Discovery of a nitrogen-rich uv-bright star in the globular cluster M5.
Bohlin, R. C.; Stecher, T. P.; Cornett, R. H.; Hill, J. K.; Smith, A. M.; Sweigart, A. V.
United States
Abstract
Ultraviolet images of the globular cluster M5 (NGC 5904) obtained with a rocket-borne telescope show a hot and luminous star ≡20arcsec from the cluster center. Spectra of this UV-bright star, obtained with the IUE satellite in the low-resolution mode, reveal an energy distribution very similar to that of μ Col, a Population I O9.5 IV star. Assuming an effective temperature of 35,000K for the UV-bright star, the authors find L = 1800 L_sun;, Mbol = -3.40, R = 1.15 R_sun;, and log g = 4.04. The N V λ1240 line is much stronger in the UV-bright star than in μ Col, indicating that the CNO cycle has converted the envelope C and O into N. A single emission line at the wavelength of the N IV intercombination line is also present, suggesting the possible existence of a planetary nebula.