ASTEROSEISMIC ANALYSIS OF THE INTERNAL STRUCTURE AND EVOLUTION OF RED GIANT BRANCH BUMP STARS

• Published in: The Astrophysical journal Vol. 804; no. 1; pp. 6 - 10
• Main Authors: Gai, Ning, Tang, Yanke
• Format: Journal Article
• Language: English
• Published: The American Astronomical Society 01.05.2015
• Subjects: Acoustics; Asymptotic properties; Envelopes; Luminosity; Mathematical models; Metallicity; Red giant stars; Stars; stars: evolution; stars: interiors; stars: oscillations
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.1088/0004-637X/804/1/6

ABSTRACT 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 d01, d10 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 in the second helium ionization zone. It induces an oscillation modulation in d01, d10 with a period of 6.4 Hz. Meanwhile, in the same model, the base of the convective envelope is located at a relatively small acoustic radius , 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 . We find that decreases monotonically with evolution. It is a reliable parameter for distinguishing stars in different positions of the RGB bump.