Search for The Possible Members of The Open Cluster NGC 3532 With Poor Astrometric Solutions of Gaia DR3

The paper estimates the number of stars with poor astrometric solutions that may be members of the NGC 3532. We select such stars by the Gaia photometry using the Hess diagram (the probability density distribution on the color-magnitude diagram). We search for stars that fall in the cluster area of the Hess diagram plotted by probable members of the NGC 3532 cluster from the Hant&Reffert sample. These stars showed a concentration towards the cluster center. We estimated the number of possible cluster members with poor astrometric solutions as 2 150 ± 230 stars. For stars with reliable parallaxes and proper motions, the cluster radius is Rc = 178 ± 3 arcminutes, and the number of cluster stars is Nc = 2 200 ± 40. Thus, when identifying probable cluster members based on parallaxes and proper motions, up to half of the cluster members can be lost.