A study of the characteristics of the blue loop

Various main factors affecting the blue loop are probed, and it is found that the form of the loop is correlated with change in the total energy production rate during the stage of core helium burning. The change comes chiefly from variations in the energy production by envelope hydrogen burning and core helium burning. Therefore, the blue loop is mainly related to changes in the energy production rates of envelope hydrogen burning and core helium burning. The variation of the energy production rate is closely connected with the radial distribution of hydrogen abundance (the X-profile) in the μ-gradient region, the temperature of the M-gradient region, and the degree of penetration of the outer convective region. Both the size and temperature of the helium core can influence variation in the rate of energy production in the helium core, and this variation not only contributes to the change of the total energy production rate, but also affects the change of energy production rate of envelope hydrogen burning.