The blue plume population in dwarf spheroidal galaxies: young stellar population or genuine blue stragglers?

Abstract

In the context of dwarf spheroidal galaxies it is hard to firmly disentangle a genuine Blue Stragglers (BSS) population from a normal young main (MS) sequence. This difficulty is persistent. For a sample of 9 non-star forming Local Group dwarf galaxies we compute the ``BSS frequency'' and compare it with that found in the Milky Way globular/open clusters and halo. The comparison shows that the BSS-frequency in dwarf galaxies, at any given Mv, is always higher than that in globular clusters of similar luminosities. Moreover, the estimated BSS-frequency for the lowest luminosity dwarf galaxies is in excellent agreement with that observed in the Milky Way halo and open clusters. We conclude that the low density, almost collision-less environment, of our dwarf galaxy sample point to their very low dynamical evolution and consequent negligible production of collisional BSS.

5 pages, 1 colour figure, contribution talk given at the Cefalu' 2007 Workshop "XXI Century Challenges for Stellar Evolution". To appear in Memorie della Societa' Astronomica Italiana, vol. 79/2, eds. S. Cassisi & M. Salaris