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Lecture 33

PHYS 183 Lecture 33: PHYS 183 - Lecture 33

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PHYS 183
Gilbert Holder

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Lecture 33 April 10, 2017 Why now? - Has been known for centuries that distant stars were suns - Obvious in hindsight that planets should be common - Why extrasolar planets = exoplanets only now? - Technologically very hard to detect - Direct detection: see planet directly via imaging o Only small handful found this way thus far - Indirect detection: observe starlight affected by planet but no the planet itself 3 techniques for detecting extrasolar planets - Direct detection - Transits - Stellar doppler wobble Direct detection of exoplanets - Stars are typically 1-10 billion times brighter than the planet o E.g. Jupiter reflects only 0.3 billionths of the Suns light o Looking for a firefly next to a search light - i.e. contrast ratios of 10 -10 at separations of 0.01-1 - contrast ratios better at infrared wavelengths but still challenging - Atmospheric blurring distorts images so impossible to see such small separations Adaptive optics - Telescope uses laser guide star to determine effect of atmospheric turbulence in real time - Corrects stellar images using guide star corrections - Demands fast local computing - Provides near diffraction-limited imaging from the ground o Can have more sensitivity as ground based telescope larger than space based Direct detection of exoplanets - Adaptive optics solve the atmospheric blurring problem o Allows near diffraction-limited imaging superb angular resolution - Doesnt solve contrast ratio problem - Solution: a coronograph o Device that blocks light from the star o Artificial eclipse - Block bright star light so faint planet becomes visible - Detection biases o Will find planets far from the star o Will find large planets that reflect a lot of light lower contrast ratio Transit detections of exoplanets
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