2005/11/30 by C. Knigge, R. L. Gilliland, Ronald L. Gilliland +7 · 14 citations
Mathematics · Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Binary number #Blue straggler #Globular cluster #Mathematics #Photometry (optics) #Physics #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/500311
published in The Astrophysical Journal 641(1), 281-287 (IOP Publishing) · 19 pages, 3 figures, accepted for publication in ApJ; revised version includes a discussion of an alternative 2-progenitor binary evolution scenario, and an appendix discussing other probable/possible BSS/X-ray matches in globular clusters and related sources
arxiv created 2005/12/10 · openalex publication_date 2006/04/10 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We show that the X-ray source W31 in the core of the globular cluster 47 Tucanae is physically associated with the bright blue straggler BSS 7. The two sources are astrometrically matched to 0 061, with a chance coincidence probability of less than 1%. We then analyze optical time-series photometry obtained with the Hubble Space Telescope ( HST ) and find that BSS 7 displays a 1.56 day periodic signal in the I band. We also construct a broadband (far-ultraviolet through far-red) spectral energy distribution for BSS 7 and fit this with single and binary models. The binary model is a better fit to the data, and we derive the corresponding stellar parameters. All of our findings are consistent with BSS 7 being a detached binary consisting of a blue straggler primary with an X-ray-active, upper-main-sequence companion. The formation of such a system would necessarily involve at least three stars, which is consistent with recent N -body models in which blue stragglers often form via multiple encounters that can involve both single and binary stars. However, we cannot yet entirely rule out the possibility that BSS 7 descended directly from a binary system via mass transfer. The system parameters needed to distinguish definitively between these scenarios may be obtainable from time-resolved spectroscopy.