NEAR-IR EXCESS OF BE STARS

The near-IR excess emission of 144 Be stars is derived from visual and near-IR observations. The quasi-simultaneous nature of the observatio ns provide colour excesses that are independent of temporal variations . Colour-colour diagrams are used to identify stars with excess colour s markedly different from the bulk of the sample stars. The near-IR em ission of four stars that have markedly different colours is attribute d to the presence of a binary companion or thermal dust emission. The percentage of stars with a significant excess increases with wavelengt h. The excess emission increases with wavelength and the largest exces ses occur in stars of earlier spectral type. The near-IR excess colour s are examined and compared to theoretical excess colours calculated f rom a simple bremsstrahlung emitting disc model with a radial density distribution of the form rho proportional to r(-beta). The effect of m odel parameters on the excess colours is discussed. The observed exces ses for the bulk of the stars are well fit by circumstellar discs with radii greater than similar to 10R and with a density index beta, in the range 2.0 - 5.0. This is very similar to the range of values previ ously determined by Waters et al. (1987) from IRAS far-IR observations . A small number of stars cannot be reconciled with discs with a const ant density index out to 10R. It is argued that the circumstellar pla sma around these stars has a change in structure at similar to 2 - 1OR . The possibilities of disc truncation or a change in the density ind ex as the cause of the structure change are discussed.