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 varia bility is thought to derive from inhomogeneities in circumstellar disks. Bo th 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 exhib its a remarkably flat spectral index in the millimeter range, with alpha (m m) similar to 2 (F-nu proportional to nu (alpha mm))Two different disk mode ls 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 (sim ilar 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 obser vational tests that will discriminate between them. The CQ Tau system exhib its a spectral index in the millimeter range of alpha (mm) similar to 2.6 c onsistent with values commonly found for disks around pre-main-sequence sta rs. The observations marginally resolve the 7 mm emission as an elongated s tructure with full width at half-maximum of 2."4 x 1."1 (240 x 110 AU at 10 0 pc distance). The size and inclination of similar to 63 degrees (implied by circular symmetry) are consistent with flared disk models that have prev iously been suggested to explain the optical colors and polarization proper ties.