Then and now: A new look at the eclipse timing variations of hierarchical triple star candidates in the primordial Kepler field, revisited by TESS

¹ Baja Astronomical Observatory of University of Szeged, H-6500 Baja, Szegedi út, Kt. 766, Hungary
² HUN-REN-SZTE Stellar Astrophysics Research Group, H-6500 Baja, Szegedi út, Kt. 766, Hungary
³ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, H-1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
⁴ Department of Physics, Kavli Institute for Astrophysics and Space Research, M.I.T., Cambridge, MA 02139, USA
⁵ Department of Astronomy, Institute of Physics and Astronomy, ELTE Eötvös Loránd University, H-1117 Budapest, Pázmány Péter sétány 1/A, Hungary
⁶ MTA CSFK Lendület Near-Field Cosmology Research Group, Research Centre for Astronomy and Earth Sciences, H-1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
⁷ Eszterházy Károly Catholic University, Department of Physics, H-3300 Eszterházy tér 1, Eger, Hungary
⁸ Institute of Physics, University of Szeged, H-6720 Szeged, Dóm tér 9., Hungary

^⋆ Corresponding author; borko@bajaobs.hu

Received: 26 December 2024
Accepted: 11 February 2025

Abstract

Context. A former analysis of eclipse timing variation (ETV) curves of eclipsing binaries (EBs) observed by the Kepler spacecraft during its ∼4-year-long prime mission has led to the discovery and characterization of 221 hierarchical triple star system with different confidence levels. Although the prime Kepler mission ended in 2013 (a little more than a decade ago), the TESS space telescope has revisited the original Kepler field on several occasions in between 2019 and 2024, thereby extending the time base of high-precision eclipse timing observations for a substantially longer interval.

Aims. In this paper, we re-analyse the extended ETV curves of the formerly identified triple star candidates and many other Kepler EBs. Besides the confirmations of the former findings and/or the improvements of the triple systems’ orbital properties, the extended time base allows us to identify several new, longer outer period triple systems, and it also makes a more detailed study of the dynamical perturbations in the tightest triple stars possible.

Methods. We extend the ETV curves of the Kepler triples with those mid-eclipse times that can be deduced from the TESS observations and, moreover, from targeted ground-based follow-up observations for a number of the objects. In general, we used the same methods that were applied for the older studies, which are described in the literature. Due to the lower quality of the TESS observations, however, for the fainter systems we averaged light curves of the EBs for 5–20 consecutive cycles, and thereby calculated ‘normal’ minima from these averaged light curves.

Results. In conclusion, we identified 243 hierarchical triple star candidates in the Kepler sample. This sample strongly overlaps our former, nine-year-old sample, confirming the older results, or providing new solutions for 193 systems of the 2016 sample. For the remaining 28 hierarchical triple candidates of that former study, we have been unable to find new solutions, either because of the disappearance of the eclipses due to orbital plane precession, or due to instrumental reasons. On the other hand, due to the extended time series, we have been able to identify 50 new, longer-period triple star candidates as well. We briefly discuss the main properties of each individual system and present statistical studies of the results.