Searching for long period pulsations in He-rich subdwarfs

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Hot subdwarf stars are He-core burning stars that have lost their H-rich envelopes. While most hot subdwarfs show almost pure H atmospheres, a small fraction of these stars show a mixed H/He surface composition. These stars are expected to be in a fast stage immediately after the He-core flash, where gravitational settling did not turn the atmosphere H-pure yet. During this phase they are expected to undergo He-core subflashes, which are predicted to drive pulsations. The confirmation of stellar pulsations driven by the He-core flash would be the first direct confirmation of the existence of the He-subflashes themselves. We granted four nights of observing time with the BUSCA instrument at the Calar Alto observatory to pursue an ad hoc search of stellar oscillations in 14 hot subdwarfs with mixed H/He atmospheres.