A Detached Eclipsing Binary near the Turnoff of the Open Cluster NGC 6819 and Determining Age Using Kepler
American Astronomical Society, AAS Meeting #221, #250.36
Published in Jan 2013
Measurements of the mass and radius of detached eclipsing binaries (DEB) can be used to accurately determine the ages of clusters if an eclipsing star is evolved enough and sits near the cluster turnoff on the color-magnitude diagram (CMD). Multiple DEBs in a cluster can constrain the age even more tightly, and can also lead to inferences about chemical composition (such as helium abundance). As part of our study of the old 2.5 Gyr) open cluster NGC 6819 in the Kepler field, we present results for the DEB Auner 665 (WOCS 24009) with a short period of 3.6 days. We make use of photometric observations from the Kepler spacecraft and from the 1 m telescope at Mount Laguna Observatory in B, V, Rc, and Ic. Radial velocities were measured as part of a long-term study of the cluster (e.g., Hole et al. 2009) using the WIYN 3.5-meter telescope. A665 is a triple-lined system, and we verify that the brightest star is physically orbiting the eclipsing binary based on radial velocities and eclipse timing variations. The stars that make up the detached eclipsing binary are almost identical in temperature, with eclipses that are only clearly distinguishable using Kepler photometry. A new astrometric study of NGC 6819 confirms the cluster membership probability of A665 at a level of P=99%. Ultimately, we will compare the masses and radii obtained with theoretical isochrones and analyze the derived age of NGC 6819, which can also be used to improve stellar theoretical models with better constraints in the mass-radius plane. Our target is to reduce the uncertainty on the cluster age to less than 10% using results from A665 and other known DEBs. The results for this system will also help produce a valuable test of the asteroseismic mass estimates for giant stars in the cluster (Stello et al. 2011). We gratefully acknowledge funding from the National Science Foundation under grant AST-0908536 and NASA under grants NNX11AC76G and NNX12AC88G.
(c) 2013: American Astronomical Society