Stellar Rotation and the Chronology of the Galaxy

Ohio State University, The, Columbus OH

Investigators

Abstract

Our understanding of how the universe around us changes with time is limited by our ability to measure ages of stars. Unlike other fundamental properties, this is not something that we are able to measure directly. We have some limited idea, at least in a statistical sense, for some stars - particularly those all formed together in "clusters". We have also developed sophisticated computer models that predict how other observed properties change in time, which we can compare to observations of real stars. Stars spin rapidly when they are formed, but their spin slows with time. A lot of effort is going into developing a better understanding of how this happens. The goal of "gyrochronology" is to be able to infer the age of a star by measuring how fast it spins, with careful consideration of its other measureable properties (not all stars with the same spin rate have the same age). This project will attempt to resolve many of the uncertainties through a careful comparison of theoretical models describing how stars spin down, measurements of long-period rotators (tens of days) using the unprecedented database from the Kepler spacecraft, and follow-up observations from ground-based observatories. The proposed activities will directly contribute to the training of a graduate student in observational and theoretical astrophysics, as well as advanced statistical analysis. It will also provide research opportunities for undergraduate students. The PI will also lead efforts to use the new Planetarium at Ohio State as a laboratory for data visualization. The CoPIs, along with a graduate student and two collaborators who are experts using the Kepler database, will conduct a careful observational and theoretical study with the goal of producing a well-calibrated rotation-age relation for field stars. This will be based on a more careful analysis of the properties of cluster stars, measurements of longer periods using Kepler data with follow-up observations at the MDM observatory at Kitt Peak, and detailed models of angular momentum loss in stars. It will benefit from the team's expertise in asteroseismology and statistics. Gyrochronology is being applied to a vast array of astrophysical problems, from planetary to extragalactic, yet there are serious complications involved in establishing a single-valued function between rotation rate and age. This team has identified all of the complications and laid out a plan that could lead to a well-constrained and widely-applicable gyrochronology law for field stars.