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Dust reverberation - A model for the infrared variations of Fairall 9
Barvainis, Richard
AA(Haystack Observatory, Westford, MA)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 400, no. 2, p. 502-509. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Active Galactic Nuclei, Cosmic Dust, Infrared Radiation, Interstellar Extinction, Light Curve, Quasars, Accretion Disks, Emission Spectra, Ultraviolet Astronomy
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A detailed model in which dust heated by the central optical/UV source is responsible for the IR emission from Fairall 9 is described. Fits to the light curves at the four measured IR wavelengths (the J, H, K, and L bands), which match both the spectral and temporal behavior of the IR light, are presented. A detailed treatment is given of the emission from clouds of significant UV and IR optical depth, illuminated on one face by a central UV continuum source. On the basis of typical grain emissivity laws, inferred sublimation temperatures for the grains lie in the range 1300-2000 K, depending on the assumed opacity of the clouds. The model is able to distinguish whether the dust lies in a spherical or disklike geometry. The clouds directly exposed to the UV exist at distances ranging from less than about 0.3 lt-yr to about 1.3 lt-yr. The variable part of the optical/UV continuum appears to have a flat spectrum extending into the near-IR, suggesting an optically thin emission mechanism rather than emission from an optically thick accretion disk.

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