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Published December 2021 | Published
Journal Article Open

Another Superdense Sub-Neptune in K2-182 b and Refined Mass Measurements for K2-199 b and c

Abstract

We combine multiple campaigns of K2 photometry with precision radial velocity measurements from Keck-HIRES to measure the masses of three sub-Neptune-sized planets. We confirm the planetary nature of the massive sub-Neptune K2-182 b (P_b = 4.7 days, R_b = 2.69 R_⊕) and derive refined parameters for K2-199 b and c (P_b = 3.2 days, R_b = 1.73 R_⊕ and P_c = 7.4 days, R_c = 2.85 R_⊕). These planets provide valuable data points in the mass–radius plane, especially as TESS continues to reveal an increasingly diverse sample of sub-Neptunes. The moderately bright (V = 12.0 mag) early K dwarf K2-182 (EPIC 211359660) was observed during K2 campaigns 5 and 18. We find that K2-182 b is potentially one of the densest sub-Neptunes known to date (20 ± 5 M_⊕ and 5.6 ± 1.4 g cm⁻³). The K5V dwarf K2-199 (EPIC 212779596; V = 12.3 mag), observed in K2 campaigns 6 and 17, hosts two recently confirmed planets. We refine the orbital and planetary parameters for K2-199 b and c by modeling both campaigns of K2 photometry and adding 12 Keck-HIRES measurements to the existing radial velocity data set (N = 33). We find that K2-199 b is likely rocky, at 6.9 ± 1.8 M_⊕ and 7.2_(-2.0)^(+2.1) g cm⁻³, and that K2-199 c has an intermediate density at 12.4 ± 2.3 M_⊕ and 2.9_(-0.6)^(+0.7) g cm⁻³. We contextualize these planets on the mass–radius plane, discuss a small but intriguing population of "superdense" sub-Neptunes (R_p < 3 R_⊕, M_p >20 M_⊕), and consider our prospects for the planets' atmospheric characterization.

Additional Information

© 2021. The American Astronomical Society. Received 2021 March 22; revised 2021 August 20; accepted 2021 September 17; published 2021 December 7. We thank the anonymous referee for a thorough reading of this work and detailed comments that improved the quality of the manuscript. J.M.A.M. is supported by the National Science Foundation Graduate Research Fellowship Program under grant No. DGE-1842400. J.M.A.M. acknowledges the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining grant No. 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. M.R.K. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1339067. A.B. is supported by the NSF Graduate Research Fellowship, grant No. DGE 1745301. L.M.W. is supported by the Beatrice Watson Parrent Fellowship and NASA ADAP grant 80NSSC19K0597. We acknowledge use of the lux supercomputer at UC Santa Cruz, funded by NSF MRI grant AST 1828315. J.M.A.M. would like to thank Brant Robertson, Josh Sonstroem, and Ryan Hausen for their help with lux access and setup. J.M.A.M. would also like to thank Jonathan Fortney for sharing computational resources and Aarynn Carter for helpful conversations. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this sacred mountain, which is now colonized land. Facilities: Keck I Telescope (HIRES) - , Keck II Telescope (NIRC2). - Software: astropy (Astropy Collaboration et al. 2013, 2018), celerite (Foreman-Mackey et al. 2017), exoplanet (Foreman-Mackey et al. 2020), isoclassify (Huber et al. 2017; Berger et al. 2020), matplotlib (Hunter 2007), numpy (Harris et al. 2020), pandas (pandas development team T 2020), pymc3 (Salvatier et al. 2016), python 3 (Van Rossum & Drake 2009), RadVel (Fulton et al. 2018), scipy (Virtanen et al. 2020), smint (Piaulet et al. 2021), SpecMatch-Syn (Petigura et al. 2017b), SpecMatch-Emp (Yee et al. 2017), starry (Luger et al. 2019), theano (Theano Development Team 2016).

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Additional details

Created:
August 22, 2023
Modified:
October 23, 2023