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

Abstract

Hubble Space Telescope 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 X 5 2.2 pm. HE(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). HE(Tau/c is therefore the first disk to be clearly resolved around an individual star 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", scale height of 3.8 AU at T = 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 lop4 Ma (w 0.1 M J~~~~~~ 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.

Visions of Nature's Planet Foundry: Images of Circumstellar Disks

“…Detailed studies of the HH 30 disk indicate a Gaussian vertical profile with a scale height comparable to that expected from local thermal equilibrium (4,50). However, a smaller than expected scale height has been measured in the disk of HK Tau B (46), possibly indicating that the dust has settled with respect to the gas in this disk. In debris disks, where gas is largely absent, the disk vertical profile traces the orbital inclination distribution for the parent bodies whose collisions are replenishing the dust population.…”

“…Most interesting are eight sources where HST directly detects the disks in scattered light. These include the edge-on disks in the HK Tau (46) and HV Tau binary systems; the circumbinary ring in UY Aur; intermediate inclination disks associated with GM Aur, GO Tau, Sz 82, and DoAr 25; and a face-on disk around TW Hya (25). Modeling of the HK Tau and TW Hya images has found a rough order-ofmagnitude agreement in disk mass estimates independently derived at optical and millimeter wavelengths.…”

Early Orbital Evolution of Binaries: Overview and Outlook

“…close binary stars and planets) is always closely associated with the presence of accretion disks (e.g., McCaughrean & O'Dell 1996;Burrows et al 1996;Stapelfeldt et al 1998). A clear decrease with time of the fraction of optically thick disks (at <3 AU from the star) from rvl00% at the age rvO.3 Myr down to a few percent at the age of rvl0 Myr has been demonstrated by Hillenbrand & Meyer (1999).…”

“…It is plausible that this instability results in nonlinear dissipation (shocks), which may lead to a near coplanarity (within the disk thickness or about 5% to 10%) on a timescale as short as the disk precessional timescale, or about 20 binary orbits (Bate et al 2000). Observations of noncoplanar disks may help resolve these issues (e.g., Stapelfeldt et al 1998;Koresko 1998 and precessing jets within binary systems also provide relevant information. Also desired are three dimensional simulations of inclined, warped disks that resolve well the internal structure of the disk.…”

High spatial resolution optical imaging of the multiple T Tauri system LkHα 262/LkHα 263

“…This discrepancy between the observed colour and the spectral class for component C probably resides in the presence of an edge-on disc in this object. It is interesting to compare the colours of LkHα 263C with those of wellknown edge-on disc systems, such as HK Tau C or HV Tau C. Stapelfeldt et al (1998) derive for HK Tau C a colour I-J = 2.4±0.1 based on HST optical images in the F814W filter and ground-based CFHT infrared images obtained one month apart. For HV Tau C we use the F814W optical and the CFHT/PUEO infrared magnitudes by Stapelfeldt et al (2003) about one year apart to derive a colour of I-J = 0.85±0.1.…”