Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Charles Hakes Fort Lewis College 1 Charles Hakes Fort Lewis College 2 Outline • • • • Remove extra folder debris Magnitudes and Distance H-R diagrams Stellar Evolution Charles Hakes Fort Lewis College 3 Magnitudes • Apparent Magnitude • how bright it looks • depends on distance • brightness depends on distance2 • Absolute Magnitude • Only depends on Luminosity (how much energy is being produced) • Does not change with distance • At 10pc, Apparent magnitude= Absolute magnitude Charles Hakes Fort Lewis College 4 Chapter 10 Star Temperatures (Colors) Charles Hakes Fort Lewis College 5 Figure 10.7 Star Colors – Orion (20°) and the Milky Way Center (2’) Charles Hakes Fort Lewis College 6 Which star would be the hottest? A) A B) B C) G D) M E) O Charles Hakes Fort Lewis College 7 Which star would be the hottest? A) A B) B C) G D) M E) O Charles Hakes Fort Lewis College 8 Star Spectral Classification • New order is: O, B, A, F, G, K ,M. • Remember the order... • Oh, Be A Fine Girl/(Guy) Kiss Me Charles Hakes Fort Lewis College 9 Chapter 10 HR Diagrams Charles Hakes Fort Lewis College 10 On the H-R diagram, red supergiants like Betelguese lie: A) top right B) top left C) about the middle D) lower left E) on the coolest portion of the main sequence Charles Hakes Fort Lewis College 11 On the H-R diagram, red supergiants like Betelguese lie: A) top right B) top left C) about the middle D) lower left E) on the coolest portion of the main sequence Charles Hakes Fort Lewis College 12 Figure 10.12 H–R Diagram of Well-Known Stars • Plot the luminosity vs. temperature. • This is called a HertzsprungRussell (H-R) diagram • Need to plot more stars! Charles Hakes Fort Lewis College 13 Figure 10.15 Hipparcos H–R Diagram Charles Hakes Fort Lewis College • Plot many stars and notice that 90% fall on the “main sequence”. • Add radius lines, and now have • luminosity • temperature • radius 14 Figure 10.14 H–R Diagram of 100 Brightest Stars • Most very bright stars are also distant Charles Hakes Fort Lewis College 15 Figure 10.13 H–R Diagram of Nearby Stars • Most close stars are very dim • Best estimate now is that 80% of stars are red dwarfs Charles Hakes Fort Lewis College 16 Chapter 10 Star Sizes Charles Hakes Fort Lewis College 17 Star Sizes • The luminosity of a star depends on the stars diameter as well as its temperature. • When radius is combined with Stefan’s Law: luminosity radius2 x T4 ( means proportional to) Charles Hakes Fort Lewis College 18 Star Sizes • The luminosity of a star depends on the stars diameter as well as its temperature. • When surface area is combined with Stefan’s Law: luminosity = 4r2 T4 (= means equal) Charles Hakes Fort Lewis College 19 Star Sizes • Can directly measure the radius on very few stars. (~dozen) • Can calculate the radius if you know the luminosity and the temperature. Charles Hakes Fort Lewis College 20 Figure 10.11 Stellar Sizes • Giants - radius between 10x and 100x solar • Supergiants larger (up to 1000x) • Dwarf - radius comparable to or smaller than the sun. Charles Hakes Fort Lewis College 21 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 22 Review • What fraction of the stars on an H-R diagram are on the main sequence. • Enter numbers 1-9 for 10%-90% Charles Hakes Fort Lewis College 23 Discussion • What fraction of the stars on an H-R diagram are on the main sequence. • Enter numbers 1-9 for 10%-90% Charles Hakes Fort Lewis College 24 Distance Scale • If you know brightness and distance, you can determine luminosity. • Turn the problem around… Charles Hakes Fort Lewis College 25 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 26 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 27 Figure 10.16 Stellar Distances Charles Hakes Fort Lewis College 28 Stellar Evolution Charles Hakes Fort Lewis College 29 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 30 Figure 11.17 Cloud Fragmentation Charles Hakes Fort Lewis College 31 Figure 11.20 Interstellar Cloud Evolution Charles Hakes Fort Lewis College 32 http://discovermagazine.com/2009/interact ive/star-formation-game/ Charles Hakes Fort Lewis College 33 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 34 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 35 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 36 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 37 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 38 Figure 11.19 Protostar on the H–R Diagram Charles Hakes Fort Lewis College 39 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 40 Figure 11.18 Orion Nebula, Up Close Charles Hakes Fort Lewis College 41 Figure 11.23 Protostars Charles Hakes Fort Lewis College 42 Figure 11.21 Newborn Star on the H–R Diagram Charles Hakes Fort Lewis College 43 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 44 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 45 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 46 Figure 10.21 Stellar Masses Charles Hakes Fort Lewis College 47 Figure 11.24 Prestellar Evolutionary Tracks Charles Hakes Fort Lewis College 48 Figure 11.25 Brown Dwarfs Charles Hakes Fort Lewis College 49 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 50