Seismology of pre-white dwarfs: Models for pulsating sdB stars

Two kinds of pre-white dwarf stars can be probed through asteroseismology: planetary nebula nuclei (PNNs) and sdB (EHB) stars. To exploit the observed pulsations requires models that incorporate state-ofthe-art input physics and realistic evolutionary histories. Pulsation analysis of extensive grids of such models provide self-consistent theoretical pulsation periods for comparison with observed pulsations in these stars. While there has been significant progress in the seismological studies of PNNs and hot white dwarfs, similar studies of the pulsating sdB stars (the EC14026 stars) have just begun. Here, I describe some preliminary results and interpretations of the pulsations of sdB stars. Eventually, we expect that the seismological constraints on their masses, luminosities, and interior compositional structure will provide a framework for exploration of this poorly understood phases of stellar evolution.