Context : The object ESO456-SC38 ( Djorgovski 2 ) is one of the globular clusters that is closest to the Galactic center .
It is on the blue horizontal branch and has a moderate metallicity of [ Fe/H ] \sim -1.0 .
It is thus similar to the very old inner bulge globular clusters NGC 6522 , NGC 6558 , and HP 1 , and therefore appears to be part of the primeval formation stages of the Milky Way .

Aims : The aim of this work is to determine an accurate distance and metallicity for ESO456-SC38 , as well as orbital parameters , in order to check similarities with other clusters in the inner bulge that have previously been well studied in terms of spectroscopy and photometry .
This is a considerably fainter cluster that is contaminated by a rich stellar field ; it is also quite absorbed by the dusty foreground .

Methods : We analyzed ESO456-SC38 based on Hubble Space Telescope photometry , with the filters F606W from ACS , F110W and F160W from WFC3 , and photometry in V and I from FORS2 at the VLT .
We combined this with identified stars that are covered by Gaia Data Release 2 .

Results : The isochrone fitting was carried out with the statistical Markov chain Monte Carlo method .
We derive an accurate distance of d _ { \odot } = 8.75 \pm 0.12 kpc and a reddening of E ( B-V ) = 0.81 ^ { +0.02 } _ { -0.02 } .
The best-fitting BaSTI isochrones correspond to an age of 12.70 ^ { +0.72 } _ { -0.69 } Gyr and a metallicity of [ Fe/H ] = -1.11 ^ { +0.03 } _ { -0.03 } .

Conclusions : ESO 456-SC38 adds to the list of moderately metal-poor globular clusters located in the inner bulge .
It is on the blue horizontal branch and is very old .
The cluster is confined to the bulge and bar region , but it does not support the Galactic bar structure .
The old stellar population represented by clusters like this has to be taken into account in models of Galactic bulge formation .
Studying them also provides indications on the formation times of the globular clusters themselves .