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Spiral waves caused by a passage of the LMC?

Published online by Cambridge University Press:  14 August 2015

A. Toomre*
Affiliation:
Massachusetts Institute of Technology, Cambridge, Mass., U.S.A.

Extract

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This progress report on the deduction of an almost grazing orbit of the Large Magellanic Cloud from the warped shape of our Galaxy focused on two issues of special relevance to this Symposium:

  1. (i) Distance R0. - An implausibly large mass (> 3 × 1010M) of the LMC is needed to account for the observed warp even with the most optimal orbit, using Schmidt's (1965) disk model of our Galaxy, or any close variant thereof. Although as yet only tentative, the inference seems to be that our distance R0 from the galactic center has been overestimated; instead of the now ‘standard’ R0 = 10 kpc, these disk-bending calculations suggest a value more like the older R0 ≅ 8 kpc.

  2. (ii) Forced spiral waves. - Even with the revised R0, the sense of the LMC orbit remains ambiguous (though not the perigalactic distance of roughly 20 kpc nor the low absolute inclination of that orbit relative to the galactic plane). Neither the detailed shapes of the vertically bent model disks, nor any computed tidal effects of the Galaxy upon the LMC and SMC, either separately or as a system, rule out an LMC passage that is retrograde with respect to the galactic rotation, but all favor a direct passage as being the more plausible. The latter kind of passage, however, presents an embarrassment of riches.

Type
Part III/Theory of Spiral Structure
Copyright
Copyright © Reidel 1970 

References

Habing, H. J.: 1966, Bull. Astron. Inst. Netherl. 18, 323.Google Scholar
Pfleiderer, J.: 1963, Z. Astrophys. 58, 12.Google Scholar
Schmidt, M.: 1965, Stars and Stellar Systems 5, 513.Google Scholar
Toomre, A.: 1969, Astrophys. J. 158, 899.CrossRefGoogle Scholar