Constraints on Properties of the Protoplanetary Disks around Ux Ori and Cq Tau

Abstract

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 α mm ∼ 2 (F ν ∝ ν αmm). Two different disk models can reproduce this property: i) a physically small disk with optically thick emission, truncated at a radius about 30 AU, or ii) a massive (∼ 0.3 − 1M ⊙) 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 α mm ∼ 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 × 1. ′′ 1 (240 × 110 AU at 100 pc distance). The size and inclination of ∼ 63 degrees (implied by circular symmetry) are consistent with flared disk models previously suggested to explain the optical colors and polarization properties.

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