• Gordon, Karl

Abstract

We propose to determine the wavelength of the photons which excite Extended Red Emission {ERE} by mapping the small scale structure of ERE and molecular hydrogen {H_2} in the reflection nebulae NGC 2023 and 7023. Both of these nebulae display sharp narrow ERE-filaments within photodissociation regions {PDR} which also show infrared H_2 fluorescence. In these opically thick filaments, different wavelength photons penetrate to different depths. By comparing the widths of these filaments in ERE and H_2 we will determine the exciting wavelength of ERE. This is possible because the combined opacity of dust and H_2 to the exciting radiation {lambda < 1100 A} of H_2 fluorescence is known, and the comparison of the thickness of the ERE and H_2 filaments will allow a determination of the dust opacity at the wavelength at which ERE is being excited. This is a sensitive test to distinguish between different materials which have been proposed as the carrier of ERE {e.g., carbon or silicon nanoparticles, polycyclic aromatic hydrocarbon molecules, hydrogenated amorphous carbon, etc.}, because the photoluminescense excitation spectra of these different materials differ by large amounts. Identifying the material which produces ERE is important as recent work on ERE in the diffuse interstellar medium has shown that the material which produces ERE comprises a significant component of dust grains.

Topics

• nanoparticle
• impedance spectroscopy
• amorphous
• Carbon
• grain
• Hydrogen
• Silicon