Computer Science – Numerical Analysis
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...284..956b&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 284, no. 3, p. 956-970
Computer Science
Numerical Analysis
43
Far Ultraviolet Radiation, Infrared Radiation, Interstellar Extinction, Interstellar Matter, Molecular Clouds, Particle Size Distribution, Brightness Distribution, Infrared Astronomy Satellite, Iue, Numerical Analysis, Photometers, Telephotometry, Telescopes
Scientific paper
We have searched for a correlation between the strength of the 12 and 25 micrometer emission measured by IRAS and the UV extinction curve for stars behind the Chamaeleon molecular complex. We find that the mid-IR emission is correlated with the area of the 2200 A bump but bump carriers are not fully depleted in matter with no mid-IR emission. We oberve an excess far-UV rise associated with matter with no mid-IR emission known to be associated with dens matter observed in emission in (13)CO. This excess may play a role in the formation of molecules by reducing the penetration of photo-dissociating far-UV light. Since none of the spectral features in the UV extinction curve show a variation which scales with the abundance of the mid-IR emitters, neither the bump nor the far-UV rise comes specifically from these particles. This suggests that when matter cycles in and out on dense regions in molecular clouds the mid-IR emitters are formed from or transformed into particles sharing the same absorption features. This interpretation of the data suggests that variations in IRAS colors result from changes in the size distribution of small particles which keep the total amount of matter within the Rayleigh limit for UV radiation (a few 100 A) roughly constant. It implies that small particles grow in dense regions of molecular clouds by accreting atoms, molecules or other small particles but do not condense on large grains. Outside these dense regions some process is effective in redistributing the matter into particles small enough to emit in the mid-infrared.
Boulanger Francois
Gry Cecile
Prevot M. L.
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