Abstract
Context.Pre-stellar cores (PSCs) are units of star formation. Besides representing early stages of the dynamical evolution leading to the formation of stars and planets, PSCs also provide a substrate for incipient chemical complexity in the interstellar space.Aims.Our aim is to understand the influence of external conditions on the chemical composition of PSCs. For this purpose, we compared molecular column densities in two typical PSCs, L183 and L1544, which are embedded in different environments.Methods.A single-pointing survey of L183 atλ= 3 mm was conducted using the IRAM 30-m single-dish antenna. This led to the detection of more than 100 emission lines from 46 molecular species. The molecular column densities and excitation temperatures derived from these lines were compared to the corresponding parameters in L1544. The data for L1544 were obtained from literature or publicly available surveys, and they were analysed using the same procedure as adopted for L183. An astrochemical model, previously developed for the interpretation of organic molecule emissions towards the methanol peak of L1544, was used to interpret the combined data.Results.Our analysis reveals clear chemical differences between the two PSCs. While L1544 is richer in carbon-bearing species, in particular carbon chains, oxygen-containing species are generally more abundant in L183. The results are well-reproduced by our chemical model.Conclusions.The observed chemical differentiation between the two PSCs is caused by the different environmental conditions: the core of L183 is deeply buried in the surrounding cloud, whereas L1544 lies close to the edge of the Taurus Molecular Cloud. The obscuration of L183 from the interstellar radiation field (ISRF) allows the carbon atoms to be locked in carbon monoxide, which ultimately leads to a large abundance of O-bearing species. In contrast, L1544, being more affected by the ISRF, can keep a fraction of carbon in atomic form, which is needed for the production of carbon chains.
Highlights
Cold dark clouds represent a very unique environment to test our knowledge of the chemical and physical evolution of the structures that led to life
The molecular column densities derived towards the dust peak of L183 with our observations were first compared with those obtained in L1544, and successively with those predicted by our astrochemical model
A sensitive, single-pointing survey of the pre-stellar core L183 was conducted in the 3 mm-wave region with the IRAM 30 m antenna
Summary
Cold dark clouds represent a very unique environment to test our knowledge of the chemical and physical evolution of the structures that led to life. Pre-stellar cores (PSCs), which are dynamically evolved starless cores (such as L183; known as L134N), represent the first phases of the star-formation process and breeding grounds of chemical complexity. Despite their apparent simplicity and the lack of internal energy sources, PSCs exhibit a surprisingly complex molecular inventory and large variations in the abundances. Spezzano et al 2016a), as well as among, different starless and pre-stellar cores Based on observations carried out with the IRAM 30m Telescope.
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