  Blue straggler star (BSS) candidates have been observed in all old dwarf
spheroidal galaxies (dSphs), however whether or not they are authentic BSSs or
young stars has been a point of debate. To both address this issue and obtain a
better understanding of the formation of BSSs in different environments we have
analysed a sample of BSS candidates in two nearby Galactic dSphs, Draco and
Ursa Minor. We have determined their radial and luminosity distributions from
wide field multicolour imaging data extending beyond the tidal radii of both
galaxies.
  BSS candidates are uniformly distributed through the host galaxy, whereas a
young population is expected to show a more clumpy distribution. Furthermore,
the observed radial distribution of BSSs, normalized to both red giant branch
(RGB) and horizontal branch (HB) stars, is almost flat, with a slight decrease
towards the centre. Such a distribution is at odds with the predictions for a
young stellar population, which should be more concentrated. Instead, it is
consistent with model predictions for BSS formation by mass transfer in
binaries (MT-BSSs). Such results, although not decisive, suggest that these
candidates are indeed BSSs and that MT-BSSs form in the same way in Draco and
Ursa Minor as in globular clusters. This favours the conclusion that Draco and
Ursa Minor are truly 'fossil' galaxies, where star formation ceased completely
more than 8 billion years ago.
