Monday, May 30, 2016

The Peculiar Orbit of a Hot-Jupiter

Močnik et al. (2016) present the discovery of WASP-157b, a hot-Jupiter in orbit around a G2V star. Transit and radial velocity observations indicate that WASP-157b has 1.045 ± 0.044 times the radius and 0.574 ± 0.093 times the mass of Jupiter. This gives WASP-157b a mean density of roughly half that of Jupiter's. WASP-157b takes only 3.95 days to orbit its host star and its estimated equilibrium temperature is 1339 ± 93 K.

Observations of the host star of WASP-157b show that it has a remarkably slow rotational speed of only ~1.0 km/s. This means that the host star of WASP-157b is either orientated pole-on or it is an exceptionally slow rotator. If the host star of WASP-157b is a slow rotator, then its rotation period is likely to be ~56 days. The average rotation period of stars similar to the host star of WASP-157b is 12.3 days, with a standard deviation of 7.2 days. If the host star is orientated pole-on, it means that WASP-157b has a highly inclined orbit that could even pass over the polar regions of its host star.

Močnik et al. (2016), "WASP-157b, a Transiting Hot Jupiter Observed with K2", arXiv:1603.05638 [astro-ph.EP]