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K. A. Marsh, T. Velusamy, C. D. Dowell (JPL), C. A. Beichman (Caltech)
We have imaged the circumstellar disk of Fomalhaut at 350 \mum wavelength, using observations made with the new SHARC II camera at the Caltech Submillimeter Observatory on 2004 Sep 18. The spatial resolution of the raw images (9 arcsec) has been enhanced by a factor of about two using the HiRes deconvolution procedure. We find that at this wavelength and signal to noise ratio (~12), the observed morphology is that of a simple inclined ring (i ~69 deg), with no other apparent structure.
We have combined our 350 \mum data with Spitzer images at 24, 70, and 160 \mum in order to estimate the 2-dimensional spatial variation of relative column density in the disk, as seen in a pole-on projection, using our DISKFIT procedure. The estimate, referred to as a ``tau map," is based on the following physical assumptions: (1) the wavelength variation of opacity is the same throughout the disk, (2) the radial variation of dust temperature is dictated by the energy balance of individual grains in the stellar radiation field, and (3) the vertical scale height of the disk follows a power-law radial variation. The resulting tau map confirms that the observations at all 4 wavelengths are consistent with a simple ring whose column density is azimuthally uniform. The estimated inner and outer radii are 120 and 210 AU, respectively, and the estimated opening angle is 7 deg. In this solution, the star is slightly displaced from the center of the ring, causing additional heating of the southwest quadrant; this accounts for the observed wavelength-dependence of the brightness asymmetry of the ansae that has been reported by others. Also apparent in the inner part of the estimated tau map is a much more diffuse component whose column density decreases inward towards the star; it is the manifestation of the central compact source visible in the 24 \mum data, and represents hot dust interior to the ring.
The implications of these results with regard to the possible existence of orbiting planetary objects in this system will be discussed.
This work was performed by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.