Discovery of O stars in the tidal Magellanic Bridge: Stellar parameters,
  abundances, and feedback of the nearest metal-poor massive stars and their
  implication for the Magellanic System ecology
  The Magellanic Bridge stretching between the SMC and LMC is the nearest
tidally stripped intergalactic environment and has a low average metallicity of
$Z~0.1Z_{\odot}$. Here we report the first discovery of three O-type stars in
the Bridge using archival spectra collected with FLAMES at ESO/VLT. We analyze
the spectra using the PoWR models, which provide the physical parameters,
ionizing photon fluxes, and surface abundances. This discovery suggests that
the tidally stripped low density gas is capable of producing massive O stars
and their ages imply ongoing star formation in the Bridge. The multi-epoch
spectra indicate that all three O stars are binaries. Despite their spatial
proximity to each other, these O stars are chemically distinct. One of them is
a fast-rotating giant with nearly LMC-like abundances. The other two are
main-sequence stars that rotate extremely slowly and are strongly metal
depleted. This includes the most nitrogen-poor O star known up to date. Taking
into account the previous analyses of B stars in the Bridge, we interpret the
various metal abundances as the signature of a chemically inhomogeneous
interstellar medium, suggesting that the gas might have accreted during
multiple episodes of tidal interaction between the Clouds. Attributing the
lowest derived metal content to the primordial gas, the time of initial
formation of the Bridge may date back to several Gyr. Using the Gaia and Galex
color-magnitude diagrams we roughly estimate the total number of O stars in the
Bridge and their total ionizing radiation. Comparing with the energetics of the
diffuse ISM, we find that the contribution of the hot stars to the ionizing
radiation field in the Bridge is less than 10%, and conclude that the main
sources of ionizing photons are leaks from the LMC and SMC. We estimate a lower
limit for the fraction of ionizing radiation that escapes from these two dwarf
galaxies.
