New OH/IR stars from color-selected IRAS sources. 3: A complete survey

Abstract

We present the results of 1612 MHz observations conducted at the Arecibo Observatory of 571 color-selected sources from the IRAS Point Source Catalog. Of these sources we detect 132, 113 for the first time. This is the third part of an Arecibo survey of color-selected IRAS sources. The earlier two parts together detected a total of 268 sources of 1612 MHz emission. An analysis of the properties of the OH/IR stars detected in all three parts of the survey is included. In particular we compute the limiting 1612 MHz peak flux of the entire survey to be approximately ˜40 mJy. The correlation between the IRAS infrared fluxes and the 1612 MHz 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 1612 MHz 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) micrometer 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=5600 L solar luminosity, and the 1612 MHz luminosity function shows a corresponding falloff above L₁₆₁₂=1.8 × 10⁻⁸ solar luminosity. We also find direct confirmation of the expectation that sources with large expansion velocity are more luminous than sources with small expansion velocity.