* Astronomy

Title: A hot Uranus transiting the nearby M dwarf GJ3470. Detected with HARPS velocimetry. Captured in transit with TRAPPIST photometry
Authors: X. Bonfils, M. Gillon, S. Udry, D. Armstrong, F. Bouchy, X. Delfosse, T. Forveille, E. Jehin, M. Lendl, C. Lovis, M. Mayor, J. McCormac, V. Neves, F. Pepe, C. Perrier, D. Pollaco, D. Queloz, N. C. Santos

We report on the discovery of GJ3470b, a transiting hot Uranus of mass m_p = 14.0±1.8 Earth masses, radius R_p = 4.2±0.6 Earth radii 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 Solar masses and radius R_s=0.50±0.06 Solar radii. 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 favourable planets for follow-up characterisations.

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