Red Clump stars in Kepler open cluster NGC 6819

¹ North-West University, Department of Physics, Private Bag X2046, Mmabatho, South Africa
² South African Astronomical Observatory, P. O Box 9, Cape Town, South Africa

^a e-mail: oyigamba@gmail.com

Published online: 23 September 2015

Abstract

We measure the large frequency separation, Δν, and the frequency of maximum amplitude, ν_max, for 10 Red Clump (RC) single member (SM) stars in the Kepler open cluster NGC 6819. We derive luminosities and masses for each individual RC star. A comparison of the observations with an isochrone of Age = 2.5 Gyr, Z = 0.017 with no mass loss using a statistical techniques is made. A fractional mass loss of 5 ± 3 percent is obtained if we assume that no correction to Δν between RC and red-giant branch (RGB) is necessary. However, models suggest that an effective correction of about 1.9 percent in Δν is required to obtain the correct mass of RC stars owing to the different internal structures of stars in the two evolutionary stages. In this case we find that the mass loss in the red giant branch is not significantly different from zero. This finding confirms that of [6]. It is clear that the mass estimate obtained by asteroseismology is not sufficient to deduce the mass loss on the red giant branch. However, it is clearly only a few percent at most.