We report the discovery of a low-mass planet orbiting Gl 15 A based on radial velocities from the Eta-Earth Survey using HIRES at Keck Observatory .
Gl 15 Ab is a planet with minimum mass M \sin i = 5.35 \pm 0.75 M _ { \earth } , orbital period P = 11.4433 \pm 0.0016 d , and an orbit that is consistent with circular .
We characterize the host star using a variety of techniques .
Photometric observations at Fairborn Observatory show no evidence for rotational modulation of spots at the orbital period to a limit of \sim 0.1 mmag , thus supporting the existence of the planet .
We detect a second RV signal with a period of 44 days that we attribute to rotational modulation of stellar surface features , as confirmed by optical photometry and the Ca ii H & K activity indicator .
Using infrared spectroscopy from Palomar-TripleSpec , we measure an M2 V spectral type and a sub-solar metallicity ( [ \mbox { M } / \mbox { H } ] = -0.22 , [ \mbox { Fe } / \mbox { H } ] = -0.32 ) .
We measure a stellar radius of \mathrm { 0.3863 } \pm \mathrm { 0.0021 } R _ { \sun } based on interferometry from CHARA .