Jeremy Buss
University of Wisconsin, Oshkosh
We present results obtained from a multi-faceted study of the LMC OB association LH 72. LH 72 lies near the geometrical center of Constellation III, a kpc-sized complex of stars and gas comprising one of the largest known superbubbles. Our study combines ultraviolet and optical spectra of the brightest blue stars, UBV photometry of the entire association, narrow-band H-alpha and H-beta images of the surrounding H II region, and will include analysis of available data of the H I gas. These data provide the necessary ingredients for characterizing the star formation history and initial mass function of the association; for mapping the distribution of dust and measuring the ultraviolet reddening law; and for exploring the interaction of the stars with the interstellar medium.
To date, we have analyzed optical spectra of 13 stars in the association in addition to IUE spectra of 7 of the same stars. We have assigned spectral and luminosity classes to the stars on the basis of the optical spectra, from which we generate an H-R diagram of the bright stars of LH 72. By fitting isochrones to the H-R diagram, we find stellar ages ranging from ~2-18 Myr. LH 72 thus contains stars as young and as old as any found in Constellation III. The observed age range spans the proposed expansion age of the surrounding superbubble, suggesting that star formation may proceed long after an initial triggering event. We also find continued evidence for propagating star formation on the scale of the association, as the center of star formation activity has drifted by ~100 pc over the past 10-15 Myr.