Seminars at FGG
The red horizontal branch: an asteroseismic and post-common-envelope perspective
Speaker: Massimiliano Matteuzzi (Universita' di Bologna (Italy))
Date and time: 2023-07-25 12:30
Asteroseismic constraints, coupled with information on photospheric chemical abundances and temperature, have given us the ability to measure radii and masses of tens of thousands of red-giant stars. Precise masses of red-giant stars enable a robust inference of their ages, given the strong relation between the initial mass of a star and the duration of the main-sequence phase, and hence its age on the red-giant branch. However, there are cases where the estimates of age can be highly precise yet very inaccurate. An example are giants that have undergone mass transfer events that have significantly altered their mass. In this context, stars with “apparent” ages significantly higher than the age of the Universe provide candidates stripped stars, or stars that have lost more mass than expected, most likely via interaction with a companion star or because of the poorly understood mass-loss mechanism along the RGB. These stars are present in the Kepler database, both in clusters and among field stars. In our study we model the structure and pulsational properties of these objects and then explore their formation through a common-envelope phase using the evolutionary code for binary stars BINARY_C and BINARY_C-PYTHON. We find that specific combinations of initial periods and secondary mass ratios can form such stars, and a possible link between these red horizontal branch stars and subdwarf B stars can exist.