A standard stellar library for evolutionary synthesis - II. The M dwarf extension

A standard library of theoretical stellar spectra intended for multiple synthetic photometry applications including spectral evolutionary synthesis is presented. The grid includes M dwarf model spectra, hence complementing the first library version established in Paper I (Lejeune et al, 1997). It covers wide ranges of fundamental parameters: T-eff: 50 000 Ii similar to 2000 K, log g: 5.5 similar to -1.02, and [M/H]: +1.0 similar to -5.0. A correction procedure is also applied to the theoretical spectra in order to provide color-calibrated flux distributions over a large domain of effective temperatures. For this purpose. empirical T-eff-color calibrations are constructed between 11500 K and 2000 K, and semi-empirical calibrations for non-solar abundances ([M/H] = -3.5 to +1.0) are established. Model colors and bolometric corrections for both the original and the corrected spectra, synthesized in the (UBV)(J)(RI)(C)JHKLL'M system, are given for the full range of stellar parameters. We find that the corrected spectra provide a more realistic representation of empirical stellar colors, though the method employed is not completely adapted to the lowest temperature models. In particular the original differential colors of the grid implied by metallicity and/or luminosity changes are not preserved below 2500 K. Limitations of the correction method used are also discussed.