@article{d676aa235ab644a2ad97010d698d3402,
title = "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. ",
keywords = "Asteroseismology, Planets and satellites: detection, Stars: horizontal-branch, Subdwarfs, Techniques: photometric",
author = "F. MacKebrandt and S. Schuh and R. Silvotti and Kim, {S. L.} and D. Kilkenny and Green, {E. M.} and R. Lutz and T. Nagel and Provencal, {J. L.} and T. Otani and Oswalt, {T. D.} and S. Benatti and L. Lanteri and A. Bonanno and A. Frasca and R. Janulis and M. Papar{\'o} and L. Moln{\'a}r and R. Claudi and {\O}stensen, {R. H.}",
note = "Funding Information: Acknowledgements. We thank Wen-Shan Hsiao for observing at the Lulin Observatory and Mike D. Reed for observing at the Baker Observatory and Elia Leibowitz for observing at the WISE observatory. F.M. conducted the work in this paper in the framework of the International Max-Planck Research School (IMPRS) for Solar System Science at the University of G{\"o}ttingen (Volkswagen Foundation project grant number VWZN3020). D.K. thanks the SAAO for generous allocations of telescope time and the National Research Foundation of South Africa and the University of the Western Cape for financial support. TDO gratefully acknowledges support from the U.S. National Science Foundation grant AST-0807919. L.M. was supported by the Premium Postdoctoral Research Program of the Hungarian Academy of Sciences. This project has been supported by the Lend{\"u}let Program of the Hungarian Academy of Sciences, project No. LP2018-7/2019. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundaci{\'o}n Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations collected at the Centro Astron{\'o}mico His-p{\'a}nico en Andaluc{\'i}a (CAHA) at Calar Alto, operated jointly by the Andalusian Universities and the Instituto de Astrof{\'i}sica de Andaluc{\'i}a (CSIC). Based on observations collected at Copernico telescope (Asiago, Italy) of the INAF – Osservatorio Astronomico di Padova. Based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. Publisher Copyright: {\textcopyright} F. Mackebrandt et al. 2020.",
year = "2020",
month = jun,
day = "1",
doi = "10.1051/0004-6361/201937172",
language = "English (US)",
volume = "638",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}