About putative Neptune-like extrasolar planetary candidates

Context. We re-analyze the precision radial velocity (RV) data of HD 208487 by the Anglo-Australian Planet Search Team, HD 190360, HD 188015, HD 114729 by the California and Carnegie Planet Search Team, and HD 147513 by the Geneva Planet Search Team. All these stars are supposed to host Jovian companions in long-period orbits. Aims. We test a hypothesis that the residuals of the 1-planet model of the RV or an irregular scatter of the measurements around the synthetic RV curve may be explained by the existence of additional planets in short-period orbits. Methods. We performed a global search for the best fits in the orbital parameters space with genetic algorithms and simplex method. This makes it possible to verify and extend the results with an application of commonly used FFT-based periodogram analysis for identifying the leading periods. Results. Our analysis confirms the presence of a periodic component in the RV of HD 190360 that may correspond to a hot-Neptune planet. We found four new cases in which the 2-planet model yields significantly better fits to the RV data than the best 1-planet solutions. If the periodic variability of the residuals of single-planet fits indeed has a planetary origin, then hot-Neptune planets may exist in these extrasolar systems. We estimate their orbital periods as in the range of 7-20 d and minimal masses of about 20 masses of the Earth.