Stellar Population Astrophysics (SPA) with the TNG: Identification of a Sulphur line at lambda(air) = 1063.600nm in GIANO-B stellar spectra

TL;DR

This study identifies a previously unlisted sulfur spectral line at 1063.600 nm in stellar spectra by revisiting laboratory data and confirming the line's presence through stellar spectrum modeling, enhancing infrared atomic data accuracy.

Contribution

The paper uncovers a sulfur line in stellar spectra by correcting historical laboratory data and demonstrates its significance for infrared stellar spectroscopy.

Findings

Identified a sulfur line at 1063.600 nm in stellar spectra.

Corrected the air-to-vacuum wavelength discrepancy in laboratory data.

Improved atomic data for infrared stellar spectroscopy.

Abstract

Context. In the advent of new infrared, high-resolution spectrometers, accurate and precise atomic data in the infrared is urgently needed. Identifications, wavelengths, strengths, broadening and hyper-fine splitting parameters of stellar lines in the near-IR are in many cases not accurate enough to model observed spectra, and in other cases even non existing. Some stellar features are unidentified. Aims. The aim with this work is to identify a spectral feature at lambda(vac) = 1063.891 nm or lambda(air) = 1063.600 nm seen in spectra of stars of different spectral types, observed with the GIANO-B spectrometer. Methods. Searching for spectral lines to match the unidentified feature in linelists from standard atomic databases was not successful. However, by investigating the original, published laboratory data we were able to identify the feature and solve the problem. To confirm its identification, we model the presumed stellar line in the solar intensity spectrum and find an excellent match. Results. We find that the observed spectral feature is a stellar line originating from the 4s'-4p' transition in S I, and that the reason for its absence in atomic line databases is a neglected air-to-vacuum correction in the original laboratory measurements from 1967 for this line only. From interpolation we determine the laboratory wavelength of the S I line to be lambda(vac) = 1063.8908 nm or lambda(air) = 1063.5993 nm, and the excitation energy of the upper level to be 9.74978 eV.