In the Trumpler Classification system, what does the letter 'r' signify for a cluster designation?
Answer
Rich in stars.
Robert Trumpler established a classification scheme in 1930 to categorize open clusters based on morphology and richness. This system uses a three-part designation. The final component, represented by a letter, specifies the stellar population density: 'p' denotes poor, 'm' denotes medium, and 'r' denotes rich in stars. For example, the Pleiades cluster, classified as I3rn, uses 'r' to indicate that it possesses a high density of stellar members relative to the other categories. The appended 'n' would further specify that nebulosity is present, but the letter 'r' itself relates purely to the richness or abundance of stars in the grouping.
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