11SchematicSchematic H-R Diagram H-R Diagram•State what an H-R Diagram is and why the information inferred from it is important to the study of stars2Main-sequence (MS)stars are fusinghydrogen into helium intheir cores.•High luminosity MSstars are hotter.•Low luminosity onesare cooler.MASS-LUMINOSITYRELATIONSHIPSignificanceSignificance of the main of the main sequence: charcteristics revealed!sequence: charcteristics revealed!•State what an H-R Diagram is and why the information inferred from it is important to the study of stars3Measurements ofmasses of MS starsshow that the hot,blue stars are muchmore massive thanthe cool, red ones.•State what an H-R Diagram is and why the information inferred from it is important to the study of stars4Summary: Fromanalysis of main-sequence stars,we find it is themassesmasses of thosecore hydrogen-fusing stars thatdetermine theirluminosities andtemperatures(spectral types).HIGH luminosityLOW luminositySizzling HOT!Moderately COOL•State what an H-R Diagram is and why the information inferred from it is important to the study of stars5• State which properties of stars can be determined directly from an H-Rdiagram and which must be inferred by indirect means.• Explain what is meant by the mass-luminosity relationship and why the“main-sequence” for stars is significant6(Part I: Solar-type stars)(Part I: Solar-type stars)27 summarize the future of the Sun on a rough timescale; apply the basics of the conservation of energy and thebattle between gravity and outward pressure to what“drives” a star to evolve at each major stage of evolution; explain what is meant by subgiant, red giant branch,electron degeneracy, helium flash, horizontal branch,planetary nebula, white dwarf.Learning goals: Be able to ….89Brown DwarfBrown Dwarfhttp://chandra.harvard.edu/xray_sources/browndwarf_fg.htmlIn between a star and a planetJupiter < BD mass < 0.08 SunRadiates in infrared due totemperature.Mass too low to start fusionin core.Slowly cools over trillions ofyears.1011Core producing energy--Fusing H to HeCore producing energy--Fusing H to He12Notice “rapid”increase inluminosityTroublestarts here!Evolution of the SunEvolution of the Sun31314Expanding Expanding SubgiantSubgiant15H He fusion shellHe ashElectrondegeneracysupports the core.[No two electrons canoccupy identicalstates.]Core collapse stopsCore collapse stopsSurface of star veryfar away!16““HumanHuman”” (molecular?) (molecular?) ““DegeneracyDegeneracy””http://www.youtube.com/watch?v=9O-u9SlnhOo17Star changes dramatically!Star changes dramatically!Today’s SunFuture Sun18Star in subgiant to giant stage:41920What initiateshelium fusion?Helium flash!What supportsthe star now?21Where is thestar on HRD?22Star is at the Star is at the ““tiptip”” of the red-giant branch of the red-giant branch2324Core runs out of helium.Core runs out of helium.Core: contracting until electrondegeneracy sets in again; givingoff energy GPE TE Shells start fusion HHe HeCC525Rest of star responding to huge luminositycoming from shell fusion Outer parts of star start to reach escapevelocity – star is unstable!2627End of the road for Sun-like stars2829 White dwarf willslowly cool to a cold,black carbon cinderof about 0.7 solarmasses “Mass sink” material does not goback into ISM.““WHITE DWARFWHITE DWARF””30Astronomers have discovered a diamond starweighing 10 billion trillion trillion carats. Thecosmic gem is the crystallized carbon core of awhite dwarf star. Credit: Travis Metcalfe andRuth Bazinet, Harvard-Smithsonian Centerfor Astrophysics.click631Final stage in the life of a sun-like starFinal stage in the life of a sun-like star323334White Dwarfs on the HR DiagramWhite Dwarfs on the HR
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