Fig. 3. The four LDC as a function of log T_eff and metallicity. The symbols have the following meaning: (continuous) log [M/H] = -5.0; (- - -) log [M/H] = -1.0; (-. -.) log [M/H] = 0.0; (....) log [M/H] = +1.0. Results for the y filter and log g = 4.5. ATLAS models, microturbulent velocity=2 km/s.