AST 251 Lecture 11

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Astronomy & Astrophysics
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AST251 Lecture 11Higher mass stars have a higher temperature and luminosity but a shorter lifetimePlanets around binary stars o A 3body system stable only if two bodies close to each other the third body much farther awayA planet may orbit a close binary system or one of the components of a wide binary systemOrbits of comparable size are unstable and the planet will be ejected Extrasolar planetsFinding an extrasolar planet will be difficult o Distances Distance to next star 44 ly280 000 AU2000x farther than any manmade craft has goneGalaxies hold a lot of stars but theres even more empty space between When galaxies collide on average no two stars crash into each other because there is so much empty space between stars o Size and MassRadius of planet 11011000 of radius of starLight from planet will be a tiny fraction of starlightMass of planet 11001100 000 of mass of starPlanets effect on motion of star tinyHistory of extrasolar planets o 1992 very first planetary system was discoveredthree planets in close orbits SunMercury distance around neutron starexception o 1995 the first planet orbiting a solartype star discovered by Swiss astronomerso By now many 100s of confirmed planet detections and more in the coming yearsPlanet detection o Directdirect imagingTake a picture of the planet exceedingly difficultfaint planet very close to bright starWorks for very large planets far from starEffective for very young and hot planets4 planetseach several Jupitermasses closest 145 AU o Indirectmeasure central stars propertiesastrometryDoppler technique transit techniqueDetect motion of central starSun moves around the common centre of gravity with all planetsextremely small displacementsmain effects12yr orbit of Jupiter and 29yr orbit of SaturnOrientation relative to Earth
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