EVIDENCE FOR AN EDGE-ON DISK AROUND THE YOUNG STAR MWC 778 FROM INFRARED IMAGING AND POLARIMETRY

MWC 778 is an unusual and little-studied young stellar object located in the IC 2144 nebula. Recent spectroscopy by Herbig and Vacca suggested the presence of an edge-on circumstellar disk around it. We present near-infrared adaptive optics imaging polarimetry and mid-infrared imaging which directly confirm the suspected nearly edge-on disk around MWC 778 (i ∼ 700-800) plus reveal a more extensive envelope pierced by bipolar outflow cavities. In addition, our mid-infrared images and near-infrared polarization maps detect a spiral-shaped structure surrounding MWC 778, with arms that extend beyond 6'' on either side of the star. Although MWC 778 has previously been classified as a Herbig Ae/Be star, the properties of its central source (including its spectral type) remain fairly uncertain. Herbig and Vacca suggested an F or G spectral type based on the presence of metallic absorption lines in the optical spectrum, which implies that MWC 778 may belong to the fairly rare class of intermediate-mass T Tauri Stars (IMTTSs) which are the evolutionary precursors to Herbig Ae/Be objects. Yet its integrated bolometric luminosity, ∼>750 L sun (for an assumed distance of 1 kpc) is surprisingly high for an F or G spectral type, even for an IMTTS. We speculate on several possible explanations for this discrepancy, including its true distance being much closer than 1 kpc, the presence of a binary companion, and/or a nonstellar origin for the observed absorption lines.