Spectrum of stars in NGC 6822 and the Milky Way galaxy

This chart displays a FORS1 spectrum of a blue supergiant in NGC 6822 (in the middle), as compared with those of supergiant stars (upper and lower) of similar atmospheric temperature in the Milky Way Galaxy. The observations were carried out by the FORS Commissioning Team on October 1, 1998, using the Multiple Object Spectroscopy (MOS) mode of FORS1. A total of 11 stars in NGC 6822 were observed simultaneously with an exposure time of 30 min. The visual magnitude of supergiant star centered on slit no. 5 is V = 18.11 and the spectral type is in the interval O9.5Ia - B0Ia. It is apparent from the figures that many spectral lines in the supergiant star in NGC 6822 are much weaker than in the Milky Way counterparts.This confirms the earlier finding that NGC 6822 has a different chemical composition - a lower content of heavy elements (or "metallicity") - than what is observed in our Galaxy.