Spectral Energy Distribution of Blue Stragglers in the Core of 47 Tucanae

Abstract

We have constructed the spectral energy distributions (SEDs) of a sample of blue straggler stars (BSSs) in the core of the globular cluster 47 Tucanae, taking advantage of the large set of high resolution images, ranging from the ultraviolet to the near-infrared, obtained with the Advanced Camera for Surveys/High Resolution Channel of the Hubble Space Telescope. Our final BSS sample consists of 22 objects, spanning the whole color and magnitude extension of the BSS sequence in 47 Tucanae. We fitted the BSS broadband SEDs with models to derive temperature, surface gravity, radius, luminosity, and mass. We show that BSSs indeed define a mass sequence, where the mass increases for increasing luminosity. Interestingly, the BSS mass estimates from the SED fitting turn out to be comparable to those derived from the projection of the stellar position in the color-magnitude diagram on standard star evolutionary tracks. We compare our results with previous, direct mass estimates of a few BSSs in 47 Tucanae. We also find a couple of supermassive BSS candidates, i.e., BSSs with masses larger than twice the turn-off mass, the formation of which must have involved more than two progenitors.