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The Hertzsprung-Russell diagrams for open clusters
Symposium - International astronomical union
The most important relationship between physical characteristics of stars is the spectrum-luminosity correlation. Investigating the character of this correlation for stars of open clusters, Trumpler has worked out a classification of clusters according to their spectral composition.doi:10.1017/s0074180900177472 fatcat:vwzp5nt67jc7hazcwzob36piwu