Disks around the Young Stars Tw Hydrae and Hd 100546 Imaged at 3.4 Millimeters with the Australia Telescope Compact Array

We present observations of the young stars TW Hya and HD 100546 made with the Australia Telescope Compact Array at 89 GHz with 200 resolution and 3 mJy continuum sensitivity. Compact thermal dust continuum emission is detected from disks surrounding both stars. HD 100546 also shows hints of extended emission, presumably a residual protostellar envelope, which is also visible in scattered light at optical wavelengths. For TWHya, HCOþ J 1⁄4 1–0 line emission from the circumstellar disk is detected and spatially resolved. The observed size and intensity are in good agreement with model calculations based on an irradiated disk with substantial depletions derived previously from single-dish observations of higher J HCOþ transitions. Subject headings: circumstellar matter — planetary systems: protoplanetary disks — stars: individual (TWHydrae, HD 100546)