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Session 10 - Interstellar Medium and Star Formation.
Display session, Monday, June 08
Hubble Space Telescope images of HK Tauri reveal that the companion star in this 2.4 arcsec (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 wavelenghts less than 2.2 microns. HK Tau/c is strikingly similar to scattered light models of an optically thick circumstellar disk seen close to edge-on, and to the HST images of HH 30 (Burrows et al. 1996, Ap.J. 473 437). HK Tau/c is therefore the first circumstellar disk to be clearly resolved in a young binary system.
The disk properties have been constrained by fitting model reflection nebulae to the HST images. The disk has a radius of 105 AU, inclination of about 5 degrees, scale height of 3.8 AU at r= 50 AU, and is flared. The absence of a point source in the near-IR requires Av > 50 mag toward the unseen central star. The thickness of the dark lane establishes a disk mass near 0.0001 solar masses of dust and gas, if the dust grains have interstellar properties and remain fully mixed vertically. With the observed disk radius equal to only 1/3 the projected separation of the binary, there is a strong possibility that tidal truncation of the circumsecondary disk has occurred in this system.
Program listing for Monday