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

Abstract

Context. 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: CH3OH, HCOOCH3, CH3OCH3, CH318OH, CH2DOH, CH3COCH3, CH3CHO, CH3CN, 13CH3CN, C2H5CN, and NH2CHO. Remarkably, we find a possible enhancement in the HCOOCH3 abundance with respect to other known hot corinos. Indeed, the [CH3OCH3]/[HCOOCH3] abundance ratio in this source is ~0.2 and, within the uncertainties, it deviates from the known correlation marginally where [CH3OCH3]/[HCOOCH3] ~1. A relatively low [CH2DOH]/[CH3OH] 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 [CH3OCH3]/[HCOOCH3] and [CH2DOH]/[CH3OH] 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.

Chemical and Physical Characterization of the Isolated Protostellar Source CB68: FAUST IV

“…Indeed, the CH 3 OCH 3 /HCOOCH 3 ratio in CB68 is 0.74 ± 0.11, which is almost comparable to those for the other sources. A trend of the constant CH 3 OCH 3 /HCOOCH 3 ratio is also reported by (Chahine et al 2022). On the other hand, the other ratios shows some variation from source to source.…”

“…CB 68 (L146) is a small, nearby, slightly comet-shaped opaque Bok globule located in the outskirts of the Ophiuchus molecular cloud complex (Nozawa et al 1991;Lemme et al 1996;Launhardt & Henning 1997;Launhardt et al 1998). The canonical distance to the Ophiuchus molecular cloud complex of 160 pc has been used historically (Chini 1981;Launhardt & Henning 1997;Launhardt et al 2010). However, Lombardi et al (2008) reported the distance to the Ophiuchus molecular cloud complex to be 119 ± 6 pc by using the Hipparcos and Tycho parallax measurements with the Two Micron All Sky Survey data.…”

The chemical nature of Orion protostars: Are ORANGES different from PEACHES? ORANGES II

“…SIMBA-a seems to have a lower methanol abundance than the other sources but since the LVG analysis has been performed with only a few data points for most of the sources, the accuracy of the fit is not very elevated. So far, only three hot corinos have been identified in the OMC-2/3 filament, the intermediate mass protostars HOPS-87 and HOPS-370 (Hsu et al 2020;Tobin et al 2019), and HOPS-108 (Tobin et al 2019;Chahine et al 2022). One of the questions we aim to answer is: how many hot corinos are present in the OMC-2/3 filament?…”

“…On the other hand, we targeted 19 solar-mass protostars located in the OMC-2/3 filament and detected only five bona fide hot corinos. Even though three other hot corinos are located in the OMC-2/3 filament (HOPS-87, HOPS-370, HOPS-108; Tobin et al 2019;Hsu et al 2020;Chahine et al 2022) we do not take them into account. Indeed, unlike the above-cited studies, we performed a blind search for hot corinos using an observational setup completely analogous to that done in Perseus by Yang et al (2021).…”

“…The closest and best analogue of our Sun's birth environment is the OMC-2/3 filament, located in the Orion A molecular cloud. Very recently, three hot corinos were detected in this region, the intermediate-mass protostars HOPS-87 (also known as MMS6) and HOPS-370 (also known as OMC2-FIR3) (Hsu et al 2020;Tobin et al 2019) and the solar-type protostar HOPS-108 located in the OMC-2 FIR4 protocluster (Tobin et al 2019;Chahine et al 2022). Although hot corinos are present in massive SFRs (Codella et al 2016;Hsu et al 2020;Chahine et al 2022), the statistics is too poor to draw any conclusion on the chemical past of our Sun.…”