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| Extended Red Emission as a Function of Optical Depth in High-latitude Interstellar Clouds |
William Dirienzo1, A. Witt2, S. Mandel3
1University of Wisconsin-Madison, 2University of Toledo, 3Hidden Valley Observatory. |
| Presentation Number: 092.17 |
Extended Red Emission is a broad component of optical spectra observed in many interstellar clouds. It was first discovered about thirty years ago, yet it is still not completely understood. Through a process of photoluminescence, dusty interstellar clouds illuminated by ultraviolet light of sufficient energy emit this extra light which peaks in the red optical wavelength range from about 540 nm to beyond 900 nm. This paper describes a study of the variation of the intensity of the ERE as a function of the optical depth in three high-latitude interstellar clouds, MBM6, MBM25, and MBM32. These data were used for a determination of the photon conversion efficiency of the process. Our results support the idea of a two-stage process of ERE excitation, initiated by UV light between 120 and 250 nm. We found that the number of ERE photons emitted is about 7% of the number of exciting UV photons absorbed by the clouds. This shows that the ERE carrier is a major contributor to the UV continuum opacity in interstellar space. The carrier must be abundant and should be incorporated more fully into comprehensive models of the dusty interstellar medium.
This work has been made possible through support from NSF Grant AST0606756 to the University of Toledo and the NSF-supported REU program in Physics and Astronomy at the University of Toledo, which we acknowledge with gratitude. |
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