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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 m to 22 m. We find that the RVs vary over 6 \ 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 q1. 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 \ and g of the star as 17\, 5001\, 000~K and 2. 370. 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. 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.
Kumar et al. (Tue,) studied this question.