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Multidimensional models of hydrogen and helium emission line profiles for classical T Tauri stars: method, tests and examples




We present multidimensional non-local thermodynamic equilibrium radiative transfer models of hydrogen and helium line profiles formed in the accretion flows and the outflows near the star–disc interaction regions of classical T Tauri stars (CTTSs). The statistical equilibrium calculations, performed under the assumption of the Sobolev approximation using the radiative transfer code torus, have been improved to include He i and He ii energy levels. This allows us to probe the physical conditions of the inner wind of CTTSs by simultaneously modelling the robust wind diagnostic line He iλ10830 and the accretion diagnostic lines such as Paβ, Brγ and He iλ5876. The code has been tested in 1D and 2D problems, and we have shown that the results are in agreement with established codes. We apply the model to the complex flow geometries of CTTSs. Example model profiles are computed using the combinations of (1) magnetospheric accretion and disc wind, and (2) magnetospheric accretion and the stellar wind. In both cases, the model produces line profiles which are qualitatively similar to those found in observations. Our models are consistent with the scenario in which the narrow blueshifted absorption component of He iλ10830 seen in observations is caused by a disc wind, and the wider blueshifted absorption component (the P-Cygni profile) is caused by a bipolar stellar wind. However, we do not have a strong constraint on the relative importance of the wind and the magnetosphere for the ‘emission’ component. Our preliminary calculations suggest that the temperature of the disc wind and stellar winds cannot be much higher than ∼10 000 K, on the basis of the strengths of hydrogen lines. Similarly the temperature of the magnetospheric accretion cannot be much higher than ∼10 000 K. With these low temperatures, we find that the photoionization by high-energy photons (e.g. X-rays) is necessary to produce He iλ10830 in emission and to produce the blueshifted absorption components.