Abstract
Abstract We report the discovery of a Neptune-size planet ( ) 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 hrs. 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.
Highlights
Most stars are thought to form in open clusters (Lada & Lada 2003), but most planets have been found around old, isolated stars that have long since left their nascent cluster families
Value 2997.0235 ± 0.0025 17.3077 ± 0.0013. We regard all these items—the lack of a secondary eclipse, the length of the transit duration, the agreement of the derived stellar density with that of a K5V star, and the vespa results— as sufficient evidence to indicate that the observed transit most likely occurs around the primary star, that it is caused by a planet, and that, given the transit depth and stellar radius (0.71R ), the transiting planet is Neptune-sized
We present the discovery of a sub-Neptune-sized (3.0 RÅ) planet in a 17.3-day orbit around a K-dwarf in the Hyades cluster
Summary
Most stars are thought to form in open clusters (Lada & Lada 2003), but most planets have been found around old, isolated stars that have long since left their nascent cluster families. Part of the reason to study planets in open clusters is that the stars are typically well understood in terms of mass, metallicity, and age (especially in comparison to field stars), and, because the derivation of planet parameters requires accurate and precise knowledge of the host stars, any planets found within open clusters would be much better understood. The first planet discovered in any open cluster was in the Hyades; ò Tauri b is a »7MJup mass planet in a 600-day orbit around an evolved K0 giant star In addition to the transit light curve of the planet, the imaging was used to detect a late M-dwarf stellar companion; spectroscopy was utilized to derive precise stellar parameters of the primary host star and show that the star is a Hyades member, based upon kinematic arguments. We show that the Neptune-sized planet most likely orbits the primary star
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