Modelling the dust grains around the peculiar Be star HD 45677

Numerical radiative transfer models are used to study circumstellar dust grains around the peculiar Be star HD 45677. The modeling technique is to fit the observed far-ultraviolet through far-infrared energy distribution with the energy distributions predicted for a spherical dust shell around a luminous hot star. Such a simultaneous multi-wavelength study makes it possible to strengthen constraints on dust-grain properties. It is found that the observations can be fitted with the emergent spectrum of a spherical shell consisting of a graphite–silicate mixture. The grain-size distribution is similar to that for diffuse cloud dust |$N(a) \approx A \enspace a^{-3.5}$|⁠, but the circumstellar dust contains large grains with a maximum size ≈ 1 µm. This result is consistent with a scenario in which HD 45677 is a young stellar object (≤ 108 yr), with the dust shell being a fossil of the molecular cloud left over from star formation.