AB Aurigae Resolved: Evidence for Spiral Structure

Abstract

We have obtained high angular resolution (~2") images of the 13CO (J=1-->0) line and 2.7 mm continuum emission and slightly lower resolution images of 12CO (J=1-->0) and C18O (J=1-->0) line emission toward the Herbig Ae star AB Aurigae. We resolve a circumstellar disk of diameter 780 AU (FWHM) with a velocity pattern consistent with a purely rotational disk at inclination 21.5d and position angle 58.6d. Using Keplerian disk models, we find a central-source dynamical mass of 2.8+/-0.1 Msolar and a cutoff radius of 615 AU for the 13CO emission. The inclination, mass, and radius determined from 12CO and C18O observations agree with these values, given optical depth and abundance effects. As a result of the high angular resolution of our observations, we confirm the existence of spiral structure suggested by near-infrared scattered-light images and show that the spiral arms represent density contrasts in the disk.