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

摘要

We present 0.35 to 2.5 micron spectra of the south and northwest filaments inthe reflection nebula NGC 7023. These spectra were used to test the theory ofSeahra & Duley that carbon nanoparticles are responsible for Extended RedEmission (ERE). Our spectra fail to show their predicted second emission bandat 1.0 micron even though both filaments exhibit strong emission in thefamiliar 0.7 micron ERE band. The northwest filament spectrum does show one,and possibly two, new dust emission features in the near-infrared. We clearlydetect a strong emission band at 1.5 micron which we tentatively attribute tobeta-FeSi_2 grains. We tentatively detect a weaker emission band at 1.15 micronwhich coincides with the location expected for transitions from the conductionband to mid-gap defect states of silicon nanoparticles. This is added evidencethat silicon nanoparticles are responsible for ERE as they already can explainthe observed behavior of the main visible ERE band.