Interstellar scintillation of pulsar B0809+74

Weak interstellar scintillations of pulsar B0809+74 were observed at two ep ochs using a 30 m EISCAT antenna at 933 MHz. These have been used to constr ain the spectrum, the distribution, and the transverse velocity of the scat tering plasma with respect to the LSR. The Kolmogorov power law is a satisf actory model for the electron density spectrum at scales between 2 x 10(7) and 10(9) m. We compare the observations with model calculations from weak scintillation theory and the known transverse velocities of the pulsar and the Earth. The simplest model is that the scattering is uniformly distribut ed along the 310 pc line of sight (l = 140 degrees, b = 32 degrees) and is stationary in the LSR. With the scattering measure as the only free paramet er, this model fits the data within the errors, and a range of about +/- 10 km s(-1) in velocity is also allowed. The integrated level of turbulence i s low, being comparable to that found toward PSR B0950+08, and suggests a r egion of low local turbulence over as much as 90 degrees in longitude, incl uding the Galactic anticenter. If, on the other hand, the scattering occurs in a compact region, the observed timescales require a specific velocity-d istance relation. In particular, enhanced scattering in a shell at the edge of the local bubble, proposed by Bhat et al. in 1998, near 72 pc toward th e pulsar, must be moving at about similar to 17 km s(-1); however, the low scattering measure argues against a shell of enhanced scattering in this di rection. The analysis also excludes scattering in the termination shock of the solar wind or in a nebula associated with the pulsar.