Group identified by applying STARGO to the data sample in the (X, Y, Z, ﹩{\mu }_{\alpha }\cos \delta ,{\mu }_{\delta }﹩) space. (a) Histogram shows the distribution of u. The dashed lines denotes the peak position of its distribution u_peak and the dotted lines show u_peak−3σ and u_peak+3σ, respectively. The left tail with u < u_peak−3σ is highlighted in cyan. (b) 2D neural map resulting from SOM, where the u value between adjacent neurons is represented by the gray scale. (c) The same as (b), where the neurons with u < u_peak−3σ are colored in cyan. Contours of two dominant neuron groups are traced with different colors (red: Coma Ber; blue: group-X).