Chemical Complexity of AFGL 2591
Caroline Gieser
Thursday December 6th, 14:00
Hot cores are ideal laboratories to study the formation of simple and complex organic molecules. Here, we present a detailed observational and modeling study of the chemistry of the prototypical hot core VLA 3 in the high-mass star-forming region AFGL 2591, where it evolves in unique conditions being isolated from other young OB stars with strong UV radiation. This region is part of the NOEMA (NOrthern Extended Millimeter Array) large program CORE targeting 20 of such regions. Observations were carried out with NOEMA from 217 GHz to 221 GHz with a spectral resolution of ~2.7 km/s and to include large-scale emission observations with the IRAM 30 m telescope were complemented. Using the high spatial resolution (0.4"", ~1300 AU at 3.3 kpc) we derived the physical structure (density and temperature) of the source using the 1.37 mm continuum, methyl cyanide and formaldehyde emission. In the spectra, we could identify in total 17 different species and 12 isotopologues among ~100 detected lines. Using XCLASS, we derived the rotation temperatures and column densities: AFGL 2591 has a high molecular abundance (e.g., SO2, SO, OCS) and shows a rich diversity in complex molecules (CH3OH, CH3CN, NH2CHO, C2H5CN, C2H3CN, CH3OCHO, CH3COCH3, CH3OCH3). Many species show an asymmetric distribution around the continuum peak which indicates a complex structure on small scales due to disk accretion and the outflow. As hot cores have a rich gas-phase chemistry, we modeled the chemical abundance with MUSCLE. The code includes the time-dependent gas-grain chemical model ALCHEMIC and finds the best-fit physical structure covering several stages of high-mass star formation. With this simplistic 1-D model, we are able to explain the abundance of ~70 % of the species with a chemical age of ~50 000 years and a best-fit physical structure comparable to the observed one. Thus, in agreement with previous studies of the region, AFGL 2591 VLA 3 seems to be in an early hot core stage. The observed chemical segregation can be partially explained by our model, but more sophisticated modeling is needed in order to explain the spatial distribution of certain species, e.g., by including shock chemistry and the complex physical structure of the source.