April
2022
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2022AJ....163..168W
Authors
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Winters, Jennifer G.
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Cloutier, Ryan
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Medina, Amber A.
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Irwin, Jonathan M.
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Charbonneau, David
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Astudillo-Defru, Nicola
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Bonfils, Xavier
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Howard, Andrew W.
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Isaacson, Howard
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Bean, Jacob L.
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Seifahrt, Andreas
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Teske, Johanna K.
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Eastman, Jason D.
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Twicken, Joseph D.
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Collins, Karen A.
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Jensen, Eric L. N.
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Quinn, Samuel N.
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Payne, Matthew J.
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Kristiansen, Martti H.
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Spencer, Alton
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Vanderburg, Andrew
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Zechmeister, Mathias
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Weiss, Lauren M.
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Wang, Sharon Xuesong
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Wang, Gavin
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Udry, Stéphane
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Terentev, Ivan A.
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Stürmer, Julian
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Stefánsson, Gudmundur
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Shporer, Avi
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Shectman, Stephen
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Sefako, Ramotholo
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Schwengeler, Hans Martin
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Schwarz, Richard P.
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Scarsdale, Nicholas
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Rubenzahl, Ryan A.
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Roy, Arpita
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Rosenthal, Lee J.
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Robertson, Paul
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Petigura, Erik A.
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Pepe, Francesco
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Omohundro, Mark
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Murphy, Joseph M. Akana
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Murgas, Felipe
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Močnik, Teo
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Montet, Benjamin T.
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Mennickent, Ronald
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Mayo, Andrew W.
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Massey, Bob
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Lubin, Jack
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Lovis, Christophe
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Lewin, Pablo
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Kasper, David
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Kane, Stephen R.
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Jenkins, Jon M.
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Huber, Daniel
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Horne, Keith
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Hill, Michelle L.
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Gorrini, Paula
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Giacalone, Steven
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Fulton, Benjamin
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Forveille, Thierry
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Figueira, Pedro
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Fetherolf, Tara
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Dressing, Courtney
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Díaz, Rodrigo F.
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Delfosse, Xavier
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Dalba, Paul A.
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Dai, Fei
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Cortés, C. C.
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Crossfield, Ian J. M.
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Crane, Jeffrey D.
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Conti, Dennis M.
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Collins, Kevin I.
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Chontos, Ashley
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Butler, R. Paul
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Brown, Peyton
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Brady, Madison
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Behmard, Aida
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Beard, Corey
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Batalha, Natalie M.
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Almenara, Jose-Manuel
Abstract
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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 ${1.304}_{-0.060}^{+0.067}$ R ⊕, consistent with an Earth-like composition. For the newly discovered LTT 1445Ac, we measure a mass of ${1.54}_{-0.19}^{+0.20}$ 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.
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