A Decade of Transit-timing Measurements Confirm Resonance in the K2-19 System
Creators
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1.
University of California, Los Angeles
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2.
Observatoire de la Côte d'Azur
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3.
California Institute of Technology
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4.
Osaka University
Abstract
K2-19 is a star, slightly smaller than the Sun, that hosts three transiting planets. Two of these, K2-19 b and c, are between the size of Neptune and Saturn and have orbital periods near a 3:2 commensurability, and exhibit strong transit-timing variations (TTVs). A previous TTV analysis reported moderate eccentricities of ≈0.20 ± 0.03 for the two planets, but such high values would imply rapid orbital decay for the innermost planet d. Here, we present an updated analysis that includes eight new transit times from TESS, which extends the time baseline from three years to a decade, and employ a gradient-aware TTV modeling code. We confirm that the system resides in resonance with a small libration amplitude, but find a broader constraints on eccentricity that range from a few percent up to 0.2. These revised eccentricities alleviate previous concerns regarding rapid tidal circularization and support the long-term dynamical stability of the system.
Copyright and License
© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
We are grateful for conversations with Konstantin Batygin that improved this manuscript. We thank the referee, Eric Agol, for a careful and thoughtful review of the manuscript. During the final preparation of this manuscript, we learned of another TTV analysis of K2-19 by J. M. Almenara et al. (2025). The two analyses proceeded independently.
Funding for this work was provided by a University of California, Los Angeles set-up award to E.A.P. and by the Heising-Simons Foundation Award #2022-3833.
This paper includes data collected with the TESS mission, obtained from the MAST data archive at the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by the NASA Explorer Program. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555.
Facilities: TESS - , Kepler - The Kepler Mission.
Software: batman (L. Kreidberg 2015), jnkepler (K. Masuda et al. 2024), lightkurve (Lightkurve Collaboration et al. 2018), NumPyro (E. Bingham et al. 2018; D. Phan et al. 2019), NumPy (C. R. Harris et al. 2020), SciPy (P. Virtanen et al. 2020), Astropy (Astropy Collaboration et al. 2013, 2018, 2022).
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Additional details
Funding
- Heising-Simons Foundation
- #2022-3833