We present 248 precise Doppler measurements of Barnard ’ s Star ( Gl 699 ) , the second nearest star system to Earth , obtained from Lick and Keck Observatories during 25 years between 1987 and 2012 .
The early precision was 20 m s ^ { -1 } but was 2 m s ^ { -1 } during the last 8 years , constituting the most extensive and sensitive search for Doppler signatures of planets around this stellar neighbor .
We carefully analyze the 136 Keck radial velocities spanning 8 years by first applying a periodogram analysis to search for nearly circular orbits .
We find no significant periodic Doppler signals with amplitudes above \sim 2 m s ^ { -1 } , setting firm upper limits on the minimum mass ( M \sin i ) of any planets with orbital periods from 0.1 to 1000 days .
Using a Monte Carlo analysis for circular orbits , we determine that planetary companions to Barnard ’ s Star with masses above 2 M _ { \oplus } and periods below 10 days would have been detected .
Planets with periods up to 2 years and masses above 10 M _ { \oplus } ( 0.0 3 M _ { Jup } ) are also ruled out .
A similar analysis allowing for eccentric orbits yields comparable mass limits .
The habitable zone of Barnard ’ s Star appears to be devoid of roughly Earth-mass planets or larger , save for face-on orbits .
Previous claims of planets around the star by van de Kamp are strongly refuted .
The radial velocity of Barnard ’ s Star increases with time at 4.515 \pm 0.002 m s ^ { -1 } yr ^ { -1 } , consistent with the predicted geometrical effect , secular acceleration , that exchanges transverse for radial components of velocity .