中国科学院云南天文台机构知识库

The "bump" is a prominent feature of the red giant branch (RGB) luminosity function of stellar clusters. Through constructing a grid of models with different masses and metallicities to study the feature of the RGB bump luminosity we find that the luminosity increases almost monotonically with increasing mass for a given metallicity and decreases monotonically with increasing metallicity. Moreover, different stars have different shapes of the RGB bump. It is correlated with the sharpness of the H discontinuity, which is left over by the convection envelope during the first dredge-up. Using the periodicity in the small separations d(01), d(10) to probe the internal structure, we find that, at about half the acoustic radius, the sound speed has a sharp variation that is caused by a local depression of the first adiabatic exponent Gamma(1) in the second helium ionization zone. It induces an oscillation modulation in d(01), d(10) with a period of 6.4 mu Hz. Meanwhile, in the same model, the base of the convective envelope is located at a relatively small acoustic radius t(envp)/T, which is about 10(-1). It is too deep to detect the exact location of the bottom of the outer convective envelope. In order to discriminate the evolutionary status of different stars, we calculate the asymptotic g-mode period spacing Delta Pi(1). We find that Delta Pi(1) decreases monotonically with evolution. It is a reliable parameter for distinguishing stars in different positions of the RGB bump.