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

TL;DR

This paper introduces an extension to the Chroma+ suite that allows in situ synthesis of exo-planet transit lightcurves for various planetary and orbital parameters, integrated with stellar atmosphere modeling without limb-darkening parameterization.

Contribution

The authors developed and integrated a new method for in situ exo-planet transit lightcurve modeling into the Chroma+ suite, applicable to multiple ports and photometric systems.

Findings

Successfully modeled transit lightcurves without limb-darkening parameterization.

Validated the model against analytic solutions for edge-on transits.

Extended the capability to various stellar and planetary configurations.

Abstract

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% of the host stellar radius, and arbitrary 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).