# A spectroscopic survey of Orion KL between 41.5 and 50 GHz

## TL;DR

This paper presents a highly sensitive spectral survey of Orion KL between 41.5 and 50 GHz, identifying numerous molecular and recombination lines, providing valuable chemical insights into this well-studied star-forming region.

## Contribution

It offers the most sensitive and wide-band spectral survey of Orion KL in this frequency range, with detailed line identification and radiative modeling of molecular emissions.

## Key findings

- Detected 66 radio recombination lines and 161 molecular lines from 20 molecules.
- Most molecules originate from low-temperature components, despite some from the hot core.
- Achieved an rms noise level of 8-12 mK, the most sensitive in this range.

## Abstract

Orion KL is one of the most frequently observed sources in the Galaxy, and the site where many molecular species have been discovered for the first time. With the availability of powerful wideband backends, it is nowadays possible to complete spectral surveys in the entire mm-range to obtain a spectroscopically unbiased chemical picture of the region. In this paper we present a sensitive spectral survey of Orion KL, made with one of the 34m antennas of the Madrid Deep Space Communications Complex in Robledo de Chavela, Spain. The spectral range surveyed is from 41.5 to 50 GHz, with a frequency spacing of 180 kHz (equivalent to about 1.2 km/s, depending on the exact frequency). The rms achieved ranges from 8 to 12 mK. The spectrum is dominated by the J=1-0 SiO maser lines and by radio recombination lines (RRLs), which were detected up to Delta_n=11. Above a 3-sigma level, we identified 66 RRLs and 161 molecular lines corresponding to 39 isotopologues from 20 molecules; a total of 18 lines remain unidentified, two of them above a 5-sigma level. Results of radiative modelling of the detected molecular lines (excluding masers) are presented. At this frequency range, this is the most sensitive survey and also the one with the widest band. Although some complex molecules like CH_3CH_2CN and CH_2CHCN arise from the hot core, most of the detected molecules originate from the low temperature components in Orion KL.