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Planet in a Close-In Orbit around a Subgiant Star

8 Jun 2016, 22:00 UTC
Planet in a Close-In Orbit around a Subgiant Star
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Figure 1: Artist’s impression of a transiting planet.K2-39b is a transiting giant planet in a close-in orbit around a subgiant star with ~3.88 times the radius and ~1.53 times the mass of the Sun. Transit and radial velocity observations indcate that K2-39b has ~50.3 times the mass and 8.3 ± 1.1 times the radius of Earth. This gives K2-39b a mean density that is only half the density of water. The orbital period of K2-39b around its host star is only 4.6 days.Currently, K2-39b is the shortest-period planet known orbiting a subgiant star. However, only a handful of evolved stars (i.e. stars larger than 3.5 times the Sun's radius) are known to host short-period (i.e. planets with orbital periods less than 100 days) transiting planets. The existence of a planet like K2-39b that is orbiting so close to its host star suggests that tidal destruction may not be that effective in removing planets in close-in orbits around subgiant stars.Figure 2: Transit light curve indicating the presence of K2-39b. Van Eylen et al. (2016)Figure 3: Radial velocity curve indicating the presence of K2-39b. Van Eylen et al. (2016)Figure 4: K2-39b compared with other confirmed planets - transiting planets (open circles) and ...

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