A Second Planet Orbiting 47 Ursae Majoris

Abstract

Precise Doppler velocity measurements during 13 yr at Lick Observatory reveal the presence of two planets orbiting the star 47 UMa. The previously detected inner planet is confirmed by the newer velocities that yield a revised orbital period P_b=1089.0+/-2.9 days, Msini=2.54 M_J, and eccentricity e_b=0.061+/-0.014. The residuals to that single-Keplerian fit exhibit a periodicity that is consistent with an additional planetary companion. A simultaneous fit for both planets implies that the outer planet has P_c=2594+/-90 days, a=3.73 AU, 0<e_c<0.2, and Msini=0.76 M_J. Its semimajor axis is the largest yet found for an extrasolar planet, and its angular separation from the host star of 0.26" makes it a good target for direct detection and astrometry. Hipparcos astrometry places limits on the masses of these planets at less than ~10 M_J, and dynamical modeling places limits on both e_c and the orbital inclinations. The outer planet induces a velocity semiamplitude of K=11.1 m s^-1 in the star during its 7 yr orbit, similar to the signal induced on the sun by Jupiter. Based on observations obtained at Lick Observatory, which is operated by the University of California.