CCD time-series photometry of the globular cluster NGC 5053: RR Lyrae,
  Blue Stragglers and SX Phoenicis stars revisited
  We report the results of CCD $V$, $r$ and $I$ time-series photometry of the
globular cluster NGC 5053. New times of maximum light are given for the eight
known RR Lyrae stars in the field of our images and their periods are revised.
Their $V$ light curves were Fourier decomposed to estimate their physical
parameters. A discussion on the accuracy of the Fourier-based iron abundances,
temperatures, masses and radii is given. New periods are found for the 5 known
SX Phe stars and a critical discussion of their secular period changes is
offered. The mean iron abundance for the RR Lyrae stars is found to be [Fe/H]
$\sim -1.97 \pm 0.16$ and lower values are not supported by the present
analysis. The absolute magnitude calibrations of the RR Lyrae stars yield an
average true distance modulus of $16.12 \pm 0.04$ or a distance of $16.7 \pm
0.3$ kpc. Comparison of the observational CMD with theoretical isochrones
indicates an age of $12.5 \pm 2.0$ Gyrs for the cluster. A careful
identification of all reported Blue Stragglers (BS) and their $V,I$ magnitudes
leads to the conclusion that BS12, BS22, BS23 and BS24 are not BS. On the other
hand, three new BS are reported. Variability was found in seven BS, very likely
of the SX Phe type in five of them, and in one red giant star. The new SX Phe
stars follow established $PL$ relationships and indicate a distance in
agreement with the distance from the RR Lyrae stars.
