Context : In the Milky Way , most globular clusters are highly conspicuous objects that were found centuries ago .
However , a few dozen of them are faint , sparsely populated systems that were identified largely during the second half of the past century .
One of the faintest is ESO 37-1 ( E 3 ) and as such it remains poorly studied , with no spectroscopic observations published so far although it was discovered in 1976 .

Aims : We investigate the globular cluster E 3 in an attempt to better constrain its fundamental parameters .
Spectroscopy of stars in the field of E 3 is shown here for the first time .

Methods : Deep , precise VI CCD photometry of E 3 down to V \sim 26 mag is presented and analysed .
Low-resolution , medium signal-to-noise ratio spectra of nine candidate members are studied to derive radial velocity and metallicity .
Proper motions from the UCAC4 catalogue are used to explore the kinematics of the bright members of E 3 .

Results : Isochrone fitting indicates that E 3 is probably very old , with an age of about 13 Gyr ; its distance from the Sun is nearly 10 kpc .
It is also somewhat metal rich with [ Fe/H ] = -0.7 .
Regarding its kinematics , our tentative estimate for the proper motions is ( \mu _ { \alpha } ~ { } \cos \delta, \mu _ { \delta } ) = ( -7.0 \pm 0.8 , 3.5 \pm 0.3 ) mas yr ^ { -1 } ( or a tangential velocity of 382 \pm 79 km s ^ { -1 } ) and for the radial velocity 45 \pm 5 km s ^ { -1 } in the solar rest frame .

Conclusions : E 3 is one of the most intriguing globular clusters in the Galaxy .
Having an old age and being metal rich is clearly a peculiar combination , only seen in a handful of objects like the far more conspicuous NGC 104 ( 47 Tucanae ) .
In addition , its low luminosity and sparse population make it a unique template for the study of the final evolutionary phases in the life of a star cluster .
Unfortunately , E 3 is among the most elusive and challenging known globular clusters because field contamination severely hampers spectroscopic studies .