Copy of Lord Nelson's Will and Codicils

Nelson, Horatio; Nicolas, Nicholas Harris

doi:10.1017/cbo9781139088039.008

Cited by 1 publication

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“…This phenomenon, known since 1957, has led to theoretical difficulties. Warps are bending waves, and we correctly understand their propagation (see Hunter, 1969a for a dispersion relation in an infinitely thin disk, and see Nelson 1976aand 1976b, Papaloizou and Lin 1995, Masset and Tagger 1995 for the dispersion relation taking into account finite thickness and compressional effects), but we do not know the mechanism responsible for their excitation. It cannot be systematically justified by tidal effects Send offprint requests to: F. Masset (Hunter and Toomre 1969), since we observe warping of very isolated spiral galaxies.…”

Section: Introductionmentioning

confidence: 99%

Non-Linear Excitation of Warps by Spiral Waves in Galaxies

Masset¹,

Tagger²

1996

International Astronomical Union Colloquium

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Abstract.We present a mechanism to explain the permanent excitation of warps in spiral or barred galaxies. We show that non-linear mode coupling with the spiral wave can be very efficient to drive two warp waves. We derive an expression of the coupling coefficient in the WKB approximation. We show that the coupling is too weak in the stellar disk, except at the Outer Lindblad Resonance where the spiral slows down and is efficiently coupled to warp waves. There, the spiral can almost completely transfer its energy and angular momentum to a "transmitted" warp, which we can observe in HI, and a "reflected" one, which we can observe as a corrugation. Our mechanism reproduces the observed amplitudes of the warp and of the corrugation.We first present side results concerning the propagation of warps in moderately thick disks. Linear results: Propagation of Warps in Moderately Thick DisksIn an infinitely thin disk, the dispersion relation of bending waves is: a) 2 = fj, 2 + 27rG£fc, where UJ is the warp's frequency in the frame of matter (if ui is its frequency in the galactocentric frame,

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