COLD DUST AROUND SOUTHERN HERBIG AE BE STARS

The results of a 1.3 millimetre continuum pilot search for cold dust a round southern Herbig Ae/Be stars are presented. Significant millimetr e flux was detected from 17 of the 33 target objects. The data show no significant correlation between the infrared spectral index and the c ircumstellar dust mass. However, the Lada class II objects have in the average lower masses compared with the class I objects pointing to an evolutionary effect. Analysing the relation between fluxes scaled to a fixed distance and luminosities, we find a linear dependence in agre ement with a relation found for less luminous young stellar objects. W e use a radiative transfer code for spherically symmetric envelopes wi th different dust components to model the spectra of selected objects and to deduce the dust mass. The spherical model fails to account for the high millimetre flux in the flat spectrum of the class II object H D 163296 even if amorphous carbon and fractal dust particles are consi dered. In this case, we applied a thin disk model which results in a f lat energy distribution and can explain the 1.3 mm flux. In addition, we discuss the R Coronae Australis region in more detail. We show that the strongest millimetre source in this area is not R CrA or T CrA bu t the deeply embedded infrared source IRS 7 which shares a number of p roperties with the well-known source L 1551-IRS5.