The CARMENES search for exoplanets around M dwarfs

LP 714-47 b (TOI 442.01): populating the Neptune desert^★,★★

¹ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
e-mail: dreizler@astro.physik.uni-goettingen.de
² Department of Physics and Astronomy, University of Kansas, Lawrence, KS, USA
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Department of Physics and Astronomy, George Mason University, 4400 University Drive MS 3F3, Fairfax, VA 22030, USA
⁵ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁶ Instituto de Astrofísica de Canarias (IAC), Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁸ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, USA
⁹ Physics & Astronomy Department, Vanderbilt University, 6301 Stevenson Center Ln., Nashville, TN 37235, USA
¹⁰ Department of Physics, and Kavli Institute for Astrophysics and Space Science, M.I.T., Cambridge, MA 02193, USA
¹¹ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹² Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University, Marrakech, Morocco
¹³ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
¹⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁵ Center for Astrophysics/Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁶ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁷ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
¹⁸ Department of Astrophysical Sciences, 4 Ivy Lane, Princeton University, Princeton, NJ 08544, USA
¹⁹ NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁰ Centro Astronómico Hispano-Alemán (CSIC-Junta de Andalucía), Observatorio Astronómico de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
²¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
²² Astrobiology Research Unit, Université de Liège, 19C Allée du 6 Août, 4000 Liège, Belgium
²³ Universidad de Atacama, Instituto de Astronomía y Ciencias Planetarias, Copiapó, Chile
²⁴ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA, USA
²⁵ Département de Physique, Université de Montréal, QC, Canada
²⁶ Department of Astronomy, California Institute of Technology, Pasadena, CA, USA
²⁷ IPAC, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
²⁸ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA, USA
²⁹ Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington, DC 20015-1305, USA
³⁰ SETI Institute, 189 Bernardo Ave, Suite 200, Mountain View, CA 94043, USA
³¹ Thomas Jefferson High School for Science and Technology, 6560 Braddock Rd, Alexandria, VA 22312, USA
³² Institute for Astronomy, University of Hawai‘i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
³³ NASA Exoplanet Science Institute Caltech/IPAC Pasadena, CA USA
³⁴ The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA
³⁵ Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM, USA
³⁶ El Sauce Observatory, Coquimbo Province, Chile
³⁷ Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
³⁸ NASA Exoplanet Science Institute, Pasadena, CA, USA
³⁹ Department of Earth Sciences, University of Hawai‘i, 1680 East-West Road, Honolulu, HI 96822, USA
⁴⁰ Mississippi State University, 355 Lee Boulevard, Mississippi State, MS 39762, USA
⁴¹ Astronomy Department, University of California, Berkeley, CA, USA
⁴² Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
⁴³ University of Southern Queensland, Toowoomba, QLD 4350, Australia
⁴⁴ Space Sciences, Technologies and Astrophysics Research Institute, Université de Liège, 19C Allée du 6 Août, 4000 Liège, Belgium
⁴⁵ Department of Physics & Astronomy, Swarthmore College, Swarthmore PA 19081, USA
⁴⁶ Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
⁴⁷ Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA
⁴⁸ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, C/ Can Magrans s/n, 08193 Bellaterra, Spain
⁴⁹ Institut d’Estudis Espacials de Catalunya (IEEC), C/ Gran Capità 2-4, 08034 Barcelona, Spain
⁵⁰ Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁵¹ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵² Department of Astronomy, University of Maryland College Park, MD 20742-2421, USA
⁵³ The University of North Carolina at Chapel Hill, Physics & Astronomy, 120 E. Cameron Ave. Phillips Hall CB3255 Chapel Hill, NC 27599, USA
⁵⁴ The United States Naval Observatory,3450 Massachusetts Avenue, NW, Washington, DC 20392-5420, USA
⁵⁵ Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
⁵⁶ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 Kanto, Japan
⁵⁷ Japan Science and Technology Agency, PRESTO, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵⁸ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁵⁹ Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019, USA
⁶⁰ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁶¹ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁶² Department of Physics & Astronomy, University of California Irvine, Irvine, CA, USA
⁶³ Exoplanets and Stellar Astrophysics Laboratory, Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁶⁴ Ankara University, Department of Astronomy and Space Sciences, 06100 Ankara, Turkey

Received: 25 March 2020
Accepted: 8 October 2020

Abstract

We report the discovery of a Neptune-like planet (LP 714-47 b, P = 4.05204 d, m_b = 30.8 ± 1.5M_⊕, R_b = 4.7 ± 0.3 R_⊕) located in the “hot Neptune desert”. Confirmation of the TESS Object of Interest (TOI 442.01) was achieved with radial-velocity follow-up using CARMENES, ESPRESSO, HIRES, iSHELL, and PFS, as well as from photometric data using TESS, Spitzer, and ground-based photometry from MuSCAT2, TRAPPIST-South, MONET-South, the George Mason University telescope, the Las Cumbres Observatory Global Telescope network, the El Sauce telescope, the TÜBİTAK National Observatory, the University of Louisville Manner Telescope, and WASP-South. We also present high-spatial resolution adaptive optics imaging with the Gemini Near-Infrared Imager. The low uncertainties in the mass and radius determination place LP 714-47 b among physically well-characterised planets, allowing for a meaningful comparison with planet structure models. The host star LP 714-47 is a slowly rotating early M dwarf (T_eff = 3950 ± 51 K) with a mass of 0.59 ± 0.02M_⊙ and a radius of 0.58 ± 0.02R_⊙. From long-term photometric monitoring and spectroscopic activity indicators, we determine a stellar rotation period of about 33 d. The stellar activity is also manifested as correlated noise in the radial-velocity data. In the power spectrum of the radial-velocity data, we detect a second signal with a period of 16 days in addition to the four-day signal of the planet. This could be shown to be a harmonic of the stellar rotation period or the signal of a second planet. It may be possible to tell the difference once more TESS data and radial-velocity data are obtained.