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Pre-stellar cores within molecular clouds provide the very initial conditionsin which stars are formed. We use the IRAM 30m telescope and the PdBI to studythe chemical and physical properties of the starless core FeSt 1-457 (Core109), in the Pipe nebula. We fit the hyperfine structure of the N2H+(1-0) IRAM30m data. This allow us to measure with high precision the velocity field, linewidths and opacity and derive the excitation temperature and column density inthe core. We use a modified Bonnor-Ebert sphere model adding a temperaturegradient towards the center to fit the 1.2 mm continuum emission and visualextinction maps. Using this model, we estimate the abundances of the N2H+ andthe rest of molecular lines detected in the 30 GHz wide line survey performedat 3 mm with IRAM 30m using ARTIST software. The core presents a rich chemistrywith emission from early (C3H2, HCN, CS) and late-time molecules (e.g., N2H+),with a clear chemical spatial differentiation for nitrogen, oxygen andsulphurated molecules. For most of the molecules detected (HCN, HCO+, CH3OH,CS, SO, 13CO and C18O), abundances are best fitted with three values,presenting a clear decrease of abundance of at least 1 or 2 orders of magnitudetowards the center of the core. The Bonnor-Ebert analysis indicates the core isgravitationally unstable and the magnetic field is not strong enough to avoidthe collapse. Depletion of molecules onto the dust grains occurs at theinterior of the core, where dust grain growth and dust depolarization alsooccurs. This suggests that these properties may be related. On the other hand,some molecules exhibit asymmetries in their integrated emission maps, whichappear to be correlated with a previously reported submillimetre polarizationasymmetry. These asymmetries could be due to a stronger interstellar radiationfield in the western side of the core.

A correlation between chemistry, polarization and dust properties in the Pipe Nebula starless core FeSt 1-457