Complex molecules toward low-mass protostars: the Serpens core

TL;DR

This study detects and analyzes complex organic molecules in the Serpens core's low-mass protostars, revealing similar abundance levels to high-mass hot cores and insights into ice photochemistry processes.

Contribution

First detection of complex organic molecules in multiple low-mass protostars within the Serpens core, expanding understanding of astrochemistry in low-mass star-forming regions.

Findings

Complex organics detected in all sources with narrow lines.

Abundances vary by an order of magnitude, highest in SMM1.

HCOOCH3 is relatively more abundant in low-mass protostars.

Abstract

Gas-phase complex organic molecules are commonly detected toward high-mass protostellar hot cores. Detections toward low-mass protostars and outflows are comparatively rare, and a larger sample is key to investigate how the chemistry responds to its environment. Guided by the prediction that complex organic molecules form in CH3OH-rich ices and thermally or non-thermally evaporate with CH3OH, we have identified three sight-lines in the Serpens core - SMM1, SMM4 and SMM4-W - which are likely to be rich in complex organics. Using the IRAM 30m telescope, narrow lines (FWHM of 1-2 km s-1) of CH3CHO and CH3OCH3 are detected toward all sources, HCOOCH3 toward SMM1 and SMM4-W, and C2H5OH not at all. Beam-averaged abundances of individual complex organics range between 0.6 and 10% with respect to CH3OH when the CH3OH rotational temperature is applied. The summed complex organic abundances also vary by an order of magnitude, with the richest chemistry toward the most luminous protostar SMM1. The range of abundances compare well with other beam-averaged observations of low-mass sources. Complex organic abundances are of the same order of magnitude toward low-mass protostars and high-mass hot cores, but HCOOCH3 is relatively more important toward low-mass protostars. This is consistent with a sequential ice photochemistry, dominated by CHO-containing products at low temperatures and early times.