WINDS FROM T-TAURI STARS .1. SPHERICALLY SYMMETRIC MODELS

As a first step toward understanding the origin of T Tauri winds, we compute emission fluxes and profiles for lines of hydrogen, Mg II, Ca II, and Na I for a sequence of spherically symmetric wind models. Our calculations indicate that the Ha emission of T Tauri stars arises in an extended and probably turbulent circumstellar envelope at temperatures ≳ 8000 K. Spherical wind models with temperatures ≲ 10,000 K tend to produce Balmer line profiles with much deeper absorption reversals than observed. The models predict that Mg II resonance line emission should be strongly correlated with Ha fluxes; observed Mg II/Hα ratios are inconsistent with the models unless extinction corrections have been underestimated. The models predict that most of the Ca II resonance line and infrared triplet emission arises in dense layers close to the star rather than in the wind. Na I resonance line emission requires either dense chromospheres or massive winds. Adopting a plausible expansion velocity field, Ha emission levels suggest mass loss rates ∼10-8 M⊙ yr-1 for most T Tauri stars, in reasonable agreement with independent analysis of forbidden emission lines. Massloss rates ≳ 10-7 M⊙ yr-1 are required to produce broad blueshifted Na I resonance line absorption, in agreement with the results of Natta and Giovanardi. Since blueshifted Na I absorption is rather rare, we infer that the mass-loss rates for most TTS are <10-7 M⊙ yr-1.