We present radiative transfer models of the circumstellar environment of classical T Tauri stars, concentrating on the formation of the Hα emission. The wide varieties of line profiles seen in observations are indicative of both inflow and outflow, and we therefore employ a circumstellar structure that includes both magnetospheric accretion and a disc wind. We perform systematic investigations of the model parameters for the wind and the magnetosphere to search for possible geometrical and physical conditions which lead to the types of profiles seen in observations. We find that the hybrid models can reproduce the wide range of profile types seen in observations, and that the most common profile types observed occupy a large volume of parameter space. Conversely, the most infrequently observed profile morphologies require a very specific set of models parameters. We find our model profiles are consistent with the canonical value of the mass-loss rate to mass-accretion rate ratio (μ = 0.1) found in earlier magnetohydrodynamic calculations and observations, but the models with 0.05 < μ < 0.2 are still in accord with observed Hα profiles. We investigate the wind contribution to the line profile as a function of model parameters, and examine the reliability of Hα as a mass-accretion diagnostic. Finally, we examine the Hα spectroscopic classification used by Reipurth et al., and discuss the basic physical conditions that are required to reproduce the profiles in each classified type.

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.

We present radiative‐transfer modelling of the dusty spiral Pinwheel Nebula observed around the Wolf–Rayet/OB‐star binary WR 104. The models are based on the three‐dimensional radiative‐transfer code torus, modified to include an adaptive mesh that allows us to adequately resolve both the inner spiral turns (subau scales) and the outer regions of the nebula (distances of 104 au from the central source). The spiral model provides a good fit to both the spectral energy distribution and Keck aperture masking interferometry, reproducing both the maximum entropy recovered images and the visibility curves. We deduce a dust creation rate of 8 ± 1 × 10−7 M⊙ yr−1, corresponding to approximately 2 per cent by mass of the carbon produced by the Wolf–Rayet star. Simultaneous modelling of the imaging and spectral data enables us to constrain both the opening angle of the wind–wind collision interface and the dust grain size. We conclude that the dust grains in the inner part of the Pinwheel Nebula are small (∼100 Å), in agreement with theoretical predictions, although we cannot rule out the presence of larger grains (∼1 μm) further from the central binary. The opening angle of the wind–wind collision interface appears to be about 40°, in broad agreement with the wind parameters estimated for the central binary. We discuss the success and deficiencies of the model, and the likely benefits of applying similar techniques to the more complex nebulae observed around other WR/O star binaries.

Context. Classical T Tauri stars are variable objects on several timescales, but just a few of them have been studied in detail, with different observational techniques and over many rotational cycles to enable the analysis of the stellar and circumstellar variations on rotational timescales. Aims. We test the dynamical predictions of the magnetospheric accretion model with synoptic data of the classical T Tauri star V2129 Oph obtained over several rotational cycles. Methods. We analyze high resolution observations obtained with the HARPS, ESPaDOnS, and SMARTS spectrographs and simultaneous photometric measurements, clearly sampling four rotational cycles, and fit them with cold/hot spot models and radiative transfer models of emission lines. Results. The photometric variability and the radial velocity variations in the photospheric lines can be explained by the rotational modulation due to cold spots, while the radial velocity variations of the He i (5876 Å) line and the veiling variability are due to hot spot rotational modulation. The hot and cold spots are located at high latitudes and about the same phase, but the hot spot is expected to sit at the chromospheric level, while the cold spot is at the photospheric level. The mass-accretion rate of the system is stable overall around (1.5 ± 0.6) × 10 −9 M yr −1 , but can increase by three times this value in a rotational cycle, during an accretion burst. The Hα and Hβ emission-line profiles vary substantially and are well-reproduced by radiative transfer models calculated from the funnel flow structure of three-dimensional magnetohydrodynamic simulations, using the dipole+octupole magnetic-field configuration previously proposed for the system. Our diskwind models do not provide a significant contribution to the emission or absorption Hα line profile of V2129 Oph. Conclusions. The global scenario proposed by magnetospheric accretion for classical T Tauri stars is able to reproduce the spectroscopic and photometric variability observed in V2129 Oph.

Classical T Tauri stars (CTTSs) are variable in different time-scales. One type of variability is possibly connected with the accretion of matter through the Rayleigh-Taylor instability that occurs at the interface between an accretion disc and a stellar magnetosphere. In this regime, matter accretes in several temporarily formed accretion streams or 'tongues' which appear in random locations, and produce stochastic photometric and line variability. We use the results of global three-dimensional magnetohydrodynamic simulations of matter flows in both stable and unstable accretion regimes to calculate time-dependent hydrogen line profiles and study their variability behaviours. In the stable regime, some hydrogen lines (e.g. Hβ, Hγ, Hδ, Paβ and Brγ) show a redshifted absorption component only during a fraction of a stellar rotation period, and its occurrence is periodic. However, in the unstable regime, the redshifted absorption component is present rather persistently during a whole stellar rotation cycle, and its strength varies non-periodically. In the stable regime, an ordered accretion funnel stream passes across the line of sight to an observer only once per stellar rotation period while in the unstable regime, several accreting streams/tongues, which are formed randomly, pass across the line of sight to an observer. The latter results in the quasi-stationarity appearance of the redshifted absorption despite the strongly unstable nature of the accretion. In the unstable regime, multiple hot spots form on the surface of the star, producing the stochastic light curve with several peaks per rotation period. This study suggests a CTTS that exhibits a stochastic light curve and a stochastic line variability, with a rather persistent redshifted absorption component, may be accreting in the unstable accretion regime.