Doppler observations from Keck Observatory have revealed a triple planet system orbiting the nearby mid-type K dwarf, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with \msini\ = 11.6 \mearth (0.036 \mjup), an orbital period of 8.135 ± 0.004 d, 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 \msini\ = 0.4 \mjup\ with an orbital period of 32.0 ±0.02 d in a nearly circular orbit, and e=0.05±0.03. The third planet has \msini\ = 0.53 \mjup\ with an orbital period of 432 ±8 d (1.18 years) and an eccentricity e=0.23±0.03. This discovery adds to the number of super Earth mass planets with \msini<12\mearth that have been detected with Doppler surveys. We find that 56 ±18% 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.
@article{arxiv.1109.2926,
title = {M2K: II. A Triple-Planet System Orbiting HIP 57274},
author = {Debra A. Fischer and Eric Gaidos and Andrew Howard and Matthew Giguere and John A. Johnson and Geoffrey W. Marcy and Jason T. Wright and Kelsey I. Clubb and Howard Isaacson and Kevin Apps and Sebastien Lepine and Andrew Mann and John Moriarty and John Brewer and Julien Spronck and Christian Schwab and Andrew Szymkowiak},
journal= {arXiv preprint arXiv:1109.2926},
year = {2015}
}