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The unveiled main-sequence splitting in omega Centauri as well as NGC 2808 suggests that matter highly-enriched in He (in terms of its mass fraction Y~0.4) was produced and made the color of some main-sequence stars bluer in these globular clusters (GCs). The potential production site for the He-rich matter is generally considered to be massive AGB stars that experience the second dredge-up. However, it is found that massive AGB stars provide the matter with Y~0.35 at most, while the observed blue-shift requires the presence of Y~0.4 matter. Here, we show that extra mixing, which operates in the red giant phase of stars less massive than ~2Msun, could be a mechanism that enhances He content in their envelopes up to Y~0.4. The extra mixing is supposed to be induced by red giant encounters with other stars in a collisional system like GCs. The Y~0.4 matter released in the AGB phase has alternative fates to (i) escape from a GC or (ii) be captured by kinematically cool stars through encounters. The AGB ejecta in omega Cen, which follows the latter case, can supply sufficient He to cause the observed blue-shift. Simultaneously, this scheme generates the extreme horizontal branch, as observed in omega Cen in response to the higher mass loss rates, which is also caused by stellar encounters.
We investigate the integrated far-ultraviolet (FUV) emission from globular clusters. We present new FUV photometry of M~87s clusters based on archival HST WFPC2 F170W observations. We use these data to test the reliability of published photometry bas
Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) s
We study the UV and optical properties of 38 massive GCs in M87, imaged using the HST/STIS and WFPC2 instruments. The majority of these GCs appear extremely bright in the FUV - roughly a magnitude brighter than their Galactic counterparts with simila
The majority of stars form in a clustered environment. This has an impact on the evolution of surrounding protoplanetary discs (PPDs) due to either photoevaporation or tidal truncation. Consequently, the development of planets depends on formation en
We investigate the long-term dynamical evolution of two distinct stellar populations of low-mass stars in globular clusters in order to study whether the energy equipartition process can explain the high number of stars harbouring abundance anomalies