A search for transiting planets around hot subdwarfs I. Methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS
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Planet-star interactionsPlanetary systemsStars: horizontal-branchSubdwarfsTechniques: photometric
V. Van Grootel et al.: A search for transiting planets around hot subdwarfs. I. A&A 650, A205 (2021). [https://doi.org/10.1051/0004-6361/202140381]
SponsorshipEuropean Space Agency European Commission PEA 4000131343; University of Liege through an ARC grant for Concerted Research Actions - Wallonia-Brussels Federation; Swiss NCCR PlanetS; Swiss National Science Foundation (SNSF) European Commission; Centre National D'etudes Spatiales; French National Research Agency (ANR) ANR-17-CE31-0018; European Research Council (ERC) 724427; Swiss National Science Foundation (SNSF); CHEOPS ASI-INAF 2019-29-HH.0; Swedish Research Council European Commission 2017-04945; Swedish National Space Agency 120/19C - DNR 65/19 - 174/18; UK Research & Innovation (UKRI) Science & Technology Facilities Council (STFC) ST/M001296/1- ST/M001040/1; SNSA; Centre National D'etudes Spatiales 837319; European Commission European Commission Joint Research Centre European Social Fund (ESF); Portuguese Foundation for Science and Technology DL 57/2016/CP1364/CT0004 - IF/01312/2014/CP1215/CT0004 - CEECIND/00826/2018; European Commission UID/FIS/04434/2019 - UIDB/04434/2020 - UIDP/04434/2020 - PTDC/FIS-AST/32113/2017 - POCI-01-0145-FEDER032113 - PTDC/FIS-AST/28953/2017 - POCI-01-0145-FEDER-028953 - PTDC/FIS-AST/28987/2017 - POCI-01-0145-FEDER-028987; Swiss National Science Foundation (SNSF) European Commission PP00P2-190080; TESS Guest Investigator Program Grant 80NSSC21K0364; Spanish Government; European Commission ESP2016-80435-C2-1-R - ESP2016-80435-C2-2-R - PGC2018-098153-B-C33 - PGC2018-098153-B-C31 - ESP2017-87676-C5-1-R - MDM-2017-0737 - PGC2018-098153-BC33; Generalitat de Catalunya/CERCA programme; European Space Agency 4000124370; CRT foundation 2018.2323; National Research, Development & Innovation Office (NRDIO) - Hungary GINOP-2.3.2-15-2016-00003 - K-119517 - K-125015; City of Szombathely 67.177-21/2016; National Aeronautics & Space Administration (NASA); Danmarks Grundforskningsfond DNRF106; European Space Agency PEA 4000119301; Stellar Astrophysics Centre (SAC) at Aarhus University; TASC/TASOC; Gaia Multilateral Agreement; DPAC
Context. Hot subdwarfs experienced strong mass loss on the red giant branch (RGB) and are now hot and small He-burning objects. These stars constitute excellent opportunities for addressing the question of the evolution of exoplanetary systems directly after the RGB phase of evolution. Aims. In this project we aim to perform a transit survey in all available light curves of hot subdwarfs from space-based telescopes (Kepler, K2, TESS, and CHEOPS) with our custom-made pipeline SHERLOCK in order to determine the occurrence rate of planets around these stars as a function of orbital period and planetary radius. We also aim to determine whether planets that were previously engulfed in the envelope of their red giant host star can survive, even partially, as a planetary remnant. Methods. For this first paper, we performed injection-and-recovery tests of synthetic transits for a selection of representative Kepler, K2, and TESS light curves to determine which transiting bodies in terms of object radius and orbital period we will be able to detect with our tools. We also provide estimates for CHEOPS data, which we analyzed with the pycheops package. Results. Transiting objects with a radius less than or similar to 1.0 R-circle times can be detected in most of the Kepler, K2, and CHEOPS targets for the shortest orbital periods (1 d and shorter), reaching values as low as similar to 0.3 R-circle times in the best cases. Sub-Earth-sized bodies are only reached for the brightest TESS targets and for those that were observed in a significant number of sectors. We also give a series of representative results for larger planets at greater distances, which strongly depend on the target magnitude and on the length and quality of the data. Conclusions. The TESS sample will provide the most important statistics for the global aim of measuring the planet occurrence rate around hot subdwarfs. The Kepler, K2, and CHEOPS data will allow us to search for planetary remnants, that is, very close and small (possibly disintegrating) objects.