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

December 2021 • 2021AJ....162..294A

Authors • Akana Murphy, Joseph M. • Kosiarek, Molly R. • Batalha, Natalie M. • Gonzales, Erica J. • Isaacson, Howard • Petigura, Erik A. • Weiss, Lauren M. • Grunblatt, Samuel K. • Ciardi, David R. • Fulton, Benjamin • Hirsch, Lea A. • Behmard, Aida • Rosenthal, Lee J.

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. * Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology.


IPAC Authors


David Ciardi

Senior Scientist


Benjamin Fulton

Assistant Scientist