Charles Hakes Fort Lewis College1

Charles Hakes Fort Lewis College2

Charles Hakes Fort Lewis College3 Outline Remove extra folder debris Magnitudes and Distance H-R diagrams Stellar Evolution

Charles Hakes Fort Lewis College4 Magnitudes Apparent Magnitude how bright it looks depends on distance brightness depends on distance 2 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 College5 Chapter 10 Star Temperatures (Colors)

Charles Hakes Fort Lewis College6 Figure 10.7 Star Colors – Orion (20°) and the Milky Way Center (2 ’ )

Charles Hakes Fort Lewis College7 Which star would be the hottest? A) A B) B C) G D) M E) O

Charles Hakes Fort Lewis College8 Which star would be the hottest? A) A B) B C) G D) M E) O

Charles Hakes Fort Lewis College9 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 College10 Chapter 10 HR Diagrams

Charles Hakes Fort Lewis College11 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 College12 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 College13 Figure H–R Diagram of Well-Known Stars Plot the luminosity vs. temperature. This is called a Hertzsprung- Russell (H-R) diagram Need to plot more stars!

Charles Hakes Fort Lewis College14 Figure Hipparcos H–R Diagram Plot many stars and notice that 90% fall on the “main sequence”. Add radius lines, and now have luminosity temperature radius

Charles Hakes Fort Lewis College15 Figure H–R Diagram of 100 Brightest Stars Most very bright stars are also distant

Charles Hakes Fort Lewis College16 Figure 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 College17 Chapter 10 Star Sizes

Charles Hakes Fort Lewis College18 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  radius 2 x T 4 (  means proportional to)

Charles Hakes Fort Lewis College19 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 = 4  r 2  T 4 (= means equal)

Charles Hakes Fort Lewis College20 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 College21 Figure 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 College22 Figure Hipparcos H–R Diagram Plot the luminosity vs. temperature. This is called a Hertzsprung- Russell (H-R) diagram

Charles Hakes Fort Lewis College23 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 College24 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 College25 Distance Scale If you know brightness and distance, you can determine luminosity. Turn the problem around…

Charles Hakes Fort Lewis College26 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 College27 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 College28 Figure Stellar Distances

Charles Hakes Fort Lewis College29 Stellar Evolution

Charles Hakes Fort Lewis College30 Figure Atomic Motions Low density clouds are too sparse for gravity. A perturbation could cause one region to start condensing.

Charles Hakes Fort Lewis College31 Figure Cloud Fragmentation

Charles Hakes Fort Lewis College32 Figure Interstellar Cloud Evolution

Charles Hakes Fort Lewis College33 l ive/star-formation-game/ ive/star-formation-game/

Charles Hakes Fort Lewis College34 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 College35 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 College36 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 College37 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 College38 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 College39 Figure Protostar on the H–R Diagram

Charles Hakes Fort Lewis College40 Figure Newborn Star on the H–R Diagram 5 - Gravity still dominates the radiation pressure, so the star continues to shrink.

Charles Hakes Fort Lewis College41 Figure Orion Nebula, Up Close

Charles Hakes Fort Lewis College42 Figure Protostars

Charles Hakes Fort Lewis College43 Figure Newborn Star on the H–R Diagram

Charles Hakes Fort Lewis College44 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 College45 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 College46 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 College47 Figure Stellar Masses

Charles Hakes Fort Lewis College48 Figure Prestellar Evolutionary Tracks

Charles Hakes Fort Lewis College49 Figure Brown Dwarfs

Charles Hakes Fort Lewis College50 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?