Observations of the Ultraviolet-bright Star ZNG 1 in the Globular Cluster M5 (NGC 5904)

We have analyzed archival spectra of the hot UV-bright star ZNG 1 in the globular cluster M5 (NGC 5904) obtained with the Far Ultraviolet Spectroscopic Explorer and the Space Telescope Imaging Spectrograph. From these data, we derive an effective temperature T eff = 43,000 ± 1400 K, a surface gravit...

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Bibliographic Details
Published in:The Astronomical journal 2024-02, Vol.167 (2), p.47
Main Author: Dixon, William V.
Format: Article
Language:English
Subjects:
Atmospheric models
Globular clusters
Helium
Helium-rich stars
Rotation
Space telescopes
Stars
Stellar abundances
Stellar atmospheres
Stellar evolution
Stellar mass
Terminal velocity
Ultraviolet astronomy
White dwarf stars
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Summary:We have analyzed archival spectra of the hot UV-bright star ZNG 1 in the globular cluster M5 (NGC 5904) obtained with the Far Ultraviolet Spectroscopic Explorer and the Space Telescope Imaging Spectrograph. From these data, we derive an effective temperature T eff = 43,000 ± 1400 K, a surface gravity log g = 4.47 ± 0.08, a rotational velocity v sin i = 157 ± 12 km s −1 , and a mass M = 0.92 ± 0.17 M ☉ . The atmosphere is helium-rich ( Y = 0.99) and enhanced in CNO (relative to the cluster). The spectrum exhibits wind features with a terminal velocity near 1500 km s −1 and strong discrete absorption components. The high helium abundance, stellar mass, and rotational velocity suggest that the star is a merger remnant, and its parameters are consistent with models of a pair of merging He-core white dwarfs.
ISSN:0004-6256
1538-3881
DOI:10.3847/1538-3881/ad11e0