The Kinematics of Gaseous Nebulae and Supergiant Stars in the Magellanic Clouds

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Abstract
Radial velocities of 42 regions of emission nebulosity in the LMC and 2 in the SMC, derived from coudé spectrograms (15.6 A/mm), are listed, together with 9 velocities in the galactic nebula M8. The results are compared with previous work. Representation of the radial velocities of 43 LMC nebulae by solid body motion yields results closely similar to a previous solution for 61 supergiants. The p.a. of the major axis of the LMC is again found close to 171°. The combined results of nebulae and stars now show differential rotation rather clearly. The optical and 21-cm rotation curves agree quite closely and define a centre of symmetry displaced 1° N of the optical bar of the LMC. With an inclined plane model (i = 27°) the mass of the LMC falls between 1.0 and 0.5 × 1010 solar masses. A velocity dispersion of 9.6 ± 1.1(s.e.) km/sec is derived for nebulae and supergiants in the LMC indicating that these objects are probably concentrated to a plane. The velocity dispersion is not significantly different from this in groups of apparently related nebulae or within the 30 Doradus nebula. 5 Supergiants in the LMC and 5 in the SMC have large velocity residuals. These stars seem similar to the high velocity O-type stars in the Galaxy since (1) they have evolved from O-type stars (2) the percentage of high velocity stars (10 per cent) is the same as for galactic O-types (3) the mean residual velocities of these stars are closely similar in the Magellanic Clouds and the Galaxy. The significance of this result is briefly discussed and it is pointed out that in the Galaxy the percentage of high velocity stars is apparently much higher amongst the Of stars than amongst O stars in general.

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