Chemical Differentiation toward the Pipe Nebula Starless Cores

TL;DR

This study used IRAM 30-m observations to classify starless cores in the Pipe Nebula based on their molecular line emissions, revealing three distinct chemical groups linked to core density and evolution.

Contribution

It introduces a new observational classification of starless cores based on molecular line emission normalized by visual extinction, highlighting chemical differentiation.

Findings

Identified three chemical groups: diffuse, oxo-sulfurated, and deuterated cores.

Revealed chemical evolution stages prior to star formation.

Suggested possible failed core based on spectral properties.

Abstract

We used the new IRAM 30-m FTS backend to perform an unbiased ~15 GHz wide survey at 3 mm toward the Pipe Nebula young diffuse starless cores. We found an unexpectedly rich chemistry. We propose a new observational classification based on the 3 mm molecular line emission normalized by the core visual extinction (Av). Based on this classification, we report a clear differentiation in terms of chemical composition and of line emission properties, which served to define three molecular core groups. The "diffuse" cores, Av<~15, show poor chemistry with mainly simple species (e.g. CS and CCH). The "oxo-sulfurated" cores, Av~15--22, appear to be abundant in species like SO and SO2, but also in HCO, which seem to disappear at higher densities. Finally, the "deuterated" cores, Av>~22, show typical evolved chemistry prior to the onset of the star formation process, with nitrogenated and deuterated species, as well as carbon chain molecules. Based on these categories, one of the "diffuse" cores (Core 47) has the spectral line properties of the "oxo-sulfurated" ones, which suggests that it is a possible failed core.