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VLT observations of interstellar comet 3I/ATLAS II

13 days ago
https://arxiv.org/abs/2508.18382
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  • #Ni I emission
  • #VLT spectroscopy
  • #interstellar comet
  • VLT spectroscopy observations of interstellar comet 3I/ATLAS (C/2025 N1) from 4.4 to 2.85 au.
  • Dust-dominated coma with a constant red optical continuum slope (~21-22%/1000Å).
  • No detection of [O I], C₂, C₃, or NH₂ at 3.17 au, but CN emission and numerous Ni I lines detected.
  • Production rates measured: log Q(CN) = 23.61±0.05 molecules s⁻¹ and log Q(Ni) = 22.67±0.07 atoms s⁻¹.
  • Steep heliocentric-distance scaling for production rates: Q(Ni) ∝ r_h⁻⁸.⁴³±⁰.⁷⁹ and Q(CN) ∝ r_h⁻⁹.³⁸±¹.².
  • Ni I emission likely driven by low-activation-energy release mechanisms (e.g., photon-stimulated desorption or thermolysis of metalated organics).
  • Future monitoring suggested to test hypotheses on Ni-CO₂ correlation and emission mechanisms.
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