A high-resolution study of gas and dust around young intermediate-mass stars: Evidence for circumstellar disks in herbig Ae systems

As part of a long-term program of observations to search for and characterize disks of gas and dust around intermediate-mass counterparts to solar-mass T Tauri stars, we have probed the environments of seven pre-main-sequence stars of spectral type Ae using millimeter-wave continuum and molecular line aperture synthesis imaging. In each case we identify a compact region of thermal continuum emission centered on the star. Upper limits to radii are in the range 200-300 AU for five members of our sample, and 680 AU for the distant source HD 245185. We identify an elongated continuum source around HD 163296, with a semimajor axis of 110 AU. Adopting relatively high values for dust grain opacities, we obtain minimum masses of circumstellar dust and gas in the range 0.005-0.034 M-circle dot for the seven sources, assuming that the observed continuum emission is optically thin. We detect molecular line emission from gas regions centered on four of the stars. Two of these regions are spatially resolved and are found to be elongated, with semimajor axes of 310 and 450 AU for HD 163296 and AB Aur, respectively. Ordered velocity gradients along the major axes of both of these structures point strongly to the presence of orbiting material in disklike configurations, and we argue that the nebular environments of our entire sample include substantial disk components.