A method for the simultaneous estimation of atmospheric parameters using the photometric indices in the uvby color system

A new method was developed to estimate the effective temperature, surface gravity, and metallicity of cool stars using only photometric indices in the uvby color system. In a graphical method, T _eff and log g were determined for all of the different values of [Fe/H] using model atmosphere grids with respect to (b - y):c ₁ and (b - y):m ₁ pair indices. Then, a three-dimensional figure where X-, Y-, and Z-axes correspond to T _eff, log g, and [Fe/H] was produced. By reading an intersection of two curves formed by a connection of three parameters obtained from the (b - y):c ₁ and (b - y):m ₁ pair indices on each of the three projected planes, T _eff, log g, and [Fe/H] were determined simultaneously. In addition, an analytical method was devised based on the same algorithm developed for the graphical method. The new method was applied to a number of field dwarfs and giants, and the results were compared with those from a spectroscopic method and other photometric calibrations.