Photometric Separation of Physical Properties of Stars

Photometry collected using Sloan Digital Sky Survey filter systems shows that it is possible to photometrically separate low metallicity stars with 0.5 < g − r < 0.8 using ugri filters, and to separate stars with −0.2 < (g − r) < 0.25 by surface gravity using ugriz filters. This confirms the result of Lenz et al. 1998, which predicted from Kurucz model atmospheres that for G/K stars there was a relationship between metallicity and the l-parameter, l = −0.436(u− g) + 0.693(g−r)+0.574(r−i)+0.199; and for A stars there was a relationship between surface gravity and the v-parameter, v = 0.283(u− g)− 0.354(g − r) + 0.455(r − i)+0.766(i−z). Photometric metallicities are a rough guide to sort metallicities, but can give very incorrect metallicities for unusual stars such as carbon stars and X-ray sources. The photometric metallicity determinations may make it possible to study the statistics of Galactic populations without time-consuming spectroscopic analysis, thus leveraging our ability to study Galactic structure and abundance gradients in the Galactic halo and thick disk. Application of the l-parameter to tens of millions of Galactic stars in the SDSS catalogs will allow us to select low metallicity candidates for further spectroscopic analysis. This technique is already being used for target selection in SEGUE, which is part of SDSS II, the three year extension to the SDSS.