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J.F. Sepinsky, R.A. Saffer, C.S. Pilman (Villanova University), G. DeMarchi, F. Paresce (ESO)
Blue Straggler Stars (BSS) in Galactic globular clusters (GCs) are thought to be formed via as-yet poorly understood interactions in binary star systems in the dense cluster cores, perhaps by the merger of two (or possibly more) stars into a single star. These stars reside on the Main Sequence beyond the cluster turn-off. NGC 6397 has six bright BSS in the cluster core, two of which are too blue, and too hot according to a model atmosphere analysis, to have been formed from mergers of only two lower-mass stars. If pure merger products, they must both have been formed by the coalescence of at least {\em three} lower mass stars. Alternatively, and more likely, is that their excess blue light is due to the presence of hitherto undetected compact hot companions, implying that they formed in heirarchical multiple star systems, or have perhaps captured an additional star at some point in their lifetimes. Other possible formation scenarios include mass accretion from their (presumed) binary companions. In this display paper, we present the results of our spectroscopic analysis of HST FOS spectra of the six BSS, namely masses and rotation rates, and we discuss the implications of our findings for their evolutionary history.
The author(s) of this abstract have provided an email address for comments about the abstract: mailto:jeremy@ast.villanova.edu