Progress in Sounding the Interior of Pulsating Hot Subdwarf Stars

Hot subdwarf stars, including helium core burning subdwarf B (sdB) stars and more evolved subdwarf O (sdO) stars, host three classes of nonradial pulsators. Two of them show rapid acoustic mode oscillations (with periods in the 60-600 s range), while the third class features slow gravity mode vibrations of period typically 1h. All three classes provide a strong potential for sounding the internal properties of stars in these evolved phases of stellar evolution through asteroseismology. This has so far been exploited mainly for the rapid p-mode sdB pulsators, but the long period g-mode sdB pulsators, with the advent of space observations, carry good promises for sounding even deeper regions inside these stars. In this review paper, we summarize the properties of pulsating hot subdwarf stars and we outline progress that have recently occured in the asteroseismic exploitation of the pulsations observed in sdB stars.