Abstract
Context. Solar-like protostars are known to be chemically rich, but it is not yet clear how much their chemical composition can vary and why. So far, two chemically distinct types of Solar-like protostars have been identified: hot corinos, which are enriched in interstellar Complex Organic Molecules, such as methanol (CH3OH) or dimethyl ether (CH3OCH3), and warm carbon chain chemistry (WCCC) objects, which are enriched in carbon chain molecules, such as butadiynyl (C4H) or ethynyl radical (CCH). However, none of these have been studied so far in environments similar to that in which our Sun was born, that is, one that is close to massive stars. Aims. In this work, we search for hot corinos and WCCC objects in the closest analogue to the Sun’s birth environment, the Orion Molecular Cloud 2/3 (OMC-2/3) filament located in the Orion A molecular cloud. Methods. We obtained single-dish observations of CCH and CH3OH line emission towards nine Solar-like protostars in this region. As in other similar studies of late, we used the [CCH]/[CH3OH] abundance ratio in order to determine the chemical nature of our protostar sample. Results. Unexpectedly, we found that the observed methanol and ethynyl radical emission (over a few thousands au scale) does not seem to originate from the protostars but rather from the parental cloud and its photo-dissociation region, illuminated by the OB stars of the region. Conclusions. Our results strongly suggest that caution should be taken before using [CCH]/[CH3OH] from single-dish observations as an indicator of the protostellar chemical nature and that there is a need for other tracers or high angular resolution observations for probing the inner protostellar layers.
Highlights
A key aspect of the chemical richness of the protostellar stage is the diversity found among Solar-like protostars
The goal of the present work is twofold: (1) to identify the nature of several protostars, hot corinos, or warm carbon chain chemistry (WCCC) objects in a region containing high-mass stars and whether it depends on the object position in the cloud; this will help us to understand whether the Sun passed through a hot corino or a WCCC object phase
To give an idea of the behaviour of the targeted sources over the full Orion Molecular Cloud 2/3 (OMC-2/3) filament, in Fig. 9 we show the gas temperature and density, CCH and CH3OH-E column densities, and the [CCH]/[CH3OH] abundance ratio derived towards each source from the non-local thermal equilibrium (LTE) analysis as a function of the source projected distance from the Trapezium OB cluster
Summary
A key aspect of the chemical richness of the protostellar stage is the diversity found among Solar-like protostars. Warm carbon chain chemistry (hereafter WCCC; Sakai et al 2008, Sakai & Yamamoto 2013) objects have an inner region deficient in iCOMs but a large (≈2000 au) zone enriched in carbon chain molecules (e.g. CCH, c-C3H2, C4H). This dichotomy does not seem to be absolute as at least one source, the protostar L483, presents both hot corino and WCCC characteristics (Oya et al 2017). We recall that the Solar System formed in a large stellar cluster in proximity to high-mass stars (M∗ ≥ 8 M ; Adams 2010, Pfalzner et al 2015)
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