Gas phase atomic metals in the circumstellar envelope of IRC+10216

The composition of the C-rich grains found in AGB stars is fundamental both for our understanding of grain formation in the atmospheres of AGB stars and for our knowledge of the composition of the grains returned to the interstellar medium. In the article highlighted here, Mauron and Huggins have succeeded in measuring the optical absorption lines of several "metals" (Na,Ca,Fe,K) in the circumstellar shell surrounding the C-rich AGB star IRC10216 towards a star in the background.They find that these species are depleted compared to solar abundances and that the pattern of the depletion is similar to what is observed in the interstellar medium. These metals moreover appear to be mainly atomic or to have a solid form in the IRC10216 envelope, but are not molecular.