Discovery of a hot post-AGB star in Galactic globular cluster E3
Abstract
We report a new hot post-asymptotic giant branch (PAGB) star in the Galactic globular cluster (GC) E3, which is one of the first of the identified PAGB stars in a GC to show a binary signature. The star stands out as the brightest source in E3 in the Astrosat/UVIT images. We confirmed its membership with the cluster E3 using Gaia DR3 kinematics and parallax measurements. We supplemented the photometric observations with radial velocities (RVs) from high-resolution spectroscopic observations at two epochs and with ground- and space-based photometric observations from 0.13 μm to 22 μm. We find that the RVs vary over ∼6 km s−1 between the two epochs. This is an indication of the star being in a binary orbit. A simulation of possible binary systems with the observed RVs suggests a binary period of either 39.12 days or 17.83 days with mass ratio q ≥ 1.0. The [Fe/H] derived using the high-resolution spectra is ∼−0.7 dex, which closely matches the cluster metallicity. The spectroscopic and photometric measurements suggest Teff and logg of the star as 17 500 ± 1000 K and 2.37 ± 0.20 dex, respectively. Various PAGB evolutionary tracks on the Hertzsprung-Russell (H-R) diagram suggest a current mass of the star in the range 0.51-0.55 M⊙. The star is enriched with C and O abundances, showing similar CNO abundances compared to the other PAGB stars in GCs with the evidence of the third dredge-up on the AGB phase.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- May 2024
- DOI:
- 10.1051/0004-6361/202449777
- arXiv:
- arXiv:2403.12907
- Bibcode:
- 2024A&A...685L...6K
- Keywords:
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- stars: abundances;
- stars: AGB and post-AGB;
- binaries: spectroscopic;
- stars: evolution;
- ultraviolet: stars;
- galaxies: star clusters: individual: E3;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- Published in A&