During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, we have serendipitously discovered a new class of low amplitude, multimode sdB pulsators with periods of the order of an hour. These periods are more than a factor of ten longer than those of previously known multimode sdB pulsators (EC 14026 stars), implying that they are due to gravity modes rather than pressure modes. The longer period pulsators are found only among cooler sdB stars, where they are surprisingly common. The iron opacity instability that drives the short period EC 14026 stars is effective only in hot sdB's, leaving the driving mechanism for the deeper gravity modes in cool sdB's currently unknown. We present the first observational results for our newly identified sdB variables, and discuss possible implications.

A new class of pulsating subdwarf B stars has recently been announced by Green and coworkers. Here we present a follow-up paper describing our observations and the pulsation structure of the class prototype PG 1716+426. The oscillations are multiperiodic with periods between 0.8 and 1.4 hr (180-340 Hz) and semiamplitudes less than 0.2%. We also observe that the periods and amplitudes appear variable, making the pulsation structure of PG 1716 complicated. The periods are an order of magnitude longer than those seen in EC 14026 (sdBV) stars, implying that they are gravity modes rather than pressure modes. As such, they represent a new class of variable star.

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