Accurate Computation of Light Curves and the Rossiter-McLaughlin Effect in Multi-Body Eclipsing Systems

Abstract

We present here an efficient method for computing the visible flux for each body during a multi-body eclipsing event for all commonly used limb darkening laws. Our approach follows the idea put forth by Pal (2012) to apply Green's Theorem on the limb darkening integral, thus transforming the two-dimensional flux integral over the visible disk into a one-dimensional integral over the visible boundary. We implement this idea through an iterative process which combines a fast method for describing the visible boundary of each body with a fast numerical integration scheme to compute the integrals. For the two-body case, our method compares well in speed with both that of Mandel & Agol (2002) and that of Gimenez (2006a). The strength of the method is that it works for any number of spherical bodies, with a computational accuracy that is adjustable through the use of a tolerance parameter. Most significantly, the method offers two main advantages over previously used techniques: (i) it can employ a multitude of limb darkening laws, including all of the commonly used ones; (ii) it can compute the Rossiter-McLaughlin effect for rigid body rotation with an arbitrary orientation of the rotation axis, using any of these limb darkening laws. In addition, we can compute the Rossiter-McLaughlin effect for stars exhibiting differential rotation, using the quadratic limb darkening law. We provide the mathematical background for the method and explain in detail how to implement the technique with the help of several examples and codes which we make available.