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 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.

We present three‐dimensional Monte Carlo radiative‐transfer models of a very young (<105 yr old) low‐mass (50 M⊙) stellar cluster containing 23 stars and 27 brown dwarfs. The models use the density and the stellar mass distributions from the large‐scale smoothed particle hydrodynamics (SPH) simulation of the formation of a low‐mass stellar cluster by Bate, Bonnell and Bromm. Using adaptive mesh refinement, the SPH density is mapped to the radiative‐transfer grid without loss of resolution. The temperature of the ISM and the circumstellar dust is computed using Lucy's Monte Carlo radiative equilibrium algorithm. Based on this temperature, we compute the spectral energy distributions of the whole cluster and the individual objects. We also compute simulated far‐infrared Spitzer Space Telescope (SST) images (24‐, 70‐, and 160‐μm bands) and construct colour–colour diagrams (near‐infrared HKL and mid‐infrared SST bands). The presence of accretion discs around the light sources influences the morphology of the dust temperature structure on a large scale (up to several 104 au). A considerable fraction of the interstellar dust is underheated compared with a model without the accretion discs because the radiation from the light sources is blocked/shadowed by the discs. The spectral energy distribution (SED) of the model cluster with accretion discs shows excess emission at λ= 3–30 μm and λ > 500 μm, compared with that without accretion discs. While the former excess is caused by the warm dust present in the discs, the latter is caused by the presence of the underheated (shadowed) dust. Our model with accretion discs around each object shows a similar distribution of spectral index (2.2–20 μm) values (i.e. Class 0–III sources) to that seen in the ρ Ophiuchus cloud. We confirm that the best diagnostics for identifying objects with accretion discs are mid‐infrared (λ= 3–10 μm) colours (e.g. SST IRAC bands) rather than HKL colours.

We present measurements of the longitudinal magnetic field in the circumstellar environment of seven classical T Tauri stars. The measurements are based on high-resolution circular spectropolarimetry of the He I 5876 emission line, which is thought to form in accretion streams controlled by a stellar magnetosphere. We detect magnetic fields in BP Tau, DF Tau and DN Tau, and detect statistically significant fields in GM Aur and RW Aur A at one epoch but not at others. We detect no field for DG Tau and GG Tau, with the caveat that these objects were observed at one epoch only. Our measurements for BP Tau and DF Tau are consistent, both in terms of sign and magnitude, with previous studies, suggesting that the characteristics of T Tauri magnetospheres are persistent over several years. We observed the magnetic field of BP Tau to decline monotonically over three nights, and have detected a peak field of 4kG in this object, the highest magnetic field yet observed in a T Tauri star. We combine our observations with results from the literature in order to perform a statistical analysis of the magnetospheric fields in BP Tau and DF Tau. Assuming a dipolar field, we determine a polar field of ~3kG and a dipole offset of 40deg for BP Tau, while DF Tau's field is consistent with a polar field of ~-4.5kG and a dipole offset of 10deg. We conclude that many classical T Tauri stars have circumstellar magnetic fields that are both strong enough and sufficiently globally-ordered to sustain large-scale magnetospheric accretion flows.Comment: 8 pages, 3 figures. Accepted by MNRAS. Corrected typo

We present hydrogen emission line profile models of magnetospheric accretion onto Classical T Tauri stars. The models are computed under the Sobolev approximation using the three-dimensional Monte Carlo radiative-transfer code TORUS. We have calculated four illustrative models in which the accretion flows are confined to azimuthal curtains - a geometry predicted by magneto-hydrodynamical simulations. Properties of the line profile variability of our models are discussed, with reference to dynamic spectra and cross-correlation images. We find that some gross characteristics of observed line profile variability are reproduced by our models, although in general the level of variability predicted is larger than that observed. We conclude that this excessive variability probably excludes dynamical simulations that predict accretion flows with low degrees of axisymmetry.Comment: 14 pages, 12 figures. Published in MNRA