The LHS 1678 System: Two Earth-sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc

Silverstein, Michele L. and Schlieder, Joshua E. and Barclay, Thomas and Hord, Benjamin J. and Jao, Wei-Chun and Vrijmoet, Eliot Halley and Henry, Todd J. and Cloutier, Ryan and Kostov, Veselin B. and Kruse, Ethan and Winters, Jennifer G. and Irwin, Jonathan M. and Kane, Stephen R. and Stassun, Keivan G. and Huang, Chelsea ORCID: https://orcid.org/0000-0003-0918-7484 and Kunimoto, Michelle and Tey, Evan and Vanderburg, Andrew and Astudillo-Defru, Nicola and Bonfils, Xavier and Brasseur, C. E. and Charbonneau, David and Ciardi, David R. and Collins, Karen A. and Collins, Kevin I. and Conti, Dennis M. and Crossfield, Ian J. M. and Daylan, Tansu and Doty, John P. and Dressing, Courtney D. and Gilbert, Emily A. and Horne, Keith and Jenkins, Jon M. and Latham, David W. and Mann, Andrew W. and Matthews, Elisabeth and Paredes, Leonardo A. and Quinn, Samuel N. and Ricker, George R. and Schwarz, Richard P. and Seager, Sara and Sefako, Ramotholo and Shporer, Avi and Smith, Jeffrey C. and Stockdale, Christopher and Tan, Thiam-Guan and Torres, Guillermo and Twicken, Joseph D. and Vanderspek, Roland and Wang, Gavin and Winn, Joshua N. (2022) The LHS 1678 System: Two Earth-sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc. The Astronomical Journal, 163 (4):151. pp. 1-31. ISSN 0004-6256

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Abstract

We present the Transiting Exoplanet Survey Satellite (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 ± 0.04 R ⊕ and 0.98 ± 0.06 R ⊕ in 0.86 day and 3.69 day orbits, respectively. Both planets are validated and characterized via ground-based follow-up observations. High Accuracy Radial Velocity Planet Searcher RV monitoring yields 97.7 percentile mass upper limits of 0.35 M ⊕ and 1.4 M ⊕ for planets b and c, respectively. The astrometric companion detected by the Cerro Tololo Inter-American Observatory/Small and Moderate Aperture Telescope System 0.9 m 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 James Webb Space Telescope and mass measurements via extreme-precision radial velocity. A third planet candidate of radius 0.9 ± 0.1 R ⊕ in a 4.97 day orbit is also identified in multicycle 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.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Date Deposited: 31 Mar 2022 05:38
Last Modified: 17 May 2022 06:32
Uncontrolled Keywords: Exoplanet systems (484); Transit photometry (1709); Low mass stars (2050); M dwarf stars (982); Astrometric binary stars (79); Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Solar and Stellar Astrophysics
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Identification Number or DOI: https://doi.org/10.3847/1538-3881/ac32e3
URI: http://eprints.usq.edu.au/id/eprint/47378

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