A High‐Resolution Study of Gas and Dust around Young Intermediate‐Mass Stars: Evidence for Circumstellar Disks in Herbig Ae Systems

Abstract

As part of a long-term program of observations to search for andcharacterize disks of gas and dust around intermediate-mass counterpartsto solar-mass T Tauri stars, we have probed the environments of sevenpre-main-sequence stars of spectral type Ae using millimeter-wavecontinuum and molecular line aperture synthesis imaging. In each case weidentify a compact region of thermal continuum emission centered on thestar. Upper limits to radii are in the range 200-300 AU for five membersof our sample, and 680 AU for the distant source HD 245185. We identifyan elongated continuum source around HD 163296, with a semimajor axis of110 AU. Adopting relatively high values for dust grain opacities, weobtain minimum masses of circumstellar dust and gas in the range0.005-0.034 M{\sun} for the seven sources, assuming that the observedcontinuum emission is optically thin. We detect molecular line emissionfrom gas regions centered on four of the stars. Two of these regions arespatially resolved and are found to be elongated, with semimajor axes of310 and 450 AU for HD 163296 and AB Aur, respectively. Ordered velocitygradients along the major axes of both of these structures pointstrongly to the presence of orbiting material in disklikeconfigurations, and we argue that the nebular environments of our entiresample include substantial disk components.