A super-Earth and sub-Neptune transiting the late-type M dwarf LP 791-18

Creators: Crossfield, Ian J. M.; Waalkes, William; Newton, Elisabeth R.; Narita, Norio; Muirhead, Philip; Ment, Kristo; Matthews, Elisabeth; Kraus, Adam; Kostov, Veselin; Kosiarek, Molly R.; Kane, Stephen R.; Isaacson, Howard; Halverson, Sam; Gonzales, Erica; Everett, Mark; Dragomir, Diana; Collins, Karen A.; Chontos, Ashley; Berardo, David; Winters, Jennifer G.; Winn, Joshua N.; Scott, Nicholas J.; Rojas-Ayala, Barbara; Rizzuto, Aaron C.; Petigura, Erik A.; Peterson, Merrin; Mocnik, Teo; Mikal-Evans, Thomas; Mehrle, Nicholas; Matson, Rachel; Kuzuhara, Masayuki; Irwin, Jonathan; Huber, Daniel; Huang, Chelsea; Howell, Steve; Howard, Andrew W.; Hirano, Teruyuki; Fulton, Benjamin J.; Dupuy, Trent; Dressing, Courtney D.; Dalba, Paul A.; Charbonneau, David; Burt, Jennifer; Berta-Thompson, Zachory; Benneke, Björn; Watanabe, Noriharu; Twicken, Joseph D.; Tamura, Motohide; Schlieder, Joshua; Seager, S.; Rose, Mark E.; Ricker, George; Quintana, Elisa; Lépine, Sébastien; Latham, David W.; Kotani, Takayuki; Jenkins, Jon M.; Hori, Yasunori; Colón, Knicole; Caldwell, Douglas A.

Abstract

Planets occur most frequently around cool dwarfs, but only a handful of specific examples are known to orbit the latest-type M stars. Using TESS photometry, we report the discovery of two planets transiting the low-mass star called LP 791-18 (identified by TESS as TOI 736). This star has spectral type M6V, effective temperature 2960 K, and radius 0.17 R⊙, making it the third-coolest star known to host planets. The two planets straddle the radius gap seen for smaller exoplanets; they include a 1.1R⊕ planet on a 0.95 day orbit and a 2.3R⊕ planet on a 5 day orbit. Because the host star is small the decrease in light during these planets' transits is fairly large (0.4% and 1.7%). This has allowed us to detect both planets' transits from ground-based photometry, refining their radii and orbital ephemerides. In the future, radial velocity observations and transmission spectroscopy can both probe these planets' bulk interior and atmospheric compositions, and additional photometric monitoring would be sensitive to even smaller transiting planets.

Additional Information

© 2019 The American Astronomical Society. Received 2019 June 21; revised 2019 August 19; accepted 2019 August 20; published 2019 September 19. The authors thank our anonymous referee for constructive comments that improved the quality of this work. We also thank Prof. N. Lewis for a stimulating and thought-provoking discussion that improved the quality of this work. We thank Hiroki Harakawa, Tomoyuki Kudo, Masashi Omiya, Aoi Takahashi, the entire IRD team, and the Subaru IRD TESS intensive follow-up project team for supporting Subaru IRD observation. I.J.M.C. acknowledges support from the NSF through grant AST-1824644, and from NASA through Caltech/JPL grant RSA-1610091. M.R.K. acknowledges support from the NSF Graduate Research Fellowship, grant No. DGE 1339067. D.H. acknowledges support by the National Aeronautics and Space Administration (80NSSC18K1585, 80NSSC19K0379) awarded through the TESS Guest Investigator Program. Work by J.N.W. was supported by the Heising-Simons Foundation. B.R-A. acknowledges support from FONDECYT through grant 11181295. W.W. acknowledges support from the NSF GRFP, DGE 1650115. N.N. is supported by JSPS KAKENHI grant Nos. JP18H01265 and JP18H05439, and JST PRESTO grant No. JPMJPR1775. A.J.C. acknowledges support from the National Science Foundation Graduate Research Fellowship Program under grant No. DGE 1842402. D.B. acknowledges support from an NSERC PGS-D scholarship. D.D. acknowledges support provided by NASA through Hubble Fellowship grant HST-HF2-51372.001-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 NAS5-26555. The MEarth Team gratefully acknowledges funding from the David and Lucille Packard Fellowship for Science and Engineering (awarded to D.C.) and the National Science Foundation under grants AST-0807690, AST-1109468, AST-1004488 (Alan T. Waterman Award), and AST-1616624. This publication was made possible through the support of 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 acknowledge the use of TESS Alert data, which is currently in a beta test phase, 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. This Letter includes data collected by the TESS mission, which are publicly available from the Multimission Archive for Space Telescopes (MAST). Some of the observations in this Letter made use of the High-Resolution Imaging instrument 'Alopeke at Gemini-North. 'Alopeke 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. 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. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Data and materials availability: All associated data products are available for download from ExoFOP-TESS website, https://exofop.ipac.caltech.edu/tess/target.php?id=181804752. Facilities: TESS - , Gaia - , Gemini ('Alopeke) - , Keck I (HIRES) - , Keck II (NIRC2) - , Subaru (IRD) - , LCO. -

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