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

Akana Murphy, Joseph M. and Kosiarek, Molly R. and Batalha, Natalie M. and Gonzales, Erica J. and Isaacson, Howard and Petigura, Erik A. and Weiss, Lauren M. and Grunblatt, Samuel K. and Ciardi, David R. and Fulton, Benjamin and Hirsch, Lea A. and Behmard, Aida and Rosenthal, Lee J. (2021) Another Superdense Sub-Neptune in K2-182 b and Refined Mass Measurements for K2-199 b and c. Astronomical Journal, 162 (6). Art. No. 294. ISSN 0004-6256. doi:10.3847/1538-3881/ac2830.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription
Akana Murphy, Joseph M.0000-0001-8898-8284
Kosiarek, Molly R.0000-0002-6115-4359
Batalha, Natalie M.0000-0002-7030-9519
Gonzales, Erica J.0000-0002-9329-2190
Isaacson, Howard0000-0002-0531-1073
Petigura, Erik A.0000-0003-0967-2893
Weiss, Lauren M.0000-0002-3725-3058
Grunblatt, Samuel K.0000-0003-4976-9980
Ciardi, David R.0000-0002-5741-3047
Fulton, Benjamin0000-0003-3504-5316
Hirsch, Lea A.0000-0001-8058-7443
Behmard, Aida0000-0003-0012-9093
Rosenthal, Lee J.0000-0001-8391-5182
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).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1842400
Large Synoptic Survey Telescope CorporationUNSPECIFIED
Brinson FoundationUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
NSF Graduate Research FellowshipDGE-1339067
NSF Graduate Research FellowshipDGE-1745301
Beatrice Watson Parrent FellowshipUNSPECIFIED
Subject Keywords:Radial velocity; Exoplanets
Issue or Number:6
Classification Code:Unified Astronomy Thesaurus concepts: Radial velocity (1332); Exoplanets (498)
Record Number:CaltechAUTHORS:20211214-988506000
Persistent URL:
Official Citation:Joseph M. Akana Murphy et al 2021 AJ 162 294
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112449
Deposited By: George Porter
Deposited On:15 Dec 2021 23:52
Last Modified:01 Feb 2022 22:54

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