A planetary system with two transiting mini-Neptunes near the radius valley transition around the bright M dwarf TOI-776

Creators: Luque, R.; Serrano, L. M.; Molaverdikhani, K.; Nixon, M. C.; Livingston, J. H.; Guenther, E. W.; Pallé, E.; Madhusudhan, N.; Nowak, G.; Korth, J.; Cochran, W. D.; Hirano, T.; Chaturvedi, P.; Goffo, E.; Albrecht, S.; Barragán, O.; Briceño, C.; Cabrera, J.; Charbonneau, D.; Cloutier, R.; Collins, K. A.; Collins, K. I.; Colón, K. D.; Crossfield, I. J. M.; Csizmadia, Sz.; Dai, F.; Deeg, H. J.; Esposito, M.; Fridlund, M.; Gandolfi, D.; Georgieva, I.; Glidden, A.; Goeke, R. F.; Grziwa, S.; Hatzes, A. P.; Henze, C. E.; Howell, S. B.; Irwin, J.; Jenkins, J. M.; Jensen, E. L. N.; Kábath, P.; Kidwell, R. C.; Kielkopf, J. F.; Knudstrup, E.; Lam, K. W. F.; Latham, D. W.; Lissauer, J. J.; Mann, A. W.; Matthews, E. C.; Mireles, I.; Narita, N.; Paegert, M.; Persson, C. M.; Redfield, S.; Ricker, G. R.; Rodler, F.; Schlieder, J. E.; Scott, N. J.; Seager, S.; Šubjak, J.; Tan, T. G.; Ting, E. B.; Vanderspek, R.; Van Eylen, V.; Winn, J. N.; Ziegler, C.

Abstract

We report the discovery and characterization of two transiting planets around the bright M1 V star LP 961-53 (TOI-776, J = 8.5 mag, M = 0.54 ± 0.03 M_⊙) detected during Sector 10 observations of the Transiting Exoplanet Survey Satellite (TESS). Combining the TESS photometry with HARPS radial velocities, as well as ground-based follow-up transit observations from the MEarth and LCOGT telescopes, for the inner planet, TOI-776 b, we measured a period of P_b = 8.25 d, a radius of R_b = 1.85 ± 0.13 R_⊕, and a mass of M_b = 4.0 ± 0.9 M_⊕; and for the outer planet, TOI-776 c, a period of P_c = 15.66 d, a radius of R_c = 2.02 ± 0.14 R ⊕, and a mass of M_c = 5.3 ± 1.8 M_⊕. The Doppler data shows one additional signal, with a period of ~34 d, associated with the rotational period of the star. The analysis of fifteen years of ground-based photometric monitoring data and the inspection of different spectral line indicators confirm this assumption. The bulk densities of TOI-776 b and c allow for a wide range of possible interior and atmospheric compositions. However, both planets have retained a significant atmosphere, with slightly different envelope mass fractions. Thanks to their location near the radius gap for M dwarfs, we can start to explore the mechanism(s) responsible for the radius valley emergence around low-mass stars as compared to solar-like stars. While a larger sample of well-characterized planets in this parameter space is still needed to draw firm conclusions, we tentatively estimate that the stellar mass below which thermally-driven mass loss is no longer the main formation pathway for sculpting the radius valley is between 0.63 and 0.54 M_⊙. Due to the brightness of the star, the TOI-776 system is also an excellent target for the James Webb Space Telescope, providing a remarkable laboratory in which to break the degeneracy in planetary interior models and to test formation and evolution theories of small planets around low-mass stars.

Additional Information

© ESO 2021. Received: 16 September 2020. Accepted: 30 November 2020. Based on observations made with ESO Telescopes at the La Silla Observatory under programs ID 1102.C-0923 and 60.A-9709. This work was supported by the KESPRINT collaboration, an international consortium devoted to the characterization and research of exoplanets discovered with space-based missions. We are very grateful to the ESO staff members for their precious support during the observations. We warmly thank Xavier Dumusque and François Bouchy for coordinating the shared observations with HARPS and Jaime Alvarado Montes, Xavier Delfosse, Guillaume Gaisné, Melissa Hobson, and Felipe Murgas who helped collecting the data. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA Explorer Program. We acknowledge the use of TESS Alert data, which is currently in a beta test phase, from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. 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 research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. 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. 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, and upon work supported by the National Aeronautics and Space Administration under Grant No. 80NSSC18K0476 issued through the XRP Program. 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 work makes use of observations from the LCOGT network. Some of the Observations in the paper made use of the High-Resolution Imaging instrument Zorro. Zorro was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Data were reduced using a software pipeline originally written by Elliott Horch and Mark Everett. Zorro was mounted on the Gemini South telescope, and NIRI was mounted on the Gemini North telescope, of the international Gemini Observatory, a program of NSF's OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Data collected under program GN-2019A-LP-101. Based in part on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia e Inovações (MCTI/LNA) do Brasil, the US National Science Foundation's NOIRLab, the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). This work was enabled by observations made from the Gemini North telescope, located within the Maunakea Science Reserve and adjacent to the summit of Maunakea. We are grateful for the privilege of observing the Universe from a place that is unique in both its astronomical quality and its cultural significance. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere under ESO programme 0103.C-0449(A). R.L. has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 713673 and financial support through the "la Caixa" INPhINIT Fellowship Grant LCF/BQ/IN17/11620033 for Doctoral studies at Spanish Research Centers of Excellence from "la Caixa" Banking Foundation, Barcelona, Spain. This work is partly financed by the Spanish Ministry of Economics and Competitiveness through projects ESP2016-80435-C2-2-R and ESP2016-80435-C2-1-R. L.M.S. and D.G. gratefully acknowledge financial support from the CRT foundation under Grant No. 2018.2323 "Gaseous or rocky? Unveiling the nature of small worlds". This work is supported by JSPS KAKENHI Grant Numbers JP19K14783, JP18H01265 and JP18H05439, and JST PRESTO Grant Number JPMJPR1775. I.J.M.C. acknowledges support from the NSF through grant AST-1824644. J.K., Sz.Cs., M.E., A.P.H., K.W.F.L., S.G. acknowledge support by DFG grants PA525/ 18-1, PA525/ 19-1, PA525/ 20-1, HA3279/ 12-1 and RA714/ 14-1 within the DFG Schwerpunkt SPP 1992, Exploring the Diversity of Extrasolar Planets. M.F, I.G. and C.M.P. gratefully acknowledge the support of the Swedish National Space Agency (DNR 65/19 and 174/18). P.K. and J.S. acknowledge the grant INTER-TRANSFER number LTT20015. S.A. knowledges support from the Danish Council for Independent Research, through a DFF Sapere Aude Starting Grant no. 4181-00487B. Funding for the Stellar Astrophysics Centre is provided by The Danish National Research Foundation (Grant agreement no.: DNRF106). H.J.D. acknowledges support by grant ESP2017-87676-C5-4-R of the Spanish Secretary of State for R&D&i (MINECO).D.G. warmly thanks Javier Alarcón, Pablo Arias, Duncan Castex, Mónica Castillo, Cecilia Farias, Mario Herrera, Francisco Labraña, Angélica León, and Ariel Sánchez (ESO La Silla) for the inspiring conversations.

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