FeH

FeH is the diatomic molecule iron hydride, consisting of one iron atom and one hydrogen atom. It forms in high-temperature, low-density gas and has been observed in laboratory plasmas as well as in various astrophysical environments.

In astronomy, FeH is notable for its presence in the atmospheres of cool stars, brown dwarfs, and to some extent sunspots. Its absorption features occur in the optical and near-infrared regions, with the Wing–Ford band near 0.99 micrometers being the most prominent feature in late-type stars. The strength and presence of FeH features depend on temperature and gravity, making them useful for spectral classification and for probing atmospheric conditions in late-type objects. FeH lines are also sensitive to magnetic fields, which allows researchers to estimate magnetic flux in M-dwarfs.

Spectroscopic data for FeH come from laboratory measurements and theoretical calculations, yielding a complex set of electronic, vibrational, and rotational transitions. The resulting line lists and opacities are incorporated into models of cool stellar atmospheres to reproduce observed spectra and to extract physical parameters. The molecule’s spectral richness requires detailed treatment in radiative transfer calculations used in stellar and substellar characterization.

Overall, FeH serves as a diagnostic tool in the study of cool stars and brown dwarfs, contributing to our understanding of atmospheric composition, temperature structure, and magnetic activity in these objects. Its prominent near-infrared features, especially the Wing–Ford band, remain a key reference point in molecular spectroscopy of late-type stars.