2000ApJ...541..959B

A new technique has been developed to remove the ionosphere's distorting effects from low-frequency VLBI data. By fitting dispersive and nondispersive components to the phases of multifrequency data, the ionosphere can be effectively removed from the data without the use of a priori calibration information. This technique, along with the new gating capability of the VLBA correlator, was used to perform accurate astrometry on pulsar B0950+08, resulting in a much improved measurement of this pulsar's proper motion (µ_α=-1.6±0.4 mas.yr^–1, µ_δ=29.5±0.5 mas.yr^–1) and parallax (π=3.6±0.3 mas). This puts the pulsar at a distance of 280±25 pc, about twice as far as previous estimates, but in good agreement with models of the electron density in the Local Bubble.