Invited Talk

Photoluminescence by Interstellar Dust: Extended Red Emission (ERE) and Blue Luminescence (BL)

Uma P. Vijh (University of Toledo)

I will review photoluminescence by interstellar dust, in particular, Extended Red Emission (ERE) and Blue Luminescence (BL).

Interstellar dust in nebulae and in the diffuse interstellar medium of galaxies contains a component which responds to illumination by ultraviolet photons with efficient luminescence in the 500 nm to 1000 nm spectral range, known as Extended Red Emission (ERE). The carrier of the dust-associated photoluminescence process causing the ERE, known now for over thirty years, remains unidentified. I will review the techniques of detection and the observational characteristics of the ERE in a wide range of astrophysical environments. I will then discuss results of the analysis of ERE observations, leading to a set of specific constraints that any proposal for the ERE carrier must confront. Newer work constrains the character of the ERE carrier by determining the wavelengths of the radiation that initiates the ERE < 118 nm. Under interstellar conditions most polycyclic aromatic hydrocarbon (PAH) molecules are ionized to the di-cation stage by photons with E > 10.5 eV and that the electronic energy level structure of PAH di-cations is consistent with fluorescence in the wavelength band of the ERE.

The last decade saw the discovery of a new dust photoluminescence phenomenon, blue luminescence (BL) with peak 370 nm in the proto-planetary nebula the Red Rectangle (RR). BL is attributed to fluorescence by small, 3-4-ringed polycyclic aromatic hydrocarbon (PAH) molecules. Detection of BL using long-slit spectroscopic observations in other ordinary reflection nebulae suggests that the BL carrier is an ubiquitous component of the ISM and is not restricted to the particular environment of the RR. Furthermore, the BL is spatially correlated with IR emission structures attributed to PAHs.

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