PX282 - E4 - turnoff points and stellar clusters

• higher mass stars 'burn out' of hydrogen faster
• clusters of stars are groups that formed at about the same time, from the same cloud
• therefore they will be of the same age, a similar composition, and the same distance
• the hertzsprung-russel diagrams for clusters have less scatter
• the age of a cluster determines what is seen

pleiades

• a young cluster $\sim 100My$r
• low-mass stars have not finished forming
• they are also further, so it may mean that low-mass stars have not been seen

hyades

• an older cluster $\sim 600Myr$
• turnoff points
• when stars end their main sequence lifetimes, they move off
• turnoff points can be used to get the age

globular cluster

• the oldest clusters
• blue stragglers: stars that break the model like binary stars, results of stellar mergers