A Second Planet Transiting LTT 1445A and a Determination of the Masses of Both Worlds

Creators: Winters, Jennifer G.; Cloutier, Ryan; Medina, Amber A.; Irwin, Jonathan M.; Charbonneau, David; Astudillo-Defru, Nicola; Bonfils, Xavier; Howard, Andrew W.; Isaacson, Howard; Bean, Jacob L.; Seifahrt, Andreas; Teske, Johanna K.; Eastman, Jason D.; Twicken, Joseph D.; Collins, Karen A.; Jensen, Eric L. N.; Quinn, Samuel N.; Payne, Matthew J.; Kristiansen, Martti H.; Spencer, Alton; Vanderburg, Andrew; Zechmeister, Mathias; Weiss, Lauren M.; Wang, Sharon Xuesong; Wang, Gavin; Udry, Stéphane; Terentev, Ivan A.; Stürmer, Julian; Stefánsson, Guðmundur; Shporer, Avi; Shectman, Stephen; Sefako, Ramotholo; Schwengeler, Hans Martin; Schwarz, Richard P.; Scarsdale, Nicholas; Rubenzahl, Ryan A.; Roy, Arpita; Rosenthal, Lee J.; Robertson, Paul; Petigura, Erik A.; Pepe, Francesco; Omohundro, Mark; Murphy, Joseph M. Akana; Murgas, Felipe; Močnik, Teo; Montet, Benjamin T.; Mennickent, Ronald; Mayo, Andrew W.; Massey, Bob; Lubin, Jack; Lovis, Christophe; Lewin, Pablo; Kasper, David; Kane, Stephen R.; Jenkins, Jon M.; Huber, Daniel; Horne, Keith; Hill, Michelle L.; Gorrini, Paula; Giacalone, Steven; Fulton, Benjamin; Forveille, Thierry; Figueira, Pedro; Fetherolf, Tara; Dressing, Courtney; Díaz, Rodrigo F.; Delfosse, Xavier; Dalba, Paul A.; Dai, Fei; Cortes, C. C.; Crossfield, Ian J. M.; Crane, Jeffrey D.; Conti, Dennis M.; Collins, Kevin I.; Chontos, Ashley; Butler, R. Paul; Brown, Peyton; Brady, Madison; Behmard, Aida; Beard, Corey; Batalha, Natalie M.; Almenara, Jose-Manuel

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Abstract

LTT 1445 is a hierarchical triple M-dwarf star system located at a distance of 6.86 pc. The primary star LTT 1445A (0.257 M_⊙) is known to host the transiting planet LTT 1445Ab with an orbital period of 5.36 days, making it the second-closest known transiting exoplanet system, and the closest one for which the host is an M dwarf. Using Transiting Exoplanet Survey Satellite data, we present the discovery of a second planet in the LTT 1445 system, with an orbital period of 3.12 days. We combine radial-velocity measurements obtained from the five spectrographs, Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, High Accuracy Radial Velocity Planet Searcher, High-Resolution Echelle Spectrometer, MAROON-X, and Planet Finder Spectrograph to establish that the new world also orbits LTT 1445A. We determine the mass and radius of LTT 1445Ab to be 2.87 ± 0.25 M_⊕ and 1.304^(+0.067)_(-0.060) R_⊕, consistent with an Earth-like composition. For the newly discovered LTT 1445Ac, we measure a mass of 1.54^(+0.20)_(-0.19) M_⊕ and a minimum radius of 1.15 R_⊕, but we cannot determine the radius directly as the signal-to-noise ratio of our light curve permits both grazing and nongrazing configurations. Using MEarth photometry and ground-based spectroscopy, we establish that star C (0.161 M_⊙) is likely the source of the 1.4 day rotation period, and star B (0.215 M_⊙) has a likely rotation period of 6.7 days. We estimate a probable rotation period of 85 days for LTT 1445A. Thus, this triple M-dwarf system appears to be in a special evolutionary stage where the most massive M dwarf has spun down, the intermediate mass M dwarf is in the process of spinning down, while the least massive stellar component has not yet begun to spin down.

Additional Information

© 2022 The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 July 30; revised 2022 January 3; accepted 2022 January 6; published 2022 March 14. We thank the referee for a thoughtful and prompt review that improved the manuscript. 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. 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 grant AST-1616624, and work supported by the National Aeronautics and Space Administration under Grant No. 80NSSC18K0476 issued through the XRP Program. This paper includes data collected by the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST). We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. 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. 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. Funding for the TESS mission is provided by the NASA's Science Mission Directorate. This work makes use of observations from the LCOGT network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-scale Innovations Program (MSIP). MSIP is funded by NSF. 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. 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 grateful for the privilege of observing the Universe from a place that is unique in both its astronomical quality and its cultural significance. The international Gemini Observatory, a program of NSF's NOIRLab, 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 Observatory 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). The MAROON-X spectrograph was funded by the David and Lucile Packard Foundation, the Heising–Simons Foundation, the Gemini Observatory, and the University of Chicago. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck 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. 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 NASA and the NSF have been used in this publication. This work has made use of the Washington Double Star Catalog maintained at the U.S. Naval Observatory. This work has made use of the Smithsonian Astrophysical Observatory/NASA Astrophysics Data System. R.C. acknowledges support from the Banting Postdoctoral Fellowship program, administered by the Government of Canada. N.A.-D. acknowledges the support of FONDECYT project 3180063. J.M.A.M. is supported by the NSF Graduate Research Fellowship, grant No. DGE-1842400. J.M.A.M. also acknowledges the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant No. 1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. D.H. acknowledges support from the Alfred P. Sloan Foundation, NASA (80NSSC21K0652), and the National Science Foundation (AST-1717000). K.H. acknowledges support from STFC grant ST/R000824/1. T.F. acknowledges support from the University of California President's Postdoctoral Fellowship Program. P.D. acknowledges support from a National Science Foundation Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1903811. Facilities: TESS - , MEarth - , LCOGT - , ESO:3.6 m (HARPS) - , Gemini:Gillett (MAROON-X) - , Keck (HIRES) - , Magellan:Clay (PFS) - , VLT (ESPRESSO) - . Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), barycorrpy (Kanodia & Wright 2018), celerite (Foreman-Mackey et al. 2017), ExoFASTv2 (Eastman et al. 2013; Eastman 2017), exoplanet (Foreman-Mackey et al. 2019), george (Ambikasaran et al. 2015), IDL, IRAF, LcTools II (Schmitt & Vanderburg 2021), PYMC3 (Salvatier et al. 2016), python, serval (Zechmeister et al. 2018), starry (Luger et al. 2019), TAPIR (Jensen 2013), Time Utilities (Eastman et al. 2010), todcor (Zucker & Mazeh 1994).

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