The N2K planet search program was designed to exploit the planet-metallicity correlation by searching for gas giant planets orbiting metal-rich stars .
Here , we present the radial velocity measurements for 378 N2K target stars that were observed with the HIRES spectrograph at Keck Observatory between 2004 and 2017 .
With this data set , we announce the discovery of six new gas giant exoplanets : a double-planet system orbiting HD 148164 ( M \sin i of 1.23 and 5.16 M _ { JUP } ) and single planet detections around HD 55696 ( M \sin i = 3.87 M _ { JUP } ) , HD 98736 ( M \sin i = 2.33 M _ { JUP } ) , HD 203473 ( M \sin i = 7.8 M _ { JUP } ) , and HD 211810 ( M \sin i = 0.67 M _ { JUP } ) .
These gas giant companions have orbital semi-major axes between 1.0 and 6.2 AU and eccentricities ranging from 0.13 to 0.71 .
We also report evidence for three gravitationally bound companions with M \sin i between 20 to 30 M _ { JUP } , placing them in the mass range of brown dwarfs , around HD 148284 , HD 214823 , and HD 217850 , and four low mass stellar companions orbiting HD 3404 , HD 24505 , HD 98630 , and HD 103459 .
In addition , we present updated orbital parameters for 42 previously announced planets .
We also report a nondetection of the putative companion HD 73256 b .
Finally , we highlight the most promising candidates for direct imaging and astrometric detection , and find that many hot Jupiters from our sample could be detectable by state-of-the-art telescopes such as Gaia .