EPSILON ERIDANI'S PLANETARY DEBRIS DISK: STRUCTURE AND DYNAMICS BASED ON SPITZER AND CALTECH SUBMILLIMETER OBSERVATORY OBSERVATIONS

Spitzer and Caltech Submillimeter Observatory images and spectrophotometry of Eridani at wavelengths from 3.5 to 350 μm reveal new details of its bright debris disk. The 350 μm map confirms the presence of a ring at r = 11"-28"(35-90 AU), observed previously at longer sub-mm wavelengths. The Spitzer mid-IR and far-IR images do not show the ring, but rather a featureless disk extending from within a few arcsec of the star across the ring to r~ 34" (110 AU). The spectral energy distribution (SED) of the debris system implies a complex structure. A model constrained by the surface brightness profiles and the SED indicates that the sub-mm ring emission is primarily from large (a~ 135 μm) grains, with smaller (a~ 15 μm) grains also present in and beyond the ring. The Spitzer Infrared Spectrograph and Multiband Imaging Photometer for Spitzer SED-mode spectrophotometry data clearly show the presence of spatially compact excess emission at λ ≳ 15 μm that requires the presence of two additional narrow belts of dust within the sub-mm ring's central void. The innermost belt at r~ 3 AU is composed of silicate dust. A simple dynamical model suggests that dust produced collisionally by a population of about 11 M_⊕ of planetesimals in the sub-mm ring could be the source of the emission from both in and beyond the sub-mm ring. Maintaining the inner belts and the inner edge to the sub-mm ring may require the presence of three planets in this system including the candidate radial velocity object.