Observed departures from LTE ionization equilibrium in late-type giants

Photoelectric scans of the Ca I line at 6572 A and the forbidden Ca II transition at 7323 A are studied in the K giant alpha Tau, the M supergiant alpha Ori, and the M giants beta And, alpha Cet, mu Gem, and beta Peg. The relative strengths of these lines are shown to be indicative of the ratio of the relative number densities of the neutral and ionized species in the photosphere. The analysis indicates an overionization relative to LTE in qualitative agreement with the theoretical calculations of Auman and Woodrow for the K and M giants. The M supergiant alpha Ori exhibits a large overionization relative to LTE.