The 1 . 2 mm image of the β Pic toris disk ⋆

We present millimeter imaging observations in the 1200 μm continuum of the disk around β Pic. With the 25′′ beam, the β Pic disk is unresolved perpendicularly to the disk plane (≤ 10′′), but slightly resolved in the northeast-southwest direction (26′′). Peak emission is observed at the stellar position. A secondary maximum is found 1000AU along the disk plane in the southwest, which does not positionally coincide with a similar feature reported earlier at 850μm. Arguments are presented which could be seen in support of the reality of these features. The observed submm/mm emission is consistent with thermal emission from dust grains, which are significantly larger than those generally found in the interstellar medium, including mm-size particles, and thus more reminiscent of the dust observed in protostellar disks. Modelling the observed scattered light in the visible and the emission in the submm/mm provides evidence for the particles dominating the scattering in the visible/NIR and those primarily responsible for the thermal emission at longer wavelengths belonging to different