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Chapter 13: Star Clusters. Stars (almost) always form in clusters. globular cluster. Open cluster. The stars all formed at the same time They are all at the same distance They formed from the same material Only difference is their masses!. h & Chi Persei – Double Cluster in Perseus.
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Chapter 13: Star Clusters Stars (almost) always form in clusters globular cluster Open cluster • The stars all formed at the same time • They are all at the same distance • They formed from the same material • Only difference is their masses!
Pleiades Open clusters: Contain < ~ 1000 stars Loosely gravitationally bound together Younger than globular (some still contain O and B stars) More enriched in heavy elements (“Population I” stars)
Open clusters that have become gravitationally unbound are stellar associations. If they continue to have similar proper motion, this is a moving group. Ursa Major moving group
globular clusters: Contains ~1000-106 stars Extremely old: billions of years Population II (low in heavy elements)
Globular cluster M2 “He who cannot see gravity at work here has no soul.” - Richard Feynman
Isochrones: Lines of ‘constant age’ for stars of different masses
Star clusters are useful to: Verify stellar evolution models Determine distances to nearby galaxies Determine chemical composition of universe in the very distant past