Constraints on properties of the protoplanetary disks around UX orionis and CQ Tauri

We present Very Large Array observations of the intermediate-mass pre-main-sequence stars UX Ori and CQ Tau at 7 mm, 3.6 cm, and 6 cm. These stars are members of the UX Ori variability class, where the origin of optical variability is thought to derive from inhomogeneities in circumstellar disks. Both stars are detected at 7 mm but not at longer wavelengths, which confirms that the millimeter emission is dominated by dust. The UX Ori system exhibits a remarkably flat spectral index in the millimeter range, with alpha (mm) similar to 2 (F-nu proportional to nu (alpha mm))Two different disk models can reproduce this property: (1) a physically small disk with optically thick emission, truncated at a radius of about 30 AU, or (2) a massive (similar to0.3-1 M-circle dot) disk mainly composed of dust particles grown to radii of 10 cm (pebbles). The observations do not spatially resolve the 7 mm emission. We discuss implications of these two models and suggest observational tests that will discriminate between them. The CQ Tau system exhibits a spectral index in the millimeter range of alpha (mm) similar to 2.6 consistent with values commonly found for disks around pre-main-sequence stars. The observations marginally resolve the 7 mm emission as an elongated structure with full width at half-maximum of 2.4 x 1.1 (240 x 110 AU at 100 pc distance). The size and inclination of similar to 63 degrees (implied by circular symmetry) are consistent with flared disk models that have previously been suggested to explain the optical colors and polarization properties.