TOI-519 b: A short-period substellar object around an M dwarf validated using multicolour photometry and phase curve analysis

¹ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
e-mail: hannu@iac.es
² Department Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³ Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejon de Ardoz, Madrid, Spain
⁴ Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁵ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁶ Japan Science and Technology Agency, PRESTO, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁷ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁹ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
¹⁰ Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹¹ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹² Rheinisches Institut für Umweltforschung an der Universität zu Köln, Abteilung Planetenforschung, Aachener Str. 209, 50931 Köln, Germany
¹³ Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, PR China
¹⁴ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹⁵ Institute of Planetary research, German Aerospace Center, Rutherfordstrasse 2, 12489 Berlin, Germany
¹⁶ Department of Astronomical Science, The Graduated University of Advanced Studies, SOKENDAI, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁷ Department of Astronomy and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹⁸ George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
¹⁹ Department of Physics & Astronomy, Swarthmore College, Swarthmore PA 19081, USA
²⁰ University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA
²¹ NASA Ames Research Center, Moffett Field, CA 94035, USA
²² SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, CA 94043, USA
²³ Noqsi Aerospace Ltd., 15 Blanchard Avenue, Billerica, MA 01821, USA
²⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
²⁵ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²⁷ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁸ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

Received: 15 July 2020
Accepted: 19 November 2020

Abstract

Context. We report the discovery of TOI-519 b (TIC 218795833), a transiting substellar object (R = 1.07 R_Jup) orbiting a faint M dwarf (V = 17.35) on a 1.26 d orbit. Brown dwarfs and massive planets orbiting M dwarfs on short-period orbits are rare, but more have already been discovered than expected from planet formation models. TOI-519 is a valuable addition to this group of unlikely systems, and it adds towards our understanding of the boundaries of planet formation.

Aims. We set out to determine the nature of the Transiting Exoplanet Survey Satellite (TESS) object of interest TOI-519 b.

Methods. Our analysis uses a SPOC-pipeline TESS light curve from Sector 7, multicolour transit photometry observed with MuSCAT2 and MuSCAT, and transit photometry observed with the LCOGT telescopes. We estimated the radius of the transiting object using multicolour transit modelling, and we set upper limits for its mass, effective temperature, and Bond albedo using a phase curve model that includes Doppler boosting, ellipsoidal variations, thermal emission, and reflected light components.

Results. TOI-519 b is a substellar object with a radius posterior median of 1.07 R_Jup and 5th and 95th percentiles of 0.66 and 1.20 R_Jup, respectively, where most of the uncertainty comes from the uncertainty in the stellar radius. The phase curve analysis sets an upper effective temperature limit of 1800 K, an upper Bond albedo limit of 0.49, and a companion mass upper limit of 14 M_Jup. The companion radius estimate combined with the T_eff and mass limits suggests that the companion is more likely a planet than a brown dwarf, but a brown-dwarf scenario is a priori more likely given the lack of known massive planets in ≈ 1 day orbits around M dwarfs with T_eff < 3800 K, and given the existence of some (but few) brown dwarfs.