Limits on the optical brightness of the ε Eridani dust ring

The STIS CCD camera on the Bubble Space Telescope (HST) was used to take deep optical images near the K2 V main-sequence star ε Eridani in an attempt to find an optical counterpart of the dust ring previously imaged by submillimeter observations. Upper limits for the optical brightness of the dust ring are determined and discussed in the context of the scattered starlight expected from plausible dust models. We find that even if the dust is smoothly distributed in symmetrical rings, the optical surface brightness of the dust, as measured with the HST STIS CCD clear aperture at 55 AU from the star, cannot be brighter than about 25 STMAG arcsec^-2. This upper limit excludes some solid-grain models for the dust ring that can fit the IR and submillimeter data. Magnitudes and positions for ≈59 discrete objects between 12″.5 and 58″ from ε En are reported. Most if not all of these objects are likely to be background stars and galaxies.