Discovery and Validation of a High-Density sub-Neptune from the K2 Mission
Abstract
We report the discovery of K2-56b, a high-density sub-Neptune exoplanet, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission, ground-based radial velocity (RV) follow-up from HARPS and high-resolution lucky and adaptive optics imaging obtained using AstraLux and MagAO, respectively. The host star is a bright (V = 11.04, K s = 9.37), slightly metal-poor ([Fe/H] = -0.15 ± 0.05 dex) solar analogue located at {152.1}-7.4+9.7 pc from Earth, for which we find a radius of {R}* ={0.928}-0.040+0.055{R}⊙ and a mass of {M}* ={0.961}-0.029+0.032{M}⊙ . A joint analysis of the K2 photometry and HARPS RVs reveal that the planet is in a ≈42 day orbit around its host star, has a radius of {2.23}-0.11+0.14{R}\oplus , and a mass of {16.3}-6.1+6.0{M}\oplus . Although the data at hand put the planet in the region of the mass-radius diagram where we could expect planets with a pure rock (I.e., magnesium silicate) composition using two-layer models (I.e., between rock/iron and rock/ice compositions), we discuss more realistic three-layer composition models which can explain the high density of the discovered exoplanet. The fact that the planet lies in the boundary between “possibly rocky” and “non-rocky” exoplanets makes it an interesting planet for future RV follow-up.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2016
- DOI:
- 10.3847/0004-637X/830/1/43
- arXiv:
- arXiv:1601.07608
- Bibcode:
- 2016ApJ...830...43E
- Keywords:
-
- planets and satellites: composition;
- planets and satellites: detection;
- planets and satellites: fundamental parameters;
- planets and satellites: terrestrial planets;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 12 pages, 11 figures. Accepted for publication in ApJ