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A Near-Infrared Spectroscopic Survey of Class I Protostars

We present the results of a near-IR spectroscopic survey of 110 Class I protostars observed from 0.80 microns to 2.43 microns at a spectroscopic resolution of R=1200. We find that Class I objects exhibit a wide range of lines and the continuum spectroscopic features. 85% of Class I protostars exhibit features indicative of mass accretion, and we found that the veiling excess, CO emission, and Br Gamma emission are closely related. We modeled the spectra to estimate the veiling excess (r_k) and extinction to each target. We also used near-IR colors and emission line ratios, when available, to also estimate extinction. In the course of this survey, we observed the spectra of 10 FU Orionis-like objects, including 2 new ones, as well as 3 Herbig Ae type stars among our Class I YSOs. We used photospheric absorption lines, when available, to estimate the spectral type of each target. Although most targets are late type stars, there are several A and F-type stars in our sample. Notably, we found no A or F class stars in the Taurus-Auriga or Perseus star forming regions. There are several cases where the observed CO and/or water absorption bands are deeper than expected from the photospheric spectral type. We find a correlation between the appearance of the reflection nebula, which traces the distribution of material on very large scales, and the near-IR spectrum, which probes smaller scales. The spectra of the components of spatially resolved protostellar binaries tend to be very similar. In particular both components tend to have similar veiling and H_2 emission, inconsistent with random selection from the sample as a whole. There is a strong correlation between [Fe II] and H_2 emission, supporting previous results showing that H_2 emission in the spectra of young stars is usually shock excited by stellar winds.