First stellar spectroscopy in Leo P
  We present the first stellar spectroscopy in the low-luminosity (M_V ~-9.3
mag), dwarf galaxy Leo P. Its significantly low oxygen abundance (3% solar) and
relative proximity (~1.6 Mpc) make it a unique galaxy to investigate the
properties of massive stars with near-primordial compositions akin to those in
the early Universe. From our VLT-MUSE spectroscopy we find the first direct
evidence for an O-type star in the prominent HII region, providing an important
test case to investigate the potential environmental dependence of the upper
end of the initial mass function in the dwarf galaxy regime. We classify 14
further sources as massive stars (and 17 more as candidate massive stars), most
likely B-type objects. From comparisons with published evolutionary models we
argue that the absolute visual magnitudes of massive stars in very metal-poor
systems such as Leo P and I Zw 18 may be fainter by ~0.5 mag compared to
Galactic stars. We also present spectroscopy of two carbon stars identified
previously as candidate asymptotic-giant-branch stars. Two of three further
candidate asymptotic-giant-branch stars display CaII absorption, confirming
them as cool, evolved stars; we also recover CaII absorption in the stacked
data of the next brightest 16 stars in the upper red giant branch. These
discoveries will provide targets for future observations to investigate the
physical properties of these objects and to calibrate evolutionary models of
luminous stars at such low metallicity. The MUSE data also reveal two
100pc-scale ring structures in Halpha emission, with the HII region located on
the northern edge of the southern ring. Lastly, we report serendipitous
observations of 20 galaxies, with redshifts ranging from z=0.39, to a close
pair of star-forming galaxies at z=2.5.
