Photoelectric radial velocities. Paper IX. The orbits of the spectroscopic binaries 81 and chi Gem.

81 and χ Gem are fifth-magnitude late-type giant stars which have been known for more than half a century to be variable in radial velocity. Systematic Cambridge observations covering well over a decade now permit reliable orbits to be determined for both stars. The periods are approximately 4.2 and 6.7 yr respectively. The high γ velocity, +83 km s^-1, of 81 Gem is noteworthy, but does not seem to be accompanied by any spectroscopic abnormality. It is likely that χ Gem is a triple system, as there appears to have been a small but significant change in its -velocity since the 1920s.