A second planet transiting LTT 1445A and a determination of the masses of both worlds
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.
Citation
Winters , J G , Cloutier , R , Medina , A A , Irwin , J M , Charbonneau , D , Astudillo-Defru , N , Bonfils , X , Howard , A W , Isaacson , H , Bean , J L , Seifahrt , A , Teske , J K , Eastman , J D , Twicken , J D , Collins , K A , Jensen , E L N , Quinn , S N , Payne , M J , Kristiansen , M H , Spencer , A , Vanderburg , A , Zechmeister , M , Weiss , L M , Wang , S X , Wang , G , Udry , S , Terentev , I A , Stürmer , J , Stefánsson , G , Shporer , A , Shectman , S , Sefako , R , Schwengeler , H M , Schwarz , R P , Scarsdale , N , Rubenzahl , R A , Roy , A , Rosenthal , L J , Robertson , P , Petigura , E A , Pepe , F , Omohundro , M , Murphy , J M A , Murgas , F , Močnik , T , Montet , B T , Mennickent , R , Mayo , A W , Massey , B , Lubin , J , Lovis , C , Lewin , P , Kasper , D , Kane , S R , Jenkins , J M , Huber , D , Horne , K , Hill , M L , Gorrini , P , Giacalone , S , Fulton , B , Forveille , T , Figueira , P , Fetherolf , T , Dressing , C , Díaz , R F , Delfosse , X , Dalba , P A , Dai , F , Cortés , C C , Crossfield , I J M , Crane , J D , Conti , D M , Collins , K I , Chontos , A , Butler , R P , Brown , P , Brady , M , Behmard , A , Beard , C , Batalha , N M & Almenara , J-M 2022 , ' A second planet transiting LTT 1445A and a determination of the masses of both worlds ' , Astronomical Journal , vol. 163 , no. 4 , 168 . https://doi.org/10.3847/1538-3881/ac50a9
Publication
Astronomical Journal
Status
Peer reviewed
ISSN
0004-6256Type
Journal article
Description
K.H. acknowledges support from STFC grant ST/R000824/1.Collections
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