Lecture21 - Discovery of extrasolar planets Discoveries...

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Discovery of extrasolar planets Discoveries regarding extrasolar planets were first published in 1989 ¾ variations in the radial velocities of HD 114762 and Alrai ( γ Cephei) were explained as being caused by possibly giant planets (11 M J J respectively). ¾ Subsequent work in 1992 however concluded that the data were not solid enough to declare the presence of a planet, although ten years later improved techniques allowed the planet to finally be confirmed. Extrasolar planets around solar-type stars began to be discovered in large numbers during the late 1990s as a result of improved telescope technology ¾ Such advances allowed for more accurate measurements of stellar motion ¾ The first definitive extrasolar planet around a main sequence star (51 Pegasi) was announced on October 6, 1995
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Detection Methods 1. Pulsar timing ¾ Pulsars are rapidly rotating neutron stars ¾ They beam radiation along a preferred axis, which is different from the rotation axis. This causes a pulse of radiation when the beam is aimed directly at Earth ¾ These pulses are normally extremely regular, and rival the best atomic clocks for precision ¾ Anomalies in the timing of these pulses can indicate the influence of a binary companion. 2. Astrometry ¾ the oldest method used in the search for extrasolar planets, used as early as 1943. ¾ Involves measuring the proper motion of a star in the search for an influence caused by its planets ¾ Changes in proper motion are so small that the best current equipment cannot produce reliable enough measurements.
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3. Radial Velocity ¾ The radial velocity can be measured from the Doppler shift of spectral lines: rest rest rest obs r c v λ = ¾ It is therefore possible to measure variations in the speed with which the star moves away from us or towards us in a binary orbit. ¾
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Lecture21 - Discovery of extrasolar planets Discoveries...

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