A Photometric Study of the Outer Halo Globular Cluster NGC 5824
  Multi-wavelength CCD photometry over 21 years has been used to produce deep
color-magnitude diagrams together with light curves for the variables in the
Galactic globular cluster NGC 5824. Twenty-one new cluster RR Lyrae stars are
identified, bringing the total to 47, of which 42 have reliable periods
determined for the first time. The color-magnitude diagram is matched using
BaSTI isochrones with age of $13$~Gyr. and reddening is found to be $E(B-V) =
0.15 \pm0.02$; using the period-Wesenheit relation in two colors the distance
modulus is $(m-M)_0=17.45 \pm 0.07$ corresponding to a distance of 30.9 Kpc.
The observations show no signs of populations that are significantly younger
than the $13$~Gyr stars. The width of the red giant branch does not allow for a
spread in [Fe/H] greater than $\sigma = 0.05$ dex, and there is no photometric
evidence for widened or parallel sequences. The $V, c_{UBI}$ pseudo-color
magnitude diagram shows a bifurcation of the red giant branch that by analogy
with other clusters is interpreted as being due to differing spectral
signatures of the first (75\%) and second (25\%) generations of stars whose age
difference is close enough that main sequence turnoffs in the color-magnitude
diagram are unresolved. The cluster main sequence is visible against the
background out to a radial distance of $\sim17$ arcmin. We conclude that NGC
5824 appears to be a classical Oosterhoff Type II globular cluster, without
overt signs of being a remnant of a now-disrupted dwarf galaxy.
