  We present observations of the young stars TW Hya and HD 100546 made with the
Australia Telescope Compact Array at 89 GHz with $\sim2''$ resolution and
$\sim3$ 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 TW Hya, HCO$^+$ J=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 HCO$^+$ transitions.
