Double stars are common.
So are stars with two names. The distance, and consequently the luminosities, of the stars are not well known. Direct measures give 735 light years, but with a large error. Rather unusual among bright naked eye stars, Sigma's light is dimmed by interstellar dust by over a magnitude, which must be corrected for. To be a giant now, one that has already started its death process, the class B star must once have been the more massive of the pair.