Self Organizing Maps (SOM) have been successfully applied in a lot of real world hard problems since their apparition. In this paper we present new topologies for SOM based on a planar graph. The design of a specific graph to encode prior information on the dataset topology is the central question addressed in this paper. In this context, star-shaped graphs are advocated for health monitoring applications, leading to a new kind of SOM that we denote by Self Organizing Star (SOS). Experiments using aircraft engine measurements show that SOS lead to meaningful and natural dataset representation.