Stellar Evolution. II. The Evolution of a 3 Mₒₔ₍ Star from the Main Sequence Through Core Helium Burning.

A 3 Mo stellar model of population I initial composition is evolved from the main sequence to the stage of helium exhaustion in the core. Out of the total time elapsed, two-thirds is spent near the main sequence with hydrogen burning in the core and one-fourth is spent in the red-giant region with helium burning in the core combined with hydrogen burning in a shell. During the hydrogen-burning phase near the main sequence, C'2 is converted into N'4 and Li is destroyed over a large fraction of the stellar interior. 016 is slowly converted into N'4 in the core. During the rise toward the red-giant tip immediately preceding the ignition of helium in the core, the extension of a convection envelope almost to the hydrogen- burning shell then leads to an increase in the surface ratio of N14 to C32 by a factor of 3.2 and to a decrease in the surface abundance of Li by a factor of 60. Surface abundances do not change further during core helium burning. Comparison with the surface Li abundance of Capella F and G permits an inference concerning the average rate of mass loss from the surface of a 3 Mo star.