Planets Around Other Stars Part 2
Planets Around Other Stars Part 2 AY 101
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This 2 page Class Notes was uploaded by Alyssa Hendrixson on Friday February 6, 2015. The Class Notes belongs to AY 101 at University of Alabama - Tuscaloosa taught by Dean Martin Townsley in Winter2015. Since its upload, it has received 72 views. For similar materials see Introduction to Astronomy in Physics 2 at University of Alabama - Tuscaloosa.
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Date Created: 02/06/15
AY 101 Lecture Notes Wednesday February 4 2015 Planets around other Stars Pt 2 0 Doppler shift 0 Wavelength of lines changed shifted by motion of emitter or absorber This allows us to measure motion of objects using spectra 0 Object moving toward observer Shifted to shorter wavelength blue 0 Object moving away from observer Shifted to longer wavelength red 0 Allows us to measure motion of objects using light 0 quotObjectquot is vague because it may be something quotemittingquot or quotabsorbing quot light as a known wavelength 0 We are interested in absorption line from cool surface layers of a star as the star moves Observing Doppler shift 0 Often shown as it would appear through a slit and prism Lines indicate intensity with wavelength increasing to the right 0 Lines are shifted by motion of emitting object with respect to the rest laboratoyO wavelengths Both absorption and emission lines can shift Larger speed implies a larger shift 0 Only motion toward or away from observer matters 0 Searching for planets 0 Most planets discovered before 1022 have been discovered from Doppler shift 0 Also used to measure planet mass Spectral lines in the star39s light are periodically shifted by its motion in response to the orbit of the planet 0 Limitation Can39t nd small planets Velocity shift is too small Can39t nd an earthlike planet but can see if there are planetary systems different from ours o What we have discovered Many planetary systems are vaguely like ours with rocky planets but a fair number have close giant planets Planets discovered from star39s Doppler shift 0 First method used to nd planets o Tends to only nd large highmass planets Solar system 0 Giant planets only in outer solar system 0 Extra mass of ices was required for them to capture gas Other stars 0 Some giant planets close to star Solar system AY 101 Lecture Notes 0 All orbits nearly circular due being formed in gas disk Other stars 0 A number of quite noncircular orbits Surprises from the rst other planetary systems 0 Masses near that ofJupiter o A wide variety of orbits 0 Some short orbits some very elliptical o Surpnse Jupitermass planets in orbits as close to the sub as Mercury 0 Limitation of this technique Could not nd small planets They are there but Doppler shift is too small 0 How do we understand these surprises 0 Planet migration Can move planets closer to star Due to interaction with the protoplanetary disk For our solar system disk was shortlived o Planetplanetinteractions Can change planets to elliptical orbits Due to interaction scattering of similar size planets Not in our solar system perhaps due to lack of migration 0 But systems like our solar system are likely more common 0 Detection of planetary transits 0 Monitor the brightness of many stars Planets that pass in front of star will change star39s brightness Only systems with particular orbital orientation will be detected Good for detecting close planets down to small masses Good for understanding general trends of planet systems Not so good for detecting nearby planetary systems OOOOO