Hubble Space Telescope WFPC2 Imaging of the Disk and Jet of HV Tauri C^{* **}

We have obtained Hubble Space Telescope (HST) WFPC2 images of the HV Tauri young triple system. The tertiary star appears as a compact bipolar nebula at visual wavelengths as already known in the near-infrared. New, deeper adaptive optics observations made at the Canada-France-Hawaii Telescope show no point source in the nebula to a limiting magnitude of K > 15. The results therefore confirm that HV Tau C is an optically thick circumstellar disk seen close to edge-on. Clear evidence for small, chromatic dust particles in the outer disk is provided by the color structure of the nebula: the thickness of the central dust lane shrinks by 30% between 0.55 and 2.2 μm. Bipolar jets extending 03-07 perpendicular to the dust lane are seen in HST narrowband [S II] and [O I] images. The continuum images are compared to multiple scattering models, with optimal density model parameters derived through χ² minimization. A disk density distribution provides a reasonable fit to the K-band image but is unable to reproduce the vertical extent of the nebula at I band without resorting to an unreasonably large scale height. Adding an envelope structure around the disk results in a much better fit to the HST image, and with a physically reasonable disk scale height. Our preferred model has a disk outer radius of 50 AU, inclination of 6°, and scale height of 6.5 AU at r = 50 AU. The thickness of the dark lane establishes a disk mass near 2 × 10^-3 M_☉ (~2M_Jup) of dust and gas, if the dust grains have interstellar properties and remain fully mixed vertically. The envelope, with a much smaller mass ~4 × 10^-5 M_☉, would be very short-lived unless replenished by new material from the star or surrounding medium.