AAS 197, January 2001
Session 91. Disks around YSOs
Oral, Wednesday, January 10, 2001, 10:30am-12:00noon, Pacific One

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[91.01] High Resolution BIMA Observations of SVS13 A and B at 1.3 mm: Evidence for Early Grain Growth in Disks

Z. T. Webster, W. J. Welch (UC Berkeley), L. W. Looney (Max-Planck-Institut für Extraterrestrische Physik), L. G. Mundy (University of Maryland)

Large and small scale flux comparisons at 1.3 mm and 2.7 mm (presented here and from Looney, Mundy, & Welch 2000 respectively) demonstrate the dust mass opacity spectral index {\betap}\approx0 for the compact structures (disks) around SVS 13A and B whereas for the large scale envelopes, {\betap}\approx 2 (defined by F\nu \propto \nu\beta_p+2, and \kappa\nu\propto\nu\beta_p, after Beckwith and Sargent 1991). High resolution 1.3 mm data in conjunction with a previously published single dish map at 1.3 mm (Chini et. al 1997) provide both the necessary resolution (0\farcs3) and large scale sensitivity to distinguish the disk from the envelopes. Of three possible scenarios to explain the shallow dust mass opacity spectral index at high resolution while also explaining the large scale dust emissivity, only particle size evolution to at least centimeter radii seems plausible. First, an optically thick disk is precluded by modeling of the disk emissivity and would require an unreasonably large disk mass. Second, reasonable chemical evolution models of small particles at high density don't lead to flat spectra. Finally, Miyake and Nakagawa (1993) show that a flat spectrum can be produced by meter sized particles. However, for large particles, the mass emissivity is very uncertain. If this result is typical, the masses inferred from millimeter fluxes for all T-Tauri disks must be in doubt.

The BIMA Array is operated by the Berkeley-Illinois-Maryland Association under funding from the National Science Foundation. Support for this work is provided by NASA.

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