Measurements of Stellar Properties through Asteroseismology: A Tool for Planet Transit Studies

Oscillations occur in stars of most masses and essentially all stages of evolution. Asteroseismology is the study of the frequencies and other properties of stellar oscillations, from which we can extract fundamental parameters such as density, mass, radius, age and rotation period. We present an overview of asteroseismic analysis methods, focusing on how this technique may be used as a tool to measure stellar properties relevant to planet transit studies. We also discuss details of the Kepler Asteroseismic Investigation -- the use of asteroseismology on the Kepler mission in order to measure basic stellar parameters. We estimate that applying asteroseismology to stars observed by Kepler will allow the determination of stellar mean densities to an accuracy of 1%, radii to 2-3%, masses to 5%, and ages to 5-10% of the main-sequence lifetime. For rotating stars, the angle of inclination can also be determined.Comment: To appear in the Proceedings of the 253rd IAU Symposium: "Transiting Planets", May 2008, Cambridge, M

Correcting stellar oscillation frequencies for near-surface effects

In helioseismology, there is a well-known offset between observed and computed oscillation frequencies. This offset is known to arise from improper modeling of the near-surface layers of the Sun, and a similar effect must occur for models of other stars. Such an effect impedes progress in asteroseismology, which involves comparing observed oscillation frequencies with those calculated from theoretical models. Here, we use data for the Sun to derive an empirical correction for the near-surface offset, which we then apply three other stars (alpha Cen A, alpha Cen B and beta Hyi). The method appears to give good results, in particular providing an accurate estimate of the mean density of each star.Comment: accepted for publication in ApJ Letter

The age at first birth and completed fertility reconsidered: findings from a sample of identical twins

In this paper we use new methods and data to reassess the relationship between the age at first birth and completed fertility. In particular we attempt to properly estimate the postponement effect, i.e., the reduction in fertility associated with a delay in childbearing, using a sample of Danish monozygotic twins born 1945--60 to control for unobserved heterogeneity. Within-MZ twin pair estimates of the postponement effect indicate that a one year delay in the first birth reduces completed fertility by about 3% for both males and females. The effect is significantly stronger for older cohorts, and it is stronger for females with a late desired entry into parenthood. Analyses that fail to control for unobservables underestimate this postponement effect between 10--25%, and they underestimate the annual decline of this effect by up to 50%. Moreover, our estimates indicate important changes across cohorts in the relevance of child-preferences and ability characteristics for the age at first birth and the pace and level of subsequent fertility. (AUTHORS)