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• Why does the sun die? • What will the sun become when it dies? • Fri & Sat, 9-11pm, if it is not cloudy. • Mar 18 & 19 • Apr 15 & 16 • May 13 & 14 • 24-inch telescope in dome • small telescopes outside Star cluster Pleiades • Evidence on giants from star clusters • All stars in a cluster are born at once. • 100,000 fraternal twins, some weighing 30 times me, the G star, some 1/10 me. 1e6 1e4 → • New policy: if you turn in more than 2 clicker paper answers, they will count 2 pts/question. • Public viewing sessions at MSU campus observatory. Giants are dying stars; white dwarfs are dead stars 100 1 Luminosity The future sun−March 18 0.01 1e-4 30,000 10,000 6,000 Temperature 3,000 HR Diagram of Clusters • Not all fainter stars were observed • In what ways are HR diagrams of H+χ Perseus, Pleiades, Hyades, & NGC188 different? • Perseus is hotter than Pleiades • Not all stars are on MS • Perseus has small range of luminosity 1 HR Diagram of Clusters 106 O star: 30M¤; 200,000L¤ Lifetime=amount of fuel/consumption rate Lifetime=21gallons/(3gallons/hr)=7hr Lifetime=30M¤/ 200,000L¤ =Lifetime¤/7000 =1.3Myr Human scale = 4days → 104 Luminosity • In what ways are HR diagrams of H+χ Perseus, Pleiades, Hyades, & NGC188 different? Stars with high mass live a short life 102 100 10-2 Sun Lifetime=10Byr Human scale 80yr Barnard’s star: 0.1M¤; 0.004L¤ 10-4 Lifetime=0.1M ¤/ 0.004L¤ =25Lifetime¤ =250Byr Human scale = 20,000yr 25,000 H-R Diagrams of star clusters 1. There are no A stars in M80 because a. they never formed. b. they died and disappeared c. all stars became redder as they get older. d. they are too faint to see. 10,000 5,000 Temperature 3,000 H-R Diagrams of star clusters 2. The hottest dwarfs in Pleiades are A stars. The hottest dwarfs in M15 are F stars. Pleiades is ___ than M15. a. older b. younger 2 Life of the sun • • • • Life of the sun Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler è Red • • • • giant. è Red HèHe burning core Inert H ç Temperature Inert He core ç Temperature • • • • Life of the sun Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler è Red • • • • giant. HèHe burning shell Inert H giant. Later Luminosity è Luminosity è Inert He core Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler è Red Few 100 Myr later ç Temperature HèHe burning shell Inert H Radius photosphere Life of the sun Radius photosphere giant. 5 Byr from now Luminosity è Luminosity è Present sun Radius photosphere Heat source moves closer to surface. Layers below surface swell up. Star becomes larger Surface becomes cooler Inert He core Radius photosphere HèHe burning shell Inert H ç Temperature 3 After helium is used up Reaction Min. Temp. 107 o K 3 4He è 12C + 4He è 2x108 16O, Ne, Na, Mg 8x108 Ne è O, Mg 1.5x109 O è Mg, S 2x109 Si èFe peak 3x109 Triple-alpha process Min. Temp. 4 1H è 4He 107 o K 3 4He è 12C 2x108 12C 4 1H è 4He 12C Reaction + 4He è 16O, Ne, Na, Mg 8x108 • Mg Following He è C, O Ne è O, for 9 O è Mg, Score never gets hot enough2x10 further reactions. Si èFe peak 3x109 Planetary nebula shell expelled. burning, 1.5x109 Stars with < 2 M• • End is He à C, O burning. • Core never gets hot enough for further reactions. • Contraction heats center • Helium starts to burn. Star continues to shrink. Surface becomes very hot. [Fig. 12.10] Solar-mass star 4