One way to probe low metallicity massive stars (less than 10% of solar) is to go to distant (> 1 Mpc) dwarf galaxies. However, the combination of distance and foreground extinction makes the observations of individual OB stars in these galaxies very challenging. On the other hand, the Magellanic Bridge, stretching between the Small and the Large Magellanic Cloud (LMC), offers a unique nearby (55 kpc) laboratory to study low-Z massive stars. A population of young stars was discovered throughout the Bridge (Demers & Battinelli 1998). This young population mainly consists of B-type stars or later. Previous studies on chemical abundances of B stars and nebula regions in the Bridge phase suggested a mean metallicity of only 10% of solar (e.g., Rolleston et al. 1999; Lehner et al. 2008).
With high resolution ESO VLT spectroscopy unveiled the presence of three O stars in the Bridge for the first time. The stars are located in the same region of the Bridge, yet they are found to be chemically distinct. One star has a metal content similar to that of LMC O stars. Another star found be in agreement with 10% of solar as observed before. On the other hand, one star in the sample is even more CNO deficient, and this is one of the most metal-poor O stars in the local group. With only 5% of solar metal content it is so far the nearest metal poor massive star!
We attribute the chemical abundance variations in the Bridge stars to insfficient ISM mixing following multiple gas accretion episodes. The HI gas accreted from the last encounter of LMC and SMC 200 Myr ago alone cannot explain the very low metal abundance of the detected O stars, suggesting that the formation of the gaseous component of the Bridge must have started many Gyr ago.
Paper link : https://www.aanda.org/articles/aa/abs/2021/02/aa39486-20/aa39486-20.html
We have obtained new HST UV spectra od these stars to understand their winds and Iron abundances. The analysis is now in progress and the results will be out soon.