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

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; MO?NIK, 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,

ASTRONOMICAL JOURNAL

IOP PUBLISHING LTD

Año: 2022 vol. 163

0004-6256

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.