Spectroastrometry and NLTE modelling of the disc around the Be star beta CMi

To understand what processes result in the creation Be star discs and how angular momentum is transported within them, 
their physical properties must be constrained. This requires comparing high spatial and spectral resolution data with detailed 
radiative transfer modelling. We present a high spectral resolution, R~80,000, sub milli-arcsecond precision, 
spectroastrometric study of the circumstellar disc around the Be star beta CMi. The data are confronted with 
three-dimensional, NLTE radiative transfer calculations to directly constrain the properties of the disc. The observed SED, 
polarisation and spectroastrometric signature of beta CMi can be well reproduced by a low density viscous disc model. The 
agreement between the model and the extensive data-set confirms that the discs around Be stars are best modelled as 
viscous decretion discs.