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

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

*Corresponding author for this work

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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 R, consistent with an Earth-like composition. For the newly discovered LTT 1445Ac, we measure a mass of 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.
Original languageEnglish
Article number168
JournalThe Astronomical Journal
Issue number4
Number of pages18
Publication statusPublished - 2022


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