학술논문
The LHS 1678 System: Two Earth-Sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc
Document Type
Working Paper
Author
Silverstein, Michele L.; Schlieder, Joshua E.; Barclay, Thomas; Hord, Benjamin J.; Jao, Wei-Chun; Vrijmoet, Eliot Halley; Henry, Todd J.; Cloutier, Ryan; Kostov, Veselin B.; Kruse, Ethan; Winters, Jennifer G.; Irwin, Jonathan M.; Kane, Stephen R.; Stassun, Keivan G.; Huang, Chelsea; Kunimoto, Michelle; Tey, Evan; Vanderburg, Andrew; Astudillo-Defru, Nicola; Bonfils, Xavier; Brasseur, C. E.; Charbonneau, David; Ciardi, David R.; Collins, Karen A.; Collins, Kevin I.; Conti, Dennis M.; Crossfield, Ian J. M.; Daylan, Tansu; Doty, John P.; Dressing, Courtney D.; Gilbert, Emily A.; Horne, Keith; Jenkins, Jon M.; Latham, David W.; Mann, Andrew W.; Matthews, Elisabeth; Paredes, Leonardo A.; Quinn, Samuel N.; Ricker, George R.; Schwarz, Richard P.; Seager, Sara; Sefako, Ramotholo; Shporer, Avi; Smith, Jeffrey C.; Stockdale, Christopher; Tan, Thiam-Guan; Torres, Guillermo; Twicken, Joseph D.; Vanderspek, Roland; Wang, Gavin; Winn, Joshua N.
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Subject
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Abstract
We present the TESS discovery of the LHS 1678 (TOI-696) exoplanet system, comprised of two approximately Earth-sized transiting planets and a likely astrometric brown dwarf orbiting a bright ($V_J$=12.5, $K_s$=8.3) M2 dwarf at 19.9 pc. The two TESS-detected planets are of radius 0.70$\pm$0.04 $R_\oplus$ and 0.98$\pm$0.06 $R_\oplus$ in 0.86-day and 3.69-day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. HARPS RV monitoring yields 97.7 percentile mass upper limits of 0.35 $M_\oplus$ and 1.4 $M_\oplus$ for planets b and c, respectively. The astrometric companion detected by the CTIO/SMARTS 0.9m has an orbital period on the order of decades and is undetected by other means. Additional ground-based observations constrain the companion to being a high-mass brown dwarf or smaller. Each planet is of unique interest; the inner planet has an ultra-short period, and the outer planet is in the Venus zone. Both are promising targets for atmospheric characterization with the JWST and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9$\pm$0.1 $R_\oplus$ in a 4.97-day orbit is also identified in multi-Cycle TESS data for validation in future work. The host star is associated with an observed gap in the lower main sequence of the Hertzsprung-Russell diagram. This gap is tied to the transition from partially- to fully-convective interiors in M dwarfs, and the effect of the associated stellar astrophysics on exoplanet evolution is currently unknown. The culmination of these system properties makes LHS 1678 a unique, compelling playground for comparative exoplanet science and understanding the formation and evolution of small, short-period exoplanets orbiting low-mass stars.
Comment: Published in The Astronomical Journal (31 pages, 21 figures, 11 tables, 3 appendices)
Comment: Published in The Astronomical Journal (31 pages, 21 figures, 11 tables, 3 appendices)