Bright Opportunities for Atmospheric Characterization of Small Planets: Masses and Radii of K2-3 b, c, d and GJ3470 b from Radial Velocity Measurements and Spitzer Transits

Creators: Kosiarek, Molly R.; Crossfield, Ian J. M.; Hardegree-Ullman, Kevin K.; Livingston, John H.; Benneke, Bjorn; Blunt, Sarah; Henry, Gregory W.; Howard, Ward S.; Berardo, David; Fulton, Benjamin J.; Hirsch, Lea A.; Howard, Andrew W.; Isaacson, Howard; Petigura, Erik A.; Sinukoff, Evan; Weiss, Lauren; Bonfils, X.; Dressing, Courtney D.; Knutson, Heather A.; Schlieder, Joshua E.; Werner, Michael; Gorjian, Varoujan; Krick, Jessica; Morales, Farisa Y.; Astudillo-Defru, Nicola; Almenara, J.-M.; Delfosse, X.; Forveille, T.; Lovis, C.; Mayor, M.; Murgas, F.; Pepe, F.; Santos, N. C.; Udry, S.; Corbett, H. T.; Fors, Octavi; Law, Nicholas M.; Ratzloff, Jeffrey K.; del Ser, Daniel

Abstract

We report improved masses, radii, and densities for four planets in two bright M-dwarf systems, K2-3 and GJ3470, derived from a combination of new radial velocity and transit observations. Supplementing K2 photometry with follow-up Spitzer transit observations refined the transit ephemerides of K2-3 b, c, and d by over a factor of 10. We analyze ground-based photometry from the Evryscope and Fairborn Observatory to determine the characteristic stellar activity timescales for our Gaussian Process fit, including the stellar rotation period and activity region decay timescale. The stellar rotation signals for both stars are evident in the radial velocity data and is included in our fit using a Gaussian process trained on the photometry. We find the masses of K2-3 b, K2-3 c, and GJ3470 b to be 6.48^(+0.99)_(-0.93), 2.14^(+1.08)_(-1.04), and 12.58^(+1.31)_(-1.28) M⊕, respectively. K2-3 d was not significantly detected and has a 3σ upper limit of 2.80 M⊕. These two systems are training cases for future TESS systems; due to the low planet densities (ρ < 3.7 g cm^(−3)) and bright host stars (K < 9 mag), they are among the best candidates for transmission spectroscopy in order to characterize the atmospheric compositions of small planets.

Additional Information

© 2019 The American Astronomical Society. Received 2018 March 13; revised 2018 November 21; accepted 2018 December 6; published 2019 February 5. M.R.K. acknowledges support from the NSF Graduate Research Fellowship, grant No. DGE 1339067. I.J.M.C. acknowledges support from NASA through K2GO grant 80NSSC18K0308 and from NSF through grant AST-1824644. G.W.H. acknowledges long-term support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence program. O.F. acknowledges funding support by the grant MDM-2014-0369 of the ICCUB (Unidad de Excelencia "María de Maeztu"). This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This research has made use of the Exoplanet Follow-up Observing Program (ExoFOP), which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Keck:I - KECK I Telescope, Spitzer - Spitzer Space Telescope satellite, TNG - Telescopio Nazionale Galileo.

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