2012ApJ...745...21F

Doppler observations from Keck Observatory have revealed a triple-planet system orbiting the nearby K4V star, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with Msin i = 11.6 M_⊕(0.036 M_Jup), an orbital period of 8.135±0.004 days, and slightly eccentric orbit e = 0.19±0.1. We calculate a transit probability of 6.5% for the inner planet. The second planet has Msin i = 0.4 M_Jup with an orbital period of 32.0±0.02 days in a nearly circular orbit (e = 0.05±0.03). The third planet has Msin i eccentricity e = 0.23±0.03. This discovery adds to the number of super-Earth mass planets with M sin i < 12 M_⊕ that have been detected with Doppler surveys. We find that 56%±18% of super-Earths are members of multi-planet systems. This is certainly a lower limit because of observational detectability limits, yet significantly higher than the fraction of Jupiter mass exoplanets, 20%±8%, that are members of Doppler-detected, multi-planet systems.