Effects of the grain temperature distribution on the organic chemistry of protostellar envelopes

Engineering Research Institute ‘Ventspils International Radio Astronomy Centre’ of Ventspils University of Applied Sciences, Inženieru 101, Ventspils, LV-3601, Latvia

^★ Corresponding author; juris.kalvans@venta.lv

Received: 11 August 2024
Accepted: 18 November 2024

Abstract

Context. Dust grains in circumstellar envelopes are likely to have a spread-out temperature distribution.

Aims. We investigate how trends in the 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 advanced treatment of the surface chemistry was used with three grain-temperature trends: a grain temperature proportional to the 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 chemistry and WCCC were investigated for a total of six models. The essence of these changes is that the main ice reservoir (small grains) has a higher (M-1/6) or lower (M1/6) temperature than the surrounding gas.

Results. The chemistry of COMs agrees better with observations in models M-1/6 and M1/6 than in Model M0. Model M-1/6 agrees best 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 reproduce the circumstellar chemistry more precisely.