Hunting pre-stellar cores with APEX: Overview

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
³ Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
⁴ Institute for Advanced Study, Kyushu University, Japan
⁵ Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
⁶ Univ. Rennes, CNRS, IPR (Institut de Physique de Rennes) – UMR 6251, 35000 Rennes, France
⁷ Department of Space, Earth, and Environment, Chalmers University of Technology, 412 96 Gothenburg, Sweden ,
⁸ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

^★ Corresponding author: caselli@mpe.mpg.de

Received: 19 June 2025
Accepted: 29 August 2025

Abstract

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 H₂ number densities higher than or equal to 3×10⁵ cm⁻³, the density of L1544 within the Herschel beam of 20″. The selected 40 (out of 1746) cores were then observed in N₂H⁺ (3–2) and N₂D⁺ (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 N₂H⁺ (3–2) and N₂D⁺ (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.