$\texttt{PyTranSpot}$ - A tool for multiband light curve modeling of planetary transits and stellar spots

TL;DR

PyTranSpot is a new tool that models multiband transit light curves with starspot anomalies, enabling accurate characterization of exoplanet and stellar properties while accounting for stellar activity effects.

Contribution

It introduces a pixellation-based modeling approach combined with MCMC to analyze starspot-affected transit data, improving parameter estimation accuracy.

Findings

Validated with synthetic light curves showing accurate parameter recovery.

Applied to real data of WASP-41b, revealing a flat transmission spectrum.

Demonstrated impact of starspots on transit parameter biases.

Abstract

Several studies have shown that stellar activity features, such as occulted and non-occulted starspots, can affect the measurement of transit parameters biasing studies of transit timing variations and transmission spectra. We present $\texttt{PyTranSpot}$, which we designed to model multiband transit light curves showing starspot anomalies, inferring both transit and spot parameters. The code follows a pixellation approach to model the star with its corresponding limb darkening, spots, and transiting planet on a two dimensional Cartesian coordinate grid. We combine $\texttt{PyTranSpot}$ with an MCMC framework to study and derive exoplanet transmission spectra, which provides statistically robust values for the physical properties and uncertainties of a transiting star-planet system. We validate $\texttt{PyTranSpot}$'s performance by analyzing eleven synthetic light curves of four different star-planet systems and 20 transit light curves of the well-studied WASP-41b system. We also investigate the impact of starspots on transit parameters and derive wavelength dependent transit depth values for WASP-41b covering a range of 6200-9200 $\AA$, indicating a flat transmission spectrum.