Abstract
We are combining images in the mid-infrared (from MSX, the US Midcourse Space Experiment) with those from the high resolution UKST/AAO Hα survey of the Galactic Plane to investigate the relationship between the mid-infrared (MIR) and optical emission line properties of candidate Planetary Nebulae (PN) discovered by the Hα survey. Preliminary results indicate that only 10–20% of likely bona fide PN have a counterpart detected in the MIR. By sharp contrast one can readily recognize pre-main- sequence objects and HII regions emitting Hα and largely embedded in dust by the simultaneous presence of 8.3 and 21.3-μm emission suggestive of dust spanning a variety of temperatures. The sharpest criteria for recognizing true PN appear to be optical morphology and spectra (particularly the presence of [OIII]), and, where detected, MIR characteristics.
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