Testing massive star evolution, star-formation history and feedback at
  low metallicity : Spectroscopic analysis of OB stars in the SMC Wing
  Stars which start their lives with spectral types O and early-B are the
progenitors of core-collapse supernovae, long gamma-ray bursts, neutron stars,
and black holes. These massive stars are the primary sources of stellar
feedback in star-forming galaxies. At low metallicities, the properties of
massive stars and their evolution are not yet fully explored. Here we report a
spectroscopic study of 320 OB stars in the Small Magellanic Cloud. The data,
which we obtained with the ESO Very Large Telescope, were analyzed using
state-of-the-art stellar atmosphere models. We find that stellar winds of our
sample stars are much weaker than theoretically expected. The stellar rotation
rates show a bi-modal distribution. The well-populated upper
Hertzsprung-Russell diagram including our sample OB stars from SMC Wing as well
as additional evolved stars all over SMC from the literature shows a strict
luminosity limit. The comparison with single-star evolutionary tracks suggests
a dichotomy in the fate of massive stars in the SMC. Only stars with
Minit<30M$_{\odot}$ seem to evolve from the main sequence to the cool side of
the HRD to become a red supergiant and to explode as type II-P supernova. In
contrast, stars with Minit>30M$_{\odot}$ appear to stay always hot and might
evolve quasi chemically homogeneously, finally collapsing to relatively massive
black holes. However, we find no indication that chemical mixing is correlated
with rapid rotation. We report extended star-formation episodes in a quiescent
low-density region of the Wing, which is progressing stochastically. We measure
the key parameters of stellar feedback and establish the links between the
rates of star formation and supernovae. Our study reveals that in metal-poor
environments the stellar feedback is dominated by core-collapse supernovae in
combination with winds and ionizing radiation supplied by a few of the most
massive stars.
