“Astrometria e fotometria de pequenos corpos do Sistema Solar em imagens com campos estelares densos”

Abstract

The accuracy in astrometric and photometric measurements of moving objects in dense stellar fields, especially for small bodies of the Solar System, is challenging due to the contamination of the target's flux by neighboring sources. This work evaluates and applies the difference imaging technique (DIA) to minimize this problem. To address this issue, a simulated astronomical image of a dense stellar field, specifically a globular cluster, was created and analyzed to compare the astrometric performance of the PRAIA and DAOPHOT packages. The results of this analysis validated the use of PRAIA for determining the centroids of astrometric reference stars, where DIA is not applicable, demonstrating competitive performance even under high stellar density conditions. Subsequently, the DIA technique, implemented with the DIAPL2 package, was applied to a sequence of images of the Centaur (10199) Chariklo obtained with the SOAR/SOI instrument in a dense stellar field. The methodology involved creating a model image without the moving object and subtracting this from the re-sampled science images. The astrometric positions of Chariklo were then determined from the difference images (isolating the target flux) in combination with the reference stars measured in the re-sampled images by PRAIA, resulting in a significant improvement in astrometric precision, with a reduction in the scatter of the residuals relative to the NIMA ephemeris (e.g., from 0.066" to 0.018" in $\Delta\alpha{\rm cos}\delta$). Additionally, the photometry extracted from the difference images allowed for the acquisition of Chariklo's rotational light curve and the precise determination of its rotational phase ($\sigma_\varphi = 0.0025$), confirming the effectiveness of DIA in dense stellar fields. The work aims to consolidate DIA as a routine tool for observations of small bodies in dense fields, crucial for predictions of stellar occultations and physical characterization.