Zinc abundances of planetary nebulae

Zinc is a useful surrogate element for measuring Fe/H as, unlike iron, it is not depleted in the gas phase media. Zn/H and O/Zn ratios have been derived using the [Zn iv] emission line at 3.625 mu m for a sample of nine Galactic planetary nebulae, seven of which are based upon new observations using the Very Large Telescope (VLT). Based on photoionization models, O/O++ is the most reliable ionization correction factor for zinc that can readily be determined from optical emission lines, with an estimated accuracy of 10 per cent or better for all targets in our sample. The majority of the sample is found to be subsolar in [Zn/H]. [O/Zn] in half of the sample is found to be consistent with solar within uncertainties, whereas the remaining half are enhanced in [O/Zn]. [Zn/H] and [O/Zn] as functions of Galactocentric distance have been investigated and there is little evidence to support a trend in either case.