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.

Links

• PREPRINT http://arxiv.org/abs/2110.05502
• ELECTR https://iopscience.iop.org/article/10.3847/1538-3881/ac2830
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2021AJ....162..294M
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/ac2830/pdf
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/162/294
• DATA https://irsa.ipac.caltech.edu/bibdata/2021/A/2021AJ....162..294A.html