We report the discovery by the WASP transit survey of a giant planet in a close orbit ( 0.0295 \pm 0.0009 AU ) around a moderately bright ( V = 11.6 , K = 10 ) G9 dwarf ( 0.89 \pm 0.08 M _ { \odot } , 0.84 \pm 0.03 R _ { \odot } ) in the Southern constellation Eridanus .
Thanks to high-precision follow-up photometry and spectroscopy obtained by the telescopes TRAPPIST and Euler , the mass and size of this planet , WASP-50 b , are well constrained to 1.47 \pm 0.09 M _ { Jup } and 1.15 \pm 0.05 R _ { Jup } , respectively .
The transit ephemeris is 2455558.6120 ( \pm 0.0002 ) + N \times 1.955096 ( \pm 0.000005 ) HJD _ { UTC } .
The size of the planet is consistent with basic models of irradiated giant planets .
The chromospheric activity ( \log R ^ { \prime } _ { HK } = -4.67 ) and rotational period ( P _ { rot } = 16.3 \pm 0.5 days ) of the host star suggest an age of 0.8 \pm 0.4 Gy that is discrepant with a stellar-evolution estimate based on the measured stellar parameters ( \rho _ { * } = 1.48 \pm 0.10 \rho _ { \odot } , T _ { eff } = 5400 \pm 100 K , [ Fe/H ] = -0.12 \pm 0.08 ) which favours an age of 7 \pm 3.5 Gy .
This discrepancy could be explained by the tidal and magnetic influence of the planet on the star , in good agreement with the observations that stars hosting hot Jupiters tend to show faster rotation and magnetic activity ( Pont 2009 ; Hartman 2010 ) .
We measure a stellar inclination of 84 _ { -31 } ^ { +6 } deg , disfavouring a high stellar obliquity .
Thanks to its large irradiation and the relatively small size of its host star , WASP-50 b is a good target for occultation spectrophotometry , making it able to constrain the relationship between hot Jupiters ’ atmospheric thermal profiles and the chromospheric activity of their host stars proposed by Knutson et al .
( 2010 ) .