Using line-depth ratios to determine surface gravity of solar-type stars

Determination of the chemical composition of stars in the Milky Way Galaxy allows us to understand galactic evolution. Large scale spectroscopic surveys are the key to determining the chemical composition of stars and thus, our galaxy’s history. In order to determine the abundance of a particular element, one must know the effective temperature, surface gravity, overall stellar metallicity, and atomic transition parameters for the corresponding absorption line. Of these parameters surface gravity remains the most elusive. Determination of the stars surface gravity is complicated by broadening effects and has degeneracies with effective temperature. By taking the ratio of two line-depths many of the dependencies can be removed. These line-depth ratios (LDR) are a function of the effective temperature, surface gravity, and line abundance, with the temperature being the dominant contributor. I will present the application of the LDR technique to solar-type stars to determine their surface gravity, and explore application to large-scale surveys.