The helium-to-hydrogen ratio of the UV-bright star Barnard 29 of Messier 13.
Adelman, S. J.; Sweigart, A. V.; Aikman, G. C. L.; Hayes, D. S.; Philip, A. G. D.
United States
Abstract
Barnard 29 is the most luminous UV-bright star of the globular cluster Messier 13. Comparison of its reddening corrected optical region spectrophotometry and IUE low dispersion fluxes and its H-gamma profile with the predictions of metal-poor model atmospheres having the metallicity of M 13 indicated Teff = 20250 K, log g = 3.15. Observations of He I lambda(4026) taken with echelle spectrograph of the Multi-Mirror telescope using a Reticon detector show that He/H = 0.055 +/- 0.020. Some astrophysical implications of this result are discussed.