VLA imaging of the disk surrounding the nearby young star TW Hydrae. Astrophys

The TW Hydrae system is perhaps the closest analog to the early solar nebula. We have used the Very Large Array to image TW Hya at wavelengths of 7 mm and 3.6 cm with resolutions of 00.1 (»5 AU) and 10.0 (»50 AU), respectively. The 7 mm emission is extended and appears dominated by a dusty disk of radius greater than 50 AU surrounding the star. The 3.6 cm emission is unresolved and likely arises from an ionized wind or gyrosynchrotron activity. The dust spectrum and spatially resolved 7 mm images of the TW Hya disk are fitted by a simple model with temperature and surface density described by radial power laws, and20.5T(r) / r. These properties are consistent with an irradiated gaseous accretion disk of mass »0.03 M, with an21S(r) / r accretion rate »1028 M, yr21 and viscosity parameter. The estimates of mass and mass accretion ratesa = 0.01 are uncertain since the gas-to-dust ratio in the TW Hya disk may have evolved from the standard interstellar value. Subject headings: accretion, accretion disks — circumstellar matter — radio continuum: stars — stars: formation — stars: individual (TW Hydrae) 1