Effects of grain temperature distribution on organic protostellar envelope chemistry

TL;DR

This study explores how different temperature distributions among dust grains in protostellar envelopes influence complex organic molecule chemistry and warm carbon-chain chemistry, improving the match with observations.

Contribution

It introduces a multi-grain astrochemical model with varied temperature trends, enhancing the understanding of grain temperature effects on envelope chemistry.

Findings

Models with varied grain temperatures better match observed COMs.

Lower temperature variation models favor WCCC at lower temperatures.

Multiple grain populations improve chemical modeling accuracy.

Abstract

Context. Dust grains in circumstellar envelopes are likely to have a spread-out temperature distribution. Aims. To investigate how trends in temperature distribution between small and large grains affect the hot corino chemistry of complex organic molecules (COMs) and warm carbon-chain chemistry (WCCC). Methods. A multi-grain multi-layer astrochemical code with an up-to-date treatment of surface chemistry was used with three grain temperature trends: grain temperature proportional to grain radius to the power -1/6 (Model M-1/6), to 0 (M0), and to 1/6 (M1/6). The cases of hot corino and WCCC chemistry were investigated, for a total of six models. The essence of these changes is for the main ice reservoir - small grains - having higher (M-1/6) or lower (M1/6) temperature than the surrounding gas. Results. The chemistry of COMs shows better agreement with observations in models M-1/6 and M1/6 than in Model M0. Model M-1/6 shows best agreement for WCCC because earlier mass-evaporation of methane ice from small grains induces the WCCC phenomenon at lower temperatures. Conclusions. Models considering several grain populations with different temperatures can more precisely reproduce circumstellar chemistry.