Near-infrared emission of protostars

Models for the thermal emission from dusty infalling envelopes around protostars indicate that the envelope emission can greatly exceed the stellar plus disk photospheric emission at wavelengths similar to 2 mu m. We argue that this thermal envelope emission accounts for the weakness of 2.3 mu m CO first-overtone absorption lines in protostellar sources. Disk emission alone is unlikely to explain the observed effect, either because disks exhibit their own CO absorption, or because inner disk holes eliminate the region of the disk that can emit in the near-infrared. We find that this near-infrared veiling is very dependent on the envelope density, increasing as mass infall rate increases and centrifugal radius decreases. The veiling also depends on the characteristics of the underlying object, and it is largest when most of the luminosity is due to accretion and the disk hole size is several stellar radii. The observed veiling indicates that dust must be falling in to distances of similar to 0.1 AU of the central star.