A hot Uranus transiting the nearby M dwarf GJ3470. Detected with HARPS velocimetry. Captured in transit with TRAPPIST photometry

TL;DR

This paper reports the discovery and characterization of GJ3470b, a hot Uranus-sized exoplanet orbiting a nearby M dwarf, using combined radial velocity and transit photometry methods, highlighting its suitability for future studies.

Contribution

First detection of a hot Uranus around an M dwarf using HARPS radial velocities and transit photometry, with detailed mass and radius measurements.

Findings

GJ3470b has a mass of 14.0±1.8 Earth masses and a radius of 4.2±0.6 Earth radii.

The planet orbits its star every 3.3371 days.

GJ3470b is among the most favorable exoplanets for follow-up characterization.

Abstract

We report on the discovery of GJ3470b, a transiting hot Uranus of mass m_p = 14.0+-1.8 Mearth, radius R_p = 4.2+-0.6 Rearth and period P=3.3371+-0.0002 day. Its host star is a nearby (d=25.2+-2.9pc) M1.5 dwarf of mass M_s=0.54+-0.07 Msol and radius R_s=0.50+-0.06 Rsol. The detection originates from a radial-velocity campaign with HARPS that focused on the search for short-period planets orbiting M dwarfs. Once the planet was discovered and the transit-search window narrowed to about 10% of an orbital period, a photometric search started with TRAPPIST and quickly detected the ingress of the planet. Additional observations with TRAPPIST, EulerCam and NITES definitely confirmed the transiting nature of GJ3470b and allow for the determination of its true mass and radius. The star's visible or infrared brightness (V=12.3, K=8.0 mag), together with a large eclipse depth D=0.57+-0.05%, ranks GJ3470b among the most favorable planets for follow-up characterizations.