VLT observations of Interstellar Comet 3I/ATLAS III: ESPRESSO HR spectroscopy

Version 2, the difference is an update on the plots. The codes were run again due a bug of non inclusion of the CN red system dv=1. Output spectra remain the same. Some new plots were added.

This repository contains the public data release of the ISO 3I/ATLAS VLT/ESPRESSO observations and data products taken during September, late November, and early December of 2025, including:

• Spectra: The reduced spectra, as described in Luco et al. 2026. Files are in csv format, and the two header rows describe column name and units in that order. The tables have 10 columns: wavelength, coadded flux, flux error, number of source spectra in the coadd, coadded flux with masked sky lines, flux error with masked sky lines, number of source spectra in the masked coadd, continuum model, ``reflectance spectrum’’ and Doppler shifted Kurucz solar irradiance spectrum. Since dedicated sky exposures were not taken on all nights, the ``reflectance`` spectra lost their physical meaning from September 16th onward, and the continuum jointly describes the reflected and sky continua.

•  "yyyymmdd_A.csv": fiber A spectra stack for a given night.

•  "yyyymmdd_B.csv": fiber B spectra stack for a given night.

•  "Full_Stack_A.csv" and "Full_Stack_B.csv": stack of all observing runs.

•  "Full_Stack_First3Post_A.csv" and "Full_Stack_Last3Pre_A.csv": First three post-perihelion night stacks and last 3 pre-perihelion night stacks.

• "Full_Stack_Pre_A.csv", "Full_Stack_Pre_B.csv",  "Full_Stack_Post_A.csv", "Full_Stack_Post_B.csv", "Full_Stack_Mid_A.csv", "Full_Stack_Mid_B.csv": The stack of all pre-perihelion spectra (fiber A and B), all post-perihelion spectra (fiber A and B), and the six closest epochs to perihelion (`Mid’; three pre- and three post-perihelion; fiber A and B).

Note: For all stacks spanning more than one night, each night’s spectra are shifted to the comet's rest-frame velocity and interpolated onto the same spectral grid before stacking.

• Supplementary Plots:

• C2:

• Fits: Fluorescence model of C2 of the Full_Stack_First3Post_A data using three different collision scenarios, no collisions, logQ=-3.12, and logQ=8.52 (Q=collisional rate).

• Corner: C2 corner plots of the previously mentioned fits.

• CN:

• Fits: Fluorescence model of CN on multiple nights. File names as "yyyymmdd_A.pdf" denoting the observed date and fiber A; One file with "yyyymmdd_B.pdf" for a fiber B fitting.  "_IR_extend" for the exercise of extending with more systems in the IR, as explained in Luco et al. 2026.

• Corner: CN corner plots of the previously mentioned fits. File names as before "yyyymmdd_A_corner.pdf". One for a fiber B fitting. "_IR_extend" for the exercise of extending with more systems in the IR, as explained in Luco et al. 2026.

• Fe:

• Fits: Iron Fluorescence fit of the nights of September 24th and December 4th on fiber A. File names as "yyyymmdd_wn_fit.pdf", “wn” denotes different wavelength windows fitted.

• Corner: Fe corner plots of the previously mentioned fits.

• Oxygen:

• Fits: 2-Voigt profile fits of the forbidden oxygen lines on fiber A. File name as "yyyymmdd_A.pdf" denoting the date observed.

• Corner: Oxygen corner plots of the previously mentioned fits.

• description.txt:

• This description.