Two small temperate planets transiting nearby M dwarfs in K2 campaigns 0 and 1

Schlieder, Joshua E. and Crossfield, Ian J M and Petigura, Erik A. and Howard, Andrew W. and Aller, Kimberly M. and Sinukoff, Evan and Isaacson, Howard T. and Fulton, Benjamin J. and Ciardi, David R. and Bonnefoy, Mickael and Ziegler, Carl and Morton, Timothy D. and Lepine, Sebastien and Obermeier, Christian and Liu, Michael C. and Bailey, Vanessa P. and Baranec, Christoph and Beichman, Charles A. and Defrere, Denis and Henning, Thomas and Hinz, Philip and Law, Nicholas and Riddle, Reed and Skemer, Andrew (2016) Two small temperate planets transiting nearby M dwarfs in K2 campaigns 0 and 1. The Astrophysical Journal, 818 (1). pp. 87-101. ISSN 0004-637X

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The prime Kepler mission revealed that small planets (<4⊕) are common, especially around low-mass M dwarfs. K2, the repurposed Kepler mission, continues this exploration of small planets around small stars. Here we combine K2 photometry with spectroscopy, adaptive optics imaging, and archival survey images to analyze two small planets orbiting the nearby field-age M dwarfs, K2-26 (EPIC 202083828) and K2-9. K2-26 is an M1.0 ± 0.5 dwarf at 93 ± 7 pc from K2 Campaign 0. We validate its planet with a day period of 14.5665 and estimate a radius of 2.67-0.42 +0.46 R⊕. K2-9 is an M2.5 ± 0.5 dwarf at 110 ± 12 pc from K2 Campaign 1. K2-9b was first identified by Montet et al.; here we present spectra and adaptive optics imaging of the host star and independently validate and characterize the planet. Our analyses indicate K2-9b is a 2.25-0.96 +0.53 R⊕ planet with a 18.4498 day period. K2-26b exhibits a transit duration that is too long to be consistent with a circular orbit given its measured stellar radius. Thus, the long transits are likely due to the photoeccentric effect and our transit fits hint at an eccentric orbit. Both planets receive low incident flux from their host stars and have estimated equilibrium temperatures <500 K. K2-9b may receive approximately Earth-like insolation. However, its host star exhibits strong GALEX UV emission which could affect any atmosphere it harbors. K2-26b and K2-9b are representatives of a poorly studied class of small planets with cool temperatures that have radii intermediate to Earth and Neptune. Future study of these systems can provide key insight into trends in bulk composition and atmospheric properties at the transition from silicate dominated to volatile rich bodies.

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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 23:15
Last Modified: 27 Jun 2017 00:22
Uncontrolled Keywords: eclipses; stars; K2-26; K2-9;photometric; spectroscopic;
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2008): E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
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