Ultraviolet and Optical Spectral Morphology of Melnick 42 and Radcliffe 136a in 30 Doradus

Abstract

HST/GHRS ultraviolet spectrograms of the individual O3 If */WN6-A object Mk 42 in 30 Dor and the adjacent, central multiple system R136a are compared with each other and with an appropriate sequence of O3 If* and WN6-A standards from the IUE archive. The analogous spectral montages covering the blue-violet region, based on new, homogeneous, digital observations of the same stars with the CTIO 4 m telescope, are also presented. These comparisons show clearly the intermediate O3/WN nature of the Mk 42 spectrum, in terms of both emission-line strength (increasing with envelope density) and stellar-wind velocity (decreasing with envelope density). It is also shown that R136a possesses stronger WN spectral characteristics than Mk 42, in agreement with HST narrow-band imaging by the WF/PC Team.