An Edge-on Circumstellar Disk in the Young Binary System HK Tauri

Abstract

Hubble Space Telescope (HST) images of HK Tauri reveal that the companion star in this 2."4 (340 AU) pre-main-sequence binary system is an entirely nebulous object at visual wavelengths. HK Tau/c appears as two elongated reflection nebulosities separated by a dark lane. Near-infrared adaptive optics observations made at the Canada-France-Hawaii Telescope show a similar morphology and no directly visible star at lambda 50 mag toward the unseen central star. The thickness of the dark lane establishes a disk mass near 10-4 Msolar (~0.1 MJupiter) of dust and gas, if the dust grains have interstellar properties and remain fully mixed vertically. With the observed disk radius equal to one-third of the projected separation of the binary, there is a strong possibility that tidal truncation of the circumsecondary disk has occurred in this system.