Radialvelocity fitting challenge. II. First results of the analysis of the data set
Abstract
Context. Radialvelocity (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 Earthtwins, 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 lowmass planets despite stellar RV signals. However, because observed RV variations at the meterpersecond 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 rednoise 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 K/N= K_{pl/RV_{rms}×√{N_{obs}}=5} with a threshold of K/N = 7.5 at the level of 8090% 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 nonnegligible 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.
Based on observations collected at the La Silla Parana Observatory, ESO (Chile), with the HARPS spectrograph at the 3.6m telescope.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 2017
 DOI:
 10.1051/00046361/201628671
 arXiv:
 arXiv:1609.03674
 Bibcode:
 2017A&A...598A.133D
 Keywords:

 techniques: radial velocities;
 planetary systems;
 stars: oscillations;
 stars: activity;
 methods: data analysis;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 36 pages (including 10 pages of appendix), 23 figures, Accepted in A&