L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf

Creators: Kostov, Veselin B.; Beichman, Charles; Christiansen, Jessie; Ciardi, David

Abstract

We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-size planets transiting L 98-59 (TOI-175, TIC 307210830)—a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broadband photometry, we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 R_⊕ to 1.6 R_⊕. All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false-positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in four more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system.

Additional Information

© 2019. The American Astronomical Society. Received 2019 March 1; revised 2019 May 15; accepted 2019 May 22; published 2019 June 27. We thank the referee for the insightful comments that helped us improve this manuscript. This manuscript includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). Funding for the TESS mission is provided by NASA's Science Mission directorate. We acknowledge the use of TESS Alerts data, as provided by the TESS Science Office. We acknowledge the use of public TESS Alert data from pipelines at the TESS Science Office and at 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. J.G.W. is supported by a grant from the John Templeton Foundation. Acquisition of the CHIRON data and the first epoch of DSSI data was 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. We thank Leonardo Paredes, Hodari James, Rodrigo Hinojosa, and Todd Henry for their work in gathering and processing the CHIRON data, as well as for the management of the CTIO/SMARTS 1.5 m telescope. We are also grateful to the observer support staff at CTIO, at ESO/VLT (for program number 0102.C-0503(A)), and Gemini (for program number GS-2018B-LP-101). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research made use of observations from the LCOGT network and the AAVSO Photometric All-sky Survey (APASS), funded by the Robert Martin Ayers Sciences Fund and NSF AST-1412587. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) ERC grant agreement No. 336480, and from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. M.G. and E.J. are FNRS Senior Research Associates. Work by B.T.M. was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. This work is partly supported by JSPS KAKENHI grant Nos. JP18H01265 and 18H05439, and JST PRESTO grant No. JPMJPR1775. K.H. acknowledges support from STFC grant ST/R000824/1. Facilities: AAVSO - American Association of Variable Star Observers International Database, LCO - , TESS. - Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), celerite (Foreman-Mackey et al. 2017; Foreman-Mackey 2018), emcee (Foreman-Mackey et al. 2013), exoplanet (Foreman-Mackey 2018), DAVE (Kostov et al. 2019), forecaster (Chen & Kipping 2017), IPython (Perez & Granger 2007), Jupyter (Kluyver et al. 2016), Lightkurve (Lightkurve Collaboration et al. 2018), Matplotlib (Hunter 2007), NumPy (van der Walt et al. 2011), Pandas (McKinney 2010), PyMC3 (Salvatier et al. 2016), SciPy (Oliphant 2007), STARRY (Luger et al. 2019), Tapir (Jensen 2013), Theano (Theano Development Team 2016), TTVFast (Deck et al. 2014), TTV2Fast2Furious (Hadden et al. 2018).

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