A Caltech Library Service

A Hot Saturn Near (but Unassociated with) the Open Cluster NGC 1817

Rampalli, Rayna and Vanderburg, Andrew and Bieryla, Allyson and Latham, David W. and Quinn, Samuel N. and Baranec, Christoph and Berlind, Perry and Calkins, Michael L. and Cochran, William D. and Duev, Dmitry A. and Endl, Michael and Esquerdo, Gilbert A. and Jensen-Clem, Rebecca and Law, Nicholas M. and Mayo, Andrew W. and Riddle, Reed and Salama, Maïssa (2019) A Hot Saturn Near (but Unassociated with) the Open Cluster NGC 1817. Astronomical Journal, 158 (2). Art. No. 62. ISSN 1538-3881.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


We report on the discovery of a hot Saturn-sized planet (9.916 ± 0.985 R ⊕) around a late F-star, K2-308, observed in Campaign 13 of the K2 mission. We began studying this planet candidate because prior to the release of Gaia DR2, the host star was thought to have been a member (⩾90% membership probability) of the ≈1 Gyr open cluster NGC 1817 based on its kinematics and photometric distance. We identify the host star (among three stars within the K2 photometric aperture) using seeing-limited photometry and rule out false-positive scenarios using adaptive optics imaging and radial velocity observations. We statistically validate K2-308b by calculating a false-positive probability rate of 0.01%. However, we also show using new kinematic measurements provided by Gaia DR2 and our measured radial velocity of the system that K2-308 is unassociated with the cluster NGC 1817. Therefore, the long running search for a giant transiting planet in an open cluster remains fruitless. Finally, we note that our use of seeing-limited photometry is a good demonstration of similar techniques that are already being used to follow up Transiting Exoplanet Survey Satellite (TESS) planet candidates, especially in crowded regions.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Rampalli, Rayna0000-0001-7337-5936
Vanderburg, Andrew0000-0001-7246-5438
Bieryla, Allyson0000-0001-6637-5401
Latham, David W.0000-0001-9911-7388
Quinn, Samuel N.0000-0002-8964-8377
Baranec, Christoph0000-0002-1917-9157
Calkins, Michael L.0000-0002-2830-5661
Cochran, William D.0000-0001-9662-3496
Duev, Dmitry A.0000-0001-5060-8733
Endl, Michael0000-0002-7714-6310
Esquerdo, Gilbert A.0000-0002-9789-5474
Jensen-Clem, Rebecca0000-0003-0054-2953
Law, Nicholas M.0000-0001-9380-6457
Mayo, Andrew W.0000-0002-7216-2135
Riddle, Reed0000-0002-0387-370X
Salama, Maïssa0000-0002-5082-6332
Additional Information:© 2019 The American Astronomical Society. Received 2019 April 23; revised 2019 June 3; accepted 2019 June 4; published 2019 July 17. We thank the anonymous referee for a quick and constructive review. R.R. gratefully acknowledges the support of the Columbia University Bridge to the Ph.D. Program in STEM. The work of A.V. was performed in part under contract with the California Institute of Technology/Jet Propulsion Laboratory funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. C.B. acknowledges support from the Alfred P. Sloan Foundation. D.W.L. acknowledges partial support from the TESS mission through a sub-award from the Massachusetts Institute of Technology to the Smithsonian Astrophysical Observatory (SAO) and from the Kepler mission under NASA Cooperative agreement NNX13AB58A with SAO. This research has made use of NASA's Astrophysics Data System and the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. The National Geographic Society–Palomar Observatory Sky Atlas (POSS-I) was made by the California Institute of Technology with grants from the National Geographic Society. The Oschin Schmidt Telescope is operated by the California Institute of Technology and Palomar Observatory. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC; Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The Robo-AO instrument was developed with support from the National Science Foundation under grants AST-0906060, AST-0960343, and AST-1207891, IUCAA, the Mt. Cuba Astronomical Foundation, and by a gift from Samuel Oschin. The Robo-AO team thanks NSF and NOAO for making the Kitt Peak 2.1 m telescope available. We thank the observatory staff at Kitt Peak for their efforts to assist Robo-AO KP operations. Robo-AO KP is a partnership between the California Institute of Technology, the University of Hawai'i, the University of North Carolina at Chapel Hill, the Inter-University Centre for Astronomy and Astrophysics (IUCAA) at Pune, India, and the National Central University, Taiwan. The Murty family feels very happy to have added a small value to this important project. Robo-AO KP is also supported by grants from the John Templeton Foundation and the Mt. Cuba Astronomical Foundation. Some data are based on observations at Kitt Peak National Observatory, National Optical Astronomy Observatory (NOAO Prop. ID: 15B-3001), which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation. We are honored to be permitted to conduct observations on Iolkam Duag (Kitt Peak), a mountain within the Tohono O'odham Nation with particular significance to the Tohono O'odham people. Facilities: Kepler/K2, FLWO:1.5 m (TRES), FLWO:1.2 m (KeplerCam), KPNO2.1 m (Robo-AO), Smith (Tull), Gaia, Exoplanet Archive, MAST, CDS, ADS. Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013), batman (Kreidberg 2015), emcee (Foreman-Mackey et al. 2013), VESPA (Morton 2015).
Funding AgencyGrant Number
Columbia UniversityUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Massachusetts Institute of Technology (MIT)UNSPECIFIED
Smithsonian Astrophysical ObservatoryUNSPECIFIED
National Geographic SocietyUNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Inter-University Centre for Astronomy and AstrophysicsUNSPECIFIED
Mt. Cuba Astronomical FoundationUNSPECIFIED
John Templeton FoundationUNSPECIFIED
Subject Keywords:planetary systems – planets and satellites: detection – stars: individual (K2-308)
Issue or Number:2
Record Number:CaltechAUTHORS:20190801-075059955
Persistent URL:
Official Citation:Rayna Rampalli et al 2019 AJ 158 62
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97569
Deposited By: Tony Diaz
Deposited On:01 Aug 2019 15:04
Last Modified:03 Oct 2019 21:32

Repository Staff Only: item control page