# Spectral Survey of the Star Formation Region DR21OH in the 4 mm Wavelength Range

**Authors:** S. V. Kalenskii, E. A. Mikheeva  
**arXiv:** [2310.03858](https://arxiv.org/abs/2310.03858)  
**Date:** 2023-10-05  
**Summary page:** https://www.summarizepaper.com/en/paper/2310.03858v1/

## Key points

- Spectral survey of massive star formation region DR21OH in the 4-mm wavelength range
- Detection of 69 molecules and their isotopologues, including simple diatomic/triatomic species and complex organic molecules
- Qualitative repetition of results from survey at 3 mm with overlap in inventories of molecules found
- Discovery of species at 4 mm with no allowed transitions in the 3-mm range (e.g., DCN, DNC, SO+)
- Presence of common dense core molecules (e.g., HC3N, CH3CCH) and hot core species (e.g., CH3OCHO, CH3CH2OH) detected at 30 K gas temperature
- Calculation of ratios Ri = Ti/Tref based on brightness temperatures for further analysis of molecular cloud composition
- Methodology involving equal line widths assumption, optical depth τi determination, and amplitude ∆Ti calculation using ∆Ti = (Tex − Tbg) × (1 − exp(−τi)) under LTE conditions.

## Summary

The results of a spectral survey of the region of massive star formation DR21OH in the 4-mm wavelength range are presented. Sixty-nine molecules and their isotopologues have been detected, ranging from simple diatomic or triatomic species such as SO, SiO and CCH, to complex organic molecules such as CH$_3$OCHO or CH$_3$OCH$_3$. The obtained results qualitatively repeat the results of the survey of the same source at 3~mm. The inventories of molecules found at 3mm and 4mm overlap to a great extent. However, at 4 mm we found a number of species that have no allowed transitions in the 3-mm wavelength range, e.g. DCN, DNC, or SO$^+$. The bulk of the molecules detected at 4~mm are those that are common for dense cores, e.g., HC$_3$N or CH$_3$CCH, but some of the detected species are typical for hot cores. The latter include complex organic molecules CH$_3$OCHO, CH$_3$CH$_2$OH, CH$_3$OCH$_3$, etc. However, the detected emission of these molecules probably arises in a gas heated to 30 K only. Nine molecules, including complex species CH$_3$C$_3$N, CH$_3$CH$_2$CN, CH$_3$COCH ... Additionally,it is assumed that all lines have equal widths in velocity units and knowingthe optical depth τi allows for findingthe amplitude ∆Ti using therelation ∆Ti = (Tex − Tbg) × (1 − exp(−τi)), where Tex and Tbg represent excitation and microwave background temperatures respectively under LTE conditions. By calculating ratios Ri = Ti/Tref based on brightness temperatures of selected lines relative to a reference line and excluding lines with Ri . 0.01 from further consideration, narrow bands centered on frequencies of chosen lines can be analyzed for further insights into molecular cloud composition and characteristics. This detailed summary provides an overview not only of the molecular species detected in DR21OH but also delves into the methodology used in analyzing spectral data to uncover valuable information about molecular clouds in star formation regions.