Observations of comet C/2020 F3 (NEOWISE) with IRAM telescopes

We present the results of millimetre-wave spectroscopic and continuum observations of the comet C/2020 F3 (NEOWISE) undertaken with the Institut de RadioAstronomie Millimétrique (IRAM) 30-m and the NOrthern Extended Millimeter Array (NOEMA) telescopes on 22, 25-27 July, and 7 August 2020. Production rates of HCN, HNC, CH₃OH CS, H₂CO, CH₃CN, H₂S, and CO were determined with upper limits on six other species. The comet shows abundances within the range observed for other comets. The CO abundance is low (3.2% relative to water), while H₂S is relatively abundant (1.1% relative to water). The H₂CO abundance shows a steep variation with heliocentric distance, possibly related to a distributed production from the dust or macro-molecular source. The CH₃OH and H₂S production rates show a slower decrease post-perihelion than water. There was no detection of the nucleus point source contribution based on the interferometric map of the continuum (implying a size of r < 4.7 km), but this yielded an estimate of the dust production rate, leading to a relatively low dust-to-gas ratio of 0.7 ± 0.3 on 22.4 July 2020.

The radio spectra are available only at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/668/A171