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Stellar Clusters Homework Problems Chapter 13
Review Questions: 1-3, 9-11 Review Problems: 1, 2, 7 Web Inquiries: 1, 4
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H-R Diagram An H-R diagram reveals three significant features. L/Lsun
The Main Sequence core hydrogen fusion Red Giants hydrogen shell source (core helium fusion) White Dwarfs carbon-oxygen core leftovers This is a snapshot in the life of many, unrelated stars. L/Lsun O B A F G K M
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H-R Diagram Other areas of the H-R diagram are
sparsely populated either because stars just don’t exist with those specific combinations of luminosity and temperature, or because the stars evolve so quickly and spend so little time in that area that the probability of seeing stars located there is very low. (Example: “Hertzsprung Gap”) L/Lsun O B A F G K M
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Clusters Formation Stars from the same formation epoch (same “birthday”) Same Age Similar Chemical Composition Same Distance from the Earth
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Stellar Clusters OPEN Cluster GLOBULAR Cluster Bright Hot, Young stars
Thousands of stars Loose Associations GLOBULAR Cluster Fainter Cooler, Older stars Hundreds of Thousands of stars Tightly Bound Systems
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Double Cluster OPEN Cluster Very few evolved stars.
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Globular Cluster Many evolved stars.
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Cluster HR Diagrams H-R diagrams revealing a variety of ages among
clusters. Who is the youngest? Who is the oldest?
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Young Cluster
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Young Cluster HR Diagram
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Cluster Evolution
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Combined Cluster H-R diagrams
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Hyades
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M44 Cluster
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M41 Cluster
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M2001 Cluster
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Globular Cluster M5
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Main Sequence Turnoff Since stellar evolution is highly dependent
upon the mass of a star, the turn-off point of a clusters main-sequence is a measure of the clusters age.
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Horizontal Giant Branch
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Pulsating Variable Stars
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Instability Strip
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The Pulsating Stars
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Cepheid Pulsation Sequence
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Pulsating Variables Light curves for two different Cepheid
variables showing the periodic changes in brightness.
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Cepheids
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Cepheid Pulsation The interplay of Radius and Temperature. L = 4pR2sT4
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Period - Luminosity Relation
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Cepheid Period - Luminosity
Observe apparent magnitude (m) Observe Period of pulsation (P) Utilize P-L relation to infer absolute magnitude (M) Use distance modulus to obtain distance: m-M = 5 log D - 5
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SMC and LMC The Milky Ways two irregular satellite galaxies.
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Distance Determinations
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Distance Indicators
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