Water protostars

Carbonates are common in hydrous meteorites and hydrous IDPs, where they are believed to have formed by parent-body aqueous processing. Since simple models of cometary evolution involve no aqueous processing, carbonates were generally presumed not to occur in comets. However, carbonates have also been detected by infrared spectroscopy in the dust shell around evolved stars and in protostars, where liquid water is not expected (Ceccarelli et al. 2002 Kemper et al. 2002). Indeed, Toppani et al. (2005) have performed experiments that indicate that carbonates can be formed by non-equilibrium condensation in circumstellar environments where water is present as vapor, not as liquid. Detections of carbonates in other exosolar systems are reported by Ceccarelli et al. (2002) and Chiavassa et al. (2005). 

Observed abundances normalized to that of water ice (=100). W33A and NGC 7538-IRS 9 are two luminous protostars which span the observed range in interstellar ice composition. The abundances for the comets are an average of those observed for comets Hyakutake and Hale-Bopp. 

Water signatures in protostars have been observed already 30 years ago. Hydroxyl and Water Masers in Protostars were discussed e.g. by Litvak, 1969 [204]. The first detection of interstellar water molecules was made by Cheung et al., 1969 [67]. They analyzed the 1.35 cm microwave emission in the sources Sgr B 2, Orion and W 49. For numerical calculations, de Jong, 1973 [100] used the abundance of water relative to hydrogen as 10 that means for 10 molecules or atoms of hydrogen there is one H2O molecule. 

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