An Astronomer Plots the H-R Diagram of a Star Cluster

question 225

Multiple Choice

An astronomer plots the H-R diagram of a star cluster and finds that it contains hot B-type stars on the main sequence and cooler G- and K-type stars noticeably above the main sequence. This cluster is

• A) very young because the G and K stars are still evolving toward the main sequence.
• B) of indeterminate age since the age of the cluster cannot be estimated from the information given.
• C) impossible because cool stars cannot exist above the main sequence when hot stars are on the main sequence.
• D) old because the G and K stars are already evolving off (away from) the main sequence.