On the Evidence of Disks around Blue Straggler Stars

Recent observations of blue stragglers by De Marco et al. (2004) haverevealed continuum deficits on the blue side of the Balmer discontinuity,leading these authors to infer the presence of discs around the stars. Thisintriguing possibility may throw light on aspects of the mechanisms responsiblefor at least some of these objects; current theories of blue stragglerformation invoke stellar collisions or interacting binaries, both of whichappear capable of forming a circumstellar disc. However, by synthesizing photospheric spectra for models of rotating bluestragglers, we demonstrate that the Balmer jump enhancements can be whollyattributed to the influence of oblateness and gravity darkening on theformation of the continuum. Therefore, we are led to conclude that theobservations of De Marco et al. can be ascribed a more prosaic explanation,that of rapid stellar rotation arising from the merger/interaction formationprocess.Comment: 4 pages, 4 figures. Accepted for publication in Ap.J. Letter