A Pair of TESS Planets Spanning the Radius Valley around the Nearby Mid-M Dwarf LTT 3780

Creators: Cloutier, Ryan; Eastman, Jason D.; Rodriguez, Joseph E.; Astudillo-Defru, Nicola; Bonfils, Xavier; Mortier, Annelies; Watson, Christopher A.; Stalport, Manu; Pinamonti, Matteo; Lienhard, Florian; Harutyunyan, Avet; Damasso, Mario; Latham, David W.; Collins, Karen A.; Massey, Robert; Irwin, Jonathan; Winters, Jennifer G.; Charbonneau, David; Ziegler, Carl; Matthews, Elisabeth; Crossfield, Ian J. M.; Kreidberg, Laura; Quinn, Samuel N.; Ricker, George; Vanderspek, Roland; Seager, Sara; Winn, Joshua; Jenkins, Jon M.; Vezie, Michael; Udry, Stéphane; Twicken, Joseph D.; Tenenbaum, Peter; Sozzetti, Alessandro; Ségransan, Damien; Schlieder, Joshua E.; Sasselov, Dimitar; Santos, Nuno C.; Rice, Ken; Rackham, Benjamin V.; Poretti, Ennio; Piotto, Giampaolo; Phillips, David; Pepe, Francesco; Molinari, Emilio; Mignon, Lucile; Micela, Giuseppina; Melo, Claudio; de Medeiros, José R.; Mayor, Michel; Matson, Rachel A.; Martinez Fiorenzano, Aldo F.; Mann, Andrew W.; Magazzú, Antonio; Lovis, Christophe; López-Morales, Mercedes; Lopez, Eric; Lissauer, Jack J.; Lépine, Sébastien; Law, Nicholas; Kielkopf, John F.; Johnson, John A.; Jensen, Eric L. N.; Howell, Steve B.; Gonzales, Erica; Ghedina, Adriano; Forveille, Thierry; Figueira, Pedro; Dumusque, Xavier; Dressing, Courtney D.; Doyon, René; Díaz, Rodrigo F.; Fabrizio, Luca Di; Delfosse, Xavier; Cosentino, Rosario; Conti, Dennis M.; Collins, Kevin I.; Cameron, Andrew Collier; Ciardi, David; Caldwell, Douglas A.; Burke, Christopher; Buchhave, Lars; Briceño, César; Boyd, Patricia; Bouchy, François; Beichman, Charles; Artigau, Étienne; Almenara, Jose M.

Abstract

We present the confirmation of two new planets transiting the nearby mid-M dwarf LTT 3780 (TIC 36724087, TOI-732, V = 13.07, K_s = 8.204, R_s = 0.374 R⊙, M_s = 0.401 M⊙, d = 22 pc). The two planet candidates are identified in a single Transiting Exoplanet Survey Satellite sector and validated with reconnaissance spectroscopy, ground-based photometric follow-up, and high-resolution imaging. With measured orbital periods of P_b = 0.77, P_c = 12.25 days and sizes r_(p,b) = 1.33 ± 0.07, r_(p,c) = 2.30 ± 0.16 R⊕, the two planets span the radius valley in period–radius space around low-mass stars, thus making the system a laboratory to test competing theories of the emergence of the radius valley in that stellar mass regime. By combining 63 precise radial velocity measurements from the High Accuracy Radial velocity Planet Searcher (HARPS) and HARPS-N, we measure planet masses of m_(p,b) = 2.62^(+0.48)_(−0.46) and m_(p,c) = 8.6^(+1.6)_(−1.3) M⊕, which indicates that LTT 3780b has a bulk composition consistent with being Earth-like, while LTT 3780c likely hosts an extended H/He envelope. We show that the recovered planetary masses are consistent with predictions from both photoevaporation and core-powered mass-loss models. The brightness and small size of LTT 3780, along with the measured planetary parameters, render LTT 3780b and c as accessible targets for atmospheric characterization of planets within the same planetary system and spanning the radius valley.

Additional Information

© 2020 The American Astronomical Society. Received 2020 March 2; revised 2020 April 27; accepted 2020 May 8; published 2020 June 4. R.C. is supported by a grant from the National Aeronautics and Space Administration in support of the TESS science mission. We thank Amber Medina for assistance with detrending the TESS light curve. We thank Sam Hadden for discussions regarding the TTV analysis. We also thank the anonymous referee for comments that helped to improve the completeness of our paper. N.A.D. acknowledges support from FONDECYT 3180063. A.M. acknowledges support from the senior Kavli Institute Fellowships. J.G.W. is supported by a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. C.Z. is supported by a Dunlap Fellowship at the Dunlap Institute for Astronomy & Astrophysics, funded through an endowment established by the Dunlap family and the University of Toronto. I.J.M.C. acknowledges support from the NSF through grant AST-1824644 and NASA through Caltech/JPL grant RSA-1610091. F.L. gratefully acknowledges a scholarship from the Fondation Zd̆nek et Michaela Bakala. M.S. thanks the Swiss National Science Foundation (SNSF) and Geneva University for their continuous support of our exoplanet researches. This work has been in particular carried out in the frame of the National Center for Competence in Research "PlanetS" supported by SNSF. C.A.W. acknowledges support from Science and Technology Facilities Council grant ST/P000312/1. N.C.S. acknowledges supported by FCT, Fundação para a Ciência e a Tecnologia, through national funds and by FEDER through COMPETE2020, Programa Operacional Competitividade e Internacionalização, by these grants: UID/FIS/04434/2019, UIDB/04434/2020, UIDP/04434/2020, PTDC/FIS-AST/32113/2017 & POCI-01-0145-FEDER-032113, PTDC/FIS-AST/28953/2017 & POCI-01-0145-FEDER-028953. M.Pi. gratefully acknowledges support from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 313014 (ETAEARTH). J.R.M. acknowledges support by the CAPES, CNPq, and FAPERN Brazilian agencies. This work has been partially supported by the National Aeronautics and Space Administration under grant No. NNX17AB59G issued through the Exoplanets Research Program. We acknowledge the use of public TESS Alert data from the pipelines at the TESS Science Office and the TESS Science Processing Operations Center. This work makes use of observations acquired with the T150 telescope at Sierra Nevada Observatory, operated by the Instituto de Astrofísica de Andalucía (IAA-CSIC). The MEarth Team gratefully acknowledges funding from the David and Lucile Packard Fellowship for Science and Engineering (awarded to D.C.). This material is based upon work supported by the National Science Foundation under grants AST-0807690, AST-1109468, AST-1004488 (Alan T. Waterman Award), and AST-1616624. This work is made possible by a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This material is based upon work supported by the National Aeronautics and Space Administration under grant No. 80NSSC18K0476 issued through the XRP Program. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work makes use of observations from the LCOGT network. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This work was supported by the French National Research Agency in the framework of the Investissements d'Avenir program (ANR-15-IDEX-02) through the funding of the "Origin of Life" project of the Univ. Grenoble-Alpes. Facilities: TESS - , FLWO:1.5m, LCOGT - , OSN - , TRAPPIST-North - , MEarth-North - , SOAR - , Gemini/NIRI - , ESO 3.6 m/HARPS - , TNG/HARPS-N. - Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), BANZAI (McCully et al. 2018), batman (Kreidberg 2015), BGLS (Mortier et al. 2015), celerite (Foreman-Mackey et al. 2017), emcee (Foreman-Mackey et al. 2013), EvapMass (Owen & Campos Estrada 2020), EXOFAST (Eastman et al. 2013), EXOFASTv2 (Eastman et al. 2019), exoplanet (Foreman-Mackey et al. 2019), forecaster (Chen & Kipping 2017), PandExo (Batalha et al. 2017), PyMC3 (Salvatier et al. 2016), scipy (Virtanen et al. 2020), STARRY (Luger et al. 2019), Tapir (Jensen 2013), TERRA (Anglada-Escudé & Butler 2012), TTV2Fast2Furious (Hadden 2019).

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