Max Service with Paul Harding, Dept. of Astronomy
Asteroseismology using Kepler
Recent advances in asteroseismology allow ages of individual stars to be measured. The ages of the stars allow us to trace the formation history of the galaxy. We are interested the and the formation of the galactic stellar halo, which should contain the oldest stars. We will identify a sample of inner halo stars suitable for age determination via asteroseismology with the Kepler satellite. The ages, combined with chemical composition and kinematics of these stars will allow the early assembly history of the Galaxy to be studied directly for the first time. Old stars cannot be indentified directly, instead we will use chemical composition as a predictor of age. Stars with a low fraction of elements other than hydrogen and helium are referred to as metal poor stars. The most metal poor stars are likely to be the oldest stars because the gas from which each generation of stars form is enriched by supernovae, thus the metallicities of more recently formed stars are generally higher. The asteroseismology data is from the Kepler satellite which continuously images a region of the sky close to the disk of the Milky Way. In this region halo stars are outnumbered by the more numerous disk stars by approximately 100,000 to 1. We plan to use imaging techniques to identify stars with an excess of ultraviolet light , as this ultraviolet excess indicates a metal poor star (Sandage et al. 1959). We use Washington filters to measure this excess as they have the best leverage (signal difference between metal poor and metal rich per measurement error) (Geisler et al. 1999). Observations have been made on the CWRU Burrell Schmidt telescope with the Washington C, M, T_2, and 51 filters. A careful error analysis will be performed, to quantify contamination of the halo sample by statistical outliers from the far more numerous disk star population. A pilot study successfully identified a sample of ten halo stars that are currently being observed by Kepler. Their ages may become available in time to discuss as part of this project. We will submit a proposal with collaborators to observe the new sample stars. Followup observations will be taken by collaborators using high-resolution spectroscopy to improve the measurements of composition and gravity.