Decreasing Systematic Errors in Estimates of Stellar Ages

Yale University, New Haven CT

Investigators

Abstract

One of the more difficult problems in astrophysics is determining how old a star is. We can measure the mass of a star and how big it is. We can find out how hot it is and what it is made of. But to find out how old a star is, we rely on computer models. Stellar models can be very uncertain; making models requires us to estimate parameters that we are unable to actually measure. Asteroseismology is the study of stars by measuring the way their surfaces pulsate. Stars like the Sun pulsate, and the frequencies of stellar pulsation carry information about the interior of the star. Asteroseismic data will be used to refine the basic parameters of stellar models and thereby obtain more reliable age estimates. These results will be important for a wide range of other astronomical topics, including studies of extrasolar planets. This program will provide student training in techniques of data analysis, statistics, and computational methods that have a wide range of technical and commercial applications. Estimates of stellar ages suffer from uncertainties, because parameters that cannot be determined from first principles need to be chosen before models can be constructed. The most important among the free parameters are the mixing length parameter and the initial helium abundance. Secondary parameters include overshoot. The aim of this investigation is to use asteroseismic data to constrain model parameters. Asteroseismic data will be used to determine whether and how the mixing length parameter varies as a function of stellar parameters, in particular with metallicity. The same will be done for the the initial helium abundance. These results will then be used to construct improved isochrones. The signature of core-overshoot will also be studied using seismic data. A related theoretical investigation will investigate whether the entropy-(metallicity, effective temperature, surface gravity) relationships determined from convection simulations match the mixing-length parameter determined with seismic data.