  We present near-infrared spectra of the excess continuum emission from the
innermost regions of classical T Tauri disks. In almost all cases, the shape of
the excess is consistent with that of a single-temperature blackbody with T ~
1400 K, similar to the expected dust sublimation temperature for typical dust
compositions. The amount of excess flux roughly correlates with the accretion
luminosity in objects with similar stellar properties. We compare our
observations with the predictions of simple disk models having an inner rim
located at the dust sublimation radius, including irradiation heating of the
dust from both the stellar and accretion luminosities. The models yield inner
rim radii in the range 0.07-0.54 AU, increasing with higher stellar and
accretion luminosities. Using typical parameters which fit our observed sample,
we predict a rim radius ~ 0.2 AU for the T Tauri star DG Tau, which agrees with
recent Keck near-infrared interferometric measurements. For large mass
accretion rates, the inner rim lies beyond the corotation radius at (or within)
which magnetospheric accretion flows are launched, which implies that pure
gaseous disks must extend inside the dust rim. Thus, for a significant fraction
of young stars, dust cannot exist in the innermost disk, calling into question
theories in which solid particles are ejected by a wind originating at the
magnetospheric radius.
