Hunting pre-stellar cores with APEX: Overview

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Context . Pre-stellar cores are centrally concentrated starless cores on the verge of star formation and they represent the initial conditions for star and planet formation. Pre-stellar cores host an active organic chemistry and isotopic fractionation, kept stored in thick icy mantles, that can be inherited by the future protoplanetary disks and planetesimals. It is therefore important to study pre-stellar cores, but this is difficult as they are short-lived, and thus rare. So far, only a few pre-stellar cores have been studied in detail, with special attention being paid to the prototypical pre-stellar core L1544 in the Taurus Molecular Cloud. Aims . Our aim is to identify nearby (<200 pc) pre-stellar cores in an unbiased way, to build a sample that can then be studied in detail. This will also allow us to explore the effect of the environment on the chemical and physical structure of pre-stellar cores. Methods . We first used the archival Herschel Gould Belt Survey data, selecting all those starless cores with central H 2 number densities higher than or equal to 3×10 5 cm −3 , the density of L1544 within the Herschel beam of 20″. The selected 40 (out of 1746) cores were then observed in N 2 H + (3–2) and N 2 D + (4–3) using the APEX antenna. Results . Following a simple analysis, a total of 17 bona fide (i.e., with a deuterium fraction larger than 10%) pre-stellar cores have been identified. Another 16 objects can also be considered pre-stellar, as they are dynamically evolved starless cores, but their deuterium fractions is relatively low (<10%); thus, they deserve further scrutiny to unveil the source of the low deuteration. Of the remaining seven objects, six have been found to be associated with a young stellar object, and one (CrA 151) presents hints of a very young (or very low-luminosity) stellar object. Conclusions . Dust continuum emission, together with spectroscopic observations of N 2 H + (3–2) and N 2 D + (4–3), is a powerful tool to identify pre-stellar cores in molecular clouds. Detailed modeling of the physical structure of the objects is now required to reconstruct the chemical composition as a function of radius. This work has provided a statistically significant sample of 33 pre-stellar cores, a crucial step in the understanding of the process of star and planet formation.

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