Dust Emission Features in NGC 7023 between 0.35 and 2.5 Microns: Extended Red Emission (0.7 Microns) and Two New Emission Features (1.15 and 1.5 Microns)

摘要

We present 0.35-2.5 μm spectra of the south and northwest filaments in the reflection nebula NGC 7023. These spectra were used to test the theory of Seahra & Duley that carbon nanoparticles are responsible for extended red emission (ERE). Our spectra fail to show their predicted second emission band at 1.0 μm even though both filaments exhibit strong emission in the familiar 0.7 μm ERE band. The northwest filament spectrum does show one, and possibly two, new dust emission features in the near-infrared. We clearly detect a strong emission band at 1.5 μm which we tentatively attribute to β-FeSi2 grains. We tentatively detect a weaker emission band at 1.15 μm which coincides with the location expected for transitions from the conduction band to midgap defect states of silicon nanoparticles. This is added evidence that silicon nanoparticles are responsible for ERE as they already can explain the observed behavior of the main visible ERE band.