Based on the long-term radial-velocity surveys carried out with the McDonald Observatory 2.7m Harlan J. Smith Telescope from 1988 to the present , we derive upper limits to long-period giant planet companions for 31 nearby stars .
Data from three phases of the McDonald Observatory 2.7m planet-search program have been merged together and for 17 objects , data from the pioneering Canada-France-Hawaii Telescope ( CFHT ) radial-velocity program have also been included in the companion-limits determination .
For those 17 objects , the baseline of observations is in excess of 23 years , enabling the detection or exclusion of giant planets in orbits beyond 8 AU .
We also consider the possibility of eccentric orbits in our computations .
At an orbital separation of 5.2 AU , we can exclude on average planets of M sin i \stackrel { \raisebox { -0.86 pt } { $ \textstyle > $ } } { \sim } 2.0 \pm 1.1 M _ { Jup } ( e = 0 ) and M sin i \stackrel { \raisebox { -0.86 pt } { $ \textstyle > $ } } { \sim } 4.0 \pm 2.8 M _ { Jup } ( e = 0.6 ) for 25 of the 31 stars in this survey .
However , we are not yet able to rule out “ true Jupiters , ” i.e .
planets of M sin i \sim 1 M _ { Jup } in 5.2 AU orbits .
These limits are of interest for the Space Interferometry Mission ( SIM ) , Terrestrial Planet Finder ( TPF ) , and Darwin missions which will search for terrestrial planets orbiting nearby stars , many of which are included in this work .