We present observations of four T Tauri stars using long baseline infrared interferometry from the Palomar Testbed Interferometer .
The target sources , T Tau N , SU Aur , RY Tau and DR Tau , are all known to be surrounded by dusty circumstellar disks .
The observations directly trace the inner regions ( < 1 AU ) of the disk and can be used to constrain the physical properties of this material .
For three of the sources observed , the infrared emission is clearly resolved .
We first use geometric models to characterize the emission region size , which ranges from 0.04 to 0.3 AU in radius .
We then use Monte Carlo radiation transfer models of accretion disks to jointly model the spectral energy distribution and the interferometric observations with disk models including accretion and scattering .
With these models , we are able to reproduce the data set with extended emission arising from structures larger than 10 milliarcseconds contributing less than 6 % of the K band emission , consistent with there being little or no envelope remaining for these Class II sources ( d \log ( \lambda F _ { \lambda } ) / d \log \lambda \approx -2 to 0 in the infrared ) .
The radiation transfer models have inner radii for the dust similar to the geometric models ; however , for RY Tau emission from gas within the inner dust radius contributes significantly to the model flux and visibility at infrared wavelengths .
The main conclusion of our modeling is that emission from inner gas disks ( between the magnetic truncation radius and the dust destruction radius ) can be a significant component in the inner disk flux for sources with large inner dust radii .