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Exoplanets Worlds Without End Copyright Lynette Cook, used with permission 8 Goals • Are there planets around other stars? • How do we know? • Are they systems like ours? Copyright Lynette Cook, used with permission 8 Are there other Earths? Copyright – Tyler Nordgren 8 How do we Know? • Two methods: 1. Radial Velocity. 2. Transit Copyright Lynette Cook, used with permission 8 1. Thermal Emission and Spectral lines • A star like our Sun has absorption lines. HOT You COOL 8 Emission Lines • Every element has a DIFFERENT finger print. 8 Doppler Shift • The greater the velocity the greater the shift. 8 Concept Test • I spin an object emitting a constant tone over my head. What do you hear? a. A constant tone. b. A tone that goes back and forth between high and low frequency. c. A constant tone of lower intensity. d. Two constant tones, one of higher frequency and one of lower frequency. e. One tone going smoothly from low to high intensity. 8 Concept Test • I spin an object emitting a constant tone over my head. What do I hear? a. A constant tone. b. A tone that goes back and forth between high and low frequency. c. A constant tone of lower intensity. d. Two constant tones, one of higher frequency and one of lower frequency. e. One tone going from smoothly from low to high intensity. 8 So Now… • From the presence and position of Spectral Lines we can know: – Composition (H, He, H2O, etc.) – Movement through space (towards or away) – How fast? c V 8 2. Reflex Motion • The Moon doesn’t orbit the Earth. • The Earth doesn’t orbit the Sun. • What do they do? • They each orbit their combined center of mass. X 8 The “Wobble” 8 3. Doppler Shifts • Movement towards or away yields Doppler shifts. X http://www.howstuffworks.com/planet-hunting2.htm You 8 4. Doppler Velocity • From Doppler shifts we get a velocity and period. 8 5. Kepler • Kepler’s Second Law: • Kepler’s Third Law: a( AU ) P( yrs ) M* 3 2 8 Copyright Lynette Cook, used with permission Result: 51 Pegasi a = 0.052 AU Mayor and Queloz 8 8 Concept Test • We know of planets around other stars because: a. We have seen the changing velocity of a star caused by the pull of a small unseen planet. b. We have seen the motion of the planet caused by the wobble of the star. c. We have seen the changing position of the star caused by the pull of the small unseen planet. d. We have seen the changing velocity of the planet caused by the motion of the star. e. We have seen the planet reflecting the star’s light. 8 Worlds without End? • Known Planets: – In our Solar System: 8 – Outside our Solar System: 680 • Known Planetary Systems: – Prior Sept. 1995: 1 (ours) Copyright Lynette Cook, used with permission – As of Feb 2012: 92 8 Concept Question What is the biggest surprise about extrasolar planetary systems? a. Most of the systems only have one planet. b. Many systems have several planets larger than Jupiter. c. Many systems have very large planets orbiting close to the star. d. Most of the planets do not fit into the categories of terrestrial or jovian planets. 8 Upsilon Andromedae Copyright Lynette Cook, used with permission 8 But Are They Real? Copyright Lynette Cook, used with permission 8 Planet Shadows 8 HD 209458 Based on Doppler curve, knew when planet might pass in front of its star. Greg Henry (Tennessee State Univ.) 8 Concept Question From the Radial Velocity Method we learn a planet’s mass. If we see that planet transit then we can also learn its: a. b. c. d. e. Size Density Composition All of the above None of the above 8 Kepler Mission 8 Kepler Systems 8 8 Smallest Kepler planets 8 8 Copyright Lynette Cook, used with permission 8 Hubble Space Telescope Savage et al. 2001 8 Homework for Friday • Find a favorite exoplanet (or exoplanetary system). Go to one of the following: http://exoplanet.eu/catalog.php http://exoplanetarchive.ipac.caltech.edu/index.html http://kepler.nasa.gov/ • Search the catalog and find your favorite. • Write down the following and bring to class: 1. Name of the Star 2. Mass or Radius of the planet (number of planets and their masses/radii if it is a system) 3. Period of the planet (periods of the planets) 4. Orbital radius of the planet (radii of their orbits) 5. Why you picked it. 8