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1 Introduction

NGC 6256 is also designated as GCL B1656-3702 , BH208 (van den Bergh & Hagen 1975) and ESO391-SC6. It is sometimes referred to in the literature as Terzan 12, however we do not recommend this nomenclature: Terzan (1971), in a revision of his original lists of new bulge clusters (Terzan 1968, 1971a), assigned the name of Terzan 12 to this cluster, where the previously named Terzan 12 became Terzan 11, because Terzan 11 of the previous list was the same as Terzan 5. Terzan 12 studied in Ortolani et al. (1998) is instead at coordinates $\alpha_{1950} = 18^{\rm h}\, 09^{\rm m}\,14.0^{\rm s}$,$\delta_{1950} = -22^{\rm o}\,45'18''$, and Terzan 5 studied in Ortolani et al. (1996) has coordinates $\alpha_{1950} = 17^{\rm h}45^{\rm m}\,00.3^{\rm s}$,$\delta_{1950} = -24^{\rm o}\,47'46''$.

NGC 6256 is at $\alpha_{1950} = 16^{\rm h}\, 56^{\rm m}\,10.2^{\rm s}$,$\delta_{1950} = -37^{\rm o}\, 02' 49''$ and $l = 347.792^{\rm o}$, $b = 3.306^{\rm o}$.

The cluster structure is very concentrated, with c = 2.50, and it presents a post core-collapse morphology (Trager et al. 1995).

Alcaino (1983) presented a photographic B vs. (B-V) CMD of the cluster, where the horizontal branch (HB) level was close to the detection limit. He suggested that the cluster is metal-rich like 47 Tucanae. He derived $V_{\rm HB} = 18.2$ and E(B-V) = 0.80, and a distance of 11.0 kpc from the Sun. Based on Alcaino's CMD, Webbink (1985) also presents $V_{\rm HB} = 18.2$, but estimated a somewhat higher reddening of E(B-V) = 0.88 which placed the cluster at $d_{\odot} = 9.1$ from the Sun. Webbink lists a rather low metallicity for the cluster, [M/H]=-1.56. The compilation by Harris (1996) indicates $V_{\rm HB} = 18.20$, E(B-V) = 0.84, $d_{\odot} = 8.9$ kpc, $\rm [Fe/H] = -0.70$.

NGC 6717, also known as GCL B1852-2245, Palomar 9, GCl-105 (Alter et al. 1970), ESO523-SC14, has coordinates $\alpha_{1950} = 18^{\rm h}\, 52^{\rm m}\,05.2^{\rm s}$,$\delta_{1950} = -22^{\rm o}\,45'55''$ and $l = 12.877^{\rm o}$, $b = -10.900^{\rm o}$.

The cluster structure is very concentrated, with c = 2.07, and it may have a post-core-collapse morphology (Trager et al. 1995).

Goranskii (1979) presented a photographic colour-magnitude diagram of NGC 6717, where the horizontal branch was close to the detection limit. He also studied a RR Lyrae star, concluding that it was a cluster member. A reddening of E(B-V) = 0.17, a distance from the Sun of $d_{\odot} = 7.6$ kpc, and an estimated metallicity of $ [M/H]\approx -1.3$ were derived. Based on Goranskii's CMD, Webbink (1985) indicated a HB level of $V_{\rm HB} = 15.7$, which combined to a reddening of E(B-V) = 0.20 from integrated colours, led to a distance from the Sun of $d_{\odot} = 7.8$ kpc. Webbink presents a lower metallicity of [M/H]=-2.19. Zinn & West (1984) obtained an integrated spectrum of the cluster in the range 3600- 5700 Å, estimating a reddening of E(B-V) = 0.22, and a metallicity of $\rm [Fe/H] = -1.32$. Harris's (1996) compilation gives $V_{\rm HB} = 15.50$, E(B-V) = 0.21, $d_{\odot} = 6.6$ kpc and $\rm [Fe/H] = -1.32$.Rutledge et al. (1997) derived a metallicity of $\rm [Fe/H] =-1.32 \pm 0.15$, based on the near-infrared CaII triplet lines.

A deep CCD BV photometry was presented by Brocato et al. (1996), showing that NGC 6717 has a moderately blue extended HB. They basically confirm the Zinn & West (1984) values of reddening and metallicity.

In the present study we report V, I photometry for NGC 6256 and B, V photometry for NGC 6717.

In Sect. 2 the observations are described. In Sects. 3 and 4 the clusters NGC 6256 and NGC 6717 are analysed respectively. The concluding remarks are provided in Sect. 5.

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