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Charles Hakes Fort Lewis College 1 Light Pollution Stellar Evolution Charles Hakes Fort Lewis College 2 Lab Notes • Be sure you have started your “report” lab. • Constellation presentations next week. • Observatory field trips… Charles Hakes Fort Lewis College 3 Night Lights • http://apod.nasa.gov/apod/ap101104.html Charles Hakes Fort Lewis College 4 Limiting Magnitude and Light Pollution Charles Hakes Fort Lewis College 5 Limiting Magnitude • Limiting Magnitude is a measure of the dimmest star visible from a given location. • • • • Center of a big city: ~2.0 Suburbs: ~4.5 Downtown Durango: ~5.5 La Plata County (FLC observatory): ~6.5 • Depends on observer experience • Depends on local glare • Depend on how dark adapted your eyes are. You should wait 20-30 minutes to measure this. Charles Hakes Fort Lewis College 6 Limiting Magnitude • Use stars of known magnitude (e.g. Little Dipper) Charles Hakes Fort Lewis College 7 Limiting Magnitude • Count the stars in a well-defined region • Chose one of the predefined star regions that is overhead • Count the number of stars visible within the region boundary • Look up the number on the published tables to find the corresponding limiting magnitude Charles Hakes Fort Lewis College 8 Limiting Magnitude Charles Hakes Fort Lewis College 9 Limiting Magnitude Alpha-Epsilon-Beta Gem stars LM 1 1.2 2 2.4 3 3.2 4 3.9 5 4.3 6 5.0 7 5.1 8 5.3 9 5.6 10 5.7 11 5.9 12 6.1 13 6.2 14 6.3 15 6.4 16 6.5 18 6.6 20 6.7 22 6.9 23 7.0 25 7.2 30 7.5 Charles Hakes Fort Lewis College 10 How many Stars Can You See? Magnitude -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Charles Hakes Fort Lewis College Range Cumulative Stars -1.50 to -0.51 -0.50 to +0.49 +0.50 to +1.49 +1.50 to +2.49 +2.50 to +3.49 +3.50 to +4.49 +4.50 to +5.49 +5.50 to +6.49 +6.50 to +7.49 +7.50 to +8.49 +8.50 to +9.49 +9.50 to +10.49 +10.50 to +11.49 +11.50 to +12.49 +12.50 to +13.49 +13.50 to +14.49 +14.50 to +15.49 +15.50 to +16.49 +16.50 to +17.49 +17.50 to +18.49 +18.50 to +19.49 +19.50 to +20.49 % Increase Seen 2 8 22 93 283 893 2,822 8,768 26,533 77,627 217,689 626,883 1,823,573 5,304,685 15,431,076 44,888,260 130,577,797 379,844,556 1,104,949,615 3,214,245,496 9,350,086,162 27,198,952,706 11 400% 275% 423% 304% 316% 316% 311% 303% 293% 280% 288% 291% 291% 291% 291% 291% 291% 291% 291% 291% 291% How many Stars Can You See? • Dark-adapted naked eye (1x7 binoculars) • Can see to magnitude 6.5 -> ~104 stars • Light gathering ability scales with area. • • • • Magnitude Increase = log10(Area increase) / 0.4 10x50 binoculars ~50x area -> +4.25 magnitudes 16” SCT ~64x area -> +4.5 magnitudes 10m Keck telescope ~625x area -> +7 magnitudes Charles Hakes Fort Lewis College 12 How many Stars Can You See? • So for naked eye observing • 10x50 binoculars • 50x area • +4.25 magnitudes (to 10.75) > 106 stars • 16” SCT • 64x area • +4.5 magnitudes (to 15.25) > 108 stars • 10m Keck telescope • 625x area • +7 magnitudes (to 22.75) > 1011 stars Charles Hakes Fort Lewis College 13 Figure 10.6 Apparent Magnitude Charles Hakes Fort Lewis College 14 Light Pollution • Generally not an issue in La Plata county. • Durango has a dark sky ordinance, but only for new construction. • Fort Lewis is making progress with outside light fixtures. Charles Hakes Fort Lewis College 15 Light Pollution Earth at Night Credit: C. Mayhew & R. Simmon (NASA/GSFC), NOAA/ NGDC, DMSP Digital Archive Charles Hakes Fort Lewis College 16 Light Pollution From IDA Website: http://www.darksky.org/images/sat.html Charles Hakes Fort Lewis College 17 Light Pollution You Are Here Observatory Charles Hakes Fort Lewis College 18 Figure 10.15 Hipparcos H–R Diagram • Plot the luminosity vs. temperature. • This is called a HertzsprungRussell (H-R) diagram Charles Hakes Fort Lewis College 19 What fraction of the stars on an H-R diagram are on the main sequence A. B. C. D. 0-50% 50-70% 70-80% >80% Charles Hakes Fort Lewis College 20 What fraction of the stars on an H-R diagram are on the main sequence A. B. C. D. 0-50% 50-70% 70-80% >80% Charles Hakes Fort Lewis College 21 Distance Scale • If you know brightness and distance, you can determine luminosity. • Turn the problem around… Charles Hakes Fort Lewis College 22 Distance Scale • If you know brightness and distance, you can determine luminosity. • Turn the problem around… • If a star is on the main sequence, then we know its luminosity. So • If you know brightness and luminosity, you can determine a star’s distance. Charles Hakes Fort Lewis College 23 Distance Scale • Spectroscopic Parallax - the process of using stellar spectra to determine distances. • Can use this distance scale out to several thousand parsecs. Charles Hakes Fort Lewis College 24 Figure 10.16 Stellar Distances Charles Hakes Fort Lewis College 25 Stellar Evolution Charles Hakes Fort Lewis College 26 Figure 11.16 Atomic Motions • Low density clouds are too sparse for gravity. • A perturbation could cause one region to start condensing. Charles Hakes Fort Lewis College 27 Figure 11.17 Cloud Fragmentation Charles Hakes Fort Lewis College 28 Figure 11.20 Interstellar Cloud Evolution Charles Hakes Fort Lewis College 29 http://discovermagazine.com/2009/interact ive/star-formation-game/ google “star formation game” Charles Hakes Fort Lewis College 30 H-R diagram review • The H-R diagram shows luminosity vs. temperature. • It is also useful for describing how stars change during their lifetime even though “time” is not on either axis. • How to do this may not be obvious. • Exercise - Get in groups of ~four and get out a blank piece of paper. Charles Hakes Fort Lewis College 31 Group Exercise • As a group, create a diagram with “financial income” on the vertical axis, and “weight” on the horizontal axis. • Use this graph to describe the past and future of a fictitious person (or a group member). • Label significant events, for example • • • • birth college retirement death Charles Hakes Fort Lewis College 32 Stellar Evolution 1 - interstellar cloud - vast (10s of parsecs) 2(and 3) - a cloud fragment may contain 1-2 solar masses and has contracted to about the size of the solar system 4 - a protostar • center ~1,000,000 K • Too cool for fusion, but hot enough to see. (photosphere ~3000 K) • radius ~100x Solar Charles Hakes Fort Lewis College 33 How would the luminosity of a one-solar-mass protostar compare to the sun? A) Less than .1x as bright B) A little lower. C) About the same. D) A little brighter E) More than 10x brighter Charles Hakes Fort Lewis College 34 How would the luminosity of a one-solar-mass protostar compare to the sun? A) Less than .1x as bright B) A little lower. C) About the same. D) A little brighter E) More than 10x brighter Charles Hakes Fort Lewis College 35 Figure 11.19 Protostar on the H–R Diagram Charles Hakes Fort Lewis College 36 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. Charles Hakes Fort Lewis College 37 Figure 11.18 Orion Nebula, Up Close Charles Hakes Fort Lewis College 38 Figure 11.23 Protostars Charles Hakes Fort Lewis College 39 Figure 11.21 Newborn Star on the H–R Diagram Charles Hakes Fort Lewis College 40 Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years Charles Hakes Fort Lewis College 41 Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years Charles Hakes Fort Lewis College 42 Stellar Lifetimes • Proportional to mass • Inversely proportional to luminosity • Big stars are MUCH more luminous, so they use their fuel MUCH faster. • The distribution of star types is representative of how long stars spend during that portion of their life. • Example - snapshots of people. Charles Hakes Fort Lewis College 43 Figure 10.21 Stellar Masses Charles Hakes Fort Lewis College 44 Figure 11.24 Prestellar Evolutionary Tracks Charles Hakes Fort Lewis College 45 Figure 11.25 Brown Dwarfs Charles Hakes Fort Lewis College 46 Figure 11.22 Protostellar Outflow Charles Hakes Fort Lewis College 47 Stellar Evolution Charles Hakes Fort Lewis College 48 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. Charles Hakes Fort Lewis College 49 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. Can have violent “winds” streaming outwards; often bipolar flow from poles; T-Tauri phase Charles Hakes Fort Lewis College 50 Figure 11.21 Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink. Can have violent “winds” streaming outwards; often bipolar flow from poles; T-Tauri phase 6 - a newborn star Core temperature high enough to ignite nuclear fusion. Charles Hakes Fort Lewis College 51 Figure 11.21 Newborn Star on the H–R Diagram Charles Hakes Fort Lewis College 52 Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years Charles Hakes Fort Lewis College 53 Stellar Lifetimes • Proportional to mass • Inversely proportional to luminosity • Big stars are MUCH more luminous, so they use their fuel MUCH faster. • The distribution of star types is representative of how long stars spend during that portion of their life. • Example - snapshots of people. Charles Hakes Fort Lewis College 54 Figure 10.21 Stellar Masses Charles Hakes Fort Lewis College 55 Figure 11.24 Prestellar Evolutionary Tracks Charles Hakes Fort Lewis College 56 Figure 12.1 Hydrostatic Equilibrium Charles Hakes Fort Lewis College 57 Figure 11.24 Prestellar Evolutionary Tracks The final location on the main sequence depends entirely on the size (mass) of the condensing cloud. Charles Hakes Fort Lewis College 58 Figure 11.25 Brown Dwarfs Not big enough to start fusion. Mass <~ 0.08 solar masses ~=80x mass of Jupiter. These are likely very numerous Charles Hakes Fort Lewis College 59 Stellar Evolution 7 - the star stays on the main sequence for most (~90%) of its lifetime. Charles Hakes Fort Lewis College 60 Figure 10.15 Hipparcos H–R Diagram Charles Hakes Fort Lewis College 61 Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years Charles Hakes Fort Lewis College 62 Stars A and B formed at the same time. Star B has 3 times the mass of star A. Star A has an expected lifetime of 3 billion years. What is the expected lifetime of star B? A) more than 9 billion years B) about 9 billion years C) 3 billion years D) about 1 billion years E) less than 1 billion years Charles Hakes Fort Lewis College 63 Figure 10.21 Stellar Masses Charles Hakes Fort Lewis College 64 What forces a star like our Sun to evolve off the main sequence? A) It loses all its neutrinos, so fusion must cease. B) It completely runs out of hydrogen. C) It builds up a core of inert helium. D) It explodes as a violent nova. E) It expels a planetary nebula to cool off and release radiation. Charles Hakes Fort Lewis College 65 What forces a star like our Sun to evolve off the main sequence? A) It loses all its neutrinos, so fusion must cease. B) It completely runs out of hydrogen. C) It builds up a core of inert helium. D) It explodes as a violent nova. E) It expels a planetary nebula to cool off and release radiation. Charles Hakes Fort Lewis College 66 Figure 12.2 Solar Composition Change 7 - fusion of H to He occurs in the core until the H is used up. Charles Hakes Fort Lewis College 67 After hydrogen fusion stops in the core of a star, the core… A) expands and cools B) expands and heats C) contracts and cools D) contracts and heats Charles Hakes Fort Lewis College 68 After hydrogen fusion stops in the core of a star, the core… A) expands and cools B) expands and heats C) contracts and cools D) contracts and heats Charles Hakes Fort Lewis College 69 After hydrogen fusion stops in the core of a star, the star as a whole… A) expands B) contracts Charles Hakes Fort Lewis College 70 After hydrogen fusion stops in the core of a star, the star as a whole… A) expands B) contracts Charles Hakes Fort Lewis College 71 Figure 12.3 Hydrogen Shell Burning Charles Hakes Fort Lewis College 7 - fusion of H to He occurs in the core until the H is used up. 8 - the He core begins to shrink (and heat!), while the Hburning region moves out into a shell 72 Figure 12.4 Red Giant on the H–R Diagram 9 - the He core continues to shrink (just a few times bigger than Earth) and heat (to 108 K) Heat pressure demo Charles Hakes Fort Lewis College 73 Figure 12.1 Hydrostatic Equilibrium Charles Hakes Fort Lewis College 74 Figure 12.5 Horizontal Branch Charles Hakes Fort Lewis College 9 - the Helium flash is when the He in the core begins to fuse into carbon. This happens when the core is ~108K. Core expands and cools. New equilibrium on the “horizontal branch.” 10 - New equilibrium on the “horizontal branch.” 75 Figure 11.27b Globular Cluster Charles Hakes Fort Lewis College 76 Note the “horizontal branch” Question What happens when the He in the core is used up? Charles Hakes Fort Lewis College 77 Figure 12.6 Helium Shell Burning In the He shell burning stage, the star expands just like in the H shell burning stage Charles Hakes Fort Lewis College 78 Figure 12.7 Reascending the Giant Branch 11 - Helium shell burning begins. Core shrinks and heats. Exterior expands and cools. Charles Hakes Fort Lewis College 79 Figure 12.10 White Dwarf on H–R Diagram 12 - For 1 solar mass stars, that is all that will fuse. (need 600 million K for the next reactions to occur.) The outer shell gets “blown off” by the hot, dense, core. Result is a planetary nebula around a white dwarf (13). Charles Hakes Fort Lewis College 80 Figure 12.9 Planetary Nebulae Charles Hakes Fort Lewis College 81 White Dwarf stage Just the core of the star remains Very small - about the size of Earth Very dense - about half as massive as the sun. Will eventually fade and become a black dwarf (stage 14). Charles Hakes Fort Lewis College 82 Figure 12.8 G-Type Star Evolution Charles Hakes Fort Lewis College 83 Three Minute Paper • Write 1-3 sentences. • What was the most important thing you learned today? • What questions do you still have about today’s topics? Charles Hakes Fort Lewis College 84 Earth Hour • Saturday, March 27, 2010. • 8:30 P.M. • Turn off lights - save energy. • http://www.myearthhour.org/ Charles Hakes Fort Lewis College 85 How many Stars Can You See? • But who uses naked eye observing any more? • High quantum efficiency CCD cameras greatly extend the depth of a telescope. • Image stacking lets you go even deeper. • Depth scales linearly until star brightness is about the same as the background sky brightness. • A dark sky on Earth is about magnitude 21/arcsec2. • For film, this would be about as deep as you could go. • 16” SCT should reach magnitude 21.5 with a 5 minute exposure using SBIG full frame CCDs • For deeper images, the signal only scales as the ~sqrt(time) Charles Hakes Fort Lewis College 86