SUBMILLIMETER CONTINUUM OBSERVATIONS OF THE T-TAURI SPECTROSCOPIC BINARY GW-ORIONIS

We have measured submillimeter fluxes from the classical T Tauri spectroscopic binary GW Orionis. Single-dish measurements were obtained at 350, 450, 800, 850, and 1100 μm with the James Clerk Maxwell Telescope, and an interferometric map (beam FWHM of 2.5″) was obtained at 1360 μm with the Owens Valley millimeter-wave array. The submillimeter luminosity of GW Ori is comparable to the largest yet found among T Tauri and Herbig Ae stars. The source is unresolved in our interferometric map implying that the emitting material is confined within a radius of 500 AU. In an optically thin, isothermal (150 K) approximation we place a lower limit of 0.3ℳ⊙ on the mass of circumbinary material, with an uncertainty of at least a factor three due to opacity normalization. The confinement of the submillimeter emission within ≈500 AU leads us to conclude that the origin of the submillimeter luminosity is a circumbinary disk. These conclusions are independent of specific disk models. Using the pure-disk model for GW Ori of Mathieu et al. [AJ, 101, 2184 (1991)], we find a disk mass of 1.5ℳ⊙, again with an uncertainty of at least a factor three. A disk mass of 1.5ℳ⊙ is 40%-50% of the total stellar mass. The circumbinary disk would be expected to drive rapid evolution of both the orbital semi-major axis and eccentricity. The low-eccentricity orbit of GW Ori is in marked contrast to this prediction, possibly indicating that the disk surface density in the vicinity of the binary may be small. The dynamical stability of such a massive disk is not clear, but stable disks of smaller mass are within the measurement uncertainty. We find the observations are well fit with a grain opacity κν∝νβ having an exponent β=2 at submillimeter wavelengths. Somewhat smaller values of β would also be acceptable, but β≈1 does not reproduce the data well. If a disk mass greater than 1.5ℳ⊙ is taken to be unstable and short-lived, then our adopted opacity normalization of Hildebrand [RAS, 24, 267 (1983)] and Pollack et al. [ApJ, 421, 615 (1994)] is an approximate lower limit to the true value for the GW Ori disk. The specific disk-shell model of Mathieu et al. [AJ, 101, 2184 (1991)] cannot reproduce these submillimeter observations. More generally, the confinement of at least 0.3ℳ⊙ within a radius of 500 AU with no evidence of extension to larger radii is problematic for origin of the submillimeter emission in an infalling envelope. Furthermore we have found that a single steady-accretion disk cannot reproduce the observed spectral energy distribution at both near-infrared and submillimeter wavelengths; a more luminous circumbinary disk is required to explain the large submillimeter luminosity. © 1995 American Astronomical Society.