The absence of the 10 μm silicate feature in the isolated Herbig Ae star HD 100453

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We analyse the optical and IR spectra, as well as the spectral energy distribution (UV to mm) of the candidate Herbig Ae star HD 100453. This star is particular, as it shows an energy distribution similar to that of other isolated Herbig Ae/Be stars (HAEBEs), but unlike most of them, it does not have a silicate emission feature at 10 μ m, as is shown in Meeus et al. ([CITE]). We confirm the HAEBE nature of HD 100453 through an analysis of its optical spectrum and derived location in the H-R diagram. The IR spectrum of HD 100453 is modelled by an optically thin radiative transfer code, from which we derive constraints on the composition, grain-size and temperature distribution of the circumstellar dust. We show that it is both possible to explain the lack of the silicate feature as (1) a grain-size effect – lack of small silicate grains, and (2) a temperature effect – lack of small, hot silicates, as proposed by Dullemmond et al. ([CITE]), and discuss both possibilities.