The Wing-Ford band as a constraint on the mass function in old galaxy populations.

Scanner measurements of the dwarf-sensitive Wing-Ford molecular band at 9910 A in 37 late-type stars show it to be a useful population indicator, giving greatest weight to the dM5dM8 stars. No detectable contribution from lower main-sequence stars could be found in scanner observations of seven E!S0/Sb galaxies at this wavelength. Analysis in terms of an isochrone population model based on evolution tracks and Tinsley's semiempirical luminosity function for the giant branch rules out power-law mass functions with an exponent x > 2. This result agrees with evidence for giant-dominated light in galaxies from the CO band at 2.3 m and a TiO band at 8548 A, but disagrees with the support for a strong dwarf component found by Spinrad and Taylor from scanner measurements of the Na I feature at 8190 A. A reexamination based on equivalent widths of the Na lines on coude' spectrograms of stars indicates that spectra of galaxies, rather than scanner indices, are required to assess the dwarf contribution. Both the UBVRIJKL colors and the mass-luminosity ratio of an E galaxy calculated from the isochrone model are compatible with recent measurements of these quantities if x 1, but disagree for a dwarf-enriched population (x > 2.7). Substitution of Larson's Gaussian initial mass function for a power law in these calculations results in a population model that is likewise compatible with observational tests. Subject headings: galaxies: stellar content - infrared: spectra - stars: late-type