Blue Straggler Masses from Pulsation Properties. I. The Case of NGC 6541

We used high spatial resolution images acquired with the Wide Field Camera 3 on board Hubble Space Telescope to probe the population of variable blue straggler stars (BSSs) in the central region of the poorly studied Galactic globular cluster NGC 6541. The time sampling of the acquired multiwavelength (F390W, F555W, and F814W) data allowed us to discover three WUMa stars and nine SX Phoenicis. Periods, mean magnitudes, and pulsation modes have been derived for the nine SX Phoenicis, and their masses have been estimated by using pulsation equations obtained from linear nonadiabatic models. We found masses in the range 1.0-1.1 M _⊙, with an average value of 1.06 ± 0.09 M _⊙ (σ = 0.04), significantly in excess of the cluster main-sequence turn-off mass (~0.75 M _⊙). A mild trend between mass and luminosity seems also to be present. The computed pulsation masses turn out to be in very good agreement with the predictions of evolutionary tracks for single stars, indicating values in the range ~1.0-1.2 M _⊙ for most of the BSS population, in agreement with what was discussed in a number of previous studies.