Context :

Aims : Dwarf spheroidal galaxies in the Local Group are usually located close to the Milky Way or M31 .
Currently , there are two clear exceptions to this rule , and the Tucana dwarf galaxy is the most distant at almost 1 Mpc from the Milky Way .
Our aim is to learn more about the nature of Tucana by measuring its radial velocity and internal kinematics .

Methods : Using the VLT/FORS2 spectrograph in multi-object mode we were able to measure the velocities of 23 individual Red Giant Branch stars in and around Tucana using the Ca triplet absorption lines .
From this sample , 17 reliable members have been identified .

Results : We measured the systemic velocity and dispersion of Tucana to be v _ { hel } = +194.0 \pm 4.3 { km s } ^ { -1 } and \sigma _ { l . o . s . } = 15.8 ^ { +4.1 } _ { -3.1 } respectively .
These measures are derived after removing the signature of rotation using a linear gradient of 6.5 \times R / R _ { core } \pm 2.9 { km s } ^ { -1 } , which corresponds to a rotation of \approx 16 { km s } ^ { -1 } at the reliable limit of our data .
Our systemic velocity corresponds to a receding velocity from the barycentre of the Local Group of v _ { LG } = +73.3 { km s } ^ { -1 } .
We also determined the mean metallicity of Tucana to be [ Fe/H ] = -1.95 \pm 0.15 with a dispersion of 0.32 \pm 0.06 dex .

Conclusions : Our study firmly excludes any obvious association of Tucana with the H I emission in the vicinity and shows that Tucana is a genuine dwarf spheroidal , with low metallicity stars , no gaseous ISM and no recent star formation .
The present location and relatively high recession velocity are consistent with Tucana having been an isolated Local Group galaxy for the majority of its existence .