Institution(s): 1. European Southern Observatory
Hot subdwarf B stars (sdBs) are the stripped cores of red giants located at the bluest extension of the horizontal branch. Several different kinds of pulsators are found among those stars. The mechanism that drives those pulsations is well known and the theoretically predicted instability regions for both the short-period p-mode and the long-period g-mode pulsators match the observed distributions fairly well. However, it remains unclear why only a few percent of the sdB stars pulsate, while most of those stars with otherwise very similar parameters do not show pulsations. From an observers perspective I will review possible candidates for the missing parameter that makes sdB stars pulsate or not (e.g. binarity, abundances, rotation).