On the Question of a Metallicity Spread in Globular Cluster M22 (NGC 6656)

Results from early photometric and spectroscopic studies for M22 showed a metallicity spread similar to, albeit significantly smaller than, that found in omega Cen, the most massive cluster in our Galaxy. Numerous studies of M22 over the last few decades have yielded conflicting results: depending upon the sample and analysis techniques, some authors find no significant variations whereas others find metallicity variations of ∼0.5 dex. In our investigation of a sample of ∼30 stars, we are employing high resolution high signal-to-noise spectra and a variety of spectroscopic approaches in determining the stellar metallicities. In this contribution, we report some of the preliminary results from our investigation of the question of metallicity variations in M22, employing a set of models derived by applying chemical constraints.