Refining the UKST Hα survey's PN database using MSX

Abstract

We are combining images in the mid-infrared (from MSX, the US Midcourse Space Experiment) with those from the high resolution UKST/AAO Halpha 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 Ha 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 Ha and largely embedded in dust by the simultaneous presence of 8.3 and 21.3 mum 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.