A possible formation channel for blue hook stars in globular cluster - II. Effects of metallicity, mass ratio, tidal enhancement efficiency and helium abundance

TL;DR

This study investigates how metallicity, helium abundance, and other factors influence the formation of blue hook stars in globular clusters using binary stellar evolution models with tidally enhanced winds.

Contribution

It provides a comprehensive analysis of the effects of multiple parameters on blue hook star formation, highlighting the significant role of helium abundance and metallicity, and compares results with observations.

Findings

Metallicity and helium abundance significantly affect BHk star formation.

Mass ratio and tidal efficiency have minimal impact on BHk formation.

Models align well with observed BHk stars in NGC 2808 and ω Cen.

Abstract

Employing tidally enhanced stellar wind, we studied in binaries the effects of metallicity, mass ratio of primary to secondary, tidal enhancement efficiency and helium abundance on the formation of blue hook (BHk) stars in globular clusters (GCs). A total of 28 sets of binary models combined with different input parameters are studied. For each set of binary model, we presented a range of initial orbital periods that is needed to produce BHk stars in binaries. All the binary models could produce BHk stars within different range of initial orbital periods. We also compared our results with the observation in the Teff-logg diagram of GC NGC 2808 and {\omega} Cen. Most of the BHk stars in these two GCs locate well in the region predicted by our theoretical models, especially when C/N-enhanced model atmospheres are considered. We found that mass ratio of primary to secondary and tidal enhancement efficiency have little effects on the formation of BHk stars in binaries, while metallicity and helium abundance would play important roles, especially for helium abundance. Specifically, with helium abundance increasing in binary models, the space range of initial orbital periods needed to produce BHk stars becomes obviously wider, regardless of other input parameters adopted. Our results were discussed with recent observations and other theoretical models.