Radial velocities of HD 166181

Our improved orbit for the G6 V primary has a period of 1.8098343days and is circular. Although the lines of additional components have not been detected, radial velocity measurements confirm that the system has additional velocity variations with a period of 2092days, or 5.73yr.

This long-period orbit has an eccentricity of 0.76. An analysis of the Hipparcos observations produces a well-determined astrometric orbit for the long-period system that has an inclination of 78{deg}. Mass estimates of the components in this zero-age main-sequence multiple system indicate that the unseen secondary in the 5.73yr orbit may also be a binary.