2001/02/27 by L. Testi, A. Natta, D. S. Shepherd +2 · 7 citations
Chemistry · Physics and Astronomy · #Astrophysics and Star Formation Studies #Molecular Spectroscopy and Structure #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/321406
22 pages, 6 figures, accepted for publication in ApJ
arxiv created 2001/02/27 · openalex publication_date 2001/06/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
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 ). 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 (~0.3-1 M ☉ ) 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° (implied by circular symmetry) are consistent with flared disk models that have previously been suggested to explain the optical colors and polarization properties.