1ASTR 1040 ASTR 1040 AccelAccelAstroAstro::Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 12 Lecture 12 ThurThur17 Feb 201117 Feb 2011zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomreEskimoEskimoplanetaryplanetarynebulanebulaTodayToday••Why O and B stars are so luminous on MS?Why O and B stars are so luminous on MS?••CC--NN--O cycleO cycledominates fusion burning of H in dominates fusion burning of H in massive stars, really pours out the energymassive stars, really pours out the energy••Explains observed Explains observed MASSMASS--LUMINOSITYLUMINOSITYrelationrelation••EstimateEstimatelifetime on the main sequence (MS)lifetime on the main sequence (MS)••First MidFirst Mid--Term ExamTerm Exambeing returnedbeing returned••Respond to discussion Q on Respond to discussion Q on ‘‘Cities of StarsCities of Stars’’••Class Class meets on Tuesmeets on Tuesin Fiske Planetarium: read in Fiske Planetarium: read Chap 16: Star BirthChap 16: Star Birthin advancein advance••Complete reading Complete reading Chap 17: Star StuffChap 17: Star Stuff, which is , which is really really ““stellar evolutionstellar evolution””So did we really love this exam?So did we really love this exam?RESULTS FROM FIRST MIDRESULTS FROM FIRST MID--TERM EXAMTERM EXAMFIRST MIDFIRST MID--TERM EXAMTERM EXAM••Grade boundariesGrade boundaries, based on 116 points:, based on 116 points:••If 100/116 (86%) If 100/116 (86%) or overor over, , AA’’ss[43%][43%]••90/116 (78%) or over, 90/116 (78%) or over, BB’’ss[32%][32%]••78/116 (67%) or over, 78/116 (67%) or over, CC’’ss[15%][15%]Also +, plain, and Also +, plain, and ––within these rangeswithin these rangesGo through answer sheetGo through answer sheet––and talk to us if and talk to us if do not understand our choices. Keep exam do not understand our choices. Keep exam + answers for future review (comp final)+ answers for future review (comp final)Dave DyerDave DyerActionAction--PackedPackedArtistryArtistryKenneth Kenneth ShellnutShellnutAwesome DensityAwesome Densityof Informationof Information(recoverable?)(recoverable?)zoomzoom--inin2Why do spectra of hottest stars (O and Why do spectra of hottest stars (O and B types) show few absorption lines?B types) show few absorption lines?••A. Many elements have been used up in these A. Many elements have been used up in these starsstars••B. These stars are old and were formed before B. These stars are old and were formed before there were many elements in the galaxythere were many elements in the galaxy••C. Many atoms in these stars are ionized C. Many atoms in these stars are ionized ––have lost electrons have lost electrons ––so canso can’’t absorbt absorb••D. Much of their absorption is in the ultravioletD. Much of their absorption is in the ultraviolet••E. C and DE. C and DE.E.Main sequence (MS) stars Main sequence (MS) stars Burning Burning hydrogenhydrogenin their coresin their coresTemperatures areTemperatures arehotterhotterfor for moremoremassive starsmassive stars(crush of gravity)(crush of gravity)More luminousMore luminous(higher fusion rates)(higher fusion rates)••Stars take Stars take millions to millions to billions of yearsbillions of yearsto go to go through their life through their life stages stages --we rarely see we rarely see a single star changea single star change••Observing many Observing many different stars lets us different stars lets us figure out figure out the the sequence of a single sequence of a single starstar’’s lifes lifeLook at broad sample, to figure out Look at broad sample, to figure out anyanylifespanlifespanL / LL / LooTemperatureTemperature1010661010--4440,00040,0003,0003,000Binary starsBinary starsshow:show:Higher on MS,Higher on MS,higher MASShigher MASSBut how longBut how longdoes a stardoes a starlive there ?live there ?10 10 MMsunsun0.3 0.3 MMsunsunLifetimes on Main Sequence (MS)Lifetimes on Main Sequence (MS)••Stars spend 90% of their lives on MSStars spend 90% of their lives on MS••Lifetime on MSLifetime on MS= amount of time star = amount of time star burns burns hydrogen (gradually) in its corehydrogen (gradually) in its core••For For SunSun, this is about 10 billion years, this is about 10 billion years••For For more massive starsmore massive stars(OBAF), lifetime is (OBAF), lifetime is (much) shorter(much) shorter••For For less massive starsless massive stars(KM), lifetime is (KM), lifetime is longer longer ••But But howhowdo we get these numbersdo we get these numbers??PP--P ChainP Chain&&CC--NN--O CycleO CycleBoth fusionBoth fusionprocessesprocessesoccur in parallel, occur in parallel, but Cbut C--NN--O makesO makesfar more energyfar more energyat at higherhighertemperaturestemperaturesStars hotter Stars hotter than F1, than F1, CC--NN--O winsO wins3CC--NN--O Fusion CycleO Fusion CycleCan provide Can provide vast luminosityvast luminosityfor massive stars on MSfor massive stars on MSCC--NN--O O CycleCycle(another view)(another view)Main SequenceMain Sequence::range of stellarrange of stellarpropertiespropertiesLLrange isrange isbiggest !biggest !““ObservedObserved””MASS MASS ----LUMINOSITYLUMINOSITYrelation forrelation formain sequencemain sequenceBut why suchBut why sucha a steepsteepvariationvariationwith mass ?with mass ?BIGGER CRUSHBIGGER CRUSHOF GRAVITY needsOF GRAVITY needsHIGHER centralHIGHER centralPRESSURE (orPRESSURE (ortemperature)temperature)FASTER BURNINGFASTER BURNING(CNO(CNO--fusionfusion--cycle cycle comes into play)comes into play)L ~ ML ~ M44How long can How long can stars burn Hstars burn Hin their cores?in their cores?More massiveMore massivestar have (very)star have (very)short livesshort livesShort lives of massive stars on MSShort lives of massive stars on MS••RockRock--star analogy: star analogy: More massive, hotter, More massive, hotter, more luminous starsmore luminous starsburn through the burn through the available fuel fasteravailable fuel faster----leading to early leading to early burnoutburnoutCC--NN--O fusion cycle is O fusion cycle is the way massive stars the way massive stars do it !do it !4EstimatingEstimatingLIFE on MSLIFE on MSFour stepsFour stepsin our estimatein our estimateSimple playSimple playwith numbers with numbers ––just be bold!just be