Resetting chemical clocks of hot cores based on S-bearing molecules

By V. Wakelam, P. Caselli, Cecilia Ceccarelli, E. Herbst, A. Castets. 2004

151 citations recorded by the source corpus.

We report a theoretical study of sulphur chemistry, as applied to hot cores, where S-bearing molecular ratios have been previously proposed and used as chemical clocks. As in previous models, we follow the S-bearing molecular composition after the injection of grain mantle components into the gas phase. For this study, we developed a time-dependent chemical model with up-to-date reaction rate coefficients. We ran several cases, using different realistic chemical compositions for the grain mantles and for the gas prior to mantle evaporation. The modeling shows that S-bearing molecular ratios depend very critically on the gas temperature and density, the abundance of atomic oxygen, and, most importantly, on the form of sulphur injected in the gas phase, which is very poorly known. Consequently, ratios of S-bearing molecules cannot be easily used as chemical clocks. However, detailed observations and careful modeling of both physical and chemical structure can give hints on the source age and constrain the mantle composition (i.e. the form of sulphur in cold molecular clouds) and, thus, help to solve the mystery of the sulphur depletion. We analyse in detail the cases of Orion and IRAS 16293-2422. The comparison of the available observations with our model suggests that the majority of sulphur released from the mantles is mainly in, or soon converted into, atomic form.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/2770a95ce2fb0e998671b8122a99d21e10fa9a10

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In Astronomy and Astrophysics

1. R. Garrod
2. V. Wakelam
3. E. Herbst
4. M. Ruaud
5. E. Dishoeck
6. J. Loison
7. Y. Aikawa
8. P. Caselli

In Instrumentation

1. R. Garrod
2. V. Wakelam
3. E. Dishoeck
4. D. Galli
5. F. Selsis
6. Y. Aikawa
7. Jonathan Tennyson
8. E. Herbst

Citations in the corpus

• Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores (2007, background): “We are dealing here with the formation of a low-mass protostar, so the hot-core stage is more aptly referred to as a “hot corino”, and short time scales have previously been discussed for such regions (Wakelam et al. 2004; Bottinelli et al. 2004a).”
• A KINETIC DATABASE FOR ASTROCHEMISTRY (KIDA) (2012, background): “Other accessible databases exist for particular cases such as Srates2 for sulfur chemistry (Wakelam et al. 2004, 2011), a database for shock models (Pineau des Forets et al. 1993) and one for photon-dominated regions3 (Le Petit et al. 2006).”
• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores (2006, background): “Moreover, the levels of sulphur-bearing species detected in the gas phase of hot cores are typically not as high as the levels detected in diffuse clouds (see e.g. Wakelam et al. 2004a).”
• On the reservoir of sulphur in dark clouds : chemistry and elemental abundance reconciled (2017, background): “…molecules are indeed often used to probe the physical structure of star-forming regions (Lada et al. 1991; Plume et al. 1997; Viti et al. 2001; Sakai et al. 2014; Podio et al. 2015) and have been proposed as chemical clocks for hot cores (Charnley 1997; Hatchell et al. 1998; Wakelam et al. 2004).”