Discussion

The planetary nebulæ  of the galactic bulge constitute the largest and nearest population of PNe. Our survey has doubled the number of known PNe in the surveyed region. Although much of our survey was done under nonphotometric conditions, subsequent photometric observations by Dopita indicate that our survey is at least two magnitudes deeper than previous work. If the luminosity function of PNe in the direction of the galactic bulge increases in the way suggested to be the case for LMC PNe, then our survey should have found at least 200 new objects, but we found only 56.

There are two possibilities for this lack of PNe: it could be that the PNe are dust-enshrouded because of their high metallicity, or that the PNe are associated with a low mass central star so that the nebula has expanded and become optically thin in the timescale over which the central star becomes hot enough to ionize it.

We have started a program to address the question of which of these two evolutionary scenarios apply to the objects in our newly-discovered sample by obtaining accurate photometry. Such data will provide a measure of the physical size, the reddening, an estimate of the luminosity in the ionizing field that is absorbed in the nebula, a determination of the excitation class, and estimates of the degree of optical thickness of the nebula and the nebular abundances.

© Copyright Astronomical Society of Australia 1997