IRAS PSC new OH/IR stars. III.

The correlation between the IRAS infrared fluxes and the 1612MHz flux of the 132 sources detected in part III of the survey is smaller than that found in the earlier parts of the survey. This is to be expected from the intrinsic variability of OH/IR stars and the longer time gap between the 1612MHz observations and the IRAS measurements. We identify a subset of 54 stars as being near the tangent point of the galactic rotation curve.

Using the kinematical distances to these stars we find that the efficiency of momentum transfer varies exponentially with the (25-12){mu}m color, consistent with the stellar outflow being driven by radiation pressure. Further the IR pump efficiency increases with increasing optical depth of the circumstellar shell, as expected for radiative pumping. The bolometric luminosity function is found to decrease sharply above L_Bol_=5600L_{sun}_, and the 1612MHz luminosity function shows a corresponding falloff above L_1612_=1.8x10^-8^L_{sun}_.

We also find direct confirmation of the expectation that sources with large expansion velocity are more luminous than sources with small expansion velocity.