2014A&A...568A..65F

This paper is dedicated to the study of the chemistry of the intermediate-mass (IM) hot core NGC 7129 FIRS 2, probably the most compact warm core found in the 2-8M_☉ stellar mass range. Our aim is to determine the chemical composition of the IM hot core NGC 7129 FIRS 2, and to provide new insights on the chemistry of hot cores in a more general context. NGC 7129 FIRS 2 (hereafter, FIRS 2) is located at a distance of 1250 pc and high spatial resolution observations are required to resolve the hot core at its center. We present a molecular survey from 218200MHz to 221800MHz carried out with the IRAM Plateau de Bure Interferometer (PdBI). These observations were complemented with a long integration single-dish spectrum taken with the IRAM 30m telescope in Pico de Veleta (Spain). We used a local thermodynamic equilibrium (LTE) single temperature code to model the whole dataset. The interferometric spectrum is crowded with a total of ≃300 lines from which a few dozen remain unidentified. The spectrum has been modeled with a total of 20 species and their isomers, isotopologues, and deuterated compounds. Complex molecules like methyl formate (CH₃OCHO), ethanol (CH₃CH₂OH), glycolaldehyde (CH₂OHCHO), acetone (CH₃COCH₃), dimethyl ether (CH₃OCH₃), ethyl cyanide (CH₃CH₂CN), and the aGg' conformer of ethylene glycol (aGg'-(CH₂OH)₂) are among the detected species. The detection of vibrationally excited lines of CH₃CN, CH₃OCHO, CH₃OH, OCS, HC₃N, and CH₃CHO proves the existence of gas and dust at high temperatures. The gas kinetic temperature estimated from the vibrational lines of CH₃CN, ∼405_–67⁺¹⁰⁰K, is similar to that measured in massive hot cores. Our data allow an extensive comparison of the chemistry in FIRS 2 and the Orion hot core. We find a quite similar chemistry in FIRS 2 and Orion. Most of the studied fractional molecular abundances agree within a factor of 5. Larger differences are only found for the deuterated compounds D₂CO and CH₂DOH and a few molecules (CH₃CH₂CN, SO₂, HNCO and CH₃CHO). Since the physical conditions are similar in both hot cores, only different initial conditions (warmer pre-collapse and collapse phase in the case of Orion) and/or different crossing times of the gas in the hot core can explain this behavior. We discuss these two scenarios.