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We have used the James Clerk Maxwell Telescope to detect strong submillimeter (350 $\mu$m - 1100 $\mu$m) continuum emission from the classical T Tauri star GW Orionis. GW Ori is a spectroscopic binary with a period of 242 days and a separation of 1 AU (Mathieu, Adams and Latham, 1991, AJ 101, 2184; MAL). It is the first pre-main sequence short-period binary system to show submillimeter emission. The submillimeter luminosity is comparable to the largest among both T Tauri and Herbig Ae stars. The emission is confined within a radius of 5 arcsec (2000 AU).
We show that the origin of the emission must be circumbinary. With an optically thin, isothermal approximation we place a lower limit of 0.1 $M_{\sun}$ on the mass of circumbinary material, assuming a maximum temperature of 150 K. Using the pure-disk models of MAL, we find disk masses between a few tenths of a solar mass and a few solar masses, depending on choice of submillimeter opacity. These values are a significant fraction of the total stellar mass (2.8 $M_{\sun}$ to 3.8 $M_{\sun}$, depending on inclination) and possibly comparable to the secondary mass alone (0.3 $M_{\sun}$ to 1.3 $M_{\sun}$). Our fluxes are inconsistent with the disk-envelope model of MAL, for typically adopted opacities. Other extended distributions of material need to be considered, particularly since GW Ori lies near the birthline.
If the circumbinary material is in a disk, then the derived masses are sufficient to drive rapid evolution of the binary orbital elements, including exciting eccentricity into the orbit. As such, the low eccentricity of GW Ori ($e=0.04\pm0.06$) may indicate that the disk matter does not populate the strong resonances near the secondary. In addition, the case of GW Ori suggests that massive circumbinary disks can survive the binary formation process, placing constraints on the degree of disk consumption and/or replenishment (e.g., if formation is the result of disk instabilities) or circuminary disk disruption (e.g.,in a disk-enhanced capture picture).
