Understanding subdwarf B stars through asteroseismology

Missouri State University, Springfield MO

Investigators

Abstract

AST 0307480 PI Reed After decades of progress in both stellar evolution theory and observational stellar astronomy, the late stages of evolution of most of the stars in our Galaxy - stages in which they shed their outer envelopes and expose their compact cores - conceal many still-unanswered questions. Recently, we have begun to exploit a powerful tool, astroseismology, for probing the interiors of stars and modeling their structure from oscillations and pulsations of the stars. Subdwarf B (sdB) stars are evolved stars located on the so-called horizontal branch of the Hertzsrung-Russell diagram, and they are thought to be the precursors of low mass white dwarf stars. Their progenitors are stars like our Sun. To date, the observational emphasis has been on discovering new pulsating sdB stars. With over 30 members discovered, the field is now mature enough to turn the success we have enjoyed applying astroseismology of white dwarfs to sdB stars. To do so requires that sufficient photometric data be obtained to resolve the often complex pulsation structure of individual objects. As horizontal branch stars, sdB stars are burning helium in their cores, With their limited hydrogen envelopes, these stars have no shell hydrogen burning simplifying their structure, and making them easier to model. Thus far only a few pulsating sdB stars have resolved pulsation spectra, some of which have revealed very interesting results. The goal of this research is to fully apply the tools of astroseismology to sdB stars by resolving the pulsation spectra of several additional members. This requires substantial telescope time to be split between national facilities, Baker Observatory (operated by our home institution), and multi-site observational campaigns with international collaborators. Pulsating stars may also be used to look for planets. Companions to sdB stars can be detected as periodic variations in the pulsation phases. Such measurements are readily sensitive to sub-Jupiter mass planets with long periods. Broader impacts. Undergraduate students will assist in obtaining and reducing the data in this research project. By exposing undergraduate students to research, they are better able to decide if astronomy is the correct career path for them. Additionally, it allows Southwest Missouri State's students to competitively apply for graduate programs based on a strong undergraduate research experience.