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Published December 2016 | Published + Submitted
Journal Article Open

K2 Discovers a Busy Bee: An Unusual Transiting Neptune Found in the Beehive Cluster


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 (K_p = 15.5 mag) M3.0 ± 0.5 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 of 3.47^(+0.78)_(-0.53) R⊕ 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.

Additional Information

© 2016 The American Astronomical Society. Received 2016 May 16; revised 2016 July 20; accepted 2016 August 3; published 2016 December 6. We thank the staff of the Wendelstein observatory for technical help and strong support during the data acquisition, including observing the target for us. We especially thank Ulrich Hopp for his constructive input during and after observations. The research of J.E.S. was supported by an appointment to the NASA Postdoctoral Program at NASA Ames Research Center, administered by Universities Space Research Association through a contract with NASA. E.A.P. acknowledges support through a Hubble Fellowship. Some of the data presented herein were obtained at the W.M. Keck Observatory (which is operated as a scientific partnership among Caltech, UC, and NASA) and at the Infrared Telescope Facility (IRTF, operated by UH under NASA contract NNH14CK55B). The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). Facilities: Kepler - The Kepler Mission, K2 - , IRTF (SpeX) - Infrared Telescope Facility, Keck: I (HIRES) - , Keck: II (NIRC2) - KECK II Telescope, Gemini-N (DSSI). - Software: vespa (Morton 2012, 2015), emcee (Foreman-Mackey et al. 2013), BATMAN (Kreidberg 2015), LDTk/pyLDTk (Parviainen & Aigrain 2015).

Attached Files

Published - Obermeier_2016_AJ_152_223.pdf

Submitted - 1608.04760v1.pdf


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