| Title: |
Observations of the Ultraviolet-bright Star III-60 in the Globular Cluster NGC 6723. |
| Authors: |
Dixon, William V.1 (AUTHOR) dixon@stsci.edu |
| Source: |
Astrophysical Journal. 2/10/2025, Vol. 980 Issue 1, p1-11. 11p. |
| Subject Terms: |
*STELLAR atmospheres, *STELLAR evolution, *STELLAR winds, *STARS, *ULTRAVIOLET spectroscopy |
| Abstract: |
We have analyzed archival far-ultraviolet spectra of the UV-bright star III-60 in the globular cluster NGC 6723 obtained with the Far Ultraviolet Spectroscopic Explorer and the Cosmic Origins Spectrograph. We find that the star's photospheric parameters (effective temperature T eff = 44,800 ± 1200 K, surface gravity log g = 4.89 ± 0.18 , and helium abundance log N (He) / N (H) = − 0.84 ± 0.29 ) are consistent with the values derived from its optical spectrum, suggesting that optically derived values are generally accurate for evolved stars with T eff ≲ 50,000 K. Relative to the cluster's red giant branch stars, III-60 is enhanced in nitrogen and depleted in carbon and oxygen. The star exhibits strong P Cygni profiles in both components of the N v λ 1240 doublet, but the resonance lines of other species show no evidence of a stellar wind. The star's effective temperature and luminosity place it on the evolutionary tracks of stars evolving from the blue horizontal branch, but its high mass (∼1.2 M ⊙) indicates that it is the product of a stellar merger. Its helium, carbon, and nitrogen abundances suggest that it is following an evolutionary path similar to that of the low-carbon, intermediate helium-rich hot subdwarfs. [ABSTRACT FROM AUTHOR] |
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