EC 10228 – 0905 is the third pulsating sdB + star to be announced. High-speed photometry reveals three periods present in the range P= 139–152 s with semi-amplitudes of less than 10 mmag. All periods show evidence of variable amplitude. Pulsation models have been calculated for sdB stars with logg ∼ 6.0 and Teff ∼ 35 000 K. These all have radial and non-radial modes with periods in the observed range. No unique mode identification is possible at present, but it is clear that at least some of the modes are non-radial. No stars have been predicted to pulsate in this region of the Hertzsprung-Russell (HR) diagram and the cause of the pulsation is not yet understood.
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Stobie et al. (1997) studied this question.