INFRARED MEASUREMENTS OF METAL-POOR SUBDWARFS AND A COMPARISON WITH MODEL ATMOSPHERES

Infrared observations of four metal-poor subdwarfs have been compared with the predictions of model stellar atmospheres. The parameters of the models were established by fitting observed and calculated spectral energy distributions at visible wavelengths. The models were used to calculate J, H, K, and L' apparent magnitudes for the subdwarfs. When compared with observation, it was found that, while the subdwarf models were internally consistent at the 1% level or better, there are systematic deviations relative to Vega in excess of 0.1 mag. These effects are far greater than would be expected from the excellent fits of the models, for both Vega and the subdwarfs, at shorter wavelengths. Various explanations are suggested for this effect.