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It is possible to measure the pattern speed Omega(p) of a barred disk galaxy without employing any particular dynamical model. The main assumption required is that the luminosity density of the tracer obey a continuity equation. In its simplest form, the method requires measuring the surface brightness and radial velocity along a strip parallel to the line of nodes. If position and velocity are measured relative to the galactic center, then the luminosity-weighted mean velocity in the strip, divided by the component of the luminosity-weighted mean position vector which is parallel to the line of nodes, is equal to Omega(p) sin i. The method has been tested on a numerical simulation of a barred disk constructed by Sellwood (1983). It is found that Omega(p) can be reliably measured to + or - 15 percent.
Tremaine et al. (Sun,) studied this question.