* Astronomy

Title: EXOFAST: A fast exoplanetary fitting suite in IDL
Authors: Jason Eastman, B. Scott Gaudi, Eric Agol

We present EXOFAST, a fast, robust suite of routines written in IDL which is designed to fit exoplanetary transits and radial velocity variations simultaneously or separately, and characterise the parameter uncertainties and covariances with a Differential Evolution Markov Chain Monte Carlo method. We describe how our code self-consistently incorporates both data sets to simultaneously derive stellar parameters along with the transit and RV parameters, resulting in consistent, but tighter constraints on an example fit of the discovery data of HAT-P-3b that is well-mixed in under two minutes on a standard desktop computer. We describe in detail how our code works and outline ways in which the code can be extended to include additional effects or generalised for the characterisation of other data sets -- including non-planetary data sets. We discuss the pros and cons of several common ways to parameterise eccentricity, highlight a subtle mistake in the implementation of MCMC that would bias the inferred eccentricity of intrinsically circular orbits to significantly non-zero results, discuss a problem with IDL's built-in random number generator in its application to large MCMC fits, and derive a method to analytically fit the linear and quadratic limb darkening coefficients of a planetary transit. Finally, we explain how we achieved improved accuracy and over a factor of 100 improvement in the execution time of the transit model calculation. Our entire source code, along with an easy-to-use online interface for several basic features of our transit and radial velocity fitting, are available online at this http URL

Read more (198kb, PDF)