NEW OH/IR STARS FROM COLOR-SELECTED IRAS SOURCES .2. AN UNBIASED 1612 MHZ SURVEY

We present the second (of three) installments of the Arecibo 1612 MHz survey of color selected IRAS sources. We investigate 1294 sources in this paper, to detect 86, 79 of them new detections. Taken together with those of Eder et al., we have an unbiased survey of sources with -0.7 ≤ (25 - 12) μm ≤ 0.25 and 0° ≤ δ ≤ 37°. While the 1612 MHz detectability of sources is independent of bII, it does exhibit a strong decrease for (25 - 12) μm ≤ -0.5. Our detections all have 25 μm fluxes >2 Jy. The special feature of this work is its coverage of high |bII| sources, so the 1612 MHz characteristics of stars with small progenitor masses are determined. This presents surprises. It provides us with direct observational evidence that radiation pressure acting on dust grains influences mass loss from red giants. It also gives us a means for tracing the response of a circumstellar shell to progressive increases in photon-momentum deposition, consequent on increases in a shell's opacity. One by-product of these results is a repertoire of models for explaining why massive stars with detached shells exhibit larger than usual expansion velocities, while low-mass stars with detached shells exhibit smaller than usual expansion velocities. We suggest a number of new, low-progenitor mass candidates for treatment as detached or "fossil" shells. These are often regarded as proto planetary nebulae. Their frequency in our sample of low-mass stars suggests that their entire "superwind" phase of mass loss is accomplished in ≈1000 yr.