K2-290: a warm Jupiter and a mini-Neptune in a triple-star system

Abstract

We report the discovery of two transiting planets orbiting K2-290 (EPIC 249624646), a bright (V=11.11) late F-type star residing in a triple-star system. It was observed during Campaign 15 of the K2 mission, and in order to confirm and characterise the system, follow-up spectroscopy and AO imaging were carried out using the FIES, HARPS, HARPS-N, and IRCS instruments. From AO imaging and Gaia data we identify two M-dwarf companions at a separation of $113\pm 2$ AU and $2467_{-155}^{+177}$ AU. From radial velocities, K2 photometry, and stellar characterisation of the host star, we find the inner planet to be a mini-Neptune with a radius of $3.06\pm 0.16R_{\oplus }$ and an orbital period of $P=9.2$ days. The radius of the mini-Neptune suggests that the planet is located above the radius valley, and with an incident flux of $F\sim 400F_{\oplus }$, it lies safely outside the super-Earth desert. The outer warm Jupiter has a mass of $0.774\pm 0.047M_{\mathrm{J}}$ and a radius of $1.006\pm 0.050R_{\mathrm{J}}$, and orbits the host star every 48.4 days on an orbit with an eccentricity $e<0.241$. Its mild eccentricity and mini-Neptune sibling suggest that the warm Jupiter originates from in situ formation or disk migration.

16 pages, 8 figures, accepted for publication in MNRAS. Updated to accepted version (including K2 name)

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