The interstellar lines and the energetics of the inner 30 Doradus nebula from the ultraviolet spectrum of R 136a

An IUE short and long wavelength absorption line spectrum (1150–3000 Å) of the central superluminous object in the 30 Doradus Nebula, R 136a, is analysed. Radial velocities and equivalent widths of the Magellanic interstellar components are given. The curve of growth of the Magellanic interstellar components displays Mn II and S II in the transition to the linear part; the corresponding column density of hydrogen (in the case of normal cosmic abundances) is |$\text{log} \enspace N_\text{H} \enspace \text{cm}^{-2} \cong 20.2$|⁠. The Magellanic interstellar components fall into four well-separated groups. The same groups show up in the velocity components of all interstellar LMC emission and absorption lines so far observed. Their average velocities are given. They can be explained by a model of the inner part of 30 Dor consisting of shells and bubbles, and warp material above the plane of the LMC. The power of R 136a alone is sufficient to energize the multitude of the 30 Dor shells and to structure the whole nebula. The wind energy supplied by R1 36a is 2–5 1039 erg s−1. The expansion velocity of the inner shell is 24 km s−1. The derived expansion age is 4 × 105 yr. The upper limit to the age of the central object is 106 yr.