The First Extensive Exploration of UV-bright Stars in the Globular Cluster NGC 2808

• Published in: The Astrophysical journal 2021-02, Vol.908 (1), p.66
• Main Authors: Prabhu, Deepthi S., Subramaniam, Annapurni, Sahu, Snehalata
• Format: Article
• Language: English
• Subjects: Astrophysics; Asymptotic giant branch stars; Effective temperatures; Globular clusters; Globular star clusters; Hertzsprung Russell diagram; Horizontal branch stars; Hubble Space Telescope; Indian spacecraft; Post-asymptotic giant branch stars; Satellites; Space telescopes; Stellar age; Stellar evolution; Ultraviolet photometry
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/abd2b5

In this study, we identified and characterized the hot and luminous UV-bright stars in the globular cluster NGC 2808. We combined data from the Ultra Violet Imaging Telescope (UVIT) on board the Indian space satellite AstroSat with the Hubble Space Telescope UV Globular Cluster Survey data for the central region (within ) and Gaia and ground-based optical photometry for the outer parts of the cluster. We constructed the UV and UV-optical color-magnitude diagrams, compared the horizontal branch (HB) members with the theoretical zero- and terminal-age HB models, and identified 34 UV-bright stars. The spectral energy distributions of the UV-bright stars were fitted with theoretical models to estimate their effective temperatures (12,500-100,000 K), radii (0.13-2.2 R ), and luminosities (∼40-3000 L ) for the first time. These stars were then placed on the Hertzsprung-Russell diagram, along with theoretical post-HB evolutionary tracks, to assess their evolutionary status. The models suggest that most of these stars are in the asymptotic giant branch (AGB)-manqué phase, and all except three have evolutionary masses