Observations of He I recombination line 10830 A are made with a newly developed bare Reticon spectrometer system. The overall system noise here is 650 rms charges/diode/readout. The observations of 5876 A from the Ulrich and Knapp line profile survey are analyzed in the context of four models: stellar wind, chromospheric, nebular, and disk. The analysis shows that the optical depth at 10830 A must be greater than unity in all cases. A spherically symmetric gas flow or a gas flow having a large scale smoothness must produce an absorption feature indicative of the velocity of the outermost layers. Such an absorption feature is found only for T Tau. The other stars that were adequately observed but found to lack such an absorption feature are LkH-alpha 264, DF Tau, RW Aur, MWC 137, and DI Cep. All of these (except DF Tau) are interpreted as chromospheric or probable chromospheric emission objects. DF Tau is considered nebular. The emission of LkH-alpha 101 is seen as arising from an extended envelope because of the very high contrast between the intensity at 10830 A and the nearby continuum.
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Ulrich et al. (1981) studied this question.