lesson星团 由十几颗至上百

1、2.2.3 星团测距、金属丰度相同昴星团中恒星HRD2014/10/23xkong1u 星团：由十几颗至上百万颗恒星组成的有共同、相互之间有较强的力系的天体系统.u 星团有很多颗恒星组成，亮度大à可以更大范围的测距；从同一气态原始物质中几乎同时形成，金属丰度一样à 可以更加精确测量距离昴星团CMD等龄线：相 T= 16 Myr等龄线T=100 Myr等龄线昴星团中恒星星团中所有恒星 具有相同的未考虑尘埃红化影响的等龄线：颜色太蓝和相同的重元素 丰度，主序很窄 2014/10/23xkong2将T=100Myr等龄线(考虑了尘埃消光影响)，移动(mM)05.6 后，可以很好的

2、拟合昴星团中恒星在HRD上的分布à距离模数(mM)0 =5log10(d/10pc) à昴星团的距离d=132pc同的各种质量的恒星在赫罗图上的位置线疏散星团Open Clustersu 光度范围：100L-30000 L；中心密度可达100Lpc-3u 核半径(面亮度下降到中心值一半处) 大小一般为数秒差距u 疏散星团中的恒星具有小的随机速度，随机速度<1 km/su 质光比M/L < 1：随大质量恒星和随星团的增加2014/10/23xkong3疏散星团Open ClustersMAI - "mean age index" in Gyr)

3、u 大多数疏散星团总是处于靠近系盘平面(or旋臂)的地方u 1200个已知OC， 5T > 1 Gyr，多数T < 300Myr2014/10/23xkong4由于星团的光大多来自其最亮的恒星，可利用其总的或估计星团光的颜色例如，昴星团有BV=-0.05，接近于其仍在 主序上的最亮恒星颜色随着大质量恒星的，的星团光来自红巨星，其颜色变得较红观测其他星系中星团时，只需测量光：将其颜色同系星团比较à河外星系中星团的和其恒星化学组成2014/10/23xkong5利用邻近星团的观测，结合恒星演化理论，把星团的颜色同其和金属丰度起来（颜色à、金属丰度）NGC 3603

4、is a very young and massive cluster：T<5Myr； SFR高；t300Myr2014/10/23xkong6在古尔德带之外，年轻于300Myr的已知疏散星团，大多处于银河中平面50pc以内。较老的星团，有较大的标高NGC 6791: one of the oldest and most massive open clusters.NGC67917年老疏散星团NGC 6791的金属丰度 Z疏散星团(不同 )的化学组成有相当大的弥散：年老的、离银心较远的疏散星团， 更可能是贫金属的年老疏散星团NGC6791金属丰度高，说明系内金属增丰过程不均匀：有些区域金

5、属元素贫乏；有些富球状星团M6open star clusterM69 globular star cluster2014/10/23xkong8球状星团u 包含的恒星数目多，结构更紧密。光度L 106-104 Lu 内部恒星具有较高随机速度sr；金属丰度贫，星族年老2014/10/23xkong9球状星团u 在核半径：rc 5pc以内，恒星的数密度大致为常数u 在潮汐半径或截断半径 rt 处，恒星数密度锐降至零2014/10/23xkong10Globular clustersTop row:M 4,Omega Cen, M 80Middle row: M 53,NGC 6752,M 13B

6、ottom row:M 4,NGC 288,47 Tuc (杜鹃座47)2014/10/23xkong11Globular cluster HR diagramMost globular cluster HR diagrams look very similar.2014/10/23xkong12球状星团的系中的球状星团，大多数都是年老的球状星团中的恒星金属丰度低，主序在比太阳稍蓝和更亮的恒星处结束u杜鹃座47M92uT=12GyrT=13Gyr所有恒星具有相同和u化学组成，主序非常狭窄较亮的恒星落在一条狭窄u的红巨星支，或者MV 0的水平支上（水平支恒星T-2 GyrT-2 Gyr燃烧其中的

7、氦和周围T+2Gyr壳层中的氢）T+2Gyr 两个GC颜色星等图：无年轻成员恒星132014/10/23xkong球状星团测距球状星团距离较远，不能利用三角视差法测量其距离uCMD方法u将观测到的CMD同恒星演化模型预期进行比较u调整假设的距离、和元u素丰度，以获得最佳拟合2014/10/23xkong14球状星团测距天琴座RR型变星u位于水平支上的小质量脉动星(它们的亮度以0.21天随半径周期、规则地变化， 易发现)u天琴座RR型星全都具有大致相同的光度，L50 Lu测定其视亮度，可求距离u2014/10/23xkong15系球状星团分布2014/10/23xkong16左图:系富金属盘球状

8、星团(实点)和不寻常天体(空菱形)右图: Fe/H-0.8的贫金属星团。实点：有蓝水平支的星团（较老）；空圈：有红水平支的球状星团（较年轻）。2014/10/23xkong17Chemical composition is one factor (usually in the sense that more m- poor clusters have bluer HBs)but other stellar properties like age, rotation and helium content have also been suggested as affecting HB morph

9、ology.系球状星团分布u 富金属球状星团在系内区为数较多，而且离中平面较近；它们可能是同核球和厚盘一起形成的。u 贫金属星团系中心形成一个大致球形u 有红水平支的球状星团(相对年轻)分布区域更加弥散u 有蓝水平支的球状星团(相对年老)朝系中心u 多数贫金属球状星团不遵循圆轨道：晕星团的轨道几乎是随机取向的，富金属球状星团像盘中的恒星一样旋转富金属球状星团贫金属球状星团2014/10/23xkong182014/10/23xkong19贫金属晕系晕中包括贫金属的球状星团和贫金属单个晕星(不属于星团)u晕星数目比球状星团多100倍，某些晕星丰度为太阳丰度105u太阳周围贫金属晕星极少，晕星轨道

10、类似于贫金属球状星团u晕对于太阳运动非常u快，可以通过高自行速度发现近邻的晕星贫金属球状星团和贫金属晕星已经在远至离银心100kpc处发现2014/10/23xkong20晕星u 多数晕星看来同贫金属球状星团一样老u 有些晕星是被系引力或撕碎的球状星团的遗迹u 球状星团帕洛马5可能已失去90的恒星；从它伸出的两条长的恒星尾跨天空大于10°u 有些贫金属晕星遵循共同的轨道，可能是被俘获的伴星系的遗迹2014/10/23xkong21贫金属晕星 实线：模型 红色三角形：薄盘星 星符号：晕星 绿色方块：厚盘星 贫金属晕星的总质量只有约109M，比盘或核球中的恒星总质量小得多2014/10/

11、23xkong22直方图：北银极附近视星等V在19 < mV < 20之间恒星数密度随BV颜色的分布2.2.4 红外观测：核球u 太阳在银盘附近，银盘中存在大量尘埃：观测研究系核球和的最佳方法是使用红外观测u 近红外图像显示系有一个扁平的核球：它贡献了银范围大河系总光20%：恒星金属丰度高，2014/10/23xkong23The bulge ageu The stellar population of the bulge is as old as the stars in the globular cluster 47 Tucanae.u Bulge stars follow t

12、he oldisochrones, with the preciseagedependingontheadopted mlicity.2014/10/23xkong24The CMD of a clean sample of bulge stars, selected on the basis of their proper motions. Also shown are isochrones for dierent ages and m licities.The bulge mlicityThe bulge mlicitydistribution function (MDF)Themeanm

13、licityisuhigher in the innermost eld,anddecreasestowardstheouter one.Thepresenceofaradialumlicity gradient along thebulgeminoraxisfavorsabulgeformationthroughdissipational collapse, againstthe bar-driven scenario.2014/10/23xkong25The bulge MDF in three elds along the minor axis, at latitudes listed

14、on the top right corners.Mean mlicities and dispersionsare labeled.系：2.2.4Galactic centerNear-IR image from 2MASS (2 Micron All Sky Survey)Extinction out of 1012by 30 magnitudesó Only 1optical photons makes its wayfrom the GC towards Earth!2014/10/23xkong26Our view (in visible light) towards th

15、e galactic center (GC) is heavily obscured by gas and dustThe Nucleus of our Galaxyu Inner 500pc of Galaxy, extinction makes optical studies impossible - use radio or IRu Observe ionized gas, line emission, dust, star clusters：stellar density is 107stars/pc3 (compared to 0.1 in the solar neighborhoo

16、d)u If the Sun were near the GCu Nearest star would be 1000AU awayu A million stars brighter than Sirius in the night skyu Total starlight more than 200 times brightness of the full Moon2014/10/23xkong27Galactic Center:Optical vs RadioobservationsStar Formation in the Galactic Centeru Molecular mate

17、rial in inner 200 pc relatively hot and denseu 104 per cm3 and 70 Ku High velocity dispersion (s 50 km/s) of moleculesu Mass: 108 Msunu High density helps star formation but high temps dontu Star formation rate (SFR) 1Msun/year2014/10/23xkong28系恒星形成率(SFR)估计对于系，取M/LV 2（星u系的M/LV 2-10）观测盘的光度LV 1.5×

18、;1010Lu由质光比à 银盘恒星质量M* 3×1010 Mu假定系IMF和太阳附近相u似à恒星演化最终将一半的物质返回星际气体中所以，为了在10Gyr内把盘建构起来，必须每年产生（35）M的恒星，即为SFRu2014/10/23xkong29由2.4节，银盘内有（510）×109 M的冷气体，所以这样的恒星诞生率可以维持至少几Gyr， t a few GyrSupermassive Black Hole in the Galactic CenterRadio image (80 pc across) shows feature SgrA and rad

19、io filamentsRadio image (10 pc across) shows feature known as SgrA West center of this is SgrA*Investigate IR stellar motions in region about 1pc across (few ly) to estimate BH mass2014/10/23xkong30The center of the Galaxy in radio wavesu 内区的射电图显示出狭窄的，数十pc长，但宽不足1pc，范围超出了系平面u 黑洞位于点状源人马座A （Sgr A *）201

20、4/10/23xkong31Central 3 lyX-ray image：Sgr A* is the bright object inthe center of the image.Radio image: center is the red ellipse at the center, called Sgr A*Infrared image：Sgr A*does not appear. Thereare about 1,000,000 stars in the area covered by this image. Stars are only 1000 AU apart.2014/10/

21、23xkong32Black HoleThe best estimate of the mass of the black hole at the galactic center was made using:Observations of nearbystar orbits in IRuRadio observations of accretion diskuOrbit of stars in spiral arms Keplers 3rd lawuX-ray observations of coronal gasuDark matter studies using rotation cur

22、vesu2014/10/23xkong33A Black Hole at the Center of Our GalaxyBy following the orbits of individual stars near the center of the Milky Way, the mass of the central black hole could be determined to 2.6 million solar masses2014/10/23xkong34u Fastest moving star moves at 2% of the speed of light, 5000

23、km/su Mass is about 3 million solar massesu Emits radio and X-raysu Almost certainly a black hole红外观测：2014/10/23xkong35X-ray View of the Galactic CenterGalactic center region contains many black- hole and neutron-star X-ray binariesSupermassive black hole in the galactic center is unusually faint in

24、 X-rays, compared to those in other galaxiesChandra X-ray image of Sgr A*LOTS of hot gas!2014/10/23xkong362.3 Galactic Rotationu 银盘中的恒星和气体是在绕银心的近圆轨道上运动u 利用有序运动，研究系气体分布、物质种类、物质分布u 气体运动à 内部引力u 物质质量à 暗物质存在2014/10/23xkong37Galaxy Rotation对于刚体转盘，有角速度w=V/R = 常数à 恒星间距离不变观测发现，太阳周围恒星速度V常数à

25、; w = V/R 随半径变化(R小，w 大；R大，w小）NOT like this.Like THIS.Our Galaxy rotates, and the center rotates faster than the outer parts do !较差自转u 较差自转：是指一个天体在自转时，不同部位的角速度互不相同的现象u 较差自转在大多数非固体的天体中存在，比如星系、巨型气体行星等等系：离银心较近的恒星转一圈所用的时间(T= 2pr/v)，少于较远的恒星uThe rotation of starsu 从太阳向内看，恒星在其轨道上超过我们；方向和太阳轨道速度V0相同u 从太阳向外看，恒

26、星落在我们后面，所以它们有相反方向的自行2.3.1 测量系转动曲线在半径R0处，太阳以速度V0运转(假定轨道为圆轨道)；而半径R处的一颗恒星P轨道速度为V(R)。该星的视向速度Vr (离开我们的速度)：Determining the MW Rotation CurveCalculate Doppler shifts for material at P moving with velocity v at a distance d from the Sun.Radial velocity is:vr = cos (90 ) o cos (90 l) Since cos(90 - x) = sin(

27、x)vr = sin o sin l = R(R) sin Ro o sin lConvert to l (since we cant measure easily)v = and vo = ovrsin (180 )/R = sin /R = sin l/RooPutting this into the above equation givesHow to map the GalaxyDifferential galactic rotation produces Doppler shifts in emission lines from gas in the Galactic disk.Ho

28、w to map the Galaxyu A cloud that is orbiting at the same radius as the Sun (B) will have a LOS velocity of zero since it is moving at the same speed as the Sun.u Clouds with orbits closer to the GC will be moving faster than the Sun and will have positive LOS velocities ( B, D )u While clouds locat

29、ed further from the GC ( A ) willhave negative line of sight velocities since they are moving slower than the Sun.Vr 与银经 l 有关To map out Vr throughout Galaxy, divide the Galaxy into quadrants based on value of galactic longitude.Quad I (0 < l < 90)：Vr=R0 sinl (w-w0)sinl > 0 à R< R0的天

30、体，Vr为正；RR0的天体，Vr变为负uLooking to material closest to GC, - 0 gets larger and Vr increases.uAt point of closest approach (subcentral orutangent point) Vr is atum for that line-of-site (los) and then continues to decrease to Suns orbit.Beyond Suns orbit, Vr becomes negative andincreases in absolute valu

31、e.uVr 与银经 l 有关Quad IV (270l360)u similar to Quad I except reverse signs.u 又重复第一象限的图案，但Vr反号Quad III (270>l>180)u sinl < 0 & V/R<V0/R0 à Vr总是正的；u similar to Quad II, but opposite signs.Quad II (180>l>90)u sinl > 0 & V/R<V0/R0 à Vr总是负的u all los pass through orb

32、its outside of the Suns.u Noum vr but increases with d.系盘内来自中性氢气体的21厘米发射线强度没有在第二象限(90l180)带正速度u第II象限第I象限第IV象限第III象限或在第三象限带负速度的气体u第I、IV象限速度刚好相反u2014/10/23xkong47Getting the Rotation Curve of the MWu Determined from 21-cm line observations (radio wavelength) sensitive to atomic Hydrogen gas that perme

33、ates the Galaxyu Assume circular orbits and that there is at least some Hydrogen all along any given LOSu Especially important to have measurable gas atsubcentral/tangent pointu Findum shift of 21-cm line along given line-of-sight (los)u Assign that Doppler shift to material at thetangent point (clo

34、sest approach to GC): Rmin = R0 sin l；(Rmin) = Vmax/(R0 sin l) + 0u By studying los longitude values from 0 to 90degrees, Rmin will range from 0 to R0Along a given line of sight, clouds with highest Doppler shift in 21-cm line are closest to center of MWGOthers will be closer or further2014/10/2349x

35、kong切点法测转动曲线转动曲线：描述星系各部分的自转速度与到自转轴距离的关系曲线。其形状由星系中的质量分布所决定u如果能够测量散布于全盘的距离已知恒星的速度，即得到转动曲线V(R)：物质分布盘星和星团的可见光被尘埃遮挡；气体原子氢的21厘米辐射受尘埃影响小，但距离难测uuT切点法测自传曲线u 对于内系(RR0)，切点法可以规避距离测量，从而求出自转曲线u 角速度w = V/R随半径增加而下降，当我们沿0l90°的一个固定方向看盘时，视向速度Vr(l,R) 在切点T处最大，在那里视线离银心最近。如果在盘内几乎每一点都有发射气体，通过测量图2.20中对于每个银经l看到的发射最大速度，则

36、可求出V(R)：（2.10）TA cloud at l=135deg, with a radial velocity of -50 km/sec (Vsun=220 km/sec and Rsun=8.5 kpc). R? d?2014/10/2352xkongA cloud at l=135deg, with a radial velocity of -50 km/sec (Vsun=220 km/sec and Rsun=8.5 kpc). R? d?d?2014/10/2353xkong实点：l270°的北边HI气体速度曲线：l90°的南边气体的速度V0220 km

37、s-1V0200 km s-1外系的自转速度用切点法求内系自转Since there is noum Doppler shift for los away from GC, rotation curvebeyond R0 is more difficult to determine. Need to measure the velocity anddistance of material independently.Use Molecular Clouds :u get V from radial velocities of CO emissionu get R (distance) from

38、 spectroscopic parallax of stars forming in cloudsUnderstanding rotation curvesV =GM(R<Ro)RadiusFor planets in the Solar System, M is dominated by Msun, so M does not change much with R - Keplarian rotation curveInside the Galaxy, M increases with radius, so velocity may stay constant or even inc

39、rease with radius.Outside the Galaxy, as in the Solar System, M remains constant with increasing R (if most mass ends at visible edge). Then we would expect the rotation curve to slope downward in Keplarian-like motion.2014/10/23xkong55系中的暗物质2.3.2What does the MW rotation curve tell us?u Since the M

40、W rotation curve shows no drop in velocities beyond the visible edge of the disk (around R=15 kpc), this indicates that some additional non-luminous material must be present à Dark Matter (matter too dim to be detected by current technology)2014/10/23xkong56What is the Dark Matter?u Neutrinos:u

41、 low mass particles that interact via gravity or weak nuclear force.u Most neutrinos, produced from nuclear fusion, pass easily through the Sun.u Common particles but low mass prevents them from contributing more than few percent of dark matter.u WIMPs - Weakly Interacting Massive Particlesu exotics

42、ubatomicparticlespredicted.viasupersymmetricextensions of the Standard Mu Predicted rest mass of 100 times that of proton.u Being searched for in particle accelerator and large detector experimentsu MACHOs - Massive Compact Halo Objectsu WhiteDwarfStars,RedDwarfs(0.2Msun),BrownDwarfs(<0.08Msun),

43、Neutron Stars, Black Holes.u Recall that the more massive remnants result from relatively rarehigh, mass stellar progenitors.2014/10/23xkong57The Search for Dark Matter (brown or white dwarfs): MACHOsThe object dwarf) thefaint (brownforegrounduorwhitebends the light ofbackgroundstarbecause of its gr

44、avitational fieldThelightfromtheubackground star is focused or “lensed” by this effectandthestarappearsbrighter.MACHO results acount for only 20% of dark matteru2014/10/23xkong582.4 Milky Way Meteorology: Interstellar Gasu 星际介质：气体和尘埃u 气体质量少于恒星质量的10%，尘埃质量更小u 气体为恒星形成提供原料u 决定了星系的特性和演化u 气体的分布、加热、运动Milky

45、 Way HI Map (21cm)Milky Way Molecule Map2.4.1 Mapping the gas layeru 运动学距离u 在银盘内做圆轨道运动的气体，由其谱线发射，可求得在银经l方向有多少气体在以视向速度Vr运动u V0、R0已知，利用自转曲线V(R)，可以估计气体的距离V = R sin l ´(V- V0)àRr0RR0u 构建系气体如何分布的图景中性氢(HI) 利用射电21厘米谱线示踪；氢(H2)是对称，利用 CO 谱线来示踪系HI和H2的面密度实点：0l180°空圈：180°l360°系MHI(48)

46、15;109 M;H质量MH21/2 MHIH2主要分布在R<R0区域，但在中心几百pc内无HI和H2HI比H2或恒星分布更延伸，垂直盘方向比H2更厚的层u 太阳处于猎户臂中，位于人马船底臂外，英仙臂里u 尘埃消光，遮挡穿过盘的视线，观测旋臂图案不连续u 和其他旋涡星系一样，致密星主要集中在星系的旋臂气体、尘埃和年轻恒2014/10/2362xkong致密气体、尘埃和年轻恒星集中在旋臂区域2014/10/2363xkong英仙臂Sun人马船底臂速度介于80 km/sVr 70 km/s的中性氢分布l- V0V = R sin l ´(V)br0RR0当l180 °时，

47、由公式，圆轨道内气体有Vr0，既不朝向也不离开我们运动观测发现，b=+70°附近的气体却以70 km/s的速度趋近我们：高纬度气流高纬度气体云：盘物质被吹走后，又回落；或者是来自系以外。不清楚星系中心气体u 离银心12 kpc之外，几乎所有气体都是热的，或者温的：可以利用在遥远类星体紫外光谱中产生的吸 收线来研究它们u 在离银心约3 kpc以内的致密气体环里面，H2的平均面密度降到5 Mpc-2以下u 在这些半径处，原子和气体都处在与b=0平面倾斜1020°的盘内：造成倾斜的不清楚4 x 4 角分 (10 pc )at 6cm radio image系核球的200pc是一个

48、u正在活跃形成恒星的富气区域，包含着至少108 M的气体u 再往里，发现致密气体接近平面b=0 (不倾斜)； 一些长弧和转动气体被拉成，环绕黑洞2014/10/2366xkong2.4.2 A Physical Pictureu 星际气体为多相介质u 在1pc-1kpc间尺度上，热相、暖相和冷相全混合在一起u 多数原子处于致密冷相，而暖、热相气体占据主要体积u 冷介质密度远高于热相，冷气体云通过弥漫介质无The cooling rate per n 2 from 1027 to 1021Herg cm3s1The interstellar gas forms a multi-phase med

49、ium, consisting basically of three components: hot (> 106K), warm (104K) and cold (102K).The different components are in approximate pressure equilibrium and the spatial transition between the phases can be quite sharp.旋臂上的巨云u H原子数密度NH1020个/cm2,或M/pc2气体云，基本变成了分子云u 巨云的尺度可以大于20pc，质量超过105 M，密度大于200个 H2cm-3云被冷HI包围，形成r100 pc、气体质量107