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We aim to investigate variations in the arrival time of coherent stellarpulsations due to the light-travel time effect to test for the presence ofsub-stellar companions. Those companions are the key to one possible formationscenario of apparently single sub-dwarf B stars. We made use of an extensiveset of ground-based observations of the four large amplitude p-mode pulsatorsDW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS spacetelescope are available on two of the targets. The timing method compares thephase of sinusoidal fits to the full multi-epoch light curves with phases fromthe fit of a number of subsets of the original time series. Observations of theTESS mission do not sample the pulsations well enough to be useful due to the(currently) fixed two-minute cadence. From the ground-based observations, weinfer evolutionary parameters from the arrival times. The residual signals showmany statistically significant periodic signals, but no clear evidence forchanges in arrival time induced by sub-stellar companions. The signals can beexplained partly by mode beating effects. We derive upper limits on companionmasses set by the observational campaign.

The EXOTIME project: Signals in the $ O-C $ diagrams of the rapidly pulsating subdwarfs DW Lyn, V1636 Ori, QQ Vir, and V541 Hya