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Circumbinary planetsYou've seen Star Wars, yes? If not, it may be helpful to visit this link and then return. Luke's home planet Tatooine is a circumbinary planet, meaning that it orbits around two stars and hence has a double sunset. We now know that such planets exist not just in science fiction but in nature too! The first 100% bonafide discovery was Kepler-16b, a Saturn-mass planet orbiting two stars that are ~65% and ~20% as big as our Sun. The Kepler space telescope has now made 11 such discoveries.
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Close binary formationStars are believed to form out of condensing clouds of gas and dust. Sometimes these clouds fragment into two, three or even more stars. This picture helps us understand the wide diversity of multi-star systems in the Galaxy. However, it is believed that two stars will not naturally form very close together. They alternatively are thought to initially form far apart and then migrate closer. I have been tackling this problem from the perspective of circumbinary planets, and how this new observable helps constrain our theories. I have also helped coordinate observational surveys of low mass binaries, obtaining observational markers of their formation history (eccentricities, orbital obliquities, rotation rates etc).
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Hot JupitersHot Jupiters are a peculiar type of planet that is a gas giant, so comparable in size and mass to Jupiter, yet orbiting in a close, "hot" orbit around its star. It may be so close that its orbital period is less than one Earth day! The first exoplanet found around a main sequence star, 51 Peg, was a hot Jupiter. Ever since then their existence and formation has puzzled astronomers. I have approached this problem as a comparison to close binary formation. By seeing the similarities and differences we may better understand both types of astrophysical system
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Planetary transitsMany surveys, e.g. Kepler from space and WASP from the ground monitor the brightness of thousands of stars. When a planet passes in front of its host star(s), known as a transit, the brightness drops and we obtain information about the planet. The separation of transits tells us the planet's period. The width and depth of the transit indicate the radius of the planet. If we also know the planet's mass, e.g. from radial velocity spectroscopy or transit timing variations, then we know the planet's bulk density and can start to probe its interior composition. Furthermore, when a planet transits its atmosphere (if it has one) will only block out part of the starlight. Based on the different wavelengths absorbed we can identify different elements and molecules within the atmosphere. In the future we may ultimately find biological markers indicative of life.
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