K2-141 b

A 5-M_⊕ super-Earth transiting a K7 V star every 6.7 h^★,★★

¹ Dipartimento di Fisica, Università degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
e-mail: oscar.barraganvil@edu.unito.it
² Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
⁴ Department of Astronomy, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
⁵ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁶ Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
⁷ Astrobiology Center, NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸ National Astronomical Observatory of Japan, NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁹ Institute of Planetary Research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
¹⁰ Departamento de Astrofísica, Universidad de La Laguna, 38206 Tenerife, Spain
¹¹ Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹² Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegrade 120, 8000 Aarhus C, Denmark
¹³ Department of Astronomy and McDonald Observatory, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712, USA
¹⁴ Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁵ Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, Asakuchi, Okayama 719-0232, Japan
¹⁶ Rheinisches Institut für Umweltforschung, Abteilung Planetenforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
¹⁷ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenberg, Germany
¹⁸ Department of Astronomy, The Ohio State University, 140 West 18th Ave., Columbus, OH 43210, USA
¹⁹ Center for Astronomy and Astrophysics, TU Berlin, Hardenbergstr. 36, 10623 Berlin, Germany

Received: 31 October 2017
Accepted: 11 January 2018

Abstract

We report on the discovery of K2-141 b (EPIC 246393474 b), an ultra-short-period super-Earth on a 6.7 h orbit transiting an active K7 V star based on data from K2 campaign 12. We confirmed the planet’s existence and measured its mass with a series of follow-up observations: seeing-limited MuSCAT imaging, NESSI high-resolution speckle observations, and FIES and HARPS high-precision radial-velocity monitoring. K2-141 b has a mass of 5.31 ± 0.46 M_⊕ and radius of 1.54_−0.09^+0.10 R_⊕, yielding a mean density of 8.00_−1.45^+1.83 g cm⁻³ and suggesting a rocky-iron composition. Models indicate that iron cannot exceed ~70% of the total mass. With an orbital period of only 6.7 h, K2-141 b is the shortest-period planet known to date with a precisely determined mass.