Investigating the composition of Halley-family comet 12P/Pons-Brooks with IRAM radio telescopes

Comet 12P/Pons-Brooks is a great Halley-family comet with an orbital period of71 years, that was first seen in 1385, and possibly earlier. It returnedto perihelion on 21 April 2024 at 0.78 au from the Sun (Fig.1)Its peak outgassing rate exceeded QH2O=1030 molec.s-1, with atotal visual magnitude of 4 in April and the comet was the focus of aworldwide observing campaign.We report observations of the comet with IRAM-30m and NOEMA facilitieson 20 January, 17, 20 March, and 22-28 April 2024. A frequency survey at3, 2 and 1 mm wavelengths, covering 8, 24 and 63 GHz respectively, was undertaken in Aprilunder average weather conditions.Several molecules and isotopologues were detected. We have derived expansionvelocity, gas temperature and production rates or upper limits on molecularabundances. Around perihelion we measured an expansion velocity around 1.1 km/sand a gas temperature of around 105 K.Lines of HCN, HNC, HC3N, CH3CN, HNCO, NH2CHO, CH3OH, H2CO, CO, HCO+, CS,H2S, OCS, SO, C34S and possibly (CH2OH)2 have been detected (Fig.2) and the molecularabundances will be presented. This is the most detailed chemicalinventory of a Halley-family comet obtained so far. The composition of 12Pwill be compared to previously investigated long- and short-periodcomets.Figure 1: Comet 12P/Pons-Brooks on 6.83 March 2024 UT. Visible image obtained with a 40.7-cm telescope, Field of view is 40x40 arcmin. (c) N. BiverFigure 2: Sample average spectra of lines observed with IRAM-30m in April 2024.The vertical scale in main beam brightness temperature (in K) is preliminary.Horizontal axis is Doppler velocity in the rest frame of the comet.Acknowledgements:This work is based on observations carried out under projects number W23AA001 and 066-23 with the IRAM NOEMA Interferometer and 30m telescopes.IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).