A Study of the 30 Doradus Region of the Large Magellanic Cloud

Abstract

The results are presented of a spectroscopic study of stars and nebulosity in the 30 Dor complex of the LMC. Intensity measurements of emission lines yield an electron temperature for the nebulosity of about 10 ⁴ °K and electron densities ranging from, 2 × 10 ² to 20 × 10 ² cm ⁻³ in different places. The Balmer decrement shows that no large amount of interstellar reddening is present in the region studied. The H/He ratio is normal. The variations in brightness within the nebulosity are probably caused by real variations in density. Internal motions in the nebulosity are discussed from radial velocity measurements at 37 different points. The velocity dispersion, corrected for observational error is 11.3 ± 3.2 (s.e.) km/sec. Though this is larger than has been found in some other nebulae it is still sufficiently small so that a stable system of large mass may eventually be formed. Despite some indications of motions of an ordered nature the results are analysed on an hypothesis of turbulent motion. The difference in radial velocity ( u ) between two points is independent of their separation in the range 9–60 pc at least and thus Kolmogoroff's law does not apply in this range, u decreases at smaller separations. The spectral types of 20 stars are given in Table V. There is a high proportion of W stars, all of which belong to the nitrogen sequence. The other stars are normal supergiants ranging from O8 to F7 Ia. A few stellar radial velocity results are listed. Some examples are given of stars showing an intimate connection with the structure of the nebulosity.