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Unstable spiral modes in the Milky Way system

Published online by Cambridge University Press:  14 August 2015

Y. Y. Lau  and
Jon Haass
Y. Y. Lau
Affiliation:
Massachusetts Institute of Technology Cambridge, Massachusetts 02139, USA
Jon Haass
Affiliation:
Massachusetts Institute of Technology Cambridge, Massachusetts 02139, USA

Extract

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Discrete spiral modes of density waves have been calculated for models of the Milky Way system. The calculation is based on a fluid dynamical formulation. (See Lau and Bertin, 1978.) The equilibrium assumes a rotation curve given by Schmidt in 1965. The surface density σ of the active disk is less than the projected value implied by the Schmidt model, because of the presence of the spheroidal component and of the finite thickness of the disk. One such model (left figure) supports a spiral mode with a pattern speed of 13.6 km/sec/kpc. The spiral pattern (right figure) is very similar to that calculated earlier by Lin and Shu (1967) who used only the short wave. The perturbation density on the contours shown equals 1/5 of the maxima. There are other unstable modes. The modes are sensitive to the assumed Q profile. The superposition of these modes opens the way to the explanation of the complicated features observed but not well explained by the single spiral pattern computed earlier.

Type
III. SPIRAL STRUCTURE
Information
Symposium - International Astronomical Union , Volume 84: The Large-Scale Characteristics of the Galaxy , 1979 , pp. 154
Copyright
Copyright © Reidel 1979 

References

Lau, Y.Y. and Bertin, G.: 1978, Astrophys. J., in press.Google Scholar
Lin, C.C. and Shu, F.H.: 1967, Proc. I.A.U. Symp. No. 31, (Noordwijk), p. 313.Google Scholar