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Photoluminescence by Interstellar Dust

by Vijh, Uma Parvathy

Abstract (Summary)
In this dissertation, we report on our study of interstellar dust through the process of photoluminescence (PL). We present the discovery of a new band of dust PL, blue luminescence (BL) with lambda_{peak} ~ 370 nm in the proto-planetary nebula known as the Red Rectangle (RR). We attribute this to fluorescence by small, 3-4-ringed polycyclic aromatic hydrocarbon (PAH) molecules. Further analysis reveals additional independent evidence for the presence of small PAHs in this nebula. 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. We present the spatial distribution of the BL in these nebulae and find that the BL is spatially correlated with IR emission structures attributed to aromatic emission features (AEFs), attributed to PAHs. The carrier of the dust-associated photoluminescence process causing the extended red emission (ERE), known now for over twenty five years, remains unidentified. We constrain the character of the ERE carrier by determining the wavelengths of the radiation that initiates the ERE – lambda < 118 nm. We note that under interstellar conditions most 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. In the last few chapters of the dissertation we present first results from ongoing work: i) Using narrow-band imaging, we present the optical detection of the circum-binary disk of the RR in the light of the BL, and show that the morphology of the BL and ERE emissions in the RR nebula are almost mutually exclusive. It is very suggestive to attribute them to different ionization stages of the same family of carriers such as PAH molecules. ii) We also present a pure spectrum of the BL free of scattered light, resolved into seven molecular emission bands, superimposed upon a broad continuum. The relative intensity of the component bands varies with position within the nebula, suggesting an origin in a set of several related molecular species, most likely small PAHs.
Bibliographical Information:

Advisor:

School:University of Toledo

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:photoluminescence polycyclic aromatic hydrocarbons fluorescence interstellar dust

ISBN:

Date of Publication:01/01/2005

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