K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

June 2017 • 2017AJ....153..271S

Authors • Sinukoff, Evan • Howard, Andrew W. • Petigura, Erik A. • Fulton, Benjamin J. • Crossfield, Ian J. M. • Isaacson, Howard • Gonzales, Erica • Crepp, Justin R. • Brewer, John M. • Hirsch, Lea • Weiss, Lauren M. • Ciardi, David R. • Schlieder, Joshua E. • Benneke, Bjoern • Christiansen, Jessie L. • Dressing, Courtney D. • Hansen, Brad M. S. • Knutson, Heather A. • Kosiarek, Molly • Livingston, John H. • Greene, Thomas P. • Rogers, Leslie A. • Lépine, Sébastien

Abstract • We report precise mass and density measurements of two extremely hot sub-Neptune-size planets from the K2 mission using radial velocities, K2 photometry, and adaptive optics imaging. K2-66 harbors a close-in sub-Neptune-sized ({2.49}_-0.24^+0.34 {R}_\oplus ) planet (K2-66b) with a mass of 21.3+/- 3.6 {M}_\oplus . Because the star is evolving up the subgiant branch, K2-66b receives a high level of irradiation, roughly twice the main-sequence value. K2-66b may reside within the so-called “photoevaporation desert,” a domain of planet size and incident flux that is almost completely devoid of planets. Its mass and radius imply that K2-66b has, at most, a meager envelope fraction (<5%) and perhaps no envelope at all, making it one of the largest planets without a significant envelope. K2-106 hosts an ultra-short-period planet (P = 13.7 hr) that is one of the hottest sub-Neptune-size planets discovered to date. Its radius ({1.82}_-0.14^+0.20 {R}_\oplus ) and mass (9.0+/- 1.6 {M}_\oplus ) are consistent with a rocky composition, as are all other small ultra-short-period planets with well-measured masses. K2-106 also hosts a larger, longer-period planet ({R}_{{p}} = {2.77}_-0.23^+0.37 {R}_\oplus , P = 13.3 days) with a mass less than 24.4 {M}_\oplus at 99.7% confidence. K2-66b and K2-106b probe planetary physics in extreme radiation environments. Their high densities reflect the challenge of retaining a substantial gas envelope in such extreme environments.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2017AJ....153..271S
• PDF https://iopscience.iop.org/article/10.3847/1538-3881/aa725f/pdf
• PDF https://stacks.iop.org/1538-3881/153/271/pdf
• PREPRINT http://arxiv.org/abs/1705.03491
• DATA http://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?type=REFERENCE&bibcode=2017AJ....153..271S
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2017AJ....153..271S
• ELECTR https://doi.org/10.3847%2F1538-3881%2Faa725f