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Kepler and the Behemoth: Three Mini-Neptunes in a 40 Million Year Old Association

Bouma, L. G. and Kerr, R. and Curtis, J. L. and Isaacson, H. and Hillenbrand, L. A. and Howard, A. W. and Kraus, A. L. and Bieryla, A. and Latham, D. W. and Petigura, E. A. and Huber, D. (2022) Kepler and the Behemoth: Three Mini-Neptunes in a 40 Million Year Old Association. . (Unpublished)

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Stellar positions and velocities from Gaia are yielding a new view of open cluster dispersal. Here we present an analysis of a group of stars spanning Cepheus to Hercules, hereafter the Cep-Her complex. The group includes four Kepler Objects of Interest: Kepler-1643 b (2.32 ± 0.14 Earth-radii, 5.3 day orbital period), KOI-7368 b (2.22 ± 0.12 Earth-radii, 6.8 days), KOI-7913 Ab (2.34 ± 0.18 Earth-radii, 24.2 days), and Kepler-1627 Ab (3.85 ± 0.11 Earth-radii, 7.2 days). The latter Neptune-sized planet is in part of the Cep-Her complex called the δ Lyr cluster (Bouma et al. 2022). Here we focus on the former three systems, which are in other regions of the association. Based on kinematic evidence from Gaia, stellar rotation periods from TESS, and spectroscopy, these three objects are also approximately 40 million years (Myr) old. More specifically, we find that Kepler-1643 is 46⁺⁹₋₇ Myr old, based on its membership in a dense sub-cluster of the complex called RSG-5. KOI-7368 and KOI-7913 are 36⁺¹⁰₋₈ Myr old, and are in a diffuse region that we call CH-2. Based on the transit shapes and high resolution imaging, all three objects are most likely planets, with false positive probabilities of 6 × 10⁻⁹, 4 × 10⁻³, and 1 × 10⁻⁴ for Kepler-1643, KOI-7368, and KOI-7913 respectively. These planets demonstrate that mini-Neptunes with sizes of approximately 2 Earth radii exist at ages of 40 million years.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper
Bouma, L. G.0000-0002-0514-5538
Kerr, R.0000-0002-6549-9792
Curtis, J. L.0000-0002-2792-134X
Isaacson, H.0000-0002-0531-1073
Howard, A. W.0000-0001-8638-0320
Kraus, A. L.0000-0001-9811-568X
Bieryla, A.0000-0001-6637-5401
Latham, D. W.0000-0001-9911-7388
Petigura, E. A.0000-0003-0967-2893
Huber, D.0000-0001-8832-4488
Additional Information:Attribution 4.0 International (CC BY 4.0). L.G.B. is supported by the Heising-Simons Foundation 51 Pegasi b Fellowship and the NASA TESS GI Program (80NSSC21K0335 and 80NSSC22K0298). R.K. is supported by the Heising-Simons Foundation. J.L.C. is supported by NSF AST-2009840 and the NASA TESS GI Program (80NSSC22K0299). D.H. is supported by the Alfred P. Sloan Foundation and NASA (80NSSC19K0597). Software: astropy (Astropy Collaboration et al. 2018), astroquery (Ginsburg et al. 2018), exoplanet (Foreman-Mackey et al. 2020), and its dependencies (Agol et al. 2020; Kipping 2013; Luger et al. 2019; Theano Development Team 2016), PyMC3 (Salvatier et al. 2016), tesscut (Brasseur et al. 2019), unpopular (Hattori et al. 2021), VESPA (Morton 2012, 2015), Facilities: Astrometry: Gaia. Imaging: Second Generation Digitized Sky Survey. Keck:II (NIRC2). Spectroscopy: Tillinghast:1.5m (TRES). Keck:I (HIRES). Photometry: Kepler, TESS, ZTF.
Group:Astronomy Department
Funding AgencyGrant Number
Heising-Simons Foundation51 Pegasi b Fellowship
Alfred P. Sloan FoundationUNSPECIFIED
Classification Code:exoplanet evolution (491), open star clusters (1160), stellar ages (1581)
Record Number:CaltechAUTHORS:20220517-214318858
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114793
Deposited By: George Porter
Deposited On:18 May 2022 15:47
Last Modified:18 May 2022 15:47

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