RedGiantEvolution红巨星演化氢燃烧壳继续向核区添加氮。Hefuaioncore氮核更密更热，直到下一种inertcarbonccreHfusionphellHie tusion shall核反应开始：Htusion shell0BMR2-100氮聚变（温度更高）：104Hie ignitionSupergiants4He+4He→8Be+Hfusion she102S8Be+4He→12C+PeeoE10-2恒星上这个过程叫HtusnshelEvoluticnd3-solar-massstrthtoughtheganttegion:10-4闪（heliumflash）-HfusioncorebasedonamathematicalmodelMain-sequence star30,00020.00010009200530002000Temperature (K)核反应并不停止··
Red Giant Evolution 红巨星演化 氦核更密更热，直到下一种 核反应开始： 氦聚变（温度更高）： 4He + 4He → 8Be + g 8Be + 4He → 12C + g 氢燃烧壳继续向核区添加氦。 恒星上这个过程叫 氦闪（helium flash） 核反应并不停止
Evidence for Stellar Evolution:StarClusters恒星演化证据：星团Stars in a starclusterall haveapproximately thesame age!星团中的恒星都有相同的年龄Moremassive stars evolve more quickly than less massiveones.质量决定寿命，大质量的恒星演化快If you put all the stars of a star cluster on a HR diagram,themostmassive stars (upperleft)will be missing如果把一个星团内的所有恒星画在一个赫罗图上，质量最大的恒星（左上）会消失
Evidence for Stellar Evolution: Star Clusters 恒星演化证据：星团 Stars in a star cluster all have approximately the same age! 星团中的恒星都有相同的年龄 More massive stars evolve more quickly than less massive ones. 质量决定寿命，大质量的恒星演化快 If you put all the stars of a star cluster on a HR diagram, the most massive stars (upper left) will be missing! 如果把一个星团内的所有恒星画在一个赫 罗图上，质量最大的恒星（左上）会消失
HR Diagram of a Star ClusterBOMKAC106The Hyades Star ClusterHigh-mass starsThe most massiveevolvedontothegiantOnlyafewstarsarestarshavedied104大质量恒星inthe giant stagebranch大质量恒星演化Main sequence102到巨星带GiantsThelower-massstarsTurn-off pointare still onthe mainsequence截断点（拐点）10-2Low-mass stars still onThefainteststarswerenotthemain sequence10-4observed inthestudy低质量恒星仍在30,000 20.0003000200010,0005000主序上Temperature (K)@2006Brooks/Cole-Thomson
High-mass stars evolved onto the giant branch 大质量恒星演化 到巨星带 Low-mass stars still on the main sequence 低质量恒星仍在 主序上 Turn-off point 截断点（拐点） HR Diagram of a Star Cluster 大质量恒星
EstimatingHighest-massstarsevolvingNGO2264/s8veryLow-massstarsyoungclustersthllstillcontrathegeuiethe Age of atromwhlchitformeatslower-massstarsarestillcontracting,andtisrichinTTaurstarsClusterLaamVisual估计星团年龄Thenebulaaroundthe Pleladeslsproducedbygasanddust主序上截断点107ythroughwhichthe cluster Ispassing.Its original nebuladissipated long ago.处的恒星：Uppermainsequencestars年龄=寿命。havedied.108yVieualTheloweronthe108Mstheturn-offpoint, the olderthe cluster.10°y3主序上截断点M67sanoldopan剩下Onlythelowercluster. In photographsmassstarsremain越低，星团越Hsuch ciusters have a uniform红矮onthemainappearancebecausethey lacksequence.not,brigntstars.ComparewiththeRESI老。星.JewelBcxonthieoppositepageVisual1010yTemperature (K)
Estimating the Age of a Cluster 估计星团年龄 The lower on the MS the turn-off point, the older the cluster. 主序上截断点 越低，星团越 老。 主序上截断点 处的恒星： 年龄=寿命。 剩下 红矮 星
（长命）RedDwarfs红矮星7solarmassesRadlativeStarswithlessthanNzone~0.4solarmassesarecompletely3.5solarmassesconvective质量小于0.4个Mass质量Convective太阳质量的恒zoneW星是完全对流1solarmass1070.8solarmass的.0.2solarma8→Hydrogen and helium remainwell mixed throughout the entire star@2006Brooks/Cole-Thomson氢和氮在整个恒星内完全混合→No phase ofshell “burning”withexpansionto giant无壳层燃烧和膨胀到巨星的过程Star not hot enough to ignite He burning恒星不足够热，不能点燃氮
Red Dwarfs 红矮星（长命） Stars with less than ~ 0.4 solar masses are completely convective 质量小于0.4个 太阳质量的恒 星是完全对流 的. → Hydrogen and helium remain well mixed throughout the entire star. 氢和氦在整个恒星内完全混合. → No phase of shell “burning” with expansion to giant. 无壳层燃烧和膨胀到巨星的过程. Star not hot enough to ignite He burning. 恒星不足够热，不能点燃氦