Sounding open clusters: Asteroseismic constraints from kepler on the properties of NGC6791 and NGC6819

Abstract

We present initial results on some of the properties of open clusters NGC6791 and NGC6819 derived from asteroseismic data obtained by NASA's Kepler mission. In addition to estimating the mass, radius, and log g of stars on the red giant branch (RGB) of these clusters, we estimate the distance to the clusters and their ages. Our model-independent estimate of the distance modulus of NGC6791 is (m - M)0 = 13.11 0.06. We find (m - M)0 = 11.85 0.05 for NGC6819. The average mass of stars on the RGB of NGC6791 is 1.20 0.01 M, while that of NGC6819 is 1.68 0.03 M. It should be noted that we do not have data that cover the entire RGB and the actual mass will be somewhat lower. We have determined model-dependent estimates of ages of these clusters. We find ages between 6.8 and 8.6 Gyr for NGC6791, however, most sets of models give ages around 7 Gyr. We obtain ages between 2 and 2.4 Gyr for NGC6819. © 2011. The American Astronomical Society. All rights reserved.