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

Abstract

We report on the discovery of a hot Saturn-sized planet (9.916 +/- 0.985 R_earth) around a late F star, EPIC 246865365, 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 approximately 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 EPIC 246865365b 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 EPIC 246865365 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 TESS planet candidates, especially in crowded regions.

11 pages, 4 figures, 1 table. Accepted in AJ

References in corpus (10)

• The Transiting Exoplanet Survey Satellite
• The K2 Mission: Characterization and Early results
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission
• A nearby M star with three transiting super-Earths discovered by K2
• The orbits of open clusters in the Galaxy
• High-efficiency Autonomous Laser Adaptive Optics
• The Monitor project: Searching for occultations in young open clusters
• Predicting the Yields of Photometric Surveys for Transiting Extrasolar Planets
• Precise Masses in the WASP-47 System
• Kinematic parameters and membership probabilities of open clusters in the Bordeaux PM2000 catalogue

Cited by in corpus (3)

• Variability in the Massive Open Cluster NGC 1817 from K2: A Rich Population of Asteroseismic Red Clump, Eclipsing Binary, and Main Sequence Pulsating Stars
• The K2 & TESS Synergy II: Revisiting 26 systems in the TESS Primary Mission
• Contemporaneous Observations of $H\alpha$ Luminosities and Photometric Amplitudes for M Dwarfs