Sodium synthesis and its abundance in yellow supergiants

In convective cores of main sequence stars sodium abundance substantially increases due to 22Ne burning in the reaction 22Ne (p,γ)23Na. On the basis of standard stellar evolution computations it is shown that due to this atmospheric sodium abundance enhances noticably at the first dredge-up phase. Simple expression giving atmospheric sodium enrichment as a function of mass of a star is derived. Atmospheric sodium abundance increases with mass. Numerical agreement with the observational data is achieved if one assumes that the initial 22Ne abundance is 3 times larger than the standard solar value