The 90-110 μm dust feature in low to intermediate mass protostars: Calcite?

We present ISO spectra between 60 and 180 μm of 32 protostars of low to intermediate mass. About half of the spectra present a dust feature between ~90 and ~110 μm. We describe the observational characteristics of this feature, which seems to be due to one single carrier. In Class 0 sources the feature peaks around 100 μm, while in AeBe stars it peaks around 95 μm. The feature peak position seems to mostly depend on the temperature of the dust of the source, suggesting reprocessing of the dust. We present arguments for the identification of the observed feature as due to calcite, and estimate that about 10% to 30% of elemental Ca is locked up in it. Therefore, calcite seems to be formed relatively easily around protostars despite the observation that on Earth it needs aqueous solutions. This rises the question of whether conditions simulating liquid water are common around forming stars and what creates them.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) with the participation of ISAS and NASA.