K2-136: A Binary System in the Hyades Cluster Hosting a Neptune-sized Planet

Abstract

We report the discovery of a Neptune-size planet (R p = 3.0R ⊕ ) in the Hyades Cluster. The host star is in a binary system, comprising a K5V star and M7/8V star with a projected separation of 40 AU. The planet orbits the primary star with an orbital period of 17.3 days and a transit duration of 3 hours. The host star is bright (V = 11.2, J = 9.1) and so may be a good target for precise radial velocity measurements. K2-136A c is the first Neptune-sized planet to be found orbiting in a binary system within an open cluster. The Hyades is the nearest star cluster to the Sun, has an age of 625-750 Myr, and forms one of the fundamental rungs in the distance ladder; understanding the planet population in such a well-studied cluster can help us understand and set constraints on the formation and evolution of planetary systems.

How Do Disks and Planetary Systems in High-mass Open Clusters Differ from Those around Field Stars?

“…Note-Column 1 indicates the cluster name, t cl its age and M cl its mass, Col. 4 gives the name of the planet-hosting star, m pl the planet mass, a pl its semi-major axis, e pl its eccentricity, and Col. 8 the references below. References: (1) Lovis & Mayor (2007), (2) Ciardi et al (2018), (20) Mann et al (2016). Comments: a) given as m pl * sin(i), where i is the inclination between the orbital plane and the line of view; b) combined planet properties from (4) and (5), errors give differences between both data sets; c) note the large error in fitted period: P = 4 850 +4560 −1750 days; d) calculated from given orbital periods; e) crude estimate for 6 000 cluster members as suggested by (10).…”

Disentangling Blended K2 Photometry: Determining the Planetary Host Star

“…For a small selection of K2 planetary hosting stars (Crossfield et al 2016) we have laid out an approach to distinguish which star the planet orbits. A few attempts have been made to determine which star a planet orbits in multi-star systems for example, Kepler-13 ; (Beatty et al 2017), Kepler-296 ; (Barclay et al 2015) and K2-136 ; (Ciardi et al 2018). Ciardi et al (2018) used the stellar density as a discriminator for which star hosts a Neptune-sized planet in a binary system in the Hyades Cluster; K2-136.…”

“…A few attempts have been made to determine which star a planet orbits in multi-star systems for example, Kepler-13 ; (Beatty et al 2017), Kepler-296 ; (Barclay et al 2015) and K2-136 ; (Ciardi et al 2018). Ciardi et al (2018) used the stellar density as a discriminator for which star hosts a Neptune-sized planet in a binary system in the Hyades Cluster; K2-136. Our approach will be to build upon the approach by Ciardi et al (2018) with the aim of publishing new radii for planets located in multi-star systems selected from Crossfield et al (2016).…”

“…Ciardi et al (2018) used the stellar density as a discriminator for which star hosts a Neptune-sized planet in a binary system in the Hyades Cluster; K2-136. Our approach will be to build upon the approach by Ciardi et al (2018) with the aim of publishing new radii for planets located in multi-star systems selected from Crossfield et al (2016). We begin by outlining our target selection in Section 2, present our approach in Section 3 and our main results in Section 4 and 5.…”

Validation of a temperate fourth planet in the K2-133 multiplanet system

“…The data were obtained using the narrow Br-γ filter (λ eff = 2.157µm, ∆λ = 0.043µm), combining 9 dithered images with integration times of 10.3 seconds each. More details of the setup used can be found in Ciardi et al (2018), Crossfield et al (2016) and Livingston et al (2018). The data are publicly available at the ExoFOP website 1 .…”