The 2175-A feature from irradiated graphitic particles

Details The 2175-A feature from irradiated graphitic particles The 2175-A feature from irradiated graphitic particles

Apr 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.243..570s&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 243, April 15, 1990, p. 570-587.

Astronomy and Astrophysics

Astronomy

99

Cosmic Dust, Graphite, Interstellar Extinction, Particle Size Distribution, Far Ultraviolet Radiation, Hydrogen Atoms, Radiation Effects

Scientific paper

In diffuse clouds, a subpopulation of the carbon grains is graphitized by UV starlight during cloud lifetimes of roughly 100 Myr. Graphitic dust created in this way will behave like monosize Rayleigh particles and produce a 2175-A absorption band showing a Lorentzian profile. A physical model is outlined in which the strength and width of the band correlate with the dust grain environment, but the central wavelength is fixed by the Froehlich frequency for surface plasmons in a homogeneous sphere. On this model, the band appears strong and narrow only in dust clouds where the flux of UV starlight is high and the H atom gas density is low. The width of the band increases from diffuse to dense clouds mainly as a result of gas-phase H atoms accreted on to the grain surface. It is shown that hydrogenation weakens the band in dense clouds, and thus explains the anticorrelation between band strength and high carbon depletion. The model as a whole uses only 30 percent of the cosmic carbon and gives good agreement with observations of the 2175-A feature and the average interstellar extinction law.

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