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A hot Uranus transiting the nearby M dwarf GJ 3470
Detected with HARPS velocimetry. Captured in transit with TRAPPIST photometry

X. Bonfils, M. Gillon, S. Udry, D. J. Armstrong, F. Bouchy, X. Delfosse, T. Forveille, A. Fumel, E. Jehin, M. Lendl, C. Lovis, M. Mayor, J. McCormac, V. Neves, F. Pepe, C. Perrier, D. Pollacco, D. Queloz, N. C. Santos

We report on the discovery of GJ 3470 b, a transiting hot Uranus of mass mp = 14.0 ± 1.8 M, radius Rp = 4.2 ± 0.6 R and period P = 3.3371 ± 0.0002 day. Its host star is a nearby (d = 25.2 ± 2.9 pc) M1.5 dwarf of mass M = 0.54 ± 0.07 M and radius R = 0.50 ± 0.06 R. The detection was made during a radial-velocity campaign with Harps that focused on the search for shortperiod 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 GJ 3470b and allowed the determination of its true mass and radius. The star’s visible or infrared brightness (Vmag = 12.3, Kmag = 8.0), together with a large eclipse depth D = 0.57 ± 0.05%, ranks GJ 3470 b among the most suitable planets for follow-up characterizations.

techniques: radial velocities – techniques: photometric – planetary systems – stars: late-type – stars: individual: GJ 3470

Based on observations made with the HARPS instrument on the ESO 3.6 m telescope under the program IDs 183.C-0437 at Cerro La Silla (Chile).
Our radial-velocity and photometric time series are only available at the CDS via anonymous ftp to ( or via

Astronomy & Astrophysics
Volume 546, Number of pages A27_1
2012 October

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia