We present the first stellar spectroscopy in the low-luminosity ( M _ { V } \sim - 9.3 mag ) , dwarf galaxy Leo P. Its significantly low oxygen abundance ( 3 % solar ) and relative proximity ( \sim 1.6 Mpc ) make it a unique galaxy in which 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 H II 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 \sim 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 Ca II absorption , confirming them as cool , evolved stars ; we also recover Ca II 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 100 pc-scale ring structures in H \alpha emission , with the H II 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 .