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arXiv · 1903.05623

The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap

Davide Gandolfi·Luca Fossati·John H. Livingston·Keivan G. Stassun·Sascha Grziwa·Oscar Barragán·Malcolm Fridlund·Daria Kubyshkina·Carina M. Persson·Fei Dai·Kristine W. F. Lam·Simon Albrecht·Natalie Batalha·Paul G. Beck·Anders Bo Justesen·Juan Cabrera·Scott Cartwright·William D. Cochran·Szilard Csizmadia·Misty D. Davies·Hans J. Deeg·Philipp Eigmüller·Michael Endl·Anders Erikson·Massimiliano Esposito·Rafael A. García·Robert Goeke·Lucía González-Cuesta·Eike W. Guenther·Artie P. Hatzes·Diego Hidalgo·Teruyuki Hirano·Maria Hjorth·Petr Kabath·Emil Knudstrup·Judith Korth·Jie Li·Rafael Luque·Savita Mathur·Pilar Montañes Rodríguez·Norio Narita·David Nespral·Prajwal Niraula·Grzegorz Nowak·Enric Palle·Martin Pätzold·Jorge Prieto-Arranz·Heike Rauer·Seth Redfield·Ignasi Ribas·Marek Skarka·Alexis M. S. Smith·Pamela Rowden·Guillermo Torres·Vincent Van Eylen·Michael L. Vezie
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Abstract

We report the discovery of a super-Earth and a sub-Neptune transiting the star HD 15337 (TOI-402, TIC 120896927), a bright (V=9) K1 dwarf observed by the Transiting Exoplanet Survey Satellite (TESS) in Sectors 3 and 4. We combine the TESS photometry with archival HARPS spectra to confirm the planetary nature of the transit signals and derive the masses of the two transiting planets. With an orbital period of 4.8 days, a mass of 7.51(+1.09)(-1.01) M_Earth, and a radius of 1.64+/-0.06 R_Earth, HD 15337b joins the growing group of short-period super-Earths known to have a rocky terrestrial composition. The sub-Neptune HD 15337c has an orbital period of 17.2 days, a mass of 8.11(+1.82)(-1.69) M_Earth, and a radius of 2.39+/-0.12 R_Earth, suggesting that the planet might be surrounded by a thick atmospheric envelope. The two planets have similar masses and lie on opposite sides of the radius gap, and are thus an excellent testbed for planet formation and evolution theories. Assuming that HD 15337c hosts a hydrogen-dominated envelope, we employ a recently developed planet atmospheric evolution algorithm in a Bayesian framework to estimate the history of the high-energy (extreme ultraviolet and X-ray) emission of the host star. We find that at an age of 150 Myr, the star possessed on average between 3.7 and 127 times the high-energy luminosity of the current Sun.

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Davide Gandolfi, Luca Fossati, John H. Livingston, Keivan G. Stassun, Sascha Grziwa, Oscar Barragán, Malcolm Fridlund, Daria Kubyshkina, Carina M. Persson, Fei Dai, Kristine W. F. Lam, Simon Albrecht, Natalie Batalha, Paul G. Beck, Anders Bo Justesen, Juan Cabrera, Scott Cartwright, William D. Cochran, Szilard Csizmadia, Misty D. Davies, Hans J. Deeg, Philipp Eigmüller, Michael Endl, Anders Erikson, Massimiliano Esposito, Rafael A. García, Robert Goeke, Lucía González-Cuesta, Eike W. Guenther, Artie P. Hatzes, Diego Hidalgo, Teruyuki Hirano, Maria Hjorth, Petr Kabath, Emil Knudstrup, Judith Korth, Jie Li, Rafael Luque, Savita Mathur, Pilar Montañes Rodríguez, Norio Narita, David Nespral, Prajwal Niraula, Grzegorz Nowak, Enric Palle, Martin Pätzold, Jorge Prieto-Arranz, Heike Rauer, Seth Redfield, Ignasi Ribas, Marek Skarka, Alexis M. S. Smith, Pamela Rowden, Guillermo Torres, Vincent Van Eylen, Michael L. Vezie. 2019-05-07. The Transiting Multi-planet System HD15337: Two Nearly Equal-mass Planets Straddling the Radius Gap. https://doi.org/10.3847/2041-8213%2Fab17d9

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