We study the FeH Wing-Ford band at λλ 9850 -10200Å by means of the fit of synthetic spectra to the observations of M stars, employing recent model atmospheres. On the basis of the spectrum synthesis, we analyze the dependence of the band upon atmospheric parameters.FeH lines are a very sensitive surface gravity indicator, being stronger in dwarfs. They are also sensitive to metallicity (Allard & Hauschildt 1995). The blending with CN lines, which are stronger in giants, does not affect the response of the Wing-Ford band to surface gravity at low resolution (or high velocity dispersions) because CN lines, which are spread all along the spectrum, are smeared out at convolutions of FWHM > ∼ 3Å. We conclude that the Wing-Ford band is a suitable dwarf/giant indicator for the study of composite stellar populations.

para a transição central. Como a equação de transferência valerá: ABSTRACT Masers are astrophysical sources in which the absorption coefficient of the corresponding spectral line is negative and the radiation is amplified. For unsaturated sources, the amplification is exponencial. For saturated sources, the mtensity of radiation increases linearly with distance, or with the cube of the path lenght of saturation.