Abstract
Aims. In order to understand the observed molecular diversity in high-mass star-forming regions, we have to determine the underlying physical and chemical structure of those regions at high angular resolution and over a range of evolutionary stages. Methods. We present a detailed observational and modeling study of the hot core VLA 3 in the high-mass star-forming region AFGL 2591, which is a target region of the NOrthern Extended Millimeter Array (NOEMA) large program CORE. Using NOEMA observations at 1.37 mm with an angular resolution of ~0″. 42 (1400 au at 3.33 kpc), we derived the physical and chemical structure of the source. We modeled the observed molecular abundances with the chemical evolution code MUSCLE (MUlti Stage ChemicaL codE). Results. With the kinetic temperature tracers CH3CN and H2CO we observe a temperature distribution with a power-law index of q = 0.41 ± 0.08. Using the visibilities of the continuum emission we derive a density structure with a power-law index of p = 1.7 ± 0.1. The hot core spectra reveal high molecular abundances and a rich diversity in complex molecules. The majority of the molecules have an asymmetric spatial distribution around the forming protostar(s), which indicates a complex physical structure on scales <1400 au. Using MUSCLE, we are able to explain the observed molecular abundance of 10 out of 14 modeled species at an estimated hot core chemical age of ~21 100 yr. In contrast to the observational analysis, our chemical modeling predicts a lower density power-law index of p < 1.4. Reasons for this discrepancy are discussed. Conclusions. Combining high spatial resolution observations with detailed chemical modeling allows us to derive a concise picture of the physical and chemical structure of the famous AFGL 2591 hot core. The next steps are to conduct a similar analysis for the whole CORE sample, and then use this analysis to constrain the chemical diversity in high-mass star formation to a much greater depth.
Highlights
The formation of the most massive stars is an active field of research
We investigate the spatial distribution of the molecular emission with line integrated intensity maps at high angular resolution
Observed and modeled density and temperature structure of the AFGL 2591 hot core In Sect. 3.3 we present the analysis of the physical environment of the hot core based on the CORE observational data
Summary
The formation of the most massive stars is an active field of research (for reviews, see, e.g., Beuther et al 2007a; Bonnell 2007; Zinnecker & Yorke 2007; Smith et al 2009; Tan et al 2014; Schilke 2015; Motte et al 2018). Based on observational and theoretical considerations, HMSF can be divided into several evolutionary stages (Beuther et al 2007a; Zinnecker & Yorke 2007): the formation of massive stars begins in infrared dark clouds (IRDCs) harboring potentially short-lived high-mass starless cores and low- to intermediatemass protostars (e.g., Pillai et al 2006; Rathborne et al 2006; Sanhueza et al 2012; Zhang et al 2015) and proceeds to form high-mass protostellar objects (HMPOs) with M > 8 M showing gas accretion and molecular outflows (e.g., Beuther et al 2002; Motte et al 2007). Ultra-compact HII (UC HII) regions form where the protostars ionize their surrounding envelope, which is observed in strong free–free emission at cm wavelengths (e.g., Garay & Lizano 1999; Palau et al 2007; Qin et al 2008; Klaassen et al 2018)
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