The Stellar Content of Nearby and Distant Starbursts

Summary

We studied the content of massive stars in the nearby HII region 30 Doradus and in the distant nuclear starburst NGC 7552. Ultraviolet imaging and ultraviolet spectroscopy with the Hubble Space Telescope and the International Ultraviolet Explorer have been obtained. The observational data have been compared with evolutionary population synthesis models in an attempt to constrain the star-formation history and mass spectrum of the two starburst regions. Despite the different physical and chemical conditions, the high-mass end of the mass functions in 30 Dor and NGC 7552 are remarkably similar.

30 Doradus and NGC 7552 — basic properties

30 Doradus in the Large Magellanic Cloud is the closest giant extragalactic HII region (GEHR). The combination of its relative proximity and its location outside the plane of our Milky Way makes 30 Dor a prime laboratory for the study of the formation and evolution of the most massive stars. Walborn (1991) reviewed the basic properties of 30 Dor, designating it the “Starburst Rosett”. 30 Dor is metal-deficient with respect to the Sun (Z = 0.3 Z_⊙) and has only a moderate interstellar reddening of E(B − V) = 0.4. At a distance of 0.05 Mpc, 1″ corresponds to a linear distance of 0.25 pc. The most massive stars are concentrated within a few arcsec of the center of 30 Dor.