The Internal Extinction Curve of NGC 6302 and its Extraordinary Spectrum

Abstract

In this paper we present a new method for obtaining the optical wavelength-dependent reddening function of planetary nebulae, using the nebular and stellar continuum. The data used was a spectrum of NGC 6302 obtained with a mean signal to noise of >10^2 A^-1 in the nebular continuum. With such a high S/N the continuum can be accurately compared with a theoretical model nebular plus stellar continuum. The nebular electron temperature and density used in the model are determined using ratios of prominent emission lines. The reddening function can then be obtained from the ratio of the theoretical and the observed continuum. We find that for NGC 6302, the visible to IR extinction law is indistinguishable from `standard' interstellar reddening, but that the UV extinction curve is much steeper than normal, suggesting that more small dust grains had been ejected into the nebula by the PN central star. Finally, using the extinction law that we have determined, we present a complete de--reddened line list of nearly 600 emission lines, and report on the detection of the He(2-10) and He(2-8) Raman Features at 4331 A and 4852 A, and the detection of Raman-Scattered OVI features at 6830 and 7087 AA.