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. * 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.
- Publication:
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The Astronomical Journal
- Pub Date:
- December 2021
- DOI:
- 10.3847/1538-3881/ac2830
- arXiv:
- arXiv:2110.05502
- Bibcode:
- 2021AJ....162..294A
- Keywords:
-
- 1332;
- 498;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 42 pages, 10 figures, 9 tables. Accepted for publication in The Astronomical Journal