Transiting planet candidate from K2 with the longest period

Abstract

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 hours 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$\pm$0.12R${}_{\mathrm{Sol}}$, the planet has a radius of 1.11${}_{-0.07}^{+0.07}$R${}_{\mathrm{Jup}}$ and a period of 3650${}_{-1130}^{+1280}$ days. The radial velocity measurements constrain the mass to be lower than 13M${}_{\mathrm{Jup}}$, 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.

arXiv comment5 pages, 3 figures. Published in A&A. Updated with correct title and full edits

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