Blue Blob in the Red Rectangle

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Science  16 Apr 2004:
Vol. 304, Issue 5669, pp. 363
DOI: 10.1126/science.304.5669.363c

The Red Rectangle nebula is an unusual protoplanetary nebula. Its central star, HD44179, is dying, and substantial mass is being blown off the star in a bipolar outflow, creating the rectangular shape and a large amount of dust. It is the brightest source of unidentified infrared band emission (UIR), and much of this comes from carbon compounds. Given that 20 to 30% of the Milky Way's infrared radiation is in the UIR and that carbon is an important component of stars, planets, and terrestrial life, it is desirable to identify the carbon species that account for the emissions.

At shorter wavelengths, in the visible to ultraviolet, the Red Rectangle looks like a blue blob, produced by dust-scattered light from the central star. Vijh et al. obtained spectra at these wavelengths, and the peaks correspond to those in fluorescence spectra of electronic transitions in neutral polycyclic aromatic hydrocarbons (PAHs) with three to four rings, such as anthracene and pyrene. Thus, not only is the Red Rectangle producing a lot of PAH dust, but blue luminescence may be used to identify many carbon and silicon species that fluoresce at specific wavelengths. — LR

Astrophys. J., in press (astro-ph/0403522).

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