Papers › Discovery and Validation of a High-Density sub-Neptune from the K2 Mission
Discovery and Validation of a High-Density sub-Neptune from the K2 Mission
Néstor Espinoza, Rafael Brahm, Andrés Jordán, James S. Jenkins, Felipe Rojas, Paula Jofré, Thomas Mädler, Markus Rabus, Julio Chanamé, Blake Pantoja, Maritza G. Soto, Katie M. Morzinski, Jared R. Males, Kimberly Ward-Duong, Laird M. Close
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We report the discovery of BD+20594b, a high density sub-Neptune exoplanet, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission, ground-based radial velocity 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, Kₛ = 9.37), slightly metal poor ([Fe/H]=-0.15±0.05 dex) solar analogue located at 152.1^(+9.7)_(-7.4) pc from Earth, for which we find a radius of R_*=0.928^(+0.055)_(-0.040)R_⊙ and a mass of M_* = 0.961^(+0.032)_(-0.029)M_⊙. A joint analysis of the K2 photometry and HARPS radial velocities reveal that the planet is in a ≈42 day orbit around its host star, has a radius of 2.23^(+0.14)_(-0.11)R_⊕, and a mass of 16.3^(+6.0)_(-6.1)M_⊕. Although the data at hand puts 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.
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