Organic chemistry in the protosolar analogue HOPS-108: Environment matters

Abstract

Hot corinos are compact regions around solar-mass protostellar objects that are very rich in interstellar Complex Organic Molecules (iCOMs). How the abundance of these molecules is affected by the environmental physical conditions is still an open question. More specifically, addressing this point is key to understand our own chemical origins since the Solar System formed in a large cluster of low- to high-mass stars and was therefore subject to external heating and ultraviolet irradiation which may have shaped the chemistry of its early formation stages. Aims. The goal of this high resolution study is to determine the abundance ratios of iCOMs in HOPS-108, which is a Class 0 protostar and a hot corino candidate located in the nearest Solar System analogue, the protostellar cluster OMC-2 FIR 4, in Orion. We aim to compare the abundance ratios to those found in other hot corinos, which are all located in less crowded environments, in order to understand the impact of environmental conditions on hot corinos' chemistry. Methods. We observed the OMC-2 FIR 4 proto-cluster using the Band 6 of the Atacama Large (sub-)Millimetre Array in Cycle 4 with an angular resolution of ~0.′′28 (110 au). We determined the abundances and temperature of the species using local thermodynamic equilibrium (LTE) and non-LTE analysis. Results. Our results reveal a rich organic chemistry towards HOPS-108, asserting that it is a hot corino where the following iCOMs are detected: CH 3 OH, HCOOCH 3 , CH 3 OCH 3 , CH 3 18OH, CHDOH, CH 3 COCH 3 , CH 3 CHO, CH 3 CN, 13CH 3 CN, CH 5 CN, and NHCHO. Remarkably, we find a possible enhancement in the HCOOCH 3 abundance with respect to other known hot corinos. Indeed, the [CH 3 OCH 3 ]/[HCOOCH 3 ] abundance ratio in this source is ~0.2 and, within the uncertainties, it deviates from the known correlation marginally where [CH 3 OCH 3 ]/[HCOOCH 3 ] ~1. A relatively low [CHDOH]/[CH 3 OH] abundance ratio of ~0.02 is also obtained, which is in agreement with that found in another Orion source, HH212, suggesting a higher gas temperature during the early phases of ice mantle formation. Conclusions. The [CH 3 OCH 3 ]/[HCOOCH 3 ] and [CHDOH]/[CH 3 OH] abundance ratios in HOPS-108 might result from different physical conditions in the Orion molecular complex compared to other regions. The former ratio cannot be reproduced with current chemical models, highlighting the importance of improving the chemical networks with theoretical calculations. More hot corinos located in heavily clustered regions such as Orion should be targeted in order to measure these ratios and evaluate whether they are an environmental product or whether HOPS-108 is an exceptional hot corino overall.