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A. N. Witt, U. P. Vijh (University of Toledo)
The Red Rectangle (RR) is a biconical proto-planetary nebula, produced by the post-AGB star system HD 44179. The system is currently in a dust/molecule producing phase and is exhibiting evidence of mixed C-rich/O-rich chemistries. The central binary source is hidden by an optically thick equatorial disk seen edge-on, which permits the direct observation of nebular emissions without undue interference from direct stellar radiation. A small fraction of residual star light emerges from the central region of the nebula only after having suffered substantial degrees of scattering and absorption by the nebular material. Thus, the absorption characteristics of the nebular dust can be studied as well.
In addition to the well-documented extended red emission (ERE) band (540 - 800 nm) that gives the RR its distinctive color and morphology, the optical spectrum of the RR also exhibits a blue luminescence (BL) component, with peak emission near a wavelength of 380 nm. We will discuss the spectra and spatial morphologies of these emissions. If both emission bands are produced by the same family of emitters, their spatial preference for mutually exclusive environments suggest that they relate to different ionization stages.
We will present observational data and comparisons with laboratory data that suggest that the BL may be the result of fluorescence by small, neutral PAH molecules with three to four carbon rings that exist preferentially in the shadow of the disk. The different excitation conditions for the ERE suggest the possible involvement of PAH dications. Laboratory data on the electronic spectra of PAH dications and their fluorescence properties are urgently needed. We gratefully acknowledge support from NSF Grant AST 0307307 which has made this research possible.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.