  We used high-spatial resolution images acquired with the WFC3 on board HST to
probe the population of variable blue straggler stars in the central region of
the poorly studied Galactic globular cluster NGC 6541. The time sampling of the
acquired multi wavelength (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 non adiabatic
models. We found masses in the range 1.0-1.1Mo, with an average value of
1.06+-0.09 Mo (sigma = 0.04), significantly in excess of the cluster Main
Sequence Turn Off mass (~ 0.75Mo). 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 Mo for most of the BSS population, in
agreement with what discussed in a number of previous studies.
