A Bayesian Kepler periodogram detects a second planet in HD 208487

• Published in: Monthly notices of the Royal Astronomical Society 2007-02, Vol.374 (4), p.1321-1333
• Main Author: Gregory, P. C.
• Format: Article
• Language: English
• Subjects: Astronomy; Bayesian analysis; Earth, ocean, space; Exact sciences and technology; methods: numerical; methods: statistical; Numerical analysis; Orbits; Planets; Stars & galaxies; stars: individual: HD 208487; stars: planetary systems; techniques: radial velocities; Velocity
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2006.11240.x

An automatic Bayesian Kepler periodogram has been developed for identifying and characterizing multiple planetary orbits in precision radial velocity data. The periodogram is powered by a parallel tempering Markov chain Monte Carlo (MCMC) algorithm which is capable of efficiently exploring a multiplanet model parameter space. The periodogram employs an alternative method for converting the time of an observation to true anomaly that enables it to handle much larger data sets without a significant increase in computation time. Improvements in the periodogram and further tests using data from HD 208487 have resulted in the detection of a second planet with a period of 90982−92 d, an eccentricity of 0.370.26−0.20, a semimajor axis of 1.870.13−0.14 au and an M sin i= 0.45+0.11−0.13MJ. The revised parameters of the first planet are period = 129.8 ± 0.4 d, eccentricity = 0.20 ± 0.09, semimajor axis = 0.51 ± 0.02 au and M sin i= 0.41 ± 0.05 MJ. Particular attention is paid to several methods for calculating the model marginal likelihood which is used to compare the probabilities of models with different numbers of planets.