# Observations of Cyanopolyynes toward Four High-Mass Star-Forming Regions Containing Hot Cores

## TL;DR

This study surveys cyanopolyynes in four high-mass star-forming regions, detecting HC5N and HC7N, revealing warm gas presence, and suggesting chemical differentiation among the regions.

## Contribution

First detection of high-excitation HC5N lines in warm regions around massive young stars, indicating its existence in warm gas within 0.07-0.1 pc radii.

## Key findings

- HC5N detected in all sources; HC7N in three.
- HC5N rotational temperatures are 13-20 K.
- Evidence of chemical differentiation among regions.

## Abstract

We carried out line survey observations at the 26-30 GHz band toward the four high-mass star-forming regions containing hot cores, G10.30-0.15, G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Robert C. Byrd Green Bank Telescope. We have detected HC5N from all of the sources, and HC7N from the three sources, except for G10.30-0.15. We further conducted observations of HC5N at the 42-46 GHz and 82-103 GHz bands toward the three sources, G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Nobeyama 45 m radio telescope. The rotational lines of HC5N with the high excitation energies (Eu/k=63-100 K), which are hardly excited in the cold dark clouds, have been detected from the three sources. The rotational temperatures of HC5N are found to be 13-20 K in the three sources. The detection of the lines with the high excitation energies and the derived rotational temperatures indicate that HC5N exists in the warm gas within 0.07-0.1 pc radii around massive young stellar objects. The column densities of HC5N in the three sources are derived to be (2.0+-2.8)*10^(13) cm-2 . We compare the ratios between N(HC5N) the column density of HC5N and W(CH3OH) the integrated intensity of the thermal CH3OH emission line among the three high-mass star-forming regions. We found a possibility of the chemical differentiation in the three high-mass star-forming regions; G28.28-0.36 shows the largest N (HC5N)/W (CH3OH) ratio of > 8.0*10^(14) in units of (K km s-1 )-1 cm-2 , while G12.89+0.49 and G16.86-2.16 show the smaller values (~2*10^(13) ).