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

April 2022 • 2022AJ....163..168W

Authors • 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, Gudmundur • 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 • Cortés, 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

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 ${1.304}_{-0.060}^{+0.067}$ 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.


IPAC Authors


Benjamin Fulton

Assistant Scientist