Letter to the Editor
Transiting planet candidate from K2 with the longest period
Observatoire de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
2 Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4 Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK
5 Centre for Exoplanet Science, SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
6 DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, 2800 Lyngby, Denmark
7 Brorfelde Observatory, Observator Gyldenkernes Vej 7, 4340 Tølløse, Denmark
Accepted: 22 June 2018
Context. We present the transit and follow-up of a single transit event from Campaign 14 of K2, EPIC248847494b, which has a duration of 54 h and a 0.18% depth.
Aims. Using photometric tools and conducting radial velocity follow-up, we vet and characterise this very strong candidate.
Methods. Owing to the long, unknown period, standard follow-up methods needed to be adapted. The transit was fitted using Namaste, and the radial velocity slope was measured and compared to a grid of planet-like orbits with varying masses and periods. These used stellar parameters measured from spectra and the distance as measured by Gaia.
Results. Orbiting around a sub-giant star with a radius of 2.70 ± 0.12 RSol, the planet has a radius of 1.11−0.07+0.07 RJup and a period of 3650−1130+1280 days. The radial velocity measurements constrain the mass to be lower than 13 MJup, which implies a planet-like object.
Conclusions. We have found a planet at 4.5 AU from a single-transit event. After a full radial velocity follow-up campaign, if confirmed, it will be the longest-period transiting planet discovered.
Key words: planets and satellites: detection / stars: individual: EPIC248847494 / planetary systems / techniques: photometric / techniques: radial velocities / techniques: spectroscopic
© ESO 2018