The wings of the calcium infrared triplet lines in late-type giant stars.

A grid of model atmospheres constructed for various combinations of T(eff), log g, and metallicity are used to investigate how the wings of the calcium infrared triplet lines in late-type giant stars are affected by changes in the stellar parameters. It appears that, over the range of metallicity investigated, the depth of absorption in the line wings is rather insensitive to a change in T(eff) of 500 K or to a change in log g of 0.5 dex. A change in metallicity of 0.5 dex has a rather larger effect which increases in magnitude with increasing temperature and decreasing surface gravity. No evidence is found to justify the use of a single-valued relationship between integrated absorption and log g even for stars of near-solar metallicity. If integrated absorption in the infrared triplet lines is to be used as an indicator of stellar surface gravity, some knowledge of the effective temperatures and metallicities of the stars concerned is essential.