Precise Doppler measurements during 4.4 yr from the Keck/HIRES spectrometer
reveal two superimposed Keplerian velocity variations for HD 168443 (G6 IV
). A simultaneous orbital Dt to both companions yields companion masses of
M sin i = 7.7 and 17.2 M-JUP, orbital periods of P = 58 days and 4.8 yr, se
mimajor axes of a = 0.29 and 2.9 AU, and eccentricities of e = 0.53 and 0.2
0. An upper limit to the mass of the outer companion of 42 M-JUP is derived
from the lack of astrometric wobble. The outer companion was not detected
with Keck adaptive optics in the near-IR. Dynamical simulations show that t
he system is remarkably stable for all possible masses of both companions.
The two orbiting companions have masses that are probably near and slightly
above the upper end of the observed mass distribution of "planets" at 10 M
-JUP. Formation in a protoplanetary disk seems plausible. But these objects
present a puzzle about their formation and dynamical history, as well as a
bout their possible kinship with planetary systems and triple-star systems.