Chapter 13 Star Clusters Stars almost always form

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Chapter 13: Star Clusters Stars (almost) always form in clusters globular cluster Open cluster

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

h & Chi Persei – Double Cluster in Perseus

Messier 35 and NGC 2158 – “open clusters” of different ages

Messier 35 and NGC 2158 – “open clusters” of different ages

Pleiades Open clusters: 1. Contain < ~ 1000 stars 2. Loosely gravitationally bound together

Pleiades Open clusters: 1. Contain < ~ 1000 stars 2. Loosely gravitationally bound together 3. Younger than globular (some still contain O and B stars) 4. More enriched in heavy elements (“Population I” stars)

Messier 50 – An “open cluster” of stars

Messier 50 – An “open cluster” of stars

Open clusters that have become gravitationally unbound are stellar associations. If they continue to

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: 1. Contains ~1000 -106 stars 2. Extremely old: billions of years 3.

globular clusters: 1. Contains ~1000 -106 stars 2. Extremely old: billions of years 3. Population II (low in heavy elements)

Globular cluster M 2 “He who cannot see gravity at work here has no

Globular cluster M 2 “He who cannot see gravity at work here has no soul. ” - Richard Feynman

HD Diagram for star clusters: only difference is mass

HD Diagram for star clusters: only difference is mass

Isochrones: Lines of ‘constant age’ for stars of different masses

Isochrones: Lines of ‘constant age’ for stars of different masses

M. S. LIFETIME for STAR at TURNOFF = AGE of CLUSTER

M. S. LIFETIME for STAR at TURNOFF = AGE of CLUSTER

Star cluster website

Star cluster website

Star clusters are useful to: 1. Verify stellar evolution models 2. Determine distances to

Star clusters are useful to: 1. Verify stellar evolution models 2. Determine distances to nearby galaxies 3. Determine chemical composition of universe in the very distant past