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

Abstract

Aims. We aim to investigate variations in the arrival time of coherent stellar pulsations due to the light-travel time effect to test for the presence of sub-stellar companions. Those companions are the key to one possible formation scenario of apparently single sub-dwarf B stars. Methods. We made use of an extensive set of ground-based observations of the four large amplitude p-mode pulsators DW Lyn, V1636 Ori, QQ Vir, and V541 Hya. Observations of the TESS space telescope are available on two of the targets. The timing method compares the phase of sinusoidal fits to the full multi-epoch light curves with phases from the fit of a number of subsets of the original time series. Results. Observations of the TESS mission do not sample the pulsations well enough to be useful due to the (currently) fixed two-minute cadence. From the ground-based observations, we infer evolutionary parameters from the arrival times. The residual signals show many statistically significant periodic signals, but no clear evidence for changes in arrival time induced by sub-stellar companions. The signals can be explained partly by mode beating effects. We derive upper limits on companion masses set by the observational campaign.

Short-period pulsating hot-subdwarf stars observed by TESS

“…The authors performed period fits and obtained structural parameters of the sdB star. Mackebrandt et al (2020) searched, with a null result, for a change in the arrival time of stellar pulsations induced by a sub-stellar companion. TESS observed the star during Sector 35.…”

A search for transiting planets around hot subdwarfs

“…To date, several planet detections around hot subdwarfs have been claimed, but none of them received confirmation. With the pulsation-timing method (variation in the oscillation periods of sdB pulsators), planets of a few Jupiter masses in orbits at about 1 AU were announced around V391 Peg and DW Lyn (Silvotti et al 2007;Lutz et al 2012), but these claims have recently been refuted (Silvotti et al 2018;Mackebrandt et al 2020). Based on weak signals that were interpreted as reflection and thermal re-emission in Kepler light curves, five very close-in (with orbital periods of a few hours) Earth-sized planets have been claimed to orbit KIC 05807616 (Charpinet et al 2011) and KIC 10001893 (Silvotti et al 2014).…”

A transit survey to search for planets around hot subdwarfs: I. methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS

“…Using the pulsation timing method (variation of the oscillation periods of sdB pulsators), planets of a few Jupiter masses in orbits about 1 AU were announced around V391 Peg and DW Lyn (Silvotti et al 2007;Lutz et al 2012), but these claims have recently been refuted (Silvotti et al 2018;Mackebrandt et al 2020). Based on weak signals interpreted as reflection and thermal re-emission in Kepler light curves, five very close-in (with orbital periods of a few hours) Earth-sized planets have been claimed to orbit KIC 05807616 (Charpinet et al 2011) andKIC 10001893 (Silvotti et al 2014).…”