Poster Open Access

Understanding Chemical Complexity in Protostellar Outflows L1157-B1 Star Forming Region

Kavak, U.; Viannet, T.


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    <subfield code="a">&lt;p&gt;During the early evolutionary stages of star formation, molecular outflows are&amp;nbsp;produced by the shocked gas interaction between high-velocity jets driven by the&amp;nbsp;protostar and the ambient material. Shocks quickly release the content of interstellar ices into the gas phase through ice sputtering and trigger a rich endothermic gas-phase chemistry. Spatially resolved molecular outflows are known to be chemically rich&amp;nbsp;with the detection of several dozens of species and provide us a laboratory to&amp;nbsp;test different chemical scenarios. Complex Organic Molecules (COMs), molecules based on carbon chemistry and probably at the origin of the prebiotic&amp;nbsp;chemistry we see in our Solar System, have been routinely detected around&amp;nbsp;protostars in large quantities. The presence of many COMs has been understood&amp;nbsp;as due to warm surface chemistry triggered by UV photolysis. The recent&amp;nbsp;detection of several COMs towards the protostellar outflow prototype L1157-B1 challenges our&amp;nbsp;current understanding of the chemistry producing these COMs. The large distance of the&amp;nbsp;source with respect to the central heating protostar (about 60 arcsec) suggests that&amp;nbsp;the pre-shock material is too cold to efficiently produce COMs through warm surface chemistry.&amp;nbsp;&lt;/p&gt;

&lt;p&gt;In this project, we theoretically studied the formation and evolution of COMs&amp;nbsp;occurring in molecular outflows. For this purpose, the results of a state-of-the-art 1D&amp;nbsp;physical shock model were applied to a gas-grain astrochemical model&amp;nbsp;in order to assess whether COMs can be produced in molecular outflows through gas-phase&amp;nbsp;chemistry. Then, the results of the model predictions were compared with recent&amp;nbsp;observations carried out with modern sub-millimeter facilities of the prototype outflow L1157-B1.&amp;nbsp;&lt;br&gt;
It is concluded that dimethyl ether (DME) and methyl formate (MF), the two most&amp;nbsp;abundant COMs in star-forming regions can be produced in significant quantities in shock regions.&lt;/p&gt;

&lt;p&gt;The production of these COMs in shocks is mostly due to of neutral-neutral chemistry, triggered&amp;nbsp;by the destruction of methanol through reactions involving atomic H forming the CH$_2$OH and&amp;nbsp;CH$_3$O radicals. Nevertheless, it seems that gas-phase chemistry alone only accounts for a&amp;nbsp;significant but not entire&amp;nbsp;part of the observed DME and MF abundances of a few percent with&amp;nbsp;respect to methanol. Alternative pathways, such as cold surface chemistry, for instance,&amp;nbsp;could also play a role.&lt;/p&gt;</subfield>
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