We present the discovery of three modestly-irradiated , roughly Neptune-mass planets orbiting three nearby Solar-type stars .
HD 42618 b has a minimum mass of 15.4 \pm 2.4 M _ { \earth } , a semi-major axis of 0.55 AU , an equilibrium temperature of 337 K , and is the first planet discovered to orbit the solar analogue host star , HD 42618 .
We also discover new planets orbiting the known exoplanet host stars HD 164922 and HD 143761 ( \rho CrB ) .
The new planet orbiting HD 164922 has a minimum mass of 12.9 \pm 1.6 M _ { \earth } and orbits interior to the previously known Jovian mass planet orbiting at 2.1 AU .
HD 164922 c has a semi-major axis of 0.34 AU and an equilibrium temperature of 418 K. HD 143761 c orbits with a semi-major axis of 0.44 AU , has a minimum mass of 25 \pm 2 M _ { \earth } , and is the warmest of the three new planets with an equilibrium temperature of 445 K. It orbits exterior to the previously known warm Jupiter in the system .
A transit search using space-based CoRoT data and ground-based photometry from the Automated Photometric Telescopes ( APTs ) at Fairborn Observatory failed to detect any transits , but the precise , high-cadence APT photometry helped to disentangle planetary-reflex motion from stellar activity .
These planets were discovered as part of an ongoing radial velocity survey of bright , nearby , chromospherically-inactive stars using the Automated Planet Finder ( APF ) telescope at Lick Observatory .
The high-cadence APF data combined with nearly two decades of radial velocity data from Keck Observatory and gives unprecedented sensitivity to both short-period low-mass , and long-period intermediate-mass planets .