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Extra-solar planets (Exoplanets) Ian Short Department of Astronomy and Physics Institute for Computational Astrophysics Saint Mary’s University Another star system?? • Nearest star 40 trillion km away • Neptune is 4.5 billion km from Sun • Planet brightness < 1/1,000,000 Star brightness • Glare of host star Host star “wobble” Planet and star both orbit centre of mass Planet and star both orbit centre of mass Doppler effect to see “wobble” Radial velocity (RV) variation Doppler effect • Orientation at least somewhat edge-on • Radial velocity (RV) change < 1 part in 1/10,000,000 • About 350 planets • Can get orbital size, shape, velocity • Lower limit to planet mass Transiting exoplanet Exoplanet transit • Edge-on orientation • Brightness change < 1 in 100 • Measure light curve • About 50 systems • Get planet radius and mass Exoplanet properties The known population (so far…) • 358 found • Almost all found since 1995 • 10% solar-type stars have planets • Most are gas giants (Jovian) (bias?) • Most have orbits smaller than Earth’s (bias?) Most are Jovian planets Gas-giants - Jupiter like May be a bias effect http://exoplanets.org Extra slides: (Not shown during presenatation) Multi-planet systems 20 known 55 Cancri: 5 planets! Multi-planet systems Future: More detections with spacebased instruments • COROT: launched Dec 2006 • MOST: launched 2003 (Canada!) Stellar spectroscopy Doppler effect to measure motion of remote object Doppler shift technique to detect stellar “wobble” Orbital plane orientation • Face-on • Edge-on Orbital plane orientation Intermediate (oblique) orientation Various types of data from extrasolar planetary system: Spectrum, light curve if transiting Adaptive optics Laser guide star and Deformable mirror Direct imaging Eg. Fomalhaut (α Piscis Austrinis) Fomalhaut’s planet (Distance = 25 Light Years) • Adaptive optics • Coronograph • Infrared (IR) band • “Roll subtraction” Fomalhaut’s planet Artist’s conception Direct imaging of extrasolar planets Habitable planets?