In situ exo-planet transit lightcurve modelling with the Chroma+ suite

We have added to the Chroma+ suite of stellar atmosphere and spectrum modelling codes the ability to synthesize the exo-planet transit lightcurve for planets of arbitrary size up to 10 planetary and stellar mass and orbital radius (thus determining orbital velocity) and arbitrary orbital inclination. The lightcurves are computed in situ, integrated with the radiative transfer solution for the radiation field emerging from the stellar surface, and there is no limb-darkening parameterization. The lightcurves are computed for the Johnson-Bessel photometric system UBVRIHJK. We describe our method of computing the transit path, and the reduction in flux caused by occultation, and compare our lightcurve to an analytic solution with a four-parameter limb-darkening parameterization for the case of an edge-on transit of the Sun by Earth. This capability has been added to all ports and variations, including the Python port, ChromaStarPy, and the version that interpolates among the fully line-blanketed ATLAS9 surface intensity distributions, ChromaStarAtlas. All codes may be accessed at www.ap.smu.ca/OpenStars and at GitHub (github.com/sevenian3).