sequence with → spectral types ranging from B2 to B9 and masses from 3 to 7 → solar masses. In the → H-R diagram the SPB group lies below → beta Cephei variables, which are more massive. SPBs show light and line-profile variations that are multi-periodic with periods of the order of days. This variability is understood in terms of non-radial → stellar pulsations, and their → oscillation modes are high-order → g modes. Theoretical models attribute the pulsational nature of SPBs to the → kappa mechanism, acting in the metal → opacity bump at 2 x 105 K. Their g-mode pulsations penetrate deep into the stellar interior, making these objects very promising for → asteroseismology. Several oscillation modes are excited simultaneously, resulting in periodicities on time scales of the order of months or even years. The prototype of this group is 53 Per. First introduced as a distinct class by Waelkens (1991, A&A 246, 453).