INTRINSIC NEAR-INFRARED EXCESSES OF T-TAURI STARS - UNDERSTANDING THECLASSICAL T-TAURI STAR LOCUS

We re-examine the observed near-infrared properties of T Tauri stars a nd interpret them with the aid of accretion disk models. Based upon a cartful analysis of the dereddened near-infrared colors, we find that T Tauri stars exhibit a surprisingly narrow range in (J-H)-(H-K) and ( H-K)-(K-L) color-color diagrams, We find that accretion disk models wi th a range of accretion rates (10(-8)M. yr(-1)<M<10(-6)M. yr(-1)), inn er-disk radii (1-6R()), and viewing angles can account for the distri bution of intrinsic near-infrared excesses, If the assumptions upon wh ich our models are based are correct, Mie find that: (i) the disk accr etion rates needed to explain the observations are consistent with tho se inferred from optical spectroscopic studies; and (ii) inner-disk ho les are required in order to explain the range of observed intrinsic n ear-infrared excesses. Our model results suggest that a given near-IR excess requires a minimum disk accretion rate, though larger accretion rates can be accommodated with specific combinations of inner disk ho le size and viewing inclinations. Further, we combine optical veiling measurements, knowledge of stellar SEDs and reddening, in order to est imate infrared photometric flux excesses for our sample of T Tauri sta rs. Assuming a distribution of mass accretion rates inferred from opti cal veiling studies, and a random distribution of viewing inclinations , we examine the plausible range of inner-disk hole sizes. The absence of inner-disk holes predicts near-IR excesses larger than those obser ved. Inner-disk holes exclusively >8R() are inconsistent with the obs ervations, whereas hole sizes between 2-6R() are well-matched to the data. Finally we examine the impact of our results on attempts to char acterize the accretion properties of embedded young star clusters. (C) 1997 American Astronomical Society.