Jiang D.(GZU), Qian L.(NAOC), Pan Z.(NAOC), Sun C.(NAOC), Yang Q.(NAOC), Huang M.(NAOC), Hao Q.(NAOC), Wang X.(NAOC), Guo M.(NAOC), Zhao L.(NAOC), Zhao Y.(NAOC), Jiang P.(NAOC)
ATel #17463; The detection of OH lambda doublet (1665. 4018 and 1667. 359 MHz) lines in the comet C/2025 A6 with FAST
on 31 Oct 2025; 07:56 UT
Credential Certification: Tong Liu (tongliu@bao.ac.cn)
Comet C/2025 A6 is a possibly non-periodic comet, however, some estimations show that its period is about 1350 years. It passed the closest approach to Earth on October 22, 2025. It is expected to reach the perihelion on November 8 from JPL horizons. On October 26, 2025, at 03:35 UT, we observed the comet with FAST (Five-hundred-meter Aperture Spherical radio Telescope, Nan et al. 2011) when it was at a heliocentric distance of 0.61 AU. The observation was done with the OnâOff switching mode with a total integration time of 1 hour. The receiver covers a frequency range of 500â3300 MHz (Zhang et al. 2023). We detected the OH lambda doublet (1665.4018 and 1667.359 MHz) with the peak intensities of 0.6(0.2) and 1.2(0.2) K, and the velocities of 28.8(0.1) and 29.0(0.1) km/s, respectively. This velocities meet the prediction of the comet ephemeris of this comet from JPL horizons.
We will continue the follow-up observations to determine the relation between OH production rate and heliocentric distance, as similar studies on OH lines from comets, e. g., the investigation of comet 12P/Pons-Brooks shows a clear dependence of OH production rate on heliocentric distance (Li et al., 2025). The detailed spectral line parameters will be released after the completion of the full analysis.
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