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L21GHW09_Extrasolar_Planets_Methods

L21GHW09_Extrasolar_Planets_Methods - Extrasolar planets...

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March 26/31, 2009 Extrasolar planets Extrasolar planets – detection methods See online Notes: •Star and Planet Formation • From Protostellar Disc to Planets
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March 26/31, 2009 Extrasolar planets Extrasolar Planets - Topics • Finding ESPs ¾ Detection methods ¾ Expectations ¾ Method biases ¾ Candidate Stars • Results ¾ What types of planets have been found? (terrestrial, jovian…) ¾ What kinds of orbits? (e, i, a) Relevance of Habitable zone • Implications, future… ¾ Relevance to planetary system formation models ¾ Relevance of habitable zone… ¾ Is our SS unique? Just unusual? Ordinary?
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March 26/31, 2009 Extrasolar planets Detection methods 1. Pulsar timing 2. Astrometric wobble 3. Radial velocities 4. Gravitational lensing 5. Transits 6. Dust disks 7. Direct detection All of these methods have been used, all are improving, and all have yielded results
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March 26/31, 2009 Extrasolar planets 1. Pulsar timing Pulsars are rapidly rotating neutron stars, with extremely regular periods Anomalies in these periods indicate the gravitational influence of a companion.
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March 26/31, 2009 Extrasolar planets Astrometric wobble observe cyclic change in motion of a star due to its motion around a common centre of mass with another body this change in position on the sky is called “proper motion” measured units: seconds of arc method requires that the planets' orbits around the star be nearly perpendicular to our line of sight, “in the plane of the sky” so planets detected by it could not be confirmed by methods like radial velocity.
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March 26/31, 2009 Extrasolar planets Astrometric wobble: limitations/constraints effect decreases with distance, so restricted to nearby stars changes in proper motion are so small that the best current equipment cannot produce reliable enough measurements an Jupiter orbit around a 1 M Sun star at 5AU would cause a wobble of 5 μ as (5x10 -6 seconds of arc) for a star at 1000pc even worse for an Earth at 1AU: 3 μ as wobble for star at 10pc requires angular resolutions unachievable from ground-based telescopes – space missions are planned
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March 26/31, 2009 Extrasolar planets Astrometric wobble: Barnard’s star Barnard’s star: second closest star to the Sun at a distance of <2pc – largest known proper motion M4V star – i.e. faint (~0.4L Sun ), low mass (0.4M Sun ) main sequence star Proper motion studies ~60yr ago showed a wobble consistent with an eccentric orbit – the first detected extrasolar planet?
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