WASP-38b: a transiting exoplanet in an eccentric, 6.87d period orbit

Aims. We report the discovery of WASP-38b, a long period transiting planet in an eccentric 6.871815 day orbit. The transit epoch is 2455335.92050�0.00074 (HJD) and the transit duration is 4.663 hours. Methods. WASP-38b’s discovery was enabled due to an upgrade to the SuperWASP-North cameras. We performed a spectral analysis of the host star HD 146389/BD+10 2980 that yielded Te f f = 6150� 80 K, log g= 4.3� 0.1, v sin i=8.6� 0.4 km s −1 , M�= 1.16� 0.04 M� and R�= 1.33�0.03 R�, consistent with a dwarf of spectral type F8. Assuming a main-sequence mass-radius relation for the star, we fitted simultaneously the radial velocity variations and th e transit light curves to estimate the orbital and planetary parameters. Results. The planet has a mass of 2.69�0.06 MJup and a radius of 1.09�0.03 RJup giving a density, �p = 2.1�0.1�J . The high precision of the eccentricity e = 0.0314�0.0044 is due to the relative transit timing from the light curv es and the RV shape. The planet equilibrium temperature is estimated at 1292�33 K. WASP-38b is the longest period planet found by SuperWASP-North and with a bright host star (V = 9.4 mag), is a good candidate for followup atmospheric studies. Conclusions.

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