Empirical determination of the integrated red giant and horizontal branch stellar mass-loss in ω Centauri

Abstract

Abstract We herein determine the average integrated mass-loss from stars belonging to the dominant metal-poor population ([Fe/H] ∼−1.7) of the Galactic globular cluster ω Centauri (NGC 5139) during their red giant and horizontal branch (HB) evolution. Masses are empirically calculated from spectroscopic measurements of surface gravity and photometric measurements of temperature and luminosity. Systematic uncertainties prevent an absolute measurement of masses at a phase of evolution. However, the relative masses of early asymptotic giant branch (AGB) stars and central red giant branch (RGB) stars can be measured, and used to derive the mass-loss between these two phases. This can then be used as a physical check of models of HB stars. For ω Centauri, the average difference is found to be 26 ± 4 per cent. Assuming initial and final masses of 0.83 and 0.53 M⊙, we determine that 0.21 ± 0.03 M⊙ is lost on the RGB and 0.09 ±∼0.05 M⊙ is lost on the AGB. The implied HB stellar mass of 0.62 ± 0.04 M⊙ is commensurate with literature determinations of the masses of the cluster’s HB stars. The accuracy of this measurement can be improved through better selection of stars and spectral coverage, and applied to other clusters where HB models do not currently agree.