Near infrared hydrogen lines as diagnostic of accretion and winds in T Tauri stars

Abstract

From a sample of 50 T Tauri stars, mostly from the Taurus-Auriga complex, Pa$\mathrm{\beta}$ line profiles were obtained for 49 of the stars and Br$\mathrm{\gamma}$ profiles for 37 of the stars. Emission at Pa$\mathrm{\beta}$ was observed for 42 stars and emission at Br$\mathrm{\gamma}$ was found for 30 stars. The most conspicuous features in the line profiles is the almost complete absence of blueshifted absorption components and the relatively high frequency of inverse P Cygni profiles (IPC). At Pa$\mathrm{\beta}$, 34% of the profiles are IPC while at Br$\mathrm{\gamma}$ 20% are IPC. The redshifted absorption features indicate infall at velocities of about $200 s}^{-1}$, compatible with free fall from a few radii out. In general, line profiles are broad centrally peaked with slightly blueshifted line peaks. Existing wind and accretion models fail, in quantitative terms, to explain the shape of the observed profiles. Magnetospheric accretion models, being the currently preferred ones, produce lines too narrow (by ∼ $100 \mathrm{km s}^{-1}$ FWHM ), wings extending to velocities too low (by at least ∼ $100 s}^{-1}$) and with maximum normalized intensities too high by factors of a few. A qualitative agreement between some of the accretion model predicted profiles and some observations hint that emission in these lines might, at least partially, arise from infalling material. Definite claims regarding the origin of the emission in these lines cannot be made until models match observations much better than they currently do.