A 1.3 cm line survey toward Orion KL

Abstract

Context. The nearby Orion Kleinmann-Low nebula is one of the most prolific sources of molecular line emission. It has served as a benchmark for spectral line searches throughout the (sub)millimeter regime. Aims. The main goal is to systematically study the spectral characteristics of Orion KL in the λ ∼ 1.3 cm band. Methods. We carried out a spectral line survey with the Effelsberg-100 m telescope toward Orion KL. It covers the frequency range between 17.9 GHz and 26.2 GHz, i.e., the radio "K band". We also examined ALMA maps to address the spatial origin of molecules detected by our 1.3 cm line survey. Results. In Orion KL, we find 261 spectral lines, yielding an average line density of about 32 spectral features per GHz above 3σ (a typical value of 3σ is 15 mJy). The identified lines include 164 radio recombination lines (RRLs) and 97 molecular lines. The RRLs, from hydrogen, helium, and carbon, stem from the ionized material of the Orion Nebula, part of which is covered by our beam. The molecular lines are assigned to 13 different molecular species including rare isotopologues. A total of 23 molecular transitions from species known to exist in Orion KL are detected for the first time in the interstellar medium. Non-metastable (J > K) 15 NH 3 transitions are detected in Orion KL for the first time. Based on the velocity information of detected lines and the ALMA images, the spatial origins of molecular emission are constrained and discussed. A narrow feature is found in SO 2 (8 1,7 −7 2,6 ), but not in other SO 2 transitions, possibly suggesting the presence of a maser line. Column densities and fractional abundances relative to H 2 are estimated for 12 molecules with local thermodynamic equilibrium (LTE) methods. Rotational diagrams of non-metastable 14 NH 3 transitions with J = K + 1 to J = K + 4 yield different results; metastable (J = K) 15 NH 3 is found to have a higher excitation temperature than non-metastable 15 NH 3 , also indicating that they may trace different regions. Elemental and isotopic abundance ratios are also estimated: He/H = (8.7 ± 0.7)% derived from the ratios between helium RRLs and hydrogen RRLs; 12 C/ 13 C = 63 ± 17 from 12 CH 3 OH/ 13 CH 3 OH; 14 N/ 15 N =100 ± 51 from 14 NH 3 / 15 NH 3 ; and D/H = (8.3 ± 4.5) × 10 −3 from NH 2 D/NH 3 . The dispersion of the He/H ratios derived from Hα/Heα pairs to Hδ/Heδ pairs is very small, which is consistent with theoretical predictions that the departure coefficients b n factors for hydrogen and helium are nearly identical. Based on a non-LTE code that neglects excitation by the infrared radiation field and a likelihood analysis, we find that the denser regions have lower kinetic temperature, which favors an external heating of the hot core.

A Broadband Digital Spectrometer for the Deep Space Network

“…On 2019 November 24 we observed eight RRLs simultaneously, from H70α to H63α, each in two polarizations. The intensities obtained for the hydrogen recombination lines in Orion KL are consistent with those observed by Gong et al (2015) with Effelsberg 100 m telescope, for a main-beam efficiency of 0.5 and n S T A *= 1.9 Jy K −1 (Kuiper et al 2019). Note the difference in frequency response for each IF is caused by the front end K-band system (see Figure 6 in Kuiper et al 2019).…”

Widespread Presence of Glycolaldehyde and Ethylene Glycol around Sagittarius B2

“…We searched for low-energy transitions of glycolaldehyde and ethylene glycol at 13.5 GHz towards IRAS 16293-2422, G31.41+0.31, G34.3+0.2 and NGC 7129 with TMRT but did not detect any emissions above 10 mK (σ ∼ 3 mK). Note that in a recent single-dish line survey of Orion KL at a frequency of 22 GHz (Gong et al 2015), which covered HOCH 2 CH 2 OH 3 0,3 (v = 0) − 2 0,2 (v = 1) (Requena-Torres et al 2008), no emission was detected either. The absence of an extended, large-scale emission for these two molecules might result from the lack of a large-scale desorption mechanism to release them from the ices into the gas phase.…”

Chemistry of the High-mass Protostellar Molecular Clump IRAS 16562–3959

“…However, by large, the best studied high-mass star formation region is Orion-KL. Interferometer mm/sub-mm studies (e.g., Blake et al 1996;Wright et al 1996;Beuther et al 2005;Feng et al 2015;Gong et al 2015) have determined the presence of a large number of COMs with a rough separation between N-bearing and O-bearing molecules, tracing the HMC and the so called compact ridge, respectively.…”