Eta Carina is one of the most massive and luminous stars known in the Milky Way. S Doradus (above Hubble Space Telescope photo) is very nearly it's counterpart in the Large Magellanic Cloud. It is an A0 star with a luminosity about 500,000 times that of the sun ,with a so-called 'P-Cygni' profile spectroscopically, indicating a massive outflow of gas from its surface. There is no positive proof that S Doradus is a single star, however. In a study by Serge Gaposhkin in 1943, he obtained a 'light curve' for S Doradus that was similar to an eclipsing binary with a period of 40 years. This interpretation remains controversial, however, S Doradus has other properties that are not consistent with an eclipsing binary system of two massive stars, such as the existence of three or more 'minima' between what were identified as the main minima in 1910 and 1940.
Is there any resemblance between Eta Carina and S Doradus? There is some superficial resemblance in that both are apparently among the handful of the most massive stars that astronomers know. Both show long, slow variations in brightness and sudden flarings, and have indications of substantial circumstellar gas. The Eta Carina nebula is 40 arcseconds across at a distance of some 3000 light years. At a distance of 170,000 light years, the corresponding S Doradus cloud would be only 40 x 3/170 = 120/170 or 0.9 arcseconds across. It would not be a very spectacular object for even the Hubble Space Telescope to try to image, so the spectroscopic evidence is probably all that we will have to work with for a while to study its circumstellar gas cloud.
Copyright 1997 Dr. Sten Odenwald
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