Toward Planetesimals in the Disk around TW Hydrae: 3.5 Centimeter Dust Emission

We present Very Large Array observations at 3.5 cm of the nearby young starTW Hya that show the emission is constant in time over weeks, months and years,and spatially resolved with peak brightness temperature ~10 K at ~0.25 (15 AU)resolution. These features are naturally explained if the emission mechanism atthis wavelength is thermal emission from dust particles in the disk surroundingthe star. To account quantitatively for the observations, we construct aself-consistent accretion disk model that incorporates a population ofcentimeter size particles that matches the long wavelength spectrum and spatialdistribution. A substantial mass fraction of orbiting particles in the TW Hyadisk must have agglomerated to centimeter size. These data provide the firstclear indication that dust emission from protoplanetary disks may be observedat centimeter wavelengths, and that changes in the spectral slope of the dustemission may be detected, providing constraints on dust evolution and theplanet formation process.Comment: 13 pages, 3 figure