Two Young Planetary Systems around Field Stars with Ages between 20 and 320 Myr from TESS

Creators: Zhou, George; Quinn, Samuel N.; Irwin, Jonathan; Huang, Chelsea X.; Collins, Karen A.; Bouma, Luke G.; Khan, Lamisha; Landrigan, Anaka; Vanderburg, Andrew M.; Rodriguez, Joseph E.; Latham, David W.; Torres, Guillermo; Douglas, Stephanie T.; Bieryla, Allyson; Esquerdo, Gilbert A.; Berlind, Perry; Calkins, Michael L.; Buchhave, Lars A.; Charbonneau, David; Collins, Kevin I.; Kielkopf, John F.; Jensen, Eric L. N.; Tan, Thiam-Guan; Hart, Rhodes; Carter, Brad; Stockdale, Christopher; Ziegler, Carl; Law, Nicholas; Mann, Andrew W.; Howell, Steve B.; Matson, Rachel A.; Scott, Nicholas J.; Furlan, Elise; White, Russel J.; Hellier, Coel; Anderson, David R.; West, Richard G.; Ricker, George; Vanderspek, Roland; Seager, Sara; Jenkins, Jon M.; Winn, Joshua N.; Mireles, Ismael; Rowden, Pamela; Yahalomi, Daniel A.; Wohler, Bill; Brasseur, Clara. E.; Daylan, Tansu; Colón, Knicole D.

Abstract

Planets around young stars trace the early evolution of planetary systems. We report the discovery and validation of two planetary systems with ages ≾300 Myr from observations by the Transiting Exoplanet Survey Satellite (TESS). The 40--320 Myr old G star TOI-251 hosts a 2.74_(-0.18)^(+0.18) R_⊕ mini-Neptune with a 4.94 day period. The 20--160 Myr old K star TOI-942 hosts a system of inflated Neptune-sized planets, with TOI-942b orbiting in a period of 4.32 days with a radius of 4.81)_(-0.20)^(+0.20) R_⊕ and TOI-942c orbiting in a period of 10.16 days with a radius of 5.79_(-0.18)^(+0.19) R_⊕. Though we cannot place either host star into a known stellar association or cluster, we can estimate their ages via their photometric and spectroscopic properties. Both stars exhibit significant photometric variability due to spot modulation, with measured rotation periods of ~3.5 days. These stars also exhibit significant chromospheric activity, with age estimates from the chromospheric calcium emission lines and X-ray fluxes matching that estimated from gyrochronology. Both stars also exhibit significant lithium absorption, similar in equivalent width to well-characterized young cluster members. TESS has the potential to deliver a population of young planet-bearing field stars, contributing significantly to tracing the properties of planets as a function of their age.

Additional Information

© 2020. The American Astronomical Society. Received 2020 July 27; revised 2020 September 11; accepted 2020 September 19; published 2020 December 2. Work by G.Z. is supported by NASA through Hubble Fellowship grant HST-HF2-51402.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. The MEarth Team gratefully acknowledges funding from the David and Lucile Packard Fellowship for Science and Engineering (awarded to D.C.). This material is based upon work supported by the National Science Foundation under grants AST-0807690, AST-1109468, AST-1004488 (Alan T. Waterman Award), and AST-1616624 and the National Aeronautics and Space Administration under grant No. 80NSSC18K0476 issued through the XRP Program. This work is made possible by a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Funding for the TESS mission is provided by NASA's Science Mission directorate. We acknowledge the use of public TESS Alert data from pipelines at the TESS Science Office and the TESS Science Processing Operations Center. This research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This paper includes data collected by the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This work makes use of data from the Mount Wilson HK Project. The HK_Project_v1995_NSO data derive from the Mount Wilson Observatory HK Project, which was supported by both public and private funds through the Carnegie Observatories, the Mount Wilson Institute, and the Harvard-Smithsonian Center for Astrophysics starting in 1966 and continuing for over 36 yr. These data are the result of the dedicated work of O. Wilson, A. Vaughan, G. Preston, D. Duncan, S. Baliunas, and many others. This work makes use of observations from the LCOGT network. Some of the observations in the paper made use of the high-resolution imaging instrument(s) Alopeke (and/or Zorro). Alopeke (and/or Zorro) was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Alopeke (and/or Zorro) was mounted on the Gemini-North (and/or South) telescope of the international Gemini Observatory, a program of NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministrio da Cincia, Tecnologia, Inovaes e Comunicaes (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Facilities: FLWO 1.5 m - , CHIRON - , TESS - , LCOGT - , MEarth - , Gemini - , Subaru. - Software: lightkurve (Barentsen et al. 2019), emcee (Foreman-Mackey et al. 2013), Astropy (Astropy Collaboration et al. 2013, 2018), AstroImageJ (Collins et al. 2017), PyAstronomy (Czesla et al. 2019), TESSCut (Brasseur et al. 2019).

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