MAMBO image of the debris disk around ε Eridani: Robustness of the azimuthal structure

Abstract

The debris disk closest to Earth is the one around the star ε Eridani at a distance of 3.2 pc. It is the prime target for detailed studies of a belt of planetesimals left from the early phase of planet formation other than the Kuiper belt. The non-uniform ring-like structure around ε Eridani, originally discovered at λ = 850 μ m with the bolometer camera SCUBA, could be the signpost of unseen longperiod planets interior to the disk that gravitationally interact with it through mean-motion resonances. However, the reliability of the structure at 850 μ m, which has been debated, has not been verified with independent observations until now.We present a high signalto-noise ratio image of this structure at λ = 1.2 mm made with the bolometer camera MAMBO and compare this with the SCUBA image. We have found that three of the four emission clumps (NE, NW, SW) and the two deep hollows to the east and west are at the same positions in the MAMBO and SCUBA images within astrometric uncertainty. The SE clump is at odds, significantly brighter and more extended in the SCUBA than in the MAMBO images, but it is possible that this mismatch is an artifact. We conclude that this degree of positional coincidence provides tentative evidence that the observed structure is robust. In addition, we present the radial brightness profile of our MAMBO image and show that the width of the planetesimal belt around ε Eridani is narrower than 22 AU, a more stringent upper limit than determined from previous observations. The corresponding relative width is 0.1 ≤ δR/R ≤ 0.4, which is lower than for the Kuiper belt.