Towards a better understanding of the distance scale from RR Lyrae
  variable stars: A case study for the inner halo globular cluster NGC 6723
  We present BV photometry for 54 variables in the metal-rich inner halo
globular cluster NGC6723. With the discovery of new RR Lyrae variables (RRLs),
we obtain <P_ab> = 0.541 +/- 0.066 and <P_c> = 0.292 +/- 0.030 day,
n(c)/n(ab+c) = 0.167, and <V(RR)>_int = 15.459 +/- 0.055. We carry out the
Fourier decomposition analysis and obtain [Fe/H]_ZW = -1.23 +/- 0.11 and E(B-V)
= 0.063 +/- 0.015 for NGC 6723. By calibrating the zero-point from the recent
absolute trigonometric parallax measurements for RR Lyr, we derive the revised
M_V(RR)-[Fe/H] relation, providing M_V(RR)= 0.52 at [Fe/H] = -1.50 and (m-M)_0
= 18.54 for Large Magellanic Cloud (LMC), in excellent agreement with others.
We obtain (m-M)_0 = 14.65 +/- 0.05, equivalent to the distance from the Sun of
8.47 +/- 0.17 kpc, for NGC 6723 from various distance measurement methods using
RRLs. We find that RRLs in NGC 6723 do not have magnitude dependency on the
radial distance, due to a not severe degree of the apparent crowdedness.
Finally, we show that there exists a relation between the degree of photometric
contamination and the apparent crowdedness of the central region of globular
cluster systems. The use of this relation can play a significantly role on
mitigating the discrepancy to establish a cosmic distance scale using RRLs in
resolved stellar populations in the near-field cosmology.
