Bipolar Symbiotic Planetary Nebulae in the Thermal Infrared: M2-9, Mz 3, and He 2-104

We present thermal-IR images of three extreme bipolar objects, M2-9, Mz3, andHe2-104. They are bipolar planetary nebulae with bright central stars and arethought to be powered by symbiotic binary systems. The mid-IR images spatiallyresolve the SEDs of the central engines from the surrounding nebulae. A warmdust component of several hundred degrees can account for the core emission,while a cooler component of about 100 K produces the more extended emissionfrom the bipolar lobes. In every case, the dust mass for the unresolved coreregion is orders of magnitude less than that in the extended lobes, raisingdoubts that the hypothetical disks in the core could have been responsible forpinching the waists of the nebulae. We find total masses of roughly 0.5-1 Msunin the nebulae of M2-9 and Mz3, requiring that this material was donated byintermediate-mass progenitor stars. The mass of He2-104's nebula is much lower,and any extended emission is too faint to detect in our images. Extended dustaround both M2-9 and Mz3 resembles the distribution of ionized gas. Our imagesof Mz3 have the highest signal-to-noise in the extended polar lobes, and weshow that the fairly uniform color temperature derived from our images canexplain the 110 K dust component that dominates the far-IR SED. In the case ofMz3, most of the mass traced by dust is concentrated at high latitudes.Comment: accepted by AJ, 18 pages, 5 figure