Precise radial velocity measurements of the star tau Boo (HR 5185, HD 120136) made by the AFOE (Advanced Fiber Optic Echelle Spectrometer) from July of 1995 to present. The radial velocity variation shows an essentially sinusoidal variation with period 3.3124 +/- 0.0004 d and amplitude 474.02 +/- 9.83 m/s. The rms value of the residuals from the fit is 28.0 m/s.
tau Boo, already suspected by Duquennoy and Mayor (1991, A & A, 248, 485) to be a spectroscopic binary, has been shown by Marcy and Butler to show a radial velocity variation with essentially the same period and amplitude as given above, consistent with the presence of a planet with semi-major axis of 0.046 AU and minimum mass 3.9 Jupiter masses; this variation has now also been detected in the data of Duquennoy and Mayor (as discussed by Marcy and Butler). Thus the AFOE data provide a second confirmation.
There is more on the AFOE's planet detection