Its evolutionary stage is unknown. HD 45677 might be an ideal star to study the dust formation process. It is different from the other stars which we studied because of the really bright near-infrared excess. This excess can be attributed to the presence of metallic iron. At longer wavelengths, however, the dust seems to be identical to that detected in the circumstellar environment of HD 179218, i.e. dominated by crystalline enstatite and forsterite.
Some evolutionary trend is apparent.
Crystalline silicate features pop up here and there. Whereas the crystalline silicates identified in HD 142527 have high temperatures, this is not the case for HD 100546, which is definitely the most evolved object, and not for HD 179218. It can be seen that pyroxene bands contribute much more than in the case of HD 100546. This migration process can as well cause the cooling of the crystalline silicates in a later stage of evolution, as seen in the other objects. Mechanisms must be found to explain how crystalline silicates are hidden or even destroyed in the interstellar medium.