2003AJ....125..801H

We present the first detailed CCD photometric study of the Galactic globular cluster NGC 6235. Our BV color-magnitude diagram extends from above the tip of the first-ascent red giant branch (RGB) to 3 mag below the horizontal branch (HB). Based on an examination of the predominantly blue HB, we conclude that there is significant differential reddening in the direction of NGC 6235. We correct the photometry for this effect. By comparing the mean location of the blue HB stars in NGC 6235 with those of other clusters of similar metallicity, we infer a mean RR Lyrae magnitude of V(RR)=16.87±0.10. The shape and location of the RGB are used to establish a metal abundance of [Fe/H]=-1.18±0.09 on the Zinn & West scale, which translates to [Fe/H]=-0.99±0.07 by using the Carretta & Gratton scale. The mean reddening of NGC 6235, estimated using the metal abundance along with the apparent color of the RGB, is E(B-V)=0.24±0.03. Lastly, we determine the distance of NGC 6235 to be in the range 15.47≤(m-M)₀≤15.57, depending on the value we adopt for the absolute magnitude of the RR Lyrae stars.