Image of Fomalhaut Dust Ring at 350 Microns: Relative Column Density Map Shows Pericenter-Apocenter Asymmetry

Astrophysics, abstract
astro-ph/0501140

From: Kenneth Marsh [view email]

Date: Sat, 8 Jan 2005 19:15:36 GMT   (139kb)

We have imaged the circumstellar disk of Fomalhaut at 350 microns wavelength,
using SHARC II at the Caltech Submillimeter Observatory. The spatial resolution
of the raw images (9 arcsec) has been enhanced by a factor of three 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 ~ 70 deg), with little or no other apparent structure; this is the first
observation that shows clearly the ring morphology of the disk. We have
combined our 350 micron data with Spitzer Space Telescope images at 24, 70, and
160 microns in order to estimate the 2-dimensional spatial variation of
relative column density ("tau map") using our DISKFIT procedure. The 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 results confirm the ring-like morphology, but
also show that the geometric center is displaced from the star by about 8 AU
and that the ring has an apocentric enhancement of approximately 14% in
integrated column density. If we interpret the displacement in terms of
elliptical orbital motion due to gravitational perturbation by an unseen
planet, then the implied forced eccentricity is ~ 0.06; dynamical modeling then
predicts an apocentric density enhancement consistent with that inferred from
the tau map.

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