The VISCACHA survey : X. A fast method to build completeness maps for Magellanic Clouds star clusters

Abstract

Photometric completeness affects the photometry of stars in crowded regions such as the cores of star clusters. Some analysis such as deriving the structural parameters of star clusters using radial density profile is heavily affected by photometric completeness and the classical techniques to map this completeness in a given field are very expensive computationally. In most surveys, for example, the large quantity of data makes it impracticable to estimate the completeness using the traditional method for the whole sample due to time and computational requirements. In this work, we present a new method that is significantly faster and results in similar completeness curves and maps as the traditional approach, providing a great first-step completeness estimator for a large sample of data. Using the completeness corrected data for each cluster we built radial density profiles improving significantly the inner portion of the profile; we also fitted the King model to them, determining the clusters’structural parameters based on a more realistic cluster profile. In this preliminary analysis, we derived structural parameters for nine selected clusters covering a range of core radii (5–40 arcesc) and tidal radii (40–180 arcesc) and discuss how the photometric completeness affects the determination of these parameters when we count stars to trace the radial profile of a star cluster.