K2 discovers a busy bee: an unusual transiting Neptune found in the beehive cluster

Obermeier, Christian and Henning, Thomas and Schlieder, Joshua E. and Crossfield, Ian J. M. and Petigura, Erik A. and Howard, Andrew W. and Sinukoff, Evan and Isaacson, Howard and Ciardi, David R. and David, Trevor J. and Hillenbrand, Lynne A. and Beichman, Charles A. and Howell, Steve B. and Horch, Elliott and Everett, Mark and Hirsch, Lea and Teske, Johanna and Christiansen, Jessie L. and Lepine, Sebastien and Aller, Kimberly M. and Liu, Michael C. and Saglia, Roberto P. and Livingston, John and Kluge, Matthias (2016) K2 discovers a busy bee: an unusual transiting Neptune found in the beehive cluster. The Astronomical Journal, 152 (6). pp. 223-234. ISSN 0004-6256

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Open clusters have been the focus of several exoplanet surveys, but only a few planets have so far been discovered. The Kepler spacecraft revealed an abundance of small planets around small cool stars, therefore, such cluster members are prime targets for exoplanet transit searches. Kepler's new mission, K2, is targeting several open clusters and star-forming regions around the ecliptic to search for transiting planets around their low-mass constituents. Here, we report the discovery of the first transiting planet in the intermediate-age (800 Myr) Beehive cluster (Praesepe). K2-95 is a faint (Kp = 15.5 mag) dwarf from K2's Campaign 5 with an effective temperature of 3471 ±124 K, approximately solar metallicity and a radius of 0.402± 0.050.R⊕ We detected a transiting planet with a radius of3.47+0.78 -0.53R⊕ and an orbital period of 10.134 days. We combined photometry, medium/high-resolution spectroscopy, adaptive optics/speckle imaging, and archival survey images to rule out any false-positive detection scenarios, validate the planet, and further characterize the system. The planet's radius is very unusual as M-dwarf field stars rarely have Neptune-sized transiting planets. The comparatively large radius of K2-95b is consistent with the other recently discovered cluster planets K2-25b (Hyades) and K2-33b (Upper Scorpius), indicating systematic differences in their evolutionary states or formation. These discoveries from K2 provide a snapshot of planet formation and evolution in cluster environments and thus make excellent laboratories to test differences between field-star and cluster planet populations.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to published version in accordance with the copyright policy of the publisher.
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 12 Jun 2017 21:27
Last Modified: 05 Feb 2018 03:17
Uncontrolled Keywords: eclipses; stars; K2-95; low-mass stars; photometric; spectroscopic;
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020102 Astronomical and Space Instrumentation
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
51 PHYSICAL SCIENCES > 5199 Other physical sciences > 519999 Other physical sciences not elsewhere classified
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: https://doi.org/10.3847/1538-3881/152/6/223
URI: http://eprints.usq.edu.au/id/eprint/32083

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