Very Large Telescope observations of interstellar comet 3I/ATLAS III: High-resolution monitoring of CN and forbidden oxygen emission across the perihelion passage with ESPRESSO

@misc{luco2026very,
  title = {{Very Large Telescope observations of interstellar comet 3I/ATLAS III: High-resolution monitoring of CN and forbidden oxygen emission across the perihelion passage with ESPRESSO}},
  author = {Baltasar Luco and Thomas H. Puzia and Rohan Rahatgaonkar and Juan Pablo Carvajal and Prasanta K. Nayak},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2607.15355},
  eprint = {2607.15355},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2607.15355},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Very Large Telescope observations of interstellar comet 3I/ATLAS III: High-resolution monitoring of CN and forbidden oxygen emission across the perihelion passage with ESPRESSO
AU  - Baltasar Luco
AU  - Thomas H. Puzia
AU  - Rohan Rahatgaonkar
AU  - Juan Pablo Carvajal
AU  - Prasanta K. Nayak
PY  - 2026
DA  - 2026/10/07
PB  - arXiv
DO  - 10.48550/arxiv.2607.15355
UR  - https://arxiv.org/abs/2607.15355
AB  - We characterize in 3I/ATLAS the heliocentric evolution of the CN production rate and the forbidden [OI] emission, describe the broader emission line inventory, and release the analysis tools and reduced data products to the community. We obtained high-resolution spectroscopy of 3I/ATLAS with VLT/ESPRESSO (r_h = 1.67 − 2.45 au). The CN production rates were derived by fitting the B^2Σ^+ − X^2Σ^+ band using CometSpec, a publicly released Python package for flexible fluorescence modeling. The three forbidden [OI] lines were modeled to derive the green-to-red (G/R) flux ratio and a CO_2 / H_2O proxy. We fit Q_CN=a (r_h/1 au)^ b to the production rate versus heliocentric distance relation. The pre-perihelion CN power-law index is b_pre = −4.62^+1.25_−1.22, which is within the range observed for Solar System comets. The CN residuals about the smooth model show substantial scatter that we attribute to a combination of systematics and possible physical drivers that the current cadence cannot disentangle. The G/R ratio decreases from ∼ 0.42 ± 0.14 at r_h ≃ 2.4 au to ∼ 0.114 ± 0.004 near perihelion. The CO_2 / H_2O proxy spans ∼ 0.06 − 1.06 and is comparable to the values reported by Subaru/HDS and SPHEREx and to those measured for 2I/Borisov. We additionally identify NiI and FeI and report post-perihelion production rates for C_2 and CH. Our high-resolution monitoring of 3I/ATLAS reveals a CO_2-rich coma that becomes progressively H_2O-dominated near perihelion. Together with the public release of CometSpec and the reduced data, these results provide an empirical reference and a methodological framework for the next generation of interstellar object monitoring campaigns.
ER  -