12. Extrasolar Planets

12. Extrasolar Planets - Extrasolar Planets Outline Our...

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Unformatted text preview: Extrasolar Planets Outline Our goals for this section: To learn about the main methods used to find planets around other stars To survey the results of planet searches so far To discuss the reasons why other planetary systems do not seem to be like our own Until about fifteen years ago, no one could say for sure whether there were planets orbiting other stars Why cant we image planets around other stars? they are too small and dim to be imaged directly, in most cases they are often too close to their parent stars to be resolved the light from their parent stars outshines them, in most cases Recent advances in technology have enabled astronomers to infer the presence of planets around many other stars Planets orbiting other stars are referred to as extrasolar planets (meaning that they are outside our solar system) or sometimes exoplanets The Search for Planets Do these solar systems look like our own? What can they tell us about the formation of stars and planets? Detection Methods If we cant see them, how do we detect planets orbiting other stars? Many methods have been proposed for locating exoplanets, but only 5 or 6 have been successful All but one of the methods used so far involve studying the properties of the extrasolar planets parent star these are indirect detections Theres still a fair bit of controversy about many of the detections and methods, but the situation is improving rapidly To date, about 250 exoplanets detected in 200 star systems with this technique Very reliable method How does it work? Recall that planets and stars actually orbit their common centre of mass or barycentre As the star orbits the barycentre of the system, the component of its orbital velocity that lies along our line of sight increases and decreases periodically We can measure the Doppler shift of the light from the star to follow the changes in its line-of-sight velocity and hence to infer the existence of an unseen companion to the star Can determine the mass of the companion The mass of the companion tells us whether or not it is a planet The Radial Velocity Technique star star-planet center of mass unseen planet in orbit around the star (too dim to see) A star with an unseen planet orbits the common star-planet barycentre. The motions of the star along the line of sight are detectable via the Doppler shift of lines in its spectrum. barycentre We represent this information as a radial velocity curve The period and amplitude of the radial velocity curve give us information about the mass, eccentricity, and orbital semimajor axis of the unseen companion (planet) The radial velocity curve of the star 51 Pegasi (the 51st brightest star in the constellation Pegasus). http://astro.unl.edu/naap/esp/animations/radialVelocitySimulator.htmlhttp://astro....
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12. Extrasolar Planets - Extrasolar Planets Outline Our...

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