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2. On structural properties of open galactic clusters and their spatial distribution;Collinder;Lund Obs. Annals,1931
3. Die offenen Sternhaufen (russ.);Barkhatova;Astron. J. UdSSR,1950
4. W. Buscombe Photometric data for galactic clusters 1963
5. H. Haffner Report IAU Comm 282 1961