Discovery and validation of a high-density sub-neptune from the K2 mission

Journal Article · Mon Oct 10 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/830/1/43· OSTI ID:22868609

Espinoza, Néstor; Brahm, Rafael; Jordán, Andrés; Rojas, Felipe; Rabus, Markus; Chanamé, Julio ^[1]; Jenkins, James S.; Pantoja, Blake; Soto, Maritza G. ^[2]; Jofré, Paula; Mädler, Thomas ^[3]; Morzinski, Katie M.; Males, Jared R.; Close, Laird M. ^[4]; Ward-Duong, Kimberly ^[5]

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1. Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile)
2. Departamento de Astronomía, Universidad de Chile, Camino al Observatorio, Cerro Calán, Santiago (Chile)
3. Institute of Astronomy, University of Cambridge (United Kingdom)
4. Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721-0065 (United States)
5. School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287 (United States)

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 {sub s} = 9.37), slightly metal-poor ([Fe/H] = −0.15 ± 0.05 dex) solar analogue located at 152.1{sub −7.4}{sup +9.7} pc from Earth, for which we find a radius of R{sub ∗}=0.928{sub −0.040}{sup +0.055}R{sub ⊙} and a mass of M{sub ∗}=0.961{sub −0.029}{sup +0.032}M{sub ⊙}. 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{sub −0.11}{sup +0.14}R{sub ⊕}, and a mass of 16.3{sub −6.1}{sup +6.0}M{sub ⊕}. 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.

• OSTI ID: 22868609
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 830; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
DENSITY
DETECTION
ICE
IRON
LAYERS
MAGNESIUM SILICATES
MASS
ORBITS
PHOTOMETRY
PLANETS
RADIAL VELOCITY
RESOLUTION
ROCKS
SATELLITES
STARS