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Today’s slides are on the web Basic Properties of Stars • Composition • Mass • Diameter = D • Measure temperature T from spectrum. Emitted energy per unit surface area • Luminosity = L [Fig. 5.10] 5000o T = 15,000K [fig 4.8]5800K 3000K 310K 4000o 3000o Wavelength Energy • Total energy emitted per unit surface area = E = T 4 • Total energy from whole star: L = E x (surface area) = ( T 4) x (D2) Measure L and T, solve for D The Hertzprung-Russell (H-R) Diagram [11.2] • Representative sample of stars. • Plot Luminosity vs. Surface Temperature. • Most stars fall along “main sequence”. M ai nS eq u en c e • Any theory about how stars work has to explain this. Hot Cool [see Fig. 11.10] 1 The H-R H-R Diagram Diagram (with with Sizes The sizes) Larg er D i a. 106 Luminosity 104 [Fig. 11.10] 102 Con stan t Dia me t 100 er 10-2 10-4 25,000 L = ( T4 ) x (D2) 10,000 5,000 Temperature 3,000 Diameter! Here’s what we observe about stars. The Mass-Luminosity Relation The H-R Diagram Hot Higher (Luminosity, Temperature, Diameter) (O) mass stars Cool (M) stars Lower mass Main sequence is a mass sequence Hot Cool 2 What is inside the Sun? energy generation (cumulative) Measure • • • • Infer Luminosity Mass Diameter Chemical composition (from our knowledge of Physics) 0 1 • Internal structure 16 million deg K H temperature composition density 4He 160 x water What is inside other stars? 3He Measure • • • • Calculate 11 atmospheres 2.5x10 Luminosity Mass Surface mass temperature (cumulative) Chemical composition 0 1 radiation Infer Diameter pressure convection • Internal Energy structure transport from Luminosity and Temperature radius 0 1 0 1 Here’s what we observe about stars. The Mass-Luminosity Relation The H-R Diagram Hot Higher (Luminosity, Temperature, Diameter) (O) mass stars Cool (M) stars Lower mass Main sequence is a mass sequence MAIN SEQUENCE: Stars convert H into He in their cores. 3 H composition 4He 3He Models of Sun show: Burning of H in center has already changed the composition a lot! Eventually, H burns outward in a shell • • • • Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler Luminosity Red giant. H He burning core Diameter Inert H Temperature 4 Eventually, H burns outward in a shell • • • • Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler Luminosity Red giant. Inert He core HHe burning shell Inert H Diameter Temperature Eventually, H burns outward in a shell • • • • Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler Luminosity Red giant. Inert He core HHe burning shell Inert H Diameter Temperature 5 Eventually, H burns outward in a shell • • • • Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler Luminosity Red giant. Inert He core HHe burning shell Inert H Diameter Temperature 6