Open Cluster

Trumpler Classification System

Degree of concentration

• I. Detached clusters with strong central concentration.
• II. Detached clusters with little central concentration.
• III. Detached clusters with no noticeable concentration.
• IV. Not well detached from surrounding star field.

Range of brightness

• 1. Most of the cluster stars are nearly the same apparent brightness.
• 2. Moderate range in brightness.
• 3. Cluster is composed of bright and faint stars.

Number of stars in cluster

• p. Poor (less than 50 stars).
• m. Medium rich (50-100 stars).
• r. Rich (more than 100 stars).

The letter 'n' following the Trumpler type means that there is nebulosity associated with the cluster.

Trumpler Classification Image Reference

image sourced from: http://www.astrophoton.com/trumpler_class.htm[1]

[1] http://www.astrophoton.com/trumpler_class.htm (HTTP)