Radial-velocity fitting challenge. II. First results of the analysis of the data set

Context. Radial-velocity (RV) signals arising from stellar photospheric phenomena are the main limitation for precise RV measurements. Those signals induce RV variations an order of magnitude larger than the signal created by the orbit of Earth-twins, thus preventing their detection. Aims. Different methods have been developed to mitigate the impact of stellar RV signals. The goal of this paper is to compare the efficiency of these different methods to recover extremely low-mass planets despite stellar RV signals. However, because observed RV variations at the meter-per-second precision level or below is a combination of signals induced by unresolved orbiting planets, by the star, and by the instrument, performing such a comparison using real data is extremely challenging. Methods. To circumvent this problem, we generated simulated RV measurements including realistic stellar and planetary signals. Different teams analyzed blindly those simulated RV measurements, using their own method to recover planetary signals despite stellar RV signals. By comparing the results obtained by the different teams with the planetary and stellar parameters used to generate the simulated RVs, it is therefore possible to compare the efficiency of these different methods. Results. The most efficient methods to recover planetary signals take into account the different activity indicators, use red-noise models to account for stellar RV signals and a Bayesian framework to provide model comparison in a robust statistical approach. Using the most efficient methodology, planets can be found down to with a threshold of K/N = 7.5 at the level of 80–90% recovery rate found for a number of methods. These recovery rates drop dramatically for K/N smaller than this threshold. In addition, for the best teams, no false positives with K/N > 7.5 were detected, while a non-negligible fraction of them appear for smaller K/N. A limit of K/N = 7.5 seems therefore a safe threshold to attest the veracity of planetary signals for RV measurements with similar properties to those of the different RV fitting challenge systems.Fil: Dumusque, X.. Université de Genève; SuizaFil: Borsa, F.. Osservatorio Astronomico di Brera; ItaliaFil: Damasso, M.. Osservatorio Astrofisico di Torino; ItaliaFil: Diaz, Rodrigo Fernando. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Université de Genève; SuizaFil: Gregory, P. C.. University Of British Columbia; CanadáFil: Hara, N. C.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Hatzes, A.. Thüringer Landessternwarte Tautenburg; AlemaniaFil: Rajpaul, V.. University of Oxford; Reino UnidoFil: Tuomi, M.. University Of Hertfordshire; Reino UnidoFil: Aigrain, S.. University of Oxford; Reino UnidoFil: Anglada Escudé, G.. Queen Mary University of London; Reino UnidoFil: Bonomo, A. S.. Osservatorio Astrofisico di Torino; ItaliaFil: Boué, G.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Dauvergne, F.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Frustagli, G.. Osservatorio Astronomico di Brera; ItaliaFil: Giacobbe, P.. Osservatorio Astrofisico di Torino; ItaliaFil: Haywood, R. D.. Harvard-Smithsonian Center for Astrophysics; Estados UnidosFil: Jones, H. R. A.. University of Hertfordshire,; Reino UnidoFil: Laskar, J.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Pinamonti, M.. Osservatorio Astronomico di Trieste; ItaliaFil: Poretti, E.. Osservatorio Astronomico di Brera; ItaliaFil: Rainer, M.. Osservatorio Astronomico di Brera; ItaliaFil: Ségransan, D.. Observatoire de Genève; SuizaFil: Sozzetti, A.. Osservatorio Astrofisico di Torino; ItaliaFil: Udry, S.. Observatoire de Genève; Suiz