Millimeter continuum observations of the giant proplyd j244-440
          D.C. Lis, Caltech
          P. Schilke, MPIfR
          H. Beuther, CfA
          D. Wilner, CfA

          The most prominent sample of disks around low-mass stars has been found in the Orion Nebula, by means of optical imaging (e.g. McCaughrean & O'Dell, 1996, AJ 111, 1977). While optical observations can determine many of the physical parameters of these “proplyds”, disk mass is not one of them, since they are optically thick at these wavelengths.  Previous attempts to determine disk masses by observations at millimeter wavelengths have been unsuccessful (Mundy et al, 1995, ApJ, 452, L137), as the 3mm fluxes were found consistent with free-free emission.

          During observations of the Orion Bar with the Plateau de Bure interferometer a 3mm point source was discovered at the position of the giant proplyd j244-440 (Bally et al., 2000, AJ 119, 2919).  Subsequent observations showed excess 1.3mm flux (23 mJy at 3mm, 55 mJy at 1.3mm). Unpublished 8.6 GHz VLA measurements (Wyrowski, private communication) show an integrated flux of 24 mJy.  Assuming optically thin free-free emission, we derive a dust flux of 4.5 mJy at 3mm, and 37.5 mJy at 1mm. The resulting dust opacity index, beta, is close to unity, consistent with grain growth in pre-main sequence disks. A preliminary disk mass estimate is ~0.007 solar masses, or ~7.5 Jupiter masses. More detailed modeling is required, but this value is well within the range of T-Tauri disks in the survey of Beckwith & Osterloh (1995, ApJ 439, 288). The scheduled 0.8mm observations with the Submillimeter Array will provide additional constraints for the dust opacity index and the disk mass.