Detection of Uv PAHs Fluorescence Bands in Halley's Innermost Coma

Details Detection of Uv PAHs Fluorescence Bands in Halley's Innermost Coma Detection of Uv PAHs Fluorescence Bands in Halley's Innermost Coma

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.5305c&link_type=abstract

American Astronomical Society, DPS meeting #39, #53.05; Bulletin of the American Astronomical Society, Vol. 39, p.521

Astronomy and Astrophysics

Astronomy

Scientific paper

In the innermost coma of P/Halley, at projected distances p<3000 km, the TKS spectrometer on board Vega detected unknown fluorescence bands in the 280-400 nm range. The cometary spectra were compared to laboratory laser-induced fluorescence spectra of PAHs having 2, 3 or 4 benzoid rings. Two PAHs, phenanthrene (C14H10) and pyrene (C16H10) were identified by the presence of three peaks in their individual spectra between 342 and 384 nm. A further examination of the data shows that anthracene (C14H10) is also present in some spectra. The optical axis of TKS scanned an angular sector of Halley's inner coma having its apex at the nucleus. Inside this region, the overall variation of the intensity was α1/p, which indicates that the polycyclic hydrocarbons are either parent molecules or are released inside the coma by dust particles. As the band intensities are not spatially homogeneous, the PAHs are probably released by dust packs.
This first identification of PAHs in a comet was also suggested by the detection of an IR emission at 3.28 μm in IKS spectra partly due to aromatic polycyclic compounds (Encrenaz et al., A&A 207, 1988, 162-173).
More recently, naphthalene, phenanthrene and pyrene were identified in 81P/Wild2 samples (Sandford et al., Science, 2006, 314, 1720-1724). Infrared signatures of PAHs have also been detected at 6.2 and 7.6 μm in Spitzer spectra of Temple1 ejecta (Lisse et al., Icarus, 2007, 187, 69-86)
The presence of PAHs in some comets, also detected in numerous interstellar nebulae gives a strong support to the fact that comets probably have kept trace of the primitive interstellar composition through the early solar system epoch.

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