[en] The prime Kepler mission revealed that small planets (<4 {R}[SUB]\oplus [/SUB]) 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 {{M}}1.0+/- 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}[SUB]-0.42[/SUB][SUP]+0.46[/SUP] {R}[SUB]\oplus [/SUB]. K2-9 is an {{M}}2.5+/- 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}[SUB]-0.96[/SUB][SUP]+0.53[/SUP] {R}[SUB]\oplus [/SUB] 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. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, La Silla Observatory, Chile during program ID 194.C-0443.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Schlieder, Joshua E.; NASA Ames Research Center, Space Science and Astrobiology Division, MS 245-6, Moffett Field, CA 94035, USA
Crossfield, Ian J. M.; Lunar & Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ, USA
Petigura, Erik A.; California Institute of Technology, Pasadena, CA 91125, USA
Howard, Andrew W.; Institute for Astronomy, University of Hawai‘i, 2680 Woodlawn Drive, Honolulu, HI, USA
Aller, Kimberly M.; Institute for Astronomy, University of Hawai‘i, 2680 Woodlawn Drive, Honolulu, HI, USA
Sinukoff, Evan; Institute for Astronomy, University of Hawai‘i, 2680 Woodlawn Drive, Honolulu, HI, USA
Isaacson, Howard T.; Astronomy Department, University of California, Berkeley, CA, USA
Fulton, Benjamin J.; Institute for Astronomy, University of Hawai‘i, 2680 Woodlawn Drive, Honolulu, HI, USA
Ciardi, David R.; NASA Exoplanet Science Institute, California Institute of Technology, 770 S. Wilson Ave., Pasadena, CA 91125, USA
Ziegler, Carl; University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
Morton, Timothy D.; Department of Astrophysics, Princeton University, Princeton NJ 08544, USA
Lépine, Sébastien; Department of Physics & Astronomy, Georgia State University, Atlanta, GA, USA
Obermeier, Christian; Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg, Germany
Liu, Michael C.; Institute for Astronomy, University of Hawai‘i, 2680 Woodlawn Drive, Honolulu, HI, USA
Bailey, Vanessa P.; Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, USA
Baranec, Christoph; Institute for Astronomy, University of Hawai‘i at Mānoa, Hilo, HI 96720-2700, USA
Beichman, Charles A.; NASA Exoplanet Science Institute, California Institute of Technology, 770 S. Wilson Ave., Pasadena, CA 91125, USA
Defrere, Denis ; Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Henning, Thomas; Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg, Germany
Hinz, Philip; Steward Observatory, Department of Astronomy, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
Law, Nicholas; University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
Riddle, Reed; California Institute of Technology, Pasadena, CA 91125, USA
Skemer, Andrew; Steward Observatory, Department of Astronomy, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA ; Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA ; )
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