massive merger in eta,chi Persei star-clusters?

[Widdekind]

According to this lecture, pp.39-41, when two MS stars merge, they make a single, new, MS star, of the combined mass; and, an anomalous star, in eta+chi Persei, is ~60 Msol, even when the MS turn-off, of those ~14 Myr old star-clusters, is ~30 Msol -- which would make the same a 'Blue Straggler' (BS). Perhaps the merger "mixes up" the stellar materials, thereby (partially) "refreshing" the fusion processes, in the combined composite resultant star? (Otherwise, why would mixing two old, H-depleted, and He-polluted, stars, which were evolving off the MS, with the rest of their stellar siblings, manage to make an effectively "rejuvinated" more massive star?)

 

Edit -- Wikipedia points to 'SX Phoenicis variable' stars, which are BSs, 'below' the MS, of their GC companions. That means, that they are hotter-and-bluer than stars of the same luminosity (and so smaller); and, dimmer than stars of the same temperature (and so smaller). They also have "high space velocities", and reside within the star-dense cores of GCs. Perhaps, then, they represent, if not a full-fledged merger (as above), a "close encounter", which ripped off their outer-envelope? Such a "skinning of a star" would "White-Dwarf-ize" the star, making it bluer-but-smaller, as hotter-but-smaller once-interior layers were now exposed to space.

 

Re-edit -- according to this article, SX Phoenicis variables reside, on the HR diagram, near the MS base, of the Instability Strip:

 

They also have "high amplitude" pulsations, characteristic of full-fledged Cepheids, which can 'puff up' to >5 AU in radius:

 

Such suggests, then, that variable SX-Ph BSs were once full-fledged, large-amplitude Cepheids, who were "caught while bloated", in a near-miss, close-encounter, with another GC companion, which ripped off much of their outer envelope. Note, tho', that the persistence of pulsations, of still-long-period, even after the outer-envelope was ripped away, implies that the pulsations are driven by deeper processes, beneath those "shed and not necessary" outer shell layers.