Structure of the Mid‐Infrared–emitting Disk around WL 16

Abstract

WL 16 is a unique member of the embedded young stellar population in the nearby ρ Ophiuchi cloud core: its extended, high surface brightness disk is visible only at mid-infrared wavelengths. We present diffraction-limited images, from 7.9 to 24.5 μm, of WL 16 acquired at the Keck II telescope. We take advantage of the ~0.3" angular resolution of the mid-infrared images to derive physical parameters for the central object by self-consistently combining them with available near-infrared spectroscopy, point-spread function fit photometry, and pre-main-sequence evolutionary tracks. We find the central star to be a 250 Lsolar, 4 Msolar, Herbig Ae star, seen through foreground material of the ρ Oph cloud core that provides an extinction of AV=31+/-1 mag. WL 16's disk is detected through all nine observed passbands, not only those four that sample polycyclic aromatic hydrocarbon (PAH) emission features. We confirm, therefore, that the emitting particles are composed of both PAHs and very small (5-100 Å) graphitic grains. The disk size as observed through the four PAH filters is 7''×3.5", corresponding to a disk diameter of ~900 AU. The disk's major axis is at a position angle of 60deg+/-2deg and is viewed at an inclination angle of 62.2d+/-0.4d to our line of sight. Our derived inclination angle is in excellent agreement with the inclination previously inferred for the inner disk (R =50-80 carbon atoms) and/or more hydrogenated PAHs than those found in the bulk of the disk. We find a disk asymmetry, observed at all nine mid-infrared wavelengths, at projected radii 1"-2.5" (corresponding to 125AU