Scientific Validation of the SPARC4 Pipeline: Multi-band Imaging, Polarimetry, and Photometric Time Series for Improved Characterization of Transiting Exoplanets

Abstract

High-cadence multi-band imaging and polarimetry have important scientific applications in astronomy. Observations of transits of exoplanets are a particular application that requires robust data reduction and analysis. We present the SPARC4 Pipeline, a suite of routines developed to process photometric and polarimetric data obtained with the instrument SPARC4 installed on the 1.6 m telescope at Pico dos Dias Observatory, Brazil. The scientific data products, up to the generation of high-cadence time series, are demonstrated using observations of several transiting exoplanetary systems in both photometric and polarimetric modes. These observations are used to produce stacked calibrated images, yielding sub-arcsecond astrometric accuracy even in sparse fields. The time series of these fields enabled a photometric characterization of the instrument. Observations of polarimetric standard stars yield an instrumental polarization below 0.06% and a linear polarization accuracy of 0.2%. Furthermore, transit observations of seven exoplanets with host-star magnitudes in the range 10.2 < V < 13.9 demonstrate that SPARC4 achieves an average photometric precision of 0.02% for a 15-minute cadence and a polarimetric precision of ~0.02% over hours-long time series. Finally, we jointly model the SPARC4 light curves together with TESS data (or K2 data in the case of HATS-9) using a Bayesian MCMC framework to refine constraints on the physical parameters of the exoplanets, enabling a more accurate determination of orbital periods and planetary radii, and providing improved constraints on the orbital and physical parameters of these hot Jupiters.