Correlations between laboratory line lists for FeH, CrH, and NiH and M-star spectra collected with ESPaDOnS and SPIRou^★

¹ Université Claude Bernard Lyon 1 & CNRS, Institut Lumière Matière, 69622 Villeurbanne, France
e-mail: amanda.ross@univ-lyon1.fr
² Université de Montpellier, CNRS, LUPM, 34095 Montpellier, France
³ Université de Toulouse CNRS, IRAP, 14 av. Belin, 31400 Toulouse, France
⁴ Science Division, Directorate of Science, European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands
⁵ Université Grenoble Alpes & CNRS, IPAG, 38000 Grenoble, France
⁶ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences (CSFK, MTA Centre of Excellence), Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁸ Department of Chemistry, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
⁹ Department of Physics, University of New Brunswick, Fredericton, NB E3B 5A3, Canada

Received: 18 July 2023
Accepted: 18 September 2023

Abstract

Context. Molecular bands of metal oxides and hydrides dominate the optical and near-infrared spectra of M dwarfs. High-resolution spectra of these bands have immense potential for determining many properties of these stars, such as effective temperature, surface gravity, elemental abundances, radial velocity, or surface magnetic fields. Techniques are being developed to do this but remain limited by the current availability and accuracy of molecular data and spectral line lists.

Aims. This paper reports metal monohydride line lists selected from near-infrared and visible laboratory data to show that specific bands in several electronic transitions can be used to identify CrH, NiH, and FeH in M stars and to determine radial velocities from Doppler shifts. The possibility of measuring magnetic fields is also investigated for FeH and CrH.

Methods. We used systematic cross-correlation analysis between unpolarised spectra from a selection of M stars and state-specific laboratory line lists. These lists were generated from a combination of existing data and new laboratory laser-excitation spectra recorded at Doppler-limited resolution, in zero-field conditions or in magnetic fields up to 0.6 tesla.

Results. We show that transitions at visible wavelengths in FeH and NiH, usually neglected in the analysis of the spectra of M-type stars, do in fact contribute to the spectra, and we demonstrate the influence of magnetic sensitivity on selected transitions in CrH and FeH.

Conclusions. Although the new line lists focus on transitions recorded at temperatures significantly lower than those of stellar objects, they remain pertinent because they cover some band-head regions of high spectral density. FeH bands can provide a useful supplement to atomic lines for the analysis of high-resolution optical and near-infrared spectra of M dwarfs. We demonstrate the influence of a magnetic field on CrH signatures around 862 nm.