We present a panchromatic study, involving a multiple technique approach, of the circumstellar disc surrounding the T Tauri star IM Lupi (Sz 82). We have undertaken a comprehensive observational study of IM Lupi using photometry, spectroscopy, millim
etre interferometry and multi-wavelength imaging. For the first time, the disc is resolved from optical and near-infrared wavelengths in scattered light, to the millimetre regime in thermal emission. Our data-set, in conjunction with existing photometric data, provides an extensive coverage of the spectral energy distribution, including a detailed spectrum of the silicate emission bands. We have performed a simultaneous modelling of the various observations, using the radiative transfer code MCFOST, and analysed a grid of models over a large fraction of the parameter space via Bayesian inference. We have constructed a model that can reproduce all of the observations of the disc. Our analysis illustrates the importance of combining a wide range of observations in order to fully constrain the disc model, with each observation providing a strong constraint only on some aspects of the disc structure and dust content. Quantitative evidence of dust evolution in the disc is obtained: grain growth up to millimetre-sized particles, vertical stratification of dust grains with micrometric grains close to the disc surface and larger grains which have settled towards the disc midplane, and possibly the formation of fluffy aggregates and/or ice mantles around grains.
For young Herbig Ae/Be stars, near-infrared interferometric measurements have revealed a correlation between the luminosity of the central object and the position of the disk inner rim. This correlation breaks down for the cooler T Tauri stars, a fac
t often interpreted in terms of disks with larger inner radii. In most cases, the conversion between the observed interferometric visibility and the calculated disk inner radius was done with a crude disk emission model. Here, we examine how the use of models that neglect scattered light can lead to an overestimation of the disk sizes. To do so, synthetic disk images (and visibilities) are calculated with a full treatment of the radiative transfer. The relative contributions of thermal emission and scattered light are compared. We find that the latter can not be neglected for cool stars. For further comparison, the model visibilities are also converted into inner disk radii using the same simple disk models as found in the literature. We find that reliable inner radii can only be estimated for Herbig Ae/Be stars with these models. However, they lead to a systematic overestimation of the disk size, by a factor of 2 to 3, for T Tauri stars. We suggest that including scattered light in the models is a simple (and sufficient) explanation of the current interferometric measurements of T Tauri stars.
Our objective is to study the vertical dust distribution in the circumbinary ring of the binary system GG Tau and to search for evidence of stratification, one of the first steps expected to occur during planet formation. We present a simultaneous
analysis of four scattered light images spanning a range of wavelength from 800 nm to 3800 nm and compare them with (i) a parametric prescription for the vertical dust stratification, and (ii) with the results of SPH bi-fluid hydrodynamic calculations. The parametric prescription and hydrodynamical calculations of stratification both reproduce the observed brightness profiles well. These models also provide a correct match for the observed star/ring integrated flux ratio. Another solution with a well-mixed, but ``exotic, dust size distribution also matches the brightness profile ratios but fails to match the star/ring flux ratio. These results give support to the presence of vertical stratification of the dust in the ring of GG Tau and further predict the presence of a radial stratification also.
