1Explain why the main sequence turn-off temperature of the stars in a cluster is a good indicator of the age of the cluster. Given actual CMDs for open clusters, rank the clusters according to ageContrast open and globular clusters when discussing age, location in the galaxy, and number of stars in the clusterGoals for today: be able to ....Wednesday, November 16, 11Describe how astronomers determine the age of a cluster of stars by reviewing its color-magnitude diagramGiven actual CMDs for open clusters, rank the clusters according to ageContrast open and globular clusters when discussing age, location in the galaxy, and number of stars in the cluster2Consider single stars on main sequence. What determines just about everything for those stars?How do we determine the masses of the stars along the main sequence?MassWe found masses through measurements of binary stars.Wednesday, November 16, 113Cosmic Perspective demonstration of individual stars leaving the main sequence:Clusters evolvingWednesday, November 16, 114The main-sequence turn-off temperature of the stars in a cluster is a good indicator of the age of the cluster because….A. we assume that stars in a cluster were born at same time with similar compositions.B. evidence indicates lifetime of a star on main sequence depends on its mass.C. evidence has shown a temperature-luminosity-mass relationship for stars on main sequence.Wednesday, November 16, 115What is the temperature, luminosity, mass relationship of stars on the main sequence? Wednesday, November 16, 116FiltersB V RB V RWednesday, November 16, 11Wednesday, November 16, 11Understanding the B - V “colors”8Hot stars are brighter at blue wavelengths than at visual. So, B apparent magnitude is a smaller number than the V magnitude number.Example: B = 4 V = 4.2B - V = -0.2 Cool stars are brighter at visual wavelengths than at blue. So, B apparent magnitude is a larger number than the V magnitude number.Example: B = 8.2 V = 7.5B - V = +0.7 Wednesday, November 16, 119 Wednesday, November 16, 1110Snapshots of many stars in 3 open clustersWednesday, November 16, 11http://www.astro.washington.edu/larson/Astro101/LecturesFraknoi/astro101s09_clustertable.htmlWednesday, November 16, 1112These are CMDs of open star clusters.Which cluster is the youngest? Oldest?What gives you confidence that your answers are correct?Youngest: Pleiades, [chi Persei, Hyades], NGC 188 OldestWednesday, November 16, 11Write down the TO values13Globular ClustersWednesday, November 16, 1114M3 Canes Venatici Wednesday, November 16, 1115Find globular clusters -- in halo of Galaxy: Extremely OLD: 9 - 12+ billion years oldFind open clusters in disk of Galaxy: Generally, young: 1 – 1,500 million years oldWhat does this tell us about the Milky Way?Wednesday, November 16, 1116Explain why the main sequence turn-off temperature of the stars in a cluster is a good indicator of the age of the cluster. Given actual CMDs for open clusters, rank the clusters according to ageContrast open and globular clusters when discussing age, location in the galaxy, and number of stars in the clusterGoals for today: be able to ....Wednesday, November 16, 11Describe how astronomers determine the age of a cluster of stars by reviewing its color-magnitude diagramGiven actual CMDs for open clusters, rank the clusters according to ageContrast open and globular clusters when discussing age, location in the galaxy, and number of stars in the
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